1/* CFG cleanup for trees. 2 Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007 3 Free Software Foundation, Inc. 4 5This file is part of GCC. 6 7GCC is free software; you can redistribute it and/or modify 8it under the terms of the GNU General Public License as published by 9the Free Software Foundation; either version 2, or (at your option) 10any later version. 11 12GCC is distributed in the hope that it will be useful, 13but WITHOUT ANY WARRANTY; without even the implied warranty of 14MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 15GNU General Public License for more details. 16 17You should have received a copy of the GNU General Public License 18along with GCC; see the file COPYING. If not, write to 19the Free Software Foundation, 51 Franklin Street, Fifth Floor, 20Boston, MA 02110-1301, USA. */ 21 22#include "config.h" 23#include "system.h" 24#include "coretypes.h" 25#include "tm.h" 26#include "tree.h" 27#include "rtl.h" 28#include "tm_p.h" 29#include "hard-reg-set.h" 30#include "basic-block.h" 31#include "output.h" 32#include "toplev.h" 33#include "flags.h" 34#include "function.h" 35#include "expr.h" 36#include "ggc.h" 37#include "langhooks.h" 38#include "diagnostic.h" 39#include "tree-flow.h" 40#include "timevar.h" 41#include "tree-dump.h" 42#include "tree-pass.h" 43#include "toplev.h" 44#include "except.h" 45#include "cfgloop.h" 46#include "cfglayout.h" 47#include "hashtab.h" 48#include "tree-ssa-propagate.h" 49#include "tree-scalar-evolution.h" 50 51/* Remove any fallthru edge from EV. Return true if an edge was removed. */ 52 53static bool 54remove_fallthru_edge (VEC(edge,gc) *ev) 55{ 56 edge_iterator ei; 57 edge e; 58 59 FOR_EACH_EDGE (e, ei, ev) 60 if ((e->flags & EDGE_FALLTHRU) != 0) 61 { 62 remove_edge (e); 63 return true; 64 } 65 return false; 66} 67 68/* Disconnect an unreachable block in the control expression starting 69 at block BB. */ 70 71static bool 72cleanup_control_expr_graph (basic_block bb, block_stmt_iterator bsi) 73{ 74 edge taken_edge; 75 bool retval = false; 76 tree expr = bsi_stmt (bsi), val; 77 78 if (!single_succ_p (bb)) 79 { 80 edge e; 81 edge_iterator ei; 82 bool warned; 83 84 fold_defer_overflow_warnings (); 85 86 switch (TREE_CODE (expr)) 87 { 88 case COND_EXPR: 89 val = fold (COND_EXPR_COND (expr)); 90 break; 91 92 case SWITCH_EXPR: 93 val = fold (SWITCH_COND (expr)); 94 if (TREE_CODE (val) != INTEGER_CST) 95 { 96 fold_undefer_and_ignore_overflow_warnings (); 97 return false; 98 } 99 break; 100 101 default: 102 gcc_unreachable (); 103 } 104 105 taken_edge = find_taken_edge (bb, val); 106 if (!taken_edge) 107 { 108 fold_undefer_and_ignore_overflow_warnings (); 109 return false; 110 } 111 112 /* Remove all the edges except the one that is always executed. */ 113 warned = false; 114 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); ) 115 { 116 if (e != taken_edge) 117 { 118 if (!warned) 119 { 120 fold_undefer_overflow_warnings 121 (true, expr, WARN_STRICT_OVERFLOW_CONDITIONAL); 122 warned = true; 123 } 124 125 taken_edge->probability += e->probability; 126 taken_edge->count += e->count; 127 remove_edge (e); 128 retval = true; 129 } 130 else 131 ei_next (&ei); 132 } 133 if (!warned) 134 fold_undefer_and_ignore_overflow_warnings (); 135 if (taken_edge->probability > REG_BR_PROB_BASE) 136 taken_edge->probability = REG_BR_PROB_BASE; 137 } 138 else 139 taken_edge = single_succ_edge (bb); 140 141 bsi_remove (&bsi, true); 142 taken_edge->flags = EDGE_FALLTHRU; 143 144 /* We removed some paths from the cfg. */ 145 free_dominance_info (CDI_DOMINATORS); 146 147 return retval; 148} 149 150/* A list of all the noreturn calls passed to modify_stmt. 151 cleanup_control_flow uses it to detect cases where a mid-block 152 indirect call has been turned into a noreturn call. When this 153 happens, all the instructions after the call are no longer 154 reachable and must be deleted as dead. */ 155 156VEC(tree,gc) *modified_noreturn_calls; 157 158/* Try to remove superfluous control structures. */ 159 160static bool 161cleanup_control_flow (void) 162{ 163 basic_block bb; 164 block_stmt_iterator bsi; 165 bool retval = false; 166 tree stmt; 167 168 /* Detect cases where a mid-block call is now known not to return. */ 169 while (VEC_length (tree, modified_noreturn_calls)) 170 { 171 stmt = VEC_pop (tree, modified_noreturn_calls); 172 bb = bb_for_stmt (stmt); 173 if (bb != NULL && last_stmt (bb) != stmt && noreturn_call_p (stmt)) 174 split_block (bb, stmt); 175 } 176 177 FOR_EACH_BB (bb) 178 { 179 bsi = bsi_last (bb); 180 181 /* If the last statement of the block could throw and now cannot, 182 we need to prune cfg. */ 183 retval |= tree_purge_dead_eh_edges (bb); 184 185 if (bsi_end_p (bsi)) 186 continue; 187 188 stmt = bsi_stmt (bsi); 189 190 if (TREE_CODE (stmt) == COND_EXPR 191 || TREE_CODE (stmt) == SWITCH_EXPR) 192 retval |= cleanup_control_expr_graph (bb, bsi); 193 /* If we had a computed goto which has a compile-time determinable 194 destination, then we can eliminate the goto. */ 195 else if (TREE_CODE (stmt) == GOTO_EXPR 196 && TREE_CODE (GOTO_DESTINATION (stmt)) == ADDR_EXPR 197 && (TREE_CODE (TREE_OPERAND (GOTO_DESTINATION (stmt), 0)) 198 == LABEL_DECL)) 199 { 200 edge e; 201 tree label; 202 edge_iterator ei; 203 basic_block target_block; 204 bool removed_edge = false; 205 206 /* First look at all the outgoing edges. Delete any outgoing 207 edges which do not go to the right block. For the one 208 edge which goes to the right block, fix up its flags. */ 209 label = TREE_OPERAND (GOTO_DESTINATION (stmt), 0); 210 target_block = label_to_block (label); 211 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); ) 212 { 213 if (e->dest != target_block) 214 { 215 removed_edge = true; 216 remove_edge (e); 217 } 218 else 219 { 220 /* Turn off the EDGE_ABNORMAL flag. */ 221 e->flags &= ~EDGE_ABNORMAL; 222 223 /* And set EDGE_FALLTHRU. */ 224 e->flags |= EDGE_FALLTHRU; 225 ei_next (&ei); 226 } 227 } 228 229 /* If we removed one or more edges, then we will need to fix the 230 dominators. It may be possible to incrementally update them. */ 231 if (removed_edge) 232 free_dominance_info (CDI_DOMINATORS); 233 234 /* Remove the GOTO_EXPR as it is not needed. The CFG has all the 235 relevant information we need. */ 236 bsi_remove (&bsi, true); 237 retval = true; 238 } 239 240 /* Check for indirect calls that have been turned into 241 noreturn calls. */ 242 else if (noreturn_call_p (stmt) && remove_fallthru_edge (bb->succs)) 243 { 244 free_dominance_info (CDI_DOMINATORS); 245 retval = true; 246 } 247 } 248 return retval; 249} 250 251/* Return true if basic block BB does nothing except pass control 252 flow to another block and that we can safely insert a label at 253 the start of the successor block. 254 255 As a precondition, we require that BB be not equal to 256 ENTRY_BLOCK_PTR. */ 257 258static bool 259tree_forwarder_block_p (basic_block bb, bool phi_wanted) 260{ 261 block_stmt_iterator bsi; 262 edge_iterator ei; 263 edge e, succ; 264 basic_block dest; 265 266 /* BB must have a single outgoing edge. */ 267 if (single_succ_p (bb) != 1 268 /* If PHI_WANTED is false, BB must not have any PHI nodes. 269 Otherwise, BB must have PHI nodes. */ 270 || (phi_nodes (bb) != NULL_TREE) != phi_wanted 271 /* BB may not be a predecessor of EXIT_BLOCK_PTR. */ 272 || single_succ (bb) == EXIT_BLOCK_PTR 273 /* Nor should this be an infinite loop. */ 274 || single_succ (bb) == bb 275 /* BB may not have an abnormal outgoing edge. */ 276 || (single_succ_edge (bb)->flags & EDGE_ABNORMAL)) 277 return false; 278 279#if ENABLE_CHECKING 280 gcc_assert (bb != ENTRY_BLOCK_PTR); 281#endif 282 283 /* Now walk through the statements backward. We can ignore labels, 284 anything else means this is not a forwarder block. */ 285 for (bsi = bsi_last (bb); !bsi_end_p (bsi); bsi_prev (&bsi)) 286 { 287 tree stmt = bsi_stmt (bsi); 288 289 switch (TREE_CODE (stmt)) 290 { 291 case LABEL_EXPR: 292 if (DECL_NONLOCAL (LABEL_EXPR_LABEL (stmt))) 293 return false; 294 break; 295 296 default: 297 return false; 298 } 299 } 300 301 if (find_edge (ENTRY_BLOCK_PTR, bb)) 302 return false; 303 304 if (current_loops) 305 { 306 basic_block dest; 307 /* Protect loop latches, headers and preheaders. */ 308 if (bb->loop_father->header == bb) 309 return false; 310 dest = EDGE_SUCC (bb, 0)->dest; 311 312 if (dest->loop_father->header == dest) 313 return false; 314 } 315 316 /* If we have an EH edge leaving this block, make sure that the 317 destination of this block has only one predecessor. This ensures 318 that we don't get into the situation where we try to remove two 319 forwarders that go to the same basic block but are handlers for 320 different EH regions. */ 321 succ = single_succ_edge (bb); 322 dest = succ->dest; 323 FOR_EACH_EDGE (e, ei, bb->preds) 324 { 325 if (e->flags & EDGE_EH) 326 { 327 if (!single_pred_p (dest)) 328 return false; 329 } 330 } 331 332 return true; 333} 334 335/* Return true if BB has at least one abnormal incoming edge. */ 336 337static inline bool 338has_abnormal_incoming_edge_p (basic_block bb) 339{ 340 edge e; 341 edge_iterator ei; 342 343 FOR_EACH_EDGE (e, ei, bb->preds) 344 if (e->flags & EDGE_ABNORMAL) 345 return true; 346 347 return false; 348} 349 350/* If all the PHI nodes in DEST have alternatives for E1 and E2 and 351 those alternatives are equal in each of the PHI nodes, then return 352 true, else return false. */ 353 354static bool 355phi_alternatives_equal (basic_block dest, edge e1, edge e2) 356{ 357 int n1 = e1->dest_idx; 358 int n2 = e2->dest_idx; 359 tree phi; 360 361 for (phi = phi_nodes (dest); phi; phi = PHI_CHAIN (phi)) 362 { 363 tree val1 = PHI_ARG_DEF (phi, n1); 364 tree val2 = PHI_ARG_DEF (phi, n2); 365 366 gcc_assert (val1 != NULL_TREE); 367 gcc_assert (val2 != NULL_TREE); 368 369 if (!operand_equal_for_phi_arg_p (val1, val2)) 370 return false; 371 } 372 373 return true; 374} 375 376/* Removes forwarder block BB. Returns false if this failed. If a new 377 forwarder block is created due to redirection of edges, it is 378 stored to worklist. */ 379 380static bool 381remove_forwarder_block (basic_block bb, basic_block **worklist) 382{ 383 edge succ = single_succ_edge (bb), e, s; 384 basic_block dest = succ->dest; 385 tree label; 386 tree phi; 387 edge_iterator ei; 388 block_stmt_iterator bsi, bsi_to; 389 bool seen_abnormal_edge = false; 390 391 /* We check for infinite loops already in tree_forwarder_block_p. 392 However it may happen that the infinite loop is created 393 afterwards due to removal of forwarders. */ 394 if (dest == bb) 395 return false; 396 397 /* If the destination block consists of a nonlocal label, do not merge 398 it. */ 399 label = first_stmt (dest); 400 if (label 401 && TREE_CODE (label) == LABEL_EXPR 402 && DECL_NONLOCAL (LABEL_EXPR_LABEL (label))) 403 return false; 404 405 /* If there is an abnormal edge to basic block BB, but not into 406 dest, problems might occur during removal of the phi node at out 407 of ssa due to overlapping live ranges of registers. 408 409 If there is an abnormal edge in DEST, the problems would occur 410 anyway since cleanup_dead_labels would then merge the labels for 411 two different eh regions, and rest of exception handling code 412 does not like it. 413 414 So if there is an abnormal edge to BB, proceed only if there is 415 no abnormal edge to DEST and there are no phi nodes in DEST. */ 416 if (has_abnormal_incoming_edge_p (bb)) 417 { 418 seen_abnormal_edge = true; 419 420 if (has_abnormal_incoming_edge_p (dest) 421 || phi_nodes (dest) != NULL_TREE) 422 return false; 423 } 424 425 /* If there are phi nodes in DEST, and some of the blocks that are 426 predecessors of BB are also predecessors of DEST, check that the 427 phi node arguments match. */ 428 if (phi_nodes (dest)) 429 { 430 FOR_EACH_EDGE (e, ei, bb->preds) 431 { 432 s = find_edge (e->src, dest); 433 if (!s) 434 continue; 435 436 if (!phi_alternatives_equal (dest, succ, s)) 437 return false; 438 } 439 } 440 441 /* Redirect the edges. */ 442 for (ei = ei_start (bb->preds); (e = ei_safe_edge (ei)); ) 443 { 444 if (e->flags & EDGE_ABNORMAL) 445 { 446 /* If there is an abnormal edge, redirect it anyway, and 447 move the labels to the new block to make it legal. */ 448 s = redirect_edge_succ_nodup (e, dest); 449 } 450 else 451 s = redirect_edge_and_branch (e, dest); 452 453 if (s == e) 454 { 455 /* Create arguments for the phi nodes, since the edge was not 456 here before. */ 457 for (phi = phi_nodes (dest); phi; phi = PHI_CHAIN (phi)) 458 add_phi_arg (phi, PHI_ARG_DEF (phi, succ->dest_idx), s); 459 } 460 else 461 { 462 /* The source basic block might become a forwarder. We know 463 that it was not a forwarder before, since it used to have 464 at least two outgoing edges, so we may just add it to 465 worklist. */ 466 if (tree_forwarder_block_p (s->src, false)) 467 *(*worklist)++ = s->src; 468 } 469 } 470 471 if (seen_abnormal_edge) 472 { 473 /* Move the labels to the new block, so that the redirection of 474 the abnormal edges works. */ 475 476 bsi_to = bsi_start (dest); 477 for (bsi = bsi_start (bb); !bsi_end_p (bsi); ) 478 { 479 label = bsi_stmt (bsi); 480 gcc_assert (TREE_CODE (label) == LABEL_EXPR); 481 bsi_remove (&bsi, false); 482 bsi_insert_before (&bsi_to, label, BSI_CONTINUE_LINKING); 483 } 484 } 485 486 /* Update the dominators. */ 487 if (dom_info_available_p (CDI_DOMINATORS)) 488 { 489 basic_block dom, dombb, domdest; 490 491 dombb = get_immediate_dominator (CDI_DOMINATORS, bb); 492 domdest = get_immediate_dominator (CDI_DOMINATORS, dest); 493 if (domdest == bb) 494 { 495 /* Shortcut to avoid calling (relatively expensive) 496 nearest_common_dominator unless necessary. */ 497 dom = dombb; 498 } 499 else 500 dom = nearest_common_dominator (CDI_DOMINATORS, domdest, dombb); 501 502 set_immediate_dominator (CDI_DOMINATORS, dest, dom); 503 } 504 505 /* And kill the forwarder block. */ 506 delete_basic_block (bb); 507 508 return true; 509} 510 511/* Removes forwarder blocks. */ 512 513static bool 514cleanup_forwarder_blocks (void) 515{ 516 basic_block bb; 517 bool changed = false; 518 basic_block *worklist = XNEWVEC (basic_block, n_basic_blocks); 519 basic_block *current = worklist; 520 521 FOR_EACH_BB (bb) 522 { 523 if (tree_forwarder_block_p (bb, false)) 524 *current++ = bb; 525 } 526 527 while (current != worklist) 528 { 529 bb = *--current; 530 changed |= remove_forwarder_block (bb, ¤t); 531 } 532 533 free (worklist); 534 return changed; 535} 536 537/* Do one round of CFG cleanup. */ 538 539static bool 540cleanup_tree_cfg_1 (void) 541{ 542 bool retval; 543 544 retval = cleanup_control_flow (); 545 retval |= delete_unreachable_blocks (); 546 547 /* Forwarder blocks can carry line number information which is 548 useful when debugging, so we only clean them up when 549 optimizing. */ 550 551 if (optimize > 0) 552 { 553 /* cleanup_forwarder_blocks can redirect edges out of 554 SWITCH_EXPRs, which can get expensive. So we want to enable 555 recording of edge to CASE_LABEL_EXPR mappings around the call 556 to cleanup_forwarder_blocks. */ 557 start_recording_case_labels (); 558 retval |= cleanup_forwarder_blocks (); 559 end_recording_case_labels (); 560 } 561 562 /* Merging the blocks may create new opportunities for folding 563 conditional branches (due to the elimination of single-valued PHI 564 nodes). */ 565 retval |= merge_seq_blocks (); 566 567 return retval; 568} 569 570 571/* Remove unreachable blocks and other miscellaneous clean up work. 572 Return true if the flowgraph was modified, false otherwise. */ 573 574bool 575cleanup_tree_cfg (void) 576{ 577 bool retval, changed; 578 579 timevar_push (TV_TREE_CLEANUP_CFG); 580 581 /* Iterate until there are no more cleanups left to do. If any 582 iteration changed the flowgraph, set CHANGED to true. */ 583 changed = false; 584 do 585 { 586 retval = cleanup_tree_cfg_1 (); 587 changed |= retval; 588 } 589 while (retval); 590 591 compact_blocks (); 592 593#ifdef ENABLE_CHECKING 594 verify_flow_info (); 595#endif 596 597 timevar_pop (TV_TREE_CLEANUP_CFG); 598 599 return changed; 600} 601 602/* Cleanup cfg and repair loop structures. */ 603 604void 605cleanup_tree_cfg_loop (void) 606{ 607 bool changed = cleanup_tree_cfg (); 608 609 if (changed) 610 { 611 bitmap changed_bbs = BITMAP_ALLOC (NULL); 612 fix_loop_structure (current_loops, changed_bbs); 613 calculate_dominance_info (CDI_DOMINATORS); 614 615 /* This usually does nothing. But sometimes parts of cfg that originally 616 were inside a loop get out of it due to edge removal (since they 617 become unreachable by back edges from latch). */ 618 rewrite_into_loop_closed_ssa (changed_bbs, TODO_update_ssa); 619 620 BITMAP_FREE (changed_bbs); 621 622#ifdef ENABLE_CHECKING 623 verify_loop_structure (current_loops); 624#endif 625 scev_reset (); 626 } 627} 628 629/* Merge the PHI nodes at BB into those at BB's sole successor. */ 630 631static void 632remove_forwarder_block_with_phi (basic_block bb) 633{ 634 edge succ = single_succ_edge (bb); 635 basic_block dest = succ->dest; 636 tree label; 637 basic_block dombb, domdest, dom; 638 639 /* We check for infinite loops already in tree_forwarder_block_p. 640 However it may happen that the infinite loop is created 641 afterwards due to removal of forwarders. */ 642 if (dest == bb) 643 return; 644 645 /* If the destination block consists of a nonlocal label, do not 646 merge it. */ 647 label = first_stmt (dest); 648 if (label 649 && TREE_CODE (label) == LABEL_EXPR 650 && DECL_NONLOCAL (LABEL_EXPR_LABEL (label))) 651 return; 652 653 /* Redirect each incoming edge to BB to DEST. */ 654 while (EDGE_COUNT (bb->preds) > 0) 655 { 656 edge e = EDGE_PRED (bb, 0), s; 657 tree phi; 658 659 s = find_edge (e->src, dest); 660 if (s) 661 { 662 /* We already have an edge S from E->src to DEST. If S and 663 E->dest's sole successor edge have the same PHI arguments 664 at DEST, redirect S to DEST. */ 665 if (phi_alternatives_equal (dest, s, succ)) 666 { 667 e = redirect_edge_and_branch (e, dest); 668 PENDING_STMT (e) = NULL_TREE; 669 continue; 670 } 671 672 /* PHI arguments are different. Create a forwarder block by 673 splitting E so that we can merge PHI arguments on E to 674 DEST. */ 675 e = single_succ_edge (split_edge (e)); 676 } 677 678 s = redirect_edge_and_branch (e, dest); 679 680 /* redirect_edge_and_branch must not create a new edge. */ 681 gcc_assert (s == e); 682 683 /* Add to the PHI nodes at DEST each PHI argument removed at the 684 destination of E. */ 685 for (phi = phi_nodes (dest); phi; phi = PHI_CHAIN (phi)) 686 { 687 tree def = PHI_ARG_DEF (phi, succ->dest_idx); 688 689 if (TREE_CODE (def) == SSA_NAME) 690 { 691 tree var; 692 693 /* If DEF is one of the results of PHI nodes removed during 694 redirection, replace it with the PHI argument that used 695 to be on E. */ 696 for (var = PENDING_STMT (e); var; var = TREE_CHAIN (var)) 697 { 698 tree old_arg = TREE_PURPOSE (var); 699 tree new_arg = TREE_VALUE (var); 700 701 if (def == old_arg) 702 { 703 def = new_arg; 704 break; 705 } 706 } 707 } 708 709 add_phi_arg (phi, def, s); 710 } 711 712 PENDING_STMT (e) = NULL; 713 } 714 715 /* Update the dominators. */ 716 dombb = get_immediate_dominator (CDI_DOMINATORS, bb); 717 domdest = get_immediate_dominator (CDI_DOMINATORS, dest); 718 if (domdest == bb) 719 { 720 /* Shortcut to avoid calling (relatively expensive) 721 nearest_common_dominator unless necessary. */ 722 dom = dombb; 723 } 724 else 725 dom = nearest_common_dominator (CDI_DOMINATORS, domdest, dombb); 726 727 set_immediate_dominator (CDI_DOMINATORS, dest, dom); 728 729 /* Remove BB since all of BB's incoming edges have been redirected 730 to DEST. */ 731 delete_basic_block (bb); 732} 733 734/* This pass merges PHI nodes if one feeds into another. For example, 735 suppose we have the following: 736 737 goto <bb 9> (<L9>); 738 739<L8>:; 740 tem_17 = foo (); 741 742 # tem_6 = PHI <tem_17(8), tem_23(7)>; 743<L9>:; 744 745 # tem_3 = PHI <tem_6(9), tem_2(5)>; 746<L10>:; 747 748 Then we merge the first PHI node into the second one like so: 749 750 goto <bb 9> (<L10>); 751 752<L8>:; 753 tem_17 = foo (); 754 755 # tem_3 = PHI <tem_23(7), tem_2(5), tem_17(8)>; 756<L10>:; 757*/ 758 759static unsigned int 760merge_phi_nodes (void) 761{ 762 basic_block *worklist = XNEWVEC (basic_block, n_basic_blocks); 763 basic_block *current = worklist; 764 basic_block bb; 765 766 calculate_dominance_info (CDI_DOMINATORS); 767 768 /* Find all PHI nodes that we may be able to merge. */ 769 FOR_EACH_BB (bb) 770 { 771 basic_block dest; 772 773 /* Look for a forwarder block with PHI nodes. */ 774 if (!tree_forwarder_block_p (bb, true)) 775 continue; 776 777 dest = single_succ (bb); 778 779 /* We have to feed into another basic block with PHI 780 nodes. */ 781 if (!phi_nodes (dest) 782 /* We don't want to deal with a basic block with 783 abnormal edges. */ 784 || has_abnormal_incoming_edge_p (bb)) 785 continue; 786 787 if (!dominated_by_p (CDI_DOMINATORS, dest, bb)) 788 { 789 /* If BB does not dominate DEST, then the PHI nodes at 790 DEST must be the only users of the results of the PHI 791 nodes at BB. */ 792 *current++ = bb; 793 } 794 else 795 { 796 tree phi; 797 unsigned int dest_idx = single_succ_edge (bb)->dest_idx; 798 799 /* BB dominates DEST. There may be many users of the PHI 800 nodes in BB. However, there is still a trivial case we 801 can handle. If the result of every PHI in BB is used 802 only by a PHI in DEST, then we can trivially merge the 803 PHI nodes from BB into DEST. */ 804 for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi)) 805 { 806 tree result = PHI_RESULT (phi); 807 use_operand_p imm_use; 808 tree use_stmt; 809 810 /* If the PHI's result is never used, then we can just 811 ignore it. */ 812 if (has_zero_uses (result)) 813 continue; 814 815 /* Get the single use of the result of this PHI node. */ 816 if (!single_imm_use (result, &imm_use, &use_stmt) 817 || TREE_CODE (use_stmt) != PHI_NODE 818 || bb_for_stmt (use_stmt) != dest 819 || PHI_ARG_DEF (use_stmt, dest_idx) != result) 820 break; 821 } 822 823 /* If the loop above iterated through all the PHI nodes 824 in BB, then we can merge the PHIs from BB into DEST. */ 825 if (!phi) 826 *current++ = bb; 827 } 828 } 829 830 /* Now let's drain WORKLIST. */ 831 while (current != worklist) 832 { 833 bb = *--current; 834 remove_forwarder_block_with_phi (bb); 835 } 836 837 free (worklist); 838 return 0; 839} 840 841static bool 842gate_merge_phi (void) 843{ 844 return 1; 845} 846 847struct tree_opt_pass pass_merge_phi = { 848 "mergephi", /* name */ 849 gate_merge_phi, /* gate */ 850 merge_phi_nodes, /* execute */ 851 NULL, /* sub */ 852 NULL, /* next */ 853 0, /* static_pass_number */ 854 TV_TREE_MERGE_PHI, /* tv_id */ 855 PROP_cfg | PROP_ssa, /* properties_required */ 856 0, /* properties_provided */ 857 0, /* properties_destroyed */ 858 0, /* todo_flags_start */ 859 TODO_dump_func | TODO_ggc_collect /* todo_flags_finish */ 860 | TODO_verify_ssa, 861 0 /* letter */ 862}; 863