1 /* RTL dead code elimination.
2 Copyright (C) 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
4 This file is part of GCC.
6 GCC is free software; you can redistribute it and/or modify it under
7 the terms of the GNU General Public License as published by the Free
8 Software Foundation; either version 3, or (at your option) any later
11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING3. If not see
18 <http://www.gnu.org/licenses/>. */
22 #include "coretypes.h"
28 #include "hard-reg-set.h"
35 #include "tree-pass.h"
38 #include "emit-rtl.h" /* FIXME: Can go away once crtl is moved to rtl.h. */
41 /* -------------------------------------------------------------------------
42 Core mark/delete routines
43 ------------------------------------------------------------------------- */
45 /* True if we are invoked while the df engine is running; in this case,
46 we don't want to reenter it. */
47 static bool df_in_progress
= false;
49 /* Instructions that have been marked but whose dependencies have not
50 yet been processed. */
51 static VEC(rtx
,heap
) *worklist
;
53 /* Bitmap of instructions marked as needed indexed by INSN_UID. */
54 static sbitmap marked
;
56 /* Bitmap obstacks used for block processing by the fast algorithm. */
57 static bitmap_obstack dce_blocks_bitmap_obstack
;
58 static bitmap_obstack dce_tmp_bitmap_obstack
;
60 static bool find_call_stack_args (rtx
, bool, bool, bitmap
);
62 /* A subroutine for which BODY is part of the instruction being tested;
63 either the top-level pattern, or an element of a PARALLEL. The
64 instruction is known not to be a bare USE or CLOBBER. */
67 deletable_insn_p_1 (rtx body
)
69 switch (GET_CODE (body
))
73 /* The UNSPEC case was added here because the ia-64 claims that
74 USEs do not work after reload and generates UNSPECS rather
75 than USEs. Since dce is run after reload we need to avoid
76 deleting these even if they are dead. If it turns out that
77 USEs really do work after reload, the ia-64 should be
78 changed, and the UNSPEC case can be removed. */
83 return !volatile_refs_p (body
);
88 /* Return true if INSN is a normal instruction that can be deleted by
92 deletable_insn_p (rtx insn
, bool fast
, bitmap arg_stores
)
98 /* We cannot delete calls inside of the recursive dce because
99 this may cause basic blocks to be deleted and this messes up
100 the rest of the stack of optimization passes. */
102 /* We cannot delete pure or const sibling calls because it is
103 hard to see the result. */
104 && (!SIBLING_CALL_P (insn
))
105 /* We can delete dead const or pure calls as long as they do not
107 && (RTL_CONST_OR_PURE_CALL_P (insn
)
108 && !RTL_LOOPING_CONST_OR_PURE_CALL_P (insn
)))
109 return find_call_stack_args (insn
, false, fast
, arg_stores
);
111 /* Don't delete jumps, notes and the like. */
112 if (!NONJUMP_INSN_P (insn
))
115 /* Don't delete insns that can throw. */
116 if (!insn_nothrow_p (insn
))
119 body
= PATTERN (insn
);
120 switch (GET_CODE (body
))
129 /* A CLOBBER of a dead pseudo register serves no purpose.
130 That is not necessarily true for hard registers until
133 return REG_P (x
) && (!HARD_REGISTER_P (x
) || reload_completed
);
136 /* Because of the way that use-def chains are built, it is not
137 possible to tell if the clobber is dead because it can
138 never be the target of a use-def chain. */
142 for (i
= XVECLEN (body
, 0) - 1; i
>= 0; i
--)
143 if (!deletable_insn_p_1 (XVECEXP (body
, 0, i
)))
148 return deletable_insn_p_1 (body
);
153 /* Return true if INSN has been marked as needed. */
156 marked_insn_p (rtx insn
)
158 /* Artificial defs are always needed and they do not have an insn.
159 We should never see them here. */
161 return TEST_BIT (marked
, INSN_UID (insn
));
165 /* If INSN has not yet been marked as needed, mark it now, and add it to
169 mark_insn (rtx insn
, bool fast
)
171 if (!marked_insn_p (insn
))
174 VEC_safe_push (rtx
, heap
, worklist
, insn
);
175 SET_BIT (marked
, INSN_UID (insn
));
177 fprintf (dump_file
, " Adding insn %d to worklist\n", INSN_UID (insn
));
180 && !SIBLING_CALL_P (insn
)
181 && (RTL_CONST_OR_PURE_CALL_P (insn
)
182 && !RTL_LOOPING_CONST_OR_PURE_CALL_P (insn
)))
183 find_call_stack_args (insn
, true, fast
, NULL
);
188 /* A note_stores callback used by mark_nonreg_stores. DATA is the
189 instruction containing DEST. */
192 mark_nonreg_stores_1 (rtx dest
, const_rtx pattern
, void *data
)
194 if (GET_CODE (pattern
) != CLOBBER
&& !REG_P (dest
))
195 mark_insn ((rtx
) data
, true);
199 /* A note_stores callback used by mark_nonreg_stores. DATA is the
200 instruction containing DEST. */
203 mark_nonreg_stores_2 (rtx dest
, const_rtx pattern
, void *data
)
205 if (GET_CODE (pattern
) != CLOBBER
&& !REG_P (dest
))
206 mark_insn ((rtx
) data
, false);
210 /* Mark INSN if BODY stores to a non-register destination. */
213 mark_nonreg_stores (rtx body
, rtx insn
, bool fast
)
216 note_stores (body
, mark_nonreg_stores_1
, insn
);
218 note_stores (body
, mark_nonreg_stores_2
, insn
);
222 /* Try to find all stack stores of CALL_INSN arguments if
223 ACCUMULATE_OUTGOING_ARGS. If all stack stores have been found
224 and it is therefore safe to eliminate the call, return true,
225 otherwise return false. This function should be first called
226 with DO_MARK false, and only when the CALL_INSN is actually
227 going to be marked called again with DO_MARK true. */
230 find_call_stack_args (rtx call_insn
, bool do_mark
, bool fast
,
233 rtx p
, insn
, prev_insn
;
235 HOST_WIDE_INT min_sp_off
, max_sp_off
;
238 gcc_assert (CALL_P (call_insn
));
239 if (!ACCUMULATE_OUTGOING_ARGS
)
244 gcc_assert (arg_stores
);
245 bitmap_clear (arg_stores
);
248 min_sp_off
= INTTYPE_MAXIMUM (HOST_WIDE_INT
);
251 /* First determine the minimum and maximum offset from sp for
253 for (p
= CALL_INSN_FUNCTION_USAGE (call_insn
); p
; p
= XEXP (p
, 1))
254 if (GET_CODE (XEXP (p
, 0)) == USE
255 && MEM_P (XEXP (XEXP (p
, 0), 0)))
257 rtx mem
= XEXP (XEXP (p
, 0), 0), addr
, size
;
258 HOST_WIDE_INT off
= 0;
259 size
= MEM_SIZE (mem
);
260 if (size
== NULL_RTX
)
262 addr
= XEXP (mem
, 0);
263 if (GET_CODE (addr
) == PLUS
264 && REG_P (XEXP (addr
, 0))
265 && CONST_INT_P (XEXP (addr
, 1)))
267 off
= INTVAL (XEXP (addr
, 1));
268 addr
= XEXP (addr
, 0);
270 if (addr
!= stack_pointer_rtx
)
274 /* If not fast, use chains to see if addr wasn't set to
279 struct df_link
*defs
;
282 for (use_rec
= DF_INSN_USES (call_insn
); *use_rec
; use_rec
++)
283 if (rtx_equal_p (addr
, DF_REF_REG (*use_rec
)))
286 if (*use_rec
== NULL
)
289 for (defs
= DF_REF_CHAIN (*use_rec
); defs
; defs
= defs
->next
)
290 if (! DF_REF_IS_ARTIFICIAL (defs
->ref
))
296 set
= single_set (DF_REF_INSN (defs
->ref
));
300 if (GET_CODE (SET_SRC (set
)) != PLUS
301 || XEXP (SET_SRC (set
), 0) != stack_pointer_rtx
302 || !CONST_INT_P (XEXP (SET_SRC (set
), 1)))
305 off
+= INTVAL (XEXP (SET_SRC (set
), 1));
310 min_sp_off
= MIN (min_sp_off
, off
);
311 max_sp_off
= MAX (max_sp_off
, off
+ INTVAL (size
));
314 if (min_sp_off
>= max_sp_off
)
316 sp_bytes
= BITMAP_ALLOC (NULL
);
318 /* Set bits in SP_BYTES bitmap for bytes relative to sp + min_sp_off
319 which contain arguments. Checking has been done in the previous
321 for (p
= CALL_INSN_FUNCTION_USAGE (call_insn
); p
; p
= XEXP (p
, 1))
322 if (GET_CODE (XEXP (p
, 0)) == USE
323 && MEM_P (XEXP (XEXP (p
, 0), 0)))
325 rtx mem
= XEXP (XEXP (p
, 0), 0), addr
;
326 HOST_WIDE_INT off
= 0, byte
;
327 addr
= XEXP (mem
, 0);
328 if (GET_CODE (addr
) == PLUS
329 && REG_P (XEXP (addr
, 0))
330 && CONST_INT_P (XEXP (addr
, 1)))
332 off
= INTVAL (XEXP (addr
, 1));
333 addr
= XEXP (addr
, 0);
335 if (addr
!= stack_pointer_rtx
)
338 struct df_link
*defs
;
341 for (use_rec
= DF_INSN_USES (call_insn
); *use_rec
; use_rec
++)
342 if (rtx_equal_p (addr
, DF_REF_REG (*use_rec
)))
345 for (defs
= DF_REF_CHAIN (*use_rec
); defs
; defs
= defs
->next
)
346 if (! DF_REF_IS_ARTIFICIAL (defs
->ref
))
349 set
= single_set (DF_REF_INSN (defs
->ref
));
350 off
+= INTVAL (XEXP (SET_SRC (set
), 1));
352 for (byte
= off
; byte
< off
+ INTVAL (MEM_SIZE (mem
)); byte
++)
354 if (!bitmap_set_bit (sp_bytes
, byte
- min_sp_off
))
359 /* Walk backwards, looking for argument stores. The search stops
360 when seeing another call, sp adjustment or memory store other than
363 for (insn
= PREV_INSN (call_insn
); insn
; insn
= prev_insn
)
366 HOST_WIDE_INT off
, byte
;
368 if (insn
== BB_HEAD (BLOCK_FOR_INSN (call_insn
)))
369 prev_insn
= NULL_RTX
;
371 prev_insn
= PREV_INSN (insn
);
379 set
= single_set (insn
);
380 if (!set
|| SET_DEST (set
) == stack_pointer_rtx
)
383 if (!MEM_P (SET_DEST (set
)))
386 mem
= SET_DEST (set
);
387 addr
= XEXP (mem
, 0);
389 if (GET_CODE (addr
) == PLUS
390 && REG_P (XEXP (addr
, 0))
391 && CONST_INT_P (XEXP (addr
, 1)))
393 off
= INTVAL (XEXP (addr
, 1));
394 addr
= XEXP (addr
, 0);
396 if (addr
!= stack_pointer_rtx
)
403 struct df_link
*defs
;
406 for (use_rec
= DF_INSN_USES (insn
); *use_rec
; use_rec
++)
407 if (rtx_equal_p (addr
, DF_REF_REG (*use_rec
)))
410 if (*use_rec
== NULL
)
413 for (defs
= DF_REF_CHAIN (*use_rec
); defs
; defs
= defs
->next
)
414 if (! DF_REF_IS_ARTIFICIAL (defs
->ref
))
420 set
= single_set (DF_REF_INSN (defs
->ref
));
424 if (GET_CODE (SET_SRC (set
)) != PLUS
425 || XEXP (SET_SRC (set
), 0) != stack_pointer_rtx
426 || !CONST_INT_P (XEXP (SET_SRC (set
), 1)))
429 off
+= INTVAL (XEXP (SET_SRC (set
), 1));
435 if (GET_MODE_SIZE (GET_MODE (mem
)) == 0)
438 for (byte
= off
; byte
< off
+ GET_MODE_SIZE (GET_MODE (mem
)); byte
++)
440 if (byte
< min_sp_off
441 || byte
>= max_sp_off
442 || !bitmap_clear_bit (sp_bytes
, byte
- min_sp_off
))
446 if (!deletable_insn_p (insn
, fast
, NULL
))
450 mark_insn (insn
, fast
);
452 bitmap_set_bit (arg_stores
, INSN_UID (insn
));
454 if (bitmap_empty_p (sp_bytes
))
461 BITMAP_FREE (sp_bytes
);
462 if (!ret
&& arg_stores
)
463 bitmap_clear (arg_stores
);
469 /* Delete all REG_EQUAL notes of the registers INSN writes, to prevent
470 bad dangling REG_EQUAL notes. */
473 delete_corresponding_reg_eq_notes (rtx insn
)
476 for (def_rec
= DF_INSN_DEFS (insn
); *def_rec
; def_rec
++)
478 df_ref def
= *def_rec
;
479 unsigned int regno
= DF_REF_REGNO (def
);
480 /* This loop is a little tricky. We cannot just go down the
481 chain because it is being modified by the actions in the
482 loop. So we just get the head. We plan to drain the list
484 while (DF_REG_EQ_USE_CHAIN (regno
))
486 df_ref eq_use
= DF_REG_EQ_USE_CHAIN (regno
);
487 rtx noted_insn
= DF_REF_INSN (eq_use
);
488 rtx note
= find_reg_note (noted_insn
, REG_EQUAL
, NULL_RTX
);
490 note
= find_reg_note (noted_insn
, REG_EQUIV
, NULL_RTX
);
492 /* This assert is generally triggered when someone deletes a
493 REG_EQUAL or REG_EQUIV note by hacking the list manually
494 rather than calling remove_note. */
496 remove_note (noted_insn
, note
);
502 /* Delete every instruction that hasn't been marked. */
505 delete_unmarked_insns (void)
509 bool must_clean
= false;
511 FOR_EACH_BB_REVERSE (bb
)
512 FOR_BB_INSNS_REVERSE_SAFE (bb
, insn
, next
)
515 /* Always delete no-op moves. */
516 if (noop_move_p (insn
))
519 /* Otherwise rely only on the DCE algorithm. */
520 else if (marked_insn_p (insn
))
523 /* Beware that reaching a dbg counter limit here can result
524 in miscompiled file. This occurs when a group of insns
525 must be deleted together, typically because the kept insn
526 depends on the output from the deleted insn. Deleting
527 this insns in reverse order (both at the bb level and
528 when looking at the blocks) minimizes this, but does not
529 eliminate it, since it is possible for the using insn to
530 be top of a block and the producer to be at the bottom of
531 the block. However, in most cases this will only result
532 in an uninitialized use of an insn that is dead anyway.
534 However, there is one rare case that will cause a
535 miscompile: deletion of non-looping pure and constant
536 calls on a machine where ACCUMULATE_OUTGOING_ARGS is true.
537 In this case it is possible to remove the call, but leave
538 the argument pushes to the stack. Because of the changes
539 to the stack pointer, this will almost always lead to a
545 fprintf (dump_file
, "DCE: Deleting insn %d\n", INSN_UID (insn
));
547 /* Before we delete the insn we have to delete REG_EQUAL notes
548 for the destination regs in order to avoid dangling notes. */
549 delete_corresponding_reg_eq_notes (insn
);
551 /* If a pure or const call is deleted, this may make the cfg
552 have unreachable blocks. We rememeber this and call
553 delete_unreachable_blocks at the end. */
557 /* Now delete the insn. */
558 delete_insn_and_edges (insn
);
561 /* Deleted a pure or const call. */
563 delete_unreachable_blocks ();
567 /* Go through the instructions and mark those whose necessity is not
568 dependent on inter-instruction information. Make sure all other
569 instructions are not marked. */
572 prescan_insns_for_dce (bool fast
)
576 bitmap arg_stores
= NULL
;
579 fprintf (dump_file
, "Finding needed instructions:\n");
581 if (!df_in_progress
&& ACCUMULATE_OUTGOING_ARGS
)
582 arg_stores
= BITMAP_ALLOC (NULL
);
586 FOR_BB_INSNS_REVERSE_SAFE (bb
, insn
, prev
)
589 /* Don't mark argument stores now. They will be marked
590 if needed when the associated CALL is marked. */
591 if (arg_stores
&& bitmap_bit_p (arg_stores
, INSN_UID (insn
)))
593 if (deletable_insn_p (insn
, fast
, arg_stores
))
594 mark_nonreg_stores (PATTERN (insn
), insn
, fast
);
596 mark_insn (insn
, fast
);
598 /* find_call_stack_args only looks at argument stores in the
601 bitmap_clear (arg_stores
);
605 BITMAP_FREE (arg_stores
);
608 fprintf (dump_file
, "Finished finding needed instructions:\n");
612 /* UD-based DSE routines. */
614 /* Mark instructions that define artificially-used registers, such as
615 the frame pointer and the stack pointer. */
618 mark_artificial_uses (void)
621 struct df_link
*defs
;
626 for (use_rec
= df_get_artificial_uses (bb
->index
);
628 for (defs
= DF_REF_CHAIN (*use_rec
); defs
; defs
= defs
->next
)
629 if (! DF_REF_IS_ARTIFICIAL (defs
->ref
))
630 mark_insn (DF_REF_INSN (defs
->ref
), false);
635 /* Mark every instruction that defines a register value that INSN uses. */
638 mark_reg_dependencies (rtx insn
)
640 struct df_link
*defs
;
643 if (DEBUG_INSN_P (insn
))
646 for (use_rec
= DF_INSN_USES (insn
); *use_rec
; use_rec
++)
648 df_ref use
= *use_rec
;
651 fprintf (dump_file
, "Processing use of ");
652 print_simple_rtl (dump_file
, DF_REF_REG (use
));
653 fprintf (dump_file
, " in insn %d:\n", INSN_UID (insn
));
655 for (defs
= DF_REF_CHAIN (use
); defs
; defs
= defs
->next
)
656 if (! DF_REF_IS_ARTIFICIAL (defs
->ref
))
657 mark_insn (DF_REF_INSN (defs
->ref
), false);
662 /* Initialize global variables for a new DCE pass. */
670 df_chain_add_problem (DF_UD_CHAIN
);
679 bitmap_obstack_initialize (&dce_blocks_bitmap_obstack
);
680 bitmap_obstack_initialize (&dce_tmp_bitmap_obstack
);
683 marked
= sbitmap_alloc (get_max_uid () + 1);
684 sbitmap_zero (marked
);
688 /* Free the data allocated by init_dce. */
693 sbitmap_free (marked
);
697 bitmap_obstack_release (&dce_blocks_bitmap_obstack
);
698 bitmap_obstack_release (&dce_tmp_bitmap_obstack
);
703 /* UD-chain based DCE. */
706 rest_of_handle_ud_dce (void)
712 prescan_insns_for_dce (false);
713 mark_artificial_uses ();
714 while (VEC_length (rtx
, worklist
) > 0)
716 insn
= VEC_pop (rtx
, worklist
);
717 mark_reg_dependencies (insn
);
719 VEC_free (rtx
, heap
, worklist
);
721 /* Before any insns are deleted, we must remove the chains since
722 they are not bidirectional. */
723 df_remove_problem (df_chain
);
724 delete_unmarked_insns ();
734 return optimize
> 1 && flag_dce
738 struct rtl_opt_pass pass_ud_rtl_dce
=
743 gate_ud_dce
, /* gate */
744 rest_of_handle_ud_dce
, /* execute */
747 0, /* static_pass_number */
749 0, /* properties_required */
750 0, /* properties_provided */
751 0, /* properties_destroyed */
752 0, /* todo_flags_start */
754 TODO_df_finish
| TODO_verify_rtl_sharing
|
755 TODO_ggc_collect
/* todo_flags_finish */
760 /* -------------------------------------------------------------------------
762 ------------------------------------------------------------------------- */
764 /* Process basic block BB. Return true if the live_in set has
765 changed. REDO_OUT is true if the info at the bottom of the block
766 needs to be recalculated before starting. AU is the proper set of
770 word_dce_process_block (basic_block bb
, bool redo_out
)
772 bitmap local_live
= BITMAP_ALLOC (&dce_tmp_bitmap_obstack
);
778 /* Need to redo the live_out set of this block if when one of
779 the succs of this block has had a change in it live in
783 df_confluence_function_n con_fun_n
= df_word_lr
->problem
->con_fun_n
;
784 bitmap_clear (DF_WORD_LR_OUT (bb
));
785 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
791 fprintf (dump_file
, "processing block %d live out = ", bb
->index
);
792 df_print_word_regset (dump_file
, DF_WORD_LR_OUT (bb
));
795 bitmap_copy (local_live
, DF_WORD_LR_OUT (bb
));
797 FOR_BB_INSNS_REVERSE (bb
, insn
)
798 if (NONDEBUG_INSN_P (insn
))
801 /* No matter if the instruction is needed or not, we remove
802 any regno in the defs from the live set. */
803 any_changed
= df_word_lr_simulate_defs (insn
, local_live
);
805 mark_insn (insn
, true);
807 /* On the other hand, we do not allow the dead uses to set
808 anything in local_live. */
809 if (marked_insn_p (insn
))
810 df_word_lr_simulate_uses (insn
, local_live
);
814 fprintf (dump_file
, "finished processing insn %d live out = ",
816 df_print_word_regset (dump_file
, local_live
);
820 block_changed
= !bitmap_equal_p (local_live
, DF_WORD_LR_IN (bb
));
822 bitmap_copy (DF_WORD_LR_IN (bb
), local_live
);
824 BITMAP_FREE (local_live
);
825 return block_changed
;
829 /* Process basic block BB. Return true if the live_in set has
830 changed. REDO_OUT is true if the info at the bottom of the block
831 needs to be recalculated before starting. AU is the proper set of
835 dce_process_block (basic_block bb
, bool redo_out
, bitmap au
)
837 bitmap local_live
= BITMAP_ALLOC (&dce_tmp_bitmap_obstack
);
844 /* Need to redo the live_out set of this block if when one of
845 the succs of this block has had a change in it live in
849 df_confluence_function_n con_fun_n
= df_lr
->problem
->con_fun_n
;
850 bitmap_clear (DF_LR_OUT (bb
));
851 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
857 fprintf (dump_file
, "processing block %d lr out = ", bb
->index
);
858 df_print_regset (dump_file
, DF_LR_OUT (bb
));
861 bitmap_copy (local_live
, DF_LR_OUT (bb
));
863 df_simulate_initialize_backwards (bb
, local_live
);
865 FOR_BB_INSNS_REVERSE (bb
, insn
)
868 bool needed
= marked_insn_p (insn
);
870 /* The insn is needed if there is someone who uses the output. */
872 for (def_rec
= DF_INSN_DEFS (insn
); *def_rec
; def_rec
++)
873 if (bitmap_bit_p (local_live
, DF_REF_REGNO (*def_rec
))
874 || bitmap_bit_p (au
, DF_REF_REGNO (*def_rec
)))
877 mark_insn (insn
, true);
881 /* No matter if the instruction is needed or not, we remove
882 any regno in the defs from the live set. */
883 df_simulate_defs (insn
, local_live
);
885 /* On the other hand, we do not allow the dead uses to set
886 anything in local_live. */
888 df_simulate_uses (insn
, local_live
);
891 df_simulate_finalize_backwards (bb
, local_live
);
893 block_changed
= !bitmap_equal_p (local_live
, DF_LR_IN (bb
));
895 bitmap_copy (DF_LR_IN (bb
), local_live
);
897 BITMAP_FREE (local_live
);
898 return block_changed
;
902 /* Perform fast DCE once initialization is done. If WORD_LEVEL is
903 true, use the word level dce, otherwise do it at the pseudo
907 fast_dce (bool word_level
)
909 int *postorder
= df_get_postorder (DF_BACKWARD
);
910 int n_blocks
= df_get_n_blocks (DF_BACKWARD
);
911 /* The set of blocks that have been seen on this iteration. */
912 bitmap processed
= BITMAP_ALLOC (&dce_blocks_bitmap_obstack
);
913 /* The set of blocks that need to have the out vectors reset because
914 the in of one of their successors has changed. */
915 bitmap redo_out
= BITMAP_ALLOC (&dce_blocks_bitmap_obstack
);
916 bitmap all_blocks
= BITMAP_ALLOC (&dce_blocks_bitmap_obstack
);
917 bool global_changed
= true;
919 /* These regs are considered always live so if they end up dying
920 because of some def, we need to bring the back again. Calling
921 df_simulate_fixup_sets has the disadvantage of calling
922 bb_has_eh_pred once per insn, so we cache the information
924 bitmap au
= &df
->regular_block_artificial_uses
;
925 bitmap au_eh
= &df
->eh_block_artificial_uses
;
928 prescan_insns_for_dce (true);
930 for (i
= 0; i
< n_blocks
; i
++)
931 bitmap_set_bit (all_blocks
, postorder
[i
]);
933 while (global_changed
)
935 global_changed
= false;
937 for (i
= 0; i
< n_blocks
; i
++)
939 int index
= postorder
[i
];
940 basic_block bb
= BASIC_BLOCK (index
);
943 if (index
< NUM_FIXED_BLOCKS
)
945 bitmap_set_bit (processed
, index
);
951 = word_dce_process_block (bb
, bitmap_bit_p (redo_out
, index
));
954 = dce_process_block (bb
, bitmap_bit_p (redo_out
, index
),
955 bb_has_eh_pred (bb
) ? au_eh
: au
);
956 bitmap_set_bit (processed
, index
);
962 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
963 if (bitmap_bit_p (processed
, e
->src
->index
))
964 /* Be tricky about when we need to iterate the
965 analysis. We only have redo the analysis if the
966 bitmaps change at the top of a block that is the
968 global_changed
= true;
970 bitmap_set_bit (redo_out
, e
->src
->index
);
976 /* Turn off the RUN_DCE flag to prevent recursive calls to
978 int old_flag
= df_clear_flags (DF_LR_RUN_DCE
);
980 /* So something was deleted that requires a redo. Do it on
982 delete_unmarked_insns ();
983 sbitmap_zero (marked
);
984 bitmap_clear (processed
);
985 bitmap_clear (redo_out
);
987 /* We do not need to rescan any instructions. We only need
988 to redo the dataflow equations for the blocks that had a
989 change at the top of the block. Then we need to redo the
992 df_analyze_problem (df_word_lr
, all_blocks
, postorder
, n_blocks
);
994 df_analyze_problem (df_lr
, all_blocks
, postorder
, n_blocks
);
996 if (old_flag
& DF_LR_RUN_DCE
)
997 df_set_flags (DF_LR_RUN_DCE
);
999 prescan_insns_for_dce (true);
1003 delete_unmarked_insns ();
1005 BITMAP_FREE (processed
);
1006 BITMAP_FREE (redo_out
);
1007 BITMAP_FREE (all_blocks
);
1011 /* Fast register level DCE. */
1014 rest_of_handle_fast_dce (void)
1023 /* Fast byte level DCE. */
1033 timevar_push (TV_DCE
);
1034 old_flags
= df_clear_flags (DF_DEFER_INSN_RESCAN
+ DF_NO_INSN_RESCAN
);
1035 df_word_lr_add_problem ();
1039 df_set_flags (old_flags
);
1040 timevar_pop (TV_DCE
);
1044 /* This is an internal call that is used by the df live register
1045 problem to run fast dce as a side effect of creating the live
1046 information. The stack is organized so that the lr problem is run,
1047 this pass is run, which updates the live info and the df scanning
1048 info, and then returns to allow the rest of the problems to be run.
1050 This can be called by elsewhere but it will not update the bit
1051 vectors for any other problems than LR. */
1054 run_fast_df_dce (void)
1058 /* If dce is able to delete something, it has to happen
1059 immediately. Otherwise there will be problems handling the
1062 df_clear_flags (DF_DEFER_INSN_RESCAN
+ DF_NO_INSN_RESCAN
);
1064 df_in_progress
= true;
1065 rest_of_handle_fast_dce ();
1066 df_in_progress
= false;
1068 df_set_flags (old_flags
);
1073 /* Run a fast DCE pass. */
1079 rest_of_handle_fast_dce ();
1084 gate_fast_dce (void)
1086 return optimize
> 0 && flag_dce
1087 && dbg_cnt (dce_fast
);
1090 struct rtl_opt_pass pass_fast_rtl_dce
=
1094 "rtl dce", /* name */
1095 gate_fast_dce
, /* gate */
1096 rest_of_handle_fast_dce
, /* execute */
1099 0, /* static_pass_number */
1101 0, /* properties_required */
1102 0, /* properties_provided */
1103 0, /* properties_destroyed */
1104 0, /* todo_flags_start */
1106 TODO_df_finish
| TODO_verify_rtl_sharing
|
1107 TODO_ggc_collect
/* todo_flags_finish */