Mercurial > hg > CbC > CbC_gcc
annotate gcc/tree-ssa-copy.c @ 59:5b5b9ea5b220
fix
| author | Shinji KONO <kono@ie.u-ryukyu.ac.jp> |
|---|---|
| date | Mon, 15 Feb 2010 17:22:24 +0900 |
| parents | 77e2b8dfacca |
| children | b7f97abdc517 |
| rev | line source |
|---|---|
| 0 | 1 /* Copy propagation and SSA_NAME replacement support routines. |
| 2 Copyright (C) 2004, 2005, 2006, 2007, 2008 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 "flags.h" | |
| 26 #include "rtl.h" | |
| 27 #include "tm_p.h" | |
| 28 #include "ggc.h" | |
| 29 #include "basic-block.h" | |
| 30 #include "output.h" | |
| 31 #include "expr.h" | |
| 32 #include "function.h" | |
| 33 #include "diagnostic.h" | |
| 34 #include "timevar.h" | |
| 35 #include "tree-dump.h" | |
| 36 #include "tree-flow.h" | |
| 37 #include "tree-pass.h" | |
| 38 #include "tree-ssa-propagate.h" | |
| 39 #include "langhooks.h" | |
|
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40 #include "cfgloop.h" |
| 0 | 41 |
| 42 /* This file implements the copy propagation pass and provides a | |
| 43 handful of interfaces for performing const/copy propagation and | |
| 44 simple expression replacement which keep variable annotations | |
| 45 up-to-date. | |
| 46 | |
| 47 We require that for any copy operation where the RHS and LHS have | |
| 48 a non-null memory tag the memory tag be the same. It is OK | |
| 49 for one or both of the memory tags to be NULL. | |
| 50 | |
| 51 We also require tracking if a variable is dereferenced in a load or | |
| 52 store operation. | |
| 53 | |
| 54 We enforce these requirements by having all copy propagation and | |
| 55 replacements of one SSA_NAME with a different SSA_NAME to use the | |
| 56 APIs defined in this file. */ | |
| 57 | |
| 58 /* Return true if we may propagate ORIG into DEST, false otherwise. */ | |
| 59 | |
| 60 bool | |
| 61 may_propagate_copy (tree dest, tree orig) | |
| 62 { | |
| 63 tree type_d = TREE_TYPE (dest); | |
| 64 tree type_o = TREE_TYPE (orig); | |
| 65 | |
| 66 /* If ORIG flows in from an abnormal edge, it cannot be propagated. */ | |
| 67 if (TREE_CODE (orig) == SSA_NAME | |
| 68 && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (orig)) | |
| 69 return false; | |
| 70 | |
| 71 /* If DEST is an SSA_NAME that flows from an abnormal edge, then it | |
| 72 cannot be replaced. */ | |
| 73 if (TREE_CODE (dest) == SSA_NAME | |
| 74 && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (dest)) | |
| 75 return false; | |
| 76 | |
| 77 /* Do not copy between types for which we *do* need a conversion. */ | |
| 78 if (!useless_type_conversion_p (type_d, type_o)) | |
| 79 return false; | |
| 80 | |
|
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81 /* Propagating virtual operands is always ok. */ |
| 0 | 82 if (TREE_CODE (dest) == SSA_NAME && !is_gimple_reg (dest)) |
| 83 { | |
|
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84 /* But only between virtual operands. */ |
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85 gcc_assert (TREE_CODE (orig) == SSA_NAME && !is_gimple_reg (orig)); |
| 0 | 86 |
|
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87 return true; |
| 0 | 88 } |
| 89 | |
| 90 /* Anything else is OK. */ | |
| 91 return true; | |
| 92 } | |
| 93 | |
| 94 /* Like may_propagate_copy, but use as the destination expression | |
| 95 the principal expression (typically, the RHS) contained in | |
| 96 statement DEST. This is more efficient when working with the | |
| 97 gimple tuples representation. */ | |
| 98 | |
| 99 bool | |
| 100 may_propagate_copy_into_stmt (gimple dest, tree orig) | |
| 101 { | |
| 102 tree type_d; | |
| 103 tree type_o; | |
| 104 | |
| 105 /* If the statement is a switch or a single-rhs assignment, | |
| 106 then the expression to be replaced by the propagation may | |
| 107 be an SSA_NAME. Fortunately, there is an explicit tree | |
| 108 for the expression, so we delegate to may_propagate_copy. */ | |
| 109 | |
| 110 if (gimple_assign_single_p (dest)) | |
| 111 return may_propagate_copy (gimple_assign_rhs1 (dest), orig); | |
| 112 else if (gimple_code (dest) == GIMPLE_SWITCH) | |
| 113 return may_propagate_copy (gimple_switch_index (dest), orig); | |
| 114 | |
| 115 /* In other cases, the expression is not materialized, so there | |
| 116 is no destination to pass to may_propagate_copy. On the other | |
| 117 hand, the expression cannot be an SSA_NAME, so the analysis | |
| 118 is much simpler. */ | |
| 119 | |
| 120 if (TREE_CODE (orig) == SSA_NAME | |
|
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121 && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (orig)) |
| 0 | 122 return false; |
| 123 | |
| 124 if (is_gimple_assign (dest)) | |
| 125 type_d = TREE_TYPE (gimple_assign_lhs (dest)); | |
| 126 else if (gimple_code (dest) == GIMPLE_COND) | |
| 127 type_d = boolean_type_node; | |
| 128 else if (is_gimple_call (dest) | |
| 129 && gimple_call_lhs (dest) != NULL_TREE) | |
| 130 type_d = TREE_TYPE (gimple_call_lhs (dest)); | |
| 131 else | |
| 132 gcc_unreachable (); | |
| 133 | |
| 134 type_o = TREE_TYPE (orig); | |
| 135 | |
| 136 if (!useless_type_conversion_p (type_d, type_o)) | |
| 137 return false; | |
| 138 | |
| 139 return true; | |
| 140 } | |
| 141 | |
| 142 /* Similarly, but we know that we're propagating into an ASM_EXPR. */ | |
| 143 | |
| 144 bool | |
| 145 may_propagate_copy_into_asm (tree dest) | |
| 146 { | |
| 147 /* Hard register operands of asms are special. Do not bypass. */ | |
| 148 return !(TREE_CODE (dest) == SSA_NAME | |
| 149 && TREE_CODE (SSA_NAME_VAR (dest)) == VAR_DECL | |
| 150 && DECL_HARD_REGISTER (SSA_NAME_VAR (dest))); | |
| 151 } | |
| 152 | |
| 153 | |
| 154 /* Common code for propagate_value and replace_exp. | |
| 155 | |
| 156 Replace use operand OP_P with VAL. FOR_PROPAGATION indicates if the | |
| 157 replacement is done to propagate a value or not. */ | |
| 158 | |
| 159 static void | |
| 160 replace_exp_1 (use_operand_p op_p, tree val, | |
| 161 bool for_propagation ATTRIBUTE_UNUSED) | |
| 162 { | |
|
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163 #if defined ENABLE_CHECKING |
| 0 | 164 tree op = USE_FROM_PTR (op_p); |
| 165 | |
| 166 gcc_assert (!(for_propagation | |
| 167 && TREE_CODE (op) == SSA_NAME | |
| 168 && TREE_CODE (val) == SSA_NAME | |
| 169 && !may_propagate_copy (op, val))); | |
| 170 #endif | |
| 171 | |
| 172 if (TREE_CODE (val) == SSA_NAME) | |
|
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173 SET_USE (op_p, val); |
| 0 | 174 else |
| 175 SET_USE (op_p, unsave_expr_now (val)); | |
| 176 } | |
| 177 | |
| 178 | |
| 179 /* Propagate the value VAL (assumed to be a constant or another SSA_NAME) | |
| 180 into the operand pointed to by OP_P. | |
| 181 | |
| 182 Use this version for const/copy propagation as it will perform additional | |
| 183 checks to ensure validity of the const/copy propagation. */ | |
| 184 | |
| 185 void | |
| 186 propagate_value (use_operand_p op_p, tree val) | |
| 187 { | |
| 188 replace_exp_1 (op_p, val, true); | |
| 189 } | |
| 190 | |
| 191 /* Replace *OP_P with value VAL (assumed to be a constant or another SSA_NAME). | |
| 192 | |
| 193 Use this version when not const/copy propagating values. For example, | |
| 194 PRE uses this version when building expressions as they would appear | |
| 195 in specific blocks taking into account actions of PHI nodes. */ | |
| 196 | |
| 197 void | |
| 198 replace_exp (use_operand_p op_p, tree val) | |
| 199 { | |
| 200 replace_exp_1 (op_p, val, false); | |
| 201 } | |
| 202 | |
| 203 | |
| 204 /* Propagate the value VAL (assumed to be a constant or another SSA_NAME) | |
| 205 into the tree pointed to by OP_P. | |
| 206 | |
| 207 Use this version for const/copy propagation when SSA operands are not | |
| 208 available. It will perform the additional checks to ensure validity of | |
| 209 the const/copy propagation, but will not update any operand information. | |
| 210 Be sure to mark the stmt as modified. */ | |
| 211 | |
| 212 void | |
| 213 propagate_tree_value (tree *op_p, tree val) | |
| 214 { | |
| 215 #if defined ENABLE_CHECKING | |
| 216 gcc_assert (!(TREE_CODE (val) == SSA_NAME | |
| 217 && *op_p | |
| 218 && TREE_CODE (*op_p) == SSA_NAME | |
| 219 && !may_propagate_copy (*op_p, val))); | |
| 220 #endif | |
| 221 | |
| 222 if (TREE_CODE (val) == SSA_NAME) | |
|
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223 *op_p = val; |
| 0 | 224 else |
| 225 *op_p = unsave_expr_now (val); | |
| 226 } | |
| 227 | |
| 228 | |
| 229 /* Like propagate_tree_value, but use as the operand to replace | |
| 230 the principal expression (typically, the RHS) contained in the | |
| 231 statement referenced by iterator GSI. Note that it is not | |
| 232 always possible to update the statement in-place, so a new | |
| 233 statement may be created to replace the original. */ | |
| 234 | |
| 235 void | |
| 236 propagate_tree_value_into_stmt (gimple_stmt_iterator *gsi, tree val) | |
| 237 { | |
| 238 gimple stmt = gsi_stmt (*gsi); | |
| 239 | |
| 240 if (is_gimple_assign (stmt)) | |
| 241 { | |
| 242 tree expr = NULL_TREE; | |
| 243 if (gimple_assign_single_p (stmt)) | |
| 244 expr = gimple_assign_rhs1 (stmt); | |
| 245 propagate_tree_value (&expr, val); | |
| 246 gimple_assign_set_rhs_from_tree (gsi, expr); | |
| 247 stmt = gsi_stmt (*gsi); | |
| 248 } | |
| 249 else if (gimple_code (stmt) == GIMPLE_COND) | |
| 250 { | |
| 251 tree lhs = NULL_TREE; | |
| 252 tree rhs = fold_convert (TREE_TYPE (val), integer_zero_node); | |
| 253 propagate_tree_value (&lhs, val); | |
| 254 gimple_cond_set_code (stmt, NE_EXPR); | |
| 255 gimple_cond_set_lhs (stmt, lhs); | |
| 256 gimple_cond_set_rhs (stmt, rhs); | |
| 257 } | |
| 258 else if (is_gimple_call (stmt) | |
| 259 && gimple_call_lhs (stmt) != NULL_TREE) | |
| 260 { | |
| 261 gimple new_stmt; | |
| 262 | |
| 263 tree expr = NULL_TREE; | |
| 264 propagate_tree_value (&expr, val); | |
|
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265 new_stmt = gimple_build_assign (gimple_call_lhs (stmt), expr); |
| 0 | 266 move_ssa_defining_stmt_for_defs (new_stmt, stmt); |
| 267 gsi_replace (gsi, new_stmt, false); | |
| 268 } | |
| 269 else if (gimple_code (stmt) == GIMPLE_SWITCH) | |
| 270 propagate_tree_value (gimple_switch_index_ptr (stmt), val); | |
| 271 else | |
| 272 gcc_unreachable (); | |
| 273 } | |
| 274 | |
| 275 /*--------------------------------------------------------------------------- | |
| 276 Copy propagation | |
| 277 ---------------------------------------------------------------------------*/ | |
| 278 /* During propagation, we keep chains of variables that are copies of | |
| 279 one another. If variable X_i is a copy of X_j and X_j is a copy of | |
| 280 X_k, COPY_OF will contain: | |
| 281 | |
| 282 COPY_OF[i].VALUE = X_j | |
| 283 COPY_OF[j].VALUE = X_k | |
| 284 COPY_OF[k].VALUE = X_k | |
| 285 | |
| 286 After propagation, the copy-of value for each variable X_i is | |
| 287 converted into the final value by walking the copy-of chains and | |
| 288 updating COPY_OF[i].VALUE to be the last element of the chain. */ | |
| 289 static prop_value_t *copy_of; | |
| 290 | |
| 291 /* Used in set_copy_of_val to determine if the last link of a copy-of | |
| 292 chain has changed. */ | |
| 293 static tree *cached_last_copy_of; | |
| 294 | |
| 295 | |
| 296 /* Return true if this statement may generate a useful copy. */ | |
| 297 | |
| 298 static bool | |
| 299 stmt_may_generate_copy (gimple stmt) | |
| 300 { | |
| 301 if (gimple_code (stmt) == GIMPLE_PHI) | |
| 302 return !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (gimple_phi_result (stmt)); | |
| 303 | |
| 304 if (gimple_code (stmt) != GIMPLE_ASSIGN) | |
| 305 return false; | |
| 306 | |
| 307 /* If the statement has volatile operands, it won't generate a | |
| 308 useful copy. */ | |
| 309 if (gimple_has_volatile_ops (stmt)) | |
| 310 return false; | |
| 311 | |
| 312 /* Statements with loads and/or stores will never generate a useful copy. */ | |
|
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313 if (gimple_vuse (stmt)) |
| 0 | 314 return false; |
| 315 | |
| 316 /* Otherwise, the only statements that generate useful copies are | |
| 317 assignments whose RHS is just an SSA name that doesn't flow | |
| 318 through abnormal edges. */ | |
| 319 return (gimple_assign_rhs_code (stmt) == SSA_NAME | |
| 320 && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (gimple_assign_rhs1 (stmt))); | |
| 321 } | |
| 322 | |
| 323 | |
| 324 /* Return the copy-of value for VAR. */ | |
| 325 | |
| 326 static inline prop_value_t * | |
| 327 get_copy_of_val (tree var) | |
| 328 { | |
| 329 prop_value_t *val = ©_of[SSA_NAME_VERSION (var)]; | |
| 330 | |
| 331 if (val->value == NULL_TREE | |
| 332 && !stmt_may_generate_copy (SSA_NAME_DEF_STMT (var))) | |
| 333 { | |
| 334 /* If the variable will never generate a useful copy relation, | |
| 335 make it its own copy. */ | |
| 336 val->value = var; | |
| 337 } | |
| 338 | |
| 339 return val; | |
| 340 } | |
| 341 | |
| 342 | |
| 343 /* Return last link in the copy-of chain for VAR. */ | |
| 344 | |
| 345 static tree | |
| 346 get_last_copy_of (tree var) | |
| 347 { | |
| 348 tree last; | |
| 349 int i; | |
| 350 | |
| 351 /* Traverse COPY_OF starting at VAR until we get to the last | |
| 352 link in the chain. Since it is possible to have cycles in PHI | |
| 353 nodes, the copy-of chain may also contain cycles. | |
|
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354 |
| 0 | 355 To avoid infinite loops and to avoid traversing lengthy copy-of |
| 356 chains, we artificially limit the maximum number of chains we are | |
| 357 willing to traverse. | |
| 358 | |
| 359 The value 5 was taken from a compiler and runtime library | |
| 360 bootstrap and a mixture of C and C++ code from various sources. | |
| 361 More than 82% of all copy-of chains were shorter than 5 links. */ | |
| 362 #define LIMIT 5 | |
| 363 | |
| 364 last = var; | |
| 365 for (i = 0; i < LIMIT; i++) | |
| 366 { | |
| 367 tree copy = copy_of[SSA_NAME_VERSION (last)].value; | |
| 368 if (copy == NULL_TREE || copy == last) | |
| 369 break; | |
| 370 last = copy; | |
| 371 } | |
| 372 | |
| 373 /* If we have reached the limit, then we are either in a copy-of | |
| 374 cycle or the copy-of chain is too long. In this case, just | |
| 375 return VAR so that it is not considered a copy of anything. */ | |
| 376 return (i < LIMIT ? last : var); | |
| 377 } | |
| 378 | |
| 379 | |
| 380 /* Set FIRST to be the first variable in the copy-of chain for DEST. | |
| 381 If DEST's copy-of value or its copy-of chain has changed, return | |
| 382 true. | |
| 383 | |
| 384 MEM_REF is the memory reference where FIRST is stored. This is | |
| 385 used when DEST is a non-register and we are copy propagating loads | |
| 386 and stores. */ | |
| 387 | |
| 388 static inline bool | |
| 389 set_copy_of_val (tree dest, tree first) | |
| 390 { | |
| 391 unsigned int dest_ver = SSA_NAME_VERSION (dest); | |
| 392 tree old_first, old_last, new_last; | |
|
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393 |
| 0 | 394 /* Set FIRST to be the first link in COPY_OF[DEST]. If that |
| 395 changed, return true. */ | |
| 396 old_first = copy_of[dest_ver].value; | |
| 397 copy_of[dest_ver].value = first; | |
| 398 | |
| 399 if (old_first != first) | |
| 400 return true; | |
| 401 | |
| 402 /* If FIRST and OLD_FIRST are the same, we need to check whether the | |
| 403 copy-of chain starting at FIRST ends in a different variable. If | |
| 404 the copy-of chain starting at FIRST ends up in a different | |
| 405 variable than the last cached value we had for DEST, then return | |
| 406 true because DEST is now a copy of a different variable. | |
| 407 | |
| 408 This test is necessary because even though the first link in the | |
| 409 copy-of chain may not have changed, if any of the variables in | |
| 410 the copy-of chain changed its final value, DEST will now be the | |
| 411 copy of a different variable, so we have to do another round of | |
| 412 propagation for everything that depends on DEST. */ | |
| 413 old_last = cached_last_copy_of[dest_ver]; | |
| 414 new_last = get_last_copy_of (dest); | |
| 415 cached_last_copy_of[dest_ver] = new_last; | |
| 416 | |
| 417 return (old_last != new_last); | |
| 418 } | |
| 419 | |
| 420 | |
| 421 /* Dump the copy-of value for variable VAR to FILE. */ | |
| 422 | |
| 423 static void | |
| 424 dump_copy_of (FILE *file, tree var) | |
| 425 { | |
| 426 tree val; | |
| 427 sbitmap visited; | |
| 428 | |
| 429 print_generic_expr (file, var, dump_flags); | |
| 430 | |
| 431 if (TREE_CODE (var) != SSA_NAME) | |
| 432 return; | |
|
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433 |
| 0 | 434 visited = sbitmap_alloc (num_ssa_names); |
| 435 sbitmap_zero (visited); | |
| 436 SET_BIT (visited, SSA_NAME_VERSION (var)); | |
|
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437 |
| 0 | 438 fprintf (file, " copy-of chain: "); |
| 439 | |
| 440 val = var; | |
| 441 print_generic_expr (file, val, 0); | |
| 442 fprintf (file, " "); | |
| 443 while (copy_of[SSA_NAME_VERSION (val)].value) | |
| 444 { | |
| 445 fprintf (file, "-> "); | |
| 446 val = copy_of[SSA_NAME_VERSION (val)].value; | |
| 447 print_generic_expr (file, val, 0); | |
| 448 fprintf (file, " "); | |
| 449 if (TEST_BIT (visited, SSA_NAME_VERSION (val))) | |
| 450 break; | |
| 451 SET_BIT (visited, SSA_NAME_VERSION (val)); | |
| 452 } | |
| 453 | |
| 454 val = get_copy_of_val (var)->value; | |
| 455 if (val == NULL_TREE) | |
| 456 fprintf (file, "[UNDEFINED]"); | |
| 457 else if (val != var) | |
| 458 fprintf (file, "[COPY]"); | |
| 459 else | |
| 460 fprintf (file, "[NOT A COPY]"); | |
|
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461 |
| 0 | 462 sbitmap_free (visited); |
| 463 } | |
| 464 | |
| 465 | |
| 466 /* Evaluate the RHS of STMT. If it produces a valid copy, set the LHS | |
| 467 value and store the LHS into *RESULT_P. If STMT generates more | |
| 468 than one name (i.e., STMT is an aliased store), it is enough to | |
| 469 store the first name in the VDEF list into *RESULT_P. After | |
| 470 all, the names generated will be VUSEd in the same statements. */ | |
| 471 | |
| 472 static enum ssa_prop_result | |
| 473 copy_prop_visit_assignment (gimple stmt, tree *result_p) | |
| 474 { | |
| 475 tree lhs, rhs; | |
| 476 prop_value_t *rhs_val; | |
| 477 | |
| 478 lhs = gimple_assign_lhs (stmt); | |
| 479 rhs = gimple_assign_rhs1 (stmt); | |
|
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480 |
| 0 | 481 |
| 482 gcc_assert (gimple_assign_rhs_code (stmt) == SSA_NAME); | |
| 483 | |
| 484 rhs_val = get_copy_of_val (rhs); | |
| 485 | |
| 486 if (TREE_CODE (lhs) == SSA_NAME) | |
| 487 { | |
| 488 /* Straight copy between two SSA names. First, make sure that | |
| 489 we can propagate the RHS into uses of LHS. */ | |
| 490 if (!may_propagate_copy (lhs, rhs)) | |
| 491 return SSA_PROP_VARYING; | |
| 492 | |
| 493 /* Notice that in the case of assignments, we make the LHS be a | |
| 494 copy of RHS's value, not of RHS itself. This avoids keeping | |
| 495 unnecessary copy-of chains (assignments cannot be in a cycle | |
| 496 like PHI nodes), speeding up the propagation process. | |
|
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497 This is different from what we do in copy_prop_visit_phi_node. |
| 0 | 498 In those cases, we are interested in the copy-of chains. */ |
| 499 *result_p = lhs; | |
| 500 if (set_copy_of_val (*result_p, rhs_val->value)) | |
| 501 return SSA_PROP_INTERESTING; | |
| 502 else | |
| 503 return SSA_PROP_NOT_INTERESTING; | |
| 504 } | |
| 505 | |
| 506 return SSA_PROP_VARYING; | |
| 507 } | |
| 508 | |
| 509 | |
| 510 /* Visit the GIMPLE_COND STMT. Return SSA_PROP_INTERESTING | |
| 511 if it can determine which edge will be taken. Otherwise, return | |
| 512 SSA_PROP_VARYING. */ | |
| 513 | |
| 514 static enum ssa_prop_result | |
| 515 copy_prop_visit_cond_stmt (gimple stmt, edge *taken_edge_p) | |
| 516 { | |
| 517 enum ssa_prop_result retval = SSA_PROP_VARYING; | |
|
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518 location_t loc = gimple_location (stmt); |
| 0 | 519 |
| 520 tree op0 = gimple_cond_lhs (stmt); | |
| 521 tree op1 = gimple_cond_rhs (stmt); | |
| 522 | |
| 523 /* The only conditionals that we may be able to compute statically | |
| 524 are predicates involving two SSA_NAMEs. */ | |
| 525 if (TREE_CODE (op0) == SSA_NAME && TREE_CODE (op1) == SSA_NAME) | |
| 526 { | |
| 527 op0 = get_last_copy_of (op0); | |
| 528 op1 = get_last_copy_of (op1); | |
| 529 | |
| 530 /* See if we can determine the predicate's value. */ | |
| 531 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 532 { | |
| 533 fprintf (dump_file, "Trying to determine truth value of "); | |
| 534 fprintf (dump_file, "predicate "); | |
| 535 print_gimple_stmt (dump_file, stmt, 0, 0); | |
| 536 } | |
| 537 | |
| 538 /* We can fold COND and get a useful result only when we have | |
| 539 the same SSA_NAME on both sides of a comparison operator. */ | |
| 540 if (op0 == op1) | |
| 541 { | |
|
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542 tree folded_cond = fold_binary_loc (loc, gimple_cond_code (stmt), |
| 0 | 543 boolean_type_node, op0, op1); |
| 544 if (folded_cond) | |
| 545 { | |
| 546 basic_block bb = gimple_bb (stmt); | |
| 547 *taken_edge_p = find_taken_edge (bb, folded_cond); | |
| 548 if (*taken_edge_p) | |
| 549 retval = SSA_PROP_INTERESTING; | |
| 550 } | |
| 551 } | |
| 552 } | |
| 553 | |
| 554 if (dump_file && (dump_flags & TDF_DETAILS) && *taken_edge_p) | |
| 555 fprintf (dump_file, "\nConditional will always take edge %d->%d\n", | |
| 556 (*taken_edge_p)->src->index, (*taken_edge_p)->dest->index); | |
| 557 | |
| 558 return retval; | |
| 559 } | |
| 560 | |
| 561 | |
| 562 /* Evaluate statement STMT. If the statement produces a new output | |
| 563 value, return SSA_PROP_INTERESTING and store the SSA_NAME holding | |
| 564 the new value in *RESULT_P. | |
| 565 | |
| 566 If STMT is a conditional branch and we can determine its truth | |
| 567 value, set *TAKEN_EDGE_P accordingly. | |
| 568 | |
| 569 If the new value produced by STMT is varying, return | |
| 570 SSA_PROP_VARYING. */ | |
| 571 | |
| 572 static enum ssa_prop_result | |
| 573 copy_prop_visit_stmt (gimple stmt, edge *taken_edge_p, tree *result_p) | |
| 574 { | |
| 575 enum ssa_prop_result retval; | |
| 576 | |
| 577 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 578 { | |
| 579 fprintf (dump_file, "\nVisiting statement:\n"); | |
| 580 print_gimple_stmt (dump_file, stmt, 0, dump_flags); | |
| 581 fprintf (dump_file, "\n"); | |
| 582 } | |
| 583 | |
| 584 if (gimple_assign_single_p (stmt) | |
| 585 && TREE_CODE (gimple_assign_lhs (stmt)) == SSA_NAME | |
| 586 && TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME) | |
| 587 { | |
| 588 /* If the statement is a copy assignment, evaluate its RHS to | |
| 589 see if the lattice value of its output has changed. */ | |
| 590 retval = copy_prop_visit_assignment (stmt, result_p); | |
| 591 } | |
| 592 else if (gimple_code (stmt) == GIMPLE_COND) | |
| 593 { | |
| 594 /* See if we can determine which edge goes out of a conditional | |
| 595 jump. */ | |
| 596 retval = copy_prop_visit_cond_stmt (stmt, taken_edge_p); | |
| 597 } | |
| 598 else | |
| 599 retval = SSA_PROP_VARYING; | |
| 600 | |
| 601 if (retval == SSA_PROP_VARYING) | |
| 602 { | |
| 603 tree def; | |
| 604 ssa_op_iter i; | |
| 605 | |
| 606 /* Any other kind of statement is not interesting for constant | |
| 607 propagation and, therefore, not worth simulating. */ | |
| 608 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 609 fprintf (dump_file, "No interesting values produced.\n"); | |
| 610 | |
| 611 /* The assignment is not a copy operation. Don't visit this | |
| 612 statement again and mark all the definitions in the statement | |
| 613 to be copies of nothing. */ | |
| 614 FOR_EACH_SSA_TREE_OPERAND (def, stmt, i, SSA_OP_ALL_DEFS) | |
| 615 set_copy_of_val (def, def); | |
| 616 } | |
| 617 | |
| 618 return retval; | |
| 619 } | |
| 620 | |
| 621 | |
| 622 /* Visit PHI node PHI. If all the arguments produce the same value, | |
| 623 set it to be the value of the LHS of PHI. */ | |
| 624 | |
| 625 static enum ssa_prop_result | |
| 626 copy_prop_visit_phi_node (gimple phi) | |
| 627 { | |
| 628 enum ssa_prop_result retval; | |
| 629 unsigned i; | |
| 630 prop_value_t phi_val = { 0, NULL_TREE }; | |
| 631 | |
| 632 tree lhs = gimple_phi_result (phi); | |
| 633 | |
| 634 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 635 { | |
| 636 fprintf (dump_file, "\nVisiting PHI node: "); | |
| 637 print_gimple_stmt (dump_file, phi, 0, dump_flags); | |
| 638 fprintf (dump_file, "\n\n"); | |
| 639 } | |
| 640 | |
| 641 for (i = 0; i < gimple_phi_num_args (phi); i++) | |
| 642 { | |
| 643 prop_value_t *arg_val; | |
| 644 tree arg = gimple_phi_arg_def (phi, i); | |
| 645 edge e = gimple_phi_arg_edge (phi, i); | |
| 646 | |
| 647 /* We don't care about values flowing through non-executable | |
| 648 edges. */ | |
| 649 if (!(e->flags & EDGE_EXECUTABLE)) | |
| 650 continue; | |
| 651 | |
| 652 /* Constants in the argument list never generate a useful copy. | |
| 653 Similarly, names that flow through abnormal edges cannot be | |
| 654 used to derive copies. */ | |
| 655 if (TREE_CODE (arg) != SSA_NAME || SSA_NAME_OCCURS_IN_ABNORMAL_PHI (arg)) | |
| 656 { | |
| 657 phi_val.value = lhs; | |
| 658 break; | |
| 659 } | |
| 660 | |
| 661 /* Avoid copy propagation from an inner into an outer loop. | |
| 662 Otherwise, this may move loop variant variables outside of | |
| 663 their loops and prevent coalescing opportunities. If the | |
| 664 value was loop invariant, it will be hoisted by LICM and | |
|
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665 exposed for copy propagation. Not a problem for virtual |
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666 operands though. */ |
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667 if (is_gimple_reg (lhs) |
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668 && loop_depth_of_name (arg) > loop_depth_of_name (lhs)) |
| 0 | 669 { |
| 670 phi_val.value = lhs; | |
| 671 break; | |
| 672 } | |
| 673 | |
| 674 /* If the LHS appears in the argument list, ignore it. It is | |
| 675 irrelevant as a copy. */ | |
| 676 if (arg == lhs || get_last_copy_of (arg) == lhs) | |
| 677 continue; | |
| 678 | |
| 679 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 680 { | |
| 681 fprintf (dump_file, "\tArgument #%d: ", i); | |
| 682 dump_copy_of (dump_file, arg); | |
| 683 fprintf (dump_file, "\n"); | |
| 684 } | |
| 685 | |
| 686 arg_val = get_copy_of_val (arg); | |
| 687 | |
| 688 /* If the LHS didn't have a value yet, make it a copy of the | |
| 689 first argument we find. Notice that while we make the LHS be | |
| 690 a copy of the argument itself, we take the memory reference | |
| 691 from the argument's value so that we can compare it to the | |
| 692 memory reference of all the other arguments. */ | |
| 693 if (phi_val.value == NULL_TREE) | |
| 694 { | |
|
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695 phi_val.value = arg_val->value ? arg_val->value : arg; |
| 0 | 696 continue; |
| 697 } | |
| 698 | |
| 699 /* If PHI_VAL and ARG don't have a common copy-of chain, then | |
| 700 this PHI node cannot be a copy operation. Also, if we are | |
| 701 copy propagating stores and these two arguments came from | |
| 702 different memory references, they cannot be considered | |
| 703 copies. */ | |
| 704 if (get_last_copy_of (phi_val.value) != get_last_copy_of (arg)) | |
| 705 { | |
| 706 phi_val.value = lhs; | |
| 707 break; | |
| 708 } | |
| 709 } | |
| 710 | |
| 711 if (phi_val.value && may_propagate_copy (lhs, phi_val.value) | |
| 712 && set_copy_of_val (lhs, phi_val.value)) | |
| 713 retval = (phi_val.value != lhs) ? SSA_PROP_INTERESTING : SSA_PROP_VARYING; | |
| 714 else | |
| 715 retval = SSA_PROP_NOT_INTERESTING; | |
| 716 | |
| 717 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 718 { | |
| 719 fprintf (dump_file, "\nPHI node "); | |
| 720 dump_copy_of (dump_file, lhs); | |
| 721 fprintf (dump_file, "\nTelling the propagator to "); | |
| 722 if (retval == SSA_PROP_INTERESTING) | |
| 723 fprintf (dump_file, "add SSA edges out of this PHI and continue."); | |
| 724 else if (retval == SSA_PROP_VARYING) | |
| 725 fprintf (dump_file, "add SSA edges out of this PHI and never visit again."); | |
| 726 else | |
| 727 fprintf (dump_file, "do nothing with SSA edges and keep iterating."); | |
| 728 fprintf (dump_file, "\n\n"); | |
| 729 } | |
| 730 | |
| 731 return retval; | |
| 732 } | |
| 733 | |
| 734 | |
| 735 /* Initialize structures used for copy propagation. PHIS_ONLY is true | |
| 736 if we should only consider PHI nodes as generating copy propagation | |
| 737 opportunities. */ | |
| 738 | |
| 739 static void | |
| 740 init_copy_prop (void) | |
| 741 { | |
| 742 basic_block bb; | |
| 743 | |
| 744 copy_of = XCNEWVEC (prop_value_t, num_ssa_names); | |
| 745 | |
| 746 cached_last_copy_of = XCNEWVEC (tree, num_ssa_names); | |
| 747 | |
| 748 FOR_EACH_BB (bb) | |
| 749 { | |
| 750 gimple_stmt_iterator si; | |
| 751 int depth = bb->loop_depth; | |
| 752 | |
| 753 for (si = gsi_start_bb (bb); !gsi_end_p (si); gsi_next (&si)) | |
| 754 { | |
| 755 gimple stmt = gsi_stmt (si); | |
| 756 ssa_op_iter iter; | |
| 757 tree def; | |
| 758 | |
| 759 /* The only statements that we care about are those that may | |
| 760 generate useful copies. We also need to mark conditional | |
| 761 jumps so that their outgoing edges are added to the work | |
| 762 lists of the propagator. | |
| 763 | |
| 764 Avoid copy propagation from an inner into an outer loop. | |
| 765 Otherwise, this may move loop variant variables outside of | |
| 766 their loops and prevent coalescing opportunities. If the | |
| 767 value was loop invariant, it will be hoisted by LICM and | |
| 768 exposed for copy propagation. */ | |
| 769 if (stmt_ends_bb_p (stmt)) | |
| 770 prop_set_simulate_again (stmt, true); | |
| 771 else if (stmt_may_generate_copy (stmt) | |
| 772 /* Since we are iterating over the statements in | |
| 773 BB, not the phi nodes, STMT will always be an | |
| 774 assignment. */ | |
| 775 && loop_depth_of_name (gimple_assign_rhs1 (stmt)) <= depth) | |
| 776 prop_set_simulate_again (stmt, true); | |
| 777 else | |
| 778 prop_set_simulate_again (stmt, false); | |
| 779 | |
| 780 /* Mark all the outputs of this statement as not being | |
| 781 the copy of anything. */ | |
| 782 FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS) | |
| 783 if (!prop_simulate_again_p (stmt)) | |
| 784 set_copy_of_val (def, def); | |
| 785 else | |
| 786 cached_last_copy_of[SSA_NAME_VERSION (def)] = def; | |
| 787 } | |
| 788 | |
| 789 for (si = gsi_start_phis (bb); !gsi_end_p (si); gsi_next (&si)) | |
| 790 { | |
| 791 gimple phi = gsi_stmt (si); | |
| 792 tree def; | |
| 793 | |
| 794 def = gimple_phi_result (phi); | |
|
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795 if (!is_gimple_reg (def) |
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796 /* In loop-closed SSA form do not copy-propagate through |
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797 PHI nodes. Technically this is only needed for loop |
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798 exit PHIs, but this is difficult to query. */ |
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799 || (current_loops |
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800 && gimple_phi_num_args (phi) == 1 |
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801 && loops_state_satisfies_p (LOOP_CLOSED_SSA))) |
| 0 | 802 prop_set_simulate_again (phi, false); |
| 803 else | |
| 804 prop_set_simulate_again (phi, true); | |
| 805 | |
| 806 if (!prop_simulate_again_p (phi)) | |
| 807 set_copy_of_val (def, def); | |
| 808 else | |
| 809 cached_last_copy_of[SSA_NAME_VERSION (def)] = def; | |
| 810 } | |
| 811 } | |
| 812 } | |
| 813 | |
| 814 | |
| 815 /* Deallocate memory used in copy propagation and do final | |
| 816 substitution. */ | |
| 817 | |
| 818 static void | |
| 819 fini_copy_prop (void) | |
| 820 { | |
| 821 size_t i; | |
| 822 prop_value_t *tmp; | |
|
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823 |
| 0 | 824 /* Set the final copy-of value for each variable by traversing the |
| 825 copy-of chains. */ | |
| 826 tmp = XCNEWVEC (prop_value_t, num_ssa_names); | |
| 827 for (i = 1; i < num_ssa_names; i++) | |
| 828 { | |
| 829 tree var = ssa_name (i); | |
|
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830 if (!var |
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831 || !copy_of[i].value |
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832 || copy_of[i].value == var) |
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833 continue; |
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834 |
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835 tmp[i].value = get_last_copy_of (var); |
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836 |
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837 /* In theory the points-to solution of all members of the |
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838 copy chain is their intersection. For now we do not bother |
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839 to compute this but only make sure we do not lose points-to |
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840 information completely by setting the points-to solution |
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841 of the representative to the first solution we find if |
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842 it doesn't have one already. */ |
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843 if (tmp[i].value != var |
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844 && POINTER_TYPE_P (TREE_TYPE (var)) |
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845 && SSA_NAME_PTR_INFO (var) |
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846 && !SSA_NAME_PTR_INFO (tmp[i].value)) |
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847 duplicate_ssa_name_ptr_info (tmp[i].value, SSA_NAME_PTR_INFO (var)); |
| 0 | 848 } |
| 849 | |
|
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850 substitute_and_fold (tmp, NULL); |
| 0 | 851 |
| 852 free (cached_last_copy_of); | |
| 853 free (copy_of); | |
| 854 free (tmp); | |
| 855 } | |
| 856 | |
| 857 | |
| 858 /* Main entry point to the copy propagator. | |
| 859 | |
| 860 PHIS_ONLY is true if we should only consider PHI nodes as generating | |
|
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861 copy propagation opportunities. |
| 0 | 862 |
| 863 The algorithm propagates the value COPY-OF using ssa_propagate. For | |
| 864 every variable X_i, COPY-OF(X_i) indicates which variable is X_i created | |
| 865 from. The following example shows how the algorithm proceeds at a | |
| 866 high level: | |
| 867 | |
| 868 1 a_24 = x_1 | |
| 869 2 a_2 = PHI <a_24, x_1> | |
| 870 3 a_5 = PHI <a_2> | |
| 871 4 x_1 = PHI <x_298, a_5, a_2> | |
| 872 | |
| 873 The end result should be that a_2, a_5, a_24 and x_1 are a copy of | |
| 874 x_298. Propagation proceeds as follows. | |
| 875 | |
| 876 Visit #1: a_24 is copy-of x_1. Value changed. | |
| 877 Visit #2: a_2 is copy-of x_1. Value changed. | |
| 878 Visit #3: a_5 is copy-of x_1. Value changed. | |
| 879 Visit #4: x_1 is copy-of x_298. Value changed. | |
| 880 Visit #1: a_24 is copy-of x_298. Value changed. | |
| 881 Visit #2: a_2 is copy-of x_298. Value changed. | |
| 882 Visit #3: a_5 is copy-of x_298. Value changed. | |
| 883 Visit #4: x_1 is copy-of x_298. Stable state reached. | |
|
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parents:
0
diff
changeset
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884 |
| 0 | 885 When visiting PHI nodes, we only consider arguments that flow |
| 886 through edges marked executable by the propagation engine. So, | |
| 887 when visiting statement #2 for the first time, we will only look at | |
| 888 the first argument (a_24) and optimistically assume that its value | |
| 889 is the copy of a_24 (x_1). | |
| 890 | |
| 891 The problem with this approach is that it may fail to discover copy | |
| 892 relations in PHI cycles. Instead of propagating copy-of | |
| 893 values, we actually propagate copy-of chains. For instance: | |
| 894 | |
| 895 A_3 = B_1; | |
| 896 C_9 = A_3; | |
| 897 D_4 = C_9; | |
| 898 X_i = D_4; | |
| 899 | |
| 900 In this code fragment, COPY-OF (X_i) = { D_4, C_9, A_3, B_1 }. | |
| 901 Obviously, we are only really interested in the last value of the | |
| 902 chain, however the propagator needs to access the copy-of chain | |
| 903 when visiting PHI nodes. | |
| 904 | |
| 905 To represent the copy-of chain, we use the array COPY_CHAINS, which | |
| 906 holds the first link in the copy-of chain for every variable. | |
| 907 If variable X_i is a copy of X_j, which in turn is a copy of X_k, | |
| 908 the array will contain: | |
| 909 | |
| 910 COPY_CHAINS[i] = X_j | |
| 911 COPY_CHAINS[j] = X_k | |
| 912 COPY_CHAINS[k] = X_k | |
| 913 | |
| 914 Keeping copy-of chains instead of copy-of values directly becomes | |
| 915 important when visiting PHI nodes. Suppose that we had the | |
| 916 following PHI cycle, such that x_52 is already considered a copy of | |
| 917 x_53: | |
| 918 | |
| 919 1 x_54 = PHI <x_53, x_52> | |
| 920 2 x_53 = PHI <x_898, x_54> | |
|
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ryoma <e075725@ie.u-ryukyu.ac.jp>
parents:
0
diff
changeset
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921 |
| 0 | 922 Visit #1: x_54 is copy-of x_53 (because x_52 is copy-of x_53) |
| 923 Visit #2: x_53 is copy-of x_898 (because x_54 is a copy of x_53, | |
| 924 so it is considered irrelevant | |
| 925 as a copy). | |
| 926 Visit #1: x_54 is copy-of nothing (x_53 is a copy-of x_898 and | |
| 927 x_52 is a copy of x_53, so | |
| 928 they don't match) | |
| 929 Visit #2: x_53 is copy-of nothing | |
| 930 | |
| 931 This problem is avoided by keeping a chain of copies, instead of | |
| 932 the final copy-of value. Propagation will now only keep the first | |
| 933 element of a variable's copy-of chain. When visiting PHI nodes, | |
| 934 arguments are considered equal if their copy-of chains end in the | |
| 935 same variable. So, as long as their copy-of chains overlap, we | |
| 936 know that they will be a copy of the same variable, regardless of | |
| 937 which variable that may be). | |
|
55
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update it from 4.4.3 to 4.5.0
ryoma <e075725@ie.u-ryukyu.ac.jp>
parents:
0
diff
changeset
|
938 |
| 0 | 939 Propagation would then proceed as follows (the notation a -> b |
| 940 means that a is a copy-of b): | |
| 941 | |
| 942 Visit #1: x_54 = PHI <x_53, x_52> | |
| 943 x_53 -> x_53 | |
| 944 x_52 -> x_53 | |
| 945 Result: x_54 -> x_53. Value changed. Add SSA edges. | |
| 946 | |
| 947 Visit #1: x_53 = PHI <x_898, x_54> | |
| 948 x_898 -> x_898 | |
| 949 x_54 -> x_53 | |
| 950 Result: x_53 -> x_898. Value changed. Add SSA edges. | |
| 951 | |
| 952 Visit #2: x_54 = PHI <x_53, x_52> | |
| 953 x_53 -> x_898 | |
| 954 x_52 -> x_53 -> x_898 | |
| 955 Result: x_54 -> x_898. Value changed. Add SSA edges. | |
| 956 | |
| 957 Visit #2: x_53 = PHI <x_898, x_54> | |
| 958 x_898 -> x_898 | |
| 959 x_54 -> x_898 | |
| 960 Result: x_53 -> x_898. Value didn't change. Stable state | |
| 961 | |
| 962 Once the propagator stabilizes, we end up with the desired result | |
| 963 x_53 and x_54 are both copies of x_898. */ | |
| 964 | |
| 965 static unsigned int | |
| 966 execute_copy_prop (void) | |
| 967 { | |
| 968 init_copy_prop (); | |
| 969 ssa_propagate (copy_prop_visit_stmt, copy_prop_visit_phi_node); | |
| 970 fini_copy_prop (); | |
| 971 return 0; | |
| 972 } | |
| 973 | |
| 974 static bool | |
| 975 gate_copy_prop (void) | |
| 976 { | |
| 977 return flag_tree_copy_prop != 0; | |
| 978 } | |
| 979 | |
| 980 struct gimple_opt_pass pass_copy_prop = | |
| 981 { | |
| 982 { | |
| 983 GIMPLE_PASS, | |
| 984 "copyprop", /* name */ | |
| 985 gate_copy_prop, /* gate */ | |
| 986 execute_copy_prop, /* execute */ | |
| 987 NULL, /* sub */ | |
| 988 NULL, /* next */ | |
| 989 0, /* static_pass_number */ | |
| 990 TV_TREE_COPY_PROP, /* tv_id */ | |
| 991 PROP_ssa | PROP_cfg, /* properties_required */ | |
| 992 0, /* properties_provided */ | |
| 993 0, /* properties_destroyed */ | |
| 994 0, /* todo_flags_start */ | |
| 995 TODO_cleanup_cfg | |
| 996 | TODO_dump_func | |
| 997 | TODO_ggc_collect | |
| 998 | TODO_verify_ssa | |
| 999 | TODO_update_ssa /* todo_flags_finish */ | |
| 1000 } | |
| 1001 }; |