1 /* CFG cleanup for trees.
2 Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
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"
28 #include "hard-reg-set.h"
29 #include "basic-block.h"
36 #include "langhooks.h"
37 #include "diagnostic.h"
38 #include "tree-flow.h"
40 #include "tree-dump.h"
41 #include "tree-pass.h"
45 #include "cfglayout.h"
47 #include "tree-ssa-propagate.h"
48 #include "tree-scalar-evolution.h"
50 /* The set of blocks in that at least one of the following changes happened:
51 -- the statement at the end of the block was changed
52 -- the block was newly created
53 -- the set of the predecessors of the block changed
54 -- the set of the successors of the block changed
55 ??? Maybe we could track these changes separately, since they determine
56 what cleanups it makes sense to try on the block. */
57 bitmap cfgcleanup_altered_bbs
;
59 /* Remove any fallthru edge from EV. Return true if an edge was removed. */
62 remove_fallthru_edge (VEC(edge
,gc
) *ev
)
67 FOR_EACH_EDGE (e
, ei
, ev
)
68 if ((e
->flags
& EDGE_FALLTHRU
) != 0)
70 remove_edge_and_dominated_blocks (e
);
77 /* Disconnect an unreachable block in the control expression starting
81 cleanup_control_expr_graph (basic_block bb
, gimple_stmt_iterator gsi
)
85 gimple stmt
= gsi_stmt (gsi
);
88 if (!single_succ_p (bb
))
95 fold_defer_overflow_warnings ();
96 loc
= gimple_location (stmt
);
97 switch (gimple_code (stmt
))
101 tree lhs
= gimple_cond_lhs (stmt
);
102 tree rhs
= gimple_cond_rhs (stmt
);
103 /* For conditions try harder and lookup single-argument
104 PHI nodes. Only do so from the same basic-block though
105 as other basic-blocks may be dead already. */
106 if (TREE_CODE (lhs
) == SSA_NAME
)
108 gimple def_stmt
= SSA_NAME_DEF_STMT (lhs
);
109 if (gimple_code (def_stmt
) == GIMPLE_PHI
110 && gimple_phi_num_args (def_stmt
) == 1
111 && gimple_bb (def_stmt
) == gimple_bb (stmt
))
112 lhs
= PHI_ARG_DEF (def_stmt
, 0);
114 if (TREE_CODE (rhs
) == SSA_NAME
)
116 gimple def_stmt
= SSA_NAME_DEF_STMT (rhs
);
117 if (gimple_code (def_stmt
) == GIMPLE_PHI
118 && gimple_phi_num_args (def_stmt
) == 1
119 && gimple_bb (def_stmt
) == gimple_bb (stmt
))
120 rhs
= PHI_ARG_DEF (def_stmt
, 0);
122 val
= fold_binary_loc (loc
, gimple_cond_code (stmt
),
123 boolean_type_node
, lhs
, rhs
);
128 val
= gimple_switch_index (stmt
);
134 taken_edge
= find_taken_edge (bb
, val
);
137 fold_undefer_and_ignore_overflow_warnings ();
141 /* Remove all the edges except the one that is always executed. */
143 for (ei
= ei_start (bb
->succs
); (e
= ei_safe_edge (ei
)); )
149 fold_undefer_overflow_warnings
150 (true, stmt
, WARN_STRICT_OVERFLOW_CONDITIONAL
);
154 taken_edge
->probability
+= e
->probability
;
155 taken_edge
->count
+= e
->count
;
156 remove_edge_and_dominated_blocks (e
);
163 fold_undefer_and_ignore_overflow_warnings ();
164 if (taken_edge
->probability
> REG_BR_PROB_BASE
)
165 taken_edge
->probability
= REG_BR_PROB_BASE
;
168 taken_edge
= single_succ_edge (bb
);
170 bitmap_set_bit (cfgcleanup_altered_bbs
, bb
->index
);
171 gsi_remove (&gsi
, true);
172 taken_edge
->flags
= EDGE_FALLTHRU
;
177 /* Try to remove superfluous control structures in basic block BB. Returns
178 true if anything changes. */
181 cleanup_control_flow_bb (basic_block bb
)
183 gimple_stmt_iterator gsi
;
187 /* If the last statement of the block could throw and now cannot,
188 we need to prune cfg. */
189 retval
|= gimple_purge_dead_eh_edges (bb
);
191 gsi
= gsi_last_bb (bb
);
195 stmt
= gsi_stmt (gsi
);
197 if (gimple_code (stmt
) == GIMPLE_COND
198 || gimple_code (stmt
) == GIMPLE_SWITCH
)
199 retval
|= cleanup_control_expr_graph (bb
, gsi
);
200 else if (gimple_code (stmt
) == GIMPLE_GOTO
201 && TREE_CODE (gimple_goto_dest (stmt
)) == ADDR_EXPR
202 && (TREE_CODE (TREE_OPERAND (gimple_goto_dest (stmt
), 0))
205 /* If we had a computed goto which has a compile-time determinable
206 destination, then we can eliminate the goto. */
210 basic_block target_block
;
212 /* First look at all the outgoing edges. Delete any outgoing
213 edges which do not go to the right block. For the one
214 edge which goes to the right block, fix up its flags. */
215 label
= TREE_OPERAND (gimple_goto_dest (stmt
), 0);
216 target_block
= label_to_block (label
);
217 for (ei
= ei_start (bb
->succs
); (e
= ei_safe_edge (ei
)); )
219 if (e
->dest
!= target_block
)
220 remove_edge_and_dominated_blocks (e
);
223 /* Turn off the EDGE_ABNORMAL flag. */
224 e
->flags
&= ~EDGE_ABNORMAL
;
226 /* And set EDGE_FALLTHRU. */
227 e
->flags
|= EDGE_FALLTHRU
;
232 bitmap_set_bit (cfgcleanup_altered_bbs
, bb
->index
);
233 bitmap_set_bit (cfgcleanup_altered_bbs
, target_block
->index
);
235 /* Remove the GOTO_EXPR as it is not needed. The CFG has all the
236 relevant information we need. */
237 gsi_remove (&gsi
, true);
241 /* Check for indirect calls that have been turned into
243 else if (is_gimple_call (stmt
)
244 && gimple_call_noreturn_p (stmt
)
245 && remove_fallthru_edge (bb
->succs
))
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.
255 As a precondition, we require that BB be not equal to
259 tree_forwarder_block_p (basic_block bb
, bool phi_wanted
)
261 gimple_stmt_iterator gsi
;
263 /* BB must have a single outgoing edge. */
264 if (single_succ_p (bb
) != 1
265 /* If PHI_WANTED is false, BB must not have any PHI nodes.
266 Otherwise, BB must have PHI nodes. */
267 || gimple_seq_empty_p (phi_nodes (bb
)) == phi_wanted
268 /* BB may not be a predecessor of EXIT_BLOCK_PTR. */
269 || single_succ (bb
) == EXIT_BLOCK_PTR
270 /* Nor should this be an infinite loop. */
271 || single_succ (bb
) == bb
272 /* BB may not have an abnormal outgoing edge. */
273 || (single_succ_edge (bb
)->flags
& EDGE_ABNORMAL
))
277 gcc_assert (bb
!= ENTRY_BLOCK_PTR
);
280 /* There should not be an edge coming from entry, or an EH edge. */
285 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
286 if (e
->src
== ENTRY_BLOCK_PTR
|| (e
->flags
& EDGE_EH
))
290 /* Now walk through the statements backward. We can ignore labels,
291 anything else means this is not a forwarder block. */
292 for (gsi
= gsi_last_bb (bb
); !gsi_end_p (gsi
); gsi_prev (&gsi
))
294 gimple stmt
= gsi_stmt (gsi
);
296 switch (gimple_code (stmt
))
299 if (DECL_NONLOCAL (gimple_label_label (stmt
)))
303 /* ??? For now, hope there's a corresponding debug
304 assignment at the destination. */
316 /* Protect loop latches, headers and preheaders. */
317 if (bb
->loop_father
->header
== bb
)
319 dest
= EDGE_SUCC (bb
, 0)->dest
;
321 if (dest
->loop_father
->header
== dest
)
327 /* Return true if BB has at least one abnormal incoming edge. */
330 has_abnormal_incoming_edge_p (basic_block bb
)
335 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
336 if (e
->flags
& EDGE_ABNORMAL
)
342 /* If all the PHI nodes in DEST have alternatives for E1 and E2 and
343 those alternatives are equal in each of the PHI nodes, then return
344 true, else return false. */
347 phi_alternatives_equal (basic_block dest
, edge e1
, edge e2
)
349 int n1
= e1
->dest_idx
;
350 int n2
= e2
->dest_idx
;
351 gimple_stmt_iterator gsi
;
353 for (gsi
= gsi_start_phis (dest
); !gsi_end_p (gsi
); gsi_next (&gsi
))
355 gimple phi
= gsi_stmt (gsi
);
356 tree val1
= gimple_phi_arg_def (phi
, n1
);
357 tree val2
= gimple_phi_arg_def (phi
, n2
);
359 gcc_assert (val1
!= NULL_TREE
);
360 gcc_assert (val2
!= NULL_TREE
);
362 if (!operand_equal_for_phi_arg_p (val1
, val2
))
369 /* Removes forwarder block BB. Returns false if this failed. */
372 remove_forwarder_block (basic_block bb
)
374 edge succ
= single_succ_edge (bb
), e
, s
;
375 basic_block dest
= succ
->dest
;
378 gimple_stmt_iterator gsi
, gsi_to
;
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 (has_abnormal_incoming_edge_p (bb
)
407 && (has_abnormal_incoming_edge_p (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 /* Redirect the edges. */
428 for (ei
= ei_start (bb
->preds
); (e
= ei_safe_edge (ei
)); )
430 bitmap_set_bit (cfgcleanup_altered_bbs
, e
->src
->index
);
432 if (e
->flags
& EDGE_ABNORMAL
)
434 /* If there is an abnormal edge, redirect it anyway, and
435 move the labels to the new block to make it legal. */
436 s
= redirect_edge_succ_nodup (e
, dest
);
439 s
= redirect_edge_and_branch (e
, dest
);
443 /* Create arguments for the phi nodes, since the edge was not
445 for (gsi
= gsi_start_phis (dest
);
449 gimple phi
= gsi_stmt (gsi
);
450 source_location l
= gimple_phi_arg_location_from_edge (phi
, succ
);
451 add_phi_arg (phi
, gimple_phi_arg_def (phi
, succ
->dest_idx
), s
, l
);
456 /* Move nonlocal labels and computed goto targets as well as user
457 defined labels and labels with an EH landing pad number to the
458 new block, so that the redirection of the abnormal edges works,
459 jump targets end up in a sane place and debug information for
460 labels is retained. */
461 gsi_to
= gsi_start_bb (dest
);
462 for (gsi
= gsi_start_bb (bb
); !gsi_end_p (gsi
); )
465 label
= gsi_stmt (gsi
);
466 if (is_gimple_debug (label
))
468 decl
= gimple_label_label (label
);
469 if (EH_LANDING_PAD_NR (decl
) != 0
470 || DECL_NONLOCAL (decl
)
471 || FORCED_LABEL (decl
)
472 || !DECL_ARTIFICIAL (decl
))
474 gsi_remove (&gsi
, false);
475 gsi_insert_before (&gsi_to
, label
, GSI_SAME_STMT
);
481 /* Move debug statements if the destination has just a single
483 if (single_pred_p (dest
))
485 gsi_to
= gsi_after_labels (dest
);
486 for (gsi
= gsi_after_labels (bb
); !gsi_end_p (gsi
); )
488 if (!is_gimple_debug (gsi_stmt (gsi
)))
490 gsi_remove (&gsi
, false);
491 gsi_insert_before (&gsi_to
, label
, GSI_SAME_STMT
);
495 bitmap_set_bit (cfgcleanup_altered_bbs
, dest
->index
);
497 /* Update the dominators. */
498 if (dom_info_available_p (CDI_DOMINATORS
))
500 basic_block dom
, dombb
, domdest
;
502 dombb
= get_immediate_dominator (CDI_DOMINATORS
, bb
);
503 domdest
= get_immediate_dominator (CDI_DOMINATORS
, dest
);
506 /* Shortcut to avoid calling (relatively expensive)
507 nearest_common_dominator unless necessary. */
511 dom
= nearest_common_dominator (CDI_DOMINATORS
, domdest
, dombb
);
513 set_immediate_dominator (CDI_DOMINATORS
, dest
, dom
);
516 /* And kill the forwarder block. */
517 delete_basic_block (bb
);
522 /* Split basic blocks on calls in the middle of a basic block that are now
523 known not to return, and remove the unreachable code. */
526 split_bbs_on_noreturn_calls (void)
528 bool changed
= false;
532 /* Detect cases where a mid-block call is now known not to return. */
534 while (VEC_length (gimple
, MODIFIED_NORETURN_CALLS (cfun
)))
536 stmt
= VEC_pop (gimple
, MODIFIED_NORETURN_CALLS (cfun
));
537 bb
= gimple_bb (stmt
);
538 /* BB might be deleted at this point, so verify first
539 BB is present in the cfg. */
541 || bb
->index
< NUM_FIXED_BLOCKS
542 || bb
->index
>= n_basic_blocks
543 || BASIC_BLOCK (bb
->index
) != bb
544 || last_stmt (bb
) == stmt
545 || !gimple_call_noreturn_p (stmt
))
549 split_block (bb
, stmt
);
550 remove_fallthru_edge (bb
->succs
);
556 /* If GIMPLE_OMP_RETURN in basic block BB is unreachable, remove it. */
559 cleanup_omp_return (basic_block bb
)
561 gimple stmt
= last_stmt (bb
);
562 basic_block control_bb
;
565 || gimple_code (stmt
) != GIMPLE_OMP_RETURN
566 || !single_pred_p (bb
))
569 control_bb
= single_pred (bb
);
570 stmt
= last_stmt (control_bb
);
572 if (stmt
== NULL
|| gimple_code (stmt
) != GIMPLE_OMP_SECTIONS_SWITCH
)
575 /* The block with the control statement normally has two entry edges -- one
576 from entry, one from continue. If continue is removed, return is
577 unreachable, so we remove it here as well. */
578 if (EDGE_COUNT (control_bb
->preds
) == 2)
581 gcc_assert (EDGE_COUNT (control_bb
->preds
) == 1);
582 remove_edge_and_dominated_blocks (single_pred_edge (bb
));
586 /* Tries to cleanup cfg in basic block BB. Returns true if anything
590 cleanup_tree_cfg_bb (basic_block bb
)
594 if (cleanup_omp_return (bb
))
597 retval
= cleanup_control_flow_bb (bb
);
599 /* Forwarder blocks can carry line number information which is
600 useful when debugging, so we only clean them up when
603 && tree_forwarder_block_p (bb
, false)
604 && remove_forwarder_block (bb
))
607 /* Merging the blocks may create new opportunities for folding
608 conditional branches (due to the elimination of single-valued PHI
610 if (single_succ_p (bb
)
611 && can_merge_blocks_p (bb
, single_succ (bb
)))
613 merge_blocks (bb
, single_succ (bb
));
620 /* Iterate the cfg cleanups, while anything changes. */
623 cleanup_tree_cfg_1 (void)
629 retval
|= split_bbs_on_noreturn_calls ();
631 /* Prepare the worklists of altered blocks. */
632 cfgcleanup_altered_bbs
= BITMAP_ALLOC (NULL
);
634 /* During forwarder block cleanup, we may redirect edges out of
635 SWITCH_EXPRs, which can get expensive. So we want to enable
636 recording of edge to CASE_LABEL_EXPR. */
637 start_recording_case_labels ();
639 /* Start by iterating over all basic blocks. We cannot use FOR_EACH_BB,
640 since the basic blocks may get removed. */
641 n
= last_basic_block
;
642 for (i
= NUM_FIXED_BLOCKS
; i
< n
; i
++)
644 bb
= BASIC_BLOCK (i
);
646 retval
|= cleanup_tree_cfg_bb (bb
);
649 /* Now process the altered blocks, as long as any are available. */
650 while (!bitmap_empty_p (cfgcleanup_altered_bbs
))
652 i
= bitmap_first_set_bit (cfgcleanup_altered_bbs
);
653 bitmap_clear_bit (cfgcleanup_altered_bbs
, i
);
654 if (i
< NUM_FIXED_BLOCKS
)
657 bb
= BASIC_BLOCK (i
);
661 retval
|= cleanup_tree_cfg_bb (bb
);
663 /* Rerun split_bbs_on_noreturn_calls, in case we have altered any noreturn
665 retval
|= split_bbs_on_noreturn_calls ();
668 end_recording_case_labels ();
669 BITMAP_FREE (cfgcleanup_altered_bbs
);
674 /* Remove unreachable blocks and other miscellaneous clean up work.
675 Return true if the flowgraph was modified, false otherwise. */
678 cleanup_tree_cfg_noloop (void)
682 timevar_push (TV_TREE_CLEANUP_CFG
);
684 /* Iterate until there are no more cleanups left to do. If any
685 iteration changed the flowgraph, set CHANGED to true.
687 If dominance information is available, there cannot be any unreachable
689 if (!dom_info_available_p (CDI_DOMINATORS
))
691 changed
= delete_unreachable_blocks ();
692 calculate_dominance_info (CDI_DOMINATORS
);
696 #ifdef ENABLE_CHECKING
697 verify_dominators (CDI_DOMINATORS
);
702 changed
|= cleanup_tree_cfg_1 ();
704 gcc_assert (dom_info_available_p (CDI_DOMINATORS
));
707 #ifdef ENABLE_CHECKING
711 timevar_pop (TV_TREE_CLEANUP_CFG
);
713 if (changed
&& current_loops
)
714 loops_state_set (LOOPS_NEED_FIXUP
);
719 /* Repairs loop structures. */
722 repair_loop_structures (void)
724 bitmap changed_bbs
= BITMAP_ALLOC (NULL
);
725 fix_loop_structure (changed_bbs
);
727 /* This usually does nothing. But sometimes parts of cfg that originally
728 were inside a loop get out of it due to edge removal (since they
729 become unreachable by back edges from latch). */
730 if (loops_state_satisfies_p (LOOP_CLOSED_SSA
))
731 rewrite_into_loop_closed_ssa (changed_bbs
, TODO_update_ssa
);
733 BITMAP_FREE (changed_bbs
);
735 #ifdef ENABLE_CHECKING
736 verify_loop_structure ();
740 loops_state_clear (LOOPS_NEED_FIXUP
);
743 /* Cleanup cfg and repair loop structures. */
746 cleanup_tree_cfg (void)
748 bool changed
= cleanup_tree_cfg_noloop ();
750 if (current_loops
!= NULL
751 && loops_state_satisfies_p (LOOPS_NEED_FIXUP
))
752 repair_loop_structures ();
757 /* Merge the PHI nodes at BB into those at BB's sole successor. */
760 remove_forwarder_block_with_phi (basic_block bb
)
762 edge succ
= single_succ_edge (bb
);
763 basic_block dest
= succ
->dest
;
765 basic_block dombb
, domdest
, dom
;
767 /* We check for infinite loops already in tree_forwarder_block_p.
768 However it may happen that the infinite loop is created
769 afterwards due to removal of forwarders. */
773 /* If the destination block consists of a nonlocal label, do not
775 label
= first_stmt (dest
);
777 && gimple_code (label
) == GIMPLE_LABEL
778 && DECL_NONLOCAL (gimple_label_label (label
)))
781 /* Redirect each incoming edge to BB to DEST. */
782 while (EDGE_COUNT (bb
->preds
) > 0)
784 edge e
= EDGE_PRED (bb
, 0), s
;
785 gimple_stmt_iterator gsi
;
787 s
= find_edge (e
->src
, dest
);
790 /* We already have an edge S from E->src to DEST. If S and
791 E->dest's sole successor edge have the same PHI arguments
792 at DEST, redirect S to DEST. */
793 if (phi_alternatives_equal (dest
, s
, succ
))
795 e
= redirect_edge_and_branch (e
, dest
);
796 redirect_edge_var_map_clear (e
);
800 /* PHI arguments are different. Create a forwarder block by
801 splitting E so that we can merge PHI arguments on E to
803 e
= single_succ_edge (split_edge (e
));
806 s
= redirect_edge_and_branch (e
, dest
);
808 /* redirect_edge_and_branch must not create a new edge. */
811 /* Add to the PHI nodes at DEST each PHI argument removed at the
813 for (gsi
= gsi_start_phis (dest
);
817 gimple phi
= gsi_stmt (gsi
);
818 tree def
= gimple_phi_arg_def (phi
, succ
->dest_idx
);
819 source_location locus
= gimple_phi_arg_location_from_edge (phi
, succ
);
821 if (TREE_CODE (def
) == SSA_NAME
)
823 edge_var_map_vector head
;
827 /* If DEF is one of the results of PHI nodes removed during
828 redirection, replace it with the PHI argument that used
830 head
= redirect_edge_var_map_vector (e
);
831 for (i
= 0; VEC_iterate (edge_var_map
, head
, i
, vm
); ++i
)
833 tree old_arg
= redirect_edge_var_map_result (vm
);
834 tree new_arg
= redirect_edge_var_map_def (vm
);
839 locus
= redirect_edge_var_map_location (vm
);
845 add_phi_arg (phi
, def
, s
, locus
);
848 redirect_edge_var_map_clear (e
);
851 /* Update the dominators. */
852 dombb
= get_immediate_dominator (CDI_DOMINATORS
, bb
);
853 domdest
= get_immediate_dominator (CDI_DOMINATORS
, dest
);
856 /* Shortcut to avoid calling (relatively expensive)
857 nearest_common_dominator unless necessary. */
861 dom
= nearest_common_dominator (CDI_DOMINATORS
, domdest
, dombb
);
863 set_immediate_dominator (CDI_DOMINATORS
, dest
, dom
);
865 /* Remove BB since all of BB's incoming edges have been redirected
867 delete_basic_block (bb
);
870 /* This pass merges PHI nodes if one feeds into another. For example,
871 suppose we have the following:
878 # tem_6 = PHI <tem_17(8), tem_23(7)>;
881 # tem_3 = PHI <tem_6(9), tem_2(5)>;
884 Then we merge the first PHI node into the second one like so:
891 # tem_3 = PHI <tem_23(7), tem_2(5), tem_17(8)>;
896 merge_phi_nodes (void)
898 basic_block
*worklist
= XNEWVEC (basic_block
, n_basic_blocks
);
899 basic_block
*current
= worklist
;
902 calculate_dominance_info (CDI_DOMINATORS
);
904 /* Find all PHI nodes that we may be able to merge. */
909 /* Look for a forwarder block with PHI nodes. */
910 if (!tree_forwarder_block_p (bb
, true))
913 dest
= single_succ (bb
);
915 /* We have to feed into another basic block with PHI
917 if (gimple_seq_empty_p (phi_nodes (dest
))
918 /* We don't want to deal with a basic block with
920 || has_abnormal_incoming_edge_p (bb
))
923 if (!dominated_by_p (CDI_DOMINATORS
, dest
, bb
))
925 /* If BB does not dominate DEST, then the PHI nodes at
926 DEST must be the only users of the results of the PHI
932 gimple_stmt_iterator gsi
;
933 unsigned int dest_idx
= single_succ_edge (bb
)->dest_idx
;
935 /* BB dominates DEST. There may be many users of the PHI
936 nodes in BB. However, there is still a trivial case we
937 can handle. If the result of every PHI in BB is used
938 only by a PHI in DEST, then we can trivially merge the
939 PHI nodes from BB into DEST. */
940 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);
943 gimple phi
= gsi_stmt (gsi
);
944 tree result
= gimple_phi_result (phi
);
945 use_operand_p imm_use
;
948 /* If the PHI's result is never used, then we can just
950 if (has_zero_uses (result
))
953 /* Get the single use of the result of this PHI node. */
954 if (!single_imm_use (result
, &imm_use
, &use_stmt
)
955 || gimple_code (use_stmt
) != GIMPLE_PHI
956 || gimple_bb (use_stmt
) != dest
957 || gimple_phi_arg_def (use_stmt
, dest_idx
) != result
)
961 /* If the loop above iterated through all the PHI nodes
962 in BB, then we can merge the PHIs from BB into DEST. */
968 /* Now let's drain WORKLIST. */
969 while (current
!= worklist
)
972 remove_forwarder_block_with_phi (bb
);
980 gate_merge_phi (void)
985 struct gimple_opt_pass pass_merge_phi
=
989 "mergephi", /* name */
990 gate_merge_phi
, /* gate */
991 merge_phi_nodes
, /* execute */
994 0, /* static_pass_number */
995 TV_TREE_MERGE_PHI
, /* tv_id */
996 PROP_cfg
| PROP_ssa
, /* properties_required */
997 0, /* properties_provided */
998 0, /* properties_destroyed */
999 0, /* todo_flags_start */
1000 TODO_dump_func
| TODO_ggc_collect
/* todo_flags_finish */