dce.c 28.5 KB
Newer Older
1
/* RTL dead code elimination.
2
   Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011
3
   Free Software Foundation, Inc.
4 5 6 7 8

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
9
Software Foundation; either version 3, or (at your option) any later
10 11 12 13 14 15 16 17
version.

GCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

You should have received a copy of the GNU General Public License
18 19
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */
20 21 22 23 24 25 26 27 28 29 30

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "hashtab.h"
#include "tm.h"
#include "rtl.h"
#include "tree.h"
#include "regs.h"
#include "hard-reg-set.h"
#include "flags.h"
31
#include "except.h"
32 33 34 35 36 37
#include "df.h"
#include "cselib.h"
#include "dce.h"
#include "timevar.h"
#include "tree-pass.h"
#include "dbgcnt.h"
38
#include "tm_p.h"
39
#include "emit-rtl.h"  /* FIXME: Can go away once crtl is moved to rtl.h.  */
40 41 42 43 44 45


/* -------------------------------------------------------------------------
   Core mark/delete routines
   ------------------------------------------------------------------------- */

46 47
/* True if we are invoked while the df engine is running; in this case,
   we don't want to reenter it.  */
48 49 50 51 52 53
static bool df_in_progress = false;

/* Instructions that have been marked but whose dependencies have not
   yet been processed.  */
static VEC(rtx,heap) *worklist;

54 55 56 57
/* Bitmap of instructions marked as needed indexed by INSN_UID.  */
static sbitmap marked;

/* Bitmap obstacks used for block processing by the fast algorithm.  */
58 59 60
static bitmap_obstack dce_blocks_bitmap_obstack;
static bitmap_obstack dce_tmp_bitmap_obstack;

61
static bool find_call_stack_args (rtx, bool, bool, bitmap);
62

Richard Sandiford committed
63 64 65
/* A subroutine for which BODY is part of the instruction being tested;
   either the top-level pattern, or an element of a PARALLEL.  The
   instruction is known not to be a bare USE or CLOBBER.  */
66 67

static bool
Richard Sandiford committed
68
deletable_insn_p_1 (rtx body)
69
{
70
  switch (GET_CODE (body))
71 72 73 74 75 76 77 78 79 80 81 82
    {
    case PREFETCH:
    case TRAP_IF:
      /* The UNSPEC case was added here because the ia-64 claims that
	 USEs do not work after reload and generates UNSPECS rather
	 than USEs.  Since dce is run after reload we need to avoid
	 deleting these even if they are dead.  If it turns out that
	 USEs really do work after reload, the ia-64 should be
	 changed, and the UNSPEC case can be removed.  */
    case UNSPEC:
      return false;

Richard Sandiford committed
83
    default:
84
      return !volatile_refs_p (body);
Richard Sandiford committed
85 86 87
    }
}

88

Richard Sandiford committed
89 90 91 92
/* Return true if INSN is a normal instruction that can be deleted by
   the DCE pass.  */

static bool
93
deletable_insn_p (rtx insn, bool fast, bitmap arg_stores)
Richard Sandiford committed
94 95 96 97
{
  rtx body, x;
  int i;

98 99 100 101 102 103 104
  if (CALL_P (insn)
      /* We cannot delete calls inside of the recursive dce because
	 this may cause basic blocks to be deleted and this messes up
	 the rest of the stack of optimization passes.  */
      && (!df_in_progress)
      /* We cannot delete pure or const sibling calls because it is
	 hard to see the result.  */
Kenneth Zadeck committed
105
      && (!SIBLING_CALL_P (insn))
106 107
      /* We can delete dead const or pure calls as long as they do not
         infinite loop.  */
Kenneth Zadeck committed
108 109
      && (RTL_CONST_OR_PURE_CALL_P (insn)
	  && !RTL_LOOPING_CONST_OR_PURE_CALL_P (insn)))
110
    return find_call_stack_args (insn, false, fast, arg_stores);
Kenneth Zadeck committed
111

112 113 114 115 116 117 118 119
  /* Don't delete jumps, notes and the like.  */
  if (!NONJUMP_INSN_P (insn))
    return false;

  /* Don't delete insns that can throw.  */
  if (!insn_nothrow_p (insn))
    return false;

Richard Sandiford committed
120 121 122 123
  body = PATTERN (insn);
  switch (GET_CODE (body))
    {
    case USE:
124
    case VAR_LOCATION:
Richard Sandiford committed
125 126
      return false;

127 128 129 130 131 132
    case CLOBBER:
      if (fast)
	{
	  /* A CLOBBER of a dead pseudo register serves no purpose.
	     That is not necessarily true for hard registers until
	     after reload.  */
133
	  x = XEXP (body, 0);
134 135
	  return REG_P (x) && (!HARD_REGISTER_P (x) || reload_completed);
	}
Richard Sandiford committed
136
      else
137 138 139 140 141
	/* Because of the way that use-def chains are built, it is not
	   possible to tell if the clobber is dead because it can
	   never be the target of a use-def chain.  */
	return false;

142
    case PARALLEL:
Richard Sandiford committed
143 144 145 146
      for (i = XVECLEN (body, 0) - 1; i >= 0; i--)
	if (!deletable_insn_p_1 (XVECEXP (body, 0, i)))
	  return false;
      return true;
147

148
    default:
Richard Sandiford committed
149
      return deletable_insn_p_1 (body);
150 151 152 153
    }
}


154
/* Return true if INSN has been marked as needed.  */
155 156 157 158

static inline int
marked_insn_p (rtx insn)
{
159 160 161 162
  /* Artificial defs are always needed and they do not have an insn.
     We should never see them here.  */
  gcc_assert (insn);
  return TEST_BIT (marked, INSN_UID (insn));
163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178
}


/* If INSN has not yet been marked as needed, mark it now, and add it to
   the worklist.  */

static void
mark_insn (rtx insn, bool fast)
{
  if (!marked_insn_p (insn))
    {
      if (!fast)
	VEC_safe_push (rtx, heap, worklist, insn);
      SET_BIT (marked, INSN_UID (insn));
      if (dump_file)
	fprintf (dump_file, "  Adding insn %d to worklist\n", INSN_UID (insn));
179 180 181 182 183 184
      if (CALL_P (insn)
	  && !df_in_progress
	  && !SIBLING_CALL_P (insn)
	  && (RTL_CONST_OR_PURE_CALL_P (insn)
	      && !RTL_LOOPING_CONST_OR_PURE_CALL_P (insn)))
	find_call_stack_args (insn, true, fast, NULL);
185 186 187 188 189 190 191 192
    }
}


/* A note_stores callback used by mark_nonreg_stores.  DATA is the
   instruction containing DEST.  */

static void
193
mark_nonreg_stores_1 (rtx dest, const_rtx pattern, void *data)
194 195 196 197 198 199 200 201 202 203
{
  if (GET_CODE (pattern) != CLOBBER && !REG_P (dest))
    mark_insn ((rtx) data, true);
}


/* A note_stores callback used by mark_nonreg_stores.  DATA is the
   instruction containing DEST.  */

static void
204
mark_nonreg_stores_2 (rtx dest, const_rtx pattern, void *data)
205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222
{
  if (GET_CODE (pattern) != CLOBBER && !REG_P (dest))
    mark_insn ((rtx) data, false);
}


/* Mark INSN if BODY stores to a non-register destination.  */

static void
mark_nonreg_stores (rtx body, rtx insn, bool fast)
{
  if (fast)
    note_stores (body, mark_nonreg_stores_1, insn);
  else
    note_stores (body, mark_nonreg_stores_2, insn);
}


223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242
/* Return true if store to MEM, starting OFF bytes from stack pointer,
   is a call argument store, and clear corresponding bits from SP_BYTES
   bitmap if it is.  */

static bool
check_argument_store (rtx mem, HOST_WIDE_INT off, HOST_WIDE_INT min_sp_off,
		      HOST_WIDE_INT max_sp_off, bitmap sp_bytes)
{
  HOST_WIDE_INT byte;
  for (byte = off; byte < off + GET_MODE_SIZE (GET_MODE (mem)); byte++)
    {
      if (byte < min_sp_off
	  || byte >= max_sp_off
	  || !bitmap_clear_bit (sp_bytes, byte - min_sp_off))
	return false;
    }
  return true;
}


243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374
/* Try to find all stack stores of CALL_INSN arguments if
   ACCUMULATE_OUTGOING_ARGS.  If all stack stores have been found
   and it is therefore safe to eliminate the call, return true,
   otherwise return false.  This function should be first called
   with DO_MARK false, and only when the CALL_INSN is actually
   going to be marked called again with DO_MARK true.  */

static bool
find_call_stack_args (rtx call_insn, bool do_mark, bool fast,
		      bitmap arg_stores)
{
  rtx p, insn, prev_insn;
  bool ret;
  HOST_WIDE_INT min_sp_off, max_sp_off;
  bitmap sp_bytes;

  gcc_assert (CALL_P (call_insn));
  if (!ACCUMULATE_OUTGOING_ARGS)
    return true;

  if (!do_mark)
    {
      gcc_assert (arg_stores);
      bitmap_clear (arg_stores);
    }

  min_sp_off = INTTYPE_MAXIMUM (HOST_WIDE_INT);
  max_sp_off = 0;

  /* First determine the minimum and maximum offset from sp for
     stored arguments.  */
  for (p = CALL_INSN_FUNCTION_USAGE (call_insn); p; p = XEXP (p, 1))
    if (GET_CODE (XEXP (p, 0)) == USE
	&& MEM_P (XEXP (XEXP (p, 0), 0)))
      {
	rtx mem = XEXP (XEXP (p, 0), 0), addr, size;
	HOST_WIDE_INT off = 0;
	size = MEM_SIZE (mem);
	if (size == NULL_RTX)
	  return false;
	addr = XEXP (mem, 0);
	if (GET_CODE (addr) == PLUS
	    && REG_P (XEXP (addr, 0))
	    && CONST_INT_P (XEXP (addr, 1)))
	  {
	    off = INTVAL (XEXP (addr, 1));
	    addr = XEXP (addr, 0);
	  }
	if (addr != stack_pointer_rtx)
	  {
	    if (!REG_P (addr))
	      return false;
	    /* If not fast, use chains to see if addr wasn't set to
	       sp + offset.  */
	    if (!fast)
	      {
		df_ref *use_rec;
		struct df_link *defs;
		rtx set;

		for (use_rec = DF_INSN_USES (call_insn); *use_rec; use_rec++)
		  if (rtx_equal_p (addr, DF_REF_REG (*use_rec)))
		    break;

		if (*use_rec == NULL)
		  return false;

		for (defs = DF_REF_CHAIN (*use_rec); defs; defs = defs->next)
		  if (! DF_REF_IS_ARTIFICIAL (defs->ref))
		    break;

		if (defs == NULL)
		  return false;

		set = single_set (DF_REF_INSN (defs->ref));
		if (!set)
		  return false;

		if (GET_CODE (SET_SRC (set)) != PLUS
		    || XEXP (SET_SRC (set), 0) != stack_pointer_rtx
		    || !CONST_INT_P (XEXP (SET_SRC (set), 1)))
		  return false;

		off += INTVAL (XEXP (SET_SRC (set), 1));
	      }
	    else
	      return false;
	  }
	min_sp_off = MIN (min_sp_off, off);
	max_sp_off = MAX (max_sp_off, off + INTVAL (size));
      }

  if (min_sp_off >= max_sp_off)
    return true;
  sp_bytes = BITMAP_ALLOC (NULL);

  /* Set bits in SP_BYTES bitmap for bytes relative to sp + min_sp_off
     which contain arguments.  Checking has been done in the previous
     loop.  */
  for (p = CALL_INSN_FUNCTION_USAGE (call_insn); p; p = XEXP (p, 1))
    if (GET_CODE (XEXP (p, 0)) == USE
	&& MEM_P (XEXP (XEXP (p, 0), 0)))
      {
	rtx mem = XEXP (XEXP (p, 0), 0), addr;
	HOST_WIDE_INT off = 0, byte;
	addr = XEXP (mem, 0);
	if (GET_CODE (addr) == PLUS
	    && REG_P (XEXP (addr, 0))
	    && CONST_INT_P (XEXP (addr, 1)))
	  {
	    off = INTVAL (XEXP (addr, 1));
	    addr = XEXP (addr, 0);
	  }
	if (addr != stack_pointer_rtx)
	  {
	    df_ref *use_rec;
	    struct df_link *defs;
	    rtx set;

	    for (use_rec = DF_INSN_USES (call_insn); *use_rec; use_rec++)
	      if (rtx_equal_p (addr, DF_REF_REG (*use_rec)))
		break;

	    for (defs = DF_REF_CHAIN (*use_rec); defs; defs = defs->next)
	      if (! DF_REF_IS_ARTIFICIAL (defs->ref))
		break;

	    set = single_set (DF_REF_INSN (defs->ref));
	    off += INTVAL (XEXP (SET_SRC (set), 1));
	  }
	for (byte = off; byte < off + INTVAL (MEM_SIZE (mem)); byte++)
	  {
375 376
	    if (!bitmap_set_bit (sp_bytes, byte - min_sp_off))
	      gcc_unreachable ();
377 378 379 380
	  }
      }

  /* Walk backwards, looking for argument stores.  The search stops
381
     when seeing another call, sp adjustment or memory store other than
382 383 384 385 386
     argument store.  */
  ret = false;
  for (insn = PREV_INSN (call_insn); insn; insn = prev_insn)
    {
      rtx set, mem, addr;
387
      HOST_WIDE_INT off;
388 389 390 391 392 393 394 395 396

      if (insn == BB_HEAD (BLOCK_FOR_INSN (call_insn)))
	prev_insn = NULL_RTX;
      else
	prev_insn = PREV_INSN (insn);

      if (CALL_P (insn))
	break;

397
      if (!NONDEBUG_INSN_P (insn))
398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455
	continue;

      set = single_set (insn);
      if (!set || SET_DEST (set) == stack_pointer_rtx)
	break;

      if (!MEM_P (SET_DEST (set)))
	continue;

      mem = SET_DEST (set);
      addr = XEXP (mem, 0);
      off = 0;
      if (GET_CODE (addr) == PLUS
	  && REG_P (XEXP (addr, 0))
	  && CONST_INT_P (XEXP (addr, 1)))
	{
	  off = INTVAL (XEXP (addr, 1));
	  addr = XEXP (addr, 0);
	}
      if (addr != stack_pointer_rtx)
	{
	  if (!REG_P (addr))
	    break;
	  if (!fast)
	    {
	      df_ref *use_rec;
	      struct df_link *defs;
	      rtx set;

	      for (use_rec = DF_INSN_USES (insn); *use_rec; use_rec++)
		if (rtx_equal_p (addr, DF_REF_REG (*use_rec)))
		  break;

	      if (*use_rec == NULL)
		break;

	      for (defs = DF_REF_CHAIN (*use_rec); defs; defs = defs->next)
		if (! DF_REF_IS_ARTIFICIAL (defs->ref))
		  break;

	      if (defs == NULL)
		break;

	      set = single_set (DF_REF_INSN (defs->ref));
	      if (!set)
		break;

	      if (GET_CODE (SET_SRC (set)) != PLUS
		  || XEXP (SET_SRC (set), 0) != stack_pointer_rtx
		  || !CONST_INT_P (XEXP (SET_SRC (set), 1)))
		break;

	      off += INTVAL (XEXP (SET_SRC (set), 1));
	    }
	  else
	    break;
	}

456 457 458
      if (GET_MODE_SIZE (GET_MODE (mem)) == 0
	  || !check_argument_store (mem, off, min_sp_off,
				    max_sp_off, sp_bytes))
459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483
	break;

      if (!deletable_insn_p (insn, fast, NULL))
	break;

      if (do_mark)
	mark_insn (insn, fast);
      else
	bitmap_set_bit (arg_stores, INSN_UID (insn));

      if (bitmap_empty_p (sp_bytes))
	{
	  ret = true;
	  break;
	}
    }

  BITMAP_FREE (sp_bytes);
  if (!ret && arg_stores)
    bitmap_clear (arg_stores);

  return ret;
}


484 485
/* Remove all REG_EQUAL and REG_EQUIV notes referring to the registers INSN
   writes to.  */
486 487

static void
488
remove_reg_equal_equiv_notes_for_defs (rtx insn)
489
{
490
  df_ref *def_rec;
491

492
  for (def_rec = DF_INSN_DEFS (insn); *def_rec; def_rec++)
493
    remove_reg_equal_equiv_notes_for_regno (DF_REF_REGNO (*def_rec));
494 495 496
}


497
/* Delete every instruction that hasn't been marked.  */
498 499 500 501 502 503

static void
delete_unmarked_insns (void)
{
  basic_block bb;
  rtx insn, next;
504
  bool must_clean = false;
505

506 507
  FOR_EACH_BB_REVERSE (bb)
    FOR_BB_INSNS_REVERSE_SAFE (bb, insn, next)
508 509
      if (INSN_P (insn))
	{
510
	  /* Always delete no-op moves.  */
511
	  if (noop_move_p (insn))
512 513 514
	    ;

	  /* Otherwise rely only on the DCE algorithm.  */
515 516 517
	  else if (marked_insn_p (insn))
	    continue;

518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535
	  /* Beware that reaching a dbg counter limit here can result
	     in miscompiled file.  This occurs when a group of insns
	     must be deleted together, typically because the kept insn
	     depends on the output from the deleted insn.  Deleting
	     this insns in reverse order (both at the bb level and
	     when looking at the blocks) minimizes this, but does not
	     eliminate it, since it is possible for the using insn to
	     be top of a block and the producer to be at the bottom of
	     the block.  However, in most cases this will only result
	     in an uninitialized use of an insn that is dead anyway.

	     However, there is one rare case that will cause a
	     miscompile: deletion of non-looping pure and constant
	     calls on a machine where ACCUMULATE_OUTGOING_ARGS is true.
	     In this case it is possible to remove the call, but leave
	     the argument pushes to the stack.  Because of the changes
	     to the stack pointer, this will almost always lead to a
	     miscompile.  */
536 537 538 539 540 541
	  if (!dbg_cnt (dce))
	    continue;

	  if (dump_file)
	    fprintf (dump_file, "DCE: Deleting insn %d\n", INSN_UID (insn));

542
	  /* Before we delete the insn we have to remove the REG_EQUAL notes
543
	     for the destination regs in order to avoid dangling notes.  */
544
	  remove_reg_equal_equiv_notes_for_defs (insn);
545

546 547 548 549 550 551
	  /* If a pure or const call is deleted, this may make the cfg
	     have unreachable blocks.  We rememeber this and call
	     delete_unreachable_blocks at the end.  */
	  if (CALL_P (insn))
	    must_clean = true;

552
	  /* Now delete the insn.  */
553 554
	  delete_insn_and_edges (insn);
	}
555 556 557 558

  /* Deleted a pure or const call.  */
  if (must_clean)
    delete_unreachable_blocks ();
559 560 561 562 563 564 565 566 567 568 569
}


/* Go through the instructions and mark those whose necessity is not
   dependent on inter-instruction information.  Make sure all other
   instructions are not marked.  */

static void
prescan_insns_for_dce (bool fast)
{
  basic_block bb;
570 571 572
  rtx insn, prev;
  bitmap arg_stores = NULL;

573 574
  if (dump_file)
    fprintf (dump_file, "Finding needed instructions:\n");
575 576 577 578

  if (!df_in_progress && ACCUMULATE_OUTGOING_ARGS)
    arg_stores = BITMAP_ALLOC (NULL);

579
  FOR_EACH_BB (bb)
580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600
    {
      FOR_BB_INSNS_REVERSE_SAFE (bb, insn, prev)
	if (INSN_P (insn))
	  {
	    /* Don't mark argument stores now.  They will be marked
	       if needed when the associated CALL is marked.  */
	    if (arg_stores && bitmap_bit_p (arg_stores, INSN_UID (insn)))
	      continue;
	    if (deletable_insn_p (insn, fast, arg_stores))
	      mark_nonreg_stores (PATTERN (insn), insn, fast);
	    else
	      mark_insn (insn, fast);
	  }
      /* find_call_stack_args only looks at argument stores in the
	 same bb.  */
      if (arg_stores)
	bitmap_clear (arg_stores);
    }

  if (arg_stores)
    BITMAP_FREE (arg_stores);
601 602 603 604 605 606 607 608

  if (dump_file)
    fprintf (dump_file, "Finished finding needed instructions:\n");
}


/* UD-based DSE routines. */

609
/* Mark instructions that define artificially-used registers, such as
610 611 612 613 614 615 616
   the frame pointer and the stack pointer.  */

static void
mark_artificial_uses (void)
{
  basic_block bb;
  struct df_link *defs;
617
  df_ref *use_rec;
618 619 620

  FOR_ALL_BB (bb)
    {
H.J. Lu committed
621
      for (use_rec = df_get_artificial_uses (bb->index);
622 623
	   *use_rec; use_rec++)
	for (defs = DF_REF_CHAIN (*use_rec); defs; defs = defs->next)
624 625
	  if (! DF_REF_IS_ARTIFICIAL (defs->ref))
	    mark_insn (DF_REF_INSN (defs->ref), false);
626 627 628
    }
}

629

630 631 632 633 634 635
/* Mark every instruction that defines a register value that INSN uses.  */

static void
mark_reg_dependencies (rtx insn)
{
  struct df_link *defs;
636
  df_ref *use_rec;
637

638 639 640
  if (DEBUG_INSN_P (insn))
    return;

641 642
  for (use_rec = DF_INSN_USES (insn); *use_rec; use_rec++)
    {
643
      df_ref use = *use_rec;
644 645 646 647 648 649 650
      if (dump_file)
	{
	  fprintf (dump_file, "Processing use of ");
	  print_simple_rtl (dump_file, DF_REF_REG (use));
	  fprintf (dump_file, " in insn %d:\n", INSN_UID (insn));
	}
      for (defs = DF_REF_CHAIN (use); defs; defs = defs->next)
651 652
	if (! DF_REF_IS_ARTIFICIAL (defs->ref))
	  mark_insn (DF_REF_INSN (defs->ref), false);
653 654 655 656
    }
}


657 658
/* Initialize global variables for a new DCE pass.  */

659
static void
660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686
init_dce (bool fast)
{
  if (!df_in_progress)
    {
      if (!fast)
	df_chain_add_problem (DF_UD_CHAIN);
      df_analyze ();
    }

  if (dump_file)
    df_dump (dump_file);

  if (fast)
    {
      bitmap_obstack_initialize (&dce_blocks_bitmap_obstack);
      bitmap_obstack_initialize (&dce_tmp_bitmap_obstack);
    }

  marked = sbitmap_alloc (get_max_uid () + 1);
  sbitmap_zero (marked);
}


/* Free the data allocated by init_dce.  */

static void
fini_dce (bool fast)
687 688
{
  sbitmap_free (marked);
689 690 691 692 693 694

  if (fast)
    {
      bitmap_obstack_release (&dce_blocks_bitmap_obstack);
      bitmap_obstack_release (&dce_tmp_bitmap_obstack);
    }
695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713
}


/* UD-chain based DCE.  */

static unsigned int
rest_of_handle_ud_dce (void)
{
  rtx insn;

  init_dce (false);

  prescan_insns_for_dce (false);
  mark_artificial_uses ();
  while (VEC_length (rtx, worklist) > 0)
    {
      insn = VEC_pop (rtx, worklist);
      mark_reg_dependencies (insn);
    }
714
  VEC_free (rtx, heap, worklist);
715

716 717 718 719 720
  /* Before any insns are deleted, we must remove the chains since
     they are not bidirectional.  */
  df_remove_problem (df_chain);
  delete_unmarked_insns ();

721
  fini_dce (false);
722 723 724 725 726 727 728
  return 0;
}


static bool
gate_ud_dce (void)
{
729 730
  return optimize > 1 && flag_dce
    && dbg_cnt (dce_ud);
731 732
}

733
struct rtl_opt_pass pass_ud_rtl_dce =
734
{
735 736
 {
  RTL_PASS,
737 738 739
  "ud dce",                             /* name */
  gate_ud_dce,                          /* gate */
  rest_of_handle_ud_dce,                /* execute */
740 741 742 743 744 745 746 747 748
  NULL,                                 /* sub */
  NULL,                                 /* next */
  0,                                    /* static_pass_number */
  TV_DCE,                               /* tv_id */
  0,                                    /* properties_required */
  0,                                    /* properties_provided */
  0,                                    /* properties_destroyed */
  0,                                    /* todo_flags_start */
  TODO_dump_func |
749
  TODO_df_finish | TODO_verify_rtl_sharing |
750 751
  TODO_ggc_collect                     /* todo_flags_finish */
 }
752 753
};

754

755 756 757 758
/* -------------------------------------------------------------------------
   Fast DCE functions
   ------------------------------------------------------------------------- */

759 760 761 762
/* Process basic block BB.  Return true if the live_in set has
   changed. REDO_OUT is true if the info at the bottom of the block
   needs to be recalculated before starting.  AU is the proper set of
   artificial uses. */
763 764

static bool
765
word_dce_process_block (basic_block bb, bool redo_out)
766 767 768 769 770 771 772 773 774 775 776 777
{
  bitmap local_live = BITMAP_ALLOC (&dce_tmp_bitmap_obstack);
  rtx insn;
  bool block_changed;

  if (redo_out)
    {
      /* Need to redo the live_out set of this block if when one of
	 the succs of this block has had a change in it live in
	 set.  */
      edge e;
      edge_iterator ei;
778 779
      df_confluence_function_n con_fun_n = df_word_lr->problem->con_fun_n;
      bitmap_clear (DF_WORD_LR_OUT (bb));
780 781 782 783 784 785 786
      FOR_EACH_EDGE (e, ei, bb->succs)
	(*con_fun_n) (e);
    }

  if (dump_file)
    {
      fprintf (dump_file, "processing block %d live out = ", bb->index);
787
      df_print_word_regset (dump_file, DF_WORD_LR_OUT (bb));
788 789
    }

790
  bitmap_copy (local_live, DF_WORD_LR_OUT (bb));
791 792

  FOR_BB_INSNS_REVERSE (bb, insn)
793
    if (NONDEBUG_INSN_P (insn))
794
      {
795
	bool any_changed;
796 797
	/* No matter if the instruction is needed or not, we remove
	   any regno in the defs from the live set.  */
798 799 800
	any_changed = df_word_lr_simulate_defs (insn, local_live);
	if (any_changed)
	  mark_insn (insn, true);
801 802 803 804

	/* On the other hand, we do not allow the dead uses to set
	   anything in local_live.  */
	if (marked_insn_p (insn))
805
	  df_word_lr_simulate_uses (insn, local_live);
806 807 808

	if (dump_file)
	  {
H.J. Lu committed
809
	    fprintf (dump_file, "finished processing insn %d live out = ",
810
		     INSN_UID (insn));
811
	    df_print_word_regset (dump_file, local_live);
812 813
	  }
      }
H.J. Lu committed
814

815
  block_changed = !bitmap_equal_p (local_live, DF_WORD_LR_IN (bb));
816
  if (block_changed)
817 818
    bitmap_copy (DF_WORD_LR_IN (bb), local_live);

819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834
  BITMAP_FREE (local_live);
  return block_changed;
}


/* Process basic block BB.  Return true if the live_in set has
   changed. REDO_OUT is true if the info at the bottom of the block
   needs to be recalculated before starting.  AU is the proper set of
   artificial uses. */

static bool
dce_process_block (basic_block bb, bool redo_out, bitmap au)
{
  bitmap local_live = BITMAP_ALLOC (&dce_tmp_bitmap_obstack);
  rtx insn;
  bool block_changed;
835
  df_ref *def_rec;
836

837
  if (redo_out)
838
    {
839 840 841 842 843 844 845 846 847
      /* Need to redo the live_out set of this block if when one of
	 the succs of this block has had a change in it live in
	 set.  */
      edge e;
      edge_iterator ei;
      df_confluence_function_n con_fun_n = df_lr->problem->con_fun_n;
      bitmap_clear (DF_LR_OUT (bb));
      FOR_EACH_EDGE (e, ei, bb->succs)
	(*con_fun_n) (e);
848 849
    }

850
  if (dump_file)
851
    {
852
      fprintf (dump_file, "processing block %d lr out = ", bb->index);
853
      df_print_regset (dump_file, DF_LR_OUT (bb));
854 855
    }

856 857
  bitmap_copy (local_live, DF_LR_OUT (bb));

858
  df_simulate_initialize_backwards (bb, local_live);
859

860 861 862
  FOR_BB_INSNS_REVERSE (bb, insn)
    if (INSN_P (insn))
      {
863
	bool needed = marked_insn_p (insn);
864 865

	/* The insn is needed if there is someone who uses the output.  */
866 867 868 869 870 871 872 873 874
	if (!needed)
	  for (def_rec = DF_INSN_DEFS (insn); *def_rec; def_rec++)
	    if (bitmap_bit_p (local_live, DF_REF_REGNO (*def_rec))
		|| bitmap_bit_p (au, DF_REF_REGNO (*def_rec)))
	      {
		needed = true;
		mark_insn (insn, true);
		break;
	      }
H.J. Lu committed
875

876 877 878 879 880 881
	/* No matter if the instruction is needed or not, we remove
	   any regno in the defs from the live set.  */
	df_simulate_defs (insn, local_live);

	/* On the other hand, we do not allow the dead uses to set
	   anything in local_live.  */
882
	if (needed)
883 884
	  df_simulate_uses (insn, local_live);
      }
H.J. Lu committed
885

886
  df_simulate_finalize_backwards (bb, local_live);
887 888 889 890 891 892 893 894 895

  block_changed = !bitmap_equal_p (local_live, DF_LR_IN (bb));
  if (block_changed)
    bitmap_copy (DF_LR_IN (bb), local_live);

  BITMAP_FREE (local_live);
  return block_changed;
}

896

897 898
/* Perform fast DCE once initialization is done.  If WORD_LEVEL is
   true, use the word level dce, otherwise do it at the pseudo
899
   level.  */
900

901
static void
902
fast_dce (bool word_level)
903 904 905 906 907 908 909 910 911 912
{
  int *postorder = df_get_postorder (DF_BACKWARD);
  int n_blocks = df_get_n_blocks (DF_BACKWARD);
  /* The set of blocks that have been seen on this iteration.  */
  bitmap processed = BITMAP_ALLOC (&dce_blocks_bitmap_obstack);
  /* The set of blocks that need to have the out vectors reset because
     the in of one of their successors has changed.  */
  bitmap redo_out = BITMAP_ALLOC (&dce_blocks_bitmap_obstack);
  bitmap all_blocks = BITMAP_ALLOC (&dce_blocks_bitmap_obstack);
  bool global_changed = true;
913 914 915 916 917 918

  /* These regs are considered always live so if they end up dying
     because of some def, we need to bring the back again.  Calling
     df_simulate_fixup_sets has the disadvantage of calling
     bb_has_eh_pred once per insn, so we cache the information
     here.  */
919 920
  bitmap au = &df->regular_block_artificial_uses;
  bitmap au_eh = &df->eh_block_artificial_uses;
921
  int i;
922 923 924 925 926 927 928 929 930

  prescan_insns_for_dce (true);

  for (i = 0; i < n_blocks; i++)
    bitmap_set_bit (all_blocks, postorder[i]);

  while (global_changed)
    {
      global_changed = false;
931

932 933 934 935 936 937 938 939 940 941 942 943
      for (i = 0; i < n_blocks; i++)
	{
	  int index = postorder[i];
	  basic_block bb = BASIC_BLOCK (index);
	  bool local_changed;

	  if (index < NUM_FIXED_BLOCKS)
	    {
	      bitmap_set_bit (processed, index);
	      continue;
	    }

944
	  if (word_level)
H.J. Lu committed
945
	    local_changed
946
	      = word_dce_process_block (bb, bitmap_bit_p (redo_out, index));
947
	  else
H.J. Lu committed
948
	    local_changed
949 950
	      = dce_process_block (bb, bitmap_bit_p (redo_out, index),
				   bb_has_eh_pred (bb) ? au_eh : au);
951
	  bitmap_set_bit (processed, index);
H.J. Lu committed
952

953 954 955 956 957 958 959 960 961 962 963 964 965 966 967
	  if (local_changed)
	    {
	      edge e;
	      edge_iterator ei;
	      FOR_EACH_EDGE (e, ei, bb->preds)
		if (bitmap_bit_p (processed, e->src->index))
		  /* Be tricky about when we need to iterate the
		     analysis.  We only have redo the analysis if the
		     bitmaps change at the top of a block that is the
		     entry to a loop.  */
		  global_changed = true;
		else
		  bitmap_set_bit (redo_out, e->src->index);
	    }
	}
H.J. Lu committed
968

969 970 971 972 973 974 975 976 977 978 979 980
      if (global_changed)
	{
	  /* Turn off the RUN_DCE flag to prevent recursive calls to
	     dce.  */
	  int old_flag = df_clear_flags (DF_LR_RUN_DCE);

	  /* So something was deleted that requires a redo.  Do it on
	     the cheap.  */
	  delete_unmarked_insns ();
	  sbitmap_zero (marked);
	  bitmap_clear (processed);
	  bitmap_clear (redo_out);
H.J. Lu committed
981

982 983 984
	  /* We do not need to rescan any instructions.  We only need
	     to redo the dataflow equations for the blocks that had a
	     change at the top of the block.  Then we need to redo the
H.J. Lu committed
985
	     iteration.  */
986 987
	  if (word_level)
	    df_analyze_problem (df_word_lr, all_blocks, postorder, n_blocks);
988 989
	  else
	    df_analyze_problem (df_lr, all_blocks, postorder, n_blocks);
990 991 992

	  if (old_flag & DF_LR_RUN_DCE)
	    df_set_flags (DF_LR_RUN_DCE);
993

994 995 996 997 998 999 1000 1001 1002 1003 1004 1005
	  prescan_insns_for_dce (true);
	}
    }

  delete_unmarked_insns ();

  BITMAP_FREE (processed);
  BITMAP_FREE (redo_out);
  BITMAP_FREE (all_blocks);
}


1006
/* Fast register level DCE.  */
1007 1008 1009 1010 1011

static unsigned int
rest_of_handle_fast_dce (void)
{
  init_dce (true);
1012 1013 1014 1015 1016 1017 1018 1019
  fast_dce (false);
  fini_dce (true);
  return 0;
}


/* Fast byte level DCE.  */

1020 1021
void
run_word_dce (void)
1022
{
1023 1024 1025 1026 1027
  int old_flags;

  if (!flag_dce)
    return;

1028
  timevar_push (TV_DCE);
1029
  old_flags = df_clear_flags (DF_DEFER_INSN_RESCAN + DF_NO_INSN_RESCAN);
1030
  df_word_lr_add_problem ();
1031 1032
  init_dce (true);
  fast_dce (true);
1033
  fini_dce (true);
1034
  df_set_flags (old_flags);
1035
  timevar_pop (TV_DCE);
1036 1037 1038 1039 1040 1041 1042 1043 1044 1045
}


/* This is an internal call that is used by the df live register
   problem to run fast dce as a side effect of creating the live
   information.  The stack is organized so that the lr problem is run,
   this pass is run, which updates the live info and the df scanning
   info, and then returns to allow the rest of the problems to be run.

   This can be called by elsewhere but it will not update the bit
1046
   vectors for any other problems than LR.  */
1047 1048 1049 1050 1051 1052 1053 1054 1055

void
run_fast_df_dce (void)
{
  if (flag_dce)
    {
      /* If dce is able to delete something, it has to happen
	 immediately.  Otherwise there will be problems handling the
	 eq_notes.  */
1056 1057 1058
      int old_flags =
	df_clear_flags (DF_DEFER_INSN_RESCAN + DF_NO_INSN_RESCAN);

1059 1060
      df_in_progress = true;
      rest_of_handle_fast_dce ();
1061 1062
      df_in_progress = false;

1063 1064 1065 1066
      df_set_flags (old_flags);
    }
}

1067

1068 1069 1070 1071
/* Run a fast DCE pass.  */

void
run_fast_dce (void)
1072
{
1073 1074
  if (flag_dce)
    rest_of_handle_fast_dce ();
1075 1076 1077
}


1078 1079
static bool
gate_fast_dce (void)
1080
{
1081 1082
  return optimize > 0 && flag_dce
    && dbg_cnt (dce_fast);
1083 1084
}

1085
struct rtl_opt_pass pass_fast_rtl_dce =
1086
{
1087 1088
 {
  RTL_PASS,
1089
  "rtl dce",                            /* name */
1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100
  gate_fast_dce,                        /* gate */
  rest_of_handle_fast_dce,              /* execute */
  NULL,                                 /* sub */
  NULL,                                 /* next */
  0,                                    /* static_pass_number */
  TV_DCE,                               /* tv_id */
  0,                                    /* properties_required */
  0,                                    /* properties_provided */
  0,                                    /* properties_destroyed */
  0,                                    /* todo_flags_start */
  TODO_dump_func |
1101
  TODO_df_finish | TODO_verify_rtl_sharing |
1102 1103
  TODO_ggc_collect                      /* todo_flags_finish */
 }
1104
};