1 /* Generic routines for manipulating SSA_NAME expressions
2 Copyright (C) 2003, 2004, 2005, 2007, 2008 Free Software Foundation, Inc.
4 This file is part of GCC.
6 GCC is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 3, or (at your option)
11 GCC is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING3. If not see
18 <http://www.gnu.org/licenses/>. */
22 #include "coretypes.h"
27 #include "tree-flow.h"
28 #include "tree-pass.h"
30 /* Rewriting a function into SSA form can create a huge number of SSA_NAMEs,
31 many of which may be thrown away shortly after their creation if jumps
32 were threaded through PHI nodes.
34 While our garbage collection mechanisms will handle this situation, it
35 is extremely wasteful to create nodes and throw them away, especially
36 when the nodes can be reused.
38 For PR 8361, we can significantly reduce the number of nodes allocated
39 and thus the total amount of memory allocated by managing SSA_NAMEs a
40 little. This additionally helps reduce the amount of work done by the
41 garbage collector. Similar results have been seen on a wider variety
42 of tests (such as the compiler itself).
44 Right now we maintain our free list on a per-function basis. It may
45 or may not make sense to maintain the free list for the duration of
48 External code should rely solely upon HIGHEST_SSA_VERSION and the
49 externally defined functions. External code should not know about
50 the details of the free list management.
52 External code should also not assume the version number on nodes is
53 monotonically increasing. We reuse the version number when we
54 reuse an SSA_NAME expression. This helps keep arrays and bitmaps
57 We could also use a zone allocator for these objects since they have
58 a very well defined lifetime. If someone wants to experiment with that
59 this is the place to try it. */
61 /* Version numbers with special meanings. We start allocating new version
62 numbers after the special ones. */
63 #define UNUSED_NAME_VERSION 0
65 #ifdef GATHER_STATISTICS
66 unsigned int ssa_name_nodes_reused;
67 unsigned int ssa_name_nodes_created;
70 /* Initialize management of SSA_NAMEs to default SIZE. If SIZE is
74 init_ssanames (struct function *fn, int size)
79 SSANAMES (fn) = VEC_alloc (tree, gc, size);
81 /* Version 0 is special, so reserve the first slot in the table. Though
82 currently unused, we may use version 0 in alias analysis as part of
83 the heuristics used to group aliases when the alias sets are too
86 We use VEC_quick_push here because we know that SSA_NAMES has at
87 least 50 elements reserved in it. */
88 VEC_quick_push (tree, SSANAMES (fn), NULL_TREE);
89 FREE_SSANAMES (fn) = NULL;
91 SYMS_TO_RENAME (fn) = BITMAP_GGC_ALLOC ();
94 /* Finalize management of SSA_NAMEs. */
99 VEC_free (tree, gc, SSANAMES (cfun));
100 FREE_SSANAMES (cfun) = NULL;
103 /* Dump some simple statistics regarding the re-use of SSA_NAME nodes. */
105 #ifdef GATHER_STATISTICS
107 ssanames_print_statistics (void)
109 fprintf (stderr, "SSA_NAME nodes allocated: %u\n", ssa_name_nodes_created);
110 fprintf (stderr, "SSA_NAME nodes reused: %u\n", ssa_name_nodes_reused);
114 /* Return an SSA_NAME node for variable VAR defined in statement STMT
115 in function FN. STMT may be an empty statement for artificial
116 references (e.g., default definitions created when a variable is
117 used without a preceding definition). */
120 make_ssa_name_fn (struct function *fn, tree var, gimple stmt)
125 gcc_assert (DECL_P (var));
127 /* If our free list has an element, then use it. */
128 if (FREE_SSANAMES (fn))
130 t = FREE_SSANAMES (fn);
131 FREE_SSANAMES (fn) = TREE_CHAIN (FREE_SSANAMES (fn));
132 #ifdef GATHER_STATISTICS
133 ssa_name_nodes_reused++;
136 /* The node was cleared out when we put it on the free list, so
137 there is no need to do so again here. */
138 gcc_assert (ssa_name (SSA_NAME_VERSION (t)) == NULL);
139 VEC_replace (tree, SSANAMES (fn), SSA_NAME_VERSION (t), t);
143 t = make_node (SSA_NAME);
144 SSA_NAME_VERSION (t) = VEC_length (tree, SSANAMES (fn));
145 VEC_safe_push (tree, gc, SSANAMES (fn), t);
146 #ifdef GATHER_STATISTICS
147 ssa_name_nodes_created++;
151 TREE_TYPE (t) = TREE_TYPE (var);
152 SSA_NAME_VAR (t) = var;
153 SSA_NAME_DEF_STMT (t) = stmt;
154 SSA_NAME_PTR_INFO (t) = NULL;
155 SSA_NAME_IN_FREE_LIST (t) = 0;
156 SSA_NAME_IS_DEFAULT_DEF (t) = 0;
157 imm = &(SSA_NAME_IMM_USE_NODE (t));
161 imm->loc.ssa_name = t;
167 /* We no longer need the SSA_NAME expression VAR, release it so that
170 Note it is assumed that no calls to make_ssa_name will be made
171 until all uses of the ssa name are released and that the only
172 use of the SSA_NAME expression is to check its SSA_NAME_VAR. All
173 other fields must be assumed clobbered. */
176 release_ssa_name (tree var)
181 /* Never release the default definition for a symbol. It's a
182 special SSA name that should always exist once it's created. */
183 if (SSA_NAME_IS_DEFAULT_DEF (var))
186 /* If VAR has been registered for SSA updating, don't remove it.
187 After update_ssa has run, the name will be released. */
188 if (name_registered_for_update_p (var))
190 release_ssa_name_after_update_ssa (var);
194 /* release_ssa_name can be called multiple times on a single SSA_NAME.
195 However, it should only end up on our free list one time. We
196 keep a status bit in the SSA_NAME node itself to indicate it has
197 been put on the free list.
199 Note that once on the freelist you can not reference the SSA_NAME's
200 defining statement. */
201 if (! SSA_NAME_IN_FREE_LIST (var))
203 tree saved_ssa_name_var = SSA_NAME_VAR (var);
204 int saved_ssa_name_version = SSA_NAME_VERSION (var);
205 use_operand_p imm = &(SSA_NAME_IMM_USE_NODE (var));
207 #ifdef ENABLE_CHECKING
208 verify_imm_links (stderr, var);
210 while (imm->next != imm)
211 delink_imm_use (imm->next);
213 VEC_replace (tree, SSANAMES (cfun),
214 SSA_NAME_VERSION (var), NULL_TREE);
215 memset (var, 0, tree_size (var));
219 imm->loc.ssa_name = var;
221 /* First put back the right tree node so that the tree checking
222 macros do not complain. */
223 TREE_SET_CODE (var, SSA_NAME);
225 /* Restore the version number. */
226 SSA_NAME_VERSION (var) = saved_ssa_name_version;
228 /* Hopefully this can go away once we have the new incremental
229 SSA updating code installed. */
230 SSA_NAME_VAR (var) = saved_ssa_name_var;
232 /* Note this SSA_NAME is now in the first list. */
233 SSA_NAME_IN_FREE_LIST (var) = 1;
235 /* And finally link it into the free list. */
236 TREE_CHAIN (var) = FREE_SSANAMES (cfun);
237 FREE_SSANAMES (cfun) = var;
241 /* Creates a duplicate of a ssa name NAME defined in statement STMT. */
244 duplicate_ssa_name (tree name, gimple stmt)
246 tree new_name = make_ssa_name (SSA_NAME_VAR (name), stmt);
247 struct ptr_info_def *old_ptr_info = SSA_NAME_PTR_INFO (name);
250 duplicate_ssa_name_ptr_info (new_name, old_ptr_info);
256 /* Creates a duplicate of the ptr_info_def at PTR_INFO for use by
257 the SSA name NAME. */
260 duplicate_ssa_name_ptr_info (tree name, struct ptr_info_def *ptr_info)
262 struct ptr_info_def *new_ptr_info;
264 gcc_assert (POINTER_TYPE_P (TREE_TYPE (name)));
265 gcc_assert (!SSA_NAME_PTR_INFO (name));
270 new_ptr_info = GGC_NEW (struct ptr_info_def);
271 *new_ptr_info = *ptr_info;
273 SSA_NAME_PTR_INFO (name) = new_ptr_info;
277 /* Release all the SSA_NAMEs created by STMT. */
280 release_defs (gimple stmt)
285 /* Make sure that we are in SSA. Otherwise, operand cache may point
287 gcc_assert (gimple_in_ssa_p (cfun));
289 FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
290 if (TREE_CODE (def) == SSA_NAME)
291 release_ssa_name (def);
295 /* Replace the symbol associated with SSA_NAME with SYM. */
298 replace_ssa_name_symbol (tree ssa_name, tree sym)
300 SSA_NAME_VAR (ssa_name) = sym;
301 TREE_TYPE (ssa_name) = TREE_TYPE (sym);
304 /* Return SSA names that are unused to GGC memory. This is used to keep
305 footprint of compiler during interprocedural optimization.
306 As a side effect the SSA_NAME_VERSION number reuse is reduced
307 so this function should not be used too often. */
309 release_dead_ssa_names (void)
313 referenced_var_iterator rvi;
315 /* Current defs point to various dead SSA names that in turn points to dead
316 statements so bunch of dead memory is held from releasing. */
317 FOR_EACH_REFERENCED_VAR (t, rvi)
318 set_current_def (t, NULL);
319 /* Now release the freelist. */
320 for (t = FREE_SSANAMES (cfun); t; t = next)
322 next = TREE_CHAIN (t);
323 /* Dangling pointers might make GGC to still see dead SSA names, so it is
324 important to unlink the list and avoid GGC from seeing all subsequent
325 SSA names. In longer run we want to have all dangling pointers here
326 removed (since they usually go through dead statements that consume
327 considerable amounts of memory). */
328 TREE_CHAIN (t) = NULL_TREE;
331 FREE_SSANAMES (cfun) = NULL;
333 /* Cgraph edges has been invalidated and point to dead statement. We need to
334 remove them now and will rebuild it before next IPA pass. */
335 cgraph_node_remove_callees (cgraph_node (current_function_decl));
338 fprintf (dump_file, "Released %i names, %.2f%%\n", n, n * 100.0 / num_ssa_names);
342 struct gimple_opt_pass pass_release_ssa_names =
346 "release_ssa", /* name */
348 release_dead_ssa_names, /* execute */
351 0, /* static_pass_number */
353 PROP_ssa, /* properties_required */
354 0, /* properties_provided */
355 0, /* properties_destroyed */
356 0, /* todo_flags_start */
357 TODO_dump_func /* todo_flags_finish */