312 lines
9.3 KiB
C
312 lines
9.3 KiB
C
/* Generic routines for manipulating SSA_NAME expressions
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Copyright (C) 2003, 2004, 2005 Free Software Foundation, Inc.
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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 "varray.h"
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#include "ggc.h"
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#include "tree-flow.h"
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/* Rewriting a function into SSA form can create a huge number of SSA_NAMEs,
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many of which may be thrown away shortly after their creation if jumps
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were threaded through PHI nodes.
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While our garbage collection mechanisms will handle this situation, it
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is extremely wasteful to create nodes and throw them away, especially
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when the nodes can be reused.
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For PR 8361, we can significantly reduce the number of nodes allocated
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and thus the total amount of memory allocated by managing SSA_NAMEs a
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little. This additionally helps reduce the amount of work done by the
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garbage collector. Similar results have been seen on a wider variety
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of tests (such as the compiler itself).
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Right now we maintain our free list on a per-function basis. It may
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or may not make sense to maintain the free list for the duration of
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a compilation unit.
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External code should rely solely upon HIGHEST_SSA_VERSION and the
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externally defined functions. External code should not know about
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the details of the free list management.
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External code should also not assume the version number on nodes is
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monotonically increasing. We reuse the version number when we
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reuse an SSA_NAME expression. This helps keep arrays and bitmaps
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more compact.
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We could also use a zone allocator for these objects since they have
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a very well defined lifetime. If someone wants to experiment with that
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this is the place to try it. */
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/* Array of all SSA_NAMEs used in the function. */
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VEC(tree,gc) *ssa_names;
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/* Free list of SSA_NAMEs. This list is wiped at the end of each function
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after we leave SSA form. */
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static GTY (()) tree free_ssanames;
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/* Version numbers with special meanings. We start allocating new version
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numbers after the special ones. */
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#define UNUSED_NAME_VERSION 0
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#ifdef GATHER_STATISTICS
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unsigned int ssa_name_nodes_reused;
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unsigned int ssa_name_nodes_created;
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#endif
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/* Initialize management of SSA_NAMEs. */
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void
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init_ssanames (void)
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{
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ssa_names = VEC_alloc (tree, gc, 50);
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/* Version 0 is special, so reserve the first slot in the table. Though
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currently unused, we may use version 0 in alias analysis as part of
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the heuristics used to group aliases when the alias sets are too
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large.
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We use VEC_quick_push here because we know that SSA_NAMES has at
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least 50 elements reserved in it. */
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VEC_quick_push (tree, ssa_names, NULL_TREE);
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free_ssanames = NULL;
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}
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/* Finalize management of SSA_NAMEs. */
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void
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fini_ssanames (void)
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{
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VEC_free (tree, gc, ssa_names);
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free_ssanames = NULL;
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}
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/* Dump some simple statistics regarding the re-use of SSA_NAME nodes. */
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#ifdef GATHER_STATISTICS
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void
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ssanames_print_statistics (void)
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{
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fprintf (stderr, "SSA_NAME nodes allocated: %u\n", ssa_name_nodes_created);
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fprintf (stderr, "SSA_NAME nodes reused: %u\n", ssa_name_nodes_reused);
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}
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#endif
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/* Return an SSA_NAME node for variable VAR defined in statement STMT.
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STMT may be an empty statement for artificial references (e.g., default
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definitions created when a variable is used without a preceding
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definition). */
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tree
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make_ssa_name (tree var, tree stmt)
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{
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tree t;
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use_operand_p imm;
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gcc_assert (DECL_P (var)
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|| TREE_CODE (var) == INDIRECT_REF);
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gcc_assert (!stmt || EXPR_P (stmt) || TREE_CODE (stmt) == PHI_NODE);
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/* If our free list has an element, then use it. */
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if (free_ssanames)
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{
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t = free_ssanames;
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free_ssanames = TREE_CHAIN (free_ssanames);
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#ifdef GATHER_STATISTICS
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ssa_name_nodes_reused++;
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#endif
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/* The node was cleared out when we put it on the free list, so
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there is no need to do so again here. */
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gcc_assert (ssa_name (SSA_NAME_VERSION (t)) == NULL);
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VEC_replace (tree, ssa_names, SSA_NAME_VERSION (t), t);
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}
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else
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{
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t = make_node (SSA_NAME);
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SSA_NAME_VERSION (t) = num_ssa_names;
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VEC_safe_push (tree, gc, ssa_names, t);
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#ifdef GATHER_STATISTICS
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ssa_name_nodes_created++;
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#endif
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}
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TREE_TYPE (t) = TREE_TYPE (var);
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SSA_NAME_VAR (t) = var;
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SSA_NAME_DEF_STMT (t) = stmt;
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SSA_NAME_PTR_INFO (t) = NULL;
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SSA_NAME_IN_FREE_LIST (t) = 0;
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imm = &(SSA_NAME_IMM_USE_NODE (t));
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imm->use = NULL;
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imm->prev = imm;
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imm->next = imm;
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imm->stmt = t;
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return t;
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}
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/* We no longer need the SSA_NAME expression VAR, release it so that
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it may be reused.
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Note it is assumed that no calls to make_ssa_name will be made
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until all uses of the ssa name are released and that the only
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use of the SSA_NAME expression is to check its SSA_NAME_VAR. All
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other fields must be assumed clobbered. */
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void
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release_ssa_name (tree var)
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{
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if (!var)
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return;
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/* Never release the default definition for a symbol. It's a
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special SSA name that should always exist once it's created. */
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if (var == default_def (SSA_NAME_VAR (var)))
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return;
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/* If VAR has been registered for SSA updating, don't remove it.
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After update_ssa has run, the name will be released. */
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if (name_registered_for_update_p (var))
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{
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release_ssa_name_after_update_ssa (var);
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return;
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}
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/* release_ssa_name can be called multiple times on a single SSA_NAME.
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However, it should only end up on our free list one time. We
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keep a status bit in the SSA_NAME node itself to indicate it has
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been put on the free list.
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Note that once on the freelist you can not reference the SSA_NAME's
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defining statement. */
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if (! SSA_NAME_IN_FREE_LIST (var))
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{
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tree saved_ssa_name_var = SSA_NAME_VAR (var);
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int saved_ssa_name_version = SSA_NAME_VERSION (var);
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use_operand_p imm = &(SSA_NAME_IMM_USE_NODE (var));
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#ifdef ENABLE_CHECKING
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verify_imm_links (stderr, var);
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#endif
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while (imm->next != imm)
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delink_imm_use (imm->next);
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VEC_replace (tree, ssa_names, SSA_NAME_VERSION (var), NULL_TREE);
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memset (var, 0, tree_size (var));
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imm->prev = imm;
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imm->next = imm;
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imm->stmt = var;
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/* First put back the right tree node so that the tree checking
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macros do not complain. */
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TREE_SET_CODE (var, SSA_NAME);
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/* Restore the version number. */
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SSA_NAME_VERSION (var) = saved_ssa_name_version;
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/* Hopefully this can go away once we have the new incremental
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SSA updating code installed. */
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SSA_NAME_VAR (var) = saved_ssa_name_var;
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/* Note this SSA_NAME is now in the first list. */
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SSA_NAME_IN_FREE_LIST (var) = 1;
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/* And finally link it into the free list. */
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TREE_CHAIN (var) = free_ssanames;
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free_ssanames = var;
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}
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}
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/* Creates a duplicate of a ssa name NAME defined in statement STMT. */
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tree
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duplicate_ssa_name (tree name, tree stmt)
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{
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tree new_name = make_ssa_name (SSA_NAME_VAR (name), stmt);
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struct ptr_info_def *old_ptr_info = SSA_NAME_PTR_INFO (name);
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if (old_ptr_info)
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duplicate_ssa_name_ptr_info (new_name, old_ptr_info);
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return new_name;
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}
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/* Creates a duplicate of the ptr_info_def at PTR_INFO for use by
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the SSA name NAME. */
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void
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duplicate_ssa_name_ptr_info (tree name, struct ptr_info_def *ptr_info)
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{
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struct ptr_info_def *new_ptr_info;
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gcc_assert (POINTER_TYPE_P (TREE_TYPE (name)));
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gcc_assert (!SSA_NAME_PTR_INFO (name));
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if (!ptr_info)
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return;
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new_ptr_info = ggc_alloc (sizeof (struct ptr_info_def));
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*new_ptr_info = *ptr_info;
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if (ptr_info->pt_vars)
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{
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new_ptr_info->pt_vars = BITMAP_GGC_ALLOC ();
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bitmap_copy (new_ptr_info->pt_vars, ptr_info->pt_vars);
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}
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SSA_NAME_PTR_INFO (name) = new_ptr_info;
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}
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/* Release all the SSA_NAMEs created by STMT. */
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void
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release_defs (tree stmt)
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{
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tree def;
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ssa_op_iter iter;
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/* Make sure that we are in SSA. Otherwise, operand cache may point
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to garbage. */
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gcc_assert (in_ssa_p);
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FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
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if (TREE_CODE (def) == SSA_NAME)
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release_ssa_name (def);
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}
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/* Replace the symbol associated with SSA_NAME with SYM. */
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void
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replace_ssa_name_symbol (tree ssa_name, tree sym)
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{
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SSA_NAME_VAR (ssa_name) = sym;
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TREE_TYPE (ssa_name) = TREE_TYPE (sym);
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}
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#include "gt-tree-ssanames.h"
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