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)
242 edge_cache
= sbitmap_alloc (last_basic_block
);
244 /* By nature of the way these get numbered, ENTRY_BLOCK_PTR->next_bb block
245 is always the entry. */
246 if (min
== ENTRY_BLOCK_PTR
->next_bb
)
247 make_edge (ENTRY_BLOCK_PTR
, min
, EDGE_FALLTHRU
);
249 FOR_BB_BETWEEN (bb
, min
, max
->next_bb
, next_bb
)
256 if (STATE (bb
) == BLOCK_ORIGINAL
)
259 /* If we have an edge cache, cache edges going out of BB. */
262 sbitmap_zero (edge_cache
);
265 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
266 if (e
->dest
!= EXIT_BLOCK_PTR
)
267 SET_BIT (edge_cache
, e
->dest
->index
);
271 if (LABEL_P (BB_HEAD (bb
))
272 && LABEL_ALT_ENTRY_P (BB_HEAD (bb
)))
273 cached_make_edge (NULL
, ENTRY_BLOCK_PTR
, bb
, 0);
275 /* Examine the last instruction of the block, and discover the
276 ways we can leave the block. */
279 code
= GET_CODE (insn
);
282 if (code
== JUMP_INSN
)
286 /* Recognize exception handling placeholders. */
287 if (GET_CODE (PATTERN (insn
)) == RESX
)
288 rtl_make_eh_edge (edge_cache
, bb
, insn
);
290 /* Recognize a non-local goto as a branch outside the
292 else if (find_reg_note (insn
, REG_NON_LOCAL_GOTO
, NULL_RTX
))
295 /* Recognize a tablejump and do the right thing. */
296 else if (tablejump_p (insn
, NULL
, &tmp
))
301 if (GET_CODE (PATTERN (tmp
)) == ADDR_VEC
)
302 vec
= XVEC (PATTERN (tmp
), 0);
304 vec
= XVEC (PATTERN (tmp
), 1);
306 for (j
= GET_NUM_ELEM (vec
) - 1; j
>= 0; --j
)
307 make_label_edge (edge_cache
, bb
,
308 XEXP (RTVEC_ELT (vec
, j
), 0), 0);
310 /* Some targets (eg, ARM) emit a conditional jump that also
311 contains the out-of-range target. Scan for these and
312 add an edge if necessary. */
313 if ((tmp
= single_set (insn
)) != NULL
314 && SET_DEST (tmp
) == pc_rtx
315 && GET_CODE (SET_SRC (tmp
)) == IF_THEN_ELSE
316 && GET_CODE (XEXP (SET_SRC (tmp
), 2)) == LABEL_REF
)
317 make_label_edge (edge_cache
, bb
,
318 XEXP (XEXP (SET_SRC (tmp
), 2), 0), 0);
321 /* If this is a computed jump, then mark it as reaching
322 everything on the forced_labels list. */
323 else if (computed_jump_p (insn
))
325 for (x
= forced_labels
; x
; x
= XEXP (x
, 1))
326 make_label_edge (edge_cache
, bb
, XEXP (x
, 0), EDGE_ABNORMAL
);
329 /* Returns create an exit out. */
330 else if (returnjump_p (insn
))
331 cached_make_edge (edge_cache
, bb
, EXIT_BLOCK_PTR
, 0);
333 /* Otherwise, we have a plain conditional or unconditional jump. */
336 gcc_assert (JUMP_LABEL (insn
));
337 make_label_edge (edge_cache
, bb
, JUMP_LABEL (insn
), 0);
341 /* If this is a sibling call insn, then this is in effect a combined call
342 and return, and so we need an edge to the exit block. No need to
343 worry about EH edges, since we wouldn't have created the sibling call
344 in the first place. */
345 if (code
== CALL_INSN
&& SIBLING_CALL_P (insn
))
346 cached_make_edge (edge_cache
, bb
, EXIT_BLOCK_PTR
,
347 EDGE_SIBCALL
| EDGE_ABNORMAL
);
349 /* If this is a CALL_INSN, then mark it as reaching the active EH
350 handler for this CALL_INSN. If we're handling non-call
351 exceptions then any insn can reach any of the active handlers.
352 Also mark the CALL_INSN as reaching any nonlocal goto handler. */
353 else if (code
== CALL_INSN
|| flag_non_call_exceptions
)
355 /* Add any appropriate EH edges. */
356 rtl_make_eh_edge (edge_cache
, bb
, insn
);
358 if (code
== CALL_INSN
&& nonlocal_goto_handler_labels
)
360 /* ??? This could be made smarter: in some cases it's possible
361 to tell that certain calls will not do a nonlocal goto.
362 For example, if the nested functions that do the nonlocal
363 gotos do not have their addresses taken, then only calls to
364 those functions or to other nested functions that use them
365 could possibly do nonlocal gotos. */
367 /* We do know that a REG_EH_REGION note with a value less
368 than 0 is guaranteed not to perform a non-local goto. */
369 rtx note
= find_reg_note (insn
, REG_EH_REGION
, NULL_RTX
);
371 if (!note
|| INTVAL (XEXP (note
, 0)) >= 0)
372 for (x
= nonlocal_goto_handler_labels
; x
; x
= XEXP (x
, 1))
373 make_label_edge (edge_cache
, bb
, XEXP (x
, 0),
374 EDGE_ABNORMAL
| EDGE_ABNORMAL_CALL
);
378 /* Find out if we can drop through to the next block. */
379 insn
= NEXT_INSN (insn
);
380 e
= find_edge (bb
, EXIT_BLOCK_PTR
);
381 if (e
&& e
->flags
& EDGE_FALLTHRU
)
386 && NOTE_LINE_NUMBER (insn
) != NOTE_INSN_BASIC_BLOCK
)
387 insn
= NEXT_INSN (insn
);
390 cached_make_edge (edge_cache
, bb
, EXIT_BLOCK_PTR
, EDGE_FALLTHRU
);
391 else if (bb
->next_bb
!= EXIT_BLOCK_PTR
)
393 if (insn
== BB_HEAD (bb
->next_bb
))
394 cached_make_edge (edge_cache
, bb
, bb
->next_bb
, EDGE_FALLTHRU
);
399 sbitmap_vector_free (edge_cache
);
402 /* Find all basic blocks of the function whose first insn is F.
404 Collect and return a list of labels whose addresses are taken. This
405 will be used in make_edges for use with computed gotos. */
408 find_basic_blocks_1 (rtx f
)
411 rtx bb_note
= NULL_RTX
;
414 basic_block prev
= ENTRY_BLOCK_PTR
;
416 /* We process the instructions in a slightly different way than we did
417 previously. This is so that we see a NOTE_BASIC_BLOCK after we have
418 closed out the previous block, so that it gets attached at the proper
419 place. Since this form should be equivalent to the previous,
420 count_basic_blocks continues to use the old form as a check. */
422 for (insn
= f
; insn
; insn
= next
)
424 enum rtx_code code
= GET_CODE (insn
);
426 next
= NEXT_INSN (insn
);
428 if ((LABEL_P (insn
) || BARRIER_P (insn
))
431 prev
= create_basic_block_structure (head
, end
, bb_note
, prev
);
432 head
= end
= NULL_RTX
;
436 if (inside_basic_block_p (insn
))
438 if (head
== NULL_RTX
)
443 if (head
&& control_flow_insn_p (insn
))
445 prev
= create_basic_block_structure (head
, end
, bb_note
, prev
);
446 head
= end
= NULL_RTX
;
454 int kind
= NOTE_LINE_NUMBER (insn
);
456 /* Look for basic block notes with which to keep the
457 basic_block_info pointers stable. Unthread the note now;
458 we'll put it back at the right place in create_basic_block.
459 Or not at all if we've already found a note in this block. */
460 if (kind
== NOTE_INSN_BASIC_BLOCK
)
462 if (bb_note
== NULL_RTX
)
465 next
= delete_insn (insn
);
482 if (head
!= NULL_RTX
)
483 create_basic_block_structure (head
, end
, bb_note
, prev
);
485 delete_insn (bb_note
);
487 gcc_assert (last_basic_block
== n_basic_blocks
);
489 clear_aux_for_blocks ();
493 /* Find basic blocks of the current function.
494 F is the first insn of the function. */
497 find_basic_blocks (rtx f
)
501 timevar_push (TV_CFG
);
503 /* Flush out existing data. */
504 if (basic_block_info
!= NULL
)
508 /* Clear bb->aux on all extant basic blocks. We'll use this as a
509 tag for reuse during create_basic_block, just in case some pass
510 copies around basic block notes improperly. */
514 basic_block_info
= NULL
;
517 n_basic_blocks
= count_basic_blocks (f
);
518 last_basic_block
= 0;
519 ENTRY_BLOCK_PTR
->next_bb
= EXIT_BLOCK_PTR
;
520 EXIT_BLOCK_PTR
->prev_bb
= ENTRY_BLOCK_PTR
;
522 /* Size the basic block table. The actual structures will be allocated
523 by find_basic_blocks_1, since we want to keep the structure pointers
524 stable across calls to find_basic_blocks. */
525 /* ??? This whole issue would be much simpler if we called find_basic_blocks
526 exactly once, and thereafter we don't have a single long chain of
527 instructions at all until close to the end of compilation when we
528 actually lay them out. */
530 VARRAY_BB_INIT (basic_block_info
, n_basic_blocks
, "basic_block_info");
532 find_basic_blocks_1 (f
);
534 profile_status
= PROFILE_ABSENT
;
537 SET_STATE (bb
, BLOCK_NEW
);
539 /* Discover the edges of our cfg. */
540 make_edges (ENTRY_BLOCK_PTR
->next_bb
, EXIT_BLOCK_PTR
->prev_bb
, 0);
542 /* Do very simple cleanup now, for the benefit of code that runs between
543 here and cleanup_cfg, e.g. thread_prologue_and_epilogue_insns. */
544 tidy_fallthru_edges ();
546 #ifdef ENABLE_CHECKING
549 timevar_pop (TV_CFG
);
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 (single_succ_p (b
))
708 e
= single_succ_edge (b
);
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
);