1 /* Control flow optimization code for GNU compiler.
2 Copyright (C) 1987, 1988, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
3 1999, 2000, 2001, 2002, 2003, 2004, 2005 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 it under
8 the terms of the GNU General Public License as published by the Free
9 Software Foundation; either version 2, or (at your option) any later
10 version.
11
12 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
13 WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
15 for more details.
16
17 You should have received a copy of the GNU General Public License
18 along with GCC; see the file COPYING. If not, write to the Free
19 Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
20 02110-1301, USA. */
21
22 /* This file contains optimizer of the control flow. The main entry point is
23 cleanup_cfg. Following optimizations are performed:
24
25 - Unreachable blocks removal
26 - Edge forwarding (edge to the forwarder block is forwarded to its
27 successor. Simplification of the branch instruction is performed by
28 underlying infrastructure so branch can be converted to simplejump or
29 eliminated).
30 - Cross jumping (tail merging)
31 - Conditional jump-around-simplejump simplification
32 - Basic block merging. */
33
34 #include "config.h"
35 #include "system.h"
36 #include "coretypes.h"
37 #include "tm.h"
38 #include "rtl.h"
39 #include "hard-reg-set.h"
40 #include "regs.h"
41 #include "timevar.h"
42 #include "output.h"
43 #include "insn-config.h"
44 #include "flags.h"
45 #include "recog.h"
46 #include "toplev.h"
47 #include "cselib.h"
48 #include "params.h"
49 #include "tm_p.h"
50 #include "target.h"
51 #include "cfglayout.h"
52 #include "emit-rtl.h"
53 #include "tree-pass.h"
54 #include "cfgloop.h"
55 #include "expr.h"
56
57 #define FORWARDER_BLOCK_P(BB) ((BB)->flags & BB_FORWARDER_BLOCK)
58
59 /* Set to true when we are running first pass of try_optimize_cfg loop. */
60 static bool first_pass;
61 static bool try_crossjump_to_edge (int, edge, edge);
62 static bool try_crossjump_bb (int, basic_block);
63 static bool outgoing_edges_match (int, basic_block, basic_block);
64 static int flow_find_cross_jump (int, basic_block, basic_block, rtx *, rtx *);
65 static bool old_insns_match_p (int, rtx, rtx);
66
67 static void merge_blocks_move_predecessor_nojumps (basic_block, basic_block);
68 static void merge_blocks_move_successor_nojumps (basic_block, basic_block);
69 static bool try_optimize_cfg (int);
70 static bool try_simplify_condjump (basic_block);
71 static bool try_forward_edges (int, basic_block);
72 static edge thread_jump (int, edge, basic_block);
73 static bool mark_effect (rtx, bitmap);
74 static void notice_new_block (basic_block);
75 static void update_forwarder_flag (basic_block);
76 static int mentions_nonequal_regs (rtx *, void *);
77 static void merge_memattrs (rtx, rtx);
78
79 /* Set flags for newly created block. */
80
81 static void
notice_new_block(basic_block bb)82 notice_new_block (basic_block bb)
83 {
84 if (!bb)
85 return;
86
87 if (forwarder_block_p (bb))
88 bb->flags |= BB_FORWARDER_BLOCK;
89 }
90
91 /* Recompute forwarder flag after block has been modified. */
92
93 static void
update_forwarder_flag(basic_block bb)94 update_forwarder_flag (basic_block bb)
95 {
96 if (forwarder_block_p (bb))
97 bb->flags |= BB_FORWARDER_BLOCK;
98 else
99 bb->flags &= ~BB_FORWARDER_BLOCK;
100 }
101
102 /* Simplify a conditional jump around an unconditional jump.
103 Return true if something changed. */
104
105 static bool
try_simplify_condjump(basic_block cbranch_block)106 try_simplify_condjump (basic_block cbranch_block)
107 {
108 basic_block jump_block, jump_dest_block, cbranch_dest_block;
109 edge cbranch_jump_edge, cbranch_fallthru_edge;
110 rtx cbranch_insn;
111
112 /* Verify that there are exactly two successors. */
113 if (EDGE_COUNT (cbranch_block->succs) != 2)
114 return false;
115
116 /* Verify that we've got a normal conditional branch at the end
117 of the block. */
118 cbranch_insn = BB_END (cbranch_block);
119 if (!any_condjump_p (cbranch_insn))
120 return false;
121
122 cbranch_fallthru_edge = FALLTHRU_EDGE (cbranch_block);
123 cbranch_jump_edge = BRANCH_EDGE (cbranch_block);
124
125 /* The next block must not have multiple predecessors, must not
126 be the last block in the function, and must contain just the
127 unconditional jump. */
128 jump_block = cbranch_fallthru_edge->dest;
129 if (!single_pred_p (jump_block)
130 || jump_block->next_bb == EXIT_BLOCK_PTR
131 || !FORWARDER_BLOCK_P (jump_block))
132 return false;
133 jump_dest_block = single_succ (jump_block);
134
135 /* If we are partitioning hot/cold basic blocks, we don't want to
136 mess up unconditional or indirect jumps that cross between hot
137 and cold sections.
138
139 Basic block partitioning may result in some jumps that appear to
140 be optimizable (or blocks that appear to be mergeable), but which really
141 must be left untouched (they are required to make it safely across
142 partition boundaries). See the comments at the top of
143 bb-reorder.c:partition_hot_cold_basic_blocks for complete details. */
144
145 if (BB_PARTITION (jump_block) != BB_PARTITION (jump_dest_block)
146 || (cbranch_jump_edge->flags & EDGE_CROSSING))
147 return false;
148
149 /* The conditional branch must target the block after the
150 unconditional branch. */
151 cbranch_dest_block = cbranch_jump_edge->dest;
152
153 if (cbranch_dest_block == EXIT_BLOCK_PTR
154 || !can_fallthru (jump_block, cbranch_dest_block))
155 return false;
156
157 /* Invert the conditional branch. */
158 if (!invert_jump (cbranch_insn, block_label (jump_dest_block), 0))
159 return false;
160
161 if (dump_file)
162 fprintf (dump_file, "Simplifying condjump %i around jump %i\n",
163 INSN_UID (cbranch_insn), INSN_UID (BB_END (jump_block)));
164
165 /* Success. Update the CFG to match. Note that after this point
166 the edge variable names appear backwards; the redirection is done
167 this way to preserve edge profile data. */
168 cbranch_jump_edge = redirect_edge_succ_nodup (cbranch_jump_edge,
169 cbranch_dest_block);
170 cbranch_fallthru_edge = redirect_edge_succ_nodup (cbranch_fallthru_edge,
171 jump_dest_block);
172 cbranch_jump_edge->flags |= EDGE_FALLTHRU;
173 cbranch_fallthru_edge->flags &= ~EDGE_FALLTHRU;
174 update_br_prob_note (cbranch_block);
175
176 /* Delete the block with the unconditional jump, and clean up the mess. */
177 delete_basic_block (jump_block);
178 tidy_fallthru_edge (cbranch_jump_edge);
179 update_forwarder_flag (cbranch_block);
180
181 return true;
182 }
183
184 /* Attempt to prove that operation is NOOP using CSElib or mark the effect
185 on register. Used by jump threading. */
186
187 static bool
mark_effect(rtx exp,regset nonequal)188 mark_effect (rtx exp, regset nonequal)
189 {
190 int regno;
191 rtx dest;
192 switch (GET_CODE (exp))
193 {
194 /* In case we do clobber the register, mark it as equal, as we know the
195 value is dead so it don't have to match. */
196 case CLOBBER:
197 if (REG_P (XEXP (exp, 0)))
198 {
199 dest = XEXP (exp, 0);
200 regno = REGNO (dest);
201 CLEAR_REGNO_REG_SET (nonequal, regno);
202 if (regno < FIRST_PSEUDO_REGISTER)
203 {
204 int n = hard_regno_nregs[regno][GET_MODE (dest)];
205 while (--n > 0)
206 CLEAR_REGNO_REG_SET (nonequal, regno + n);
207 }
208 }
209 return false;
210
211 case SET:
212 if (rtx_equal_for_cselib_p (SET_DEST (exp), SET_SRC (exp)))
213 return false;
214 dest = SET_DEST (exp);
215 if (dest == pc_rtx)
216 return false;
217 if (!REG_P (dest))
218 return true;
219 regno = REGNO (dest);
220 SET_REGNO_REG_SET (nonequal, regno);
221 if (regno < FIRST_PSEUDO_REGISTER)
222 {
223 int n = hard_regno_nregs[regno][GET_MODE (dest)];
224 while (--n > 0)
225 SET_REGNO_REG_SET (nonequal, regno + n);
226 }
227 return false;
228
229 default:
230 return false;
231 }
232 }
233
234 /* Return nonzero if X is a register set in regset DATA.
235 Called via for_each_rtx. */
236 static int
mentions_nonequal_regs(rtx * x,void * data)237 mentions_nonequal_regs (rtx *x, void *data)
238 {
239 regset nonequal = (regset) data;
240 if (REG_P (*x))
241 {
242 int regno;
243
244 regno = REGNO (*x);
245 if (REGNO_REG_SET_P (nonequal, regno))
246 return 1;
247 if (regno < FIRST_PSEUDO_REGISTER)
248 {
249 int n = hard_regno_nregs[regno][GET_MODE (*x)];
250 while (--n > 0)
251 if (REGNO_REG_SET_P (nonequal, regno + n))
252 return 1;
253 }
254 }
255 return 0;
256 }
257 /* Attempt to prove that the basic block B will have no side effects and
258 always continues in the same edge if reached via E. Return the edge
259 if exist, NULL otherwise. */
260
261 static edge
thread_jump(int mode,edge e,basic_block b)262 thread_jump (int mode, edge e, basic_block b)
263 {
264 rtx set1, set2, cond1, cond2, insn;
265 enum rtx_code code1, code2, reversed_code2;
266 bool reverse1 = false;
267 unsigned i;
268 regset nonequal;
269 bool failed = false;
270 reg_set_iterator rsi;
271
272 if (b->flags & BB_NONTHREADABLE_BLOCK)
273 return NULL;
274
275 /* At the moment, we do handle only conditional jumps, but later we may
276 want to extend this code to tablejumps and others. */
277 if (EDGE_COUNT (e->src->succs) != 2)
278 return NULL;
279 if (EDGE_COUNT (b->succs) != 2)
280 {
281 b->flags |= BB_NONTHREADABLE_BLOCK;
282 return NULL;
283 }
284
285 /* Second branch must end with onlyjump, as we will eliminate the jump. */
286 if (!any_condjump_p (BB_END (e->src)))
287 return NULL;
288
289 if (!any_condjump_p (BB_END (b)) || !onlyjump_p (BB_END (b)))
290 {
291 b->flags |= BB_NONTHREADABLE_BLOCK;
292 return NULL;
293 }
294
295 set1 = pc_set (BB_END (e->src));
296 set2 = pc_set (BB_END (b));
297 if (((e->flags & EDGE_FALLTHRU) != 0)
298 != (XEXP (SET_SRC (set1), 1) == pc_rtx))
299 reverse1 = true;
300
301 cond1 = XEXP (SET_SRC (set1), 0);
302 cond2 = XEXP (SET_SRC (set2), 0);
303 if (reverse1)
304 code1 = reversed_comparison_code (cond1, BB_END (e->src));
305 else
306 code1 = GET_CODE (cond1);
307
308 code2 = GET_CODE (cond2);
309 reversed_code2 = reversed_comparison_code (cond2, BB_END (b));
310
311 if (!comparison_dominates_p (code1, code2)
312 && !comparison_dominates_p (code1, reversed_code2))
313 return NULL;
314
315 /* Ensure that the comparison operators are equivalent.
316 ??? This is far too pessimistic. We should allow swapped operands,
317 different CCmodes, or for example comparisons for interval, that
318 dominate even when operands are not equivalent. */
319 if (!rtx_equal_p (XEXP (cond1, 0), XEXP (cond2, 0))
320 || !rtx_equal_p (XEXP (cond1, 1), XEXP (cond2, 1)))
321 return NULL;
322
323 /* Short circuit cases where block B contains some side effects, as we can't
324 safely bypass it. */
325 for (insn = NEXT_INSN (BB_HEAD (b)); insn != NEXT_INSN (BB_END (b));
326 insn = NEXT_INSN (insn))
327 if (INSN_P (insn) && side_effects_p (PATTERN (insn)))
328 {
329 b->flags |= BB_NONTHREADABLE_BLOCK;
330 return NULL;
331 }
332
333 cselib_init (false);
334
335 /* First process all values computed in the source basic block. */
336 for (insn = NEXT_INSN (BB_HEAD (e->src));
337 insn != NEXT_INSN (BB_END (e->src));
338 insn = NEXT_INSN (insn))
339 if (INSN_P (insn))
340 cselib_process_insn (insn);
341
342 nonequal = BITMAP_ALLOC (NULL);
343 CLEAR_REG_SET (nonequal);
344
345 /* Now assume that we've continued by the edge E to B and continue
346 processing as if it were same basic block.
347 Our goal is to prove that whole block is an NOOP. */
348
349 for (insn = NEXT_INSN (BB_HEAD (b));
350 insn != NEXT_INSN (BB_END (b)) && !failed;
351 insn = NEXT_INSN (insn))
352 {
353 if (INSN_P (insn))
354 {
355 rtx pat = PATTERN (insn);
356
357 if (GET_CODE (pat) == PARALLEL)
358 {
359 for (i = 0; i < (unsigned)XVECLEN (pat, 0); i++)
360 failed |= mark_effect (XVECEXP (pat, 0, i), nonequal);
361 }
362 else
363 failed |= mark_effect (pat, nonequal);
364 }
365
366 cselib_process_insn (insn);
367 }
368
369 /* Later we should clear nonequal of dead registers. So far we don't
370 have life information in cfg_cleanup. */
371 if (failed)
372 {
373 b->flags |= BB_NONTHREADABLE_BLOCK;
374 goto failed_exit;
375 }
376
377 /* cond2 must not mention any register that is not equal to the
378 former block. */
379 if (for_each_rtx (&cond2, mentions_nonequal_regs, nonequal))
380 goto failed_exit;
381
382 /* In case liveness information is available, we need to prove equivalence
383 only of the live values. */
384 if (mode & CLEANUP_UPDATE_LIFE)
385 AND_REG_SET (nonequal, b->il.rtl->global_live_at_end);
386
387 EXECUTE_IF_SET_IN_REG_SET (nonequal, 0, i, rsi)
388 goto failed_exit;
389
390 BITMAP_FREE (nonequal);
391 cselib_finish ();
392 if ((comparison_dominates_p (code1, code2) != 0)
393 != (XEXP (SET_SRC (set2), 1) == pc_rtx))
394 return BRANCH_EDGE (b);
395 else
396 return FALLTHRU_EDGE (b);
397
398 failed_exit:
399 BITMAP_FREE (nonequal);
400 cselib_finish ();
401 return NULL;
402 }
403
404 /* Attempt to forward edges leaving basic block B.
405 Return true if successful. */
406
407 static bool
try_forward_edges(int mode,basic_block b)408 try_forward_edges (int mode, basic_block b)
409 {
410 bool changed = false;
411 edge_iterator ei;
412 edge e, *threaded_edges = NULL;
413
414 /* If we are partitioning hot/cold basic blocks, we don't want to
415 mess up unconditional or indirect jumps that cross between hot
416 and cold sections.
417
418 Basic block partitioning may result in some jumps that appear to
419 be optimizable (or blocks that appear to be mergeable), but which really m
420 ust be left untouched (they are required to make it safely across
421 partition boundaries). See the comments at the top of
422 bb-reorder.c:partition_hot_cold_basic_blocks for complete details. */
423
424 if (find_reg_note (BB_END (b), REG_CROSSING_JUMP, NULL_RTX))
425 return false;
426
427 for (ei = ei_start (b->succs); (e = ei_safe_edge (ei)); )
428 {
429 basic_block target, first;
430 int counter;
431 bool threaded = false;
432 int nthreaded_edges = 0;
433 bool may_thread = first_pass | (b->flags & BB_DIRTY);
434
435 /* Skip complex edges because we don't know how to update them.
436
437 Still handle fallthru edges, as we can succeed to forward fallthru
438 edge to the same place as the branch edge of conditional branch
439 and turn conditional branch to an unconditional branch. */
440 if (e->flags & EDGE_COMPLEX)
441 {
442 ei_next (&ei);
443 continue;
444 }
445
446 target = first = e->dest;
447 counter = NUM_FIXED_BLOCKS;
448
449 /* If we are partitioning hot/cold basic_blocks, we don't want to mess
450 up jumps that cross between hot/cold sections.
451
452 Basic block partitioning may result in some jumps that appear
453 to be optimizable (or blocks that appear to be mergeable), but which
454 really must be left untouched (they are required to make it safely
455 across partition boundaries). See the comments at the top of
456 bb-reorder.c:partition_hot_cold_basic_blocks for complete
457 details. */
458
459 if (first != EXIT_BLOCK_PTR
460 && find_reg_note (BB_END (first), REG_CROSSING_JUMP, NULL_RTX))
461 return false;
462
463 while (counter < n_basic_blocks)
464 {
465 basic_block new_target = NULL;
466 bool new_target_threaded = false;
467 may_thread |= target->flags & BB_DIRTY;
468
469 if (FORWARDER_BLOCK_P (target)
470 && !(single_succ_edge (target)->flags & EDGE_CROSSING)
471 && single_succ (target) != EXIT_BLOCK_PTR)
472 {
473 /* Bypass trivial infinite loops. */
474 new_target = single_succ (target);
475 if (target == new_target)
476 counter = n_basic_blocks;
477 }
478
479 /* Allow to thread only over one edge at time to simplify updating
480 of probabilities. */
481 else if ((mode & CLEANUP_THREADING) && may_thread)
482 {
483 edge t = thread_jump (mode, e, target);
484 if (t)
485 {
486 if (!threaded_edges)
487 threaded_edges = XNEWVEC (edge, n_basic_blocks);
488 else
489 {
490 int i;
491
492 /* Detect an infinite loop across blocks not
493 including the start block. */
494 for (i = 0; i < nthreaded_edges; ++i)
495 if (threaded_edges[i] == t)
496 break;
497 if (i < nthreaded_edges)
498 {
499 counter = n_basic_blocks;
500 break;
501 }
502 }
503
504 /* Detect an infinite loop across the start block. */
505 if (t->dest == b)
506 break;
507
508 gcc_assert (nthreaded_edges < n_basic_blocks - NUM_FIXED_BLOCKS);
509 threaded_edges[nthreaded_edges++] = t;
510
511 new_target = t->dest;
512 new_target_threaded = true;
513 }
514 }
515
516 if (!new_target)
517 break;
518
519 counter++;
520 target = new_target;
521 threaded |= new_target_threaded;
522 }
523
524 if (counter >= n_basic_blocks)
525 {
526 if (dump_file)
527 fprintf (dump_file, "Infinite loop in BB %i.\n",
528 target->index);
529 }
530 else if (target == first)
531 ; /* We didn't do anything. */
532 else
533 {
534 /* Save the values now, as the edge may get removed. */
535 gcov_type edge_count = e->count;
536 int edge_probability = e->probability;
537 int edge_frequency;
538 int n = 0;
539
540 /* Don't force if target is exit block. */
541 if (threaded && target != EXIT_BLOCK_PTR)
542 {
543 notice_new_block (redirect_edge_and_branch_force (e, target));
544 if (dump_file)
545 fprintf (dump_file, "Conditionals threaded.\n");
546 }
547 else if (!redirect_edge_and_branch (e, target))
548 {
549 if (dump_file)
550 fprintf (dump_file,
551 "Forwarding edge %i->%i to %i failed.\n",
552 b->index, e->dest->index, target->index);
553 ei_next (&ei);
554 continue;
555 }
556
557 /* We successfully forwarded the edge. Now update profile
558 data: for each edge we traversed in the chain, remove
559 the original edge's execution count. */
560 edge_frequency = ((edge_probability * b->frequency
561 + REG_BR_PROB_BASE / 2)
562 / REG_BR_PROB_BASE);
563
564 if (!FORWARDER_BLOCK_P (b) && forwarder_block_p (b))
565 b->flags |= BB_FORWARDER_BLOCK;
566
567 do
568 {
569 edge t;
570
571 if (!single_succ_p (first))
572 {
573 gcc_assert (n < nthreaded_edges);
574 t = threaded_edges [n++];
575 gcc_assert (t->src == first);
576 update_bb_profile_for_threading (first, edge_frequency,
577 edge_count, t);
578 update_br_prob_note (first);
579 }
580 else
581 {
582 first->count -= edge_count;
583 if (first->count < 0)
584 first->count = 0;
585 first->frequency -= edge_frequency;
586 if (first->frequency < 0)
587 first->frequency = 0;
588 /* It is possible that as the result of
589 threading we've removed edge as it is
590 threaded to the fallthru edge. Avoid
591 getting out of sync. */
592 if (n < nthreaded_edges
593 && first == threaded_edges [n]->src)
594 n++;
595 t = single_succ_edge (first);
596 }
597
598 t->count -= edge_count;
599 if (t->count < 0)
600 t->count = 0;
601 first = t->dest;
602 }
603 while (first != target);
604
605 changed = true;
606 continue;
607 }
608 ei_next (&ei);
609 }
610
611 if (threaded_edges)
612 free (threaded_edges);
613 return changed;
614 }
615
616
617 /* Blocks A and B are to be merged into a single block. A has no incoming
618 fallthru edge, so it can be moved before B without adding or modifying
619 any jumps (aside from the jump from A to B). */
620
621 static void
merge_blocks_move_predecessor_nojumps(basic_block a,basic_block b)622 merge_blocks_move_predecessor_nojumps (basic_block a, basic_block b)
623 {
624 rtx barrier;
625 bool only_notes;
626
627 /* If we are partitioning hot/cold basic blocks, we don't want to
628 mess up unconditional or indirect jumps that cross between hot
629 and cold sections.
630
631 Basic block partitioning may result in some jumps that appear to
632 be optimizable (or blocks that appear to be mergeable), but which really
633 must be left untouched (they are required to make it safely across
634 partition boundaries). See the comments at the top of
635 bb-reorder.c:partition_hot_cold_basic_blocks for complete details. */
636
637 if (BB_PARTITION (a) != BB_PARTITION (b))
638 return;
639
640 barrier = next_nonnote_insn (BB_END (a));
641 gcc_assert (BARRIER_P (barrier));
642 delete_insn (barrier);
643
644 /* Move block and loop notes out of the chain so that we do not
645 disturb their order.
646
647 ??? A better solution would be to squeeze out all the non-nested notes
648 and adjust the block trees appropriately. Even better would be to have
649 a tighter connection between block trees and rtl so that this is not
650 necessary. */
651 only_notes = squeeze_notes (&BB_HEAD (a), &BB_END (a));
652 gcc_assert (!only_notes);
653
654 /* Scramble the insn chain. */
655 if (BB_END (a) != PREV_INSN (BB_HEAD (b)))
656 reorder_insns_nobb (BB_HEAD (a), BB_END (a), PREV_INSN (BB_HEAD (b)));
657 a->flags |= BB_DIRTY;
658
659 if (dump_file)
660 fprintf (dump_file, "Moved block %d before %d and merged.\n",
661 a->index, b->index);
662
663 /* Swap the records for the two blocks around. */
664
665 unlink_block (a);
666 link_block (a, b->prev_bb);
667
668 /* Now blocks A and B are contiguous. Merge them. */
669 merge_blocks (a, b);
670 }
671
672 /* Blocks A and B are to be merged into a single block. B has no outgoing
673 fallthru edge, so it can be moved after A without adding or modifying
674 any jumps (aside from the jump from A to B). */
675
676 static void
merge_blocks_move_successor_nojumps(basic_block a,basic_block b)677 merge_blocks_move_successor_nojumps (basic_block a, basic_block b)
678 {
679 rtx barrier, real_b_end;
680 rtx label, table;
681 bool only_notes;
682
683 /* If we are partitioning hot/cold basic blocks, we don't want to
684 mess up unconditional or indirect jumps that cross between hot
685 and cold sections.
686
687 Basic block partitioning may result in some jumps that appear to
688 be optimizable (or blocks that appear to be mergeable), but which really
689 must be left untouched (they are required to make it safely across
690 partition boundaries). See the comments at the top of
691 bb-reorder.c:partition_hot_cold_basic_blocks for complete details. */
692
693 if (BB_PARTITION (a) != BB_PARTITION (b))
694 return;
695
696 real_b_end = BB_END (b);
697
698 /* If there is a jump table following block B temporarily add the jump table
699 to block B so that it will also be moved to the correct location. */
700 if (tablejump_p (BB_END (b), &label, &table)
701 && prev_active_insn (label) == BB_END (b))
702 {
703 BB_END (b) = table;
704 }
705
706 /* There had better have been a barrier there. Delete it. */
707 barrier = NEXT_INSN (BB_END (b));
708 if (barrier && BARRIER_P (barrier))
709 delete_insn (barrier);
710
711 /* Move block and loop notes out of the chain so that we do not
712 disturb their order.
713
714 ??? A better solution would be to squeeze out all the non-nested notes
715 and adjust the block trees appropriately. Even better would be to have
716 a tighter connection between block trees and rtl so that this is not
717 necessary. */
718 only_notes = squeeze_notes (&BB_HEAD (b), &BB_END (b));
719 gcc_assert (!only_notes);
720
721
722 /* Scramble the insn chain. */
723 reorder_insns_nobb (BB_HEAD (b), BB_END (b), BB_END (a));
724
725 /* Restore the real end of b. */
726 BB_END (b) = real_b_end;
727
728 if (dump_file)
729 fprintf (dump_file, "Moved block %d after %d and merged.\n",
730 b->index, a->index);
731
732 /* Now blocks A and B are contiguous. Merge them. */
733 merge_blocks (a, b);
734 }
735
736 /* Attempt to merge basic blocks that are potentially non-adjacent.
737 Return NULL iff the attempt failed, otherwise return basic block
738 where cleanup_cfg should continue. Because the merging commonly
739 moves basic block away or introduces another optimization
740 possibility, return basic block just before B so cleanup_cfg don't
741 need to iterate.
742
743 It may be good idea to return basic block before C in the case
744 C has been moved after B and originally appeared earlier in the
745 insn sequence, but we have no information available about the
746 relative ordering of these two. Hopefully it is not too common. */
747
748 static basic_block
merge_blocks_move(edge e,basic_block b,basic_block c,int mode)749 merge_blocks_move (edge e, basic_block b, basic_block c, int mode)
750 {
751 basic_block next;
752
753 /* If we are partitioning hot/cold basic blocks, we don't want to
754 mess up unconditional or indirect jumps that cross between hot
755 and cold sections.
756
757 Basic block partitioning may result in some jumps that appear to
758 be optimizable (or blocks that appear to be mergeable), but which really
759 must be left untouched (they are required to make it safely across
760 partition boundaries). See the comments at the top of
761 bb-reorder.c:partition_hot_cold_basic_blocks for complete details. */
762
763 if (BB_PARTITION (b) != BB_PARTITION (c))
764 return NULL;
765
766
767
768 /* If B has a fallthru edge to C, no need to move anything. */
769 if (e->flags & EDGE_FALLTHRU)
770 {
771 int b_index = b->index, c_index = c->index;
772 merge_blocks (b, c);
773 update_forwarder_flag (b);
774
775 if (dump_file)
776 fprintf (dump_file, "Merged %d and %d without moving.\n",
777 b_index, c_index);
778
779 return b->prev_bb == ENTRY_BLOCK_PTR ? b : b->prev_bb;
780 }
781
782 /* Otherwise we will need to move code around. Do that only if expensive
783 transformations are allowed. */
784 else if (mode & CLEANUP_EXPENSIVE)
785 {
786 edge tmp_edge, b_fallthru_edge;
787 bool c_has_outgoing_fallthru;
788 bool b_has_incoming_fallthru;
789 edge_iterator ei;
790
791 /* Avoid overactive code motion, as the forwarder blocks should be
792 eliminated by edge redirection instead. One exception might have
793 been if B is a forwarder block and C has no fallthru edge, but
794 that should be cleaned up by bb-reorder instead. */
795 if (FORWARDER_BLOCK_P (b) || FORWARDER_BLOCK_P (c))
796 return NULL;
797
798 /* We must make sure to not munge nesting of lexical blocks,
799 and loop notes. This is done by squeezing out all the notes
800 and leaving them there to lie. Not ideal, but functional. */
801
802 FOR_EACH_EDGE (tmp_edge, ei, c->succs)
803 if (tmp_edge->flags & EDGE_FALLTHRU)
804 break;
805
806 c_has_outgoing_fallthru = (tmp_edge != NULL);
807
808 FOR_EACH_EDGE (tmp_edge, ei, b->preds)
809 if (tmp_edge->flags & EDGE_FALLTHRU)
810 break;
811
812 b_has_incoming_fallthru = (tmp_edge != NULL);
813 b_fallthru_edge = tmp_edge;
814 next = b->prev_bb;
815 if (next == c)
816 next = next->prev_bb;
817
818 /* Otherwise, we're going to try to move C after B. If C does
819 not have an outgoing fallthru, then it can be moved
820 immediately after B without introducing or modifying jumps. */
821 if (! c_has_outgoing_fallthru)
822 {
823 merge_blocks_move_successor_nojumps (b, c);
824 return next == ENTRY_BLOCK_PTR ? next->next_bb : next;
825 }
826
827 /* If B does not have an incoming fallthru, then it can be moved
828 immediately before C without introducing or modifying jumps.
829 C cannot be the first block, so we do not have to worry about
830 accessing a non-existent block. */
831
832 if (b_has_incoming_fallthru)
833 {
834 basic_block bb;
835
836 if (b_fallthru_edge->src == ENTRY_BLOCK_PTR)
837 return NULL;
838 bb = force_nonfallthru (b_fallthru_edge);
839 if (bb)
840 notice_new_block (bb);
841 }
842
843 merge_blocks_move_predecessor_nojumps (b, c);
844 return next == ENTRY_BLOCK_PTR ? next->next_bb : next;
845 }
846
847 return NULL;
848 }
849
850
851 /* Removes the memory attributes of MEM expression
852 if they are not equal. */
853
854 void
merge_memattrs(rtx x,rtx y)855 merge_memattrs (rtx x, rtx y)
856 {
857 int i;
858 int j;
859 enum rtx_code code;
860 const char *fmt;
861
862 if (x == y)
863 return;
864 if (x == 0 || y == 0)
865 return;
866
867 code = GET_CODE (x);
868
869 if (code != GET_CODE (y))
870 return;
871
872 if (GET_MODE (x) != GET_MODE (y))
873 return;
874
875 if (code == MEM && MEM_ATTRS (x) != MEM_ATTRS (y))
876 {
877 if (! MEM_ATTRS (x))
878 MEM_ATTRS (y) = 0;
879 else if (! MEM_ATTRS (y))
880 MEM_ATTRS (x) = 0;
881 else
882 {
883 rtx mem_size;
884
885 if (MEM_ALIAS_SET (x) != MEM_ALIAS_SET (y))
886 {
887 set_mem_alias_set (x, 0);
888 set_mem_alias_set (y, 0);
889 }
890
891 if (! mem_expr_equal_p (MEM_EXPR (x), MEM_EXPR (y)))
892 {
893 set_mem_expr (x, 0);
894 set_mem_expr (y, 0);
895 set_mem_offset (x, 0);
896 set_mem_offset (y, 0);
897 }
898 else if (MEM_OFFSET (x) != MEM_OFFSET (y))
899 {
900 set_mem_offset (x, 0);
901 set_mem_offset (y, 0);
902 }
903
904 if (!MEM_SIZE (x))
905 mem_size = NULL_RTX;
906 else if (!MEM_SIZE (y))
907 mem_size = NULL_RTX;
908 else
909 mem_size = GEN_INT (MAX (INTVAL (MEM_SIZE (x)),
910 INTVAL (MEM_SIZE (y))));
911 set_mem_size (x, mem_size);
912 set_mem_size (y, mem_size);
913
914 set_mem_align (x, MIN (MEM_ALIGN (x), MEM_ALIGN (y)));
915 set_mem_align (y, MEM_ALIGN (x));
916 }
917 }
918
919 fmt = GET_RTX_FORMAT (code);
920 for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
921 {
922 switch (fmt[i])
923 {
924 case 'E':
925 /* Two vectors must have the same length. */
926 if (XVECLEN (x, i) != XVECLEN (y, i))
927 return;
928
929 for (j = 0; j < XVECLEN (x, i); j++)
930 merge_memattrs (XVECEXP (x, i, j), XVECEXP (y, i, j));
931
932 break;
933
934 case 'e':
935 merge_memattrs (XEXP (x, i), XEXP (y, i));
936 }
937 }
938 return;
939 }
940
941
942 /* Return true if I1 and I2 are equivalent and thus can be crossjumped. */
943
944 static bool
old_insns_match_p(int mode ATTRIBUTE_UNUSED,rtx i1,rtx i2)945 old_insns_match_p (int mode ATTRIBUTE_UNUSED, rtx i1, rtx i2)
946 {
947 rtx p1, p2;
948
949 /* Verify that I1 and I2 are equivalent. */
950 if (GET_CODE (i1) != GET_CODE (i2))
951 return false;
952
953 p1 = PATTERN (i1);
954 p2 = PATTERN (i2);
955
956 if (GET_CODE (p1) != GET_CODE (p2))
957 return false;
958
959 /* If this is a CALL_INSN, compare register usage information.
960 If we don't check this on stack register machines, the two
961 CALL_INSNs might be merged leaving reg-stack.c with mismatching
962 numbers of stack registers in the same basic block.
963 If we don't check this on machines with delay slots, a delay slot may
964 be filled that clobbers a parameter expected by the subroutine.
965
966 ??? We take the simple route for now and assume that if they're
967 equal, they were constructed identically. */
968
969 if (CALL_P (i1)
970 && (!rtx_equal_p (CALL_INSN_FUNCTION_USAGE (i1),
971 CALL_INSN_FUNCTION_USAGE (i2))
972 || SIBLING_CALL_P (i1) != SIBLING_CALL_P (i2)))
973 return false;
974
975 #ifdef STACK_REGS
976 /* If cross_jump_death_matters is not 0, the insn's mode
977 indicates whether or not the insn contains any stack-like
978 regs. */
979
980 if ((mode & CLEANUP_POST_REGSTACK) && stack_regs_mentioned (i1))
981 {
982 /* If register stack conversion has already been done, then
983 death notes must also be compared before it is certain that
984 the two instruction streams match. */
985
986 rtx note;
987 HARD_REG_SET i1_regset, i2_regset;
988
989 CLEAR_HARD_REG_SET (i1_regset);
990 CLEAR_HARD_REG_SET (i2_regset);
991
992 for (note = REG_NOTES (i1); note; note = XEXP (note, 1))
993 if (REG_NOTE_KIND (note) == REG_DEAD && STACK_REG_P (XEXP (note, 0)))
994 SET_HARD_REG_BIT (i1_regset, REGNO (XEXP (note, 0)));
995
996 for (note = REG_NOTES (i2); note; note = XEXP (note, 1))
997 if (REG_NOTE_KIND (note) == REG_DEAD && STACK_REG_P (XEXP (note, 0)))
998 SET_HARD_REG_BIT (i2_regset, REGNO (XEXP (note, 0)));
999
1000 GO_IF_HARD_REG_EQUAL (i1_regset, i2_regset, done);
1001
1002 return false;
1003
1004 done:
1005 ;
1006 }
1007 #endif
1008
1009 if (reload_completed
1010 ? rtx_renumbered_equal_p (p1, p2) : rtx_equal_p (p1, p2))
1011 return true;
1012
1013 /* Do not do EQUIV substitution after reload. First, we're undoing the
1014 work of reload_cse. Second, we may be undoing the work of the post-
1015 reload splitting pass. */
1016 /* ??? Possibly add a new phase switch variable that can be used by
1017 targets to disallow the troublesome insns after splitting. */
1018 if (!reload_completed)
1019 {
1020 /* The following code helps take care of G++ cleanups. */
1021 rtx equiv1 = find_reg_equal_equiv_note (i1);
1022 rtx equiv2 = find_reg_equal_equiv_note (i2);
1023
1024 if (equiv1 && equiv2
1025 /* If the equivalences are not to a constant, they may
1026 reference pseudos that no longer exist, so we can't
1027 use them. */
1028 && (! reload_completed
1029 || (CONSTANT_P (XEXP (equiv1, 0))
1030 && rtx_equal_p (XEXP (equiv1, 0), XEXP (equiv2, 0)))))
1031 {
1032 rtx s1 = single_set (i1);
1033 rtx s2 = single_set (i2);
1034 if (s1 != 0 && s2 != 0
1035 && rtx_renumbered_equal_p (SET_DEST (s1), SET_DEST (s2)))
1036 {
1037 validate_change (i1, &SET_SRC (s1), XEXP (equiv1, 0), 1);
1038 validate_change (i2, &SET_SRC (s2), XEXP (equiv2, 0), 1);
1039 if (! rtx_renumbered_equal_p (p1, p2))
1040 cancel_changes (0);
1041 else if (apply_change_group ())
1042 return true;
1043 }
1044 }
1045 }
1046
1047 return false;
1048 }
1049
1050 /* Look through the insns at the end of BB1 and BB2 and find the longest
1051 sequence that are equivalent. Store the first insns for that sequence
1052 in *F1 and *F2 and return the sequence length.
1053
1054 To simplify callers of this function, if the blocks match exactly,
1055 store the head of the blocks in *F1 and *F2. */
1056
1057 static int
flow_find_cross_jump(int mode ATTRIBUTE_UNUSED,basic_block bb1,basic_block bb2,rtx * f1,rtx * f2)1058 flow_find_cross_jump (int mode ATTRIBUTE_UNUSED, basic_block bb1,
1059 basic_block bb2, rtx *f1, rtx *f2)
1060 {
1061 rtx i1, i2, last1, last2, afterlast1, afterlast2;
1062 int ninsns = 0;
1063
1064 /* Skip simple jumps at the end of the blocks. Complex jumps still
1065 need to be compared for equivalence, which we'll do below. */
1066
1067 i1 = BB_END (bb1);
1068 last1 = afterlast1 = last2 = afterlast2 = NULL_RTX;
1069 if (onlyjump_p (i1)
1070 || (returnjump_p (i1) && !side_effects_p (PATTERN (i1))))
1071 {
1072 last1 = i1;
1073 i1 = PREV_INSN (i1);
1074 }
1075
1076 i2 = BB_END (bb2);
1077 if (onlyjump_p (i2)
1078 || (returnjump_p (i2) && !side_effects_p (PATTERN (i2))))
1079 {
1080 last2 = i2;
1081 /* Count everything except for unconditional jump as insn. */
1082 if (!simplejump_p (i2) && !returnjump_p (i2) && last1)
1083 ninsns++;
1084 i2 = PREV_INSN (i2);
1085 }
1086
1087 while (true)
1088 {
1089 /* Ignore notes. */
1090 while (!INSN_P (i1) && i1 != BB_HEAD (bb1))
1091 i1 = PREV_INSN (i1);
1092
1093 while (!INSN_P (i2) && i2 != BB_HEAD (bb2))
1094 i2 = PREV_INSN (i2);
1095
1096 if (i1 == BB_HEAD (bb1) || i2 == BB_HEAD (bb2))
1097 break;
1098
1099 if (!old_insns_match_p (mode, i1, i2))
1100 break;
1101
1102 merge_memattrs (i1, i2);
1103
1104 /* Don't begin a cross-jump with a NOTE insn. */
1105 if (INSN_P (i1))
1106 {
1107 /* If the merged insns have different REG_EQUAL notes, then
1108 remove them. */
1109 rtx equiv1 = find_reg_equal_equiv_note (i1);
1110 rtx equiv2 = find_reg_equal_equiv_note (i2);
1111
1112 if (equiv1 && !equiv2)
1113 remove_note (i1, equiv1);
1114 else if (!equiv1 && equiv2)
1115 remove_note (i2, equiv2);
1116 else if (equiv1 && equiv2
1117 && !rtx_equal_p (XEXP (equiv1, 0), XEXP (equiv2, 0)))
1118 {
1119 remove_note (i1, equiv1);
1120 remove_note (i2, equiv2);
1121 }
1122
1123 afterlast1 = last1, afterlast2 = last2;
1124 last1 = i1, last2 = i2;
1125 ninsns++;
1126 }
1127
1128 i1 = PREV_INSN (i1);
1129 i2 = PREV_INSN (i2);
1130 }
1131
1132 #ifdef HAVE_cc0
1133 /* Don't allow the insn after a compare to be shared by
1134 cross-jumping unless the compare is also shared. */
1135 if (ninsns && reg_mentioned_p (cc0_rtx, last1) && ! sets_cc0_p (last1))
1136 last1 = afterlast1, last2 = afterlast2, ninsns--;
1137 #endif
1138
1139 /* Include preceding notes and labels in the cross-jump. One,
1140 this may bring us to the head of the blocks as requested above.
1141 Two, it keeps line number notes as matched as may be. */
1142 if (ninsns)
1143 {
1144 while (last1 != BB_HEAD (bb1) && !INSN_P (PREV_INSN (last1)))
1145 last1 = PREV_INSN (last1);
1146
1147 if (last1 != BB_HEAD (bb1) && LABEL_P (PREV_INSN (last1)))
1148 last1 = PREV_INSN (last1);
1149
1150 while (last2 != BB_HEAD (bb2) && !INSN_P (PREV_INSN (last2)))
1151 last2 = PREV_INSN (last2);
1152
1153 if (last2 != BB_HEAD (bb2) && LABEL_P (PREV_INSN (last2)))
1154 last2 = PREV_INSN (last2);
1155
1156 *f1 = last1;
1157 *f2 = last2;
1158 }
1159
1160 return ninsns;
1161 }
1162
1163 /* Return true iff the condbranches at the end of BB1 and BB2 match. */
1164 bool
condjump_equiv_p(struct equiv_info * info,bool call_init)1165 condjump_equiv_p (struct equiv_info *info, bool call_init)
1166 {
1167 basic_block bb1 = info->x_block;
1168 basic_block bb2 = info->y_block;
1169 edge b1 = BRANCH_EDGE (bb1);
1170 edge b2 = BRANCH_EDGE (bb2);
1171 edge f1 = FALLTHRU_EDGE (bb1);
1172 edge f2 = FALLTHRU_EDGE (bb2);
1173 bool reverse, match;
1174 rtx set1, set2, cond1, cond2;
1175 rtx src1, src2;
1176 enum rtx_code code1, code2;
1177
1178 /* Get around possible forwarders on fallthru edges. Other cases
1179 should be optimized out already. */
1180 if (FORWARDER_BLOCK_P (f1->dest))
1181 f1 = single_succ_edge (f1->dest);
1182
1183 if (FORWARDER_BLOCK_P (f2->dest))
1184 f2 = single_succ_edge (f2->dest);
1185
1186 /* To simplify use of this function, return false if there are
1187 unneeded forwarder blocks. These will get eliminated later
1188 during cleanup_cfg. */
1189 if (FORWARDER_BLOCK_P (f1->dest)
1190 || FORWARDER_BLOCK_P (f2->dest)
1191 || FORWARDER_BLOCK_P (b1->dest)
1192 || FORWARDER_BLOCK_P (b2->dest))
1193 return false;
1194
1195 if (f1->dest == f2->dest && b1->dest == b2->dest)
1196 reverse = false;
1197 else if (f1->dest == b2->dest && b1->dest == f2->dest)
1198 reverse = true;
1199 else
1200 return false;
1201
1202 set1 = pc_set (BB_END (bb1));
1203 set2 = pc_set (BB_END (bb2));
1204 if ((XEXP (SET_SRC (set1), 1) == pc_rtx)
1205 != (XEXP (SET_SRC (set2), 1) == pc_rtx))
1206 reverse = !reverse;
1207
1208 src1 = SET_SRC (set1);
1209 src2 = SET_SRC (set2);
1210 cond1 = XEXP (src1, 0);
1211 cond2 = XEXP (src2, 0);
1212 code1 = GET_CODE (cond1);
1213 if (reverse)
1214 code2 = reversed_comparison_code (cond2, BB_END (bb2));
1215 else
1216 code2 = GET_CODE (cond2);
1217
1218 if (code2 == UNKNOWN)
1219 return false;
1220
1221 if (call_init && !struct_equiv_init (STRUCT_EQUIV_START | info->mode, info))
1222 gcc_unreachable ();
1223 /* Make the sources of the pc sets unreadable so that when we call
1224 insns_match_p it won't process them.
1225 The death_notes_match_p from insns_match_p won't see the local registers
1226 used for the pc set, but that could only cause missed optimizations when
1227 there are actually condjumps that use stack registers. */
1228 SET_SRC (set1) = pc_rtx;
1229 SET_SRC (set2) = pc_rtx;
1230 /* Verify codes and operands match. */
1231 if (code1 == code2)
1232 {
1233 match = (insns_match_p (BB_END (bb1), BB_END (bb2), info)
1234 && rtx_equiv_p (&XEXP (cond1, 0), XEXP (cond2, 0), 1, info)
1235 && rtx_equiv_p (&XEXP (cond1, 1), XEXP (cond2, 1), 1, info));
1236
1237 }
1238 else if (code1 == swap_condition (code2))
1239 {
1240 match = (insns_match_p (BB_END (bb1), BB_END (bb2), info)
1241 && rtx_equiv_p (&XEXP (cond1, 1), XEXP (cond2, 0), 1, info)
1242 && rtx_equiv_p (&XEXP (cond1, 0), XEXP (cond2, 1), 1, info));
1243
1244 }
1245 else
1246 match = false;
1247 SET_SRC (set1) = src1;
1248 SET_SRC (set2) = src2;
1249 match &= verify_changes (0);
1250
1251 /* If we return true, we will join the blocks. Which means that
1252 we will only have one branch prediction bit to work with. Thus
1253 we require the existing branches to have probabilities that are
1254 roughly similar. */
1255 if (match
1256 && !optimize_size
1257 && maybe_hot_bb_p (bb1)
1258 && maybe_hot_bb_p (bb2))
1259 {
1260 int prob2;
1261
1262 if (b1->dest == b2->dest)
1263 prob2 = b2->probability;
1264 else
1265 /* Do not use f2 probability as f2 may be forwarded. */
1266 prob2 = REG_BR_PROB_BASE - b2->probability;
1267
1268 /* Fail if the difference in probabilities is greater than 50%.
1269 This rules out two well-predicted branches with opposite
1270 outcomes. */
1271 if (abs (b1->probability - prob2) > REG_BR_PROB_BASE / 2)
1272 {
1273 if (dump_file)
1274 fprintf (dump_file,
1275 "Outcomes of branch in bb %i and %i differ too much (%i %i)\n",
1276 bb1->index, bb2->index, b1->probability, prob2);
1277
1278 match = false;
1279 }
1280 }
1281
1282 if (dump_file && match)
1283 fprintf (dump_file, "Conditionals in bb %i and %i match.\n",
1284 bb1->index, bb2->index);
1285
1286 if (!match)
1287 cancel_changes (0);
1288 return match;
1289 }
1290
1291 /* Return true iff outgoing edges of BB1 and BB2 match, together with
1292 the branch instruction. This means that if we commonize the control
1293 flow before end of the basic block, the semantic remains unchanged.
1294
1295 We may assume that there exists one edge with a common destination. */
1296
1297 static bool
outgoing_edges_match(int mode,basic_block bb1,basic_block bb2)1298 outgoing_edges_match (int mode, basic_block bb1, basic_block bb2)
1299 {
1300 int nehedges1 = 0, nehedges2 = 0;
1301 edge fallthru1 = 0, fallthru2 = 0;
1302 edge e1, e2;
1303 edge_iterator ei;
1304
1305 /* If BB1 has only one successor, we may be looking at either an
1306 unconditional jump, or a fake edge to exit. */
1307 if (single_succ_p (bb1)
1308 && (single_succ_edge (bb1)->flags & (EDGE_COMPLEX | EDGE_FAKE)) == 0
1309 && (!JUMP_P (BB_END (bb1)) || simplejump_p (BB_END (bb1))))
1310 return (single_succ_p (bb2)
1311 && (single_succ_edge (bb2)->flags
1312 & (EDGE_COMPLEX | EDGE_FAKE)) == 0
1313 && (!JUMP_P (BB_END (bb2)) || simplejump_p (BB_END (bb2))));
1314
1315 /* Match conditional jumps - this may get tricky when fallthru and branch
1316 edges are crossed. */
1317 if (EDGE_COUNT (bb1->succs) == 2
1318 && any_condjump_p (BB_END (bb1))
1319 && onlyjump_p (BB_END (bb1)))
1320 {
1321 edge b1, f1, b2, f2;
1322 bool reverse, match;
1323 rtx set1, set2, cond1, cond2;
1324 enum rtx_code code1, code2;
1325
1326 if (EDGE_COUNT (bb2->succs) != 2
1327 || !any_condjump_p (BB_END (bb2))
1328 || !onlyjump_p (BB_END (bb2)))
1329 return false;
1330
1331 b1 = BRANCH_EDGE (bb1);
1332 b2 = BRANCH_EDGE (bb2);
1333 f1 = FALLTHRU_EDGE (bb1);
1334 f2 = FALLTHRU_EDGE (bb2);
1335
1336 /* Get around possible forwarders on fallthru edges. Other cases
1337 should be optimized out already. */
1338 if (FORWARDER_BLOCK_P (f1->dest))
1339 f1 = single_succ_edge (f1->dest);
1340
1341 if (FORWARDER_BLOCK_P (f2->dest))
1342 f2 = single_succ_edge (f2->dest);
1343
1344 /* To simplify use of this function, return false if there are
1345 unneeded forwarder blocks. These will get eliminated later
1346 during cleanup_cfg. */
1347 if (FORWARDER_BLOCK_P (f1->dest)
1348 || FORWARDER_BLOCK_P (f2->dest)
1349 || FORWARDER_BLOCK_P (b1->dest)
1350 || FORWARDER_BLOCK_P (b2->dest))
1351 return false;
1352
1353 if (f1->dest == f2->dest && b1->dest == b2->dest)
1354 reverse = false;
1355 else if (f1->dest == b2->dest && b1->dest == f2->dest)
1356 reverse = true;
1357 else
1358 return false;
1359
1360 set1 = pc_set (BB_END (bb1));
1361 set2 = pc_set (BB_END (bb2));
1362 if ((XEXP (SET_SRC (set1), 1) == pc_rtx)
1363 != (XEXP (SET_SRC (set2), 1) == pc_rtx))
1364 reverse = !reverse;
1365
1366 cond1 = XEXP (SET_SRC (set1), 0);
1367 cond2 = XEXP (SET_SRC (set2), 0);
1368 code1 = GET_CODE (cond1);
1369 if (reverse)
1370 code2 = reversed_comparison_code (cond2, BB_END (bb2));
1371 else
1372 code2 = GET_CODE (cond2);
1373
1374 if (code2 == UNKNOWN)
1375 return false;
1376
1377 /* Verify codes and operands match. */
1378 match = ((code1 == code2
1379 && rtx_renumbered_equal_p (XEXP (cond1, 0), XEXP (cond2, 0))
1380 && rtx_renumbered_equal_p (XEXP (cond1, 1), XEXP (cond2, 1)))
1381 || (code1 == swap_condition (code2)
1382 && rtx_renumbered_equal_p (XEXP (cond1, 1),
1383 XEXP (cond2, 0))
1384 && rtx_renumbered_equal_p (XEXP (cond1, 0),
1385 XEXP (cond2, 1))));
1386
1387 /* If we return true, we will join the blocks. Which means that
1388 we will only have one branch prediction bit to work with. Thus
1389 we require the existing branches to have probabilities that are
1390 roughly similar. */
1391 if (match
1392 && !optimize_size
1393 && maybe_hot_bb_p (bb1)
1394 && maybe_hot_bb_p (bb2))
1395 {
1396 int prob2;
1397
1398 if (b1->dest == b2->dest)
1399 prob2 = b2->probability;
1400 else
1401 /* Do not use f2 probability as f2 may be forwarded. */
1402 prob2 = REG_BR_PROB_BASE - b2->probability;
1403
1404 /* Fail if the difference in probabilities is greater than 50%.
1405 This rules out two well-predicted branches with opposite
1406 outcomes. */
1407 if (abs (b1->probability - prob2) > REG_BR_PROB_BASE / 2)
1408 {
1409 if (dump_file)
1410 fprintf (dump_file,
1411 "Outcomes of branch in bb %i and %i differ too much (%i %i)\n",
1412 bb1->index, bb2->index, b1->probability, prob2);
1413
1414 return false;
1415 }
1416 }
1417
1418 if (dump_file && match)
1419 fprintf (dump_file, "Conditionals in bb %i and %i match.\n",
1420 bb1->index, bb2->index);
1421
1422 return match;
1423 }
1424
1425 /* Generic case - we are seeing a computed jump, table jump or trapping
1426 instruction. */
1427
1428 /* Check whether there are tablejumps in the end of BB1 and BB2.
1429 Return true if they are identical. */
1430 {
1431 rtx label1, label2;
1432 rtx table1, table2;
1433
1434 if (tablejump_p (BB_END (bb1), &label1, &table1)
1435 && tablejump_p (BB_END (bb2), &label2, &table2)
1436 && GET_CODE (PATTERN (table1)) == GET_CODE (PATTERN (table2)))
1437 {
1438 /* The labels should never be the same rtx. If they really are same
1439 the jump tables are same too. So disable crossjumping of blocks BB1
1440 and BB2 because when deleting the common insns in the end of BB1
1441 by delete_basic_block () the jump table would be deleted too. */
1442 /* If LABEL2 is referenced in BB1->END do not do anything
1443 because we would loose information when replacing
1444 LABEL1 by LABEL2 and then LABEL2 by LABEL1 in BB1->END. */
1445 if (label1 != label2 && !rtx_referenced_p (label2, BB_END (bb1)))
1446 {
1447 /* Set IDENTICAL to true when the tables are identical. */
1448 bool identical = false;
1449 rtx p1, p2;
1450
1451 p1 = PATTERN (table1);
1452 p2 = PATTERN (table2);
1453 if (GET_CODE (p1) == ADDR_VEC && rtx_equal_p (p1, p2))
1454 {
1455 identical = true;
1456 }
1457 else if (GET_CODE (p1) == ADDR_DIFF_VEC
1458 && (XVECLEN (p1, 1) == XVECLEN (p2, 1))
1459 && rtx_equal_p (XEXP (p1, 2), XEXP (p2, 2))
1460 && rtx_equal_p (XEXP (p1, 3), XEXP (p2, 3)))
1461 {
1462 int i;
1463
1464 identical = true;
1465 for (i = XVECLEN (p1, 1) - 1; i >= 0 && identical; i--)
1466 if (!rtx_equal_p (XVECEXP (p1, 1, i), XVECEXP (p2, 1, i)))
1467 identical = false;
1468 }
1469
1470 if (identical)
1471 {
1472 replace_label_data rr;
1473 bool match;
1474
1475 /* Temporarily replace references to LABEL1 with LABEL2
1476 in BB1->END so that we could compare the instructions. */
1477 rr.r1 = label1;
1478 rr.r2 = label2;
1479 rr.update_label_nuses = false;
1480 for_each_rtx (&BB_END (bb1), replace_label, &rr);
1481
1482 match = old_insns_match_p (mode, BB_END (bb1), BB_END (bb2));
1483 if (dump_file && match)
1484 fprintf (dump_file,
1485 "Tablejumps in bb %i and %i match.\n",
1486 bb1->index, bb2->index);
1487
1488 /* Set the original label in BB1->END because when deleting
1489 a block whose end is a tablejump, the tablejump referenced
1490 from the instruction is deleted too. */
1491 rr.r1 = label2;
1492 rr.r2 = label1;
1493 for_each_rtx (&BB_END (bb1), replace_label, &rr);
1494
1495 return match;
1496 }
1497 }
1498 return false;
1499 }
1500 }
1501
1502 /* First ensure that the instructions match. There may be many outgoing
1503 edges so this test is generally cheaper. */
1504 if (!old_insns_match_p (mode, BB_END (bb1), BB_END (bb2)))
1505 return false;
1506
1507 /* Search the outgoing edges, ensure that the counts do match, find possible
1508 fallthru and exception handling edges since these needs more
1509 validation. */
1510 if (EDGE_COUNT (bb1->succs) != EDGE_COUNT (bb2->succs))
1511 return false;
1512
1513 FOR_EACH_EDGE (e1, ei, bb1->succs)
1514 {
1515 e2 = EDGE_SUCC (bb2, ei.index);
1516
1517 if (e1->flags & EDGE_EH)
1518 nehedges1++;
1519
1520 if (e2->flags & EDGE_EH)
1521 nehedges2++;
1522
1523 if (e1->flags & EDGE_FALLTHRU)
1524 fallthru1 = e1;
1525 if (e2->flags & EDGE_FALLTHRU)
1526 fallthru2 = e2;
1527 }
1528
1529 /* If number of edges of various types does not match, fail. */
1530 if (nehedges1 != nehedges2
1531 || (fallthru1 != 0) != (fallthru2 != 0))
1532 return false;
1533
1534 /* fallthru edges must be forwarded to the same destination. */
1535 if (fallthru1)
1536 {
1537 basic_block d1 = (forwarder_block_p (fallthru1->dest)
1538 ? single_succ (fallthru1->dest): fallthru1->dest);
1539 basic_block d2 = (forwarder_block_p (fallthru2->dest)
1540 ? single_succ (fallthru2->dest): fallthru2->dest);
1541
1542 if (d1 != d2)
1543 return false;
1544 }
1545
1546 /* Ensure the same EH region. */
1547 {
1548 rtx n1 = find_reg_note (BB_END (bb1), REG_EH_REGION, 0);
1549 rtx n2 = find_reg_note (BB_END (bb2), REG_EH_REGION, 0);
1550
1551 if (!n1 && n2)
1552 return false;
1553
1554 if (n1 && (!n2 || XEXP (n1, 0) != XEXP (n2, 0)))
1555 return false;
1556 }
1557
1558 /* The same checks as in try_crossjump_to_edge. It is required for RTL
1559 version of sequence abstraction. */
1560 FOR_EACH_EDGE (e1, ei, bb2->succs)
1561 {
1562 edge e2;
1563 edge_iterator ei;
1564 basic_block d1 = e1->dest;
1565
1566 if (FORWARDER_BLOCK_P (d1))
1567 d1 = EDGE_SUCC (d1, 0)->dest;
1568
1569 FOR_EACH_EDGE (e2, ei, bb1->succs)
1570 {
1571 basic_block d2 = e2->dest;
1572 if (FORWARDER_BLOCK_P (d2))
1573 d2 = EDGE_SUCC (d2, 0)->dest;
1574 if (d1 == d2)
1575 break;
1576 }
1577
1578 if (!e2)
1579 return false;
1580 }
1581
1582 return true;
1583 }
1584
1585 /* Returns true if BB basic block has a preserve label. */
1586
1587 static bool
block_has_preserve_label(basic_block bb)1588 block_has_preserve_label (basic_block bb)
1589 {
1590 return (bb
1591 && block_label (bb)
1592 && LABEL_PRESERVE_P (block_label (bb)));
1593 }
1594
1595 /* E1 and E2 are edges with the same destination block. Search their
1596 predecessors for common code. If found, redirect control flow from
1597 (maybe the middle of) E1->SRC to (maybe the middle of) E2->SRC. */
1598
1599 static bool
try_crossjump_to_edge(int mode,edge e1,edge e2)1600 try_crossjump_to_edge (int mode, edge e1, edge e2)
1601 {
1602 int nmatch;
1603 basic_block src1 = e1->src, src2 = e2->src;
1604 basic_block redirect_to, redirect_from, to_remove;
1605 rtx newpos1, newpos2;
1606 edge s;
1607 edge_iterator ei;
1608
1609 newpos1 = newpos2 = NULL_RTX;
1610
1611 /* If we have partitioned hot/cold basic blocks, it is a bad idea
1612 to try this optimization.
1613
1614 Basic block partitioning may result in some jumps that appear to
1615 be optimizable (or blocks that appear to be mergeable), but which really
1616 must be left untouched (they are required to make it safely across
1617 partition boundaries). See the comments at the top of
1618 bb-reorder.c:partition_hot_cold_basic_blocks for complete details. */
1619
1620 if (flag_reorder_blocks_and_partition && no_new_pseudos)
1621 return false;
1622
1623 /* Search backward through forwarder blocks. We don't need to worry
1624 about multiple entry or chained forwarders, as they will be optimized
1625 away. We do this to look past the unconditional jump following a
1626 conditional jump that is required due to the current CFG shape. */
1627 if (single_pred_p (src1)
1628 && FORWARDER_BLOCK_P (src1))
1629 e1 = single_pred_edge (src1), src1 = e1->src;
1630
1631 if (single_pred_p (src2)
1632 && FORWARDER_BLOCK_P (src2))
1633 e2 = single_pred_edge (src2), src2 = e2->src;
1634
1635 /* Nothing to do if we reach ENTRY, or a common source block. */
1636 if (src1 == ENTRY_BLOCK_PTR || src2 == ENTRY_BLOCK_PTR)
1637 return false;
1638 if (src1 == src2)
1639 return false;
1640
1641 /* Seeing more than 1 forwarder blocks would confuse us later... */
1642 if (FORWARDER_BLOCK_P (e1->dest)
1643 && FORWARDER_BLOCK_P (single_succ (e1->dest)))
1644 return false;
1645
1646 if (FORWARDER_BLOCK_P (e2->dest)
1647 && FORWARDER_BLOCK_P (single_succ (e2->dest)))
1648 return false;
1649
1650 /* Likewise with dead code (possibly newly created by the other optimizations
1651 of cfg_cleanup). */
1652 if (EDGE_COUNT (src1->preds) == 0 || EDGE_COUNT (src2->preds) == 0)
1653 return false;
1654
1655 /* Look for the common insn sequence, part the first ... */
1656 if (!outgoing_edges_match (mode, src1, src2))
1657 return false;
1658
1659 /* ... and part the second. */
1660 nmatch = flow_find_cross_jump (mode, src1, src2, &newpos1, &newpos2);
1661
1662 /* Don't proceed with the crossjump unless we found a sufficient number
1663 of matching instructions or the 'from' block was totally matched
1664 (such that its predecessors will hopefully be redirected and the
1665 block removed). */
1666 if ((nmatch < PARAM_VALUE (PARAM_MIN_CROSSJUMP_INSNS))
1667 && (newpos1 != BB_HEAD (src1)))
1668 return false;
1669
1670 /* Avoid deleting preserve label when redirecting ABNORMAL edges. */
1671 if (block_has_preserve_label (e1->dest)
1672 && (e1->flags & EDGE_ABNORMAL))
1673 return false;
1674
1675 /* Here we know that the insns in the end of SRC1 which are common with SRC2
1676 will be deleted.
1677 If we have tablejumps in the end of SRC1 and SRC2
1678 they have been already compared for equivalence in outgoing_edges_match ()
1679 so replace the references to TABLE1 by references to TABLE2. */
1680 {
1681 rtx label1, label2;
1682 rtx table1, table2;
1683
1684 if (tablejump_p (BB_END (src1), &label1, &table1)
1685 && tablejump_p (BB_END (src2), &label2, &table2)
1686 && label1 != label2)
1687 {
1688 replace_label_data rr;
1689 rtx insn;
1690
1691 /* Replace references to LABEL1 with LABEL2. */
1692 rr.r1 = label1;
1693 rr.r2 = label2;
1694 rr.update_label_nuses = true;
1695 for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
1696 {
1697 /* Do not replace the label in SRC1->END because when deleting
1698 a block whose end is a tablejump, the tablejump referenced
1699 from the instruction is deleted too. */
1700 if (insn != BB_END (src1))
1701 for_each_rtx (&insn, replace_label, &rr);
1702 }
1703 }
1704 }
1705
1706 /* Avoid splitting if possible. We must always split when SRC2 has
1707 EH predecessor edges, or we may end up with basic blocks with both
1708 normal and EH predecessor edges. */
1709 if (newpos2 == BB_HEAD (src2)
1710 && !(EDGE_PRED (src2, 0)->flags & EDGE_EH))
1711 redirect_to = src2;
1712 else
1713 {
1714 if (newpos2 == BB_HEAD (src2))
1715 {
1716 /* Skip possible basic block header. */
1717 if (LABEL_P (newpos2))
1718 newpos2 = NEXT_INSN (newpos2);
1719 if (NOTE_P (newpos2))
1720 newpos2 = NEXT_INSN (newpos2);
1721 }
1722
1723 if (dump_file)
1724 fprintf (dump_file, "Splitting bb %i before %i insns\n",
1725 src2->index, nmatch);
1726 redirect_to = split_block (src2, PREV_INSN (newpos2))->dest;
1727 }
1728
1729 if (dump_file)
1730 fprintf (dump_file,
1731 "Cross jumping from bb %i to bb %i; %i common insns\n",
1732 src1->index, src2->index, nmatch);
1733
1734 redirect_to->count += src1->count;
1735 redirect_to->frequency += src1->frequency;
1736 /* We may have some registers visible through the block. */
1737 redirect_to->flags |= BB_DIRTY;
1738
1739 /* Recompute the frequencies and counts of outgoing edges. */
1740 FOR_EACH_EDGE (s, ei, redirect_to->succs)
1741 {
1742 edge s2;
1743 edge_iterator ei;
1744 basic_block d = s->dest;
1745
1746 if (FORWARDER_BLOCK_P (d))
1747 d = single_succ (d);
1748
1749 FOR_EACH_EDGE (s2, ei, src1->succs)
1750 {
1751 basic_block d2 = s2->dest;
1752 if (FORWARDER_BLOCK_P (d2))
1753 d2 = single_succ (d2);
1754 if (d == d2)
1755 break;
1756 }
1757
1758 s->count += s2->count;
1759
1760 /* Take care to update possible forwarder blocks. We verified
1761 that there is no more than one in the chain, so we can't run
1762 into infinite loop. */
1763 if (FORWARDER_BLOCK_P (s->dest))
1764 {
1765 single_succ_edge (s->dest)->count += s2->count;
1766 s->dest->count += s2->count;
1767 s->dest->frequency += EDGE_FREQUENCY (s);
1768 }
1769
1770 if (FORWARDER_BLOCK_P (s2->dest))
1771 {
1772 single_succ_edge (s2->dest)->count -= s2->count;
1773 if (single_succ_edge (s2->dest)->count < 0)
1774 single_succ_edge (s2->dest)->count = 0;
1775 s2->dest->count -= s2->count;
1776 s2->dest->frequency -= EDGE_FREQUENCY (s);
1777 if (s2->dest->frequency < 0)
1778 s2->dest->frequency = 0;
1779 if (s2->dest->count < 0)
1780 s2->dest->count = 0;
1781 }
1782
1783 if (!redirect_to->frequency && !src1->frequency)
1784 s->probability = (s->probability + s2->probability) / 2;
1785 else
1786 s->probability
1787 = ((s->probability * redirect_to->frequency +
1788 s2->probability * src1->frequency)
1789 / (redirect_to->frequency + src1->frequency));
1790 }
1791
1792 update_br_prob_note (redirect_to);
1793
1794 /* Edit SRC1 to go to REDIRECT_TO at NEWPOS1. */
1795
1796 /* Skip possible basic block header. */
1797 if (LABEL_P (newpos1))
1798 newpos1 = NEXT_INSN (newpos1);
1799
1800 if (NOTE_P (newpos1))
1801 newpos1 = NEXT_INSN (newpos1);
1802
1803 redirect_from = split_block (src1, PREV_INSN (newpos1))->src;
1804 to_remove = single_succ (redirect_from);
1805
1806 redirect_edge_and_branch_force (single_succ_edge (redirect_from), redirect_to);
1807 delete_basic_block (to_remove);
1808
1809 update_forwarder_flag (redirect_from);
1810 if (redirect_to != src2)
1811 update_forwarder_flag (src2);
1812
1813 return true;
1814 }
1815
1816 /* Search the predecessors of BB for common insn sequences. When found,
1817 share code between them by redirecting control flow. Return true if
1818 any changes made. */
1819
1820 static bool
try_crossjump_bb(int mode,basic_block bb)1821 try_crossjump_bb (int mode, basic_block bb)
1822 {
1823 edge e, e2, fallthru;
1824 bool changed;
1825 unsigned max, ix, ix2;
1826 basic_block ev, ev2;
1827 edge_iterator ei;
1828
1829 /* Nothing to do if there is not at least two incoming edges. */
1830 if (EDGE_COUNT (bb->preds) < 2)
1831 return false;
1832
1833 /* Don't crossjump if this block ends in a computed jump,
1834 unless we are optimizing for size. */
1835 if (!optimize_size
1836 && bb != EXIT_BLOCK_PTR
1837 && computed_jump_p (BB_END (bb)))
1838 return false;
1839
1840 /* If we are partitioning hot/cold basic blocks, we don't want to
1841 mess up unconditional or indirect jumps that cross between hot
1842 and cold sections.
1843
1844 Basic block partitioning may result in some jumps that appear to
1845 be optimizable (or blocks that appear to be mergeable), but which really
1846 must be left untouched (they are required to make it safely across
1847 partition boundaries). See the comments at the top of
1848 bb-reorder.c:partition_hot_cold_basic_blocks for complete details. */
1849
1850 if (BB_PARTITION (EDGE_PRED (bb, 0)->src) !=
1851 BB_PARTITION (EDGE_PRED (bb, 1)->src)
1852 || (EDGE_PRED (bb, 0)->flags & EDGE_CROSSING))
1853 return false;
1854
1855 /* It is always cheapest to redirect a block that ends in a branch to
1856 a block that falls through into BB, as that adds no branches to the
1857 program. We'll try that combination first. */
1858 fallthru = NULL;
1859 max = PARAM_VALUE (PARAM_MAX_CROSSJUMP_EDGES);
1860
1861 if (EDGE_COUNT (bb->preds) > max)
1862 return false;
1863
1864 FOR_EACH_EDGE (e, ei, bb->preds)
1865 {
1866 if (e->flags & EDGE_FALLTHRU)
1867 fallthru = e;
1868 }
1869
1870 changed = false;
1871 for (ix = 0, ev = bb; ix < EDGE_COUNT (ev->preds); )
1872 {
1873 e = EDGE_PRED (ev, ix);
1874 ix++;
1875
1876 /* As noted above, first try with the fallthru predecessor. */
1877 if (fallthru)
1878 {
1879 /* Don't combine the fallthru edge into anything else.
1880 If there is a match, we'll do it the other way around. */
1881 if (e == fallthru)
1882 continue;
1883 /* If nothing changed since the last attempt, there is nothing
1884 we can do. */
1885 if (!first_pass
1886 && (!(e->src->flags & BB_DIRTY)
1887 && !(fallthru->src->flags & BB_DIRTY)))
1888 continue;
1889
1890 if (try_crossjump_to_edge (mode, e, fallthru))
1891 {
1892 changed = true;
1893 ix = 0;
1894 ev = bb;
1895 continue;
1896 }
1897 }
1898
1899 /* Non-obvious work limiting check: Recognize that we're going
1900 to call try_crossjump_bb on every basic block. So if we have
1901 two blocks with lots of outgoing edges (a switch) and they
1902 share lots of common destinations, then we would do the
1903 cross-jump check once for each common destination.
1904
1905 Now, if the blocks actually are cross-jump candidates, then
1906 all of their destinations will be shared. Which means that
1907 we only need check them for cross-jump candidacy once. We
1908 can eliminate redundant checks of crossjump(A,B) by arbitrarily
1909 choosing to do the check from the block for which the edge
1910 in question is the first successor of A. */
1911 if (EDGE_SUCC (e->src, 0) != e)
1912 continue;
1913
1914 for (ix2 = 0, ev2 = bb; ix2 < EDGE_COUNT (ev2->preds); )
1915 {
1916 e2 = EDGE_PRED (ev2, ix2);
1917 ix2++;
1918
1919 if (e2 == e)
1920 continue;
1921
1922 /* We've already checked the fallthru edge above. */
1923 if (e2 == fallthru)
1924 continue;
1925
1926 /* The "first successor" check above only prevents multiple
1927 checks of crossjump(A,B). In order to prevent redundant
1928 checks of crossjump(B,A), require that A be the block
1929 with the lowest index. */
1930 if (e->src->index > e2->src->index)
1931 continue;
1932
1933 /* If nothing changed since the last attempt, there is nothing
1934 we can do. */
1935 if (!first_pass
1936 && (!(e->src->flags & BB_DIRTY)
1937 && !(e2->src->flags & BB_DIRTY)))
1938 continue;
1939
1940 if (try_crossjump_to_edge (mode, e, e2))
1941 {
1942 changed = true;
1943 ev2 = bb;
1944 ix = 0;
1945 break;
1946 }
1947 }
1948 }
1949
1950 return changed;
1951 }
1952
1953 /* Do simple CFG optimizations - basic block merging, simplifying of jump
1954 instructions etc. Return nonzero if changes were made. */
1955
1956 static bool
try_optimize_cfg(int mode)1957 try_optimize_cfg (int mode)
1958 {
1959 bool changed_overall = false;
1960 bool changed;
1961 int iterations = 0;
1962 basic_block bb, b, next;
1963
1964 if (mode & CLEANUP_CROSSJUMP)
1965 add_noreturn_fake_exit_edges ();
1966
1967 if (mode & (CLEANUP_UPDATE_LIFE | CLEANUP_CROSSJUMP | CLEANUP_THREADING))
1968 clear_bb_flags ();
1969
1970 FOR_EACH_BB (bb)
1971 update_forwarder_flag (bb);
1972
1973 if (! targetm.cannot_modify_jumps_p ())
1974 {
1975 first_pass = true;
1976 /* Attempt to merge blocks as made possible by edge removal. If
1977 a block has only one successor, and the successor has only
1978 one predecessor, they may be combined. */
1979 do
1980 {
1981 changed = false;
1982 iterations++;
1983
1984 if (dump_file)
1985 fprintf (dump_file,
1986 "\n\ntry_optimize_cfg iteration %i\n\n",
1987 iterations);
1988
1989 for (b = ENTRY_BLOCK_PTR->next_bb; b != EXIT_BLOCK_PTR;)
1990 {
1991 basic_block c;
1992 edge s;
1993 bool changed_here = false;
1994
1995 /* Delete trivially dead basic blocks. */
1996 while (EDGE_COUNT (b->preds) == 0)
1997 {
1998 c = b->prev_bb;
1999 if (dump_file)
2000 fprintf (dump_file, "Deleting block %i.\n",
2001 b->index);
2002
2003 delete_basic_block (b);
2004 if (!(mode & CLEANUP_CFGLAYOUT))
2005 changed = true;
2006 b = c;
2007 }
2008
2009 /* Remove code labels no longer used. */
2010 if (single_pred_p (b)
2011 && (single_pred_edge (b)->flags & EDGE_FALLTHRU)
2012 && !(single_pred_edge (b)->flags & EDGE_COMPLEX)
2013 && LABEL_P (BB_HEAD (b))
2014 /* If the previous block ends with a branch to this
2015 block, we can't delete the label. Normally this
2016 is a condjump that is yet to be simplified, but
2017 if CASE_DROPS_THRU, this can be a tablejump with
2018 some element going to the same place as the
2019 default (fallthru). */
2020 && (single_pred (b) == ENTRY_BLOCK_PTR
2021 || !JUMP_P (BB_END (single_pred (b)))
2022 || ! label_is_jump_target_p (BB_HEAD (b),
2023 BB_END (single_pred (b)))))
2024 {
2025 rtx label = BB_HEAD (b);
2026
2027 delete_insn_chain (label, label);
2028 /* In the case label is undeletable, move it after the
2029 BASIC_BLOCK note. */
2030 if (NOTE_LINE_NUMBER (BB_HEAD (b)) == NOTE_INSN_DELETED_LABEL)
2031 {
2032 rtx bb_note = NEXT_INSN (BB_HEAD (b));
2033
2034 reorder_insns_nobb (label, label, bb_note);
2035 BB_HEAD (b) = bb_note;
2036 }
2037 if (dump_file)
2038 fprintf (dump_file, "Deleted label in block %i.\n",
2039 b->index);
2040 }
2041
2042 /* If we fall through an empty block, we can remove it. */
2043 if (!(mode & CLEANUP_CFGLAYOUT)
2044 && single_pred_p (b)
2045 && (single_pred_edge (b)->flags & EDGE_FALLTHRU)
2046 && !LABEL_P (BB_HEAD (b))
2047 && FORWARDER_BLOCK_P (b)
2048 /* Note that forwarder_block_p true ensures that
2049 there is a successor for this block. */
2050 && (single_succ_edge (b)->flags & EDGE_FALLTHRU)
2051 && n_basic_blocks > NUM_FIXED_BLOCKS + 1)
2052 {
2053 if (dump_file)
2054 fprintf (dump_file,
2055 "Deleting fallthru block %i.\n",
2056 b->index);
2057
2058 c = b->prev_bb == ENTRY_BLOCK_PTR ? b->next_bb : b->prev_bb;
2059 redirect_edge_succ_nodup (single_pred_edge (b),
2060 single_succ (b));
2061 delete_basic_block (b);
2062 changed = true;
2063 b = c;
2064 }
2065
2066 if (single_succ_p (b)
2067 && (s = single_succ_edge (b))
2068 && !(s->flags & EDGE_COMPLEX)
2069 && (c = s->dest) != EXIT_BLOCK_PTR
2070 && single_pred_p (c)
2071 && b != c)
2072 {
2073 /* When not in cfg_layout mode use code aware of reordering
2074 INSN. This code possibly creates new basic blocks so it
2075 does not fit merge_blocks interface and is kept here in
2076 hope that it will become useless once more of compiler
2077 is transformed to use cfg_layout mode. */
2078
2079 if ((mode & CLEANUP_CFGLAYOUT)
2080 && can_merge_blocks_p (b, c))
2081 {
2082 merge_blocks (b, c);
2083 update_forwarder_flag (b);
2084 changed_here = true;
2085 }
2086 else if (!(mode & CLEANUP_CFGLAYOUT)
2087 /* If the jump insn has side effects,
2088 we can't kill the edge. */
2089 && (!JUMP_P (BB_END (b))
2090 || (reload_completed
2091 ? simplejump_p (BB_END (b))
2092 : (onlyjump_p (BB_END (b))
2093 && !tablejump_p (BB_END (b),
2094 NULL, NULL))))
2095 && (next = merge_blocks_move (s, b, c, mode)))
2096 {
2097 b = next;
2098 changed_here = true;
2099 }
2100 }
2101
2102 /* Simplify branch over branch. */
2103 if ((mode & CLEANUP_EXPENSIVE)
2104 && !(mode & CLEANUP_CFGLAYOUT)
2105 && try_simplify_condjump (b))
2106 changed_here = true;
2107
2108 /* If B has a single outgoing edge, but uses a
2109 non-trivial jump instruction without side-effects, we
2110 can either delete the jump entirely, or replace it
2111 with a simple unconditional jump. */
2112 if (single_succ_p (b)
2113 && single_succ (b) != EXIT_BLOCK_PTR
2114 && onlyjump_p (BB_END (b))
2115 && !find_reg_note (BB_END (b), REG_CROSSING_JUMP, NULL_RTX)
2116 && try_redirect_by_replacing_jump (single_succ_edge (b),
2117 single_succ (b),
2118 (mode & CLEANUP_CFGLAYOUT) != 0))
2119 {
2120 update_forwarder_flag (b);
2121 changed_here = true;
2122 }
2123
2124 /* Simplify branch to branch. */
2125 if (try_forward_edges (mode, b))
2126 changed_here = true;
2127
2128 /* Look for shared code between blocks. */
2129 if ((mode & CLEANUP_CROSSJUMP)
2130 && try_crossjump_bb (mode, b))
2131 changed_here = true;
2132
2133 /* Don't get confused by the index shift caused by
2134 deleting blocks. */
2135 if (!changed_here)
2136 b = b->next_bb;
2137 else
2138 changed = true;
2139 }
2140
2141 if ((mode & CLEANUP_CROSSJUMP)
2142 && try_crossjump_bb (mode, EXIT_BLOCK_PTR))
2143 changed = true;
2144
2145 #ifdef ENABLE_CHECKING
2146 if (changed)
2147 verify_flow_info ();
2148 #endif
2149
2150 changed_overall |= changed;
2151 first_pass = false;
2152 }
2153 while (changed);
2154 }
2155
2156 if (mode & CLEANUP_CROSSJUMP)
2157 remove_fake_exit_edges ();
2158
2159 FOR_ALL_BB (b)
2160 b->flags &= ~(BB_FORWARDER_BLOCK | BB_NONTHREADABLE_BLOCK);
2161
2162 return changed_overall;
2163 }
2164
2165 /* Delete all unreachable basic blocks. */
2166
2167 bool
delete_unreachable_blocks(void)2168 delete_unreachable_blocks (void)
2169 {
2170 bool changed = false;
2171 basic_block b, next_bb;
2172
2173 find_unreachable_blocks ();
2174
2175 /* Delete all unreachable basic blocks. */
2176
2177 for (b = ENTRY_BLOCK_PTR->next_bb; b != EXIT_BLOCK_PTR; b = next_bb)
2178 {
2179 next_bb = b->next_bb;
2180
2181 if (!(b->flags & BB_REACHABLE))
2182 {
2183 delete_basic_block (b);
2184 changed = true;
2185 }
2186 }
2187
2188 if (changed)
2189 tidy_fallthru_edges ();
2190 return changed;
2191 }
2192
2193 /* Merges sequential blocks if possible. */
2194
2195 bool
merge_seq_blocks(void)2196 merge_seq_blocks (void)
2197 {
2198 basic_block bb;
2199 bool changed = false;
2200
2201 for (bb = ENTRY_BLOCK_PTR->next_bb; bb != EXIT_BLOCK_PTR; )
2202 {
2203 if (single_succ_p (bb)
2204 && can_merge_blocks_p (bb, single_succ (bb)))
2205 {
2206 /* Merge the blocks and retry. */
2207 merge_blocks (bb, single_succ (bb));
2208 changed = true;
2209 continue;
2210 }
2211
2212 bb = bb->next_bb;
2213 }
2214
2215 return changed;
2216 }
2217
2218 /* Tidy the CFG by deleting unreachable code and whatnot. */
2219
2220 bool
cleanup_cfg(int mode)2221 cleanup_cfg (int mode)
2222 {
2223 bool changed = false;
2224
2225 timevar_push (TV_CLEANUP_CFG);
2226 if (delete_unreachable_blocks ())
2227 {
2228 changed = true;
2229 /* We've possibly created trivially dead code. Cleanup it right
2230 now to introduce more opportunities for try_optimize_cfg. */
2231 if (!(mode & (CLEANUP_NO_INSN_DEL | CLEANUP_UPDATE_LIFE))
2232 && !reload_completed)
2233 delete_trivially_dead_insns (get_insns(), max_reg_num ());
2234 }
2235
2236 compact_blocks ();
2237
2238 while (try_optimize_cfg (mode))
2239 {
2240 delete_unreachable_blocks (), changed = true;
2241 if (mode & CLEANUP_UPDATE_LIFE)
2242 {
2243 /* Cleaning up CFG introduces more opportunities for dead code
2244 removal that in turn may introduce more opportunities for
2245 cleaning up the CFG. */
2246 if (!update_life_info_in_dirty_blocks (UPDATE_LIFE_GLOBAL_RM_NOTES,
2247 PROP_DEATH_NOTES
2248 | PROP_SCAN_DEAD_CODE
2249 | PROP_KILL_DEAD_CODE
2250 | ((mode & CLEANUP_LOG_LINKS)
2251 ? PROP_LOG_LINKS : 0)))
2252 break;
2253 }
2254 else if (!(mode & CLEANUP_NO_INSN_DEL)
2255 && (mode & CLEANUP_EXPENSIVE)
2256 && !reload_completed)
2257 {
2258 if (!delete_trivially_dead_insns (get_insns(), max_reg_num ()))
2259 break;
2260 }
2261 else
2262 break;
2263 delete_dead_jumptables ();
2264 }
2265
2266 timevar_pop (TV_CLEANUP_CFG);
2267
2268 return changed;
2269 }
2270
2271 static unsigned int
rest_of_handle_jump(void)2272 rest_of_handle_jump (void)
2273 {
2274 delete_unreachable_blocks ();
2275
2276 if (cfun->tail_call_emit)
2277 fixup_tail_calls ();
2278 return 0;
2279 }
2280
2281 struct tree_opt_pass pass_jump =
2282 {
2283 "sibling", /* name */
2284 NULL, /* gate */
2285 rest_of_handle_jump, /* execute */
2286 NULL, /* sub */
2287 NULL, /* next */
2288 0, /* static_pass_number */
2289 TV_JUMP, /* tv_id */
2290 0, /* properties_required */
2291 0, /* properties_provided */
2292 0, /* properties_destroyed */
2293 TODO_ggc_collect, /* todo_flags_start */
2294 TODO_dump_func |
2295 TODO_verify_flow, /* todo_flags_finish */
2296 'i' /* letter */
2297 };
2298
2299
2300 static unsigned int
rest_of_handle_jump2(void)2301 rest_of_handle_jump2 (void)
2302 {
2303 /* Turn NOTE_INSN_EXPECTED_VALUE into REG_BR_PROB. Do this
2304 before jump optimization switches branch directions. */
2305 if (flag_guess_branch_prob)
2306 expected_value_to_br_prob ();
2307
2308 delete_trivially_dead_insns (get_insns (), max_reg_num ());
2309 reg_scan (get_insns (), max_reg_num ());
2310 if (dump_file)
2311 dump_flow_info (dump_file, dump_flags);
2312 cleanup_cfg ((optimize ? CLEANUP_EXPENSIVE : 0)
2313 | (flag_thread_jumps ? CLEANUP_THREADING : 0));
2314
2315 purge_line_number_notes ();
2316
2317 if (optimize)
2318 cleanup_cfg (CLEANUP_EXPENSIVE);
2319
2320 /* Jump optimization, and the removal of NULL pointer checks, may
2321 have reduced the number of instructions substantially. CSE, and
2322 future passes, allocate arrays whose dimensions involve the
2323 maximum instruction UID, so if we can reduce the maximum UID
2324 we'll save big on memory. */
2325 renumber_insns ();
2326 return 0;
2327 }
2328
2329
2330 struct tree_opt_pass pass_jump2 =
2331 {
2332 "jump", /* name */
2333 NULL, /* gate */
2334 rest_of_handle_jump2, /* execute */
2335 NULL, /* sub */
2336 NULL, /* next */
2337 0, /* static_pass_number */
2338 TV_JUMP, /* tv_id */
2339 0, /* properties_required */
2340 0, /* properties_provided */
2341 0, /* properties_destroyed */
2342 TODO_ggc_collect, /* todo_flags_start */
2343 TODO_dump_func, /* todo_flags_finish */
2344 'j' /* letter */
2345 };
2346
2347
2348