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, 51 Franklin Street, Fifth Floor, 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 /* Treat trap instructions like noreturn calls (same provision). */
124 if (GET_CODE (PATTERN (insn)) == TRAP_IF
125 && XEXP (PATTERN (insn), 0) == const1_rtx)
128 return (flag_non_call_exceptions && can_throw_internal (insn));
131 /* It is nonsense to reach barrier when looking for the
132 end of basic block, but before dead code is eliminated
141 /* Count the basic blocks of the function. */
144 count_basic_blocks (rtx f)
146 int count = NUM_FIXED_BLOCKS;
147 bool saw_insn = false;
150 for (insn = f; insn; insn = NEXT_INSN (insn))
152 /* Code labels and barriers causes current basic block to be
153 terminated at previous real insn. */
154 if ((LABEL_P (insn) || BARRIER_P (insn))
156 count++, saw_insn = false;
158 /* Start basic block if needed. */
159 if (!saw_insn && inside_basic_block_p (insn))
162 /* Control flow insn causes current basic block to be terminated. */
163 if (saw_insn && control_flow_insn_p (insn))
164 count++, saw_insn = false;
170 /* The rest of the compiler works a bit smoother when we don't have to
171 check for the edge case of do-nothing functions with no basic blocks. */
172 if (count == NUM_FIXED_BLOCKS)
174 emit_insn (gen_rtx_USE (VOIDmode, const0_rtx));
175 count = NUM_FIXED_BLOCKS + 1;
181 /* Create an edge between two basic blocks. FLAGS are auxiliary information
182 about the edge that is accumulated between calls. */
184 /* Create an edge from a basic block to a label. */
187 make_label_edge (sbitmap edge_cache, basic_block src, rtx label, int flags)
189 gcc_assert (LABEL_P (label));
191 /* If the label was never emitted, this insn is junk, but avoid a
192 crash trying to refer to BLOCK_FOR_INSN (label). This can happen
193 as a result of a syntax error and a diagnostic has already been
196 if (INSN_UID (label) == 0)
199 cached_make_edge (edge_cache, src, BLOCK_FOR_INSN (label), flags);
202 /* Create the edges generated by INSN in REGION. */
205 rtl_make_eh_edge (sbitmap edge_cache, basic_block src, rtx insn)
207 int is_call = CALL_P (insn) ? EDGE_ABNORMAL_CALL : 0;
210 handlers = reachable_handlers (insn);
212 for (i = handlers; i; i = XEXP (i, 1))
213 make_label_edge (edge_cache, src, XEXP (i, 0),
214 EDGE_ABNORMAL | EDGE_EH | is_call);
216 free_INSN_LIST_list (&handlers);
219 /* States of basic block as seen by find_many_sub_basic_blocks. */
221 /* Basic blocks created via split_block belong to this state.
222 make_edges will examine these basic blocks to see if we need to
223 create edges going out of them. */
226 /* Basic blocks that do not need examining belong to this state.
227 These blocks will be left intact. In particular, make_edges will
228 not create edges going out of these basic blocks. */
231 /* Basic blocks that may need splitting (due to a label appearing in
232 the middle, etc) belong to this state. After splitting them,
233 make_edges will create edges going out of them as needed. */
237 #define STATE(BB) (enum state) ((size_t) (BB)->aux)
238 #define SET_STATE(BB, STATE) ((BB)->aux = (void *) (size_t) (STATE))
240 /* Used internally by purge_dead_tablejump_edges, ORed into state. */
241 #define BLOCK_USED_BY_TABLEJUMP 32
242 #define FULL_STATE(BB) ((size_t) (BB)->aux)
244 /* Identify the edges going out of basic blocks between MIN and MAX,
245 inclusive, that have their states set to BLOCK_NEW or
248 UPDATE_P should be nonzero if we are updating CFG and zero if we
249 are building CFG from scratch. */
252 make_edges (basic_block min, basic_block max, int update_p)
255 sbitmap edge_cache = NULL;
257 /* Heavy use of computed goto in machine-generated code can lead to
258 nearly fully-connected CFGs. In that case we spend a significant
259 amount of time searching the edge lists for duplicates. */
260 if (forced_labels || cfun->max_jumptable_ents > 100)
261 edge_cache = sbitmap_alloc (last_basic_block);
263 /* By nature of the way these get numbered, ENTRY_BLOCK_PTR->next_bb block
264 is always the entry. */
265 if (min == ENTRY_BLOCK_PTR->next_bb)
266 make_edge (ENTRY_BLOCK_PTR, min, EDGE_FALLTHRU);
268 FOR_BB_BETWEEN (bb, min, max->next_bb, next_bb)
275 if (STATE (bb) == BLOCK_ORIGINAL)
278 /* If we have an edge cache, cache edges going out of BB. */
281 sbitmap_zero (edge_cache);
284 FOR_EACH_EDGE (e, ei, bb->succs)
285 if (e->dest != EXIT_BLOCK_PTR)
286 SET_BIT (edge_cache, e->dest->index);
290 if (LABEL_P (BB_HEAD (bb))
291 && LABEL_ALT_ENTRY_P (BB_HEAD (bb)))
292 cached_make_edge (NULL, ENTRY_BLOCK_PTR, bb, 0);
294 /* Examine the last instruction of the block, and discover the
295 ways we can leave the block. */
298 code = GET_CODE (insn);
301 if (code == JUMP_INSN)
305 /* Recognize exception handling placeholders. */
306 if (GET_CODE (PATTERN (insn)) == RESX)
307 rtl_make_eh_edge (edge_cache, bb, insn);
309 /* Recognize a non-local goto as a branch outside the
311 else if (find_reg_note (insn, REG_NON_LOCAL_GOTO, NULL_RTX))
314 /* Recognize a tablejump and do the right thing. */
315 else if (tablejump_p (insn, NULL, &tmp))
320 if (GET_CODE (PATTERN (tmp)) == ADDR_VEC)
321 vec = XVEC (PATTERN (tmp), 0);
323 vec = XVEC (PATTERN (tmp), 1);
325 for (j = GET_NUM_ELEM (vec) - 1; j >= 0; --j)
326 make_label_edge (edge_cache, bb,
327 XEXP (RTVEC_ELT (vec, j), 0), 0);
329 /* Some targets (eg, ARM) emit a conditional jump that also
330 contains the out-of-range target. Scan for these and
331 add an edge if necessary. */
332 if ((tmp = single_set (insn)) != NULL
333 && SET_DEST (tmp) == pc_rtx
334 && GET_CODE (SET_SRC (tmp)) == IF_THEN_ELSE
335 && GET_CODE (XEXP (SET_SRC (tmp), 2)) == LABEL_REF)
336 make_label_edge (edge_cache, bb,
337 XEXP (XEXP (SET_SRC (tmp), 2), 0), 0);
340 /* If this is a computed jump, then mark it as reaching
341 everything on the forced_labels list. */
342 else if (computed_jump_p (insn))
344 for (x = forced_labels; x; x = XEXP (x, 1))
345 make_label_edge (edge_cache, bb, XEXP (x, 0), EDGE_ABNORMAL);
348 /* Returns create an exit out. */
349 else if (returnjump_p (insn))
350 cached_make_edge (edge_cache, bb, EXIT_BLOCK_PTR, 0);
352 /* Otherwise, we have a plain conditional or unconditional jump. */
355 gcc_assert (JUMP_LABEL (insn));
356 make_label_edge (edge_cache, bb, JUMP_LABEL (insn), 0);
360 /* If this is a sibling call insn, then this is in effect a combined call
361 and return, and so we need an edge to the exit block. No need to
362 worry about EH edges, since we wouldn't have created the sibling call
363 in the first place. */
364 if (code == CALL_INSN && SIBLING_CALL_P (insn))
365 cached_make_edge (edge_cache, bb, EXIT_BLOCK_PTR,
366 EDGE_SIBCALL | EDGE_ABNORMAL);
368 /* If this is a CALL_INSN, then mark it as reaching the active EH
369 handler for this CALL_INSN. If we're handling non-call
370 exceptions then any insn can reach any of the active handlers.
371 Also mark the CALL_INSN as reaching any nonlocal goto handler. */
372 else if (code == CALL_INSN || flag_non_call_exceptions)
374 /* Add any appropriate EH edges. */
375 rtl_make_eh_edge (edge_cache, bb, insn);
377 if (code == CALL_INSN && nonlocal_goto_handler_labels)
379 /* ??? This could be made smarter: in some cases it's possible
380 to tell that certain calls will not do a nonlocal goto.
381 For example, if the nested functions that do the nonlocal
382 gotos do not have their addresses taken, then only calls to
383 those functions or to other nested functions that use them
384 could possibly do nonlocal gotos. */
386 /* We do know that a REG_EH_REGION note with a value less
387 than 0 is guaranteed not to perform a non-local goto. */
388 rtx note = find_reg_note (insn, REG_EH_REGION, NULL_RTX);
390 if (!note || INTVAL (XEXP (note, 0)) >= 0)
391 for (x = nonlocal_goto_handler_labels; x; x = XEXP (x, 1))
392 make_label_edge (edge_cache, bb, XEXP (x, 0),
393 EDGE_ABNORMAL | EDGE_ABNORMAL_CALL);
397 /* Find out if we can drop through to the next block. */
398 insn = NEXT_INSN (insn);
399 e = find_edge (bb, EXIT_BLOCK_PTR);
400 if (e && e->flags & EDGE_FALLTHRU)
405 && NOTE_KIND (insn) != NOTE_INSN_BASIC_BLOCK)
406 insn = NEXT_INSN (insn);
409 cached_make_edge (edge_cache, bb, EXIT_BLOCK_PTR, EDGE_FALLTHRU);
410 else if (bb->next_bb != EXIT_BLOCK_PTR)
412 if (insn == BB_HEAD (bb->next_bb))
413 cached_make_edge (edge_cache, bb, bb->next_bb, EDGE_FALLTHRU);
418 sbitmap_vector_free (edge_cache);
421 /* Find all basic blocks of the function whose first insn is F.
423 Collect and return a list of labels whose addresses are taken. This
424 will be used in make_edges for use with computed gotos. */
427 find_basic_blocks_1 (rtx f)
430 rtx bb_note = NULL_RTX;
433 basic_block prev = ENTRY_BLOCK_PTR;
435 /* We process the instructions in a slightly different way than we did
436 previously. This is so that we see a NOTE_BASIC_BLOCK after we have
437 closed out the previous block, so that it gets attached at the proper
438 place. Since this form should be equivalent to the previous,
439 count_basic_blocks continues to use the old form as a check. */
441 for (insn = f; insn; insn = next)
443 enum rtx_code code = GET_CODE (insn);
445 next = NEXT_INSN (insn);
447 if ((LABEL_P (insn) || BARRIER_P (insn))
450 prev = create_basic_block_structure (head, end, bb_note, prev);
451 head = end = NULL_RTX;
455 if (inside_basic_block_p (insn))
457 if (head == NULL_RTX)
462 if (head && control_flow_insn_p (insn))
464 prev = create_basic_block_structure (head, end, bb_note, prev);
465 head = end = NULL_RTX;
472 /* Look for basic block notes with which to keep the
473 basic_block_info pointers stable. Unthread the note now;
474 we'll put it back at the right place in create_basic_block.
475 Or not at all if we've already found a note in this block. */
476 if (NOTE_INSN_BASIC_BLOCK_P (insn))
478 if (bb_note == NULL_RTX)
481 next = delete_insn (insn);
497 if (head != NULL_RTX)
498 create_basic_block_structure (head, end, bb_note, prev);
500 delete_insn (bb_note);
502 gcc_assert (last_basic_block == n_basic_blocks);
504 clear_aux_for_blocks ();
508 /* Find basic blocks of the current function.
509 F is the first insn of the function. */
512 find_basic_blocks (rtx f)
516 timevar_push (TV_CFG);
518 /* Flush out existing data. */
519 if (basic_block_info != NULL)
523 /* Clear bb->aux on all extant basic blocks. We'll use this as a
524 tag for reuse during create_basic_block, just in case some pass
525 copies around basic block notes improperly. */
529 basic_block_info = NULL;
532 n_basic_blocks = count_basic_blocks (f);
533 last_basic_block = NUM_FIXED_BLOCKS;
534 ENTRY_BLOCK_PTR->next_bb = EXIT_BLOCK_PTR;
535 EXIT_BLOCK_PTR->prev_bb = ENTRY_BLOCK_PTR;
538 /* Size the basic block table. The actual structures will be allocated
539 by find_basic_blocks_1, since we want to keep the structure pointers
540 stable across calls to find_basic_blocks. */
541 /* ??? This whole issue would be much simpler if we called find_basic_blocks
542 exactly once, and thereafter we don't have a single long chain of
543 instructions at all until close to the end of compilation when we
544 actually lay them out. */
546 basic_block_info = VEC_alloc (basic_block, gc, n_basic_blocks);
547 VEC_safe_grow_cleared (basic_block, gc, basic_block_info, n_basic_blocks);
548 SET_BASIC_BLOCK (ENTRY_BLOCK, ENTRY_BLOCK_PTR);
549 SET_BASIC_BLOCK (EXIT_BLOCK, EXIT_BLOCK_PTR);
551 find_basic_blocks_1 (f);
553 profile_status = PROFILE_ABSENT;
555 /* Tell make_edges to examine every block for out-going edges. */
557 SET_STATE (bb, BLOCK_NEW);
559 /* Discover the edges of our cfg. */
560 make_edges (ENTRY_BLOCK_PTR->next_bb, EXIT_BLOCK_PTR->prev_bb, 0);
562 /* Do very simple cleanup now, for the benefit of code that runs between
563 here and cleanup_cfg, e.g. thread_prologue_and_epilogue_insns. */
564 tidy_fallthru_edges ();
566 #ifdef ENABLE_CHECKING
569 timevar_pop (TV_CFG);
573 mark_tablejump_edge (rtx label)
577 gcc_assert (LABEL_P (label));
578 /* See comment in make_label_edge. */
579 if (INSN_UID (label) == 0)
581 bb = BLOCK_FOR_INSN (label);
582 SET_STATE (bb, FULL_STATE (bb) | BLOCK_USED_BY_TABLEJUMP);
586 purge_dead_tablejump_edges (basic_block bb, rtx table)
588 rtx insn = BB_END (bb), tmp;
594 if (GET_CODE (PATTERN (table)) == ADDR_VEC)
595 vec = XVEC (PATTERN (table), 0);
597 vec = XVEC (PATTERN (table), 1);
599 for (j = GET_NUM_ELEM (vec) - 1; j >= 0; --j)
600 mark_tablejump_edge (XEXP (RTVEC_ELT (vec, j), 0));
602 /* Some targets (eg, ARM) emit a conditional jump that also
603 contains the out-of-range target. Scan for these and
604 add an edge if necessary. */
605 if ((tmp = single_set (insn)) != NULL
606 && SET_DEST (tmp) == pc_rtx
607 && GET_CODE (SET_SRC (tmp)) == IF_THEN_ELSE
608 && GET_CODE (XEXP (SET_SRC (tmp), 2)) == LABEL_REF)
609 mark_tablejump_edge (XEXP (XEXP (SET_SRC (tmp), 2), 0));
611 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
613 if (FULL_STATE (e->dest) & BLOCK_USED_BY_TABLEJUMP)
614 SET_STATE (e->dest, FULL_STATE (e->dest)
615 & ~(size_t) BLOCK_USED_BY_TABLEJUMP);
616 else if (!(e->flags & (EDGE_ABNORMAL | EDGE_EH)))
625 /* Scan basic block BB for possible BB boundaries inside the block
626 and create new basic blocks in the progress. */
629 find_bb_boundaries (basic_block bb)
631 basic_block orig_bb = bb;
632 rtx insn = BB_HEAD (bb);
633 rtx end = BB_END (bb);
635 rtx flow_transfer_insn = NULL_RTX;
636 edge fallthru = NULL;
638 if (insn == BB_END (bb))
642 insn = NEXT_INSN (insn);
644 /* Scan insn chain and try to find new basic block boundaries. */
647 enum rtx_code code = GET_CODE (insn);
649 /* On code label, split current basic block. */
650 if (code == CODE_LABEL)
652 fallthru = split_block (bb, PREV_INSN (insn));
653 if (flow_transfer_insn)
654 BB_END (bb) = flow_transfer_insn;
657 remove_edge (fallthru);
658 flow_transfer_insn = NULL_RTX;
659 if (LABEL_ALT_ENTRY_P (insn))
660 make_edge (ENTRY_BLOCK_PTR, bb, 0);
663 /* In case we've previously seen an insn that effects a control
664 flow transfer, split the block. */
665 if (flow_transfer_insn && inside_basic_block_p (insn))
667 fallthru = split_block (bb, PREV_INSN (insn));
668 BB_END (bb) = flow_transfer_insn;
670 remove_edge (fallthru);
671 flow_transfer_insn = NULL_RTX;
674 if (control_flow_insn_p (insn))
675 flow_transfer_insn = insn;
678 insn = NEXT_INSN (insn);
681 /* In case expander replaced normal insn by sequence terminating by
682 return and barrier, or possibly other sequence not behaving like
683 ordinary jump, we need to take care and move basic block boundary. */
684 if (flow_transfer_insn)
685 BB_END (bb) = flow_transfer_insn;
687 /* We've possibly replaced the conditional jump by conditional jump
688 followed by cleanup at fallthru edge, so the outgoing edges may
690 purge_dead_edges (bb);
692 /* purge_dead_edges doesn't handle tablejump's, but if we have split the
693 basic block, we might need to kill some edges. */
694 if (bb != orig_bb && tablejump_p (BB_END (bb), NULL, &table))
695 purge_dead_tablejump_edges (bb, table);
698 /* Assume that frequency of basic block B is known. Compute frequencies
699 and probabilities of outgoing edges. */
702 compute_outgoing_frequencies (basic_block b)
707 if (EDGE_COUNT (b->succs) == 2)
709 rtx note = find_reg_note (BB_END (b), REG_BR_PROB, NULL);
714 probability = INTVAL (XEXP (note, 0));
716 e->probability = probability;
717 e->count = ((b->count * probability + REG_BR_PROB_BASE / 2)
719 f = FALLTHRU_EDGE (b);
720 f->probability = REG_BR_PROB_BASE - probability;
721 f->count = b->count - e->count;
726 if (single_succ_p (b))
728 e = single_succ_edge (b);
729 e->probability = REG_BR_PROB_BASE;
733 guess_outgoing_edge_probabilities (b);
735 FOR_EACH_EDGE (e, ei, b->succs)
736 e->count = ((b->count * e->probability + REG_BR_PROB_BASE / 2)
740 /* Assume that some pass has inserted labels or control flow
741 instructions within a basic block. Split basic blocks as needed
745 find_many_sub_basic_blocks (sbitmap blocks)
747 basic_block bb, min, max;
751 TEST_BIT (blocks, bb->index) ? BLOCK_TO_SPLIT : BLOCK_ORIGINAL);
754 if (STATE (bb) == BLOCK_TO_SPLIT)
755 find_bb_boundaries (bb);
758 if (STATE (bb) != BLOCK_ORIGINAL)
762 for (; bb != EXIT_BLOCK_PTR; bb = bb->next_bb)
763 if (STATE (bb) != BLOCK_ORIGINAL)
766 /* Now re-scan and wire in all edges. This expect simple (conditional)
767 jumps at the end of each new basic blocks. */
768 make_edges (min, max, 1);
770 /* Update branch probabilities. Expect only (un)conditional jumps
771 to be created with only the forward edges. */
772 if (profile_status != PROFILE_ABSENT)
773 FOR_BB_BETWEEN (bb, min, max->next_bb, next_bb)
778 if (STATE (bb) == BLOCK_ORIGINAL)
780 if (STATE (bb) == BLOCK_NEW)
784 FOR_EACH_EDGE (e, ei, bb->preds)
786 bb->count += e->count;
787 bb->frequency += EDGE_FREQUENCY (e);
791 compute_outgoing_frequencies (bb);