2013-08-14 Paolo Carlini <paolo.carlini@oracle.com>
[official-gcc.git] / gcc / cfgbuild.c
blobac6aefb86dfbc329b738b75c47d93e85923a5a58
1 /* Control flow graph building code for GNU compiler.
2 Copyright (C) 1987-2013 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 "tm.h"
25 #include "tree.h"
26 #include "rtl.h"
27 #include "hard-reg-set.h"
28 #include "basic-block.h"
29 #include "regs.h"
30 #include "flags.h"
31 #include "function.h"
32 #include "except.h"
33 #include "expr.h"
34 #include "diagnostic-core.h"
35 #include "timevar.h"
36 #include "sbitmap.h"
38 static void make_edges (basic_block, basic_block, int);
39 static void make_label_edge (sbitmap, basic_block, rtx, int);
40 static void find_bb_boundaries (basic_block);
41 static void compute_outgoing_frequencies (basic_block);
43 /* Return true if insn is something that should be contained inside basic
44 block. */
46 bool
47 inside_basic_block_p (const_rtx insn)
49 switch (GET_CODE (insn))
51 case CODE_LABEL:
52 /* Avoid creating of basic block for jumptables. */
53 return (NEXT_INSN (insn) == 0
54 || ! JUMP_TABLE_DATA_P (NEXT_INSN (insn)));
56 case JUMP_INSN:
57 case CALL_INSN:
58 case INSN:
59 case DEBUG_INSN:
60 return true;
62 case JUMP_TABLE_DATA:
63 case BARRIER:
64 case NOTE:
65 return false;
67 default:
68 gcc_unreachable ();
72 /* Return true if INSN may cause control flow transfer, so it should be last in
73 the basic block. */
75 bool
76 control_flow_insn_p (const_rtx insn)
78 switch (GET_CODE (insn))
80 case NOTE:
81 case CODE_LABEL:
82 case DEBUG_INSN:
83 return false;
85 case JUMP_INSN:
86 return true;
88 case CALL_INSN:
89 /* Noreturn and sibling call instructions terminate the basic blocks
90 (but only if they happen unconditionally). */
91 if ((SIBLING_CALL_P (insn)
92 || find_reg_note (insn, REG_NORETURN, 0))
93 && GET_CODE (PATTERN (insn)) != COND_EXEC)
94 return true;
96 /* Call insn may return to the nonlocal goto handler. */
97 if (can_nonlocal_goto (insn))
98 return true;
99 break;
101 case INSN:
102 /* Treat trap instructions like noreturn calls (same provision). */
103 if (GET_CODE (PATTERN (insn)) == TRAP_IF
104 && XEXP (PATTERN (insn), 0) == const1_rtx)
105 return true;
106 if (!cfun->can_throw_non_call_exceptions)
107 return false;
108 break;
110 case JUMP_TABLE_DATA:
111 case BARRIER:
112 /* It is nonsense to reach this when looking for the
113 end of basic block, but before dead code is eliminated
114 this may happen. */
115 return false;
117 default:
118 gcc_unreachable ();
121 return can_throw_internal (insn);
125 /* Create an edge between two basic blocks. FLAGS are auxiliary information
126 about the edge that is accumulated between calls. */
128 /* Create an edge from a basic block to a label. */
130 static void
131 make_label_edge (sbitmap edge_cache, basic_block src, rtx label, int flags)
133 gcc_assert (LABEL_P (label));
135 /* If the label was never emitted, this insn is junk, but avoid a
136 crash trying to refer to BLOCK_FOR_INSN (label). This can happen
137 as a result of a syntax error and a diagnostic has already been
138 printed. */
140 if (INSN_UID (label) == 0)
141 return;
143 cached_make_edge (edge_cache, src, BLOCK_FOR_INSN (label), flags);
146 /* Create the edges generated by INSN in REGION. */
148 void
149 rtl_make_eh_edge (sbitmap edge_cache, basic_block src, rtx insn)
151 eh_landing_pad lp = get_eh_landing_pad_from_rtx (insn);
153 if (lp)
155 rtx label = lp->landing_pad;
157 /* During initial rtl generation, use the post_landing_pad. */
158 if (label == NULL)
160 gcc_assert (lp->post_landing_pad);
161 label = label_rtx (lp->post_landing_pad);
164 make_label_edge (edge_cache, src, label,
165 EDGE_ABNORMAL | EDGE_EH
166 | (CALL_P (insn) ? EDGE_ABNORMAL_CALL : 0));
170 /* States of basic block as seen by find_many_sub_basic_blocks. */
171 enum state {
172 /* Basic blocks created via split_block belong to this state.
173 make_edges will examine these basic blocks to see if we need to
174 create edges going out of them. */
175 BLOCK_NEW = 0,
177 /* Basic blocks that do not need examining belong to this state.
178 These blocks will be left intact. In particular, make_edges will
179 not create edges going out of these basic blocks. */
180 BLOCK_ORIGINAL,
182 /* Basic blocks that may need splitting (due to a label appearing in
183 the middle, etc) belong to this state. After splitting them,
184 make_edges will create edges going out of them as needed. */
185 BLOCK_TO_SPLIT
188 #define STATE(BB) (enum state) ((size_t) (BB)->aux)
189 #define SET_STATE(BB, STATE) ((BB)->aux = (void *) (size_t) (STATE))
191 /* Used internally by purge_dead_tablejump_edges, ORed into state. */
192 #define BLOCK_USED_BY_TABLEJUMP 32
193 #define FULL_STATE(BB) ((size_t) (BB)->aux)
195 /* Identify the edges going out of basic blocks between MIN and MAX,
196 inclusive, that have their states set to BLOCK_NEW or
197 BLOCK_TO_SPLIT.
199 UPDATE_P should be nonzero if we are updating CFG and zero if we
200 are building CFG from scratch. */
202 static void
203 make_edges (basic_block min, basic_block max, int update_p)
205 basic_block bb;
206 sbitmap edge_cache = NULL;
208 /* Heavy use of computed goto in machine-generated code can lead to
209 nearly fully-connected CFGs. In that case we spend a significant
210 amount of time searching the edge lists for duplicates. */
211 if (forced_labels || cfun->cfg->max_jumptable_ents > 100)
212 edge_cache = sbitmap_alloc (last_basic_block);
214 /* By nature of the way these get numbered, ENTRY_BLOCK_PTR->next_bb block
215 is always the entry. */
216 if (min == ENTRY_BLOCK_PTR->next_bb)
217 make_edge (ENTRY_BLOCK_PTR, min, EDGE_FALLTHRU);
219 FOR_BB_BETWEEN (bb, min, max->next_bb, next_bb)
221 rtx insn, x;
222 enum rtx_code code;
223 edge e;
224 edge_iterator ei;
226 if (STATE (bb) == BLOCK_ORIGINAL)
227 continue;
229 /* If we have an edge cache, cache edges going out of BB. */
230 if (edge_cache)
232 bitmap_clear (edge_cache);
233 if (update_p)
235 FOR_EACH_EDGE (e, ei, bb->succs)
236 if (e->dest != EXIT_BLOCK_PTR)
237 bitmap_set_bit (edge_cache, e->dest->index);
241 if (LABEL_P (BB_HEAD (bb))
242 && LABEL_ALT_ENTRY_P (BB_HEAD (bb)))
243 cached_make_edge (NULL, ENTRY_BLOCK_PTR, bb, 0);
245 /* Examine the last instruction of the block, and discover the
246 ways we can leave the block. */
248 insn = BB_END (bb);
249 code = GET_CODE (insn);
251 /* A branch. */
252 if (code == JUMP_INSN)
254 rtx tmp;
256 /* Recognize a non-local goto as a branch outside the
257 current function. */
258 if (find_reg_note (insn, REG_NON_LOCAL_GOTO, NULL_RTX))
261 /* Recognize a tablejump and do the right thing. */
262 else if (tablejump_p (insn, NULL, &tmp))
264 rtvec vec;
265 int j;
267 if (GET_CODE (PATTERN (tmp)) == ADDR_VEC)
268 vec = XVEC (PATTERN (tmp), 0);
269 else
270 vec = XVEC (PATTERN (tmp), 1);
272 for (j = GET_NUM_ELEM (vec) - 1; j >= 0; --j)
273 make_label_edge (edge_cache, bb,
274 XEXP (RTVEC_ELT (vec, j), 0), 0);
276 /* Some targets (eg, ARM) emit a conditional jump that also
277 contains the out-of-range target. Scan for these and
278 add an edge if necessary. */
279 if ((tmp = single_set (insn)) != NULL
280 && SET_DEST (tmp) == pc_rtx
281 && GET_CODE (SET_SRC (tmp)) == IF_THEN_ELSE
282 && GET_CODE (XEXP (SET_SRC (tmp), 2)) == LABEL_REF)
283 make_label_edge (edge_cache, bb,
284 XEXP (XEXP (SET_SRC (tmp), 2), 0), 0);
287 /* If this is a computed jump, then mark it as reaching
288 everything on the forced_labels list. */
289 else if (computed_jump_p (insn))
291 for (x = forced_labels; x; x = XEXP (x, 1))
292 make_label_edge (edge_cache, bb, XEXP (x, 0), EDGE_ABNORMAL);
295 /* Returns create an exit out. */
296 else if (returnjump_p (insn))
297 cached_make_edge (edge_cache, bb, EXIT_BLOCK_PTR, 0);
299 /* Recognize asm goto and do the right thing. */
300 else if ((tmp = extract_asm_operands (PATTERN (insn))) != NULL)
302 int i, n = ASM_OPERANDS_LABEL_LENGTH (tmp);
303 for (i = 0; i < n; ++i)
304 make_label_edge (edge_cache, bb,
305 XEXP (ASM_OPERANDS_LABEL (tmp, i), 0), 0);
308 /* Otherwise, we have a plain conditional or unconditional jump. */
309 else
311 gcc_assert (JUMP_LABEL (insn));
312 make_label_edge (edge_cache, bb, JUMP_LABEL (insn), 0);
316 /* If this is a sibling call insn, then this is in effect a combined call
317 and return, and so we need an edge to the exit block. No need to
318 worry about EH edges, since we wouldn't have created the sibling call
319 in the first place. */
320 if (code == CALL_INSN && SIBLING_CALL_P (insn))
321 cached_make_edge (edge_cache, bb, EXIT_BLOCK_PTR,
322 EDGE_SIBCALL | EDGE_ABNORMAL);
324 /* If this is a CALL_INSN, then mark it as reaching the active EH
325 handler for this CALL_INSN. If we're handling non-call
326 exceptions then any insn can reach any of the active handlers.
327 Also mark the CALL_INSN as reaching any nonlocal goto handler. */
328 else if (code == CALL_INSN || cfun->can_throw_non_call_exceptions)
330 /* Add any appropriate EH edges. */
331 rtl_make_eh_edge (edge_cache, bb, insn);
333 if (code == CALL_INSN)
335 if (can_nonlocal_goto (insn))
337 /* ??? This could be made smarter: in some cases it's
338 possible to tell that certain calls will not do a
339 nonlocal goto. For example, if the nested functions
340 that do the nonlocal gotos do not have their addresses
341 taken, then only calls to those functions or to other
342 nested functions that use them could possibly do
343 nonlocal gotos. */
344 for (x = nonlocal_goto_handler_labels; x; x = XEXP (x, 1))
345 make_label_edge (edge_cache, bb, XEXP (x, 0),
346 EDGE_ABNORMAL | EDGE_ABNORMAL_CALL);
349 if (flag_tm)
351 rtx note;
352 for (note = REG_NOTES (insn); note; note = XEXP (note, 1))
353 if (REG_NOTE_KIND (note) == REG_TM)
354 make_label_edge (edge_cache, bb, XEXP (note, 0),
355 EDGE_ABNORMAL | EDGE_ABNORMAL_CALL);
360 /* Find out if we can drop through to the next block. */
361 insn = NEXT_INSN (insn);
362 e = find_edge (bb, EXIT_BLOCK_PTR);
363 if (e && e->flags & EDGE_FALLTHRU)
364 insn = NULL;
366 while (insn
367 && NOTE_P (insn)
368 && NOTE_KIND (insn) != NOTE_INSN_BASIC_BLOCK)
369 insn = NEXT_INSN (insn);
371 if (!insn)
372 cached_make_edge (edge_cache, bb, EXIT_BLOCK_PTR, EDGE_FALLTHRU);
373 else if (bb->next_bb != EXIT_BLOCK_PTR)
375 if (insn == BB_HEAD (bb->next_bb))
376 cached_make_edge (edge_cache, bb, bb->next_bb, EDGE_FALLTHRU);
380 if (edge_cache)
381 sbitmap_free (edge_cache);
384 static void
385 mark_tablejump_edge (rtx label)
387 basic_block bb;
389 gcc_assert (LABEL_P (label));
390 /* See comment in make_label_edge. */
391 if (INSN_UID (label) == 0)
392 return;
393 bb = BLOCK_FOR_INSN (label);
394 SET_STATE (bb, FULL_STATE (bb) | BLOCK_USED_BY_TABLEJUMP);
397 static void
398 purge_dead_tablejump_edges (basic_block bb, rtx table)
400 rtx insn = BB_END (bb), tmp;
401 rtvec vec;
402 int j;
403 edge_iterator ei;
404 edge e;
406 if (GET_CODE (PATTERN (table)) == ADDR_VEC)
407 vec = XVEC (PATTERN (table), 0);
408 else
409 vec = XVEC (PATTERN (table), 1);
411 for (j = GET_NUM_ELEM (vec) - 1; j >= 0; --j)
412 mark_tablejump_edge (XEXP (RTVEC_ELT (vec, j), 0));
414 /* Some targets (eg, ARM) emit a conditional jump that also
415 contains the out-of-range target. Scan for these and
416 add an edge if necessary. */
417 if ((tmp = single_set (insn)) != NULL
418 && SET_DEST (tmp) == pc_rtx
419 && GET_CODE (SET_SRC (tmp)) == IF_THEN_ELSE
420 && GET_CODE (XEXP (SET_SRC (tmp), 2)) == LABEL_REF)
421 mark_tablejump_edge (XEXP (XEXP (SET_SRC (tmp), 2), 0));
423 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
425 if (FULL_STATE (e->dest) & BLOCK_USED_BY_TABLEJUMP)
426 SET_STATE (e->dest, FULL_STATE (e->dest)
427 & ~(size_t) BLOCK_USED_BY_TABLEJUMP);
428 else if (!(e->flags & (EDGE_ABNORMAL | EDGE_EH)))
430 remove_edge (e);
431 continue;
433 ei_next (&ei);
437 /* Scan basic block BB for possible BB boundaries inside the block
438 and create new basic blocks in the progress. */
440 static void
441 find_bb_boundaries (basic_block bb)
443 basic_block orig_bb = bb;
444 rtx insn = BB_HEAD (bb);
445 rtx end = BB_END (bb), x;
446 rtx table;
447 rtx flow_transfer_insn = NULL_RTX;
448 edge fallthru = NULL;
450 if (insn == BB_END (bb))
451 return;
453 if (LABEL_P (insn))
454 insn = NEXT_INSN (insn);
456 /* Scan insn chain and try to find new basic block boundaries. */
457 while (1)
459 enum rtx_code code = GET_CODE (insn);
461 /* In case we've previously seen an insn that effects a control
462 flow transfer, split the block. */
463 if ((flow_transfer_insn || code == CODE_LABEL)
464 && inside_basic_block_p (insn))
466 fallthru = split_block (bb, PREV_INSN (insn));
467 if (flow_transfer_insn)
469 BB_END (bb) = flow_transfer_insn;
471 /* Clean up the bb field for the insns between the blocks. */
472 for (x = NEXT_INSN (flow_transfer_insn);
473 x != BB_HEAD (fallthru->dest);
474 x = NEXT_INSN (x))
475 if (!BARRIER_P (x))
476 set_block_for_insn (x, NULL);
479 bb = fallthru->dest;
480 remove_edge (fallthru);
481 flow_transfer_insn = NULL_RTX;
482 if (code == CODE_LABEL && LABEL_ALT_ENTRY_P (insn))
483 make_edge (ENTRY_BLOCK_PTR, bb, 0);
485 else if (code == BARRIER)
487 /* __builtin_unreachable () may cause a barrier to be emitted in
488 the middle of a BB. We need to split it in the same manner as
489 if the barrier were preceded by a control_flow_insn_p insn. */
490 if (!flow_transfer_insn)
491 flow_transfer_insn = prev_nonnote_insn_bb (insn);
494 if (control_flow_insn_p (insn))
495 flow_transfer_insn = insn;
496 if (insn == end)
497 break;
498 insn = NEXT_INSN (insn);
501 /* In case expander replaced normal insn by sequence terminating by
502 return and barrier, or possibly other sequence not behaving like
503 ordinary jump, we need to take care and move basic block boundary. */
504 if (flow_transfer_insn)
506 BB_END (bb) = flow_transfer_insn;
508 /* Clean up the bb field for the insns that do not belong to BB. */
509 x = flow_transfer_insn;
510 while (x != end)
512 x = NEXT_INSN (x);
513 if (!BARRIER_P (x))
514 set_block_for_insn (x, NULL);
518 /* We've possibly replaced the conditional jump by conditional jump
519 followed by cleanup at fallthru edge, so the outgoing edges may
520 be dead. */
521 purge_dead_edges (bb);
523 /* purge_dead_edges doesn't handle tablejump's, but if we have split the
524 basic block, we might need to kill some edges. */
525 if (bb != orig_bb && tablejump_p (BB_END (bb), NULL, &table))
526 purge_dead_tablejump_edges (bb, table);
529 /* Assume that frequency of basic block B is known. Compute frequencies
530 and probabilities of outgoing edges. */
532 static void
533 compute_outgoing_frequencies (basic_block b)
535 edge e, f;
536 edge_iterator ei;
538 if (EDGE_COUNT (b->succs) == 2)
540 rtx note = find_reg_note (BB_END (b), REG_BR_PROB, NULL);
541 int probability;
543 if (note)
545 probability = INTVAL (XEXP (note, 0));
546 e = BRANCH_EDGE (b);
547 e->probability = probability;
548 e->count = apply_probability (b->count, probability);
549 f = FALLTHRU_EDGE (b);
550 f->probability = REG_BR_PROB_BASE - probability;
551 f->count = b->count - e->count;
552 return;
554 else
556 guess_outgoing_edge_probabilities (b);
559 else if (single_succ_p (b))
561 e = single_succ_edge (b);
562 e->probability = REG_BR_PROB_BASE;
563 e->count = b->count;
564 return;
566 else
568 /* We rely on BBs with more than two successors to have sane probabilities
569 and do not guess them here. For BBs terminated by switch statements
570 expanded to jump-table jump, we have done the right thing during
571 expansion. For EH edges, we still guess the probabilities here. */
572 bool complex_edge = false;
573 FOR_EACH_EDGE (e, ei, b->succs)
574 if (e->flags & EDGE_COMPLEX)
576 complex_edge = true;
577 break;
579 if (complex_edge)
580 guess_outgoing_edge_probabilities (b);
583 if (b->count)
584 FOR_EACH_EDGE (e, ei, b->succs)
585 e->count = apply_probability (b->count, e->probability);
588 /* Assume that some pass has inserted labels or control flow
589 instructions within a basic block. Split basic blocks as needed
590 and create edges. */
592 void
593 find_many_sub_basic_blocks (sbitmap blocks)
595 basic_block bb, min, max;
597 FOR_EACH_BB (bb)
598 SET_STATE (bb,
599 bitmap_bit_p (blocks, bb->index) ? BLOCK_TO_SPLIT : BLOCK_ORIGINAL);
601 FOR_EACH_BB (bb)
602 if (STATE (bb) == BLOCK_TO_SPLIT)
603 find_bb_boundaries (bb);
605 FOR_EACH_BB (bb)
606 if (STATE (bb) != BLOCK_ORIGINAL)
607 break;
609 min = max = bb;
610 for (; bb != EXIT_BLOCK_PTR; bb = bb->next_bb)
611 if (STATE (bb) != BLOCK_ORIGINAL)
612 max = bb;
614 /* Now re-scan and wire in all edges. This expect simple (conditional)
615 jumps at the end of each new basic blocks. */
616 make_edges (min, max, 1);
618 /* Update branch probabilities. Expect only (un)conditional jumps
619 to be created with only the forward edges. */
620 if (profile_status != PROFILE_ABSENT)
621 FOR_BB_BETWEEN (bb, min, max->next_bb, next_bb)
623 edge e;
624 edge_iterator ei;
626 if (STATE (bb) == BLOCK_ORIGINAL)
627 continue;
628 if (STATE (bb) == BLOCK_NEW)
630 bb->count = 0;
631 bb->frequency = 0;
632 FOR_EACH_EDGE (e, ei, bb->preds)
634 bb->count += e->count;
635 bb->frequency += EDGE_FREQUENCY (e);
639 compute_outgoing_frequencies (bb);
642 FOR_EACH_BB (bb)
643 SET_STATE (bb, 0);