Copyright 1988-2015 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being Funding Free Software, the Front-Cover Texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the section entitled GNU Free Documentation License.
The FSFs Front-Cover Text is:
A GNU Manual
The FSFs Back-Cover Text is:
You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development.
Software development
The GNU Compiler Collection. <(gcc)> The GNU C++ compiler. <(gcc)> :command:`gcov`a test coverage program. <(gcc)-gcov> :command:`gcov-tool`an offline gcda profile processing program. <(gcc)-gcov-tool>
This file documents the use of the GNU compilers.
Using the GNU Compiler Collection For gcc version 6.0.0 (pre-release)
(GCC)
Richard M. Stallman and the GCC Developer Community
0pt plus 1filll
Published by:
GNU Press Website: http://www.gnupress.org a division of the General: pressgnu.org Free Software Foundation Orders: salesgnu.org 51 Franklin Street, Fifth Floor Tel 617-542-5942 Boston, MA 02110-1301 USA Fax 617-542-2652
Last printed October 2003 for GCC 3.3.1. Printed copies are available for $45 each.
:: _top:
This manual documents how to use the GNU compilers, as well as their features and incompatibilities, and how to report bugs. It corresponds to the compilers (GCC) version 6.0.0. The internals of the GNU compilers, including how to port them to new targets and some information about how to write front ends for new languages, are documented in a separate manual. TopIntroductiongccintGNU Compiler Collection (GCC) Internals.
:: _g++-and-gcc:
GCC stands for GNU Compiler Collection. GCC is an integrated distribution of compilers for several major programming languages. These languages currently include C, C++, Objective-C, Objective-C++, Java, Fortran, Ada, and Go.
The abbreviation GCC has multiple meanings in common use. The current official meaning is GNU Compiler Collection, which refers generically to the complete suite of tools. The name historically stood for GNU C Compiler, and this usage is still common when the emphasis is on compiling C programs. Finally, the name is also used when speaking of the language-independent component of GCC: code shared among the compilers for all supported languages.
The language-independent component of GCC includes the majority of the optimizers, as well as the back ends that generate machine code for various processors.
The part of a compiler that is specific to a particular language is called the front end. In addition to the front ends that are integrated components of GCC, there are several other front ends that are maintained separately. These support languages such as Pascal, Mercury, and COBOL To use these, they must be built together with GCC proper.
Most of the compilers for languages other than C have their own names. The C++ compiler is G++, the Ada compiler is GNAT, and so on. When we talk about compiling one of those languages, we might refer to that compiler by its own name, or as GCC Either is correct.
Historically, compilers for many languages, including C++ and Fortran, have been implemented as preprocessors which emit another high level language such as C None of the compilers included in GCC are implemented this way; they all generate machine code directly. This sort of preprocessor should not be confused with the C preprocessor, which is an integral feature of the C, C++, Objective-C and Objective-C++ languages.
:: _standards:
For each language compiled by GCC for which there is a standard, GCC attempts to follow one or more versions of that standard, possibly with some exceptions, and possibly with some extensions.
GCC supports three versions of the C standard, although support for the most recent version is not yet complete.
The original ANSI C standard (X3.159-1989) was ratified in 1989 and published in 1990. This standard was ratified as an ISO standard (ISO/IEC 9899:1990) later in 1990. There were no technical differences between these publications, although the sections of the ANSI standard were renumbered and became clauses in the ISO standard. This standard, in both its forms, is commonly known as C89, or occasionally as C90, from the dates of ratification. The ANSI standard, but not the ISO standard, also came with a Rationale document. To select this standard in GCC, use one of the options -ansi, -std=c90 or -std=iso9899:1990; to obtain all the diagnostics required by the standard, you should also specify -pedantic (or -pedantic-errors if you want them to be errors rather than warnings). C Dialect OptionsOptions Controlling C Dialect.
Errors in the 1990 ISO C standard were corrected in two Technical Corrigenda published in 1994 and 1996. GCC does not support the uncorrected version.
An amendment to the 1990 standard was published in 1995. This amendment added digraphs and __STDC_VERSION__ to the language, but otherwise concerned the library. This amendment is commonly known as AMD1; the amended standard is sometimes known as C94 or C95. To select this standard in GCC, use the option -std=iso9899:199409 (with, as for other standard versions, -pedantic to receive all required diagnostics).
A new edition of the ISO C standard was published in 1999 as ISO/IEC 9899:1999, and is commonly known as C99. GCC has substantially complete support for this standard version; see http://gcc.gnu.org/c99status.html for details. To select this standard, use -std=c99 or -std=iso9899:1999. (While in development, drafts of this standard version were referred to as C9X.)
Errors in the 1999 ISO C standard were corrected in three Technical Corrigenda published in 2001, 2004 and 2007. GCC does not support the uncorrected version.
A fourth version of the C standard, known as C11, was published in 2011 as ISO/IEC 9899:2011. GCC has substantially complete support for this standard, enabled with -std=c11 or -std=iso9899:2011. (While in development, drafts of this standard version were referred to as C1X.)
By default, GCC provides some extensions to the C language that on rare occasions conflict with the C standard. C ExtensionsExtensions to the C Language Family. Use of the -std options listed above will disable these extensions where they conflict with the C standard version selected. You may also select an extended version of the C language explicitly with -std=gnu90 (for C90 with GNU extensions), -std=gnu99 (for C99 with GNU extensions) or -std=gnu11 (for C11 with GNU extensions). The default, if no C language dialect options are given, is -std=gnu11. Some features that are part of the C99 standard are accepted as extensions in C90 mode, and some features that are part of the C11 standard are accepted as extensions in C90 and C99 modes.
The ISO C standard defines (in clause 4) two classes of conforming implementation. A conforming hosted implementation supports the whole standard including all the library facilities; a conforming freestanding implementation is only required to provide certain library facilities: those in <float.h>, <limits.h>, <stdarg.h>, and <stddef.h>; since AMD1, also those in <iso646.h>; since C99, also those in <stdbool.h> and <stdint.h>; and since C11, also those in <stdalign.h> and <stdnoreturn.h>. In addition, complex types, added in C99, are not required for freestanding implementations. The standard also defines two environments for programs, a freestanding environment, required of all implementations and which may not have library facilities beyond those required of freestanding implementations, where the handling of program startup and termination are implementation-defined, and a hosted environment, which is not required, in which all the library facilities are provided and startup is through a function int main (void) or int main (int, char *[]). An OS kernel would be a freestanding environment; a program using the facilities of an operating system would normally be in a hosted implementation.
GCC aims towards being usable as a conforming freestanding implementation, or as the compiler for a conforming hosted implementation. By default, it will act as the compiler for a hosted implementation, defining __STDC_HOSTED__ as 1 and presuming that when the names of ISO C functions are used, they have the semantics defined in the standard. To make it act as a conforming freestanding implementation for a freestanding environment, use the option -ffreestanding; it will then define __STDC_HOSTED__ to 0 and not make assumptions about the meanings of function names from the standard library, with exceptions noted below. To build an OS kernel, you may well still need to make your own arrangements for linking and startup. C Dialect OptionsOptions Controlling C Dialect.
GCC does not provide the library facilities required only of hosted implementations, nor yet all the facilities required by C99 of freestanding implementations on all platforms; to use the facilities of a hosted environment, you will need to find them elsewhere (for example, in the GNU C library). Standard LibrariesStandard Libraries.
Most of the compiler support routines used by GCC are present in libgcc, but there are a few exceptions. GCC requires the freestanding environment provide memcpy, memmove, memset and memcmp. Finally, if __builtin_trap is used, and the target does not implement the trap pattern, then GCC will emit a call to abort.
For references to Technical Corrigenda, Rationale documents and information concerning the history of C that is available online, see http://gcc.gnu.org/readings.html
GCC supports the original ISO C++ standard (1998) and contains experimental support for the second ISO C++ standard (2011).
The original ISO C++ standard was published as the ISO standard (ISO/IEC 14882:1998) and amended by a Technical Corrigenda published in 2003 (ISO/IEC 14882:2003). These standards are referred to as C++98 and C++03, respectively. GCC implements the majority of C++98 (export is a notable exception) and most of the changes in C++03. To select this standard in GCC, use one of the options -ansi, -std=c++98, or -std=c++03; to obtain all the diagnostics required by the standard, you should also specify -pedantic (or -pedantic-errors if you want them to be errors rather than warnings).
A revised ISO C++ standard was published in 2011 as ISO/IEC 14882:2011, and is referred to as C++11; before its publication it was commonly referred to as C++0x. C++11 contains several changes to the C++ language, most of which have been implemented in an experimental C++11 mode in GCC For information regarding the C++11 features available in the experimental C++11 mode, see http://gcc.gnu.org/projects/cxx0x.html. To select this standard in GCC, use the option -std=c++11; to obtain all the diagnostics required by the standard, you should also specify -pedantic (or -pedantic-errors if you want them to be errors rather than warnings).
More information about the C++ standards is available on the ISO C++ committees web site at http://www.open-std.org/jtc1/sc22/wg21/.
By default, GCC provides some extensions to the C++ language; C++ Dialect OptionsOptions Controlling C++ Dialect. Use of the -std option listed above will disable these extensions. You may also select an extended version of the C++ language explicitly with -std=gnu++98 (for C++98 with GNU extensions) or -std=gnu++11 (for C++11 with GNU extensions). The default, if no C++ language dialect options are given, is -std=gnu++98.
GCC supports traditional Objective-C (also known as Objective-C 1.0) and contains support for the Objective-C exception and synchronization syntax. It has also support for a number of Objective-C 2.0 language extensions, including properties, fast enumeration (only for Objective-C), method attributes and the optional and required keywords in protocols. GCC supports Objective-C++ and features available in Objective-C are also available in Objective-C++
GCC by default uses the GNU Objective-C runtime library, which is part of GCC and is not the same as the Apple/NeXT Objective-C runtime library used on Apple systems. There are a number of differences documented in this manual. The options -fgnu-runtime and -fnext-runtime allow you to switch between producing output that works with the GNU Objective-C runtime library and output that works with the Apple/NeXT Objective-C runtime library.
There is no formal written standard for Objective-C or Objective-C++ The authoritative manual on traditional Objective-C (1.0) is Object-Oriented Programming and the Objective-C Language, available at a number of web sites:
The Objective-C exception and synchronization syntax (that is, the keywords try, throw, catch, finally and synchronized) is supported by GCC and is enabled with the option -fobjc-exceptions. The syntax is briefly documented in this manual and in the Objective-C 2.0 manuals from Apple.
The Objective-C 2.0 language extensions and features are automatically enabled; they include properties (via the property, synthesize and dynamic keywords), fast enumeration (not available in Objective-C++), attributes for methods (such as deprecated, noreturn, sentinel, format), the unused attribute for method arguments, the package keyword for instance variables and the optional and required keywords in protocols. You can disable all these Objective-C 2.0 language extensions with the option -fobjc-std=objc1, which causes the compiler to recognize the same Objective-C language syntax recognized by GCC 4.0, and to produce an error if one of the new features is used.
GCC has currently no support for non-fragile instance variables.
The authoritative manual on Objective-C 2.0 is available from Apple:
For more information concerning the history of Objective-C that is available online, see http://gcc.gnu.org/readings.html
As of the GCC 4.7.1 release, GCC supports the Go 1 language standard, described at http://golang.org/doc/go1.html.
TopGNAT Reference ManualAbout This Guidegnat_rmGNAT Reference Manual, for information on standard conformance and compatibility of the Ada compiler.
StandardsStandardsgfortranThe GNU Fortran Compiler, for details of standards supported by GNU Fortran.
CompatibilityCompatibility with the Java PlatformgcjGNU gcj, for details of compatibility between gcj and the Java Platform.
@c man begin INCLUDE @include gcc-vers.texi @c man end
@c man begin COPYRIGHT Copyright @copyright{} 1988-2015 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being ``GNU General Public License’’ and ``Funding Free Software’‘, the Front-Cover texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the gfdl(7) man page.
The FSF’s Front-Cover Text is:
A GNU Manual
The FSF’s Back-Cover Text is:
You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development.
@c man end @c Set file name and title for the man page. @setfilename gcc @settitle GNU project C and C++ compiler @c man begin SYNOPSIS gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}]
[@option{-g}] [@option{-pg}] [@option{-O}@var{level}] [@option{-W}@var{warn}@dots{}] [@option{-Wpedantic}] [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}] [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}] [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}] [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{}
Only the most useful options are listed here; see below for the remainder. @command{g++} accepts mostly the same options as @command{gcc}. @c man end @c man begin SEEALSO gpl(7), gfdl(7), fsf-funding(7), cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1) and the Info entries for @file{gcc}, @file{cpp}, @file{as}, @file{ld}, @file{binutils} and @file{gdb}. @c man end @c man begin BUGS For instructions on reporting bugs, see @w{@value{BUGURL}}. @c man end @c man begin AUTHOR See the Info entry for @command{gcc}, or @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}}, for contributors to GCC@. @c man end
:: _invoking-gcc:
When you invoke GCC, it normally does preprocessing, compilation, assembly and linking. The overall options allow you to stop this process at an intermediate stage. For example, the -c option says not to run the linker. Then the output consists of object files output by the assembler.
Other options are passed on to one stage of processing. Some options control the preprocessor and others the compiler itself. Yet other options control the assembler and linker; most of these are not documented here, since you rarely need to use any of them.
Most of the command-line options that you can use with GCC are useful for C programs; when an option is only useful with another language (usually C++), the explanation says so explicitly. If the description for a particular option does not mention a source language, you can use that option with all supported languages.
Invoking G++Compiling C++ Programs, for a summary of special options for compiling C++ programs.
The gcc program accepts options and file names as operands. Many options have multi-letter names; therefore multiple single-letter options may not be grouped: -dv is very different from -d -v.
You can mix options and other arguments. For the most part, the order you use doesnt matter. Order does matter when you use several options of the same kind; for example, if you specify -L more than once, the directories are searched in the order specified. Also, the placement of the -l option is significant.
Many options have long names starting with -f or with -Wfor example, -fmove-loop-invariants, -Wformat and so on. Most of these have both positive and negative forms; the negative form of -ffoo is -fno-foo. This manual documents only one of these two forms, whichever one is not the default.
Option Index, for an index to GCCs options.
:: _option-summary:
Here is a summary of all the options, grouped by type. Explanations are in the following sections.
Overall OptionsOptions Controlling the Kind of Output.
-c -S -E -o file -no-canonical-prefixes -pipe -pass-exit-codes -x language -v -### --help`[=``class``[,...]] :option:–target-help` --version -wrapper file -fplugin=```file` -fplugin-arg-```name``=``arg` -fdump-ada-spec`[:option:-slim`] -fada-spec-parent=```unit` -fdump-go-spec=```file`
C Dialect OptionsOptions Controlling C Dialect.
-ansi -std=```standard` -fgnu89-inline -aux-info filename -fallow-parameterless-variadic-functions -fno-asm -fno-builtin -fno-builtin-```function` -fhosted -ffreestanding -fopenacc -fopenmp -fopenmp-simd -fms-extensions -fplan9-extensions -trigraphs -traditional -traditional-cpp -fallow-single-precision -fcond-mismatch -flax-vector-conversions -fsigned-bitfields -fsigned-char -funsigned-bitfields -funsigned-char
C++ Dialect OptionsOptions Controlling C++ Dialect.
-fabi-version=```n` -fno-access-control -fcheck-new -fconstexpr-depth=```n` -ffriend-injection -fno-elide-constructors -fno-enforce-eh-specs -ffor-scope -fno-for-scope -fno-gnu-keywords -fno-implicit-templates -fno-implicit-inline-templates -fno-implement-inlines -fms-extensions -fno-nonansi-builtins -fnothrow-opt -fno-operator-names -fno-optional-diags -fpermissive -fno-pretty-templates -frepo -fno-rtti -fsized-deallocation -fstats -ftemplate-backtrace-limit=```n` -ftemplate-depth=```n` -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ -fvisibility-inlines-hidden -fvtable-verify=`[std|preinit|none] :option:-fvtv-counts` -fvtv-debug -fvisibility-ms-compat -fext-numeric-literals -Wabi=```n` -Wabi-tag -Wconversion-null -Wctor-dtor-privacy -Wdelete-non-virtual-dtor -Wliteral-suffix -Wnarrowing -Wnoexcept -Wnon-virtual-dtor -Wreorder -Weffc++ -Wstrict-null-sentinel -Wno-non-template-friend -Wold-style-cast -Woverloaded-virtual -Wno-pmf-conversions -Wsign-promo
Objective-C and Objective-C++ Dialect OptionsOptions Controlling Objective-C and Objective-C++ Dialects.
-fconstant-string-class=```class:option:-name``` -fgnu-runtime -fnext-runtime -fno-nil-receivers -fobjc-abi-version=```n` -fobjc-call-cxx-cdtors -fobjc-direct-dispatch -fobjc-exceptions -fobjc-gc -fobjc-nilcheck -fobjc-std=objc1 -fno-local-ivars -fivar-visibility=`[public|protected|private|package] :option:-freplace-objc-classes` -fzero-link -gen-decls -Wassign-intercept -Wno-protocol -Wselector -Wstrict-selector-match -Wundeclared-selector
Language Independent OptionsOptions to Control Diagnostic Messages Formatting.
-fmessage-length=```n` -fdiagnostics-show-location=`[once|every:option:-line`] -fdiagnostics-color=`[auto|never|always] :option:-fno-diagnostics-show-option` -fno-diagnostics-show-caret
Warning OptionsOptions to Request or Suppress Warnings.
-fsyntax-only -fmax-errors=```n` -Wpedantic -pedantic-errors -w -Wextra -Wall -Waddress -Waggregate-return -Waggressive-loop-optimizations -Warray-bounds -Warray-bounds=```n` -Wbool-compare -Wno-attributes -Wno-builtin-macro-redefined -Wc90-c99-compat -Wc99-c11-compat -Wc++-compat -Wc++11-compat -Wc++14-compat -Wcast-align -Wcast-qual -Wchar-subscripts -Wclobbered -Wcomment -Wconditionally-supported -Wconversion -Wcoverage-mismatch -Wdate-time -Wdelete-incomplete -Wno-cpp -Wno-deprecated -Wno-deprecated-declarations -Wno-designated-init -Wdisabled-optimization -Wno-discarded-qualifiers -Wno-discarded-array-qualifiers -Wno-div-by-zero -Wdouble-promotion -Wempty-body -Wenum-compare -Wno-endif-labels -Werror -Werror=* -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 -Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral -Wformat-security -Wformat-signedness -Wformat-y2k -Wframe-larger-than=```len` -Wno-free-nonheap-object -Wjump-misses-init -Wignored-qualifiers -Wincompatible-pointer-types -Wimplicit -Wimplicit-function-declaration -Wimplicit-int -Winit-self -Winline -Wno-int-conversion -Wno-int-to-pointer-cast -Wno-invalid-offsetof -Winvalid-pch -Wlarger-than=```len` -Wunsafe-loop-optimizations -Wlogical-op -Wlogical-not-parentheses -Wlong-long -Wmain -Wmaybe-uninitialized -Wmemset-transposed-args -Wmissing-braces -Wmissing-field-initializers -Wmissing-include-dirs -Wno-multichar -Wnonnull -Wnormalized=`[none|id|nfc|nfkc] :option:-Wodr` -Wno-overflow -Wopenmp-simd -Woverride-init-side-effects -Woverlength-strings -Wpacked -Wpacked-bitfield-compat -Wpadded -Wparentheses -Wpedantic-ms-format -Wno-pedantic-ms-format -Wpointer-arith -Wno-pointer-to-int-cast -Wredundant-decls -Wno-return-local-addr -Wreturn-type -Wsequence-point -Wshadow -Wno-shadow-ivar -Wshift-count-negative -Wshift-count-overflow -Wshift-negative-value -Wsign-compare -Wsign-conversion -Wfloat-conversion -Wsizeof-pointer-memaccess -Wsizeof-array-argument -Wstack-protector -Wstack-usage=```len` -Wstrict-aliasing -Wstrict-aliasing=n -Wstrict-overflow -Wstrict-overflow=```n` -Wsuggest-attribute=`[pure|const|noreturn|format] :option:-Wsuggest-final-types` -Wsuggest-final-methods -Wsuggest-override -Wmissing-format-attribute -Wswitch -Wswitch-default -Wswitch-enum -Wswitch-bool -Wsync-nand -Wsystem-headers -Wtrampolines -Wtrigraphs -Wtype-limits -Wundef -Wuninitialized -Wunknown-pragmas -Wno-pragmas -Wunsuffixed-float-constants -Wunused -Wunused-function -Wunused-label -Wunused-local-typedefs -Wunused-parameter -Wno-unused-result -Wunused-value -Wunused-variable -Wunused-but-set-parameter -Wunused-but-set-variable -Wuseless-cast -Wvariadic-macros -Wvector-operation-performance -Wvla -Wvolatile-register-var -Wwrite-strings -Wzero-as-null-pointer-constant
-Wbad-function-cast -Wmissing-declarations -Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs -Wold-style-declaration -Wold-style-definition -Wstrict-prototypes -Wtraditional -Wtraditional-conversion -Wdeclaration-after-statement -Wpointer-sign
Debugging OptionsOptions for Debugging Your Program or GCC.
-d```letters` -dumpspecs -dumpmachine -dumpversion -fsanitize=```style` -fsanitize-recover -fsanitize-recover=```style` -fasan-shadow-offset=```number` -fsanitize-sections=```s1,s2,...` -fsanitize-undefined-trap-on-error -fcheck-pointer-bounds -fchkp-check-incomplete-type -fchkp-first-field-has-own-bounds -fchkp-narrow-bounds -fchkp-narrow-to-innermost-array -fchkp-optimize -fchkp-use-fast-string-functions -fchkp-use-nochk-string-functions -fchkp-use-static-bounds -fchkp-use-static-const-bounds -fchkp-treat-zero-dynamic-size-as-infinite -fchkp-check-read -fchkp-check-read -fchkp-check-write -fchkp-store-bounds -fchkp-instrument-calls -fchkp-instrument-marked-only -fchkp-use-wrappers -fdbg-cnt-list -fdbg-cnt=```counter:option:-value-list``` -fdisable-ipa-```pass_name` -fdisable-rtl-```pass_name` -fdisable-rtl-```pass:option:-name```=``range:option:-list`` -fdisable-tree-```pass_name` -fdisable-tree-```pass:option:-name```=``range:option:-list`` -fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links -fdump-translation-unit`[-``n`] -fdump-class-hierarchy`[-``n`] -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline -fdump-passes -fdump-statistics -fdump-tree-all -fdump-tree-original`[-``n`] -fdump-tree-optimized`[-``n`] -fdump-tree-cfg -fdump-tree-alias -fdump-tree-ch -fdump-tree-ssa`[-``n`] -fdump-tree-pre`[-``n`] -fdump-tree-ccp`[-``n`] -fdump-tree-dce`[-``n`] -fdump-tree-gimple`[:option:-raw`] -fdump-tree-dom`[-``n`] -fdump-tree-dse`[-``n`] -fdump-tree-phiprop`[-``n`] -fdump-tree-phiopt`[-``n`] -fdump-tree-forwprop`[-``n`] -fdump-tree-copyrename`[-``n`] -fdump-tree-nrv -fdump-tree-vect -fdump-tree-sink -fdump-tree-sra`[-``n`] -fdump-tree-forwprop`[-``n`] -fdump-tree-fre`[-``n`] -fdump-tree-vtable-verify -fdump-tree-vrp`[-``n`] -fdump-tree-storeccp`[-``n`] -fdump-final-insns=```file` -fcompare-debug`[=``opts`] -fcompare-debug-second -feliminate-dwarf2-dups -fno-eliminate-unused-debug-types -feliminate-unused-debug-symbols -femit-class-debug-always -fenable-```kind`-pass -fenable-```kind`-pass``=``range:option:`-list` -fdebug-types-section -fmem-report-wpa -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs -fopt-info -fopt-info-```options``[=``file`] -frandom-seed=```number` -fsched-verbose=```n` -fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose -fstack-usage -ftest-coverage -ftime-report -fvar-tracking -fvar-tracking-assignments -fvar-tracking-assignments-toggle -g -g```level` -gtoggle -gcoff -gdwarf-```version` -ggdb -grecord-gcc-switches -gno-record-gcc-switches -gstabs -gstabs+ -gstrict-dwarf -gno-strict-dwarf -gvms -gxcoff -gxcoff+ -gz`[=``type`] -fno-merge-debug-strings -fno-dwarf2-cfi-asm -fdebug-prefix-map=```old``=``new` -femit-struct-debug-baseonly -femit-struct-debug-reduced -femit-struct-debug-detailed`[=``spec:option:-list```] -p -pg -print-file-name=```library` -print-libgcc-file-name -print-multi-directory -print-multi-lib -print-multi-os-directory -print-prog-name=```program` -print-search-dirs -Q -print-sysroot -print-sysroot-headers-suffix -save-temps -save-temps=cwd -save-temps=obj -time`[=``file`]
Optimize OptionsOptions that Control Optimization.
-faggressive-loop-optimizations -falign-functions[=```n`] -falign-jumps[=```n`] -falign-labels[=```n`] -falign-loops[=```n`] -fassociative-math -fauto-profile -fauto-profile[=```path`] -fauto-inc-dec -fbranch-probabilities -fbranch-target-load-optimize -fbranch-target-load-optimize2 -fbtr-bb-exclusive -fcaller-saves -fcheck-data-deps -fcombine-stack-adjustments -fconserve-stack -fcompare-elim -fcprop-registers -fcrossjumping -fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules -fcx-limited-range -fdata-sections -fdce -fdelayed-branch -fdelete-null-pointer-checks -fdevirtualize -fdevirtualize-speculatively -fdevirtualize-at-ltrans -fdse -fearly-inlining -fipa-sra -fexpensive-optimizations -ffat-lto-objects -ffast-math -ffinite-math-only -ffloat-store -fexcess-precision=```style` -fforward-propagate -ffp-contract=```style` -ffunction-sections -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity -fgcse-sm -fhoist-adjacent-loads -fif-conversion -fif-conversion2 -findirect-inlining -finline-functions -finline-functions-called-once -finline-limit=```n` -finline-small-functions -fipa-cp -fipa-cp-clone -fipa-cp-alignment -fipa-pta -fipa-profile -fipa-pure-const -fipa-reference -fipa-icf -fira-algorithm=```algorithm` -fira-region=```region` -fira-hoist-pressure -fira-loop-pressure -fno-ira-share-save-slots -fno-ira-share-spill-slots -fira-verbose=```n` -fisolate-erroneous-paths-dereference -fisolate-erroneous-paths-attribute -fivopts -fkeep-inline-functions -fkeep-static-consts -flive-range-shrinkage -floop-block -floop-interchange -floop-strip-mine -floop-unroll-and-jam -floop-nest-optimize -floop-parallelize-all -flra-remat -flto -flto-compression-level -flto-partition=```alg` -flto-report -flto-report-wpa -fmerge-all-constants -fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves -fmove-loop-invariants -fno-branch-count-reg -fno-defer-pop -fno-function-cse -fno-guess-branch-probability -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 -fno-sched-interblock -fno-sched-spec -fno-signed-zeros -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss -fomit-frame-pointer -foptimize-sibling-calls -fpartial-inlining -fpeel-loops -fpredictive-commoning -fprefetch-loop-arrays -fprofile-report -fprofile-correction -fprofile-dir=```path` -fprofile-generate -fprofile-generate=```path` -fprofile-use -fprofile-use=```path` -fprofile-values -fprofile-reorder-functions -freciprocal-math -free -frename-registers -freorder-blocks -freorder-blocks-and-partition -freorder-functions -frerun-cse-after-loop -freschedule-modulo-scheduled-loops -frounding-math -fsched2-use-superblocks -fsched-pressure -fsched-spec-load -fsched-spec-load-dangerous -fsched-stalled-insns-dep[=```n`] -fsched-stalled-insns[=```n`] -fsched-group-heuristic -fsched-critical-path-heuristic -fsched-spec-insn-heuristic -fsched-rank-heuristic -fsched-last-insn-heuristic -fsched-dep-count-heuristic -fschedule-fusion -fschedule-insns -fschedule-insns2 -fsection-anchors -fselective-scheduling -fselective-scheduling2 -fsel-sched-pipelining -fsel-sched-pipelining-outer-loops -fsemantic-interposition -fshrink-wrap -fsignaling-nans -fsingle-precision-constant -fsplit-ivs-in-unroller -fsplit-wide-types -fssa-phiopt -fstack-protector -fstack-protector-all -fstack-protector-strong -fstack-protector-explicit -fstdarg-opt -fstrict-aliasing -fstrict-overflow -fthread-jumps -ftracer -ftree-bit-ccp -ftree-builtin-call-dce -ftree-ccp -ftree-ch -ftree-coalesce-inline-vars -ftree-coalesce-vars -ftree-copy-prop -ftree-copyrename -ftree-dce -ftree-dominator-opts -ftree-dse -ftree-forwprop -ftree-fre -ftree-loop-if-convert -ftree-loop-if-convert-stores -ftree-loop-im -ftree-phiprop -ftree-loop-distribution -ftree-loop-distribute-patterns -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize -ftree-loop-vectorize -ftree-parallelize-loops=```n` -ftree-pre -ftree-partial-pre -ftree-pta -ftree-reassoc -ftree-sink -ftree-slsr -ftree-sra -ftree-switch-conversion -ftree-tail-merge -ftree-ter -ftree-vectorize -ftree-vrp -funit-at-a-time -funroll-all-loops -funroll-loops -funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops -fipa-ra -fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb -fwhole-program -fwpa -fuse-linker-plugin --param name``=``value -O -O0 -O1 -O2 -O3 -Os -Ofast -Og
Preprocessor OptionsOptions Controlling the Preprocessor.
-A```question``=``answer` -A-```question``[=``answer`] -C -dD -dI -dM -dN -D```macro``[=``defn`] -E -H -idirafter dir -include file -imacros file -iprefix file -iwithprefix dir -iwithprefixbefore dir -isystem dir -imultilib dir -isysroot dir -M -MM -MF -MG -MP -MQ -MT -nostdinc -P -fdebug-cpp -ftrack-macro-expansion -fworking-directory -remap -trigraphs -undef -U```macro` -Wp,```option` -Xpreprocessor option -no-integrated-cpp
Assembler OptionsPassing Options to the Assembler.
-Wa,```option` -Xassembler option
Link OptionsOptions for Linking.
``object-file-name`` -fuse-ld=``linker`` -l``library``
-nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic
-s -static -static-libgcc -static-libstdc++
-static-libasan -static-libtsan -static-liblsan -static-libubsan
-static-libmpx -static-libmpxwrappers
-shared -shared-libgcc -symbolic
-T ``script`` -Wl,``option`` -Xlinker ``option``
-u ``symbol`` -z ``keyword``
Directory OptionsOptions for Directory Search.
-B```prefix` -I```dir` -iplugindir=```dir` -iquote```dir` -L```dir` -specs=```file` -I- --sysroot=```dir` --no-sysroot-suffix
Submodel OptionsHardware Models and Configurations.
AArch64 Options
-mabi=```name` -mbig-endian -mlittle-endian -mgeneral-regs-only -mcmodel=tiny -mcmodel=small -mcmodel=large -mstrict-align -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer -mtls-dialect=desc -mtls-dialect=traditional -mfix-cortex-a53-835769 -mno-fix-cortex-a53-835769 -mfix-cortex-a53-843419 -mno-fix-cortex-a53-843419 -march=```name` -mcpu=```name` -mtune=```name`
Adapteva Epiphany Options
-mhalf-reg-file -mprefer-short-insn-regs -mbranch-cost=```num` -mcmove -mnops=```num` -msoft-cmpsf -msplit-lohi -mpost-inc -mpost-modify -mstack-offset=```num` -mround-nearest -mlong-calls -mshort-calls -msmall16 -mfp-mode=```mode` -mvect-double -max-vect-align=```num` -msplit-vecmove-early -m1reg-```reg`
ARC Options
-mbarrel-shifter -mcpu=```cpu` -mA6 -mARC600 -mA7 -mARC700 -mdpfp -mdpfp-compact -mdpfp-fast -mno-dpfp-lrsr -mea -mno-mpy -mmul32x16 -mmul64 -mnorm -mspfp -mspfp-compact -mspfp-fast -msimd -msoft-float -mswap -mcrc -mdsp-packa -mdvbf -mlock -mmac-d16 -mmac-24 -mrtsc -mswape -mtelephony -mxy -misize -mannotate-align -marclinux -marclinux_prof -mepilogue-cfi -mlong-calls -mmedium-calls -msdata -mucb-mcount -mvolatile-cache -malign-call -mauto-modify-reg -mbbit-peephole -mno-brcc -mcase-vector-pcrel -mcompact-casesi -mno-cond-exec -mearly-cbranchsi -mexpand-adddi -mindexed-loads -mlra -mlra-priority-none -mlra-priority-compact mlra:option:-priority-noncompact -mno-millicode -mmixed-code -mq-class -mRcq -mRcw -msize-level=```level` -mtune=```cpu` -mmultcost=```num` -munalign-prob-threshold=```probability`
ARM Options
-mapcs-frame -mno-apcs-frame -mabi=```name` -mapcs-stack-check -mno-apcs-stack-check -mapcs-float -mno-apcs-float -mapcs-reentrant -mno-apcs-reentrant -msched-prolog -mno-sched-prolog -mlittle-endian -mbig-endian -mfloat-abi=```name` -mfp16-format=```name` -mthumb-interwork -mno-thumb-interwork -mcpu=```name` -march=```name` -mfpu=```name` -mtune=```name` -mprint-tune-info -mstructure-size-boundary=```n` -mabort-on-noreturn -mlong-calls -mno-long-calls -msingle-pic-base -mno-single-pic-base -mpic-register=```reg` -mnop-fun-dllimport -mpoke-function-name -mthumb -marm -mtpcs-frame -mtpcs-leaf-frame -mcaller-super-interworking -mcallee-super-interworking -mtp=```name` -mtls-dialect=```dialect` -mword-relocations -mfix-cortex-m3-ldrd -munaligned-access -mneon-for-64bits -mslow-flash-data -masm-syntax-unified -mrestrict-it
AVR Options
-mmcu=```mcu` -maccumulate-args -mbranch-cost=```cost` -mcall-prologues -mint8 -mn_flash=```size` -mno-interrupts -mrelax -mrmw -mstrict-X -mtiny-stack -nodevicelib -Waddr-space-convert
Blackfin Options
-mcpu=```cpu``[-``sirevision`] -msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly -mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library -mno-id-shared-library -mshared-library-id=```n` -mleaf-id-shared-library -mno-leaf-id-shared-library -msep-data -mno-sep-data -mlong-calls -mno-long-calls -mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram -micplb
C6X Options
-mbig-endian -mlittle-endian -march=```cpu` -msim -msdata=```sdata:option:-type```
CRIS Options
-mcpu=```cpu` -march=```cpu` -mtune=```cpu` -mmax-stack-frame=```n` -melinux-stacksize=```n` -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects -mstack-align -mdata-align -mconst-align -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt -melf -maout -melinux -mlinux -sim -sim2 -mmul-bug-workaround -mno-mul-bug-workaround
CR16 Options
-mmac -mcr16cplus -mcr16c -msim -mint32 -mbit-ops -mdata-model=```model`
Darwin Options
-all_load -allowable_client -arch -arch_errors_fatal -arch_only -bind_at_load -bundle -bundle_loader -client_name -compatibility_version -current_version -dead_strip -dependency-file -dylib_file -dylinker_install_name -dynamic -dynamiclib -exported_symbols_list -filelist -flat_namespace -force_cpusubtype_ALL -force_flat_namespace -headerpad_max_install_names -iframework -image_base -init -install_name -keep_private_externs -multi_module -multiply_defined -multiply_defined_unused -noall_load -no_dead_strip_inits_and_terms -nofixprebinding -nomultidefs -noprebind -noseglinkedit -pagezero_size -prebind -prebind_all_twolevel_modules -private_bundle -read_only_relocs -sectalign -sectobjectsymbols -whyload -seg1addr -sectcreate -sectobjectsymbols -sectorder -segaddr -segs_read_only_addr -segs_read_write_addr -seg_addr_table -seg_addr_table_filename -seglinkedit -segprot -segs_read_only_addr -segs_read_write_addr -single_module -static -sub_library -sub_umbrella -twolevel_namespace -umbrella -undefined -unexported_symbols_list -weak_reference_mismatches -whatsloaded -F -gused -gfull -mmacosx-version-min=```version` -mkernel -mone-byte-bool
DEC Alpha Options
-mno-fp-regs -msoft-float -mieee -mieee-with-inexact -mieee-conformant -mfp-trap-mode=```mode` -mfp-rounding-mode=```mode` -mtrap-precision=```mode` -mbuild-constants -mcpu=```cpu:option:-type``` -mtune=```cpu:option:-type``` -mbwx -mmax -mfix -mcix -mfloat-vax -mfloat-ieee -mexplicit-relocs -msmall-data -mlarge-data -msmall-text -mlarge-text -mmemory-latency=```time`
FR30 Options
FRV Options
-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 -mhard-float -msoft-float -malloc-cc -mfixed-cc -mdword -mno-dword -mdouble -mno-double -mmedia -mno-media -mmuladd -mno-muladd -mfdpic -minline-plt -mgprel-ro -multilib-library-pic -mlinked-fp -mlong-calls -malign-labels -mlibrary-pic -macc-4 -macc-8 -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move -moptimize-membar -mno-optimize-membar -mscc -mno-scc -mcond-exec -mno-cond-exec -mvliw-branch -mno-vliw-branch -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec -mno-nested-cond-exec -mtomcat-stats -mTLS -mtls -mcpu=```cpu`
GNU/Linux Options
-mglibc -muclibc -mmusl -mbionic -mandroid -tno-android-cc -tno-android-ld
H8/300 Options
-mrelax -mh -ms -mn -mexr -mno-exr -mint32 -malign-300
HPPA Options
-march=```architecture:option:-type``` -mdisable-fpregs -mdisable-indexing -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld -mfixed-range=```register:option:-range``` -mjump-in-delay -mlinker-opt -mlong-calls -mlong-load-store -mno-disable-fpregs -mno-disable-indexing -mno-fast-indirect-calls -mno-gas -mno-jump-in-delay -mno-long-load-store -mno-portable-runtime -mno-soft-float -mno-space-regs -msoft-float -mpa-risc-1-0 -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime -mschedule=```cpu:option:-type``` -mspace-regs -msio -mwsio -munix=```unix:option:-std``` -nolibdld -static -threads
IA-64 Options
-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic -mvolatile-asm-stop -mregister-names -msdata -mno-sdata -mconstant-gp -mauto-pic -mfused-madd -minline-float-divide-min-latency -minline-float-divide-max-throughput -mno-inline-float-divide -minline-int-divide-min-latency -minline-int-divide-max-throughput -mno-inline-int-divide -minline-sqrt-min-latency -minline-sqrt-max-throughput -mno-inline-sqrt -mdwarf2-asm -mearly-stop-bits -mfixed-range=```register:option:-range``` -mtls-size=```tls:option:-size``` -mtune=```cpu:option:-type``` -milp32 -mlp64 -msched-br-data-spec -msched-ar-data-spec -msched-control-spec -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec -msched-spec-ldc -msched-spec-control-ldc -msched-prefer-non-data-spec-insns -msched-prefer-non-control-spec-insns -msched-stop-bits-after-every-cycle -msched-count-spec-in-critical-path -msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost -msched-max-memory-insns-hard-limit -msched-max-memory-insns=```max:option:-insns```
LM32 Options
-mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled -msign-extend-enabled -muser-enabled
M32R/D Options
-m32r2 -m32rx -m32r -mdebug -malign-loops -mno-align-loops -missue-rate=```number` -mbranch-cost=```number` -mmodel=```code:option:-size-model-type``` -msdata=```sdata:option:-type``` -mno-flush-func -mflush-func=```name` -mno-flush-trap -mflush-trap=```number` -G num
M32C Options
-mcpu=```cpu` -msim -memregs=```number`
M680x0 Options
-march=```arch` -mcpu=```cpu` -mtune=```tune` -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 -m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 -mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 -mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort -mno-short -mhard-float -m68881 -msoft-float -mpcrel -malign-int -mstrict-align -msep-data -mno-sep-data -mshared-library-id=n -mid-shared-library -mno-id-shared-library -mxgot -mno-xgot
MCore Options
-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields -m4byte-functions -mno-4byte-functions -mcallgraph-data -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment
MeP Options
-mabsdiff -mall-opts -maverage -mbased=```n` -mbitops -mc=```n` -mclip -mconfig=```name` -mcop -mcop32 -mcop64 -mivc2 -mdc -mdiv -meb -mel -mio-volatile -ml -mleadz -mm -mminmax -mmult -mno-opts -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf -mtiny=```n`
MicroBlaze Options
-msoft-float -mhard-float -msmall-divides -mcpu=```cpu` -mmemcpy -mxl-soft-mul -mxl-soft-div -mxl-barrel-shift -mxl-pattern-compare -mxl-stack-check -mxl-gp-opt -mno-clearbss -mxl-multiply-high -mxl-float-convert -mxl-float-sqrt -mbig-endian -mlittle-endian -mxl-reorder -mxl-mode-```app:option:-model```
MIPS Options
-EL -EB -march=```arch` -mtune=```arch` -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 -mips32r3 -mips32r5 -mips32r6 -mips64 -mips64r2 -mips64r3 -mips64r5 -mips64r6 -mips16 -mno-mips16 -mflip-mips16 -minterlink-compressed -mno-interlink-compressed -minterlink-mips16 -mno-interlink-mips16 -mabi=```abi` -mabicalls -mno-abicalls -mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot -mgp32 -mgp64 -mfp32 -mfpxx -mfp64 -mhard-float -msoft-float -mno-float -msingle-float -mdouble-float -modd-spreg -mno-odd-spreg -mabs=```mode` -mnan=```encoding` -mdsp -mno-dsp -mdspr2 -mno-dspr2 -mmcu -mmno-mcu -meva -mno-eva -mvirt -mno-virt -mxpa -mno-xpa -mmicromips -mno-micromips -mfpu=```fpu:option:-type``` -msmartmips -mno-smartmips -mpaired-single -mno-paired-single -mdmx -mno-mdmx -mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc -mlong64 -mlong32 -msym32 -mno-sym32 -G```num` -mlocal-sdata -mno-local-sdata -mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt -membedded-data -mno-embedded-data -muninit-const-in-rodata -mno-uninit-const-in-rodata -mcode-readable=```setting` -msplit-addresses -mno-split-addresses -mexplicit-relocs -mno-explicit-relocs -mcheck-zero-division -mno-check-zero-division -mdivide-traps -mdivide-breaks -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls -mmad -mno-mad -mimadd -mno-imadd -mfused-madd -mno-fused-madd -nocpp -mfix-24k -mno-fix-24k -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 -mfix-r10000 -mno-fix-r10000 -mfix-rm7000 -mno-fix-rm7000 -mfix-vr4120 -mno-fix-vr4120 -mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 -mflush-func=```func` -mno-flush-func -mbranch-cost=```num` -mbranch-likely -mno-branch-likely -mfp-exceptions -mno-fp-exceptions -mvr4130-align -mno-vr4130-align -msynci -mno-synci -mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address
MMIX Options
-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols -melf -mbranch-predict -mno-branch-predict -mbase-addresses -mno-base-addresses -msingle-exit -mno-single-exit
MN10300 Options
-mmult-bug -mno-mult-bug -mno-am33 -mam33 -mam33-2 -mam34 -mtune=```cpu:option:-type``` -mreturn-pointer-on-d0 -mno-crt0 -mrelax -mliw -msetlb
Moxie Options
MSP430 Options
-msim -masm-hex -mmcu= -mcpu= -mlarge -msmall -mrelax -mcode-region= -mdata-region= -mhwmult= -minrt
NDS32 Options
-mbig-endian -mlittle-endian -mreduced-regs -mfull-regs -mcmov -mno-cmov -mperf-ext -mno-perf-ext -mv3push -mno-v3push -m16bit -mno-16bit -misr-vector-size=```num` -mcache-block-size=```num` -march=```arch` -mcmodel=```code:option:-model``` -mctor-dtor -mrelax
Nios II Options
-G num -mgpopt=```option` -mgpopt -mno-gpopt -mel -meb -mno-bypass-cache -mbypass-cache -mno-cache-volatile -mcache-volatile -mno-fast-sw-div -mfast-sw-div -mhw-mul -mno-hw-mul -mhw-mulx -mno-hw-mulx -mno-hw-div -mhw-div -mcustom-```insn``=``N` -mno-custom-```insn` -mcustom-fpu-cfg=```name` -mhal -msmallc -msys-crt0=```name` -msys-lib=```name`
Nvidia PTX Options
PDP-11 Options
-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 -mbcopy -mbcopy-builtin -mint32 -mno-int16 -mint16 -mno-int32 -mfloat32 -mno-float64 -mfloat64 -mno-float32 -mabshi -mno-abshi -mbranch-expensive -mbranch-cheap -munix-asm -mdec-asm
picoChip Options
-mae=```ae_type` -mvliw-lookahead=```N` -msymbol-as-address -mno-inefficient-warnings
PowerPC Options See RS/6000 and PowerPC Options.
RL78 Options
-msim -mmul=none -mmul=g13 -mmul=g14 -mallregs -mcpu=g10 -mcpu=g13 -mcpu=g14 -mg10 -mg13 -mg14 -m64bit-doubles -m32bit-doubles
RS/6000 and PowerPC Options
-mcpu=```cpu:option:-type``` -mtune=```cpu:option:-type``` -mcmodel=```code:option:-model``` -mpowerpc64 -maltivec -mno-altivec -mpowerpc-gpopt -mno-powerpc-gpopt -mpowerpc-gfxopt -mno-powerpc-gfxopt -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd -mfprnd -mno-fprnd -mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc -m64 -m32 -mxl-compat -mno-xl-compat -mpe -malign-power -malign-natural -msoft-float -mhard-float -mmultiple -mno-multiple -msingle-float -mdouble-float -msimple-fpu -mstring -mno-string -mupdate -mno-update -mavoid-indexed-addresses -mno-avoid-indexed-addresses -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align -mstrict-align -mno-strict-align -mrelocatable -mno-relocatable -mrelocatable-lib -mno-relocatable-lib -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian -mdynamic-no-pic -maltivec -mswdiv -msingle-pic-base -mprioritize-restricted-insns=```priority` -msched-costly-dep=```dependence_type` -minsert-sched-nops=```scheme` -mcall-sysv -mcall-netbsd -maix-struct-return -msvr4-struct-return -mabi=```abi:option:-type``` -msecure-plt -mbss-plt -mblock-move-inline-limit=```num` -misel -mno-isel -misel=yes -misel=no -mspe -mno-spe -mspe=yes -mspe=no -mpaired -mgen-cell-microcode -mwarn-cell-microcode -mvrsave -mno-vrsave -mmulhw -mno-mulhw -mdlmzb -mno-dlmzb -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double -mprototype -mno-prototype -msim -mmvme -mads -myellowknife -memb -msdata -msdata=```opt` -mvxworks -G num -pthread -mrecip -mrecip=```opt` -mno-recip -mrecip-precision -mno-recip-precision -mveclibabi=```type` -mfriz -mno-friz -mpointers-to-nested-functions -mno-pointers-to-nested-functions -msave-toc-indirect -mno-save-toc-indirect -mpower8-fusion -mno-mpower8-fusion -mpower8-vector -mno-power8-vector -mcrypto -mno-crypto -mdirect-move -mno-direct-move -mquad-memory -mno-quad-memory -mquad-memory-atomic -mno-quad-memory-atomic -mcompat-align-parm -mno-compat-align-parm -mupper-regs-df -mno-upper-regs-df -mupper-regs-sf -mno-upper-regs-sf -mupper-regs -mno-upper-regs
RX Options
-m64bit-doubles -m32bit-doubles -fpu -nofpu -mcpu= -mbig-endian-data -mlittle-endian-data -msmall-data -msim -mno-sim -mas100-syntax -mno-as100-syntax -mrelax -mmax-constant-size= -mint-register= -mpid -mallow-string-insns -mno-allow-string-insns -mno-warn-multiple-fast-interrupts -msave-acc-in-interrupts
S/390 and zSeries Options
-mtune=```cpu:option:-type``` -march=```cpu:option:-type``` -mhard-float -msoft-float -mhard-dfp -mno-hard-dfp -mlong-double-64 -mlong-double-128 -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack -msmall-exec -mno-small-exec -mmvcle -mno-mvcle -m64 -m31 -mdebug -mno-debug -mesa -mzarch -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard -mhotpatch=```halfwords`,``halfwords``
Score Options
-meb -mel -mnhwloop -muls -mmac -mscore5 -mscore5u -mscore7 -mscore7d
SH Options
-m1 -m2 -m2e -m2a-nofpu -m2a-single-only -m2a-single -m2a -m3 -m3e -m4-nofpu -m4-single-only -m4-single -m4 -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al -m5-64media -m5-64media-nofpu -m5-32media -m5-32media-nofpu -m5-compact -m5-compact-nofpu -mb -ml -mdalign -mrelax -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave -mieee -mno-ieee -mbitops -misize -minline-ic_invalidate -mpadstruct -mspace -mprefergot -musermode -multcost=```number` -mdiv=```strategy` -mdivsi3_libfunc=```name` -mfixed-range=```register:option:-range``` -mindexed-addressing -mgettrcost=```number` -mpt-fixed -maccumulate-outgoing-args -minvalid-symbols -matomic-model=```atomic:option:-model``` -mbranch-cost=```num` -mzdcbranch -mno-zdcbranch -mcbranch-force-delay-slot -mfused-madd -mno-fused-madd -mfsca -mno-fsca -mfsrra -mno-fsrra -mpretend-cmove -mtas
Solaris 2 Options
-mclear-hwcap -mno-clear-hwcap -mimpure-text -mno-impure-text -pthreads -pthread
SPARC Options
-mcpu=```cpu:option:-type``` -mtune=```cpu:option:-type``` -mcmodel=```code:option:-model``` -mmemory-model=```mem:option:-model``` -m32 -m64 -mapp-regs -mno-app-regs -mfaster-structs -mno-faster-structs -mflat -mno-flat -mfpu -mno-fpu -mhard-float -msoft-float -mhard-quad-float -msoft-quad-float -mstack-bias -mno-stack-bias -munaligned-doubles -mno-unaligned-doubles -muser-mode -mno-user-mode -mv8plus -mno-v8plus -mvis -mno-vis -mvis2 -mno-vis2 -mvis3 -mno-vis3 -mcbcond -mno-cbcond -mfmaf -mno-fmaf -mpopc -mno-popc -mfix-at697f -mfix-ut699
SPU Options
-mwarn-reloc -merror-reloc -msafe-dma -munsafe-dma -mbranch-hints -msmall-mem -mlarge-mem -mstdmain -mfixed-range=```register:option:-range``` -mea32 -mea64 -maddress-space-conversion -mno-address-space-conversion -mcache-size=```cache:option:-size``` -matomic-updates -mno-atomic-updates
System V Options
-Qy -Qn -YP,```paths` -Ym,```dir`
TILE-Gx Options
-mcpu=CPU -m32 -m64 -mbig-endian -mlittle-endian -mcmodel=```code:option:-model```
TILEPro Options
-mcpu=```cpu` -m32
V850 Options
-mlong-calls -mno-long-calls -mep -mno-ep -mprolog-function -mno-prolog-function -mspace -mtda=```n` -msda=```n` -mzda=```n` -mapp-regs -mno-app-regs -mdisable-callt -mno-disable-callt -mv850e2v3 -mv850e2 -mv850e1 -mv850es -mv850e -mv850 -mv850e3v5 -mloop -mrelax -mlong-jumps -msoft-float -mhard-float -mgcc-abi -mrh850-abi -mbig-switch
VAX Options
Visium Options
-mdebug -msim -mfpu -mno-fpu -mhard-float -msoft-float -mcpu=```cpu:option:-type``` -mtune=```cpu:option:-type``` -msv-mode -muser-mode
VMS Options
-mvms-return-codes -mdebug-main=```prefix` -mmalloc64 -mpointer-size=```size`
VxWorks Options
-mrtp -non-static -Bstatic -Bdynamic -Xbind-lazy -Xbind-now
x86 Options
-mtune=```cpu:option:-type``` -march=```cpu:option:-type``` -mtune-ctrl=```feature:option:-list``` -mdump-tune-features -mno-default -mfpmath=```unit` -masm=```dialect` -mno-fancy-math-387 -mno-fp-ret-in-387 -msoft-float -mno-wide-multiply -mrtd -malign-double -mpreferred-stack-boundary=```num` -mincoming-stack-boundary=```num` -mcld -mcx16 -msahf -mmovbe -mcrc32 -mrecip -mrecip=```opt` -mvzeroupper -mprefer-avx128 -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx -mavx2 -mavx512f -mavx512pf -mavx512er -mavx512cd -msha -maes -mpclmul -mfsgsbase -mrdrnd -mf16c -mfma -mprefetchwt1 -mclflushopt -mxsavec -mxsaves -msse4a -m3dnow -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop -mlzcnt -mbmi2 -mfxsr -mxsave -mxsaveopt -mrtm -mlwp -mmpx -mthreads -mno-align-stringops -minline-all-stringops -minline-stringops-dynamically -mstringop-strategy=```alg` -mmemcpy-strategy=```strategy` -mmemset-strategy=```strategy` -mpush-args -maccumulate-outgoing-args -m128bit-long-double -m96bit-long-double -mlong-double-64 -mlong-double-80 -mlong-double-128 -mregparm=```num` -msseregparm -mveclibabi=```type` -mvect8-ret-in-mem -mpc32 -mpc64 -mpc80 -mstackrealign -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs -mcmodel=```code:option:-model``` -mabi=```name` -maddress-mode=```mode` -m32 -m64 -mx32 -m16 -mlarge-data-threshold=```num` -msse2avx -mfentry -mrecord-mcount -mnop-mcount -m8bit-idiv -mavx256-split-unaligned-load -mavx256-split-unaligned-store -malign-data=```type` -mstack-protector-guard=```guard`
x86 Windows Options
-mconsole -mcygwin -mno-cygwin -mdll -mnop-fun-dllimport -mthread -municode -mwin32 -mwindows -fno-set-stack-executable
Xstormy16 Options
Xtensa Options
-mconst16 -mno-const16 -mfused-madd -mno-fused-madd -mforce-no-pic -mserialize-volatile -mno-serialize-volatile -mtext-section-literals -mno-text-section-literals -mtarget-align -mno-target-align -mlongcalls -mno-longcalls
zSeries Options See S/390 and zSeries Options.
Code Gen OptionsOptions for Code Generation Conventions.
-fcall-saved-```reg` -fcall-used-```reg` -ffixed-```reg` -fexceptions -fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables -fasynchronous-unwind-tables -fno-gnu-unique -finhibit-size-directive -finstrument-functions -finstrument-functions-exclude-function-list=```sym`,``sym``,... -finstrument-functions-exclude-file-list=```file`,``file``,... -fno-common -fno-ident -fpcc-struct-return -fpic -fPIC -fpie -fPIE -fno-plt -fno-jump-tables -frecord-gcc-switches -freg-struct-return -fshort-enums -fshort-double -fshort-wchar -fverbose-asm -fpack-struct[=```n`] -fstack-check -fstack-limit-register=```reg` -fstack-limit-symbol=```sym` -fno-stack-limit -fsplit-stack -fleading-underscore -ftls-model=```model` -fstack-reuse=```reuse_level` -ftrapv -fwrapv -fbounds-check -fvisibility=`[default|internal|hidden|protected] :option:-fstrict-volatile-bitfields` -fsync-libcalls
:: _overall-options:
Compilation can involve up to four stages: preprocessing, compilation proper, assembly and linking, always in that order. GCC is capable of preprocessing and compiling several files either into several assembler input files, or into one assembler input file; then each assembler input file produces an object file, and linking combines all the object files (those newly compiled, and those specified as input) into an executable file.
For any given input file, the file name suffix determines what kind of compilation is done:
file.c C source code that must be preprocessed.
file.i C source code that should not be preprocessed.
file.ii C++ source code that should not be preprocessed.
file.m Objective-C source code. Note that you must link with the libobjc library to make an Objective-C program work.
file.mi Objective-C source code that should not be preprocessed.
file.mm file.M Objective-C++ source code. Note that you must link with the libobjc library to make an Objective-C++ program work. Note that .M refers to a literal capital M
file.mii Objective-C++ source code that should not be preprocessed.
file.h C, C++, Objective-C or Objective-C++ header file to be turned into a precompiled header (default), or C, C++ header file to be turned into an Ada spec (via the -fdump-ada-spec switch).
file.cc file.cp file.cxx file.cpp file.CPP file.c++ file.C C++ source code that must be preprocessed. Note that in .cxx, the last two letters must both be literally x. Likewise, .C refers to a literal capital C
file.mm file.M Objective-C++ source code that must be preprocessed.
file.mii Objective-C++ source code that should not be preprocessed.
file.hh file.H file.hp file.hxx file.hpp file.HPP file.h++ file.tcc C++ header file to be turned into a precompiled header or Ada spec.
file.f file.for file.ftn Fixed form Fortran source code that should not be preprocessed.
file.F file.FOR file.fpp file.FPP file.FTN Fixed form Fortran source code that must be preprocessed (with the traditional preprocessor).
file.f90 file.f95 file.f03 file.f08 Free form Fortran source code that should not be preprocessed.
file.F90 file.F95 file.F03 file.F08 Free form Fortran source code that must be preprocessed (with the traditional preprocessor).
file.go Go source code.
file.ads Ada source code file that contains a library unit declaration (a declaration of a package, subprogram, or generic, or a generic instantiation), or a library unit renaming declaration (a package, generic, or subprogram renaming declaration). Such files are also called specs.
file.adb Ada source code file containing a library unit body (a subprogram or package body). Such files are also called bodies.
file.s Assembler code.
file.S file.sx Assembler code that must be preprocessed.
other An object file to be fed straight into linking. Any file name with no recognized suffix is treated this way.
You can specify the input language explicitly with the -x option:
-x language Specify explicitly the language for the following input files (rather than letting the compiler choose a default based on the file name suffix). This option applies to all following input files until the next -x option. Possible values for language are:
c c-header cpp-output
c++ c++-header c++-cpp-output
objective-c objective-c-header objective-c-cpp-output
objective-c++ objective-c++-header objective-c++-cpp-output
assembler assembler-with-cpp
ada
f77 f77-cpp-input f95 f95-cpp-input
go
java
Turn off any specification of a language, so that subsequent files are handled according to their file name suffixes (as they are if -x has not been used at all).
Normally the gcc program exits with the code of 1 if any phase of the compiler returns a non-success return code. If you specify -pass-exit-codes, the gcc program instead returns with the numerically highest error produced by any phase returning an error indication. The C, C++, and Fortran front ends return 4 if an internal compiler error is encountered.
If you only want some of the stages of compilation, you can use -x (or filename suffixes) to tell gcc where to start, and one of the options -c, -S, or -E to say where gcc is to stop. Note that some combinations (for example, -x cpp-output -E) instruct gcc to do nothing at all.
Compile or assemble the source files, but do not link. The linking stage simply is not done. The ultimate output is in the form of an object file for each source file.
By default, the object file name for a source file is made by replacing the suffix .c, .i, .s, etc., with .o.
Unrecognized input files, not requiring compilation or assembly, are ignored.
Stop after the stage of compilation proper; do not assemble. The output is in the form of an assembler code file for each non-assembler input file specified.
By default, the assembler file name for a source file is made by replacing the suffix .c, .i, etc., with .s.
Input files that dont require compilation are ignored.
Stop after the preprocessing stage; do not run the compiler proper. The output is in the form of preprocessed source code, which is sent to the standard output.
Input files that dont require preprocessing are ignored.
-o file
Place output in file file. This applies to whatever sort of output is being produced, whether it be an executable file, an object file, an assembler file or preprocessed C code.
If -o is not specified, the default is to put an executable file in a.out, the object file for source.``suffix`` in source.o, its assembler file in source.s, a precompiled header file in source.``suffix``.gch, and all preprocessed C source on standard output.
Print (on standard error output) the commands executed to run the stages of compilation. Also print the version number of the compiler driver program and of the preprocessor and the compiler proper.
Like -v except the commands are not executed and arguments are quoted unless they contain only alphanumeric characters or ./-_. This is useful for shell scripts to capture the driver-generated command lines.
Use pipes rather than temporary files for communication between the various stages of compilation. This fails to work on some systems where the assembler is unable to read from a pipe; but the GNU assembler has no trouble.
Print (on the standard output) a description of the command-line options understood by gcc. If the -v option is also specified then --help is also passed on to the various processes invoked by gcc, so that they can display the command-line options they accept. If the -Wextra option has also been specified (prior to the --help option), then command-line options that have no documentation associated with them are also displayed.
Print (on the standard output) a description of target-specific command-line options for each tool. For some targets extra target-specific information may also be printed.
–help={class``|[^]``qualifier}[,...]
Print (on the standard output) a description of the command-line options understood by the compiler that fit into all specified classes and qualifiers. These are the supported classes:
optimizers Display all of the optimization options supported by the compiler.
warnings Display all of the options controlling warning messages produced by the compiler.
target Display target-specific options. Unlike the --target-help option however, target-specific options of the linker and assembler are not displayed. This is because those tools do not currently support the extended --help= syntax.
params Display the values recognized by the --param option.
language Display the options supported for language, where language is the name of one of the languages supported in this version of GCC
common Display the options that are common to all languages.
These are the supported qualifiers:
undocumented Display only those options that are undocumented.
joined Display options taking an argument that appears after an equal sign in the same continuous piece of text, such as: –help=target.
separate Display options taking an argument that appears as a separate word following the original option, such as: -o output-file.
Thus for example to display all the undocumented target-specific switches supported by the compiler, use:
--help=target,undocumented
The sense of a qualifier can be inverted by prefixing it with the ^ character, so for example to display all binary warning options (i.e., ones that are either on or off and that do not take an argument) that have a description, use:
--help=warnings,^joined,^undocumented
The argument to --help= should not consist solely of inverted qualifiers.
Combining several classes is possible, although this usually restricts the output so much that there is nothing to display. One case where it does work, however, is when one of the classes is target. For example, to display all the target-specific optimization options, use:
--help=target,optimizers
The --help= option can be repeated on the command line. Each successive use displays its requested class of options, skipping those that have already been displayed.
If the -Q option appears on the command line before the --help= option, then the descriptive text displayed by --help= is changed. Instead of describing the displayed options, an indication is given as to whether the option is enabled, disabled or set to a specific value (assuming that the compiler knows this at the point where the --help= option is used).
Here is a truncated example from the ARM port of gcc:
% gcc -Q -mabi=2 --help=target -c
The following options are target specific:
-mabi= 2
-mabort-on-noreturn [disabled]
-mapcs [disabled]
The output is sensitive to the effects of previous command-line options, so for example it is possible to find out which optimizations are enabled at -O2 by using:
Alternatively you can discover which binary optimizations are enabled by -O3 by using:
gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
diff /tmp/O2-opts /tmp/O3-opts | grep enabled
Do not expand any symbolic links, resolve references to /../ or /./, or make the path absolute when generating a relative prefix.
Display the version number and copyrights of the invoked GCC
Invoke all subcommands under a wrapper program. The name of the wrapper program and its parameters are passed as a comma separated list.
gcc -c t.c -wrapper gdb,--args
This invokes all subprograms of gcc under gdb –args, thus the invocation of cc1 is gdb –args cc1 ....
-fplugin=``name``.so
Load the plugin code in file name.so, assumed to be a shared object to be dlopend by the compiler. The base name of the shared object file is used to identify the plugin for the purposes of argument parsing (See -fplugin-arg-``name`-key``=``value` below). Each plugin should define the callback functions specified in the Plugins API.
-fplugin-arg-name-key``=``value
Define an argument called key with a value of value for the plugin called name.
-fdump-ada-spec[-slim]
For C and C++ source and include files, generate corresponding Ada specs. Generating Ada Bindings for C and C++ headersgnat_ugnGNAT Users Guide, which provides detailed documentation on this feature.
-fada-spec-parent=``unit``
In conjunction with -fdump-ada-spec[-slim] above, generate Ada specs as child units of parent unit.
-fdump-go-spec=``file``
For input files in any language, generate corresponding Go declarations in file. This generates Go const, type, var, and func declarations which may be a useful way to start writing a Go interface to code written in some other language.
file Read command-line options from file. The options read are inserted in place of the original file option. If file does not exist, or cannot be read, then the option will be treated literally, and not removed.
Options in file are separated by whitespace. A whitespace character may be included in an option by surrounding the entire option in either single or double quotes. Any character (including a backslash) may be included by prefixing the character to be included with a backslash. The file may itself contain additional file options; any such options will be processed recursively.
:: _invoking-g++:
C++ source files conventionally use one of the suffixes .C, .cc, .cpp, .CPP, .c++, .cp, or .cxx; C++ header files often use .hh, .hpp, .H, or (for shared template code) .tcc; and preprocessed C++ files use the suffix .ii. GCC recognizes files with these names and compiles them as C++ programs even if you call the compiler the same way as for compiling C programs (usually with the name gcc).
However, the use of gcc does not add the C++ library. g++ is a program that calls GCC and automatically specifies linking against the C++ library. It treats .c, .h and .i files as C++ source files instead of C source files unless -x is used. This program is also useful when precompiling a C header file with a .h extension for use in C++ compilations. On many systems, g++ is also installed with the name c++.
invoking g++ When you compile C++ programs, you may specify many of the same command-line options that you use for compiling programs in any language; or command-line options meaningful for C and related languages; or options that are meaningful only for C++ programs. C Dialect OptionsOptions Controlling C Dialect, for explanations of options for languages related to C C++ Dialect OptionsOptions Controlling C++ Dialect, for explanations of options that are meaningful only for C++ programs.
:: _c-dialect-options:
The following options control the dialect of C (or languages derived from C, such as C++, Objective-C and Objective-C++) that the compiler accepts:
In C mode, this is equivalent to -std=c90. In C++ mode, it is equivalent to -std=c++98.
This turns off certain features of GCC that are incompatible with ISO C90 (when compiling C code), or of standard C++ (when compiling C++ code), such as the asm and typeof keywords, and predefined macros such as unix and vax that identify the type of system you are using. It also enables the undesirable and rarely used ISO trigraph feature. For the C compiler, it disables recognition of C++ style // comments as well as the inline keyword.
The alternate keywords __asm__, __extension__, __inline__ and __typeof__ continue to work despite -ansi. You would not want to use them in an ISO C program, of course, but it is useful to put them in header files that might be included in compilations done with -ansi. Alternate predefined macros such as __unix__ and __vax__ are also available, with or without -ansi.
The -ansi option does not cause non-ISO programs to be rejected gratuitously. For that, -Wpedantic is required in addition to -ansi. Warning Options.
The macro __STRICT_ANSI__ is predefined when the -ansi option is used. Some header files may notice this macro and refrain from declaring certain functions or defining certain macros that the ISO standard doesnt call for; this is to avoid interfering with any programs that might use these names for other things.
Functions that are normally built in but do not have semantics defined by ISO C (such as alloca and ffs) are not built-in functions when -ansi is used. Other BuiltinsOther built-in functions provided by GCC, for details of the functions affected.
Determine the language standard. StandardsLanguage Standards Supported by GCC, for details of these standard versions. This option is currently only supported when compiling C or C++.
The compiler can accept several base standards, such as c90 or c++98, and GNU dialects of those standards, such as gnu90 or gnu++98. When a base standard is specified, the compiler accepts all programs following that standard plus those using GNU extensions that do not contradict it. For example, -std=c90 turns off certain features of GCC that are incompatible with ISO C90, such as the asm and typeof keywords, but not other GNU extensions that do not have a meaning in ISO C90, such as omitting the middle term of a ?: expression. On the other hand, when a GNU dialect of a standard is specified, all features supported by the compiler are enabled, even when those features change the meaning of the base standard. As a result, some strict-conforming programs may be rejected. The particular standard is used by -Wpedantic to identify which features are GNU extensions given that version of the standard. For example -std=gnu90 -Wpedantic warns about C++ style // comments, while -std=gnu99 -Wpedantic does not.
A value for this option must be provided; possible values are
Support all ISO C90 programs (certain GNU extensions that conflict with ISO C90 are disabled). Same as -ansi for C code.
ISO C90 as modified in amendment 1.
ISO C99. This standard is substantially completely supported, modulo bugs and floating-point issues (mainly but not entirely relating to optional C99 features from Annexes F and G). See http://gcc.gnu.org/c99status.html for more information. The names c9x and iso9899:199x are deprecated.
ISO C11, the 2011 revision of the ISO C standard. This standard is substantially completely supported, modulo bugs, floating-point issues (mainly but not entirely relating to optional C11 features from Annexes F and G) and the optional Annexes K (Bounds-checking interfaces) and L (Analyzability). The name c1x is deprecated.
GNU dialect of ISO C90 (including some C99 features).
GNU dialect of ISO C99. The name gnu9x is deprecated.
GNU dialect of ISO C11. This is the default for C code. The name gnu1x is deprecated.
The 1998 ISO C++ standard plus the 2003 technical corrigendum and some additional defect reports. Same as -ansi for C++ code.
GNU dialect of -std=c++98. This is the default for C++ code.
The 2011 ISO C++ standard plus amendments. The name c++0x is deprecated.
GNU dialect of -std=c++11. The name gnu++0x is deprecated.
The 2014 ISO C++ standard plus amendments. The name c++1y is deprecated.
GNU dialect of -std=c++14. The name gnu++1y is deprecated.
The next revision of the ISO C++ standard, tentatively planned for 2017. Support is highly experimental, and will almost certainly change in incompatible ways in future releases.
GNU dialect of -std=c++1z. Support is highly experimental, and will almost certainly change in incompatible ways in future releases.
The option -fgnu89-inline tells GCC to use the traditional GNU semantics for inline functions when in C99 mode. InlineAn Inline Function is As Fast As a Macro. Using this option is roughly equivalent to adding the gnu_inline function attribute to all inline functions (Function Attributes).
The option -fno-gnu89-inline explicitly tells GCC to use the C99 semantics for inline when in C99 or gnu99 mode (i.e., it specifies the default behavior). This option is not supported in -std=c90 or -std=gnu90 mode.
The preprocessor macros __GNUC_GNU_INLINE__ and __GNUC_STDC_INLINE__ may be used to check which semantics are in effect for inline functions. Common Predefined MacroscppThe C Preprocessor.
-aux-info filename
Output to the given filename prototyped declarations for all functions declared and/or defined in a translation unit, including those in header files. This option is silently ignored in any language other than C
Besides declarations, the file indicates, in comments, the origin of each declaration (source file and line), whether the declaration was implicit, prototyped or unprototyped (I, N for new or O for old, respectively, in the first character after the line number and the colon), and whether it came from a declaration or a definition (C or F, respectively, in the following character). In the case of function definitions, a K&R-style list of arguments followed by their declarations is also provided, inside comments, after the declaration.
Accept variadic functions without named parameters.
Although it is possible to define such a function, this is not very useful as it is not possible to read the arguments. This is only supported for C as this construct is allowed by C++.
Do not recognize asm, inline or typeof as a keyword, so that code can use these words as identifiers. You can use the keywords __asm__, __inline__ and __typeof__ instead. -ansi implies -fno-asm.
In C++, this switch only affects the typeof keyword, since asm and inline are standard keywords. You may want to use the -fno-gnu-keywords flag instead, which has the same effect. In C99 mode (-std=c99 or -std=gnu99), this switch only affects the asm and typeof keywords, since inline is a standard keyword in ISO C99.
Dont recognize built-in functions that do not begin with __builtin_ as prefix. Other BuiltinsOther built-in functions provided by GCC, for details of the functions affected, including those which are not built-in functions when -ansi or -std options for strict ISO C conformance are used because they do not have an ISO standard meaning.
GCC normally generates special code to handle certain built-in functions more efficiently; for instance, calls to alloca may become single instructions which adjust the stack directly, and calls to memcpy may become inline copy loops. The resulting code is often both smaller and faster, but since the function calls no longer appear as such, you cannot set a breakpoint on those calls, nor can you change the behavior of the functions by linking with a different library. In addition, when a function is recognized as a built-in function, GCC may use information about that function to warn about problems with calls to that function, or to generate more efficient code, even if the resulting code still contains calls to that function. For example, warnings are given with -Wformat for bad calls to printf when printf is built in and strlen is known not to modify global memory.
With the -fno-builtin-``function`` option only the built-in function function is disabled. function must not begin with __builtin_. If a function is named that is not built-in in this version of GCC, this option is ignored. There is no corresponding -fbuiltin-``function`` option; if you wish to enable built-in functions selectively when using -fno-builtin or -ffreestanding, you may define macros such as:
#define abs(n) __builtin_abs ((n))
#define strcpy(d, s) __builtin_strcpy ((d), (s))
Assert that compilation targets a hosted environment. This implies -fbuiltin. A hosted environment is one in which the entire standard library is available, and in which main has a return type of int. Examples are nearly everything except a kernel. This is equivalent to -fno-freestanding.
Assert that compilation targets a freestanding environment. This implies -fno-builtin. A freestanding environment is one in which the standard library may not exist, and program startup may not necessarily be at main. The most obvious example is an OS kernel. This is equivalent to -fno-hosted.
StandardsLanguage Standards Supported by GCC, for details of freestanding and hosted environments.
Enable handling of OpenACC directives #pragma acc in C/C++ and !$acc in Fortran. When -fopenacc is specified, the compiler generates accelerated code according to the OpenACC Application Programming Interface v2.0 http://www.openacc.org/. This option implies -pthread, and thus is only supported on targets that have support for -pthread.
Note that this is an experimental feature, incomplete, and subject to change in future versions of GCC. See https://gcc.gnu.org/wiki/OpenACC for more information.
Enable handling of OpenMP directives #pragma omp in C/C++ and !$omp in Fortran. When -fopenmp is specified, the compiler generates parallel code according to the OpenMP Application Program Interface v4.0 http://www.openmp.org/. This option implies -pthread, and thus is only supported on targets that have support for -pthread. -fopenmp implies -fopenmp-simd.
Enable handling of OpenMPs SIMD directives with #pragma omp in C/C++ and !$omp in Fortran. Other OpenMP directives are ignored.
Enable the usage of Cilk Plus language extension features for C/C++. When the option -fcilkplus is specified, enable the usage of the Cilk Plus Language extension features for C/C++. The present implementation follows ABI version 1.2. This is an experimental feature that is only partially complete, and whose interface may change in future versions of GCC as the official specification changes. Currently, all features but _Cilk_for have been implemented.
When the option -fgnu-tm is specified, the compiler generates code for the Linux variant of Intels current Transactional Memory ABI specification document (Revision 1.1, May 6 2009). This is an experimental feature whose interface may change in future versions of GCC, as the official specification changes. Please note that not all architectures are supported for this feature.
For more information on GCCs support for transactional memory, Enabling libitmThe GNU Transactional Memory LibrarylibitmGNU Transactional Memory Library.
Note that the transactional memory feature is not supported with non-call exceptions (-fnon-call-exceptions).
Accept some non-standard constructs used in Microsoft header files.
In C++ code, this allows member names in structures to be similar to previous types declarations.
typedef int UOW;
struct ABC {
UOW UOW;
};
Some cases of unnamed fields in structures and unions are only accepted with this option. Unnamed FieldsUnnamed struct/union fields within structs/unions, for details.
Note that this option is off for all targets but x86 targets using ms-abi.
Accept some non-standard constructs used in Plan 9 code.
This enables -fms-extensions, permits passing pointers to structures with anonymous fields to functions that expect pointers to elements of the type of the field, and permits referring to anonymous fields declared using a typedef. Unnamed FieldsUnnamed struct/union fields within structs/unions, for details. This is only supported for C, not C++.
Support ISO C trigraphs. The -ansi option (and -std options for strict ISO C conformance) implies -trigraphs.
Formerly, these options caused GCC to attempt to emulate a pre-standard C compiler. They are now only supported with the -E switch. The preprocessor continues to support a pre-standard mode. See the GNU CPP manual for details.
Allow conditional expressions with mismatched types in the second and third arguments. The value of such an expression is void. This option is not supported for C++.
Allow implicit conversions between vectors with differing numbers of elements and/or incompatible element types. This option should not be used for new code.
Let the type char be unsigned, like unsigned char.
Each kind of machine has a default for what char should be. It is either like unsigned char by default or like signed char by default.
Ideally, a portable program should always use signed char or unsigned char when it depends on the signedness of an object. But many programs have been written to use plain char and expect it to be signed, or expect it to be unsigned, depending on the machines they were written for. This option, and its inverse, let you make such a program work with the opposite default.
The type char is always a distinct type from each of signed char or unsigned char, even though its behavior is always just like one of those two.
Let the type char be signed, like signed char.
Note that this is equivalent to -fno-unsigned-char, which is the negative form of -funsigned-char. Likewise, the option -fno-signed-char is equivalent to -funsigned-char.
These options control whether a bit-field is signed or unsigned, when the declaration does not use either signed or unsigned. By default, such a bit-field is signed, because this is consistent: the basic integer types such as int are signed types.
:: _c++-dialect-options:
This section describes the command-line options that are only meaningful for C++ programs. You can also use most of the GNU compiler options regardless of what language your program is in. For example, you might compile a file firstClass.C like this:
g++ -g -frepo -O -c firstClass.C
In this example, only -frepo is an option meant only for C++ programs; you can use the other options with any language supported by GCC
Here is a list of options that are only for compiling C++ programs:
-fabi-version=``n``
Use version n of the C++ ABI The default is version 0.
Version 0 refers to the version conforming most closely to the C++ ABI specification. Therefore, the ABI obtained using version 0 will change in different versions of G++ as ABI bugs are fixed.
Version 1 is the version of the C++ ABI that first appeared in G++ 3.2.
Version 2 is the version of the C++ ABI that first appeared in G++ 3.4, and was the default through G++ 4.9.
Version 3 corrects an error in mangling a constant address as a template argument.
Version 4, which first appeared in G++ 4.5, implements a standard mangling for vector types.
Version 5, which first appeared in G++ 4.6, corrects the mangling of attribute const/volatile on function pointer types, decltype of a plain decl, and use of a function parameter in the declaration of another parameter.
Version 6, which first appeared in G++ 4.7, corrects the promotion behavior of C++11 scoped enums and the mangling of template argument packs, const/static_cast, prefix ++ and , and a class scope function used as a template argument.
Version 7, which first appeared in G++ 4.8, that treats nullptr_t as a builtin type and corrects the mangling of lambdas in default argument scope.
Version 8, which first appeared in G++ 4.9, corrects the substitution behavior of function types with function-cv-qualifiers.
See also -Wabi.
-fabi-compat-version=``n``
On targets that support strong aliases, G++ works around mangling changes by creating an alias with the correct mangled name when defining a symbol with an incorrect mangled name. This switch specifies which ABI version to use for the alias.
With -fabi-version=0 (the default), this defaults to 2. If another ABI version is explicitly selected, this defaults to 0.
The compatibility version is also set by -Wabi=``n``.
Turn off all access checking. This switch is mainly useful for working around bugs in the access control code.
Check that the pointer returned by operator new is non-null before attempting to modify the storage allocated. This check is normally unnecessary because the C++ standard specifies that operator new only returns 0 if it is declared throw(), in which case the compiler always checks the return value even without this option. In all other cases, when operator new has a non-empty exception specification, memory exhaustion is signalled by throwing std::bad_alloc. See also new (nothrow).
-fconstexpr-depth=``n``
Set the maximum nested evaluation depth for C++11 constexpr functions to n. A limit is needed to detect endless recursion during constant expression evaluation. The minimum specified by the standard is 512.
Enable deduction of a template type parameter as std::initializer_list from a brace-enclosed initializer list, i.e.
template <class T> auto forward(T t) -> decltype (realfn (t))
{
return realfn (t);
}
void f()
{
forward({1,2}); // call forward<std::initializer_list<int>>
}
This deduction was implemented as a possible extension to the originally proposed semantics for the C++11 standard, but was not part of the final standard, so it is disabled by default. This option is deprecated, and may be removed in a future version of G++.
Inject friend functions into the enclosing namespace, so that they are visible outside the scope of the class in which they are declared. Friend functions were documented to work this way in the old Annotated C++ Reference Manual. However, in ISO C++ a friend function that is not declared in an enclosing scope can only be found using argument dependent lookup. GCC defaults to the standard behavior.
This option is for compatibility, and may be removed in a future release of G++.
The C++ standard allows an implementation to omit creating a temporary that is only used to initialize another object of the same type. Specifying this option disables that optimization, and forces G++ to call the copy constructor in all cases.
Dont generate code to check for violation of exception specifications at run time. This option violates the C++ standard, but may be useful for reducing code size in production builds, much like defining NDEBUG. This does not give user code permission to throw exceptions in violation of the exception specifications; the compiler still optimizes based on the specifications, so throwing an unexpected exception results in undefined behavior at run time.
The C++11 and OpenMP standards allow thread_local and threadprivate variables to have dynamic (runtime) initialization. To support this, any use of such a variable goes through a wrapper function that performs any necessary initialization. When the use and definition of the variable are in the same translation unit, this overhead can be optimized away, but when the use is in a different translation unit there is significant overhead even if the variable doesnt actually need dynamic initialization. If the programmer can be sure that no use of the variable in a non-defining TU needs to trigger dynamic initialization (either because the variable is statically initialized, or a use of the variable in the defining TU will be executed before any uses in another TU), they can avoid this overhead with the -fno-extern-tls-init option.
On targets that support symbol aliases, the default is -fextern-tls-init. On targets that do not support symbol aliases, the default is -fno-extern-tls-init.
If -ffor-scope is specified, the scope of variables declared in a for-init-statement is limited to the for loop itself, as specified by the C++ standard. If -fno-for-scope is specified, the scope of variables declared in a for-init-statement extends to the end of the enclosing scope, as was the case in old versions of G++, and other (traditional) implementations of C++.
If neither flag is given, the default is to follow the standard, but to allow and give a warning for old-style code that would otherwise be invalid, or have different behavior.
Do not recognize typeof as a keyword, so that code can use this word as an identifier. You can use the keyword __typeof__ instead. -ansi implies -fno-gnu-keywords.
Never emit code for non-inline templates that are instantiated implicitly (i.e. by use); only emit code for explicit instantiations. Template Instantiation, for more information.
Dont emit code for implicit instantiations of inline templates, either. The default is to handle inlines differently so that compiles with and without optimization need the same set of explicit instantiations.
To save space, do not emit out-of-line copies of inline functions controlled by #pragma implementation. This causes linker errors if these functions are not inlined everywhere they are called.
Disable Wpedantic warnings about constructs used in MFC, such as implicit int and getting a pointer to member function via non-standard syntax.
Disable built-in declarations of functions that are not mandated by ANSI/ISO C These include ffs, alloca, _exit, index, bzero, conjf, and other related functions.
Treat a throw() exception specification as if it were a noexcept specification to reduce or eliminate the text size overhead relative to a function with no exception specification. If the function has local variables of types with non-trivial destructors, the exception specification actually makes the function smaller because the EH cleanups for those variables can be optimized away. The semantic effect is that an exception thrown out of a function with such an exception specification results in a call to terminate rather than unexpected.
Do not treat the operator name keywords and, bitand, bitor, compl, not, or and xor as synonyms as keywords.
Disable diagnostics that the standard says a compiler does not need to issue. Currently, the only such diagnostic issued by G++ is the one for a name having multiple meanings within a class.
Downgrade some diagnostics about nonconformant code from errors to warnings. Thus, using -fpermissive allows some nonconforming code to compile.
When an error message refers to a specialization of a function template, the compiler normally prints the signature of the template followed by the template arguments and any typedefs or typenames in the signature (e.g. void f(T) [with T = int] rather than void f(int)) so that its clear which template is involved. When an error message refers to a specialization of a class template, the compiler omits any template arguments that match the default template arguments for that template. If either of these behaviors make it harder to understand the error message rather than easier, you can use -fno-pretty-templates to disable them.
Enable automatic template instantiation at link time. This option also implies -fno-implicit-templates. Template Instantiation, for more information.
Disable generation of information about every class with virtual functions for use by the C++ run-time type identification features (dynamic_cast and typeid). If you dont use those parts of the language, you can save some space by using this flag. Note that exception handling uses the same information, but G++ generates it as needed. The dynamic_cast operator can still be used for casts that do not require run-time type information, i.e. casts to void * or to unambiguous base classes.
Enable the built-in global declarations
void operator delete (void *, std::size_t) noexcept;
void operator delete[] (void *, std::size_t) noexcept;
as introduced in C++14. This is useful for user-defined replacement deallocation functions that, for example, use the size of the object to make deallocation faster. Enabled by default under -std=c++14 and above. The flag -Wsized-deallocation warns about places that might want to add a definition.
Emit statistics about front-end processing at the end of the compilation. This information is generally only useful to the G++ development team.
Allow the compiler to optimize using the assumption that a value of enumerated type can only be one of the values of the enumeration (as defined in the C++ standard; basically, a value that can be represented in the minimum number of bits needed to represent all the enumerators). This assumption may not be valid if the program uses a cast to convert an arbitrary integer value to the enumerated type.
-ftemplate-backtrace-limit=``n``
Set the maximum number of template instantiation notes for a single warning or error to n. The default value is 10.
-ftemplate-depth=``n``
Set the maximum instantiation depth for template classes to n. A limit on the template instantiation depth is needed to detect endless recursions during template class instantiation. ANSI/ISO C++ conforming programs must not rely on a maximum depth greater than 17 (changed to 1024 in C++11). The default value is 900, as the compiler can run out of stack space before hitting 1024 in some situations.
Do not emit the extra code to use the routines specified in the C++ ABI for thread-safe initialization of local statics. You can use this option to reduce code size slightly in code that doesnt need to be thread-safe.
Register destructors for objects with static storage duration with the __cxa_atexit function rather than the atexit function. This option is required for fully standards-compliant handling of static destructors, but only works if your C library supports __cxa_atexit.
Dont use the __cxa_get_exception_ptr runtime routine. This causes std::uncaught_exception to be incorrect, but is necessary if the runtime routine is not available.
This switch declares that the user does not attempt to compare pointers to inline functions or methods where the addresses of the two functions are taken in different shared objects.
The effect of this is that GCC may, effectively, mark inline methods with __attribute__ ((visibility ("hidden"))) so that they do not appear in the export table of a DSO and do not require a PLT indirection when used within the DSO Enabling this option can have a dramatic effect on load and link times of a DSO as it massively reduces the size of the dynamic export table when the library makes heavy use of templates.
The behavior of this switch is not quite the same as marking the methods as hidden directly, because it does not affect static variables local to the function or cause the compiler to deduce that the function is defined in only one shared object.
You may mark a method as having a visibility explicitly to negate the effect of the switch for that method. For example, if you do want to compare pointers to a particular inline method, you might mark it as having default visibility. Marking the enclosing class with explicit visibility has no effect.
Explicitly instantiated inline methods are unaffected by this option as their linkage might otherwise cross a shared library boundary. Template Instantiation.
This flag attempts to use visibility settings to make GCCs C++ linkage model compatible with that of Microsoft Visual Studio.
The flag makes these changes to GCCs linkage model:
In new code it is better to use -fvisibility=hidden and export those classes that are intended to be externally visible. Unfortunately it is possible for code to rely, perhaps accidentally, on the Visual Studio behavior.
Among the consequences of these changes are that static data members of the same type with the same name but defined in different shared objects are different, so changing one does not change the other; and that pointers to function members defined in different shared objects may not compare equal. When this flag is given, it is a violation of the ODR to define types with the same name differently.
-fvtable-verify=[std|preinit|none]
Turn on (or off, if using -fvtable-verify=none) the security feature that verifies at run time, for every virtual call, that the vtable pointer through which the call is made is valid for the type of the object, and has not been corrupted or overwritten. If an invalid vtable pointer is detected at run time, an error is reported and execution of the program is immediately halted.
This option causes run-time data structures to be built at program startup, which are used for verifying the vtable pointers. The options std and preinit control the timing of when these data structures are built. In both cases the data structures are built before execution reaches main. Using -fvtable-verify=std causes the data structures to be built after shared libraries have been loaded and initialized. -fvtable-verify=preinit causes them to be built before shared libraries have been loaded and initialized.
If this option appears multiple times in the command line with different values specified, none takes highest priority over both std and preinit; preinit takes priority over std.
When used in conjunction with -fvtable-verify=std or -fvtable-verify=preinit, causes debug versions of the runtime functions for the vtable verification feature to be called. This flag also causes the compiler to log information about which vtable pointers it finds for each class. This information is written to a file named vtv_set_ptr_data.log in the directory named by the environment variable VTV_LOGS_DIR if that is defined or the current working directory otherwise.
Note: This feature appends data to the log file. If you want a fresh log file, be sure to delete any existing one.
This is a debugging flag. When used in conjunction with -fvtable-verify=std or -fvtable-verify=preinit, this causes the compiler to keep track of the total number of virtual calls it encounters and the number of verifications it inserts. It also counts the number of calls to certain run-time library functions that it inserts and logs this information for each compilation unit. The compiler writes this information to a file named vtv_count_data.log in the directory named by the environment variable VTV_LOGS_DIR if that is defined or the current working directory otherwise. It also counts the size of the vtable pointer sets for each class, and writes this information to vtv_class_set_sizes.log in the same directory.
Note: This feature appends data to the log files. To get fresh log files, be sure to delete any existing ones.
Do not use weak symbol support, even if it is provided by the linker. By default, G++ uses weak symbols if they are available. This option exists only for testing, and should not be used by end-users; it results in inferior code and has no benefits. This option may be removed in a future release of G++.
Do not search for header files in the standard directories specific to C++, but do still search the other standard directories. (This option is used when building the C++ library.)
In addition, these optimization, warning, and code generation options have meanings only for C++ programs:
Note
(C, Objective-C, C++ and Objective-C++ only)
When an explicit -fabi-version=``n`` option is used, causes G++ to warn when it generates code that is probably not compatible with the vendor-neutral C++ ABI Since G++ now defaults to -fabi-version=0, -Wabi has no effect unless either an older ABI version is selected (with -fabi-version=``n``) or an older compatibility version is selected (with -Wabi=``n`` or -fabi-compat-version=``n``).
Although an effort has been made to warn about all such cases, there are probably some cases that are not warned about, even though G++ is generating incompatible code. There may also be cases where warnings are emitted even though the code that is generated is compatible.
You should rewrite your code to avoid these warnings if you are concerned about the fact that code generated by G++ may not be binary compatible with code generated by other compilers.
-Wabi can also be used with an explicit version number to warn about compatibility with a particular -fabi-version level, e.g. -Wabi=2 to warn about changes relative to -fabi-version=2. Specifying a version number also sets -fabi-compat-version=``n``.
The known incompatibilities in -fabi-version=2 (which was the default from GCC 3.4 to 4.9) include:
A template with a non-type template parameter of reference type was mangled incorrectly:
extern int N;
template <int &> struct S {};
void n (S<N>) {2}
This was fixed in -fabi-version=3.
SIMD vector types declared using __attribute ((vector_size)) were mangled in a non-standard way that does not allow for overloading of functions taking vectors of different sizes.
The mangling was changed in -fabi-version=4.
__attribute ((const)) and noreturn were mangled as type qualifiers, and decltype of a plain declaration was folded away.
These mangling issues were fixed in -fabi-version=5.
Scoped enumerators passed as arguments to a variadic function are promoted like unscoped enumerators, causing va_arg to complain. On most targets this does not actually affect the parameter passing ABI, as there is no way to pass an argument smaller than int.
Also, the ABI changed the mangling of template argument packs, const_cast, static_cast, prefix increment/decrement, and a class scope function used as a template argument.
These issues were corrected in -fabi-version=6.
Lambdas in default argument scope were mangled incorrectly, and the ABI changed the mangling of nullptr_t.
These issues were corrected in -fabi-version=7.
When mangling a function type with function-cv-qualifiers, the un-qualified function type was incorrectly treated as a substitution candidate.
This was fixed in -fabi-version=8.
It also warns about psABI-related changes. The known psABI changes at this point include:
For SysV/x86-64, unions with long double members are passed in memory as specified in psABI. For example:
union U {
long double ld;
int i;
};
union U is always passed in memory.
Note
(C++ and Objective-C++ only)
Warn when a type with an ABI tag is used in a context that does not have that ABI tag. See C++ Attributes for more information about ABI tags.
Note
(C++ and Objective-C++ only)
Warn when a class seems unusable because all the constructors or destructors in that class are private, and it has neither friends nor public static member functions. Also warn if there are no non-private methods, and theres at least one private member function that isnt a constructor or destructor.
Note
(C++ and Objective-C++ only)
Warn when delete is used to destroy an instance of a class that has virtual functions and non-virtual destructor. It is unsafe to delete an instance of a derived class through a pointer to a base class if the base class does not have a virtual destructor. This warning is enabled by -Wall.
Note
(C++ and Objective-C++ only)
Warn when a string or character literal is followed by a ud-suffix which does not begin with an underscore. As a conforming extension, GCC treats such suffixes as separate preprocessing tokens in order to maintain backwards compatibility with code that uses formatting macros from <inttypes.h>. For example:
#define __STDC_FORMAT_MACROS
#include <inttypes.h>
#include <stdio.h>
int main() {
int64_t i64 = 123;
printf("My int64: %" PRId64"\n", i64);
}
In this case, PRId64 is treated as a separate preprocessing token.
This warning is enabled by default.
Note
(C++ and Objective-C++ only)
Warn when a narrowing conversion prohibited by C++11 occurs within { }, e.g.
int i = { 2.2 }; // error: narrowing from double to int
This flag is included in -Wall and -Wc++11-compat.
With -std=c++11, -Wno-narrowing suppresses the diagnostic required by the standard. Note that this does not affect the meaning of well-formed code; narrowing conversions are still considered ill-formed in SFINAE context.
Note
(C++ and Objective-C++ only)
Warn when a noexcept-expression evaluates to false because of a call to a function that does not have a non-throwing exception specification (i.e. throw() or noexcept) but is known by the compiler to never throw an exception.
Note
(C++ and Objective-C++ only)
Warn when a class has virtual functions and an accessible non-virtual destructor itself or in an accessible polymorphic base class, in which case it is possible but unsafe to delete an instance of a derived class through a pointer to the class itself or base class. This warning is automatically enabled if -Weffc++ is specified.
Note
(C++ and Objective-C++ only)
Warn when the order of member initializers given in the code does not match the order in which they must be executed. For instance:
struct A {
int i;
int j;
A(): j (0), i (1) { }
};
The compiler rearranges the member initializers for i and j to match the declaration order of the members, emitting a warning to that effect. This warning is enabled by -Wall.
Note
(C++ and Objective-C++ only)
Accept imaginary, fixed-point, or machine-defined literal number suffixes as GNU extensions. When this option is turned off these suffixes are treated as C++11 user-defined literal numeric suffixes. This is on by default for all pre-C++11 dialects and all GNU dialects: -std=c++98, -std=gnu++98, -std=gnu++11, -std=gnu++14. This option is off by default for ISO C++11 onwards (-std=c++11, ...).
The following -W... options are not affected by -Wall.
Note
(C++ and Objective-C++ only)
Warn about violations of the following style guidelines from Scott Meyers Effective C++ series of books:
This option also enables -Wnon-virtual-dtor, which is also one of the effective C++ recommendations. However, the check is extended to warn about the lack of virtual destructor in accessible non-polymorphic bases classes too.
When selecting this option, be aware that the standard library headers do not obey all of these guidelines; use grep -v to filter out those warnings.
Note
(C++ and Objective-C++ only)
Warn about the use of an uncasted NULL as sentinel. When compiling only with GCC this is a valid sentinel, as NULL is defined to __null. Although it is a null pointer constant rather than a null pointer, it is guaranteed to be of the same size as a pointer. But this use is not portable across different compilers.
Note
(C++ and Objective-C++ only)
Disable warnings when non-templatized friend functions are declared within a template. Since the advent of explicit template specification support in G++, if the name of the friend is an unqualified-id (i.e., friend foo(int)), the C++ language specification demands that the friend declare or define an ordinary, nontemplate function. (Section 14.5.3). Before G++ implemented explicit specification, unqualified-ids could be interpreted as a particular specialization of a templatized function. Because this non-conforming behavior is no longer the default behavior for G++, -Wnon-template-friend allows the compiler to check existing code for potential trouble spots and is on by default. This new compiler behavior can be turned off with -Wno-non-template-friend, which keeps the conformant compiler code but disables the helpful warning.
Note
(C++ and Objective-C++ only)
Warn if an old-style (C-style) cast to a non-void type is used within a C++ program. The new-style casts (dynamic_cast, static_cast, reinterpret_cast, and const_cast) are less vulnerable to unintended effects and much easier to search for.
Note
(C++ and Objective-C++ only)
Warn when a function declaration hides virtual functions from a base class. For example, in:
struct A {
virtual void f();
};
struct B: public A {
void f(int);
};
the A class version of f is hidden in B, and code like:
B* b;
b->f();
fails to compile.
Note
(C++ and Objective-C++ only)
Disable the diagnostic for converting a bound pointer to member function to a plain pointer.
Note
(C++ and Objective-C++ only)
Warn when overload resolution chooses a promotion from unsigned or enumerated type to a signed type, over a conversion to an unsigned type of the same size. Previous versions of G++ tried to preserve unsignedness, but the standard mandates the current behavior.
Note
(C++ and Objective-C++ only)
Disable the warning about a throw-expression that will immediately result in a call to terminate.
:: _objective-c-and-objective-c++-dialect-options:
(NOTE: This manual does not describe the Objective-C and Objective-C++ languages themselves. StandardsLanguage Standards Supported by GCC, for references.)
This section describes the command-line options that are only meaningful for Objective-C and Objective-C++ programs. You can also use most of the language-independent GNU compiler options. For example, you might compile a file some_class.m like this:
gcc -g -fgnu-runtime -O -c some_class.m
In this example, -fgnu-runtime is an option meant only for Objective-C and Objective-C++ programs; you can use the other options with any language supported by GCC
Note that since Objective-C is an extension of the C language, Objective-C compilations may also use options specific to the C front-end (e.g., -Wtraditional). Similarly, Objective-C++ compilations may use C++-specific options (e.g., -Wabi).
Here is a list of options that are only for compiling Objective-C and Objective-C++ programs:
-fconstant-string-class=``class-name``
Use class-name as the name of the class to instantiate for each literal string specified with the syntax "...". The default class name is NXConstantString if the GNU runtime is being used, and NSConstantString if the NeXT runtime is being used (see below). The -fconstant-cfstrings option, if also present, overrides the -fconstant-string-class setting and cause "..." literals to be laid out as constant CoreFoundation strings.
Generate object code compatible with the standard GNU Objective-C runtime. This is the default for most types of systems.
Generate output compatible with the NeXT runtime. This is the default for NeXT-based systems, including Darwin and Mac OS X The macro __NEXT_RUNTIME__ is predefined if (and only if) this option is used.
Assume that all Objective-C message dispatches ([receiver message:arg]) in this translation unit ensure that the receiver is not nil. This allows for more efficient entry points in the runtime to be used. This option is only available in conjunction with the NeXT runtime and ABI version 0 or 1.
-fobjc-abi-version=``n``
Use version n of the Objective-C ABI for the selected runtime. This option is currently supported only for the NeXT runtime. In that case, Version 0 is the traditional (32-bit) ABI without support for properties and other Objective-C 2.0 additions. Version 1 is the traditional (32-bit) ABI with support for properties and other Objective-C 2.0 additions. Version 2 is the modern (64-bit) ABI. If nothing is specified, the default is Version 0 on 32-bit target machines, and Version 2 on 64-bit target machines.
For each Objective-C class, check if any of its instance variables is a C++ object with a non-trivial default constructor. If so, synthesize a special - (id) .cxx_construct instance method which runs non-trivial default constructors on any such instance variables, in order, and then return self. Similarly, check if any instance variable is a C++ object with a non-trivial destructor, and if so, synthesize a special - (void) .cxx_destruct method which runs all such default destructors, in reverse order.
The - (id) .cxx_construct and - (void) .cxx_destruct methods thusly generated only operate on instance variables declared in the current Objective-C class, and not those inherited from superclasses. It is the responsibility of the Objective-C runtime to invoke all such methods in an objects inheritance hierarchy. The - (id) .cxx_construct methods are invoked by the runtime immediately after a new object instance is allocated; the - (void) .cxx_destruct methods are invoked immediately before the runtime deallocates an object instance.
As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has support for invoking the - (id) .cxx_construct and - (void) .cxx_destruct methods.
Allow fast jumps to the message dispatcher. On Darwin this is accomplished via the comm page.
Enable syntactic support for structured exception handling in Objective-C, similar to what is offered by C++ and Java. This option is required to use the Objective-C keywords try, throw, catch, finally and synchronized. This option is available with both the GNU runtime and the NeXT runtime (but not available in conjunction with the NeXT runtime on Mac OS X 10.2 and earlier).
Enable garbage collection (GC) in Objective-C and Objective-C++ programs. This option is only available with the NeXT runtime; the GNU runtime has a different garbage collection implementation that does not require special compiler flags.
For the NeXT runtime with version 2 of the ABI, check for a nil receiver in method invocations before doing the actual method call. This is the default and can be disabled using -fno-objc-nilcheck. Class methods and super calls are never checked for nil in this way no matter what this flag is set to. Currently this flag does nothing when the GNU runtime, or an older version of the NeXT runtime ABI, is used.
Conform to the language syntax of Objective-C 1.0, the language recognized by GCC 4.0. This only affects the Objective-C additions to the C/C++ language; it does not affect conformance to C/C++ standards, which is controlled by the separate C/C++ dialect option flags. When this option is used with the Objective-C or Objective-C++ compiler, any Objective-C syntax that is not recognized by GCC 4.0 is rejected. This is useful if you need to make sure that your Objective-C code can be compiled with older versions of GCC
Emit a special marker instructing ld(1) not to statically link in the resulting object file, and allow dyld(1) to load it in at run time instead. This is used in conjunction with the Fix-and-Continue debugging mode, where the object file in question may be recompiled and dynamically reloaded in the course of program execution, without the need to restart the program itself. Currently, Fix-and-Continue functionality is only available in conjunction with the NeXT runtime on Mac OS X 10.3 and later.
When compiling for the NeXT runtime, the compiler ordinarily replaces calls to objc_getClass("...") (when the name of the class is known at compile time) with static class references that get initialized at load time, which improves run-time performance. Specifying the -fzero-link flag suppresses this behavior and causes calls to objc_getClass("...") to be retained. This is useful in Zero-Link debugging mode, since it allows for individual class implementations to be modified during program execution. The GNU runtime currently always retains calls to objc_get_class("...") regardless of command-line options.
By default instance variables in Objective-C can be accessed as if they were local variables from within the methods of the class theyre declared in. This can lead to shadowing between instance variables and other variables declared either locally inside a class method or globally with the same name. Specifying the -fno-local-ivars flag disables this behavior thus avoiding variable shadowing issues.
-fivar-visibility=[public|protected|private|package]
Set the default instance variable visibility to the specified option so that instance variables declared outside the scope of any access modifier directives default to the specified visibility.
Dump interface declarations for all classes seen in the source file to a file named sourcename.decl.
Note
(Objective-C and Objective-C++ only)
Warn whenever an Objective-C assignment is being intercepted by the garbage collector.
Note
(Objective-C and Objective-C++ only)
If a class is declared to implement a protocol, a warning is issued for every method in the protocol that is not implemented by the class. The default behavior is to issue a warning for every method not explicitly implemented in the class, even if a method implementation is inherited from the superclass. If you use the -Wno-protocol option, then methods inherited from the superclass are considered to be implemented, and no warning is issued for them.
Note
(Objective-C and Objective-C++ only)
Warn if multiple methods of different types for the same selector are found during compilation. The check is performed on the list of methods in the final stage of compilation. Additionally, a check is performed for each selector appearing in a selector(...) expression, and a corresponding method for that selector has been found during compilation. Because these checks scan the method table only at the end of compilation, these warnings are not produced if the final stage of compilation is not reached, for example because an error is found during compilation, or because the -fsyntax-only option is being used.
Note
(Objective-C and Objective-C++ only)
Warn if multiple methods with differing argument and/or return types are found for a given selector when attempting to send a message using this selector to a receiver of type id or Class. When this flag is off (which is the default behavior), the compiler omits such warnings if any differences found are confined to types that share the same size and alignment.
Note
(Objective-C and Objective-C++ only)
Warn if a selector(...) expression referring to an undeclared selector is found. A selector is considered undeclared if no method with that name has been declared before the selector(...) expression, either explicitly in an interface or protocol declaration, or implicitly in an implementation section. This option always performs its checks as soon as a selector(...) expression is found, while -Wselector only performs its checks in the final stage of compilation. This also enforces the coding style convention that methods and selectors must be declared before being used.
Generate C header describing the largest structure that is passed by value, if any.
:: _language-independent-options:
Traditionally, diagnostic messages have been formatted irrespective of the output devices aspect (e.g. its width, ...). You can use the options described below to control the formatting algorithm for diagnostic messages, e.g. how many characters per line, how often source location information should be reported. Note that some language front ends may not honor these options.
-fmessage-length=``n``
Try to format error messages so that they fit on lines of about n characters. If n is zero, then no line-wrapping is done; each error message appears on a single line. This is the default for all front ends.
Only meaningful in line-wrapping mode. Instructs the diagnostic messages reporter to emit source location information once; that is, in case the message is too long to fit on a single physical line and has to be wrapped, the source location wont be emitted (as prefix) again, over and over, in subsequent continuation lines. This is the default behavior.
Only meaningful in line-wrapping mode. Instructs the diagnostic messages reporter to emit the same source location information (as prefix) for physical lines that result from the process of breaking a message which is too long to fit on a single line.
-fdiagnostics-color[=``WHEN``]
-fno-diagnostics-color
GCC_COLORS environment variable Use color in diagnostics. WHEN is never, always, or auto. The default depends on how the compiler has been configured, it can be any of the above WHEN options or also never if GCC_COLORS environment variable isnt present in the environment, and auto otherwise. auto means to use color only when the standard error is a terminal. The forms -fdiagnostics-color and -fno-diagnostics-color are aliases for -fdiagnostics-color=always and -fdiagnostics-color=never, respectively.
The colors are defined by the environment variable GCC_COLORS. Its value is a colon-separated list of capabilities and Select Graphic Rendition (SGR) substrings. SGR commands are interpreted by the terminal or terminal emulator. (See the section in the documentation of your text terminal for permitted values and their meanings as character attributes.) These substring values are integers in decimal representation and can be concatenated with semicolons. Common values to concatenate include 1 for bold, 4 for underline, 5 for blink, 7 for inverse, 39 for default foreground color, 30 to 37 for foreground colors, 90 to 97 for 16-color mode foreground colors, 38;5;0 to 38;5;255 for 88-color and 256-color modes foreground colors, 49 for default background color, 40 to 47 for background colors, 100 to 107 for 16-color mode background colors, and 48;5;0 to 48;5;255 for 88-color and 256-color modes background colors.
The default GCC_COLORS is
error=01;31:warning=01;35:note=01;36:caret=01;32:locus=01:quote=01
where 01;31 is bold red, 01;35 is bold magenta, 01;36 is bold cyan, 01;32 is bold green and 01 is bold. Setting GCC_COLORS to the empty string disables colors. Supported capabilities are as follows.
error GCC_COLORS capability SGR substring for error: markers.
warning GCC_COLORS capability SGR substring for warning: markers.
note GCC_COLORS capability SGR substring for note: markers.
caret GCC_COLORS capability SGR substring for caret line.
locus GCC_COLORS capability SGR substring for location information, file:line or file:line:column etc.
quote GCC_COLORS capability SGR substring for information printed within quotes.
By default, each diagnostic emitted includes text indicating the command-line option that directly controls the diagnostic (if such an option is known to the diagnostic machinery). Specifying the -fno-diagnostics-show-option flag suppresses that behavior.
By default, each diagnostic emitted includes the original source line and a caret ^ indicating the column. This option suppresses this information. The source line is truncated to n characters, if the -fmessage-length=n option is given. When the output is done to the terminal, the width is limited to the width given by the COLUMNS environment variable or, if not set, to the terminal width.
:: _warning-options:
Warnings are diagnostic messages that report constructions that are not inherently erroneous but that are risky or suggest there may have been an error.
The following language-independent options do not enable specific warnings but control the kinds of diagnostics produced by GCC
Check the code for syntax errors, but dont do anything beyond that.
-fmax-errors=``n``
Limits the maximum number of error messages to n, at which point GCC bails out rather than attempting to continue processing the source code. If n is 0 (the default), there is no limit on the number of error messages produced. If -Wfatal-errors is also specified, then -Wfatal-errors takes precedence over this option.
Inhibit all warning messages.
Make all warnings into errors.
Make the specified warning into an error. The specifier for a warning is appended; for example -Werror=switch turns the warnings controlled by -Wswitch into errors. This switch takes a negative form, to be used to negate -Werror for specific warnings; for example -Wno-error=switch makes -Wswitch warnings not be errors, even when -Werror is in effect.
The warning message for each controllable warning includes the option that controls the warning. That option can then be used with -Werror= and -Wno-error= as described above. (Printing of the option in the warning message can be disabled using the -fno-diagnostics-show-option flag.)
Note that specifying -Werror=```foo` automatically implies -W```foo`. However, -Wno-error=```foo` does not imply anything.
This option causes the compiler to abort compilation on the first error occurred rather than trying to keep going and printing further error messages.
You can request many specific warnings with options beginning with -W, for example -Wimplicit to request warnings on implicit declarations. Each of these specific warning options also has a negative form beginning -Wno- to turn off warnings; for example, -Wno-implicit. This manual lists only one of the two forms, whichever is not the default. For further language-specific options also refer to C++ Dialect Options and Objective-C and Objective-C++ Dialect Options.
Some options, such as -Wall and -Wextra, turn on other options, such as -Wunused, which may turn on further options, such as -Wunused-value. The combined effect of positive and negative forms is that more specific options have priority over less specific ones, independently of their position in the command-line. For options of the same specificity, the last one takes effect. Options enabled or disabled via pragmas (Diagnostic Pragmas) take effect as if they appeared at the end of the command-line.
When an unrecognized warning option is requested (e.g., -Wunknown-warning), GCC emits a diagnostic stating that the option is not recognized. However, if the -Wno- form is used, the behavior is slightly different: no diagnostic is produced for -Wno-unknown-warning unless other diagnostics are being produced. This allows the use of new -Wno- options with old compilers, but if something goes wrong, the compiler warns that an unrecognized option is present.
Issue all the warnings demanded by strict ISO C and ISO C++; reject all programs that use forbidden extensions, and some other programs that do not follow ISO C and ISO C++. For ISO C, follows the version of the ISO C standard specified by any -std option used.
Valid ISO C and ISO C++ programs should compile properly with or without this option (though a rare few require -ansi or a -std option specifying the required version of ISO C) However, without this option, certain GNU extensions and traditional C and C++ features are supported as well. With this option, they are rejected.
-Wpedantic does not cause warning messages for use of the alternate keywords whose names begin and end with __. Pedantic warnings are also disabled in the expression that follows __extension__. However, only system header files should use these escape routes; application programs should avoid them. Alternate Keywords.
Some users try to use -Wpedantic to check programs for strict ISO C conformance. They soon find that it does not do quite what they want: it finds some non-ISO practices, but not allonly those for which ISO C requires a diagnostic, and some others for which diagnostics have been added.
A feature to report any failure to conform to ISO C might be useful in some instances, but would require considerable additional work and would be quite different from -Wpedantic. We dont have plans to support such a feature in the near future.
Where the standard specified with -std represents a GNU extended dialect of C, such as gnu90 or gnu99, there is a corresponding base standard, the version of ISO C on which the GNU extended dialect is based. Warnings from -Wpedantic are given where they are required by the base standard. (It does not make sense for such warnings to be given only for features not in the specified GNU C dialect, since by definition the GNU dialects of C include all features the compiler supports with the given option, and there would be nothing to warn about.)
Give an error whenever the base standard (see -Wpedantic) requires a diagnostic, in some cases where there is undefined behavior at compile-time and in some other cases that do not prevent compilation of programs that are valid according to the standard. This is not equivalent to -Werror=pedantic, since there are errors enabled by this option and not enabled by the latter and vice versa.
This enables all the warnings about constructions that some users consider questionable, and that are easy to avoid (or modify to prevent the warning), even in conjunction with macros. This also enables some language-specific warnings described in C++ Dialect Options and Objective-C and Objective-C++ Dialect Options.
-Wall turns on the following warning flags:
-Waddress -Warray-bounds=1 (only with :option:-O2``) -Wc++11-compat -Wc++14-compat -Wchar-subscripts -Wenum-compare (in C/ObjC; this is on by default in C++) -Wimplicit-int (C and Objective:option:-C only) -Wimplicit-function-declaration (C and Objective:option:-C only) -Wcomment -Wformat -Wmain (only for C/ObjC and unless :option:-ffreestanding``) -Wmaybe-uninitialized -Wmissing-braces (only for C/ObjC) -Wnonnull -Wopenmp-simd -Wparentheses -Wpointer-sign -Wreorder -Wreturn-type -Wsequence-point -Wsign-compare (only in C++) -Wstrict-aliasing -Wstrict-overflow=1 -Wswitch -Wtrigraphs -Wuninitialized -Wunknown-pragmas -Wunused-function -Wunused-label -Wunused-value -Wunused-variable -Wvolatile-register-var
Note that some warning flags are not implied by -Wall. Some of them warn about constructions that users generally do not consider questionable, but which occasionally you might wish to check for; others warn about constructions that are necessary or hard to avoid in some cases, and there is no simple way to modify the code to suppress the warning. Some of them are enabled by -Wextra but many of them must be enabled individually.
This enables some extra warning flags that are not enabled by -Wall. (This option used to be called -W. The older name is still supported, but the newer name is more descriptive.)
-Wclobbered -Wempty-body -Wignored-qualifiers -Wmissing-field-initializers -Wmissing-parameter-type (C only) -Wold-style-declaration (C only) -Woverride-init -Wsign-compare -Wtype-limits -Wuninitialized -Wshift-negative-value -Wunused-parameter (only with :option:-Wunused`` or :option:-Wall``) -Wunused-but-set-parameter (only with :option:-Wunused`` or :option:-Wall``)
The option -Wextra also prints warning messages for the following cases:
Warn if an array subscript has type char. This is a common cause of error, as programmers often forget that this type is signed on some machines. This warning is enabled by -Wall.
Warn whenever a comment-start sequence /* appears in a /* comment, or whenever a Backslash-Newline appears in a // comment. This warning is enabled by -Wall.
Warn if feedback profiles do not match when using the -fprofile-use option. If a source file is changed between compiling with -fprofile-gen and with -fprofile-use, the files with the profile feedback can fail to match the source file and GCC cannot use the profile feedback information. By default, this warning is enabled and is treated as an error. -Wno-coverage-mismatch can be used to disable the warning or -Wno-error=coverage-mismatch can be used to disable the error. Disabling the error for this warning can result in poorly optimized code and is useful only in the case of very minor changes such as bug fixes to an existing code-base. Completely disabling the warning is not recommended.
(C, Objective-C, C++, Objective-C++ and Fortran only)
Suppress warning messages emitted by #warning directives.
Note
(C, C++, Objective-C and Objective-C++ only)
Give a warning when a value of type float is implicitly promoted to double. CPUs with a 32-bit single-precision floating-point unit implement float in hardware, but emulate double in software. On such a machine, doing computations using double values is much more expensive because of the overhead required for software emulation.
It is easy to accidentally do computations with double because floating-point literals are implicitly of type double. For example, in:
float area(float radius)
{
return 3.14159 * radius * radius;
}
the compiler performs the entire computation with double because the floating-point literal is a double.
Check calls to printf and scanf, etc., to make sure that the arguments supplied have types appropriate to the format string specified, and that the conversions specified in the format string make sense. This includes standard functions, and others specified by format attributes (Function Attributes), in the printf, scanf, strftime and strfmon (an X/Open extension, not in the C standard) families (or other target-specific families). Which functions are checked without format attributes having been specified depends on the standard version selected, and such checks of functions without the attribute specified are disabled by -ffreestanding or -fno-builtin.
The formats are checked against the format features supported by GNU libc version 2.2. These include all ISO C90 and C99 features, as well as features from the Single Unix Specification and some BSD and GNU extensions. Other library implementations may not support all these features; GCC does not support warning about features that go beyond a particular librarys limitations. However, if -Wpedantic is used with -Wformat, warnings are given about format features not in the selected standard version (but not for strfmon formats, since those are not in any version of the C standard). C Dialect OptionsOptions Controlling C Dialect.
Option -Wformat is equivalent to -Wformat=1, and -Wno-format is equivalent to -Wformat=0. Since -Wformat also checks for null format arguments for several functions, -Wformat also implies -Wnonnull. Some aspects of this level of format checking can be disabled by the options: -Wno-format-contains-nul, -Wno-format-extra-args, and -Wno-format-zero-length. -Wformat is enabled by -Wall.
If -Wformat is specified, do not warn about format strings that contain NUL bytes.
If -Wformat is specified, do not warn about excess arguments to a printf or scanf format function. The C standard specifies that such arguments are ignored.
Where the unused arguments lie between used arguments that are specified with $ operand number specifications, normally warnings are still given, since the implementation could not know what type to pass to va_arg to skip the unused arguments. However, in the case of scanf formats, this option suppresses the warning if the unused arguments are all pointers, since the Single Unix Specification says that such unused arguments are allowed.
If -Wformat is specified, do not warn about zero-length formats. The C standard specifies that zero-length formats are allowed.
Enable -Wformat plus additional format checks. Currently equivalent to -Wformat -Wformat-nonliteral -Wformat-security -Wformat-y2k.
If -Wformat is specified, also warn if the format string is not a string literal and so cannot be checked, unless the format function takes its format arguments as a va_list.
If -Wformat is specified, also warn about uses of format functions that represent possible security problems. At present, this warns about calls to printf and scanf functions where the format string is not a string literal and there are no format arguments, as in printf (foo);. This may be a security hole if the format string came from untrusted input and contains %n. (This is currently a subset of what -Wformat-nonliteral warns about, but in future warnings may be added to -Wformat-security that are not included in -Wformat-nonliteral.)
Warn about passing a null pointer for arguments marked as requiring a non-null value by the nonnull function attribute.
-Wnonnull is included in -Wall and -Wformat. It can be disabled with the -Wno-nonnull option.
Note
(C, C++, Objective-C and Objective-C++ only)
Warn about uninitialized variables that are initialized with themselves. Note this option can only be used with the -Wuninitialized option.
For example, GCC warns about i being uninitialized in the following snippet only when -Winit-self has been specified:
int f()
{
int i = i;
return i;
}
This warning is enabled by -Wall in C++.
Note
(C and Objective-C only)
Warn when a declaration does not specify a type. This warning is enabled by -Wall.
Note
(C and Objective-C only)
Give a warning whenever a function is used before being declared. In C99 mode (-std=c99 or -std=gnu99), this warning is enabled by default and it is made into an error by -pedantic-errors. This warning is also enabled by -Wall.
Note
(C and Objective-C only)
Same as -Wimplicit-int and -Wimplicit-function-declaration. This warning is enabled by -Wall.
Note
(C and C++ only)
Warn if the return type of a function has a type qualifier such as const. For ISO C such a type qualifier has no effect, since the value returned by a function is not an lvalue. For C++, the warning is only emitted for scalar types or void. ISO C prohibits qualified void return types on function definitions, so such return types always receive a warning even without this option.
This warning is also enabled by -Wextra.
Warn if the type of main is suspicious. main should be a function with external linkage, returning int, taking either zero arguments, two, or three arguments of appropriate types. This warning is enabled by default in C++ and is enabled by either -Wall or -Wpedantic.
Warn if an aggregate or union initializer is not fully bracketed. In the following example, the initializer for a is not fully bracketed, but that for b is fully bracketed. This warning is enabled by -Wall in C.
int a[2][2] = { 0, 1, 2, 3 };
int b[2][2] = { { 0, 1 }, { 2, 3 } };
This warning is enabled by -Wall.
Note
(C, C++, Objective-C and Objective-C++ only)
Warn if a user-supplied include directory does not exist.
Warn if parentheses are omitted in certain contexts, such as when there is an assignment in a context where a truth value is expected, or when operators are nested whose precedence people often get confused about.
Also warn if a comparison like x<=y<=z appears; this is equivalent to (x<=y ? 1 : 0) <= z, which is a different interpretation from that of ordinary mathematical notation.
Also warn about constructions where there may be confusion to which if statement an else branch belongs. Here is an example of such a case:
{
if (a)
if (b)
foo ();
else
bar ();
}
In C/C++, every else branch belongs to the innermost possible if statement, which in this example is if (b). This is often not what the programmer expected, as illustrated in the above example by indentation the programmer chose. When there is the potential for this confusion, GCC issues a warning when this flag is specified. To eliminate the warning, add explicit braces around the innermost if statement so there is no way the else can belong to the enclosing if. The resulting code looks like this:
{
if (a)
{
if (b)
foo ();
else
bar ();
}
}
Also warn for dangerous uses of the GNU extension to ?: with omitted middle operand. When the condition in the ?: operator is a boolean expression, the omitted value is always 1. Often programmers expect it to be a value computed inside the conditional expression instead.
This warning is enabled by -Wall.
Warn about code that may have undefined semantics because of violations of sequence point rules in the C and C++ standards.
The C and C++ standards define the order in which expressions in a C/C++ program are evaluated in terms of sequence points, which represent a partial ordering between the execution of parts of the program: those executed before the sequence point, and those executed after it. These occur after the evaluation of a full expression (one which is not part of a larger expression), after the evaluation of the first operand of a &&, ||, ? : or , (comma) operator, before a function is called (but after the evaluation of its arguments and the expression denoting the called function), and in certain other places. Other than as expressed by the sequence point rules, the order of evaluation of subexpressions of an expression is not specified. All these rules describe only a partial order rather than a total order, since, for example, if two functions are called within one expression with no sequence point between them, the order in which the functions are called is not specified. However, the standards committee have ruled that function calls do not overlap.
It is not specified when between sequence points modifications to the values of objects take effect. Programs whose behavior depends on this have undefined behavior; the C and C++ standards specify that Between the previous and next sequence point an object shall have its stored value modified at most once by the evaluation of an expression. Furthermore, the prior value shall be read only to determine the value to be stored.. If a program breaks these rules, the results on any particular implementation are entirely unpredictable.
Examples of code with undefined behavior are a = a++;, a[n] = b[n++] and a[i++] = i;. Some more complicated cases are not diagnosed by this option, and it may give an occasional false positive result, but in general it has been found fairly effective at detecting this sort of problem in programs.
The standard is worded confusingly, therefore there is some debate over the precise meaning of the sequence point rules in subtle cases. Links to discussions of the problem, including proposed formal definitions, may be found on the GCC readings page, at http://gcc.gnu.org/readings.html.
This warning is enabled by -Wall for C and C++.
Do not warn about returning a pointer (or in C++, a reference) to a variable that goes out of scope after the function returns.
Warn whenever a function is defined with a return type that defaults to int. Also warn about any return statement with no return value in a function whose return type is not void (falling off the end of the function body is considered returning without a value), and about a return statement with an expression in a function whose return type is void.
For C++, a function without return type always produces a diagnostic message, even when -Wno-return-type is specified. The only exceptions are main and functions defined in system headers.
This warning is enabled by -Wall.
Warn if shift count is negative. This warning is enabled by default.
Warn if shift count >= width of type. This warning is enabled by default.
Warn if left shifting a negative value. This warning is enabled by -Wextra in C99 and C++11 modes (and newer).
Warn whenever a switch statement has an index of enumerated type and lacks a case for one or more of the named codes of that enumeration. (The presence of a default label prevents this warning.) case labels outside the enumeration range also provoke warnings when this option is used (even if there is a default label). This warning is enabled by -Wall.
Warn whenever a switch statement does not have a default case.
Warn whenever a switch statement has an index of enumerated type and lacks a case for one or more of the named codes of that enumeration. case labels outside the enumeration range also provoke warnings when this option is used. The only difference between -Wswitch and this option is that this option gives a warning about an omitted enumeration code even if there is a default label.
Warn whenever a switch statement has an index of boolean type. It is possible to suppress this warning by casting the controlling expression to a type other than bool. For example:
switch ((int) (a == 4))
{
...
}
This warning is enabled by default for C and C++ programs.
Note
(C and C++ only)
Warn when __sync_fetch_and_nand and __sync_nand_and_fetch built-in functions are used. These functions changed semantics in GCC 4.4.
Warn if any trigraphs are encountered that might change the meaning of the program (trigraphs within comments are not warned about). This warning is enabled by -Wall.
Warn whenever a function parameter is assigned to, but otherwise unused (aside from its declaration).
To suppress this warning use the unused attribute (Variable Attributes).
This warning is also enabled by -Wunused together with -Wextra.
Warn whenever a local variable is assigned to, but otherwise unused (aside from its declaration). This warning is enabled by -Wall.
To suppress this warning use the unused attribute (Variable Attributes).
This warning is also enabled by -Wunused, which is enabled by -Wall.
Warn whenever a static function is declared but not defined or a non-inline static function is unused. This warning is enabled by -Wall.
Warn whenever a label is declared but not used. This warning is enabled by -Wall.
To suppress this warning use the unused attribute (Variable Attributes).
Note
(C, Objective-C, C++ and Objective-C++ only)
Warn when a typedef locally defined in a function is not used. This warning is enabled by -Wall.
Warn whenever a function parameter is unused aside from its declaration.
To suppress this warning use the unused attribute (Variable Attributes).
Do not warn if a caller of a function marked with attribute warn_unused_result (Function Attributes) does not use its return value. The default is -Wunused-result.
Warn whenever a local variable or non-constant static variable is unused aside from its declaration. This warning is enabled by -Wall.
To suppress this warning use the unused attribute (Variable Attributes).
Warn whenever a statement computes a result that is explicitly not used. To suppress this warning cast the unused expression to void. This includes an expression-statement or the left-hand side of a comma expression that contains no side effects. For example, an expression such as x[i,j] causes a warning, while x[(void)i,j] does not.
This warning is enabled by -Wall.
All the above -Wunused options combined.
In order to get a warning about an unused function parameter, you must either specify -Wextra -Wunused (note that -Wall implies -Wunused), or separately specify -Wunused-parameter.
Warn if an automatic variable is used without first being initialized or if a variable may be clobbered by a setjmp call. In C++, warn if a non-static reference or non-static const member appears in a class without constructors.
If you want to warn about code that uses the uninitialized value of the variable in its own initializer, use the -Winit-self option.
These warnings occur for individual uninitialized or clobbered elements of structure, union or array variables as well as for variables that are uninitialized or clobbered as a whole. They do not occur for variables or elements declared volatile. Because these warnings depend on optimization, the exact variables or elements for which there are warnings depends on the precise optimization options and version of GCC used.
Note that there may be no warning about a variable that is used only to compute a value that itself is never used, because such computations may be deleted by data flow analysis before the warnings are printed.
For an automatic variable, if there exists a path from the function entry to a use of the variable that is initialized, but there exist some other paths for which the variable is not initialized, the compiler emits a warning if it cannot prove the uninitialized paths are not executed at run time. These warnings are made optional because GCC is not smart enough to see all the reasons why the code might be correct in spite of appearing to have an error. Here is one example of how this can happen:
{
int x;
switch (y)
{
case 1: x = 1;
break;
case 2: x = 4;
break;
case 3: x = 5;
}
foo (x);
}
If the value of y is always 1, 2 or 3, then x is always initialized, but GCC doesnt know this. To suppress the warning, you need to provide a default case with assert(0) or similar code.
longjmp warnings This option also warns when a non-volatile automatic variable might be changed by a call to longjmp. These warnings as well are possible only in optimizing compilation.
The compiler sees only the calls to setjmp. It cannot know where longjmp will be called; in fact, a signal handler could call it at any point in the code. As a result, you may get a warning even when there is in fact no problem because longjmp cannot in fact be called at the place that would cause a problem.
Some spurious warnings can be avoided if you declare all the functions you use that never return as noreturn. Function Attributes.
Warn when a #pragma directive is encountered that is not understood by GCC If this command-line option is used, warnings are even issued for unknown pragmas in system header files. This is not the case if the warnings are only enabled by the -Wall command-line option.
Do not warn about misuses of pragmas, such as incorrect parameters, invalid syntax, or conflicts between pragmas. See also -Wunknown-pragmas.
This option is only active when -fstrict-aliasing is active. It warns about code that might break the strict aliasing rules that the compiler is using for optimization. The warning does not catch all cases, but does attempt to catch the more common pitfalls. It is included in -Wall. It is equivalent to -Wstrict-aliasing=3
This option is only active when -fstrict-aliasing is active. It warns about code that might break the strict aliasing rules that the compiler is using for optimization. Higher levels correspond to higher accuracy (fewer false positives). Higher levels also correspond to more effort, similar to the way -O works. -Wstrict-aliasing is equivalent to -Wstrict-aliasing=3.
Level 1: Most aggressive, quick, least accurate. Possibly useful when higher levels do not warn but -fstrict-aliasing still breaks the code, as it has very few false negatives. However, it has many false positives. Warns for all pointer conversions between possibly incompatible types, even if never dereferenced. Runs in the front end only.
Level 2: Aggressive, quick, not too precise. May still have many false positives (not as many as level 1 though), and few false negatives (but possibly more than level 1). Unlike level 1, it only warns when an address is taken. Warns about incomplete types. Runs in the front end only.
Level 3 (default for -Wstrict-aliasing): Should have very few false positives and few false negatives. Slightly slower than levels 1 or 2 when optimization is enabled. Takes care of the common pun+dereference pattern in the front end: *(int*)&some_float. If optimization is enabled, it also runs in the back end, where it deals with multiple statement cases using flow-sensitive points-to information. Only warns when the converted pointer is dereferenced. Does not warn about incomplete types.
This option is only active when -fstrict-overflow is active. It warns about cases where the compiler optimizes based on the assumption that signed overflow does not occur. Note that it does not warn about all cases where the code might overflow: it only warns about cases where the compiler implements some optimization. Thus this warning depends on the optimization level.
An optimization that assumes that signed overflow does not occur is perfectly safe if the values of the variables involved are such that overflow never does, in fact, occur. Therefore this warning can easily give a false positive: a warning about code that is not actually a problem. To help focus on important issues, several warning levels are defined. No warnings are issued for the use of undefined signed overflow when estimating how many iterations a loop requires, in particular when determining whether a loop will be executed at all.
Warn about cases that are both questionable and easy to avoid. For example, with -fstrict-overflow, the compiler simplifies x + 1 > x to 1. This level of -Wstrict-overflow is enabled by -Wall; higher levels are not, and must be explicitly requested.
Also warn about other cases where a comparison is simplified to a constant. For example: abs (x) >= 0. This can only be simplified when -fstrict-overflow is in effect, because abs (INT_MIN) overflows to INT_MIN, which is less than zero. -Wstrict-overflow (with no level) is the same as -Wstrict-overflow=2.
Also warn about other cases where a comparison is simplified. For example: x + 1 > 1 is simplified to x > 0.
Also warn about other simplifications not covered by the above cases. For example: (x * 10) / 5 is simplified to x * 2.
Also warn about cases where the compiler reduces the magnitude of a constant involved in a comparison. For example: x + 2 > y is simplified to x + 1 >= y. This is reported only at the highest warning level because this simplification applies to many comparisons, so this warning level gives a very large number of false positives.
-Wsuggest-attribute=[pure|const|noreturn|format]
Warn for cases where adding an attribute may be beneficial. The attributes currently supported are listed below.
Warn about functions that might be candidates for attributes pure, const or noreturn. The compiler only warns for functions visible in other compilation units or (in the case of pure and const) if it cannot prove that the function returns normally. A function returns normally if it doesnt contain an infinite loop or return abnormally by throwing, calling abort or trapping. This analysis requires option -fipa-pure-const, which is enabled by default at -O and higher. Higher optimization levels improve the accuracy of the analysis.
Warn about function pointers that might be candidates for format attributes. Note these are only possible candidates, not absolute ones. GCC guesses that function pointers with format attributes that are used in assignment, initialization, parameter passing or return statements should have a corresponding format attribute in the resulting type. I.e. the left-hand side of the assignment or initialization, the type of the parameter variable, or the return type of the containing function respectively should also have a format attribute to avoid the warning.
GCC also warns about function definitions that might be candidates for format attributes. Again, these are only possible candidates. GCC guesses that format attributes might be appropriate for any function that calls a function like vprintf or vscanf, but this might not always be the case, and some functions for which format attributes are appropriate may not be detected.
Warn about types with virtual methods where code quality would be improved if the type were declared with the C++11 final specifier, or, if possible, declared in an anonymous namespace. This allows GCC to more aggressively devirtualize the polymorphic calls. This warning is more effective with link time optimization, where the information about the class hierarchy graph is more complete.
Warn about virtual methods where code quality would be improved if the method were declared with the C++11 final specifier, or, if possible, its type were declared in an anonymous namespace or with the final specifier. This warning is more effective with link time optimization, where the information about the class hierarchy graph is more complete. It is recommended to first consider suggestions of -Wsuggest-final-types and then rebuild with new annotations.
Warn about overriding virtual functions that are not marked with the override keyword.
This option is only active when -ftree-vrp is active (default for -O2 and above). It warns about subscripts to arrays that are always out of bounds. This warning is enabled by -Wall.
This is the warning level of -Warray-bounds and is enabled by -Wall; higher levels are not, and must be explicitly requested.
This warning level also warns about out of bounds access for arrays at the end of a struct and for arrays accessed through pointers. This warning level may give a larger number of false positives and is deactivated by default.
Warn about boolean expression compared with an integer value different from true/false. For instance, the following comparison is always false:
int n = 5;
...
if ((n > 1) == 2) { ... }
This warning is enabled by -Wall.
Note
(C and Objective-C only)
Do not warn if type qualifiers on pointers are being discarded. Typically, the compiler warns if a const char * variable is passed to a function that takes a char * parameter. This option can be used to suppress such a warning.
Note
(C and Objective-C only)
Do not warn if type qualifiers on arrays which are pointer targets are being discarded. Typically, the compiler warns if a const int (*)[] variable is passed to a function that takes a int (*)[] parameter. This option can be used to suppress such a warning.
Note
(C and Objective-C only)
Do not warn when there is a conversion between pointers that have incompatible types. This warning is for cases not covered by -Wno-pointer-sign, which warns for pointer argument passing or assignment with different signedness.
Note
(C and Objective-C only)
Do not warn about incompatible integer to pointer and pointer to integer conversions. This warning is about implicit conversions; for explicit conversions the warnings -Wno-int-to-pointer-cast and -Wno-pointer-to-int-cast may be used.
Do not warn about compile-time integer division by zero. Floating-point division by zero is not warned about, as it can be a legitimate way of obtaining infinities and NaNs.
Print warning messages for constructs found in system header files. Warnings from system headers are normally suppressed, on the assumption that they usually do not indicate real problems and would only make the compiler output harder to read. Using this command-line option tells GCC to emit warnings from system headers as if they occurred in user code. However, note that using -Wall in conjunction with this option does not warn about unknown pragmas in system headersfor that, -Wunknown-pragmas must also be used.
Warn about trampolines generated for pointers to nested functions. A trampoline is a small piece of data or code that is created at run time on the stack when the address of a nested function is taken, and is used to call the nested function indirectly. For some targets, it is made up of data only and thus requires no special treatment. But, for most targets, it is made up of code and thus requires the stack to be made executable in order for the program to work properly.
Warn if floating-point values are used in equality comparisons.
The idea behind this is that sometimes it is convenient (for the programmer) to consider floating-point values as approximations to infinitely precise real numbers. If you are doing this, then you need to compute (by analyzing the code, or in some other way) the maximum or likely maximum error that the computation introduces, and allow for it when performing comparisons (and when producing output, but thats a different problem). In particular, instead of testing for equality, you should check to see whether the two values have ranges that overlap; and this is done with the relational operators, so equality comparisons are probably mistaken.
Note
(C and Objective-C only)
Warn about certain constructs that behave differently in traditional and ISO C Also warn about ISO C constructs that have no traditional C equivalent, and/or problematic constructs that should be avoided.
Note
(C and Objective-C only)
Warn if a prototype causes a type conversion that is different from what would happen to the same argument in the absence of a prototype. This includes conversions of fixed point to floating and vice versa, and conversions changing the width or signedness of a fixed-point argument except when the same as the default promotion.
Note
(C and Objective-C only)
Warn when a declaration is found after a statement in a block. This construct, known from C++, was introduced with ISO C99 and is by default allowed in GCC It is not supported by ISO C90. Mixed Declarations.
Warn if an undefined identifier is evaluated in an #if directive.
Do not warn whenever an #else or an #endif are followed by text.
Warn whenever a local variable or type declaration shadows another variable, parameter, type, class member (in C++), or instance variable (in Objective-C) or whenever a built-in function is shadowed. Note that in C++, the compiler warns if a local variable shadows an explicit typedef, but not if it shadows a struct/class/enum.
Note
(Objective-C only)
Do not warn whenever a local variable shadows an instance variable in an Objective-C method.
-Wlarger-than=``len``
Wlarger-than=``len`` Wlarger-than-len Warn whenever an object of larger than len bytes is defined.
-Wframe-larger-than=``len``
Warn if the size of a function frame is larger than len bytes. The computation done to determine the stack frame size is approximate and not conservative. The actual requirements may be somewhat greater than len even if you do not get a warning. In addition, any space allocated via alloca, variable-length arrays, or related constructs is not included by the compiler when determining whether or not to issue a warning.
Do not warn when attempting to free an object that was not allocated on the heap.
-Wstack-usage=``len``
Warn if the stack usage of a function might be larger than len bytes. The computation done to determine the stack usage is conservative. Any space allocated via alloca, variable-length arrays, or related constructs is included by the compiler when determining whether or not to issue a warning.
The message is in keeping with the output of -fstack-usage.
If the stack usage is fully static but exceeds the specified amount, its:
warning: stack usage is 1120 bytes
If the stack usage is (partly) dynamic but bounded, its:
warning: stack usage might be 1648 bytes
If the stack usage is (partly) dynamic and not bounded, its:
warning: stack usage might be unbounded
Warn if the loop cannot be optimized because the compiler cannot assume anything on the bounds of the loop indices. With -funsafe-loop-optimizations warn if the compiler makes such assumptions.
Note
(MinGW targets only)
When used in combination with -Wformat and -pedantic without GNU extensions, this option disables the warnings about non-ISO printf / scanf format width specifiers I32, I64, and I used on Windows targets, which depend on the MS runtime.
Warn about anything that depends on the size of a function type or of void. GNU C assigns these types a size of 1, for convenience in calculations with void * pointers and pointers to functions. In C++, warn also when an arithmetic operation involves NULL. This warning is also enabled by -Wpedantic.
Warn if a comparison is always true or always false due to the limited range of the data type, but do not warn for constant expressions. For example, warn if an unsigned variable is compared against zero with < or >=. This warning is also enabled by -Wextra.
Note
(C and Objective-C only)
Warn when a function call is cast to a non-matching type. For example, warn if a call to a function returning an integer type is cast to a pointer type.
Note
(C and Objective-C only)
Warn about features not present in ISO C90, but present in ISO C99. For instance, warn about use of variable length arrays, long long type, bool type, compound literals, designated initializers, and so on. This option is independent of the standards mode. Warnings are disabled in the expression that follows __extension__.
Note
(C and Objective-C only)
Warn about features not present in ISO C99, but present in ISO C11. For instance, warn about use of anonymous structures and unions, _Atomic type qualifier, _Thread_local storage-class specifier, _Alignas specifier, Alignof operator, _Generic keyword, and so on. This option is independent of the standards mode. Warnings are disabled in the expression that follows __extension__.
Note
(C and Objective-C only)
Warn about ISO C constructs that are outside of the common subset of ISO C and ISO C++, e.g. request for implicit conversion from void * to a pointer to non-void type.
Note
(C++ and Objective-C++ only)
Warn about C++ constructs whose meaning differs between ISO C++ 1998 and ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are keywords in ISO C++ 2011. This warning turns on -Wnarrowing and is enabled by -Wall.
Note
(C++ and Objective-C++ only)
Warn about C++ constructs whose meaning differs between ISO C++ 2011 and ISO C++ 2014. This warning is enabled by -Wall.
Warn whenever a pointer is cast so as to remove a type qualifier from the target type. For example, warn if a const char * is cast to an ordinary char *.
Also warn when making a cast that introduces a type qualifier in an unsafe way. For example, casting char ** to const char ** is unsafe, as in this example:
/* p is char ** value. */
const char **q = (const char **) p;
/* Assignment of readonly string to const char * is OK. */
*q = "string";
/* Now char** pointer points to read-only memory. */
**p = 'b';
Warn whenever a pointer is cast such that the required alignment of the target is increased. For example, warn if a char * is cast to an int * on machines where integers can only be accessed at two- or four-byte boundaries.
When compiling C, give string constants the type const char[``length]`` so that copying the address of one into a non-const char * pointer produces a warning. These warnings help you find at compile time code that can try to write into a string constant, but only if you have been very careful about using const in declarations and prototypes. Otherwise, it is just a nuisance. This is why we did not make -Wall request these warnings.
When compiling C++, warn about the deprecated conversion from string literals to char *. This warning is enabled by default for C++ programs.
Warn for variables that might be changed by longjmp or vfork. This warning is also enabled by -Wextra.
Note
(C++ and Objective-C++ only)
Warn for conditionally-supported (C++11 [intro.defs]) constructs.
Warn for implicit conversions that may alter a value. This includes conversions between real and integer, like abs (x) when x is double; conversions between signed and unsigned, like unsigned ui = -1; and conversions to smaller types, like sqrtf (M_PI). Do not warn for explicit casts like abs ((int) x) and ui = (unsigned) -1, or if the value is not changed by the conversion like in abs (2.0). Warnings about conversions between signed and unsigned integers can be disabled by using -Wno-sign-conversion.
For C++, also warn for confusing overload resolution for user-defined conversions; and conversions that never use a type conversion operator: conversions to void, the same type, a base class or a reference to them. Warnings about conversions between signed and unsigned integers are disabled by default in C++ unless -Wsign-conversion is explicitly enabled.
Note
(C++ and Objective-C++ only)
Do not warn for conversions between NULL and non-pointer types. -Wconversion-null is enabled by default.
Note
(C++ and Objective-C++ only)
Warn when a literal 0 is used as null pointer constant. This can be useful to facilitate the conversion to nullptr in C++11.
Warn when macros __TIME__, __DATE__ or __TIMESTAMP__ are encountered as they might prevent bit-wise-identical reproducible compilations.
Note
(C++ and Objective-C++ only)
Warn when deleting a pointer to incomplete type, which may cause undefined behavior at runtime. This warning is enabled by default.
Note
(C++ and Objective-C++ only)
Warn when an expression is casted to its own type.
Warn if an empty body occurs in an if, else or do while statement. This warning is also enabled by -Wextra.
Warn about a comparison between values of different enumerated types. In C++ enumeral mismatches in conditional expressions are also diagnosed and the warning is enabled by default. In C this warning is enabled by -Wall.
Note
(C, Objective-C only)
Warn if a goto statement or a switch statement jumps forward across the initialization of a variable, or jumps backward to a label after the variable has been initialized. This only warns about variables that are initialized when they are declared. This warning is only supported for C and Objective-C; in C++ this sort of branch is an error in any case.
-Wjump-misses-init is included in -Wc++-compat. It can be disabled with the -Wno-jump-misses-init option.
Warn when a comparison between signed and unsigned values could produce an incorrect result when the signed value is converted to unsigned. This warning is also enabled by -Wextra; to get the other warnings of -Wextra without this warning, use -Wextra -Wno-sign-compare.
Warn for implicit conversions that may change the sign of an integer value, like assigning a signed integer expression to an unsigned integer variable. An explicit cast silences the warning. In C, this option is enabled also by -Wconversion.
Warn for implicit conversions that reduce the precision of a real value. This includes conversions from real to integer, and from higher precision real to lower precision real values. This option is also enabled by -Wconversion.
Note
(C++ and Objective-C++ only)
Warn about a definition of an unsized deallocation function
void operator delete (void *) noexcept;
void operator delete[] (void *) noexcept;
without a definition of the corresponding sized deallocation function
void operator delete (void *, std::size_t) noexcept;
void operator delete[] (void *, std::size_t) noexcept;
or vice versa. Enabled by -Wextra along with -fsized-deallocation.
Warn for suspicious length parameters to certain string and memory built-in functions if the argument uses sizeof. This warning warns e.g. about memset (ptr, 0, sizeof (ptr)); if ptr is not an array, but a pointer, and suggests a possible fix, or about memcpy (&foo, ptr, sizeof (&foo));. This warning is enabled by -Wall.
Warn when the sizeof operator is applied to a parameter that is declared as an array in a function definition. This warning is enabled by default for C and C++ programs.
Warn for suspicious calls to the memset built-in function, if the second argument is not zero and the third argument is zero. This warns e.g.about memset (buf, sizeof buf, 0) where most probably memset (buf, 0, sizeof buf) was meant instead. The diagnostics is only emitted if the third argument is literal zero. If it is some expression that is folded to zero, a cast of zero to some type, etc., it is far less likely that the user has mistakenly exchanged the arguments and no warning is emitted. This warning is enabled by -Wall.
Warn about suspicious uses of memory addresses. These include using the address of a function in a conditional expression, such as void func(void); if (func), and comparisons against the memory address of a string literal, such as if (x == "abc"). Such uses typically indicate a programmer error: the address of a function always evaluates to true, so their use in a conditional usually indicate that the programmer forgot the parentheses in a function call; and comparisons against string literals result in unspecified behavior and are not portable in C, so they usually indicate that the programmer intended to use strcmp. This warning is enabled by -Wall.
Warn about suspicious uses of logical operators in expressions. This includes using logical operators in contexts where a bit-wise operator is likely to be expected. Also warns when the operands of a logical operator are the same:
extern int a;
if (a < 0 && a < 0) { ... }
Warn about logical not used on the left hand side operand of a comparison. This option does not warn if the RHS operand is of a boolean type. Its purpose is to detect suspicious code like the following:
int a;
...
if (!a > 1) { ... }
It is possible to suppress the warning by wrapping the LHS into parentheses:
if ((!a) > 1) { ... }
This warning is enabled by -Wall.
Warn if any functions that return structures or unions are defined or called. (In languages where you can return an array, this also elicits a warning.)
Warn if in a loop with constant number of iterations the compiler detects undefined behavior in some statement during one or more of the iterations.
Do not warn if an unexpected __attribute__ is used, such as unrecognized attributes, function attributes applied to variables, etc. This does not stop errors for incorrect use of supported attributes.
Do not warn if certain built-in macros are redefined. This suppresses warnings for redefinition of __TIMESTAMP__, __TIME__, __DATE__, __FILE__, and __BASE_FILE__.
Note
(C and Objective-C only)
Warn if a function is declared or defined without specifying the argument types. (An old-style function definition is permitted without a warning if preceded by a declaration that specifies the argument types.)
Note
(C and Objective-C only)
Warn for obsolescent usages, according to the C Standard, in a declaration. For example, warn if storage-class specifiers like static are not the first things in a declaration. This warning is also enabled by -Wextra.
Note
(C and Objective-C only)
Warn if an old-style function definition is used. A warning is given even if there is a previous prototype.
Note
(C and Objective-C only)
A function parameter is declared without a type specifier in K&R-style functions:
void foo(bar) { }
This warning is also enabled by -Wextra.
Note
(C and Objective-C only)
Warn if a global function is defined without a previous prototype declaration. This warning is issued even if the definition itself provides a prototype. Use this option to detect global functions that do not have a matching prototype declaration in a header file. This option is not valid for C++ because all function declarations provide prototypes and a non-matching declaration declares an overload rather than conflict with an earlier declaration. Use -Wmissing-declarations to detect missing declarations in C++.
Warn if a global function is defined without a previous declaration. Do so even if the definition itself provides a prototype. Use this option to detect global functions that are not declared in header files. In C, no warnings are issued for functions with previous non-prototype declarations; use -Wmissing-prototypes to detect missing prototypes. In C++, no warnings are issued for function templates, or for inline functions, or for functions in anonymous namespaces.
Warn if a structures initializer has some fields missing. For example, the following code causes such a warning, because x.h is implicitly zero:
struct s { int f, g, h; };
struct s x = { 3, 4 };
This option does not warn about designated initializers, so the following modification does not trigger a warning:
struct s { int f, g, h; };
struct s x = { .f = 3, .g = 4 };
In C++ this option does not warn either about the empty { } initializer, for example:
struct s { int f, g, h; };
s x = { };
This warning is included in -Wextra. To get other -Wextra warnings without this one, use -Wextra -Wno-missing-field-initializers.
Do not warn if a multicharacter constant (‘FOOF’) is used. Usually they indicate a typo in the users code, as they have implementation-defined values, and should not be used in portable code.
-Wnormalized[=<none|id|nfc|nfkc>]
In ISO C and ISO C++, two identifiers are different if they are different sequences of characters. However, sometimes when characters outside the basic ASCII character set are used, you can have two different character sequences that look the same. To avoid confusion, the ISO 10646 standard sets out some normalization rules which when applied ensure that two sequences that look the same are turned into the same sequence. GCC can warn you if you are using identifiers that have not been normalized; this option controls that warning.
There are four levels of warning supported by GCC The default is -Wnormalized=nfc, which warns about any identifier that is not in the ISO 10646 C normalized form, NFC. NFC is the recommended form for most uses. It is equivalent to -Wnormalized.
Unfortunately, there are some characters allowed in identifiers by ISO C and ISO C++ that, when turned into NFC, are not allowed in identifiers. That is, theres no way to use these symbols in portable ISO C or C++ and have all your identifiers in NFC -Wnormalized=id suppresses the warning for these characters. It is hoped that future versions of the standards involved will correct this, which is why this option is not the default.
You can switch the warning off for all characters by writing -Wnormalized=none or -Wno-normalized. You should only do this if you are using some other normalization scheme (like D), because otherwise you can easily create bugs that are literally impossible to see.
Some characters in ISO 10646 have distinct meanings but look identical in some fonts or display methodologies, especially once formatting has been applied. For instance \u207F, SUPERSCRIPT LATIN SMALL LETTER N, displays just like a regular n that has been placed in a superscript. ISO 10646 defines the NFKC normalization scheme to convert all these into a standard form as well, and GCC warns if your code is not in NFKC if you use -Wnormalized=nfkc. This warning is comparable to warning about every identifier that contains the letter O because it might be confused with the digit 0, and so is not the default, but may be useful as a local coding convention if the programming environment cannot be fixed to display these characters distinctly.
Do not warn about usage of deprecated features. Deprecated Features.
Do not warn about uses of functions (Function Attributes), variables (Variable Attributes), and types (Type Attributes) marked as deprecated by using the deprecated attribute.
Do not warn about compile-time overflow in constant expressions.
Warn about One Definition Rule violations during link-time optimization. Requires -flto-odr-type-merging to be enabled. Enabled by default.
Warn if the vectorizer cost model overrides the OpenMP or the Cilk Plus simd directive set by user. The -fsimd-cost-model=unlimited option can be used to relax the cost model.
Note
(C and Objective-C only)
Warn if an initialized field without side effects is overridden when using designated initializers (Designated InitsDesignated Initializers).
This warning is included in -Wextra. To get other -Wextra warnings without this one, use -Wextra -Wno-override-init.
Note
(C and Objective-C only)
Warn if an initialized field with side effects is overridden when using designated initializers (Designated InitsDesignated Initializers). This warning is enabled by default.
Warn if a structure is given the packed attribute, but the packed attribute has no effect on the layout or size of the structure. Such structures may be mis-aligned for little benefit. For instance, in this code, the variable f.x in struct bar is misaligned even though struct bar does not itself have the packed attribute:
struct foo {
int x;
char a, b, c, d;
} __attribute__((packed));
struct bar {
char z;
struct foo f;
};
The 4.1, 4.2 and 4.3 series of GCC ignore the packed attribute on bit-fields of type char. This has been fixed in GCC 4.4 but the change can lead to differences in the structure layout. GCC informs you when the offset of such a field has changed in GCC 4.4. For example there is no longer a 4-bit padding between field a and b in this structure:
struct foo
{
char a:4;
char b:8;
} __attribute__ ((packed));
This warning is enabled by default. Use -Wno-packed-bitfield-compat to disable this warning.
Warn if padding is included in a structure, either to align an element of the structure or to align the whole structure. Sometimes when this happens it is possible to rearrange the fields of the structure to reduce the padding and so make the structure smaller.
Warn if anything is declared more than once in the same scope, even in cases where multiple declaration is valid and changes nothing.
Note
(C and Objective-C only)
Warn if an extern declaration is encountered within a function.
Suppress warnings about use of C++11 inheriting constructors when the base class inherited from has a C variadic constructor; the warning is on by default because the ellipsis is not inherited.
Warn if a function that is declared as inline cannot be inlined. Even with this option, the compiler does not warn about failures to inline functions declared in system headers.
The compiler uses a variety of heuristics to determine whether or not to inline a function. For example, the compiler takes into account the size of the function being inlined and the amount of inlining that has already been done in the current function. Therefore, seemingly insignificant changes in the source program can cause the warnings produced by -Winline to appear or disappear.
Note
(C++ and Objective-C++ only)
Suppress warnings from applying the offsetof macro to a non-POD type. According to the 2014 ISO C++ standard, applying offsetof to a non-standard-layout type is undefined. In existing C++ implementations, however, offsetof typically gives meaningful results. This flag is for users who are aware that they are writing nonportable code and who have deliberately chosen to ignore the warning about it.
The restrictions on offsetof may be relaxed in a future version of the C++ standard.
Suppress warnings from casts to pointer type of an integer of a different size. In C++, casting to a pointer type of smaller size is an error. Wint-to-pointer-cast is enabled by default.
Note
(C and Objective-C only)
Suppress warnings from casts from a pointer to an integer type of a different size.
Warn if a precompiled header (Precompiled Headers) is found in the search path but cant be used.
Warn if long long type is used. This is enabled by either -Wpedantic or -Wtraditional in ISO C90 and C++98 modes. To inhibit the warning messages, use -Wno-long-long.
Warn if variadic macros are used in ISO C90 mode, or if the GNU alternate syntax is used in ISO C99 mode. This is enabled by either -Wpedantic or -Wtraditional. To inhibit the warning messages, use -Wno-variadic-macros.
Warn upon questionable usage of the macros used to handle variable arguments like va_start. This is default. To inhibit the warning messages, use -Wno-varargs.
Warn if vector operation is not implemented via SIMD capabilities of the architecture. Mainly useful for the performance tuning. Vector operation can be implemented piecewise, which means that the scalar operation is performed on every vector element; in parallel, which means that the vector operation is implemented using scalars of wider type, which normally is more performance efficient; and as a single scalar, which means that vector fits into a scalar type.
Suppress warnings about inheriting from a virtual base with a non-trivial C++11 move assignment operator. This is dangerous because if the virtual base is reachable along more than one path, it is moved multiple times, which can mean both objects end up in the moved-from state. If the move assignment operator is written to avoid moving from a moved-from object, this warning can be disabled.
Warn if variable length array is used in the code. -Wno-vla prevents the -Wpedantic warning of the variable length array.
Warn if a register variable is declared volatile. The volatile modifier does not inhibit all optimizations that may eliminate reads and/or writes to register variables. This warning is enabled by -Wall.
Warn if a requested optimization pass is disabled. This warning does not generally indicate that there is anything wrong with your code; it merely indicates that GCCs optimizers are unable to handle the code effectively. Often, the problem is that your code is too big or too complex; GCC refuses to optimize programs when the optimization itself is likely to take inordinate amounts of time.
Note
(C and Objective-C only)
Warn for pointer argument passing or assignment with different signedness. This option is only supported for C and Objective-C It is implied by -Wall and by -Wpedantic, which can be disabled with -Wno-pointer-sign.
This option is only active when -fstack-protector is active. It warns about functions that are not protected against stack smashing.
Warn about string constants that are longer than the minimum maximum length specified in the C standard. Modern compilers generally allow string constants that are much longer than the standards minimum limit, but very portable programs should avoid using longer strings.
The limit applies after string constant concatenation, and does not count the trailing NUL In C90, the limit was 509 characters; in C99, it was raised to 4095. C++98 does not specify a normative minimum maximum, so we do not diagnose overlength strings in C++
This option is implied by -Wpedantic, and can be disabled with -Wno-overlength-strings.
Note
(C and Objective-C only)
Issue a warning for any floating constant that does not have a suffix. When used together with -Wsystem-headers it warns about such constants in system header files. This can be useful when preparing code to use with the FLOAT_CONST_DECIMAL64 pragma from the decimal floating-point extension to C99.
Note
(C and Objective-C only)Suppress warnings when a positional initializer is used to initialize
a structure that has been marked with the designated_init attribute.
:: _debugging-options:
GCC has various special options that are used for debugging either your program or GCC:
Produce debugging information in the operating systems native format (stabs, COFF, XCOFF, or DWARF 2) GDB can work with this debugging information.
On most systems that use stabs format, -g enables use of extra debugging information that only GDB can use; this extra information makes debugging work better in GDB but probably makes other debuggers crash or refuse to read the program. If you want to control for certain whether to generate the extra information, use -gstabs+, -gstabs, -gxcoff+, -gxcoff, or -gvms (see below).
GCC allows you to use -g with -O. The shortcuts taken by optimized code may occasionally produce surprising results: some variables you declared may not exist at all; flow of control may briefly move where you did not expect it; some statements may not be executed because they compute constant results or their values are already at hand; some statements may execute in different places because they have been moved out of loops.
Nevertheless it proves possible to debug optimized output. This makes it reasonable to use the optimizer for programs that might have bugs.
The following options are useful when GCC is generated with the capability for more than one debugging format.
Separate as much dwarf debugging information as possible into a separate output file with the extension .dwo. This option allows the build system to avoid linking files with debug information. To be useful, this option requires a debugger capable of reading .dwo files.
Produce debugging information for use by GDB This means to use the most expressive format available (DWARF 2, stabs, or the native format if neither of those are supported), including GDB extensions if at all possible.
Generate dwarf .debug_pubnames and .debug_pubtypes sections.
Generate .debug_pubnames and .debug_pubtypes sections in a format suitable for conversion into a GDBindex. This option is only useful with a linker that can produce GDBindex version 7.
Produce debugging information in stabs format (if that is supported), without GDB extensions. This is the format used by DBX on most BSD systems. On MIPS, Alpha and System V Release 4 systems this option produces stabs debugging output that is not understood by DBX or SDB On System V Release 4 systems this option requires the GNU assembler.
Produce debugging information in stabs format (if that is supported), for only symbols that are actually used.
Instead of emitting debugging information for a C++ class in only one object file, emit it in all object files using the class. This option should be used only with debuggers that are unable to handle the way GCC normally emits debugging information for classes because using this option increases the size of debugging information by as much as a factor of two.
When using DWARF Version 4 or higher, type DIEs can be put into their own .debug_types section instead of making them part of the .debug_info section. It is more efficient to put them in a separate comdat sections since the linker can then remove duplicates. But not all DWARF consumers support .debug_types sections yet and on some objects .debug_types produces larger instead of smaller debugging information.
Produce debugging information in stabs format (if that is supported), using GNU extensions understood only by the GNU debugger (GDB) The use of these extensions is likely to make other debuggers crash or refuse to read the program.
Produce debugging information in COFF format (if that is supported). This is the format used by SDB on most System V systems prior to System V Release 4.
Produce debugging information in XCOFF format (if that is supported). This is the format used by the DBX debugger on IBM RS/6000 systems.
Produce debugging information in XCOFF format (if that is supported), using GNU extensions understood only by the GNU debugger (GDB) The use of these extensions is likely to make other debuggers crash or refuse to read the program, and may cause assemblers other than the GNU assembler (GAS) to fail with an error.
-gdwarf-version
gdwarf-version Produce debugging information in DWARF format (if that is supported). The value of version may be either 2, 3, 4 or 5; the default version for most targets is 4. DWARF Version 5 is only experimental.
Note that with DWARF Version 2, some ports require and always use some non-conflicting DWARF 3 extensions in the unwind tables.
Version 4 may require GDB 7.0 and -fvar-tracking-assignments for maximum benefit.
This switch causes the command-line options used to invoke the compiler that may affect code generation to be appended to the DW_AT_producer attribute in DWARF debugging information. The options are concatenated with spaces separating them from each other and from the compiler version. See also -frecord-gcc-switches for another way of storing compiler options into the object file. This is the default.
Disallow appending command-line options to the DW_AT_producer attribute in DWARF debugging information.
Disallow using extensions of later DWARF standard version than selected with -gdwarf-``version``. On most targets using non-conflicting DWARF extensions from later standard versions is allowed.
Allow using extensions of later DWARF standard version than selected with -gdwarf-``version``.
-gz[=``type``]
Produce compressed debug sections in DWARF format, if that is supported. If type is not given, the default type depends on the capabilities of the assembler and linker used. type may be one of none (dont compress debug sections), zlib (use zlib compression in ELF gABI format), or zlib-gnu (use zlib compression in traditional GNU format). If the linker doesnt support writing compressed debug sections, the option is rejected. Otherwise, if the assembler does not support them, -gz is silently ignored when producing object files.
Produce debugging information in Alpha/VMS debug format (if that is supported). This is the format used by DEBUG on Alpha/VMS systems.
-g``level``
-ggdb``level`` -gstabs``level`` -gcoff``level`` -gxcoff``level`` -gvms``level`` Request debugging information and also use level to specify how much information. The default level is 2.
Level 0 produces no debug information at all. Thus, -g0 negates -g.
Level 1 produces minimal information, enough for making backtraces in parts of the program that you dont plan to debug. This includes descriptions of functions and external variables, and line number tables, but no information about local variables.
Level 3 includes extra information, such as all the macro definitions present in the program. Some debuggers support macro expansion when you use -g3.
-gdwarf-2 does not accept a concatenated debug level, because GCC used to support an option -gdwarf that meant to generate debug information in version 1 of the DWARF format (which is very different from version 2), and it would have been too confusing. That debug format is long obsolete, but the option cannot be changed now. Instead use an additional -g``level`` option to change the debug level for DWARF.
Turn off generation of debug info, if leaving out this option generates it, or turn it on at level 2 otherwise. The position of this argument in the command line does not matter; it takes effect after all other options are processed, and it does so only once, no matter how many times it is given. This is mainly intended to be used with -fcompare-debug.
Enable AddressSanitizer, a fast memory error detector. Memory access instructions are instrumented to detect out-of-bounds and use-after-free bugs. See http://code.google.com/p/address-sanitizer/ for more details. The run-time behavior can be influenced using the ASAN_OPTIONS environment variable; see https://code.google.com/p/address-sanitizer/wiki/Flags#Run-time_flags for a list of supported options.
Enable AddressSanitizer for Linux kernel. See http://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel for more details.
Enable ThreadSanitizer, a fast data race detector. Memory access instructions are instrumented to detect data race bugs. See http://code.google.com/p/thread-sanitizer/ for more details. The run-time behavior can be influenced using the TSAN_OPTIONS environment variable; see https://code.google.com/p/thread-sanitizer/wiki/Flags for a list of supported options.
Enable LeakSanitizer, a memory leak detector. This option only matters for linking of executables and if neither -fsanitize=address nor -fsanitize=thread is used. In that case the executable is linked against a library that overrides malloc and other allocator functions. See https://code.google.com/p/address-sanitizer/wiki/LeakSanitizer for more details. The run-time behavior can be influenced using the LSAN_OPTIONS environment variable.
Enable UndefinedBehaviorSanitizer, a fast undefined behavior detector. Various computations are instrumented to detect undefined behavior at runtime. Current suboptions are:
This option enables checking that the result of a shift operation is not undefined. Note that what exactly is considered undefined differs slightly between C and C++, as well as between ISO C90 and C99, etc.
Detect integer division by zero as well as INT_MIN / -1 division.
With this option, the compiler turns the __builtin_unreachable call into a diagnostics message call instead. When reaching the __builtin_unreachable call, the behavior is undefined.
This option instructs the compiler to check that the size of a variable length array is positive.
This option enables pointer checking. Particularly, the application built with this option turned on will issue an error message when it tries to dereference a NULL pointer, or if a reference (possibly an rvalue reference) is bound to a NULL pointer, or if a method is invoked on an object pointed by a NULL pointer.
This option enables return statement checking. Programs built with this option turned on will issue an error message when the end of a non-void function is reached without actually returning a value. This option works in C++ only.
This option enables signed integer overflow checking. We check that the result of +, *, and both unary and binary - does not overflow in the signed arithmetics. Note, integer promotion rules must be taken into account. That is, the following is not an overflow:
signed char a = SCHAR_MAX;
a++;
This option enables instrumentation of array bounds. Various out of bounds accesses are detected. Flexible array members, flexible array member-like arrays, and initializers of variables with static storage are not instrumented.
This option enables strict instrumentation of array bounds. Most out of bounds accesses are detected, including flexible array members and flexible array member-like arrays. Initializers of variables with static storage are not instrumented.
This option enables checking of alignment of pointers when they are dereferenced, or when a reference is bound to insufficiently aligned target, or when a method or constructor is invoked on insufficiently aligned object.
This option enables instrumentation of memory references using the __builtin_object_size function. Various out of bounds pointer accesses are detected.
Detect floating-point division by zero. Unlike other similar options, -fsanitize=float-divide-by-zero is not enabled by -fsanitize=undefined, since floating-point division by zero can be a legitimate way of obtaining infinities and NaNs.
This option enables floating-point type to integer conversion checking. We check that the result of the conversion does not overflow. Unlike other similar options, -fsanitize=float-cast-overflow is not enabled by -fsanitize=undefined. This option does not work well with FE_INVALID exceptions enabled.
This option enables instrumentation of calls, checking whether null values are not passed to arguments marked as requiring a non-null value by the nonnull function attribute.
This option enables instrumentation of return statements in functions marked with returns_nonnull function attribute, to detect returning of null values from such functions.
This option enables instrumentation of loads from bool. If a value other than 0/1 is loaded, a run-time error is issued.
This option enables instrumentation of loads from an enum type. If a value outside the range of values for the enum type is loaded, a run-time error is issued.
This option enables instrumentation of C++ member function calls, member accesses and some conversions between pointers to base and derived classes, to verify the referenced object has the correct dynamic type.
While -ftrapv causes traps for signed overflows to be emitted, -fsanitize=undefined gives a diagnostic message. This currently works only for the C family of languages.
This option disables all previously enabled sanitizers. -fsanitize=all is not allowed, as some sanitizers cannot be used together.
-fasan-shadow-offset=``number``
This option forces GCC to use custom shadow offset in AddressSanitizer checks. It is useful for experimenting with different shadow memory layouts in Kernel AddressSanitizer.
-fsanitize-sections=``s1,s2,...``
Sanitize global variables in selected user-defined sections. si may contain wildcards.
-fsanitize-recover[=``opts``]
-fsanitize-recover= controls error recovery mode for sanitizers mentioned in comma-separated list of opts. Enabling this option for a sanitizer component causes it to attempt to continue running the program as if no error happened. This means multiple runtime errors can be reported in a single program run, and the exit code of the program may indicate success even when errors have been reported. The -fno-sanitize-recover= option can be used to alter this behavior: only the first detected error is reported and program then exits with a non-zero exit code.
Currently this feature only works for -fsanitize=undefined (and its suboptions except for -fsanitize=unreachable and -fsanitize=return), -fsanitize=float-cast-overflow, -fsanitize=float-divide-by-zero and -fsanitize=kernel-address. For these sanitizers error recovery is turned on by default. -fsanitize-recover=all and -fno-sanitize-recover=all is also accepted, the former enables recovery for all sanitizers that support it, the latter disables recovery for all sanitizers that support it.
Syntax without explicit opts parameter is deprecated. It is equivalent to
-fsanitize-recover=undefined,float-cast-overflow,float-divide-by-zero
Similarly -fno-sanitize-recover is equivalent to
-fno-sanitize-recover=undefined,float-cast-overflow,float-divide-by-zero
The -fsanitize-undefined-trap-on-error option instructs the compiler to report undefined behavior using __builtin_trap rather than a libubsan library routine. The advantage of this is that the libubsan library is not needed and is not linked in, so this is usable even in freestanding environments.
Enable Pointer Bounds Checker instrumentation. Each memory reference is instrumented with checks of the pointer used for memory access against bounds associated with that pointer.
Currently there is only an implementation for Intel MPX available, thus x86 target and -mmpx are required to enable this feature. MPX-based instrumentation requires a runtime library to enable MPX in hardware and handle bounds violation signals. By default when -fcheck-pointer-bounds and -mmpx options are used to link a program, the GCC driver links against the libmpx runtime library and libmpxwrappers library. It also passes -z bndplt to a linker in case it supports this option (which is checked on libmpx configuration). Note that old versions of linker may ignore option. Gold linker doesnt support -z bndplt option. With no -z bndplt support in linker all calls to dynamic libraries lose passed bounds reducing overall protection level. Its highly recommended to use linker with -z bndplt support. In case such linker is not available it is adviced to always use -static-libmpxwrappers for better protection level or use -static to completely avoid external calls to dynamic libraries. MPX-based instrumentation may be used for debugging and also may be included in production code to increase program security. Depending on usage, you may have different requirements for the runtime library. The current version of the MPX runtime library is more oriented for use as a debugging tool. MPX runtime library usage implies -lpthread. See also -static-libmpx. The runtime library behavior can be influenced using various CHKP_RT_* environment variables. See https://gcc.gnu.org/wiki/Intel%20MPX%20support%20in%20the%20GCC%20compiler for more details.
Generated instrumentation may be controlled by various -fchkp-* options and by the bnd_variable_size structure field attribute (Type Attributes) and bnd_legacy, and bnd_instrument function attributes (Function Attributes). GCC also provides a number of built-in functions for controlling the Pointer Bounds Checker. Pointer Bounds Checker builtins, for more information.
Generate pointer bounds checks for variables with incomplete type. Enabled by default.
Controls bounds used by Pointer Bounds Checker for pointers to object fields. If narrowing is enabled then field bounds are used. Otherwise object bounds are used. See also -fchkp-narrow-to-innermost-array and -fchkp-first-field-has-own-bounds. Enabled by default.
Forces Pointer Bounds Checker to use narrowed bounds for the address of the first field in the structure. By default a pointer to the first field has the same bounds as a pointer to the whole structure.
Forces Pointer Bounds Checker to use bounds of the innermost arrays in case of nested static array access. By default this option is disabled and bounds of the outermost array are used.
Enables Pointer Bounds Checker optimizations. Enabled by default at optimization levels -O, -O2, -O3.
Enables use of *_nobnd versions of string functions (not copying bounds) by Pointer Bounds Checker. Disabled by default.
Enables use of *_nochk versions of string functions (not checking bounds) by Pointer Bounds Checker. Disabled by default.
Allow Pointer Bounds Checker to generate static bounds holding bounds of static variables. Enabled by default.
Use statically-initialized bounds for constant bounds instead of generating them each time they are required. By default enabled when -fchkp-use-static-bounds is enabled.
With this option, objects with incomplete type whose dynamically-obtained size is zero are treated as having infinite size instead by Pointer Bounds Checker. This option may be helpful if a program is linked with a library missing size information for some symbols. Disabled by default.
Instructs Pointer Bounds Checker to generate checks for all read accesses to memory. Enabled by default.
Instructs Pointer Bounds Checker to generate checks for all write accesses to memory. Enabled by default.
Instructs Pointer Bounds Checker to generate bounds stores for pointer writes. Enabled by default.
Instructs Pointer Bounds Checker to pass pointer bounds to calls. Enabled by default.
Instructs Pointer Bounds Checker to instrument only functions marked with the bnd_instrument attribute (Function Attributes). Disabled by default.
Allows Pointer Bounds Checker to replace calls to built-in functions with calls to wrapper functions. When -fchkp-use-wrappers is used to link a program, the GCC driver automatically links against libmpxwrappers. See also -static-libmpxwrappers. Enabled by default.
-fdump-final-insns[=``file``]
Dump the final internal representation (RTL) to file. If the optional argument is omitted (or if file is .), the name of the dump file is determined by appending .gkd to the compilation output file name.
-fcompare-debug[=``opts``]
If no error occurs during compilation, run the compiler a second time, adding opts and -fcompare-debug-second to the arguments passed to the second compilation. Dump the final internal representation in both compilations, and print an error if they differ.
If the equal sign is omitted, the default -gtoggle is used.
The environment variable GCC_COMPARE_DEBUG, if defined, non-empty and nonzero, implicitly enables -fcompare-debug. If GCC_COMPARE_DEBUG is defined to a string starting with a dash, then it is used for opts, otherwise the default -gtoggle is used.
-fcompare-debug=, with the equal sign but without opts, is equivalent to -fno-compare-debug, which disables the dumping of the final representation and the second compilation, preventing even GCC_COMPARE_DEBUG from taking effect.
To verify full coverage during -fcompare-debug testing, set GCC_COMPARE_DEBUG to say -fcompare-debug-not-overridden, which GCC rejects as an invalid option in any actual compilation (rather than preprocessing, assembly or linking). To get just a warning, setting GCC_COMPARE_DEBUG to -w%n-fcompare-debug not overridden will do.
This option is implicitly passed to the compiler for the second compilation requested by -fcompare-debug, along with options to silence warnings, and omitting other options that would cause side-effect compiler outputs to files or to the standard output. Dump files and preserved temporary files are renamed so as to contain the .gk additional extension during the second compilation, to avoid overwriting those generated by the first.
When this option is passed to the compiler driver, it causes the first compilation to be skipped, which makes it useful for little other than debugging the compiler proper.
Compress DWARF 2 debugging information by eliminating duplicated information about each symbol. This option only makes sense when generating DWARF 2 debugging information with -gdwarf-2.
Emit debug information for struct-like types only when the base name of the compilation source file matches the base name of file in which the struct is defined.
This option substantially reduces the size of debugging information, but at significant potential loss in type information to the debugger. See -femit-struct-debug-reduced for a less aggressive option. See -femit-struct-debug-detailed for more detailed control.
This option works only with DWARF 2.
Emit debug information for struct-like types only when the base name of the compilation source file matches the base name of file in which the type is defined, unless the struct is a template or defined in a system header.
This option significantly reduces the size of debugging information, with some potential loss in type information to the debugger. See -femit-struct-debug-baseonly for a more aggressive option. See -femit-struct-debug-detailed for more detailed control.
This option works only with DWARF 2.
-femit-struct-debug-detailed[=``spec-list``]
Specify the struct-like types for which the compiler generates debug information. The intent is to reduce duplicate struct debug information between different object files within the same program.
This option is a detailed version of -femit-struct-debug-reduced and -femit-struct-debug-baseonly, which serves for most needs.
A specification has the syntax [dir:|ind:][ord:|gen:](any|sys|base|none)
The optional first word limits the specification to structs that are used directly (dir:) or used indirectly (ind:). A struct type is used directly when it is the type of a variable, member. Indirect uses arise through pointers to structs. That is, when use of an incomplete struct is valid, the use is indirect. An example is struct one direct; struct two * indirect;.
The optional second word limits the specification to ordinary structs (ord:) or generic structs (gen:). Generic structs are a bit complicated to explain. For C++, these are non-explicit specializations of template classes, or non-template classes within the above. Other programming languages have generics, but -femit-struct-debug-detailed does not yet implement them.
The third word specifies the source files for those structs for which the compiler should emit debug information. The values none and any have the normal meaning. The value base means that the base of name of the file in which the type declaration appears must match the base of the name of the main compilation file. In practice, this means that when compiling foo.c, debug information is generated for types declared in that file and foo.h, but not other header files. The value sys means those types satisfying base or declared in system or compiler headers.
You may need to experiment to determine the best settings for your application.
The default is -femit-struct-debug-detailed=all.
This option works only with DWARF 2.
Direct the linker to not merge together strings in the debugging information that are identical in different object files. Merging is not supported by all assemblers or linkers. Merging decreases the size of the debug information in the output file at the cost of increasing link processing time. Merging is enabled by default.
-fdebug-prefix-map=``old``=``new``
When compiling files in directory old, record debugging information describing them as in new instead.
Emit DWARF 2 unwind info as compiler generated .eh_frame section instead of using GAS .cfi_* directives.
prof
Generate extra code to write profile information suitable for the analysis program prof. You must use this option when compiling the source files you want data about, and you must also use it when linking.
gprof
Generate extra code to write profile information suitable for the analysis program gprof. You must use this option when compiling the source files you want data about, and you must also use it when linking.
Makes the compiler print out each function name as it is compiled, and print some statistics about each pass when it finishes.
Makes the compiler print some statistics about the time consumed by each pass when it finishes.
Makes the compiler print some statistics about permanent memory allocation when it finishes.
Makes the compiler print some statistics about permanent memory allocation for the WPA phase only.
Makes the compiler print some statistics about permanent memory allocation before or after interprocedural optimization.
Makes the compiler print some statistics about consistency of the (estimated) profile and effect of individual passes.
Makes the compiler output stack usage information for the program, on a per-function basis. The filename for the dump is made by appending .su to the auxname. auxname is generated from the name of the output file, if explicitly specified and it is not an executable, otherwise it is the basename of the source file. An entry is made up of three fields:
The qualifier static means that the function manipulates the stack statically: a fixed number of bytes are allocated for the frame on function entry and released on function exit; no stack adjustments are otherwise made in the function. The second field is this fixed number of bytes.
The qualifier dynamic means that the function manipulates the stack dynamically: in addition to the static allocation described above, stack adjustments are made in the body of the function, for example to push/pop arguments around function calls. If the qualifier bounded is also present, the amount of these adjustments is bounded at compile time and the second field is an upper bound of the total amount of stack used by the function. If it is not present, the amount of these adjustments is not bounded at compile time and the second field only represents the bounded part.
Add code so that program flow arcs are instrumented. During execution the program records how many times each branch and call is executed and how many times it is taken or returns. When the compiled program exits it saves this data to a file called auxname.gcda for each source file. The data may be used for profile-directed optimizations (-fbranch-probabilities), or for test coverage analysis (-ftest-coverage). Each object files auxname is generated from the name of the output file, if explicitly specified and it is not the final executable, otherwise it is the basename of the source file. In both cases any suffix is removed (e.g. foo.gcda for input file dir/foo.c, or dir/foo.gcda for output file specified as -o dir/foo.o). Cross-profiling.
gcov
This option is used to compile and link code instrumented for coverage analysis. The option is a synonym for -fprofile-arcs -ftest-coverage (when compiling) and -lgcov (when linking). See the documentation for those options for more details.
With -fprofile-arcs, for each function of your program GCC creates a program flow graph, then finds a spanning tree for the graph. Only arcs that are not on the spanning tree have to be instrumented: the compiler adds code to count the number of times that these arcs are executed. When an arc is the only exit or only entrance to a block, the instrumentation code can be added to the block; otherwise, a new basic block must be created to hold the instrumentation code.
Produce a notes file that the gcov code-coverage utility (Gcov:command:gcov`a Test Coverage Program) can use to show program coverage. Each source files note file is called ``auxname`.gcno. Refer to the -fprofile-arcs option above for a description of auxname and instructions on how to generate test coverage data. Coverage data matches the source files more closely if you do not optimize.
Print the name and the counter upper bound for all debug counters.
-fdbg-cnt=``counter-value-list``
Set the internal debug counter upper bound. counter-value-list is a comma-separated list of name:value pairs which sets the upper bound of each debug counter name to value. All debug counters have the initial upper bound of UINT_MAX; thus dbg_cnt returns true always unless the upper bound is set by this option. For example, with -fdbg-cnt=dce:10,tail_call:0, dbg_cnt(dce) returns true only for first 10 invocations.
-fenable-kind-pass -fdisable-kind-pass``=``range-list
This is a set of options that are used to explicitly disable/enable optimization passes. These options are intended for use for debugging GCC. Compiler users should use regular options for enabling/disabling passes instead.
-fdisable-ipa-pass Disable IPA pass pass. pass is the pass name. If the same pass is statically invoked in the compiler multiple times, the pass name should be appended with a sequential number starting from 1.
-fdisable-rtl-pass -fdisable-rtl-pass``=``range-list Disable RTL pass pass. pass is the pass name. If the same pass is statically invoked in the compiler multiple times, the pass name should be appended with a sequential number starting from 1. range-list is a comma-separated list of function ranges or assembler names. Each range is a number pair separated by a colon. The range is inclusive in both ends. If the range is trivial, the number pair can be simplified as a single number. If the functions call graph nodes uid falls within one of the specified ranges, the pass is disabled for that function. The uid is shown in the function header of a dump file, and the pass names can be dumped by using option -fdump-passes.
-fdisable-tree-pass -fdisable-tree-pass``=``range-list Disable tree pass pass. See -fdisable-rtl for the description of option arguments.
-fenable-ipa-pass Enable IPA pass pass. pass is the pass name. If the same pass is statically invoked in the compiler multiple times, the pass name should be appended with a sequential number starting from 1.
-fenable-rtl-pass -fenable-rtl-pass``=``range-list Enable RTL pass pass. See -fdisable-rtl for option argument description and examples.
-fenable-tree-pass -fenable-tree-pass``=``range-list Enable tree pass pass. See -fdisable-rtl for the description of option arguments.
Here are some examples showing uses of these options.
# disable ccp1 for all functions
-fdisable-tree-ccp1
# disable complete unroll for function whose cgraph node uid is 1
-fenable-tree-cunroll=1
# disable gcse2 for functions at the following ranges [1,1],
# [300,400], and [400,1000]
# disable gcse2 for functions foo and foo2
-fdisable-rtl-gcse2=foo,foo2
# disable early inlining
-fdisable-tree-einline
# disable ipa inlining
-fdisable-ipa-inline
# enable tree full unroll
-fenable-tree-unroll
-d``letters`` -fdump-rtl-pass -fdump-rtl-pass``=``filename
fdump-rtl-pass Says to make debugging dumps during compilation at times specified by letters. This is used for debugging the RTL-based passes of the compiler. The file names for most of the dumps are made by appending a pass number and a word to the dumpname, and the files are created in the directory of the output file. In case of =``filename`` option, the dump is output on the given file instead of the pass numbered dump files. Note that the pass number is computed statically as passes get registered into the pass manager. Thus the numbering is not related to the dynamic order of execution of passes. In particular, a pass installed by a plugin could have a number over 200 even if it executed quite early. dumpname is generated from the name of the output file, if explicitly specified and it is not an executable, otherwise it is the basename of the source file. These switches may have different effects when -E is used for preprocessing.
Debug dumps can be enabled with a -fdump-rtl switch or some -d option letters. Here are the possible letters for use in pass and letters, and their meanings:
Dump after branch alignments have been computed.
Dump after fixing rtl statements that have unsatisfied in/out constraints.
Dump after auto-inc-dec discovery. This pass is only run on architectures that have auto inc or auto dec instructions.
Dump after cleaning up the barrier instructions.
Dump after partitioning hot and cold basic blocks.
Dump after block reordering.
-fdump-rtl-btl1 and -fdump-rtl-btl2 enable dumping after the two branch target load optimization passes.
Dump after jump bypassing and control flow optimizations.
Dump after the RTL instruction combination pass.
Dump after duplicating the computed gotos.
-fdump-rtl-ce1, -fdump-rtl-ce2, and -fdump-rtl-ce3 enable dumping after the three if conversion passes.
Dump after hard register copy propagation.
Dump after combining stack adjustments.
-fdump-rtl-cse1 and -fdump-rtl-cse2 enable dumping after the two common subexpression elimination passes.
Dump after the standalone dead code elimination passes.
Dump after delayed branch scheduling.
-fdump-rtl-dce1 and -fdump-rtl-dce2 enable dumping after the two dead store elimination passes.
Dump after finalization of EH handling code.
Dump after conversion of EH handling range regions.
Dump after RTL generation.
-fdump-rtl-fwprop1 and -fdump-rtl-fwprop2 enable dumping after the two forward propagation passes.
-fdump-rtl-gcse1 and -fdump-rtl-gcse2 enable dumping after global common subexpression elimination.
Dump after the initialization of the registers.
Dump after the computation of the initial value sets.
Dump after converting to cfglayout mode.
Dump after iterated register allocation.
Dump after the second jump optimization.
-fdump-rtl-loop2 enables dumping after the rtl loop optimization passes.
Dump after performing the machine dependent reorganization pass, if that pass exists.
Dump after removing redundant mode switches.
Dump after register renumbering.
Dump after converting from cfglayout mode.
Dump after the peephole pass.
Dump after post-reload optimizations.
Dump after generating the function prologues and epilogues.
-fdump-rtl-sched1 and -fdump-rtl-sched2 enable dumping after the basic block scheduling passes.
Dump after sign/zero extension elimination.
Dump after common sequence discovery.
Dump after shortening branches.
Dump after sibling call optimizations.
These options enable dumping after five rounds of instruction splitting.
Dump after modulo scheduling. This pass is only run on some architectures.
Dump after conversion from GCCs flat register file registers to the x87s stack-like registers. This pass is only run on x86 variants.
-fdump-rtl-subreg1 and -fdump-rtl-subreg2 enable dumping after the two subreg expansion passes.
Dump after all rtl has been unshared.
Dump after variable tracking.
Dump after converting virtual registers to hard registers.
Dump after live range splitting.
These dumps are defined but always produce empty files.
Produce all the dumps listed above.
Annotate the assembler output with miscellaneous debugging information.
Dump all macro definitions, at the end of preprocessing, in addition to normal output.
Produce a core dump whenever an error occurs.
Annotate the assembler output with a comment indicating which pattern and alternative is used. The length of each instruction is also printed.
Dump the RTL in the assembler output as a comment before each instruction. Also turns on -dp annotation.
Just generate RTL for a function instead of compiling it. Usually used with -fdump-rtl-expand.
When doing debugging dumps, suppress address output. This makes it more feasible to use diff on debugging dumps for compiler invocations with different compiler binaries and/or different text / bss / data / heap / stack / dso start locations.
Collect and dump debug information into temporary file if ICE in C/C++ compiler occured.
When doing debugging dumps, suppress instruction numbers and address output. This makes it more feasible to use diff on debugging dumps for compiler invocations with different options, in particular with and without -g.
When doing debugging dumps (see -d option above), suppress instruction numbers for the links to the previous and next instructions in a sequence.
Note
(C++ only)
Dump a representation of the tree structure for the entire translation unit to a file. The file name is made by appending .tu to the source file name, and the file is created in the same directory as the output file. If the -options form is used, options controls the details of the dump as described for the -fdump-tree options.
Note
(C++ only)
Dump a representation of each classs hierarchy and virtual function table layout to a file. The file name is made by appending .class to the source file name, and the file is created in the same directory as the output file. If the -options form is used, options controls the details of the dump as described for the -fdump-tree options.
-fdump-ipa-switch
Control the dumping at various stages of inter-procedural analysis language tree to a file. The file name is generated by appending a switch specific suffix to the source file name, and the file is created in the same directory as the output file. The following dumps are possible:
Enables all inter-procedural analysis dumps.
Dumps information about call-graph optimization, unused function removal, and inlining decisions.
Dump after function inlining.
Dump the list of optimization passes that are turned on and off by the current command-line options.
-fdump-statistics-option
Enable and control dumping of pass statistics in a separate file. The file name is generated by appending a suffix ending in .statistics to the source file name, and the file is created in the same directory as the output file. If the -option form is used, -stats causes counters to be summed over the whole compilation unit while -details dumps every event as the passes generate them. The default with no option is to sum counters for each function compiled.
-fdump-tree-switch -fdump-tree-switch-options -fdump-tree-switch-options``=``filename
Control the dumping at various stages of processing the intermediate language tree to a file. The file name is generated by appending a switch-specific suffix to the source file name, and the file is created in the same directory as the output file. In case of =``filename`` option, the dump is output on the given file instead of the auto named dump files. If the -options form is used, options is a list of - separated options which control the details of the dump. Not all options are applicable to all dumps; those that are not meaningful are ignored. The following options are available
Print the address of each node. Usually this is not meaningful as it changes according to the environment and source file. Its primary use is for tying up a dump file with a debug environment.
If DECL_ASSEMBLER_NAME has been set for a given decl, use that in the dump instead of DECL_NAME. Its primary use is ease of use working backward from mangled names in the assembly file.
When dumping front-end intermediate representations, inhibit dumping of members of a scope or body of a function merely because that scope has been reached. Only dump such items when they are directly reachable by some other path.
When dumping pretty-printed trees, this option inhibits dumping the bodies of control structures.
When dumping RTL, print the RTL in slim (condensed) form instead of the default LISP-like representation.
Print a raw representation of the tree. By default, trees are pretty-printed into a C-like representation.
Enable more detailed dumps (not honored by every dump option). Also include information from the optimization passes.
Enable dumping various statistics about the pass (not honored by every dump option).
Enable showing basic block boundaries (disabled in raw dumps).
For each of the other indicated dump files (-fdump-rtl-``pass``), dump a representation of the control flow graph suitable for viewing with GraphViz to file.``passid``.``pass``.dot. Each function in the file is pretty-printed as a subgraph, so that GraphViz can render them all in a single plot.
This option currently only works for RTL dumps, and the RTL is always dumped in slim form.
Enable showing virtual operands for every statement.
Enable showing line numbers for statements.
Enable showing the unique ID (DECL_UID) for each variable.
Enable showing the tree dump for each statement.
Enable showing the EH region number holding each statement.
Enable showing scalar evolution analysis details.
Enable showing optimization information (only available in certain passes).
Enable showing missed optimization information (only available in certain passes).
Enable other detailed optimization information (only available in certain passes). =``filename``
Instead of an auto named dump file, output into the given file name. The file names stdout and stderr are treated specially and are considered already open standard streams. For example,
gcc -O2 -ftree-vectorize -fdump-tree-vect-blocks=foo.dump
-fdump-tree-pre=stderr file.c
outputs vectorizer dump into foo.dump, while the PRE dump is output on to stderr. If two conflicting dump filenames are given for the same pass, then the latter option overrides the earlier one.
Turn on all options, except raw, slim, verbose and lineno.
Turn on all optimization options, i.e., optimized, missed, and note.
The following tree dumps are possible:
Dump before any tree based optimization, to file.original.
Dump after all tree based optimization, to file.optimized.
Dump each function before and after the gimplification pass to a file. The file name is made by appending .gimple to the source file name.
Dump the control flow graph of each function to a file. The file name is made by appending .cfg to the source file name.
Dump each function after copying loop headers. The file name is made by appending .ch to the source file name.
Dump SSA related information to a file. The file name is made by appending .ssa to the source file name.
Dump aliasing information for each function. The file name is made by appending .alias to the source file name.
Dump each function after CCP The file name is made by appending .ccp to the source file name.
Dump each function after STORE-CCP The file name is made by appending .storeccp to the source file name.
Dump trees after partial redundancy elimination. The file name is made by appending .pre to the source file name.
Dump trees after full redundancy elimination. The file name is made by appending .fre to the source file name.
Dump trees after copy propagation. The file name is made by appending .copyprop to the source file name.
Dump trees after store copy-propagation. The file name is made by appending .store_copyprop to the source file name.
Dump each function after dead code elimination. The file name is made by appending .dce to the source file name.
Dump each function after performing scalar replacement of aggregates. The file name is made by appending .sra to the source file name.
Dump each function after performing code sinking. The file name is made by appending .sink to the source file name.
Dump each function after applying dominator tree optimizations. The file name is made by appending .dom to the source file name.
Dump each function after applying dead store elimination. The file name is made by appending .dse to the source file name.
Dump each function after optimizing PHI nodes into straightline code. The file name is made by appending .phiopt to the source file name.
Dump each function after forward propagating single use variables. The file name is made by appending .forwprop to the source file name.
Dump each function after applying the copy rename optimization. The file name is made by appending .copyrename to the source file name.
Dump each function after applying the named return value optimization on generic trees. The file name is made by appending .nrv to the source file name.
Dump each function after applying vectorization of loops. The file name is made by appending .vect to the source file name.
Dump each function after applying vectorization of basic blocks. The file name is made by appending .slp to the source file name.
Dump each function after Value Range Propagation (VRP). The file name is made by appending .vrp to the source file name.
Enable all the available tree dumps with the flags provided in this option.
Controls optimization dumps from various optimization passes. If the -options form is used, options is a list of - separated option keywords to select the dump details and optimizations.
The options can be divided into two groups: options describing the verbosity of the dump, and options describing which optimizations should be included. The options from both the groups can be freely mixed as they are non-overlapping. However, in case of any conflicts, the later options override the earlier options on the command line.
The following options control the dump verbosity:
Print information when an optimization is successfully applied. It is up to a pass to decide which information is relevant. For example, the vectorizer passes print the source location of loops which are successfully vectorized.
Print information about missed optimizations. Individual passes control which information to include in the output.
Print verbose information about optimizations, such as certain transformations, more detailed messages about decisions etc.
Print detailed optimization information. This includes optimized, missed, and note.
One or more of the following option keywords can be used to describe a group of optimizations:
Enable dumps from all interprocedural optimizations.
Enable dumps from all loop optimizations.
Enable dumps from all inlining optimizations.
Enable dumps from all vectorization optimizations.
Enable dumps from all optimizations. This is a superset of the optimization groups listed above.
If options is omitted, it defaults to optimized-optall, which means to dump all info about successful optimizations from all the passes.
If the filename is provided, then the dumps from all the applicable optimizations are concatenated into the filename. Otherwise the dump is output onto stderr. Though multiple -fopt-info options are accepted, only one of them can include a filename. If other filenames are provided then all but the first such option are ignored.
Note that the output filename is overwritten in case of multiple translation units. If a combined output from multiple translation units is desired, stderr should be used instead.
In the following example, the optimization info is output to stderr:
gcc -O3 -fopt-info
This example:
gcc -O3 -fopt-info-missed=missed.all
outputs missed optimization report from all the passes into missed.all, and this one:
gcc -O2 -ftree-vectorize -fopt-info-vec-missed
prints information about missed optimization opportunities from vectorization passes on stderr. Note that -fopt-info-vec-missed is equivalent to -fopt-info-missed-vec.
As another example,
gcc -O3 -fopt-info-inline-optimized-missed=inline.txt
outputs information about missed optimizations as well as optimized locations from all the inlining passes into inline.txt.
Finally, consider:
gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt
Here the two output filenames vec.miss and loop.opt are in conflict since only one output file is allowed. In this case, only the first option takes effect and the subsequent options are ignored. Thus only vec.miss is produced which contains dumps from the vectorizer about missed opportunities.
-frandom-seed=``number``
This option provides a seed that GCC uses in place of random numbers in generating certain symbol names that have to be different in every compiled file. It is also used to place unique stamps in coverage data files and the object files that produce them. You can use the -frandom-seed option to produce reproducibly identical object files.
The number should be different for every file you compile.
-fsched-verbose=``n``
On targets that use instruction scheduling, this option controls the amount of debugging output the scheduler prints. This information is written to standard error, unless -fdump-rtl-sched1 or -fdump-rtl-sched2 is specified, in which case it is output to the usual dump listing file, .sched1 or .sched2 respectively. However for n greater than nine, the output is always printed to standard error.
For n greater than zero, -fsched-verbose outputs the same information as -fdump-rtl-sched1 and -fdump-rtl-sched2. For n greater than one, it also output basic block probabilities, detailed ready list information and unit/insn info. For n greater than two, it includes RTL at abort point, control-flow and regions info. And for n over four, -fsched-verbose also includes dependence info.
Store the usual temporary intermediate files permanently; place them in the current directory and name them based on the source file. Thus, compiling foo.c with -c -save-temps produces files foo.i and foo.s, as well as foo.o. This creates a preprocessed foo.i output file even though the compiler now normally uses an integrated preprocessor.
When used in combination with the -x command-line option, -save-temps is sensible enough to avoid over writing an input source file with the same extension as an intermediate file. The corresponding intermediate file may be obtained by renaming the source file before using -save-temps.
If you invoke GCC in parallel, compiling several different source files that share a common base name in different subdirectories or the same source file compiled for multiple output destinations, it is likely that the different parallel compilers will interfere with each other, and overwrite the temporary files. For instance:
gcc -save-temps -o outdir1/foo.o indir1/foo.c&
gcc -save-temps -o outdir2/foo.o indir2/foo.c&
may result in foo.i and foo.o being written to simultaneously by both compilers.
Store the usual temporary intermediate files permanently. If the -o option is used, the temporary files are based on the object file. If the -o option is not used, the -save-temps=obj switch behaves like -save-temps.
For example:
gcc -save-temps=obj -c foo.c
gcc -save-temps=obj -c bar.c -o dir/xbar.o
gcc -save-temps=obj foobar.c -o dir2/yfoobar
creates foo.i, foo.s, dir/xbar.i, dir/xbar.s, dir2/yfoobar.i, dir2/yfoobar.s, and dir2/yfoobar.o.
-time[=``file``]
Report the CPU time taken by each subprocess in the compilation sequence. For C source files, this is the compiler proper and assembler (plus the linker if linking is done).
Without the specification of an output file, the output looks like this:
# cc1 0.12 0.01
# as 0.00 0.01
The first number on each line is the user time, that is time spent executing the program itself. The second number is system time, time spent executing operating system routines on behalf of the program. Both numbers are in seconds.
With the specification of an output file, the output is appended to the named file, and it looks like this:
0.12 0.01 cc1 ``options``
0.00 0.01 as ``options``
The user time and the system time are moved before the program name, and the options passed to the program are displayed, so that one can later tell what file was being compiled, and with which options.
Run variable tracking pass. It computes where variables are stored at each position in code. Better debugging information is then generated (if the debugging information format supports this information).
It is enabled by default when compiling with optimization (-Os, -O, -O2, ...), debugging information (-g) and the debug info format supports it.
Annotate assignments to user variables early in the compilation and attempt to carry the annotations over throughout the compilation all the way to the end, in an attempt to improve debug information while optimizing. Use of -gdwarf-4 is recommended along with it.
It can be enabled even if var-tracking is disabled, in which case annotations are created and maintained, but discarded at the end. By default, this flag is enabled together with -fvar-tracking, except when selective scheduling is enabled.
Toggle -fvar-tracking-assignments, in the same way that -gtoggle toggles -g.
-print-file-name=``library``
Print the full absolute name of the library file library that would be used when linkingand dont do anything else. With this option, GCC does not compile or link anything; it just prints the file name.
Print the directory name corresponding to the multilib selected by any other switches present in the command line. This directory is supposed to exist in GCC_EXEC_PREFIX.
Print the mapping from multilib directory names to compiler switches that enable them. The directory name is separated from the switches by ;, and each switch starts with an instead of the -, without spaces between multiple switches. This is supposed to ease shell processing.
Print the path to OS libraries for the selected multilib, relative to some lib subdirectory. If OS libraries are present in the lib subdirectory and no multilibs are used, this is usually just ., if OS libraries are present in lib``suffix`` sibling directories this prints e.g. ../lib64, ../lib or ../lib32, or if OS libraries are present in lib/subdir subdirectories it prints e.g. amd64, sparcv9 or ev6.
Print the path to OS libraries for the selected multiarch, relative to some lib subdirectory.
-print-prog-name=``program``
Like -print-file-name, but searches for a program such as cpp.
Same as -print-file-name=libgcc.a.
This is useful when you use -nostdlib or -nodefaultlibs but you do want to link with libgcc.a. You can do:
gcc -nostdlib ``files``... `gcc -print-libgcc-file-name`
Print the name of the configured installation directory and a list of program and library directories gcc searchesand dont do anything else.
This is useful when gcc prints the error message installation problem, cannot exec cpp0: No such file or directory. To resolve this you either need to put cpp0 and the other compiler components where gcc expects to find them, or you can set the environment variable GCC_EXEC_PREFIX to the directory where you installed them. Dont forget the trailing /. Environment Variables.
Print the target sysroot directory that is used during compilation. This is the target sysroot specified either at configure time or using the --sysroot option, possibly with an extra suffix that depends on compilation options. If no target sysroot is specified, the option prints nothing.
Print the suffix added to the target sysroot when searching for headers, or give an error if the compiler is not configured with such a suffixand dont do anything else.
Print the compilers target machine (for example, i686-pc-linux-gnu)and dont do anything else.
Print the compiler version (for example, 3.0)and dont do anything else.
Print the compilers built-in specsand dont do anything else. (This is used when GCC itself is being built.) Spec Files.
Normally, when producing DWARF 2 output, GCC avoids producing debug symbol output for types that are nowhere used in the source file being compiled. Sometimes it is useful to have GCC emit debugging information for all types declared in a compilation unit, regardless of whether or not they are actually used in that compilation unit, for example if, in the debugger, you want to cast a value to a type that is not actually used in your program (but is declared). More often, however, this results in a significant amount of wasted space.
:: _optimize-options:
These options control various sorts of optimizations.
Without any optimization option, the compilers goal is to reduce the cost of compilation and to make debugging produce the expected results. Statements are independent: if you stop the program with a breakpoint between statements, you can then assign a new value to any variable or change the program counter to any other statement in the function and get exactly the results you expect from the source code.
Turning on optimization flags makes the compiler attempt to improve the performance and/or code size at the expense of compilation time and possibly the ability to debug the program.
The compiler performs optimization based on the knowledge it has of the program. Compiling multiple files at once to a single output file mode allows the compiler to use information gained from all of the files when compiling each of them.
Not all optimizations are controlled directly by a flag. Only optimizations that have a flag are listed in this section.
Most optimizations are only enabled if an -O level is set on the command line. Otherwise they are disabled, even if individual optimization flags are specified.
Depending on the target and how GCC was configured, a slightly different set of optimizations may be enabled at each -O level than those listed here. You can invoke GCC with -Q --help=optimizers to find out the exact set of optimizations that are enabled at each level. Overall Options, for examples.
Optimize. Optimizing compilation takes somewhat more time, and a lot more memory for a large function.
With -O, the compiler tries to reduce code size and execution time, without performing any optimizations that take a great deal of compilation time.
-O turns on the following optimization flags:
-fauto-inc-dec -fbranch-count-reg -fcombine-stack-adjustments -fcompare-elim -fcprop-registers -fdce -fdefer-pop -fdelayed-branch -fdse -fforward-propagate -fguess-branch-probability -fif-conversion2 -fif-conversion -finline-functions-called-once -fipa-pure-const -fipa-profile -fipa-reference -fmerge-constants -fmove-loop-invariants -fshrink-wrap -fsplit-wide-types -ftree-bit-ccp -ftree-ccp -fssa-phiopt -ftree-ch -ftree-copy-prop -ftree-copyrename -ftree-dce -ftree-dominator-opts -ftree-dse -ftree-forwprop -ftree-fre -ftree-phiprop -ftree-sink -ftree-slsr -ftree-sra -ftree-pta -ftree-ter -funit-at-a-time
-O also turns on -fomit-frame-pointer on machines where doing so does not interfere with debugging.
Optimize even more. GCC performs nearly all supported optimizations that do not involve a space-speed tradeoff. As compared to -O, this option increases both compilation time and the performance of the generated code.
-O2 turns on all optimization flags specified by -O. It also turns on the following optimization flags:
-fthread-jumps -falign-functions -falign-jumps -falign-loops -falign-labels -fcaller-saves -fcrossjumping -fcse-follow-jumps -fcse-skip-blocks -fdelete-null-pointer-checks -fdevirtualize -fdevirtualize-speculatively -fexpensive-optimizations -fgcse -fgcse-lm -fhoist-adjacent-loads -finline-small-functions -findirect-inlining -fipa-cp -fipa-cp-alignment -fipa-sra -fipa-icf -fisolate-erroneous-paths-dereference -flra-remat -foptimize-sibling-calls -foptimize-strlen -fpartial-inlining -fpeephole2 -freorder-blocks -freorder-blocks-and-partition -freorder-functions -frerun-cse-after-loop -fsched-interblock -fsched-spec -fschedule-insns -fschedule-insns2 -fstrict-aliasing -fstrict-overflow -ftree-builtin-call-dce -ftree-switch-conversion -ftree-tail-merge -ftree-pre -ftree-vrp -fipa-ra
Please note the warning under -fgcse about invoking -O2 on programs that use computed gotos.
Optimize yet more. -O3 turns on all optimizations specified by -O2 and also turns on the -finline-functions, -funswitch-loops, -fpredictive-commoning, -fgcse-after-reload, -ftree-loop-vectorize, -ftree-loop-distribute-patterns, -ftree-slp-vectorize, -fvect-cost-model, -ftree-partial-pre and -fipa-cp-clone options.
Reduce compilation time and make debugging produce the expected results. This is the default.
Optimize for size. -Os enables all -O2 optimizations that do not typically increase code size. It also performs further optimizations designed to reduce code size.
-Os disables the following optimization flags:
-falign-functions -falign-jumps -falign-loops -falign-labels -freorder-blocks -freorder-blocks-and-partition -fprefetch-loop-arrays
Disregard strict standards compliance. -Ofast enables all -O3 optimizations. It also enables optimizations that are not valid for all standard-compliant programs. It turns on -ffast-math and the Fortran-specific -fno-protect-parens and -fstack-arrays.
Optimize debugging experience. -Og enables optimizations that do not interfere with debugging. It should be the optimization level of choice for the standard edit-compile-debug cycle, offering a reasonable level of optimization while maintaining fast compilation and a good debugging experience.
If you use multiple -O options, with or without level numbers, the last such option is the one that is effective.
Options of the form -f``flag`` specify machine-independent flags. Most flags have both positive and negative forms; the negative form of -ffoo is -fno-foo. In the table below, only one of the forms is listedthe one you typically use. You can figure out the other form by either removing no- or adding it.
The following options control specific optimizations. They are either activated by -O options or are related to ones that are. You can use the following flags in the rare cases when fine-tuning of optimizations to be performed is desired.
Always pop the arguments to each function call as soon as that function returns. For machines that must pop arguments after a function call, the compiler normally lets arguments accumulate on the stack for several function calls and pops them all at once.
Perform a forward propagation pass on RTL The pass tries to combine two instructions and checks if the result can be simplified. If loop unrolling is active, two passes are performed and the second is scheduled after loop unrolling.
This option is enabled by default at optimization levels -O, -O2, -O3, -Os.
-ffp-contract=``style``
-ffp-contract=off disables floating-point expression contraction. -ffp-contract=fast enables floating-point expression contraction such as forming of fused multiply-add operations if the target has native support for them. -ffp-contract=on enables floating-point expression contraction if allowed by the language standard. This is currently not implemented and treated equal to -ffp-contract=off.
The default is -ffp-contract=fast.
Dont keep the frame pointer in a register for functions that dont need one. This avoids the instructions to save, set up and restore frame pointers; it also makes an extra register available in many functions. It also makes debugging impossible on some machines.
On some machines, such as the VAX, this flag has no effect, because the standard calling sequence automatically handles the frame pointer and nothing is saved by pretending it doesnt exist. The machine-description macro FRAME_POINTER_REQUIRED controls whether a target machine supports this flag. RegistersRegister UsagegccintGNU Compiler Collection (GCC) Internals.
The default setting (when not optimizing for size) for 32-bit GNU/Linux x86 and 32-bit Darwin x86 targets is -fomit-frame-pointer. You can configure GCC with the --enable-frame-pointer configure option to change the default.
Optimize sibling and tail recursive calls.
Optimize various standard C string functions (e.g. strlen, strchr or strcpy) and their _FORTIFY_SOURCE counterparts into faster alternatives.
Do not expand any functions inline apart from those marked with the always_inline attribute. This is the default when not optimizing.
Single functions can be exempted from inlining by marking them with the noinline attribute.
Integrate functions into their callers when their body is smaller than expected function call code (so overall size of program gets smaller). The compiler heuristically decides which functions are simple enough to be worth integrating in this way. This inlining applies to all functions, even those not declared inline.
Enabled at level -O2.
Inline also indirect calls that are discovered to be known at compile time thanks to previous inlining. This option has any effect only when inlining itself is turned on by the -finline-functions or -finline-small-functions options.
Enabled at level -O2.
Consider all functions for inlining, even if they are not declared inline. The compiler heuristically decides which functions are worth integrating in this way.
If all calls to a given function are integrated, and the function is declared static, then the function is normally not output as assembler code in its own right.
Enabled at level -O3.
Consider all static functions called once for inlining into their caller even if they are not marked inline. If a call to a given function is integrated, then the function is not output as assembler code in its own right.
Inline functions marked by always_inline and functions whose body seems smaller than the function call overhead early before doing -fprofile-generate instrumentation and real inlining pass. Doing so makes profiling significantly cheaper and usually inlining faster on programs having large chains of nested wrapper functions.
Enabled by default.
Perform interprocedural scalar replacement of aggregates, removal of unused parameters and replacement of parameters passed by reference by parameters passed by value.
Enabled at levels -O2, -O3 and -Os.
-finline-limit=``n``
By default, GCC limits the size of functions that can be inlined. This flag allows coarse control of this limit. n is the size of functions that can be inlined in number of pseudo instructions.
Inlining is actually controlled by a number of parameters, which may be specified individually by using --param ``name``=``value``. The -finline-limit=``n`` option sets some of these parameters as follows:
is set to n/2.
is set to n/2.
See below for a documentation of the individual parameters controlling inlining and for the defaults of these parameters.
Note: there may be no value to -finline-limit that results in default behavior.
Note: pseudo instruction represents, in this particular context, an abstract measurement of functions size. In no way does it represent a count of assembly instructions and as such its exact meaning might change from one release to an another.
This is a more fine-grained version of -fkeep-inline-functions, which applies only to functions that are declared using the dllexport attribute or declspec (Function AttributesDeclaring Attributes of Functions.)
In C, emit static functions that are declared inline into the object file, even if the function has been inlined into all of its callers. This switch does not affect functions using the extern inline extension in GNU C90 In C++, emit any and all inline functions into the object file.
Emit variables declared static const when optimization isnt turned on, even if the variables arent referenced.
GCC enables this option by default. If you want to force the compiler to check if a variable is referenced, regardless of whether or not optimization is turned on, use the -fno-keep-static-consts option.
Attempt to merge identical constants (string constants and floating-point constants) across compilation units.
This option is the default for optimized compilation if the assembler and linker support it. Use -fno-merge-constants to inhibit this behavior.
Attempt to merge identical constants and identical variables.
This option implies -fmerge-constants. In addition to -fmerge-constants this considers e.g. even constant initialized arrays or initialized constant variables with integral or floating-point types. Languages like C or C++ require each variable, including multiple instances of the same variable in recursive calls, to have distinct locations, so using this option results in non-conforming behavior.
Perform swing modulo scheduling immediately before the first scheduling pass. This pass looks at innermost loops and reorders their instructions by overlapping different iterations.
Perform more aggressive SMS-based modulo scheduling with register moves allowed. By setting this flag certain anti-dependences edges are deleted, which triggers the generation of reg-moves based on the life-range analysis. This option is effective only with -fmodulo-sched enabled.
Do not use decrement and branch instructions on a count register, but instead generate a sequence of instructions that decrement a register, compare it against zero, then branch based upon the result. This option is only meaningful on architectures that support such instructions, which include x86, PowerPC, IA-64 and S/390.
Enabled by default at -O1 and higher.
The default is -fbranch-count-reg.
Do not put function addresses in registers; make each instruction that calls a constant function contain the functions address explicitly.
This option results in less efficient code, but some strange hacks that alter the assembler output may be confused by the optimizations performed when this option is not used.
The default is -ffunction-cse
If the target supports a BSS section, GCC by default puts variables that are initialized to zero into BSS This can save space in the resulting code.
This option turns off this behavior because some programs explicitly rely on variables going to the data sectione.g., so that the resulting executable can find the beginning of that section and/or make assumptions based on that.
The default is -fzero-initialized-in-bss.
Perform optimizations that check to see if a jump branches to a location where another comparison subsumed by the first is found. If so, the first branch is redirected to either the destination of the second branch or a point immediately following it, depending on whether the condition is known to be true or false.
When using a type that occupies multiple registers, such as long long on a 32-bit system, split the registers apart and allocate them independently. This normally generates better code for those types, but may make debugging more difficult.
In common subexpression elimination (CSE), scan through jump instructions when the target of the jump is not reached by any other path. For example, when CSE encounters an if statement with an else clause, CSE follows the jump when the condition tested is false.
This is similar to -fcse-follow-jumps, but causes CSE to follow jumps that conditionally skip over blocks. When CSE encounters a simple if statement with no else clause, -fcse-skip-blocks causes CSE to follow the jump around the body of the if.
Re-run common subexpression elimination after loop optimizations are performed.
Perform a global common subexpression elimination pass. This pass also performs global constant and copy propagation.
Note: When compiling a program using computed gotos, a GCC extension, you may get better run-time performance if you disable the global common subexpression elimination pass by adding -fno-gcse to the command line.
When -fgcse-lm is enabled, global common subexpression elimination attempts to move loads that are only killed by stores into themselves. This allows a loop containing a load/store sequence to be changed to a load outside the loop, and a copy/store within the loop.
Enabled by default when -fgcse is enabled.
When -fgcse-sm is enabled, a store motion pass is run after global common subexpression elimination. This pass attempts to move stores out of loops. When used in conjunction with -fgcse-lm, loops containing a load/store sequence can be changed to a load before the loop and a store after the loop.
Not enabled at any optimization level.
When -fgcse-las is enabled, the global common subexpression elimination pass eliminates redundant loads that come after stores to the same memory location (both partial and full redundancies).
Not enabled at any optimization level.
When -fgcse-after-reload is enabled, a redundant load elimination pass is performed after reload. The purpose of this pass is to clean up redundant spilling.
This option tells the loop optimizer to use language constraints to derive bounds for the number of iterations of a loop. This assumes that loop code does not invoke undefined behavior by for example causing signed integer overflows or out-of-bound array accesses. The bounds for the number of iterations of a loop are used to guide loop unrolling and peeling and loop exit test optimizations. This option is enabled by default.
This option tells the loop optimizer to assume that loop indices do not overflow, and that loops with nontrivial exit condition are not infinite. This enables a wider range of loop optimizations even if the loop optimizer itself cannot prove that these assumptions are valid. If you use -Wunsafe-loop-optimizations, the compiler warns you if it finds this kind of loop.
Perform cross-jumping transformation. This transformation unifies equivalent code and saves code size. The resulting code may or may not perform better than without cross-jumping.
Combine increments or decrements of addresses with memory accesses. This pass is always skipped on architectures that do not have instructions to support this. Enabled by default at -O and higher on architectures that support this.
Attempt to transform conditional jumps into branch-less equivalents. This includes use of conditional moves, min, max, set flags and abs instructions, and some tricks doable by standard arithmetics. The use of conditional execution on chips where it is available is controlled by -fif-conversion2.
Use conditional execution (where available) to transform conditional jumps into branch-less equivalents.
The C++ ABI requires multiple entry points for constructors and destructors: one for a base subobject, one for a complete object, and one for a virtual destructor that calls operator delete afterwards. For a hierarchy with virtual bases, the base and complete variants are clones, which means two copies of the function. With this option, the base and complete variants are changed to be thunks that call a common implementation.
Enabled by -Os.
Assume that programs cannot safely dereference null pointers, and that no code or data element resides at address zero. This option enables simple constant folding optimizations at all optimization levels. In addition, other optimization passes in GCC use this flag to control global dataflow analyses that eliminate useless checks for null pointers; these assume that a memory access to address zero always results in a trap, so that if a pointer is checked after it has already been dereferenced, it cannot be null.
Note however that in some environments this assumption is not true. Use -fno-delete-null-pointer-checks to disable this optimization for programs that depend on that behavior.
This option is enabled by default on most targets. On Nios II ELF, it defaults to off. On AVR and CR16, this option is completely disabled.
Passes that use the dataflow information are enabled independently at different optimization levels.
Attempt to convert calls to virtual functions to direct calls. This is done both within a procedure and interprocedurally as part of indirect inlining (-findirect-inlining) and interprocedural constant propagation (-fipa-cp). Enabled at levels -O2, -O3, -Os.
Attempt to convert calls to virtual functions to speculative direct calls. Based on the analysis of the type inheritance graph, determine for a given call the set of likely targets. If the set is small, preferably of size 1, change the call into a conditional deciding between direct and indirect calls. The speculative calls enable more optimizations, such as inlining. When they seem useless after further optimization, they are converted back into original form.
Stream extra information needed for aggressive devirtualization when running the link-time optimizer in local transformation mode. This option enables more devirtualization but significantly increases the size of streamed data. For this reason it is disabled by default.
Perform a number of minor optimizations that are relatively expensive.
Attempt to remove redundant extension instructions. This is especially helpful for the x86-64 architecture, which implicitly zero-extends in 64-bit registers after writing to their lower 32-bit half.
In C++ the value of an object is only affected by changes within its lifetime: when the constructor begins, the object has an indeterminate value, and any changes during the lifetime of the object are dead when the object is destroyed. Normally dead store elimination will take advantage of this; if your code relies on the value of the object storage persisting beyond the lifetime of the object, you can use this flag to disable this optimization.
Attempt to decrease register pressure through register live range shrinkage. This is helpful for fast processors with small or moderate size register sets.
-fira-algorithm=``algorithm``
Use the specified coloring algorithm for the integrated register allocator. The algorithm argument can be priority, which specifies Chows priority coloring, or CB, which specifies Chaitin-Briggs coloring. Chaitin-Briggs coloring is not implemented for all architectures, but for those targets that do support it, it is the default because it generates better code.
-fira-region=``region``
Use specified regions for the integrated register allocator. The region argument should be one of the following:
Use all loops as register allocation regions. This can give the best results for machines with a small and/or irregular register set.
Use all loops except for loops with small register pressure as the regions. This value usually gives the best results in most cases and for most architectures, and is enabled by default when compiling with optimization for speed (-O, -O2, ...).
Use all functions as a single region. This typically results in the smallest code size, and is enabled by default for -Os or -O0.
Use IRA to evaluate register pressure in the code hoisting pass for decisions to hoist expressions. This option usually results in smaller code, but it can slow the compiler down.
This option is enabled at level -Os for all targets.
Use IRA to evaluate register pressure in loops for decisions to move loop invariants. This option usually results in generation of faster and smaller code on machines with large register files (>= 32 registers), but it can slow the compiler down.
This option is enabled at level -O3 for some targets.
Disable sharing of stack slots used for saving call-used hard registers living through a call. Each hard register gets a separate stack slot, and as a result function stack frames are larger.
Disable sharing of stack slots allocated for pseudo-registers. Each pseudo-register that does not get a hard register gets a separate stack slot, and as a result function stack frames are larger.
-fira-verbose=``n``
Control the verbosity of the dump file for the integrated register allocator. The default value is 5. If the value n is greater or equal to 10, the dump output is sent to stderr using the same format as n minus 10.
Enable CFG-sensitive rematerialization in LRA. Instead of loading values of spilled pseudos, LRA tries to rematerialize (recalculate) values if it is profitable.
If supported for the target machine, attempt to reorder instructions to exploit instruction slots available after delayed branch instructions.
If supported for the target machine, attempt to reorder instructions to eliminate execution stalls due to required data being unavailable. This helps machines that have slow floating point or memory load instructions by allowing other instructions to be issued until the result of the load or floating-point instruction is required.
Similar to -fschedule-insns, but requests an additional pass of instruction scheduling after register allocation has been done. This is especially useful on machines with a relatively small number of registers and where memory load instructions take more than one cycle.
Dont schedule instructions across basic blocks. This is normally enabled by default when scheduling before register allocation, i.e. with -fschedule-insns or at -O2 or higher.
Dont allow speculative motion of non-load instructions. This is normally enabled by default when scheduling before register allocation, i.e. with -fschedule-insns or at -O2 or higher.
Enable register pressure sensitive insn scheduling before register allocation. This only makes sense when scheduling before register allocation is enabled, i.e. with -fschedule-insns or at -O2 or higher. Usage of this option can improve the generated code and decrease its size by preventing register pressure increase above the number of available hard registers and subsequent spills in register allocation.
Allow speculative motion of some load instructions. This only makes sense when scheduling before register allocation, i.e. with -fschedule-insns or at -O2 or higher.
Allow speculative motion of more load instructions. This only makes sense when scheduling before register allocation, i.e. with -fschedule-insns or at -O2 or higher.
Define how many insns (if any) can be moved prematurely from the queue of stalled insns into the ready list during the second scheduling pass. -fno-sched-stalled-insns means that no insns are moved prematurely, -fsched-stalled-insns=0 means there is no limit on how many queued insns can be moved prematurely. -fsched-stalled-insns without a value is equivalent to -fsched-stalled-insns=1.
Define how many insn groups (cycles) are examined for a dependency on a stalled insn that is a candidate for premature removal from the queue of stalled insns. This has an effect only during the second scheduling pass, and only if -fsched-stalled-insns is used. -fno-sched-stalled-insns-dep is equivalent to -fsched-stalled-insns-dep=0. -fsched-stalled-insns-dep without a value is equivalent to -fsched-stalled-insns-dep=1.
When scheduling after register allocation, use superblock scheduling. This allows motion across basic block boundaries, resulting in faster schedules. This option is experimental, as not all machine descriptions used by GCC model the CPU closely enough to avoid unreliable results from the algorithm.
This only makes sense when scheduling after register allocation, i.e. with -fschedule-insns2 or at -O2 or higher.
Enable the group heuristic in the scheduler. This heuristic favors the instruction that belongs to a schedule group. This is enabled by default when scheduling is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher.
Enable the critical-path heuristic in the scheduler. This heuristic favors instructions on the critical path. This is enabled by default when scheduling is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher.
Enable the speculative instruction heuristic in the scheduler. This heuristic favors speculative instructions with greater dependency weakness. This is enabled by default when scheduling is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher.
Enable the rank heuristic in the scheduler. This heuristic favors the instruction belonging to a basic block with greater size or frequency. This is enabled by default when scheduling is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher.
Enable the last-instruction heuristic in the scheduler. This heuristic favors the instruction that is less dependent on the last instruction scheduled. This is enabled by default when scheduling is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher.
Enable the dependent-count heuristic in the scheduler. This heuristic favors the instruction that has more instructions depending on it. This is enabled by default when scheduling is enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher.
Modulo scheduling is performed before traditional scheduling. If a loop is modulo scheduled, later scheduling passes may change its schedule. Use this option to control that behavior.
Schedule instructions using selective scheduling algorithm. Selective scheduling runs instead of the first scheduler pass.
Schedule instructions using selective scheduling algorithm. Selective scheduling runs instead of the second scheduler pass.
Enable software pipelining of innermost loops during selective scheduling. This option has no effect unless one of -fselective-scheduling or -fselective-scheduling2 is turned on.
When pipelining loops during selective scheduling, also pipeline outer loops. This option has no effect unless -fsel-sched-pipelining is turned on.
Some object formats, like ELF, allow interposing of symbols by the dynamic linker. This means that for symbols exported from the DSO, the compiler cannot perform interprocedural propagation, inlining and other optimizations in anticipation that the function or variable in question may change. While this feature is useful, for example, to rewrite memory allocation functions by a debugging implementation, it is expensive in the terms of code quality. With -fno-semantic-interposition the compiler assumes that if interposition happens for functions the overwriting function will have precisely the same semantics (and side effects). Similarly if interposition happens for variables, the constructor of the variable will be the same. The flag has no effect for functions explicitly declared inline (where it is never allowed for interposition to change semantics) and for symbols explicitly declared weak.
Emit function prologues only before parts of the function that need it, rather than at the top of the function. This flag is enabled by default at -O and higher.
Enable allocation of values to registers that are clobbered by function calls, by emitting extra instructions to save and restore the registers around such calls. Such allocation is done only when it seems to result in better code.
This option is always enabled by default on certain machines, usually those which have no call-preserved registers to use instead.
Tracks stack adjustments (pushes and pops) and stack memory references and then tries to find ways to combine them.
Enabled by default at -O1 and higher.
Use caller save registers for allocation if those registers are not used by any called function. In that case it is not necessary to save and restore them around calls. This is only possible if called functions are part of same compilation unit as current function and they are compiled before it.
Attempt to minimize stack usage. The compiler attempts to use less stack space, even if that makes the program slower. This option implies setting the large-stack-frame parameter to 100 and the large-stack-frame-growth parameter to 400.
Perform partial redundancy elimination (PRE) on trees. This flag is enabled by default at -O2 and -O3.
Make partial redundancy elimination (PRE) more aggressive. This flag is enabled by default at -O3.
Perform forward propagation on trees. This flag is enabled by default at -O and higher.
Perform full redundancy elimination (FRE) on trees. The difference between FRE and PRE is that FRE only considers expressions that are computed on all paths leading to the redundant computation. This analysis is faster than PRE, though it exposes fewer redundancies. This flag is enabled by default at -O and higher.
Perform hoisting of loads from conditional pointers on trees. This pass is enabled by default at -O and higher.
Speculatively hoist loads from both branches of an if-then-else if the loads are from adjacent locations in the same structure and the target architecture has a conditional move instruction. This flag is enabled by default at -O2 and higher.
Perform copy propagation on trees. This pass eliminates unnecessary copy operations. This flag is enabled by default at -O and higher.
Discover which functions are pure or constant. Enabled by default at -O and higher.
Discover which static variables do not escape the compilation unit. Enabled by default at -O and higher.
Perform interprocedural pointer analysis and interprocedural modification and reference analysis. This option can cause excessive memory and compile-time usage on large compilation units. It is not enabled by default at any optimization level.
Perform interprocedural profile propagation. The functions called only from cold functions are marked as cold. Also functions executed once (such as cold, noreturn, static constructors or destructors) are identified. Cold functions and loop less parts of functions executed once are then optimized for size. Enabled by default at -O and higher.
Perform interprocedural constant propagation. This optimization analyzes the program to determine when values passed to functions are constants and then optimizes accordingly. This optimization can substantially increase performance if the application has constants passed to functions. This flag is enabled by default at -O2, -Os and -O3.
Perform function cloning to make interprocedural constant propagation stronger. When enabled, interprocedural constant propagation performs function cloning when externally visible function can be called with constant arguments. Because this optimization can create multiple copies of functions, it may significantly increase code size (see --param ipcp-unit-growth=``value``). This flag is enabled by default at -O3.
When enabled, this optimization propagates alignment of function parameters to support better vectorization and string operations.
This flag is enabled by default at -O2 and -Os. It requires that -fipa-cp is enabled.
Perform Identical Code Folding for functions and read-only variables. The optimization reduces code size and may disturb unwind stacks by replacing a function by equivalent one with a different name. The optimization works more effectively with link time optimization enabled.
Nevertheless the behavior is similar to Gold Linker ICF optimization, GCC ICF works on different levels and thus the optimizations are not same - there are equivalences that are found only by GCC and equivalences found only by Gold.
Detect paths that trigger erroneous or undefined behavior due to dereferencing a null pointer. Isolate those paths from the main control flow and turn the statement with erroneous or undefined behavior into a trap. This flag is enabled by default at -O2 and higher and depends on -fdelete-null-pointer-checks also being enabled.
Detect paths that trigger erroneous or undefined behavior due a null value being used in a way forbidden by a returns_nonnull or nonnull attribute. Isolate those paths from the main control flow and turn the statement with erroneous or undefined behavior into a trap. This is not currently enabled, but may be enabled by -O2 in the future.
Perform forward store motion on trees. This flag is enabled by default at -O and higher.
Perform sparse conditional bit constant propagation on trees and propagate pointer alignment information. This pass only operates on local scalar variables and is enabled by default at -O and higher. It requires that -ftree-ccp is enabled.
Perform sparse conditional constant propagation (CCP) on trees. This pass only operates on local scalar variables and is enabled by default at -O and higher.
Perform pattern matching on SSA PHI nodes to optimize conditional code. This pass is enabled by default at -O and higher.
Perform conversion of simple initializations in a switch to initializations from a scalar array. This flag is enabled by default at -O2 and higher.
Look for identical code sequences. When found, replace one with a jump to the other. This optimization is known as tail merging or cross jumping. This flag is enabled by default at -O2 and higher. The compilation time in this pass can be limited using max-tail-merge-comparisons parameter and max-tail-merge-iterations parameter.
Perform dead code elimination (DCE) on trees. This flag is enabled by default at -O and higher.
Perform conditional dead code elimination (DCE) for calls to built-in functions that may set errno but are otherwise side-effect free. This flag is enabled by default at -O2 and higher if -Os is not also specified.
Perform a variety of simple scalar cleanups (constant/copy propagation, redundancy elimination, range propagation and expression simplification) based on a dominator tree traversal. This also performs jump threading (to reduce jumps to jumps). This flag is enabled by default at -O and higher.
Perform dead store elimination (DSE) on trees. A dead store is a store into a memory location that is later overwritten by another store without any intervening loads. In this case the earlier store can be deleted. This flag is enabled by default at -O and higher.
Perform loop header copying on trees. This is beneficial since it increases effectiveness of code motion optimizations. It also saves one jump. This flag is enabled by default at -O and higher. It is not enabled for -Os, since it usually increases code size.
Perform loop optimizations on trees. This flag is enabled by default at -O and higher.
Perform loop interchange transformations on tree. Same as -floop-interchange. To use this code transformation, GCC has to be configured with --with-isl to enable the Graphite loop transformation infrastructure.
Perform loop interchange transformations on loops. Interchanging two nested loops switches the inner and outer loops. For example, given a loop like:
DO J = 1, M
DO I = 1, N
A(J, I) = A(J, I) * C
ENDDO
ENDDO
loop interchange transforms the loop as if it were written:
DO I = 1, N
DO J = 1, M
A(J, I) = A(J, I) * C
ENDDO
ENDDO
which can be beneficial when N is larger than the caches, because in Fortran, the elements of an array are stored in memory contiguously by column, and the original loop iterates over rows, potentially creating at each access a cache miss. This optimization applies to all the languages supported by GCC and is not limited to Fortran. To use this code transformation, GCC has to be configured with --with-isl to enable the Graphite loop transformation infrastructure.
Perform loop strip mining transformations on loops. Strip mining splits a loop into two nested loops. The outer loop has strides equal to the strip size and the inner loop has strides of the original loop within a strip. The strip length can be changed using the loop-block-tile-size parameter. For example, given a loop like:
DO I = 1, N
A(I) = A(I) + C
ENDDO
loop strip mining transforms the loop as if it were written:
DO II = 1, N, 51
DO I = II, min (II + 50, N)
A(I) = A(I) + C
ENDDO
ENDDO
This optimization applies to all the languages supported by GCC and is not limited to Fortran. To use this code transformation, GCC has to be configured with --with-isl to enable the Graphite loop transformation infrastructure.
Perform loop blocking transformations on loops. Blocking strip mines each loop in the loop nest such that the memory accesses of the element loops fit inside caches. The strip length can be changed using the loop-block-tile-size parameter. For example, given a loop like:
DO I = 1, N
DO J = 1, M
A(J, I) = B(I) + C(J)
ENDDO
ENDDO
loop blocking transforms the loop as if it were written:
DO II = 1, N, 51
DO JJ = 1, M, 51
DO I = II, min (II + 50, N)
DO J = JJ, min (JJ + 50, M)
A(J, I) = B(I) + C(J)
ENDDO
ENDDO
ENDDO
ENDDO
which can be beneficial when M is larger than the caches, because the innermost loop iterates over a smaller amount of data which can be kept in the caches. This optimization applies to all the languages supported by GCC and is not limited to Fortran. To use this code transformation, GCC has to be configured with --with-isl to enable the Graphite loop transformation infrastructure.
Enable the identity transformation for graphite. For every SCoP we generate the polyhedral representation and transform it back to gimple. Using -fgraphite-identity we can check the costs or benefits of the GIMPLE -> GRAPHITE -> GIMPLE transformation. Some minimal optimizations are also performed by the code generator ISL, like index splitting and dead code elimination in loops.
Enable the ISL based loop nest optimizer. This is a generic loop nest optimizer based on the Pluto optimization algorithms. It calculates a loop structure optimized for data-locality and parallelism. This option is experimental.
Enable unroll and jam for the ISL based loop nest optimizer. The unroll factor can be changed using the loop-unroll-jam-size parameter. The unrolled dimension (counting from the most inner one) can be changed using the loop-unroll-jam-depth parameter. .
Use the Graphite data dependence analysis to identify loops that can be parallelized. Parallelize all the loops that can be analyzed to not contain loop carried dependences without checking that it is profitable to parallelize the loops.
Compare the results of several data dependence analyzers. This option is used for debugging the data dependence analyzers.
Attempt to transform conditional jumps in the innermost loops to branch-less equivalents. The intent is to remove control-flow from the innermost loops in order to improve the ability of the vectorization pass to handle these loops. This is enabled by default if vectorization is enabled.
Attempt to also if-convert conditional jumps containing memory writes. This transformation can be unsafe for multi-threaded programs as it transforms conditional memory writes into unconditional memory writes. For example,
for (i = 0; i < N; i++)
if (cond)
A[i] = expr;
is transformed to
for (i = 0; i < N; i++)
A[i] = cond ? expr : A[i];
potentially producing data races.
Perform loop distribution. This flag can improve cache performance on big loop bodies and allow further loop optimizations, like parallelization or vectorization, to take place. For example, the loop
DO I = 1, N
A(I) = B(I) + C
D(I) = E(I) * F
ENDDO
is transformed to
DO I = 1, N
A(I) = B(I) + C
ENDDO
DO I = 1, N
D(I) = E(I) * F
ENDDO
Perform loop distribution of patterns that can be code generated with calls to a library. This flag is enabled by default at -O3.
This pass distributes the initialization loops and generates a call to memset zero. For example, the loop
DO I = 1, N
A(I) = 0
B(I) = A(I) + I
ENDDO
is transformed to
DO I = 1, N
A(I) = 0
ENDDO
DO I = 1, N
B(I) = A(I) + I
ENDDO
and the initialization loop is transformed into a call to memset zero.
Perform loop invariant motion on trees. This pass moves only invariants that are hard to handle at RTL level (function calls, operations that expand to nontrivial sequences of insns). With -funswitch-loops it also moves operands of conditions that are invariant out of the loop, so that we can use just trivial invariantness analysis in loop unswitching. The pass also includes store motion.
Create a canonical counter for number of iterations in loops for which determining number of iterations requires complicated analysis. Later optimizations then may determine the number easily. Useful especially in connection with unrolling.
Perform induction variable optimizations (strength reduction, induction variable merging and induction variable elimination) on trees.
Parallelize loops, i.e., split their iteration space to run in n threads. This is only possible for loops whose iterations are independent and can be arbitrarily reordered. The optimization is only profitable on multiprocessor machines, for loops that are CPU-intensive, rather than constrained e.g. by memory bandwidth. This option implies -pthread, and thus is only supported on targets that have support for -pthread.
Perform function-local points-to analysis on trees. This flag is enabled by default at -O and higher.
Perform scalar replacement of aggregates. This pass replaces structure references with scalars to prevent committing structures to memory too early. This flag is enabled by default at -O and higher.
Perform copy renaming on trees. This pass attempts to rename compiler temporaries to other variables at copy locations, usually resulting in variable names which more closely resemble the original variables. This flag is enabled by default at -O and higher.
Tell the copyrename pass (see -ftree-copyrename) to attempt to combine small user-defined variables too, but only if they are inlined from other functions. It is a more limited form of -ftree-coalesce-vars. This may harm debug information of such inlined variables, but it keeps variables of the inlined-into function apart from each other, such that they are more likely to contain the expected values in a debugging session.
Tell the copyrename pass (see -ftree-copyrename) to attempt to combine small user-defined variables too, instead of just compiler temporaries. This may severely limit the ability to debug an optimized program compiled with -fno-var-tracking-assignments. In the negated form, this flag prevents SSA coalescing of user variables, including inlined ones. This option is enabled by default.
Perform temporary expression replacement during the SSA->normal phase. Single use/single def temporaries are replaced at their use location with their defining expression. This results in non-GIMPLE code, but gives the expanders much more complex trees to work on resulting in better RTL generation. This is enabled by default at -O and higher.
Perform straight-line strength reduction on trees. This recognizes related expressions involving multiplications and replaces them by less expensive calculations when possible. This is enabled by default at -O and higher.
Perform vectorization on trees. This flag enables -ftree-loop-vectorize and -ftree-slp-vectorize if not explicitly specified.
Perform loop vectorization on trees. This flag is enabled by default at -O3 and when -ftree-vectorize is enabled.
Perform basic block vectorization on trees. This flag is enabled by default at -O3 and when -ftree-vectorize is enabled.
-fvect-cost-model=``model``
Alter the cost model used for vectorization. The model argument should be one of unlimited, dynamic or cheap. With the unlimited model the vectorized code-path is assumed to be profitable while with the dynamic model a runtime check guards the vectorized code-path to enable it only for iteration counts that will likely execute faster than when executing the original scalar loop. The cheap model disables vectorization of loops where doing so would be cost prohibitive for example due to required runtime checks for data dependence or alignment but otherwise is equal to the dynamic model. The default cost model depends on other optimization flags and is either dynamic or cheap.
-fsimd-cost-model=``model``
Alter the cost model used for vectorization of loops marked with the OpenMP or Cilk Plus simd directive. The model argument should be one of unlimited, dynamic, cheap. All values of model have the same meaning as described in -fvect-cost-model and by default a cost model defined with -fvect-cost-model is used.
Perform Value Range Propagation on trees. This is similar to the constant propagation pass, but instead of values, ranges of values are propagated. This allows the optimizers to remove unnecessary range checks like array bound checks and null pointer checks. This is enabled by default at -O2 and higher. Null pointer check elimination is only done if -fdelete-null-pointer-checks is enabled.
Enables expression of values of induction variables in later iterations of the unrolled loop using the value in the first iteration. This breaks long dependency chains, thus improving efficiency of the scheduling passes.
A combination of -fweb and CSE is often sufficient to obtain the same effect. However, that is not reliable in cases where the loop body is more complicated than a single basic block. It also does not work at all on some architectures due to restrictions in the CSE pass.
This optimization is enabled by default.
With this option, the compiler creates multiple copies of some local variables when unrolling a loop, which can result in superior code.
Inline parts of functions. This option has any effect only when inlining itself is turned on by the -finline-functions or -finline-small-functions options.
Enabled at level -O2.
Perform predictive commoning optimization, i.e., reusing computations (especially memory loads and stores) performed in previous iterations of loops.
This option is enabled at level -O3.
If supported by the target machine, generate instructions to prefetch memory to improve the performance of loops that access large arrays.
This option may generate better or worse code; results are highly dependent on the structure of loops within the source code.
Disabled at level -Os.
Disable any machine-specific peephole optimizations. The difference between -fno-peephole and -fno-peephole2 is in how they are implemented in the compiler; some targets use one, some use the other, a few use both.
-fpeephole is enabled by default. -fpeephole2 enabled at levels -O2, -O3, -Os.
Do not guess branch probabilities using heuristics.
GCC uses heuristics to guess branch probabilities if they are not provided by profiling feedback (-fprofile-arcs). These heuristics are based on the control flow graph. If some branch probabilities are specified by __builtin_expect, then the heuristics are used to guess branch probabilities for the rest of the control flow graph, taking the __builtin_expect info into account. The interactions between the heuristics and __builtin_expect can be complex, and in some cases, it may be useful to disable the heuristics so that the effects of __builtin_expect are easier to understand.
The default is -fguess-branch-probability at levels -O, -O2, -O3, -Os.
Reorder basic blocks in the compiled function in order to reduce number of taken branches and improve code locality.
In addition to reordering basic blocks in the compiled function, in order to reduce number of taken branches, partitions hot and cold basic blocks into separate sections of the assembly and .o files, to improve paging and cache locality performance.
This optimization is automatically turned off in the presence of exception handling, for linkonce sections, for functions with a user-defined section attribute and on any architecture that does not support named sections.
Reorder functions in the object file in order to improve code locality. This is implemented by using special subsections .text.hot for most frequently executed functions and .text.unlikely for unlikely executed functions. Reordering is done by the linker so object file format must support named sections and linker must place them in a reasonable way.
Also profile feedback must be available to make this option effective. See -fprofile-arcs for details.
Allow the compiler to assume the strictest aliasing rules applicable to the language being compiled. For C (and C++), this activates optimizations based on the type of expressions. In particular, an object of one type is assumed never to reside at the same address as an object of a different type, unless the types are almost the same. For example, an unsigned int can alias an int, but not a void* or a double. A character type may alias any other type.
Type-punningPay special attention to code like this:
union a_union {
int i;
double d;
};
int f() {
union a_union t;
t.d = 3.0;
return t.i;
}
The practice of reading from a different union member than the one most recently written to (called type-punning) is common. Even with -fstrict-aliasing, type-punning is allowed, provided the memory is accessed through the union type. So, the code above works as expected. Structures unions enumerations and bit-fields implementation. However, this code might not:
int f() {
union a_union t;
int* ip;
t.d = 3.0;
ip = &t.i;
return *ip;
}
Similarly, access by taking the address, casting the resulting pointer and dereferencing the result has undefined behavior, even if the cast uses a union type, e.g.:
int f() {
double d = 3.0;
return ((union a_union *) &d)->i;
}
The -fstrict-aliasing option is enabled at levels -O2, -O3, -Os.
Allow the compiler to assume strict signed overflow rules, depending on the language being compiled. For C (and C++) this means that overflow when doing arithmetic with signed numbers is undefined, which means that the compiler may assume that it does not happen. This permits various optimizations. For example, the compiler assumes that an expression like i + 10 > i is always true for signed i. This assumption is only valid if signed overflow is undefined, as the expression is false if i + 10 overflows when using twos complement arithmetic. When this option is in effect any attempt to determine whether an operation on signed numbers overflows must be written carefully to not actually involve overflow.
This option also allows the compiler to assume strict pointer semantics: given a pointer to an object, if adding an offset to that pointer does not produce a pointer to the same object, the addition is undefined. This permits the compiler to conclude that p + u > p is always true for a pointer p and unsigned integer u. This assumption is only valid because pointer wraparound is undefined, as the expression is false if p + u overflows using twos complement arithmetic.
See also the -fwrapv option. Using -fwrapv means that integer signed overflow is fully defined: it wraps. When -fwrapv is used, there is no difference between -fstrict-overflow and -fno-strict-overflow for integers. With -fwrapv certain types of overflow are permitted. For example, if the compiler gets an overflow when doing arithmetic on constants, the overflowed value can still be used with -fwrapv, but not otherwise.
The -fstrict-overflow option is enabled at levels -O2, -O3, -Os.
Align the start of functions to the next power-of-two greater than n, skipping up to n bytes. For instance, -falign-functions=32 aligns functions to the next 32-byte boundary, but -falign-functions=24 aligns to the next 32-byte boundary only if this can be done by skipping 23 bytes or less.
-fno-align-functions and -falign-functions=1 are equivalent and mean that functions are not aligned.
Some assemblers only support this flag when n is a power of two; in that case, it is rounded up.
If n is not specified or is zero, use a machine-dependent default.
Align all branch targets to a power-of-two boundary, skipping up to n bytes like -falign-functions. This option can easily make code slower, because it must insert dummy operations for when the branch target is reached in the usual flow of the code.
-fno-align-labels and -falign-labels=1 are equivalent and mean that labels are not aligned.
If -falign-loops or -falign-jumps are applicable and are greater than this value, then their values are used instead.
If n is not specified or is zero, use a machine-dependent default which is very likely to be 1, meaning no alignment.
Align loops to a power-of-two boundary, skipping up to n bytes like -falign-functions. If the loops are executed many times, this makes up for any execution of the dummy operations.
-fno-align-loops and -falign-loops=1 are equivalent and mean that loops are not aligned.
If n is not specified or is zero, use a machine-dependent default.
Align branch targets to a power-of-two boundary, for branch targets where the targets can only be reached by jumping, skipping up to n bytes like -falign-functions. In this case, no dummy operations need be executed.
-fno-align-jumps and -falign-jumps=1 are equivalent and mean that loops are not aligned.
If n is not specified or is zero, use a machine-dependent default.
This option is left for compatibility reasons. -funit-at-a-time has no effect, while -fno-unit-at-a-time implies -fno-toplevel-reorder and -fno-section-anchors.
Enabled by default.
Do not reorder top-level functions, variables, and asm statements. Output them in the same order that they appear in the input file. When this option is used, unreferenced static variables are not removed. This option is intended to support existing code that relies on a particular ordering. For new code, it is better to use attributes when possible.
Enabled at level -O0. When disabled explicitly, it also implies -fno-section-anchors, which is otherwise enabled at -O0 on some targets.
Constructs webs as commonly used for register allocation purposes and assign each web individual pseudo register. This allows the register allocation pass to operate on pseudos directly, but also strengthens several other optimization passes, such as CSE, loop optimizer and trivial dead code remover. It can, however, make debugging impossible, since variables no longer stay in a home register.
Enabled by default with -funroll-loops.
Assume that the current compilation unit represents the whole program being compiled. All public functions and variables with the exception of main and those merged by attribute externally_visible become static functions and in effect are optimized more aggressively by interprocedural optimizers.
This option should not be used in combination with -flto. Instead relying on a linker plugin should provide safer and more precise information.
-flto[=``n``]
This option runs the standard link-time optimizer. When invoked with source code, it generates GIMPLE (one of GCCs internal representations) and writes it to special ELF sections in the object file. When the object files are linked together, all the function bodies are read from these ELF sections and instantiated as if they had been part of the same translation unit.
To use the link-time optimizer, -flto and optimization options should be specified at compile time and during the final link. For example:
gcc -c -O2 -flto foo.c
gcc -c -O2 -flto bar.c
gcc -o myprog -flto -O2 foo.o bar.o
The first two invocations to GCC save a bytecode representation of GIMPLE into special ELF sections inside foo.o and bar.o. The final invocation reads the GIMPLE bytecode from foo.o and bar.o, merges the two files into a single internal image, and compiles the result as usual. Since both foo.o and bar.o are merged into a single image, this causes all the interprocedural analyses and optimizations in GCC to work across the two files as if they were a single one. This means, for example, that the inliner is able to inline functions in bar.o into functions in foo.o and vice-versa.
Another (simpler) way to enable link-time optimization is:
gcc -o myprog -flto -O2 foo.c bar.c
The above generates bytecode for foo.c and bar.c, merges them together into a single GIMPLE representation and optimizes them as usual to produce myprog.
The only important thing to keep in mind is that to enable link-time optimizations you need to use the GCC driver to perform the link-step. GCC then automatically performs link-time optimization if any of the objects involved were compiled with the -flto command-line option. You generally should specify the optimization options to be used for link-time optimization though GCC tries to be clever at guessing an optimization level to use from the options used at compile-time if you fail to specify one at link-time. You can always override the automatic decision to do link-time optimization at link-time by passing -fno-lto to the link command.
To make whole program optimization effective, it is necessary to make certain whole program assumptions. The compiler needs to know what functions and variables can be accessed by libraries and runtime outside of the link-time optimized unit. When supported by the linker, the linker plugin (see -fuse-linker-plugin) passes information to the compiler about used and externally visible symbols. When the linker plugin is not available, -fwhole-program should be used to allow the compiler to make these assumptions, which leads to more aggressive optimization decisions.
When -fuse-linker-plugin is not enabled then, when a file is compiled with -flto, the generated object file is larger than a regular object file because it contains GIMPLE bytecodes and the usual final code (see -ffat-lto-objects. This means that object files with LTO information can be linked as normal object files; if -fno-lto is passed to the linker, no interprocedural optimizations are applied. Note that when -fno-fat-lto-objects is enabled the compile-stage is faster but you cannot perform a regular, non-LTO link on them.
Additionally, the optimization flags used to compile individual files are not necessarily related to those used at link time. For instance,
gcc -c -O0 -ffat-lto-objects -flto foo.c
gcc -c -O0 -ffat-lto-objects -flto bar.c
gcc -o myprog -O3 foo.o bar.o
This produces individual object files with unoptimized assembler code, but the resulting binary myprog is optimized at -O3. If, instead, the final binary is generated with -fno-lto, then myprog is not optimized.
When producing the final binary, GCC only applies link-time optimizations to those files that contain bytecode. Therefore, you can mix and match object files and libraries with GIMPLE bytecodes and final object code. GCC automatically selects which files to optimize in LTO mode and which files to link without further processing.
There are some code generation flags preserved by GCC when generating bytecodes, as they need to be used during the final link stage. Generally options specified at link-time override those specified at compile-time.
If you do not specify an optimization level option -O at link-time then GCC computes one based on the optimization levels used when compiling the object files. The highest optimization level wins here.
Currently, the following options and their setting are take from the first object file that explicitely specified it: -fPIC, -fpic, -fpie, -fcommon, -fexceptions, -fnon-call-exceptions, -fgnu-tm and all the -m target flags.
Certain ABI changing flags are required to match in all compilation-units and trying to override this at link-time with a conflicting value is ignored. This includes options such as -freg-struct-return and -fpcc-struct-return.
Other options such as -ffp-contract, -fno-strict-overflow, -fwrapv, -fno-trapv or -fno-strict-aliasing are passed through to the link stage and merged conservatively for conflicting translation units. Specifically -fno-strict-overflow, -fwrapv and -fno-trapv take precedence and for example -ffp-contract=off takes precedence over -ffp-contract=fast. You can override them at linke-time.
It is recommended that you compile all the files participating in the same link with the same options and also specify those options at link time.
If LTO encounters objects with C linkage declared with incompatible types in separate translation units to be linked together (undefined behavior according to ISO C99 6.2.7), a non-fatal diagnostic may be issued. The behavior is still undefined at run time. Similar diagnostics may be raised for other languages.
Another feature of LTO is that it is possible to apply interprocedural optimizations on files written in different languages:
gcc -c -flto foo.c
g++ -c -flto bar.cc
gfortran -c -flto baz.f90
g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran
Notice that the final link is done with g++ to get the C++ runtime libraries and -lgfortran is added to get the Fortran runtime libraries. In general, when mixing languages in LTO mode, you should use the same link command options as when mixing languages in a regular (non-LTO) compilation.
If object files containing GIMPLE bytecode are stored in a library archive, say libfoo.a, it is possible to extract and use them in an LTO link if you are using a linker with plugin support. To create static libraries suitable for LTO, use gcc-ar and gcc-ranlib instead of ar and ranlib; to show the symbols of object files with GIMPLE bytecode, use gcc-nm. Those commands require that ar, ranlib and nm have been compiled with plugin support. At link time, use the the flag -fuse-linker-plugin to ensure that the library participates in the LTO optimization process:
gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo
With the linker plugin enabled, the linker extracts the needed GIMPLE files from libfoo.a and passes them on to the running GCC to make them part of the aggregated GIMPLE image to be optimized.
If you are not using a linker with plugin support and/or do not enable the linker plugin, then the objects inside libfoo.a are extracted and linked as usual, but they do not participate in the LTO optimization process. In order to make a static library suitable for both LTO optimization and usual linkage, compile its object files with -flto -ffat-lto-objects.
Link-time optimizations do not require the presence of the whole program to operate. If the program does not require any symbols to be exported, it is possible to combine -flto and -fwhole-program to allow the interprocedural optimizers to use more aggressive assumptions which may lead to improved optimization opportunities. Use of -fwhole-program is not needed when linker plugin is active (see -fuse-linker-plugin).
The current implementation of LTO makes no attempt to generate bytecode that is portable between different types of hosts. The bytecode files are versioned and there is a strict version check, so bytecode files generated in one version of GCC do not work with an older or newer version of GCC.
Link-time optimization does not work well with generation of debugging information. Combining -flto with -g is currently experimental and expected to produce unexpected results.
If you specify the optional n, the optimization and code generation done at link time is executed in parallel using n parallel jobs by utilizing an installed make program. The environment variable MAKE may be used to override the program used. The default value for n is 1.
You can also specify -flto=jobserver to use GNU makes job server mode to determine the number of parallel jobs. This is useful when the Makefile calling GCC is already executing in parallel. You must prepend a + to the command recipe in the parent Makefile for this to work. This option likely only works if MAKE is GNU make.
-flto-partition=``alg``
Specify the partitioning algorithm used by the link-time optimizer. The value is either 1to1 to specify a partitioning mirroring the original source files or balanced to specify partitioning into equally sized chunks (whenever possible) or max to create new partition for every symbol where possible. Specifying none as an algorithm disables partitioning and streaming completely. The default value is balanced. While 1to1 can be used as an workaround for various code ordering issues, the max partitioning is intended for internal testing only. The value one specifies that exactly one partition should be used while the value none bypasses partitioning and executes the link-time optimization step directly from the WPA phase.
Enable streaming of mangled types names of C++ types and their unification at linktime. This increases size of LTO object files, but enable diagnostics about One Definition Rule violations.
-flto-compression-level=``n``
This option specifies the level of compression used for intermediate language written to LTO object files, and is only meaningful in conjunction with LTO mode (-flto). Valid values are 0 (no compression) to 9 (maximum compression). Values outside this range are clamped to either 0 or 9. If the option is not given, a default balanced compression setting is used.
Prints a report with internal details on the workings of the link-time optimizer. The contents of this report vary from version to version. It is meant to be useful to GCC developers when processing object files in LTO mode (via -flto).
Disabled by default.
Like -flto-report, but only print for the WPA phase of Link Time Optimization.
Enables the use of a linker plugin during link-time optimization. This option relies on plugin support in the linker, which is available in gold or in GNU ld 2.21 or newer.
This option enables the extraction of object files with GIMPLE bytecode out of library archives. This improves the quality of optimization by exposing more code to the link-time optimizer. This information specifies what symbols can be accessed externally (by non-LTO object or during dynamic linking). Resulting code quality improvements on binaries (and shared libraries that use hidden visibility) are similar to -fwhole-program. See -flto for a description of the effect of this flag and how to use it.
This option is enabled by default when LTO support in GCC is enabled and GCC was configured for use with a linker supporting plugins (GNU ld 2.21 or newer or gold).
Fat LTO objects are object files that contain both the intermediate language and the object code. This makes them usable for both LTO linking and normal linking. This option is effective only when compiling with -flto and is ignored at link time.
-fno-fat-lto-objects improves compilation time over plain LTO, but requires the complete toolchain to be aware of LTO. It requires a linker with linker plugin support for basic functionality. Additionally, nm, ar and ranlib need to support linker plugins to allow a full-featured build environment (capable of building static libraries etc). GCC provides the gcc-ar, gcc-nm, gcc-ranlib wrappers to pass the right options to these tools. With non fat LTO makefiles need to be modified to use them.
The default is -fno-fat-lto-objects on targets with linker plugin support.
After register allocation and post-register allocation instruction splitting, identify arithmetic instructions that compute processor flags similar to a comparison operation based on that arithmetic. If possible, eliminate the explicit comparison operation.
This pass only applies to certain targets that cannot explicitly represent the comparison operation before register allocation is complete.
After register allocation and post-register allocation instruction splitting, perform a copy-propagation pass to try to reduce scheduling dependencies and occasionally eliminate the copy.
Profiles collected using an instrumented binary for multi-threaded programs may be inconsistent due to missed counter updates. When this option is specified, GCC uses heuristics to correct or smooth out such inconsistencies. By default, GCC emits an error message when an inconsistent profile is detected.
-fprofile-dir=``path``
Set the directory to search for the profile data files in to path. This option affects only the profile data generated by -fprofile-generate, -ftest-coverage, -fprofile-arcs and used by -fprofile-use and -fbranch-probabilities and its related options. Both absolute and relative paths can be used. By default, GCC uses the current directory as path, thus the profile data file appears in the same directory as the object file.
Enable options usually used for instrumenting application to produce profile useful for later recompilation with profile feedback based optimization. You must use -fprofile-generate both when compiling and when linking your program.
The following options are enabled: -fprofile-arcs, -fprofile-values, -fvpt.
If path is specified, GCC looks at the path to find the profile feedback data files. See -fprofile-dir.
Enable profile feedback-directed optimizations, and the following optimizations which are generally profitable only with profile feedback available: -fbranch-probabilities, -fvpt, -funroll-loops, -fpeel-loops, -ftracer, -ftree-vectorize, and ftree-loop-distribute-patterns.
By default, GCC emits an error message if the feedback profiles do not match the source code. This error can be turned into a warning by using -Wcoverage-mismatch. Note this may result in poorly optimized code.
If path is specified, GCC looks at the path to find the profile feedback data files. See -fprofile-dir.
Enable sampling-based feedback-directed optimizations, and the following optimizations which are generally profitable only with profile feedback available: -fbranch-probabilities, -fvpt, -funroll-loops, -fpeel-loops, -ftracer, -ftree-vectorize, -finline-functions, -fipa-cp, -fipa-cp-clone, -fpredictive-commoning, -funswitch-loops, -fgcse-after-reload, and -ftree-loop-distribute-patterns.
path is the name of a file containing AutoFDO profile information. If omitted, it defaults to fbdata.afdo in the current directory.
Producing an AutoFDO profile data file requires running your program with the perf utility on a supported GNU/Linux target system. For more information, see https://perf.wiki.kernel.org/.
E.g.
perf record -e br_inst_retired:near_taken -b -o perf.data \
-- your_program
Then use the create_gcov tool to convert the raw profile data to a format that can be used by GCC. You must also supply the unstripped binary for your program to this tool. See https://github.com/google/autofdo.
E.g.
create_gcov --binary=your_program.unstripped --profile=perf.data \
--gcov=profile.afdo
The following options control compiler behavior regarding floating-point arithmetic. These options trade off between speed and correctness. All must be specifically enabled.
Do not store floating-point variables in registers, and inhibit other options that might change whether a floating-point value is taken from a register or memory.
This option prevents undesirable excess precision on machines such as the 68000 where the floating registers (of the 68881) keep more precision than a double is supposed to have. Similarly for the x86 architecture. For most programs, the excess precision does only good, but a few programs rely on the precise definition of IEEE floating point. Use -ffloat-store for such programs, after modifying them to store all pertinent intermediate computations into variables.
-fexcess-precision=``style``
This option allows further control over excess precision on machines where floating-point registers have more precision than the IEEE float and double types and the processor does not support operations rounding to those types. By default, -fexcess-precision=fast is in effect; this means that operations are carried out in the precision of the registers and that it is unpredictable when rounding to the types specified in the source code takes place. When compiling C, if -fexcess-precision=standard is specified then excess precision follows the rules specified in ISO C99; in particular, both casts and assignments cause values to be rounded to their semantic types (whereas -ffloat-store only affects assignments). This option is enabled by default for C if a strict conformance option such as -std=c99 is used.
-fexcess-precision=standard is not implemented for languages other than C, and has no effect if -funsafe-math-optimizations or -ffast-math is specified. On the x86, it also has no effect if -mfpmath=sse or -mfpmath=sse+387 is specified; in the former case, IEEE semantics apply without excess precision, and in the latter, rounding is unpredictable.
Sets the options -fno-math-errno, -funsafe-math-optimizations, -ffinite-math-only, -fno-rounding-math, -fno-signaling-nans and -fcx-limited-range.
This option causes the preprocessor macro __FAST_MATH__ to be defined.
This option is not turned on by any -O option besides -Ofast since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications.
Do not set errno after calling math functions that are executed with a single instruction, e.g., sqrt. A program that relies on IEEE exceptions for math error handling may want to use this flag for speed while maintaining IEEE arithmetic compatibility.
This option is not turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications.
The default is -fmath-errno.
On Darwin systems, the math library never sets errno. There is therefore no reason for the compiler to consider the possibility that it might, and -fno-math-errno is the default.
Allow optimizations for floating-point arithmetic that (a) assume that arguments and results are valid and (b) may violate IEEE or ANSI standards. When used at link-time, it may include libraries or startup files that change the default FPU control word or other similar optimizations.
This option is not turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications. Enables -fno-signed-zeros, -fno-trapping-math, -fassociative-math and -freciprocal-math.
The default is -fno-unsafe-math-optimizations.
Allow re-association of operands in series of floating-point operations. This violates the ISO C and C++ language standard by possibly changing computation result. NOTE: re-ordering may change the sign of zero as well as ignore NaNs and inhibit or create underflow or overflow (and thus cannot be used on code that relies on rounding behavior like (x + 2**52) - 2**52. May also reorder floating-point comparisons and thus may not be used when ordered comparisons are required. This option requires that both -fno-signed-zeros and -fno-trapping-math be in effect. Moreover, it doesnt make much sense with -frounding-math. For Fortran the option is automatically enabled when both -fno-signed-zeros and -fno-trapping-math are in effect.
The default is -fno-associative-math.
Allow the reciprocal of a value to be used instead of dividing by the value if this enables optimizations. For example x / y can be replaced with x * (1/y), which is useful if (1/y) is subject to common subexpression elimination. Note that this loses precision and increases the number of flops operating on the value.
The default is -fno-reciprocal-math.
Allow optimizations for floating-point arithmetic that assume that arguments and results are not NaNs or +-Infs.
This option is not turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions. It may, however, yield faster code for programs that do not require the guarantees of these specifications.
The default is -fno-finite-math-only.
Allow optimizations for floating-point arithmetic that ignore the signedness of zero. IEEE arithmetic specifies the behavior of distinct +0.0 and 0.0 values, which then prohibits simplification of expressions such as x+0.0 or 0.0*x (even with -ffinite-math-only). This option implies that the sign of a zero result isnt significant.
The default is -fsigned-zeros.
Compile code assuming that floating-point operations cannot generate user-visible traps. These traps include division by zero, overflow, underflow, inexact result and invalid operation. This option requires that -fno-signaling-nans be in effect. Setting this option may allow faster code if one relies on non-stop IEEE arithmetic, for example.
This option should never be turned on by any -O option since it can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions.
The default is -ftrapping-math.
Disable transformations and optimizations that assume default floating-point rounding behavior. This is round-to-zero for all floating point to integer conversions, and round-to-nearest for all other arithmetic truncations. This option should be specified for programs that change the FP rounding mode dynamically, or that may be executed with a non-default rounding mode. This option disables constant folding of floating-point expressions at compile time (which may be affected by rounding mode) and arithmetic transformations that are unsafe in the presence of sign-dependent rounding modes.
The default is -fno-rounding-math.
This option is experimental and does not currently guarantee to disable all GCC optimizations that are affected by rounding mode. Future versions of GCC may provide finer control of this setting using C99s FENV_ACCESS pragma. This command-line option will be used to specify the default state for FENV_ACCESS.
Compile code assuming that IEEE signaling NaNs may generate user-visible traps during floating-point operations. Setting this option disables optimizations that may change the number of exceptions visible with signaling NaNs. This option implies -ftrapping-math.
This option causes the preprocessor macro __SUPPORT_SNAN__ to be defined.
The default is -fno-signaling-nans.
This option is experimental and does not currently guarantee to disable all GCC optimizations that affect signaling NaN behavior.
Treat floating-point constants as single precision instead of implicitly converting them to double-precision constants.
When enabled, this option states that a range reduction step is not needed when performing complex division. Also, there is no checking whether the result of a complex multiplication or division is NaN + I*NaN, with an attempt to rescue the situation in that case. The default is -fno-cx-limited-range, but is enabled by -ffast-math.
This option controls the default setting of the ISO C99 CX_LIMITED_RANGE pragma. Nevertheless, the option applies to all languages.
Complex multiplication and division follow Fortran rules. Range reduction is done as part of complex division, but there is no checking whether the result of a complex multiplication or division is NaN + I*NaN, with an attempt to rescue the situation in that case.
The default is -fno-cx-fortran-rules.
The following options control optimizations that may improve performance, but are not enabled by any -O options. This section includes experimental options that may produce broken code.
After running a program compiled with -fprofile-arcs (Debugging OptionsOptions for Debugging Your Program or gcc), you can compile it a second time using -fbranch-probabilities, to improve optimizations based on the number of times each branch was taken. When a program compiled with -fprofile-arcs exits, it saves arc execution counts to a file called sourcename.gcda for each source file. The information in this data file is very dependent on the structure of the generated code, so you must use the same source code and the same optimization options for both compilations.
With -fbranch-probabilities, GCC puts a REG_BR_PROB note on each JUMP_INSN and CALL_INSN. These can be used to improve optimization. Currently, they are only used in one place: in reorg.c, instead of guessing which path a branch is most likely to take, the REG_BR_PROB values are used to exactly determine which path is taken more often.
If combined with -fprofile-arcs, it adds code so that some data about values of expressions in the program is gathered.
With -fbranch-probabilities, it reads back the data gathered from profiling values of expressions for usage in optimizations.
Enabled with -fprofile-generate and -fprofile-use.
Function reordering based on profile instrumentation collects first time of execution of a function and orders these functions in ascending order.
Enabled with -fprofile-use.
If combined with -fprofile-arcs, this option instructs the compiler to add code to gather information about values of expressions.
With -fbranch-probabilities, it reads back the data gathered and actually performs the optimizations based on them. Currently the optimizations include specialization of division operations using the knowledge about the value of the denominator.
Attempt to avoid false dependencies in scheduled code by making use of registers left over after register allocation. This optimization most benefits processors with lots of registers. Depending on the debug information format adopted by the target, however, it can make debugging impossible, since variables no longer stay in a home register.
Enabled by default with -funroll-loops and -fpeel-loops.
Performs a target dependent pass over the instruction stream to schedule instructions of same type together because target machine can execute them more efficiently if they are adjacent to each other in the instruction flow.
Perform tail duplication to enlarge superblock size. This transformation simplifies the control flow of the function allowing other optimizations to do a better job.
Enabled with -fprofile-use.
Unroll loops whose number of iterations can be determined at compile time or upon entry to the loop. -funroll-loops implies -frerun-cse-after-loop, -fweb and -frename-registers. It also turns on complete loop peeling (i.e. complete removal of loops with a small constant number of iterations). This option makes code larger, and may or may not make it run faster.
Enabled with -fprofile-use.
Unroll all loops, even if their number of iterations is uncertain when the loop is entered. This usually makes programs run more slowly. -funroll-all-loops implies the same options as -funroll-loops.
Peels loops for which there is enough information that they do not roll much (from profile feedback). It also turns on complete loop peeling (i.e. complete removal of loops with small constant number of iterations).
Enabled with -fprofile-use.
Enables the loop invariant motion pass in the RTL loop optimizer. Enabled at level -O1
Move branches with loop invariant conditions out of the loop, with duplicates of the loop on both branches (modified according to result of the condition).
Place each function or data item into its own section in the output file if the target supports arbitrary sections. The name of the function or the name of the data item determines the sections name in the output file.
Use these options on systems where the linker can perform optimizations to improve locality of reference in the instruction space. Most systems using the ELF object format and SPARC processors running Solaris 2 have linkers with such optimizations. AIX may have these optimizations in the future.
Only use these options when there are significant benefits from doing so. When you specify these options, the assembler and linker create larger object and executable files and are also slower. You cannot use gprof on all systems if you specify this option, and you may have problems with debugging if you specify both this option and -g.
Perform branch target register load optimization before prologue / epilogue threading. The use of target registers can typically be exposed only during reload, thus hoisting loads out of loops and doing inter-block scheduling needs a separate optimization pass.
Perform branch target register load optimization after prologue / epilogue threading.
When performing branch target register load optimization, dont reuse branch target registers within any basic block.
Emit extra code to check for buffer overflows, such as stack smashing attacks. This is done by adding a guard variable to functions with vulnerable objects. This includes functions that call alloca, and functions with buffers larger than 8 bytes. The guards are initialized when a function is entered and then checked when the function exits. If a guard check fails, an error message is printed and the program exits.
Like -fstack-protector except that all functions are protected.
Like -fstack-protector but includes additional functions to be protected those that have local array definitions, or have references to local frame addresses.
Like -fstack-protector but only protects those functions which have the stack_protect attribute
Optimize the prologue of variadic argument functions with respect to usage of those arguments.
Try to reduce the number of symbolic address calculations by using shared anchor symbols to address nearby objects. This transformation can help to reduce the number of GOT entries and GOT accesses on some targets.
For example, the implementation of the following function foo:
static int a, b, c;
int foo (void) { return a + b + c; }
usually calculates the addresses of all three variables, but if you compile it with -fsection-anchors, it accesses the variables from a common anchor point instead. The effect is similar to the following pseudocode (which isnt valid C):
int foo (void)
{
register int *xr = &x;
return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
}
Not all targets support this option.
–param name``=``value
In some places, GCC uses various constants to control the amount of optimization that is done. For example, GCC does not inline functions that contain more than a certain number of instructions. You can control some of these constants on the command line using the --param option.
The names of specific parameters, and the meaning of the values, are tied to the internals of the compiler, and are subject to change without notice in future releases.
In each case, the value is an integer. The allowable choices for name are:
When branch is predicted to be taken with probability lower than this threshold (in percent), then it is considered well predictable. The default is 10.
The maximum number of incoming edges to consider for cross-jumping. The algorithm used by -fcrossjumping is O(N^2) in the number of edges incoming to each block. Increasing values mean more aggressive optimization, making the compilation time increase with probably small improvement in executable size.
The minimum number of instructions that must be matched at the end of two blocks before cross-jumping is performed on them. This value is ignored in the case where all instructions in the block being cross-jumped from are matched. The default value is 5.
The maximum code size expansion factor when copying basic blocks instead of jumping. The expansion is relative to a jump instruction. The default value is 8.
The maximum number of instructions to duplicate to a block that jumps to a computed goto. To avoid O(N^2) behavior in a number of passes, GCC factors computed gotos early in the compilation process, and unfactors them as late as possible. Only computed jumps at the end of a basic blocks with no more than max-goto-duplication-insns are unfactored. The default value is 8.
The maximum number of instructions to consider when looking for an instruction to fill a delay slot. If more than this arbitrary number of instructions are searched, the time savings from filling the delay slot are minimal, so stop searching. Increasing values mean more aggressive optimization, making the compilation time increase with probably small improvement in execution time.
When trying to fill delay slots, the maximum number of instructions to consider when searching for a block with valid live register information. Increasing this arbitrarily chosen value means more aggressive optimization, increasing the compilation time. This parameter should be removed when the delay slot code is rewritten to maintain the control-flow graph.
The approximate maximum amount of memory that can be allocated in order to perform the global common subexpression elimination optimization. If more memory than specified is required, the optimization is not done.
If the ratio of expression insertions to deletions is larger than this value for any expression, then RTL PRE inserts or removes the expression and thus leaves partially redundant computations in the instruction stream. The default value is 20.
The maximum number of pending dependencies scheduling allows before flushing the current state and starting over. Large functions with few branches or calls can create excessively large lists which needlessly consume memory and resources.
The maximum number of backtrack attempts the scheduler should make when modulo scheduling a loop. Larger values can exponentially increase compilation time.
Several parameters control the tree inliner used in GCC This number sets the maximum number of instructions (counted in GCCs internal representation) in a single function that the tree inliner considers for inlining. This only affects functions declared inline and methods implemented in a class declaration (C++). The default value is 400.
When you use -finline-functions (included in -O3), a lot of functions that would otherwise not be considered for inlining by the compiler are investigated. To those functions, a different (more restrictive) limit compared to functions declared inline can be applied. The default value is 40.
When estimated performance improvement of caller + callee runtime exceeds this threshold (in precent), the function can be inlined regardless the limit on --param max-inline-insns-single and --param max-inline-insns-auto.
The limit specifying really large functions. For functions larger than this limit after inlining, inlining is constrained by --param large-function-growth. This parameter is useful primarily to avoid extreme compilation time caused by non-linear algorithms used by the back end. The default value is 2700.
Specifies maximal growth of large function caused by inlining in percents. The default value is 100 which limits large function growth to 2.0 times the original size.
The limit specifying large translation unit. Growth caused by inlining of units larger than this limit is limited by --param inline-unit-growth. For small units this might be too tight. For example, consider a unit consisting of function A that is inline and B that just calls A three times. If B is small relative to A, the growth of unit is 300% and yet such inlining is very sane. For very large units consisting of small inlineable functions, however, the overall unit growth limit is needed to avoid exponential explosion of code size. Thus for smaller units, the size is increased to --param large-unit-insns before applying --param inline-unit-growth. The default is 10000.
Specifies maximal overall growth of the compilation unit caused by inlining. The default value is 20 which limits unit growth to 1.2 times the original size. Cold functions (either marked cold via an attribute or by profile feedback) are not accounted into the unit size.
Specifies maximal overall growth of the compilation unit caused by interprocedural constant propagation. The default value is 10 which limits unit growth to 1.1 times the original size.
The limit specifying large stack frames. While inlining the algorithm is trying to not grow past this limit too much. The default value is 256 bytes.
Specifies maximal growth of large stack frames caused by inlining in percents. The default value is 1000 which limits large stack frame growth to 11 times the original size.
Specifies the maximum number of instructions an out-of-line copy of a self-recursive inline function can grow into by performing recursive inlining.
--param max-inline-insns-recursive applies to functions declared inline. For functions not declared inline, recursive inlining happens only when -finline-functions (included in -O3) is enabled; --param max-inline-insns-recursive-auto applies instead. The default value is 450.
Specifies the maximum recursion depth used for recursive inlining.
--param max-inline-recursive-depth applies to functions declared inline. For functions not declared inline, recursive inlining happens only when -finline-functions (included in -O3) is enabled; --param max-inline-recursive-depth-auto applies instead. The default value is 8.
Recursive inlining is profitable only for function having deep recursion in average and can hurt for function having little recursion depth by increasing the prologue size or complexity of function body to other optimizers.
When profile feedback is available (see -fprofile-generate) the actual recursion depth can be guessed from probability that function recurses via a given call expression. This parameter limits inlining only to call expressions whose probability exceeds the given threshold (in percents). The default value is 10.
Specify growth that the early inliner can make. In effect it increases the amount of inlining for code having a large abstraction penalty. The default value is 14.
Limit of iterations of the early inliner. This basically bounds the number of nested indirect calls the early inliner can resolve. Deeper chains are still handled by late inlining.
Probability (in percent) that C++ inline function with comdat visibility are shared across multiple compilation units. The default value is 20.
A parameter to control whether to use function internal id in profile database lookup. If the value is 0, the compiler uses an id that is based on function assembler name and filename, which makes old profile data more tolerant to source changes such as function reordering etc. The default value is 0.
The minimum number of iterations under which loops are not vectorized when -ftree-vectorize is used. The number of iterations after vectorization needs to be greater than the value specified by this option to allow vectorization. The default value is 0.
Scaling factor in calculation of maximum distance an expression can be moved by GCSE optimizations. This is currently supported only in the code hoisting pass. The bigger the ratio, the more aggressive code hoisting is with simple expressions, i.e., the expressions that have cost less than gcse-unrestricted-cost. Specifying 0 disables hoisting of simple expressions. The default value is 10.
Cost, roughly measured as the cost of a single typical machine instruction, at which GCSE optimizations do not constrain the distance an expression can travel. This is currently supported only in the code hoisting pass. The lesser the cost, the more aggressive code hoisting is. Specifying 0 allows all expressions to travel unrestricted distances. The default value is 3.
The depth of search in the dominator tree for expressions to hoist. This is used to avoid quadratic behavior in hoisting algorithm. The value of 0 does not limit on the search, but may slow down compilation of huge functions. The default value is 30.
The maximum amount of similar bbs to compare a bb with. This is used to avoid quadratic behavior in tree tail merging. The default value is 10.
The maximum amount of iterations of the pass over the function. This is used to limit compilation time in tree tail merging. The default value is 2.
The maximum number of instructions that a loop may have to be unrolled. If a loop is unrolled, this parameter also determines how many times the loop code is unrolled.
The maximum number of instructions biased by probabilities of their execution that a loop may have to be unrolled. If a loop is unrolled, this parameter also determines how many times the loop code is unrolled.
The maximum number of unrollings of a single loop.
The maximum number of instructions that a loop may have to be peeled. If a loop is peeled, this parameter also determines how many times the loop code is peeled.
The maximum number of peelings of a single loop.
The maximum number of branches on the hot path through the peeled sequence.
The maximum number of insns of a completely peeled loop.
The maximum number of iterations of a loop to be suitable for complete peeling.
The maximum depth of a loop nest suitable for complete peeling.
The maximum number of insns of an unswitched loop.
The maximum number of branches unswitched in a single loop.
The minimum cost of an expensive expression in the loop invariant motion.
Bound on number of candidates for induction variables, below which all candidates are considered for each use in induction variable optimizations. If there are more candidates than this, only the most relevant ones are considered to avoid quadratic time complexity.
The induction variable optimizations give up on loops that contain more induction variable uses.
If the number of candidates in the set is smaller than this value, always try to remove unnecessary ivs from the set when adding a new one.
Bound on size of expressions used in the scalar evolutions analyzer. Large expressions slow the analyzer.
Bound on the complexity of the expressions in the scalar evolutions analyzer. Complex expressions slow the analyzer.
The maximum number of variables in an Omega constraint system. The default value is 128.
The maximum number of inequalities in an Omega constraint system. The default value is 256.
The maximum number of equalities in an Omega constraint system. The default value is 128.
The maximum number of wildcard variables that the Omega solver is able to insert. The default value is 18.
The size of the hash table in the Omega solver. The default value is 550.
The maximal number of keys used by the Omega solver. The default value is 500.
When set to 1, use expensive methods to eliminate all redundant constraints. The default value is 0.
The maximum number of run-time checks that can be performed when doing loop versioning for alignment in the vectorizer.
The maximum number of run-time checks that can be performed when doing loop versioning for alias in the vectorizer.
The maximum number of loop peels to enhance access alignment for vectorizer. Value -1 means no limit.
The maximum number of iterations of a loop the brute-force algorithm for analysis of the number of iterations of the loop tries to evaluate.
A basic block profile count is considered hot if it contributes to the given permillage (i.e. 0...1000) of the entire profiled execution.
Select fraction of the entry block frequency of executions of basic block in function given basic block needs to have to be considered hot.
The maximum number of loop iterations we predict statically. This is useful in cases where a function contains a single loop with known bound and another loop with unknown bound. The known number of iterations is predicted correctly, while the unknown number of iterations average to roughly 10. This means that the loop without bounds appears artificially cold relative to the other one.
Control the probability of the expression having the specified value. This parameter takes a percentage (i.e. 0 ... 100) as input. The default probability of 90 is obtained empirically.
Select fraction of the maximal frequency of executions of a basic block in a function to align the basic block.
A loop expected to iterate at least the selected number of iterations is aligned.
This value is used to limit superblock formation once the given percentage of executed instructions is covered. This limits unnecessary code size expansion.
The tracer-dynamic-coverage-feedback parameter is used only when profile feedback is available. The real profiles (as opposed to statically estimated ones) are much less balanced allowing the threshold to be larger value.
Stop tail duplication once code growth has reached given percentage. This is a rather artificial limit, as most of the duplicates are eliminated later in cross jumping, so it may be set to much higher values than is the desired code growth.
Stop reverse growth when the reverse probability of best edge is less than this threshold (in percent).
Stop forward growth if the best edge has probability lower than this threshold.
Similarly to tracer-dynamic-coverage two values are present, one for compilation for profile feedback and one for compilation without. The value for compilation with profile feedback needs to be more conservative (higher) in order to make tracer effective.
The maximum number of basic blocks on path that CSE considers. The default is 10.
The maximum number of instructions CSE processes before flushing. The default is 1000.
GCC uses a garbage collector to manage its own memory allocation. This parameter specifies the minimum percentage by which the garbage collectors heap should be allowed to expand between collections. Tuning this may improve compilation speed; it has no effect on code generation.
The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when RAM >= 1GB If getrlimit is available, the notion of RAM is the smallest of actual RAM and RLIMIT_DATA or RLIMIT_AS. If GCC is not able to calculate RAM on a particular platform, the lower bound of 30% is used. Setting this parameter and ggc-min-heapsize to zero causes a full collection to occur at every opportunity. This is extremely slow, but can be useful for debugging.
Minimum size of the garbage collectors heap before it begins bothering to collect garbage. The first collection occurs after the heap expands by ggc-min-expand% beyond ggc-min-heapsize. Again, tuning this may improve compilation speed, and has no effect on code generation.
The default is the smaller of RAM/8, RLIMIT_RSS, or a limit that tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but with a lower bound of 4096 (four megabytes) and an upper bound of 131072 (128 megabytes). If GCC is not able to calculate RAM on a particular platform, the lower bound is used. Setting this parameter very large effectively disables garbage collection. Setting this parameter and ggc-min-expand to zero causes a full collection to occur at every opportunity.
The maximum number of instruction reload should look backward for equivalent register. Increasing values mean more aggressive optimization, making the compilation time increase with probably slightly better performance. The default value is 100.
The maximum number of memory locations cselib should take into account. Increasing values mean more aggressive optimization, making the compilation time increase with probably slightly better performance. The default value is 500.
Used by the basic block reordering pass to decide whether to use unconditional branch or duplicate the code on its destination. Code is duplicated when its estimated size is smaller than this value multiplied by the estimated size of unconditional jump in the hot spots of the program.
The reorder-block-duplicate-feedback parameter is used only when profile feedback is available. It may be set to higher values than reorder-block-duplicate since information about the hot spots is more accurate.
The maximum number of instructions ready to be issued the scheduler should consider at any given time during the first scheduling pass. Increasing values mean more thorough searches, making the compilation time increase with probably little benefit. The default value is 100.
The maximum number of blocks in a region to be considered for interblock scheduling. The default value is 10.
The maximum number of blocks in a region to be considered for pipelining in the selective scheduler. The default value is 15.
The maximum number of insns in a region to be considered for interblock scheduling. The default value is 100.
The maximum number of insns in a region to be considered for pipelining in the selective scheduler. The default value is 200.
The minimum probability (in percents) of reaching a source block for interblock speculative scheduling. The default value is 40.
The maximum number of iterations through CFG to extend regions. A value of 0 (the default) disables region extensions.
The maximum conflict delay for an insn to be considered for speculative motion. The default value is 3.
The minimal probability of speculation success (in percents), so that speculative insns are scheduled. The default value is 40.
The minimum probability an edge must have for the scheduler to save its state across it. The default value is 10.
Minimal distance (in CPU cycles) between store and load targeting same memory locations. The default value is 1.
The maximum size of the lookahead window of selective scheduling. It is a depth of search for available instructions. The default value is 50.
The maximum number of times that an instruction is scheduled during selective scheduling. This is the limit on the number of iterations through which the instruction may be pipelined. The default value is 2.
The maximum number of best instructions in the ready list that are considered for renaming in the selective scheduler. The default value is 2.
The minimum value of stage count that swing modulo scheduler generates. The default value is 2.
The maximum size measured as number of RTLs that can be recorded in an expression in combiner for a pseudo register as last known value of that register. The default is 10000.
The maximum number of instructions the RTL combiner tries to combine. The default value is 2 at -Og and 4 otherwise.
Small integer constants can use a shared data structure, reducing the compilers memory usage and increasing its speed. This sets the maximum value of a shared integer constant. The default value is 256.
The minimum size of buffers (i.e. arrays) that receive stack smashing protection when -fstack-protection is used.
The minimum size of variables taking part in stack slot sharing when not optimizing. The default value is 32.
Maximum number of statements allowed in a block that needs to be duplicated when threading jumps.
Maximum number of fields in a structure treated in a field sensitive manner during pointer analysis. The default is zero for -O0 and -O1, and 100 for -Os, -O2, and -O3.
Estimate on average number of instructions that are executed before prefetch finishes. The distance prefetched ahead is proportional to this constant. Increasing this number may also lead to less streams being prefetched (see simultaneous-prefetches).
Maximum number of prefetches that can run at the same time.
The size of cache line in L1 cache, in bytes.
The size of L1 cache, in kilobytes.
The size of L2 cache, in kilobytes.
The minimum ratio between the number of instructions and the number of prefetches to enable prefetching in a loop.
The minimum ratio between the number of instructions and the number of memory references to enable prefetching in a loop.
Whether the compiler should use the canonical type system. By default, this should always be 1, which uses a more efficient internal mechanism for comparing types in C++ and Objective-C++. However, if bugs in the canonical type system are causing compilation failures, set this value to 0 to disable canonical types.
Switch initialization conversion refuses to create arrays that are bigger than switch-conversion-max-branch-ratio times the number of branches in the switch.
Maximum length of the partial antic set computed during the tree partial redundancy elimination optimization (-ftree-pre) when optimizing at -O3 and above. For some sorts of source code the enhanced partial redundancy elimination optimization can run away, consuming all of the memory available on the host machine. This parameter sets a limit on the length of the sets that are computed, which prevents the runaway behavior. Setting a value of 0 for this parameter allows an unlimited set length.
Maximum size of a strongly connected component (SCC) during SCCVN processing. If this limit is hit, SCCVN processing for the whole function is not done and optimizations depending on it are disabled. The default maximum SCC size is 10000.
Maximum number of alias-oracle queries we perform when looking for redundancies for loads and stores. If this limit is hit the search is aborted and the load or store is not considered redundant. The number of queries is algorithmically limited to the number of stores on all paths from the load to the function entry. The default maxmimum number of queries is 1000.
IRA uses regional register allocation by default. If a function contains more loops than the number given by this parameter, only at most the given number of the most frequently-executed loops form regions for regional register allocation. The default value of the parameter is 100.
Although IRA uses a sophisticated algorithm to compress the conflict table, the table can still require excessive amounts of memory for huge functions. If the conflict table for a function could be more than the size in MB given by this parameter, the register allocator instead uses a faster, simpler, and lower-quality algorithm that does not require building a pseudo-register conflict table. The default value of the parameter is 2000.
IRA can be used to evaluate more accurate register pressure in loops for decisions to move loop invariants (see -O3). The number of available registers reserved for some other purposes is given by this parameter. The default value of the parameter is 2, which is the minimal number of registers needed by typical instructions. This value is the best found from numerous experiments.
LRA tries to reuse values reloaded in registers in subsequent insns. This optimization is called inheritance. EBB is used as a region to do this optimization. The parameter defines a minimal fall-through edge probability in percentage used to add BB to inheritance EBB in LRA. The default value of the parameter is 40. The value was chosen from numerous runs of SPEC2000 on x86-64.
Loop invariant motion can be very expensive, both in compilation time and in amount of needed compile-time memory, with very large loops. Loops with more basic blocks than this parameter wont have loop invariant motion optimization performed on them. The default value of the parameter is 1000 for -O1 and 10000 for -O2 and above.
Building data dapendencies is expensive for very large loops. This parameter limits the number of data references in loops that are considered for data dependence analysis. These large loops are no handled by the optimizations using loop data dependencies. The default value is 1000.
Sets a maximum number of hash table slots to use during variable tracking dataflow analysis of any function. If this limit is exceeded with variable tracking at assignments enabled, analysis for that function is retried without it, after removing all debug insns from the function. If the limit is exceeded even without debug insns, var tracking analysis is completely disabled for the function. Setting the parameter to zero makes it unlimited.
Sets a maximum number of recursion levels when attempting to map variable names or debug temporaries to value expressions. This trades compilation time for more complete debug information. If this is set too low, value expressions that are available and could be represented in debug information may end up not being used; setting this higher may enable the compiler to find more complex debug expressions, but compile time and memory use may grow. The default is 12.
Use uids starting at this parameter for nondebug insns. The range below the parameter is reserved exclusively for debug insns created by -fvar-tracking-assignments, but debug insns may get (non-overlapping) uids above it if the reserved range is exhausted.
IPA-SRA replaces a pointer to an aggregate with one or more new parameters only when their cumulative size is less or equal to ipa-sra-ptr-growth-factor times the size of the original pointer parameter.
sra-max-scalarization-size-Ospeed
The two Scalar Reduction of Aggregates passes (SRA and IPA-SRA) aim to replace scalar parts of aggregates with uses of independent scalar variables. These parameters control the maximum size, in storage units, of aggregate which is considered for replacement when compiling for speed (sra-max-scalarization-size-Ospeed) or size (sra-max-scalarization-size-Osize) respectively.
When making copies of thread-local variables in a transaction, this parameter specifies the size in bytes after which variables are saved with the logging functions as opposed to save/restore code sequence pairs. This option only applies when using -fgnu-tm.
To avoid exponential effects in the Graphite loop transforms, the number of parameters in a Static Control Part (SCoP) is bounded. The default value is 10 parameters. A variable whose value is unknown at compilation time and defined outside a SCoP is a parameter of the SCoP.
To avoid exponential effects in the detection of SCoPs, the size of the functions analyzed by Graphite is bounded. The default value is 100 basic blocks.
Loop blocking or strip mining transforms, enabled with -floop-block or -floop-strip-mine, strip mine each loop in the loop nest by a given number of iterations. The strip length can be changed using the loop-block-tile-size parameter. The default value is 51 iterations.
Specify the unroll factor for the -floop-unroll-and-jam option. The default value is 4.
Specify the dimension to be unrolled (counting from the most inner loop) for the -floop-unroll-and-jam. The default value is 2.
IPA-CP attempts to track all possible values and types passed to a functions parameter in order to propagate them and perform devirtualization. ipa-cp-value-list-size is the maximum number of values and types it stores per one formal parameter of a function.
IPA-CP calculates its own score of cloning profitability heuristics and performs those cloning opportunities with scores that exceed ipa-cp-eval-threshold.
Percentage penalty the recursive functions will receive when they are evaluated for cloning.
Percentage penalty functions containg a single call to another function will receive when they are evaluated for cloning.
IPA-CP is also capable to propagate a number of scalar values passed in an aggregate. ipa-max-agg-items controls the maximum number of such values per one parameter.
When IPA-CP determines that a cloning candidate would make the number of iterations of a loop known, it adds a bonus of ipa-cp-loop-hint-bonus to the profitability score of the candidate.
When IPA-CP determines that a cloning candidate would make the index of an array access known, it adds a bonus of ipa-cp-array-index-hint-bonus to the profitability score of the candidate.
During its analysis of function bodies, IPA-CP employs alias analysis in order to track values pointed to by function parameters. In order not spend too much time analyzing huge functions, it gives up and consider all memory clobbered after examining ipa-max-aa-steps statements modifying memory.
Specify desired number of partitions produced during WHOPR compilation. The number of partitions should exceed the number of CPUs used for compilation. The default value is 32.
Size of minimal partition for WHOPR (in estimated instructions). This prevents expenses of splitting very small programs into too many partitions.
The maximum number of namespaces to consult for suggestions when C++ name lookup fails for an identifier. The default is 1000.
The maximum relative execution frequency (in percents) of the target block relative to a statements original block to allow statement sinking of a statement. Larger numbers result in more aggressive statement sinking. The default value is 75. A small positive adjustment is applied for statements with memory operands as those are even more profitable so sink.
The maximum number of conditional stores paires that can be sunk. Set to 0 if either vectorization (-ftree-vectorize) or if-conversion (-ftree-loop-if-convert) is disabled. The default is 2.
Allow optimizers to introduce new data races on stores. Set to 1 to allow, otherwise to 0. This option is enabled by default at optimization level -Ofast.
The smallest number of different values for which it is best to use a jump-table instead of a tree of conditional branches. If the value is 0, use the default for the machine. The default is 0.
Set the maximum number of instructions executed in parallel in reassociated tree. This parameter overrides target dependent heuristics used by default if has non zero value.
Choose between the two available implementations of -fsched-pressure. Algorithm 1 is the original implementation and is the more likely to prevent instructions from being reordered. Algorithm 2 was designed to be a compromise between the relatively conservative approach taken by algorithm 1 and the rather aggressive approach taken by the default scheduler. It relies more heavily on having a regular register file and accurate register pressure classes. See haifa-sched.c in the GCC sources for more details.
The default choice depends on the target.
Set the maximum number of existing candidates that are considered when seeking a basis for a new straight-line strength reduction candidate.
Enable buffer overflow detection for global objects. This kind of protection is enabled by default if you are using -fsanitize=address option. To disable global objects protection use --param asan-globals=0.
Enable buffer overflow detection for stack objects. This kind of protection is enabled by default when using:option:-fsanitize=address. To disable stack protection use --param asan-stack=0 option.
Enable buffer overflow detection for memory reads. This kind of protection is enabled by default when using -fsanitize=address. To disable memory reads protection use --param asan-instrument-reads=0.
Enable buffer overflow detection for memory writes. This kind of protection is enabled by default when using -fsanitize=address. To disable memory writes protection use --param asan-instrument-writes=0 option.
Enable detection for built-in functions. This kind of protection is enabled by default when using -fsanitize=address. To disable built-in functions protection use --param asan-memintrin=0.
Enable detection of use-after-return. This kind of protection is enabled by default when using -fsanitize=address option. To disable use-after-return detection use --param asan-use-after-return=0.
If number of memory accesses in function being instrumented is greater or equal to this number, use callbacks instead of inline checks. E.g. to disable inline code use --param asan-instrumentation-with-call-threshold=0.
Static constructors generated by Pointer Bounds Checker may become very large and significantly increase compile time at optimization level -O1 and higher. This parameter is a maximum nubmer of statements in a single generated constructor. Default value is 5000.
Maximum number of instructions to copy when duplicating blocks on a finite state automaton jump thread path. The default is 100.
Maximum number of basic blocks on a finite state automaton jump thread path. The default is 10.
Maximum number of new jump thread paths to create for a finite state automaton. The default is 50.
:: _preprocessor-options:
These options control the C preprocessor, which is run on each C source file before actual compilation.
If you use the -E option, nothing is done except preprocessing. Some of these options make sense only together with -E because they cause the preprocessor output to be unsuitable for actual compilation.
-Wp,``option``
You can use -Wp,``option`` to bypass the compiler driver and pass option directly through to the preprocessor. If option contains commas, it is split into multiple options at the commas. However, many options are modified, translated or interpreted by the compiler driver before being passed to the preprocessor, and -Wp forcibly bypasses this phase. The preprocessors direct interface is undocumented and subject to change, so whenever possible you should avoid using -Wp and let the driver handle the options instead.
-Xpreprocessor option
Pass option as an option to the preprocessor. You can use this to supply system-specific preprocessor options that GCC does not recognize.
If you want to pass an option that takes an argument, you must use -Xpreprocessor twice, once for the option and once for the argument.
Perform preprocessing as a separate pass before compilation. By default, GCC performs preprocessing as an integrated part of input tokenization and parsing. If this option is provided, the appropriate language front end (cc1, cc1plus, or cc1obj for C, C++, and Objective-C, respectively) is instead invoked twice, once for preprocessing only and once for actual compilation of the preprocessed input. This option may be useful in conjunction with the -B or -wrapper options to specify an alternate preprocessor or perform additional processing of the program source between normal preprocessing and compilation.
:: _assembler-options:
You can pass options to the assembler.
-Wa,``option``
Pass option as an option to the assembler. If option contains commas, it is split into multiple options at the commas.
-Xassembler option
Pass option as an option to the assembler. You can use this to supply system-specific assembler options that GCC does not recognize.
If you want to pass an option that takes an argument, you must use -Xassembler twice, once for the option and once for the argument.
:: _link-options:
These options come into play when the compiler links object files into an executable output file. They are meaningless if the compiler is not doing a link step.
object-file-name A file name that does not end in a special recognized suffix is considered to name an object file or library. (Object files are distinguished from libraries by the linker according to the file contents.) If linking is done, these object files are used as input to the linker.
If any of these options is used, then the linker is not run, and object file names should not be used as arguments. Overall Options.
Use the bfd linker instead of the default linker.
Use the gold linker instead of the default linker.
-l``library``
-l library
Search the library named library when linking. (The second alternative with the library as a separate argument is only for POSIX compliance and is not recommended.)
It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified. Thus, foo.o -lz bar.o searches library z after file foo.o but before bar.o. If bar.o refers to functions in z, those functions may not be loaded.
The linker searches a standard list of directories for the library, which is actually a file named lib``library``.a. The linker then uses this file as if it had been specified precisely by name.
The directories searched include several standard system directories plus any that you specify with -L.
Normally the files found this way are library filesarchive files whose members are object files. The linker handles an archive file by scanning through it for members which define symbols that have so far been referenced but not defined. But if the file that is found is an ordinary object file, it is linked in the usual fashion. The only difference between using an -l option and specifying a file name is that -l surrounds library with lib and .a and searches several directories.
You need this special case of the -l option in order to link an Objective-C or Objective-C++ program.
Do not use the standard system startup files when linking. The standard system libraries are used normally, unless -nostdlib or -nodefaultlibs is used.
Do not use the standard system libraries when linking. Only the libraries you specify are passed to the linker, and options specifying linkage of the system libraries, such as -static-libgcc or -shared-libgcc, are ignored. The standard startup files are used normally, unless -nostartfiles is used.
The compiler may generate calls to memcmp, memset, memcpy and memmove. These entries are usually resolved by entries in libc. These entry points should be supplied through some other mechanism when this option is specified.
Do not use the standard system startup files or libraries when linking. No startup files and only the libraries you specify are passed to the linker, and options specifying linkage of the system libraries, such as -static-libgcc or -shared-libgcc, are ignored.
The compiler may generate calls to memcmp, memset, memcpy and memmove. These entries are usually resolved by entries in libc. These entry points should be supplied through some other mechanism when this option is specified.
-lgcc, use with -nostdlib -nostdlib and unresolved references unresolved references and -nostdlib -lgcc, use with -nodefaultlibs -nodefaultlibs and unresolved references unresolved references and -nodefaultlibs One of the standard libraries bypassed by -nostdlib and -nodefaultlibs is libgcc.a, a library of internal subroutines which GCC uses to overcome shortcomings of particular machines, or special needs for some languages. (InterfaceInterfacing to GCC OutputgccintGNU Compiler Collection (GCC) Internals, for more discussion of libgcc.a.) In most cases, you need libgcc.a even when you want to avoid other standard libraries. In other words, when you specify -nostdlib or -nodefaultlibs you should usually specify -lgcc as well. This ensures that you have no unresolved references to internal GCC library subroutines. (An example of such an internal subroutine is __main, used to ensure C++ constructors are called; Collect2``collect2``gccintGNU Compiler Collection (GCC) Internals.)
Produce a position independent executable on targets that support it. For predictable results, you must also specify the same set of options used for compilation (-fpie, -fPIE, or model suboptions) when you specify this linker option.
Pass the flag -export-dynamic to the ELF linker, on targets that support it. This instructs the linker to add all symbols, not only used ones, to the dynamic symbol table. This option is needed for some uses of dlopen or to allow obtaining backtraces from within a program.
Remove all symbol table and relocation information from the executable.
On systems that support dynamic linking, this prevents linking with the shared libraries. On other systems, this option has no effect.
Produce a shared object which can then be linked with other objects to form an executable. Not all systems support this option. For predictable results, you must also specify the same set of options used for compilation (-fpic, -fPIC, or model suboptions) when you specify this linker option.On some systems, gcc -shared needs to build supplementary stub code for constructors to work. On multi-libbed systems, gcc -shared must select the correct support libraries to link against. Failing to supply the correct flags may lead to subtle defects. Supplying them in cases where they are not necessary is innocuous.
On systems that provide libgcc as a shared library, these options force the use of either the shared or static version, respectively. If no shared version of libgcc was built when the compiler was configured, these options have no effect.
There are several situations in which an application should use the shared libgcc instead of the static version. The most common of these is when the application wishes to throw and catch exceptions across different shared libraries. In that case, each of the libraries as well as the application itself should use the shared libgcc.
Therefore, the G++ and GCJ drivers automatically add -shared-libgcc whenever you build a shared library or a main executable, because C++ and Java programs typically use exceptions, so this is the right thing to do.
If, instead, you use the GCC driver to create shared libraries, you may find that they are not always linked with the shared libgcc. If GCC finds, at its configuration time, that you have a non-GNU linker or a GNU linker that does not support option --eh-frame-hdr, it links the shared version of libgcc into shared libraries by default. Otherwise, it takes advantage of the linker and optimizes away the linking with the shared version of libgcc, linking with the static version of libgcc by default. This allows exceptions to propagate through such shared libraries, without incurring relocation costs at library load time.
However, if a library or main executable is supposed to throw or catch exceptions, you must link it using the G++ or GCJ driver, as appropriate for the languages used in the program, or using the option -shared-libgcc, such that it is linked with the shared libgcc.
When the -fsanitize=address option is used to link a program, the GCC driver automatically links against libasan. If libasan is available as a shared library, and the -static option is not used, then this links against the shared version of libasan. The -static-libasan option directs the GCC driver to link libasan statically, without necessarily linking other libraries statically.
When the -fsanitize=thread option is used to link a program, the GCC driver automatically links against libtsan. If libtsan is available as a shared library, and the -static option is not used, then this links against the shared version of libtsan. The -static-libtsan option directs the GCC driver to link libtsan statically, without necessarily linking other libraries statically.
When the -fsanitize=leak option is used to link a program, the GCC driver automatically links against liblsan. If liblsan is available as a shared library, and the -static option is not used, then this links against the shared version of liblsan. The -static-liblsan option directs the GCC driver to link liblsan statically, without necessarily linking other libraries statically.
When the -fsanitize=undefined option is used to link a program, the GCC driver automatically links against libubsan. If libubsan is available as a shared library, and the -static option is not used, then this links against the shared version of libubsan. The -static-libubsan option directs the GCC driver to link libubsan statically, without necessarily linking other libraries statically.
When the -fcheck-pointer bounds and -mmpx options are used to link a program, the GCC driver automatically links against libmpx. If libmpx is available as a shared library, and the -static option is not used, then this links against the shared version of libmpx. The -static-libmpx option directs the GCC driver to link libmpx statically, without necessarily linking other libraries statically.
When the -fcheck-pointer bounds and -mmpx options are used to link a program without also using -fno-chkp-use-wrappers, the GCC driver automatically links against libmpxwrappers. If libmpxwrappers is available as a shared library, and the -static option is not used, then this links against the shared version of libmpxwrappers. The -static-libmpxwrappers option directs the GCC driver to link libmpxwrappers statically, without necessarily linking other libraries statically.
When the g++ program is used to link a C++ program, it normally automatically links against libstdc++. If libstdc++ is available as a shared library, and the -static option is not used, then this links against the shared version of libstdc++. That is normally fine. However, it is sometimes useful to freeze the version of libstdc++ used by the program without going all the way to a fully static link. The -static-libstdc++ option directs the g++ driver to link libstdc++ statically, without necessarily linking other libraries statically.
Bind references to global symbols when building a shared object. Warn about any unresolved references (unless overridden by the link editor option -Xlinker -z -Xlinker defs). Only a few systems support this option.
-T script
Use script as the linker script. This option is supported by most systems using the GNU linker. On some targets, such as bare-board targets without an operating system, the -T option may be required when linking to avoid references to undefined symbols.
-Xlinker option
Pass option as an option to the linker. You can use this to supply system-specific linker options that GCC does not recognize.
If you want to pass an option that takes a separate argument, you must use -Xlinker twice, once for the option and once for the argument. For example, to pass -assert definitions, you must write -Xlinker -assert -Xlinker definitions. It does not work to write -Xlinker "-assert definitions", because this passes the entire string as a single argument, which is not what the linker expects.
When using the GNU linker, it is usually more convenient to pass arguments to linker options using the option``=``value syntax than as separate arguments. For example, you can specify -Xlinker -Map=output.map rather than -Xlinker -Map -Xlinker output.map. Other linkers may not support this syntax for command-line options.
-Wl,``option``
Pass option as an option to the linker. If option contains commas, it is split into multiple options at the commas. You can use this syntax to pass an argument to the option. For example, -Wl,-Map,output.map passes -Map output.map to the linker. When using the GNU linker, you can also get the same effect with -Wl,-Map=output.map.
-u symbol
Pretend the symbol symbol is undefined, to force linking of library modules to define it. You can use -u multiple times with different symbols to force loading of additional library modules.
-z keyword
-z is passed directly on to the linker along with the keyword keyword. See the section in the documentation of your linker for permitted values and their meanings.
:: _directory-options:
These options specify directories to search for header files, for libraries and for parts of the compiler:
-I``dir``
Add the directory dir to the head of the list of directories to be searched for header files. This can be used to override a system header file, substituting your own version, since these directories are searched before the system header file directories. However, you should not use this option to add directories that contain vendor-supplied system header files (use -isystem for that). If you use more than one -I option, the directories are scanned in left-to-right order; the standard system directories come after.
If a standard system include directory, or a directory specified with -isystem, is also specified with -I, the -I option is ignored. The directory is still searched but as a system directory at its normal position in the system include chain. This is to ensure that GCCs procedure to fix buggy system headers and the ordering for the include_next directive are not inadvertently changed. If you really need to change the search order for system directories, use the -nostdinc and/or -isystem options.
-iplugindir=``dir``
Set the directory to search for plugins that are passed by -fplugin=``name`` instead of -fplugin=``path`/name.so`. This option is not meant to be used by the user, but only passed by the driver.
-iquote``dir``
Add the directory dir to the head of the list of directories to be searched for header files only for the case of #include "``file“; they are not searched for ``#include <``file>``, otherwise just like -I.
-L``dir``
Add directory dir to the list of directories to be searched for -l.
-B``prefix``
This option specifies where to find the executables, libraries, include files, and data files of the compiler itself.
The compiler driver program runs one or more of the subprograms cpp, cc1, as and ld. It tries prefix as a prefix for each program it tries to run, both with and without machine/version/ (Target Options).
For each subprogram to be run, the compiler driver first tries the -B prefix, if any. If that name is not found, or if -B is not specified, the driver tries two standard prefixes, /usr/lib/gcc/ and /usr/local/lib/gcc/. If neither of those results in a file name that is found, the unmodified program name is searched for using the directories specified in your PATH environment variable.
The compiler checks to see if the path provided by -B refers to a directory, and if necessary it adds a directory separator character at the end of the path.
-B prefixes that effectively specify directory names also apply to libraries in the linker, because the compiler translates these options into -L options for the linker. They also apply to include files in the preprocessor, because the compiler translates these options into -isystem options for the preprocessor. In this case, the compiler appends include to the prefix.
The runtime support file libgcc.a can also be searched for using the -B prefix, if needed. If it is not found there, the two standard prefixes above are tried, and that is all. The file is left out of the link if it is not found by those means.
Another way to specify a prefix much like the -B prefix is to use the environment variable GCC_EXEC_PREFIX. Environment Variables.
As a special kludge, if the path provided by -B is [dir/]stage``N``/, where N is a number in the range 0 to 9, then it is replaced by [dir/]include. This is to help with boot-strapping the compiler.
-specs=``file``
Process file after the compiler reads in the standard specs file, in order to override the defaults which the gcc driver program uses when determining what switches to pass to cc1, cc1plus, as, ld, etc. More than one -specs=``file`` can be specified on the command line, and they are processed in order, from left to right.
–sysroot=``dir``
Use dir as the logical root directory for headers and libraries. For example, if the compiler normally searches for headers in /usr/include and libraries in /usr/lib, it instead searches dir/usr/include and dir/usr/lib.
If you use both this option and the -isysroot option, then the --sysroot option applies to libraries, but the -isysroot option applies to header files.
The GNU linker (beginning with version 2.16) has the necessary support for this option. If your linker does not support this option, the header file aspect of --sysroot still works, but the library aspect does not.
For some targets, a suffix is added to the root directory specified with --sysroot, depending on the other options used, so that headers may for example be found in dir/suffix/usr/include instead of dir/usr/include. This option disables the addition of such a suffix.
This option has been deprecated. Please use -iquote instead for -I directories before the -I- and remove the -I- option. Any directories you specify with -I options before the -I- option are searched only for the case of #include "``file“; they are not searched for ``#include <``file>``.
If additional directories are specified with -I options after the -I- option, these directories are searched for all #include directives. (Ordinarily all -I directories are used this way.)
In addition, the -I- option inhibits the use of the current directory (where the current input file came from) as the first search directory for #include "``file“``. There is no way to override this effect of -I-. With -I. you can specify searching the directory that is current when the compiler is invoked. That is not exactly the same as what the preprocessor does by default, but it is often satisfactory.
-I- does not inhibit the use of the standard system directories for header files. Thus, -I- and -nostdinc are independent.
:: _spec-files:
gcc is a driver program. It performs its job by invoking a sequence of other programs to do the work of compiling, assembling and linking. GCC interprets its command-line parameters and uses these to deduce which programs it should invoke, and which command-line options it ought to place on their command lines. This behavior is controlled by spec strings. In most cases there is one spec string for each program that GCC can invoke, but a few programs have multiple spec strings to control their behavior. The spec strings built into GCC can be overridden by using the -specs= command-line switch to specify a spec file.
Spec files are plaintext files that are used to construct spec strings. They consist of a sequence of directives separated by blank lines. The type of directive is determined by the first non-whitespace character on the line, which can be one of the following:
%``command`` Issues a command to the spec file processor. The commands that can appear here are:
%include <file> %include Search for file and insert its text at the current point in the specs file.
%include_noerr <file> %include_noerr Just like %include, but do not generate an error message if the include file cannot be found.
%rename old_name new_name %rename Rename the spec string old_name to new_name.
*[spec_name]: This tells the compiler to create, override or delete the named spec string. All lines after this directive up to the next directive or blank line are considered to be the text for the spec string. If this results in an empty string then the spec is deleted. (Or, if the spec did not exist, then nothing happens.) Otherwise, if the spec does not currently exist a new spec is created. If the spec does exist then its contents are overridden by the text of this directive, unless the first character of that text is the + character, in which case the text is appended to the spec.
[suffix]: Creates a new [suffix] spec pair. All lines after this directive and up to the next directive or blank line are considered to make up the spec string for the indicated suffix. When the compiler encounters an input file with the named suffix, it processes the spec string in order to work out how to compile that file. For example:
.ZZ:
z-compile -input %i
This says that any input file whose name ends in .ZZ should be passed to the program z-compile, which should be invoked with the command-line switch -input and with the result of performing the %i substitution. (See below.)
As an alternative to providing a spec string, the text following a suffix directive can be one of the following:
language This says that the suffix is an alias for a known language. This is similar to using the -x command-line switch to GCC to specify a language explicitly. For example:
.ZZ:
c++
Says that .ZZ files are, in fact, C++ source files.
#``name`` This causes an error messages saying:
``name`` compiler not installed on this system.
GCC already has an extensive list of suffixes built into it. This directive adds an entry to the end of the list of suffixes, but since the list is searched from the end backwards, it is effectively possible to override earlier entries using this technique.
GCC has the following spec strings built into it. Spec files can override these strings or create their own. Note that individual targets can also add their own spec strings to this list.
asm Options to pass to the assembler
asm_final Options to pass to the assembler post-processor
cpp Options to pass to the C preprocessor
cc1 Options to pass to the C compiler
cc1plus Options to pass to the C++ compiler
endfile Object files to include at the end of the link
link Options to pass to the linker
lib Libraries to include on the command line to the linker
libgcc Decides which GCC support library to pass to the linker
linker Sets the name of the linker
predefines Defines to be passed to the C preprocessor
signed_char Defines to pass to CPP to say whether ``char`` is signed
by default
startfile Object files to include at the start of the link
Here is a small example of a spec file:
%rename lib old_lib
*lib:
--start-group -lgcc -lc -leval1 --end-group %(old_lib)
This example renames the spec called lib to old_lib and then overrides the previous definition of lib with a new one. The new definition adds in some extra command-line options before including the text of the old definition.
Spec strings are a list of command-line options to be passed to their corresponding program. In addition, the spec strings can contain %-prefixed sequences to substitute variable text or to conditionally insert text into the command line. Using these constructs it is possible to generate quite complex command lines.
Here is a table of all defined %-sequences for spec strings. Note that spaces are not generated automatically around the results of expanding these sequences. Therefore you can concatenate them together or combine them with constant text in a single argument.
Substitute one % into the program name or argument.
Substitute the name of the input file being processed.
Substitute the basename of the input file being processed. This is the substring up to (and not including) the last period and not including the directory.
This is the same as %b, but include the file suffix (text after the last period).
Marks the argument containing or following the %d as a temporary file name, so that that file is deleted if GCC exits successfully. Unlike %g, this contributes no text to the argument.
%g``suffix``
Substitute a file name that has suffix suffix and is chosen once per compilation, and mark the argument in the same way as %d. To reduce exposure to denial-of-service attacks, the file name is now chosen in a way that is hard to predict even when previously chosen file names are known. For example, %g.s ... %g.o ... %g.s might turn into ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s. suffix matches the regexp [.A-Za-z]* or the special string %O, which is treated exactly as if %O had been preprocessed. Previously, %g was simply substituted with a file name chosen once per compilation, without regard to any appended suffix (which was therefore treated just like ordinary text), making such attacks more likely to succeed.
%u``suffix`` Like %g, but generates a new temporary file name each time it appears instead of once per compilation.
%U``suffix`` Substitutes the last file name generated with %u``suffix``, generating a new one if there is no such last file name. In the absence of any %u``suffix``, this is just like %g``suffix``, except they dont share the same suffix space, so %g.s ... %U.s ... %g.s ... %U.s involves the generation of two distinct file names, one for each %g.s and another for each %U.s. Previously, %U was simply substituted with a file name chosen for the previous %u, without regard to any appended suffix.
%j``suffix`` Substitutes the name of the HOST_BIT_BUCKET, if any, and if it is writable, and if -save-temps is not used; otherwise, substitute the name of a temporary file, just like %u. This temporary file is not meant for communication between processes, but rather as a junk disposal mechanism.
%|``suffix`` %m``suffix`` Like %g, except if -pipe is in effect. In that case %| substitutes a single dash and %m substitutes nothing at all. These are the two most common ways to instruct a program that it should read from standard input or write to standard output. If you need something more elaborate you can use an %{pipe:X} construct: see for example f/lang-specs.h.
%.``SUFFIX`` Substitutes .SUFFIX for the suffixes of a matched switchs args when it is subsequently output with %*. SUFFIX is terminated by the next space or %.
Marks the argument containing or following the %w as the designated output file of this compilation. This puts the argument into the sequence of arguments that %o substitutes.
Substitutes the names of all the output files, with spaces automatically placed around them. You should write spaces around the %o as well or the results are undefined. %o is for use in the specs for running the linker. Input files whose names have no recognized suffix are not compiled at all, but they are included among the output files, so they are linked.
Substitutes the suffix for object files. Note that this is handled specially when it immediately follows %g, %u, or %U, because of the need for those to form complete file names. The handling is such that %O is treated exactly as if it had already been substituted, except that %g, %u, and %U do not currently support additional suffix characters following %O as they do following, for example, .o.
Substitutes the standard macro predefinitions for the current target machine. Use this when running cpp.
Like %p, but puts __ before and after the name of each predefined macro, except for macros that start with __ or with `L`, where L is an uppercase letter. This is for ISO C
Substitute any of -iprefix (made from GCC_EXEC_PREFIX), -isysroot (made from TARGET_SYSTEM_ROOT), -isystem (made from COMPILER_PATH and -B options) and -imultilib as necessary.
Current argument is the name of a library or startup file of some sort. Search for that file in a standard list of directories and substitute the full name found. The current working directory is included in the list of directories scanned.
Current argument is the name of a linker script. Search for that file in the current list of directories to scan for libraries. If the file is located insert a --script option into the command line followed by the full path name found. If the file is not found then generate an error message. Note: the current working directory is not searched.
%e``str``
Print str as an error message. str is terminated by a newline. Use this when inconsistent options are detected.
%(name) Substitute the contents of spec string name at this point.
%x{option} Accumulate an option for %X.
Output the accumulated linker options specified by -Wl or a %x spec string.
Output the accumulated assembler options specified by -Wa.
Output the accumulated preprocessor options specified by -Wp.
Process the asm spec. This is used to compute the switches to be passed to the assembler.
Process the asm_final spec. This is a spec string for passing switches to an assembler post-processor, if such a program is needed.
Process the link spec. This is the spec for computing the command line passed to the linker. Typically it makes use of the %L %G %S %D and %E sequences.
Dump out a -L option for each directory that GCC believes might contain startup files. If the target supports multilibs then the current multilib directory is prepended to each of these paths.
Process the lib spec. This is a spec string for deciding which libraries are included on the command line to the linker.
Process the libgcc spec. This is a spec string for deciding which GCC support library is included on the command line to the linker.
Process the startfile spec. This is a spec for deciding which object files are the first ones passed to the linker. Typically this might be a file named crt0.o.
Process the endfile spec. This is a spec string that specifies the last object files that are passed to the linker.
Process the cpp spec. This is used to construct the arguments to be passed to the C preprocessor.
Process the cc1 spec. This is used to construct the options to be passed to the actual C compiler (cc1).
Process the cc1plus spec. This is used to construct the options to be passed to the actual C++ compiler (cc1plus).
Substitute the variable part of a matched option. See below. Note that each comma in the substituted string is replaced by a single space.
%<S
Remove all occurrences of -S from the command line. Notethis command is position dependent. % commands in the spec string before this one see -S, % commands in the spec string after this one do not.
%:function``(``args) Call the named function function, passing it args. args is first processed as a nested spec string, then split into an argument vector in the usual fashion. The function returns a string which is processed as if it had appeared literally as part of the current spec.
The following built-in spec functions are provided:
getenv The getenv spec function takes two arguments: an environment variable name and a string. If the environment variable is not defined, a fatal error is issued. Otherwise, the return value is the value of the environment variable concatenated with the string. For example, if TOPDIR is defined as /path/to/top, then:
%:getenv(TOPDIR /include)
expands to /path/to/top/include.
if-exists The if-exists spec function takes one argument, an absolute pathname to a file. If the file exists, if-exists returns the pathname. Here is a small example of its usage:
*startfile:
crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s
if-exists-else The if-exists-else spec function is similar to the if-exists spec function, except that it takes two arguments. The first argument is an absolute pathname to a file. If the file exists, if-exists-else returns the pathname. If it does not exist, it returns the second argument. This way, if-exists-else can be used to select one file or another, based on the existence of the first. Here is a small example of its usage:
*startfile:
crt0%O%s %:if-exists(crti%O%s) \
%:if-exists-else(crtbeginT%O%s crtbegin%O%s)
replace-outfile The replace-outfile spec function takes two arguments. It looks for the first argument in the outfiles array and replaces it with the second argument. Here is a small example of its usage:
%{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)}
remove-outfile The remove-outfile spec function takes one argument. It looks for the first argument in the outfiles array and removes it. Here is a small example its usage:
%:remove-outfile(-lm)
pass-through-libs The pass-through-libs spec function takes any number of arguments. It finds any -l options and any non-options ending in .a (which it assumes are the names of linker input library archive files) and returns a result containing all the found arguments each prepended by -plugin-opt=-pass-through= and joined by spaces. This list is intended to be passed to the LTO linker plugin.
%:pass-through-libs(%G %L %G)
print-asm-header The print-asm-header function takes no arguments and simply prints a banner like:
Assembler options
=================
Use "-Wa,OPTION" to pass "OPTION" to the assembler.
It is used to separate compiler options from assembler options in the --target-help output.
%{S} Substitutes the -S switch, if that switch is given to GCC If that switch is not specified, this substitutes nothing. Note that the leading dash is omitted when specifying this option, and it is automatically inserted if the substitution is performed. Thus the spec string %{foo} matches the command-line option -foo and outputs the command-line option -foo.
%W{S} Like %{S} but mark last argument supplied within as a file to be deleted on failure.
%{S``*} Substitutes all the switches specified to GCC whose names start with ``-S, but which also take an argument. This is used for switches like -o, -D, -I, etc. GCC considers -o foo as being one switch whose name starts with o. %{o*} substitutes this text, including the space. Thus two arguments are generated.
%{S``*&``T``*} Like %{``S``*}, but preserve order of ``S and T options (the order of S and T in the spec is not significant). There can be any number of ampersand-separated variables; for each the wild card is optional. Useful for CPP as %{D*&U*&A*}.
%{S:X} Substitutes X, if the -S switch is given to GCC
%{!``S``:X} Substitutes X, if the -S switch is not given to GCC
%{S``*:``X} Substitutes X if one or more switches whose names start with -S are specified to GCC Normally X is substituted only once, no matter how many such switches appeared. However, if %* appears somewhere in X, then X is substituted once for each matching switch, with the %* replaced by the part of that switch matching the *.
If %* appears as the last part of a spec sequence then a space is added after the end of the last substitution. If there is more text in the sequence, however, then a space is not generated. This allows the %* substitution to be used as part of a larger string. For example, a spec string like this:
%{mcu=*:--script=%*/memory.ld}
when matching an option like -mcu=newchip produces:
--script=newchip/memory.ld
%{.``S``:X} Substitutes X, if processing a file with suffix S.
%{!.``S``:X} Substitutes X, if not processing a file with suffix S.
%{,``S``:X} Substitutes X, if processing a file for language S.
%{!,``S``:X} Substitutes X, if not processing a file for language S.
%{S``|``P:X} Substitutes X if either -S or -P is given to GCC This may be combined with !, ., ,, and * sequences as well, although they have a stronger binding than the |. If %* appears in X, all of the alternatives must be starred, and only the first matching alternative is substituted.
For example, a spec string like this:
%{.c:-foo} %{!.c:-bar} %{.c|d:-baz} %{!.c|d:-boggle}
outputs the following command-line options from the following input command-line options:
fred.c -foo -baz
jim.d -bar -boggle
-d fred.c -foo -baz -boggle
-d jim.d -bar -baz -boggle
If S is given to GCC, substitutes X; else if T is given to GCC, substitutes Y; else substitutes D. There can be as many clauses as you need. This may be combined with ., ,, !, |, and * as needed.
The conditional text X in a %{S:X} or similar construct may contain other nested % constructs or spaces, or even newlines. They are processed as usual, as described above. Trailing white space in X is ignored. White space may also appear anywhere on the left side of the colon in these constructs, except between . or * and the corresponding word.
The -O, -f, -m, and -W switches are handled specifically in these constructs. If another value of -O or the negated form of a -f, -m, or -W switch is found later in the command line, the earlier switch value is ignored, except with {S``*} where ``S is just one letter, which passes all matching options.
The character | at the beginning of the predicate text is used to indicate that a command should be piped to the following command, but only if -pipe is specified.
It is built into GCC which switches take arguments and which do not. (You might think it would be useful to generalize this to allow each compilers spec to say which switches take arguments. But this cannot be done in a consistent fashion. GCC cannot even decide which input files have been specified without knowing which switches take arguments, and it must know which input files to compile in order to tell which compilers to run).
GCC also knows implicitly that arguments starting in -l are to be treated as compiler output files, and passed to the linker in their proper position among the other output files.
:: _target-options:
The usual way to run GCC is to run the executable called gcc, or :command:`machine-gcc` when cross-compiling, or :command:`machine-gcc-version` to run a version other than the one that was installed last.
:: _submodel-options:
Each target machine types can have its own special options, starting with -m, to choose among various hardware models or configurationsfor example, 68010 vs 68020, floating coprocessor or none. A single installed version of the compiler can compile for any model or configuration, according to the options specified.
Some configurations of the compiler also support additional special options, usually for compatibility with other compilers on the same platform.
:: _aarch64-options:
These options are defined for AArch64 implementations:
-mabi=``name``
Generate code for the specified data model. Permissible values are ilp32 for SysV-like data model where int, long int and pointer are 32-bit, and lp64 for SysV-like data model where int is 32-bit, but long int and pointer are 64-bit.
The default depends on the specific target configuration. Note that the LP64 and ILP32 ABIs are not link-compatible; you must compile your entire program with the same ABI, and link with a compatible set of libraries.
Generate big-endian code. This is the default when GCC is configured for an aarch64_be-- target.
Generate code which uses only the general registers.
Generate little-endian code. This is the default when GCC is configured for an aarch64-- but not an aarch64_be-- target.
Generate code for the tiny code model. The program and its statically defined symbols must be within 1GB of each other. Pointers are 64 bits. Programs can be statically or dynamically linked. This model is not fully implemented and mostly treated as small.
Generate code for the small code model. The program and its statically defined symbols must be within 4GB of each other. Pointers are 64 bits. Programs can be statically or dynamically linked. This is the default code model.
Generate code for the large code model. This makes no assumptions about addresses and sizes of sections. Pointers are 64 bits. Programs can be statically linked only.
Do not assume that unaligned memory references are handled by the system.
Omit or keep the frame pointer in leaf functions. The former behaviour is the default.
Use TLS descriptors as the thread-local storage mechanism for dynamic accesses of TLS variables. This is the default.
Use traditional TLS as the thread-local storage mechanism for dynamic accesses of TLS variables.
Enable or disable the workaround for the ARM Cortex-A53 erratum number 835769. This involves inserting a NOP instruction between memory instructions and 64-bit integer multiply-accumulate instructions.
Enable or disable the workaround for the ARM Cortex-A53 erratum number 843419. This erratum workaround is made at link time and this will only pass the corresponding flag to the linker.
-march=``name``
Specify the name of the target architecture, optionally suffixed by one or more feature modifiers. This option has the form -march=``arch``{+[no]``feature`}*`, where the only permissible value for arch is armv8-a. The permissible values for feature are documented in the sub-section below. Additionally on native AArch64 GNU/Linux systems the value native is available. This option causes the compiler to pick the architecture of the host system. If the compiler is unable to recognize the architecture of the host system this option has no effect.
Where conflicting feature modifiers are specified, the right-most feature is used.
GCC uses this name to determine what kind of instructions it can emit when generating assembly code.
Where -march is specified without either of -mtune or -mcpu also being specified, the code is tuned to perform well across a range of target processors implementing the target architecture.
-mtune=``name``
Specify the name of the target processor for which GCC should tune the performance of the code. Permissible values for this option are: generic, cortex-a53, cortex-a57, cortex-a72, exynos-m1, thunderx, xgene1.
Additionally, this option can specify that GCC should tune the performance of the code for a big.LITTLE system. Permissible values for this option are: cortex-a57.cortex-a53, cortex-a72.cortex-a53.
Additionally on native AArch64 GNU/Linux systems the value native is available. This option causes the compiler to pick the architecture of and tune the performance of the code for the processor of the host system. If the compiler is unable to recognize the processor of the host system this option has no effect.
Where none of -mtune=, -mcpu= or -march= are specified, the code is tuned to perform well across a range of target processors.
This option cannot be suffixed by feature modifiers.
-mcpu=``name``
Specify the name of the target processor, optionally suffixed by one or more feature modifiers. This option has the form -mcpu=``cpu``{+[no]``feature`}*`, where the permissible values for cpu are the same as those available for -mtune. Additionally on native AArch64 GNU/Linux systems the value native is available. This option causes the compiler to tune the performance of the code for the processor of the host system. If the compiler is unable to recognize the processor of the host system this option has no effect.
The permissible values for feature are documented in the sub-section below.
Where conflicting feature modifiers are specified, the right-most feature is used.
GCC uses this name to determine what kind of instructions it can emit when generating assembly code (as if by -march) and to determine the target processor for which to tune for performance (as if by -mtune). Where this option is used in conjunction with -march or -mtune, those options take precedence over the appropriate part of this option.
-march and -mcpu Feature Modifiers -march feature modifiers -mcpu feature modifiers Feature modifiers used with -march and -mcpu can be one the following:
Enable CRC extension.
Enable Crypto extension. This implies Advanced SIMD is enabled.
Enable floating-point instructions.
Enable Advanced SIMD instructions. This implies floating-point instructions are enabled. This is the default for all current possible values for options -march and -mcpu=.
:: _adapteva-epiphany-options:
These -m options are defined for Adapteva Epiphany:
Dont allocate any register in the range r32...``r63``. That allows code to run on hardware variants that lack these registers.
Preferrentially allocate registers that allow short instruction generation. This can result in increased instruction count, so this may either reduce or increase overall code size.
-mbranch-cost=``num``
Set the cost of branches to roughly num simple instructions. This cost is only a heuristic and is not guaranteed to produce consistent results across releases.
Enable the generation of conditional moves.
-mnops=``num``
Emit num NOPs before every other generated instruction.
For single-precision floating-point comparisons, emit an fsub instruction and test the flags. This is faster than a software comparison, but can get incorrect results in the presence of NaNs, or when two different small numbers are compared such that their difference is calculated as zero. The default is -msoft-cmpsf, which uses slower, but IEEE-compliant, software comparisons.
-mstack-offset=``num``
Set the offset between the top of the stack and the stack pointer. E.g., a value of 8 means that the eight bytes in the range sp+0...sp+7 can be used by leaf functions without stack allocation. Values other than 8 or 16 are untested and unlikely to work. Note also that this option changes the ABI; compiling a program with a different stack offset than the libraries have been compiled with generally does not work. This option can be useful if you want to evaluate if a different stack offset would give you better code, but to actually use a different stack offset to build working programs, it is recommended to configure the toolchain with the appropriate --with-stack-offset=``num`` option.
Make the scheduler assume that the rounding mode has been set to truncating. The default is -mround-nearest.
If not otherwise specified by an attribute, assume all calls might be beyond the offset range of the b / bl instructions, and therefore load the function address into a register before performing a (otherwise direct) call. This is the default.
If not otherwise specified by an attribute, assume all direct calls are in the range of the b / bl instructions, so use these instructions for direct calls. The default is -mlong-calls.
Assume addresses can be loaded as 16-bit unsigned values. This does not apply to function addresses for which -mlong-calls semantics are in effect.
-mfp-mode=``mode``
Set the prevailing mode of the floating-point unit. This determines the floating-point mode that is provided and expected at function call and return time. Making this mode match the mode you predominantly need at function start can make your programs smaller and faster by avoiding unnecessary mode switches.
mode can be set to one the following values:
Any mode at function entry is valid, and retained or restored when the function returns, and when it calls other functions. This mode is useful for compiling libraries or other compilation units you might want to incorporate into different programs with different prevailing FPU modes, and the convenience of being able to use a single object file outweighs the size and speed overhead for any extra mode switching that might be needed, compared with what would be needed with a more specific choice of prevailing FPU mode.
This is the mode used for floating-point calculations with truncating (i.e. round towards zero) rounding mode. That includes conversion from floating point to integer.
This is the mode used for floating-point calculations with round-to-nearest-or-even rounding mode.
This is the mode used to perform integer calculations in the FPU, e.g. integer multiply, or integer multiply-and-accumulate.
The default is -mfp-mode=caller
Code generation tweaks that disable, respectively, splitting of 32-bit loads, generation of post-increment addresses, and generation of post-modify addresses. The defaults are msplit-lohi, -mpost-inc, and -mpost-modify.
Change the preferred SIMD mode to SImode. The default is -mvect-double, which uses DImode as preferred SIMD mode.
-max-vect-align=``num``
The maximum alignment for SIMD vector mode types. num may be 4 or 8. The default is 8. Note that this is an ABI change, even though many library function interfaces are unaffected if they dont use SIMD vector modes in places that affect size and/or alignment of relevant types.
Split vector moves into single word moves before reload. In theory this can give better register allocation, but so far the reverse seems to be generally the case.
-m1reg-reg
Specify a register to hold the constant 1, which makes loading small negative constants and certain bitmasks faster. Allowable values for reg are r43 and r63, which specify use of that register as a fixed register, and none, which means that no register is used for this purpose. The default is -m1reg-none.
:: _arc-options:
The following options control the architecture variant for which code is being compiled:
Generate instructions supported by barrel shifter. This is the default unless -mcpu=ARC601 is in effect.
-mcpu=``cpu``
Set architecture type, register usage, and instruction scheduling parameters for cpu. There are also shortcut alias options available for backward compatibility and convenience. Supported values for cpu are
Compile for ARC600. Aliases: -mA6, -mARC600.
Compile for ARC700. Aliases: -mA7, -mARC700. This is the default when configured with --with-cpu=arc700
FPX: Generate Double Precision FPX instructions, tuned for the compact implementation.
FPX: Generate Double Precision FPX instructions, tuned for the fast implementation.
Disable LR and SR instructions from using FPX extension aux registers.
Generate Extended arithmetic instructions. Currently only divaw, adds, subs, and sat16 are supported. This is always enabled for -mcpu=ARC700.
Do not generate mpy instructions for ARC700.
Generate 32x16 bit multiply and mac instructions.
Generate mul64 and mulu64 instructions. Only valid for -mcpu=ARC600.
Generate norm instruction. This is the default if -mcpu=ARC700 is in effect.
FPX: Generate Single Precision FPX instructions, tuned for the compact implementation.
FPX: Generate Single Precision FPX instructions, tuned for the fast implementation.
Enable generation of ARC SIMD instructions via target-specific builtins. Only valid for -mcpu=ARC700.
This option ignored; it is provided for compatibility purposes only. Software floating point code is emitted by default, and this default can overridden by FPX options; mspfp, mspfp-compact, or mspfp-fast for single precision, and mdpfp, mdpfp-compact, or mdpfp-fast for double precision.
Generate swap instructions.
The following options are passed through to the assembler, and also define preprocessor macro symbols.
Passed down to the assembler to enable the DSP Pack A extensions. Also sets the preprocessor symbol __Xdsp_packa.
Passed down to the assembler to enable the dual viterbi butterfly extension. Also sets the preprocessor symbol __Xdvbf.
Passed down to the assembler to enable the Locked Load/Store Conditional extension. Also sets the preprocessor symbol __Xlock.
Passed down to the assembler. Also sets the preprocessor symbol __Xxmac_d16.
Passed down to the assembler. Also sets the preprocessor symbol __Xxmac_24.
Passed down to the assembler to enable the 64-bit Time-Stamp Counter extension instruction. Also sets the preprocessor symbol __Xrtsc.
Passed down to the assembler to enable the swap byte ordering extension instruction. Also sets the preprocessor symbol __Xswape.
Passed down to the assembler to enable dual and single operand instructions for telephony. Also sets the preprocessor symbol __Xtelephony.
Passed down to the assembler to enable the XY Memory extension. Also sets the preprocessor symbol __Xxy.
The following options control how the assembly code is annotated:
Annotate assembler instructions with estimated addresses.
Explain what alignment considerations lead to the decision to make an instruction short or long.
The following options are passed through to the linker:
Passed through to the linker, to specify use of the arclinux emulation. This option is enabled by default in tool chains built for arc-linux-uclibc and arceb-linux-uclibc targets when profiling is not requested.
Passed through to the linker, to specify use of the arclinux_prof emulation. This option is enabled by default in tool chains built for arc-linux-uclibc and arceb-linux-uclibc targets when profiling is requested.
The following options control the semantics of generated code:
Enable generation of call frame information for epilogues.
Disable generation of call frame information for epilogues.
Generate call insns as register indirect calls, thus providing access to the full 32-bit address range.
Dont use less than 25 bit addressing range for calls, which is the offset available for an unconditional branch-and-link instruction. Conditional execution of function calls is suppressed, to allow use of the 25-bit range, rather than the 21-bit range with conditional branch-and-link. This is the default for tool chains built for arc-linux-uclibc and arceb-linux-uclibc targets.
Do not generate sdata references. This is the default for tool chains built for arc-linux-uclibc and arceb-linux-uclibc targets.
Instrument with mcount calls as used in UCB code. I.e. do the counting in the callee, not the caller. By default ARC instrumentation counts in the caller.
Use ordinarily cached memory accesses for volatile references. This is the default.
Enable cache bypass for volatile references.
The following options fine tune code generation:
Do alignment optimizations for call instructions.
Enable the use of pre/post modify with register displacement.
Enable bbit peephole2.
This option disables a target-specific pass in arc_reorg to generate BRcc instructions. It has no effect on BRcc generation driven by the combiner pass.
Use pc-relative switch case tables - this enables case table shortening. This is the default for -Os.
Disable ARCompact specific pass to generate conditional execution instructions. Due to delay slot scheduling and interactions between operand numbers, literal sizes, instruction lengths, and the support for conditional execution, the target-independent pass to generate conditional execution is often lacking, so the ARC port has kept a special pass around that tries to find more conditional execution generating opportunities after register allocation, branch shortening, and delay slot scheduling have been done. This pass generally, but not always, improves performance and code size, at the cost of extra compilation time, which is why there is an option to switch it off. If you have a problem with call instructions exceeding their allowable offset range because they are conditionalized, you should consider using -mmedium-calls instead.
Enable pre-reload use of the cbranchsi pattern.
Expand adddi3 and subdi3 at rtl generation time into add.f, adc etc.
Enable the use of indexed loads. This can be problematic because some optimizers then assume that indexed stores exist, which is not the case.
Enable Local Register Allocation. This is still experimental for ARC, so by default the compiler uses standard reload (i.e. -mno-lra).
Dont indicate any priority for target registers.
Indicate target register priority for r0..r3 / r12..r15.
Reduce target regsiter priority for r0..r3 / r12..r15.
When optimizing for size (using -Os), prologues and epilogues that have to save or restore a large number of registers are often shortened by using call to a special function in libgcc; this is referred to as a millicode call. As these calls can pose performance issues, and/or cause linking issues when linking in a nonstandard way, this option is provided to turn off millicode call generation.
Tweak register allocation to help 16-bit instruction generation. This generally has the effect of decreasing the average instruction size while increasing the instruction count.
Enable Rcq constraint handling - most short code generation depends on this. This is the default.
Enable Rcw constraint handling - ccfsm condexec mostly depends on this. This is the default.
-msize-level=``level``
Fine-tune size optimization with regards to instruction lengths and alignment. The recognized values for level are:
No size optimization. This level is deprecated and treated like 1.
Short instructions are used opportunistically.
In addition, alignment of loops and of code after barriers are dropped.
In addition, optional data alignment is dropped, and the option Os is enabled.
This defaults to 3 when -Os is in effect. Otherwise, the behavior when this is not set is equivalent to level 1.
-mtune=``cpu``
Set instruction scheduling parameters for cpu, overriding any implied by -mcpu=.
Supported values for cpu are
Tune for ARC600 cpu.
Tune for ARC601 cpu.
Tune for ARC700 cpu with standard multiplier block.
Tune for ARC700 cpu with XMAC block.
Tune for ARC725D cpu.
Tune for ARC750D cpu.
-mmultcost=``num``
Cost to assume for a multiply instruction, with 4 being equal to a normal instruction.
-munalign-prob-threshold=``probability``
Set probability threshold for unaligning branches. When tuning for ARC700 and optimizing for speed, branches without filled delay slot are preferably emitted unaligned and long, unless profiling indicates that the probability for the branch to be taken is below probability. Cross-profiling. The default is (REG_BR_PROB_BASE/2), i.e. 5000.
The following options are maintained for backward compatibility, but are now deprecated and will be removed in a future release:
Obsolete FPX.
Compile code for big endian targets. Use of these options is now deprecated. Users wanting big-endian code, should use the arceb-elf32 and arceb-linux-uclibc targets when building the tool chain, for which big-endian is the default.
Compile code for little endian targets. Use of these options is now deprecated. Users wanting little-endian code should use the arc-elf32 and arc-linux-uclibc targets when building the tool chain, for which little-endian is the default.
Replaced by -mbarrel-shifter.
Replaced by -mdpfp-compact.
Replaced by -mdpfp-fast.
Replaced by -mdsp-packa.
Replaced by -mspfp-compact.
Replaced by -mspfp-fast.
-mtune=``cpu``
Values arc600, arc601, arc700 and arc700-xmac for cpu are replaced by ARC600, ARC601, ARC700 and ARC700-xmac respectively
-multcost=``num``
Replaced by -mmultcost.
:: _arm-options:
These -m options are defined for the ARM port:
-mabi=``name``
Generate code for the specified ABI Permissible values are: apcs-gnu, atpcs, aapcs, aapcs-linux and iwmmxt.
Generate a stack frame that is compliant with the ARM Procedure Call Standard for all functions, even if this is not strictly necessary for correct execution of the code. Specifying -fomit-frame-pointer with this option causes the stack frames not to be generated for leaf functions. The default is -mno-apcs-frame. This option is deprecated.
This is a synonym for -mapcs-frame and is deprecated.
@c not currently implemented @item -mapcs-stack-check @opindex mapcs-stack-check Generate code to check the amount of stack space available upon entry to every function (that actually uses some stack space). If there is insufficient space available then either the function @code{__rt_stkovf_split_small} or @code{__rt_stkovf_split_big} is called, depending upon the amount of stack space required. The runtime system is required to provide these functions. The default is @option{-mno-apcs-stack-check}, since this produces smaller code.
@c not currently implemented @item -mapcs-float @opindex mapcs-float Pass floating-point arguments using the floating-point registers. This is one of the variants of the APCS@. This option is recommended if the target hardware has a floating-point unit or if a lot of floating-point arithmetic is going to be performed by the code. The default is @option{-mno-apcs-float}, since the size of integer-only code is slightly increased if @option{-mapcs-float} is used.
@c not currently implemented @item -mapcs-reentrant @opindex mapcs-reentrant Generate reentrant, position-independent code. The default is @option{-mno-apcs-reentrant}.
Generate code that supports calling between the ARM and Thumb instruction sets. Without this option, on pre-v5 architectures, the two instruction sets cannot be reliably used inside one program. The default is -mno-thumb-interwork, since slightly larger code is generated when -mthumb-interwork is specified. In AAPCS configurations this option is meaningless.
Prevent the reordering of instructions in the function prologue, or the merging of those instruction with the instructions in the functions body. This means that all functions start with a recognizable set of instructions (or in fact one of a choice from a small set of different function prologues), and this information can be used to locate the start of functions inside an executable piece of code. The default is -msched-prolog.
-mfloat-abi=``name``
Specifies which floating-point ABI to use. Permissible values are: soft, softfp and hard.
Specifying soft causes GCC to generate output containing library calls for floating-point operations. softfp allows the generation of code using hardware floating-point instructions, but still uses the soft-float calling conventions. hard allows generation of floating-point instructions and uses FPU-specific calling conventions.
The default depends on the specific target configuration. Note that the hard-float and soft-float ABIs are not link-compatible; you must compile your entire program with the same ABI, and link with a compatible set of libraries.
Generate code for a processor running in little-endian mode. This is the default for all standard configurations.
Generate code for a processor running in big-endian mode; the default is to compile code for a little-endian processor.
-march=``name``
This specifies the name of the target ARM architecture. GCC uses this name to determine what kind of instructions it can emit when generating assembly code. This option can be used in conjunction with or instead of the -mcpu= option. Permissible names are: armv2, armv2a, armv3, armv3m, armv4, armv4t, armv5, armv5t, armv5e, armv5te, armv6, armv6j, armv6t2, armv6z, armv6zk, armv6-m, armv7, armv7-a, armv7-r, armv7-m, armv7e-m, armv7ve, armv8-a, armv8-a+crc, iwmmxt, iwmmxt2, ep9312.
-march=armv7ve is the armv7-a architecture with virtualization extensions.
-march=armv8-a+crc enables code generation for the ARMv8-A architecture together with the optional CRC32 extensions.
-march=native causes the compiler to auto-detect the architecture of the build computer. At present, this feature is only supported on GNU/Linux, and not all architectures are recognized. If the auto-detect is unsuccessful the option has no effect.
-mtune=``name``
This option specifies the name of the target ARM processor for which GCC should tune the performance of the code. For some ARM implementations better performance can be obtained by using this option. Permissible names are: arm2, arm250, arm3, arm6, arm60, arm600, arm610, arm620, arm7, arm7m, arm7d, arm7dm, arm7di, arm7dmi, arm70, arm700, arm700i, arm710, arm710c, arm7100, arm720, arm7500, arm7500fe, arm7tdmi, arm7tdmi-s, arm710t, arm720t, arm740t, strongarm, strongarm110, strongarm1100, strongarm1110, arm8, arm810, arm9, arm9e, arm920, arm920t, arm922t, arm946e-s, arm966e-s, arm968e-s, arm926ej-s, arm940t, arm9tdmi, arm10tdmi, arm1020t, arm1026ej-s, arm10e, arm1020e, arm1022e, arm1136j-s, arm1136jf-s, mpcore, mpcorenovfp, arm1156t2-s, arm1156t2f-s, arm1176jz-s, arm1176jzf-s, cortex-a5, cortex-a7, cortex-a8, cortex-a9, cortex-a12, cortex-a15, cortex-a53, cortex-a57, cortex-a72, cortex-r4, cortex-r4f, cortex-r5, cortex-r7, cortex-m7, cortex-m4, cortex-m3, cortex-m1, cortex-m0, cortex-m0plus, cortex-m1.small-multiply, cortex-m0.small-multiply, cortex-m0plus.small-multiply, exynos-m1, marvell-pj4, xscale, iwmmxt, iwmmxt2, ep9312, fa526, fa626, fa606te, fa626te, fmp626, fa726te, xgene1.
Additionally, this option can specify that GCC should tune the performance of the code for a big.LITTLE system. Permissible names are: cortex-a15.cortex-a7, cortex-a57.cortex-a53, cortex-a72.cortex-a53.
-mtune=generic-``arch`` specifies that GCC should tune the performance for a blend of processors within architecture arch. The aim is to generate code that run well on the current most popular processors, balancing between optimizations that benefit some CPUs in the range, and avoiding performance pitfalls of other CPUs. The effects of this option may change in future GCC versions as CPU models come and go.
-mtune=native causes the compiler to auto-detect the CPU of the build computer. At present, this feature is only supported on GNU/Linux, and not all architectures are recognized. If the auto-detect is unsuccessful the option has no effect.
-mcpu=``name``
This specifies the name of the target ARM processor. GCC uses this name to derive the name of the target ARM architecture (as if specified by -march) and the ARM processor type for which to tune for performance (as if specified by -mtune). Where this option is used in conjunction with -march or -mtune, those options take precedence over the appropriate part of this option.
Permissible names for this option are the same as those for -mtune.
-mcpu=generic-``arch`` is also permissible, and is equivalent to -march=``arch` -mtune=generic-arch`. See -mtune for more information.
-mcpu=native causes the compiler to auto-detect the CPU of the build computer. At present, this feature is only supported on GNU/Linux, and not all architectures are recognized. If the auto-detect is unsuccessful the option has no effect.
-mfpu=``name``
This specifies what floating-point hardware (or hardware emulation) is available on the target. Permissible names are: vfp, vfpv3, vfpv3-fp16, vfpv3-d16, vfpv3-d16-fp16, vfpv3xd, vfpv3xd-fp16, neon, neon-fp16, vfpv4, vfpv4-d16, fpv4-sp-d16, neon-vfpv4, fpv5-d16, fpv5-sp-d16, fp-armv8, neon-fp-armv8, and crypto-neon-fp-armv8.
If -msoft-float is specified this specifies the format of floating-point values.
If the selected floating-point hardware includes the NEON extension (e.g. -mfpu`=neon), note that floating-point operations are not generated by GCCs auto-vectorization pass unless :option:-funsafe-math-optimizations` is also specified. This is because NEON hardware does not fully implement the IEEE 754 standard for floating-point arithmetic (in particular denormal values are treated as zero), so the use of NEON instructions may lead to a loss of precision.
-mfp16-format=``name``
Specify the format of the __fp16 half-precision floating-point type. Permissible names are none, ieee, and alternative; the default is none, in which case the __fp16 type is not defined. Half-Precision, for more information.
-mstructure-size-boundary=``n``
The sizes of all structures and unions are rounded up to a multiple of the number of bits set by this option. Permissible values are 8, 32 and 64. The default value varies for different toolchains. For the COFF targeted toolchain the default value is 8. A value of 64 is only allowed if the underlying ABI supports it.
Specifying a larger number can produce faster, more efficient code, but can also increase the size of the program. Different values are potentially incompatible. Code compiled with one value cannot necessarily expect to work with code or libraries compiled with another value, if they exchange information using structures or unions.
Generate a call to the function abort at the end of a noreturn function. It is executed if the function tries to return.
Tells the compiler to perform function calls by first loading the address of the function into a register and then performing a subroutine call on this register. This switch is needed if the target function lies outside of the 64-megabyte addressing range of the offset-based version of subroutine call instruction.
Even if this switch is enabled, not all function calls are turned into long calls. The heuristic is that static functions, functions that have the short_call attribute, functions that are inside the scope of a #pragma no_long_calls directive, and functions whose definitions have already been compiled within the current compilation unit are not turned into long calls. The exceptions to this rule are that weak function definitions, functions with the long_call attribute or the section attribute, and functions that are within the scope of a #pragma long_calls directive are always turned into long calls.
This feature is not enabled by default. Specifying -mno-long-calls restores the default behavior, as does placing the function calls within the scope of a #pragma long_calls_off directive. Note these switches have no effect on how the compiler generates code to handle function calls via function pointers.
Treat the register used for PIC addressing as read-only, rather than loading it in the prologue for each function. The runtime system is responsible for initializing this register with an appropriate value before execution begins.
-mpic-register=``reg``
Specify the register to be used for PIC addressing. For standard PIC base case, the default is any suitable register determined by compiler. For single PIC base case, the default is R9 if target is EABI based or stack-checking is enabled, otherwise the default is R10.
Assume that each data segments are relative to text segment at load time. Therefore, it permits addressing data using PC-relative operations. This option is on by default for targets other than VxWorks RTP.
Write the name of each function into the text section, directly preceding the function prologue. The generated code is similar to this:
t0
.ascii "arm_poke_function_name", 0
.align
t1
.word 0xff000000 + (t1 - t0)
arm_poke_function_name
mov ip, sp
stmfd sp!, {fp, ip, lr, pc}
sub fp, ip, #4
When performing a stack backtrace, code can inspect the value of pc stored at fp + 0. If the trace function then looks at location pc - 12 and the top 8 bits are set, then we know that there is a function name embedded immediately preceding this location and has length ((pc[-3]) & 0xff000000).
Select between generating code that executes in ARM and Thumb states. The default for most configurations is to generate code that executes in ARM state, but the default can be changed by configuring GCC with the --with-mode=```state` configure option.
Generate a stack frame that is compliant with the Thumb Procedure Call Standard for all non-leaf functions. (A leaf function is one that does not call any other functions.) The default is -mno-tpcs-frame.
Generate a stack frame that is compliant with the Thumb Procedure Call Standard for all leaf functions. (A leaf function is one that does not call any other functions.) The default is -mno-apcs-leaf-frame.
Gives all externally visible functions in the file being compiled an ARM instruction set header which switches to Thumb mode before executing the rest of the function. This allows these functions to be called from non-interworking code. This option is not valid in AAPCS configurations because interworking is enabled by default.
Allows calls via function pointers (including virtual functions) to execute correctly regardless of whether the target code has been compiled for interworking or not. There is a small overhead in the cost of executing a function pointer if this option is enabled. This option is not valid in AAPCS configurations because interworking is enabled by default.
-mtp=``name``
Specify the access model for the thread local storage pointer. The valid models are soft, which generates calls to __aeabi_read_tp, cp15, which fetches the thread pointer from cp15 directly (supported in the arm6k architecture), and auto, which uses the best available method for the selected processor. The default setting is auto.
-mtls-dialect=``dialect``
Specify the dialect to use for accessing thread local storage. Two ``dialect``s are supportedgnu and gnu2. The gnu dialect selects the original GNU scheme for supporting local and global dynamic TLS models. The gnu2 dialect selects the GNU descriptor scheme, which provides better performance for shared libraries. The GNU descriptor scheme is compatible with the original scheme, but does require new assembler, linker and library support. Initial and local exec TLS models are unaffected by this option and always use the original scheme.
Only generate absolute relocations on word-sized values (i.e. R_ARM_ABS32). This is enabled by default on targets (uClinux, SymbianOS) where the runtime loader imposes this restriction, and when -fpic or -fPIC is specified.
Some Cortex-M3 cores can cause data corruption when ldrd instructions with overlapping destination and base registers are used. This option avoids generating these instructions. This option is enabled by default when -mcpu=cortex-m3 is specified.
Enables (or disables) reading and writing of 16- and 32- bit values from addresses that are not 16- or 32- bit aligned. By default unaligned access is disabled for all pre-ARMv6 and all ARMv6-M architectures, and enabled for all other architectures. If unaligned access is not enabled then words in packed data structures are accessed a byte at a time.
The ARM attribute Tag_CPU_unaligned_access is set in the generated object file to either true or false, depending upon the setting of this option. If unaligned access is enabled then the preprocessor symbol __ARM_FEATURE_UNALIGNED is also defined.
Enables using Neon to handle scalar 64-bits operations. This is disabled by default since the cost of moving data from core registers to Neon is high.
Assume loading data from flash is slower than fetching instruction. Therefore literal load is minimized for better performance. This option is only supported when compiling for ARMv7 M-profile and off by default.
Assume inline assembler is using unified asm syntax. The default is currently off which implies divided syntax. Currently this option is available only for Thumb1 and has no effect on ARM state and Thumb2. However, this may change in future releases of GCC. Divided syntax should be considered deprecated.
Restricts generation of IT blocks to conform to the rules of ARMv8. IT blocks can only contain a single 16-bit instruction from a select set of instructions. This option is on by default for ARMv8 Thumb mode.
Print CPU tuning information as comment in assembler file. This is an option used only for regression testing of the compiler and not intended for ordinary use in compiling code. This option is disabled by default.
:: _avr-options:
These options are defined for AVR implementations:
-mmcu=``mcu``
Specify Atmel AVR instruction set architectures (ISA) or MCU type.
The default for this option isavr2.
GCC supports the following AVR devices and ISAs:
Accumulate outgoing function arguments and acquire/release the needed stack space for outgoing function arguments once in function prologue/epilogue. Without this option, outgoing arguments are pushed before calling a function and popped afterwards.
Popping the arguments after the function call can be expensive on AVR so that accumulating the stack space might lead to smaller executables because arguments need not to be removed from the stack after such a function call.
This option can lead to reduced code size for functions that perform several calls to functions that get their arguments on the stack like calls to printf-like functions.
-mbranch-cost=``cost``
Set the branch costs for conditional branch instructions to cost. Reasonable values for cost are small, non-negative integers. The default branch cost is 0.
Functions prologues/epilogues are expanded as calls to appropriate subroutines. Code size is smaller.
Assume int to be 8-bit integer. This affects the sizes of all types: a char is 1 byte, an int is 1 byte, a long is 2 bytes, and long long is 4 bytes. Please note that this option does not conform to the C standards, but it results in smaller code size.
-mn-flash=``num``
Assume that the flash memory has a size of num times 64KiB.
Generated code is not compatible with hardware interrupts. Code size is smaller.
Try to replace CALL resp. JMP instruction by the shorter RCALL resp. RJMP instruction if applicable. Setting -mrelax just adds the --mlink-relax option to the assemblers command line and the --relax option to the linkers command line.
Jump relaxing is performed by the linker because jump offsets are not known before code is located. Therefore, the assembler code generated by the compiler is the same, but the instructions in the executable may differ from instructions in the assembler code.
Relaxing must be turned on if linker stubs are needed, see the section on EIND and linker stubs below.
Assume that the device supports the Read-Modify-Write instructions XCH, LAC, LAS and LAT.
Treat the stack pointer register as an 8-bit register, i.e. assume the high byte of the stack pointer is zero. In general, you dont need to set this option by hand.
This option is used internally by the compiler to select and build multilibs for architectures avr2 and avr25. These architectures mix devices with and without SPH. For any setting other than -mmcu=avr2 or -mmcu=avr25 the compiler driver adds or removes this option from the compiler propers command line, because the compiler then knows if the device or architecture has an 8-bit stack pointer and thus no SPH register or not.
Use address register X in a way proposed by the hardware. This means that X is only used in indirect, post-increment or pre-decrement addressing.
Without this option, the X register may be used in the same way as Y or Z which then is emulated by additional instructions. For example, loading a value with X+const addressing with a small non-negative const < 64 to a register Rn is performed as
adiw r26, const ; X += const
ld ``Rn``, X ; ``Rn`` = *X
sbiw r26, const ; X -= const
Only change the lower 8bits of the stack pointer.
Dont link against AVR-LibCs device specific library libdev.a.
Warn about conversions between address spaces in the case where the resulting address space is not contained in the incoming address space.
EIND and Devices with More Than 128 Ki Bytes of Flash EIND Pointers in the implementation are 16bits wide. The address of a function or label is represented as word address so that indirect jumps and calls can target any code address in the range of 64Ki words.
In order to facilitate indirect jump on devices with more than 128Ki bytes of program memory space, there is a special function register called EIND that serves as most significant part of the target address when EICALL or EIJMP instructions are used.
Indirect jumps and calls on these devices are handled as follows by the compiler and are subject to some limitations:
The compiler never sets EIND.
The compiler uses EIND implicitely in EICALL/EIJMP instructions or might read EIND directly in order to emulate an indirect call/jump by means of a RET instruction.
The compiler assumes that EIND never changes during the startup code or during the application. In particular, EIND is not saved/restored in function or interrupt service routine prologue/epilogue.
For indirect calls to functions and computed goto, the linker generates stubs. Stubs are jump pads sometimes also called trampolines. Thus, the indirect call/jump jumps to such a stub. The stub contains a direct jump to the desired address.
Linker relaxation must be turned on so that the linker generates the stubs correctly in all situations. See the compiler option -mrelax and the linker option --relax. There are corner cases where the linker is supposed to generate stubs but aborts without relaxation and without a helpful error message.
The default linker script is arranged for code with EIND = 0. If code is supposed to work for a setup with EIND != 0, a custom linker script has to be used in order to place the sections whose name start with .trampolines into the segment where EIND points to.
The startup code from libgcc never sets EIND. Notice that startup code is a blend of code from libgcc and AVR-LibC. For the impact of AVR-LibC on EIND, see the http://nongnu.org/avr-libc/user-manual/AVR-LibC user manual.
It is legitimate for user-specific startup code to set up EIND early, for example by means of initialization code located in section .init3. Such code runs prior to general startup code that initializes RAM and calls constructors, but after the bit of startup code from AVR-LibC that sets EIND to the segment where the vector table is located.
#include <avr/io.h>
static void
__attribute__((section(".init3"),naked,used,no_instrument_function))
init3_set_eind (void)
{
__asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t"
"out %i0,r24" :: "n" (&EIND) : "r24","memory");
}
The __trampolines_start symbol is defined in the linker script.
Stubs are generated automatically by the linker if the following two conditions are met:
The address of a label is taken by means of the gs modifier (short for generate stubs) like so:
LDI r24, lo8(gs(``func``))
LDI r25, hi8(gs(``func``))
The final location of that label is in a code segment outside the segment where the stubs are located.
The compiler emits such gs modifiers for code labels in the following situations:
Jumping to non-symbolic addresses like so is not supported:
int main (void)
{
/* Call function at word address 0x2 */
return ((int(*)(void)) 0x2)();
}
Instead, a stub has to be set up, i.e. the function has to be called through a symbol (func_4 in the example):
int main (void)
{
extern int func_4 (void);
/* Call function at byte address 0x4 */
return func_4();
}
and the application be linked with -Wl,--defsym,func_4=0x4. Alternatively, func_4 can be defined in the linker script.
Handling of the RAMPD, RAMPX, RAMPY and RAMPZ Special Function Registers RAMPD RAMPX RAMPY RAMPZ Some AVR devices support memories larger than the 64KiB range that can be accessed with 16-bit pointers. To access memory locations outside this 64KiB range, the contentent of a RAMP register is used as high part of the address: The X, Y, Z address register is concatenated with the RAMPX, RAMPY, RAMPZ special function register, respectively, to get a wide address. Similarly, RAMPD is used together with direct addressing.
GCC defines several built-in macros so that the user code can test for the presence or absence of features. Almost any of the following built-in macros are deduced from device capabilities and thus triggered by the -mmcu= command-line option.
For even more AVR-specific built-in macros see AVR Named Address Spaces and AVR Built-in Functions.
Build-in macro that resolves to a decimal number that identifies the architecture and depends on the -mmcu=``mcu`` option. Possible values are:
2, 25, 3, 31, 35, 4, 5, 51, 6
for mcu``=``avr2, avr25, avr3, avr31, avr35, avr4, avr5, avr51, avr6,
respectively and
100, 102, 104, 105, 106, 107
for mcu``=``avrtiny, avrxmega2, avrxmega4, avrxmega5, avrxmega6, avrxmega7, respectively. If mcu specifies a device, this built-in macro is set accordingly. For example, with -mmcu=atmega8 the macro is defined to 4.
__AVR_``Device``__
Setting -mmcu=``device`` defines this built-in macro which reflects the devices name. For example, -mmcu=atmega8 defines the built-in macro __AVR_ATmega8__, -mmcu=attiny261a defines __AVR_ATtiny261A__, etc.
The built-in macros names follow the scheme __AVR_``Device``__ where Device is the device name as from the AVR user manual. The difference between Device in the built-in macro and device in -mmcu=``device`` is that the latter is always lowercase.
If device is not a device but only a core architecture like avr51, this macro is not defined.
Setting -mmcu=``device`` defines this built-in macro to the devices name. For example, with -mmcu=atmega8 the macro is defined to atmega8.
If device is not a device but only a core architecture like avr51, this macro is not defined.
The device / architecture belongs to the XMEGA family of devices.
The device has the the ELPM instruction.
The device has the ELPM R``n,Z`` and ELPM R``n,Z+`` instructions.
The device has the MOVW instruction to perform 16-bit register-register moves.
The device has the LPM R``n,Z`` and LPM R``n,Z+`` instructions.
The device has a hardware multiplier.
The device has the JMP and CALL instructions. This is the case for devices with at least 16KiB of program memory.
The device has the EIJMP and EICALL instructions. This is the case for devices with more than 128KiB of program memory. This also means that the program counter (PC) is 3bytes wide.
The program counter (PC) is 2bytes wide. This is the case for devices with up to 128KiB of program memory.
The stack pointer (SP) register is treated as 8-bit respectively 16-bit register by the compiler. The definition of these macros is affected by -mtiny-stack.
The device has the SPH (high part of stack pointer) special function register or has an 8-bit stack pointer, respectively. The definition of these macros is affected by -mmcu= and in the cases of -mmcu=avr2 and -mmcu=avr25 also by -msp8.
The device has the RAMPD, RAMPX, RAMPY, RAMPZ special function register, respectively.
This macro reflects the -mno-interrupts command-line option.
Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit instructions because of a hardware erratum. Skip instructions are SBRS, SBRC, SBIS, SBIC and CPSE. The second macro is only defined if __AVR_HAVE_JMP_CALL__ is also set.
The device has Read-Modify-Write instructions (XCH, LAC, LAS and LAT).
__AVR_SFR_OFFSET__=``offset``
Instructions that can address I/O special function registers directly like IN, OUT, SBI, etc. may use a different address as if addressed by an instruction to access RAM like LD or STS. This offset depends on the device architecture and has to be subtracted from the RAM address in order to get the respective I/Oaddress.
The compiler is configured to be used together with AVR-Libc. See the --with-avrlibc configure option.
:: _blackfin-options:
-mcpu=``cpu``[-sirevision]
Specifies the name of the target Blackfin processor. Currently, cpu can be one of bf512, bf514, bf516, bf518, bf522, bf523, bf524, bf525, bf526, bf527, bf531, bf532, bf533, bf534, bf536, bf537, bf538, bf539, bf542, bf544, bf547, bf548, bf549, bf542m, bf544m, bf547m, bf548m, bf549m, bf561, bf592.
The optional sirevision specifies the silicon revision of the target Blackfin processor. Any workarounds available for the targeted silicon revision are enabled. If sirevision is none, no workarounds are enabled. If sirevision is any, all workarounds for the targeted processor are enabled. The __SILICON_REVISION__ macro is defined to two hexadecimal digits representing the major and minor numbers in the silicon revision. If sirevision is none, the __SILICON_REVISION__ is not defined. If sirevision is any, the __SILICON_REVISION__ is defined to be 0xffff. If this optional sirevision is not used, GCC assumes the latest known silicon revision of the targeted Blackfin processor.
GCC defines a preprocessor macro for the specified cpu. For the bfin-elf toolchain, this option causes the hardware BSP provided by libgloss to be linked in if -msim is not given.
Without this option, bf532 is used as the processor by default.
Note that support for bf561 is incomplete. For bf561, only the preprocessor macro is defined.
Specifies that the program will be run on the simulator. This causes the simulator BSP provided by libgloss to be linked in. This option has effect only for bfin-elf toolchain. Certain other options, such as -mid-shared-library and -mfdpic, imply -msim.
Dont keep the frame pointer in a register for leaf functions. This avoids the instructions to save, set up and restore frame pointers and makes an extra register available in leaf functions. The option -fomit-frame-pointer removes the frame pointer for all functions, which might make debugging harder.
When enabled, the compiler ensures that the generated code does not contain speculative loads after jump instructions. If this option is used, __WORKAROUND_SPECULATIVE_LOADS is defined.
Dont generate extra code to prevent speculative loads from occurring.
When enabled, the compiler ensures that the generated code does not contain CSYNC or SSYNC instructions too soon after conditional branches. If this option is used, __WORKAROUND_SPECULATIVE_SYNCS is defined.
Dont generate extra code to prevent CSYNC or SSYNC instructions from occurring too soon after a conditional branch.
When enabled, the compiler is free to take advantage of the knowledge that the entire program fits into the low 64k of memory.
Assume that the program is arbitrarily large. This is the default.
Do stack checking using information placed into L1 scratchpad memory by the uClinux kernel.
Generate code that supports shared libraries via the library ID method. This allows for execute in place and shared libraries in an environment without virtual memory management. This option implies -fPIC. With a bfin-elf target, this option implies -msim.
Generate code that doesnt assume ID-based shared libraries are being used. This is the default.
Generate code that supports shared libraries via the library ID method, but assumes that this library or executable wont link against any other ID shared libraries. That allows the compiler to use faster code for jumps and calls.
Do not assume that the code being compiled wont link against any ID shared libraries. Slower code is generated for jump and call insns.
Specifies the identification number of the ID-based shared library being compiled. Specifying a value of 0 generates more compact code; specifying other values forces the allocation of that number to the current library but is no more space- or time-efficient than omitting this option.
Generate code that allows the data segment to be located in a different area of memory from the text segment. This allows for execute in place in an environment without virtual memory management by eliminating relocations against the text section.
Generate code that assumes that the data segment follows the text segment. This is the default.
Tells the compiler to perform function calls by first loading the address of the function into a register and then performing a subroutine call on this register. This switch is needed if the target function lies outside of the 24-bit addressing range of the offset-based version of subroutine call instruction.
This feature is not enabled by default. Specifying -mno-long-calls restores the default behavior. Note these switches have no effect on how the compiler generates code to handle function calls via function pointers.
Link with the fast floating-point library. This library relaxes some of the IEEE floating-point standards rules for checking inputs against Not-a-Number (NAN), in the interest of performance.
Enable inlining of PLT entries in function calls to functions that are not known to bind locally. It has no effect without -mfdpic.
Build a standalone application for multicore Blackfin processors. This option causes proper start files and link scripts supporting multicore to be used, and defines the macro __BFIN_MULTICORE. It can only be used with -mcpu=bf561[-``sirevision`]`.
This option can be used with -mcorea or -mcoreb, which selects the one-application-per-core programming model. Without -mcorea or -mcoreb, the single-application/dual-core programming model is used. In this model, the main function of Core B should be named as coreb_main.
If this option is not used, the single-core application programming model is used.
Build a standalone application for Core A of BF561 when using the one-application-per-core programming model. Proper start files and link scripts are used to support Core A, and the macro __BFIN_COREA is defined. This option can only be used in conjunction with -mmulticore.
Build a standalone application for Core B of BF561 when using the one-application-per-core programming model. Proper start files and link scripts are used to support Core B, and the macro __BFIN_COREB is defined. When this option is used, coreb_main should be used instead of main. This option can only be used in conjunction with -mmulticore.
Build a standalone application for SDRAM. Proper start files and link scripts are used to put the application into SDRAM, and the macro __BFIN_SDRAM is defined. The loader should initialize SDRAM before loading the application.
Assume that ICPLBs are enabled at run time. This has an effect on certain anomaly workarounds. For Linux targets, the default is to assume ICPLBs are enabled; for standalone applications the default is off.
:: _c6x-options:
-march=``name``
This specifies the name of the target architecture. GCC uses this name to determine what kind of instructions it can emit when generating assembly code. Permissible names are: c62x, c64x, c64x+, c67x, c67x+, c674x.
Generate code for a big-endian target.
Generate code for a little-endian target. This is the default.
Choose startup files and linker script suitable for the simulator.
Put small global and static data in the .neardata section, which is pointed to by register B14. Put small uninitialized global and static data in the .bss section, which is adjacent to the .neardata section. Put small read-only data into the .rodata section. The corresponding sections used for large pieces of data are .fardata, .far and .const.
Put all data, not just small objects, into the sections reserved for small data, and use addressing relative to the B14 register to access them.
Make no use of the sections reserved for small data, and use absolute addresses to access all data. Put all initialized global and static data in the .fardata section, and all uninitialized data in the .far section. Put all constant data into the .const section.
:: _cris-options:
These options are defined specifically for the CRIS ports.
-march=``architecture-type`` -mcpu=``architecture-type``
Generate code for the specified architecture. The choices for architecture-type are v3, v8 and v10 for respectively ETRAX 4, ETRAX 100, and ETRAX 100 LX Default is v0 except for cris-axis-linux-gnu, where the default is v10.
-mtune=``architecture-type``
Tune to architecture-type everything applicable about the generated code, except for the ABI and the set of available instructions. The choices for architecture-type are the same as for -march=``architecture-type``.
-mmax-stack-frame=``n``
Warn when the stack frame of a function exceeds n bytes.
The options -metrax4 and -metrax100 are synonyms for -march=v3 and -march=v8 respectively.
Work around a bug in the muls and mulu instructions for CPU models where it applies. This option is active by default.
Enable CRIS-specific verbose debug-related information in the assembly code. This option also has the effect of turning off the #NO_APP formatted-code indicator to the assembler at the beginning of the assembly file.
Do not use condition-code results from previous instruction; always emit compare and test instructions before use of condition codes.
Do not emit instructions with side effects in addressing modes other than post-increment.
These options (no- options) arrange (eliminate arrangements) for the stack frame, individual data and constants to be aligned for the maximum single data access size for the chosen CPU model. The default is to arrange for 32-bit alignment. ABI details such as structure layout are not affected by these options.
Similar to the stack- data- and const-align options above, these options arrange for stack frame, writable data and constants to all be 32-bit, 16-bit or 8-bit aligned. The default is 32-bit alignment.
With -mno-prologue-epilogue, the normal function prologue and epilogue which set up the stack frame are omitted and no return instructions or return sequences are generated in the code. Use this option only together with visual inspection of the compiled code: no warnings or errors are generated when call-saved registers must be saved, or storage for local variables needs to be allocated.
With -fpic and -fPIC, dont generate (do generate) instruction sequences that load addresses for functions from the PLT part of the GOT rather than (traditional on other architectures) calls to the PLT The default is -mgotplt.
Legacy no-op option only recognized with the cris-axis-elf and cris-axis-linux-gnu targets.
Legacy no-op option only recognized with the cris-axis-linux-gnu target.
This option, recognized for the cris-axis-elf, arranges to link with input-output functions from a simulator library. Code, initialized data and zero-initialized data are allocated consecutively.
Like -sim, but pass linker options to locate initialized data at 0x40000000 and zero-initialized data at 0x80000000.
:: _cr16-options:
These options are defined specifically for the CR16 ports.
Enable the use of multiply-accumulate instructions. Disabled by default.
Generate code for CR16C or CR16C+ architecture. CR16C+ architecture is default.
Links the library libsim.a which is in compatible with simulator. Applicable to ELF compiler only.
Choose integer type as 32-bit wide.
Generates sbit/cbit instructions for bit manipulations.
-mdata-model=``model``
Choose a data model. The choices for model are near, far or medium. medium is default. However, far is not valid with -mcr16c, as the CR16C architecture does not support the far data model.
:: _darwin-options:
These options are defined for all architectures running the Darwin operating system.
FSF GCC on Darwin does not create fat object files; it creates an object file for the single architecture that GCC was built to target. Apples GCC on Darwin does create fat files if multiple -arch options are used; it does so by running the compiler or linker multiple times and joining the results together with lipo.
The subtype of the file created (like ppc7400 or ppc970 or i686) is determined by the flags that specify the ISA that GCC is targeting, like -mcpu or -march. The -force_cpusubtype_ALL option can be used to override this.
The Darwin tools vary in their behavior when presented with an ISA mismatch. The assembler, as, only permits instructions to be used that are valid for the subtype of the file it is generating, so you cannot put 64-bit instructions in a ppc750 object file. The linker for shared libraries, /usr/bin/libtool, fails and prints an error if asked to create a shared library with a less restrictive subtype than its input files (for instance, trying to put a ppc970 object file in a ppc7400 library). The linker for executables, ld, quietly gives the executable the most restrictive subtype of any of its input files.
-F``dir``
Add the framework directory dir to the head of the list of directories to be searched for header files. These directories are interleaved with those specified by -I options and are scanned in a left-to-right order.
A framework directory is a directory with frameworks in it. A framework is a directory with a Headers and/or PrivateHeaders directory contained directly in it that ends in .framework. The name of a framework is the name of this directory excluding the .framework. Headers associated with the framework are found in one of those two directories, with Headers being searched first. A subframework is a framework directory that is in a frameworks Frameworks directory. Includes of subframework headers can only appear in a header of a framework that contains the subframework, or in a sibling subframework header. Two subframeworks are siblings if they occur in the same framework. A subframework should not have the same name as a framework; a warning is issued if this is violated. Currently a subframework cannot have subframeworks; in the future, the mechanism may be extended to support this. The standard frameworks can be found in /System/Library/Frameworks and /Library/Frameworks. An example include looks like #include <Framework/header.h>, where Framework denotes the name of the framework and header.h is found in the PrivateHeaders or Headers directory.
-iframework``dir``
Like -F except the directory is a treated as a system directory. The main difference between this -iframework and -F is that with -iframework the compiler does not warn about constructs contained within header files found via dir. This option is valid only for the C family of languages.
Emit debugging information for symbols that are used. For stabs debugging format, this enables -feliminate-unused-debug-symbols. This is by default ON
Emit debugging information for all symbols and types.
-mmacosx-version-min=``version``
The earliest version of MacOS X that this executable will run on is version. Typical values of version include 10.1, 10.2, and 10.3.9.
If the compiler was built to use the systems headers by default, then the default for this option is the system version on which the compiler is running, otherwise the default is to make choices that are compatible with as many systems and code bases as possible.
Enable kernel development mode. The -mkernel option sets -static, -fno-common, -fno-use-cxa-atexit, -fno-exceptions, -fno-non-call-exceptions, -fapple-kext, -fno-weak and -fno-rtti where applicable. This mode also sets -mno-altivec, -msoft-float, -fno-builtin and -mlong-branch for PowerPC targets.
Override the defaults for bool so that sizeof(bool)==1. By default sizeof(bool) is 4 when compiling for Darwin/PowerPC and 1 when compiling for Darwin/x86, so this option has no effect on x86.
Warning: The -mone-byte-bool switch causes GCC to generate code that is not binary compatible with code generated without that switch. Using this switch may require recompiling all other modules in a program, including system libraries. Use this switch to conform to a non-default data model.
Generate code suitable for fast turnaround development, such as to allow GDB to dynamically load .o files into already-running programs. -findirect-data and -ffix-and-continue are provided for backwards compatibility.
Loads all members of static archive libraries. See man ld(1) for more information.
Cause the errors having to do with files that have the wrong architecture to be fatal.
Causes the output file to be marked such that the dynamic linker will bind all undefined references when the file is loaded or launched.
Produce a Mach-o bundle format file. See man ld(1) for more information.
-bundle_loader executable
This option specifies the executable that will load the build output file being linked. See man ld(1) for more information.
When passed this option, GCC produces a dynamic library instead of an executable when linking, using the Darwin libtool command.
This causes GCCs output file to have the ALL subtype, instead of one controlled by the -mcpu or -march option.
| -allowable_client | |
| client_name | |
-client_name -compatibility_version -current_version -dead_strip -dependency-file -dylib_file -dylinker_install_name -dynamic -exported_symbols_list -filelist
-flat_namespace -force_flat_namespace -headerpad_max_install_names -image_base -init -install_name -keep_private_externs -multi_module -multiply_defined -multiply_defined_unused
-noall_load -no_dead_strip_inits_and_terms -nofixprebinding -nomultidefs -noprebind -noseglinkedit -pagezero_size -prebind -prebind_all_twolevel_modules -private_bundle
-read_only_relocs -sectalign -sectobjectsymbols -whyload -seg1addr -sectcreate -sectobjectsymbols -sectorder -segaddr -segs_read_only_addr
-segs_read_write_addr -seg_addr_table -seg_addr_table_filename -seglinkedit -segprot -segs_read_only_addr -segs_read_write_addr -single_module -static -sub_library
-sub_umbrella -twolevel_namespace -umbrella -undefined -unexported_symbols_list -weak_reference_mismatches -whatsloaded
These options are passed to the Darwin linker. The Darwin linker man page describes them in detail.
:: _dec-alpha-options:
These -m options are defined for the DEC Alpha implementations:
Use (do not use) the hardware floating-point instructions for floating-point operations. When -msoft-float is specified, functions in libgcc.a are used to perform floating-point operations. Unless they are replaced by routines that emulate the floating-point operations, or compiled in such a way as to call such emulations routines, these routines issue floating-point operations. If you are compiling for an Alpha without floating-point operations, you must ensure that the library is built so as not to call them.
Note that Alpha implementations without floating-point operations are required to have floating-point registers.
Generate code that uses (does not use) the floating-point register set. -mno-fp-regs implies -msoft-float. If the floating-point register set is not used, floating-point operands are passed in integer registers as if they were integers and floating-point results are passed in $0 instead of $f0. This is a non-standard calling sequence, so any function with a floating-point argument or return value called by code compiled with -mno-fp-regs must also be compiled with that option.
A typical use of this option is building a kernel that does not use, and hence need not save and restore, any floating-point registers.
The Alpha architecture implements floating-point hardware optimized for maximum performance. It is mostly compliant with the IEEE floating-point standard. However, for full compliance, software assistance is required. This option generates code fully IEEE-compliant code except that the inexact-flag is not maintained (see below). If this option is turned on, the preprocessor macro _IEEE_FP is defined during compilation. The resulting code is less efficient but is able to correctly support denormalized numbers and exceptional IEEE values such as not-a-number and plus/minus infinity. Other Alpha compilers call this option -ieee_with_no_inexact.
This is like -mieee except the generated code also maintains the IEEE inexact-flag. Turning on this option causes the generated code to implement fully-compliant IEEE math. In addition to _IEEE_FP, _IEEE_FP_EXACT is defined as a preprocessor macro. On some Alpha implementations the resulting code may execute significantly slower than the code generated by default. Since there is very little code that depends on the inexact-flag, you should normally not specify this option. Other Alpha compilers call this option -ieee_with_inexact.
-mfp-trap-mode=``trap-mode``
This option controls what floating-point related traps are enabled. Other Alpha compilers call this option -fptm ``trap-mode``. The trap mode can be set to one of four values:
This is the default (normal) setting. The only traps that are enabled are the ones that cannot be disabled in software (e.g., division by zero trap).
In addition to the traps enabled by n, underflow traps are enabled as well.
Like u, but the instructions are marked to be safe for software completion (see Alpha architecture manual for details).
Like su, but inexact traps are enabled as well.
-mfp-rounding-mode=``rounding-mode``
Selects the IEEE rounding mode. Other Alpha compilers call this option -fprm ``rounding-mode``. The rounding-mode can be one of:
Normal IEEE rounding mode. Floating-point numbers are rounded towards the nearest machine number or towards the even machine number in case of a tie.
Round towards minus infinity.
Chopped rounding mode. Floating-point numbers are rounded towards zero.
Dynamic rounding mode. A field in the floating-point control register (fpcr, see Alpha architecture reference manual) controls the rounding mode in effect. The C library initializes this register for rounding towards plus infinity. Thus, unless your program modifies the fpcr, d corresponds to round towards plus infinity.
-mtrap-precision=``trap-precision``
In the Alpha architecture, floating-point traps are imprecise. This means without software assistance it is impossible to recover from a floating trap and program execution normally needs to be terminated. GCC can generate code that can assist operating system trap handlers in determining the exact location that caused a floating-point trap. Depending on the requirements of an application, different levels of precisions can be selected:
Program precision. This option is the default and means a trap handler can only identify which program caused a floating-point exception.
Function precision. The trap handler can determine the function that caused a floating-point exception.
Instruction precision. The trap handler can determine the exact instruction that caused a floating-point exception.
Other Alpha compilers provide the equivalent options called -scope_safe and -resumption_safe.
This option marks the generated code as IEEE conformant. You must not use this option unless you also specify -mtrap-precision=i and either -mfp-trap-mode=su or -mfp-trap-mode=sui. Its only effect is to emit the line .eflag 48 in the function prologue of the generated assembly file.
Normally GCC examines a 32- or 64-bit integer constant to see if it can construct it from smaller constants in two or three instructions. If it cannot, it outputs the constant as a literal and generates code to load it from the data segment at run time.
Use this option to require GCC to construct all integer constants using code, even if it takes more instructions (the maximum is six).
You typically use this option to build a shared library dynamic loader. Itself a shared library, it must relocate itself in memory before it can find the variables and constants in its own data segment.
Indicate whether GCC should generate code to use the optional BWX, CIX, FIX and MAX instruction sets. The default is to use the instruction sets supported by the CPU type specified via -mcpu= option or that of the CPU on which GCC was built if none is specified.
Generate code that uses (does not use) VAX F and G floating-point arithmetic instead of IEEE single and double precision.
Older Alpha assemblers provided no way to generate symbol relocations except via assembler macros. Use of these macros does not allow optimal instruction scheduling. GNU binutils as of version 2.12 supports a new syntax that allows the compiler to explicitly mark which relocations should apply to which instructions. This option is mostly useful for debugging, as GCC detects the capabilities of the assembler when it is built and sets the default accordingly.
When -mexplicit-relocs is in effect, static data is accessed via gp-relative relocations. When -msmall-data is used, objects 8 bytes long or smaller are placed in a small data area (the .sdata and .sbss sections) and are accessed via 16-bit relocations off of the $gp register. This limits the size of the small data area to 64KB, but allows the variables to be directly accessed via a single instruction.
The default is -mlarge-data. With this option the data area is limited to just below 2GB Programs that require more than 2GB of data must use malloc or mmap to allocate the data in the heap instead of in the programs data segment.
When generating code for shared libraries, -fpic implies -msmall-data and -fPIC implies -mlarge-data.
When -msmall-text is used, the compiler assumes that the code of the entire program (or shared library) fits in 4MB, and is thus reachable with a branch instruction. When -msmall-data is used, the compiler can assume that all local symbols share the same $gp value, and thus reduce the number of instructions required for a function call from 4 to 1.
The default is -mlarge-text.
-mcpu=``cpu_type``
Set the instruction set and instruction scheduling parameters for machine type cpu_type. You can specify either the EV style name or the corresponding chip number. GCC supports scheduling parameters for the EV4, EV5 and EV6 family of processors and chooses the default values for the instruction set from the processor you specify. If you do not specify a processor type, GCC defaults to the processor on which the compiler was built.
Supported values for cpu_type are
Schedules as an EV4 and has no instruction set extensions.
Schedules as an EV5 and has no instruction set extensions.
Schedules as an EV5 and supports the BWX extension.
Schedules as an EV5 and supports the BWX and MAX extensions.
Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.
Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.
Native toolchains also support the value native, which selects the best architecture option for the host processor. -mcpu=native has no effect if GCC does not recognize the processor.
-mtune=``cpu_type``
Set only the instruction scheduling parameters for machine type cpu_type. The instruction set is not changed.
Native toolchains also support the value native, which selects the best architecture option for the host processor. -mtune=native has no effect if GCC does not recognize the processor.
-mmemory-latency=``time``
Sets the latency the scheduler should assume for typical memory references as seen by the application. This number is highly dependent on the memory access patterns used by the application and the size of the external cache on the machine.
Valid options for time are
number A decimal number representing clock cycles.
The compiler contains estimates of the number of clock cycles for typical EV4 & EV5 hardware for the Level 1, 2 & 3 caches (also called Dcache, Scache, and Bcache), as well as to main memory. Note that L3 is only valid for EV5.
:: _fr30-options:
These options are defined specifically for the FR30 port.
Use the small address space model. This can produce smaller code, but it does assume that all symbolic values and addresses fit into a 20-bit range.
Assume that runtime support has been provided and so there is no need to include the simulator library (libsim.a) on the linker command line.
:: _frv-options:
Only use the first 32 general-purpose registers.
Use all 64 general-purpose registers.
Use only the first 32 floating-point registers.
Use all 64 floating-point registers.
Use hardware instructions for floating-point operations.
Use library routines for floating-point operations.
Dynamically allocate condition code registers.
Do not try to dynamically allocate condition code registers, only use icc0 and fcc0.
Change ABI to use double word insns.
Do not use double word instructions.
Use floating-point double instructions.
Do not use floating-point double instructions.
Use media instructions.
Do not use media instructions.
Use multiply and add/subtract instructions.
Do not use multiply and add/subtract instructions.
Select the FDPIC ABI, which uses function descriptors to represent pointers to functions. Without any PIC/PIE-related options, it implies -fPIE. With -fpic or -fpie, it assumes GOT entries and small data are within a 12-bit range from the GOT base address; with -fPIC or -fPIE, GOT offsets are computed with 32 bits. With a bfin-elf target, this option implies -msim.
Enable inlining of PLT entries in function calls to functions that are not known to bind locally. It has no effect without -mfdpic. Its enabled by default if optimizing for speed and compiling for shared libraries (i.e., -fPIC or -fpic), or when an optimization option such as -O3 or above is present in the command line.
Assume a large TLS segment when generating thread-local code.
Do not assume a large TLS segment when generating thread-local code.
Enable the use of GPREL relocations in the FDPIC ABI for data that is known to be in read-only sections. Its enabled by default, except for -fpic or -fpie: even though it may help make the global offset table smaller, it trades 1 instruction for 4. With -fPIC or -fPIE, it trades 3 instructions for 4, one of which may be shared by multiple symbols, and it avoids the need for a GOT entry for the referenced symbol, so its more likely to be a win. If it is not, -mno-gprel-ro can be used to disable it.
Link with the (library, not FD) pic libraries. Its implied by -mlibrary-pic, as well as by -fPIC and -fpic without -mfdpic. You should never have to use it explicitly.
Follow the EABI requirement of always creating a frame pointer whenever a stack frame is allocated. This option is enabled by default and can be disabled with -mno-linked-fp.
Use indirect addressing to call functions outside the current compilation unit. This allows the functions to be placed anywhere within the 32-bit address space.
Try to align labels to an 8-byte boundary by inserting NOPs into the previous packet. This option only has an effect when VLIW packing is enabled. It doesnt create new packets; it merely adds NOPs to existing ones.
Generate position-independent EABI code.
Use only the first four media accumulator registers.
Use all eight media accumulator registers.
Pack VLIW instructions.
Do not pack VLIW instructions.
Do not mark ABI switches in e_flags.
Enable the use of conditional-move instructions (default).
This switch is mainly for debugging the compiler and will likely be removed in a future version.
Disable the use of conditional-move instructions.
This switch is mainly for debugging the compiler and will likely be removed in a future version.
Enable the use of conditional set instructions (default).
This switch is mainly for debugging the compiler and will likely be removed in a future version.
Disable the use of conditional set instructions.
This switch is mainly for debugging the compiler and will likely be removed in a future version.
Enable the use of conditional execution (default).
This switch is mainly for debugging the compiler and will likely be removed in a future version.
Disable the use of conditional execution.
This switch is mainly for debugging the compiler and will likely be removed in a future version.
Run a pass to pack branches into VLIW instructions (default).
This switch is mainly for debugging the compiler and will likely be removed in a future version.
Do not run a pass to pack branches into VLIW instructions.
This switch is mainly for debugging the compiler and will likely be removed in a future version.
Enable optimization of && and || in conditional execution (default).
This switch is mainly for debugging the compiler and will likely be removed in a future version.
Disable optimization of && and || in conditional execution.
This switch is mainly for debugging the compiler and will likely be removed in a future version.
Enable nested conditional execution optimizations (default).
This switch is mainly for debugging the compiler and will likely be removed in a future version.
Disable nested conditional execution optimizations.
This switch is mainly for debugging the compiler and will likely be removed in a future version.
This switch removes redundant membar instructions from the compiler-generated code. It is enabled by default.
This switch disables the automatic removal of redundant membar instructions from the generated code.
Cause gas to print out tomcat statistics.
-mcpu=``cpu``
Select the processor type for which to generate code. Possible values are frv, fr550, tomcat, fr500, fr450, fr405, fr400, fr300 and simple.
:: _gnu/linux-options:
These -m options are defined for GNU/Linux targets:
Use the GNU C library. This is the default except on --linux-uclibc, --linux-musl and --linux-android targets.
Use uClibc C library. This is the default on --linux-uclibc targets.
Use the musl C library. This is the default on --linux-musl targets.
Use Bionic C library. This is the default on --linux-android targets.
Compile code compatible with Android platform. This is the default on --linux-android targets.
When compiling, this option enables -mbionic, -fPIC, -fno-exceptions and -fno-rtti by default. When linking, this option makes the GCC driver pass Android-specific options to the linker. Finally, this option causes the preprocessor macro __ANDROID__ to be defined.
Disable compilation effects of -mandroid, i.e., do not enable -mbionic, -fPIC, -fno-exceptions and -fno-rtti by default.
Disable linking effects of -mandroid, i.e., pass standard Linux linking options to the linker.
:: _h8/300-options:
These -m options are defined for the H8/300 implementations:
Shorten some address references at link time, when possible; uses the linker option -relax. H8/300``ld`` and the H8/300ldUsing ld, for a fuller description.
Generate code for the H8/300H
Generate code for the H8S
Generate code for the H8S and H8/300H in the normal mode. This switch must be used either with -mh or -ms.
Extended registers are stored on stack before execution of function with monitor attribute. Default option is -mexr. This option is valid only for H8S targets.
Extended registers are not stored on stack before execution of function with monitor attribute. Default option is -mno-exr. This option is valid only for H8S targets.
Make int data 32 bits by default.
On the H8/300H and H8S, use the same alignment rules as for the H8/300. The default for the H8/300H and H8S is to align longs and floats on 4-byte boundaries. -malign-300 causes them to be aligned on 2-byte boundaries. This option has no effect on the H8/300.
:: _hppa-options:
These -m options are defined for the HPPA family of computers:
-march=``architecture-type``
Generate code for the specified architecture. The choices for architecture-type are 1.0 for PA 1.0, 1.1 for PA 1.1, and 2.0 for PA 2.0 processors. Refer to /usr/lib/sched.models on an HP-UX system to determine the proper architecture option for your machine. Code compiled for lower numbered architectures runs on higher numbered architectures, but not the other way around.
Synonyms for -march=1.0, -march=1.1, and -march=2.0 respectively.
This option is ignored and provided for compatibility purposes only.
Prevent floating-point registers from being used in any manner. This is necessary for compiling kernels that perform lazy context switching of floating-point registers. If you use this option and attempt to perform floating-point operations, the compiler aborts.
Prevent the compiler from using indexing address modes. This avoids some rather obscure problems when compiling MIG generated code under MACH
Generate code that assumes the target has no space registers. This allows GCC to generate faster indirect calls and use unscaled index address modes.
Such code is suitable for level 0 PA systems and kernels.
Generate code that assumes calls never cross space boundaries. This allows GCC to emit code that performs faster indirect calls.
This option does not work in the presence of shared libraries or nested functions.
-mfixed-range=``register-range``
Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator cannot use. This is useful when compiling kernel code. A register range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma.
Generate 3-instruction load and store sequences as sometimes required by the HP-UX 10 linker. This is equivalent to the +k option to the HP compilers.
Use the portable calling conventions proposed by HP for ELF systems.
Enable the use of assembler directives only GAS understands.
-mschedule=``cpu-type``
Schedule code according to the constraints for the machine type cpu-type. The choices for cpu-type are 700 7100, 7100LC, 7200, 7300 and 8000. Refer to /usr/lib/sched.models on an HP-UX system to determine the proper scheduling option for your machine. The default scheduling is 8000.
Enable the optimization pass in the HP-UX linker. Note this makes symbolic debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9 linkers in which they give bogus error messages when linking some programs.
Generate output containing library calls for floating point. Warning: the requisite libraries are not available for all HPPA targets. Normally the facilities of the machines usual C compiler are used, but this cannot be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation.
-msoft-float changes the calling convention in the output file; therefore, it is only useful if you compile all of a program with this option. In particular, you need to compile libgcc.a, the library that comes with GCC, with -msoft-float in order for this to work.
Generate the predefine, _SIO, for server IO The default is -mwsio. This generates the predefines, __hp9000s700, __hp9000s700__ and _WSIO, for workstation IO These options are available under HP-UX and HI-UX
Use options specific to GNU ld. This passes -shared to ld when building a shared library. It is the default when GCC is configured, explicitly or implicitly, with the GNU linker. This option does not affect which ld is called; it only changes what parameters are passed to that ld. The ld that is called is determined by the --with-ld configure option, GCCs program search path, and finally by the users PATH. The linker used by GCC can be printed using which gcc -print-prog-name=ld. This option is only available on the 64-bit HP-UX GCC, i.e. configured with hppa*64*--hpux.
Use options specific to HP ld. This passes -b to ld when building a shared library and passes +Accept TypeMismatch to ld on all links. It is the default when GCC is configured, explicitly or implicitly, with the HP linker. This option does not affect which ld is called; it only changes what parameters are passed to that ld. The ld that is called is determined by the --with-ld configure option, GCCs program search path, and finally by the users PATH. The linker used by GCC can be printed using which gcc -print-prog-name=ld. This option is only available on the 64-bit HP-UX GCC, i.e. configured with hppa*64*--hpux.
Generate code that uses long call sequences. This ensures that a call is always able to reach linker generated stubs. The default is to generate long calls only when the distance from the call site to the beginning of the function or translation unit, as the case may be, exceeds a predefined limit set by the branch type being used. The limits for normal calls are 7,600,000 and 240,000 bytes, respectively for the PA 2.0 and PA 1.X architectures. Sibcalls are always limited at 240,000 bytes.
Distances are measured from the beginning of functions when using the -ffunction-sections option, or when using the -mgas and -mno-portable-runtime options together under HP-UX with the SOM linker.
It is normally not desirable to use this option as it degrades performance. However, it may be useful in large applications, particularly when partial linking is used to build the application.
The types of long calls used depends on the capabilities of the assembler and linker, and the type of code being generated. The impact on systems that support long absolute calls, and long pic symbol-difference or pc-relative calls should be relatively small. However, an indirect call is used on 32-bit ELF systems in pic code and it is quite long.
-munix=``unix-std``
Generate compiler predefines and select a startfile for the specified UNIX standard. The choices for unix-std are 93, 95 and 98. 93 is supported on all HP-UX versions. 95 is available on HP-UX 10.10 and later. 98 is available on HP-UX 11.11 and later. The default values are 93 for HP-UX 10.00, 95 for HP-UX 10.10 though to 11.00, and 98 for HP-UX 11.11 and later.
-munix=93 provides the same predefines as GCC 3.3 and 3.4. -munix=95 provides additional predefines for XOPEN_UNIX and _XOPEN_SOURCE_EXTENDED, and the startfile unix95.o. -munix=98 provides additional predefines for _XOPEN_UNIX, _XOPEN_SOURCE_EXTENDED, _INCLUDE__STDC_A1_SOURCE and _INCLUDE_XOPEN_SOURCE_500, and the startfile unix98.o.
It is important to note that this option changes the interfaces for various library routines. It also affects the operational behavior of the C library. Thus, extreme care is needed in using this option.
Library code that is intended to operate with more than one UNIX standard must test, set and restore the variable __xpg4_extended_mask as appropriate. Most GNU software doesnt provide this capability.
Suppress the generation of link options to search libdld.sl when the -static option is specified on HP-UX 10 and later.
The HP-UX implementation of setlocale in libc has a dependency on libdld.sl. There isnt an archive version of libdld.sl. Thus, when the -static option is specified, special link options are needed to resolve this dependency.
On HP-UX 10 and later, the GCC driver adds the necessary options to link with libdld.sl when the -static option is specified. This causes the resulting binary to be dynamic. On the 64-bit port, the linkers generate dynamic binaries by default in any case. The -nolibdld option can be used to prevent the GCC driver from adding these link options.
Add support for multithreading with the dce thread library under HP-UX This option sets flags for both the preprocessor and linker.
:: _ia-64-options:
These are the -m options defined for the Intel IA-64 architecture.
Generate code for a big-endian target. This is the default for HP-UX
Generate code for a little-endian target. This is the default for AIX5 and GNU/Linux.
Generate (or dont) code for the GNU assembler. This is the default.
Generate (or dont) code for the GNU linker. This is the default.
Generate code that does not use a global pointer register. The result is not position independent code, and violates the IA-64 ABI
Generate (or dont) a stop bit immediately before and after volatile asm statements.
Generate (or dont) in, loc, and out register names for the stacked registers. This may make assembler output more readable.
Disable (or enable) optimizations that use the small data section. This may be useful for working around optimizer bugs.
Generate code that uses a single constant global pointer value. This is useful when compiling kernel code.
Generate code that is self-relocatable. This implies -mconstant-gp. This is useful when compiling firmware code.
Generate code for inline divides of floating-point values using the minimum latency algorithm.
Generate code for inline divides of floating-point values using the maximum throughput algorithm.
Do not generate inline code for divides of floating-point values.
Generate code for inline divides of integer values using the minimum latency algorithm.
Generate code for inline divides of integer values using the maximum throughput algorithm.
Do not generate inline code for divides of integer values.
Generate code for inline square roots using the minimum latency algorithm.
Generate code for inline square roots using the maximum throughput algorithm.
Do not generate inline code for sqrt.
Do (dont) generate code that uses the fused multiply/add or multiply/subtract instructions. The default is to use these instructions.
Dont (or do) generate assembler code for the DWARF 2 line number debugging info. This may be useful when not using the GNU assembler.
Allow stop bits to be placed earlier than immediately preceding the instruction that triggered the stop bit. This can improve instruction scheduling, but does not always do so.
-mfixed-range=``register-range``
Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator cannot use. This is useful when compiling kernel code. A register range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma.
-mtls-size=``tls-size``
Specify bit size of immediate TLS offsets. Valid values are 14, 22, and 64.
-mtune=``cpu-type``
Tune the instruction scheduling for a particular CPU, Valid values are itanium, itanium1, merced, itanium2, and mckinley.
Generate code for a 32-bit or 64-bit environment. The 32-bit environment sets int, long and pointer to 32 bits. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits. These are HP-UX specific flags.
(Dis/En)able data speculative scheduling before reload. This results in generation of ld.a instructions and the corresponding check instructions (ld.c / chk.a). The default is disable.
(En/Dis)able data speculative scheduling after reload. This results in generation of ld.a instructions and the corresponding check instructions (ld.c / chk.a). The default is enable.
(Dis/En)able control speculative scheduling. This feature is available only during region scheduling (i.e. before reload). This results in generation of the ld.s instructions and the corresponding check instructions chk.s. The default is disable.
(En/Dis)able speculative scheduling of the instructions that are dependent on the data speculative loads before reload. This is effective only with -msched-br-data-spec enabled. The default is enable.
(En/Dis)able speculative scheduling of the instructions that are dependent on the data speculative loads after reload. This is effective only with -msched-ar-data-spec enabled. The default is enable.
(En/Dis)able speculative scheduling of the instructions that are dependent on the control speculative loads. This is effective only with -msched-control-spec enabled. The default is enable.
If enabled, data-speculative instructions are chosen for schedule only if there are no other choices at the moment. This makes the use of the data speculation much more conservative. The default is disable.
If enabled, control-speculative instructions are chosen for schedule only if there are no other choices at the moment. This makes the use of the control speculation much more conservative. The default is disable.
If enabled, speculative dependencies are considered during computation of the instructions priorities. This makes the use of the speculation a bit more conservative. The default is disable.
Use a simple data speculation check. This option is on by default.
Use a simple check for control speculation. This option is on by default.
Place a stop bit after every cycle when scheduling. This option is on by default.
Assume that floating-point stores and loads are not likely to cause a conflict when placed into the same instruction group. This option is disabled by default.
Generate checks for control speculation in selective scheduling. This flag is disabled by default.
-msched-max-memory-insns=``max-insns``
Limit on the number of memory insns per instruction group, giving lower priority to subsequent memory insns attempting to schedule in the same instruction group. Frequently useful to prevent cache bank conflicts. The default value is 1.
Makes the limit specified by msched-max-memory-insns a hard limit, disallowing more than that number in an instruction group. Otherwise, the limit is soft, meaning that non-memory operations are preferred when the limit is reached, but memory operations may still be scheduled.
:: _lm32-options:
These -m options are defined for the LatticeMico32 architecture:
Enable barrel-shift instructions.
Enable divide and modulus instructions.
Enable multiply instructions.
Enable sign extend instructions.
Enable user-defined instructions.
:: _m32c-options:
-mcpu=``name``
Select the CPU for which code is generated. name may be one of r8c for the R8C/Tiny series, m16c for the M16C (up to /60) series, m32cm for the M16C/80 series, or m32c for the M32C/80 series.
Specifies that the program will be run on the simulator. This causes an alternate runtime library to be linked in which supports, for example, file I/O You must not use this option when generating programs that will run on real hardware; you must provide your own runtime library for whatever I/O functions are needed.
-memregs=``number``
Specifies the number of memory-based pseudo-registers GCC uses during code generation. These pseudo-registers are used like real registers, so there is a tradeoff between GCCs ability to fit the code into available registers, and the performance penalty of using memory instead of registers. Note that all modules in a program must be compiled with the same value for this option. Because of that, you must not use this option with GCCs default runtime libraries.
:: _m32r/d-options:
These -m options are defined for Renesas M32R/D architectures:
Generate code for the M32R/2
Generate code for the M32R/X
Generate code for the M32R This is the default.
Assume all objects live in the lower 16MB of memory (so that their addresses can be loaded with the ld24 instruction), and assume all subroutines are reachable with the bl instruction. This is the default.
The addressability of a particular object can be set with the model attribute.
Assume objects may be anywhere in the 32-bit address space (the compiler generates seth/add3 instructions to load their addresses), and assume all subroutines are reachable with the bl instruction.
Assume objects may be anywhere in the 32-bit address space (the compiler generates seth/add3 instructions to load their addresses), and assume subroutines may not be reachable with the bl instruction (the compiler generates the much slower seth/add3/jl instruction sequence).
Disable use of the small data area. Variables are put into one of .data, .bss, or .rodata (unless the section attribute has been specified). This is the default.
The small data area consists of sections .sdata and .sbss. Objects may be explicitly put in the small data area with the section attribute using one of these sections.
Put small global and static data in the small data area, but do not generate special code to reference them.
Put small global and static data in the small data area, and generate special instructions to reference them.
-G num
Put global and static objects less than or equal to num bytes into the small data or BSS sections instead of the normal data or BSS sections. The default value of num is 8. The -msdata option must be set to one of sdata or use for this option to have any effect.
All modules should be compiled with the same -G ``num`` value. Compiling with different values of num may or may not work; if it doesnt the linker gives an error messageincorrect code is not generated.
Makes the M32R-specific code in the compiler display some statistics that might help in debugging programs.
Align all loops to a 32-byte boundary.
Do not enforce a 32-byte alignment for loops. This is the default.
-missue-rate=``number``
missue-rate=``number`` Issue number instructions per cycle. number can only be 1 or 2.
-mbranch-cost=``number`` mbranch-cost=``number`` number can only be 1 or 2. If it is 1 then branches are preferred over conditional code, if it is 2, then the opposite applies.
-mflush-trap=``number`` mflush-trap=``number`` Specifies the trap number to use to flush the cache. The default is 12. Valid numbers are between 0 and 15 inclusive.
Specifies that the cache cannot be flushed by using a trap.
-mflush-func=``name``
mflush-func=``name`` Specifies the name of the operating system function to call to flush the cache. The default is _flush_cache, but a function call is only used if a trap is not available.
Indicates that there is no OS function for flushing the cache.
:: _m680x0-options:
These are the -m options defined for M680x0 and ColdFire processors. The default settings depend on which architecture was selected when the compiler was configured; the defaults for the most common choices are given below.
-march=``arch``
Generate code for a specific M680x0 or ColdFire instruction set architecture. Permissible values of arch for M680x0 architectures are: 68000, 68010, 68020, 68030, 68040, 68060 and cpu32. ColdFire architectures are selected according to Freescales ISA classification and the permissible values are: isaa, isaaplus, isab and isac.
GCC defines a macro __mcf``arch``__ whenever it is generating code for a ColdFire target. The arch in this macro is one of the -march arguments given above.
When used together, -march and -mtune select code that runs on a family of similar processors but that is optimized for a particular microarchitecture.
-mcpu=``cpu``
Generate code for a specific M680x0 or ColdFire processor. The M680x0 ``cpu``s are: 68000, 68010, 68020, 68030, 68040, 68060, 68302, 68332 and cpu32. The ColdFire ``cpu``s are given by the table below, which also classifies the CPUs into families:
Family -mcpu arguments 51 51 51ac 51ag 51cn 51em 51je 51jf 51jg 51jm 51mm 51qe 51qm 5206 5202 5204 5206 5206e 5206e 5208 5207 5208 5211a 5210a 5211a 5213 5211 5212 5213 5216 5214 5216 52235 52230 52231 52232 52233 52234 52235 5225 5224 5225 52259 52252 52254 52255 52256 52258 52259 5235 5232 5233 5234 5235 523x 5249 5249 5250 5250 5271 5270 5271 5272 5272 5275 5274 5275 5282 5280 5281 5282 528x 53017 53011 53012 53013 53014 53015 53016 53017 5307 5307 5329 5327 5328 5329 532x 5373 5372 5373 537x 5407 5407 5475 5470 5471 5472 5473 5474 5475 547x 5480 5481 5482 5483 5484 5485
-mcpu=``cpu`` overrides -march=``arch`` if arch is compatible with cpu. Other combinations of -mcpu and -march are rejected.
GCC defines the macro __mcf_cpu_``cpu`` when ColdFire target cpu is selected. It also defines __mcf_family_``family``, where the value of family is given by the table above.
-mtune=``tune``
Tune the code for a particular microarchitecture within the constraints set by -march and -mcpu. The M680x0 microarchitectures are: 68000, 68010, 68020, 68030, 68040, 68060 and cpu32. The ColdFire microarchitectures are: cfv1, cfv2, cfv3, cfv4 and cfv4e.
You can also use -mtune=68020-40 for code that needs to run relatively well on 68020, 68030 and 68040 targets. -mtune=68020-60 is similar but includes 68060 targets as well. These two options select the same tuning decisions as -m68020-40 and -m68020-60 respectively.
GCC defines the macros __mc``arch`` and __mc``arch``__ when tuning for 680x0 architecture arch. It also defines mc``arch`` unless either -ansi or a non-GNU -std option is used. If GCC is tuning for a range of architectures, as selected by -mtune=68020-40 or -mtune=68020-60, it defines the macros for every architecture in the range.
GCC also defines the macro __m``uarch``__ when tuning for ColdFire microarchitecture uarch, where uarch is one of the arguments given above.
Generate output for a 68000. This is the default when the compiler is configured for 68000-based systems. It is equivalent to -march=68000.
Use this option for microcontrollers with a 68000 or EC000 core, including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.
Generate output for a 68010. This is the default when the compiler is configured for 68010-based systems. It is equivalent to -march=68010.
Generate output for a 68020. This is the default when the compiler is configured for 68020-based systems. It is equivalent to -march=68020.
Generate output for a 68030. This is the default when the compiler is configured for 68030-based systems. It is equivalent to -march=68030.
Generate output for a 68040. This is the default when the compiler is configured for 68040-based systems. It is equivalent to -march=68040.
This option inhibits the use of 68881/68882 instructions that have to be emulated by software on the 68040. Use this option if your 68040 does not have code to emulate those instructions.
Generate output for a 68060. This is the default when the compiler is configured for 68060-based systems. It is equivalent to -march=68060.
This option inhibits the use of 68020 and 68881/68882 instructions that have to be emulated by software on the 68060. Use this option if your 68060 does not have code to emulate those instructions.
Generate output for a CPU32. This is the default when the compiler is configured for CPU32-based systems. It is equivalent to -march=cpu32.
Use this option for microcontrollers with a CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334, 68336, 68340, 68341, 68349 and 68360.
Generate output for a 520X ColdFire CPU This is the default when the compiler is configured for 520X-based systems. It is equivalent to -mcpu=5206, and is now deprecated in favor of that option.
Use this option for microcontroller with a 5200 core, including the MCF5202, MCF5203, MCF5204 and MCF5206.
Generate output for a 5206e ColdFire CPU The option is now deprecated in favor of the equivalent -mcpu=5206e.
Generate output for a member of the ColdFire 528X family. The option is now deprecated in favor of the equivalent -mcpu=528x.
Generate output for a ColdFire 5307 CPU The option is now deprecated in favor of the equivalent -mcpu=5307.
Generate output for a ColdFire 5407 CPU The option is now deprecated in favor of the equivalent -mcpu=5407.
Generate output for a ColdFire V4e family CPU (e.g. 547x/548x). This includes use of hardware floating-point instructions. The option is equivalent to -mcpu=547x, and is now deprecated in favor of that option.
Generate output for a 68040, without using any of the new instructions. This results in code that can run relatively efficiently on either a 68020/68881 or a 68030 or a 68040. The generated code does use the 68881 instructions that are emulated on the 68040.
The option is equivalent to -march=68020 -mtune=68020-40.
Generate output for a 68060, without using any of the new instructions. This results in code that can run relatively efficiently on either a 68020/68881 or a 68030 or a 68040. The generated code does use the 68881 instructions that are emulated on the 68060.
The option is equivalent to -march=68020 -mtune=68020-60.
Generate floating-point instructions. This is the default for 68020 and above, and for ColdFire devices that have an FPU It defines the macro __HAVE_68881__ on M680x0 targets and __mcffpu__ on ColdFire targets.
Do not generate floating-point instructions; use library calls instead. This is the default for 68000, 68010, and 68832 targets. It is also the default for ColdFire devices that have no FPU.
Generate (do not generate) ColdFire hardware divide and remainder instructions. If -march is used without -mcpu, the default is on for ColdFire architectures and off for M680x0 architectures. Otherwise, the default is taken from the target CPU (either the default CPU, or the one specified by -mcpu). For example, the default is off for -mcpu=5206 and on for -mcpu=5206e.
GCC defines the macro __mcfhwdiv__ when this option is enabled.
Consider type int to be 16 bits wide, like short int. Additionally, parameters passed on the stack are also aligned to a 16-bit boundary even on targets whose API mandates promotion to 32-bit.
Do not consider type int to be 16 bits wide. This is the default.
Do not use the bit-field instructions. The -m68000, -mcpu32 and -m5200 options imply -mnobitfield.
Do use the bit-field instructions. The -m68020 option implies -mbitfield. This is the default if you use a configuration designed for a 68020.
Use a different function-calling convention, in which functions that take a fixed number of arguments return with the rtd instruction, which pops their arguments while returning. This saves one instruction in the caller since there is no need to pop the arguments there.
This calling convention is incompatible with the one normally used on Unix, so you cannot use it if you need to call libraries compiled with the Unix compiler.
Also, you must provide function prototypes for all functions that take variable numbers of arguments (including printf); otherwise incorrect code is generated for calls to those functions.
In addition, seriously incorrect code results if you call a function with too many arguments. (Normally, extra arguments are harmlessly ignored.)
The rtd instruction is supported by the 68010, 68020, 68030, 68040, 68060 and CPU32 processors, but not by the 68000 or 5200.
Control whether GCC aligns int, long, long long, float, double, and long double variables on a 32-bit boundary (-malign-int) or a 16-bit boundary (-mno-align-int). Aligning variables on 32-bit boundaries produces code that runs somewhat faster on processors with 32-bit busses at the expense of more memory.
Warning: if you use the -malign-int switch, GCC aligns structures containing the above types differently than most published application binary interface specifications for the m68k.
Use the pc-relative addressing mode of the 68000 directly, instead of using a global offset table. At present, this option implies -fpic, allowing at most a 16-bit offset for pc-relative addressing. -fPIC is not presently supported with -mpcrel, though this could be supported for 68020 and higher processors.
Do not (do) assume that unaligned memory references are handled by the system.
Generate code that allows the data segment to be located in a different area of memory from the text segment. This allows for execute-in-place in an environment without virtual memory management. This option implies -fPIC.
Generate code that assumes that the data segment follows the text segment. This is the default.
Generate code that supports shared libraries via the library ID method. This allows for execute-in-place and shared libraries in an environment without virtual memory management. This option implies -fPIC.
Generate code that doesnt assume ID-based shared libraries are being used. This is the default.
Specifies the identification number of the ID-based shared library being compiled. Specifying a value of 0 generates more compact code; specifying other values forces the allocation of that number to the current library, but is no more space- or time-efficient than omitting this option.
When generating position-independent code for ColdFire, generate code that works if the GOT has more than 8192 entries. This code is larger and slower than code generated without this option. On M680x0 processors, this option is not needed; -fPIC suffices.
GCC normally uses a single instruction to load values from the GOT While this is relatively efficient, it only works if the GOT is smaller than about 64k. Anything larger causes the linker to report an error such as:
relocation truncated to fit: R_68K_GOT16O foobar
If this happens, you should recompile your code with -mxgot. It should then work with very large GOTs. However, code generated with -mxgot is less efficient, since it takes 4 instructions to fetch the value of a global symbol.
Note that some linkers, including newer versions of the GNU linker, can create multiple GOTs and sort GOT entries. If you have such a linker, you should only need to use -mxgot when compiling a single object file that accesses more than 8192 GOT entries. Very few do.
These options have no effect unless GCC is generating position-independent code.
:: _mcore-options:
These are the -m options defined for the Motorola M*Core processors.
Inline constants into the code stream if it can be done in two instructions or less.
Use the divide instruction. (Enabled by default).
Allow arbitrary-sized immediates in bit operations.
Always treat bit-fields as int-sized.
Force all functions to be aligned to a 4-byte boundary.
Emit callgraph information.
Prefer word access when reading byte quantities.
Generate code for a little-endian target.
Generate code for the 210 processor.
Assume that runtime support has been provided and so omit the simulator library (libsim.a) from the linker command line.
-mstack-increment=``size``
Set the maximum amount for a single stack increment operation. Large values can increase the speed of programs that contain functions that need a large amount of stack space, but they can also trigger a segmentation fault if the stack is extended too much. The default value is 0x1000.
:: _mep-options:
Enables the abs instruction, which is the absolute difference between two registers.
Enables all the optional instructionsaverage, multiply, divide, bit operations, leading zero, absolute difference, min/max, clip, and saturation.
Enables the ave instruction, which computes the average of two registers.
-mbased=``n``
Variables of size n bytes or smaller are placed in the .based section by default. Based variables use the $tp register as a base register, and there is a 128-byte limit to the .based section.
Enables the bit operation instructionsbit test (btstm), set (bsetm), clear (bclrm), invert (bnotm), and test-and-set (tas).
-mc=``name``
Selects which section constant data is placed in. name may be tiny, near, or far.
Enables the clip instruction. Note that -mclip is not useful unless you also provide -mminmax.
-mconfig=``name``
Selects one of the built-in core configurations. Each MeP chip has one or more modules in it; each module has a core CPU and a variety of coprocessors, optional instructions, and peripherals. The MeP-Integrator tool, not part of GCC, provides these configurations through this option; using this option is the same as using all the corresponding command-line options. The default configuration is default.
Enables the coprocessor instructions. By default, this is a 32-bit coprocessor. Note that the coprocessor is normally enabled via the -mconfig= option.
Enables the 32-bit coprocessors instructions.
Enables the 64-bit coprocessors instructions.
Enables IVC2 scheduling. IVC2 is a 64-bit VLIW coprocessor.
Causes constant variables to be placed in the .near section.
Enables the div and divu instructions.
Generate big-endian code.
Generate little-endian code.
Tells the compiler that any variable marked with the io attribute is to be considered volatile.
Causes variables to be assigned to the .far section by default.
Enables the leadz (leading zero) instruction.
Causes variables to be assigned to the .near section by default.
Enables the min and max instructions.
Enables the multiplication and multiply-accumulate instructions.
Disables all the optional instructions enabled by -mall-opts.
Enables the repeat and erepeat instructions, used for low-overhead looping.
Causes all variables to default to the .tiny section. Note that there is a 65536-byte limit to this section. Accesses to these variables use the %gp base register.
Enables the saturation instructions. Note that the compiler does not currently generate these itself, but this option is included for compatibility with other tools, like as.
Link the SDRAM-based runtime instead of the default ROM-based runtime.
Link the simulator run-time libraries.
Link the simulator runtime libraries, excluding built-in support for reset and exception vectors and tables.
Causes all functions to default to the .far section. Without this option, functions default to the .near section.
-mtiny=``n``
Variables that are n bytes or smaller are allocated to the .tiny section. These variables use the $gp base register. The default for this option is 4, but note that theres a 65536-byte limit to the .tiny section.
:: _microblaze-options:
Use software emulation for floating point (default).
Use hardware floating-point instructions.
Do not optimize block moves, use memcpy.
This option is deprecated. Use -fno-zero-initialized-in-bss instead.
-mcpu=``cpu-type``
Use features of, and schedule code for, the given CPU. Supported values are in the format v``X``.``YY``.``Z``, where X is a major version, YY is the minor version, and Z is compatibility code. Example values are v3.00.a, v4.00.b, v5.00.a, v5.00.b, v5.00.b, v6.00.a.
Use software multiply emulation (default).
Use software emulation for divides (default).
Use the hardware barrel shifter.
Use pattern compare instructions.
Use table lookup optimization for small signed integer divisions.
This option is deprecated. Use -fstack-check instead.
Use GP-relative .sdata/.sbss sections.
Use multiply high instructions for high part of 32x32 multiply.
Use hardware floating-point conversion instructions.
Use hardware floating-point square root instruction.
Generate code for a big-endian target.
Generate code for a little-endian target.
Use reorder instructions (swap and byte reversed load/store).
-mxl-mode-app-model
Select application model app-model. Valid models are
normal executable (default), uses startup code crt0.o.
for use with Xilinx Microprocessor Debugger (XMD) based software intrusive debug agent called xmdstub. This uses startup file crt1.o and sets the start address of the program to 0x800.
for applications that are loaded using a bootloader. This model uses startup file crt2.o which does not contain a processor reset vector handler. This is suitable for transferring control on a processor reset to the bootloader rather than the application.
for applications that do not require any of the MicroBlaze vectors. This option may be useful for applications running within a monitoring application. This model uses crt3.o as a startup file.
Option -xl-mode-``app-model`` is a deprecated alias for -mxl-mode-``app-model``.
:: _mips-options:
Generate big-endian code.
Generate little-endian code. This is the default for mips*el-- configurations.
-march=``arch``
Generate code that runs on arch, which can be the name of a generic MIPS ISA, or the name of a particular processor. The ISA names are: mips1, mips2, mips3, mips4, mips32, mips32r2, mips32r3, mips32r5, mips32r6, mips64, mips64r2, mips64r3, mips64r5 and mips64r6. The processor names are: 4kc, 4km, 4kp, 4ksc, 4kec, 4kem, 4kep, 4ksd, 5kc, 5kf, 20kc, 24kc, 24kf2_1, 24kf1_1, 24kec, 24kef2_1, 24kef1_1, 34kc, 34kf2_1, 34kf1_1, 34kn, 74kc, 74kf2_1, 74kf1_1, 74kf3_2, 1004kc, 1004kf2_1, 1004kf1_1, loongson2e, loongson2f, loongson3a, m4k, m14k, m14kc, m14ke, m14kec, octeon, octeon+, octeon2, octeon3, orion, p5600, r2000, r3000, r3900, r4000, r4400, r4600, r4650, r4700, r6000, r8000, rm7000, rm9000, r10000, r12000, r14000, r16000, sb1, sr71000, vr4100, vr4111, vr4120, vr4130, vr4300, vr5000, vr5400, vr5500, xlr and xlp. The special value from-abi selects the most compatible architecture for the selected ABI (that is, mips1 for 32-bit ABIs and mips3 for 64-bit ABIs)
The native Linux/GNU toolchain also supports the value native, which selects the best architecture option for the host processor. -march=native has no effect if GCC does not recognize the processor.
In processor names, a final 000 can be abbreviated as k (for example, -march=r2k). Prefixes are optional, and vr may be written r.
Names of the form ``n``f2_1 refer to processors with FPUs clocked at half the rate of the core, names of the form ``n``f1_1 refer to processors with FPUs clocked at the same rate as the core, and names of the form ``n``f3_2 refer to processors with FPUs clocked a ratio of 3:2 with respect to the core. For compatibility reasons, ``n``f is accepted as a synonym for ``n``f2_1 while ``n``x and ``b``fx are accepted as synonyms for ``n``f1_1.
GCC defines two macros based on the value of this option. The first is _MIPS_ARCH, which gives the name of target architecture, as a string. The second has the form _MIPS_ARCH_``foo``, where foo is the capitalized value of _MIPS_ARCH For example, -march=r2000 sets _MIPS_ARCH to "r2000" and defines the macro _MIPS_ARCH_R2000.
Note that the _MIPS_ARCH macro uses the processor names given above. In other words, it has the full prefix and does not abbreviate 000 as k. In the case of from-abi, the macro names the resolved architecture (either "mips1" or "mips3"). It names the default architecture when no -march option is given.
-mtune=``arch``
Optimize for arch. Among other things, this option controls the way instructions are scheduled, and the perceived cost of arithmetic operations. The list of arch values is the same as for -march.
When this option is not used, GCC optimizes for the processor specified by -march. By using -march and -mtune together, it is possible to generate code that runs on a family of processors, but optimize the code for one particular member of that family.
-mtune defines the macros _MIPS_TUNE and _MIPS_TUNE_``foo``, which work in the same way as the -march ones described above.
Equivalent to -march=mips1.
Equivalent to -march=mips2.
Equivalent to -march=mips3.
Equivalent to -march=mips4.
Equivalent to -march=mips32.
Equivalent to -march=mips32r3.
Equivalent to -march=mips32r5.
Equivalent to -march=mips32r6.
Equivalent to -march=mips64.
Equivalent to -march=mips64r2.
Equivalent to -march=mips64r3.
Equivalent to -march=mips64r5.
Equivalent to -march=mips64r6.
Generate (do not generate) MIPS16 code. If GCC is targeting a MIPS32 or MIPS64 architecture, it makes use of the MIPS16e ASE
MIPS16 code generation can also be controlled on a per-function basis by means of mips16 and nomips16 attributes. Function Attributes, for more information.
Generate MIPS16 code on alternating functions. This option is provided for regression testing of mixed MIPS16/non-MIPS16 code generation, and is not intended for ordinary use in compiling user code.
-minterlink-compressed
Require (do not require) that code using the standard (uncompressed) MIPS ISA be link-compatible with MIPS16 and microMIPS code, and vice versa.
For example, code using the standard ISA encoding cannot jump directly to MIPS16 or microMIPS code; it must either use a call or an indirect jump. -minterlink-compressed therefore disables direct jumps unless GCC knows that the target of the jump is not compressed.
Aliases of -minterlink-compressed and -mno-interlink-compressed. These options predate the microMIPS ASE and are retained for backwards compatibility.
Generate code for the given ABI
Note that the EABI has a 32-bit and a 64-bit variant. GCC normally generates 64-bit code when you select a 64-bit architecture, but you can use -mgp32 to get 32-bit code instead.
For information about the O64 ABI, see http://gcc.gnu.org/projects/mipso64-abi.html.
GCC supports a variant of the o32 ABI in which floating-point registers are 64 rather than 32 bits wide. You can select this combination with -mabi=32 -mfp64. This ABI relies on the mthc1 and mfhc1 instructions and is therefore only supported for MIPS32R2, MIPS32R3 and MIPS32R5 processors.
The register assignments for arguments and return values remain the same, but each scalar value is passed in a single 64-bit register rather than a pair of 32-bit registers. For example, scalar floating-point values are returned in $f0 only, not a $f0/$f1 pair. The set of call-saved registers also remains the same in that the even-numbered double-precision registers are saved.
Two additional variants of the o32 ABI are supported to enable a transition from 32-bit to 64-bit registers. These are FPXX (-mfpxx) and FP64A (-mfp64 -mno-odd-spreg). The FPXX extension mandates that all code must execute correctly when run using 32-bit or 64-bit registers. The code can be interlinked with either FP32 or FP64, but not both. The FP64A extension is similar to the FP64 extension but forbids the use of odd-numbered single-precision registers. This can be used in conjunction with the FRE mode of FPUs in MIPS32R5 processors and allows both FP32 and FP64A code to interlink and run in the same process without changing FPU modes.
Generate (do not generate) code that is suitable for SVR4-style dynamic objects. -mabicalls is the default for SVR4-based systems.
Generate (do not generate) code that is fully position-independent, and that can therefore be linked into shared libraries. This option only affects -mabicalls.
All -mabicalls code has traditionally been position-independent, regardless of options like -fPIC and -fpic. However, as an extension, the GNU toolchain allows executables to use absolute accesses for locally-binding symbols. It can also use shorter GP initialization sequences and generate direct calls to locally-defined functions. This mode is selected by -mno-shared.
-mno-shared depends on binutils 2.16 or higher and generates objects that can only be linked by the GNU linker. However, the option does not affect the ABI of the final executable; it only affects the ABI of relocatable objects. Using -mno-shared generally makes executables both smaller and quicker.
-mshared is the default.
Assume (do not assume) that the static and dynamic linkers support PLTs and copy relocations. This option only affects -mno-shared -mabicalls. For the n64 ABI, this option has no effect without -msym32.
You can make -mplt the default by configuring GCC with --with-mips-plt. The default is -mno-plt otherwise.
Lift (do not lift) the usual restrictions on the size of the global offset table.
GCC normally uses a single instruction to load values from the GOT While this is relatively efficient, it only works if the GOT is smaller than about 64k. Anything larger causes the linker to report an error such as:
relocation truncated to fit: R_MIPS_GOT16 foobar
If this happens, you should recompile your code with -mxgot. This works with very large GOTs, although the code is also less efficient, since it takes three instructions to fetch the value of a global symbol.
Note that some linkers can create multiple GOTs. If you have such a linker, you should only need to use -mxgot when a single object file accesses more than 64ks worth of GOT entries. Very few do.
These options have no effect unless GCC is generating position independent code.
Assume that general-purpose registers are 32 bits wide.
Assume that general-purpose registers are 64 bits wide.
Assume that floating-point registers are 32 bits wide.
Assume that floating-point registers are 64 bits wide.
Do not assume the width of floating-point registers.
Use floating-point coprocessor instructions.
Do not use floating-point coprocessor instructions. Implement floating-point calculations using library calls instead.
Equivalent to -msoft-float, but additionally asserts that the program being compiled does not perform any floating-point operations. This option is presently supported only by some bare-metal MIPS configurations, where it may select a special set of libraries that lack all floating-point support (including, for example, the floating-point printf formats). If code compiled with -mno-float accidentally contains floating-point operations, it is likely to suffer a link-time or run-time failure.
Assume that the floating-point coprocessor only supports single-precision operations.
Assume that the floating-point coprocessor supports double-precision operations. This is the default.
Enable the use of odd-numbered single-precision floating-point registers for the o32 ABI. This is the default for processors that are known to support these registers. When using the o32 FPXX ABI, -mno-odd-spreg is set by default.
These options control the treatment of the special not-a-number (NaN) IEEE 754 floating-point data with the abs.fmt and neg.fmt machine instructions.
By default or when -mabs=legacy is used the legacy treatment is selected. In this case these instructions are considered arithmetic and avoided where correct operation is required and the input operand might be a NaN. A longer sequence of instructions that manipulate the sign bit of floating-point datum manually is used instead unless the -ffinite-math-only option has also been specified.
The -mabs=2008 option selects the IEEE 754-2008 treatment. In this case these instructions are considered non-arithmetic and therefore operating correctly in all cases, including in particular where the input operand is a NaN. These instructions are therefore always used for the respective operations.
These options control the encoding of the special not-a-number (NaN) IEEE 754 floating-point data.
The -mnan=legacy option selects the legacy encoding. In this case quiet NaNs (qNaNs) are denoted by the first bit of their trailing significand field being 0, whereas signalling NaNs (sNaNs) are denoted by the first bit of their trailing significand field being 1.
The -mnan=2008 option selects the IEEE 754-2008 encoding. In this case qNaNs are denoted by the first bit of their trailing significand field being 1, whereas sNaNs are denoted by the first bit of their trailing significand field being 0.
The default is -mnan=legacy unless GCC has been configured with --with-nan=2008.
Use (do not use) ll, sc, and sync instructions to implement atomic memory built-in functions. When neither option is specified, GCC uses the instructions if the target architecture supports them.
-mllsc is useful if the runtime environment can emulate the instructions and -mno-llsc can be useful when compiling for nonstandard ISAs. You can make either option the default by configuring GCC with --with-llsc and --without-llsc respectively. --with-llsc is the default for some configurations; see the installation documentation for details.
Use (do not use) revision 1 of the MIPS DSP ASE MIPS DSP Built-in Functions. This option defines the preprocessor macro __mips_dsp. It also defines __mips_dsp_rev to 1.
Use (do not use) revision 2 of the MIPS DSP ASE MIPS DSP Built-in Functions. This option defines the preprocessor macros __mips_dsp and __mips_dspr2. It also defines __mips_dsp_rev to 2.
Use (do not use) the MIPS SmartMIPS ASE.
Use (do not use) paired-single floating-point instructions. MIPS Paired-Single Support. This option requires hardware floating-point support to be enabled.
Use (do not use) MIPS Digital Media Extension instructions. This option can only be used when generating 64-bit code and requires hardware floating-point support to be enabled.
Use (do not use) the MIPS-3D ASE MIPS-3D Built-in Functions. The option -mips3d implies -mpaired-single.
Generate (do not generate) microMIPS code.
MicroMIPS code generation can also be controlled on a per-function basis by means of micromips and nomicromips attributes. Function Attributes, for more information.
Use (do not use) MT Multithreading instructions.
Use (do not use) the MIPS MCU ASE instructions.
Use (do not use) the MIPS Enhanced Virtual Addressing instructions.
Use (do not use) the MIPS Virtualization Application Specific instructions.
Use (do not use) the MIPS eXtended Physical Address (XPA) instructions.
Force long types to be 64 bits wide. See -mlong32 for an explanation of the default and the way that the pointer size is determined.
Force long, int, and pointer types to be 32 bits wide.
The default size of ``int``s, ``long``s and pointers depends on the ABI All the supported ABIs use 32-bit ``int``s. The n64 ABI uses 64-bit ``long``s, as does the 64-bit EABI; the others use 32-bit ``long``s. Pointers are the same size as ``long``s, or the same size as integer registers, whichever is smaller.
Assume (do not assume) that all symbols have 32-bit values, regardless of the selected ABI This option is useful in combination with -mabi=64 and -mno-abicalls because it allows GCC to generate shorter and faster references to symbolic addresses.
-G num
Put definitions of externally-visible data in a small data section if that data is no bigger than num bytes. GCC can then generate more efficient accesses to the data; see -mgpopt for details.
The default -G option depends on the configuration.
Extend (do not extend) the -G behavior to local data too, such as to static variables in C -mlocal-sdata is the default for all configurations.
If the linker complains that an application is using too much small data, you might want to try rebuilding the less performance-critical parts with -mno-local-sdata. You might also want to build large libraries with -mno-local-sdata, so that the libraries leave more room for the main program.
Assume (do not assume) that externally-defined data is in a small data section if the size of that data is within the -G limit. -mextern-sdata is the default for all configurations.
If you compile a module Mod with -mextern-sdata -G ``num`` -mgpopt, and Mod references a variable Var that is no bigger than num bytes, you must make sure that Var is placed in a small data section. If Var is defined by another module, you must either compile that module with a high-enough -G setting or attach a section attribute to Var``s definition. If ``Var is common, you must link the application with a high-enough -G setting.
The easiest way of satisfying these restrictions is to compile and link every module with the same -G option. However, you may wish to build a library that supports several different small data limits. You can do this by compiling the library with the highest supported -G setting and additionally using -mno-extern-sdata to stop the library from making assumptions about externally-defined data.
Use (do not use) GP-relative accesses for symbols that are known to be in a small data section; see -G, -mlocal-sdata and -mextern-sdata. -mgpopt is the default for all configurations.
-mno-gpopt is useful for cases where the $gp register might not hold the value of _gp. For example, if the code is part of a library that might be used in a boot monitor, programs that call boot monitor routines pass an unknown value in $gp. (In such situations, the boot monitor itself is usually compiled with -G0.)
-mno-gpopt implies -mno-local-sdata and -mno-extern-sdata.
Allocate variables to the read-only data section first if possible, then next in the small data section if possible, otherwise in data. This gives slightly slower code than the default, but reduces the amount of RAM required when executing, and thus may be preferred for some embedded systems.
Put uninitialized const variables in the read-only data section. This option is only meaningful in conjunction with -membedded-data.
-mcode-readable=``setting``
Specify whether GCC may generate code that reads from executable sections. There are three possible settings:
Instructions may freely access executable sections. This is the default setting.
MIPS16 PC-relative load instructions can access executable sections, but other instructions must not do so. This option is useful on 4KSc and 4KSd processors when the code TLBs have the Read Inhibit bit set. It is also useful on processors that can be configured to have a dual instruction/data SRAM interface and that, like the M4K, automatically redirect PC-relative loads to the instruction RAM.
Instructions must not access executable sections. This option can be useful on targets that are configured to have a dual instruction/data SRAM interface but that (unlike the M4K) do not automatically redirect PC-relative loads to the instruction RAM.
Enable (disable) use of the %hi() and %lo() assembler relocation operators. This option has been superseded by -mexplicit-relocs but is retained for backwards compatibility.
Use (do not use) assembler relocation operators when dealing with symbolic addresses. The alternative, selected by -mno-explicit-relocs, is to use assembler macros instead.
-mexplicit-relocs is the default if GCC was configured to use an assembler that supports relocation operators.
Trap (do not trap) on integer division by zero.
The default is -mcheck-zero-division.
MIPS systems check for division by zero by generating either a conditional trap or a break instruction. Using traps results in smaller code, but is only supported on MIPS II and later. Also, some versions of the Linux kernel have a bug that prevents trap from generating the proper signal (SIGFPE). Use -mdivide-traps to allow conditional traps on architectures that support them and -mdivide-breaks to force the use of breaks.
The default is usually -mdivide-traps, but this can be overridden at configure time using --with-divide=breaks. Divide-by-zero checks can be completely disabled using -mno-check-zero-division.
Force (do not force) the use of memcpy for non-trivial block moves. The default is -mno-memcpy, which allows GCC to inline most constant-sized copies.
Disable (do not disable) use of the jal instruction. Calling functions using jal is more efficient but requires the caller and callee to be in the same 256 megabyte segment.
This option has no effect on abicalls code. The default is -mno-long-calls.
Enable (disable) use of the mad, madu and mul instructions, as provided by the R4650 ISA
Enable (disable) use of the madd and msub integer instructions. The default is -mimadd on architectures that support madd and msub except for the 74k architecture where it was found to generate slower code.
Enable (disable) use of the floating-point multiply-accumulate instructions, when they are available. The default is -mfused-madd.
On the R8000 CPU when multiply-accumulate instructions are used, the intermediate product is calculated to infinite precision and is not subject to the FCSR Flush to Zero bit. This may be undesirable in some circumstances. On other processors the result is numerically identical to the equivalent computation using separate multiply, add, subtract and negate instructions.
Tell the MIPS assembler to not run its preprocessor over user assembler files (with a .s suffix) when assembling them.
-mfix-24k
Work around the 24K E48 (lost data on stores during refill) errata. The workarounds are implemented by the assembler rather than by GCC
Work around certain R4000 CPU errata:
Work around certain R4400 CPU errata:
Work around certain R10000 errata:
This option can only be used if the target architecture supports branch-likely instructions. -mfix-r10000 is the default when -march=r10000 is used; -mno-fix-r10000 is the default otherwise.
Work around the RM7000 dmult/dmultu errata. The workarounds are implemented by the assembler rather than by GCC
Work around certain VR4120 errata:
The workarounds for the division errata rely on special functions in libgcc.a. At present, these functions are only provided by the mips64vr*-elf configurations.
Other VR4120 errata require a NOP to be inserted between certain pairs of instructions. These errata are handled by the assembler, not by GCC itself.
Work around the VR4130 mflo/mfhi errata. The workarounds are implemented by the assembler rather than by GCC, although GCC avoids using mflo and mfhi if the VR4130 macc, macchi, dmacc and dmacchi instructions are available instead.
Work around certain SB-1 CPU core errata. (This flag currently works around the SB-1 revision 2 F1 and F2 floating-point errata.)
-mr10k-cache-barrier=``setting``
Specify whether GCC should insert cache barriers to avoid the side-effects of speculation on R10K processors.
In common with many processors, the R10K tries to predict the outcome of a conditional branch and speculatively executes instructions from the taken branch. It later aborts these instructions if the predicted outcome is wrong. However, on the R10K, even aborted instructions can have side effects.
This problem only affects kernel stores and, depending on the system, kernel loads. As an example, a speculatively-executed store may load the target memory into cache and mark the cache line as dirty, even if the store itself is later aborted. If a DMA operation writes to the same area of memory before the dirty line is flushed, the cached data overwrites the DMA-ed data. See the R10K processor manual for a full description, including other potential problems.
One workaround is to insert cache barrier instructions before every memory access that might be speculatively executed and that might have side effects even if aborted. -mr10k-cache-barrier=``setting`` controls GCCs implementation of this workaround. It assumes that aborted accesses to any byte in the following regions does not have side effects:
It is the kernels responsibility to ensure that speculative accesses to these regions are indeed safe.
If the input program contains a function declaration such as:
void foo (void);
then the implementation of foo must allow j foo and jal foo to be executed speculatively. GCC honors this restriction for functions it compiles itself. It expects non-GCC functions (such as hand-written assembly code) to do the same.
The option has three forms:
Insert a cache barrier before a load or store that might be speculatively executed and that might have side effects even if aborted.
Insert a cache barrier before a store that might be speculatively executed and that might have side effects even if aborted.
Disable the insertion of cache barriers. This is the default setting.
-mflush-func=``func`` -mno-flush-func
Specifies the function to call to flush the I and D caches, or to not call any such function. If called, the function must take the same arguments as the common _flush_func, that is, the address of the memory range for which the cache is being flushed, the size of the memory range, and the number 3 (to flush both caches). The default depends on the target GCC was configured for, but commonly is either _flush_func or __cpu_flush.
mbranch-cost=``num``
Set the cost of branches to roughly num simple instructions. This cost is only a heuristic and is not guaranteed to produce consistent results across releases. A zero cost redundantly selects the default, which is based on the -mtune setting.
Enable or disable use of Branch Likely instructions, regardless of the default for the selected architecture. By default, Branch Likely instructions may be generated if they are supported by the selected architecture. An exception is for the MIPS32 and MIPS64 architectures and processors that implement those architectures; for those, Branch Likely instructions are not be generated by default because the MIPS32 and MIPS64 architectures specifically deprecate their use.
Specifies whether FP exceptions are enabled. This affects how FP instructions are scheduled for some processors. The default is that FP exceptions are enabled.
For instance, on the SB-1, if FP exceptions are disabled, and we are emitting 64-bit code, then we can use both FP pipes. Otherwise, we can only use one FP pipe.
The VR4130 pipeline is two-way superscalar, but can only issue two instructions together if the first one is 8-byte aligned. When this option is enabled, GCC aligns pairs of instructions that it thinks should execute in parallel.
This option only has an effect when optimizing for the VR4130. It normally makes code faster, but at the expense of making it bigger. It is enabled by default at optimization level -O3.
Enable (disable) generation of synci instructions on architectures that support it. The synci instructions (if enabled) are generated when __builtin___clear_cache is compiled.
This option defaults to -mno-synci, but the default can be overridden by configuring GCC with --with-synci.
When compiling code for single processor systems, it is generally safe to use synci. However, on many multi-core (SMP) systems, it does not invalidate the instruction caches on all cores and may lead to undefined behavior.
Try to turn PIC calls that are normally dispatched via register $25 into direct calls. This is only possible if the linker can resolve the destination at link-time and if the destination is within range for a direct call.
-mrelax-pic-calls is the default if GCC was configured to use an assembler and a linker that support the .reloc assembly directive and -mexplicit-relocs is in effect. With -mno-explicit-relocs, this optimization can be performed by the assembler and the linker alone without help from the compiler.
Emit (do not emit) code that allows _mcount to modify the calling functions return address. When enabled, this option extends the usual _mcount interface with a new ra-address parameter, which has type intptr_t * and is passed in register $12. _mcount can then modify the return address by doing both of the following:
The default is -mno-mcount-ra-address.
:: _mmix-options:
These options are defined for the MMIX:
Specify that intrinsic library functions are being compiled, passing all values in registers, no matter the size.
Generate floating-point comparison instructions that compare with respect to the rE epsilon register.
Generate code that passes function parameters and return values that (in the called function) are seen as registers $0 and up, as opposed to the GNU ABI which uses global registers $231 and up.
When reading data from memory in sizes shorter than 64 bits, use (do not use) zero-extending load instructions by default, rather than sign-extending ones.
Make the result of a division yielding a remainder have the same sign as the divisor. With the default, -mno-knuthdiv, the sign of the remainder follows the sign of the dividend. Both methods are arithmetically valid, the latter being almost exclusively used.
Prepend (do not prepend) a : to all global symbols, so the assembly code can be used with the PREFIX assembly directive.
Generate an executable in the ELF format, rather than the default mmo format used by the mmix simulator.
Use (do not use) the probable-branch instructions, when static branch prediction indicates a probable branch.
Generate (do not generate) code that uses base addresses. Using a base address automatically generates a request (handled by the assembler and the linker) for a constant to be set up in a global register. The register is used for one or more base address requests within the range 0 to 255 from the value held in the register. The generally leads to short and fast code, but the number of different data items that can be addressed is limited. This means that a program that uses lots of static data may require -mno-base-addresses.
Force (do not force) generated code to have a single exit point in each function.
:: _mn10300-options:
These -m options are defined for Matsushita MN10300 architectures:
Generate code to avoid bugs in the multiply instructions for the MN10300 processors. This is the default.
Do not generate code to avoid bugs in the multiply instructions for the MN10300 processors.
Generate code using features specific to the AM33 processor.
Do not generate code using features specific to the AM33 processor. This is the default.
Generate code using features specific to the AM33/2.0 processor.
Generate code using features specific to the AM34 processor.
-mtune=``cpu-type``
Use the timing characteristics of the indicated CPU type when scheduling instructions. This does not change the targeted processor type. The CPU type must be one of mn10300, am33, am33-2 or am34.
When generating a function that returns a pointer, return the pointer in both a0 and d0. Otherwise, the pointer is returned only in a0, and attempts to call such functions without a prototype result in errors. Note that this option is on by default; use -mno-return-pointer-on-d0 to disable it.
Do not link in the C run-time initialization object file.
Indicate to the linker that it should perform a relaxation optimization pass to shorten branches, calls and absolute memory addresses. This option only has an effect when used on the command line for the final link step.
This option makes symbolic debugging impossible.
Allow the compiler to generate Long Instruction Word instructions if the target is the AM33 or later. This is the default. This option defines the preprocessor macro __LIW__.
Do not allow the compiler to generate Long Instruction Word instructions. This option defines the preprocessor macro __NO_LIW__.
Allow the compiler to generate the SETLB and Lcc instructions if the target is the AM33 or later. This is the default. This option defines the preprocessor macro __SETLB__.
Do not allow the compiler to generate SETLB or Lcc instructions. This option defines the preprocessor macro __NO_SETLB__.
:: _moxie-options:
Generate big-endian code. This is the default for moxie-- configurations.
Generate little-endian code.
Generate mul.x and umul.x instructions. This is the default for moxiebox-- configurations.
Do not link in the C run-time initialization object file.
:: _msp430-options:
These options are defined for the MSP430:
Force assembly output to always use hex constants. Normally such constants are signed decimals, but this option is available for testsuite and/or aesthetic purposes.
Select the MCU to target. This is used to create a C preprocessor symbol based upon the MCU name, converted to upper case and pre- and post-fixed with __. This in turn is used by the msp430.h header file to select an MCU-specific supplementary header file.
The option also sets the ISA to use. If the MCU name is one that is known to only support the 430 ISA then that is selected, otherwise the 430X ISA is selected. A generic MCU name of msp430 can also be used to select the 430 ISA. Similarly the generic msp430x MCU name selects the 430X ISA.
In addition an MCU-specific linker script is added to the linker command line. The scripts name is the name of the MCU with .ld appended. Thus specifying -mmcu=xxx on the gcc command line defines the C preprocessor symbol __XXX__ and cause the linker to search for a script called xxx.ld.
This option is also passed on to the assembler.
Specifies the ISA to use. Accepted values are msp430, msp430x and msp430xv2. This option is deprecated. The -mmcu= option should be used to select the ISA.
Link to the simulator runtime libraries and linker script. Overrides any scripts that would be selected by the -mmcu= option.
Use large-model addressing (20-bit pointers, 32-bit size_t).
Use small-model addressing (16-bit pointers, 16-bit size_t).
This option is passed to the assembler and linker, and allows the linker to perform certain optimizations that cannot be done until the final link.
Describes the type of hardware multiply supported by the target. Accepted values are none for no hardware multiply, 16bit for the original 16-bit-only multiply supported by early MCUs. 32bit for the 16/32-bit multiply supported by later MCUs and f5series for the 16/32-bit multiply supported by F5-series MCUs. A value of auto can also be given. This tells GCC to deduce the hardware multiply support based upon the MCU name provided by the -mmcu option. If no -mmcu option is specified then 32bit hardware multiply support is assumed. auto is the default setting.
Hardware multiplies are normally performed by calling a library routine. This saves space in the generated code. When compiling at -O3 or higher however the hardware multiplier is invoked inline. This makes for bigger, but faster code.
The hardware multiply routines disable interrupts whilst running and restore the previous interrupt state when they finish. This makes them safe to use inside interrupt handlers as well as in normal code.
Enable the use of a minimum runtime environment - no static initializers or constructors. This is intended for memory-constrained devices. The compiler includes special symbols in some objects that tell the linker and runtime which code fragments are required.
These options tell the compiler where to place functions and data that do not have one of the lower, upper, either or section attributes. Possible values are lower, upper, either or any. The first three behave like the corresponding attribute. The fourth possible value - any - is the default. It leaves placement entirely up to the linker script and how it assigns the standard sections (.text, .data etc) to the memory regions.
:: _nds32-options:
These options are defined for NDS32 implementations:
Generate code in big-endian mode.
Generate code in little-endian mode.
Use reduced-set registers for register allocation.
Use full-set registers for register allocation.
Generate conditional move instructions.
Do not generate conditional move instructions.
Generate performance extension instructions.
Do not generate performance extension instructions.
Generate v3 push25/pop25 instructions.
Do not generate v3 push25/pop25 instructions.
Generate 16-bit instructions.
Do not generate 16-bit instructions.
-misr-vector-size=``num``
Specify the size of each interrupt vector, which must be 4 or 16.
-mcache-block-size=``num``
Specify the size of each cache block, which must be a power of 2 between 4 and 512.
-march=``arch``
Specify the name of the target architecture.
-mcmodel=``code-model``
Set the code model to one of
small All the data and read-only data segments must be within 512KB addressing space. The text segment must be within 16MB addressing space. medium The data segment must be within 512KB while the read-only data segment can be within 4GB addressing space. The text segment should be still within 16MB addressing space. large All the text and data segments can be within 4GB addressing space.
Enable constructor/destructor feature.
Guide linker to relax instructions.
:: _nios-ii-options:
These are the options defined for the Altera Nios II processor.
-G num
Put global and static objects less than or equal to num bytes into the small data or BSS sections instead of the normal data or BSS sections. The default value of num is 8.
-mgpopt=``option``
Generate (do not generate) GP-relative accesses. The following option names are recognized:
Do not generate GP-relative accesses.
Generate GP-relative accesses for small data objects that are not external or weak. Also use GP-relative addressing for objects that have been explicitly placed in a small data section via a section attribute.
As for local, but also generate GP-relative accesses for small data objects that are external or weak. If you use this option, you must ensure that all parts of your program (including libraries) are compiled with the same -G setting.
Generate GP-relative accesses for all data objects in the program. If you use this option, the entire data and BSS segments of your program must fit in 64K of memory and you must use an appropriate linker script to allocate them within the addressible range of the global pointer.
Generate GP-relative addresses for function pointers as well as data pointers. If you use this option, the entire text, data, and BSS segments of your program must fit in 64K of memory and you must use an appropriate linker script to allocate them within the addressible range of the global pointer.
-mgpopt is equivalent to -mgpopt=local, and -mno-gpopt is equivalent to -mgpopt=none.
The default is -mgpopt except when -fpic or -fPIC is specified to generate position-independent code. Note that the Nios II ABI does not permit GP-relative accesses from shared libraries.
You may need to specify -mno-gpopt explicitly when building programs that include large amounts of small data, including large GOT data sections. In this case, the 16-bit offset for GP-relative addressing may not be large enough to allow access to the entire small data section.
Generate little-endian (default) or big-endian (experimental) code, respectively.
Force all load and store instructions to always bypass cache by using I/O variants of the instructions. The default is not to bypass the cache.
Volatile memory access bypass the cache using the I/O variants of the load and store instructions. The default is not to bypass the cache.
Do not use table-based fast divide for small numbers. The default is to use the fast divide at -O3 and above.
Enable or disable emitting mul, mulx and div family of instructions by the compiler. The default is to emit mul and not emit div and mulx.
-mcustom-insn``=``N
-mno-custom-insn mcustom-insn mno-custom-insn Each -mcustom-``insn``=``N`` option enables use of a custom instruction with encoding N when generating code that uses insn. For example, -mcustom-fadds=253 generates custom instruction 253 for single-precision floating-point add operations instead of the default behavior of using a library call.
The following values of insn are supported. Except as otherwise noted, floating-point operations are expected to be implemented with normal IEEE 754 semantics and correspond directly to the C operators or the equivalent GCC built-in functions (Other Builtins).
Single-precision floating point:
fadds, fsubs, fdivs, fmuls Binary arithmetic operations.
fnegs Unary negation.
fabss Unary absolute value.
fcmpeqs, fcmpges, fcmpgts, fcmples, fcmplts, fcmpnes Comparison operations.
fmins, fmaxs Floating-point minimum and maximum. These instructions are only generated if -ffinite-math-only is specified.
fsqrts Unary square root operation.
fcoss, fsins, ftans, fatans, fexps, flogs Floating-point trigonometric and exponential functions. These instructions are only generated if -funsafe-math-optimizations is also specified.
Double-precision floating point:
faddd, fsubd, fdivd, fmuld Binary arithmetic operations.
fnegd Unary negation.
fabsd Unary absolute value.
fcmpeqd, fcmpged, fcmpgtd, fcmpled, fcmpltd, fcmpned Comparison operations.
fmind, fmaxd Double-precision minimum and maximum. These instructions are only generated if -ffinite-math-only is specified.
fsqrtd Unary square root operation.
fcosd, fsind, ftand, fatand, fexpd, flogd Double-precision trigonometric and exponential functions. These instructions are only generated if -funsafe-math-optimizations is also specified.
Conversions:
fextsd Conversion from single precision to double precision.
ftruncds Conversion from double precision to single precision.
fixsi, fixsu, fixdi, fixdu Conversion from floating point to signed or unsigned integer types, with truncation towards zero.
round Conversion from single-precision floating point to signed integer, rounding to the nearest integer and ties away from zero. This corresponds to the __builtin_lroundf function when -fno-math-errno is used.
floatis, floatus, floatid, floatud Conversion from signed or unsigned integer types to floating-point types.
In addition, all of the following transfer instructions for internal registers X and Y must be provided to use any of the double-precision floating-point instructions. Custom instructions taking two double-precision source operands expect the first operand in the 64-bit register X. The other operand (or only operand of a unary operation) is given to the custom arithmetic instruction with the least significant half in source register src1 and the most significant half in src2. A custom instruction that returns a double-precision result returns the most significant 32 bits in the destination register and the other half in 32-bit register Y. GCC automatically generates the necessary code sequences to write register X and/or read register Y when double-precision floating-point instructions are used.
fwrx Write src1 into the least significant half of X and src2 into the most significant half of X.
fwry Write src1 into Y.
frdxhi, frdxlo Read the most or least (respectively) significant half of X and store it in dest.
frdy Read the value of Y and store it into dest.
Note that you can gain more local control over generation of Nios II custom instructions by using the target("custom-``insn``=``N”)`` and target("no-custom-``insn”)`` function attributes (Function Attributes) or pragmas (Function Specific Option Pragmas).
-mcustom-fpu-cfg=``name``
This option enables a predefined, named set of custom instruction encodings (see -mcustom-``insn`` above). Currently, the following sets are defined:
-mcustom-fpu-cfg=60-1 is equivalent to:
-mcustom-fmuls=252 -mcustom-fadds=253 -mcustom-fsubs=254 -fsingle-precision-constant
-mcustom-fpu-cfg=60-2 is equivalent to:
-mcustom-fmuls=252 -mcustom-fadds=253 -mcustom-fsubs=254 -mcustom-fdivs=255 -fsingle-precision-constant
-mcustom-fpu-cfg=72-3 is equivalent to:
-mcustom-floatus=243 -mcustom-fixsi=244 -mcustom-floatis=245 -mcustom-fcmpgts=246 -mcustom-fcmples=249 -mcustom-fcmpeqs=250 -mcustom-fcmpnes=251 -mcustom-fmuls=252 -mcustom-fadds=253 -mcustom-fsubs=254 -mcustom-fdivs=255 -fsingle-precision-constant
Custom instruction assignments given by individual -mcustom-``insn``= options override those given by -mcustom-fpu-cfg=, regardless of the order of the options on the command line.
Note that you can gain more local control over selection of a FPU configuration by using the target("custom-fpu-cfg=``name”)`` function attribute (Function Attributes) or pragma (Function Specific Option Pragmas).
These additional -m options are available for the Altera Nios II ELF (bare-metal) target:
Link with HAL BSP. This suppresses linking with the GCC-provided C runtime startup and termination code, and is typically used in conjunction with -msys-crt0= to specify the location of the alternate startup code provided by the HAL BSP.
Link with a limited version of the C library, -lsmallc, rather than Newlib.
-msys-crt0=``startfile``
startfile is the file name of the startfile (crt0) to use when linking. This option is only useful in conjunction with -mhal.
-msys-lib=``systemlib``
systemlib is the library name of the library that provides low-level system calls required by the C library, e.g. read and write. This option is typically used to link with a library provided by a HAL BSP.
:: _nvidia-ptx-options:
These options are defined for Nvidia PTX:
Generate code for 32-bit or 64-bit ABI.
Link in code for a __main kernel. This is for stand-alone instead of offloading execution.
:: _pdp-11-options:
These options are defined for the PDP-11:
Use hardware FPP floating point. This is the default. (FIS floating point on the PDP-11/40 is not supported.)
Do not use hardware floating point.
Return floating-point results in ac0 (fr0 in Unix assembler syntax).
Return floating-point results in memory. This is the default.
Generate code for a PDP-11/40.
Generate code for a PDP-11/45. This is the default.
Generate code for a PDP-11/10.
Use inline movmemhi patterns for copying memory. This is the default.
Do not use inline movmemhi patterns for copying memory.
Use 16-bit int. This is the default.
Use 32-bit int.
Use 64-bit float. This is the default.
Use 32-bit float.
Use abshi2 pattern. This is the default.
Do not use abshi2 pattern.
Pretend that branches are expensive. This is for experimenting with code generation only.
Do not pretend that branches are expensive. This is the default.
Use DEC assembler syntax. This is the default when configured for any PDP-11 target other than pdp11-*-bsd.
:: _picochip-options:
These -m options are defined for picoChip implementations:
-mae=``ae_type``
Set the instruction set, register set, and instruction scheduling parameters for array element type ae_type. Supported values for ae_type are ANY, MUL, and MAC.
-mae=ANY selects a completely generic AE type. Code generated with this option runs on any of the other AE types. The code is not as efficient as it would be if compiled for a specific AE type, and some types of operation (e.g., multiplication) do not work properly on all types of AE.
-mae=MUL selects a MUL AE type. This is the most useful AE type for compiled code, and is the default.
-mae=MAC selects a DSP-style MAC AE. Code compiled with this option may suffer from poor performance of byte (char) manipulation, since the DSP AE does not provide hardware support for byte load/stores.
Enable the compiler to directly use a symbol name as an address in a load/store instruction, without first loading it into a register. Typically, the use of this option generates larger programs, which run faster than when the option isnt used. However, the results vary from program to program, so it is left as a user option, rather than being permanently enabled.
Disables warnings about the generation of inefficient code. These warnings can be generated, for example, when compiling code that performs byte-level memory operations on the MAC AE type. The MAC AE has no hardware support for byte-level memory operations, so all byte load/stores must be synthesized from word load/store operations. This is inefficient and a warning is generated to indicate that you should rewrite the code to avoid byte operations, or to target an AE type that has the necessary hardware support. This option disables these warnings.
:: _powerpc-options:
Links in additional target libraries to support operation within a simulator.
Specifies the type of hardware multiplication and division support to be used. The simplest is none, which uses software for both multiplication and division. This is the default. The g13 value is for the hardware multiply/divide peripheral found on the RL78/G13 (S2 core) targets. The g14 value selects the use of the multiplication and division instructions supported by the RL78/G14 (S3 core) parts. The value rl78 is an alias for g14 and the value mg10 is an alias for none.
In addition a C preprocessor macro is defined, based upon the setting of this option. Possible values are: __RL78_MUL_NONE__, __RL78_MUL_G13__ or __RL78_MUL_G14__.
Specifies the RL78 core to target. The default is the G14 core, also known as an S3 core or just RL78. The G13 or S2 core does not have multiply or divide instructions, instead it uses a hardware peripheral for these operations. The G10 or S1 core does not have register banks, so it uses a different calling convention.
If this option is set it also selects the type of hardware multiply support to use, unless this is overridden by an explicit -mmul=none option on the command line. Thus specifying -mcpu=g13 enables the use of the G13 hardware multiply peripheral and specifying -mcpu=g10 disables the use of hardware multipications altogether.
Note, although the RL78/G14 core is the default target, specifying -mcpu=g14 or -mcpu=rl78 on the command line does change the behaviour of the toolchain since it also enables G14 hardware multiply support. If these options are not specified on the command line then software multiplication routines will be used even though the code targets the RL78 core. This is for backwards compatibility with older toolchains which did not have hardware multiply and divide support.
In addition a C preprocessor macro is defined, based upon the setting of this option. Possible values are: __RL78_G10__, __RL78_G13__ or __RL78_G14__.
These are aliases for the corresponding -mcpu= option. They are provided for backwards compatibility.
Allow the compiler to use all of the available registers. By default registers r24..r31 are reserved for use in interrupt handlers. With this option enabled these registers can be used in ordinary functions as well.
Make the double data type be 64 bits (-m64bit-doubles) or 32 bits (-m32bit-doubles) in size. The default is -m32bit-doubles.
:: _rs/6000-and-powerpc-options:
These -m options are defined for the IBM RS/6000 and PowerPC:
You use these options to specify which instructions are available on the processor you are using. The default value of these options is determined when configuring GCC Specifying the -mcpu=``cpu_type`` overrides the specification of these options. We recommend you use the -mcpu=``cpu_type`` option rather than the options listed above.
Specifying -mpowerpc-gpopt allows GCC to use the optional PowerPC architecture instructions in the General Purpose group, including floating-point square root. Specifying -mpowerpc-gfxopt allows GCC to use the optional PowerPC architecture instructions in the Graphics group, including floating-point select.
The -mmfcrf option allows GCC to generate the move from condition register field instruction implemented on the POWER4 processor and other processors that support the PowerPC V2.01 architecture. The -mpopcntb option allows GCC to generate the popcount and double-precision FP reciprocal estimate instruction implemented on the POWER5 processor and other processors that support the PowerPC V2.02 architecture. The -mpopcntd option allows GCC to generate the popcount instruction implemented on the POWER7 processor and other processors that support the PowerPC V2.06 architecture. The -mfprnd option allows GCC to generate the FP round to integer instructions implemented on the POWER5+ processor and other processors that support the PowerPC V2.03 architecture. The -mcmpb option allows GCC to generate the compare bytes instruction implemented on the POWER6 processor and other processors that support the PowerPC V2.05 architecture. The -mmfpgpr option allows GCC to generate the FP move to/from general-purpose register instructions implemented on the POWER6X processor and other processors that support the extended PowerPC V2.05 architecture. The -mhard-dfp option allows GCC to generate the decimal floating-point instructions implemented on some POWER processors.
The -mpowerpc64 option allows GCC to generate the additional 64-bit instructions that are found in the full PowerPC64 architecture and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to -mno-powerpc64.
-mcpu=``cpu_type``
Set architecture type, register usage, and instruction scheduling parameters for machine type cpu_type. Supported values for cpu_type are 401, 403, 405, 405fp, 440, 440fp, 464, 464fp, 476, 476fp, 505, 601, 602, 603, 603e, 604, 604e, 620, 630, 740, 7400, 7450, 750, 801, 821, 823, 860, 970, 8540, a2, e300c2, e300c3, e500mc, e500mc64, e5500, e6500, ec603e, G3, G4, G5, titan, power3, power4, power5, power5+, power6, power6x, power7, power8, powerpc, powerpc64, powerpc64le, and rs64.
-mcpu=powerpc, -mcpu=powerpc64, and -mcpu=powerpc64le specify pure 32-bit PowerPC (either endian), 64-bit big endian PowerPC and 64-bit little endian PowerPC architecture machine types, with an appropriate, generic processor model assumed for scheduling purposes.
The other options specify a specific processor. Code generated under those options runs best on that processor, and may not run at all on others.
The -mcpu options automatically enable or disable the following options:
-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple -mpopcntb -mpopcntd -mpowerpc64 -mpowerpc-gpopt -mpowerpc-gfxopt -msingle-float -mdouble-float -msimple-fpu -mstring -mmulhw -mdlmzb -mmfpgpr -mvsx -mcrypto -mdirect-move -mpower8-fusion -mpower8-vector -mquad-memory -mquad-memory-atomic
The particular options set for any particular CPU varies between compiler versions, depending on what setting seems to produce optimal code for that CPU; it doesnt necessarily reflect the actual hardwares capabilities. If you wish to set an individual option to a particular value, you may specify it after the -mcpu option, like -mcpu=970 -mno-altivec.
On AIX, the -maltivec and -mpowerpc64 options are not enabled or disabled by the -mcpu option at present because AIX does not have full support for these options. You may still enable or disable them individually if youre sure itll work in your environment.
-mtune=``cpu_type``
Set the instruction scheduling parameters for machine type cpu_type, but do not set the architecture type or register usage, as -mcpu=``cpu_type`` does. The same values for cpu_type are used for -mtune as for -mcpu. If both are specified, the code generated uses the architecture and registers set by -mcpu, but the scheduling parameters set by -mtune.
Generate PowerPC64 code for the small model: The TOC is limited to 64k.
Generate PowerPC64 code for the medium model: The TOC and other static data may be up to a total of 4G in size.
Generate PowerPC64 code for the large model: The TOC may be up to 4G in size. Other data and code is only limited by the 64-bit address space.
Generate code that uses (does not use) AltiVec instructions, and also enable the use of built-in functions that allow more direct access to the AltiVec instruction set. You may also need to set -mabi=altivec to adjust the current ABI with AltiVec ABI enhancements.
When -maltivec is used, rather than -maltivec=le or -maltivec=be, the element order for Altivec intrinsics such as vec_splat, vec_extract, and vec_insert match array element order corresponding to the endianness of the target. That is, element zero identifies the leftmost element in a vector register when targeting a big-endian platform, and identifies the rightmost element in a vector register when targeting a little-endian platform.
Generate Altivec instructions using big-endian element order, regardless of whether the target is big- or little-endian. This is the default when targeting a big-endian platform.
The element order is used to interpret element numbers in Altivec intrinsics such as vec_splat, vec_extract, and vec_insert. By default, these match array element order corresponding to the endianness for the target.
Generate Altivec instructions using little-endian element order, regardless of whether the target is big- or little-endian. This is the default when targeting a little-endian platform. This option is currently ignored when targeting a big-endian platform.
The element order is used to interpret element numbers in Altivec intrinsics such as vec_splat, vec_extract, and vec_insert. By default, these match array element order corresponding to the endianness for the target.
Generate VRSAVE instructions when generating AltiVec code.
Generate Cell microcode instructions.
Warn when a Cell microcode instruction is emitted. An example of a Cell microcode instruction is a variable shift.
Generate code that allows ld and ld.so to build executables and shared libraries with non-executable .plt and .got sections. This is a PowerPC 32-bit SYSV ABI option.
Generate code that uses a BSS .plt section that ld.so fills in, and requires .plt and .got sections that are both writable and executable. This is a PowerPC 32-bit SYSV ABI option.
This switch enables or disables the generation of ISEL instructions.
-misel=``yes/no``
This switch has been deprecated. Use -misel and -mno-isel instead.
This switch enables or disables the generation of SPE simd instructions.
This switch enables or disables the generation of PAIRED simd instructions.
-mspe=``yes/no``
This option has been deprecated. Use -mspe and -mno-spe instead.
Generate code that uses (does not use) vector/scalar (VSX) instructions, and also enable the use of built-in functions that allow more direct access to the VSX instruction set.
Enable the use (disable) of the built-in functions that allow direct access to the cryptographic instructions that were added in version 2.07 of the PowerPC ISA.
Generate code that uses (does not use) the instructions to move data between the general purpose registers and the vector/scalar (VSX) registers that were added in version 2.07 of the PowerPC ISA.
Generate code that keeps (does not keeps) some integer operations adjacent so that the instructions can be fused together on power8 and later processors.
Generate code that uses (does not use) the vector and scalar instructions that were added in version 2.07 of the PowerPC ISA. Also enable the use of built-in functions that allow more direct access to the vector instructions.
Generate code that uses (does not use) the non-atomic quad word memory instructions. The -mquad-memory option requires use of 64-bit mode.
Generate code that uses (does not use) the atomic quad word memory instructions. The -mquad-memory-atomic option requires use of 64-bit mode.
Generate code that uses (does not use) the scalar double precision instructions that target all 64 registers in the vector/scalar floating point register set that were added in version 2.06 of the PowerPC ISA. -mupper-regs-df is turned on by default if you use any of the -mcpu=power7, -mcpu=power8, or -mvsx options.
Generate code that uses (does not use) the scalar single precision instructions that target all 64 registers in the vector/scalar floating point register set that were added in version 2.07 of the PowerPC ISA. -mupper-regs-sf is turned on by default if you use either of the -mcpu=power8 or -mpower8-vector options.
Generate code that uses (does not use) the scalar instructions that target all 64 registers in the vector/scalar floating point register set, depending on the model of the machine.
If the -mno-upper-regs option is used, it turns off both -mupper-regs-sf and -mupper-regs-df options.
-mfloat-gprs=``yes/single/double/no``
-mfloat-gprs
This switch enables or disables the generation of floating-point operations on the general-purpose registers for architectures that support it.
The argument yes or single enables the use of single-precision floating-point operations.
The argument double enables the use of single and double-precision floating-point operations.
The argument no disables floating-point operations on the general-purpose registers.
This option is currently only available on the MPC854x.
Generate code for 32-bit or 64-bit environments of Darwin and SVR4 targets (including GNU/Linux). The 32-bit environment sets int, long and pointer to 32 bits and generates code that runs on any PowerPC variant. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits, and generates code for PowerPC64, as for -mpowerpc64.
Modify generation of the TOC (Table Of Contents), which is created for every executable file. The -mfull-toc option is selected by default. In that case, GCC allocates at least one TOC entry for each unique non-automatic variable reference in your program. GCC also places floating-point constants in the TOC However, only 16,384 entries are available in the TOC
If you receive a linker error message that saying you have overflowed the available TOC space, you can reduce the amount of TOC space used with the -mno-fp-in-toc and -mno-sum-in-toc options. -mno-fp-in-toc prevents GCC from putting floating-point constants in the TOC and -mno-sum-in-toc forces GCC to generate code to calculate the sum of an address and a constant at run time instead of putting that sum into the TOC You may specify one or both of these options. Each causes GCC to produce very slightly slower and larger code at the expense of conserving TOC space.
If you still run out of space in the TOC even when you specify both of these options, specify -mminimal-toc instead. This option causes GCC to make only one TOC entry for every file. When you specify this option, GCC produces code that is slower and larger but which uses extremely little TOC space. You may wish to use this option only on files that contain less frequently-executed code.
Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit long type, and the infrastructure needed to support them. Specifying -maix64 implies -mpowerpc64, while -maix32 disables the 64-bit ABI and implies -mno-powerpc64. GCC defaults to -maix32.
Produce code that conforms more closely to IBM XL compiler semantics when using AIX-compatible ABI Pass floating-point arguments to prototyped functions beyond the register save area (RSA) on the stack in addition to argument FPRs. Do not assume that most significant double in 128-bit long double value is properly rounded when comparing values and converting to double. Use XL symbol names for long double support routines.
The AIX calling convention was extended but not initially documented to handle an obscure K&R C case of calling a function that takes the address of its arguments with fewer arguments than declared. IBM XL compilers access floating-point arguments that do not fit in the RSA from the stack when a subroutine is compiled without optimization. Because always storing floating-point arguments on the stack is inefficient and rarely needed, this option is not enabled by default and only is necessary when calling subroutines compiled by IBM XL compilers without optimization.
Support IBM RS/6000 SP Parallel Environment (PE) Link an application written to use message passing with special startup code to enable the application to run. The system must have PE installed in the standard location (/usr/lpp/ppe.poe/), or the specs file must be overridden with the -specs= option to specify the appropriate directory location. The Parallel Environment does not support threads, so the -mpe option and the -pthread option are incompatible.
On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option -malign-natural overrides the ABI-defined alignment of larger types, such as floating-point doubles, on their natural size-based boundary. The option -malign-power instructs GCC to follow the ABI-specified alignment rules. GCC defaults to the standard alignment defined in the ABI
On 64-bit Darwin, natural alignment is the default, and -malign-power is not supported.
Generate code that does not use (uses) the floating-point register set. Software floating-point emulation is provided if you use the -msoft-float option, and pass the option to GCC when linking.
Generate code for single- or double-precision floating-point operations. -mdouble-float implies -msingle-float.
Do not generate sqrt and div instructions for hardware floating-point unit.
-mfpu=``name``
Specify type of floating-point unit. Valid values for name are sp_lite (equivalent to -msingle-float -msimple-fpu), dp_lite (equivalent to -mdouble-float -msimple-fpu), sp_full (equivalent to -msingle-float), and dp_full (equivalent to -mdouble-float).
Perform optimizations for the floating-point unit on Xilinx PPC 405/440.
Generate code that uses (does not use) the load multiple word instructions and the store multiple word instructions. These instructions are generated by default on POWER systems, and not generated on PowerPC systems. Do not use -mmultiple on little-endian PowerPC systems, since those instructions do not work when the processor is in little-endian mode. The exceptions are PPC740 and PPC750 which permit these instructions in little-endian mode.
Generate code that uses (does not use) the load string instructions and the store string word instructions to save multiple registers and do small block moves. These instructions are generated by default on POWER systems, and not generated on PowerPC systems. Do not use -mstring on little-endian PowerPC systems, since those instructions do not work when the processor is in little-endian mode. The exceptions are PPC740 and PPC750 which permit these instructions in little-endian mode.
Generate code that uses (does not use) the load or store instructions that update the base register to the address of the calculated memory location. These instructions are generated by default. If you use -mno-update, there is a small window between the time that the stack pointer is updated and the address of the previous frame is stored, which means code that walks the stack frame across interrupts or signals may get corrupted data.
Generate code that tries to avoid (not avoid) the use of indexed load or store instructions. These instructions can incur a performance penalty on Power6 processors in certain situations, such as when stepping through large arrays that cross a 16M boundary. This option is enabled by default when targeting Power6 and disabled otherwise.
Generate code that uses (does not use) the floating-point multiply and accumulate instructions. These instructions are generated by default if hardware floating point is used. The machine-dependent -mfused-madd option is now mapped to the machine-independent -ffp-contract=fast option, and -mno-fused-madd is mapped to -ffp-contract=off.
Generate code that uses (does not use) the half-word multiply and multiply-accumulate instructions on the IBM 405, 440, 464 and 476 processors. These instructions are generated by default when targeting those processors.
Generate code that uses (does not use) the string-search dlmzb instruction on the IBM 405, 440, 464 and 476 processors. This instruction is generated by default when targeting those processors.
On System V.4 and embedded PowerPC systems do not (do) force structures and unions that contain bit-fields to be aligned to the base type of the bit-field.
For example, by default a structure containing nothing but 8 unsigned bit-fields of length 1 is aligned to a 4-byte boundary and has a size of 4 bytes. By using -mno-bit-align, the structure is aligned to a 1-byte boundary and is 1 byte in size.
On System V.4 and embedded PowerPC systems do not (do) assume that unaligned memory references are handled by the system.
Generate code that allows (does not allow) a static executable to be relocated to a different address at run time. A simple embedded PowerPC system loader should relocate the entire contents of .got2 and 4-byte locations listed in the .fixup section, a table of 32-bit addresses generated by this option. For this to work, all objects linked together must be compiled with -mrelocatable or -mrelocatable-lib. -mrelocatable code aligns the stack to an 8-byte boundary.
Like -mrelocatable, -mrelocatable-lib generates a .fixup section to allow static executables to be relocated at run time, but -mrelocatable-lib does not use the smaller stack alignment of -mrelocatable. Objects compiled with -mrelocatable-lib may be linked with objects compiled with any combination of the -mrelocatable options.
On System V.4 and embedded PowerPC systems do not (do) assume that register 2 contains a pointer to a global area pointing to the addresses used in the program.
On System V.4 and embedded PowerPC systems compile code for the processor in little-endian mode. The -mlittle-endian option is the same as -mlittle.
On System V.4 and embedded PowerPC systems compile code for the processor in big-endian mode. The -mbig-endian option is the same as -mbig.
On Darwin and Mac OS X systems, compile code so that it is not relocatable, but that its external references are relocatable. The resulting code is suitable for applications, but not shared libraries.
Treat the register used for PIC addressing as read-only, rather than loading it in the prologue for each function. The runtime system is responsible for initializing this register with an appropriate value before execution begins.
-mprioritize-restricted-insns=``priority``
This option controls the priority that is assigned to dispatch-slot restricted instructions during the second scheduling pass. The argument priority takes the value 0, 1, or 2 to assign no, highest, or second-highest (respectively) priority to dispatch-slot restricted instructions.
-msched-costly-dep=``dependence_type``
This option controls which dependences are considered costly by the target during instruction scheduling. The argument dependence_type takes one of the following values:
no No dependence is costly.
all All dependences are costly.
true_store_to_load A true dependence from store to load is costly.
store_to_load Any dependence from store to load is costly.
number Any dependence for which the latency is greater than or equal to number is costly.
-minsert-sched-nops=``scheme``
This option controls which NOP insertion scheme is used during the second scheduling pass. The argument scheme takes one of the following values:
no Dont insert NOPs.
pad Pad with NOPs any dispatch group that has vacant issue slots, according to the schedulers grouping.
regroup_exact Insert NOPs to force costly dependent insns into separate groups. Insert exactly as many NOPs as needed to force an insn to a new group, according to the estimated processor grouping.
number Insert NOPs to force costly dependent insns into separate groups. Insert number NOPs to force an insn to a new group.
On System V.4 and embedded PowerPC systems compile code using calling conventions that adhere to the March 1995 draft of the System V Application Binary Interface, PowerPC processor supplement. This is the default unless you configured GCC using powerpc-*-eabiaix.
Specify both -mcall-sysv and -meabi options.
Specify both -mcall-sysv and -mno-eabi options.
On System V.4 and embedded PowerPC systems compile code for the AIX operating system.
On System V.4 and embedded PowerPC systems compile code for the Linux-based GNU system.
On System V.4 and embedded PowerPC systems compile code for the FreeBSD operating system.
On System V.4 and embedded PowerPC systems compile code for the NetBSD operating system.
On System V.4 and embedded PowerPC systems compile code for the OpenBSD operating system.
Return all structures in memory (as specified by the AIX ABI)
Return structures smaller than 8 bytes in registers (as specified by the SVR4 ABI)
-mabi=``abi-type``
Extend the current ABI with a particular extension, or remove such extension. Valid values are altivec, no-altivec, spe, no-spe, ibmlongdouble, ieeelongdouble, elfv1, elfv2
Extend the current ABI with SPE ABI extensions. This does not change the default ABI, instead it adds the SPE ABI extensions to the current ABI
Disable Book-E SPE ABI extensions for the current ABI
Change the current ABI to use IBM extended-precision long double. This is a PowerPC 32-bit SYSV ABI option.
Change the current ABI to use IEEE extended-precision long double. This is a PowerPC 32-bit Linux ABI option.
Change the current ABI to use the ELFv1 ABI. This is the default ABI for big-endian PowerPC 64-bit Linux. Overriding the default ABI requires special system support and is likely to fail in spectacular ways.
Change the current ABI to use the ELFv2 ABI. This is the default ABI for little-endian PowerPC 64-bit Linux. Overriding the default ABI requires special system support and is likely to fail in spectacular ways.
On System V.4 and embedded PowerPC systems assume that all calls to variable argument functions are properly prototyped. Otherwise, the compiler must insert an instruction before every non-prototyped call to set or clear bit 6 of the condition code register (CR) to indicate whether floating-point values are passed in the floating-point registers in case the function takes variable arguments. With -mprototype, only calls to prototyped variable argument functions set or clear the bit.
On embedded PowerPC systems, assume that the startup module is called sim-crt0.o and that the standard C libraries are libsim.a and libc.a. This is the default for powerpc-*-eabisim configurations.
On embedded PowerPC systems, assume that the startup module is called crt0.o and the standard C libraries are libmvme.a and libc.a.
On embedded PowerPC systems, assume that the startup module is called crt0.o and the standard C libraries are libads.a and libc.a.
On embedded PowerPC systems, assume that the startup module is called crt0.o and the standard C libraries are libyk.a and libc.a.
On System V.4 and embedded PowerPC systems, specify that you are compiling for a VxWorks system.
On embedded PowerPC systems, set the PPC_EMB bit in the ELF flags header to indicate that eabi extended relocations are used.
On System V.4 and embedded PowerPC systems do (do not) adhere to the Embedded Applications Binary Interface (EABI), which is a set of modifications to the System V.4 specifications. Selecting -meabi means that the stack is aligned to an 8-byte boundary, a function __eabi is called from main to set up the EABI environment, and the -msdata option can use both r2 and r13 to point to two separate small data areas. Selecting -mno-eabi means that the stack is aligned to a 16-byte boundary, no EABI initialization function is called from main, and the -msdata option only uses r13 to point to a single small data area. The -meabi option is on by default if you configured GCC using one of the powerpc*--eabi options.
On System V.4 and embedded PowerPC systems, put small initialized const global and static data in the .sdata2 section, which is pointed to by register r2. Put small initialized non-const global and static data in the .sdata section, which is pointed to by register r13. Put small uninitialized global and static data in the .sbss section, which is adjacent to the .sdata section. The -msdata=eabi option is incompatible with the -mrelocatable option. The -msdata=eabi option also sets the -memb option.
On System V.4 and embedded PowerPC systems, put small global and static data in the .sdata section, which is pointed to by register r13. Put small uninitialized global and static data in the .sbss section, which is adjacent to the .sdata section. The -msdata=sysv option is incompatible with the -mrelocatable option.
On System V.4 and embedded PowerPC systems, if -meabi is used, compile code the same as -msdata=eabi, otherwise compile code the same as -msdata=sysv.
On System V.4 and embedded PowerPC systems, put small global data in the .sdata section. Put small uninitialized global data in the .sbss section. Do not use register r13 to address small data however. This is the default behavior unless other -msdata options are used.
On embedded PowerPC systems, put all initialized global and static data in the .data section, and all uninitialized data in the .bss section.
-mblock-move-inline-limit=``num``
Inline all block moves (such as calls to memcpy or structure copies) less than or equal to num bytes. The minimum value for num is 32 bytes on 32-bit targets and 64 bytes on 64-bit targets. The default value is target-specific.
-G num
On embedded PowerPC systems, put global and static items less than or equal to num bytes into the small data or BSS sections instead of the normal data or BSS section. By default, num is 8. The -G ``num`` switch is also passed to the linker. All modules should be compiled with the same -G ``num`` value.
On System V.4 and embedded PowerPC systems do (do not) emit register names in the assembly language output using symbolic forms.
By default assume that all calls are far away so that a longer and more expensive calling sequence is required. This is required for calls farther than 32 megabytes (33,554,432 bytes) from the current location. A short call is generated if the compiler knows the call cannot be that far away. This setting can be overridden by the shortcall function attribute, or by #pragma longcall(0).
Some linkers are capable of detecting out-of-range calls and generating glue code on the fly. On these systems, long calls are unnecessary and generate slower code. As of this writing, the AIX linker can do this, as can the GNU linker for PowerPC/64. It is planned to add this feature to the GNU linker for 32-bit PowerPC systems as well.
On Darwin/PPC systems, #pragma longcall generates jbsr callee, L42, plus a branch island (glue code). The two target addresses represent the callee and the branch island. The Darwin/PPC linker prefers the first address and generates a bl callee if the PPC bl instruction reaches the callee directly; otherwise, the linker generates bl L42 to call the branch island. The branch island is appended to the body of the calling function; it computes the full 32-bit address of the callee and jumps to it.
On Mach-O (Darwin) systems, this option directs the compiler emit to the glue for every direct call, and the Darwin linker decides whether to use or discard it.
In the future, GCC may ignore all longcall specifications when the linker is known to generate glue.
Mark (do not mark) calls to __tls_get_addr with a relocation specifying the function argument. The relocation allows the linker to reliably associate function call with argument setup instructions for TLS optimization, which in turn allows GCC to better schedule the sequence.
Adds support for multithreading with the pthreads library. This option sets flags for both the preprocessor and linker.
This option enables use of the reciprocal estimate and reciprocal square root estimate instructions with additional Newton-Raphson steps to increase precision instead of doing a divide or square root and divide for floating-point arguments. You should use the -ffast-math option when using -mrecip (or at least -funsafe-math-optimizations, -finite-math-only, -freciprocal-math and -fno-trapping-math). Note that while the throughput of the sequence is generally higher than the throughput of the non-reciprocal instruction, the precision of the sequence can be decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994) for reciprocal square roots.
-mrecip=``opt``
This option controls which reciprocal estimate instructions may be used. opt is a comma-separated list of options, which may be preceded by a ! to invert the option:
Enable all estimate instructions.
Enable the default instructions, equivalent to -mrecip.
Disable all estimate instructions, equivalent to -mno-recip.
Enable the reciprocal approximation instructions for both single and double precision.
Enable the single-precision reciprocal approximation instructions.
Enable the double-precision reciprocal approximation instructions.
Enable the reciprocal square root approximation instructions for both single and double precision.
Enable the single-precision reciprocal square root approximation instructions.
Enable the double-precision reciprocal square root approximation instructions.
So, for example, -mrecip=all,!rsqrtd enables all of the reciprocal estimate instructions, except for the FRSQRTE, XSRSQRTEDP, and XVRSQRTEDP instructions which handle the double-precision reciprocal square root calculations.
Assume (do not assume) that the reciprocal estimate instructions provide higher-precision estimates than is mandated by the PowerPC ABI. Selecting -mcpu=power6, -mcpu=power7 or -mcpu=power8 automatically selects -mrecip-precision. The double-precision square root estimate instructions are not generated by default on low-precision machines, since they do not provide an estimate that converges after three steps.
-mveclibabi=``type``
Specifies the ABI type to use for vectorizing intrinsics using an external library. The only type supported at present is mass, which specifies to use IBMs Mathematical Acceleration Subsystem (MASS) libraries for vectorizing intrinsics using external libraries. GCC currently emits calls to acosd2, acosf4, acoshd2, acoshf4, asind2, asinf4, asinhd2, asinhf4, atan2d2, atan2f4, atand2, atanf4, atanhd2, atanhf4, cbrtd2, cbrtf4, cosd2, cosf4, coshd2, coshf4, erfcd2, erfcf4, erfd2, erff4, exp2d2, exp2f4, expd2, expf4, expm1d2, expm1f4, hypotd2, hypotf4, lgammad2, lgammaf4, log10d2, log10f4, log1pd2, log1pf4, log2d2, log2f4, logd2, logf4, powd2, powf4, sind2, sinf4, sinhd2, sinhf4, sqrtd2, sqrtf4, tand2, tanf4, tanhd2, and tanhf4 when generating code for power7. Both -ftree-vectorize and -funsafe-math-optimizations must also be enabled. The MASS libraries must be specified at link time.
Generate (do not generate) the friz instruction when the -funsafe-math-optimizations option is used to optimize rounding of floating-point values to 64-bit integer and back to floating point. The friz instruction does not return the same value if the floating-point number is too large to fit in an integer.
Generate (do not generate) code to load up the static chain register (r11) when calling through a pointer on AIX and 64-bit Linux systems where a function pointer points to a 3-word descriptor giving the function address, TOC value to be loaded in register r2, and static chain value to be loaded in register r11. The -mpointers-to-nested-functions is on by default. You cannot call through pointers to nested functions or pointers to functions compiled in other languages that use the static chain if you use -mno-pointers-to-nested-functions.
Generate (do not generate) code to save the TOC value in the reserved stack location in the function prologue if the function calls through a pointer on AIX and 64-bit Linux systems. If the TOC value is not saved in the prologue, it is saved just before the call through the pointer. The -mno-save-toc-indirect option is the default.
Generate (do not generate) code to pass structure parameters with a maximum alignment of 64 bits, for compatibility with older versions of GCC.
Older versions of GCC (prior to 4.9.0) incorrectly did not align a structure parameter on a 128-bit boundary when that structure contained a member requiring 128-bit alignment. This is corrected in more recent versions of GCC. This option may be used to generate code that is compatible with functions compiled with older versions of GCC.
The -mno-compat-align-parm option is the default.
:: _rx-options:
These command-line options are defined for RX targets:
Make the double data type be 64 bits (-m64bit-doubles) or 32 bits (-m32bit-doubles) in size. The default is -m32bit-doubles. Note RX floating-point hardware only works on 32-bit values, which is why the default is -m32bit-doubles.
Enables (-fpu) or disables (-nofpu) the use of RX floating-point hardware. The default is enabled for the RX600 series and disabled for the RX200 series.
Floating-point instructions are only generated for 32-bit floating-point values, however, so the FPU hardware is not used for doubles if the -m64bit-doubles option is used.
Note If the -fpu option is enabled then -funsafe-math-optimizations is also enabled automatically. This is because the RX FPU instructions are themselves unsafe.
-mcpu=``name``
Selects the type of RX CPU to be targeted. Currently three types are supported, the generic RX600 and RX200 series hardware and the specific RX610 CPU. The default is RX600.
The only difference between RX600 and RX610 is that the RX610 does not support the MVTIPL instruction.
The RX200 series does not have a hardware floating-point unit and so -nofpu is enabled by default when this type is selected.
Store data (but not code) in the big-endian format. The default is -mlittle-endian-data, i.e. to store data in the little-endian format.
-msmall-data-limit=``N``
Specifies the maximum size in bytes of global and static variables which can be placed into the small data area. Using the small data area can lead to smaller and faster code, but the size of area is limited and it is up to the programmer to ensure that the area does not overflow. Also when the small data area is used one of the RXs registers (usually r13) is reserved for use pointing to this area, so it is no longer available for use by the compiler. This could result in slower and/or larger code if variables are pushed onto the stack instead of being held in this register.
Note, common variables (variables that have not been initialized) and constants are not placed into the small data area as they are assigned to other sections in the output executable.
The default value is zero, which disables this feature. Note, this feature is not enabled by default with higher optimization levels (-O2 etc) because of the potentially detrimental effects of reserving a register. It is up to the programmer to experiment and discover whether this feature is of benefit to their program. See the description of the -mpid option for a description of how the actual register to hold the small data area pointer is chosen.
Use the simulator runtime. The default is to use the libgloss board-specific runtime.
When generating assembler output use a syntax that is compatible with Renesass AS100 assembler. This syntax can also be handled by the GAS assembler, but it has some restrictions so it is not generated by default.
-mmax-constant-size=``N``
Specifies the maximum size, in bytes, of a constant that can be used as an operand in a RX instruction. Although the RX instruction set does allow constants of up to 4 bytes in length to be used in instructions, a longer value equates to a longer instruction. Thus in some circumstances it can be beneficial to restrict the size of constants that are used in instructions. Constants that are too big are instead placed into a constant pool and referenced via register indirection.
The value N can be between 0 and 4. A value of 0 (the default) or 4 means that constants of any size are allowed.
Enable linker relaxation. Linker relaxation is a process whereby the linker attempts to reduce the size of a program by finding shorter versions of various instructions. Disabled by default.
-mint-register=``N``
Specify the number of registers to reserve for fast interrupt handler functions. The value N can be between 0 and 4. A value of 1 means that register r13 is reserved for the exclusive use of fast interrupt handlers. A value of 2 reserves r13 and r12. A value of 3 reserves r13, r12 and r11, and a value of 4 reserves r13 through r10. A value of 0, the default, does not reserve any registers.
Specifies that interrupt handler functions should preserve the accumulator register. This is only necessary if normal code might use the accumulator register, for example because it performs 64-bit multiplications. The default is to ignore the accumulator as this makes the interrupt handlers faster.
Enables the generation of position independent data. When enabled any access to constant data is done via an offset from a base address held in a register. This allows the location of constant data to be determined at run time without requiring the executable to be relocated, which is a benefit to embedded applications with tight memory constraints. Data that can be modified is not affected by this option.
Note, using this feature reserves a register, usually r13, for the constant data base address. This can result in slower and/or larger code, especially in complicated functions.
The actual register chosen to hold the constant data base address depends upon whether the -msmall-data-limit and/or the -mint-register command-line options are enabled. Starting with register r13 and proceeding downwards, registers are allocated first to satisfy the requirements of -mint-register, then -mpid and finally -msmall-data-limit. Thus it is possible for the small data area register to be r8 if both -mint-register=4 and -mpid are specified on the command line.
By default this feature is not enabled. The default can be restored via the -mno-pid command-line option.
Prevents GCC from issuing a warning message if it finds more than one fast interrupt handler when it is compiling a file. The default is to issue a warning for each extra fast interrupt handler found, as the RX only supports one such interrupt.
Enables or disables the use of the string manipulation instructions SMOVF, SCMPU, SMOVB, SMOVU, SUNTIL SWHILE and also the RMPA instruction. These instructions may prefetch data, which is not safe to do if accessing an I/O register. (See section 12.2.7 of the RX62N Group Users Manual for more information).
The default is to allow these instructions, but it is not possible for GCC to reliably detect all circumstances where a string instruction might be used to access an I/O register, so their use cannot be disabled automatically. Instead it is reliant upon the programmer to use the -mno-allow-string-insns option if their program accesses I/O space.
When the instructions are enabled GCC defines the C preprocessor symbol __RX_ALLOW_STRING_INSNS__, otherwise it defines the symbol __RX_DISALLOW_STRING_INSNS__.
Note: The generic GCC command-line option -ffixed-``reg`` has special significance to the RX port when used with the interrupt function attribute. This attribute indicates a function intended to process fast interrupts. GCC ensures that it only uses the registers r10, r11, r12 and/or r13 and only provided that the normal use of the corresponding registers have been restricted via the -ffixed-``reg`` or -mint-register command-line options.
:: _s/390-and-zseries-options:
These are the -m options defined for the S/390 and zSeries architecture.
Use (do not use) the hardware floating-point instructions and registers for floating-point operations. When -msoft-float is specified, functions in libgcc.a are used to perform floating-point operations. When -mhard-float is specified, the compiler generates IEEE floating-point instructions. This is the default.
Use (do not use) the hardware decimal-floating-point instructions for decimal-floating-point operations. When -mno-hard-dfp is specified, functions in libgcc.a are used to perform decimal-floating-point operations. When -mhard-dfp is specified, the compiler generates decimal-floating-point hardware instructions. This is the default for -march=z9-ec or higher.
These switches control the size of long double type. A size of 64 bits makes the long double type equivalent to the double type. This is the default.
Store (do not store) the address of the callers frame as backchain pointer into the callees stack frame. A backchain may be needed to allow debugging using tools that do not understand DWARF 2 call frame information. When -mno-packed-stack is in effect, the backchain pointer is stored at the bottom of the stack frame; when -mpacked-stack is in effect, the backchain is placed into the topmost word of the 96/160 byte register save area.
In general, code compiled with -mbackchain is call-compatible with code compiled with -mmo-backchain; however, use of the backchain for debugging purposes usually requires that the whole binary is built with -mbackchain. Note that the combination of -mbackchain, -mpacked-stack and -mhard-float is not supported. In order to build a linux kernel use -msoft-float.
The default is to not maintain the backchain.
Use (do not use) the packed stack layout. When -mno-packed-stack is specified, the compiler uses the all fields of the 96/160 byte register save area only for their default purpose; unused fields still take up stack space. When -mpacked-stack is specified, register save slots are densely packed at the top of the register save area; unused space is reused for other purposes, allowing for more efficient use of the available stack space. However, when -mbackchain is also in effect, the topmost word of the save area is always used to store the backchain, and the return address register is always saved two words below the backchain.
As long as the stack frame backchain is not used, code generated with -mpacked-stack is call-compatible with code generated with -mno-packed-stack. Note that some non-FSF releases of GCC 2.95 for S/390 or zSeries generated code that uses the stack frame backchain at run time, not just for debugging purposes. Such code is not call-compatible with code compiled with -mpacked-stack. Also, note that the combination of -mbackchain, -mpacked-stack and -mhard-float is not supported. In order to build a linux kernel use -msoft-float.
The default is to not use the packed stack layout.
Generate (or do not generate) code using the bras instruction to do subroutine calls. This only works reliably if the total executable size does not exceed 64k. The default is to use the basr instruction instead, which does not have this limitation.
When -m31 is specified, generate code compliant to the GNU/Linux for S/390 ABI When -m64 is specified, generate code compliant to the GNU/Linux for zSeries ABI This allows GCC in particular to generate 64-bit instructions. For the s390 targets, the default is -m31, while the s390x targets default to -m64.
When -mzarch is specified, generate code using the instructions available on z/Architecture. When -mesa is specified, generate code using the instructions available on ESA/390. Note that -mesa is not possible with -m64. When generating code compliant to the GNU/Linux for S/390 ABI, the default is -mesa. When generating code compliant to the GNU/Linux for zSeries ABI, the default is -mzarch.
Generate (or do not generate) code using the mvcle instruction to perform block moves. When -mno-mvcle is specified, use a mvc loop instead. This is the default unless optimizing for size.
Print (or do not print) additional debug information when compiling. The default is to not print debug information.
-march=``cpu-type``
Generate code that runs on cpu-type, which is the name of a system representing a certain processor type. Possible values for cpu-type are g5, g6, z900, z990, z9-109, z9-ec, z10, z196, and zEC12. When generating code using the instructions available on z/Architecture, the default is -march=z900. Otherwise, the default is -march=g5.
-mtune=``cpu-type``
Tune to cpu-type everything applicable about the generated code, except for the ABI and the set of available instructions. The list of cpu-type values is the same as for -march. The default is the value used for -march.
Generate code that adds (does not add) in TPF OS specific branches to trace routines in the operating system. This option is off by default, even when compiling for the TPF OS
Generate code that uses (does not use) the floating-point multiply and accumulate instructions. These instructions are generated by default if hardware floating point is used.
-mwarn-framesize=``framesize``
Emit a warning if the current function exceeds the given frame size. Because this is a compile-time check it doesnt need to be a real problem when the program runs. It is intended to identify functions that most probably cause a stack overflow. It is useful to be used in an environment with limited stack size e.g. the linux kernel.
Emit a warning if the function calls alloca or uses dynamically-sized arrays. This is generally a bad idea with a limited stack size.
-mstack-guard=``stack-guard``
-mstack-size=``stack-size``
If these options are provided the S/390 back end emits additional instructions in the function prologue that trigger a trap if the stack size is stack-guard bytes above the stack-size (remember that the stack on S/390 grows downward). If the stack-guard option is omitted the smallest power of 2 larger than the frame size of the compiled function is chosen. These options are intended to be used to help debugging stack overflow problems. The additionally emitted code causes only little overhead and hence can also be used in production-like systems without greater performance degradation. The given values have to be exact powers of 2 and stack-size has to be greater than stack-guard without exceeding 64k. In order to be efficient the extra code makes the assumption that the stack starts at an address aligned to the value given by stack-size. The stack-guard option can only be used in conjunction with stack-size.
-mhotpatch=``pre-halfwords``,``post-halfwords``
If the hotpatch option is enabled, a hot-patching function prologue is generated for all functions in the compilation unit. The funtion label is prepended with the given number of two-byte NOP instructions (pre-halfwords, maximum 1000000). After the label, 2 * post-halfwords bytes are appended, using the largest NOP like instructions the architecture allows (maximum 1000000).
If both arguments are zero, hotpatching is disabled.
This option can be overridden for individual functions with the hotpatch attribute.
:: _score-options:
These options are defined for Score implementations:
Compile code for big-endian mode. This is the default.
Compile code for little-endian mode.
Disable generation of bcnz instructions.
Enable generation of unaligned load and store instructions.
Enable the use of multiply-accumulate instructions. Disabled by default.
Specify the SCORE5 as the target architecture.
Specify the SCORE5U of the target architecture.
Specify the SCORE7 as the target architecture. This is the default.
Specify the SCORE7D as the target architecture.
:: _sh-options:
These -m options are defined for the SH implementations:
Generate code for the SH1.
Generate code for the SH2.
Generate code for the SH2e.
Generate code for the SH2a without FPU, or for a SH2a-FPU in such a way that the floating-point unit is not used.
Generate code for the SH2a-FPU, in such a way that no double-precision floating-point operations are used.
Generate code for the SH2a-FPU assuming the floating-point unit is in single-precision mode by default.
Generate code for the SH2a-FPU assuming the floating-point unit is in double-precision mode by default.
Generate code for the SH3.
Generate code for the SH3e.
Generate code for the SH4 without a floating-point unit.
Generate code for the SH4 with a floating-point unit that only supports single-precision arithmetic.
Generate code for the SH4 assuming the floating-point unit is in single-precision mode by default.
Generate code for the SH4.
Generate code for SH4-100.
Generate code for SH4-100 in such a way that the floating-point unit is not used.
Generate code for SH4-100 assuming the floating-point unit is in single-precision mode by default.
Generate code for SH4-100 in such a way that no double-precision floating-point operations are used.
Generate code for SH4-200.
Generate code for SH4-200 without in such a way that the floating-point unit is not used.
Generate code for SH4-200 assuming the floating-point unit is in single-precision mode by default.
Generate code for SH4-200 in such a way that no double-precision floating-point operations are used.
Generate code for SH4-300.
Generate code for SH4-300 without in such a way that the floating-point unit is not used.
Generate code for SH4-300 in such a way that no double-precision floating-point operations are used.
Generate code for SH4-300 in such a way that no double-precision floating-point operations are used.
Generate code for SH4-340 (no MMU, no FPU).
Generate code for SH4-500 (no FPU). Passes -isa=sh4-nofpu to the assembler.
Generate code for the SH4al-dsp, or for a SH4a in such a way that the floating-point unit is not used.
Generate code for the SH4a, in such a way that no double-precision floating-point operations are used.
Generate code for the SH4a assuming the floating-point unit is in single-precision mode by default.
Generate code for the SH4a.
Same as -m4a-nofpu, except that it implicitly passes -dsp to the assembler. GCC doesnt generate any DSP instructions at the moment.
Generate 32-bit code for SHmedia.
Generate 32-bit code for SHmedia in such a way that the floating-point unit is not used.
Generate 64-bit code for SHmedia.
Generate 64-bit code for SHmedia in such a way that the floating-point unit is not used.
Generate code for SHcompact.
Generate code for SHcompact in such a way that the floating-point unit is not used.
Compile code for the processor in big-endian mode.
Compile code for the processor in little-endian mode.
Align doubles at 64-bit boundaries. Note that this changes the calling conventions, and thus some functions from the standard C library do not work unless you recompile it first with -mdalign.
Shorten some address references at link time, when possible; uses the linker option -relax.
Use 32-bit offsets in switch tables. The default is to use 16-bit offsets.
Enable the use of bit manipulation instructions on SH2A.
Comply with the calling conventions defined by Renesas.
Comply with the calling conventions defined for GCC before the Renesas conventions were available. This option is the default for all targets of the SH toolchain.
Control the IEEE compliance of floating-point comparisons, which affects the handling of cases where the result of a comparison is unordered. By default -mieee is implicitly enabled. If -ffinite-math-only is enabled -mno-ieee is implicitly set, which results in faster floating-point greater-equal and less-equal comparisons. The implcit settings can be overridden by specifying either -mieee or -mno-ieee.
Inline code to invalidate instruction cache entries after setting up nested function trampolines. This option has no effect if -musermode is in effect and the selected code generation option (e.g. -m4) does not allow the use of the icbi instruction. If the selected code generation option does not allow the use of the icbi instruction, and -musermode is not in effect, the inlined code manipulates the instruction cache address array directly with an associative write. This not only requires privileged mode at run time, but it also fails if the cache line had been mapped via the TLB and has become unmapped.
Dump instruction size and location in the assembly code.
This option is deprecated. It pads structures to multiple of 4 bytes, which is incompatible with the SH ABI
-matomic-model=``model``
matomic-model=``model`` Sets the model of atomic operations and additional parameters as a comma separated list. For details on the atomic built-in functions see __atomic Builtins. The following models and parameters are supported:
Disable compiler generated atomic sequences and emit library calls for atomic operations. This is the default if the target is not sh*-*-linux*.
Generate GNU/Linux compatible gUSA software atomic sequences for the atomic built-in functions. The generated atomic sequences require additional support from the interrupt/exception handling code of the system and are only suitable for SH3* and SH4* single-core systems. This option is enabled by default when the target is sh*-*-linux* and SH3* or SH4*. When the target is SH4A, this option also partially utilizes the hardware atomic instructions movli.l and movco.l to create more efficient code, unless strict is specified.
Generate software atomic sequences that use a variable in the thread control block. This is a variation of the gUSA sequences which can also be used on SH1* and SH2* targets. The generated atomic sequences require additional support from the interrupt/exception handling code of the system and are only suitable for single-core systems. When using this model, the gbr-offset= parameter has to be specified as well.
Generate software atomic sequences that temporarily disable interrupts by setting SR.IMASK = 1111. This model works only when the program runs in privileged mode and is only suitable for single-core systems. Additional support from the interrupt/exception handling code of the system is not required. This model is enabled by default when the target is sh*-*-linux* and SH1* or SH2*.
Generate hardware atomic sequences using the movli.l and movco.l instructions only. This is only available on SH4A and is suitable for multi-core systems. Since the hardware instructions support only 32 bit atomic variables access to 8 or 16 bit variables is emulated with 32 bit accesses. Code compiled with this option is also compatible with other software atomic model interrupt/exception handling systems if executed on an SH4A system. Additional support from the interrupt/exception handling code of the system is not required for this model.
This parameter specifies the offset in bytes of the variable in the thread control block structure that should be used by the generated atomic sequences when the soft-tcb model has been selected. For other models this parameter is ignored. The specified value must be an integer multiple of four and in the range 0-1020.
This parameter prevents mixed usage of multiple atomic models, even if they are compatible, and makes the compiler generate atomic sequences of the specified model only.
Generate the tas.b opcode for __atomic_test_and_set. Notice that depending on the particular hardware and software configuration this can degrade overall performance due to the operand cache line flushes that are implied by the tas.b instruction. On multi-core SH4A processors the tas.b instruction must be used with caution since it can result in data corruption for certain cache configurations.
When generating position-independent code, emit function calls using the Global Offset Table instead of the Procedure Linkage Table.
Dont allow (allow) the compiler generating privileged mode code. Specifying -musermode also implies -mno-inline-ic_invalidate if the inlined code would not work in user mode. -musermode is the default when the target is sh*-*-linux*. If the target is SH1* or SH2* -musermode has no effect, since there is no user mode.
-multcost=``number``
multcost=``number`` Set the cost to assume for a multiply insn.
-mdiv=``strategy`` mdiv=``strategy`` Set the division strategy to be used for integer division operations. For SHmedia strategy can be one of:
Performs the operation in floating point. This has a very high latency, but needs only a few instructions, so it might be a good choice if your code has enough easily-exploitable ILP to allow the compiler to schedule the floating-point instructions together with other instructions. Division by zero causes a floating-point exception.
Uses integer operations to calculate the inverse of the divisor, and then multiplies the dividend with the inverse. This strategy allows CSE and hoisting of the inverse calculation. Division by zero calculates an unspecified result, but does not trap.
A variant of inv where, if no CSE or hoisting opportunities have been found, or if the entire operation has been hoisted to the same place, the last stages of the inverse calculation are intertwined with the final multiply to reduce the overall latency, at the expense of using a few more instructions, and thus offering fewer scheduling opportunities with other code.
Calls a library function that usually implements the inv:minlat strategy. This gives high code density for m5-*media-nofpu compilations.
Uses a different entry point of the same library function, where it assumes that a pointer to a lookup table has already been set up, which exposes the pointer load to CSE and code hoisting optimizations.
Use the inv algorithm for initial code generation, but if the code stays unoptimized, revert to the call, call2, or fp strategies, respectively. Note that the potentially-trapping side effect of division by zero is carried by a separate instruction, so it is possible that all the integer instructions are hoisted out, but the marker for the side effect stays where it is. A recombination to floating-point operations or a call is not possible in that case.
Variants of the inv:minlat strategy. In the case that the inverse calculation is not separated from the multiply, they speed up division where the dividend fits into 20 bits (plus sign where applicable) by inserting a test to skip a number of operations in this case; this test slows down the case of larger dividends. inv20u assumes the case of a such a small dividend to be unlikely, and inv20l assumes it to be likely.
For targets other than SHmedia strategy can be one of:
Calls a library function that uses the single-step division instruction div1 to perform the operation. Division by zero calculates an unspecified result and does not trap. This is the default except for SH4, SH2A and SHcompact.
Calls a library function that performs the operation in double precision floating point. Division by zero causes a floating-point exception. This is the default for SHcompact with FPU. Specifying this for targets that do not have a double precision FPU defaults to call-div1.
Calls a library function that uses a lookup table for small divisors and the div1 instruction with case distinction for larger divisors. Division by zero calculates an unspecified result and does not trap. This is the default for SH4. Specifying this for targets that do not have dynamic shift instructions defaults to call-div1.
When a division strategy has not been specified the default strategy is selected based on the current target. For SH2A the default strategy is to use the divs and divu instructions instead of library function calls.
Reserve space once for outgoing arguments in the function prologue rather than around each call. Generally beneficial for performance and size. Also needed for unwinding to avoid changing the stack frame around conditional code.
-mdivsi3_libfunc=``name``
mdivsi3_libfunc=``name`` Set the name of the library function used for 32-bit signed division to name. This only affects the name used in the call and inv:call division strategies, and the compiler still expects the same sets of input/output/clobbered registers as if this option were not present.
-mfixed-range=``register-range``
Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator can not use. This is useful when compiling kernel code. A register range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma.
Enable the use of the indexed addressing mode for SHmedia32/SHcompact. This is only safe if the hardware and/or OS implement 32-bit wrap-around semantics for the indexed addressing mode. The architecture allows the implementation of processors with 64-bit MMU, which the OS could use to get 32-bit addressing, but since no current hardware implementation supports this or any other way to make the indexed addressing mode safe to use in the 32-bit ABI, the default is -mno-indexed-addressing.
-mgettrcost=``number``
mgettrcost=``number`` Set the cost assumed for the gettr instruction to number. The default is 2 if -mpt-fixed is in effect, 100 otherwise.
Assume pt* instructions wont trap. This generally generates better-scheduled code, but is unsafe on current hardware. The current architecture definition says that ptabs and ptrel trap when the target anded with 3 is 3. This has the unintentional effect of making it unsafe to schedule these instructions before a branch, or hoist them out of a loop. For example, __do_global_ctors, a part of libgcc that runs constructors at program startup, calls functions in a list which is delimited by 1. With the -mpt-fixed option, the ptabs is done before testing against 1. That means that all the constructors run a bit more quickly, but when the loop comes to the end of the list, the program crashes because ptabs loads 1 into a target register.
Since this option is unsafe for any hardware implementing the current architecture specification, the default is -mno-pt-fixed. Unless specified explicitly with -mgettrcost, -mno-pt-fixed also implies -mgettrcost=100; this deters register allocation from using target registers for storing ordinary integers.
Assume symbols might be invalid. Ordinary function symbols generated by the compiler are always valid to load with movi/shori/ptabs or movi/shori/ptrel, but with assembler and/or linker tricks it is possible to generate symbols that cause ptabs or ptrel to trap. This option is only meaningful when -mno-pt-fixed is in effect. It prevents cross-basic-block CSE, hoisting and most scheduling of symbol loads. The default is -mno-invalid-symbols.
-mbranch-cost=``num``
mbranch-cost=``num`` Assume num to be the cost for a branch instruction. Higher numbers make the compiler try to generate more branch-free code if possible. If not specified the value is selected depending on the processor type that is being compiled for.
Assume (do not assume) that zero displacement conditional branch instructions bt and bf are fast. If -mzdcbranch is specified, the compiler prefers zero displacement branch code sequences. This is enabled by default when generating code for SH4 and SH4A. It can be explicitly disabled by specifying -mno-zdcbranch.
Force the usage of delay slots for conditional branches, which stuffs the delay slot with a nop if a suitable instruction cant be found. By default this option is disabled. It can be enabled to work around hardware bugs as found in the original SH7055.
Generate code that uses (does not use) the floating-point multiply and accumulate instructions. These instructions are generated by default if hardware floating point is used. The machine-dependent -mfused-madd option is now mapped to the machine-independent -ffp-contract=fast option, and -mno-fused-madd is mapped to -ffp-contract=off.
Allow or disallow the compiler to emit the fsca instruction for sine and cosine approximations. The option -mfsca must be used in combination with -funsafe-math-optimizations. It is enabled by default when generating code for SH4A. Using -mno-fsca disables sine and cosine approximations even if -funsafe-math-optimizations is in effect.
Allow or disallow the compiler to emit the fsrra instruction for reciprocal square root approximations. The option -mfsrra must be used in combination with -funsafe-math-optimizations and -ffinite-math-only. It is enabled by default when generating code for SH4A. Using -mno-fsrra disables reciprocal square root approximations even if -funsafe-math-optimizations and -ffinite-math-only are in effect.
Prefer zero-displacement conditional branches for conditional move instruction patterns. This can result in faster code on the SH4 processor.
:: _solaris-2-options:
These -m options are supported on Solaris 2:
-mclear-hwcap tells the compiler to remove the hardware capabilities generated by the Solaris assembler. This is only necessary when object files use ISA extensions not supported by the current machine, but check at runtime whether or not to use them.
-mimpure-text, used in addition to -shared, tells the compiler to not pass -z text to the linker when linking a shared object. Using this option, you can link position-dependent code into a shared object.
-mimpure-text suppresses the relocations remain against allocatable but non-writable sections linker error message. However, the necessary relocations trigger copy-on-write, and the shared object is not actually shared across processes. Instead of using -mimpure-text, you should compile all source code with -fpic or -fPIC.
These switches are supported in addition to the above on Solaris 2:
Add support for multithreading using the POSIX threads library. This option sets flags for both the preprocessor and linker. This option does not affect the thread safety of object code produced by the compiler or that of libraries supplied with it.
:: _sparc-options:
These -m options are supported on the SPARC:
Specify -mapp-regs to generate output using the global registers 2 through 4, which the SPARC SVR4 ABI reserves for applications. Like the global register 1, each global register 2 through 4 is then treated as an allocable register that is clobbered by function calls. This is the default.
To be fully SVR4 ABI-compliant at the cost of some performance loss, specify -mno-app-regs. You should compile libraries and system software with this option.
With -mflat, the compiler does not generate save/restore instructions and uses a flat or single register window model. This model is compatible with the regular register window model. The local registers and the input registers (05) are still treated as call-saved registers and are saved on the stack as needed.
With -mno-flat (the default), the compiler generates save/restore instructions (except for leaf functions). This is the normal operating mode.
Generate output containing floating-point instructions. This is the default.
Generate output containing library calls for floating point. Warning: the requisite libraries are not available for all SPARC targets. Normally the facilities of the machines usual C compiler are used, but this cannot be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation. The embedded targets sparc--aout and sparclite--* do provide software floating-point support.
-msoft-float changes the calling convention in the output file; therefore, it is only useful if you compile all of a program with this option. In particular, you need to compile libgcc.a, the library that comes with GCC, with -msoft-float in order for this to work.
Generate output containing quad-word (long double) floating-point instructions.
Generate output containing library calls for quad-word (long double) floating-point instructions. The functions called are those specified in the SPARC ABI This is the default.
As of this writing, there are no SPARC implementations that have hardware support for the quad-word floating-point instructions. They all invoke a trap handler for one of these instructions, and then the trap handler emulates the effect of the instruction. Because of the trap handler overhead, this is much slower than calling the ABI library routines. Thus the -msoft-quad-float option is the default.
Assume that doubles have 8-byte alignment. This is the default.
With -munaligned-doubles, GCC assumes that doubles have 8-byte alignment only if they are contained in another type, or if they have an absolute address. Otherwise, it assumes they have 4-byte alignment. Specifying this option avoids some rare compatibility problems with code generated by other compilers. It is not the default because it results in a performance loss, especially for floating-point code.
Do not generate code that can only run in supervisor mode. This is relevant only for the casa instruction emitted for the LEON3 processor. The default is -mno-user-mode.
With -mfaster-structs, the compiler assumes that structures should have 8-byte alignment. This enables the use of pairs of ldd and std instructions for copies in structure assignment, in place of twice as many ld and st pairs. However, the use of this changed alignment directly violates the SPARC ABI Thus, its intended only for use on targets where the developer acknowledges that their resulting code is not directly in line with the rules of the ABI
-mcpu=``cpu_type``
Set the instruction set, register set, and instruction scheduling parameters for machine type cpu_type. Supported values for cpu_type are v7, cypress, v8, supersparc, hypersparc, leon, leon3, leon3v7, sparclite, f930, f934, sparclite86x, sparclet, tsc701, v9, ultrasparc, ultrasparc3, niagara, niagara2, niagara3 and niagara4.
Native Solaris and GNU/Linux toolchains also support the value native, which selects the best architecture option for the host processor. -mcpu=native has no effect if GCC does not recognize the processor.
Default instruction scheduling parameters are used for values that select an architecture and not an implementation. These are v7, v8, sparclite, sparclet, v9.
Here is a list of each supported architecture and their supported implementations.
cypress, leon3v7
supersparc, hypersparc, leon, leon3
f930, f934, sparclite86x
tsc701
ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4
By default (unless configured otherwise), GCC generates code for the V7 variant of the SPARC architecture. With -mcpu=cypress, the compiler additionally optimizes it for the Cypress CY7C602 chip, as used in the SPARCStation/SPARCServer 3xx series. This is also appropriate for the older SPARCStation 1, 2, IPX etc.
With -mcpu=v8, GCC generates code for the V8 variant of the SPARC architecture. The only difference from V7 code is that the compiler emits the integer multiply and integer divide instructions which exist in SPARC-V8 but not in SPARC-V7. With -mcpu=supersparc, the compiler additionally optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and 2000 series.
With -mcpu=sparclite, GCC generates code for the SPARClite variant of the SPARC architecture. This adds the integer multiply, integer divide step and scan (ffs) instructions which exist in SPARClite but not in SPARC-V7. With -mcpu=f930, the compiler additionally optimizes it for the Fujitsu MB86930 chip, which is the original SPARClite, with no FPU With -mcpu=f934, the compiler additionally optimizes it for the Fujitsu MB86934 chip, which is the more recent SPARClite with FPU
With -mcpu=sparclet, GCC generates code for the SPARClet variant of the SPARC architecture. This adds the integer multiply, multiply/accumulate, integer divide step and scan (ffs) instructions which exist in SPARClet but not in SPARC-V7. With -mcpu=tsc701, the compiler additionally optimizes it for the TEMIC SPARClet chip.
With -mcpu=v9, GCC generates code for the V9 variant of the SPARC architecture. This adds 64-bit integer and floating-point move instructions, 3 additional floating-point condition code registers and conditional move instructions. With -mcpu=ultrasparc, the compiler additionally optimizes it for the Sun UltraSPARC I/II/IIi chips. With -mcpu=ultrasparc3, the compiler additionally optimizes it for the Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With -mcpu=niagara, the compiler additionally optimizes it for Sun UltraSPARC T1 chips. With -mcpu=niagara2, the compiler additionally optimizes it for Sun UltraSPARC T2 chips. With -mcpu=niagara3, the compiler additionally optimizes it for Sun UltraSPARC T3 chips. With -mcpu=niagara4, the compiler additionally optimizes it for Sun UltraSPARC T4 chips.
-mtune=``cpu_type``
Set the instruction scheduling parameters for machine type cpu_type, but do not set the instruction set or register set that the option -mcpu=``cpu_type`` does.
The same values for -mcpu=``cpu_type`` can be used for -mtune=``cpu_type``, but the only useful values are those that select a particular CPU implementation. Those are cypress, supersparc, hypersparc, leon, leon3, leon3v7, f930, f934, sparclite86x, tsc701, ultrasparc, ultrasparc3, niagara, niagara2, niagara3 and niagara4. With native Solaris and GNU/Linux toolchains, native can also be used.
With -mv8plus, GCC generates code for the SPARC-V8+ ABI The difference from the V8 ABI is that the global and out registers are considered 64 bits wide. This is enabled by default on Solaris in 32-bit mode for all SPARC-V9 processors.
With -mvis, GCC generates code that takes advantage of the UltraSPARC Visual Instruction Set extensions. The default is -mno-vis.
With -mvis2, GCC generates code that takes advantage of version 2.0 of the UltraSPARC Visual Instruction Set extensions. The default is -mvis2 when targeting a cpu that supports such instructions, such as UltraSPARC-III and later. Setting -mvis2 also sets -mvis.
With -mvis3, GCC generates code that takes advantage of version 3.0 of the UltraSPARC Visual Instruction Set extensions. The default is -mvis3 when targeting a cpu that supports such instructions, such as niagara-3 and later. Setting -mvis3 also sets -mvis2 and -mvis.
With -mcbcond, GCC generates code that takes advantage of compare-and-branch instructions, as defined in the Sparc Architecture 2011. The default is -mcbcond when targeting a cpu that supports such instructions, such as niagara-4 and later.
With -mpopc, GCC generates code that takes advantage of the UltraSPARC population count instruction. The default is -mpopc when targeting a cpu that supports such instructions, such as Niagara-2 and later.
With -mfmaf, GCC generates code that takes advantage of the UltraSPARC Fused Multiply-Add Floating-point extensions. The default is -mfmaf when targeting a cpu that supports such instructions, such as Niagara-3 and later.
Enable the documented workaround for the single erratum of the Atmel AT697F processor (which corresponds to erratum #13 of the AT697E processor).
Enable the documented workarounds for the floating-point errata and the data cache nullify errata of the UT699 processor.
These -m options are supported in addition to the above on SPARC-V9 processors in 64-bit environments:
Generate code for a 32-bit or 64-bit environment. The 32-bit environment sets int, long and pointer to 32 bits. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits.
-mcmodel=``which``
Set the code model to one of
The Medium/Low code model: 64-bit addresses, programs must be linked in the low 32 bits of memory. Programs can be statically or dynamically linked.
The Medium/Middle code model: 64-bit addresses, programs must be linked in the low 44 bits of memory, the text and data segments must be less than 2GB in size and the data segment must be located within 2GB of the text segment.
The Medium/Anywhere code model: 64-bit addresses, programs may be linked anywhere in memory, the text and data segments must be less than 2GB in size and the data segment must be located within 2GB of the text segment.
The Medium/Anywhere code model for embedded systems: 64-bit addresses, the text and data segments must be less than 2GB in size, both starting anywhere in memory (determined at link time). The global register %g4 points to the base of the data segment. Programs are statically linked and PIC is not supported.
-mmemory-model=``mem-model``
Set the memory model in force on the processor to one of
The default memory model for the processor and operating system.
Relaxed Memory Order
Partial Store Order
Total Store Order
Sequential Consistency
These memory models are formally defined in Appendix D of the Sparc V9 architecture manual, as set in the processors PSTATE.MM field.
With -mstack-bias, GCC assumes that the stack pointer, and frame pointer if present, are offset by 2047 which must be added back when making stack frame references. This is the default in 64-bit mode. Otherwise, assume no such offset is present.
:: _spu-options:
These -m options are supported on the SPU:
The loader for SPU does not handle dynamic relocations. By default, GCC gives an error when it generates code that requires a dynamic relocation. -mno-error-reloc disables the error, -mwarn-reloc generates a warning instead.
Instructions that initiate or test completion of DMA must not be reordered with respect to loads and stores of the memory that is being accessed. With -munsafe-dma you must use the volatile keyword to protect memory accesses, but that can lead to inefficient code in places where the memory is known to not change. Rather than mark the memory as volatile, you can use -msafe-dma to tell the compiler to treat the DMA instructions as potentially affecting all memory.
By default, GCC generates a branch hint instruction to avoid pipeline stalls for always-taken or probably-taken branches. A hint is not generated closer than 8 instructions away from its branch. There is little reason to disable them, except for debugging purposes, or to make an object a little bit smaller.
By default, GCC generates code assuming that addresses are never larger than 18 bits. With -mlarge-mem code is generated that assumes a full 32-bit address.
By default, GCC links against startup code that assumes the SPU-style main function interface (which has an unconventional parameter list). With -mstdmain, GCC links your program against startup code that assumes a C99-style interface to main, including a local copy of argv strings.
-mfixed-range=``register-range``
Generate code treating the given register range as fixed registers. A fixed register is one that the register allocator cannot use. This is useful when compiling kernel code. A register range is specified as two registers separated by a dash. Multiple register ranges can be specified separated by a comma.
Compile code assuming that pointers to the PPU address space accessed via the __ea named address space qualifier are either 32 or 64 bits wide. The default is 32 bits. As this is an ABI-changing option, all object code in an executable must be compiled with the same setting.
Allow/disallow treating the __ea address space as superset of the generic address space. This enables explicit type casts between __ea and generic pointer as well as implicit conversions of generic pointers to __ea pointers. The default is to allow address space pointer conversions.
-mcache-size=``cache-size``
This option controls the version of libgcc that the compiler links to an executable and selects a software-managed cache for accessing variables in the __ea address space with a particular cache size. Possible options for cache-size are 8, 16, 32, 64 and 128. The default cache size is 64KB.
This option controls the version of libgcc that the compiler links to an executable and selects whether atomic updates to the software-managed cache of PPU-side variables are used. If you use atomic updates, changes to a PPU variable from SPU code using the __ea named address space qualifier do not interfere with changes to other PPU variables residing in the same cache line from PPU code. If you do not use atomic updates, such interference may occur; however, writing back cache lines is more efficient. The default behavior is to use atomic updates.
By default, GCC inserts nops to increase dual issue when it expects it to increase performance. n can be a value from 0 to 10. A smaller n inserts fewer nops. 10 is the default, 0 is the same as -mno-dual-nops. Disabled with -Os.
-mhint-max-nops=``n``
Maximum number of nops to insert for a branch hint. A branch hint must be at least 8 instructions away from the branch it is affecting. GCC inserts up to n nops to enforce this, otherwise it does not generate the branch hint.
-mhint-max-distance=``n``
The encoding of the branch hint instruction limits the hint to be within 256 instructions of the branch it is affecting. By default, GCC makes sure it is within 125.
Work around a hardware bug that causes the SPU to stall indefinitely. By default, GCC inserts the hbrp instruction to make sure this stall wont happen.
:: _system-v-options:
These additional options are available on System V Release 4 for compatibility with other compilers on those systems:
Identify the versions of each tool used by the compiler, in a .ident assembler directive in the output.
Refrain from adding .ident directives to the output file (this is the default).
-YP,``dirs``
Search the directories dirs, and no others, for libraries specified with -l.
-Ym,``dir``
Look in the directory dir to find the M4 preprocessor. The assembler uses this option.
:: _tile-gx-options:
These -m options are supported on the TILE-Gx:
Generate code for the small model. The distance for direct calls is limited to 500M in either direction. PC-relative addresses are 32 bits. Absolute addresses support the full address range.
Generate code for the large model. There is no limitation on call distance, pc-relative addresses, or absolute addresses.
-mcpu=``name``
Selects the type of CPU to be targeted. Currently the only supported type is tilegx.
Generate code for a 32-bit or 64-bit environment. The 32-bit environment sets int, long, and pointer to 32 bits. The 64-bit environment sets int to 32 bits and long and pointer to 64 bits.
Generate code in big/little endian mode, respectively.
:: _tilepro-options:
These -m options are supported on the TILEPro:
-mcpu=``name``
Selects the type of CPU to be targeted. Currently the only supported type is tilepro.
Generate code for a 32-bit environment, which sets int, long, and pointer to 32 bits. This is the only supported behavior so the flag is essentially ignored.
:: _v850-options:
These -m options are defined for V850 implementations:
Treat all calls as being far away (near). If calls are assumed to be far away, the compiler always loads the functions address into a register, and calls indirect through the pointer.
Do not optimize (do optimize) basic blocks that use the same index pointer 4 or more times to copy pointer into the ep register, and use the shorter sld and sst instructions. The -mep option is on by default if you optimize.
Do not use (do use) external functions to save and restore registers at the prologue and epilogue of a function. The external functions are slower, but use less code space if more than one function saves the same number of registers. The -mprolog-function option is on by default if you optimize.
Try to make the code as small as possible. At present, this just turns on the -mep and -mprolog-function options.
-mtda=``n``
Put static or global variables whose size is n bytes or less into the tiny data area that register ep points to. The tiny data area can hold up to 256 bytes in total (128 bytes for byte references).
-msda=``n``
Put static or global variables whose size is n bytes or less into the small data area that register gp points to. The small data area can hold up to 64 kilobytes.
-mzda=``n``
Put static or global variables whose size is n bytes or less into the first 32 kilobytes of memory.
Specify that the target processor is the V850.
Specify that the target processor is the V850E3V5. The preprocessor constant __v850e3v5__ is defined if this option is used.
Specify that the target processor is the V850E3V5. This is an alias for the -mv850e3v5 option.
Specify that the target processor is the V850E2V3. The preprocessor constant __v850e2v3__ is defined if this option is used.
Specify that the target processor is the V850E2. The preprocessor constant __v850e2__ is defined if this option is used.
Specify that the target processor is the V850E1. The preprocessor constants __v850e1__ and __v850e__ are defined if this option is used.
Specify that the target processor is the V850ES. This is an alias for the -mv850e1 option.
Specify that the target processor is the V850E The preprocessor constant __v850e__ is defined if this option is used.
If neither -mv850 nor -mv850e nor -mv850e1 nor -mv850e2 nor -mv850e2v3 nor -mv850e3v5 are defined then a default target processor is chosen and the relevant __v850*__ preprocessor constant is defined.
The preprocessor constants __v850 and __v851__ are always defined, regardless of which processor variant is the target.
This option suppresses generation of the CALLT instruction for the v850e, v850e1, v850e2, v850e2v3 and v850e3v5 flavors of the v850 architecture.
This option is enabled by default when the RH850 ABI is in use (see -mrh850-abi), and disabled by default when the GCC ABI is in use. If CALLT instructions are being generated then the C preprocessor symbol __V850_CALLT__ is defined.
Disable (or re-enable) the generation of PC-relative jump instructions.
Disable (or re-enable) the generation of hardware floating point instructions. This option is only significant when the target architecture is V850E2V3 or higher. If hardware floating point instructions are being generated then the C preprocessor symbol __FPU_OK__ is defined, otherwise the symbol __NO_FPU__ is defined.
Enables the use of the e3v5 LOOP instruction. The use of this instruction is not enabled by default when the e3v5 architecture is selected because its use is still experimental.
Enables support for the RH850 version of the V850 ABI. This is the default. With this version of the ABI the following rules apply:
When this version of the ABI is enabled the C preprocessor symbol __V850_RH850_ABI__ is defined.
Enables support for the old GCC version of the V850 ABI. With this version of the ABI the following rules apply:
When this version of the ABI is enabled the C preprocessor symbol __V850_GCC_ABI__ is defined.
Enables support for double and long long types to be aligned on 8-byte boundaries. The default is to restrict the alignment of all objects to at most 4-bytes. When -m8byte-align is in effect the C preprocessor symbol __V850_8BYTE_ALIGN__ is defined.
Generate code suitable for big switch tables. Use this option only if the assembler/linker complain about out of range branches within a switch table.
This option causes r2 and r5 to be used in the code generated by the compiler. This setting is the default.
This option causes r2 and r5 to be treated as fixed registers.
:: _vax-options:
These -m options are defined for the VAX:
Do not output certain jump instructions (aobleq and so on) that the Unix assembler for the VAX cannot handle across long ranges.
Do output those jump instructions, on the assumption that the GNU assembler is being used.
Output code for G-format floating-point numbers instead of D-format.
:: _visium-options:
A program which performs file I/O and is destined to run on an MCM target should be linked with this option. It causes the libraries libc.a and libdebug.a to be linked. The program should be run on the target under the control of the GDB remote debugging stub.
A program which performs file I/O and is destined to run on the simulator should be linked with option. This causes libraries libc.a and libsim.a to be linked.
Generate code containing floating-point instructions. This is the default.
Generate code containing library calls for floating-point.
-msoft-float changes the calling convention in the output file; therefore, it is only useful if you compile all of a program with this option. In particular, you need to compile libgcc.a, the library that comes with GCC, with -msoft-float in order for this to work.
-mcpu=``cpu_type``
Set the instruction set, register set, and instruction scheduling parameters for machine type cpu_type. Supported values for cpu_type are mcm, gr5 and gr6.
mcm is a synonym of gr5 present for backward compatibility.
By default (unless configured otherwise), GCC generates code for the GR5 variant of the Visium architecture.
With -mcpu=gr6, GCC generates code for the GR6 variant of the Visium architecture. The only difference from GR5 code is that the compiler will generate block move instructions.
-mtune=``cpu_type``
Set the instruction scheduling parameters for machine type cpu_type, but do not set the instruction set or register set that the option -mcpu=``cpu_type`` would.
Generate code for the supervisor mode, where there are no restrictions on the access to general registers. This is the default.
Generate code for the user mode, where the access to some general registers is forbidden: on the GR5, registers r24 to r31 cannot be accessed in this mode; on the GR6, only registers r29 to r31 are affected.
:: _vms-options:
These -m options are defined for the VMS implementations:
Return VMS condition codes from main. The default is to return POSIX-style condition (e.g.error) codes.
-mdebug-main=``prefix``
mdebug-main=``prefix`` Flag the first routine whose name starts with prefix as the main routine for the debugger.
Default to 64-bit memory allocation routines.
-mpointer-size=``size``
mpointer-size=``size`` Set the default size of pointers. Possible options for size are 32 or short for 32 bit pointers, 64 or long for 64 bit pointers, and no for supporting only 32 bit pointers. The later option disables pragma pointer_size.
:: _vxworks-options:
The options in this section are defined for all VxWorks targets. Options specific to the target hardware are listed with the other options for that target.
GCC can generate code for both VxWorks kernels and real time processes (RTPs). This option switches from the former to the latter. It also defines the preprocessor macro __RTP__.
Link an RTP executable against shared libraries rather than static libraries. The options -static and -shared can also be used for RTPs (Link Options); -static is the default.
These options are passed down to the linker. They are defined for compatibility with Diab.
Enable lazy binding of function calls. This option is equivalent to -Wl,-z,now and is defined for compatibility with Diab.
Disable lazy binding of function calls. This option is the default and is defined for compatibility with Diab.
:: _x86-options:
These -m options are defined for the x86 family of computers.
-march=``cpu-type``
Generate instructions for the machine type cpu-type. In contrast to -mtune=``cpu-type``, which merely tunes the generated code for the specified cpu-type, -march=``cpu-type`` allows GCC to generate code that may not run at all on processors other than the one indicated. Specifying -march=``cpu-type`` implies -mtune=``cpu-type``.
The choices for cpu-type are:
This selects the CPU to generate code for at compilation time by determining the processor type of the compiling machine. Using -march=native enables all instruction subsets supported by the local machine (hence the result might not run on different machines). Using -mtune=native produces code optimized for the local machine under the constraints of the selected instruction set.
Original Intel i386 CPU
Intel i486 CPU (No scheduling is implemented for this chip.)
Intel Pentium CPU with no MMX support.
Intel Pentium MMX CPU, based on Pentium core with MMX instruction set support.
Intel Pentium Pro CPU
When used with -march, the Pentium Pro instruction set is used, so the code runs on all i686 family chips. When used with -mtune, it has the same meaning as generic.
Intel Pentium II CPU, based on Pentium Pro core with MMX instruction set support.
Intel Pentium III CPU, based on Pentium Pro core with MMX and SSE instruction set support.
Intel Pentium M; low-power version of Intel Pentium III CPU with MMX, SSE and SSE2 instruction set support. Used by Centrino notebooks.
Intel Pentium 4 CPU with MMX, SSE and SSE2 instruction set support.
Improved version of Intel Pentium 4 CPU with MMX, SSE, SSE2 and SSE3 instruction set support.
Improved version of Intel Pentium 4 CPU with 64-bit extensions, MMX, SSE, SSE2 and SSE3 instruction set support.
Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3 instruction set support.
Intel Nehalem CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2 and POPCNT instruction set support.
Intel Westmere CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES and PCLMUL instruction set support.
Intel Sandy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AES and PCLMUL instruction set support.
Intel Ivy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AES, PCLMUL, FSGSBASE, RDRND and F16C instruction set support.
Intel Haswell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2 and F16C instruction set support.
Intel Broadwell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX and PREFETCHW instruction set support.
Intel Bonnell CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3 and SSSE3 instruction set support.
Intel Silvermont CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AES, PCLMUL and RDRND instruction set support.
Intel Knights Landing CPU with 64-bit extensions, MOVBE, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, FMA, BMI, BMI2, F16C, RDSEED, ADCX, PREFETCHW, AVX512F, AVX512PF, AVX512ER and AVX512CD instruction set support.
AMD K6 CPU with MMX instruction set support.
Improved versions of AMD K6 CPU with MMX and 3DNow! instruction set support.
AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow! and SSE prefetch instructions support.
Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow! and full SSE instruction set support.
Processors based on the AMD K8 core with x86-64 instruction set support, including the AMD Opteron, Athlon 64, and Athlon 64 FX processors. (This supersets MMX, SSE, SSE2, 3DNow!, enhanced 3DNow! and 64-bit instruction set extensions.)
Improved versions of AMD K8 cores with SSE3 instruction set support.
CPUs based on AMD Family 10h cores with x86-64 instruction set support. (This supersets MMX, SSE, SSE2, SSE3, SSE4A, 3DNow!, enhanced 3DNow!, ABM and 64-bit instruction set extensions.)
CPUs based on AMD Family 15h cores with x86-64 instruction set support. (This supersets FMA4, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.)
AMD Family 15h core based CPUs with x86-64 instruction set support. (This supersets BMI, TBM, F16C, FMA, FMA4, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.)
AMD Family 15h core based CPUs with x86-64 instruction set support. (This supersets BMI, TBM, F16C, FMA, FMA4, FSGSBASE, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.
AMD Family 15h core based CPUs with x86-64 instruction set support. (This supersets BMI, BMI2, TBM, F16C, FMA, FMA4, FSGSBASE, AVX, AVX2, XOP, LWP, AES, PCL_MUL, CX16, MOVBE, MMX, SSE, SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.
CPUs based on AMD Family 14h cores with x86-64 instruction set support. (This supersets MMX, SSE, SSE2, SSE3, SSSE3, SSE4A, CX16, ABM and 64-bit instruction set extensions.)
CPUs based on AMD Family 16h cores with x86-64 instruction set support. This includes MOVBE, F16C, BMI, AVX, PCL_MUL, AES, SSE4.2, SSE4.1, CX16, ABM, SSE4A, SSSE3, SSE3, SSE2, SSE, MMX and 64-bit instruction set extensions.
IDT WinChip C6 CPU, dealt in same way as i486 with additional MMX instruction set support.
IDT WinChip 2 CPU, dealt in same way as i486 with additional MMX and 3DNow! instruction set support.
VIA C3 CPU with MMX and 3DNow! instruction set support. (No scheduling is implemented for this chip.)
VIA C3-2 (Nehemiah/C5XL) CPU with MMX and SSE instruction set support. (No scheduling is implemented for this chip.)
AMD Geode embedded processor with MMX and 3DNow! instruction set support.
-mtune=``cpu-type``
Tune to cpu-type everything applicable about the generated code, except for the ABI and the set of available instructions. While picking a specific cpu-type schedules things appropriately for that particular chip, the compiler does not generate any code that cannot run on the default machine type unless you use a -march=``cpu-type`` option. For example, if GCC is configured for i686-pc-linux-gnu then -mtune=pentium4 generates code that is tuned for Pentium 4 but still runs on i686 machines.
The choices for cpu-type are the same as for -march. In addition, -mtune supports 2 extra choices for cpu-type:
Produce code optimized for the most common IA32/AMD64/EM64T processors. If you know the CPU on which your code will run, then you should use the corresponding -mtune or -march option instead of -mtune=generic. But, if you do not know exactly what CPU users of your application will have, then you should use this option.
As new processors are deployed in the marketplace, the behavior of this option will change. Therefore, if you upgrade to a newer version of GCC, code generation controlled by this option will change to reflect the processors that are most common at the time that version of GCC is released.
There is no -march=generic option because -march indicates the instruction set the compiler can use, and there is no generic instruction set applicable to all processors. In contrast, -mtune indicates the processor (or, in this case, collection of processors) for which the code is optimized.
Produce code optimized for the most current Intel processors, which are Haswell and Silvermont for this version of GCC. If you know the CPU on which your code will run, then you should use the corresponding -mtune or -march option instead of -mtune=intel. But, if you want your application performs better on both Haswell and Silvermont, then you should use this option.
As new Intel processors are deployed in the marketplace, the behavior of this option will change. Therefore, if you upgrade to a newer version of GCC, code generation controlled by this option will change to reflect the most current Intel processors at the time that version of GCC is released.
There is no -march=intel option because -march indicates the instruction set the compiler can use, and there is no common instruction set applicable to all processors. In contrast, -mtune indicates the processor (or, in this case, collection of processors) for which the code is optimized.
-mcpu=``cpu-type``
A deprecated synonym for -mtune.
-mfpmath=``unit``
Generate floating-point arithmetic for selected unit unit. The choices for unit are:
Use the standard 387 floating-point coprocessor present on the majority of chips and emulated otherwise. Code compiled with this option runs almost everywhere. The temporary results are computed in 80-bit precision instead of the precision specified by the type, resulting in slightly different results compared to most of other chips. See -ffloat-store for more detailed description.
This is the default choice for x86-32 targets.
Use scalar floating-point instructions present in the SSE instruction set. This instruction set is supported by Pentium III and newer chips, and in the AMD line by Athlon-4, Athlon XP and Athlon MP chips. The earlier version of the SSE instruction set supports only single-precision arithmetic, thus the double and extended-precision arithmetic are still done using 387. A later version, present only in Pentium 4 and AMD x86-64 chips, supports double-precision arithmetic too.
For the x86-32 compiler, you must use -march=``cpu-type``, -msse or -msse2 switches to enable SSE extensions and make this option effective. For the x86-64 compiler, these extensions are enabled by default.
The resulting code should be considerably faster in the majority of cases and avoid the numerical instability problems of 387 code, but may break some existing code that expects temporaries to be 80 bits.
This is the default choice for the x86-64 compiler.
Attempt to utilize both instruction sets at once. This effectively doubles the amount of available registers, and on chips with separate execution units for 387 and SSE the execution resources too. Use this option with care, as it is still experimental, because the GCC register allocator does not model separate functional units well, resulting in unstable performance.
-masm=``dialect`` masm=``dialect`` Output assembly instructions using selected dialect. Also affects which dialect is used for basic asm (Basic Asm) and extended asm (Extended Asm). Supported choices (in dialect order) are att or intel. The default is att. Darwin does not support intel.
Control whether or not the compiler uses IEEE floating-point comparisons. These correctly handle the case where the result of a comparison is unordered.
Generate output containing library calls for floating point.
Warning: the requisite libraries are not part of GCC Normally the facilities of the machines usual C compiler are used, but this cant be done directly in cross-compilation. You must make your own arrangements to provide suitable library functions for cross-compilation.
On machines where a function returns floating-point results in the 80387 register stack, some floating-point opcodes may be emitted even if -msoft-float is used.
Do not use the FPU registers for return values of functions.
The usual calling convention has functions return values of types float and double in an FPU register, even if there is no FPU The idea is that the operating system should emulate an FPU
The option -mno-fp-ret-in-387 causes such values to be returned in ordinary CPU registers instead.
Some 387 emulators do not support the sin, cos and sqrt instructions for the 387. Specify this option to avoid generating those instructions. This option is the default on FreeBSD, OpenBSD and NetBSD This option is overridden when -march indicates that the target CPU always has an FPU and so the instruction does not need emulation. These instructions are not generated unless you also use the -funsafe-math-optimizations switch.
Control whether GCC aligns double, long double, and long long variables on a two-word boundary or a one-word boundary. Aligning double variables on a two-word boundary produces code that runs somewhat faster on a Pentium at the expense of more memory.
On x86-64, -malign-double is enabled by default.
Warning: if you use the -malign-double switch, structures containing the above types are aligned differently than the published application binary interface specifications for the x86-32 and are not binary compatible with structures in code compiled without that switch.
These switches control the size of long double type. The x86-32 application binary interface specifies the size to be 96 bits, so -m96bit-long-double is the default in 32-bit mode.
Modern architectures (Pentium and newer) prefer long double to be aligned to an 8- or 16-byte boundary. In arrays or structures conforming to the ABI, this is not possible. So specifying -m128bit-long-double aligns long double to a 16-byte boundary by padding the long double with an additional 32-bit zero.
In the x86-64 compiler, -m128bit-long-double is the default choice as its ABI specifies that long double is aligned on 16-byte boundary.
Notice that neither of these options enable any extra precision over the x87 standard of 80 bits for a long double.
Warning: if you override the default value for your target ABI, this changes the size of structures and arrays containing long double variables, as well as modifying the function calling convention for functions taking long double. Hence they are not binary-compatible with code compiled without that switch.
These switches control the size of long double type. A size of 64 bits makes the long double type equivalent to the double type. This is the default for 32-bit Bionic C library. A size of 128 bits makes the long double type equivalent to the __float128 type. This is the default for 64-bit Bionic C library.
Warning: if you override the default value for your target ABI, this changes the size of structures and arrays containing long double variables, as well as modifying the function calling convention for functions taking long double. Hence they are not binary-compatible with code compiled without that switch.
-malign-data=``type``
Control how GCC aligns variables. Supported values for type are compat uses increased alignment value compatible uses GCC 4.8 and earlier, abi uses alignment value as specified by the psABI, and cacheline uses increased alignment value to match the cache line size. compat is the default.
-mlarge-data-threshold=``threshold``
When -mcmodel=medium is specified, data objects larger than threshold are placed in the large data section. This value must be the same across all objects linked into the binary, and defaults to 65535.
Use a different function-calling convention, in which functions that take a fixed number of arguments return with the ret ``num`` instruction, which pops their arguments while returning. This saves one instruction in the caller since there is no need to pop the arguments there.
You can specify that an individual function is called with this calling sequence with the function attribute stdcall. You can also override the -mrtd option by using the function attribute cdecl. Function Attributes.
Warning: this calling convention is incompatible with the one normally used on Unix, so you cannot use it if you need to call libraries compiled with the Unix compiler.
Also, you must provide function prototypes for all functions that take variable numbers of arguments (including printf); otherwise incorrect code is generated for calls to those functions.
In addition, seriously incorrect code results if you call a function with too many arguments. (Normally, extra arguments are harmlessly ignored.)
-mregparm=``num``
Control how many registers are used to pass integer arguments. By default, no registers are used to pass arguments, and at most 3 registers can be used. You can control this behavior for a specific function by using the function attribute regparm. Function Attributes.
Warning: if you use this switch, and num is nonzero, then you must build all modules with the same value, including any libraries. This includes the system libraries and startup modules.
Use SSE register passing conventions for float and double arguments and return values. You can control this behavior for a specific function by using the function attribute sseregparm. Function Attributes.
Warning: if you use this switch then you must build all modules with the same value, including any libraries. This includes the system libraries and startup modules.
Return 8-byte vectors in memory instead of MMX registers. This is the default on Solaris8 and 9 and VxWorks to match the ABI of the Sun Studio compilers until version 12. Later compiler versions (starting with Studio 12 Update1) follow the ABI used by other x86 targets, which is the default on Solaris10 and later. Only use this option if you need to remain compatible with existing code produced by those previous compiler versions or older versions of GCC
Set 80387 floating-point precision to 32, 64 or 80 bits. When -mpc32 is specified, the significands of results of floating-point operations are rounded to 24 bits (single precision); -mpc64 rounds the significands of results of floating-point operations to 53 bits (double precision) and -mpc80 rounds the significands of results of floating-point operations to 64 bits (extended double precision), which is the default. When this option is used, floating-point operations in higher precisions are not available to the programmer without setting the FPU control word explicitly.
Setting the rounding of floating-point operations to less than the default 80 bits can speed some programs by 2% or more. Note that some mathematical libraries assume that extended-precision (80-bit) floating-point operations are enabled by default; routines in such libraries could suffer significant loss of accuracy, typically through so-called catastrophic cancellation, when this option is used to set the precision to less than extended precision.
Realign the stack at entry. On the x86, the -mstackrealign option generates an alternate prologue and epilogue that realigns the run-time stack if necessary. This supports mixing legacy codes that keep 4-byte stack alignment with modern codes that keep 16-byte stack alignment for SSE compatibility. See also the attribute force_align_arg_pointer, applicable to individual functions.
-mpreferred-stack-boundary=``num``
Attempt to keep the stack boundary aligned to a 2 raised to num byte boundary. If -mpreferred-stack-boundary is not specified, the default is 4 (16 bytes or 128 bits).
Warning: When generating code for the x86-64 architecture with SSE extensions disabled, -mpreferred-stack-boundary=3 can be used to keep the stack boundary aligned to 8 byte boundary. Since x86-64 ABI require 16 byte stack alignment, this is ABI incompatible and intended to be used in controlled environment where stack space is important limitation. This option leads to wrong code when functions compiled with 16 byte stack alignment (such as functions from a standard library) are called with misaligned stack. In this case, SSE instructions may lead to misaligned memory access traps. In addition, variable arguments are handled incorrectly for 16 byte aligned objects (including x87 long double and __int128), leading to wrong results. You must build all modules with -mpreferred-stack-boundary=3, including any libraries. This includes the system libraries and startup modules.
-mincoming-stack-boundary=``num``
Assume the incoming stack is aligned to a 2 raised to num byte boundary. If -mincoming-stack-boundary is not specified, the one specified by -mpreferred-stack-boundary is used.
On Pentium and Pentium Pro, double and long double values should be aligned to an 8-byte boundary (see -malign-double) or suffer significant run time performance penalties. On Pentium III, the Streaming SIMD Extension (SSE) data type __m128 may not work properly if it is not 16-byte aligned.
To ensure proper alignment of this values on the stack, the stack boundary must be as aligned as that required by any value stored on the stack. Further, every function must be generated such that it keeps the stack aligned. Thus calling a function compiled with a higher preferred stack boundary from a function compiled with a lower preferred stack boundary most likely misaligns the stack. It is recommended that libraries that use callbacks always use the default setting.
This extra alignment does consume extra stack space, and generally increases code size. Code that is sensitive to stack space usage, such as embedded systems and operating system kernels, may want to reduce the preferred alignment to -mpreferred-stack-boundary=2.
These switches enable the use of instructions in the MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, AVX, AVX2, AVX512F, AVX512PF, AVX512ER, AVX512CD, SHA, AES, PCLMUL, FSGSBASE, RDRND, F16C, FMA, SSE4A, FMA4, XOP, LWP, ABM, BMI, BMI2, FXSR, XSAVE, XSAVEOPT, LZCNT, RTM, MPX or 3DNow! extended instruction sets. Each has a corresponding -mno- option to disable use of these instructions.
These extensions are also available as built-in functions: see x86 Built-in Functions, for details of the functions enabled and disabled by these switches.
To generate SSE/SSE2 instructions automatically from floating-point code (as opposed to 387 instructions), see -mfpmath=sse.
GCC depresses SSEx instructions when -mavx is used. Instead, it generates new AVX instructions or AVX equivalence for all SSEx instructions when needed.
These options enable GCC to use these extended instructions in generated code, even without -mfpmath=sse. Applications that perform run-time CPU detection must compile separate files for each supported architecture, using the appropriate flags. In particular, the file containing the CPU detection code should be compiled without these options.
This option instructs GCC to dump the names of the x86 performance tuning features and default settings. The names can be used in -mtune-ctrl=``feature-list``.
-mtune-ctrl=``feature-list``
mtune-ctrl=``feature-list`` This option is used to do fine grain control of x86 code generation features. feature-list is a comma separated list of feature names. See also -mdump-tune-features. When specified, the feature is turned on if it is not preceded with ^, otherwise, it is turned off. -mtune-ctrl=``feature-list`` is intended to be used by GCC developers. Using it may lead to code paths not covered by testing and can potentially result in compiler ICEs or runtime errors.
This option instructs GCC to turn off all tunable features. See also -mtune-ctrl=``feature-list`` and -mdump-tune-features.
This option instructs GCC to emit a cld instruction in the prologue of functions that use string instructions. String instructions depend on the DF flag to select between autoincrement or autodecrement mode. While the ABI specifies the DF flag to be cleared on function entry, some operating systems violate this specification by not clearing the DF flag in their exception dispatchers. The exception handler can be invoked with the DF flag set, which leads to wrong direction mode when string instructions are used. This option can be enabled by default on 32-bit x86 targets by configuring GCC with the --enable-cld configure option. Generation of cld instructions can be suppressed with the -mno-cld compiler option in this case.
This option instructs GCC to emit a vzeroupper instruction before a transfer of control flow out of the function to minimize the AVX to SSE transition penalty as well as remove unnecessary zeroupper intrinsics.
This option instructs GCC to use 128-bit AVX instructions instead of 256-bit AVX instructions in the auto-vectorizer.
This option enables GCC to generate CMPXCHG16B instructions. CMPXCHG16B allows for atomic operations on 128-bit double quadword (or oword) data types. This is useful for high-resolution counters that can be updated by multiple processors (or cores). This instruction is generated as part of atomic built-in functions: see __sync Builtins or __atomic Builtins for details.
This option enables generation of SAHF instructions in 64-bit code. Early Intel Pentium 4 CPUs with Intel 64 support, prior to the introduction of Pentium 4 G1 step in December 2005, lacked the LAHF and SAHF instructions which are supported by AMD64. These are load and store instructions, respectively, for certain status flags. In 64-bit mode, the SAHF instruction is used to optimize fmod, drem, and remainder built-in functions; see Other Builtins for details.
This option enables use of the movbe instruction to implement __builtin_bswap32 and __builtin_bswap64.
This option enables built-in functions __builtin_ia32_crc32qi, __builtin_ia32_crc32hi, __builtin_ia32_crc32si and __builtin_ia32_crc32di to generate the crc32 machine instruction.
This option enables use of RCPSS and RSQRTSS instructions (and their vectorized variants RCPPS and RSQRTPS) with an additional Newton-Raphson step to increase precision instead of DIVSS and SQRTSS (and their vectorized variants) for single-precision floating-point arguments. These instructions are generated only when -funsafe-math-optimizations is enabled together with -finite-math-only and -fno-trapping-math. Note that while the throughput of the sequence is higher than the throughput of the non-reciprocal instruction, the precision of the sequence can be decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994).
Note that GCC implements 1.0f/sqrtf(``x)`` in terms of RSQRTSS (or RSQRTPS) already with -ffast-math (or the above option combination), and doesnt need -mrecip.
Also note that GCC emits the above sequence with additional Newton-Raphson step for vectorized single-float division and vectorized sqrtf(``x)`` already with -ffast-math (or the above option combination), and doesnt need -mrecip.
-mrecip=``opt``
This option controls which reciprocal estimate instructions may be used. opt is a comma-separated list of options, which may be preceded by a ! to invert the option:
Enable all estimate instructions.
Enable the default instructions, equivalent to -mrecip.
Disable all estimate instructions, equivalent to -mno-recip.
Enable the approximation for scalar division.
Enable the approximation for vectorized division.
Enable the approximation for scalar square root.
Enable the approximation for vectorized square root.
So, for example, -mrecip=all,!sqrt enables all of the reciprocal approximations, except for square root.
-mveclibabi=``type``
Specifies the ABI type to use for vectorizing intrinsics using an external library. Supported values for type are svml for the Intel short vector math library and acml for the AMD math core library. To use this option, both -ftree-vectorize and -funsafe-math-optimizations have to be enabled, and an SVML or ACML ABI-compatible library must be specified at link time.
GCC currently emits calls to vmldExp2, vmldLn2, vmldLog102, vmldLog102, vmldPow2, vmldTanh2, vmldTan2, vmldAtan2, vmldAtanh2, vmldCbrt2, vmldSinh2, vmldSin2, vmldAsinh2, vmldAsin2, vmldCosh2, vmldCos2, vmldAcosh2, vmldAcos2, vmlsExp4, vmlsLn4, vmlsLog104, vmlsLog104, vmlsPow4, vmlsTanh4, vmlsTan4, vmlsAtan4, vmlsAtanh4, vmlsCbrt4, vmlsSinh4, vmlsSin4, vmlsAsinh4, vmlsAsin4, vmlsCosh4, vmlsCos4, vmlsAcosh4 and vmlsAcos4 for corresponding function type when -mveclibabi=svml is used, and __vrd2_sin, __vrd2_cos, __vrd2_exp, __vrd2_log, __vrd2_log2, __vrd2_log10, __vrs4_sinf, __vrs4_cosf, __vrs4_expf, __vrs4_logf, __vrs4_log2f, __vrs4_log10f and __vrs4_powf for the corresponding function type when -mveclibabi=acml is used.
-mabi=``name``
Generate code for the specified calling convention. Permissible values are sysv for the ABI used on GNU/Linux and other systems, and ms for the Microsoft ABI. The default is to use the Microsoft ABI when targeting Microsoft Windows and the SysV ABI on all other systems. You can control this behavior for specific functions by using the function attributes ms_abi and sysv_abi. Function Attributes.
-mtls-dialect=``type``
Generate code to access thread-local storage using the gnu or gnu2 conventions. gnu is the conservative default; gnu2 is more efficient, but it may add compile- and run-time requirements that cannot be satisfied on all systems.
Use PUSH operations to store outgoing parameters. This method is shorter and usually equally fast as method using SUB/MOV operations and is enabled by default. In some cases disabling it may improve performance because of improved scheduling and reduced dependencies.
If enabled, the maximum amount of space required for outgoing arguments is computed in the function prologue. This is faster on most modern CPUs because of reduced dependencies, improved scheduling and reduced stack usage when the preferred stack boundary is not equal to 2. The drawback is a notable increase in code size. This switch implies -mno-push-args.
Support thread-safe exception handling on MinGW. Programs that rely on thread-safe exception handling must compile and link all code with the -mthreads option. When compiling, -mthreads defines -D_MT; when linking, it links in a special thread helper library -lmingwthrd which cleans up per-thread exception-handling data.
Do not align the destination of inlined string operations. This switch reduces code size and improves performance in case the destination is already aligned, but GCC doesnt know about it.
By default GCC inlines string operations only when the destination is known to be aligned to least a 4-byte boundary. This enables more inlining and increases code size, but may improve performance of code that depends on fast memcpy, strlen, and memset for short lengths.
For string operations of unknown size, use run-time checks with inline code for small blocks and a library call for large blocks.
-mstringop-strategy=``alg``
mstringop-strategy=``alg`` Override the internal decision heuristic for the particular algorithm to use for inlining string operations. The allowed values for alg are:
Expand using i386 rep prefix of the specified size.
Expand into an inline loop.
Always use a library call.
-mmemcpy-strategy=``strategy`` mmemcpy-strategy=``strategy`` Override the internal decision heuristic to decide if __builtin_memcpy should be inlined and what inline algorithm to use when the expected size of the copy operation is known. strategy is a comma-separated list of alg:max_size:dest_align triplets. alg is specified in -mstringop-strategy, max_size specifies the max byte size with which inline algorithm alg is allowed. For the last triplet, the max_size must be -1. The max_size of the triplets in the list must be specified in increasing order. The minimal byte size for alg is 0 for the first triplet and ``max_size + 1`` of the preceding range.
-mmemset-strategy=``strategy`` mmemset-strategy=``strategy`` The option is similar to -mmemcpy-strategy= except that it is to control __builtin_memset expansion.
Dont keep the frame pointer in a register for leaf functions. This avoids the instructions to save, set up, and restore frame pointers and makes an extra register available in leaf functions. The option -fomit-leaf-frame-pointer removes the frame pointer for leaf functions, which might make debugging harder.
Controls whether TLS variables may be accessed with offsets from the TLS segment register (%gs for 32-bit, %fs for 64-bit), or whether the thread base pointer must be added. Whether or not this is valid depends on the operating system, and whether it maps the segment to cover the entire TLS area.
For systems that use the GNU C Library, the default is on.
Specify that the assembler should encode SSE instructions with VEX prefix. The option -mavx turns this on by default.
If profiling is active (-pg), put the profiling counter call before the prologue. Note: On x86 architectures the attribute ms_hook_prologue isnt possible at the moment for -mfentry and -pg.
If profiling is active (-pg), generate a __mcount_loc section that contains pointers to each profiling call. This is useful for automatically patching and out calls.
If profiling is active (-pg), generate the calls to the profiling functions as nops. This is useful when they should be patched in later dynamically. This is likely only useful together with -mrecord-mcount.
When generating code for the x86-64 architecture with SSE extensions disabled, -skip-rax-setup can be used to skip setting up RAX register when there are no variable arguments passed in vector registers.
Warning: Since RAX register is used to avoid unnecessarily saving vector registers on stack when passing variable arguments, the impacts of this option are callees may waste some stack space, misbehave or jump to a random location. GCC 4.4 or newer dont have those issues, regardless the RAX register value.
On some processors, like Intel Atom, 8-bit unsigned integer divide is much faster than 32-bit/64-bit integer divide. This option generates a run-time check. If both dividend and divisor are within range of 0 to 255, 8-bit unsigned integer divide is used instead of 32-bit/64-bit integer divide.
Split 32-byte AVX unaligned load and store.
-mstack-protector-guard=``guard``
mstack-protector-guard=``guard`` Generate stack protection code using canary at guard. Supported locations are global for global canary or tls for per-thread canary in the TLS block (the default). This option has effect only when -fstack-protector or -fstack-protector-all is specified.
These -m switches are supported in addition to the above on x86-64 processors in 64-bit environments.
Generate code for a 16-bit, 32-bit or 64-bit environment. The -m32 option sets int, long, and pointer types to 32 bits, and generates code that runs on any i386 system.
The -m64 option sets int to 32 bits and long and pointer types to 64 bits, and generates code for the x86-64 architecture. For Darwin only the -m64 option also turns off the -fno-pic and -mdynamic-no-pic options.
The -mx32 option sets int, long, and pointer types to 32 bits, and generates code for the x86-64 architecture.
The -m16 option is the same as -m32, except for that it outputs the .code16gcc assembly directive at the beginning of the assembly output so that the binary can run in 16-bit mode.
Do not use a so-called red zone for x86-64 code. The red zone is mandated by the x86-64 ABI; it is a 128-byte area beyond the location of the stack pointer that is not modified by signal or interrupt handlers and therefore can be used for temporary data without adjusting the stack pointer. The flag -mno-red-zone disables this red zone.
Generate code for the small code model: the program and its symbols must be linked in the lower 2 GB of the address space. Pointers are 64 bits. Programs can be statically or dynamically linked. This is the default code model.
Generate code for the kernel code model. The kernel runs in the negative 2 GB of the address space. This model has to be used for Linux kernel code.
Generate code for the medium model: the program is linked in the lower 2 GB of the address space. Small symbols are also placed there. Symbols with sizes larger than -mlarge-data-threshold are put into large data or BSS sections and can be located above 2GB. Programs can be statically or dynamically linked.
Generate code for the large model. This model makes no assumptions about addresses and sizes of sections.
Generate code for long address mode. This is only supported for 64-bit and x32 environments. It is the default address mode for 64-bit environments.
Generate code for short address mode. This is only supported for 32-bit and x32 environments. It is the default address mode for 32-bit and x32 environments.
:: _x86-windows-options:
These additional options are available for Microsoft Windows targets:
This option specifies that a console application is to be generated, by instructing the linker to set the PE header subsystem type required for console applications. This option is available for Cygwin and MinGW targets and is enabled by default on those targets.
This option is available for Cygwin and MinGW targets. It specifies that a DLLa dynamic link libraryis to be generated, enabling the selection of the required runtime startup object and entry point.
This option is available for Cygwin and MinGW targets. It specifies that the dllimport attribute should be ignored.
This option is available for MinGW targets. It specifies that MinGW-specific thread support is to be used.
This option is available for MinGW-w64 targets. It causes the UNICODE preprocessor macro to be predefined, and chooses Unicode-capable runtime startup code.
This option is available for Cygwin and MinGW targets. It specifies that the typical Microsoft Windows predefined macros are to be set in the pre-processor, but does not influence the choice of runtime library/startup code.
This option is available for Cygwin and MinGW targets. It specifies that a GUI application is to be generated by instructing the linker to set the PE header subsystem type appropriately.
This option is available for MinGW targets. It specifies that the executable flag for the stack used by nested functions isnt set. This is necessary for binaries running in kernel mode of Microsoft Windows, as there the User32 API, which is used to set executable privileges, isnt available.
This option is available for MinGW and Cygwin targets. It specifies that relocated-data in read-only section is put into .data section. This is a necessary for older runtimes not supporting modification of .rdata sections for pseudo-relocation.
This option is available for Cygwin and MinGW targets. It specifies that the GNU extension to the PE file format that permits the correct alignment of COMMON variables should be used when generating code. It is enabled by default if GCC detects that the target assembler found during configuration supports the feature.
See also under x86 Options for standard options.
:: _xstormy16-options:
These options are defined for Xstormy16:
Choose startup files and linker script suitable for the simulator.
:: _xtensa-options:
These options are supported for Xtensa targets:
Enable or disable use of CONST16 instructions for loading constant values. The CONST16 instruction is currently not a standard option from Tensilica. When enabled, CONST16 instructions are always used in place of the standard L32R instructions. The use of CONST16 is enabled by default only if the L32R instruction is not available.
Enable or disable use of fused multiply/add and multiply/subtract instructions in the floating-point option. This has no effect if the floating-point option is not also enabled. Disabling fused multiply/add and multiply/subtract instructions forces the compiler to use separate instructions for the multiply and add/subtract operations. This may be desirable in some cases where strict IEEE 754-compliant results are required: the fused multiply add/subtract instructions do not round the intermediate result, thereby producing results with more bits of precision than specified by the IEEE standard. Disabling fused multiply add/subtract instructions also ensures that the program output is not sensitive to the compilers ability to combine multiply and add/subtract operations.
When this option is enabled, GCC inserts MEMW instructions before volatile memory references to guarantee sequential consistency. The default is -mserialize-volatile. Use -mno-serialize-volatile to omit the MEMW instructions.
For targets, like GNU/Linux, where all user-mode Xtensa code must be position-independent code (PIC), this option disables PIC for compiling kernel code.
These options control the treatment of literal pools. The default is -mno-text-section-literals, which places literals in a separate section in the output file. This allows the literal pool to be placed in a data RAM/ROM, and it also allows the linker to combine literal pools from separate object files to remove redundant literals and improve code size. With -mtext-section-literals, the literals are interspersed in the text section in order to keep them as close as possible to their references. This may be necessary for large assembly files.
When this option is enabled, GCC instructs the assembler to automatically align instructions to reduce branch penalties at the expense of some code density. The assembler attempts to widen density instructions to align branch targets and the instructions following call instructions. If there are not enough preceding safe density instructions to align a target, no widening is performed. The default is -mtarget-align. These options do not affect the treatment of auto-aligned instructions like LOOP, which the assembler always aligns, either by widening density instructions or by inserting NOP instructions.
When this option is enabled, GCC instructs the assembler to translate direct calls to indirect calls unless it can determine that the target of a direct call is in the range allowed by the call instruction. This translation typically occurs for calls to functions in other source files. Specifically, the assembler translates a direct CALL instruction into an L32R followed by a CALLX instruction. The default is -mno-longcalls. This option should be used in programs where the call target can potentially be out of range. This option is implemented in the assembler, not the compiler, so the assembly code generated by GCC still shows direct call instructionslook at the disassembled object code to see the actual instructions. Note that the assembler uses an indirect call for every cross-file call, not just those that really are out of range.
:: _zseries-options:
These machine-independent options control the interface conventions used in code generation.
Most of them have both positive and negative forms; the negative form of -ffoo is -fno-foo. In the table below, only one of the forms is listedthe one that is not the default. You can figure out the other form by either removing no- or adding it.
For front ends that support it, generate additional code to check that indices used to access arrays are within the declared range. This is currently only supported by the Java and Fortran front ends, where this option defaults to true and false respectively.
-fstack-reuse=``reuse-level``
This option controls stack space reuse for user declared local/auto variables and compiler generated temporaries. reuse_level can be all, named_vars, or none. all enables stack reuse for all local variables and temporaries, named_vars enables the reuse only for user defined local variables with names, and none disables stack reuse completely. The default value is all. The option is needed when the program extends the lifetime of a scoped local variable or a compiler generated temporary beyond the end point defined by the language. When a lifetime of a variable ends, and if the variable lives in memory, the optimizing compiler has the freedom to reuse its stack space with other temporaries or scoped local variables whose live range does not overlap with it. Legacy code extending local lifetime is likely to break with the stack reuse optimization.
For example,
int *p;
{
int local1;
p = &local1;
local1 = 10;
....
}
{
int local2;
local2 = 20;
...
}
if (*p == 10) // out of scope use of local1
{
}
Another example:
struct A
{
A(int k) : i(k), j(k) { }
int i;
int j;
};
A *ap;
void foo(const A& ar)
{
ap = &ar;
}
void bar()
{
foo(A(10)); // temp object's lifetime ends when foo returns
{
A a(20);
....
}
ap->i+= 10; // ap references out of scope temp whose space
// is reused with a. What is the value of ap->i?
}
The lifetime of a compiler generated temporary is well defined by the C++ standard. When a lifetime of a temporary ends, and if the temporary lives in memory, the optimizing compiler has the freedom to reuse its stack space with other temporaries or scoped local variables whose live range does not overlap with it. However some of the legacy code relies on the behavior of older compilers in which temporaries stack space is not reused, the aggressive stack reuse can lead to runtime errors. This option is used to control the temporary stack reuse optimization.
This option generates traps for signed overflow on addition, subtraction, multiplication operations.
This option instructs the compiler to assume that signed arithmetic overflow of addition, subtraction and multiplication wraps around using twos-complement representation. This flag enables some optimizations and disables others. This option is enabled by default for the Java front end, as required by the Java language specification.
Enable exception handling. Generates extra code needed to propagate exceptions. For some targets, this implies GCC generates frame unwind information for all functions, which can produce significant data size overhead, although it does not affect execution. If you do not specify this option, GCC enables it by default for languages like C++ that normally require exception handling, and disables it for languages like C that do not normally require it. However, you may need to enable this option when compiling C code that needs to interoperate properly with exception handlers written in C++. You may also wish to disable this option if you are compiling older C++ programs that dont use exception handling.
Generate code that allows trapping instructions to throw exceptions. Note that this requires platform-specific runtime support that does not exist everywhere. Moreover, it only allows trapping instructions to throw exceptions, i.e. memory references or floating-point instructions. It does not allow exceptions to be thrown from arbitrary signal handlers such as SIGALRM.
Consider that instructions that may throw exceptions but dont otherwise contribute to the execution of the program can be optimized away. This option is enabled by default for the Ada front end, as permitted by the Ada language specification. Optimization passes that cause dead exceptions to be removed are enabled independently at different optimization levels.
Similar to -fexceptions, except that it just generates any needed static data, but does not affect the generated code in any other way. You normally do not need to enable this option; instead, a language processor that needs this handling enables it on your behalf.
Generate unwind table in DWARF 2 format, if supported by target machine. The table is exact at each instruction boundary, so it can be used for stack unwinding from asynchronous events (such as debugger or garbage collector).
On systems with recent GNU assembler and C library, the C++ compiler uses the STB_GNU_UNIQUE binding to make sure that definitions of template static data members and static local variables in inline functions are unique even in the presence of RTLD_LOCAL; this is necessary to avoid problems with a library used by two different RTLD_LOCAL plugins depending on a definition in one of them and therefore disagreeing with the other one about the binding of the symbol. But this causes dlclose to be ignored for affected DSOs; if your program relies on reinitialization of a DSO via dlclose and dlopen, you can use -fno-gnu-unique.
Return short struct and union values in memory like longer ones, rather than in registers. This convention is less efficient, but it has the advantage of allowing intercallability between GCC-compiled files and files compiled with other compilers, particularly the Portable C Compiler (pcc).
The precise convention for returning structures in memory depends on the target configuration macros.
Short structures and unions are those whose size and alignment match that of some integer type.
Warning: code compiled with the -fpcc-struct-return switch is not binary compatible with code compiled with the -freg-struct-return switch. Use it to conform to a non-default application binary interface.
Return struct and union values in registers when possible. This is more efficient for small structures than -fpcc-struct-return.
If you specify neither -fpcc-struct-return nor -freg-struct-return, GCC defaults to whichever convention is standard for the target. If there is no standard convention, GCC defaults to -fpcc-struct-return, except on targets where GCC is the principal compiler. In those cases, we can choose the standard, and we chose the more efficient register return alternative.
Warning: code compiled with the -freg-struct-return switch is not binary compatible with code compiled with the -fpcc-struct-return switch. Use it to conform to a non-default application binary interface.
Allocate to an enum type only as many bytes as it needs for the declared range of possible values. Specifically, the enum type is equivalent to the smallest integer type that has enough room.
Warning: the -fshort-enums switch causes GCC to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface.
Use the same size for double as for float.
Warning: the -fshort-double switch causes GCC to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface.
Override the underlying type for wchar_t to be short unsigned int instead of the default for the target. This option is useful for building programs to run under WINE
Warning: the -fshort-wchar switch causes GCC to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface.
In C code, controls the placement of uninitialized global variables. Unix C compilers have traditionally permitted multiple definitions of such variables in different compilation units by placing the variables in a common block. This is the behavior specified by -fcommon, and is the default for GCC on most targets. On the other hand, this behavior is not required by ISO C, and on some targets may carry a speed or code size penalty on variable references. The -fno-common option specifies that the compiler should place uninitialized global variables in the data section of the object file, rather than generating them as common blocks. This has the effect that if the same variable is declared (without extern) in two different compilations, you get a multiple-definition error when you link them. In this case, you must compile with -fcommon instead. Compiling with -fno-common is useful on targets for which it provides better performance, or if you wish to verify that the program will work on other systems that always treat uninitialized variable declarations this way.
Ignore the #ident directive.
Dont output a .size assembler directive, or anything else that would cause trouble if the function is split in the middle, and the two halves are placed at locations far apart in memory. This option is used when compiling crtstuff.c; you should not need to use it for anything else.
Put extra commentary information in the generated assembly code to make it more readable. This option is generally only of use to those who actually need to read the generated assembly code (perhaps while debugging the compiler itself).
-fno-verbose-asm, the default, causes the extra information to be omitted and is useful when comparing two assembler files.
This switch causes the command line used to invoke the compiler to be recorded into the object file that is being created. This switch is only implemented on some targets and the exact format of the recording is target and binary file format dependent, but it usually takes the form of a section containing ASCII text. This switch is related to the -fverbose-asm switch, but that switch only records information in the assembler output file as comments, so it never reaches the object file. See also -grecord-gcc-switches for another way of storing compiler options into the object file.
Generate position-independent code (PIC) suitable for use in a shared library, if supported for the target machine. Such code accesses all constant addresses through a global offset table (GOT) The dynamic loader resolves the GOT entries when the program starts (the dynamic loader is not part of GCC; it is part of the operating system). If the GOT size for the linked executable exceeds a machine-specific maximum size, you get an error message from the linker indicating that -fpic does not work; in that case, recompile with -fPIC instead. (These maximums are 8k on the SPARC and 32k on the m68k and RS/6000. The x86 has no such limit.)
Position-independent code requires special support, and therefore works only on certain machines. For the x86, GCC supports PIC for System V but not for the Sun 386i. Code generated for the IBM RS/6000 is always position-independent.
When this flag is set, the macros __pic__ and __PIC__ are defined to 1.
If supported for the target machine, emit position-independent code, suitable for dynamic linking and avoiding any limit on the size of the global offset table. This option makes a difference on the m68k, PowerPC and SPARC
Position-independent code requires special support, and therefore works only on certain machines.
When this flag is set, the macros __pic__ and __PIC__ are defined to 2.
These options are similar to -fpic and -fPIC, but generated position independent code can be only linked into executables. Usually these options are used when -pie GCC option is used during linking.
-fpie and -fPIE both define the macros __pie__ and __PIE__. The macros have the value 1 for -fpie and 2 for -fPIE.
Do not use PLT for external function calls in position-independent code. Instead, load callee address at call site from GOT and branch to it. This leads to more efficient code by eliminating PLT stubs and exposing GOT load to optimizations. On architectures such as 32-bit x86 where PLT stubs expect GOT pointer in a specific register, this gives more register allocation freedom to the compiler. Lazy binding requires PLT: with -fno-plt all external symbols are resolved at load time.
Do not use jump tables for switch statements even where it would be more efficient than other code generation strategies. This option is of use in conjunction with -fpic or -fPIC for building code that forms part of a dynamic linker and cannot reference the address of a jump table. On some targets, jump tables do not require a GOT and this option is not needed.
-ffixed-reg
Treat the register named reg as a fixed register; generated code should never refer to it (except perhaps as a stack pointer, frame pointer or in some other fixed role).
reg must be the name of a register. The register names accepted are machine-specific and are defined in the REGISTER_NAMES macro in the machine description macro file.
This flag does not have a negative form, because it specifies a three-way choice.
-fcall-used-reg
Treat the register named reg as an allocable register that is clobbered by function calls. It may be allocated for temporaries or variables that do not live across a call. Functions compiled this way do not save and restore the register reg.
It is an error to use this flag with the frame pointer or stack pointer. Use of this flag for other registers that have fixed pervasive roles in the machines execution model produces disastrous results.
This flag does not have a negative form, because it specifies a three-way choice.
-fcall-saved-reg
Treat the register named reg as an allocable register saved by functions. It may be allocated even for temporaries or variables that live across a call. Functions compiled this way save and restore the register reg if they use it.
It is an error to use this flag with the frame pointer or stack pointer. Use of this flag for other registers that have fixed pervasive roles in the machines execution model produces disastrous results.
A different sort of disaster results from the use of this flag for a register in which function values may be returned.
This flag does not have a negative form, because it specifies a three-way choice.
-fpack-struct[=``n``]
Without a value specified, pack all structure members together without holes. When a value is specified (which must be a small power of two), pack structure members according to this value, representing the maximum alignment (that is, objects with default alignment requirements larger than this are output potentially unaligned at the next fitting location.
Warning: the -fpack-struct switch causes GCC to generate code that is not binary compatible with code generated without that switch. Additionally, it makes the code suboptimal. Use it to conform to a non-default application binary interface.
Generate instrumentation calls for entry and exit to functions. Just after function entry and just before function exit, the following profiling functions are called with the address of the current function and its call site. (On some platforms, __builtin_return_address does not work beyond the current function, so the call site information may not be available to the profiling functions otherwise.)
void __cyg_profile_func_enter (void *this_fn,
void *call_site);
void __cyg_profile_func_exit (void *this_fn,
void *call_site);
The first argument is the address of the start of the current function, which may be looked up exactly in the symbol table.
This instrumentation is also done for functions expanded inline in other functions. The profiling calls indicate where, conceptually, the inline function is entered and exited. This means that addressable versions of such functions must be available. If all your uses of a function are expanded inline, this may mean an additional expansion of code size. If you use extern inline in your C code, an addressable version of such functions must be provided. (This is normally the case anyway, but if you get lucky and the optimizer always expands the functions inline, you might have gotten away without providing static copies.)
A function may be given the attribute no_instrument_function, in which case this instrumentation is not done. This can be used, for example, for the profiling functions listed above, high-priority interrupt routines, and any functions from which the profiling functions cannot safely be called (perhaps signal handlers, if the profiling routines generate output or allocate memory).
-finstrument-functions-exclude-file-list=``file``,``file``,...
Set the list of functions that are excluded from instrumentation (see the description of -finstrument-functions). If the file that contains a function definition matches with one of file, then that function is not instrumented. The match is done on substrings: if the file parameter is a substring of the file name, it is considered to be a match.
For example:
-finstrument-functions-exclude-file-list=/bits/stl,include/sys
excludes any inline function defined in files whose pathnames contain /bits/stl or include/sys.
If, for some reason, you want to include letter , in one of sym, write ,. For example, -finstrument-functions-exclude-file-list=',,tmp' (note the single quote surrounding the option).
-finstrument-functions-exclude-function-list=``sym``,``sym``,...
This is similar to -finstrument-functions-exclude-file-list, but this option sets the list of function names to be excluded from instrumentation. The function name to be matched is its user-visible name, such as vector<int> blah(const vector<int> &), not the internal mangled name (e.g., _Z4blahRSt6vectorIiSaIiEE). The match is done on substrings: if the sym parameter is a substring of the function name, it is considered to be a match. For C99 and C++ extended identifiers, the function name must be given in UTF-8, not using universal character names.
Generate code to verify that you do not go beyond the boundary of the stack. You should specify this flag if you are running in an environment with multiple threads, but you only rarely need to specify it in a single-threaded environment since stack overflow is automatically detected on nearly all systems if there is only one stack.
Note that this switch does not actually cause checking to be done; the operating system or the language runtime must do that. The switch causes generation of code to ensure that they see the stack being extended.
You can additionally specify a string parameter: no means no checking, generic means force the use of old-style checking, specific means use the best checking method and is equivalent to bare -fstack-check.
Old-style checking is a generic mechanism that requires no specific target support in the compiler but comes with the following drawbacks:
Note that old-style stack checking is also the fallback method for specific if no target support has been added in the compiler.
-fstack-limit-register=``reg``
-fstack-limit-symbol=``sym`` -fno-stack-limit
Generate code to ensure that the stack does not grow beyond a certain value, either the value of a register or the address of a symbol. If a larger stack is required, a signal is raised at run time. For most targets, the signal is raised before the stack overruns the boundary, so it is possible to catch the signal without taking special precautions.
For instance, if the stack starts at absolute address 0x80000000 and grows downwards, you can use the flags -fstack-limit-symbol=__stack_limit and -Wl,--defsym,__stack_limit=0x7ffe0000 to enforce a stack limit of 128KB Note that this may only work with the GNU linker.
Generate code to automatically split the stack before it overflows. The resulting program has a discontiguous stack which can only overflow if the program is unable to allocate any more memory. This is most useful when running threaded programs, as it is no longer necessary to calculate a good stack size to use for each thread. This is currently only implemented for the x86 targets running GNU/Linux.
When code compiled with -fsplit-stack calls code compiled without -fsplit-stack, there may not be much stack space available for the latter code to run. If compiling all code, including library code, with -fsplit-stack is not an option, then the linker can fix up these calls so that the code compiled without -fsplit-stack always has a large stack. Support for this is implemented in the gold linker in GNU binutils release 2.21 and later.
This option and its counterpart, -fno-leading-underscore, forcibly change the way C symbols are represented in the object file. One use is to help link with legacy assembly code.
Warning: the -fleading-underscore switch causes GCC to generate code that is not binary compatible with code generated without that switch. Use it to conform to a non-default application binary interface. Not all targets provide complete support for this switch.
-ftls-model=``model``
Alter the thread-local storage model to be used (Thread-Local). The model argument should be one of global-dynamic, local-dynamic, initial-exec or local-exec. Note that the choice is subject to optimization: the compiler may use a more efficient model for symbols not visible outside of the translation unit, or if -fpic is not given on the command line.
The default without -fpic is initial-exec; with -fpic the default is global-dynamic.
-fvisibility=[default|internal|hidden|protected]
Set the default ELF image symbol visibility to the specified optionall symbols are marked with this unless overridden within the code. Using this feature can very substantially improve linking and load times of shared object libraries, produce more optimized code, provide near-perfect API export and prevent symbol clashes. It is strongly recommended that you use this in any shared objects you distribute.
Despite the nomenclature, default always means public; i.e., available to be linked against from outside the shared object. protected and internal are pretty useless in real-world usage so the only other commonly used option is hidden. The default if -fvisibility isnt specified is default, i.e., make every symbol public.
A good explanation of the benefits offered by ensuring ELF symbols have the correct visibility is given by How To Write Shared Libraries by Ulrich Drepper (which can be found at http://www.akkadia.org/drepper/)however a superior solution made possible by this option to marking things hidden when the default is public is to make the default hidden and mark things public. This is the norm with DLLs on Windows and with -fvisibility=hidden and __attribute__ ((visibility("default"))) instead of __declspec(dllexport) you get almost identical semantics with identical syntax. This is a great boon to those working with cross-platform projects.
For those adding visibility support to existing code, you may find #pragma GCC visibility of use. This works by you enclosing the declarations you wish to set visibility for with (for example) #pragma GCC visibility push(hidden) and #pragma GCC visibility pop. Bear in mind that symbol visibility should be viewed as part of the API interface contract and thus all new code should always specify visibility when it is not the default; i.e., declarations only for use within the local DSO should always be marked explicitly as hidden as so to avoid PLT indirection overheadsmaking this abundantly clear also aids readability and self-documentation of the code. Note that due to ISO C++ specification requirements, operator new and operator delete must always be of default visibility.
Be aware that headers from outside your project, in particular system headers and headers from any other library you use, may not be expecting to be compiled with visibility other than the default. You may need to explicitly say #pragma GCC visibility push(default) before including any such headers.
extern declarations are not affected by -fvisibility, so a lot of code can be recompiled with -fvisibility=hidden with no modifications. However, this means that calls to extern functions with no explicit visibility use the PLT, so it is more effective to use __attribute ((visibility)) and/or #pragma GCC visibility to tell the compiler which extern declarations should be treated as hidden.
Note that -fvisibility does affect C++ vague linkage entities. This means that, for instance, an exception class that is be thrown between DSOs must be explicitly marked with default visibility so that the type_info nodes are unified between the DSOs.
An overview of these techniques, their benefits and how to use them is at http://gcc.gnu.org/wiki/Visibility.
This option should be used if accesses to volatile bit-fields (or other structure fields, although the compiler usually honors those types anyway) should use a single access of the width of the fields type, aligned to a natural alignment if possible. For example, targets with memory-mapped peripheral registers might require all such accesses to be 16 bits wide; with this flag you can declare all peripheral bit-fields as unsigned short (assuming short is 16 bits on these targets) to force GCC to use 16-bit accesses instead of, perhaps, a more efficient 32-bit access.
If this option is disabled, the compiler uses the most efficient instruction. In the previous example, that might be a 32-bit load instruction, even though that accesses bytes that do not contain any portion of the bit-field, or memory-mapped registers unrelated to the one being updated.
In some cases, such as when the packed attribute is applied to a structure field, it may not be possible to access the field with a single read or write that is correctly aligned for the target machine. In this case GCC falls back to generating multiple accesses rather than code that will fault or truncate the result at run time.
Note: Due to restrictions of the C/C++11 memory model, write accesses are not allowed to touch non bit-field members. It is therefore recommended to define all bits of the fields type as bit-field members.
The default value of this option is determined by the application binary interface for the target processor.
This option controls whether any out-of-line instance of the __sync family of functions may be used to implement the C++11 __atomic family of functions.
The default value of this option is enabled, thus the only useful form of the option is -fno-sync-libcalls. This option is used in the implementation of the libatomic runtime library.
:: _environment-variables:
This section describes several environment variables that affect how GCC operates. Some of them work by specifying directories or prefixes to use when searching for various kinds of files. Some are used to specify other aspects of the compilation environment.
Note that you can also specify places to search using options such as -B, -I and -L (Directory Options). These take precedence over places specified using environment variables, which in turn take precedence over those specified by the configuration of GCC DriverControlling the Compilation Driver gccgccintGNU Compiler Collection (GCC) Internals.
These environment variables control the way that GCC uses localization information which allows GCC to work with different national conventions. GCC inspects the locale categories LC_CTYPE and LC_MESSAGES if it has been configured to do so. These locale categories can be set to any value supported by your installation. A typical value is en_GB.UTF-8 for English in the United Kingdom encoded in UTF-8.
The LC_CTYPE environment variable specifies character classification. GCC uses it to determine the character boundaries in a string; this is needed for some multibyte encodings that contain quote and escape characters that are otherwise interpreted as a string end or escape.
The LC_MESSAGES environment variable specifies the language to use in diagnostic messages.
If the LC_ALL environment variable is set, it overrides the value of LC_CTYPE and LC_MESSAGES; otherwise, LC_CTYPE and LC_MESSAGES default to the value of the LANG environment variable. If none of these variables are set, GCC defaults to traditional C English behavior.
If TMPDIR is set, it specifies the directory to use for temporary files. GCC uses temporary files to hold the output of one stage of compilation which is to be used as input to the next stage: for example, the output of the preprocessor, which is the input to the compiler proper.
Setting GCC_COMPARE_DEBUG is nearly equivalent to passing -fcompare-debug to the compiler driver. See the documentation of this option for more details.
If GCC_EXEC_PREFIX is set, it specifies a prefix to use in the names of the subprograms executed by the compiler. No slash is added when this prefix is combined with the name of a subprogram, but you can specify a prefix that ends with a slash if you wish.
If GCC_EXEC_PREFIX is not set, GCC attempts to figure out an appropriate prefix to use based on the pathname it is invoked with.
If GCC cannot find the subprogram using the specified prefix, it tries looking in the usual places for the subprogram.
The default value of GCC_EXEC_PREFIX is prefix/lib/gcc/ where prefix is the prefix to the installed compiler. In many cases prefix is the value of prefix when you ran the configure script.
Other prefixes specified with -B take precedence over this prefix.
This prefix is also used for finding files such as crt0.o that are used for linking.
In addition, the prefix is used in an unusual way in finding the directories to search for header files. For each of the standard directories whose name normally begins with /usr/local/lib/gcc (more precisely, with the value of GCC_INCLUDE_DIR), GCC tries replacing that beginning with the specified prefix to produce an alternate directory name. Thus, with -Bfoo/, GCC searches foo/bar just before it searches the standard directory /usr/local/lib/bar. If a standard directory begins with the configured prefix then the value of prefix is replaced by GCC_EXEC_PREFIX when looking for header files.
The value of COMPILER_PATH is a colon-separated list of directories, much like PATH. GCC tries the directories thus specified when searching for subprograms, if it cant find the subprograms using GCC_EXEC_PREFIX.
The value of LIBRARY_PATH is a colon-separated list of directories, much like PATH. When configured as a native compiler, GCC tries the directories thus specified when searching for special linker files, if it cant find them using GCC_EXEC_PREFIX. Linking using GCC also uses these directories when searching for ordinary libraries for the -l option (but directories specified with -L come first).
This variable is used to pass locale information to the compiler. One way in which this information is used is to determine the character set to be used when character literals, string literals and comments are parsed in C and C++. When the compiler is configured to allow multibyte characters, the following values for LANG are recognized:
Recognize JIS characters.
Recognize SJIS characters.
Recognize EUCJP characters.
If LANG is not defined, or if it has some other value, then the compiler uses mblen and mbtowc as defined by the default locale to recognize and translate multibyte characters.
Some additional environment variables affect the behavior of the preprocessor.
:: _precompiled-headers:
Often large projects have many header files that are included in every source file. The time the compiler takes to process these header files over and over again can account for nearly all of the time required to build the project. To make builds faster, GCC allows you to precompile a header file.
To create a precompiled header file, simply compile it as you would any other file, if necessary using the -x option to make the driver treat it as a C or C++ header file. You may want to use a tool like make to keep the precompiled header up-to-date when the headers it contains change.
A precompiled header file is searched for when #include is seen in the compilation. As it searches for the included file (Search PathSearch PathcppThe C Preprocessor) the compiler looks for a precompiled header in each directory just before it looks for the include file in that directory. The name searched for is the name specified in the #include with .gch appended. If the precompiled header file cant be used, it is ignored.
For instance, if you have #include "all.h", and you have all.h.gch in the same directory as all.h, then the precompiled header file is used if possible, and the original header is used otherwise.
Alternatively, you might decide to put the precompiled header file in a directory and use -I to ensure that directory is searched before (or instead of) the directory containing the original header. Then, if you want to check that the precompiled header file is always used, you can put a file of the same name as the original header in this directory containing an #error command.
This also works with -include. So yet another way to use precompiled headers, good for projects not designed with precompiled header files in mind, is to simply take most of the header files used by a project, include them from another header file, precompile that header file, and -include the precompiled header. If the header files have guards against multiple inclusion, they are skipped because theyve already been included (in the precompiled header).
If you need to precompile the same header file for different languages, targets, or compiler options, you can instead make a directory named like all.h.gch, and put each precompiled header in the directory, perhaps using -o. It doesnt matter what you call the files in the directory; every precompiled header in the directory is considered. The first precompiled header encountered in the directory that is valid for this compilation is used; theyre searched in no particular order.
There are many other possibilities, limited only by your imagination, good sense, and the constraints of your build system.
A precompiled header file can be used only when these conditions apply:
Only one precompiled header can be used in a particular compilation.
A precompiled header cant be used once the first C token is seen. You can have preprocessor directives before a precompiled header; you cannot include a precompiled header from inside another header.
The precompiled header file must be produced for the same language as the current compilation. You cant use a C precompiled header for a C++ compilation.
The precompiled header file must have been produced by the same compiler binary as the current compilation is using.
Any macros defined before the precompiled header is included must either be defined in the same way as when the precompiled header was generated, or must not affect the precompiled header, which usually means that they dont appear in the precompiled header at all.
The -D option is one way to define a macro before a precompiled header is included; using a #define can also do it. There are also some options that define macros implicitly, like -O and -Wdeprecated; the same rule applies to macros defined this way.
If debugging information is output when using the precompiled header, using -g or similar, the same kind of debugging information must have been output when building the precompiled header. However, a precompiled header built using -g can be used in a compilation when no debugging information is being output.
The same -m options must generally be used when building and using the precompiled header. Submodel Options, for any cases where this rule is relaxed.
Each of the following options must be the same when building and using the precompiled header:
Some other command-line options starting with -f, -p, or -O must be defined in the same way as when the precompiled header was generated. At present, its not clear which options are safe to change and which are not; the safest choice is to use exactly the same options when generating and using the precompiled header. The following are known to be safe:
-fmessage-length= -fpreprocessed -fsched-interblock -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous -fsched-verbose=```number` -fschedule-insns -fvisibility= -pedantic-errors
For all of these except the last, the compiler automatically ignores the precompiled header if the conditions arent met. If you find an option combination that doesnt work and doesnt cause the precompiled header to be ignored, please consider filing a bug report, see Bugs.
If you do use differing options when generating and using the precompiled header, the actual behavior is a mixture of the behavior for the options. For instance, if you use -g to generate the precompiled header but not when using it, you may or may not get debugging information for routines in the precompiled header.
:: _c-implementation:
A conforming implementation of ISO C is required to document its choice of behavior in each of the areas that are designated implementation defined. The following lists all such areas, along with the section numbers from the ISO/IEC 9899:1990, ISO/IEC 9899:1999 and ISO/IEC 9899:2011 standards. Some areas are only implementation-defined in one version of the standard.
Some choices depend on the externally determined ABI for the platform (including standard character encodings) which GCC follows; these are listed as determined by ABI below. CompatibilityBinary Compatibility, and http://gcc.gnu.org/readings.html. Some choices are documented in the preprocessor manual. Implementation-defined behaviorImplementation-defined behaviorcppThe C Preprocessor. Some choices are made by the library and operating system (or other environment when compiling for a freestanding environment); refer to their documentation for details.
:: _translation-implementation:
How a diagnostic is identified (C90 3.7, C99 and C11 3.10, C90, C99 and C11 5.1.1.3).
Diagnostics consist of all the output sent to stderr by GCC
Whether each nonempty sequence of white-space characters other than new-line is retained or replaced by one space character in translation phase 3 (C90, C99 and C11 5.1.1.2).
Implementation-defined behaviorImplementation-defined behaviorcppThe C Preprocessor.
:: _environment-implementation:
The behavior of most of these points are dependent on the implementation of the C library, and are not defined by GCC itself.
The mapping between physical source file multibyte characters and the source character set in translation phase 1 (C90, C99 and C11 5.1.1.2).
Implementation-defined behaviorImplementation-defined behaviorcppThe C Preprocessor.
:: _identifiers-implementation:
Which additional multibyte characters may appear in identifiers and their correspondence to universal character names (C99 and C11 6.4.2).
Implementation-defined behaviorImplementation-defined behaviorcppThe C Preprocessor.
The number of significant initial characters in an identifier (C90 6.1.2, C90, C99 and C11 5.2.4.1, C99 and C11 6.4.2).
For internal names, all characters are significant. For external names, the number of significant characters are defined by the linker; for almost all targets, all characters are significant.
Whether case distinctions are significant in an identifier with external linkage (C90 6.1.2).
This is a property of the linker. C99 and C11 require that case distinctions are always significant in identifiers with external linkage and systems without this property are not supported by GCC
:: _characters-implementation:
The number of bits in a byte (C90 3.4, C99 and C11 3.6).
Determined by ABI
The values of the members of the execution character set (C90, C99 and C11 5.2.1).
Determined by ABI
The unique value of the member of the execution character set produced for each of the standard alphabetic escape sequences (C90, C99 and C11 5.2.2).
Determined by ABI
The value of a char object into which has been stored any character other than a member of the basic execution character set (C90 6.1.2.5, C99 and C11 6.2.5).
Determined by ABI
Which of signed char or unsigned char has the same range, representation, and behavior as plain char (C90 6.1.2.5, C90 6.2.1.1, C99 and C11 6.2.5, C99 and C11 6.3.1.1).
Determined by ABI The options -funsigned-char and -fsigned-char change the default. C Dialect OptionsOptions Controlling C Dialect.
The mapping of members of the source character set (in character constants and string literals) to members of the execution character set (C90 6.1.3.4, C99 and C11 6.4.4.4, C90, C99 and C11 5.1.1.2).
Determined by ABI
The value of an integer character constant containing more than one character or containing a character or escape sequence that does not map to a single-byte execution character (C90 6.1.3.4, C99 and C11 6.4.4.4).
Implementation-defined behaviorImplementation-defined behaviorcppThe C Preprocessor.
The value of a wide character constant containing more than one multibyte character or a single multibyte character that maps to multiple members of the extended execution character set, or containing a multibyte character or escape sequence not represented in the extended execution character set (C90 6.1.3.4, C99 and C11 6.4.4.4).
Implementation-defined behaviorImplementation-defined behaviorcppThe C Preprocessor.
The current locale used to convert a wide character constant consisting of a single multibyte character that maps to a member of the extended execution character set into a corresponding wide character code (C90 6.1.3.4, C99 and C11 6.4.4.4).
Implementation-defined behaviorImplementation-defined behaviorcppThe C Preprocessor.
Whether differently-prefixed wide string literal tokens can be concatenated and, if so, the treatment of the resulting multibyte character sequence (C11 6.4.5).
Such tokens may not be concatenated.
The current locale used to convert a wide string literal into corresponding wide character codes (C90 6.1.4, C99 and C11 6.4.5).
Implementation-defined behaviorImplementation-defined behaviorcppThe C Preprocessor.
The value of a string literal containing a multibyte character or escape sequence not represented in the execution character set (C90 6.1.4, C99 and C11 6.4.5).
Implementation-defined behaviorImplementation-defined behaviorcppThe C Preprocessor.
The encoding of any of wchar_t, char16_t, and char32_t where the corresponding standard encoding macro (__STDC_ISO_10646__, __STDC_UTF_16__, or __STDC_UTF_32__) is not defined (C11 6.10.8.2).
Implementation-defined behaviorImplementation-defined behaviorcppThe C Preprocessor. char16_t and char32_t literals are always encoded in UTF-16 and UTF-32 respectively.
:: _integers-implementation:
Any extended integer types that exist in the implementation (C99 and C11 6.2.5).
GCC does not support any extended integer types.
Whether signed integer types are represented using sign and magnitude, twos complement, or ones complement, and whether the extraordinary value is a trap representation or an ordinary value (C99 and C11 6.2.6.2).
GCC supports only twos complement integer types, and all bit patterns are ordinary values.
The rank of any extended integer type relative to another extended integer type with the same precision (C99 and C11 6.3.1.1).
GCC does not support any extended integer types.
The result of, or the signal raised by, converting an integer to a signed integer type when the value cannot be represented in an object of that type (C90 6.2.1.2, C99 and C11 6.3.1.3).
For conversion to a type of width N, the value is reduced modulo 2^N to be within range of the type; no signal is raised.
The results of some bitwise operations on signed integers (C90 6.3, C99 and C11 6.5).
Bitwise operators act on the representation of the value including both the sign and value bits, where the sign bit is considered immediately above the highest-value value bit. Signed >> acts on negative numbers by sign extension.
GCC does not use the latitude given in C99 and C11 only to treat certain aspects of signed << as undefined, but this is subject to change.
The sign of the remainder on integer division (C90 6.3.5).
GCC always follows the C99 and C11 requirement that the result of division is truncated towards zero.
:: _floating-point-implementation:
The accuracy of the floating-point operations and of the library functions in <math.h> and <complex.h> that return floating-point results (C90, C99 and C11 5.2.4.2.2).
The accuracy is unknown.
The rounding behaviors characterized by non-standard values of FLT_ROUNDS (C90, C99 and C11 5.2.4.2.2).
GCC does not use such values.
The evaluation methods characterized by non-standard negative values of FLT_EVAL_METHOD (C99 and C11 5.2.4.2.2).
GCC does not use such values.
The direction of rounding when an integer is converted to a floating-point number that cannot exactly represent the original value (C90 6.2.1.3, C99 and C11 6.3.1.4).
C99 Annex F is followed.
The direction of rounding when a floating-point number is converted to a narrower floating-point number (C90 6.2.1.4, C99 and C11 6.3.1.5).
C99 Annex F is followed.
How the nearest representable value or the larger or smaller representable value immediately adjacent to the nearest representable value is chosen for certain floating constants (C90 6.1.3.1, C99 and C11 6.4.4.2).
C99 Annex F is followed.
Whether and how floating expressions are contracted when not disallowed by the FP_CONTRACT pragma (C99 and C11 6.5).
Expressions are currently only contracted if -ffp-contract=fast, -funsafe-math-optimizations or -ffast-math are used. This is subject to change.
The default state for the FENV_ACCESS pragma (C99 and C11 7.6.1).
This pragma is not implemented, but the default is to off unless -frounding-math is used in which case it is on.
Additional floating-point exceptions, rounding modes, environments, and classifications, and their macro names (C99 and C11 7.6, C99 and C11 7.12).
This is dependent on the implementation of the C library, and is not defined by GCC itself.
The default state for the FP_CONTRACT pragma (C99 and C11 7.12.2).
This pragma is not implemented. Expressions are currently only contracted if -ffp-contract=fast, -funsafe-math-optimizations or -ffast-math are used. This is subject to change.
Whether the inexact floating-point exception can be raised when the rounded result actually does equal the mathematical result in an IEC 60559 conformant implementation (C99 F.9).
This is dependent on the implementation of the C library, and is not defined by GCC itself.
Whether the underflow (and inexact) floating-point exception can be raised when a result is tiny but not inexact in an IEC 60559 conformant implementation (C99 F.9).
This is dependent on the implementation of the C library, and is not defined by GCC itself.
:: _arrays-and-pointers-implementation:
The result of converting a pointer to an integer or vice versa (C90 6.3.4, C99 and C11 6.3.2.3).
A cast from pointer to integer discards most-significant bits if the pointer representation is larger than the integer type, sign-extendsFuture versions of GCC may zero-extend, or use a target-defined ptr_extend pattern. Do not rely on sign extension. if the pointer representation is smaller than the integer type, otherwise the bits are unchanged.
A cast from integer to pointer discards most-significant bits if the pointer representation is smaller than the integer type, extends according to the signedness of the integer type if the pointer representation is larger than the integer type, otherwise the bits are unchanged.
When casting from pointer to integer and back again, the resulting pointer must reference the same object as the original pointer, otherwise the behavior is undefined. That is, one may not use integer arithmetic to avoid the undefined behavior of pointer arithmetic as proscribed in C99 and C11 6.5.6/8.
The size of the result of subtracting two pointers to elements of the same array (C90 6.3.6, C99 and C11 6.5.6).
The value is as specified in the standard and the type is determined by the ABI
:: _hints-implementation:
The extent to which suggestions made by using the register storage-class specifier are effective (C90 6.5.1, C99 and C11 6.7.1).
The register specifier affects code generation only in these ways:
The extent to which suggestions made by using the inline function specifier are effective (C99 and C11 6.7.4).
GCC will not inline any functions if the -fno-inline option is used or if -O0 is used. Otherwise, GCC may still be unable to inline a function for many reasons; the -Winline option may be used to determine if a function has not been inlined and why not.
:: _structures-unions-enumerations-and-bit-fields-implementation:
A member of a union object is accessed using a member of a different type (C90 6.3.2.3).
The relevant bytes of the representation of the object are treated as an object of the type used for the access. Type-punning. This may be a trap representation.
Whether a plain int bit-field is treated as a signed int bit-field or as an unsigned int bit-field (C90 6.5.2, C90 6.5.2.1, C99 and C11 6.7.2, C99 and C11 6.7.2.1).
By default it is treated as signed int but this may be changed by the -funsigned-bitfields option.
Allowable bit-field types other than _Bool, signed int, and unsigned int (C99 and C11 6.7.2.1).
Other integer types, such as long int, and enumerated types are permitted even in strictly conforming mode.
Whether atomic types are permitted for bit-fields (C11 6.7.2.1).
Atomic types are not permitted for bit-fields.
Whether a bit-field can straddle a storage-unit boundary (C90 6.5.2.1, C99 and C11 6.7.2.1).
Determined by ABI
The order of allocation of bit-fields within a unit (C90 6.5.2.1, C99 and C11 6.7.2.1).
Determined by ABI
The alignment of non-bit-field members of structures (C90 6.5.2.1, C99 and C11 6.7.2.1).
Determined by ABI
The integer type compatible with each enumerated type (C90 6.5.2.2, C99 and C11 6.7.2.2).
Normally, the type is unsigned int if there are no negative values in the enumeration, otherwise int. If -fshort-enums is specified, then if there are negative values it is the first of signed char, short and int that can represent all the values, otherwise it is the first of unsigned char, unsigned short and unsigned int that can represent all the values.
On some targets, -fshort-enums is the default; this is determined by the ABI
:: _qualifiers-implementation:
What constitutes an access to an object that has volatile-qualified type (C90 6.5.3, C99 and C11 6.7.3).
Such an object is normally accessed by pointers and used for accessing hardware. In most expressions, it is intuitively obvious what is a read and what is a write. For example
volatile int *dst = ``somevalue``;
volatile int *src = ``someothervalue``;
*dst = *src;
will cause a read of the volatile object pointed to by src and store the value into the volatile object pointed to by dst. There is no guarantee that these reads and writes are atomic, especially for objects larger than int.
However, if the volatile storage is not being modified, and the value of the volatile storage is not used, then the situation is less obvious. For example
volatile int *src = ``somevalue``;
*src;
According to the C standard, such an expression is an rvalue whose type is the unqualified version of its original type, i.e. int. Whether GCC interprets this as a read of the volatile object being pointed to or only as a request to evaluate the expression for its side-effects depends on this type.
If it is a scalar type, or on most targets an aggregate type whose only member object is of a scalar type, or a union type whose member objects are of scalar types, the expression is interpreted by GCC as a read of the volatile object; in the other cases, the expression is only evaluated for its side-effects.
:: _declarators-implementation:
The maximum number of declarators that may modify an arithmetic, structure or union type (C90 6.5.4).
GCC is only limited by available memory.
:: _statements-implementation:
The maximum number of case values in a switch statement (C90 6.6.4.2).
GCC is only limited by available memory.
:: _preprocessing-directives-implementation:
Implementation-defined behaviorImplementation-defined behaviorcppThe C Preprocessor, for details of these aspects of implementation-defined behavior.
The locations within #pragma directives where header name preprocessing tokens are recognized (C11 6.4, C11 6.4.7).
How sequences in both forms of header names are mapped to headers or external source file names (C90 6.1.7, C99 and C11 6.4.7).
Whether the value of a character constant in a constant expression that controls conditional inclusion matches the value of the same character constant in the execution character set (C90 6.8.1, C99 and C11 6.10.1).
Whether the value of a single-character character constant in a constant expression that controls conditional inclusion may have a negative value (C90 6.8.1, C99 and C11 6.10.1).
The places that are searched for an included <> delimited header, and how the places are specified or the header is identified (C90 6.8.2, C99 and C11 6.10.2).
How the named source file is searched for in an included “” delimited header (C90 6.8.2, C99 and C11 6.10.2).
The method by which preprocessing tokens (possibly resulting from macro expansion) in a #include directive are combined into a header name (C90 6.8.2, C99 and C11 6.10.2).
The nesting limit for #include processing (C90 6.8.2, C99 and C11 6.10.2).
Whether the # operator inserts a character before the character that begins a universal character name in a character constant or string literal (C99 and C11 6.10.3.2).
The behavior on each recognized non-STDC #pragma directive (C90 6.8.6, C99 and C11 6.10.6).
PragmasPragmascppThe C Preprocessor, for details of pragmas accepted by GCC on all targets. PragmasPragmas Accepted by GCC, for details of target-specific pragmas.
The definitions for __DATE__ and __TIME__ when respectively, the date and time of translation are not available (C90 6.8.8, C99 6.10.8, C11 6.10.8.1).
:: _library-functions-implementation:
The behavior of most of these points are dependent on the implementation of the C library, and are not defined by GCC itself.
The null pointer constant to which the macro NULL expands (C90 7.1.6, C99 7.17, C11 7.19).
In <stddef.h>, NULL expands to ((void *)0). GCC does not provide the other headers which define NULL and some library implementations may use other definitions in those headers.
:: _architecture-implementation:
The values or expressions assigned to the macros specified in the headers <float.h>, <limits.h>, and <stdint.h> (C90, C99 and C11 5.2.4.2, C99 7.18.2, C99 7.18.3, C11 7.20.2, C11 7.20.3).
Determined by ABI
The result of attempting to indirectly access an object with automatic or thread storage duration from a thread other than the one with which it is associated (C11 6.2.4).
Such accesses are supported, subject to the same requirements for synchronization for concurrent accesses as for concurrent accesses to any object.
The number, order, and encoding of bytes in any object (when not explicitly specified in this International Standard) (C99 and C11 6.2.6.1).
Determined by ABI
Whether any extended alignments are supported and the contexts in which they are supported (C11 6.2.8).
Extended alignments up to 2^{28} (bytes) are supported for objects of automatic storage duration. Alignments supported for objects of static and thread storage duration are determined by the ABI.
Valid alignment values other than those returned by an _Alignof expression for fundamental types, if any (C11 6.2.8).
Valid alignments are powers of 2 up to and including 2^{28}.
The value of the result of the sizeof and _Alignof operators (C90 6.3.3.4, C99 and C11 6.5.3.4).
Determined by ABI
:: _locale-specific-behavior-implementation:
The behavior of these points are dependent on the implementation of the C library, and are not defined by GCC itself.
:: _c++-implementation:
A conforming implementation of ISO C++ is required to document its choice of behavior in each of the areas that are designated implementation defined. The following lists all such areas, along with the section numbers from the ISO/IEC 14882:1998 and ISO/IEC 14882:2003 standards. Some areas are only implementation-defined in one version of the standard.
Some choices depend on the externally determined ABI for the platform (including standard character encodings) which GCC follows; these are listed as determined by ABI below. CompatibilityBinary Compatibility, and http://gcc.gnu.org/readings.html. Some choices are documented in the preprocessor manual. Implementation-defined behaviorImplementation-defined behaviorcppThe C Preprocessor. Some choices are documented in the corresponding document for the C language. C Implementation. Some choices are made by the library and operating system (or other environment when compiling for a freestanding environment); refer to their documentation for details.
:: _conditionally-supported-behavior:
Each implementation shall include documentation that identifies all conditionally-supported constructs that it does not support (C++0x 1.4).
Whether an argument of class type with a non-trivial copy constructor or destructor can be passed to ... (C++0x 5.2.2).
Such argument passing is supported, using the same pass-by-invisible-reference approach used for normal function arguments of such types.
:: _exception-handling:
In the situation where no matching handler is found, it is implementation-defined whether or not the stack is unwound before std::terminate() is called (C++98 15.5.1).
The stack is not unwound before std::terminate is called.
:: _c-extensions:
GNU C provides several language features not found in ISO standard C (The -pedantic option directs GCC to print a warning message if any of these features is used.) To test for the availability of these features in conditional compilation, check for a predefined macro __GNUC__, which is always defined under GCC
These extensions are available in C and Objective-C Most of them are also available in C++. C++ ExtensionsExtensions to the C++ Language, for extensions that apply only to C++.
Some features that are in ISO C99 but not C90 or C++ are also, as extensions, accepted by GCC in C90 mode and in C++.
:: _statement-exprs:
A compound statement enclosed in parentheses may appear as an expression in GNU C This allows you to use loops, switches, and local variables within an expression.
Recall that a compound statement is a sequence of statements surrounded by braces; in this construct, parentheses go around the braces. For example:
({ int y = foo (); int z;
if (y > 0) z = y;
else z = - y;
z; })
is a valid (though slightly more complex than necessary) expression for the absolute value of foo ().
The last thing in the compound statement should be an expression followed by a semicolon; the value of this subexpression serves as the value of the entire construct. (If you use some other kind of statement last within the braces, the construct has type void, and thus effectively no value.)
This feature is especially useful in making macro definitions safe (so that they evaluate each operand exactly once). For example, the maximum function is commonly defined as a macro in standard C as follows:
#define max(a,b) ((a) > (b) ? (a) : (b))
But this definition computes either a or b twice, with bad results if the operand has side effects. In GNU C, if you know the type of the operands (here taken as int), you can define the macro safely as follows:
#define maxint(a,b) \
({int _a = (a), _b = (b); _a > _b ? _a : _b; })
Embedded statements are not allowed in constant expressions, such as the value of an enumeration constant, the width of a bit-field, or the initial value of a static variable.
If you dont know the type of the operand, you can still do this, but you must use typeof or __auto_type (Typeof).
In G++, the result value of a statement expression undergoes array and function pointer decay, and is returned by value to the enclosing expression. For instance, if A is a class, then
A a;
({a;}).Foo ()
constructs a temporary A object to hold the result of the statement expression, and that is used to invoke Foo. Therefore the this pointer observed by Foo is not the address of a.
In a statement expression, any temporaries created within a statement are destroyed at that statements end. This makes statement expressions inside macros slightly different from function calls. In the latter case temporaries introduced during argument evaluation are destroyed at the end of the statement that includes the function call. In the statement expression case they are destroyed during the statement expression. For instance,
#define macro(a) ({__typeof__(a) b = (a); b + 3; })
template<typename T> T function(T a) { T b = a; return b + 3; }
void foo ()
{
macro (X ());
function (X ());
}
has different places where temporaries are destroyed. For the macro case, the temporary X is destroyed just after the initialization of b. In the function case that temporary is destroyed when the function returns.
These considerations mean that it is probably a bad idea to use statement expressions of this form in header files that are designed to work with C++. (Note that some versions of the GNU C Library contained header files using statement expressions that lead to precisely this bug.)
Jumping into a statement expression with goto or using a switch statement outside the statement expression with a case or default label inside the statement expression is not permitted. Jumping into a statement expression with a computed goto (Labels as Values) has undefined behavior. Jumping out of a statement expression is permitted, but if the statement expression is part of a larger expression then it is unspecified which other subexpressions of that expression have been evaluated except where the language definition requires certain subexpressions to be evaluated before or after the statement expression. In any case, as with a function call, the evaluation of a statement expression is not interleaved with the evaluation of other parts of the containing expression. For example,
foo (), (({ bar1 (); goto a; 0; }) + bar2 ()), baz();
calls foo and bar1 and does not call baz but may or may not call bar2. If bar2 is called, it is called after foo and before bar1.
:: _local-labels:
GCC allows you to declare local labels in any nested block scope. A local label is just like an ordinary label, but you can only reference it (with a goto statement, or by taking its address) within the block in which it is declared.
A local label declaration looks like this:
__label__ ``label``;
or
__label__ ``label1``, ``label2``, /* ... */;
Local label declarations must come at the beginning of the block, before any ordinary declarations or statements.
The label declaration defines the label name, but does not define the label itself. You must do this in the usual way, with ``label:``, within the statements of the statement expression.
The local label feature is useful for complex macros. If a macro contains nested loops, a goto can be useful for breaking out of them. However, an ordinary label whose scope is the whole function cannot be used: if the macro can be expanded several times in one function, the label is multiply defined in that function. A local label avoids this problem. For example:
#define SEARCH(value, array, target) \
do { \
__label__ found; \
typeof (target) _SEARCH_target = (target); \
typeof (*(array)) *_SEARCH_array = (array); \
int i, j; \
int value; \
for (i = 0; i < max; i++) \
for (j = 0; j < max; j++) \
if (_SEARCH_array[i][j] == _SEARCH_target) \
{ (value) = i; goto found; } \
(value) = -1; \
found:; \
} while (0)
This could also be written using a statement expression:
#define SEARCH(array, target) \
({ \
__label__ found; \
typeof (target) _SEARCH_target = (target); \
typeof (*(array)) *_SEARCH_array = (array); \
int i, j; \
int value; \
for (i = 0; i < max; i++) \
for (j = 0; j < max; j++) \
if (_SEARCH_array[i][j] == _SEARCH_target) \
{ value = i; goto found; } \
value = -1; \
found: \
value; \
})
Local label declarations also make the labels they declare visible to nested functions, if there are any. Nested Functions, for details.
:: _labels-as-values:
You can get the address of a label defined in the current function (or a containing function) with the unary operator &&. The value has type void *. This value is a constant and can be used wherever a constant of that type is valid. For example:
void *ptr;
/* ... */
ptr = &&foo;
To use these values, you need to be able to jump to one. This is done with the computed goto statementThe analogous feature in Fortran is called an assigned goto, but that name seems inappropriate in C, where one can do more than simply store label addresses in label variables., goto *``exp;``. For example,
goto *ptr;
Any expression of type void * is allowed.
One way of using these constants is in initializing a static array that serves as a jump table:
static void *array[] = { &&foo, &&bar, &&hack };
Then you can select a label with indexing, like this:
goto *array[i];
Note that this does not check whether the subscript is in boundsarray indexing in C never does that.
Such an array of label values serves a purpose much like that of the switch statement. The switch statement is cleaner, so use that rather than an array unless the problem does not fit a switch statement very well.
Another use of label values is in an interpreter for threaded code. The labels within the interpreter function can be stored in the threaded code for super-fast dispatching.
You may not use this mechanism to jump to code in a different function. If you do that, totally unpredictable things happen. The best way to avoid this is to store the label address only in automatic variables and never pass it as an argument.
An alternate way to write the above example is
static const int array[] = { &&foo - &&foo, &&bar - &&foo,
&&hack - &&foo };
goto *(&&foo + array[i]);
This is more friendly to code living in shared libraries, as it reduces the number of dynamic relocations that are needed, and by consequence, allows the data to be read-only. This alternative with label differences is not supported for the AVR target, please use the first approach for AVR programs.
The &&foo expressions for the same label might have different values if the containing function is inlined or cloned. If a program relies on them being always the same, __attribute__((__noinline__,__noclone__)) should be used to prevent inlining and cloning. If &&foo is used in a static variable initializer, inlining and cloning is forbidden.
:: _nested-functions:
A nested function is a function defined inside another function. Nested functions are supported as an extension in GNU C, but are not supported by GNU C++.
The nested functions name is local to the block where it is defined. For example, here we define a nested function named square, and call it twice:
foo (double a, double b)
{
double square (double z) { return z * z; }
return square (a) + square (b);
}
The nested function can access all the variables of the containing function that are visible at the point of its definition. This is called lexical scoping. For example, here we show a nested function which uses an inherited variable named offset:
bar (int *array, int offset, int size)
{
int access (int *array, int index)
{ return array[index + offset]; }
int i;
/* ... */
for (i = 0; i < size; i++)
/* ... */ access (array, i) /* ... */
}
Nested function definitions are permitted within functions in the places where variable definitions are allowed; that is, in any block, mixed with the other declarations and statements in the block.
It is possible to call the nested function from outside the scope of its name by storing its address or passing the address to another function:
hack (int *array, int size)
{
void store (int index, int value)
{ array[index] = value; }
intermediate (store, size);
}
Here, the function intermediate receives the address of store as an argument. If intermediate calls store, the arguments given to store are used to store into array. But this technique works only so long as the containing function (hack, in this example) does not exit.
If you try to call the nested function through its address after the containing function exits, all hell breaks loose. If you try to call it after a containing scope level exits, and if it refers to some of the variables that are no longer in scope, you may be lucky, but its not wise to take the risk. If, however, the nested function does not refer to anything that has gone out of scope, you should be safe.
GCC implements taking the address of a nested function using a technique called trampolines. This technique was described in Lexical Closures for C++ (Thomas M. Breuel, USENIX C++ Conference Proceedings, October 17-21, 1988).
A nested function can jump to a label inherited from a containing function, provided the label is explicitly declared in the containing function (Local Labels). Such a jump returns instantly to the containing function, exiting the nested function that did the goto and any intermediate functions as well. Here is an example:
bar (int *array, int offset, int size)
{
__label__ failure;
int access (int *array, int index)
{
if (index > size)
goto failure;
return array[index + offset];
}
int i;
/* ... */
for (i = 0; i < size; i++)
/* ... */ access (array, i) /* ... */
/* ... */
return 0;
/* Control comes here from ``access``
if it detects an error. */
failure:
return -1;
}
A nested function always has no linkage. Declaring one with extern or static is erroneous. If you need to declare the nested function before its definition, use auto (which is otherwise meaningless for function declarations).
bar (int *array, int offset, int size)
{
__label__ failure;
auto int access (int *, int);
/* ... */
int access (int *array, int index)
{
if (index > size)
goto failure;
return array[index + offset];
}
/* ... */
}
:: _constructing-calls:
Using the built-in functions described below, you can record the arguments a function received, and call another function with the same arguments, without knowing the number or types of the arguments.
You can also record the return value of that function call, and later return that value, without knowing what data type the function tried to return (as long as your caller expects that data type).
However, these built-in functions may interact badly with some sophisticated features or other extensions of the language. It is, therefore, not recommended to use them outside very simple functions acting as mere forwarders for their arguments.
This built-in function returns a pointer to data describing how to perform a call with the same arguments as are passed to the current function.
The function saves the arg pointer register, structure value address, and all registers that might be used to pass arguments to a function into a block of memory allocated on the stack. Then it returns the address of that block.
This built-in function invokes function with a copy of the parameters described by arguments and size.
The value of arguments should be the value returned by __builtin_apply_args. The argument size specifies the size of the stack argument data, in bytes.
This function returns a pointer to data describing how to return whatever value is returned by function. The data is saved in a block of memory allocated on the stack.
It is not always simple to compute the proper value for size. The value is used by __builtin_apply to compute the amount of data that should be pushed on the stack and copied from the incoming argument area.
This built-in function returns the value described by result from the containing function. You should specify, for result, a value returned by __builtin_apply.
This built-in function represents all anonymous arguments of an inline function. It can be used only in inline functions that are always inlined, never compiled as a separate function, such as those using __attribute__ ((__always_inline__)) or __attribute__ ((__gnu_inline__)) extern inline functions. It must be only passed as last argument to some other function with variable arguments. This is useful for writing small wrapper inlines for variable argument functions, when using preprocessor macros is undesirable. For example:
extern int myprintf (FILE *f, const char *format, ...);
extern inline __attribute__ ((__gnu_inline__)) int
myprintf (FILE *f, const char *format, ...)
{
int r = fprintf (f, "myprintf: ");
if (r < 0)
return r;
int s = fprintf (f, format, __builtin_va_arg_pack ());
if (s < 0)
return s;
return r + s;
}
This built-in function returns the number of anonymous arguments of an inline function. It can be used only in inline functions that are always inlined, never compiled as a separate function, such as those using __attribute__ ((__always_inline__)) or __attribute__ ((__gnu_inline__)) extern inline functions. For example following does link- or run-time checking of open arguments for optimized code:
#ifdef __OPTIMIZE__
extern inline __attribute__((__gnu_inline__)) int
myopen (const char *path, int oflag, ...)
{
if (__builtin_va_arg_pack_len () > 1)
warn_open_too_many_arguments ();
if (__builtin_constant_p (oflag))
{
if ((oflag & O_CREAT) != 0 && __builtin_va_arg_pack_len () < 1)
{
warn_open_missing_mode ();
return __open_2 (path, oflag);
}
return open (path, oflag, __builtin_va_arg_pack ());
}
if (__builtin_va_arg_pack_len () < 1)
return __open_2 (path, oflag);
return open (path, oflag, __builtin_va_arg_pack ());
}
#endif
:: _typeof:
Referring to a Type with typeof
Another way to refer to the type of an expression is with typeof. The syntax of using of this keyword looks like sizeof, but the construct acts semantically like a type name defined with typedef.
There are two ways of writing the argument to typeof: with an expression or with a type. Here is an example with an expression:
typeof (x[0](1))
This assumes that x is an array of pointers to functions; the type described is that of the values of the functions.
Here is an example with a typename as the argument:
typeof (int *)
Here the type described is that of pointers to int.
If you are writing a header file that must work when included in ISO C programs, write __typeof__ instead of typeof. Alternate Keywords.
A typeof construct can be used anywhere a typedef name can be used. For example, you can use it in a declaration, in a cast, or inside of sizeof or typeof.
The operand of typeof is evaluated for its side effects if and only if it is an expression of variably modified type or the name of such a type.
typeof is often useful in conjunction with statement expressions (Statement Exprs). Here is how the two together can be used to define a safe maximum macro which operates on any arithmetic type and evaluates each of its arguments exactly once:
#define max(a,b) \
({ typeof (a) _a = (a); \
typeof (b) _b = (b); \
_a > _b ? _a : _b; })
_ in variables in macros
The reason for using names that start with underscores for the local variables is to avoid conflicts with variable names that occur within the expressions that are substituted for a and b. Eventually we hope to design a new form of declaration syntax that allows you to declare variables whose scopes start only after their initializers; this will be a more reliable way to prevent such conflicts.
Some more examples of the use of typeof:
This declares y with the type of what x points to.
typeof (*x) y;
This declares y as an array of such values.
typeof (*x) y[4];
This declares y as an array of pointers to characters:
typeof (typeof (char *)[4]) y;
It is equivalent to the following traditional C declaration:
char *y[4];
To see the meaning of the declaration using typeof, and why it might be a useful way to write, rewrite it with these macros:
#define pointer(T) typeof(T *)
#define array(T, N) typeof(T [N])
Now the declaration can be rewritten this way:
array (pointer (char), 4) y;
Thus, array (pointer (char), 4) is the type of arrays of 4 pointers to char.
In GNU C, but not GNU C++, you may also declare the type of a variable as __auto_type. In that case, the declaration must declare only one variable, whose declarator must just be an identifier, the declaration must be initialized, and the type of the variable is determined by the initializer; the name of the variable is not in scope until after the initializer. (In C++, you should use C++11 auto for this purpose.) Using __auto_type, the maximum macro above could be written as:
#define max(a,b) \
({ __auto_type _a = (a); \
__auto_type _b = (b); \
_a > _b ? _a : _b; })
Using __auto_type instead of typeof has two advantages:
:: _conditionals:
extensions, ?: ?: extensions
The middle operand in a conditional expression may be omitted. Then if the first operand is nonzero, its value is the value of the conditional expression.
Therefore, the expression
x ? : y
has the value of x if that is nonzero; otherwise, the value of y.
This example is perfectly equivalent to
x ? x : y
side effect in ?: ?: side effect
In this simple case, the ability to omit the middle operand is not especially useful. When it becomes useful is when the first operand does, or may (if it is a macro argument), contain a side effect. Then repeating the operand in the middle would perform the side effect twice. Omitting the middle operand uses the value already computed without the undesirable effects of recomputing it.
:: ___int128:
__int128 data types
As an extension the integer scalar type __int128 is supported for targets which have an integer mode wide enough to hold 128 bits. Simply write __int128 for a signed 128-bit integer, or unsigned __int128 for an unsigned 128-bit integer. There is no support in GCC for expressing an integer constant of type __int128 for targets with long long integer less than 128 bits wide.
:: _long-long:
long long data types
LL integer suffix ULL integer suffix
ISO C99 supports data types for integers that are at least 64 bits wide, and as an extension GCC supports them in C90 mode and in C++. Simply write long long int for a signed integer, or unsigned long long int for an unsigned integer. To make an integer constant of type long long int, add the suffix LL to the integer. To make an integer constant of type unsigned long long int, add the suffix ULL to the integer.
You can use these types in arithmetic like any other integer types. Addition, subtraction, and bitwise boolean operations on these types are open-coded on all types of machines. Multiplication is open-coded if the machine supports a fullword-to-doubleword widening multiply instruction. Division and shifts are open-coded only on machines that provide special support. The operations that are not open-coded use special library routines that come with GCC
There may be pitfalls when you use long long types for function arguments without function prototypes. If a function expects type int for its argument, and you pass a value of type long long int, confusion results because the caller and the subroutine disagree about the number of bytes for the argument. Likewise, if the function expects long long int and you pass int. The best way to avoid such problems is to use prototypes.
:: _complex:
_Complex keyword __complex__ keyword
ISO C99 supports complex floating data types, and as an extension GCC supports them in C90 mode and in C++. GCC also supports complex integer data types which are not part of ISO C99. You can declare complex types using the keyword _Complex. As an extension, the older GNU keyword __complex__ is also supported.
For example, _Complex double x; declares x as a variable whose real part and imaginary part are both of type double. _Complex short int y; declares y to have real and imaginary parts of type short int; this is not likely to be useful, but it shows that the set of complex types is complete.
To write a constant with a complex data type, use the suffix i or j (either one; they are equivalent). For example, 2.5fi has type _Complex float and 3i has type _Complex int. Such a constant always has a pure imaginary value, but you can form any complex value you like by adding one to a real constant. This is a GNU extension; if you have an ISO C99 conforming C library (such as the GNU C Library), and want to construct complex constants of floating type, you should include <complex.h> and use the macros I or _Complex_I instead.
__real__ keyword __imag__ keyword To extract the real part of a complex-valued expression exp, write __real__ ``exp``. Likewise, use __imag__ to extract the imaginary part. This is a GNU extension; for values of floating type, you should use the ISO C99 functions crealf, creal, creall, cimagf, cimag and cimagl, declared in <complex.h> and also provided as built-in functions by GCC
The operator ~ performs complex conjugation when used on a value with a complex type. This is a GNU extension; for values of floating type, you should use the ISO C99 functions conjf, conj and conjl, declared in <complex.h> and also provided as built-in functions by GCC
GCC can allocate complex automatic variables in a noncontiguous fashion; its even possible for the real part to be in a register while the imaginary part is on the stack (or vice versa). Only the DWARF 2 debug info format can represent this, so use of DWARF 2 is recommended. If you are using the stabs debug info format, GCC describes a noncontiguous complex variable as if it were two separate variables of noncomplex type. If the variables actual name is foo, the two fictitious variables are named foo$real and foo$imag. You can examine and set these two fictitious variables with your debugger.
:: _floating-types:
__float80 data type __float128 data type w floating point suffix q floating point suffix W floating point suffix Q floating point suffix
As an extension, GNU C supports additional floating types, __float80 and __float128 to support 80-bit (XFmode) and 128-bit (TFmode) floating types. Support for additional types includes the arithmetic operators: add, subtract, multiply, divide; unary arithmetic operators; relational operators; equality operators; and conversions to and from integer and other floating types. Use a suffix w or W in a literal constant of type __float80 and q or Q for _float128. You can declare complex types using the corresponding internal complex type, XCmode for __float80 type and TCmode for __float128 type:
typedef _Complex float __attribute__((mode(TC))) _Complex128;
typedef _Complex float __attribute__((mode(XC))) _Complex80;
Not all targets support additional floating-point types. __float80 and __float128 types are supported on x86 and IA-64 targets. The __float128 type is supported on hppa HP-UX targets.
:: _half-precision:
__fp16 data type
On ARM targets, GCC supports half-precision (16-bit) floating point via the __fp16 type. You must enable this type explicitly with the -mfp16-format command-line option in order to use it.
ARM supports two incompatible representations for half-precision floating-point values. You must choose one of the representations and use it consistently in your program.
Specifying -mfp16-format=ieee selects the IEEE 754-2008 format. This format can represent normalized values in the range of 2^{-14} to 65504. There are 11 bits of significand precision, approximately 3 decimal digits.
Specifying -mfp16-format=alternative selects the ARM alternative format. This representation is similar to the IEEE format, but does not support infinities or NaNs. Instead, the range of exponents is extended, so that this format can represent normalized values in the range of 2^{-14} to 131008.
The __fp16 type is a storage format only. For purposes of arithmetic and other operations, __fp16 values in C or C++ expressions are automatically promoted to float. In addition, you cannot declare a function with a return value or parameters of type __fp16.
Note that conversions from double to __fp16 involve an intermediate conversion to float. Because of rounding, this can sometimes produce a different result than a direct conversion.
ARM provides hardware support for conversions between __fp16 and float values as an extension to VFP and NEON (Advanced SIMD). GCC generates code using these hardware instructions if you compile with options to select an FPU that provides them; for example, -mfpu=neon-fp16 -mfloat-abi=softfp, in addition to the -mfp16-format option to select a half-precision format.
Language-level support for the __fp16 data type is independent of whether GCC generates code using hardware floating-point instructions. In cases where hardware support is not specified, GCC implements conversions between __fp16 and float values as library calls.
:: _decimal-float:
_Decimal32 data type _Decimal64 data type _Decimal128 data type df integer suffix dd integer suffix dl integer suffix DF integer suffix DD integer suffix DL integer suffix
As an extension, GNU C supports decimal floating types as defined in the N1312 draft of ISO/IEC WDTR24732. Support for decimal floating types in GCC will evolve as the draft technical report changes. Calling conventions for any target might also change. Not all targets support decimal floating types.
The decimal floating types are _Decimal32, _Decimal64, and _Decimal128. They use a radix of ten, unlike the floating types float, double, and long double whose radix is not specified by the C standard but is usually two.
Support for decimal floating types includes the arithmetic operators add, subtract, multiply, divide; unary arithmetic operators; relational operators; equality operators; and conversions to and from integer and other floating types. Use a suffix df or DF in a literal constant of type _Decimal32, dd or DD for _Decimal64, and dl or DL for _Decimal128.
GCC support of decimal float as specified by the draft technical report is incomplete:
Types _Decimal32, _Decimal64, and _Decimal128 are supported by the DWARF 2 debug information format.
:: _hex-floats:
ISO C99 supports floating-point numbers written not only in the usual decimal notation, such as 1.55e1, but also numbers such as 0x1.fp3 written in hexadecimal format. As a GNU extension, GCC supports this in C90 mode (except in some cases when strictly conforming) and in C++. In that format the 0x hex introducer and the p or P exponent field are mandatory. The exponent is a decimal number that indicates the power of 2 by which the significant part is multiplied. Thus 0x1.f is
$1 {15over16}$,
1 15/16, p3 multiplies it by 8, and the value of 0x1.fp3 is the same as 1.55e1.
Unlike for floating-point numbers in the decimal notation the exponent is always required in the hexadecimal notation. Otherwise the compiler would not be able to resolve the ambiguity of, e.g., 0x1.f. This could mean 1.0f or 1.9375 since f is also the extension for floating-point constants of type float.
:: _fixed-point:
_Fract data type _Accum data type _Sat data type hr fixed-suffix r fixed-suffix lr fixed-suffix llr fixed-suffix uhr fixed-suffix ur fixed-suffix ulr fixed-suffix ullr fixed-suffix hk fixed-suffix k fixed-suffix lk fixed-suffix llk fixed-suffix uhk fixed-suffix uk fixed-suffix ulk fixed-suffix ullk fixed-suffix HR fixed-suffix R fixed-suffix LR fixed-suffix LLR fixed-suffix UHR fixed-suffix UR fixed-suffix ULR fixed-suffix ULLR fixed-suffix HK fixed-suffix K fixed-suffix LK fixed-suffix LLK fixed-suffix UHK fixed-suffix UK fixed-suffix ULK fixed-suffix ULLK fixed-suffix
As an extension, GNU C supports fixed-point types as defined in the N1169 draft of ISO/IEC DTR 18037. Support for fixed-point types in GCC will evolve as the draft technical report changes. Calling conventions for any target might also change. Not all targets support fixed-point types.
The fixed-point types are short _Fract, _Fract, long _Fract, long long _Fract, unsigned short _Fract, unsigned _Fract, unsigned long _Fract, unsigned long long _Fract, _Sat short _Fract, _Sat _Fract, _Sat long _Fract, _Sat long long _Fract, _Sat unsigned short _Fract, _Sat unsigned _Fract, _Sat unsigned long _Fract, _Sat unsigned long long _Fract, short _Accum, _Accum, long _Accum, long long _Accum, unsigned short _Accum, unsigned _Accum, unsigned long _Accum, unsigned long long _Accum, _Sat short _Accum, _Sat _Accum, _Sat long _Accum, _Sat long long _Accum, _Sat unsigned short _Accum, _Sat unsigned _Accum, _Sat unsigned long _Accum, _Sat unsigned long long _Accum.
Fixed-point data values contain fractional and optional integral parts. The format of fixed-point data varies and depends on the target machine.
Support for fixed-point types includes:
Use a suffix in a fixed-point literal constant:
GCC support of fixed-point types as specified by the draft technical report is incomplete:
Fixed-point types are supported by the DWARF 2 debug information format.
:: _named-address-spaces:
As an extension, GNU C supports named address spaces as defined in the N1275 draft of ISO/IEC DTR 18037. Support for named address spaces in GCC will evolve as the draft technical report changes. Calling conventions for any target might also change. At present, only the AVR, SPU, M32C, and RL78 targets support address spaces other than the generic address space.
Address space identifiers may be used exactly like any other C type qualifier (e.g., const or volatile). See the N1275 document for more details.
AVR Named Address Spaces
On the AVR target, there are several address spaces that can be used in order to put read-only data into the flash memory and access that data by means of the special instructions LPM or ELPM needed to read from flash.
Per default, any data including read-only data is located in RAM (the generic address space) so that non-generic address spaces are needed to locate read-only data in flash memory and to generate the right instructions to access this data without using (inline) assembler code.
__flash AVR Named Address Spaces The __flash qualifier locates data in the .progmem.data section. Data is read using the LPM instruction. Pointers to this address space are 16 bits wide.
__flash1 AVR Named Address Spaces __flash2 AVR Named Address Spaces __flash3 AVR Named Address Spaces __flash4 AVR Named Address Spaces __flash5 AVR Named Address Spaces These are 16-bit address spaces locating data in section .progmem``N.data`` where N refers to address space __flash``N``. The compiler sets the RAMPZ segment register appropriately before reading data by means of the ELPM instruction.
__memx AVR Named Address Spaces This is a 24-bit address space that linearizes flash and RAM: If the high bit of the address is set, data is read from RAM using the lower two bytes as RAM address. If the high bit of the address is clear, data is read from flash with RAMPZ set according to the high byte of the address. AVR Built-in Functions``__builtin_avr_flash_segment``.
Objects in this address space are located in .progmemx.data.
Example
char my_read (const __flash char ** p)
{
/* p is a pointer to RAM that points to a pointer to flash.
The first indirection of p reads that flash pointer
from RAM and the second indirection reads a char from this
flash address. */
return **p;
}
/* Locate array[] in flash memory */
const __flash int array[] = { 3, 5, 7, 11, 13, 17, 19 };
int i = 1;
int main (void)
{
/* Return 17 by reading from flash memory */
return array[array[i]];
}
For each named address space supported by avr-gcc there is an equally named but uppercase built-in macro defined. The purpose is to facilitate testing if respective address space support is available or not:
#ifdef __FLASH
const __flash int var = 1;
int read_var (void)
{
return var;
}
#else
#include <avr/pgmspace.h> /* From AVR-LibC */
const int var PROGMEM = 1;
int read_var (void)
{
return (int) pgm_read_word (&var);
}
#endif /* __FLASH */
Notice that attribute AVR Variable Attributes``progmem`` locates data in flash but accesses to these data read from generic address space, i.e. from RAM, so that you need special accessors like pgm_read_byte from http://nongnu.org/avr-libc/user-manual/AVR-LibC together with attribute progmem.
Limitations and caveats
Reading across the 64KiB section boundary of the __flash or __flash``N`` address spaces shows undefined behavior. The only address space that supports reading across the 64KiB flash segment boundaries is __memx.
If you use one of the __flash``N`` address spaces you must arrange your linker script to locate the .progmem``N.data`` sections according to your needs.
Any data or pointers to the non-generic address spaces must be qualified as const, i.e. as read-only data. This still applies if the data in one of these address spaces like software version number or calibration lookup table are intended to be changed after load time by, say, a boot loader. In this case the right qualification is const volatile so that the compiler must not optimize away known values or insert them as immediates into operands of instructions.
The following code initializes a variable pfoo located in static storage with a 24-bit address:
extern const __memx char foo;
const __memx void *pfoo = &foo;
Such code requires at least binutils 2.23, see http://sourceware.org/PR13503PR13503.
__far M32C Named Address Spaces
On the M32C target, with the R8C and M16C CPU variants, variables qualified with __far are accessed using 32-bit addresses in order to access memory beyond the first 64Ki bytes. If __far is used with the M32CM or M32C CPU variants, it has no effect.
__far RL78 Named Address Spaces
On the RL78 target, variables qualified with __far are accessed with 32-bit pointers (20-bit addresses) rather than the default 16-bit addresses. Non-far variables are assumed to appear in the topmost 64KiB of the address space.
__ea SPU Named Address Spaces
On the SPU target variables may be declared as belonging to another address space by qualifying the type with the __ea address space identifier:
extern int __ea i;
The compiler generates special code to access the variable i. It may use runtime library support, or generate special machine instructions to access that address space.
:: _zero-length:
Zero-length arrays are allowed in GNU C They are very useful as the last element of a structure that is really a header for a variable-length object:
struct line {
int length;
char contents[0];
};
struct line *thisline = (struct line *)
malloc (sizeof (struct line) + this_length);
thisline->length = this_length;
In ISO C90, you would have to give contents a length of 1, which means either you waste space or complicate the argument to malloc.
In ISO C99, you would use a flexible array member, which is slightly different in syntax and semantics:
Non-empty initialization of zero-length arrays is treated like any case where there are more initializer elements than the array holds, in that a suitable warning about excess elements in array is given, and the excess elements (all of them, in this case) are ignored.
GCC allows static initialization of flexible array members. This is equivalent to defining a new structure containing the original structure followed by an array of sufficient size to contain the data. E.g. in the following, f1 is constructed as if it were declared like f2.
struct f1 {
int x; int y[];
} f1 = { 1, { 2, 3, 4 } };
struct f2 {
struct f1 f1; int data[3];
} f2 = { { 1 }, { 2, 3, 4 } };
The convenience of this extension is that f1 has the desired type, eliminating the need to consistently refer to f2.f1.
This has symmetry with normal static arrays, in that an array of unknown size is also written with [].
Of course, this extension only makes sense if the extra data comes at the end of a top-level object, as otherwise we would be overwriting data at subsequent offsets. To avoid undue complication and confusion with initialization of deeply nested arrays, we simply disallow any non-empty initialization except when the structure is the top-level object. For example:
struct foo { int x; int y[]; };
struct bar { struct foo z; };
struct foo a = { 1, { 2, 3, 4 } }; // Valid.
struct bar b = { { 1, { 2, 3, 4 } } }; // Invalid.
struct bar c = { { 1, { } } }; // Valid.
struct foo d[1] = { { 1, { 2, 3, 4 } } }; // Invalid.
:: _empty-structures:
GCC permits a C structure to have no members:
struct empty {
};
The structure has size zero. In C++, empty structures are part of the language. G++ treats empty structures as if they had a single member of type char.
:: _variable-length:
Variable-length automatic arrays are allowed in ISO C99, and as an extension GCC accepts them in C90 mode and in C++. These arrays are declared like any other automatic arrays, but with a length that is not a constant expression. The storage is allocated at the point of declaration and deallocated when the block scope containing the declaration exits. For example:
FILE *
concat_fopen (char *s1, char *s2, char *mode)
{
char str[strlen (s1) + strlen (s2) + 1];
strcpy (str, s1);
strcat (str, s2);
return fopen (str, mode);
}
Jumping or breaking out of the scope of the array name deallocates the storage. Jumping into the scope is not allowed; you get an error message for it.
As an extension, GCC accepts variable-length arrays as a member of a structure or a union. For example:
void
foo (int n)
{
struct S { int x[n]; };
}
alloca vs variable-length arrays You can use the function alloca to get an effect much like variable-length arrays. The function alloca is available in many other C implementations (but not in all). On the other hand, variable-length arrays are more elegant.
There are other differences between these two methods. Space allocated with alloca exists until the containing function returns. The space for a variable-length array is deallocated as soon as the array names scope ends. (If you use both variable-length arrays and alloca in the same function, deallocation of a variable-length array also deallocates anything more recently allocated with alloca.)
You can also use variable-length arrays as arguments to functions:
struct entry
tester (int len, char data[len][len])
{
/* ... */
}
The length of an array is computed once when the storage is allocated and is remembered for the scope of the array in case you access it with sizeof.
If you want to pass the array first and the length afterward, you can use a forward declaration in the parameter listanother GNU extension.
struct entry
tester (int len; char data[len][len], int len)
{
/* ... */
}
The int len before the semicolon is a parameter forward declaration, and it serves the purpose of making the name len known when the declaration of data is parsed.
You can write any number of such parameter forward declarations in the parameter list. They can be separated by commas or semicolons, but the last one must end with a semicolon, which is followed by the real parameter declarations. Each forward declaration must match a real declaration in parameter name and data type. ISO C99 does not support parameter forward declarations.
:: _variadic-macros:
In the ISO C standard of 1999, a macro can be declared to accept a variable number of arguments much as a function can. The syntax for defining the macro is similar to that of a function. Here is an example:
#define debug(format, ...) fprintf (stderr, format, __VA_ARGS__)
Here ... is a variable argument. In the invocation of such a macro, it represents the zero or more tokens until the closing parenthesis that ends the invocation, including any commas. This set of tokens replaces the identifier __VA_ARGS__ in the macro body wherever it appears. See the CPP manual for more information.
GCC has long supported variadic macros, and used a different syntax that allowed you to give a name to the variable arguments just like any other argument. Here is an example:
#define debug(format, args...) fprintf (stderr, format, args)
This is in all ways equivalent to the ISO C example above, but arguably more readable and descriptive.
GNU CPP has two further variadic macro extensions, and permits them to be used with either of the above forms of macro definition.
In standard C, you are not allowed to leave the variable argument out entirely; but you are allowed to pass an empty argument. For example, this invocation is invalid in ISO C, because there is no comma after the string:
debug ("A message")
GNU CPP permits you to completely omit the variable arguments in this way. In the above examples, the compiler would complain, though since the expansion of the macro still has the extra comma after the format string.
To help solve this problem, CPP behaves specially for variable arguments used with the token paste operator, ##. If instead you write
#define debug(format, ...) fprintf (stderr, format, ## __VA_ARGS__)
and if the variable arguments are omitted or empty, the ## operator causes the preprocessor to remove the comma before it. If you do provide some variable arguments in your macro invocation, GNU CPP does not complain about the paste operation and instead places the variable arguments after the comma. Just like any other pasted macro argument, these arguments are not macro expanded.
:: _escaped-newlines:
The preprocessor treatment of escaped newlines is more relaxed than that specified by the C90 standard, which requires the newline to immediately follow a backslash. GCCs implementation allows whitespace in the form of spaces, horizontal and vertical tabs, and form feeds between the backslash and the subsequent newline. The preprocessor issues a warning, but treats it as a valid escaped newline and combines the two lines to form a single logical line. This works within comments and tokens, as well as between tokens. Comments are not treated as whitespace for the purposes of this relaxation, since they have not yet been replaced with spaces.
:: _subscripting:
In ISO C99, arrays that are not lvalues still decay to pointers, and may be subscripted, although they may not be modified or used after the next sequence point and the unary & operator may not be applied to them. As an extension, GNU C allows such arrays to be subscripted in C90 mode, though otherwise they do not decay to pointers outside C99 mode. For example, this is valid in GNU C though not valid in C90:
struct foo {int a[4];};
struct foo f();
bar (int index)
{
return f().a[index];
}
:: _pointer-arith:
Arithmetic on void- and Function-Pointers
In GNU C, addition and subtraction operations are supported on pointers to void and on pointers to functions. This is done by treating the size of a void or of a function as 1.
A consequence of this is that sizeof is also allowed on void and on function types, and returns 1.
The option -Wpointer-arith requests a warning if these extensions are used.
:: _pointers-to-arrays:
In GNU C, pointers to arrays with qualifiers work similar to pointers to other qualified types. For example, a value of type int (*)[5] can be used to initialize a variable of type const int (*)[5]. These types are incompatible in ISO C because the const qualifier is formally attached to the element type of the array and not the array itself.
extern void
transpose (int N, int M, double out[M][N], const double in[N][M]);
double x[3][2];
double y[2][3];
...
transpose(3, 2, y, x);
:: _initializers:
As in standard C++ and ISO C99, the elements of an aggregate initializer for an automatic variable are not required to be constant expressions in GNU C Here is an example of an initializer with run-time varying elements:
foo (float f, float g)
{
float beat_freqs[2] = { f-g, f+g };
/* ... */
}
:: _compound-literals:
ISO C99 supports compound literals. A compound literal looks like a cast containing an initializer. Its value is an object of the type specified in the cast, containing the elements specified in the initializer; it is an lvalue. As an extension, GCC supports compound literals in C90 mode and in C++, though the semantics are somewhat different in C++.
Usually, the specified type is a structure. Assume that struct foo and structure are declared as shown:
struct foo {int a; char b[2];} structure;
Here is an example of constructing a struct foo with a compound literal:
structure = ((struct foo) {x + y, 'a', 0});
This is equivalent to writing the following:
{
struct foo temp = {x + y, 'a', 0};
structure = temp;
}
You can also construct an array, though this is dangerous in C++, as explained below. If all the elements of the compound literal are (made up of) simple constant expressions, suitable for use in initializers of objects of static storage duration, then the compound literal can be coerced to a pointer to its first element and used in such an initializer, as shown here:
char **foo = (char *[]) { "x", "y", "z" };
Compound literals for scalar types and union types are also allowed, but then the compound literal is equivalent to a cast.
As a GNU extension, GCC allows initialization of objects with static storage duration by compound literals (which is not possible in ISO C99, because the initializer is not a constant). It is handled as if the object is initialized only with the bracket enclosed list if the types of the compound literal and the object match. The initializer list of the compound literal must be constant. If the object being initialized has array type of unknown size, the size is determined by compound literal size.
static struct foo x = (struct foo) {1, 'a', 'b'};
static int y[] = (int []) {1, 2, 3};
static int z[] = (int [3]) {1};
The above lines are equivalent to the following:
static struct foo x = {1, 'a', 'b'};
static int y[] = {1, 2, 3};
static int z[] = {1, 0, 0};
In C, a compound literal designates an unnamed object with static or automatic storage duration. In C++, a compound literal designates a temporary object, which only lives until the end of its full-expression. As a result, well-defined C code that takes the address of a subobject of a compound literal can be undefined in C++, so the C++ compiler rejects the conversion of a temporary array to a pointer. For instance, if the array compound literal example above appeared inside a function, any subsequent use of foo in C++ has undefined behavior because the lifetime of the array ends after the declaration of foo.
As an optimization, the C++ compiler sometimes gives array compound literals longer lifetimes: when the array either appears outside a function or has const-qualified type. If foo and its initializer had elements of char *const type rather than char *, or if foo were a global variable, the array would have static storage duration. But it is probably safest just to avoid the use of array compound literals in code compiled as C++.
:: _designated-inits:
Standard C90 requires the elements of an initializer to appear in a fixed order, the same as the order of the elements in the array or structure being initialized.
In ISO C99 you can give the elements in any order, specifying the array indices or structure field names they apply to, and GNU C allows this as an extension in C90 mode as well. This extension is not implemented in GNU C++.
To specify an array index, write [index] = before the element value. For example,
int a[6] = { [4] = 29, [2] = 15 };
is equivalent to
int a[6] = { 0, 0, 15, 0, 29, 0 };
The index values must be constant expressions, even if the array being initialized is automatic.
An alternative syntax for this that has been obsolete since GCC 2.5 but GCC still accepts is to write [index] before the element value, with no =.
To initialize a range of elements to the same value, write [first ... last] = value. This is a GNU extension. For example,
int widths[] = { [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 };
If the value in it has side-effects, the side-effects happen only once, not for each initialized field by the range initializer.
Note that the length of the array is the highest value specified plus one.
In a structure initializer, specify the name of a field to initialize with .``fieldname`` = before the element value. For example, given the following structure,
struct point { int x, y; };
the following initialization
struct point p = { .y = yvalue, .x = xvalue };
is equivalent to
struct point p = { xvalue, yvalue };
Another syntax that has the same meaning, obsolete since GCC 2.5, is fieldname:, as shown here:
struct point p = { y: yvalue, x: xvalue };
Omitted field members are implicitly initialized the same as objects that have static storage duration.
The [index] or .``fieldname`` is known as a designator. You can also use a designator (or the obsolete colon syntax) when initializing a union, to specify which element of the union should be used. For example,
union foo { int i; double d; };
union foo f = { .d = 4 };
converts 4 to a double to store it in the union using the second element. By contrast, casting 4 to type union foo stores it into the union as the integer i, since it is an integer. (Cast to Union.)
You can combine this technique of naming elements with ordinary C initialization of successive elements. Each initializer element that does not have a designator applies to the next consecutive element of the array or structure. For example,
int a[6] = { [1] = v1, v2, [4] = v4 };
is equivalent to
int a[6] = { 0, v1, v2, 0, v4, 0 };
Labeling the elements of an array initializer is especially useful when the indices are characters or belong to an enum type. For example:
int whitespace[256]
= { [' '] = 1, ['\t'] = 1, ['\h'] = 1,
['\f'] = 1, ['\n'] = 1, ['\r'] = 1 };
You can also write a series of .``fieldname`` and [index] designators before an = to specify a nested subobject to initialize; the list is taken relative to the subobject corresponding to the closest surrounding brace pair. For example, with the struct point declaration above:
struct point ptarray[10] = { [2].y = yv2, [2].x = xv2, [0].x = xv0 };
If the same field is initialized multiple times, it has the value from the last initialization. If any such overridden initialization has side-effect, it is unspecified whether the side-effect happens or not. Currently, GCC discards them and issues a warning.
:: _case-ranges:
You can specify a range of consecutive values in a single case label, like this:
case ``low`` ... ``high``:
This has the same effect as the proper number of individual case labels, one for each integer value from low to high, inclusive.
This feature is especially useful for ranges of ASCII character codes:
case 'A' ... 'Z':
Be careful: Write spaces around the ..., for otherwise it may be parsed wrong when you use it with integer values. For example, write this:
case 1 ... 5:
rather than this:
case 1...5:
:: _cast-to-union:
A cast to union type is similar to other casts, except that the type specified is a union type. You can specify the type either with union ``tag`` or with a typedef name. A cast to union is actually a constructor, not a cast, and hence does not yield an lvalue like normal casts. (Compound Literals.)
The types that may be cast to the union type are those of the members of the union. Thus, given the following union and variables:
union foo { int i; double d; };
int x;
double y;
both x and y can be cast to type union foo.
Using the cast as the right-hand side of an assignment to a variable of union type is equivalent to storing in a member of the union:
union foo u;
/* ... */
u = (union foo) x u.i = x
u = (union foo) y u.d = y
You can also use the union cast as a function argument:
void hack (union foo);
/* ... */
hack ((union foo) x);
:: _mixed-declarations:
ISO C99 and ISO C++ allow declarations and code to be freely mixed within compound statements. As an extension, GNU C also allows this in C90 mode. For example, you could do:
int i;
/* ... */
i++;
int j = i + 2;
Each identifier is visible from where it is declared until the end of the enclosing block.
:: _function-attributes:
volatile applied to function const applied to function
In GNU C, you can use function attributes to declare certain things about functions called in your program which help the compiler optimize calls and check your code more carefully. For example, you can use attributes to declare that a function never returns (noreturn), returns a value depending only on its arguments (pure), or has printf-style arguments (format).
You can also use attributes to control memory placement, code generation options or call/return conventions within the function being annotated. Many of these attributes are target-specific. For example, many targets support attributes for defining interrupt handler functions, which typically must follow special register usage and return conventions.
Function attributes are introduced by the __attribute__ keyword on a declaration, followed by an attribute specification inside double parentheses. You can specify multiple attributes in a declaration by separating them by commas within the double parentheses or by immediately following an attribute declaration with another attribute declaration. Attribute Syntax, for the exact rules on attribute syntax and placement.
GCC also supports attributes on variable declarations (Variable Attributes), labels (Label Attributes), and types (Type Attributes).
There is some overlap between the purposes of attributes and pragmas (PragmasPragmas Accepted by GCC). It has been found convenient to use __attribute__ to achieve a natural attachment of attributes to their corresponding declarations, whereas #pragma is of use for compatibility with other compilers or constructs that do not naturally form part of the grammar.
In addition to the attributes documented here, GCC plugins may provide their own attributes.
:: _common-function-attributes:
The following attributes are supported on most targets.
alias (“target”) alias function attribute The alias attribute causes the declaration to be emitted as an alias for another symbol, which must be specified. For instance,
void __f () { /* Do something. */; }
void f () __attribute__ ((weak, alias ("__f")));
defines f to be a weak alias for __f. In C++, the mangled name for the target must be used. It is an error if __f is not defined in the same translation unit.
This attribute requires assembler and object file support, and may not be available on all targets.
aligned (alignment) aligned function attribute This attribute specifies a minimum alignment for the function, measured in bytes.
You cannot use this attribute to decrease the alignment of a function, only to increase it. However, when you explicitly specify a function alignment this overrides the effect of the -falign-functions (Optimize Options) option for this function.
Note that the effectiveness of aligned attributes may be limited by inherent limitations in your linker. On many systems, the linker is only able to arrange for functions to be aligned up to a certain maximum alignment. (For some linkers, the maximum supported alignment may be very very small.) See your linker documentation for further information.
The aligned attribute can also be used for variables and fields (Variable Attributes.)
alloc_align function attribute The alloc_align attribute is used to tell the compiler that the function return value points to memory, where the returned pointer minimum alignment is given by one of the functions parameters. GCC uses this information to improve pointer alignment analysis.
The function parameter denoting the allocated alignment is specified by one integer argument, whose number is the argument of the attribute. Argument numbering starts at one.
For instance,
void* my_memalign(size_t, size_t) __attribute__((alloc_align(1)))
declares that my_memalign returns memory with minimum alignment given by parameter 1.
alloc_size function attribute The alloc_size attribute is used to tell the compiler that the function return value points to memory, where the size is given by one or two of the functions parameters. GCC uses this information to improve the correctness of __builtin_object_size.
The function parameter(s) denoting the allocated size are specified by one or two integer arguments supplied to the attribute. The allocated size is either the value of the single function argument specified or the product of the two function arguments specified. Argument numbering starts at one.
For instance,
void* my_calloc(size_t, size_t) __attribute__((alloc_size(1,2)))
void* my_realloc(void*, size_t) __attribute__((alloc_size(2)))
declares that my_calloc returns memory of the size given by the product of parameter 1 and 2 and that my_realloc returns memory of the size given by parameter 2.
always_inline function attribute Generally, functions are not inlined unless optimization is specified. For functions declared inline, this attribute inlines the function independent of any restrictions that otherwise apply to inlining. Failure to inline such a function is diagnosed as an error. Note that if such a function is called indirectly the compiler may or may not inline it depending on optimization level and a failure to inline an indirect call may or may not be diagnosed.
artificial function attribute This attribute is useful for small inline wrappers that if possible should appear during debugging as a unit. Depending on the debug info format it either means marking the function as artificial or using the caller location for all instructions within the inlined body.
assume_aligned function attribute The assume_aligned attribute is used to tell the compiler that the function return value points to memory, where the returned pointer minimum alignment is given by the first argument. If the attribute has two arguments, the second argument is misalignment offset.
For instance
void* my_alloc1(size_t) __attribute__((assume_aligned(16)))
void* my_alloc2(size_t) __attribute__((assume_aligned(32, 8)))
declares that my_alloc1 returns 16-byte aligned pointer and that my_alloc2 returns a pointer whose value modulo 32 is equal to 8.
bnd_instrument function attribute The bnd_instrument attribute on functions is used to inform the compiler that the function should be instrumented when compiled with the -fchkp-instrument-marked-only option.
bnd_legacy function attribute
The bnd_legacy attribute on functions is used to inform the compiler that the function should not be instrumented when compiled with the -fcheck-pointer-bounds option.
cold function attribute The cold attribute on functions is used to inform the compiler that the function is unlikely to be executed. The function is optimized for size rather than speed and on many targets it is placed into a special subsection of the text section so all cold functions appear close together, improving code locality of non-cold parts of program. The paths leading to calls of cold functions within code are marked as unlikely by the branch prediction mechanism. It is thus useful to mark functions used to handle unlikely conditions, such as perror, as cold to improve optimization of hot functions that do call marked functions in rare occasions.
When profile feedback is available, via -fprofile-use, cold functions are automatically detected and this attribute is ignored.
const function attribute
Many functions do not examine any values except their arguments, and have no effects except the return value. Basically this is just slightly more strict class than the pure attribute below, since function is not allowed to read global memory.
Note that a function that has pointer arguments and examines the data pointed to must not be declared const. Likewise, a function that calls a non-const function usually must not be const. It does not make sense for a const function to return void.
constructor function attribute destructor function attribute The constructor attribute causes the function to be called automatically before execution enters main (). Similarly, the destructor attribute causes the function to be called automatically after main () completes or exit () is called. Functions with these attributes are useful for initializing data that is used implicitly during the execution of the program.
You may provide an optional integer priority to control the order in which constructor and destructor functions are run. A constructor with a smaller priority number runs before a constructor with a larger priority number; the opposite relationship holds for destructors. So, if you have a constructor that allocates a resource and a destructor that deallocates the same resource, both functions typically have the same priority. The priorities for constructor and destructor functions are the same as those specified for namespace-scope C++ objects (C++ Attributes).
These attributes are not currently implemented for Objective-C
deprecated function attribute The deprecated attribute results in a warning if the function is used anywhere in the source file. This is useful when identifying functions that are expected to be removed in a future version of a program. The warning also includes the location of the declaration of the deprecated function, to enable users to easily find further information about why the function is deprecated, or what they should do instead. Note that the warnings only occurs for uses:
int old_fn () __attribute__ ((deprecated));
int old_fn ();
int (*fn_ptr)() = old_fn;
results in a warning on line 3 but not line 2. The optional msg argument, which must be a string, is printed in the warning if present.
The deprecated attribute can also be used for variables and types (Variable Attributes, Type Attributes.)
error (“message”)
warning (“message”) error function attribute warning function attribute If the error or warning attribute is used on a function declaration and a call to such a function is not eliminated through dead code elimination or other optimizations, an error or warning (respectively) that includes message is diagnosed. This is useful for compile-time checking, especially together with __builtin_constant_p and inline functions where checking the inline function arguments is not possible through extern char [(condition) ? 1 : -1]; tricks.
While it is possible to leave the function undefined and thus invoke a link failure (to define the function with a message in .gnu.warning* section), when using these attributes the problem is diagnosed earlier and with exact location of the call even in presence of inline functions or when not emitting debugging information.
externally_visible function attribute This attribute, attached to a global variable or function, nullifies the effect of the -fwhole-program command-line option, so the object remains visible outside the current compilation unit.
If -fwhole-program is used together with -flto and gold is used as the linker plugin, externally_visible attributes are automatically added to functions (not variable yet due to a current gold issue) that are accessed outside of LTO objects according to resolution file produced by gold. For other linkers that cannot generate resolution file, explicit externally_visible attributes are still necessary.
flatten function attribute Generally, inlining into a function is limited. For a function marked with this attribute, every call inside this function is inlined, if possible. Whether the function itself is considered for inlining depends on its size and the current inlining parameters.
format (archetype, string-index, first-to-check)
format function attribute functions with printf, scanf, strftime or strfmon style arguments
The format attribute specifies that a function takes printf, scanf, strftime or strfmon style arguments that should be type-checked against a format string. For example, the declaration:
extern int
my_printf (void *my_object, const char *my_format, ...)
__attribute__ ((format (printf, 2, 3)));
causes the compiler to check the arguments in calls to my_printf for consistency with the printf style format string argument my_format.
The parameter archetype determines how the format string is interpreted, and should be printf, scanf, strftime, gnu_printf, gnu_scanf, gnu_strftime or strfmon. (You can also use __printf__, __scanf__, __strftime__ or __strfmon__.) On MinGW targets, ms_printf, ms_scanf, and ms_strftime are also present. archetype values such as printf refer to the formats accepted by the systems C runtime library, while values prefixed with gnu_ always refer to the formats accepted by the GNU C Library. On Microsoft Windows targets, values prefixed with ms_ refer to the formats accepted by the msvcrt.dll library. The parameter string-index specifies which argument is the format string argument (starting from 1), while first-to-check is the number of the first argument to check against the format string. For functions where the arguments are not available to be checked (such as vprintf), specify the third parameter as zero. In this case the compiler only checks the format string for consistency. For strftime formats, the third parameter is required to be zero. Since non-static C++ methods have an implicit this argument, the arguments of such methods should be counted from two, not one, when giving values for string-index and first-to-check.
In the example above, the format string (my_format) is the second argument of the function my_print, and the arguments to check start with the third argument, so the correct parameters for the format attribute are 2 and 3.
The format attribute allows you to identify your own functions that take format strings as arguments, so that GCC can check the calls to these functions for errors. The compiler always (unless -ffreestanding or -fno-builtin is used) checks formats for the standard library functions printf, fprintf, sprintf, scanf, fscanf, sscanf, strftime, vprintf, vfprintf and vsprintf whenever such warnings are requested (using -Wformat), so there is no need to modify the header file stdio.h. In C99 mode, the functions snprintf, vsnprintf, vscanf, vfscanf and vsscanf are also checked. Except in strictly conforming C standard modes, the X/Open function strfmon is also checked as are printf_unlocked and fprintf_unlocked. C Dialect OptionsOptions Controlling C Dialect.
For Objective-C dialects, NSString (or __NSString__) is recognized in the same context. Declarations including these format attributes are parsed for correct syntax, however the result of checking of such format strings is not yet defined, and is not carried out by this version of the compiler.
The target may also provide additional types of format checks. Target Format ChecksFormat Checks Specific to Particular Target Machines.
format_arg (string-index) format_arg function attribute
The format_arg attribute specifies that a function takes a format string for a printf, scanf, strftime or strfmon style function and modifies it (for example, to translate it into another language), so the result can be passed to a printf, scanf, strftime or strfmon style function (with the remaining arguments to the format function the same as they would have been for the unmodified string). For example, the declaration:
extern char *
my_dgettext (char *my_domain, const char *my_format)
__attribute__ ((format_arg (2)));
causes the compiler to check the arguments in calls to a printf, scanf, strftime or strfmon type function, whose format string argument is a call to the my_dgettext function, for consistency with the format string argument my_format. If the format_arg attribute had not been specified, all the compiler could tell in such calls to format functions would be that the format string argument is not constant; this would generate a warning when -Wformat-nonliteral is used, but the calls could not be checked without the attribute.
The parameter string-index specifies which argument is the format string argument (starting from one). Since non-static C++ methods have an implicit this argument, the arguments of such methods should be counted from two.
The format_arg attribute allows you to identify your own functions that modify format strings, so that GCC can check the calls to printf, scanf, strftime or strfmon type function whose operands are a call to one of your own function. The compiler always treats gettext, dgettext, and dcgettext in this manner except when strict ISO C support is requested by -ansi or an appropriate -std option, or -ffreestanding or -fno-builtin is used. C Dialect OptionsOptions Controlling C Dialect.
For Objective-C dialects, the format-arg attribute may refer to an NSString reference for compatibility with the format attribute above.
The target may also allow additional types in format-arg attributes. Target Format ChecksFormat Checks Specific to Particular Target Machines.
gnu_inline function attribute This attribute should be used with a function that is also declared with the inline keyword. It directs GCC to treat the function as if it were defined in gnu90 mode even when compiling in C99 or gnu99 mode.
If the function is declared extern, then this definition of the function is used only for inlining. In no case is the function compiled as a standalone function, not even if you take its address explicitly. Such an address becomes an external reference, as if you had only declared the function, and had not defined it. This has almost the effect of a macro. The way to use this is to put a function definition in a header file with this attribute, and put another copy of the function, without extern, in a library file. The definition in the header file causes most calls to the function to be inlined. If any uses of the function remain, they refer to the single copy in the library. Note that the two definitions of the functions need not be precisely the same, although if they do not have the same effect your program may behave oddly.
In C, if the function is neither extern nor static, then the function is compiled as a standalone function, as well as being inlined where possible.
This is how GCC traditionally handled functions declared inline. Since ISO C99 specifies a different semantics for inline, this function attribute is provided as a transition measure and as a useful feature in its own right. This attribute is available in GCC 4.1.3 and later. It is available if either of the preprocessor macros __GNUC_GNU_INLINE__ or __GNUC_STDC_INLINE__ are defined. InlineAn Inline Function is As Fast As a Macro.
In C++, this attribute does not depend on extern in any way, but it still requires the inline keyword to enable its special behavior.
hot function attribute The hot attribute on a function is used to inform the compiler that the function is a hot spot of the compiled program. The function is optimized more aggressively and on many targets it is placed into a special subsection of the text section so all hot functions appear close together, improving locality.
When profile feedback is available, via -fprofile-use, hot functions are automatically detected and this attribute is ignored.
ifunc (“resolver”)
ifunc function attribute
The ifunc attribute is used to mark a function as an indirect function using the STT_GNU_IFUNC symbol type extension to the ELF standard. This allows the resolution of the symbol value to be determined dynamically at load time, and an optimized version of the routine can be selected for the particular processor or other system characteristics determined then. To use this attribute, first define the implementation functions available, and a resolver function that returns a pointer to the selected implementation function. The implementation functions declarations must match the API of the function being implemented, the resolvers declaration is be a function returning pointer to void function returning void:
void *my_memcpy (void *dst, const void *src, size_t len)
{
...
}
static void (*resolve_memcpy (void)) (void)
{
return my_memcpy; // we'll just always select this routine
}
The exported header file declaring the function the user calls would contain:
extern void *memcpy (void *, const void *, size_t);
allowing the user to call this as a regular function, unaware of the implementation. Finally, the indirect function needs to be defined in the same translation unit as the resolver function:
void *memcpy (void *, const void *, size_t)
__attribute__ ((ifunc ("resolve_memcpy")));
Indirect functions cannot be weak. Binutils version 2.20.1 or higher and GNU C Library version 2.11.1 are required to use this feature.
Many GCC back ends support attributes to indicate that a function is an interrupt handler, which tells the compiler to generate function entry and exit sequences that differ from those from regular functions. The exact syntax and behavior are target-specific; refer to the following subsections for details.
leaf function attribute Calls to external functions with this attribute must return to the current compilation unit only by return or by exception handling. In particular, leaf functions are not allowed to call callback function passed to it from the current compilation unit or directly call functions exported by the unit or longjmp into the unit. Leaf function might still call functions from other compilation units and thus they are not necessarily leaf in the sense that they contain no function calls at all.
The attribute is intended for library functions to improve dataflow analysis. The compiler takes the hint that any data not escaping the current compilation unit can not be used or modified by the leaf function. For example, the sin function is a leaf function, but qsort is not.
Note that leaf functions might invoke signals and signal handlers might be defined in the current compilation unit and use static variables. The only compliant way to write such a signal handler is to declare such variables volatile.
The attribute has no effect on functions defined within the current compilation unit. This is to allow easy merging of multiple compilation units into one, for example, by using the link-time optimization. For this reason the attribute is not allowed on types to annotate indirect calls.
malloc function attribute
This tells the compiler that a function is malloc-like, i.e., that the pointer P returned by the function cannot alias any other pointer valid when the function returns, and moreover no pointers to valid objects occur in any storage addressed by P.
Using this attribute can improve optimization. Functions like malloc and calloc have this property because they return a pointer to uninitialized or zeroed-out storage. However, functions like realloc do not have this property, as they can return a pointer to storage containing pointers.
no_icf function attribute This function attribute prevents a functions from being merged with another semantically equivalent function.
no_instrument_function function attribute
If -finstrument-functions is given, profiling function calls are generated at entry and exit of most user-compiled functions. Functions with this attribute are not so instrumented.
no_reorder function attribute Do not reorder functions or variables marked no_reorder against each other or top level assembler statements the executable. The actual order in the program will depend on the linker command line. Static variables marked like this are also not removed. This has a similar effect as the -fno-toplevel-reorder option, but only applies to the marked symbols.
no_sanitize_address function attribute The no_sanitize_address attribute on functions is used to inform the compiler that it should not instrument memory accesses in the function when compiling with the -fsanitize=address option. The no_address_safety_analysis is a deprecated alias of the no_sanitize_address attribute, new code should use no_sanitize_address.
no_sanitize_thread function attribute The no_sanitize_thread attribute on functions is used to inform the compiler that it should not instrument memory accesses in the function when compiling with the -fsanitize=thread option.
no_sanitize_undefined function attribute The no_sanitize_undefined attribute on functions is used to inform the compiler that it should not check for undefined behavior in the function when compiling with the -fsanitize=undefined option.
no_split_stack function attribute
If -fsplit-stack is given, functions have a small prologue which decides whether to split the stack. Functions with the no_split_stack attribute do not have that prologue, and thus may run with only a small amount of stack space available.
noclone function attribute This function attribute prevents a function from being considered for cloninga mechanism that produces specialized copies of functions and which is (currently) performed by interprocedural constant propagation.
noinline function attribute This function attribute prevents a function from being considered for inlining.
asm ("");
(Extended Asm) in the called function, to serve as a special side-effect.
nonnull (arg-index, ...)
nonnull function attribute
The nonnull attribute specifies that some function parameters should be non-null pointers. For instance, the declaration:
extern void *
my_memcpy (void *dest, const void *src, size_t len)
__attribute__((nonnull (1, 2)));
causes the compiler to check that, in calls to my_memcpy, arguments dest and src are non-null. If the compiler determines that a null pointer is passed in an argument slot marked as non-null, and the -Wnonnull option is enabled, a warning is issued. The compiler may also choose to make optimizations based on the knowledge that certain function arguments will never be null.
If no argument index list is given to the nonnull attribute, all pointer arguments are marked as non-null. To illustrate, the following declaration is equivalent to the previous example:
extern void *
my_memcpy (void *dest, const void *src, size_t len)
__attribute__((nonnull));
noreturn function attribute
A few standard library functions, such as abort and exit, cannot return. GCC knows this automatically. Some programs define their own functions that never return. You can declare them noreturn to tell the compiler this fact. For example,
void fatal () __attribute__ ((noreturn));
void
fatal (/* ... */)
{
/* ... */ /* Print error message. */ /* ... */
exit (1);
}
The noreturn keyword tells the compiler to assume that fatal cannot return. It can then optimize without regard to what would happen if fatal ever did return. This makes slightly better code. More importantly, it helps avoid spurious warnings of uninitialized variables.
The noreturn keyword does not affect the exceptional path when that applies: a noreturn-marked function may still return to the caller by throwing an exception or calling longjmp.
Do not assume that registers saved by the calling function are restored before calling the noreturn function.
It does not make sense for a noreturn function to have a return type other than void.
nothrow function attribute The nothrow attribute is used to inform the compiler that a function cannot throw an exception. For example, most functions in the standard C library can be guaranteed not to throw an exception with the notable exceptions of qsort and bsearch that take function pointer arguments.
optimize function attribute The optimize attribute is used to specify that a function is to be compiled with different optimization options than specified on the command line. Arguments can either be numbers or strings. Numbers are assumed to be an optimization level. Strings that begin with O are assumed to be an optimization option, while other options are assumed to be used with a -f prefix. You can also use the #pragma GCC optimize pragma to set the optimization options that affect more than one function. Function Specific Option Pragmas, for details about the #pragma GCC optimize pragma.
This can be used for instance to have frequently-executed functions compiled with more aggressive optimization options that produce faster and larger code, while other functions can be compiled with less aggressive options.
pure function attribute
Many functions have no effects except the return value and their return value depends only on the parameters and/or global variables. Such a function can be subject to common subexpression elimination and loop optimization just as an arithmetic operator would be. These functions should be declared with the attribute pure. For example,
int square (int) __attribute__ ((pure));
says that the hypothetical function square is safe to call fewer times than the program says.
Some of common examples of pure functions are strlen or memcmp. Interesting non-pure functions are functions with infinite loops or those depending on volatile memory or other system resource, that may change between two consecutive calls (such as feof in a multithreading environment).
returns_nonnull function attribute The returns_nonnull attribute specifies that the function return value should be a non-null pointer. For instance, the declaration:
extern void *
mymalloc (size_t len) __attribute__((returns_nonnull));
lets the compiler optimize callers based on the knowledge that the return value will never be null.
returns_twice function attribute
The returns_twice attribute tells the compiler that a function may return more than one time. The compiler ensures that all registers are dead before calling such a function and emits a warning about the variables that may be clobbered after the second return from the function. Examples of such functions are setjmp and vfork. The longjmp-like counterpart of such function, if any, might need to be marked with the noreturn attribute.
section (“section-name”)
section function attribute
Normally, the compiler places the code it generates in the text section. Sometimes, however, you need additional sections, or you need certain particular functions to appear in special sections. The section attribute specifies that a function lives in a particular section. For example, the declaration:
extern void foobar (void) __attribute__ ((section ("bar")));
puts the function foobar in the bar section.
Some file formats do not support arbitrary sections so the section attribute is not available on all platforms. If you need to map the entire contents of a module to a particular section, consider using the facilities of the linker instead.
sentinel function attribute This function attribute ensures that a parameter in a function call is an explicit NULL. The attribute is only valid on variadic functions. By default, the sentinel is located at position zero, the last parameter of the function call. If an optional integer position argument P is supplied to the attribute, the sentinel must be located at position P counting backwards from the end of the argument list.
__attribute__ ((sentinel))
is equivalent to
__attribute__ ((sentinel(0)))
The attribute is automatically set with a position of 0 for the built-in functions execl and execlp. The built-in function execle has the attribute set with a position of 1.
A valid NULL in this context is defined as zero with any pointer type. If your system defines the NULL macro with an integer type then you need to add an explicit cast. GCC replaces stddef.h with a copy that redefines NULL appropriately.
The warnings for missing or incorrect sentinels are enabled with -Wformat.
stack_protect function attribute This function attribute make a stack protection of the function if flags fstack-protector or fstack-protector-strong or fstack-protector-explicit are set.
target (options)
target function attribute Multiple target back ends implement the target attribute to specify that a function is to be compiled with different target options than specified on the command line. This can be used for instance to have functions compiled with a different ISA (instruction set architecture) than the default. You can also use the #pragma GCC target pragma to set more than one function to be compiled with specific target options. Function Specific Option Pragmas, for details about the #pragma GCC target pragma.
For instance, on an x86, you could declare one function with the target("sse4.1,arch=core2") attribute and another with target("sse4a,arch=amdfam10"). This is equivalent to compiling the first function with -msse4.1 and -march=core2 options, and the second function with -msse4a and -march=amdfam10 options. It is up to you to make sure that a function is only invoked on a machine that supports the particular ISA it is compiled for (for example by using cpuid on x86 to determine what feature bits and architecture family are used).
int core2_func (void) __attribute__ ((__target__ ("arch=core2")));
int sse3_func (void) __attribute__ ((__target__ ("sse3")));
You can either use multiple strings separated by commas to specify multiple options, or separate the options with a comma (,) within a single string.
The options supported are specific to each target; refer to x86 Function Attributes, PowerPC Function Attributes, and Nios II Function Attributes, for details.
unused function attribute This attribute, attached to a function, means that the function is meant to be possibly unused. GCC does not produce a warning for this function.
used function attribute This attribute, attached to a function, means that code must be emitted for the function even if it appears that the function is not referenced. This is useful, for example, when the function is referenced only in inline assembly.
When applied to a member function of a C++ class template, the attribute also means that the function is instantiated if the class itself is instantiated.
visibility (“visibility_type”)
visibility function attribute This attribute affects the linkage of the declaration to which it is attached. There are four supported visibility_type values: default, hidden, protected or internal visibility.
void __attribute__ ((visibility ("protected")))
f () { /* Do something. */; }
int i __attribute__ ((visibility ("hidden")));
The possible values of visibility_type correspond to the visibility settings in the ELF gABI.
Default visibility is the normal case for the object file format. This value is available for the visibility attribute to override other options that may change the assumed visibility of entities.
On ELF, default visibility means that the declaration is visible to other modules and, in shared libraries, means that the declared entity may be overridden.
On Darwin, default visibility means that the declaration is visible to other modules.
Default visibility corresponds to external linkage in the language.
Hidden visibility indicates that the entity declared has a new form of linkage, which we call hidden linkage. Two declarations of an object with hidden linkage refer to the same object if they are in the same shared object.
Internal visibility is like hidden visibility, but with additional processor specific semantics. Unless otherwise specified by the psABI, GCC defines internal visibility to mean that a function is never called from another module. Compare this with hidden functions which, while they cannot be referenced directly by other modules, can be referenced indirectly via function pointers. By indicating that a function cannot be called from outside the module, GCC may for instance omit the load of a PIC register since it is known that the calling function loaded the correct value.
Protected visibility is like default visibility except that it indicates that references within the defining module bind to the definition in that module. That is, the declared entity cannot be overridden by another module.
All visibilities are supported on many, but not all, ELF targets (supported when the assembler supports the .visibility pseudo-op). Default visibility is supported everywhere. Hidden visibility is supported on Darwin targets.
The visibility attribute should be applied only to declarations that would otherwise have external linkage. The attribute should be applied consistently, so that the same entity should not be declared with different settings of the attribute.
In C++, the visibility attribute applies to types as well as functions and objects, because in C++ types have linkage. A class must not have greater visibility than its non-static data member types and bases, and class members default to the visibility of their class. Also, a declaration without explicit visibility is limited to the visibility of its type.
In C++, you can mark member functions and static member variables of a class with the visibility attribute. This is useful if you know a particular method or static member variable should only be used from one shared object; then you can mark it hidden while the rest of the class has default visibility. Care must be taken to avoid breaking the One Definition Rule; for example, it is usually not useful to mark an inline method as hidden without marking the whole class as hidden.
A C++ namespace declaration can also have the visibility attribute.
namespace nspace1 __attribute__ ((visibility ("protected")))
{ /* Do something. */; }
This attribute applies only to the particular namespace body, not to other definitions of the same namespace; it is equivalent to using #pragma GCC visibility before and after the namespace definition (Visibility Pragmas).
In C++, if a template argument has limited visibility, this restriction is implicitly propagated to the template instantiation. Otherwise, template instantiations and specializations default to the visibility of their template.
If both the template and enclosing class have explicit visibility, the visibility from the template is used.
warn_unused_result function attribute The warn_unused_result attribute causes a warning to be emitted if a caller of the function with this attribute does not use its return value. This is useful for functions where not checking the result is either a security problem or always a bug, such as realloc.
int fn () __attribute__ ((warn_unused_result));
int foo ()
{
if (fn () < 0) return -1;
fn ();
return 0;
}
results in warning on line 5.
weak function attribute The weak attribute causes the declaration to be emitted as a weak symbol rather than a global. This is primarily useful in defining library functions that can be overridden in user code, though it can also be used with non-function declarations. Weak symbols are supported for ELF targets, and also for a.out targets when using the GNU assembler and linker.
weakref function attribute The weakref attribute marks a declaration as a weak reference. Without arguments, it should be accompanied by an alias attribute naming the target symbol. Optionally, the target may be given as an argument to weakref itself. In either case, weakref implicitly marks the declaration as weak. Without a target, given as an argument to weakref or to alias, weakref is equivalent to weak.
static int x() __attribute__ ((weakref ("y")));
/* is equivalent to... */
static int x() __attribute__ ((weak, weakref, alias ("y")));
/* and to... */
static int x() __attribute__ ((weakref));
static int x() __attribute__ ((alias ("y")));
A weak reference is an alias that does not by itself require a definition to be given for the target symbol. If the target symbol is only referenced through weak references, then it becomes a weak undefined symbol. If it is directly referenced, however, then such strong references prevail, and a definition is required for the symbol, not necessarily in the same translation unit.
The effect is equivalent to moving all references to the alias to a separate translation unit, renaming the alias to the aliased symbol, declaring it as weak, compiling the two separate translation units and performing a reloadable link on them.
At present, a declaration to which weakref is attached can only be static.
On the MSP430 target these attributes can be used to specify whether the function or variable should be placed into low memory, high memory, or the placement should be left to the linker to decide. The attributes are only significant if compiling for the MSP430X architecture.
The attributes work in conjunction with a linker script that has been augmented to specify where to place sections with a .lower and a .upper prefix. So for example as well as placing the .data section the script would also specify the placement of a .lower.data and a .upper.data section. The intention being that lower sections are placed into a small but easier to access memory region and the upper sections are placed into a larger, but slower to access region.
The either attribute is special. It tells the linker to place the object into the corresponding lower section if there is room for it. If there is insufficient room then the object is placed into the corresponding upper section instead. Note - the placement algorithm is not very sophisticated. It will not attempt to find an optimal packing of the lower sections. It just makes one pass over the objects and does the best that it can. Using the -ffunction-sections and -fdata-sections command line options can help the packing however, since they produce smaller, easier to pack regions.
:: _arc-function-attributes:
These function attributes are supported by the ARC back end:
interrupt function attribute, ARC Use this attribute to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.
On the ARC, you must specify the kind of interrupt to be handled in a parameter to the interrupt attribute like this:
void f () __attribute__ ((interrupt ("ilink1")));
Permissible values for this parameter are: ilink1 and ilink2.
long_call function attribute, ARC medium_call function attribute, ARC short_call function attribute, ARC
These attributes specify how a particular function is called. These attributes override the -mlong-calls and -mmedium-calls (ARC Options) command-line switches and #pragma long_calls settings.
For ARC, a function marked with the long_call attribute is always called using register-indirect jump-and-link instructions, thereby enabling the called function to be placed anywhere within the 32-bit address space. A function marked with the medium_call attribute will always be close enough to be called with an unconditional branch-and-link instruction, which has a 25-bit offset from the call site. A function marked with the short_call attribute will always be close enough to be called with a conditional branch-and-link instruction, which has a 21-bit offset from the call site.
:: _arm-function-attributes:
These function attributes are supported for ARM targets:
interrupt function attribute, ARM Use this attribute to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.
You can specify the kind of interrupt to be handled by adding an optional parameter to the interrupt attribute like this:
void f () __attribute__ ((interrupt ("IRQ")));
Permissible values for this parameter are: IRQ, FIQ, SWI, ABORT and UNDEF.
On ARMv7-M the interrupt type is ignored, and the attribute means the function may be called with a word-aligned stack pointer.
isr function attribute, ARM Use this attribute on ARM to write Interrupt Service Routines. This is an alias to the interrupt attribute above.
long_call function attribute, ARM short_call function attribute, ARM
These attributes specify how a particular function is called. These attributes override the -mlong-calls (ARM Options) command-line switch and #pragma long_calls settings. For ARM, the long_call attribute indicates that the function might be far away from the call site and require a different (more expensive) calling sequence. The short_call attribute always places the offset to the function from the call site into the BL instruction directly.
naked function attribute, ARM This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The specified function will not have prologue/epilogue sequences generated by the compiler. Only basic asm statements can safely be included in naked functions (Basic Asm). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended upon to work reliably and are not supported.
pcs function attribute, ARM
The pcs attribute can be used to control the calling convention used for a function on ARM. The attribute takes an argument that specifies the calling convention to use.
When compiling using the AAPCS ABI (or a variant of it) then valid values for the argument are "aapcs" and "aapcs-vfp". In order to use a variant other than "aapcs" then the compiler must be permitted to use the appropriate co-processor registers (i.e., the VFP registers must be available in order to use "aapcs-vfp"). For example,
/* Argument passed in r0, and result returned in r0+r1. */
double f2d (float) __attribute__((pcs("aapcs")));
Variadic functions always use the "aapcs" calling convention and the compiler rejects attempts to specify an alternative.
:: _avr-function-attributes:
These function attributes are supported by the AVR back end:
interrupt function attribute, AVR Use this attribute to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.
On the AVR, the hardware globally disables interrupts when an interrupt is executed. The first instruction of an interrupt handler declared with this attribute is a SEI instruction to re-enable interrupts. See also the signal function attribute that does not insert a SEI instruction. If both signal and interrupt are specified for the same function, signal is silently ignored.
naked function attribute, AVR This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The specified function will not have prologue/epilogue sequences generated by the compiler. Only basic asm statements can safely be included in naked functions (Basic Asm). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended upon to work reliably and are not supported.
OS_main function attribute, AVR OS_task function attribute, AVR On AVR, functions with the OS_main or OS_task attribute do not save/restore any call-saved register in their prologue/epilogue.
The OS_main attribute can be used when there is guarantee that interrupts are disabled at the time when the function is entered. This saves resources when the stack pointer has to be changed to set up a frame for local variables.
The OS_task attribute can be used when there is no guarantee that interrupts are disabled at that time when the function is entered like for, eg task functions in a multi-threading operating system. In that case, changing the stack pointer register is guarded by save/clear/restore of the global interrupt enable flag.
The differences to the naked function attribute are:
signal function attribute, AVR Use this attribute on the AVR to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.
See also the interrupt function attribute.
The AVR hardware globally disables interrupts when an interrupt is executed. Interrupt handler functions defined with the signal attribute do not re-enable interrupts. It is save to enable interrupts in a signal handler. This save only applies to the code generated by the compiler and not to the IRQ layout of the application which is responsibility of the application.
If both signal and interrupt are specified for the same function, signal is silently ignored.
:: _blackfin-function-attributes:
These function attributes are supported by the Blackfin back end:
exception_handler function attribute
Use this attribute on the Blackfin to indicate that the specified function is an exception handler. The compiler generates function entry and exit sequences suitable for use in an exception handler when this attribute is present.
interrupt_handler function attribute, Blackfin Use this attribute to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.
kspisusp function attribute, Blackfin
When used together with interrupt_handler, exception_handler or nmi_handler, code is generated to load the stack pointer from the USP register in the function prologue.
l1_text function attribute, Blackfin This attribute specifies a function to be placed into L1 Instruction SRAM The function is put into a specific section named .l1.text. With -mfdpic, function calls with a such function as the callee or caller uses inlined PLT.
l2 function attribute, Blackfin This attribute specifies a function to be placed into L2 SRAM. The function is put into a specific section named .l2.text. With -mfdpic, callers of such functions use an inlined PLT.
longcall function attribute, Blackfin shortcall function attribute, Blackfin The longcall attribute indicates that the function might be far away from the call site and require a different (more expensive) calling sequence. The shortcall attribute indicates that the function is always close enough for the shorter calling sequence to be used. These attributes override the -mlongcall switch.
nesting function attribute, Blackfin
Use this attribute together with interrupt_handler, exception_handler or nmi_handler to indicate that the function entry code should enable nested interrupts or exceptions.
nmi_handler function attribute, Blackfin
Use this attribute on the Blackfin to indicate that the specified function is an NMI handler. The compiler generates function entry and exit sequences suitable for use in an NMI handler when this attribute is present.
saveall function attribute, Blackfin
Use this attribute to indicate that all registers except the stack pointer should be saved in the prologue regardless of whether they are used or not.
:: _cr16-function-attributes:
These function attributes are supported by the CR16 back end:
interrupt function attribute, CR16 Use this attribute to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.
:: _epiphany-function-attributes:
These function attributes are supported by the Epiphany back end:
disinterrupt function attribute, Epiphany This attribute causes the compiler to emit instructions to disable interrupts for the duration of the given function.
forwarder_section function attribute, Epiphany This attribute modifies the behavior of an interrupt handler. The interrupt handler may be in external memory which cannot be reached by a branch instruction, so generate a local memory trampoline to transfer control. The single parameter identifies the section where the trampoline is placed.
interrupt function attribute, Epiphany Use this attribute to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present. It may also generate a special section with code to initialize the interrupt vector table.
On Epiphany targets one or more optional parameters can be added like this:
void __attribute__ ((interrupt ("dma0, dma1"))) universal_dma_handler ();
Permissible values for these parameters are: reset, software_exception, page_miss, timer0, timer1, message, dma0, dma1, wand and swi. Multiple parameters indicate that multiple entries in the interrupt vector table should be initialized for this function, i.e. for each parameter name, a jump to the function is emitted in the section ivt_entry_``name``. The parameter(s) may be omitted entirely, in which case no interrupt vector table entry is provided.
Note that interrupts are enabled inside the function unless the disinterrupt attribute is also specified.
The following examples are all valid uses of these attributes on Epiphany targets:
void __attribute__ ((interrupt)) universal_handler ();
void __attribute__ ((interrupt ("dma1"))) dma1_handler ();
void __attribute__ ((interrupt ("dma0, dma1")))
universal_dma_handler ();
void __attribute__ ((interrupt ("timer0"), disinterrupt))
fast_timer_handler ();
void __attribute__ ((interrupt ("dma0, dma1"),
forwarder_section ("tramp")))
external_dma_handler ();
long_call function attribute, Epiphany short_call function attribute, Epiphany
These attributes specify how a particular function is called. These attributes override the -mlong-calls (Adapteva Epiphany Options) command-line switch and #pragma long_calls settings.
:: _h8/300-function-attributes:
These function attributes are available for H8/300 targets:
function_vector function attribute, H8/300 Use this attribute on the H8/300, H8/300H, and H8S to indicate that the specified function should be called through the function vector. Calling a function through the function vector reduces code size; however, the function vector has a limited size (maximum 128 entries on the H8/300 and 64 entries on the H8/300H and H8S) and shares space with the interrupt vector.
interrupt_handler function attribute, H8/300 Use this attribute on the H8/300, H8/300H, and H8S to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.
saveall function attribute, H8/300
Use this attribute on the H8/300, H8/300H, and H8S to indicate that all registers except the stack pointer should be saved in the prologue regardless of whether they are used or not.
:: _ia-64-function-attributes:
These function attributes are supported on IA-64 targets:
syscall_linkage function attribute, IA-64 This attribute is used to modify the IA-64 calling convention by marking all input registers as live at all function exits. This makes it possible to restart a system call after an interrupt without having to save/restore the input registers. This also prevents kernel data from leaking into application code.
version_id function attribute, IA-64 This IA-64 HP-UX attribute, attached to a global variable or function, renames a symbol to contain a version string, thus allowing for function level versioning. HP-UX system header files may use function level versioning for some system calls.
extern int foo () __attribute__((version_id ("20040821")));
Calls to foo are mapped to calls to foo{20040821}.
:: _m32c-function-attributes:
These function attributes are supported by the M32C back end:
bank_switch function attribute, M32C When added to an interrupt handler with the M32C port, causes the prologue and epilogue to use bank switching to preserve the registers rather than saving them on the stack.
fast_interrupt function attribute, M32C Use this attribute on the M32C port to indicate that the specified function is a fast interrupt handler. This is just like the interrupt attribute, except that freit is used to return instead of reit.
function_vector function attribute, M16C/M32C On M16C/M32C targets, the function_vector attribute declares a special page subroutine call function. Use of this attribute reduces the code size by 2 bytes for each call generated to the subroutine. The argument to the attribute is the vector number entry from the special page vector table which contains the 16 low-order bits of the subroutines entry address. Each vector table has special page number (18 to 255) that is used in jsrs instructions. Jump addresses of the routines are generated by adding 0x0F0000 (in case of M16C targets) or 0xFF0000 (in case of M32C targets), to the 2-byte addresses set in the vector table. Therefore you need to ensure that all the special page vector routines should get mapped within the address range 0x0F0000 to 0x0FFFFF (for M16C) and 0xFF0000 to 0xFFFFFF (for M32C).
In the following example 2 bytes are saved for each call to function foo.
void foo (void) __attribute__((function_vector(0x18)));
void foo (void)
{
}
void bar (void)
{
foo();
}
If functions are defined in one file and are called in another file, then be sure to write this declaration in both files.
This attribute is ignored for R8C target.
interrupt function attribute, M32C Use this attribute to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.
:: _m32r/d-function-attributes:
These function attributes are supported by the M32R/D back end:
interrupt function attribute, M32R/D Use this attribute to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.
model (model-name)
model function attribute, M32R/D
On the M32R/D, use this attribute to set the addressability of an object, and of the code generated for a function. The identifier model-name is one of small, medium, or large, representing each of the code models.
Small model objects live in the lower 16MB of memory (so that their addresses can be loaded with the ld24 instruction), and are callable with the bl instruction.
Medium model objects may live anywhere in the 32-bit address space (the compiler generates seth/add3 instructions to load their addresses), and are callable with the bl instruction.
Large model objects may live anywhere in the 32-bit address space (the compiler generates seth/add3 instructions to load their addresses), and may not be reachable with the bl instruction (the compiler generates the much slower seth/add3/jl instruction sequence).
:: _m68k-function-attributes:
These function attributes are supported by the m68k back end:
interrupt function attribute, m68k interrupt_handler function attribute, m68k Use this attribute to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present. Either name may be used.
interrupt_thread function attribute, fido Use this attribute on fido, a subarchitecture of the m68k, to indicate that the specified function is an interrupt handler that is designed to run as a thread. The compiler omits generate prologue/epilogue sequences and replaces the return instruction with a sleep instruction. This attribute is available only on fido.
:: _mcore-function-attributes:
These function attributes are supported by the MCORE back end:
naked function attribute, MCORE This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The specified function will not have prologue/epilogue sequences generated by the compiler. Only basic asm statements can safely be included in naked functions (Basic Asm). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended upon to work reliably and are not supported.
:: _mep-function-attributes:
These function attributes are supported by the MeP back end:
disinterrupt function attribute, MeP On MeP targets, this attribute causes the compiler to emit instructions to disable interrupts for the duration of the given function.
interrupt function attribute, MeP Use this attribute to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.
near function attribute, MeP This attribute causes the compiler to assume the called function is close enough to use the normal calling convention, overriding the -mtf command-line option.
far function attribute, MeP On MeP targets this causes the compiler to use a calling convention that assumes the called function is too far away for the built-in addressing modes.
vliw function attribute, MeP The vliw attribute tells the compiler to emit instructions in VLIW mode instead of core mode. Note that this attribute is not allowed unless a VLIW coprocessor has been configured and enabled through command-line options.
:: _microblaze-function-attributes:
These function attributes are supported on MicroBlaze targets:
save_volatiles function attribute, MicroBlaze Use this attribute to indicate that the function is an interrupt handler. All volatile registers (in addition to non-volatile registers) are saved in the function prologue. If the function is a leaf function, only volatiles used by the function are saved. A normal function return is generated instead of a return from interrupt.
break_handler function attribute, MicroBlaze
Use this attribute to indicate that the specified function is a break handler. The compiler generates function entry and exit sequences suitable for use in an break handler when this attribute is present. The return from break_handler is done through the rtbd instead of rtsd.
void f () __attribute__ ((break_handler));
:: _microsoft-windows-function-attributes:
The following attributes are available on Microsoft Windows and Symbian OS targets.
dllexport function attribute __declspec(dllexport) On Microsoft Windows targets and Symbian OS targets the dllexport attribute causes the compiler to provide a global pointer to a pointer in a DLL, so that it can be referenced with the dllimport attribute. On Microsoft Windows targets, the pointer name is formed by combining _imp__ and the function or variable name.
You can use __declspec(dllexport) as a synonym for __attribute__ ((dllexport)) for compatibility with other compilers.
On systems that support the visibility attribute, this attribute also implies default visibility. It is an error to explicitly specify any other visibility.
GCCs default behavior is to emit all inline functions with the dllexport attribute. Since this can cause object file-size bloat, you can use -fno-keep-inline-dllexport, which tells GCC to ignore the attribute for inlined functions unless the -fkeep-inline-functions flag is used instead.
The attribute is ignored for undefined symbols.
When applied to C++ classes, the attribute marks defined non-inlined member functions and static data members as exports. Static consts initialized in-class are not marked unless they are also defined out-of-class.
For Microsoft Windows targets there are alternative methods for including the symbol in the DLLs export table such as using a .def file with an EXPORTS section or, with GNU ld, using the --export-all linker flag.
dllimport function attribute __declspec(dllimport) On Microsoft Windows and Symbian OS targets, the dllimport attribute causes the compiler to reference a function or variable via a global pointer to a pointer that is set up by the DLL exporting the symbol. The attribute implies extern. On Microsoft Windows targets, the pointer name is formed by combining _imp__ and the function or variable name.
You can use __declspec(dllimport) as a synonym for __attribute__ ((dllimport)) for compatibility with other compilers.
On systems that support the visibility attribute, this attribute also implies default visibility. It is an error to explicitly specify any other visibility.
Currently, the attribute is ignored for inlined functions. If the attribute is applied to a symbol definition, an error is reported. If a symbol previously declared dllimport is later defined, the attribute is ignored in subsequent references, and a warning is emitted. The attribute is also overridden by a subsequent declaration as dllexport.
When applied to C++ classes, the attribute marks non-inlined member functions and static data members as imports. However, the attribute is ignored for virtual methods to allow creation of vtables using thunks.
On the SH Symbian OS target the dllimport attribute also has another affectit can cause the vtable and run-time type information for a class to be exported. This happens when the class has a dllimported constructor or a non-inline, non-pure virtual function and, for either of those two conditions, the class also has an inline constructor or destructor and has a key function that is defined in the current translation unit.
For Microsoft Windows targets the use of the dllimport attribute on functions is not necessary, but provides a small performance benefit by eliminating a thunk in the DLL The use of the dllimport attribute on imported variables can be avoided by passing the --enable-auto-import switch to the GNU linker. As with functions, using the attribute for a variable eliminates a thunk in the DLL
One drawback to using this attribute is that a pointer to a variable marked as dllimport cannot be used as a constant address. However, a pointer to a function with the dllimport attribute can be used as a constant initializer; in this case, the address of a stub function in the import lib is referenced. On Microsoft Windows targets, the attribute can be disabled for functions by setting the -mnop-fun-dllimport flag.
:: _mips-function-attributes:
These function attributes are supported by the MIPS back end:
interrupt function attribute, MIPS Use this attribute to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.
You can use the following attributes to modify the behavior of an interrupt handler:
use_shadow_register_set function attribute, MIPS Assume that the handler uses a shadow register set, instead of the main general-purpose registers.
keep_interrupts_masked function attribute, MIPS Keep interrupts masked for the whole function. Without this attribute, GCC tries to reenable interrupts for as much of the function as it can.
use_debug_exception_return function attribute, MIPS Return using the deret instruction. Interrupt handlers that dont have this attribute return using eret instead.
You can use any combination of these attributes, as shown below:
void __attribute__ ((interrupt)) v0 ();
void __attribute__ ((interrupt, use_shadow_register_set)) v1 ();
void __attribute__ ((interrupt, keep_interrupts_masked)) v2 ();
void __attribute__ ((interrupt, use_debug_exception_return)) v3 ();
void __attribute__ ((interrupt, use_shadow_register_set,
keep_interrupts_masked)) v4 ();
void __attribute__ ((interrupt, use_shadow_register_set,
use_debug_exception_return)) v5 ();
void __attribute__ ((interrupt, keep_interrupts_masked,
use_debug_exception_return)) v6 ();
void __attribute__ ((interrupt, use_shadow_register_set,
keep_interrupts_masked,
use_debug_exception_return)) v7 ();
long_call function attribute, MIPS near function attribute, MIPS far function attribute, MIPS These attributes specify how a particular function is called on MIPS The attributes override the -mlong-calls (MIPS Options) command-line switch. The long_call and far attributes are synonyms, and cause the compiler to always call the function by first loading its address into a register, and then using the contents of that register. The near attribute has the opposite effect; it specifies that non-PIC calls should be made using the more efficient jal instruction.
mips16 function attribute, MIPS nomips16 function attribute, MIPS
On MIPS targets, you can use the mips16 and nomips16 function attributes to locally select or turn off MIPS16 code generation. A function with the mips16 attribute is emitted as MIPS16 code, while MIPS16 code generation is disabled for functions with the nomips16 attribute. These attributes override the -mips16 and -mno-mips16 options on the command line (MIPS Options).
When compiling files containing mixed MIPS16 and non-MIPS16 code, the preprocessor symbol __mips16 reflects the setting on the command line, not that within individual functions. Mixed MIPS16 and non-MIPS16 code may interact badly with some GCC extensions such as __builtin_apply (Constructing Calls).
micromips function attribute nomicromips function attribute
On MIPS targets, you can use the micromips and nomicromips function attributes to locally select or turn off microMIPS code generation. A function with the micromips attribute is emitted as microMIPS code, while microMIPS code generation is disabled for functions with the nomicromips attribute. These attributes override the -mmicromips and -mno-micromips options on the command line (MIPS Options).
When compiling files containing mixed microMIPS and non-microMIPS code, the preprocessor symbol __mips_micromips reflects the setting on the command line, not that within individual functions. Mixed microMIPS and non-microMIPS code may interact badly with some GCC extensions such as __builtin_apply (Constructing Calls).
nocompression function attribute, MIPS On MIPS targets, you can use the nocompression function attribute to locally turn off MIPS16 and microMIPS code generation. This attribute overrides the -mips16 and -mmicromips options on the command line (MIPS Options).
:: _msp430-function-attributes:
These function attributes are supported by the MSP430 back end:
critical function attribute, MSP430 Critical functions disable interrupts upon entry and restore the previous interrupt state upon exit. Critical functions cannot also have the naked or reentrant attributes. They can have the interrupt attribute.
interrupt function attribute, MSP430 Use this attribute to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.
You can provide an argument to the interrupt attribute which specifies a name or number. If the argument is a number it indicates the slot in the interrupt vector table (0 - 31) to which this handler should be assigned. If the argument is a name it is treated as a symbolic name for the vector slot. These names should match up with appropriate entries in the linker script. By default the names watchdog for vector 26, nmi for vector 30 and reset for vector 31 are recognized.
naked function attribute, MSP430 This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The specified function will not have prologue/epilogue sequences generated by the compiler. Only basic asm statements can safely be included in naked functions (Basic Asm). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended upon to work reliably and are not supported.
reentrant function attribute, MSP430 Reentrant functions disable interrupts upon entry and enable them upon exit. Reentrant functions cannot also have the naked or critical attributes. They can have the interrupt attribute.
wakeup function attribute, MSP430 This attribute only applies to interrupt functions. It is silently ignored if applied to a non-interrupt function. A wakeup interrupt function will rouse the processor from any low-power state that it might be in when the function exits.
:: _nds32-function-attributes:
These function attributes are supported by the NDS32 back end:
exception function attribute
Use this attribute on the NDS32 target to indicate that the specified function is an exception handler. The compiler will generate corresponding sections for use in an exception handler.
interrupt function attribute, NDS32 On NDS32 target, this attribute indicates that the specified function is an interrupt handler. The compiler generates corresponding sections for use in an interrupt handler. You can use the following attributes to modify the behavior:
nested function attribute, NDS32 This interrupt service routine is interruptible.
not_nested function attribute, NDS32 This interrupt service routine is not interruptible.
nested_ready function attribute, NDS32 This interrupt service routine is interruptible after PSW.GIE (global interrupt enable) is set. This allows interrupt service routine to finish some short critical code before enabling interrupts.
save_all function attribute, NDS32 The system will help save all registers into stack before entering interrupt handler.
partial_save function attribute, NDS32 The system will help save caller registers into stack before entering interrupt handler.
naked function attribute, NDS32 This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The specified function will not have prologue/epilogue sequences generated by the compiler. Only basic asm statements can safely be included in naked functions (Basic Asm). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended upon to work reliably and are not supported.
reset function attribute, NDS32
Use this attribute on the NDS32 target to indicate that the specified function is a reset handler. The compiler will generate corresponding sections for use in a reset handler. You can use the following attributes to provide extra exception handling:
nmi function attribute, NDS32 Provide a user-defined function to handle NMI exception.
warm function attribute, NDS32 Provide a user-defined function to handle warm reset exception.
:: _nios-ii-function-attributes:
These function attributes are supported by the Nios II back end:
target (options) target function attribute As discussed in Common Function Attributes, this attribute allows specification of target-specific compilation options.
When compiling for Nios II, the following options are allowed:
custom-insn``=``N no-custom-insn target("custom-``insn``=``N”)`` function attribute, Nios II target("no-custom-``insn”)`` function attribute, Nios II Each custom-insn``=``N attribute locally enables use of a custom instruction with encoding N when generating code that uses insn. Similarly, no-custom-insn locally inhibits use of the custom instruction insn. These target attributes correspond to the -mcustom-``insn``=``N`` and -mno-custom-``insn`` command-line options, and support the same set of insn keywords. Nios II Options, for more information.
custom-fpu-cfg=``name`` target("custom-fpu-cfg=``name”)`` function attribute, Nios II This attribute corresponds to the -mcustom-fpu-cfg=``name`` command-line option, to select a predefined set of custom instructions named name. Nios II Options, for more information.
:: _powerpc-function-attributes:
These function attributes are supported by the PowerPC back end:
longcall function attribute, PowerPC shortcall function attribute, PowerPC The longcall attribute indicates that the function might be far away from the call site and require a different (more expensive) calling sequence. The shortcall attribute indicates that the function is always close enough for the shorter calling sequence to be used. These attributes override both the -mlongcall switch and the #pragma longcall setting.
RS/6000 and PowerPC Options, for more information on whether long calls are necessary.
target (options)
target function attribute As discussed in Common Function Attributes, this attribute allows specification of target-specific compilation options.
On the PowerPC, the following options are allowed:
target("altivec") function attribute, PowerPC Generate code that uses (does not use) AltiVec instructions. In 32-bit code, you cannot enable AltiVec instructions unless -mabi=altivec is used on the command line.
target("cmpb") function attribute, PowerPC Generate code that uses (does not use) the compare bytes instruction implemented on the POWER6 processor and other processors that support the PowerPC V2.05 architecture.
target("dlmzb") function attribute, PowerPC Generate code that uses (does not use) the string-search dlmzb instruction on the IBM 405, 440, 464 and 476 processors. This instruction is generated by default when targeting those processors.
target("fprnd") function attribute, PowerPC Generate code that uses (does not use) the FP round to integer instructions implemented on the POWER5+ processor and other processors that support the PowerPC V2.03 architecture.
target("hard-dfp") function attribute, PowerPC Generate code that uses (does not use) the decimal floating-point instructions implemented on some POWER processors.
target("isel") function attribute, PowerPC Generate code that uses (does not use) ISEL instruction.
target("mfcrf") function attribute, PowerPC Generate code that uses (does not use) the move from condition register field instruction implemented on the POWER4 processor and other processors that support the PowerPC V2.01 architecture.
target("mfpgpr") function attribute, PowerPC Generate code that uses (does not use) the FP move to/from general purpose register instructions implemented on the POWER6X processor and other processors that support the extended PowerPC V2.05 architecture.
target("mulhw") function attribute, PowerPC Generate code that uses (does not use) the half-word multiply and multiply-accumulate instructions on the IBM 405, 440, 464 and 476 processors. These instructions are generated by default when targeting those processors.
target("multiple") function attribute, PowerPC Generate code that uses (does not use) the load multiple word instructions and the store multiple word instructions.
target("update") function attribute, PowerPC Generate code that uses (does not use) the load or store instructions that update the base register to the address of the calculated memory location.
target("popcntb") function attribute, PowerPC Generate code that uses (does not use) the popcount and double-precision FP reciprocal estimate instruction implemented on the POWER5 processor and other processors that support the PowerPC V2.02 architecture.
target("popcntd") function attribute, PowerPC Generate code that uses (does not use) the popcount instruction implemented on the POWER7 processor and other processors that support the PowerPC V2.06 architecture.
target("powerpc-gfxopt") function attribute, PowerPC Generate code that uses (does not use) the optional PowerPC architecture instructions in the Graphics group, including floating-point select.
target("powerpc-gpopt") function attribute, PowerPC Generate code that uses (does not use) the optional PowerPC architecture instructions in the General Purpose group, including floating-point square root.
target("recip-precision") function attribute, PowerPC Assume (do not assume) that the reciprocal estimate instructions provide higher-precision estimates than is mandated by the PowerPC ABI.
target("string") function attribute, PowerPC Generate code that uses (does not use) the load string instructions and the store string word instructions to save multiple registers and do small block moves.
target("vsx") function attribute, PowerPC Generate code that uses (does not use) vector/scalar (VSX) instructions, and also enable the use of built-in functions that allow more direct access to the VSX instruction set. In 32-bit code, you cannot enable VSX or AltiVec instructions unless -mabi=altivec is used on the command line.
target("friz") function attribute, PowerPC Generate (do not generate) the friz instruction when the -funsafe-math-optimizations option is used to optimize rounding a floating-point value to 64-bit integer and back to floating point. The friz instruction does not return the same value if the floating-point number is too large to fit in an integer.
target("avoid-indexed-addresses") function attribute, PowerPC Generate code that tries to avoid (not avoid) the use of indexed load or store instructions.
target("paired") function attribute, PowerPC Generate code that uses (does not use) the generation of PAIRED simd instructions.
target("longcall") function attribute, PowerPC Generate code that assumes (does not assume) that all calls are far away so that a longer more expensive calling sequence is required.
cpu=``CPU``
target("cpu=``CPU”)`` function attribute, PowerPC Specify the architecture to generate code for when compiling the function. If you select the target("cpu=power7") attribute when generating 32-bit code, VSX and AltiVec instructions are not generated unless you use the -mabi=altivec option on the command line.
tune=``TUNE`` target("tune=``TUNE”)`` function attribute, PowerPC Specify the architecture to tune for when compiling the function. If you do not specify the target("tune=``TUNE”)`` attribute and you do specify the target("cpu=``CPU”)`` attribute, compilation tunes for the CPU architecture, and not the default tuning specified on the command line.
On the PowerPC, the inliner does not inline a function that has different target options than the caller, unless the callee has a subset of the target options of the caller.
:: _rl78-function-attributes:
These function attributes are supported by the RL78 back end:
interrupt function attribute, RL78 brk_interrupt function attribute, RL78 These attributes indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.
Use brk_interrupt instead of interrupt for handlers intended to be used with the BRK opcode (i.e. those that must end with RETB instead of RETI).
naked function attribute, RL78 This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The specified function will not have prologue/epilogue sequences generated by the compiler. Only basic asm statements can safely be included in naked functions (Basic Asm). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended upon to work reliably and are not supported.
:: _rx-function-attributes:
These function attributes are supported by the RX back end:
fast_interrupt function attribute, RX Use this attribute on the RX port to indicate that the specified function is a fast interrupt handler. This is just like the interrupt attribute, except that freit is used to return instead of reit.
interrupt function attribute, RX Use this attribute to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.
On RX targets, you may specify one or more vector numbers as arguments to the attribute, as well as naming an alternate table name. Parameters are handled sequentially, so one handler can be assigned to multiple entries in multiple tables. One may also pass the magic string "$default" which causes the function to be used for any unfilled slots in the current table.
This example shows a simple assignment of a function to one vector in the default table (note that preprocessor macros may be used for chip-specific symbolic vector names):
void __attribute__ ((interrupt (5))) txd1_handler ();
This example assigns a function to two slots in the default table (using preprocessor macros defined elsewhere) and makes it the default for the dct table:
void __attribute__ ((interrupt (RXD1_VECT,RXD2_VECT,"dct","$default")))
txd1_handler ();
naked function attribute, RX This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The specified function will not have prologue/epilogue sequences generated by the compiler. Only basic asm statements can safely be included in naked functions (Basic Asm). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended upon to work reliably and are not supported.
vector function attribute, RX This RX attribute is similar to the interrupt attribute, including its parameters, but does not make the function an interrupt-handler type function (i.e. it retains the normal C function calling ABI). See the interrupt attribute for a description of its arguments.
:: _s/390-function-attributes:
These function attributes are supported on the S/390:
hotpatch (halfwords-before-function-label,``halfwords-after-function-label``) hotpatch function attribute, S/390
On S/390 System z targets, you can use this function attribute to make GCC generate a hot-patching function prologue. If the -mhotpatch= command-line option is used at the same time, the hotpatch attribute takes precedence. The first of the two arguments specifies the number of halfwords to be added before the function label. A second argument can be used to specify the number of halfwords to be added after the function label. For both arguments the maximum allowed value is 1000000.
If both arguments are zero, hotpatching is disabled.
:: _sh-function-attributes:
These function attributes are supported on the SH family of processors:
function_vector function attribute, SH
On SH2A targets, this attribute declares a function to be called using the TBR relative addressing mode. The argument to this attribute is the entry number of the same function in a vector table containing all the TBR relative addressable functions. For correct operation the TBR must be setup accordingly to point to the start of the vector table before any functions with this attribute are invoked. Usually a good place to do the initialization is the startup routine. The TBR relative vector table can have at max 256 function entries. The jumps to these functions are generated using a SH2A specific, non delayed branch instruction JSR/N (disp8,TBR). You must use GAS and GLD from GNU binutils version 2.7 or later for this attribute to work correctly.
In an application, for a function being called once, this attribute saves at least 8 bytes of code; and if other successive calls are being made to the same function, it saves 2 bytes of code per each of these calls.
interrupt_handler function attribute, SH Use this attribute to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.
nosave_low_regs function attribute, SH Use this attribute on SH targets to indicate that an interrupt_handler function should not save and restore registers R0..R7. This can be used on SH3* and SH4* targets that have a second R0..R7 register bank for non-reentrant interrupt handlers.
renesas function attribute, SH On SH targets this attribute specifies that the function or struct follows the Renesas ABI.
resbank function attribute, SH On the SH2A target, this attribute enables the high-speed register saving and restoration using a register bank for interrupt_handler routines. Saving to the bank is performed automatically after the CPU accepts an interrupt that uses a register bank.
The nineteen 32-bit registers comprising general register R0 to R14, control register GBR, and system registers MACH, MACL, and PR and the vector table address offset are saved into a register bank. Register banks are stacked in first-in last-out (FILO) sequence. Restoration from the bank is executed by issuing a RESBANK instruction.
sp_switch function attribute, SH Use this attribute on the SH to indicate an interrupt_handler function should switch to an alternate stack. It expects a string argument that names a global variable holding the address of the alternate stack.
void *alt_stack;
void f () __attribute__ ((interrupt_handler,
sp_switch ("alt_stack")));
trap_exit function attribute, SH Use this attribute on the SH for an interrupt_handler to return using trapa instead of rte. This attribute expects an integer argument specifying the trap number to be used.
trapa_handler function attribute, SH On SH targets this function attribute is similar to interrupt_handler but it does not save and restore all registers.
:: _spu-function-attributes:
These function attributes are supported by the SPU back end:
naked function attribute, SPU This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The specified function will not have prologue/epilogue sequences generated by the compiler. Only basic asm statements can safely be included in naked functions (Basic Asm). While using extended asm or a mixture of basic asm and C code may appear to work, they cannot be depended upon to work reliably and are not supported.
:: _symbian-os-function-attributes:
Microsoft Windows Function Attributes, for discussion of the dllexport and dllimport attributes.
:: _visium-function-attributes:
These function attributes are supported by the Visium back end:
interrupt function attribute, Visium Use this attribute to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.
:: _x86-function-attributes:
These function attributes are supported by the x86 back end:
cdecl function attribute, x86-32
On the x86-32 targets, the cdecl attribute causes the compiler to assume that the calling function pops off the stack space used to pass arguments. This is useful to override the effects of the -mrtd switch.
fastcall function attribute, x86-32
On x86-32 targets, the fastcall attribute causes the compiler to pass the first argument (if of integral type) in the register ECX and the second argument (if of integral type) in the register EDX Subsequent and other typed arguments are passed on the stack. The called function pops the arguments off the stack. If the number of arguments is variable all arguments are pushed on the stack.
thiscall function attribute, x86-32
On x86-32 targets, the thiscall attribute causes the compiler to pass the first argument (if of integral type) in the register ECX. Subsequent and other typed arguments are passed on the stack. The called function pops the arguments off the stack. If the number of arguments is variable all arguments are pushed on the stack. The thiscall attribute is intended for C++ non-static member functions. As a GCC extension, this calling convention can be used for C functions and for static member methods.
ms_abi function attribute, x86 sysv_abi function attribute, x86
On 32-bit and 64-bit x86 targets, you can use an ABI attribute to indicate which calling convention should be used for a function. The ms_abi attribute tells the compiler to use the Microsoft ABI, while the sysv_abi attribute tells the compiler to use the ABI used on GNU/Linux and other systems. The default is to use the Microsoft ABI when targeting Windows. On all other systems, the default is the x86/AMD ABI.
Note, the ms_abi attribute for Microsoft Windows 64-bit targets currently requires the -maccumulate-outgoing-args option.
callee_pop_aggregate_return (number)
callee_pop_aggregate_return function attribute, x86
On x86-32 targets, you can use this attribute to control how aggregates are returned in memory. If the caller is responsible for popping the hidden pointer together with the rest of the arguments, specify number equal to zero. If callee is responsible for popping the hidden pointer, specify number equal to one.
The default x86-32 ABI assumes that the callee pops the stack for hidden pointer. However, on x86-32 Microsoft Windows targets, the compiler assumes that the caller pops the stack for hidden pointer.
ms_hook_prologue function attribute, x86
On 32-bit and 64-bit x86 targets, you can use this function attribute to make GCC generate the hot-patching function prologue used in Win32 API functions in Microsoft Windows XP Service Pack 2 and newer.
regparm (number)
regparm function attribute, x86
On x86-32 targets, the regparm attribute causes the compiler to pass arguments number one to number if they are of integral type in registers EAX, EDX, and ECX instead of on the stack. Functions that take a variable number of arguments continue to be passed all of their arguments on the stack.
Beware that on some ELF systems this attribute is unsuitable for global functions in shared libraries with lazy binding (which is the default). Lazy binding sends the first call via resolving code in the loader, which might assume EAX, EDX and ECX can be clobbered, as per the standard calling conventions. Solaris 8 is affected by this. Systems with the GNU C Library version 2.1 or higher and FreeBSD are believed to be safe since the loaders there save EAX, EDX and ECX. (Lazy binding can be disabled with the linker or the loader if desired, to avoid the problem.)
sseregparm function attribute, x86 On x86-32 targets with SSE support, the sseregparm attribute causes the compiler to pass up to 3 floating-point arguments in SSE registers instead of on the stack. Functions that take a variable number of arguments continue to pass all of their floating-point arguments on the stack.
force_align_arg_pointer function attribute, x86 On x86 targets, the force_align_arg_pointer attribute may be applied to individual function definitions, generating an alternate prologue and epilogue that realigns the run-time stack if necessary. This supports mixing legacy codes that run with a 4-byte aligned stack with modern codes that keep a 16-byte stack for SSE compatibility.
stdcall function attribute, x86-32
On x86-32 targets, the stdcall attribute causes the compiler to assume that the called function pops off the stack space used to pass arguments, unless it takes a variable number of arguments.
target (options)
target function attribute As discussed in Common Function Attributes, this attribute allows specification of target-specific compilation options.
On the x86, the following options are allowed:
target("abm") function attribute, x86 Enable/disable the generation of the advanced bit instructions.
target("aes") function attribute, x86 Enable/disable the generation of the AES instructions.
target("default") function attribute, x86 Function Multiversioning, where it is used to specify the default function version.
target("mmx") function attribute, x86 Enable/disable the generation of the MMX instructions.
target("pclmul") function attribute, x86 Enable/disable the generation of the PCLMUL instructions.
target("popcnt") function attribute, x86 Enable/disable the generation of the POPCNT instruction.
target("sse") function attribute, x86 Enable/disable the generation of the SSE instructions.
target("sse2") function attribute, x86 Enable/disable the generation of the SSE2 instructions.
target("sse3") function attribute, x86 Enable/disable the generation of the SSE3 instructions.
target("sse4") function attribute, x86 Enable/disable the generation of the SSE4 instructions (both SSE4.1 and SSE4.2).
target("sse4.1") function attribute, x86 Enable/disable the generation of the sse4.1 instructions.
target("sse4.2") function attribute, x86 Enable/disable the generation of the sse4.2 instructions.
target("sse4a") function attribute, x86 Enable/disable the generation of the SSE4A instructions.
target("fma4") function attribute, x86 Enable/disable the generation of the FMA4 instructions.
target("xop") function attribute, x86 Enable/disable the generation of the XOP instructions.
target("lwp") function attribute, x86 Enable/disable the generation of the LWP instructions.
target("ssse3") function attribute, x86 Enable/disable the generation of the SSSE3 instructions.
target("cld") function attribute, x86 Enable/disable the generation of the CLD before string moves.
target("fancy-math-387") function attribute, x86 Enable/disable the generation of the sin, cos, and sqrt instructions on the 387 floating-point unit.
target("fused-madd") function attribute, x86 Enable/disable the generation of the fused multiply/add instructions.
target("ieee-fp") function attribute, x86 Enable/disable the generation of floating point that depends on IEEE arithmetic.
target("inline-all-stringops") function attribute, x86 Enable/disable inlining of string operations.
target("inline-stringops-dynamically") function attribute, x86 Enable/disable the generation of the inline code to do small string operations and calling the library routines for large operations.
target("align-stringops") function attribute, x86 Do/do not align destination of inlined string operations.
target("recip") function attribute, x86 Enable/disable the generation of RCPSS, RCPPS, RSQRTSS and RSQRTPS instructions followed an additional Newton-Raphson step instead of doing a floating-point division.
arch=``ARCH``
target("arch=``ARCH”)`` function attribute, x86 Specify the architecture to generate code for in compiling the function.
tune=``TUNE`` target("tune=``TUNE”)`` function attribute, x86 Specify the architecture to tune for in compiling the function.
fpmath=``FPMATH`` target("fpmath=``FPMATH”)`` function attribute, x86 Specify which floating-point unit to use. You must specify the target("fpmath=sse,387") option as target("fpmath=sse+387") because the comma would separate different options.
On the x86, the inliner does not inline a function that has different target options than the caller, unless the callee has a subset of the target options of the caller. For example a function declared with target("sse3") can inline a function with target("sse2"), since -msse3 implies -msse2.
:: _xstormy16-function-attributes:
These function attributes are supported by the Xstormy16 back end:
interrupt function attribute, Xstormy16 Use this attribute to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.
:: _variable-attributes:
The keyword __attribute__ allows you to specify special attributes of variables or structure fields. This keyword is followed by an attribute specification inside double parentheses. Some attributes are currently defined generically for variables. Other attributes are defined for variables on particular target systems. Other attributes are available for functions (Function Attributes), labels (Label Attributes) and for types (Type Attributes). Other front ends might define more attributes (C++ ExtensionsExtensions to the C++ Language).
Attribute Syntax, for details of the exact syntax for using attributes.
:: _common-variable-attributes:
The following attributes are supported on most targets.
aligned variable attribute aligned (alignment) This attribute specifies a minimum alignment for the variable or structure field, measured in bytes. For example, the declaration:
int x __attribute__ ((aligned (16))) = 0;
causes the compiler to allocate the global variable x on a 16-byte boundary. On a 68040, this could be used in conjunction with an asm expression to access the move16 instruction which requires 16-byte aligned operands.
You can also specify the alignment of structure fields. For example, to create a double-word aligned int pair, you could write:
struct foo { int x[2] __attribute__ ((aligned (8))); };
This is an alternative to creating a union with a double member, which forces the union to be double-word aligned.
As in the preceding examples, you can explicitly specify the alignment (in bytes) that you wish the compiler to use for a given variable or structure field. Alternatively, you can leave out the alignment factor and just ask the compiler to align a variable or field to the default alignment for the target architecture you are compiling for. The default alignment is sufficient for all scalar types, but may not be enough for all vector types on a target that supports vector operations. The default alignment is fixed for a particular target ABI.
GCC also provides a target specific macro __BIGGEST_ALIGNMENT__, which is the largest alignment ever used for any data type on the target machine you are compiling for. For example, you could write:
short array[3] __attribute__ ((aligned (__BIGGEST_ALIGNMENT__)));
The compiler automatically sets the alignment for the declared variable or field to __BIGGEST_ALIGNMENT__. Doing this can often make copy operations more efficient, because the compiler can use whatever instructions copy the biggest chunks of memory when performing copies to or from the variables or fields that you have aligned this way. Note that the value of __BIGGEST_ALIGNMENT__ may change depending on command-line options.
When used on a struct, or struct member, the aligned attribute can only increase the alignment; in order to decrease it, the packed attribute must be specified as well. When used as part of a typedef, the aligned attribute can both increase and decrease alignment, and specifying the packed attribute generates a warning.
Note that the effectiveness of aligned attributes may be limited by inherent limitations in your linker. On many systems, the linker is only able to arrange for variables to be aligned up to a certain maximum alignment. (For some linkers, the maximum supported alignment may be very very small.) If your linker is only able to align variables up to a maximum of 8-byte alignment, then specifying aligned(16) in an __attribute__ still only provides you with 8-byte alignment. See your linker documentation for further information.
The aligned attribute can also be used for functions (Common Function Attributes.)
cleanup (cleanup_function) cleanup variable attribute The cleanup attribute runs a function when the variable goes out of scope. This attribute can only be applied to auto function scope variables; it may not be applied to parameters or variables with static storage duration. The function must take one parameter, a pointer to a type compatible with the variable. The return value of the function (if any) is ignored.
If -fexceptions is enabled, then cleanup_function is run during the stack unwinding that happens during the processing of the exception. Note that the cleanup attribute does not allow the exception to be caught, only to perform an action. It is undefined what happens if cleanup_function does not return normally.
common variable attribute nocommon variable attribute
The common attribute requests GCC to place a variable in common storage. The nocommon attribute requests the oppositeto allocate space for it directly.
These attributes override the default chosen by the -fno-common and -fcommon flags respectively.
deprecated variable attribute The deprecated attribute results in a warning if the variable is used anywhere in the source file. This is useful when identifying variables that are expected to be removed in a future version of a program. The warning also includes the location of the declaration of the deprecated variable, to enable users to easily find further information about why the variable is deprecated, or what they should do instead. Note that the warning only occurs for uses:
extern int old_var __attribute__ ((deprecated));
extern int old_var;
int new_fn () { return old_var; }
results in a warning on line 3 but not line 2. The optional msg argument, which must be a string, is printed in the warning if present.
The deprecated attribute can also be used for functions and types (Common Function Attributes, Common Type Attributes).
mode (mode)
mode variable attribute This attribute specifies the data type for the declarationwhichever type corresponds to the mode mode. This in effect lets you request an integer or floating-point type according to its width.
You may also specify a mode of byte or __byte__ to indicate the mode corresponding to a one-byte integer, word or __word__ for the mode of a one-word integer, and pointer or __pointer__ for the mode used to represent pointers.
packed variable attribute The packed attribute specifies that a variable or structure field should have the smallest possible alignmentone byte for a variable, and one bit for a field, unless you specify a larger value with the aligned attribute.
Here is a structure in which the field x is packed, so that it immediately follows a:
struct foo
{
char a;
int x[2] __attribute__ ((packed));
};
Note: The 4.1, 4.2 and 4.3 series of GCC ignore the packed attribute on bit-fields of type char. This has been fixed in GCC 4.4 but the change can lead to differences in the structure layout. See the documentation of -Wpacked-bitfield-compat for more information.
section (“section-name”)
section variable attribute Normally, the compiler places the objects it generates in sections like data and bss. Sometimes, however, you need additional sections, or you need certain particular variables to appear in special sections, for example to map to special hardware. The section attribute specifies that a variable (or function) lives in a particular section. For example, this small program uses several specific section names:
struct duart a __attribute__ ((section ("DUART_A"))) = { 0 };
struct duart b __attribute__ ((section ("DUART_B"))) = { 0 };
char stack[10000] __attribute__ ((section ("STACK"))) = { 0 };
int init_data __attribute__ ((section ("INITDATA")));
main()
{
/* Initialize stack pointer */
init_sp (stack + sizeof (stack));
/* Initialize initialized data */
memcpy (&init_data, &data, &edata - &data);
/* Turn on the serial ports */
init_duart (&a);
init_duart (&b);
}
Use the section attribute with global variables and not local variables, as shown in the example.
You may use the section attribute with initialized or uninitialized global variables but the linker requires each object be defined once, with the exception that uninitialized variables tentatively go in the common (or bss) section and can be multiply defined. Using the section attribute changes what section the variable goes into and may cause the linker to issue an error if an uninitialized variable has multiple definitions. You can force a variable to be initialized with the -fno-common flag or the nocommon attribute.
Some file formats do not support arbitrary sections so the section attribute is not available on all platforms. If you need to map the entire contents of a module to a particular section, consider using the facilities of the linker instead.
tls_model (“tls_model”) tls_model variable attribute The tls_model attribute sets thread-local storage model (Thread-Local) of a particular __thread variable, overriding -ftls-model= command-line switch on a per-variable basis. The tls_model argument should be one of global-dynamic, local-dynamic, initial-exec or local-exec.
Not all targets support this attribute.
unused variable attribute This attribute, attached to a variable, means that the variable is meant to be possibly unused. GCC does not produce a warning for this variable.
used variable attribute This attribute, attached to a variable with static storage, means that the variable must be emitted even if it appears that the variable is not referenced.
When applied to a static data member of a C++ class template, the attribute also means that the member is instantiated if the class itself is instantiated.
vector_size (bytes)
vector_size variable attribute This attribute specifies the vector size for the variable, measured in bytes. For example, the declaration:
int foo __attribute__ ((vector_size (16)));
causes the compiler to set the mode for foo, to be 16 bytes, divided into int sized units. Assuming a 32-bit int (a vector of 4 units of 4 bytes), the corresponding mode of foo is V4SI
This attribute is only applicable to integral and float scalars, although arrays, pointers, and function return values are allowed in conjunction with this construct.
Aggregates with this attribute are invalid, even if they are of the same size as a corresponding scalar. For example, the declaration:
struct S { int a; };
struct S __attribute__ ((vector_size (16))) foo;
is invalid even if the size of the structure is the same as the size of the int.
weak variable attribute The weak attribute is described in Common Function Attributes.
:: _avr-variable-attributes:
progmem variable attribute, AVR The progmem attribute is used on the AVR to place read-only data in the non-volatile program memory (flash). The progmem attribute accomplishes this by putting respective variables into a section whose name starts with .progmem.
This attribute works similar to the section attribute but adds additional checking. Notice that just like the section attribute, progmem affects the location of the data but not how this data is accessed.
In order to read data located with the progmem attribute (inline) assembler must be used.
/* Use custom macros from http://nongnu.org/avr-libc/user-manual/AVR-LibC */
#include <avr/pgmspace.h>
/* Locate var in flash memory */
const int var[2] PROGMEM = { 1, 2 };
int read_var (int i)
{
/* Access var[] by accessor macro from avr/pgmspace.h */
return (int) pgm_read_word (& var[i]);
}
AVR is a Harvard architecture processor and data and read-only data normally resides in the data memory (RAM).
See also the AVR Named Address Spaces section for an alternate way to locate and access data in flash memory.
io variable attribute, AVR Variables with the io attribute are used to address memory-mapped peripherals in the io address range. If an address is specified, the variable is assigned that address, and the value is interpreted as an address in the data address space. Example:
volatile int porta __attribute__((io (0x22)));
The address specified in the address in the data address range.
Otherwise, the variable it is not assigned an address, but the compiler will still use in/out instructions where applicable, assuming some other module assigns an address in the io address range. Example:
extern volatile int porta __attribute__((io));
io_low variable attribute, AVR This is like the io attribute, but additionally it informs the compiler that the object lies in the lower half of the I/O area, allowing the use of cbi, sbi, sbic and sbis instructions.
address variable attribute, AVR Variables with the address attribute are used to address memory-mapped peripherals that may lie outside the io address range.
volatile int porta __attribute__((address (0x600)));
:: _blackfin-variable-attributes:
Three attributes are currently defined for the Blackfin.
l1_data variable attribute, Blackfin l1_data_A variable attribute, Blackfin l1_data_B variable attribute, Blackfin Use these attributes on the Blackfin to place the variable into L1 Data SRAM. Variables with l1_data attribute are put into the specific section named .l1.data. Those with l1_data_A attribute are put into the specific section named .l1.data.A. Those with l1_data_B attribute are put into the specific section named .l1.data.B.
l2 variable attribute, Blackfin Use this attribute on the Blackfin to place the variable into L2 SRAM. Variables with l2 attribute are put into the specific section named .l2.data.
:: _h8/300-variable-attributes:
These variable attributes are available for H8/300 targets:
eightbit_data variable attribute, H8/300
Use this attribute on the H8/300, H8/300H, and H8S to indicate that the specified variable should be placed into the eight-bit data section. The compiler generates more efficient code for certain operations on data in the eight-bit data area. Note the eight-bit data area is limited to 256 bytes of data.
You must use GAS and GLD from GNU binutils version 2.7 or later for this attribute to work correctly.
tiny_data variable attribute, H8/300
Use this attribute on the H8/300H and H8S to indicate that the specified variable should be placed into the tiny data section. The compiler generates more efficient code for loads and stores on data in the tiny data section. Note the tiny data area is limited to slightly under 32KB of data.
:: _ia-64-variable-attributes:
The IA-64 back end supports the following variable attribute:
model (model-name) model variable attribute, IA-64
On IA-64, use this attribute to set the addressability of an object. At present, the only supported identifier for model-name is small, indicating addressability via small (22-bit) addresses (so that their addresses can be loaded with the addl instruction). Caveat: such addressing is by definition not position independent and hence this attribute must not be used for objects defined by shared libraries.
:: _m32r/d-variable-attributes:
One attribute is currently defined for the M32R/D
model (model-name) model-name variable attribute, M32R/D
Use this attribute on the M32R/D to set the addressability of an object. The identifier model-name is one of small, medium, or large, representing each of the code models.
Small model objects live in the lower 16MB of memory (so that their addresses can be loaded with the ld24 instruction).
Medium and large model objects may live anywhere in the 32-bit address space (the compiler generates seth/add3 instructions to load their addresses).
:: _mep-variable-attributes:
The MeP target has a number of addressing modes and busses. The near space spans the standard memory spaces first 16 megabytes (24 bits). The far space spans the entire 32-bit memory space. The based space is a 128-byte region in the memory space that is addressed relative to the $tp register. The tiny space is a 65536-byte region relative to the $gp register. In addition to these memory regions, the MeP target has a separate 16-bit control bus which is specified with cb attributes.
based variable attribute, MeP Any variable with the based attribute is assigned to the .based section, and is accessed with relative to the $tp register.
tiny variable attribute, MeP Likewise, the tiny attribute assigned variables to the .tiny section, relative to the $gp register.
near variable attribute, MeP Variables with the near attribute are assumed to have addresses that fit in a 24-bit addressing mode. This is the default for large variables (-mtiny=4 is the default) but this attribute can override -mtiny= for small variables, or override -ml.
far variable attribute, MeP Variables with the far attribute are addressed using a full 32-bit address. Since this covers the entire memory space, this allows modules to make no assumptions about where variables might be stored.
Variables with the io attribute are used to address memory-mapped peripherals. If an address is specified, the variable is assigned that address, else it is not assigned an address (it is assumed some other module assigns an address). Example:
int timer_count __attribute__((io(0x123)));
cb variable attribute, MeP Variables with the cb attribute are used to access the control bus, using special instructions. addr indicates the control bus address. Example:
int cpu_clock __attribute__((cb(0x123)));
:: _microsoft-windows-variable-attributes:
You can use these attributes on Microsoft Windows targets. x86 Variable Attributes for additional Windows compatibility attributes available on all x86 targets.
dllimport variable attribute dllexport variable attribute The dllimport and dllexport attributes are described in Microsoft Windows Function Attributes.
selectany variable attribute The selectany attribute causes an initialized global variable to have link-once semantics. When multiple definitions of the variable are encountered by the linker, the first is selected and the remainder are discarded. Following usage by the Microsoft compiler, the linker is told not to warn about size or content differences of the multiple definitions.
Although the primary usage of this attribute is for POD types, the attribute can also be applied to global C++ objects that are initialized by a constructor. In this case, the static initialization and destruction code for the object is emitted in each translation defining the object, but the calls to the constructor and destructor are protected by a link-once guard variable.
The selectany attribute is only available on Microsoft Windows targets. You can use __declspec (selectany) as a synonym for __attribute__ ((selectany)) for compatibility with other compilers.
shared variable attribute On Microsoft Windows, in addition to putting variable definitions in a named section, the section can also be shared among all running copies of an executable or DLL For example, this small program defines shared data by putting it in a named section shared and marking the section shareable:
int foo __attribute__((section ("shared"), shared)) = 0;
int
main()
{
/* Read and write foo. All running
copies see the same value. */
return 0;
}
You may only use the shared attribute along with section attribute with a fully-initialized global definition because of the way linkers work. See section attribute for more information.
The shared attribute is only available on Microsoft Windows
:: _powerpc-variable-attributes:
Three attributes currently are defined for PowerPC configurations: altivec, ms_struct and gcc_struct.
ms_struct variable attribute, PowerPC gcc_struct variable attribute, PowerPC For full documentation of the struct attributes please see the documentation in x86 Variable Attributes.
altivec variable attribute, PowerPC For documentation of altivec attribute please see the documentation in PowerPC Type Attributes.
:: _spu-variable-attributes:
spu_vector variable attribute, SPU The SPU supports the spu_vector attribute for variables. For documentation of this attribute please see the documentation in SPU Type Attributes.
:: _x86-variable-attributes:
Two attributes are currently defined for x86 configurations: ms_struct and gcc_struct.
ms_struct variable attribute, x86 gcc_struct variable attribute, x86
If packed is used on a structure, or if bit-fields are used, it may be that the Microsoft ABI lays out the structure differently than the way GCC normally does. Particularly when moving packed data between functions compiled with GCC and the native Microsoft compiler (either via function call or as data in a file), it may be necessary to access either format.
Currently -m[no-]ms-bitfields is provided for the Microsoft Windows x86 compilers to match the native Microsoft compiler.
The Microsoft structure layout algorithm is fairly simple with the exception of the bit-field packing. The padding and alignment of members of structures and whether a bit-field can straddle a storage-unit boundary are determine by these rules:
Structure members are stored sequentially in the order in which they are declared: the first member has the lowest memory address and the last member the highest.
Every data object has an alignment requirement. The alignment requirement for all data except structures, unions, and arrays is either the size of the object or the current packing size (specified with either the aligned attribute or the pack pragma), whichever is less. For structures, unions, and arrays, the alignment requirement is the largest alignment requirement of its members. Every object is allocated an offset so that:
offset % alignment_requirement == 0
Adjacent bit-fields are packed into the same 1-, 2-, or 4-byte allocation unit if the integral types are the same size and if the next bit-field fits into the current allocation unit without crossing the boundary imposed by the common alignment requirements of the bit-fields.
MSVC interprets zero-length bit-fields in the following ways:
If a zero-length bit-field is inserted between two bit-fields that are normally coalesced, the bit-fields are not coalesced.
For example:
struct
{
unsigned long bf_1 : 12;
unsigned long : 0;
unsigned long bf_2 : 12;
} t1;
The size of t1 is 8 bytes with the zero-length bit-field. If the zero-length bit-field were removed, ``t1``s size would be 4 bytes.
If a zero-length bit-field is inserted after a bit-field, foo, and the alignment of the zero-length bit-field is greater than the member that follows it, bar, bar is aligned as the type of the zero-length bit-field.
For example:
struct
{
char foo : 4;
short : 0;
char bar;
} t2;
struct
{
char foo : 4;
short : 0;
double bar;
} t3;
For t2, bar is placed at offset 2, rather than offset 1. Accordingly, the size of t2 is 4. For t3, the zero-length bit-field does not affect the alignment of bar or, as a result, the size of the structure.
Taking this into account, it is important to note the following:
If a zero-length bit-field follows a normal bit-field, the type of the zero-length bit-field may affect the alignment of the structure as whole. For example, t2 has a size of 4 bytes, since the zero-length bit-field follows a normal bit-field, and is of type short.
Even if a zero-length bit-field is not followed by a normal bit-field, it may still affect the alignment of the structure:
struct
{
char foo : 6;
long : 0;
} t4;
Here, t4 takes up 4 bytes.
Zero-length bit-fields following non-bit-field members are ignored:
struct
{
char foo;
long : 0;
char bar;
} t5;
Here, t5 takes up 2 bytes.
:: _xstormy16-variable-attributes:
One attribute is currently defined for xstormy16 configurations: below100.
below100 variable attribute, Xstormy16
If a variable has the below100 attribute (BELOW100 is allowed also), GCC places the variable in the first 0x100 bytes of memory and use special opcodes to access it. Such variables are placed in either the .bss_below100 section or the .data_below100 section.
:: _type-attributes:
The keyword __attribute__ allows you to specify special attributes of types. Some type attributes apply only to struct and union types, while others can apply to any type defined via a typedef declaration. Other attributes are defined for functions (Function Attributes), labels (Label Attributes) and for variables (Variable Attributes).
The __attribute__ keyword is followed by an attribute specification inside double parentheses.
You may specify type attributes in an enum, struct or union type declaration or definition by placing them immediately after the struct, union or enum keyword. A less preferred syntax is to place them just past the closing curly brace of the definition.
You can also include type attributes in a typedef declaration. Attribute Syntax, for details of the exact syntax for using attributes.
:: _common-type-attributes:
The following type attributes are supported on most targets.
aligned type attribute aligned (alignment) This attribute specifies a minimum alignment (in bytes) for variables of the specified type. For example, the declarations:
struct S { short f[3]; } __attribute__ ((aligned (8)));
typedef int more_aligned_int __attribute__ ((aligned (8)));
force the compiler to ensure (as far as it can) that each variable whose type is struct S or more_aligned_int is allocated and aligned at least on a 8-byte boundary. On a SPARC, having all variables of type struct S aligned to 8-byte boundaries allows the compiler to use the ldd and std (doubleword load and store) instructions when copying one variable of type struct S to another, thus improving run-time efficiency.
Note that the alignment of any given struct or union type is required by the ISO C standard to be at least a perfect multiple of the lowest common multiple of the alignments of all of the members of the struct or union in question. This means that you can effectively adjust the alignment of a struct or union type by attaching an aligned attribute to any one of the members of such a type, but the notation illustrated in the example above is a more obvious, intuitive, and readable way to request the compiler to adjust the alignment of an entire struct or union type.
As in the preceding example, you can explicitly specify the alignment (in bytes) that you wish the compiler to use for a given struct or union type. Alternatively, you can leave out the alignment factor and just ask the compiler to align a type to the maximum useful alignment for the target machine you are compiling for. For example, you could write:
struct S { short f[3]; } __attribute__ ((aligned));
Whenever you leave out the alignment factor in an aligned attribute specification, the compiler automatically sets the alignment for the type to the largest alignment that is ever used for any data type on the target machine you are compiling for. Doing this can often make copy operations more efficient, because the compiler can use whatever instructions copy the biggest chunks of memory when performing copies to or from the variables that have types that you have aligned this way.
In the example above, if the size of each short is 2 bytes, then the size of the entire struct S type is 6 bytes. The smallest power of two that is greater than or equal to that is 8, so the compiler sets the alignment for the entire struct S type to 8 bytes.
Note that although you can ask the compiler to select a time-efficient alignment for a given type and then declare only individual stand-alone objects of that type, the compilers ability to select a time-efficient alignment is primarily useful only when you plan to create arrays of variables having the relevant (efficiently aligned) type. If you declare or use arrays of variables of an efficiently-aligned type, then it is likely that your program also does pointer arithmetic (or subscripting, which amounts to the same thing) on pointers to the relevant type, and the code that the compiler generates for these pointer arithmetic operations is often more efficient for efficiently-aligned types than for other types.
The aligned attribute can only increase the alignment; but you can decrease it by specifying packed as well. See below.
Note that the effectiveness of aligned attributes may be limited by inherent limitations in your linker. On many systems, the linker is only able to arrange for variables to be aligned up to a certain maximum alignment. (For some linkers, the maximum supported alignment may be very very small.) If your linker is only able to align variables up to a maximum of 8-byte alignment, then specifying aligned(16) in an __attribute__ still only provides you with 8-byte alignment. See your linker documentation for further information.
Specifying this attribute for struct and union types is equivalent to specifying the packed attribute on each of the structure or union members. Specifying the -fshort-enums flag on the line is equivalent to specifying the packed attribute on all enum definitions.
In the following example struct my_packed_struct``s members are packed closely together, but the internal layout of its ``s member is not packedto do that, struct my_unpacked_struct needs to be packed too.
struct my_unpacked_struct
{
char c;
int i;
};
struct __attribute__ ((__packed__)) my_packed_struct
{
char c;
int i;
struct my_unpacked_struct s;
};
You may only specify this attribute on the definition of an enum, struct or union, not on a typedef that does not also define the enumerated type, structure or union.
bnd_variable_size type attribute
When applied to a structure field, this attribute tells Pointer Bounds Checker that the size of this field should not be computed using static type information. It may be used to mark variably-sized static array fields placed at the end of a structure.
struct S
{
int size;
char data[1];
}
S *p = (S *)malloc (sizeof(S) + 100);
p->data[10] = 0; //Bounds violation
By using an attribute for the field we may avoid unwanted bound violation checks:
struct S
{
int size;
char data[1] __attribute__((bnd_variable_size));
}
S *p = (S *)malloc (sizeof(S) + 100);
p->data[10] = 0; //OK
deprecated type attribute The deprecated attribute results in a warning if the type is used anywhere in the source file. This is useful when identifying types that are expected to be removed in a future version of a program. If possible, the warning also includes the location of the declaration of the deprecated type, to enable users to easily find further information about why the type is deprecated, or what they should do instead. Note that the warnings only occur for uses and then only if the type is being applied to an identifier that itself is not being declared as deprecated.
typedef int T1 __attribute__ ((deprecated));
T1 x;
typedef T1 T2;
T2 y;
typedef T1 T3 __attribute__ ((deprecated));
T3 z __attribute__ ((deprecated));
results in a warning on line 2 and 3 but not lines 4, 5, or 6. No warning is issued for line 4 because T2 is not explicitly deprecated. Line 5 has no warning because T3 is explicitly deprecated. Similarly for line 6. The optional msg argument, which must be a string, is printed in the warning if present.
The deprecated attribute can also be used for functions and variables (Function Attributes, Variable Attributes.)
designated_init type attribute This attribute may only be applied to structure types. It indicates that any initialization of an object of this type must use designated initializers rather than positional initializers. The intent of this attribute is to allow the programmer to indicate that a structures layout may change, and that therefore relying on positional initialization will result in future breakage.
GCC emits warnings based on this attribute by default; use -Wno-designated-init to suppress them.
may_alias type attribute Accesses through pointers to types with this attribute are not subject to type-based alias analysis, but are instead assumed to be able to alias any other type of objects. In the context of section 6.5 paragraph 7 of the C99 standard, an lvalue expression dereferencing such a pointer is treated like having a character type. See -fstrict-aliasing for more information on aliasing issues. This extension exists to support some vector APIs, in which pointers to one vector type are permitted to alias pointers to a different vector type.
Note that an object of a type with this attribute does not have any special semantics.
Example of use:
typedef short __attribute__((__may_alias__)) short_a;
int
main (void)
{
int a = 0x12345678;
short_a *b = (short_a *) &a;
b[1] = 0;
if (a == 0x12345678)
abort();
exit(0);
}
If you replaced short_a with short in the variable declaration, the above program would abort when compiled with -fstrict-aliasing, which is on by default at -O2 or above.
packed type attribute This attribute, attached to struct or union type definition, specifies that each member (other than zero-width bit-fields) of the structure or union is placed to minimize the memory required. When attached to an enum definition, it indicates that the smallest integral type should be used.
transparent_union type attribute
This attribute, attached to a union type definition, indicates that any function parameter having that union type causes calls to that function to be treated in a special way.
First, the argument corresponding to a transparent union type can be of any type in the union; no cast is required. Also, if the union contains a pointer type, the corresponding argument can be a null pointer constant or a void pointer expression; and if the union contains a void pointer type, the corresponding argument can be any pointer expression. If the union member type is a pointer, qualifiers like const on the referenced type must be respected, just as with normal pointer conversions.
Second, the argument is passed to the function using the calling conventions of the first member of the transparent union, not the calling conventions of the union itself. All members of the union must have the same machine representation; this is necessary for this argument passing to work properly.
Transparent unions are designed for library functions that have multiple interfaces for compatibility reasons. For example, suppose the wait function must accept either a value of type int * to comply with POSIX, or a value of type union wait * to comply with the 4.1BSD interface. If wait``s parameter were ``void *, wait would accept both kinds of arguments, but it would also accept any other pointer type and this would make argument type checking less useful. Instead, <sys/wait.h> might define the interface as follows:
typedef union __attribute__ ((__transparent_union__))
{
int *__ip;
union wait *__up;
} wait_status_ptr_t;
pid_t wait (wait_status_ptr_t);
This interface allows either int * or union wait * arguments to be passed, using the int * calling convention. The program can call wait with arguments of either type:
int w1 () { int w; return wait (&w); }
int w2 () { union wait w; return wait (&w); }
With this interface, ``wait``s implementation might look like this:
pid_t wait (wait_status_ptr_t p)
{
return waitpid (-1, p.__ip, 0);
}
unused type attribute When attached to a type (including a union or a struct), this attribute means that variables of that type are meant to appear possibly unused. GCC does not produce a warning for any variables of that type, even if the variable appears to do nothing. This is often the case with lock or thread classes, which are usually defined and then not referenced, but contain constructors and destructors that have nontrivial bookkeeping functions.
visibility type attribute In C++, attribute visibility (Function Attributes) can also be applied to class, struct, union and enum types. Unlike other type attributes, the attribute must appear between the initial keyword and the name of the type; it cannot appear after the body of the type.
Note that the type visibility is applied to vague linkage entities associated with the class (vtable, typeinfo node, etc.). In particular, if a class is thrown as an exception in one shared object and caught in another, the class must have default visibility. Otherwise the two shared objects are unable to use the same typeinfo node and exception handling will break.
To specify multiple attributes, separate them by commas within the double parentheses: for example, __attribute__ ((aligned (16), packed)).
:: _arm-type-attributes:
notshared type attribute, ARM On those ARM targets that support dllimport (such as Symbian OS), you can use the notshared attribute to indicate that the virtual table and other similar data for a class should not be exported from a DLL For example:
class __declspec(notshared) C {
public:
__declspec(dllimport) C();
virtual void f();
}
__declspec(dllexport)
C::C() {}
In this code, C::C is exported from the current DLL, but the virtual table for C is not exported. (You can use __attribute__ instead of __declspec if you prefer, but most Symbian OS code uses __declspec.)
:: _mep-type-attributes:
based type attribute, MeP tiny type attribute, MeP near type attribute, MeP far type attribute, MeP Many of the MeP variable attributes may be applied to types as well. Specifically, the based, tiny, near, and far attributes may be applied to either. The io and cb attributes may not be applied to types.
:: _powerpc-type-attributes:
Three attributes currently are defined for PowerPC configurations: altivec, ms_struct and gcc_struct.
ms_struct type attribute, PowerPC gcc_struct type attribute, PowerPC For full documentation of the ms_struct and gcc_struct attributes please see the documentation in x86 Type Attributes.
altivec type attribute, PowerPC The altivec attribute allows one to declare AltiVec vector data types supported by the AltiVec Programming Interface Manual. The attribute requires an argument to specify one of three vector types: vector__, pixel__ (always followed by unsigned short), and bool__ (always followed by unsigned).
__attribute__((altivec(vector__)))
__attribute__((altivec(pixel__))) unsigned short
__attribute__((altivec(bool__))) unsigned
These attributes mainly are intended to support the __vector, __pixel, and __bool AltiVec keywords.
:: _spu-type-attributes:
spu_vector type attribute, SPU The SPU supports the spu_vector attribute for types. This attribute allows one to declare vector data types supported by the Sony/Toshiba/IBM SPU Language Extensions Specification. It is intended to support the __vector keyword.
:: _x86-type-attributes:
Two attributes are currently defined for x86 configurations: ms_struct and gcc_struct.
ms_struct type attribute, x86 gcc_struct type attribute, x86
If packed is used on a structure, or if bit-fields are used it may be that the Microsoft ABI packs them differently than GCC normally packs them. Particularly when moving packed data between functions compiled with GCC and the native Microsoft compiler (either via function call or as data in a file), it may be necessary to access either format.
Currently -m[no-]ms-bitfields is provided for the Microsoft Windows x86 compilers to match the native Microsoft compiler.
:: _label-attributes:
GCC allows attributes to be set on C labels. Attribute Syntax, for details of the exact syntax for using attributes. Other attributes are available for functions (Function Attributes), variables (Variable Attributes) and for types (Type Attributes).
This example uses the cold label attribute to indicate the ErrorHandling branch is unlikely to be taken and that the ErrorHandling label is unused:
asm goto ("some asm" : : : : NoError);
/* This branch (the fall-through from the asm) is less commonly used */
ErrorHandling:
__attribute__((cold, unused)); /* Semi-colon is required here */
printf("error\n");
return 0;
NoError:
printf("no error\n");
return 1;
unused label attribute This feature is intended for program-generated code that may contain unused labels, but which is compiled with -Wall. It is not normally appropriate to use in it human-written code, though it could be useful in cases where the code that jumps to the label is contained within an #ifdef conditional.
hot label attribute The hot attribute on a label is used to inform the compiler that the path following the label is more likely than paths that are not so annotated. This attribute is used in cases where __builtin_expect cannot be used, for instance with computed goto or asm goto.
cold label attribute The cold attribute on labels is used to inform the compiler that the path following the label is unlikely to be executed. This attribute is used in cases where __builtin_expect cannot be used, for instance with computed goto or asm goto.
:: _attribute-syntax:
This section describes the syntax with which __attribute__ may be used, and the constructs to which attribute specifiers bind, for the C language. Some details may vary for C++ and Objective-C Because of infelicities in the grammar for attributes, some forms described here may not be successfully parsed in all cases.
There are some problems with the semantics of attributes in C++. For example, there are no manglings for attributes, although they may affect code generation, so problems may arise when attributed types are used in conjunction with templates or overloading. Similarly, typeid does not distinguish between types with different attributes. Support for attributes in C++ may be restricted in future to attributes on declarations only, but not on nested declarators.
Function Attributes, for details of the semantics of attributes applying to functions. Variable Attributes, for details of the semantics of attributes applying to variables. Type Attributes, for details of the semantics of attributes applying to structure, union and enumerated types. Label Attributes, for details of the semantics of attributes applying to labels.
An attribute specifier is of the form __attribute__ ((``attribute-list))``. An attribute list is a possibly empty comma-separated sequence of attributes, where each attribute is one of the following:
An attribute specifier list is a sequence of one or more attribute specifiers, not separated by any other tokens.
You may optionally specify attribute names with __ preceding and following the name. This allows you to use them in header files without being concerned about a possible macro of the same name. For example, you may use the attribute name __noreturn__ instead of noreturn.
In GNU C, an attribute specifier list may appear after the colon following a label, other than a case or default label. GNU C++ only permits attributes on labels if the attribute specifier is immediately followed by a semicolon (i.e., the label applies to an empty statement). If the semicolon is missing, C++ label attributes are ambiguous, as it is permissible for a declaration, which could begin with an attribute list, to be labelled in C++. Declarations cannot be labelled in C90 or C99, so the ambiguity does not arise there.
An attribute specifier list may appear as part of a struct, union or enum specifier. It may go either immediately after the struct, union or enum keyword, or after the closing brace. The former syntax is preferred. Where attribute specifiers follow the closing brace, they are considered to relate to the structure, union or enumerated type defined, not to any enclosing declaration the type specifier appears in, and the type defined is not complete until after the attribute specifiers.
Otherwise, an attribute specifier appears as part of a declaration, counting declarations of unnamed parameters and type names, and relates to that declaration (which may be nested in another declaration, for example in the case of a parameter declaration), or to a particular declarator within a declaration. Where an attribute specifier is applied to a parameter declared as a function or an array, it should apply to the function or array rather than the pointer to which the parameter is implicitly converted, but this is not yet correctly implemented.
Any list of specifiers and qualifiers at the start of a declaration may contain attribute specifiers, whether or not such a list may in that context contain storage class specifiers. (Some attributes, however, are essentially in the nature of storage class specifiers, and only make sense where storage class specifiers may be used; for example, section.) There is one necessary limitation to this syntax: the first old-style parameter declaration in a function definition cannot begin with an attribute specifier, because such an attribute applies to the function instead by syntax described below (which, however, is not yet implemented in this case). In some other cases, attribute specifiers are permitted by this grammar but not yet supported by the compiler. All attribute specifiers in this place relate to the declaration as a whole. In the obsolescent usage where a type of int is implied by the absence of type specifiers, such a list of specifiers and qualifiers may be an attribute specifier list with no other specifiers or qualifiers.
At present, the first parameter in a function prototype must have some type specifier that is not an attribute specifier; this resolves an ambiguity in the interpretation of void f(int (__attribute__((foo)) x)), but is subject to change. At present, if the parentheses of a function declarator contain only attributes then those attributes are ignored, rather than yielding an error or warning or implying a single parameter of type int, but this is subject to change.
An attribute specifier list may appear immediately before a declarator (other than the first) in a comma-separated list of declarators in a declaration of more than one identifier using a single list of specifiers and qualifiers. Such attribute specifiers apply only to the identifier before whose declarator they appear. For example, in
__attribute__((noreturn)) void d0 (void),
__attribute__((format(printf, 1, 2))) d1 (const char *, ...),
d2 (void);
the noreturn attribute applies to all the functions declared; the format attribute only applies to d1.
An attribute specifier list may appear immediately before the comma, = or semicolon terminating the declaration of an identifier other than a function definition. Such attribute specifiers apply to the declared object or function. Where an assembler name for an object or function is specified (Asm Labels), the attribute must follow the asm specification.
An attribute specifier list may, in future, be permitted to appear after the declarator in a function definition (before any old-style parameter declarations or the function body).
Attribute specifiers may be mixed with type qualifiers appearing inside the [] of a parameter array declarator, in the C99 construct by which such qualifiers are applied to the pointer to which the array is implicitly converted. Such attribute specifiers apply to the pointer, not to the array, but at present this is not implemented and they are ignored.
An attribute specifier list may appear at the start of a nested declarator. At present, there are some limitations in this usage: the attributes correctly apply to the declarator, but for most individual attributes the semantics this implies are not implemented. When attribute specifiers follow the * of a pointer declarator, they may be mixed with any type qualifiers present. The following describes the formal semantics of this syntax. It makes the most sense if you are familiar with the formal specification of declarators in the ISO C standard.
Consider (as in C99 subclause 6.7.5 paragraph 4) a declaration T D1, where T contains declaration specifiers that specify a type Type (such as int) and D1 is a declarator that contains an identifier ident. The type specified for ident for derived declarators whose type does not include an attribute specifier is as in the ISO C standard.
If D1 has the form ( ``attribute-specifier-list D )``, and the declaration T D specifies the type derived-declarator-type-list Type for ident, then T D1 specifies the type derived-declarator-type-list attribute-specifier-list Type for ident.
If D1 has the form * ``type-qualifier-and-attribute-specifier-list D``, and the declaration T D specifies the type derived-declarator-type-list Type for ident, then T D1 specifies the type derived-declarator-type-list type-qualifier-and-attribute-specifier-list pointer to Type for ident.
For example,
void (__attribute__((noreturn)) ****f) (void);
specifies the type pointer to pointer to pointer to pointer to non-returning function returning void. As another example,
char *__attribute__((aligned(8))) *f;
specifies the type pointer to 8-byte-aligned pointer to char. Note again that this does not work with most attributes; for example, the usage of aligned and noreturn attributes given above is not yet supported.
For compatibility with existing code written for compiler versions that did not implement attributes on nested declarators, some laxity is allowed in the placing of attributes. If an attribute that only applies to types is applied to a declaration, it is treated as applying to the type of that declaration. If an attribute that only applies to declarations is applied to the type of a declaration, it is treated as applying to that declaration; and, for compatibility with code placing the attributes immediately before the identifier declared, such an attribute applied to a function return type is treated as applying to the function type, and such an attribute applied to an array element type is treated as applying to the array type. If an attribute that only applies to function types is applied to a pointer-to-function type, it is treated as applying to the pointer target type; if such an attribute is applied to a function return type that is not a pointer-to-function type, it is treated as applying to the function type.
:: _function-prototypes:
GNU C extends ISO C to allow a function prototype to override a later old-style non-prototype definition. Consider the following example:
/* Use prototypes unless the compiler is old-fashioned. */
#ifdef __STDC__
#define P(x) x
#else
#define P(x) ()
#endif
/* Prototype function declaration. */
int isroot P((uid_t));
/* Old-style function definition. */
int
isroot (x) /* ??? lossage here ??? */
uid_t x;
{
return x == 0;
}
Suppose the type uid_t happens to be short. ISO C does not allow this example, because subword arguments in old-style non-prototype definitions are promoted. Therefore in this example the function definitions argument is really an int, which does not match the prototype argument type of short.
This restriction of ISO C makes it hard to write code that is portable to traditional C compilers, because the programmer does not know whether the uid_t type is short, int, or long. Therefore, in cases like these GNU C allows a prototype to override a later old-style definition. More precisely, in GNU C, a function prototype argument type overrides the argument type specified by a later old-style definition if the former type is the same as the latter type before promotion. Thus in GNU C the above example is equivalent to the following:
int isroot (uid_t);
int
isroot (uid_t x)
{
return x == 0;
}
GNU C++ does not support old-style function definitions, so this extension is irrelevant.
:: _c++-comments:
//
In GNU C, you may use C++ style comments, which start with // and continue until the end of the line. Many other C implementations allow such comments, and they are included in the 1999 C standard. However, C++ style comments are not recognized if you specify an -std option specifying a version of ISO C before C99, or -ansi (equivalent to -std=c90).
:: _dollar-signs:
In GNU C, you may normally use dollar signs in identifier names. This is because many traditional C implementations allow such identifiers. However, dollar signs in identifiers are not supported on a few target machines, typically because the target assembler does not allow them.
:: _character-escapes:
The Character ESC in Constants
You can use the sequence e in a string or character constant to stand for the ASCII character ESC.
:: _alignment:
The keyword __alignof__ allows you to inquire about how an object is aligned, or the minimum alignment usually required by a type. Its syntax is just like sizeof.
For example, if the target machine requires a double value to be aligned on an 8-byte boundary, then __alignof__ (double) is 8. This is true on many RISC machines. On more traditional machine designs, __alignof__ (double) is 4 or even 2.
Some machines never actually require alignment; they allow reference to any data type even at an odd address. For these machines, __alignof__ reports the smallest alignment that GCC gives the data type, usually as mandated by the target ABI.
If the operand of __alignof__ is an lvalue rather than a type, its value is the required alignment for its type, taking into account any minimum alignment specified with GCCs __attribute__ extension (Variable Attributes). For example, after this declaration:
struct foo { int x; char y; } foo1;
the value of __alignof__ (foo1.y) is 1, even though its actual alignment is probably 2 or 4, the same as __alignof__ (int).
It is an error to ask for the alignment of an incomplete type.
:: _inline:
By declaring a function inline, you can direct GCC to make calls to that function faster. One way GCC can achieve this is to integrate that functions code into the code for its callers. This makes execution faster by eliminating the function-call overhead; in addition, if any of the actual argument values are constant, their known values may permit simplifications at compile time so that not all of the inline functions code needs to be included. The effect on code size is less predictable; object code may be larger or smaller with function inlining, depending on the particular case. You can also direct GCC to try to integrate all simple enough functions into their callers with the option -finline-functions.
GCC implements three different semantics of declaring a function inline. One is available with -std=gnu89 or -fgnu89-inline or when gnu_inline attribute is present on all inline declarations, another when -std=c99, -std=c11, -std=gnu99 or -std=gnu11 (without -fgnu89-inline), and the third is used when compiling C++.
To declare a function inline, use the inline keyword in its declaration, like this:
static inline int
inc (int *a)
{
return (*a)++;
}
If you are writing a header file to be included in ISO C90 programs, write __inline__ instead of inline. Alternate Keywords.
The three types of inlining behave similarly in two important cases: when the inline keyword is used on a static function, like the example above, and when a function is first declared without using the inline keyword and then is defined with inline, like this:
extern int inc (int *a);
inline int
inc (int *a)
{
return (*a)++;
}
In both of these common cases, the program behaves the same as if you had not used the inline keyword, except for its speed.
When a function is both inline and static, if all calls to the function are integrated into the caller, and the functions address is never used, then the functions own assembler code is never referenced. In this case, GCC does not actually output assembler code for the function, unless you specify the option -fkeep-inline-functions. Some calls cannot be integrated for various reasons (in particular, calls that precede the functions definition cannot be integrated, and neither can recursive calls within the definition). If there is a nonintegrated call, then the function is compiled to assembler code as usual. The function must also be compiled as usual if the program refers to its address, because that cant be inlined.
Note that certain usages in a function definition can make it unsuitable for inline substitution. Among these usages are: variadic functions, use of alloca, use of variable-length data types (Variable Length), use of computed goto (Labels as Values), use of nonlocal goto, and nested functions (Nested Functions). Using -Winline warns when a function marked inline could not be substituted, and gives the reason for the failure.
automatic inline for C++ member fns inline automatic for C++ member fns member fns, automatically inline C++ member fns, automatically inline
As required by ISO C++, GCC considers member functions defined within the body of a class to be marked inline even if they are not explicitly declared with the inline keyword. You can override this with -fno-default-inline; C++ Dialect OptionsOptions Controlling C++ Dialect.
GCC does not inline any functions when not optimizing unless you specify the always_inline attribute for the function, like this:
/* Prototype. */
inline void foo (const char) __attribute__((always_inline));
The remainder of this section is specific to GNU C90 inlining.
When an inline function is not static, then the compiler must assume that there may be calls from other source files; since a global symbol can be defined only once in any program, the function must not be defined in the other source files, so the calls therein cannot be integrated. Therefore, a non-static inline function is always compiled on its own in the usual fashion.
If you specify both inline and extern in the function definition, then the definition is used only for inlining. In no case is the function compiled on its own, not even if you refer to its address explicitly. Such an address becomes an external reference, as if you had only declared the function, and had not defined it.
This combination of inline and extern has almost the effect of a macro. The way to use it is to put a function definition in a header file with these keywords, and put another copy of the definition (lacking inline and extern) in a library file. The definition in the header file causes most calls to the function to be inlined. If any uses of the function remain, they refer to the single copy in the library.
:: _volatiles:
C has the concept of volatile objects. These are normally accessed by pointers and used for accessing hardware or inter-thread communication. The standard encourages compilers to refrain from optimizations concerning accesses to volatile objects, but leaves it implementation defined as to what constitutes a volatile access. The minimum requirement is that at a sequence point all previous accesses to volatile objects have stabilized and no subsequent accesses have occurred. Thus an implementation is free to reorder and combine volatile accesses that occur between sequence points, but cannot do so for accesses across a sequence point. The use of volatile does not allow you to violate the restriction on updating objects multiple times between two sequence points.
Accesses to non-volatile objects are not ordered with respect to volatile accesses. You cannot use a volatile object as a memory barrier to order a sequence of writes to non-volatile memory. For instance:
int *ptr = ``something``;
volatile int vobj;
*ptr = ``something``;
vobj = 1;
Unless *ptr and vobj can be aliased, it is not guaranteed that the write to *ptr occurs by the time the update of vobj happens. If you need this guarantee, you must use a stronger memory barrier such as:
int *ptr = ``something``;
volatile int vobj;
*ptr = ``something``;
asm volatile ("" : : : "memory");
vobj = 1;
A scalar volatile object is read when it is accessed in a void context:
volatile int *src = ``somevalue``;
*src;
Such expressions are rvalues, and GCC implements this as a read of the volatile object being pointed to.
Assignments are also expressions and have an rvalue. However when assigning to a scalar volatile, the volatile object is not reread, regardless of whether the assignment expressions rvalue is used or not. If the assignments rvalue is used, the value is that assigned to the volatile object. For instance, there is no read of vobj in all the following cases:
int obj;
volatile int vobj;
vobj = ``something``;
obj = vobj = ``something``;
obj ? vobj = ``onething`` : vobj = ``anotherthing``;
obj = (``something``, vobj = ``anotherthing``);
If you need to read the volatile object after an assignment has occurred, you must use a separate expression with an intervening sequence point.
As bit-fields are not individually addressable, volatile bit-fields may be implicitly read when written to, or when adjacent bit-fields are accessed. Bit-field operations may be optimized such that adjacent bit-fields are only partially accessed, if they straddle a storage unit boundary. For these reasons it is unwise to use volatile bit-fields to access hardware.
:: _using-assembly-language-with-c:
asm keyword
The asm keyword allows you to embed assembler instructions within C code. GCC provides two forms of inline asm statements. A basic asm statement is one with no operands (Basic Asm), while an extended asm statement (Extended Asm) includes one or more operands. The extended form is preferred for mixing C and assembly language within a function, but to include assembly language at top level you must use basic asm.
You can also use the asm keyword to override the assembler name for a C symbol, or to place a C variable in a specific register.
:: _basic-asm:
basic asm
A basic asm statement has the following syntax:
asm [ volatile ] ( ``AssemblerInstructions`` )
The asm keyword is a GNU extension. When writing code that can be compiled with -ansi and the various -std options, use __asm__ instead of asm (Alternate Keywords).
The optional volatile qualifier has no effect. All basic asm blocks are implicitly volatile.
This is a literal string that specifies the assembler code. The string can contain any instructions recognized by the assembler, including directives. GCC does not parse the assembler instructions themselves and does not know what they mean or even whether they are valid assembler input.
You may place multiple assembler instructions together in a single asm string, separated by the characters normally used in assembly code for the system. A combination that works in most places is a newline to break the line, plus a tab character (written as nt). Some assemblers allow semicolons as a line separator. However, note that some assembler dialects use semicolons to start a comment.
Using extended asm typically produces smaller, safer, and more efficient code, and in most cases it is a better solution than basic asm. However, there are two situations where only basic asm can be used:
Safely accessing C data and calling functions from basic asm is more complex than it may appear. To access C data, it is better to use extended asm.
Do not expect a sequence of asm statements to remain perfectly consecutive after compilation. If certain instructions need to remain consecutive in the output, put them in a single multi-instruction asm statement. Note that GCCs optimizers can move asm statements relative to other code, including across jumps.
asm statements may not perform jumps into other asm statements. GCC does not know about these jumps, and therefore cannot take account of them when deciding how to optimize. Jumps from asm to C labels are only supported in extended asm.
Under certain circumstances, GCC may duplicate (or remove duplicates of) your assembly code when optimizing. This can lead to unexpected duplicate symbol errors during compilation if your assembly code defines symbols or labels.
Since GCC does not parse the AssemblerInstructions, it has no visibility of any symbols it references. This may result in GCC discarding those symbols as unreferenced.
The compiler copies the assembler instructions in a basic asm verbatim to the assembly language output file, without processing dialects or any of the % operators that are available with extended asm. This results in minor differences between basic asm strings and extended asm templates. For example, to refer to registers you might use %eax in basic asm and %%eax in extended asm.
On targets such as x86 that support multiple assembler dialects, all basic asm blocks use the assembler dialect specified by the -masm command-line option (x86 Options). Basic asm provides no mechanism to provide different assembler strings for different dialects.
Here is an example of basic asm for i386:
/* Note that this code will not compile with -masm=intel */
#define DebugBreak() asm("int $3")
:: _extended-asm:
extended asm
With extended asm you can read and write C variables from assembler and perform jumps from assembler code to C labels. Extended asm syntax uses colons (:) to delimit the operand parameters after the assembler template:
asm [volatile] ( ``AssemblerTemplate``
: ``OutputOperands``
[ : ``InputOperands``
[ : ``Clobbers`` ] ])
asm [volatile] goto ( ``AssemblerTemplate``
:
: ``InputOperands``
: ``Clobbers``
: ``GotoLabels``)
The asm keyword is a GNU extension. When writing code that can be compiled with -ansi and the various -std options, use __asm__ instead of asm (Alternate Keywords).
The typical use of extended asm statements is to manipulate input values to produce output values. However, your asm statements may also produce side effects. If so, you may need to use the volatile qualifier to disable certain optimizations. Volatile.
This qualifier informs the compiler that the asm statement may perform a jump to one of the labels listed in the GotoLabels. GotoLabels.
This is a literal string that is the template for the assembler code. It is a combination of fixed text and tokens that refer to the input, output, and goto parameters. AssemblerTemplate.
A comma-separated list of the C variables modified by the instructions in the AssemblerTemplate. An empty list is permitted. OutputOperands.
A comma-separated list of C expressions read by the instructions in the AssemblerTemplate. An empty list is permitted. InputOperands.
A comma-separated list of registers or other values changed by the AssemblerTemplate, beyond those listed as outputs. An empty list is permitted. Clobbers.
When you are using the goto form of asm, this section contains the list of all C labels to which the code in the AssemblerTemplate may jump. GotoLabels.
asm statements may not perform jumps into other asm statements, only to the listed GotoLabels. GCCs optimizers do not know about other jumps; therefore they cannot take account of them when deciding how to optimize.
The total number of input + output + goto operands is limited to 30.
The asm statement allows you to include assembly instructions directly within C code. This may help you to maximize performance in time-sensitive code or to access assembly instructions that are not readily available to C programs.
Note that extended asm statements must be inside a function. Only basic asm may be outside functions (Basic Asm). Functions declared with the naked attribute also require basic asm (Function Attributes).
While the uses of asm are many and varied, it may help to think of an asm statement as a series of low-level instructions that convert input parameters to output parameters. So a simple (if not particularly useful) example for i386 using asm might look like this:
int src = 1;
int dst;
asm ("mov %1, %0\n\t"
"add $1, %0"
: "=r" (dst)
: "r" (src));
printf("%d\n", dst);
This code copies src to dst and add 1 to dst.
Volatile
volatile asm asm volatile
GCCs optimizers sometimes discard asm statements if they determine there is no need for the output variables. Also, the optimizers may move code out of loops if they believe that the code will always return the same result (i.e. none of its input values change between calls). Using the volatile qualifier disables these optimizations. asm statements that have no output operands, including asm goto statements, are implicitly volatile.
This i386 code demonstrates a case that does not use (or require) the volatile qualifier. If it is performing assertion checking, this code uses asm to perform the validation. Otherwise, dwRes is unreferenced by any code. As a result, the optimizers can discard the asm statement, which in turn removes the need for the entire DoCheck routine. By omitting the volatile qualifier when it isnt needed you allow the optimizers to produce the most efficient code possible.
void DoCheck(uint32_t dwSomeValue)
{
uint32_t dwRes;
// Assumes dwSomeValue is not zero.
asm ("bsfl %1,%0"
: "=r" (dwRes)
: "r" (dwSomeValue)
: "cc");
assert(dwRes > 3);
}
The next example shows a case where the optimizers can recognize that the input (dwSomeValue) never changes during the execution of the function and can therefore move the asm outside the loop to produce more efficient code. Again, using volatile disables this type of optimization.
void do_print(uint32_t dwSomeValue)
{
uint32_t dwRes;
for (uint32_t x=0; x < 5; x++)
{
// Assumes dwSomeValue is not zero.
asm ("bsfl %1,%0"
: "=r" (dwRes)
: "r" (dwSomeValue)
: "cc");
printf("%u: %u %u\n", x, dwSomeValue, dwRes);
}
}
The following example demonstrates a case where you need to use the volatile qualifier. It uses the x86 rdtsc instruction, which reads the computers time-stamp counter. Without the volatile qualifier, the optimizers might assume that the asm block will always return the same value and therefore optimize away the second call.
uint64_t msr;
asm volatile ( "rdtsc\n\t" // Returns the time in EDX:EAX.
"shl $32, %%rdx\n\t" // Shift the upper bits left.
"or %%rdx, %0" // 'Or' in the lower bits.
: "=a" (msr)
:
: "rdx");
printf("msr: %llx\n", msr);
// Do other work...
// Reprint the timestamp
asm volatile ( "rdtsc\n\t" // Returns the time in EDX:EAX.
"shl $32, %%rdx\n\t" // Shift the upper bits left.
"or %%rdx, %0" // 'Or' in the lower bits.
: "=a" (msr)
:
: "rdx");
printf("msr: %llx\n", msr);
GCCs optimizers do not treat this code like the non-volatile code in the earlier examples. They do not move it out of loops or omit it on the assumption that the result from a previous call is still valid.
Note that the compiler can move even volatile asm instructions relative to other code, including across jump instructions. For example, on many targets there is a system register that controls the rounding mode of floating-point operations. Setting it with a volatile asm, as in the following PowerPC example, does not work reliably.
asm volatile("mtfsf 255, %0" : : "f" (fpenv));
sum = x + y;
The compiler may move the addition back before the volatile asm. To make it work as expected, add an artificial dependency to the asm by referencing a variable in the subsequent code, for example:
asm volatile ("mtfsf 255,%1" : "=X" (sum) : "f" (fpenv));
sum = x + y;
Under certain circumstances, GCC may duplicate (or remove duplicates of) your assembly code when optimizing. This can lead to unexpected duplicate symbol errors during compilation if your asm code defines symbols or labels. Using %= (AssemblerTemplate) may help resolve this problem.
AssemblerTemplate
asm assembler template
An assembler template is a literal string containing assembler instructions. The compiler replaces tokens in the template that refer to inputs, outputs, and goto labels, and then outputs the resulting string to the assembler. The string can contain any instructions recognized by the assembler, including directives. GCC does not parse the assembler instructions themselves and does not know what they mean or even whether they are valid assembler input. However, it does count the statements (Size of an asm).
You may place multiple assembler instructions together in a single asm string, separated by the characters normally used in assembly code for the system. A combination that works in most places is a newline to break the line, plus a tab character to move to the instruction field (written as nt). Some assemblers allow semicolons as a line separator. However, note that some assembler dialects use semicolons to start a comment.
Do not expect a sequence of asm statements to remain perfectly consecutive after compilation, even when you are using the volatile qualifier. If certain instructions need to remain consecutive in the output, put them in a single multi-instruction asm statement.
Accessing data from C programs without using input/output operands (such as by using global symbols directly from the assembler template) may not work as expected. Similarly, calling functions directly from an assembler template requires a detailed understanding of the target assembler and ABI.
Since GCC does not parse the assembler template, it has no visibility of any symbols it references. This may result in GCC discarding those symbols as unreferenced unless they are also listed as input, output, or goto operands.
In addition to the tokens described by the input, output, and goto operands, these tokens have special meanings in the assembler template:
Outputs a single % into the assembler code.
Outputs a number that is unique to each instance of the asm statement in the entire compilation. This option is useful when creating local labels and referring to them multiple times in a single template that generates multiple assembler instructions.
Outputs {, |, and } characters (respectively) into the assembler code. When unescaped, these characters have special meaning to indicate multiple assembler dialects, as described below.
Multiple assembler dialects in asm templates
On targets such as x86, GCC supports multiple assembler dialects. The -masm option controls which dialect GCC uses as its default for inline assembler. The target-specific documentation for the -masm option contains the list of supported dialects, as well as the default dialect if the option is not specified. This information may be important to understand, since assembler code that works correctly when compiled using one dialect will likely fail if compiled using another. x86 Options.
If your code needs to support multiple assembler dialects (for example, if you are writing public headers that need to support a variety of compilation options), use constructs of this form:
{ dialect0 | dialect1 | dialect2... }
This construct outputs dialect0 when using dialect #0 to compile the code, dialect1 for dialect #1, etc. If there are fewer alternatives within the braces than the number of dialects the compiler supports, the construct outputs nothing.
For example, if an x86 compiler supports two dialects (att, intel), an assembler template such as this:
"bt{l %[Offset],%[Base] | %[Base],%[Offset]}; jc %l2"
is equivalent to one of
"btl %[Offset],%[Base] ; jc %l2" /* att dialect */
"bt %[Base],%[Offset]; jc %l2" /* intel dialect */
Using that same compiler, this code:
"xchg{l}\t{%%}ebx, %1"
corresponds to either
"xchgl\t%%ebx, %1" /* att dialect */
"xchg\tebx, %1" /* intel dialect */
There is no support for nesting dialect alternatives.
OutputOperands
asm output operands
An asm statement has zero or more output operands indicating the names of C variables modified by the assembler code.
In this i386 example, old (referred to in the template string as %0) and *Base (as %1) are outputs and Offset (%2) is an input:
bool old;
__asm__ ("btsl %2,%1\n\t" // Turn on zero-based bit #Offset in Base.
"sbb %0,%0" // Use the CF to calculate old.
: "=r" (old), "+rm" (*Base)
: "Ir" (Offset)
: "cc");
return old;
Operands are separated by commas. Each operand has this format:
[ [``asmSymbolicName``] ] ``constraint`` (``cvariablename``)
Specifies a symbolic name for the operand. Reference the name in the assembler template by enclosing it in square brackets (i.e. %[Value]). The scope of the name is the asm statement that contains the definition. Any valid C variable name is acceptable, including names already defined in the surrounding code. No two operands within the same asm statement can use the same symbolic name.
When not using an asmSymbolicName, use the (zero-based) position of the operand in the list of operands in the assembler template. For example if there are three output operands, use %0 in the template to refer to the first, %1 for the second, and %2 for the third.
A string constant specifying constraints on the placement of the operand; Constraints, for details.
Output constraints must begin with either = (a variable overwriting an existing value) or + (when reading and writing). When using =, do not assume the location contains the existing value on entry to the asm, except when the operand is tied to an input; InputOperandsInput Operands.
After the prefix, there must be one or more additional constraints (Constraints) that describe where the value resides. Common constraints include r for register and m for memory. When you list more than one possible location (for example, "=rm"), the compiler chooses the most efficient one based on the current context. If you list as many alternates as the asm statement allows, you permit the optimizers to produce the best possible code. If you must use a specific register, but your Machine Constraints do not provide sufficient control to select the specific register you want, local register variables may provide a solution (Local Reg Vars).
Specifies a C lvalue expression to hold the output, typically a variable name. The enclosing parentheses are a required part of the syntax.
When the compiler selects the registers to use to represent the output operands, it does not use any of the clobbered registers (Clobbers).
Output operand expressions must be lvalues. The compiler cannot check whether the operands have data types that are reasonable for the instruction being executed. For output expressions that are not directly addressable (for example a bit-field), the constraint must allow a register. In that case, GCC uses the register as the output of the asm, and then stores that register into the output.
Operands using the + constraint modifier count as two operands (that is, both as input and output) towards the total maximum of 30 operands per asm statement.
Use the & constraint modifier (Modifiers) on all output operands that must not overlap an input. Otherwise, GCC may allocate the output operand in the same register as an unrelated input operand, on the assumption that the assembler code consumes its inputs before producing outputs. This assumption may be false if the assembler code actually consists of more than one instruction.
The same problem can occur if one output parameter (a) allows a register constraint and another output parameter (b) allows a memory constraint. The code generated by GCC to access the memory address in b can contain registers which might be shared by a, and GCC considers those registers to be inputs to the asm. As above, GCC assumes that such input registers are consumed before any outputs are written. This assumption may result in incorrect behavior if the asm writes to a before using b. Combining the & modifier with the register constraint on a ensures that modifying a does not affect the address referenced by b. Otherwise, the location of b is undefined if a is modified before using b.
asm supports operand modifiers on operands (for example %k2 instead of simply %2). Typically these qualifiers are hardware dependent. The list of supported modifiers for x86 is found at x86Operandmodifiersx86 Operand modifiers.
If the C code that follows the asm makes no use of any of the output operands, use volatile for the asm statement to prevent the optimizers from discarding the asm statement as unneeded (see Volatile).
This code makes no use of the optional asmSymbolicName. Therefore it references the first output operand as %0 (were there a second, it would be %1, etc). The number of the first input operand is one greater than that of the last output operand. In this i386 example, that makes Mask referenced as %1:
uint32_t Mask = 1234;
uint32_t Index;
asm ("bsfl %1, %0"
: "=r" (Index)
: "r" (Mask)
: "cc");
That code overwrites the variable Index (=), placing the value in a register (r). Using the generic r constraint instead of a constraint for a specific register allows the compiler to pick the register to use, which can result in more efficient code. This may not be possible if an assembler instruction requires a specific register.
The following i386 example uses the asmSymbolicName syntax. It produces the same result as the code above, but some may consider it more readable or more maintainable since reordering index numbers is not necessary when adding or removing operands. The names aIndex and aMask are only used in this example to emphasize which names get used where. It is acceptable to reuse the names Index and Mask.
uint32_t Mask = 1234;
uint32_t Index;
asm ("bsfl %[aMask], %[aIndex]"
: [aIndex] "=r" (Index)
: [aMask] "r" (Mask)
: "cc");
Here are some more examples of output operands.
uint32_t c = 1;
uint32_t d;
uint32_t *e = &c;
asm ("mov %[e], %[d]"
: [d] "=rm" (d)
: [e] "rm" (*e));
Here, d may either be in a register or in memory. Since the compiler might already have the current value of the uint32_t location pointed to by e in a register, you can enable it to choose the best location for d by specifying both constraints.
InputOperands
asm input operands asm expressions
Input operands make values from C variables and expressions available to the assembly code.
Operands are separated by commas. Each operand has this format:
[ [``asmSymbolicName``] ] ``constraint`` (``cexpression``)
Specifies a symbolic name for the operand. Reference the name in the assembler template by enclosing it in square brackets (i.e. %[Value]). The scope of the name is the asm statement that contains the definition. Any valid C variable name is acceptable, including names already defined in the surrounding code. No two operands within the same asm statement can use the same symbolic name.
When not using an asmSymbolicName, use the (zero-based) position of the operand in the list of operands in the assembler template. For example if there are two output operands and three inputs, use %2 in the template to refer to the first input operand, %3 for the second, and %4 for the third.
A string constant specifying constraints on the placement of the operand; Constraints, for details.
Input constraint strings may not begin with either = or +. When you list more than one possible location (for example, “irm”), the compiler chooses the most efficient one based on the current context. If you must use a specific register, but your Machine Constraints do not provide sufficient control to select the specific register you want, local register variables may provide a solution (Local Reg Vars).
Input constraints can also be digits (for example, "0"). This indicates that the specified input must be in the same place as the output constraint at the (zero-based) index in the output constraint list. When using asmSymbolicName syntax for the output operands, you may use these names (enclosed in brackets []) instead of digits.
This is the C variable or expression being passed to the asm statement as input. The enclosing parentheses are a required part of the syntax.
When the compiler selects the registers to use to represent the input operands, it does not use any of the clobbered registers (Clobbers).
If there are no output operands but there are input operands, place two consecutive colons where the output operands would go:
__asm__ ("some instructions"
: /* No outputs. */
: "r" (Offset / 8));
Warning: Do not modify the contents of input-only operands (except for inputs tied to outputs). The compiler assumes that on exit from the asm statement these operands contain the same values as they had before executing the statement. It is not possible to use clobbers to inform the compiler that the values in these inputs are changing. One common work-around is to tie the changing input variable to an output variable that never gets used. Note, however, that if the code that follows the asm statement makes no use of any of the output operands, the GCC optimizers may discard the asm statement as unneeded (see Volatile).
asm supports operand modifiers on operands (for example %k2 instead of simply %2). Typically these qualifiers are hardware dependent. The list of supported modifiers for x86 is found at x86Operandmodifiersx86 Operand modifiers.
In this example using the fictitious combine instruction, the constraint "0" for input operand 1 says that it must occupy the same location as output operand 0. Only input operands may use numbers in constraints, and they must each refer to an output operand. Only a number (or the symbolic assembler name) in the constraint can guarantee that one operand is in the same place as another. The mere fact that foo is the value of both operands is not enough to guarantee that they are in the same place in the generated assembler code.
asm ("combine %2, %0"
: "=r" (foo)
: "0" (foo), "g" (bar));
Here is an example using symbolic names.
asm ("cmoveq %1, %2, %[result]"
: [result] "=r"(result)
: "r" (test), "r" (new), "[result]" (old));
Clobbers
asm clobbers
While the compiler is aware of changes to entries listed in the output operands, the inline asm code may modify more than just the outputs. For example, calculations may require additional registers, or the processor may overwrite a register as a side effect of a particular assembler instruction. In order to inform the compiler of these changes, list them in the clobber list. Clobber list items are either register names or the special clobbers (listed below). Each clobber list item is a string constant enclosed in double quotes and separated by commas.
Clobber descriptions may not in any way overlap with an input or output operand. For example, you may not have an operand describing a register class with one member when listing that register in the clobber list. Variables declared to live in specific registers (Explicit Reg Vars) and used as asm input or output operands must have no part mentioned in the clobber description. In particular, there is no way to specify that input operands get modified without also specifying them as output operands.
When the compiler selects which registers to use to represent input and output operands, it does not use any of the clobbered registers. As a result, clobbered registers are available for any use in the assembler code.
Here is a realistic example for the VAX showing the use of clobbered registers:
asm volatile ("movc3 %0, %1, %2"
: /* No outputs. */
: "g" (from), "g" (to), "g" (count)
: "r0", "r1", "r2", "r3", "r4", "r5");
Also, there are two special clobber arguments:
The "cc" clobber indicates that the assembler code modifies the flags register. On some machines, GCC represents the condition codes as a specific hardware register; "cc" serves to name this register. On other machines, condition code handling is different, and specifying "cc" has no effect. But it is valid no matter what the target.
The "memory" clobber tells the compiler that the assembly code performs memory reads or writes to items other than those listed in the input and output operands (for example, accessing the memory pointed to by one of the input parameters). To ensure memory contains correct values, GCC may need to flush specific register values to memory before executing the asm. Further, the compiler does not assume that any values read from memory before an asm remain unchanged after that asm; it reloads them as needed. Using the "memory" clobber effectively forms a read/write memory barrier for the compiler.
Note that this clobber does not prevent the processor from doing speculative reads past the asm statement. To prevent that, you need processor-specific fence instructions.
Flushing registers to memory has performance implications and may be an issue for time-sensitive code. You can use a trick to avoid this if the size of the memory being accessed is known at compile time. For example, if accessing ten bytes of a string, use a memory input like:
{"m"( ({ struct { char x[10]; } *p = (void *)ptr ; *p; }) )}.
GotoLabels
asm goto labels
asm goto allows assembly code to jump to one or more C labels. The GotoLabels section in an asm goto statement contains a comma-separated list of all C labels to which the assembler code may jump. GCC assumes that asm execution falls through to the next statement (if this is not the case, consider using the __builtin_unreachable intrinsic after the asm statement). Optimization of asm goto may be improved by using the hot and cold label attributes (Label Attributes).
An asm goto statement cannot have outputs. This is due to an internal restriction of the compiler: control transfer instructions cannot have outputs. If the assembler code does modify anything, use the "memory" clobber to force the optimizers to flush all register values to memory and reload them if necessary after the asm statement.
Also note that an asm goto statement is always implicitly considered volatile.
To reference a label in the assembler template, prefix it with %l (lowercase L) followed by its (zero-based) position in GotoLabels plus the number of input operands. For example, if the asm has three inputs and references two labels, refer to the first label as %l3 and the second as %l4).
Alternately, you can reference labels using the actual C label name enclosed in brackets. For example, to reference a label named carry, you can use %l[carry]. The label must still be listed in the GotoLabels section when using this approach.
Here is an example of asm goto for i386:
asm goto (
"btl %1, %0\n\t"
"jc %l2"
: /* No outputs. */
: "r" (p1), "r" (p2)
: "cc"
: carry);
return 0;
carry:
return 1;
The following example shows an asm goto that uses a memory clobber.
int frob(int x)
{
int y;
asm goto ("frob %%r5, %1; jc %l[error]; mov (%2), %%r5"
: /* No outputs. */
: "r"(x), "r"(&y)
: "r5", "memory"
: error);
return y;
error:
return -1;
}
x86Operandmodifiers
References to input, output, and goto operands in the assembler template of extended asm statements can use modifiers to affect the way the operands are formatted in the code output to the assembler. For example, the following code uses the h and b modifiers for x86:
uint16_t num;
asm volatile ("xchg %h0, %b0" : "+a" (num) );
These modifiers generate this assembler code:
xchg %ah, %al
The rest of this discussion uses the following code for illustrative purposes.
int main()
{
int iInt = 1;
top:
asm volatile goto ("some assembler instructions here"
: /* No outputs. */
: "q" (iInt), "X" (sizeof(unsigned char) + 1)
: /* No clobbers. */
: top);
}
With no modifiers, this is what the output from the operands would be for the att and intel dialects of assembler:
Operand masm=att OFFSET FLAT:.L2 Operand masm=att masm=intel %0 %eax eax %1 $2 2 %2 $.L2 OFFSET FLAT:.L2
The table below shows the list of supported modifiers and their effects.
Modifier Print the opcode suffix for the size of th Operand masm=att masm=intel Modifier Description Operand masm=att masm=intel z Print the opcode suffix for the size of the current integer operand (one of b/w/l/q). %z0 l
b Print the QImode name of the register. %b0 %al al h Print the QImode name for a high register. %h0 %ah ah w Print the HImode name of the register. %w0 %ax ax k Print the SImode name of the register. %k0 %eax eax q Print the DImode name of the register. %q0 %rax rax l Print the label name with no punctuation. %l2 .L2 .L2 c Require a constant operand and print the constant expression with no punctuation. %c1 2 2
x86floatingpointasmoperands
x86 Floating-Point asm Operands
On x86 targets, there are several rules on the usage of stack-like registers in the operands of an asm. These rules apply only to the operands that are stack-like registers:
Given a set of input registers that die in an asm, it is necessary to know which are implicitly popped by the asm, and which must be explicitly popped by GCC
An input register that is implicitly popped by the asm must be explicitly clobbered, unless it is constrained to match an output operand.
For any input register that is implicitly popped by an asm, it is necessary to know how to adjust the stack to compensate for the pop. If any non-popped input is closer to the top of the reg-stack than the implicitly popped register, it would not be possible to know what the stack looked likeits not clear how the rest of the stack slides up.
All implicitly popped input registers must be closer to the top of the reg-stack than any input that is not implicitly popped.
It is possible that if an input dies in an asm, the compiler might use the input register for an output reload. Consider this example:
asm ("foo" : "=t" (a) : "f" (b));
This code says that input b is not popped by the asm, and that the asm pushes a result onto the reg-stack, i.e., the stack is one deeper after the asm than it was before. But, it is possible that reload may think that it can use the same register for both the input and the output.
To prevent this from happening, if any input operand uses the f constraint, all output register constraints must use the & early-clobber modifier.
The example above is correctly written as:
asm ("foo" : "=&t" (a) : "f" (b));
Some operands need to be in particular places on the stack. All output operands fall in this categoryGCC has no other way to know which registers the outputs appear in unless you indicate this in the constraints.
Output operands must specifically indicate which register an output appears in after an asm. =f is not allowed: the operand constraints must select a class with a single register.
Output operands may not be inserted between existing stack registers. Since no 387 opcode uses a read/write operand, all output operands are dead before the asm, and are pushed by the asm. It makes no sense to push anywhere but the top of the reg-stack.
Output operands must start at the top of the reg-stack: output operands may not skip a register.
Some asm statements may need extra stack space for internal calculations. This can be guaranteed by clobbering stack registers unrelated to the inputs and outputs.
This asm takes one input, which is internally popped, and produces two outputs.
asm ("fsincos" : "=t" (cos), "=u" (sin) : "0" (inp));
This asm takes two inputs, which are popped by the fyl2xp1 opcode, and replaces them with one output. The st(1) clobber is necessary for the compiler to know that fyl2xp1 pops both inputs.
asm ("fyl2xp1" : "=t" (result) : "0" (x), "u" (y) : "st(1)");
:: _constraints:
Constraints for asm Operands operand constraints, asm constraints, asm asm constraints
Here are specific details on what constraint letters you can use with asm operands. Constraints can say whether an operand may be in a register, and which kinds of register; whether the operand can be a memory reference, and which kinds of address; whether the operand may be an immediate constant, and which possible values it may have. Constraints can also require two operands to match. Side-effects arent allowed in operands of inline asm, unless < or > constraints are used, because there is no guarantee that the side-effects will happen exactly once in an instruction that can update the addressing register.
:: _simple-constraints:
The simplest kind of constraint is a string full of letters, each of which describes one kind of operand that is permitted. Here are the letters that are allowed:
Whitespace characters are ignored and can be inserted at any position except the first. This enables each alternative for different operands to be visually aligned in the machine description even if they have different number of constraints and modifiers.
m in constraint
m
A memory operand is allowed, with any kind of address that the machine supports in general. Note that the letter used for the general memory constraint can be re-defined by a back end using the TARGET_MEM_CONSTRAINT macro.
o in constraint o A memory operand is allowed, but only if the address is offsettable. This means that adding a small integer (actually, the width in bytes of the operand, as determined by its machine mode) may be added to the address and the result is also a valid memory address.
For example, an address which is constant is offsettable; so is an address that is the sum of a register and a constant (as long as a slightly larger constant is also within the range of address-offsets supported by the machine); but an autoincrement or autodecrement address is not offsettable. More complicated indirect/indexed addresses may or may not be offsettable depending on the other addressing modes that the machine supports.
Note that in an output operand which can be matched by another operand, the constraint letter o is valid only when accompanied by both < (if the target machine has predecrement addressing) and > (if the target machine has preincrement addressing).
V in constraint V A memory operand that is not offsettable. In other words, anything that would fit the m constraint but not the o constraint.
< in constraint < A memory operand with autodecrement addressing (either predecrement or postdecrement) is allowed. In inline asm this constraint is only allowed if the operand is used exactly once in an instruction that can handle the side-effects. Not using an operand with < in constraint string in the inline asm pattern at all or using it in multiple instructions isnt valid, because the side-effects wouldnt be performed or would be performed more than once. Furthermore, on some targets the operand with < in constraint string must be accompanied by special instruction suffixes like %U0 instruction suffix on PowerPC or %P0 on IA-64.
> in constraint > A memory operand with autoincrement addressing (either preincrement or postincrement) is allowed. In inline asm the same restrictions as for < apply.
r in constraint
r A register operand is allowed provided that it is in a general register.
i in constraint i An immediate integer operand (one with constant value) is allowed. This includes symbolic constants whose values will be known only at assembly time or later.
n in constraint n An immediate integer operand with a known numeric value is allowed. Many systems cannot support assembly-time constants for operands less than a word wide. Constraints for these operands should use n rather than i.
I in constraint I, J, K, ... P Other letters in the range I through P may be defined in a machine-dependent fashion to permit immediate integer operands with explicit integer values in specified ranges. For example, on the 68000, I is defined to stand for the range of values 1 to 8. This is the range permitted as a shift count in the shift instructions.
E in constraint E An immediate floating operand (expression code const_double) is allowed, but only if the target floating point format is the same as that of the host machine (on which the compiler is running).
F in constraint F An immediate floating operand (expression code const_double or const_vector) is allowed.
G in constraint H in constraint G, H G and H may be defined in a machine-dependent fashion to permit immediate floating operands in particular ranges of values.
s in constraint s An immediate integer operand whose value is not an explicit integer is allowed.
This might appear strange; if an insn allows a constant operand with a value not known at compile time, it certainly must allow any known value. So why use s instead of i? Sometimes it allows better code to be generated.
For example, on the 68000 in a fullword instruction it is possible to use an immediate operand; but if the immediate value is between 128 and 127, better code results from loading the value into a register and using the register. This is because the load into the register can be done with a moveq instruction. We arrange for this to happen by defining the letter K to mean any integer outside the range 128 to 127, and then specifying Ks in the operand constraints.
g in constraint g Any register, memory or immediate integer operand is allowed, except for registers that are not general registers.
X in constraint X Any operand whatsoever is allowed.
0 in constraint
0, 1, 2, ... 9 An operand that matches the specified operand number is allowed. If a digit is used together with letters within the same alternative, the digit should come last.
This number is allowed to be more than a single digit. If multiple digits are encountered consecutively, they are interpreted as a single decimal integer. There is scant chance for ambiguity, since to-date it has never been desirable that 10 be interpreted as matching either operand 1 or operand 0. Should this be desired, one can use multiple alternatives instead.
This is called a matching constraint and what it really means is that the assembler has only a single operand that fills two roles which asm distinguishes. For example, an add instruction uses two input operands and an output operand, but on most CISC machines an add instruction really has only two operands, one of them an input-output operand:
addl #35,r12
Matching constraints are used in these circumstances. More precisely, the two operands that match must include one input-only operand and one output-only operand. Moreover, the digit must be a smaller number than the number of the operand that uses it in the constraint.
p in constraint p An operand that is a valid memory address is allowed. This is for load address and push address instructions.
p in the constraint must be accompanied by address_operand as the predicate in the match_operand. This predicate interprets the mode specified in the match_operand as the mode of the memory reference for which the address would be valid.
other-letters Other letters can be defined in machine-dependent fashion to stand for particular classes of registers or other arbitrary operand types. d, a and f are defined on the 68000/68020 to stand for data, address and floating point registers.
:: _multi-alternative:
Sometimes a single instruction has multiple alternative sets of possible operands. For example, on the 68000, a logical-or instruction can combine register or an immediate value into memory, or it can combine any kind of operand into a register; but it cannot combine one memory location into another.
These constraints are represented as multiple alternatives. An alternative can be described by a series of letters for each operand. The overall constraint for an operand is made from the letters for this operand from the first alternative, a comma, the letters for this operand from the second alternative, a comma, and so on until the last alternative.
If all the operands fit any one alternative, the instruction is valid. Otherwise, for each alternative, the compiler counts how many instructions must be added to copy the operands so that that alternative applies. The alternative requiring the least copying is chosen. If two alternatives need the same amount of copying, the one that comes first is chosen. These choices can be altered with the ? and ! characters:
? in constraint
Disparage slightly the alternative that the ? appears in, as a choice when no alternative applies exactly. The compiler regards this alternative as one unit more costly for each ? that appears in it.
! in constraint
Disparage severely the alternative that the ! appears in. This alternative can still be used if it fits without reloading, but if reloading is needed, some other alternative will be used.
^ in constraint
This constraint is analogous to ? but it disparages slightly the alternative only if the operand with the ^ needs a reload.
$ in constraint
This constraint is analogous to ! but it disparages severely the alternative only if the operand with the $ needs a reload.
:: _modifiers:
Here are constraint modifier characters.
= in constraint
Means that this operand is written to by this instruction: the previous value is discarded and replaced by new data.
Means that this operand is both read and written by the instruction.
When the compiler fixes up the operands to satisfy the constraints, it needs to know which operands are read by the instruction and which are written by it. = identifies an operand which is only written; + identifies an operand that is both read and written; all other operands are assumed to only be read.
If you specify = or + in a constraint, you put it in the first character of the constraint string.
& in constraint
Means (in a particular alternative) that this operand is an earlyclobber operand, which is written before the instruction is finished using the input operands. Therefore, this operand may not lie in a register that is read by the instruction or as part of any memory address.
& applies only to the alternative in which it is written. In constraints with multiple alternatives, sometimes one alternative requires & while others do not. See, for example, the movdf insn of the 68000.
A operand which is read by the instruction can be tied to an earlyclobber operand if its only use as an input occurs before the early result is written. Adding alternatives of this form often allows GCC to produce better code when only some of the read operands can be affected by the earlyclobber. See, for example, the mulsi3 insn of the ARM
Furthermore, if the earlyclobber operand is also a read/write operand, then that operand is written only after its used.
& does not obviate the need to write = or +. As earlyclobber operands are always written, a read-only earlyclobber operand is ill-formed and will be rejected by the compiler.
% in constraint
Declares the instruction to be commutative for this operand and the following operand. This means that the compiler may interchange the two operands if that is the cheapest way to make all operands fit the constraints. % applies to all alternatives and must appear as the first character in the constraint. Only read-only operands can use %.
GCC can only handle one commutative pair in an asm; if you use more, the compiler may fail. Note that you need not use the modifier if the two alternatives are strictly identical; this would only waste time in the reload pass. The modifier is not operational after register allocation, so the result of define_peephole2 and ``define_split``s performed after reload cannot rely on % to make the intended insn match.
# in constraint
Says that all following characters, up to the next comma, are to be ignored as a constraint. They are significant only for choosing register preferences.
Says that the following character should be ignored when choosing register preferences. * has no effect on the meaning of the constraint as a constraint, and no effect on reloading. For LRA * additionally disparages slightly the alternative if the following character matches the operand.
:: _machine-constraints:
Whenever possible, you should use the general-purpose constraint letters in asm arguments, since they will convey meaning more readily to people reading your code. Failing that, use the constraint letters that usually have very similar meanings across architectures. The most commonly used constraints are m and r (for memory and general-purpose registers respectively; Simple Constraints), and I, usually the letter indicating the most common immediate-constant format.
Each architecture defines additional constraints. These constraints are used by the compiler itself for instruction generation, as well as for asm statements; therefore, some of the constraints are not particularly useful for asm. Here is a summary of some of the machine-dependent constraints available on some particular machines; it includes both constraints that are useful for asm and constraints that arent. The compiler source file mentioned in the table heading for each architecture is the definitive reference for the meanings of that architectures constraints.
AArch64 familyconfig/aarch64/constraints.md
The stack pointer register (SP)
Floating point or SIMD vector register
Integer constant that is valid as an immediate operand in an ADD instruction
Integer constant that is valid as an immediate operand in a SUB instruction (once negated)
Integer constant that can be used with a 32-bit logical instruction
Integer constant that can be used with a 64-bit logical instruction
Integer constant that is valid as an immediate operand in a 32-bit MOV pseudo instruction. The MOV may be assembled to one of several different machine instructions depending on the value
Integer constant that is valid as an immediate operand in a 64-bit MOV pseudo instruction
An absolute symbolic address or a label reference
Floating point constant zero
Integer constant zero
The high part (bits 12 and upwards) of the pc-relative address of a symbol within 4GB of the instruction
A memory address which uses a single base register with no offset
A memory address suitable for a load/store pair instruction in SI, DI, SF and DF modes
ARC config/arc/constraints.md
Registers usable in ARCompact 16-bit instructions: r0-r3, r12-r15. This constraint can only match when the -mq option is in effect.
Registers usable as base-regs of memory addresses in ARCompact 16-bit memory instructions: r0-r3, r12-r15, sp. This constraint can only match when the -mq option is in effect.
ARC FPX (dpfp) 64-bit registers. D0, D1.
A signed 12-bit integer constant.
constant for arithmetic/logical operations. This might be any constant that can be put into a long immediate by the assmbler or linker without involving a PIC relocation.
A 3-bit unsigned integer constant.
A 6-bit unsigned integer constant.
Ones complement of a 6-bit unsigned integer constant.
Twos complement of a 6-bit unsigned integer constant.
A 5-bit unsigned integer constant.
A 7-bit unsigned integer constant.
A 8-bit unsigned integer constant.
Any const_double value.
ARM familyconfig/arm/constraints.md
In Thumb state, the core registers r8-r15.
The stack pointer register.
In Thumb State the core registers r0-r7. In ARM state this is an alias for the r constraint.
VFP floating-point registers s0-s31. Used for 32 bit values.
VFP floating-point registers d0-d31 and the appropriate subset d0-d15 based on command line options. Used for 64 bit values only. Not valid for Thumb1.
The iWMMX co-processor registers.
The iWMMX GR registers.
The floating-point constant 0.0
Integer that is valid as an immediate operand in a data processing instruction. That is, an integer in the range 0 to 255 rotated by a multiple of 2
Integer in the range 4095 to 4095
Integer that satisfies constraint I when inverted (ones complement)
Integer that satisfies constraint I when negated (twos complement)
Integer in the range 0 to 32
A memory reference where the exact address is in a single register (m is preferable for asm statements)
An item in the constant pool
A symbol in the text segment of the current file
A memory reference suitable for VFP load/store insns (reg+constant offset)
A memory reference suitable for iWMMXt load/store instructions.
A memory reference suitable for the ARMv4 ldrsb instruction.
AVR familyconfig/avr/constraints.md
Registers from r0 to r15
Registers from r16 to r23
Registers from r16 to r31
Registers from r24 to r31. These registers can be used in adiw command
Pointer register (r26r31)
Base pointer register (r28r31)
Stack pointer register (SPH:SPL)
Temporary register r0
Register pair X (r27:r26)
Register pair Y (r29:r28)
Register pair Z (r31:r30)
Constant greater than 1, less than 64
Constant greater than 64, less than 1
Constant integer 2
Constant integer 0
Constant that fits in 8 bits
Constant integer 1
Constant integer 8, 16, or 24
Constant integer 1
A floating point constant 0.0
A memory address based on Y or Z pointer with displacement.
Blackfin familyconfig/bfin/constraints.md
P register
D register
A call clobbered P register.
q``n``
A single register. If n is in the range 0 to 7, the corresponding D register. If it is A, then the register P0.
Even-numbered D register
Odd-numbered D register
Accumulator register.
Even-numbered accumulator register.
Odd-numbered accumulator register.
I register
B register
M register
Registers used for circular buffering, i.e. I, B, or L registers.
The CC register.
LT0 or LT1.
LC0 or LC1.
LB0 or LB1.
Any D, P, B, M, I or L register.
Additional registers typically used only in prologues and epilogues: RETS, RETN, RETI, RETX, RETE, ASTAT, SEQSTAT and USP.
Any register except accumulators or CC.
Signed 16 bit integer (in the range 32768 to 32767)
Unsigned 16 bit integer (in the range 0 to 65535)
Signed 7 bit integer (in the range 64 to 63)
Unsigned 7 bit integer (in the range 0 to 127)
Unsigned 5 bit integer (in the range 0 to 31)
Signed 4 bit integer (in the range 8 to 7)
Signed 3 bit integer (in the range 3 to 4)
Unsigned 3 bit integer (in the range 0 to 7)
P``n``
Constant n, where n is a single-digit constant in the range 0 to 4.
An integer equal to one of the MACFLAG_XXX constants that is suitable for use with either accumulator.
An integer equal to one of the MACFLAG_XXX constants that is suitable for use only with accumulator A1.
Constant 255.
Constant 65535.
An integer constant with exactly a single bit set.
An integer constant with all bits set except exactly one.
Any SYMBOL_REF.
CR16 Architectureconfig/cr16/cr16.h
Registers from r0 to r14 (registers without stack pointer)
Register from r0 to r11 (all 16-bit registers)
Register from r12 to r15 (all 32-bit registers)
Signed constant that fits in 4 bits
Signed constant that fits in 5 bits
Signed constant that fits in 6 bits
Unsigned constant that fits in 4 bits
Signed constant that fits in 32 bits
Check for 64 bits wide constants for add/sub instructions
Floating point constant that is legal for store immediate
Epiphanyconfig/epiphany/constraints.md
An unsigned 16-bit constant.
An unsigned 5-bit constant.
A signed 11-bit constant.
A signed 11-bit constant added to 1. Can only match when the -m1reg-``reg`` option is active.
Left-shift of 1, i.e., a bit mask with a block of leading ones, the rest being a block of trailing zeroes. Can only match when the -m1reg-``reg`` option is active.
Right-shift of 1, i.e., a bit mask with a trailing block of ones, the rest being zeroes. Or to put it another way, one less than a power of two. Can only match when the -m1reg-``reg`` option is active.
Constant for arithmetic/logical operations. This is like i, except that for position independent code, no symbols / expressions needing relocations are allowed.
Symbolic constant for call/jump instruction.
The register class usable in short insns. This is a register class constraint, and can thus drive register allocation. This constraint wont match unless -mprefer-short-insn-regs is in effect.
The the register class of registers that can be used to hold a sibcall call address. I.e., a caller-saved register.
Core control register class.
The register group usable in short insns. This constraint does not use a register class, so that it only passively matches suitable registers, and doesnt drive register allocation.
Matches the return address if it can be replaced with the link register.
Matches the integer condition code register.
Matches the return address if it is in a stack slot.
Matches control register values to switch fp mode, which are encapsulated in UNSPEC_FP_MODE.
FRVconfig/frv/frv.h
Register in the class ACC_REGS (acc0 to acc7).
Register in the class EVEN_ACC_REGS (acc0 to acc7).
Register in the class CC_REGS (fcc0 to fcc3 and icc0 to icc3).
Register in the class GPR_REGS (gr0 to gr63).
Register in the class EVEN_REGS (gr0 to gr63). Odd registers are excluded not in the class but through the use of a machine mode larger than 4 bytes.
Register in the class FPR_REGS (fr0 to fr63).
Register in the class FEVEN_REGS (fr0 to fr63). Odd registers are excluded not in the class but through the use of a machine mode larger than 4 bytes.
Register in the class LR_REG (the lr register).
Register in the class QUAD_REGS (gr2 to gr63). Register numbers not divisible by 4 are excluded not in the class but through the use of a machine mode larger than 8 bytes.
Register in the class ICC_REGS (icc0 to icc3).
Register in the class FCC_REGS (fcc0 to fcc3).
Register in the class ICR_REGS (cc4 to cc7).
Register in the class FCR_REGS (cc0 to cc3).
Register in the class QUAD_FPR_REGS (fr0 to fr63). Register numbers not divisible by 4 are excluded not in the class but through the use of a machine mode larger than 8 bytes.
Register in the class SPR_REGS (lcr and lr).
Register in the class QUAD_ACC_REGS (acc0 to acc7).
Register in the class ACCG_REGS (accg0 to accg7).
Register in the class CR_REGS (cc0 to cc7).
Floating point constant zero
6-bit signed integer constant
10-bit signed integer constant
16-bit signed integer constant
16-bit unsigned integer constant
12-bit signed integer constant that is negativei.e. in the range of 2048 to 1
Constant zero
12-bit signed integer constant that is greater than zeroi.e. in the range of 1 to 2047.
Hewlett-Packard PA-RISCconfig/pa/pa.h
General register 1
Floating point register
Shift amount register
Floating point register (deprecated)
Upper floating point register (32-bit), floating point register (64-bit)
Any register
Signed 11-bit integer constant
Signed 14-bit integer constant
Integer constant that can be deposited with a zdepi instruction
Signed 5-bit integer constant
Integer constant 0
Integer constant that can be loaded with a ldil instruction
Integer constant whose value plus one is a power of 2
Integer constant that can be used for and operations in depi and extru instructions
Integer constant 31
Integer constant 63
Floating-point constant 0.0
A lo_sum data-linkage-table memory operand
A memory operand that can be used as the destination operand of an integer store instruction
A scaled or unscaled indexed memory operand
A memory operand for floating-point loads and stores
A register indirect memory operand
Intel IA-64config/ia64/ia64.h
General register r0 to r3 for addl instruction
Branch register
Predicate register (c as in conditional)
Application register residing in M-unit
Application register residing in I-unit
Floating-point register
Memory operand. If used together with < or >, the operand can have postincrement and postdecrement which require printing with %Pn on IA-64.
Floating-point constant 0.0 or 1.0
14-bit signed integer constant
22-bit signed integer constant
8-bit signed integer constant for logical instructions
8-bit adjusted signed integer constant for compare pseudo-ops
6-bit unsigned integer constant for shift counts
9-bit signed integer constant for load and store postincrements
The constant zero
0 or 1 for dep instruction
Non-volatile memory for floating-point loads and stores
Integer constant in the range 1 to 4 for shladd instruction
Memory operand except postincrement and postdecrement. This is now roughly the same as m when not used together with < or >.
M32Cconfig/m32c/m32c.c
$sp, $fb, $sb.
Any control register, when theyre 16 bits wide (nothing if control registers are 24 bits wide)
Any control register, when theyre 24 bits wide.
$r0, $r1, $r2, $r3.
$r0 or $r2, or $r2r0 for 32 bit values.
$r1 or $r3, or $r3r1 for 32 bit values.
A register that can hold a 64 bit value.
$r0 or $r1 (registers with addressable high/low bytes)
$r2 or $r3
Address registers
Address registers when theyre 16 bits wide.
Address registers when theyre 24 bits wide.
Registers that can hold QI values.
Registers that can be used with displacements ($a0, $a1, $sb).
Registers that can hold 32 bit values.
Registers that can hold 16 bit values.
Registers chat can hold 16 bit values, including all control registers.
$r0 through R1, plus $a0 and $a1.
The flags register.
The memory-based pseudo-registers $mem0 through $mem15.
Registers that can hold pointers (16 bit registers for r8c, m16c; 24 bit registers for m32cm, m32c).
Matches multiple registers in a PARALLEL to form a larger register. Used to match function return values.
8 ... 7
128 ... 127
32768 ... 32767
0 ... 65535
8 ... 1 or 1 ... 8
16 ... 1 or 1 ... 16
32 ... 1 or 1 ... 32
65536 ... 1
An 8 bit value with exactly one bit set.
A 16 bit value with exactly one bit set.
The common src/dest memory addressing modes.
Memory addressed using $a0 or $a1.
Memory addressed with immediate addresses.
Memory addressed using the stack pointer ($sp).
Memory addressed using the frame base register ($fb).
Memory addressed using the small base register ($sb).
$r1h
MePconfig/mep/constraints.md
The $sp register.
The $tp register.
Any control register.
Either the $hi or the $lo register.
Coprocessor registers that can be directly loaded ($c0-$c15).
Coprocessor registers that can be moved to each other.
Coprocessor registers that can be moved to core registers.
The $hi register.
The $rpc register.
The $lo register.
Registers which can be used in $tp-relative addressing.
The $gp register.
The coprocessor registers.
The coprocessor control registers.
The $0 register.
User-defined register set A.
User-defined register set B.
User-defined register set C.
User-defined register set D.
Offsets for $gp-rel addressing.
Constants that can be used directly with boolean insns.
Constants that can be moved directly to registers.
Small constants that can be added to registers.
Long shift counts.
Small constants that can be compared to registers.
Constants that can be loaded into the top half of registers.
Signed 8-bit immediates.
Symbols encoded for $tp-rel or $gp-rel addressing.
Non-constant addresses for loading/saving coprocessor registers.
The top half of a symbols value.
A register indirect address without offset.
Symbolic references to the control bus.
MicroBlazeconfig/microblaze/constraints.md
A general register (r0 to r31).
A status register (rmsr, $fcc1 to $fcc7).
MIPSconfig/mips/constraints.md
An address register. This is equivalent to r unless generating MIPS16 code.
A floating-point register (if available).
Formerly the hi register. This constraint is no longer supported.
The lo register. Use this register to store values that are no bigger than a word.
The concatenated hi and lo registers. Use this register to store doubleword values.
A register suitable for use in an indirect jump. This will always be $25 for -mabicalls.
Register $3. Do not use this constraint in new code; it is retained only for compatibility with glibc.
Equivalent to r; retained for backwards compatibility.
A floating-point condition code register.
A signed 16-bit constant (for arithmetic instructions).
Integer zero.
An unsigned 16-bit constant (for logic instructions).
A signed 32-bit constant in which the lower 16 bits are zero. Such constants can be loaded using lui.
A constant that cannot be loaded using lui, addiu or ori.
A constant in the range 65535 to 1 (inclusive).
A signed 15-bit constant.
A constant in the range 1 to 65535 (inclusive).
Floating-point zero.
An address that can be used in a non-macro load or store.
A memory operand whose address is formed by a base register and offset that is suitable for use in instructions with the same addressing mode as ll and sc.
An address suitable for a prefetch instruction, or for any other instruction with the same addressing mode as prefetch.
Motorola 680x0config/m68k/constraints.md
Address register
Data register
68881 floating-point register, if available
Integer in the range 1 to 8
16-bit signed number
Signed number whose magnitude is greater than 0x80
Integer in the range 8 to 1
Signed number whose magnitude is greater than 0x100
Range 24 to 31, rotatert:SI 8 to 1 expressed as rotate
16 (for rotate using swap)
Range 8 to 15, rotatert:HI 8 to 1 expressed as rotate
Numbers that mov3q can handle
Floating point constant that is not a 68881 constant
Operands that satisfy m when -mpcrel is in effect
Operands that satisfy s when -mpcrel is not in effect
Address register indirect addressing mode
Register offset addressing
const_call_operand
symbol_ref or const
const_int
const_int 0
Range of signed numbers that dont fit in 16 bits
Integers valid for mvq
Integers valid for a moveq followed by a swap
Integers valid for mvz
Integers valid for mvs
push_operand
Non-register operands allowed in clr
Moxieconfig/moxie/constraints.md
An absolute address
An offset address
A register indirect memory operand
A constant in the range of 0 to 255.
A constant in the range of 0 to 255.
MSP430config/msp430/constraints.md
Register R12.
Register R13.
Integer constant 1.
Integer constant -1^20..1^19.
Integer constant 1-4.
Memory references which do not require an extended MOVX instruction.
Memory reference, labels only.
Memory reference, stack only.
NDS32config/nds32/constraints.md
LOW register class $r0 to $r7 constraint for V3/V3M ISA.
LOW register class $r0 to $r7.
MIDDLE register class $r0 to $r11, $r16 to $r19.
HIGH register class $r12 to $r14, $r20 to $r31.
Temporary assist register $ta (i.e. $r15).
Stack register $sp.
Unsigned immediate 3-bit value.
Negative immediate 3-bit value in the range of 70.
Unsigned immediate 4-bit value.
Signed immediate 5-bit value.
Unsigned immediate 5-bit value.
Negative immediate 5-bit value in the range of 310.
Unsigned immediate 5-bit value for movpi45 instruction with range 1647.
Unsigned immediate 6-bit value constraint for addri36.sp instruction.
Unsigned immediate 8-bit value.
Unsigned immediate 9-bit value.
Signed immediate 10-bit value.
Signed immediate 11-bit value.
Signed immediate 15-bit value.
Unsigned immediate 15-bit value.
A constant which is not in the range of imm15u but ok for bclr instruction.
A constant which is not in the range of imm15u but ok for bset instruction.
A constant which is not in the range of imm15u but ok for btgl instruction.
A constant whose compliment value is in the range of imm15u and ok for bitci instruction.
Signed immediate 16-bit value.
Signed immediate 17-bit value.
Signed immediate 19-bit value.
Signed immediate 20-bit value.
The immediate value that can be simply set high 20-bit.
The immediate value 0xff.
The immediate value 0xffff.
The immediate value 0x01.
The immediate value 0x7ff.
The immediate value with power of 2.
The immediate value with power of 2 minus 1.
Memory constraint for 333 format.
Memory constraint for 45 format.
Memory constraint for 37 format.
Nios II familyconfig/nios2/constraints.md
Integer that is valid as an immediate operand in an instruction taking a signed 16-bit number. Range 32768 to 32767.
Integer that is valid as an immediate operand in an instruction taking an unsigned 16-bit number. Range 0 to 65535.
Integer that is valid as an immediate operand in an instruction taking only the upper 16-bits of a 32-bit number. Range 32-bit numbers with the lower 16-bits being 0.
Integer that is valid as an immediate operand for a shift instruction. Range 0 to 31.
Integer that is valid as an immediate operand for only the value 0. Can be used in conjunction with the format modifier z to use r0 instead of 0 in the assembly output.
Integer that is valid as an immediate operand for a custom instruction opcode. Range 0 to 255.
Matches immediates which are addresses in the small data section and therefore can be added to gp as a 16-bit immediate to re-create their 32-bit value.
PDP-11config/pdp11/constraints.md
Floating point registers AC0 through AC3. These can be loaded from/to memory with a single instruction.
Odd numbered general registers (R1, R3, R5). These are used for 16-bit multiply operations.
Any of the floating point registers (AC0 through AC5).
Floating point constant 0.
An integer constant that fits in 16 bits.
An integer constant whose low order 16 bits are zero.
An integer constant that does not meet the constraints for codes I or J.
The integer constant 1.
The integer constant 1.
The integer constant 0.
Integer constants 4 through 1 and 1 through 4; shifts by these amounts are handled as multiple single-bit shifts rather than a single variable-length shift.
A memory reference which requires an additional word (address or offset) after the opcode.
A memory reference that is encoded within the opcode.
PowerPC and IBM RS6000config/rs6000/constraints.md
Address base register
Floating point register (containing 64-bit value)
Floating point register (containing 32-bit value)
Altivec vector register
Any VSX register if the -mvsx option was used or NO_REGS.
VSX vector register to hold vector double data or NO_REGS.
VSX vector register to hold vector float data or NO_REGS.
If -mmfpgpr was used, a floating point register or NO_REGS.
Floating point register if direct moves are available, or NO_REGS.
FP or VSX register to hold 64-bit integers for VSX insns or NO_REGS.
FP or VSX register to hold 64-bit integers for direct moves or NO_REGS.
FP or VSX register to hold 64-bit doubles for direct moves or NO_REGS.
Floating point register if the LFIWAX instruction is enabled or NO_REGS.
VSX register if direct move instructions are enabled, or NO_REGS.
No register (NO_REGS).
General purpose register if 64-bit instructions are enabled or NO_REGS.
VSX vector register to hold scalar double values or NO_REGS.
VSX vector register to hold 128 bit integer or NO_REGS.
Altivec register to use for float/32-bit int loads/stores or NO_REGS.
Altivec register to use for double loads/stores or NO_REGS.
FP or VSX register to perform float operations under -mvsx or NO_REGS.
Floating point register if the STFIWX instruction is enabled or NO_REGS.
FP or VSX register to perform ISA 2.07 float ops or NO_REGS.
Floating point register if the LFIWZX instruction is enabled or NO_REGS.
Int constant that is the element number of the 64-bit scalar in a vector.
A memory address that will work with the lq and stq instructions.
MQ, CTR, or LINK register
MQ register
CTR register
LINK register
CR register (condition register) number 0
CR register (condition register)
XER[CA] carry bit (part of the XER register)
Signed 16-bit constant
Unsigned 16-bit constant shifted left 16 bits (use L instead for SImode constants)
Unsigned 16-bit constant
Signed 16-bit constant shifted left 16 bits
Constant larger than 31
Exact power of 2
Zero
Constant whose negation is a signed 16-bit constant
Floating point constant that can be loaded into a register with one instruction per word
Integer/Floating point constant that can be loaded into a register using three instructions
Memory operand. Normally, m does not allow addresses that update the base register. If < or > constraint is also used, they are allowed and therefore on PowerPC targets in that case it is only safe to use m<> in an asm statement if that asm statement accesses the operand exactly once. The asm statement must also use %U``<opno>`` as a placeholder for the update flag in the corresponding load or store instruction. For example:
asm ("st%U0 %1,%0" : "=m<>" (mem) : "r" (val));
is correct but:
asm ("st %1,%0" : "=m<>" (mem) : "r" (val));
is not.
A stable memory operand; that is, one which does not include any automodification of the base register. This used to be useful when m allowed automodification of the base register, but as those are now only allowed when < or > is used, es is basically the same as m without < and >.
Memory operand that is an offset from a register (it is usually better to use m or es in asm statements)
Memory operand that is an indexed or indirect from a register (it is usually better to use m or es in asm statements)
AIX TOC entry
Address operand that is an indexed or indirect from a register (p is preferable for asm statements)
Constant suitable as a 64-bit mask operand
Constant suitable as a 32-bit mask operand
System V Release 4 small data area reference
AND masks that can be performed by two rldic{l, r} instructions
Vector constant that does not require memory
Vector constant that is all zeros.
RL78config/rl78/constraints.md
An integer constant in the range 1 ... 7.
An integer constant in the range 0 ... 255.
An integer constant in the range 255 ... 0
The integer constant 1.
The integer constant -1.
The integer constant 0.
The integer constant 2.
The integer constant -2.
An integer constant in the range 1 ... 15.
The built-in compare typeseq, ne, gtu, ltu, geu, and leu.
The synthetic compare typesgt, lt, ge, and le.
A memory reference with an absolute address.
A memory reference using BC as a base register, with an optional offset.
A memory reference using AX, BC, DE, or HL for the address, for calls.
A memory reference using any 16-bit register pair for the address, for calls.
A memory reference using DE as a base register, with an optional offset.
A memory reference using DE as a base register, without any offset.
Any memory reference to an address in the far address space.
A memory reference using HL as a base register, with an optional one-byte offset.
A memory reference using HL as a base register, with B or C as the index register.
A memory reference using HL as a base register, without any offset.
A memory reference using SP as a base register, with an optional one-byte offset.
Any memory reference to an address in the near address space.
The AX register.
The BC register.
The DE register.
A through L registers.
The SP register.
The HL register.
The 16-bit R8 register.
The 16-bit R10 register.
The registers reserved for interrupts (R24 to R31).
The A register.
The B register.
The C register.
The D register.
The E register.
The H register.
The L register.
The virtual registers.
The PSW register.
The X register.
RXconfig/rx/constraints.md
An address which does not involve register indirect addressing or pre/post increment/decrement addressing.
A symbol reference.
A constant in the range 256 to 255, inclusive.
A constant in the range 128 to 127, inclusive.
A constant in the range 32768 to 32767, inclusive.
A constant in the range 8388608 to 8388607, inclusive.
A constant in the range 0 to 15, inclusive.
S/390 and zSeriesconfig/s390/s390.h
Address register (general purpose register except r0)
Condition code register
Data register (arbitrary general purpose register)
Floating-point register
Unsigned 8-bit constant (0255)
Unsigned 12-bit constant (04095)
Signed 16-bit constant (3276832767)
Value appropriate as displacement.
for short displacement
for long displacement
Constant integer with a value of 0x7fffffff.
Multiple letter constraint followed by 4 parameter letters.
number of the part counting from most to least significant
mode of the part
mode of the containing operand
value of the other parts (Fall bits set)
The constraint matches if the specified part of a constant has a value different from its other parts.
Memory reference without index register and with short displacement.
Memory reference with index register and short displacement.
Memory reference without index register but with long displacement.
Memory reference with index register and long displacement.
Pointer with short displacement.
Pointer with long displacement.
Shift count operand.
SPARCconfig/sparc/sparc.h
Floating-point register on the SPARC-V8 architecture and lower floating-point register on the SPARC-V9 architecture.
Floating-point register. It is equivalent to f on the SPARC-V8 architecture and contains both lower and upper floating-point registers on the SPARC-V9 architecture.
Floating-point condition code register.
Lower floating-point register. It is only valid on the SPARC-V9 architecture when the Visual Instruction Set is available.
Floating-point register. It is only valid on the SPARC-V9 architecture when the Visual Instruction Set is available.
64-bit global or out register for the SPARC-V8+ architecture.
The constant all-ones, for floating-point.
Signed 5-bit constant
A vector constant
Signed 13-bit constant
Zero
32-bit constant with the low 12 bits clear (a constant that can be loaded with the sethi instruction)
A constant in the range supported by movcc instructions (11-bit signed immediate)
A constant in the range supported by movrcc instructions (10-bit signed immediate)
Same as K, except that it verifies that bits that are not in the lower 32-bit range are all zero. Must be used instead of K for modes wider than SImode
The constant 4096
Floating-point zero
Signed 13-bit constant, sign-extended to 32 or 64 bits
The constant -1
Floating-point constant whose integral representation can be moved into an integer register using a single sethi instruction
Floating-point constant whose integral representation can be moved into an integer register using a single mov instruction
Floating-point constant whose integral representation can be moved into an integer register using a high/lo_sum instruction sequence
Memory address aligned to an 8-byte boundary
Even register
Memory address for e constraint registers
Memory address with only a base register
Vector zero
SPUconfig/spu/spu.h
An immediate which can be loaded with the il/ila/ilh/ilhu instructions. const_int is treated as a 64 bit value.
An immediate for and/xor/or instructions. const_int is treated as a 64 bit value.
An immediate for the iohl instruction. const_int is treated as a 64 bit value.
An immediate which can be loaded with fsmbi.
An immediate which can be loaded with the il/ila/ilh/ilhu instructions. const_int is treated as a 32 bit value.
An immediate for most arithmetic instructions. const_int is treated as a 32 bit value.
An immediate for and/xor/or instructions. const_int is treated as a 32 bit value.
An immediate for the iohl instruction. const_int is treated as a 32 bit value.
A constant in the range [64, 63] for shift/rotate instructions.
An unsigned 7-bit constant for conversion/nop/channel instructions.
A signed 10-bit constant for most arithmetic instructions.
A signed 16 bit immediate for stop.
An unsigned 16-bit constant for iohl and fsmbi.
An unsigned 7-bit constant whose 3 least significant bits are 0.
An unsigned 3-bit constant for 16-byte rotates and shifts
Call operand, reg, for indirect calls
Call operand, symbol, for relative calls.
Call operand, const_int, for absolute calls.
An immediate which can be loaded with the il/ila/ilh/ilhu instructions. const_int is sign extended to 128 bit.
An immediate for shift and rotate instructions. const_int is treated as a 32 bit value.
An immediate for and/xor/or instructions. const_int is sign extended as a 128 bit.
An immediate for the iohl instruction. const_int is sign extended to 128 bit.
TI C6X familyconfig/c6x/constraints.md
Register file A (A0A31).
Register file B (B0B31).
Predicate registers in register file A (A0A2 on C64X and higher, A1 and A2 otherwise).
Predicate registers in register file B (B0B2).
A call-used register in register file B (B0B9, B16B31).
Register file A, excluding predicate registers (A3A31, plus A0 if not C64X or higher).
Register file B, excluding predicate registers (B3B31).
Integer constant in the range 0 ... 15.
Integer constant in the range 0 ... 31.
Integer constant in the range 31 ... 0.
Integer constant in the range 16 ... 15.
Integer constant that can be the operand of an ADDA or a SUBA insn.
Integer constant in the range 0 ... 65535.
Integer constant in the range 32768 ... 32767.
Integer constant in the range -2^{20} ... 2^{20} - 1.
Integer constant that is a valid mask for the clr instruction.
Integer constant that is a valid mask for the set instruction.
Memory location with A base register.
Memory location with B base register.
Register B14 (aka DP).
TILE-Gxconfig/tilegx/constraints.md
Each of these represents a register constraint for an individual register, from r0 to r10.
Signed 8-bit integer constant.
Signed 16-bit integer constant.
Unsigned 16-bit integer constant.
Integer constant that fits in one signed byte when incremented by one (129 ... 126).
Memory operand. If used together with < or >, the operand can have postincrement which requires printing with %In and %in on TILE-Gx. For example:
asm ("st_add %I0,%1,%i0" : "=m<>" (*mem) : "r" (val));
A bit mask suitable for the BFINS instruction.
Integer constant that is a byte tiled out eight times.
The integer zero constant.
Integer constant that is a sign-extended byte tiled out as four shorts.
Integer constant that fits in one signed byte when incremented (129 ... 126), but excluding -1.
Integer constant that has all 1 bits consecutive and starting at bit 0.
A 16-bit fragment of a got, tls, or pc-relative reference.
Memory operand except postincrement. This is roughly the same as m when not used together with < or >.
An 8-element vector constant with identical elements.
A 4-element vector constant with identical elements.
The integer constant 0xffffffff.
The integer constant 0xffffffff00000000.
TILEProconfig/tilepro/constraints.md
Each of these represents a register constraint for an individual register, from r0 to r10.
Signed 8-bit integer constant.
Signed 16-bit integer constant.
Nonzero integer constant with low 16 bits zero.
Integer constant that fits in one signed byte when incremented by one (129 ... 126).
Memory operand. If used together with < or >, the operand can have postincrement which requires printing with %In and %in on TILEPro. For example:
asm ("swadd %I0,%1,%i0" : "=m<>" (mem) : "r" (val));
A bit mask suitable for the MM instruction.
Integer constant that is a byte tiled out four times.
The integer zero constant.
Integer constant that is a sign-extended byte tiled out as two shorts.
Integer constant that fits in one signed byte when incremented (129 ... 126), but excluding -1.
A symbolic operand, or a 16-bit fragment of a got, tls, or pc-relative reference.
Memory operand except postincrement. This is roughly the same as m when not used together with < or >.
A 4-element vector constant with identical elements.
A 2-element vector constant with identical elements.
Visiumconfig/visium/constraints.md
EAM register mdb
EAM register mdc
Floating point register
General register, but not r29, r30 and r31
Register r1
Register r2
Register r3
Floating-point constant 0.0
Integer constant in the range 0 .. 65535 (16-bit immediate)
Integer constant in the range 1 .. 31 (5-bit immediate)
Integer constant in the range 65535 .. 1 (16-bit negative immediate)
Integer constant 1
Integer constant 0
Integer constant 32
x86 familyconfig/i386/constraints.md
Legacy registerthe eight integer registers available on all i386 processors (a, b, c, d, si, di, bp, sp).
Any register accessible as ``r``l. In 32-bit mode, a, b, c, and d; in 64-bit mode, any integer register.
Any register accessible as ``r``h: a, b, c, and d.
The a register.
The b register.
The c register.
The d register.
The si register.
The di register.
The a and d registers. This class is used for instructions that return double word results in the ax:dx register pair. Single word values will be allocated either in ax or dx. For example on i386 the following implements rdtsc:
unsigned long long rdtsc (void)
{
unsigned long long tick;
__asm__ __volatile__("rdtsc":"=A"(tick));
return tick;
}
This is not correct on x86-64 as it would allocate tick in either ax or dx. You have to use the following variant instead:
unsigned long long rdtsc (void)
{
unsigned int tickl, tickh;
__asm__ __volatile__("rdtsc":"=a"(tickl),"=d"(tickh));
return ((unsigned long long)tickh << 32)|tickl;
}
Any 80387 floating-point (stack) register.
Top of 80387 floating-point stack (%st(0)).
Second from top of 80387 floating-point stack (%st(1)).
Any MMX register.
Any SSE register.
First SSE register (%xmm0).
Integer constant in the range 0 ... 31, for 32-bit shifts.
Integer constant in the range 0 ... 63, for 64-bit shifts.
Signed 8-bit integer constant.
0xFF or 0xFFFF, for andsi as a zero-extending move.
0, 1, 2, or 3 (shifts for the lea instruction).
Unsigned 8-bit integer constant (for in and out instructions).
Standard 80387 floating point constant.
Standard SSE floating point constant.
32-bit signed integer constant, or a symbolic reference known to fit that range (for immediate operands in sign-extending x86-64 instructions).
32-bit unsigned integer constant, or a symbolic reference known to fit that range (for immediate operands in zero-extending x86-64 instructions).
Xstormy16config/stormy16/stormy16.h
Register r0.
Register r1.
Register r2.
Register r8.
Registers r0 through r7.
Registers r0 and r1.
The carry register.
Registers r8 and r9.
A constant between 0 and 3 inclusive.
A constant that has exactly one bit set.
A constant that has exactly one bit clear.
A constant between 0 and 255 inclusive.
A constant between 255 and 0 inclusive.
A constant between 3 and 0 inclusive.
A constant between 1 and 4 inclusive.
A constant between 4 and 1 inclusive.
A memory reference that is a stack push.
A memory reference that is a stack pop.
A memory reference that refers to a constant address of known value.
The register indicated by Rx (not implemented yet).
A constant that is not between 2 and 15 inclusive.
The constant 0.
Xtensaconfig/xtensa/constraints.md
General-purpose 32-bit register
One-bit boolean register
MAC16 40-bit accumulator register
Signed 12-bit integer constant, for use in MOVI instructions
Signed 8-bit integer constant, for use in ADDI instructions
Integer constant valid for BccI instructions
Unsigned constant valid for BccUI instructions
:: _asm-labels:
You can specify the name to be used in the assembler code for a C function or variable by writing the asm (or __asm__) keyword after the declarator as follows:
int foo asm ("myfoo") = 2;
This specifies that the name to be used for the variable foo in the assembler code should be myfoo rather than the usual _foo.
On systems where an underscore is normally prepended to the name of a C function or variable, this feature allows you to define names for the linker that do not start with an underscore.
It does not make sense to use this feature with a non-static local variable since such variables do not have assembler names. If you are trying to put the variable in a particular register, see Explicit Reg Vars. GCC presently accepts such code with a warning, but will probably be changed to issue an error, rather than a warning, in the future.
You cannot use asm in this way in a function definition; but you can get the same effect by writing a declaration for the function before its definition and putting asm there, like this:
extern func () asm ("FUNC");
func (x, y)
int x, y;
/* ... */
It is up to you to make sure that the assembler names you choose do not conflict with any other assembler symbols. Also, you must not use a register name; that would produce completely invalid assembler code. GCC does not as yet have the ability to store static variables in registers. Perhaps that will be added.
:: _explicit-reg-vars:
GNU C allows you to put a few global variables into specified hardware registers. You can also specify the register in which an ordinary register variable should be allocated.
Global register variables reserve registers throughout the program. This may be useful in programs such as programming language interpreters that have a couple of global variables that are accessed very often.
Local register variables in specific registers do not reserve the registers, except at the point where they are used as input or output operands in an asm statement and the asm statement itself is not deleted. The compilers data flow analysis is capable of determining where the specified registers contain live values, and where they are available for other uses. Stores into local register variables may be deleted when they appear to be dead according to dataflow analysis. References to local register variables may be deleted or moved or simplified.
These local variables are sometimes convenient for use with the extended asm feature (Extended Asm), if you want to write one output of the assembler instruction directly into a particular register. (This works provided the register you specify fits the constraints specified for that operand in the asm.)
:: _global-reg-vars:
You can define a global register variable in GNU C like this:
register int *foo asm ("a5");
Here a5 is the name of the register that should be used. Choose a register that is normally saved and restored by function calls on your machine, so that library routines will not clobber it.
Naturally the register name is CPU-dependent, so you need to conditionalize your program according to CPU type. The register a5 is a good choice on a 68000 for a variable of pointer type. On machines with register windows, be sure to choose a global register that is not affected magically by the function call mechanism.
In addition, different operating systems on the same CPU may differ in how they name the registers; then you need additional conditionals. For example, some 68000 operating systems call this register %a5.
Eventually there may be a way of asking the compiler to choose a register automatically, but first we need to figure out how it should choose and how to enable you to guide the choice. No solution is evident.
Defining a global register variable in a certain register reserves that register entirely for this use, at least within the current compilation. The register is not allocated for any other purpose in the functions in the current compilation, and is not saved and restored by these functions. Stores into this register are never deleted even if they appear to be dead, but references may be deleted or moved or simplified.
It is not safe to access the global register variables from signal handlers, or from more than one thread of control, because the system library routines may temporarily use the register for other things (unless you recompile them specially for the task at hand).
qsort, and global register variables It is not safe for one function that uses a global register variable to call another such function foo by way of a third function lose that is compiled without knowledge of this variable (i.e. in a different source file in which the variable isnt declared). This is because lose might save the register and put some other value there. For example, you cant expect a global register variable to be available in the comparison-function that you pass to qsort, since qsort might have put something else in that register. (If you are prepared to recompile qsort with the same global register variable, you can solve this problem.)
If you want to recompile qsort or other source files that do not actually use your global register variable, so that they do not use that register for any other purpose, then it suffices to specify the compiler option -ffixed-``reg``. You need not actually add a global register declaration to their source code.
A function that can alter the value of a global register variable cannot safely be called from a function compiled without this variable, because it could clobber the value the caller expects to find there on return. Therefore, the function that is the entry point into the part of the program that uses the global register variable must explicitly save and restore the value that belongs to its caller.
register variable after longjmp global register after longjmp value after longjmp
On most machines, longjmp restores to each global register variable the value it had at the time of the setjmp. On some machines, however, longjmp does not change the value of global register variables. To be portable, the function that called setjmp should make other arrangements to save the values of the global register variables, and to restore them in a longjmp. This way, the same thing happens regardless of what longjmp does.
All global register variable declarations must precede all function definitions. If such a declaration could appear after function definitions, the declaration would be too late to prevent the register from being used for other purposes in the preceding functions.
Global register variables may not have initial values, because an executable file has no means to supply initial contents for a register.
On the SPARC, there are reports that g3 ... g7 are suitable registers, but certain library functions, such as getwd, as well as the subroutines for division and remainder, modify g3 and g4. g1 and g2 are local temporaries.
On the 68000, a2 ... a5 should be suitable, as should d2 ... d7. Of course, it does not do to use more than a few of those.
:: _local-reg-vars:
You can define a local register variable with a specified register like this:
register int *foo asm ("a5");
Here a5 is the name of the register that should be used. Note that this is the same syntax used for defining global register variables, but for a local variable it appears within a function.
Naturally the register name is CPU-dependent, but this is not a problem, since specific registers are most often useful with explicit assembler instructions (Extended Asm). Both of these things generally require that you conditionalize your program according to CPU type.
In addition, operating systems on one type of CPU may differ in how they name the registers; then you need additional conditionals. For example, some 68000 operating systems call this register %a5.
Defining such a register variable does not reserve the register; it remains available for other uses in places where flow control determines the variables value is not live.
This option does not guarantee that GCC generates code that has this variable in the register you specify at all times. You may not code an explicit reference to this register in the assembler instruction template part of an asm statement and assume it always refers to this variable. However, using the variable as an input or output operand to the asm guarantees that the specified register is used for that operand. Extended Asm, for more information.
Stores into local register variables may be deleted when they appear to be dead according to dataflow analysis. References to local register variables may be deleted or moved or simplified.
As with global register variables, it is recommended that you choose a register that is normally saved and restored by function calls on your machine, so that library routines will not clobber it.
Sometimes when writing inline asm code, you need to make an operand be a specific register, but theres no matching constraint letter for that register. To force the operand into that register, create a local variable and specify the register in the variables declaration. Then use the local variable for the asm operand and specify any constraint letter that matches the register:
register int *p1 asm ("r0") = ...;
register int *p2 asm ("r1") = ...;
register int *result asm ("r0");
asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));
Warning: In the above example, be aware that a register (for example r0) can be call-clobbered by subsequent code, including function calls and library calls for arithmetic operators on other variables (for example the initialization of p2). In this case, use temporary variables for expressions between the register assignments:
int t1 = ...;
register int *p1 asm ("r0") = ...;
register int *p2 asm ("r1") = t1;
register int *result asm ("r0");
asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));
:: _size-of-an-asm:
Size of an asm
Some targets require that GCC track the size of each instruction used in order to generate correct code. Because the final length of the code produced by an asm statement is only known by the assembler, GCC must make an estimate as to how big it will be. It does this by counting the number of instructions in the pattern of the asm and multiplying that by the length of the longest instruction supported by that processor. (When working out the number of instructions, it assumes that any occurrence of a newline or of whatever statement separator character is supported by the assembler typically ; indicates the end of an instruction.)
Normally, GCCs estimate is adequate to ensure that correct code is generated, but it is possible to confuse the compiler if you use pseudo instructions or assembler macros that expand into multiple real instructions, or if you use assembler directives that expand to more space in the object file than is needed for a single instruction. If this happens then the assembler may produce a diagnostic saying that a label is unreachable.
:: _alternate-keywords:
-ansi and the various -std options disable certain keywords. This causes trouble when you want to use GNU C extensions, or a general-purpose header file that should be usable by all programs, including ISO C programs. The keywords asm, typeof and inline are not available in programs compiled with -ansi or -std (although inline can be used in a program compiled with -std=c99 or -std=c11). The ISO C99 keyword restrict is only available when -std=gnu99 (which will eventually be the default) or -std=c99 (or the equivalent -std=iso9899:1999), or an option for a later standard version, is used.
The way to solve these problems is to put __ at the beginning and end of each problematical keyword. For example, use __asm__ instead of asm, and __inline__ instead of inline.
Other C compilers wont accept these alternative keywords; if you want to compile with another compiler, you can define the alternate keywords as macros to replace them with the customary keywords. It looks like this:
#ifndef __GNUC__
#define __asm__ asm
#endif
-pedantic and other options cause warnings for many GNU C extensions. You can prevent such warnings within one expression by writing __extension__ before the expression. __extension__ has no effect aside from this.
:: _incomplete-enums:
Incomplete enum Types
You can define an enum tag without specifying its possible values. This results in an incomplete type, much like what you get if you write struct foo without describing the elements. A later declaration that does specify the possible values completes the type.
You cant allocate variables or storage using the type while it is incomplete. However, you can work with pointers to that type.
This extension may not be very useful, but it makes the handling of enum more consistent with the way struct and union are handled.
This extension is not supported by GNU C++.
:: _function-names:
__func__ identifier __FUNCTION__ identifier __PRETTY_FUNCTION__ identifier
GCC provides three magic variables that hold the name of the current function, as a string. The first of these is __func__, which is part of the C99 standard:
The identifier __func__ is implicitly declared by the translator as if, immediately following the opening brace of each function definition, the declaration
static const char __func__[] = "function-name";
appeared, where function-name is the name of the lexically-enclosing function. This name is the unadorned name of the function.
__FUNCTION__ is another name for __func__, provided for backward compatibility with old versions of GCC.
In C, __PRETTY_FUNCTION__ is yet another name for __func__. However, in C++, __PRETTY_FUNCTION__ contains the type signature of the function as well as its bare name. For example, this program:
extern "C" {
extern int printf (char *, ...);
}
class a {
public:
void sub (int i)
{
printf ("__FUNCTION__ = %s\n", __FUNCTION__);
printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__);
}
};
int
main (void)
{
a ax;
ax.sub (0);
return 0;
}
gives this output:
__FUNCTION__ = sub
__PRETTY_FUNCTION__ = void a::sub(int)
These identifiers are variables, not preprocessor macros, and may not be used to initialize char arrays or be concatenated with other string literals.
:: _return-address:
These functions may be used to get information about the callers of a function.
This function returns the return address of the current function, or of one of its callers. The level argument is number of frames to scan up the call stack. A value of 0 yields the return address of the current function, a value of 1 yields the return address of the caller of the current function, and so forth. When inlining the expected behavior is that the function returns the address of the function that is returned to. To work around this behavior use the noinline function attribute.
The level argument must be a constant integer.
On some machines it may be impossible to determine the return address of any function other than the current one; in such cases, or when the top of the stack has been reached, this function returns 0 or a random value. In addition, __builtin_frame_address may be used to determine if the top of the stack has been reached.
Additional post-processing of the returned value may be needed, see __builtin_extract_return_addr.
This function should only be used with a nonzero argument for debugging purposes.
The address as returned by __builtin_return_address may have to be fed through this function to get the actual encoded address. For example, on the 31-bit S/390 platform the highest bit has to be masked out, or on SPARC platforms an offset has to be added for the true next instruction to be executed.
If no fixup is needed, this function simply passes through addr.
This function does the reverse of __builtin_extract_return_addr.
This function is similar to __builtin_return_address, but it returns the address of the function frame rather than the return address of the function. Calling __builtin_frame_address with a value of 0 yields the frame address of the current function, a value of 1 yields the frame address of the caller of the current function, and so forth.
The frame is the area on the stack that holds local variables and saved registers. The frame address is normally the address of the first word pushed on to the stack by the function. However, the exact definition depends upon the processor and the calling convention. If the processor has a dedicated frame pointer register, and the function has a frame, then __builtin_frame_address returns the value of the frame pointer register.
On some machines it may be impossible to determine the frame address of any function other than the current one; in such cases, or when the top of the stack has been reached, this function returns 0 if the first frame pointer is properly initialized by the startup code.
This function should only be used with a nonzero argument for debugging purposes.
:: _vector-extensions:
On some targets, the instruction set contains SIMD vector instructions which operate on multiple values contained in one large register at the same time. For example, on the x86 the MMX, 3DNow! and SSE extensions can be used this way.
The first step in using these extensions is to provide the necessary data types. This should be done using an appropriate typedef:
typedef int v4si __attribute__ ((vector_size (16)));
The int type specifies the base type, while the attribute specifies the vector size for the variable, measured in bytes. For example, the declaration above causes the compiler to set the mode for the v4si type to be 16 bytes wide and divided into int sized units. For a 32-bit int this means a vector of 4 units of 4 bytes, and the corresponding mode of foo is V4SI.
The vector_size attribute is only applicable to integral and float scalars, although arrays, pointers, and function return values are allowed in conjunction with this construct. Only sizes that are a power of two are currently allowed.
All the basic integer types can be used as base types, both as signed and as unsigned: char, short, int, long, long long. In addition, float and double can be used to build floating-point vector types.
Specifying a combination that is not valid for the current architecture causes GCC to synthesize the instructions using a narrower mode. For example, if you specify a variable of type V4SI and your architecture does not allow for this specific SIMD type, GCC produces code that uses 4 SIs.
The types defined in this manner can be used with a subset of normal C operations. Currently, GCC allows using the following operators on these types: +, -, *, /, unary minus, ^, |, &, ~, %
The operations behave like C++ valarrays. Addition is defined as the addition of the corresponding elements of the operands. For example, in the code below, each of the 4 elements in a is added to the corresponding 4 elements in b and the resulting vector is stored in c.
typedef int v4si __attribute__ ((vector_size (16)));
v4si a, b, c;
c = a + b;
Subtraction, multiplication, division, and the logical operations operate in a similar manner. Likewise, the result of using the unary minus or complement operators on a vector type is a vector whose elements are the negative or complemented values of the corresponding elements in the operand.
It is possible to use shifting operators <<, >> on integer-type vectors. The operation is defined as following: {a0, a1, ..., an} >> {b0, b1, ..., bn} == {a0 >> b0, a1 >> b1, ..., an >> bn} Vector operands must have the same number of elements.
For convenience, it is allowed to use a binary vector operation where one operand is a scalar. In that case the compiler transforms the scalar operand into a vector where each element is the scalar from the operation. The transformation happens only if the scalar could be safely converted to the vector-element type. Consider the following code.
typedef int v4si __attribute__ ((vector_size (16)));
v4si a, b, c;
long l;
a = b + 1; /* a = b + {1,1,1,1}; */
a = 2 * b; /* a = {2,2,2,2} * b; */
a = l + a; /* Error, cannot convert long to int. */
Vectors can be subscripted as if the vector were an array with the same number of elements and base type. Out of bound accesses invoke undefined behavior at run time. Warnings for out of bound accesses for vector subscription can be enabled with -Warray-bounds.
Vector comparison is supported with standard comparison operators: ==, !=, <, <=, >, >=. Comparison operands can be vector expressions of integer-type or real-type. Comparison between integer-type vectors and real-type vectors are not supported. The result of the comparison is a vector of the same width and number of elements as the comparison operands with a signed integral element type.
Vectors are compared element-wise producing 0 when comparison is false and -1 (constant of the appropriate type where all bits are set) otherwise. Consider the following example.
typedef int v4si __attribute__ ((vector_size (16)));
v4si a = {1,2,3,4};
v4si b = {3,2,1,4};
v4si c;
c = a > b; /* The result would be {0, 0,-1, 0} */
c = a == b; /* The result would be {0,-1, 0,-1} */
In C++, the ternary operator ?: is available. a?b:c, where b and c are vectors of the same type and a is an integer vector with the same number of elements of the same size as b and c, computes all three arguments and creates a vector {a[0]?b[0]:c[0], a[1]?b[1]:c[1], ...}. Note that unlike in OpenCL, a is thus interpreted as a != 0 and not a < 0. As in the case of binary operations, this syntax is also accepted when one of b or c is a scalar that is then transformed into a vector. If both b and c are scalars and the type of true?b:c has the same size as the element type of a, then b and c are converted to a vector type whose elements have this type and with the same number of elements as a.
In C++, the logic operators !, &&, || are available for vectors. !v is equivalent to v == 0, a && b is equivalent to a!=0 & b!=0 and a || b is equivalent to a!=0 | b!=0. For mixed operations between a scalar s and a vector v, s && v is equivalent to s?v!=0:0 (the evaluation is short-circuit) and v && s is equivalent to v!=0 & (s?-1:0).
Vector shuffling is available using functions __builtin_shuffle (vec, mask) and __builtin_shuffle (vec0, vec1, mask). Both functions construct a permutation of elements from one or two vectors and return a vector of the same type as the input vector(s). The mask is an integral vector with the same width (W) and element count (N) as the output vector.
The elements of the input vectors are numbered in memory ordering of vec0 beginning at 0 and vec1 beginning at N. The elements of mask are considered modulo N in the single-operand case and modulo 2*``N`` in the two-operand case.
Consider the following example,
typedef int v4si __attribute__ ((vector_size (16)));
v4si a = {1,2,3,4};
v4si b = {5,6,7,8};
v4si mask1 = {0,1,1,3};
v4si mask2 = {0,4,2,5};
v4si res;
res = __builtin_shuffle (a, mask1); /* res is {1,2,2,4} */
res = __builtin_shuffle (a, b, mask2); /* res is {1,5,3,6} */
Note that __builtin_shuffle is intentionally semantically compatible with the OpenCL shuffle and shuffle2 functions.
You can declare variables and use them in function calls and returns, as well as in assignments and some casts. You can specify a vector type as a return type for a function. Vector types can also be used as function arguments. It is possible to cast from one vector type to another, provided they are of the same size (in fact, you can also cast vectors to and from other datatypes of the same size).
You cannot operate between vectors of different lengths or different signedness without a cast.
:: _offsetof:
Support for offsetof
GCC implements for both C and C++ a syntactic extension to implement the offsetof macro.
primary:
"__builtin_offsetof" "(" ``typename`` "," offsetof_member_designator ")"
offsetof_member_designator:
``identifier``
| offsetof_member_designator "." ``identifier``
| offsetof_member_designator "[" ``expr`` "]"
This extension is sufficient such that
#define offsetof(``type``, ``member``) __builtin_offsetof (``type``, ``member``)
is a suitable definition of the offsetof macro. In C++, type may be dependent. In either case, member may consist of a single identifier, or a sequence of member accesses and array references.
:: ___sync-builtins:
Legacy __sync Built-in Functions for Atomic Memory Access
The following built-in functions are intended to be compatible with those described in the Intel Itanium Processor-specific Application Binary Interface, section 7.4. As such, they depart from normal GCC practice by not using the __builtin_ prefix and also by being overloaded so that they work on multiple types.
The definition given in the Intel documentation allows only for the use of the types int, long, long long or their unsigned counterparts. GCC allows any integral scalar or pointer type that is 1, 2, 4 or 8 bytes in length.
These functions are implemented in terms of the __atomic builtins (__atomic Builtins). They should not be used for new code which should use the __atomic builtins instead.
Not all operations are supported by all target processors. If a particular operation cannot be implemented on the target processor, a warning is generated and a call to an external function is generated. The external function carries the same name as the built-in version, with an additional suffix `n` where n is the size of the data type.
In most cases, these built-in functions are considered a full barrier. That is, no memory operand is moved across the operation, either forward or backward. Further, instructions are issued as necessary to prevent the processor from speculating loads across the operation and from queuing stores after the operation.
All of the routines are described in the Intel documentation to take an optional list of variables protected by the memory barrier. Its not clear what is meant by that; it could mean that only the listed variables are protected, or it could mean a list of additional variables to be protected. The list is ignored by GCC which treats it as empty. GCC interprets an empty list as meaning that all globally accessible variables should be protected.
type __sync_fetch_and_add (type *ptr, type value, ...) type __sync_fetch_and_sub (type *ptr, type value, ...) type __sync_fetch_and_or (type *ptr, type value, ...) type __sync_fetch_and_and (type *ptr, type value, ...) type __sync_fetch_and_xor (type *ptr, type value, ...) type __sync_fetch_and_nand (type *ptr, type value, ...)
These built-in functions perform the operation suggested by the name, and returns the value that had previously been in memory. That is,
{ tmp = *ptr; *ptr ``op``= value; return tmp; }
{ tmp = *ptr; *ptr = ~(tmp & value); return tmp; } // nand
Note: GCC 4.4 and later implement __sync_fetch_and_nand as *ptr = ~(tmp & value) instead of *ptr = ~tmp & value.
type __sync_add_and_fetch (type *ptr, type value, ...) type __sync_sub_and_fetch (type *ptr, type value, ...) type __sync_or_and_fetch (type *ptr, type value, ...) type __sync_and_and_fetch (type *ptr, type value, ...) type __sync_xor_and_fetch (type *ptr, type value, ...) type __sync_nand_and_fetch (type *ptr, type value, ...)
These built-in functions perform the operation suggested by the name, and return the new value. That is,
{ *ptr ``op``= value; return *ptr; }
{ *ptr = ~(*ptr & value); return *ptr; } // nand
Note: GCC 4.4 and later implement __sync_nand_and_fetch as *ptr = ~(*ptr & value) instead of *ptr = ~*ptr & value.
bool __sync_bool_compare_and_swap (type *ptr, type oldval, type newval, ...) type __sync_val_compare_and_swap (type *ptr, type oldval, type newval, ...)
These built-in functions perform an atomic compare and swap. That is, if the current value of *``ptr`` is oldval, then write newval into *``ptr``.
The bool version returns true if the comparison is successful and newval is written. The val version returns the contents of *``ptr`` before the operation.
This built-in function issues a full memory barrier.
type __sync_lock_test_and_set (type *ptr, type value, ...)
This built-in function, as described by Intel, is not a traditional test-and-set operation, but rather an atomic exchange operation. It writes value into *``ptr``, and returns the previous contents of *``ptr``.
Many targets have only minimal support for such locks, and do not support a full exchange operation. In this case, a target may support reduced functionality here by which the only valid value to store is the immediate constant 1. The exact value actually stored in *``ptr`` is implementation defined.
This built-in function is not a full barrier, but rather an acquire barrier. This means that references after the operation cannot move to (or be speculated to) before the operation, but previous memory stores may not be globally visible yet, and previous memory loads may not yet be satisfied.
void __sync_lock_release (type *ptr, ...)
This built-in function releases the lock acquired by __sync_lock_test_and_set. Normally this means writing the constant 0 to *``ptr``.
This built-in function is not a full barrier, but rather a release barrier. This means that all previous memory stores are globally visible, and all previous memory loads have been satisfied, but following memory reads are not prevented from being speculated to before the barrier.
:: ___atomic-builtins:
The following built-in functions approximately match the requirements for C++11 concurrency and memory models. They are all identified by being prefixed with __atomic and most are overloaded so that they work with multiple types.
These functions are intended to replace the legacy __sync builtins. The main difference is that the memory model to be used is a parameter to the functions. New code should always use the __atomic builtins rather than the __sync builtins.
Note that the __atomic builtins assume that programs will conform to the C++11 model for concurrency. In particular, they assume that programs are free of data races. See the C++11 standard for detailed definitions.
The __atomic builtins can be used with any integral scalar or pointer type that is 1, 2, 4, or 8 bytes in length. 16-byte integral types are also allowed if __int128 (__int128) is supported by the architecture.
The four non-arithmetic functions (load, store, exchange, and compare_exchange) all have a generic version as well. This generic version works on any data type. If the data type size maps to one of the integral sizes that may have lock free support, the generic version uses the lock free built-in function. Otherwise an external call is left to be resolved at run time. This external call is the same format with the addition of a size_t parameter inserted as the first parameter indicating the size of the object being pointed to. All objects must be the same size.
There are 6 different memory models that can be specified. These map to the C++11 memory models with the same names, see the C++11 standard or the http://gcc.gnu.org/wiki/Atomic/GCCMM/AtomicSyncGCC wiki on atomic synchronization for detailed definitions. Individual targets may also support additional memory models for use on specific architectures. Refer to the target documentation for details of these.
The memory models integrate both barriers to code motion as well as synchronization requirements with other threads. They are listed here in approximately ascending order of strength.
No barriers or synchronization.
Data dependency only for both barrier and synchronization with another thread.
Barrier to hoisting of code and synchronizes with release (or stronger) semantic stores from another thread.
Barrier to sinking of code and synchronizes with acquire (or stronger) semantic loads from another thread.
Barrier in both directions and synchronizes with acquire loads and release stores in another thread.
Barrier in both directions and synchronizes with acquire loads and release stores in all threads.
Note that the scope of a C++11 memory model depends on whether or not the function being called is a fence (such as __atomic_thread_fence). In a fence, all memory accesses are subject to the restrictions of the memory model. When the function is an operation on a location, the restrictions apply only to those memory accesses that could affect or that could depend on the location.
Target architectures are encouraged to provide their own patterns for each of these built-in functions. If no target is provided, the original non-memory model set of __sync atomic built-in functions are used, along with any required synchronization fences surrounding it in order to achieve the proper behavior. Execution in this case is subject to the same restrictions as those built-in functions.
If there is no pattern or mechanism to provide a lock free instruction sequence, a call is made to an external routine with the same parameters to be resolved at run time.
When implementing patterns for these built-in functions, the memory model parameter can be ignored as long as the pattern implements the most restrictive __ATOMIC_SEQ_CST model. Any of the other memory models execute correctly with this memory model but they may not execute as efficiently as they could with a more appropriate implementation of the relaxed requirements.
Note that the C++11 standard allows for the memory model parameter to be determined at run time rather than at compile time. These built-in functions map any run-time value to __ATOMIC_SEQ_CST rather than invoke a runtime library call or inline a switch statement. This is standard compliant, safe, and the simplest approach for now.
The memory model parameter is a signed int, but only the lower 16 bits are reserved for the memory model. The remainder of the signed int is reserved for target use and should be 0. Use of the predefined atomic values ensures proper usage.
This built-in function implements an atomic load operation. It returns the contents of *``ptr``.
The valid memory model variants are __ATOMIC_RELAXED, __ATOMIC_SEQ_CST, __ATOMIC_ACQUIRE, and __ATOMIC_CONSUME.
This is the generic version of an atomic load. It returns the contents of *``ptr`` in *``ret``.
This built-in function implements an atomic store operation. It writes ``val`` into *``ptr``.
The valid memory model variants are __ATOMIC_RELAXED, __ATOMIC_SEQ_CST, and __ATOMIC_RELEASE.
This is the generic version of an atomic store. It stores the value of *``val`` into *``ptr``.
This built-in function implements an atomic exchange operation. It writes val into *``ptr``, and returns the previous contents of *``ptr``.
The valid memory model variants are __ATOMIC_RELAXED, __ATOMIC_SEQ_CST, __ATOMIC_ACQUIRE, __ATOMIC_RELEASE, and __ATOMIC_ACQ_REL.
This is the generic version of an atomic exchange. It stores the contents of *``val`` into *``ptr``. The original value of *``ptr`` is copied into *``ret``.
This built-in function implements an atomic compare and exchange operation. This compares the contents of *``ptr`` with the contents of *``expected``. If equal, the operation is a read-modify-write which writes desired into *``ptr``. If they are not equal, the operation is a read and the current contents of *``ptr`` is written into *``expected``. weak is true for weak compare_exchange, and false for the strong variation. Many targets only offer the strong variation and ignore the parameter. When in doubt, use the strong variation.
True is returned if desired is written into *``ptr`` and the operation is considered to conform to the memory model specified by success_memmodel. There are no restrictions on what memory model can be used here.
False is returned otherwise, and the operation is considered to conform to failure_memmodel. This memory model cannot be __ATOMIC_RELEASE nor __ATOMIC_ACQ_REL. It also cannot be a stronger model than that specified by success_memmodel.
This built-in function implements the generic version of __atomic_compare_exchange. The function is virtually identical to __atomic_compare_exchange_n, except the desired value is also a pointer.
These built-in functions perform the operation suggested by the name, and return the result of the operation. That is,
{ *ptr ``op``= val; return *ptr; }
All memory models are valid.
These built-in functions perform the operation suggested by the name, and return the value that had previously been in *``ptr``. That is,
{ tmp = *ptr; *ptr ``op``= val; return tmp; }
All memory models are valid.
This built-in function performs an atomic test-and-set operation on the byte at *``ptr``. The byte is set to some implementation defined nonzero set value and the return value is true if and only if the previous contents were set. It should be only used for operands of type bool or char. For other types only part of the value may be set.
All memory models are valid.
This built-in function performs an atomic clear operation on *``ptr``. After the operation, *``ptr`` contains 0. It should be only used for operands of type bool or char and in conjunction with __atomic_test_and_set. For other types it may only clear partially. If the type is not bool prefer using __atomic_store.
The valid memory model variants are __ATOMIC_RELAXED, __ATOMIC_SEQ_CST, and __ATOMIC_RELEASE.
This built-in function acts as a synchronization fence between threads based on the specified memory model.
All memory orders are valid.
This built-in function acts as a synchronization fence between a thread and signal handlers based in the same thread.
All memory orders are valid.
This built-in function returns true if objects of size bytes always generate lock free atomic instructions for the target architecture. size must resolve to a compile-time constant and the result also resolves to a compile-time constant.
ptr is an optional pointer to the object that may be used to determine alignment. A value of 0 indicates typical alignment should be used. The compiler may also ignore this parameter.
if (_atomic_always_lock_free (sizeof (long long), 0))
This built-in function returns true if objects of size bytes always generate lock free atomic instructions for the target architecture. If it is not known to be lock free a call is made to a runtime routine named __atomic_is_lock_free.
ptr is an optional pointer to the object that may be used to determine alignment. A value of 0 indicates typical alignment should be used. The compiler may also ignore this parameter.
:: _integer-overflow-builtins:
The following built-in functions allow performing simple arithmetic operations together with checking whether the operations overflowed.
These built-in functions promote the first two operands into infinite precision signed type and perform addition on those promoted operands. The result is then cast to the type the third pointer argument points to and stored there. If the stored result is equal to the infinite precision result, the built-in functions return false, otherwise they return true. As the addition is performed in infinite signed precision, these built-in functions have fully defined behavior for all argument values.
The first built-in function allows arbitrary integral types for operands and the result type must be pointer to some integer type, the rest of the built-in functions have explicit integer types.
The compiler will attempt to use hardware instructions to implement these built-in functions where possible, like conditional jump on overflow after addition, conditional jump on carry etc.
These built-in functions are similar to the add overflow checking built-in functions above, except they perform subtraction, subtract the second argument from the first one, instead of addition.
These built-in functions are similar to the add overflow checking built-in functions above, except they perform multiplication, instead of addition.
:: _x86-specific-memory-model-extensions-for-transactional-memory:
The x86 architecture supports additional memory ordering flags to mark lock critical sections for hardware lock elision. These must be specified in addition to an existing memory model to atomic intrinsics.
Start lock elision on a lock variable. Memory model must be __ATOMIC_ACQUIRE or stronger.
End lock elision on a lock variable. Memory model must be __ATOMIC_RELEASE or stronger.
When a lock acquire fails it is required for good performance to abort the transaction quickly. This can be done with a _mm_pause
#include <immintrin.h> // For _mm_pause
int lockvar;
/* Acquire lock with lock elision */
while (__atomic_exchange_n(&lockvar, 1, __ATOMIC_ACQUIRE|__ATOMIC_HLE_ACQUIRE))
_mm_pause(); /* Abort failed transaction */
...
/* Free lock with lock elision */
__atomic_store_n(&lockvar, 0, __ATOMIC_RELEASE|__ATOMIC_HLE_RELEASE);
:: _object-size-checking:
GCC implements a limited buffer overflow protection mechanism that can prevent some buffer overflow attacks.
is a built-in construct that returns a constant number of bytes from ptr to the end of the object ptr pointer points to (if known at compile time). __builtin_object_size never evaluates its arguments for side-effects. If there are any side-effects in them, it returns (size_t) -1 for type 0 or 1 and (size_t) 0 for type 2 or 3. If there are multiple objects ptr can point to and all of them are known at compile time, the returned number is the maximum of remaining byte counts in those objects if type & 2 is 0 and minimum if nonzero. If it is not possible to determine which objects ptr points to at compile time, __builtin_object_size should return (size_t) -1 for type 0 or 1 and (size_t) 0 for type 2 or 3.
type is an integer constant from 0 to 3. If the least significant bit is clear, objects are whole variables, if it is set, a closest surrounding subobject is considered the object a pointer points to. The second bit determines if maximum or minimum of remaining bytes is computed.
struct V { char buf1[10]; int b; char buf2[10]; } var;
char *p = &var.buf1[1], *q = &var.b;
/* Here the object p points to is var. */
assert (__builtin_object_size (p, 0) == sizeof (var) - 1);
/* The subobject p points to is var.buf1. */
assert (__builtin_object_size (p, 1) == sizeof (var.buf1) - 1);
/* The object q points to is var. */
assert (__builtin_object_size (q, 0)
== (char *) (&var + 1) - (char *) &var.b);
/* The subobject q points to is var.b. */
assert (__builtin_object_size (q, 1) == sizeof (var.b));
There are built-in functions added for many common string operation functions, e.g., for memcpy __builtin___memcpy_chk built-in is provided. This built-in has an additional last argument, which is the number of bytes remaining in object the dest argument points to or (size_t) -1 if the size is not known.
The built-in functions are optimized into the normal string functions like memcpy if the last argument is (size_t) -1 or if it is known at compile time that the destination object will not be overflown. If the compiler can determine at compile time the object will be always overflown, it issues a warning.
The intended use can be e.g.
#undef memcpy
#define bos0(dest) __builtin_object_size (dest, 0)
#define memcpy(dest, src, n) \
__builtin___memcpy_chk (dest, src, n, bos0 (dest))
char *volatile p;
char buf[10];
/* It is unknown what object p points to, so this is optimized
into plain memcpy - no checking is possible. */
memcpy (p, "abcde", n);
/* Destination is known and length too. It is known at compile
time there will be no overflow. */
memcpy (&buf[5], "abcde", 5);
/* Destination is known, but the length is not known at compile time.
This will result in __memcpy_chk call that can check for overflow
at run time. */
memcpy (&buf[5], "abcde", n);
/* Destination is known and it is known at compile time there will
be overflow. There will be a warning and __memcpy_chk call that
will abort the program at run time. */
memcpy (&buf[6], "abcde", 5);
Such built-in functions are provided for memcpy, mempcpy, memmove, memset, strcpy, stpcpy, strncpy, strcat and strncat.
There are also checking built-in functions for formatted output functions.
int __builtin___sprintf_chk (char *s, int flag, size_t os, const char *fmt, ...);
int __builtin___snprintf_chk (char *s, size_t maxlen, int flag, size_t os,
const char *fmt, ...);
int __builtin___vsprintf_chk (char *s, int flag, size_t os, const char *fmt,
va_list ap);
int __builtin___vsnprintf_chk (char *s, size_t maxlen, int flag, size_t os,
const char *fmt, va_list ap);
The added flag argument is passed unchanged to __sprintf_chk etc. functions and can contain implementation specific flags on what additional security measures the checking function might take, such as handling %n differently.
The os argument is the object size s points to, like in the other built-in functions. There is a small difference in the behavior though, if os is (size_t) -1, the built-in functions are optimized into the non-checking functions only if flag is 0, otherwise the checking function is called with os argument set to (size_t) -1.
In addition to this, there are checking built-in functions __builtin___printf_chk, __builtin___vprintf_chk, __builtin___fprintf_chk and __builtin___vfprintf_chk. These have just one additional argument, flag, right before format string fmt. If the compiler is able to optimize them to fputc etc. functions, it does, otherwise the checking function is called and the flag argument passed to it.
:: _pointer-bounds-checker-builtins:
GCC provides a set of built-in functions to control Pointer Bounds Checker instrumentation. Note that all Pointer Bounds Checker builtins can be used even if you compile with Pointer Bounds Checker off (-fno-check-pointer-bounds). The behavior may differ in such case as documented below.
This built-in function returns a new pointer with the value of q, and associate it with the bounds [q, q``+``size-1]. With Pointer Bounds Checker off, the built-in function just returns the first argument.
extern void *__wrap_malloc (size_t n)
{
void *p = (void *)__real_malloc (n);
if (!p) return __builtin___bnd_null_ptr_bounds (p);
return __builtin___bnd_set_ptr_bounds (p, n);
}
This built-in function returns a new pointer with the value of p and associates it with the narrowed bounds formed by the intersection of bounds associated with q and the bounds [p, p + size - 1]. With Pointer Bounds Checker off, the built-in function just returns the first argument.
void init_objects (object *objs, size_t size)
{
size_t i;
/* Initialize objects one-by-one passing pointers with bounds of
an object, not the full array of objects. */
for (i = 0; i < size; i++)
init_object (__builtin___bnd_narrow_ptr_bounds (objs + i, objs,
sizeof(object)));
}
This built-in function returns a new pointer with the value of q, and associates it with the bounds already associated with pointer r. With Pointer Bounds Checker off, the built-in function just returns the first argument.
/* Here is a way to get pointer to object's field but
still with the full object's bounds. */
int *field_ptr = __builtin___bnd_copy_ptr_bounds (&objptr->int_field,
objptr);
This built-in function returns a new pointer with the value of q, and associates it with INIT (allowing full memory access) bounds. With Pointer Bounds Checker off, the built-in function just returns the first argument.
This built-in function returns a new pointer with the value of q, and associates it with NULL (allowing no memory access) bounds. With Pointer Bounds Checker off, the built-in function just returns the first argument.
This built-in function stores the bounds associated with pointer ptr_val and location ptr_addr into Bounds Table. This can be useful to propagate bounds from legacy code without touching the associated pointers memory when pointers are copied as integers. With Pointer Bounds Checker off, the built-in function call is ignored.
This built-in function checks if the pointer q is within the lower bound of its associated bounds. With Pointer Bounds Checker off, the built-in function call is ignored.
extern void *__wrap_memset (void *dst, int c, size_t len)
{
if (len > 0)
{
__builtin___bnd_chk_ptr_lbounds (dst);
__builtin___bnd_chk_ptr_ubounds ((char *)dst + len - 1);
__real_memset (dst, c, len);
}
return dst;
}
This built-in function checks if the pointer q is within the upper bound of its associated bounds. With Pointer Bounds Checker off, the built-in function call is ignored.
This built-in function checks if [q, q + size - 1] is within the lower and upper bounds associated with q. With Pointer Bounds Checker off, the built-in function call is ignored.
extern void *__wrap_memcpy (void *dst, const void *src, size_t n)
{
if (n > 0)
{
__bnd_chk_ptr_bounds (dst, n);
__bnd_chk_ptr_bounds (src, n);
__real_memcpy (dst, src, n);
}
return dst;
}
This built-in function returns the lower bound associated with the pointer q, as a pointer value. This is useful for debugging using printf. With Pointer Bounds Checker off, the built-in function returns 0.
void *lb = __builtin___bnd_get_ptr_lbound (q);
void *ub = __builtin___bnd_get_ptr_ubound (q);
printf ("q = %p lb(q) = %p ub(q) = %p", q, lb, ub);
This built-in function returns the upper bound (which is a pointer) associated with the pointer q. With Pointer Bounds Checker off, the built-in function returns -1.
:: _cilk-plus-builtins:
GCC provides support for the following built-in reduction functions if Cilk Plus is enabled. Cilk Plus can be enabled using the -fcilkplus flag.
Further details and examples about these built-in functions are described in the Cilk Plus language manual which can be found at http://www.cilkplus.org.
:: _other-builtins:
GCC provides a large number of built-in functions other than the ones mentioned above. Some of these are for internal use in the processing of exceptions or variable-length argument lists and are not documented here because they may change from time to time; we do not recommend general use of these functions.
The remaining functions are provided for optimization purposes.
GCC includes built-in versions of many of the functions in the standard C library. The versions prefixed with __builtin_ are always treated as having the same meaning as the C library function even if you specify the -fno-builtin option. (C Dialect Options) Many of these functions are only optimized in certain cases; if they are not optimized in a particular case, a call to the library function is emitted.
Outside strict ISO C mode (-ansi, -std=c90, -std=c99 or -std=c11), the functions _exit, alloca, bcmp, bzero, dcgettext, dgettext, dremf, dreml, drem, exp10f, exp10l, exp10, ffsll, ffsl, ffs, fprintf_unlocked, fputs_unlocked, gammaf, gammal, gamma, gammaf_r, gammal_r, gamma_r, gettext, index, isascii, j0f, j0l, j0, j1f, j1l, j1, jnf, jnl, jn, lgammaf_r, lgammal_r, lgamma_r, mempcpy, pow10f, pow10l, pow10, printf_unlocked, rindex, scalbf, scalbl, scalb, signbit, signbitf, signbitl, signbitd32, signbitd64, signbitd128, significandf, significandl, significand, sincosf, sincosl, sincos, stpcpy, stpncpy, strcasecmp, strdup, strfmon, strncasecmp, strndup, toascii, y0f, y0l, y0, y1f, y1l, y1, ynf, ynl and yn may be handled as built-in functions. All these functions have corresponding versions prefixed with __builtin_, which may be used even in strict C90 mode.
The ISO C99 functions _Exit, acoshf, acoshl, acosh, asinhf, asinhl, asinh, atanhf, atanhl, atanh, cabsf, cabsl, cabs, cacosf, cacoshf, cacoshl, cacosh, cacosl, cacos, cargf, cargl, carg, casinf, casinhf, casinhl, casinh, casinl, casin, catanf, catanhf, catanhl, catanh, catanl, catan, cbrtf, cbrtl, cbrt, ccosf, ccoshf, ccoshl, ccosh, ccosl, ccos, cexpf, cexpl, cexp, cimagf, cimagl, cimag, clogf, clogl, clog, conjf, conjl, conj, copysignf, copysignl, copysign, cpowf, cpowl, cpow, cprojf, cprojl, cproj, crealf, creall, creal, csinf, csinhf, csinhl, csinh, csinl, csin, csqrtf, csqrtl, csqrt, ctanf, ctanhf, ctanhl, ctanh, ctanl, ctan, erfcf, erfcl, erfc, erff, erfl, erf, exp2f, exp2l, exp2, expm1f, expm1l, expm1, fdimf, fdiml, fdim, fmaf, fmal, fmaxf, fmaxl, fmax, fma, fminf, fminl, fmin, hypotf, hypotl, hypot, ilogbf, ilogbl, ilogb, imaxabs, isblank, iswblank, lgammaf, lgammal, lgamma, llabs, llrintf, llrintl, llrint, llroundf, llroundl, llround, log1pf, log1pl, log1p, log2f, log2l, log2, logbf, logbl, logb, lrintf, lrintl, lrint, lroundf, lroundl, lround, nearbyintf, nearbyintl, nearbyint, nextafterf, nextafterl, nextafter, nexttowardf, nexttowardl, nexttoward, remainderf, remainderl, remainder, remquof, remquol, remquo, rintf, rintl, rint, roundf, roundl, round, scalblnf, scalblnl, scalbln, scalbnf, scalbnl, scalbn, snprintf, tgammaf, tgammal, tgamma, truncf, truncl, trunc, vfscanf, vscanf, vsnprintf and vsscanf are handled as built-in functions except in strict ISO C90 mode (-ansi or -std=c90).
There are also built-in versions of the ISO C99 functions acosf, acosl, asinf, asinl, atan2f, atan2l, atanf, atanl, ceilf, ceill, cosf, coshf, coshl, cosl, expf, expl, fabsf, fabsl, floorf, floorl, fmodf, fmodl, frexpf, frexpl, ldexpf, ldexpl, log10f, log10l, logf, logl, modfl, modf, powf, powl, sinf, sinhf, sinhl, sinl, sqrtf, sqrtl, tanf, tanhf, tanhl and tanl that are recognized in any mode since ISO C90 reserves these names for the purpose to which ISO C99 puts them. All these functions have corresponding versions prefixed with __builtin_.
The ISO C94 functions iswalnum, iswalpha, iswcntrl, iswdigit, iswgraph, iswlower, iswprint, iswpunct, iswspace, iswupper, iswxdigit, towlower and towupper are handled as built-in functions except in strict ISO C90 mode (-ansi or -std=c90).
The ISO C90 functions abort, abs, acos, asin, atan2, atan, calloc, ceil, cosh, cos, exit, exp, fabs, floor, fmod, fprintf, fputs, frexp, fscanf, isalnum, isalpha, iscntrl, isdigit, isgraph, islower, isprint, ispunct, isspace, isupper, isxdigit, tolower, toupper, labs, ldexp, log10, log, malloc, memchr, memcmp, memcpy, memset, modf, pow, printf, putchar, puts, scanf, sinh, sin, snprintf, sprintf, sqrt, sscanf, strcat, strchr, strcmp, strcpy, strcspn, strlen, strncat, strncmp, strncpy, strpbrk, strrchr, strspn, strstr, tanh, tan, vfprintf, vprintf and vsprintf are all recognized as built-in functions unless -fno-builtin is specified (or -fno-builtin-``function`` is specified for an individual function). All of these functions have corresponding versions prefixed with __builtin_.
GCC provides built-in versions of the ISO C99 floating-point comparison macros that avoid raising exceptions for unordered operands. They have the same names as the standard macros ( isgreater, isgreaterequal, isless, islessequal, islessgreater, and isunordered) , with __builtin_ prefixed. We intend for a library implementor to be able to simply #define each standard macro to its built-in equivalent. In the same fashion, GCC provides fpclassify, isfinite, isinf_sign and isnormal built-ins used with __builtin_ prefixed. The isinf and isnan built-in functions appear both with and without the __builtin_ prefix.
You can use the built-in function __builtin_types_compatible_p to determine whether two types are the same.
This built-in function returns 1 if the unqualified versions of the types type1 and type2 (which are types, not expressions) are compatible, 0 otherwise. The result of this built-in function can be used in integer constant expressions.
This built-in function ignores top level qualifiers (e.g., const, volatile). For example, int is equivalent to const int.
The type int[] and int[5] are compatible. On the other hand, int and char * are not compatible, even if the size of their types, on the particular architecture are the same. Also, the amount of pointer indirection is taken into account when determining similarity. Consequently, short * is not similar to short **. Furthermore, two types that are typedefed are considered compatible if their underlying types are compatible.
An enum type is not considered to be compatible with another enum type even if both are compatible with the same integer type; this is what the C standard specifies. For example, enum {foo, bar} is not similar to enum {hot, dog}.
You typically use this function in code whose execution varies depending on the arguments types. For example:
#define foo(x) \
({ \
typeof (x) tmp = (x); \
if (__builtin_types_compatible_p (typeof (x), long double)) \
tmp = foo_long_double (tmp); \
else if (__builtin_types_compatible_p (typeof (x), double)) \
tmp = foo_double (tmp); \
else if (__builtin_types_compatible_p (typeof (x), float)) \
tmp = foo_float (tmp); \
else \
abort (); \
tmp; \
})
Note: This construct is only available for C
The call_exp expression must be a function call, and the pointer_exp expression must be a pointer. The pointer_exp is passed to the function call in the targets static chain location. The result of builtin is the result of the function call.
Note: This builtin is only available for C This builtin can be used to call Go closures from C.
You can use the built-in function __builtin_choose_expr to evaluate code depending on the value of a constant expression. This built-in function returns exp1 if const_exp, which is an integer constant expression, is nonzero. Otherwise it returns exp2.
This built-in function is analogous to the ? : operator in C, except that the expression returned has its type unaltered by promotion rules. Also, the built-in function does not evaluate the expression that is not chosen. For example, if const_exp evaluates to true, exp2 is not evaluated even if it has side-effects.
This built-in function can return an lvalue if the chosen argument is an lvalue.
If exp1 is returned, the return type is the same as exp1``s type. Similarly, if ``exp2 is returned, its return type is the same as exp2.
Example:
#define foo(x) \
__builtin_choose_expr ( \
__builtin_types_compatible_p (typeof (x), double), \
foo_double (x), \
__builtin_choose_expr ( \
__builtin_types_compatible_p (typeof (x), float), \
foo_float (x), \
/* The void expression results in a compile-time error \
when assigning the result to something. */ \
(void)0))
Note: This construct is only available for C Furthermore, the unused expression (exp1 or exp2 depending on the value of const_exp) may still generate syntax errors. This may change in future revisions.
The built-in function __builtin_complex is provided for use in implementing the ISO C11 macros CMPLXF, CMPLX and CMPLXL. real and imag must have the same type, a real binary floating-point type, and the result has the corresponding complex type with real and imaginary parts real and imag. Unlike real + I * imag, this works even when infinities, NaNs and negative zeros are involved.
You can use the built-in function __builtin_constant_p to determine if a value is known to be constant at compile time and hence that GCC can perform constant-folding on expressions involving that value. The argument of the function is the value to test. The function returns the integer 1 if the argument is known to be a compile-time constant and 0 if it is not known to be a compile-time constant. A return of 0 does not indicate that the value is not a constant, but merely that GCC cannot prove it is a constant with the specified value of the -O option.
You typically use this function in an embedded application where memory is a critical resource. If you have some complex calculation, you may want it to be folded if it involves constants, but need to call a function if it does not. For example:
#define Scale_Value(X) \
(__builtin_constant_p (X) \
? ((X) * SCALE + OFFSET) : Scale (X))
You may use this built-in function in either a macro or an inline function. However, if you use it in an inlined function and pass an argument of the function as the argument to the built-in, GCC never returns 1 when you call the inline function with a string constant or compound literal (Compound Literals) and does not return 1 when you pass a constant numeric value to the inline function unless you specify the -O option.
You may also use __builtin_constant_p in initializers for static data. For instance, you can write
static const int table[] = {
__builtin_constant_p (EXPRESSION) ? (EXPRESSION) : -1,
/* ... */
};
This is an acceptable initializer even if EXPRESSION is not a constant expression, including the case where __builtin_constant_p returns 1 because EXPRESSION can be folded to a constant but EXPRESSION contains operands that are not otherwise permitted in a static initializer (for example, 0 && foo ()). GCC must be more conservative about evaluating the built-in in this case, because it has no opportunity to perform optimization.
You may use __builtin_expect to provide the compiler with branch prediction information. In general, you should prefer to use actual profile feedback for this (-fprofile-arcs), as programmers are notoriously bad at predicting how their programs actually perform. However, there are applications in which this data is hard to collect.
The return value is the value of exp, which should be an integral expression. The semantics of the built-in are that it is expected that exp == c. For example:
if (__builtin_expect (x, 0))
foo ();
indicates that we do not expect to call foo, since we expect x to be zero. Since you are limited to integral expressions for exp, you should use constructions such as
if (__builtin_expect (ptr != NULL, 1))
foo (*ptr);
when testing pointer or floating-point values.
This function causes the program to exit abnormally. GCC implements this function by using a target-dependent mechanism (such as intentionally executing an illegal instruction) or by calling abort. The mechanism used may vary from release to release so you should not rely on any particular implementation.
If control flow reaches the point of the __builtin_unreachable, the program is undefined. It is useful in situations where the compiler cannot deduce the unreachability of the code.
One such case is immediately following an asm statement that either never terminates, or one that transfers control elsewhere and never returns. In this example, without the __builtin_unreachable, GCC issues a warning that control reaches the end of a non-void function. It also generates code to return after the asm.
int f (int c, int v)
{
if (c)
{
return v;
}
else
{
asm("jmp error_handler");
__builtin_unreachable ();
}
}
Because the asm statement unconditionally transfers control out of the function, control never reaches the end of the function body. The __builtin_unreachable is in fact unreachable and communicates this fact to the compiler.
Another use for __builtin_unreachable is following a call a function that never returns but that is not declared __attribute__((noreturn)), as in this example:
void function_that_never_returns (void);
int g (int c)
{
if (c)
{
return 1;
}
else
{
function_that_never_returns ();
__builtin_unreachable ();
}
}
This function returns its first argument, and allows the compiler to assume that the returned pointer is at least align bytes aligned. This built-in can have either two or three arguments, if it has three, the third argument should have integer type, and if it is nonzero means misalignment offset. For example:
void *x = __builtin_assume_aligned (arg, 16);
means that the compiler can assume x, set to arg, is at least 16-byte aligned, while:
void *x = __builtin_assume_aligned (arg, 32, 8);
means that the compiler can assume for x, set to arg, that (char *) x - 8 is 32-byte aligned.
This function is the equivalent to the preprocessor __LINE__ macro and returns the line number of the invocation of the built-in. In a C++ default argument for a function F, it gets the line number of the call to F.
This function is the equivalent to the preprocessor __FUNCTION__ macro and returns the function name the invocation of the built-in is in.
This function is the equivalent to the preprocessor __FILE__ macro and returns the file name the invocation of the built-in is in. In a C++ default argument for a function F, it gets the file name of the call to F.
This function is used to flush the processors instruction cache for the region of memory between begin inclusive and end exclusive. Some targets require that the instruction cache be flushed, after modifying memory containing code, in order to obtain deterministic behavior.
If the target does not require instruction cache flushes, __builtin___clear_cache has no effect. Otherwise either instructions are emitted in-line to clear the instruction cache or a call to the __clear_cache function in libgcc is made.
This function is used to minimize cache-miss latency by moving data into a cache before it is accessed. You can insert calls to __builtin_prefetch into code for which you know addresses of data in memory that is likely to be accessed soon. If the target supports them, data prefetch instructions are generated. If the prefetch is done early enough before the access then the data will be in the cache by the time it is accessed.
The value of addr is the address of the memory to prefetch. There are two optional arguments, rw and locality. The value of rw is a compile-time constant one or zero; one means that the prefetch is preparing for a write to the memory address and zero, the default, means that the prefetch is preparing for a read. The value locality must be a compile-time constant integer between zero and three. A value of zero means that the data has no temporal locality, so it need not be left in the cache after the access. A value of three means that the data has a high degree of temporal locality and should be left in all levels of cache possible. Values of one and two mean, respectively, a low or moderate degree of temporal locality. The default is three.
for (i = 0; i < n; i++)
{
a[i] = a[i] + b[i];
__builtin_prefetch (&a[i+j], 1, 1);
__builtin_prefetch (&b[i+j], 0, 1);
/* ... */
}
Data prefetch does not generate faults if addr is invalid, but the address expression itself must be valid. For example, a prefetch of p->next does not fault if p->next is not a valid address, but evaluation faults if p is not a valid address.
If the target does not support data prefetch, the address expression is evaluated if it includes side effects but no other code is generated and GCC does not issue a warning.
Returns a positive infinity, if supported by the floating-point format, else DBL_MAX. This function is suitable for implementing the ISO C macro HUGE_VAL.
Similar to __builtin_huge_val, except the return type is float.
Similar to __builtin_huge_val, except the return type is long double.
This built-in implements the C99 fpclassify functionality. The first five int arguments should be the target librarys notion of the possible FP classes and are used for return values. They must be constant values and they must appear in this order: FP_NAN, FP_INFINITE, FP_NORMAL, FP_SUBNORMAL and FP_ZERO. The ellipsis is for exactly one floating-point value to classify. GCC treats the last argument as type-generic, which means it does not do default promotion from float to double.
Similar to __builtin_huge_val, except a warning is generated if the target floating-point format does not support infinities.
Similar to __builtin_inf, except the return type is _Decimal32.
Similar to __builtin_inf, except the return type is _Decimal64.
Similar to __builtin_inf, except the return type is _Decimal128.
Similar to __builtin_inf, except the return type is float. This function is suitable for implementing the ISO C99 macro INFINITY.
Similar to __builtin_inf, except the return type is long double.
Similar to isinf, except the return value is -1 for an argument of -Inf and 1 for an argument of +Inf. Note while the parameter list is an ellipsis, this function only accepts exactly one floating-point argument. GCC treats this parameter as type-generic, which means it does not do default promotion from float to double.
This is an implementation of the ISO C99 function nan.
Since ISO C99 defines this function in terms of strtod, which we do not implement, a description of the parsing is in order. The string is parsed as by strtol; that is, the base is recognized by leading 0 or 0x prefixes. The number parsed is placed in the significand such that the least significant bit of the number is at the least significant bit of the significand. The number is truncated to fit the significand field provided. The significand is forced to be a quiet NaN
This function, if given a string literal all of which would have been consumed by strtol, is evaluated early enough that it is considered a compile-time constant.
Similar to __builtin_nan, except the return type is _Decimal32.
Similar to __builtin_nan, except the return type is _Decimal64.
Similar to __builtin_nan, except the return type is _Decimal128.
Similar to __builtin_nan, except the return type is float.
Similar to __builtin_nan, except the return type is long double.
Similar to __builtin_nan, except the significand is forced to be a signaling NaN The nans function is proposed by http://www.open-std.org/jtc1/sc22/wg14/www/docs/n965.htmWG14 N965.
Similar to __builtin_nans, except the return type is float.
Similar to __builtin_nans, except the return type is long double.
Returns one plus the index of the least significant 1-bit of x, or if x is zero, returns zero.
Returns the number of leading 0-bits in x, starting at the most significant bit position. If x is 0, the result is undefined.
Returns the number of trailing 0-bits in x, starting at the least significant bit position. If x is 0, the result is undefined.
Returns the number of leading redundant sign bits in x, i.e. the number of bits following the most significant bit that are identical to it. There are no special cases for 0 or other values.
Returns the number of 1-bits in x.
Returns the parity of x, i.e. the number of 1-bits in x modulo 2.
Similar to __builtin_ffs, except the argument type is long.
Similar to __builtin_clz, except the argument type is unsigned long.
Similar to __builtin_ctz, except the argument type is unsigned long.
Similar to __builtin_clrsb, except the argument type is long.
Similar to __builtin_popcount, except the argument type is unsigned long.
Similar to __builtin_parity, except the argument type is unsigned long.
Similar to __builtin_ffs, except the argument type is long long.
Similar to __builtin_clz, except the argument type is unsigned long long.
Similar to __builtin_ctz, except the argument type is unsigned long long.
Similar to __builtin_clrsb, except the argument type is long long.
Similar to __builtin_popcount, except the argument type is unsigned long long.
Similar to __builtin_parity, except the argument type is unsigned long long.
Returns the first argument raised to the power of the second. Unlike the pow function no guarantees about precision and rounding are made.
Similar to __builtin_powi, except the argument and return types are float.
Similar to __builtin_powi, except the argument and return types are long double.
Returns x with the order of the bytes reversed; for example, 0xaabb becomes 0xbbaa. Byte here always means exactly 8 bits.
Similar to __builtin_bswap16, except the argument and return types are 32 bit.
Similar to __builtin_bswap32, except the argument and return types are 64 bit.
:: _target-builtins:
On some target machines, GCC supports many built-in functions specific to those machines. Generally these generate calls to specific machine instructions, but allow the compiler to schedule those calls.
:: _aarch64-built-in-functions:
These built-in functions are available for the AArch64 family of processors.
unsigned int __builtin_aarch64_get_fpcr ()
void __builtin_aarch64_set_fpcr (unsigned int)
unsigned int __builtin_aarch64_get_fpsr ()
void __builtin_aarch64_set_fpsr (unsigned int)
:: _alpha-built-in-functions:
These built-in functions are available for the Alpha family of processors, depending on the command-line switches used.
The following built-in functions are always available. They all generate the machine instruction that is part of the name.
long __builtin_alpha_implver (void)
long __builtin_alpha_rpcc (void)
long __builtin_alpha_amask (long)
long __builtin_alpha_cmpbge (long, long)
long __builtin_alpha_extbl (long, long)
long __builtin_alpha_extwl (long, long)
long __builtin_alpha_extll (long, long)
long __builtin_alpha_extql (long, long)
long __builtin_alpha_extwh (long, long)
long __builtin_alpha_extlh (long, long)
long __builtin_alpha_extqh (long, long)
long __builtin_alpha_insbl (long, long)
long __builtin_alpha_inswl (long, long)
long __builtin_alpha_insll (long, long)
long __builtin_alpha_insql (long, long)
long __builtin_alpha_inswh (long, long)
long __builtin_alpha_inslh (long, long)
long __builtin_alpha_insqh (long, long)
long __builtin_alpha_mskbl (long, long)
long __builtin_alpha_mskwl (long, long)
long __builtin_alpha_mskll (long, long)
long __builtin_alpha_mskql (long, long)
long __builtin_alpha_mskwh (long, long)
long __builtin_alpha_msklh (long, long)
long __builtin_alpha_mskqh (long, long)
long __builtin_alpha_umulh (long, long)
long __builtin_alpha_zap (long, long)
long __builtin_alpha_zapnot (long, long)
The following built-in functions are always with -mmax or -mcpu=``cpu`` where cpu is pca56 or later. They all generate the machine instruction that is part of the name.
long __builtin_alpha_pklb (long)
long __builtin_alpha_pkwb (long)
long __builtin_alpha_unpkbl (long)
long __builtin_alpha_unpkbw (long)
long __builtin_alpha_minub8 (long, long)
long __builtin_alpha_minsb8 (long, long)
long __builtin_alpha_minuw4 (long, long)
long __builtin_alpha_minsw4 (long, long)
long __builtin_alpha_maxub8 (long, long)
long __builtin_alpha_maxsb8 (long, long)
long __builtin_alpha_maxuw4 (long, long)
long __builtin_alpha_maxsw4 (long, long)
long __builtin_alpha_perr (long, long)
The following built-in functions are always with -mcix or -mcpu=``cpu`` where cpu is ev67 or later. They all generate the machine instruction that is part of the name.
long __builtin_alpha_cttz (long)
long __builtin_alpha_ctlz (long)
long __builtin_alpha_ctpop (long)
The following built-in functions are available on systems that use the OSF/1 PALcode. Normally they invoke the rduniq and wruniq PAL calls, but when invoked with -mtls-kernel, they invoke rdval and wrval.
void *__builtin_thread_pointer (void)
void __builtin_set_thread_pointer (void *)
:: _altera-nios-ii-built-in-functions:
These built-in functions are available for the Altera Nios II family of processors.
The following built-in functions are always available. They all generate the machine instruction that is part of the name.
int __builtin_ldbio (volatile const void *)
int __builtin_ldbuio (volatile const void *)
int __builtin_ldhio (volatile const void *)
int __builtin_ldhuio (volatile const void *)
int __builtin_ldwio (volatile const void *)
void __builtin_stbio (volatile void *, int)
void __builtin_sthio (volatile void *, int)
void __builtin_stwio (volatile void *, int)
void __builtin_sync (void)
int __builtin_rdctl (int)
void __builtin_wrctl (int, int)
The following built-in functions are always available. They all generate a Nios II Custom Instruction. The name of the function represents the types that the function takes and returns. The letter before the n is the return type or void if absent. The n represents the first parameter to all the custom instructions, the custom instruction number. The two letters after the n represent the up to two parameters to the function.
The letters represent the following data types:
void for return type and no parameter for parameter types.
int for return type and parameter type
float for return type and parameter type
void * for return type and parameter type
And the function names are:
void __builtin_custom_n (void)
void __builtin_custom_ni (int)
void __builtin_custom_nf (float)
void __builtin_custom_np (void *)
void __builtin_custom_nii (int, int)
void __builtin_custom_nif (int, float)
void __builtin_custom_nip (int, void *)
void __builtin_custom_nfi (float, int)
void __builtin_custom_nff (float, float)
void __builtin_custom_nfp (float, void *)
void __builtin_custom_npi (void *, int)
void __builtin_custom_npf (void *, float)
void __builtin_custom_npp (void *, void *)
int __builtin_custom_in (void)
int __builtin_custom_ini (int)
int __builtin_custom_inf (float)
int __builtin_custom_inp (void *)
int __builtin_custom_inii (int, int)
int __builtin_custom_inif (int, float)
int __builtin_custom_inip (int, void *)
int __builtin_custom_infi (float, int)
int __builtin_custom_inff (float, float)
int __builtin_custom_infp (float, void *)
int __builtin_custom_inpi (void *, int)
int __builtin_custom_inpf (void *, float)
int __builtin_custom_inpp (void *, void *)
float __builtin_custom_fn (void)
float __builtin_custom_fni (int)
float __builtin_custom_fnf (float)
float __builtin_custom_fnp (void *)
float __builtin_custom_fnii (int, int)
float __builtin_custom_fnif (int, float)
float __builtin_custom_fnip (int, void *)
float __builtin_custom_fnfi (float, int)
float __builtin_custom_fnff (float, float)
float __builtin_custom_fnfp (float, void *)
float __builtin_custom_fnpi (void *, int)
float __builtin_custom_fnpf (void *, float)
float __builtin_custom_fnpp (void *, void *)
void * __builtin_custom_pn (void)
void * __builtin_custom_pni (int)
void * __builtin_custom_pnf (float)
void * __builtin_custom_pnp (void *)
void * __builtin_custom_pnii (int, int)
void * __builtin_custom_pnif (int, float)
void * __builtin_custom_pnip (int, void *)
void * __builtin_custom_pnfi (float, int)
void * __builtin_custom_pnff (float, float)
void * __builtin_custom_pnfp (float, void *)
void * __builtin_custom_pnpi (void *, int)
void * __builtin_custom_pnpf (void *, float)
void * __builtin_custom_pnpp (void *, void *)
:: _arc-built-in-functions:
The following built-in functions are provided for ARC targets. The built-ins generate the corresponding assembly instructions. In the examples given below, the generated code often requires an operand or result to be in a register. Where necessary further code will be generated to ensure this is true, but for brevity this is not described in each case.
Note: Using a built-in to generate an instruction not supported by a target may cause problems. At present the compiler is not guaranteed to detect such misuse, and as a result an internal compiler error may be generated.
Return 1 if val is known to have the byte alignment given by alignval, otherwise return 0. Note that this is different from
__alignof__(*(char *)``val``) >= alignval
because __alignof__ sees only the type of the dereference, whereas __builtin_arc_align uses alignment information from the pointer as well as from the pointed-to type. The information available will depend on optimization level.
Generates
brk
The operand is the number of a register to be read. Generates:
mov ``dest``, r``regno``
where the value in dest will be the result returned from the built-in.
The first operand is the number of a register to be written, the second operand is a compile time constant to write into that register. Generates:
mov r``regno``, ``val``
Only available if either -mcpu=ARC700 or -meA is set. Generates:
divaw ``dest``, ``a``, ``b``
where the value in dest will be the result returned from the built-in.
Generates
flag ``a``
The operand, auxv, is the address of an auxiliary register and must be a compile time constant. Generates:
lr ``dest``, [``auxr``]
Where the value in dest will be the result returned from the built-in.
Only available with -mmul64. Generates:
mul64 ``a``, ``b``
Only available with -mmul64. Generates:
mulu64 ``a``, ``b``
Generates:
nop
Only valid if the norm instruction is available through the -mnorm option or by default with -mcpu=ARC700. Generates:
norm ``dest``, ``src``
Where the value in dest will be the result returned from the built-in.
Only valid if the normw instruction is available through the -mnorm option or by default with -mcpu=ARC700. Generates:
normw ``dest``, ``src``
Where the value in dest will be the result returned from the built-in.
Generates:
rtie
Generates:
sleep ``a``
The first argument, auxv, is the address of an auxiliary register, the second argument, val, is a compile time constant to be written to the register. Generates:
sr ``auxr``, [``val``]
Only valid with -mswap. Generates:
swap ``dest``, ``src``
Where the value in dest will be the result returned from the built-in.
Generates:
swi
Only available with -mcpu=ARC700. Generates:
sync
Only available with -mcpu=ARC700. Generates:
trap_s ``c``
Only available with -mcpu=ARC700. Generates:
unimp_s
The instructions generated by the following builtins are not considered as candidates for scheduling. They are not moved around by the compiler during scheduling, and thus can be expected to appear where they are put in the C code:
__builtin_arc_brk()
__builtin_arc_core_read()
__builtin_arc_core_write()
__builtin_arc_flag()
__builtin_arc_lr()
__builtin_arc_sleep()
__builtin_arc_sr()
__builtin_arc_swi()
:: _arc-simd-built-in-functions:
SIMD builtins provided by the compiler can be used to generate the vector instructions. This section describes the available builtins and their usage in programs. With the -msimd option, the compiler provides 128-bit vector types, which can be specified using the vector_size attribute. The header file arc-simd.h can be included to use the following predefined types:
typedef int __v4si __attribute__((vector_size(16)));
typedef short __v8hi __attribute__((vector_size(16)));
These types can be used to define 128-bit variables. The built-in functions listed in the following section can be used on these variables to generate the vector operations.
For all builtins, __builtin_arc_``someinsn``, the header file arc-simd.h also provides equivalent macros called _``someinsn`` that can be used for programming ease and improved readability. The following macros for DMA control are also provided:
#define _setup_dma_in_channel_reg _vdiwr
#define _setup_dma_out_channel_reg _vdowr
The following is a complete list of all the SIMD built-ins provided for ARC, grouped by calling signature.
The following take two __v8hi arguments and return a __v8hi result:
__v8hi __builtin_arc_vaddaw (__v8hi, __v8hi)
__v8hi __builtin_arc_vaddw (__v8hi, __v8hi)
__v8hi __builtin_arc_vand (__v8hi, __v8hi)
__v8hi __builtin_arc_vandaw (__v8hi, __v8hi)
__v8hi __builtin_arc_vavb (__v8hi, __v8hi)
__v8hi __builtin_arc_vavrb (__v8hi, __v8hi)
__v8hi __builtin_arc_vbic (__v8hi, __v8hi)
__v8hi __builtin_arc_vbicaw (__v8hi, __v8hi)
__v8hi __builtin_arc_vdifaw (__v8hi, __v8hi)
__v8hi __builtin_arc_vdifw (__v8hi, __v8hi)
__v8hi __builtin_arc_veqw (__v8hi, __v8hi)
__v8hi __builtin_arc_vh264f (__v8hi, __v8hi)
__v8hi __builtin_arc_vh264ft (__v8hi, __v8hi)
__v8hi __builtin_arc_vh264fw (__v8hi, __v8hi)
__v8hi __builtin_arc_vlew (__v8hi, __v8hi)
__v8hi __builtin_arc_vltw (__v8hi, __v8hi)
__v8hi __builtin_arc_vmaxaw (__v8hi, __v8hi)
__v8hi __builtin_arc_vmaxw (__v8hi, __v8hi)
__v8hi __builtin_arc_vminaw (__v8hi, __v8hi)
__v8hi __builtin_arc_vminw (__v8hi, __v8hi)
__v8hi __builtin_arc_vmr1aw (__v8hi, __v8hi)
__v8hi __builtin_arc_vmr1w (__v8hi, __v8hi)
__v8hi __builtin_arc_vmr2aw (__v8hi, __v8hi)
__v8hi __builtin_arc_vmr2w (__v8hi, __v8hi)
__v8hi __builtin_arc_vmr3aw (__v8hi, __v8hi)
__v8hi __builtin_arc_vmr3w (__v8hi, __v8hi)
__v8hi __builtin_arc_vmr4aw (__v8hi, __v8hi)
__v8hi __builtin_arc_vmr4w (__v8hi, __v8hi)
__v8hi __builtin_arc_vmr5aw (__v8hi, __v8hi)
__v8hi __builtin_arc_vmr5w (__v8hi, __v8hi)
__v8hi __builtin_arc_vmr6aw (__v8hi, __v8hi)
__v8hi __builtin_arc_vmr6w (__v8hi, __v8hi)
__v8hi __builtin_arc_vmr7aw (__v8hi, __v8hi)
__v8hi __builtin_arc_vmr7w (__v8hi, __v8hi)
__v8hi __builtin_arc_vmrb (__v8hi, __v8hi)
__v8hi __builtin_arc_vmulaw (__v8hi, __v8hi)
__v8hi __builtin_arc_vmulfaw (__v8hi, __v8hi)
__v8hi __builtin_arc_vmulfw (__v8hi, __v8hi)
__v8hi __builtin_arc_vmulw (__v8hi, __v8hi)
__v8hi __builtin_arc_vnew (__v8hi, __v8hi)
__v8hi __builtin_arc_vor (__v8hi, __v8hi)
__v8hi __builtin_arc_vsubaw (__v8hi, __v8hi)
__v8hi __builtin_arc_vsubw (__v8hi, __v8hi)
__v8hi __builtin_arc_vsummw (__v8hi, __v8hi)
__v8hi __builtin_arc_vvc1f (__v8hi, __v8hi)
__v8hi __builtin_arc_vvc1ft (__v8hi, __v8hi)
__v8hi __builtin_arc_vxor (__v8hi, __v8hi)
__v8hi __builtin_arc_vxoraw (__v8hi, __v8hi)
The following take one __v8hi and one int argument and return a __v8hi result:
__v8hi __builtin_arc_vbaddw (__v8hi, int)
__v8hi __builtin_arc_vbmaxw (__v8hi, int)
__v8hi __builtin_arc_vbminw (__v8hi, int)
__v8hi __builtin_arc_vbmulaw (__v8hi, int)
__v8hi __builtin_arc_vbmulfw (__v8hi, int)
__v8hi __builtin_arc_vbmulw (__v8hi, int)
__v8hi __builtin_arc_vbrsubw (__v8hi, int)
__v8hi __builtin_arc_vbsubw (__v8hi, int)
The following take one __v8hi argument and one int argument which must be a 3-bit compile time constant indicating a register number I0-I7. They return a __v8hi result.
__v8hi __builtin_arc_vasrw (__v8hi, const int)
__v8hi __builtin_arc_vsr8 (__v8hi, const int)
__v8hi __builtin_arc_vsr8aw (__v8hi, const int)
The following take one __v8hi argument and one int argument which must be a 6-bit compile time constant. They return a __v8hi result.
__v8hi __builtin_arc_vasrpwbi (__v8hi, const int)
__v8hi __builtin_arc_vasrrpwbi (__v8hi, const int)
__v8hi __builtin_arc_vasrrwi (__v8hi, const int)
__v8hi __builtin_arc_vasrsrwi (__v8hi, const int)
__v8hi __builtin_arc_vasrwi (__v8hi, const int)
__v8hi __builtin_arc_vsr8awi (__v8hi, const int)
__v8hi __builtin_arc_vsr8i (__v8hi, const int)
The following take one __v8hi argument and one int argument which must be a 8-bit compile time constant. They return a __v8hi result.
__v8hi __builtin_arc_vd6tapf (__v8hi, const int)
__v8hi __builtin_arc_vmvaw (__v8hi, const int)
__v8hi __builtin_arc_vmvw (__v8hi, const int)
__v8hi __builtin_arc_vmvzw (__v8hi, const int)
The following take two int arguments, the second of which which must be a 8-bit compile time constant. They return a __v8hi result:
__v8hi __builtin_arc_vmovaw (int, const int)
__v8hi __builtin_arc_vmovw (int, const int)
__v8hi __builtin_arc_vmovzw (int, const int)
The following take a single __v8hi argument and return a __v8hi result:
__v8hi __builtin_arc_vabsaw (__v8hi)
__v8hi __builtin_arc_vabsw (__v8hi)
__v8hi __builtin_arc_vaddsuw (__v8hi)
__v8hi __builtin_arc_vexch1 (__v8hi)
__v8hi __builtin_arc_vexch2 (__v8hi)
__v8hi __builtin_arc_vexch4 (__v8hi)
__v8hi __builtin_arc_vsignw (__v8hi)
__v8hi __builtin_arc_vupbaw (__v8hi)
__v8hi __builtin_arc_vupbw (__v8hi)
__v8hi __builtin_arc_vupsbaw (__v8hi)
__v8hi __builtin_arc_vupsbw (__v8hi)
The following take two int arguments and return no result:
void __builtin_arc_vdirun (int, int)
void __builtin_arc_vdorun (int, int)
The following take two int arguments and return no result. The first argument must a 3-bit compile time constant indicating one of the DR0-DR7 DMA setup channels:
void __builtin_arc_vdiwr (const int, int)
void __builtin_arc_vdowr (const int, int)
The following take an int argument and return no result:
void __builtin_arc_vendrec (int)
void __builtin_arc_vrec (int)
void __builtin_arc_vrecrun (int)
void __builtin_arc_vrun (int)
The following take a __v8hi argument and two int arguments and return a __v8hi result. The second argument must be a 3-bit compile time constants, indicating one the registers I0-I7, and the third argument must be an 8-bit compile time constant.
Note: Although the equivalent hardware instructions do not take an SIMD register as an operand, these builtins overwrite the relevant bits of the __v8hi register provided as the first argument with the value loaded from the [Ib, u8] location in the SDM.
__v8hi __builtin_arc_vld32 (__v8hi, const int, const int)
__v8hi __builtin_arc_vld32wh (__v8hi, const int, const int)
__v8hi __builtin_arc_vld32wl (__v8hi, const int, const int)
__v8hi __builtin_arc_vld64 (__v8hi, const int, const int)
The following take two int arguments and return a __v8hi result. The first argument must be a 3-bit compile time constants, indicating one the registers I0-I7, and the second argument must be an 8-bit compile time constant.
__v8hi __builtin_arc_vld128 (const int, const int)
__v8hi __builtin_arc_vld64w (const int, const int)
The following take a __v8hi argument and two int arguments and return no result. The second argument must be a 3-bit compile time constants, indicating one the registers I0-I7, and the third argument must be an 8-bit compile time constant.
void __builtin_arc_vst128 (__v8hi, const int, const int)
void __builtin_arc_vst64 (__v8hi, const int, const int)
The following take a __v8hi argument and three int arguments and return no result. The second argument must be a 3-bit compile-time constant, identifying the 16-bit sub-register to be stored, the third argument must be a 3-bit compile time constants, indicating one the registers I0-I7, and the fourth argument must be an 8-bit compile time constant.
void __builtin_arc_vst16_n (__v8hi, const int, const int, const int)
void __builtin_arc_vst32_n (__v8hi, const int, const int, const int)
:: _arm-iwmmxt-built-in-functions:
These built-in functions are available for the ARM family of processors when the -mcpu=iwmmxt switch is used:
typedef int v2si __attribute__ ((vector_size (8)));
typedef short v4hi __attribute__ ((vector_size (8)));
typedef char v8qi __attribute__ ((vector_size (8)));
int __builtin_arm_getwcgr0 (void)
void __builtin_arm_setwcgr0 (int)
int __builtin_arm_getwcgr1 (void)
void __builtin_arm_setwcgr1 (int)
int __builtin_arm_getwcgr2 (void)
void __builtin_arm_setwcgr2 (int)
int __builtin_arm_getwcgr3 (void)
void __builtin_arm_setwcgr3 (int)
int __builtin_arm_textrmsb (v8qi, int)
int __builtin_arm_textrmsh (v4hi, int)
int __builtin_arm_textrmsw (v2si, int)
int __builtin_arm_textrmub (v8qi, int)
int __builtin_arm_textrmuh (v4hi, int)
int __builtin_arm_textrmuw (v2si, int)
v8qi __builtin_arm_tinsrb (v8qi, int, int)
v4hi __builtin_arm_tinsrh (v4hi, int, int)
v2si __builtin_arm_tinsrw (v2si, int, int)
long long __builtin_arm_tmia (long long, int, int)
long long __builtin_arm_tmiabb (long long, int, int)
long long __builtin_arm_tmiabt (long long, int, int)
long long __builtin_arm_tmiaph (long long, int, int)
long long __builtin_arm_tmiatb (long long, int, int)
long long __builtin_arm_tmiatt (long long, int, int)
int __builtin_arm_tmovmskb (v8qi)
int __builtin_arm_tmovmskh (v4hi)
int __builtin_arm_tmovmskw (v2si)
long long __builtin_arm_waccb (v8qi)
long long __builtin_arm_wacch (v4hi)
long long __builtin_arm_waccw (v2si)
v8qi __builtin_arm_waddb (v8qi, v8qi)
v8qi __builtin_arm_waddbss (v8qi, v8qi)
v8qi __builtin_arm_waddbus (v8qi, v8qi)
v4hi __builtin_arm_waddh (v4hi, v4hi)
v4hi __builtin_arm_waddhss (v4hi, v4hi)
v4hi __builtin_arm_waddhus (v4hi, v4hi)
v2si __builtin_arm_waddw (v2si, v2si)
v2si __builtin_arm_waddwss (v2si, v2si)
v2si __builtin_arm_waddwus (v2si, v2si)
v8qi __builtin_arm_walign (v8qi, v8qi, int)
long long __builtin_arm_wand(long long, long long)
long long __builtin_arm_wandn (long long, long long)
v8qi __builtin_arm_wavg2b (v8qi, v8qi)
v8qi __builtin_arm_wavg2br (v8qi, v8qi)
v4hi __builtin_arm_wavg2h (v4hi, v4hi)
v4hi __builtin_arm_wavg2hr (v4hi, v4hi)
v8qi __builtin_arm_wcmpeqb (v8qi, v8qi)
v4hi __builtin_arm_wcmpeqh (v4hi, v4hi)
v2si __builtin_arm_wcmpeqw (v2si, v2si)
v8qi __builtin_arm_wcmpgtsb (v8qi, v8qi)
v4hi __builtin_arm_wcmpgtsh (v4hi, v4hi)
v2si __builtin_arm_wcmpgtsw (v2si, v2si)
v8qi __builtin_arm_wcmpgtub (v8qi, v8qi)
v4hi __builtin_arm_wcmpgtuh (v4hi, v4hi)
v2si __builtin_arm_wcmpgtuw (v2si, v2si)
long long __builtin_arm_wmacs (long long, v4hi, v4hi)
long long __builtin_arm_wmacsz (v4hi, v4hi)
long long __builtin_arm_wmacu (long long, v4hi, v4hi)
long long __builtin_arm_wmacuz (v4hi, v4hi)
v4hi __builtin_arm_wmadds (v4hi, v4hi)
v4hi __builtin_arm_wmaddu (v4hi, v4hi)
v8qi __builtin_arm_wmaxsb (v8qi, v8qi)
v4hi __builtin_arm_wmaxsh (v4hi, v4hi)
v2si __builtin_arm_wmaxsw (v2si, v2si)
v8qi __builtin_arm_wmaxub (v8qi, v8qi)
v4hi __builtin_arm_wmaxuh (v4hi, v4hi)
v2si __builtin_arm_wmaxuw (v2si, v2si)
v8qi __builtin_arm_wminsb (v8qi, v8qi)
v4hi __builtin_arm_wminsh (v4hi, v4hi)
v2si __builtin_arm_wminsw (v2si, v2si)
v8qi __builtin_arm_wminub (v8qi, v8qi)
v4hi __builtin_arm_wminuh (v4hi, v4hi)
v2si __builtin_arm_wminuw (v2si, v2si)
v4hi __builtin_arm_wmulsm (v4hi, v4hi)
v4hi __builtin_arm_wmulul (v4hi, v4hi)
v4hi __builtin_arm_wmulum (v4hi, v4hi)
long long __builtin_arm_wor (long long, long long)
v2si __builtin_arm_wpackdss (long long, long long)
v2si __builtin_arm_wpackdus (long long, long long)
v8qi __builtin_arm_wpackhss (v4hi, v4hi)
v8qi __builtin_arm_wpackhus (v4hi, v4hi)
v4hi __builtin_arm_wpackwss (v2si, v2si)
v4hi __builtin_arm_wpackwus (v2si, v2si)
long long __builtin_arm_wrord (long long, long long)
long long __builtin_arm_wrordi (long long, int)
v4hi __builtin_arm_wrorh (v4hi, long long)
v4hi __builtin_arm_wrorhi (v4hi, int)
v2si __builtin_arm_wrorw (v2si, long long)
v2si __builtin_arm_wrorwi (v2si, int)
v2si __builtin_arm_wsadb (v2si, v8qi, v8qi)
v2si __builtin_arm_wsadbz (v8qi, v8qi)
v2si __builtin_arm_wsadh (v2si, v4hi, v4hi)
v2si __builtin_arm_wsadhz (v4hi, v4hi)
v4hi __builtin_arm_wshufh (v4hi, int)
long long __builtin_arm_wslld (long long, long long)
long long __builtin_arm_wslldi (long long, int)
v4hi __builtin_arm_wsllh (v4hi, long long)
v4hi __builtin_arm_wsllhi (v4hi, int)
v2si __builtin_arm_wsllw (v2si, long long)
v2si __builtin_arm_wsllwi (v2si, int)
long long __builtin_arm_wsrad (long long, long long)
long long __builtin_arm_wsradi (long long, int)
v4hi __builtin_arm_wsrah (v4hi, long long)
v4hi __builtin_arm_wsrahi (v4hi, int)
v2si __builtin_arm_wsraw (v2si, long long)
v2si __builtin_arm_wsrawi (v2si, int)
long long __builtin_arm_wsrld (long long, long long)
long long __builtin_arm_wsrldi (long long, int)
v4hi __builtin_arm_wsrlh (v4hi, long long)
v4hi __builtin_arm_wsrlhi (v4hi, int)
v2si __builtin_arm_wsrlw (v2si, long long)
v2si __builtin_arm_wsrlwi (v2si, int)
v8qi __builtin_arm_wsubb (v8qi, v8qi)
v8qi __builtin_arm_wsubbss (v8qi, v8qi)
v8qi __builtin_arm_wsubbus (v8qi, v8qi)
v4hi __builtin_arm_wsubh (v4hi, v4hi)
v4hi __builtin_arm_wsubhss (v4hi, v4hi)
v4hi __builtin_arm_wsubhus (v4hi, v4hi)
v2si __builtin_arm_wsubw (v2si, v2si)
v2si __builtin_arm_wsubwss (v2si, v2si)
v2si __builtin_arm_wsubwus (v2si, v2si)
v4hi __builtin_arm_wunpckehsb (v8qi)
v2si __builtin_arm_wunpckehsh (v4hi)
long long __builtin_arm_wunpckehsw (v2si)
v4hi __builtin_arm_wunpckehub (v8qi)
v2si __builtin_arm_wunpckehuh (v4hi)
long long __builtin_arm_wunpckehuw (v2si)
v4hi __builtin_arm_wunpckelsb (v8qi)
v2si __builtin_arm_wunpckelsh (v4hi)
long long __builtin_arm_wunpckelsw (v2si)
v4hi __builtin_arm_wunpckelub (v8qi)
v2si __builtin_arm_wunpckeluh (v4hi)
long long __builtin_arm_wunpckeluw (v2si)
v8qi __builtin_arm_wunpckihb (v8qi, v8qi)
v4hi __builtin_arm_wunpckihh (v4hi, v4hi)
v2si __builtin_arm_wunpckihw (v2si, v2si)
v8qi __builtin_arm_wunpckilb (v8qi, v8qi)
v4hi __builtin_arm_wunpckilh (v4hi, v4hi)
v2si __builtin_arm_wunpckilw (v2si, v2si)
long long __builtin_arm_wxor (long long, long long)
long long __builtin_arm_wzero ()
:: _arm-c-language-extensions-(acle):
GCC implements extensions for C as described in the ARM C Language Extensions (ACLE) specification, which can be found at http://infocenter.arm.com/help/topic/com.arm.doc.ihi0053c/IHI0053C_acle_2_0.pdf.
As a part of ACLE, GCC implements extensions for Advanced SIMD as described in the ARM C Language Extensions Specification. The complete list of Advanced SIMD intrinsics can be found at http://infocenter.arm.com/help/topic/com.arm.doc.ihi0073a/IHI0073A_arm_neon_intrinsics_ref.pdf. The built-in intrinsics for the Advanced SIMD extension are available when NEON is enabled.
Currently, ARM and AArch64 back ends do not support ACLE 2.0 fully. Both back ends support CRC32 intrinsics from arm_acle.h. The ARM back ends 16-bit floating-point Advanced SIMD intrinsics currently comply to ACLE v1.1. AArch64s back end does not have support for 16-bit floating point Advanced SIMD intrinsics yet.
See ARM Options and AArch64 Options for more information on the availability of extensions.
:: _arm-floating-point-status-and-control-intrinsics:
These built-in functions are available for the ARM family of processors with floating-point unit.
unsigned int __builtin_arm_get_fpscr ()
void __builtin_arm_set_fpscr (unsigned int)
:: _avr-built-in-functions:
For each built-in function for AVR, there is an equally named, uppercase built-in macro defined. That way users can easily query if or if not a specific built-in is implemented or not. For example, if __builtin_avr_nop is available the macro __BUILTIN_AVR_NOP is defined to 1 and undefined otherwise.
The following built-in functions map to the respective machine instruction, i.e. nop, sei, cli, sleep, wdr, swap, fmul, fmuls resp. fmulsu. The three fmul* built-ins are implemented as library call if no hardware multiplier is available.
void __builtin_avr_nop (void)
void __builtin_avr_sei (void)
void __builtin_avr_cli (void)
void __builtin_avr_sleep (void)
void __builtin_avr_wdr (void)
unsigned char __builtin_avr_swap (unsigned char)
unsigned int __builtin_avr_fmul (unsigned char, unsigned char)
int __builtin_avr_fmuls (char, char)
int __builtin_avr_fmulsu (char, unsigned char)
In order to delay execution for a specific number of cycles, GCC implements
void __builtin_avr_delay_cycles (unsigned long ticks)
ticks is the number of ticks to delay execution. Note that this built-in does not take into account the effect of interrupts that might increase delay time. ticks must be a compile-time integer constant; delays with a variable number of cycles are not supported.
char __builtin_avr_flash_segment (const __memx void*)
This built-in takes a byte address to the 24-bit AVR Named Address Spacesaddress space __memx and returns the number of the flash segment (the 64 KiB chunk) where the address points to. Counting starts at 0. If the address does not point to flash memory, return -1.
unsigned char __builtin_avr_insert_bits (unsigned long map, unsigned char bits, unsigned char val)
Insert bits from bits into val and return the resulting value. The nibbles of map determine how the insertion is performed: Let X be the n-th nibble of map
One typical use case for this built-in is adjusting input and output values to non-contiguous port layouts. Some examples:
// same as val, bits is unused
__builtin_avr_insert_bits (0xffffffff, bits, val)
// same as bits, val is unused
__builtin_avr_insert_bits (0x76543210, bits, val)
// same as rotating bits by 4
__builtin_avr_insert_bits (0x32107654, bits, 0)
// high nibble of result is the high nibble of val
// low nibble of result is the low nibble of bits
__builtin_avr_insert_bits (0xffff3210, bits, val)
// reverse the bit order of bits
__builtin_avr_insert_bits (0x01234567, bits, 0)
:: _blackfin-built-in-functions:
Currently, there are two Blackfin-specific built-in functions. These are used for generating CSYNC and SSYNC machine insns without using inline assembly; by using these built-in functions the compiler can automatically add workarounds for hardware errata involving these instructions. These functions are named as follows:
void __builtin_bfin_csync (void)
void __builtin_bfin_ssync (void)
:: _fr-v-built-in-functions:
GCC provides many FR-V-specific built-in functions. In general, these functions are intended to be compatible with those described by FR-V Family, Softune C/C++ Compiler Manual (V6), Fujitsu Semiconductor. The two exceptions are __MDUNPACKH and __MBTOHE, the GCC forms of which pass 128-bit values by pointer rather than by value.
Most of the functions are named after specific FR-V instructions. Such functions are said to be directly mapped and are summarized here in tabular form.
:: _argument-types:
The arguments to the built-in functions can be divided into three groups: register numbers, compile-time constants and run-time values. In order to make this classification clear at a glance, the arguments and return values are given the following pseudo types:
Pseudo type Real C type Constant? Description uh unsigned short No an unsigned halfword uw1 unsigned int No an unsigned word sw1 int No a signed word uw2 unsigned long long No an unsigned doubleword sw2 long long No a signed doubleword const int Yes an integer constant acc int Yes an ACC register number iacc int Yes an IACC register number
These pseudo types are not defined by GCC, they are simply a notational convenience used in this manual.
Arguments of type uh, uw1, sw1, uw2 and sw2 are evaluated at run time. They correspond to register operands in the underlying FR-V instructions.
const arguments represent immediate operands in the underlying FR-V instructions. They must be compile-time constants.
acc arguments are evaluated at compile time and specify the number of an accumulator register. For example, an acc argument of 2 selects the ACC2 register.
iacc arguments are similar to acc arguments but specify the number of an IACC register. See Other Built-in Functions for more details.
:: _directly-mapped-integer-functions:
The functions listed below map directly to FR-V I-type instructions.
Function prototype Example usage Assembly output sw1 __ADDSS (sw1, sw1) ``c = __ADDSS (a, b)`` ADDSS ``a,``b``,``c```` sw1 __SCAN (sw1, sw1) ``c = __SCAN (a, b)`` SCAN ``a,``b``,``c```` sw1 __SCUTSS (sw1) ``b = __SCUTSS (a)`` SCUTSS ``a,``b```` sw1 __SLASS (sw1, sw1) ``c = __SLASS (a, b)`` SLASS ``a,``b``,``c```` void __SMASS (sw1, sw1) __SMASS (``a, b)`` SMASS ``a,``b```` void __SMSSS (sw1, sw1) __SMSSS (``a, b)`` SMSSS ``a,``b```` void __SMU (sw1, sw1) __SMU (``a, b)`` SMU ``a,``b```` sw2 __SMUL (sw1, sw1) ``c = __SMUL (a, b)`` SMUL ``a,``b``,``c```` sw1 __SUBSS (sw1, sw1) ``c = __SUBSS (a, b)`` SUBSS ``a,``b``,``c```` uw2 __UMUL (uw1, uw1) ``c = __UMUL (a, b)`` UMUL ``a,``b``,``c````
:: _directly-mapped-media-functions:
The functions listed below map directly to FR-V M-type instructions.
Function prototype Example usage Assembly output uw1 __MABSHS (sw1) ``b = __MABSHS (a)`` MABSHS ``a,``b```` void __MADDACCS (acc, acc) __MADDACCS (``b, a)`` MADDACCS ``a,``b```` sw1 __MADDHSS (sw1, sw1) ``c = __MADDHSS (a, b)`` MADDHSS ``a,``b``,``c```` uw1 __MADDHUS (uw1, uw1) ``c = __MADDHUS (a, b)`` MADDHUS ``a,``b``,``c```` uw1 __MAND (uw1, uw1) ``c = __MAND (a, b)`` MAND ``a,``b``,``c```` void __MASACCS (acc, acc) __MASACCS (``b, a)`` MASACCS ``a,``b```` uw1 __MAVEH (uw1, uw1) ``c = __MAVEH (a, b)`` MAVEH ``a,``b``,``c```` uw2 __MBTOH (uw1) ``b = __MBTOH (a)`` MBTOH ``a,``b```` void __MBTOHE (uw1 *, uw1) __MBTOHE (&``b, a)`` MBTOHE ``a,``b```` void __MCLRACC (acc) __MCLRACC (``a)`` MCLRACC ``a`` void __MCLRACCA (void) __MCLRACCA () MCLRACCA uw1 __Mcop1 (uw1, uw1) ``c = __Mcop1 (a, b)`` Mcop1 ``a,``b``,``c```` uw1 __Mcop2 (uw1, uw1) ``c = __Mcop2 (a, b)`` Mcop2 ``a,``b``,``c```` uw1 __MCPLHI (uw2, const) ``c = __MCPLHI (a, b)`` MCPLHI ``a,#``b``,``c```` uw1 __MCPLI (uw2, const) ``c = __MCPLI (a, b)`` MCPLI ``a,#``b``,``c```` void __MCPXIS (acc, sw1, sw1) __MCPXIS (``c, a, b)`` MCPXIS ``a,``b``,``c```` void __MCPXIU (acc, uw1, uw1) __MCPXIU (``c, a, b)`` MCPXIU ``a,``b``,``c```` void __MCPXRS (acc, sw1, sw1) __MCPXRS (``c, a, b)`` MCPXRS ``a,``b``,``c```` void __MCPXRU (acc, uw1, uw1) __MCPXRU (``c, a, b)`` MCPXRU ``a,``b``,``c```` uw1 __MCUT (acc, uw1) ``c = __MCUT (a, b)`` MCUT ``a,``b``,``c```` uw1 __MCUTSS (acc, sw1) ``c = __MCUTSS (a, b)`` MCUTSS ``a,``b``,``c```` void __MDADDACCS (acc, acc) __MDADDACCS (``b, a)`` MDADDACCS ``a,``b```` void __MDASACCS (acc, acc) __MDASACCS (``b, a)`` MDASACCS ``a,``b```` uw2 __MDCUTSSI (acc, const) ``c = __MDCUTSSI (a, b)`` MDCUTSSI ``a,#``b``,``c```` uw2 __MDPACKH (uw2, uw2) ``c = __MDPACKH (a, b)`` MDPACKH ``a,``b``,``c```` uw2 __MDROTLI (uw2, const) ``c = __MDROTLI (a, b)`` MDROTLI ``a,#``b``,``c```` void __MDSUBACCS (acc, acc) __MDSUBACCS (``b, a)`` MDSUBACCS ``a,``b```` void __MDUNPACKH (uw1 *, uw2) __MDUNPACKH (&``b, a)`` MDUNPACKH ``a,``b```` uw2 __MEXPDHD (uw1, const) ``c = __MEXPDHD (a, b)`` MEXPDHD ``a,#``b``,``c```` uw1 __MEXPDHW (uw1, const) ``c = __MEXPDHW (a, b)`` MEXPDHW ``a,#``b``,``c```` uw1 __MHDSETH (uw1, const) ``c = __MHDSETH (a, b)`` MHDSETH ``a,#``b``,``c```` sw1 __MHDSETS (const) ``b = __MHDSETS (a)`` MHDSETS #``a,``b```` uw1 __MHSETHIH (uw1, const) ``b = __MHSETHIH (b, a)`` MHSETHIH #``a,``b```` sw1 __MHSETHIS (sw1, const) ``b = __MHSETHIS (b, a)`` MHSETHIS #``a,``b```` uw1 __MHSETLOH (uw1, const) ``b = __MHSETLOH (b, a)`` MHSETLOH #``a,``b```` sw1 __MHSETLOS (sw1, const) ``b = __MHSETLOS (b, a)`` MHSETLOS #``a,``b```` uw1 __MHTOB (uw2) ``b = __MHTOB (a)`` MHTOB ``a,``b```` void __MMACHS (acc, sw1, sw1) __MMACHS (``c, a, b)`` MMACHS ``a,``b``,``c```` void __MMACHU (acc, uw1, uw1) __MMACHU (``c, a, b)`` MMACHU ``a,``b``,``c```` void __MMRDHS (acc, sw1, sw1) __MMRDHS (``c, a, b)`` MMRDHS ``a,``b``,``c```` void __MMRDHU (acc, uw1, uw1) __MMRDHU (``c, a, b)`` MMRDHU ``a,``b``,``c```` void __MMULHS (acc, sw1, sw1) __MMULHS (``c, a, b)`` MMULHS ``a,``b``,``c```` void __MMULHU (acc, uw1, uw1) __MMULHU (``c, a, b)`` MMULHU ``a,``b``,``c```` void __MMULXHS (acc, sw1, sw1) __MMULXHS (``c, a, b)`` MMULXHS ``a,``b``,``c```` void __MMULXHU (acc, uw1, uw1) __MMULXHU (``c, a, b)`` MMULXHU ``a,``b``,``c```` uw1 __MNOT (uw1) ``b = __MNOT (a)`` MNOT ``a,``b```` uw1 __MOR (uw1, uw1) ``c = __MOR (a, b)`` MOR ``a,``b``,``c```` uw1 __MPACKH (uh, uh) ``c = __MPACKH (a, b)`` MPACKH ``a,``b``,``c```` sw2 __MQADDHSS (sw2, sw2) ``c = __MQADDHSS (a, b)`` MQADDHSS ``a,``b``,``c```` uw2 __MQADDHUS (uw2, uw2) ``c = __MQADDHUS (a, b)`` MQADDHUS ``a,``b``,``c```` void __MQCPXIS (acc, sw2, sw2) __MQCPXIS (``c, a, b)`` MQCPXIS ``a,``b``,``c```` void __MQCPXIU (acc, uw2, uw2) __MQCPXIU (``c, a, b)`` MQCPXIU ``a,``b``,``c```` void __MQCPXRS (acc, sw2, sw2) __MQCPXRS (``c, a, b)`` MQCPXRS ``a,``b``,``c```` void __MQCPXRU (acc, uw2, uw2) __MQCPXRU (``c, a, b)`` MQCPXRU ``a,``b``,``c```` sw2 __MQLCLRHS (sw2, sw2) ``c = __MQLCLRHS (a, b)`` MQLCLRHS ``a,``b``,``c```` sw2 __MQLMTHS (sw2, sw2) ``c = __MQLMTHS (a, b)`` MQLMTHS ``a,``b``,``c```` void __MQMACHS (acc, sw2, sw2) __MQMACHS (``c, a, b)`` MQMACHS ``a,``b``,``c```` void __MQMACHU (acc, uw2, uw2) __MQMACHU (``c, a, b)`` MQMACHU ``a,``b``,``c```` void __MQMACXHS (acc, sw2, sw2) __MQMACXHS (``c, a, b)`` MQMACXHS ``a,``b``,``c```` void __MQMULHS (acc, sw2, sw2) __MQMULHS (``c, a, b)`` MQMULHS ``a,``b``,``c```` void __MQMULHU (acc, uw2, uw2) __MQMULHU (``c, a, b)`` MQMULHU ``a,``b``,``c```` void __MQMULXHS (acc, sw2, sw2) __MQMULXHS (``c, a, b)`` MQMULXHS ``a,``b``,``c```` void __MQMULXHU (acc, uw2, uw2) __MQMULXHU (``c, a, b)`` MQMULXHU ``a,``b``,``c```` sw2 __MQSATHS (sw2, sw2) ``c = __MQSATHS (a, b)`` MQSATHS ``a,``b``,``c```` uw2 __MQSLLHI (uw2, int) ``c = __MQSLLHI (a, b)`` MQSLLHI ``a,``b``,``c```` sw2 __MQSRAHI (sw2, int) ``c = __MQSRAHI (a, b)`` MQSRAHI ``a,``b``,``c```` sw2 __MQSUBHSS (sw2, sw2) ``c = __MQSUBHSS (a, b)`` MQSUBHSS ``a,``b``,``c```` uw2 __MQSUBHUS (uw2, uw2) ``c = __MQSUBHUS (a, b)`` MQSUBHUS ``a,``b``,``c```` void __MQXMACHS (acc, sw2, sw2) __MQXMACHS (``c, a, b)`` MQXMACHS ``a,``b``,``c```` void __MQXMACXHS (acc, sw2, sw2) __MQXMACXHS (``c, a, b)`` MQXMACXHS ``a,``b``,``c```` uw1 __MRDACC (acc) ``b = __MRDACC (a)`` MRDACC ``a,``b```` uw1 __MRDACCG (acc) ``b = __MRDACCG (a)`` MRDACCG ``a,``b```` uw1 __MROTLI (uw1, const) ``c = __MROTLI (a, b)`` MROTLI ``a,#``b``,``c```` uw1 __MROTRI (uw1, const) ``c = __MROTRI (a, b)`` MROTRI ``a,#``b``,``c```` sw1 __MSATHS (sw1, sw1) ``c = __MSATHS (a, b)`` MSATHS ``a,``b``,``c```` uw1 __MSATHU (uw1, uw1) ``c = __MSATHU (a, b)`` MSATHU ``a,``b``,``c```` uw1 __MSLLHI (uw1, const) ``c = __MSLLHI (a, b)`` MSLLHI ``a,#``b``,``c```` sw1 __MSRAHI (sw1, const) ``c = __MSRAHI (a, b)`` MSRAHI ``a,#``b``,``c```` uw1 __MSRLHI (uw1, const) ``c = __MSRLHI (a, b)`` MSRLHI ``a,#``b``,``c```` void __MSUBACCS (acc, acc) __MSUBACCS (``b, a)`` MSUBACCS ``a,``b```` sw1 __MSUBHSS (sw1, sw1) ``c = __MSUBHSS (a, b)`` MSUBHSS ``a,``b``,``c```` uw1 __MSUBHUS (uw1, uw1) ``c = __MSUBHUS (a, b)`` MSUBHUS ``a,``b``,``c```` void __MTRAP (void) __MTRAP () MTRAP uw2 __MUNPACKH (uw1) ``b = __MUNPACKH (a)`` MUNPACKH ``a,``b```` uw1 __MWCUT (uw2, uw1) ``c = __MWCUT (a, b)`` MWCUT ``a,``b``,``c```` void __MWTACC (acc, uw1) __MWTACC (``b, a)`` MWTACC ``a,``b```` void __MWTACCG (acc, uw1) __MWTACCG (``b, a)`` MWTACCG ``a,``b```` uw1 __MXOR (uw1, uw1) ``c = __MXOR (a, b)`` MXOR ``a,``b``,``c````
:: _raw-read/write-functions:
This sections describes built-in functions related to read and write instructions to access memory. These functions generate membar instructions to flush the I/O load and stores where appropriate, as described in Fujitsus manual described above.
unsigned char __builtin_read8 (void *data) unsigned short __builtin_read16 (void *data) unsigned long __builtin_read32 (void *data) unsigned long long __builtin_read64 (void *data)
void __builtin_write8 (void *data, unsigned char datum) void __builtin_write16 (void *data, unsigned short datum) void __builtin_write32 (void *data, unsigned long datum) void __builtin_write64 (void *data, unsigned long long datum)
:: _other-built-in-functions:
This section describes built-in functions that are not named after a specific FR-V instruction.
sw2 __IACCreadll (iacc reg) Return the full 64-bit value of IACC0 The reg argument is reserved for future expansion and must be 0.
sw1 __IACCreadl (iacc reg) Return the value of IACC0H if reg is 0 and IACC0L if reg is 1. Other values of reg are rejected as invalid.
void __IACCsetll (iacc reg, sw2 x) Set the full 64-bit value of IACC0 to x. The reg argument is reserved for future expansion and must be 0.
void __IACCsetl (iacc reg, sw1 x) Set IACC0H to x if reg is 0 and IACC0L to x if reg is 1. Other values of reg are rejected as invalid.
void __data_prefetch0 (const void *x) Use the dcpl instruction to load the contents of address x into the data cache.
void __data_prefetch (const void *x) Use the nldub instruction to load the contents of address x into the data cache. The instruction is issued in slot I1
:: _mips-dsp-built-in-functions:
The MIPS DSP Application-Specific Extension (ASE) includes new instructions that are designed to improve the performance of DSP and media applications. It provides instructions that operate on packed 8-bit/16-bit integer data, Q7, Q15 and Q31 fractional data.
GCC supports MIPS DSP operations using both the generic vector extensions (Vector Extensions) and a collection of MIPS-specific built-in functions. Both kinds of support are enabled by the -mdsp command-line option.
Revision 2 of the ASE was introduced in the second half of 2006. This revision adds extra instructions to the original ASE, but is otherwise backwards-compatible with it. You can select revision 2 using the command-line option -mdspr2; this option implies -mdsp.
The SCOUNT and POS bits of the DSP control register are global. The WRDSP, EXTPDP, EXTPDPV and MTHLIP instructions modify the SCOUNT and POS bits. During optimization, the compiler does not delete these instructions and it does not delete calls to functions containing these instructions.
At present, GCC only provides support for operations on 32-bit vectors. The vector type associated with 8-bit integer data is usually called v4i8, the vector type associated with Q7 is usually called v4q7, the vector type associated with 16-bit integer data is usually called v2i16, and the vector type associated with Q15 is usually called v2q15. They can be defined in C as follows:
typedef signed char v4i8 __attribute__ ((vector_size(4)));
typedef signed char v4q7 __attribute__ ((vector_size(4)));
typedef short v2i16 __attribute__ ((vector_size(4)));
typedef short v2q15 __attribute__ ((vector_size(4)));
v4i8, v4q7, v2i16 and v2q15 values are initialized in the same way as aggregates. For example:
v4i8 a = {1, 2, 3, 4};
v4i8 b;
b = (v4i8) {5, 6, 7, 8};
v2q15 c = {0x0fcb, 0x3a75};
v2q15 d;
d = (v2q15) {0.1234 * 0x1.0p15, 0.4567 * 0x1.0p15};
Note: The CPUs endianness determines the order in which values are packed. On little-endian targets, the first value is the least significant and the last value is the most significant. The opposite order applies to big-endian targets. For example, the code above sets the lowest byte of a to 1 on little-endian targets and 4 on big-endian targets.
Note: Q7, Q15 and Q31 values must be initialized with their integer representation. As shown in this example, the integer representation of a Q7 value can be obtained by multiplying the fractional value by 0x1.0p7. The equivalent for Q15 values is to multiply by 0x1.0p15. The equivalent for Q31 values is to multiply by 0x1.0p31.
The table below lists the v4i8 and v2q15 operations for which hardware support exists. a and b are v4i8 values, and c and d are v2q15 values.
C code MIPS instruction a + b addu.qb c + d addq.ph a - b subu.qb c - d subq.ph
The table below lists the v2i16 operation for which hardware support exists for the DSP ASE REV 2. e and f are v2i16 values.
C code MIPS instruction e * f mul.ph
It is easier to describe the DSP built-in functions if we first define the following types:
typedef int q31;
typedef int i32;
typedef unsigned int ui32;
typedef long long a64;
q31 and i32 are actually the same as int, but we use q31 to indicate a Q31 fractional value and i32 to indicate a 32-bit integer value. Similarly, a64 is the same as long long, but we use a64 to indicate values that are placed in one of the four DSP accumulators ($ac0, $ac1, $ac2 or $ac3).
Also, some built-in functions prefer or require immediate numbers as parameters, because the corresponding DSP instructions accept both immediate numbers and register operands, or accept immediate numbers only. The immediate parameters are listed as follows.
imm0_3: 0 to 3.
imm0_7: 0 to 7.
imm0_15: 0 to 15.
imm0_31: 0 to 31.
imm0_63: 0 to 63.
imm0_255: 0 to 255.
imm_n32_31: -32 to 31.
imm_n512_511: -512 to 511.
The following built-in functions map directly to a particular MIPS DSP instruction. Please refer to the architecture specification for details on what each instruction does.
v2q15 __builtin_mips_addq_ph (v2q15, v2q15)
v2q15 __builtin_mips_addq_s_ph (v2q15, v2q15)
q31 __builtin_mips_addq_s_w (q31, q31)
v4i8 __builtin_mips_addu_qb (v4i8, v4i8)
v4i8 __builtin_mips_addu_s_qb (v4i8, v4i8)
v2q15 __builtin_mips_subq_ph (v2q15, v2q15)
v2q15 __builtin_mips_subq_s_ph (v2q15, v2q15)
q31 __builtin_mips_subq_s_w (q31, q31)
v4i8 __builtin_mips_subu_qb (v4i8, v4i8)
v4i8 __builtin_mips_subu_s_qb (v4i8, v4i8)
i32 __builtin_mips_addsc (i32, i32)
i32 __builtin_mips_addwc (i32, i32)
i32 __builtin_mips_modsub (i32, i32)
i32 __builtin_mips_raddu_w_qb (v4i8)
v2q15 __builtin_mips_absq_s_ph (v2q15)
q31 __builtin_mips_absq_s_w (q31)
v4i8 __builtin_mips_precrq_qb_ph (v2q15, v2q15)
v2q15 __builtin_mips_precrq_ph_w (q31, q31)
v2q15 __builtin_mips_precrq_rs_ph_w (q31, q31)
v4i8 __builtin_mips_precrqu_s_qb_ph (v2q15, v2q15)
q31 __builtin_mips_preceq_w_phl (v2q15)
q31 __builtin_mips_preceq_w_phr (v2q15)
v2q15 __builtin_mips_precequ_ph_qbl (v4i8)
v2q15 __builtin_mips_precequ_ph_qbr (v4i8)
v2q15 __builtin_mips_precequ_ph_qbla (v4i8)
v2q15 __builtin_mips_precequ_ph_qbra (v4i8)
v2q15 __builtin_mips_preceu_ph_qbl (v4i8)
v2q15 __builtin_mips_preceu_ph_qbr (v4i8)
v2q15 __builtin_mips_preceu_ph_qbla (v4i8)
v2q15 __builtin_mips_preceu_ph_qbra (v4i8)
v4i8 __builtin_mips_shll_qb (v4i8, imm0_7)
v4i8 __builtin_mips_shll_qb (v4i8, i32)
v2q15 __builtin_mips_shll_ph (v2q15, imm0_15)
v2q15 __builtin_mips_shll_ph (v2q15, i32)
v2q15 __builtin_mips_shll_s_ph (v2q15, imm0_15)
v2q15 __builtin_mips_shll_s_ph (v2q15, i32)
q31 __builtin_mips_shll_s_w (q31, imm0_31)
q31 __builtin_mips_shll_s_w (q31, i32)
v4i8 __builtin_mips_shrl_qb (v4i8, imm0_7)
v4i8 __builtin_mips_shrl_qb (v4i8, i32)
v2q15 __builtin_mips_shra_ph (v2q15, imm0_15)
v2q15 __builtin_mips_shra_ph (v2q15, i32)
v2q15 __builtin_mips_shra_r_ph (v2q15, imm0_15)
v2q15 __builtin_mips_shra_r_ph (v2q15, i32)
q31 __builtin_mips_shra_r_w (q31, imm0_31)
q31 __builtin_mips_shra_r_w (q31, i32)
v2q15 __builtin_mips_muleu_s_ph_qbl (v4i8, v2q15)
v2q15 __builtin_mips_muleu_s_ph_qbr (v4i8, v2q15)
v2q15 __builtin_mips_mulq_rs_ph (v2q15, v2q15)
q31 __builtin_mips_muleq_s_w_phl (v2q15, v2q15)
q31 __builtin_mips_muleq_s_w_phr (v2q15, v2q15)
a64 __builtin_mips_dpau_h_qbl (a64, v4i8, v4i8)
a64 __builtin_mips_dpau_h_qbr (a64, v4i8, v4i8)
a64 __builtin_mips_dpsu_h_qbl (a64, v4i8, v4i8)
a64 __builtin_mips_dpsu_h_qbr (a64, v4i8, v4i8)
a64 __builtin_mips_dpaq_s_w_ph (a64, v2q15, v2q15)
a64 __builtin_mips_dpaq_sa_l_w (a64, q31, q31)
a64 __builtin_mips_dpsq_s_w_ph (a64, v2q15, v2q15)
a64 __builtin_mips_dpsq_sa_l_w (a64, q31, q31)
a64 __builtin_mips_mulsaq_s_w_ph (a64, v2q15, v2q15)
a64 __builtin_mips_maq_s_w_phl (a64, v2q15, v2q15)
a64 __builtin_mips_maq_s_w_phr (a64, v2q15, v2q15)
a64 __builtin_mips_maq_sa_w_phl (a64, v2q15, v2q15)
a64 __builtin_mips_maq_sa_w_phr (a64, v2q15, v2q15)
i32 __builtin_mips_bitrev (i32)
i32 __builtin_mips_insv (i32, i32)
v4i8 __builtin_mips_repl_qb (imm0_255)
v4i8 __builtin_mips_repl_qb (i32)
v2q15 __builtin_mips_repl_ph (imm_n512_511)
v2q15 __builtin_mips_repl_ph (i32)
void __builtin_mips_cmpu_eq_qb (v4i8, v4i8)
void __builtin_mips_cmpu_lt_qb (v4i8, v4i8)
void __builtin_mips_cmpu_le_qb (v4i8, v4i8)
i32 __builtin_mips_cmpgu_eq_qb (v4i8, v4i8)
i32 __builtin_mips_cmpgu_lt_qb (v4i8, v4i8)
i32 __builtin_mips_cmpgu_le_qb (v4i8, v4i8)
void __builtin_mips_cmp_eq_ph (v2q15, v2q15)
void __builtin_mips_cmp_lt_ph (v2q15, v2q15)
void __builtin_mips_cmp_le_ph (v2q15, v2q15)
v4i8 __builtin_mips_pick_qb (v4i8, v4i8)
v2q15 __builtin_mips_pick_ph (v2q15, v2q15)
v2q15 __builtin_mips_packrl_ph (v2q15, v2q15)
i32 __builtin_mips_extr_w (a64, imm0_31)
i32 __builtin_mips_extr_w (a64, i32)
i32 __builtin_mips_extr_r_w (a64, imm0_31)
i32 __builtin_mips_extr_s_h (a64, i32)
i32 __builtin_mips_extr_rs_w (a64, imm0_31)
i32 __builtin_mips_extr_rs_w (a64, i32)
i32 __builtin_mips_extr_s_h (a64, imm0_31)
i32 __builtin_mips_extr_r_w (a64, i32)
i32 __builtin_mips_extp (a64, imm0_31)
i32 __builtin_mips_extp (a64, i32)
i32 __builtin_mips_extpdp (a64, imm0_31)
i32 __builtin_mips_extpdp (a64, i32)
a64 __builtin_mips_shilo (a64, imm_n32_31)
a64 __builtin_mips_shilo (a64, i32)
a64 __builtin_mips_mthlip (a64, i32)
void __builtin_mips_wrdsp (i32, imm0_63)
i32 __builtin_mips_rddsp (imm0_63)
i32 __builtin_mips_lbux (void *, i32)
i32 __builtin_mips_lhx (void *, i32)
i32 __builtin_mips_lwx (void *, i32)
a64 __builtin_mips_ldx (void *, i32) [MIPS64 only]
i32 __builtin_mips_bposge32 (void)
a64 __builtin_mips_madd (a64, i32, i32);
a64 __builtin_mips_maddu (a64, ui32, ui32);
a64 __builtin_mips_msub (a64, i32, i32);
a64 __builtin_mips_msubu (a64, ui32, ui32);
a64 __builtin_mips_mult (i32, i32);
a64 __builtin_mips_multu (ui32, ui32);
The following built-in functions map directly to a particular MIPS DSP REV 2 instruction. Please refer to the architecture specification for details on what each instruction does.
v4q7 __builtin_mips_absq_s_qb (v4q7);
v2i16 __builtin_mips_addu_ph (v2i16, v2i16);
v2i16 __builtin_mips_addu_s_ph (v2i16, v2i16);
v4i8 __builtin_mips_adduh_qb (v4i8, v4i8);
v4i8 __builtin_mips_adduh_r_qb (v4i8, v4i8);
i32 __builtin_mips_append (i32, i32, imm0_31);
i32 __builtin_mips_balign (i32, i32, imm0_3);
i32 __builtin_mips_cmpgdu_eq_qb (v4i8, v4i8);
i32 __builtin_mips_cmpgdu_lt_qb (v4i8, v4i8);
i32 __builtin_mips_cmpgdu_le_qb (v4i8, v4i8);
a64 __builtin_mips_dpa_w_ph (a64, v2i16, v2i16);
a64 __builtin_mips_dps_w_ph (a64, v2i16, v2i16);
v2i16 __builtin_mips_mul_ph (v2i16, v2i16);
v2i16 __builtin_mips_mul_s_ph (v2i16, v2i16);
q31 __builtin_mips_mulq_rs_w (q31, q31);
v2q15 __builtin_mips_mulq_s_ph (v2q15, v2q15);
q31 __builtin_mips_mulq_s_w (q31, q31);
a64 __builtin_mips_mulsa_w_ph (a64, v2i16, v2i16);
v4i8 __builtin_mips_precr_qb_ph (v2i16, v2i16);
v2i16 __builtin_mips_precr_sra_ph_w (i32, i32, imm0_31);
v2i16 __builtin_mips_precr_sra_r_ph_w (i32, i32, imm0_31);
i32 __builtin_mips_prepend (i32, i32, imm0_31);
v4i8 __builtin_mips_shra_qb (v4i8, imm0_7);
v4i8 __builtin_mips_shra_r_qb (v4i8, imm0_7);
v4i8 __builtin_mips_shra_qb (v4i8, i32);
v4i8 __builtin_mips_shra_r_qb (v4i8, i32);
v2i16 __builtin_mips_shrl_ph (v2i16, imm0_15);
v2i16 __builtin_mips_shrl_ph (v2i16, i32);
v2i16 __builtin_mips_subu_ph (v2i16, v2i16);
v2i16 __builtin_mips_subu_s_ph (v2i16, v2i16);
v4i8 __builtin_mips_subuh_qb (v4i8, v4i8);
v4i8 __builtin_mips_subuh_r_qb (v4i8, v4i8);
v2q15 __builtin_mips_addqh_ph (v2q15, v2q15);
v2q15 __builtin_mips_addqh_r_ph (v2q15, v2q15);
q31 __builtin_mips_addqh_w (q31, q31);
q31 __builtin_mips_addqh_r_w (q31, q31);
v2q15 __builtin_mips_subqh_ph (v2q15, v2q15);
v2q15 __builtin_mips_subqh_r_ph (v2q15, v2q15);
q31 __builtin_mips_subqh_w (q31, q31);
q31 __builtin_mips_subqh_r_w (q31, q31);
a64 __builtin_mips_dpax_w_ph (a64, v2i16, v2i16);
a64 __builtin_mips_dpsx_w_ph (a64, v2i16, v2i16);
a64 __builtin_mips_dpaqx_s_w_ph (a64, v2q15, v2q15);
a64 __builtin_mips_dpaqx_sa_w_ph (a64, v2q15, v2q15);
a64 __builtin_mips_dpsqx_s_w_ph (a64, v2q15, v2q15);
a64 __builtin_mips_dpsqx_sa_w_ph (a64, v2q15, v2q15);
:: _mips-paired-single-support:
The MIPS64 architecture includes a number of instructions that operate on pairs of single-precision floating-point values. Each pair is packed into a 64-bit floating-point register, with one element being designated the upper half and the other being designated the lower half.
GCC supports paired-single operations using both the generic vector extensions (Vector Extensions) and a collection of MIPS-specific built-in functions. Both kinds of support are enabled by the -mpaired-single command-line option.
The vector type associated with paired-single values is usually called v2sf. It can be defined in C as follows:
typedef float v2sf __attribute__ ((vector_size (8)));
v2sf values are initialized in the same way as aggregates. For example:
v2sf a = {1.5, 9.1};
v2sf b;
float e, f;
b = (v2sf) {e, f};
Note: The CPUs endianness determines which value is stored in the upper half of a register and which value is stored in the lower half. On little-endian targets, the first value is the lower one and the second value is the upper one. The opposite order applies to big-endian targets. For example, the code above sets the lower half of a to 1.5 on little-endian targets and 9.1 on big-endian targets.
:: _mips-loongson-built-in-functions:
GCC provides intrinsics to access the SIMD instructions provided by the ST Microelectronics Loongson-2E and -2F processors. These intrinsics, available after inclusion of the loongson.h header file, operate on the following 64-bit vector types:
The intrinsics provided are listed below; each is named after the machine instruction to which it corresponds, with suffixes added as appropriate to distinguish intrinsics that expand to the same machine instruction yet have different argument types. Refer to the architecture documentation for a description of the functionality of each instruction.
int16x4_t packsswh (int32x2_t s, int32x2_t t);
int8x8_t packsshb (int16x4_t s, int16x4_t t);
uint8x8_t packushb (uint16x4_t s, uint16x4_t t);
uint32x2_t paddw_u (uint32x2_t s, uint32x2_t t);
uint16x4_t paddh_u (uint16x4_t s, uint16x4_t t);
uint8x8_t paddb_u (uint8x8_t s, uint8x8_t t);
int32x2_t paddw_s (int32x2_t s, int32x2_t t);
int16x4_t paddh_s (int16x4_t s, int16x4_t t);
int8x8_t paddb_s (int8x8_t s, int8x8_t t);
uint64_t paddd_u (uint64_t s, uint64_t t);
int64_t paddd_s (int64_t s, int64_t t);
int16x4_t paddsh (int16x4_t s, int16x4_t t);
int8x8_t paddsb (int8x8_t s, int8x8_t t);
uint16x4_t paddush (uint16x4_t s, uint16x4_t t);
uint8x8_t paddusb (uint8x8_t s, uint8x8_t t);
uint64_t pandn_ud (uint64_t s, uint64_t t);
uint32x2_t pandn_uw (uint32x2_t s, uint32x2_t t);
uint16x4_t pandn_uh (uint16x4_t s, uint16x4_t t);
uint8x8_t pandn_ub (uint8x8_t s, uint8x8_t t);
int64_t pandn_sd (int64_t s, int64_t t);
int32x2_t pandn_sw (int32x2_t s, int32x2_t t);
int16x4_t pandn_sh (int16x4_t s, int16x4_t t);
int8x8_t pandn_sb (int8x8_t s, int8x8_t t);
uint16x4_t pavgh (uint16x4_t s, uint16x4_t t);
uint8x8_t pavgb (uint8x8_t s, uint8x8_t t);
uint32x2_t pcmpeqw_u (uint32x2_t s, uint32x2_t t);
uint16x4_t pcmpeqh_u (uint16x4_t s, uint16x4_t t);
uint8x8_t pcmpeqb_u (uint8x8_t s, uint8x8_t t);
int32x2_t pcmpeqw_s (int32x2_t s, int32x2_t t);
int16x4_t pcmpeqh_s (int16x4_t s, int16x4_t t);
int8x8_t pcmpeqb_s (int8x8_t s, int8x8_t t);
uint32x2_t pcmpgtw_u (uint32x2_t s, uint32x2_t t);
uint16x4_t pcmpgth_u (uint16x4_t s, uint16x4_t t);
uint8x8_t pcmpgtb_u (uint8x8_t s, uint8x8_t t);
int32x2_t pcmpgtw_s (int32x2_t s, int32x2_t t);
int16x4_t pcmpgth_s (int16x4_t s, int16x4_t t);
int8x8_t pcmpgtb_s (int8x8_t s, int8x8_t t);
uint16x4_t pextrh_u (uint16x4_t s, int field);
int16x4_t pextrh_s (int16x4_t s, int field);
uint16x4_t pinsrh_0_u (uint16x4_t s, uint16x4_t t);
uint16x4_t pinsrh_1_u (uint16x4_t s, uint16x4_t t);
uint16x4_t pinsrh_2_u (uint16x4_t s, uint16x4_t t);
uint16x4_t pinsrh_3_u (uint16x4_t s, uint16x4_t t);
int16x4_t pinsrh_0_s (int16x4_t s, int16x4_t t);
int16x4_t pinsrh_1_s (int16x4_t s, int16x4_t t);
int16x4_t pinsrh_2_s (int16x4_t s, int16x4_t t);
int16x4_t pinsrh_3_s (int16x4_t s, int16x4_t t);
int32x2_t pmaddhw (int16x4_t s, int16x4_t t);
int16x4_t pmaxsh (int16x4_t s, int16x4_t t);
uint8x8_t pmaxub (uint8x8_t s, uint8x8_t t);
int16x4_t pminsh (int16x4_t s, int16x4_t t);
uint8x8_t pminub (uint8x8_t s, uint8x8_t t);
uint8x8_t pmovmskb_u (uint8x8_t s);
int8x8_t pmovmskb_s (int8x8_t s);
uint16x4_t pmulhuh (uint16x4_t s, uint16x4_t t);
int16x4_t pmulhh (int16x4_t s, int16x4_t t);
int16x4_t pmullh (int16x4_t s, int16x4_t t);
int64_t pmuluw (uint32x2_t s, uint32x2_t t);
uint8x8_t pasubub (uint8x8_t s, uint8x8_t t);
uint16x4_t biadd (uint8x8_t s);
uint16x4_t psadbh (uint8x8_t s, uint8x8_t t);
uint16x4_t pshufh_u (uint16x4_t dest, uint16x4_t s, uint8_t order);
int16x4_t pshufh_s (int16x4_t dest, int16x4_t s, uint8_t order);
uint16x4_t psllh_u (uint16x4_t s, uint8_t amount);
int16x4_t psllh_s (int16x4_t s, uint8_t amount);
uint32x2_t psllw_u (uint32x2_t s, uint8_t amount);
int32x2_t psllw_s (int32x2_t s, uint8_t amount);
uint16x4_t psrlh_u (uint16x4_t s, uint8_t amount);
int16x4_t psrlh_s (int16x4_t s, uint8_t amount);
uint32x2_t psrlw_u (uint32x2_t s, uint8_t amount);
int32x2_t psrlw_s (int32x2_t s, uint8_t amount);
uint16x4_t psrah_u (uint16x4_t s, uint8_t amount);
int16x4_t psrah_s (int16x4_t s, uint8_t amount);
uint32x2_t psraw_u (uint32x2_t s, uint8_t amount);
int32x2_t psraw_s (int32x2_t s, uint8_t amount);
uint32x2_t psubw_u (uint32x2_t s, uint32x2_t t);
uint16x4_t psubh_u (uint16x4_t s, uint16x4_t t);
uint8x8_t psubb_u (uint8x8_t s, uint8x8_t t);
int32x2_t psubw_s (int32x2_t s, int32x2_t t);
int16x4_t psubh_s (int16x4_t s, int16x4_t t);
int8x8_t psubb_s (int8x8_t s, int8x8_t t);
uint64_t psubd_u (uint64_t s, uint64_t t);
int64_t psubd_s (int64_t s, int64_t t);
int16x4_t psubsh (int16x4_t s, int16x4_t t);
int8x8_t psubsb (int8x8_t s, int8x8_t t);
uint16x4_t psubush (uint16x4_t s, uint16x4_t t);
uint8x8_t psubusb (uint8x8_t s, uint8x8_t t);
uint32x2_t punpckhwd_u (uint32x2_t s, uint32x2_t t);
uint16x4_t punpckhhw_u (uint16x4_t s, uint16x4_t t);
uint8x8_t punpckhbh_u (uint8x8_t s, uint8x8_t t);
int32x2_t punpckhwd_s (int32x2_t s, int32x2_t t);
int16x4_t punpckhhw_s (int16x4_t s, int16x4_t t);
int8x8_t punpckhbh_s (int8x8_t s, int8x8_t t);
uint32x2_t punpcklwd_u (uint32x2_t s, uint32x2_t t);
uint16x4_t punpcklhw_u (uint16x4_t s, uint16x4_t t);
uint8x8_t punpcklbh_u (uint8x8_t s, uint8x8_t t);
int32x2_t punpcklwd_s (int32x2_t s, int32x2_t t);
int16x4_t punpcklhw_s (int16x4_t s, int16x4_t t);
int8x8_t punpcklbh_s (int8x8_t s, int8x8_t t);
:: _paired-single-arithmetic:
The table below lists the v2sf operations for which hardware support exists. a, b and c are v2sf values and x is an integral value.
C code MIPS instruction a + b add.ps a - b sub.ps -a neg.ps a * b mul.ps a * b + c madd.ps a * b - c msub.ps -(a * b + c) nmadd.ps -(a * b - c) nmsub.ps x ? a : b movn.ps/movz.ps
Note that the multiply-accumulate instructions can be disabled using the command-line option -mno-fused-madd.
:: _paired-single-built-in-functions:
The following paired-single functions map directly to a particular MIPS instruction. Please refer to the architecture specification for details on what each instruction does.
Pair lower lower (pll.ps).
Pair upper lower (pul.ps).
Pair lower upper (plu.ps).
Pair upper upper (puu.ps).
Convert pair to paired single (cvt.ps.s).
Convert pair lower to single (cvt.s.pl).
Convert pair upper to single (cvt.s.pu).
Absolute value (abs.ps).
Align variable (alnv.ps).
Note: The value of the third parameter must be 0 or 4 modulo 8, otherwise the result is unpredictable. Please read the instruction description for details.
The following multi-instruction functions are also available. In each case, cond can be any of the 16 floating-point conditions: f, un, eq, ueq, olt, ult, ole, ule, sf, ngle, seq, ngl, lt, nge, le or ngt.
v2sf __builtin_mips_movt_c_``cond``_ps (v2sf a, v2sf b, v2sf c, v2sf d) v2sf __builtin_mips_movf_c_``cond``_ps (v2sf a, v2sf b, v2sf c, v2sf d) Conditional move based on floating-point comparison (c.``cond.ps``, movt.ps/movf.ps).
The movt functions return the value x computed by:
c.``cond``.ps ``cc``,``a``,``b``
mov.ps ``x``,``c``
movt.ps ``x``,``d``,``cc``
The movf functions are similar but use movf.ps instead of movt.ps.
int __builtin_mips_upper_c_``cond``_ps (v2sf a, v2sf b) int __builtin_mips_lower_c_``cond``_ps (v2sf a, v2sf b) Comparison of two paired-single values (c.``cond.ps``, bc1t/bc1f).
These functions compare a and b using c.``cond.ps`` and return either the upper or lower half of the result. For example:
v2sf a, b;
if (__builtin_mips_upper_c_eq_ps (a, b))
upper_halves_are_equal ();
else
upper_halves_are_unequal ();
if (__builtin_mips_lower_c_eq_ps (a, b))
lower_halves_are_equal ();
else
lower_halves_are_unequal ();
:: _mips-3d-built-in-functions:
The MIPS-3D Application-Specific Extension (ASE) includes additional paired-single instructions that are designed to improve the performance of 3D graphics operations. Support for these instructions is controlled by the -mips3d command-line option.
The functions listed below map directly to a particular MIPS-3D instruction. Please refer to the architecture specification for more details on what each instruction does.
Reduction add (addr.ps).
Reduction multiply (mulr.ps).
Convert paired single to paired word (cvt.pw.ps).
Convert paired word to paired single (cvt.ps.pw).
Reduced-precision reciprocal (sequence step 1) (recip1.``fmt``).
Reduced-precision reciprocal (sequence step 2) (recip2.``fmt``).
Reduced-precision reciprocal square root (sequence step 1) (rsqrt1.``fmt``).
Reduced-precision reciprocal square root (sequence step 2) (rsqrt2.``fmt``).
The following multi-instruction functions are also available. In each case, cond can be any of the 16 floating-point conditions: f, un, eq, ueq, olt, ult, ole, ule, sf, ngle, seq, ngl, lt, nge, le or ngt.
int __builtin_mips_cabs_``cond``_s (float a, float b) int __builtin_mips_cabs_``cond``_d (double a, double b) Absolute comparison of two scalar values (cabs.``cond.``fmt````, bc1t/bc1f).
These functions compare a and b using cabs.``cond.s`` or cabs.``cond.d`` and return the result as a boolean value. For example:
float a, b;
if (__builtin_mips_cabs_eq_s (a, b))
true ();
else
false ();
int __builtin_mips_upper_cabs_``cond``_ps (v2sf a, v2sf b) int __builtin_mips_lower_cabs_``cond``_ps (v2sf a, v2sf b) Absolute comparison of two paired-single values (cabs.``cond.ps``, bc1t/bc1f).
These functions compare a and b using cabs.``cond.ps`` and return either the upper or lower half of the result. For example:
v2sf a, b;
if (__builtin_mips_upper_cabs_eq_ps (a, b))
upper_halves_are_equal ();
else
upper_halves_are_unequal ();
if (__builtin_mips_lower_cabs_eq_ps (a, b))
lower_halves_are_equal ();
else
lower_halves_are_unequal ();
v2sf __builtin_mips_movt_cabs_``cond``_ps (v2sf a, v2sf b, v2sf c, v2sf d) v2sf __builtin_mips_movf_cabs_``cond``_ps (v2sf a, v2sf b, v2sf c, v2sf d) Conditional move based on absolute comparison (cabs.``cond.ps``, movt.ps/movf.ps).
The movt functions return the value x computed by:
cabs.``cond``.ps ``cc``,``a``,``b``
mov.ps ``x``,``c``
movt.ps ``x``,``d``,``cc``
The movf functions are similar but use movf.ps instead of movt.ps.
int __builtin_mips_any_c_``cond``_ps (v2sf a, v2sf b) int __builtin_mips_all_c_``cond``_ps (v2sf a, v2sf b) int __builtin_mips_any_cabs_``cond``_ps (v2sf a, v2sf b) int __builtin_mips_all_cabs_``cond``_ps (v2sf a, v2sf b) Comparison of two paired-single values (c.``cond.ps``/cabs.``cond.ps``, bc1any2t/bc1any2f).
These functions compare a and b using c.``cond.ps`` or cabs.``cond.ps``. The any forms return true if either result is true and the all forms return true if both results are true. For example:
v2sf a, b;
if (__builtin_mips_any_c_eq_ps (a, b))
one_is_true ();
else
both_are_false ();
if (__builtin_mips_all_c_eq_ps (a, b))
both_are_true ();
else
one_is_false ();
int __builtin_mips_any_c_``cond``_4s (v2sf a, v2sf b, v2sf c, v2sf d) int __builtin_mips_all_c_``cond``_4s (v2sf a, v2sf b, v2sf c, v2sf d) int __builtin_mips_any_cabs_``cond``_4s (v2sf a, v2sf b, v2sf c, v2sf d) int __builtin_mips_all_cabs_``cond``_4s (v2sf a, v2sf b, v2sf c, v2sf d) Comparison of four paired-single values (c.``cond.ps``/cabs.``cond.ps``, bc1any4t/bc1any4f).
These functions use c.``cond.ps`` or cabs.``cond.ps`` to compare a with b and to compare c with d. The any forms return true if any of the four results are true and the all forms return true if all four results are true. For example:
v2sf a, b, c, d;
if (__builtin_mips_any_c_eq_4s (a, b, c, d))
some_are_true ();
else
all_are_false ();
if (__builtin_mips_all_c_eq_4s (a, b, c, d))
all_are_true ();
else
some_are_false ();
:: _other-mips-built-in-functions:
GCC provides other MIPS-specific built-in functions:
void __builtin_mips_cache (int op, const volatile void *addr) Insert a cache instruction with operands op and addr. GCC defines the preprocessor macro ___GCC_HAVE_BUILTIN_MIPS_CACHE when this function is available.
Get and set the contents of the floating-point control and status register (FPU control register 31). These functions are only available in hard-float code but can be called in both MIPS16 and non-MIPS16 contexts.
__builtin_mips_set_fcsr can be used to change any bit of the register except the condition codes, which GCC assumes are preserved.
:: _msp430-built-in-functions:
GCC provides a couple of special builtin functions to aid in the writing of interrupt handlers in C.
__bic_SR_register_on_exit (int mask) This clears the indicated bits in the saved copy of the status register currently residing on the stack. This only works inside interrupt handlers and the changes to the status register will only take affect once the handler returns.
__bis_SR_register_on_exit (int mask) This sets the indicated bits in the saved copy of the status register currently residing on the stack. This only works inside interrupt handlers and the changes to the status register will only take affect once the handler returns.
__delay_cycles (long long cycles) This inserts an instruction sequence that takes exactly cycles cycles (between 0 and about 17E9) to complete. The inserted sequence may use jumps, loops, or no-ops, and does not interfere with any other instructions. Note that cycles must be a compile-time constant integer - that is, you must pass a number, not a variable that may be optimized to a constant later. The number of cycles delayed by this builtin is exact.
:: _nds32-built-in-functions:
These built-in functions are available for the NDS32 target:
Insert an ISYNC instruction into the instruction stream where addr is an instruction address for serialization.
Insert an ISB instruction into the instruction stream.
Return the content of a system register which is mapped by sr.
Return the content of a user space register which is mapped by usr.
Move the value to a system register which is mapped by sr.
Move the value to a user space register which is mapped by usr.
Enable global interrupt.
Disable global interrupt.
:: _picochip-built-in-functions:
GCC provides an interface to selected machine instructions from the picoChip instruction set.
int __builtin_sbc (int value) Sign bit count. Return the number of consecutive bits in value that have the same value as the sign bit. The result is the number of leading sign bits minus one, giving the number of redundant sign bits in value.
int __builtin_byteswap (int value) Byte swap. Return the result of swapping the upper and lower bytes of value.
int __builtin_brev (int value) Bit reversal. Return the result of reversing the bits in value. Bit 15 is swapped with bit 0, bit 14 is swapped with bit 1, and so on.
int __builtin_adds (int x, int y) Saturating addition. Return the result of adding x and y, storing the value 32767 if the result overflows.
int __builtin_subs (int x, int y) Saturating subtraction. Return the result of subtracting y from x, storing the value 32768 if the result overflows.
Halt. The processor stops execution. This built-in is useful for implementing assertions.
:: _powerpc-built-in-functions:
These built-in functions are available for the PowerPC family of processors:
float __builtin_recipdivf (float, float);
float __builtin_rsqrtf (float);
double __builtin_recipdiv (double, double);
double __builtin_rsqrt (double);
uint64_t __builtin_ppc_get_timebase ();
unsigned long __builtin_ppc_mftb ();
double __builtin_unpack_longdouble (long double, int);
long double __builtin_pack_longdouble (double, double);
The vec_rsqrt, __builtin_rsqrt, and __builtin_rsqrtf functions generate multiple instructions to implement the reciprocal sqrt functionality using reciprocal sqrt estimate instructions.
The __builtin_recipdiv, and __builtin_recipdivf functions generate multiple instructions to implement division using the reciprocal estimate instructions.
The __builtin_ppc_get_timebase and __builtin_ppc_mftb functions generate instructions to read the Time Base Register. The __builtin_ppc_get_timebase function may generate multiple instructions and always returns the 64 bits of the Time Base Register. The __builtin_ppc_mftb function always generates one instruction and returns the Time Base Register value as an unsigned long, throwing away the most significant word on 32-bit environments.
The following built-in functions are available for the PowerPC family of processors, starting with ISA 2.06 or later (-mcpu=power7 or -mpopcntd):
long __builtin_bpermd (long, long);
int __builtin_divwe (int, int);
int __builtin_divweo (int, int);
unsigned int __builtin_divweu (unsigned int, unsigned int);
unsigned int __builtin_divweuo (unsigned int, unsigned int);
long __builtin_divde (long, long);
long __builtin_divdeo (long, long);
unsigned long __builtin_divdeu (unsigned long, unsigned long);
unsigned long __builtin_divdeuo (unsigned long, unsigned long);
unsigned int cdtbcd (unsigned int);
unsigned int cbcdtd (unsigned int);
unsigned int addg6s (unsigned int, unsigned int);
The __builtin_divde, __builtin_divdeo, __builtin_divdeu, __builtin_divdeou functions require a 64-bit environment support ISA 2.06 or later.
The following built-in functions are available for the PowerPC family of processors when hardware decimal floating point (-mhard-dfp) is available:
_Decimal64 __builtin_dxex (_Decimal64);
_Decimal128 __builtin_dxexq (_Decimal128);
_Decimal64 __builtin_ddedpd (int, _Decimal64);
_Decimal128 __builtin_ddedpdq (int, _Decimal128);
_Decimal64 __builtin_denbcd (int, _Decimal64);
_Decimal128 __builtin_denbcdq (int, _Decimal128);
_Decimal64 __builtin_diex (_Decimal64, _Decimal64);
_Decimal128 _builtin_diexq (_Decimal128, _Decimal128);
_Decimal64 __builtin_dscli (_Decimal64, int);
_Decimal128 __builtin_dscliq (_Decimal128, int);
_Decimal64 __builtin_dscri (_Decimal64, int);
_Decimal128 __builtin_dscriq (_Decimal128, int);
unsigned long long __builtin_unpack_dec128 (_Decimal128, int);
_Decimal128 __builtin_pack_dec128 (unsigned long long, unsigned long long);
The following built-in functions are available for the PowerPC family of processors when the Vector Scalar (vsx) instruction set is available:
unsigned long long __builtin_unpack_vector_int128 (vector __int128_t, int);
vector __int128_t __builtin_pack_vector_int128 (unsigned long long,
unsigned long long);
:: _powerpc-altivec/vsx-built-in-functions:
GCC provides an interface for the PowerPC family of processors to access the AltiVec operations described in Motorolas AltiVec Programming Interface Manual. The interface is made available by including <altivec.h> and using -maltivec and -mabi=altivec. The interface supports the following vector types.
vector unsigned char
vector signed char
vector bool char
vector unsigned short
vector signed short
vector bool short
vector pixel
vector unsigned int
vector signed int
vector bool int
vector float
If -mvsx is used the following additional vector types are implemented.
vector unsigned long
vector signed long
vector double
The long types are only implemented for 64-bit code generation, and the long type is only used in the floating point/integer conversion instructions.
GCCs implementation of the high-level language interface available from C and C++ code differs from Motorolas documentation in several ways.
A vector constant is a list of constant expressions within curly braces.
A vector initializer requires no cast if the vector constant is of the same type as the variable it is initializing.
If signed or unsigned is omitted, the signedness of the vector type is the default signedness of the base type. The default varies depending on the operating system, so a portable program should always specify the signedness.
Compiling with -maltivec adds keywords __vector, vector, __pixel, pixel, __bool and bool. When compiling ISO C, the context-sensitive substitution of the keywords vector, pixel and bool is disabled. To use them, you must include <altivec.h> instead.
GCC allows using a typedef name as the type specifier for a vector type.
For C, overloaded functions are implemented with macros so the following does not work:
vec_add ((vector signed int){1, 2, 3, 4}, foo);
Since vec_add is a macro, the vector constant in the example is treated as four separate arguments. Wrap the entire argument in parentheses for this to work.
Note: Only the <altivec.h> interface is supported. Internally, GCC uses built-in functions to achieve the functionality in the aforementioned header file, but they are not supported and are subject to change without notice.
The following interfaces are supported for the generic and specific AltiVec operations and the AltiVec predicates. In cases where there is a direct mapping between generic and specific operations, only the generic names are shown here, although the specific operations can also be used.
Arguments that are documented as const int require literal integral values within the range required for that operation.
vector signed char vec_abs (vector signed char);
vector signed short vec_abs (vector signed short);
vector signed int vec_abs (vector signed int);
vector float vec_abs (vector float);
vector signed char vec_abss (vector signed char);
vector signed short vec_abss (vector signed short);
vector signed int vec_abss (vector signed int);
vector signed char vec_add (vector bool char, vector signed char);
vector signed char vec_add (vector signed char, vector bool char);
vector signed char vec_add (vector signed char, vector signed char);
vector unsigned char vec_add (vector bool char, vector unsigned char);
vector unsigned char vec_add (vector unsigned char, vector bool char);
vector unsigned char vec_add (vector unsigned char,
vector unsigned char);
vector signed short vec_add (vector bool short, vector signed short);
vector signed short vec_add (vector signed short, vector bool short);
vector signed short vec_add (vector signed short, vector signed short);
vector unsigned short vec_add (vector bool short,
vector unsigned short);
vector unsigned short vec_add (vector unsigned short,
vector bool short);
vector unsigned short vec_add (vector unsigned short,
vector unsigned short);
vector signed int vec_add (vector bool int, vector signed int);
vector signed int vec_add (vector signed int, vector bool int);
vector signed int vec_add (vector signed int, vector signed int);
vector unsigned int vec_add (vector bool int, vector unsigned int);
vector unsigned int vec_add (vector unsigned int, vector bool int);
vector unsigned int vec_add (vector unsigned int, vector unsigned int);
vector float vec_add (vector float, vector float);
vector float vec_vaddfp (vector float, vector float);
vector signed int vec_vadduwm (vector bool int, vector signed int);
vector signed int vec_vadduwm (vector signed int, vector bool int);
vector signed int vec_vadduwm (vector signed int, vector signed int);
vector unsigned int vec_vadduwm (vector bool int, vector unsigned int);
vector unsigned int vec_vadduwm (vector unsigned int, vector bool int);
vector unsigned int vec_vadduwm (vector unsigned int,
vector unsigned int);
vector signed short vec_vadduhm (vector bool short,
vector signed short);
vector signed short vec_vadduhm (vector signed short,
vector bool short);
vector signed short vec_vadduhm (vector signed short,
vector signed short);
vector unsigned short vec_vadduhm (vector bool short,
vector unsigned short);
vector unsigned short vec_vadduhm (vector unsigned short,
vector bool short);
vector unsigned short vec_vadduhm (vector unsigned short,
vector unsigned short);
vector signed char vec_vaddubm (vector bool char, vector signed char);
vector signed char vec_vaddubm (vector signed char, vector bool char);
vector signed char vec_vaddubm (vector signed char, vector signed char);
vector unsigned char vec_vaddubm (vector bool char,
vector unsigned char);
vector unsigned char vec_vaddubm (vector unsigned char,
vector bool char);
vector unsigned char vec_vaddubm (vector unsigned char,
vector unsigned char);
vector unsigned int vec_addc (vector unsigned int, vector unsigned int);
vector unsigned char vec_adds (vector bool char, vector unsigned char);
vector unsigned char vec_adds (vector unsigned char, vector bool char);
vector unsigned char vec_adds (vector unsigned char,
vector unsigned char);
vector signed char vec_adds (vector bool char, vector signed char);
vector signed char vec_adds (vector signed char, vector bool char);
vector signed char vec_adds (vector signed char, vector signed char);
vector unsigned short vec_adds (vector bool short,
vector unsigned short);
vector unsigned short vec_adds (vector unsigned short,
vector bool short);
vector unsigned short vec_adds (vector unsigned short,
vector unsigned short);
vector signed short vec_adds (vector bool short, vector signed short);
vector signed short vec_adds (vector signed short, vector bool short);
vector signed short vec_adds (vector signed short, vector signed short);
vector unsigned int vec_adds (vector bool int, vector unsigned int);
vector unsigned int vec_adds (vector unsigned int, vector bool int);
vector unsigned int vec_adds (vector unsigned int, vector unsigned int);
vector signed int vec_adds (vector bool int, vector signed int);
vector signed int vec_adds (vector signed int, vector bool int);
vector signed int vec_adds (vector signed int, vector signed int);
vector signed int vec_vaddsws (vector bool int, vector signed int);
vector signed int vec_vaddsws (vector signed int, vector bool int);
vector signed int vec_vaddsws (vector signed int, vector signed int);
vector unsigned int vec_vadduws (vector bool int, vector unsigned int);
vector unsigned int vec_vadduws (vector unsigned int, vector bool int);
vector unsigned int vec_vadduws (vector unsigned int,
vector unsigned int);
vector signed short vec_vaddshs (vector bool short,
vector signed short);
vector signed short vec_vaddshs (vector signed short,
vector bool short);
vector signed short vec_vaddshs (vector signed short,
vector signed short);
vector unsigned short vec_vadduhs (vector bool short,
vector unsigned short);
vector unsigned short vec_vadduhs (vector unsigned short,
vector bool short);
vector unsigned short vec_vadduhs (vector unsigned short,
vector unsigned short);
vector signed char vec_vaddsbs (vector bool char, vector signed char);
vector signed char vec_vaddsbs (vector signed char, vector bool char);
vector signed char vec_vaddsbs (vector signed char, vector signed char);
vector unsigned char vec_vaddubs (vector bool char,
vector unsigned char);
vector unsigned char vec_vaddubs (vector unsigned char,
vector bool char);
vector unsigned char vec_vaddubs (vector unsigned char,
vector unsigned char);
vector float vec_and (vector float, vector float);
vector float vec_and (vector float, vector bool int);
vector float vec_and (vector bool int, vector float);
vector bool int vec_and (vector bool int, vector bool int);
vector signed int vec_and (vector bool int, vector signed int);
vector signed int vec_and (vector signed int, vector bool int);
vector signed int vec_and (vector signed int, vector signed int);
vector unsigned int vec_and (vector bool int, vector unsigned int);
vector unsigned int vec_and (vector unsigned int, vector bool int);
vector unsigned int vec_and (vector unsigned int, vector unsigned int);
vector bool short vec_and (vector bool short, vector bool short);
vector signed short vec_and (vector bool short, vector signed short);
vector signed short vec_and (vector signed short, vector bool short);
vector signed short vec_and (vector signed short, vector signed short);
vector unsigned short vec_and (vector bool short,
vector unsigned short);
vector unsigned short vec_and (vector unsigned short,
vector bool short);
vector unsigned short vec_and (vector unsigned short,
vector unsigned short);
vector signed char vec_and (vector bool char, vector signed char);
vector bool char vec_and (vector bool char, vector bool char);
vector signed char vec_and (vector signed char, vector bool char);
vector signed char vec_and (vector signed char, vector signed char);
vector unsigned char vec_and (vector bool char, vector unsigned char);
vector unsigned char vec_and (vector unsigned char, vector bool char);
vector unsigned char vec_and (vector unsigned char,
vector unsigned char);
vector float vec_andc (vector float, vector float);
vector float vec_andc (vector float, vector bool int);
vector float vec_andc (vector bool int, vector float);
vector bool int vec_andc (vector bool int, vector bool int);
vector signed int vec_andc (vector bool int, vector signed int);
vector signed int vec_andc (vector signed int, vector bool int);
vector signed int vec_andc (vector signed int, vector signed int);
vector unsigned int vec_andc (vector bool int, vector unsigned int);
vector unsigned int vec_andc (vector unsigned int, vector bool int);
vector unsigned int vec_andc (vector unsigned int, vector unsigned int);
vector bool short vec_andc (vector bool short, vector bool short);
vector signed short vec_andc (vector bool short, vector signed short);
vector signed short vec_andc (vector signed short, vector bool short);
vector signed short vec_andc (vector signed short, vector signed short);
vector unsigned short vec_andc (vector bool short,
vector unsigned short);
vector unsigned short vec_andc (vector unsigned short,
vector bool short);
vector unsigned short vec_andc (vector unsigned short,
vector unsigned short);
vector signed char vec_andc (vector bool char, vector signed char);
vector bool char vec_andc (vector bool char, vector bool char);
vector signed char vec_andc (vector signed char, vector bool char);
vector signed char vec_andc (vector signed char, vector signed char);
vector unsigned char vec_andc (vector bool char, vector unsigned char);
vector unsigned char vec_andc (vector unsigned char, vector bool char);
vector unsigned char vec_andc (vector unsigned char,
vector unsigned char);
vector unsigned char vec_avg (vector unsigned char,
vector unsigned char);
vector signed char vec_avg (vector signed char, vector signed char);
vector unsigned short vec_avg (vector unsigned short,
vector unsigned short);
vector signed short vec_avg (vector signed short, vector signed short);
vector unsigned int vec_avg (vector unsigned int, vector unsigned int);
vector signed int vec_avg (vector signed int, vector signed int);
vector signed int vec_vavgsw (vector signed int, vector signed int);
vector unsigned int vec_vavguw (vector unsigned int,
vector unsigned int);
vector signed short vec_vavgsh (vector signed short,
vector signed short);
vector unsigned short vec_vavguh (vector unsigned short,
vector unsigned short);
vector signed char vec_vavgsb (vector signed char, vector signed char);
vector unsigned char vec_vavgub (vector unsigned char,
vector unsigned char);
vector float vec_copysign (vector float);
vector float vec_ceil (vector float);
vector signed int vec_cmpb (vector float, vector float);
vector bool char vec_cmpeq (vector signed char, vector signed char);
vector bool char vec_cmpeq (vector unsigned char, vector unsigned char);
vector bool short vec_cmpeq (vector signed short, vector signed short);
vector bool short vec_cmpeq (vector unsigned short,
vector unsigned short);
vector bool int vec_cmpeq (vector signed int, vector signed int);
vector bool int vec_cmpeq (vector unsigned int, vector unsigned int);
vector bool int vec_cmpeq (vector float, vector float);
vector bool int vec_vcmpeqfp (vector float, vector float);
vector bool int vec_vcmpequw (vector signed int, vector signed int);
vector bool int vec_vcmpequw (vector unsigned int, vector unsigned int);
vector bool short vec_vcmpequh (vector signed short,
vector signed short);
vector bool short vec_vcmpequh (vector unsigned short,
vector unsigned short);
vector bool char vec_vcmpequb (vector signed char, vector signed char);
vector bool char vec_vcmpequb (vector unsigned char,
vector unsigned char);
vector bool int vec_cmpge (vector float, vector float);
vector bool char vec_cmpgt (vector unsigned char, vector unsigned char);
vector bool char vec_cmpgt (vector signed char, vector signed char);
vector bool short vec_cmpgt (vector unsigned short,
vector unsigned short);
vector bool short vec_cmpgt (vector signed short, vector signed short);
vector bool int vec_cmpgt (vector unsigned int, vector unsigned int);
vector bool int vec_cmpgt (vector signed int, vector signed int);
vector bool int vec_cmpgt (vector float, vector float);
vector bool int vec_vcmpgtfp (vector float, vector float);
vector bool int vec_vcmpgtsw (vector signed int, vector signed int);
vector bool int vec_vcmpgtuw (vector unsigned int, vector unsigned int);
vector bool short vec_vcmpgtsh (vector signed short,
vector signed short);
vector bool short vec_vcmpgtuh (vector unsigned short,
vector unsigned short);
vector bool char vec_vcmpgtsb (vector signed char, vector signed char);
vector bool char vec_vcmpgtub (vector unsigned char,
vector unsigned char);
vector bool int vec_cmple (vector float, vector float);
vector bool char vec_cmplt (vector unsigned char, vector unsigned char);
vector bool char vec_cmplt (vector signed char, vector signed char);
vector bool short vec_cmplt (vector unsigned short,
vector unsigned short);
vector bool short vec_cmplt (vector signed short, vector signed short);
vector bool int vec_cmplt (vector unsigned int, vector unsigned int);
vector bool int vec_cmplt (vector signed int, vector signed int);
vector bool int vec_cmplt (vector float, vector float);
vector float vec_cpsgn (vector float, vector float);
vector float vec_ctf (vector unsigned int, const int);
vector float vec_ctf (vector signed int, const int);
vector double vec_ctf (vector unsigned long, const int);
vector double vec_ctf (vector signed long, const int);
vector float vec_vcfsx (vector signed int, const int);
vector float vec_vcfux (vector unsigned int, const int);
vector signed int vec_cts (vector float, const int);
vector signed long vec_cts (vector double, const int);
vector unsigned int vec_ctu (vector float, const int);
vector unsigned long vec_ctu (vector double, const int);
void vec_dss (const int);
void vec_dssall (void);
void vec_dst (const vector unsigned char *, int, const int);
void vec_dst (const vector signed char *, int, const int);
void vec_dst (const vector bool char *, int, const int);
void vec_dst (const vector unsigned short *, int, const int);
void vec_dst (const vector signed short *, int, const int);
void vec_dst (const vector bool short *, int, const int);
void vec_dst (const vector pixel *, int, const int);
void vec_dst (const vector unsigned int *, int, const int);
void vec_dst (const vector signed int *, int, const int);
void vec_dst (const vector bool int *, int, const int);
void vec_dst (const vector float *, int, const int);
void vec_dst (const unsigned char *, int, const int);
void vec_dst (const signed char *, int, const int);
void vec_dst (const unsigned short *, int, const int);
void vec_dst (const short *, int, const int);
void vec_dst (const unsigned int *, int, const int);
void vec_dst (const int *, int, const int);
void vec_dst (const unsigned long *, int, const int);
void vec_dst (const long *, int, const int);
void vec_dst (const float *, int, const int);
void vec_dstst (const vector unsigned char *, int, const int);
void vec_dstst (const vector signed char *, int, const int);
void vec_dstst (const vector bool char *, int, const int);
void vec_dstst (const vector unsigned short *, int, const int);
void vec_dstst (const vector signed short *, int, const int);
void vec_dstst (const vector bool short *, int, const int);
void vec_dstst (const vector pixel *, int, const int);
void vec_dstst (const vector unsigned int *, int, const int);
void vec_dstst (const vector signed int *, int, const int);
void vec_dstst (const vector bool int *, int, const int);
void vec_dstst (const vector float *, int, const int);
void vec_dstst (const unsigned char *, int, const int);
void vec_dstst (const signed char *, int, const int);
void vec_dstst (const unsigned short *, int, const int);
void vec_dstst (const short *, int, const int);
void vec_dstst (const unsigned int *, int, const int);
void vec_dstst (const int *, int, const int);
void vec_dstst (const unsigned long *, int, const int);
void vec_dstst (const long *, int, const int);
void vec_dstst (const float *, int, const int);
void vec_dststt (const vector unsigned char *, int, const int);
void vec_dststt (const vector signed char *, int, const int);
void vec_dststt (const vector bool char *, int, const int);
void vec_dststt (const vector unsigned short *, int, const int);
void vec_dststt (const vector signed short *, int, const int);
void vec_dststt (const vector bool short *, int, const int);
void vec_dststt (const vector pixel *, int, const int);
void vec_dststt (const vector unsigned int *, int, const int);
void vec_dststt (const vector signed int *, int, const int);
void vec_dststt (const vector bool int *, int, const int);
void vec_dststt (const vector float *, int, const int);
void vec_dststt (const unsigned char *, int, const int);
void vec_dststt (const signed char *, int, const int);
void vec_dststt (const unsigned short *, int, const int);
void vec_dststt (const short *, int, const int);
void vec_dststt (const unsigned int *, int, const int);
void vec_dststt (const int *, int, const int);
void vec_dststt (const unsigned long *, int, const int);
void vec_dststt (const long *, int, const int);
void vec_dststt (const float *, int, const int);
void vec_dstt (const vector unsigned char *, int, const int);
void vec_dstt (const vector signed char *, int, const int);
void vec_dstt (const vector bool char *, int, const int);
void vec_dstt (const vector unsigned short *, int, const int);
void vec_dstt (const vector signed short *, int, const int);
void vec_dstt (const vector bool short *, int, const int);
void vec_dstt (const vector pixel *, int, const int);
void vec_dstt (const vector unsigned int *, int, const int);
void vec_dstt (const vector signed int *, int, const int);
void vec_dstt (const vector bool int *, int, const int);
void vec_dstt (const vector float *, int, const int);
void vec_dstt (const unsigned char *, int, const int);
void vec_dstt (const signed char *, int, const int);
void vec_dstt (const unsigned short *, int, const int);
void vec_dstt (const short *, int, const int);
void vec_dstt (const unsigned int *, int, const int);
void vec_dstt (const int *, int, const int);
void vec_dstt (const unsigned long *, int, const int);
void vec_dstt (const long *, int, const int);
void vec_dstt (const float *, int, const int);
vector float vec_expte (vector float);
vector float vec_floor (vector float);
vector float vec_ld (int, const vector float *);
vector float vec_ld (int, const float *);
vector bool int vec_ld (int, const vector bool int *);
vector signed int vec_ld (int, const vector signed int *);
vector signed int vec_ld (int, const int *);
vector signed int vec_ld (int, const long *);
vector unsigned int vec_ld (int, const vector unsigned int *);
vector unsigned int vec_ld (int, const unsigned int *);
vector unsigned int vec_ld (int, const unsigned long *);
vector bool short vec_ld (int, const vector bool short *);
vector pixel vec_ld (int, const vector pixel *);
vector signed short vec_ld (int, const vector signed short *);
vector signed short vec_ld (int, const short *);
vector unsigned short vec_ld (int, const vector unsigned short *);
vector unsigned short vec_ld (int, const unsigned short *);
vector bool char vec_ld (int, const vector bool char *);
vector signed char vec_ld (int, const vector signed char *);
vector signed char vec_ld (int, const signed char *);
vector unsigned char vec_ld (int, const vector unsigned char *);
vector unsigned char vec_ld (int, const unsigned char *);
vector signed char vec_lde (int, const signed char *);
vector unsigned char vec_lde (int, const unsigned char *);
vector signed short vec_lde (int, const short *);
vector unsigned short vec_lde (int, const unsigned short *);
vector float vec_lde (int, const float *);
vector signed int vec_lde (int, const int *);
vector unsigned int vec_lde (int, const unsigned int *);
vector signed int vec_lde (int, const long *);
vector unsigned int vec_lde (int, const unsigned long *);
vector float vec_lvewx (int, float *);
vector signed int vec_lvewx (int, int *);
vector unsigned int vec_lvewx (int, unsigned int *);
vector signed int vec_lvewx (int, long *);
vector unsigned int vec_lvewx (int, unsigned long *);
vector signed short vec_lvehx (int, short *);
vector unsigned short vec_lvehx (int, unsigned short *);
vector signed char vec_lvebx (int, char *);
vector unsigned char vec_lvebx (int, unsigned char *);
vector float vec_ldl (int, const vector float *);
vector float vec_ldl (int, const float *);
vector bool int vec_ldl (int, const vector bool int *);
vector signed int vec_ldl (int, const vector signed int *);
vector signed int vec_ldl (int, const int *);
vector signed int vec_ldl (int, const long *);
vector unsigned int vec_ldl (int, const vector unsigned int *);
vector unsigned int vec_ldl (int, const unsigned int *);
vector unsigned int vec_ldl (int, const unsigned long *);
vector bool short vec_ldl (int, const vector bool short *);
vector pixel vec_ldl (int, const vector pixel *);
vector signed short vec_ldl (int, const vector signed short *);
vector signed short vec_ldl (int, const short *);
vector unsigned short vec_ldl (int, const vector unsigned short *);
vector unsigned short vec_ldl (int, const unsigned short *);
vector bool char vec_ldl (int, const vector bool char *);
vector signed char vec_ldl (int, const vector signed char *);
vector signed char vec_ldl (int, const signed char *);
vector unsigned char vec_ldl (int, const vector unsigned char *);
vector unsigned char vec_ldl (int, const unsigned char *);
vector float vec_loge (vector float);
vector unsigned char vec_lvsl (int, const volatile unsigned char *);
vector unsigned char vec_lvsl (int, const volatile signed char *);
vector unsigned char vec_lvsl (int, const volatile unsigned short *);
vector unsigned char vec_lvsl (int, const volatile short *);
vector unsigned char vec_lvsl (int, const volatile unsigned int *);
vector unsigned char vec_lvsl (int, const volatile int *);
vector unsigned char vec_lvsl (int, const volatile unsigned long *);
vector unsigned char vec_lvsl (int, const volatile long *);
vector unsigned char vec_lvsl (int, const volatile float *);
vector unsigned char vec_lvsr (int, const volatile unsigned char *);
vector unsigned char vec_lvsr (int, const volatile signed char *);
vector unsigned char vec_lvsr (int, const volatile unsigned short *);
vector unsigned char vec_lvsr (int, const volatile short *);
vector unsigned char vec_lvsr (int, const volatile unsigned int *);
vector unsigned char vec_lvsr (int, const volatile int *);
vector unsigned char vec_lvsr (int, const volatile unsigned long *);
vector unsigned char vec_lvsr (int, const volatile long *);
vector unsigned char vec_lvsr (int, const volatile float *);
vector float vec_madd (vector float, vector float, vector float);
vector signed short vec_madds (vector signed short,
vector signed short,
vector signed short);
vector unsigned char vec_max (vector bool char, vector unsigned char);
vector unsigned char vec_max (vector unsigned char, vector bool char);
vector unsigned char vec_max (vector unsigned char,
vector unsigned char);
vector signed char vec_max (vector bool char, vector signed char);
vector signed char vec_max (vector signed char, vector bool char);
vector signed char vec_max (vector signed char, vector signed char);
vector unsigned short vec_max (vector bool short,
vector unsigned short);
vector unsigned short vec_max (vector unsigned short,
vector bool short);
vector unsigned short vec_max (vector unsigned short,
vector unsigned short);
vector signed short vec_max (vector bool short, vector signed short);
vector signed short vec_max (vector signed short, vector bool short);
vector signed short vec_max (vector signed short, vector signed short);
vector unsigned int vec_max (vector bool int, vector unsigned int);
vector unsigned int vec_max (vector unsigned int, vector bool int);
vector unsigned int vec_max (vector unsigned int, vector unsigned int);
vector signed int vec_max (vector bool int, vector signed int);
vector signed int vec_max (vector signed int, vector bool int);
vector signed int vec_max (vector signed int, vector signed int);
vector float vec_max (vector float, vector float);
vector float vec_vmaxfp (vector float, vector float);
vector signed int vec_vmaxsw (vector bool int, vector signed int);
vector signed int vec_vmaxsw (vector signed int, vector bool int);
vector signed int vec_vmaxsw (vector signed int, vector signed int);
vector unsigned int vec_vmaxuw (vector bool int, vector unsigned int);
vector unsigned int vec_vmaxuw (vector unsigned int, vector bool int);
vector unsigned int vec_vmaxuw (vector unsigned int,
vector unsigned int);
vector signed short vec_vmaxsh (vector bool short, vector signed short);
vector signed short vec_vmaxsh (vector signed short, vector bool short);
vector signed short vec_vmaxsh (vector signed short,
vector signed short);
vector unsigned short vec_vmaxuh (vector bool short,
vector unsigned short);
vector unsigned short vec_vmaxuh (vector unsigned short,
vector bool short);
vector unsigned short vec_vmaxuh (vector unsigned short,
vector unsigned short);
vector signed char vec_vmaxsb (vector bool char, vector signed char);
vector signed char vec_vmaxsb (vector signed char, vector bool char);
vector signed char vec_vmaxsb (vector signed char, vector signed char);
vector unsigned char vec_vmaxub (vector bool char,
vector unsigned char);
vector unsigned char vec_vmaxub (vector unsigned char,
vector bool char);
vector unsigned char vec_vmaxub (vector unsigned char,
vector unsigned char);
vector bool char vec_mergeh (vector bool char, vector bool char);
vector signed char vec_mergeh (vector signed char, vector signed char);
vector unsigned char vec_mergeh (vector unsigned char,
vector unsigned char);
vector bool short vec_mergeh (vector bool short, vector bool short);
vector pixel vec_mergeh (vector pixel, vector pixel);
vector signed short vec_mergeh (vector signed short,
vector signed short);
vector unsigned short vec_mergeh (vector unsigned short,
vector unsigned short);
vector float vec_mergeh (vector float, vector float);
vector bool int vec_mergeh (vector bool int, vector bool int);
vector signed int vec_mergeh (vector signed int, vector signed int);
vector unsigned int vec_mergeh (vector unsigned int,
vector unsigned int);
vector float vec_vmrghw (vector float, vector float);
vector bool int vec_vmrghw (vector bool int, vector bool int);
vector signed int vec_vmrghw (vector signed int, vector signed int);
vector unsigned int vec_vmrghw (vector unsigned int,
vector unsigned int);
vector bool short vec_vmrghh (vector bool short, vector bool short);
vector signed short vec_vmrghh (vector signed short,
vector signed short);
vector unsigned short vec_vmrghh (vector unsigned short,
vector unsigned short);
vector pixel vec_vmrghh (vector pixel, vector pixel);
vector bool char vec_vmrghb (vector bool char, vector bool char);
vector signed char vec_vmrghb (vector signed char, vector signed char);
vector unsigned char vec_vmrghb (vector unsigned char,
vector unsigned char);
vector bool char vec_mergel (vector bool char, vector bool char);
vector signed char vec_mergel (vector signed char, vector signed char);
vector unsigned char vec_mergel (vector unsigned char,
vector unsigned char);
vector bool short vec_mergel (vector bool short, vector bool short);
vector pixel vec_mergel (vector pixel, vector pixel);
vector signed short vec_mergel (vector signed short,
vector signed short);
vector unsigned short vec_mergel (vector unsigned short,
vector unsigned short);
vector float vec_mergel (vector float, vector float);
vector bool int vec_mergel (vector bool int, vector bool int);
vector signed int vec_mergel (vector signed int, vector signed int);
vector unsigned int vec_mergel (vector unsigned int,
vector unsigned int);
vector float vec_vmrglw (vector float, vector float);
vector signed int vec_vmrglw (vector signed int, vector signed int);
vector unsigned int vec_vmrglw (vector unsigned int,
vector unsigned int);
vector bool int vec_vmrglw (vector bool int, vector bool int);
vector bool short vec_vmrglh (vector bool short, vector bool short);
vector signed short vec_vmrglh (vector signed short,
vector signed short);
vector unsigned short vec_vmrglh (vector unsigned short,
vector unsigned short);
vector pixel vec_vmrglh (vector pixel, vector pixel);
vector bool char vec_vmrglb (vector bool char, vector bool char);
vector signed char vec_vmrglb (vector signed char, vector signed char);
vector unsigned char vec_vmrglb (vector unsigned char,
vector unsigned char);
vector unsigned short vec_mfvscr (void);
vector unsigned char vec_min (vector bool char, vector unsigned char);
vector unsigned char vec_min (vector unsigned char, vector bool char);
vector unsigned char vec_min (vector unsigned char,
vector unsigned char);
vector signed char vec_min (vector bool char, vector signed char);
vector signed char vec_min (vector signed char, vector bool char);
vector signed char vec_min (vector signed char, vector signed char);
vector unsigned short vec_min (vector bool short,
vector unsigned short);
vector unsigned short vec_min (vector unsigned short,
vector bool short);
vector unsigned short vec_min (vector unsigned short,
vector unsigned short);
vector signed short vec_min (vector bool short, vector signed short);
vector signed short vec_min (vector signed short, vector bool short);
vector signed short vec_min (vector signed short, vector signed short);
vector unsigned int vec_min (vector bool int, vector unsigned int);
vector unsigned int vec_min (vector unsigned int, vector bool int);
vector unsigned int vec_min (vector unsigned int, vector unsigned int);
vector signed int vec_min (vector bool int, vector signed int);
vector signed int vec_min (vector signed int, vector bool int);
vector signed int vec_min (vector signed int, vector signed int);
vector float vec_min (vector float, vector float);
vector float vec_vminfp (vector float, vector float);
vector signed int vec_vminsw (vector bool int, vector signed int);
vector signed int vec_vminsw (vector signed int, vector bool int);
vector signed int vec_vminsw (vector signed int, vector signed int);
vector unsigned int vec_vminuw (vector bool int, vector unsigned int);
vector unsigned int vec_vminuw (vector unsigned int, vector bool int);
vector unsigned int vec_vminuw (vector unsigned int,
vector unsigned int);
vector signed short vec_vminsh (vector bool short, vector signed short);
vector signed short vec_vminsh (vector signed short, vector bool short);
vector signed short vec_vminsh (vector signed short,
vector signed short);
vector unsigned short vec_vminuh (vector bool short,
vector unsigned short);
vector unsigned short vec_vminuh (vector unsigned short,
vector bool short);
vector unsigned short vec_vminuh (vector unsigned short,
vector unsigned short);
vector signed char vec_vminsb (vector bool char, vector signed char);
vector signed char vec_vminsb (vector signed char, vector bool char);
vector signed char vec_vminsb (vector signed char, vector signed char);
vector unsigned char vec_vminub (vector bool char,
vector unsigned char);
vector unsigned char vec_vminub (vector unsigned char,
vector bool char);
vector unsigned char vec_vminub (vector unsigned char,
vector unsigned char);
vector signed short vec_mladd (vector signed short,
vector signed short,
vector signed short);
vector signed short vec_mladd (vector signed short,
vector unsigned short,
vector unsigned short);
vector signed short vec_mladd (vector unsigned short,
vector signed short,
vector signed short);
vector unsigned short vec_mladd (vector unsigned short,
vector unsigned short,
vector unsigned short);
vector signed short vec_mradds (vector signed short,
vector signed short,
vector signed short);
vector unsigned int vec_msum (vector unsigned char,
vector unsigned char,
vector unsigned int);
vector signed int vec_msum (vector signed char,
vector unsigned char,
vector signed int);
vector unsigned int vec_msum (vector unsigned short,
vector unsigned short,
vector unsigned int);
vector signed int vec_msum (vector signed short,
vector signed short,
vector signed int);
vector signed int vec_vmsumshm (vector signed short,
vector signed short,
vector signed int);
vector unsigned int vec_vmsumuhm (vector unsigned short,
vector unsigned short,
vector unsigned int);
vector signed int vec_vmsummbm (vector signed char,
vector unsigned char,
vector signed int);
vector unsigned int vec_vmsumubm (vector unsigned char,
vector unsigned char,
vector unsigned int);
vector unsigned int vec_msums (vector unsigned short,
vector unsigned short,
vector unsigned int);
vector signed int vec_msums (vector signed short,
vector signed short,
vector signed int);
vector signed int vec_vmsumshs (vector signed short,
vector signed short,
vector signed int);
vector unsigned int vec_vmsumuhs (vector unsigned short,
vector unsigned short,
vector unsigned int);
void vec_mtvscr (vector signed int);
void vec_mtvscr (vector unsigned int);
void vec_mtvscr (vector bool int);
void vec_mtvscr (vector signed short);
void vec_mtvscr (vector unsigned short);
void vec_mtvscr (vector bool short);
void vec_mtvscr (vector pixel);
void vec_mtvscr (vector signed char);
void vec_mtvscr (vector unsigned char);
void vec_mtvscr (vector bool char);
vector unsigned short vec_mule (vector unsigned char,
vector unsigned char);
vector signed short vec_mule (vector signed char,
vector signed char);
vector unsigned int vec_mule (vector unsigned short,
vector unsigned short);
vector signed int vec_mule (vector signed short, vector signed short);
vector signed int vec_vmulesh (vector signed short,
vector signed short);
vector unsigned int vec_vmuleuh (vector unsigned short,
vector unsigned short);
vector signed short vec_vmulesb (vector signed char,
vector signed char);
vector unsigned short vec_vmuleub (vector unsigned char,
vector unsigned char);
vector unsigned short vec_mulo (vector unsigned char,
vector unsigned char);
vector signed short vec_mulo (vector signed char, vector signed char);
vector unsigned int vec_mulo (vector unsigned short,
vector unsigned short);
vector signed int vec_mulo (vector signed short, vector signed short);
vector signed int vec_vmulosh (vector signed short,
vector signed short);
vector unsigned int vec_vmulouh (vector unsigned short,
vector unsigned short);
vector signed short vec_vmulosb (vector signed char,
vector signed char);
vector unsigned short vec_vmuloub (vector unsigned char,
vector unsigned char);
vector float vec_nmsub (vector float, vector float, vector float);
vector float vec_nor (vector float, vector float);
vector signed int vec_nor (vector signed int, vector signed int);
vector unsigned int vec_nor (vector unsigned int, vector unsigned int);
vector bool int vec_nor (vector bool int, vector bool int);
vector signed short vec_nor (vector signed short, vector signed short);
vector unsigned short vec_nor (vector unsigned short,
vector unsigned short);
vector bool short vec_nor (vector bool short, vector bool short);
vector signed char vec_nor (vector signed char, vector signed char);
vector unsigned char vec_nor (vector unsigned char,
vector unsigned char);
vector bool char vec_nor (vector bool char, vector bool char);
vector float vec_or (vector float, vector float);
vector float vec_or (vector float, vector bool int);
vector float vec_or (vector bool int, vector float);
vector bool int vec_or (vector bool int, vector bool int);
vector signed int vec_or (vector bool int, vector signed int);
vector signed int vec_or (vector signed int, vector bool int);
vector signed int vec_or (vector signed int, vector signed int);
vector unsigned int vec_or (vector bool int, vector unsigned int);
vector unsigned int vec_or (vector unsigned int, vector bool int);
vector unsigned int vec_or (vector unsigned int, vector unsigned int);
vector bool short vec_or (vector bool short, vector bool short);
vector signed short vec_or (vector bool short, vector signed short);
vector signed short vec_or (vector signed short, vector bool short);
vector signed short vec_or (vector signed short, vector signed short);
vector unsigned short vec_or (vector bool short, vector unsigned short);
vector unsigned short vec_or (vector unsigned short, vector bool short);
vector unsigned short vec_or (vector unsigned short,
vector unsigned short);
vector signed char vec_or (vector bool char, vector signed char);
vector bool char vec_or (vector bool char, vector bool char);
vector signed char vec_or (vector signed char, vector bool char);
vector signed char vec_or (vector signed char, vector signed char);
vector unsigned char vec_or (vector bool char, vector unsigned char);
vector unsigned char vec_or (vector unsigned char, vector bool char);
vector unsigned char vec_or (vector unsigned char,
vector unsigned char);
vector signed char vec_pack (vector signed short, vector signed short);
vector unsigned char vec_pack (vector unsigned short,
vector unsigned short);
vector bool char vec_pack (vector bool short, vector bool short);
vector signed short vec_pack (vector signed int, vector signed int);
vector unsigned short vec_pack (vector unsigned int,
vector unsigned int);
vector bool short vec_pack (vector bool int, vector bool int);
vector bool short vec_vpkuwum (vector bool int, vector bool int);
vector signed short vec_vpkuwum (vector signed int, vector signed int);
vector unsigned short vec_vpkuwum (vector unsigned int,
vector unsigned int);
vector bool char vec_vpkuhum (vector bool short, vector bool short);
vector signed char vec_vpkuhum (vector signed short,
vector signed short);
vector unsigned char vec_vpkuhum (vector unsigned short,
vector unsigned short);
vector pixel vec_packpx (vector unsigned int, vector unsigned int);
vector unsigned char vec_packs (vector unsigned short,
vector unsigned short);
vector signed char vec_packs (vector signed short, vector signed short);
vector unsigned short vec_packs (vector unsigned int,
vector unsigned int);
vector signed short vec_packs (vector signed int, vector signed int);
vector signed short vec_vpkswss (vector signed int, vector signed int);
vector unsigned short vec_vpkuwus (vector unsigned int,
vector unsigned int);
vector signed char vec_vpkshss (vector signed short,
vector signed short);
vector unsigned char vec_vpkuhus (vector unsigned short,
vector unsigned short);
vector unsigned char vec_packsu (vector unsigned short,
vector unsigned short);
vector unsigned char vec_packsu (vector signed short,
vector signed short);
vector unsigned short vec_packsu (vector unsigned int,
vector unsigned int);
vector unsigned short vec_packsu (vector signed int, vector signed int);
vector unsigned short vec_vpkswus (vector signed int,
vector signed int);
vector unsigned char vec_vpkshus (vector signed short,
vector signed short);
vector float vec_perm (vector float,
vector float,
vector unsigned char);
vector signed int vec_perm (vector signed int,
vector signed int,
vector unsigned char);
vector unsigned int vec_perm (vector unsigned int,
vector unsigned int,
vector unsigned char);
vector bool int vec_perm (vector bool int,
vector bool int,
vector unsigned char);
vector signed short vec_perm (vector signed short,
vector signed short,
vector unsigned char);
vector unsigned short vec_perm (vector unsigned short,
vector unsigned short,
vector unsigned char);
vector bool short vec_perm (vector bool short,
vector bool short,
vector unsigned char);
vector pixel vec_perm (vector pixel,
vector pixel,
vector unsigned char);
vector signed char vec_perm (vector signed char,
vector signed char,
vector unsigned char);
vector unsigned char vec_perm (vector unsigned char,
vector unsigned char,
vector unsigned char);
vector bool char vec_perm (vector bool char,
vector bool char,
vector unsigned char);
vector float vec_re (vector float);
vector signed char vec_rl (vector signed char,
vector unsigned char);
vector unsigned char vec_rl (vector unsigned char,
vector unsigned char);
vector signed short vec_rl (vector signed short, vector unsigned short);
vector unsigned short vec_rl (vector unsigned short,
vector unsigned short);
vector signed int vec_rl (vector signed int, vector unsigned int);
vector unsigned int vec_rl (vector unsigned int, vector unsigned int);
vector signed int vec_vrlw (vector signed int, vector unsigned int);
vector unsigned int vec_vrlw (vector unsigned int, vector unsigned int);
vector signed short vec_vrlh (vector signed short,
vector unsigned short);
vector unsigned short vec_vrlh (vector unsigned short,
vector unsigned short);
vector signed char vec_vrlb (vector signed char, vector unsigned char);
vector unsigned char vec_vrlb (vector unsigned char,
vector unsigned char);
vector float vec_round (vector float);
vector float vec_recip (vector float, vector float);
vector float vec_rsqrt (vector float);
vector float vec_rsqrte (vector float);
vector float vec_sel (vector float, vector float, vector bool int);
vector float vec_sel (vector float, vector float, vector unsigned int);
vector signed int vec_sel (vector signed int,
vector signed int,
vector bool int);
vector signed int vec_sel (vector signed int,
vector signed int,
vector unsigned int);
vector unsigned int vec_sel (vector unsigned int,
vector unsigned int,
vector bool int);
vector unsigned int vec_sel (vector unsigned int,
vector unsigned int,
vector unsigned int);
vector bool int vec_sel (vector bool int,
vector bool int,
vector bool int);
vector bool int vec_sel (vector bool int,
vector bool int,
vector unsigned int);
vector signed short vec_sel (vector signed short,
vector signed short,
vector bool short);
vector signed short vec_sel (vector signed short,
vector signed short,
vector unsigned short);
vector unsigned short vec_sel (vector unsigned short,
vector unsigned short,
vector bool short);
vector unsigned short vec_sel (vector unsigned short,
vector unsigned short,
vector unsigned short);
vector bool short vec_sel (vector bool short,
vector bool short,
vector bool short);
vector bool short vec_sel (vector bool short,
vector bool short,
vector unsigned short);
vector signed char vec_sel (vector signed char,
vector signed char,
vector bool char);
vector signed char vec_sel (vector signed char,
vector signed char,
vector unsigned char);
vector unsigned char vec_sel (vector unsigned char,
vector unsigned char,
vector bool char);
vector unsigned char vec_sel (vector unsigned char,
vector unsigned char,
vector unsigned char);
vector bool char vec_sel (vector bool char,
vector bool char,
vector bool char);
vector bool char vec_sel (vector bool char,
vector bool char,
vector unsigned char);
vector signed char vec_sl (vector signed char,
vector unsigned char);
vector unsigned char vec_sl (vector unsigned char,
vector unsigned char);
vector signed short vec_sl (vector signed short, vector unsigned short);
vector unsigned short vec_sl (vector unsigned short,
vector unsigned short);
vector signed int vec_sl (vector signed int, vector unsigned int);
vector unsigned int vec_sl (vector unsigned int, vector unsigned int);
vector signed int vec_vslw (vector signed int, vector unsigned int);
vector unsigned int vec_vslw (vector unsigned int, vector unsigned int);
vector signed short vec_vslh (vector signed short,
vector unsigned short);
vector unsigned short vec_vslh (vector unsigned short,
vector unsigned short);
vector signed char vec_vslb (vector signed char, vector unsigned char);
vector unsigned char vec_vslb (vector unsigned char,
vector unsigned char);
vector float vec_sld (vector float, vector float, const int);
vector signed int vec_sld (vector signed int,
vector signed int,
const int);
vector unsigned int vec_sld (vector unsigned int,
vector unsigned int,
const int);
vector bool int vec_sld (vector bool int,
vector bool int,
const int);
vector signed short vec_sld (vector signed short,
vector signed short,
const int);
vector unsigned short vec_sld (vector unsigned short,
vector unsigned short,
const int);
vector bool short vec_sld (vector bool short,
vector bool short,
const int);
vector pixel vec_sld (vector pixel,
vector pixel,
const int);
vector signed char vec_sld (vector signed char,
vector signed char,
const int);
vector unsigned char vec_sld (vector unsigned char,
vector unsigned char,
const int);
vector bool char vec_sld (vector bool char,
vector bool char,
const int);
vector signed int vec_sll (vector signed int,
vector unsigned int);
vector signed int vec_sll (vector signed int,
vector unsigned short);
vector signed int vec_sll (vector signed int,
vector unsigned char);
vector unsigned int vec_sll (vector unsigned int,
vector unsigned int);
vector unsigned int vec_sll (vector unsigned int,
vector unsigned short);
vector unsigned int vec_sll (vector unsigned int,
vector unsigned char);
vector bool int vec_sll (vector bool int,
vector unsigned int);
vector bool int vec_sll (vector bool int,
vector unsigned short);
vector bool int vec_sll (vector bool int,
vector unsigned char);
vector signed short vec_sll (vector signed short,
vector unsigned int);
vector signed short vec_sll (vector signed short,
vector unsigned short);
vector signed short vec_sll (vector signed short,
vector unsigned char);
vector unsigned short vec_sll (vector unsigned short,
vector unsigned int);
vector unsigned short vec_sll (vector unsigned short,
vector unsigned short);
vector unsigned short vec_sll (vector unsigned short,
vector unsigned char);
vector bool short vec_sll (vector bool short, vector unsigned int);
vector bool short vec_sll (vector bool short, vector unsigned short);
vector bool short vec_sll (vector bool short, vector unsigned char);
vector pixel vec_sll (vector pixel, vector unsigned int);
vector pixel vec_sll (vector pixel, vector unsigned short);
vector pixel vec_sll (vector pixel, vector unsigned char);
vector signed char vec_sll (vector signed char, vector unsigned int);
vector signed char vec_sll (vector signed char, vector unsigned short);
vector signed char vec_sll (vector signed char, vector unsigned char);
vector unsigned char vec_sll (vector unsigned char,
vector unsigned int);
vector unsigned char vec_sll (vector unsigned char,
vector unsigned short);
vector unsigned char vec_sll (vector unsigned char,
vector unsigned char);
vector bool char vec_sll (vector bool char, vector unsigned int);
vector bool char vec_sll (vector bool char, vector unsigned short);
vector bool char vec_sll (vector bool char, vector unsigned char);
vector float vec_slo (vector float, vector signed char);
vector float vec_slo (vector float, vector unsigned char);
vector signed int vec_slo (vector signed int, vector signed char);
vector signed int vec_slo (vector signed int, vector unsigned char);
vector unsigned int vec_slo (vector unsigned int, vector signed char);
vector unsigned int vec_slo (vector unsigned int, vector unsigned char);
vector signed short vec_slo (vector signed short, vector signed char);
vector signed short vec_slo (vector signed short, vector unsigned char);
vector unsigned short vec_slo (vector unsigned short,
vector signed char);
vector unsigned short vec_slo (vector unsigned short,
vector unsigned char);
vector pixel vec_slo (vector pixel, vector signed char);
vector pixel vec_slo (vector pixel, vector unsigned char);
vector signed char vec_slo (vector signed char, vector signed char);
vector signed char vec_slo (vector signed char, vector unsigned char);
vector unsigned char vec_slo (vector unsigned char, vector signed char);
vector unsigned char vec_slo (vector unsigned char,
vector unsigned char);
vector signed char vec_splat (vector signed char, const int);
vector unsigned char vec_splat (vector unsigned char, const int);
vector bool char vec_splat (vector bool char, const int);
vector signed short vec_splat (vector signed short, const int);
vector unsigned short vec_splat (vector unsigned short, const int);
vector bool short vec_splat (vector bool short, const int);
vector pixel vec_splat (vector pixel, const int);
vector float vec_splat (vector float, const int);
vector signed int vec_splat (vector signed int, const int);
vector unsigned int vec_splat (vector unsigned int, const int);
vector bool int vec_splat (vector bool int, const int);
vector signed long vec_splat (vector signed long, const int);
vector unsigned long vec_splat (vector unsigned long, const int);
vector signed char vec_splats (signed char);
vector unsigned char vec_splats (unsigned char);
vector signed short vec_splats (signed short);
vector unsigned short vec_splats (unsigned short);
vector signed int vec_splats (signed int);
vector unsigned int vec_splats (unsigned int);
vector float vec_splats (float);
vector float vec_vspltw (vector float, const int);
vector signed int vec_vspltw (vector signed int, const int);
vector unsigned int vec_vspltw (vector unsigned int, const int);
vector bool int vec_vspltw (vector bool int, const int);
vector bool short vec_vsplth (vector bool short, const int);
vector signed short vec_vsplth (vector signed short, const int);
vector unsigned short vec_vsplth (vector unsigned short, const int);
vector pixel vec_vsplth (vector pixel, const int);
vector signed char vec_vspltb (vector signed char, const int);
vector unsigned char vec_vspltb (vector unsigned char, const int);
vector bool char vec_vspltb (vector bool char, const int);
vector signed char vec_splat_s8 (const int);
vector signed short vec_splat_s16 (const int);
vector signed int vec_splat_s32 (const int);
vector unsigned char vec_splat_u8 (const int);
vector unsigned short vec_splat_u16 (const int);
vector unsigned int vec_splat_u32 (const int);
vector signed char vec_sr (vector signed char, vector unsigned char);
vector unsigned char vec_sr (vector unsigned char,
vector unsigned char);
vector signed short vec_sr (vector signed short,
vector unsigned short);
vector unsigned short vec_sr (vector unsigned short,
vector unsigned short);
vector signed int vec_sr (vector signed int, vector unsigned int);
vector unsigned int vec_sr (vector unsigned int, vector unsigned int);
vector signed int vec_vsrw (vector signed int, vector unsigned int);
vector unsigned int vec_vsrw (vector unsigned int, vector unsigned int);
vector signed short vec_vsrh (vector signed short,
vector unsigned short);
vector unsigned short vec_vsrh (vector unsigned short,
vector unsigned short);
vector signed char vec_vsrb (vector signed char, vector unsigned char);
vector unsigned char vec_vsrb (vector unsigned char,
vector unsigned char);
vector signed char vec_sra (vector signed char, vector unsigned char);
vector unsigned char vec_sra (vector unsigned char,
vector unsigned char);
vector signed short vec_sra (vector signed short,
vector unsigned short);
vector unsigned short vec_sra (vector unsigned short,
vector unsigned short);
vector signed int vec_sra (vector signed int, vector unsigned int);
vector unsigned int vec_sra (vector unsigned int, vector unsigned int);
vector signed int vec_vsraw (vector signed int, vector unsigned int);
vector unsigned int vec_vsraw (vector unsigned int,
vector unsigned int);
vector signed short vec_vsrah (vector signed short,
vector unsigned short);
vector unsigned short vec_vsrah (vector unsigned short,
vector unsigned short);
vector signed char vec_vsrab (vector signed char, vector unsigned char);
vector unsigned char vec_vsrab (vector unsigned char,
vector unsigned char);
vector signed int vec_srl (vector signed int, vector unsigned int);
vector signed int vec_srl (vector signed int, vector unsigned short);
vector signed int vec_srl (vector signed int, vector unsigned char);
vector unsigned int vec_srl (vector unsigned int, vector unsigned int);
vector unsigned int vec_srl (vector unsigned int,
vector unsigned short);
vector unsigned int vec_srl (vector unsigned int, vector unsigned char);
vector bool int vec_srl (vector bool int, vector unsigned int);
vector bool int vec_srl (vector bool int, vector unsigned short);
vector bool int vec_srl (vector bool int, vector unsigned char);
vector signed short vec_srl (vector signed short, vector unsigned int);
vector signed short vec_srl (vector signed short,
vector unsigned short);
vector signed short vec_srl (vector signed short, vector unsigned char);
vector unsigned short vec_srl (vector unsigned short,
vector unsigned int);
vector unsigned short vec_srl (vector unsigned short,
vector unsigned short);
vector unsigned short vec_srl (vector unsigned short,
vector unsigned char);
vector bool short vec_srl (vector bool short, vector unsigned int);
vector bool short vec_srl (vector bool short, vector unsigned short);
vector bool short vec_srl (vector bool short, vector unsigned char);
vector pixel vec_srl (vector pixel, vector unsigned int);
vector pixel vec_srl (vector pixel, vector unsigned short);
vector pixel vec_srl (vector pixel, vector unsigned char);
vector signed char vec_srl (vector signed char, vector unsigned int);
vector signed char vec_srl (vector signed char, vector unsigned short);
vector signed char vec_srl (vector signed char, vector unsigned char);
vector unsigned char vec_srl (vector unsigned char,
vector unsigned int);
vector unsigned char vec_srl (vector unsigned char,
vector unsigned short);
vector unsigned char vec_srl (vector unsigned char,
vector unsigned char);
vector bool char vec_srl (vector bool char, vector unsigned int);
vector bool char vec_srl (vector bool char, vector unsigned short);
vector bool char vec_srl (vector bool char, vector unsigned char);
vector float vec_sro (vector float, vector signed char);
vector float vec_sro (vector float, vector unsigned char);
vector signed int vec_sro (vector signed int, vector signed char);
vector signed int vec_sro (vector signed int, vector unsigned char);
vector unsigned int vec_sro (vector unsigned int, vector signed char);
vector unsigned int vec_sro (vector unsigned int, vector unsigned char);
vector signed short vec_sro (vector signed short, vector signed char);
vector signed short vec_sro (vector signed short, vector unsigned char);
vector unsigned short vec_sro (vector unsigned short,
vector signed char);
vector unsigned short vec_sro (vector unsigned short,
vector unsigned char);
vector pixel vec_sro (vector pixel, vector signed char);
vector pixel vec_sro (vector pixel, vector unsigned char);
vector signed char vec_sro (vector signed char, vector signed char);
vector signed char vec_sro (vector signed char, vector unsigned char);
vector unsigned char vec_sro (vector unsigned char, vector signed char);
vector unsigned char vec_sro (vector unsigned char,
vector unsigned char);
void vec_st (vector float, int, vector float *);
void vec_st (vector float, int, float *);
void vec_st (vector signed int, int, vector signed int *);
void vec_st (vector signed int, int, int *);
void vec_st (vector unsigned int, int, vector unsigned int *);
void vec_st (vector unsigned int, int, unsigned int *);
void vec_st (vector bool int, int, vector bool int *);
void vec_st (vector bool int, int, unsigned int *);
void vec_st (vector bool int, int, int *);
void vec_st (vector signed short, int, vector signed short *);
void vec_st (vector signed short, int, short *);
void vec_st (vector unsigned short, int, vector unsigned short *);
void vec_st (vector unsigned short, int, unsigned short *);
void vec_st (vector bool short, int, vector bool short *);
void vec_st (vector bool short, int, unsigned short *);
void vec_st (vector pixel, int, vector pixel *);
void vec_st (vector pixel, int, unsigned short *);
void vec_st (vector pixel, int, short *);
void vec_st (vector bool short, int, short *);
void vec_st (vector signed char, int, vector signed char *);
void vec_st (vector signed char, int, signed char *);
void vec_st (vector unsigned char, int, vector unsigned char *);
void vec_st (vector unsigned char, int, unsigned char *);
void vec_st (vector bool char, int, vector bool char *);
void vec_st (vector bool char, int, unsigned char *);
void vec_st (vector bool char, int, signed char *);
void vec_ste (vector signed char, int, signed char *);
void vec_ste (vector unsigned char, int, unsigned char *);
void vec_ste (vector bool char, int, signed char *);
void vec_ste (vector bool char, int, unsigned char *);
void vec_ste (vector signed short, int, short *);
void vec_ste (vector unsigned short, int, unsigned short *);
void vec_ste (vector bool short, int, short *);
void vec_ste (vector bool short, int, unsigned short *);
void vec_ste (vector pixel, int, short *);
void vec_ste (vector pixel, int, unsigned short *);
void vec_ste (vector float, int, float *);
void vec_ste (vector signed int, int, int *);
void vec_ste (vector unsigned int, int, unsigned int *);
void vec_ste (vector bool int, int, int *);
void vec_ste (vector bool int, int, unsigned int *);
void vec_stvewx (vector float, int, float *);
void vec_stvewx (vector signed int, int, int *);
void vec_stvewx (vector unsigned int, int, unsigned int *);
void vec_stvewx (vector bool int, int, int *);
void vec_stvewx (vector bool int, int, unsigned int *);
void vec_stvehx (vector signed short, int, short *);
void vec_stvehx (vector unsigned short, int, unsigned short *);
void vec_stvehx (vector bool short, int, short *);
void vec_stvehx (vector bool short, int, unsigned short *);
void vec_stvehx (vector pixel, int, short *);
void vec_stvehx (vector pixel, int, unsigned short *);
void vec_stvebx (vector signed char, int, signed char *);
void vec_stvebx (vector unsigned char, int, unsigned char *);
void vec_stvebx (vector bool char, int, signed char *);
void vec_stvebx (vector bool char, int, unsigned char *);
void vec_stl (vector float, int, vector float *);
void vec_stl (vector float, int, float *);
void vec_stl (vector signed int, int, vector signed int *);
void vec_stl (vector signed int, int, int *);
void vec_stl (vector unsigned int, int, vector unsigned int *);
void vec_stl (vector unsigned int, int, unsigned int *);
void vec_stl (vector bool int, int, vector bool int *);
void vec_stl (vector bool int, int, unsigned int *);
void vec_stl (vector bool int, int, int *);
void vec_stl (vector signed short, int, vector signed short *);
void vec_stl (vector signed short, int, short *);
void vec_stl (vector unsigned short, int, vector unsigned short *);
void vec_stl (vector unsigned short, int, unsigned short *);
void vec_stl (vector bool short, int, vector bool short *);
void vec_stl (vector bool short, int, unsigned short *);
void vec_stl (vector bool short, int, short *);
void vec_stl (vector pixel, int, vector pixel *);
void vec_stl (vector pixel, int, unsigned short *);
void vec_stl (vector pixel, int, short *);
void vec_stl (vector signed char, int, vector signed char *);
void vec_stl (vector signed char, int, signed char *);
void vec_stl (vector unsigned char, int, vector unsigned char *);
void vec_stl (vector unsigned char, int, unsigned char *);
void vec_stl (vector bool char, int, vector bool char *);
void vec_stl (vector bool char, int, unsigned char *);
void vec_stl (vector bool char, int, signed char *);
vector signed char vec_sub (vector bool char, vector signed char);
vector signed char vec_sub (vector signed char, vector bool char);
vector signed char vec_sub (vector signed char, vector signed char);
vector unsigned char vec_sub (vector bool char, vector unsigned char);
vector unsigned char vec_sub (vector unsigned char, vector bool char);
vector unsigned char vec_sub (vector unsigned char,
vector unsigned char);
vector signed short vec_sub (vector bool short, vector signed short);
vector signed short vec_sub (vector signed short, vector bool short);
vector signed short vec_sub (vector signed short, vector signed short);
vector unsigned short vec_sub (vector bool short,
vector unsigned short);
vector unsigned short vec_sub (vector unsigned short,
vector bool short);
vector unsigned short vec_sub (vector unsigned short,
vector unsigned short);
vector signed int vec_sub (vector bool int, vector signed int);
vector signed int vec_sub (vector signed int, vector bool int);
vector signed int vec_sub (vector signed int, vector signed int);
vector unsigned int vec_sub (vector bool int, vector unsigned int);
vector unsigned int vec_sub (vector unsigned int, vector bool int);
vector unsigned int vec_sub (vector unsigned int, vector unsigned int);
vector float vec_sub (vector float, vector float);
vector float vec_vsubfp (vector float, vector float);
vector signed int vec_vsubuwm (vector bool int, vector signed int);
vector signed int vec_vsubuwm (vector signed int, vector bool int);
vector signed int vec_vsubuwm (vector signed int, vector signed int);
vector unsigned int vec_vsubuwm (vector bool int, vector unsigned int);
vector unsigned int vec_vsubuwm (vector unsigned int, vector bool int);
vector unsigned int vec_vsubuwm (vector unsigned int,
vector unsigned int);
vector signed short vec_vsubuhm (vector bool short,
vector signed short);
vector signed short vec_vsubuhm (vector signed short,
vector bool short);
vector signed short vec_vsubuhm (vector signed short,
vector signed short);
vector unsigned short vec_vsubuhm (vector bool short,
vector unsigned short);
vector unsigned short vec_vsubuhm (vector unsigned short,
vector bool short);
vector unsigned short vec_vsubuhm (vector unsigned short,
vector unsigned short);
vector signed char vec_vsububm (vector bool char, vector signed char);
vector signed char vec_vsububm (vector signed char, vector bool char);
vector signed char vec_vsububm (vector signed char, vector signed char);
vector unsigned char vec_vsububm (vector bool char,
vector unsigned char);
vector unsigned char vec_vsububm (vector unsigned char,
vector bool char);
vector unsigned char vec_vsububm (vector unsigned char,
vector unsigned char);
vector unsigned int vec_subc (vector unsigned int, vector unsigned int);
vector unsigned char vec_subs (vector bool char, vector unsigned char);
vector unsigned char vec_subs (vector unsigned char, vector bool char);
vector unsigned char vec_subs (vector unsigned char,
vector unsigned char);
vector signed char vec_subs (vector bool char, vector signed char);
vector signed char vec_subs (vector signed char, vector bool char);
vector signed char vec_subs (vector signed char, vector signed char);
vector unsigned short vec_subs (vector bool short,
vector unsigned short);
vector unsigned short vec_subs (vector unsigned short,
vector bool short);
vector unsigned short vec_subs (vector unsigned short,
vector unsigned short);
vector signed short vec_subs (vector bool short, vector signed short);
vector signed short vec_subs (vector signed short, vector bool short);
vector signed short vec_subs (vector signed short, vector signed short);
vector unsigned int vec_subs (vector bool int, vector unsigned int);
vector unsigned int vec_subs (vector unsigned int, vector bool int);
vector unsigned int vec_subs (vector unsigned int, vector unsigned int);
vector signed int vec_subs (vector bool int, vector signed int);
vector signed int vec_subs (vector signed int, vector bool int);
vector signed int vec_subs (vector signed int, vector signed int);
vector signed int vec_vsubsws (vector bool int, vector signed int);
vector signed int vec_vsubsws (vector signed int, vector bool int);
vector signed int vec_vsubsws (vector signed int, vector signed int);
vector unsigned int vec_vsubuws (vector bool int, vector unsigned int);
vector unsigned int vec_vsubuws (vector unsigned int, vector bool int);
vector unsigned int vec_vsubuws (vector unsigned int,
vector unsigned int);
vector signed short vec_vsubshs (vector bool short,
vector signed short);
vector signed short vec_vsubshs (vector signed short,
vector bool short);
vector signed short vec_vsubshs (vector signed short,
vector signed short);
vector unsigned short vec_vsubuhs (vector bool short,
vector unsigned short);
vector unsigned short vec_vsubuhs (vector unsigned short,
vector bool short);
vector unsigned short vec_vsubuhs (vector unsigned short,
vector unsigned short);
vector signed char vec_vsubsbs (vector bool char, vector signed char);
vector signed char vec_vsubsbs (vector signed char, vector bool char);
vector signed char vec_vsubsbs (vector signed char, vector signed char);
vector unsigned char vec_vsububs (vector bool char,
vector unsigned char);
vector unsigned char vec_vsububs (vector unsigned char,
vector bool char);
vector unsigned char vec_vsububs (vector unsigned char,
vector unsigned char);
vector unsigned int vec_sum4s (vector unsigned char,
vector unsigned int);
vector signed int vec_sum4s (vector signed char, vector signed int);
vector signed int vec_sum4s (vector signed short, vector signed int);
vector signed int vec_vsum4shs (vector signed short, vector signed int);
vector signed int vec_vsum4sbs (vector signed char, vector signed int);
vector unsigned int vec_vsum4ubs (vector unsigned char,
vector unsigned int);
vector signed int vec_sum2s (vector signed int, vector signed int);
vector signed int vec_sums (vector signed int, vector signed int);
vector float vec_trunc (vector float);
vector signed short vec_unpackh (vector signed char);
vector bool short vec_unpackh (vector bool char);
vector signed int vec_unpackh (vector signed short);
vector bool int vec_unpackh (vector bool short);
vector unsigned int vec_unpackh (vector pixel);
vector bool int vec_vupkhsh (vector bool short);
vector signed int vec_vupkhsh (vector signed short);
vector unsigned int vec_vupkhpx (vector pixel);
vector bool short vec_vupkhsb (vector bool char);
vector signed short vec_vupkhsb (vector signed char);
vector signed short vec_unpackl (vector signed char);
vector bool short vec_unpackl (vector bool char);
vector unsigned int vec_unpackl (vector pixel);
vector signed int vec_unpackl (vector signed short);
vector bool int vec_unpackl (vector bool short);
vector unsigned int vec_vupklpx (vector pixel);
vector bool int vec_vupklsh (vector bool short);
vector signed int vec_vupklsh (vector signed short);
vector bool short vec_vupklsb (vector bool char);
vector signed short vec_vupklsb (vector signed char);
vector float vec_xor (vector float, vector float);
vector float vec_xor (vector float, vector bool int);
vector float vec_xor (vector bool int, vector float);
vector bool int vec_xor (vector bool int, vector bool int);
vector signed int vec_xor (vector bool int, vector signed int);
vector signed int vec_xor (vector signed int, vector bool int);
vector signed int vec_xor (vector signed int, vector signed int);
vector unsigned int vec_xor (vector bool int, vector unsigned int);
vector unsigned int vec_xor (vector unsigned int, vector bool int);
vector unsigned int vec_xor (vector unsigned int, vector unsigned int);
vector bool short vec_xor (vector bool short, vector bool short);
vector signed short vec_xor (vector bool short, vector signed short);
vector signed short vec_xor (vector signed short, vector bool short);
vector signed short vec_xor (vector signed short, vector signed short);
vector unsigned short vec_xor (vector bool short,
vector unsigned short);
vector unsigned short vec_xor (vector unsigned short,
vector bool short);
vector unsigned short vec_xor (vector unsigned short,
vector unsigned short);
vector signed char vec_xor (vector bool char, vector signed char);
vector bool char vec_xor (vector bool char, vector bool char);
vector signed char vec_xor (vector signed char, vector bool char);
vector signed char vec_xor (vector signed char, vector signed char);
vector unsigned char vec_xor (vector bool char, vector unsigned char);
vector unsigned char vec_xor (vector unsigned char, vector bool char);
vector unsigned char vec_xor (vector unsigned char,
vector unsigned char);
int vec_all_eq (vector signed char, vector bool char);
int vec_all_eq (vector signed char, vector signed char);
int vec_all_eq (vector unsigned char, vector bool char);
int vec_all_eq (vector unsigned char, vector unsigned char);
int vec_all_eq (vector bool char, vector bool char);
int vec_all_eq (vector bool char, vector unsigned char);
int vec_all_eq (vector bool char, vector signed char);
int vec_all_eq (vector signed short, vector bool short);
int vec_all_eq (vector signed short, vector signed short);
int vec_all_eq (vector unsigned short, vector bool short);
int vec_all_eq (vector unsigned short, vector unsigned short);
int vec_all_eq (vector bool short, vector bool short);
int vec_all_eq (vector bool short, vector unsigned short);
int vec_all_eq (vector bool short, vector signed short);
int vec_all_eq (vector pixel, vector pixel);
int vec_all_eq (vector signed int, vector bool int);
int vec_all_eq (vector signed int, vector signed int);
int vec_all_eq (vector unsigned int, vector bool int);
int vec_all_eq (vector unsigned int, vector unsigned int);
int vec_all_eq (vector bool int, vector bool int);
int vec_all_eq (vector bool int, vector unsigned int);
int vec_all_eq (vector bool int, vector signed int);
int vec_all_eq (vector float, vector float);
int vec_all_ge (vector bool char, vector unsigned char);
int vec_all_ge (vector unsigned char, vector bool char);
int vec_all_ge (vector unsigned char, vector unsigned char);
int vec_all_ge (vector bool char, vector signed char);
int vec_all_ge (vector signed char, vector bool char);
int vec_all_ge (vector signed char, vector signed char);
int vec_all_ge (vector bool short, vector unsigned short);
int vec_all_ge (vector unsigned short, vector bool short);
int vec_all_ge (vector unsigned short, vector unsigned short);
int vec_all_ge (vector signed short, vector signed short);
int vec_all_ge (vector bool short, vector signed short);
int vec_all_ge (vector signed short, vector bool short);
int vec_all_ge (vector bool int, vector unsigned int);
int vec_all_ge (vector unsigned int, vector bool int);
int vec_all_ge (vector unsigned int, vector unsigned int);
int vec_all_ge (vector bool int, vector signed int);
int vec_all_ge (vector signed int, vector bool int);
int vec_all_ge (vector signed int, vector signed int);
int vec_all_ge (vector float, vector float);
int vec_all_gt (vector bool char, vector unsigned char);
int vec_all_gt (vector unsigned char, vector bool char);
int vec_all_gt (vector unsigned char, vector unsigned char);
int vec_all_gt (vector bool char, vector signed char);
int vec_all_gt (vector signed char, vector bool char);
int vec_all_gt (vector signed char, vector signed char);
int vec_all_gt (vector bool short, vector unsigned short);
int vec_all_gt (vector unsigned short, vector bool short);
int vec_all_gt (vector unsigned short, vector unsigned short);
int vec_all_gt (vector bool short, vector signed short);
int vec_all_gt (vector signed short, vector bool short);
int vec_all_gt (vector signed short, vector signed short);
int vec_all_gt (vector bool int, vector unsigned int);
int vec_all_gt (vector unsigned int, vector bool int);
int vec_all_gt (vector unsigned int, vector unsigned int);
int vec_all_gt (vector bool int, vector signed int);
int vec_all_gt (vector signed int, vector bool int);
int vec_all_gt (vector signed int, vector signed int);
int vec_all_gt (vector float, vector float);
int vec_all_in (vector float, vector float);
int vec_all_le (vector bool char, vector unsigned char);
int vec_all_le (vector unsigned char, vector bool char);
int vec_all_le (vector unsigned char, vector unsigned char);
int vec_all_le (vector bool char, vector signed char);
int vec_all_le (vector signed char, vector bool char);
int vec_all_le (vector signed char, vector signed char);
int vec_all_le (vector bool short, vector unsigned short);
int vec_all_le (vector unsigned short, vector bool short);
int vec_all_le (vector unsigned short, vector unsigned short);
int vec_all_le (vector bool short, vector signed short);
int vec_all_le (vector signed short, vector bool short);
int vec_all_le (vector signed short, vector signed short);
int vec_all_le (vector bool int, vector unsigned int);
int vec_all_le (vector unsigned int, vector bool int);
int vec_all_le (vector unsigned int, vector unsigned int);
int vec_all_le (vector bool int, vector signed int);
int vec_all_le (vector signed int, vector bool int);
int vec_all_le (vector signed int, vector signed int);
int vec_all_le (vector float, vector float);
int vec_all_lt (vector bool char, vector unsigned char);
int vec_all_lt (vector unsigned char, vector bool char);
int vec_all_lt (vector unsigned char, vector unsigned char);
int vec_all_lt (vector bool char, vector signed char);
int vec_all_lt (vector signed char, vector bool char);
int vec_all_lt (vector signed char, vector signed char);
int vec_all_lt (vector bool short, vector unsigned short);
int vec_all_lt (vector unsigned short, vector bool short);
int vec_all_lt (vector unsigned short, vector unsigned short);
int vec_all_lt (vector bool short, vector signed short);
int vec_all_lt (vector signed short, vector bool short);
int vec_all_lt (vector signed short, vector signed short);
int vec_all_lt (vector bool int, vector unsigned int);
int vec_all_lt (vector unsigned int, vector bool int);
int vec_all_lt (vector unsigned int, vector unsigned int);
int vec_all_lt (vector bool int, vector signed int);
int vec_all_lt (vector signed int, vector bool int);
int vec_all_lt (vector signed int, vector signed int);
int vec_all_lt (vector float, vector float);
int vec_all_nan (vector float);
int vec_all_ne (vector signed char, vector bool char);
int vec_all_ne (vector signed char, vector signed char);
int vec_all_ne (vector unsigned char, vector bool char);
int vec_all_ne (vector unsigned char, vector unsigned char);
int vec_all_ne (vector bool char, vector bool char);
int vec_all_ne (vector bool char, vector unsigned char);
int vec_all_ne (vector bool char, vector signed char);
int vec_all_ne (vector signed short, vector bool short);
int vec_all_ne (vector signed short, vector signed short);
int vec_all_ne (vector unsigned short, vector bool short);
int vec_all_ne (vector unsigned short, vector unsigned short);
int vec_all_ne (vector bool short, vector bool short);
int vec_all_ne (vector bool short, vector unsigned short);
int vec_all_ne (vector bool short, vector signed short);
int vec_all_ne (vector pixel, vector pixel);
int vec_all_ne (vector signed int, vector bool int);
int vec_all_ne (vector signed int, vector signed int);
int vec_all_ne (vector unsigned int, vector bool int);
int vec_all_ne (vector unsigned int, vector unsigned int);
int vec_all_ne (vector bool int, vector bool int);
int vec_all_ne (vector bool int, vector unsigned int);
int vec_all_ne (vector bool int, vector signed int);
int vec_all_ne (vector float, vector float);
int vec_all_nge (vector float, vector float);
int vec_all_ngt (vector float, vector float);
int vec_all_nle (vector float, vector float);
int vec_all_nlt (vector float, vector float);
int vec_all_numeric (vector float);
int vec_any_eq (vector signed char, vector bool char);
int vec_any_eq (vector signed char, vector signed char);
int vec_any_eq (vector unsigned char, vector bool char);
int vec_any_eq (vector unsigned char, vector unsigned char);
int vec_any_eq (vector bool char, vector bool char);
int vec_any_eq (vector bool char, vector unsigned char);
int vec_any_eq (vector bool char, vector signed char);
int vec_any_eq (vector signed short, vector bool short);
int vec_any_eq (vector signed short, vector signed short);
int vec_any_eq (vector unsigned short, vector bool short);
int vec_any_eq (vector unsigned short, vector unsigned short);
int vec_any_eq (vector bool short, vector bool short);
int vec_any_eq (vector bool short, vector unsigned short);
int vec_any_eq (vector bool short, vector signed short);
int vec_any_eq (vector pixel, vector pixel);
int vec_any_eq (vector signed int, vector bool int);
int vec_any_eq (vector signed int, vector signed int);
int vec_any_eq (vector unsigned int, vector bool int);
int vec_any_eq (vector unsigned int, vector unsigned int);
int vec_any_eq (vector bool int, vector bool int);
int vec_any_eq (vector bool int, vector unsigned int);
int vec_any_eq (vector bool int, vector signed int);
int vec_any_eq (vector float, vector float);
int vec_any_ge (vector signed char, vector bool char);
int vec_any_ge (vector unsigned char, vector bool char);
int vec_any_ge (vector unsigned char, vector unsigned char);
int vec_any_ge (vector signed char, vector signed char);
int vec_any_ge (vector bool char, vector unsigned char);
int vec_any_ge (vector bool char, vector signed char);
int vec_any_ge (vector unsigned short, vector bool short);
int vec_any_ge (vector unsigned short, vector unsigned short);
int vec_any_ge (vector signed short, vector signed short);
int vec_any_ge (vector signed short, vector bool short);
int vec_any_ge (vector bool short, vector unsigned short);
int vec_any_ge (vector bool short, vector signed short);
int vec_any_ge (vector signed int, vector bool int);
int vec_any_ge (vector unsigned int, vector bool int);
int vec_any_ge (vector unsigned int, vector unsigned int);
int vec_any_ge (vector signed int, vector signed int);
int vec_any_ge (vector bool int, vector unsigned int);
int vec_any_ge (vector bool int, vector signed int);
int vec_any_ge (vector float, vector float);
int vec_any_gt (vector bool char, vector unsigned char);
int vec_any_gt (vector unsigned char, vector bool char);
int vec_any_gt (vector unsigned char, vector unsigned char);
int vec_any_gt (vector bool char, vector signed char);
int vec_any_gt (vector signed char, vector bool char);
int vec_any_gt (vector signed char, vector signed char);
int vec_any_gt (vector bool short, vector unsigned short);
int vec_any_gt (vector unsigned short, vector bool short);
int vec_any_gt (vector unsigned short, vector unsigned short);
int vec_any_gt (vector bool short, vector signed short);
int vec_any_gt (vector signed short, vector bool short);
int vec_any_gt (vector signed short, vector signed short);
int vec_any_gt (vector bool int, vector unsigned int);
int vec_any_gt (vector unsigned int, vector bool int);
int vec_any_gt (vector unsigned int, vector unsigned int);
int vec_any_gt (vector bool int, vector signed int);
int vec_any_gt (vector signed int, vector bool int);
int vec_any_gt (vector signed int, vector signed int);
int vec_any_gt (vector float, vector float);
int vec_any_le (vector bool char, vector unsigned char);
int vec_any_le (vector unsigned char, vector bool char);
int vec_any_le (vector unsigned char, vector unsigned char);
int vec_any_le (vector bool char, vector signed char);
int vec_any_le (vector signed char, vector bool char);
int vec_any_le (vector signed char, vector signed char);
int vec_any_le (vector bool short, vector unsigned short);
int vec_any_le (vector unsigned short, vector bool short);
int vec_any_le (vector unsigned short, vector unsigned short);
int vec_any_le (vector bool short, vector signed short);
int vec_any_le (vector signed short, vector bool short);
int vec_any_le (vector signed short, vector signed short);
int vec_any_le (vector bool int, vector unsigned int);
int vec_any_le (vector unsigned int, vector bool int);
int vec_any_le (vector unsigned int, vector unsigned int);
int vec_any_le (vector bool int, vector signed int);
int vec_any_le (vector signed int, vector bool int);
int vec_any_le (vector signed int, vector signed int);
int vec_any_le (vector float, vector float);
int vec_any_lt (vector bool char, vector unsigned char);
int vec_any_lt (vector unsigned char, vector bool char);
int vec_any_lt (vector unsigned char, vector unsigned char);
int vec_any_lt (vector bool char, vector signed char);
int vec_any_lt (vector signed char, vector bool char);
int vec_any_lt (vector signed char, vector signed char);
int vec_any_lt (vector bool short, vector unsigned short);
int vec_any_lt (vector unsigned short, vector bool short);
int vec_any_lt (vector unsigned short, vector unsigned short);
int vec_any_lt (vector bool short, vector signed short);
int vec_any_lt (vector signed short, vector bool short);
int vec_any_lt (vector signed short, vector signed short);
int vec_any_lt (vector bool int, vector unsigned int);
int vec_any_lt (vector unsigned int, vector bool int);
int vec_any_lt (vector unsigned int, vector unsigned int);
int vec_any_lt (vector bool int, vector signed int);
int vec_any_lt (vector signed int, vector bool int);
int vec_any_lt (vector signed int, vector signed int);
int vec_any_lt (vector float, vector float);
int vec_any_nan (vector float);
int vec_any_ne (vector signed char, vector bool char);
int vec_any_ne (vector signed char, vector signed char);
int vec_any_ne (vector unsigned char, vector bool char);
int vec_any_ne (vector unsigned char, vector unsigned char);
int vec_any_ne (vector bool char, vector bool char);
int vec_any_ne (vector bool char, vector unsigned char);
int vec_any_ne (vector bool char, vector signed char);
int vec_any_ne (vector signed short, vector bool short);
int vec_any_ne (vector signed short, vector signed short);
int vec_any_ne (vector unsigned short, vector bool short);
int vec_any_ne (vector unsigned short, vector unsigned short);
int vec_any_ne (vector bool short, vector bool short);
int vec_any_ne (vector bool short, vector unsigned short);
int vec_any_ne (vector bool short, vector signed short);
int vec_any_ne (vector pixel, vector pixel);
int vec_any_ne (vector signed int, vector bool int);
int vec_any_ne (vector signed int, vector signed int);
int vec_any_ne (vector unsigned int, vector bool int);
int vec_any_ne (vector unsigned int, vector unsigned int);
int vec_any_ne (vector bool int, vector bool int);
int vec_any_ne (vector bool int, vector unsigned int);
int vec_any_ne (vector bool int, vector signed int);
int vec_any_ne (vector float, vector float);
int vec_any_nge (vector float, vector float);
int vec_any_ngt (vector float, vector float);
int vec_any_nle (vector float, vector float);
int vec_any_nlt (vector float, vector float);
int vec_any_numeric (vector float);
int vec_any_out (vector float, vector float);
If the vector/scalar (VSX) instruction set is available, the following additional functions are available:
vector double vec_abs (vector double);
vector double vec_add (vector double, vector double);
vector double vec_and (vector double, vector double);
vector double vec_and (vector double, vector bool long);
vector double vec_and (vector bool long, vector double);
vector long vec_and (vector long, vector long);
vector long vec_and (vector long, vector bool long);
vector long vec_and (vector bool long, vector long);
vector unsigned long vec_and (vector unsigned long, vector unsigned long);
vector unsigned long vec_and (vector unsigned long, vector bool long);
vector unsigned long vec_and (vector bool long, vector unsigned long);
vector double vec_andc (vector double, vector double);
vector double vec_andc (vector double, vector bool long);
vector double vec_andc (vector bool long, vector double);
vector long vec_andc (vector long, vector long);
vector long vec_andc (vector long, vector bool long);
vector long vec_andc (vector bool long, vector long);
vector unsigned long vec_andc (vector unsigned long, vector unsigned long);
vector unsigned long vec_andc (vector unsigned long, vector bool long);
vector unsigned long vec_andc (vector bool long, vector unsigned long);
vector double vec_ceil (vector double);
vector bool long vec_cmpeq (vector double, vector double);
vector bool long vec_cmpge (vector double, vector double);
vector bool long vec_cmpgt (vector double, vector double);
vector bool long vec_cmple (vector double, vector double);
vector bool long vec_cmplt (vector double, vector double);
vector double vec_cpsgn (vector double, vector double);
vector float vec_div (vector float, vector float);
vector double vec_div (vector double, vector double);
vector long vec_div (vector long, vector long);
vector unsigned long vec_div (vector unsigned long, vector unsigned long);
vector double vec_floor (vector double);
vector double vec_ld (int, const vector double *);
vector double vec_ld (int, const double *);
vector double vec_ldl (int, const vector double *);
vector double vec_ldl (int, const double *);
vector unsigned char vec_lvsl (int, const volatile double *);
vector unsigned char vec_lvsr (int, const volatile double *);
vector double vec_madd (vector double, vector double, vector double);
vector double vec_max (vector double, vector double);
vector signed long vec_mergeh (vector signed long, vector signed long);
vector signed long vec_mergeh (vector signed long, vector bool long);
vector signed long vec_mergeh (vector bool long, vector signed long);
vector unsigned long vec_mergeh (vector unsigned long, vector unsigned long);
vector unsigned long vec_mergeh (vector unsigned long, vector bool long);
vector unsigned long vec_mergeh (vector bool long, vector unsigned long);
vector signed long vec_mergel (vector signed long, vector signed long);
vector signed long vec_mergel (vector signed long, vector bool long);
vector signed long vec_mergel (vector bool long, vector signed long);
vector unsigned long vec_mergel (vector unsigned long, vector unsigned long);
vector unsigned long vec_mergel (vector unsigned long, vector bool long);
vector unsigned long vec_mergel (vector bool long, vector unsigned long);
vector double vec_min (vector double, vector double);
vector float vec_msub (vector float, vector float, vector float);
vector double vec_msub (vector double, vector double, vector double);
vector float vec_mul (vector float, vector float);
vector double vec_mul (vector double, vector double);
vector long vec_mul (vector long, vector long);
vector unsigned long vec_mul (vector unsigned long, vector unsigned long);
vector float vec_nearbyint (vector float);
vector double vec_nearbyint (vector double);
vector float vec_nmadd (vector float, vector float, vector float);
vector double vec_nmadd (vector double, vector double, vector double);
vector double vec_nmsub (vector double, vector double, vector double);
vector double vec_nor (vector double, vector double);
vector long vec_nor (vector long, vector long);
vector long vec_nor (vector long, vector bool long);
vector long vec_nor (vector bool long, vector long);
vector unsigned long vec_nor (vector unsigned long, vector unsigned long);
vector unsigned long vec_nor (vector unsigned long, vector bool long);
vector unsigned long vec_nor (vector bool long, vector unsigned long);
vector double vec_or (vector double, vector double);
vector double vec_or (vector double, vector bool long);
vector double vec_or (vector bool long, vector double);
vector long vec_or (vector long, vector long);
vector long vec_or (vector long, vector bool long);
vector long vec_or (vector bool long, vector long);
vector unsigned long vec_or (vector unsigned long, vector unsigned long);
vector unsigned long vec_or (vector unsigned long, vector bool long);
vector unsigned long vec_or (vector bool long, vector unsigned long);
vector double vec_perm (vector double, vector double, vector unsigned char);
vector long vec_perm (vector long, vector long, vector unsigned char);
vector unsigned long vec_perm (vector unsigned long, vector unsigned long,
vector unsigned char);
vector double vec_rint (vector double);
vector double vec_recip (vector double, vector double);
vector double vec_rsqrt (vector double);
vector double vec_rsqrte (vector double);
vector double vec_sel (vector double, vector double, vector bool long);
vector double vec_sel (vector double, vector double, vector unsigned long);
vector long vec_sel (vector long, vector long, vector long);
vector long vec_sel (vector long, vector long, vector unsigned long);
vector long vec_sel (vector long, vector long, vector bool long);
vector unsigned long vec_sel (vector unsigned long, vector unsigned long,
vector long);
vector unsigned long vec_sel (vector unsigned long, vector unsigned long,
vector unsigned long);
vector unsigned long vec_sel (vector unsigned long, vector unsigned long,
vector bool long);
vector double vec_splats (double);
vector signed long vec_splats (signed long);
vector unsigned long vec_splats (unsigned long);
vector float vec_sqrt (vector float);
vector double vec_sqrt (vector double);
void vec_st (vector double, int, vector double *);
void vec_st (vector double, int, double *);
vector double vec_sub (vector double, vector double);
vector double vec_trunc (vector double);
vector double vec_xor (vector double, vector double);
vector double vec_xor (vector double, vector bool long);
vector double vec_xor (vector bool long, vector double);
vector long vec_xor (vector long, vector long);
vector long vec_xor (vector long, vector bool long);
vector long vec_xor (vector bool long, vector long);
vector unsigned long vec_xor (vector unsigned long, vector unsigned long);
vector unsigned long vec_xor (vector unsigned long, vector bool long);
vector unsigned long vec_xor (vector bool long, vector unsigned long);
int vec_all_eq (vector double, vector double);
int vec_all_ge (vector double, vector double);
int vec_all_gt (vector double, vector double);
int vec_all_le (vector double, vector double);
int vec_all_lt (vector double, vector double);
int vec_all_nan (vector double);
int vec_all_ne (vector double, vector double);
int vec_all_nge (vector double, vector double);
int vec_all_ngt (vector double, vector double);
int vec_all_nle (vector double, vector double);
int vec_all_nlt (vector double, vector double);
int vec_all_numeric (vector double);
int vec_any_eq (vector double, vector double);
int vec_any_ge (vector double, vector double);
int vec_any_gt (vector double, vector double);
int vec_any_le (vector double, vector double);
int vec_any_lt (vector double, vector double);
int vec_any_nan (vector double);
int vec_any_ne (vector double, vector double);
int vec_any_nge (vector double, vector double);
int vec_any_ngt (vector double, vector double);
int vec_any_nle (vector double, vector double);
int vec_any_nlt (vector double, vector double);
int vec_any_numeric (vector double);
vector double vec_vsx_ld (int, const vector double *);
vector double vec_vsx_ld (int, const double *);
vector float vec_vsx_ld (int, const vector float *);
vector float vec_vsx_ld (int, const float *);
vector bool int vec_vsx_ld (int, const vector bool int *);
vector signed int vec_vsx_ld (int, const vector signed int *);
vector signed int vec_vsx_ld (int, const int *);
vector signed int vec_vsx_ld (int, const long *);
vector unsigned int vec_vsx_ld (int, const vector unsigned int *);
vector unsigned int vec_vsx_ld (int, const unsigned int *);
vector unsigned int vec_vsx_ld (int, const unsigned long *);
vector bool short vec_vsx_ld (int, const vector bool short *);
vector pixel vec_vsx_ld (int, const vector pixel *);
vector signed short vec_vsx_ld (int, const vector signed short *);
vector signed short vec_vsx_ld (int, const short *);
vector unsigned short vec_vsx_ld (int, const vector unsigned short *);
vector unsigned short vec_vsx_ld (int, const unsigned short *);
vector bool char vec_vsx_ld (int, const vector bool char *);
vector signed char vec_vsx_ld (int, const vector signed char *);
vector signed char vec_vsx_ld (int, const signed char *);
vector unsigned char vec_vsx_ld (int, const vector unsigned char *);
vector unsigned char vec_vsx_ld (int, const unsigned char *);
void vec_vsx_st (vector double, int, vector double *);
void vec_vsx_st (vector double, int, double *);
void vec_vsx_st (vector float, int, vector float *);
void vec_vsx_st (vector float, int, float *);
void vec_vsx_st (vector signed int, int, vector signed int *);
void vec_vsx_st (vector signed int, int, int *);
void vec_vsx_st (vector unsigned int, int, vector unsigned int *);
void vec_vsx_st (vector unsigned int, int, unsigned int *);
void vec_vsx_st (vector bool int, int, vector bool int *);
void vec_vsx_st (vector bool int, int, unsigned int *);
void vec_vsx_st (vector bool int, int, int *);
void vec_vsx_st (vector signed short, int, vector signed short *);
void vec_vsx_st (vector signed short, int, short *);
void vec_vsx_st (vector unsigned short, int, vector unsigned short *);
void vec_vsx_st (vector unsigned short, int, unsigned short *);
void vec_vsx_st (vector bool short, int, vector bool short *);
void vec_vsx_st (vector bool short, int, unsigned short *);
void vec_vsx_st (vector pixel, int, vector pixel *);
void vec_vsx_st (vector pixel, int, unsigned short *);
void vec_vsx_st (vector pixel, int, short *);
void vec_vsx_st (vector bool short, int, short *);
void vec_vsx_st (vector signed char, int, vector signed char *);
void vec_vsx_st (vector signed char, int, signed char *);
void vec_vsx_st (vector unsigned char, int, vector unsigned char *);
void vec_vsx_st (vector unsigned char, int, unsigned char *);
void vec_vsx_st (vector bool char, int, vector bool char *);
void vec_vsx_st (vector bool char, int, unsigned char *);
void vec_vsx_st (vector bool char, int, signed char *);
vector double vec_xxpermdi (vector double, vector double, int);
vector float vec_xxpermdi (vector float, vector float, int);
vector long long vec_xxpermdi (vector long long, vector long long, int);
vector unsigned long long vec_xxpermdi (vector unsigned long long,
vector unsigned long long, int);
vector int vec_xxpermdi (vector int, vector int, int);
vector unsigned int vec_xxpermdi (vector unsigned int,
vector unsigned int, int);
vector short vec_xxpermdi (vector short, vector short, int);
vector unsigned short vec_xxpermdi (vector unsigned short,
vector unsigned short, int);
vector signed char vec_xxpermdi (vector signed char, vector signed char, int);
vector unsigned char vec_xxpermdi (vector unsigned char,
vector unsigned char, int);
vector double vec_xxsldi (vector double, vector double, int);
vector float vec_xxsldi (vector float, vector float, int);
vector long long vec_xxsldi (vector long long, vector long long, int);
vector unsigned long long vec_xxsldi (vector unsigned long long,
vector unsigned long long, int);
vector int vec_xxsldi (vector int, vector int, int);
vector unsigned int vec_xxsldi (vector unsigned int, vector unsigned int, int);
vector short vec_xxsldi (vector short, vector short, int);
vector unsigned short vec_xxsldi (vector unsigned short,
vector unsigned short, int);
vector signed char vec_xxsldi (vector signed char, vector signed char, int);
vector unsigned char vec_xxsldi (vector unsigned char,
vector unsigned char, int);
Note that the vec_ld and vec_st built-in functions always generate the AltiVec LVX and STVX instructions even if the VSX instruction set is available. The vec_vsx_ld and vec_vsx_st built-in functions always generate the VSX LXVD2X, LXVW4X, STXVD2X, and STXVW4X instructions.
If the ISA 2.07 additions to the vector/scalar (power8-vector) instruction set is available, the following additional functions are available for both 32-bit and 64-bit targets. For 64-bit targets, you can use vector long instead of vector long long, vector bool long instead of vector bool long long, and vector unsigned long instead of vector unsigned long long.
vector long long vec_abs (vector long long);
vector long long vec_add (vector long long, vector long long);
vector unsigned long long vec_add (vector unsigned long long,
vector unsigned long long);
int vec_all_eq (vector long long, vector long long);
int vec_all_eq (vector unsigned long long, vector unsigned long long);
int vec_all_ge (vector long long, vector long long);
int vec_all_ge (vector unsigned long long, vector unsigned long long);
int vec_all_gt (vector long long, vector long long);
int vec_all_gt (vector unsigned long long, vector unsigned long long);
int vec_all_le (vector long long, vector long long);
int vec_all_le (vector unsigned long long, vector unsigned long long);
int vec_all_lt (vector long long, vector long long);
int vec_all_lt (vector unsigned long long, vector unsigned long long);
int vec_all_ne (vector long long, vector long long);
int vec_all_ne (vector unsigned long long, vector unsigned long long);
int vec_any_eq (vector long long, vector long long);
int vec_any_eq (vector unsigned long long, vector unsigned long long);
int vec_any_ge (vector long long, vector long long);
int vec_any_ge (vector unsigned long long, vector unsigned long long);
int vec_any_gt (vector long long, vector long long);
int vec_any_gt (vector unsigned long long, vector unsigned long long);
int vec_any_le (vector long long, vector long long);
int vec_any_le (vector unsigned long long, vector unsigned long long);
int vec_any_lt (vector long long, vector long long);
int vec_any_lt (vector unsigned long long, vector unsigned long long);
int vec_any_ne (vector long long, vector long long);
int vec_any_ne (vector unsigned long long, vector unsigned long long);
vector long long vec_eqv (vector long long, vector long long);
vector long long vec_eqv (vector bool long long, vector long long);
vector long long vec_eqv (vector long long, vector bool long long);
vector unsigned long long vec_eqv (vector unsigned long long,
vector unsigned long long);
vector unsigned long long vec_eqv (vector bool long long,
vector unsigned long long);
vector unsigned long long vec_eqv (vector unsigned long long,
vector bool long long);
vector int vec_eqv (vector int, vector int);
vector int vec_eqv (vector bool int, vector int);
vector int vec_eqv (vector int, vector bool int);
vector unsigned int vec_eqv (vector unsigned int, vector unsigned int);
vector unsigned int vec_eqv (vector bool unsigned int,
vector unsigned int);
vector unsigned int vec_eqv (vector unsigned int,
vector bool unsigned int);
vector short vec_eqv (vector short, vector short);
vector short vec_eqv (vector bool short, vector short);
vector short vec_eqv (vector short, vector bool short);
vector unsigned short vec_eqv (vector unsigned short, vector unsigned short);
vector unsigned short vec_eqv (vector bool unsigned short,
vector unsigned short);
vector unsigned short vec_eqv (vector unsigned short,
vector bool unsigned short);
vector signed char vec_eqv (vector signed char, vector signed char);
vector signed char vec_eqv (vector bool signed char, vector signed char);
vector signed char vec_eqv (vector signed char, vector bool signed char);
vector unsigned char vec_eqv (vector unsigned char, vector unsigned char);
vector unsigned char vec_eqv (vector bool unsigned char, vector unsigned char);
vector unsigned char vec_eqv (vector unsigned char, vector bool unsigned char);
vector long long vec_max (vector long long, vector long long);
vector unsigned long long vec_max (vector unsigned long long,
vector unsigned long long);
vector signed int vec_mergee (vector signed int, vector signed int);
vector unsigned int vec_mergee (vector unsigned int, vector unsigned int);
vector bool int vec_mergee (vector bool int, vector bool int);
vector signed int vec_mergeo (vector signed int, vector signed int);
vector unsigned int vec_mergeo (vector unsigned int, vector unsigned int);
vector bool int vec_mergeo (vector bool int, vector bool int);
vector long long vec_min (vector long long, vector long long);
vector unsigned long long vec_min (vector unsigned long long,
vector unsigned long long);
vector long long vec_nand (vector long long, vector long long);
vector long long vec_nand (vector bool long long, vector long long);
vector long long vec_nand (vector long long, vector bool long long);
vector unsigned long long vec_nand (vector unsigned long long,
vector unsigned long long);
vector unsigned long long vec_nand (vector bool long long,
vector unsigned long long);
vector unsigned long long vec_nand (vector unsigned long long,
vector bool long long);
vector int vec_nand (vector int, vector int);
vector int vec_nand (vector bool int, vector int);
vector int vec_nand (vector int, vector bool int);
vector unsigned int vec_nand (vector unsigned int, vector unsigned int);
vector unsigned int vec_nand (vector bool unsigned int,
vector unsigned int);
vector unsigned int vec_nand (vector unsigned int,
vector bool unsigned int);
vector short vec_nand (vector short, vector short);
vector short vec_nand (vector bool short, vector short);
vector short vec_nand (vector short, vector bool short);
vector unsigned short vec_nand (vector unsigned short, vector unsigned short);
vector unsigned short vec_nand (vector bool unsigned short,
vector unsigned short);
vector unsigned short vec_nand (vector unsigned short,
vector bool unsigned short);
vector signed char vec_nand (vector signed char, vector signed char);
vector signed char vec_nand (vector bool signed char, vector signed char);
vector signed char vec_nand (vector signed char, vector bool signed char);
vector unsigned char vec_nand (vector unsigned char, vector unsigned char);
vector unsigned char vec_nand (vector bool unsigned char, vector unsigned char);
vector unsigned char vec_nand (vector unsigned char, vector bool unsigned char);
vector long long vec_orc (vector long long, vector long long);
vector long long vec_orc (vector bool long long, vector long long);
vector long long vec_orc (vector long long, vector bool long long);
vector unsigned long long vec_orc (vector unsigned long long,
vector unsigned long long);
vector unsigned long long vec_orc (vector bool long long,
vector unsigned long long);
vector unsigned long long vec_orc (vector unsigned long long,
vector bool long long);
vector int vec_orc (vector int, vector int);
vector int vec_orc (vector bool int, vector int);
vector int vec_orc (vector int, vector bool int);
vector unsigned int vec_orc (vector unsigned int, vector unsigned int);
vector unsigned int vec_orc (vector bool unsigned int,
vector unsigned int);
vector unsigned int vec_orc (vector unsigned int,
vector bool unsigned int);
vector short vec_orc (vector short, vector short);
vector short vec_orc (vector bool short, vector short);
vector short vec_orc (vector short, vector bool short);
vector unsigned short vec_orc (vector unsigned short, vector unsigned short);
vector unsigned short vec_orc (vector bool unsigned short,
vector unsigned short);
vector unsigned short vec_orc (vector unsigned short,
vector bool unsigned short);
vector signed char vec_orc (vector signed char, vector signed char);
vector signed char vec_orc (vector bool signed char, vector signed char);
vector signed char vec_orc (vector signed char, vector bool signed char);
vector unsigned char vec_orc (vector unsigned char, vector unsigned char);
vector unsigned char vec_orc (vector bool unsigned char, vector unsigned char);
vector unsigned char vec_orc (vector unsigned char, vector bool unsigned char);
vector int vec_pack (vector long long, vector long long);
vector unsigned int vec_pack (vector unsigned long long,
vector unsigned long long);
vector bool int vec_pack (vector bool long long, vector bool long long);
vector int vec_packs (vector long long, vector long long);
vector unsigned int vec_packs (vector unsigned long long,
vector unsigned long long);
vector unsigned int vec_packsu (vector long long, vector long long);
vector unsigned int vec_packsu (vector unsigned long long,
vector unsigned long long);
vector long long vec_rl (vector long long,
vector unsigned long long);
vector long long vec_rl (vector unsigned long long,
vector unsigned long long);
vector long long vec_sl (vector long long, vector unsigned long long);
vector long long vec_sl (vector unsigned long long,
vector unsigned long long);
vector long long vec_sr (vector long long, vector unsigned long long);
vector unsigned long long char vec_sr (vector unsigned long long,
vector unsigned long long);
vector long long vec_sra (vector long long, vector unsigned long long);
vector unsigned long long vec_sra (vector unsigned long long,
vector unsigned long long);
vector long long vec_sub (vector long long, vector long long);
vector unsigned long long vec_sub (vector unsigned long long,
vector unsigned long long);
vector long long vec_unpackh (vector int);
vector unsigned long long vec_unpackh (vector unsigned int);
vector long long vec_unpackl (vector int);
vector unsigned long long vec_unpackl (vector unsigned int);
vector long long vec_vaddudm (vector long long, vector long long);
vector long long vec_vaddudm (vector bool long long, vector long long);
vector long long vec_vaddudm (vector long long, vector bool long long);
vector unsigned long long vec_vaddudm (vector unsigned long long,
vector unsigned long long);
vector unsigned long long vec_vaddudm (vector bool unsigned long long,
vector unsigned long long);
vector unsigned long long vec_vaddudm (vector unsigned long long,
vector bool unsigned long long);
vector long long vec_vbpermq (vector signed char, vector signed char);
vector long long vec_vbpermq (vector unsigned char, vector unsigned char);
vector long long vec_cntlz (vector long long);
vector unsigned long long vec_cntlz (vector unsigned long long);
vector int vec_cntlz (vector int);
vector unsigned int vec_cntlz (vector int);
vector short vec_cntlz (vector short);
vector unsigned short vec_cntlz (vector unsigned short);
vector signed char vec_cntlz (vector signed char);
vector unsigned char vec_cntlz (vector unsigned char);
vector long long vec_vclz (vector long long);
vector unsigned long long vec_vclz (vector unsigned long long);
vector int vec_vclz (vector int);
vector unsigned int vec_vclz (vector int);
vector short vec_vclz (vector short);
vector unsigned short vec_vclz (vector unsigned short);
vector signed char vec_vclz (vector signed char);
vector unsigned char vec_vclz (vector unsigned char);
vector signed char vec_vclzb (vector signed char);
vector unsigned char vec_vclzb (vector unsigned char);
vector long long vec_vclzd (vector long long);
vector unsigned long long vec_vclzd (vector unsigned long long);
vector short vec_vclzh (vector short);
vector unsigned short vec_vclzh (vector unsigned short);
vector int vec_vclzw (vector int);
vector unsigned int vec_vclzw (vector int);
vector signed char vec_vgbbd (vector signed char);
vector unsigned char vec_vgbbd (vector unsigned char);
vector long long vec_vmaxsd (vector long long, vector long long);
vector unsigned long long vec_vmaxud (vector unsigned long long,
unsigned vector long long);
vector long long vec_vminsd (vector long long, vector long long);
vector unsigned long long vec_vminud (vector long long,
vector long long);
vector int vec_vpksdss (vector long long, vector long long);
vector unsigned int vec_vpksdss (vector long long, vector long long);
vector unsigned int vec_vpkudus (vector unsigned long long,
vector unsigned long long);
vector int vec_vpkudum (vector long long, vector long long);
vector unsigned int vec_vpkudum (vector unsigned long long,
vector unsigned long long);
vector bool int vec_vpkudum (vector bool long long, vector bool long long);
vector long long vec_vpopcnt (vector long long);
vector unsigned long long vec_vpopcnt (vector unsigned long long);
vector int vec_vpopcnt (vector int);
vector unsigned int vec_vpopcnt (vector int);
vector short vec_vpopcnt (vector short);
vector unsigned short vec_vpopcnt (vector unsigned short);
vector signed char vec_vpopcnt (vector signed char);
vector unsigned char vec_vpopcnt (vector unsigned char);
vector signed char vec_vpopcntb (vector signed char);
vector unsigned char vec_vpopcntb (vector unsigned char);
vector long long vec_vpopcntd (vector long long);
vector unsigned long long vec_vpopcntd (vector unsigned long long);
vector short vec_vpopcnth (vector short);
vector unsigned short vec_vpopcnth (vector unsigned short);
vector int vec_vpopcntw (vector int);
vector unsigned int vec_vpopcntw (vector int);
vector long long vec_vrld (vector long long, vector unsigned long long);
vector unsigned long long vec_vrld (vector unsigned long long,
vector unsigned long long);
vector long long vec_vsld (vector long long, vector unsigned long long);
vector long long vec_vsld (vector unsigned long long,
vector unsigned long long);
vector long long vec_vsrad (vector long long, vector unsigned long long);
vector unsigned long long vec_vsrad (vector unsigned long long,
vector unsigned long long);
vector long long vec_vsrd (vector long long, vector unsigned long long);
vector unsigned long long char vec_vsrd (vector unsigned long long,
vector unsigned long long);
vector long long vec_vsubudm (vector long long, vector long long);
vector long long vec_vsubudm (vector bool long long, vector long long);
vector long long vec_vsubudm (vector long long, vector bool long long);
vector unsigned long long vec_vsubudm (vector unsigned long long,
vector unsigned long long);
vector unsigned long long vec_vsubudm (vector bool long long,
vector unsigned long long);
vector unsigned long long vec_vsubudm (vector unsigned long long,
vector bool long long);
vector long long vec_vupkhsw (vector int);
vector unsigned long long vec_vupkhsw (vector unsigned int);
vector long long vec_vupklsw (vector int);
vector unsigned long long vec_vupklsw (vector int);
If the ISA 2.07 additions to the vector/scalar (power8-vector) instruction set is available, the following additional functions are available for 64-bit targets. New vector types (vector __int128_t and vector __uint128_t) are available to hold the __int128_t and __uint128_t types to use these builtins.
The normal vector extract, and set operations work on vector __int128_t and vector __uint128_t types, but the index value must be 0.
vector __int128_t vec_vaddcuq (vector __int128_t, vector __int128_t);
vector __uint128_t vec_vaddcuq (vector __uint128_t, vector __uint128_t);
vector __int128_t vec_vadduqm (vector __int128_t, vector __int128_t);
vector __uint128_t vec_vadduqm (vector __uint128_t, vector __uint128_t);
vector __int128_t vec_vaddecuq (vector __int128_t, vector __int128_t,
vector __int128_t);
vector __uint128_t vec_vaddecuq (vector __uint128_t, vector __uint128_t,
vector __uint128_t);
vector __int128_t vec_vaddeuqm (vector __int128_t, vector __int128_t,
vector __int128_t);
vector __uint128_t vec_vaddeuqm (vector __uint128_t, vector __uint128_t,
vector __uint128_t);
vector __int128_t vec_vsubecuq (vector __int128_t, vector __int128_t,
vector __int128_t);
vector __uint128_t vec_vsubecuq (vector __uint128_t, vector __uint128_t,
vector __uint128_t);
vector __int128_t vec_vsubeuqm (vector __int128_t, vector __int128_t,
vector __int128_t);
vector __uint128_t vec_vsubeuqm (vector __uint128_t, vector __uint128_t,
vector __uint128_t);
vector __int128_t vec_vsubcuq (vector __int128_t, vector __int128_t);
vector __uint128_t vec_vsubcuq (vector __uint128_t, vector __uint128_t);
__int128_t vec_vsubuqm (__int128_t, __int128_t);
__uint128_t vec_vsubuqm (__uint128_t, __uint128_t);
vector __int128_t __builtin_bcdadd (vector __int128_t, vector__int128_t);
int __builtin_bcdadd_lt (vector __int128_t, vector__int128_t);
int __builtin_bcdadd_eq (vector __int128_t, vector__int128_t);
int __builtin_bcdadd_gt (vector __int128_t, vector__int128_t);
int __builtin_bcdadd_ov (vector __int128_t, vector__int128_t);
vector __int128_t bcdsub (vector __int128_t, vector__int128_t);
int __builtin_bcdsub_lt (vector __int128_t, vector__int128_t);
int __builtin_bcdsub_eq (vector __int128_t, vector__int128_t);
int __builtin_bcdsub_gt (vector __int128_t, vector__int128_t);
int __builtin_bcdsub_ov (vector __int128_t, vector__int128_t);
If the cryptographic instructions are enabled (-mcrypto or -mcpu=power8), the following builtins are enabled.
vector unsigned long long __builtin_crypto_vsbox (vector unsigned long long);
vector unsigned long long __builtin_crypto_vcipher (vector unsigned long long,
vector unsigned long long);
vector unsigned long long __builtin_crypto_vcipherlast
(vector unsigned long long,
vector unsigned long long);
vector unsigned long long __builtin_crypto_vncipher (vector unsigned long long,
vector unsigned long long);
vector unsigned long long __builtin_crypto_vncipherlast
(vector unsigned long long,
vector unsigned long long);
vector unsigned char __builtin_crypto_vpermxor (vector unsigned char,
vector unsigned char,
vector unsigned char);
vector unsigned short __builtin_crypto_vpermxor (vector unsigned short,
vector unsigned short,
vector unsigned short);
vector unsigned int __builtin_crypto_vpermxor (vector unsigned int,
vector unsigned int,
vector unsigned int);
vector unsigned long long __builtin_crypto_vpermxor (vector unsigned long long,
vector unsigned long long,
vector unsigned long long);
vector unsigned char __builtin_crypto_vpmsumb (vector unsigned char,
vector unsigned char);
vector unsigned short __builtin_crypto_vpmsumb (vector unsigned short,
vector unsigned short);
vector unsigned int __builtin_crypto_vpmsumb (vector unsigned int,
vector unsigned int);
vector unsigned long long __builtin_crypto_vpmsumb (vector unsigned long long,
vector unsigned long long);
vector unsigned long long __builtin_crypto_vshasigmad
(vector unsigned long long, int, int);
vector unsigned int __builtin_crypto_vshasigmaw (vector unsigned int,
int, int);
The second argument to the __builtin_crypto_vshasigmad and __builtin_crypto_vshasigmaw builtin functions must be a constant integer that is 0 or 1. The third argument to these builtin functions must be a constant integer in the range of 0 to 15.
:: _powerpc-hardware-transactional-memory-built-in-functions:
GCC provides two interfaces for accessing the Hardware Transactional Memory (HTM) instructions available on some of the PowerPC family of processors (eg, POWER8). The two interfaces come in a low level interface, consisting of built-in functions specific to PowerPC and a higher level interface consisting of inline functions that are common between PowerPC and S/390.
The following low level built-in functions are available with -mhtm or -mcpu=CPU where CPU is power8 or later. They all generate the machine instruction that is part of the name.
The HTM builtins (with the exception of __builtin_tbegin) return the full 4-bit condition register value set by their associated hardware instruction. The header file htmintrin.h defines some macros that can be used to decipher the return value. The __builtin_tbegin builtin returns a simple true or false value depending on whether a transaction was successfully started or not. The arguments of the builtins match exactly the type and order of the associated hardware instructions operands, except for the __builtin_tcheck builtin, which does not take any input arguments. Refer to the ISA manual for a description of each instructions operands.
unsigned int __builtin_tbegin (unsigned int)
unsigned int __builtin_tend (unsigned int)
unsigned int __builtin_tabort (unsigned int)
unsigned int __builtin_tabortdc (unsigned int, unsigned int, unsigned int)
unsigned int __builtin_tabortdci (unsigned int, unsigned int, int)
unsigned int __builtin_tabortwc (unsigned int, unsigned int, unsigned int)
unsigned int __builtin_tabortwci (unsigned int, unsigned int, int)
unsigned int __builtin_tcheck (void)
unsigned int __builtin_treclaim (unsigned int)
unsigned int __builtin_trechkpt (void)
unsigned int __builtin_tsr (unsigned int)
In addition to the above HTM built-ins, we have added built-ins for some common extended mnemonics of the HTM instructions:
unsigned int __builtin_tendall (void)
unsigned int __builtin_tresume (void)
unsigned int __builtin_tsuspend (void)
The following set of built-in functions are available to gain access to the HTM specific special purpose registers.
unsigned long __builtin_get_texasr (void)
unsigned long __builtin_get_texasru (void)
unsigned long __builtin_get_tfhar (void)
unsigned long __builtin_get_tfiar (void)
void __builtin_set_texasr (unsigned long);
void __builtin_set_texasru (unsigned long);
void __builtin_set_tfhar (unsigned long);
void __builtin_set_tfiar (unsigned long);
Example usage of these low level built-in functions may look like:
#include <htmintrin.h>
int num_retries = 10;
while (1)
{
if (__builtin_tbegin (0))
{
/* Transaction State Initiated. */
if (is_locked (lock))
__builtin_tabort (0);
... transaction code...
__builtin_tend (0);
break;
}
else
{
/* Transaction State Failed. Use locks if the transaction
failure is "persistent" or we've tried too many times. */
if (num_retries-- <= 0
|| _TEXASRU_FAILURE_PERSISTENT (__builtin_get_texasru ()))
{
acquire_lock (lock);
... non transactional fallback path...
release_lock (lock);
break;
}
}
}
One final built-in function has been added that returns the value of the 2-bit Transaction State field of the Machine Status Register (MSR) as stored in CR0.
unsigned long __builtin_ttest (void)
This built-in can be used to determine the current transaction state using the following code example:
#include <htmintrin.h>
unsigned char tx_state = _HTM_STATE (__builtin_ttest ());
if (tx_state == _HTM_TRANSACTIONAL)
{
/* Code to use in transactional state. */
}
else if (tx_state == _HTM_NONTRANSACTIONAL)
{
/* Code to use in non-transactional state. */
}
else if (tx_state == _HTM_SUSPENDED)
{
/* Code to use in transaction suspended state. */
}
The following high level HTM interface is made available by including <htmxlintrin.h> and using -mhtm or -mcpu=CPU where CPU is power8 or later. This interface is common between PowerPC and S/390, allowing users to write one HTM source implementation that can be compiled and executed on either system.
long __TM_simple_begin (void)
long __TM_begin (void* const TM_buff)
long __TM_end (void)
void __TM_abort (void)
void __TM_named_abort (unsigned char const code)
void __TM_resume (void)
void __TM_suspend (void)
long __TM_is_user_abort (void* const TM_buff)
long __TM_is_named_user_abort (void* const TM_buff, unsigned char *code)
long __TM_is_illegal (void* const TM_buff)
long __TM_is_footprint_exceeded (void* const TM_buff)
long __TM_nesting_depth (void* const TM_buff)
long __TM_is_nested_too_deep(void* const TM_buff)
long __TM_is_conflict(void* const TM_buff)
long __TM_is_failure_persistent(void* const TM_buff)
long __TM_failure_address(void* const TM_buff)
long long __TM_failure_code(void* const TM_buff)
Using these common set of HTM inline functions, we can create a more portable version of the HTM example in the previous section that will work on either PowerPC or S/390:
#include <htmxlintrin.h>
int num_retries = 10;
TM_buff_type TM_buff;
while (1)
{
if (__TM_begin (TM_buff) == _HTM_TBEGIN_STARTED)
{
/* Transaction State Initiated. */
if (is_locked (lock))
__TM_abort ();
... transaction code...
__TM_end ();
break;
}
else
{
/* Transaction State Failed. Use locks if the transaction
failure is "persistent" or we've tried too many times. */
if (num_retries-- <= 0
|| __TM_is_failure_persistent (TM_buff))
{
acquire_lock (lock);
... non transactional fallback path...
release_lock (lock);
break;
}
}
}
:: _rx-built-in-functions:
GCC supports some of the RX instructions which cannot be expressed in the C programming language via the use of built-in functions. The following functions are supported:
Generates the brk machine instruction.
Generates the clrpsw machine instruction to clear the specified bit in the processor status word.
Generates the int machine instruction to generate an interrupt with the specified value.
Generates the machi machine instruction to add the result of multiplying the top 16 bits of the two arguments into the accumulator.
Generates the maclo machine instruction to add the result of multiplying the bottom 16 bits of the two arguments into the accumulator.
Generates the mulhi machine instruction to place the result of multiplying the top 16 bits of the two arguments into the accumulator.
Generates the mullo machine instruction to place the result of multiplying the bottom 16 bits of the two arguments into the accumulator.
Generates the mvfachi machine instruction to read the top 32 bits of the accumulator.
Generates the mvfacmi machine instruction to read the middle 32 bits of the accumulator.
Generates the mvfc machine instruction which reads the control register specified in its argument and returns its value.
Generates the mvtachi machine instruction to set the top 32 bits of the accumulator.
Generates the mvtaclo machine instruction to set the bottom 32 bits of the accumulator.
Generates the mvtc machine instruction which sets control register number reg to val.
Generates the mvtipl machine instruction set the interrupt priority level.
Generates the racw machine instruction to round the accumulator according to the specified mode.
Generates the revw machine instruction which swaps the bytes in the argument so that bits 07 now occupy bits 815 and vice versa, and also bits 1623 occupy bits 2431 and vice versa.
Generates the rmpa machine instruction which initiates a repeated multiply and accumulate sequence.
Generates the round machine instruction which returns the floating-point argument rounded according to the current rounding mode set in the floating-point status word register.
Generates the sat machine instruction which returns the saturated value of the argument.
Generates the setpsw machine instruction to set the specified bit in the processor status word.
Generates the wait machine instruction.
:: _s/390-system-z-built-in-functions:
Generates the tbegin machine instruction starting a non-constraint hardware transaction. If the parameter is non-NULL the memory area is used to store the transaction diagnostic buffer and will be passed as first operand to tbegin. This buffer can be defined using the struct __htm_tdb C struct defined in htmintrin.h and must reside on a double-word boundary. The second tbegin operand is set to 0xff0c. This enables save/restore of all GPRs and disables aborts for FPR and AR manipulations inside the transaction body. The condition code set by the tbegin instruction is returned as integer value. The tbegin instruction by definition overwrites the content of all FPRs. The compiler will generate code which saves and restores the FPRs. For soft-float code it is recommended to used the *_nofloat variant. In order to prevent a TDB from being written it is required to pass an constant zero value as parameter. Passing the zero value through a variable is not sufficient. Although modifications of access registers inside the transaction will not trigger an transaction abort it is not supported to actually modify them. Access registers do not get saved when entering a transaction. They will have undefined state when reaching the abort code.
Macros for the possible return codes of tbegin are defined in the htmintrin.h header file:
tbegin has been executed as part of normal processing. The transaction body is supposed to be executed.
The transaction was aborted due to an indeterminate condition which might be persistent.
The transaction aborted due to a transient failure. The transaction should be re-executed in that case.
The transaction aborted due to a persistent failure. Re-execution under same circumstances will not be productive.
The _HTM_FIRST_USER_ABORT_CODE defined in htmintrin.h specifies the first abort code which can be used for __builtin_tabort. Values below this threshold are reserved for machine use.
The struct __htm_tdb defined in htmintrin.h describes the structure of the transaction diagnostic block as specified in the Principles of Operation manual chapter 5-91.
Same as __builtin_tbegin but without FPR saves and restores. Using this variant in code making use of FPRs will leave the FPRs in undefined state when entering the transaction abort handler code.
In addition to __builtin_tbegin a loop for transient failures is generated. If tbegin returns a condition code of 2 the transaction will be retried as often as specified in the second argument. The perform processor assist instruction is used to tell the CPU about the number of fails so far.
Same as __builtin_tbegin_retry but without FPR saves and restores. Using this variant in code making use of FPRs will leave the FPRs in undefined state when entering the transaction abort handler code.
Generates the tbeginc machine instruction starting a constraint hardware transaction. The second operand is set to 0xff08.
Generates the tend machine instruction finishing a transaction and making the changes visible to other threads. The condition code generated by tend is returned as integer value.
Generates the tabort machine instruction with the specified abort code. Abort codes from 0 through 255 are reserved and will result in an error message.
Generates the ppa rX,rY,1 machine instruction. Where the integer parameter is loaded into rX and a value of zero is loaded into rY. The integer parameter specifies the number of times the transaction repeatedly aborted.
Generates the etnd machine instruction. The current nesting depth is returned as integer value. For a nesting depth of 0 the code is not executed as part of an transaction.
Generates the ntstg machine instruction. The second argument is written to the first arguments location. The store operation will not be rolled-back in case of an transaction abort.
:: _sh-built-in-functions:
The following built-in functions are supported on the SH1, SH2, SH3 and SH4 families of processors:
Sets the GBR register to the specified value ptr. This is usually used by system code that manages threads and execution contexts. The compiler normally does not generate code that modifies the contents of GBR and thus the value is preserved across function calls. Changing the GBR value in user code must be done with caution, since the compiler might use GBR in order to access thread local variables.
Returns the value that is currently set in the GBR register. Memory loads and stores that use the thread pointer as a base address are turned into GBR based displacement loads and stores, if possible. For example:
struct my_tcb
{
int a, b, c, d, e;
};
int get_tcb_value (void)
{
// Generate mov.l (8,gbr),r0 instruction
return ((my_tcb*)__builtin_thread_pointer ())->c;
}
Returns the value that is currently set in the FPSCR register.
Sets the FPSCR register to the specified value val, while preserving the current values of the FR, SZ and PR bits.
:: _sparc-vis-built-in-functions:
GCC supports SIMD operations on the SPARC using both the generic vector extensions (Vector Extensions) as well as built-in functions for the SPARC Visual Instruction Set (VIS). When you use the -mvis switch, the VIS extension is exposed as the following built-in functions:
typedef int v1si __attribute__ ((vector_size (4)));
typedef int v2si __attribute__ ((vector_size (8)));
typedef short v4hi __attribute__ ((vector_size (8)));
typedef short v2hi __attribute__ ((vector_size (4)));
typedef unsigned char v8qi __attribute__ ((vector_size (8)));
typedef unsigned char v4qi __attribute__ ((vector_size (4)));
void __builtin_vis_write_gsr (int64_t);
int64_t __builtin_vis_read_gsr (void);
void * __builtin_vis_alignaddr (void *, long);
void * __builtin_vis_alignaddrl (void *, long);
int64_t __builtin_vis_faligndatadi (int64_t, int64_t);
v2si __builtin_vis_faligndatav2si (v2si, v2si);
v4hi __builtin_vis_faligndatav4hi (v4si, v4si);
v8qi __builtin_vis_faligndatav8qi (v8qi, v8qi);
v4hi __builtin_vis_fexpand (v4qi);
v4hi __builtin_vis_fmul8x16 (v4qi, v4hi);
v4hi __builtin_vis_fmul8x16au (v4qi, v2hi);
v4hi __builtin_vis_fmul8x16al (v4qi, v2hi);
v4hi __builtin_vis_fmul8sux16 (v8qi, v4hi);
v4hi __builtin_vis_fmul8ulx16 (v8qi, v4hi);
v2si __builtin_vis_fmuld8sux16 (v4qi, v2hi);
v2si __builtin_vis_fmuld8ulx16 (v4qi, v2hi);
v4qi __builtin_vis_fpack16 (v4hi);
v8qi __builtin_vis_fpack32 (v2si, v8qi);
v2hi __builtin_vis_fpackfix (v2si);
v8qi __builtin_vis_fpmerge (v4qi, v4qi);
int64_t __builtin_vis_pdist (v8qi, v8qi, int64_t);
long __builtin_vis_edge8 (void *, void *);
long __builtin_vis_edge8l (void *, void *);
long __builtin_vis_edge16 (void *, void *);
long __builtin_vis_edge16l (void *, void *);
long __builtin_vis_edge32 (void *, void *);
long __builtin_vis_edge32l (void *, void *);
long __builtin_vis_fcmple16 (v4hi, v4hi);
long __builtin_vis_fcmple32 (v2si, v2si);
long __builtin_vis_fcmpne16 (v4hi, v4hi);
long __builtin_vis_fcmpne32 (v2si, v2si);
long __builtin_vis_fcmpgt16 (v4hi, v4hi);
long __builtin_vis_fcmpgt32 (v2si, v2si);
long __builtin_vis_fcmpeq16 (v4hi, v4hi);
long __builtin_vis_fcmpeq32 (v2si, v2si);
v4hi __builtin_vis_fpadd16 (v4hi, v4hi);
v2hi __builtin_vis_fpadd16s (v2hi, v2hi);
v2si __builtin_vis_fpadd32 (v2si, v2si);
v1si __builtin_vis_fpadd32s (v1si, v1si);
v4hi __builtin_vis_fpsub16 (v4hi, v4hi);
v2hi __builtin_vis_fpsub16s (v2hi, v2hi);
v2si __builtin_vis_fpsub32 (v2si, v2si);
v1si __builtin_vis_fpsub32s (v1si, v1si);
long __builtin_vis_array8 (long, long);
long __builtin_vis_array16 (long, long);
long __builtin_vis_array32 (long, long);
When you use the -mvis2 switch, the VIS version 2.0 built-in functions also become available:
long __builtin_vis_bmask (long, long);
int64_t __builtin_vis_bshuffledi (int64_t, int64_t);
v2si __builtin_vis_bshufflev2si (v2si, v2si);
v4hi __builtin_vis_bshufflev2si (v4hi, v4hi);
v8qi __builtin_vis_bshufflev2si (v8qi, v8qi);
long __builtin_vis_edge8n (void *, void *);
long __builtin_vis_edge8ln (void *, void *);
long __builtin_vis_edge16n (void *, void *);
long __builtin_vis_edge16ln (void *, void *);
long __builtin_vis_edge32n (void *, void *);
long __builtin_vis_edge32ln (void *, void *);
When you use the -mvis3 switch, the VIS version 3.0 built-in functions also become available:
void __builtin_vis_cmask8 (long);
void __builtin_vis_cmask16 (long);
void __builtin_vis_cmask32 (long);
v4hi __builtin_vis_fchksm16 (v4hi, v4hi);
v4hi __builtin_vis_fsll16 (v4hi, v4hi);
v4hi __builtin_vis_fslas16 (v4hi, v4hi);
v4hi __builtin_vis_fsrl16 (v4hi, v4hi);
v4hi __builtin_vis_fsra16 (v4hi, v4hi);
v2si __builtin_vis_fsll16 (v2si, v2si);
v2si __builtin_vis_fslas16 (v2si, v2si);
v2si __builtin_vis_fsrl16 (v2si, v2si);
v2si __builtin_vis_fsra16 (v2si, v2si);
long __builtin_vis_pdistn (v8qi, v8qi);
v4hi __builtin_vis_fmean16 (v4hi, v4hi);
int64_t __builtin_vis_fpadd64 (int64_t, int64_t);
int64_t __builtin_vis_fpsub64 (int64_t, int64_t);
v4hi __builtin_vis_fpadds16 (v4hi, v4hi);
v2hi __builtin_vis_fpadds16s (v2hi, v2hi);
v4hi __builtin_vis_fpsubs16 (v4hi, v4hi);
v2hi __builtin_vis_fpsubs16s (v2hi, v2hi);
v2si __builtin_vis_fpadds32 (v2si, v2si);
v1si __builtin_vis_fpadds32s (v1si, v1si);
v2si __builtin_vis_fpsubs32 (v2si, v2si);
v1si __builtin_vis_fpsubs32s (v1si, v1si);
long __builtin_vis_fucmple8 (v8qi, v8qi);
long __builtin_vis_fucmpne8 (v8qi, v8qi);
long __builtin_vis_fucmpgt8 (v8qi, v8qi);
long __builtin_vis_fucmpeq8 (v8qi, v8qi);
float __builtin_vis_fhadds (float, float);
double __builtin_vis_fhaddd (double, double);
float __builtin_vis_fhsubs (float, float);
double __builtin_vis_fhsubd (double, double);
float __builtin_vis_fnhadds (float, float);
double __builtin_vis_fnhaddd (double, double);
int64_t __builtin_vis_umulxhi (int64_t, int64_t);
int64_t __builtin_vis_xmulx (int64_t, int64_t);
int64_t __builtin_vis_xmulxhi (int64_t, int64_t);
:: _spu-built-in-functions:
GCC provides extensions for the SPU processor as described in the Sony/Toshiba/IBM SPU Language Extensions Specification, which can be found at http://cell.scei.co.jp/ or http://www.ibm.com/developerworks/power/cell/. GCCs implementation differs in several ways.
The optional extension of specifying vector constants in parentheses is not supported.
A vector initializer requires no cast if the vector constant is of the same type as the variable it is initializing.
If signed or unsigned is omitted, the signedness of the vector type is the default signedness of the base type. The default varies depending on the operating system, so a portable program should always specify the signedness.
By default, the keyword __vector is added. The macro vector is defined in <spu_intrinsics.h> and can be undefined.
GCC allows using a typedef name as the type specifier for a vector type.
For C, overloaded functions are implemented with macros so the following does not work:
spu_add ((vector signed int){1, 2, 3, 4}, foo);
Since spu_add is a macro, the vector constant in the example is treated as four separate arguments. Wrap the entire argument in parentheses for this to work.
The extended version of __builtin_expect is not supported.
Note: Only the interface described in the aforementioned specification is supported. Internally, GCC uses built-in functions to implement the required functionality, but these are not supported and are subject to change without notice.
:: _ti-c6x-built-in-functions:
GCC provides intrinsics to access certain instructions of the TI C6X processors. These intrinsics, listed below, are available after inclusion of the c6x_intrinsics.h header file. They map directly to C6X instructions.
int _sadd (int, int)
int _ssub (int, int)
int _sadd2 (int, int)
int _ssub2 (int, int)
long long _mpy2 (int, int)
long long _smpy2 (int, int)
int _add4 (int, int)
int _sub4 (int, int)
int _saddu4 (int, int)
int _smpy (int, int)
int _smpyh (int, int)
int _smpyhl (int, int)
int _smpylh (int, int)
int _sshl (int, int)
int _subc (int, int)
int _avg2 (int, int)
int _avgu4 (int, int)
int _clrr (int, int)
int _extr (int, int)
int _extru (int, int)
int _abs (int)
int _abs2 (int)
:: _tile-gx-built-in-functions:
GCC provides intrinsics to access every instruction of the TILE-Gx processor. The intrinsics are of the form:
unsigned long long __insn_``op`` (...)
Where op is the name of the instruction. Refer to the ISA manual for the complete list of instructions.
GCC also provides intrinsics to directly access the network registers. The intrinsics are:
unsigned long long __tile_idn0_receive (void)
unsigned long long __tile_idn1_receive (void)
unsigned long long __tile_udn0_receive (void)
unsigned long long __tile_udn1_receive (void)
unsigned long long __tile_udn2_receive (void)
unsigned long long __tile_udn3_receive (void)
void __tile_idn_send (unsigned long long)
void __tile_udn_send (unsigned long long)
The intrinsic void __tile_network_barrier (void) is used to guarantee that no network operations before it are reordered with those after it.
:: _tilepro-built-in-functions:
GCC provides intrinsics to access every instruction of the TILEPro processor. The intrinsics are of the form:
unsigned __insn_``op`` (...)
where op is the name of the instruction. Refer to the ISA manual for the complete list of instructions.
GCC also provides intrinsics to directly access the network registers. The intrinsics are:
unsigned __tile_idn0_receive (void)
unsigned __tile_idn1_receive (void)
unsigned __tile_sn_receive (void)
unsigned __tile_udn0_receive (void)
unsigned __tile_udn1_receive (void)
unsigned __tile_udn2_receive (void)
unsigned __tile_udn3_receive (void)
void __tile_idn_send (unsigned)
void __tile_sn_send (unsigned)
void __tile_udn_send (unsigned)
The intrinsic void __tile_network_barrier (void) is used to guarantee that no network operations before it are reordered with those after it.
:: _x86-built-in-functions:
These built-in functions are available for the x86-32 and x86-64 family of computers, depending on the command-line switches used.
If you specify command-line switches such as -msse, the compiler could use the extended instruction sets even if the built-ins are not used explicitly in the program. For this reason, applications that perform run-time CPU detection must compile separate files for each supported architecture, using the appropriate flags. In particular, the file containing the CPU detection code should be compiled without these options.
The following machine modes are available for use with MMX built-in functions (Vector Extensions): V2SI for a vector of two 32-bit integers, V4HI for a vector of four 16-bit integers, and V8QI for a vector of eight 8-bit integers. Some of the built-in functions operate on MMX registers as a whole 64-bit entity, these use V1DI as their mode.
If 3DNow! extensions are enabled, V2SF is used as a mode for a vector of two 32-bit floating-point values.
If SSE extensions are enabled, V4SF is used for a vector of four 32-bit floating-point values. Some instructions use a vector of four 32-bit integers, these use V4SI. Finally, some instructions operate on an entire vector register, interpreting it as a 128-bit integer, these use mode TI.
In 64-bit mode, the x86-64 family of processors uses additional built-in functions for efficient use of TF (__float128) 128-bit floating point and TC 128-bit complex floating-point values.
The following floating-point built-in functions are available in 64-bit mode. All of them implement the function that is part of the name.
__float128 __builtin_fabsq (__float128)
__float128 __builtin_copysignq (__float128, __float128)
The following built-in function is always available.
Generates the pause machine instruction with a compiler memory barrier.
The following floating-point built-in functions are made available in the 64-bit mode.
Similar to __builtin_inf, except the return type is __float128.
Similar to __builtin_huge_val, except the return type is __float128.
The following built-in functions are always available and can be used to check the target platform type.
This function runs the CPU detection code to check the type of CPU and the features supported. This built-in function needs to be invoked along with the built-in functions to check CPU type and features, __builtin_cpu_is and __builtin_cpu_supports, only when used in a function that is executed before any constructors are called. The CPU detection code is automatically executed in a very high priority constructor.
For example, this function has to be used in ifunc resolvers that check for CPU type using the built-in functions __builtin_cpu_is and __builtin_cpu_supports, or in constructors on targets that dont support constructor priority.
static void (*resolve_memcpy (void)) (void)
{
// ifunc resolvers fire before constructors, explicitly call the init
// function.
__builtin_cpu_init ();
if (__builtin_cpu_supports ("ssse3"))
return ssse3_memcpy; // super fast memcpy with ssse3 instructions.
else
return default_memcpy;
}
void *memcpy (void *, const void *, size_t)
__attribute__ ((ifunc ("resolve_memcpy")));
This function returns a positive integer if the run-time CPU is of type cpuname and returns 0 otherwise. The following CPU names can be detected:
Intel CPU.
Intel Atom CPU.
Intel Core 2 CPU.
Intel Core i7 CPU.
Intel Core i7 Nehalem CPU.
Intel Core i7 Westmere CPU.
Intel Core i7 Sandy Bridge CPU.
AMD CPU.
AMD Family 10h CPU.
AMD Family 10h Barcelona CPU.
AMD Family 10h Shanghai CPU.
AMD Family 10h Istanbul CPU.
AMD Family 14h CPU.
AMD Family 15h CPU.
AMD Family 15h Bulldozer version 1.
AMD Family 15h Bulldozer version 2.
AMD Family 15h Bulldozer version 3.
AMD Family 15h Bulldozer version 4.
AMD Family 16h CPU.
Here is an example:
if (__builtin_cpu_is ("corei7"))
{
do_corei7 (); // Core i7 specific implementation.
}
else
{
do_generic (); // Generic implementation.
}
This function returns a positive integer if the run-time CPU supports feature and returns 0 otherwise. The following features can be detected:
CMOV instruction.
MMX instructions.
POPCNT instruction.
SSE instructions.
SSE2 instructions.
SSE3 instructions.
SSSE3 instructions.
SSE4.1 instructions.
SSE4.2 instructions.
AVX instructions.
AVX2 instructions.
AVX512F instructions.
Here is an example:
if (__builtin_cpu_supports ("popcnt"))
{
asm("popcnt %1,%0" : "=r"(count) : "rm"(n) : "cc");
}
else
{
count = generic_countbits (n); //generic implementation.
}
The following built-in functions are made available by -mmmx. All of them generate the machine instruction that is part of the name.
v8qi __builtin_ia32_paddb (v8qi, v8qi)
v4hi __builtin_ia32_paddw (v4hi, v4hi)
v2si __builtin_ia32_paddd (v2si, v2si)
v8qi __builtin_ia32_psubb (v8qi, v8qi)
v4hi __builtin_ia32_psubw (v4hi, v4hi)
v2si __builtin_ia32_psubd (v2si, v2si)
v8qi __builtin_ia32_paddsb (v8qi, v8qi)
v4hi __builtin_ia32_paddsw (v4hi, v4hi)
v8qi __builtin_ia32_psubsb (v8qi, v8qi)
v4hi __builtin_ia32_psubsw (v4hi, v4hi)
v8qi __builtin_ia32_paddusb (v8qi, v8qi)
v4hi __builtin_ia32_paddusw (v4hi, v4hi)
v8qi __builtin_ia32_psubusb (v8qi, v8qi)
v4hi __builtin_ia32_psubusw (v4hi, v4hi)
v4hi __builtin_ia32_pmullw (v4hi, v4hi)
v4hi __builtin_ia32_pmulhw (v4hi, v4hi)
di __builtin_ia32_pand (di, di)
di __builtin_ia32_pandn (di,di)
di __builtin_ia32_por (di, di)
di __builtin_ia32_pxor (di, di)
v8qi __builtin_ia32_pcmpeqb (v8qi, v8qi)
v4hi __builtin_ia32_pcmpeqw (v4hi, v4hi)
v2si __builtin_ia32_pcmpeqd (v2si, v2si)
v8qi __builtin_ia32_pcmpgtb (v8qi, v8qi)
v4hi __builtin_ia32_pcmpgtw (v4hi, v4hi)
v2si __builtin_ia32_pcmpgtd (v2si, v2si)
v8qi __builtin_ia32_punpckhbw (v8qi, v8qi)
v4hi __builtin_ia32_punpckhwd (v4hi, v4hi)
v2si __builtin_ia32_punpckhdq (v2si, v2si)
v8qi __builtin_ia32_punpcklbw (v8qi, v8qi)
v4hi __builtin_ia32_punpcklwd (v4hi, v4hi)
v2si __builtin_ia32_punpckldq (v2si, v2si)
v8qi __builtin_ia32_packsswb (v4hi, v4hi)
v4hi __builtin_ia32_packssdw (v2si, v2si)
v8qi __builtin_ia32_packuswb (v4hi, v4hi)
v4hi __builtin_ia32_psllw (v4hi, v4hi)
v2si __builtin_ia32_pslld (v2si, v2si)
v1di __builtin_ia32_psllq (v1di, v1di)
v4hi __builtin_ia32_psrlw (v4hi, v4hi)
v2si __builtin_ia32_psrld (v2si, v2si)
v1di __builtin_ia32_psrlq (v1di, v1di)
v4hi __builtin_ia32_psraw (v4hi, v4hi)
v2si __builtin_ia32_psrad (v2si, v2si)
v4hi __builtin_ia32_psllwi (v4hi, int)
v2si __builtin_ia32_pslldi (v2si, int)
v1di __builtin_ia32_psllqi (v1di, int)
v4hi __builtin_ia32_psrlwi (v4hi, int)
v2si __builtin_ia32_psrldi (v2si, int)
v1di __builtin_ia32_psrlqi (v1di, int)
v4hi __builtin_ia32_psrawi (v4hi, int)
v2si __builtin_ia32_psradi (v2si, int)
The following built-in functions are made available either with -msse, or with a combination of -m3dnow and -march=athlon. All of them generate the machine instruction that is part of the name.
v4hi __builtin_ia32_pmulhuw (v4hi, v4hi)
v8qi __builtin_ia32_pavgb (v8qi, v8qi)
v4hi __builtin_ia32_pavgw (v4hi, v4hi)
v1di __builtin_ia32_psadbw (v8qi, v8qi)
v8qi __builtin_ia32_pmaxub (v8qi, v8qi)
v4hi __builtin_ia32_pmaxsw (v4hi, v4hi)
v8qi __builtin_ia32_pminub (v8qi, v8qi)
v4hi __builtin_ia32_pminsw (v4hi, v4hi)
int __builtin_ia32_pmovmskb (v8qi)
void __builtin_ia32_maskmovq (v8qi, v8qi, char *)
void __builtin_ia32_movntq (di *, di)
void __builtin_ia32_sfence (void)
The following built-in functions are available when -msse is used. All of them generate the machine instruction that is part of the name.
int __builtin_ia32_comieq (v4sf, v4sf)
int __builtin_ia32_comineq (v4sf, v4sf)
int __builtin_ia32_comilt (v4sf, v4sf)
int __builtin_ia32_comile (v4sf, v4sf)
int __builtin_ia32_comigt (v4sf, v4sf)
int __builtin_ia32_comige (v4sf, v4sf)
int __builtin_ia32_ucomieq (v4sf, v4sf)
int __builtin_ia32_ucomineq (v4sf, v4sf)
int __builtin_ia32_ucomilt (v4sf, v4sf)
int __builtin_ia32_ucomile (v4sf, v4sf)
int __builtin_ia32_ucomigt (v4sf, v4sf)
int __builtin_ia32_ucomige (v4sf, v4sf)
v4sf __builtin_ia32_addps (v4sf, v4sf)
v4sf __builtin_ia32_subps (v4sf, v4sf)
v4sf __builtin_ia32_mulps (v4sf, v4sf)
v4sf __builtin_ia32_divps (v4sf, v4sf)
v4sf __builtin_ia32_addss (v4sf, v4sf)
v4sf __builtin_ia32_subss (v4sf, v4sf)
v4sf __builtin_ia32_mulss (v4sf, v4sf)
v4sf __builtin_ia32_divss (v4sf, v4sf)
v4sf __builtin_ia32_cmpeqps (v4sf, v4sf)
v4sf __builtin_ia32_cmpltps (v4sf, v4sf)
v4sf __builtin_ia32_cmpleps (v4sf, v4sf)
v4sf __builtin_ia32_cmpgtps (v4sf, v4sf)
v4sf __builtin_ia32_cmpgeps (v4sf, v4sf)
v4sf __builtin_ia32_cmpunordps (v4sf, v4sf)
v4sf __builtin_ia32_cmpneqps (v4sf, v4sf)
v4sf __builtin_ia32_cmpnltps (v4sf, v4sf)
v4sf __builtin_ia32_cmpnleps (v4sf, v4sf)
v4sf __builtin_ia32_cmpngtps (v4sf, v4sf)
v4sf __builtin_ia32_cmpngeps (v4sf, v4sf)
v4sf __builtin_ia32_cmpordps (v4sf, v4sf)
v4sf __builtin_ia32_cmpeqss (v4sf, v4sf)
v4sf __builtin_ia32_cmpltss (v4sf, v4sf)
v4sf __builtin_ia32_cmpless (v4sf, v4sf)
v4sf __builtin_ia32_cmpunordss (v4sf, v4sf)
v4sf __builtin_ia32_cmpneqss (v4sf, v4sf)
v4sf __builtin_ia32_cmpnltss (v4sf, v4sf)
v4sf __builtin_ia32_cmpnless (v4sf, v4sf)
v4sf __builtin_ia32_cmpordss (v4sf, v4sf)
v4sf __builtin_ia32_maxps (v4sf, v4sf)
v4sf __builtin_ia32_maxss (v4sf, v4sf)
v4sf __builtin_ia32_minps (v4sf, v4sf)
v4sf __builtin_ia32_minss (v4sf, v4sf)
v4sf __builtin_ia32_andps (v4sf, v4sf)
v4sf __builtin_ia32_andnps (v4sf, v4sf)
v4sf __builtin_ia32_orps (v4sf, v4sf)
v4sf __builtin_ia32_xorps (v4sf, v4sf)
v4sf __builtin_ia32_movss (v4sf, v4sf)
v4sf __builtin_ia32_movhlps (v4sf, v4sf)
v4sf __builtin_ia32_movlhps (v4sf, v4sf)
v4sf __builtin_ia32_unpckhps (v4sf, v4sf)
v4sf __builtin_ia32_unpcklps (v4sf, v4sf)
v4sf __builtin_ia32_cvtpi2ps (v4sf, v2si)
v4sf __builtin_ia32_cvtsi2ss (v4sf, int)
v2si __builtin_ia32_cvtps2pi (v4sf)
int __builtin_ia32_cvtss2si (v4sf)
v2si __builtin_ia32_cvttps2pi (v4sf)
int __builtin_ia32_cvttss2si (v4sf)
v4sf __builtin_ia32_rcpps (v4sf)
v4sf __builtin_ia32_rsqrtps (v4sf)
v4sf __builtin_ia32_sqrtps (v4sf)
v4sf __builtin_ia32_rcpss (v4sf)
v4sf __builtin_ia32_rsqrtss (v4sf)
v4sf __builtin_ia32_sqrtss (v4sf)
v4sf __builtin_ia32_shufps (v4sf, v4sf, int)
void __builtin_ia32_movntps (float *, v4sf)
int __builtin_ia32_movmskps (v4sf)
The following built-in functions are available when -msse is used.
Generates the movups machine instruction as a load from memory.
Generates the movups machine instruction as a store to memory.
Generates the movss machine instruction as a load from memory.
Generates the movhps machine instruction as a load from memory.
Generates the movlps machine instruction as a load from memory
Generates the movhps machine instruction as a store to memory.
Generates the movlps machine instruction as a store to memory.
The following built-in functions are available when -msse2 is used. All of them generate the machine instruction that is part of the name.
int __builtin_ia32_comisdeq (v2df, v2df)
int __builtin_ia32_comisdlt (v2df, v2df)
int __builtin_ia32_comisdle (v2df, v2df)
int __builtin_ia32_comisdgt (v2df, v2df)
int __builtin_ia32_comisdge (v2df, v2df)
int __builtin_ia32_comisdneq (v2df, v2df)
int __builtin_ia32_ucomisdeq (v2df, v2df)
int __builtin_ia32_ucomisdlt (v2df, v2df)
int __builtin_ia32_ucomisdle (v2df, v2df)
int __builtin_ia32_ucomisdgt (v2df, v2df)
int __builtin_ia32_ucomisdge (v2df, v2df)
int __builtin_ia32_ucomisdneq (v2df, v2df)
v2df __builtin_ia32_cmpeqpd (v2df, v2df)
v2df __builtin_ia32_cmpltpd (v2df, v2df)
v2df __builtin_ia32_cmplepd (v2df, v2df)
v2df __builtin_ia32_cmpgtpd (v2df, v2df)
v2df __builtin_ia32_cmpgepd (v2df, v2df)
v2df __builtin_ia32_cmpunordpd (v2df, v2df)
v2df __builtin_ia32_cmpneqpd (v2df, v2df)
v2df __builtin_ia32_cmpnltpd (v2df, v2df)
v2df __builtin_ia32_cmpnlepd (v2df, v2df)
v2df __builtin_ia32_cmpngtpd (v2df, v2df)
v2df __builtin_ia32_cmpngepd (v2df, v2df)
v2df __builtin_ia32_cmpordpd (v2df, v2df)
v2df __builtin_ia32_cmpeqsd (v2df, v2df)
v2df __builtin_ia32_cmpltsd (v2df, v2df)
v2df __builtin_ia32_cmplesd (v2df, v2df)
v2df __builtin_ia32_cmpunordsd (v2df, v2df)
v2df __builtin_ia32_cmpneqsd (v2df, v2df)
v2df __builtin_ia32_cmpnltsd (v2df, v2df)
v2df __builtin_ia32_cmpnlesd (v2df, v2df)
v2df __builtin_ia32_cmpordsd (v2df, v2df)
v2di __builtin_ia32_paddq (v2di, v2di)
v2di __builtin_ia32_psubq (v2di, v2di)
v2df __builtin_ia32_addpd (v2df, v2df)
v2df __builtin_ia32_subpd (v2df, v2df)
v2df __builtin_ia32_mulpd (v2df, v2df)
v2df __builtin_ia32_divpd (v2df, v2df)
v2df __builtin_ia32_addsd (v2df, v2df)
v2df __builtin_ia32_subsd (v2df, v2df)
v2df __builtin_ia32_mulsd (v2df, v2df)
v2df __builtin_ia32_divsd (v2df, v2df)
v2df __builtin_ia32_minpd (v2df, v2df)
v2df __builtin_ia32_maxpd (v2df, v2df)
v2df __builtin_ia32_minsd (v2df, v2df)
v2df __builtin_ia32_maxsd (v2df, v2df)
v2df __builtin_ia32_andpd (v2df, v2df)
v2df __builtin_ia32_andnpd (v2df, v2df)
v2df __builtin_ia32_orpd (v2df, v2df)
v2df __builtin_ia32_xorpd (v2df, v2df)
v2df __builtin_ia32_movsd (v2df, v2df)
v2df __builtin_ia32_unpckhpd (v2df, v2df)
v2df __builtin_ia32_unpcklpd (v2df, v2df)
v16qi __builtin_ia32_paddb128 (v16qi, v16qi)
v8hi __builtin_ia32_paddw128 (v8hi, v8hi)
v4si __builtin_ia32_paddd128 (v4si, v4si)
v2di __builtin_ia32_paddq128 (v2di, v2di)
v16qi __builtin_ia32_psubb128 (v16qi, v16qi)
v8hi __builtin_ia32_psubw128 (v8hi, v8hi)
v4si __builtin_ia32_psubd128 (v4si, v4si)
v2di __builtin_ia32_psubq128 (v2di, v2di)
v8hi __builtin_ia32_pmullw128 (v8hi, v8hi)
v8hi __builtin_ia32_pmulhw128 (v8hi, v8hi)
v2di __builtin_ia32_pand128 (v2di, v2di)
v2di __builtin_ia32_pandn128 (v2di, v2di)
v2di __builtin_ia32_por128 (v2di, v2di)
v2di __builtin_ia32_pxor128 (v2di, v2di)
v16qi __builtin_ia32_pavgb128 (v16qi, v16qi)
v8hi __builtin_ia32_pavgw128 (v8hi, v8hi)
v16qi __builtin_ia32_pcmpeqb128 (v16qi, v16qi)
v8hi __builtin_ia32_pcmpeqw128 (v8hi, v8hi)
v4si __builtin_ia32_pcmpeqd128 (v4si, v4si)
v16qi __builtin_ia32_pcmpgtb128 (v16qi, v16qi)
v8hi __builtin_ia32_pcmpgtw128 (v8hi, v8hi)
v4si __builtin_ia32_pcmpgtd128 (v4si, v4si)
v16qi __builtin_ia32_pmaxub128 (v16qi, v16qi)
v8hi __builtin_ia32_pmaxsw128 (v8hi, v8hi)
v16qi __builtin_ia32_pminub128 (v16qi, v16qi)
v8hi __builtin_ia32_pminsw128 (v8hi, v8hi)
v16qi __builtin_ia32_punpckhbw128 (v16qi, v16qi)
v8hi __builtin_ia32_punpckhwd128 (v8hi, v8hi)
v4si __builtin_ia32_punpckhdq128 (v4si, v4si)
v2di __builtin_ia32_punpckhqdq128 (v2di, v2di)
v16qi __builtin_ia32_punpcklbw128 (v16qi, v16qi)
v8hi __builtin_ia32_punpcklwd128 (v8hi, v8hi)
v4si __builtin_ia32_punpckldq128 (v4si, v4si)
v2di __builtin_ia32_punpcklqdq128 (v2di, v2di)
v16qi __builtin_ia32_packsswb128 (v8hi, v8hi)
v8hi __builtin_ia32_packssdw128 (v4si, v4si)
v16qi __builtin_ia32_packuswb128 (v8hi, v8hi)
v8hi __builtin_ia32_pmulhuw128 (v8hi, v8hi)
void __builtin_ia32_maskmovdqu (v16qi, v16qi)
v2df __builtin_ia32_loadupd (double *)
void __builtin_ia32_storeupd (double *, v2df)
v2df __builtin_ia32_loadhpd (v2df, double const *)
v2df __builtin_ia32_loadlpd (v2df, double const *)
int __builtin_ia32_movmskpd (v2df)
int __builtin_ia32_pmovmskb128 (v16qi)
void __builtin_ia32_movnti (int *, int)
void __builtin_ia32_movnti64 (long long int *, long long int)
void __builtin_ia32_movntpd (double *, v2df)
void __builtin_ia32_movntdq (v2df *, v2df)
v4si __builtin_ia32_pshufd (v4si, int)
v8hi __builtin_ia32_pshuflw (v8hi, int)
v8hi __builtin_ia32_pshufhw (v8hi, int)
v2di __builtin_ia32_psadbw128 (v16qi, v16qi)
v2df __builtin_ia32_sqrtpd (v2df)
v2df __builtin_ia32_sqrtsd (v2df)
v2df __builtin_ia32_shufpd (v2df, v2df, int)
v2df __builtin_ia32_cvtdq2pd (v4si)
v4sf __builtin_ia32_cvtdq2ps (v4si)
v4si __builtin_ia32_cvtpd2dq (v2df)
v2si __builtin_ia32_cvtpd2pi (v2df)
v4sf __builtin_ia32_cvtpd2ps (v2df)
v4si __builtin_ia32_cvttpd2dq (v2df)
v2si __builtin_ia32_cvttpd2pi (v2df)
v2df __builtin_ia32_cvtpi2pd (v2si)
int __builtin_ia32_cvtsd2si (v2df)
int __builtin_ia32_cvttsd2si (v2df)
long long __builtin_ia32_cvtsd2si64 (v2df)
long long __builtin_ia32_cvttsd2si64 (v2df)
v4si __builtin_ia32_cvtps2dq (v4sf)
v2df __builtin_ia32_cvtps2pd (v4sf)
v4si __builtin_ia32_cvttps2dq (v4sf)
v2df __builtin_ia32_cvtsi2sd (v2df, int)
v2df __builtin_ia32_cvtsi642sd (v2df, long long)
v4sf __builtin_ia32_cvtsd2ss (v4sf, v2df)
v2df __builtin_ia32_cvtss2sd (v2df, v4sf)
void __builtin_ia32_clflush (const void *)
void __builtin_ia32_lfence (void)
void __builtin_ia32_mfence (void)
v16qi __builtin_ia32_loaddqu (const char *)
void __builtin_ia32_storedqu (char *, v16qi)
v1di __builtin_ia32_pmuludq (v2si, v2si)
v2di __builtin_ia32_pmuludq128 (v4si, v4si)
v8hi __builtin_ia32_psllw128 (v8hi, v8hi)
v4si __builtin_ia32_pslld128 (v4si, v4si)
v2di __builtin_ia32_psllq128 (v2di, v2di)
v8hi __builtin_ia32_psrlw128 (v8hi, v8hi)
v4si __builtin_ia32_psrld128 (v4si, v4si)
v2di __builtin_ia32_psrlq128 (v2di, v2di)
v8hi __builtin_ia32_psraw128 (v8hi, v8hi)
v4si __builtin_ia32_psrad128 (v4si, v4si)
v2di __builtin_ia32_pslldqi128 (v2di, int)
v8hi __builtin_ia32_psllwi128 (v8hi, int)
v4si __builtin_ia32_pslldi128 (v4si, int)
v2di __builtin_ia32_psllqi128 (v2di, int)
v2di __builtin_ia32_psrldqi128 (v2di, int)
v8hi __builtin_ia32_psrlwi128 (v8hi, int)
v4si __builtin_ia32_psrldi128 (v4si, int)
v2di __builtin_ia32_psrlqi128 (v2di, int)
v8hi __builtin_ia32_psrawi128 (v8hi, int)
v4si __builtin_ia32_psradi128 (v4si, int)
v4si __builtin_ia32_pmaddwd128 (v8hi, v8hi)
v2di __builtin_ia32_movq128 (v2di)
The following built-in functions are available when -msse3 is used. All of them generate the machine instruction that is part of the name.
v2df __builtin_ia32_addsubpd (v2df, v2df)
v4sf __builtin_ia32_addsubps (v4sf, v4sf)
v2df __builtin_ia32_haddpd (v2df, v2df)
v4sf __builtin_ia32_haddps (v4sf, v4sf)
v2df __builtin_ia32_hsubpd (v2df, v2df)
v4sf __builtin_ia32_hsubps (v4sf, v4sf)
v16qi __builtin_ia32_lddqu (char const *)
void __builtin_ia32_monitor (void *, unsigned int, unsigned int)
v4sf __builtin_ia32_movshdup (v4sf)
v4sf __builtin_ia32_movsldup (v4sf)
void __builtin_ia32_mwait (unsigned int, unsigned int)
The following built-in functions are available when -mssse3 is used. All of them generate the machine instruction that is part of the name.
v2si __builtin_ia32_phaddd (v2si, v2si)
v4hi __builtin_ia32_phaddw (v4hi, v4hi)
v4hi __builtin_ia32_phaddsw (v4hi, v4hi)
v2si __builtin_ia32_phsubd (v2si, v2si)
v4hi __builtin_ia32_phsubw (v4hi, v4hi)
v4hi __builtin_ia32_phsubsw (v4hi, v4hi)
v4hi __builtin_ia32_pmaddubsw (v8qi, v8qi)
v4hi __builtin_ia32_pmulhrsw (v4hi, v4hi)
v8qi __builtin_ia32_pshufb (v8qi, v8qi)
v8qi __builtin_ia32_psignb (v8qi, v8qi)
v2si __builtin_ia32_psignd (v2si, v2si)
v4hi __builtin_ia32_psignw (v4hi, v4hi)
v1di __builtin_ia32_palignr (v1di, v1di, int)
v8qi __builtin_ia32_pabsb (v8qi)
v2si __builtin_ia32_pabsd (v2si)
v4hi __builtin_ia32_pabsw (v4hi)
The following built-in functions are available when -mssse3 is used. All of them generate the machine instruction that is part of the name.
v4si __builtin_ia32_phaddd128 (v4si, v4si)
v8hi __builtin_ia32_phaddw128 (v8hi, v8hi)
v8hi __builtin_ia32_phaddsw128 (v8hi, v8hi)
v4si __builtin_ia32_phsubd128 (v4si, v4si)
v8hi __builtin_ia32_phsubw128 (v8hi, v8hi)
v8hi __builtin_ia32_phsubsw128 (v8hi, v8hi)
v8hi __builtin_ia32_pmaddubsw128 (v16qi, v16qi)
v8hi __builtin_ia32_pmulhrsw128 (v8hi, v8hi)
v16qi __builtin_ia32_pshufb128 (v16qi, v16qi)
v16qi __builtin_ia32_psignb128 (v16qi, v16qi)
v4si __builtin_ia32_psignd128 (v4si, v4si)
v8hi __builtin_ia32_psignw128 (v8hi, v8hi)
v2di __builtin_ia32_palignr128 (v2di, v2di, int)
v16qi __builtin_ia32_pabsb128 (v16qi)
v4si __builtin_ia32_pabsd128 (v4si)
v8hi __builtin_ia32_pabsw128 (v8hi)
The following built-in functions are available when -msse4.1 is used. All of them generate the machine instruction that is part of the name.
v2df __builtin_ia32_blendpd (v2df, v2df, const int)
v4sf __builtin_ia32_blendps (v4sf, v4sf, const int)
v2df __builtin_ia32_blendvpd (v2df, v2df, v2df)
v4sf __builtin_ia32_blendvps (v4sf, v4sf, v4sf)
v2df __builtin_ia32_dppd (v2df, v2df, const int)
v4sf __builtin_ia32_dpps (v4sf, v4sf, const int)
v4sf __builtin_ia32_insertps128 (v4sf, v4sf, const int)
v2di __builtin_ia32_movntdqa (v2di *);
v16qi __builtin_ia32_mpsadbw128 (v16qi, v16qi, const int)
v8hi __builtin_ia32_packusdw128 (v4si, v4si)
v16qi __builtin_ia32_pblendvb128 (v16qi, v16qi, v16qi)
v8hi __builtin_ia32_pblendw128 (v8hi, v8hi, const int)
v2di __builtin_ia32_pcmpeqq (v2di, v2di)
v8hi __builtin_ia32_phminposuw128 (v8hi)
v16qi __builtin_ia32_pmaxsb128 (v16qi, v16qi)
v4si __builtin_ia32_pmaxsd128 (v4si, v4si)
v4si __builtin_ia32_pmaxud128 (v4si, v4si)
v8hi __builtin_ia32_pmaxuw128 (v8hi, v8hi)
v16qi __builtin_ia32_pminsb128 (v16qi, v16qi)
v4si __builtin_ia32_pminsd128 (v4si, v4si)
v4si __builtin_ia32_pminud128 (v4si, v4si)
v8hi __builtin_ia32_pminuw128 (v8hi, v8hi)
v4si __builtin_ia32_pmovsxbd128 (v16qi)
v2di __builtin_ia32_pmovsxbq128 (v16qi)
v8hi __builtin_ia32_pmovsxbw128 (v16qi)
v2di __builtin_ia32_pmovsxdq128 (v4si)
v4si __builtin_ia32_pmovsxwd128 (v8hi)
v2di __builtin_ia32_pmovsxwq128 (v8hi)
v4si __builtin_ia32_pmovzxbd128 (v16qi)
v2di __builtin_ia32_pmovzxbq128 (v16qi)
v8hi __builtin_ia32_pmovzxbw128 (v16qi)
v2di __builtin_ia32_pmovzxdq128 (v4si)
v4si __builtin_ia32_pmovzxwd128 (v8hi)
v2di __builtin_ia32_pmovzxwq128 (v8hi)
v2di __builtin_ia32_pmuldq128 (v4si, v4si)
v4si __builtin_ia32_pmulld128 (v4si, v4si)
int __builtin_ia32_ptestc128 (v2di, v2di)
int __builtin_ia32_ptestnzc128 (v2di, v2di)
int __builtin_ia32_ptestz128 (v2di, v2di)
v2df __builtin_ia32_roundpd (v2df, const int)
v4sf __builtin_ia32_roundps (v4sf, const int)
v2df __builtin_ia32_roundsd (v2df, v2df, const int)
v4sf __builtin_ia32_roundss (v4sf, v4sf, const int)
The following built-in functions are available when -msse4.1 is used.
Generates the insertps machine instruction.
Generates the pextrb machine instruction.
Generates the pinsrb machine instruction.
Generates the pinsrd machine instruction.
Generates the pinsrq machine instruction in 64bit mode.
The following built-in functions are changed to generate new SSE4.1 instructions when -msse4.1 is used.
Generates the extractps machine instruction.
Generates the pextrd machine instruction.
Generates the pextrq machine instruction in 64bit mode.
The following built-in functions are available when -msse4.2 is used. All of them generate the machine instruction that is part of the name.
v16qi __builtin_ia32_pcmpestrm128 (v16qi, int, v16qi, int, const int)
int __builtin_ia32_pcmpestri128 (v16qi, int, v16qi, int, const int)
int __builtin_ia32_pcmpestria128 (v16qi, int, v16qi, int, const int)
int __builtin_ia32_pcmpestric128 (v16qi, int, v16qi, int, const int)
int __builtin_ia32_pcmpestrio128 (v16qi, int, v16qi, int, const int)
int __builtin_ia32_pcmpestris128 (v16qi, int, v16qi, int, const int)
int __builtin_ia32_pcmpestriz128 (v16qi, int, v16qi, int, const int)
v16qi __builtin_ia32_pcmpistrm128 (v16qi, v16qi, const int)
int __builtin_ia32_pcmpistri128 (v16qi, v16qi, const int)
int __builtin_ia32_pcmpistria128 (v16qi, v16qi, const int)
int __builtin_ia32_pcmpistric128 (v16qi, v16qi, const int)
int __builtin_ia32_pcmpistrio128 (v16qi, v16qi, const int)
int __builtin_ia32_pcmpistris128 (v16qi, v16qi, const int)
int __builtin_ia32_pcmpistriz128 (v16qi, v16qi, const int)
v2di __builtin_ia32_pcmpgtq (v2di, v2di)
The following built-in functions are available when -msse4.2 is used.
Generates the crc32b machine instruction.
Generates the crc32w machine instruction.
Generates the crc32l machine instruction.
Generates the crc32q machine instruction.
The following built-in functions are changed to generate new SSE4.2 instructions when -msse4.2 is used.
Generates the popcntl machine instruction.
Generates the popcntl or popcntq machine instruction, depending on the size of unsigned long.
Generates the popcntq machine instruction.
The following built-in functions are available when -mavx is used. All of them generate the machine instruction that is part of the name.
v4df __builtin_ia32_addpd256 (v4df,v4df)
v8sf __builtin_ia32_addps256 (v8sf,v8sf)
v4df __builtin_ia32_addsubpd256 (v4df,v4df)
v8sf __builtin_ia32_addsubps256 (v8sf,v8sf)
v4df __builtin_ia32_andnpd256 (v4df,v4df)
v8sf __builtin_ia32_andnps256 (v8sf,v8sf)
v4df __builtin_ia32_andpd256 (v4df,v4df)
v8sf __builtin_ia32_andps256 (v8sf,v8sf)
v4df __builtin_ia32_blendpd256 (v4df,v4df,int)
v8sf __builtin_ia32_blendps256 (v8sf,v8sf,int)
v4df __builtin_ia32_blendvpd256 (v4df,v4df,v4df)
v8sf __builtin_ia32_blendvps256 (v8sf,v8sf,v8sf)
v2df __builtin_ia32_cmppd (v2df,v2df,int)
v4df __builtin_ia32_cmppd256 (v4df,v4df,int)
v4sf __builtin_ia32_cmpps (v4sf,v4sf,int)
v8sf __builtin_ia32_cmpps256 (v8sf,v8sf,int)
v2df __builtin_ia32_cmpsd (v2df,v2df,int)
v4sf __builtin_ia32_cmpss (v4sf,v4sf,int)
v4df __builtin_ia32_cvtdq2pd256 (v4si)
v8sf __builtin_ia32_cvtdq2ps256 (v8si)
v4si __builtin_ia32_cvtpd2dq256 (v4df)
v4sf __builtin_ia32_cvtpd2ps256 (v4df)
v8si __builtin_ia32_cvtps2dq256 (v8sf)
v4df __builtin_ia32_cvtps2pd256 (v4sf)
v4si __builtin_ia32_cvttpd2dq256 (v4df)
v8si __builtin_ia32_cvttps2dq256 (v8sf)
v4df __builtin_ia32_divpd256 (v4df,v4df)
v8sf __builtin_ia32_divps256 (v8sf,v8sf)
v8sf __builtin_ia32_dpps256 (v8sf,v8sf,int)
v4df __builtin_ia32_haddpd256 (v4df,v4df)
v8sf __builtin_ia32_haddps256 (v8sf,v8sf)
v4df __builtin_ia32_hsubpd256 (v4df,v4df)
v8sf __builtin_ia32_hsubps256 (v8sf,v8sf)
v32qi __builtin_ia32_lddqu256 (pcchar)
v32qi __builtin_ia32_loaddqu256 (pcchar)
v4df __builtin_ia32_loadupd256 (pcdouble)
v8sf __builtin_ia32_loadups256 (pcfloat)
v2df __builtin_ia32_maskloadpd (pcv2df,v2df)
v4df __builtin_ia32_maskloadpd256 (pcv4df,v4df)
v4sf __builtin_ia32_maskloadps (pcv4sf,v4sf)
v8sf __builtin_ia32_maskloadps256 (pcv8sf,v8sf)
void __builtin_ia32_maskstorepd (pv2df,v2df,v2df)
void __builtin_ia32_maskstorepd256 (pv4df,v4df,v4df)
void __builtin_ia32_maskstoreps (pv4sf,v4sf,v4sf)
void __builtin_ia32_maskstoreps256 (pv8sf,v8sf,v8sf)
v4df __builtin_ia32_maxpd256 (v4df,v4df)
v8sf __builtin_ia32_maxps256 (v8sf,v8sf)
v4df __builtin_ia32_minpd256 (v4df,v4df)
v8sf __builtin_ia32_minps256 (v8sf,v8sf)
v4df __builtin_ia32_movddup256 (v4df)
int __builtin_ia32_movmskpd256 (v4df)
int __builtin_ia32_movmskps256 (v8sf)
v8sf __builtin_ia32_movshdup256 (v8sf)
v8sf __builtin_ia32_movsldup256 (v8sf)
v4df __builtin_ia32_mulpd256 (v4df,v4df)
v8sf __builtin_ia32_mulps256 (v8sf,v8sf)
v4df __builtin_ia32_orpd256 (v4df,v4df)
v8sf __builtin_ia32_orps256 (v8sf,v8sf)
v2df __builtin_ia32_pd_pd256 (v4df)
v4df __builtin_ia32_pd256_pd (v2df)
v4sf __builtin_ia32_ps_ps256 (v8sf)
v8sf __builtin_ia32_ps256_ps (v4sf)
int __builtin_ia32_ptestc256 (v4di,v4di,ptest)
int __builtin_ia32_ptestnzc256 (v4di,v4di,ptest)
int __builtin_ia32_ptestz256 (v4di,v4di,ptest)
v8sf __builtin_ia32_rcpps256 (v8sf)
v4df __builtin_ia32_roundpd256 (v4df,int)
v8sf __builtin_ia32_roundps256 (v8sf,int)
v8sf __builtin_ia32_rsqrtps_nr256 (v8sf)
v8sf __builtin_ia32_rsqrtps256 (v8sf)
v4df __builtin_ia32_shufpd256 (v4df,v4df,int)
v8sf __builtin_ia32_shufps256 (v8sf,v8sf,int)
v4si __builtin_ia32_si_si256 (v8si)
v8si __builtin_ia32_si256_si (v4si)
v4df __builtin_ia32_sqrtpd256 (v4df)
v8sf __builtin_ia32_sqrtps_nr256 (v8sf)
v8sf __builtin_ia32_sqrtps256 (v8sf)
void __builtin_ia32_storedqu256 (pchar,v32qi)
void __builtin_ia32_storeupd256 (pdouble,v4df)
void __builtin_ia32_storeups256 (pfloat,v8sf)
v4df __builtin_ia32_subpd256 (v4df,v4df)
v8sf __builtin_ia32_subps256 (v8sf,v8sf)
v4df __builtin_ia32_unpckhpd256 (v4df,v4df)
v8sf __builtin_ia32_unpckhps256 (v8sf,v8sf)
v4df __builtin_ia32_unpcklpd256 (v4df,v4df)
v8sf __builtin_ia32_unpcklps256 (v8sf,v8sf)
v4df __builtin_ia32_vbroadcastf128_pd256 (pcv2df)
v8sf __builtin_ia32_vbroadcastf128_ps256 (pcv4sf)
v4df __builtin_ia32_vbroadcastsd256 (pcdouble)
v4sf __builtin_ia32_vbroadcastss (pcfloat)
v8sf __builtin_ia32_vbroadcastss256 (pcfloat)
v2df __builtin_ia32_vextractf128_pd256 (v4df,int)
v4sf __builtin_ia32_vextractf128_ps256 (v8sf,int)
v4si __builtin_ia32_vextractf128_si256 (v8si,int)
v4df __builtin_ia32_vinsertf128_pd256 (v4df,v2df,int)
v8sf __builtin_ia32_vinsertf128_ps256 (v8sf,v4sf,int)
v8si __builtin_ia32_vinsertf128_si256 (v8si,v4si,int)
v4df __builtin_ia32_vperm2f128_pd256 (v4df,v4df,int)
v8sf __builtin_ia32_vperm2f128_ps256 (v8sf,v8sf,int)
v8si __builtin_ia32_vperm2f128_si256 (v8si,v8si,int)
v2df __builtin_ia32_vpermil2pd (v2df,v2df,v2di,int)
v4df __builtin_ia32_vpermil2pd256 (v4df,v4df,v4di,int)
v4sf __builtin_ia32_vpermil2ps (v4sf,v4sf,v4si,int)
v8sf __builtin_ia32_vpermil2ps256 (v8sf,v8sf,v8si,int)
v2df __builtin_ia32_vpermilpd (v2df,int)
v4df __builtin_ia32_vpermilpd256 (v4df,int)
v4sf __builtin_ia32_vpermilps (v4sf,int)
v8sf __builtin_ia32_vpermilps256 (v8sf,int)
v2df __builtin_ia32_vpermilvarpd (v2df,v2di)
v4df __builtin_ia32_vpermilvarpd256 (v4df,v4di)
v4sf __builtin_ia32_vpermilvarps (v4sf,v4si)
v8sf __builtin_ia32_vpermilvarps256 (v8sf,v8si)
int __builtin_ia32_vtestcpd (v2df,v2df,ptest)
int __builtin_ia32_vtestcpd256 (v4df,v4df,ptest)
int __builtin_ia32_vtestcps (v4sf,v4sf,ptest)
int __builtin_ia32_vtestcps256 (v8sf,v8sf,ptest)
int __builtin_ia32_vtestnzcpd (v2df,v2df,ptest)
int __builtin_ia32_vtestnzcpd256 (v4df,v4df,ptest)
int __builtin_ia32_vtestnzcps (v4sf,v4sf,ptest)
int __builtin_ia32_vtestnzcps256 (v8sf,v8sf,ptest)
int __builtin_ia32_vtestzpd (v2df,v2df,ptest)
int __builtin_ia32_vtestzpd256 (v4df,v4df,ptest)
int __builtin_ia32_vtestzps (v4sf,v4sf,ptest)
int __builtin_ia32_vtestzps256 (v8sf,v8sf,ptest)
void __builtin_ia32_vzeroall (void)
void __builtin_ia32_vzeroupper (void)
v4df __builtin_ia32_xorpd256 (v4df,v4df)
v8sf __builtin_ia32_xorps256 (v8sf,v8sf)
The following built-in functions are available when -mavx2 is used. All of them generate the machine instruction that is part of the name.
v32qi __builtin_ia32_mpsadbw256 (v32qi,v32qi,int)
v32qi __builtin_ia32_pabsb256 (v32qi)
v16hi __builtin_ia32_pabsw256 (v16hi)
v8si __builtin_ia32_pabsd256 (v8si)
v16hi __builtin_ia32_packssdw256 (v8si,v8si)
v32qi __builtin_ia32_packsswb256 (v16hi,v16hi)
v16hi __builtin_ia32_packusdw256 (v8si,v8si)
v32qi __builtin_ia32_packuswb256 (v16hi,v16hi)
v32qi __builtin_ia32_paddb256 (v32qi,v32qi)
v16hi __builtin_ia32_paddw256 (v16hi,v16hi)
v8si __builtin_ia32_paddd256 (v8si,v8si)
v4di __builtin_ia32_paddq256 (v4di,v4di)
v32qi __builtin_ia32_paddsb256 (v32qi,v32qi)
v16hi __builtin_ia32_paddsw256 (v16hi,v16hi)
v32qi __builtin_ia32_paddusb256 (v32qi,v32qi)
v16hi __builtin_ia32_paddusw256 (v16hi,v16hi)
v4di __builtin_ia32_palignr256 (v4di,v4di,int)
v4di __builtin_ia32_andsi256 (v4di,v4di)
v4di __builtin_ia32_andnotsi256 (v4di,v4di)
v32qi __builtin_ia32_pavgb256 (v32qi,v32qi)
v16hi __builtin_ia32_pavgw256 (v16hi,v16hi)
v32qi __builtin_ia32_pblendvb256 (v32qi,v32qi,v32qi)
v16hi __builtin_ia32_pblendw256 (v16hi,v16hi,int)
v32qi __builtin_ia32_pcmpeqb256 (v32qi,v32qi)
v16hi __builtin_ia32_pcmpeqw256 (v16hi,v16hi)
v8si __builtin_ia32_pcmpeqd256 (c8si,v8si)
v4di __builtin_ia32_pcmpeqq256 (v4di,v4di)
v32qi __builtin_ia32_pcmpgtb256 (v32qi,v32qi)
v16hi __builtin_ia32_pcmpgtw256 (16hi,v16hi)
v8si __builtin_ia32_pcmpgtd256 (v8si,v8si)
v4di __builtin_ia32_pcmpgtq256 (v4di,v4di)
v16hi __builtin_ia32_phaddw256 (v16hi,v16hi)
v8si __builtin_ia32_phaddd256 (v8si,v8si)
v16hi __builtin_ia32_phaddsw256 (v16hi,v16hi)
v16hi __builtin_ia32_phsubw256 (v16hi,v16hi)
v8si __builtin_ia32_phsubd256 (v8si,v8si)
v16hi __builtin_ia32_phsubsw256 (v16hi,v16hi)
v32qi __builtin_ia32_pmaddubsw256 (v32qi,v32qi)
v16hi __builtin_ia32_pmaddwd256 (v16hi,v16hi)
v32qi __builtin_ia32_pmaxsb256 (v32qi,v32qi)
v16hi __builtin_ia32_pmaxsw256 (v16hi,v16hi)
v8si __builtin_ia32_pmaxsd256 (v8si,v8si)
v32qi __builtin_ia32_pmaxub256 (v32qi,v32qi)
v16hi __builtin_ia32_pmaxuw256 (v16hi,v16hi)
v8si __builtin_ia32_pmaxud256 (v8si,v8si)
v32qi __builtin_ia32_pminsb256 (v32qi,v32qi)
v16hi __builtin_ia32_pminsw256 (v16hi,v16hi)
v8si __builtin_ia32_pminsd256 (v8si,v8si)
v32qi __builtin_ia32_pminub256 (v32qi,v32qi)
v16hi __builtin_ia32_pminuw256 (v16hi,v16hi)
v8si __builtin_ia32_pminud256 (v8si,v8si)
int __builtin_ia32_pmovmskb256 (v32qi)
v16hi __builtin_ia32_pmovsxbw256 (v16qi)
v8si __builtin_ia32_pmovsxbd256 (v16qi)
v4di __builtin_ia32_pmovsxbq256 (v16qi)
v8si __builtin_ia32_pmovsxwd256 (v8hi)
v4di __builtin_ia32_pmovsxwq256 (v8hi)
v4di __builtin_ia32_pmovsxdq256 (v4si)
v16hi __builtin_ia32_pmovzxbw256 (v16qi)
v8si __builtin_ia32_pmovzxbd256 (v16qi)
v4di __builtin_ia32_pmovzxbq256 (v16qi)
v8si __builtin_ia32_pmovzxwd256 (v8hi)
v4di __builtin_ia32_pmovzxwq256 (v8hi)
v4di __builtin_ia32_pmovzxdq256 (v4si)
v4di __builtin_ia32_pmuldq256 (v8si,v8si)
v16hi __builtin_ia32_pmulhrsw256 (v16hi, v16hi)
v16hi __builtin_ia32_pmulhuw256 (v16hi,v16hi)
v16hi __builtin_ia32_pmulhw256 (v16hi,v16hi)
v16hi __builtin_ia32_pmullw256 (v16hi,v16hi)
v8si __builtin_ia32_pmulld256 (v8si,v8si)
v4di __builtin_ia32_pmuludq256 (v8si,v8si)
v4di __builtin_ia32_por256 (v4di,v4di)
v16hi __builtin_ia32_psadbw256 (v32qi,v32qi)
v32qi __builtin_ia32_pshufb256 (v32qi,v32qi)
v8si __builtin_ia32_pshufd256 (v8si,int)
v16hi __builtin_ia32_pshufhw256 (v16hi,int)
v16hi __builtin_ia32_pshuflw256 (v16hi,int)
v32qi __builtin_ia32_psignb256 (v32qi,v32qi)
v16hi __builtin_ia32_psignw256 (v16hi,v16hi)
v8si __builtin_ia32_psignd256 (v8si,v8si)
v4di __builtin_ia32_pslldqi256 (v4di,int)
v16hi __builtin_ia32_psllwi256 (16hi,int)
v16hi __builtin_ia32_psllw256(v16hi,v8hi)
v8si __builtin_ia32_pslldi256 (v8si,int)
v8si __builtin_ia32_pslld256(v8si,v4si)
v4di __builtin_ia32_psllqi256 (v4di,int)
v4di __builtin_ia32_psllq256(v4di,v2di)
v16hi __builtin_ia32_psrawi256 (v16hi,int)
v16hi __builtin_ia32_psraw256 (v16hi,v8hi)
v8si __builtin_ia32_psradi256 (v8si,int)
v8si __builtin_ia32_psrad256 (v8si,v4si)
v4di __builtin_ia32_psrldqi256 (v4di, int)
v16hi __builtin_ia32_psrlwi256 (v16hi,int)
v16hi __builtin_ia32_psrlw256 (v16hi,v8hi)
v8si __builtin_ia32_psrldi256 (v8si,int)
v8si __builtin_ia32_psrld256 (v8si,v4si)
v4di __builtin_ia32_psrlqi256 (v4di,int)
v4di __builtin_ia32_psrlq256(v4di,v2di)
v32qi __builtin_ia32_psubb256 (v32qi,v32qi)
v32hi __builtin_ia32_psubw256 (v16hi,v16hi)
v8si __builtin_ia32_psubd256 (v8si,v8si)
v4di __builtin_ia32_psubq256 (v4di,v4di)
v32qi __builtin_ia32_psubsb256 (v32qi,v32qi)
v16hi __builtin_ia32_psubsw256 (v16hi,v16hi)
v32qi __builtin_ia32_psubusb256 (v32qi,v32qi)
v16hi __builtin_ia32_psubusw256 (v16hi,v16hi)
v32qi __builtin_ia32_punpckhbw256 (v32qi,v32qi)
v16hi __builtin_ia32_punpckhwd256 (v16hi,v16hi)
v8si __builtin_ia32_punpckhdq256 (v8si,v8si)
v4di __builtin_ia32_punpckhqdq256 (v4di,v4di)
v32qi __builtin_ia32_punpcklbw256 (v32qi,v32qi)
v16hi __builtin_ia32_punpcklwd256 (v16hi,v16hi)
v8si __builtin_ia32_punpckldq256 (v8si,v8si)
v4di __builtin_ia32_punpcklqdq256 (v4di,v4di)
v4di __builtin_ia32_pxor256 (v4di,v4di)
v4di __builtin_ia32_movntdqa256 (pv4di)
v4sf __builtin_ia32_vbroadcastss_ps (v4sf)
v8sf __builtin_ia32_vbroadcastss_ps256 (v4sf)
v4df __builtin_ia32_vbroadcastsd_pd256 (v2df)
v4di __builtin_ia32_vbroadcastsi256 (v2di)
v4si __builtin_ia32_pblendd128 (v4si,v4si)
v8si __builtin_ia32_pblendd256 (v8si,v8si)
v32qi __builtin_ia32_pbroadcastb256 (v16qi)
v16hi __builtin_ia32_pbroadcastw256 (v8hi)
v8si __builtin_ia32_pbroadcastd256 (v4si)
v4di __builtin_ia32_pbroadcastq256 (v2di)
v16qi __builtin_ia32_pbroadcastb128 (v16qi)
v8hi __builtin_ia32_pbroadcastw128 (v8hi)
v4si __builtin_ia32_pbroadcastd128 (v4si)
v2di __builtin_ia32_pbroadcastq128 (v2di)
v8si __builtin_ia32_permvarsi256 (v8si,v8si)
v4df __builtin_ia32_permdf256 (v4df,int)
v8sf __builtin_ia32_permvarsf256 (v8sf,v8sf)
v4di __builtin_ia32_permdi256 (v4di,int)
v4di __builtin_ia32_permti256 (v4di,v4di,int)
v4di __builtin_ia32_extract128i256 (v4di,int)
v4di __builtin_ia32_insert128i256 (v4di,v2di,int)
v8si __builtin_ia32_maskloadd256 (pcv8si,v8si)
v4di __builtin_ia32_maskloadq256 (pcv4di,v4di)
v4si __builtin_ia32_maskloadd (pcv4si,v4si)
v2di __builtin_ia32_maskloadq (pcv2di,v2di)
void __builtin_ia32_maskstored256 (pv8si,v8si,v8si)
void __builtin_ia32_maskstoreq256 (pv4di,v4di,v4di)
void __builtin_ia32_maskstored (pv4si,v4si,v4si)
void __builtin_ia32_maskstoreq (pv2di,v2di,v2di)
v8si __builtin_ia32_psllv8si (v8si,v8si)
v4si __builtin_ia32_psllv4si (v4si,v4si)
v4di __builtin_ia32_psllv4di (v4di,v4di)
v2di __builtin_ia32_psllv2di (v2di,v2di)
v8si __builtin_ia32_psrav8si (v8si,v8si)
v4si __builtin_ia32_psrav4si (v4si,v4si)
v8si __builtin_ia32_psrlv8si (v8si,v8si)
v4si __builtin_ia32_psrlv4si (v4si,v4si)
v4di __builtin_ia32_psrlv4di (v4di,v4di)
v2di __builtin_ia32_psrlv2di (v2di,v2di)
v2df __builtin_ia32_gathersiv2df (v2df, pcdouble,v4si,v2df,int)
v4df __builtin_ia32_gathersiv4df (v4df, pcdouble,v4si,v4df,int)
v2df __builtin_ia32_gatherdiv2df (v2df, pcdouble,v2di,v2df,int)
v4df __builtin_ia32_gatherdiv4df (v4df, pcdouble,v4di,v4df,int)
v4sf __builtin_ia32_gathersiv4sf (v4sf, pcfloat,v4si,v4sf,int)
v8sf __builtin_ia32_gathersiv8sf (v8sf, pcfloat,v8si,v8sf,int)
v4sf __builtin_ia32_gatherdiv4sf (v4sf, pcfloat,v2di,v4sf,int)
v4sf __builtin_ia32_gatherdiv4sf256 (v4sf, pcfloat,v4di,v4sf,int)
v2di __builtin_ia32_gathersiv2di (v2di, pcint64,v4si,v2di,int)
v4di __builtin_ia32_gathersiv4di (v4di, pcint64,v4si,v4di,int)
v2di __builtin_ia32_gatherdiv2di (v2di, pcint64,v2di,v2di,int)
v4di __builtin_ia32_gatherdiv4di (v4di, pcint64,v4di,v4di,int)
v4si __builtin_ia32_gathersiv4si (v4si, pcint,v4si,v4si,int)
v8si __builtin_ia32_gathersiv8si (v8si, pcint,v8si,v8si,int)
v4si __builtin_ia32_gatherdiv4si (v4si, pcint,v2di,v4si,int)
v4si __builtin_ia32_gatherdiv4si256 (v4si, pcint,v4di,v4si,int)
The following built-in functions are available when -maes is used. All of them generate the machine instruction that is part of the name.
v2di __builtin_ia32_aesenc128 (v2di, v2di)
v2di __builtin_ia32_aesenclast128 (v2di, v2di)
v2di __builtin_ia32_aesdec128 (v2di, v2di)
v2di __builtin_ia32_aesdeclast128 (v2di, v2di)
v2di __builtin_ia32_aeskeygenassist128 (v2di, const int)
v2di __builtin_ia32_aesimc128 (v2di)
The following built-in function is available when -mpclmul is used.
Generates the pclmulqdq machine instruction.
The following built-in function is available when -mfsgsbase is used. All of them generate the machine instruction that is part of the name.
unsigned int __builtin_ia32_rdfsbase32 (void)
unsigned long long __builtin_ia32_rdfsbase64 (void)
unsigned int __builtin_ia32_rdgsbase32 (void)
unsigned long long __builtin_ia32_rdgsbase64 (void)
void _writefsbase_u32 (unsigned int)
void _writefsbase_u64 (unsigned long long)
void _writegsbase_u32 (unsigned int)
void _writegsbase_u64 (unsigned long long)
The following built-in function is available when -mrdrnd is used. All of them generate the machine instruction that is part of the name.
unsigned int __builtin_ia32_rdrand16_step (unsigned short *)
unsigned int __builtin_ia32_rdrand32_step (unsigned int *)
unsigned int __builtin_ia32_rdrand64_step (unsigned long long *)
The following built-in functions are available when -msse4a is used. All of them generate the machine instruction that is part of the name.
void __builtin_ia32_movntsd (double *, v2df)
void __builtin_ia32_movntss (float *, v4sf)
v2di __builtin_ia32_extrq (v2di, v16qi)
v2di __builtin_ia32_extrqi (v2di, const unsigned int, const unsigned int)
v2di __builtin_ia32_insertq (v2di, v2di)
v2di __builtin_ia32_insertqi (v2di, v2di, const unsigned int, const unsigned int)
The following built-in functions are available when -mxop is used.
v2df __builtin_ia32_vfrczpd (v2df)
v4sf __builtin_ia32_vfrczps (v4sf)
v2df __builtin_ia32_vfrczsd (v2df)
v4sf __builtin_ia32_vfrczss (v4sf)
v4df __builtin_ia32_vfrczpd256 (v4df)
v8sf __builtin_ia32_vfrczps256 (v8sf)
v2di __builtin_ia32_vpcmov (v2di, v2di, v2di)
v2di __builtin_ia32_vpcmov_v2di (v2di, v2di, v2di)
v4si __builtin_ia32_vpcmov_v4si (v4si, v4si, v4si)
v8hi __builtin_ia32_vpcmov_v8hi (v8hi, v8hi, v8hi)
v16qi __builtin_ia32_vpcmov_v16qi (v16qi, v16qi, v16qi)
v2df __builtin_ia32_vpcmov_v2df (v2df, v2df, v2df)
v4sf __builtin_ia32_vpcmov_v4sf (v4sf, v4sf, v4sf)
v4di __builtin_ia32_vpcmov_v4di256 (v4di, v4di, v4di)
v8si __builtin_ia32_vpcmov_v8si256 (v8si, v8si, v8si)
v16hi __builtin_ia32_vpcmov_v16hi256 (v16hi, v16hi, v16hi)
v32qi __builtin_ia32_vpcmov_v32qi256 (v32qi, v32qi, v32qi)
v4df __builtin_ia32_vpcmov_v4df256 (v4df, v4df, v4df)
v8sf __builtin_ia32_vpcmov_v8sf256 (v8sf, v8sf, v8sf)
v16qi __builtin_ia32_vpcomeqb (v16qi, v16qi)
v8hi __builtin_ia32_vpcomeqw (v8hi, v8hi)
v4si __builtin_ia32_vpcomeqd (v4si, v4si)
v2di __builtin_ia32_vpcomeqq (v2di, v2di)
v16qi __builtin_ia32_vpcomequb (v16qi, v16qi)
v4si __builtin_ia32_vpcomequd (v4si, v4si)
v2di __builtin_ia32_vpcomequq (v2di, v2di)
v8hi __builtin_ia32_vpcomequw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomeqw (v8hi, v8hi)
v16qi __builtin_ia32_vpcomfalseb (v16qi, v16qi)
v4si __builtin_ia32_vpcomfalsed (v4si, v4si)
v2di __builtin_ia32_vpcomfalseq (v2di, v2di)
v16qi __builtin_ia32_vpcomfalseub (v16qi, v16qi)
v4si __builtin_ia32_vpcomfalseud (v4si, v4si)
v2di __builtin_ia32_vpcomfalseuq (v2di, v2di)
v8hi __builtin_ia32_vpcomfalseuw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomfalsew (v8hi, v8hi)
v16qi __builtin_ia32_vpcomgeb (v16qi, v16qi)
v4si __builtin_ia32_vpcomged (v4si, v4si)
v2di __builtin_ia32_vpcomgeq (v2di, v2di)
v16qi __builtin_ia32_vpcomgeub (v16qi, v16qi)
v4si __builtin_ia32_vpcomgeud (v4si, v4si)
v2di __builtin_ia32_vpcomgeuq (v2di, v2di)
v8hi __builtin_ia32_vpcomgeuw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomgew (v8hi, v8hi)
v16qi __builtin_ia32_vpcomgtb (v16qi, v16qi)
v4si __builtin_ia32_vpcomgtd (v4si, v4si)
v2di __builtin_ia32_vpcomgtq (v2di, v2di)
v16qi __builtin_ia32_vpcomgtub (v16qi, v16qi)
v4si __builtin_ia32_vpcomgtud (v4si, v4si)
v2di __builtin_ia32_vpcomgtuq (v2di, v2di)
v8hi __builtin_ia32_vpcomgtuw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomgtw (v8hi, v8hi)
v16qi __builtin_ia32_vpcomleb (v16qi, v16qi)
v4si __builtin_ia32_vpcomled (v4si, v4si)
v2di __builtin_ia32_vpcomleq (v2di, v2di)
v16qi __builtin_ia32_vpcomleub (v16qi, v16qi)
v4si __builtin_ia32_vpcomleud (v4si, v4si)
v2di __builtin_ia32_vpcomleuq (v2di, v2di)
v8hi __builtin_ia32_vpcomleuw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomlew (v8hi, v8hi)
v16qi __builtin_ia32_vpcomltb (v16qi, v16qi)
v4si __builtin_ia32_vpcomltd (v4si, v4si)
v2di __builtin_ia32_vpcomltq (v2di, v2di)
v16qi __builtin_ia32_vpcomltub (v16qi, v16qi)
v4si __builtin_ia32_vpcomltud (v4si, v4si)
v2di __builtin_ia32_vpcomltuq (v2di, v2di)
v8hi __builtin_ia32_vpcomltuw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomltw (v8hi, v8hi)
v16qi __builtin_ia32_vpcomneb (v16qi, v16qi)
v4si __builtin_ia32_vpcomned (v4si, v4si)
v2di __builtin_ia32_vpcomneq (v2di, v2di)
v16qi __builtin_ia32_vpcomneub (v16qi, v16qi)
v4si __builtin_ia32_vpcomneud (v4si, v4si)
v2di __builtin_ia32_vpcomneuq (v2di, v2di)
v8hi __builtin_ia32_vpcomneuw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomnew (v8hi, v8hi)
v16qi __builtin_ia32_vpcomtrueb (v16qi, v16qi)
v4si __builtin_ia32_vpcomtrued (v4si, v4si)
v2di __builtin_ia32_vpcomtrueq (v2di, v2di)
v16qi __builtin_ia32_vpcomtrueub (v16qi, v16qi)
v4si __builtin_ia32_vpcomtrueud (v4si, v4si)
v2di __builtin_ia32_vpcomtrueuq (v2di, v2di)
v8hi __builtin_ia32_vpcomtrueuw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomtruew (v8hi, v8hi)
v4si __builtin_ia32_vphaddbd (v16qi)
v2di __builtin_ia32_vphaddbq (v16qi)
v8hi __builtin_ia32_vphaddbw (v16qi)
v2di __builtin_ia32_vphadddq (v4si)
v4si __builtin_ia32_vphaddubd (v16qi)
v2di __builtin_ia32_vphaddubq (v16qi)
v8hi __builtin_ia32_vphaddubw (v16qi)
v2di __builtin_ia32_vphaddudq (v4si)
v4si __builtin_ia32_vphadduwd (v8hi)
v2di __builtin_ia32_vphadduwq (v8hi)
v4si __builtin_ia32_vphaddwd (v8hi)
v2di __builtin_ia32_vphaddwq (v8hi)
v8hi __builtin_ia32_vphsubbw (v16qi)
v2di __builtin_ia32_vphsubdq (v4si)
v4si __builtin_ia32_vphsubwd (v8hi)
v4si __builtin_ia32_vpmacsdd (v4si, v4si, v4si)
v2di __builtin_ia32_vpmacsdqh (v4si, v4si, v2di)
v2di __builtin_ia32_vpmacsdql (v4si, v4si, v2di)
v4si __builtin_ia32_vpmacssdd (v4si, v4si, v4si)
v2di __builtin_ia32_vpmacssdqh (v4si, v4si, v2di)
v2di __builtin_ia32_vpmacssdql (v4si, v4si, v2di)
v4si __builtin_ia32_vpmacsswd (v8hi, v8hi, v4si)
v8hi __builtin_ia32_vpmacssww (v8hi, v8hi, v8hi)
v4si __builtin_ia32_vpmacswd (v8hi, v8hi, v4si)
v8hi __builtin_ia32_vpmacsww (v8hi, v8hi, v8hi)
v4si __builtin_ia32_vpmadcsswd (v8hi, v8hi, v4si)
v4si __builtin_ia32_vpmadcswd (v8hi, v8hi, v4si)
v16qi __builtin_ia32_vpperm (v16qi, v16qi, v16qi)
v16qi __builtin_ia32_vprotb (v16qi, v16qi)
v4si __builtin_ia32_vprotd (v4si, v4si)
v2di __builtin_ia32_vprotq (v2di, v2di)
v8hi __builtin_ia32_vprotw (v8hi, v8hi)
v16qi __builtin_ia32_vpshab (v16qi, v16qi)
v4si __builtin_ia32_vpshad (v4si, v4si)
v2di __builtin_ia32_vpshaq (v2di, v2di)
v8hi __builtin_ia32_vpshaw (v8hi, v8hi)
v16qi __builtin_ia32_vpshlb (v16qi, v16qi)
v4si __builtin_ia32_vpshld (v4si, v4si)
v2di __builtin_ia32_vpshlq (v2di, v2di)
v8hi __builtin_ia32_vpshlw (v8hi, v8hi)
The following built-in functions are available when -mfma4 is used. All of them generate the machine instruction that is part of the name.
v2df __builtin_ia32_vfmaddpd (v2df, v2df, v2df)
v4sf __builtin_ia32_vfmaddps (v4sf, v4sf, v4sf)
v2df __builtin_ia32_vfmaddsd (v2df, v2df, v2df)
v4sf __builtin_ia32_vfmaddss (v4sf, v4sf, v4sf)
v2df __builtin_ia32_vfmsubpd (v2df, v2df, v2df)
v4sf __builtin_ia32_vfmsubps (v4sf, v4sf, v4sf)
v2df __builtin_ia32_vfmsubsd (v2df, v2df, v2df)
v4sf __builtin_ia32_vfmsubss (v4sf, v4sf, v4sf)
v2df __builtin_ia32_vfnmaddpd (v2df, v2df, v2df)
v4sf __builtin_ia32_vfnmaddps (v4sf, v4sf, v4sf)
v2df __builtin_ia32_vfnmaddsd (v2df, v2df, v2df)
v4sf __builtin_ia32_vfnmaddss (v4sf, v4sf, v4sf)
v2df __builtin_ia32_vfnmsubpd (v2df, v2df, v2df)
v4sf __builtin_ia32_vfnmsubps (v4sf, v4sf, v4sf)
v2df __builtin_ia32_vfnmsubsd (v2df, v2df, v2df)
v4sf __builtin_ia32_vfnmsubss (v4sf, v4sf, v4sf)
v2df __builtin_ia32_vfmaddsubpd (v2df, v2df, v2df)
v4sf __builtin_ia32_vfmaddsubps (v4sf, v4sf, v4sf)
v2df __builtin_ia32_vfmsubaddpd (v2df, v2df, v2df)
v4sf __builtin_ia32_vfmsubaddps (v4sf, v4sf, v4sf)
v4df __builtin_ia32_vfmaddpd256 (v4df, v4df, v4df)
v8sf __builtin_ia32_vfmaddps256 (v8sf, v8sf, v8sf)
v4df __builtin_ia32_vfmsubpd256 (v4df, v4df, v4df)
v8sf __builtin_ia32_vfmsubps256 (v8sf, v8sf, v8sf)
v4df __builtin_ia32_vfnmaddpd256 (v4df, v4df, v4df)
v8sf __builtin_ia32_vfnmaddps256 (v8sf, v8sf, v8sf)
v4df __builtin_ia32_vfnmsubpd256 (v4df, v4df, v4df)
v8sf __builtin_ia32_vfnmsubps256 (v8sf, v8sf, v8sf)
v4df __builtin_ia32_vfmaddsubpd256 (v4df, v4df, v4df)
v8sf __builtin_ia32_vfmaddsubps256 (v8sf, v8sf, v8sf)
v4df __builtin_ia32_vfmsubaddpd256 (v4df, v4df, v4df)
v8sf __builtin_ia32_vfmsubaddps256 (v8sf, v8sf, v8sf)
The following built-in functions are available when -mlwp is used.
void __builtin_ia32_llwpcb16 (void *);
void __builtin_ia32_llwpcb32 (void *);
void __builtin_ia32_llwpcb64 (void *);
void * __builtin_ia32_llwpcb16 (void);
void * __builtin_ia32_llwpcb32 (void);
void * __builtin_ia32_llwpcb64 (void);
void __builtin_ia32_lwpval16 (unsigned short, unsigned int, unsigned short)
void __builtin_ia32_lwpval32 (unsigned int, unsigned int, unsigned int)
void __builtin_ia32_lwpval64 (unsigned __int64, unsigned int, unsigned int)
unsigned char __builtin_ia32_lwpins16 (unsigned short, unsigned int, unsigned short)
unsigned char __builtin_ia32_lwpins32 (unsigned int, unsigned int, unsigned int)
unsigned char __builtin_ia32_lwpins64 (unsigned __int64, unsigned int, unsigned int)
The following built-in functions are available when -mbmi is used. All of them generate the machine instruction that is part of the name.
unsigned int __builtin_ia32_bextr_u32(unsigned int, unsigned int);
unsigned long long __builtin_ia32_bextr_u64 (unsigned long long, unsigned long long);
The following built-in functions are available when -mbmi2 is used. All of them generate the machine instruction that is part of the name.
unsigned int _bzhi_u32 (unsigned int, unsigned int)
unsigned int _pdep_u32 (unsigned int, unsigned int)
unsigned int _pext_u32 (unsigned int, unsigned int)
unsigned long long _bzhi_u64 (unsigned long long, unsigned long long)
unsigned long long _pdep_u64 (unsigned long long, unsigned long long)
unsigned long long _pext_u64 (unsigned long long, unsigned long long)
The following built-in functions are available when -mlzcnt is used. All of them generate the machine instruction that is part of the name.
unsigned short __builtin_ia32_lzcnt_16(unsigned short);
unsigned int __builtin_ia32_lzcnt_u32(unsigned int);
unsigned long long __builtin_ia32_lzcnt_u64 (unsigned long long);
The following built-in functions are available when -mfxsr is used. All of them generate the machine instruction that is part of the name.
void __builtin_ia32_fxsave (void *)
void __builtin_ia32_fxrstor (void *)
void __builtin_ia32_fxsave64 (void *)
void __builtin_ia32_fxrstor64 (void *)
The following built-in functions are available when -mxsave is used. All of them generate the machine instruction that is part of the name.
void __builtin_ia32_xsave (void *, long long)
void __builtin_ia32_xrstor (void *, long long)
void __builtin_ia32_xsave64 (void *, long long)
void __builtin_ia32_xrstor64 (void *, long long)
The following built-in functions are available when -mxsaveopt is used. All of them generate the machine instruction that is part of the name.
void __builtin_ia32_xsaveopt (void *, long long)
void __builtin_ia32_xsaveopt64 (void *, long long)
The following built-in functions are available when -mtbm is used. Both of them generate the immediate form of the bextr machine instruction.
unsigned int __builtin_ia32_bextri_u32 (unsigned int, const unsigned int);
unsigned long long __builtin_ia32_bextri_u64 (unsigned long long, const unsigned long long);
The following built-in functions are available when -m3dnow is used. All of them generate the machine instruction that is part of the name.
void __builtin_ia32_femms (void)
v8qi __builtin_ia32_pavgusb (v8qi, v8qi)
v2si __builtin_ia32_pf2id (v2sf)
v2sf __builtin_ia32_pfacc (v2sf, v2sf)
v2sf __builtin_ia32_pfadd (v2sf, v2sf)
v2si __builtin_ia32_pfcmpeq (v2sf, v2sf)
v2si __builtin_ia32_pfcmpge (v2sf, v2sf)
v2si __builtin_ia32_pfcmpgt (v2sf, v2sf)
v2sf __builtin_ia32_pfmax (v2sf, v2sf)
v2sf __builtin_ia32_pfmin (v2sf, v2sf)
v2sf __builtin_ia32_pfmul (v2sf, v2sf)
v2sf __builtin_ia32_pfrcp (v2sf)
v2sf __builtin_ia32_pfrcpit1 (v2sf, v2sf)
v2sf __builtin_ia32_pfrcpit2 (v2sf, v2sf)
v2sf __builtin_ia32_pfrsqrt (v2sf)
v2sf __builtin_ia32_pfsub (v2sf, v2sf)
v2sf __builtin_ia32_pfsubr (v2sf, v2sf)
v2sf __builtin_ia32_pi2fd (v2si)
v4hi __builtin_ia32_pmulhrw (v4hi, v4hi)
The following built-in functions are available when both -m3dnow and -march=athlon are used. All of them generate the machine instruction that is part of the name.
v2si __builtin_ia32_pf2iw (v2sf)
v2sf __builtin_ia32_pfnacc (v2sf, v2sf)
v2sf __builtin_ia32_pfpnacc (v2sf, v2sf)
v2sf __builtin_ia32_pi2fw (v2si)
v2sf __builtin_ia32_pswapdsf (v2sf)
v2si __builtin_ia32_pswapdsi (v2si)
The following built-in functions are available when -mrtm is used They are used for restricted transactional memory. These are the internal low level functions. Normally the functions in x86 transactional memory intrinsics should be used instead.
int __builtin_ia32_xbegin ()
void __builtin_ia32_xend ()
void __builtin_ia32_xabort (status)
int __builtin_ia32_xtest ()
:: _x86-transactional-memory-intrinsics:
These hardware transactional memory intrinsics for x86 allow you to use memory transactions with RTM (Restricted Transactional Memory). This support is enabled with the -mrtm option. For using HLE (Hardware Lock Elision) see x86 specific memory model extensions for transactional memory instead.
A memory transaction commits all changes to memory in an atomic way, as visible to other threads. If the transaction fails it is rolled back and all side effects discarded.
Generally there is no guarantee that a memory transaction ever succeeds and suitable fallback code always needs to be supplied.
Start a RTM (Restricted Transactional Memory) transaction. Returns _XBEGIN_STARTED when the transaction started successfully (note this is not 0, so the constant has to be explicitly tested).
If the transaction aborts, all side-effects are undone and an abort code encoded as a bit mask is returned. The following macros are defined:
Transaction was explicitly aborted with _xabort. The parameter passed to _xabort is available with _XABORT_CODE(status).
Transaction retry is possible.
Transaction abort due to a memory conflict with another thread.
Transaction abort due to the transaction using too much memory.
Transaction abort due to a debug trap.
Transaction abort in an inner nested transaction.
There is no guarantee any transaction ever succeeds, so there always needs to be a valid fallback path.
Commit the current transaction. When no transaction is active this faults. All memory side-effects of the transaction become visible to other threads in an atomic manner.
Return a nonzero value if a transaction is currently active, otherwise 0.
Abort the current transaction. When no transaction is active this is a no-op. The status is an 8-bit constant; its value is encoded in the return value from _xbegin.
Here is an example showing handling for _XABORT_RETRY and a fallback path for other failures:
#include <immintrin.h>
int n_tries, max_tries;
unsigned status = _XABORT_EXPLICIT;
...
for (n_tries = 0; n_tries < max_tries; n_tries++)
{
status = _xbegin ();
if (status == _XBEGIN_STARTED || !(status & _XABORT_RETRY))
break;
}
if (status == _XBEGIN_STARTED)
{
... transaction code...
_xend ();
}
else
{
... non-transactional fallback path...
}
Note that, in most cases, the transactional and non-transactional code must synchronize together to ensure consistency.
:: _target-format-checks:
For some target machines, GCC supports additional options to the format attribute (Function AttributesDeclaring Attributes of Functions).
:: _solaris-format-checks:
Solaris targets support the cmn_err (or __cmn_err__) format check. cmn_err accepts a subset of the standard printf conversions, and the two-argument %b conversion for displaying bit-fields. See the Solaris man page for cmn_err for more information.
:: _darwin-format-checks:
Darwin targets support the CFString (or __CFString__) in the format attribute context. Declarations made with such attribution are parsed for correct syntax and format argument types. However, parsing of the format string itself is currently undefined and is not carried out by this version of the compiler.
Additionally, CFStringRefs (defined by the CoreFoundation headers) may also be used as format arguments. Note that the relevant headers are only likely to be available on Darwin (OSX) installations. On such installations, the XCode and system documentation provide descriptions of CFString, CFStringRefs and associated functions.
:: _pragmas:
#pragma
GCC supports several types of pragmas, primarily in order to compile code originally written for other compilers. Note that in general we do not recommend the use of pragmas; Function Attributes, for further explanation.
:: _arm-pragmas:
The ARM target defines pragmas for controlling the default addition of long_call and short_call attributes to functions. Function Attributes, for information about the effects of these attributes.
Set all subsequent functions to have the long_call attribute.
Set all subsequent functions to have the short_call attribute.
Do not affect the long_call or short_call attributes of subsequent functions.
:: _m32c-pragmas:
GCC memregs number
Overrides the command-line option -memregs= for the current file. Use with care! This pragma must be before any function in the file, and mixing different memregs values in different objects may make them incompatible. This pragma is useful when a performance-critical function uses a memreg for temporary values, as it may allow you to reduce the number of memregs used.
ADDRESS name address
For any declared symbols matching name, this does three things to that symbol: it forces the symbol to be located at the given address (a number), it forces the symbol to be volatile, and it changes the symbols scope to be static. This pragma exists for compatibility with other compilers, but note that the common 1234H numeric syntax is not supported (use 0x1234 instead). Example:
#pragma ADDRESS port3 0x103
char port3;
:: _mep-pragmas:
Overrides the command-line option -mio-volatile for the current file. Note that for compatibility with future GCC releases, this option should only be used once before any io variables in each file.
GCC coprocessor available registers
Specifies which coprocessor registers are available to the register allocator. registers may be a single register, register range separated by ellipses, or comma-separated list of those. Example:
#pragma GCC coprocessor available $c0...$c10, $c28
GCC coprocessor call_saved registers
Specifies which coprocessor registers are to be saved and restored by any function using them. registers may be a single register, register range separated by ellipses, or comma-separated list of those. Example:
#pragma GCC coprocessor call_saved $c4...$c6, $c31
GCC coprocessor subclass ‘(A|B|C|D)’ = registers
Creates and defines a register class. These register classes can be used by inline asm constructs. registers may be a single register, register range separated by ellipses, or comma-separated list of those. Example:
#pragma GCC coprocessor subclass 'B' = $c2, $c4, $c6
asm ("cpfoo %0" : "=B" (x));
GCC disinterrupt name , name ...
For the named functions, the compiler adds code to disable interrupts for the duration of those functions. If any functions so named are not encountered in the source, a warning is emitted that the pragma is not used. Examples:
#pragma disinterrupt foo
#pragma disinterrupt bar, grill
int foo () { ... }
GCC call name , name ...
For the named functions, the compiler always uses a register-indirect call model when calling the named functions. Examples:
extern int foo ();
#pragma call foo
:: _rs/6000-and-powerpc-pragmas:
The RS/6000 and PowerPC targets define one pragma for controlling whether or not the longcall attribute is added to function declarations by default. This pragma overrides the -mlongcall option, but not the longcall and shortcall attributes. RS/6000 and PowerPC Options, for more information about when long calls are and are not necessary.
Apply the longcall attribute to all subsequent function declarations.
Do not apply the longcall attribute to subsequent function declarations.
:: _darwin-pragmas:
The following pragmas are available for all architectures running the Darwin operating system. These are useful for compatibility with other Mac OS compilers.
mark tokens...
This pragma is accepted, but has no effect.
options align=``alignment``
This pragma sets the alignment of fields in structures. The values of alignment may be mac68k, to emulate m68k alignment, or power, to emulate PowerPC alignment. Uses of this pragma nest properly; to restore the previous setting, use reset for the alignment.
segment tokens...
This pragma is accepted, but has no effect.
unused (var [, var]...)
This pragma declares variables to be possibly unused. GCC does not produce warnings for the listed variables. The effect is similar to that of the unused attribute, except that this pragma may appear anywhere within the variables scopes.
:: _solaris-pragmas:
The Solaris target supports #pragma redefine_extname (Symbol-Renaming Pragmas). It also supports additional #pragma directives for compatibility with the system compiler.
align alignment (variable [, variable]...)
Increase the minimum alignment of each variable to alignment. This is the same as GCCs aligned attribute Variable Attributes). Macro expansion occurs on the arguments to this pragma when compiling C and Objective-C It does not currently occur when compiling C++, but this is a bug which may be fixed in a future release.
fini (function [, function]...)
This pragma causes each listed function to be called after main, or during shared module unloading, by adding a call to the .fini section.
init (function [, function]...)
This pragma causes each listed function to be called during initialization (before main) or during shared module loading, by adding a call to the .init section.
:: _symbol-renaming-pragmas:
GCC supports a #pragma directive that changes the name used in assembly for a given declaration. While this pragma is supported on all platforms, it is intended primarily to provide compatibility with the Solaris system headers. This effect can also be achieved using the asm labels extension (Asm Labels).
redefine_extname oldname newname
This pragma gives the C function oldname the assembly symbol newname. The preprocessor macro __PRAGMA_REDEFINE_EXTNAME is defined if this pragma is available (currently on all platforms).
This pragma and the asm labels extension interact in a complicated manner. Here are some corner cases you may want to be aware of:
:: _structure-packing-pragmas:
For compatibility with Microsoft Windows compilers, GCC supports a set of #pragma directives that change the maximum alignment of members of structures (other than zero-width bit-fields), unions, and classes subsequently defined. The n value below always is required to be a small power of two and specifies the new alignment in bytes.
Some targets, e.g. x86 and PowerPC, support the ms_struct #pragma which lays out a structure as the documented __attribute__ ((ms_struct)).
:: _weak-pragmas:
For compatibility with SVR4, GCC supports a set of #pragma directives for declaring symbols to be weak, and defining weak aliases.
#pragma weak symbol
This pragma declares symbol to be weak, as if the declaration had the attribute of the same name. The pragma may appear before or after the declaration of symbol. It is not an error for symbol to never be defined at all.
#pragma weak symbol1 = symbol2 This pragma declares symbol1 to be a weak alias of symbol2. It is an error if symbol2 is not defined in the current translation unit.
:: _diagnostic-pragmas:
GCC allows the user to selectively enable or disable certain types of diagnostics, and change the kind of the diagnostic. For example, a projects policy might require that all sources compile with -Werror but certain files might have exceptions allowing specific types of warnings. Or, a project might selectively enable diagnostics and treat them as errors depending on which preprocessor macros are defined.
#pragma GCC diagnostic kind option
Modifies the disposition of a diagnostic. Note that not all diagnostics are modifiable; at the moment only warnings (normally controlled by -W...) can be controlled, and not all of them. Use -fdiagnostics-show-option to determine which diagnostics are controllable and which option controls them.
kind is error to treat this diagnostic as an error, warning to treat it like a warning (even if -Werror is in effect), or ignored if the diagnostic is to be ignored. option is a double quoted string that matches the command-line option.
#pragma GCC diagnostic warning "-Wformat"
#pragma GCC diagnostic error "-Wformat"
#pragma GCC diagnostic ignored "-Wformat"
Note that these pragmas override any command-line options. GCC keeps track of the location of each pragma, and issues diagnostics according to the state as of that point in the source file. Thus, pragmas occurring after a line do not affect diagnostics caused by that line.
Causes GCC to remember the state of the diagnostics as of each push, and restore to that point at each pop. If a pop has no matching push, the command-line options are restored.
#pragma GCC diagnostic error "-Wuninitialized"
foo(a); /* error is given for this one */
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wuninitialized"
foo(b); /* no diagnostic for this one */
#pragma GCC diagnostic pop
foo(c); /* error is given for this one */
#pragma GCC diagnostic pop
foo(d); /* depends on command-line options */
GCC also offers a simple mechanism for printing messages during compilation.
#pragma message string
Prints string as a compiler message on compilation. The message is informational only, and is neither a compilation warning nor an error.
#pragma message "Compiling " __FILE__ "..."
string may be parenthesized, and is printed with location information. For example,
#define DO_PRAGMA(x) _Pragma (#x)
#define TODO(x) DO_PRAGMA(message ("TODO - " #x))
TODO(Remember to fix this)
prints /tmp/file.c:4: note: #pragma message: TODO - Remember to fix this.
:: _visibility-pragmas:
#pragma GCC visibility push(visibility) #pragma GCC visibility pop
This pragma allows the user to set the visibility for multiple declarations without having to give each a visibility attribute (Function Attributes).
In C++, #pragma GCC visibility affects only namespace-scope declarations. Class members and template specializations are not affected; if you want to override the visibility for a particular member or instantiation, you must use an attribute.
:: _push/pop-macro-pragmas:
For compatibility with Microsoft Windows compilers, GCC supports #pragma push_macro("macro_name") and #pragma pop_macro("macro_name").
#pragma push_macro("macro_name")
This pragma saves the value of the macro named as macro_name to the top of the stack for this macro.
#pragma pop_macro("macro_name")
This pragma sets the value of the macro named as macro_name to the value on top of the stack for this macro. If the stack for macro_name is empty, the value of the macro remains unchanged.
For example:
#define X 1
#pragma push_macro("X")
#undef X
#define X -1
#pragma pop_macro("X")
int x [X];
In this example, the definition of X as 1 is saved by #pragma push_macro and restored by #pragma pop_macro.
:: _function-specific-option-pragmas:
#pragma GCC target ("string"...)
This pragma allows you to set target specific options for functions defined later in the source file. One or more strings can be specified. Each function that is defined after this point is as if attribute((target("STRING"))) was specified for that function. The parenthesis around the options is optional. Function Attributes, for more information about the target attribute and the attribute syntax.
The #pragma GCC target pragma is presently implemented for x86, PowerPC, and Nios II targets only.
#pragma GCC optimize ("string"...)
This pragma allows you to set global optimization options for functions defined later in the source file. One or more strings can be specified. Each function that is defined after this point is as if attribute((optimize("STRING"))) was specified for that function. The parenthesis around the options is optional. Function Attributes, for more information about the optimize attribute and the attribute syntax.
These pragmas maintain a stack of the current target and optimization options. It is intended for include files where you temporarily want to switch to using a different #pragma GCC target or #pragma GCC optimize and then to pop back to the previous options.
This pragma clears the current #pragma GCC target and #pragma GCC optimize to use the default switches as specified on the command line.
:: _loop-specific-pragmas:
With this pragma, the programmer asserts that there are no loop-carried dependencies which would prevent consecutive iterations of the following loop from executing concurrently with SIMD (single instruction multiple data) instructions.
For example, the compiler can only unconditionally vectorize the following loop with the pragma:
void foo (int n, int *a, int *b, int *c)
{
int i, j;
#pragma GCC ivdep
for (i = 0; i < n; ++i)
a[i] = b[i] + c[i];
}
In this example, using the restrict qualifier had the same effect. In the following example, that would not be possible. Assume k < -m or k >= m. Only with the pragma, the compiler knows that it can unconditionally vectorize the following loop:
void ignore_vec_dep (int *a, int k, int c, int m)
{
#pragma GCC ivdep
for (int i = 0; i < m; i++)
a[i] = a[i + k] * c;
}
:: _unnamed-fields:
struct union
As permitted by ISO C11 and for compatibility with other compilers, GCC allows you to define a structure or union that contains, as fields, structures and unions without names. For example:
struct {
int a;
union {
int b;
float c;
};
int d;
} foo;
In this example, you are able to access members of the unnamed union with code like foo.b. Note that only unnamed structs and unions are allowed, you may not have, for example, an unnamed int.
You must never create such structures that cause ambiguous field definitions. For example, in this structure:
struct {
int a;
struct {
int a;
};
} foo;
it is ambiguous which a is being referred to with foo.a. The compiler gives errors for such constructs.
Unless -fms-extensions is used, the unnamed field must be a structure or union definition without a tag (for example, struct { int a; };). If -fms-extensions is used, the field may also be a definition with a tag such as struct foo { int a; };, a reference to a previously defined structure or union such as struct foo;, or a reference to a typedef name for a previously defined structure or union type.
The option -fplan9-extensions enables -fms-extensions as well as two other extensions. First, a pointer to a structure is automatically converted to a pointer to an anonymous field for assignments and function calls. For example:
struct s1 { int a; };
struct s2 { struct s1; };
extern void f1 (struct s1 *);
void f2 (struct s2 *p) { f1 (p); }
In the call to f1 inside f2, the pointer p is converted into a pointer to the anonymous field.
Second, when the type of an anonymous field is a typedef for a struct or union, code may refer to the field using the name of the typedef.
typedef struct { int a; } s1;
struct s2 { s1; };
s1 f1 (struct s2 *p) { return p->s1; }
These usages are only permitted when they are not ambiguous.
:: _thread-local:
TLS __thread
Thread-local storage (TLS) is a mechanism by which variables are allocated such that there is one instance of the variable per extant thread. The runtime model GCC uses to implement this originates in the IA-64 processor-specific ABI, but has since been migrated to other processors as well. It requires significant support from the linker (ld), dynamic linker (ld.so), and system libraries (libc.so and libpthread.so), so it is not available everywhere.
At the user level, the extension is visible with a new storage class keyword: __thread. For example:
__thread int i;
extern __thread struct state s;
static __thread char *p;
The __thread specifier may be used alone, with the extern or static specifiers, but with no other storage class specifier. When used with extern or static, __thread must appear immediately after the other storage class specifier.
The __thread specifier may be applied to any global, file-scoped static, function-scoped static, or static data member of a class. It may not be applied to block-scoped automatic or non-static data member.
When the address-of operator is applied to a thread-local variable, it is evaluated at run time and returns the address of the current threads instance of that variable. An address so obtained may be used by any thread. When a thread terminates, any pointers to thread-local variables in that thread become invalid.
No static initialization may refer to the address of a thread-local variable.
In C++, if an initializer is present for a thread-local variable, it must be a constant-expression, as defined in 5.19.2 of the ANSI/ISO C++ standard.
See http://www.akkadia.org/drepper/tls.pdfELF Handling For Thread-Local Storage for a detailed explanation of the four thread-local storage addressing models, and how the runtime is expected to function.
:: _c99-thread-local-edits:
The following are a set of changes to ISO/IEC 9899:1999 (aka C99) that document the exact semantics of the language extension.
5.1.2 Execution environments
Add new text after paragraph 1
Within either execution environment, a thread is a flow of control within a program. It is implementation defined whether or not there may be more than one thread associated with a program. It is implementation defined how threads beyond the first are created, the name and type of the function called at thread startup, and how threads may be terminated. However, objects with thread storage duration shall be initialized before thread startup.
6.2.4 Storage durations of objects
Add new text before paragraph 3
An object whose identifier is declared with the storage-class specifier __thread has thread storage duration. Its lifetime is the entire execution of the thread, and its stored value is initialized only once, prior to thread startup.
6.4.1 Keywords
Add __thread.
6.7.1 Storage-class specifiers
Add __thread to the list of storage class specifiers in paragraph 1.
Change paragraph 2 to
With the exception of __thread, at most one storage-class specifier may be given [...]. The __thread specifier may be used alone, or immediately following extern or static.
Add new text after paragraph 6
The declaration of an identifier for a variable that has block scope that specifies __thread shall also specify either extern or static.
The __thread specifier shall be used only with variables.
:: _c++98-thread-local-edits:
The following are a set of changes to ISO/IEC 14882:1998 (aka C++98) that document the exact semantics of the language extension.
[intro.execution]
New text after paragraph 4
A thread is a flow of control within the abstract machine. It is implementation defined whether or not there may be more than one thread.
New text after paragraph 7
It is unspecified whether additional action must be taken to ensure when and whether side effects are visible to other threads.
[lex.key]
Add __thread.
[basic.start.main]
Add after paragraph 5
The thread that begins execution at the main function is called the main thread. It is implementation defined how functions beginning threads other than the main thread are designated or typed. A function so designated, as well as the main function, is called a thread startup function. It is implementation defined what happens if a thread startup function returns. It is implementation defined what happens to other threads when any thread calls exit.
[basic.start.init]
Add after paragraph 4
The storage for an object of thread storage duration shall be statically initialized before the first statement of the thread startup function. An object of thread storage duration shall not require dynamic initialization.
[basic.start.term]
Add after paragraph 3
The type of an object with thread storage duration shall not have a non-trivial destructor, nor shall it be an array type whose elements (directly or indirectly) have non-trivial destructors.
[basic.stc]
Add thread storage duration to the list in paragraph 1.
Change paragraph 2
Thread, static, and automatic storage durations are associated with objects introduced by declarations [...].
Add __thread to the list of specifiers in paragraph 3.
[basic.stc.thread]
New section before [basic.stc.static]
The keyword __thread applied to a non-local object gives the object thread storage duration.
A local variable or class data member declared both static and __thread gives the variable or member thread storage duration.
[basic.stc.static]
Change paragraph 1
All objects that have neither thread storage duration, dynamic storage duration nor are local [...].
[dcl.stc]
Add __thread to the list in paragraph 1.
Change paragraph 1
With the exception of __thread, at most one storage-class-specifier shall appear in a given decl-specifier-seq. The __thread specifier may be used alone, or immediately following the extern or static specifiers. [...]
Add after paragraph 5
The __thread specifier can be applied only to the names of objects and to anonymous unions.
[class.mem]
Add after paragraph 6
Non-static members shall not be __thread.
:: _binary-constants:
Binary Constants using the 0b Prefix Binary constants using the 0b prefix
Integer constants can be written as binary constants, consisting of a sequence of 0 and 1 digits, prefixed by 0b or 0B. This is particularly useful in environments that operate a lot on the bit level (like microcontrollers).
The following statements are identical:
i = 42;
i = 0x2a;
i = 052;
i = 0b101010;
The type of these constants follows the same rules as for octal or hexadecimal integer constants, so suffixes like L or UL can be applied.
:: _c++-extensions:
The GNU compiler provides these extensions to the C++ language (and you can also use most of the C language extensions in your C++ programs). If you want to write code that checks whether these features are available, you can test for the GNU compiler the same way as for C programs: check for a predefined macro __GNUC__. You can also use __GNUG__ to test specifically for GNU C++ (Common Predefined MacrosPredefined MacroscppThe GNU C Preprocessor).
:: _c++-volatiles:
The C++ standard differs from the C standard in its treatment of volatile objects. It fails to specify what constitutes a volatile access, except to say that C++ should behave in a similar manner to C with respect to volatiles, where possible. However, the different lvalueness of expressions between C and C++ complicate the behavior. G++ behaves the same as GCC for volatile access, C ExtensionsVolatiles, for a description of GCCs behavior.
The C and C++ language specifications differ when an object is accessed in a void context:
volatile int *src = ``somevalue``;
*src;
The C++ standard specifies that such expressions do not undergo lvalue to rvalue conversion, and that the type of the dereferenced object may be incomplete. The C++ standard does not specify explicitly that it is lvalue to rvalue conversion that is responsible for causing an access. There is reason to believe that it is, because otherwise certain simple expressions become undefined. However, because it would surprise most programmers, G++ treats dereferencing a pointer to volatile object of complete type as GCC would do for an equivalent type in C When the object has incomplete type, G++ issues a warning; if you wish to force an error, you must force a conversion to rvalue with, for instance, a static cast.
When using a reference to volatile, G++ does not treat equivalent expressions as accesses to volatiles, but instead issues a warning that no volatile is accessed. The rationale for this is that otherwise it becomes difficult to determine where volatile access occur, and not possible to ignore the return value from functions returning volatile references. Again, if you wish to force a read, cast the reference to an rvalue.
G++ implements the same behavior as GCC does when assigning to a volatile objectthere is no reread of the assigned-to object, the assigned rvalue is reused. Note that in C++ assignment expressions are lvalues, and if used as an lvalue, the volatile object is referred to. For instance, vref refers to vobj, as expected, in the following example:
volatile int vobj;
volatile int &vref = vobj = ``something``;
:: _restricted-pointers:
As with the C front end, G++ understands the C99 feature of restricted pointers, specified with the __restrict__, or __restrict type qualifier. Because you cannot compile C++ by specifying the -std=c99 language flag, restrict is not a keyword in C++.
In addition to allowing restricted pointers, you can specify restricted references, which indicate that the reference is not aliased in the local context.
void fn (int *__restrict__ rptr, int &__restrict__ rref)
{
/* ... */
}
In the body of fn, rptr points to an unaliased integer and rref refers to a (different) unaliased integer.
You may also specify whether a member functions this pointer is unaliased by using __restrict__ as a member function qualifier.
void T::fn () __restrict__
{
/* ... */
}
Within the body of T::fn, this has the effective definition T *__restrict__ const this. Notice that the interpretation of a __restrict__ member function qualifier is different to that of const or volatile qualifier, in that it is applied to the pointer rather than the object. This is consistent with other compilers that implement restricted pointers.
As with all outermost parameter qualifiers, __restrict__ is ignored in function definition matching. This means you only need to specify __restrict__ in a function definition, rather than in a function prototype as well.
:: _vague-linkage:
There are several constructs in C++ that require space in the object file but are not clearly tied to a single translation unit. We say that these constructs have vague linkage. Typically such constructs are emitted wherever they are needed, though sometimes we can be more clever.
Inline functions are typically defined in a header file which can be included in many different compilations. Hopefully they can usually be inlined, but sometimes an out-of-line copy is necessary, if the address of the function is taken or if inlining fails. In general, we emit an out-of-line copy in all translation units where one is needed. As an exception, we only emit inline virtual functions with the vtable, since it always requires a copy.
Local static variables and string constants used in an inline function are also considered to have vague linkage, since they must be shared between all inlined and out-of-line instances of the function.
C++ virtual functions are implemented in most compilers using a lookup table, known as a vtable. The vtable contains pointers to the virtual functions provided by a class, and each object of the class contains a pointer to its vtable (or vtables, in some multiple-inheritance situations). If the class declares any non-inline, non-pure virtual functions, the first one is chosen as the key method for the class, and the vtable is only emitted in the translation unit where the key method is defined.
Note: If the chosen key method is later defined as inline, the vtable is still emitted in every translation unit that defines it. Make sure that any inline virtuals are declared inline in the class body, even if they are not defined there.
type_info objects
type_info
C++ requires information about types to be written out in order to implement dynamic_cast, typeid and exception handling. For polymorphic classes (classes with virtual functions), the type_info object is written out along with the vtable so that dynamic_cast can determine the dynamic type of a class object at run time. For all other types, we write out the type_info object when it is used: when applying typeid to an expression, throwing an object, or referring to a type in a catch clause or exception specification.
Most everything in this section also applies to template instantiations, but there are other options as well. Template InstantiationWheres the Template?.
When used with GNU ld version 2.8 or later on an ELF system such as GNU/Linux or Solaris 2, or on Microsoft Windows, duplicate copies of these constructs will be discarded at link time. This is known as COMDAT support.
On targets that dont support COMDAT, but do support weak symbols, GCC uses them. This way one copy overrides all the others, but the unused copies still take up space in the executable.
For targets that do not support either COMDAT or weak symbols, most entities with vague linkage are emitted as local symbols to avoid duplicate definition errors from the linker. This does not happen for local statics in inlines, however, as having multiple copies almost certainly breaks things.
C++ InterfaceDeclarations and Definitions in One Header, for another way to control placement of these constructs.
:: _c++-interface:
#pragma interface and #pragma implementation provide the user with a way of explicitly directing the compiler to emit entities with vague linkage (and debugging information) in a particular translation unit.
Note: These ``#pragma``s have been superceded as of GCC 2.7.2 by COMDAT support and the key method heuristic mentioned in Vague Linkage. Using them can actually cause your program to grow due to unnecessary out-of-line copies of inline functions.
Use this directive in header files that define object classes, to save space in most of the object files that use those classes. Normally, local copies of certain information (backup copies of inline member functions, debugging information, and the internal tables that implement virtual functions) must be kept in each object file that includes class definitions. You can use this pragma to avoid such duplication. When a header file containing #pragma interface is included in a compilation, this auxiliary information is not generated (unless the main input source file itself uses #pragma implementation). Instead, the object files contain references to be resolved at link time.
The second form of this directive is useful for the case where you have multiple headers with the same name in different directories. If you use this form, you must specify the same string to #pragma implementation.
Use this pragma in a main input file, when you want full output from included header files to be generated (and made globally visible). The included header file, in turn, should use #pragma interface. Backup copies of inline member functions, debugging information, and the internal tables used to implement virtual functions are all generated in implementation files.
implied #pragma implementation #pragma implementation, implied
If you use #pragma implementation with no argument, it applies to an include file with the same basenameA files basename is the name stripped of all leading path information and of trailing suffixes, such as .h or .C or .cc. as your source file. For example, in allclass.cc, giving just #pragma implementation by itself is equivalent to #pragma implementation “allclass.h”.
Use the string argument if you want a single implementation file to include code from multiple header files. (You must also use #include to include the header file; #pragma implementation only specifies how to use the fileit doesnt actually include it.)
There is no way to split up the contents of a single header file into multiple implementation files.
#pragma implementation and #pragma interface also have an effect on function inlining.
If you define a class in a header file marked with #pragma interface, the effect on an inline function defined in that class is similar to an explicit extern declarationthe compiler emits no code at all to define an independent version of the function. Its definition is used only for inlining with its callers.
Conversely, when you include the same header file in a main source file that declares it as #pragma implementation, the compiler emits code for the function itself; this defines a version of the function that can be found via pointers (or by callers compiled without inlining). If all calls to the function can be inlined, you can avoid emitting the function by compiling with -fno-implement-inlines. If any calls are not inlined, you will get linker errors.
:: _template-instantiation:
C++ templates are the first language feature to require more intelligence from the environment than one usually finds on a UNIX system. Somehow the compiler and linker have to make sure that each template instance occurs exactly once in the executable if it is needed, and not at all otherwise. There are two basic approaches to this problem, which are referred to as the Borland model and the Cfront model.
Borland C++ solved the template instantiation problem by adding the code equivalent of common blocks to their linker; the compiler emits template instances in each translation unit that uses them, and the linker collapses them together. The advantage of this model is that the linker only has to consider the object files themselves; there is no external complexity to worry about. This disadvantage is that compilation time is increased because the template code is being compiled repeatedly. Code written for this model tends to include definitions of all templates in the header file, since they must be seen to be instantiated.
The AT&T C++ translator, Cfront, solved the template instantiation problem by creating the notion of a template repository, an automatically maintained place where template instances are stored. A more modern version of the repository works as follows: As individual object files are built, the compiler places any template definitions and instantiations encountered in the repository. At link time, the link wrapper adds in the objects in the repository and compiles any needed instances that were not previously emitted. The advantages of this model are more optimal compilation speed and the ability to use the system linker; to implement the Borland model a compiler vendor also needs to replace the linker. The disadvantages are vastly increased complexity, and thus potential for error; for some code this can be just as transparent, but in practice it can been very difficult to build multiple programs in one directory and one program in multiple directories. Code written for this model tends to separate definitions of non-inline member templates into a separate file, which should be compiled separately.
When used with GNU ld version 2.8 or later on an ELF system such as GNU/Linux or Solaris 2, or on Microsoft Windows, G++ supports the Borland model. On other systems, G++ implements neither automatic model.
You have the following options for dealing with template instantiations:
Compile your template-using code with -frepo. The compiler generates files with the extension .rpo listing all of the template instantiations used in the corresponding object files that could be instantiated there; the link wrapper, collect2, then updates the .rpo files to tell the compiler where to place those instantiations and rebuild any affected object files. The link-time overhead is negligible after the first pass, as the compiler continues to place the instantiations in the same files.
This is your best option for application code written for the Borland model, as it just works. Code written for the Cfront model needs to be modified so that the template definitions are available at one or more points of instantiation; usually this is as simple as adding #include <tmethods.cc> to the end of each template header.
For library code, if you want the library to provide all of the template instantiations it needs, just try to link all of its object files together; the link will fail, but cause the instantiations to be generated as a side effect. Be warned, however, that this may cause conflicts if multiple libraries try to provide the same instantiations. For greater control, use explicit instantiation as described in the next option.
Compile your code with -fno-implicit-templates to disable the implicit generation of template instances, and explicitly instantiate all the ones you use. This approach requires more knowledge of exactly which instances you need than do the others, but its less mysterious and allows greater control. You can scatter the explicit instantiations throughout your program, perhaps putting them in the translation units where the instances are used or the translation units that define the templates themselves; you can put all of the explicit instantiations you need into one big file; or you can create small files like
#include "Foo.h"
#include "Foo.cc"
template class Foo<int>;
template ostream& operator <<
(ostream&, const Foo<int>&);
for each of the instances you need, and create a template instantiation library from those.
If you are using Cfront-model code, you can probably get away with not using -fno-implicit-templates when compiling files that dont #include the member template definitions.
If you use one big file to do the instantiations, you may want to compile it without -fno-implicit-templates so you get all of the instances required by your explicit instantiations (but not by any other files) without having to specify them as well.
The ISO C++ 2011 standard allows forward declaration of explicit instantiations (with extern). G++ supports explicit instantiation declarations in C++98 mode and has extended the template instantiation syntax to support instantiation of the compiler support data for a template class (i.e. the vtable) without instantiating any of its members (with inline), and instantiation of only the static data members of a template class, without the support data or member functions (with static):
extern template int max (int, int);
inline template class Foo<int>;
static template class Foo<int>;
Do nothing. Pretend G++ does implement automatic instantiation management. Code written for the Borland model works fine, but each translation unit contains instances of each of the templates it uses. In a large program, this can lead to an unacceptable amount of code duplication.
:: _bound-member-functions:
In C++, pointer to member functions (PMFs) are implemented using a wide pointer of sorts to handle all the possible call mechanisms; the PMF needs to store information about how to adjust the this pointer, and if the function pointed to is virtual, where to find the vtable, and where in the vtable to look for the member function. If you are using PMFs in an inner loop, you should really reconsider that decision. If that is not an option, you can extract the pointer to the function that would be called for a given object/PMF pair and call it directly inside the inner loop, to save a bit of time.
Note that you still pay the penalty for the call through a function pointer; on most modern architectures, such a call defeats the branch prediction features of the CPU This is also true of normal virtual function calls.
The syntax for this extension is
extern A a;
extern int (A::*fp)();
typedef int (*fptr)(A *);
fptr p = (fptr)(a.*fp);
For PMF constants (i.e. expressions of the form &Klasse::Member), no object is needed to obtain the address of the function. They can be converted to function pointers directly:
fptr p1 = (fptr)(&A::foo);
You must specify -Wno-pmf-conversions to use this extension.
:: _c++-attributes:
Some attributes only make sense for C++ programs.
abi_tag (“tag”, ...) abi_tag function attribute abi_tag variable attribute abi_tag type attribute The abi_tag attribute can be applied to a function, variable, or class declaration. It modifies the mangled name of the entity to incorporate the tag name, in order to distinguish the function or class from an earlier version with a different ABI; perhaps the class has changed size, or the function has a different return type that is not encoded in the mangled name.
The attribute can also be applied to an inline namespace, but does not affect the mangled name of the namespace; in this case it is only used for -Wabi-tag warnings and automatic tagging of functions and variables. Tagging inline namespaces is generally preferable to tagging individual declarations, but the latter is sometimes necessary, such as when only certain members of a class need to be tagged.
The argument can be a list of strings of arbitrary length. The strings are sorted on output, so the order of the list is unimportant.
A redeclaration of an entity must not add new ABI tags, since doing so would change the mangled name.
The ABI tags apply to a name, so all instantiations and specializations of a template have the same tags. The attribute will be ignored if applied to an explicit specialization or instantiation.
The -Wabi-tag flag enables a warning about a class which does not have all the ABI tags used by its subobjects and virtual functions; for users with code that needs to coexist with an earlier ABI, using this option can help to find all affected types that need to be tagged.
When a type involving an ABI tag is used as the type of a variable or return type of a function where that tag is not already present in the signature of the function, the tag is automatically applied to the variable or function. -Wabi-tag also warns about this situation; this warning can be avoided by explicitly tagging the variable or function or moving it into a tagged inline namespace.
init_priority (priority) init_priority variable attribute
In Standard C++, objects defined at namespace scope are guaranteed to be initialized in an order in strict accordance with that of their definitions in a given translation unit. No guarantee is made for initializations across translation units. However, GNU C++ allows users to control the order of initialization of objects defined at namespace scope with the init_priority attribute by specifying a relative priority, a constant integral expression currently bounded between 101 and 65535 inclusive. Lower numbers indicate a higher priority.
In the following example, A would normally be created before B, but the init_priority attribute reverses that order:
Some_Class A __attribute__ ((init_priority (2000)));
Some_Class B __attribute__ ((init_priority (543)));
Note that the particular values of priority do not matter; only their relative ordering.
java_interface type attribute
This type attribute informs C++ that the class is a Java interface. It may only be applied to classes declared within an extern "Java" block. Calls to methods declared in this interface are dispatched using GCJs interface table mechanism, instead of regular virtual table dispatch.
warn_unused type attribute
For C++ types with non-trivial constructors and/or destructors it is impossible for the compiler to determine whether a variable of this type is truly unused if it is not referenced. This type attribute informs the compiler that variables of this type should be warned about if they appear to be unused, just like variables of fundamental types.
This attribute is appropriate for types which just represent a value, such as std::string; it is not appropriate for types which control a resource, such as std::mutex.
This attribute is also accepted in C, but it is unnecessary because C does not have constructors or destructors.
See also Namespace Association.
:: _function-multiversioning:
With the GNU C++ front end, for x86 targets, you may specify multiple versions of a function, where each function is specialized for a specific target feature. At runtime, the appropriate version of the function is automatically executed depending on the characteristics of the execution platform. Here is an example.
__attribute__ ((target ("default")))
int foo ()
{
// The default version of foo.
return 0;
}
__attribute__ ((target ("sse4.2")))
int foo ()
{
// foo version for SSE4.2
return 1;
}
__attribute__ ((target ("arch=atom")))
int foo ()
{
// foo version for the Intel ATOM processor
return 2;
}
__attribute__ ((target ("arch=amdfam10")))
int foo ()
{
// foo version for the AMD Family 0x10 processors.
return 3;
}
int main ()
{
int (*p)() = &foo;
assert ((*p) () == foo ());
return 0;
}
In the above example, four versions of function foo are created. The first version of foo with the target attribute “default” is the default version. This version gets executed when no other target specific version qualifies for execution on a particular platform. A new version of foo is created by using the same function signature but with a different target string. Function foo is called or a pointer to it is taken just like a regular function. GCC takes care of doing the dispatching to call the right version at runtime. Refer to the http://gcc.gnu.org/wiki/FunctionMultiVersioningGCC wiki on Function Multiversioning for more details.
:: _namespace-association:
Caution: The semantics of this extension are equivalent to C++ 2011 inline namespaces. Users should use inline namespaces instead as this extension will be removed in future versions of G++.
A using-directive with __attribute ((strong)) is stronger than a normal using-directive in two ways:
The used namespace must be nested within the using namespace so that normal unqualified lookup works properly.
This is useful for composing a namespace transparently from implementation namespaces. For example:
namespace std {
namespace debug {
template <class T> struct A { };
}
using namespace debug __attribute ((__strong__));
template <> struct A<int> { }; // OK to specialize
template <class T> void f (A<T>);
}
int main()
{
f (std::A<float>()); // lookup finds std::f
f (std::A<int>());
}
:: _type-traits:
The C++ front end implements syntactic extensions that allow compile-time determination of various characteristics of a type (or of a pair of types).
If type is const qualified or is a reference type then the trait is false. Otherwise if __has_trivial_assign (type) is true then the trait is true, else if type is a cv class or union type with copy assignment operators that are known not to throw an exception then the trait is true, else it is false. Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.
If __has_trivial_copy (type) is true then the trait is true, else if type is a cv class or union type with copy constructors that are known not to throw an exception then the trait is true, else it is false. Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.
If __has_trivial_constructor (type) is true then the trait is true, else if type is a cv class or union type (or array thereof) with a default constructor that is known not to throw an exception then the trait is true, else it is false. Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.
If type is const qualified or is a reference type then the trait is false. Otherwise if __is_pod (type) is true then the trait is true, else if type is a cv class or union type with a trivial copy assignment ([class.copy]) then the trait is true, else it is false. Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.
If __is_pod (type) is true or type is a reference type then the trait is true, else if type is a cv class or union type with a trivial copy constructor ([class.copy]) then the trait is true, else it is false. Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.
If __is_pod (type) is true then the trait is true, else if type is a cv class or union type (or array thereof) with a trivial default constructor ([class.ctor]) then the trait is true, else it is false. Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.
If __is_pod (type) is true or type is a reference type then the trait is true, else if type is a cv class or union type (or array thereof) with a trivial destructor ([class.dtor]) then the trait is true, else it is false. Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.
If type is a class type with a virtual destructor ([class.dtor]) then the trait is true, else it is false. Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.
If type is an abstract class ([class.abstract]) then the trait is true, else it is false. Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.
If base_type is a base class of derived_type ([class.derived]) then the trait is true, otherwise it is false. Top-level cv qualifications of base_type and derived_type are ignored. For the purposes of this trait, a class type is considered is own base. Requires: if __is_class (base_type) and __is_class (derived_type) are true and base_type and derived_type are not the same type (disregarding cv-qualifiers), derived_type shall be a complete type. Diagnostic is produced if this requirement is not met.
If type is a cv class type, and not a union type ([basic.compound]) the trait is true, else it is false.
If __is_class (type) is false then the trait is false. Otherwise type is considered empty if and only if: type has no non-static data members, or all non-static data members, if any, are bit-fields of length 0, and type has no virtual members, and type has no virtual base classes, and type has no base classes base_type for which __is_empty (base_type) is false. Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.
If type is a cv enumeration type ([basic.compound]) the trait is true, else it is false.
If type is a literal type ([basic.types]) the trait is true, else it is false. Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.
If type is a cv POD type ([basic.types]) then the trait is true, else it is false. Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.
If type is a polymorphic class ([class.virtual]) then the trait is true, else it is false. Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.
If type is a standard-layout type ([basic.types]) the trait is true, else it is false. Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.
If type is a trivial type ([basic.types]) the trait is true, else it is false. Requires: type shall be a complete type, (possibly cv-qualified) void, or an array of unknown bound.
If type is a cv union type ([basic.compound]) the trait is true, else it is false.
The underlying type of type. Requires: type shall be an enumeration type ([dcl.enum]).
:: _java-exceptions:
The Java language uses a slightly different exception handling model from C++. Normally, GNU C++ automatically detects when you are writing C++ code that uses Java exceptions, and handle them appropriately. However, if C++ code only needs to execute destructors when Java exceptions are thrown through it, GCC guesses incorrectly. Sample problematic code is:
struct S { ~S(); };
extern void bar(); // is written in Java, and may throw exceptions
void foo()
{
S s;
bar();
}
The usual effect of an incorrect guess is a link failure, complaining of a missing routine called __gxx_personality_v0.
You can inform the compiler that Java exceptions are to be used in a translation unit, irrespective of what it might think, by writing #pragma GCC java_exceptions at the head of the file. This #pragma must appear before any functions that throw or catch exceptions, or run destructors when exceptions are thrown through them.
You cannot mix Java and C++ exceptions in the same translation unit. It is believed to be safe to throw a C++ exception from one file through another file compiled for the Java exception model, or vice versa, but there may be bugs in this area.
:: _deprecated-features:
In the past, the GNU C++ compiler was extended to experiment with new features, at a time when the C++ language was still evolving. Now that the C++ standard is complete, some of those features are superseded by superior alternatives. Using the old features might cause a warning in some cases that the feature will be dropped in the future. In other cases, the feature might be gone already.
While the list below is not exhaustive, it documents some of the options that are now deprecated:
These are two of the many ways for G++ to implement template instantiation. Template Instantiation. The C++ standard clearly defines how template definitions have to be organized across implementation units. G++ has an implicit instantiation mechanism that should work just fine for standard-conforming code.
Previously it was possible to use an empty prototype parameter list to indicate an unspecified number of parameters (like C), rather than no parameters, as C++ demands. This feature has been removed, except where it is required for backwards compatibility. Backwards Compatibility.
G++ allows a virtual function returning void * to be overridden by one returning a different pointer type. This extension to the covariant return type rules is now deprecated and will be removed from a future version.
The G++ minimum and maximum operators (<? and >?) and their compound forms (<?=) and >?=) have been deprecated and are now removed from G++. Code using these operators should be modified to use std::min and std::max instead.
The named return value extension has been deprecated, and is now removed from G++.
The use of initializer lists with new expressions has been deprecated, and is now removed from G++.
Floating and complex non-type template parameters have been deprecated, and are now removed from G++.
The implicit typename extension has been deprecated and is now removed from G++.
The use of default arguments in function pointers, function typedefs and other places where they are not permitted by the standard is deprecated and will be removed from a future version of G++.
G++ allows floating-point literals to appear in integral constant expressions, e.g. enum E { e = int(2.2 * 3.7) } This extension is deprecated and will be removed from a future version.
G++ allows static data members of const floating-point type to be declared with an initializer in a class definition. The standard only allows initializers for static members of const integral types and const enumeration types so this extension has been deprecated and will be removed from a future version.
:: _backwards-compatibility:
Now that there is a definitive ISO standard C++, G++ has a specification to adhere to. The C++ language evolved over time, and features that used to be acceptable in previous drafts of the standard, such as the ARM [Annotated C++ Reference Manual], are no longer accepted. In order to allow compilation of C++ written to such drafts, G++ contains some backwards compatibilities. All such backwards compatibility features are liable to disappear in future versions of G++. They should be considered deprecated. Deprecated Features.
If a variable is declared at for scope, it used to remain in scope until the end of the scope that contained the for statement (rather than just within the for scope). G++ retains this, but issues a warning, if such a variable is accessed outside the for scope.
Old C system header files did not contain an extern "C" {...} scope to set the language. On such systems, all header files are implicitly scoped inside a C language scope. Also, an empty prototype () is treated as an unspecified number of arguments, rather than no arguments, as C++ demands.
:: _objective-c:
This document is meant to describe some of the GNU Objective-C features. It is not intended to teach you Objective-C. There are several resources on the Internet that present the language.
:: _gnu-objective-c-runtime-api:
This section is specific for the GNU Objective-C runtime. If you are using a different runtime, you can skip it.
The GNU Objective-C runtime provides an API that allows you to interact with the Objective-C runtime system, querying the live runtime structures and even manipulating them. This allows you for example to inspect and navigate classes, methods and protocols; to define new classes or new methods, and even to modify existing classes or protocols.
If you are using a Foundation library such as GNUstep-Base, this library will provide you with a rich set of functionality to do most of the inspection tasks, and you probably will only need direct access to the GNU Objective-C runtime API to define new classes or methods.
:: _modern-gnu-objective-c-runtime-api:
The GNU Objective-C runtime provides an API which is similar to the one provided by the Objective-C 2.0 Apple/NeXT Objective-C runtime. The API is documented in the public header files of the GNU Objective-C runtime:
The header files contain detailed documentation for each function in the GNU Objective-C runtime API.
:: _traditional-gnu-objective-c-runtime-api:
The GNU Objective-C runtime used to provide a different API, which we call the traditional GNU Objective-C runtime API. Functions belonging to this API are easy to recognize because they use a different naming convention, such as class_get_super_class() (traditional API) instead of class_getSuperclass() (modern API). Software using this API includes the file objc/objc-api.h where it is declared.
Starting with GCC 4.7.0, the traditional GNU runtime API is no longer available.
:: _executing-code-before-main:
+load: Executing Code before main
This section is specific for the GNU Objective-C runtime. If you are using a different runtime, you can skip it.
The GNU Objective-C runtime provides a way that allows you to execute code before the execution of the program enters the main function. The code is executed on a per-class and a per-category basis, through a special class method +load.
This facility is very useful if you want to initialize global variables which can be accessed by the program directly, without sending a message to the class first. The usual way to initialize global variables, in the +initialize method, might not be useful because +initialize is only called when the first message is sent to a class object, which in some cases could be too late.
Suppose for example you have a FileStream class that declares Stdin, Stdout and Stderr as global variables, like below:
FileStream *Stdin = nil;
FileStream *Stdout = nil;
FileStream *Stderr = nil;
implementation FileStream
+ (void)initialize
{
Stdin = [[FileStream new] initWithFd:0];
Stdout = [[FileStream new] initWithFd:1];
Stderr = [[FileStream new] initWithFd:2];
}
/* Other methods here */
end
In this example, the initialization of Stdin, Stdout and Stderr in +initialize occurs too late. The programmer can send a message to one of these objects before the variables are actually initialized, thus sending messages to the nil object. The +initialize method which actually initializes the global variables is not invoked until the first message is sent to the class object. The solution would require these variables to be initialized just before entering main.
The correct solution of the above problem is to use the +load method instead of +initialize:
implementation FileStream
+ (void)load
{
Stdin = [[FileStream new] initWithFd:0];
Stdout = [[FileStream new] initWithFd:1];
Stderr = [[FileStream new] initWithFd:2];
}
/* Other methods here */
end
The +load is a method that is not overridden by categories. If a class and a category of it both implement +load, both methods are invoked. This allows some additional initializations to be performed in a category.
This mechanism is not intended to be a replacement for +initialize. You should be aware of its limitations when you decide to use it instead of +initialize.
:: _what-you-can-and-what-you-cannot-do-in-+load:
What You Can and Cannot Do in +load
+load is to be used only as a last resort. Because it is executed very early, most of the Objective-C runtime machinery will not be ready when +load is executed; hence +load works best for executing C code that is independent on the Objective-C runtime.
The +load implementation in the GNU runtime guarantees you the following things:
In particular, the following things, even if they can work in a particular case, are not guaranteed:
You should make no assumptions about receiving +load in sibling classes when you write +load of a class. The order in which sibling classes receive +load is not guaranteed.
The order in which +load and +initialize are called could be problematic if this matters. If you dont allocate objects inside +load, it is guaranteed that +load is called before +initialize. If you create an object inside +load the +initialize method of objects class is invoked even if +load was not invoked. Note if you explicitly call +load on a class, +initialize will be called first. To avoid possible problems try to implement only one of these methods.
The +load method is also invoked when a bundle is dynamically loaded into your running program. This happens automatically without any intervening operation from you. When you write bundles and you need to write +load you can safely create and send messages to objects whose classes already exist in the running program. The same restrictions as above apply to classes defined in bundle.
:: _type-encoding:
This is an advanced section. Type encodings are used extensively by the compiler and by the runtime, but you generally do not need to know about them to use Objective-C.
The Objective-C compiler generates type encodings for all the types. These type encodings are used at runtime to find out information about selectors and methods and about objects and classes.
The types are encoded in the following way:
_Bool B char c unsigned char C short s unsigned short S int i unsigned int I long l unsigned long L long long q unsigned long long Q float f double d long double D void v id ```` Class # SEL : char* * enum an enum is encoded exactly as the integer type that the compiler uses for it, which depends on the enumeration values. Often the compiler users unsigned int, which is then encoded as I. unknown type ? Complex types j followed by the inner type. For example _Complex double is encoded as “jd”. bit-fields b followed by the starting position of the bit-field, the type of the bit-field and the size of the bit-field (the bit-fields encoding was changed from the NeXTs compiler encoding, see below)
The encoding of bit-fields has changed to allow bit-fields to be properly handled by the runtime functions that compute sizes and alignments of types that contain bit-fields. The previous encoding contained only the size of the bit-field. Using only this information it is not possible to reliably compute the size occupied by the bit-field. This is very important in the presence of the Boehms garbage collector because the objects are allocated using the typed memory facility available in this collector. The typed memory allocation requires information about where the pointers are located inside the object.
The position in the bit-field is the position, counting in bits, of the bit closest to the beginning of the structure.
The non-atomic types are encoded as follows:
pointers ^ followed by the pointed type. arrays [ followed by the number of elements in the array followed by the type of the elements followed by ] structures { followed by the name of the structure (or ? if the structure is unnamed), the = sign, the type of the members and by } unions ( followed by the name of the structure (or ? if the union is unnamed), the = sign, the type of the members followed by ) vectors ![ followed by the vector_size (the number of bytes composing the vector) followed by a comma, followed by the alignment (in bytes) of the vector, followed by the type of the elements followed by ]
Here are some types and their encodings, as they are generated by the compiler on an i386 machine:
Objective-C type Compiler encoding
int a[10];
[10i]
struct {
int i;
float f[3];
int a:3;
int b:2;
char c;
}
{?=i[3f]b128i3b131i2c}
int a __attribute__ ((vector_size (16)));
![16,16i] (alignment would depend on the machine)
In addition to the types the compiler also encodes the type specifiers. The table below describes the encoding of the current Objective-C type specifiers:
Specifier Encoding const r in n inout N out o bycopy O byref R oneway V
The type specifiers are encoded just before the type. Unlike types however, the type specifiers are only encoded when they appear in method argument types.
Note how const interacts with pointers:
Objective-C type Compiler encoding
const int
ri
const int*
^ri
int *const
r^i
const int* is a pointer to a const int, and so is encoded as ^ri. int* const, instead, is a const pointer to an int, and so is encoded as r^i.
Finally, there is a complication when encoding const char * versus char * const. Because char * is encoded as * and not as ^c, there is no way to express the fact that r applies to the pointer or to the pointee.
Hence, it is assumed as a convention that r* means const char * (since it is what is most often meant), and there is no way to encode char *const. char *const would simply be encoded as *, and the const is lost.
:: _legacy-type-encoding:
Unfortunately, historically GCC used to have a number of bugs in its encoding code. The NeXT runtime expects GCC to emit type encodings in this historical format (compatible with GCC-3.3), so when using the NeXT runtime, GCC will introduce on purpose a number of incorrect encodings:
In addition to that, the NeXT runtime uses a different encoding for bitfields. It encodes them as b followed by the size, without a bit offset or the underlying field type.
:: _encode:
encode
GNU Objective-C supports the encode syntax that allows you to create a type encoding from a C/Objective-C type. For example, encode(int) is compiled by the compiler into "i".
encode does not support type qualifiers other than const. For example, encode(const char*) is valid and is compiled into "r*", while encode(bycopy char *) is invalid and will cause a compilation error.
:: _method-signatures:
This section documents the encoding of method types, which is rarely needed to use Objective-C. You should skip it at a first reading; the runtime provides functions that will work on methods and can walk through the list of parameters and interpret them for you. These functions are part of the public API and are the preferred way to interact with method signatures from user code.
But if you need to debug a problem with method signatures and need to know how they are implemented (i.e., the ABI), read on.
Methods have their signature encoded and made available to the runtime. The signature encodes all the information required to dynamically build invocations of the method at runtime: return type and arguments.
The signature is a null-terminated string, composed of the following:
For example, a method with no arguments and returning int would have the signature i80:4 if the size of a pointer is 4. The signature is interpreted as follows: the i is the return type (an int), the 8 is the total size of the parameters in bytes (two pointers each of size 4), the 0 is the first parameter (an object at byte offset 0) and :4 is the second parameter (a SEL at byte offset 4).
You can easily find more examples by running the strings program on an Objective-C object file compiled by GCC. Youll see a lot of strings that look very much like i80:4. They are signatures of Objective-C methods.
:: _garbage-collection:
This section is specific for the GNU Objective-C runtime. If you are using a different runtime, you can skip it.
Support for garbage collection with the GNU runtime has been added by using a powerful conservative garbage collector, known as the Boehm-Demers-Weiser conservative garbage collector.
To enable the support for it you have to configure the compiler using an additional argument, --enable-objc-gc. This will build the boehm-gc library, and build an additional runtime library which has several enhancements to support the garbage collector. The new library has a new name, libobjc_gc.a to not conflict with the non-garbage-collected library.
When the garbage collector is used, the objects are allocated using the so-called typed memory allocation mechanism available in the Boehm-Demers-Weiser collector. This mode requires precise information on where pointers are located inside objects. This information is computed once per class, immediately after the class has been initialized.
There is a new runtime function class_ivar_set_gcinvisible() which can be used to declare a so-called weak pointer reference. Such a pointer is basically hidden for the garbage collector; this can be useful in certain situations, especially when you want to keep track of the allocated objects, yet allow them to be collected. This kind of pointers can only be members of objects, you cannot declare a global pointer as a weak reference. Every type which is a pointer type can be declared a weak pointer, including id, Class and SEL.
Here is an example of how to use this feature. Suppose you want to implement a class whose instances hold a weak pointer reference; the following class does this:
interface WeakPointer : Object
{
const void* weakPointer;
}
- initWithPointer:(const void*)p;
- (const void*)weakPointer;
end
implementation WeakPointer
+ (void)initialize
{
if (self == objc_lookUpClass ("WeakPointer"))
class_ivar_set_gcinvisible (self, "weakPointer", YES);
}
- initWithPointer:(const void*)p
{
weakPointer = p;
return self;
}
- (const void*)weakPointer
{
return weakPointer;
}
end
Weak pointers are supported through a new type character specifier represented by the ! character. The class_ivar_set_gcinvisible() function adds or removes this specifier to the string type description of the instance variable named as argument.
:: _constant-string-objects:
GNU Objective-C provides constant string objects that are generated directly by the compiler. You declare a constant string object by prefixing a C constant string with the character :
id myString = "this is a constant string object";
The constant string objects are by default instances of the NXConstantString class which is provided by the GNU Objective-C runtime. To get the definition of this class you must include the objc/NXConstStr.h header file.
User defined libraries may want to implement their own constant string class. To be able to support them, the GNU Objective-C compiler provides a new command line options -fconstant-string-class=``class-name``. The provided class should adhere to a strict structure, the same as ``NXConstantString``s structure:
interface MyConstantStringClass
{
Class isa;
char *c_string;
unsigned int len;
}
end
NXConstantString inherits from Object; user class libraries may choose to inherit the customized constant string class from a different class than Object. There is no requirement in the methods the constant string class has to implement, but the final ivar layout of the class must be the compatible with the given structure.
When the compiler creates the statically allocated constant string object, the c_string field will be filled by the compiler with the string; the length field will be filled by the compiler with the string length; the isa pointer will be filled with NULL by the compiler, and it will later be fixed up automatically at runtime by the GNU Objective-C runtime library to point to the class which was set by the -fconstant-string-class option when the object file is loaded (if you wonder how it works behind the scenes, the name of the class to use, and the list of static objects to fixup, are stored by the compiler in the object file in a place where the GNU runtime library will find them at runtime).
As a result, when a file is compiled with the -fconstant-string-class option, all the constant string objects will be instances of the class specified as argument to this option. It is possible to have multiple compilation units referring to different constant string classes, neither the compiler nor the linker impose any restrictions in doing this.
:: _compatibility_alias:
compatibility_alias
The keyword compatibility_alias allows you to define a class name as equivalent to another class name. For example:
compatibility_alias WOApplication GSWApplication;
tells the compiler that each time it encounters WOApplication as a class name, it should replace it with GSWApplication (that is, WOApplication is just an alias for GSWApplication).
There are some constraints on how this can be used
:: _exceptions:
GNU Objective-C provides exception support built into the language, as in the following example:
try {
...
throw expr;
...
}
catch (AnObjCClass *exc) {
...
throw expr;
...
throw;
...
}
catch (AnotherClass *exc) {
...
}
catch (id allOthers) {
...
}
finally {
...
throw expr;
...
}
The throw statement may appear anywhere in an Objective-C or Objective-C++ program; when used inside of a catch block, the throw may appear without an argument (as shown above), in which case the object caught by the catch will be rethrown.
Note that only (pointers to) Objective-C objects may be thrown and caught using this scheme. When an object is thrown, it will be caught by the nearest catch clause capable of handling objects of that type, analogously to how catch blocks work in C++ and Java. A catch(id ...) clause (as shown above) may also be provided to catch any and all Objective-C exceptions not caught by previous catch clauses (if any).
The finally clause, if present, will be executed upon exit from the immediately preceding try ... catch section. This will happen regardless of whether any exceptions are thrown, caught or rethrown inside the try ... catch section, analogously to the behavior of the finally clause in Java.
There are several caveats to using the new exception mechanism:
:: _synchronization:
GNU Objective-C provides support for synchronized blocks:
synchronized (ObjCClass *guard) {
...
}
Upon entering the synchronized block, a thread of execution shall first check whether a lock has been placed on the corresponding guard object by another thread. If it has, the current thread shall wait until the other thread relinquishes its lock. Once guard becomes available, the current thread will place its own lock on it, execute the code contained in the synchronized block, and finally relinquish the lock (thereby making guard available to other threads).
Unlike Java, Objective-C does not allow for entire methods to be marked synchronized. Note that throwing exceptions out of synchronized blocks is allowed, and will cause the guarding object to be unlocked properly.
Because of the interactions between synchronization and exception handling, you can only use synchronized when compiling with exceptions enabled, that is with the command line option -fobjc-exceptions.
:: _fast-enumeration:
GNU Objective-C provides support for the fast enumeration syntax:
id array = ...;
id object;
for (object in array)
{
/* Do something with 'object' */
}
array needs to be an Objective-C object (usually a collection object, for example an array, a dictionary or a set) which implements the Fast Enumeration Protocol (see below). If you are using a Foundation library such as GNUstep Base or Apple Cocoa Foundation, all collection objects in the library implement this protocol and can be used in this way.
The code above would iterate over all objects in array. For each of them, it assigns it to object, then executes the Do something with 'object' statements.
Here is a fully worked-out example using a Foundation library (which provides the implementation of NSArray, NSString and NSLog):
NSArray *array = [NSArray arrayWithObjects: "1", "2", "3", nil];
NSString *object;
for (object in array)
NSLog ("Iterating over %", object);
:: _c99-like-fast-enumeration-syntax:
A c99-like declaration syntax is also allowed:
id array = ...;
for (id object in array)
{
/* Do something with 'object' */
}
this is completely equivalent to:
id array = ...;
{
id object;
for (object in array)
{
/* Do something with 'object' */
}
}
but can save some typing.
Note that the option -std=c99 is not required to allow this syntax in Objective-C.
:: _fast-enumeration-details:
Here is a more technical description with the gory details. Consider the code
for (``object expression`` in ``collection expression``)
{
``statements``
}
here is what happens when you run it:
:: _fast-enumeration-protocol:
If you want your own collection object to be usable with fast enumeration, you need to have it implement the method
where NSFastEnumerationState must be defined in your code as follows:
typedef struct
{
unsigned long state;
id *itemsPtr;
unsigned long *mutationsPtr;
unsigned long extra[5];
} NSFastEnumerationState;
If no NSFastEnumerationState is defined in your code, the compiler will automatically replace NSFastEnumerationState * with struct __objcFastEnumerationState *, where that type is silently defined by the compiler in an identical way. This can be confusing and we recommend that you define NSFastEnumerationState (as shown above) instead.
The method is called repeatedly during a fast enumeration to retrieve batches of objects. Each invocation of the method should retrieve the next batch of objects.
The return value of the method is the number of objects in the current batch; this should not exceed len, which is the maximum size of a batch as requested by the caller. The batch itself is returned in the itemsPtr field of the NSFastEnumerationState struct.
To help with returning the objects, the objects array is a C array preallocated by the caller (on the stack) of size len. In many cases you can put the objects you want to return in that objects array, then do itemsPtr = objects. But you dont have to; if your collection already has the objects to return in some form of C array, it could return them from there instead.
The state and extra fields of the NSFastEnumerationState structure allows your collection object to keep track of the state of the enumeration. In a simple array implementation, state may keep track of the index of the last object that was returned, and extra may be unused.
The mutationsPtr field of the NSFastEnumerationState is used to keep track of mutations. It should point to a number; before working on each object, the fast enumeration loop will check that this number has not changed. If it has, a mutation has happened and the fast enumeration will abort. So, mutationsPtr could be set to point to some sort of version number of your collection, which is increased by one every time there is a change (for example when an object is added or removed). Or, if you are content with less strict mutation checks, it could point to the number of objects in your collection or some other value that can be checked to perform an approximate check that the collection has not been mutated.
Finally, note how we declared the len argument and the return value to be of type unsigned long. They could also be declared to be of type unsigned int and everything would still work.
:: _messaging-with-the-gnu-objective-c-runtime:
This section is specific for the GNU Objective-C runtime. If you are using a different runtime, you can skip it.
The implementation of messaging in the GNU Objective-C runtime is designed to be portable, and so is based on standard C.
Sending a message in the GNU Objective-C runtime is composed of two separate steps. First, there is a call to the lookup function, objc_msg_lookup () (or, in the case of messages to super, objc_msg_lookup_super ()). This runtime function takes as argument the receiver and the selector of the method to be called; it returns the IMP, that is a pointer to the function implementing the method. The second step of method invocation consists of casting this pointer function to the appropriate function pointer type, and calling the function pointed to it with the right arguments.
For example, when the compiler encounters a method invocation such as [object init], it compiles it into a call to objc_msg_lookup (object, selector(init)) followed by a cast of the returned value to the appropriate function pointer type, and then it calls it.
:: _dynamically-registering-methods:
If objc_msg_lookup() does not find a suitable method implementation, because the receiver does not implement the required method, it tries to see if the class can dynamically register the method.
To do so, the runtime checks if the class of the receiver implements the method
+ (BOOL) resolveInstanceMethod: (SEL)selector;
in the case of an instance method, or
+ (BOOL) resolveClassMethod: (SEL)selector;
in the case of a class method. If the class implements it, the runtime invokes it, passing as argument the selector of the original method, and if it returns YES, the runtime tries the lookup again, which could now succeed if a matching method was added dynamically by +resolveInstanceMethod: or +resolveClassMethod:.
This allows classes to dynamically register methods (by adding them to the class using class_addMethod) when they are first called. To do so, a class should implement +resolveInstanceMethod: (or, depending on the case, +resolveClassMethod:) and have it recognize the selectors of methods that can be registered dynamically at runtime, register them, and return YES. It should return NO for methods that it does not dynamically registered at runtime.
If +resolveInstanceMethod: (or +resolveClassMethod:) is not implemented or returns NO, the runtime then tries the forwarding hook.
Support for +resolveInstanceMethod: and resolveClassMethod: was added to the GNU Objective-C runtime in GCC version 4.6.
:: _forwarding-hook:
The GNU Objective-C runtime provides a hook, called __objc_msg_forward2, which is called by objc_msg_lookup() when it cant find a method implementation in the runtime tables and after calling +resolveInstanceMethod: and +resolveClassMethod: has been attempted and did not succeed in dynamically registering the method.
To configure the hook, you set the global variable __objc_msg_forward2 to a function with the same argument and return types of objc_msg_lookup(). When objc_msg_lookup() can not find a method implementation, it invokes the hook function you provided to get a method implementation to return. So, in practice __objc_msg_forward2 allows you to extend objc_msg_lookup() by adding some custom code that is called to do a further lookup when no standard method implementation can be found using the normal lookup.
This hook is generally reserved for Foundation libraries such as GNUstep Base, which use it to implement their high-level method forwarding API, typically based around the forwardInvocation: method. So, unless you are implementing your own Foundation library, you should not set this hook.
In a typical forwarding implementation, the __objc_msg_forward2 hook function determines the argument and return type of the method that is being looked up, and then creates a function that takes these arguments and has that return type, and returns it to the caller. Creating this function is non-trivial and is typically performed using a dedicated library such as libffi.
The forwarding method implementation thus created is returned by objc_msg_lookup() and is executed as if it was a normal method implementation. When the forwarding method implementation is called, it is usually expected to pack all arguments into some sort of object (typically, an NSInvocation in a Foundation library), and hand it over to the programmer (forwardInvocation:) who is then allowed to manipulate the method invocation using a high-level API provided by the Foundation library. For example, the programmer may want to examine the method invocation arguments and name and potentially change them before forwarding the method invocation to one or more local objects (performInvocation:) or even to remote objects (by using Distributed Objects or some other mechanism). When all this completes, the return value is passed back and must be returned correctly to the original caller.
Note that the GNU Objective-C runtime currently provides no support for method forwarding or method invocations other than the __objc_msg_forward2 hook.
If the forwarding hook does not exist or returns NULL, the runtime currently attempts forwarding using an older, deprecated API, and if that fails, it aborts the program. In future versions of the GNU Objective-C runtime, the runtime will immediately abort.
:: _compatibility:
Binary compatibility encompasses several related concepts:
The set of runtime conventions followed by all of the tools that deal with binary representations of a program, including compilers, assemblers, linkers, and language runtime support. Some ABIs are formal with a written specification, possibly designed by multiple interested parties. Others are simply the way things are actually done by a particular set of tools.
A compiler conforms to an ABI if it generates code that follows all of the specifications enumerated by that ABI A library conforms to an ABI if it is implemented according to that ABI An application conforms to an ABI if it is built using tools that conform to that ABI and does not contain source code that specifically changes behavior specified by the ABI
Calling conventions are a subset of an ABI that specify of how arguments are passed and function results are returned.
Different sets of tools are interoperable if they generate files that can be used in the same program. The set of tools includes compilers, assemblers, linkers, libraries, header files, startup files, and debuggers. Binaries produced by different sets of tools are not interoperable unless they implement the same ABI This applies to different versions of the same tools as well as tools from different vendors.
Whether a function in a binary built by one set of tools can call a function in a binary built by a different set of tools is a subset of interoperability.
Language standards include lists of implementation-defined features whose behavior can vary from one implementation to another. Some of these features are normally covered by a platforms ABI and others are not. The features that are not covered by an ABI generally affect how a program behaves, but not intercallability.
Conformance to the same ABI and the same behavior of implementation-defined features are both relevant for compatibility.
The application binary interface implemented by a C or C++ compiler affects code generation and runtime support for:
In addition, the application binary interface implemented by a C++ compiler affects code generation and runtime support for:
Some GCC compilation options cause the compiler to generate code that does not conform to the platforms default ABI Other options cause different program behavior for implementation-defined features that are not covered by an ABI These options are provided for consistency with other compilers that do not follow the platforms default ABI or the usual behavior of implementation-defined features for the platform. Be very careful about using such options.
Most platforms have a well-defined ABI that covers C code, but ABIs that cover C++ functionality are not yet common.
Starting with GCC 3.2, GCC binary conventions for C++ are based on a written, vendor-neutral C++ ABI that was designed to be specific to 64-bit Itanium but also includes generic specifications that apply to any platform. This C++ ABI is also implemented by other compiler vendors on some platforms, notably GNU/Linux and BSD systems. We have tried hard to provide a stable ABI that will be compatible with future GCC releases, but it is possible that we will encounter problems that make this difficult. Such problems could include different interpretations of the C++ ABI by different vendors, bugs in the ABI, or bugs in the implementation of the ABI in different compilers. GCCs -Wabi switch warns when G++ generates code that is probably not compatible with the C++ ABI
The C++ library used with a C++ compiler includes the Standard C++ Library, with functionality defined in the C++ Standard, plus language runtime support. The runtime support is included in a C++ ABI, but there is no formal ABI for the Standard C++ Library. Two implementations of that library are interoperable if one follows the de-facto ABI of the other and if they are both built with the same compiler, or with compilers that conform to the same ABI for C++ compiler and runtime support.
When G++ and another C++ compiler conform to the same C++ ABI, but the implementations of the Standard C++ Library that they normally use do not follow the same ABI for the Standard C++ Library, object files built with those compilers can be used in the same program only if they use the same C++ library. This requires specifying the location of the C++ library header files when invoking the compiler whose usual library is not being used. The location of GCCs C++ header files depends on how the GCC build was configured, but can be seen by using the G++ -v option. With default configuration options for G++ 3.3 the compile line for a different C++ compiler needs to include
-I``gcc_install_directory``/include/c++/3.3
Similarly, compiling code with G++ that must use a C++ library other than the GNU C++ library requires specifying the location of the header files for that other library.
The most straightforward way to link a program to use a particular C++ library is to use a C++ driver that specifies that C++ library by default. The g++ driver, for example, tells the linker where to find GCCs C++ library (libstdc++) plus the other libraries and startup files it needs, in the proper order.
If a program must use a different C++ library and its not possible to do the final link using a C++ driver that uses that library by default, it is necessary to tell g++ the location and name of that library. It might also be necessary to specify different startup files and other runtime support libraries, and to suppress the use of GCCs support libraries with one or more of the options -nostdlib, -nostartfiles, and -nodefaultlibs.
@c man begin COPYRIGHT Copyright @copyright{} 1996-2015 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being ``GNU General Public License’’ and ``Funding Free Software’‘, the Front-Cover texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the gfdl(7) man page.
The FSF’s Front-Cover Text is:
A GNU Manual
The FSF’s Back-Cover Text is:
You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development.
@c man end @c Set file name and title for the man page. @setfilename gcov @settitle coverage testing tool
:: _gcov:
:command:`gcov`a Test Coverage Program
gcov is a tool you can use in conjunction with GCC to test code coverage in your programs.
:: _gcov-intro:
Introduction to gcov
gcov is a test coverage program. Use it in concert with GCC to analyze your programs to help create more efficient, faster running code and to discover untested parts of your program. You can use gcov as a profiling tool to help discover where your optimization efforts will best affect your code. You can also use gcov along with the other profiling tool, gprof, to assess which parts of your code use the greatest amount of computing time.
Profiling tools help you analyze your codes performance. Using a profiler such as gcov or gprof, you can find out some basic performance statistics, such as:
Once you know these things about how your code works when compiled, you can look at each module to see which modules should be optimized. gcov helps you determine where to work on optimization.
Software developers also use coverage testing in concert with testsuites, to make sure software is actually good enough for a release. Testsuites can verify that a program works as expected; a coverage program tests to see how much of the program is exercised by the testsuite. Developers can then determine what kinds of test cases need to be added to the testsuites to create both better testing and a better final product.
You should compile your code without optimization if you plan to use gcov because the optimization, by combining some lines of code into one function, may not give you as much information as you need to look for hot spots where the code is using a great deal of computer time. Likewise, because gcov accumulates statistics by line (at the lowest resolution), it works best with a programming style that places only one statement on each line. If you use complicated macros that expand to loops or to other control structures, the statistics are less helpfulthey only report on the line where the macro call appears. If your complex macros behave like functions, you can replace them with inline functions to solve this problem.
gcov creates a logfile called sourcefile.gcov which indicates how many times each line of a source file sourcefile.c has executed. You can use these logfiles along with gprof to aid in fine-tuning the performance of your programs. gprof gives timing information you can use along with the information you get from gcov.
gcov works only on code compiled with GCC It is not compatible with any other profiling or test coverage mechanism.
:: _invoking-gcov:
Invoking gcov
gcov [``options``] ``files``
gcov accepts the following options:
@c man begin SYNOPSIS gcov [@option{-v}|@option{--version}] [@option{-h}|@option{--help}]
[@option{-a}|@option{--all-blocks}] [@option{-b}|@option{--branch-probabilities}] [@option{-c}|@option{--branch-counts}] [@option{-d}|@option{--display-progress}] [@option{-f}|@option{--function-summaries}] [@option{-i}|@option{--intermediate-format}] [@option{-l}|@option{--long-file-names}] [@option{-m}|@option{--demangled-names}] [@option{-n}|@option{--no-output}] [@option{-o}|@option{--object-directory} @var{directory|file}] [@option{-p}|@option{--preserve-paths}] [@option{-r}|@option{--relative-only}] [@option{-s}|@option{--source-prefix} @var{directory}] [@option{-u}|@option{--unconditional-branches}] @var{files}
@c man end @c man begin SEEALSO gpl(7), gfdl(7), fsf-funding(7), gcc(1) and the Info entry for @file{gcc}. @c man end
Display help about using gcov (on the standard output), and exit without doing any further processing.
Display the gcov version number (on the standard output), and exit without doing any further processing.
Write individual execution counts for every basic block. Normally gcov outputs execution counts only for the main blocks of a line. With this option you can determine if blocks within a single line are not being executed.
Write branch frequencies to the output file, and write branch summary info to the standard output. This option allows you to see how often each branch in your program was taken. Unconditional branches will not be shown, unless the -u option is given.
Write branch frequencies as the number of branches taken, rather than the percentage of branches taken.
Do not create the gcov output file.
Create long file names for included source files. For example, if the header file x.h contains code, and was included in the file a.c, then running gcov on the file a.c will produce an output file called a.c##x.h.gcov instead of x.h.gcov. This can be useful if x.h is included in multiple source files and you want to see the individual contributions. If you use the -p option, both the including and included file names will be complete path names.
Preserve complete path information in the names of generated .gcov files. Without this option, just the filename component is used. With this option, all directories are used, with / characters translated to # characters, . directory components removed and unremoveable .. components renamed to ^. This is useful if sourcefiles are in several different directories.
Only output information about source files with a relative pathname (after source prefix elision). Absolute paths are usually system header files and coverage of any inline functions therein is normally uninteresting.
Output summaries for each function in addition to the file level summary.
-o directory|file
–object-directory directory –object-file file Specify either the directory containing the gcov data files, or the object path name. The .gcno, and .gcda data files are searched for using this option. If a directory is specified, the data files are in that directory and named after the input file name, without its extension. If a file is specified here, the data files are named after that file, without its extension.
-s directory –source-prefix directory A prefix for source file names to remove when generating the output coverage files. This option is useful when building in a separate directory, and the pathname to the source directory is not wanted when determining the output file names. Note that this prefix detection is applied before determining whether the source file is absolute.
When branch probabilities are given, include those of unconditional branches. Unconditional branches are normally not interesting.
Display the progress on the standard output.
Output gcov file in an easy-to-parse intermediate text format that can be used by lcov or other tools. The output is a single .gcov file per .gcda file. No source code is required.
The format of the intermediate .gcov file is plain text with one entry per line
file:``source_file_name``
function:``line_number``,``execution_count``,``function_name``
lcount:``line number``,``execution_count``
branch:``line_number``,``branch_coverage_type``
Where the ``branch_coverage_type`` is
notexec (Branch not executed)
taken (Branch executed and taken)
nottaken (Branch executed, but not taken)
There can be multiple ``file`` entries in an intermediate gcov
file. All entries following a ``file`` pertain to that source file
until the next ``file`` entry.
Here is a sample when -i is used in conjunction with -b option:
file:array.cc
function:11,1,_Z3sumRKSt6vectorIPiSaIS0_EE
function:22,1,main
lcount:11,1
lcount:12,1
lcount:14,1
branch:14,taken
lcount:26,1
branch:28,nottaken
Display demangled function names in output. The default is to show mangled function names.
gcov should be run with the current directory the same as that when you invoked the compiler. Otherwise it will not be able to locate the source files. gcov produces files called mangledname.gcov in the current directory. These contain the coverage information of the source file they correspond to. One .gcov file is produced for each source (or header) file containing code, which was compiled to produce the data files. The mangledname part of the output file name is usually simply the source file name, but can be something more complicated if the -l or -p options are given. Refer to those options for details.
If you invoke gcov with multiple input files, the contributions from each input file are summed. Typically you would invoke it with the same list of files as the final link of your executable.
The .gcov files contain the : separated fields along with program source code. The format is
``execution_count``:``line_number``:``source line text``
Additional block information may succeed each line, when requested by command line option. The execution_count is - for lines containing no code. Unexecuted lines are marked ##### or ====, depending on whether they are reachable by non-exceptional paths or only exceptional paths such as C++ exception handlers, respectively.
Some lines of information at the start have line_number of zero. These preamble lines are of the form
-:0:```tag`:value
The ordering and number of these preamble lines will be augmented as gcov development progresses do not rely on them remaining unchanged. Use tag to locate a particular preamble line.
The additional block information is of the form
``tag`` ``information``
The information is human readable, but designed to be simple enough for machine parsing too.
When printing percentages, 0% and 100% are only printed when the values are exactly 0% and 100% respectively. Other values which would conventionally be rounded to 0% or 100% are instead printed as the nearest non-boundary value.
When using gcov, you must first compile your program with two special GCC options: -fprofile-arcs -ftest-coverage. This tells the compiler to generate additional information needed by gcov (basically a flow graph of the program) and also includes additional code in the object files for generating the extra profiling information needed by gcov. These additional files are placed in the directory where the object file is located.
Running the program will cause profile output to be generated. For each source file compiled with -fprofile-arcs, an accompanying .gcda file will be placed in the object file directory.
Running gcov with your programs source file names as arguments will now produce a listing of the code along with frequency of execution for each line. For example, if your program is called tmp.c, this is what you see when you use the basic gcov facility:
$ gcc -fprofile-arcs -ftest-coverage tmp.c
$ a.out
$ gcov tmp.c
90.00% of 10 source lines executed in file tmp.c
Creating tmp.c.gcov.
The file tmp.c.gcov contains output from gcov. Here is a sample:
-: 0:Source:tmp.c
-: 0:Graph:tmp.gcno
-: 0:Data:tmp.gcda
-: 0:Runs:1
-: 0:Programs:1
-: 1:#include <stdio.h>
-: 2:
-: 3:int main (void)
1: 4:{
1: 5: int i, total;
-: 6:
1: 7: total = 0;
-: 8:
11: 9: for (i = 0; i < 10; i++)
10: 10: total += i;
-: 11:
1: 12: if (total != 45)
#####: 13: printf ("Failure\n");
-: 14: else
1: 15: printf ("Success\n");
1: 16: return 0;
-: 17:}
When you use the -a option, you will get individual block counts, and the output looks like this:
-: 0:Source:tmp.c
-: 0:Graph:tmp.gcno
-: 0:Data:tmp.gcda
-: 0:Runs:1
-: 0:Programs:1
-: 1:#include <stdio.h>
-: 2:
-: 3:int main (void)
1: 4:{
1: 4-block 0
1: 5: int i, total;
-: 6:
1: 7: total = 0;
-: 8:
11: 9: for (i = 0; i < 10; i++)
11: 9-block 0
10: 10: total += i;
10: 10-block 0
-: 11:
1: 12: if (total != 45)
1: 12-block 0
#####: 13: printf ("Failure\n");
$$$$$: 13-block 0
-: 14: else
1: 15: printf ("Success\n");
1: 15-block 0
1: 16: return 0;
1: 16-block 0
-: 17:}
In this mode, each basic block is only shown on one line the last line of the block. A multi-line block will only contribute to the execution count of that last line, and other lines will not be shown to contain code, unless previous blocks end on those lines. The total execution count of a line is shown and subsequent lines show the execution counts for individual blocks that end on that line. After each block, the branch and call counts of the block will be shown, if the -b option is given.
Because of the way GCC instruments calls, a call count can be shown after a line with no individual blocks. As you can see, line 13 contains a basic block that was not executed.
When you use the -b option, your output looks like this:
$ gcov -b tmp.c
90.00% of 10 source lines executed in file tmp.c
80.00% of 5 branches executed in file tmp.c
80.00% of 5 branches taken at least once in file tmp.c
50.00% of 2 calls executed in file tmp.c
Creating tmp.c.gcov.
Here is a sample of a resulting tmp.c.gcov file:
-: 0:Source:tmp.c
-: 0:Graph:tmp.gcno
-: 0:Data:tmp.gcda
-: 0:Runs:1
-: 0:Programs:1
-: 1:#include <stdio.h>
-: 2:
-: 3:int main (void)
function main called 1 returned 1 blocks executed 75%
1: 4:{
1: 5: int i, total;
-: 6:
1: 7: total = 0;
-: 8:
11: 9: for (i = 0; i < 10; i++)
branch 0 taken 91% (fallthrough)
branch 1 taken 9%
10: 10: total += i;
-: 11:
1: 12: if (total != 45)
branch 0 taken 0% (fallthrough)
branch 1 taken 100%
#####: 13: printf ("Failure\n");
call 0 never executed
-: 14: else
1: 15: printf ("Success\n");
call 0 called 1 returned 100%
1: 16: return 0;
-: 17:}
For each function, a line is printed showing how many times the function is called, how many times it returns and what percentage of the functions blocks were executed.
For each basic block, a line is printed after the last line of the basic block describing the branch or call that ends the basic block. There can be multiple branches and calls listed for a single source line if there are multiple basic blocks that end on that line. In this case, the branches and calls are each given a number. There is no simple way to map these branches and calls back to source constructs. In general, though, the lowest numbered branch or call will correspond to the leftmost construct on the source line.
For a branch, if it was executed at least once, then a percentage indicating the number of times the branch was taken divided by the number of times the branch was executed will be printed. Otherwise, the message never executed is printed.
For a call, if it was executed at least once, then a percentage indicating the number of times the call returned divided by the number of times the call was executed will be printed. This will usually be 100%, but may be less for functions that call exit or longjmp, and thus may not return every time they are called.
The execution counts are cumulative. If the example program were executed again without removing the .gcda file, the count for the number of times each line in the source was executed would be added to the results of the previous run(s). This is potentially useful in several ways. For example, it could be used to accumulate data over a number of program runs as part of a test verification suite, or to provide more accurate long-term information over a large number of program runs.
The data in the .gcda files is saved immediately before the program exits. For each source file compiled with -fprofile-arcs, the profiling code first attempts to read in an existing .gcda file; if the file doesnt match the executable (differing number of basic block counts) it will ignore the contents of the file. It then adds in the new execution counts and finally writes the data to the file.
:: _gcov-and-optimization:
Using gcov with GCC Optimization
If you plan to use gcov to help optimize your code, you must first compile your program with two special GCC options: -fprofile-arcs -ftest-coverage. Aside from that, you can use any other GCC options; but if you want to prove that every single line in your program was executed, you should not compile with optimization at the same time. On some machines the optimizer can eliminate some simple code lines by combining them with other lines. For example, code like this:
if (a != b)
c = 1;
else
c = 0;
can be compiled into one instruction on some machines. In this case, there is no way for gcov to calculate separate execution counts for each line because there isnt separate code for each line. Hence the gcov output looks like this if you compiled the program with optimization:
100: 12:if (a != b)
100: 13: c = 1;
100: 14:else
100: 15: c = 0;
The output shows that this block of code, combined by optimization, executed 100 times. In one sense this result is correct, because there was only one instruction representing all four of these lines. However, the output does not indicate how many times the result was 0 and how many times the result was 1.
Inlineable functions can create unexpected line counts. Line counts are shown for the source code of the inlineable function, but what is shown depends on where the function is inlined, or if it is not inlined at all.
If the function is not inlined, the compiler must emit an out of line copy of the function, in any object file that needs it. If fileA.o and fileB.o both contain out of line bodies of a particular inlineable function, they will also both contain coverage counts for that function. When fileA.o and fileB.o are linked together, the linker will, on many systems, select one of those out of line bodies for all calls to that function, and remove or ignore the other. Unfortunately, it will not remove the coverage counters for the unused function body. Hence when instrumented, all but one use of that function will show zero counts.
If the function is inlined in several places, the block structure in each location might not be the same. For instance, a condition might now be calculable at compile time in some instances. Because the coverage of all the uses of the inline function will be shown for the same source lines, the line counts themselves might seem inconsistent.
Long-running applications can use the _gcov_reset and _gcov_dump facilities to restrict profile collection to the program region of interest. Calling _gcov_reset(void) will clear all profile counters to zero, and calling _gcov_dump(void) will cause the profile information collected at that point to be dumped to .gcda output files.
:: _gcov-data-files:
Brief Description of gcov Data Files
gcov uses two files for profiling. The names of these files are derived from the original object file by substituting the file suffix with either .gcno, or .gcda. The files contain coverage and profile data stored in a platform-independent format. The .gcno files are placed in the same directory as the object file. By default, the .gcda files are also stored in the same directory as the object file, but the GCC -fprofile-dir option may be used to store the .gcda files in a separate directory.
The .gcno notes file is generated when the source file is compiled with the GCC -ftest-coverage option. It contains information to reconstruct the basic block graphs and assign source line numbers to blocks.
The .gcda count data file is generated when a program containing object files built with the GCC -fprofile-arcs option is executed. A separate .gcda file is created for each object file compiled with this option. It contains arc transition counts, value profile counts, and some summary information.
The full details of the file format is specified in gcov-io.h, and functions provided in that header file should be used to access the coverage files.
:: _cross-profiling:
Running the program will cause profile output to be generated. For each source file compiled with -fprofile-arcs, an accompanying .gcda file will be placed in the object file directory. That implicitly requires running the program on the same system as it was built or having the same absolute directory structure on the target system. The program will try to create the needed directory structure, if it is not already present.
To support cross-profiling, a program compiled with -fprofile-arcs can relocate the data files based on two environment variables:
GCOV_PREFIX contains the prefix to add to the absolute paths in the object file. Prefix can be absolute, or relative. The default is no prefix.
GCOV_PREFIX_STRIP indicates the how many initial directory names to strip off the hardwired absolute paths. Default value is 0.
then a relative path is made out of the hardwired absolute paths.
For example, if the object file /user/build/foo.o was built with -fprofile-arcs, the final executable will try to create the data file /user/build/foo.gcda when running on the target system. This will fail if the corresponding directory does not exist and it is unable to create it. This can be overcome by, for example, setting the environment as GCOV_PREFIX=/target/run and GCOV_PREFIX_STRIP=1. Such a setting will name the data file /target/run/build/foo.gcda.
You must move the data files to the expected directory tree in order to use them for profile directed optimizations (--use-profile), or to use the gcov tool.
@c man begin COPYRIGHT Copyright @copyright{} 2014-2015 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being ``GNU General Public License’’ and ``Funding Free Software’‘, the Front-Cover texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the gfdl(7) man page.
The FSF’s Front-Cover Text is:
A GNU Manual
The FSF’s Back-Cover Text is:
You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development.
@c man end @c Set file name and title for the man page. @setfilename gcov-tool @settitle offline gcda profile processing tool
:: _gcov-tool:
:command:`gcov-tool`an Offline Gcda Profile Processing Tool
gcov-tool is a tool you can use in conjunction with GCC to manipulate or process gcda profile files offline.
:: _gcov-tool-intro:
Introduction to gcov-tool
gcov-tool is an offline tool to process gccs gcda profile files.
Current gcov-tool supports the following functionalities:
Examples of the use cases for this tool are:
Note that for the merging operation, this profile generated offline may contain slight different values from the online merged profile. Here are a list of typical differences:
:: _invoking-gcov-tool:
Invoking gcov-tool
gcov-tool [``global-options``] SUB_COMMAND [``sub_command-options``] ``profile_dir``
gcov-tool accepts the following options:
@c man begin SYNOPSIS gcov-tool [@option{-v}|@option{--version}] [@option{-h}|@option{--help}]
@c man end @c man begin SEEALSO gpl(7), gfdl(7), fsf-funding(7), gcc(1), gcov(1) and the Info entry for @file{gcc}. @c man end
Display help about using gcov-tool (on the standard output), and exit without doing any further processing.
Display the gcov-tool version number (on the standard output), and exit without doing any further processing.
Merge two profile directories.
Set the verbose mode.
-o directory
–output directory Set the output profile directory. Default output directory name is merged_profile.
-w w1,``w2`` –weight w1,``w2`` Set the merge weights of the directory1 and directory2, respectively. The default weights are 1 for both.
Read the specified profile directory and rewrite to a new directory.
Set the verbose mode.
-o directory
–output directory Set the output profile directory. Default output name is rewrite_profile.
-s float_or_simple-frac_value –scale float_or_simple-frac_value Scale the profile counters. The specified value can be in floating point value, or simple fraction value form, such 1, 2, 2/3, and 5/3.
-n long_long_value –normalize <long_long_value> Normalize the profile. The specified value is the max counter value in the new profile.
Computer the overlap score between the two specified profile directories. The overlap score is computed based on the arc profiles. It is defined as the sum of min (p1_counter[i] / p1_sum_all, p2_counter[i] / p2_sum_all), for all arc counter i, where p1_counter[i] and p2_counter[i] are two matched counters and p1_sum_all and p2_sum_all are the sum of counter values in profile 1 and profile 2, respectively.
Set the verbose mode.
Only print info for hot objects/functions.
Print function level overlap score.
Print full gcda filename.
Print object level overlap score.
-t float
–hot_threshold <float> Set the threshold for hot counter value.
:: _trouble:
This section describes known problems that affect users of GCC Most of these are not GCC bugs per seif they were, we would fix them. But the result for a user may be like the result of a bug.
Some of these problems are due to bugs in other software, some are missing features that are too much work to add, and some are places where peoples opinions differ as to what is best.
:: _actual-bugs:
:: _interoperation:
This section lists various difficulties encountered in using GCC together with other compilers or with the assemblers, linkers, libraries and debuggers on certain systems.
On many platforms, GCC supports a different ABI for C++ than do other compilers, so the object files compiled by GCC cannot be used with object files generated by another C++ compiler.
An area where the difference is most apparent is name mangling. The use of different name mangling is intentional, to protect you from more subtle problems. Compilers differ as to many internal details of C++ implementation, including: how class instances are laid out, how multiple inheritance is implemented, and how virtual function calls are handled. If the name encoding were made the same, your programs would link against libraries provided from other compilersbut the programs would then crash when run. Incompatible libraries are then detected at link time, rather than at run time.
On some BSD systems, including some versions of Ultrix, use of profiling causes static variable destructors (currently used only in C++) not to be run.
On a SPARC, GCC aligns all values of type double on an 8-byte boundary, and it expects every double to be so aligned. The Sun compiler usually gives double values 8-byte alignment, with one exception: function arguments of type double may not be aligned.
As a result, if a function compiled with Sun CC takes the address of an argument of type double and passes this pointer of type double * to a function compiled with GCC, dereferencing the pointer may cause a fatal signal.
One way to solve this problem is to compile your entire program with GCC Another solution is to modify the function that is compiled with Sun CC to copy the argument into a local variable; local variables are always properly aligned. A third solution is to modify the function that uses the pointer to dereference it via the following function access_double instead of directly with *:
inline double
access_double (double *unaligned_ptr)
{
union d2i { double d; int i[2]; };
union d2i *p = (union d2i *) unaligned_ptr;
union d2i u;
u.i[0] = p->i[0];
u.i[1] = p->i[1];
return u.d;
}
Storing into the pointer can be done likewise with the same union.
On Solaris, the malloc function in the libmalloc.a library may allocate memory that is only 4 byte aligned. Since GCC on the SPARC assumes that doubles are 8 byte aligned, this may result in a fatal signal if doubles are stored in memory allocated by the libmalloc.a library.
The solution is to not use the libmalloc.a library. Use instead malloc and related functions from libc.a; they do not have this problem.
On the HP PA machine, ADB sometimes fails to work on functions compiled with GCC Specifically, it fails to work on functions that use alloca or variable-size arrays. This is because GCC doesnt generate HP-UX unwind descriptors for such functions. It may even be impossible to generate them.
Debugging (-g) is not supported on the HP PA machine, unless you use the preliminary GNU tools.
Taking the address of a label may generate errors from the HP-UX PA assembler. GAS for the PA does not have this problem.
Using floating point parameters for indirect calls to static functions will not work when using the HP assembler. There simply is no way for GCC to specify what registers hold arguments for static functions when using the HP assembler. GAS for the PA does not have this problem.
In extremely rare cases involving some very large functions you may receive errors from the HP linker complaining about an out of bounds unconditional branch offset. This used to occur more often in previous versions of GCC, but is now exceptionally rare. If you should run into it, you can work around by making your function smaller.
GCC compiled code sometimes emits warnings from the HP-UX assembler of the form:
(warning) Use of GR3 when
frame >= 8192 may cause conflict.
These warnings are harmless and can be safely ignored.
In extremely rare cases involving some very large functions you may receive errors from the AIX Assembler complaining about a displacement that is too large. If you should run into it, you can work around by making your function smaller.
The libstdc++.a library in GCC relies on the SVR4 dynamic linker semantics which merges global symbols between libraries and applications, especially necessary for C++ streams functionality. This is not the default behavior of AIX shared libraries and dynamic linking. libstdc++.a is built on AIX with runtime-linking enabled so that symbol merging can occur. To utilize this feature, the application linked with libstdc++.a must include the -Wl,-brtl flag on the link line. G++ cannot impose this because this option may interfere with the semantics of the user program and users may not always use g++ to link his or her application. Applications are not required to use the -Wl,-brtl flag on the link linethe rest of the libstdc++.a library which is not dependent on the symbol merging semantics will continue to function correctly.
An application can interpose its own definition of functions for functions invoked by libstdc++.a with runtime-linking enabled on AIX To accomplish this the application must be linked with runtime-linking option and the functions explicitly must be exported by the application (-Wl,-brtl,-bE:exportfile).
AIX on the RS/6000 provides support (NLS) for environments outside of the United States. Compilers and assemblers use NLS to support locale-specific representations of various objects including floating-point numbers (. vs , for separating decimal fractions). There have been problems reported where the library linked with GCC does not produce the same floating-point formats that the assembler accepts. If you have this problem, set the LANG environment variable to C or En_US.
Even if you specify -fdollars-in-identifiers, you cannot successfully use $ in identifiers on the RS/6000 due to a restriction in the IBM assembler. GAS supports these identifiers.
:: _incompatibilities:
There are several noteworthy incompatibilities between GNU C and K&R (non-ISO) versions of C
GCC normally makes string constants read-only. If several identical-looking string constants are used, GCC stores only one copy of the string.
mktemp, and constant strings One consequence is that you cannot call mktemp with a string constant argument. The function mktemp always alters the string its argument points to.
sscanf, and constant strings fscanf, and constant strings scanf, and constant strings Another consequence is that sscanf does not work on some very old systems when passed a string constant as its format control string or input. This is because sscanf incorrectly tries to write into the string constant. Likewise fscanf and scanf.
The solution to these problems is to change the program to use char-array variables with initialization strings for these purposes instead of string constants.
-2147483648 is positive.
This is because 2147483648 cannot fit in the type int, so (following the ISO C rules) its data type is unsigned long int. Negating this value yields 2147483648 again.
GCC does not substitute macro arguments when they appear inside of string constants. For example, the following macro in GCC
#define foo(a) "a"
will produce output "a" regardless of what the argument a is.
setjmp incompatibilities longjmp incompatibilities
When you use setjmp and longjmp, the only automatic variables guaranteed to remain valid are those declared volatile. This is a consequence of automatic register allocation. Consider this function:
jmp_buf j;
foo ()
{
int a, b;
a = fun1 ();
if (setjmp (j))
return a;
a = fun2 ();
/* ``longjmp (j)`` may occur in ``fun3``. */
return a + fun3 ();
}
Here a may or may not be restored to its first value when the longjmp occurs. If a is allocated in a register, then its first value is restored; otherwise, it keeps the last value stored in it.
If you use the -W option with the -O option, you will get a warning when GCC thinks such a problem might be possible.
Programs that use preprocessing directives in the middle of macro arguments do not work with GCC For example, a program like this will not work:
foobar (
#define luser
hack)
ISO C does not permit such a construct.
K&R compilers allow comments to cross over an inclusion boundary (i.e. started in an include file and ended in the including file).
Declarations of external variables and functions within a block apply only to the block containing the declaration. In other words, they have the same scope as any other declaration in the same place.
In some other C compilers, an extern declaration affects all the rest of the file even if it happens within a block.
In traditional C, you can combine long, etc., with a typedef name, as shown here:
typedef int foo;
typedef long foo bar;
In ISO C, this is not allowed: long and other type modifiers require an explicit int.
PCC allows typedef names to be used as function parameters.
Traditional C allows the following erroneous pair of declarations to appear together in a given scope:
typedef int foo;
typedef foo foo;
GCC treats all characters of identifiers as significant. According to K&R-1 (2.2), No more than the first eight characters are significant, although more may be used.. Also according to K&R-1 (2.2), An identifier is a sequence of letters and digits; the first character must be a letter. The underscore _ counts as a letter., but GCC also allows dollar signs in identifiers.
PCC allows whitespace in the middle of compound assignment operators such as +=. GCC, following the ISO standard, does not allow this.
'
GCC complains about unterminated character constants inside of preprocessing conditionals that fail. Some programs have English comments enclosed in conditionals that are guaranteed to fail; if these comments contain apostrophes, GCC will probably report an error. For example, this code would produce an error:
#if 0
You can't expect this to work.
#endif
The best solution to such a problem is to put the text into an actual C comment delimited by /.../.
Many user programs contain the declaration long time ();. In the past, the system header files on many systems did not actually declare time, so it did not matter what type your program declared it to return. But in systems with ISO C headers, time is declared to return time_t, and if that is not the same as long, then long time (); is erroneous.
The solution is to change your program to use appropriate system headers (<time.h> on systems with ISO C headers) and not to declare time if the system header files declare it, or failing that to use time_t as the return type of time.
float as function value type
When compiling functions that return float, PCC converts it to a double. GCC actually returns a float. If you are concerned with PCC compatibility, you should declare your functions to return double; you might as well say what you mean.
When compiling functions that return structures or unions, GCC output code normally uses a method different from that used on most versions of Unix. As a result, code compiled with GCC cannot call a structure-returning function compiled with PCC, and vice versa.
The method used by GCC is as follows: a structure or union which is 1, 2, 4 or 8 bytes long is returned like a scalar. A structure or union with any other size is stored into an address supplied by the caller (usually in a special, fixed register, but on some machines it is passed on the stack). The target hook TARGET_STRUCT_VALUE_RTX tells GCC where to pass this address.
By contrast, PCC on most target machines returns structures and unions of any size by copying the data into an area of static storage, and then returning the address of that storage as if it were a pointer value. The caller must copy the data from that memory area to the place where the value is wanted. GCC does not use this method because it is slower and nonreentrant.
On some newer machines, PCC uses a reentrant convention for all structure and union returning. GCC on most of these machines uses a compatible convention when returning structures and unions in memory, but still returns small structures and unions in registers.
You can tell GCC to use a compatible convention for all structure and union returning with the option -fpcc-struct-return.
GCC complains about program fragments such as 0x74ae-0x4000 which appear to be two hexadecimal constants separated by the minus operator. Actually, this string is a single preprocessing token. Each such token must correspond to one token in C Since this does not, GCC prints an error message. Although it may appear obvious that what is meant is an operator and two values, the ISO C standard specifically requires that this be treated as erroneous.
A preprocessing token is a preprocessing number if it begins with a digit and is followed by letters, underscores, digits, periods and e+, e-, E+, E-, p+, p-, P+, or P- character sequences. (In strict C90 mode, the sequences p+, p-, P+ and P- cannot appear in preprocessing numbers.)
To make the above program fragment valid, place whitespace in front of the minus sign. This whitespace will end the preprocessing number.
:: _fixed-headers:
GCC needs to install corrected versions of some system header files. This is because most target systems have some header files that wont work with GCC unless they are changed. Some have bugs, some are incompatible with ISO C, and some depend on special features of other compilers.
Installing GCC automatically creates and installs the fixed header files, by running a program called fixincludes. Normally, you dont need to pay attention to this. But there are cases where it doesnt do the right thing automatically.
If you update the systems header files, such as by installing a new system version, the fixed header files of GCC are not automatically updated. They can be updated using the mkheaders script installed in libexecdir/gcc/target/version/install-tools/.
On some systems, header file directories contain machine-specific symbolic links in certain places. This makes it possible to share most of the header files among hosts running the same version of the system on different machine models.
The programs that fix the header files do not understand this special way of using symbolic links; therefore, the directory of fixed header files is good only for the machine model used to build it.
It is possible to make separate sets of fixed header files for the different machine models, and arrange a structure of symbolic links so as to use the proper set, but youll have to do this by hand.
:: _standard-libraries:
GCC by itself attempts to be a conforming freestanding implementation. StandardsLanguage Standards Supported by GCC, for details of what this means. Beyond the library facilities required of such an implementation, the rest of the C library is supplied by the vendor of the operating system. If that C library doesnt conform to the C standards, then your programs might get warnings (especially when using -Wall) that you dont expect.
For example, the sprintf function on SunOS 4.1.3 returns char * while the C standard says that sprintf returns an int. The fixincludes program could make the prototype for this function match the Standard, but that would be wrong, since the function will still return char *.
If you need a Standard compliant library, then you need to find one, as GCC does not provide one. The GNU C library (called glibc) provides ISO C, POSIX, BSD, SystemV and X/Open compatibility for GNU/Linux and HURD-based GNU systems; no recent version of it supports other systems, though some very old versions did. Version 2.2 of the GNU C library includes nearly complete C99 support. You could also ask your operating system vendor if newer libraries are available.
:: _disappointments:
These problems are perhaps regrettable, but we dont know any practical way around them.
Certain local variables arent recognized by debuggers when you compile with optimization.
This occurs because sometimes GCC optimizes the variable out of existence. There is no way to tell the debugger how to compute the value such a variable would have had, and it is not clear that would be desirable anyway. So GCC simply does not mention the eliminated variable when it writes debugging information.
You have to expect a certain amount of disagreement between the executable and your source code, when you use optimization.
Users often think it is a bug when GCC reports an error for code like this:
int foo (struct mumble *);
struct mumble { ... };
int foo (struct mumble *x)
{ ... }
This code really is erroneous, because the scope of struct mumble in the prototype is limited to the argument list containing it. It does not refer to the struct mumble defined with file scope immediately belowthey are two unrelated types with similar names in different scopes.
But in the definition of foo, the file-scope type is used because that is available to be inherited. Thus, the definition and the prototype do not match, and you get an error.
This behavior may seem silly, but its what the ISO standard specifies. It is easy enough for you to make your code work by moving the definition of struct mumble above the prototype. Its not worth being incompatible with ISO C just to avoid an error for the example shown above.
Accesses to bit-fields even in volatile objects works by accessing larger objects, such as a byte or a word. You cannot rely on what size of object is accessed in order to read or write the bit-field; it may even vary for a given bit-field according to the precise usage.
If you care about controlling the amount of memory that is accessed, use volatile but do not use bit-fields.
GCC comes with shell scripts to fix certain known problems in system header files. They install corrected copies of various header files in a special directory where only GCC will normally look for them. The scripts adapt to various systems by searching all the system header files for the problem cases that we know about.
If new system header files are installed, nothing automatically arranges to update the corrected header files. They can be updated using the mkheaders script installed in libexecdir/gcc/target/version/install-tools/.
On 68000 and x86 systems, for instance, you can get paradoxical results if you test the precise values of floating point numbers. For example, you can find that a floating point value which is not a NaN is not equal to itself. This results from the fact that the floating point registers hold a few more bits of precision than fit in a double in memory. Compiled code moves values between memory and floating point registers at its convenience, and moving them into memory truncates them.
You can partially avoid this problem by using the -ffloat-store option (Optimize Options).
On AIX and other platforms without weak symbol support, templates need to be instantiated explicitly and symbols for static members of templates will not be generated.
On AIX, GCC scans object files and library archives for static constructors and destructors when linking an application before the linker prunes unreferenced symbols. This is necessary to prevent the AIX linker from mistakenly assuming that static constructor or destructor are unused and removing them before the scanning can occur. All static constructors and destructors found will be referenced even though the modules in which they occur may not be used by the program. This may lead to both increased executable size and unexpected symbol references.
:: _c++-misunderstandings:
C++ is a complex language and an evolving one, and its standard definition (the ISO C++ standard) was only recently completed. As a result, your C++ compiler may occasionally surprise you, even when its behavior is correct. This section discusses some areas that frequently give rise to questions of this sort.
:: _static-definitions:
Declare and Define Static Members
When a class has static data members, it is not enough to declare the static member; you must also define it. For example:
class Foo
{
...
void method();
static int bar;
};
This declaration only establishes that the class Foo has an int named Foo::bar, and a member function named Foo::method. But you still need to define both method and bar elsewhere. According to the ISO standard, you must supply an initializer in one (and only one) source file, such as:
int Foo::bar = 0;
Other C++ compilers may not correctly implement the standard behavior. As a result, when you switch to g++ from one of these compilers, you may discover that a program that appeared to work correctly in fact does not conform to the standard: g++ reports as undefined symbols any static data members that lack definitions.
:: _name-lookup:
The C++ standard prescribes that all names that are not dependent on template parameters are bound to their present definitions when parsing a template function or class.The C++ standard just uses the term dependent for names that depend on the type or value of template parameters. This shorter term will also be used in the rest of this section. Only names that are dependent are looked up at the point of instantiation. For example, consider
void foo(double);
struct A {
template <typename T>
void f () {
foo (1); // 1
int i = N; // 2
T t;
t.bar(); // 3
foo (t); // 4
}
static const int N;
};
Here, the names foo and N appear in a context that does not depend on the type of T. The compiler will thus require that they are defined in the context of use in the template, not only before the point of instantiation, and will here use ::foo(double) and A::N, respectively. In particular, it will convert the integer value to a double when passing it to ::foo(double).
Conversely, bar and the call to foo in the fourth marked line are used in contexts that do depend on the type of T, so they are only looked up at the point of instantiation, and you can provide declarations for them after declaring the template, but before instantiating it. In particular, if you instantiate A::f<int>, the last line will call an overloaded ::foo(int) if one was provided, even if after the declaration of struct A.
This distinction between lookup of dependent and non-dependent names is called two-stage (or dependent) name lookup. G++ implements it since version 3.4.
Two-stage name lookup sometimes leads to situations with behavior different from non-template codes. The most common is probably this:
template <typename T> struct Base {
int i;
};
template <typename T> struct Derived : public Base<T> {
int get_i() { return i; }
};
In get_i(), i is not used in a dependent context, so the compiler will look for a name declared at the enclosing namespace scope (which is the global scope here). It will not look into the base class, since that is dependent and you may declare specializations of Base even after declaring Derived, so the compiler cant really know what i would refer to. If there is no global variable i, then you will get an error message.
In order to make it clear that you want the member of the base class, you need to defer lookup until instantiation time, at which the base class is known. For this, you need to access i in a dependent context, by either using this->i (remember that this is of type Derived<T>*, so is obviously dependent), or using Base<T>::i. Alternatively, Base<T>::i might be brought into scope by a using-declaration.
Another, similar example involves calling member functions of a base class:
template <typename T> struct Base {
int f();
};
template <typename T> struct Derived : Base<T> {
int g() { return f(); };
};
Again, the call to f() is not dependent on template arguments (there are no arguments that depend on the type T, and it is also not otherwise specified that the call should be in a dependent context). Thus a global declaration of such a function must be available, since the one in the base class is not visible until instantiation time. The compiler will consequently produce the following error message:
x.cc: In member function `int Derived<T>::g()':
x.cc:6: error: there are no arguments to `f' that depend on a template
parameter, so a declaration of `f' must be available
x.cc:6: error: (if you use `-fpermissive', G++ will accept your code, but
allowing the use of an undeclared name is deprecated)
To make the code valid either use this->f(), or Base<T>::f(). Using the -fpermissive flag will also let the compiler accept the code, by marking all function calls for which no declaration is visible at the time of definition of the template for later lookup at instantiation time, as if it were a dependent call. We do not recommend using -fpermissive to work around invalid code, and it will also only catch cases where functions in base classes are called, not where variables in base classes are used (as in the example above).
Note that some compilers (including G++ versions prior to 3.4) get these examples wrong and accept above code without an error. Those compilers do not implement two-stage name lookup correctly.
:: _temporaries:
It is dangerous to use pointers or references to portions of a temporary object. The compiler may very well delete the object before you expect it to, leaving a pointer to garbage. The most common place where this problem crops up is in classes like string classes, especially ones that define a conversion function to type char * or const char *``which is one reason why the standard ``string class requires you to call the c_str member function. However, any class that returns a pointer to some internal structure is potentially subject to this problem.
For example, a program may use a function strfunc that returns string objects, and another function charfunc that operates on pointers to char:
string strfunc ();
void charfunc (const char *);
void
f ()
{
const char *p = strfunc().c_str();
...
charfunc (p);
...
charfunc (p);
}
In this situation, it may seem reasonable to save a pointer to the C string returned by the c_str member function and use that rather than call c_str repeatedly. However, the temporary string created by the call to strfunc is destroyed after p is initialized, at which point p is left pointing to freed memory.
Code like this may run successfully under some other compilers, particularly obsolete cfront-based compilers that delete temporaries along with normal local variables. However, the GNU C++ behavior is standard-conforming, so if your program depends on late destruction of temporaries it is not portable.
The safe way to write such code is to give the temporary a name, which forces it to remain until the end of the scope of the name. For example:
const string& tmp = strfunc ();
charfunc (tmp.c_str ());
:: _copy-assignment:
When a base class is virtual, only one subobject of the base class belongs to each full object. Also, the constructors and destructors are invoked only once, and called from the most-derived class. However, such objects behave unspecified when being assigned. For example:
struct Base{
char *name;
Base(char *n) : name(strdup(n)){}
Base& operator= (const Base& other){
free (name);
name = strdup (other.name);
}
};
struct A:virtual Base{
int val;
A():Base("A"){}
};
struct B:virtual Base{
int bval;
B():Base("B"){}
};
struct Derived:public A, public B{
Derived():Base("Derived"){}
};
void func(Derived &d1, Derived &d2)
{
d1 = d2;
}
The C++ standard specifies that Base::Base is only called once when constructing or copy-constructing a Derived object. It is unspecified whether Base::operator= is called more than once when the implicit copy-assignment for Derived objects is invoked (as it is inside func in the example).
G++ implements the intuitive algorithm for copy-assignment: assign all direct bases, then assign all members. In that algorithm, the virtual base subobject can be encountered more than once. In the example, copying proceeds in the following order: val, name (via strdup), bval, and name again.
If application code relies on copy-assignment, a user-defined copy-assignment operator removes any uncertainties. With such an operator, the application can define whether and how the virtual base subobject is assigned.
:: _non-bugs:
This section lists changes that people frequently request, but which we do not make because we think GCC is better without them.
Checking the number and type of arguments to a function which has an old-fashioned definition and no prototype.
Such a feature would work only occasionallyonly for calls that appear in the same file as the called function, following the definition. The only way to check all calls reliably is to add a prototype for the function. But adding a prototype eliminates the motivation for this feature. So the feature is not worthwhile.
Warning about using an expression whose type is signed as a shift count.
Shift count operands are probably signed more often than unsigned. Warning about this would cause far more annoyance than good.
Warning about assigning a signed value to an unsigned variable.
Such assignments must be very common; warning about them would cause more annoyance than good.
Warning when a non-void function value is ignored.
C contains many standard functions that return a value that most programs choose to ignore. One obvious example is printf. Warning about this practice only leads the defensive programmer to clutter programs with dozens of casts to void. Such casts are required so frequently that they become visual noise. Writing those casts becomes so automatic that they no longer convey useful information about the intentions of the programmer. For functions where the return value should never be ignored, use the warn_unused_result function attribute (Function Attributes).
Making -fshort-enums the default.
This would cause storage layout to be incompatible with most other C compilers. And it doesnt seem very important, given that you can get the same result in other ways. The case where it matters most is when the enumeration-valued object is inside a structure, and in that case you can specify a field width explicitly.
Making bit-fields unsigned by default on particular machines where the ABI standard says to do so.
The ISO C standard leaves it up to the implementation whether a bit-field declared plain int is signed or not. This in effect creates two alternative dialects of C
The GNU C compiler supports both dialects; you can specify the signed dialect with -fsigned-bitfields and the unsigned dialect with -funsigned-bitfields. However, this leaves open the question of which dialect to use by default.
Currently, the preferred dialect makes plain bit-fields signed, because this is simplest. Since int is the same as signed int in every other context, it is cleanest for them to be the same in bit-fields as well.
Some computer manufacturers have published Application Binary Interface standards which specify that plain bit-fields should be unsigned. It is a mistake, however, to say anything about this issue in an ABI This is because the handling of plain bit-fields distinguishes two dialects of C Both dialects are meaningful on every type of machine. Whether a particular object file was compiled using signed bit-fields or unsigned is of no concern to other object files, even if they access the same bit-fields in the same data structures.
A given program is written in one or the other of these two dialects. The program stands a chance to work on most any machine if it is compiled with the proper dialect. It is unlikely to work at all if compiled with the wrong dialect.
Many users appreciate the GNU C compiler because it provides an environment that is uniform across machines. These users would be inconvenienced if the compiler treated plain bit-fields differently on certain machines.
Occasionally users write programs intended only for a particular machine type. On these occasions, the users would benefit if the GNU C compiler were to support by default the same dialect as the other compilers on that machine. But such applications are rare. And users writing a program to run on more than one type of machine cannot possibly benefit from this kind of compatibility.
This is why GCC does and will treat plain bit-fields in the same fashion on all types of machines (by default).
There are some arguments for making bit-fields unsigned by default on all machines. If, for example, this becomes a universal de facto standard, it would make sense for GCC to go along with it. This is something to be considered in the future.
(Of course, users strongly concerned about portability should indicate explicitly in each bit-field whether it is signed or not. In this way, they write programs which have the same meaning in both C dialects.)
Undefining __STDC__ when -ansi is not used.
Currently, GCC defines __STDC__ unconditionally. This provides good results in practice.
Programmers normally use conditionals on __STDC__ to ask whether it is safe to use certain features of ISO C, such as function prototypes or ISO token concatenation. Since plain gcc supports all the features of ISO C, the correct answer to these questions is yes.
Some users try to use __STDC__ to check for the availability of certain library facilities. This is actually incorrect usage in an ISO C program, because the ISO C standard says that a conforming freestanding implementation should define __STDC__ even though it does not have the library facilities. gcc -ansi -pedantic is a conforming freestanding implementation, and it is therefore required to define __STDC__, even though it does not come with an ISO C library.
Sometimes people say that defining __STDC__ in a compiler that does not completely conform to the ISO C standard somehow violates the standard. This is illogical. The standard is a standard for compilers that claim to support ISO C, such as gcc -ansinot for other compilers such as plain gcc. Whatever the ISO C standard says is relevant to the design of plain gcc without -ansi only for pragmatic reasons, not as a requirement.
GCC normally defines __STDC__ to be 1, and in addition defines __STRICT_ANSI__ if you specify the -ansi option, or a -std option for strict conformance to some version of ISO C On some hosts, system include files use a different convention, where __STDC__ is normally 0, but is 1 if the user specifies strict conformance to the C Standard. GCC follows the host convention when processing system include files, but when processing user files it follows the usual GNU C convention.
Undefining __STDC__ in C++.
Programs written to compile with C++-to-C translators get the value of __STDC__ that goes with the C compiler that is subsequently used. These programs must test __STDC__ to determine what kind of C preprocessor that compiler uses: whether they should concatenate tokens in the ISO C fashion or in the traditional fashion.
These programs work properly with GNU C++ if __STDC__ is defined. They would not work otherwise.
In addition, many header files are written to provide prototypes in ISO C but not in traditional C Many of these header files can work without change in C++ provided __STDC__ is defined. If __STDC__ is not defined, they will all fail, and will all need to be changed to test explicitly for C++ as well.
Deleting empty loops.
Historically, GCC has not deleted empty loops under the assumption that the most likely reason you would put one in a program is to have a delay, so deleting them will not make real programs run any faster.
However, the rationale here is that optimization of a nonempty loop cannot produce an empty one. This held for carefully written C compiled with less powerful optimizers but is not always the case for carefully written C++ or with more powerful optimizers. Thus GCC will remove operations from loops whenever it can determine those operations are not externally visible (apart from the time taken to execute them, of course). In case the loop can be proved to be finite, GCC will also remove the loop itself.
Be aware of this when performing timing tests, for instance the following loop can be completely removed, provided some_expression can provably not change any global state.
{
int sum = 0;
int ix;
for (ix = 0; ix != 10000; ix++)
sum += some_expression;
}
Even though sum is accumulated in the loop, no use is made of that summation, so the accumulation can be removed.
Making side effects happen in the same order as in some other compiler.
It is never safe to depend on the order of evaluation of side effects. For example, a function call like this may very well behave differently from one compiler to another:
void func (int, int);
int i = 2;
func (i++, i++);
There is no guarantee (in either the C or the C++ standard language definitions) that the increments will be evaluated in any particular order. Either increment might happen first. func might get the arguments 2, 3, or it might get 3, 2, or even 2, 2.
Making certain warnings into errors by default.
Some ISO C testsuites report failure when the compiler does not produce an error message for a certain program.
ISO C requires a diagnostic message for certain kinds of invalid programs, but a warning is defined by GCC to count as a diagnostic. If GCC produces a warning but not an error, that is correct ISO C support. If testsuites call this failure, they should be run with the GCC option -pedantic-errors, which will turn these warnings into errors.
:: _warnings-and-errors:
The GNU compiler can produce two kinds of diagnostics: errors and warnings. Each kind has a different purpose:
Warnings may indicate danger points where you should check to make sure that your program really does what you intend; or the use of obsolete features; or the use of nonstandard features of GNU C or C++. Many warnings are issued only if you ask for them, with one of the -W options (for instance, -Wall requests a variety of useful warnings).
GCC always tries to compile your program if possible; it never gratuitously rejects a program whose meaning is clear merely because (for instance) it fails to conform to a standard. In some cases, however, the C and C++ standards specify that certain extensions are forbidden, and a diagnostic must be issued by a conforming compiler. The -pedantic option tells GCC to issue warnings in such cases; -pedantic-errors says to make them errors instead. This does not mean that all non-ISO constructs get warnings or errors.
Warning OptionsOptions to Request or Suppress Warnings, for more detail on these and related command-line options.
:: _bugs:
Your bug reports play an essential role in making GCC reliable.
When you encounter a problem, the first thing to do is to see if it is already known. Trouble. If it isnt known, then you should report the problem.
:: _bug-criteria:
If you are not sure whether you have found a bug, here are some guidelines:
If the compiler gets a fatal signal, for any input whatever, that is a compiler bug. Reliable compilers never crash.
If the compiler produces invalid assembly code, for any input whatever (except an asm statement), that is a compiler bug, unless the compiler reports errors (not just warnings) which would ordinarily prevent the assembler from being run.
If the compiler produces valid assembly code that does not correctly execute the input source code, that is a compiler bug.
However, you must double-check to make sure, because you may have a program whose behavior is undefined, which happened by chance to give the desired results with another C or C++ compiler.
For example, in many nonoptimizing compilers, you can write x; at the end of a function instead of return x;, with the same results. But the value of the function is undefined if return is omitted; it is not a bug when GCC produces different results.
Problems often result from expressions with two increment operators, as in f (*p++, *p++). Your previous compiler might have interpreted that expression the way you intended; GCC might interpret it another way. Neither compiler is wrong. The bug is in your code.
After you have localized the error to a single source line, it should be easy to check for these things. If your program is correct and well defined, you have found a compiler bug.
If the compiler produces an error message for valid input, that is a compiler bug.
If the compiler does not produce an error message for invalid input, that is a compiler bug. However, you should note that your idea of invalid input might be someone elses idea of an extension or support for traditional practice.
If you are an experienced user of one of the languages GCC supports, your suggestions for improvement of GCC are welcome in any case.
:: _bug-reporting:
Bugs should be reported to the bug database at http://gcc.gnu.org/bugs.html.
:: _service:
If you need help installing, using or changing GCC, there are two ways to find it:
For further information, see http://gcc.gnu.org/faq.html#support.
:: _contributing:
If you would like to help pretest GCC releases to assure they work well, current development sources are available by SVN (see http://gcc.gnu.org/svn.html). Source and binary snapshots are also available for FTP; see http://gcc.gnu.org/snapshots.html.
If you would like to work on improvements to GCC, please read the advice at these URLs:
http://gcc.gnu.org/contribute.html
http://gcc.gnu.org/contributewhy.html
for information on how to make useful contributions and avoid duplication of effort. Suggested projects are listed at http://gcc.gnu.org/projects/.
@c Set file name and title for man page. @setfilename fsf-funding @settitle Funding Free Software @c man begin SEEALSO gpl(7), gfdl(7). @c man end
:: _funding:
If you want to have more free software a few years from now, it makes sense for you to help encourage people to contribute funds for its development. The most effective approach known is to encourage commercial redistributors to donate.
Users of free software systems can boost the pace of development by encouraging for-a-fee distributors to donate part of their selling price to free software developersthe Free Software Foundation, and others.
The way to convince distributors to do this is to demand it and expect it from them. So when you compare distributors, judge them partly by how much they give to free software development. Show distributors they must compete to be the one who gives the most.
To make this approach work, you must insist on numbers that you can compare, such as, We will donate ten dollars to the Frobnitz project for each disk sold. Dont be satisfied with a vague promise, such as A portion of the profits are donated, since it doesnt give a basis for comparison.
Even a precise fraction of the profits from this disk is not very meaningful, since creative accounting and unrelated business decisions can greatly alter what fraction of the sales price counts as profit. If the price you pay is $50, ten percent of the profit is probably less than a dollar; it might be a few cents, or nothing at all.
Some redistributors do development work themselves. This is useful too; but to keep everyone honest, you need to inquire how much they do, and what kind. Some kinds of development make much more long-term difference than others. For example, maintaining a separate version of a program contributes very little; maintaining the standard version of a program for the whole community contributes much. Easy new ports contribute little, since someone else would surely do them; difficult ports such as adding a new CPU to the GNU Compiler Collection contribute more; major new features or packages contribute the most.
By establishing the idea that supporting further development is the proper thing to do when distributing free software for a fee, we can assure a steady flow of resources into making more free software.
Copyright 1994 Free Software Foundation, Inc. Verbatim copying and redistribution of this section is permitted without royalty; alteration is not permitted.
:: _gnu-project:
The GNU Project was launched in 1984 to develop a complete Unix-like operating system which is free software: the GNU system. (GNU is a recursive acronym for GNUs Not Unix; it is pronounced guh-NEW) Variants of the GNU operating system, which use the kernel Linux, are now widely used; though these systems are often referred to as Linux, they are more accurately called GNU/Linux systems.
For more information, see:
http://www.gnu.org/
http://www.gnu.org/gnu/linux-and-gnu.html
@c Set file name and title for man page. @setfilename gpl @settitle GNU General Public License @c man begin SEEALSO gfdl(7), fsf-funding(7). @c man end @c man begin COPYRIGHT Copyright @copyright{} 2007 Free Software Foundation, Inc.
Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. @c man end
:: _copying:
Version 3, 29 June 2007
Copyright 2007 Free Software Foundation, Inc. http://fsf.org/
Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.
Preamble
The GNU General Public License is a free, copyleft license for software and other kinds of works.
The licenses for most software and other practical works are designed to take away your freedom to share and change the works. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change all versions of a programto make sure it remains free software for all its users. We, the Free Software Foundation, use the GNU General Public License for most of our software; it applies also to any other work released this way by its authors. You can apply it to your programs, too.
When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for them if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs, and that you know you can do these things.
To protect your rights, we need to prevent others from denying you these rights or asking you to surrender the rights. Therefore, you have certain responsibilities if you distribute copies of the software, or if you modify it: responsibilities to respect the freedom of others.
For example, if you distribute copies of such a program, whether gratis or for a fee, you must pass on to the recipients the same freedoms that you received. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.
Developers that use the GNU GPL protect your rights with two steps: (1) assert copyright on the software, and (2) offer you this License giving you legal permission to copy, distribute and/or modify it.
For the developers and authors protection, the GPL clearly explains that there is no warranty for this free software. For both users and authors sake, the GPL requires that modified versions be marked as changed, so that their problems will not be attributed erroneously to authors of previous versions.
Some devices are designed to deny users access to install or run modified versions of the software inside them, although the manufacturer can do so. This is fundamentally incompatible with the aim of protecting users freedom to change the software. The systematic pattern of such abuse occurs in the area of products for individuals to use, which is precisely where it is most unacceptable. Therefore, we have designed this version of the GPL to prohibit the practice for those products. If such problems arise substantially in other domains, we stand ready to extend this provision to those domains in future versions of the GPL, as needed to protect the freedom of users.
Finally, every program is threatened constantly by software patents. States should not allow patents to restrict development and use of software on general-purpose computers, but in those that do, we wish to avoid the special danger that patents applied to a free program could make it effectively proprietary. To prevent this, the GPL assures that patents cannot be used to render the program non-free.
The precise terms and conditions for copying, distribution and modification follow.
TERMS AND CONDITIONS
0 * Definitions.
This License refers to version 3 of the GNU General Public License.
Copyright also means copyright-like laws that apply to other kinds of works, such as semiconductor masks.
The Program refers to any copyrightable work licensed under this License. Each licensee is addressed as you. Licensees and recipients may be individuals or organizations.
To modify a work means to copy from or adapt all or part of the work in a fashion requiring copyright permission, other than the making of an exact copy. The resulting work is called a modified version of the earlier work or a work based on the earlier work.
A covered work means either the unmodified Program or a work based on the Program.
To propagate a work means to do anything with it that, without permission, would make you directly or secondarily liable for infringement under applicable copyright law, except executing it on a computer or modifying a private copy. Propagation includes copying, distribution (with or without modification), making available to the public, and in some countries other activities as well.
To convey a work means any kind of propagation that enables other parties to make or receive copies. Mere interaction with a user through a computer network, with no transfer of a copy, is not conveying.
An interactive user interface displays Appropriate Legal Notices to the extent that it includes a convenient and prominently visible feature that (1) displays an appropriate copyright notice, and (2) tells the user that there is no warranty for the work (except to the extent that warranties are provided), that licensees may convey the work under this License, and how to view a copy of this License. If the interface presents a list of user commands or options, such as a menu, a prominent item in the list meets this criterion.
Source Code.
The source code for a work means the preferred form of the work for making modifications to it. Object code means any non-source form of a work.
A Standard Interface means an interface that either is an official standard defined by a recognized standards body, or, in the case of interfaces specified for a particular programming language, one that is widely used among developers working in that language.
The System Libraries of an executable work include anything, other than the work as a whole, that (a) is included in the normal form of packaging a Major Component, but which is not part of that Major Component, and (b) serves only to enable use of the work with that Major Component, or to implement a Standard Interface for which an implementation is available to the public in source code form. A Major Component, in this context, means a major essential component (kernel, window system, and so on) of the specific operating system (if any) on which the executable work runs, or a compiler used to produce the work, or an object code interpreter used to run it.
The Corresponding Source for a work in object code form means all the source code needed to generate, install, and (for an executable work) run the object code and to modify the work, including scripts to control those activities. However, it does not include the works System Libraries, or general-purpose tools or generally available free programs which are used unmodified in performing those activities but which are not part of the work. For example, Corresponding Source includes interface definition files associated with source files for the work, and the source code for shared libraries and dynamically linked subprograms that the work is specifically designed to require, such as by intimate data communication or control flow between those subprograms and other parts of the work.
The Corresponding Source need not include anything that users can regenerate automatically from other parts of the Corresponding Source.
The Corresponding Source for a work in source code form is that same work.
Basic Permissions.
All rights granted under this License are granted for the term of copyright on the Program, and are irrevocable provided the stated conditions are met. This License explicitly affirms your unlimited permission to run the unmodified Program. The output from running a covered work is covered by this License only if the output, given its content, constitutes a covered work. This License acknowledges your rights of fair use or other equivalent, as provided by copyright law.
You may make, run and propagate covered works that you do not convey, without conditions so long as your license otherwise remains in force. You may convey covered works to others for the sole purpose of having them make modifications exclusively for you, or provide you with facilities for running those works, provided that you comply with the terms of this License in conveying all material for which you do not control copyright. Those thus making or running the covered works for you must do so exclusively on your behalf, under your direction and control, on terms that prohibit them from making any copies of your copyrighted material outside their relationship with you.
Conveying under any other circumstances is permitted solely under the conditions stated below. Sublicensing is not allowed; section 10 makes it unnecessary.
Protecting Users Legal Rights From Anti-Circumvention Law.
No covered work shall be deemed part of an effective technological measure under any applicable law fulfilling obligations under article 11 of the WIPO copyright treaty adopted on 20 December 1996, or similar laws prohibiting or restricting circumvention of such measures.
When you convey a covered work, you waive any legal power to forbid circumvention of technological measures to the extent such circumvention is effected by exercising rights under this License with respect to the covered work, and you disclaim any intention to limit operation or modification of the work as a means of enforcing, against the works users, your or third parties legal rights to forbid circumvention of technological measures.
Conveying Verbatim Copies.
You may convey verbatim copies of the Programs source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice; keep intact all notices stating that this License and any non-permissive terms added in accord with section 7 apply to the code; keep intact all notices of the absence of any warranty; and give all recipients a copy of this License along with the Program.
You may charge any price or no price for each copy that you convey, and you may offer support or warranty protection for a fee.
Conveying Modified Source Versions.
You may convey a work based on the Program, or the modifications to produce it from the Program, in the form of source code under the terms of section 4, provided that you also meet all of these conditions:
a * The work must carry prominent notices stating that you modified it,
and giving a relevant date.
A compilation of a covered work with other separate and independent works, which are not by their nature extensions of the covered work, and which are not combined with it such as to form a larger program, in or on a volume of a storage or distribution medium, is called an aggregate if the compilation and its resulting copyright are not used to limit the access or legal rights of the compilations users beyond what the individual works permit. Inclusion of a covered work in an aggregate does not cause this License to apply to the other parts of the aggregate.
Conveying Non-Source Forms.
You may convey a covered work in object code form under the terms of sections 4 and 5, provided that you also convey the machine-readable Corresponding Source under the terms of this License, in one of these ways:
a * Convey the object code in, or embodied in, a physical product
(including a physical distribution medium), accompanied by the Corresponding Source fixed on a durable physical medium customarily used for software interchange.
A separable portion of the object code, whose source code is excluded from the Corresponding Source as a System Library, need not be included in conveying the object code work.
A User Product is either (1) a consumer product, which means any tangible personal property which is normally used for personal, family, or household purposes, or (2) anything designed or sold for incorporation into a dwelling. In determining whether a product is a consumer product, doubtful cases shall be resolved in favor of coverage. For a particular product received by a particular user, normally used refers to a typical or common use of that class of product, regardless of the status of the particular user or of the way in which the particular user actually uses, or expects or is expected to use, the product. A product is a consumer product regardless of whether the product has substantial commercial, industrial or non-consumer uses, unless such uses represent the only significant mode of use of the product.
Installation Information for a User Product means any methods, procedures, authorization keys, or other information required to install and execute modified versions of a covered work in that User Product from a modified version of its Corresponding Source. The information must suffice to ensure that the continued functioning of the modified object code is in no case prevented or interfered with solely because modification has been made.
If you convey an object code work under this section in, or with, or specifically for use in, a User Product, and the conveying occurs as part of a transaction in which the right of possession and use of the User Product is transferred to the recipient in perpetuity or for a fixed term (regardless of how the transaction is characterized), the Corresponding Source conveyed under this section must be accompanied by the Installation Information. But this requirement does not apply if neither you nor any third party retains the ability to install modified object code on the User Product (for example, the work has been installed in ROM).
The requirement to provide Installation Information does not include a requirement to continue to provide support service, warranty, or updates for a work that has been modified or installed by the recipient, or for the User Product in which it has been modified or installed. Access to a network may be denied when the modification itself materially and adversely affects the operation of the network or violates the rules and protocols for communication across the network.
Corresponding Source conveyed, and Installation Information provided, in accord with this section must be in a format that is publicly documented (and with an implementation available to the public in source code form), and must require no special password or key for unpacking, reading or copying.
Additional Terms.
Additional permissions are terms that supplement the terms of this License by making exceptions from one or more of its conditions. Additional permissions that are applicable to the entire Program shall be treated as though they were included in this License, to the extent that they are valid under applicable law. If additional permissions apply only to part of the Program, that part may be used separately under those permissions, but the entire Program remains governed by this License without regard to the additional permissions.
When you convey a copy of a covered work, you may at your option remove any additional permissions from that copy, or from any part of it. (Additional permissions may be written to require their own removal in certain cases when you modify the work.) You may place additional permissions on material, added by you to a covered work, for which you have or can give appropriate copyright permission.
Notwithstanding any other provision of this License, for material you add to a covered work, you may (if authorized by the copyright holders of that material) supplement the terms of this License with terms:
a * Disclaiming warranty or limiting liability differently from the terms
of sections 15 and 16 of this License; or
All other non-permissive additional terms are considered further restrictions within the meaning of section 10. If the Program as you received it, or any part of it, contains a notice stating that it is governed by this License along with a term that is a further restriction, you may remove that term. If a license document contains a further restriction but permits relicensing or conveying under this License, you may add to a covered work material governed by the terms of that license document, provided that the further restriction does not survive such relicensing or conveying.
If you add terms to a covered work in accord with this section, you must place, in the relevant source files, a statement of the additional terms that apply to those files, or a notice indicating where to find the applicable terms.
Additional terms, permissive or non-permissive, may be stated in the form of a separately written license, or stated as exceptions; the above requirements apply either way.
Termination.
You may not propagate or modify a covered work except as expressly provided under this License. Any attempt otherwise to propagate or modify it is void, and will automatically terminate your rights under this License (including any patent licenses granted under the third paragraph of section 11).
However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.
Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.
Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, you do not qualify to receive new licenses for the same material under section 10.
Acceptance Not Required for Having Copies.
You are not required to accept this License in order to receive or run a copy of the Program. Ancillary propagation of a covered work occurring solely as a consequence of using peer-to-peer transmission to receive a copy likewise does not require acceptance. However, nothing other than this License grants you permission to propagate or modify any covered work. These actions infringe copyright if you do not accept this License. Therefore, by modifying or propagating a covered work, you indicate your acceptance of this License to do so.
Automatic Licensing of Downstream Recipients.
Each time you convey a covered work, the recipient automatically receives a license from the original licensors, to run, modify and propagate that work, subject to this License. You are not responsible for enforcing compliance by third parties with this License.
An entity transaction is a transaction transferring control of an organization, or substantially all assets of one, or subdividing an organization, or merging organizations. If propagation of a covered work results from an entity transaction, each party to that transaction who receives a copy of the work also receives whatever licenses to the work the partys predecessor in interest had or could give under the previous paragraph, plus a right to possession of the Corresponding Source of the work from the predecessor in interest, if the predecessor has it or can get it with reasonable efforts.
You may not impose any further restrictions on the exercise of the rights granted or affirmed under this License. For example, you may not impose a license fee, royalty, or other charge for exercise of rights granted under this License, and you may not initiate litigation (including a cross-claim or counterclaim in a lawsuit) alleging that any patent claim is infringed by making, using, selling, offering for sale, or importing the Program or any portion of it.
Patents.
A contributor is a copyright holder who authorizes use under this License of the Program or a work on which the Program is based. The work thus licensed is called the contributors contributor version.
A contributors essential patent claims are all patent claims owned or controlled by the contributor, whether already acquired or hereafter acquired, that would be infringed by some manner, permitted by this License, of making, using, or selling its contributor version, but do not include claims that would be infringed only as a consequence of further modification of the contributor version. For purposes of this definition, control includes the right to grant patent sublicenses in a manner consistent with the requirements of this License.
Each contributor grants you a non-exclusive, worldwide, royalty-free patent license under the contributors essential patent claims, to make, use, sell, offer for sale, import and otherwise run, modify and propagate the contents of its contributor version.
In the following three paragraphs, a patent license is any express agreement or commitment, however denominated, not to enforce a patent (such as an express permission to practice a patent or covenant not to sue for patent infringement). To grant such a patent license to a party means to make such an agreement or commitment not to enforce a patent against the party.
If you convey a covered work, knowingly relying on a patent license, and the Corresponding Source of the work is not available for anyone to copy, free of charge and under the terms of this License, through a publicly available network server or other readily accessible means, then you must either (1) cause the Corresponding Source to be so available, or (2) arrange to deprive yourself of the benefit of the patent license for this particular work, or (3) arrange, in a manner consistent with the requirements of this License, to extend the patent license to downstream recipients. Knowingly relying means you have actual knowledge that, but for the patent license, your conveying the covered work in a country, or your recipients use of the covered work in a country, would infringe one or more identifiable patents in that country that you have reason to believe are valid.
If, pursuant to or in connection with a single transaction or arrangement, you convey, or propagate by procuring conveyance of, a covered work, and grant a patent license to some of the parties receiving the covered work authorizing them to use, propagate, modify or convey a specific copy of the covered work, then the patent license you grant is automatically extended to all recipients of the covered work and works based on it.
A patent license is discriminatory if it does not include within the scope of its coverage, prohibits the exercise of, or is conditioned on the non-exercise of one or more of the rights that are specifically granted under this License. You may not convey a covered work if you are a party to an arrangement with a third party that is in the business of distributing software, under which you make payment to the third party based on the extent of your activity of conveying the work, and under which the third party grants, to any of the parties who would receive the covered work from you, a discriminatory patent license (a) in connection with copies of the covered work conveyed by you (or copies made from those copies), or (b) primarily for and in connection with specific products or compilations that contain the covered work, unless you entered into that arrangement, or that patent license was granted, prior to 28 March 2007.
Nothing in this License shall be construed as excluding or limiting any implied license or other defenses to infringement that may otherwise be available to you under applicable patent law.
No Surrender of Others Freedom.
If conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot convey a covered work so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not convey it at all. For example, if you agree to terms that obligate you to collect a royalty for further conveying from those to whom you convey the Program, the only way you could satisfy both those terms and this License would be to refrain entirely from conveying the Program.
Use with the GNU Affero General Public License.
Notwithstanding any other provision of this License, you have permission to link or combine any covered work with a work licensed under version 3 of the GNU Affero General Public License into a single combined work, and to convey the resulting work. The terms of this License will continue to apply to the part which is the covered work, but the special requirements of the GNU Affero General Public License, section 13, concerning interaction through a network will apply to the combination as such.
Revised Versions of this License.
The Free Software Foundation may publish revised and/or new versions of the GNU General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.
Each version is given a distinguishing version number. If the Program specifies that a certain numbered version of the GNU General Public License or any later version applies to it, you have the option of following the terms and conditions either of that numbered version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of the GNU General Public License, you may choose any version ever published by the Free Software Foundation.
If the Program specifies that a proxy can decide which future versions of the GNU General Public License can be used, that proxys public statement of acceptance of a version permanently authorizes you to choose that version for the Program.
Later license versions may give you additional or different permissions. However, no additional obligations are imposed on any author or copyright holder as a result of your choosing to follow a later version.
Disclaimer of Warranty.
THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM AS IS WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
Limitation of Liability.
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
Interpretation of Sections 15 and 16.
If the disclaimer of warranty and limitation of liability provided above cannot be given local legal effect according to their terms, reviewing courts shall apply local law that most closely approximates an absolute waiver of all civil liability in connection with the Program, unless a warranty or assumption of liability accompanies a copy of the Program in return for a fee.
END OF TERMS AND CONDITIONS
How to Apply These Terms to Your New Programs
If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.
To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively state the exclusion of warranty; and each file should have at least the copyright line and a pointer to where the full notice is found.
``one line to give the program's name and a brief idea of what it does.``
Copyright (C) ``year`` ``name of author``
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at
your option) any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see http://www.gnu.org/licenses/.
Also add information on how to contact you by electronic and paper mail.
If the program does terminal interaction, make it output a short notice like this when it starts in an interactive mode:
``program`` Copyright (C) ``year`` ``name of author``
This program comes with ABSOLUTELY NO WARRANTY; for details type show w.
This is free software, and you are welcome to redistribute it
under certain conditions; type show c for details.
The hypothetical commands show w and show c should show the appropriate parts of the General Public License. Of course, your programs commands might be different; for a GUI interface, you would use an about box.
You should also get your employer (if you work as a programmer) or school, if any, to sign a copyright disclaimer for the program, if necessary. For more information on this, and how to apply and follow the GNU GPL, see http://www.gnu.org/licenses/.
The GNU General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Lesser General Public License instead of this License. But first, please read http://www.gnu.org/philosophy/why-not-lgpl.html.
@c Set file name and title for man page. @setfilename gfdl @settitle GNU Free Documentation License @c man begin SEEALSO gpl(7), fsf-funding(7). @c man end @c man begin COPYRIGHT Copyright @copyright{} 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. @uref{http://fsf.org/}
Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. @c This file is intended to be included within another document, @c hence no sectioning command or @node. @c man end
:: _gnu-free-documentation-license: