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:
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 /* Heavy use of computed goto in machine-generated code can lead to
231 nearly fully-connected CFGs. In that case we spend a significant
232 amount of time searching the edge lists for duplicates. */
233 if (forced_labels
|| cfun
->max_jumptable_ents
> 100)
235 edge_cache
= sbitmap_vector_alloc (last_basic_block
, last_basic_block
);
236 sbitmap_vector_zero (edge_cache
, last_basic_block
);
239 FOR_BB_BETWEEN (bb
, min
, max
->next_bb
, next_bb
)
244 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
245 if (e
->dest
!= EXIT_BLOCK_PTR
)
246 SET_BIT (edge_cache
[bb
->index
], e
->dest
->index
);
250 /* By nature of the way these get numbered, ENTRY_BLOCK_PTR->next_bb block
251 is always the entry. */
252 if (min
== ENTRY_BLOCK_PTR
->next_bb
)
253 cached_make_edge (edge_cache
, ENTRY_BLOCK_PTR
, min
,
256 FOR_BB_BETWEEN (bb
, min
, max
->next_bb
, next_bb
)
262 if (LABEL_P (BB_HEAD (bb
))
263 && LABEL_ALT_ENTRY_P (BB_HEAD (bb
)))
264 cached_make_edge (NULL
, ENTRY_BLOCK_PTR
, bb
, 0);
266 /* Examine the last instruction of the block, and discover the
267 ways we can leave the block. */
270 code
= GET_CODE (insn
);
273 if (code
== JUMP_INSN
)
277 /* Recognize exception handling placeholders. */
278 if (GET_CODE (PATTERN (insn
)) == RESX
)
279 rtl_make_eh_edge (edge_cache
, bb
, insn
);
281 /* Recognize a non-local goto as a branch outside the
283 else if (find_reg_note (insn
, REG_NON_LOCAL_GOTO
, NULL_RTX
))
286 /* Recognize a tablejump and do the right thing. */
287 else if (tablejump_p (insn
, NULL
, &tmp
))
292 if (GET_CODE (PATTERN (tmp
)) == ADDR_VEC
)
293 vec
= XVEC (PATTERN (tmp
), 0);
295 vec
= XVEC (PATTERN (tmp
), 1);
297 for (j
= GET_NUM_ELEM (vec
) - 1; j
>= 0; --j
)
298 make_label_edge (edge_cache
, bb
,
299 XEXP (RTVEC_ELT (vec
, j
), 0), 0);
301 /* Some targets (eg, ARM) emit a conditional jump that also
302 contains the out-of-range target. Scan for these and
303 add an edge if necessary. */
304 if ((tmp
= single_set (insn
)) != NULL
305 && SET_DEST (tmp
) == pc_rtx
306 && GET_CODE (SET_SRC (tmp
)) == IF_THEN_ELSE
307 && GET_CODE (XEXP (SET_SRC (tmp
), 2)) == LABEL_REF
)
308 make_label_edge (edge_cache
, bb
,
309 XEXP (XEXP (SET_SRC (tmp
), 2), 0), 0);
312 /* If this is a computed jump, then mark it as reaching
313 everything on the forced_labels list. */
314 else if (computed_jump_p (insn
))
316 for (x
= forced_labels
; x
; x
= XEXP (x
, 1))
317 make_label_edge (edge_cache
, bb
, XEXP (x
, 0), EDGE_ABNORMAL
);
320 /* Returns create an exit out. */
321 else if (returnjump_p (insn
))
322 cached_make_edge (edge_cache
, bb
, EXIT_BLOCK_PTR
, 0);
324 /* Otherwise, we have a plain conditional or unconditional jump. */
327 gcc_assert (JUMP_LABEL (insn
));
328 make_label_edge (edge_cache
, bb
, JUMP_LABEL (insn
), 0);
332 /* If this is a sibling call insn, then this is in effect a combined call
333 and return, and so we need an edge to the exit block. No need to
334 worry about EH edges, since we wouldn't have created the sibling call
335 in the first place. */
336 if (code
== CALL_INSN
&& SIBLING_CALL_P (insn
))
337 cached_make_edge (edge_cache
, bb
, EXIT_BLOCK_PTR
,
338 EDGE_SIBCALL
| EDGE_ABNORMAL
);
340 /* If this is a CALL_INSN, then mark it as reaching the active EH
341 handler for this CALL_INSN. If we're handling non-call
342 exceptions then any insn can reach any of the active handlers.
343 Also mark the CALL_INSN as reaching any nonlocal goto handler. */
344 else if (code
== CALL_INSN
|| flag_non_call_exceptions
)
346 /* Add any appropriate EH edges. */
347 rtl_make_eh_edge (edge_cache
, bb
, insn
);
349 if (code
== CALL_INSN
&& nonlocal_goto_handler_labels
)
351 /* ??? This could be made smarter: in some cases it's possible
352 to tell that certain calls will not do a nonlocal goto.
353 For example, if the nested functions that do the nonlocal
354 gotos do not have their addresses taken, then only calls to
355 those functions or to other nested functions that use them
356 could possibly do nonlocal gotos. */
358 /* We do know that a REG_EH_REGION note with a value less
359 than 0 is guaranteed not to perform a non-local goto. */
360 rtx note
= find_reg_note (insn
, REG_EH_REGION
, NULL_RTX
);
362 if (!note
|| INTVAL (XEXP (note
, 0)) >= 0)
363 for (x
= nonlocal_goto_handler_labels
; x
; x
= XEXP (x
, 1))
364 make_label_edge (edge_cache
, bb
, XEXP (x
, 0),
365 EDGE_ABNORMAL
| EDGE_ABNORMAL_CALL
);
369 /* Find out if we can drop through to the next block. */
370 insn
= NEXT_INSN (insn
);
371 e
= find_edge (bb
, EXIT_BLOCK_PTR
);
372 if (e
&& e
->flags
& EDGE_FALLTHRU
)
377 && NOTE_LINE_NUMBER (insn
) != NOTE_INSN_BASIC_BLOCK
)
378 insn
= NEXT_INSN (insn
);
381 cached_make_edge (edge_cache
, bb
, EXIT_BLOCK_PTR
, EDGE_FALLTHRU
);
382 else if (bb
->next_bb
!= EXIT_BLOCK_PTR
)
384 if (insn
== BB_HEAD (bb
->next_bb
))
385 cached_make_edge (edge_cache
, bb
, bb
->next_bb
, EDGE_FALLTHRU
);
390 sbitmap_vector_free (edge_cache
);
393 /* Find all basic blocks of the function whose first insn is F.
395 Collect and return a list of labels whose addresses are taken. This
396 will be used in make_edges for use with computed gotos. */
399 find_basic_blocks_1 (rtx f
)
402 rtx bb_note
= NULL_RTX
;
405 basic_block prev
= ENTRY_BLOCK_PTR
;
407 /* We process the instructions in a slightly different way than we did
408 previously. This is so that we see a NOTE_BASIC_BLOCK after we have
409 closed out the previous block, so that it gets attached at the proper
410 place. Since this form should be equivalent to the previous,
411 count_basic_blocks continues to use the old form as a check. */
413 for (insn
= f
; insn
; insn
= next
)
415 enum rtx_code code
= GET_CODE (insn
);
417 next
= NEXT_INSN (insn
);
419 if ((LABEL_P (insn
) || BARRIER_P (insn
))
422 prev
= create_basic_block_structure (head
, end
, bb_note
, prev
);
423 head
= end
= NULL_RTX
;
427 if (inside_basic_block_p (insn
))
429 if (head
== NULL_RTX
)
434 if (head
&& control_flow_insn_p (insn
))
436 prev
= create_basic_block_structure (head
, end
, bb_note
, prev
);
437 head
= end
= NULL_RTX
;
445 int kind
= NOTE_LINE_NUMBER (insn
);
447 /* Look for basic block notes with which to keep the
448 basic_block_info pointers stable. Unthread the note now;
449 we'll put it back at the right place in create_basic_block.
450 Or not at all if we've already found a note in this block. */
451 if (kind
== NOTE_INSN_BASIC_BLOCK
)
453 if (bb_note
== NULL_RTX
)
456 next
= delete_insn (insn
);
473 if (head
!= NULL_RTX
)
474 create_basic_block_structure (head
, end
, bb_note
, prev
);
476 delete_insn (bb_note
);
478 gcc_assert (last_basic_block
== n_basic_blocks
);
480 clear_aux_for_blocks ();
484 /* Find basic blocks of the current function.
485 F is the first insn of the function and NREGS the number of register
489 find_basic_blocks (rtx f
, int nregs ATTRIBUTE_UNUSED
,
490 FILE *file ATTRIBUTE_UNUSED
)
494 timevar_push (TV_CFG
);
496 /* Flush out existing data. */
497 if (basic_block_info
!= NULL
)
501 /* Clear bb->aux on all extant basic blocks. We'll use this as a
502 tag for reuse during create_basic_block, just in case some pass
503 copies around basic block notes improperly. */
507 basic_block_info
= NULL
;
510 n_basic_blocks
= count_basic_blocks (f
);
511 last_basic_block
= 0;
512 ENTRY_BLOCK_PTR
->next_bb
= EXIT_BLOCK_PTR
;
513 EXIT_BLOCK_PTR
->prev_bb
= ENTRY_BLOCK_PTR
;
515 /* Size the basic block table. The actual structures will be allocated
516 by find_basic_blocks_1, since we want to keep the structure pointers
517 stable across calls to find_basic_blocks. */
518 /* ??? This whole issue would be much simpler if we called find_basic_blocks
519 exactly once, and thereafter we don't have a single long chain of
520 instructions at all until close to the end of compilation when we
521 actually lay them out. */
523 VARRAY_BB_INIT (basic_block_info
, n_basic_blocks
, "basic_block_info");
525 find_basic_blocks_1 (f
);
527 profile_status
= PROFILE_ABSENT
;
529 /* Discover the edges of our cfg. */
530 make_edges (ENTRY_BLOCK_PTR
->next_bb
, EXIT_BLOCK_PTR
->prev_bb
, 0);
532 /* Do very simple cleanup now, for the benefit of code that runs between
533 here and cleanup_cfg, e.g. thread_prologue_and_epilogue_insns. */
534 tidy_fallthru_edges ();
536 #ifdef ENABLE_CHECKING
539 timevar_pop (TV_CFG
);
542 /* State of basic block as seen by find_sub_basic_blocks. */
543 enum state
{BLOCK_NEW
= 0, BLOCK_ORIGINAL
, BLOCK_TO_SPLIT
};
545 #define STATE(BB) (enum state) ((size_t) (BB)->aux)
546 #define SET_STATE(BB, STATE) ((BB)->aux = (void *) (size_t) (STATE))
548 /* Used internally by purge_dead_tablejump_edges, ORed into state. */
549 #define BLOCK_USED_BY_TABLEJUMP 32
550 #define FULL_STATE(BB) ((size_t) (BB)->aux)
553 mark_tablejump_edge (rtx label
)
557 gcc_assert (LABEL_P (label
));
558 /* See comment in make_label_edge. */
559 if (INSN_UID (label
) == 0)
561 bb
= BLOCK_FOR_INSN (label
);
562 SET_STATE (bb
, FULL_STATE (bb
) | BLOCK_USED_BY_TABLEJUMP
);
566 purge_dead_tablejump_edges (basic_block bb
, rtx table
)
568 rtx insn
= BB_END (bb
), tmp
;
574 if (GET_CODE (PATTERN (table
)) == ADDR_VEC
)
575 vec
= XVEC (PATTERN (table
), 0);
577 vec
= XVEC (PATTERN (table
), 1);
579 for (j
= GET_NUM_ELEM (vec
) - 1; j
>= 0; --j
)
580 mark_tablejump_edge (XEXP (RTVEC_ELT (vec
, j
), 0));
582 /* Some targets (eg, ARM) emit a conditional jump that also
583 contains the out-of-range target. Scan for these and
584 add an edge if necessary. */
585 if ((tmp
= single_set (insn
)) != NULL
586 && SET_DEST (tmp
) == pc_rtx
587 && GET_CODE (SET_SRC (tmp
)) == IF_THEN_ELSE
588 && GET_CODE (XEXP (SET_SRC (tmp
), 2)) == LABEL_REF
)
589 mark_tablejump_edge (XEXP (XEXP (SET_SRC (tmp
), 2), 0));
591 for (ei
= ei_start (bb
->succs
); (e
= ei_safe_edge (ei
)); )
593 if (FULL_STATE (e
->dest
) & BLOCK_USED_BY_TABLEJUMP
)
594 SET_STATE (e
->dest
, FULL_STATE (e
->dest
)
595 & ~(size_t) BLOCK_USED_BY_TABLEJUMP
);
596 else if (!(e
->flags
& (EDGE_ABNORMAL
| EDGE_EH
)))
605 /* Scan basic block BB for possible BB boundaries inside the block
606 and create new basic blocks in the progress. */
609 find_bb_boundaries (basic_block bb
)
611 basic_block orig_bb
= bb
;
612 rtx insn
= BB_HEAD (bb
);
613 rtx end
= BB_END (bb
);
615 rtx flow_transfer_insn
= NULL_RTX
;
616 edge fallthru
= NULL
;
618 if (insn
== BB_END (bb
))
622 insn
= NEXT_INSN (insn
);
624 /* Scan insn chain and try to find new basic block boundaries. */
627 enum rtx_code code
= GET_CODE (insn
);
629 /* On code label, split current basic block. */
630 if (code
== CODE_LABEL
)
632 fallthru
= split_block (bb
, PREV_INSN (insn
));
633 if (flow_transfer_insn
)
634 BB_END (bb
) = flow_transfer_insn
;
637 remove_edge (fallthru
);
638 flow_transfer_insn
= NULL_RTX
;
639 if (LABEL_ALT_ENTRY_P (insn
))
640 make_edge (ENTRY_BLOCK_PTR
, bb
, 0);
643 /* In case we've previously seen an insn that effects a control
644 flow transfer, split the block. */
645 if (flow_transfer_insn
&& inside_basic_block_p (insn
))
647 fallthru
= split_block (bb
, PREV_INSN (insn
));
648 BB_END (bb
) = flow_transfer_insn
;
650 remove_edge (fallthru
);
651 flow_transfer_insn
= NULL_RTX
;
654 if (control_flow_insn_p (insn
))
655 flow_transfer_insn
= insn
;
658 insn
= NEXT_INSN (insn
);
661 /* In case expander replaced normal insn by sequence terminating by
662 return and barrier, or possibly other sequence not behaving like
663 ordinary jump, we need to take care and move basic block boundary. */
664 if (flow_transfer_insn
)
665 BB_END (bb
) = flow_transfer_insn
;
667 /* We've possibly replaced the conditional jump by conditional jump
668 followed by cleanup at fallthru edge, so the outgoing edges may
670 purge_dead_edges (bb
);
672 /* purge_dead_edges doesn't handle tablejump's, but if we have split the
673 basic block, we might need to kill some edges. */
674 if (bb
!= orig_bb
&& tablejump_p (BB_END (bb
), NULL
, &table
))
675 purge_dead_tablejump_edges (bb
, table
);
678 /* Assume that frequency of basic block B is known. Compute frequencies
679 and probabilities of outgoing edges. */
682 compute_outgoing_frequencies (basic_block b
)
687 if (EDGE_COUNT (b
->succs
) == 2)
689 rtx note
= find_reg_note (BB_END (b
), REG_BR_PROB
, NULL
);
694 probability
= INTVAL (XEXP (note
, 0));
696 e
->probability
= probability
;
697 e
->count
= ((b
->count
* probability
+ REG_BR_PROB_BASE
/ 2)
699 f
= FALLTHRU_EDGE (b
);
700 f
->probability
= REG_BR_PROB_BASE
- probability
;
701 f
->count
= b
->count
- e
->count
;
706 if (EDGE_COUNT (b
->succs
) == 1)
708 e
= EDGE_SUCC (b
, 0);
709 e
->probability
= REG_BR_PROB_BASE
;
713 guess_outgoing_edge_probabilities (b
);
715 FOR_EACH_EDGE (e
, ei
, b
->succs
)
716 e
->count
= ((b
->count
* e
->probability
+ REG_BR_PROB_BASE
/ 2)
720 /* Assume that someone emitted code with control flow instructions to the
721 basic block. Update the data structure. */
724 find_many_sub_basic_blocks (sbitmap blocks
)
726 basic_block bb
, min
, max
;
730 TEST_BIT (blocks
, bb
->index
) ? BLOCK_TO_SPLIT
: BLOCK_ORIGINAL
);
733 if (STATE (bb
) == BLOCK_TO_SPLIT
)
734 find_bb_boundaries (bb
);
737 if (STATE (bb
) != BLOCK_ORIGINAL
)
741 for (; bb
!= EXIT_BLOCK_PTR
; bb
= bb
->next_bb
)
742 if (STATE (bb
) != BLOCK_ORIGINAL
)
745 /* Now re-scan and wire in all edges. This expect simple (conditional)
746 jumps at the end of each new basic blocks. */
747 make_edges (min
, max
, 1);
749 /* Update branch probabilities. Expect only (un)conditional jumps
750 to be created with only the forward edges. */
751 if (profile_status
!= PROFILE_ABSENT
)
752 FOR_BB_BETWEEN (bb
, min
, max
->next_bb
, next_bb
)
757 if (STATE (bb
) == BLOCK_ORIGINAL
)
759 if (STATE (bb
) == BLOCK_NEW
)
763 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
765 bb
->count
+= e
->count
;
766 bb
->frequency
+= EDGE_FREQUENCY (e
);
770 compute_outgoing_frequencies (bb
);
777 /* Like above but for single basic block only. */
780 find_sub_basic_blocks (basic_block bb
)
782 basic_block min
, max
, b
;
783 basic_block next
= bb
->next_bb
;
786 find_bb_boundaries (bb
);
789 /* Now re-scan and wire in all edges. This expect simple (conditional)
790 jumps at the end of each new basic blocks. */
791 make_edges (min
, max
, 1);
793 /* Update branch probabilities. Expect only (un)conditional jumps
794 to be created with only the forward edges. */
795 FOR_BB_BETWEEN (b
, min
, max
->next_bb
, next_bb
)
804 FOR_EACH_EDGE (e
, ei
, b
->preds
)
806 b
->count
+= e
->count
;
807 b
->frequency
+= EDGE_FREQUENCY (e
);
811 compute_outgoing_frequencies (b
);