gcc/combine-stack-adj.cc

   1 /* Combine stack adjustments.
   2    Copyright (C) 1987-2022 Free Software Foundation, Inc.
   3
   4 This file is part of GCC.
   5
   6 GCC is free software; you can redistribute it and/or modify it under
   7 the terms of the GNU General Public License as published by the Free
   8 Software Foundation; either version 3, or (at your option) any later
   9 version.
  10
  11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14 for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GCC; see the file COPYING3.  If not see
  18 <http://www.gnu.org/licenses/>.  */
  19
  20 /* Track stack adjustments and stack memory references.  Attempt to
  21    reduce the number of stack adjustments by back-propagating across
  22    the memory references.
  23
  24    This is intended primarily for use with targets that do not define
  25    ACCUMULATE_OUTGOING_ARGS.  It is of significantly more value to
  26    targets that define PREFERRED_STACK_BOUNDARY more aligned than
  27    STACK_BOUNDARY (e.g. x86), or if not all registers can be pushed
  28    (e.g. x86 fp regs) which would ordinarily have to be implemented
  29    as a sub/mov pair due to restrictions in calls.cc.
  30
  31    Propagation stops when any of the insns that need adjusting are
  32    (a) no longer valid because we've exceeded their range, (b) a
  33    non-trivial push instruction, or (c) a call instruction.
  34
  35    Restriction B is based on the assumption that push instructions
  36    are smaller or faster.  If a port really wants to remove all
  37    pushes, it should have defined ACCUMULATE_OUTGOING_ARGS.  The
  38    one exception that is made is for an add immediately followed
  39    by a push.  */
  40
  41 #include "config.h"
  42 #include "system.h"
  43 #include "coretypes.h"
  44 #include "backend.h"
  45 #include "rtl.h"
  46 #include "df.h"
  47 #include "insn-config.h"
  48 #include "memmodel.h"
  49 #include "emit-rtl.h"
  50 #include "recog.h"
  51 #include "cfgrtl.h"
  52 #include "tree-pass.h"
  53 #include "rtl-iter.h"
  54
  55 \f
  56 /* This structure records two kinds of stack references between stack
  57    adjusting instructions: stack references in memory addresses for
  58    regular insns and all stack references for debug insns.  */
  59
  60 struct csa_reflist
  61 {
  62   HOST_WIDE_INT sp_offset;
  63   rtx_insn *insn;
  64   rtx *ref;
  65   struct csa_reflist *next;
  66 };
  67
  68 static int stack_memref_p (rtx);
  69 static rtx single_set_for_csa (rtx_insn *);
  70 static void free_csa_reflist (struct csa_reflist *);
  71 static struct csa_reflist *record_one_stack_ref (rtx_insn *, rtx *,
  72                                                  struct csa_reflist *);
  73 static bool try_apply_stack_adjustment (rtx_insn *, struct csa_reflist *,
  74                                         HOST_WIDE_INT, HOST_WIDE_INT,
  75                                         bitmap, rtx_insn *);
  76 static void combine_stack_adjustments_for_block (basic_block, bitmap);
  77
  78
  79 /* Main entry point for stack adjustment combination.  */
  80
  81 static void
  82 combine_stack_adjustments (void)
  83 {
  84   basic_block bb;
  85   bitmap live = BITMAP_ALLOC (&reg_obstack);
  86
  87   FOR_EACH_BB_FN (bb, cfun)
  88     combine_stack_adjustments_for_block (bb, live);
  89
  90   BITMAP_FREE (live);
  91 }
  92
  93 /* Recognize a MEM of the form (sp) or (plus sp const).  */
  94
  95 static int
  96 stack_memref_p (rtx x)
  97 {
  98   if (!MEM_P (x))
  99     return 0;
 100   x = XEXP (x, 0);
 101
 102   if (x == stack_pointer_rtx)
 103     return 1;
 104   if (GET_CODE (x) == PLUS
 105       && XEXP (x, 0) == stack_pointer_rtx
 106       && CONST_INT_P (XEXP (x, 1)))
 107     return 1;
 108
 109   return 0;
 110 }
 111
 112 /* Recognize either normal single_set or the hack in i386.md for
 113    tying fp and sp adjustments.  */
 114
 115 static rtx
 116 single_set_for_csa (rtx_insn *insn)
 117 {
 118   int i;
 119   rtx tmp = single_set (insn);
 120   if (tmp)
 121     return tmp;
 122
 123   if (!NONJUMP_INSN_P (insn)
 124       || GET_CODE (PATTERN (insn)) != PARALLEL)
 125     return NULL_RTX;
 126
 127   tmp = PATTERN (insn);
 128   if (GET_CODE (XVECEXP (tmp, 0, 0)) != SET)
 129     return NULL_RTX;
 130
 131   for (i = 1; i < XVECLEN (tmp, 0); ++i)
 132     {
 133       rtx this_rtx = XVECEXP (tmp, 0, i);
 134
 135       /* The special case is allowing a no-op set.  */
 136       if (GET_CODE (this_rtx) == SET
 137           && SET_SRC (this_rtx) == SET_DEST (this_rtx))
 138         ;
 139       else if (GET_CODE (this_rtx) != CLOBBER
 140                && GET_CODE (this_rtx) != USE)
 141         return NULL_RTX;
 142     }
 143
 144   return XVECEXP (tmp, 0, 0);
 145 }
 146
 147 /* Free the list of csa_reflist nodes.  */
 148
 149 static void
 150 free_csa_reflist (struct csa_reflist *reflist)
 151 {
 152   struct csa_reflist *next;
 153   for (; reflist ; reflist = next)
 154     {
 155       next = reflist->next;
 156       free (reflist);
 157     }
 158 }
 159
 160 /* Create a new csa_reflist node from the given stack reference.
 161    It is already known that the reference is either a MEM satisfying the
 162    predicate stack_memref_p or a REG representing the stack pointer.  */
 163
 164 static struct csa_reflist *
 165 record_one_stack_ref (rtx_insn *insn, rtx *ref, struct csa_reflist *next_reflist)
 166 {
 167   struct csa_reflist *ml;
 168
 169   ml = XNEW (struct csa_reflist);
 170
 171   if (REG_P (*ref) || XEXP (*ref, 0) == stack_pointer_rtx)
 172     ml->sp_offset = 0;
 173   else
 174     ml->sp_offset = INTVAL (XEXP (XEXP (*ref, 0), 1));
 175
 176   ml->insn = insn;
 177   ml->ref = ref;
 178   ml->next = next_reflist;
 179
 180   return ml;
 181 }
 182
 183 /* We only know how to adjust the CFA; no other frame-related changes
 184    may appear in any insn to be deleted.  */
 185
 186 static bool
 187 no_unhandled_cfa (rtx_insn *insn)
 188 {
 189   if (!RTX_FRAME_RELATED_P (insn))
 190     return true;
 191
 192   /* No CFA notes at all is a legacy interpretation like
 193      FRAME_RELATED_EXPR, and is context sensitive within
 194      the prologue state machine.  We can't handle that here.  */
 195   bool has_cfa_adjust = false;
 196
 197   for (rtx link = REG_NOTES (insn); link; link = XEXP (link, 1))
 198     switch (REG_NOTE_KIND (link))
 199       {
 200       default:
 201         break;
 202       case REG_CFA_ADJUST_CFA:
 203         has_cfa_adjust = true;
 204         break;
 205
 206       case REG_FRAME_RELATED_EXPR:
 207       case REG_CFA_DEF_CFA:
 208       case REG_CFA_OFFSET:
 209       case REG_CFA_REGISTER:
 210       case REG_CFA_EXPRESSION:
 211       case REG_CFA_RESTORE:
 212       case REG_CFA_SET_VDRAP:
 213       case REG_CFA_WINDOW_SAVE:
 214       case REG_CFA_FLUSH_QUEUE:
 215       case REG_CFA_TOGGLE_RA_MANGLE:
 216         return false;
 217       }
 218
 219   return has_cfa_adjust;
 220 }
 221
 222 /* Attempt to apply ADJUST to the stack adjusting insn INSN, as well
 223    as each of the memories and stack references in REFLIST.  Return true
 224    on success.  */
 225
 226 static bool
 227 try_apply_stack_adjustment (rtx_insn *insn, struct csa_reflist *reflist,
 228                             HOST_WIDE_INT new_adjust, HOST_WIDE_INT delta,
 229                             bitmap live, rtx_insn *other_insn)
 230 {
 231   struct csa_reflist *ml;
 232   rtx set;
 233   bool remove_equal = false;
 234
 235   set = single_set_for_csa (insn);
 236   if (MEM_P (SET_DEST (set)))
 237     validate_change (insn, &SET_DEST (set),
 238                      replace_equiv_address (SET_DEST (set), stack_pointer_rtx),
 239                      1);
 240   else if (REG_P (SET_SRC (set)))
 241     {
 242       if (other_insn == NULL_RTX || live == NULL)
 243         return false;
 244       rtx other_set = single_set_for_csa (other_insn);
 245       if (SET_DEST (other_set) != stack_pointer_rtx
 246           || GET_CODE (SET_SRC (other_set)) != PLUS
 247           || XEXP (SET_SRC (other_set), 0) != stack_pointer_rtx
 248           || !CONST_INT_P (XEXP (SET_SRC (other_set), 1)))
 249         return false;
 250       if (PATTERN (other_insn) != other_set)
 251         {
 252           if (GET_CODE (PATTERN (other_insn)) != PARALLEL)
 253             return false;
 254           int i;
 255           rtx p = PATTERN (other_insn);
 256           for (i = 0; i < XVECLEN (p, 0); ++i)
 257             {
 258               rtx this_rtx = XVECEXP (p, 0, i);
 259               if (this_rtx == other_set)
 260                 continue;
 261               if (GET_CODE (this_rtx) != CLOBBER)
 262                 return false;
 263               if (!REG_P (XEXP (this_rtx, 0))
 264                   || !HARD_REGISTER_P (XEXP (this_rtx, 0)))
 265                 return false;
 266               unsigned int end_regno = END_REGNO (XEXP (this_rtx, 0));
 267               for (unsigned int regno = REGNO (XEXP (this_rtx, 0));
 268                    regno < end_regno; ++regno)
 269                 if (bitmap_bit_p (live, regno))
 270                   return false;
 271             }
 272         }
 273       validate_change (insn, &PATTERN (insn), copy_rtx (PATTERN (other_insn)),
 274                        1);
 275       set = single_set_for_csa (insn);
 276       validate_change (insn, &XEXP (SET_SRC (set), 1), GEN_INT (new_adjust),
 277                        1);
 278       remove_equal = true;
 279     }
 280   else
 281     validate_change (insn, &XEXP (SET_SRC (set), 1), GEN_INT (new_adjust), 1);
 282
 283   for (ml = reflist; ml ; ml = ml->next)
 284     {
 285       rtx new_addr = plus_constant (Pmode, stack_pointer_rtx,
 286                                     ml->sp_offset - delta);
 287       rtx new_val;
 288
 289       if (MEM_P (*ml->ref))
 290         new_val = replace_equiv_address_nv (*ml->ref, new_addr);
 291       else if (GET_MODE (*ml->ref) == GET_MODE (stack_pointer_rtx))
 292         new_val = new_addr;
 293       else
 294         new_val = lowpart_subreg (GET_MODE (*ml->ref), new_addr,
 295                                   GET_MODE (new_addr));
 296       validate_change (ml->insn, ml->ref, new_val, 1);
 297     }
 298
 299   if (apply_change_group ())
 300     {
 301       /* Succeeded.  Update our knowledge of the stack references.  */
 302       for (ml = reflist; ml ; ml = ml->next)
 303         ml->sp_offset -= delta;
 304
 305       if (remove_equal)
 306         remove_reg_equal_equiv_notes (insn);
 307       return true;
 308     }
 309   else
 310     return false;
 311 }
 312
 313 /* For non-debug insns, record all stack memory references in INSN
 314    and return true if there were no other (unrecorded) references to the
 315    stack pointer.  For debug insns, record all stack references regardless
 316    of context and unconditionally return true.  */
 317
 318 static bool
 319 record_stack_refs (rtx_insn *insn, struct csa_reflist **reflist)
 320 {
 321   subrtx_ptr_iterator::array_type array;
 322   FOR_EACH_SUBRTX_PTR (iter, array, &PATTERN (insn), NONCONST)
 323     {
 324       rtx *loc = *iter;
 325       rtx x = *loc;
 326       switch (GET_CODE (x))
 327         {
 328         case MEM:
 329           if (!reg_mentioned_p (stack_pointer_rtx, x))
 330             iter.skip_subrtxes ();
 331           /* We are not able to handle correctly all possible memrefs
 332              containing stack pointer, so this check is necessary.  */
 333           else if (stack_memref_p (x))
 334             {
 335               *reflist = record_one_stack_ref (insn, loc, *reflist);
 336               iter.skip_subrtxes ();
 337             }
 338           /* Try harder for DEBUG_INSNs, handle e.g.
 339              (mem (mem (sp + 16) + 4).  */
 340           else if (!DEBUG_INSN_P (insn))
 341             return false;
 342           break;
 343
 344         case REG:
 345           /* ??? We want be able to handle non-memory stack pointer
 346              references later.  For now just discard all insns referring to
 347              stack pointer outside mem expressions.  We would probably
 348              want to teach validate_replace to simplify expressions first.
 349
 350              We can't just compare with STACK_POINTER_RTX because the
 351              reference to the stack pointer might be in some other mode.
 352              In particular, an explicit clobber in an asm statement will
 353              result in a QImode clobber.
 354
 355              In DEBUG_INSNs, we want to replace all occurrences, otherwise
 356              they will cause -fcompare-debug failures.  */
 357           if (REGNO (x) == STACK_POINTER_REGNUM)
 358             {
 359               if (!DEBUG_INSN_P (insn))
 360                 return false;
 361               *reflist = record_one_stack_ref (insn, loc, *reflist);
 362             }
 363           break;
 364
 365         default:
 366           break;
 367         }
 368     }
 369   return true;
 370 }
 371
 372 /* If INSN has a REG_ARGS_SIZE note, move it to LAST.
 373    AFTER is true iff LAST follows INSN in the instruction stream.  */
 374
 375 static void
 376 maybe_move_args_size_note (rtx_insn *last, rtx_insn *insn, bool after)
 377 {
 378   rtx note, last_note;
 379
 380   note = find_reg_note (insn, REG_ARGS_SIZE, NULL_RTX);
 381   if (note == NULL)
 382     return;
 383
 384   last_note = find_reg_note (last, REG_ARGS_SIZE, NULL_RTX);
 385   if (last_note)
 386     {
 387       /* The ARGS_SIZE notes are *not* cumulative.  They represent an
 388          absolute value, and the "most recent" note wins.  */
 389       if (!after)
 390         XEXP (last_note, 0) = XEXP (note, 0);
 391     }
 392   else
 393     add_reg_note (last, REG_ARGS_SIZE, XEXP (note, 0));
 394 }
 395
 396 /* Merge any REG_CFA_ADJUST_CFA note from SRC into DST.
 397    AFTER is true iff DST follows SRC in the instruction stream.  */
 398
 399 static void
 400 maybe_merge_cfa_adjust (rtx_insn *dst, rtx_insn *src, bool after)
 401 {
 402   rtx snote = NULL, dnote = NULL;
 403   rtx sexp, dexp;
 404   rtx exp1, exp2;
 405
 406   if (RTX_FRAME_RELATED_P (src))
 407     snote = find_reg_note (src, REG_CFA_ADJUST_CFA, NULL_RTX);
 408   if (snote == NULL)
 409     return;
 410   sexp = XEXP (snote, 0);
 411
 412   if (RTX_FRAME_RELATED_P (dst))
 413     dnote = find_reg_note (dst, REG_CFA_ADJUST_CFA, NULL_RTX);
 414   if (dnote == NULL)
 415     {
 416       add_reg_note (dst, REG_CFA_ADJUST_CFA, sexp);
 417       return;
 418     }
 419   dexp = XEXP (dnote, 0);
 420
 421   gcc_assert (GET_CODE (sexp) == SET);
 422   gcc_assert (GET_CODE (dexp) == SET);
 423
 424   if (after)
 425     exp1 = dexp, exp2 = sexp;
 426   else
 427     exp1 = sexp, exp2 = dexp;
 428
 429   SET_SRC (exp1) = simplify_replace_rtx (SET_SRC (exp1), SET_DEST (exp2),
 430                                          SET_SRC (exp2));
 431   XEXP (dnote, 0) = exp1;
 432 }
 433
 434 /* Return the next (or previous) active insn within BB.  */
 435
 436 static rtx_insn *
 437 prev_active_insn_bb (basic_block bb, rtx_insn *insn)
 438 {
 439   for (insn = PREV_INSN (insn);
 440        insn != PREV_INSN (BB_HEAD (bb));
 441        insn = PREV_INSN (insn))
 442     if (active_insn_p (insn))
 443       return insn;
 444   return NULL;
 445 }
 446
 447 static rtx_insn *
 448 next_active_insn_bb (basic_block bb, rtx_insn *insn)
 449 {
 450   for (insn = NEXT_INSN (insn);
 451        insn != NEXT_INSN (BB_END (bb));
 452        insn = NEXT_INSN (insn))
 453     if (active_insn_p (insn))
 454       return insn;
 455   return NULL;
 456 }
 457
 458 /* If INSN has a REG_ARGS_SIZE note, if possible move it to PREV.  Otherwise
 459    search for a nearby candidate within BB where we can stick the note.  */
 460
 461 static void
 462 force_move_args_size_note (basic_block bb, rtx_insn *prev, rtx_insn *insn)
 463 {
 464   rtx note;
 465   rtx_insn *test, *next_candidate, *prev_candidate;
 466
 467   /* If PREV exists, tail-call to the logic in the other function.  */
 468   if (prev)
 469     {
 470       maybe_move_args_size_note (prev, insn, false);
 471       return;
 472     }
 473
 474   /* First, make sure there's anything that needs doing.  */
 475   note = find_reg_note (insn, REG_ARGS_SIZE, NULL_RTX);
 476   if (note == NULL)
 477     return;
 478
 479   /* We need to find a spot between the previous and next exception points
 480      where we can place the note and "properly" deallocate the arguments.  */
 481   next_candidate = prev_candidate = NULL;
 482
 483   /* It is often the case that we have insns in the order:
 484         call
 485         add sp (previous deallocation)
 486         sub sp (align for next arglist)
 487         push arg
 488      and the add/sub cancel.  Therefore we begin by searching forward.  */
 489
 490   test = insn;
 491   while ((test = next_active_insn_bb (bb, test)) != NULL)
 492     {
 493       /* Found an existing note: nothing to do.  */
 494       if (find_reg_note (test, REG_ARGS_SIZE, NULL_RTX))
 495         return;
 496       /* Found something that affects unwinding.  Stop searching.  */
 497       if (CALL_P (test) || !insn_nothrow_p (test))
 498         break;
 499       if (next_candidate == NULL)
 500         next_candidate = test;
 501     }
 502
 503   test = insn;
 504   while ((test = prev_active_insn_bb (bb, test)) != NULL)
 505     {
 506       rtx tnote;
 507       /* Found a place that seems logical to adjust the stack.  */
 508       tnote = find_reg_note (test, REG_ARGS_SIZE, NULL_RTX);
 509       if (tnote)
 510         {
 511           XEXP (tnote, 0) = XEXP (note, 0);
 512           return;
 513         }
 514       if (prev_candidate == NULL)
 515         prev_candidate = test;
 516       /* Found something that affects unwinding.  Stop searching.  */
 517       if (CALL_P (test) || !insn_nothrow_p (test))
 518         break;
 519     }
 520
 521   if (prev_candidate)
 522     test = prev_candidate;
 523   else if (next_candidate)
 524     test = next_candidate;
 525   else
 526     {
 527       /* ??? We *must* have a place, lest we ICE on the lost adjustment.
 528          Options are: dummy clobber insn, nop, or prevent the removal of
 529          the sp += 0 insn.  */
 530       /* TODO: Find another way to indicate to the dwarf2 code that we
 531          have not in fact lost an adjustment.  */
 532       test = emit_insn_before (gen_rtx_CLOBBER (VOIDmode, const0_rtx), insn);
 533     }
 534   add_reg_note (test, REG_ARGS_SIZE, XEXP (note, 0));
 535 }
 536
 537 /* Subroutine of combine_stack_adjustments, called for each basic block.  */
 538
 539 static void
 540 combine_stack_adjustments_for_block (basic_block bb, bitmap live)
 541 {
 542   HOST_WIDE_INT last_sp_adjust = 0;
 543   rtx_insn *last_sp_set = NULL;
 544   rtx_insn *last2_sp_set = NULL;
 545   bitmap last_sp_live = NULL;
 546   struct csa_reflist *reflist = NULL;
 547   bitmap copy = NULL;
 548   rtx_insn *insn, *next;
 549   rtx set;
 550   bool end_of_block = false;
 551
 552   bitmap_copy (live, DF_LR_IN (bb));
 553   df_simulate_initialize_forwards (bb, live);
 554
 555   for (insn = BB_HEAD (bb); !end_of_block ; insn = next)
 556     {
 557       end_of_block = insn == BB_END (bb);
 558       next = NEXT_INSN (insn);
 559
 560       if (! INSN_P (insn))
 561         continue;
 562
 563       set = single_set_for_csa (insn);
 564       if (set && find_reg_note (insn, REG_STACK_CHECK, NULL_RTX))
 565         set = NULL_RTX;
 566       if (set)
 567         {
 568           rtx dest = SET_DEST (set);
 569           rtx src = SET_SRC (set);
 570           HOST_WIDE_INT this_adjust = 0;
 571
 572           /* Find constant additions to the stack pointer.  */
 573           if (dest == stack_pointer_rtx
 574               && GET_CODE (src) == PLUS
 575               && XEXP (src, 0) == stack_pointer_rtx
 576               && CONST_INT_P (XEXP (src, 1)))
 577             this_adjust = INTVAL (XEXP (src, 1));
 578           /* Or such additions turned by postreload into a store of
 579              equivalent register.  */
 580           else if (dest == stack_pointer_rtx
 581                    && REG_P (src)
 582                    && REGNO (src) != STACK_POINTER_REGNUM)
 583             if (rtx equal = find_reg_note (insn, REG_EQUAL, NULL_RTX))
 584               if (GET_CODE (XEXP (equal, 0)) == PLUS
 585                   && XEXP (XEXP (equal, 0), 0) == stack_pointer_rtx
 586                   && CONST_INT_P (XEXP (XEXP (equal, 0), 1)))
 587                 this_adjust = INTVAL (XEXP (XEXP (equal, 0), 1));
 588
 589           if (this_adjust)
 590             {
 591               /* If we've not seen an adjustment previously, record
 592                  it now and continue.  */
 593               if (! last_sp_set)
 594                 {
 595                   last_sp_set = insn;
 596                   last_sp_adjust = this_adjust;
 597                   if (REG_P (src))
 598                     {
 599                       if (copy == NULL)
 600                         copy = BITMAP_ALLOC (&reg_obstack);
 601                       last_sp_live = copy;
 602                       bitmap_copy (last_sp_live, live);
 603                     }
 604                   else
 605                     last_sp_live = NULL;
 606                   df_simulate_one_insn_forwards (bb, insn, live);
 607                   continue;
 608                 }
 609
 610               /* If not all recorded refs can be adjusted, or the
 611                  adjustment is now too large for a constant addition,
 612                  we cannot merge the two stack adjustments.
 613
 614                  Also we need to be careful to not move stack pointer
 615                  such that we create stack accesses outside the allocated
 616                  area.  We can combine an allocation into the first insn,
 617                  or a deallocation into the second insn.  We cannot
 618                  combine an allocation followed by a deallocation.
 619
 620                  The only somewhat frequent occurrence of the later is when
 621                  a function allocates a stack frame but does not use it.
 622                  For this case, we would need to analyze rtl stream to be
 623                  sure that allocated area is really unused.  This means not
 624                  only checking the memory references, but also all registers
 625                  or global memory references possibly containing a stack
 626                  frame address.
 627
 628                  Perhaps the best way to address this problem is to teach
 629                  gcc not to allocate stack for objects never used.  */
 630
 631               /* Combine an allocation into the first instruction.  */
 632               if (STACK_GROWS_DOWNWARD ? this_adjust <= 0 : this_adjust >= 0)
 633                 {
 634                   if (no_unhandled_cfa (insn)
 635                       && try_apply_stack_adjustment (last_sp_set, reflist,
 636                                                      last_sp_adjust
 637                                                      + this_adjust,
 638                                                      this_adjust,
 639                                                      last_sp_live,
 640                                                      insn))
 641                     {
 642                       /* It worked!  */
 643                       maybe_move_args_size_note (last_sp_set, insn, false);
 644                       maybe_merge_cfa_adjust (last_sp_set, insn, false);
 645                       delete_insn (insn);
 646                       last_sp_adjust += this_adjust;
 647                       last_sp_live = NULL;
 648                       continue;
 649                     }
 650                 }
 651
 652               /* Otherwise we have a deallocation.  Do not combine with
 653                  a previous allocation.  Combine into the second insn.  */
 654               else if (STACK_GROWS_DOWNWARD
 655                        ? last_sp_adjust >= 0 : last_sp_adjust <= 0)
 656                 {
 657                   if (no_unhandled_cfa (last_sp_set)
 658                       && !REG_P (src)
 659                       && try_apply_stack_adjustment (insn, reflist,
 660                                                      last_sp_adjust
 661                                                      + this_adjust,
 662                                                      -last_sp_adjust,
 663                                                      NULL, NULL))
 664                     {
 665                       /* It worked!  */
 666                       maybe_move_args_size_note (insn, last_sp_set, true);
 667                       maybe_merge_cfa_adjust (insn, last_sp_set, true);
 668                       delete_insn (last_sp_set);
 669                       last_sp_set = insn;
 670                       last_sp_adjust += this_adjust;
 671                       last_sp_live = NULL;
 672                       free_csa_reflist (reflist);
 673                       reflist = NULL;
 674                       df_simulate_one_insn_forwards (bb, insn, live);
 675                       continue;
 676                     }
 677                 }
 678
 679               /* Combination failed.  Restart processing from here.  If
 680                  deallocation+allocation conspired to cancel, we can
 681                  delete the old deallocation insn.  */
 682               if (last_sp_set)
 683                 {
 684                   if (last_sp_adjust == 0 && no_unhandled_cfa (last_sp_set))
 685                     {
 686                       maybe_move_args_size_note (insn, last_sp_set, true);
 687                       maybe_merge_cfa_adjust (insn, last_sp_set, true);
 688                       delete_insn (last_sp_set);
 689                     }
 690                   else
 691                     last2_sp_set = last_sp_set;
 692                 }
 693               free_csa_reflist (reflist);
 694               reflist = NULL;
 695               last_sp_set = insn;
 696               last_sp_adjust = this_adjust;
 697               if (REG_P (src))
 698                 {
 699                   if (copy == NULL)
 700                     copy = BITMAP_ALLOC (&reg_obstack);
 701                   last_sp_live = copy;
 702                   bitmap_copy (last_sp_live, live);
 703                 }
 704               else
 705                 last_sp_live = NULL;
 706               df_simulate_one_insn_forwards (bb, insn, live);
 707               continue;
 708             }
 709
 710           /* Find a store with pre-(dec|inc)rement or pre-modify of exactly
 711              the previous adjustment and turn it into a simple store.  This
 712              is equivalent to anticipating the stack adjustment so this must
 713              be an allocation.  */
 714           if (MEM_P (dest)
 715               && ((STACK_GROWS_DOWNWARD
 716                    ? (GET_CODE (XEXP (dest, 0)) == PRE_DEC
 717                       && known_eq (last_sp_adjust,
 718                                    GET_MODE_SIZE (GET_MODE (dest))))
 719                    : (GET_CODE (XEXP (dest, 0)) == PRE_INC
 720                       && known_eq (-last_sp_adjust,
 721                                    GET_MODE_SIZE (GET_MODE (dest)))))
 722                   || ((STACK_GROWS_DOWNWARD
 723                        ? last_sp_adjust >= 0 : last_sp_adjust <= 0)
 724                       && GET_CODE (XEXP (dest, 0)) == PRE_MODIFY
 725                       && GET_CODE (XEXP (XEXP (dest, 0), 1)) == PLUS
 726                       && XEXP (XEXP (XEXP (dest, 0), 1), 0)
 727                          == stack_pointer_rtx
 728                       && GET_CODE (XEXP (XEXP (XEXP (dest, 0), 1), 1))
 729                          == CONST_INT
 730                       && INTVAL (XEXP (XEXP (XEXP (dest, 0), 1), 1))
 731                          == -last_sp_adjust))
 732               && XEXP (XEXP (dest, 0), 0) == stack_pointer_rtx
 733               && !reg_mentioned_p (stack_pointer_rtx, src)
 734               && memory_address_p (GET_MODE (dest), stack_pointer_rtx)
 735               && try_apply_stack_adjustment (insn, reflist, 0,
 736                                              -last_sp_adjust,
 737                                              NULL, NULL))
 738             {
 739               if (last2_sp_set)
 740                 maybe_move_args_size_note (last2_sp_set, last_sp_set, false);
 741               else
 742                 maybe_move_args_size_note (insn, last_sp_set, true);
 743               delete_insn (last_sp_set);
 744               free_csa_reflist (reflist);
 745               reflist = NULL;
 746               last_sp_set = NULL;
 747               last_sp_adjust = 0;
 748               last_sp_live = NULL;
 749               df_simulate_one_insn_forwards (bb, insn, live);
 750               continue;
 751             }
 752         }
 753
 754       if (!CALL_P (insn) && last_sp_set && record_stack_refs (insn, &reflist))
 755         {
 756           df_simulate_one_insn_forwards (bb, insn, live);
 757           continue;
 758         }
 759
 760       /* Otherwise, we were not able to process the instruction.
 761          Do not continue collecting data across such a one.  */
 762       if (last_sp_set
 763           && (CALL_P (insn)
 764               || reg_mentioned_p (stack_pointer_rtx, PATTERN (insn))))
 765         {
 766           if (last_sp_set && last_sp_adjust == 0)
 767             {
 768               force_move_args_size_note (bb, last2_sp_set, last_sp_set);
 769               delete_insn (last_sp_set);
 770             }
 771           free_csa_reflist (reflist);
 772           reflist = NULL;
 773           last2_sp_set = NULL;
 774           last_sp_set = NULL;
 775           last_sp_adjust = 0;
 776           last_sp_live = NULL;
 777         }
 778
 779       df_simulate_one_insn_forwards (bb, insn, live);
 780     }
 781
 782   if (last_sp_set && last_sp_adjust == 0)
 783     {
 784       force_move_args_size_note (bb, last2_sp_set, last_sp_set);
 785       delete_insn (last_sp_set);
 786     }
 787
 788   if (reflist)
 789     free_csa_reflist (reflist);
 790   if (copy)
 791     BITMAP_FREE (copy);
 792 }
 793 \f
 794 static unsigned int
 795 rest_of_handle_stack_adjustments (void)
 796 {
 797   df_note_add_problem ();
 798   df_analyze ();
 799   combine_stack_adjustments ();
 800   return 0;
 801 }
 802
 803 namespace {
 804
 805 const pass_data pass_data_stack_adjustments =
 806 {
 807   RTL_PASS, /* type */
 808   "csa", /* name */
 809   OPTGROUP_NONE, /* optinfo_flags */
 810   TV_COMBINE_STACK_ADJUST, /* tv_id */
 811   0, /* properties_required */
 812   0, /* properties_provided */
 813   0, /* properties_destroyed */
 814   0, /* todo_flags_start */
 815   TODO_df_finish, /* todo_flags_finish */
 816 };
 817
 818 class pass_stack_adjustments : public rtl_opt_pass
 819 {
 820 public:
 821   pass_stack_adjustments (gcc::context *ctxt)
 822     : rtl_opt_pass (pass_data_stack_adjustments, ctxt)
 823   {}
 824
 825   /* opt_pass methods: */
 826   virtual bool gate (function *);
 827   virtual unsigned int execute (function *)
 828     {
 829       return rest_of_handle_stack_adjustments ();
 830     }
 831
 832 }; // class pass_stack_adjustments
 833
 834 bool
 835 pass_stack_adjustments::gate (function *)
 836 {
 837   /* This is kind of a heuristic.  We need to run combine_stack_adjustments
 838      even for machines with possibly nonzero TARGET_RETURN_POPS_ARGS
 839      and ACCUMULATE_OUTGOING_ARGS.  We expect that only ports having
 840      push instructions will have popping returns.  */
 841 #ifndef PUSH_ROUNDING
 842   if (ACCUMULATE_OUTGOING_ARGS)
 843     return false;
 844 #endif
 845   return flag_combine_stack_adjustments;
 846 }
 847
 848 } // anon namespace
 849
 850 rtl_opt_pass *
 851 make_pass_stack_adjustments (gcc::context *ctxt)
 852 {
 853   return new pass_stack_adjustments (ctxt);
 854 }