1/* RTL dead code elimination.
2 Copyright (C) 2005-2017 Free Software Foundation, Inc.
3
4This file is part of GCC.
5
6GCC is free software; you can redistribute it and/or modify it under
7the terms of the GNU General Public License as published by the Free
8Software Foundation; either version 3, or (at your option) any later
9version.
10
11GCC is distributed in the hope that it will be useful, but WITHOUT ANY
12WARRANTY; without even the implied warranty of MERCHANTABILITY or
13FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14for more details.
15
16You should have received a copy of the GNU General Public License
17along with GCC; see the file COPYING3. If not see
18<http://www.gnu.org/licenses/>. */
19
20#include "config.h"
21#include "system.h"
22#include "coretypes.h"
23#include "backend.h"
24#include "rtl.h"
25#include "tree.h"
26#include "predict.h"
27#include "df.h"
28#include "memmodel.h"
29#include "tm_p.h"
30#include "emit-rtl.h" /* FIXME: Can go away once crtl is moved to rtl.h. */
31#include "cfgrtl.h"
32#include "cfgbuild.h"
33#include "cfgcleanup.h"
34#include "dce.h"
35#include "valtrack.h"
36#include "tree-pass.h"
37#include "dbgcnt.h"
38
39
40/* -------------------------------------------------------------------------
41 Core mark/delete routines
42 ------------------------------------------------------------------------- */
43
44/* True if we are invoked while the df engine is running; in this case,
45 we don't want to reenter it. */
46static bool df_in_progress = false;
47
48/* True if we are allowed to alter the CFG in this pass. */
49static bool can_alter_cfg = false;
50
51/* Instructions that have been marked but whose dependencies have not
52 yet been processed. */
53static vec<rtx_insn *> worklist;
54
55/* Bitmap of instructions marked as needed indexed by INSN_UID. */
56static sbitmap marked;
57
58/* Bitmap obstacks used for block processing by the fast algorithm. */
59static bitmap_obstack dce_blocks_bitmap_obstack;
60static bitmap_obstack dce_tmp_bitmap_obstack;
61
62static bool find_call_stack_args (rtx_call_insn *, bool, bool, bitmap);
63
64/* A subroutine for which BODY is part of the instruction being tested;
65 either the top-level pattern, or an element of a PARALLEL. The
66 instruction is known not to be a bare USE or CLOBBER. */
67
68static bool
69deletable_insn_p_1 (rtx body)
70{
71 switch (GET_CODE (body))
72 {
73 case PREFETCH:
74 case TRAP_IF:
75 /* The UNSPEC case was added here because the ia-64 claims that
76 USEs do not work after reload and generates UNSPECS rather
77 than USEs. Since dce is run after reload we need to avoid
78 deleting these even if they are dead. If it turns out that
79 USEs really do work after reload, the ia-64 should be
80 changed, and the UNSPEC case can be removed. */
81 case UNSPEC:
82 return false;
83
84 default:
85 return !volatile_refs_p (body);
86 }
87}
88
89
90/* Return true if INSN is a normal instruction that can be deleted by
91 the DCE pass. */
92
93static bool
94deletable_insn_p (rtx_insn *insn, bool fast, bitmap arg_stores)
95{
96 rtx body, x;
97 int i;
98 df_ref def;
99
100 if (CALL_P (insn)
101 /* We cannot delete calls inside of the recursive dce because
102 this may cause basic blocks to be deleted and this messes up
103 the rest of the stack of optimization passes. */
104 && (!df_in_progress)
105 /* We cannot delete pure or const sibling calls because it is
106 hard to see the result. */
107 && (!SIBLING_CALL_P (insn))
108 /* We can delete dead const or pure calls as long as they do not
109 infinite loop. */
110 && (RTL_CONST_OR_PURE_CALL_P (insn)
111 && !RTL_LOOPING_CONST_OR_PURE_CALL_P (insn)))
112 return find_call_stack_args (as_a <rtx_call_insn *> (insn), false,
113 fast, arg_stores);
114
115 /* Don't delete jumps, notes and the like. */
116 if (!NONJUMP_INSN_P (insn))
117 return false;
118
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;
123
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;
129 /* Initialization of pseudo PIC register should never be removed. */
130 else if (DF_REF_REG (def) == pic_offset_table_rtx
131 && REGNO (pic_offset_table_rtx) >= FIRST_PSEUDO_REGISTER)
132 return false;
133
134 body = PATTERN (insn);
135 switch (GET_CODE (body))
136 {
137 case USE:
138 case VAR_LOCATION:
139 return false;
140
141 case CLOBBER:
142 if (fast)
143 {
144 /* A CLOBBER of a dead pseudo register serves no purpose.
145 That is not necessarily true for hard registers until
146 after reload. */
147 x = XEXP (body, 0);
148 return REG_P (x) && (!HARD_REGISTER_P (x) || reload_completed);
149 }
150 else
151 /* Because of the way that use-def chains are built, it is not
152 possible to tell if the clobber is dead because it can
153 never be the target of a use-def chain. */
154 return false;
155
156 case PARALLEL:
157 for (i = XVECLEN (body, 0) - 1; i >= 0; i--)
158 if (!deletable_insn_p_1 (XVECEXP (body, 0, i)))
159 return false;
160 return true;
161
162 default:
163 return deletable_insn_p_1 (body);
164 }
165}
166
167
168/* Return true if INSN has been marked as needed. */
169
170static inline int
171marked_insn_p (rtx_insn *insn)
172{
173 /* Artificial defs are always needed and they do not have an insn.
174 We should never see them here. */
175 gcc_assert (insn);
176 return bitmap_bit_p (marked, INSN_UID (insn));
177}
178
179
180/* If INSN has not yet been marked as needed, mark it now, and add it to
181 the worklist. */
182
183static void
184mark_insn (rtx_insn *insn, bool fast)
185{
186 if (!marked_insn_p (insn))
187 {
188 if (!fast)
189 worklist.safe_push (insn);
190 bitmap_set_bit (marked, INSN_UID (insn));
191 if (dump_file)
192 fprintf (dump_file, " Adding insn %d to worklist\n", INSN_UID (insn));
193 if (CALL_P (insn)
194 && !df_in_progress
195 && !SIBLING_CALL_P (insn)
196 && (RTL_CONST_OR_PURE_CALL_P (insn)
197 && !RTL_LOOPING_CONST_OR_PURE_CALL_P (insn)))
198 find_call_stack_args (as_a <rtx_call_insn *> (insn), true, fast, NULL);
199 }
200}
201
202
203/* A note_stores callback used by mark_nonreg_stores. DATA is the
204 instruction containing DEST. */
205
206static void
207mark_nonreg_stores_1 (rtx dest, const_rtx pattern, void *data)
208{
209 if (GET_CODE (pattern) != CLOBBER && !REG_P (dest))
210 mark_insn ((rtx_insn *) data, true);
211}
212
213
214/* A note_stores callback used by mark_nonreg_stores. DATA is the
215 instruction containing DEST. */
216
217static void
218mark_nonreg_stores_2 (rtx dest, const_rtx pattern, void *data)
219{
220 if (GET_CODE (pattern) != CLOBBER && !REG_P (dest))
221 mark_insn ((rtx_insn *) data, false);
222}
223
224
225/* Mark INSN if BODY stores to a non-register destination. */
226
227static void
228mark_nonreg_stores (rtx body, rtx_insn *insn, bool fast)
229{
230 if (fast)
231 note_stores (body, mark_nonreg_stores_1, insn);
232 else
233 note_stores (body, mark_nonreg_stores_2, insn);
234}
235
236
237/* Return true if a store to SIZE bytes, starting OFF bytes from stack pointer,
238 is a call argument store, and clear corresponding bits from SP_BYTES
239 bitmap if it is. */
240
241static bool
242check_argument_store (HOST_WIDE_INT size, HOST_WIDE_INT off,
243 HOST_WIDE_INT min_sp_off, HOST_WIDE_INT max_sp_off,
244 bitmap sp_bytes)
245{
246 HOST_WIDE_INT byte;
247 for (byte = off; byte < off + size; byte++)
248 {
249 if (byte < min_sp_off
250 || byte >= max_sp_off
251 || !bitmap_clear_bit (sp_bytes, byte - min_sp_off))
252 return false;
253 }
254 return true;
255}
256
257
258/* Try to find all stack stores of CALL_INSN arguments if
259 ACCUMULATE_OUTGOING_ARGS. If all stack stores have been found
260 and it is therefore safe to eliminate the call, return true,
261 otherwise return false. This function should be first called
262 with DO_MARK false, and only when the CALL_INSN is actually
263 going to be marked called again with DO_MARK true. */
264
265static bool
266find_call_stack_args (rtx_call_insn *call_insn, bool do_mark, bool fast,
267 bitmap arg_stores)
268{
269 rtx p;
270 rtx_insn *insn, *prev_insn;
271 bool ret;
272 HOST_WIDE_INT min_sp_off, max_sp_off;
273 bitmap sp_bytes;
274
275 gcc_assert (CALL_P (call_insn));
276 if (!ACCUMULATE_OUTGOING_ARGS)
277 return true;
278
279 if (!do_mark)
280 {
281 gcc_assert (arg_stores);
282 bitmap_clear (arg_stores);
283 }
284
285 min_sp_off = INTTYPE_MAXIMUM (HOST_WIDE_INT);
286 max_sp_off = 0;
287
288 /* First determine the minimum and maximum offset from sp for
289 stored arguments. */
290 for (p = CALL_INSN_FUNCTION_USAGE (call_insn); p; p = XEXP (p, 1))
291 if (GET_CODE (XEXP (p, 0)) == USE
292 && MEM_P (XEXP (XEXP (p, 0), 0)))
293 {
294 rtx mem = XEXP (XEXP (p, 0), 0), addr;
295 HOST_WIDE_INT off = 0, size;
296 if (!MEM_SIZE_KNOWN_P (mem))
297 return false;
298 size = MEM_SIZE (mem);
299 addr = XEXP (mem, 0);
300 if (GET_CODE (addr) == PLUS
301 && REG_P (XEXP (addr, 0))
302 && CONST_INT_P (XEXP (addr, 1)))
303 {
304 off = INTVAL (XEXP (addr, 1));
305 addr = XEXP (addr, 0);
306 }
307 if (addr != stack_pointer_rtx)
308 {
309 if (!REG_P (addr))
310 return false;
311 /* If not fast, use chains to see if addr wasn't set to
312 sp + offset. */
313 if (!fast)
314 {
315 df_ref use;
316 struct df_link *defs;
317 rtx set;
318
319 FOR_EACH_INSN_USE (use, call_insn)
320 if (rtx_equal_p (addr, DF_REF_REG (use)))
321 break;
322
323 if (use == NULL)
324 return false;
325
326 for (defs = DF_REF_CHAIN (use); defs; defs = defs->next)
327 if (! DF_REF_IS_ARTIFICIAL (defs->ref))
328 break;
329
330 if (defs == NULL)
331 return false;
332
333 set = single_set (DF_REF_INSN (defs->ref));
334 if (!set)
335 return false;
336
337 if (GET_CODE (SET_SRC (set)) != PLUS
338 || XEXP (SET_SRC (set), 0) != stack_pointer_rtx
339 || !CONST_INT_P (XEXP (SET_SRC (set), 1)))
340 return false;
341
342 off += INTVAL (XEXP (SET_SRC (set), 1));
343 }
344 else
345 return false;
346 }
347 min_sp_off = MIN (min_sp_off, off);
348 max_sp_off = MAX (max_sp_off, off + size);
349 }
350
351 if (min_sp_off >= max_sp_off)
352 return true;
353 sp_bytes = BITMAP_ALLOC (NULL);
354
355 /* Set bits in SP_BYTES bitmap for bytes relative to sp + min_sp_off
356 which contain arguments. Checking has been done in the previous
357 loop. */
358 for (p = CALL_INSN_FUNCTION_USAGE (call_insn); p; p = XEXP (p, 1))
359 if (GET_CODE (XEXP (p, 0)) == USE
360 && MEM_P (XEXP (XEXP (p, 0), 0)))
361 {
362 rtx mem = XEXP (XEXP (p, 0), 0), addr;
363 HOST_WIDE_INT off = 0, byte;
364 addr = XEXP (mem, 0);
365 if (GET_CODE (addr) == PLUS
366 && REG_P (XEXP (addr, 0))
367 && CONST_INT_P (XEXP (addr, 1)))
368 {
369 off = INTVAL (XEXP (addr, 1));
370 addr = XEXP (addr, 0);
371 }
372 if (addr != stack_pointer_rtx)
373 {
374 df_ref use;
375 struct df_link *defs;
376 rtx set;
377
378 FOR_EACH_INSN_USE (use, call_insn)
379 if (rtx_equal_p (addr, DF_REF_REG (use)))
380 break;
381
382 for (defs = DF_REF_CHAIN (use); defs; defs = defs->next)
383 if (! DF_REF_IS_ARTIFICIAL (defs->ref))
384 break;
385
386 set = single_set (DF_REF_INSN (defs->ref));
387 off += INTVAL (XEXP (SET_SRC (set), 1));
388 }
389 for (byte = off; byte < off + MEM_SIZE (mem); byte++)
390 {
391 if (!bitmap_set_bit (sp_bytes, byte - min_sp_off))
392 gcc_unreachable ();
393 }
394 }
395
396 /* Walk backwards, looking for argument stores. The search stops
397 when seeing another call, sp adjustment or memory store other than
398 argument store. */
399 ret = false;
400 for (insn = PREV_INSN (call_insn); insn; insn = prev_insn)
401 {
402 rtx set, mem, addr;
403 HOST_WIDE_INT off;
404
405 if (insn == BB_HEAD (BLOCK_FOR_INSN (call_insn)))
406 prev_insn = NULL;
407 else
408 prev_insn = PREV_INSN (insn);
409
410 if (CALL_P (insn))
411 break;
412
413 if (!NONDEBUG_INSN_P (insn))
414 continue;
415
416 set = single_set (insn);
417 if (!set || SET_DEST (set) == stack_pointer_rtx)
418 break;
419
420 if (!MEM_P (SET_DEST (set)))
421 continue;
422
423 mem = SET_DEST (set);
424 addr = XEXP (mem, 0);
425 off = 0;
426 if (GET_CODE (addr) == PLUS
427 && REG_P (XEXP (addr, 0))
428 && CONST_INT_P (XEXP (addr, 1)))
429 {
430 off = INTVAL (XEXP (addr, 1));
431 addr = XEXP (addr, 0);
432 }
433 if (addr != stack_pointer_rtx)
434 {
435 if (!REG_P (addr))
436 break;
437 if (!fast)
438 {
439 df_ref use;
440 struct df_link *defs;
441 rtx set;
442
443 FOR_EACH_INSN_USE (use, insn)
444 if (rtx_equal_p (addr, DF_REF_REG (use)))
445 break;
446
447 if (use == NULL)
448 break;
449
450 for (defs = DF_REF_CHAIN (use); defs; defs = defs->next)
451 if (! DF_REF_IS_ARTIFICIAL (defs->ref))
452 break;
453
454 if (defs == NULL)
455 break;
456
457 set = single_set (DF_REF_INSN (defs->ref));
458 if (!set)
459 break;
460
461 if (GET_CODE (SET_SRC (set)) != PLUS
462 || XEXP (SET_SRC (set), 0) != stack_pointer_rtx
463 || !CONST_INT_P (XEXP (SET_SRC (set), 1)))
464 break;
465
466 off += INTVAL (XEXP (SET_SRC (set), 1));
467 }
468 else
469 break;
470 }
471
472 if (!MEM_SIZE_KNOWN_P (mem)
473 || !check_argument_store (MEM_SIZE (mem), off, min_sp_off,
474 max_sp_off, sp_bytes))
475 break;
476
477 if (!deletable_insn_p (insn, fast, NULL))
478 break;
479
480 if (do_mark)
481 mark_insn (insn, fast);
482 else
483 bitmap_set_bit (arg_stores, INSN_UID (insn));
484
485 if (bitmap_empty_p (sp_bytes))
486 {
487 ret = true;
488 break;
489 }
490 }
491
492 BITMAP_FREE (sp_bytes);
493 if (!ret && arg_stores)
494 bitmap_clear (arg_stores);
495
496 return ret;
497}
498
499
500/* Remove all REG_EQUAL and REG_EQUIV notes referring to the registers INSN
501 writes to. */
502
503static void
504remove_reg_equal_equiv_notes_for_defs (rtx_insn *insn)
505{
506 df_ref def;
507
508 FOR_EACH_INSN_DEF (def, insn)
509 remove_reg_equal_equiv_notes_for_regno (DF_REF_REGNO (def));
510}
511
512/* Scan all BBs for debug insns and reset those that reference values
513 defined in unmarked insns. */
514
515static void
516reset_unmarked_insns_debug_uses (void)
517{
518 basic_block bb;
519 rtx_insn *insn, *next;
520
521 FOR_EACH_BB_REVERSE_FN (bb, cfun)
522 FOR_BB_INSNS_REVERSE_SAFE (bb, insn, next)
523 if (DEBUG_INSN_P (insn))
524 {
525 df_ref use;
526
527 FOR_EACH_INSN_USE (use, insn)
528 {
529 struct df_link *defs;
530 for (defs = DF_REF_CHAIN (use); defs; defs = defs->next)
531 {
532 rtx_insn *ref_insn;
533 if (DF_REF_IS_ARTIFICIAL (defs->ref))
534 continue;
535 ref_insn = DF_REF_INSN (defs->ref);
536 if (!marked_insn_p (ref_insn))
537 break;
538 }
539 if (!defs)
540 continue;
541 /* ??? FIXME could we propagate the values assigned to
542 each of the DEFs? */
543 INSN_VAR_LOCATION_LOC (insn) = gen_rtx_UNKNOWN_VAR_LOC ();
544 df_insn_rescan_debug_internal (insn);
545 break;
546 }
547 }
548}
549
550/* Delete every instruction that hasn't been marked. */
551
552static void
553delete_unmarked_insns (void)
554{
555 basic_block bb;
556 rtx_insn *insn, *next;
557 bool must_clean = false;
558
559 FOR_EACH_BB_REVERSE_FN (bb, cfun)
560 FOR_BB_INSNS_REVERSE_SAFE (bb, insn, next)
561 if (NONDEBUG_INSN_P (insn))
562 {
563 /* Always delete no-op moves. */
564 if (noop_move_p (insn))
565 ;
566
567 /* Otherwise rely only on the DCE algorithm. */
568 else if (marked_insn_p (insn))
569 continue;
570
571 /* Beware that reaching a dbg counter limit here can result
572 in miscompiled file. This occurs when a group of insns
573 must be deleted together, typically because the kept insn
574 depends on the output from the deleted insn. Deleting
575 this insns in reverse order (both at the bb level and
576 when looking at the blocks) minimizes this, but does not
577 eliminate it, since it is possible for the using insn to
578 be top of a block and the producer to be at the bottom of
579 the block. However, in most cases this will only result
580 in an uninitialized use of an insn that is dead anyway.
581
582 However, there is one rare case that will cause a
583 miscompile: deletion of non-looping pure and constant
584 calls on a machine where ACCUMULATE_OUTGOING_ARGS is true.
585 In this case it is possible to remove the call, but leave
586 the argument pushes to the stack. Because of the changes
587 to the stack pointer, this will almost always lead to a
588 miscompile. */
589 if (!dbg_cnt (dce))
590 continue;
591
592 if (crtl->shrink_wrapped_separate
593 && find_reg_note (insn, REG_CFA_RESTORE, NULL))
594 {
595 if (dump_file)
596 fprintf (dump_file, "DCE: NOT deleting insn %d, it's a "
597 "callee-save restore\n", INSN_UID (insn));
598 continue;
599 }
600
601 if (dump_file)
602 fprintf (dump_file, "DCE: Deleting insn %d\n", INSN_UID (insn));
603
604 /* Before we delete the insn we have to remove the REG_EQUAL notes
605 for the destination regs in order to avoid dangling notes. */
606 remove_reg_equal_equiv_notes_for_defs (insn);
607
608 /* If a pure or const call is deleted, this may make the cfg
609 have unreachable blocks. We rememeber this and call
610 delete_unreachable_blocks at the end. */
611 if (CALL_P (insn))
612 must_clean = true;
613
614 /* Now delete the insn. */
615 delete_insn_and_edges (insn);
616 }
617
618 /* Deleted a pure or const call. */
619 if (must_clean)
620 delete_unreachable_blocks ();
621}
622
623
624/* Go through the instructions and mark those whose necessity is not
625 dependent on inter-instruction information. Make sure all other
626 instructions are not marked. */
627
628static void
629prescan_insns_for_dce (bool fast)
630{
631 basic_block bb;
632 rtx_insn *insn, *prev;
633 bitmap arg_stores = NULL;
634
635 if (dump_file)
636 fprintf (dump_file, "Finding needed instructions:\n");
637
638 if (!df_in_progress && ACCUMULATE_OUTGOING_ARGS)
639 arg_stores = BITMAP_ALLOC (NULL);
640
641 FOR_EACH_BB_FN (bb, cfun)
642 {
643 FOR_BB_INSNS_REVERSE_SAFE (bb, insn, prev)
644 if (NONDEBUG_INSN_P (insn))
645 {
646 /* Don't mark argument stores now. They will be marked
647 if needed when the associated CALL is marked. */
648 if (arg_stores && bitmap_bit_p (arg_stores, INSN_UID (insn)))
649 continue;
650 if (deletable_insn_p (insn, fast, arg_stores))
651 mark_nonreg_stores (PATTERN (insn), insn, fast);
652 else
653 mark_insn (insn, fast);
654 }
655 /* find_call_stack_args only looks at argument stores in the
656 same bb. */
657 if (arg_stores)
658 bitmap_clear (arg_stores);
659 }
660
661 if (arg_stores)
662 BITMAP_FREE (arg_stores);
663
664 if (dump_file)
665 fprintf (dump_file, "Finished finding needed instructions:\n");
666}
667
668
669/* UD-based DSE routines. */
670
671/* Mark instructions that define artificially-used registers, such as
672 the frame pointer and the stack pointer. */
673
674static void
675mark_artificial_uses (void)
676{
677 basic_block bb;
678 struct df_link *defs;
679 df_ref use;
680
681 FOR_ALL_BB_FN (bb, cfun)
682 FOR_EACH_ARTIFICIAL_USE (use, bb->index)
683 for (defs = DF_REF_CHAIN (use); defs; defs = defs->next)
684 if (!DF_REF_IS_ARTIFICIAL (defs->ref))
685 mark_insn (DF_REF_INSN (defs->ref), false);
686}
687
688
689/* Mark every instruction that defines a register value that INSN uses. */
690
691static void
692mark_reg_dependencies (rtx_insn *insn)
693{
694 struct df_link *defs;
695 df_ref use;
696
697 if (DEBUG_INSN_P (insn))
698 return;
699
700 FOR_EACH_INSN_USE (use, insn)
701 {
702 if (dump_file)
703 {
704 fprintf (dump_file, "Processing use of ");
705 print_simple_rtl (dump_file, DF_REF_REG (use));
706 fprintf (dump_file, " in insn %d:\n", INSN_UID (insn));
707 }
708 for (defs = DF_REF_CHAIN (use); defs; defs = defs->next)
709 if (! DF_REF_IS_ARTIFICIAL (defs->ref))
710 mark_insn (DF_REF_INSN (defs->ref), false);
711 }
712}
713
714
715/* Initialize global variables for a new DCE pass. */
716
717static void
718init_dce (bool fast)
719{
720 if (!df_in_progress)
721 {
722 if (!fast)
723 {
724 df_set_flags (DF_RD_PRUNE_DEAD_DEFS);
725 df_chain_add_problem (DF_UD_CHAIN);
726 }
727 df_analyze ();
728 }
729
730 if (dump_file)
731 df_dump (dump_file);
732
733 if (fast)
734 {
735 bitmap_obstack_initialize (&dce_blocks_bitmap_obstack);
736 bitmap_obstack_initialize (&dce_tmp_bitmap_obstack);
737 can_alter_cfg = false;
738 }
739 else
740 can_alter_cfg = true;
741
742 marked = sbitmap_alloc (get_max_uid () + 1);
743 bitmap_clear (marked);
744}
745
746
747/* Free the data allocated by init_dce. */
748
749static void
750fini_dce (bool fast)
751{
752 sbitmap_free (marked);
753
754 if (fast)
755 {
756 bitmap_obstack_release (&dce_blocks_bitmap_obstack);
757 bitmap_obstack_release (&dce_tmp_bitmap_obstack);
758 }
759}
760
761
762/* UD-chain based DCE. */
763
764static unsigned int
765rest_of_handle_ud_dce (void)
766{
767 rtx_insn *insn;
768
769 init_dce (false);
770
771 prescan_insns_for_dce (false);
772 mark_artificial_uses ();
773 while (worklist.length () > 0)
774 {
775 insn = worklist.pop ();
776 mark_reg_dependencies (insn);
777 }
778 worklist.release ();
779
780 if (MAY_HAVE_DEBUG_BIND_INSNS)
781 reset_unmarked_insns_debug_uses ();
782
783 /* Before any insns are deleted, we must remove the chains since
784 they are not bidirectional. */
785 df_remove_problem (df_chain);
786 delete_unmarked_insns ();
787
788 fini_dce (false);
789 return 0;
790}
791
792
793namespace {
794
795const pass_data pass_data_ud_rtl_dce =
796{
797 RTL_PASS, /* type */
798 "ud_dce", /* name */
799 OPTGROUP_NONE, /* optinfo_flags */
800 TV_DCE, /* tv_id */
801 0, /* properties_required */
802 0, /* properties_provided */
803 0, /* properties_destroyed */
804 0, /* todo_flags_start */
805 TODO_df_finish, /* todo_flags_finish */
806};
807
808class pass_ud_rtl_dce : public rtl_opt_pass
809{
810public:
811 pass_ud_rtl_dce (gcc::context *ctxt)
812 : rtl_opt_pass (pass_data_ud_rtl_dce, ctxt)
813 {}
814
815 /* opt_pass methods: */
816 virtual bool gate (function *)
817 {
818 return optimize > 1 && flag_dce && dbg_cnt (dce_ud);
819 }
820
821 virtual unsigned int execute (function *)
822 {
823 return rest_of_handle_ud_dce ();
824 }
825
826}; // class pass_ud_rtl_dce
827
828} // anon namespace
829
830rtl_opt_pass *
831make_pass_ud_rtl_dce (gcc::context *ctxt)
832{
833 return new pass_ud_rtl_dce (ctxt);
834}
835
836
837/* -------------------------------------------------------------------------
838 Fast DCE functions
839 ------------------------------------------------------------------------- */
840
841/* Process basic block BB. Return true if the live_in set has
842 changed. REDO_OUT is true if the info at the bottom of the block
843 needs to be recalculated before starting. AU is the proper set of
844 artificial uses. Track global substitution of uses of dead pseudos
845 in debug insns using GLOBAL_DEBUG. */
846
847static bool
848word_dce_process_block (basic_block bb, bool redo_out,
849 struct dead_debug_global *global_debug)
850{
851 bitmap local_live = BITMAP_ALLOC (&dce_tmp_bitmap_obstack);
852 rtx_insn *insn;
853 bool block_changed;
854 struct dead_debug_local debug;
855
856 if (redo_out)
857 {
858 /* Need to redo the live_out set of this block if when one of
859 the succs of this block has had a change in it live in
860 set. */
861 edge e;
862 edge_iterator ei;
863 df_confluence_function_n con_fun_n = df_word_lr->problem->con_fun_n;
864 bitmap_clear (DF_WORD_LR_OUT (bb));
865 FOR_EACH_EDGE (e, ei, bb->succs)
866 (*con_fun_n) (e);
867 }
868
869 if (dump_file)
870 {
871 fprintf (dump_file, "processing block %d live out = ", bb->index);
872 df_print_word_regset (dump_file, DF_WORD_LR_OUT (bb));
873 }
874
875 bitmap_copy (local_live, DF_WORD_LR_OUT (bb));
876 dead_debug_local_init (&debug, NULL, global_debug);
877
878 FOR_BB_INSNS_REVERSE (bb, insn)
879 if (DEBUG_INSN_P (insn))
880 {
881 df_ref use;
882 FOR_EACH_INSN_USE (use, insn)
883 if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER
884 && (GET_MODE_SIZE (GET_MODE (DF_REF_REAL_REG (use)))
885 == 2 * UNITS_PER_WORD)
886 && !bitmap_bit_p (local_live, 2 * DF_REF_REGNO (use))
887 && !bitmap_bit_p (local_live, 2 * DF_REF_REGNO (use) + 1))
888 dead_debug_add (&debug, use, DF_REF_REGNO (use));
889 }
890 else if (INSN_P (insn))
891 {
892 bool any_changed;
893
894 /* No matter if the instruction is needed or not, we remove
895 any regno in the defs from the live set. */
896 any_changed = df_word_lr_simulate_defs (insn, local_live);
897 if (any_changed)
898 mark_insn (insn, true);
899
900 /* On the other hand, we do not allow the dead uses to set
901 anything in local_live. */
902 if (marked_insn_p (insn))
903 df_word_lr_simulate_uses (insn, local_live);
904
905 /* Insert debug temps for dead REGs used in subsequent debug
906 insns. We may have to emit a debug temp even if the insn
907 was marked, in case the debug use was after the point of
908 death. */
909 if (debug.used && !bitmap_empty_p (debug.used))
910 {
911 df_ref def;
912
913 FOR_EACH_INSN_DEF (def, insn)
914 dead_debug_insert_temp (&debug, DF_REF_REGNO (def), insn,
915 marked_insn_p (insn)
916 && !control_flow_insn_p (insn)
917 ? DEBUG_TEMP_AFTER_WITH_REG_FORCE
918 : DEBUG_TEMP_BEFORE_WITH_VALUE);
919 }
920
921 if (dump_file)
922 {
923 fprintf (dump_file, "finished processing insn %d live out = ",
924 INSN_UID (insn));
925 df_print_word_regset (dump_file, local_live);
926 }
927 }
928
929 block_changed = !bitmap_equal_p (local_live, DF_WORD_LR_IN (bb));
930 if (block_changed)
931 bitmap_copy (DF_WORD_LR_IN (bb), local_live);
932
933 dead_debug_local_finish (&debug, NULL);
934 BITMAP_FREE (local_live);
935 return block_changed;
936}
937
938
939/* Process basic block BB. Return true if the live_in set has
940 changed. REDO_OUT is true if the info at the bottom of the block
941 needs to be recalculated before starting. AU is the proper set of
942 artificial uses. Track global substitution of uses of dead pseudos
943 in debug insns using GLOBAL_DEBUG. */
944
945static bool
946dce_process_block (basic_block bb, bool redo_out, bitmap au,
947 struct dead_debug_global *global_debug)
948{
949 bitmap local_live = BITMAP_ALLOC (&dce_tmp_bitmap_obstack);
950 rtx_insn *insn;
951 bool block_changed;
952 df_ref def;
953 struct dead_debug_local debug;
954
955 if (redo_out)
956 {
957 /* Need to redo the live_out set of this block if when one of
958 the succs of this block has had a change in it live in
959 set. */
960 edge e;
961 edge_iterator ei;
962 df_confluence_function_n con_fun_n = df_lr->problem->con_fun_n;
963 bitmap_clear (DF_LR_OUT (bb));
964 FOR_EACH_EDGE (e, ei, bb->succs)
965 (*con_fun_n) (e);
966 }
967
968 if (dump_file)
969 {
970 fprintf (dump_file, "processing block %d lr out = ", bb->index);
971 df_print_regset (dump_file, DF_LR_OUT (bb));
972 }
973
974 bitmap_copy (local_live, DF_LR_OUT (bb));
975
976 df_simulate_initialize_backwards (bb, local_live);
977 dead_debug_local_init (&debug, NULL, global_debug);
978
979 FOR_BB_INSNS_REVERSE (bb, insn)
980 if (DEBUG_INSN_P (insn))
981 {
982 df_ref use;
983 FOR_EACH_INSN_USE (use, insn)
984 if (!bitmap_bit_p (local_live, DF_REF_REGNO (use))
985 && !bitmap_bit_p (au, DF_REF_REGNO (use)))
986 dead_debug_add (&debug, use, DF_REF_REGNO (use));
987 }
988 else if (INSN_P (insn))
989 {
990 bool needed = marked_insn_p (insn);
991
992 /* The insn is needed if there is someone who uses the output. */
993 if (!needed)
994 FOR_EACH_INSN_DEF (def, insn)
995 if (bitmap_bit_p (local_live, DF_REF_REGNO (def))
996 || bitmap_bit_p (au, DF_REF_REGNO (def)))
997 {
998 needed = true;
999 mark_insn (insn, true);
1000 break;
1001 }
1002
1003 /* No matter if the instruction is needed or not, we remove
1004 any regno in the defs from the live set. */
1005 df_simulate_defs (insn, local_live);
1006
1007 /* On the other hand, we do not allow the dead uses to set
1008 anything in local_live. */
1009 if (needed)
1010 df_simulate_uses (insn, local_live);
1011
1012 /* Insert debug temps for dead REGs used in subsequent debug
1013 insns. We may have to emit a debug temp even if the insn
1014 was marked, in case the debug use was after the point of
1015 death. */
1016 if (debug.used && !bitmap_empty_p (debug.used))
1017 FOR_EACH_INSN_DEF (def, insn)
1018 dead_debug_insert_temp (&debug, DF_REF_REGNO (def), insn,
1019 needed && !control_flow_insn_p (insn)
1020 ? DEBUG_TEMP_AFTER_WITH_REG_FORCE
1021 : DEBUG_TEMP_BEFORE_WITH_VALUE);
1022 }
1023
1024 dead_debug_local_finish (&debug, NULL);
1025 df_simulate_finalize_backwards (bb, local_live);
1026
1027 block_changed = !bitmap_equal_p (local_live, DF_LR_IN (bb));
1028 if (block_changed)
1029 bitmap_copy (DF_LR_IN (bb), local_live);
1030
1031 BITMAP_FREE (local_live);
1032 return block_changed;
1033}
1034
1035
1036/* Perform fast DCE once initialization is done. If WORD_LEVEL is
1037 true, use the word level dce, otherwise do it at the pseudo
1038 level. */
1039
1040static void
1041fast_dce (bool word_level)
1042{
1043 int *postorder = df_get_postorder (DF_BACKWARD);
1044 int n_blocks = df_get_n_blocks (DF_BACKWARD);
1045 /* The set of blocks that have been seen on this iteration. */
1046 bitmap processed = BITMAP_ALLOC (&dce_blocks_bitmap_obstack);
1047 /* The set of blocks that need to have the out vectors reset because
1048 the in of one of their successors has changed. */
1049 bitmap redo_out = BITMAP_ALLOC (&dce_blocks_bitmap_obstack);
1050 bitmap all_blocks = BITMAP_ALLOC (&dce_blocks_bitmap_obstack);
1051 bool global_changed = true;
1052
1053 /* These regs are considered always live so if they end up dying
1054 because of some def, we need to bring the back again. Calling
1055 df_simulate_fixup_sets has the disadvantage of calling
1056 bb_has_eh_pred once per insn, so we cache the information
1057 here. */
1058 bitmap au = &df->regular_block_artificial_uses;
1059 bitmap au_eh = &df->eh_block_artificial_uses;
1060 int i;
1061 struct dead_debug_global global_debug;
1062
1063 prescan_insns_for_dce (true);
1064
1065 for (i = 0; i < n_blocks; i++)
1066 bitmap_set_bit (all_blocks, postorder[i]);
1067
1068 dead_debug_global_init (&global_debug, NULL);
1069
1070 while (global_changed)
1071 {
1072 global_changed = false;
1073
1074 for (i = 0; i < n_blocks; i++)
1075 {
1076 int index = postorder[i];
1077 basic_block bb = BASIC_BLOCK_FOR_FN (cfun, index);
1078 bool local_changed;
1079
1080 if (index < NUM_FIXED_BLOCKS)
1081 {
1082 bitmap_set_bit (processed, index);
1083 continue;
1084 }
1085
1086 if (word_level)
1087 local_changed
1088 = word_dce_process_block (bb, bitmap_bit_p (redo_out, index),
1089 &global_debug);
1090 else
1091 local_changed
1092 = dce_process_block (bb, bitmap_bit_p (redo_out, index),
1093 bb_has_eh_pred (bb) ? au_eh : au,
1094 &global_debug);
1095 bitmap_set_bit (processed, index);
1096
1097 if (local_changed)
1098 {
1099 edge e;
1100 edge_iterator ei;
1101 FOR_EACH_EDGE (e, ei, bb->preds)
1102 if (bitmap_bit_p (processed, e->src->index))
1103 /* Be tricky about when we need to iterate the
1104 analysis. We only have redo the analysis if the
1105 bitmaps change at the top of a block that is the
1106 entry to a loop. */
1107 global_changed = true;
1108 else
1109 bitmap_set_bit (redo_out, e->src->index);
1110 }
1111 }
1112
1113 if (global_changed)
1114 {
1115 /* Turn off the RUN_DCE flag to prevent recursive calls to
1116 dce. */
1117 int old_flag = df_clear_flags (DF_LR_RUN_DCE);
1118
1119 /* So something was deleted that requires a redo. Do it on
1120 the cheap. */
1121 delete_unmarked_insns ();
1122 bitmap_clear (marked);
1123 bitmap_clear (processed);
1124 bitmap_clear (redo_out);
1125
1126 /* We do not need to rescan any instructions. We only need
1127 to redo the dataflow equations for the blocks that had a
1128 change at the top of the block. Then we need to redo the
1129 iteration. */
1130 if (word_level)
1131 df_analyze_problem (df_word_lr, all_blocks, postorder, n_blocks);
1132 else
1133 df_analyze_problem (df_lr, all_blocks, postorder, n_blocks);
1134
1135 if (old_flag & DF_LR_RUN_DCE)
1136 df_set_flags (DF_LR_RUN_DCE);
1137
1138 prescan_insns_for_dce (true);
1139 }
1140 }
1141
1142 dead_debug_global_finish (&global_debug, NULL);
1143
1144 delete_unmarked_insns ();
1145
1146 BITMAP_FREE (processed);
1147 BITMAP_FREE (redo_out);
1148 BITMAP_FREE (all_blocks);
1149}
1150
1151
1152/* Fast register level DCE. */
1153
1154static unsigned int
1155rest_of_handle_fast_dce (void)
1156{
1157 init_dce (true);
1158 fast_dce (false);
1159 fini_dce (true);
1160 return 0;
1161}
1162
1163
1164/* Fast byte level DCE. */
1165
1166void
1167run_word_dce (void)
1168{
1169 int old_flags;
1170
1171 if (!flag_dce)
1172 return;
1173
1174 timevar_push (TV_DCE);
1175 old_flags = df_clear_flags (DF_DEFER_INSN_RESCAN + DF_NO_INSN_RESCAN);
1176 df_word_lr_add_problem ();
1177 init_dce (true);
1178 fast_dce (true);
1179 fini_dce (true);
1180 df_set_flags (old_flags);
1181 timevar_pop (TV_DCE);
1182}
1183
1184
1185/* This is an internal call that is used by the df live register
1186 problem to run fast dce as a side effect of creating the live
1187 information. The stack is organized so that the lr problem is run,
1188 this pass is run, which updates the live info and the df scanning
1189 info, and then returns to allow the rest of the problems to be run.
1190
1191 This can be called by elsewhere but it will not update the bit
1192 vectors for any other problems than LR. */
1193
1194void
1195run_fast_df_dce (void)
1196{
1197 if (flag_dce)
1198 {
1199 /* If dce is able to delete something, it has to happen
1200 immediately. Otherwise there will be problems handling the
1201 eq_notes. */
1202 int old_flags =
1203 df_clear_flags (DF_DEFER_INSN_RESCAN + DF_NO_INSN_RESCAN);
1204
1205 df_in_progress = true;
1206 rest_of_handle_fast_dce ();
1207 df_in_progress = false;
1208
1209 df_set_flags (old_flags);
1210 }
1211}
1212
1213
1214/* Run a fast DCE pass. */
1215
1216void
1217run_fast_dce (void)
1218{
1219 if (flag_dce)
1220 rest_of_handle_fast_dce ();
1221}
1222
1223
1224namespace {
1225
1226const pass_data pass_data_fast_rtl_dce =
1227{
1228 RTL_PASS, /* type */
1229 "rtl_dce", /* name */
1230 OPTGROUP_NONE, /* optinfo_flags */
1231 TV_DCE, /* tv_id */
1232 0, /* properties_required */
1233 0, /* properties_provided */
1234 0, /* properties_destroyed */
1235 0, /* todo_flags_start */
1236 TODO_df_finish, /* todo_flags_finish */
1237};
1238
1239class pass_fast_rtl_dce : public rtl_opt_pass
1240{
1241public:
1242 pass_fast_rtl_dce (gcc::context *ctxt)
1243 : rtl_opt_pass (pass_data_fast_rtl_dce, ctxt)
1244 {}
1245
1246 /* opt_pass methods: */
1247 virtual bool gate (function *)
1248 {
1249 return optimize > 0 && flag_dce && dbg_cnt (dce_fast);
1250 }
1251
1252 virtual unsigned int execute (function *)
1253 {
1254 return rest_of_handle_fast_dce ();
1255 }
1256
1257}; // class pass_fast_rtl_dce
1258
1259} // anon namespace
1260
1261rtl_opt_pass *
1262make_pass_fast_rtl_dce (gcc::context *ctxt)
1263{
1264 return new pass_fast_rtl_dce (ctxt);
1265}
1266