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"
34 #include "langhooks.h"
35 #include "diagnostic.h"
36 #include "tree-flow.h"
38 #include "tree-dump.h"
39 #include "tree-pass.h"
43 #include "cfglayout.h"
45 #include "tree-ssa-propagate.h"
46 #include "tree-scalar-evolution.h"
48 /* The set of blocks in that at least one of the following changes happened:
49 -- the statement at the end of the block was changed
50 -- the block was newly created
51 -- the set of the predecessors of the block changed
52 -- the set of the successors of the block changed
53 ??? Maybe we could track these changes separately, since they determine
54 what cleanups it makes sense to try on the block. */
55 bitmap cfgcleanup_altered_bbs;
57 /* Remove any fallthru edge from EV. Return true if an edge was removed. */
60 remove_fallthru_edge (VEC(edge,gc) *ev)
65 FOR_EACH_EDGE (e, ei, ev)
66 if ((e->flags & EDGE_FALLTHRU) != 0)
68 remove_edge_and_dominated_blocks (e);
75 /* Disconnect an unreachable block in the control expression starting
79 cleanup_control_expr_graph (basic_block bb, gimple_stmt_iterator gsi)
83 gimple stmt = gsi_stmt (gsi);
86 if (!single_succ_p (bb))
93 fold_defer_overflow_warnings ();
94 loc = gimple_location (stmt);
95 switch (gimple_code (stmt))
99 tree lhs = gimple_cond_lhs (stmt);
100 tree rhs = gimple_cond_rhs (stmt);
101 /* For conditions try harder and lookup single-argument
102 PHI nodes. Only do so from the same basic-block though
103 as other basic-blocks may be dead already. */
104 if (TREE_CODE (lhs) == SSA_NAME
105 && !name_registered_for_update_p (lhs))
107 gimple def_stmt = SSA_NAME_DEF_STMT (lhs);
108 if (gimple_code (def_stmt) == GIMPLE_PHI
109 && gimple_phi_num_args (def_stmt) == 1
110 && gimple_bb (def_stmt) == gimple_bb (stmt)
111 && (TREE_CODE (PHI_ARG_DEF (def_stmt, 0)) != SSA_NAME
112 || !name_registered_for_update_p (PHI_ARG_DEF (def_stmt,
114 lhs = PHI_ARG_DEF (def_stmt, 0);
116 if (TREE_CODE (rhs) == SSA_NAME
117 && !name_registered_for_update_p (rhs))
119 gimple def_stmt = SSA_NAME_DEF_STMT (rhs);
120 if (gimple_code (def_stmt) == GIMPLE_PHI
121 && gimple_phi_num_args (def_stmt) == 1
122 && gimple_bb (def_stmt) == gimple_bb (stmt)
123 && (TREE_CODE (PHI_ARG_DEF (def_stmt, 0)) != SSA_NAME
124 || !name_registered_for_update_p (PHI_ARG_DEF (def_stmt,
126 rhs = PHI_ARG_DEF (def_stmt, 0);
128 val = fold_binary_loc (loc, gimple_cond_code (stmt),
129 boolean_type_node, lhs, rhs);
134 val = gimple_switch_index (stmt);
140 taken_edge = find_taken_edge (bb, val);
143 fold_undefer_and_ignore_overflow_warnings ();
147 /* Remove all the edges except the one that is always executed. */
149 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
155 fold_undefer_overflow_warnings
156 (true, stmt, WARN_STRICT_OVERFLOW_CONDITIONAL);
160 taken_edge->probability += e->probability;
161 taken_edge->count += e->count;
162 remove_edge_and_dominated_blocks (e);
169 fold_undefer_and_ignore_overflow_warnings ();
170 if (taken_edge->probability > REG_BR_PROB_BASE)
171 taken_edge->probability = REG_BR_PROB_BASE;
174 taken_edge = single_succ_edge (bb);
176 bitmap_set_bit (cfgcleanup_altered_bbs, bb->index);
177 gsi_remove (&gsi, true);
178 taken_edge->flags = EDGE_FALLTHRU;
183 /* Try to remove superfluous control structures in basic block BB. Returns
184 true if anything changes. */
187 cleanup_control_flow_bb (basic_block bb)
189 gimple_stmt_iterator gsi;
193 /* If the last statement of the block could throw and now cannot,
194 we need to prune cfg. */
195 retval |= gimple_purge_dead_eh_edges (bb);
197 gsi = gsi_last_bb (bb);
201 stmt = gsi_stmt (gsi);
203 if (gimple_code (stmt) == GIMPLE_COND
204 || gimple_code (stmt) == GIMPLE_SWITCH)
205 retval |= cleanup_control_expr_graph (bb, gsi);
206 else if (gimple_code (stmt) == GIMPLE_GOTO
207 && TREE_CODE (gimple_goto_dest (stmt)) == ADDR_EXPR
208 && (TREE_CODE (TREE_OPERAND (gimple_goto_dest (stmt), 0))
211 /* If we had a computed goto which has a compile-time determinable
212 destination, then we can eliminate the goto. */
216 basic_block target_block;
218 /* First look at all the outgoing edges. Delete any outgoing
219 edges which do not go to the right block. For the one
220 edge which goes to the right block, fix up its flags. */
221 label = TREE_OPERAND (gimple_goto_dest (stmt), 0);
222 target_block = label_to_block (label);
223 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
225 if (e->dest != target_block)
226 remove_edge_and_dominated_blocks (e);
229 /* Turn off the EDGE_ABNORMAL flag. */
230 e->flags &= ~EDGE_ABNORMAL;
232 /* And set EDGE_FALLTHRU. */
233 e->flags |= EDGE_FALLTHRU;
238 bitmap_set_bit (cfgcleanup_altered_bbs, bb->index);
239 bitmap_set_bit (cfgcleanup_altered_bbs, target_block->index);
241 /* Remove the GOTO_EXPR as it is not needed. The CFG has all the
242 relevant information we need. */
243 gsi_remove (&gsi, true);
247 /* Check for indirect calls that have been turned into
249 else if (is_gimple_call (stmt)
250 && gimple_call_noreturn_p (stmt)
251 && remove_fallthru_edge (bb->succs))
257 /* Return true if basic block BB does nothing except pass control
258 flow to another block and that we can safely insert a label at
259 the start of the successor block.
261 As a precondition, we require that BB be not equal to
265 tree_forwarder_block_p (basic_block bb, bool phi_wanted)
267 gimple_stmt_iterator gsi;
270 /* BB must have a single outgoing edge. */
271 if (single_succ_p (bb) != 1
272 /* If PHI_WANTED is false, BB must not have any PHI nodes.
273 Otherwise, BB must have PHI nodes. */
274 || gimple_seq_empty_p (phi_nodes (bb)) == phi_wanted
275 /* BB may not be a predecessor of EXIT_BLOCK_PTR. */
276 || single_succ (bb) == EXIT_BLOCK_PTR
277 /* Nor should this be an infinite loop. */
278 || single_succ (bb) == bb
279 /* BB may not have an abnormal outgoing edge. */
280 || (single_succ_edge (bb)->flags & EDGE_ABNORMAL))
284 gcc_assert (bb != ENTRY_BLOCK_PTR);
287 locus = single_succ_edge (bb)->goto_locus;
289 /* There should not be an edge coming from entry, or an EH edge. */
294 FOR_EACH_EDGE (e, ei, bb->preds)
295 if (e->src == ENTRY_BLOCK_PTR || (e->flags & EDGE_EH))
297 /* If goto_locus of any of the edges differs, prevent removing
298 the forwarder block for -O0. */
299 else if (optimize == 0 && e->goto_locus != locus)
303 /* Now walk through the statements backward. We can ignore labels,
304 anything else means this is not a forwarder block. */
305 for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi_prev (&gsi))
307 gimple stmt = gsi_stmt (gsi);
309 switch (gimple_code (stmt))
312 if (DECL_NONLOCAL (gimple_label_label (stmt)))
314 if (optimize == 0 && gimple_location (stmt) != locus)
318 /* ??? For now, hope there's a corresponding debug
319 assignment at the destination. */
331 /* Protect loop latches, headers and preheaders. */
332 if (bb->loop_father->header == bb)
334 dest = EDGE_SUCC (bb, 0)->dest;
336 if (dest->loop_father->header == dest)
342 /* Return true if BB has at least one abnormal incoming edge. */
345 has_abnormal_incoming_edge_p (basic_block bb)
350 FOR_EACH_EDGE (e, ei, bb->preds)
351 if (e->flags & EDGE_ABNORMAL)
357 /* If all the PHI nodes in DEST have alternatives for E1 and E2 and
358 those alternatives are equal in each of the PHI nodes, then return
359 true, else return false. */
362 phi_alternatives_equal (basic_block dest, edge e1, edge e2)
364 int n1 = e1->dest_idx;
365 int n2 = e2->dest_idx;
366 gimple_stmt_iterator gsi;
368 for (gsi = gsi_start_phis (dest); !gsi_end_p (gsi); gsi_next (&gsi))
370 gimple phi = gsi_stmt (gsi);
371 tree val1 = gimple_phi_arg_def (phi, n1);
372 tree val2 = gimple_phi_arg_def (phi, n2);
374 gcc_assert (val1 != NULL_TREE);
375 gcc_assert (val2 != NULL_TREE);
377 if (!operand_equal_for_phi_arg_p (val1, val2))
384 /* Removes forwarder block BB. Returns false if this failed. */
387 remove_forwarder_block (basic_block bb)
389 edge succ = single_succ_edge (bb), e, s;
390 basic_block dest = succ->dest;
393 gimple_stmt_iterator gsi, gsi_to;
394 bool can_move_debug_stmts;
396 /* We check for infinite loops already in tree_forwarder_block_p.
397 However it may happen that the infinite loop is created
398 afterwards due to removal of forwarders. */
402 /* If the destination block consists of a nonlocal label or is a
403 EH landing pad, do not merge it. */
404 label = first_stmt (dest);
406 && gimple_code (label) == GIMPLE_LABEL
407 && (DECL_NONLOCAL (gimple_label_label (label))
408 || EH_LANDING_PAD_NR (gimple_label_label (label)) != 0))
411 /* If there is an abnormal edge to basic block BB, but not into
412 dest, problems might occur during removal of the phi node at out
413 of ssa due to overlapping live ranges of registers.
415 If there is an abnormal edge in DEST, the problems would occur
416 anyway since cleanup_dead_labels would then merge the labels for
417 two different eh regions, and rest of exception handling code
420 So if there is an abnormal edge to BB, proceed only if there is
421 no abnormal edge to DEST and there are no phi nodes in DEST. */
422 if (has_abnormal_incoming_edge_p (bb)
423 && (has_abnormal_incoming_edge_p (dest)
424 || !gimple_seq_empty_p (phi_nodes (dest))))
427 /* If there are phi nodes in DEST, and some of the blocks that are
428 predecessors of BB are also predecessors of DEST, check that the
429 phi node arguments match. */
430 if (!gimple_seq_empty_p (phi_nodes (dest)))
432 FOR_EACH_EDGE (e, ei, bb->preds)
434 s = find_edge (e->src, dest);
438 if (!phi_alternatives_equal (dest, succ, s))
443 can_move_debug_stmts = single_pred_p (dest);
445 /* Redirect the edges. */
446 for (ei = ei_start (bb->preds); (e = ei_safe_edge (ei)); )
448 bitmap_set_bit (cfgcleanup_altered_bbs, e->src->index);
450 if (e->flags & EDGE_ABNORMAL)
452 /* If there is an abnormal edge, redirect it anyway, and
453 move the labels to the new block to make it legal. */
454 s = redirect_edge_succ_nodup (e, dest);
457 s = redirect_edge_and_branch (e, dest);
461 /* Create arguments for the phi nodes, since the edge was not
463 for (gsi = gsi_start_phis (dest);
467 gimple phi = gsi_stmt (gsi);
468 source_location l = gimple_phi_arg_location_from_edge (phi, succ);
469 add_phi_arg (phi, gimple_phi_arg_def (phi, succ->dest_idx), s, l);
474 /* Move nonlocal labels and computed goto targets as well as user
475 defined labels and labels with an EH landing pad number to the
476 new block, so that the redirection of the abnormal edges works,
477 jump targets end up in a sane place and debug information for
478 labels is retained. */
479 gsi_to = gsi_start_bb (dest);
480 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); )
483 label = gsi_stmt (gsi);
484 if (is_gimple_debug (label))
486 decl = gimple_label_label (label);
487 if (EH_LANDING_PAD_NR (decl) != 0
488 || DECL_NONLOCAL (decl)
489 || FORCED_LABEL (decl)
490 || !DECL_ARTIFICIAL (decl))
492 gsi_remove (&gsi, false);
493 gsi_insert_before (&gsi_to, label, GSI_SAME_STMT);
499 /* Move debug statements if the destination has just a single
501 if (can_move_debug_stmts)
503 gsi_to = gsi_after_labels (dest);
504 for (gsi = gsi_after_labels (bb); !gsi_end_p (gsi); )
506 gimple debug = gsi_stmt (gsi);
507 if (!is_gimple_debug (debug))
509 gsi_remove (&gsi, false);
510 gsi_insert_before (&gsi_to, debug, GSI_SAME_STMT);
514 bitmap_set_bit (cfgcleanup_altered_bbs, dest->index);
516 /* Update the dominators. */
517 if (dom_info_available_p (CDI_DOMINATORS))
519 basic_block dom, dombb, domdest;
521 dombb = get_immediate_dominator (CDI_DOMINATORS, bb);
522 domdest = get_immediate_dominator (CDI_DOMINATORS, dest);
525 /* Shortcut to avoid calling (relatively expensive)
526 nearest_common_dominator unless necessary. */
530 dom = nearest_common_dominator (CDI_DOMINATORS, domdest, dombb);
532 set_immediate_dominator (CDI_DOMINATORS, dest, dom);
535 /* And kill the forwarder block. */
536 delete_basic_block (bb);
541 /* STMT is a call that has been discovered noreturn. Fixup the CFG
542 and remove LHS. Return true if something changed. */
545 fixup_noreturn_call (gimple stmt)
547 basic_block bb = gimple_bb (stmt);
548 bool changed = false;
550 if (gimple_call_builtin_p (stmt, BUILT_IN_RETURN))
553 /* First split basic block if stmt is not last. */
554 if (stmt != gsi_stmt (gsi_last_bb (bb)))
555 split_block (bb, stmt);
557 changed |= remove_fallthru_edge (bb->succs);
559 /* If there is LHS, remove it. */
560 if (gimple_call_lhs (stmt))
562 tree op = gimple_call_lhs (stmt);
563 gimple_call_set_lhs (stmt, NULL_TREE);
564 /* We need to remove SSA name to avoid checking.
565 All uses are dominated by the noreturn and thus will
566 be removed afterwards. */
567 if (TREE_CODE (op) == SSA_NAME)
570 imm_use_iterator iter;
573 FOR_EACH_IMM_USE_STMT (use_stmt, iter, op)
574 FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
575 SET_USE (use_p, error_mark_node);
584 /* Split basic blocks on calls in the middle of a basic block that are now
585 known not to return, and remove the unreachable code. */
588 split_bbs_on_noreturn_calls (void)
590 bool changed = false;
594 /* Detect cases where a mid-block call is now known not to return. */
596 while (VEC_length (gimple, MODIFIED_NORETURN_CALLS (cfun)))
598 stmt = VEC_pop (gimple, MODIFIED_NORETURN_CALLS (cfun));
599 bb = gimple_bb (stmt);
600 /* BB might be deleted at this point, so verify first
601 BB is present in the cfg. */
603 || bb->index < NUM_FIXED_BLOCKS
604 || bb->index >= n_basic_blocks
605 || BASIC_BLOCK (bb->index) != bb
606 || !gimple_call_noreturn_p (stmt))
609 changed |= fixup_noreturn_call (stmt);
615 /* If GIMPLE_OMP_RETURN in basic block BB is unreachable, remove it. */
618 cleanup_omp_return (basic_block bb)
620 gimple stmt = last_stmt (bb);
621 basic_block control_bb;
624 || gimple_code (stmt) != GIMPLE_OMP_RETURN
625 || !single_pred_p (bb))
628 control_bb = single_pred (bb);
629 stmt = last_stmt (control_bb);
631 if (stmt == NULL || gimple_code (stmt) != GIMPLE_OMP_SECTIONS_SWITCH)
634 /* The block with the control statement normally has two entry edges -- one
635 from entry, one from continue. If continue is removed, return is
636 unreachable, so we remove it here as well. */
637 if (EDGE_COUNT (control_bb->preds) == 2)
640 gcc_assert (EDGE_COUNT (control_bb->preds) == 1);
641 remove_edge_and_dominated_blocks (single_pred_edge (bb));
645 /* Tries to cleanup cfg in basic block BB. Returns true if anything
649 cleanup_tree_cfg_bb (basic_block bb)
653 if (cleanup_omp_return (bb))
656 retval = cleanup_control_flow_bb (bb);
658 if (tree_forwarder_block_p (bb, false)
659 && remove_forwarder_block (bb))
662 /* Merging the blocks may create new opportunities for folding
663 conditional branches (due to the elimination of single-valued PHI
665 if (single_succ_p (bb)
666 && can_merge_blocks_p (bb, single_succ (bb)))
668 merge_blocks (bb, single_succ (bb));
675 /* Iterate the cfg cleanups, while anything changes. */
678 cleanup_tree_cfg_1 (void)
684 retval |= split_bbs_on_noreturn_calls ();
686 /* Prepare the worklists of altered blocks. */
687 cfgcleanup_altered_bbs = BITMAP_ALLOC (NULL);
689 /* During forwarder block cleanup, we may redirect edges out of
690 SWITCH_EXPRs, which can get expensive. So we want to enable
691 recording of edge to CASE_LABEL_EXPR. */
692 start_recording_case_labels ();
694 /* Start by iterating over all basic blocks. We cannot use FOR_EACH_BB,
695 since the basic blocks may get removed. */
696 n = last_basic_block;
697 for (i = NUM_FIXED_BLOCKS; i < n; i++)
699 bb = BASIC_BLOCK (i);
701 retval |= cleanup_tree_cfg_bb (bb);
704 /* Now process the altered blocks, as long as any are available. */
705 while (!bitmap_empty_p (cfgcleanup_altered_bbs))
707 i = bitmap_first_set_bit (cfgcleanup_altered_bbs);
708 bitmap_clear_bit (cfgcleanup_altered_bbs, i);
709 if (i < NUM_FIXED_BLOCKS)
712 bb = BASIC_BLOCK (i);
716 retval |= cleanup_tree_cfg_bb (bb);
718 /* Rerun split_bbs_on_noreturn_calls, in case we have altered any noreturn
720 retval |= split_bbs_on_noreturn_calls ();
723 end_recording_case_labels ();
724 BITMAP_FREE (cfgcleanup_altered_bbs);
729 /* Remove unreachable blocks and other miscellaneous clean up work.
730 Return true if the flowgraph was modified, false otherwise. */
733 cleanup_tree_cfg_noloop (void)
737 timevar_push (TV_TREE_CLEANUP_CFG);
739 /* Iterate until there are no more cleanups left to do. If any
740 iteration changed the flowgraph, set CHANGED to true.
742 If dominance information is available, there cannot be any unreachable
744 if (!dom_info_available_p (CDI_DOMINATORS))
746 changed = delete_unreachable_blocks ();
747 calculate_dominance_info (CDI_DOMINATORS);
751 #ifdef ENABLE_CHECKING
752 verify_dominators (CDI_DOMINATORS);
757 changed |= cleanup_tree_cfg_1 ();
759 gcc_assert (dom_info_available_p (CDI_DOMINATORS));
762 #ifdef ENABLE_CHECKING
766 timevar_pop (TV_TREE_CLEANUP_CFG);
768 if (changed && current_loops)
769 loops_state_set (LOOPS_NEED_FIXUP);
774 /* Repairs loop structures. */
777 repair_loop_structures (void)
779 bitmap changed_bbs = BITMAP_ALLOC (NULL);
780 fix_loop_structure (changed_bbs);
782 /* This usually does nothing. But sometimes parts of cfg that originally
783 were inside a loop get out of it due to edge removal (since they
784 become unreachable by back edges from latch). */
785 if (loops_state_satisfies_p (LOOP_CLOSED_SSA))
786 rewrite_into_loop_closed_ssa (changed_bbs, TODO_update_ssa);
788 BITMAP_FREE (changed_bbs);
790 #ifdef ENABLE_CHECKING
791 verify_loop_structure ();
795 loops_state_clear (LOOPS_NEED_FIXUP);
798 /* Cleanup cfg and repair loop structures. */
801 cleanup_tree_cfg (void)
803 bool changed = cleanup_tree_cfg_noloop ();
805 if (current_loops != NULL
806 && loops_state_satisfies_p (LOOPS_NEED_FIXUP))
807 repair_loop_structures ();
812 /* Merge the PHI nodes at BB into those at BB's sole successor. */
815 remove_forwarder_block_with_phi (basic_block bb)
817 edge succ = single_succ_edge (bb);
818 basic_block dest = succ->dest;
820 basic_block dombb, domdest, dom;
822 /* We check for infinite loops already in tree_forwarder_block_p.
823 However it may happen that the infinite loop is created
824 afterwards due to removal of forwarders. */
828 /* If the destination block consists of a nonlocal label, do not
830 label = first_stmt (dest);
832 && gimple_code (label) == GIMPLE_LABEL
833 && DECL_NONLOCAL (gimple_label_label (label)))
836 /* Redirect each incoming edge to BB to DEST. */
837 while (EDGE_COUNT (bb->preds) > 0)
839 edge e = EDGE_PRED (bb, 0), s;
840 gimple_stmt_iterator gsi;
842 s = find_edge (e->src, dest);
845 /* We already have an edge S from E->src to DEST. If S and
846 E->dest's sole successor edge have the same PHI arguments
847 at DEST, redirect S to DEST. */
848 if (phi_alternatives_equal (dest, s, succ))
850 e = redirect_edge_and_branch (e, dest);
851 redirect_edge_var_map_clear (e);
855 /* PHI arguments are different. Create a forwarder block by
856 splitting E so that we can merge PHI arguments on E to
858 e = single_succ_edge (split_edge (e));
861 s = redirect_edge_and_branch (e, dest);
863 /* redirect_edge_and_branch must not create a new edge. */
866 /* Add to the PHI nodes at DEST each PHI argument removed at the
868 for (gsi = gsi_start_phis (dest);
872 gimple phi = gsi_stmt (gsi);
873 tree def = gimple_phi_arg_def (phi, succ->dest_idx);
874 source_location locus = gimple_phi_arg_location_from_edge (phi, succ);
876 if (TREE_CODE (def) == SSA_NAME)
878 edge_var_map_vector head;
882 /* If DEF is one of the results of PHI nodes removed during
883 redirection, replace it with the PHI argument that used
885 head = redirect_edge_var_map_vector (e);
886 for (i = 0; VEC_iterate (edge_var_map, head, i, vm); ++i)
888 tree old_arg = redirect_edge_var_map_result (vm);
889 tree new_arg = redirect_edge_var_map_def (vm);
894 locus = redirect_edge_var_map_location (vm);
900 add_phi_arg (phi, def, s, locus);
903 redirect_edge_var_map_clear (e);
906 /* Update the dominators. */
907 dombb = get_immediate_dominator (CDI_DOMINATORS, bb);
908 domdest = get_immediate_dominator (CDI_DOMINATORS, dest);
911 /* Shortcut to avoid calling (relatively expensive)
912 nearest_common_dominator unless necessary. */
916 dom = nearest_common_dominator (CDI_DOMINATORS, domdest, dombb);
918 set_immediate_dominator (CDI_DOMINATORS, dest, dom);
920 /* Remove BB since all of BB's incoming edges have been redirected
922 delete_basic_block (bb);
925 /* This pass merges PHI nodes if one feeds into another. For example,
926 suppose we have the following:
933 # tem_6 = PHI <tem_17(8), tem_23(7)>;
936 # tem_3 = PHI <tem_6(9), tem_2(5)>;
939 Then we merge the first PHI node into the second one like so:
946 # tem_3 = PHI <tem_23(7), tem_2(5), tem_17(8)>;
951 merge_phi_nodes (void)
953 basic_block *worklist = XNEWVEC (basic_block, n_basic_blocks);
954 basic_block *current = worklist;
957 calculate_dominance_info (CDI_DOMINATORS);
959 /* Find all PHI nodes that we may be able to merge. */
964 /* Look for a forwarder block with PHI nodes. */
965 if (!tree_forwarder_block_p (bb, true))
968 dest = single_succ (bb);
970 /* We have to feed into another basic block with PHI
972 if (gimple_seq_empty_p (phi_nodes (dest))
973 /* We don't want to deal with a basic block with
975 || has_abnormal_incoming_edge_p (bb))
978 if (!dominated_by_p (CDI_DOMINATORS, dest, bb))
980 /* If BB does not dominate DEST, then the PHI nodes at
981 DEST must be the only users of the results of the PHI
987 gimple_stmt_iterator gsi;
988 unsigned int dest_idx = single_succ_edge (bb)->dest_idx;
990 /* BB dominates DEST. There may be many users of the PHI
991 nodes in BB. However, there is still a trivial case we
992 can handle. If the result of every PHI in BB is used
993 only by a PHI in DEST, then we can trivially merge the
994 PHI nodes from BB into DEST. */
995 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi);
998 gimple phi = gsi_stmt (gsi);
999 tree result = gimple_phi_result (phi);
1000 use_operand_p imm_use;
1003 /* If the PHI's result is never used, then we can just
1005 if (has_zero_uses (result))
1008 /* Get the single use of the result of this PHI node. */
1009 if (!single_imm_use (result, &imm_use, &use_stmt)
1010 || gimple_code (use_stmt) != GIMPLE_PHI
1011 || gimple_bb (use_stmt) != dest
1012 || gimple_phi_arg_def (use_stmt, dest_idx) != result)
1016 /* If the loop above iterated through all the PHI nodes
1017 in BB, then we can merge the PHIs from BB into DEST. */
1018 if (gsi_end_p (gsi))
1023 /* Now let's drain WORKLIST. */
1024 while (current != worklist)
1027 remove_forwarder_block_with_phi (bb);
1035 gate_merge_phi (void)
1040 struct gimple_opt_pass pass_merge_phi =
1044 "mergephi", /* name */
1045 gate_merge_phi, /* gate */
1046 merge_phi_nodes, /* execute */
1049 0, /* static_pass_number */
1050 TV_TREE_MERGE_PHI, /* tv_id */
1051 PROP_cfg | PROP_ssa, /* properties_required */
1052 0, /* properties_provided */
1053 0, /* properties_destroyed */
1054 0, /* todo_flags_start */
1055 TODO_dump_func | TODO_ggc_collect /* todo_flags_finish */