1 /* Control flow optimization code for GNU compiler.
2 Copyright (C) 1987, 1988, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
3 1999, 2000, 2001, 2002 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 /* This file contains optimizer of the control flow. The main entrypoint is
23 cleanup_cfg. Following optimizations are performed:
25 - Unreachable blocks removal
26 - Edge forwarding (edge to the forwarder block is forwarded to it's
27 successor. Simplification of the branch instruction is performed by
28 underlying infrastructure so branch can be converted to simplejump or
30 - Cross jumping (tail merging)
31 - Conditional jump-around-simplejump simplification
32 - Basic block merging. */
37 #include "hard-reg-set.h"
38 #include "basic-block.h"
41 #include "insn-config.h"
51 /* cleanup_cfg maintains following flags for each basic block. */
55 /* Set if BB is the forwarder block to avoid too many
56 forwarder_block_p calls. */
57 BB_FORWARDER_BLOCK
= 1,
58 BB_NONTHREADABLE_BLOCK
= 2
61 #define BB_FLAGS(BB) (enum bb_flags) (BB)->aux
62 #define BB_SET_FLAG(BB, FLAG) \
63 (BB)->aux = (void *) (long) ((enum bb_flags) (BB)->aux | (FLAG))
64 #define BB_CLEAR_FLAG(BB, FLAG) \
65 (BB)->aux = (void *) (long) ((enum bb_flags) (BB)->aux & ~(FLAG))
67 #define FORWARDER_BLOCK_P(BB) (BB_FLAGS (BB) & BB_FORWARDER_BLOCK)
69 static bool try_crossjump_to_edge
PARAMS ((int, edge
, edge
));
70 static bool try_crossjump_bb
PARAMS ((int, basic_block
));
71 static bool outgoing_edges_match
PARAMS ((int,
72 basic_block
, basic_block
));
73 static int flow_find_cross_jump
PARAMS ((int, basic_block
, basic_block
,
75 static bool insns_match_p
PARAMS ((int, rtx
, rtx
));
77 static bool label_is_jump_target_p
PARAMS ((rtx
, rtx
));
78 static bool tail_recursion_label_p
PARAMS ((rtx
));
79 static void merge_blocks_move_predecessor_nojumps
PARAMS ((basic_block
,
81 static void merge_blocks_move_successor_nojumps
PARAMS ((basic_block
,
83 static bool merge_blocks
PARAMS ((edge
,basic_block
,basic_block
,
85 static bool try_optimize_cfg
PARAMS ((int));
86 static bool try_simplify_condjump
PARAMS ((basic_block
));
87 static bool try_forward_edges
PARAMS ((int, basic_block
));
88 static edge thread_jump
PARAMS ((int, edge
, basic_block
));
89 static bool mark_effect
PARAMS ((rtx
, bitmap
));
90 static void notice_new_block
PARAMS ((basic_block
));
91 static void update_forwarder_flag
PARAMS ((basic_block
));
92 static int mentions_nonequal_regs
PARAMS ((rtx
*, void *));
94 /* Set flags for newly created block. */
103 if (forwarder_block_p (bb
))
104 BB_SET_FLAG (bb
, BB_FORWARDER_BLOCK
);
107 /* Recompute forwarder flag after block has been modified. */
110 update_forwarder_flag (bb
)
113 if (forwarder_block_p (bb
))
114 BB_SET_FLAG (bb
, BB_FORWARDER_BLOCK
);
116 BB_CLEAR_FLAG (bb
, BB_FORWARDER_BLOCK
);
119 /* Simplify a conditional jump around an unconditional jump.
120 Return true if something changed. */
123 try_simplify_condjump (cbranch_block
)
124 basic_block cbranch_block
;
126 basic_block jump_block
, jump_dest_block
, cbranch_dest_block
;
127 edge cbranch_jump_edge
, cbranch_fallthru_edge
;
130 /* Verify that there are exactly two successors. */
131 if (!cbranch_block
->succ
132 || !cbranch_block
->succ
->succ_next
133 || cbranch_block
->succ
->succ_next
->succ_next
)
136 /* Verify that we've got a normal conditional branch at the end
138 cbranch_insn
= cbranch_block
->end
;
139 if (!any_condjump_p (cbranch_insn
))
142 cbranch_fallthru_edge
= FALLTHRU_EDGE (cbranch_block
);
143 cbranch_jump_edge
= BRANCH_EDGE (cbranch_block
);
145 /* The next block must not have multiple predecessors, must not
146 be the last block in the function, and must contain just the
147 unconditional jump. */
148 jump_block
= cbranch_fallthru_edge
->dest
;
149 if (jump_block
->pred
->pred_next
150 || jump_block
->next_bb
== EXIT_BLOCK_PTR
151 || !FORWARDER_BLOCK_P (jump_block
))
153 jump_dest_block
= jump_block
->succ
->dest
;
155 /* The conditional branch must target the block after the
156 unconditional branch. */
157 cbranch_dest_block
= cbranch_jump_edge
->dest
;
159 if (!can_fallthru (jump_block
, cbranch_dest_block
))
162 /* Invert the conditional branch. */
163 if (!invert_jump (cbranch_insn
, block_label (jump_dest_block
), 0))
167 fprintf (rtl_dump_file
, "Simplifying condjump %i around jump %i\n",
168 INSN_UID (cbranch_insn
), INSN_UID (jump_block
->end
));
170 /* Success. Update the CFG to match. Note that after this point
171 the edge variable names appear backwards; the redirection is done
172 this way to preserve edge profile data. */
173 cbranch_jump_edge
= redirect_edge_succ_nodup (cbranch_jump_edge
,
175 cbranch_fallthru_edge
= redirect_edge_succ_nodup (cbranch_fallthru_edge
,
177 cbranch_jump_edge
->flags
|= EDGE_FALLTHRU
;
178 cbranch_fallthru_edge
->flags
&= ~EDGE_FALLTHRU
;
179 update_br_prob_note (cbranch_block
);
181 /* Delete the block with the unconditional jump, and clean up the mess. */
182 flow_delete_block (jump_block
);
183 tidy_fallthru_edge (cbranch_jump_edge
, cbranch_block
, cbranch_dest_block
);
188 /* Attempt to prove that operation is NOOP using CSElib or mark the effect
189 on register. Used by jump threading. */
192 mark_effect (exp
, nonequal
)
198 switch (GET_CODE (exp
))
200 /* In case we do clobber the register, mark it as equal, as we know the
201 value is dead so it don't have to match. */
203 if (REG_P (XEXP (exp
, 0)))
205 dest
= XEXP (exp
, 0);
206 regno
= REGNO (dest
);
207 CLEAR_REGNO_REG_SET (nonequal
, regno
);
208 if (regno
< FIRST_PSEUDO_REGISTER
)
210 int n
= HARD_REGNO_NREGS (regno
, GET_MODE (dest
));
212 CLEAR_REGNO_REG_SET (nonequal
, regno
+ n
);
218 if (rtx_equal_for_cselib_p (SET_DEST (exp
), SET_SRC (exp
)))
220 dest
= SET_DEST (exp
);
225 regno
= REGNO (dest
);
226 SET_REGNO_REG_SET (nonequal
, regno
);
227 if (regno
< FIRST_PSEUDO_REGISTER
)
229 int n
= HARD_REGNO_NREGS (regno
, GET_MODE (dest
));
231 SET_REGNO_REG_SET (nonequal
, regno
+ n
);
240 /* Return nonzero if X is an register set in regset DATA.
241 Called via for_each_rtx. */
243 mentions_nonequal_regs (x
, data
)
247 regset nonequal
= (regset
) data
;
253 if (REGNO_REG_SET_P (nonequal
, regno
))
255 if (regno
< FIRST_PSEUDO_REGISTER
)
257 int n
= HARD_REGNO_NREGS (regno
, GET_MODE (*x
));
259 if (REGNO_REG_SET_P (nonequal
, regno
+ n
))
265 /* Attempt to prove that the basic block B will have no side effects and
266 allways continues in the same edge if reached via E. Return the edge
267 if exist, NULL otherwise. */
270 thread_jump (mode
, e
, b
)
275 rtx set1
, set2
, cond1
, cond2
, insn
;
276 enum rtx_code code1
, code2
, reversed_code2
;
277 bool reverse1
= false;
282 if (BB_FLAGS (b
) & BB_NONTHREADABLE_BLOCK
)
285 /* At the moment, we do handle only conditional jumps, but later we may
286 want to extend this code to tablejumps and others. */
287 if (!e
->src
->succ
->succ_next
|| e
->src
->succ
->succ_next
->succ_next
)
289 if (!b
->succ
|| !b
->succ
->succ_next
|| b
->succ
->succ_next
->succ_next
)
291 BB_SET_FLAG (b
, BB_NONTHREADABLE_BLOCK
);
295 /* Second branch must end with onlyjump, as we will eliminate the jump. */
296 if (!any_condjump_p (e
->src
->end
))
299 if (!any_condjump_p (b
->end
) || !onlyjump_p (b
->end
))
301 BB_SET_FLAG (b
, BB_NONTHREADABLE_BLOCK
);
305 set1
= pc_set (e
->src
->end
);
306 set2
= pc_set (b
->end
);
307 if (((e
->flags
& EDGE_FALLTHRU
) != 0)
308 != (XEXP (SET_SRC (set1
), 1) == pc_rtx
))
311 cond1
= XEXP (SET_SRC (set1
), 0);
312 cond2
= XEXP (SET_SRC (set2
), 0);
314 code1
= reversed_comparison_code (cond1
, e
->src
->end
);
316 code1
= GET_CODE (cond1
);
318 code2
= GET_CODE (cond2
);
319 reversed_code2
= reversed_comparison_code (cond2
, b
->end
);
321 if (!comparison_dominates_p (code1
, code2
)
322 && !comparison_dominates_p (code1
, reversed_code2
))
325 /* Ensure that the comparison operators are equivalent.
326 ??? This is far too pesimistic. We should allow swapped operands,
327 different CCmodes, or for example comparisons for interval, that
328 dominate even when operands are not equivalent. */
329 if (!rtx_equal_p (XEXP (cond1
, 0), XEXP (cond2
, 0))
330 || !rtx_equal_p (XEXP (cond1
, 1), XEXP (cond2
, 1)))
333 /* Short circuit cases where block B contains some side effects, as we can't
335 for (insn
= NEXT_INSN (b
->head
); insn
!= NEXT_INSN (b
->end
);
336 insn
= NEXT_INSN (insn
))
337 if (INSN_P (insn
) && side_effects_p (PATTERN (insn
)))
339 BB_SET_FLAG (b
, BB_NONTHREADABLE_BLOCK
);
345 /* First process all values computed in the source basic block. */
346 for (insn
= NEXT_INSN (e
->src
->head
); insn
!= NEXT_INSN (e
->src
->end
);
347 insn
= NEXT_INSN (insn
))
349 cselib_process_insn (insn
);
351 nonequal
= BITMAP_XMALLOC();
352 CLEAR_REG_SET (nonequal
);
354 /* Now assume that we've continued by the edge E to B and continue
355 processing as if it were same basic block.
356 Our goal is to prove that whole block is an NOOP. */
358 for (insn
= NEXT_INSN (b
->head
); insn
!= NEXT_INSN (b
->end
) && !failed
;
359 insn
= NEXT_INSN (insn
))
363 rtx pat
= PATTERN (insn
);
365 if (GET_CODE (pat
) == PARALLEL
)
367 for (i
= 0; i
< XVECLEN (pat
, 0); i
++)
368 failed
|= mark_effect (XVECEXP (pat
, 0, i
), nonequal
);
371 failed
|= mark_effect (pat
, nonequal
);
374 cselib_process_insn (insn
);
377 /* Later we should clear nonequal of dead registers. So far we don't
378 have life information in cfg_cleanup. */
381 BB_SET_FLAG (b
, BB_NONTHREADABLE_BLOCK
);
385 /* cond2 must not mention any register that is not equal to the
387 if (for_each_rtx (&cond2
, mentions_nonequal_regs
, nonequal
))
390 /* In case liveness information is available, we need to prove equivalence
391 only of the live values. */
392 if (mode
& CLEANUP_UPDATE_LIFE
)
393 AND_REG_SET (nonequal
, b
->global_live_at_end
);
395 EXECUTE_IF_SET_IN_REG_SET (nonequal
, 0, i
, goto failed_exit
;);
397 BITMAP_XFREE (nonequal
);
399 if ((comparison_dominates_p (code1
, code2
) != 0)
400 != (XEXP (SET_SRC (set2
), 1) == pc_rtx
))
401 return BRANCH_EDGE (b
);
403 return FALLTHRU_EDGE (b
);
406 BITMAP_XFREE (nonequal
);
411 /* Attempt to forward edges leaving basic block B.
412 Return true if successful. */
415 try_forward_edges (mode
, b
)
419 bool changed
= false;
420 edge e
, next
, *threaded_edges
= NULL
;
422 for (e
= b
->succ
; e
; e
= next
)
424 basic_block target
, first
;
426 bool threaded
= false;
427 int nthreaded_edges
= 0;
431 /* Skip complex edges because we don't know how to update them.
433 Still handle fallthru edges, as we can succeed to forward fallthru
434 edge to the same place as the branch edge of conditional branch
435 and turn conditional branch to an unconditional branch. */
436 if (e
->flags
& EDGE_COMPLEX
)
439 target
= first
= e
->dest
;
442 while (counter
< n_basic_blocks
)
444 basic_block new_target
= NULL
;
445 bool new_target_threaded
= false;
447 if (FORWARDER_BLOCK_P (target
)
448 && target
->succ
->dest
!= EXIT_BLOCK_PTR
)
450 /* Bypass trivial infinite loops. */
451 if (target
== target
->succ
->dest
)
452 counter
= n_basic_blocks
;
453 new_target
= target
->succ
->dest
;
456 /* Allow to thread only over one edge at time to simplify updating
458 else if (mode
& CLEANUP_THREADING
)
460 edge t
= thread_jump (mode
, e
, target
);
464 threaded_edges
= xmalloc (sizeof (*threaded_edges
)
470 /* Detect an infinite loop across blocks not
471 including the start block. */
472 for (i
= 0; i
< nthreaded_edges
; ++i
)
473 if (threaded_edges
[i
] == t
)
475 if (i
< nthreaded_edges
)
477 counter
= n_basic_blocks
;
482 /* Detect an infinite loop across the start block. */
486 if (nthreaded_edges
>= n_basic_blocks
)
488 threaded_edges
[nthreaded_edges
++] = t
;
490 new_target
= t
->dest
;
491 new_target_threaded
= true;
498 /* Avoid killing of loop pre-headers, as it is the place loop
499 optimizer wants to hoist code to.
501 For fallthru forwarders, the LOOP_BEG note must appear between
502 the header of block and CODE_LABEL of the loop, for non forwarders
503 it must appear before the JUMP_INSN. */
504 if (mode
& CLEANUP_PRE_LOOP
)
506 rtx insn
= (target
->succ
->flags
& EDGE_FALLTHRU
507 ? target
->head
: prev_nonnote_insn (target
->end
));
509 if (GET_CODE (insn
) != NOTE
)
510 insn
= NEXT_INSN (insn
);
512 for (; insn
&& GET_CODE (insn
) != CODE_LABEL
&& !INSN_P (insn
);
513 insn
= NEXT_INSN (insn
))
514 if (GET_CODE (insn
) == NOTE
515 && NOTE_LINE_NUMBER (insn
) == NOTE_INSN_LOOP_BEG
)
518 if (GET_CODE (insn
) == NOTE
)
524 threaded
|= new_target_threaded
;
527 if (counter
>= n_basic_blocks
)
530 fprintf (rtl_dump_file
, "Infinite loop in BB %i.\n",
533 else if (target
== first
)
534 ; /* We didn't do anything. */
537 /* Save the values now, as the edge may get removed. */
538 gcov_type edge_count
= e
->count
;
539 int edge_probability
= e
->probability
;
543 /* Don't force if target is exit block. */
544 if (threaded
&& target
!= EXIT_BLOCK_PTR
)
546 notice_new_block (redirect_edge_and_branch_force (e
, target
));
548 fprintf (rtl_dump_file
, "Conditionals threaded.\n");
550 else if (!redirect_edge_and_branch (e
, target
))
553 fprintf (rtl_dump_file
,
554 "Forwarding edge %i->%i to %i failed.\n",
555 b
->index
, e
->dest
->index
, target
->index
);
559 /* We successfully forwarded the edge. Now update profile
560 data: for each edge we traversed in the chain, remove
561 the original edge's execution count. */
562 edge_frequency
= ((edge_probability
* b
->frequency
563 + REG_BR_PROB_BASE
/ 2)
566 if (!FORWARDER_BLOCK_P (b
) && forwarder_block_p (b
))
567 BB_SET_FLAG (b
, BB_FORWARDER_BLOCK
);
573 first
->count
-= edge_count
;
574 if (first
->count
< 0)
576 first
->frequency
-= edge_frequency
;
577 if (first
->frequency
< 0)
578 first
->frequency
= 0;
579 if (first
->succ
->succ_next
)
583 if (n
>= nthreaded_edges
)
585 t
= threaded_edges
[n
++];
588 if (first
->frequency
)
589 prob
= edge_frequency
* REG_BR_PROB_BASE
/ first
->frequency
;
592 if (prob
> t
->probability
)
593 prob
= t
->probability
;
594 t
->probability
-= prob
;
595 prob
= REG_BR_PROB_BASE
- prob
;
598 first
->succ
->probability
= REG_BR_PROB_BASE
;
599 first
->succ
->succ_next
->probability
= 0;
602 for (e
= first
->succ
; e
; e
= e
->succ_next
)
603 e
->probability
= ((e
->probability
* REG_BR_PROB_BASE
)
605 update_br_prob_note (first
);
609 /* It is possible that as the result of
610 threading we've removed edge as it is
611 threaded to the fallthru edge. Avoid
612 getting out of sync. */
613 if (n
< nthreaded_edges
614 && first
== threaded_edges
[n
]->src
)
619 t
->count
-= edge_count
;
624 while (first
!= target
);
631 free (threaded_edges
);
635 /* Return true if LABEL is a target of JUMP_INSN. This applies only
636 to non-complex jumps. That is, direct unconditional, conditional,
637 and tablejumps, but not computed jumps or returns. It also does
638 not apply to the fallthru case of a conditional jump. */
641 label_is_jump_target_p (label
, jump_insn
)
642 rtx label
, jump_insn
;
644 rtx tmp
= JUMP_LABEL (jump_insn
);
650 && (tmp
= NEXT_INSN (tmp
)) != NULL_RTX
651 && GET_CODE (tmp
) == JUMP_INSN
652 && (tmp
= PATTERN (tmp
),
653 GET_CODE (tmp
) == ADDR_VEC
654 || GET_CODE (tmp
) == ADDR_DIFF_VEC
))
656 rtvec vec
= XVEC (tmp
, GET_CODE (tmp
) == ADDR_DIFF_VEC
);
657 int i
, veclen
= GET_NUM_ELEM (vec
);
659 for (i
= 0; i
< veclen
; ++i
)
660 if (XEXP (RTVEC_ELT (vec
, i
), 0) == label
)
667 /* Return true if LABEL is used for tail recursion. */
670 tail_recursion_label_p (label
)
675 for (x
= tail_recursion_label_list
; x
; x
= XEXP (x
, 1))
676 if (label
== XEXP (x
, 0))
682 /* Blocks A and B are to be merged into a single block. A has no incoming
683 fallthru edge, so it can be moved before B without adding or modifying
684 any jumps (aside from the jump from A to B). */
687 merge_blocks_move_predecessor_nojumps (a
, b
)
693 barrier
= next_nonnote_insn (a
->end
);
694 if (GET_CODE (barrier
) != BARRIER
)
696 delete_insn (barrier
);
698 /* Move block and loop notes out of the chain so that we do not
701 ??? A better solution would be to squeeze out all the non-nested notes
702 and adjust the block trees appropriately. Even better would be to have
703 a tighter connection between block trees and rtl so that this is not
705 if (squeeze_notes (&a
->head
, &a
->end
))
708 /* Scramble the insn chain. */
709 if (a
->end
!= PREV_INSN (b
->head
))
710 reorder_insns_nobb (a
->head
, a
->end
, PREV_INSN (b
->head
));
711 a
->flags
|= BB_DIRTY
;
714 fprintf (rtl_dump_file
, "Moved block %d before %d and merged.\n",
717 /* Swap the records for the two blocks around. Although we are deleting B,
718 A is now where B was and we want to compact the BB array from where
720 BASIC_BLOCK (a
->index
) = b
;
721 BASIC_BLOCK (b
->index
) = a
;
727 link_block (a
, b
->prev_bb
);
729 /* Now blocks A and B are contiguous. Merge them. */
730 merge_blocks_nomove (a
, b
);
733 /* Blocks A and B are to be merged into a single block. B has no outgoing
734 fallthru edge, so it can be moved after A without adding or modifying
735 any jumps (aside from the jump from A to B). */
738 merge_blocks_move_successor_nojumps (a
, b
)
741 rtx barrier
, real_b_end
;
744 barrier
= NEXT_INSN (b
->end
);
746 /* Recognize a jump table following block B. */
748 && GET_CODE (barrier
) == CODE_LABEL
749 && NEXT_INSN (barrier
)
750 && GET_CODE (NEXT_INSN (barrier
)) == JUMP_INSN
751 && (GET_CODE (PATTERN (NEXT_INSN (barrier
))) == ADDR_VEC
752 || GET_CODE (PATTERN (NEXT_INSN (barrier
))) == ADDR_DIFF_VEC
))
754 /* Temporarily add the table jump insn to b, so that it will also
755 be moved to the correct location. */
756 b
->end
= NEXT_INSN (barrier
);
757 barrier
= NEXT_INSN (b
->end
);
760 /* There had better have been a barrier there. Delete it. */
761 if (barrier
&& GET_CODE (barrier
) == BARRIER
)
762 delete_insn (barrier
);
764 /* Move block and loop notes out of the chain so that we do not
767 ??? A better solution would be to squeeze out all the non-nested notes
768 and adjust the block trees appropriately. Even better would be to have
769 a tighter connection between block trees and rtl so that this is not
771 if (squeeze_notes (&b
->head
, &b
->end
))
774 /* Scramble the insn chain. */
775 reorder_insns_nobb (b
->head
, b
->end
, a
->end
);
777 /* Restore the real end of b. */
781 fprintf (rtl_dump_file
, "Moved block %d after %d and merged.\n",
784 /* Now blocks A and B are contiguous. Merge them. */
785 merge_blocks_nomove (a
, b
);
788 /* Attempt to merge basic blocks that are potentially non-adjacent.
789 Return true iff the attempt succeeded. */
792 merge_blocks (e
, b
, c
, mode
)
797 /* If C has a tail recursion label, do not merge. There is no
798 edge recorded from the call_placeholder back to this label, as
799 that would make optimize_sibling_and_tail_recursive_calls more
800 complex for no gain. */
801 if ((mode
& CLEANUP_PRE_SIBCALL
)
802 && GET_CODE (c
->head
) == CODE_LABEL
803 && tail_recursion_label_p (c
->head
))
806 /* If B has a fallthru edge to C, no need to move anything. */
807 if (e
->flags
& EDGE_FALLTHRU
)
809 int b_index
= b
->index
, c_index
= c
->index
;
810 merge_blocks_nomove (b
, c
);
811 update_forwarder_flag (b
);
814 fprintf (rtl_dump_file
, "Merged %d and %d without moving.\n",
820 /* Otherwise we will need to move code around. Do that only if expensive
821 transformations are allowed. */
822 else if (mode
& CLEANUP_EXPENSIVE
)
824 edge tmp_edge
, b_fallthru_edge
;
825 bool c_has_outgoing_fallthru
;
826 bool b_has_incoming_fallthru
;
828 /* Avoid overactive code motion, as the forwarder blocks should be
829 eliminated by edge redirection instead. One exception might have
830 been if B is a forwarder block and C has no fallthru edge, but
831 that should be cleaned up by bb-reorder instead. */
832 if (FORWARDER_BLOCK_P (b
) || FORWARDER_BLOCK_P (c
))
835 /* We must make sure to not munge nesting of lexical blocks,
836 and loop notes. This is done by squeezing out all the notes
837 and leaving them there to lie. Not ideal, but functional. */
839 for (tmp_edge
= c
->succ
; tmp_edge
; tmp_edge
= tmp_edge
->succ_next
)
840 if (tmp_edge
->flags
& EDGE_FALLTHRU
)
843 c_has_outgoing_fallthru
= (tmp_edge
!= NULL
);
845 for (tmp_edge
= b
->pred
; tmp_edge
; tmp_edge
= tmp_edge
->pred_next
)
846 if (tmp_edge
->flags
& EDGE_FALLTHRU
)
849 b_has_incoming_fallthru
= (tmp_edge
!= NULL
);
850 b_fallthru_edge
= tmp_edge
;
852 /* Otherwise, we're going to try to move C after B. If C does
853 not have an outgoing fallthru, then it can be moved
854 immediately after B without introducing or modifying jumps. */
855 if (! c_has_outgoing_fallthru
)
857 merge_blocks_move_successor_nojumps (b
, c
);
861 /* If B does not have an incoming fallthru, then it can be moved
862 immediately before C without introducing or modifying jumps.
863 C cannot be the first block, so we do not have to worry about
864 accessing a non-existent block. */
866 if (b_has_incoming_fallthru
)
870 if (b_fallthru_edge
->src
== ENTRY_BLOCK_PTR
)
872 bb
= force_nonfallthru (b_fallthru_edge
);
874 notice_new_block (bb
);
877 merge_blocks_move_predecessor_nojumps (b
, c
);
885 /* Return true if I1 and I2 are equivalent and thus can be crossjumped. */
888 insns_match_p (mode
, i1
, i2
)
889 int mode ATTRIBUTE_UNUSED
;
894 /* Verify that I1 and I2 are equivalent. */
895 if (GET_CODE (i1
) != GET_CODE (i2
))
901 if (GET_CODE (p1
) != GET_CODE (p2
))
904 /* If this is a CALL_INSN, compare register usage information.
905 If we don't check this on stack register machines, the two
906 CALL_INSNs might be merged leaving reg-stack.c with mismatching
907 numbers of stack registers in the same basic block.
908 If we don't check this on machines with delay slots, a delay slot may
909 be filled that clobbers a parameter expected by the subroutine.
911 ??? We take the simple route for now and assume that if they're
912 equal, they were constructed identically. */
914 if (GET_CODE (i1
) == CALL_INSN
915 && !rtx_equal_p (CALL_INSN_FUNCTION_USAGE (i1
),
916 CALL_INSN_FUNCTION_USAGE (i2
)))
920 /* If cross_jump_death_matters is not 0, the insn's mode
921 indicates whether or not the insn contains any stack-like
924 if ((mode
& CLEANUP_POST_REGSTACK
) && stack_regs_mentioned (i1
))
926 /* If register stack conversion has already been done, then
927 death notes must also be compared before it is certain that
928 the two instruction streams match. */
931 HARD_REG_SET i1_regset
, i2_regset
;
933 CLEAR_HARD_REG_SET (i1_regset
);
934 CLEAR_HARD_REG_SET (i2_regset
);
936 for (note
= REG_NOTES (i1
); note
; note
= XEXP (note
, 1))
937 if (REG_NOTE_KIND (note
) == REG_DEAD
&& STACK_REG_P (XEXP (note
, 0)))
938 SET_HARD_REG_BIT (i1_regset
, REGNO (XEXP (note
, 0)));
940 for (note
= REG_NOTES (i2
); note
; note
= XEXP (note
, 1))
941 if (REG_NOTE_KIND (note
) == REG_DEAD
&& STACK_REG_P (XEXP (note
, 0)))
942 SET_HARD_REG_BIT (i2_regset
, REGNO (XEXP (note
, 0)));
944 GO_IF_HARD_REG_EQUAL (i1_regset
, i2_regset
, done
);
954 ? ! rtx_renumbered_equal_p (p1
, p2
) : ! rtx_equal_p (p1
, p2
))
956 /* The following code helps take care of G++ cleanups. */
957 rtx equiv1
= find_reg_equal_equiv_note (i1
);
958 rtx equiv2
= find_reg_equal_equiv_note (i2
);
961 /* If the equivalences are not to a constant, they may
962 reference pseudos that no longer exist, so we can't
964 && (! reload_completed
965 || (CONSTANT_P (XEXP (equiv1
, 0))
966 && rtx_equal_p (XEXP (equiv1
, 0), XEXP (equiv2
, 0)))))
968 rtx s1
= single_set (i1
);
969 rtx s2
= single_set (i2
);
970 if (s1
!= 0 && s2
!= 0
971 && rtx_renumbered_equal_p (SET_DEST (s1
), SET_DEST (s2
)))
973 validate_change (i1
, &SET_SRC (s1
), XEXP (equiv1
, 0), 1);
974 validate_change (i2
, &SET_SRC (s2
), XEXP (equiv2
, 0), 1);
975 if (! rtx_renumbered_equal_p (p1
, p2
))
977 else if (apply_change_group ())
988 /* Look through the insns at the end of BB1 and BB2 and find the longest
989 sequence that are equivalent. Store the first insns for that sequence
990 in *F1 and *F2 and return the sequence length.
992 To simplify callers of this function, if the blocks match exactly,
993 store the head of the blocks in *F1 and *F2. */
996 flow_find_cross_jump (mode
, bb1
, bb2
, f1
, f2
)
997 int mode ATTRIBUTE_UNUSED
;
998 basic_block bb1
, bb2
;
1001 rtx i1
, i2
, last1
, last2
, afterlast1
, afterlast2
;
1004 /* Skip simple jumps at the end of the blocks. Complex jumps still
1005 need to be compared for equivalence, which we'll do below. */
1008 last1
= afterlast1
= last2
= afterlast2
= NULL_RTX
;
1010 || (returnjump_p (i1
) && !side_effects_p (PATTERN (i1
))))
1013 i1
= PREV_INSN (i1
);
1018 || (returnjump_p (i2
) && !side_effects_p (PATTERN (i2
))))
1021 /* Count everything except for unconditional jump as insn. */
1022 if (!simplejump_p (i2
) && !returnjump_p (i2
) && last1
)
1024 i2
= PREV_INSN (i2
);
1030 while (!active_insn_p (i1
) && i1
!= bb1
->head
)
1031 i1
= PREV_INSN (i1
);
1033 while (!active_insn_p (i2
) && i2
!= bb2
->head
)
1034 i2
= PREV_INSN (i2
);
1036 if (i1
== bb1
->head
|| i2
== bb2
->head
)
1039 if (!insns_match_p (mode
, i1
, i2
))
1042 /* Don't begin a cross-jump with a USE or CLOBBER insn. */
1043 if (active_insn_p (i1
))
1045 /* If the merged insns have different REG_EQUAL notes, then
1047 rtx equiv1
= find_reg_equal_equiv_note (i1
);
1048 rtx equiv2
= find_reg_equal_equiv_note (i2
);
1050 if (equiv1
&& !equiv2
)
1051 remove_note (i1
, equiv1
);
1052 else if (!equiv1
&& equiv2
)
1053 remove_note (i2
, equiv2
);
1054 else if (equiv1
&& equiv2
1055 && !rtx_equal_p (XEXP (equiv1
, 0), XEXP (equiv2
, 0)))
1057 remove_note (i1
, equiv1
);
1058 remove_note (i2
, equiv2
);
1061 afterlast1
= last1
, afterlast2
= last2
;
1062 last1
= i1
, last2
= i2
;
1066 i1
= PREV_INSN (i1
);
1067 i2
= PREV_INSN (i2
);
1071 /* Don't allow the insn after a compare to be shared by
1072 cross-jumping unless the compare is also shared. */
1073 if (ninsns
&& reg_mentioned_p (cc0_rtx
, last1
) && ! sets_cc0_p (last1
))
1074 last1
= afterlast1
, last2
= afterlast2
, ninsns
--;
1077 /* Include preceding notes and labels in the cross-jump. One,
1078 this may bring us to the head of the blocks as requested above.
1079 Two, it keeps line number notes as matched as may be. */
1082 while (last1
!= bb1
->head
&& !active_insn_p (PREV_INSN (last1
)))
1083 last1
= PREV_INSN (last1
);
1085 if (last1
!= bb1
->head
&& GET_CODE (PREV_INSN (last1
)) == CODE_LABEL
)
1086 last1
= PREV_INSN (last1
);
1088 while (last2
!= bb2
->head
&& !active_insn_p (PREV_INSN (last2
)))
1089 last2
= PREV_INSN (last2
);
1091 if (last2
!= bb2
->head
&& GET_CODE (PREV_INSN (last2
)) == CODE_LABEL
)
1092 last2
= PREV_INSN (last2
);
1101 /* Return true iff outgoing edges of BB1 and BB2 match, together with
1102 the branch instruction. This means that if we commonize the control
1103 flow before end of the basic block, the semantic remains unchanged.
1105 We may assume that there exists one edge with a common destination. */
1108 outgoing_edges_match (mode
, bb1
, bb2
)
1113 int nehedges1
= 0, nehedges2
= 0;
1114 edge fallthru1
= 0, fallthru2
= 0;
1117 /* If BB1 has only one successor, we may be looking at either an
1118 unconditional jump, or a fake edge to exit. */
1119 if (bb1
->succ
&& !bb1
->succ
->succ_next
1120 && !(bb1
->succ
->flags
& (EDGE_COMPLEX
| EDGE_FAKE
)))
1121 return (bb2
->succ
&& !bb2
->succ
->succ_next
1122 && (bb2
->succ
->flags
& (EDGE_COMPLEX
| EDGE_FAKE
)) == 0);
1124 /* Match conditional jumps - this may get tricky when fallthru and branch
1125 edges are crossed. */
1127 && bb1
->succ
->succ_next
1128 && !bb1
->succ
->succ_next
->succ_next
1129 && any_condjump_p (bb1
->end
)
1130 && onlyjump_p (bb1
->end
))
1132 edge b1
, f1
, b2
, f2
;
1133 bool reverse
, match
;
1134 rtx set1
, set2
, cond1
, cond2
;
1135 enum rtx_code code1
, code2
;
1138 || !bb2
->succ
->succ_next
1139 || bb2
->succ
->succ_next
->succ_next
1140 || !any_condjump_p (bb2
->end
)
1141 || !onlyjump_p (bb2
->end
))
1144 /* Do not crossjump across loop boundaries. This is a temporary
1145 workaround for the common scenario in which crossjumping results
1146 in killing the duplicated loop condition, making bb-reorder rotate
1147 the loop incorectly, leaving an extra unconditional jump inside
1150 This check should go away once bb-reorder knows how to duplicate
1151 code in this case or rotate the loops to avoid this scenario. */
1152 if (bb1
->loop_depth
!= bb2
->loop_depth
)
1155 b1
= BRANCH_EDGE (bb1
);
1156 b2
= BRANCH_EDGE (bb2
);
1157 f1
= FALLTHRU_EDGE (bb1
);
1158 f2
= FALLTHRU_EDGE (bb2
);
1160 /* Get around possible forwarders on fallthru edges. Other cases
1161 should be optimized out already. */
1162 if (FORWARDER_BLOCK_P (f1
->dest
))
1163 f1
= f1
->dest
->succ
;
1165 if (FORWARDER_BLOCK_P (f2
->dest
))
1166 f2
= f2
->dest
->succ
;
1168 /* To simplify use of this function, return false if there are
1169 unneeded forwarder blocks. These will get eliminated later
1170 during cleanup_cfg. */
1171 if (FORWARDER_BLOCK_P (f1
->dest
)
1172 || FORWARDER_BLOCK_P (f2
->dest
)
1173 || FORWARDER_BLOCK_P (b1
->dest
)
1174 || FORWARDER_BLOCK_P (b2
->dest
))
1177 if (f1
->dest
== f2
->dest
&& b1
->dest
== b2
->dest
)
1179 else if (f1
->dest
== b2
->dest
&& b1
->dest
== f2
->dest
)
1184 set1
= pc_set (bb1
->end
);
1185 set2
= pc_set (bb2
->end
);
1186 if ((XEXP (SET_SRC (set1
), 1) == pc_rtx
)
1187 != (XEXP (SET_SRC (set2
), 1) == pc_rtx
))
1190 cond1
= XEXP (SET_SRC (set1
), 0);
1191 cond2
= XEXP (SET_SRC (set2
), 0);
1192 code1
= GET_CODE (cond1
);
1194 code2
= reversed_comparison_code (cond2
, bb2
->end
);
1196 code2
= GET_CODE (cond2
);
1198 if (code2
== UNKNOWN
)
1201 /* Verify codes and operands match. */
1202 match
= ((code1
== code2
1203 && rtx_renumbered_equal_p (XEXP (cond1
, 0), XEXP (cond2
, 0))
1204 && rtx_renumbered_equal_p (XEXP (cond1
, 1), XEXP (cond2
, 1)))
1205 || (code1
== swap_condition (code2
)
1206 && rtx_renumbered_equal_p (XEXP (cond1
, 1),
1208 && rtx_renumbered_equal_p (XEXP (cond1
, 0),
1211 /* If we return true, we will join the blocks. Which means that
1212 we will only have one branch prediction bit to work with. Thus
1213 we require the existing branches to have probabilities that are
1217 && maybe_hot_bb_p (bb1
)
1218 && maybe_hot_bb_p (bb2
))
1222 if (b1
->dest
== b2
->dest
)
1223 prob2
= b2
->probability
;
1225 /* Do not use f2 probability as f2 may be forwarded. */
1226 prob2
= REG_BR_PROB_BASE
- b2
->probability
;
1228 /* Fail if the difference in probabilities is greater than 50%.
1229 This rules out two well-predicted branches with opposite
1231 if (abs (b1
->probability
- prob2
) > REG_BR_PROB_BASE
/ 2)
1234 fprintf (rtl_dump_file
,
1235 "Outcomes of branch in bb %i and %i differs to much (%i %i)\n",
1236 bb1
->index
, bb2
->index
, b1
->probability
, prob2
);
1242 if (rtl_dump_file
&& match
)
1243 fprintf (rtl_dump_file
, "Conditionals in bb %i and %i match.\n",
1244 bb1
->index
, bb2
->index
);
1249 /* Generic case - we are seeing an computed jump, table jump or trapping
1252 /* First ensure that the instructions match. There may be many outgoing
1253 edges so this test is generally cheaper.
1254 ??? Currently the tablejumps will never match, as they do have
1255 different tables. */
1256 if (!insns_match_p (mode
, bb1
->end
, bb2
->end
))
1259 /* Search the outgoing edges, ensure that the counts do match, find possible
1260 fallthru and exception handling edges since these needs more
1262 for (e1
= bb1
->succ
, e2
= bb2
->succ
; e1
&& e2
;
1263 e1
= e1
->succ_next
, e2
= e2
->succ_next
)
1265 if (e1
->flags
& EDGE_EH
)
1268 if (e2
->flags
& EDGE_EH
)
1271 if (e1
->flags
& EDGE_FALLTHRU
)
1273 if (e2
->flags
& EDGE_FALLTHRU
)
1277 /* If number of edges of various types does not match, fail. */
1279 || nehedges1
!= nehedges2
1280 || (fallthru1
!= 0) != (fallthru2
!= 0))
1283 /* fallthru edges must be forwarded to the same destination. */
1286 basic_block d1
= (forwarder_block_p (fallthru1
->dest
)
1287 ? fallthru1
->dest
->succ
->dest
: fallthru1
->dest
);
1288 basic_block d2
= (forwarder_block_p (fallthru2
->dest
)
1289 ? fallthru2
->dest
->succ
->dest
: fallthru2
->dest
);
1295 /* In case we do have EH edges, ensure we are in the same region. */
1298 rtx n1
= find_reg_note (bb1
->end
, REG_EH_REGION
, 0);
1299 rtx n2
= find_reg_note (bb2
->end
, REG_EH_REGION
, 0);
1301 if (XEXP (n1
, 0) != XEXP (n2
, 0))
1305 /* We don't need to match the rest of edges as above checks should be enought
1306 to ensure that they are equivalent. */
1310 /* E1 and E2 are edges with the same destination block. Search their
1311 predecessors for common code. If found, redirect control flow from
1312 (maybe the middle of) E1->SRC to (maybe the middle of) E2->SRC. */
1315 try_crossjump_to_edge (mode
, e1
, e2
)
1320 basic_block src1
= e1
->src
, src2
= e2
->src
;
1321 basic_block redirect_to
;
1322 rtx newpos1
, newpos2
;
1327 /* Search backward through forwarder blocks. We don't need to worry
1328 about multiple entry or chained forwarders, as they will be optimized
1329 away. We do this to look past the unconditional jump following a
1330 conditional jump that is required due to the current CFG shape. */
1332 && !src1
->pred
->pred_next
1333 && FORWARDER_BLOCK_P (src1
))
1334 e1
= src1
->pred
, src1
= e1
->src
;
1337 && !src2
->pred
->pred_next
1338 && FORWARDER_BLOCK_P (src2
))
1339 e2
= src2
->pred
, src2
= e2
->src
;
1341 /* Nothing to do if we reach ENTRY, or a common source block. */
1342 if (src1
== ENTRY_BLOCK_PTR
|| src2
== ENTRY_BLOCK_PTR
)
1347 /* Seeing more than 1 forwarder blocks would confuse us later... */
1348 if (FORWARDER_BLOCK_P (e1
->dest
)
1349 && FORWARDER_BLOCK_P (e1
->dest
->succ
->dest
))
1352 if (FORWARDER_BLOCK_P (e2
->dest
)
1353 && FORWARDER_BLOCK_P (e2
->dest
->succ
->dest
))
1356 /* Likewise with dead code (possibly newly created by the other optimizations
1358 if (!src1
->pred
|| !src2
->pred
)
1361 /* Look for the common insn sequence, part the first ... */
1362 if (!outgoing_edges_match (mode
, src1
, src2
))
1365 /* ... and part the second. */
1366 nmatch
= flow_find_cross_jump (mode
, src1
, src2
, &newpos1
, &newpos2
);
1370 /* Avoid splitting if possible. */
1371 if (newpos2
== src2
->head
)
1376 fprintf (rtl_dump_file
, "Splitting bb %i before %i insns\n",
1377 src2
->index
, nmatch
);
1378 redirect_to
= split_block (src2
, PREV_INSN (newpos2
))->dest
;
1382 fprintf (rtl_dump_file
,
1383 "Cross jumping from bb %i to bb %i; %i common insns\n",
1384 src1
->index
, src2
->index
, nmatch
);
1386 redirect_to
->count
+= src1
->count
;
1387 redirect_to
->frequency
+= src1
->frequency
;
1388 /* We may have some registers visible trought the block. */
1389 redirect_to
->flags
|= BB_DIRTY
;
1391 /* Recompute the frequencies and counts of outgoing edges. */
1392 for (s
= redirect_to
->succ
; s
; s
= s
->succ_next
)
1395 basic_block d
= s
->dest
;
1397 if (FORWARDER_BLOCK_P (d
))
1400 for (s2
= src1
->succ
; ; s2
= s2
->succ_next
)
1402 basic_block d2
= s2
->dest
;
1403 if (FORWARDER_BLOCK_P (d2
))
1404 d2
= d2
->succ
->dest
;
1409 s
->count
+= s2
->count
;
1411 /* Take care to update possible forwarder blocks. We verified
1412 that there is no more than one in the chain, so we can't run
1413 into infinite loop. */
1414 if (FORWARDER_BLOCK_P (s
->dest
))
1416 s
->dest
->succ
->count
+= s2
->count
;
1417 s
->dest
->count
+= s2
->count
;
1418 s
->dest
->frequency
+= EDGE_FREQUENCY (s
);
1421 if (FORWARDER_BLOCK_P (s2
->dest
))
1423 s2
->dest
->succ
->count
-= s2
->count
;
1424 if (s2
->dest
->succ
->count
< 0)
1425 s2
->dest
->succ
->count
= 0;
1426 s2
->dest
->count
-= s2
->count
;
1427 s2
->dest
->frequency
-= EDGE_FREQUENCY (s
);
1428 if (s2
->dest
->frequency
< 0)
1429 s2
->dest
->frequency
= 0;
1430 if (s2
->dest
->count
< 0)
1431 s2
->dest
->count
= 0;
1434 if (!redirect_to
->frequency
&& !src1
->frequency
)
1435 s
->probability
= (s
->probability
+ s2
->probability
) / 2;
1438 = ((s
->probability
* redirect_to
->frequency
+
1439 s2
->probability
* src1
->frequency
)
1440 / (redirect_to
->frequency
+ src1
->frequency
));
1443 update_br_prob_note (redirect_to
);
1445 /* Edit SRC1 to go to REDIRECT_TO at NEWPOS1. */
1447 /* Skip possible basic block header. */
1448 if (GET_CODE (newpos1
) == CODE_LABEL
)
1449 newpos1
= NEXT_INSN (newpos1
);
1451 if (GET_CODE (newpos1
) == NOTE
)
1452 newpos1
= NEXT_INSN (newpos1
);
1455 /* Emit the jump insn. */
1456 label
= block_label (redirect_to
);
1457 emit_jump_insn_after (gen_jump (label
), src1
->end
);
1458 JUMP_LABEL (src1
->end
) = label
;
1459 LABEL_NUSES (label
)++;
1461 /* Delete the now unreachable instructions. */
1462 delete_insn_chain (newpos1
, last
);
1464 /* Make sure there is a barrier after the new jump. */
1465 last
= next_nonnote_insn (src1
->end
);
1466 if (!last
|| GET_CODE (last
) != BARRIER
)
1467 emit_barrier_after (src1
->end
);
1471 remove_edge (src1
->succ
);
1472 make_single_succ_edge (src1
, redirect_to
, 0);
1474 update_forwarder_flag (src1
);
1479 /* Search the predecessors of BB for common insn sequences. When found,
1480 share code between them by redirecting control flow. Return true if
1481 any changes made. */
1484 try_crossjump_bb (mode
, bb
)
1488 edge e
, e2
, nexte2
, nexte
, fallthru
;
1492 /* Nothing to do if there is not at least two incoming edges. */
1493 if (!bb
->pred
|| !bb
->pred
->pred_next
)
1496 /* It is always cheapest to redirect a block that ends in a branch to
1497 a block that falls through into BB, as that adds no branches to the
1498 program. We'll try that combination first. */
1499 for (fallthru
= bb
->pred
; fallthru
; fallthru
= fallthru
->pred_next
, n
++)
1501 if (fallthru
->flags
& EDGE_FALLTHRU
)
1508 for (e
= bb
->pred
; e
; e
= nexte
)
1510 nexte
= e
->pred_next
;
1512 /* As noted above, first try with the fallthru predecessor. */
1515 /* Don't combine the fallthru edge into anything else.
1516 If there is a match, we'll do it the other way around. */
1520 if (try_crossjump_to_edge (mode
, e
, fallthru
))
1528 /* Non-obvious work limiting check: Recognize that we're going
1529 to call try_crossjump_bb on every basic block. So if we have
1530 two blocks with lots of outgoing edges (a switch) and they
1531 share lots of common destinations, then we would do the
1532 cross-jump check once for each common destination.
1534 Now, if the blocks actually are cross-jump candidates, then
1535 all of their destinations will be shared. Which means that
1536 we only need check them for cross-jump candidacy once. We
1537 can eliminate redundant checks of crossjump(A,B) by arbitrarily
1538 choosing to do the check from the block for which the edge
1539 in question is the first successor of A. */
1540 if (e
->src
->succ
!= e
)
1543 for (e2
= bb
->pred
; e2
; e2
= nexte2
)
1545 nexte2
= e2
->pred_next
;
1550 /* We've already checked the fallthru edge above. */
1554 /* The "first successor" check above only prevents multiple
1555 checks of crossjump(A,B). In order to prevent redundant
1556 checks of crossjump(B,A), require that A be the block
1557 with the lowest index. */
1558 if (e
->src
->index
> e2
->src
->index
)
1561 if (try_crossjump_to_edge (mode
, e
, e2
))
1573 /* Do simple CFG optimizations - basic block merging, simplifying of jump
1574 instructions etc. Return nonzero if changes were made. */
1577 try_optimize_cfg (mode
)
1580 bool changed_overall
= false;
1585 if (mode
& CLEANUP_CROSSJUMP
)
1586 add_noreturn_fake_exit_edges ();
1589 update_forwarder_flag (bb
);
1591 if (mode
& CLEANUP_UPDATE_LIFE
)
1594 if (! (* targetm
.cannot_modify_jumps_p
) ())
1596 /* Attempt to merge blocks as made possible by edge removal. If
1597 a block has only one successor, and the successor has only
1598 one predecessor, they may be combined. */
1605 fprintf (rtl_dump_file
,
1606 "\n\ntry_optimize_cfg iteration %i\n\n",
1609 for (b
= ENTRY_BLOCK_PTR
->next_bb
; b
!= EXIT_BLOCK_PTR
;)
1613 bool changed_here
= false;
1615 /* Delete trivially dead basic blocks. */
1616 while (b
->pred
== NULL
)
1620 fprintf (rtl_dump_file
, "Deleting block %i.\n",
1623 flow_delete_block (b
);
1628 /* Remove code labels no longer used. Don't do this
1629 before CALL_PLACEHOLDER is removed, as some branches
1630 may be hidden within. */
1631 if (b
->pred
->pred_next
== NULL
1632 && (b
->pred
->flags
& EDGE_FALLTHRU
)
1633 && !(b
->pred
->flags
& EDGE_COMPLEX
)
1634 && GET_CODE (b
->head
) == CODE_LABEL
1635 && (!(mode
& CLEANUP_PRE_SIBCALL
)
1636 || !tail_recursion_label_p (b
->head
))
1637 /* If the previous block ends with a branch to this
1638 block, we can't delete the label. Normally this
1639 is a condjump that is yet to be simplified, but
1640 if CASE_DROPS_THRU, this can be a tablejump with
1641 some element going to the same place as the
1642 default (fallthru). */
1643 && (b
->pred
->src
== ENTRY_BLOCK_PTR
1644 || GET_CODE (b
->pred
->src
->end
) != JUMP_INSN
1645 || ! label_is_jump_target_p (b
->head
,
1646 b
->pred
->src
->end
)))
1648 rtx label
= b
->head
;
1650 b
->head
= NEXT_INSN (b
->head
);
1651 delete_insn_chain (label
, label
);
1653 fprintf (rtl_dump_file
, "Deleted label in block %i.\n",
1657 /* If we fall through an empty block, we can remove it. */
1658 if (b
->pred
->pred_next
== NULL
1659 && (b
->pred
->flags
& EDGE_FALLTHRU
)
1660 && GET_CODE (b
->head
) != CODE_LABEL
1661 && FORWARDER_BLOCK_P (b
)
1662 /* Note that forwarder_block_p true ensures that
1663 there is a successor for this block. */
1664 && (b
->succ
->flags
& EDGE_FALLTHRU
)
1665 && n_basic_blocks
> 1)
1668 fprintf (rtl_dump_file
,
1669 "Deleting fallthru block %i.\n",
1672 c
= b
->prev_bb
== ENTRY_BLOCK_PTR
? b
->next_bb
: b
->prev_bb
;
1673 redirect_edge_succ_nodup (b
->pred
, b
->succ
->dest
);
1674 flow_delete_block (b
);
1679 /* Merge blocks. Loop because chains of blocks might be
1681 while ((s
= b
->succ
) != NULL
1682 && s
->succ_next
== NULL
1683 && !(s
->flags
& EDGE_COMPLEX
)
1684 && (c
= s
->dest
) != EXIT_BLOCK_PTR
1685 && c
->pred
->pred_next
== NULL
1686 /* If the jump insn has side effects,
1687 we can't kill the edge. */
1688 && (GET_CODE (b
->end
) != JUMP_INSN
1689 || simplejump_p (b
->end
))
1690 && merge_blocks (s
, b
, c
, mode
))
1691 changed_here
= true;
1693 /* Simplify branch over branch. */
1694 if ((mode
& CLEANUP_EXPENSIVE
) && try_simplify_condjump (b
))
1695 changed_here
= true;
1697 /* If B has a single outgoing edge, but uses a
1698 non-trivial jump instruction without side-effects, we
1699 can either delete the jump entirely, or replace it
1700 with a simple unconditional jump. Use
1701 redirect_edge_and_branch to do the dirty work. */
1703 && ! b
->succ
->succ_next
1704 && b
->succ
->dest
!= EXIT_BLOCK_PTR
1705 && onlyjump_p (b
->end
)
1706 && redirect_edge_and_branch (b
->succ
, b
->succ
->dest
))
1708 update_forwarder_flag (b
);
1709 changed_here
= true;
1712 /* Simplify branch to branch. */
1713 if (try_forward_edges (mode
, b
))
1714 changed_here
= true;
1716 /* Look for shared code between blocks. */
1717 if ((mode
& CLEANUP_CROSSJUMP
)
1718 && try_crossjump_bb (mode
, b
))
1719 changed_here
= true;
1721 /* Don't get confused by the index shift caused by
1729 if ((mode
& CLEANUP_CROSSJUMP
)
1730 && try_crossjump_bb (mode
, EXIT_BLOCK_PTR
))
1733 #ifdef ENABLE_CHECKING
1735 verify_flow_info ();
1738 changed_overall
|= changed
;
1743 if (mode
& CLEANUP_CROSSJUMP
)
1744 remove_fake_edges ();
1746 clear_aux_for_blocks ();
1748 return changed_overall
;
1751 /* Delete all unreachable basic blocks. */
1754 delete_unreachable_blocks ()
1756 bool changed
= false;
1757 basic_block b
, next_bb
;
1760 find_unreachable_blocks ();
1762 /* Delete all unreachable basic blocks. Do compaction concurrently,
1763 as otherwise we can wind up with O(N^2) behaviour here when we
1764 have oodles of dead code. */
1766 for (b
= ENTRY_BLOCK_PTR
->next_bb
; b
!= EXIT_BLOCK_PTR
; b
= next_bb
)
1768 next_bb
= b
->next_bb
;
1770 if (!(b
->flags
& BB_REACHABLE
))
1772 flow_delete_block_noexpunge (b
);
1773 expunge_block_nocompact (b
);
1778 BASIC_BLOCK (j
) = b
;
1783 basic_block_info
->num_elements
= j
;
1786 tidy_fallthru_edges ();
1790 /* Tidy the CFG by deleting unreachable code and whatnot. */
1796 bool changed
= false;
1798 timevar_push (TV_CLEANUP_CFG
);
1799 if (delete_unreachable_blocks ())
1802 /* We've possibly created trivially dead code. Cleanup it right
1803 now to introduce more oppurtunities for try_optimize_cfg. */
1804 if (!(mode
& (CLEANUP_NO_INSN_DEL
1805 | CLEANUP_UPDATE_LIFE
| CLEANUP_PRE_SIBCALL
))
1806 && !reload_completed
)
1807 delete_trivially_dead_insns (get_insns(), max_reg_num ());
1809 while (try_optimize_cfg (mode
))
1811 delete_unreachable_blocks (), changed
= true;
1812 if (mode
& CLEANUP_UPDATE_LIFE
)
1814 /* Cleaning up CFG introduces more oppurtunities for dead code
1815 removal that in turn may introduce more oppurtunities for
1816 cleaning up the CFG. */
1817 if (!update_life_info_in_dirty_blocks (UPDATE_LIFE_GLOBAL_RM_NOTES
,
1819 | PROP_SCAN_DEAD_CODE
1820 | PROP_KILL_DEAD_CODE
1824 else if (!(mode
& (CLEANUP_NO_INSN_DEL
| CLEANUP_PRE_SIBCALL
))
1825 && !reload_completed
)
1827 if (!delete_trivially_dead_insns (get_insns(), max_reg_num ()))
1832 delete_dead_jumptables ();
1835 /* Kill the data we won't maintain. */
1836 free_EXPR_LIST_list (&label_value_list
);
1837 timevar_pop (TV_CLEANUP_CFG
);