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[official-gcc.git] / gcc / tree-ssanames.c
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1 /* Generic routines for manipulating SSA_NAME expressions
2 Copyright (C) 2003, 2004, 2005 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 2, or (at your option)
9 any later version.
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 COPYING. If not, write to
18 the Free Software Foundation, 51 Franklin Street, Fifth Floor,
19 Boston, MA 02110-1301, USA. */
21 #include "config.h"
22 #include "system.h"
23 #include "coretypes.h"
24 #include "tm.h"
25 #include "tree.h"
26 #include "varray.h"
27 #include "ggc.h"
28 #include "tree-flow.h"
29 #include "tree-pass.h"
31 /* Rewriting a function into SSA form can create a huge number of SSA_NAMEs,
32 many of which may be thrown away shortly after their creation if jumps
33 were threaded through PHI nodes.
35 While our garbage collection mechanisms will handle this situation, it
36 is extremely wasteful to create nodes and throw them away, especially
37 when the nodes can be reused.
39 For PR 8361, we can significantly reduce the number of nodes allocated
40 and thus the total amount of memory allocated by managing SSA_NAMEs a
41 little. This additionally helps reduce the amount of work done by the
42 garbage collector. Similar results have been seen on a wider variety
43 of tests (such as the compiler itself).
45 Right now we maintain our free list on a per-function basis. It may
46 or may not make sense to maintain the free list for the duration of
47 a compilation unit.
49 External code should rely solely upon HIGHEST_SSA_VERSION and the
50 externally defined functions. External code should not know about
51 the details of the free list management.
53 External code should also not assume the version number on nodes is
54 monotonically increasing. We reuse the version number when we
55 reuse an SSA_NAME expression. This helps keep arrays and bitmaps
56 more compact.
58 We could also use a zone allocator for these objects since they have
59 a very well defined lifetime. If someone wants to experiment with that
60 this is the place to try it. */
62 /* Version numbers with special meanings. We start allocating new version
63 numbers after the special ones. */
64 #define UNUSED_NAME_VERSION 0
66 #ifdef GATHER_STATISTICS
67 unsigned int ssa_name_nodes_reused;
68 unsigned int ssa_name_nodes_created;
69 #endif
71 /* Initialize management of SSA_NAMEs. */
73 void
74 init_ssanames (void)
76 SSANAMES (cfun) = VEC_alloc (tree, gc, 50);
78 /* Version 0 is special, so reserve the first slot in the table. Though
79 currently unused, we may use version 0 in alias analysis as part of
80 the heuristics used to group aliases when the alias sets are too
81 large.
83 We use VEC_quick_push here because we know that SSA_NAMES has at
84 least 50 elements reserved in it. */
85 VEC_quick_push (tree, SSANAMES (cfun), NULL_TREE);
86 FREE_SSANAMES (cfun) = NULL;
89 /* Finalize management of SSA_NAMEs. */
91 void
92 fini_ssanames (void)
94 VEC_free (tree, gc, SSANAMES (cfun));
95 FREE_SSANAMES (cfun) = NULL;
98 /* Dump some simple statistics regarding the re-use of SSA_NAME nodes. */
100 #ifdef GATHER_STATISTICS
101 void
102 ssanames_print_statistics (void)
104 fprintf (stderr, "SSA_NAME nodes allocated: %u\n", ssa_name_nodes_created);
105 fprintf (stderr, "SSA_NAME nodes reused: %u\n", ssa_name_nodes_reused);
107 #endif
109 /* Return an SSA_NAME node for variable VAR defined in statement STMT.
110 STMT may be an empty statement for artificial references (e.g., default
111 definitions created when a variable is used without a preceding
112 definition). */
114 tree
115 make_ssa_name (tree var, tree stmt)
117 tree t;
118 use_operand_p imm;
120 gcc_assert (DECL_P (var)
121 || TREE_CODE (var) == INDIRECT_REF);
123 gcc_assert (!stmt
124 || EXPR_P (stmt) || GIMPLE_STMT_P (stmt)
125 || TREE_CODE (stmt) == PHI_NODE);
127 /* If our free list has an element, then use it. */
128 if (FREE_SSANAMES (cfun))
130 t = FREE_SSANAMES (cfun);
131 FREE_SSANAMES (cfun) = TREE_CHAIN (FREE_SSANAMES (cfun));
132 #ifdef GATHER_STATISTICS
133 ssa_name_nodes_reused++;
134 #endif
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 (cfun), SSA_NAME_VERSION (t), t);
141 else
143 t = make_node (SSA_NAME);
144 SSA_NAME_VERSION (t) = num_ssa_names;
145 VEC_safe_push (tree, gc, SSANAMES (cfun), t);
146 #ifdef GATHER_STATISTICS
147 ssa_name_nodes_created++;
148 #endif
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));
158 imm->use = NULL;
159 imm->prev = imm;
160 imm->next = imm;
161 imm->stmt = t;
163 return t;
167 /* We no longer need the SSA_NAME expression VAR, release it so that
168 it may be reused.
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. */
175 void
176 release_ssa_name (tree var)
178 if (!var)
179 return;
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))
184 return;
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);
191 return;
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);
209 #endif
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));
217 imm->prev = imm;
218 imm->next = imm;
219 imm->stmt = var;
220 /* First put back the right tree node so that the tree checking
221 macros do not complain. */
222 TREE_SET_CODE (var, SSA_NAME);
224 /* Restore the version number. */
225 SSA_NAME_VERSION (var) = saved_ssa_name_version;
227 /* Hopefully this can go away once we have the new incremental
228 SSA updating code installed. */
229 SSA_NAME_VAR (var) = saved_ssa_name_var;
231 /* Note this SSA_NAME is now in the first list. */
232 SSA_NAME_IN_FREE_LIST (var) = 1;
234 /* And finally link it into the free list. */
235 TREE_CHAIN (var) = FREE_SSANAMES (cfun);
236 FREE_SSANAMES (cfun) = var;
240 /* Creates a duplicate of a ssa name NAME defined in statement STMT. */
242 tree
243 duplicate_ssa_name (tree name, tree stmt)
245 tree new_name = make_ssa_name (SSA_NAME_VAR (name), stmt);
246 struct ptr_info_def *old_ptr_info = SSA_NAME_PTR_INFO (name);
248 if (old_ptr_info)
249 duplicate_ssa_name_ptr_info (new_name, old_ptr_info);
251 return new_name;
255 /* Creates a duplicate of the ptr_info_def at PTR_INFO for use by
256 the SSA name NAME. */
258 void
259 duplicate_ssa_name_ptr_info (tree name, struct ptr_info_def *ptr_info)
261 struct ptr_info_def *new_ptr_info;
263 gcc_assert (POINTER_TYPE_P (TREE_TYPE (name)));
264 gcc_assert (!SSA_NAME_PTR_INFO (name));
266 if (!ptr_info)
267 return;
269 new_ptr_info = ggc_alloc (sizeof (struct ptr_info_def));
270 *new_ptr_info = *ptr_info;
272 if (ptr_info->pt_vars)
274 new_ptr_info->pt_vars = BITMAP_GGC_ALLOC ();
275 bitmap_copy (new_ptr_info->pt_vars, ptr_info->pt_vars);
278 SSA_NAME_PTR_INFO (name) = new_ptr_info;
282 /* Release all the SSA_NAMEs created by STMT. */
284 void
285 release_defs (tree stmt)
287 tree def;
288 ssa_op_iter iter;
290 /* Make sure that we are in SSA. Otherwise, operand cache may point
291 to garbage. */
292 gcc_assert (gimple_in_ssa_p (cfun));
294 FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
295 if (TREE_CODE (def) == SSA_NAME)
296 release_ssa_name (def);
300 /* Replace the symbol associated with SSA_NAME with SYM. */
302 void
303 replace_ssa_name_symbol (tree ssa_name, tree sym)
305 SSA_NAME_VAR (ssa_name) = sym;
306 TREE_TYPE (ssa_name) = TREE_TYPE (sym);
309 /* Return SSA names that are unused to GGC memory. This is used to keep
310 footprint of compiler during interprocedural optimization.
311 As a side effect the SSA_NAME_VERSION number reuse is reduced
312 so this function should not be used too often. */
313 static unsigned int
314 release_dead_ssa_names (void)
316 tree t, next;
317 int n = 0;
318 referenced_var_iterator rvi;
320 /* Current defs point to various dead SSA names that in turn points to dead
321 statements so bunch of dead memory is held from releasing. */
322 FOR_EACH_REFERENCED_VAR (t, rvi)
323 set_current_def (t, NULL);
324 /* Now release the freelist. */
325 for (t = FREE_SSANAMES (cfun); t; t = next)
327 next = TREE_CHAIN (t);
328 /* Dangling pointers might make GGC to still see dead SSA names, so it is
329 important to unlink the list and avoid GGC from seeing all subsequent
330 SSA names. In longer run we want to have all dangling pointers here
331 removed (since they usually go through dead statements that consume
332 considerable amounts of memory). */
333 TREE_CHAIN (t) = NULL_TREE;
334 n++;
336 FREE_SSANAMES (cfun) = NULL;
338 /* Cgraph edges has been invalidated and point to dead statement. We need to
339 remove them now and will rebuild it before next IPA pass. */
340 cgraph_node_remove_callees (cgraph_node (current_function_decl));
342 if (dump_file)
343 fprintf (dump_file, "Released %i names, %.2f%%\n", n, n * 100.0 / num_ssa_names);
344 return 0;
347 struct tree_opt_pass pass_release_ssa_names =
349 "release_ssa", /* name */
350 NULL, /* gate */
351 release_dead_ssa_names, /* execute */
352 NULL, /* sub */
353 NULL, /* next */
354 0, /* static_pass_number */
355 0, /* tv_id */
356 PROP_ssa, /* properties_required */
357 0, /* properties_provided */
358 0, /* properties_destroyed */
359 0, /* todo_flags_start */
360 0, /* todo_flags_finish */
361 0 /* letter */