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/* Combine stack adjustments.

   Copyright (C) 1987, 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997,

   1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009,

   2010 Free Software Foundation, Inc.

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

Software Foundation; either version 3, or (at your option) any later

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

along with GCC; see the file COPYING3.  If not see

<http://www.gnu.org/licenses/>.  */

/* Track stack adjustments and stack memory references.  Attempt to

   reduce the number of stack adjustments by back-propagating across

   the memory references.

   This is intended primarily for use with targets that do not define

   ACCUMULATE_OUTGOING_ARGS.  It is of significantly more value to

   targets that define PREFERRED_STACK_BOUNDARY more aligned than

   STACK_BOUNDARY (e.g. x86), or if not all registers can be pushed

   (e.g. x86 fp regs) which would ordinarily have to be implemented

   as a sub/mov pair due to restrictions in calls.c.

   Propagation stops when any of the insns that need adjusting are

   (a) no longer valid because we've exceeded their range, (b) a

   non-trivial push instruction, or (c) a call instruction.

   Restriction B is based on the assumption that push instructions

   are smaller or faster.  If a port really wants to remove all

   pushes, it should have defined ACCUMULATE_OUTGOING_ARGS.  The

   one exception that is made is for an add immediately followed

   by a push.  */

#include "config.h"

#include "system.h"

#include "coretypes.h"

#include "tm.h"

#include "rtl.h"

#include "tm_p.h"

#include "insn-config.h"

#include "recog.h"

#include "output.h"

#include "regs.h"

#include "hard-reg-set.h"

#include "flags.h"

#include "function.h"

#include "expr.h"

#include "basic-block.h"

#include "df.h"

#include "except.h"

#include "reload.h"

#include "timevar.h"

#include "tree-pass.h"

/* Turn STACK_GROWS_DOWNWARD into a boolean.  */

#ifdef STACK_GROWS_DOWNWARD

#undef STACK_GROWS_DOWNWARD

#define STACK_GROWS_DOWNWARD 1

#else

#define STACK_GROWS_DOWNWARD 0

#endif

/* This structure records two kinds of stack references between stack

   adjusting instructions: stack references in memory addresses for

   regular insns and all stack references for debug insns.  */

struct csa_reflist

{

  HOST_WIDE_INT sp_offset;

  rtx insn, *ref;

  struct csa_reflist *next;

};

static int stack_memref_p (rtx);

static rtx single_set_for_csa (rtx);

static void free_csa_reflist (struct csa_reflist *);

static struct csa_reflist *record_one_stack_ref (rtx, rtx *,

                                                 struct csa_reflist *);

static int try_apply_stack_adjustment (rtx, struct csa_reflist *,

                                       HOST_WIDE_INT, HOST_WIDE_INT);

static void combine_stack_adjustments_for_block (basic_block);

static int record_stack_refs (rtx *, void *);

/* Main entry point for stack adjustment combination.  */

static void

combine_stack_adjustments (void)

{

  basic_block bb;

  FOR_EACH_BB (bb)

    combine_stack_adjustments_for_block (bb);

}

/* Recognize a MEM of the form (sp) or (plus sp const).  */

static int

stack_memref_p (rtx x)

{

  if (!MEM_P (x))

    return 0;

  x = XEXP (x, 0);

  if (x == stack_pointer_rtx)

    return 1;

  if (GET_CODE (x) == PLUS

      && XEXP (x, 0) == stack_pointer_rtx

      && CONST_INT_P (XEXP (x, 1)))

    return 1;

  return 0;

}

/* Recognize either normal single_set or the hack in i386.md for

   tying fp and sp adjustments.  */

static rtx

single_set_for_csa (rtx insn)

{

  int i;

  rtx tmp = single_set (insn);

  if (tmp)

    return tmp;

  if (!NONJUMP_INSN_P (insn)

      || GET_CODE (PATTERN (insn)) != PARALLEL)

    return NULL_RTX;

  tmp = PATTERN (insn);

  if (GET_CODE (XVECEXP (tmp, 0, 0)) != SET)

    return NULL_RTX;

  for (i = 1; i < XVECLEN (tmp, 0); ++i)

    {

      rtx this_rtx = XVECEXP (tmp, 0, i);

      /* The special case is allowing a no-op set.  */

      if (GET_CODE (this_rtx) == SET

          && SET_SRC (this_rtx) == SET_DEST (this_rtx))

        ;

      else if (GET_CODE (this_rtx) != CLOBBER

               && GET_CODE (this_rtx) != USE)

        return NULL_RTX;

    }

  return XVECEXP (tmp, 0, 0);

}

/* Free the list of csa_reflist nodes.  */

static void

free_csa_reflist (struct csa_reflist *reflist)

{

  struct csa_reflist *next;

  for (; reflist ; reflist = next)

    {

      next = reflist->next;

      free (reflist);

    }

}

/* Create a new csa_reflist node from the given stack reference.

   It is already known that the reference is either a MEM satisfying the

   predicate stack_memref_p or a REG representing the stack pointer.  */

static struct csa_reflist *

record_one_stack_ref (rtx insn, rtx *ref, struct csa_reflist *next_reflist)

{

  struct csa_reflist *ml;

  ml = XNEW (struct csa_reflist);

  if (REG_P (*ref) || XEXP (*ref, 0) == stack_pointer_rtx)

    ml->sp_offset = 0;

  else

    ml->sp_offset = INTVAL (XEXP (XEXP (*ref, 0), 1));

  ml->insn = insn;

  ml->ref = ref;

  ml->next = next_reflist;

  return ml;

}

/* Attempt to apply ADJUST to the stack adjusting insn INSN, as well

   as each of the memories and stack references in REFLIST.  Return true

   on success.  */

static int

try_apply_stack_adjustment (rtx insn, struct csa_reflist *reflist,

                            HOST_WIDE_INT new_adjust, HOST_WIDE_INT delta)

{

  struct csa_reflist *ml;

  rtx set;

  set = single_set_for_csa (insn);

  if (MEM_P (SET_DEST (set)))

    validate_change (insn, &SET_DEST (set),

                     replace_equiv_address (SET_DEST (set), stack_pointer_rtx),

                     1);

  else

    validate_change (insn, &XEXP (SET_SRC (set), 1), GEN_INT (new_adjust), 1);

  for (ml = reflist; ml ; ml = ml->next)

    {

      rtx new_addr = plus_constant (stack_pointer_rtx, ml->sp_offset - delta);

      rtx new_val;

      if (MEM_P (*ml->ref))

        new_val = replace_equiv_address_nv (*ml->ref, new_addr);

      else if (GET_MODE (*ml->ref) == GET_MODE (stack_pointer_rtx))

        new_val = new_addr;

      else

        new_val = lowpart_subreg (GET_MODE (*ml->ref), new_addr,

                                  GET_MODE (new_addr));

      validate_change (ml->insn, ml->ref, new_val, 1);

    }

  if (apply_change_group ())

    {

      /* Succeeded.  Update our knowledge of the stack references.  */

      for (ml = reflist; ml ; ml = ml->next)

        ml->sp_offset -= delta;

      return 1;

    }

  else

    return 0;

}

/* Called via for_each_rtx and used to record all stack memory and other

   references in the insn and discard all other stack pointer references.  */

struct record_stack_refs_data

{

  rtx insn;

  struct csa_reflist *reflist;

};

static int

record_stack_refs (rtx *xp, void *data)

{

  rtx x = *xp;

  struct record_stack_refs_data *d =

    (struct record_stack_refs_data *) data;

  if (!x)

    return 0;

  switch (GET_CODE (x))

    {

    case MEM:

      if (!reg_mentioned_p (stack_pointer_rtx, x))

        return -1;

      /* We are not able to handle correctly all possible memrefs containing

         stack pointer, so this check is necessary.  */

      if (stack_memref_p (x))

        {

          d->reflist = record_one_stack_ref (d->insn, xp, d->reflist);

          return -1;

        }

      /* Try harder for DEBUG_INSNs, handle e.g. (mem (mem (sp + 16) + 4).  */

      return !DEBUG_INSN_P (d->insn);

    case REG:

      /* ??? We want be able to handle non-memory stack pointer

         references later.  For now just discard all insns referring to

         stack pointer outside mem expressions.  We would probably

         want to teach validate_replace to simplify expressions first.

         We can't just compare with STACK_POINTER_RTX because the

         reference to the stack pointer might be in some other mode.

         In particular, an explicit clobber in an asm statement will

         result in a QImode clobber.

         In DEBUG_INSNs, we want to replace all occurrences, otherwise

         they will cause -fcompare-debug failures.  */

      if (REGNO (x) == STACK_POINTER_REGNUM)

        {

          if (!DEBUG_INSN_P (d->insn))

            return 1;

          d->reflist = record_one_stack_ref (d->insn, xp, d->reflist);

          return -1;

        }

      break;

    default:

      break;

    }

  return 0;

}

/* If INSN has a REG_ARGS_SIZE note, move it to LAST.

   AFTER is true iff LAST follows INSN in the instruction stream.  */

static void

maybe_move_args_size_note (rtx last, rtx insn, bool after)

{

  rtx note, last_note;

  note = find_reg_note (insn, REG_ARGS_SIZE, NULL_RTX);

  if (note == NULL)

    return;

  last_note = find_reg_note (last, REG_ARGS_SIZE, NULL_RTX);

  if (last_note)

    {

      /* The ARGS_SIZE notes are *not* cumulative.  They represent an

         absolute value, and the "most recent" note wins.  */

      if (!after)

        XEXP (last_note, 0) = XEXP (note, 0);

    }

  else

    add_reg_note (last, REG_ARGS_SIZE, XEXP (note, 0));

}

/* Subroutine of combine_stack_adjustments, called for each basic block.  */

static void

combine_stack_adjustments_for_block (basic_block bb)

{

  HOST_WIDE_INT last_sp_adjust = 0;

  rtx last_sp_set = NULL_RTX;

  struct csa_reflist *reflist = NULL;

  rtx insn, next, set;

  struct record_stack_refs_data data;

  bool end_of_block = false;

  for (insn = BB_HEAD (bb); !end_of_block ; insn = next)

    {

      end_of_block = insn == BB_END (bb);

      next = NEXT_INSN (insn);

      if (! INSN_P (insn))

        continue;

      set = single_set_for_csa (insn);

      if (set)

        {

          rtx dest = SET_DEST (set);

          rtx src = SET_SRC (set);

          /* Find constant additions to the stack pointer.  */

          if (dest == stack_pointer_rtx

              && GET_CODE (src) == PLUS

              && XEXP (src, 0) == stack_pointer_rtx

              && CONST_INT_P (XEXP (src, 1)))

            {

              HOST_WIDE_INT this_adjust = INTVAL (XEXP (src, 1));

              /* If we've not seen an adjustment previously, record

                 it now and continue.  */

              if (! last_sp_set)

                {

                  last_sp_set = insn;

                  last_sp_adjust = this_adjust;

                  continue;

                }

              /* If not all recorded refs can be adjusted, or the

                 adjustment is now too large for a constant addition,

                 we cannot merge the two stack adjustments.

                 Also we need to be careful to not move stack pointer

                 such that we create stack accesses outside the allocated

                 area.  We can combine an allocation into the first insn,

                 or a deallocation into the second insn.  We can not

                 combine an allocation followed by a deallocation.

                 The only somewhat frequent occurrence of the later is when

                 a function allocates a stack frame but does not use it.

                 For this case, we would need to analyze rtl stream to be

                 sure that allocated area is really unused.  This means not

                 only checking the memory references, but also all registers

                 or global memory references possibly containing a stack

                 frame address.

                 Perhaps the best way to address this problem is to teach

                 gcc not to allocate stack for objects never used.  */

              /* Combine an allocation into the first instruction.  */

              if (STACK_GROWS_DOWNWARD ? this_adjust <= 0 : this_adjust >= 0)

                {

                  if (try_apply_stack_adjustment (last_sp_set, reflist,

                                                  last_sp_adjust + this_adjust,

                                                  this_adjust))

                    {

                      maybe_move_args_size_note (last_sp_set, insn, false);

                      /* It worked!  */

                      delete_insn (insn);

                      last_sp_adjust += this_adjust;

                      continue;

                    }

                }

              /* Otherwise we have a deallocation.  Do not combine with

                 a previous allocation.  Combine into the second insn.  */

              else if (STACK_GROWS_DOWNWARD

                       ? last_sp_adjust >= 0 : last_sp_adjust <= 0)

                {

                  if (try_apply_stack_adjustment (insn, reflist,

                                                  last_sp_adjust + this_adjust,

                                                  -last_sp_adjust))

                    {

                      maybe_move_args_size_note (insn, last_sp_set, true);

                      /* It worked!  */

                      delete_insn (last_sp_set);

                      last_sp_set = insn;

                      last_sp_adjust += this_adjust;

                      free_csa_reflist (reflist);

                      reflist = NULL;

                      continue;

                    }

                }

              /* Combination failed.  Restart processing from here.  If

                 deallocation+allocation conspired to cancel, we can

                 delete the old deallocation insn.  */

              if (last_sp_set && last_sp_adjust == 0)

                delete_insn (last_sp_set);

              free_csa_reflist (reflist);

              reflist = NULL;

              last_sp_set = insn;

              last_sp_adjust = this_adjust;

              continue;

            }

          /* Find a store with pre-(dec|inc)rement or pre-modify of exactly

             the previous adjustment and turn it into a simple store.  This

             is equivalent to anticipating the stack adjustment so this must

             be an allocation.  */

          if (MEM_P (dest)

              && ((STACK_GROWS_DOWNWARD

                   ? (GET_CODE (XEXP (dest, 0)) == PRE_DEC

                      && last_sp_adjust

                         == (HOST_WIDE_INT) GET_MODE_SIZE (GET_MODE (dest)))

                   : (GET_CODE (XEXP (dest, 0)) == PRE_INC

                      && last_sp_adjust

                         == -(HOST_WIDE_INT) GET_MODE_SIZE (GET_MODE (dest))))

                  || ((STACK_GROWS_DOWNWARD

                       ? last_sp_adjust >= 0 : last_sp_adjust <= 0)

                      && GET_CODE (XEXP (dest, 0)) == PRE_MODIFY

                      && GET_CODE (XEXP (XEXP (dest, 0), 1)) == PLUS

                      && XEXP (XEXP (XEXP (dest, 0), 1), 0)

                         == stack_pointer_rtx

                      && GET_CODE (XEXP (XEXP (XEXP (dest, 0), 1), 1))

                         == CONST_INT

                      && INTVAL (XEXP (XEXP (XEXP (dest, 0), 1), 1))

                         == -last_sp_adjust))

              && XEXP (XEXP (dest, 0), 0) == stack_pointer_rtx

              && !reg_mentioned_p (stack_pointer_rtx, src)

              && memory_address_p (GET_MODE (dest), stack_pointer_rtx)

              && try_apply_stack_adjustment (insn, reflist, 0,

                                             -last_sp_adjust))

            {

              delete_insn (last_sp_set);

              free_csa_reflist (reflist);

              reflist = NULL;

              last_sp_set = NULL_RTX;

              last_sp_adjust = 0;

              continue;

            }

        }

      data.insn = insn;

      data.reflist = reflist;

      if (!CALL_P (insn) && last_sp_set

          && !for_each_rtx (&PATTERN (insn), record_stack_refs, &data))

        {

           reflist = data.reflist;

           continue;

        }

      reflist = data.reflist;

      /* Otherwise, we were not able to process the instruction.

         Do not continue collecting data across such a one.  */

      if (last_sp_set

          && (CALL_P (insn)

              || reg_mentioned_p (stack_pointer_rtx, PATTERN (insn))))

        {

          if (last_sp_set && last_sp_adjust == 0)

            delete_insn (last_sp_set);

          free_csa_reflist (reflist);

          reflist = NULL;

          last_sp_set = NULL_RTX;

          last_sp_adjust = 0;

        }

    }

  if (last_sp_set && last_sp_adjust == 0)

    delete_insn (last_sp_set);

  if (reflist)

    free_csa_reflist (reflist);

}

static bool

gate_handle_stack_adjustments (void)

{

  return flag_combine_stack_adjustments;

}

static unsigned int

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 */

 }

};