1 /* Generic routines for manipulating SSA_NAME expressions 2 Copyright (C) 2003-2013 Free Software Foundation, Inc. 3 4 This file is part of GCC. 5 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) 9 any later version. 10 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. 15 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/>. */ 19 20 #include "config.h" 21 #include "system.h" 22 #include "coretypes.h" 23 #include "tm.h" 24 #include "tree.h" 25 #include "tree-flow.h" 26 #include "tree-pass.h" 27 28 /* Rewriting a function into SSA form can create a huge number of SSA_NAMEs, 29 many of which may be thrown away shortly after their creation if jumps 30 were threaded through PHI nodes. 31 32 While our garbage collection mechanisms will handle this situation, it 33 is extremely wasteful to create nodes and throw them away, especially 34 when the nodes can be reused. 35 36 For PR 8361, we can significantly reduce the number of nodes allocated 37 and thus the total amount of memory allocated by managing SSA_NAMEs a 38 little. This additionally helps reduce the amount of work done by the 39 garbage collector. Similar results have been seen on a wider variety 40 of tests (such as the compiler itself). 41 42 Right now we maintain our free list on a per-function basis. It may 43 or may not make sense to maintain the free list for the duration of 44 a compilation unit. 45 46 External code should rely solely upon HIGHEST_SSA_VERSION and the 47 externally defined functions. External code should not know about 48 the details of the free list management. 49 50 External code should also not assume the version number on nodes is 51 monotonically increasing. We reuse the version number when we 52 reuse an SSA_NAME expression. This helps keep arrays and bitmaps 53 more compact. */ 54 55 56 /* Version numbers with special meanings. We start allocating new version 57 numbers after the special ones. */ 58 #define UNUSED_NAME_VERSION 0 59 60 unsigned int ssa_name_nodes_reused; 61 unsigned int ssa_name_nodes_created; 62 63 /* Initialize management of SSA_NAMEs to default SIZE. If SIZE is 64 zero use default. */ 65 66 void 67 init_ssanames (struct function *fn, int size) 68 { 69 if (size < 50) 70 size = 50; 71 72 vec_alloc (SSANAMES (fn), size); 73 74 /* Version 0 is special, so reserve the first slot in the table. Though 75 currently unused, we may use version 0 in alias analysis as part of 76 the heuristics used to group aliases when the alias sets are too 77 large. 78 79 We use vec::quick_push here because we know that SSA_NAMES has at 80 least 50 elements reserved in it. */ 81 SSANAMES (fn)->quick_push (NULL_TREE); 82 FREE_SSANAMES (fn) = NULL; 83 84 fn->gimple_df->ssa_renaming_needed = 0; 85 fn->gimple_df->rename_vops = 0; 86 } 87 88 /* Finalize management of SSA_NAMEs. */ 89 90 void 91 fini_ssanames (void) 92 { 93 vec_free (SSANAMES (cfun)); 94 vec_free (FREE_SSANAMES (cfun)); 95 } 96 97 /* Dump some simple statistics regarding the re-use of SSA_NAME nodes. */ 98 99 void 100 ssanames_print_statistics (void) 101 { 102 fprintf (stderr, "SSA_NAME nodes allocated: %u\n", ssa_name_nodes_created); 103 fprintf (stderr, "SSA_NAME nodes reused: %u\n", ssa_name_nodes_reused); 104 } 105 106 /* Return an SSA_NAME node for variable VAR defined in statement STMT 107 in function FN. STMT may be an empty statement for artificial 108 references (e.g., default definitions created when a variable is 109 used without a preceding definition). */ 110 111 tree 112 make_ssa_name_fn (struct function *fn, tree var, gimple stmt) 113 { 114 tree t; 115 use_operand_p imm; 116 117 gcc_assert (TREE_CODE (var) == VAR_DECL 118 || TREE_CODE (var) == PARM_DECL 119 || TREE_CODE (var) == RESULT_DECL 120 || (TYPE_P (var) && is_gimple_reg_type (var))); 121 122 /* If our free list has an element, then use it. */ 123 if (!vec_safe_is_empty (FREE_SSANAMES (fn))) 124 { 125 t = FREE_SSANAMES (fn)->pop (); 126 if (GATHER_STATISTICS) 127 ssa_name_nodes_reused++; 128 129 /* The node was cleared out when we put it on the free list, so 130 there is no need to do so again here. */ 131 gcc_assert ((*SSANAMES (fn))[SSA_NAME_VERSION (t)] == NULL); 132 (*SSANAMES (fn))[SSA_NAME_VERSION (t)] = t; 133 } 134 else 135 { 136 t = make_node (SSA_NAME); 137 SSA_NAME_VERSION (t) = SSANAMES (fn)->length (); 138 vec_safe_push (SSANAMES (fn), t); 139 if (GATHER_STATISTICS) 140 ssa_name_nodes_created++; 141 } 142 143 if (TYPE_P (var)) 144 { 145 TREE_TYPE (t) = var; 146 SET_SSA_NAME_VAR_OR_IDENTIFIER (t, NULL_TREE); 147 } 148 else 149 { 150 TREE_TYPE (t) = TREE_TYPE (var); 151 SET_SSA_NAME_VAR_OR_IDENTIFIER (t, var); 152 } 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->loc.ssa_name = t; 162 163 return t; 164 } 165 166 167 /* We no longer need the SSA_NAME expression VAR, release it so that 168 it may be reused. 169 170 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. */ 174 175 void 176 release_ssa_name (tree var) 177 { 178 if (!var) 179 return; 180 181 /* 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; 185 186 /* 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)) 189 { 190 release_ssa_name_after_update_ssa (var); 191 return; 192 } 193 194 /* 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. 198 199 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)) 202 { 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)); 206 207 if (MAY_HAVE_DEBUG_STMTS) 208 insert_debug_temp_for_var_def (NULL, var); 209 210 #ifdef ENABLE_CHECKING 211 verify_imm_links (stderr, var); 212 #endif 213 while (imm->next != imm) 214 delink_imm_use (imm->next); 215 216 (*SSANAMES (cfun))[SSA_NAME_VERSION (var)] = NULL_TREE; 217 memset (var, 0, tree_size (var)); 218 219 imm->prev = imm; 220 imm->next = imm; 221 imm->loc.ssa_name = var; 222 223 /* First put back the right tree node so that the tree checking 224 macros do not complain. */ 225 TREE_SET_CODE (var, SSA_NAME); 226 227 /* Restore the version number. */ 228 SSA_NAME_VERSION (var) = saved_ssa_name_version; 229 230 /* Hopefully this can go away once we have the new incremental 231 SSA updating code installed. */ 232 SET_SSA_NAME_VAR_OR_IDENTIFIER (var, saved_ssa_name_var); 233 234 /* Note this SSA_NAME is now in the first list. */ 235 SSA_NAME_IN_FREE_LIST (var) = 1; 236 237 /* And finally put it on the free list. */ 238 vec_safe_push (FREE_SSANAMES (cfun), var); 239 } 240 } 241 242 /* If the alignment of the pointer described by PI is known, return true and 243 store the alignment and the deviation from it into *ALIGNP and *MISALIGNP 244 respectively. Otherwise return false. */ 245 246 bool 247 get_ptr_info_alignment (struct ptr_info_def *pi, unsigned int *alignp, 248 unsigned int *misalignp) 249 { 250 if (pi->align) 251 { 252 *alignp = pi->align; 253 *misalignp = pi->misalign; 254 return true; 255 } 256 else 257 return false; 258 } 259 260 /* State that the pointer described by PI has unknown alignment. */ 261 262 void 263 mark_ptr_info_alignment_unknown (struct ptr_info_def *pi) 264 { 265 pi->align = 0; 266 pi->misalign = 0; 267 } 268 269 /* Store the the power-of-two byte alignment and the deviation from that 270 alignment of pointer described by PI to ALIOGN and MISALIGN 271 respectively. */ 272 273 void 274 set_ptr_info_alignment (struct ptr_info_def *pi, unsigned int align, 275 unsigned int misalign) 276 { 277 gcc_checking_assert (align != 0); 278 gcc_assert ((align & (align - 1)) == 0); 279 gcc_assert ((misalign & ~(align - 1)) == 0); 280 281 pi->align = align; 282 pi->misalign = misalign; 283 } 284 285 /* If pointer described by PI has known alignment, increase its known 286 misalignment by INCREMENT modulo its current alignment. */ 287 288 void 289 adjust_ptr_info_misalignment (struct ptr_info_def *pi, 290 unsigned int increment) 291 { 292 if (pi->align != 0) 293 { 294 pi->misalign += increment; 295 pi->misalign &= (pi->align - 1); 296 } 297 } 298 299 /* Return the alias information associated with pointer T. It creates a 300 new instance if none existed. */ 301 302 struct ptr_info_def * 303 get_ptr_info (tree t) 304 { 305 struct ptr_info_def *pi; 306 307 gcc_assert (POINTER_TYPE_P (TREE_TYPE (t))); 308 309 pi = SSA_NAME_PTR_INFO (t); 310 if (pi == NULL) 311 { 312 pi = ggc_alloc_cleared_ptr_info_def (); 313 pt_solution_reset (&pi->pt); 314 mark_ptr_info_alignment_unknown (pi); 315 SSA_NAME_PTR_INFO (t) = pi; 316 } 317 318 return pi; 319 } 320 321 322 /* Creates a new SSA name using the template NAME tobe defined by 323 statement STMT in function FN. */ 324 325 tree 326 copy_ssa_name_fn (struct function *fn, tree name, gimple stmt) 327 { 328 tree new_name; 329 330 if (SSA_NAME_VAR (name)) 331 new_name = make_ssa_name_fn (fn, SSA_NAME_VAR (name), stmt); 332 else 333 { 334 new_name = make_ssa_name_fn (fn, TREE_TYPE (name), stmt); 335 SET_SSA_NAME_VAR_OR_IDENTIFIER (new_name, SSA_NAME_IDENTIFIER (name)); 336 } 337 338 return new_name; 339 } 340 341 342 /* Creates a duplicate of the ptr_info_def at PTR_INFO for use by 343 the SSA name NAME. */ 344 345 void 346 duplicate_ssa_name_ptr_info (tree name, struct ptr_info_def *ptr_info) 347 { 348 struct ptr_info_def *new_ptr_info; 349 350 gcc_assert (POINTER_TYPE_P (TREE_TYPE (name))); 351 gcc_assert (!SSA_NAME_PTR_INFO (name)); 352 353 if (!ptr_info) 354 return; 355 356 new_ptr_info = ggc_alloc_ptr_info_def (); 357 *new_ptr_info = *ptr_info; 358 359 SSA_NAME_PTR_INFO (name) = new_ptr_info; 360 } 361 362 363 /* Creates a duplicate of a ssa name NAME tobe defined by statement STMT 364 in function FN. */ 365 366 tree 367 duplicate_ssa_name_fn (struct function *fn, tree name, gimple stmt) 368 { 369 tree new_name = copy_ssa_name_fn (fn, name, stmt); 370 struct ptr_info_def *old_ptr_info = SSA_NAME_PTR_INFO (name); 371 372 if (old_ptr_info) 373 duplicate_ssa_name_ptr_info (new_name, old_ptr_info); 374 375 return new_name; 376 } 377 378 379 /* Release all the SSA_NAMEs created by STMT. */ 380 381 void 382 release_defs (gimple stmt) 383 { 384 tree def; 385 ssa_op_iter iter; 386 387 /* Make sure that we are in SSA. Otherwise, operand cache may point 388 to garbage. */ 389 gcc_assert (gimple_in_ssa_p (cfun)); 390 391 FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS) 392 if (TREE_CODE (def) == SSA_NAME) 393 release_ssa_name (def); 394 } 395 396 397 /* Replace the symbol associated with SSA_NAME with SYM. */ 398 399 void 400 replace_ssa_name_symbol (tree ssa_name, tree sym) 401 { 402 SET_SSA_NAME_VAR_OR_IDENTIFIER (ssa_name, sym); 403 TREE_TYPE (ssa_name) = TREE_TYPE (sym); 404 } 405 406 /* Return SSA names that are unused to GGC memory and compact the SSA 407 version namespace. This is used to keep footprint of compiler during 408 interprocedural optimization. */ 409 static unsigned int 410 release_dead_ssa_names (void) 411 { 412 unsigned i, j; 413 int n = vec_safe_length (FREE_SSANAMES (cfun)); 414 415 /* Now release the freelist. */ 416 vec_free (FREE_SSANAMES (cfun)); 417 418 /* And compact the SSA number space. We make sure to not change the 419 relative order of SSA versions. */ 420 for (i = 1, j = 1; i < cfun->gimple_df->ssa_names->length (); ++i) 421 { 422 tree name = ssa_name (i); 423 if (name) 424 { 425 if (i != j) 426 { 427 SSA_NAME_VERSION (name) = j; 428 (*cfun->gimple_df->ssa_names)[j] = name; 429 } 430 j++; 431 } 432 } 433 cfun->gimple_df->ssa_names->truncate (j); 434 435 statistics_counter_event (cfun, "SSA names released", n); 436 statistics_counter_event (cfun, "SSA name holes removed", i - j); 437 if (dump_file) 438 fprintf (dump_file, "Released %i names, %.2f%%, removed %i holes\n", 439 n, n * 100.0 / num_ssa_names, i - j); 440 return 0; 441 } 442 443 struct gimple_opt_pass pass_release_ssa_names = 444 { 445 { 446 GIMPLE_PASS, 447 "release_ssa", /* name */ 448 OPTGROUP_NONE, /* optinfo_flags */ 449 NULL, /* gate */ 450 release_dead_ssa_names, /* execute */ 451 NULL, /* sub */ 452 NULL, /* next */ 453 0, /* static_pass_number */ 454 TV_TREE_SSA_OTHER, /* tv_id */ 455 PROP_ssa, /* properties_required */ 456 0, /* properties_provided */ 457 0, /* properties_destroyed */ 458 TODO_remove_unused_locals, /* todo_flags_start */ 459 0 /* todo_flags_finish */ 460 } 461 }; 462