1 /* CFG cleanup for trees.
2 Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
3 Free Software Foundation, Inc.
5 This file is part of GCC.
7 GCC is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 3, or (at your option)
12 GCC is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with GCC; see the file COPYING3. If not see
19 <http://www.gnu.org/licenses/>. */
23 #include "coretypes.h"
27 #include "basic-block.h"
29 #include "diagnostic-core.h"
34 #include "langhooks.h"
35 #include "tree-flow.h"
37 #include "tree-dump.h"
38 #include "tree-pass.h"
42 #include "cfglayout.h"
44 #include "tree-ssa-propagate.h"
45 #include "tree-scalar-evolution.h"
47 /* The set of blocks in that at least one of the following changes happened:
48 -- the statement at the end of the block was changed
49 -- the block was newly created
50 -- the set of the predecessors of the block changed
51 -- the set of the successors of the block changed
52 ??? Maybe we could track these changes separately, since they determine
53 what cleanups it makes sense to try on the block. */
54 bitmap cfgcleanup_altered_bbs;
56 /* Remove any fallthru edge from EV. Return true if an edge was removed. */
59 remove_fallthru_edge (VEC(edge,gc) *ev)
64 FOR_EACH_EDGE (e, ei, ev)
65 if ((e->flags & EDGE_FALLTHRU) != 0)
67 remove_edge_and_dominated_blocks (e);
74 /* Disconnect an unreachable block in the control expression starting
78 cleanup_control_expr_graph (basic_block bb, gimple_stmt_iterator gsi)
82 gimple stmt = gsi_stmt (gsi);
85 if (!single_succ_p (bb))
92 fold_defer_overflow_warnings ();
93 loc = gimple_location (stmt);
94 switch (gimple_code (stmt))
98 tree lhs = gimple_cond_lhs (stmt);
99 tree rhs = gimple_cond_rhs (stmt);
100 /* For conditions try harder and lookup single-argument
101 PHI nodes. Only do so from the same basic-block though
102 as other basic-blocks may be dead already. */
103 if (TREE_CODE (lhs) == SSA_NAME
104 && !name_registered_for_update_p (lhs))
106 gimple def_stmt = SSA_NAME_DEF_STMT (lhs);
107 if (gimple_code (def_stmt) == GIMPLE_PHI
108 && gimple_phi_num_args (def_stmt) == 1
109 && gimple_bb (def_stmt) == gimple_bb (stmt)
110 && (TREE_CODE (PHI_ARG_DEF (def_stmt, 0)) != SSA_NAME
111 || !name_registered_for_update_p (PHI_ARG_DEF (def_stmt,
113 lhs = PHI_ARG_DEF (def_stmt, 0);
115 if (TREE_CODE (rhs) == SSA_NAME
116 && !name_registered_for_update_p (rhs))
118 gimple def_stmt = SSA_NAME_DEF_STMT (rhs);
119 if (gimple_code (def_stmt) == GIMPLE_PHI
120 && gimple_phi_num_args (def_stmt) == 1
121 && gimple_bb (def_stmt) == gimple_bb (stmt)
122 && (TREE_CODE (PHI_ARG_DEF (def_stmt, 0)) != SSA_NAME
123 || !name_registered_for_update_p (PHI_ARG_DEF (def_stmt,
125 rhs = PHI_ARG_DEF (def_stmt, 0);
127 val = fold_binary_loc (loc, gimple_cond_code (stmt),
128 boolean_type_node, lhs, rhs);
133 val = gimple_switch_index (stmt);
139 taken_edge = find_taken_edge (bb, val);
142 fold_undefer_and_ignore_overflow_warnings ();
146 /* Remove all the edges except the one that is always executed. */
148 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
154 fold_undefer_overflow_warnings
155 (true, stmt, WARN_STRICT_OVERFLOW_CONDITIONAL);
159 taken_edge->probability += e->probability;
160 taken_edge->count += e->count;
161 remove_edge_and_dominated_blocks (e);
168 fold_undefer_and_ignore_overflow_warnings ();
169 if (taken_edge->probability > REG_BR_PROB_BASE)
170 taken_edge->probability = REG_BR_PROB_BASE;
173 taken_edge = single_succ_edge (bb);
175 bitmap_set_bit (cfgcleanup_altered_bbs, bb->index);
176 gsi_remove (&gsi, true);
177 taken_edge->flags = EDGE_FALLTHRU;
182 /* Try to remove superfluous control structures in basic block BB. Returns
183 true if anything changes. */
186 cleanup_control_flow_bb (basic_block bb)
188 gimple_stmt_iterator gsi;
192 /* If the last statement of the block could throw and now cannot,
193 we need to prune cfg. */
194 retval |= gimple_purge_dead_eh_edges (bb);
196 gsi = gsi_last_bb (bb);
200 stmt = gsi_stmt (gsi);
202 if (gimple_code (stmt) == GIMPLE_COND
203 || gimple_code (stmt) == GIMPLE_SWITCH)
204 retval |= cleanup_control_expr_graph (bb, gsi);
205 else if (gimple_code (stmt) == GIMPLE_GOTO
206 && TREE_CODE (gimple_goto_dest (stmt)) == ADDR_EXPR
207 && (TREE_CODE (TREE_OPERAND (gimple_goto_dest (stmt), 0))
210 /* If we had a computed goto which has a compile-time determinable
211 destination, then we can eliminate the goto. */
215 basic_block target_block;
217 /* First look at all the outgoing edges. Delete any outgoing
218 edges which do not go to the right block. For the one
219 edge which goes to the right block, fix up its flags. */
220 label = TREE_OPERAND (gimple_goto_dest (stmt), 0);
221 target_block = label_to_block (label);
222 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
224 if (e->dest != target_block)
225 remove_edge_and_dominated_blocks (e);
228 /* Turn off the EDGE_ABNORMAL flag. */
229 e->flags &= ~EDGE_ABNORMAL;
231 /* And set EDGE_FALLTHRU. */
232 e->flags |= EDGE_FALLTHRU;
237 bitmap_set_bit (cfgcleanup_altered_bbs, bb->index);
238 bitmap_set_bit (cfgcleanup_altered_bbs, target_block->index);
240 /* Remove the GOTO_EXPR as it is not needed. The CFG has all the
241 relevant information we need. */
242 gsi_remove (&gsi, true);
246 /* Check for indirect calls that have been turned into
248 else if (is_gimple_call (stmt)
249 && gimple_call_noreturn_p (stmt)
250 && remove_fallthru_edge (bb->succs))
256 /* Return true if basic block BB does nothing except pass control
257 flow to another block and that we can safely insert a label at
258 the start of the successor block.
260 As a precondition, we require that BB be not equal to
264 tree_forwarder_block_p (basic_block bb, bool phi_wanted)
266 gimple_stmt_iterator gsi;
269 /* BB must have a single outgoing edge. */
270 if (single_succ_p (bb) != 1
271 /* If PHI_WANTED is false, BB must not have any PHI nodes.
272 Otherwise, BB must have PHI nodes. */
273 || gimple_seq_empty_p (phi_nodes (bb)) == phi_wanted
274 /* BB may not be a predecessor of EXIT_BLOCK_PTR. */
275 || single_succ (bb) == EXIT_BLOCK_PTR
276 /* Nor should this be an infinite loop. */
277 || single_succ (bb) == bb
278 /* BB may not have an abnormal outgoing edge. */
279 || (single_succ_edge (bb)->flags & EDGE_ABNORMAL))
283 gcc_assert (bb != ENTRY_BLOCK_PTR);
286 locus = single_succ_edge (bb)->goto_locus;
288 /* There should not be an edge coming from entry, or an EH edge. */
293 FOR_EACH_EDGE (e, ei, bb->preds)
294 if (e->src == ENTRY_BLOCK_PTR || (e->flags & EDGE_EH))
296 /* If goto_locus of any of the edges differs, prevent removing
297 the forwarder block for -O0. */
298 else if (optimize == 0 && e->goto_locus != locus)
302 /* Now walk through the statements backward. We can ignore labels,
303 anything else means this is not a forwarder block. */
304 for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi_prev (&gsi))
306 gimple stmt = gsi_stmt (gsi);
308 switch (gimple_code (stmt))
311 if (DECL_NONLOCAL (gimple_label_label (stmt)))
313 if (optimize == 0 && gimple_location (stmt) != locus)
317 /* ??? For now, hope there's a corresponding debug
318 assignment at the destination. */
330 /* Protect loop latches, headers and preheaders. */
331 if (bb->loop_father->header == bb)
333 dest = EDGE_SUCC (bb, 0)->dest;
335 if (dest->loop_father->header == dest)
341 /* If all the PHI nodes in DEST have alternatives for E1 and E2 and
342 those alternatives are equal in each of the PHI nodes, then return
343 true, else return false. */
346 phi_alternatives_equal (basic_block dest, edge e1, edge e2)
348 int n1 = e1->dest_idx;
349 int n2 = e2->dest_idx;
350 gimple_stmt_iterator gsi;
352 for (gsi = gsi_start_phis (dest); !gsi_end_p (gsi); gsi_next (&gsi))
354 gimple phi = gsi_stmt (gsi);
355 tree val1 = gimple_phi_arg_def (phi, n1);
356 tree val2 = gimple_phi_arg_def (phi, n2);
358 gcc_assert (val1 != NULL_TREE);
359 gcc_assert (val2 != NULL_TREE);
361 if (!operand_equal_for_phi_arg_p (val1, val2))
368 /* Removes forwarder block BB. Returns false if this failed. */
371 remove_forwarder_block (basic_block bb)
373 edge succ = single_succ_edge (bb), e, s;
374 basic_block dest = succ->dest;
377 gimple_stmt_iterator gsi, gsi_to;
378 bool can_move_debug_stmts;
380 /* We check for infinite loops already in tree_forwarder_block_p.
381 However it may happen that the infinite loop is created
382 afterwards due to removal of forwarders. */
386 /* If the destination block consists of a nonlocal label or is a
387 EH landing pad, do not merge it. */
388 label = first_stmt (dest);
390 && gimple_code (label) == GIMPLE_LABEL
391 && (DECL_NONLOCAL (gimple_label_label (label))
392 || EH_LANDING_PAD_NR (gimple_label_label (label)) != 0))
395 /* If there is an abnormal edge to basic block BB, but not into
396 dest, problems might occur during removal of the phi node at out
397 of ssa due to overlapping live ranges of registers.
399 If there is an abnormal edge in DEST, the problems would occur
400 anyway since cleanup_dead_labels would then merge the labels for
401 two different eh regions, and rest of exception handling code
404 So if there is an abnormal edge to BB, proceed only if there is
405 no abnormal edge to DEST and there are no phi nodes in DEST. */
406 if (bb_has_abnormal_pred (bb)
407 && (bb_has_abnormal_pred (dest)
408 || !gimple_seq_empty_p (phi_nodes (dest))))
411 /* If there are phi nodes in DEST, and some of the blocks that are
412 predecessors of BB are also predecessors of DEST, check that the
413 phi node arguments match. */
414 if (!gimple_seq_empty_p (phi_nodes (dest)))
416 FOR_EACH_EDGE (e, ei, bb->preds)
418 s = find_edge (e->src, dest);
422 if (!phi_alternatives_equal (dest, succ, s))
427 can_move_debug_stmts = single_pred_p (dest);
429 /* Redirect the edges. */
430 for (ei = ei_start (bb->preds); (e = ei_safe_edge (ei)); )
432 bitmap_set_bit (cfgcleanup_altered_bbs, e->src->index);
434 if (e->flags & EDGE_ABNORMAL)
436 /* If there is an abnormal edge, redirect it anyway, and
437 move the labels to the new block to make it legal. */
438 s = redirect_edge_succ_nodup (e, dest);
441 s = redirect_edge_and_branch (e, dest);
445 /* Create arguments for the phi nodes, since the edge was not
447 for (gsi = gsi_start_phis (dest);
451 gimple phi = gsi_stmt (gsi);
452 source_location l = gimple_phi_arg_location_from_edge (phi, succ);
453 add_phi_arg (phi, gimple_phi_arg_def (phi, succ->dest_idx), s, l);
458 /* Move nonlocal labels and computed goto targets as well as user
459 defined labels and labels with an EH landing pad number to the
460 new block, so that the redirection of the abnormal edges works,
461 jump targets end up in a sane place and debug information for
462 labels is retained. */
463 gsi_to = gsi_start_bb (dest);
464 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); )
467 label = gsi_stmt (gsi);
468 if (is_gimple_debug (label))
470 decl = gimple_label_label (label);
471 if (EH_LANDING_PAD_NR (decl) != 0
472 || DECL_NONLOCAL (decl)
473 || FORCED_LABEL (decl)
474 || !DECL_ARTIFICIAL (decl))
476 gsi_remove (&gsi, false);
477 gsi_insert_before (&gsi_to, label, GSI_SAME_STMT);
483 /* Move debug statements if the destination has just a single
485 if (can_move_debug_stmts)
487 gsi_to = gsi_after_labels (dest);
488 for (gsi = gsi_after_labels (bb); !gsi_end_p (gsi); )
490 gimple debug = gsi_stmt (gsi);
491 if (!is_gimple_debug (debug))
493 gsi_remove (&gsi, false);
494 gsi_insert_before (&gsi_to, debug, GSI_SAME_STMT);
498 bitmap_set_bit (cfgcleanup_altered_bbs, dest->index);
500 /* Update the dominators. */
501 if (dom_info_available_p (CDI_DOMINATORS))
503 basic_block dom, dombb, domdest;
505 dombb = get_immediate_dominator (CDI_DOMINATORS, bb);
506 domdest = get_immediate_dominator (CDI_DOMINATORS, dest);
509 /* Shortcut to avoid calling (relatively expensive)
510 nearest_common_dominator unless necessary. */
514 dom = nearest_common_dominator (CDI_DOMINATORS, domdest, dombb);
516 set_immediate_dominator (CDI_DOMINATORS, dest, dom);
519 /* And kill the forwarder block. */
520 delete_basic_block (bb);
525 /* STMT is a call that has been discovered noreturn. Fixup the CFG
526 and remove LHS. Return true if something changed. */
529 fixup_noreturn_call (gimple stmt)
531 basic_block bb = gimple_bb (stmt);
532 bool changed = false;
534 if (gimple_call_builtin_p (stmt, BUILT_IN_RETURN))
537 /* First split basic block if stmt is not last. */
538 if (stmt != gsi_stmt (gsi_last_bb (bb)))
539 split_block (bb, stmt);
541 changed |= remove_fallthru_edge (bb->succs);
543 /* If there is LHS, remove it. */
544 if (gimple_call_lhs (stmt))
546 tree op = gimple_call_lhs (stmt);
547 gimple_call_set_lhs (stmt, NULL_TREE);
549 /* We need to remove SSA name to avoid checking errors.
550 All uses are dominated by the noreturn and thus will
551 be removed afterwards.
552 We proactively remove affected non-PHI statements to avoid
553 fixup_cfg from trying to update them and crashing. */
554 if (TREE_CODE (op) == SSA_NAME)
557 imm_use_iterator iter;
560 unsigned int bb_index;
562 bitmap blocks = BITMAP_ALLOC (NULL);
564 FOR_EACH_IMM_USE_STMT (use_stmt, iter, op)
566 if (gimple_code (use_stmt) != GIMPLE_PHI)
567 bitmap_set_bit (blocks, gimple_bb (use_stmt)->index);
569 FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
570 SET_USE (use_p, error_mark_node);
572 EXECUTE_IF_SET_IN_BITMAP (blocks, 0, bb_index, bi)
573 delete_basic_block (BASIC_BLOCK (bb_index));
574 BITMAP_FREE (blocks);
575 release_ssa_name (op);
580 /* Similarly remove VDEF if there is any. */
581 else if (gimple_vdef (stmt))
587 /* Split basic blocks on calls in the middle of a basic block that are now
588 known not to return, and remove the unreachable code. */
591 split_bbs_on_noreturn_calls (void)
593 bool changed = false;
597 /* Detect cases where a mid-block call is now known not to return. */
599 while (VEC_length (gimple, MODIFIED_NORETURN_CALLS (cfun)))
601 stmt = VEC_pop (gimple, MODIFIED_NORETURN_CALLS (cfun));
602 bb = gimple_bb (stmt);
603 /* BB might be deleted at this point, so verify first
604 BB is present in the cfg. */
606 || bb->index < NUM_FIXED_BLOCKS
607 || bb->index >= n_basic_blocks
608 || BASIC_BLOCK (bb->index) != bb
609 || !gimple_call_noreturn_p (stmt))
612 changed |= fixup_noreturn_call (stmt);
618 /* If GIMPLE_OMP_RETURN in basic block BB is unreachable, remove it. */
621 cleanup_omp_return (basic_block bb)
623 gimple stmt = last_stmt (bb);
624 basic_block control_bb;
627 || gimple_code (stmt) != GIMPLE_OMP_RETURN
628 || !single_pred_p (bb))
631 control_bb = single_pred (bb);
632 stmt = last_stmt (control_bb);
634 if (stmt == NULL || gimple_code (stmt) != GIMPLE_OMP_SECTIONS_SWITCH)
637 /* The block with the control statement normally has two entry edges -- one
638 from entry, one from continue. If continue is removed, return is
639 unreachable, so we remove it here as well. */
640 if (EDGE_COUNT (control_bb->preds) == 2)
643 gcc_assert (EDGE_COUNT (control_bb->preds) == 1);
644 remove_edge_and_dominated_blocks (single_pred_edge (bb));
648 /* Tries to cleanup cfg in basic block BB. Returns true if anything
652 cleanup_tree_cfg_bb (basic_block bb)
656 if (cleanup_omp_return (bb))
659 retval = cleanup_control_flow_bb (bb);
661 if (tree_forwarder_block_p (bb, false)
662 && remove_forwarder_block (bb))
665 /* Merging the blocks may create new opportunities for folding
666 conditional branches (due to the elimination of single-valued PHI
668 if (single_succ_p (bb)
669 && can_merge_blocks_p (bb, single_succ (bb)))
671 merge_blocks (bb, single_succ (bb));
678 /* Iterate the cfg cleanups, while anything changes. */
681 cleanup_tree_cfg_1 (void)
687 retval |= split_bbs_on_noreturn_calls ();
689 /* Prepare the worklists of altered blocks. */
690 cfgcleanup_altered_bbs = BITMAP_ALLOC (NULL);
692 /* During forwarder block cleanup, we may redirect edges out of
693 SWITCH_EXPRs, which can get expensive. So we want to enable
694 recording of edge to CASE_LABEL_EXPR. */
695 start_recording_case_labels ();
697 /* Start by iterating over all basic blocks. We cannot use FOR_EACH_BB,
698 since the basic blocks may get removed. */
699 n = last_basic_block;
700 for (i = NUM_FIXED_BLOCKS; i < n; i++)
702 bb = BASIC_BLOCK (i);
704 retval |= cleanup_tree_cfg_bb (bb);
707 /* Now process the altered blocks, as long as any are available. */
708 while (!bitmap_empty_p (cfgcleanup_altered_bbs))
710 i = bitmap_first_set_bit (cfgcleanup_altered_bbs);
711 bitmap_clear_bit (cfgcleanup_altered_bbs, i);
712 if (i < NUM_FIXED_BLOCKS)
715 bb = BASIC_BLOCK (i);
719 retval |= cleanup_tree_cfg_bb (bb);
721 /* Rerun split_bbs_on_noreturn_calls, in case we have altered any noreturn
723 retval |= split_bbs_on_noreturn_calls ();
726 end_recording_case_labels ();
727 BITMAP_FREE (cfgcleanup_altered_bbs);
732 /* Remove unreachable blocks and other miscellaneous clean up work.
733 Return true if the flowgraph was modified, false otherwise. */
736 cleanup_tree_cfg_noloop (void)
740 timevar_push (TV_TREE_CLEANUP_CFG);
742 /* Iterate until there are no more cleanups left to do. If any
743 iteration changed the flowgraph, set CHANGED to true.
745 If dominance information is available, there cannot be any unreachable
747 if (!dom_info_available_p (CDI_DOMINATORS))
749 changed = delete_unreachable_blocks ();
750 calculate_dominance_info (CDI_DOMINATORS);
754 #ifdef ENABLE_CHECKING
755 verify_dominators (CDI_DOMINATORS);
760 changed |= cleanup_tree_cfg_1 ();
762 gcc_assert (dom_info_available_p (CDI_DOMINATORS));
765 #ifdef ENABLE_CHECKING
769 timevar_pop (TV_TREE_CLEANUP_CFG);
771 if (changed && current_loops)
772 loops_state_set (LOOPS_NEED_FIXUP);
777 /* Repairs loop structures. */
780 repair_loop_structures (void)
782 bitmap changed_bbs = BITMAP_ALLOC (NULL);
783 fix_loop_structure (changed_bbs);
785 /* This usually does nothing. But sometimes parts of cfg that originally
786 were inside a loop get out of it due to edge removal (since they
787 become unreachable by back edges from latch). */
788 if (loops_state_satisfies_p (LOOP_CLOSED_SSA))
789 rewrite_into_loop_closed_ssa (changed_bbs, TODO_update_ssa);
791 BITMAP_FREE (changed_bbs);
793 #ifdef ENABLE_CHECKING
794 verify_loop_structure ();
798 loops_state_clear (LOOPS_NEED_FIXUP);
801 /* Cleanup cfg and repair loop structures. */
804 cleanup_tree_cfg (void)
806 bool changed = cleanup_tree_cfg_noloop ();
808 if (current_loops != NULL
809 && loops_state_satisfies_p (LOOPS_NEED_FIXUP))
810 repair_loop_structures ();
815 /* Merge the PHI nodes at BB into those at BB's sole successor. */
818 remove_forwarder_block_with_phi (basic_block bb)
820 edge succ = single_succ_edge (bb);
821 basic_block dest = succ->dest;
823 basic_block dombb, domdest, dom;
825 /* We check for infinite loops already in tree_forwarder_block_p.
826 However it may happen that the infinite loop is created
827 afterwards due to removal of forwarders. */
831 /* If the destination block consists of a nonlocal label, do not
833 label = first_stmt (dest);
835 && gimple_code (label) == GIMPLE_LABEL
836 && DECL_NONLOCAL (gimple_label_label (label)))
839 /* Redirect each incoming edge to BB to DEST. */
840 while (EDGE_COUNT (bb->preds) > 0)
842 edge e = EDGE_PRED (bb, 0), s;
843 gimple_stmt_iterator gsi;
845 s = find_edge (e->src, dest);
848 /* We already have an edge S from E->src to DEST. If S and
849 E->dest's sole successor edge have the same PHI arguments
850 at DEST, redirect S to DEST. */
851 if (phi_alternatives_equal (dest, s, succ))
853 e = redirect_edge_and_branch (e, dest);
854 redirect_edge_var_map_clear (e);
858 /* PHI arguments are different. Create a forwarder block by
859 splitting E so that we can merge PHI arguments on E to
861 e = single_succ_edge (split_edge (e));
864 s = redirect_edge_and_branch (e, dest);
866 /* redirect_edge_and_branch must not create a new edge. */
869 /* Add to the PHI nodes at DEST each PHI argument removed at the
871 for (gsi = gsi_start_phis (dest);
875 gimple phi = gsi_stmt (gsi);
876 tree def = gimple_phi_arg_def (phi, succ->dest_idx);
877 source_location locus = gimple_phi_arg_location_from_edge (phi, succ);
879 if (TREE_CODE (def) == SSA_NAME)
881 edge_var_map_vector head;
885 /* If DEF is one of the results of PHI nodes removed during
886 redirection, replace it with the PHI argument that used
888 head = redirect_edge_var_map_vector (e);
889 FOR_EACH_VEC_ELT (edge_var_map, head, i, vm)
891 tree old_arg = redirect_edge_var_map_result (vm);
892 tree new_arg = redirect_edge_var_map_def (vm);
897 locus = redirect_edge_var_map_location (vm);
903 add_phi_arg (phi, def, s, locus);
906 redirect_edge_var_map_clear (e);
909 /* Update the dominators. */
910 dombb = get_immediate_dominator (CDI_DOMINATORS, bb);
911 domdest = get_immediate_dominator (CDI_DOMINATORS, dest);
914 /* Shortcut to avoid calling (relatively expensive)
915 nearest_common_dominator unless necessary. */
919 dom = nearest_common_dominator (CDI_DOMINATORS, domdest, dombb);
921 set_immediate_dominator (CDI_DOMINATORS, dest, dom);
923 /* Remove BB since all of BB's incoming edges have been redirected
925 delete_basic_block (bb);
928 /* This pass merges PHI nodes if one feeds into another. For example,
929 suppose we have the following:
936 # tem_6 = PHI <tem_17(8), tem_23(7)>;
939 # tem_3 = PHI <tem_6(9), tem_2(5)>;
942 Then we merge the first PHI node into the second one like so:
949 # tem_3 = PHI <tem_23(7), tem_2(5), tem_17(8)>;
954 merge_phi_nodes (void)
956 basic_block *worklist = XNEWVEC (basic_block, n_basic_blocks);
957 basic_block *current = worklist;
960 calculate_dominance_info (CDI_DOMINATORS);
962 /* Find all PHI nodes that we may be able to merge. */
967 /* Look for a forwarder block with PHI nodes. */
968 if (!tree_forwarder_block_p (bb, true))
971 dest = single_succ (bb);
973 /* We have to feed into another basic block with PHI
975 if (gimple_seq_empty_p (phi_nodes (dest))
976 /* We don't want to deal with a basic block with
978 || bb_has_abnormal_pred (bb))
981 if (!dominated_by_p (CDI_DOMINATORS, dest, bb))
983 /* If BB does not dominate DEST, then the PHI nodes at
984 DEST must be the only users of the results of the PHI
990 gimple_stmt_iterator gsi;
991 unsigned int dest_idx = single_succ_edge (bb)->dest_idx;
993 /* BB dominates DEST. There may be many users of the PHI
994 nodes in BB. However, there is still a trivial case we
995 can handle. If the result of every PHI in BB is used
996 only by a PHI in DEST, then we can trivially merge the
997 PHI nodes from BB into DEST. */
998 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi);
1001 gimple phi = gsi_stmt (gsi);
1002 tree result = gimple_phi_result (phi);
1003 use_operand_p imm_use;
1006 /* If the PHI's result is never used, then we can just
1008 if (has_zero_uses (result))
1011 /* Get the single use of the result of this PHI node. */
1012 if (!single_imm_use (result, &imm_use, &use_stmt)
1013 || gimple_code (use_stmt) != GIMPLE_PHI
1014 || gimple_bb (use_stmt) != dest
1015 || gimple_phi_arg_def (use_stmt, dest_idx) != result)
1019 /* If the loop above iterated through all the PHI nodes
1020 in BB, then we can merge the PHIs from BB into DEST. */
1021 if (gsi_end_p (gsi))
1026 /* Now let's drain WORKLIST. */
1027 while (current != worklist)
1030 remove_forwarder_block_with_phi (bb);
1038 gate_merge_phi (void)
1043 struct gimple_opt_pass pass_merge_phi =
1047 "mergephi", /* name */
1048 gate_merge_phi, /* gate */
1049 merge_phi_nodes, /* execute */
1052 0, /* static_pass_number */
1053 TV_TREE_MERGE_PHI, /* tv_id */
1054 PROP_cfg | PROP_ssa, /* properties_required */
1055 0, /* properties_provided */
1056 0, /* properties_destroyed */
1057 0, /* todo_flags_start */
1058 TODO_dump_func | TODO_ggc_collect /* todo_flags_finish */