* cfghooks.c (verify_flow_info): Disable check that all probabilities
[official-gcc.git] / gcc / cfgbuild.c
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1 /* Control flow graph building code for GNU compiler.
2 Copyright (C) 1987-2017 Free Software Foundation, Inc.
4 This file is part of GCC.
6 GCC is free software; you can redistribute it and/or modify it under
7 the terms of the GNU General Public License as published by the Free
8 Software Foundation; either version 3, or (at your option) any later
9 version.
11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 for more details.
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING3. If not see
18 <http://www.gnu.org/licenses/>. */
21 #include "config.h"
22 #include "system.h"
23 #include "coretypes.h"
24 #include "backend.h"
25 #include "rtl.h"
26 #include "cfghooks.h"
27 #include "memmodel.h"
28 #include "emit-rtl.h"
29 #include "cfgrtl.h"
30 #include "cfganal.h"
31 #include "cfgbuild.h"
32 #include "except.h"
33 #include "stmt.h"
35 static void make_edges (basic_block, basic_block, int);
36 static void make_label_edge (sbitmap, basic_block, rtx, int);
37 static void find_bb_boundaries (basic_block);
38 static void compute_outgoing_frequencies (basic_block);
40 /* Return true if insn is something that should be contained inside basic
41 block. */
43 bool
44 inside_basic_block_p (const rtx_insn *insn)
46 switch (GET_CODE (insn))
48 case CODE_LABEL:
49 /* Avoid creating of basic block for jumptables. */
50 return (NEXT_INSN (insn) == 0
51 || ! JUMP_TABLE_DATA_P (NEXT_INSN (insn)));
53 case JUMP_INSN:
54 case CALL_INSN:
55 case INSN:
56 case DEBUG_INSN:
57 return true;
59 case JUMP_TABLE_DATA:
60 case BARRIER:
61 case NOTE:
62 return false;
64 default:
65 gcc_unreachable ();
69 /* Return true if INSN may cause control flow transfer, so it should be last in
70 the basic block. */
72 bool
73 control_flow_insn_p (const rtx_insn *insn)
75 switch (GET_CODE (insn))
77 case NOTE:
78 case CODE_LABEL:
79 case DEBUG_INSN:
80 return false;
82 case JUMP_INSN:
83 return true;
85 case CALL_INSN:
86 /* Noreturn and sibling call instructions terminate the basic blocks
87 (but only if they happen unconditionally). */
88 if ((SIBLING_CALL_P (insn)
89 || find_reg_note (insn, REG_NORETURN, 0))
90 && GET_CODE (PATTERN (insn)) != COND_EXEC)
91 return true;
93 /* Call insn may return to the nonlocal goto handler. */
94 if (can_nonlocal_goto (insn))
95 return true;
96 break;
98 case INSN:
99 /* Treat trap instructions like noreturn calls (same provision). */
100 if (GET_CODE (PATTERN (insn)) == TRAP_IF
101 && XEXP (PATTERN (insn), 0) == const1_rtx)
102 return true;
103 if (!cfun->can_throw_non_call_exceptions)
104 return false;
105 break;
107 case JUMP_TABLE_DATA:
108 case BARRIER:
109 /* It is nonsense to reach this when looking for the
110 end of basic block, but before dead code is eliminated
111 this may happen. */
112 return false;
114 default:
115 gcc_unreachable ();
118 return can_throw_internal (insn);
122 /* Create an edge between two basic blocks. FLAGS are auxiliary information
123 about the edge that is accumulated between calls. */
125 /* Create an edge from a basic block to a label. */
127 static void
128 make_label_edge (sbitmap edge_cache, basic_block src, rtx label, int flags)
130 gcc_assert (LABEL_P (label));
132 /* If the label was never emitted, this insn is junk, but avoid a
133 crash trying to refer to BLOCK_FOR_INSN (label). This can happen
134 as a result of a syntax error and a diagnostic has already been
135 printed. */
137 if (INSN_UID (label) == 0)
138 return;
140 cached_make_edge (edge_cache, src, BLOCK_FOR_INSN (label), flags);
143 /* Create the edges generated by INSN in REGION. */
145 void
146 rtl_make_eh_edge (sbitmap edge_cache, basic_block src, rtx insn)
148 eh_landing_pad lp = get_eh_landing_pad_from_rtx (insn);
150 if (lp)
152 rtx_insn *label = lp->landing_pad;
154 /* During initial rtl generation, use the post_landing_pad. */
155 if (label == NULL)
157 gcc_assert (lp->post_landing_pad);
158 label = label_rtx (lp->post_landing_pad);
161 make_label_edge (edge_cache, src, label,
162 EDGE_ABNORMAL | EDGE_EH
163 | (CALL_P (insn) ? EDGE_ABNORMAL_CALL : 0));
167 /* States of basic block as seen by find_many_sub_basic_blocks. */
168 enum state {
169 /* Basic blocks created via split_block belong to this state.
170 make_edges will examine these basic blocks to see if we need to
171 create edges going out of them. */
172 BLOCK_NEW = 0,
174 /* Basic blocks that do not need examining belong to this state.
175 These blocks will be left intact. In particular, make_edges will
176 not create edges going out of these basic blocks. */
177 BLOCK_ORIGINAL,
179 /* Basic blocks that may need splitting (due to a label appearing in
180 the middle, etc) belong to this state. After splitting them,
181 make_edges will create edges going out of them as needed. */
182 BLOCK_TO_SPLIT
185 #define STATE(BB) (enum state) ((size_t) (BB)->aux)
186 #define SET_STATE(BB, STATE) ((BB)->aux = (void *) (size_t) (STATE))
188 /* Used internally by purge_dead_tablejump_edges, ORed into state. */
189 #define BLOCK_USED_BY_TABLEJUMP 32
190 #define FULL_STATE(BB) ((size_t) (BB)->aux)
192 /* Identify the edges going out of basic blocks between MIN and MAX,
193 inclusive, that have their states set to BLOCK_NEW or
194 BLOCK_TO_SPLIT.
196 UPDATE_P should be nonzero if we are updating CFG and zero if we
197 are building CFG from scratch. */
199 static void
200 make_edges (basic_block min, basic_block max, int update_p)
202 basic_block bb;
203 sbitmap edge_cache = NULL;
205 /* Heavy use of computed goto in machine-generated code can lead to
206 nearly fully-connected CFGs. In that case we spend a significant
207 amount of time searching the edge lists for duplicates. */
208 if (!vec_safe_is_empty (forced_labels)
209 || cfun->cfg->max_jumptable_ents > 100)
210 edge_cache = sbitmap_alloc (last_basic_block_for_fn (cfun));
212 /* By nature of the way these get numbered, ENTRY_BLOCK_PTR->next_bb block
213 is always the entry. */
214 if (min == ENTRY_BLOCK_PTR_FOR_FN (cfun)->next_bb)
215 make_edge (ENTRY_BLOCK_PTR_FOR_FN (cfun), min, EDGE_FALLTHRU);
217 FOR_BB_BETWEEN (bb, min, max->next_bb, next_bb)
219 rtx_insn *insn;
220 enum rtx_code code;
221 edge e;
222 edge_iterator ei;
224 if (STATE (bb) == BLOCK_ORIGINAL)
225 continue;
227 /* If we have an edge cache, cache edges going out of BB. */
228 if (edge_cache)
230 bitmap_clear (edge_cache);
231 if (update_p)
233 FOR_EACH_EDGE (e, ei, bb->succs)
234 if (e->dest != EXIT_BLOCK_PTR_FOR_FN (cfun))
235 bitmap_set_bit (edge_cache, e->dest->index);
239 if (LABEL_P (BB_HEAD (bb))
240 && LABEL_ALT_ENTRY_P (BB_HEAD (bb)))
241 cached_make_edge (NULL, ENTRY_BLOCK_PTR_FOR_FN (cfun), bb, 0);
243 /* Examine the last instruction of the block, and discover the
244 ways we can leave the block. */
246 insn = BB_END (bb);
247 code = GET_CODE (insn);
249 /* A branch. */
250 if (code == JUMP_INSN)
252 rtx tmp;
253 rtx_jump_table_data *table;
255 /* Recognize a non-local goto as a branch outside the
256 current function. */
257 if (find_reg_note (insn, REG_NON_LOCAL_GOTO, NULL_RTX))
260 /* Recognize a tablejump and do the right thing. */
261 else if (tablejump_p (insn, NULL, &table))
263 rtvec vec = table->get_labels ();
264 int j;
266 for (j = GET_NUM_ELEM (vec) - 1; j >= 0; --j)
267 make_label_edge (edge_cache, bb,
268 XEXP (RTVEC_ELT (vec, j), 0), 0);
270 /* Some targets (eg, ARM) emit a conditional jump that also
271 contains the out-of-range target. Scan for these and
272 add an edge if necessary. */
273 if ((tmp = single_set (insn)) != NULL
274 && SET_DEST (tmp) == pc_rtx
275 && GET_CODE (SET_SRC (tmp)) == IF_THEN_ELSE
276 && GET_CODE (XEXP (SET_SRC (tmp), 2)) == LABEL_REF)
277 make_label_edge (edge_cache, bb,
278 label_ref_label (XEXP (SET_SRC (tmp), 2)), 0);
281 /* If this is a computed jump, then mark it as reaching
282 everything on the forced_labels list. */
283 else if (computed_jump_p (insn))
285 rtx_insn *insn;
286 unsigned int i;
287 FOR_EACH_VEC_SAFE_ELT (forced_labels, i, insn)
288 make_label_edge (edge_cache, bb, insn, EDGE_ABNORMAL);
291 /* Returns create an exit out. */
292 else if (returnjump_p (insn))
293 cached_make_edge (edge_cache, bb, EXIT_BLOCK_PTR_FOR_FN (cfun), 0);
295 /* Recognize asm goto and do the right thing. */
296 else if ((tmp = extract_asm_operands (PATTERN (insn))) != NULL)
298 int i, n = ASM_OPERANDS_LABEL_LENGTH (tmp);
299 for (i = 0; i < n; ++i)
300 make_label_edge (edge_cache, bb,
301 XEXP (ASM_OPERANDS_LABEL (tmp, i), 0), 0);
304 /* Otherwise, we have a plain conditional or unconditional jump. */
305 else
307 gcc_assert (JUMP_LABEL (insn));
308 make_label_edge (edge_cache, bb, JUMP_LABEL (insn), 0);
312 /* If this is a sibling call insn, then this is in effect a combined call
313 and return, and so we need an edge to the exit block. No need to
314 worry about EH edges, since we wouldn't have created the sibling call
315 in the first place. */
316 if (code == CALL_INSN && SIBLING_CALL_P (insn))
317 cached_make_edge (edge_cache, bb, EXIT_BLOCK_PTR_FOR_FN (cfun),
318 EDGE_SIBCALL | EDGE_ABNORMAL);
320 /* If this is a CALL_INSN, then mark it as reaching the active EH
321 handler for this CALL_INSN. If we're handling non-call
322 exceptions then any insn can reach any of the active handlers.
323 Also mark the CALL_INSN as reaching any nonlocal goto handler. */
324 else if (code == CALL_INSN || cfun->can_throw_non_call_exceptions)
326 /* Add any appropriate EH edges. */
327 rtl_make_eh_edge (edge_cache, bb, insn);
329 if (code == CALL_INSN)
331 if (can_nonlocal_goto (insn))
333 /* ??? This could be made smarter: in some cases it's
334 possible to tell that certain calls will not do a
335 nonlocal goto. For example, if the nested functions
336 that do the nonlocal gotos do not have their addresses
337 taken, then only calls to those functions or to other
338 nested functions that use them could possibly do
339 nonlocal gotos. */
340 for (rtx_insn_list *x = nonlocal_goto_handler_labels;
342 x = x->next ())
343 make_label_edge (edge_cache, bb, x->insn (),
344 EDGE_ABNORMAL | EDGE_ABNORMAL_CALL);
347 if (flag_tm)
349 rtx note;
350 for (note = REG_NOTES (insn); note; note = XEXP (note, 1))
351 if (REG_NOTE_KIND (note) == REG_TM)
352 make_label_edge (edge_cache, bb, XEXP (note, 0),
353 EDGE_ABNORMAL | EDGE_ABNORMAL_CALL);
358 /* Find out if we can drop through to the next block. */
359 insn = NEXT_INSN (insn);
360 e = find_edge (bb, EXIT_BLOCK_PTR_FOR_FN (cfun));
361 if (e && e->flags & EDGE_FALLTHRU)
362 insn = NULL;
364 while (insn
365 && NOTE_P (insn)
366 && NOTE_KIND (insn) != NOTE_INSN_BASIC_BLOCK)
367 insn = NEXT_INSN (insn);
369 if (!insn)
370 cached_make_edge (edge_cache, bb, EXIT_BLOCK_PTR_FOR_FN (cfun),
371 EDGE_FALLTHRU);
372 else if (bb->next_bb != EXIT_BLOCK_PTR_FOR_FN (cfun))
374 if (insn == BB_HEAD (bb->next_bb))
375 cached_make_edge (edge_cache, bb, bb->next_bb, EDGE_FALLTHRU);
379 if (edge_cache)
380 sbitmap_free (edge_cache);
383 static void
384 mark_tablejump_edge (rtx label)
386 basic_block bb;
388 gcc_assert (LABEL_P (label));
389 /* See comment in make_label_edge. */
390 if (INSN_UID (label) == 0)
391 return;
392 bb = BLOCK_FOR_INSN (label);
393 SET_STATE (bb, FULL_STATE (bb) | BLOCK_USED_BY_TABLEJUMP);
396 static void
397 purge_dead_tablejump_edges (basic_block bb, rtx_jump_table_data *table)
399 rtx_insn *insn = BB_END (bb);
400 rtx tmp;
401 rtvec vec;
402 int j;
403 edge_iterator ei;
404 edge e;
406 vec = table->get_labels ();
408 for (j = GET_NUM_ELEM (vec) - 1; j >= 0; --j)
409 mark_tablejump_edge (XEXP (RTVEC_ELT (vec, j), 0));
411 /* Some targets (eg, ARM) emit a conditional jump that also
412 contains the out-of-range target. Scan for these and
413 add an edge if necessary. */
414 if ((tmp = single_set (insn)) != NULL
415 && SET_DEST (tmp) == pc_rtx
416 && GET_CODE (SET_SRC (tmp)) == IF_THEN_ELSE
417 && GET_CODE (XEXP (SET_SRC (tmp), 2)) == LABEL_REF)
418 mark_tablejump_edge (label_ref_label (XEXP (SET_SRC (tmp), 2)));
420 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
422 if (FULL_STATE (e->dest) & BLOCK_USED_BY_TABLEJUMP)
423 SET_STATE (e->dest, FULL_STATE (e->dest)
424 & ~(size_t) BLOCK_USED_BY_TABLEJUMP);
425 else if (!(e->flags & (EDGE_ABNORMAL | EDGE_EH)))
427 remove_edge (e);
428 continue;
430 ei_next (&ei);
434 /* Scan basic block BB for possible BB boundaries inside the block
435 and create new basic blocks in the progress. */
437 static void
438 find_bb_boundaries (basic_block bb)
440 basic_block orig_bb = bb;
441 rtx_insn *insn = BB_HEAD (bb);
442 rtx_insn *end = BB_END (bb), *x;
443 rtx_jump_table_data *table;
444 rtx_insn *flow_transfer_insn = NULL;
445 rtx_insn *debug_insn = NULL;
446 edge fallthru = NULL;
448 if (insn == end)
449 return;
451 if (LABEL_P (insn))
452 insn = NEXT_INSN (insn);
454 /* Scan insn chain and try to find new basic block boundaries. */
455 while (1)
457 enum rtx_code code = GET_CODE (insn);
459 if (code == DEBUG_INSN)
461 if (flow_transfer_insn && !debug_insn)
462 debug_insn = insn;
464 /* In case we've previously seen an insn that effects a control
465 flow transfer, split the block. */
466 else if ((flow_transfer_insn || code == CODE_LABEL)
467 && inside_basic_block_p (insn))
469 rtx_insn *prev = PREV_INSN (insn);
471 /* If the first non-debug inside_basic_block_p insn after a control
472 flow transfer is not a label, split the block before the debug
473 insn instead of before the non-debug insn, so that the debug
474 insns are not lost. */
475 if (debug_insn && code != CODE_LABEL && code != BARRIER)
476 prev = PREV_INSN (debug_insn);
477 fallthru = split_block (bb, prev);
478 if (flow_transfer_insn)
480 BB_END (bb) = flow_transfer_insn;
482 rtx_insn *next;
483 /* Clean up the bb field for the insns between the blocks. */
484 for (x = NEXT_INSN (flow_transfer_insn);
485 x != BB_HEAD (fallthru->dest);
486 x = next)
488 next = NEXT_INSN (x);
489 /* Debug insns should not be in between basic blocks,
490 drop them on the floor. */
491 if (DEBUG_INSN_P (x))
492 delete_insn (x);
493 else if (!BARRIER_P (x))
494 set_block_for_insn (x, NULL);
498 bb = fallthru->dest;
499 remove_edge (fallthru);
500 /* BB is unreachable at this point - we need to determine its profile
501 once edges are built. */
502 bb->frequency = 0;
503 bb->count = profile_count::uninitialized ();
504 flow_transfer_insn = NULL;
505 debug_insn = NULL;
506 if (code == CODE_LABEL && LABEL_ALT_ENTRY_P (insn))
507 make_edge (ENTRY_BLOCK_PTR_FOR_FN (cfun), bb, 0);
509 else if (code == BARRIER)
511 /* __builtin_unreachable () may cause a barrier to be emitted in
512 the middle of a BB. We need to split it in the same manner as
513 if the barrier were preceded by a control_flow_insn_p insn. */
514 if (!flow_transfer_insn)
515 flow_transfer_insn = prev_nonnote_insn_bb (insn);
518 if (control_flow_insn_p (insn))
519 flow_transfer_insn = insn;
520 if (insn == end)
521 break;
522 insn = NEXT_INSN (insn);
525 /* In case expander replaced normal insn by sequence terminating by
526 return and barrier, or possibly other sequence not behaving like
527 ordinary jump, we need to take care and move basic block boundary. */
528 if (flow_transfer_insn && flow_transfer_insn != end)
530 BB_END (bb) = flow_transfer_insn;
532 /* Clean up the bb field for the insns that do not belong to BB. */
533 rtx_insn *next;
534 for (x = NEXT_INSN (flow_transfer_insn); ; x = next)
536 next = NEXT_INSN (x);
537 /* Debug insns should not be in between basic blocks,
538 drop them on the floor. */
539 if (DEBUG_INSN_P (x))
540 delete_insn (x);
541 else if (!BARRIER_P (x))
542 set_block_for_insn (x, NULL);
543 if (x == end)
544 break;
548 /* We've possibly replaced the conditional jump by conditional jump
549 followed by cleanup at fallthru edge, so the outgoing edges may
550 be dead. */
551 purge_dead_edges (bb);
553 /* purge_dead_edges doesn't handle tablejump's, but if we have split the
554 basic block, we might need to kill some edges. */
555 if (bb != orig_bb && tablejump_p (BB_END (bb), NULL, &table))
556 purge_dead_tablejump_edges (bb, table);
559 /* Assume that frequency of basic block B is known. Compute frequencies
560 and probabilities of outgoing edges. */
562 static void
563 compute_outgoing_frequencies (basic_block b)
565 edge e, f;
566 edge_iterator ei;
568 if (EDGE_COUNT (b->succs) == 2)
570 rtx note = find_reg_note (BB_END (b), REG_BR_PROB, NULL);
571 int probability;
573 if (note)
575 probability = XINT (note, 0);
576 e = BRANCH_EDGE (b);
577 e->probability
578 = profile_probability::from_reg_br_prob_note (probability);
579 e->count = b->count.apply_probability (e->probability);
580 f = FALLTHRU_EDGE (b);
581 f->probability = e->probability.invert ();
582 f->count = b->count - e->count;
583 return;
585 else
587 guess_outgoing_edge_probabilities (b);
590 else if (single_succ_p (b))
592 e = single_succ_edge (b);
593 e->probability = profile_probability::always ();
594 e->count = b->count;
595 return;
597 else
599 /* We rely on BBs with more than two successors to have sane probabilities
600 and do not guess them here. For BBs terminated by switch statements
601 expanded to jump-table jump, we have done the right thing during
602 expansion. For EH edges, we still guess the probabilities here. */
603 bool complex_edge = false;
604 FOR_EACH_EDGE (e, ei, b->succs)
605 if (e->flags & EDGE_COMPLEX)
607 complex_edge = true;
608 break;
610 if (complex_edge)
611 guess_outgoing_edge_probabilities (b);
614 if (b->count.initialized_p ())
615 FOR_EACH_EDGE (e, ei, b->succs)
616 e->count = b->count.apply_probability (e->probability);
619 /* Assume that some pass has inserted labels or control flow
620 instructions within a basic block. Split basic blocks as needed
621 and create edges. */
623 void
624 find_many_sub_basic_blocks (sbitmap blocks)
626 basic_block bb, min, max;
627 bool found = false;
628 auto_vec<unsigned int> n_succs;
629 n_succs.safe_grow_cleared (last_basic_block_for_fn (cfun));
631 FOR_EACH_BB_FN (bb, cfun)
632 SET_STATE (bb,
633 bitmap_bit_p (blocks, bb->index) ? BLOCK_TO_SPLIT : BLOCK_ORIGINAL);
635 FOR_EACH_BB_FN (bb, cfun)
636 if (STATE (bb) == BLOCK_TO_SPLIT)
638 int n = last_basic_block_for_fn (cfun);
639 unsigned int ns = EDGE_COUNT (bb->succs);
641 find_bb_boundaries (bb);
642 if (n == last_basic_block_for_fn (cfun) && ns == EDGE_COUNT (bb->succs))
643 n_succs[bb->index] = EDGE_COUNT (bb->succs);
646 FOR_EACH_BB_FN (bb, cfun)
647 if (STATE (bb) != BLOCK_ORIGINAL)
649 found = true;
650 break;
653 if (!found)
654 return;
656 min = max = bb;
657 for (; bb != EXIT_BLOCK_PTR_FOR_FN (cfun); bb = bb->next_bb)
658 if (STATE (bb) != BLOCK_ORIGINAL)
659 max = bb;
661 /* Now re-scan and wire in all edges. This expect simple (conditional)
662 jumps at the end of each new basic blocks. */
663 make_edges (min, max, 1);
665 /* Update branch probabilities. Expect only (un)conditional jumps
666 to be created with only the forward edges. */
667 if (profile_status_for_fn (cfun) != PROFILE_ABSENT)
668 FOR_BB_BETWEEN (bb, min, max->next_bb, next_bb)
670 edge e;
671 edge_iterator ei;
673 if (STATE (bb) == BLOCK_ORIGINAL)
674 continue;
675 if (STATE (bb) == BLOCK_NEW)
677 bool initialized_src = false, uninitialized_src = false;
678 bb->count = profile_count::zero ();
679 bb->frequency = 0;
680 FOR_EACH_EDGE (e, ei, bb->preds)
682 if (e->count.initialized_p ())
684 bb->count += e->count;
685 initialized_src = true;
687 else
688 uninitialized_src = true;
689 if (e->probability.initialized_p ())
690 bb->frequency += EDGE_FREQUENCY (e);
692 /* When some edges are missing with read profile, this is
693 most likely because RTL expansion introduced loop.
694 When profile is guessed we may have BB that is reachable
695 from unlikely path as well as from normal path.
697 TODO: We should handle loops created during BB expansion
698 correctly here. For now we assume all those loop to cycle
699 precisely once. */
700 if (!initialized_src
701 || (uninitialized_src
702 && profile_status_for_fn (cfun) != PROFILE_READ))
703 bb->count = profile_count::uninitialized ();
705 /* If nothing changed, there is no need to create new BBs. */
706 else if (EDGE_COUNT (bb->succs) == n_succs[bb->index])
708 /* In rare occassions RTL expansion might have mistakely assigned
709 a probabilities different from what is in CFG. This happens
710 when we try to split branch to two but optimize out the
711 second branch during the way. See PR81030. */
712 if (JUMP_P (BB_END (bb)) && any_condjump_p (BB_END (bb))
713 && EDGE_COUNT (bb->succs) >= 2)
714 update_br_prob_note (bb);
715 continue;
718 compute_outgoing_frequencies (bb);
721 FOR_EACH_BB_FN (bb, cfun)
722 SET_STATE (bb, 0);