1 /* CFG cleanup for trees.
2 Copyright (C) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010
3 Free Software Foundation, Inc.
4
5 This file is part of GCC.
6
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)
10 any later version.
11
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.
16
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/>. */
20
21 #include "config.h"
22 #include "system.h"
23 #include "coretypes.h"
24 #include "tm.h"
25 #include "tree.h"
26 #include "tm_p.h"
27 #include "basic-block.h"
28 #include "output.h"
29 #include "diagnostic-core.h"
30 #include "flags.h"
31 #include "function.h"
32 #include "ggc.h"
33 #include "langhooks.h"
34 #include "tree-flow.h"
35 #include "timevar.h"
36 #include "tree-dump.h"
37 #include "tree-pass.h"
38 #include "except.h"
39 #include "cfgloop.h"
40 #include "cfglayout.h"
41 #include "hashtab.h"
42 #include "tree-ssa-propagate.h"
43 #include "tree-scalar-evolution.h"
44
45 /* The set of blocks in that at least one of the following changes happened:
46 -- the statement at the end of the block was changed
47 -- the block was newly created
48 -- the set of the predecessors of the block changed
49 -- the set of the successors of the block changed
50 ??? Maybe we could track these changes separately, since they determine
51 what cleanups it makes sense to try on the block. */
52 bitmap cfgcleanup_altered_bbs;
53
54 /* Remove any fallthru edge from EV. Return true if an edge was removed. */
55
56 static bool
remove_fallthru_edge(VEC (edge,gc)* ev)57 remove_fallthru_edge (VEC(edge,gc) *ev)
58 {
59 edge_iterator ei;
60 edge e;
61
62 FOR_EACH_EDGE (e, ei, ev)
63 if ((e->flags & EDGE_FALLTHRU) != 0)
64 {
65 remove_edge_and_dominated_blocks (e);
66 return true;
67 }
68 return false;
69 }
70
71
72 /* Disconnect an unreachable block in the control expression starting
73 at block BB. */
74
75 static bool
cleanup_control_expr_graph(basic_block bb,gimple_stmt_iterator gsi)76 cleanup_control_expr_graph (basic_block bb, gimple_stmt_iterator gsi)
77 {
78 edge taken_edge;
79 bool retval = false;
80 gimple stmt = gsi_stmt (gsi);
81 tree val;
82
83 if (!single_succ_p (bb))
84 {
85 edge e;
86 edge_iterator ei;
87 bool warned;
88 location_t loc;
89
90 fold_defer_overflow_warnings ();
91 loc = gimple_location (stmt);
92 switch (gimple_code (stmt))
93 {
94 case GIMPLE_COND:
95 {
96 tree lhs = gimple_cond_lhs (stmt);
97 tree rhs = gimple_cond_rhs (stmt);
98 /* For conditions try harder and lookup single-argument
99 PHI nodes. Only do so from the same basic-block though
100 as other basic-blocks may be dead already. */
101 if (TREE_CODE (lhs) == SSA_NAME
102 && !name_registered_for_update_p (lhs))
103 {
104 gimple def_stmt = SSA_NAME_DEF_STMT (lhs);
105 if (gimple_code (def_stmt) == GIMPLE_PHI
106 && gimple_phi_num_args (def_stmt) == 1
107 && gimple_bb (def_stmt) == gimple_bb (stmt)
108 && (TREE_CODE (PHI_ARG_DEF (def_stmt, 0)) != SSA_NAME
109 || !name_registered_for_update_p (PHI_ARG_DEF (def_stmt,
110 0))))
111 lhs = PHI_ARG_DEF (def_stmt, 0);
112 }
113 if (TREE_CODE (rhs) == SSA_NAME
114 && !name_registered_for_update_p (rhs))
115 {
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 && (TREE_CODE (PHI_ARG_DEF (def_stmt, 0)) != SSA_NAME
121 || !name_registered_for_update_p (PHI_ARG_DEF (def_stmt,
122 0))))
123 rhs = PHI_ARG_DEF (def_stmt, 0);
124 }
125 val = fold_binary_loc (loc, gimple_cond_code (stmt),
126 boolean_type_node, lhs, rhs);
127 break;
128 }
129
130 case GIMPLE_SWITCH:
131 val = gimple_switch_index (stmt);
132 break;
133
134 default:
135 val = NULL_TREE;
136 }
137 taken_edge = find_taken_edge (bb, val);
138 if (!taken_edge)
139 {
140 fold_undefer_and_ignore_overflow_warnings ();
141 return false;
142 }
143
144 /* Remove all the edges except the one that is always executed. */
145 warned = false;
146 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
147 {
148 if (e != taken_edge)
149 {
150 if (!warned)
151 {
152 fold_undefer_overflow_warnings
153 (true, stmt, WARN_STRICT_OVERFLOW_CONDITIONAL);
154 warned = true;
155 }
156
157 taken_edge->probability += e->probability;
158 taken_edge->count += e->count;
159 remove_edge_and_dominated_blocks (e);
160 retval = true;
161 }
162 else
163 ei_next (&ei);
164 }
165 if (!warned)
166 fold_undefer_and_ignore_overflow_warnings ();
167 if (taken_edge->probability > REG_BR_PROB_BASE)
168 taken_edge->probability = REG_BR_PROB_BASE;
169 }
170 else
171 taken_edge = single_succ_edge (bb);
172
173 bitmap_set_bit (cfgcleanup_altered_bbs, bb->index);
174 gsi_remove (&gsi, true);
175 taken_edge->flags = EDGE_FALLTHRU;
176
177 return retval;
178 }
179
180 /* Try to remove superfluous control structures in basic block BB. Returns
181 true if anything changes. */
182
183 static bool
cleanup_control_flow_bb(basic_block bb)184 cleanup_control_flow_bb (basic_block bb)
185 {
186 gimple_stmt_iterator gsi;
187 bool retval = false;
188 gimple stmt;
189
190 /* If the last statement of the block could throw and now cannot,
191 we need to prune cfg. */
192 retval |= gimple_purge_dead_eh_edges (bb);
193
194 gsi = gsi_last_bb (bb);
195 if (gsi_end_p (gsi))
196 return retval;
197
198 stmt = gsi_stmt (gsi);
199
200 if (gimple_code (stmt) == GIMPLE_COND
201 || gimple_code (stmt) == GIMPLE_SWITCH)
202 retval |= cleanup_control_expr_graph (bb, gsi);
203 else if (gimple_code (stmt) == GIMPLE_GOTO
204 && TREE_CODE (gimple_goto_dest (stmt)) == ADDR_EXPR
205 && (TREE_CODE (TREE_OPERAND (gimple_goto_dest (stmt), 0))
206 == LABEL_DECL))
207 {
208 /* If we had a computed goto which has a compile-time determinable
209 destination, then we can eliminate the goto. */
210 edge e;
211 tree label;
212 edge_iterator ei;
213 basic_block target_block;
214
215 /* First look at all the outgoing edges. Delete any outgoing
216 edges which do not go to the right block. For the one
217 edge which goes to the right block, fix up its flags. */
218 label = TREE_OPERAND (gimple_goto_dest (stmt), 0);
219 target_block = label_to_block (label);
220 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
221 {
222 if (e->dest != target_block)
223 remove_edge_and_dominated_blocks (e);
224 else
225 {
226 /* Turn off the EDGE_ABNORMAL flag. */
227 e->flags &= ~EDGE_ABNORMAL;
228
229 /* And set EDGE_FALLTHRU. */
230 e->flags |= EDGE_FALLTHRU;
231 ei_next (&ei);
232 }
233 }
234
235 bitmap_set_bit (cfgcleanup_altered_bbs, bb->index);
236 bitmap_set_bit (cfgcleanup_altered_bbs, target_block->index);
237
238 /* Remove the GOTO_EXPR as it is not needed. The CFG has all the
239 relevant information we need. */
240 gsi_remove (&gsi, true);
241 retval = true;
242 }
243
244 /* Check for indirect calls that have been turned into
245 noreturn calls. */
246 else if (is_gimple_call (stmt)
247 && gimple_call_noreturn_p (stmt)
248 && remove_fallthru_edge (bb->succs))
249 retval = true;
250
251 return retval;
252 }
253
254 /* Return true if basic block BB does nothing except pass control
255 flow to another block and that we can safely insert a label at
256 the start of the successor block.
257
258 As a precondition, we require that BB be not equal to
259 ENTRY_BLOCK_PTR. */
260
261 static bool
tree_forwarder_block_p(basic_block bb,bool phi_wanted)262 tree_forwarder_block_p (basic_block bb, bool phi_wanted)
263 {
264 gimple_stmt_iterator gsi;
265 location_t locus;
266
267 /* BB must have a single outgoing edge. */
268 if (single_succ_p (bb) != 1
269 /* If PHI_WANTED is false, BB must not have any PHI nodes.
270 Otherwise, BB must have PHI nodes. */
271 || gimple_seq_empty_p (phi_nodes (bb)) == phi_wanted
272 /* BB may not be a predecessor of EXIT_BLOCK_PTR. */
273 || single_succ (bb) == EXIT_BLOCK_PTR
274 /* Nor should this be an infinite loop. */
275 || single_succ (bb) == bb
276 /* BB may not have an abnormal outgoing edge. */
277 || (single_succ_edge (bb)->flags & EDGE_ABNORMAL))
278 return false;
279
280 gcc_checking_assert (bb != ENTRY_BLOCK_PTR);
281
282 locus = single_succ_edge (bb)->goto_locus;
283
284 /* There should not be an edge coming from entry, or an EH edge. */
285 {
286 edge_iterator ei;
287 edge e;
288
289 FOR_EACH_EDGE (e, ei, bb->preds)
290 if (e->src == ENTRY_BLOCK_PTR || (e->flags & EDGE_EH))
291 return false;
292 /* If goto_locus of any of the edges differs, prevent removing
293 the forwarder block for -O0. */
294 else if (optimize == 0 && e->goto_locus != locus)
295 return false;
296 }
297
298 /* Now walk through the statements backward. We can ignore labels,
299 anything else means this is not a forwarder block. */
300 for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi_prev (&gsi))
301 {
302 gimple stmt = gsi_stmt (gsi);
303
304 switch (gimple_code (stmt))
305 {
306 case GIMPLE_LABEL:
307 if (DECL_NONLOCAL (gimple_label_label (stmt)))
308 return false;
309 if (optimize == 0 && gimple_location (stmt) != locus)
310 return false;
311 break;
312
313 /* ??? For now, hope there's a corresponding debug
314 assignment at the destination. */
315 case GIMPLE_DEBUG:
316 break;
317
318 default:
319 return false;
320 }
321 }
322
323 if (current_loops)
324 {
325 basic_block dest;
326 /* Protect loop latches, headers and preheaders. */
327 if (bb->loop_father->header == bb)
328 return false;
329 dest = EDGE_SUCC (bb, 0)->dest;
330
331 if (dest->loop_father->header == dest)
332 return false;
333 }
334 return true;
335 }
336
337 /* If all the PHI nodes in DEST have alternatives for E1 and E2 and
338 those alternatives are equal in each of the PHI nodes, then return
339 true, else return false. */
340
341 static bool
phi_alternatives_equal(basic_block dest,edge e1,edge e2)342 phi_alternatives_equal (basic_block dest, edge e1, edge e2)
343 {
344 int n1 = e1->dest_idx;
345 int n2 = e2->dest_idx;
346 gimple_stmt_iterator gsi;
347
348 for (gsi = gsi_start_phis (dest); !gsi_end_p (gsi); gsi_next (&gsi))
349 {
350 gimple phi = gsi_stmt (gsi);
351 tree val1 = gimple_phi_arg_def (phi, n1);
352 tree val2 = gimple_phi_arg_def (phi, n2);
353
354 gcc_assert (val1 != NULL_TREE);
355 gcc_assert (val2 != NULL_TREE);
356
357 if (!operand_equal_for_phi_arg_p (val1, val2))
358 return false;
359 }
360
361 return true;
362 }
363
364 /* Removes forwarder block BB. Returns false if this failed. */
365
366 static bool
remove_forwarder_block(basic_block bb)367 remove_forwarder_block (basic_block bb)
368 {
369 edge succ = single_succ_edge (bb), e, s;
370 basic_block dest = succ->dest;
371 gimple label;
372 edge_iterator ei;
373 gimple_stmt_iterator gsi, gsi_to;
374 bool can_move_debug_stmts;
375
376 /* We check for infinite loops already in tree_forwarder_block_p.
377 However it may happen that the infinite loop is created
378 afterwards due to removal of forwarders. */
379 if (dest == bb)
380 return false;
381
382 /* If the destination block consists of a nonlocal label or is a
383 EH landing pad, do not merge it. */
384 label = first_stmt (dest);
385 if (label
386 && gimple_code (label) == GIMPLE_LABEL
387 && (DECL_NONLOCAL (gimple_label_label (label))
388 || EH_LANDING_PAD_NR (gimple_label_label (label)) != 0))
389 return false;
390
391 /* If there is an abnormal edge to basic block BB, but not into
392 dest, problems might occur during removal of the phi node at out
393 of ssa due to overlapping live ranges of registers.
394
395 If there is an abnormal edge in DEST, the problems would occur
396 anyway since cleanup_dead_labels would then merge the labels for
397 two different eh regions, and rest of exception handling code
398 does not like it.
399
400 So if there is an abnormal edge to BB, proceed only if there is
401 no abnormal edge to DEST and there are no phi nodes in DEST. */
402 if (bb_has_abnormal_pred (bb)
403 && (bb_has_abnormal_pred (dest)
404 || !gimple_seq_empty_p (phi_nodes (dest))))
405 return false;
406
407 /* If there are phi nodes in DEST, and some of the blocks that are
408 predecessors of BB are also predecessors of DEST, check that the
409 phi node arguments match. */
410 if (!gimple_seq_empty_p (phi_nodes (dest)))
411 {
412 FOR_EACH_EDGE (e, ei, bb->preds)
413 {
414 s = find_edge (e->src, dest);
415 if (!s)
416 continue;
417
418 if (!phi_alternatives_equal (dest, succ, s))
419 return false;
420 }
421 }
422
423 can_move_debug_stmts = MAY_HAVE_DEBUG_STMTS && single_pred_p (dest);
424
425 /* Redirect the edges. */
426 for (ei = ei_start (bb->preds); (e = ei_safe_edge (ei)); )
427 {
428 bitmap_set_bit (cfgcleanup_altered_bbs, e->src->index);
429
430 if (e->flags & EDGE_ABNORMAL)
431 {
432 /* If there is an abnormal edge, redirect it anyway, and
433 move the labels to the new block to make it legal. */
434 s = redirect_edge_succ_nodup (e, dest);
435 }
436 else
437 s = redirect_edge_and_branch (e, dest);
438
439 if (s == e)
440 {
441 /* Create arguments for the phi nodes, since the edge was not
442 here before. */
443 for (gsi = gsi_start_phis (dest);
444 !gsi_end_p (gsi);
445 gsi_next (&gsi))
446 {
447 gimple phi = gsi_stmt (gsi);
448 source_location l = gimple_phi_arg_location_from_edge (phi, succ);
449 add_phi_arg (phi, gimple_phi_arg_def (phi, succ->dest_idx), s, l);
450 }
451 }
452 }
453
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); )
461 {
462 tree decl;
463 label = gsi_stmt (gsi);
464 if (is_gimple_debug (label))
465 break;
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))
471 {
472 gsi_remove (&gsi, false);
473 gsi_insert_before (&gsi_to, label, GSI_SAME_STMT);
474 }
475 else
476 gsi_next (&gsi);
477 }
478
479 /* Move debug statements if the destination has a single predecessor. */
480 if (can_move_debug_stmts)
481 {
482 gsi_to = gsi_after_labels (dest);
483 for (gsi = gsi_after_labels (bb); !gsi_end_p (gsi); )
484 {
485 gimple debug = gsi_stmt (gsi);
486 if (!is_gimple_debug (debug))
487 break;
488 gsi_remove (&gsi, false);
489 gsi_insert_before (&gsi_to, debug, GSI_SAME_STMT);
490 }
491 }
492
493 bitmap_set_bit (cfgcleanup_altered_bbs, dest->index);
494
495 /* Update the dominators. */
496 if (dom_info_available_p (CDI_DOMINATORS))
497 {
498 basic_block dom, dombb, domdest;
499
500 dombb = get_immediate_dominator (CDI_DOMINATORS, bb);
501 domdest = get_immediate_dominator (CDI_DOMINATORS, dest);
502 if (domdest == bb)
503 {
504 /* Shortcut to avoid calling (relatively expensive)
505 nearest_common_dominator unless necessary. */
506 dom = dombb;
507 }
508 else
509 dom = nearest_common_dominator (CDI_DOMINATORS, domdest, dombb);
510
511 set_immediate_dominator (CDI_DOMINATORS, dest, dom);
512 }
513
514 /* And kill the forwarder block. */
515 delete_basic_block (bb);
516
517 return true;
518 }
519
520 /* STMT is a call that has been discovered noreturn. Fixup the CFG
521 and remove LHS. Return true if something changed. */
522
523 bool
fixup_noreturn_call(gimple stmt)524 fixup_noreturn_call (gimple stmt)
525 {
526 basic_block bb = gimple_bb (stmt);
527 bool changed = false;
528
529 if (gimple_call_builtin_p (stmt, BUILT_IN_RETURN))
530 return false;
531
532 /* First split basic block if stmt is not last. */
533 if (stmt != gsi_stmt (gsi_last_bb (bb)))
534 split_block (bb, stmt);
535
536 changed |= remove_fallthru_edge (bb->succs);
537
538 /* If there is LHS, remove it. */
539 if (gimple_call_lhs (stmt))
540 {
541 tree op = gimple_call_lhs (stmt);
542 gimple_call_set_lhs (stmt, NULL_TREE);
543
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)
550 {
551 use_operand_p use_p;
552 imm_use_iterator iter;
553 gimple use_stmt;
554 bitmap_iterator bi;
555 unsigned int bb_index;
556
557 bitmap blocks = BITMAP_ALLOC (NULL);
558
559 FOR_EACH_IMM_USE_STMT (use_stmt, iter, op)
560 {
561 if (gimple_code (use_stmt) != GIMPLE_PHI)
562 bitmap_set_bit (blocks, gimple_bb (use_stmt)->index);
563 else
564 FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
565 SET_USE (use_p, error_mark_node);
566 }
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);
571 }
572 update_stmt (stmt);
573 changed = true;
574 }
575 /* Similarly remove VDEF if there is any. */
576 else if (gimple_vdef (stmt))
577 update_stmt (stmt);
578 return changed;
579 }
580
581
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. */
584
585 static bool
split_bbs_on_noreturn_calls(void)586 split_bbs_on_noreturn_calls (void)
587 {
588 bool changed = false;
589 gimple stmt;
590 basic_block bb;
591
592 /* Detect cases where a mid-block call is now known not to return. */
593 if (cfun->gimple_df)
594 while (VEC_length (gimple, MODIFIED_NORETURN_CALLS (cfun)))
595 {
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. */
600 if (bb == NULL
601 || bb->index < NUM_FIXED_BLOCKS
602 || bb->index >= last_basic_block
603 || BASIC_BLOCK (bb->index) != bb
604 || !gimple_call_noreturn_p (stmt))
605 continue;
606
607 changed |= fixup_noreturn_call (stmt);
608 }
609
610 return changed;
611 }
612
613 /* Tries to cleanup cfg in basic block BB. Returns true if anything
614 changes. */
615
616 static bool
cleanup_tree_cfg_bb(basic_block bb)617 cleanup_tree_cfg_bb (basic_block bb)
618 {
619 bool retval = cleanup_control_flow_bb (bb);
620
621 if (tree_forwarder_block_p (bb, false)
622 && remove_forwarder_block (bb))
623 return true;
624
625 /* Merging the blocks may create new opportunities for folding
626 conditional branches (due to the elimination of single-valued PHI
627 nodes). */
628 if (single_succ_p (bb)
629 && can_merge_blocks_p (bb, single_succ (bb)))
630 {
631 merge_blocks (bb, single_succ (bb));
632 return true;
633 }
634
635 return retval;
636 }
637
638 /* Iterate the cfg cleanups, while anything changes. */
639
640 static bool
cleanup_tree_cfg_1(void)641 cleanup_tree_cfg_1 (void)
642 {
643 bool retval = false;
644 basic_block bb;
645 unsigned i, n;
646
647 retval |= split_bbs_on_noreturn_calls ();
648
649 /* Prepare the worklists of altered blocks. */
650 cfgcleanup_altered_bbs = BITMAP_ALLOC (NULL);
651
652 /* During forwarder block cleanup, we may redirect edges out of
653 SWITCH_EXPRs, which can get expensive. So we want to enable
654 recording of edge to CASE_LABEL_EXPR. */
655 start_recording_case_labels ();
656
657 /* Start by iterating over all basic blocks. We cannot use FOR_EACH_BB,
658 since the basic blocks may get removed. */
659 n = last_basic_block;
660 for (i = NUM_FIXED_BLOCKS; i < n; i++)
661 {
662 bb = BASIC_BLOCK (i);
663 if (bb)
664 retval |= cleanup_tree_cfg_bb (bb);
665 }
666
667 /* Now process the altered blocks, as long as any are available. */
668 while (!bitmap_empty_p (cfgcleanup_altered_bbs))
669 {
670 i = bitmap_first_set_bit (cfgcleanup_altered_bbs);
671 bitmap_clear_bit (cfgcleanup_altered_bbs, i);
672 if (i < NUM_FIXED_BLOCKS)
673 continue;
674
675 bb = BASIC_BLOCK (i);
676 if (!bb)
677 continue;
678
679 retval |= cleanup_tree_cfg_bb (bb);
680
681 /* Rerun split_bbs_on_noreturn_calls, in case we have altered any noreturn
682 calls. */
683 retval |= split_bbs_on_noreturn_calls ();
684 }
685
686 end_recording_case_labels ();
687 BITMAP_FREE (cfgcleanup_altered_bbs);
688 return retval;
689 }
690
691
692 /* Remove unreachable blocks and other miscellaneous clean up work.
693 Return true if the flowgraph was modified, false otherwise. */
694
695 static bool
cleanup_tree_cfg_noloop(void)696 cleanup_tree_cfg_noloop (void)
697 {
698 bool changed;
699
700 timevar_push (TV_TREE_CLEANUP_CFG);
701
702 /* Iterate until there are no more cleanups left to do. If any
703 iteration changed the flowgraph, set CHANGED to true.
704
705 If dominance information is available, there cannot be any unreachable
706 blocks. */
707 if (!dom_info_available_p (CDI_DOMINATORS))
708 {
709 changed = delete_unreachable_blocks ();
710 calculate_dominance_info (CDI_DOMINATORS);
711 }
712 else
713 {
714 #ifdef ENABLE_CHECKING
715 verify_dominators (CDI_DOMINATORS);
716 #endif
717 changed = false;
718 }
719
720 changed |= cleanup_tree_cfg_1 ();
721
722 gcc_assert (dom_info_available_p (CDI_DOMINATORS));
723 compact_blocks ();
724
725 #ifdef ENABLE_CHECKING
726 verify_flow_info ();
727 #endif
728
729 timevar_pop (TV_TREE_CLEANUP_CFG);
730
731 if (changed && current_loops)
732 loops_state_set (LOOPS_NEED_FIXUP);
733
734 return changed;
735 }
736
737 /* Repairs loop structures. */
738
739 static void
repair_loop_structures(void)740 repair_loop_structures (void)
741 {
742 bitmap changed_bbs;
743
744 timevar_push (TV_REPAIR_LOOPS);
745 changed_bbs = BITMAP_ALLOC (NULL);
746 fix_loop_structure (changed_bbs);
747
748 /* This usually does nothing. But sometimes parts of cfg that originally
749 were inside a loop get out of it due to edge removal (since they
750 become unreachable by back edges from latch). */
751 if (loops_state_satisfies_p (LOOP_CLOSED_SSA))
752 rewrite_into_loop_closed_ssa (changed_bbs, TODO_update_ssa);
753
754 BITMAP_FREE (changed_bbs);
755
756 #ifdef ENABLE_CHECKING
757 verify_loop_structure ();
758 #endif
759 scev_reset ();
760
761 loops_state_clear (LOOPS_NEED_FIXUP);
762 timevar_pop (TV_REPAIR_LOOPS);
763 }
764
765 /* Cleanup cfg and repair loop structures. */
766
767 bool
cleanup_tree_cfg(void)768 cleanup_tree_cfg (void)
769 {
770 bool changed = cleanup_tree_cfg_noloop ();
771
772 if (current_loops != NULL
773 && loops_state_satisfies_p (LOOPS_NEED_FIXUP))
774 repair_loop_structures ();
775
776 return changed;
777 }
778
779 /* Merge the PHI nodes at BB into those at BB's sole successor. */
780
781 static void
remove_forwarder_block_with_phi(basic_block bb)782 remove_forwarder_block_with_phi (basic_block bb)
783 {
784 edge succ = single_succ_edge (bb);
785 basic_block dest = succ->dest;
786 gimple label;
787 basic_block dombb, domdest, dom;
788
789 /* We check for infinite loops already in tree_forwarder_block_p.
790 However it may happen that the infinite loop is created
791 afterwards due to removal of forwarders. */
792 if (dest == bb)
793 return;
794
795 /* If the destination block consists of a nonlocal label, do not
796 merge it. */
797 label = first_stmt (dest);
798 if (label
799 && gimple_code (label) == GIMPLE_LABEL
800 && DECL_NONLOCAL (gimple_label_label (label)))
801 return;
802
803 /* Redirect each incoming edge to BB to DEST. */
804 while (EDGE_COUNT (bb->preds) > 0)
805 {
806 edge e = EDGE_PRED (bb, 0), s;
807 gimple_stmt_iterator gsi;
808
809 s = find_edge (e->src, dest);
810 if (s)
811 {
812 /* We already have an edge S from E->src to DEST. If S and
813 E->dest's sole successor edge have the same PHI arguments
814 at DEST, redirect S to DEST. */
815 if (phi_alternatives_equal (dest, s, succ))
816 {
817 e = redirect_edge_and_branch (e, dest);
818 redirect_edge_var_map_clear (e);
819 continue;
820 }
821
822 /* PHI arguments are different. Create a forwarder block by
823 splitting E so that we can merge PHI arguments on E to
824 DEST. */
825 e = single_succ_edge (split_edge (e));
826 }
827
828 s = redirect_edge_and_branch (e, dest);
829
830 /* redirect_edge_and_branch must not create a new edge. */
831 gcc_assert (s == e);
832
833 /* Add to the PHI nodes at DEST each PHI argument removed at the
834 destination of E. */
835 for (gsi = gsi_start_phis (dest);
836 !gsi_end_p (gsi);
837 gsi_next (&gsi))
838 {
839 gimple phi = gsi_stmt (gsi);
840 tree def = gimple_phi_arg_def (phi, succ->dest_idx);
841 source_location locus = gimple_phi_arg_location_from_edge (phi, succ);
842
843 if (TREE_CODE (def) == SSA_NAME)
844 {
845 edge_var_map_vector head;
846 edge_var_map *vm;
847 size_t i;
848
849 /* If DEF is one of the results of PHI nodes removed during
850 redirection, replace it with the PHI argument that used
851 to be on E. */
852 head = redirect_edge_var_map_vector (e);
853 FOR_EACH_VEC_ELT (edge_var_map, head, i, vm)
854 {
855 tree old_arg = redirect_edge_var_map_result (vm);
856 tree new_arg = redirect_edge_var_map_def (vm);
857
858 if (def == old_arg)
859 {
860 def = new_arg;
861 locus = redirect_edge_var_map_location (vm);
862 break;
863 }
864 }
865 }
866
867 add_phi_arg (phi, def, s, locus);
868 }
869
870 redirect_edge_var_map_clear (e);
871 }
872
873 /* Update the dominators. */
874 dombb = get_immediate_dominator (CDI_DOMINATORS, bb);
875 domdest = get_immediate_dominator (CDI_DOMINATORS, dest);
876 if (domdest == bb)
877 {
878 /* Shortcut to avoid calling (relatively expensive)
879 nearest_common_dominator unless necessary. */
880 dom = dombb;
881 }
882 else
883 dom = nearest_common_dominator (CDI_DOMINATORS, domdest, dombb);
884
885 set_immediate_dominator (CDI_DOMINATORS, dest, dom);
886
887 /* Remove BB since all of BB's incoming edges have been redirected
888 to DEST. */
889 delete_basic_block (bb);
890 }
891
892 /* This pass merges PHI nodes if one feeds into another. For example,
893 suppose we have the following:
894
895 goto <bb 9> (<L9>);
896
897 <L8>:;
898 tem_17 = foo ();
899
900 # tem_6 = PHI <tem_17(8), tem_23(7)>;
901 <L9>:;
902
903 # tem_3 = PHI <tem_6(9), tem_2(5)>;
904 <L10>:;
905
906 Then we merge the first PHI node into the second one like so:
907
908 goto <bb 9> (<L10>);
909
910 <L8>:;
911 tem_17 = foo ();
912
913 # tem_3 = PHI <tem_23(7), tem_2(5), tem_17(8)>;
914 <L10>:;
915 */
916
917 static unsigned int
merge_phi_nodes(void)918 merge_phi_nodes (void)
919 {
920 basic_block *worklist = XNEWVEC (basic_block, n_basic_blocks);
921 basic_block *current = worklist;
922 basic_block bb;
923
924 calculate_dominance_info (CDI_DOMINATORS);
925
926 /* Find all PHI nodes that we may be able to merge. */
927 FOR_EACH_BB (bb)
928 {
929 basic_block dest;
930
931 /* Look for a forwarder block with PHI nodes. */
932 if (!tree_forwarder_block_p (bb, true))
933 continue;
934
935 dest = single_succ (bb);
936
937 /* We have to feed into another basic block with PHI
938 nodes. */
939 if (gimple_seq_empty_p (phi_nodes (dest))
940 /* We don't want to deal with a basic block with
941 abnormal edges. */
942 || bb_has_abnormal_pred (bb))
943 continue;
944
945 if (!dominated_by_p (CDI_DOMINATORS, dest, bb))
946 {
947 /* If BB does not dominate DEST, then the PHI nodes at
948 DEST must be the only users of the results of the PHI
949 nodes at BB. */
950 *current++ = bb;
951 }
952 else
953 {
954 gimple_stmt_iterator gsi;
955 unsigned int dest_idx = single_succ_edge (bb)->dest_idx;
956
957 /* BB dominates DEST. There may be many users of the PHI
958 nodes in BB. However, there is still a trivial case we
959 can handle. If the result of every PHI in BB is used
960 only by a PHI in DEST, then we can trivially merge the
961 PHI nodes from BB into DEST. */
962 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi);
963 gsi_next (&gsi))
964 {
965 gimple phi = gsi_stmt (gsi);
966 tree result = gimple_phi_result (phi);
967 use_operand_p imm_use;
968 gimple use_stmt;
969
970 /* If the PHI's result is never used, then we can just
971 ignore it. */
972 if (has_zero_uses (result))
973 continue;
974
975 /* Get the single use of the result of this PHI node. */
976 if (!single_imm_use (result, &imm_use, &use_stmt)
977 || gimple_code (use_stmt) != GIMPLE_PHI
978 || gimple_bb (use_stmt) != dest
979 || gimple_phi_arg_def (use_stmt, dest_idx) != result)
980 break;
981 }
982
983 /* If the loop above iterated through all the PHI nodes
984 in BB, then we can merge the PHIs from BB into DEST. */
985 if (gsi_end_p (gsi))
986 *current++ = bb;
987 }
988 }
989
990 /* Now let's drain WORKLIST. */
991 while (current != worklist)
992 {
993 bb = *--current;
994 remove_forwarder_block_with_phi (bb);
995 }
996
997 free (worklist);
998 return 0;
999 }
1000
1001 static bool
gate_merge_phi(void)1002 gate_merge_phi (void)
1003 {
1004 return 1;
1005 }
1006
1007 struct gimple_opt_pass pass_merge_phi =
1008 {
1009 {
1010 GIMPLE_PASS,
1011 "mergephi", /* name */
1012 gate_merge_phi, /* gate */
1013 merge_phi_nodes, /* execute */
1014 NULL, /* sub */
1015 NULL, /* next */
1016 0, /* static_pass_number */
1017 TV_TREE_MERGE_PHI, /* tv_id */
1018 PROP_cfg | PROP_ssa, /* properties_required */
1019 0, /* properties_provided */
1020 0, /* properties_destroyed */
1021 0, /* todo_flags_start */
1022 TODO_ggc_collect /* todo_flags_finish */
1023 | TODO_verify_ssa
1024 }
1025 };
1026