machmode.h File Reference
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Data Structures | |
| class | bit_field_mode_iterator |
Enumerations | |
| enum | mode_class { MODE_CLASSES, MAX_MODE_CLASS, MODE_CLASSES, MAX_MODE_CLASS } |
Functions | |
| enum machine_mode | mode_for_size (unsigned int, enum mode_class, int) |
| enum machine_mode | smallest_mode_for_size (unsigned int, enum mode_class) |
| enum machine_mode | int_mode_for_mode (enum machine_mode) |
| enum machine_mode | mode_for_vector (enum machine_mode, unsigned) |
| enum machine_mode | get_best_mode (int, int, unsigned HOST_WIDE_INT, unsigned HOST_WIDE_INT, unsigned int, enum machine_mode, bool) |
| unsigned | get_mode_alignment (enum machine_mode) |
| unsigned int | element_precision (enum machine_mode) |
| void | init_adjust_machine_modes (void) |
Variables | |
| const char *const | mode_name [NUM_MACHINE_MODES] |
| const unsigned char | mode_class [NUM_MACHINE_MODES] |
| CONST_MODE_SIZE unsigned char | mode_size [NUM_MACHINE_MODES] |
| const unsigned short | mode_precision [NUM_MACHINE_MODES] |
| CONST_MODE_IBIT unsigned char | mode_ibit [NUM_MACHINE_MODES] |
| CONST_MODE_FBIT unsigned char | mode_fbit [NUM_MACHINE_MODES] |
| const unsigned HOST_WIDE_INT | mode_mask_array [NUM_MACHINE_MODES] |
| const unsigned char | mode_inner [NUM_MACHINE_MODES] |
| const unsigned char | mode_nunits [NUM_MACHINE_MODES] |
| const unsigned char | mode_wider [NUM_MACHINE_MODES] |
| const unsigned char | mode_2xwider [NUM_MACHINE_MODES] |
| CONST_MODE_BASE_ALIGN unsigned char | mode_base_align [NUM_MACHINE_MODES] |
| const unsigned char | class_narrowest_mode [MAX_MODE_CLASS] |
| enum machine_mode | byte_mode |
| enum machine_mode | word_mode |
| enum machine_mode | ptr_mode |
Enumeration Type Documentation
| enum mode_class |
Function Documentation
| unsigned int element_precision | ( | enum | machine_mode | ) |
Get the precision of the mode or its inner mode if it has one.
| enum machine_mode get_best_mode | ( | int | bitsize, |
| int | bitpos, | ||
| unsigned HOST_WIDE_INT | bitregion_start, | ||
| unsigned HOST_WIDE_INT | bitregion_end, | ||
| unsigned int | align, | ||
| enum machine_mode | largest_mode, | ||
| bool | volatilep | ||
| ) |
Find the best mode to use to access a bit field.
Find the best machine mode to use when referencing a bit field of length BITSIZE bits starting at BITPOS. BITREGION_START is the bit position of the first bit in this sequence of bit fields. BITREGION_END is the last bit in this sequence. If these two fields are non-zero, we should restrict the memory access to that range. Otherwise, we are allowed to touch any adjacent non bit-fields. The underlying object is known to be aligned to a boundary of ALIGN bits. If LARGEST_MODE is not VOIDmode, it means that we should not use a mode larger than LARGEST_MODE (usually SImode). If no mode meets all these conditions, we return VOIDmode. If VOLATILEP is false and SLOW_BYTE_ACCESS is false, we return the smallest mode meeting these conditions. If VOLATILEP is false and SLOW_BYTE_ACCESS is true, we return the largest mode (but a mode no wider than UNITS_PER_WORD) that meets all the conditions. If VOLATILEP is true the narrow_volatile_bitfields target hook is used to decide which of the above modes should be used.
??? For historical reasons, reject modes that would normally
receive greater alignment, even if unaligned accesses are
acceptable. This has both advantages and disadvantages.
Removing this check means that something like:
struct s { unsigned int x; unsigned int y; };
int f (struct s *s) { return s->x == 0 && s->y == 0; }
can be implemented using a single load and compare on
64-bit machines that have no alignment restrictions.
For example, on powerpc64-linux-gnu, we would generate:
ld 3,0(3)
cntlzd 3,3
srdi 3,3,6
blr
rather than:
lwz 9,0(3)
cmpwi 7,9,0
bne 7,.L3
lwz 3,4(3)
cntlzw 3,3
srwi 3,3,5
extsw 3,3
blr
.p2align 4,,15
.L3:
li 3,0
blr
However, accessing more than one field can make life harder
for the gimple optimizers. For example, gcc.dg/vect/bb-slp-5.c
has a series of unsigned short copies followed by a series of
unsigned short comparisons. With this check, both the copies
and comparisons remain 16-bit accesses and FRE is able
to eliminate the latter. Without the check, the comparisons
can be done using 2 64-bit operations, which FRE isn't able
to handle in the same way.
Either way, it would probably be worth disabling this check
during expand. One particular example where removing the
check would help is the get_best_mode call in store_bit_field.
If we are given a memory bitregion of 128 bits that is aligned
to a 64-bit boundary, and the bitfield we want to modify is
in the second half of the bitregion, this check causes
store_bitfield to turn the memory into a 64-bit reference
to the _first_ half of the region. We later use
adjust_bitfield_address to get a reference to the correct half,
but doing so looks to adjust_bitfield_address as though we are
moving past the end of the original object, so it drops the
associated MEM_EXPR and MEM_OFFSET. Removing the check
causes store_bit_field to keep a 128-bit memory reference,
so that the final bitfield reference still has a MEM_EXPR
and MEM_OFFSET.
Referenced by store_bit_field().
| unsigned get_mode_alignment | ( | enum | machine_mode | ) |
Referenced by emit_move_change_mode().
| void init_adjust_machine_modes | ( | void | ) |
Target-dependent machine mode initialization - in insn-modes.c.
| enum machine_mode int_mode_for_mode | ( | enum | machine_mode | ) |
Return an integer mode of the exact same size as the input mode, or BLKmode on failure.
Referenced by expand_abs(), find_shift_sequence(), and make_compound_operation().
| enum machine_mode mode_for_size | ( | unsigned | int, |
| enum | mode_class, | ||
| int | |||
| ) |
Return the mode for data of a given size SIZE and mode class CLASS. If LIMIT is nonzero, then don't use modes bigger than MAX_FIXED_MODE_SIZE. The value is BLKmode if no other mode is found.
Referenced by assign_mem_slot(), decompose_register(), distribute_and_simplify_rtx(), expand_builtin___clear_cache(), expand_builtin_compare_and_swap(), finish_bitfield_layout(), int_mode_for_mode(), and spill_failure().
| enum machine_mode mode_for_vector | ( | enum | machine_mode, |
| unsigned | |||
| ) |
Return a mode that is suitable for representing a vector, or BLKmode on failure.
Referenced by finish_bitfield_layout(), and init_optabs().
| enum machine_mode smallest_mode_for_size | ( | unsigned | int, |
| enum | mode_class | ||
| ) |
Similar, but find the smallest mode for a given width.
Referenced by finish_bitfield_layout().
Variable Documentation
| enum machine_mode byte_mode |
Define the integer modes whose sizes are BITS_PER_UNIT and BITS_PER_WORD and the mode whose class is Pmode and whose size is POINTER_SIZE.
Commonly used modes.
Referenced by clear_storage_hints().
| const unsigned char class_narrowest_mode[MAX_MODE_CLASS] |
For each class, get the narrowest mode in that class.
| const unsigned char mode_2xwider[NUM_MACHINE_MODES] |
For scalars, this is a mode with twice the precision. For vectors, this is a mode with the same inner mode but with twice the elements.
| CONST_MODE_BASE_ALIGN unsigned char mode_base_align[NUM_MACHINE_MODES] |
Determine alignment, 1<=result<=BIGGEST_ALIGNMENT.
Referenced by mode_for_vector().
| const unsigned char mode_class[NUM_MACHINE_MODES] |
Get the general kind of object that mode MODE represents (integer, floating, complex, etc.)
| CONST_MODE_FBIT unsigned char mode_fbit[NUM_MACHINE_MODES] |
Get the number of fractional bits of an object of mode MODE.
| CONST_MODE_IBIT unsigned char mode_ibit[NUM_MACHINE_MODES] |
Get the number of integral bits of an object of mode MODE.
| const unsigned char mode_inner[NUM_MACHINE_MODES] |
Return the mode of the inner elements in a vector.
| const unsigned HOST_WIDE_INT mode_mask_array[NUM_MACHINE_MODES] |
Get a bitmask containing 1 for all bits in a word that fit within mode MODE.
| const char* const mode_name[NUM_MACHINE_MODES] |
Make an enum class that gives all the machine modes.
Get the name of mode MODE as a string.
| const unsigned char mode_nunits[NUM_MACHINE_MODES] |
Get the number of units in the object.
| const unsigned short mode_precision[NUM_MACHINE_MODES] |
Get the number of value bits of an object of mode MODE.
| CONST_MODE_SIZE unsigned char mode_size[NUM_MACHINE_MODES] |
Get the size in bytes and bits of an object of mode MODE.
| const unsigned char mode_wider[NUM_MACHINE_MODES] |
Get the next wider natural mode (eg, QI -> HI -> SI -> DI -> TI).
| enum machine_mode ptr_mode |
Referenced by default_asm_output_anchor(), expand_builtin_prefetch(), expand_omp_atomic_load(), and lookup_tramp_for_decl().
| enum machine_mode word_mode |
Referenced by assign_parm_adjust_entry_rtl(), default_eh_return_filter_mode(), default_libgcc_cmp_return_mode(), default_libgcc_shift_count_mode(), default_vector_alignment(), do_jump_by_parts_zero_rtx(), emit_block_move_libcall_fn(), emit_block_move_via_loop(), expand_abs(), expand_absneg_bit(), expand_builtin_assume_aligned(), expand_vector_broadcast(), find_defs(), mathfn_built_in_1(), mem_overlaps_already_clobbered_arg_p(), resolve_reg_notes(), restore_fixed_argument_area(), store_bit_field(), and subreg_lowpart_offset().
