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[official-gcc.git] / gcc / dce.c
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1 /* RTL dead code elimination.
2 Copyright (C) 2005-2014 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
9 version.
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
14 for more details.
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/>. */
20 #include "config.h"
21 #include "system.h"
22 #include "coretypes.h"
23 #include "hashtab.h"
24 #include "tm.h"
25 #include "rtl.h"
26 #include "tree.h"
27 #include "regs.h"
28 #include "hard-reg-set.h"
29 #include "flags.h"
30 #include "except.h"
31 #include "df.h"
32 #include "cselib.h"
33 #include "dce.h"
34 #include "valtrack.h"
35 #include "tree-pass.h"
36 #include "dbgcnt.h"
37 #include "tm_p.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 /* True if we are allowed to alter the CFG in this pass. */
50 static bool can_alter_cfg = false;
52 /* Instructions that have been marked but whose dependencies have not
53 yet been processed. */
54 static vec<rtx> worklist;
56 /* Bitmap of instructions marked as needed indexed by INSN_UID. */
57 static sbitmap marked;
59 /* Bitmap obstacks used for block processing by the fast algorithm. */
60 static bitmap_obstack dce_blocks_bitmap_obstack;
61 static bitmap_obstack dce_tmp_bitmap_obstack;
63 static bool find_call_stack_args (rtx, bool, bool, bitmap);
65 /* A subroutine for which BODY is part of the instruction being tested;
66 either the top-level pattern, or an element of a PARALLEL. The
67 instruction is known not to be a bare USE or CLOBBER. */
69 static bool
70 deletable_insn_p_1 (rtx body)
72 switch (GET_CODE (body))
74 case PREFETCH:
75 case TRAP_IF:
76 /* The UNSPEC case was added here because the ia-64 claims that
77 USEs do not work after reload and generates UNSPECS rather
78 than USEs. Since dce is run after reload we need to avoid
79 deleting these even if they are dead. If it turns out that
80 USEs really do work after reload, the ia-64 should be
81 changed, and the UNSPEC case can be removed. */
82 case UNSPEC:
83 return false;
85 default:
86 return !volatile_refs_p (body);
91 /* Return true if INSN is a normal instruction that can be deleted by
92 the DCE pass. */
94 static bool
95 deletable_insn_p (rtx insn, bool fast, bitmap arg_stores)
97 rtx body, x;
98 int i;
99 df_ref def;
101 if (CALL_P (insn)
102 /* We cannot delete calls inside of the recursive dce because
103 this may cause basic blocks to be deleted and this messes up
104 the rest of the stack of optimization passes. */
105 && (!df_in_progress)
106 /* We cannot delete pure or const sibling calls because it is
107 hard to see the result. */
108 && (!SIBLING_CALL_P (insn))
109 /* We can delete dead const or pure calls as long as they do not
110 infinite loop. */
111 && (RTL_CONST_OR_PURE_CALL_P (insn)
112 && !RTL_LOOPING_CONST_OR_PURE_CALL_P (insn)))
113 return find_call_stack_args (insn, false, fast, arg_stores);
115 /* Don't delete jumps, notes and the like. */
116 if (!NONJUMP_INSN_P (insn))
117 return false;
119 /* Don't delete insns that may throw if we cannot do so. */
120 if (!(cfun->can_delete_dead_exceptions && can_alter_cfg)
121 && !insn_nothrow_p (insn))
122 return false;
124 /* If INSN sets a global_reg, leave it untouched. */
125 FOR_EACH_INSN_DEF (def, insn)
126 if (HARD_REGISTER_NUM_P (DF_REF_REGNO (def))
127 && global_regs[DF_REF_REGNO (def)])
128 return false;
130 body = PATTERN (insn);
131 switch (GET_CODE (body))
133 case USE:
134 case VAR_LOCATION:
135 return false;
137 case CLOBBER:
138 if (fast)
140 /* A CLOBBER of a dead pseudo register serves no purpose.
141 That is not necessarily true for hard registers until
142 after reload. */
143 x = XEXP (body, 0);
144 return REG_P (x) && (!HARD_REGISTER_P (x) || reload_completed);
146 else
147 /* Because of the way that use-def chains are built, it is not
148 possible to tell if the clobber is dead because it can
149 never be the target of a use-def chain. */
150 return false;
152 case PARALLEL:
153 for (i = XVECLEN (body, 0) - 1; i >= 0; i--)
154 if (!deletable_insn_p_1 (XVECEXP (body, 0, i)))
155 return false;
156 return true;
158 default:
159 return deletable_insn_p_1 (body);
164 /* Return true if INSN has been marked as needed. */
166 static inline int
167 marked_insn_p (rtx insn)
169 /* Artificial defs are always needed and they do not have an insn.
170 We should never see them here. */
171 gcc_assert (insn);
172 return bitmap_bit_p (marked, INSN_UID (insn));
176 /* If INSN has not yet been marked as needed, mark it now, and add it to
177 the worklist. */
179 static void
180 mark_insn (rtx insn, bool fast)
182 if (!marked_insn_p (insn))
184 if (!fast)
185 worklist.safe_push (insn);
186 bitmap_set_bit (marked, INSN_UID (insn));
187 if (dump_file)
188 fprintf (dump_file, " Adding insn %d to worklist\n", INSN_UID (insn));
189 if (CALL_P (insn)
190 && !df_in_progress
191 && !SIBLING_CALL_P (insn)
192 && (RTL_CONST_OR_PURE_CALL_P (insn)
193 && !RTL_LOOPING_CONST_OR_PURE_CALL_P (insn)))
194 find_call_stack_args (insn, true, fast, NULL);
199 /* A note_stores callback used by mark_nonreg_stores. DATA is the
200 instruction containing DEST. */
202 static void
203 mark_nonreg_stores_1 (rtx dest, const_rtx pattern, void *data)
205 if (GET_CODE (pattern) != CLOBBER && !REG_P (dest))
206 mark_insn ((rtx) data, true);
210 /* A note_stores callback used by mark_nonreg_stores. DATA is the
211 instruction containing DEST. */
213 static void
214 mark_nonreg_stores_2 (rtx dest, const_rtx pattern, void *data)
216 if (GET_CODE (pattern) != CLOBBER && !REG_P (dest))
217 mark_insn ((rtx) data, false);
221 /* Mark INSN if BODY stores to a non-register destination. */
223 static void
224 mark_nonreg_stores (rtx body, rtx insn, bool fast)
226 if (fast)
227 note_stores (body, mark_nonreg_stores_1, insn);
228 else
229 note_stores (body, mark_nonreg_stores_2, insn);
233 /* Return true if store to MEM, starting OFF bytes from stack pointer,
234 is a call argument store, and clear corresponding bits from SP_BYTES
235 bitmap if it is. */
237 static bool
238 check_argument_store (rtx mem, HOST_WIDE_INT off, HOST_WIDE_INT min_sp_off,
239 HOST_WIDE_INT max_sp_off, bitmap sp_bytes)
241 HOST_WIDE_INT byte;
242 for (byte = off; byte < off + GET_MODE_SIZE (GET_MODE (mem)); byte++)
244 if (byte < min_sp_off
245 || byte >= max_sp_off
246 || !bitmap_clear_bit (sp_bytes, byte - min_sp_off))
247 return false;
249 return true;
253 /* Try to find all stack stores of CALL_INSN arguments if
254 ACCUMULATE_OUTGOING_ARGS. If all stack stores have been found
255 and it is therefore safe to eliminate the call, return true,
256 otherwise return false. This function should be first called
257 with DO_MARK false, and only when the CALL_INSN is actually
258 going to be marked called again with DO_MARK true. */
260 static bool
261 find_call_stack_args (rtx call_insn, bool do_mark, bool fast,
262 bitmap arg_stores)
264 rtx p, insn, prev_insn;
265 bool ret;
266 HOST_WIDE_INT min_sp_off, max_sp_off;
267 bitmap sp_bytes;
269 gcc_assert (CALL_P (call_insn));
270 if (!ACCUMULATE_OUTGOING_ARGS)
271 return true;
273 if (!do_mark)
275 gcc_assert (arg_stores);
276 bitmap_clear (arg_stores);
279 min_sp_off = INTTYPE_MAXIMUM (HOST_WIDE_INT);
280 max_sp_off = 0;
282 /* First determine the minimum and maximum offset from sp for
283 stored arguments. */
284 for (p = CALL_INSN_FUNCTION_USAGE (call_insn); p; p = XEXP (p, 1))
285 if (GET_CODE (XEXP (p, 0)) == USE
286 && MEM_P (XEXP (XEXP (p, 0), 0)))
288 rtx mem = XEXP (XEXP (p, 0), 0), addr;
289 HOST_WIDE_INT off = 0, size;
290 if (!MEM_SIZE_KNOWN_P (mem))
291 return false;
292 size = MEM_SIZE (mem);
293 addr = XEXP (mem, 0);
294 if (GET_CODE (addr) == PLUS
295 && REG_P (XEXP (addr, 0))
296 && CONST_INT_P (XEXP (addr, 1)))
298 off = INTVAL (XEXP (addr, 1));
299 addr = XEXP (addr, 0);
301 if (addr != stack_pointer_rtx)
303 if (!REG_P (addr))
304 return false;
305 /* If not fast, use chains to see if addr wasn't set to
306 sp + offset. */
307 if (!fast)
309 df_ref use;
310 struct df_link *defs;
311 rtx set;
313 FOR_EACH_INSN_USE (use, call_insn)
314 if (rtx_equal_p (addr, DF_REF_REG (use)))
315 break;
317 if (use == NULL)
318 return false;
320 for (defs = DF_REF_CHAIN (use); defs; defs = defs->next)
321 if (! DF_REF_IS_ARTIFICIAL (defs->ref))
322 break;
324 if (defs == NULL)
325 return false;
327 set = single_set (DF_REF_INSN (defs->ref));
328 if (!set)
329 return false;
331 if (GET_CODE (SET_SRC (set)) != PLUS
332 || XEXP (SET_SRC (set), 0) != stack_pointer_rtx
333 || !CONST_INT_P (XEXP (SET_SRC (set), 1)))
334 return false;
336 off += INTVAL (XEXP (SET_SRC (set), 1));
338 else
339 return false;
341 min_sp_off = MIN (min_sp_off, off);
342 max_sp_off = MAX (max_sp_off, off + size);
345 if (min_sp_off >= max_sp_off)
346 return true;
347 sp_bytes = BITMAP_ALLOC (NULL);
349 /* Set bits in SP_BYTES bitmap for bytes relative to sp + min_sp_off
350 which contain arguments. Checking has been done in the previous
351 loop. */
352 for (p = CALL_INSN_FUNCTION_USAGE (call_insn); p; p = XEXP (p, 1))
353 if (GET_CODE (XEXP (p, 0)) == USE
354 && MEM_P (XEXP (XEXP (p, 0), 0)))
356 rtx mem = XEXP (XEXP (p, 0), 0), addr;
357 HOST_WIDE_INT off = 0, byte;
358 addr = XEXP (mem, 0);
359 if (GET_CODE (addr) == PLUS
360 && REG_P (XEXP (addr, 0))
361 && CONST_INT_P (XEXP (addr, 1)))
363 off = INTVAL (XEXP (addr, 1));
364 addr = XEXP (addr, 0);
366 if (addr != stack_pointer_rtx)
368 df_ref use;
369 struct df_link *defs;
370 rtx set;
372 FOR_EACH_INSN_USE (use, call_insn)
373 if (rtx_equal_p (addr, DF_REF_REG (use)))
374 break;
376 for (defs = DF_REF_CHAIN (use); defs; defs = defs->next)
377 if (! DF_REF_IS_ARTIFICIAL (defs->ref))
378 break;
380 set = single_set (DF_REF_INSN (defs->ref));
381 off += INTVAL (XEXP (SET_SRC (set), 1));
383 for (byte = off; byte < off + MEM_SIZE (mem); byte++)
385 if (!bitmap_set_bit (sp_bytes, byte - min_sp_off))
386 gcc_unreachable ();
390 /* Walk backwards, looking for argument stores. The search stops
391 when seeing another call, sp adjustment or memory store other than
392 argument store. */
393 ret = false;
394 for (insn = PREV_INSN (call_insn); insn; insn = prev_insn)
396 rtx set, mem, addr;
397 HOST_WIDE_INT off;
399 if (insn == BB_HEAD (BLOCK_FOR_INSN (call_insn)))
400 prev_insn = NULL_RTX;
401 else
402 prev_insn = PREV_INSN (insn);
404 if (CALL_P (insn))
405 break;
407 if (!NONDEBUG_INSN_P (insn))
408 continue;
410 set = single_set (insn);
411 if (!set || SET_DEST (set) == stack_pointer_rtx)
412 break;
414 if (!MEM_P (SET_DEST (set)))
415 continue;
417 mem = SET_DEST (set);
418 addr = XEXP (mem, 0);
419 off = 0;
420 if (GET_CODE (addr) == PLUS
421 && REG_P (XEXP (addr, 0))
422 && CONST_INT_P (XEXP (addr, 1)))
424 off = INTVAL (XEXP (addr, 1));
425 addr = XEXP (addr, 0);
427 if (addr != stack_pointer_rtx)
429 if (!REG_P (addr))
430 break;
431 if (!fast)
433 df_ref use;
434 struct df_link *defs;
435 rtx set;
437 FOR_EACH_INSN_USE (use, insn)
438 if (rtx_equal_p (addr, DF_REF_REG (use)))
439 break;
441 if (use == NULL)
442 break;
444 for (defs = DF_REF_CHAIN (use); defs; defs = defs->next)
445 if (! DF_REF_IS_ARTIFICIAL (defs->ref))
446 break;
448 if (defs == NULL)
449 break;
451 set = single_set (DF_REF_INSN (defs->ref));
452 if (!set)
453 break;
455 if (GET_CODE (SET_SRC (set)) != PLUS
456 || XEXP (SET_SRC (set), 0) != stack_pointer_rtx
457 || !CONST_INT_P (XEXP (SET_SRC (set), 1)))
458 break;
460 off += INTVAL (XEXP (SET_SRC (set), 1));
462 else
463 break;
466 if (GET_MODE_SIZE (GET_MODE (mem)) == 0
467 || !check_argument_store (mem, off, min_sp_off,
468 max_sp_off, sp_bytes))
469 break;
471 if (!deletable_insn_p (insn, fast, NULL))
472 break;
474 if (do_mark)
475 mark_insn (insn, fast);
476 else
477 bitmap_set_bit (arg_stores, INSN_UID (insn));
479 if (bitmap_empty_p (sp_bytes))
481 ret = true;
482 break;
486 BITMAP_FREE (sp_bytes);
487 if (!ret && arg_stores)
488 bitmap_clear (arg_stores);
490 return ret;
494 /* Remove all REG_EQUAL and REG_EQUIV notes referring to the registers INSN
495 writes to. */
497 static void
498 remove_reg_equal_equiv_notes_for_defs (rtx insn)
500 df_ref def;
502 FOR_EACH_INSN_DEF (def, insn)
503 remove_reg_equal_equiv_notes_for_regno (DF_REF_REGNO (def));
506 /* Scan all BBs for debug insns and reset those that reference values
507 defined in unmarked insns. */
509 static void
510 reset_unmarked_insns_debug_uses (void)
512 basic_block bb;
513 rtx insn, next;
515 FOR_EACH_BB_REVERSE_FN (bb, cfun)
516 FOR_BB_INSNS_REVERSE_SAFE (bb, insn, next)
517 if (DEBUG_INSN_P (insn))
519 df_ref use;
521 FOR_EACH_INSN_USE (use, insn)
523 struct df_link *defs;
524 for (defs = DF_REF_CHAIN (use); defs; defs = defs->next)
526 rtx ref_insn;
527 if (DF_REF_IS_ARTIFICIAL (defs->ref))
528 continue;
529 ref_insn = DF_REF_INSN (defs->ref);
530 if (!marked_insn_p (ref_insn))
531 break;
533 if (!defs)
534 continue;
535 /* ??? FIXME could we propagate the values assigned to
536 each of the DEFs? */
537 INSN_VAR_LOCATION_LOC (insn) = gen_rtx_UNKNOWN_VAR_LOC ();
538 df_insn_rescan_debug_internal (insn);
539 break;
544 /* Delete every instruction that hasn't been marked. */
546 static void
547 delete_unmarked_insns (void)
549 basic_block bb;
550 rtx insn, next;
551 bool must_clean = false;
553 FOR_EACH_BB_REVERSE_FN (bb, cfun)
554 FOR_BB_INSNS_REVERSE_SAFE (bb, insn, next)
555 if (NONDEBUG_INSN_P (insn))
557 /* Always delete no-op moves. */
558 if (noop_move_p (insn))
561 /* Otherwise rely only on the DCE algorithm. */
562 else if (marked_insn_p (insn))
563 continue;
565 /* Beware that reaching a dbg counter limit here can result
566 in miscompiled file. This occurs when a group of insns
567 must be deleted together, typically because the kept insn
568 depends on the output from the deleted insn. Deleting
569 this insns in reverse order (both at the bb level and
570 when looking at the blocks) minimizes this, but does not
571 eliminate it, since it is possible for the using insn to
572 be top of a block and the producer to be at the bottom of
573 the block. However, in most cases this will only result
574 in an uninitialized use of an insn that is dead anyway.
576 However, there is one rare case that will cause a
577 miscompile: deletion of non-looping pure and constant
578 calls on a machine where ACCUMULATE_OUTGOING_ARGS is true.
579 In this case it is possible to remove the call, but leave
580 the argument pushes to the stack. Because of the changes
581 to the stack pointer, this will almost always lead to a
582 miscompile. */
583 if (!dbg_cnt (dce))
584 continue;
586 if (dump_file)
587 fprintf (dump_file, "DCE: Deleting insn %d\n", INSN_UID (insn));
589 /* Before we delete the insn we have to remove the REG_EQUAL notes
590 for the destination regs in order to avoid dangling notes. */
591 remove_reg_equal_equiv_notes_for_defs (insn);
593 /* If a pure or const call is deleted, this may make the cfg
594 have unreachable blocks. We rememeber this and call
595 delete_unreachable_blocks at the end. */
596 if (CALL_P (insn))
597 must_clean = true;
599 /* Now delete the insn. */
600 delete_insn_and_edges (insn);
603 /* Deleted a pure or const call. */
604 if (must_clean)
605 delete_unreachable_blocks ();
609 /* Go through the instructions and mark those whose necessity is not
610 dependent on inter-instruction information. Make sure all other
611 instructions are not marked. */
613 static void
614 prescan_insns_for_dce (bool fast)
616 basic_block bb;
617 rtx insn, prev;
618 bitmap arg_stores = NULL;
620 if (dump_file)
621 fprintf (dump_file, "Finding needed instructions:\n");
623 if (!df_in_progress && ACCUMULATE_OUTGOING_ARGS)
624 arg_stores = BITMAP_ALLOC (NULL);
626 FOR_EACH_BB_FN (bb, cfun)
628 FOR_BB_INSNS_REVERSE_SAFE (bb, insn, prev)
629 if (NONDEBUG_INSN_P (insn))
631 /* Don't mark argument stores now. They will be marked
632 if needed when the associated CALL is marked. */
633 if (arg_stores && bitmap_bit_p (arg_stores, INSN_UID (insn)))
634 continue;
635 if (deletable_insn_p (insn, fast, arg_stores))
636 mark_nonreg_stores (PATTERN (insn), insn, fast);
637 else
638 mark_insn (insn, fast);
640 /* find_call_stack_args only looks at argument stores in the
641 same bb. */
642 if (arg_stores)
643 bitmap_clear (arg_stores);
646 if (arg_stores)
647 BITMAP_FREE (arg_stores);
649 if (dump_file)
650 fprintf (dump_file, "Finished finding needed instructions:\n");
654 /* UD-based DSE routines. */
656 /* Mark instructions that define artificially-used registers, such as
657 the frame pointer and the stack pointer. */
659 static void
660 mark_artificial_uses (void)
662 basic_block bb;
663 struct df_link *defs;
664 df_ref use;
666 FOR_ALL_BB_FN (bb, cfun)
667 FOR_EACH_ARTIFICIAL_USE (use, bb->index)
668 for (defs = DF_REF_CHAIN (use); defs; defs = defs->next)
669 if (!DF_REF_IS_ARTIFICIAL (defs->ref))
670 mark_insn (DF_REF_INSN (defs->ref), false);
674 /* Mark every instruction that defines a register value that INSN uses. */
676 static void
677 mark_reg_dependencies (rtx insn)
679 struct df_link *defs;
680 df_ref use;
682 if (DEBUG_INSN_P (insn))
683 return;
685 FOR_EACH_INSN_USE (use, insn)
687 if (dump_file)
689 fprintf (dump_file, "Processing use of ");
690 print_simple_rtl (dump_file, DF_REF_REG (use));
691 fprintf (dump_file, " in insn %d:\n", INSN_UID (insn));
693 for (defs = DF_REF_CHAIN (use); defs; defs = defs->next)
694 if (! DF_REF_IS_ARTIFICIAL (defs->ref))
695 mark_insn (DF_REF_INSN (defs->ref), false);
700 /* Initialize global variables for a new DCE pass. */
702 static void
703 init_dce (bool fast)
705 if (!df_in_progress)
707 if (!fast)
709 df_set_flags (DF_RD_PRUNE_DEAD_DEFS);
710 df_chain_add_problem (DF_UD_CHAIN);
712 df_analyze ();
715 if (dump_file)
716 df_dump (dump_file);
718 if (fast)
720 bitmap_obstack_initialize (&dce_blocks_bitmap_obstack);
721 bitmap_obstack_initialize (&dce_tmp_bitmap_obstack);
722 can_alter_cfg = false;
724 else
725 can_alter_cfg = true;
727 marked = sbitmap_alloc (get_max_uid () + 1);
728 bitmap_clear (marked);
732 /* Free the data allocated by init_dce. */
734 static void
735 fini_dce (bool fast)
737 sbitmap_free (marked);
739 if (fast)
741 bitmap_obstack_release (&dce_blocks_bitmap_obstack);
742 bitmap_obstack_release (&dce_tmp_bitmap_obstack);
747 /* UD-chain based DCE. */
749 static unsigned int
750 rest_of_handle_ud_dce (void)
752 rtx insn;
754 init_dce (false);
756 prescan_insns_for_dce (false);
757 mark_artificial_uses ();
758 while (worklist.length () > 0)
760 insn = worklist.pop ();
761 mark_reg_dependencies (insn);
763 worklist.release ();
765 if (MAY_HAVE_DEBUG_INSNS)
766 reset_unmarked_insns_debug_uses ();
768 /* Before any insns are deleted, we must remove the chains since
769 they are not bidirectional. */
770 df_remove_problem (df_chain);
771 delete_unmarked_insns ();
773 fini_dce (false);
774 return 0;
778 namespace {
780 const pass_data pass_data_ud_rtl_dce =
782 RTL_PASS, /* type */
783 "ud_dce", /* name */
784 OPTGROUP_NONE, /* optinfo_flags */
785 TV_DCE, /* tv_id */
786 0, /* properties_required */
787 0, /* properties_provided */
788 0, /* properties_destroyed */
789 0, /* todo_flags_start */
790 TODO_df_finish, /* todo_flags_finish */
793 class pass_ud_rtl_dce : public rtl_opt_pass
795 public:
796 pass_ud_rtl_dce (gcc::context *ctxt)
797 : rtl_opt_pass (pass_data_ud_rtl_dce, ctxt)
800 /* opt_pass methods: */
801 virtual bool gate (function *)
803 return optimize > 1 && flag_dce && dbg_cnt (dce_ud);
806 virtual unsigned int execute (function *)
808 return rest_of_handle_ud_dce ();
811 }; // class pass_ud_rtl_dce
813 } // anon namespace
815 rtl_opt_pass *
816 make_pass_ud_rtl_dce (gcc::context *ctxt)
818 return new pass_ud_rtl_dce (ctxt);
822 /* -------------------------------------------------------------------------
823 Fast DCE functions
824 ------------------------------------------------------------------------- */
826 /* Process basic block BB. Return true if the live_in set has
827 changed. REDO_OUT is true if the info at the bottom of the block
828 needs to be recalculated before starting. AU is the proper set of
829 artificial uses. Track global substitution of uses of dead pseudos
830 in debug insns using GLOBAL_DEBUG. */
832 static bool
833 word_dce_process_block (basic_block bb, bool redo_out,
834 struct dead_debug_global *global_debug)
836 bitmap local_live = BITMAP_ALLOC (&dce_tmp_bitmap_obstack);
837 rtx insn;
838 bool block_changed;
839 struct dead_debug_local debug;
841 if (redo_out)
843 /* Need to redo the live_out set of this block if when one of
844 the succs of this block has had a change in it live in
845 set. */
846 edge e;
847 edge_iterator ei;
848 df_confluence_function_n con_fun_n = df_word_lr->problem->con_fun_n;
849 bitmap_clear (DF_WORD_LR_OUT (bb));
850 FOR_EACH_EDGE (e, ei, bb->succs)
851 (*con_fun_n) (e);
854 if (dump_file)
856 fprintf (dump_file, "processing block %d live out = ", bb->index);
857 df_print_word_regset (dump_file, DF_WORD_LR_OUT (bb));
860 bitmap_copy (local_live, DF_WORD_LR_OUT (bb));
861 dead_debug_local_init (&debug, NULL, global_debug);
863 FOR_BB_INSNS_REVERSE (bb, insn)
864 if (DEBUG_INSN_P (insn))
866 df_ref use;
867 FOR_EACH_INSN_USE (use, insn)
868 if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER
869 && (GET_MODE_SIZE (GET_MODE (DF_REF_REAL_REG (use)))
870 == 2 * UNITS_PER_WORD)
871 && !bitmap_bit_p (local_live, 2 * DF_REF_REGNO (use))
872 && !bitmap_bit_p (local_live, 2 * DF_REF_REGNO (use) + 1))
873 dead_debug_add (&debug, use, DF_REF_REGNO (use));
875 else if (INSN_P (insn))
877 bool any_changed;
879 /* No matter if the instruction is needed or not, we remove
880 any regno in the defs from the live set. */
881 any_changed = df_word_lr_simulate_defs (insn, local_live);
882 if (any_changed)
883 mark_insn (insn, true);
885 /* On the other hand, we do not allow the dead uses to set
886 anything in local_live. */
887 if (marked_insn_p (insn))
888 df_word_lr_simulate_uses (insn, local_live);
890 /* Insert debug temps for dead REGs used in subsequent debug
891 insns. We may have to emit a debug temp even if the insn
892 was marked, in case the debug use was after the point of
893 death. */
894 if (debug.used && !bitmap_empty_p (debug.used))
896 df_ref def;
898 FOR_EACH_INSN_DEF (def, insn)
899 dead_debug_insert_temp (&debug, DF_REF_REGNO (def), insn,
900 marked_insn_p (insn)
901 && !control_flow_insn_p (insn)
902 ? DEBUG_TEMP_AFTER_WITH_REG_FORCE
903 : DEBUG_TEMP_BEFORE_WITH_VALUE);
906 if (dump_file)
908 fprintf (dump_file, "finished processing insn %d live out = ",
909 INSN_UID (insn));
910 df_print_word_regset (dump_file, local_live);
914 block_changed = !bitmap_equal_p (local_live, DF_WORD_LR_IN (bb));
915 if (block_changed)
916 bitmap_copy (DF_WORD_LR_IN (bb), local_live);
918 dead_debug_local_finish (&debug, NULL);
919 BITMAP_FREE (local_live);
920 return block_changed;
924 /* Process basic block BB. Return true if the live_in set has
925 changed. REDO_OUT is true if the info at the bottom of the block
926 needs to be recalculated before starting. AU is the proper set of
927 artificial uses. Track global substitution of uses of dead pseudos
928 in debug insns using GLOBAL_DEBUG. */
930 static bool
931 dce_process_block (basic_block bb, bool redo_out, bitmap au,
932 struct dead_debug_global *global_debug)
934 bitmap local_live = BITMAP_ALLOC (&dce_tmp_bitmap_obstack);
935 rtx insn;
936 bool block_changed;
937 df_ref def;
938 struct dead_debug_local debug;
940 if (redo_out)
942 /* Need to redo the live_out set of this block if when one of
943 the succs of this block has had a change in it live in
944 set. */
945 edge e;
946 edge_iterator ei;
947 df_confluence_function_n con_fun_n = df_lr->problem->con_fun_n;
948 bitmap_clear (DF_LR_OUT (bb));
949 FOR_EACH_EDGE (e, ei, bb->succs)
950 (*con_fun_n) (e);
953 if (dump_file)
955 fprintf (dump_file, "processing block %d lr out = ", bb->index);
956 df_print_regset (dump_file, DF_LR_OUT (bb));
959 bitmap_copy (local_live, DF_LR_OUT (bb));
961 df_simulate_initialize_backwards (bb, local_live);
962 dead_debug_local_init (&debug, NULL, global_debug);
964 FOR_BB_INSNS_REVERSE (bb, insn)
965 if (DEBUG_INSN_P (insn))
967 df_ref use;
968 FOR_EACH_INSN_USE (use, insn)
969 if (!bitmap_bit_p (local_live, DF_REF_REGNO (use))
970 && !bitmap_bit_p (au, DF_REF_REGNO (use)))
971 dead_debug_add (&debug, use, DF_REF_REGNO (use));
973 else if (INSN_P (insn))
975 bool needed = marked_insn_p (insn);
977 /* The insn is needed if there is someone who uses the output. */
978 if (!needed)
979 FOR_EACH_INSN_DEF (def, insn)
980 if (bitmap_bit_p (local_live, DF_REF_REGNO (def))
981 || bitmap_bit_p (au, DF_REF_REGNO (def)))
983 needed = true;
984 mark_insn (insn, true);
985 break;
988 /* No matter if the instruction is needed or not, we remove
989 any regno in the defs from the live set. */
990 df_simulate_defs (insn, local_live);
992 /* On the other hand, we do not allow the dead uses to set
993 anything in local_live. */
994 if (needed)
995 df_simulate_uses (insn, local_live);
997 /* Insert debug temps for dead REGs used in subsequent debug
998 insns. We may have to emit a debug temp even if the insn
999 was marked, in case the debug use was after the point of
1000 death. */
1001 if (debug.used && !bitmap_empty_p (debug.used))
1002 FOR_EACH_INSN_DEF (def, insn)
1003 dead_debug_insert_temp (&debug, DF_REF_REGNO (def), insn,
1004 needed && !control_flow_insn_p (insn)
1005 ? DEBUG_TEMP_AFTER_WITH_REG_FORCE
1006 : DEBUG_TEMP_BEFORE_WITH_VALUE);
1009 dead_debug_local_finish (&debug, NULL);
1010 df_simulate_finalize_backwards (bb, local_live);
1012 block_changed = !bitmap_equal_p (local_live, DF_LR_IN (bb));
1013 if (block_changed)
1014 bitmap_copy (DF_LR_IN (bb), local_live);
1016 BITMAP_FREE (local_live);
1017 return block_changed;
1021 /* Perform fast DCE once initialization is done. If WORD_LEVEL is
1022 true, use the word level dce, otherwise do it at the pseudo
1023 level. */
1025 static void
1026 fast_dce (bool word_level)
1028 int *postorder = df_get_postorder (DF_BACKWARD);
1029 int n_blocks = df_get_n_blocks (DF_BACKWARD);
1030 /* The set of blocks that have been seen on this iteration. */
1031 bitmap processed = BITMAP_ALLOC (&dce_blocks_bitmap_obstack);
1032 /* The set of blocks that need to have the out vectors reset because
1033 the in of one of their successors has changed. */
1034 bitmap redo_out = BITMAP_ALLOC (&dce_blocks_bitmap_obstack);
1035 bitmap all_blocks = BITMAP_ALLOC (&dce_blocks_bitmap_obstack);
1036 bool global_changed = true;
1038 /* These regs are considered always live so if they end up dying
1039 because of some def, we need to bring the back again. Calling
1040 df_simulate_fixup_sets has the disadvantage of calling
1041 bb_has_eh_pred once per insn, so we cache the information
1042 here. */
1043 bitmap au = &df->regular_block_artificial_uses;
1044 bitmap au_eh = &df->eh_block_artificial_uses;
1045 int i;
1046 struct dead_debug_global global_debug;
1048 prescan_insns_for_dce (true);
1050 for (i = 0; i < n_blocks; i++)
1051 bitmap_set_bit (all_blocks, postorder[i]);
1053 dead_debug_global_init (&global_debug, NULL);
1055 while (global_changed)
1057 global_changed = false;
1059 for (i = 0; i < n_blocks; i++)
1061 int index = postorder[i];
1062 basic_block bb = BASIC_BLOCK_FOR_FN (cfun, index);
1063 bool local_changed;
1065 if (index < NUM_FIXED_BLOCKS)
1067 bitmap_set_bit (processed, index);
1068 continue;
1071 if (word_level)
1072 local_changed
1073 = word_dce_process_block (bb, bitmap_bit_p (redo_out, index),
1074 &global_debug);
1075 else
1076 local_changed
1077 = dce_process_block (bb, bitmap_bit_p (redo_out, index),
1078 bb_has_eh_pred (bb) ? au_eh : au,
1079 &global_debug);
1080 bitmap_set_bit (processed, index);
1082 if (local_changed)
1084 edge e;
1085 edge_iterator ei;
1086 FOR_EACH_EDGE (e, ei, bb->preds)
1087 if (bitmap_bit_p (processed, e->src->index))
1088 /* Be tricky about when we need to iterate the
1089 analysis. We only have redo the analysis if the
1090 bitmaps change at the top of a block that is the
1091 entry to a loop. */
1092 global_changed = true;
1093 else
1094 bitmap_set_bit (redo_out, e->src->index);
1098 if (global_changed)
1100 /* Turn off the RUN_DCE flag to prevent recursive calls to
1101 dce. */
1102 int old_flag = df_clear_flags (DF_LR_RUN_DCE);
1104 /* So something was deleted that requires a redo. Do it on
1105 the cheap. */
1106 delete_unmarked_insns ();
1107 bitmap_clear (marked);
1108 bitmap_clear (processed);
1109 bitmap_clear (redo_out);
1111 /* We do not need to rescan any instructions. We only need
1112 to redo the dataflow equations for the blocks that had a
1113 change at the top of the block. Then we need to redo the
1114 iteration. */
1115 if (word_level)
1116 df_analyze_problem (df_word_lr, all_blocks, postorder, n_blocks);
1117 else
1118 df_analyze_problem (df_lr, all_blocks, postorder, n_blocks);
1120 if (old_flag & DF_LR_RUN_DCE)
1121 df_set_flags (DF_LR_RUN_DCE);
1123 prescan_insns_for_dce (true);
1127 dead_debug_global_finish (&global_debug, NULL);
1129 delete_unmarked_insns ();
1131 BITMAP_FREE (processed);
1132 BITMAP_FREE (redo_out);
1133 BITMAP_FREE (all_blocks);
1137 /* Fast register level DCE. */
1139 static unsigned int
1140 rest_of_handle_fast_dce (void)
1142 init_dce (true);
1143 fast_dce (false);
1144 fini_dce (true);
1145 return 0;
1149 /* Fast byte level DCE. */
1151 void
1152 run_word_dce (void)
1154 int old_flags;
1156 if (!flag_dce)
1157 return;
1159 timevar_push (TV_DCE);
1160 old_flags = df_clear_flags (DF_DEFER_INSN_RESCAN + DF_NO_INSN_RESCAN);
1161 df_word_lr_add_problem ();
1162 init_dce (true);
1163 fast_dce (true);
1164 fini_dce (true);
1165 df_set_flags (old_flags);
1166 timevar_pop (TV_DCE);
1170 /* This is an internal call that is used by the df live register
1171 problem to run fast dce as a side effect of creating the live
1172 information. The stack is organized so that the lr problem is run,
1173 this pass is run, which updates the live info and the df scanning
1174 info, and then returns to allow the rest of the problems to be run.
1176 This can be called by elsewhere but it will not update the bit
1177 vectors for any other problems than LR. */
1179 void
1180 run_fast_df_dce (void)
1182 if (flag_dce)
1184 /* If dce is able to delete something, it has to happen
1185 immediately. Otherwise there will be problems handling the
1186 eq_notes. */
1187 int old_flags =
1188 df_clear_flags (DF_DEFER_INSN_RESCAN + DF_NO_INSN_RESCAN);
1190 df_in_progress = true;
1191 rest_of_handle_fast_dce ();
1192 df_in_progress = false;
1194 df_set_flags (old_flags);
1199 /* Run a fast DCE pass. */
1201 void
1202 run_fast_dce (void)
1204 if (flag_dce)
1205 rest_of_handle_fast_dce ();
1209 namespace {
1211 const pass_data pass_data_fast_rtl_dce =
1213 RTL_PASS, /* type */
1214 "rtl_dce", /* name */
1215 OPTGROUP_NONE, /* optinfo_flags */
1216 TV_DCE, /* tv_id */
1217 0, /* properties_required */
1218 0, /* properties_provided */
1219 0, /* properties_destroyed */
1220 0, /* todo_flags_start */
1221 TODO_df_finish, /* todo_flags_finish */
1224 class pass_fast_rtl_dce : public rtl_opt_pass
1226 public:
1227 pass_fast_rtl_dce (gcc::context *ctxt)
1228 : rtl_opt_pass (pass_data_fast_rtl_dce, ctxt)
1231 /* opt_pass methods: */
1232 virtual bool gate (function *)
1234 return optimize > 0 && flag_dce && dbg_cnt (dce_fast);
1237 virtual unsigned int execute (function *)
1239 return rest_of_handle_fast_dce ();
1242 }; // class pass_fast_rtl_dce
1244 } // anon namespace
1246 rtl_opt_pass *
1247 make_pass_fast_rtl_dce (gcc::context *ctxt)
1249 return new pass_fast_rtl_dce (ctxt);