1 /* Generic routines for manipulating SSA_NAME expressions 2 Copyright (C) 2003, 2004, 2005, 2007, 2008, 2009 3 Free Software Foundation, Inc. 4 5 This file is part of GCC. 6 7 GCC is free software; you can redistribute it and/or modify 8 it under the terms of the GNU General Public License as published by 9 the Free Software Foundation; either version 3, or (at your option) 10 any later version. 11 12 GCC is distributed in the hope that it will be useful, 13 but WITHOUT ANY WARRANTY; without even the implied warranty of 14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 15 GNU General Public License for more details. 16 17 You should have received a copy of the GNU General Public License 18 along with GCC; see the file COPYING3. If not see 19 <http://www.gnu.org/licenses/>. */ 20 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" 30 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. 34 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. 38 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). 44 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. 48 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. 52 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. 57 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. */ 61 62 /* Version numbers with special meanings. We start allocating new version 63 numbers after the special ones. */ 64 #define UNUSED_NAME_VERSION 0 65 66 #ifdef GATHER_STATISTICS 67 unsigned int ssa_name_nodes_reused; 68 unsigned int ssa_name_nodes_created; 69 #endif 70 71 /* Initialize management of SSA_NAMEs to default SIZE. If SIZE is 72 zero use default. */ 73 74 void 75 init_ssanames (struct function *fn, int size) 76 { 77 if (size < 50) 78 size = 50; 79 80 SSANAMES (fn) = VEC_alloc (tree, gc, size); 81 82 /* Version 0 is special, so reserve the first slot in the table. Though 83 currently unused, we may use version 0 in alias analysis as part of 84 the heuristics used to group aliases when the alias sets are too 85 large. 86 87 We use VEC_quick_push here because we know that SSA_NAMES has at 88 least 50 elements reserved in it. */ 89 VEC_quick_push (tree, SSANAMES (fn), NULL_TREE); 90 FREE_SSANAMES (fn) = NULL; 91 92 SYMS_TO_RENAME (fn) = BITMAP_GGC_ALLOC (); 93 } 94 95 /* Finalize management of SSA_NAMEs. */ 96 97 void 98 fini_ssanames (void) 99 { 100 VEC_free (tree, gc, SSANAMES (cfun)); 101 FREE_SSANAMES (cfun) = NULL; 102 } 103 104 /* Dump some simple statistics regarding the re-use of SSA_NAME nodes. */ 105 106 #ifdef GATHER_STATISTICS 107 void 108 ssanames_print_statistics (void) 109 { 110 fprintf (stderr, "SSA_NAME nodes allocated: %u\n", ssa_name_nodes_created); 111 fprintf (stderr, "SSA_NAME nodes reused: %u\n", ssa_name_nodes_reused); 112 } 113 #endif 114 115 /* Return an SSA_NAME node for variable VAR defined in statement STMT 116 in function FN. STMT may be an empty statement for artificial 117 references (e.g., default definitions created when a variable is 118 used without a preceding definition). */ 119 120 tree 121 make_ssa_name_fn (struct function *fn, tree var, gimple stmt) 122 { 123 tree t; 124 use_operand_p imm; 125 126 gcc_assert (DECL_P (var)); 127 128 /* If our free list has an element, then use it. */ 129 if (FREE_SSANAMES (fn)) 130 { 131 t = FREE_SSANAMES (fn); 132 FREE_SSANAMES (fn) = TREE_CHAIN (FREE_SSANAMES (fn)); 133 #ifdef GATHER_STATISTICS 134 ssa_name_nodes_reused++; 135 #endif 136 137 /* The node was cleared out when we put it on the free list, so 138 there is no need to do so again here. */ 139 gcc_assert (ssa_name (SSA_NAME_VERSION (t)) == NULL); 140 VEC_replace (tree, SSANAMES (fn), SSA_NAME_VERSION (t), t); 141 } 142 else 143 { 144 t = make_node (SSA_NAME); 145 SSA_NAME_VERSION (t) = VEC_length (tree, SSANAMES (fn)); 146 VEC_safe_push (tree, gc, SSANAMES (fn), t); 147 #ifdef GATHER_STATISTICS 148 ssa_name_nodes_created++; 149 #endif 150 } 151 152 TREE_TYPE (t) = TREE_TYPE (var); 153 SSA_NAME_VAR (t) = var; 154 SSA_NAME_DEF_STMT (t) = stmt; 155 SSA_NAME_PTR_INFO (t) = NULL; 156 SSA_NAME_IN_FREE_LIST (t) = 0; 157 SSA_NAME_IS_DEFAULT_DEF (t) = 0; 158 imm = &(SSA_NAME_IMM_USE_NODE (t)); 159 imm->use = NULL; 160 imm->prev = imm; 161 imm->next = imm; 162 imm->loc.ssa_name = t; 163 164 return t; 165 } 166 167 168 /* We no longer need the SSA_NAME expression VAR, release it so that 169 it may be reused. 170 171 Note it is assumed that no calls to make_ssa_name will be made 172 until all uses of the ssa name are released and that the only 173 use of the SSA_NAME expression is to check its SSA_NAME_VAR. All 174 other fields must be assumed clobbered. */ 175 176 void 177 release_ssa_name (tree var) 178 { 179 if (!var) 180 return; 181 182 /* Never release the default definition for a symbol. It's a 183 special SSA name that should always exist once it's created. */ 184 if (SSA_NAME_IS_DEFAULT_DEF (var)) 185 return; 186 187 /* If VAR has been registered for SSA updating, don't remove it. 188 After update_ssa has run, the name will be released. */ 189 if (name_registered_for_update_p (var)) 190 { 191 release_ssa_name_after_update_ssa (var); 192 return; 193 } 194 195 /* release_ssa_name can be called multiple times on a single SSA_NAME. 196 However, it should only end up on our free list one time. We 197 keep a status bit in the SSA_NAME node itself to indicate it has 198 been put on the free list. 199 200 Note that once on the freelist you can not reference the SSA_NAME's 201 defining statement. */ 202 if (! SSA_NAME_IN_FREE_LIST (var)) 203 { 204 tree saved_ssa_name_var = SSA_NAME_VAR (var); 205 int saved_ssa_name_version = SSA_NAME_VERSION (var); 206 use_operand_p imm = &(SSA_NAME_IMM_USE_NODE (var)); 207 208 if (MAY_HAVE_DEBUG_STMTS) 209 insert_debug_temp_for_var_def (NULL, var); 210 211 #ifdef ENABLE_CHECKING 212 verify_imm_links (stderr, var); 213 #endif 214 while (imm->next != imm) 215 delink_imm_use (imm->next); 216 217 VEC_replace (tree, SSANAMES (cfun), 218 SSA_NAME_VERSION (var), NULL_TREE); 219 memset (var, 0, tree_size (var)); 220 221 imm->prev = imm; 222 imm->next = imm; 223 imm->loc.ssa_name = var; 224 225 /* First put back the right tree node so that the tree checking 226 macros do not complain. */ 227 TREE_SET_CODE (var, SSA_NAME); 228 229 /* Restore the version number. */ 230 SSA_NAME_VERSION (var) = saved_ssa_name_version; 231 232 /* Hopefully this can go away once we have the new incremental 233 SSA updating code installed. */ 234 SSA_NAME_VAR (var) = saved_ssa_name_var; 235 236 /* Note this SSA_NAME is now in the first list. */ 237 SSA_NAME_IN_FREE_LIST (var) = 1; 238 239 /* And finally link it into the free list. */ 240 TREE_CHAIN (var) = FREE_SSANAMES (cfun); 241 FREE_SSANAMES (cfun) = var; 242 } 243 } 244 245 /* Creates a duplicate of a ssa name NAME defined in statement STMT. */ 246 247 tree 248 duplicate_ssa_name (tree name, gimple stmt) 249 { 250 tree new_name = make_ssa_name (SSA_NAME_VAR (name), stmt); 251 struct ptr_info_def *old_ptr_info = SSA_NAME_PTR_INFO (name); 252 253 if (old_ptr_info) 254 duplicate_ssa_name_ptr_info (new_name, old_ptr_info); 255 256 return new_name; 257 } 258 259 260 /* Creates a duplicate of the ptr_info_def at PTR_INFO for use by 261 the SSA name NAME. */ 262 263 void 264 duplicate_ssa_name_ptr_info (tree name, struct ptr_info_def *ptr_info) 265 { 266 struct ptr_info_def *new_ptr_info; 267 268 gcc_assert (POINTER_TYPE_P (TREE_TYPE (name))); 269 gcc_assert (!SSA_NAME_PTR_INFO (name)); 270 271 if (!ptr_info) 272 return; 273 274 new_ptr_info = GGC_NEW (struct ptr_info_def); 275 *new_ptr_info = *ptr_info; 276 277 SSA_NAME_PTR_INFO (name) = new_ptr_info; 278 } 279 280 281 /* Release all the SSA_NAMEs created by STMT. */ 282 283 void 284 release_defs (gimple stmt) 285 { 286 tree def; 287 ssa_op_iter iter; 288 289 /* Make sure that we are in SSA. Otherwise, operand cache may point 290 to garbage. */ 291 gcc_assert (gimple_in_ssa_p (cfun)); 292 293 FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS) 294 if (TREE_CODE (def) == SSA_NAME) 295 release_ssa_name (def); 296 } 297 298 299 /* Replace the symbol associated with SSA_NAME with SYM. */ 300 301 void 302 replace_ssa_name_symbol (tree ssa_name, tree sym) 303 { 304 SSA_NAME_VAR (ssa_name) = sym; 305 TREE_TYPE (ssa_name) = TREE_TYPE (sym); 306 } 307 308 /* Return SSA names that are unused to GGC memory. This is used to keep 309 footprint of compiler during interprocedural optimization. 310 As a side effect the SSA_NAME_VERSION number reuse is reduced 311 so this function should not be used too often. */ 312 static unsigned int 313 release_dead_ssa_names (void) 314 { 315 tree t, next; 316 int n = 0; 317 referenced_var_iterator rvi; 318 319 /* Current defs point to various dead SSA names that in turn points to dead 320 statements so bunch of dead memory is held from releasing. */ 321 FOR_EACH_REFERENCED_VAR (t, rvi) 322 set_current_def (t, NULL); 323 /* Now release the freelist. */ 324 for (t = FREE_SSANAMES (cfun); t; t = next) 325 { 326 next = TREE_CHAIN (t); 327 /* Dangling pointers might make GGC to still see dead SSA names, so it is 328 important to unlink the list and avoid GGC from seeing all subsequent 329 SSA names. In longer run we want to have all dangling pointers here 330 removed (since they usually go through dead statements that consume 331 considerable amounts of memory). */ 332 TREE_CHAIN (t) = NULL_TREE; 333 n++; 334 } 335 FREE_SSANAMES (cfun) = NULL; 336 337 /* Cgraph edges has been invalidated and point to dead statement. We need to 338 remove them now and will rebuild it before next IPA pass. */ 339 cgraph_node_remove_callees (cgraph_node (current_function_decl)); 340 341 if (dump_file) 342 fprintf (dump_file, "Released %i names, %.2f%%\n", n, n * 100.0 / num_ssa_names); 343 return 0; 344 } 345 346 struct gimple_opt_pass pass_release_ssa_names = 347 { 348 { 349 GIMPLE_PASS, 350 "release_ssa", /* name */ 351 NULL, /* gate */ 352 release_dead_ssa_names, /* execute */ 353 NULL, /* sub */ 354 NULL, /* next */ 355 0, /* static_pass_number */ 356 TV_NONE, /* tv_id */ 357 PROP_ssa, /* properties_required */ 358 0, /* properties_provided */ 359 0, /* properties_destroyed */ 360 0, /* todo_flags_start */ 361 TODO_dump_func /* todo_flags_finish */ 362 } 363 }; 364