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"
28 #include "diagnostic-core.h"
32 #include "langhooks.h"
33 #include "tree-flow.h"
35 #include "tree-dump.h"
36 #include "tree-pass.h"
40 #include "tree-ssa-propagate.h"
41 #include "tree-scalar-evolution.h"
43 /* The set of blocks in that at least one of the following changes happened:
44 -- the statement at the end of the block was changed
45 -- the block was newly created
46 -- the set of the predecessors of the block changed
47 -- the set of the successors of the block changed
48 ??? Maybe we could track these changes separately, since they determine
49 what cleanups it makes sense to try on the block. */
50 bitmap cfgcleanup_altered_bbs
;
52 /* Remove any fallthru edge from EV. Return true if an edge was removed. */
55 remove_fallthru_edge (VEC(edge
,gc
) *ev
)
60 FOR_EACH_EDGE (e
, ei
, ev
)
61 if ((e
->flags
& EDGE_FALLTHRU
) != 0)
63 remove_edge_and_dominated_blocks (e
);
70 /* Disconnect an unreachable block in the control expression starting
74 cleanup_control_expr_graph (basic_block bb
, gimple_stmt_iterator gsi
)
78 gimple stmt
= gsi_stmt (gsi
);
81 if (!single_succ_p (bb
))
88 fold_defer_overflow_warnings ();
89 loc
= gimple_location (stmt
);
90 switch (gimple_code (stmt
))
94 tree lhs
= gimple_cond_lhs (stmt
);
95 tree rhs
= gimple_cond_rhs (stmt
);
96 /* For conditions try harder and lookup single-argument
97 PHI nodes. Only do so from the same basic-block though
98 as other basic-blocks may be dead already. */
99 if (TREE_CODE (lhs
) == SSA_NAME
100 && !name_registered_for_update_p (lhs
))
102 gimple def_stmt
= SSA_NAME_DEF_STMT (lhs
);
103 if (gimple_code (def_stmt
) == GIMPLE_PHI
104 && gimple_phi_num_args (def_stmt
) == 1
105 && gimple_bb (def_stmt
) == gimple_bb (stmt
)
106 && (TREE_CODE (PHI_ARG_DEF (def_stmt
, 0)) != SSA_NAME
107 || !name_registered_for_update_p (PHI_ARG_DEF (def_stmt
,
109 lhs
= PHI_ARG_DEF (def_stmt
, 0);
111 if (TREE_CODE (rhs
) == SSA_NAME
112 && !name_registered_for_update_p (rhs
))
114 gimple def_stmt
= SSA_NAME_DEF_STMT (rhs
);
115 if (gimple_code (def_stmt
) == GIMPLE_PHI
116 && gimple_phi_num_args (def_stmt
) == 1
117 && gimple_bb (def_stmt
) == gimple_bb (stmt
)
118 && (TREE_CODE (PHI_ARG_DEF (def_stmt
, 0)) != SSA_NAME
119 || !name_registered_for_update_p (PHI_ARG_DEF (def_stmt
,
121 rhs
= PHI_ARG_DEF (def_stmt
, 0);
123 val
= fold_binary_loc (loc
, gimple_cond_code (stmt
),
124 boolean_type_node
, lhs
, rhs
);
129 val
= gimple_switch_index (stmt
);
135 taken_edge
= find_taken_edge (bb
, val
);
138 fold_undefer_and_ignore_overflow_warnings ();
142 /* Remove all the edges except the one that is always executed. */
144 for (ei
= ei_start (bb
->succs
); (e
= ei_safe_edge (ei
)); )
150 fold_undefer_overflow_warnings
151 (true, stmt
, WARN_STRICT_OVERFLOW_CONDITIONAL
);
155 taken_edge
->probability
+= e
->probability
;
156 taken_edge
->count
+= e
->count
;
157 remove_edge_and_dominated_blocks (e
);
164 fold_undefer_and_ignore_overflow_warnings ();
165 if (taken_edge
->probability
> REG_BR_PROB_BASE
)
166 taken_edge
->probability
= REG_BR_PROB_BASE
;
169 taken_edge
= single_succ_edge (bb
);
171 bitmap_set_bit (cfgcleanup_altered_bbs
, bb
->index
);
172 gsi_remove (&gsi
, true);
173 taken_edge
->flags
= EDGE_FALLTHRU
;
178 /* Try to remove superfluous control structures in basic block BB. Returns
179 true if anything changes. */
182 cleanup_control_flow_bb (basic_block bb
)
184 gimple_stmt_iterator gsi
;
188 /* If the last statement of the block could throw and now cannot,
189 we need to prune cfg. */
190 retval
|= gimple_purge_dead_eh_edges (bb
);
192 gsi
= gsi_last_bb (bb
);
196 stmt
= gsi_stmt (gsi
);
198 if (gimple_code (stmt
) == GIMPLE_COND
199 || gimple_code (stmt
) == GIMPLE_SWITCH
)
200 retval
|= cleanup_control_expr_graph (bb
, gsi
);
201 else if (gimple_code (stmt
) == GIMPLE_GOTO
202 && TREE_CODE (gimple_goto_dest (stmt
)) == ADDR_EXPR
203 && (TREE_CODE (TREE_OPERAND (gimple_goto_dest (stmt
), 0))
206 /* If we had a computed goto which has a compile-time determinable
207 destination, then we can eliminate the goto. */
211 basic_block target_block
;
213 /* First look at all the outgoing edges. Delete any outgoing
214 edges which do not go to the right block. For the one
215 edge which goes to the right block, fix up its flags. */
216 label
= TREE_OPERAND (gimple_goto_dest (stmt
), 0);
217 target_block
= label_to_block (label
);
218 for (ei
= ei_start (bb
->succs
); (e
= ei_safe_edge (ei
)); )
220 if (e
->dest
!= target_block
)
221 remove_edge_and_dominated_blocks (e
);
224 /* Turn off the EDGE_ABNORMAL flag. */
225 e
->flags
&= ~EDGE_ABNORMAL
;
227 /* And set EDGE_FALLTHRU. */
228 e
->flags
|= EDGE_FALLTHRU
;
233 bitmap_set_bit (cfgcleanup_altered_bbs
, bb
->index
);
234 bitmap_set_bit (cfgcleanup_altered_bbs
, target_block
->index
);
236 /* Remove the GOTO_EXPR as it is not needed. The CFG has all the
237 relevant information we need. */
238 gsi_remove (&gsi
, true);
242 /* Check for indirect calls that have been turned into
244 else if (is_gimple_call (stmt
)
245 && gimple_call_noreturn_p (stmt
)
246 && remove_fallthru_edge (bb
->succs
))
252 /* Return true if basic block BB does nothing except pass control
253 flow to another block and that we can safely insert a label at
254 the start of the successor block.
256 As a precondition, we require that BB be not equal to
260 tree_forwarder_block_p (basic_block bb
, bool phi_wanted
)
262 gimple_stmt_iterator gsi
;
265 /* BB must have a single outgoing edge. */
266 if (single_succ_p (bb
) != 1
267 /* If PHI_WANTED is false, BB must not have any PHI nodes.
268 Otherwise, BB must have PHI nodes. */
269 || gimple_seq_empty_p (phi_nodes (bb
)) == phi_wanted
270 /* BB may not be a predecessor of EXIT_BLOCK_PTR. */
271 || single_succ (bb
) == EXIT_BLOCK_PTR
272 /* Nor should this be an infinite loop. */
273 || single_succ (bb
) == bb
274 /* BB may not have an abnormal outgoing edge. */
275 || (single_succ_edge (bb
)->flags
& EDGE_ABNORMAL
))
278 gcc_checking_assert (bb
!= ENTRY_BLOCK_PTR
);
280 locus
= single_succ_edge (bb
)->goto_locus
;
282 /* There should not be an edge coming from entry, or an EH edge. */
287 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
288 if (e
->src
== ENTRY_BLOCK_PTR
|| (e
->flags
& EDGE_EH
))
290 /* If goto_locus of any of the edges differs, prevent removing
291 the forwarder block for -O0. */
292 else if (optimize
== 0 && e
->goto_locus
!= locus
)
296 /* Now walk through the statements backward. We can ignore labels,
297 anything else means this is not a forwarder block. */
298 for (gsi
= gsi_last_bb (bb
); !gsi_end_p (gsi
); gsi_prev (&gsi
))
300 gimple stmt
= gsi_stmt (gsi
);
302 switch (gimple_code (stmt
))
305 if (DECL_NONLOCAL (gimple_label_label (stmt
)))
307 if (optimize
== 0 && gimple_location (stmt
) != locus
)
311 /* ??? For now, hope there's a corresponding debug
312 assignment at the destination. */
324 /* Protect loop latches, headers and preheaders. */
325 if (bb
->loop_father
->header
== bb
)
327 dest
= EDGE_SUCC (bb
, 0)->dest
;
329 if (dest
->loop_father
->header
== dest
)
335 /* If all the PHI nodes in DEST have alternatives for E1 and E2 and
336 those alternatives are equal in each of the PHI nodes, then return
337 true, else return false. */
340 phi_alternatives_equal (basic_block dest
, edge e1
, edge e2
)
342 int n1
= e1
->dest_idx
;
343 int n2
= e2
->dest_idx
;
344 gimple_stmt_iterator gsi
;
346 for (gsi
= gsi_start_phis (dest
); !gsi_end_p (gsi
); gsi_next (&gsi
))
348 gimple phi
= gsi_stmt (gsi
);
349 tree val1
= gimple_phi_arg_def (phi
, n1
);
350 tree val2
= gimple_phi_arg_def (phi
, n2
);
352 gcc_assert (val1
!= NULL_TREE
);
353 gcc_assert (val2
!= NULL_TREE
);
355 if (!operand_equal_for_phi_arg_p (val1
, val2
))
362 /* Removes forwarder block BB. Returns false if this failed. */
365 remove_forwarder_block (basic_block bb
)
367 edge succ
= single_succ_edge (bb
), e
, s
;
368 basic_block dest
= succ
->dest
;
371 gimple_stmt_iterator gsi
, gsi_to
;
372 bool can_move_debug_stmts
;
374 /* We check for infinite loops already in tree_forwarder_block_p.
375 However it may happen that the infinite loop is created
376 afterwards due to removal of forwarders. */
380 /* If the destination block consists of a nonlocal label or is a
381 EH landing pad, do not merge it. */
382 label
= first_stmt (dest
);
384 && gimple_code (label
) == GIMPLE_LABEL
385 && (DECL_NONLOCAL (gimple_label_label (label
))
386 || EH_LANDING_PAD_NR (gimple_label_label (label
)) != 0))
389 /* If there is an abnormal edge to basic block BB, but not into
390 dest, problems might occur during removal of the phi node at out
391 of ssa due to overlapping live ranges of registers.
393 If there is an abnormal edge in DEST, the problems would occur
394 anyway since cleanup_dead_labels would then merge the labels for
395 two different eh regions, and rest of exception handling code
398 So if there is an abnormal edge to BB, proceed only if there is
399 no abnormal edge to DEST and there are no phi nodes in DEST. */
400 if (bb_has_abnormal_pred (bb
)
401 && (bb_has_abnormal_pred (dest
)
402 || !gimple_seq_empty_p (phi_nodes (dest
))))
405 /* If there are phi nodes in DEST, and some of the blocks that are
406 predecessors of BB are also predecessors of DEST, check that the
407 phi node arguments match. */
408 if (!gimple_seq_empty_p (phi_nodes (dest
)))
410 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
412 s
= find_edge (e
->src
, dest
);
416 if (!phi_alternatives_equal (dest
, succ
, s
))
421 can_move_debug_stmts
= MAY_HAVE_DEBUG_STMTS
&& single_pred_p (dest
);
423 /* Redirect the edges. */
424 for (ei
= ei_start (bb
->preds
); (e
= ei_safe_edge (ei
)); )
426 bitmap_set_bit (cfgcleanup_altered_bbs
, e
->src
->index
);
428 if (e
->flags
& EDGE_ABNORMAL
)
430 /* If there is an abnormal edge, redirect it anyway, and
431 move the labels to the new block to make it legal. */
432 s
= redirect_edge_succ_nodup (e
, dest
);
435 s
= redirect_edge_and_branch (e
, dest
);
439 /* Create arguments for the phi nodes, since the edge was not
441 for (gsi
= gsi_start_phis (dest
);
445 gimple phi
= gsi_stmt (gsi
);
446 source_location l
= gimple_phi_arg_location_from_edge (phi
, succ
);
447 tree b
= gimple_phi_arg_block_from_edge (phi
, succ
);
448 add_phi_arg (phi
, gimple_phi_arg_def (phi
, succ
->dest_idx
), s
, l
,
454 /* Move nonlocal labels and computed goto targets as well as user
455 defined labels and labels with an EH landing pad number to the
456 new block, so that the redirection of the abnormal edges works,
457 jump targets end up in a sane place and debug information for
458 labels is retained. */
459 gsi_to
= gsi_start_bb (dest
);
460 for (gsi
= gsi_start_bb (bb
); !gsi_end_p (gsi
); )
463 label
= gsi_stmt (gsi
);
464 if (is_gimple_debug (label
))
466 decl
= gimple_label_label (label
);
467 if (EH_LANDING_PAD_NR (decl
) != 0
468 || DECL_NONLOCAL (decl
)
469 || FORCED_LABEL (decl
)
470 || !DECL_ARTIFICIAL (decl
))
472 gsi_remove (&gsi
, false);
473 gsi_insert_before (&gsi_to
, label
, GSI_SAME_STMT
);
479 /* Move debug statements if the destination has a single predecessor. */
480 if (can_move_debug_stmts
)
482 gsi_to
= gsi_after_labels (dest
);
483 for (gsi
= gsi_after_labels (bb
); !gsi_end_p (gsi
); )
485 gimple debug
= gsi_stmt (gsi
);
486 if (!is_gimple_debug (debug
))
488 gsi_remove (&gsi
, false);
489 gsi_insert_before (&gsi_to
, debug
, GSI_SAME_STMT
);
493 bitmap_set_bit (cfgcleanup_altered_bbs
, dest
->index
);
495 /* Update the dominators. */
496 if (dom_info_available_p (CDI_DOMINATORS
))
498 basic_block dom
, dombb
, domdest
;
500 dombb
= get_immediate_dominator (CDI_DOMINATORS
, bb
);
501 domdest
= get_immediate_dominator (CDI_DOMINATORS
, dest
);
504 /* Shortcut to avoid calling (relatively expensive)
505 nearest_common_dominator unless necessary. */
509 dom
= nearest_common_dominator (CDI_DOMINATORS
, domdest
, dombb
);
511 set_immediate_dominator (CDI_DOMINATORS
, dest
, dom
);
514 /* And kill the forwarder block. */
515 delete_basic_block (bb
);
520 /* STMT is a call that has been discovered noreturn. Fixup the CFG
521 and remove LHS. Return true if something changed. */
524 fixup_noreturn_call (gimple stmt
)
526 basic_block bb
= gimple_bb (stmt
);
527 bool changed
= false;
529 if (gimple_call_builtin_p (stmt
, BUILT_IN_RETURN
))
532 /* First split basic block if stmt is not last. */
533 if (stmt
!= gsi_stmt (gsi_last_bb (bb
)))
534 split_block (bb
, stmt
);
536 changed
|= remove_fallthru_edge (bb
->succs
);
538 /* If there is LHS, remove it. */
539 if (gimple_call_lhs (stmt
))
541 tree op
= gimple_call_lhs (stmt
);
542 gimple_call_set_lhs (stmt
, NULL_TREE
);
544 /* We need to remove SSA name to avoid checking errors.
545 All uses are dominated by the noreturn and thus will
546 be removed afterwards.
547 We proactively remove affected non-PHI statements to avoid
548 fixup_cfg from trying to update them and crashing. */
549 if (TREE_CODE (op
) == SSA_NAME
)
552 imm_use_iterator iter
;
555 unsigned int bb_index
;
557 bitmap blocks
= BITMAP_ALLOC (NULL
);
559 FOR_EACH_IMM_USE_STMT (use_stmt
, iter
, op
)
561 if (gimple_code (use_stmt
) != GIMPLE_PHI
)
562 bitmap_set_bit (blocks
, gimple_bb (use_stmt
)->index
);
564 FOR_EACH_IMM_USE_ON_STMT (use_p
, iter
)
565 SET_USE (use_p
, error_mark_node
);
567 EXECUTE_IF_SET_IN_BITMAP (blocks
, 0, bb_index
, bi
)
568 delete_basic_block (BASIC_BLOCK (bb_index
));
569 BITMAP_FREE (blocks
);
570 release_ssa_name (op
);
575 /* Similarly remove VDEF if there is any. */
576 else if (gimple_vdef (stmt
))
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
>= last_basic_block
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)
779 timevar_push (TV_REPAIR_LOOPS
);
780 changed_bbs
= BITMAP_ALLOC (NULL
);
781 fix_loop_structure (changed_bbs
);
783 /* This usually does nothing. But sometimes parts of cfg that originally
784 were inside a loop get out of it due to edge removal (since they
785 become unreachable by back edges from latch). */
786 if (loops_state_satisfies_p (LOOP_CLOSED_SSA
))
787 rewrite_into_loop_closed_ssa (changed_bbs
, TODO_update_ssa
);
789 BITMAP_FREE (changed_bbs
);
791 #ifdef ENABLE_CHECKING
792 verify_loop_structure ();
796 timevar_pop (TV_REPAIR_LOOPS
);
799 /* Cleanup cfg and repair loop structures. */
802 cleanup_tree_cfg (void)
804 bool changed
= cleanup_tree_cfg_noloop ();
806 if (current_loops
!= NULL
807 && loops_state_satisfies_p (LOOPS_NEED_FIXUP
))
808 repair_loop_structures ();
813 /* Merge the PHI nodes at BB into those at BB's sole successor. */
816 remove_forwarder_block_with_phi (basic_block bb
)
818 edge succ
= single_succ_edge (bb
);
819 basic_block dest
= succ
->dest
;
821 basic_block dombb
, domdest
, dom
;
823 /* We check for infinite loops already in tree_forwarder_block_p.
824 However it may happen that the infinite loop is created
825 afterwards due to removal of forwarders. */
829 /* If the destination block consists of a nonlocal label, do not
831 label
= first_stmt (dest
);
833 && gimple_code (label
) == GIMPLE_LABEL
834 && DECL_NONLOCAL (gimple_label_label (label
)))
837 /* Redirect each incoming edge to BB to DEST. */
838 while (EDGE_COUNT (bb
->preds
) > 0)
840 edge e
= EDGE_PRED (bb
, 0), s
;
841 gimple_stmt_iterator gsi
;
843 s
= find_edge (e
->src
, dest
);
846 /* We already have an edge S from E->src to DEST. If S and
847 E->dest's sole successor edge have the same PHI arguments
848 at DEST, redirect S to DEST. */
849 if (phi_alternatives_equal (dest
, s
, succ
))
851 e
= redirect_edge_and_branch (e
, dest
);
852 redirect_edge_var_map_clear (e
);
856 /* PHI arguments are different. Create a forwarder block by
857 splitting E so that we can merge PHI arguments on E to
859 e
= single_succ_edge (split_edge (e
));
862 s
= redirect_edge_and_branch (e
, dest
);
864 /* redirect_edge_and_branch must not create a new edge. */
867 /* Add to the PHI nodes at DEST each PHI argument removed at the
869 for (gsi
= gsi_start_phis (dest
);
873 gimple phi
= gsi_stmt (gsi
);
874 tree def
= gimple_phi_arg_def (phi
, succ
->dest_idx
);
875 source_location locus
= gimple_phi_arg_location_from_edge (phi
, succ
);
876 tree block
= gimple_phi_arg_block_from_edge (phi
, succ
);
878 if (TREE_CODE (def
) == SSA_NAME
)
880 edge_var_map_vector head
;
884 /* If DEF is one of the results of PHI nodes removed during
885 redirection, replace it with the PHI argument that used
887 head
= redirect_edge_var_map_vector (e
);
888 FOR_EACH_VEC_ELT (edge_var_map
, head
, i
, vm
)
890 tree old_arg
= redirect_edge_var_map_result (vm
);
891 tree new_arg
= redirect_edge_var_map_def (vm
);
896 locus
= redirect_edge_var_map_location (vm
);
897 block
= redirect_edge_var_map_block (vm
);
903 add_phi_arg (phi
, def
, s
, locus
, block
);
906 redirect_edge_var_map_clear (e
);
909 /* Update the dominators. */
910 dombb
= get_immediate_dominator (CDI_DOMINATORS
, bb
);
911 domdest
= get_immediate_dominator (CDI_DOMINATORS
, dest
);
914 /* Shortcut to avoid calling (relatively expensive)
915 nearest_common_dominator unless necessary. */
919 dom
= nearest_common_dominator (CDI_DOMINATORS
, domdest
, dombb
);
921 set_immediate_dominator (CDI_DOMINATORS
, dest
, dom
);
923 /* Remove BB since all of BB's incoming edges have been redirected
925 delete_basic_block (bb
);
928 /* This pass merges PHI nodes if one feeds into another. For example,
929 suppose we have the following:
936 # tem_6 = PHI <tem_17(8), tem_23(7)>;
939 # tem_3 = PHI <tem_6(9), tem_2(5)>;
942 Then we merge the first PHI node into the second one like so:
949 # tem_3 = PHI <tem_23(7), tem_2(5), tem_17(8)>;
954 merge_phi_nodes (void)
956 basic_block
*worklist
= XNEWVEC (basic_block
, n_basic_blocks
);
957 basic_block
*current
= worklist
;
960 calculate_dominance_info (CDI_DOMINATORS
);
962 /* Find all PHI nodes that we may be able to merge. */
967 /* Look for a forwarder block with PHI nodes. */
968 if (!tree_forwarder_block_p (bb
, true))
971 dest
= single_succ (bb
);
973 /* We have to feed into another basic block with PHI
975 if (gimple_seq_empty_p (phi_nodes (dest
))
976 /* We don't want to deal with a basic block with
978 || bb_has_abnormal_pred (bb
))
981 if (!dominated_by_p (CDI_DOMINATORS
, dest
, bb
))
983 /* If BB does not dominate DEST, then the PHI nodes at
984 DEST must be the only users of the results of the PHI
990 gimple_stmt_iterator gsi
;
991 unsigned int dest_idx
= single_succ_edge (bb
)->dest_idx
;
993 /* BB dominates DEST. There may be many users of the PHI
994 nodes in BB. However, there is still a trivial case we
995 can handle. If the result of every PHI in BB is used
996 only by a PHI in DEST, then we can trivially merge the
997 PHI nodes from BB into DEST. */
998 for (gsi
= gsi_start_phis (bb
); !gsi_end_p (gsi
);
1001 gimple phi
= gsi_stmt (gsi
);
1002 tree result
= gimple_phi_result (phi
);
1003 use_operand_p imm_use
;
1006 /* If the PHI's result is never used, then we can just
1008 if (has_zero_uses (result
))
1011 /* Get the single use of the result of this PHI node. */
1012 if (!single_imm_use (result
, &imm_use
, &use_stmt
)
1013 || gimple_code (use_stmt
) != GIMPLE_PHI
1014 || gimple_bb (use_stmt
) != dest
1015 || gimple_phi_arg_def (use_stmt
, dest_idx
) != result
)
1019 /* If the loop above iterated through all the PHI nodes
1020 in BB, then we can merge the PHIs from BB into DEST. */
1021 if (gsi_end_p (gsi
))
1026 /* Now let's drain WORKLIST. */
1027 while (current
!= worklist
)
1030 remove_forwarder_block_with_phi (bb
);
1038 gate_merge_phi (void)
1043 struct gimple_opt_pass pass_merge_phi
=
1047 "mergephi", /* name */
1048 gate_merge_phi
, /* gate */
1049 merge_phi_nodes
, /* execute */
1052 0, /* static_pass_number */
1053 TV_TREE_MERGE_PHI
, /* tv_id */
1054 PROP_cfg
| PROP_ssa
, /* properties_required */
1055 0, /* properties_provided */
1056 0, /* properties_destroyed */
1057 0, /* todo_flags_start */
1058 TODO_ggc_collect
/* todo_flags_finish */