#include "config.h"#include "system.h"#include "coretypes.h"#include "tm.h"#include "tree.h"#include "gimple-pretty-print.h"#include "bitmap.h"#include "gimple.h"#include "gimple-ssa.h"#include "tree-phinodes.h"#include "ssa-iterators.h"#include "tree-ssanames.h"#include "dumpfile.h"#include "tree-ssa-live.h"#include "tree-ssa-ter.h"#include "tree-outof-ssa.h"#include "flags.h"
Data Structures | |
| struct | temp_expr_table_d |
Macros | |
| #define | VIRTUAL_PARTITION(table) (table->virtual_partition) |
Typedefs | |
| typedef struct temp_expr_table_d * | temp_expr_table_p |
Functions | |
| static temp_expr_table_p | new_temp_expr_table () |
| static bitmap | free_temp_expr_table () |
| static bool | version_to_be_replaced_p () |
| static void | make_dependent_on_partition () |
| static void | add_to_partition_kill_list () |
| static void | remove_from_partition_kill_list () |
| static void | add_dependence () |
| static void | finished_with_expr () |
| static bool | ter_is_replaceable_p () |
| static void | process_replaceable () |
| static void | kill_expr () |
| static void | kill_virtual_exprs () |
| static void | mark_replaceable () |
| static void | find_replaceable_in_bb () |
| bitmap | find_replaceable_exprs () |
| void | dump_replaceable_exprs () |
Variables | |
| static bitmap_obstack | ter_bitmap_obstack |
Macro Definition Documentation
Used to indicate a dependency on VDEFs.
Referenced by find_replaceable_exprs().
Typedef Documentation
| typedef struct temp_expr_table_d * temp_expr_table_p |
Routines for performing Temporary Expression Replacement (TER) in SSA trees. Copyright (C) 2003-2013 Free Software Foundation, Inc. Contributed by Andrew MacLeod amacleod@redhat.com
This file is part of GCC.
GCC 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, or (at your option) any later version.
GCC 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 GCC; see the file COPYING3. If not see http://www.gnu.org/licenses/. Temporary Expression Replacement (TER)
Replace SSA version variables during out-of-ssa with their defining expression if there is only one use of the variable.
This pass is required in order for the RTL expansion pass to see larger chunks of code. This allows it to make better choices on RTL pattern selection. When expand is rewritten and merged with out-of-ssa, and understands SSA, this should be eliminated.
A pass is made through the function, one block at a time. No cross block information is tracked.
Variables which only have one use, and whose defining stmt is considered a replaceable expression (see ssa_is_replaceable_p) are tracked to see whether they can be replaced at their use location.
n_12 = C * 10 a_2 = b_5 + 6 v_9 = a_2 * n_12
if there are the only use of n_12 and a_2, TER will substitute in their expressions in v_9, and end up with:
v_9 = (b_5 + 6) * (C * 10)
which will then have the ssa_name assigned to regular variables, and the resulting code which will be passed to the expander looks something like:
v = (b + 6) * (C * 10)
This requires ensuring that none of the variables used by the expression change between the def point and where it is used. Furthermore, if any of the ssa_names used in this expression are themselves replaceable, we have to ensure none of that expressions' arguments change either. Although SSA_NAMES themselves don't change, this pass is performed after coalescing has coalesced different SSA_NAMES together, so there could be a definition of an SSA_NAME which is coalesced with a use that causes a problem, i.e.,
PHI b_5 = <b_8(2), b_14(1)> <...> a_2 = b_5 + 6 b_8 = c_4 + 4 v_9 = a_2 * n_12 <...>
If b_5, b_8 and b_14 are all coalesced together... The expression b_5 + 6 CANNOT replace the use in the statement defining v_9 because b_8 is in fact killing the value of b_5 since they share a partition and will be assigned the same memory or register location.
TER implements this but stepping through the instructions in a block and tracking potential expressions for replacement, and the partitions they are dependent on. Expressions are represented by the SSA_NAME_VERSION of the DEF on the LHS of a GIMPLE_ASSIGN and the expression is the RHS.
When a stmt is determined to be a possible replacement expression, the following steps are taken:
EXPR_DECL_UID bitmap is allocated and set to the base variable UID of the def and any uses in the expression. non-NULL means the expression is being tracked. The UID's themselves are used to prevent TER substitution into accumulating sequences, i.e.,
x = x + y x = x + z x = x + w etc. this can result in very large expressions which don't accomplish anything see PR tree-optimization/17549.
PARTITION_DEPENDENCIES is another bitmap array, and it has a bit set for any partition which is used in the expression. This is primarily used to remove an expression from the partition kill lists when a decision is made whether to replace it or not. This is indexed by ssa version number as well, and indicates a partition number. virtual operands are not tracked individually, but they are summarized by an artificial partition called VIRTUAL_PARTITION. This means a MAY or MUST def will kill ALL expressions that are dependent on a virtual operand. Note that the EXPR_DECL_UID and this bitmap represent very similar information, but the info in one is not easy to obtain from the other.
KILL_LIST is yet another bitmap array, this time it is indexed by partition number, and represents a list of active expressions which will will no longer be valid if a definition into this partition takes place.
PARTITION_IN_USE is simply a bitmap which is used to track which partitions currently have something in their kill list. This is used at the end of a block to clear out the KILL_LIST bitmaps at the end of each block.
NEW_REPLACEABLE_DEPENDENCIES is used as a temporary place to store dependencies which will be reused by the current definition. All the uses on an expression are processed before anything else is done. If a use is determined to be a replaceable expression AND the current stmt is also going to be replaceable, all the dependencies of this replaceable use will be picked up by the current stmt's expression. Rather than recreate them, they are simply copied here and then copied into the new expression when it is processed.
a_2 = b_5 + 6 v_8 = a_2 + c_4
a_2's expression 'b_5 + 6' is determined to be replaceable at the use location. It is dependent on the partition 'b_5' is in. This is cached into the NEW_REPLACEABLE_DEPENDENCIES bitmap, and when v_8 is examined for replaceability, it is a candidate, and it is dependent on the partition b_5 is in NOT a_2, as well as c_4's partition.
if v_8 is also replaceable:
x_9 = v_8 * 5
x_9 is dependent on partitions b_5, and c_4
if a statement is found which has either of those partitions written to before x_9 is used, then x_9 itself is NOT replaceable. Temporary Expression Replacement (TER) table information.
Function Documentation
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Add a dependency between the def of ssa VERSION and VAR. If VAR is replaceable by an expression, add a dependence each of the elements of the expression. These are contained in the new_replaceable list. TAB is the expression table.
Version will now be killed by a write to any partition the
substituted expression would have been killed by.
Rather than set partition_dependencies and in_use lists bit by
bit, simply OR in the new_replaceable_dependencies bits. It is only necessary to add these once.
Only dependencies on ssa_names which are coalesced with something need
to be tracked. Partitions with containing only a single SSA_NAME
*cannot* have their value changed.
References add_to_partition_kill_list(), gcc_checking_assert, make_dependent_on_partition(), NO_PARTITION, and var_to_partition().
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inlinestatic |
Add VER to the kill list for P. TAB is the expression table
References bitmap_clear_bit(), bitmap_empty_p(), BITMAP_FREE, gcc_checking_assert, temp_expr_table_d::kill_list, and temp_expr_table_d::partition_in_use.
Referenced by add_dependence().
| void dump_replaceable_exprs | ( | ) |
Dump TER expression table EXPR to file F.
References EXECUTE_IF_SET_IN_BITMAP, and temp_expr_table_d::kill_list.
Referenced by expand_phi_nodes(), and find_replaceable_exprs().
| bitmap find_replaceable_exprs | ( | ) |
This function is the driver routine for replacement of temporary expressions in the SSA->normal phase, operating on MAP. If there are replaceable expressions, a table is returned which maps SSA versions to the expressions they should be replaced with. A NULL_TREE indicates no replacement should take place. If there are no replacements at all, NULL is returned by the function, otherwise an expression vector indexed by SSA_NAME version numbers.
References bitmap_empty_p(), dump_replaceable_exprs(), temp_expr_table_d::expr_decl_uids, num_ssa_names, temp_expr_table_d::partition_dependencies, print_generic_expr(), temp_expr_table_d::replaceable_expressions, ssa_name, TDF_SLIM, and VIRTUAL_PARTITION.
Referenced by expand_phi_nodes().
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This function processes basic block BB, and looks for variables which can be replaced by their expressions. Results are stored in the table TAB.
Determine if this stmt finishes an existing expression.
If this use is a potential replacement variable, process it.
See if the root variables are the same. If they are, we
do not want to do the replacement to avoid problems with
code size, see PR tree-optimization/17549. If the stmt does a memory store and the replacement
is a load aliasing it avoid creating overlapping
assignments which we cannot expand correctly. Mark expression as replaceable unless stmt is volatile, or the
def variable has the same root variable as something in the
substitution list, or the def and use span a call such that
we'll expand lifetimes across a call. Next, see if this stmt kills off an active expression.
Increment counter if this is a non BUILT_IN call. We allow
replacement over BUILT_IN calls since many will expand to inline
insns instead of a true call. Now see if we are creating a new expression or not.
Free any unused dependency lists.
A V_{MAY,MUST}_DEF kills any expression using a virtual operand,
including the current stmt.
References bitmap_bit_p, DECL_UID, and SSA_NAME_VAR.
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This function will remove the expression for VERSION from replacement consideration in table TAB. If FREE_EXPR is true, then remove the expression from consideration as well by freeing the decl uid bitmap.
Remove this expression from its dependent lists. The partition dependence list is retained and transferred later to whomever uses this version.
References single_imm_use(), SINGLE_SSA_TREE_OPERAND, ssa_is_replaceable_p(), and SSA_OP_DEF.
Referenced by kill_expr().
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Free TER table T. If there are valid replacements, return the expression vector.
References temp_expr_table_d::expr_decl_uids, gcc_assert, NULL, and temp_expr_table_d::partition_dependencies.
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inlinestatic |
This function removes any expression in TAB which is dependent on PARTITION from consideration, making it not replaceable.
Mark every active expr dependent on this var as not replaceable. finished_with_expr can modify the bitmap, so we can't execute over it.
References BITMAP_ALLOC, bitmap_ior_into(), bitmap_set_bit, finished_with_expr(), temp_expr_table_d::new_replaceable_dependencies, NULL, temp_expr_table_d::partition_dependencies, temp_expr_table_d::replaceable_expressions, and SSA_NAME_VERSION.
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inlinestatic |
This function kills all expressions in TAB which are dependent on virtual partitions.
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inlinestatic |
Add partition P to the list if partitions VERSION is dependent on. TAB is the expression table
References BITMAP_ALLOC, bitmap_set_bit, temp_expr_table_d::kill_list, and temp_expr_table_d::partition_in_use.
Referenced by add_dependence().
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Mark the expression associated with VAR as replaceable, and enter the defining stmt into the partition_dependencies table TAB. If MORE_REPLACING is true, accumulate the pending partition dependencies.
Move the dependence list to the pending listpending.
Set the replaceable expression. The bitmap for this "escapes" from this file so it's allocated on the default obstack.
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Create a new TER table for MAP.
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Create an expression entry for a replaceable expression.
Add this expression to the dependency list for each use partition.
If there are VUSES, add a dependence on virtual defs.
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Remove VER from the partition kill list for P. TAB is the expression table.
References bitmap_empty_p(), temp_expr_table_d::new_replaceable_dependencies, SSA_NAME_VERSION, and version_to_be_replaced_p().
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inlinestatic |
Return TRUE if expression STMT is suitable for replacement. In addition to ssa_is_replaceable_p, require the same bb, and for -O0 same locus and same BLOCK), Considers memory loads as replaceable if aliasing is available.
Only consider definitions which have a single use. ssa_is_replaceable_p
already performed this check, but the use stmt pointer is required for
further checks.
If the use isn't in this block, it wont be replaced either.
Without alias info we can't move around loads.
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inlinestatic |
Return TRUE if VERSION is to be replaced by an expression in TAB.
References BITMAP_ALLOC, bitmap_set_bit, and temp_expr_table_d::partition_dependencies.
Referenced by remove_from_partition_kill_list().
Variable Documentation
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A place for the many, many bitmaps we create.
