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/* Control flow optimization code for GNU compiler.

   Copyright (C) 1987, 1988, 1992, 1993, 1994, 1995, 1996, 1997, 1998,

   1999, 2000, 2001, 2002, 2003, 2004, 2005, 2007

   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/>.  */

/* Try to match two basic blocks - or their ends - for structural equivalence.

   We scan the blocks from their ends backwards, and expect that insns are

   identical, except for certain cases involving registers.  A mismatch

   We scan the blocks from their ends backwards, hoping to find a match, I.e.

   insns are identical, except for certain cases involving registers.  A

   mismatch between register number RX (used in block X) and RY (used in the

   same way in block Y) can be handled in one of the following cases:

   1. RX and RY are local to their respective blocks; they are set there and

      die there.  If so, they can effectively be ignored.

   2. RX and RY die in their blocks, but live at the start.  If any path

      gets redirected through X instead of Y, the caller must emit

      compensation code to move RY to RX.  If there are overlapping inputs,

      the function resolve_input_conflict ensures that this can be done.

      Information about these registers are tracked in the X_LOCAL, Y_LOCAL,

      LOCAL_COUNT and LOCAL_RVALUE fields.

   3. RX and RY live throughout their blocks, including the start and the end.

      Either RX and RY must be identical, or we have to replace all uses in

      block X with a new pseudo, which is stored in the INPUT_REG field.  The

      caller can then use block X instead of block Y by copying RY to the new

      pseudo.

   The main entry point to this file is struct_equiv_block_eq.  This function

   uses a struct equiv_info to accept some of its inputs, to keep track of its

   internal state, to pass down to its helper functions, and to communicate

   some of the results back to the caller.

   Most scans will result in a failure to match a sufficient number of insns

   to make any optimization worth while, therefore the process is geared more

   to quick scanning rather than the ability to exactly backtrack when we

   find a mismatch.  The information gathered is still meaningful to make a

   preliminary decision if we want to do an optimization, we might only

   slightly overestimate the number of matchable insns, and underestimate

   the number of inputs an miss an input conflict.  Sufficient information

   is gathered so that when we make another pass, we won't have to backtrack

   at the same point.

   Another issue is that information in memory attributes and/or REG_NOTES

   might have to be merged or discarded to make a valid match.  We don't want

   to discard such information when we are not certain that we want to merge

   the two (partial) blocks.

   For these reasons, struct_equiv_block_eq has to be called first with the

   STRUCT_EQUIV_START bit set in the mode parameter.  This will calculate the

   number of matched insns and the number and types of inputs.  If the

   need_rerun field is set, the results are only tentative, and the caller

   has to call again with STRUCT_EQUIV_RERUN till need_rerun is false in

   order to get a reliable match.

   To install the changes necessary for the match, the function has to be

   called again with STRUCT_EQUIV_FINAL.

   While scanning an insn, we process first all the SET_DESTs, then the

   SET_SRCes, then the REG_NOTES, in order to keep the register liveness

   information consistent.

   If we were to mix up the order for sources / destinations in an insn where

   a source is also a destination, we'd end up being mistaken to think that

   the register is not live in the preceding insn.  */

#include "config.h"

#include "system.h"

#include "coretypes.h"

#include "tm.h"

#include "rtl.h"

#include "regs.h"

#include "output.h"

#include "insn-config.h"

#include "flags.h"

#include "recog.h"

#include "tm_p.h"

#include "target.h"

#include "emit-rtl.h"

#include "reload.h"

static void merge_memattrs (rtx, rtx);

static bool set_dest_equiv_p (rtx x, rtx y, struct equiv_info *info);

static bool set_dest_addr_equiv_p (rtx x, rtx y, struct equiv_info *info);

static void find_dying_inputs (struct equiv_info *info);

static bool resolve_input_conflict (struct equiv_info *info);

/* After reload, some moves, as indicated by SECONDARY_RELOAD_CLASS and

   SECONDARY_MEMORY_NEEDED, cannot be done directly.  For our purposes, we

   consider them impossible to generate after reload (even though some

   might be synthesized when you throw enough code at them).

   Since we don't know while processing a cross-jump if a local register

   that is currently live will eventually be live and thus be an input,

   we keep track of potential inputs that would require an impossible move

   by using a prohibitively high cost for them.

   This number, multiplied with the larger of STRUCT_EQUIV_MAX_LOCAL and

   FIRST_PSEUDO_REGISTER, must fit in the input_cost field of

   struct equiv_info.  */

#define IMPOSSIBLE_MOVE_FACTOR 20000

/* Removes the memory attributes of MEM expression

   if they are not equal.  */

void

merge_memattrs (rtx x, rtx y)

{

  int i;

  int j;

  enum rtx_code code;

  const char *fmt;

  if (x == y)

    return;

  if (x == 0 || y == 0)

    return;

  code = GET_CODE (x);

  if (code != GET_CODE (y))

    return;

  if (GET_MODE (x) != GET_MODE (y))

    return;

  if (code == MEM && MEM_ATTRS (x) != MEM_ATTRS (y))

    {

      if (! MEM_ATTRS (x))

        MEM_ATTRS (y) = 0;

      else if (! MEM_ATTRS (y))

        MEM_ATTRS (x) = 0;

      else

        {

          rtx mem_size;

          if (MEM_ALIAS_SET (x) != MEM_ALIAS_SET (y))

            {

              set_mem_alias_set (x, 0);

              set_mem_alias_set (y, 0);

            }

          if (! mem_expr_equal_p (MEM_EXPR (x), MEM_EXPR (y)))

            {

              set_mem_expr (x, 0);

              set_mem_expr (y, 0);

              set_mem_offset (x, 0);

              set_mem_offset (y, 0);

            }

          else if (MEM_OFFSET (x) != MEM_OFFSET (y))

            {

              set_mem_offset (x, 0);

              set_mem_offset (y, 0);

            }

          if (!MEM_SIZE (x))

            mem_size = NULL_RTX;

          else if (!MEM_SIZE (y))

            mem_size = NULL_RTX;

          else

            mem_size = GEN_INT (MAX (INTVAL (MEM_SIZE (x)),

                                     INTVAL (MEM_SIZE (y))));

          set_mem_size (x, mem_size);

          set_mem_size (y, mem_size);

          set_mem_align (x, MIN (MEM_ALIGN (x), MEM_ALIGN (y)));

          set_mem_align (y, MEM_ALIGN (x));

        }

    }

  fmt = GET_RTX_FORMAT (code);

  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)

    {

      switch (fmt[i])

        {

        case 'E':

          /* Two vectors must have the same length.  */

          if (XVECLEN (x, i) != XVECLEN (y, i))

            return;

          for (j = 0; j < XVECLEN (x, i); j++)

            merge_memattrs (XVECEXP (x, i, j), XVECEXP (y, i, j));

          break;

        case 'e':

          merge_memattrs (XEXP (x, i), XEXP (y, i));

        }

    }

  return;

}

/* In SET, assign the bit for the register number of REG the value VALUE.

   If REG is a hard register, do so for all its constituent registers.

   Return the number of registers that have become included (as a positive

   number) or excluded (as a negative number).  */

static int

assign_reg_reg_set (regset set, rtx reg, int value)

{

  unsigned regno = REGNO (reg);

  int nregs, i, old;

  if (regno >= FIRST_PSEUDO_REGISTER)

    {

      gcc_assert (!reload_completed);

      nregs = 1;

    }

  else

    nregs = hard_regno_nregs[regno][GET_MODE (reg)];

  for (old = 0, i = nregs; --i >= 0; regno++)

    {

      if ((value != 0) == REGNO_REG_SET_P (set, regno))

        continue;

      if (value)

        old++, SET_REGNO_REG_SET (set, regno);

      else

        old--, CLEAR_REGNO_REG_SET (set, regno);

    }

  return old;

}

/* Record state about current inputs / local registers / liveness

   in *P.  */

static inline void

struct_equiv_make_checkpoint (struct struct_equiv_checkpoint *p,

                              struct equiv_info *info)

{

  *p = info->cur;

}

/* Call struct_equiv_make_checkpoint (P, INFO) if the current partial block

   is suitable to split off - i.e. there is no dangling cc0 user - and

   if the current cost of the common instructions, minus the cost for

   setting up the inputs, is higher than what has been recorded before

   in CHECKPOINT[N].  Also, if we do so, confirm or cancel any pending

   changes.  */

static void

struct_equiv_improve_checkpoint (struct struct_equiv_checkpoint *p,

                                 struct equiv_info *info)

{

#ifdef HAVE_cc0

  if (reg_mentioned_p (cc0_rtx, info->cur.x_start)

      && !sets_cc0_p (info->cur.x_start))

    return;

#endif

  if (info->cur.input_count >= IMPOSSIBLE_MOVE_FACTOR)

    return;

  if (info->input_cost >= 0

      ? (COSTS_N_INSNS(info->cur.ninsns - p->ninsns)

         > info->input_cost * (info->cur.input_count - p->input_count))

      : info->cur.ninsns > p->ninsns && !info->cur.input_count)

    {

      if (info->check_input_conflict && ! resolve_input_conflict (info))

        return;

      /* We have a profitable set of changes.  If this is the final pass,

         commit them now.  Otherwise, we don't know yet if we can make any

         change, so put the old code back for now.  */

      if (info->mode & STRUCT_EQUIV_FINAL)

        confirm_change_group ();

      else

        cancel_changes (0);

      struct_equiv_make_checkpoint (p, info);

    }

}

/* Restore state about current inputs / local registers / liveness

   from P.  */

static void

struct_equiv_restore_checkpoint (struct struct_equiv_checkpoint *p,

                                 struct equiv_info *info)

{

  info->cur.ninsns = p->ninsns;

  info->cur.x_start = p->x_start;

  info->cur.y_start = p->y_start;

  info->cur.input_count = p->input_count;

  info->cur.input_valid = p->input_valid;

  while (info->cur.local_count > p->local_count)

    {

      info->cur.local_count--;

      info->cur.version--;

      if (REGNO_REG_SET_P (info->x_local_live,

                           REGNO (info->x_local[info->cur.local_count])))

        {

          assign_reg_reg_set (info->x_local_live,

                              info->x_local[info->cur.local_count], 0);

          assign_reg_reg_set (info->y_local_live,

                              info->y_local[info->cur.local_count], 0);

          info->cur.version--;

        }

    }

  if (info->cur.version != p->version)

    info->need_rerun = true;

}

/* Update register liveness to reflect that X is now life (if rvalue is

   nonzero) or dead (if rvalue is zero) in INFO->x_block, and likewise Y

   in INFO->y_block.  Return the number of registers the liveness of which

   changed in each block (as a negative number if registers became dead).  */

static int

note_local_live (struct equiv_info *info, rtx x, rtx y, int rvalue)

{

  unsigned x_regno = REGNO (x);

  unsigned y_regno = REGNO (y);

  int x_nominal_nregs = (x_regno >= FIRST_PSEUDO_REGISTER

                         ? 1 : hard_regno_nregs[x_regno][GET_MODE (x)]);

  int y_nominal_nregs = (y_regno >= FIRST_PSEUDO_REGISTER

                         ? 1 : hard_regno_nregs[y_regno][GET_MODE (y)]);

  int x_change = assign_reg_reg_set (info->x_local_live, x, rvalue);

  int y_change = assign_reg_reg_set (info->y_local_live, y, rvalue);

  gcc_assert (x_nominal_nregs && y_nominal_nregs);

  gcc_assert (x_change * y_nominal_nregs == y_change * x_nominal_nregs);

  if (y_change)

    {

      if (reload_completed)

        {

          unsigned x_regno ATTRIBUTE_UNUSED = REGNO (x);

          unsigned y_regno = REGNO (y);

          enum machine_mode x_mode = GET_MODE (x);

          if (secondary_reload_class (0, REGNO_REG_CLASS (y_regno), x_mode, x)

              != NO_REGS

#ifdef SECONDARY_MEMORY_NEEDED

              || SECONDARY_MEMORY_NEEDED (REGNO_REG_CLASS (y_regno),

                                          REGNO_REG_CLASS (x_regno), x_mode)

#endif

              )

          y_change *= IMPOSSIBLE_MOVE_FACTOR;

        }

      info->cur.input_count += y_change;

      info->cur.version++;

    }

  return x_change;

}

/* Check if *XP is equivalent to Y.  Until an an unreconcilable difference is

   found, use in-group changes with validate_change on *XP to make register

   assignments agree.  It is the (not necessarily direct) callers

   responsibility to verify / confirm / cancel these changes, as appropriate.

   RVALUE indicates if the processed piece of rtl is used as a destination, in

   which case we can't have different registers being an input.  Returns

   nonzero if the two blocks have been identified as equivalent, zero otherwise.

   RVALUE == 0: destination

   RVALUE == 1: source

   RVALUE == -1: source, ignore SET_DEST of SET / clobber.  */

bool

rtx_equiv_p (rtx *xp, rtx y, int rvalue, struct equiv_info *info)

{

  rtx x = *xp;

  enum rtx_code code;

  int length;

  const char *format;

  int i;

  if (!y || !x)

    return x == y;

  code = GET_CODE (y);

  if (code != REG && x == y)

    return true;

  if (GET_CODE (x) != code

      || GET_MODE (x) != GET_MODE (y))

    return false;

  /* ??? could extend to allow CONST_INT inputs.  */

  switch (code)

    {

    case REG:

      {

        unsigned x_regno = REGNO (x);

        unsigned y_regno = REGNO (y);

        int x_common_live, y_common_live;

        if (reload_completed

            && (x_regno >= FIRST_PSEUDO_REGISTER

                || y_regno >= FIRST_PSEUDO_REGISTER))

          {

            /* We should only see this in REG_NOTEs.  */

            gcc_assert (!info->live_update);

            /* Returning false will cause us to remove the notes.  */

            return false;

          }

#ifdef STACK_REGS

        /* After reg-stack, can only accept literal matches of stack regs.  */

        if (info->mode & CLEANUP_POST_REGSTACK

            && (IN_RANGE (x_regno, FIRST_STACK_REG, LAST_STACK_REG)

                || IN_RANGE (y_regno, FIRST_STACK_REG, LAST_STACK_REG)))

          return x_regno == y_regno;

#endif

        /* If the register is a locally live one in one block, the

           corresponding one must be locally live in the other, too, and

           match of identical regnos doesn't apply.  */

        if (REGNO_REG_SET_P (info->x_local_live, x_regno))

          {

            if (!REGNO_REG_SET_P (info->y_local_live, y_regno))

              return false;

          }

        else if (REGNO_REG_SET_P (info->y_local_live, y_regno))

          return false;

        else if (x_regno == y_regno)

          {

            if (!rvalue && info->cur.input_valid

                && (reg_overlap_mentioned_p (x, info->x_input)

                    || reg_overlap_mentioned_p (x, info->y_input)))

              return false;

            /* Update liveness information.  */

            if (info->live_update

                && assign_reg_reg_set (info->common_live, x, rvalue))

              info->cur.version++;

            return true;

          }

        x_common_live = REGNO_REG_SET_P (info->common_live, x_regno);

        y_common_live = REGNO_REG_SET_P (info->common_live, y_regno);

        if (x_common_live != y_common_live)

          return false;

        else if (x_common_live)

          {

            if (! rvalue || info->input_cost < 0 || no_new_pseudos)

              return false;

            /* If info->live_update is not set, we are processing notes.

               We then allow a match with x_input / y_input found in a

               previous pass.  */

            if (info->live_update && !info->cur.input_valid)

              {

                info->cur.input_valid = true;

                info->x_input = x;

                info->y_input = y;

                info->cur.input_count += optimize_size ? 2 : 1;

                if (info->input_reg

                    && GET_MODE (info->input_reg) != GET_MODE (info->x_input))

                  info->input_reg = NULL_RTX;

                if (!info->input_reg)

                  info->input_reg = gen_reg_rtx (GET_MODE (info->x_input));

              }

            else if ((info->live_update

                      ? ! info->cur.input_valid : ! info->x_input)

                     || ! rtx_equal_p (x, info->x_input)

                     || ! rtx_equal_p (y, info->y_input))

              return false;

            validate_change (info->cur.x_start, xp, info->input_reg, 1);

          }

        else

          {

            int x_nregs = (x_regno >= FIRST_PSEUDO_REGISTER

                           ? 1 : hard_regno_nregs[x_regno][GET_MODE (x)]);

            int y_nregs = (y_regno >= FIRST_PSEUDO_REGISTER

                           ? 1 : hard_regno_nregs[y_regno][GET_MODE (y)]);

            int size = GET_MODE_SIZE (GET_MODE (x));

            enum machine_mode x_mode = GET_MODE (x);

            unsigned x_regno_i, y_regno_i;

            int x_nregs_i, y_nregs_i, size_i;

            int local_count = info->cur.local_count;

            /* This might be a register local to each block.  See if we have

               it already registered.  */

            for (i = local_count - 1; i >= 0; i--)

              {

                x_regno_i = REGNO (info->x_local[i]);

                x_nregs_i = (x_regno_i >= FIRST_PSEUDO_REGISTER

                             ? 1 : hard_regno_nregs[x_regno_i][GET_MODE (x)]);

                y_regno_i = REGNO (info->y_local[i]);

                y_nregs_i = (y_regno_i >= FIRST_PSEUDO_REGISTER

                             ? 1 : hard_regno_nregs[y_regno_i][GET_MODE (y)]);

                size_i = GET_MODE_SIZE (GET_MODE (info->x_local[i]));

                /* If we have a new pair of registers that is wider than an

                   old pair and enclosing it with matching offsets,

                   remove the old pair.  If we find a matching, wider, old

                   pair, use the old one.  If the width is the same, use the

                   old one if the modes match, but the new if they don't.

                   We don't want to get too fancy with subreg_regno_offset

                   here, so we just test two straightforward cases each.  */

                if (info->live_update

                    && (x_mode != GET_MODE (info->x_local[i])

                        ? size >= size_i : size > size_i))

                  {

                    /* If the new pair is fully enclosing a matching

                       existing pair, remove the old one.  N.B. because

                       we are removing one entry here, the check below

                       if we have space for a new entry will succeed.  */

                    if ((x_regno <= x_regno_i

                         && x_regno + x_nregs >= x_regno_i + x_nregs_i

                         && x_nregs == y_nregs && x_nregs_i == y_nregs_i

                         && x_regno - x_regno_i == y_regno - y_regno_i)

                        || (x_regno == x_regno_i && y_regno == y_regno_i

                            && x_nregs >= x_nregs_i && y_nregs >= y_nregs_i))

                      {

                        info->cur.local_count = --local_count;

                        info->x_local[i] = info->x_local[local_count];

                        info->y_local[i] = info->y_local[local_count];

                        continue;

                      }

                  }

                else

                  {

                    /* If the new pair is fully enclosed within a matching

                       existing pair, succeed.  */

                    if (x_regno >= x_regno_i

                        && x_regno + x_nregs <= x_regno_i + x_nregs_i

                        && x_nregs == y_nregs && x_nregs_i == y_nregs_i

                        && x_regno - x_regno_i == y_regno - y_regno_i)

                      break;

                    if (x_regno == x_regno_i && y_regno == y_regno_i

                        && x_nregs <= x_nregs_i && y_nregs <= y_nregs_i)

                      break;

                }

                /* Any other overlap causes a match failure.  */

                if (x_regno + x_nregs > x_regno_i

                    && x_regno_i + x_nregs_i > x_regno)

                  return false;

                if (y_regno + y_nregs > y_regno_i

                    && y_regno_i + y_nregs_i > y_regno)

                  return false;

              }

            if (i < 0)

              {

                /* Not found.  Create a new entry if possible.  */

                if (!info->live_update

                    || info->cur.local_count >= STRUCT_EQUIV_MAX_LOCAL)

                  return false;

                info->x_local[info->cur.local_count] = x;

                info->y_local[info->cur.local_count] = y;

                info->cur.local_count++;

                info->cur.version++;

              }

            note_local_live (info, x, y, rvalue);

          }

        return true;

      }

    case SET:

      gcc_assert (rvalue < 0);

      /* Ignore the destinations role as a destination.  Still, we have

         to consider input registers embedded in the addresses of a MEM.

         N.B., we process the rvalue aspect of STRICT_LOW_PART /

         ZERO_EXTEND / SIGN_EXTEND along with their lvalue aspect.  */

      if(!set_dest_addr_equiv_p (SET_DEST (x), SET_DEST (y), info))

        return false;

      /* Process source.  */

      return rtx_equiv_p (&SET_SRC (x), SET_SRC (y), 1, info);

    case PRE_MODIFY:

      /* Process destination.  */

      if (!rtx_equiv_p (&XEXP (x, 0), XEXP (y, 0), 0, info))

        return false;

      /* Process source.  */

      return rtx_equiv_p (&XEXP (x, 1), XEXP (y, 1), 1, info);

    case POST_MODIFY:

      {

        rtx x_dest0, x_dest1;

        /* Process destination.  */

        x_dest0 = XEXP (x, 0);

        gcc_assert (REG_P (x_dest0));

        if (!rtx_equiv_p (&XEXP (x, 0), XEXP (y, 0), 0, info))

          return false;

        x_dest1 = XEXP (x, 0);

        /* validate_change might have changed the destination.  Put it back

           so that we can do a proper match for its role a an input.  */

        XEXP (x, 0) = x_dest0;

        if (!rtx_equiv_p (&XEXP (x, 0), XEXP (y, 0), 1, info))

          return false;

        gcc_assert (x_dest1 == XEXP (x, 0));

        /* Process source.  */

        return rtx_equiv_p (&XEXP (x, 1), XEXP (y, 1), 1, info);

      }

    case CLOBBER:

      gcc_assert (rvalue < 0);

      return true;

    /* Some special forms are also rvalues when they appear in lvalue

       positions.  However, we must ont try to match a register after we

       have already altered it with validate_change, consider the rvalue

       aspect while we process the lvalue.  */

    case STRICT_LOW_PART:

    case ZERO_EXTEND:

    case SIGN_EXTEND:

      {

        rtx x_inner, y_inner;

        enum rtx_code code;

        int change;

        if (rvalue)

          break;

        x_inner = XEXP (x, 0);

        y_inner = XEXP (y, 0);

        if (GET_MODE (x_inner) != GET_MODE (y_inner))

          return false;

        code = GET_CODE (x_inner);

        if (code != GET_CODE (y_inner))

          return false;

        /* The address of a MEM is an input that will be processed during

           rvalue == -1 processing.  */

        if (code == SUBREG)

          {

            if (SUBREG_BYTE (x_inner) != SUBREG_BYTE (y_inner))

              return false;

            x = x_inner;

            x_inner = SUBREG_REG (x_inner);

            y_inner = SUBREG_REG (y_inner);

            if (GET_MODE (x_inner) != GET_MODE (y_inner))

              return false;

            code = GET_CODE (x_inner);

            if (code != GET_CODE (y_inner))

              return false;

          }

        if (code == MEM)

          return true;

        gcc_assert (code == REG);

        if (! rtx_equiv_p (&XEXP (x, 0), y_inner, rvalue, info))

          return false;

        if (REGNO (x_inner) == REGNO (y_inner))

          {

            change = assign_reg_reg_set (info->common_live, x_inner, 1);

            info->cur.version++;

          }

        else

          change = note_local_live (info, x_inner, y_inner, 1);

        gcc_assert (change);

        return true;

      }

    /* The AUTO_INC / POST_MODIFY / PRE_MODIFY sets are modelled to take

       place during input processing, however, that is benign, since they

       are paired with reads.  */

    case MEM:

      return !rvalue || rtx_equiv_p (&XEXP (x, 0), XEXP (y, 0), rvalue, info);

    case POST_INC: case POST_DEC: case PRE_INC: case PRE_DEC:

      return (rtx_equiv_p (&XEXP (x, 0), XEXP (y, 0), 0, info)

              && rtx_equiv_p (&XEXP (x, 0), XEXP (y, 0), 1, info));

    case PARALLEL:

      /* If this is a top-level PATTERN PARALLEL, we expect the caller to

         have handled the SET_DESTs.  A complex or vector PARALLEL can be

         identified by having a mode.  */

      gcc_assert (rvalue < 0 || GET_MODE (x) != VOIDmode);

      break;

    case LABEL_REF:

      /* Check special tablejump match case.  */

      if (XEXP (y, 0) == info->y_label)

        return (XEXP (x, 0) == info->x_label);

      /* We can't assume nonlocal labels have their following insns yet.  */

      if (LABEL_REF_NONLOCAL_P (x) || LABEL_REF_NONLOCAL_P (y))

        return XEXP (x, 0) == XEXP (y, 0);

      /* Two label-refs are equivalent if they point at labels

         in the same position in the instruction stream.  */

      return (next_real_insn (XEXP (x, 0))

              == next_real_insn (XEXP (y, 0)));

    case SYMBOL_REF: