1 /* CFG cleanup for trees.
2 Copyright (C) 2001-2013 Free Software Foundation, Inc.
4 This file is part of GCC.
6 GCC is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 3, or (at your option)
11 GCC is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING3. If not see
18 <http://www.gnu.org/licenses/>. */
22 #include "coretypes.h"
26 #include "basic-block.h"
27 #include "diagnostic-core.h"
31 #include "langhooks.h"
32 #include "tree-flow.h"
33 #include "tree-pass.h"
37 #include "tree-ssa-propagate.h"
38 #include "tree-scalar-evolution.h"
40 /* The set of blocks in that at least one of the following changes happened:
41 -- the statement at the end of the block was changed
42 -- the block was newly created
43 -- the set of the predecessors of the block changed
44 -- the set of the successors of the block changed
45 ??? Maybe we could track these changes separately, since they determine
46 what cleanups it makes sense to try on the block. */
47 bitmap cfgcleanup_altered_bbs
;
49 /* Remove any fallthru edge from EV. Return true if an edge was removed. */
52 remove_fallthru_edge (vec
<edge
, va_gc
> *ev
)
57 FOR_EACH_EDGE (e
, ei
, ev
)
58 if ((e
->flags
& EDGE_FALLTHRU
) != 0)
60 remove_edge_and_dominated_blocks (e
);
67 /* Disconnect an unreachable block in the control expression starting
71 cleanup_control_expr_graph (basic_block bb
, gimple_stmt_iterator gsi
)
75 gimple stmt
= gsi_stmt (gsi
);
78 if (!single_succ_p (bb
))
85 fold_defer_overflow_warnings ();
86 loc
= gimple_location (stmt
);
87 switch (gimple_code (stmt
))
90 val
= fold_binary_loc (loc
, gimple_cond_code (stmt
),
92 gimple_cond_lhs (stmt
),
93 gimple_cond_rhs (stmt
));
97 val
= gimple_switch_index (stmt
);
103 taken_edge
= find_taken_edge (bb
, val
);
106 fold_undefer_and_ignore_overflow_warnings ();
110 /* Remove all the edges except the one that is always executed. */
112 for (ei
= ei_start (bb
->succs
); (e
= ei_safe_edge (ei
)); )
118 fold_undefer_overflow_warnings
119 (true, stmt
, WARN_STRICT_OVERFLOW_CONDITIONAL
);
123 taken_edge
->probability
+= e
->probability
;
124 taken_edge
->count
+= e
->count
;
125 remove_edge_and_dominated_blocks (e
);
132 fold_undefer_and_ignore_overflow_warnings ();
133 if (taken_edge
->probability
> REG_BR_PROB_BASE
)
134 taken_edge
->probability
= REG_BR_PROB_BASE
;
137 taken_edge
= single_succ_edge (bb
);
139 bitmap_set_bit (cfgcleanup_altered_bbs
, bb
->index
);
140 gsi_remove (&gsi
, true);
141 taken_edge
->flags
= EDGE_FALLTHRU
;
146 /* Try to remove superfluous control structures in basic block BB. Returns
147 true if anything changes. */
150 cleanup_control_flow_bb (basic_block bb
)
152 gimple_stmt_iterator gsi
;
156 /* If the last statement of the block could throw and now cannot,
157 we need to prune cfg. */
158 retval
|= gimple_purge_dead_eh_edges (bb
);
160 gsi
= gsi_last_bb (bb
);
164 stmt
= gsi_stmt (gsi
);
166 if (gimple_code (stmt
) == GIMPLE_COND
167 || gimple_code (stmt
) == GIMPLE_SWITCH
)
168 retval
|= cleanup_control_expr_graph (bb
, gsi
);
169 else if (gimple_code (stmt
) == GIMPLE_GOTO
170 && TREE_CODE (gimple_goto_dest (stmt
)) == ADDR_EXPR
171 && (TREE_CODE (TREE_OPERAND (gimple_goto_dest (stmt
), 0))
174 /* If we had a computed goto which has a compile-time determinable
175 destination, then we can eliminate the goto. */
179 basic_block target_block
;
181 /* First look at all the outgoing edges. Delete any outgoing
182 edges which do not go to the right block. For the one
183 edge which goes to the right block, fix up its flags. */
184 label
= TREE_OPERAND (gimple_goto_dest (stmt
), 0);
185 target_block
= label_to_block (label
);
186 for (ei
= ei_start (bb
->succs
); (e
= ei_safe_edge (ei
)); )
188 if (e
->dest
!= target_block
)
189 remove_edge_and_dominated_blocks (e
);
192 /* Turn off the EDGE_ABNORMAL flag. */
193 e
->flags
&= ~EDGE_ABNORMAL
;
195 /* And set EDGE_FALLTHRU. */
196 e
->flags
|= EDGE_FALLTHRU
;
201 bitmap_set_bit (cfgcleanup_altered_bbs
, bb
->index
);
202 bitmap_set_bit (cfgcleanup_altered_bbs
, target_block
->index
);
204 /* Remove the GOTO_EXPR as it is not needed. The CFG has all the
205 relevant information we need. */
206 gsi_remove (&gsi
, true);
210 /* Check for indirect calls that have been turned into
212 else if (is_gimple_call (stmt
)
213 && gimple_call_noreturn_p (stmt
)
214 && remove_fallthru_edge (bb
->succs
))
220 /* Return true if basic block BB does nothing except pass control
221 flow to another block and that we can safely insert a label at
222 the start of the successor block.
224 As a precondition, we require that BB be not equal to
228 tree_forwarder_block_p (basic_block bb
, bool phi_wanted
)
230 gimple_stmt_iterator gsi
;
233 /* BB must have a single outgoing edge. */
234 if (single_succ_p (bb
) != 1
235 /* If PHI_WANTED is false, BB must not have any PHI nodes.
236 Otherwise, BB must have PHI nodes. */
237 || gimple_seq_empty_p (phi_nodes (bb
)) == phi_wanted
238 /* BB may not be a predecessor of EXIT_BLOCK_PTR. */
239 || single_succ (bb
) == EXIT_BLOCK_PTR
240 /* Nor should this be an infinite loop. */
241 || single_succ (bb
) == bb
242 /* BB may not have an abnormal outgoing edge. */
243 || (single_succ_edge (bb
)->flags
& EDGE_ABNORMAL
))
246 gcc_checking_assert (bb
!= ENTRY_BLOCK_PTR
);
248 locus
= single_succ_edge (bb
)->goto_locus
;
250 /* There should not be an edge coming from entry, or an EH edge. */
255 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
256 if (e
->src
== ENTRY_BLOCK_PTR
|| (e
->flags
& EDGE_EH
))
258 /* If goto_locus of any of the edges differs, prevent removing
259 the forwarder block for -O0. */
260 else if (optimize
== 0 && e
->goto_locus
!= locus
)
264 /* Now walk through the statements backward. We can ignore labels,
265 anything else means this is not a forwarder block. */
266 for (gsi
= gsi_last_bb (bb
); !gsi_end_p (gsi
); gsi_prev (&gsi
))
268 gimple stmt
= gsi_stmt (gsi
);
270 switch (gimple_code (stmt
))
273 if (DECL_NONLOCAL (gimple_label_label (stmt
)))
275 if (optimize
== 0 && gimple_location (stmt
) != locus
)
279 /* ??? For now, hope there's a corresponding debug
280 assignment at the destination. */
292 /* Protect loop latches, headers and preheaders. */
293 if (bb
->loop_father
->header
== bb
)
295 dest
= EDGE_SUCC (bb
, 0)->dest
;
297 if (dest
->loop_father
->header
== dest
)
303 /* If all the PHI nodes in DEST have alternatives for E1 and E2 and
304 those alternatives are equal in each of the PHI nodes, then return
305 true, else return false. */
308 phi_alternatives_equal (basic_block dest
, edge e1
, edge e2
)
310 int n1
= e1
->dest_idx
;
311 int n2
= e2
->dest_idx
;
312 gimple_stmt_iterator gsi
;
314 for (gsi
= gsi_start_phis (dest
); !gsi_end_p (gsi
); gsi_next (&gsi
))
316 gimple phi
= gsi_stmt (gsi
);
317 tree val1
= gimple_phi_arg_def (phi
, n1
);
318 tree val2
= gimple_phi_arg_def (phi
, n2
);
320 gcc_assert (val1
!= NULL_TREE
);
321 gcc_assert (val2
!= NULL_TREE
);
323 if (!operand_equal_for_phi_arg_p (val1
, val2
))
330 /* Removes forwarder block BB. Returns false if this failed. */
333 remove_forwarder_block (basic_block bb
)
335 edge succ
= single_succ_edge (bb
), e
, s
;
336 basic_block dest
= succ
->dest
;
339 gimple_stmt_iterator gsi
, gsi_to
;
340 bool can_move_debug_stmts
;
342 /* We check for infinite loops already in tree_forwarder_block_p.
343 However it may happen that the infinite loop is created
344 afterwards due to removal of forwarders. */
348 /* If the destination block consists of a nonlocal label or is a
349 EH landing pad, do not merge it. */
350 label
= first_stmt (dest
);
352 && gimple_code (label
) == GIMPLE_LABEL
353 && (DECL_NONLOCAL (gimple_label_label (label
))
354 || EH_LANDING_PAD_NR (gimple_label_label (label
)) != 0))
357 /* If there is an abnormal edge to basic block BB, but not into
358 dest, problems might occur during removal of the phi node at out
359 of ssa due to overlapping live ranges of registers.
361 If there is an abnormal edge in DEST, the problems would occur
362 anyway since cleanup_dead_labels would then merge the labels for
363 two different eh regions, and rest of exception handling code
366 So if there is an abnormal edge to BB, proceed only if there is
367 no abnormal edge to DEST and there are no phi nodes in DEST. */
368 if (bb_has_abnormal_pred (bb
)
369 && (bb_has_abnormal_pred (dest
)
370 || !gimple_seq_empty_p (phi_nodes (dest
))))
373 /* If there are phi nodes in DEST, and some of the blocks that are
374 predecessors of BB are also predecessors of DEST, check that the
375 phi node arguments match. */
376 if (!gimple_seq_empty_p (phi_nodes (dest
)))
378 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
380 s
= find_edge (e
->src
, dest
);
384 if (!phi_alternatives_equal (dest
, succ
, s
))
389 can_move_debug_stmts
= MAY_HAVE_DEBUG_STMTS
&& single_pred_p (dest
);
391 /* Redirect the edges. */
392 for (ei
= ei_start (bb
->preds
); (e
= ei_safe_edge (ei
)); )
394 bitmap_set_bit (cfgcleanup_altered_bbs
, e
->src
->index
);
396 if (e
->flags
& EDGE_ABNORMAL
)
398 /* If there is an abnormal edge, redirect it anyway, and
399 move the labels to the new block to make it legal. */
400 s
= redirect_edge_succ_nodup (e
, dest
);
403 s
= redirect_edge_and_branch (e
, dest
);
407 /* Create arguments for the phi nodes, since the edge was not
409 for (gsi
= gsi_start_phis (dest
);
413 gimple phi
= gsi_stmt (gsi
);
414 source_location l
= gimple_phi_arg_location_from_edge (phi
, succ
);
415 add_phi_arg (phi
, gimple_phi_arg_def (phi
, succ
->dest_idx
), s
, l
);
420 /* Move nonlocal labels and computed goto targets as well as user
421 defined labels and labels with an EH landing pad number to the
422 new block, so that the redirection of the abnormal edges works,
423 jump targets end up in a sane place and debug information for
424 labels is retained. */
425 gsi_to
= gsi_start_bb (dest
);
426 for (gsi
= gsi_start_bb (bb
); !gsi_end_p (gsi
); )
429 label
= gsi_stmt (gsi
);
430 if (is_gimple_debug (label
))
432 decl
= gimple_label_label (label
);
433 if (EH_LANDING_PAD_NR (decl
) != 0
434 || DECL_NONLOCAL (decl
)
435 || FORCED_LABEL (decl
)
436 || !DECL_ARTIFICIAL (decl
))
438 gsi_remove (&gsi
, false);
439 gsi_insert_before (&gsi_to
, label
, GSI_SAME_STMT
);
445 /* Move debug statements if the destination has a single predecessor. */
446 if (can_move_debug_stmts
)
448 gsi_to
= gsi_after_labels (dest
);
449 for (gsi
= gsi_after_labels (bb
); !gsi_end_p (gsi
); )
451 gimple debug
= gsi_stmt (gsi
);
452 if (!is_gimple_debug (debug
))
454 gsi_remove (&gsi
, false);
455 gsi_insert_before (&gsi_to
, debug
, GSI_SAME_STMT
);
459 bitmap_set_bit (cfgcleanup_altered_bbs
, dest
->index
);
461 /* Update the dominators. */
462 if (dom_info_available_p (CDI_DOMINATORS
))
464 basic_block dom
, dombb
, domdest
;
466 dombb
= get_immediate_dominator (CDI_DOMINATORS
, bb
);
467 domdest
= get_immediate_dominator (CDI_DOMINATORS
, dest
);
470 /* Shortcut to avoid calling (relatively expensive)
471 nearest_common_dominator unless necessary. */
475 dom
= nearest_common_dominator (CDI_DOMINATORS
, domdest
, dombb
);
477 set_immediate_dominator (CDI_DOMINATORS
, dest
, dom
);
480 /* And kill the forwarder block. */
481 delete_basic_block (bb
);
486 /* STMT is a call that has been discovered noreturn. Fixup the CFG
487 and remove LHS. Return true if something changed. */
490 fixup_noreturn_call (gimple stmt
)
492 basic_block bb
= gimple_bb (stmt
);
493 bool changed
= false;
495 if (gimple_call_builtin_p (stmt
, BUILT_IN_RETURN
))
498 /* First split basic block if stmt is not last. */
499 if (stmt
!= gsi_stmt (gsi_last_bb (bb
)))
500 split_block (bb
, stmt
);
502 changed
|= remove_fallthru_edge (bb
->succs
);
504 /* If there is LHS, remove it. */
505 if (gimple_call_lhs (stmt
))
507 tree op
= gimple_call_lhs (stmt
);
508 gimple_call_set_lhs (stmt
, NULL_TREE
);
510 /* We need to remove SSA name to avoid checking errors.
511 All uses are dominated by the noreturn and thus will
512 be removed afterwards.
513 We proactively remove affected non-PHI statements to avoid
514 fixup_cfg from trying to update them and crashing. */
515 if (TREE_CODE (op
) == SSA_NAME
)
518 imm_use_iterator iter
;
521 unsigned int bb_index
;
523 bitmap blocks
= BITMAP_ALLOC (NULL
);
525 FOR_EACH_IMM_USE_STMT (use_stmt
, iter
, op
)
527 if (gimple_code (use_stmt
) != GIMPLE_PHI
)
528 bitmap_set_bit (blocks
, gimple_bb (use_stmt
)->index
);
530 FOR_EACH_IMM_USE_ON_STMT (use_p
, iter
)
531 SET_USE (use_p
, error_mark_node
);
533 EXECUTE_IF_SET_IN_BITMAP (blocks
, 0, bb_index
, bi
)
534 delete_basic_block (BASIC_BLOCK (bb_index
));
535 BITMAP_FREE (blocks
);
536 release_ssa_name (op
);
541 /* Similarly remove VDEF if there is any. */
542 else if (gimple_vdef (stmt
))
548 /* Split basic blocks on calls in the middle of a basic block that are now
549 known not to return, and remove the unreachable code. */
552 split_bbs_on_noreturn_calls (void)
554 bool changed
= false;
558 /* Detect cases where a mid-block call is now known not to return. */
560 while (vec_safe_length (MODIFIED_NORETURN_CALLS (cfun
)))
562 stmt
= MODIFIED_NORETURN_CALLS (cfun
)->pop ();
563 bb
= gimple_bb (stmt
);
564 /* BB might be deleted at this point, so verify first
565 BB is present in the cfg. */
567 || bb
->index
< NUM_FIXED_BLOCKS
568 || bb
->index
>= last_basic_block
569 || BASIC_BLOCK (bb
->index
) != bb
570 || !gimple_call_noreturn_p (stmt
))
573 changed
|= fixup_noreturn_call (stmt
);
579 /* Tries to cleanup cfg in basic block BB. Returns true if anything
583 cleanup_tree_cfg_bb (basic_block bb
)
585 bool retval
= cleanup_control_flow_bb (bb
);
587 if (tree_forwarder_block_p (bb
, false)
588 && remove_forwarder_block (bb
))
591 /* Merging the blocks may create new opportunities for folding
592 conditional branches (due to the elimination of single-valued PHI
594 if (single_succ_p (bb
)
595 && can_merge_blocks_p (bb
, single_succ (bb
)))
597 merge_blocks (bb
, single_succ (bb
));
604 /* Iterate the cfg cleanups, while anything changes. */
607 cleanup_tree_cfg_1 (void)
613 retval
|= split_bbs_on_noreturn_calls ();
615 /* Prepare the worklists of altered blocks. */
616 cfgcleanup_altered_bbs
= BITMAP_ALLOC (NULL
);
618 /* During forwarder block cleanup, we may redirect edges out of
619 SWITCH_EXPRs, which can get expensive. So we want to enable
620 recording of edge to CASE_LABEL_EXPR. */
621 start_recording_case_labels ();
623 /* Start by iterating over all basic blocks. We cannot use FOR_EACH_BB,
624 since the basic blocks may get removed. */
625 n
= last_basic_block
;
626 for (i
= NUM_FIXED_BLOCKS
; i
< n
; i
++)
628 bb
= BASIC_BLOCK (i
);
630 retval
|= cleanup_tree_cfg_bb (bb
);
633 /* Now process the altered blocks, as long as any are available. */
634 while (!bitmap_empty_p (cfgcleanup_altered_bbs
))
636 i
= bitmap_first_set_bit (cfgcleanup_altered_bbs
);
637 bitmap_clear_bit (cfgcleanup_altered_bbs
, i
);
638 if (i
< NUM_FIXED_BLOCKS
)
641 bb
= BASIC_BLOCK (i
);
645 retval
|= cleanup_tree_cfg_bb (bb
);
647 /* Rerun split_bbs_on_noreturn_calls, in case we have altered any noreturn
649 retval
|= split_bbs_on_noreturn_calls ();
652 end_recording_case_labels ();
653 BITMAP_FREE (cfgcleanup_altered_bbs
);
658 /* Remove unreachable blocks and other miscellaneous clean up work.
659 Return true if the flowgraph was modified, false otherwise. */
662 cleanup_tree_cfg_noloop (void)
666 timevar_push (TV_TREE_CLEANUP_CFG
);
668 /* Iterate until there are no more cleanups left to do. If any
669 iteration changed the flowgraph, set CHANGED to true.
671 If dominance information is available, there cannot be any unreachable
673 if (!dom_info_available_p (CDI_DOMINATORS
))
675 changed
= delete_unreachable_blocks ();
676 calculate_dominance_info (CDI_DOMINATORS
);
680 #ifdef ENABLE_CHECKING
681 verify_dominators (CDI_DOMINATORS
);
686 changed
|= cleanup_tree_cfg_1 ();
688 gcc_assert (dom_info_available_p (CDI_DOMINATORS
));
691 #ifdef ENABLE_CHECKING
695 timevar_pop (TV_TREE_CLEANUP_CFG
);
697 if (changed
&& current_loops
)
698 loops_state_set (LOOPS_NEED_FIXUP
);
703 /* Repairs loop structures. */
706 repair_loop_structures (void)
710 calculate_dominance_info (CDI_DOMINATORS
);
712 timevar_push (TV_REPAIR_LOOPS
);
713 changed_bbs
= BITMAP_ALLOC (NULL
);
714 fix_loop_structure (changed_bbs
);
716 /* This usually does nothing. But sometimes parts of cfg that originally
717 were inside a loop get out of it due to edge removal (since they
718 become unreachable by back edges from latch). */
719 if (loops_state_satisfies_p (LOOP_CLOSED_SSA
))
720 rewrite_into_loop_closed_ssa (changed_bbs
, TODO_update_ssa
);
722 BITMAP_FREE (changed_bbs
);
724 #ifdef ENABLE_CHECKING
725 verify_loop_structure ();
729 timevar_pop (TV_REPAIR_LOOPS
);
732 /* Cleanup cfg and repair loop structures. */
735 cleanup_tree_cfg (void)
737 bool changed
= cleanup_tree_cfg_noloop ();
739 if (current_loops
!= NULL
740 && loops_state_satisfies_p (LOOPS_NEED_FIXUP
))
741 repair_loop_structures ();
746 /* Merge the PHI nodes at BB into those at BB's sole successor. */
749 remove_forwarder_block_with_phi (basic_block bb
)
751 edge succ
= single_succ_edge (bb
);
752 basic_block dest
= succ
->dest
;
754 basic_block dombb
, domdest
, dom
;
756 /* We check for infinite loops already in tree_forwarder_block_p.
757 However it may happen that the infinite loop is created
758 afterwards due to removal of forwarders. */
762 /* If the destination block consists of a nonlocal label, do not
764 label
= first_stmt (dest
);
766 && gimple_code (label
) == GIMPLE_LABEL
767 && DECL_NONLOCAL (gimple_label_label (label
)))
770 /* Redirect each incoming edge to BB to DEST. */
771 while (EDGE_COUNT (bb
->preds
) > 0)
773 edge e
= EDGE_PRED (bb
, 0), s
;
774 gimple_stmt_iterator gsi
;
776 s
= find_edge (e
->src
, dest
);
779 /* We already have an edge S from E->src to DEST. If S and
780 E->dest's sole successor edge have the same PHI arguments
781 at DEST, redirect S to DEST. */
782 if (phi_alternatives_equal (dest
, s
, succ
))
784 e
= redirect_edge_and_branch (e
, dest
);
785 redirect_edge_var_map_clear (e
);
789 /* PHI arguments are different. Create a forwarder block by
790 splitting E so that we can merge PHI arguments on E to
792 e
= single_succ_edge (split_edge (e
));
795 s
= redirect_edge_and_branch (e
, dest
);
797 /* redirect_edge_and_branch must not create a new edge. */
800 /* Add to the PHI nodes at DEST each PHI argument removed at the
802 for (gsi
= gsi_start_phis (dest
);
806 gimple phi
= gsi_stmt (gsi
);
807 tree def
= gimple_phi_arg_def (phi
, succ
->dest_idx
);
808 source_location locus
= gimple_phi_arg_location_from_edge (phi
, succ
);
810 if (TREE_CODE (def
) == SSA_NAME
)
812 edge_var_map_vector
*head
;
816 /* If DEF is one of the results of PHI nodes removed during
817 redirection, replace it with the PHI argument that used
819 head
= redirect_edge_var_map_vector (e
);
820 FOR_EACH_VEC_ELT (*head
, i
, vm
)
822 tree old_arg
= redirect_edge_var_map_result (vm
);
823 tree new_arg
= redirect_edge_var_map_def (vm
);
828 locus
= redirect_edge_var_map_location (vm
);
834 add_phi_arg (phi
, def
, s
, locus
);
837 redirect_edge_var_map_clear (e
);
840 /* Update the dominators. */
841 dombb
= get_immediate_dominator (CDI_DOMINATORS
, bb
);
842 domdest
= get_immediate_dominator (CDI_DOMINATORS
, dest
);
845 /* Shortcut to avoid calling (relatively expensive)
846 nearest_common_dominator unless necessary. */
850 dom
= nearest_common_dominator (CDI_DOMINATORS
, domdest
, dombb
);
852 set_immediate_dominator (CDI_DOMINATORS
, dest
, dom
);
854 /* Remove BB since all of BB's incoming edges have been redirected
856 delete_basic_block (bb
);
859 /* This pass merges PHI nodes if one feeds into another. For example,
860 suppose we have the following:
867 # tem_6 = PHI <tem_17(8), tem_23(7)>;
870 # tem_3 = PHI <tem_6(9), tem_2(5)>;
873 Then we merge the first PHI node into the second one like so:
880 # tem_3 = PHI <tem_23(7), tem_2(5), tem_17(8)>;
885 merge_phi_nodes (void)
887 basic_block
*worklist
= XNEWVEC (basic_block
, n_basic_blocks
);
888 basic_block
*current
= worklist
;
891 calculate_dominance_info (CDI_DOMINATORS
);
893 /* Find all PHI nodes that we may be able to merge. */
898 /* Look for a forwarder block with PHI nodes. */
899 if (!tree_forwarder_block_p (bb
, true))
902 dest
= single_succ (bb
);
904 /* We have to feed into another basic block with PHI
906 if (gimple_seq_empty_p (phi_nodes (dest
))
907 /* We don't want to deal with a basic block with
909 || bb_has_abnormal_pred (bb
))
912 if (!dominated_by_p (CDI_DOMINATORS
, dest
, bb
))
914 /* If BB does not dominate DEST, then the PHI nodes at
915 DEST must be the only users of the results of the PHI
921 gimple_stmt_iterator gsi
;
922 unsigned int dest_idx
= single_succ_edge (bb
)->dest_idx
;
924 /* BB dominates DEST. There may be many users of the PHI
925 nodes in BB. However, there is still a trivial case we
926 can handle. If the result of every PHI in BB is used
927 only by a PHI in DEST, then we can trivially merge the
928 PHI nodes from BB into DEST. */
929 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);
932 gimple phi
= gsi_stmt (gsi
);
933 tree result
= gimple_phi_result (phi
);
934 use_operand_p imm_use
;
937 /* If the PHI's result is never used, then we can just
939 if (has_zero_uses (result
))
942 /* Get the single use of the result of this PHI node. */
943 if (!single_imm_use (result
, &imm_use
, &use_stmt
)
944 || gimple_code (use_stmt
) != GIMPLE_PHI
945 || gimple_bb (use_stmt
) != dest
946 || gimple_phi_arg_def (use_stmt
, dest_idx
) != result
)
950 /* If the loop above iterated through all the PHI nodes
951 in BB, then we can merge the PHIs from BB into DEST. */
957 /* Now let's drain WORKLIST. */
958 while (current
!= worklist
)
961 remove_forwarder_block_with_phi (bb
);
969 gate_merge_phi (void)
974 struct gimple_opt_pass pass_merge_phi
=
978 "mergephi", /* name */
979 OPTGROUP_NONE
, /* optinfo_flags */
980 gate_merge_phi
, /* gate */
981 merge_phi_nodes
, /* execute */
984 0, /* static_pass_number */
985 TV_TREE_MERGE_PHI
, /* tv_id */
986 PROP_cfg
| PROP_ssa
, /* properties_required */
987 0, /* properties_provided */
988 0, /* properties_destroyed */
989 0, /* todo_flags_start */
990 TODO_ggc_collect
/* todo_flags_finish */