1 /* Control flow graph building 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.
5 This file is part of GCC.
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
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
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, 59 Temple Place - Suite 330, Boston, MA
22 /* find_basic_blocks divides the current function's rtl into basic
23 blocks and constructs the CFG. The blocks are recorded in the
24 basic_block_info array; the CFG exists in the edge structures
25 referenced by the blocks.
27 find_basic_blocks also finds any unreachable loops and deletes them.
29 Available functionality:
35 #include "coretypes.h"
39 #include "hard-reg-set.h"
40 #include "basic-block.h"
49 static int count_basic_blocks (rtx);
50 static void find_basic_blocks_1 (rtx);
51 static void make_edges (basic_block, basic_block, int);
52 static void make_label_edge (sbitmap *, basic_block, rtx, int);
53 static void find_bb_boundaries (basic_block);
54 static void compute_outgoing_frequencies (basic_block);
56 /* Return true if insn is something that should be contained inside basic
60 inside_basic_block_p (rtx insn)
62 switch (GET_CODE (insn))
65 /* Avoid creating of basic block for jumptables. */
66 return (NEXT_INSN (insn) == 0
67 || !JUMP_P (NEXT_INSN (insn))
68 || (GET_CODE (PATTERN (NEXT_INSN (insn))) != ADDR_VEC
69 && GET_CODE (PATTERN (NEXT_INSN (insn))) != ADDR_DIFF_VEC));
72 return (GET_CODE (PATTERN (insn)) != ADDR_VEC
73 && GET_CODE (PATTERN (insn)) != ADDR_DIFF_VEC);
88 /* Return true if INSN may cause control flow transfer, so it should be last in
92 control_flow_insn_p (rtx insn)
96 switch (GET_CODE (insn))
103 /* Jump insn always causes control transfer except for tablejumps. */
104 return (GET_CODE (PATTERN (insn)) != ADDR_VEC
105 && GET_CODE (PATTERN (insn)) != ADDR_DIFF_VEC);
108 /* Noreturn and sibling call instructions terminate the basic blocks
109 (but only if they happen unconditionally). */
110 if ((SIBLING_CALL_P (insn)
111 || find_reg_note (insn, REG_NORETURN, 0))
112 && GET_CODE (PATTERN (insn)) != COND_EXEC)
114 /* Call insn may return to the nonlocal goto handler. */
115 return ((nonlocal_goto_handler_labels
116 && (0 == (note = find_reg_note (insn, REG_EH_REGION,
118 || INTVAL (XEXP (note, 0)) >= 0))
120 || can_throw_internal (insn));
123 return (flag_non_call_exceptions && can_throw_internal (insn));
126 /* It is nonsense to reach barrier when looking for the
127 end of basic block, but before dead code is eliminated
136 /* Count the basic blocks of the function. */
139 count_basic_blocks (rtx f)
142 bool saw_insn = false;
145 for (insn = f; insn; insn = NEXT_INSN (insn))
147 /* Code labels and barriers causes current basic block to be
148 terminated at previous real insn. */
149 if ((LABEL_P (insn) || BARRIER_P (insn))
151 count++, saw_insn = false;
153 /* Start basic block if needed. */
154 if (!saw_insn && inside_basic_block_p (insn))
157 /* Control flow insn causes current basic block to be terminated. */
158 if (saw_insn && control_flow_insn_p (insn))
159 count++, saw_insn = false;
165 /* The rest of the compiler works a bit smoother when we don't have to
166 check for the edge case of do-nothing functions with no basic blocks. */
169 emit_insn (gen_rtx_USE (VOIDmode, const0_rtx));
176 /* Create an edge between two basic blocks. FLAGS are auxiliary information
177 about the edge that is accumulated between calls. */
179 /* Create an edge from a basic block to a label. */
182 make_label_edge (sbitmap *edge_cache, basic_block src, rtx label, int flags)
184 gcc_assert (LABEL_P (label));
186 /* If the label was never emitted, this insn is junk, but avoid a
187 crash trying to refer to BLOCK_FOR_INSN (label). This can happen
188 as a result of a syntax error and a diagnostic has already been
191 if (INSN_UID (label) == 0)
194 cached_make_edge (edge_cache, src, BLOCK_FOR_INSN (label), flags);
197 /* Create the edges generated by INSN in REGION. */
200 rtl_make_eh_edge (sbitmap *edge_cache, basic_block src, rtx insn)
202 int is_call = CALL_P (insn) ? EDGE_ABNORMAL_CALL : 0;
205 handlers = reachable_handlers (insn);
207 for (i = handlers; i; i = XEXP (i, 1))
208 make_label_edge (edge_cache, src, XEXP (i, 0),
209 EDGE_ABNORMAL | EDGE_EH | is_call);
211 free_INSN_LIST_list (&handlers);
214 /* State of basic block as seen by find_many_sub_basic_blocks. */
215 enum state {BLOCK_NEW = 0, BLOCK_ORIGINAL, BLOCK_TO_SPLIT};
217 #define STATE(BB) (enum state) ((size_t) (BB)->aux)
218 #define SET_STATE(BB, STATE) ((BB)->aux = (void *) (size_t) (STATE))
220 /* Used internally by purge_dead_tablejump_edges, ORed into state. */
221 #define BLOCK_USED_BY_TABLEJUMP 32
222 #define FULL_STATE(BB) ((size_t) (BB)->aux)
224 /* Identify the edges between basic blocks MIN to MAX.
226 NONLOCAL_LABEL_LIST is a list of non-local labels in the function. Blocks
227 that are otherwise unreachable may be reachable with a non-local goto.
229 BB_EH_END is an array indexed by basic block number in which we record
230 the list of exception regions active at the end of the basic block. */
233 make_edges (basic_block min, basic_block max, int update_p)
236 sbitmap *edge_cache = NULL;
238 /* Heavy use of computed goto in machine-generated code can lead to
239 nearly fully-connected CFGs. In that case we spend a significant
240 amount of time searching the edge lists for duplicates. */
241 if (forced_labels || cfun->max_jumptable_ents > 100)
243 edge_cache = sbitmap_vector_alloc (last_basic_block, last_basic_block);
244 sbitmap_vector_zero (edge_cache, last_basic_block);
248 FOR_BB_BETWEEN (bb, min, max->next_bb, next_bb)
249 if (STATE (bb) != BLOCK_ORIGINAL)
254 FOR_EACH_EDGE (e, ei, bb->succs)
255 if (e->dest != EXIT_BLOCK_PTR)
256 SET_BIT (edge_cache[bb->index], e->dest->index);
261 /* By nature of the way these get numbered, ENTRY_BLOCK_PTR->next_bb block
262 is always the entry. */
263 if (min == ENTRY_BLOCK_PTR->next_bb)
264 cached_make_edge (edge_cache, ENTRY_BLOCK_PTR, min,
267 FOR_BB_BETWEEN (bb, min, max->next_bb, next_bb)
273 if (STATE (bb) == BLOCK_ORIGINAL)
276 if (LABEL_P (BB_HEAD (bb))
277 && LABEL_ALT_ENTRY_P (BB_HEAD (bb)))
278 cached_make_edge (NULL, ENTRY_BLOCK_PTR, bb, 0);
280 /* Examine the last instruction of the block, and discover the
281 ways we can leave the block. */
284 code = GET_CODE (insn);
287 if (code == JUMP_INSN)
291 /* Recognize exception handling placeholders. */
292 if (GET_CODE (PATTERN (insn)) == RESX)
293 rtl_make_eh_edge (edge_cache, bb, insn);
295 /* Recognize a non-local goto as a branch outside the
297 else if (find_reg_note (insn, REG_NON_LOCAL_GOTO, NULL_RTX))
300 /* Recognize a tablejump and do the right thing. */
301 else if (tablejump_p (insn, NULL, &tmp))
306 if (GET_CODE (PATTERN (tmp)) == ADDR_VEC)
307 vec = XVEC (PATTERN (tmp), 0);
309 vec = XVEC (PATTERN (tmp), 1);
311 for (j = GET_NUM_ELEM (vec) - 1; j >= 0; --j)
312 make_label_edge (edge_cache, bb,
313 XEXP (RTVEC_ELT (vec, j), 0), 0);
315 /* Some targets (eg, ARM) emit a conditional jump that also
316 contains the out-of-range target. Scan for these and
317 add an edge if necessary. */
318 if ((tmp = single_set (insn)) != NULL
319 && SET_DEST (tmp) == pc_rtx
320 && GET_CODE (SET_SRC (tmp)) == IF_THEN_ELSE
321 && GET_CODE (XEXP (SET_SRC (tmp), 2)) == LABEL_REF)
322 make_label_edge (edge_cache, bb,
323 XEXP (XEXP (SET_SRC (tmp), 2), 0), 0);
326 /* If this is a computed jump, then mark it as reaching
327 everything on the forced_labels list. */
328 else if (computed_jump_p (insn))
330 for (x = forced_labels; x; x = XEXP (x, 1))
331 make_label_edge (edge_cache, bb, XEXP (x, 0), EDGE_ABNORMAL);
334 /* Returns create an exit out. */
335 else if (returnjump_p (insn))
336 cached_make_edge (edge_cache, bb, EXIT_BLOCK_PTR, 0);
338 /* Otherwise, we have a plain conditional or unconditional jump. */
341 gcc_assert (JUMP_LABEL (insn));
342 make_label_edge (edge_cache, bb, JUMP_LABEL (insn), 0);
346 /* If this is a sibling call insn, then this is in effect a combined call
347 and return, and so we need an edge to the exit block. No need to
348 worry about EH edges, since we wouldn't have created the sibling call
349 in the first place. */
350 if (code == CALL_INSN && SIBLING_CALL_P (insn))
351 cached_make_edge (edge_cache, bb, EXIT_BLOCK_PTR,
352 EDGE_SIBCALL | EDGE_ABNORMAL);
354 /* If this is a CALL_INSN, then mark it as reaching the active EH
355 handler for this CALL_INSN. If we're handling non-call
356 exceptions then any insn can reach any of the active handlers.
357 Also mark the CALL_INSN as reaching any nonlocal goto handler. */
358 else if (code == CALL_INSN || flag_non_call_exceptions)
360 /* Add any appropriate EH edges. */
361 rtl_make_eh_edge (edge_cache, bb, insn);
363 if (code == CALL_INSN && nonlocal_goto_handler_labels)
365 /* ??? This could be made smarter: in some cases it's possible
366 to tell that certain calls will not do a nonlocal goto.
367 For example, if the nested functions that do the nonlocal
368 gotos do not have their addresses taken, then only calls to
369 those functions or to other nested functions that use them
370 could possibly do nonlocal gotos. */
372 /* We do know that a REG_EH_REGION note with a value less
373 than 0 is guaranteed not to perform a non-local goto. */
374 rtx note = find_reg_note (insn, REG_EH_REGION, NULL_RTX);
376 if (!note || INTVAL (XEXP (note, 0)) >= 0)
377 for (x = nonlocal_goto_handler_labels; x; x = XEXP (x, 1))
378 make_label_edge (edge_cache, bb, XEXP (x, 0),
379 EDGE_ABNORMAL | EDGE_ABNORMAL_CALL);
383 /* Find out if we can drop through to the next block. */
384 insn = NEXT_INSN (insn);
385 e = find_edge (bb, EXIT_BLOCK_PTR);
386 if (e && e->flags & EDGE_FALLTHRU)
391 && NOTE_LINE_NUMBER (insn) != NOTE_INSN_BASIC_BLOCK)
392 insn = NEXT_INSN (insn);
395 cached_make_edge (edge_cache, bb, EXIT_BLOCK_PTR, EDGE_FALLTHRU);
396 else if (bb->next_bb != EXIT_BLOCK_PTR)
398 if (insn == BB_HEAD (bb->next_bb))
399 cached_make_edge (edge_cache, bb, bb->next_bb, EDGE_FALLTHRU);
404 sbitmap_vector_free (edge_cache);
407 /* Find all basic blocks of the function whose first insn is F.
409 Collect and return a list of labels whose addresses are taken. This
410 will be used in make_edges for use with computed gotos. */
413 find_basic_blocks_1 (rtx f)
416 rtx bb_note = NULL_RTX;
419 basic_block prev = ENTRY_BLOCK_PTR;
421 /* We process the instructions in a slightly different way than we did
422 previously. This is so that we see a NOTE_BASIC_BLOCK after we have
423 closed out the previous block, so that it gets attached at the proper
424 place. Since this form should be equivalent to the previous,
425 count_basic_blocks continues to use the old form as a check. */
427 for (insn = f; insn; insn = next)
429 enum rtx_code code = GET_CODE (insn);
431 next = NEXT_INSN (insn);
433 if ((LABEL_P (insn) || BARRIER_P (insn))
436 prev = create_basic_block_structure (head, end, bb_note, prev);
437 head = end = NULL_RTX;
441 if (inside_basic_block_p (insn))
443 if (head == NULL_RTX)
448 if (head && control_flow_insn_p (insn))
450 prev = create_basic_block_structure (head, end, bb_note, prev);
451 head = end = NULL_RTX;
459 int kind = NOTE_LINE_NUMBER (insn);
461 /* Look for basic block notes with which to keep the
462 basic_block_info pointers stable. Unthread the note now;
463 we'll put it back at the right place in create_basic_block.
464 Or not at all if we've already found a note in this block. */
465 if (kind == NOTE_INSN_BASIC_BLOCK)
467 if (bb_note == NULL_RTX)
470 next = delete_insn (insn);
487 if (head != NULL_RTX)
488 create_basic_block_structure (head, end, bb_note, prev);
490 delete_insn (bb_note);
492 gcc_assert (last_basic_block == n_basic_blocks);
494 clear_aux_for_blocks ();
498 /* Find basic blocks of the current function.
499 F is the first insn of the function. */
502 find_basic_blocks (rtx f)
506 timevar_push (TV_CFG);
508 /* Flush out existing data. */
509 if (basic_block_info != NULL)
513 /* Clear bb->aux on all extant basic blocks. We'll use this as a
514 tag for reuse during create_basic_block, just in case some pass
515 copies around basic block notes improperly. */
519 basic_block_info = NULL;
522 n_basic_blocks = count_basic_blocks (f);
523 last_basic_block = 0;
524 ENTRY_BLOCK_PTR->next_bb = EXIT_BLOCK_PTR;
525 EXIT_BLOCK_PTR->prev_bb = ENTRY_BLOCK_PTR;
527 /* Size the basic block table. The actual structures will be allocated
528 by find_basic_blocks_1, since we want to keep the structure pointers
529 stable across calls to find_basic_blocks. */
530 /* ??? This whole issue would be much simpler if we called find_basic_blocks
531 exactly once, and thereafter we don't have a single long chain of
532 instructions at all until close to the end of compilation when we
533 actually lay them out. */
535 VARRAY_BB_INIT (basic_block_info, n_basic_blocks, "basic_block_info");
537 find_basic_blocks_1 (f);
539 profile_status = PROFILE_ABSENT;
542 SET_STATE (bb, BLOCK_NEW);
544 /* Discover the edges of our cfg. */
545 make_edges (ENTRY_BLOCK_PTR->next_bb, EXIT_BLOCK_PTR->prev_bb, 0);
547 /* Do very simple cleanup now, for the benefit of code that runs between
548 here and cleanup_cfg, e.g. thread_prologue_and_epilogue_insns. */
549 tidy_fallthru_edges ();
551 #ifdef ENABLE_CHECKING
554 timevar_pop (TV_CFG);
558 mark_tablejump_edge (rtx label)
562 gcc_assert (LABEL_P (label));
563 /* See comment in make_label_edge. */
564 if (INSN_UID (label) == 0)
566 bb = BLOCK_FOR_INSN (label);
567 SET_STATE (bb, FULL_STATE (bb) | BLOCK_USED_BY_TABLEJUMP);
571 purge_dead_tablejump_edges (basic_block bb, rtx table)
573 rtx insn = BB_END (bb), tmp;
579 if (GET_CODE (PATTERN (table)) == ADDR_VEC)
580 vec = XVEC (PATTERN (table), 0);
582 vec = XVEC (PATTERN (table), 1);
584 for (j = GET_NUM_ELEM (vec) - 1; j >= 0; --j)
585 mark_tablejump_edge (XEXP (RTVEC_ELT (vec, j), 0));
587 /* Some targets (eg, ARM) emit a conditional jump that also
588 contains the out-of-range target. Scan for these and
589 add an edge if necessary. */
590 if ((tmp = single_set (insn)) != NULL
591 && SET_DEST (tmp) == pc_rtx
592 && GET_CODE (SET_SRC (tmp)) == IF_THEN_ELSE
593 && GET_CODE (XEXP (SET_SRC (tmp), 2)) == LABEL_REF)
594 mark_tablejump_edge (XEXP (XEXP (SET_SRC (tmp), 2), 0));
596 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
598 if (FULL_STATE (e->dest) & BLOCK_USED_BY_TABLEJUMP)
599 SET_STATE (e->dest, FULL_STATE (e->dest)
600 & ~(size_t) BLOCK_USED_BY_TABLEJUMP);
601 else if (!(e->flags & (EDGE_ABNORMAL | EDGE_EH)))
610 /* Scan basic block BB for possible BB boundaries inside the block
611 and create new basic blocks in the progress. */
614 find_bb_boundaries (basic_block bb)
616 basic_block orig_bb = bb;
617 rtx insn = BB_HEAD (bb);
618 rtx end = BB_END (bb);
620 rtx flow_transfer_insn = NULL_RTX;
621 edge fallthru = NULL;
623 if (insn == BB_END (bb))
627 insn = NEXT_INSN (insn);
629 /* Scan insn chain and try to find new basic block boundaries. */
632 enum rtx_code code = GET_CODE (insn);
634 /* On code label, split current basic block. */
635 if (code == CODE_LABEL)
637 fallthru = split_block (bb, PREV_INSN (insn));
638 if (flow_transfer_insn)
639 BB_END (bb) = flow_transfer_insn;
642 remove_edge (fallthru);
643 flow_transfer_insn = NULL_RTX;
644 if (LABEL_ALT_ENTRY_P (insn))
645 make_edge (ENTRY_BLOCK_PTR, bb, 0);
648 /* In case we've previously seen an insn that effects a control
649 flow transfer, split the block. */
650 if (flow_transfer_insn && inside_basic_block_p (insn))
652 fallthru = split_block (bb, PREV_INSN (insn));
653 BB_END (bb) = flow_transfer_insn;
655 remove_edge (fallthru);
656 flow_transfer_insn = NULL_RTX;
659 if (control_flow_insn_p (insn))
660 flow_transfer_insn = insn;
663 insn = NEXT_INSN (insn);
666 /* In case expander replaced normal insn by sequence terminating by
667 return and barrier, or possibly other sequence not behaving like
668 ordinary jump, we need to take care and move basic block boundary. */
669 if (flow_transfer_insn)
670 BB_END (bb) = flow_transfer_insn;
672 /* We've possibly replaced the conditional jump by conditional jump
673 followed by cleanup at fallthru edge, so the outgoing edges may
675 purge_dead_edges (bb);
677 /* purge_dead_edges doesn't handle tablejump's, but if we have split the
678 basic block, we might need to kill some edges. */
679 if (bb != orig_bb && tablejump_p (BB_END (bb), NULL, &table))
680 purge_dead_tablejump_edges (bb, table);
683 /* Assume that frequency of basic block B is known. Compute frequencies
684 and probabilities of outgoing edges. */
687 compute_outgoing_frequencies (basic_block b)
692 if (EDGE_COUNT (b->succs) == 2)
694 rtx note = find_reg_note (BB_END (b), REG_BR_PROB, NULL);
699 probability = INTVAL (XEXP (note, 0));
701 e->probability = probability;
702 e->count = ((b->count * probability + REG_BR_PROB_BASE / 2)
704 f = FALLTHRU_EDGE (b);
705 f->probability = REG_BR_PROB_BASE - probability;
706 f->count = b->count - e->count;
711 if (EDGE_COUNT (b->succs) == 1)
713 e = EDGE_SUCC (b, 0);
714 e->probability = REG_BR_PROB_BASE;
718 guess_outgoing_edge_probabilities (b);
720 FOR_EACH_EDGE (e, ei, b->succs)
721 e->count = ((b->count * e->probability + REG_BR_PROB_BASE / 2)
725 /* Assume that someone emitted code with control flow instructions to the
726 basic block. Update the data structure. */
729 find_many_sub_basic_blocks (sbitmap blocks)
731 basic_block bb, min, max;
735 TEST_BIT (blocks, bb->index) ? BLOCK_TO_SPLIT : BLOCK_ORIGINAL);
738 if (STATE (bb) == BLOCK_TO_SPLIT)
739 find_bb_boundaries (bb);
742 if (STATE (bb) != BLOCK_ORIGINAL)
746 for (; bb != EXIT_BLOCK_PTR; bb = bb->next_bb)
747 if (STATE (bb) != BLOCK_ORIGINAL)
750 /* Now re-scan and wire in all edges. This expect simple (conditional)
751 jumps at the end of each new basic blocks. */
752 make_edges (min, max, 1);
754 /* Update branch probabilities. Expect only (un)conditional jumps
755 to be created with only the forward edges. */
756 if (profile_status != PROFILE_ABSENT)
757 FOR_BB_BETWEEN (bb, min, max->next_bb, next_bb)
762 if (STATE (bb) == BLOCK_ORIGINAL)
764 if (STATE (bb) == BLOCK_NEW)
768 FOR_EACH_EDGE (e, ei, bb->preds)
770 bb->count += e->count;
771 bb->frequency += EDGE_FREQUENCY (e);
775 compute_outgoing_frequencies (bb);