551 lines
16 KiB
C
551 lines
16 KiB
C
/* Combine stack adjustments.
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Copyright (C) 1987, 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997,
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1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009,
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2010 Free Software Foundation, Inc.
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify it under
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the terms of the GNU General Public License as published by the Free
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Software Foundation; either version 3, or (at your option) any later
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version.
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GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with GCC; see the file COPYING3. If not see
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<http://www.gnu.org/licenses/>. */
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/* Track stack adjustments and stack memory references. Attempt to
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reduce the number of stack adjustments by back-propagating across
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the memory references.
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This is intended primarily for use with targets that do not define
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ACCUMULATE_OUTGOING_ARGS. It is of significantly more value to
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targets that define PREFERRED_STACK_BOUNDARY more aligned than
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STACK_BOUNDARY (e.g. x86), or if not all registers can be pushed
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(e.g. x86 fp regs) which would ordinarily have to be implemented
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as a sub/mov pair due to restrictions in calls.c.
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Propagation stops when any of the insns that need adjusting are
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(a) no longer valid because we've exceeded their range, (b) a
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non-trivial push instruction, or (c) a call instruction.
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Restriction B is based on the assumption that push instructions
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are smaller or faster. If a port really wants to remove all
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pushes, it should have defined ACCUMULATE_OUTGOING_ARGS. The
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one exception that is made is for an add immediately followed
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by a push. */
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#include "config.h"
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#include "system.h"
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#include "coretypes.h"
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#include "tm.h"
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#include "rtl.h"
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#include "tm_p.h"
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#include "insn-config.h"
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#include "recog.h"
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#include "output.h"
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#include "regs.h"
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#include "hard-reg-set.h"
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#include "flags.h"
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#include "function.h"
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#include "expr.h"
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#include "basic-block.h"
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#include "df.h"
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#include "except.h"
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#include "reload.h"
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#include "timevar.h"
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#include "tree-pass.h"
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/* Turn STACK_GROWS_DOWNWARD into a boolean. */
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#ifdef STACK_GROWS_DOWNWARD
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#undef STACK_GROWS_DOWNWARD
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#define STACK_GROWS_DOWNWARD 1
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#else
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#define STACK_GROWS_DOWNWARD 0
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#endif
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/* This structure records two kinds of stack references between stack
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adjusting instructions: stack references in memory addresses for
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regular insns and all stack references for debug insns. */
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struct csa_reflist
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{
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HOST_WIDE_INT sp_offset;
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rtx insn, *ref;
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struct csa_reflist *next;
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};
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static int stack_memref_p (rtx);
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static rtx single_set_for_csa (rtx);
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static void free_csa_reflist (struct csa_reflist *);
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static struct csa_reflist *record_one_stack_ref (rtx, rtx *,
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struct csa_reflist *);
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static int try_apply_stack_adjustment (rtx, struct csa_reflist *,
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HOST_WIDE_INT, HOST_WIDE_INT);
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static void combine_stack_adjustments_for_block (basic_block);
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static int record_stack_refs (rtx *, void *);
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/* Main entry point for stack adjustment combination. */
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static void
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combine_stack_adjustments (void)
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{
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basic_block bb;
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FOR_EACH_BB (bb)
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combine_stack_adjustments_for_block (bb);
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}
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/* Recognize a MEM of the form (sp) or (plus sp const). */
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static int
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stack_memref_p (rtx x)
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{
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if (!MEM_P (x))
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return 0;
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x = XEXP (x, 0);
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if (x == stack_pointer_rtx)
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return 1;
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if (GET_CODE (x) == PLUS
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&& XEXP (x, 0) == stack_pointer_rtx
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&& CONST_INT_P (XEXP (x, 1)))
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return 1;
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return 0;
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}
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/* Recognize either normal single_set or the hack in i386.md for
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tying fp and sp adjustments. */
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static rtx
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single_set_for_csa (rtx insn)
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{
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int i;
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rtx tmp = single_set (insn);
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if (tmp)
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return tmp;
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if (!NONJUMP_INSN_P (insn)
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|| GET_CODE (PATTERN (insn)) != PARALLEL)
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return NULL_RTX;
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tmp = PATTERN (insn);
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if (GET_CODE (XVECEXP (tmp, 0, 0)) != SET)
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return NULL_RTX;
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for (i = 1; i < XVECLEN (tmp, 0); ++i)
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{
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rtx this_rtx = XVECEXP (tmp, 0, i);
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/* The special case is allowing a no-op set. */
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if (GET_CODE (this_rtx) == SET
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&& SET_SRC (this_rtx) == SET_DEST (this_rtx))
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;
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else if (GET_CODE (this_rtx) != CLOBBER
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&& GET_CODE (this_rtx) != USE)
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return NULL_RTX;
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}
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return XVECEXP (tmp, 0, 0);
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}
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/* Free the list of csa_reflist nodes. */
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static void
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free_csa_reflist (struct csa_reflist *reflist)
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{
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struct csa_reflist *next;
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for (; reflist ; reflist = next)
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{
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next = reflist->next;
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free (reflist);
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}
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}
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/* Create a new csa_reflist node from the given stack reference.
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It is already known that the reference is either a MEM satisfying the
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predicate stack_memref_p or a REG representing the stack pointer. */
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static struct csa_reflist *
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record_one_stack_ref (rtx insn, rtx *ref, struct csa_reflist *next_reflist)
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{
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struct csa_reflist *ml;
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ml = XNEW (struct csa_reflist);
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if (REG_P (*ref) || XEXP (*ref, 0) == stack_pointer_rtx)
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ml->sp_offset = 0;
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else
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ml->sp_offset = INTVAL (XEXP (XEXP (*ref, 0), 1));
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ml->insn = insn;
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ml->ref = ref;
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ml->next = next_reflist;
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return ml;
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}
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/* Attempt to apply ADJUST to the stack adjusting insn INSN, as well
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as each of the memories and stack references in REFLIST. Return true
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on success. */
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static int
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try_apply_stack_adjustment (rtx insn, struct csa_reflist *reflist,
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HOST_WIDE_INT new_adjust, HOST_WIDE_INT delta)
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{
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struct csa_reflist *ml;
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rtx set;
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set = single_set_for_csa (insn);
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if (MEM_P (SET_DEST (set)))
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validate_change (insn, &SET_DEST (set),
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replace_equiv_address (SET_DEST (set), stack_pointer_rtx),
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1);
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else
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validate_change (insn, &XEXP (SET_SRC (set), 1), GEN_INT (new_adjust), 1);
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for (ml = reflist; ml ; ml = ml->next)
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{
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rtx new_addr = plus_constant (stack_pointer_rtx, ml->sp_offset - delta);
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rtx new_val;
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if (MEM_P (*ml->ref))
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new_val = replace_equiv_address_nv (*ml->ref, new_addr);
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else if (GET_MODE (*ml->ref) == GET_MODE (stack_pointer_rtx))
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new_val = new_addr;
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else
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new_val = lowpart_subreg (GET_MODE (*ml->ref), new_addr,
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GET_MODE (new_addr));
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validate_change (ml->insn, ml->ref, new_val, 1);
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}
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if (apply_change_group ())
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{
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/* Succeeded. Update our knowledge of the stack references. */
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for (ml = reflist; ml ; ml = ml->next)
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ml->sp_offset -= delta;
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return 1;
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}
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else
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return 0;
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}
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/* Called via for_each_rtx and used to record all stack memory and other
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references in the insn and discard all other stack pointer references. */
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struct record_stack_refs_data
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{
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rtx insn;
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struct csa_reflist *reflist;
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};
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static int
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record_stack_refs (rtx *xp, void *data)
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{
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rtx x = *xp;
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struct record_stack_refs_data *d =
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(struct record_stack_refs_data *) data;
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if (!x)
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return 0;
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switch (GET_CODE (x))
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{
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case MEM:
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if (!reg_mentioned_p (stack_pointer_rtx, x))
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return -1;
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/* We are not able to handle correctly all possible memrefs containing
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stack pointer, so this check is necessary. */
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if (stack_memref_p (x))
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{
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d->reflist = record_one_stack_ref (d->insn, xp, d->reflist);
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return -1;
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}
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/* Try harder for DEBUG_INSNs, handle e.g. (mem (mem (sp + 16) + 4). */
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return !DEBUG_INSN_P (d->insn);
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case REG:
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/* ??? We want be able to handle non-memory stack pointer
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references later. For now just discard all insns referring to
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stack pointer outside mem expressions. We would probably
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want to teach validate_replace to simplify expressions first.
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We can't just compare with STACK_POINTER_RTX because the
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reference to the stack pointer might be in some other mode.
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In particular, an explicit clobber in an asm statement will
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result in a QImode clobber.
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In DEBUG_INSNs, we want to replace all occurrences, otherwise
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they will cause -fcompare-debug failures. */
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if (REGNO (x) == STACK_POINTER_REGNUM)
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{
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if (!DEBUG_INSN_P (d->insn))
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return 1;
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d->reflist = record_one_stack_ref (d->insn, xp, d->reflist);
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return -1;
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}
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break;
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default:
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break;
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}
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return 0;
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}
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/* If INSN has a REG_ARGS_SIZE note, move it to LAST.
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AFTER is true iff LAST follows INSN in the instruction stream. */
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static void
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maybe_move_args_size_note (rtx last, rtx insn, bool after)
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{
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rtx note, last_note;
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note = find_reg_note (insn, REG_ARGS_SIZE, NULL_RTX);
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if (note == NULL)
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return;
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last_note = find_reg_note (last, REG_ARGS_SIZE, NULL_RTX);
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if (last_note)
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{
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/* The ARGS_SIZE notes are *not* cumulative. They represent an
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absolute value, and the "most recent" note wins. */
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if (!after)
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XEXP (last_note, 0) = XEXP (note, 0);
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}
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else
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add_reg_note (last, REG_ARGS_SIZE, XEXP (note, 0));
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}
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/* Subroutine of combine_stack_adjustments, called for each basic block. */
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static void
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combine_stack_adjustments_for_block (basic_block bb)
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{
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HOST_WIDE_INT last_sp_adjust = 0;
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rtx last_sp_set = NULL_RTX;
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struct csa_reflist *reflist = NULL;
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rtx insn, next, set;
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struct record_stack_refs_data data;
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bool end_of_block = false;
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for (insn = BB_HEAD (bb); !end_of_block ; insn = next)
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{
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end_of_block = insn == BB_END (bb);
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next = NEXT_INSN (insn);
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if (! INSN_P (insn))
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continue;
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set = single_set_for_csa (insn);
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if (set)
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{
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rtx dest = SET_DEST (set);
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rtx src = SET_SRC (set);
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/* Find constant additions to the stack pointer. */
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if (dest == stack_pointer_rtx
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&& GET_CODE (src) == PLUS
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&& XEXP (src, 0) == stack_pointer_rtx
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&& CONST_INT_P (XEXP (src, 1)))
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{
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HOST_WIDE_INT this_adjust = INTVAL (XEXP (src, 1));
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/* If we've not seen an adjustment previously, record
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it now and continue. */
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if (! last_sp_set)
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{
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last_sp_set = insn;
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last_sp_adjust = this_adjust;
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continue;
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}
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/* If not all recorded refs can be adjusted, or the
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adjustment is now too large for a constant addition,
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we cannot merge the two stack adjustments.
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Also we need to be careful to not move stack pointer
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such that we create stack accesses outside the allocated
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area. We can combine an allocation into the first insn,
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or a deallocation into the second insn. We can not
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combine an allocation followed by a deallocation.
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The only somewhat frequent occurrence of the later is when
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a function allocates a stack frame but does not use it.
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For this case, we would need to analyze rtl stream to be
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sure that allocated area is really unused. This means not
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only checking the memory references, but also all registers
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or global memory references possibly containing a stack
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frame address.
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Perhaps the best way to address this problem is to teach
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gcc not to allocate stack for objects never used. */
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/* Combine an allocation into the first instruction. */
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if (STACK_GROWS_DOWNWARD ? this_adjust <= 0 : this_adjust >= 0)
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{
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if (try_apply_stack_adjustment (last_sp_set, reflist,
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last_sp_adjust + this_adjust,
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this_adjust))
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{
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maybe_move_args_size_note (last_sp_set, insn, false);
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/* It worked! */
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delete_insn (insn);
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last_sp_adjust += this_adjust;
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continue;
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}
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}
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/* Otherwise we have a deallocation. Do not combine with
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a previous allocation. Combine into the second insn. */
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else if (STACK_GROWS_DOWNWARD
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? last_sp_adjust >= 0 : last_sp_adjust <= 0)
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{
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if (try_apply_stack_adjustment (insn, reflist,
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last_sp_adjust + this_adjust,
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-last_sp_adjust))
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{
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maybe_move_args_size_note (insn, last_sp_set, true);
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/* It worked! */
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delete_insn (last_sp_set);
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last_sp_set = insn;
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last_sp_adjust += this_adjust;
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free_csa_reflist (reflist);
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reflist = NULL;
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continue;
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}
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}
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/* Combination failed. Restart processing from here. If
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deallocation+allocation conspired to cancel, we can
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delete the old deallocation insn. */
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if (last_sp_set && last_sp_adjust == 0)
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delete_insn (last_sp_set);
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free_csa_reflist (reflist);
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reflist = NULL;
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last_sp_set = insn;
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last_sp_adjust = this_adjust;
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continue;
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}
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/* Find a store with pre-(dec|inc)rement or pre-modify of exactly
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the previous adjustment and turn it into a simple store. This
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is equivalent to anticipating the stack adjustment so this must
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be an allocation. */
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if (MEM_P (dest)
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&& ((STACK_GROWS_DOWNWARD
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? (GET_CODE (XEXP (dest, 0)) == PRE_DEC
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&& last_sp_adjust
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== (HOST_WIDE_INT) GET_MODE_SIZE (GET_MODE (dest)))
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: (GET_CODE (XEXP (dest, 0)) == PRE_INC
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&& last_sp_adjust
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== -(HOST_WIDE_INT) GET_MODE_SIZE (GET_MODE (dest))))
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|| ((STACK_GROWS_DOWNWARD
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? last_sp_adjust >= 0 : last_sp_adjust <= 0)
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&& GET_CODE (XEXP (dest, 0)) == PRE_MODIFY
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&& GET_CODE (XEXP (XEXP (dest, 0), 1)) == PLUS
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&& XEXP (XEXP (XEXP (dest, 0), 1), 0)
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== stack_pointer_rtx
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&& GET_CODE (XEXP (XEXP (XEXP (dest, 0), 1), 1))
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== CONST_INT
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&& INTVAL (XEXP (XEXP (XEXP (dest, 0), 1), 1))
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== -last_sp_adjust))
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&& XEXP (XEXP (dest, 0), 0) == stack_pointer_rtx
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&& !reg_mentioned_p (stack_pointer_rtx, src)
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&& memory_address_p (GET_MODE (dest), stack_pointer_rtx)
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&& try_apply_stack_adjustment (insn, reflist, 0,
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-last_sp_adjust))
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{
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delete_insn (last_sp_set);
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free_csa_reflist (reflist);
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reflist = NULL;
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last_sp_set = NULL_RTX;
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last_sp_adjust = 0;
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continue;
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}
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}
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data.insn = insn;
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data.reflist = reflist;
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if (!CALL_P (insn) && last_sp_set
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&& !for_each_rtx (&PATTERN (insn), record_stack_refs, &data))
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{
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reflist = data.reflist;
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continue;
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}
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reflist = data.reflist;
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/* Otherwise, we were not able to process the instruction.
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Do not continue collecting data across such a one. */
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if (last_sp_set
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&& (CALL_P (insn)
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|| reg_mentioned_p (stack_pointer_rtx, PATTERN (insn))))
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{
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if (last_sp_set && last_sp_adjust == 0)
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delete_insn (last_sp_set);
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free_csa_reflist (reflist);
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reflist = NULL;
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last_sp_set = NULL_RTX;
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last_sp_adjust = 0;
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}
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}
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if (last_sp_set && last_sp_adjust == 0)
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delete_insn (last_sp_set);
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if (reflist)
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free_csa_reflist (reflist);
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}
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static bool
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gate_handle_stack_adjustments (void)
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{
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return flag_combine_stack_adjustments;
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}
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static unsigned int
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rest_of_handle_stack_adjustments (void)
|
||
{
|
||
cleanup_cfg (flag_crossjumping ? CLEANUP_CROSSJUMP : 0);
|
||
|
||
/* This is kind of a heuristic. We need to run combine_stack_adjustments
|
||
even for machines with possibly nonzero TARGET_RETURN_POPS_ARGS
|
||
and ACCUMULATE_OUTGOING_ARGS. We expect that only ports having
|
||
push instructions will have popping returns. */
|
||
#ifndef PUSH_ROUNDING
|
||
if (!ACCUMULATE_OUTGOING_ARGS)
|
||
#endif
|
||
{
|
||
df_note_add_problem ();
|
||
df_analyze ();
|
||
combine_stack_adjustments ();
|
||
}
|
||
return 0;
|
||
}
|
||
|
||
struct rtl_opt_pass pass_stack_adjustments =
|
||
{
|
||
{
|
||
RTL_PASS,
|
||
"csa", /* name */
|
||
gate_handle_stack_adjustments, /* gate */
|
||
rest_of_handle_stack_adjustments, /* execute */
|
||
NULL, /* sub */
|
||
NULL, /* next */
|
||
0, /* static_pass_number */
|
||
TV_COMBINE_STACK_ADJUST, /* tv_id */
|
||
0, /* properties_required */
|
||
0, /* properties_provided */
|
||
0, /* properties_destroyed */
|
||
0, /* todo_flags_start */
|
||
TODO_df_finish | TODO_verify_rtl_sharing |
|
||
TODO_ggc_collect, /* todo_flags_finish */
|
||
}
|
||
};
|