1 /* Dead code elimination pass for the GNU compiler. 2 Copyright (C) 2002-2019 Free Software Foundation, Inc. 3 Contributed by Ben Elliston <bje@redhat.com> 4 and Andrew MacLeod <amacleod@redhat.com> 5 Adapted to use control dependence by Steven Bosscher, SUSE Labs. 6 7 This file is part of GCC. 8 9 GCC is free software; you can redistribute it and/or modify it 10 under the terms of the GNU General Public License as published by the 11 Free Software Foundation; either version 3, or (at your option) any 12 later version. 13 14 GCC is distributed in the hope that it will be useful, but WITHOUT 15 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 16 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 17 for more details. 18 19 You should have received a copy of the GNU General Public License 20 along with GCC; see the file COPYING3. If not see 21 <http://www.gnu.org/licenses/>. */ 22 23 /* Dead code elimination. 24 25 References: 26 27 Building an Optimizing Compiler, 28 Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9. 29 30 Advanced Compiler Design and Implementation, 31 Steven Muchnick, Morgan Kaufmann, 1997, Section 18.10. 32 33 Dead-code elimination is the removal of statements which have no 34 impact on the program's output. "Dead statements" have no impact 35 on the program's output, while "necessary statements" may have 36 impact on the output. 37 38 The algorithm consists of three phases: 39 1. Marking as necessary all statements known to be necessary, 40 e.g. most function calls, writing a value to memory, etc; 41 2. Propagating necessary statements, e.g., the statements 42 giving values to operands in necessary statements; and 43 3. Removing dead statements. */ 44 45 #include "config.h" 46 #include "system.h" 47 #include "coretypes.h" 48 #include "backend.h" 49 #include "rtl.h" 50 #include "tree.h" 51 #include "gimple.h" 52 #include "cfghooks.h" 53 #include "tree-pass.h" 54 #include "ssa.h" 55 #include "gimple-pretty-print.h" 56 #include "fold-const.h" 57 #include "calls.h" 58 #include "cfganal.h" 59 #include "tree-eh.h" 60 #include "gimplify.h" 61 #include "gimple-iterator.h" 62 #include "tree-cfg.h" 63 #include "tree-ssa-loop-niter.h" 64 #include "tree-into-ssa.h" 65 #include "tree-dfa.h" 66 #include "cfgloop.h" 67 #include "tree-scalar-evolution.h" 68 #include "tree-ssa-propagate.h" 69 #include "gimple-fold.h" 70 71 static struct stmt_stats 72 { 73 int total; 74 int total_phis; 75 int removed; 76 int removed_phis; 77 } stats; 78 79 #define STMT_NECESSARY GF_PLF_1 80 81 static vec<gimple *> worklist; 82 83 /* Vector indicating an SSA name has already been processed and marked 84 as necessary. */ 85 static sbitmap processed; 86 87 /* Vector indicating that the last statement of a basic block has already 88 been marked as necessary. */ 89 static sbitmap last_stmt_necessary; 90 91 /* Vector indicating that BB contains statements that are live. */ 92 static sbitmap bb_contains_live_stmts; 93 94 /* Before we can determine whether a control branch is dead, we need to 95 compute which blocks are control dependent on which edges. 96 97 We expect each block to be control dependent on very few edges so we 98 use a bitmap for each block recording its edges. An array holds the 99 bitmap. The Ith bit in the bitmap is set if that block is dependent 100 on the Ith edge. */ 101 static control_dependences *cd; 102 103 /* Vector indicating that a basic block has already had all the edges 104 processed that it is control dependent on. */ 105 static sbitmap visited_control_parents; 106 107 /* TRUE if this pass alters the CFG (by removing control statements). 108 FALSE otherwise. 109 110 If this pass alters the CFG, then it will arrange for the dominators 111 to be recomputed. */ 112 static bool cfg_altered; 113 114 /* When non-NULL holds map from basic block index into the postorder. */ 115 static int *bb_postorder; 116 117 118 /* If STMT is not already marked necessary, mark it, and add it to the 119 worklist if ADD_TO_WORKLIST is true. */ 120 121 static inline void 122 mark_stmt_necessary (gimple *stmt, bool add_to_worklist) 123 { 124 gcc_assert (stmt); 125 126 if (gimple_plf (stmt, STMT_NECESSARY)) 127 return; 128 129 if (dump_file && (dump_flags & TDF_DETAILS)) 130 { 131 fprintf (dump_file, "Marking useful stmt: "); 132 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM); 133 fprintf (dump_file, "\n"); 134 } 135 136 gimple_set_plf (stmt, STMT_NECESSARY, true); 137 if (add_to_worklist) 138 worklist.safe_push (stmt); 139 if (add_to_worklist && bb_contains_live_stmts && !is_gimple_debug (stmt)) 140 bitmap_set_bit (bb_contains_live_stmts, gimple_bb (stmt)->index); 141 } 142 143 144 /* Mark the statement defining operand OP as necessary. */ 145 146 static inline void 147 mark_operand_necessary (tree op) 148 { 149 gimple *stmt; 150 int ver; 151 152 gcc_assert (op); 153 154 ver = SSA_NAME_VERSION (op); 155 if (bitmap_bit_p (processed, ver)) 156 { 157 stmt = SSA_NAME_DEF_STMT (op); 158 gcc_assert (gimple_nop_p (stmt) 159 || gimple_plf (stmt, STMT_NECESSARY)); 160 return; 161 } 162 bitmap_set_bit (processed, ver); 163 164 stmt = SSA_NAME_DEF_STMT (op); 165 gcc_assert (stmt); 166 167 if (gimple_plf (stmt, STMT_NECESSARY) || gimple_nop_p (stmt)) 168 return; 169 170 if (dump_file && (dump_flags & TDF_DETAILS)) 171 { 172 fprintf (dump_file, "marking necessary through "); 173 print_generic_expr (dump_file, op); 174 fprintf (dump_file, " stmt "); 175 print_gimple_stmt (dump_file, stmt, 0); 176 } 177 178 gimple_set_plf (stmt, STMT_NECESSARY, true); 179 if (bb_contains_live_stmts) 180 bitmap_set_bit (bb_contains_live_stmts, gimple_bb (stmt)->index); 181 worklist.safe_push (stmt); 182 } 183 184 185 /* Mark STMT as necessary if it obviously is. Add it to the worklist if 186 it can make other statements necessary. 187 188 If AGGRESSIVE is false, control statements are conservatively marked as 189 necessary. */ 190 191 static void 192 mark_stmt_if_obviously_necessary (gimple *stmt, bool aggressive) 193 { 194 /* With non-call exceptions, we have to assume that all statements could 195 throw. If a statement could throw, it can be deemed necessary. */ 196 if (cfun->can_throw_non_call_exceptions 197 && !cfun->can_delete_dead_exceptions 198 && stmt_could_throw_p (cfun, stmt)) 199 { 200 mark_stmt_necessary (stmt, true); 201 return; 202 } 203 204 /* Statements that are implicitly live. Most function calls, asm 205 and return statements are required. Labels and GIMPLE_BIND nodes 206 are kept because they are control flow, and we have no way of 207 knowing whether they can be removed. DCE can eliminate all the 208 other statements in a block, and CFG can then remove the block 209 and labels. */ 210 switch (gimple_code (stmt)) 211 { 212 case GIMPLE_PREDICT: 213 case GIMPLE_LABEL: 214 mark_stmt_necessary (stmt, false); 215 return; 216 217 case GIMPLE_ASM: 218 case GIMPLE_RESX: 219 case GIMPLE_RETURN: 220 mark_stmt_necessary (stmt, true); 221 return; 222 223 case GIMPLE_CALL: 224 { 225 tree callee = gimple_call_fndecl (stmt); 226 if (callee != NULL_TREE 227 && fndecl_built_in_p (callee, BUILT_IN_NORMAL)) 228 switch (DECL_FUNCTION_CODE (callee)) 229 { 230 case BUILT_IN_MALLOC: 231 case BUILT_IN_ALIGNED_ALLOC: 232 case BUILT_IN_CALLOC: 233 CASE_BUILT_IN_ALLOCA: 234 case BUILT_IN_STRDUP: 235 case BUILT_IN_STRNDUP: 236 return; 237 238 default:; 239 } 240 /* Most, but not all function calls are required. Function calls that 241 produce no result and have no side effects (i.e. const pure 242 functions) are unnecessary. */ 243 if (gimple_has_side_effects (stmt)) 244 { 245 mark_stmt_necessary (stmt, true); 246 return; 247 } 248 if (!gimple_call_lhs (stmt)) 249 return; 250 break; 251 } 252 253 case GIMPLE_DEBUG: 254 /* Debug temps without a value are not useful. ??? If we could 255 easily locate the debug temp bind stmt for a use thereof, 256 would could refrain from marking all debug temps here, and 257 mark them only if they're used. */ 258 if (gimple_debug_nonbind_marker_p (stmt) 259 || !gimple_debug_bind_p (stmt) 260 || gimple_debug_bind_has_value_p (stmt) 261 || TREE_CODE (gimple_debug_bind_get_var (stmt)) != DEBUG_EXPR_DECL) 262 mark_stmt_necessary (stmt, false); 263 return; 264 265 case GIMPLE_GOTO: 266 gcc_assert (!simple_goto_p (stmt)); 267 mark_stmt_necessary (stmt, true); 268 return; 269 270 case GIMPLE_COND: 271 gcc_assert (EDGE_COUNT (gimple_bb (stmt)->succs) == 2); 272 /* Fall through. */ 273 274 case GIMPLE_SWITCH: 275 if (! aggressive) 276 mark_stmt_necessary (stmt, true); 277 break; 278 279 case GIMPLE_ASSIGN: 280 if (gimple_clobber_p (stmt)) 281 return; 282 break; 283 284 default: 285 break; 286 } 287 288 /* If the statement has volatile operands, it needs to be preserved. 289 Same for statements that can alter control flow in unpredictable 290 ways. */ 291 if (gimple_has_volatile_ops (stmt) || is_ctrl_altering_stmt (stmt)) 292 { 293 mark_stmt_necessary (stmt, true); 294 return; 295 } 296 297 if (stmt_may_clobber_global_p (stmt)) 298 { 299 mark_stmt_necessary (stmt, true); 300 return; 301 } 302 303 return; 304 } 305 306 307 /* Mark the last statement of BB as necessary. */ 308 309 static void 310 mark_last_stmt_necessary (basic_block bb) 311 { 312 gimple *stmt = last_stmt (bb); 313 314 bitmap_set_bit (last_stmt_necessary, bb->index); 315 bitmap_set_bit (bb_contains_live_stmts, bb->index); 316 317 /* We actually mark the statement only if it is a control statement. */ 318 if (stmt && is_ctrl_stmt (stmt)) 319 mark_stmt_necessary (stmt, true); 320 } 321 322 323 /* Mark control dependent edges of BB as necessary. We have to do this only 324 once for each basic block so we set the appropriate bit after we're done. 325 326 When IGNORE_SELF is true, ignore BB in the list of control dependences. */ 327 328 static void 329 mark_control_dependent_edges_necessary (basic_block bb, bool ignore_self) 330 { 331 bitmap_iterator bi; 332 unsigned edge_number; 333 bool skipped = false; 334 335 gcc_assert (bb != EXIT_BLOCK_PTR_FOR_FN (cfun)); 336 337 if (bb == ENTRY_BLOCK_PTR_FOR_FN (cfun)) 338 return; 339 340 EXECUTE_IF_SET_IN_BITMAP (cd->get_edges_dependent_on (bb->index), 341 0, edge_number, bi) 342 { 343 basic_block cd_bb = cd->get_edge_src (edge_number); 344 345 if (ignore_self && cd_bb == bb) 346 { 347 skipped = true; 348 continue; 349 } 350 351 if (!bitmap_bit_p (last_stmt_necessary, cd_bb->index)) 352 mark_last_stmt_necessary (cd_bb); 353 } 354 355 if (!skipped) 356 bitmap_set_bit (visited_control_parents, bb->index); 357 } 358 359 360 /* Find obviously necessary statements. These are things like most function 361 calls, and stores to file level variables. 362 363 If EL is NULL, control statements are conservatively marked as 364 necessary. Otherwise it contains the list of edges used by control 365 dependence analysis. */ 366 367 static void 368 find_obviously_necessary_stmts (bool aggressive) 369 { 370 basic_block bb; 371 gimple_stmt_iterator gsi; 372 edge e; 373 gimple *phi, *stmt; 374 int flags; 375 376 FOR_EACH_BB_FN (bb, cfun) 377 { 378 /* PHI nodes are never inherently necessary. */ 379 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi)) 380 { 381 phi = gsi_stmt (gsi); 382 gimple_set_plf (phi, STMT_NECESSARY, false); 383 } 384 385 /* Check all statements in the block. */ 386 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi)) 387 { 388 stmt = gsi_stmt (gsi); 389 gimple_set_plf (stmt, STMT_NECESSARY, false); 390 mark_stmt_if_obviously_necessary (stmt, aggressive); 391 } 392 } 393 394 /* Pure and const functions are finite and thus have no infinite loops in 395 them. */ 396 flags = flags_from_decl_or_type (current_function_decl); 397 if ((flags & (ECF_CONST|ECF_PURE)) && !(flags & ECF_LOOPING_CONST_OR_PURE)) 398 return; 399 400 /* Prevent the empty possibly infinite loops from being removed. */ 401 if (aggressive) 402 { 403 struct loop *loop; 404 if (mark_irreducible_loops ()) 405 FOR_EACH_BB_FN (bb, cfun) 406 { 407 edge_iterator ei; 408 FOR_EACH_EDGE (e, ei, bb->succs) 409 if ((e->flags & EDGE_DFS_BACK) 410 && (e->flags & EDGE_IRREDUCIBLE_LOOP)) 411 { 412 if (dump_file) 413 fprintf (dump_file, "Marking back edge of irreducible loop %i->%i\n", 414 e->src->index, e->dest->index); 415 mark_control_dependent_edges_necessary (e->dest, false); 416 } 417 } 418 419 FOR_EACH_LOOP (loop, 0) 420 if (!finite_loop_p (loop)) 421 { 422 if (dump_file) 423 fprintf (dump_file, "cannot prove finiteness of loop %i\n", loop->num); 424 mark_control_dependent_edges_necessary (loop->latch, false); 425 } 426 } 427 } 428 429 430 /* Return true if REF is based on an aliased base, otherwise false. */ 431 432 static bool 433 ref_may_be_aliased (tree ref) 434 { 435 gcc_assert (TREE_CODE (ref) != WITH_SIZE_EXPR); 436 while (handled_component_p (ref)) 437 ref = TREE_OPERAND (ref, 0); 438 if (TREE_CODE (ref) == MEM_REF 439 && TREE_CODE (TREE_OPERAND (ref, 0)) == ADDR_EXPR) 440 ref = TREE_OPERAND (TREE_OPERAND (ref, 0), 0); 441 return !(DECL_P (ref) 442 && !may_be_aliased (ref)); 443 } 444 445 static bitmap visited = NULL; 446 static unsigned int longest_chain = 0; 447 static unsigned int total_chain = 0; 448 static unsigned int nr_walks = 0; 449 static bool chain_ovfl = false; 450 451 /* Worker for the walker that marks reaching definitions of REF, 452 which is based on a non-aliased decl, necessary. It returns 453 true whenever the defining statement of the current VDEF is 454 a kill for REF, as no dominating may-defs are necessary for REF 455 anymore. DATA points to the basic-block that contains the 456 stmt that refers to REF. */ 457 458 static bool 459 mark_aliased_reaching_defs_necessary_1 (ao_ref *ref, tree vdef, void *data) 460 { 461 gimple *def_stmt = SSA_NAME_DEF_STMT (vdef); 462 463 /* All stmts we visit are necessary. */ 464 if (! gimple_clobber_p (def_stmt)) 465 mark_operand_necessary (vdef); 466 467 /* If the stmt lhs kills ref, then we can stop walking. */ 468 if (gimple_has_lhs (def_stmt) 469 && TREE_CODE (gimple_get_lhs (def_stmt)) != SSA_NAME 470 /* The assignment is not necessarily carried out if it can throw 471 and we can catch it in the current function where we could inspect 472 the previous value. 473 ??? We only need to care about the RHS throwing. For aggregate 474 assignments or similar calls and non-call exceptions the LHS 475 might throw as well. */ 476 && !stmt_can_throw_internal (cfun, def_stmt)) 477 { 478 tree base, lhs = gimple_get_lhs (def_stmt); 479 poly_int64 size, offset, max_size; 480 bool reverse; 481 ao_ref_base (ref); 482 base 483 = get_ref_base_and_extent (lhs, &offset, &size, &max_size, &reverse); 484 /* We can get MEM[symbol: sZ, index: D.8862_1] here, 485 so base == refd->base does not always hold. */ 486 if (base == ref->base) 487 { 488 /* For a must-alias check we need to be able to constrain 489 the accesses properly. */ 490 if (known_eq (size, max_size) 491 && known_subrange_p (ref->offset, ref->max_size, offset, size)) 492 return true; 493 /* Or they need to be exactly the same. */ 494 else if (ref->ref 495 /* Make sure there is no induction variable involved 496 in the references (gcc.c-torture/execute/pr42142.c). 497 The simplest way is to check if the kill dominates 498 the use. */ 499 /* But when both are in the same block we cannot 500 easily tell whether we came from a backedge 501 unless we decide to compute stmt UIDs 502 (see PR58246). */ 503 && (basic_block) data != gimple_bb (def_stmt) 504 && dominated_by_p (CDI_DOMINATORS, (basic_block) data, 505 gimple_bb (def_stmt)) 506 && operand_equal_p (ref->ref, lhs, 0)) 507 return true; 508 } 509 } 510 511 /* Otherwise keep walking. */ 512 return false; 513 } 514 515 static void 516 mark_aliased_reaching_defs_necessary (gimple *stmt, tree ref) 517 { 518 unsigned int chain; 519 ao_ref refd; 520 gcc_assert (!chain_ovfl); 521 ao_ref_init (&refd, ref); 522 chain = walk_aliased_vdefs (&refd, gimple_vuse (stmt), 523 mark_aliased_reaching_defs_necessary_1, 524 gimple_bb (stmt), NULL); 525 if (chain > longest_chain) 526 longest_chain = chain; 527 total_chain += chain; 528 nr_walks++; 529 } 530 531 /* Worker for the walker that marks reaching definitions of REF, which 532 is not based on a non-aliased decl. For simplicity we need to end 533 up marking all may-defs necessary that are not based on a non-aliased 534 decl. The only job of this walker is to skip may-defs based on 535 a non-aliased decl. */ 536 537 static bool 538 mark_all_reaching_defs_necessary_1 (ao_ref *ref ATTRIBUTE_UNUSED, 539 tree vdef, void *data ATTRIBUTE_UNUSED) 540 { 541 gimple *def_stmt = SSA_NAME_DEF_STMT (vdef); 542 543 /* We have to skip already visited (and thus necessary) statements 544 to make the chaining work after we dropped back to simple mode. */ 545 if (chain_ovfl 546 && bitmap_bit_p (processed, SSA_NAME_VERSION (vdef))) 547 { 548 gcc_assert (gimple_nop_p (def_stmt) 549 || gimple_plf (def_stmt, STMT_NECESSARY)); 550 return false; 551 } 552 553 /* We want to skip stores to non-aliased variables. */ 554 if (!chain_ovfl 555 && gimple_assign_single_p (def_stmt)) 556 { 557 tree lhs = gimple_assign_lhs (def_stmt); 558 if (!ref_may_be_aliased (lhs)) 559 return false; 560 } 561 562 /* We want to skip statments that do not constitute stores but have 563 a virtual definition. */ 564 if (is_gimple_call (def_stmt)) 565 { 566 tree callee = gimple_call_fndecl (def_stmt); 567 if (callee != NULL_TREE 568 && fndecl_built_in_p (callee, BUILT_IN_NORMAL)) 569 switch (DECL_FUNCTION_CODE (callee)) 570 { 571 case BUILT_IN_MALLOC: 572 case BUILT_IN_ALIGNED_ALLOC: 573 case BUILT_IN_CALLOC: 574 CASE_BUILT_IN_ALLOCA: 575 case BUILT_IN_FREE: 576 return false; 577 578 default:; 579 } 580 } 581 582 if (! gimple_clobber_p (def_stmt)) 583 mark_operand_necessary (vdef); 584 585 return false; 586 } 587 588 static void 589 mark_all_reaching_defs_necessary (gimple *stmt) 590 { 591 walk_aliased_vdefs (NULL, gimple_vuse (stmt), 592 mark_all_reaching_defs_necessary_1, NULL, &visited); 593 } 594 595 /* Return true for PHI nodes with one or identical arguments 596 can be removed. */ 597 static bool 598 degenerate_phi_p (gimple *phi) 599 { 600 unsigned int i; 601 tree op = gimple_phi_arg_def (phi, 0); 602 for (i = 1; i < gimple_phi_num_args (phi); i++) 603 if (gimple_phi_arg_def (phi, i) != op) 604 return false; 605 return true; 606 } 607 608 /* Propagate necessity using the operands of necessary statements. 609 Process the uses on each statement in the worklist, and add all 610 feeding statements which contribute to the calculation of this 611 value to the worklist. 612 613 In conservative mode, EL is NULL. */ 614 615 static void 616 propagate_necessity (bool aggressive) 617 { 618 gimple *stmt; 619 620 if (dump_file && (dump_flags & TDF_DETAILS)) 621 fprintf (dump_file, "\nProcessing worklist:\n"); 622 623 while (worklist.length () > 0) 624 { 625 /* Take STMT from worklist. */ 626 stmt = worklist.pop (); 627 628 if (dump_file && (dump_flags & TDF_DETAILS)) 629 { 630 fprintf (dump_file, "processing: "); 631 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM); 632 fprintf (dump_file, "\n"); 633 } 634 635 if (aggressive) 636 { 637 /* Mark the last statement of the basic blocks on which the block 638 containing STMT is control dependent, but only if we haven't 639 already done so. */ 640 basic_block bb = gimple_bb (stmt); 641 if (bb != ENTRY_BLOCK_PTR_FOR_FN (cfun) 642 && !bitmap_bit_p (visited_control_parents, bb->index)) 643 mark_control_dependent_edges_necessary (bb, false); 644 } 645 646 if (gimple_code (stmt) == GIMPLE_PHI 647 /* We do not process virtual PHI nodes nor do we track their 648 necessity. */ 649 && !virtual_operand_p (gimple_phi_result (stmt))) 650 { 651 /* PHI nodes are somewhat special in that each PHI alternative has 652 data and control dependencies. All the statements feeding the 653 PHI node's arguments are always necessary. In aggressive mode, 654 we also consider the control dependent edges leading to the 655 predecessor block associated with each PHI alternative as 656 necessary. */ 657 gphi *phi = as_a <gphi *> (stmt); 658 size_t k; 659 660 for (k = 0; k < gimple_phi_num_args (stmt); k++) 661 { 662 tree arg = PHI_ARG_DEF (stmt, k); 663 if (TREE_CODE (arg) == SSA_NAME) 664 mark_operand_necessary (arg); 665 } 666 667 /* For PHI operands it matters from where the control flow arrives 668 to the BB. Consider the following example: 669 670 a=exp1; 671 b=exp2; 672 if (test) 673 ; 674 else 675 ; 676 c=PHI(a,b) 677 678 We need to mark control dependence of the empty basic blocks, since they 679 contains computation of PHI operands. 680 681 Doing so is too restrictive in the case the predecestor block is in 682 the loop. Consider: 683 684 if (b) 685 { 686 int i; 687 for (i = 0; i<1000; ++i) 688 ; 689 j = 0; 690 } 691 return j; 692 693 There is PHI for J in the BB containing return statement. 694 In this case the control dependence of predecestor block (that is 695 within the empty loop) also contains the block determining number 696 of iterations of the block that would prevent removing of empty 697 loop in this case. 698 699 This scenario can be avoided by splitting critical edges. 700 To save the critical edge splitting pass we identify how the control 701 dependence would look like if the edge was split. 702 703 Consider the modified CFG created from current CFG by splitting 704 edge B->C. In the postdominance tree of modified CFG, C' is 705 always child of C. There are two cases how chlids of C' can look 706 like: 707 708 1) C' is leaf 709 710 In this case the only basic block C' is control dependent on is B. 711 712 2) C' has single child that is B 713 714 In this case control dependence of C' is same as control 715 dependence of B in original CFG except for block B itself. 716 (since C' postdominate B in modified CFG) 717 718 Now how to decide what case happens? There are two basic options: 719 720 a) C postdominate B. Then C immediately postdominate B and 721 case 2 happens iff there is no other way from B to C except 722 the edge B->C. 723 724 There is other way from B to C iff there is succesor of B that 725 is not postdominated by B. Testing this condition is somewhat 726 expensive, because we need to iterate all succesors of B. 727 We are safe to assume that this does not happen: we will mark B 728 as needed when processing the other path from B to C that is 729 conrol dependent on B and marking control dependencies of B 730 itself is harmless because they will be processed anyway after 731 processing control statement in B. 732 733 b) C does not postdominate B. Always case 1 happens since there is 734 path from C to exit that does not go through B and thus also C'. */ 735 736 if (aggressive && !degenerate_phi_p (stmt)) 737 { 738 for (k = 0; k < gimple_phi_num_args (stmt); k++) 739 { 740 basic_block arg_bb = gimple_phi_arg_edge (phi, k)->src; 741 742 if (gimple_bb (stmt) 743 != get_immediate_dominator (CDI_POST_DOMINATORS, arg_bb)) 744 { 745 if (!bitmap_bit_p (last_stmt_necessary, arg_bb->index)) 746 mark_last_stmt_necessary (arg_bb); 747 } 748 else if (arg_bb != ENTRY_BLOCK_PTR_FOR_FN (cfun) 749 && !bitmap_bit_p (visited_control_parents, 750 arg_bb->index)) 751 mark_control_dependent_edges_necessary (arg_bb, true); 752 } 753 } 754 } 755 else 756 { 757 /* Propagate through the operands. Examine all the USE, VUSE and 758 VDEF operands in this statement. Mark all the statements 759 which feed this statement's uses as necessary. */ 760 ssa_op_iter iter; 761 tree use; 762 763 /* If this is a call to free which is directly fed by an 764 allocation function do not mark that necessary through 765 processing the argument. */ 766 if (gimple_call_builtin_p (stmt, BUILT_IN_FREE)) 767 { 768 tree ptr = gimple_call_arg (stmt, 0); 769 gimple *def_stmt; 770 tree def_callee; 771 /* If the pointer we free is defined by an allocation 772 function do not add the call to the worklist. */ 773 if (TREE_CODE (ptr) == SSA_NAME 774 && is_gimple_call (def_stmt = SSA_NAME_DEF_STMT (ptr)) 775 && (def_callee = gimple_call_fndecl (def_stmt)) 776 && DECL_BUILT_IN_CLASS (def_callee) == BUILT_IN_NORMAL 777 && (DECL_FUNCTION_CODE (def_callee) == BUILT_IN_ALIGNED_ALLOC 778 || DECL_FUNCTION_CODE (def_callee) == BUILT_IN_MALLOC 779 || DECL_FUNCTION_CODE (def_callee) == BUILT_IN_CALLOC)) 780 continue; 781 } 782 783 FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE) 784 mark_operand_necessary (use); 785 786 use = gimple_vuse (stmt); 787 if (!use) 788 continue; 789 790 /* If we dropped to simple mode make all immediately 791 reachable definitions necessary. */ 792 if (chain_ovfl) 793 { 794 mark_all_reaching_defs_necessary (stmt); 795 continue; 796 } 797 798 /* For statements that may load from memory (have a VUSE) we 799 have to mark all reaching (may-)definitions as necessary. 800 We partition this task into two cases: 801 1) explicit loads based on decls that are not aliased 802 2) implicit loads (like calls) and explicit loads not 803 based on decls that are not aliased (like indirect 804 references or loads from globals) 805 For 1) we mark all reaching may-defs as necessary, stopping 806 at dominating kills. For 2) we want to mark all dominating 807 references necessary, but non-aliased ones which we handle 808 in 1). By keeping a global visited bitmap for references 809 we walk for 2) we avoid quadratic behavior for those. */ 810 811 if (is_gimple_call (stmt)) 812 { 813 tree callee = gimple_call_fndecl (stmt); 814 unsigned i; 815 816 /* Calls to functions that are merely acting as barriers 817 or that only store to memory do not make any previous 818 stores necessary. */ 819 if (callee != NULL_TREE 820 && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL 821 && (DECL_FUNCTION_CODE (callee) == BUILT_IN_MEMSET 822 || DECL_FUNCTION_CODE (callee) == BUILT_IN_MEMSET_CHK 823 || DECL_FUNCTION_CODE (callee) == BUILT_IN_MALLOC 824 || DECL_FUNCTION_CODE (callee) == BUILT_IN_ALIGNED_ALLOC 825 || DECL_FUNCTION_CODE (callee) == BUILT_IN_CALLOC 826 || DECL_FUNCTION_CODE (callee) == BUILT_IN_FREE 827 || DECL_FUNCTION_CODE (callee) == BUILT_IN_VA_END 828 || ALLOCA_FUNCTION_CODE_P (DECL_FUNCTION_CODE (callee)) 829 || DECL_FUNCTION_CODE (callee) == BUILT_IN_STACK_SAVE 830 || DECL_FUNCTION_CODE (callee) == BUILT_IN_STACK_RESTORE 831 || DECL_FUNCTION_CODE (callee) == BUILT_IN_ASSUME_ALIGNED)) 832 continue; 833 834 /* Calls implicitly load from memory, their arguments 835 in addition may explicitly perform memory loads. */ 836 mark_all_reaching_defs_necessary (stmt); 837 for (i = 0; i < gimple_call_num_args (stmt); ++i) 838 { 839 tree arg = gimple_call_arg (stmt, i); 840 if (TREE_CODE (arg) == SSA_NAME 841 || is_gimple_min_invariant (arg)) 842 continue; 843 if (TREE_CODE (arg) == WITH_SIZE_EXPR) 844 arg = TREE_OPERAND (arg, 0); 845 if (!ref_may_be_aliased (arg)) 846 mark_aliased_reaching_defs_necessary (stmt, arg); 847 } 848 } 849 else if (gimple_assign_single_p (stmt)) 850 { 851 tree rhs; 852 /* If this is a load mark things necessary. */ 853 rhs = gimple_assign_rhs1 (stmt); 854 if (TREE_CODE (rhs) != SSA_NAME 855 && !is_gimple_min_invariant (rhs) 856 && TREE_CODE (rhs) != CONSTRUCTOR) 857 { 858 if (!ref_may_be_aliased (rhs)) 859 mark_aliased_reaching_defs_necessary (stmt, rhs); 860 else 861 mark_all_reaching_defs_necessary (stmt); 862 } 863 } 864 else if (greturn *return_stmt = dyn_cast <greturn *> (stmt)) 865 { 866 tree rhs = gimple_return_retval (return_stmt); 867 /* A return statement may perform a load. */ 868 if (rhs 869 && TREE_CODE (rhs) != SSA_NAME 870 && !is_gimple_min_invariant (rhs) 871 && TREE_CODE (rhs) != CONSTRUCTOR) 872 { 873 if (!ref_may_be_aliased (rhs)) 874 mark_aliased_reaching_defs_necessary (stmt, rhs); 875 else 876 mark_all_reaching_defs_necessary (stmt); 877 } 878 } 879 else if (gasm *asm_stmt = dyn_cast <gasm *> (stmt)) 880 { 881 unsigned i; 882 mark_all_reaching_defs_necessary (stmt); 883 /* Inputs may perform loads. */ 884 for (i = 0; i < gimple_asm_ninputs (asm_stmt); ++i) 885 { 886 tree op = TREE_VALUE (gimple_asm_input_op (asm_stmt, i)); 887 if (TREE_CODE (op) != SSA_NAME 888 && !is_gimple_min_invariant (op) 889 && TREE_CODE (op) != CONSTRUCTOR 890 && !ref_may_be_aliased (op)) 891 mark_aliased_reaching_defs_necessary (stmt, op); 892 } 893 } 894 else if (gimple_code (stmt) == GIMPLE_TRANSACTION) 895 { 896 /* The beginning of a transaction is a memory barrier. */ 897 /* ??? If we were really cool, we'd only be a barrier 898 for the memories touched within the transaction. */ 899 mark_all_reaching_defs_necessary (stmt); 900 } 901 else 902 gcc_unreachable (); 903 904 /* If we over-used our alias oracle budget drop to simple 905 mode. The cost metric allows quadratic behavior 906 (number of uses times number of may-defs queries) up to 907 a constant maximal number of queries and after that falls back to 908 super-linear complexity. */ 909 if (/* Constant but quadratic for small functions. */ 910 total_chain > 128 * 128 911 /* Linear in the number of may-defs. */ 912 && total_chain > 32 * longest_chain 913 /* Linear in the number of uses. */ 914 && total_chain > nr_walks * 32) 915 { 916 chain_ovfl = true; 917 if (visited) 918 bitmap_clear (visited); 919 } 920 } 921 } 922 } 923 924 /* Remove dead PHI nodes from block BB. */ 925 926 static bool 927 remove_dead_phis (basic_block bb) 928 { 929 bool something_changed = false; 930 gphi *phi; 931 gphi_iterator gsi; 932 933 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi);) 934 { 935 stats.total_phis++; 936 phi = gsi.phi (); 937 938 /* We do not track necessity of virtual PHI nodes. Instead do 939 very simple dead PHI removal here. */ 940 if (virtual_operand_p (gimple_phi_result (phi))) 941 { 942 /* Virtual PHI nodes with one or identical arguments 943 can be removed. */ 944 if (degenerate_phi_p (phi)) 945 { 946 tree vdef = gimple_phi_result (phi); 947 tree vuse = gimple_phi_arg_def (phi, 0); 948 949 use_operand_p use_p; 950 imm_use_iterator iter; 951 gimple *use_stmt; 952 FOR_EACH_IMM_USE_STMT (use_stmt, iter, vdef) 953 FOR_EACH_IMM_USE_ON_STMT (use_p, iter) 954 SET_USE (use_p, vuse); 955 if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vdef) 956 && TREE_CODE (vuse) == SSA_NAME) 957 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (vuse) = 1; 958 } 959 else 960 gimple_set_plf (phi, STMT_NECESSARY, true); 961 } 962 963 if (!gimple_plf (phi, STMT_NECESSARY)) 964 { 965 something_changed = true; 966 if (dump_file && (dump_flags & TDF_DETAILS)) 967 { 968 fprintf (dump_file, "Deleting : "); 969 print_gimple_stmt (dump_file, phi, 0, TDF_SLIM); 970 fprintf (dump_file, "\n"); 971 } 972 973 remove_phi_node (&gsi, true); 974 stats.removed_phis++; 975 continue; 976 } 977 978 gsi_next (&gsi); 979 } 980 return something_changed; 981 } 982 983 984 /* Remove dead statement pointed to by iterator I. Receives the basic block BB 985 containing I so that we don't have to look it up. */ 986 987 static void 988 remove_dead_stmt (gimple_stmt_iterator *i, basic_block bb, 989 vec<edge> &to_remove_edges) 990 { 991 gimple *stmt = gsi_stmt (*i); 992 993 if (dump_file && (dump_flags & TDF_DETAILS)) 994 { 995 fprintf (dump_file, "Deleting : "); 996 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM); 997 fprintf (dump_file, "\n"); 998 } 999 1000 stats.removed++; 1001 1002 /* If we have determined that a conditional branch statement contributes 1003 nothing to the program, then we not only remove it, but we need to update 1004 the CFG. We can chose any of edges out of BB as long as we are sure to not 1005 close infinite loops. This is done by always choosing the edge closer to 1006 exit in inverted_post_order_compute order. */ 1007 if (is_ctrl_stmt (stmt)) 1008 { 1009 edge_iterator ei; 1010 edge e = NULL, e2; 1011 1012 /* See if there is only one non-abnormal edge. */ 1013 if (single_succ_p (bb)) 1014 e = single_succ_edge (bb); 1015 /* Otherwise chose one that is closer to bb with live statement in it. 1016 To be able to chose one, we compute inverted post order starting from 1017 all BBs with live statements. */ 1018 if (!e) 1019 { 1020 if (!bb_postorder) 1021 { 1022 auto_vec<int, 20> postorder; 1023 inverted_post_order_compute (&postorder, 1024 &bb_contains_live_stmts); 1025 bb_postorder = XNEWVEC (int, last_basic_block_for_fn (cfun)); 1026 for (unsigned int i = 0; i < postorder.length (); ++i) 1027 bb_postorder[postorder[i]] = i; 1028 } 1029 FOR_EACH_EDGE (e2, ei, bb->succs) 1030 if (!e || e2->dest == EXIT_BLOCK_PTR_FOR_FN (cfun) 1031 || bb_postorder [e->dest->index] 1032 < bb_postorder [e2->dest->index]) 1033 e = e2; 1034 } 1035 gcc_assert (e); 1036 e->probability = profile_probability::always (); 1037 1038 /* The edge is no longer associated with a conditional, so it does 1039 not have TRUE/FALSE flags. 1040 We are also safe to drop EH/ABNORMAL flags and turn them into 1041 normal control flow, because we know that all the destinations (including 1042 those odd edges) are equivalent for program execution. */ 1043 e->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE | EDGE_EH | EDGE_ABNORMAL); 1044 1045 /* The lone outgoing edge from BB will be a fallthru edge. */ 1046 e->flags |= EDGE_FALLTHRU; 1047 1048 /* Remove the remaining outgoing edges. */ 1049 FOR_EACH_EDGE (e2, ei, bb->succs) 1050 if (e != e2) 1051 { 1052 /* If we made a BB unconditionally exit a loop or removed 1053 an entry into an irreducible region, then this transform 1054 alters the set of BBs in the loop. Schedule a fixup. */ 1055 if (loop_exit_edge_p (bb->loop_father, e) 1056 || (e2->dest->flags & BB_IRREDUCIBLE_LOOP)) 1057 loops_state_set (LOOPS_NEED_FIXUP); 1058 to_remove_edges.safe_push (e2); 1059 } 1060 } 1061 1062 /* If this is a store into a variable that is being optimized away, 1063 add a debug bind stmt if possible. */ 1064 if (MAY_HAVE_DEBUG_BIND_STMTS 1065 && gimple_assign_single_p (stmt) 1066 && is_gimple_val (gimple_assign_rhs1 (stmt))) 1067 { 1068 tree lhs = gimple_assign_lhs (stmt); 1069 if ((VAR_P (lhs) || TREE_CODE (lhs) == PARM_DECL) 1070 && !DECL_IGNORED_P (lhs) 1071 && is_gimple_reg_type (TREE_TYPE (lhs)) 1072 && !is_global_var (lhs) 1073 && !DECL_HAS_VALUE_EXPR_P (lhs)) 1074 { 1075 tree rhs = gimple_assign_rhs1 (stmt); 1076 gdebug *note 1077 = gimple_build_debug_bind (lhs, unshare_expr (rhs), stmt); 1078 gsi_insert_after (i, note, GSI_SAME_STMT); 1079 } 1080 } 1081 1082 unlink_stmt_vdef (stmt); 1083 gsi_remove (i, true); 1084 release_defs (stmt); 1085 } 1086 1087 /* Helper for maybe_optimize_arith_overflow. Find in *TP if there are any 1088 uses of data (SSA_NAME) other than REALPART_EXPR referencing it. */ 1089 1090 static tree 1091 find_non_realpart_uses (tree *tp, int *walk_subtrees, void *data) 1092 { 1093 if (TYPE_P (*tp) || TREE_CODE (*tp) == REALPART_EXPR) 1094 *walk_subtrees = 0; 1095 if (*tp == (tree) data) 1096 return *tp; 1097 return NULL_TREE; 1098 } 1099 1100 /* If the IMAGPART_EXPR of the {ADD,SUB,MUL}_OVERFLOW result is never used, 1101 but REALPART_EXPR is, optimize the {ADD,SUB,MUL}_OVERFLOW internal calls 1102 into plain unsigned {PLUS,MINUS,MULT}_EXPR, and if needed reset debug 1103 uses. */ 1104 1105 static void 1106 maybe_optimize_arith_overflow (gimple_stmt_iterator *gsi, 1107 enum tree_code subcode) 1108 { 1109 gimple *stmt = gsi_stmt (*gsi); 1110 tree lhs = gimple_call_lhs (stmt); 1111 1112 if (lhs == NULL || TREE_CODE (lhs) != SSA_NAME) 1113 return; 1114 1115 imm_use_iterator imm_iter; 1116 use_operand_p use_p; 1117 bool has_debug_uses = false; 1118 bool has_realpart_uses = false; 1119 bool has_other_uses = false; 1120 FOR_EACH_IMM_USE_FAST (use_p, imm_iter, lhs) 1121 { 1122 gimple *use_stmt = USE_STMT (use_p); 1123 if (is_gimple_debug (use_stmt)) 1124 has_debug_uses = true; 1125 else if (is_gimple_assign (use_stmt) 1126 && gimple_assign_rhs_code (use_stmt) == REALPART_EXPR 1127 && TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0) == lhs) 1128 has_realpart_uses = true; 1129 else 1130 { 1131 has_other_uses = true; 1132 break; 1133 } 1134 } 1135 1136 if (!has_realpart_uses || has_other_uses) 1137 return; 1138 1139 tree arg0 = gimple_call_arg (stmt, 0); 1140 tree arg1 = gimple_call_arg (stmt, 1); 1141 location_t loc = gimple_location (stmt); 1142 tree type = TREE_TYPE (TREE_TYPE (lhs)); 1143 tree utype = type; 1144 if (!TYPE_UNSIGNED (type)) 1145 utype = build_nonstandard_integer_type (TYPE_PRECISION (type), 1); 1146 tree result = fold_build2_loc (loc, subcode, utype, 1147 fold_convert_loc (loc, utype, arg0), 1148 fold_convert_loc (loc, utype, arg1)); 1149 result = fold_convert_loc (loc, type, result); 1150 1151 if (has_debug_uses) 1152 { 1153 gimple *use_stmt; 1154 FOR_EACH_IMM_USE_STMT (use_stmt, imm_iter, lhs) 1155 { 1156 if (!gimple_debug_bind_p (use_stmt)) 1157 continue; 1158 tree v = gimple_debug_bind_get_value (use_stmt); 1159 if (walk_tree (&v, find_non_realpart_uses, lhs, NULL)) 1160 { 1161 gimple_debug_bind_reset_value (use_stmt); 1162 update_stmt (use_stmt); 1163 } 1164 } 1165 } 1166 1167 if (TREE_CODE (result) == INTEGER_CST && TREE_OVERFLOW (result)) 1168 result = drop_tree_overflow (result); 1169 tree overflow = build_zero_cst (type); 1170 tree ctype = build_complex_type (type); 1171 if (TREE_CODE (result) == INTEGER_CST) 1172 result = build_complex (ctype, result, overflow); 1173 else 1174 result = build2_loc (gimple_location (stmt), COMPLEX_EXPR, 1175 ctype, result, overflow); 1176 1177 if (dump_file && (dump_flags & TDF_DETAILS)) 1178 { 1179 fprintf (dump_file, "Transforming call: "); 1180 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM); 1181 fprintf (dump_file, "because the overflow result is never used into: "); 1182 print_generic_stmt (dump_file, result, TDF_SLIM); 1183 fprintf (dump_file, "\n"); 1184 } 1185 1186 if (!update_call_from_tree (gsi, result)) 1187 gimplify_and_update_call_from_tree (gsi, result); 1188 } 1189 1190 /* Eliminate unnecessary statements. Any instruction not marked as necessary 1191 contributes nothing to the program, and can be deleted. */ 1192 1193 static bool 1194 eliminate_unnecessary_stmts (void) 1195 { 1196 bool something_changed = false; 1197 basic_block bb; 1198 gimple_stmt_iterator gsi, psi; 1199 gimple *stmt; 1200 tree call; 1201 vec<basic_block> h; 1202 auto_vec<edge> to_remove_edges; 1203 1204 if (dump_file && (dump_flags & TDF_DETAILS)) 1205 fprintf (dump_file, "\nEliminating unnecessary statements:\n"); 1206 1207 clear_special_calls (); 1208 1209 /* Walking basic blocks and statements in reverse order avoids 1210 releasing SSA names before any other DEFs that refer to them are 1211 released. This helps avoid loss of debug information, as we get 1212 a chance to propagate all RHSs of removed SSAs into debug uses, 1213 rather than only the latest ones. E.g., consider: 1214 1215 x_3 = y_1 + z_2; 1216 a_5 = x_3 - b_4; 1217 # DEBUG a => a_5 1218 1219 If we were to release x_3 before a_5, when we reached a_5 and 1220 tried to substitute it into the debug stmt, we'd see x_3 there, 1221 but x_3's DEF, type, etc would have already been disconnected. 1222 By going backwards, the debug stmt first changes to: 1223 1224 # DEBUG a => x_3 - b_4 1225 1226 and then to: 1227 1228 # DEBUG a => y_1 + z_2 - b_4 1229 1230 as desired. */ 1231 gcc_assert (dom_info_available_p (CDI_DOMINATORS)); 1232 h = get_all_dominated_blocks (CDI_DOMINATORS, 1233 single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun))); 1234 1235 while (h.length ()) 1236 { 1237 bb = h.pop (); 1238 1239 /* Remove dead statements. */ 1240 auto_bitmap debug_seen; 1241 for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi = psi) 1242 { 1243 stmt = gsi_stmt (gsi); 1244 1245 psi = gsi; 1246 gsi_prev (&psi); 1247 1248 stats.total++; 1249 1250 /* We can mark a call to free as not necessary if the 1251 defining statement of its argument is not necessary 1252 (and thus is getting removed). */ 1253 if (gimple_plf (stmt, STMT_NECESSARY) 1254 && gimple_call_builtin_p (stmt, BUILT_IN_FREE)) 1255 { 1256 tree ptr = gimple_call_arg (stmt, 0); 1257 if (TREE_CODE (ptr) == SSA_NAME) 1258 { 1259 gimple *def_stmt = SSA_NAME_DEF_STMT (ptr); 1260 if (!gimple_nop_p (def_stmt) 1261 && !gimple_plf (def_stmt, STMT_NECESSARY)) 1262 gimple_set_plf (stmt, STMT_NECESSARY, false); 1263 } 1264 } 1265 1266 /* If GSI is not necessary then remove it. */ 1267 if (!gimple_plf (stmt, STMT_NECESSARY)) 1268 { 1269 /* Keep clobbers that we can keep live live. */ 1270 if (gimple_clobber_p (stmt)) 1271 { 1272 ssa_op_iter iter; 1273 use_operand_p use_p; 1274 bool dead = false; 1275 FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_USE) 1276 { 1277 tree name = USE_FROM_PTR (use_p); 1278 if (!SSA_NAME_IS_DEFAULT_DEF (name) 1279 && !bitmap_bit_p (processed, SSA_NAME_VERSION (name))) 1280 { 1281 dead = true; 1282 break; 1283 } 1284 } 1285 if (!dead) 1286 { 1287 bitmap_clear (debug_seen); 1288 continue; 1289 } 1290 } 1291 if (!is_gimple_debug (stmt)) 1292 something_changed = true; 1293 remove_dead_stmt (&gsi, bb, to_remove_edges); 1294 continue; 1295 } 1296 else if (is_gimple_call (stmt)) 1297 { 1298 tree name = gimple_call_lhs (stmt); 1299 1300 notice_special_calls (as_a <gcall *> (stmt)); 1301 1302 /* When LHS of var = call (); is dead, simplify it into 1303 call (); saving one operand. */ 1304 if (name 1305 && TREE_CODE (name) == SSA_NAME 1306 && !bitmap_bit_p (processed, SSA_NAME_VERSION (name)) 1307 /* Avoid doing so for allocation calls which we 1308 did not mark as necessary, it will confuse the 1309 special logic we apply to malloc/free pair removal. */ 1310 && (!(call = gimple_call_fndecl (stmt)) 1311 || DECL_BUILT_IN_CLASS (call) != BUILT_IN_NORMAL 1312 || (DECL_FUNCTION_CODE (call) != BUILT_IN_ALIGNED_ALLOC 1313 && DECL_FUNCTION_CODE (call) != BUILT_IN_MALLOC 1314 && DECL_FUNCTION_CODE (call) != BUILT_IN_CALLOC 1315 && !ALLOCA_FUNCTION_CODE_P 1316 (DECL_FUNCTION_CODE (call))))) 1317 { 1318 something_changed = true; 1319 if (dump_file && (dump_flags & TDF_DETAILS)) 1320 { 1321 fprintf (dump_file, "Deleting LHS of call: "); 1322 print_gimple_stmt (dump_file, stmt, 0, TDF_SLIM); 1323 fprintf (dump_file, "\n"); 1324 } 1325 1326 gimple_call_set_lhs (stmt, NULL_TREE); 1327 maybe_clean_or_replace_eh_stmt (stmt, stmt); 1328 update_stmt (stmt); 1329 release_ssa_name (name); 1330 1331 /* GOMP_SIMD_LANE (unless two argument) or ASAN_POISON 1332 without lhs is not needed. */ 1333 if (gimple_call_internal_p (stmt)) 1334 switch (gimple_call_internal_fn (stmt)) 1335 { 1336 case IFN_GOMP_SIMD_LANE: 1337 if (gimple_call_num_args (stmt) >= 2 1338 && !integer_nonzerop (gimple_call_arg (stmt, 1))) 1339 break; 1340 /* FALLTHRU */ 1341 case IFN_ASAN_POISON: 1342 remove_dead_stmt (&gsi, bb, to_remove_edges); 1343 break; 1344 default: 1345 break; 1346 } 1347 } 1348 else if (gimple_call_internal_p (stmt)) 1349 switch (gimple_call_internal_fn (stmt)) 1350 { 1351 case IFN_ADD_OVERFLOW: 1352 maybe_optimize_arith_overflow (&gsi, PLUS_EXPR); 1353 break; 1354 case IFN_SUB_OVERFLOW: 1355 maybe_optimize_arith_overflow (&gsi, MINUS_EXPR); 1356 break; 1357 case IFN_MUL_OVERFLOW: 1358 maybe_optimize_arith_overflow (&gsi, MULT_EXPR); 1359 break; 1360 default: 1361 break; 1362 } 1363 } 1364 else if (gimple_debug_bind_p (stmt)) 1365 { 1366 /* We are only keeping the last debug-bind of a 1367 non-DEBUG_EXPR_DECL variable in a series of 1368 debug-bind stmts. */ 1369 tree var = gimple_debug_bind_get_var (stmt); 1370 if (TREE_CODE (var) != DEBUG_EXPR_DECL 1371 && !bitmap_set_bit (debug_seen, DECL_UID (var))) 1372 remove_dead_stmt (&gsi, bb, to_remove_edges); 1373 continue; 1374 } 1375 bitmap_clear (debug_seen); 1376 } 1377 1378 /* Remove dead PHI nodes. */ 1379 something_changed |= remove_dead_phis (bb); 1380 } 1381 1382 h.release (); 1383 1384 /* Since we don't track liveness of virtual PHI nodes, it is possible that we 1385 rendered some PHI nodes unreachable while they are still in use. 1386 Mark them for renaming. */ 1387 if (!to_remove_edges.is_empty ()) 1388 { 1389 basic_block prev_bb; 1390 1391 /* Remove edges. We've delayed this to not get bogus debug stmts 1392 during PHI node removal. */ 1393 for (unsigned i = 0; i < to_remove_edges.length (); ++i) 1394 remove_edge (to_remove_edges[i]); 1395 cfg_altered = true; 1396 1397 find_unreachable_blocks (); 1398 1399 /* Delete all unreachable basic blocks in reverse dominator order. */ 1400 for (bb = EXIT_BLOCK_PTR_FOR_FN (cfun)->prev_bb; 1401 bb != ENTRY_BLOCK_PTR_FOR_FN (cfun); bb = prev_bb) 1402 { 1403 prev_bb = bb->prev_bb; 1404 1405 if (!bitmap_bit_p (bb_contains_live_stmts, bb->index) 1406 || !(bb->flags & BB_REACHABLE)) 1407 { 1408 for (gphi_iterator gsi = gsi_start_phis (bb); !gsi_end_p (gsi); 1409 gsi_next (&gsi)) 1410 if (virtual_operand_p (gimple_phi_result (gsi.phi ()))) 1411 { 1412 bool found = false; 1413 imm_use_iterator iter; 1414 1415 FOR_EACH_IMM_USE_STMT (stmt, iter, 1416 gimple_phi_result (gsi.phi ())) 1417 { 1418 if (!(gimple_bb (stmt)->flags & BB_REACHABLE)) 1419 continue; 1420 if (gimple_code (stmt) == GIMPLE_PHI 1421 || gimple_plf (stmt, STMT_NECESSARY)) 1422 { 1423 found = true; 1424 BREAK_FROM_IMM_USE_STMT (iter); 1425 } 1426 } 1427 if (found) 1428 mark_virtual_phi_result_for_renaming (gsi.phi ()); 1429 } 1430 1431 if (!(bb->flags & BB_REACHABLE)) 1432 { 1433 /* Speed up the removal of blocks that don't 1434 dominate others. Walking backwards, this should 1435 be the common case. ??? Do we need to recompute 1436 dominators because of cfg_altered? */ 1437 if (!first_dom_son (CDI_DOMINATORS, bb)) 1438 delete_basic_block (bb); 1439 else 1440 { 1441 h = get_all_dominated_blocks (CDI_DOMINATORS, bb); 1442 1443 while (h.length ()) 1444 { 1445 bb = h.pop (); 1446 prev_bb = bb->prev_bb; 1447 /* Rearrangements to the CFG may have failed 1448 to update the dominators tree, so that 1449 formerly-dominated blocks are now 1450 otherwise reachable. */ 1451 if (!!(bb->flags & BB_REACHABLE)) 1452 continue; 1453 delete_basic_block (bb); 1454 } 1455 1456 h.release (); 1457 } 1458 } 1459 } 1460 } 1461 } 1462 1463 if (bb_postorder) 1464 free (bb_postorder); 1465 bb_postorder = NULL; 1466 1467 return something_changed; 1468 } 1469 1470 1471 /* Print out removed statement statistics. */ 1472 1473 static void 1474 print_stats (void) 1475 { 1476 float percg; 1477 1478 percg = ((float) stats.removed / (float) stats.total) * 100; 1479 fprintf (dump_file, "Removed %d of %d statements (%d%%)\n", 1480 stats.removed, stats.total, (int) percg); 1481 1482 if (stats.total_phis == 0) 1483 percg = 0; 1484 else 1485 percg = ((float) stats.removed_phis / (float) stats.total_phis) * 100; 1486 1487 fprintf (dump_file, "Removed %d of %d PHI nodes (%d%%)\n", 1488 stats.removed_phis, stats.total_phis, (int) percg); 1489 } 1490 1491 /* Initialization for this pass. Set up the used data structures. */ 1492 1493 static void 1494 tree_dce_init (bool aggressive) 1495 { 1496 memset ((void *) &stats, 0, sizeof (stats)); 1497 1498 if (aggressive) 1499 { 1500 last_stmt_necessary = sbitmap_alloc (last_basic_block_for_fn (cfun)); 1501 bitmap_clear (last_stmt_necessary); 1502 bb_contains_live_stmts = sbitmap_alloc (last_basic_block_for_fn (cfun)); 1503 bitmap_clear (bb_contains_live_stmts); 1504 } 1505 1506 processed = sbitmap_alloc (num_ssa_names + 1); 1507 bitmap_clear (processed); 1508 1509 worklist.create (64); 1510 cfg_altered = false; 1511 } 1512 1513 /* Cleanup after this pass. */ 1514 1515 static void 1516 tree_dce_done (bool aggressive) 1517 { 1518 if (aggressive) 1519 { 1520 delete cd; 1521 sbitmap_free (visited_control_parents); 1522 sbitmap_free (last_stmt_necessary); 1523 sbitmap_free (bb_contains_live_stmts); 1524 bb_contains_live_stmts = NULL; 1525 } 1526 1527 sbitmap_free (processed); 1528 1529 worklist.release (); 1530 } 1531 1532 /* Main routine to eliminate dead code. 1533 1534 AGGRESSIVE controls the aggressiveness of the algorithm. 1535 In conservative mode, we ignore control dependence and simply declare 1536 all but the most trivially dead branches necessary. This mode is fast. 1537 In aggressive mode, control dependences are taken into account, which 1538 results in more dead code elimination, but at the cost of some time. 1539 1540 FIXME: Aggressive mode before PRE doesn't work currently because 1541 the dominance info is not invalidated after DCE1. This is 1542 not an issue right now because we only run aggressive DCE 1543 as the last tree SSA pass, but keep this in mind when you 1544 start experimenting with pass ordering. */ 1545 1546 static unsigned int 1547 perform_tree_ssa_dce (bool aggressive) 1548 { 1549 bool something_changed = 0; 1550 1551 calculate_dominance_info (CDI_DOMINATORS); 1552 1553 /* Preheaders are needed for SCEV to work. 1554 Simple lateches and recorded exits improve chances that loop will 1555 proved to be finite in testcases such as in loop-15.c and loop-24.c */ 1556 bool in_loop_pipeline = scev_initialized_p (); 1557 if (aggressive && ! in_loop_pipeline) 1558 { 1559 scev_initialize (); 1560 loop_optimizer_init (LOOPS_NORMAL 1561 | LOOPS_HAVE_RECORDED_EXITS); 1562 } 1563 1564 tree_dce_init (aggressive); 1565 1566 if (aggressive) 1567 { 1568 /* Compute control dependence. */ 1569 calculate_dominance_info (CDI_POST_DOMINATORS); 1570 cd = new control_dependences (); 1571 1572 visited_control_parents = 1573 sbitmap_alloc (last_basic_block_for_fn (cfun)); 1574 bitmap_clear (visited_control_parents); 1575 1576 mark_dfs_back_edges (); 1577 } 1578 1579 find_obviously_necessary_stmts (aggressive); 1580 1581 if (aggressive && ! in_loop_pipeline) 1582 { 1583 loop_optimizer_finalize (); 1584 scev_finalize (); 1585 } 1586 1587 longest_chain = 0; 1588 total_chain = 0; 1589 nr_walks = 0; 1590 chain_ovfl = false; 1591 visited = BITMAP_ALLOC (NULL); 1592 propagate_necessity (aggressive); 1593 BITMAP_FREE (visited); 1594 1595 something_changed |= eliminate_unnecessary_stmts (); 1596 something_changed |= cfg_altered; 1597 1598 /* We do not update postdominators, so free them unconditionally. */ 1599 free_dominance_info (CDI_POST_DOMINATORS); 1600 1601 /* If we removed paths in the CFG, then we need to update 1602 dominators as well. I haven't investigated the possibility 1603 of incrementally updating dominators. */ 1604 if (cfg_altered) 1605 free_dominance_info (CDI_DOMINATORS); 1606 1607 statistics_counter_event (cfun, "Statements deleted", stats.removed); 1608 statistics_counter_event (cfun, "PHI nodes deleted", stats.removed_phis); 1609 1610 /* Debugging dumps. */ 1611 if (dump_file && (dump_flags & (TDF_STATS|TDF_DETAILS))) 1612 print_stats (); 1613 1614 tree_dce_done (aggressive); 1615 1616 if (something_changed) 1617 { 1618 free_numbers_of_iterations_estimates (cfun); 1619 if (in_loop_pipeline) 1620 scev_reset (); 1621 return TODO_update_ssa | TODO_cleanup_cfg; 1622 } 1623 return 0; 1624 } 1625 1626 /* Pass entry points. */ 1627 static unsigned int 1628 tree_ssa_dce (void) 1629 { 1630 return perform_tree_ssa_dce (/*aggressive=*/false); 1631 } 1632 1633 static unsigned int 1634 tree_ssa_cd_dce (void) 1635 { 1636 return perform_tree_ssa_dce (/*aggressive=*/optimize >= 2); 1637 } 1638 1639 namespace { 1640 1641 const pass_data pass_data_dce = 1642 { 1643 GIMPLE_PASS, /* type */ 1644 "dce", /* name */ 1645 OPTGROUP_NONE, /* optinfo_flags */ 1646 TV_TREE_DCE, /* tv_id */ 1647 ( PROP_cfg | PROP_ssa ), /* properties_required */ 1648 0, /* properties_provided */ 1649 0, /* properties_destroyed */ 1650 0, /* todo_flags_start */ 1651 0, /* todo_flags_finish */ 1652 }; 1653 1654 class pass_dce : public gimple_opt_pass 1655 { 1656 public: 1657 pass_dce (gcc::context *ctxt) 1658 : gimple_opt_pass (pass_data_dce, ctxt) 1659 {} 1660 1661 /* opt_pass methods: */ 1662 opt_pass * clone () { return new pass_dce (m_ctxt); } 1663 virtual bool gate (function *) { return flag_tree_dce != 0; } 1664 virtual unsigned int execute (function *) { return tree_ssa_dce (); } 1665 1666 }; // class pass_dce 1667 1668 } // anon namespace 1669 1670 gimple_opt_pass * 1671 make_pass_dce (gcc::context *ctxt) 1672 { 1673 return new pass_dce (ctxt); 1674 } 1675 1676 namespace { 1677 1678 const pass_data pass_data_cd_dce = 1679 { 1680 GIMPLE_PASS, /* type */ 1681 "cddce", /* name */ 1682 OPTGROUP_NONE, /* optinfo_flags */ 1683 TV_TREE_CD_DCE, /* tv_id */ 1684 ( PROP_cfg | PROP_ssa ), /* properties_required */ 1685 0, /* properties_provided */ 1686 0, /* properties_destroyed */ 1687 0, /* todo_flags_start */ 1688 0, /* todo_flags_finish */ 1689 }; 1690 1691 class pass_cd_dce : public gimple_opt_pass 1692 { 1693 public: 1694 pass_cd_dce (gcc::context *ctxt) 1695 : gimple_opt_pass (pass_data_cd_dce, ctxt) 1696 {} 1697 1698 /* opt_pass methods: */ 1699 opt_pass * clone () { return new pass_cd_dce (m_ctxt); } 1700 virtual bool gate (function *) { return flag_tree_dce != 0; } 1701 virtual unsigned int execute (function *) { return tree_ssa_cd_dce (); } 1702 1703 }; // class pass_cd_dce 1704 1705 } // anon namespace 1706 1707 gimple_opt_pass * 1708 make_pass_cd_dce (gcc::context *ctxt) 1709 { 1710 return new pass_cd_dce (ctxt); 1711 } 1712 1713 1714 /* A cheap DCE interface. WORKLIST is a list of possibly dead stmts and 1715 is consumed by this function. The function has linear complexity in 1716 the number of dead stmts with a constant factor like the average SSA 1717 use operands number. */ 1718 1719 void 1720 simple_dce_from_worklist (bitmap worklist) 1721 { 1722 while (! bitmap_empty_p (worklist)) 1723 { 1724 /* Pop item. */ 1725 unsigned i = bitmap_first_set_bit (worklist); 1726 bitmap_clear_bit (worklist, i); 1727 1728 tree def = ssa_name (i); 1729 /* Removed by somebody else or still in use. */ 1730 if (! def || ! has_zero_uses (def)) 1731 continue; 1732 1733 gimple *t = SSA_NAME_DEF_STMT (def); 1734 if (gimple_has_side_effects (t)) 1735 continue; 1736 1737 /* Add uses to the worklist. */ 1738 ssa_op_iter iter; 1739 use_operand_p use_p; 1740 FOR_EACH_PHI_OR_STMT_USE (use_p, t, iter, SSA_OP_USE) 1741 { 1742 tree use = USE_FROM_PTR (use_p); 1743 if (TREE_CODE (use) == SSA_NAME 1744 && ! SSA_NAME_IS_DEFAULT_DEF (use)) 1745 bitmap_set_bit (worklist, SSA_NAME_VERSION (use)); 1746 } 1747 1748 /* Remove stmt. */ 1749 if (dump_file && (dump_flags & TDF_DETAILS)) 1750 { 1751 fprintf (dump_file, "Removing dead stmt:"); 1752 print_gimple_stmt (dump_file, t, 0); 1753 } 1754 gimple_stmt_iterator gsi = gsi_for_stmt (t); 1755 if (gimple_code (t) == GIMPLE_PHI) 1756 remove_phi_node (&gsi, true); 1757 else 1758 { 1759 gsi_remove (&gsi, true); 1760 release_defs (t); 1761 } 1762 } 1763 } 1764