2004-04-29 Paolo Bonzini <bonzini@gnu.org>

[gcc/gcc.git] / gcc / combine.c

/* Optimize by combining instructions for GNU compiler.
   Copyright (C) 1987, 1988, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
   1999, 2000, 2001, 2002, 2003, 2004 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 2, 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 COPYING.  If not, write to the Free
Software Foundation, 59 Temple Place - Suite 330, Boston, MA
02111-1307, USA.  */

/* This module is essentially the "combiner" phase of the U. of Arizona
   Portable Optimizer, but redone to work on our list-structured
   representation for RTL instead of their string representation.

   The LOG_LINKS of each insn identify the most recent assignment
   to each REG used in the insn.  It is a list of previous insns,
   each of which contains a SET for a REG that is used in this insn
   and not used or set in between.  LOG_LINKs never cross basic blocks.
   They were set up by the preceding pass (lifetime analysis).

   We try to combine each pair of insns joined by a logical link.
   We also try to combine triples of insns A, B and C when
   C has a link back to B and B has a link back to A.

   LOG_LINKS does not have links for use of the CC0.  They don't
   need to, because the insn that sets the CC0 is always immediately
   before the insn that tests it.  So we always regard a branch
   insn as having a logical link to the preceding insn.  The same is true
   for an insn explicitly using CC0.

   We check (with use_crosses_set_p) to avoid combining in such a way
   as to move a computation to a place where its value would be different.

   Combination is done by mathematically substituting the previous
   insn(s) values for the regs they set into the expressions in
   the later insns that refer to these regs.  If the result is a valid insn
   for our target machine, according to the machine description,
   we install it, delete the earlier insns, and update the data flow
   information (LOG_LINKS and REG_NOTES) for what we did.

   There are a few exceptions where the dataflow information created by
   flow.c aren't completely updated:

   - reg_live_length is not updated
   - a LOG_LINKS entry that refers to an insn with multiple SETs may be
     removed because there is no way to know which register it was
     linking

   To simplify substitution, we combine only when the earlier insn(s)
   consist of only a single assignment.  To simplify updating afterward,
   we never combine when a subroutine call appears in the middle.

   Since we do not represent assignments to CC0 explicitly except when that
   is all an insn does, there is no LOG_LINKS entry in an insn that uses
   the condition code for the insn that set the condition code.
   Fortunately, these two insns must be consecutive.
   Therefore, every JUMP_INSN is taken to have an implicit logical link
   to the preceding insn.  This is not quite right, since non-jumps can
   also use the condition code; but in practice such insns would not
   combine anyway.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "rtl.h"
#include "tree.h"
#include "tm_p.h"
#include "flags.h"
#include "regs.h"
#include "hard-reg-set.h"
#include "basic-block.h"
#include "insn-config.h"
#include "function.h"
/* Include expr.h after insn-config.h so we get HAVE_conditional_move.  */
#include "expr.h"
#include "insn-attr.h"
#include "recog.h"
#include "real.h"
#include "toplev.h"
#include "target.h"

/* Number of attempts to combine instructions in this function.  */

static int combine_attempts;

/* Number of attempts that got as far as substitution in this function.  */

static int combine_merges;

/* Number of instructions combined with added SETs in this function.  */

static int combine_extras;

/* Number of instructions combined in this function.  */

static int combine_successes;

/* Totals over entire compilation.  */

static int total_attempts, total_merges, total_extras, total_successes;

\f
/* Vector mapping INSN_UIDs to cuids.
   The cuids are like uids but increase monotonically always.
   Combine always uses cuids so that it can compare them.
   But actually renumbering the uids, which we used to do,
   proves to be a bad idea because it makes it hard to compare
   the dumps produced by earlier passes with those from later passes.  */

static int *uid_cuid;
static int max_uid_cuid;

/* Get the cuid of an insn.  */

#define INSN_CUID(INSN) \
(INSN_UID (INSN) > max_uid_cuid ? insn_cuid (INSN) : uid_cuid[INSN_UID (INSN)])

/* In case BITS_PER_WORD == HOST_BITS_PER_WIDE_INT, shifting by
   BITS_PER_WORD would invoke undefined behavior.  Work around it.  */

#define UWIDE_SHIFT_LEFT_BY_BITS_PER_WORD(val) \
  (((unsigned HOST_WIDE_INT) (val) << (BITS_PER_WORD - 1)) << 1)

#define nonzero_bits(X, M) \
  cached_nonzero_bits (X, M, NULL_RTX, VOIDmode, 0)

#define num_sign_bit_copies(X, M) \
  cached_num_sign_bit_copies (X, M, NULL_RTX, VOIDmode, 0)

/* Maximum register number, which is the size of the tables below.  */

static unsigned int combine_max_regno;

struct reg_stat {
  /* Record last point of death of (hard or pseudo) register n.  */
  rtx                           last_death;

  /* Record last point of modification of (hard or pseudo) register n.  */
  rtx                           last_set;

  /* The next group of fields allows the recording of the last value assigned
     to (hard or pseudo) register n.  We use this information to see if an
     operation being processed is redundant given a prior operation performed
     on the register.  For example, an `and' with a constant is redundant if
     all the zero bits are already known to be turned off.

     We use an approach similar to that used by cse, but change it in the
     following ways:

     (1) We do not want to reinitialize at each label.
     (2) It is useful, but not critical, to know the actual value assigned
         to a register.  Often just its form is helpful.

     Therefore, we maintain the following fields:

     last_set_value             the last value assigned
     last_set_label             records the value of label_tick when the
                                register was assigned
     last_set_table_tick        records the value of label_tick when a
                                value using the register is assigned
     last_set_invalid           set to nonzero when it is not valid
                                to use the value of this register in some
                                register's value

     To understand the usage of these tables, it is important to understand
     the distinction between the value in last_set_value being valid and
     the register being validly contained in some other expression in the
     table.

     (The next two parameters are out of date).

     reg_stat[i].last_set_value is valid if it is nonzero, and either
     reg_n_sets[i] is 1 or reg_stat[i].last_set_label == label_tick.

     Register I may validly appear in any expression returned for the value
     of another register if reg_n_sets[i] is 1.  It may also appear in the
     value for register J if reg_stat[j].last_set_invalid is zero, or
     reg_stat[i].last_set_label < reg_stat[j].last_set_label.

     If an expression is found in the table containing a register which may
     not validly appear in an expression, the register is replaced by
     something that won't match, (clobber (const_int 0)).  */

  /* Record last value assigned to (hard or pseudo) register n.  */

  rtx                           last_set_value;

  /* Record the value of label_tick when an expression involving register n
     is placed in last_set_value.  */

  int                           last_set_table_tick;

  /* Record the value of label_tick when the value for register n is placed in
     last_set_value.  */

  int                           last_set_label;

  /* These fields are maintained in parallel with last_set_value and are
     used to store the mode in which the register was last set, te bits
     that were known to be zero when it was last set, and the number of
     sign bits copies it was known to have when it was last set.  */

  unsigned HOST_WIDE_INT        last_set_nonzero_bits;
  char                          last_set_sign_bit_copies;
  ENUM_BITFIELD(machine_mode)   last_set_mode : 8; 

  /* Set nonzero if references to register n in expressions should not be
     used.  last_set_invalid is set nonzero when this register is being
     assigned to and last_set_table_tick == label_tick.  */

  char                          last_set_invalid;

  /* Some registers that are set more than once and used in more than one
     basic block are nevertheless always set in similar ways.  For example,
     a QImode register may be loaded from memory in two places on a machine
     where byte loads zero extend.

     We record in the following fields if a register has some leading bits
     that are always equal to the sign bit, and what we know about the
     nonzero bits of a register, specifically which bits are known to be
     zero.

     If an entry is zero, it means that we don't know anything special.  */

  unsigned char                 sign_bit_copies;

  unsigned HOST_WIDE_INT        nonzero_bits;
};

static struct reg_stat *reg_stat;

/* Record the cuid of the last insn that invalidated memory
   (anything that writes memory, and subroutine calls, but not pushes).  */

static int mem_last_set;

/* Record the cuid of the last CALL_INSN
   so we can tell whether a potential combination crosses any calls.  */

static int last_call_cuid;

/* When `subst' is called, this is the insn that is being modified
   (by combining in a previous insn).  The PATTERN of this insn
   is still the old pattern partially modified and it should not be
   looked at, but this may be used to examine the successors of the insn
   to judge whether a simplification is valid.  */

static rtx subst_insn;

/* This is the lowest CUID that `subst' is currently dealing with.
   get_last_value will not return a value if the register was set at or
   after this CUID.  If not for this mechanism, we could get confused if
   I2 or I1 in try_combine were an insn that used the old value of a register
   to obtain a new value.  In that case, we might erroneously get the
   new value of the register when we wanted the old one.  */

static int subst_low_cuid;

/* This contains any hard registers that are used in newpat; reg_dead_at_p
   must consider all these registers to be always live.  */

static HARD_REG_SET newpat_used_regs;

/* This is an insn to which a LOG_LINKS entry has been added.  If this
   insn is the earlier than I2 or I3, combine should rescan starting at
   that location.  */

static rtx added_links_insn;

/* Basic block in which we are performing combines.  */
static basic_block this_basic_block;

/* A bitmap indicating which blocks had registers go dead at entry.
   After combine, we'll need to re-do global life analysis with
   those blocks as starting points.  */
static sbitmap refresh_blocks;
\f
/* Incremented for each label.  */

static int label_tick;

/* Mode used to compute significance in reg_stat[].nonzero_bits.  It is the
   largest integer mode that can fit in HOST_BITS_PER_WIDE_INT.  */

static enum machine_mode nonzero_bits_mode;

/* Nonzero when reg_stat[].nonzero_bits and reg_stat[].sign_bit_copies can
   be safely used.  It is zero while computing them and after combine has
   completed.  This former test prevents propagating values based on
   previously set values, which can be incorrect if a variable is modified
   in a loop.  */

static int nonzero_sign_valid;

\f
/* Record one modification to rtl structure
   to be undone by storing old_contents into *where.
   is_int is 1 if the contents are an int.  */

struct undo
{
  struct undo *next;
  int is_int;
  union {rtx r; int i;} old_contents;
  union {rtx *r; int *i;} where;
};

/* Record a bunch of changes to be undone, up to MAX_UNDO of them.
   num_undo says how many are currently recorded.

   other_insn is nonzero if we have modified some other insn in the process
   of working on subst_insn.  It must be verified too.  */

struct undobuf
{
  struct undo *undos;
  struct undo *frees;
  rtx other_insn;
};

static struct undobuf undobuf;

/* Number of times the pseudo being substituted for
   was found and replaced.  */

static int n_occurrences;

static void do_SUBST (rtx *, rtx);
static void do_SUBST_INT (int *, int);
static void init_reg_last (void);
static void setup_incoming_promotions (void);
static void set_nonzero_bits_and_sign_copies (rtx, rtx, void *);
static int cant_combine_insn_p (rtx);
static int can_combine_p (rtx, rtx, rtx, rtx, rtx *, rtx *);
static int combinable_i3pat (rtx, rtx *, rtx, rtx, int, rtx *);
static int contains_muldiv (rtx);
static rtx try_combine (rtx, rtx, rtx, int *);
static void undo_all (void);
static void undo_commit (void);
static rtx *find_split_point (rtx *, rtx);
static rtx subst (rtx, rtx, rtx, int, int);
static rtx combine_simplify_rtx (rtx, enum machine_mode, int);
static rtx simplify_if_then_else (rtx);
static rtx simplify_set (rtx);
static rtx simplify_logical (rtx);
static rtx expand_compound_operation (rtx);
static rtx expand_field_assignment (rtx);
static rtx make_extraction (enum machine_mode, rtx, HOST_WIDE_INT,
                            rtx, unsigned HOST_WIDE_INT, int, int, int);
static rtx extract_left_shift (rtx, int);
static rtx make_compound_operation (rtx, enum rtx_code);
static int get_pos_from_mask (unsigned HOST_WIDE_INT,
                              unsigned HOST_WIDE_INT *);
static rtx force_to_mode (rtx, enum machine_mode,
                          unsigned HOST_WIDE_INT, rtx, int);
static rtx if_then_else_cond (rtx, rtx *, rtx *);
static rtx known_cond (rtx, enum rtx_code, rtx, rtx);
static int rtx_equal_for_field_assignment_p (rtx, rtx);
static rtx make_field_assignment (rtx);
static rtx apply_distributive_law (rtx);
static rtx simplify_and_const_int (rtx, enum machine_mode, rtx,
                                   unsigned HOST_WIDE_INT);
static unsigned HOST_WIDE_INT cached_nonzero_bits (rtx, enum machine_mode,
                                                   rtx, enum machine_mode,
                                                   unsigned HOST_WIDE_INT);
static unsigned HOST_WIDE_INT nonzero_bits1 (rtx, enum machine_mode, rtx,
                                             enum machine_mode,
                                             unsigned HOST_WIDE_INT);
static unsigned int cached_num_sign_bit_copies (rtx, enum machine_mode, rtx,
                                                enum machine_mode,
                                                unsigned int);
static unsigned int num_sign_bit_copies1 (rtx, enum machine_mode, rtx,
                                          enum machine_mode, unsigned int);
static int merge_outer_ops (enum rtx_code *, HOST_WIDE_INT *, enum rtx_code,
                            HOST_WIDE_INT, enum machine_mode, int *);
static rtx simplify_shift_const (rtx, enum rtx_code, enum machine_mode, rtx,
                                 int);
static int recog_for_combine (rtx *, rtx, rtx *);
static rtx gen_lowpart_for_combine (enum machine_mode, rtx);
static rtx gen_binary (enum rtx_code, enum machine_mode, rtx, rtx);
static enum rtx_code simplify_comparison (enum rtx_code, rtx *, rtx *);
static void update_table_tick (rtx);
static void record_value_for_reg (rtx, rtx, rtx);
static void check_promoted_subreg (rtx, rtx);
static void record_dead_and_set_regs_1 (rtx, rtx, void *);
static void record_dead_and_set_regs (rtx);
static int get_last_value_validate (rtx *, rtx, int, int);
static rtx get_last_value (rtx);
static int use_crosses_set_p (rtx, int);
static void reg_dead_at_p_1 (rtx, rtx, void *);
static int reg_dead_at_p (rtx, rtx);
static void move_deaths (rtx, rtx, int, rtx, rtx *);
static int reg_bitfield_target_p (rtx, rtx);
static void distribute_notes (rtx, rtx, rtx, rtx);
static void distribute_links (rtx);
static void mark_used_regs_combine (rtx);
static int insn_cuid (rtx);
static void record_promoted_value (rtx, rtx);
static rtx reversed_comparison (rtx, enum machine_mode, rtx, rtx);
static enum rtx_code combine_reversed_comparison_code (rtx);
static int unmentioned_reg_p_1 (rtx *, void *);
static bool unmentioned_reg_p (rtx, rtx);
\f
/* Substitute NEWVAL, an rtx expression, into INTO, a place in some
   insn.  The substitution can be undone by undo_all.  If INTO is already
   set to NEWVAL, do not record this change.  Because computing NEWVAL might
   also call SUBST, we have to compute it before we put anything into
   the undo table.  */

static void
do_SUBST (rtx *into, rtx newval)
{
  struct undo *buf;
  rtx oldval = *into;

  if (oldval == newval)
    return;

  /* We'd like to catch as many invalid transformations here as
     possible.  Unfortunately, there are way too many mode changes
     that are perfectly valid, so we'd waste too much effort for
     little gain doing the checks here.  Focus on catching invalid
     transformations involving integer constants.  */
  if (GET_MODE_CLASS (GET_MODE (oldval)) == MODE_INT
      && GET_CODE (newval) == CONST_INT)
    {
      /* Sanity check that we're replacing oldval with a CONST_INT
         that is a valid sign-extension for the original mode.  */
      if (INTVAL (newval) != trunc_int_for_mode (INTVAL (newval),
                                                 GET_MODE (oldval)))
        abort ();

      /* Replacing the operand of a SUBREG or a ZERO_EXTEND with a
         CONST_INT is not valid, because after the replacement, the
         original mode would be gone.  Unfortunately, we can't tell
         when do_SUBST is called to replace the operand thereof, so we
         perform this test on oldval instead, checking whether an
         invalid replacement took place before we got here.  */
      if ((GET_CODE (oldval) == SUBREG
           && GET_CODE (SUBREG_REG (oldval)) == CONST_INT)
          || (GET_CODE (oldval) == ZERO_EXTEND
              && GET_CODE (XEXP (oldval, 0)) == CONST_INT))
        abort ();
    }

  if (undobuf.frees)
    buf = undobuf.frees, undobuf.frees = buf->next;
  else
    buf = xmalloc (sizeof (struct undo));

  buf->is_int = 0;
  buf->where.r = into;
  buf->old_contents.r = oldval;
  *into = newval;

  buf->next = undobuf.undos, undobuf.undos = buf;
}

#define SUBST(INTO, NEWVAL)     do_SUBST(&(INTO), (NEWVAL))

/* Similar to SUBST, but NEWVAL is an int expression.  Note that substitution
   for the value of a HOST_WIDE_INT value (including CONST_INT) is
   not safe.  */

static void
do_SUBST_INT (int *into, int newval)
{
  struct undo *buf;
  int oldval = *into;

  if (oldval == newval)
    return;

  if (undobuf.frees)
    buf = undobuf.frees, undobuf.frees = buf->next;
  else
    buf = xmalloc (sizeof (struct undo));

  buf->is_int = 1;
  buf->where.i = into;
  buf->old_contents.i = oldval;
  *into = newval;

  buf->next = undobuf.undos, undobuf.undos = buf;
}

#define SUBST_INT(INTO, NEWVAL)  do_SUBST_INT(&(INTO), (NEWVAL))
\f
/* Main entry point for combiner.  F is the first insn of the function.
   NREGS is the first unused pseudo-reg number.

   Return nonzero if the combiner has turned an indirect jump
   instruction into a direct jump.  */
int
combine_instructions (rtx f, unsigned int nregs)
{
  rtx insn, next;
#ifdef HAVE_cc0
  rtx prev;
#endif
  int i;
  rtx links, nextlinks;

  int new_direct_jump_p = 0;

  combine_attempts = 0;
  combine_merges = 0;
  combine_extras = 0;
  combine_successes = 0;

  combine_max_regno = nregs;

  /* It is not safe to use ordinary gen_lowpart in combine.
     See comments in gen_lowpart_for_combine.  */
  gen_lowpart = gen_lowpart_for_combine;

  reg_stat = xcalloc (nregs, sizeof (struct reg_stat));

  init_recog_no_volatile ();

  /* Compute maximum uid value so uid_cuid can be allocated.  */

  for (insn = f, i = 0; insn; insn = NEXT_INSN (insn))
    if (INSN_UID (insn) > i)
      i = INSN_UID (insn);

  uid_cuid = xmalloc ((i + 1) * sizeof (int));
  max_uid_cuid = i;

  nonzero_bits_mode = mode_for_size (HOST_BITS_PER_WIDE_INT, MODE_INT, 0);

  /* Don't use reg_stat[].nonzero_bits when computing it.  This can cause
     problems when, for example, we have j <<= 1 in a loop.  */

  nonzero_sign_valid = 0;

  /* Compute the mapping from uids to cuids.
     Cuids are numbers assigned to insns, like uids,
     except that cuids increase monotonically through the code.

     Scan all SETs and see if we can deduce anything about what
     bits are known to be zero for some registers and how many copies
     of the sign bit are known to exist for those registers.

     Also set any known values so that we can use it while searching
     for what bits are known to be set.  */

  label_tick = 1;

  setup_incoming_promotions ();

  refresh_blocks = sbitmap_alloc (last_basic_block);
  sbitmap_zero (refresh_blocks);

  for (insn = f, i = 0; insn; insn = NEXT_INSN (insn))
    {
      uid_cuid[INSN_UID (insn)] = ++i;
      subst_low_cuid = i;
      subst_insn = insn;

      if (INSN_P (insn))
        {
          note_stores (PATTERN (insn), set_nonzero_bits_and_sign_copies,
                       NULL);
          record_dead_and_set_regs (insn);

#ifdef AUTO_INC_DEC
          for (links = REG_NOTES (insn); links; links = XEXP (links, 1))
            if (REG_NOTE_KIND (links) == REG_INC)
              set_nonzero_bits_and_sign_copies (XEXP (links, 0), NULL_RTX,
                                                NULL);
#endif
        }

      if (GET_CODE (insn) == CODE_LABEL)
        label_tick++;
    }

  nonzero_sign_valid = 1;

  /* Now scan all the insns in forward order.  */

  label_tick = 1;
  last_call_cuid = 0;
  mem_last_set = 0;
  init_reg_last ();
  setup_incoming_promotions ();

  FOR_EACH_BB (this_basic_block)
    {
      for (insn = BB_HEAD (this_basic_block);
           insn != NEXT_INSN (BB_END (this_basic_block));
           insn = next ? next : NEXT_INSN (insn))
        {
          next = 0;

          if (GET_CODE (insn) == CODE_LABEL)
            label_tick++;

          else if (INSN_P (insn))
            {
              /* See if we know about function return values before this
                 insn based upon SUBREG flags.  */
              check_promoted_subreg (insn, PATTERN (insn));

              /* Try this insn with each insn it links back to.  */

              for (links = LOG_LINKS (insn); links; links = XEXP (links, 1))
                if ((next = try_combine (insn, XEXP (links, 0),
                                         NULL_RTX, &new_direct_jump_p)) != 0)
                  goto retry;

              /* Try each sequence of three linked insns ending with this one.  */

              for (links = LOG_LINKS (insn); links; links = XEXP (links, 1))
                {
                  rtx link = XEXP (links, 0);

                  /* If the linked insn has been replaced by a note, then there
                     is no point in pursuing this chain any further.  */
                  if (GET_CODE (link) == NOTE)
                    continue;

                  for (nextlinks = LOG_LINKS (link);
                       nextlinks;
                       nextlinks = XEXP (nextlinks, 1))
                    if ((next = try_combine (insn, link,
                                             XEXP (nextlinks, 0),
                                             &new_direct_jump_p)) != 0)
                      goto retry;
                }

#ifdef HAVE_cc0
              /* Try to combine a jump insn that uses CC0
                 with a preceding insn that sets CC0, and maybe with its
                 logical predecessor as well.
                 This is how we make decrement-and-branch insns.
                 We need this special code because data flow connections
                 via CC0 do not get entered in LOG_LINKS.  */

              if (GET_CODE (insn) == JUMP_INSN
                  && (prev = prev_nonnote_insn (insn)) != 0
                  && GET_CODE (prev) == INSN
                  && sets_cc0_p (PATTERN (prev)))
                {
                  if ((next = try_combine (insn, prev,
                                           NULL_RTX, &new_direct_jump_p)) != 0)
                    goto retry;

                  for (nextlinks = LOG_LINKS (prev); nextlinks;
                       nextlinks = XEXP (nextlinks, 1))
                    if ((next = try_combine (insn, prev,
                                             XEXP (nextlinks, 0),
                                             &new_direct_jump_p)) != 0)
                      goto retry;
                }

              /* Do the same for an insn that explicitly references CC0.  */
              if (GET_CODE (insn) == INSN
                  && (prev = prev_nonnote_insn (insn)) != 0
                  && GET_CODE (prev) == INSN
                  && sets_cc0_p (PATTERN (prev))
                  && GET_CODE (PATTERN (insn)) == SET
                  && reg_mentioned_p (cc0_rtx, SET_SRC (PATTERN (insn))))
                {
                  if ((next = try_combine (insn, prev,
                                           NULL_RTX, &new_direct_jump_p)) != 0)
                    goto retry;

                  for (nextlinks = LOG_LINKS (prev); nextlinks;
                       nextlinks = XEXP (nextlinks, 1))
                    if ((next = try_combine (insn, prev,
                                             XEXP (nextlinks, 0),
                                             &new_direct_jump_p)) != 0)
                      goto retry;
                }

              /* Finally, see if any of the insns that this insn links to
                 explicitly references CC0.  If so, try this insn, that insn,
                 and its predecessor if it sets CC0.  */
              for (links = LOG_LINKS (insn); links; links = XEXP (links, 1))
                if (GET_CODE (XEXP (links, 0)) == INSN
                    && GET_CODE (PATTERN (XEXP (links, 0))) == SET
                    && reg_mentioned_p (cc0_rtx, SET_SRC (PATTERN (XEXP (links, 0))))
                    && (prev = prev_nonnote_insn (XEXP (links, 0))) != 0
                    && GET_CODE (prev) == INSN
                    && sets_cc0_p (PATTERN (prev))
                    && (next = try_combine (insn, XEXP (links, 0),
                                            prev, &new_direct_jump_p)) != 0)
                  goto retry;
#endif

              /* Try combining an insn with two different insns whose results it
                 uses.  */
              for (links = LOG_LINKS (insn); links; links = XEXP (links, 1))
                for (nextlinks = XEXP (links, 1); nextlinks;
                     nextlinks = XEXP (nextlinks, 1))
                  if ((next = try_combine (insn, XEXP (links, 0),
                                           XEXP (nextlinks, 0),
                                           &new_direct_jump_p)) != 0)
                    goto retry;

              /* Try this insn with each REG_EQUAL note it links back to.  */
              for (links = LOG_LINKS (insn); links; links = XEXP (links, 1))
                {
                  rtx set, note;
                  rtx temp = XEXP (links, 0);
                  if ((set = single_set (temp)) != 0
                      && (note = find_reg_equal_equiv_note (temp)) != 0
                      && GET_CODE (XEXP (note, 0)) != EXPR_LIST
                      /* Avoid using a register that may already been marked
                         dead by an earlier instruction.  */
                      && ! unmentioned_reg_p (XEXP (note, 0), SET_SRC (set)))
                    {
                      /* Temporarily replace the set's source with the
                         contents of the REG_EQUAL note.  The insn will
                         be deleted or recognized by try_combine.  */
                      rtx orig = SET_SRC (set);
                      SET_SRC (set) = XEXP (note, 0);
                      next = try_combine (insn, temp, NULL_RTX,
                                          &new_direct_jump_p);
                      if (next)
                        goto retry;
                      SET_SRC (set) = orig;
                    }
                }

              if (GET_CODE (insn) != NOTE)
                record_dead_and_set_regs (insn);

            retry:
              ;
            }
        }
    }
  clear_bb_flags ();

  EXECUTE_IF_SET_IN_SBITMAP (refresh_blocks, 0, i,
                             BASIC_BLOCK (i)->flags |= BB_DIRTY);
  new_direct_jump_p |= purge_all_dead_edges (0);
  delete_noop_moves (f);

  update_life_info_in_dirty_blocks (UPDATE_LIFE_GLOBAL_RM_NOTES,
                                    PROP_DEATH_NOTES | PROP_SCAN_DEAD_CODE
                                    | PROP_KILL_DEAD_CODE);

  /* Clean up.  */
  sbitmap_free (refresh_blocks);
  free (reg_stat);
  free (uid_cuid);

  {
    struct undo *undo, *next;
    for (undo = undobuf.frees; undo; undo = next)
      {
        next = undo->next;
        free (undo);
      }
    undobuf.frees = 0;
  }

  total_attempts += combine_attempts;
  total_merges += combine_merges;
  total_extras += combine_extras;
  total_successes += combine_successes;

  nonzero_sign_valid = 0;
  gen_lowpart = gen_lowpart_general;

  /* Make recognizer allow volatile MEMs again.  */
  init_recog ();

  return new_direct_jump_p;
}

/* Wipe the last_xxx fields of reg_stat in preparation for another pass.  */

static void
init_reg_last (void)
{
  unsigned int i;
  for (i = 0; i < combine_max_regno; i++)
    memset (reg_stat + i, 0, offsetof (struct reg_stat, sign_bit_copies));
}
\f
/* Set up any promoted values for incoming argument registers.  */

static void
setup_incoming_promotions (void)
{
  unsigned int regno;
  rtx reg;
  enum machine_mode mode;
  int unsignedp;
  rtx first = get_insns ();

  if (targetm.calls.promote_function_args (TREE_TYPE (cfun->decl)))
    {
      for (regno = 0; regno < FIRST_PSEUDO_REGISTER; regno++)
        /* Check whether this register can hold an incoming pointer
           argument.  FUNCTION_ARG_REGNO_P tests outgoing register
           numbers, so translate if necessary due to register windows.  */
        if (FUNCTION_ARG_REGNO_P (OUTGOING_REGNO (regno))
            && (reg = promoted_input_arg (regno, &mode, &unsignedp)) != 0)
          {
            record_value_for_reg
              (reg, first, gen_rtx_fmt_e ((unsignedp ? ZERO_EXTEND
                                           : SIGN_EXTEND),
                                          GET_MODE (reg),
                                          gen_rtx_CLOBBER (mode, const0_rtx)));
          }
    }
}
\f
/* Called via note_stores.  If X is a pseudo that is narrower than
   HOST_BITS_PER_WIDE_INT and is being set, record what bits are known zero.

   If we are setting only a portion of X and we can't figure out what
   portion, assume all bits will be used since we don't know what will
   be happening.

   Similarly, set how many bits of X are known to be copies of the sign bit
   at all locations in the function.  This is the smallest number implied
   by any set of X.  */

static void
set_nonzero_bits_and_sign_copies (rtx x, rtx set,
                                  void *data ATTRIBUTE_UNUSED)
{
  unsigned int num;

  if (GET_CODE (x) == REG
      && REGNO (x) >= FIRST_PSEUDO_REGISTER
      /* If this register is undefined at the start of the file, we can't
         say what its contents were.  */
      && ! REGNO_REG_SET_P (ENTRY_BLOCK_PTR->next_bb->global_live_at_start, REGNO (x))
      && GET_MODE_BITSIZE (GET_MODE (x)) <= HOST_BITS_PER_WIDE_INT)
    {
      if (set == 0 || GET_CODE (set) == CLOBBER)
        {
          reg_stat[REGNO (x)].nonzero_bits = GET_MODE_MASK (GET_MODE (x));
          reg_stat[REGNO (x)].sign_bit_copies = 1;
          return;
        }

      /* If this is a complex assignment, see if we can convert it into a
         simple assignment.  */
      set = expand_field_assignment (set);

      /* If this is a simple assignment, or we have a paradoxical SUBREG,
         set what we know about X.  */

      if (SET_DEST (set) == x
          || (GET_CODE (SET_DEST (set)) == SUBREG
              && (GET_MODE_SIZE (GET_MODE (SET_DEST (set)))
                  > GET_MODE_SIZE (GET_MODE (SUBREG_REG (SET_DEST (set)))))
              && SUBREG_REG (SET_DEST (set)) == x))
        {
          rtx src = SET_SRC (set);

#ifdef SHORT_IMMEDIATES_SIGN_EXTEND
          /* If X is narrower than a word and SRC is a non-negative
             constant that would appear negative in the mode of X,
             sign-extend it for use in reg_stat[].nonzero_bits because some
             machines (maybe most) will actually do the sign-extension
             and this is the conservative approach.

             ??? For 2.5, try to tighten up the MD files in this regard
             instead of this kludge.  */

          if (GET_MODE_BITSIZE (GET_MODE (x)) < BITS_PER_WORD
              && GET_CODE (src) == CONST_INT
              && INTVAL (src) > 0
              && 0 != (INTVAL (src)
                       & ((HOST_WIDE_INT) 1
                          << (GET_MODE_BITSIZE (GET_MODE (x)) - 1))))
            src = GEN_INT (INTVAL (src)
                           | ((HOST_WIDE_INT) (-1)
                              << GET_MODE_BITSIZE (GET_MODE (x))));
#endif

          /* Don't call nonzero_bits if it cannot change anything.  */
          if (reg_stat[REGNO (x)].nonzero_bits != ~(unsigned HOST_WIDE_INT) 0)
            reg_stat[REGNO (x)].nonzero_bits
              |= nonzero_bits (src, nonzero_bits_mode);
          num = num_sign_bit_copies (SET_SRC (set), GET_MODE (x));
          if (reg_stat[REGNO (x)].sign_bit_copies == 0
              || reg_stat[REGNO (x)].sign_bit_copies > num)
            reg_stat[REGNO (x)].sign_bit_copies = num;
        }
      else
        {
          reg_stat[REGNO (x)].nonzero_bits = GET_MODE_MASK (GET_MODE (x));
          reg_stat[REGNO (x)].sign_bit_copies = 1;
        }
    }
}
\f
/* See if INSN can be combined into I3.  PRED and SUCC are optionally
   insns that were previously combined into I3 or that will be combined
   into the merger of INSN and I3.

   Return 0 if the combination is not allowed for any reason.

   If the combination is allowed, *PDEST will be set to the single
   destination of INSN and *PSRC to the single source, and this function
   will return 1.  */

static int
can_combine_p (rtx insn, rtx i3, rtx pred ATTRIBUTE_UNUSED, rtx succ,
               rtx *pdest, rtx *psrc)
{
  int i;
  rtx set = 0, src, dest;
  rtx p;
#ifdef AUTO_INC_DEC
  rtx link;
#endif
  int all_adjacent = (succ ? (next_active_insn (insn) == succ
                              && next_active_insn (succ) == i3)
                      : next_active_insn (insn) == i3);

  /* Can combine only if previous insn is a SET of a REG, a SUBREG or CC0.
     or a PARALLEL consisting of such a SET and CLOBBERs.

     If INSN has CLOBBER parallel parts, ignore them for our processing.
     By definition, these happen during the execution of the insn.  When it
     is merged with another insn, all bets are off.  If they are, in fact,
     needed and aren't also supplied in I3, they may be added by
     recog_for_combine.  Otherwise, it won't match.

     We can also ignore a SET whose SET_DEST is mentioned in a REG_UNUSED
     note.

     Get the source and destination of INSN.  If more than one, can't
     combine.  */

  if (GET_CODE (PATTERN (insn)) == SET)
    set = PATTERN (insn);
  else if (GET_CODE (PATTERN (insn)) == PARALLEL
           && GET_CODE (XVECEXP (PATTERN (insn), 0, 0)) == SET)
    {
      for (i = 0; i < XVECLEN (PATTERN (insn), 0); i++)
        {
          rtx elt = XVECEXP (PATTERN (insn), 0, i);
          rtx note;

          switch (GET_CODE (elt))
            {
            /* This is important to combine floating point insns
               for the SH4 port.  */
            case USE:
              /* Combining an isolated USE doesn't make sense.
                 We depend here on combinable_i3pat to reject them.  */
              /* The code below this loop only verifies that the inputs of
                 the SET in INSN do not change.  We call reg_set_between_p
                 to verify that the REG in the USE does not change between
                 I3 and INSN.
                 If the USE in INSN was for a pseudo register, the matching
                 insn pattern will likely match any register; combining this
                 with any other USE would only be safe if we knew that the
                 used registers have identical values, or if there was
                 something to tell them apart, e.g. different modes.  For
                 now, we forgo such complicated tests and simply disallow
                 combining of USES of pseudo registers with any other USE.  */
              if (GET_CODE (XEXP (elt, 0)) == REG
                  && GET_CODE (PATTERN (i3)) == PARALLEL)
                {
                  rtx i3pat = PATTERN (i3);
                  int i = XVECLEN (i3pat, 0) - 1;
                  unsigned int regno = REGNO (XEXP (elt, 0));

                  do
                    {
                      rtx i3elt = XVECEXP (i3pat, 0, i);

                      if (GET_CODE (i3elt) == USE
                          && GET_CODE (XEXP (i3elt, 0)) == REG
                          && (REGNO (XEXP (i3elt, 0)) == regno
                              ? reg_set_between_p (XEXP (elt, 0),
                                                   PREV_INSN (insn), i3)
                              : regno >= FIRST_PSEUDO_REGISTER))
                        return 0;
                    }
                  while (--i >= 0);
                }
              break;

              /* We can ignore CLOBBERs.  */
            case CLOBBER:
              break;

            case SET:
              /* Ignore SETs whose result isn't used but not those that
                 have side-effects.  */
              if (find_reg_note (insn, REG_UNUSED, SET_DEST (elt))
                  && (!(note = find_reg_note (insn, REG_EH_REGION, NULL_RTX))
                      || INTVAL (XEXP (note, 0)) <= 0)
                  && ! side_effects_p (elt))
                break;

              /* If we have already found a SET, this is a second one and
                 so we cannot combine with this insn.  */
              if (set)
                return 0;

              set = elt;
              break;

            default:
              /* Anything else means we can't combine.  */
              return 0;
            }
        }

      if (set == 0
          /* If SET_SRC is an ASM_OPERANDS we can't throw away these CLOBBERs,
             so don't do anything with it.  */
          || GET_CODE (SET_SRC (set)) == ASM_OPERANDS)
        return 0;
    }
  else
    return 0;

  if (set == 0)
    return 0;

  set = expand_field_assignment (set);
  src = SET_SRC (set), dest = SET_DEST (set);

  /* Don't eliminate a store in the stack pointer.  */
  if (dest == stack_pointer_rtx
      /* Don't combine with an insn that sets a register to itself if it has
         a REG_EQUAL note.  This may be part of a REG_NO_CONFLICT sequence.  */
      || (rtx_equal_p (src, dest) && find_reg_note (insn, REG_EQUAL, NULL_RTX))
      /* Can't merge an ASM_OPERANDS.  */
      || GET_CODE (src) == ASM_OPERANDS
      /* Can't merge a function call.  */
      || GET_CODE (src) == CALL
      /* Don't eliminate a function call argument.  */
      || (GET_CODE (i3) == CALL_INSN
          && (find_reg_fusage (i3, USE, dest)
              || (GET_CODE (dest) == REG
                  && REGNO (dest) < FIRST_PSEUDO_REGISTER
                  && global_regs[REGNO (dest)])))
      /* Don't substitute into an incremented register.  */
      || FIND_REG_INC_NOTE (i3, dest)
      || (succ && FIND_REG_INC_NOTE (succ, dest))
#if 0
      /* Don't combine the end of a libcall into anything.  */
      /* ??? This gives worse code, and appears to be unnecessary, since no
         pass after flow uses REG_LIBCALL/REG_RETVAL notes.  Local-alloc does
         use REG_RETVAL notes for noconflict blocks, but other code here
         makes sure that those insns don't disappear.  */
      || find_reg_note (insn, REG_RETVAL, NULL_RTX)
#endif
      /* Make sure that DEST is not used after SUCC but before I3.  */
      || (succ && ! all_adjacent
          && reg_used_between_p (dest, succ, i3))
      /* Make sure that the value that is to be substituted for the register
         does not use any registers whose values alter in between.  However,
         If the insns are adjacent, a use can't cross a set even though we
         think it might (this can happen for a sequence of insns each setting
         the same destination; last_set of that register might point to
         a NOTE).  If INSN has a REG_EQUIV note, the register is always
         equivalent to the memory so the substitution is valid even if there
         are intervening stores.  Also, don't move a volatile asm or
         UNSPEC_VOLATILE across any other insns.  */
      || (! all_adjacent
          && (((GET_CODE (src) != MEM
                || ! find_reg_note (insn, REG_EQUIV, src))
               && use_crosses_set_p (src, INSN_CUID (insn)))
              || (GET_CODE (src) == ASM_OPERANDS && MEM_VOLATILE_P (src))
              || GET_CODE (src) == UNSPEC_VOLATILE))
      /* If there is a REG_NO_CONFLICT note for DEST in I3 or SUCC, we get
         better register allocation by not doing the combine.  */
      || find_reg_note (i3, REG_NO_CONFLICT, dest)
      || (succ && find_reg_note (succ, REG_NO_CONFLICT, dest))
      /* Don't combine across a CALL_INSN, because that would possibly
         change whether the life span of some REGs crosses calls or not,
         and it is a pain to update that information.
         Exception: if source is a constant, moving it later can't hurt.
         Accept that special case, because it helps -fforce-addr a lot.  */
      || (INSN_CUID (insn) < last_call_cuid && ! CONSTANT_P (src)))
    return 0;

  /* DEST must either be a REG or CC0.  */
  if (GET_CODE (dest) == REG)
    {
      /* If register alignment is being enforced for multi-word items in all
         cases except for parameters, it is possible to have a register copy
         insn referencing a hard register that is not allowed to contain the
         mode being copied and which would not be valid as an operand of most
         insns.  Eliminate this problem by not combining with such an insn.

         Also, on some machines we don't want to extend the life of a hard
         register.  */

      if (GET_CODE (src) == REG
          && ((REGNO (dest) < FIRST_PSEUDO_REGISTER
               && ! HARD_REGNO_MODE_OK (REGNO (dest), GET_MODE (dest)))
              /* Don't extend the life of a hard register unless it is
                 user variable (if we have few registers) or it can't
                 fit into the desired register (meaning something special
                 is going on).
                 Also avoid substituting a return register into I3, because
                 reload can't handle a conflict with constraints of other
                 inputs.  */
              || (REGNO (src) < FIRST_PSEUDO_REGISTER
                  && ! HARD_REGNO_MODE_OK (REGNO (src), GET_MODE (src)))))
        return 0;
    }
  else if (GET_CODE (dest) != CC0)
    return 0;

  /* Don't substitute for a register intended as a clobberable operand.
     Similarly, don't substitute an expression containing a register that
     will be clobbered in I3.  */
  if (GET_CODE (PATTERN (i3)) == PARALLEL)
    for (i = XVECLEN (PATTERN (i3), 0) - 1; i >= 0; i--)
      if (GET_CODE (XVECEXP (PATTERN (i3), 0, i)) == CLOBBER
          && (reg_overlap_mentioned_p (XEXP (XVECEXP (PATTERN (i3), 0, i), 0),
                                       src)
              || rtx_equal_p (XEXP (XVECEXP (PATTERN (i3), 0, i), 0), dest)))
        return 0;

  /* If INSN contains anything volatile, or is an `asm' (whether volatile
     or not), reject, unless nothing volatile comes between it and I3 */

  if (GET_CODE (src) == ASM_OPERANDS || volatile_refs_p (src))
    {
      /* Make sure succ doesn't contain a volatile reference.  */
      if (succ != 0 && volatile_refs_p (PATTERN (succ)))
        return 0;

      for (p = NEXT_INSN (insn); p != i3; p = NEXT_INSN (p))
        if (INSN_P (p) && p != succ && volatile_refs_p (PATTERN (p)))
          return 0;
    }

  /* If INSN is an asm, and DEST is a hard register, reject, since it has
     to be an explicit register variable, and was chosen for a reason.  */

  if (GET_CODE (src) == ASM_OPERANDS
      && GET_CODE (dest) == REG && REGNO (dest) < FIRST_PSEUDO_REGISTER)
    return 0;

  /* If there are any volatile insns between INSN and I3, reject, because
     they might affect machine state.  */

  for (p = NEXT_INSN (insn); p != i3; p = NEXT_INSN (p))
    if (INSN_P (p) && p != succ && volatile_insn_p (PATTERN (p)))
      return 0;

  /* If INSN or I2 contains an autoincrement or autodecrement,
     make sure that register is not used between there and I3,
     and not already used in I3 either.
     Also insist that I3 not be a jump; if it were one
     and the incremented register were spilled, we would lose.  */

#ifdef AUTO_INC_DEC
  for (link = REG_NOTES (insn); link; link = XEXP (link, 1))
    if (REG_NOTE_KIND (link) == REG_INC
        && (GET_CODE (i3) == JUMP_INSN
            || reg_used_between_p (XEXP (link, 0), insn, i3)
            || reg_overlap_mentioned_p (XEXP (link, 0), PATTERN (i3))))
      return 0;
#endif

#ifdef HAVE_cc0
  /* Don't combine an insn that follows a CC0-setting insn.
     An insn that uses CC0 must not be separated from the one that sets it.
     We do, however, allow I2 to follow a CC0-setting insn if that insn
     is passed as I1; in that case it will be deleted also.
     We also allow combining in this case if all the insns are adjacent
     because that would leave the two CC0 insns adjacent as well.
     It would be more logical to test whether CC0 occurs inside I1 or I2,
     but that would be much slower, and this ought to be equivalent.  */

  p = prev_nonnote_insn (insn);
  if (p && p != pred && GET_CODE (p) == INSN && sets_cc0_p (PATTERN (p))
      && ! all_adjacent)
    return 0;
#endif

  /* If we get here, we have passed all the tests and the combination is
     to be allowed.  */

  *pdest = dest;
  *psrc = src;

  return 1;
}
\f
/* LOC is the location within I3 that contains its pattern or the component
   of a PARALLEL of the pattern.  We validate that it is valid for combining.

   One problem is if I3 modifies its output, as opposed to replacing it
   entirely, we can't allow the output to contain I2DEST or I1DEST as doing
   so would produce an insn that is not equivalent to the original insns.

   Consider:

         (set (reg:DI 101) (reg:DI 100))
         (set (subreg:SI (reg:DI 101) 0) <foo>)

   This is NOT equivalent to:

         (parallel [(set (subreg:SI (reg:DI 100) 0) <foo>)
                    (set (reg:DI 101) (reg:DI 100))])

   Not only does this modify 100 (in which case it might still be valid
   if 100 were dead in I2), it sets 101 to the ORIGINAL value of 100.

   We can also run into a problem if I2 sets a register that I1
   uses and I1 gets directly substituted into I3 (not via I2).  In that
   case, we would be getting the wrong value of I2DEST into I3, so we
   must reject the combination.  This case occurs when I2 and I1 both
   feed into I3, rather than when I1 feeds into I2, which feeds into I3.
   If I1_NOT_IN_SRC is nonzero, it means that finding I1 in the source
   of a SET must prevent combination from occurring.

   Before doing the above check, we first try to expand a field assignment
   into a set of logical operations.

   If PI3_DEST_KILLED is nonzero, it is a pointer to a location in which
   we place a register that is both set and used within I3.  If more than one
   such register is detected, we fail.

   Return 1 if the combination is valid, zero otherwise.  */

static int
combinable_i3pat (rtx i3, rtx *loc, rtx i2dest, rtx i1dest,
                  int i1_not_in_src, rtx *pi3dest_killed)
{
  rtx x = *loc;

  if (GET_CODE (x) == SET)
    {
      rtx set = x ;
      rtx dest = SET_DEST (set);
      rtx src = SET_SRC (set);
      rtx inner_dest = dest;

      while (GET_CODE (inner_dest) == STRICT_LOW_PART
             || GET_CODE (inner_dest) == SUBREG
             || GET_CODE (inner_dest) == ZERO_EXTRACT)
        inner_dest = XEXP (inner_dest, 0);

      /* Check for the case where I3 modifies its output, as discussed
         above.  We don't want to prevent pseudos from being combined
         into the address of a MEM, so only prevent the combination if
         i1 or i2 set the same MEM.  */
      if ((inner_dest != dest &&
           (GET_CODE (inner_dest) != MEM
            || rtx_equal_p (i2dest, inner_dest)
            || (i1dest && rtx_equal_p (i1dest, inner_dest)))
           && (reg_overlap_mentioned_p (i2dest, inner_dest)
               || (i1dest && reg_overlap_mentioned_p (i1dest, inner_dest))))

          /* This is the same test done in can_combine_p except we can't test
             all_adjacent; we don't have to, since this instruction will stay
             in place, thus we are not considering increasing the lifetime of
             INNER_DEST.

             Also, if this insn sets a function argument, combining it with
             something that might need a spill could clobber a previous
             function argument; the all_adjacent test in can_combine_p also
             checks this; here, we do a more specific test for this case.  */

          || (GET_CODE (inner_dest) == REG
              && REGNO (inner_dest) < FIRST_PSEUDO_REGISTER
              && (! HARD_REGNO_MODE_OK (REGNO (inner_dest),
                                        GET_MODE (inner_dest))))
          || (i1_not_in_src && reg_overlap_mentioned_p (i1dest, src)))
        return 0;

      /* If DEST is used in I3, it is being killed in this insn,
         so record that for later.
         Never add REG_DEAD notes for the FRAME_POINTER_REGNUM or the
         STACK_POINTER_REGNUM, since these are always considered to be
         live.  Similarly for ARG_POINTER_REGNUM if it is fixed.  */
      if (pi3dest_killed && GET_CODE (dest) == REG
          && reg_referenced_p (dest, PATTERN (i3))
          && REGNO (dest) != FRAME_POINTER_REGNUM
#if HARD_FRAME_POINTER_REGNUM != FRAME_POINTER_REGNUM
          && REGNO (dest) != HARD_FRAME_POINTER_REGNUM
#endif
#if ARG_POINTER_REGNUM != FRAME_POINTER_REGNUM
          && (REGNO (dest) != ARG_POINTER_REGNUM
              || ! fixed_regs [REGNO (dest)])
#endif
          && REGNO (dest) != STACK_POINTER_REGNUM)
        {
          if (*pi3dest_killed)
            return 0;

          *pi3dest_killed = dest;
        }
    }

  else if (GET_CODE (x) == PARALLEL)
    {
      int i;

      for (i = 0; i < XVECLEN (x, 0); i++)
        if (! combinable_i3pat (i3, &XVECEXP (x, 0, i), i2dest, i1dest,
                                i1_not_in_src, pi3dest_killed))
          return 0;
    }

  return 1;
}
\f
/* Return 1 if X is an arithmetic expression that contains a multiplication
   and division.  We don't count multiplications by powers of two here.  */

static int
contains_muldiv (rtx x)
{
  switch (GET_CODE (x))
    {
    case MOD:  case DIV:  case UMOD:  case UDIV:
      return 1;

    case MULT:
      return ! (GET_CODE (XEXP (x, 1)) == CONST_INT
                && exact_log2 (INTVAL (XEXP (x, 1))) >= 0);
    default:
      if (BINARY_P (x))
        return contains_muldiv (XEXP (x, 0))
            || contains_muldiv (XEXP (x, 1));

      if (UNARY_P (x))
        return contains_muldiv (XEXP (x, 0));

      return 0;
    }
}
\f
/* Determine whether INSN can be used in a combination.  Return nonzero if
   not.  This is used in try_combine to detect early some cases where we
   can't perform combinations.  */

static int
cant_combine_insn_p (rtx insn)
{
  rtx set;
  rtx src, dest;

  /* If this isn't really an insn, we can't do anything.
     This can occur when flow deletes an insn that it has merged into an
     auto-increment address.  */
  if (! INSN_P (insn))
    return 1;

  /* Never combine loads and stores involving hard regs that are likely
     to be spilled.  The register allocator can usually handle such
     reg-reg moves by tying.  If we allow the combiner to make
     substitutions of likely-spilled regs, we may abort in reload.
     As an exception, we allow combinations involving fixed regs; these are
     not available to the register allocator so there's no risk involved.  */

  set = single_set (insn);
  if (! set)
    return 0;
  src = SET_SRC (set);
  dest = SET_DEST (set);
  if (GET_CODE (src) == SUBREG)
    src = SUBREG_REG (src);
  if (GET_CODE (dest) == SUBREG)
    dest = SUBREG_REG (dest);
  if (REG_P (src) && REG_P (dest)
      && ((REGNO (src) < FIRST_PSEUDO_REGISTER
           && ! fixed_regs[REGNO (src)]
           && CLASS_LIKELY_SPILLED_P (REGNO_REG_CLASS (REGNO (src))))
          || (REGNO (dest) < FIRST_PSEUDO_REGISTER
              && ! fixed_regs[REGNO (dest)]
              && CLASS_LIKELY_SPILLED_P (REGNO_REG_CLASS (REGNO (dest))))))
    return 1;

  return 0;
}

/* Adjust INSN after we made a change to its destination.

   Changing the destination can invalidate notes that say something about
   the results of the insn and a LOG_LINK pointing to the insn.  */

static void
adjust_for_new_dest (rtx insn)
{
  rtx *loc;

  /* For notes, be conservative and simply remove them.  */
  loc = &REG_NOTES (insn);
  while (*loc)
    {
      enum reg_note kind = REG_NOTE_KIND (*loc);
      if (kind == REG_EQUAL || kind == REG_EQUIV)
        *loc = XEXP (*loc, 1);
      else
        loc = &XEXP (*loc, 1);
    }

  /* The new insn will have a destination that was previously the destination
     of an insn just above it.  Call distribute_links to make a LOG_LINK from
     the next use of that destination.  */
  distribute_links (gen_rtx_INSN_LIST (VOIDmode, insn, NULL_RTX));
}

/* Try to combine the insns I1 and I2 into I3.
   Here I1 and I2 appear earlier than I3.
   I1 can be zero; then we combine just I2 into I3.

   If we are combining three insns and the resulting insn is not recognized,
   try splitting it into two insns.  If that happens, I2 and I3 are retained
   and I1 is pseudo-deleted by turning it into a NOTE.  Otherwise, I1 and I2
   are pseudo-deleted.

   Return 0 if the combination does not work.  Then nothing is changed.
   If we did the combination, return the insn at which combine should
   resume scanning.

   Set NEW_DIRECT_JUMP_P to a nonzero value if try_combine creates a
   new direct jump instruction.  */

static rtx
try_combine (rtx i3, rtx i2, rtx i1, int *new_direct_jump_p)
{
  /* New patterns for I3 and I2, respectively.  */
  rtx newpat, newi2pat = 0;
  int substed_i2 = 0, substed_i1 = 0;
  /* Indicates need to preserve SET in I1 or I2 in I3 if it is not dead.  */
  int added_sets_1, added_sets_2;
  /* Total number of SETs to put into I3.  */
  int total_sets;
  /* Nonzero if I2's body now appears in I3.  */
  int i2_is_used;
  /* INSN_CODEs for new I3, new I2, and user of condition code.  */
  int insn_code_number, i2_code_number = 0, other_code_number = 0;
  /* Contains I3 if the destination of I3 is used in its source, which means
     that the old life of I3 is being killed.  If that usage is placed into
     I2 and not in I3, a REG_DEAD note must be made.  */
  rtx i3dest_killed = 0;
  /* SET_DEST and SET_SRC of I2 and I1.  */
  rtx i2dest, i2src, i1dest = 0, i1src = 0;
  /* PATTERN (I2), or a copy of it in certain cases.  */
  rtx i2pat;
  /* Indicates if I2DEST or I1DEST is in I2SRC or I1_SRC.  */
  int i2dest_in_i2src = 0, i1dest_in_i1src = 0, i2dest_in_i1src = 0;
  int i1_feeds_i3 = 0;
  /* Notes that must be added to REG_NOTES in I3 and I2.  */
  rtx new_i3_notes, new_i2_notes;
  /* Notes that we substituted I3 into I2 instead of the normal case.  */
  int i3_subst_into_i2 = 0;
  /* Notes that I1, I2 or I3 is a MULT operation.  */
  int have_mult = 0;

  int maxreg;
  rtx temp;
  rtx link;
  int i;

  /* Exit early if one of the insns involved can't be used for
     combinations.  */
  if (cant_combine_insn_p (i3)
      || cant_combine_insn_p (i2)
      || (i1 && cant_combine_insn_p (i1))
      /* We also can't do anything if I3 has a
         REG_LIBCALL note since we don't want to disrupt the contiguity of a
         libcall.  */
#if 0
      /* ??? This gives worse code, and appears to be unnecessary, since no
         pass after flow uses REG_LIBCALL/REG_RETVAL notes.  */
      || find_reg_note (i3, REG_LIBCALL, NULL_RTX)
#endif
      )
    return 0;

  combine_attempts++;
  undobuf.other_insn = 0;

  /* Reset the hard register usage information.  */
  CLEAR_HARD_REG_SET (newpat_used_regs);

  /* If I1 and I2 both feed I3, they can be in any order.  To simplify the
     code below, set I1 to be the earlier of the two insns.  */
  if (i1 && INSN_CUID (i1) > INSN_CUID (i2))
    temp = i1, i1 = i2, i2 = temp;

  added_links_insn = 0;

  /* First check for one important special-case that the code below will
     not handle.  Namely, the case where I1 is zero, I2 is a PARALLEL
     and I3 is a SET whose SET_SRC is a SET_DEST in I2.  In that case,
     we may be able to replace that destination with the destination of I3.
     This occurs in the common code where we compute both a quotient and
     remainder into a structure, in which case we want to do the computation
     directly into the structure to avoid register-register copies.

     Note that this case handles both multiple sets in I2 and also
     cases where I2 has a number of CLOBBER or PARALLELs.

     We make very conservative checks below and only try to handle the
     most common cases of this.  For example, we only handle the case
     where I2 and I3 are adjacent to avoid making difficult register
     usage tests.  */

  if (i1 == 0 && GET_CODE (i3) == INSN && GET_CODE (PATTERN (i3)) == SET
      && GET_CODE (SET_SRC (PATTERN (i3))) == REG
      && REGNO (SET_SRC (PATTERN (i3))) >= FIRST_PSEUDO_REGISTER
      && find_reg_note (i3, REG_DEAD, SET_SRC (PATTERN (i3)))
      && GET_CODE (PATTERN (i2)) == PARALLEL
      && ! side_effects_p (SET_DEST (PATTERN (i3)))
      /* If the dest of I3 is a ZERO_EXTRACT or STRICT_LOW_PART, the code
         below would need to check what is inside (and reg_overlap_mentioned_p
         doesn't support those codes anyway).  Don't allow those destinations;
         the resulting insn isn't likely to be recognized anyway.  */
      && GET_CODE (SET_DEST (PATTERN (i3))) != ZERO_EXTRACT
      && GET_CODE (SET_DEST (PATTERN (i3))) != STRICT_LOW_PART
      && ! reg_overlap_mentioned_p (SET_SRC (PATTERN (i3)),
                                    SET_DEST (PATTERN (i3)))
      && next_real_insn (i2) == i3)
    {
      rtx p2 = PATTERN (i2);

      /* Make sure that the destination of I3,
         which we are going to substitute into one output of I2,
         is not used within another output of I2.  We must avoid making this:
         (parallel [(set (mem (reg 69)) ...)
                    (set (reg 69) ...)])
         which is not well-defined as to order of actions.
         (Besides, reload can't handle output reloads for this.)

         The problem can also happen if the dest of I3 is a memory ref,
         if another dest in I2 is an indirect memory ref.  */
      for (i = 0; i < XVECLEN (p2, 0); i++)
        if ((GET_CODE (XVECEXP (p2, 0, i)) == SET
             || GET_CODE (XVECEXP (p2, 0, i)) == CLOBBER)
            && reg_overlap_mentioned_p (SET_DEST (PATTERN (i3)),
                                        SET_DEST (XVECEXP (p2, 0, i))))
          break;

      if (i == XVECLEN (p2, 0))
        for (i = 0; i < XVECLEN (p2, 0); i++)
          if ((GET_CODE (XVECEXP (p2, 0, i)) == SET
               || GET_CODE (XVECEXP (p2, 0, i)) == CLOBBER)
              && SET_DEST (XVECEXP (p2, 0, i)) == SET_SRC (PATTERN (i3)))
            {
              combine_merges++;

              subst_insn = i3;
              subst_low_cuid = INSN_CUID (i2);

              added_sets_2 = added_sets_1 = 0;
              i2dest = SET_SRC (PATTERN (i3));

              /* Replace the dest in I2 with our dest and make the resulting
                 insn the new pattern for I3.  Then skip to where we
                 validate the pattern.  Everything was set up above.  */
              SUBST (SET_DEST (XVECEXP (p2, 0, i)),
                     SET_DEST (PATTERN (i3)));

              newpat = p2;
              i3_subst_into_i2 = 1;
              goto validate_replacement;
            }
    }

  /* If I2 is setting a double-word pseudo to a constant and I3 is setting
     one of those words to another constant, merge them by making a new
     constant.  */
  if (i1 == 0
      && (temp = single_set (i2)) != 0
      && (GET_CODE (SET_SRC (temp)) == CONST_INT
          || GET_CODE (SET_SRC (temp)) == CONST_DOUBLE)
      && GET_CODE (SET_DEST (temp)) == REG
      && GET_MODE_CLASS (GET_MODE (SET_DEST (temp))) == MODE_INT
      && GET_MODE_SIZE (GET_MODE (SET_DEST (temp))) == 2 * UNITS_PER_WORD
      && GET_CODE (PATTERN (i3)) == SET
      && GET_CODE (SET_DEST (PATTERN (i3))) == SUBREG
      && SUBREG_REG (SET_DEST (PATTERN (i3))) == SET_DEST (temp)
      && GET_MODE_CLASS (GET_MODE (SET_DEST (PATTERN (i3)))) == MODE_INT
      && GET_MODE_SIZE (GET_MODE (SET_DEST (PATTERN (i3)))) == UNITS_PER_WORD
      && GET_CODE (SET_SRC (PATTERN (i3))) == CONST_INT)
    {
      HOST_WIDE_INT lo, hi;

      if (GET_CODE (SET_SRC (temp)) == CONST_INT)
        lo = INTVAL (SET_SRC (temp)), hi = lo < 0 ? -1 : 0;
      else
        {
          lo = CONST_DOUBLE_LOW (SET_SRC (temp));
          hi = CONST_DOUBLE_HIGH (SET_SRC (temp));
        }

      if (subreg_lowpart_p (SET_DEST (PATTERN (i3))))
        {
          /* We don't handle the case of the target word being wider
             than a host wide int.  */
          if (HOST_BITS_PER_WIDE_INT < BITS_PER_WORD)
            abort ();

          lo &= ~(UWIDE_SHIFT_LEFT_BY_BITS_PER_WORD (1) - 1);
          lo |= (INTVAL (SET_SRC (PATTERN (i3)))
                 & (UWIDE_SHIFT_LEFT_BY_BITS_PER_WORD (1) - 1));
        }
      else if (HOST_BITS_PER_WIDE_INT == BITS_PER_WORD)
        hi = INTVAL (SET_SRC (PATTERN (i3)));
      else if (HOST_BITS_PER_WIDE_INT >= 2 * BITS_PER_WORD)
        {
          int sign = -(int) ((unsigned HOST_WIDE_INT) lo
                             >> (HOST_BITS_PER_WIDE_INT - 1));

          lo &= ~ (UWIDE_SHIFT_LEFT_BY_BITS_PER_WORD
                   (UWIDE_SHIFT_LEFT_BY_BITS_PER_WORD (1) - 1));
          lo |= (UWIDE_SHIFT_LEFT_BY_BITS_PER_WORD
                 (INTVAL (SET_SRC (PATTERN (i3)))));
          if (hi == sign)
            hi = lo < 0 ? -1 : 0;
        }
      else
        /* We don't handle the case of the higher word not fitting
           entirely in either hi or lo.  */
        abort ();

      combine_merges++;
      subst_insn = i3;
      subst_low_cuid = INSN_CUID (i2);
      added_sets_2 = added_sets_1 = 0;
      i2dest = SET_DEST (temp);

      SUBST (SET_SRC (temp),
             immed_double_const (lo, hi, GET_MODE (SET_DEST (temp))));

      newpat = PATTERN (i2);
      goto validate_replacement;
    }

#ifndef HAVE_cc0
  /* If we have no I1 and I2 looks like:
        (parallel [(set (reg:CC X) (compare:CC OP (const_int 0)))
                   (set Y OP)])
     make up a dummy I1 that is
        (set Y OP)
     and change I2 to be
        (set (reg:CC X) (compare:CC Y (const_int 0)))

     (We can ignore any trailing CLOBBERs.)

     This undoes a previous combination and allows us to match a branch-and-
     decrement insn.  */

  if (i1 == 0 && GET_CODE (PATTERN (i2)) == PARALLEL
      && XVECLEN (PATTERN (i2), 0) >= 2
      && GET_CODE (XVECEXP (PATTERN (i2), 0, 0)) == SET
      && (GET_MODE_CLASS (GET_MODE (SET_DEST (XVECEXP (PATTERN (i2), 0, 0))))
          == MODE_CC)
      && GET_CODE (SET_SRC (XVECEXP (PATTERN (i2), 0, 0))) == COMPARE
      && XEXP (SET_SRC (XVECEXP (PATTERN (i2), 0, 0)), 1) == const0_rtx
      && GET_CODE (XVECEXP (PATTERN (i2), 0, 1)) == SET
      && GET_CODE (SET_DEST (XVECEXP (PATTERN (i2), 0, 1))) == REG
      && rtx_equal_p (XEXP (SET_SRC (XVECEXP (PATTERN (i2), 0, 0)), 0),
                      SET_SRC (XVECEXP (PATTERN (i2), 0, 1))))
    {
      for (i = XVECLEN (PATTERN (i2), 0) - 1; i >= 2; i--)
        if (GET_CODE (XVECEXP (PATTERN (i2), 0, i)) != CLOBBER)
          break;

      if (i == 1)
        {
          /* We make I1 with the same INSN_UID as I2.  This gives it
             the same INSN_CUID for value tracking.  Our fake I1 will
             never appear in the insn stream so giving it the same INSN_UID
             as I2 will not cause a problem.  */

          i1 = gen_rtx_INSN (VOIDmode, INSN_UID (i2), NULL_RTX, i2,
                             BLOCK_FOR_INSN (i2), INSN_LOCATOR (i2),
                             XVECEXP (PATTERN (i2), 0, 1), -1, NULL_RTX,
                             NULL_RTX);

          SUBST (PATTERN (i2), XVECEXP (PATTERN (i2), 0, 0));
          SUBST (XEXP (SET_SRC (PATTERN (i2)), 0),
                 SET_DEST (PATTERN (i1)));
        }
    }
#endif

  /* Verify that I2 and I1 are valid for combining.  */
  if (! can_combine_p (i2, i3, i1, NULL_RTX, &i2dest, &i2src)
      || (i1 && ! can_combine_p (i1, i3, NULL_RTX, i2, &i1dest, &i1src)))
    {
      undo_all ();
      return 0;
    }

  /* Record whether I2DEST is used in I2SRC and similarly for the other
     cases.  Knowing this will help in register status updating below.  */
  i2dest_in_i2src = reg_overlap_mentioned_p (i2dest, i2src);
  i1dest_in_i1src = i1 && reg_overlap_mentioned_p (i1dest, i1src);
  i2dest_in_i1src = i1 && reg_overlap_mentioned_p (i2dest, i1src);

  /* See if I1 directly feeds into I3.  It does if I1DEST is not used
     in I2SRC.  */
  i1_feeds_i3 = i1 && ! reg_overlap_mentioned_p (i1dest, i2src);

  /* Ensure that I3's pattern can be the destination of combines.  */
  if (! combinable_i3pat (i3, &PATTERN (i3), i2dest, i1dest,
                          i1 && i2dest_in_i1src && i1_feeds_i3,
                          &i3dest_killed))
    {
      undo_all ();
      return 0;
    }

  /* See if any of the insns is a MULT operation.  Unless one is, we will
     reject a combination that is, since it must be slower.  Be conservative
     here.  */
  if (GET_CODE (i2src) == MULT
      || (i1 != 0 && GET_CODE (i1src) == MULT)
      || (GET_CODE (PATTERN (i3)) == SET
          && GET_CODE (SET_SRC (PATTERN (i3))) == MULT))
    have_mult = 1;

  /* If I3 has an inc, then give up if I1 or I2 uses the reg that is inc'd.
     We used to do this EXCEPT in one case: I3 has a post-inc in an
     output operand.  However, that exception can give rise to insns like
        mov r3,(r3)+
     which is a famous insn on the PDP-11 where the value of r3 used as the
     source was model-dependent.  Avoid this sort of thing.  */

#if 0
  if (!(GET_CODE (PATTERN (i3)) == SET
        && GET_CODE (SET_SRC (PATTERN (i3))) == REG
        && GET_CODE (SET_DEST (PATTERN (i3))) == MEM
        && (GET_CODE (XEXP (SET_DEST (PATTERN (i3)), 0)) == POST_INC
            || GET_CODE (XEXP (SET_DEST (PATTERN (i3)), 0)) == POST_DEC)))
    /* It's not the exception.  */
#endif
#ifdef AUTO_INC_DEC
    for (link = REG_NOTES (i3); link; link = XEXP (link, 1))
      if (REG_NOTE_KIND (link) == REG_INC
          && (reg_overlap_mentioned_p (XEXP (link, 0), PATTERN (i2))
              || (i1 != 0
                  && reg_overlap_mentioned_p (XEXP (link, 0), PATTERN (i1)))))
        {
          undo_all ();
          return 0;
        }
#endif

  /* See if the SETs in I1 or I2 need to be kept around in the merged
     instruction: whenever the value set there is still needed past I3.
     For the SETs in I2, this is easy: we see if I2DEST dies or is set in I3.

     For the SET in I1, we have two cases:  If I1 and I2 independently
     feed into I3, the set in I1 needs to be kept around if I1DEST dies
     or is set in I3.  Otherwise (if I1 feeds I2 which feeds I3), the set
     in I1 needs to be kept around unless I1DEST dies or is set in either
     I2 or I3.  We can distinguish these cases by seeing if I2SRC mentions
     I1DEST.  If so, we know I1 feeds into I2.  */

  added_sets_2 = ! dead_or_set_p (i3, i2dest);

  added_sets_1
    = i1 && ! (i1_feeds_i3 ? dead_or_set_p (i3, i1dest)
               : (dead_or_set_p (i3, i1dest) || dead_or_set_p (i2, i1dest)));

  /* If the set in I2 needs to be kept around, we must make a copy of
     PATTERN (I2), so that when we substitute I1SRC for I1DEST in
     PATTERN (I2), we are only substituting for the original I1DEST, not into
     an already-substituted copy.  This also prevents making self-referential
     rtx.  If I2 is a PARALLEL, we just need the piece that assigns I2SRC to
     I2DEST.  */

  i2pat = (GET_CODE (PATTERN (i2)) == PARALLEL
           ? gen_rtx_SET (VOIDmode, i2dest, i2src)
           : PATTERN (i2));

  if (added_sets_2)
    i2pat = copy_rtx (i2pat);

  combine_merges++;

  /* Substitute in the latest insn for the regs set by the earlier ones.  */

  maxreg = max_reg_num ();

  subst_insn = i3;

  /* It is possible that the source of I2 or I1 may be performing an
     unneeded operation, such as a ZERO_EXTEND of something that is known
     to have the high part zero.  Handle that case by letting subst look at
     the innermost one of them.

     Another way to do this would be to have a function that tries to
     simplify a single insn instead of merging two or more insns.  We don't
     do this because of the potential of infinite loops and because
     of the potential extra memory required.  However, doing it the way
     we are is a bit of a kludge and doesn't catch all cases.

     But only do this if -fexpensive-optimizations since it slows things down
     and doesn't usually win.  */

  if (flag_expensive_optimizations)
    {
      /* Pass pc_rtx so no substitutions are done, just simplifications.  */
      if (i1)
        {
          subst_low_cuid = INSN_CUID (i1);
          i1src = subst (i1src, pc_rtx, pc_rtx, 0, 0);
        }
      else
        {
          subst_low_cuid = INSN_CUID (i2);
          i2src = subst (i2src, pc_rtx, pc_rtx, 0, 0);
        }
    }

#ifndef HAVE_cc0
  /* Many machines that don't use CC0 have insns that can both perform an
     arithmetic operation and set the condition code.  These operations will
     be represented as a PARALLEL with the first element of the vector
     being a COMPARE of an arithmetic operation with the constant zero.
     The second element of the vector will set some pseudo to the result
     of the same arithmetic operation.  If we simplify the COMPARE, we won't
     match such a pattern and so will generate an extra insn.   Here we test
     for this case, where both the comparison and the operation result are
     needed, and make the PARALLEL by just replacing I2DEST in I3SRC with
     I2SRC.  Later we will make the PARALLEL that contains I2.  */

  if (i1 == 0 && added_sets_2 && GET_CODE (PATTERN (i3)) == SET
      && GET_CODE (SET_SRC (PATTERN (i3))) == COMPARE
      && XEXP (SET_SRC (PATTERN (i3)), 1) == const0_rtx
      && rtx_equal_p (XEXP (SET_SRC (PATTERN (i3)), 0), i2dest))
    {
#ifdef SELECT_CC_MODE
      rtx *cc_use;
      enum machine_mode compare_mode;
#endif

      newpat = PATTERN (i3);
      SUBST (XEXP (SET_SRC (newpat), 0), i2src);

      i2_is_used = 1;

#ifdef SELECT_CC_MODE
      /* See if a COMPARE with the operand we substituted in should be done
         with the mode that is currently being used.  If not, do the same
         processing we do in `subst' for a SET; namely, if the destination
         is used only once, try to replace it with a register of the proper
         mode and also replace the COMPARE.  */
      if (undobuf.other_insn == 0
          && (cc_use = find_single_use (SET_DEST (newpat), i3,
                                        &undobuf.other_insn))
          && ((compare_mode = SELECT_CC_MODE (GET_CODE (*cc_use),
                                              i2src, const0_rtx))
              != GET_MODE (SET_DEST (newpat))))
        {
          unsigned int regno = REGNO (SET_DEST (newpat));
          rtx new_dest = gen_rtx_REG (compare_mode, regno);

          if (regno < FIRST_PSEUDO_REGISTER
              || (REG_N_SETS (regno) == 1 && ! added_sets_2
                  && ! REG_USERVAR_P (SET_DEST (newpat))))
            {
              if (regno >= FIRST_PSEUDO_REGISTER)
                SUBST (regno_reg_rtx[regno], new_dest);

              SUBST (SET_DEST (newpat), new_dest);
              SUBST (XEXP (*cc_use, 0), new_dest);
              SUBST (SET_SRC (newpat),
                     gen_rtx_COMPARE (compare_mode, i2src, const0_rtx));
            }
          else
            undobuf.other_insn = 0;
        }
#endif
    }
  else
#endif
    {
      n_occurrences = 0;                /* `subst' counts here */

      /* If I1 feeds into I2 (not into I3) and I1DEST is in I1SRC, we
         need to make a unique copy of I2SRC each time we substitute it
         to avoid self-referential rtl.  */

      subst_low_cuid = INSN_CUID (i2);
      newpat = subst (PATTERN (i3), i2dest, i2src, 0,
                      ! i1_feeds_i3 && i1dest_in_i1src);
      substed_i2 = 1;

      /* Record whether i2's body now appears within i3's body.  */
      i2_is_used = n_occurrences;
    }

  /* If we already got a failure, don't try to do more.  Otherwise,
     try to substitute in I1 if we have it.  */

  if (i1 && GET_CODE (newpat) != CLOBBER)
    {
      /* Before we can do this substitution, we must redo the test done
         above (see detailed comments there) that ensures  that I1DEST
         isn't mentioned in any SETs in NEWPAT that are field assignments.  */

      if (! combinable_i3pat (NULL_RTX, &newpat, i1dest, NULL_RTX,
                              0, (rtx*) 0))
        {
          undo_all ();
          return 0;
        }

      n_occurrences = 0;
      subst_low_cuid = INSN_CUID (i1);
      newpat = subst (newpat, i1dest, i1src, 0, 0);
      substed_i1 = 1;
    }

  /* Fail if an autoincrement side-effect has been duplicated.  Be careful
     to count all the ways that I2SRC and I1SRC can be used.  */
  if ((FIND_REG_INC_NOTE (i2, NULL_RTX) != 0
       && i2_is_used + added_sets_2 > 1)
      || (i1 != 0 && FIND_REG_INC_NOTE (i1, NULL_RTX) != 0
          && (n_occurrences + added_sets_1 + (added_sets_2 && ! i1_feeds_i3)
              > 1))
      /* Fail if we tried to make a new register (we used to abort, but there's
         really no reason to).  */
      || max_reg_num () != maxreg
      /* Fail if we couldn't do something and have a CLOBBER.  */
      || GET_CODE (newpat) == CLOBBER
      /* Fail if this new pattern is a MULT and we didn't have one before
         at the outer level.  */
      || (GET_CODE (newpat) == SET && GET_CODE (SET_SRC (newpat)) == MULT
          && ! have_mult))
    {
      undo_all ();
      return 0;
    }

  /* If the actions of the earlier insns must be kept
     in addition to substituting them into the latest one,
     we must make a new PARALLEL for the latest insn
     to hold additional the SETs.  */

  if (added_sets_1 || added_sets_2)
    {
      combine_extras++;

      if (GET_CODE (newpat) == PARALLEL)
        {
          rtvec old = XVEC (newpat, 0);
          total_sets = XVECLEN (newpat, 0) + added_sets_1 + added_sets_2;
          newpat = gen_rtx_PARALLEL (VOIDmode, rtvec_alloc (total_sets));
          memcpy (XVEC (newpat, 0)->elem, &old->elem[0],
                  sizeof (old->elem[0]) * old->num_elem);
        }
      else
        {
          rtx old = newpat;
          total_sets = 1 + added_sets_1 + added_sets_2;
          newpat = gen_rtx_PARALLEL (VOIDmode, rtvec_alloc (total_sets));
          XVECEXP (newpat, 0, 0) = old;
        }

      if (added_sets_1)
        XVECEXP (newpat, 0, --total_sets)
          = (GET_CODE (PATTERN (i1)) == PARALLEL
             ? gen_rtx_SET (VOIDmode, i1dest, i1src) : PATTERN (i1));

      if (added_sets_2)
        {
          /* If there is no I1, use I2's body as is.  We used to also not do
             the subst call below if I2 was substituted into I3,
             but that could lose a simplification.  */
          if (i1 == 0)
            XVECEXP (newpat, 0, --total_sets) = i2pat;
          else
            /* See comment where i2pat is assigned.  */
            XVECEXP (newpat, 0, --total_sets)
              = subst (i2pat, i1dest, i1src, 0, 0);
        }
    }

  /* We come here when we are replacing a destination in I2 with the
     destination of I3.  */
 validate_replacement:

  /* Note which hard regs this insn has as inputs.  */
  mark_used_regs_combine (newpat);

  /* Is the result of combination a valid instruction?  */
  insn_code_number = recog_for_combine (&newpat, i3, &new_i3_notes);

  /* If the result isn't valid, see if it is a PARALLEL of two SETs where
     the second SET's destination is a register that is unused and isn't
     marked as an instruction that might trap in an EH region.  In that case,
     we just need the first SET.   This can occur when simplifying a divmod
     insn.  We *must* test for this case here because the code below that
     splits two independent SETs doesn't handle this case correctly when it
     updates the register status.

     It's pointless doing this if we originally had two sets, one from
     i3, and one from i2.  Combining then splitting the parallel results
     in the original i2 again plus an invalid insn (which we delete).
     The net effect is only to move instructions around, which makes
     debug info less accurate.

     Also check the case where the first SET's destination is unused.
     That would not cause incorrect code, but does cause an unneeded
     insn to remain.  */

  if (insn_code_number < 0
      && !(added_sets_2 && i1 == 0)
      && GET_CODE (newpat) == PARALLEL
      && XVECLEN (newpat, 0) == 2
      && GET_CODE (XVECEXP (newpat, 0, 0)) == SET
      && GET_CODE (XVECEXP (newpat, 0, 1)) == SET
      && asm_noperands (newpat) < 0)
    {
      rtx set0 = XVECEXP (newpat, 0, 0);
      rtx set1 = XVECEXP (newpat, 0, 1);
      rtx note;

      if (((GET_CODE (SET_DEST (set1)) == REG
            && find_reg_note (i3, REG_UNUSED, SET_DEST (set1)))
           || (GET_CODE (SET_DEST (set1)) == SUBREG
               && find_reg_note (i3, REG_UNUSED, SUBREG_REG (SET_DEST (set1)))))
          && (!(note = find_reg_note (i3, REG_EH_REGION, NULL_RTX))
              || INTVAL (XEXP (note, 0)) <= 0)
          && ! side_effects_p (SET_SRC (set1)))
        {
          newpat = set0;
          insn_code_number = recog_for_combine (&newpat, i3, &new_i3_notes);
        }

      else if (((GET_CODE (SET_DEST (set0)) == REG
                 && find_reg_note (i3, REG_UNUSED, SET_DEST (set0)))
                || (GET_CODE (SET_DEST (set0)) == SUBREG
                    && find_reg_note (i3, REG_UNUSED,
                                      SUBREG_REG (SET_DEST (set0)))))
               && (!(note = find_reg_note (i3, REG_EH_REGION, NULL_RTX))
                   || INTVAL (XEXP (note, 0)) <= 0)
               && ! side_effects_p (SET_SRC (set0)))
        {
          newpat = set1;
          insn_code_number = recog_for_combine (&newpat, i3, &new_i3_notes);

          if (insn_code_number >= 0)
            {
              /* If we will be able to accept this, we have made a
                 change to the destination of I3.  This requires us to
                 do a few adjustments.  */

              PATTERN (i3) = newpat;
              adjust_for_new_dest (i3);
            }
        }
    }

  /* If we were combining three insns and the result is a simple SET
     with no ASM_OPERANDS that wasn't recognized, try to split it into two
     insns.  There are two ways to do this.  It can be split using a
     machine-specific method (like when you have an addition of a large
     constant) or by combine in the function find_split_point.  */

  if (i1 && insn_code_number < 0 && GET_CODE (newpat) == SET
      && asm_noperands (newpat) < 0)
    {
      rtx m_split, *split;
      rtx ni2dest = i2dest;

      /* See if the MD file can split NEWPAT.  If it can't, see if letting it
         use I2DEST as a scratch register will help.  In the latter case,
         convert I2DEST to the mode of the source of NEWPAT if we can.  */

      m_split = split_insns (newpat, i3);

      /* We can only use I2DEST as a scratch reg if it doesn't overlap any
         inputs of NEWPAT.  */

      /* ??? If I2DEST is not safe, and I1DEST exists, then it would be
         possible to try that as a scratch reg.  This would require adding
         more code to make it work though.  */

      if (m_split == 0 && ! reg_overlap_mentioned_p (ni2dest, newpat))
        {
          /* If I2DEST is a hard register or the only use of a pseudo,
             we can change its mode.  */
          if (GET_MODE (SET_DEST (newpat)) != GET_MODE (i2dest)
              && GET_MODE (SET_DEST (newpat)) != VOIDmode
              && GET_CODE (i2dest) == REG
              && (REGNO (i2dest) < FIRST_PSEUDO_REGISTER
                  || (REG_N_SETS (REGNO (i2dest)) == 1 && ! added_sets_2
                      && ! REG_USERVAR_P (i2dest))))
            ni2dest = gen_rtx_REG (GET_MODE (SET_DEST (newpat)),
                                   REGNO (i2dest));

          m_split = split_insns (gen_rtx_PARALLEL
                                 (VOIDmode,
                                  gen_rtvec (2, newpat,
                                             gen_rtx_CLOBBER (VOIDmode,
                                                              ni2dest))),
                                 i3);
          /* If the split with the mode-changed register didn't work, try
             the original register.  */
          if (! m_split && ni2dest != i2dest)
            {
              ni2dest = i2dest;
              m_split = split_insns (gen_rtx_PARALLEL
                                     (VOIDmode,
                                      gen_rtvec (2, newpat,
                                                 gen_rtx_CLOBBER (VOIDmode,
                                                                  i2dest))),
                                     i3);
            }
        }

      if (m_split && NEXT_INSN (m_split) == NULL_RTX)
        {
          m_split = PATTERN (m_split);
          insn_code_number = recog_for_combine (&m_split, i3, &new_i3_notes);
          if (insn_code_number >= 0)
            newpat = m_split;
        }
      else if (m_split && NEXT_INSN (NEXT_INSN (m_split)) == NULL_RTX
               && (next_real_insn (i2) == i3
                   || ! use_crosses_set_p (PATTERN (m_split), INSN_CUID (i2))))
        {
          rtx i2set, i3set;
          rtx newi3pat = PATTERN (NEXT_INSN (m_split));
          newi2pat = PATTERN (m_split);

          i3set = single_set (NEXT_INSN (m_split));
          i2set = single_set (m_split);

          /* In case we changed the mode of I2DEST, replace it in the
             pseudo-register table here.  We can't do it above in case this
             code doesn't get executed and we do a split the other way.  */

          if (REGNO (i2dest) >= FIRST_PSEUDO_REGISTER)
            SUBST (regno_reg_rtx[REGNO (i2dest)], ni2dest);

          i2_code_number = recog_for_combine (&newi2pat, i2, &new_i2_notes);

          /* If I2 or I3 has multiple SETs, we won't know how to track
             register status, so don't use these insns.  If I2's destination
             is used between I2 and I3, we also can't use these insns.  */

          if (i2_code_number >= 0 && i2set && i3set
              && (next_real_insn (i2) == i3
                  || ! reg_used_between_p (SET_DEST (i2set), i2, i3)))
            insn_code_number = recog_for_combine (&newi3pat, i3,
                                                  &new_i3_notes);
          if (insn_code_number >= 0)
            newpat = newi3pat;

          /* It is possible that both insns now set the destination of I3.
             If so, we must show an extra use of it.  */

          if (insn_code_number >= 0)
            {
              rtx new_i3_dest = SET_DEST (i3set);
              rtx new_i2_dest = SET_DEST (i2set);

              while (GET_CODE (new_i3_dest) == ZERO_EXTRACT
                     || GET_CODE (new_i3_dest) == STRICT_LOW_PART
                     || GET_CODE (new_i3_dest) == SUBREG)
                new_i3_dest = XEXP (new_i3_dest, 0);

              while (GET_CODE (new_i2_dest) == ZERO_EXTRACT
                     || GET_CODE (new_i2_dest) == STRICT_LOW_PART
                     || GET_CODE (new_i2_dest) == SUBREG)
                new_i2_dest = XEXP (new_i2_dest, 0);

              if (GET_CODE (new_i3_dest) == REG
                  && GET_CODE (new_i2_dest) == REG
                  && REGNO (new_i3_dest) == REGNO (new_i2_dest))
                REG_N_SETS (REGNO (new_i2_dest))++;
            }
        }

      /* If we can split it and use I2DEST, go ahead and see if that
         helps things be recognized.  Verify that none of the registers
         are set between I2 and I3.  */
      if (insn_code_number < 0 && (split = find_split_point (&newpat, i3)) != 0
#ifdef HAVE_cc0
          && GET_CODE (i2dest) == REG
#endif
          /* We need I2DEST in the proper mode.  If it is a hard register
             or the only use of a pseudo, we can change its mode.  */
          && (GET_MODE (*split) == GET_MODE (i2dest)
              || GET_MODE (*split) == VOIDmode
              || REGNO (i2dest) < FIRST_PSEUDO_REGISTER
              || (REG_N_SETS (REGNO (i2dest)) == 1 && ! added_sets_2
                  && ! REG_USERVAR_P (i2dest)))
          && (next_real_insn (i2) == i3
              || ! use_crosses_set_p (*split, INSN_CUID (i2)))
          /* We can't overwrite I2DEST if its value is still used by
             NEWPAT.  */
          && ! reg_referenced_p (i2dest, newpat))
        {
          rtx newdest = i2dest;
          enum rtx_code split_code = GET_CODE (*split);
          enum machine_mode split_mode = GET_MODE (*split);

          /* Get NEWDEST as a register in the proper mode.  We have already
             validated that we can do this.  */
          if (GET_MODE (i2dest) != split_mode && split_mode != VOIDmode)
            {
              newdest = gen_rtx_REG (split_mode, REGNO (i2dest));

              if (REGNO (i2dest) >= FIRST_PSEUDO_REGISTER)
                SUBST (regno_reg_rtx[REGNO (i2dest)], newdest);
            }

          /* If *SPLIT is a (mult FOO (const_int pow2)), convert it to
             an ASHIFT.  This can occur if it was inside a PLUS and hence
             appeared to be a memory address.  This is a kludge.  */
          if (split_code == MULT
              && GET_CODE (XEXP (*split, 1)) == CONST_INT
              && INTVAL (XEXP (*split, 1)) > 0
              && (i = exact_log2 (INTVAL (XEXP (*split, 1)))) >= 0)
            {
              SUBST (*split, gen_rtx_ASHIFT (split_mode,
                                             XEXP (*split, 0), GEN_INT (i)));
              /* Update split_code because we may not have a multiply
                 anymore.  */
              split_code = GET_CODE (*split);
            }

#ifdef INSN_SCHEDULING
          /* If *SPLIT is a paradoxical SUBREG, when we split it, it should
             be written as a ZERO_EXTEND.  */
          if (split_code == SUBREG && GET_CODE (SUBREG_REG (*split)) == MEM)
            {
#ifdef LOAD_EXTEND_OP
              /* Or as a SIGN_EXTEND if LOAD_EXTEND_OP says that that's
                 what it really is.  */
              if (LOAD_EXTEND_OP (GET_MODE (SUBREG_REG (*split)))
                  == SIGN_EXTEND)
                SUBST (*split, gen_rtx_SIGN_EXTEND (split_mode,
                                                    SUBREG_REG (*split)));
              else
#endif
                SUBST (*split, gen_rtx_ZERO_EXTEND (split_mode,
                                                    SUBREG_REG (*split)));
            }
#endif

          newi2pat = gen_rtx_SET (VOIDmode, newdest, *split);
          SUBST (*split, newdest);
          i2_code_number = recog_for_combine (&newi2pat, i2, &new_i2_notes);

          /* If the split point was a MULT and we didn't have one before,
             don't use one now.  */
          if (i2_code_number >= 0 && ! (split_code == MULT && ! have_mult))
            insn_code_number = recog_for_combine (&newpat, i3, &new_i3_notes);
        }
    }

  /* Check for a case where we loaded from memory in a narrow mode and
     then sign extended it, but we need both registers.  In that case,
     we have a PARALLEL with both loads from the same memory location.
     We can split this into a load from memory followed by a register-register
     copy.  This saves at least one insn, more if register allocation can
     eliminate the copy.

     We cannot do this if the destination of the first assignment is a
     condition code register or cc0.  We eliminate this case by making sure
     the SET_DEST and SET_SRC have the same mode.

     We cannot do this if the destination of the second assignment is
     a register that we have already assumed is zero-extended.  Similarly
     for a SUBREG of such a register.  */

  else if (i1 && insn_code_number < 0 && asm_noperands (newpat) < 0
           && GET_CODE (newpat) == PARALLEL
           && XVECLEN (newpat, 0) == 2
           && GET_CODE (XVECEXP (newpat, 0, 0)) == SET
           && GET_CODE (SET_SRC (XVECEXP (newpat, 0, 0))) == SIGN_EXTEND
           && (GET_MODE (SET_DEST (XVECEXP (newpat, 0, 0)))
               == GET_MODE (SET_SRC (XVECEXP (newpat, 0, 0))))
           && GET_CODE (XVECEXP (newpat, 0, 1)) == SET
           && rtx_equal_p (SET_SRC (XVECEXP (newpat, 0, 1)),
                           XEXP (SET_SRC (XVECEXP (newpat, 0, 0)), 0))
           && ! use_crosses_set_p (SET_SRC (XVECEXP (newpat, 0, 1)),
                                   INSN_CUID (i2))
           && GET_CODE (SET_DEST (XVECEXP (newpat, 0, 1))) != ZERO_EXTRACT
           && GET_CODE (SET_DEST (XVECEXP (newpat, 0, 1))) != STRICT_LOW_PART
           && ! (temp = SET_DEST (XVECEXP (newpat, 0, 1)),
                 (GET_CODE (temp) == REG
                  && reg_stat[REGNO (temp)].nonzero_bits != 0
                  && GET_MODE_BITSIZE (GET_MODE (temp)) < BITS_PER_WORD
                  && GET_MODE_BITSIZE (GET_MODE (temp)) < HOST_BITS_PER_INT
                  && (reg_stat[REGNO (temp)].nonzero_bits
                      != GET_MODE_MASK (word_mode))))
           && ! (GET_CODE (SET_DEST (XVECEXP (newpat, 0, 1))) == SUBREG
                 && (temp = SUBREG_REG (SET_DEST (XVECEXP (newpat, 0, 1))),
                     (GET_CODE (temp) == REG
                      && reg_stat[REGNO (temp)].nonzero_bits != 0
                      && GET_MODE_BITSIZE (GET_MODE (temp)) < BITS_PER_WORD
                      && GET_MODE_BITSIZE (GET_MODE (temp)) < HOST_BITS_PER_INT
                      && (reg_stat[REGNO (temp)].nonzero_bits
                          != GET_MODE_MASK (word_mode)))))
           && ! reg_overlap_mentioned_p (SET_DEST (XVECEXP (newpat, 0, 1)),
                                         SET_SRC (XVECEXP (newpat, 0, 1)))
           && ! find_reg_note (i3, REG_UNUSED,
                               SET_DEST (XVECEXP (newpat, 0, 0))))
    {
      rtx ni2dest;

      newi2pat = XVECEXP (newpat, 0, 0);
      ni2dest = SET_DEST (XVECEXP (newpat, 0, 0));
      newpat = XVECEXP (newpat, 0, 1);
      SUBST (SET_SRC (newpat),
             gen_lowpart (GET_MODE (SET_SRC (newpat)), ni2dest));
      i2_code_number = recog_for_combine (&newi2pat, i2, &new_i2_notes);

      if (i2_code_number >= 0)
        insn_code_number = recog_for_combine (&newpat, i3, &new_i3_notes);

      if (insn_code_number >= 0)
        {
          rtx insn;
          rtx link;

          /* If we will be able to accept this, we have made a change to the
             destination of I3.  This requires us to do a few adjustments.  */
          PATTERN (i3) = newpat;
          adjust_for_new_dest (i3);

          /* I3 now uses what used to be its destination and which is
             now I2's destination.  That means we need a LOG_LINK from
             I3 to I2.  But we used to have one, so we still will.

             However, some later insn might be using I2's dest and have
             a LOG_LINK pointing at I3.  We must remove this link.
             The simplest way to remove the link is to point it at I1,
             which we know will be a NOTE.  */

          for (insn = NEXT_INSN (i3);
               insn && (this_basic_block->next_bb == EXIT_BLOCK_PTR
                        || insn != BB_HEAD (this_basic_block->next_bb));
               insn = NEXT_INSN (insn))
            {
              if (INSN_P (insn) && reg_referenced_p (ni2dest, PATTERN (insn)))
                {
                  for (link = LOG_LINKS (insn); link;
                       link = XEXP (link, 1))
                    if (XEXP (link, 0) == i3)
                      XEXP (link, 0) = i1;

                  break;
                }
            }
        }
    }

  /* Similarly, check for a case where we have a PARALLEL of two independent
     SETs but we started with three insns.  In this case, we can do the sets
     as two separate insns.  This case occurs when some SET allows two
     other insns to combine, but the destination of that SET is still live.  */

  else if (i1 && insn_code_number < 0 && asm_noperands (newpat) < 0
           && GET_CODE (newpat) == PARALLEL
           && XVECLEN (newpat, 0) == 2
           && GET_CODE (XVECEXP (newpat, 0, 0)) == SET
           && GET_CODE (SET_DEST (XVECEXP (newpat, 0, 0))) != ZERO_EXTRACT
           && GET_CODE (SET_DEST (XVECEXP (newpat, 0, 0))) != STRICT_LOW_PART
           && GET_CODE (XVECEXP (newpat, 0, 1)) == SET
           && GET_CODE (SET_DEST (XVECEXP (newpat, 0, 1))) != ZERO_EXTRACT
           && GET_CODE (SET_DEST (XVECEXP (newpat, 0, 1))) != STRICT_LOW_PART
           && ! use_crosses_set_p (SET_SRC (XVECEXP (newpat, 0, 1)),
                                   INSN_CUID (i2))
           /* Don't pass sets with (USE (MEM ...)) dests to the following.  */
           && GET_CODE (SET_DEST (XVECEXP (newpat, 0, 1))) != USE
           && GET_CODE (SET_DEST (XVECEXP (newpat, 0, 0))) != USE
           && ! reg_referenced_p (SET_DEST (XVECEXP (newpat, 0, 1)),
                                  XVECEXP (newpat, 0, 0))
           && ! reg_referenced_p (SET_DEST (XVECEXP (newpat, 0, 0)),
                                  XVECEXP (newpat, 0, 1))
           && ! (contains_muldiv (SET_SRC (XVECEXP (newpat, 0, 0)))
                 && contains_muldiv (SET_SRC (XVECEXP (newpat, 0, 1)))))
    {
      /* Normally, it doesn't matter which of the two is done first,
         but it does if one references cc0.  In that case, it has to
         be first.  */
#ifdef HAVE_cc0
      if (reg_referenced_p (cc0_rtx, XVECEXP (newpat, 0, 0)))
        {
          newi2pat = XVECEXP (newpat, 0, 0);
          newpat = XVECEXP (newpat, 0, 1);
        }
      else
#endif
        {
          newi2pat = XVECEXP (newpat, 0, 1);
          newpat = XVECEXP (newpat, 0, 0);
        }

      i2_code_number = recog_for_combine (&newi2pat, i2, &new_i2_notes);

      if (i2_code_number >= 0)
        insn_code_number = recog_for_combine (&newpat, i3, &new_i3_notes);
    }

  /* If it still isn't recognized, fail and change things back the way they
     were.  */
  if ((insn_code_number < 0
       /* Is the result a reasonable ASM_OPERANDS?  */
       && (! check_asm_operands (newpat) || added_sets_1 || added_sets_2)))
    {
      undo_all ();
      return 0;
    }

  /* If we had to change another insn, make sure it is valid also.  */
  if (undobuf.other_insn)
    {
      rtx other_pat = PATTERN (undobuf.other_insn);
      rtx new_other_notes;
      rtx note, next;

      CLEAR_HARD_REG_SET (newpat_used_regs);

      other_code_number = recog_for_combine (&other_pat, undobuf.other_insn,
                                             &new_other_notes);

      if (other_code_number < 0 && ! check_asm_operands (other_pat))
        {
          undo_all ();
          return 0;
        }

      PATTERN (undobuf.other_insn) = other_pat;

      /* If any of the notes in OTHER_INSN were REG_UNUSED, ensure that they
         are still valid.  Then add any non-duplicate notes added by
         recog_for_combine.  */
      for (note = REG_NOTES (undobuf.other_insn); note; note = next)
        {
          next = XEXP (note, 1);

          if (REG_NOTE_KIND (note) == REG_UNUSED
              && ! reg_set_p (XEXP (note, 0), PATTERN (undobuf.other_insn)))
            {
              if (GET_CODE (XEXP (note, 0)) == REG)
                REG_N_DEATHS (REGNO (XEXP (note, 0)))--;

              remove_note (undobuf.other_insn, note);
            }
        }

      for (note = new_other_notes; note; note = XEXP (note, 1))
        if (GET_CODE (XEXP (note, 0)) == REG)
          REG_N_DEATHS (REGNO (XEXP (note, 0)))++;

      distribute_notes (new_other_notes, undobuf.other_insn,
                        undobuf.other_insn, NULL_RTX);
    }
#ifdef HAVE_cc0
  /* If I2 is the CC0 setter and I3 is the CC0 user then check whether
     they are adjacent to each other or not.  */
  {
    rtx p = prev_nonnote_insn (i3);
    if (p && p != i2 && GET_CODE (p) == INSN && newi2pat
        && sets_cc0_p (newi2pat))
      {
        undo_all ();
        return 0;
      }
  }
#endif

  /* We now know that we can do this combination.  Merge the insns and
     update the status of registers and LOG_LINKS.  */

  {
    rtx i3notes, i2notes, i1notes = 0;
    rtx i3links, i2links, i1links = 0;
    rtx midnotes = 0;
    unsigned int regno;

    /* Get the old REG_NOTES and LOG_LINKS from all our insns and
       clear them.  */
    i3notes = REG_NOTES (i3), i3links = LOG_LINKS (i3);
    i2notes = REG_NOTES (i2), i2links = LOG_LINKS (i2);
    if (i1)
      i1notes = REG_NOTES (i1), i1links = LOG_LINKS (i1);

    /* Ensure that we do not have something that should not be shared but
       occurs multiple times in the new insns.  Check this by first
       resetting all the `used' flags and then copying anything is shared.  */

    reset_used_flags (i3notes);
    reset_used_flags (i2notes);
    reset_used_flags (i1notes);
    reset_used_flags (newpat);
    reset_used_flags (newi2pat);
    if (undobuf.other_insn)
      reset_used_flags (PATTERN (undobuf.other_insn));

    i3notes = copy_rtx_if_shared (i3notes);
    i2notes = copy_rtx_if_shared (i2notes);
    i1notes = copy_rtx_if_shared (i1notes);
    newpat = copy_rtx_if_shared (newpat);
    newi2pat = copy_rtx_if_shared (newi2pat);
    if (undobuf.other_insn)
      reset_used_flags (PATTERN (undobuf.other_insn));

    INSN_CODE (i3) = insn_code_number;
    PATTERN (i3) = newpat;

    if (GET_CODE (i3) == CALL_INSN && CALL_INSN_FUNCTION_USAGE (i3))
      {
        rtx call_usage = CALL_INSN_FUNCTION_USAGE (i3);

        reset_used_flags (call_usage);
        call_usage = copy_rtx (call_usage);

        if (substed_i2)
          replace_rtx (call_usage, i2dest, i2src);

        if (substed_i1)
          replace_rtx (call_usage, i1dest, i1src);

        CALL_INSN_FUNCTION_USAGE (i3) = call_usage;
      }

    if (undobuf.other_insn)
      INSN_CODE (undobuf.other_insn) = other_code_number;

    /* We had one special case above where I2 had more than one set and
       we replaced a destination of one of those sets with the destination
       of I3.  In that case, we have to update LOG_LINKS of insns later
       in this basic block.  Note that this (expensive) case is rare.

       Also, in this case, we must pretend that all REG_NOTEs for I2
       actually came from I3, so that REG_UNUSED notes from I2 will be
       properly handled.  */

    if (i3_subst_into_i2)
      {
        for (i = 0; i < XVECLEN (PATTERN (i2), 0); i++)
          if (GET_CODE (XVECEXP (PATTERN (i2), 0, i)) != USE
              && GET_CODE (SET_DEST (XVECEXP (PATTERN (i2), 0, i))) == REG
              && SET_DEST (XVECEXP (PATTERN (i2), 0, i)) != i2dest
              && ! find_reg_note (i2, REG_UNUSED,
                                  SET_DEST (XVECEXP (PATTERN (i2), 0, i))))
            for (temp = NEXT_INSN (i2);
                 temp && (this_basic_block->next_bb == EXIT_BLOCK_PTR
                          || BB_HEAD (this_basic_block) != temp);
                 temp = NEXT_INSN (temp))
              if (temp != i3 && INSN_P (temp))
                for (link = LOG_LINKS (temp); link; link = XEXP (link, 1))
                  if (XEXP (link, 0) == i2)
                    XEXP (link, 0) = i3;

        if (i3notes)
          {
            rtx link = i3notes;
            while (XEXP (link, 1))
              link = XEXP (link, 1);
            XEXP (link, 1) = i2notes;
          }
        else
          i3notes = i2notes;
        i2notes = 0;
      }

    LOG_LINKS (i3) = 0;
    REG_NOTES (i3) = 0;
    LOG_LINKS (i2) = 0;
    REG_NOTES (i2) = 0;

    if (newi2pat)
      {
        INSN_CODE (i2) = i2_code_number;
        PATTERN (i2) = newi2pat;
      }
    else
      {
        PUT_CODE (i2, NOTE);
        NOTE_LINE_NUMBER (i2) = NOTE_INSN_DELETED;
        NOTE_SOURCE_FILE (i2) = 0;
      }

    if (i1)
      {
        LOG_LINKS (i1) = 0;
        REG_NOTES (i1) = 0;
        PUT_CODE (i1, NOTE);
        NOTE_LINE_NUMBER (i1) = NOTE_INSN_DELETED;
        NOTE_SOURCE_FILE (i1) = 0;
      }

    /* Get death notes for everything that is now used in either I3 or
       I2 and used to die in a previous insn.  If we built two new
       patterns, move from I1 to I2 then I2 to I3 so that we get the
       proper movement on registers that I2 modifies.  */

    if (newi2pat)
      {
        move_deaths (newi2pat, NULL_RTX, INSN_CUID (i1), i2, &midnotes);
        move_deaths (newpat, newi2pat, INSN_CUID (i1), i3, &midnotes);
      }
    else
      move_deaths (newpat, NULL_RTX, i1 ? INSN_CUID (i1) : INSN_CUID (i2),
                   i3, &midnotes);

    /* Distribute all the LOG_LINKS and REG_NOTES from I1, I2, and I3.  */
    if (i3notes)
      distribute_notes (i3notes, i3, i3, newi2pat ? i2 : NULL_RTX);
    if (i2notes)
      distribute_notes (i2notes, i2, i3, newi2pat ? i2 : NULL_RTX);
    if (i1notes)
      distribute_notes (i1notes, i1, i3, newi2pat ? i2 : NULL_RTX);
    if (midnotes)
      distribute_notes (midnotes, NULL_RTX, i3, newi2pat ? i2 : NULL_RTX);

    /* Distribute any notes added to I2 or I3 by recog_for_combine.  We
       know these are REG_UNUSED and want them to go to the desired insn,
       so we always pass it as i3.  We have not counted the notes in
       reg_n_deaths yet, so we need to do so now.  */

    if (newi2pat && new_i2_notes)
      {
        for (temp = new_i2_notes; temp; temp = XEXP (temp, 1))
          if (GET_CODE (XEXP (temp, 0)) == REG)
            REG_N_DEATHS (REGNO (XEXP (temp, 0)))++;

        distribute_notes (new_i2_notes, i2, i2, NULL_RTX);
      }

    if (new_i3_notes)
      {
        for (temp = new_i3_notes; temp; temp = XEXP (temp, 1))
          if (GET_CODE (XEXP (temp, 0)) == REG)
            REG_N_DEATHS (REGNO (XEXP (temp, 0)))++;

        distribute_notes (new_i3_notes, i3, i3, NULL_RTX);
      }

    /* If I3DEST was used in I3SRC, it really died in I3.  We may need to
       put a REG_DEAD note for it somewhere.  If NEWI2PAT exists and sets
       I3DEST, the death must be somewhere before I2, not I3.  If we passed I3
       in that case, it might delete I2.  Similarly for I2 and I1.
       Show an additional death due to the REG_DEAD note we make here.  If
       we discard it in distribute_notes, we will decrement it again.  */

    if (i3dest_killed)
      {
        if (GET_CODE (i3dest_killed) == REG)
          REG_N_DEATHS (REGNO (i3dest_killed))++;

        if (newi2pat && reg_set_p (i3dest_killed, newi2pat))
          distribute_notes (gen_rtx_EXPR_LIST (REG_DEAD, i3dest_killed,
                                               NULL_RTX),
                            NULL_RTX, i2, NULL_RTX);
        else
          distribute_notes (gen_rtx_EXPR_LIST (REG_DEAD, i3dest_killed,
                                               NULL_RTX),
                            NULL_RTX, i3, newi2pat ? i2 : NULL_RTX);
      }

    if (i2dest_in_i2src)
      {
        if (GET_CODE (i2dest) == REG)
          REG_N_DEATHS (REGNO (i2dest))++;

        if (newi2pat && reg_set_p (i2dest, newi2pat))
          distribute_notes (gen_rtx_EXPR_LIST (REG_DEAD, i2dest, NULL_RTX),
                            NULL_RTX, i2, NULL_RTX);
        else
          distribute_notes (gen_rtx_EXPR_LIST (REG_DEAD, i2dest, NULL_RTX),
                            NULL_RTX, i3, newi2pat ? i2 : NULL_RTX);
      }

    if (i1dest_in_i1src)
      {
        if (GET_CODE (i1dest) == REG)
          REG_N_DEATHS (REGNO (i1dest))++;

        if (newi2pat && reg_set_p (i1dest, newi2pat))
          distribute_notes (gen_rtx_EXPR_LIST (REG_DEAD, i1dest, NULL_RTX),
                            NULL_RTX, i2, NULL_RTX);
        else
          distribute_notes (gen_rtx_EXPR_LIST (REG_DEAD, i1dest, NULL_RTX),
                            NULL_RTX, i3, newi2pat ? i2 : NULL_RTX);
      }

    distribute_links (i3links);
    distribute_links (i2links);
    distribute_links (i1links);

    if (GET_CODE (i2dest) == REG)
      {
        rtx link;
        rtx i2_insn = 0, i2_val = 0, set;

        /* The insn that used to set this register doesn't exist, and
           this life of the register may not exist either.  See if one of
           I3's links points to an insn that sets I2DEST.  If it does,
           that is now the last known value for I2DEST. If we don't update
           this and I2 set the register to a value that depended on its old
           contents, we will get confused.  If this insn is used, thing
           will be set correctly in combine_instructions.  */

        for (link = LOG_LINKS (i3); link; link = XEXP (link, 1))
          if ((set = single_set (XEXP (link, 0))) != 0
              && rtx_equal_p (i2dest, SET_DEST (set)))
            i2_insn = XEXP (link, 0), i2_val = SET_SRC (set);

        record_value_for_reg (i2dest, i2_insn, i2_val);

        /* If the reg formerly set in I2 died only once and that was in I3,
           zero its use count so it won't make `reload' do any work.  */
        if (! added_sets_2
            && (newi2pat == 0 || ! reg_mentioned_p (i2dest, newi2pat))
            && ! i2dest_in_i2src)
          {
            regno = REGNO (i2dest);
            REG_N_SETS (regno)--;
          }
      }

    if (i1 && GET_CODE (i1dest) == REG)
      {
        rtx link;
        rtx i1_insn = 0, i1_val = 0, set;

        for (link = LOG_LINKS (i3); link; link = XEXP (link, 1))
          if ((set = single_set (XEXP (link, 0))) != 0
              && rtx_equal_p (i1dest, SET_DEST (set)))
            i1_insn = XEXP (link, 0), i1_val = SET_SRC (set);

        record_value_for_reg (i1dest, i1_insn, i1_val);

        regno = REGNO (i1dest);
        if (! added_sets_1 && ! i1dest_in_i1src)
          REG_N_SETS (regno)--;
      }

    /* Update reg_stat[].nonzero_bits et al for any changes that may have
       been made to this insn.  The order of
       set_nonzero_bits_and_sign_copies() is important.  Because newi2pat
       can affect nonzero_bits of newpat */
    if (newi2pat)
      note_stores (newi2pat, set_nonzero_bits_and_sign_copies, NULL);
    note_stores (newpat, set_nonzero_bits_and_sign_copies, NULL);

    /* Set new_direct_jump_p if a new return or simple jump instruction
       has been created.

       If I3 is now an unconditional jump, ensure that it has a
       BARRIER following it since it may have initially been a
       conditional jump.  It may also be the last nonnote insn.  */

    if (returnjump_p (i3) || any_uncondjump_p (i3))
      {
        *new_direct_jump_p = 1;
        mark_jump_label (PATTERN (i3), i3, 0);

        if ((temp = next_nonnote_insn (i3)) == NULL_RTX
            || GET_CODE (temp) != BARRIER)
          emit_barrier_after (i3);
      }

    if (undobuf.other_insn != NULL_RTX
        && (returnjump_p (undobuf.other_insn)
            || any_uncondjump_p (undobuf.other_insn)))
      {
        *new_direct_jump_p = 1;

        if ((temp = next_nonnote_insn (undobuf.other_insn)) == NULL_RTX
            || GET_CODE (temp) != BARRIER)
          emit_barrier_after (undobuf.other_insn);
      }

    /* An NOOP jump does not need barrier, but it does need cleaning up
       of CFG.  */
    if (GET_CODE (newpat) == SET
        && SET_SRC (newpat) == pc_rtx
        && SET_DEST (newpat) == pc_rtx)
      *new_direct_jump_p = 1;
  }

  combine_successes++;
  undo_commit ();

  if (added_links_insn
      && (newi2pat == 0 || INSN_CUID (added_links_insn) < INSN_CUID (i2))
      && INSN_CUID (added_links_insn) < INSN_CUID (i3))
    return added_links_insn;
  else
    return newi2pat ? i2 : i3;
}
\f
/* Undo all the modifications recorded in undobuf.  */

static void
undo_all (void)
{
  struct undo *undo, *next;

  for (undo = undobuf.undos; undo; undo = next)
    {
      next = undo->next;
      if (undo->is_int)
        *undo->where.i = undo->old_contents.i;
      else
        *undo->where.r = undo->old_contents.r;

      undo->next = undobuf.frees;
      undobuf.frees = undo;
    }

  undobuf.undos = 0;
}

/* We've committed to accepting the changes we made.  Move all
   of the undos to the free list.  */

static void
undo_commit (void)
{
  struct undo *undo, *next;

  for (undo = undobuf.undos; undo; undo = next)
    {
      next = undo->next;
      undo->next = undobuf.frees;
      undobuf.frees = undo;
    }
  undobuf.undos = 0;
}

\f
/* Find the innermost point within the rtx at LOC, possibly LOC itself,
   where we have an arithmetic expression and return that point.  LOC will
   be inside INSN.

   try_combine will call this function to see if an insn can be split into
   two insns.  */

static rtx *
find_split_point (rtx *loc, rtx insn)
{
  rtx x = *loc;
  enum rtx_code code = GET_CODE (x);
  rtx *split;
  unsigned HOST_WIDE_INT len = 0;
  HOST_WIDE_INT pos = 0;
  int unsignedp = 0;
  rtx inner = NULL_RTX;

  /* First special-case some codes.  */
  switch (code)
    {
    case SUBREG:
#ifdef INSN_SCHEDULING
      /* If we are making a paradoxical SUBREG invalid, it becomes a split
         point.  */
      if (GET_CODE (SUBREG_REG (x)) == MEM)
        return loc;
#endif
      return find_split_point (&SUBREG_REG (x), insn);

    case MEM:
#ifdef HAVE_lo_sum
      /* If we have (mem (const ..)) or (mem (symbol_ref ...)), split it
         using LO_SUM and HIGH.  */
      if (GET_CODE (XEXP (x, 0)) == CONST
          || GET_CODE (XEXP (x, 0)) == SYMBOL_REF)
        {
          SUBST (XEXP (x, 0),
                 gen_rtx_LO_SUM (Pmode,
                                 gen_rtx_HIGH (Pmode, XEXP (x, 0)),
                                 XEXP (x, 0)));
          return &XEXP (XEXP (x, 0), 0);
        }
#endif

      /* If we have a PLUS whose second operand is a constant and the
         address is not valid, perhaps will can split it up using
         the machine-specific way to split large constants.  We use
         the first pseudo-reg (one of the virtual regs) as a placeholder;
         it will not remain in the result.  */
      if (GET_CODE (XEXP (x, 0)) == PLUS
          && GET_CODE (XEXP (XEXP (x, 0), 1)) == CONST_INT
          && ! memory_address_p (GET_MODE (x), XEXP (x, 0)))
        {
          rtx reg = regno_reg_rtx[FIRST_PSEUDO_REGISTER];
          rtx seq = split_insns (gen_rtx_SET (VOIDmode, reg, XEXP (x, 0)),
                                 subst_insn);

          /* This should have produced two insns, each of which sets our
             placeholder.  If the source of the second is a valid address,
             we can make put both sources together and make a split point
             in the middle.  */

          if (seq
              && NEXT_INSN (seq) != NULL_RTX
              && NEXT_INSN (NEXT_INSN (seq)) == NULL_RTX
              && GET_CODE (seq) == INSN
              && GET_CODE (PATTERN (seq)) == SET
              && SET_DEST (PATTERN (seq)) == reg
              && ! reg_mentioned_p (reg,
                                    SET_SRC (PATTERN (seq)))
              && GET_CODE (NEXT_INSN (seq)) == INSN
              && GET_CODE (PATTERN (NEXT_INSN (seq))) == SET
              && SET_DEST (PATTERN (NEXT_INSN (seq))) == reg
              && memory_address_p (GET_MODE (x),
                                   SET_SRC (PATTERN (NEXT_INSN (seq)))))
            {
              rtx src1 = SET_SRC (PATTERN (seq));
              rtx src2 = SET_SRC (PATTERN (NEXT_INSN (seq)));

              /* Replace the placeholder in SRC2 with SRC1.  If we can
                 find where in SRC2 it was placed, that can become our
                 split point and we can replace this address with SRC2.
                 Just try two obvious places.  */

              src2 = replace_rtx (src2, reg, src1);
              split = 0;
              if (XEXP (src2, 0) == src1)
                split = &XEXP (src2, 0);
              else if (GET_RTX_FORMAT (GET_CODE (XEXP (src2, 0)))[0] == 'e'
                       && XEXP (XEXP (src2, 0), 0) == src1)
                split = &XEXP (XEXP (src2, 0), 0);

              if (split)
                {
                  SUBST (XEXP (x, 0), src2);
                  return split;
                }
            }

          /* If that didn't work, perhaps the first operand is complex and
             needs to be computed separately, so make a split point there.
             This will occur on machines that just support REG + CONST
             and have a constant moved through some previous computation.  */

          else if (!OBJECT_P (XEXP (XEXP (x, 0), 0))
                   && ! (GET_CODE (XEXP (XEXP (x, 0), 0)) == SUBREG
                         && OBJECT_P (SUBREG_REG (XEXP (XEXP (x, 0), 0)))))
            return &XEXP (XEXP (x, 0), 0);
        }
      break;

    case SET:
#ifdef HAVE_cc0
      /* If SET_DEST is CC0 and SET_SRC is not an operand, a COMPARE, or a
         ZERO_EXTRACT, the most likely reason why this doesn't match is that
         we need to put the operand into a register.  So split at that
         point.  */

      if (SET_DEST (x) == cc0_rtx
          && GET_CODE (SET_SRC (x)) != COMPARE
          && GET_CODE (SET_SRC (x)) != ZERO_EXTRACT
          && !OBJECT_P (SET_SRC (x))
          && ! (GET_CODE (SET_SRC (x)) == SUBREG
                && OBJECT_P (SUBREG_REG (SET_SRC (x)))))
        return &SET_SRC (x);
#endif

      /* See if we can split SET_SRC as it stands.  */
      split = find_split_point (&SET_SRC (x), insn);
      if (split && split != &SET_SRC (x))
        return split;

      /* See if we can split SET_DEST as it stands.  */
      split = find_split_point (&SET_DEST (x), insn);
      if (split && split != &SET_DEST (x))
        return split;

      /* See if this is a bitfield assignment with everything constant.  If
         so, this is an IOR of an AND, so split it into that.  */
      if (GET_CODE (SET_DEST (x)) == ZERO_EXTRACT
          && (GET_MODE_BITSIZE (GET_MODE (XEXP (SET_DEST (x), 0)))
              <= HOST_BITS_PER_WIDE_INT)
          && GET_CODE (XEXP (SET_DEST (x), 1)) == CONST_INT
          && GET_CODE (XEXP (SET_DEST (x), 2)) == CONST_INT
          && GET_CODE (SET_SRC (x)) == CONST_INT
          && ((INTVAL (XEXP (SET_DEST (x), 1))
               + INTVAL (XEXP (SET_DEST (x), 2)))
              <= GET_MODE_BITSIZE (GET_MODE (XEXP (SET_DEST (x), 0))))
          && ! side_effects_p (XEXP (SET_DEST (x), 0)))
        {
          HOST_WIDE_INT pos = INTVAL (XEXP (SET_DEST (x), 2));
          unsigned HOST_WIDE_INT len = INTVAL (XEXP (SET_DEST (x), 1));
          unsigned HOST_WIDE_INT src = INTVAL (SET_SRC (x));
          rtx dest = XEXP (SET_DEST (x), 0);
          enum machine_mode mode = GET_MODE (dest);
          unsigned HOST_WIDE_INT mask = ((HOST_WIDE_INT) 1 << len) - 1;

          if (BITS_BIG_ENDIAN)
            pos = GET_MODE_BITSIZE (mode) - len - pos;

          if (src == mask)
            SUBST (SET_SRC (x),
                   gen_binary (IOR, mode, dest, GEN_INT (src << pos)));
          else
            SUBST (SET_SRC (x),
                   gen_binary (IOR, mode,
                               gen_binary (AND, mode, dest,
                                           gen_int_mode (~(mask << pos),
                                                         mode)),
                               GEN_INT (src << pos)));

          SUBST (SET_DEST (x), dest);

          split = find_split_point (&SET_SRC (x), insn);
          if (split && split != &SET_SRC (x))
            return split;
        }

      /* Otherwise, see if this is an operation that we can split into two.
         If so, try to split that.  */
      code = GET_CODE (SET_SRC (x));

      switch (code)
        {
        case AND:
          /* If we are AND'ing with a large constant that is only a single
             bit and the result is only being used in a context where we
             need to know if it is zero or nonzero, replace it with a bit
             extraction.  This will avoid the large constant, which might
             have taken more than one insn to make.  If the constant were
             not a valid argument to the AND but took only one insn to make,
             this is no worse, but if it took more than one insn, it will
             be better.  */

          if (GET_CODE (XEXP (SET_SRC (x), 1)) == CONST_INT
              && GET_CODE (XEXP (SET_SRC (x), 0)) == REG
              && (pos = exact_log2 (INTVAL (XEXP (SET_SRC (x), 1)))) >= 7
              && GET_CODE (SET_DEST (x)) == REG
              && (split = find_single_use (SET_DEST (x), insn, (rtx*) 0)) != 0
              && (GET_CODE (*split) == EQ || GET_CODE (*split) == NE)
              && XEXP (*split, 0) == SET_DEST (x)
              && XEXP (*split, 1) == const0_rtx)
            {
              rtx extraction = make_extraction (GET_MODE (SET_DEST (x)),
                                                XEXP (SET_SRC (x), 0),
                                                pos, NULL_RTX, 1, 1, 0, 0);
              if (extraction != 0)
                {
                  SUBST (SET_SRC (x), extraction);
                  return find_split_point (loc, insn);
                }
            }
          break;

        case NE:
          /* If STORE_FLAG_VALUE is -1, this is (NE X 0) and only one bit of X
             is known to be on, this can be converted into a NEG of a shift.  */
          if (STORE_FLAG_VALUE == -1 && XEXP (SET_SRC (x), 1) == const0_rtx
              && GET_MODE (SET_SRC (x)) == GET_MODE (XEXP (SET_SRC (x), 0))
              && 1 <= (pos = exact_log2
                       (nonzero_bits (XEXP (SET_SRC (x), 0),
                                      GET_MODE (XEXP (SET_SRC (x), 0))))))
            {
              enum machine_mode mode = GET_MODE (XEXP (SET_SRC (x), 0));

              SUBST (SET_SRC (x),
                     gen_rtx_NEG (mode,
                                  gen_rtx_LSHIFTRT (mode,
                                                    XEXP (SET_SRC (x), 0),
                                                    GEN_INT (pos))));

              split = find_split_point (&SET_SRC (x), insn);
              if (split && split != &SET_SRC (x))
                return split;
            }
          break;

        case SIGN_EXTEND:
          inner = XEXP (SET_SRC (x), 0);

          /* We can't optimize if either mode is a partial integer
             mode as we don't know how many bits are significant
             in those modes.  */
          if (GET_MODE_CLASS (GET_MODE (inner)) == MODE_PARTIAL_INT
              || GET_MODE_CLASS (GET_MODE (SET_SRC (x))) == MODE_PARTIAL_INT)
            break;

          pos = 0;
          len = GET_MODE_BITSIZE (GET_MODE (inner));
          unsignedp = 0;
          break;

        case SIGN_EXTRACT:
        case ZERO_EXTRACT:
          if (GET_CODE (XEXP (SET_SRC (x), 1)) == CONST_INT
              && GET_CODE (XEXP (SET_SRC (x), 2)) == CONST_INT)
            {
              inner = XEXP (SET_SRC (x), 0);
              len = INTVAL (XEXP (SET_SRC (x), 1));
              pos = INTVAL (XEXP (SET_SRC (x), 2));

              if (BITS_BIG_ENDIAN)
                pos = GET_MODE_BITSIZE (GET_MODE (inner)) - len - pos;
              unsignedp = (code == ZERO_EXTRACT);
            }
          break;

        default:
          break;
        }

      if (len && pos >= 0 && pos + len <= GET_MODE_BITSIZE (GET_MODE (inner)))
        {
          enum machine_mode mode = GET_MODE (SET_SRC (x));

          /* For unsigned, we have a choice of a shift followed by an
             AND or two shifts.  Use two shifts for field sizes where the
             constant might be too large.  We assume here that we can
             always at least get 8-bit constants in an AND insn, which is
             true for every current RISC.  */

          if (unsignedp && len <= 8)
            {
              SUBST (SET_SRC (x),
                     gen_rtx_AND (mode,
                                  gen_rtx_LSHIFTRT
                                  (mode, gen_lowpart (mode, inner),
                                   GEN_INT (pos)),
                                  GEN_INT (((HOST_WIDE_INT) 1 << len) - 1)));

              split = find_split_point (&SET_SRC (x), insn);
              if (split && split != &SET_SRC (x))
                return split;
            }
          else
            {
              SUBST (SET_SRC (x),
                     gen_rtx_fmt_ee
                     (unsignedp ? LSHIFTRT : ASHIFTRT, mode,
                      gen_rtx_ASHIFT (mode,
                                      gen_lowpart (mode, inner),
                                      GEN_INT (GET_MODE_BITSIZE (mode)
                                               - len - pos)),
                      GEN_INT (GET_MODE_BITSIZE (mode) - len)));

              split = find_split_point (&SET_SRC (x), insn);
              if (split && split != &SET_SRC (x))
                return split;
            }
        }

      /* See if this is a simple operation with a constant as the second
         operand.  It might be that this constant is out of range and hence
         could be used as a split point.  */
      if (BINARY_P (SET_SRC (x))
          && CONSTANT_P (XEXP (SET_SRC (x), 1))
          && (OBJECT_P (XEXP (SET_SRC (x), 0))
              || (GET_CODE (XEXP (SET_SRC (x), 0)) == SUBREG
                  && OBJECT_P (SUBREG_REG (XEXP (SET_SRC (x), 0))))))
        return &XEXP (SET_SRC (x), 1);

      /* Finally, see if this is a simple operation with its first operand
         not in a register.  The operation might require this operand in a
         register, so return it as a split point.  We can always do this
         because if the first operand were another operation, we would have
         already found it as a split point.  */
      if ((BINARY_P (SET_SRC (x)) || UNARY_P (SET_SRC (x)))
          && ! register_operand (XEXP (SET_SRC (x), 0), VOIDmode))
        return &XEXP (SET_SRC (x), 0);

      return 0;

    case AND:
    case IOR:
      /* We write NOR as (and (not A) (not B)), but if we don't have a NOR,
         it is better to write this as (not (ior A B)) so we can split it.
         Similarly for IOR.  */
      if (GET_CODE (XEXP (x, 0)) == NOT && GET_CODE (XEXP (x, 1)) == NOT)
        {
          SUBST (*loc,
                 gen_rtx_NOT (GET_MODE (x),
                              gen_rtx_fmt_ee (code == IOR ? AND : IOR,
                                              GET_MODE (x),
                                              XEXP (XEXP (x, 0), 0),
                                              XEXP (XEXP (x, 1), 0))));
          return find_split_point (loc, insn);
        }

      /* Many RISC machines have a large set of logical insns.  If the
         second operand is a NOT, put it first so we will try to split the
         other operand first.  */
      if (GET_CODE (XEXP (x, 1)) == NOT)
        {
          rtx tem = XEXP (x, 0);
          SUBST (XEXP (x, 0), XEXP (x, 1));
          SUBST (XEXP (x, 1), tem);
        }
      break;

    default:
      break;
    }

  /* Otherwise, select our actions depending on our rtx class.  */
  switch (GET_RTX_CLASS (code))
    {
    case RTX_BITFIELD_OPS:              /* This is ZERO_EXTRACT and SIGN_EXTRACT.  */
    case RTX_TERNARY:
      split = find_split_point (&XEXP (x, 2), insn);
      if (split)
        return split;
      /* ... fall through ...  */
    case RTX_BIN_ARITH:
    case RTX_COMM_ARITH:
    case RTX_COMPARE:
    case RTX_COMM_COMPARE:
      split = find_split_point (&XEXP (x, 1), insn);
      if (split)
        return split;
      /* ... fall through ...  */
    case RTX_UNARY:
      /* Some machines have (and (shift ...) ...) insns.  If X is not
         an AND, but XEXP (X, 0) is, use it as our split point.  */
      if (GET_CODE (x) != AND && GET_CODE (XEXP (x, 0)) == AND)
        return &XEXP (x, 0);

      split = find_split_point (&XEXP (x, 0), insn);
      if (split)
        return split;
      return loc;

    default:
      /* Otherwise, we don't have a split point.  */
      return 0;
    }
}
\f
/* Throughout X, replace FROM with TO, and return the result.
   The result is TO if X is FROM;
   otherwise the result is X, but its contents may have been modified.
   If they were modified, a record was made in undobuf so that
   undo_all will (among other things) return X to its original state.

   If the number of changes necessary is too much to record to undo,
   the excess changes are not made, so the result is invalid.
   The changes already made can still be undone.
   undobuf.num_undo is incremented for such changes, so by testing that
   the caller can tell whether the result is valid.

   `n_occurrences' is incremented each time FROM is replaced.

   IN_DEST is nonzero if we are processing the SET_DEST of a SET.

   UNIQUE_COPY is nonzero if each substitution must be unique.  We do this
   by copying if `n_occurrences' is nonzero.  */

static rtx
subst (rtx x, rtx from, rtx to, int in_dest, int unique_copy)
{
  enum rtx_code code = GET_CODE (x);
  enum machine_mode op0_mode = VOIDmode;
  const char *fmt;
  int len, i;
  rtx new;

/* Two expressions are equal if they are identical copies of a shared
   RTX or if they are both registers with the same register number
   and mode.  */

#define COMBINE_RTX_EQUAL_P(X,Y)                        \
  ((X) == (Y)                                           \
   || (GET_CODE (X) == REG && GET_CODE (Y) == REG       \
       && REGNO (X) == REGNO (Y) && GET_MODE (X) == GET_MODE (Y)))

  if (! in_dest && COMBINE_RTX_EQUAL_P (x, from))
    {
      n_occurrences++;
      return (unique_copy && n_occurrences > 1 ? copy_rtx (to) : to);
    }

  /* If X and FROM are the same register but different modes, they will
     not have been seen as equal above.  However, flow.c will make a
     LOG_LINKS entry for that case.  If we do nothing, we will try to
     rerecognize our original insn and, when it succeeds, we will
     delete the feeding insn, which is incorrect.

     So force this insn not to match in this (rare) case.  */
  if (! in_dest && code == REG && GET_CODE (from) == REG
      && REGNO (x) == REGNO (from))
    return gen_rtx_CLOBBER (GET_MODE (x), const0_rtx);

  /* If this is an object, we are done unless it is a MEM or LO_SUM, both
     of which may contain things that can be combined.  */
  if (code != MEM && code != LO_SUM && OBJECT_P (x))
    return x;

  /* It is possible to have a subexpression appear twice in the insn.
     Suppose that FROM is a register that appears within TO.
     Then, after that subexpression has been scanned once by `subst',
     the second time it is scanned, TO may be found.  If we were
     to scan TO here, we would find FROM within it and create a
     self-referent rtl structure which is completely wrong.  */
  if (COMBINE_RTX_EQUAL_P (x, to))
    return to;

  /* Parallel asm_operands need special attention because all of the
     inputs are shared across the arms.  Furthermore, unsharing the
     rtl results in recognition failures.  Failure to handle this case
     specially can result in circular rtl.

     Solve this by doing a normal pass across the first entry of the
     parallel, and only processing the SET_DESTs of the subsequent
     entries.  Ug.  */

  if (code == PARALLEL
      && GET_CODE (XVECEXP (x, 0, 0)) == SET
      && GET_CODE (SET_SRC (XVECEXP (x, 0, 0))) == ASM_OPERANDS)
    {
      new = subst (XVECEXP (x, 0, 0), from, to, 0, unique_copy);

      /* If this substitution failed, this whole thing fails.  */
      if (GET_CODE (new) == CLOBBER
          && XEXP (new, 0) == const0_rtx)
        return new;

      SUBST (XVECEXP (x, 0, 0), new);

      for (i = XVECLEN (x, 0) - 1; i >= 1; i--)
        {
          rtx dest = SET_DEST (XVECEXP (x, 0, i));

          if (GET_CODE (dest) != REG
              && GET_CODE (dest) != CC0
              && GET_CODE (dest) != PC)
            {
              new = subst (dest, from, to, 0, unique_copy);

              /* If this substitution failed, this whole thing fails.  */
              if (GET_CODE (new) == CLOBBER
                  && XEXP (new, 0) == const0_rtx)
                return new;

              SUBST (SET_DEST (XVECEXP (x, 0, i)), new);
            }
        }
    }
  else
    {
      len = GET_RTX_LENGTH (code);
      fmt = GET_RTX_FORMAT (code);

      /* We don't need to process a SET_DEST that is a register, CC0,
         or PC, so set up to skip this common case.  All other cases
         where we want to suppress replacing something inside a
         SET_SRC are handled via the IN_DEST operand.  */
      if (code == SET
          && (GET_CODE (SET_DEST (x)) == REG
              || GET_CODE (SET_DEST (x)) == CC0
              || GET_CODE (SET_DEST (x)) == PC))
        fmt = "ie";

      /* Get the mode of operand 0 in case X is now a SIGN_EXTEND of a
         constant.  */
      if (fmt[0] == 'e')
        op0_mode = GET_MODE (XEXP (x, 0));

      for (i = 0; i < len; i++)
        {
          if (fmt[i] == 'E')
            {
              int j;
              for (j = XVECLEN (x, i) - 1; j >= 0; j--)
                {
                  if (COMBINE_RTX_EQUAL_P (XVECEXP (x, i, j), from))
                    {
                      new = (unique_copy && n_occurrences
                             ? copy_rtx (to) : to);
                      n_occurrences++;
                    }
                  else
                    {
                      new = subst (XVECEXP (x, i, j), from, to, 0,
                                   unique_copy);

                      /* If this substitution failed, this whole thing
                         fails.  */
                      if (GET_CODE (new) == CLOBBER
                          && XEXP (new, 0) == const0_rtx)
                        return new;
                    }

                  SUBST (XVECEXP (x, i, j), new);
                }
            }
          else if (fmt[i] == 'e')
            {
              /* If this is a register being set, ignore it.  */
              new = XEXP (x, i);
              if (in_dest
                  && (code == SUBREG || code == STRICT_LOW_PART
                      || code == ZERO_EXTRACT)
                  && i == 0
                  && GET_CODE (new) == REG)
                ;

              else if (COMBINE_RTX_EQUAL_P (XEXP (x, i), from))
                {
                  /* In general, don't install a subreg involving two
                     modes not tieable.  It can worsen register
                     allocation, and can even make invalid reload
                     insns, since the reg inside may need to be copied
                     from in the outside mode, and that may be invalid
                     if it is an fp reg copied in integer mode.

                     We allow two exceptions to this: It is valid if
                     it is inside another SUBREG and the mode of that
                     SUBREG and the mode of the inside of TO is
                     tieable and it is valid if X is a SET that copies
                     FROM to CC0.  */

                  if (GET_CODE (to) == SUBREG
                      && ! MODES_TIEABLE_P (GET_MODE (to),
                                            GET_MODE (SUBREG_REG (to)))
                      && ! (code == SUBREG
                            && MODES_TIEABLE_P (GET_MODE (x),
                                                GET_MODE (SUBREG_REG (to))))
#ifdef HAVE_cc0
                      && ! (code == SET && i == 1 && XEXP (x, 0) == cc0_rtx)
#endif
                      )
                    return gen_rtx_CLOBBER (VOIDmode, const0_rtx);

#ifdef CANNOT_CHANGE_MODE_CLASS
                  if (code == SUBREG
                      && GET_CODE (to) == REG
                      && REGNO (to) < FIRST_PSEUDO_REGISTER
                      && REG_CANNOT_CHANGE_MODE_P (REGNO (to),
                                                   GET_MODE (to),
                                                   GET_MODE (x)))
                    return gen_rtx_CLOBBER (VOIDmode, const0_rtx);
#endif

                  new = (unique_copy && n_occurrences ? copy_rtx (to) : to);
                  n_occurrences++;
                }
              else
                /* If we are in a SET_DEST, suppress most cases unless we
                   have gone inside a MEM, in which case we want to
                   simplify the address.  We assume here that things that
                   are actually part of the destination have their inner
                   parts in the first expression.  This is true for SUBREG,
                   STRICT_LOW_PART, and ZERO_EXTRACT, which are the only
                   things aside from REG and MEM that should appear in a
                   SET_DEST.  */
                new = subst (XEXP (x, i), from, to,
                             (((in_dest
                                && (code == SUBREG || code == STRICT_LOW_PART
                                    || code == ZERO_EXTRACT))
                               || code == SET)
                              && i == 0), unique_copy);

              /* If we found that we will have to reject this combination,
                 indicate that by returning the CLOBBER ourselves, rather than
                 an expression containing it.  This will speed things up as
                 well as prevent accidents where two CLOBBERs are considered
                 to be equal, thus producing an incorrect simplification.  */

              if (GET_CODE (new) == CLOBBER && XEXP (new, 0) == const0_rtx)
                return new;

              if (GET_CODE (x) == SUBREG
                  && (GET_CODE (new) == CONST_INT
                      || GET_CODE (new) == CONST_DOUBLE))
                {
                  enum machine_mode mode = GET_MODE (x);

                  x = simplify_subreg (GET_MODE (x), new,
                                       GET_MODE (SUBREG_REG (x)),
                                       SUBREG_BYTE (x));
                  if (! x)
                    x = gen_rtx_CLOBBER (mode, const0_rtx);
                }
              else if (GET_CODE (new) == CONST_INT
                       && GET_CODE (x) == ZERO_EXTEND)
                {
                  x = simplify_unary_operation (ZERO_EXTEND, GET_MODE (x),
                                                new, GET_MODE (XEXP (x, 0)));
                  if (! x)
                    abort ();
                }
              else
                SUBST (XEXP (x, i), new);
            }
        }
    }

  /* Try to simplify X.  If the simplification changed the code, it is likely
     that further simplification will help, so loop, but limit the number
     of repetitions that will be performed.  */

  for (i = 0; i < 4; i++)
    {
      /* If X is sufficiently simple, don't bother trying to do anything
         with it.  */
      if (code != CONST_INT && code != REG && code != CLOBBER)
        x = combine_simplify_rtx (x, op0_mode, in_dest);

      if (GET_CODE (x) == code)
        break;

      code = GET_CODE (x);

      /* We no longer know the original mode of operand 0 since we
         have changed the form of X)  */
      op0_mode = VOIDmode;
    }

  return x;
}
\f
/* Simplify X, a piece of RTL.  We just operate on the expression at the
   outer level; call `subst' to simplify recursively.  Return the new
   expression.

   OP0_MODE is the original mode of XEXP (x, 0).  IN_DEST is nonzero
   if we are inside a SET_DEST.  */

static rtx
combine_simplify_rtx (rtx x, enum machine_mode op0_mode, int in_dest)
{
  enum rtx_code code = GET_CODE (x);
  enum machine_mode mode = GET_MODE (x);
  rtx temp;
  rtx reversed;
  int i;

  /* If this is a commutative operation, put a constant last and a complex
     expression first.  We don't need to do this for comparisons here.  */
  if (COMMUTATIVE_ARITH_P (x)
      && swap_commutative_operands_p (XEXP (x, 0), XEXP (x, 1)))
    {
      temp = XEXP (x, 0);
      SUBST (XEXP (x, 0), XEXP (x, 1));
      SUBST (XEXP (x, 1), temp);
    }

  /* If this is a PLUS, MINUS, or MULT, and the first operand is the
     sign extension of a PLUS with a constant, reverse the order of the sign
     extension and the addition. Note that this not the same as the original
     code, but overflow is undefined for signed values.  Also note that the
     PLUS will have been partially moved "inside" the sign-extension, so that
     the first operand of X will really look like:
         (ashiftrt (plus (ashift A C4) C5) C4).
     We convert this to
         (plus (ashiftrt (ashift A C4) C2) C4)
     and replace the first operand of X with that expression.  Later parts
     of this function may simplify the expression further.

     For example, if we start with (mult (sign_extend (plus A C1)) C2),
     we swap the SIGN_EXTEND and PLUS.  Later code will apply the
     distributive law to produce (plus (mult (sign_extend X) C1) C3).

     We do this to simplify address expressions.  */

  if ((code == PLUS || code == MINUS || code == MULT)
      && GET_CODE (XEXP (x, 0)) == ASHIFTRT
      && GET_CODE (XEXP (XEXP (x, 0), 0)) == PLUS
      && GET_CODE (XEXP (XEXP (XEXP (x, 0), 0), 0)) == ASHIFT
      && GET_CODE (XEXP (XEXP (XEXP (XEXP (x, 0), 0), 0), 1)) == CONST_INT
      && GET_CODE (XEXP (XEXP (x, 0), 1)) == CONST_INT
      && XEXP (XEXP (XEXP (XEXP (x, 0), 0), 0), 1) == XEXP (XEXP (x, 0), 1)
      && GET_CODE (XEXP (XEXP (XEXP (x, 0), 0), 1)) == CONST_INT
      && (temp = simplify_binary_operation (ASHIFTRT, mode,
                                            XEXP (XEXP (XEXP (x, 0), 0), 1),
                                            XEXP (XEXP (x, 0), 1))) != 0)
    {
      rtx new
        = simplify_shift_const (NULL_RTX, ASHIFT, mode,
                                XEXP (XEXP (XEXP (XEXP (x, 0), 0), 0), 0),
                                INTVAL (XEXP (XEXP (x, 0), 1)));

      new = simplify_shift_const (NULL_RTX, ASHIFTRT, mode, new,
                                  INTVAL (XEXP (XEXP (x, 0), 1)));

      SUBST (XEXP (x, 0), gen_binary (PLUS, mode, new, temp));
    }

  /* If this is a simple operation applied to an IF_THEN_ELSE, try
     applying it to the arms of the IF_THEN_ELSE.  This often simplifies
     things.  Check for cases where both arms are testing the same
     condition.

     Don't do anything if all operands are very simple.  */

  if ((BINARY_P (x)
       && ((!OBJECT_P (XEXP (x, 0))
            && ! (GET_CODE (XEXP (x, 0)) == SUBREG
                  && OBJECT_P (SUBREG_REG (XEXP (x, 0)))))
           || (!OBJECT_P (XEXP (x, 1))
               && ! (GET_CODE (XEXP (x, 1)) == SUBREG
                     && OBJECT_P (SUBREG_REG (XEXP (x, 1)))))))
      || (UNARY_P (x)
          && (!OBJECT_P (XEXP (x, 0))
               && ! (GET_CODE (XEXP (x, 0)) == SUBREG
                     && OBJECT_P (SUBREG_REG (XEXP (x, 0)))))))
    {
      rtx cond, true_rtx, false_rtx;

      cond = if_then_else_cond (x, &true_rtx, &false_rtx);
      if (cond != 0
          /* If everything is a comparison, what we have is highly unlikely
             to be simpler, so don't use it.  */
          && ! (COMPARISON_P (x)
                && (COMPARISON_P (true_rtx) || COMPARISON_P (false_rtx))))
        {
          rtx cop1 = const0_rtx;
          enum rtx_code cond_code = simplify_comparison (NE, &cond, &cop1);

          if (cond_code == NE && COMPARISON_P (cond))
            return x;

          /* Simplify the alternative arms; this may collapse the true and
             false arms to store-flag values.  Be careful to use copy_rtx
             here since true_rtx or false_rtx might share RTL with x as a
             result of the if_then_else_cond call above.  */
          true_rtx = subst (copy_rtx (true_rtx), pc_rtx, pc_rtx, 0, 0);
          false_rtx = subst (copy_rtx (false_rtx), pc_rtx, pc_rtx, 0, 0);

          /* If true_rtx and false_rtx are not general_operands, an if_then_else
             is unlikely to be simpler.  */
          if (general_operand (true_rtx, VOIDmode)
              && general_operand (false_rtx, VOIDmode))
            {
              enum rtx_code reversed;

              /* Restarting if we generate a store-flag expression will cause
                 us to loop.  Just drop through in this case.  */

              /* If the result values are STORE_FLAG_VALUE and zero, we can
                 just make the comparison operation.  */
              if (true_rtx == const_true_rtx && false_rtx == const0_rtx)
                x = gen_binary (cond_code, mode, cond, cop1);
              else if (true_rtx == const0_rtx && false_rtx == const_true_rtx
                       && ((reversed = reversed_comparison_code_parts
                                        (cond_code, cond, cop1, NULL))
                           != UNKNOWN))
                x = gen_binary (reversed, mode, cond, cop1);

              /* Likewise, we can make the negate of a comparison operation
                 if the result values are - STORE_FLAG_VALUE and zero.  */
              else if (GET_CODE (true_rtx) == CONST_INT
                       && INTVAL (true_rtx) == - STORE_FLAG_VALUE
                       && false_rtx == const0_rtx)
                x = simplify_gen_unary (NEG, mode,
                                        gen_binary (cond_code, mode, cond,
                                                    cop1),
                                        mode);
              else if (GET_CODE (false_rtx) == CONST_INT
                       && INTVAL (false_rtx) == - STORE_FLAG_VALUE
                       && true_rtx == const0_rtx
                       && ((reversed = reversed_comparison_code_parts
                                        (cond_code, cond, cop1, NULL))
                           != UNKNOWN))
                x = simplify_gen_unary (NEG, mode,
                                        gen_binary (reversed, mode,
                                                    cond, cop1),
                                        mode);
              else
                return gen_rtx_IF_THEN_ELSE (mode,
                                             gen_binary (cond_code, VOIDmode,
                                                         cond, cop1),
                                             true_rtx, false_rtx);

              code = GET_CODE (x);
              op0_mode = VOIDmode;
            }
        }
    }

  /* Try to fold this expression in case we have constants that weren't
     present before.  */
  temp = 0;
  switch (GET_RTX_CLASS (code))
    {
    case RTX_UNARY:
      if (op0_mode == VOIDmode)
        op0_mode = GET_MODE (XEXP (x, 0));
      temp = simplify_unary_operation (code, mode, XEXP (x, 0), op0_mode);
      break;
    case RTX_COMPARE:
    case RTX_COMM_COMPARE:
      {
        enum machine_mode cmp_mode = GET_MODE (XEXP (x, 0));
        if (cmp_mode == VOIDmode)
          {
            cmp_mode = GET_MODE (XEXP (x, 1));
            if (cmp_mode == VOIDmode)
              cmp_mode = op0_mode;
          }
        temp = simplify_relational_operation (code, mode, cmp_mode,
                                              XEXP (x, 0), XEXP (x, 1));
      }
      break;
    case RTX_COMM_ARITH:
    case RTX_BIN_ARITH:
      temp = simplify_binary_operation (code, mode, XEXP (x, 0), XEXP (x, 1));
      break;
    case RTX_BITFIELD_OPS:
    case RTX_TERNARY:
      temp = simplify_ternary_operation (code, mode, op0_mode, XEXP (x, 0),
                                         XEXP (x, 1), XEXP (x, 2));
      break;
    default:
      break;
    }

  if (temp)
    {
      x = temp;
      code = GET_CODE (temp);
      op0_mode = VOIDmode;
      mode = GET_MODE (temp);
    }

  /* First see if we can apply the inverse distributive law.  */
  if (code == PLUS || code == MINUS
      || code == AND || code == IOR || code == XOR)
    {
      x = apply_distributive_law (x);
      code = GET_CODE (x);
      op0_mode = VOIDmode;
    }

  /* If CODE is an associative operation not otherwise handled, see if we
     can associate some operands.  This can win if they are constants or
     if they are logically related (i.e. (a & b) & a).  */
  if ((code == PLUS || code == MINUS || code == MULT || code == DIV
       || code == AND || code == IOR || code == XOR
       || code == SMAX || code == SMIN || code == UMAX || code == UMIN)
      && ((INTEGRAL_MODE_P (mode) && code != DIV)
          || (flag_unsafe_math_optimizations && FLOAT_MODE_P (mode))))
    {
      if (GET_CODE (XEXP (x, 0)) == code)
        {
          rtx other = XEXP (XEXP (x, 0), 0);
          rtx inner_op0 = XEXP (XEXP (x, 0), 1);
          rtx inner_op1 = XEXP (x, 1);
          rtx inner;

          /* Make sure we pass the constant operand if any as the second
             one if this is a commutative operation.  */
          if (CONSTANT_P (inner_op0) && COMMUTATIVE_ARITH_P (x))
            {
              rtx tem = inner_op0;
              inner_op0 = inner_op1;
              inner_op1 = tem;
            }
          inner = simplify_binary_operation (code == MINUS ? PLUS
                                             : code == DIV ? MULT
                                             : code,
                                             mode, inner_op0, inner_op1);

          /* For commutative operations, try the other pair if that one
             didn't simplify.  */
          if (inner == 0 && COMMUTATIVE_ARITH_P (x))
            {
              other = XEXP (XEXP (x, 0), 1);
              inner = simplify_binary_operation (code, mode,
                                                 XEXP (XEXP (x, 0), 0),
                                                 XEXP (x, 1));
            }

          if (inner)
            return gen_binary (code, mode, other, inner);
        }
    }

  /* A little bit of algebraic simplification here.  */
  switch (code)
    {
    case MEM:
      /* Ensure that our address has any ASHIFTs converted to MULT in case
         address-recognizing predicates are called later.  */
      temp = make_compound_operation (XEXP (x, 0), MEM);
      SUBST (XEXP (x, 0), temp);
      break;

    case SUBREG:
      if (op0_mode == VOIDmode)
        op0_mode = GET_MODE (SUBREG_REG (x));

      /* See if this can be moved to simplify_subreg.  */
      if (CONSTANT_P (SUBREG_REG (x))
          && subreg_lowpart_offset (mode, op0_mode) == SUBREG_BYTE (x)
             /* Don't call gen_lowpart if the inner mode
                is VOIDmode and we cannot simplify it, as SUBREG without
                inner mode is invalid.  */
          && (GET_MODE (SUBREG_REG (x)) != VOIDmode
              || gen_lowpart_common (mode, SUBREG_REG (x))))
        return gen_lowpart (mode, SUBREG_REG (x));

      if (GET_MODE_CLASS (GET_MODE (SUBREG_REG (x))) == MODE_CC)
        break;
      {
        rtx temp;
        temp = simplify_subreg (mode, SUBREG_REG (x), op0_mode,
                                SUBREG_BYTE (x));
        if (temp)
          return temp;
      }