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annotate gcc/tree-ssa-uncprop.c @ 158:494b0b89df80 default tip
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| author | Shinji KONO <kono@ie.u-ryukyu.ac.jp> |
|---|---|
| date | Mon, 25 May 2020 18:13:55 +0900 |
| parents | 1830386684a0 |
| children |
| rev | line source |
|---|---|
| 0 | 1 /* Routines for discovering and unpropagating edge equivalences. |
| 145 | 2 Copyright (C) 2005-2020 Free Software Foundation, Inc. |
| 0 | 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" | |
| 111 | 23 #include "backend.h" |
| 0 | 24 #include "tree.h" |
| 111 | 25 #include "gimple.h" |
| 26 #include "tree-pass.h" | |
| 27 #include "ssa.h" | |
| 28 #include "fold-const.h" | |
| 29 #include "cfganal.h" | |
| 30 #include "gimple-iterator.h" | |
| 31 #include "tree-cfg.h" | |
| 0 | 32 #include "domwalk.h" |
| 111 | 33 #include "tree-hash-traits.h" |
| 34 #include "tree-ssa-live.h" | |
| 35 #include "tree-ssa-coalesce.h" | |
| 0 | 36 |
| 37 /* The basic structure describing an equivalency created by traversing | |
| 38 an edge. Traversing the edge effectively means that we can assume | |
| 39 that we've seen an assignment LHS = RHS. */ | |
| 40 struct edge_equivalency | |
| 41 { | |
| 42 tree rhs; | |
| 43 tree lhs; | |
| 44 }; | |
| 45 | |
| 46 /* This routine finds and records edge equivalences for every edge | |
| 47 in the CFG. | |
| 48 | |
| 49 When complete, each edge that creates an equivalency will have an | |
|
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50 EDGE_EQUIVALENCY structure hanging off the edge's AUX field. |
| 0 | 51 The caller is responsible for freeing the AUX fields. */ |
| 52 | |
| 53 static void | |
| 54 associate_equivalences_with_edges (void) | |
| 55 { | |
| 56 basic_block bb; | |
| 57 | |
| 58 /* Walk over each block. If the block ends with a control statement, | |
| 59 then it might create a useful equivalence. */ | |
| 111 | 60 FOR_EACH_BB_FN (bb, cfun) |
| 0 | 61 { |
| 62 gimple_stmt_iterator gsi = gsi_last_bb (bb); | |
| 111 | 63 gimple *stmt; |
| 0 | 64 |
| 65 /* If the block does not end with a COND_EXPR or SWITCH_EXPR | |
| 66 then there is nothing to do. */ | |
| 67 if (gsi_end_p (gsi)) | |
| 68 continue; | |
| 69 | |
| 70 stmt = gsi_stmt (gsi); | |
| 71 | |
| 72 if (!stmt) | |
| 73 continue; | |
| 74 | |
| 75 /* A COND_EXPR may create an equivalency in a variety of different | |
| 76 ways. */ | |
| 77 if (gimple_code (stmt) == GIMPLE_COND) | |
| 78 { | |
| 79 edge true_edge; | |
| 80 edge false_edge; | |
| 81 struct edge_equivalency *equivalency; | |
| 82 enum tree_code code = gimple_cond_code (stmt); | |
| 83 | |
| 84 extract_true_false_edges_from_block (bb, &true_edge, &false_edge); | |
| 85 | |
| 86 /* Equality tests may create one or two equivalences. */ | |
| 87 if (code == EQ_EXPR || code == NE_EXPR) | |
| 88 { | |
| 89 tree op0 = gimple_cond_lhs (stmt); | |
| 90 tree op1 = gimple_cond_rhs (stmt); | |
| 91 | |
| 92 /* Special case comparing booleans against a constant as we | |
| 93 know the value of OP0 on both arms of the branch. i.e., we | |
| 94 can record an equivalence for OP0 rather than COND. */ | |
| 95 if (TREE_CODE (op0) == SSA_NAME | |
| 96 && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (op0) | |
| 111 | 97 && ssa_name_has_boolean_range (op0) |
| 98 && is_gimple_min_invariant (op1) | |
| 99 && (integer_zerop (op1) || integer_onep (op1))) | |
| 0 | 100 { |
| 111 | 101 tree true_val = constant_boolean_node (true, TREE_TYPE (op0)); |
| 102 tree false_val = constant_boolean_node (false, | |
| 103 TREE_TYPE (op0)); | |
| 0 | 104 if (code == EQ_EXPR) |
| 105 { | |
| 106 equivalency = XNEW (struct edge_equivalency); | |
| 107 equivalency->lhs = op0; | |
| 108 equivalency->rhs = (integer_zerop (op1) | |
| 111 | 109 ? false_val |
| 110 : true_val); | |
| 0 | 111 true_edge->aux = equivalency; |
| 112 | |
| 113 equivalency = XNEW (struct edge_equivalency); | |
| 114 equivalency->lhs = op0; | |
| 115 equivalency->rhs = (integer_zerop (op1) | |
| 111 | 116 ? true_val |
| 117 : false_val); | |
| 0 | 118 false_edge->aux = equivalency; |
| 119 } | |
| 120 else | |
| 121 { | |
| 122 equivalency = XNEW (struct edge_equivalency); | |
| 123 equivalency->lhs = op0; | |
| 124 equivalency->rhs = (integer_zerop (op1) | |
| 111 | 125 ? true_val |
| 126 : false_val); | |
| 0 | 127 true_edge->aux = equivalency; |
| 128 | |
| 129 equivalency = XNEW (struct edge_equivalency); | |
| 130 equivalency->lhs = op0; | |
| 131 equivalency->rhs = (integer_zerop (op1) | |
| 111 | 132 ? false_val |
| 133 : true_val); | |
| 0 | 134 false_edge->aux = equivalency; |
| 135 } | |
| 136 } | |
| 137 | |
| 138 else if (TREE_CODE (op0) == SSA_NAME | |
| 139 && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (op0) | |
| 140 && (is_gimple_min_invariant (op1) | |
| 141 || (TREE_CODE (op1) == SSA_NAME | |
| 142 && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (op1)))) | |
| 143 { | |
| 144 /* For IEEE, -0.0 == 0.0, so we don't necessarily know | |
| 145 the sign of a variable compared against zero. If | |
| 146 we're honoring signed zeros, then we cannot record | |
| 147 this value unless we know that the value is nonzero. */ | |
| 111 | 148 if (HONOR_SIGNED_ZEROS (op0) |
| 0 | 149 && (TREE_CODE (op1) != REAL_CST |
| 111 | 150 || real_equal (&dconst0, &TREE_REAL_CST (op1)))) |
| 0 | 151 continue; |
| 152 | |
| 153 equivalency = XNEW (struct edge_equivalency); | |
| 154 equivalency->lhs = op0; | |
| 155 equivalency->rhs = op1; | |
| 156 if (code == EQ_EXPR) | |
| 157 true_edge->aux = equivalency; | |
|
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158 else |
| 0 | 159 false_edge->aux = equivalency; |
| 160 | |
| 161 } | |
| 162 } | |
| 163 | |
| 164 /* ??? TRUTH_NOT_EXPR can create an equivalence too. */ | |
| 165 } | |
| 166 | |
| 167 /* For a SWITCH_EXPR, a case label which represents a single | |
| 168 value and which is the only case label which reaches the | |
| 169 target block creates an equivalence. */ | |
| 170 else if (gimple_code (stmt) == GIMPLE_SWITCH) | |
| 171 { | |
| 111 | 172 gswitch *switch_stmt = as_a <gswitch *> (stmt); |
| 173 tree cond = gimple_switch_index (switch_stmt); | |
| 0 | 174 |
| 175 if (TREE_CODE (cond) == SSA_NAME | |
| 176 && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (cond)) | |
| 177 { | |
| 111 | 178 int i, n_labels = gimple_switch_num_labels (switch_stmt); |
| 179 tree *info = XCNEWVEC (tree, last_basic_block_for_fn (cfun)); | |
| 0 | 180 |
| 181 /* Walk over the case label vector. Record blocks | |
| 182 which are reached by a single case label which represents | |
| 183 a single value. */ | |
| 184 for (i = 0; i < n_labels; i++) | |
| 185 { | |
| 111 | 186 tree label = gimple_switch_label (switch_stmt, i); |
| 131 | 187 basic_block bb = label_to_block (cfun, CASE_LABEL (label)); |
| 0 | 188 |
| 189 if (CASE_HIGH (label) | |
| 190 || !CASE_LOW (label) | |
| 191 || info[bb->index]) | |
| 192 info[bb->index] = error_mark_node; | |
| 193 else | |
| 194 info[bb->index] = label; | |
| 195 } | |
| 196 | |
| 197 /* Now walk over the blocks to determine which ones were | |
| 198 marked as being reached by a useful case label. */ | |
| 111 | 199 for (i = 0; i < n_basic_blocks_for_fn (cfun); i++) |
| 0 | 200 { |
| 201 tree node = info[i]; | |
| 202 | |
| 203 if (node != NULL | |
| 204 && node != error_mark_node) | |
| 205 { | |
| 206 tree x = fold_convert (TREE_TYPE (cond), CASE_LOW (node)); | |
| 207 struct edge_equivalency *equivalency; | |
| 208 | |
| 209 /* Record an equivalency on the edge from BB to basic | |
| 210 block I. */ | |
| 211 equivalency = XNEW (struct edge_equivalency); | |
| 212 equivalency->rhs = x; | |
| 213 equivalency->lhs = cond; | |
| 111 | 214 find_edge (bb, BASIC_BLOCK_FOR_FN (cfun, i))->aux = |
| 215 equivalency; | |
| 0 | 216 } |
| 217 } | |
| 218 free (info); | |
| 219 } | |
| 220 } | |
| 221 | |
| 222 } | |
| 223 } | |
| 224 | |
| 225 | |
| 226 /* Translating out of SSA sometimes requires inserting copies and | |
| 227 constant initializations on edges to eliminate PHI nodes. | |
| 228 | |
| 229 In some cases those copies and constant initializations are | |
| 230 redundant because the target already has the value on the | |
| 231 RHS of the assignment. | |
| 232 | |
| 233 We previously tried to catch these cases after translating | |
| 234 out of SSA form. However, that code often missed cases. Worse | |
| 235 yet, the cases it missed were also often missed by the RTL | |
| 236 optimizers. Thus the resulting code had redundant instructions. | |
| 237 | |
| 238 This pass attempts to detect these situations before translating | |
| 239 out of SSA form. | |
| 240 | |
| 241 The key concept that this pass is built upon is that these | |
| 242 redundant copies and constant initializations often occur | |
| 243 due to constant/copy propagating equivalences resulting from | |
| 244 COND_EXPRs and SWITCH_EXPRs. | |
| 245 | |
| 246 We want to do those propagations as they can sometimes allow | |
| 247 the SSA optimizers to do a better job. However, in the cases | |
| 248 where such propagations do not result in further optimization, | |
| 249 we would like to "undo" the propagation to avoid the redundant | |
| 250 copies and constant initializations. | |
| 251 | |
| 252 This pass works by first associating equivalences with edges in | |
| 253 the CFG. For example, the edge leading from a SWITCH_EXPR to | |
| 254 its associated CASE_LABEL will have an equivalency between | |
| 255 SWITCH_COND and the value in the case label. | |
| 256 | |
| 257 Once we have found the edge equivalences, we proceed to walk | |
| 258 the CFG in dominator order. As we traverse edges we record | |
| 259 equivalences associated with those edges we traverse. | |
| 260 | |
| 261 When we encounter a PHI node, we walk its arguments to see if we | |
| 262 have an equivalence for the PHI argument. If so, then we replace | |
| 263 the argument. | |
| 264 | |
| 265 Equivalences are looked up based on their value (think of it as | |
| 266 the RHS of an assignment). A value may be an SSA_NAME or an | |
| 267 invariant. We may have several SSA_NAMEs with the same value, | |
| 268 so with each value we have a list of SSA_NAMEs that have the | |
| 269 same value. */ | |
| 270 | |
| 145 | 271 typedef hash_map<tree_operand_hash, auto_vec<tree> > val_ssa_equiv_t; |
| 0 | 272 |
| 111 | 273 /* Global hash table implementing a mapping from invariant values |
| 274 to a list of SSA_NAMEs which have the same value. We might be | |
| 275 able to reuse tree-vn for this code. */ | |
| 145 | 276 val_ssa_equiv_t *val_ssa_equiv; |
| 0 | 277 |
| 111 | 278 static void uncprop_into_successor_phis (basic_block); |
| 0 | 279 |
| 280 /* Remove the most recently recorded equivalency for VALUE. */ | |
| 281 | |
| 282 static void | |
| 283 remove_equivalence (tree value) | |
| 284 { | |
| 111 | 285 val_ssa_equiv->get (value)->pop (); |
| 0 | 286 } |
| 287 | |
| 288 /* Record EQUIVALENCE = VALUE into our hash table. */ | |
| 289 | |
| 290 static void | |
| 291 record_equiv (tree value, tree equivalence) | |
| 292 { | |
| 111 | 293 val_ssa_equiv->get_or_insert (value).safe_push (equivalence); |
| 0 | 294 } |
| 295 | |
| 111 | 296 class uncprop_dom_walker : public dom_walker |
| 0 | 297 { |
| 111 | 298 public: |
| 299 uncprop_dom_walker (cdi_direction direction) : dom_walker (direction) {} | |
| 0 | 300 |
| 111 | 301 virtual edge before_dom_children (basic_block); |
| 302 virtual void after_dom_children (basic_block); | |
| 0 | 303 |
| 111 | 304 private: |
| 0 | 305 |
| 111 | 306 /* As we enter each block we record the value for any edge equivalency |
| 307 leading to this block. If no such edge equivalency exists, then we | |
| 308 record NULL. These equivalences are live until we leave the dominator | |
| 309 subtree rooted at the block where we record the equivalency. */ | |
| 310 auto_vec<tree, 2> m_equiv_stack; | |
| 311 }; | |
| 0 | 312 |
| 313 /* We have finished processing the dominator children of BB, perform | |
| 314 any finalization actions in preparation for leaving this node in | |
| 315 the dominator tree. */ | |
| 316 | |
| 111 | 317 void |
| 318 uncprop_dom_walker::after_dom_children (basic_block bb ATTRIBUTE_UNUSED) | |
| 0 | 319 { |
| 320 /* Pop the topmost value off the equiv stack. */ | |
| 111 | 321 tree value = m_equiv_stack.pop (); |
| 0 | 322 |
| 323 /* If that value was non-null, then pop the topmost equivalency off | |
| 324 its equivalency stack. */ | |
| 325 if (value != NULL) | |
| 326 remove_equivalence (value); | |
| 327 } | |
| 328 | |
| 329 /* Unpropagate values from PHI nodes in successor blocks of BB. */ | |
| 330 | |
| 331 static void | |
|
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332 uncprop_into_successor_phis (basic_block bb) |
| 0 | 333 { |
| 334 edge e; | |
| 335 edge_iterator ei; | |
| 336 | |
| 337 /* For each successor edge, first temporarily record any equivalence | |
| 338 on that edge. Then unpropagate values in any PHI nodes at the | |
| 339 destination of the edge. Then remove the temporary equivalence. */ | |
| 340 FOR_EACH_EDGE (e, ei, bb->succs) | |
| 341 { | |
| 342 gimple_seq phis = phi_nodes (e->dest); | |
| 343 gimple_stmt_iterator gsi; | |
| 344 | |
| 345 /* If there are no PHI nodes in this destination, then there is | |
| 346 no sense in recording any equivalences. */ | |
|
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347 if (gimple_seq_empty_p (phis)) |
| 0 | 348 continue; |
| 349 | |
| 350 /* Record any equivalency associated with E. */ | |
| 351 if (e->aux) | |
| 352 { | |
| 353 struct edge_equivalency *equiv = (struct edge_equivalency *) e->aux; | |
| 354 record_equiv (equiv->rhs, equiv->lhs); | |
| 355 } | |
| 356 | |
| 357 /* Walk over the PHI nodes, unpropagating values. */ | |
| 358 for (gsi = gsi_start (phis) ; !gsi_end_p (gsi); gsi_next (&gsi)) | |
| 359 { | |
| 111 | 360 gimple *phi = gsi_stmt (gsi); |
| 0 | 361 tree arg = PHI_ARG_DEF (phi, e->dest_idx); |
| 111 | 362 tree res = PHI_RESULT (phi); |
| 0 | 363 |
| 111 | 364 /* If the argument is not an invariant and can be potentially |
| 365 coalesced with the result, then there's no point in | |
| 366 un-propagating the argument. */ | |
| 0 | 367 if (!is_gimple_min_invariant (arg) |
| 111 | 368 && gimple_can_coalesce_p (arg, res)) |
| 0 | 369 continue; |
| 370 | |
| 371 /* Lookup this argument's value in the hash table. */ | |
| 111 | 372 vec<tree> *equivalences = val_ssa_equiv->get (arg); |
| 373 if (equivalences) | |
| 0 | 374 { |
| 375 /* Walk every equivalence with the same value. If we find | |
| 111 | 376 one that can potentially coalesce with the PHI rsult, |
| 0 | 377 then replace the value in the argument with its equivalent |
| 378 SSA_NAME. Use the most recent equivalence as hopefully | |
| 379 that results in shortest lifetimes. */ | |
| 111 | 380 for (int j = equivalences->length () - 1; j >= 0; j--) |
| 0 | 381 { |
| 111 | 382 tree equiv = (*equivalences)[j]; |
| 0 | 383 |
| 111 | 384 if (gimple_can_coalesce_p (equiv, res)) |
| 0 | 385 { |
| 386 SET_PHI_ARG_DEF (phi, e->dest_idx, equiv); | |
| 387 break; | |
| 388 } | |
| 389 } | |
| 390 } | |
| 391 } | |
| 392 | |
| 393 /* If we had an equivalence associated with this edge, remove it. */ | |
| 394 if (e->aux) | |
| 395 { | |
| 396 struct edge_equivalency *equiv = (struct edge_equivalency *) e->aux; | |
| 397 remove_equivalence (equiv->rhs); | |
| 398 } | |
| 399 } | |
| 400 } | |
| 401 | |
| 111 | 402 edge |
| 403 uncprop_dom_walker::before_dom_children (basic_block bb) | |
| 0 | 404 { |
| 405 basic_block parent; | |
| 406 bool recorded = false; | |
| 407 | |
| 408 /* If this block is dominated by a single incoming edge and that edge | |
| 409 has an equivalency, then record the equivalency and push the | |
| 410 VALUE onto EQUIV_STACK. Else push a NULL entry on EQUIV_STACK. */ | |
| 411 parent = get_immediate_dominator (CDI_DOMINATORS, bb); | |
| 412 if (parent) | |
| 413 { | |
| 131 | 414 edge e = single_pred_edge_ignoring_loop_edges (bb, false); |
| 0 | 415 |
| 416 if (e && e->src == parent && e->aux) | |
| 417 { | |
| 418 struct edge_equivalency *equiv = (struct edge_equivalency *) e->aux; | |
| 419 | |
| 420 record_equiv (equiv->rhs, equiv->lhs); | |
| 111 | 421 m_equiv_stack.safe_push (equiv->rhs); |
| 0 | 422 recorded = true; |
| 423 } | |
| 424 } | |
| 425 | |
| 426 if (!recorded) | |
| 111 | 427 m_equiv_stack.safe_push (NULL_TREE); |
|
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diff
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428 |
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77e2b8dfacca
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parents:
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diff
changeset
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429 uncprop_into_successor_phis (bb); |
| 111 | 430 return NULL; |
| 0 | 431 } |
| 432 | |
| 111 | 433 namespace { |
| 434 | |
| 435 const pass_data pass_data_uncprop = | |
| 0 | 436 { |
| 111 | 437 GIMPLE_PASS, /* type */ |
| 438 "uncprop", /* name */ | |
| 439 OPTGROUP_NONE, /* optinfo_flags */ | |
| 440 TV_TREE_SSA_UNCPROP, /* tv_id */ | |
| 441 ( PROP_cfg | PROP_ssa ), /* properties_required */ | |
| 442 0, /* properties_provided */ | |
| 443 0, /* properties_destroyed */ | |
| 444 0, /* todo_flags_start */ | |
| 445 0, /* todo_flags_finish */ | |
| 0 | 446 }; |
| 447 | |
| 111 | 448 class pass_uncprop : public gimple_opt_pass |
| 449 { | |
| 450 public: | |
| 451 pass_uncprop (gcc::context *ctxt) | |
| 452 : gimple_opt_pass (pass_data_uncprop, ctxt) | |
| 453 {} | |
| 454 | |
| 455 /* opt_pass methods: */ | |
| 456 opt_pass * clone () { return new pass_uncprop (m_ctxt); } | |
| 457 virtual bool gate (function *) { return flag_tree_dom != 0; } | |
| 458 virtual unsigned int execute (function *); | |
| 459 | |
| 460 }; // class pass_uncprop | |
| 461 | |
| 462 unsigned int | |
| 463 pass_uncprop::execute (function *fun) | |
| 464 { | |
| 465 basic_block bb; | |
| 466 | |
| 467 associate_equivalences_with_edges (); | |
| 468 | |
| 469 /* Create our global data structures. */ | |
| 145 | 470 val_ssa_equiv = new val_ssa_equiv_t (1024); |
| 111 | 471 |
| 472 /* We're going to do a dominator walk, so ensure that we have | |
| 473 dominance information. */ | |
| 474 calculate_dominance_info (CDI_DOMINATORS); | |
| 475 | |
| 476 /* Recursively walk the dominator tree undoing unprofitable | |
| 477 constant/copy propagations. */ | |
| 478 uncprop_dom_walker (CDI_DOMINATORS).walk (fun->cfg->x_entry_block_ptr); | |
| 479 | |
| 480 /* we just need to empty elements out of the hash table, and cleanup the | |
| 481 AUX field on the edges. */ | |
| 482 delete val_ssa_equiv; | |
| 483 val_ssa_equiv = NULL; | |
| 484 FOR_EACH_BB_FN (bb, fun) | |
| 485 { | |
| 486 edge e; | |
| 487 edge_iterator ei; | |
| 488 | |
| 489 FOR_EACH_EDGE (e, ei, bb->succs) | |
| 490 { | |
| 491 if (e->aux) | |
| 492 { | |
| 493 free (e->aux); | |
| 494 e->aux = NULL; | |
| 495 } | |
| 496 } | |
| 497 } | |
| 498 return 0; | |
| 499 } | |
| 500 | |
| 501 } // anon namespace | |
| 502 | |
| 503 gimple_opt_pass * | |
| 504 make_pass_uncprop (gcc::context *ctxt) | |
| 505 { | |
| 506 return new pass_uncprop (ctxt); | |
| 507 } |