405 lines
11 KiB
C
405 lines
11 KiB
C
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/* Rename SSA copies.
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Copyright (C) 2004 Free Software Foundation, Inc.
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Contributed by Andrew MacLeod <amacleod@redhat.com>
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GCC is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GCC; see the file COPYING. If not, write to
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the Free Software Foundation, 51 Franklin Street, Fifth Floor,
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Boston, MA 02110-1301, USA. */
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#include "config.h"
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#include "system.h"
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#include "coretypes.h"
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#include "tm.h"
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#include "tree.h"
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#include "flags.h"
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#include "basic-block.h"
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#include "function.h"
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#include "diagnostic.h"
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#include "bitmap.h"
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#include "tree-flow.h"
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#include "tree-gimple.h"
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#include "tree-inline.h"
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#include "timevar.h"
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#include "hashtab.h"
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#include "tree-dump.h"
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#include "tree-ssa-live.h"
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#include "tree-pass.h"
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#include "langhooks.h"
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/* The following routines implement the SSA copy renaming phase.
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This optimization looks for copies between 2 SSA_NAMES, either through a
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direct copy, or an implicit one via a PHI node result and its arguments.
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Each copy is examined to determine if it is possible to rename the base
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variable of one of the operands to the same variable as the other operand.
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i.e.
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T.3_5 = <blah>
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a_1 = T.3_5
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If this copy couldn't be copy propagated, it could possibly remain in the
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program throughout the optimization phases. After SSA->normal, it would
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become:
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T.3 = <blah>
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a = T.3
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Since T.3_5 is distinct from all other SSA versions of T.3, there is no
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fundamental reason why the base variable needs to be T.3, subject to
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certain restrictions. This optimization attempts to determine if we can
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change the base variable on copies like this, and result in code such as:
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a_5 = <blah>
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a_1 = a_5
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This gives the SSA->normal pass a shot at coalescing a_1 and a_5. If it is
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possible, the copy goes away completely. If it isn't possible, a new temp
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will be created for a_5, and you will end up with the exact same code:
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a.8 = <blah>
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a = a.8
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The other benefit of performing this optimization relates to what variables
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are chosen in copies. Gimplification of the program uses temporaries for
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a lot of things. expressions like
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a_1 = <blah>
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<blah2> = a_1
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get turned into
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T.3_5 = <blah>
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a_1 = T.3_5
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<blah2> = a_1
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Copy propagation is done in a forward direction, and if we can propagate
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through the copy, we end up with:
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T.3_5 = <blah>
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<blah2> = T.3_5
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The copy is gone, but so is all reference to the user variable 'a'. By
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performing this optimization, we would see the sequence:
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a_5 = <blah>
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a_1 = a_5
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<blah2> = a_1
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which copy propagation would then turn into:
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a_5 = <blah>
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<blah2> = a_5
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and so we still retain the user variable whenever possible. */
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/* Coalesce the partitions in MAP representing VAR1 and VAR2 if it is valid.
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Choose a representative for the partition, and send debug info to DEBUG. */
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static void
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copy_rename_partition_coalesce (var_map map, tree var1, tree var2, FILE *debug)
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{
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int p1, p2, p3;
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tree root1, root2;
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tree rep1, rep2;
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var_ann_t ann1, ann2, ann3;
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bool ign1, ign2, abnorm;
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gcc_assert (TREE_CODE (var1) == SSA_NAME);
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gcc_assert (TREE_CODE (var2) == SSA_NAME);
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register_ssa_partition (map, var1, false);
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register_ssa_partition (map, var2, true);
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p1 = partition_find (map->var_partition, SSA_NAME_VERSION (var1));
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p2 = partition_find (map->var_partition, SSA_NAME_VERSION (var2));
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if (debug)
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{
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fprintf (debug, "Try : ");
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print_generic_expr (debug, var1, TDF_SLIM);
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fprintf (debug, "(P%d) & ", p1);
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print_generic_expr (debug, var2, TDF_SLIM);
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fprintf (debug, "(P%d)", p2);
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}
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gcc_assert (p1 != NO_PARTITION);
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gcc_assert (p2 != NO_PARTITION);
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rep1 = partition_to_var (map, p1);
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rep2 = partition_to_var (map, p2);
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root1 = SSA_NAME_VAR (rep1);
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root2 = SSA_NAME_VAR (rep2);
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ann1 = var_ann (root1);
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ann2 = var_ann (root2);
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if (p1 == p2)
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{
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if (debug)
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fprintf (debug, " : Already coalesced.\n");
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return;
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}
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/* Don't coalesce if one of the variables occurs in an abnormal PHI. */
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abnorm = (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rep1)
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|| SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rep2));
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if (abnorm)
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{
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if (debug)
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fprintf (debug, " : Abnormal PHI barrier. No coalesce.\n");
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return;
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}
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/* Partitions already have the same root, simply merge them. */
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if (root1 == root2)
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{
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p1 = partition_union (map->var_partition, p1, p2);
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if (debug)
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fprintf (debug, " : Same root, coalesced --> P%d.\n", p1);
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return;
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}
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/* Never attempt to coalesce 2 difference parameters. */
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if (TREE_CODE (root1) == PARM_DECL && TREE_CODE (root2) == PARM_DECL)
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{
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if (debug)
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fprintf (debug, " : 2 different PARM_DECLS. No coalesce.\n");
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return;
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}
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if ((TREE_CODE (root1) == RESULT_DECL) != (TREE_CODE (root2) == RESULT_DECL))
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{
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if (debug)
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fprintf (debug, " : One root a RESULT_DECL. No coalesce.\n");
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return;
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}
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ign1 = TREE_CODE (root1) == VAR_DECL && DECL_IGNORED_P (root1);
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ign2 = TREE_CODE (root2) == VAR_DECL && DECL_IGNORED_P (root2);
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/* Never attempt to coalesce 2 user variables unless one is an inline
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variable. */
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if (!ign1 && !ign2)
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{
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if (DECL_FROM_INLINE (root2))
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ign2 = true;
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else if (DECL_FROM_INLINE (root1))
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ign1 = true;
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else
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{
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if (debug)
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fprintf (debug, " : 2 different USER vars. No coalesce.\n");
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return;
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}
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}
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/* Don't coalesce if there are two different memory tags. */
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if (ann1->symbol_mem_tag
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&& ann2->symbol_mem_tag
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&& ann1->symbol_mem_tag != ann2->symbol_mem_tag)
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{
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if (debug)
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fprintf (debug, " : 2 memory tags. No coalesce.\n");
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return;
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}
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/* If both values have default defs, we can't coalesce. If only one has a
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tag, make sure that variable is the new root partition. */
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if (default_def (root1))
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{
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if (default_def (root2))
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{
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if (debug)
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fprintf (debug, " : 2 default defs. No coalesce.\n");
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return;
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}
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else
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{
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ign2 = true;
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ign1 = false;
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}
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}
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else if (default_def (root2))
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{
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ign1 = true;
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ign2 = false;
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}
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/* Don't coalesce if the two variables aren't type compatible. */
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if (!lang_hooks.types_compatible_p (TREE_TYPE (root1), TREE_TYPE (root2)))
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{
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if (debug)
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fprintf (debug, " : Incompatible types. No coalesce.\n");
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return;
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}
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/* Don't coalesce if the aliasing sets of the types are different. */
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if (POINTER_TYPE_P (TREE_TYPE (root1))
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&& POINTER_TYPE_P (TREE_TYPE (root2))
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&& get_alias_set (TREE_TYPE (TREE_TYPE (root1)))
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!= get_alias_set (TREE_TYPE (TREE_TYPE (root2))))
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{
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if (debug)
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fprintf (debug, " : 2 different aliasing sets. No coalesce.\n");
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return;
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}
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/* Merge the two partitions. */
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p3 = partition_union (map->var_partition, p1, p2);
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/* Set the root variable of the partition to the better choice, if there is
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one. */
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if (!ign2)
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replace_ssa_name_symbol (partition_to_var (map, p3), root2);
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else if (!ign1)
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replace_ssa_name_symbol (partition_to_var (map, p3), root1);
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/* Update the various flag widgitry of the current base representative. */
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ann3 = var_ann (SSA_NAME_VAR (partition_to_var (map, p3)));
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if (ann1->symbol_mem_tag)
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ann3->symbol_mem_tag = ann1->symbol_mem_tag;
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else
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ann3->symbol_mem_tag = ann2->symbol_mem_tag;
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if (debug)
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{
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fprintf (debug, " --> P%d ", p3);
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print_generic_expr (debug, SSA_NAME_VAR (partition_to_var (map, p3)),
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TDF_SLIM);
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fprintf (debug, "\n");
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}
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}
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/* This function will make a pass through the IL, and attempt to coalesce any
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SSA versions which occur in PHI's or copies. Coalescing is accomplished by
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changing the underlying root variable of all coalesced version. This will
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then cause the SSA->normal pass to attempt to coalesce them all to the same
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variable. */
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static unsigned int
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rename_ssa_copies (void)
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{
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var_map map;
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basic_block bb;
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block_stmt_iterator bsi;
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tree phi, stmt, var, part_var;
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unsigned x;
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FILE *debug;
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if (dump_file && (dump_flags & TDF_DETAILS))
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debug = dump_file;
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else
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debug = NULL;
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map = init_var_map (num_ssa_names + 1);
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FOR_EACH_BB (bb)
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{
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/* Scan for real copies. */
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for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
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{
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stmt = bsi_stmt (bsi);
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if (TREE_CODE (stmt) == MODIFY_EXPR)
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{
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tree lhs = TREE_OPERAND (stmt, 0);
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tree rhs = TREE_OPERAND (stmt, 1);
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if (TREE_CODE (lhs) == SSA_NAME && TREE_CODE (rhs) == SSA_NAME)
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copy_rename_partition_coalesce (map, lhs, rhs, debug);
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}
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}
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}
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FOR_EACH_BB (bb)
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{
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/* Treat PHI nodes as copies between the result and each argument. */
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for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
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{
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int i;
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tree res = PHI_RESULT (phi);
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/* Do not process virtual SSA_NAMES. */
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if (!is_gimple_reg (SSA_NAME_VAR (res)))
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continue;
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for (i = 0; i < PHI_NUM_ARGS (phi); i++)
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{
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tree arg = PHI_ARG_DEF (phi, i);
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if (TREE_CODE (arg) == SSA_NAME)
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copy_rename_partition_coalesce (map, res, arg, debug);
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}
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}
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}
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if (debug)
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dump_var_map (debug, map);
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/* Now one more pass to make all elements of a partition share the same
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root variable. */
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for (x = 1; x <= num_ssa_names; x++)
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{
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part_var = partition_to_var (map, x);
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if (!part_var)
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continue;
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var = map->partition_to_var[x];
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if (debug)
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{
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if (SSA_NAME_VAR (var) != SSA_NAME_VAR (part_var))
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{
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fprintf (debug, "Coalesced ");
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print_generic_expr (debug, var, TDF_SLIM);
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fprintf (debug, " to ");
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print_generic_expr (debug, part_var, TDF_SLIM);
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fprintf (debug, "\n");
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}
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}
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replace_ssa_name_symbol (var, SSA_NAME_VAR (part_var));
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}
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delete_var_map (map);
|
||
|
|
return 0;
|
||
|
|
}
|
||
|
|
|
||
|
|
/* Return true if copy rename is to be performed. */
|
||
|
|
|
||
|
|
static bool
|
||
|
|
gate_copyrename (void)
|
||
|
|
{
|
||
|
|
return flag_tree_copyrename != 0;
|
||
|
|
}
|
||
|
|
|
||
|
|
struct tree_opt_pass pass_rename_ssa_copies =
|
||
|
|
{
|
||
|
|
"copyrename", /* name */
|
||
|
|
gate_copyrename, /* gate */
|
||
|
|
rename_ssa_copies, /* execute */
|
||
|
|
NULL, /* sub */
|
||
|
|
NULL, /* next */
|
||
|
|
0, /* static_pass_number */
|
||
|
|
TV_TREE_COPY_RENAME, /* tv_id */
|
||
|
|
PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */
|
||
|
|
0, /* properties_provided */
|
||
|
|
0, /* properties_destroyed */
|
||
|
|
0, /* todo_flags_start */
|
||
|
|
TODO_dump_func | TODO_verify_ssa, /* todo_flags_finish */
|
||
|
|
0 /* letter */
|
||
|
|
};
|
||
|
|
|