1/* RTL dead code elimination.
2 Copyright (C) 2005-2025 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#include "rtl-iter.h"
39
40
41/* -------------------------------------------------------------------------
42 Core mark/delete routines
43 ------------------------------------------------------------------------- */
44
45/* True if we are invoked while the df engine is running; in this case,
46 we don't want to reenter it. */
47static bool df_in_progress = false;
48
49/* True if we are allowed to alter the CFG in this pass. */
50static bool can_alter_cfg = false;
51
52/* Instructions that have been marked but whose dependencies have not
53 yet been processed. */
54static vec<rtx_insn *> worklist;
55
56/* Bitmap of instructions marked as needed indexed by INSN_UID. */
57static sbitmap marked;
58
59/* Bitmap obstacks used for block processing by the fast algorithm. */
60static bitmap_obstack dce_blocks_bitmap_obstack;
61static bitmap_obstack dce_tmp_bitmap_obstack;
62
63static bool find_call_stack_args (rtx_call_insn *, bool, bool, bitmap);
64
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. */
68
69static bool
70deletable_insn_p_1 (rtx body)
71{
72 switch (GET_CODE (body))
73 {
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;
84
85 default:
86 return !volatile_refs_p (body);
87 }
88}
89
90/* Don't delete calls that may throw if we cannot do so. */
91
92static bool
93can_delete_call (rtx_insn *insn)
94{
95 if (cfun->can_delete_dead_exceptions && can_alter_cfg)
96 return true;
97 if (!insn_nothrow_p (insn))
98 return false;
99 if (can_alter_cfg)
100 return true;
101 /* If we can't alter cfg, even when the call can't throw exceptions, it
102 might have EDGE_ABNORMAL_CALL edges and so we shouldn't delete such
103 calls. */
104 gcc_assert (CALL_P (insn));
105 if (BLOCK_FOR_INSN (insn) && BB_END (BLOCK_FOR_INSN (insn)) == insn)
106 {
107 edge e;
108 edge_iterator ei;
109
110 FOR_EACH_EDGE (e, ei, BLOCK_FOR_INSN (insn)->succs)
111 if ((e->flags & EDGE_ABNORMAL_CALL) != 0)
112 return false;
113 }
114 return true;
115}
116
117/* Return true if INSN is a normal instruction that can be deleted by
118 the DCE pass. */
119
120static bool
121deletable_insn_p (rtx_insn *insn, bool fast, bitmap arg_stores)
122{
123 rtx body, x;
124 int i;
125 df_ref def;
126
127 if (CALL_P (insn)
128 /* We cannot delete calls inside of the recursive dce because
129 this may cause basic blocks to be deleted and this messes up
130 the rest of the stack of optimization passes. */
131 && (!df_in_progress)
132 /* We cannot delete pure or const sibling calls because it is
133 hard to see the result. */
134 && (!SIBLING_CALL_P (insn))
135 /* We can delete dead const or pure calls as long as they do not
136 infinite loop. */
137 && (RTL_CONST_OR_PURE_CALL_P (insn)
138 && !RTL_LOOPING_CONST_OR_PURE_CALL_P (insn))
139 /* Don't delete calls that may throw if we cannot do so. */
140 && can_delete_call (insn))
141 return find_call_stack_args (as_a <rtx_call_insn *> (p: insn), false,
142 fast, arg_stores);
143
144 /* Don't delete jumps, notes and the like. */
145 if (!NONJUMP_INSN_P (insn))
146 return false;
147
148 /* Don't delete insns that may throw if we cannot do so. */
149 if (!(cfun->can_delete_dead_exceptions && can_alter_cfg)
150 && !insn_nothrow_p (insn))
151 return false;
152
153 /* If INSN sets a global_reg, leave it untouched. */
154 FOR_EACH_INSN_DEF (def, insn)
155 if (HARD_REGISTER_NUM_P (DF_REF_REGNO (def))
156 && global_regs[DF_REF_REGNO (def)])
157 return false;
158 /* Initialization of pseudo PIC register should never be removed. */
159 else if (DF_REF_REG (def) == pic_offset_table_rtx
160 && REGNO (pic_offset_table_rtx) >= FIRST_PSEUDO_REGISTER)
161 return false;
162
163 /* Callee-save restores are needed. */
164 if (RTX_FRAME_RELATED_P (insn)
165 && crtl->shrink_wrapped_separate
166 && find_reg_note (insn, REG_CFA_RESTORE, NULL))
167 return false;
168
169 body = PATTERN (insn);
170 switch (GET_CODE (body))
171 {
172 case USE:
173 case VAR_LOCATION:
174 return false;
175
176 case CLOBBER:
177 if (fast)
178 {
179 /* A CLOBBER of a dead pseudo register serves no purpose.
180 That is not necessarily true for hard registers until
181 after reload. */
182 x = XEXP (body, 0);
183 return REG_P (x) && (!HARD_REGISTER_P (x) || reload_completed);
184 }
185 else
186 /* Because of the way that use-def chains are built, it is not
187 possible to tell if the clobber is dead because it can
188 never be the target of a use-def chain. */
189 return false;
190
191 case PARALLEL:
192 for (i = XVECLEN (body, 0) - 1; i >= 0; i--)
193 if (!deletable_insn_p_1 (XVECEXP (body, 0, i)))
194 return false;
195 return true;
196
197 default:
198 return deletable_insn_p_1 (body);
199 }
200}
201
202
203/* Return true if INSN has been marked as needed. */
204
205static inline int
206marked_insn_p (rtx_insn *insn)
207{
208 /* Artificial defs are always needed and they do not have an insn.
209 We should never see them here. */
210 gcc_assert (insn);
211 return bitmap_bit_p (map: marked, bitno: INSN_UID (insn));
212}
213
214
215/* If INSN has not yet been marked as needed, mark it now, and add it to
216 the worklist. */
217
218static void
219mark_insn (rtx_insn *insn, bool fast)
220{
221 if (!marked_insn_p (insn))
222 {
223 if (!fast)
224 worklist.safe_push (obj: insn);
225 bitmap_set_bit (map: marked, bitno: INSN_UID (insn));
226 if (dump_file)
227 fprintf (stream: dump_file, format: " Adding insn %d to worklist\n", INSN_UID (insn));
228 if (CALL_P (insn)
229 && !df_in_progress
230 && !SIBLING_CALL_P (insn)
231 && (RTL_CONST_OR_PURE_CALL_P (insn)
232 && !RTL_LOOPING_CONST_OR_PURE_CALL_P (insn))
233 && can_delete_call (insn))
234 find_call_stack_args (as_a <rtx_call_insn *> (p: insn), true, fast, NULL);
235 }
236}
237
238
239/* A note_stores callback used by mark_nonreg_stores. DATA is the
240 instruction containing DEST. */
241
242static void
243mark_nonreg_stores_1 (rtx dest, const_rtx pattern, void *data)
244{
245 if (GET_CODE (pattern) != CLOBBER && !REG_P (dest))
246 mark_insn (insn: (rtx_insn *) data, fast: true);
247}
248
249
250/* A note_stores callback used by mark_nonreg_stores. DATA is the
251 instruction containing DEST. */
252
253static void
254mark_nonreg_stores_2 (rtx dest, const_rtx pattern, void *data)
255{
256 if (GET_CODE (pattern) != CLOBBER && !REG_P (dest))
257 mark_insn (insn: (rtx_insn *) data, fast: false);
258}
259
260
261/* Mark INSN if it stores to a non-register destination. */
262
263static void
264mark_nonreg_stores (rtx_insn *insn, bool fast)
265{
266 if (fast)
267 note_stores (insn, mark_nonreg_stores_1, insn);
268 else
269 note_stores (insn, mark_nonreg_stores_2, insn);
270}
271
272
273/* Return true if a store to SIZE bytes, starting OFF bytes from stack pointer,
274 is a call argument store, and clear corresponding bits from SP_BYTES
275 bitmap if it is. */
276
277static bool
278check_argument_store (HOST_WIDE_INT size, HOST_WIDE_INT off,
279 HOST_WIDE_INT min_sp_off, HOST_WIDE_INT max_sp_off,
280 bitmap sp_bytes)
281{
282 HOST_WIDE_INT byte;
283 for (byte = off; byte < off + size; byte++)
284 {
285 if (byte < min_sp_off
286 || byte >= max_sp_off
287 || !bitmap_clear_bit (sp_bytes, byte - min_sp_off))
288 return false;
289 }
290 return true;
291}
292
293/* If MEM has sp address, return 0, if it has sp + const address,
294 return that const, if it has reg address where reg is set to sp + const
295 and FAST is false, return const, otherwise return
296 INTTYPE_MINUMUM (HOST_WIDE_INT). */
297
298static HOST_WIDE_INT
299sp_based_mem_offset (rtx_call_insn *call_insn, const_rtx mem, bool fast)
300{
301 HOST_WIDE_INT off = 0;
302 rtx addr = XEXP (mem, 0);
303 if (GET_CODE (addr) == PLUS
304 && REG_P (XEXP (addr, 0))
305 && CONST_INT_P (XEXP (addr, 1)))
306 {
307 off = INTVAL (XEXP (addr, 1));
308 addr = XEXP (addr, 0);
309 }
310 if (addr == stack_pointer_rtx)
311 return off;
312
313 if (!REG_P (addr) || fast)
314 return INTTYPE_MINIMUM (HOST_WIDE_INT);
315
316 /* If not fast, use chains to see if addr wasn't set to sp + offset. */
317 df_ref use;
318 FOR_EACH_INSN_USE (use, call_insn)
319 if (rtx_equal_p (addr, DF_REF_REG (use)))
320 break;
321
322 if (use == NULL)
323 return INTTYPE_MINIMUM (HOST_WIDE_INT);
324
325 struct df_link *defs;
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 INTTYPE_MINIMUM (HOST_WIDE_INT);
332
333 rtx set = single_set (DF_REF_INSN (defs->ref));
334 if (!set)
335 return INTTYPE_MINIMUM (HOST_WIDE_INT);
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 INTTYPE_MINIMUM (HOST_WIDE_INT);
341
342 off += INTVAL (XEXP (SET_SRC (set), 1));
343 return off;
344}
345
346/* Data for check_argument_load called via note_uses. */
347struct check_argument_load_data {
348 bitmap sp_bytes;
349 HOST_WIDE_INT min_sp_off, max_sp_off;
350 rtx_call_insn *call_insn;
351 bool fast;
352 bool load_found;
353};
354
355/* Helper function for find_call_stack_args. Check if there are
356 any loads from the argument slots in between the const/pure call
357 and store to the argument slot, set LOAD_FOUND if any is found. */
358
359static void
360check_argument_load (rtx *loc, void *data)
361{
362 struct check_argument_load_data *d
363 = (struct check_argument_load_data *) data;
364 subrtx_iterator::array_type array;
365 FOR_EACH_SUBRTX (iter, array, *loc, NONCONST)
366 {
367 const_rtx mem = *iter;
368 HOST_WIDE_INT size;
369 if (MEM_P (mem)
370 && MEM_SIZE_KNOWN_P (mem)
371 && MEM_SIZE (mem).is_constant (const_value: &size))
372 {
373 HOST_WIDE_INT off = sp_based_mem_offset (call_insn: d->call_insn, mem, fast: d->fast);
374 if (off != INTTYPE_MINIMUM (HOST_WIDE_INT)
375 && off < d->max_sp_off
376 && off + size > d->min_sp_off)
377 for (HOST_WIDE_INT byte = MAX (off, d->min_sp_off);
378 byte < MIN (off + size, d->max_sp_off); byte++)
379 if (bitmap_bit_p (d->sp_bytes, byte - d->min_sp_off))
380 {
381 d->load_found = true;
382 return;
383 }
384 }
385 }
386}
387
388/* Try to find all stack stores of CALL_INSN arguments if
389 ACCUMULATE_OUTGOING_ARGS. If all stack stores have been found
390 and it is therefore safe to eliminate the call, return true,
391 otherwise return false. This function should be first called
392 with DO_MARK false, and only when the CALL_INSN is actually
393 going to be marked called again with DO_MARK true. */
394
395static bool
396find_call_stack_args (rtx_call_insn *call_insn, bool do_mark, bool fast,
397 bitmap arg_stores)
398{
399 rtx p;
400 rtx_insn *insn, *prev_insn;
401 bool ret;
402 HOST_WIDE_INT min_sp_off, max_sp_off;
403 bitmap sp_bytes;
404
405 gcc_assert (CALL_P (call_insn));
406 if (!ACCUMULATE_OUTGOING_ARGS)
407 return true;
408
409 if (!do_mark)
410 {
411 gcc_assert (arg_stores);
412 bitmap_clear (arg_stores);
413 }
414
415 min_sp_off = INTTYPE_MAXIMUM (HOST_WIDE_INT);
416 max_sp_off = 0;
417
418 /* First determine the minimum and maximum offset from sp for
419 stored arguments. */
420 for (p = CALL_INSN_FUNCTION_USAGE (call_insn); p; p = XEXP (p, 1))
421 if (GET_CODE (XEXP (p, 0)) == USE
422 && MEM_P (XEXP (XEXP (p, 0), 0)))
423 {
424 rtx mem = XEXP (XEXP (p, 0), 0);
425 HOST_WIDE_INT size;
426 if (!MEM_SIZE_KNOWN_P (mem) || !MEM_SIZE (mem).is_constant (const_value: &size))
427 return false;
428 HOST_WIDE_INT off = sp_based_mem_offset (call_insn, mem, fast);
429 if (off == INTTYPE_MINIMUM (HOST_WIDE_INT))
430 return false;
431 min_sp_off = MIN (min_sp_off, off);
432 max_sp_off = MAX (max_sp_off, off + size);
433 }
434
435 if (min_sp_off >= max_sp_off)
436 return true;
437 sp_bytes = BITMAP_ALLOC (NULL);
438
439 /* Set bits in SP_BYTES bitmap for bytes relative to sp + min_sp_off
440 which contain arguments. Checking has been done in the previous
441 loop. */
442 for (p = CALL_INSN_FUNCTION_USAGE (call_insn); p; p = XEXP (p, 1))
443 if (GET_CODE (XEXP (p, 0)) == USE
444 && MEM_P (XEXP (XEXP (p, 0), 0)))
445 {
446 rtx mem = XEXP (XEXP (p, 0), 0);
447 /* Checked in the previous iteration. */
448 HOST_WIDE_INT size = MEM_SIZE (mem).to_constant ();
449 HOST_WIDE_INT off = sp_based_mem_offset (call_insn, mem, fast);
450 gcc_checking_assert (off != INTTYPE_MINIMUM (HOST_WIDE_INT));
451 for (HOST_WIDE_INT byte = off; byte < off + size; byte++)
452 if (!bitmap_set_bit (sp_bytes, byte - min_sp_off))
453 gcc_unreachable ();
454 }
455
456 /* Walk backwards, looking for argument stores. The search stops
457 when seeing another call, sp adjustment, memory store other than
458 argument store or a read from an argument stack slot. */
459 struct check_argument_load_data data
460 = { .sp_bytes: sp_bytes, .min_sp_off: min_sp_off, .max_sp_off: max_sp_off, .call_insn: call_insn, .fast: fast, .load_found: false };
461 ret = false;
462 for (insn = PREV_INSN (insn: call_insn); insn; insn = prev_insn)
463 {
464 if (insn == BB_HEAD (BLOCK_FOR_INSN (call_insn)))
465 prev_insn = NULL;
466 else
467 prev_insn = PREV_INSN (insn);
468
469 if (CALL_P (insn))
470 break;
471
472 if (!NONDEBUG_INSN_P (insn))
473 continue;
474
475 rtx set = single_set (insn);
476 if (!set || SET_DEST (set) == stack_pointer_rtx)
477 break;
478
479 note_uses (&PATTERN (insn), check_argument_load, &data);
480 if (data.load_found)
481 break;
482
483 if (!MEM_P (SET_DEST (set)))
484 continue;
485
486 rtx mem = SET_DEST (set);
487 HOST_WIDE_INT off = sp_based_mem_offset (call_insn, mem, fast);
488 if (off == INTTYPE_MINIMUM (HOST_WIDE_INT))
489 break;
490
491 HOST_WIDE_INT size;
492 if (!MEM_SIZE_KNOWN_P (mem)
493 || !MEM_SIZE (mem).is_constant (const_value: &size)
494 || !check_argument_store (size, off, min_sp_off,
495 max_sp_off, sp_bytes))
496 break;
497
498 if (!deletable_insn_p (insn, fast, NULL))
499 break;
500
501 if (do_mark)
502 mark_insn (insn, fast);
503 else
504 bitmap_set_bit (arg_stores, INSN_UID (insn));
505
506 if (bitmap_empty_p (map: sp_bytes))
507 {
508 ret = true;
509 break;
510 }
511 }
512
513 BITMAP_FREE (sp_bytes);
514 if (!ret && arg_stores)
515 bitmap_clear (arg_stores);
516
517 return ret;
518}
519
520
521/* Remove all REG_EQUAL and REG_EQUIV notes referring to the registers INSN
522 writes to. */
523
524static void
525remove_reg_equal_equiv_notes_for_defs (rtx_insn *insn)
526{
527 df_ref def;
528
529 FOR_EACH_INSN_DEF (def, insn)
530 remove_reg_equal_equiv_notes_for_regno (DF_REF_REGNO (def));
531}
532
533/* Scan all BBs for debug insns and reset those that reference values
534 defined in unmarked insns. */
535
536static void
537reset_unmarked_insns_debug_uses (void)
538{
539 basic_block bb;
540 rtx_insn *insn, *next;
541
542 FOR_EACH_BB_REVERSE_FN (bb, cfun)
543 FOR_BB_INSNS_REVERSE_SAFE (bb, insn, next)
544 if (DEBUG_INSN_P (insn))
545 {
546 df_ref use;
547
548 FOR_EACH_INSN_USE (use, insn)
549 {
550 struct df_link *defs;
551 for (defs = DF_REF_CHAIN (use); defs; defs = defs->next)
552 {
553 rtx_insn *ref_insn;
554 if (DF_REF_IS_ARTIFICIAL (defs->ref))
555 continue;
556 ref_insn = DF_REF_INSN (defs->ref);
557 if (!marked_insn_p (insn: ref_insn))
558 break;
559 }
560 if (!defs)
561 continue;
562 /* ??? FIXME could we propagate the values assigned to
563 each of the DEFs? */
564 INSN_VAR_LOCATION_LOC (insn) = gen_rtx_UNKNOWN_VAR_LOC ();
565 df_insn_rescan_debug_internal (insn);
566 break;
567 }
568 }
569}
570
571/* Delete every instruction that hasn't been marked. */
572
573static void
574delete_unmarked_insns (void)
575{
576 basic_block bb;
577 rtx_insn *insn, *next;
578 bool must_clean = false;
579
580 FOR_EACH_BB_REVERSE_FN (bb, cfun)
581 FOR_BB_INSNS_REVERSE_SAFE (bb, insn, next)
582 if (NONDEBUG_INSN_P (insn))
583 {
584 rtx turn_into_use = NULL_RTX;
585
586 /* Always delete no-op moves. */
587 if (noop_move_p (insn)
588 /* Unless the no-op move can throw and we are not allowed
589 to alter cfg. */
590 && (!cfun->can_throw_non_call_exceptions
591 || (cfun->can_delete_dead_exceptions && can_alter_cfg)
592 || insn_nothrow_p (insn)))
593 {
594 if (RTX_FRAME_RELATED_P (insn))
595 turn_into_use
596 = find_reg_note (insn, REG_CFA_RESTORE, NULL);
597 if (turn_into_use && REG_P (XEXP (turn_into_use, 0)))
598 turn_into_use = XEXP (turn_into_use, 0);
599 else
600 turn_into_use = NULL_RTX;
601 }
602
603 /* Otherwise rely only on the DCE algorithm. */
604 else if (marked_insn_p (insn))
605 continue;
606
607 /* Beware that reaching a dbg counter limit here can result
608 in miscompiled file. This occurs when a group of insns
609 must be deleted together, typically because the kept insn
610 depends on the output from the deleted insn. Deleting
611 this insns in reverse order (both at the bb level and
612 when looking at the blocks) minimizes this, but does not
613 eliminate it, since it is possible for the using insn to
614 be top of a block and the producer to be at the bottom of
615 the block. However, in most cases this will only result
616 in an uninitialized use of an insn that is dead anyway.
617
618 However, there is one rare case that will cause a
619 miscompile: deletion of non-looping pure and constant
620 calls on a machine where ACCUMULATE_OUTGOING_ARGS is true.
621 In this case it is possible to remove the call, but leave
622 the argument pushes to the stack. Because of the changes
623 to the stack pointer, this will almost always lead to a
624 miscompile. */
625 if (!dbg_cnt (index: dce))
626 continue;
627
628 if (dump_file)
629 fprintf (stream: dump_file, format: "DCE: Deleting insn %d\n", INSN_UID (insn));
630
631 /* Before we delete the insn we have to remove the REG_EQUAL notes
632 for the destination regs in order to avoid dangling notes. */
633 remove_reg_equal_equiv_notes_for_defs (insn);
634
635 if (turn_into_use)
636 {
637 /* Don't remove frame related noop moves if they cary
638 REG_CFA_RESTORE note, while we don't need to emit any code,
639 we need it to emit the CFI restore note. */
640 PATTERN (insn)
641 = gen_rtx_USE (GET_MODE (turn_into_use), turn_into_use);
642 INSN_CODE (insn) = -1;
643 df_insn_rescan (insn);
644 }
645 else
646 /* Now delete the insn. */
647 must_clean |= delete_insn_and_edges (insn);
648 }
649
650 /* Deleted a pure or const call. */
651 if (must_clean)
652 {
653 gcc_assert (can_alter_cfg);
654 delete_unreachable_blocks ();
655 free_dominance_info (CDI_DOMINATORS);
656 }
657}
658
659
660/* Go through the instructions and mark those whose necessity is not
661 dependent on inter-instruction information. Make sure all other
662 instructions are not marked. */
663
664static void
665prescan_insns_for_dce (bool fast)
666{
667 basic_block bb;
668 rtx_insn *insn, *prev;
669 bitmap arg_stores = NULL;
670
671 if (dump_file)
672 fprintf (stream: dump_file, format: "Finding needed instructions:\n");
673
674 if (!df_in_progress && ACCUMULATE_OUTGOING_ARGS)
675 arg_stores = BITMAP_ALLOC (NULL);
676
677 FOR_EACH_BB_FN (bb, cfun)
678 {
679 FOR_BB_INSNS_REVERSE_SAFE (bb, insn, prev)
680 if (NONDEBUG_INSN_P (insn))
681 {
682 /* Don't mark argument stores now. They will be marked
683 if needed when the associated CALL is marked. */
684 if (arg_stores && bitmap_bit_p (arg_stores, INSN_UID (insn)))
685 continue;
686 if (deletable_insn_p (insn, fast, arg_stores))
687 mark_nonreg_stores (insn, fast);
688 else
689 mark_insn (insn, fast);
690 }
691 /* find_call_stack_args only looks at argument stores in the
692 same bb. */
693 if (arg_stores)
694 bitmap_clear (arg_stores);
695 }
696
697 if (arg_stores)
698 BITMAP_FREE (arg_stores);
699
700 if (dump_file)
701 fprintf (stream: dump_file, format: "Finished finding needed instructions:\n");
702}
703
704
705/* UD-based DSE routines. */
706
707/* Mark instructions that define artificially-used registers, such as
708 the frame pointer and the stack pointer. */
709
710static void
711mark_artificial_uses (void)
712{
713 basic_block bb;
714 struct df_link *defs;
715 df_ref use;
716
717 FOR_ALL_BB_FN (bb, cfun)
718 FOR_EACH_ARTIFICIAL_USE (use, bb->index)
719 for (defs = DF_REF_CHAIN (use); defs; defs = defs->next)
720 if (!DF_REF_IS_ARTIFICIAL (defs->ref))
721 mark_insn (DF_REF_INSN (defs->ref), fast: false);
722}
723
724
725/* Mark every instruction that defines a register value that INSN uses. */
726
727static void
728mark_reg_dependencies (rtx_insn *insn)
729{
730 struct df_link *defs;
731 df_ref use;
732
733 if (DEBUG_INSN_P (insn))
734 return;
735
736 FOR_EACH_INSN_USE (use, insn)
737 {
738 if (dump_file)
739 {
740 fprintf (stream: dump_file, format: "Processing use of ");
741 print_simple_rtl (dump_file, DF_REF_REG (use));
742 fprintf (stream: dump_file, format: " in insn %d:\n", INSN_UID (insn));
743 }
744 for (defs = DF_REF_CHAIN (use); defs; defs = defs->next)
745 if (! DF_REF_IS_ARTIFICIAL (defs->ref))
746 mark_insn (DF_REF_INSN (defs->ref), fast: false);
747 }
748}
749
750
751/* Initialize global variables for a new DCE pass. */
752
753static void
754init_dce (bool fast)
755{
756 if (!df_in_progress)
757 {
758 if (!fast)
759 {
760 df_set_flags (DF_RD_PRUNE_DEAD_DEFS);
761 df_chain_add_problem (DF_UD_CHAIN);
762 }
763 df_analyze ();
764 }
765
766 if (dump_file)
767 df_dump (dump_file);
768
769 if (fast)
770 {
771 bitmap_obstack_initialize (&dce_blocks_bitmap_obstack);
772 bitmap_obstack_initialize (&dce_tmp_bitmap_obstack);
773 can_alter_cfg = false;
774 }
775 else
776 can_alter_cfg = true;
777
778 marked = sbitmap_alloc (get_max_uid () + 1);
779 bitmap_clear (marked);
780}
781
782
783/* Free the data allocated by init_dce. */
784
785static void
786fini_dce (bool fast)
787{
788 sbitmap_free (map: marked);
789
790 if (fast)
791 {
792 bitmap_obstack_release (&dce_blocks_bitmap_obstack);
793 bitmap_obstack_release (&dce_tmp_bitmap_obstack);
794 }
795}
796
797
798/* UD-chain based DCE. */
799
800static unsigned int
801rest_of_handle_ud_dce (void)
802{
803 rtx_insn *insn;
804
805 init_dce (fast: false);
806
807 prescan_insns_for_dce (fast: false);
808 mark_artificial_uses ();
809 while (worklist.length () > 0)
810 {
811 insn = worklist.pop ();
812 mark_reg_dependencies (insn);
813 }
814 worklist.release ();
815
816 if (MAY_HAVE_DEBUG_BIND_INSNS)
817 reset_unmarked_insns_debug_uses ();
818
819 /* Before any insns are deleted, we must remove the chains since
820 they are not bidirectional. */
821 df_remove_problem (df_chain);
822 delete_unmarked_insns ();
823
824 fini_dce (fast: false);
825 return 0;
826}
827
828
829namespace {
830
831const pass_data pass_data_ud_rtl_dce =
832{
833 .type: RTL_PASS, /* type */
834 .name: "ud_dce", /* name */
835 .optinfo_flags: OPTGROUP_NONE, /* optinfo_flags */
836 .tv_id: TV_DCE, /* tv_id */
837 .properties_required: 0, /* properties_required */
838 .properties_provided: 0, /* properties_provided */
839 .properties_destroyed: 0, /* properties_destroyed */
840 .todo_flags_start: 0, /* todo_flags_start */
841 TODO_df_finish, /* todo_flags_finish */
842};
843
844class pass_ud_rtl_dce : public rtl_opt_pass
845{
846public:
847 pass_ud_rtl_dce (gcc::context *ctxt)
848 : rtl_opt_pass (pass_data_ud_rtl_dce, ctxt)
849 {}
850
851 /* opt_pass methods: */
852 bool gate (function *) final override
853 {
854 return optimize > 1 && flag_dce && dbg_cnt (index: dce_ud);
855 }
856
857 unsigned int execute (function *) final override
858 {
859 return rest_of_handle_ud_dce ();
860 }
861
862}; // class pass_ud_rtl_dce
863
864} // anon namespace
865
866rtl_opt_pass *
867make_pass_ud_rtl_dce (gcc::context *ctxt)
868{
869 return new pass_ud_rtl_dce (ctxt);
870}
871
872
873/* -------------------------------------------------------------------------
874 Fast DCE functions
875 ------------------------------------------------------------------------- */
876
877/* Process basic block BB. Return true if the live_in set has
878 changed. REDO_OUT is true if the info at the bottom of the block
879 needs to be recalculated before starting. AU is the proper set of
880 artificial uses. Track global substitution of uses of dead pseudos
881 in debug insns using GLOBAL_DEBUG. */
882
883static bool
884word_dce_process_block (basic_block bb, bool redo_out,
885 struct dead_debug_global *global_debug)
886{
887 bitmap local_live = BITMAP_ALLOC (obstack: &dce_tmp_bitmap_obstack);
888 rtx_insn *insn;
889 bool block_changed;
890 struct dead_debug_local debug;
891
892 if (redo_out)
893 {
894 /* Need to redo the live_out set of this block if when one of
895 the succs of this block has had a change in it live in
896 set. */
897 edge e;
898 edge_iterator ei;
899 df_confluence_function_n con_fun_n = df_word_lr->problem->con_fun_n;
900 bitmap_clear (DF_WORD_LR_OUT (bb));
901 FOR_EACH_EDGE (e, ei, bb->succs)
902 (*con_fun_n) (e);
903 }
904
905 if (dump_file)
906 {
907 fprintf (stream: dump_file, format: "processing block %d live out = ", bb->index);
908 df_print_word_regset (file: dump_file, DF_WORD_LR_OUT (bb));
909 }
910
911 bitmap_copy (local_live, DF_WORD_LR_OUT (bb));
912 dead_debug_local_init (&debug, NULL, global_debug);
913
914 FOR_BB_INSNS_REVERSE (bb, insn)
915 if (DEBUG_INSN_P (insn))
916 {
917 df_ref use;
918 FOR_EACH_INSN_USE (use, insn)
919 if (DF_REF_REGNO (use) >= FIRST_PSEUDO_REGISTER
920 && known_eq (GET_MODE_SIZE (GET_MODE (DF_REF_REAL_REG (use))),
921 2 * UNITS_PER_WORD)
922 && !bitmap_bit_p (local_live, 2 * DF_REF_REGNO (use))
923 && !bitmap_bit_p (local_live, 2 * DF_REF_REGNO (use) + 1))
924 dead_debug_add (&debug, use, DF_REF_REGNO (use));
925 }
926 else if (INSN_P (insn))
927 {
928 bool any_changed;
929
930 /* No matter if the instruction is needed or not, we remove
931 any regno in the defs from the live set. */
932 any_changed = df_word_lr_simulate_defs (insn, local_live);
933 if (any_changed)
934 mark_insn (insn, fast: true);
935
936 /* On the other hand, we do not allow the dead uses to set
937 anything in local_live. */
938 if (marked_insn_p (insn))
939 df_word_lr_simulate_uses (insn, local_live);
940
941 /* Insert debug temps for dead REGs used in subsequent debug
942 insns. We may have to emit a debug temp even if the insn
943 was marked, in case the debug use was after the point of
944 death. */
945 if (debug.used && !bitmap_empty_p (map: debug.used))
946 {
947 df_ref def;
948
949 FOR_EACH_INSN_DEF (def, insn)
950 dead_debug_insert_temp (&debug, DF_REF_REGNO (def), insn,
951 marked_insn_p (insn)
952 && !control_flow_insn_p (insn)
953 ? DEBUG_TEMP_AFTER_WITH_REG_FORCE
954 : DEBUG_TEMP_BEFORE_WITH_VALUE);
955 }
956
957 if (dump_file)
958 {
959 fprintf (stream: dump_file, format: "finished processing insn %d live out = ",
960 INSN_UID (insn));
961 df_print_word_regset (file: dump_file, r: local_live);
962 }
963 }
964
965 block_changed = !bitmap_equal_p (local_live, DF_WORD_LR_IN (bb));
966 if (block_changed)
967 bitmap_copy (DF_WORD_LR_IN (bb), local_live);
968
969 dead_debug_local_finish (&debug, NULL);
970 BITMAP_FREE (local_live);
971 return block_changed;
972}
973
974
975/* Process basic block BB. Return true if the live_in set has
976 changed. REDO_OUT is true if the info at the bottom of the block
977 needs to be recalculated before starting. AU is the proper set of
978 artificial uses. Track global substitution of uses of dead pseudos
979 in debug insns using GLOBAL_DEBUG. */
980
981static bool
982dce_process_block (basic_block bb, bool redo_out, bitmap au,
983 struct dead_debug_global *global_debug)
984{
985 bitmap local_live = BITMAP_ALLOC (obstack: &dce_tmp_bitmap_obstack);
986 rtx_insn *insn;
987 bool block_changed;
988 df_ref def;
989 struct dead_debug_local debug;
990
991 if (redo_out)
992 {
993 /* Need to redo the live_out set of this block if when one of
994 the succs of this block has had a change in it live in
995 set. */
996 edge e;
997 edge_iterator ei;
998 df_confluence_function_n con_fun_n = df_lr->problem->con_fun_n;
999 bitmap_clear (DF_LR_OUT (bb));
1000 FOR_EACH_EDGE (e, ei, bb->succs)
1001 (*con_fun_n) (e);
1002 }
1003
1004 if (dump_file)
1005 {
1006 fprintf (stream: dump_file, format: "processing block %d lr out = ", bb->index);
1007 df_print_regset (file: dump_file, DF_LR_OUT (bb));
1008 }
1009
1010 bitmap_copy (local_live, DF_LR_OUT (bb));
1011
1012 df_simulate_initialize_backwards (bb, local_live);
1013 dead_debug_local_init (&debug, NULL, global_debug);
1014
1015 FOR_BB_INSNS_REVERSE (bb, insn)
1016 if (DEBUG_INSN_P (insn))
1017 {
1018 df_ref use;
1019 FOR_EACH_INSN_USE (use, insn)
1020 if (!bitmap_bit_p (local_live, DF_REF_REGNO (use))
1021 && !bitmap_bit_p (au, DF_REF_REGNO (use)))
1022 dead_debug_add (&debug, use, DF_REF_REGNO (use));
1023 }
1024 else if (INSN_P (insn))
1025 {
1026 bool needed = marked_insn_p (insn);
1027
1028 /* The insn is needed if there is someone who uses the output. */
1029 if (!needed)
1030 FOR_EACH_INSN_DEF (def, insn)
1031 if (bitmap_bit_p (local_live, DF_REF_REGNO (def))
1032 || bitmap_bit_p (au, DF_REF_REGNO (def)))
1033 {
1034 needed = true;
1035 mark_insn (insn, fast: true);
1036 break;
1037 }
1038
1039 /* No matter if the instruction is needed or not, we remove
1040 any regno in the defs from the live set. */
1041 df_simulate_defs (insn, local_live);
1042
1043 /* On the other hand, we do not allow the dead uses to set
1044 anything in local_live. */
1045 if (needed)
1046 df_simulate_uses (insn, local_live);
1047
1048 /* Insert debug temps for dead REGs used in subsequent debug
1049 insns. We may have to emit a debug temp even if the insn
1050 was marked, in case the debug use was after the point of
1051 death. */
1052 if (debug.used && !bitmap_empty_p (map: debug.used))
1053 FOR_EACH_INSN_DEF (def, insn)
1054 dead_debug_insert_temp (&debug, DF_REF_REGNO (def), insn,
1055 needed && !control_flow_insn_p (insn)
1056 ? DEBUG_TEMP_AFTER_WITH_REG_FORCE
1057 : DEBUG_TEMP_BEFORE_WITH_VALUE);
1058 }
1059
1060 dead_debug_local_finish (&debug, NULL);
1061 df_simulate_finalize_backwards (bb, local_live);
1062
1063 block_changed = !bitmap_equal_p (local_live, DF_LR_IN (bb));
1064 if (block_changed)
1065 bitmap_copy (DF_LR_IN (bb), local_live);
1066
1067 BITMAP_FREE (local_live);
1068 return block_changed;
1069}
1070
1071
1072/* Perform fast DCE once initialization is done. If WORD_LEVEL is
1073 true, use the word level dce, otherwise do it at the pseudo
1074 level. */
1075
1076static void
1077fast_dce (bool word_level)
1078{
1079 int *postorder = df_get_postorder (DF_BACKWARD);
1080 int n_blocks = df_get_n_blocks (DF_BACKWARD);
1081 /* The set of blocks that have been seen on this iteration. */
1082 bitmap processed = BITMAP_ALLOC (obstack: &dce_blocks_bitmap_obstack);
1083 /* The set of blocks that need to have the out vectors reset because
1084 the in of one of their successors has changed. */
1085 bitmap redo_out = BITMAP_ALLOC (obstack: &dce_blocks_bitmap_obstack);
1086 bitmap all_blocks = BITMAP_ALLOC (obstack: &dce_blocks_bitmap_obstack);
1087 bool global_changed = true;
1088
1089 /* These regs are considered always live so if they end up dying
1090 because of some def, we need to bring the back again. Calling
1091 df_simulate_fixup_sets has the disadvantage of calling
1092 bb_has_eh_pred once per insn, so we cache the information
1093 here. */
1094 bitmap au = &df->regular_block_artificial_uses;
1095 bitmap au_eh = &df->eh_block_artificial_uses;
1096 int i;
1097 struct dead_debug_global global_debug;
1098
1099 prescan_insns_for_dce (fast: true);
1100
1101 for (i = 0; i < n_blocks; i++)
1102 bitmap_set_bit (all_blocks, postorder[i]);
1103
1104 dead_debug_global_init (&global_debug, NULL);
1105
1106 while (global_changed)
1107 {
1108 global_changed = false;
1109
1110 for (i = 0; i < n_blocks; i++)
1111 {
1112 int index = postorder[i];
1113 basic_block bb = BASIC_BLOCK_FOR_FN (cfun, index);
1114 bool local_changed;
1115
1116 if (index < NUM_FIXED_BLOCKS)
1117 {
1118 bitmap_set_bit (processed, index);
1119 continue;
1120 }
1121
1122 if (word_level)
1123 local_changed
1124 = word_dce_process_block (bb, redo_out: bitmap_bit_p (redo_out, index),
1125 global_debug: &global_debug);
1126 else
1127 local_changed
1128 = dce_process_block (bb, redo_out: bitmap_bit_p (redo_out, index),
1129 au: bb_has_eh_pred (bb) ? au_eh : au,
1130 global_debug: &global_debug);
1131 bitmap_set_bit (processed, index);
1132
1133 if (local_changed)
1134 {
1135 edge e;
1136 edge_iterator ei;
1137 FOR_EACH_EDGE (e, ei, bb->preds)
1138 if (bitmap_bit_p (processed, e->src->index))
1139 /* Be tricky about when we need to iterate the
1140 analysis. We only have redo the analysis if the
1141 bitmaps change at the top of a block that is the
1142 entry to a loop. */
1143 global_changed = true;
1144 else
1145 bitmap_set_bit (redo_out, e->src->index);
1146 }
1147 }
1148
1149 if (global_changed)
1150 {
1151 /* Turn off the RUN_DCE flag to prevent recursive calls to
1152 dce. */
1153 int old_flag = df_clear_flags (DF_LR_RUN_DCE);
1154
1155 /* So something was deleted that requires a redo. Do it on
1156 the cheap. */
1157 delete_unmarked_insns ();
1158 bitmap_clear (marked);
1159 bitmap_clear (processed);
1160 bitmap_clear (redo_out);
1161
1162 /* We do not need to rescan any instructions. We only need
1163 to redo the dataflow equations for the blocks that had a
1164 change at the top of the block. Then we need to redo the
1165 iteration. */
1166 if (word_level)
1167 df_analyze_problem (df_word_lr, all_blocks, postorder, n_blocks);
1168 else
1169 df_analyze_problem (df_lr, all_blocks, postorder, n_blocks);
1170
1171 if (old_flag & DF_LR_RUN_DCE)
1172 df_set_flags (DF_LR_RUN_DCE);
1173
1174 prescan_insns_for_dce (fast: true);
1175 }
1176 }
1177
1178 dead_debug_global_finish (&global_debug, NULL);
1179
1180 delete_unmarked_insns ();
1181
1182 BITMAP_FREE (processed);
1183 BITMAP_FREE (redo_out);
1184 BITMAP_FREE (all_blocks);
1185
1186 /* Both forms of DCE should make further DCE unnecessary. */
1187 df_lr_dce->solutions_dirty = false;
1188}
1189
1190
1191/* Fast register level DCE. */
1192
1193static unsigned int
1194rest_of_handle_fast_dce (void)
1195{
1196 init_dce (fast: true);
1197 fast_dce (word_level: false);
1198 fini_dce (fast: true);
1199 return 0;
1200}
1201
1202
1203/* Fast byte level DCE. */
1204
1205void
1206run_word_dce (void)
1207{
1208 int old_flags;
1209
1210 if (!flag_dce)
1211 return;
1212
1213 timevar_push (tv: TV_DCE);
1214 old_flags = df_clear_flags (DF_DEFER_INSN_RESCAN + DF_NO_INSN_RESCAN);
1215 df_word_lr_add_problem ();
1216 init_dce (fast: true);
1217 fast_dce (word_level: true);
1218 fini_dce (fast: true);
1219 df_set_flags (old_flags);
1220 timevar_pop (tv: TV_DCE);
1221}
1222
1223
1224/* This is an internal call that is used by the df live register
1225 problem to run fast dce as a side effect of creating the live
1226 information. The stack is organized so that the lr problem is run,
1227 this pass is run, which updates the live info and the df scanning
1228 info, and then returns to allow the rest of the problems to be run.
1229
1230 This can be called by elsewhere but it will not update the bit
1231 vectors for any other problems than LR. */
1232
1233void
1234run_fast_df_dce (void)
1235{
1236 if (flag_dce)
1237 {
1238 /* If dce is able to delete something, it has to happen
1239 immediately. Otherwise there will be problems handling the
1240 eq_notes. */
1241 int old_flags =
1242 df_clear_flags (DF_DEFER_INSN_RESCAN + DF_NO_INSN_RESCAN);
1243
1244 df_in_progress = true;
1245 rest_of_handle_fast_dce ();
1246 df_in_progress = false;
1247
1248 df_set_flags (old_flags);
1249 }
1250}
1251
1252
1253/* Run a fast DCE pass. */
1254
1255void
1256run_fast_dce (void)
1257{
1258 if (flag_dce)
1259 rest_of_handle_fast_dce ();
1260}
1261
1262
1263namespace {
1264
1265const pass_data pass_data_fast_rtl_dce =
1266{
1267 .type: RTL_PASS, /* type */
1268 .name: "rtl_dce", /* name */
1269 .optinfo_flags: OPTGROUP_NONE, /* optinfo_flags */
1270 .tv_id: TV_DCE, /* tv_id */
1271 .properties_required: 0, /* properties_required */
1272 .properties_provided: 0, /* properties_provided */
1273 .properties_destroyed: 0, /* properties_destroyed */
1274 .todo_flags_start: 0, /* todo_flags_start */
1275 TODO_df_finish, /* todo_flags_finish */
1276};
1277
1278class pass_fast_rtl_dce : public rtl_opt_pass
1279{
1280public:
1281 pass_fast_rtl_dce (gcc::context *ctxt)
1282 : rtl_opt_pass (pass_data_fast_rtl_dce, ctxt)
1283 {}
1284
1285 /* opt_pass methods: */
1286 bool gate (function *) final override
1287 {
1288 return optimize > 0 && flag_dce && dbg_cnt (index: dce_fast);
1289 }
1290
1291 unsigned int execute (function *) final override
1292 {
1293 return rest_of_handle_fast_dce ();
1294 }
1295
1296}; // class pass_fast_rtl_dce
1297
1298} // anon namespace
1299
1300rtl_opt_pass *
1301make_pass_fast_rtl_dce (gcc::context *ctxt)
1302{
1303 return new pass_fast_rtl_dce (ctxt);
1304}
1305

source code of gcc/dce.cc