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 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:
32 - Local CFG construction
33 find_sub_basic_blocks */
37 #include "coretypes.h"
41 #include "hard-reg-set.h"
42 #include "basic-block.h"
51 static int count_basic_blocks (rtx);
52 static void find_basic_blocks_1 (rtx);
53 static void make_edges (basic_block, basic_block, int);
54 static void make_label_edge (sbitmap *, basic_block, rtx, int);
55 static void find_bb_boundaries (basic_block);
56 static void compute_outgoing_frequencies (basic_block);
58 /* Return true if insn is something that should be contained inside basic
62 inside_basic_block_p (rtx insn)
64 switch (GET_CODE (insn))
67 /* Avoid creating of basic block for jumptables. */
68 return (NEXT_INSN (insn) == 0
69 || !JUMP_P (NEXT_INSN (insn))
70 || (GET_CODE (PATTERN (NEXT_INSN (insn))) != ADDR_VEC
71 && GET_CODE (PATTERN (NEXT_INSN (insn))) != ADDR_DIFF_VEC));
74 return (GET_CODE (PATTERN (insn)) != ADDR_VEC
75 && GET_CODE (PATTERN (insn)) != ADDR_DIFF_VEC);
90 /* Return true if INSN may cause control flow transfer, so it should be last in
94 control_flow_insn_p (rtx insn)
98 switch (GET_CODE (insn))
105 /* Jump insn always causes control transfer except for tablejumps. */
106 return (GET_CODE (PATTERN (insn)) != ADDR_VEC
107 && GET_CODE (PATTERN (insn)) != ADDR_DIFF_VEC);
110 /* Noreturn and sibling call instructions terminate the basic blocks
111 (but only if they happen unconditionally). */
112 if ((SIBLING_CALL_P (insn)
113 || find_reg_note (insn, REG_NORETURN, 0))
114 && GET_CODE (PATTERN (insn)) != COND_EXEC)
116 /* Call insn may return to the nonlocal goto handler. */
117 return ((nonlocal_goto_handler_labels
118 && (0 == (note = find_reg_note (insn, REG_EH_REGION,
120 || INTVAL (XEXP (note, 0)) >= 0))
122 || can_throw_internal (insn));
125 return (flag_non_call_exceptions && can_throw_internal (insn));
128 /* It is nonsense to reach barrier when looking for the
129 end of basic block, but before dead code is eliminated
138 /* Count the basic blocks of the function. */
141 count_basic_blocks (rtx f)
144 bool saw_insn = false;
147 for (insn = f; insn; insn = NEXT_INSN (insn))
149 /* Code labels and barriers causes current basic block to be
150 terminated at previous real insn. */
151 if ((LABEL_P (insn) || BARRIER_P (insn))
153 count++, saw_insn = false;
155 /* Start basic block if needed. */
156 if (!saw_insn && inside_basic_block_p (insn))
159 /* Control flow insn causes current basic block to be terminated. */
160 if (saw_insn && control_flow_insn_p (insn))
161 count++, saw_insn = false;
167 /* The rest of the compiler works a bit smoother when we don't have to
168 check for the edge case of do-nothing functions with no basic blocks. */
171 emit_insn (gen_rtx_USE (VOIDmode, const0_rtx));
178 /* Create an edge between two basic blocks. FLAGS are auxiliary information
179 about the edge that is accumulated between calls. */
181 /* Create an edge from a basic block to a label. */
184 make_label_edge (sbitmap *edge_cache, basic_block src, rtx label, int flags)
186 gcc_assert (LABEL_P (label));
188 /* If the label was never emitted, this insn is junk, but avoid a
189 crash trying to refer to BLOCK_FOR_INSN (label). This can happen
190 as a result of a syntax error and a diagnostic has already been
193 if (INSN_UID (label) == 0)
196 cached_make_edge (edge_cache, src, BLOCK_FOR_INSN (label), flags);
199 /* Create the edges generated by INSN in REGION. */
202 rtl_make_eh_edge (sbitmap *edge_cache, basic_block src, rtx insn)
204 int is_call = CALL_P (insn) ? EDGE_ABNORMAL_CALL : 0;
207 handlers = reachable_handlers (insn);
209 for (i = handlers; i; i = XEXP (i, 1))
210 make_label_edge (edge_cache, src, XEXP (i, 0),
211 EDGE_ABNORMAL | EDGE_EH | is_call);
213 free_INSN_LIST_list (&handlers);
216 /* Identify the edges between basic blocks MIN to MAX.
218 NONLOCAL_LABEL_LIST is a list of non-local labels in the function. Blocks
219 that are otherwise unreachable may be reachable with a non-local goto.
221 BB_EH_END is an array indexed by basic block number in which we record
222 the list of exception regions active at the end of the basic block. */
225 make_edges (basic_block min, basic_block max, int update_p)
228 sbitmap *edge_cache = NULL;
230 /* Assume no computed jump; revise as we create edges. */
231 current_function_has_computed_jump = 0;
233 /* If we are partitioning hot and cold basic blocks into separate
234 sections, we cannot assume there is no computed jump (partitioning
235 sometimes requires the use of indirect jumps; see comments about
236 partitioning at the top of bb-reorder.c:partition_hot_cold_basic_blocks
237 for complete details). */
239 if (flag_reorder_blocks_and_partition)
240 current_function_has_computed_jump = 1;
242 /* Heavy use of computed goto in machine-generated code can lead to
243 nearly fully-connected CFGs. In that case we spend a significant
244 amount of time searching the edge lists for duplicates. */
245 if (forced_labels || cfun->max_jumptable_ents > 100)
247 edge_cache = sbitmap_vector_alloc (last_basic_block, last_basic_block);
248 sbitmap_vector_zero (edge_cache, last_basic_block);
251 FOR_BB_BETWEEN (bb, min, max->next_bb, next_bb)
256 FOR_EACH_EDGE (e, ei, bb->succs)
257 if (e->dest != EXIT_BLOCK_PTR)
258 SET_BIT (edge_cache[bb->index], e->dest->index);
262 /* By nature of the way these get numbered, ENTRY_BLOCK_PTR->next_bb block
263 is always the entry. */
264 if (min == ENTRY_BLOCK_PTR->next_bb)
265 cached_make_edge (edge_cache, ENTRY_BLOCK_PTR, min,
268 FOR_BB_BETWEEN (bb, min, max->next_bb, next_bb)
274 if (LABEL_P (BB_HEAD (bb))
275 && LABEL_ALT_ENTRY_P (BB_HEAD (bb)))
276 cached_make_edge (NULL, ENTRY_BLOCK_PTR, bb, 0);
278 /* Examine the last instruction of the block, and discover the
279 ways we can leave the block. */
282 code = GET_CODE (insn);
285 if (code == JUMP_INSN)
289 /* Recognize exception handling placeholders. */
290 if (GET_CODE (PATTERN (insn)) == RESX)
291 rtl_make_eh_edge (edge_cache, bb, insn);
293 /* Recognize a non-local goto as a branch outside the
295 else if (find_reg_note (insn, REG_NON_LOCAL_GOTO, NULL_RTX))
298 /* Recognize a tablejump and do the right thing. */
299 else if (tablejump_p (insn, NULL, &tmp))
304 if (GET_CODE (PATTERN (tmp)) == ADDR_VEC)
305 vec = XVEC (PATTERN (tmp), 0);
307 vec = XVEC (PATTERN (tmp), 1);
309 for (j = GET_NUM_ELEM (vec) - 1; j >= 0; --j)
310 make_label_edge (edge_cache, bb,
311 XEXP (RTVEC_ELT (vec, j), 0), 0);
313 /* Some targets (eg, ARM) emit a conditional jump that also
314 contains the out-of-range target. Scan for these and
315 add an edge if necessary. */
316 if ((tmp = single_set (insn)) != NULL
317 && SET_DEST (tmp) == pc_rtx
318 && GET_CODE (SET_SRC (tmp)) == IF_THEN_ELSE
319 && GET_CODE (XEXP (SET_SRC (tmp), 2)) == LABEL_REF)
320 make_label_edge (edge_cache, bb,
321 XEXP (XEXP (SET_SRC (tmp), 2), 0), 0);
324 /* If this is a computed jump, then mark it as reaching
325 everything on the forced_labels list. */
326 else if (computed_jump_p (insn))
328 current_function_has_computed_jump = 1;
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 and NREGS the number of register
503 find_basic_blocks (rtx f, int nregs ATTRIBUTE_UNUSED,
504 FILE *file ATTRIBUTE_UNUSED)
508 timevar_push (TV_CFG);
510 /* Flush out existing data. */
511 if (basic_block_info != NULL)
515 /* Clear bb->aux on all extant basic blocks. We'll use this as a
516 tag for reuse during create_basic_block, just in case some pass
517 copies around basic block notes improperly. */
521 basic_block_info = NULL;
524 n_basic_blocks = count_basic_blocks (f);
525 last_basic_block = 0;
526 ENTRY_BLOCK_PTR->next_bb = EXIT_BLOCK_PTR;
527 EXIT_BLOCK_PTR->prev_bb = ENTRY_BLOCK_PTR;
529 /* Size the basic block table. The actual structures will be allocated
530 by find_basic_blocks_1, since we want to keep the structure pointers
531 stable across calls to find_basic_blocks. */
532 /* ??? This whole issue would be much simpler if we called find_basic_blocks
533 exactly once, and thereafter we don't have a single long chain of
534 instructions at all until close to the end of compilation when we
535 actually lay them out. */
537 VARRAY_BB_INIT (basic_block_info, n_basic_blocks, "basic_block_info");
539 find_basic_blocks_1 (f);
541 profile_status = PROFILE_ABSENT;
543 /* Discover the edges of our cfg. */
544 make_edges (ENTRY_BLOCK_PTR->next_bb, EXIT_BLOCK_PTR->prev_bb, 0);
546 /* Do very simple cleanup now, for the benefit of code that runs between
547 here and cleanup_cfg, e.g. thread_prologue_and_epilogue_insns. */
548 tidy_fallthru_edges ();
550 #ifdef ENABLE_CHECKING
553 timevar_pop (TV_CFG);
556 /* State of basic block as seen by find_sub_basic_blocks. */
557 enum state {BLOCK_NEW = 0, BLOCK_ORIGINAL, BLOCK_TO_SPLIT};
559 #define STATE(BB) (enum state) ((size_t) (BB)->aux)
560 #define SET_STATE(BB, STATE) ((BB)->aux = (void *) (size_t) (STATE))
562 /* Scan basic block BB for possible BB boundaries inside the block
563 and create new basic blocks in the progress. */
566 find_bb_boundaries (basic_block bb)
568 rtx insn = BB_HEAD (bb);
569 rtx end = BB_END (bb);
570 rtx flow_transfer_insn = NULL_RTX;
571 edge fallthru = NULL;
573 if (insn == BB_END (bb))
577 insn = NEXT_INSN (insn);
579 /* Scan insn chain and try to find new basic block boundaries. */
582 enum rtx_code code = GET_CODE (insn);
584 /* On code label, split current basic block. */
585 if (code == CODE_LABEL)
587 fallthru = split_block (bb, PREV_INSN (insn));
588 if (flow_transfer_insn)
589 BB_END (bb) = flow_transfer_insn;
592 remove_edge (fallthru);
593 flow_transfer_insn = NULL_RTX;
594 if (LABEL_ALT_ENTRY_P (insn))
595 make_edge (ENTRY_BLOCK_PTR, bb, 0);
598 /* In case we've previously seen an insn that effects a control
599 flow transfer, split the block. */
600 if (flow_transfer_insn && inside_basic_block_p (insn))
602 fallthru = split_block (bb, PREV_INSN (insn));
603 BB_END (bb) = flow_transfer_insn;
605 remove_edge (fallthru);
606 flow_transfer_insn = NULL_RTX;
609 if (control_flow_insn_p (insn))
610 flow_transfer_insn = insn;
613 insn = NEXT_INSN (insn);
616 /* In case expander replaced normal insn by sequence terminating by
617 return and barrier, or possibly other sequence not behaving like
618 ordinary jump, we need to take care and move basic block boundary. */
619 if (flow_transfer_insn)
620 BB_END (bb) = flow_transfer_insn;
622 /* We've possibly replaced the conditional jump by conditional jump
623 followed by cleanup at fallthru edge, so the outgoing edges may
625 purge_dead_edges (bb);
628 /* Assume that frequency of basic block B is known. Compute frequencies
629 and probabilities of outgoing edges. */
632 compute_outgoing_frequencies (basic_block b)
637 if (EDGE_COUNT (b->succs) == 2)
639 rtx note = find_reg_note (BB_END (b), REG_BR_PROB, NULL);
644 probability = INTVAL (XEXP (note, 0));
646 e->probability = probability;
647 e->count = ((b->count * probability + REG_BR_PROB_BASE / 2)
649 f = FALLTHRU_EDGE (b);
650 f->probability = REG_BR_PROB_BASE - probability;
651 f->count = b->count - e->count;
656 if (EDGE_COUNT (b->succs) == 1)
658 e = EDGE_SUCC (b, 0);
659 e->probability = REG_BR_PROB_BASE;
663 guess_outgoing_edge_probabilities (b);
665 FOR_EACH_EDGE (e, ei, b->succs)
666 e->count = ((b->count * e->probability + REG_BR_PROB_BASE / 2)
670 /* Assume that someone emitted code with control flow instructions to the
671 basic block. Update the data structure. */
674 find_many_sub_basic_blocks (sbitmap blocks)
676 basic_block bb, min, max;
680 TEST_BIT (blocks, bb->index) ? BLOCK_TO_SPLIT : BLOCK_ORIGINAL);
683 if (STATE (bb) == BLOCK_TO_SPLIT)
684 find_bb_boundaries (bb);
687 if (STATE (bb) != BLOCK_ORIGINAL)
691 for (; bb != EXIT_BLOCK_PTR; bb = bb->next_bb)
692 if (STATE (bb) != BLOCK_ORIGINAL)
695 /* Now re-scan and wire in all edges. This expect simple (conditional)
696 jumps at the end of each new basic blocks. */
697 make_edges (min, max, 1);
699 /* Update branch probabilities. Expect only (un)conditional jumps
700 to be created with only the forward edges. */
701 if (profile_status != PROFILE_ABSENT)
702 FOR_BB_BETWEEN (bb, min, max->next_bb, next_bb)
707 if (STATE (bb) == BLOCK_ORIGINAL)
709 if (STATE (bb) == BLOCK_NEW)
713 FOR_EACH_EDGE (e, ei, bb->preds)
715 bb->count += e->count;
716 bb->frequency += EDGE_FREQUENCY (e);
720 compute_outgoing_frequencies (bb);
727 /* Like above but for single basic block only. */
730 find_sub_basic_blocks (basic_block bb)
732 basic_block min, max, b;
733 basic_block next = bb->next_bb;
736 find_bb_boundaries (bb);
739 /* Now re-scan and wire in all edges. This expect simple (conditional)
740 jumps at the end of each new basic blocks. */
741 make_edges (min, max, 1);
743 /* Update branch probabilities. Expect only (un)conditional jumps
744 to be created with only the forward edges. */
745 FOR_BB_BETWEEN (b, min, max->next_bb, next_bb)
754 FOR_EACH_EDGE (e, ei, b->preds)
756 b->count += e->count;
757 b->frequency += EDGE_FREQUENCY (e);
761 compute_outgoing_frequencies (b);