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"
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))
94 fold_defer_overflow_warnings ();
95 val = gimple_fold (stmt);
96 taken_edge = find_taken_edge (bb, val);
99 fold_undefer_and_ignore_overflow_warnings ();
103 /* Remove all the edges except the one that is always executed. */
105 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
111 fold_undefer_overflow_warnings
112 (true, stmt, WARN_STRICT_OVERFLOW_CONDITIONAL);
116 taken_edge->probability += e->probability;
117 taken_edge->count += e->count;
118 remove_edge_and_dominated_blocks (e);
125 fold_undefer_and_ignore_overflow_warnings ();
126 if (taken_edge->probability > REG_BR_PROB_BASE)
127 taken_edge->probability = REG_BR_PROB_BASE;
130 taken_edge = single_succ_edge (bb);
132 bitmap_set_bit (cfgcleanup_altered_bbs, bb->index);
133 gsi_remove (&gsi, true);
134 taken_edge->flags = EDGE_FALLTHRU;
139 /* Try to remove superfluous control structures in basic block BB. Returns
140 true if anything changes. */
143 cleanup_control_flow_bb (basic_block bb)
145 gimple_stmt_iterator gsi;
149 /* If the last statement of the block could throw and now cannot,
150 we need to prune cfg. */
151 retval |= gimple_purge_dead_eh_edges (bb);
153 gsi = gsi_last_bb (bb);
157 stmt = gsi_stmt (gsi);
159 if (gimple_code (stmt) == GIMPLE_COND
160 || gimple_code (stmt) == GIMPLE_SWITCH)
161 retval |= cleanup_control_expr_graph (bb, gsi);
162 else if (gimple_code (stmt) == GIMPLE_GOTO
163 && TREE_CODE (gimple_goto_dest (stmt)) == ADDR_EXPR
164 && (TREE_CODE (TREE_OPERAND (gimple_goto_dest (stmt), 0))
167 /* If we had a computed goto which has a compile-time determinable
168 destination, then we can eliminate the goto. */
172 basic_block target_block;
174 /* First look at all the outgoing edges. Delete any outgoing
175 edges which do not go to the right block. For the one
176 edge which goes to the right block, fix up its flags. */
177 label = TREE_OPERAND (gimple_goto_dest (stmt), 0);
178 target_block = label_to_block (label);
179 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
181 if (e->dest != target_block)
182 remove_edge_and_dominated_blocks (e);
185 /* Turn off the EDGE_ABNORMAL flag. */
186 e->flags &= ~EDGE_ABNORMAL;
188 /* And set EDGE_FALLTHRU. */
189 e->flags |= EDGE_FALLTHRU;
194 bitmap_set_bit (cfgcleanup_altered_bbs, bb->index);
195 bitmap_set_bit (cfgcleanup_altered_bbs, target_block->index);
197 /* Remove the GOTO_EXPR as it is not needed. The CFG has all the
198 relevant information we need. */
199 gsi_remove (&gsi, true);
203 /* Check for indirect calls that have been turned into
205 else if (is_gimple_call (stmt)
206 && gimple_call_noreturn_p (stmt)
207 && remove_fallthru_edge (bb->succs))
213 /* Return true if basic block BB does nothing except pass control
214 flow to another block and that we can safely insert a label at
215 the start of the successor block.
217 As a precondition, we require that BB be not equal to
221 tree_forwarder_block_p (basic_block bb, bool phi_wanted)
223 gimple_stmt_iterator gsi;
229 /* BB must have a single outgoing edge. */
230 if (single_succ_p (bb) != 1
231 /* If PHI_WANTED is false, BB must not have any PHI nodes.
232 Otherwise, BB must have PHI nodes. */
233 || gimple_seq_empty_p (phi_nodes (bb)) == phi_wanted
234 /* BB may not be a predecessor of EXIT_BLOCK_PTR. */
235 || single_succ (bb) == EXIT_BLOCK_PTR
236 /* Nor should this be an infinite loop. */
237 || single_succ (bb) == bb
238 /* BB may not have an abnormal outgoing edge. */
239 || (single_succ_edge (bb)->flags & EDGE_ABNORMAL))
243 gcc_assert (bb != ENTRY_BLOCK_PTR);
246 locus = single_succ_edge (bb)->goto_locus;
248 /* Now walk through the statements backward. We can ignore labels,
249 anything else means this is not a forwarder block. */
250 for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi_prev (&gsi))
252 gimple stmt = gsi_stmt (gsi);
254 switch (gimple_code (stmt))
257 if (DECL_NONLOCAL (gimple_label_label (stmt)))
259 if (optimize == 0 && gimple_location (stmt) != locus)
268 if (find_edge (ENTRY_BLOCK_PTR, bb))
274 /* Protect loop latches, headers and preheaders. */
275 if (bb->loop_father->header == bb)
277 dest = EDGE_SUCC (bb, 0)->dest;
279 if (dest->loop_father->header == dest)
283 /* If we have an EH edge leaving this block, make sure that the
284 destination of this block has only one predecessor. This ensures
285 that we don't get into the situation where we try to remove two
286 forwarders that go to the same basic block but are handlers for
287 different EH regions. */
288 succ = single_succ_edge (bb);
290 FOR_EACH_EDGE (e, ei, bb->preds)
292 if (e->flags & EDGE_EH)
294 if (!single_pred_p (dest))
297 /* If goto_locus of any of the edges differs, prevent removing
298 the forwarder block for -O0. */
299 if (optimize == 0 && e->goto_locus != locus)
306 /* Return true if BB has at least one abnormal incoming edge. */
309 has_abnormal_incoming_edge_p (basic_block bb)
314 FOR_EACH_EDGE (e, ei, bb->preds)
315 if (e->flags & EDGE_ABNORMAL)
321 /* If all the PHI nodes in DEST have alternatives for E1 and E2 and
322 those alternatives are equal in each of the PHI nodes, then return
323 true, else return false. */
326 phi_alternatives_equal (basic_block dest, edge e1, edge e2)
328 int n1 = e1->dest_idx;
329 int n2 = e2->dest_idx;
330 gimple_stmt_iterator gsi;
332 for (gsi = gsi_start_phis (dest); !gsi_end_p (gsi); gsi_next (&gsi))
334 gimple phi = gsi_stmt (gsi);
335 tree val1 = gimple_phi_arg_def (phi, n1);
336 tree val2 = gimple_phi_arg_def (phi, n2);
338 gcc_assert (val1 != NULL_TREE);
339 gcc_assert (val2 != NULL_TREE);
341 if (!operand_equal_for_phi_arg_p (val1, val2))
348 /* Removes forwarder block BB. Returns false if this failed. */
351 remove_forwarder_block (basic_block bb)
353 edge succ = single_succ_edge (bb), e, s;
354 basic_block dest = succ->dest;
357 gimple_stmt_iterator gsi, gsi_to;
358 bool seen_abnormal_edge = false;
360 /* We check for infinite loops already in tree_forwarder_block_p.
361 However it may happen that the infinite loop is created
362 afterwards due to removal of forwarders. */
366 /* If the destination block consists of a nonlocal label, do not merge
368 label = first_stmt (dest);
370 && gimple_code (label) == GIMPLE_LABEL
371 && DECL_NONLOCAL (gimple_label_label (label)))
374 /* If there is an abnormal edge to basic block BB, but not into
375 dest, problems might occur during removal of the phi node at out
376 of ssa due to overlapping live ranges of registers.
378 If there is an abnormal edge in DEST, the problems would occur
379 anyway since cleanup_dead_labels would then merge the labels for
380 two different eh regions, and rest of exception handling code
383 So if there is an abnormal edge to BB, proceed only if there is
384 no abnormal edge to DEST and there are no phi nodes in DEST. */
385 if (has_abnormal_incoming_edge_p (bb))
387 seen_abnormal_edge = true;
389 if (has_abnormal_incoming_edge_p (dest)
390 || !gimple_seq_empty_p (phi_nodes (dest)))
394 /* If there are phi nodes in DEST, and some of the blocks that are
395 predecessors of BB are also predecessors of DEST, check that the
396 phi node arguments match. */
397 if (!gimple_seq_empty_p (phi_nodes (dest)))
399 FOR_EACH_EDGE (e, ei, bb->preds)
401 s = find_edge (e->src, dest);
405 if (!phi_alternatives_equal (dest, succ, s))
410 /* Redirect the edges. */
411 for (ei = ei_start (bb->preds); (e = ei_safe_edge (ei)); )
413 bitmap_set_bit (cfgcleanup_altered_bbs, e->src->index);
415 if (e->flags & EDGE_ABNORMAL)
417 /* If there is an abnormal edge, redirect it anyway, and
418 move the labels to the new block to make it legal. */
419 s = redirect_edge_succ_nodup (e, dest);
422 s = redirect_edge_and_branch (e, dest);
426 /* Create arguments for the phi nodes, since the edge was not
428 for (gsi = gsi_start_phis (dest);
432 gimple phi = gsi_stmt (gsi);
433 add_phi_arg (phi, gimple_phi_arg_def (phi, succ->dest_idx), s);
438 if (seen_abnormal_edge)
440 /* Move the labels to the new block, so that the redirection of
441 the abnormal edges works. */
442 gsi_to = gsi_start_bb (dest);
443 for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); )
445 label = gsi_stmt (gsi);
446 gcc_assert (gimple_code (label) == GIMPLE_LABEL);
447 gsi_remove (&gsi, false);
448 gsi_insert_before (&gsi_to, label, GSI_CONTINUE_LINKING);
452 bitmap_set_bit (cfgcleanup_altered_bbs, dest->index);
454 /* Update the dominators. */
455 if (dom_info_available_p (CDI_DOMINATORS))
457 basic_block dom, dombb, domdest;
459 dombb = get_immediate_dominator (CDI_DOMINATORS, bb);
460 domdest = get_immediate_dominator (CDI_DOMINATORS, dest);
463 /* Shortcut to avoid calling (relatively expensive)
464 nearest_common_dominator unless necessary. */
468 dom = nearest_common_dominator (CDI_DOMINATORS, domdest, dombb);
470 set_immediate_dominator (CDI_DOMINATORS, dest, dom);
473 /* And kill the forwarder block. */
474 delete_basic_block (bb);
479 /* Split basic blocks on calls in the middle of a basic block that are now
480 known not to return, and remove the unreachable code. */
483 split_bbs_on_noreturn_calls (void)
485 bool changed = false;
489 /* Detect cases where a mid-block call is now known not to return. */
491 while (VEC_length (gimple, MODIFIED_NORETURN_CALLS (cfun)))
493 stmt = VEC_pop (gimple, MODIFIED_NORETURN_CALLS (cfun));
494 bb = gimple_bb (stmt);
495 /* BB might be deleted at this point, so verify first
496 BB is present in the cfg. */
498 || bb->index < NUM_FIXED_BLOCKS
499 || bb->index >= last_basic_block
500 || BASIC_BLOCK (bb->index) != bb
501 || last_stmt (bb) == stmt
502 || !gimple_call_noreturn_p (stmt))
506 split_block (bb, stmt);
507 remove_fallthru_edge (bb->succs);
513 /* If GIMPLE_OMP_RETURN in basic block BB is unreachable, remove it. */
516 cleanup_omp_return (basic_block bb)
518 gimple stmt = last_stmt (bb);
519 basic_block control_bb;
522 || gimple_code (stmt) != GIMPLE_OMP_RETURN
523 || !single_pred_p (bb))
526 control_bb = single_pred (bb);
527 stmt = last_stmt (control_bb);
529 if (stmt == NULL || gimple_code (stmt) != GIMPLE_OMP_SECTIONS_SWITCH)
532 /* The block with the control statement normally has two entry edges -- one
533 from entry, one from continue. If continue is removed, return is
534 unreachable, so we remove it here as well. */
535 if (EDGE_COUNT (control_bb->preds) == 2)
538 gcc_assert (EDGE_COUNT (control_bb->preds) == 1);
539 remove_edge_and_dominated_blocks (single_pred_edge (bb));
543 /* Tries to cleanup cfg in basic block BB. Returns true if anything
547 cleanup_tree_cfg_bb (basic_block bb)
551 if (cleanup_omp_return (bb))
554 retval = cleanup_control_flow_bb (bb);
556 if (tree_forwarder_block_p (bb, false)
557 && remove_forwarder_block (bb))
560 /* Merging the blocks may create new opportunities for folding
561 conditional branches (due to the elimination of single-valued PHI
563 if (single_succ_p (bb)
564 && can_merge_blocks_p (bb, single_succ (bb)))
566 merge_blocks (bb, single_succ (bb));
573 /* Iterate the cfg cleanups, while anything changes. */
576 cleanup_tree_cfg_1 (void)
582 retval |= split_bbs_on_noreturn_calls ();
584 /* Prepare the worklists of altered blocks. */
585 cfgcleanup_altered_bbs = BITMAP_ALLOC (NULL);
587 /* During forwarder block cleanup, we may redirect edges out of
588 SWITCH_EXPRs, which can get expensive. So we want to enable
589 recording of edge to CASE_LABEL_EXPR. */
590 start_recording_case_labels ();
592 /* Start by iterating over all basic blocks. We cannot use FOR_EACH_BB,
593 since the basic blocks may get removed. */
594 n = last_basic_block;
595 for (i = NUM_FIXED_BLOCKS; i < n; i++)
597 bb = BASIC_BLOCK (i);
599 retval |= cleanup_tree_cfg_bb (bb);
602 /* Now process the altered blocks, as long as any are available. */
603 while (!bitmap_empty_p (cfgcleanup_altered_bbs))
605 i = bitmap_first_set_bit (cfgcleanup_altered_bbs);
606 bitmap_clear_bit (cfgcleanup_altered_bbs, i);
607 if (i < NUM_FIXED_BLOCKS)
610 bb = BASIC_BLOCK (i);
614 retval |= cleanup_tree_cfg_bb (bb);
616 /* Rerun split_bbs_on_noreturn_calls, in case we have altered any noreturn
618 retval |= split_bbs_on_noreturn_calls ();
621 end_recording_case_labels ();
622 BITMAP_FREE (cfgcleanup_altered_bbs);
627 /* Remove unreachable blocks and other miscellaneous clean up work.
628 Return true if the flowgraph was modified, false otherwise. */
631 cleanup_tree_cfg_noloop (void)
635 timevar_push (TV_TREE_CLEANUP_CFG);
637 /* Iterate until there are no more cleanups left to do. If any
638 iteration changed the flowgraph, set CHANGED to true.
640 If dominance information is available, there cannot be any unreachable
642 if (!dom_info_available_p (CDI_DOMINATORS))
644 changed = delete_unreachable_blocks ();
645 calculate_dominance_info (CDI_DOMINATORS);
649 #ifdef ENABLE_CHECKING
650 verify_dominators (CDI_DOMINATORS);
655 changed |= cleanup_tree_cfg_1 ();
657 gcc_assert (dom_info_available_p (CDI_DOMINATORS));
660 #ifdef ENABLE_CHECKING
664 timevar_pop (TV_TREE_CLEANUP_CFG);
666 if (changed && current_loops)
667 loops_state_set (LOOPS_NEED_FIXUP);
672 /* Repairs loop structures. */
675 repair_loop_structures (void)
677 bitmap changed_bbs = BITMAP_ALLOC (NULL);
678 fix_loop_structure (changed_bbs);
680 /* This usually does nothing. But sometimes parts of cfg that originally
681 were inside a loop get out of it due to edge removal (since they
682 become unreachable by back edges from latch). */
683 if (loops_state_satisfies_p (LOOP_CLOSED_SSA))
684 rewrite_into_loop_closed_ssa (changed_bbs, TODO_update_ssa);
686 BITMAP_FREE (changed_bbs);
688 #ifdef ENABLE_CHECKING
689 verify_loop_structure ();
693 loops_state_clear (LOOPS_NEED_FIXUP);
696 /* Cleanup cfg and repair loop structures. */
699 cleanup_tree_cfg (void)
701 bool changed = cleanup_tree_cfg_noloop ();
703 if (current_loops != NULL
704 && loops_state_satisfies_p (LOOPS_NEED_FIXUP))
705 repair_loop_structures ();
710 /* Merge the PHI nodes at BB into those at BB's sole successor. */
713 remove_forwarder_block_with_phi (basic_block bb)
715 edge succ = single_succ_edge (bb);
716 basic_block dest = succ->dest;
718 basic_block dombb, domdest, dom;
720 /* We check for infinite loops already in tree_forwarder_block_p.
721 However it may happen that the infinite loop is created
722 afterwards due to removal of forwarders. */
726 /* If the destination block consists of a nonlocal label, do not
728 label = first_stmt (dest);
730 && gimple_code (label) == GIMPLE_LABEL
731 && DECL_NONLOCAL (gimple_label_label (label)))
734 /* Redirect each incoming edge to BB to DEST. */
735 while (EDGE_COUNT (bb->preds) > 0)
737 edge e = EDGE_PRED (bb, 0), s;
738 gimple_stmt_iterator gsi;
740 s = find_edge (e->src, dest);
743 /* We already have an edge S from E->src to DEST. If S and
744 E->dest's sole successor edge have the same PHI arguments
745 at DEST, redirect S to DEST. */
746 if (phi_alternatives_equal (dest, s, succ))
748 e = redirect_edge_and_branch (e, dest);
749 redirect_edge_var_map_clear (e);
753 /* PHI arguments are different. Create a forwarder block by
754 splitting E so that we can merge PHI arguments on E to
756 e = single_succ_edge (split_edge (e));
759 s = redirect_edge_and_branch (e, dest);
761 /* redirect_edge_and_branch must not create a new edge. */
764 /* Add to the PHI nodes at DEST each PHI argument removed at the
766 for (gsi = gsi_start_phis (dest);
770 gimple phi = gsi_stmt (gsi);
771 tree def = gimple_phi_arg_def (phi, succ->dest_idx);
773 if (TREE_CODE (def) == SSA_NAME)
775 edge_var_map_vector head;
779 /* If DEF is one of the results of PHI nodes removed during
780 redirection, replace it with the PHI argument that used
782 head = redirect_edge_var_map_vector (e);
783 for (i = 0; VEC_iterate (edge_var_map, head, i, vm); ++i)
785 tree old_arg = redirect_edge_var_map_result (vm);
786 tree new_arg = redirect_edge_var_map_def (vm);
796 add_phi_arg (phi, def, s);
799 redirect_edge_var_map_clear (e);
802 /* Update the dominators. */
803 dombb = get_immediate_dominator (CDI_DOMINATORS, bb);
804 domdest = get_immediate_dominator (CDI_DOMINATORS, dest);
807 /* Shortcut to avoid calling (relatively expensive)
808 nearest_common_dominator unless necessary. */
812 dom = nearest_common_dominator (CDI_DOMINATORS, domdest, dombb);
814 set_immediate_dominator (CDI_DOMINATORS, dest, dom);
816 /* Remove BB since all of BB's incoming edges have been redirected
818 delete_basic_block (bb);
821 /* This pass merges PHI nodes if one feeds into another. For example,
822 suppose we have the following:
829 # tem_6 = PHI <tem_17(8), tem_23(7)>;
832 # tem_3 = PHI <tem_6(9), tem_2(5)>;
835 Then we merge the first PHI node into the second one like so:
842 # tem_3 = PHI <tem_23(7), tem_2(5), tem_17(8)>;
847 merge_phi_nodes (void)
849 basic_block *worklist = XNEWVEC (basic_block, n_basic_blocks);
850 basic_block *current = worklist;
853 calculate_dominance_info (CDI_DOMINATORS);
855 /* Find all PHI nodes that we may be able to merge. */
860 /* Look for a forwarder block with PHI nodes. */
861 if (!tree_forwarder_block_p (bb, true))
864 dest = single_succ (bb);
866 /* We have to feed into another basic block with PHI
868 if (!phi_nodes (dest)
869 /* We don't want to deal with a basic block with
871 || has_abnormal_incoming_edge_p (bb))
874 if (!dominated_by_p (CDI_DOMINATORS, dest, bb))
876 /* If BB does not dominate DEST, then the PHI nodes at
877 DEST must be the only users of the results of the PHI
883 gimple_stmt_iterator gsi;
884 unsigned int dest_idx = single_succ_edge (bb)->dest_idx;
886 /* BB dominates DEST. There may be many users of the PHI
887 nodes in BB. However, there is still a trivial case we
888 can handle. If the result of every PHI in BB is used
889 only by a PHI in DEST, then we can trivially merge the
890 PHI nodes from BB into DEST. */
891 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi);
894 gimple phi = gsi_stmt (gsi);
895 tree result = gimple_phi_result (phi);
896 use_operand_p imm_use;
899 /* If the PHI's result is never used, then we can just
901 if (has_zero_uses (result))
904 /* Get the single use of the result of this PHI node. */
905 if (!single_imm_use (result, &imm_use, &use_stmt)
906 || gimple_code (use_stmt) != GIMPLE_PHI
907 || gimple_bb (use_stmt) != dest
908 || gimple_phi_arg_def (use_stmt, dest_idx) != result)
912 /* If the loop above iterated through all the PHI nodes
913 in BB, then we can merge the PHIs from BB into DEST. */
919 /* Now let's drain WORKLIST. */
920 while (current != worklist)
923 remove_forwarder_block_with_phi (bb);
931 gate_merge_phi (void)
936 struct gimple_opt_pass pass_merge_phi =
940 "mergephi", /* name */
941 gate_merge_phi, /* gate */
942 merge_phi_nodes, /* execute */
945 0, /* static_pass_number */
946 TV_TREE_MERGE_PHI, /* tv_id */
947 PROP_cfg | PROP_ssa, /* properties_required */
948 0, /* properties_provided */
949 0, /* properties_destroyed */
950 0, /* todo_flags_start */
951 TODO_dump_func | TODO_ggc_collect /* todo_flags_finish */