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"
33 #include "langhooks.h"
34 #include "tree-flow.h"
36 #include "tree-dump.h"
37 #include "tree-pass.h"
41 #include "cfglayout.h"
43 #include "tree-ssa-propagate.h"
44 #include "tree-scalar-evolution.h"
46 /* The set of blocks in that at least one of the following changes happened:
47 -- the statement at the end of the block was changed
48 -- the block was newly created
49 -- the set of the predecessors of the block changed
50 -- the set of the successors of the block changed
51 ??? Maybe we could track these changes separately, since they determine
52 what cleanups it makes sense to try on the block. */
53 bitmap cfgcleanup_altered_bbs;
55 /* Remove any fallthru edge from EV. Return true if an edge was removed. */
58 remove_fallthru_edge (VEC(edge,gc) *ev)
63 FOR_EACH_EDGE (e, ei, ev)
64 if ((e->flags & EDGE_FALLTHRU) != 0)
66 remove_edge_and_dominated_blocks (e);
73 /* Disconnect an unreachable block in the control expression starting
77 cleanup_control_expr_graph (basic_block bb, gimple_stmt_iterator gsi)
81 gimple stmt = gsi_stmt (gsi);
84 if (!single_succ_p (bb))
91 fold_defer_overflow_warnings ();
92 loc = gimple_location (stmt);
93 switch (gimple_code (stmt))
97 tree lhs = gimple_cond_lhs (stmt);
98 tree rhs = gimple_cond_rhs (stmt);
99 /* For conditions try harder and lookup single-argument
100 PHI nodes. Only do so from the same basic-block though
101 as other basic-blocks may be dead already. */
102 if (TREE_CODE (lhs) == SSA_NAME
103 && !name_registered_for_update_p (lhs))
105 gimple def_stmt = SSA_NAME_DEF_STMT (lhs);
106 if (gimple_code (def_stmt) == GIMPLE_PHI
107 && gimple_phi_num_args (def_stmt) == 1
108 && gimple_bb (def_stmt) == gimple_bb (stmt)
109 && (TREE_CODE (PHI_ARG_DEF (def_stmt, 0)) != SSA_NAME
110 || !name_registered_for_update_p (PHI_ARG_DEF (def_stmt,
112 lhs = PHI_ARG_DEF (def_stmt, 0);
114 if (TREE_CODE (rhs) == SSA_NAME
115 && !name_registered_for_update_p (rhs))
117 gimple def_stmt = SSA_NAME_DEF_STMT (rhs);
118 if (gimple_code (def_stmt) == GIMPLE_PHI
119 && gimple_phi_num_args (def_stmt) == 1
120 && gimple_bb (def_stmt) == gimple_bb (stmt)
121 && (TREE_CODE (PHI_ARG_DEF (def_stmt, 0)) != SSA_NAME
122 || !name_registered_for_update_p (PHI_ARG_DEF (def_stmt,
124 rhs = PHI_ARG_DEF (def_stmt, 0);
126 val = fold_binary_loc (loc, gimple_cond_code (stmt),
127 boolean_type_node, lhs, rhs);
132 val = gimple_switch_index (stmt);
138 taken_edge = find_taken_edge (bb, val);
141 fold_undefer_and_ignore_overflow_warnings ();
145 /* Remove all the edges except the one that is always executed. */
147 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
153 fold_undefer_overflow_warnings
154 (true, stmt, WARN_STRICT_OVERFLOW_CONDITIONAL);
158 taken_edge->probability += e->probability;
159 taken_edge->count += e->count;
160 remove_edge_and_dominated_blocks (e);
167 fold_undefer_and_ignore_overflow_warnings ();
168 if (taken_edge->probability > REG_BR_PROB_BASE)
169 taken_edge->probability = REG_BR_PROB_BASE;
172 taken_edge = single_succ_edge (bb);
174 bitmap_set_bit (cfgcleanup_altered_bbs, bb->index);
175 gsi_remove (&gsi, true);
176 taken_edge->flags = EDGE_FALLTHRU;
181 /* Try to remove superfluous control structures in basic block BB. Returns
182 true if anything changes. */
185 cleanup_control_flow_bb (basic_block bb)
187 gimple_stmt_iterator gsi;
191 /* If the last statement of the block could throw and now cannot,
192 we need to prune cfg. */
193 retval |= gimple_purge_dead_eh_edges (bb);
195 gsi = gsi_last_bb (bb);
199 stmt = gsi_stmt (gsi);
201 if (gimple_code (stmt) == GIMPLE_COND
202 || gimple_code (stmt) == GIMPLE_SWITCH)
203 retval |= cleanup_control_expr_graph (bb, gsi);
204 else if (gimple_code (stmt) == GIMPLE_GOTO
205 && TREE_CODE (gimple_goto_dest (stmt)) == ADDR_EXPR
206 && (TREE_CODE (TREE_OPERAND (gimple_goto_dest (stmt), 0))
209 /* If we had a computed goto which has a compile-time determinable
210 destination, then we can eliminate the goto. */
214 basic_block target_block;
216 /* First look at all the outgoing edges. Delete any outgoing
217 edges which do not go to the right block. For the one
218 edge which goes to the right block, fix up its flags. */
219 label = TREE_OPERAND (gimple_goto_dest (stmt), 0);
220 target_block = label_to_block (label);
221 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
223 if (e->dest != target_block)
224 remove_edge_and_dominated_blocks (e);
227 /* Turn off the EDGE_ABNORMAL flag. */
228 e->flags &= ~EDGE_ABNORMAL;
230 /* And set EDGE_FALLTHRU. */
231 e->flags |= EDGE_FALLTHRU;
236 bitmap_set_bit (cfgcleanup_altered_bbs, bb->index);
237 bitmap_set_bit (cfgcleanup_altered_bbs, target_block->index);
239 /* Remove the GOTO_EXPR as it is not needed. The CFG has all the
240 relevant information we need. */
241 gsi_remove (&gsi, true);
245 /* Check for indirect calls that have been turned into
247 else if (is_gimple_call (stmt)
248 && gimple_call_noreturn_p (stmt)
249 && remove_fallthru_edge (bb->succs))
255 /* Return true if basic block BB does nothing except pass control
256 flow to another block and that we can safely insert a label at
257 the start of the successor block.
259 As a precondition, we require that BB be not equal to
263 tree_forwarder_block_p (basic_block bb, bool phi_wanted)
265 gimple_stmt_iterator gsi;
268 /* BB must have a single outgoing edge. */
269 if (single_succ_p (bb) != 1
270 /* If PHI_WANTED is false, BB must not have any PHI nodes.
271 Otherwise, BB must have PHI nodes. */
272 || gimple_seq_empty_p (phi_nodes (bb)) == phi_wanted
273 /* BB may not be a predecessor of EXIT_BLOCK_PTR. */
274 || single_succ (bb) == EXIT_BLOCK_PTR
275 /* Nor should this be an infinite loop. */
276 || single_succ (bb) == bb
277 /* BB may not have an abnormal outgoing edge. */
278 || (single_succ_edge (bb)->flags & EDGE_ABNORMAL))
282 gcc_assert (bb != ENTRY_BLOCK_PTR);
285 locus = single_succ_edge (bb)->goto_locus;
287 /* There should not be an edge coming from entry, or an EH edge. */
292 FOR_EACH_EDGE (e, ei, bb->preds)
293 if (e->src == ENTRY_BLOCK_PTR || (e->flags & EDGE_EH))
295 /* If goto_locus of any of the edges differs, prevent removing
296 the forwarder block for -O0. */
297 else if (optimize == 0 && e->goto_locus != locus)
301 /* Now walk through the statements backward. We can ignore labels,
302 anything else means this is not a forwarder block. */
303 for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi_prev (&gsi))
305 gimple stmt = gsi_stmt (gsi);
307 switch (gimple_code (stmt))
310 if (DECL_NONLOCAL (gimple_label_label (stmt)))
312 if (optimize == 0 && gimple_location (stmt) != locus)
316 /* ??? For now, hope there's a corresponding debug
317 assignment at the destination. */
329 /* Protect loop latches, headers and preheaders. */
330 if (bb->loop_father->header == bb)
332 dest = EDGE_SUCC (bb, 0)->dest;
334 if (dest->loop_father->header == dest)
340 /* Return true if BB has at least one abnormal incoming edge. */
343 has_abnormal_incoming_edge_p (basic_block bb)
348 FOR_EACH_EDGE (e, ei, bb->preds)
349 if (e->flags & EDGE_ABNORMAL)
355 /* If all the PHI nodes in DEST have alternatives for E1 and E2 and
356 those alternatives are equal in each of the PHI nodes, then return
357 true, else return false. */
360 phi_alternatives_equal (basic_block dest, edge e1, edge e2)
362 int n1 = e1->dest_idx;
363 int n2 = e2->dest_idx;
364 gimple_stmt_iterator gsi;
366 for (gsi = gsi_start_phis (dest); !gsi_end_p (gsi); gsi_next (&gsi))
368 gimple phi = gsi_stmt (gsi);
369 tree val1 = gimple_phi_arg_def (phi, n1);
370 tree val2 = gimple_phi_arg_def (phi, n2);
372 gcc_assert (val1 != NULL_TREE);
373 gcc_assert (val2 != NULL_TREE);
375 if (!operand_equal_for_phi_arg_p (val1, val2))
382 /* Removes forwarder block BB. Returns false if this failed. */
385 remove_forwarder_block (basic_block bb)
387 edge succ = single_succ_edge (bb), e, s;
388 basic_block dest = succ->dest;
391 gimple_stmt_iterator gsi, gsi_to;
392 bool can_move_debug_stmts;
394 /* We check for infinite loops already in tree_forwarder_block_p.
395 However it may happen that the infinite loop is created
396 afterwards due to removal of forwarders. */
400 /* If the destination block consists of a nonlocal label or is a
401 EH landing pad, do not merge it. */
402 label = first_stmt (dest);
404 && gimple_code (label) == GIMPLE_LABEL
405 && (DECL_NONLOCAL (gimple_label_label (label))
406 || EH_LANDING_PAD_NR (gimple_label_label (label)) != 0))
409 /* If there is an abnormal edge to basic block BB, but not into
410 dest, problems might occur during removal of the phi node at out
411 of ssa due to overlapping live ranges of registers.
413 If there is an abnormal edge in DEST, the problems would occur
414 anyway since cleanup_dead_labels would then merge the labels for
415 two different eh regions, and rest of exception handling code
418 So if there is an abnormal edge to BB, proceed only if there is
419 no abnormal edge to DEST and there are no phi nodes in DEST. */
420 if (has_abnormal_incoming_edge_p (bb)
421 && (has_abnormal_incoming_edge_p (dest)
422 || !gimple_seq_empty_p (phi_nodes (dest))))
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 (!gimple_seq_empty_p (phi_nodes (dest)))
430 FOR_EACH_EDGE (e, ei, bb->preds)
432 s = find_edge (e->src, dest);
436 if (!phi_alternatives_equal (dest, succ, s))
441 can_move_debug_stmts = single_pred_p (dest);
443 /* Redirect the edges. */
444 for (ei = ei_start (bb->preds); (e = ei_safe_edge (ei)); )
446 bitmap_set_bit (cfgcleanup_altered_bbs, e->src->index);
448 if (e->flags & EDGE_ABNORMAL)
450 /* If there is an abnormal edge, redirect it anyway, and
451 move the labels to the new block to make it legal. */
452 s = redirect_edge_succ_nodup (e, dest);
455 s = redirect_edge_and_branch (e, dest);
459 /* Create arguments for the phi nodes, since the edge was not
461 for (gsi = gsi_start_phis (dest);
465 gimple phi = gsi_stmt (gsi);
466 source_location l = gimple_phi_arg_location_from_edge (phi, succ);
467 add_phi_arg (phi, gimple_phi_arg_def (phi, succ->dest_idx), s, l);
472 /* Move nonlocal labels and computed goto targets as well as user
473 defined labels and labels with an EH landing pad number to the
474 new block, so that the redirection of the abnormal edges works,
475 jump targets end up in a sane place and debug information for
476 labels is retained. */
477 gsi_to = gsi_start_bb (dest);
478 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); )
481 label = gsi_stmt (gsi);
482 if (is_gimple_debug (label))
484 decl = gimple_label_label (label);
485 if (EH_LANDING_PAD_NR (decl) != 0
486 || DECL_NONLOCAL (decl)
487 || FORCED_LABEL (decl)
488 || !DECL_ARTIFICIAL (decl))
490 gsi_remove (&gsi, false);
491 gsi_insert_before (&gsi_to, label, GSI_SAME_STMT);
497 /* Move debug statements if the destination has just a single
499 if (can_move_debug_stmts)
501 gsi_to = gsi_after_labels (dest);
502 for (gsi = gsi_after_labels (bb); !gsi_end_p (gsi); )
504 gimple debug = gsi_stmt (gsi);
505 if (!is_gimple_debug (debug))
507 gsi_remove (&gsi, false);
508 gsi_insert_before (&gsi_to, debug, GSI_SAME_STMT);
512 bitmap_set_bit (cfgcleanup_altered_bbs, dest->index);
514 /* Update the dominators. */
515 if (dom_info_available_p (CDI_DOMINATORS))
517 basic_block dom, dombb, domdest;
519 dombb = get_immediate_dominator (CDI_DOMINATORS, bb);
520 domdest = get_immediate_dominator (CDI_DOMINATORS, dest);
523 /* Shortcut to avoid calling (relatively expensive)
524 nearest_common_dominator unless necessary. */
528 dom = nearest_common_dominator (CDI_DOMINATORS, domdest, dombb);
530 set_immediate_dominator (CDI_DOMINATORS, dest, dom);
533 /* And kill the forwarder block. */
534 delete_basic_block (bb);
539 /* STMT is a call that has been discovered noreturn. Fixup the CFG
540 and remove LHS. Return true if something changed. */
543 fixup_noreturn_call (gimple stmt)
545 basic_block bb = gimple_bb (stmt);
546 bool changed = false;
548 if (gimple_call_builtin_p (stmt, BUILT_IN_RETURN))
551 /* First split basic block if stmt is not last. */
552 if (stmt != gsi_stmt (gsi_last_bb (bb)))
553 split_block (bb, stmt);
555 changed |= remove_fallthru_edge (bb->succs);
557 /* If there is LHS, remove it. */
558 if (gimple_call_lhs (stmt))
560 tree op = gimple_call_lhs (stmt);
561 gimple_call_set_lhs (stmt, NULL_TREE);
562 /* We need to remove SSA name to avoid checking.
563 All uses are dominated by the noreturn and thus will
564 be removed afterwards. */
565 if (TREE_CODE (op) == SSA_NAME)
568 imm_use_iterator iter;
571 FOR_EACH_IMM_USE_STMT (use_stmt, iter, op)
572 FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
573 SET_USE (use_p, error_mark_node);
582 /* Split basic blocks on calls in the middle of a basic block that are now
583 known not to return, and remove the unreachable code. */
586 split_bbs_on_noreturn_calls (void)
588 bool changed = false;
592 /* Detect cases where a mid-block call is now known not to return. */
594 while (VEC_length (gimple, MODIFIED_NORETURN_CALLS (cfun)))
596 stmt = VEC_pop (gimple, MODIFIED_NORETURN_CALLS (cfun));
597 bb = gimple_bb (stmt);
598 /* BB might be deleted at this point, so verify first
599 BB is present in the cfg. */
601 || bb->index < NUM_FIXED_BLOCKS
602 || bb->index >= n_basic_blocks
603 || BASIC_BLOCK (bb->index) != bb
604 || !gimple_call_noreturn_p (stmt))
607 changed |= fixup_noreturn_call (stmt);
613 /* If GIMPLE_OMP_RETURN in basic block BB is unreachable, remove it. */
616 cleanup_omp_return (basic_block bb)
618 gimple stmt = last_stmt (bb);
619 basic_block control_bb;
622 || gimple_code (stmt) != GIMPLE_OMP_RETURN
623 || !single_pred_p (bb))
626 control_bb = single_pred (bb);
627 stmt = last_stmt (control_bb);
629 if (stmt == NULL || gimple_code (stmt) != GIMPLE_OMP_SECTIONS_SWITCH)
632 /* The block with the control statement normally has two entry edges -- one
633 from entry, one from continue. If continue is removed, return is
634 unreachable, so we remove it here as well. */
635 if (EDGE_COUNT (control_bb->preds) == 2)
638 gcc_assert (EDGE_COUNT (control_bb->preds) == 1);
639 remove_edge_and_dominated_blocks (single_pred_edge (bb));
643 /* Tries to cleanup cfg in basic block BB. Returns true if anything
647 cleanup_tree_cfg_bb (basic_block bb)
651 if (cleanup_omp_return (bb))
654 retval = cleanup_control_flow_bb (bb);
656 if (tree_forwarder_block_p (bb, false)
657 && remove_forwarder_block (bb))
660 /* Merging the blocks may create new opportunities for folding
661 conditional branches (due to the elimination of single-valued PHI
663 if (single_succ_p (bb)
664 && can_merge_blocks_p (bb, single_succ (bb)))
666 merge_blocks (bb, single_succ (bb));
673 /* Iterate the cfg cleanups, while anything changes. */
676 cleanup_tree_cfg_1 (void)
682 retval |= split_bbs_on_noreturn_calls ();
684 /* Prepare the worklists of altered blocks. */
685 cfgcleanup_altered_bbs = BITMAP_ALLOC (NULL);
687 /* During forwarder block cleanup, we may redirect edges out of
688 SWITCH_EXPRs, which can get expensive. So we want to enable
689 recording of edge to CASE_LABEL_EXPR. */
690 start_recording_case_labels ();
692 /* Start by iterating over all basic blocks. We cannot use FOR_EACH_BB,
693 since the basic blocks may get removed. */
694 n = last_basic_block;
695 for (i = NUM_FIXED_BLOCKS; i < n; i++)
697 bb = BASIC_BLOCK (i);
699 retval |= cleanup_tree_cfg_bb (bb);
702 /* Now process the altered blocks, as long as any are available. */
703 while (!bitmap_empty_p (cfgcleanup_altered_bbs))
705 i = bitmap_first_set_bit (cfgcleanup_altered_bbs);
706 bitmap_clear_bit (cfgcleanup_altered_bbs, i);
707 if (i < NUM_FIXED_BLOCKS)
710 bb = BASIC_BLOCK (i);
714 retval |= cleanup_tree_cfg_bb (bb);
716 /* Rerun split_bbs_on_noreturn_calls, in case we have altered any noreturn
718 retval |= split_bbs_on_noreturn_calls ();
721 end_recording_case_labels ();
722 BITMAP_FREE (cfgcleanup_altered_bbs);
727 /* Remove unreachable blocks and other miscellaneous clean up work.
728 Return true if the flowgraph was modified, false otherwise. */
731 cleanup_tree_cfg_noloop (void)
735 timevar_push (TV_TREE_CLEANUP_CFG);
737 /* Iterate until there are no more cleanups left to do. If any
738 iteration changed the flowgraph, set CHANGED to true.
740 If dominance information is available, there cannot be any unreachable
742 if (!dom_info_available_p (CDI_DOMINATORS))
744 changed = delete_unreachable_blocks ();
745 calculate_dominance_info (CDI_DOMINATORS);
749 #ifdef ENABLE_CHECKING
750 verify_dominators (CDI_DOMINATORS);
755 changed |= cleanup_tree_cfg_1 ();
757 gcc_assert (dom_info_available_p (CDI_DOMINATORS));
760 #ifdef ENABLE_CHECKING
764 timevar_pop (TV_TREE_CLEANUP_CFG);
766 if (changed && current_loops)
767 loops_state_set (LOOPS_NEED_FIXUP);
772 /* Repairs loop structures. */
775 repair_loop_structures (void)
777 bitmap changed_bbs = BITMAP_ALLOC (NULL);
778 fix_loop_structure (changed_bbs);
780 /* This usually does nothing. But sometimes parts of cfg that originally
781 were inside a loop get out of it due to edge removal (since they
782 become unreachable by back edges from latch). */
783 if (loops_state_satisfies_p (LOOP_CLOSED_SSA))
784 rewrite_into_loop_closed_ssa (changed_bbs, TODO_update_ssa);
786 BITMAP_FREE (changed_bbs);
788 #ifdef ENABLE_CHECKING
789 verify_loop_structure ();
793 loops_state_clear (LOOPS_NEED_FIXUP);
796 /* Cleanup cfg and repair loop structures. */
799 cleanup_tree_cfg (void)
801 bool changed = cleanup_tree_cfg_noloop ();
803 if (current_loops != NULL
804 && loops_state_satisfies_p (LOOPS_NEED_FIXUP))
805 repair_loop_structures ();
810 /* Merge the PHI nodes at BB into those at BB's sole successor. */
813 remove_forwarder_block_with_phi (basic_block bb)
815 edge succ = single_succ_edge (bb);
816 basic_block dest = succ->dest;
818 basic_block dombb, domdest, dom;
820 /* We check for infinite loops already in tree_forwarder_block_p.
821 However it may happen that the infinite loop is created
822 afterwards due to removal of forwarders. */
826 /* If the destination block consists of a nonlocal label, do not
828 label = first_stmt (dest);
830 && gimple_code (label) == GIMPLE_LABEL
831 && DECL_NONLOCAL (gimple_label_label (label)))
834 /* Redirect each incoming edge to BB to DEST. */
835 while (EDGE_COUNT (bb->preds) > 0)
837 edge e = EDGE_PRED (bb, 0), s;
838 gimple_stmt_iterator gsi;
840 s = find_edge (e->src, dest);
843 /* We already have an edge S from E->src to DEST. If S and
844 E->dest's sole successor edge have the same PHI arguments
845 at DEST, redirect S to DEST. */
846 if (phi_alternatives_equal (dest, s, succ))
848 e = redirect_edge_and_branch (e, dest);
849 redirect_edge_var_map_clear (e);
853 /* PHI arguments are different. Create a forwarder block by
854 splitting E so that we can merge PHI arguments on E to
856 e = single_succ_edge (split_edge (e));
859 s = redirect_edge_and_branch (e, dest);
861 /* redirect_edge_and_branch must not create a new edge. */
864 /* Add to the PHI nodes at DEST each PHI argument removed at the
866 for (gsi = gsi_start_phis (dest);
870 gimple phi = gsi_stmt (gsi);
871 tree def = gimple_phi_arg_def (phi, succ->dest_idx);
872 source_location locus = gimple_phi_arg_location_from_edge (phi, succ);
874 if (TREE_CODE (def) == SSA_NAME)
876 edge_var_map_vector head;
880 /* If DEF is one of the results of PHI nodes removed during
881 redirection, replace it with the PHI argument that used
883 head = redirect_edge_var_map_vector (e);
884 for (i = 0; VEC_iterate (edge_var_map, head, i, vm); ++i)
886 tree old_arg = redirect_edge_var_map_result (vm);
887 tree new_arg = redirect_edge_var_map_def (vm);
892 locus = redirect_edge_var_map_location (vm);
898 add_phi_arg (phi, def, s, locus);
901 redirect_edge_var_map_clear (e);
904 /* Update the dominators. */
905 dombb = get_immediate_dominator (CDI_DOMINATORS, bb);
906 domdest = get_immediate_dominator (CDI_DOMINATORS, dest);
909 /* Shortcut to avoid calling (relatively expensive)
910 nearest_common_dominator unless necessary. */
914 dom = nearest_common_dominator (CDI_DOMINATORS, domdest, dombb);
916 set_immediate_dominator (CDI_DOMINATORS, dest, dom);
918 /* Remove BB since all of BB's incoming edges have been redirected
920 delete_basic_block (bb);
923 /* This pass merges PHI nodes if one feeds into another. For example,
924 suppose we have the following:
931 # tem_6 = PHI <tem_17(8), tem_23(7)>;
934 # tem_3 = PHI <tem_6(9), tem_2(5)>;
937 Then we merge the first PHI node into the second one like so:
944 # tem_3 = PHI <tem_23(7), tem_2(5), tem_17(8)>;
949 merge_phi_nodes (void)
951 basic_block *worklist = XNEWVEC (basic_block, n_basic_blocks);
952 basic_block *current = worklist;
955 calculate_dominance_info (CDI_DOMINATORS);
957 /* Find all PHI nodes that we may be able to merge. */
962 /* Look for a forwarder block with PHI nodes. */
963 if (!tree_forwarder_block_p (bb, true))
966 dest = single_succ (bb);
968 /* We have to feed into another basic block with PHI
970 if (gimple_seq_empty_p (phi_nodes (dest))
971 /* We don't want to deal with a basic block with
973 || has_abnormal_incoming_edge_p (bb))
976 if (!dominated_by_p (CDI_DOMINATORS, dest, bb))
978 /* If BB does not dominate DEST, then the PHI nodes at
979 DEST must be the only users of the results of the PHI
985 gimple_stmt_iterator gsi;
986 unsigned int dest_idx = single_succ_edge (bb)->dest_idx;
988 /* BB dominates DEST. There may be many users of the PHI
989 nodes in BB. However, there is still a trivial case we
990 can handle. If the result of every PHI in BB is used
991 only by a PHI in DEST, then we can trivially merge the
992 PHI nodes from BB into DEST. */
993 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi);
996 gimple phi = gsi_stmt (gsi);
997 tree result = gimple_phi_result (phi);
998 use_operand_p imm_use;
1001 /* If the PHI's result is never used, then we can just
1003 if (has_zero_uses (result))
1006 /* Get the single use of the result of this PHI node. */
1007 if (!single_imm_use (result, &imm_use, &use_stmt)
1008 || gimple_code (use_stmt) != GIMPLE_PHI
1009 || gimple_bb (use_stmt) != dest
1010 || gimple_phi_arg_def (use_stmt, dest_idx) != result)
1014 /* If the loop above iterated through all the PHI nodes
1015 in BB, then we can merge the PHIs from BB into DEST. */
1016 if (gsi_end_p (gsi))
1021 /* Now let's drain WORKLIST. */
1022 while (current != worklist)
1025 remove_forwarder_block_with_phi (bb);
1033 gate_merge_phi (void)
1038 struct gimple_opt_pass pass_merge_phi =
1042 "mergephi", /* name */
1043 gate_merge_phi, /* gate */
1044 merge_phi_nodes, /* execute */
1047 0, /* static_pass_number */
1048 TV_TREE_MERGE_PHI, /* tv_id */
1049 PROP_cfg | PROP_ssa, /* properties_required */
1050 0, /* properties_provided */
1051 0, /* properties_destroyed */
1052 0, /* todo_flags_start */
1053 TODO_dump_func | TODO_ggc_collect /* todo_flags_finish */