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"
40 /* -------------------------------------------------------------------------
41 Core mark/delete routines
42 ------------------------------------------------------------------------- */
44 /* True if we are invoked while the df engine is running; in this case,
45 we don't want to reenter it. */
46 static bool df_in_progress
= false;
48 /* Instructions that have been marked but whose dependencies have not
49 yet been processed. */
50 static VEC(rtx
,heap
) *worklist
;
52 /* Bitmap of instructions marked as needed indexed by INSN_UID. */
53 static sbitmap marked
;
55 /* Bitmap obstacks used for block processing by the fast algorithm. */
56 static bitmap_obstack dce_blocks_bitmap_obstack
;
57 static bitmap_obstack dce_tmp_bitmap_obstack
;
59 static bool find_call_stack_args (rtx
, bool, bool, bitmap
);
61 /* A subroutine for which BODY is part of the instruction being tested;
62 either the top-level pattern, or an element of a PARALLEL. The
63 instruction is known not to be a bare USE or CLOBBER. */
66 deletable_insn_p_1 (rtx body
)
68 switch (GET_CODE (body
))
72 /* The UNSPEC case was added here because the ia-64 claims that
73 USEs do not work after reload and generates UNSPECS rather
74 than USEs. Since dce is run after reload we need to avoid
75 deleting these even if they are dead. If it turns out that
76 USEs really do work after reload, the ia-64 should be
77 changed, and the UNSPEC case can be removed. */
82 if (volatile_refs_p (body
))
85 if (flag_non_call_exceptions
&& may_trap_p (body
))
93 /* Return true if INSN is a normal instruction that can be deleted by
97 deletable_insn_p (rtx insn
, bool fast
, bitmap arg_stores
)
103 /* We cannot delete calls inside of the recursive dce because
104 this may cause basic blocks to be deleted and this messes up
105 the rest of the stack of optimization passes. */
107 /* We cannot delete pure or const sibling calls because it is
108 hard to see the result. */
109 && (!SIBLING_CALL_P (insn
))
110 /* We can delete dead const or pure calls as long as they do not
112 && (RTL_CONST_OR_PURE_CALL_P (insn
)
113 && !RTL_LOOPING_CONST_OR_PURE_CALL_P (insn
)))
114 return find_call_stack_args (insn
, false, fast
, arg_stores
);
116 if (!NONJUMP_INSN_P (insn
))
119 /* Similarly, we cannot delete other insns that can throw either. */
120 if (df_in_progress
&& flag_non_call_exceptions
&& can_throw_internal (insn
))
123 body
= PATTERN (insn
);
124 switch (GET_CODE (body
))
132 /* A CLOBBER of a dead pseudo register serves no purpose.
133 That is not necessarily true for hard registers until
136 return REG_P (x
) && (!HARD_REGISTER_P (x
) || reload_completed
);
139 /* Because of the way that use-def chains are built, it is not
140 possible to tell if the clobber is dead because it can
141 never be the target of a use-def chain. */
145 for (i
= XVECLEN (body
, 0) - 1; i
>= 0; i
--)
146 if (!deletable_insn_p_1 (XVECEXP (body
, 0, i
)))
151 return deletable_insn_p_1 (body
);
156 /* Return true if INSN has been marked as needed. */
159 marked_insn_p (rtx insn
)
161 /* Artificial defs are always needed and they do not have an insn.
162 We should never see them here. */
164 return TEST_BIT (marked
, INSN_UID (insn
));
168 /* If INSN has not yet been marked as needed, mark it now, and add it to
172 mark_insn (rtx insn
, bool fast
)
174 if (!marked_insn_p (insn
))
177 VEC_safe_push (rtx
, heap
, worklist
, insn
);
178 SET_BIT (marked
, INSN_UID (insn
));
180 fprintf (dump_file
, " Adding insn %d to worklist\n", INSN_UID (insn
));
183 && !SIBLING_CALL_P (insn
)
184 && (RTL_CONST_OR_PURE_CALL_P (insn
)
185 && !RTL_LOOPING_CONST_OR_PURE_CALL_P (insn
)))
186 find_call_stack_args (insn
, true, fast
, NULL
);
191 /* A note_stores callback used by mark_nonreg_stores. DATA is the
192 instruction containing DEST. */
195 mark_nonreg_stores_1 (rtx dest
, const_rtx pattern
, void *data
)
197 if (GET_CODE (pattern
) != CLOBBER
&& !REG_P (dest
))
198 mark_insn ((rtx
) data
, true);
202 /* A note_stores callback used by mark_nonreg_stores. DATA is the
203 instruction containing DEST. */
206 mark_nonreg_stores_2 (rtx dest
, const_rtx pattern
, void *data
)
208 if (GET_CODE (pattern
) != CLOBBER
&& !REG_P (dest
))
209 mark_insn ((rtx
) data
, false);
213 /* Mark INSN if BODY stores to a non-register destination. */
216 mark_nonreg_stores (rtx body
, rtx insn
, bool fast
)
219 note_stores (body
, mark_nonreg_stores_1
, insn
);
221 note_stores (body
, mark_nonreg_stores_2
, insn
);
225 /* Try to find all stack stores of CALL_INSN arguments if
226 ACCUMULATE_OUTGOING_ARGS. If all stack stores have been found
227 and it is therefore safe to eliminate the call, return true,
228 otherwise return false. This function should be first called
229 with DO_MARK false, and only when the CALL_INSN is actually
230 going to be marked called again with DO_MARK true. */
233 find_call_stack_args (rtx call_insn
, bool do_mark
, bool fast
,
236 rtx p
, insn
, prev_insn
;
238 HOST_WIDE_INT min_sp_off
, max_sp_off
;
241 gcc_assert (CALL_P (call_insn
));
242 if (!ACCUMULATE_OUTGOING_ARGS
)
247 gcc_assert (arg_stores
);
248 bitmap_clear (arg_stores
);
251 min_sp_off
= INTTYPE_MAXIMUM (HOST_WIDE_INT
);
254 /* First determine the minimum and maximum offset from sp for
256 for (p
= CALL_INSN_FUNCTION_USAGE (call_insn
); p
; p
= XEXP (p
, 1))
257 if (GET_CODE (XEXP (p
, 0)) == USE
258 && MEM_P (XEXP (XEXP (p
, 0), 0)))
260 rtx mem
= XEXP (XEXP (p
, 0), 0), addr
, size
;
261 HOST_WIDE_INT off
= 0;
262 size
= MEM_SIZE (mem
);
263 if (size
== NULL_RTX
)
265 addr
= XEXP (mem
, 0);
266 if (GET_CODE (addr
) == PLUS
267 && REG_P (XEXP (addr
, 0))
268 && CONST_INT_P (XEXP (addr
, 1)))
270 off
= INTVAL (XEXP (addr
, 1));
271 addr
= XEXP (addr
, 0);
273 if (addr
!= stack_pointer_rtx
)
277 /* If not fast, use chains to see if addr wasn't set to
282 struct df_link
*defs
;
285 for (use_rec
= DF_INSN_USES (call_insn
); *use_rec
; use_rec
++)
286 if (rtx_equal_p (addr
, DF_REF_REG (*use_rec
)))
289 if (*use_rec
== NULL
)
292 for (defs
= DF_REF_CHAIN (*use_rec
); defs
; defs
= defs
->next
)
293 if (! DF_REF_IS_ARTIFICIAL (defs
->ref
))
299 set
= single_set (DF_REF_INSN (defs
->ref
));
303 if (GET_CODE (SET_SRC (set
)) != PLUS
304 || XEXP (SET_SRC (set
), 0) != stack_pointer_rtx
305 || !CONST_INT_P (XEXP (SET_SRC (set
), 1)))
308 off
+= INTVAL (XEXP (SET_SRC (set
), 1));
313 min_sp_off
= MIN (min_sp_off
, off
);
314 max_sp_off
= MAX (max_sp_off
, off
+ INTVAL (size
));
317 if (min_sp_off
>= max_sp_off
)
319 sp_bytes
= BITMAP_ALLOC (NULL
);
321 /* Set bits in SP_BYTES bitmap for bytes relative to sp + min_sp_off
322 which contain arguments. Checking has been done in the previous
324 for (p
= CALL_INSN_FUNCTION_USAGE (call_insn
); p
; p
= XEXP (p
, 1))
325 if (GET_CODE (XEXP (p
, 0)) == USE
326 && MEM_P (XEXP (XEXP (p
, 0), 0)))
328 rtx mem
= XEXP (XEXP (p
, 0), 0), addr
;
329 HOST_WIDE_INT off
= 0, byte
;
330 addr
= XEXP (mem
, 0);
331 if (GET_CODE (addr
) == PLUS
332 && REG_P (XEXP (addr
, 0))
333 && CONST_INT_P (XEXP (addr
, 1)))
335 off
= INTVAL (XEXP (addr
, 1));
336 addr
= XEXP (addr
, 0);
338 if (addr
!= stack_pointer_rtx
)
341 struct df_link
*defs
;
344 for (use_rec
= DF_INSN_USES (call_insn
); *use_rec
; use_rec
++)
345 if (rtx_equal_p (addr
, DF_REF_REG (*use_rec
)))
348 for (defs
= DF_REF_CHAIN (*use_rec
); defs
; defs
= defs
->next
)
349 if (! DF_REF_IS_ARTIFICIAL (defs
->ref
))
352 set
= single_set (DF_REF_INSN (defs
->ref
));
353 off
+= INTVAL (XEXP (SET_SRC (set
), 1));
355 for (byte
= off
; byte
< off
+ INTVAL (MEM_SIZE (mem
)); byte
++)
357 if (!bitmap_set_bit (sp_bytes
, byte
- min_sp_off
))
362 /* Walk backwards, looking for argument stores. The search stops
363 when seeing another call, sp adjustment or memory store other than
366 for (insn
= PREV_INSN (call_insn
); insn
; insn
= prev_insn
)
369 HOST_WIDE_INT off
, byte
;
371 if (insn
== BB_HEAD (BLOCK_FOR_INSN (call_insn
)))
372 prev_insn
= NULL_RTX
;
374 prev_insn
= PREV_INSN (insn
);
382 set
= single_set (insn
);
383 if (!set
|| SET_DEST (set
) == stack_pointer_rtx
)
386 if (!MEM_P (SET_DEST (set
)))
389 mem
= SET_DEST (set
);
390 addr
= XEXP (mem
, 0);
392 if (GET_CODE (addr
) == PLUS
393 && REG_P (XEXP (addr
, 0))
394 && CONST_INT_P (XEXP (addr
, 1)))
396 off
= INTVAL (XEXP (addr
, 1));
397 addr
= XEXP (addr
, 0);
399 if (addr
!= stack_pointer_rtx
)
406 struct df_link
*defs
;
409 for (use_rec
= DF_INSN_USES (insn
); *use_rec
; use_rec
++)
410 if (rtx_equal_p (addr
, DF_REF_REG (*use_rec
)))
413 if (*use_rec
== NULL
)
416 for (defs
= DF_REF_CHAIN (*use_rec
); defs
; defs
= defs
->next
)
417 if (! DF_REF_IS_ARTIFICIAL (defs
->ref
))
423 set
= single_set (DF_REF_INSN (defs
->ref
));
427 if (GET_CODE (SET_SRC (set
)) != PLUS
428 || XEXP (SET_SRC (set
), 0) != stack_pointer_rtx
429 || !CONST_INT_P (XEXP (SET_SRC (set
), 1)))
432 off
+= INTVAL (XEXP (SET_SRC (set
), 1));
438 if (GET_MODE_SIZE (GET_MODE (mem
)) == 0)
441 for (byte
= off
; byte
< off
+ GET_MODE_SIZE (GET_MODE (mem
)); byte
++)
443 if (byte
< min_sp_off
444 || byte
>= max_sp_off
445 || !bitmap_clear_bit (sp_bytes
, byte
- min_sp_off
))
449 if (!deletable_insn_p (insn
, fast
, NULL
))
453 mark_insn (insn
, fast
);
455 bitmap_set_bit (arg_stores
, INSN_UID (insn
));
457 if (bitmap_empty_p (sp_bytes
))
464 BITMAP_FREE (sp_bytes
);
465 if (!ret
&& arg_stores
)
466 bitmap_clear (arg_stores
);
472 /* Delete all REG_EQUAL notes of the registers INSN writes, to prevent
473 bad dangling REG_EQUAL notes. */
476 delete_corresponding_reg_eq_notes (rtx insn
)
479 for (def_rec
= DF_INSN_DEFS (insn
); *def_rec
; def_rec
++)
481 df_ref def
= *def_rec
;
482 unsigned int regno
= DF_REF_REGNO (def
);
483 /* This loop is a little tricky. We cannot just go down the
484 chain because it is being modified by the actions in the
485 loop. So we just get the head. We plan to drain the list
487 while (DF_REG_EQ_USE_CHAIN (regno
))
489 df_ref eq_use
= DF_REG_EQ_USE_CHAIN (regno
);
490 rtx noted_insn
= DF_REF_INSN (eq_use
);
491 rtx note
= find_reg_note (noted_insn
, REG_EQUAL
, NULL_RTX
);
493 note
= find_reg_note (noted_insn
, REG_EQUIV
, NULL_RTX
);
495 /* This assert is generally triggered when someone deletes a
496 REG_EQUAL or REG_EQUIV note by hacking the list manually
497 rather than calling remove_note. */
499 remove_note (noted_insn
, note
);
505 /* Delete every instruction that hasn't been marked. */
508 delete_unmarked_insns (void)
512 bool must_clean
= false;
514 FOR_EACH_BB_REVERSE (bb
)
515 FOR_BB_INSNS_REVERSE_SAFE (bb
, insn
, next
)
518 /* Always delete no-op moves. */
519 if (noop_move_p (insn
))
522 /* Otherwise rely only on the DCE algorithm. */
523 else if (marked_insn_p (insn
))
526 /* Beware that reaching a dbg counter limit here can result
527 in miscompiled file. This occurs when a group of insns
528 must be deleted together, typically because the kept insn
529 depends on the output from the deleted insn. Deleting
530 this insns in reverse order (both at the bb level and
531 when looking at the blocks) minimizes this, but does not
532 eliminate it, since it is possible for the using insn to
533 be top of a block and the producer to be at the bottom of
534 the block. However, in most cases this will only result
535 in an uninitialized use of an insn that is dead anyway.
537 However, there is one rare case that will cause a
538 miscompile: deletion of non-looping pure and constant
539 calls on a machine where ACCUMULATE_OUTGOING_ARGS is true.
540 In this case it is possible to remove the call, but leave
541 the argument pushes to the stack. Because of the changes
542 to the stack pointer, this will almost always lead to a
548 fprintf (dump_file
, "DCE: Deleting insn %d\n", INSN_UID (insn
));
550 /* Before we delete the insn we have to delete REG_EQUAL notes
551 for the destination regs in order to avoid dangling notes. */
552 delete_corresponding_reg_eq_notes (insn
);
554 /* If a pure or const call is deleted, this may make the cfg
555 have unreachable blocks. We rememeber this and call
556 delete_unreachable_blocks at the end. */
560 /* Now delete the insn. */
561 delete_insn_and_edges (insn
);
564 /* Deleted a pure or const call. */
566 delete_unreachable_blocks ();
570 /* Go through the instructions and mark those whose necessity is not
571 dependent on inter-instruction information. Make sure all other
572 instructions are not marked. */
575 prescan_insns_for_dce (bool fast
)
579 bitmap arg_stores
= NULL
;
582 fprintf (dump_file
, "Finding needed instructions:\n");
584 if (!df_in_progress
&& ACCUMULATE_OUTGOING_ARGS
)
585 arg_stores
= BITMAP_ALLOC (NULL
);
589 FOR_BB_INSNS_REVERSE_SAFE (bb
, insn
, prev
)
592 /* Don't mark argument stores now. They will be marked
593 if needed when the associated CALL is marked. */
594 if (arg_stores
&& bitmap_bit_p (arg_stores
, INSN_UID (insn
)))
596 if (deletable_insn_p (insn
, fast
, arg_stores
))
597 mark_nonreg_stores (PATTERN (insn
), insn
, fast
);
599 mark_insn (insn
, fast
);
601 /* find_call_stack_args only looks at argument stores in the
604 bitmap_clear (arg_stores
);
608 BITMAP_FREE (arg_stores
);
611 fprintf (dump_file
, "Finished finding needed instructions:\n");
615 /* UD-based DSE routines. */
617 /* Mark instructions that define artificially-used registers, such as
618 the frame pointer and the stack pointer. */
621 mark_artificial_uses (void)
624 struct df_link
*defs
;
629 for (use_rec
= df_get_artificial_uses (bb
->index
);
631 for (defs
= DF_REF_CHAIN (*use_rec
); defs
; defs
= defs
->next
)
632 if (! DF_REF_IS_ARTIFICIAL (defs
->ref
))
633 mark_insn (DF_REF_INSN (defs
->ref
), false);
638 /* Mark every instruction that defines a register value that INSN uses. */
641 mark_reg_dependencies (rtx insn
)
643 struct df_link
*defs
;
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 byte_dce_process_block (basic_block bb
, bool redo_out
, bitmap au
)
772 bitmap local_live
= BITMAP_ALLOC (&dce_tmp_bitmap_obstack
);
779 /* Need to redo the live_out set of this block if when one of
780 the succs of this block has had a change in it live in
784 df_confluence_function_n con_fun_n
= df_byte_lr
->problem
->con_fun_n
;
785 bitmap_clear (DF_BYTE_LR_OUT (bb
));
786 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
792 fprintf (dump_file
, "processing block %d live out = ", bb
->index
);
793 df_print_byte_regset (dump_file
, DF_BYTE_LR_OUT (bb
));
796 bitmap_copy (local_live
, DF_BYTE_LR_OUT (bb
));
798 df_byte_lr_simulate_artificial_refs_at_end (bb
, local_live
);
800 FOR_BB_INSNS_REVERSE (bb
, insn
)
803 /* The insn is needed if there is someone who uses the output. */
804 for (def_rec
= DF_INSN_DEFS (insn
); *def_rec
; def_rec
++)
806 df_ref def
= *def_rec
;
808 unsigned int dregno
= DF_REF_REGNO (def
);
809 unsigned int start
= df_byte_lr_get_regno_start (dregno
);
810 unsigned int len
= df_byte_lr_get_regno_len (dregno
);
814 /* This is one of the only places where DF_MM_MAY should
815 be used for defs. Need to make sure that we are
816 checking for all of the bits that may be used. */
818 if (!df_compute_accessed_bytes (def
, DF_MM_MAY
, &sb
, &lb
))
824 if (bitmap_bit_p (au
, dregno
))
826 mark_insn (insn
, true);
832 if (bitmap_bit_p (local_live
, start
++))
834 mark_insn (insn
, true);
841 /* No matter if the instruction is needed or not, we remove
842 any regno in the defs from the live set. */
843 df_byte_lr_simulate_defs (insn
, local_live
);
845 /* On the other hand, we do not allow the dead uses to set
846 anything in local_live. */
847 if (marked_insn_p (insn
))
848 df_byte_lr_simulate_uses (insn
, local_live
);
852 fprintf (dump_file
, "finished processing insn %d live out = ",
854 df_print_byte_regset (dump_file
, local_live
);
858 df_byte_lr_simulate_artificial_refs_at_top (bb
, local_live
);
860 block_changed
= !bitmap_equal_p (local_live
, DF_BYTE_LR_IN (bb
));
862 bitmap_copy (DF_BYTE_LR_IN (bb
), local_live
);
863 BITMAP_FREE (local_live
);
864 return block_changed
;
868 /* Process basic block BB. Return true if the live_in set has
869 changed. REDO_OUT is true if the info at the bottom of the block
870 needs to be recalculated before starting. AU is the proper set of
874 dce_process_block (basic_block bb
, bool redo_out
, bitmap au
)
876 bitmap local_live
= BITMAP_ALLOC (&dce_tmp_bitmap_obstack
);
883 /* Need to redo the live_out set of this block if when one of
884 the succs of this block has had a change in it live in
888 df_confluence_function_n con_fun_n
= df_lr
->problem
->con_fun_n
;
889 bitmap_clear (DF_LR_OUT (bb
));
890 FOR_EACH_EDGE (e
, ei
, bb
->succs
)
896 fprintf (dump_file
, "processing block %d lr out = ", bb
->index
);
897 df_print_regset (dump_file
, DF_LR_OUT (bb
));
900 bitmap_copy (local_live
, DF_LR_OUT (bb
));
902 df_simulate_initialize_backwards (bb
, local_live
);
904 FOR_BB_INSNS_REVERSE (bb
, insn
)
909 /* The insn is needed if there is someone who uses the output. */
910 for (def_rec
= DF_INSN_DEFS (insn
); *def_rec
; def_rec
++)
911 if (bitmap_bit_p (local_live
, DF_REF_REGNO (*def_rec
))
912 || bitmap_bit_p (au
, DF_REF_REGNO (*def_rec
)))
919 mark_insn (insn
, true);
921 /* No matter if the instruction is needed or not, we remove
922 any regno in the defs from the live set. */
923 df_simulate_defs (insn
, local_live
);
925 /* On the other hand, we do not allow the dead uses to set
926 anything in local_live. */
927 if (marked_insn_p (insn
))
928 df_simulate_uses (insn
, local_live
);
931 df_simulate_finalize_backwards (bb
, local_live
);
933 block_changed
= !bitmap_equal_p (local_live
, DF_LR_IN (bb
));
935 bitmap_copy (DF_LR_IN (bb
), local_live
);
937 BITMAP_FREE (local_live
);
938 return block_changed
;
942 /* Perform fast DCE once initialization is done. If BYTE_LEVEL is
943 true, use the byte level dce, otherwise do it at the pseudo
947 fast_dce (bool byte_level
)
949 int *postorder
= df_get_postorder (DF_BACKWARD
);
950 int n_blocks
= df_get_n_blocks (DF_BACKWARD
);
951 /* The set of blocks that have been seen on this iteration. */
952 bitmap processed
= BITMAP_ALLOC (&dce_blocks_bitmap_obstack
);
953 /* The set of blocks that need to have the out vectors reset because
954 the in of one of their successors has changed. */
955 bitmap redo_out
= BITMAP_ALLOC (&dce_blocks_bitmap_obstack
);
956 bitmap all_blocks
= BITMAP_ALLOC (&dce_blocks_bitmap_obstack
);
957 bool global_changed
= true;
959 /* These regs are considered always live so if they end up dying
960 because of some def, we need to bring the back again. Calling
961 df_simulate_fixup_sets has the disadvantage of calling
962 bb_has_eh_pred once per insn, so we cache the information
964 bitmap au
= df
->regular_block_artificial_uses
;
965 bitmap au_eh
= df
->eh_block_artificial_uses
;
968 prescan_insns_for_dce (true);
970 for (i
= 0; i
< n_blocks
; i
++)
971 bitmap_set_bit (all_blocks
, postorder
[i
]);
973 while (global_changed
)
975 global_changed
= false;
977 for (i
= 0; i
< n_blocks
; i
++)
979 int index
= postorder
[i
];
980 basic_block bb
= BASIC_BLOCK (index
);
983 if (index
< NUM_FIXED_BLOCKS
)
985 bitmap_set_bit (processed
, index
);
991 = byte_dce_process_block (bb
, bitmap_bit_p (redo_out
, index
),
992 bb_has_eh_pred (bb
) ? au_eh
: au
);
995 = dce_process_block (bb
, bitmap_bit_p (redo_out
, index
),
996 bb_has_eh_pred (bb
) ? au_eh
: au
);
997 bitmap_set_bit (processed
, index
);
1003 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
1004 if (bitmap_bit_p (processed
, e
->src
->index
))
1005 /* Be tricky about when we need to iterate the
1006 analysis. We only have redo the analysis if the
1007 bitmaps change at the top of a block that is the
1009 global_changed
= true;
1011 bitmap_set_bit (redo_out
, e
->src
->index
);
1017 /* Turn off the RUN_DCE flag to prevent recursive calls to
1019 int old_flag
= df_clear_flags (DF_LR_RUN_DCE
);
1021 /* So something was deleted that requires a redo. Do it on
1023 delete_unmarked_insns ();
1024 sbitmap_zero (marked
);
1025 bitmap_clear (processed
);
1026 bitmap_clear (redo_out
);
1028 /* We do not need to rescan any instructions. We only need
1029 to redo the dataflow equations for the blocks that had a
1030 change at the top of the block. Then we need to redo the
1033 df_analyze_problem (df_byte_lr
, all_blocks
, postorder
, n_blocks
);
1035 df_analyze_problem (df_lr
, all_blocks
, postorder
, n_blocks
);
1037 if (old_flag
& DF_LR_RUN_DCE
)
1038 df_set_flags (DF_LR_RUN_DCE
);
1040 prescan_insns_for_dce (true);
1044 delete_unmarked_insns ();
1046 BITMAP_FREE (processed
);
1047 BITMAP_FREE (redo_out
);
1048 BITMAP_FREE (all_blocks
);
1052 /* Fast register level DCE. */
1055 rest_of_handle_fast_dce (void)
1064 /* Fast byte level DCE. */
1067 rest_of_handle_fast_byte_dce (void)
1069 df_byte_lr_add_problem ();
1077 /* This is an internal call that is used by the df live register
1078 problem to run fast dce as a side effect of creating the live
1079 information. The stack is organized so that the lr problem is run,
1080 this pass is run, which updates the live info and the df scanning
1081 info, and then returns to allow the rest of the problems to be run.
1083 This can be called by elsewhere but it will not update the bit
1084 vectors for any other problems than LR. */
1087 run_fast_df_dce (void)
1091 /* If dce is able to delete something, it has to happen
1092 immediately. Otherwise there will be problems handling the
1095 df_clear_flags (DF_DEFER_INSN_RESCAN
+ DF_NO_INSN_RESCAN
);
1097 df_in_progress
= true;
1098 rest_of_handle_fast_dce ();
1099 df_in_progress
= false;
1101 df_set_flags (old_flags
);
1106 /* Run a fast DCE pass. */
1112 rest_of_handle_fast_dce ();
1117 gate_fast_dce (void)
1119 return optimize
> 0 && flag_dce
1120 && dbg_cnt (dce_fast
);
1123 struct rtl_opt_pass pass_fast_rtl_dce
=
1128 gate_fast_dce
, /* gate */
1129 rest_of_handle_fast_dce
, /* execute */
1132 0, /* static_pass_number */
1134 0, /* properties_required */
1135 0, /* properties_provided */
1136 0, /* properties_destroyed */
1137 0, /* todo_flags_start */
1139 TODO_df_finish
| TODO_verify_rtl_sharing
|
1140 TODO_ggc_collect
/* todo_flags_finish */
1144 struct rtl_opt_pass pass_fast_rtl_byte_dce
=
1148 "byte-dce", /* name */
1149 gate_fast_dce
, /* gate */
1150 rest_of_handle_fast_byte_dce
, /* execute */
1153 0, /* static_pass_number */
1155 0, /* properties_required */
1156 0, /* properties_provided */
1157 0, /* properties_destroyed */
1158 0, /* todo_flags_start */
1160 TODO_df_finish
| TODO_verify_rtl_sharing
|
1161 TODO_ggc_collect
/* todo_flags_finish */