Add movdi pattern to FR30 port.

[official-gcc.git] / gcc / simplify-rtx.c

/* RTL simplification functions for GNU compiler.
   Copyright (C) 1987, 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
   1999, 2000 Free Software Foundation, Inc.

This file is part of GNU CC.

GNU CC 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.

GNU CC 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 GNU CC; see the file COPYING.  If not, write to
the Free Software Foundation, 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */


#include "config.h"
#include "system.h"
#include <setjmp.h>

#include "rtl.h"
#include "tm_p.h"
#include "regs.h"
#include "hard-reg-set.h"
#include "flags.h"
#include "real.h"
#include "insn-config.h"
#include "recog.h"
#include "function.h"
#include "expr.h"
#include "toplev.h"
#include "output.h"
#include "ggc.h"
#include "obstack.h"
#include "hashtab.h"
#include "cselib.h"

/* Simplification and canonicalization of RTL.  */

/* Nonzero if X has the form (PLUS frame-pointer integer).  We check for
   virtual regs here because the simplify_*_operation routines are called
   by integrate.c, which is called before virtual register instantiation.

   ?!? FIXED_BASE_PLUS_P and NONZERO_BASE_PLUS_P need to move into 
   a header file so that their definitions can be shared with the
   simplification routines in simplify-rtx.c.  Until then, do not
   change these macros without also changing the copy in simplify-rtx.c.  */

#define FIXED_BASE_PLUS_P(X)                                    \
  ((X) == frame_pointer_rtx || (X) == hard_frame_pointer_rtx    \
   || ((X) == arg_pointer_rtx && fixed_regs[ARG_POINTER_REGNUM])\
   || (X) == virtual_stack_vars_rtx                             \
   || (X) == virtual_incoming_args_rtx                          \
   || (GET_CODE (X) == PLUS && GET_CODE (XEXP (X, 1)) == CONST_INT \
       && (XEXP (X, 0) == frame_pointer_rtx                     \
           || XEXP (X, 0) == hard_frame_pointer_rtx             \
           || ((X) == arg_pointer_rtx                           \
               && fixed_regs[ARG_POINTER_REGNUM])               \
           || XEXP (X, 0) == virtual_stack_vars_rtx             \
           || XEXP (X, 0) == virtual_incoming_args_rtx))        \
   || GET_CODE (X) == ADDRESSOF)

/* Similar, but also allows reference to the stack pointer.

   This used to include FIXED_BASE_PLUS_P, however, we can't assume that
   arg_pointer_rtx by itself is nonzero, because on at least one machine,
   the i960, the arg pointer is zero when it is unused.  */

#define NONZERO_BASE_PLUS_P(X)                                  \
  ((X) == frame_pointer_rtx || (X) == hard_frame_pointer_rtx    \
   || (X) == virtual_stack_vars_rtx                             \
   || (X) == virtual_incoming_args_rtx                          \
   || (GET_CODE (X) == PLUS && GET_CODE (XEXP (X, 1)) == CONST_INT \
       && (XEXP (X, 0) == frame_pointer_rtx                     \
           || XEXP (X, 0) == hard_frame_pointer_rtx             \
           || ((X) == arg_pointer_rtx                           \
               && fixed_regs[ARG_POINTER_REGNUM])               \
           || XEXP (X, 0) == virtual_stack_vars_rtx             \
           || XEXP (X, 0) == virtual_incoming_args_rtx))        \
   || (X) == stack_pointer_rtx                                  \
   || (X) == virtual_stack_dynamic_rtx                          \
   || (X) == virtual_outgoing_args_rtx                          \
   || (GET_CODE (X) == PLUS && GET_CODE (XEXP (X, 1)) == CONST_INT \
       && (XEXP (X, 0) == stack_pointer_rtx                     \
           || XEXP (X, 0) == virtual_stack_dynamic_rtx          \
           || XEXP (X, 0) == virtual_outgoing_args_rtx))        \
   || GET_CODE (X) == ADDRESSOF)


static rtx simplify_plus_minus          PARAMS ((enum rtx_code,
                                                 enum machine_mode, rtx, rtx));
static void check_fold_consts           PARAMS ((PTR));
static int entry_and_rtx_equal_p        PARAMS ((const void *, const void *));
static unsigned int get_value_hash      PARAMS ((const void *));
static struct elt_list *new_elt_list    PARAMS ((struct elt_list *,
                                                 cselib_val *));
static struct elt_loc_list *new_elt_loc_list PARAMS ((struct elt_loc_list *,
                                                      rtx));
static void unchain_one_value           PARAMS ((cselib_val *));
static void unchain_one_elt_list        PARAMS ((struct elt_list **));
static void unchain_one_elt_loc_list    PARAMS ((struct elt_loc_list **));
static void clear_table                 PARAMS ((void));
static int discard_useless_locs         PARAMS ((void **, void *));
static int discard_useless_values       PARAMS ((void **, void *));
static void remove_useless_values       PARAMS ((void));
static unsigned int hash_rtx            PARAMS ((rtx, enum machine_mode, int));
static cselib_val *new_cselib_val       PARAMS ((unsigned int,
                                                 enum machine_mode));
static void add_mem_for_addr            PARAMS ((cselib_val *, cselib_val *,
                                                 rtx));
static cselib_val *cselib_lookup_mem    PARAMS ((rtx, int));
static rtx cselib_subst_to_values       PARAMS ((rtx));
static void cselib_invalidate_regno     PARAMS ((unsigned int,
                                                 enum machine_mode));
static int cselib_mem_conflict_p        PARAMS ((rtx, rtx));
static int cselib_invalidate_mem_1      PARAMS ((void **, void *));
static void cselib_invalidate_mem       PARAMS ((rtx));
static void cselib_invalidate_rtx       PARAMS ((rtx, rtx, void *));
static void cselib_record_set           PARAMS ((rtx, cselib_val *,
                                                 cselib_val *));
static void cselib_record_sets          PARAMS ((rtx));

/* There are three ways in which cselib can look up an rtx:
   - for a REG, the reg_values table (which is indexed by regno) is used
   - for a MEM, we recursively look up its address and then follow the
     addr_list of that value
   - for everything else, we compute a hash value and go through the hash
     table.  Since different rtx's can still have the same hash value,
     this involves walking the table entries for a given value and comparing
     the locations of the entries with the rtx we are looking up.  */

/* A table that enables us to look up elts by their value.  */
static htab_t hash_table;

/* This is a global so we don't have to pass this through every function.
   It is used in new_elt_loc_list to set SETTING_INSN.  */
static rtx cselib_current_insn;

/* Every new unknown value gets a unique number.  */
static unsigned int next_unknown_value;

/* The number of registers we had when the varrays were last resized.  */
static unsigned int cselib_nregs;

/* Count values without known locations.  Whenever this grows too big, we
   remove these useless values from the table.  */
static int n_useless_values;

/* Number of useless values before we remove them from the hash table.  */
#define MAX_USELESS_VALUES 32

/* This table maps from register number to values.  It does not contain
   pointers to cselib_val structures, but rather elt_lists.  The purpose is
   to be able to refer to the same register in different modes.  */
static varray_type reg_values;
#define REG_VALUES(I) VARRAY_ELT_LIST (reg_values, (I))

/* We pass this to cselib_invalidate_mem to invalidate all of
   memory for a non-const call instruction.  */
static rtx callmem;

/* Memory for our structures is allocated from this obstack.  */
static struct obstack cselib_obstack;

/* Used to quickly free all memory.  */
static char *cselib_startobj;

/* Caches for unused structures.  */
static cselib_val *empty_vals;
static struct elt_list *empty_elt_lists;
static struct elt_loc_list *empty_elt_loc_lists;

/* Set by discard_useless_locs if it deleted the last location of any
   value.  */
static int values_became_useless;
\f
/* Make a binary operation by properly ordering the operands and 
   seeing if the expression folds.  */

rtx
simplify_gen_binary (code, mode, op0, op1)
     enum rtx_code code;
     enum machine_mode mode;
     rtx op0, op1;
{
  rtx tem;

  /* Put complex operands first and constants second if commutative.  */
  if (GET_RTX_CLASS (code) == 'c'
      && ((CONSTANT_P (op0) && GET_CODE (op1) != CONST_INT)
          || (GET_RTX_CLASS (GET_CODE (op0)) == 'o'
              && GET_RTX_CLASS (GET_CODE (op1)) != 'o')
          || (GET_CODE (op0) == SUBREG
              && GET_RTX_CLASS (GET_CODE (SUBREG_REG (op0))) == 'o'
              && GET_RTX_CLASS (GET_CODE (op1)) != 'o')))
    tem = op0, op0 = op1, op1 = tem;

  /* If this simplifies, do it.  */
  tem = simplify_binary_operation (code, mode, op0, op1);

  if (tem)
    return tem;

  /* Handle addition and subtraction of CONST_INT specially.  Otherwise,
     just form the operation.  */

  if (code == PLUS && GET_CODE (op1) == CONST_INT
      && GET_MODE (op0) != VOIDmode)
    return plus_constant (op0, INTVAL (op1));
  else if (code == MINUS && GET_CODE (op1) == CONST_INT
           && GET_MODE (op0) != VOIDmode)
    return plus_constant (op0, - INTVAL (op1));
  else
    return gen_rtx_fmt_ee (code, mode, op0, op1);
}
\f
/* Try to simplify a unary operation CODE whose output mode is to be
   MODE with input operand OP whose mode was originally OP_MODE.
   Return zero if no simplification can be made.  */

rtx
simplify_unary_operation (code, mode, op, op_mode)
     enum rtx_code code;
     enum machine_mode mode;
     rtx op;
     enum machine_mode op_mode;
{
  unsigned int width = GET_MODE_BITSIZE (mode);

  /* The order of these tests is critical so that, for example, we don't
     check the wrong mode (input vs. output) for a conversion operation,
     such as FIX.  At some point, this should be simplified.  */

#if !defined(REAL_IS_NOT_DOUBLE) || defined(REAL_ARITHMETIC)

  if (code == FLOAT && GET_MODE (op) == VOIDmode
      && (GET_CODE (op) == CONST_DOUBLE || GET_CODE (op) == CONST_INT))
    {
      HOST_WIDE_INT hv, lv;
      REAL_VALUE_TYPE d;

      if (GET_CODE (op) == CONST_INT)
        lv = INTVAL (op), hv = INTVAL (op) < 0 ? -1 : 0;
      else
        lv = CONST_DOUBLE_LOW (op),  hv = CONST_DOUBLE_HIGH (op);

#ifdef REAL_ARITHMETIC
      REAL_VALUE_FROM_INT (d, lv, hv, mode);
#else
      if (hv < 0)
        {
          d = (double) (~ hv);
          d *= ((double) ((HOST_WIDE_INT) 1 << (HOST_BITS_PER_WIDE_INT / 2))
                * (double) ((HOST_WIDE_INT) 1 << (HOST_BITS_PER_WIDE_INT / 2)));
          d += (double) (unsigned HOST_WIDE_INT) (~ lv);
          d = (- d - 1.0);
        }
      else
        {
          d = (double) hv;
          d *= ((double) ((HOST_WIDE_INT) 1 << (HOST_BITS_PER_WIDE_INT / 2))
                * (double) ((HOST_WIDE_INT) 1 << (HOST_BITS_PER_WIDE_INT / 2)));
          d += (double) (unsigned HOST_WIDE_INT) lv;
        }
#endif  /* REAL_ARITHMETIC */
      d = real_value_truncate (mode, d);
      return CONST_DOUBLE_FROM_REAL_VALUE (d, mode);
    }
  else if (code == UNSIGNED_FLOAT && GET_MODE (op) == VOIDmode
           && (GET_CODE (op) == CONST_DOUBLE || GET_CODE (op) == CONST_INT))
    {
      HOST_WIDE_INT hv, lv;
      REAL_VALUE_TYPE d;

      if (GET_CODE (op) == CONST_INT)
        lv = INTVAL (op), hv = INTVAL (op) < 0 ? -1 : 0;
      else
        lv = CONST_DOUBLE_LOW (op),  hv = CONST_DOUBLE_HIGH (op);

      if (op_mode == VOIDmode)
        {
          /* We don't know how to interpret negative-looking numbers in
             this case, so don't try to fold those.  */
          if (hv < 0)
            return 0;
        }
      else if (GET_MODE_BITSIZE (op_mode) >= HOST_BITS_PER_WIDE_INT * 2)
        ;
      else
        hv = 0, lv &= GET_MODE_MASK (op_mode);

#ifdef REAL_ARITHMETIC
      REAL_VALUE_FROM_UNSIGNED_INT (d, lv, hv, mode);
#else

      d = (double) (unsigned HOST_WIDE_INT) hv;
      d *= ((double) ((HOST_WIDE_INT) 1 << (HOST_BITS_PER_WIDE_INT / 2))
            * (double) ((HOST_WIDE_INT) 1 << (HOST_BITS_PER_WIDE_INT / 2)));
      d += (double) (unsigned HOST_WIDE_INT) lv;
#endif  /* REAL_ARITHMETIC */
      d = real_value_truncate (mode, d);
      return CONST_DOUBLE_FROM_REAL_VALUE (d, mode);
    }
#endif

  if (GET_CODE (op) == CONST_INT
      && width <= HOST_BITS_PER_WIDE_INT && width > 0)
    {
      register HOST_WIDE_INT arg0 = INTVAL (op);
      register HOST_WIDE_INT val;

      switch (code)
        {
        case NOT:
          val = ~ arg0;
          break;

        case NEG:
          val = - arg0;
          break;

        case ABS:
          val = (arg0 >= 0 ? arg0 : - arg0);
          break;

        case FFS:
          /* Don't use ffs here.  Instead, get low order bit and then its
             number.  If arg0 is zero, this will return 0, as desired.  */
          arg0 &= GET_MODE_MASK (mode);
          val = exact_log2 (arg0 & (- arg0)) + 1;
          break;

        case TRUNCATE:
          val = arg0;
          break;

        case ZERO_EXTEND:
          if (op_mode == VOIDmode)
            op_mode = mode;
          if (GET_MODE_BITSIZE (op_mode) == HOST_BITS_PER_WIDE_INT)
            {
              /* If we were really extending the mode,
                 we would have to distinguish between zero-extension
                 and sign-extension.  */
              if (width != GET_MODE_BITSIZE (op_mode))
                abort ();
              val = arg0;
            }
          else if (GET_MODE_BITSIZE (op_mode) < HOST_BITS_PER_WIDE_INT)
            val = arg0 & ~((HOST_WIDE_INT) (-1) << GET_MODE_BITSIZE (op_mode));
          else
            return 0;
          break;

        case SIGN_EXTEND:
          if (op_mode == VOIDmode)
            op_mode = mode;
          if (GET_MODE_BITSIZE (op_mode) == HOST_BITS_PER_WIDE_INT)
            {
              /* If we were really extending the mode,
                 we would have to distinguish between zero-extension
                 and sign-extension.  */
              if (width != GET_MODE_BITSIZE (op_mode))
                abort ();
              val = arg0;
            }
          else if (GET_MODE_BITSIZE (op_mode) < HOST_BITS_PER_WIDE_INT)
            {
              val
                = arg0 & ~((HOST_WIDE_INT) (-1) << GET_MODE_BITSIZE (op_mode));
              if (val
                  & ((HOST_WIDE_INT) 1 << (GET_MODE_BITSIZE (op_mode) - 1)))
                val -= (HOST_WIDE_INT) 1 << GET_MODE_BITSIZE (op_mode);
            }
          else
            return 0;
          break;

        case SQRT:
          return 0;

        default:
          abort ();
        }

      val = trunc_int_for_mode (val, mode);

      return GEN_INT (val);
    }

  /* We can do some operations on integer CONST_DOUBLEs.  Also allow
     for a DImode operation on a CONST_INT.  */
  else if (GET_MODE (op) == VOIDmode && width <= HOST_BITS_PER_INT * 2
           && (GET_CODE (op) == CONST_DOUBLE || GET_CODE (op) == CONST_INT))
    {
      HOST_WIDE_INT l1, h1, lv, hv;

      if (GET_CODE (op) == CONST_DOUBLE)
        l1 = CONST_DOUBLE_LOW (op), h1 = CONST_DOUBLE_HIGH (op);
      else
        l1 = INTVAL (op), h1 = l1 < 0 ? -1 : 0;

      switch (code)
        {
        case NOT:
          lv = ~ l1;
          hv = ~ h1;
          break;

        case NEG:
          neg_double (l1, h1, &lv, &hv);
          break;

        case ABS:
          if (h1 < 0)
            neg_double (l1, h1, &lv, &hv);
          else
            lv = l1, hv = h1;
          break;

        case FFS:
          hv = 0;
          if (l1 == 0)
            lv = HOST_BITS_PER_WIDE_INT + exact_log2 (h1 & (-h1)) + 1;
          else
            lv = exact_log2 (l1 & (-l1)) + 1;
          break;

        case TRUNCATE:
          /* This is just a change-of-mode, so do nothing.  */
          lv = l1, hv = h1;
          break;

        case ZERO_EXTEND:
          if (op_mode == VOIDmode
              || GET_MODE_BITSIZE (op_mode) > HOST_BITS_PER_WIDE_INT)
            return 0;

          hv = 0;
          lv = l1 & GET_MODE_MASK (op_mode);
          break;

        case SIGN_EXTEND:
          if (op_mode == VOIDmode
              || GET_MODE_BITSIZE (op_mode) > HOST_BITS_PER_WIDE_INT)
            return 0;
          else
            {
              lv = l1 & GET_MODE_MASK (op_mode);
              if (GET_MODE_BITSIZE (op_mode) < HOST_BITS_PER_WIDE_INT
                  && (lv & ((HOST_WIDE_INT) 1
                            << (GET_MODE_BITSIZE (op_mode) - 1))) != 0)
                lv -= (HOST_WIDE_INT) 1 << GET_MODE_BITSIZE (op_mode);

              hv = (lv < 0) ? ~ (HOST_WIDE_INT) 0 : 0;
            }
          break;

        case SQRT:
          return 0;

        default:
          return 0;
        }

      return immed_double_const (lv, hv, mode);
    }

#if ! defined (REAL_IS_NOT_DOUBLE) || defined (REAL_ARITHMETIC)
  else if (GET_CODE (op) == CONST_DOUBLE
           && GET_MODE_CLASS (mode) == MODE_FLOAT)
    {
      REAL_VALUE_TYPE d;
      jmp_buf handler;
      rtx x;

      if (setjmp (handler))
        /* There used to be a warning here, but that is inadvisable.
           People may want to cause traps, and the natural way
           to do it should not get a warning.  */
        return 0;

      set_float_handler (handler);

      REAL_VALUE_FROM_CONST_DOUBLE (d, op);

      switch (code)
        {
        case NEG:
          d = REAL_VALUE_NEGATE (d);
          break;

        case ABS:
          if (REAL_VALUE_NEGATIVE (d))
            d = REAL_VALUE_NEGATE (d);
          break;

        case FLOAT_TRUNCATE:
          d = real_value_truncate (mode, d);
          break;

        case FLOAT_EXTEND:
          /* All this does is change the mode.  */
          break;

        case FIX:
          d = REAL_VALUE_RNDZINT (d);
          break;

        case UNSIGNED_FIX:
          d = REAL_VALUE_UNSIGNED_RNDZINT (d);
          break;

        case SQRT:
          return 0;

        default:
          abort ();
        }

      x = CONST_DOUBLE_FROM_REAL_VALUE (d, mode);
      set_float_handler (NULL_PTR);
      return x;
    }

  else if (GET_CODE (op) == CONST_DOUBLE
           && GET_MODE_CLASS (GET_MODE (op)) == MODE_FLOAT
           && GET_MODE_CLASS (mode) == MODE_INT
           && width <= HOST_BITS_PER_WIDE_INT && width > 0)
    {
      REAL_VALUE_TYPE d;
      jmp_buf handler;
      HOST_WIDE_INT val;

      if (setjmp (handler))
        return 0;

      set_float_handler (handler);

      REAL_VALUE_FROM_CONST_DOUBLE (d, op);

      switch (code)
        {
        case FIX:
          val = REAL_VALUE_FIX (d);
          break;

        case UNSIGNED_FIX:
          val = REAL_VALUE_UNSIGNED_FIX (d);
          break;

        default:
          abort ();
        }

      set_float_handler (NULL_PTR);

      val = trunc_int_for_mode (val, mode);

      return GEN_INT (val);
    }
#endif
  /* This was formerly used only for non-IEEE float.
     eggert@twinsun.com says it is safe for IEEE also.  */
  else
    {
      /* There are some simplifications we can do even if the operands
         aren't constant.  */
      switch (code)
        {
        case NEG:
        case NOT:
          /* (not (not X)) == X, similarly for NEG.  */
          if (GET_CODE (op) == code)
            return XEXP (op, 0);
          break;

        case SIGN_EXTEND:
          /* (sign_extend (truncate (minus (label_ref L1) (label_ref L2))))
             becomes just the MINUS if its mode is MODE.  This allows
             folding switch statements on machines using casesi (such as
             the Vax).  */
          if (GET_CODE (op) == TRUNCATE
              && GET_MODE (XEXP (op, 0)) == mode
              && GET_CODE (XEXP (op, 0)) == MINUS
              && GET_CODE (XEXP (XEXP (op, 0), 0)) == LABEL_REF
              && GET_CODE (XEXP (XEXP (op, 0), 1)) == LABEL_REF)
            return XEXP (op, 0);

#ifdef POINTERS_EXTEND_UNSIGNED
          if (! POINTERS_EXTEND_UNSIGNED
              && mode == Pmode && GET_MODE (op) == ptr_mode
              && CONSTANT_P (op))
            return convert_memory_address (Pmode, op);
#endif
          break;

#ifdef POINTERS_EXTEND_UNSIGNED
        case ZERO_EXTEND:
          if (POINTERS_EXTEND_UNSIGNED
              && mode == Pmode && GET_MODE (op) == ptr_mode
              && CONSTANT_P (op))
            return convert_memory_address (Pmode, op);
          break;
#endif
          
        default:
          break;
        }

      return 0;
    }
}
\f
/* Simplify a binary operation CODE with result mode MODE, operating on OP0
   and OP1.  Return 0 if no simplification is possible.

   Don't use this for relational operations such as EQ or LT.
   Use simplify_relational_operation instead.  */

rtx
simplify_binary_operation (code, mode, op0, op1)
     enum rtx_code code;
     enum machine_mode mode;
     rtx op0, op1;
{
  register HOST_WIDE_INT arg0, arg1, arg0s, arg1s;
  HOST_WIDE_INT val;
  unsigned int width = GET_MODE_BITSIZE (mode);
  rtx tem;

  /* Relational operations don't work here.  We must know the mode
     of the operands in order to do the comparison correctly.
     Assuming a full word can give incorrect results.
     Consider comparing 128 with -128 in QImode.  */

  if (GET_RTX_CLASS (code) == '<')
    abort ();

#if ! defined (REAL_IS_NOT_DOUBLE) || defined (REAL_ARITHMETIC)
  if (GET_MODE_CLASS (mode) == MODE_FLOAT
      && GET_CODE (op0) == CONST_DOUBLE && GET_CODE (op1) == CONST_DOUBLE
      && mode == GET_MODE (op0) && mode == GET_MODE (op1))
    {
      REAL_VALUE_TYPE f0, f1, value;
      jmp_buf handler;

      if (setjmp (handler))
        return 0;

      set_float_handler (handler);

      REAL_VALUE_FROM_CONST_DOUBLE (f0, op0);
      REAL_VALUE_FROM_CONST_DOUBLE (f1, op1);
      f0 = real_value_truncate (mode, f0);
      f1 = real_value_truncate (mode, f1);

#ifdef REAL_ARITHMETIC
#ifndef REAL_INFINITY
      if (code == DIV && REAL_VALUES_EQUAL (f1, dconst0))
        return 0;
#endif
      REAL_ARITHMETIC (value, rtx_to_tree_code (code), f0, f1);
#else
      switch (code)
        {
        case PLUS:
          value = f0 + f1;
          break;
        case MINUS:
          value = f0 - f1;
          break;
        case MULT:
          value = f0 * f1;
          break;
        case DIV:
#ifndef REAL_INFINITY
          if (f1 == 0)
            return 0;
#endif
          value = f0 / f1;
          break;
        case SMIN:
          value = MIN (f0, f1);
          break;
        case SMAX:
          value = MAX (f0, f1);
          break;
        default:
          abort ();
        }
#endif

      value = real_value_truncate (mode, value);
      set_float_handler (NULL_PTR);
      return CONST_DOUBLE_FROM_REAL_VALUE (value, mode);
    }
#endif  /* not REAL_IS_NOT_DOUBLE, or REAL_ARITHMETIC */

  /* We can fold some multi-word operations.  */
  if (GET_MODE_CLASS (mode) == MODE_INT
      && width == HOST_BITS_PER_WIDE_INT * 2
      && (GET_CODE (op0) == CONST_DOUBLE || GET_CODE (op0) == CONST_INT)
      && (GET_CODE (op1) == CONST_DOUBLE || GET_CODE (op1) == CONST_INT))
    {
      HOST_WIDE_INT l1, l2, h1, h2, lv, hv;

      if (GET_CODE (op0) == CONST_DOUBLE)
        l1 = CONST_DOUBLE_LOW (op0), h1 = CONST_DOUBLE_HIGH (op0);
      else
        l1 = INTVAL (op0), h1 = l1 < 0 ? -1 : 0;

      if (GET_CODE (op1) == CONST_DOUBLE)
        l2 = CONST_DOUBLE_LOW (op1), h2 = CONST_DOUBLE_HIGH (op1);
      else
        l2 = INTVAL (op1), h2 = l2 < 0 ? -1 : 0;

      switch (code)
        {
        case MINUS:
          /* A - B == A + (-B).  */
          neg_double (l2, h2, &lv, &hv);
          l2 = lv, h2 = hv;

          /* .. fall through ...  */

        case PLUS:
          add_double (l1, h1, l2, h2, &lv, &hv);
          break;

        case MULT:
          mul_double (l1, h1, l2, h2, &lv, &hv);
          break;

        case DIV:  case MOD:   case UDIV:  case UMOD:
          /* We'd need to include tree.h to do this and it doesn't seem worth
             it.  */
          return 0;

        case AND:
          lv = l1 & l2, hv = h1 & h2;
          break;

        case IOR:
          lv = l1 | l2, hv = h1 | h2;
          break;

        case XOR:
          lv = l1 ^ l2, hv = h1 ^ h2;
          break;

        case SMIN:
          if (h1 < h2
              || (h1 == h2
                  && ((unsigned HOST_WIDE_INT) l1
                      < (unsigned HOST_WIDE_INT) l2)))
            lv = l1, hv = h1;
          else
            lv = l2, hv = h2;
          break;

        case SMAX:
          if (h1 > h2
              || (h1 == h2
                  && ((unsigned HOST_WIDE_INT) l1
                      > (unsigned HOST_WIDE_INT) l2)))
            lv = l1, hv = h1;
          else
            lv = l2, hv = h2;
          break;

        case UMIN:
          if ((unsigned HOST_WIDE_INT) h1 < (unsigned HOST_WIDE_INT) h2
              || (h1 == h2
                  && ((unsigned HOST_WIDE_INT) l1
                      < (unsigned HOST_WIDE_INT) l2)))
            lv = l1, hv = h1;
          else
            lv = l2, hv = h2;
          break;

        case UMAX:
          if ((unsigned HOST_WIDE_INT) h1 > (unsigned HOST_WIDE_INT) h2
              || (h1 == h2
                  && ((unsigned HOST_WIDE_INT) l1
                      > (unsigned HOST_WIDE_INT) l2)))
            lv = l1, hv = h1;
          else
            lv = l2, hv = h2;
          break;

        case LSHIFTRT:   case ASHIFTRT:
        case ASHIFT:
        case ROTATE:     case ROTATERT:
#ifdef SHIFT_COUNT_TRUNCATED
          if (SHIFT_COUNT_TRUNCATED)
            l2 &= (GET_MODE_BITSIZE (mode) - 1), h2 = 0;
#endif

          if (h2 != 0 || l2 < 0 || l2 >= GET_MODE_BITSIZE (mode))
            return 0;

          if (code == LSHIFTRT || code == ASHIFTRT)
            rshift_double (l1, h1, l2, GET_MODE_BITSIZE (mode), &lv, &hv,
                           code == ASHIFTRT);
          else if (code == ASHIFT)
            lshift_double (l1, h1, l2, GET_MODE_BITSIZE (mode), &lv, &hv, 1);
          else if (code == ROTATE)
            lrotate_double (l1, h1, l2, GET_MODE_BITSIZE (mode), &lv, &hv);
          else /* code == ROTATERT */
            rrotate_double (l1, h1, l2, GET_MODE_BITSIZE (mode), &lv, &hv);
          break;

        default:
          return 0;
        }

      return immed_double_const (lv, hv, mode);
    }

  if (GET_CODE (op0) != CONST_INT || GET_CODE (op1) != CONST_INT
      || width > HOST_BITS_PER_WIDE_INT || width == 0)
    {
      /* Even if we can't compute a constant result,
         there are some cases worth simplifying.  */

      switch (code)
        {
        case PLUS:
          /* In IEEE floating point, x+0 is not the same as x.  Similarly
             for the other optimizations below.  */
          if (TARGET_FLOAT_FORMAT == IEEE_FLOAT_FORMAT
              && FLOAT_MODE_P (mode) && ! flag_fast_math)
            break;

          if (op1 == CONST0_RTX (mode))
            return op0;

          /* ((-a) + b) -> (b - a) and similarly for (a + (-b)) */
          if (GET_CODE (op0) == NEG)
            return simplify_gen_binary (MINUS, mode, op1, XEXP (op0, 0));
          else if (GET_CODE (op1) == NEG)
            return simplify_gen_binary (MINUS, mode, op0, XEXP (op1, 0));

          /* Handle both-operands-constant cases.  We can only add
             CONST_INTs to constants since the sum of relocatable symbols
             can't be handled by most assemblers.  Don't add CONST_INT
             to CONST_INT since overflow won't be computed properly if wider
             than HOST_BITS_PER_WIDE_INT.  */

          if (CONSTANT_P (op0) && GET_MODE (op0) != VOIDmode
              && GET_CODE (op1) == CONST_INT)
            return plus_constant (op0, INTVAL (op1));
          else if (CONSTANT_P (op1) && GET_MODE (op1) != VOIDmode
                   && GET_CODE (op0) == CONST_INT)
            return plus_constant (op1, INTVAL (op0));

          /* See if this is something like X * C - X or vice versa or
             if the multiplication is written as a shift.  If so, we can
             distribute and make a new multiply, shift, or maybe just
             have X (if C is 2 in the example above).  But don't make
             real multiply if we didn't have one before.  */

          if (! FLOAT_MODE_P (mode))
            {
              HOST_WIDE_INT coeff0 = 1, coeff1 = 1;
              rtx lhs = op0, rhs = op1;
              int had_mult = 0;

              if (GET_CODE (lhs) == NEG)
                coeff0 = -1, lhs = XEXP (lhs, 0);
              else if (GET_CODE (lhs) == MULT
                       && GET_CODE (XEXP (lhs, 1)) == CONST_INT)
                {
                  coeff0 = INTVAL (XEXP (lhs, 1)), lhs = XEXP (lhs, 0);
                  had_mult = 1;
                }
              else if (GET_CODE (lhs) == ASHIFT
                       && GET_CODE (XEXP (lhs, 1)) == CONST_INT
                       && INTVAL (XEXP (lhs, 1)) >= 0
                       && INTVAL (XEXP (lhs, 1)) < HOST_BITS_PER_WIDE_INT)
                {
                  coeff0 = ((HOST_WIDE_INT) 1) << INTVAL (XEXP (lhs, 1));
                  lhs = XEXP (lhs, 0);
                }

              if (GET_CODE (rhs) == NEG)
                coeff1 = -1, rhs = XEXP (rhs, 0);
              else if (GET_CODE (rhs) == MULT
                       && GET_CODE (XEXP (rhs, 1)) == CONST_INT)
                {
                  coeff1 = INTVAL (XEXP (rhs, 1)), rhs = XEXP (rhs, 0);
                  had_mult = 1;
                }
              else if (GET_CODE (rhs) == ASHIFT
                       && GET_CODE (XEXP (rhs, 1)) == CONST_INT
                       && INTVAL (XEXP (rhs, 1)) >= 0
                       && INTVAL (XEXP (rhs, 1)) < HOST_BITS_PER_WIDE_INT)
                {
                  coeff1 = ((HOST_WIDE_INT) 1) << INTVAL (XEXP (rhs, 1));
                  rhs = XEXP (rhs, 0);
                }

              if (rtx_equal_p (lhs, rhs))
                {
                  tem = simplify_gen_binary (MULT, mode, lhs,
                                        GEN_INT (coeff0 + coeff1));
                  return (GET_CODE (tem) == MULT && ! had_mult) ? 0 : tem;
                }
            }

          /* If one of the operands is a PLUS or a MINUS, see if we can
             simplify this by the associative law. 
             Don't use the associative law for floating point.
             The inaccuracy makes it nonassociative,
             and subtle programs can break if operations are associated.  */

          if (INTEGRAL_MODE_P (mode)
              && (GET_CODE (op0) == PLUS || GET_CODE (op0) == MINUS
                  || GET_CODE (op1) == PLUS || GET_CODE (op1) == MINUS)
              && (tem = simplify_plus_minus (code, mode, op0, op1)) != 0)
            return tem;
          break;

        case COMPARE:
#ifdef HAVE_cc0
          /* Convert (compare FOO (const_int 0)) to FOO unless we aren't
             using cc0, in which case we want to leave it as a COMPARE
             so we can distinguish it from a register-register-copy.

             In IEEE floating point, x-0 is not the same as x.  */

          if ((TARGET_FLOAT_FORMAT != IEEE_FLOAT_FORMAT
               || ! FLOAT_MODE_P (mode) || flag_fast_math)
              && op1 == CONST0_RTX (mode))
            return op0;
#else
          /* Do nothing here.  */
#endif
          break;
              
        case MINUS:
          /* None of these optimizations can be done for IEEE
             floating point.  */
          if (TARGET_FLOAT_FORMAT == IEEE_FLOAT_FORMAT
              && FLOAT_MODE_P (mode) && ! flag_fast_math)
            break;

          /* We can't assume x-x is 0 even with non-IEEE floating point,
             but since it is zero except in very strange circumstances, we
             will treat it as zero with -ffast-math.  */
          if (rtx_equal_p (op0, op1)
              && ! side_effects_p (op0)
              && (! FLOAT_MODE_P (mode) || flag_fast_math))
            return CONST0_RTX (mode);

          /* Change subtraction from zero into negation.  */
          if (op0 == CONST0_RTX (mode))
            return gen_rtx_NEG (mode, op1);

          /* (-1 - a) is ~a.  */
          if (op0 == constm1_rtx)
            return gen_rtx_NOT (mode, op1);

          /* Subtracting 0 has no effect.  */
          if (op1 == CONST0_RTX (mode))
            return op0;

          /* See if this is something like X * C - X or vice versa or
             if the multiplication is written as a shift.  If so, we can
             distribute and make a new multiply, shift, or maybe just
             have X (if C is 2 in the example above).  But don't make
             real multiply if we didn't have one before.  */

          if (! FLOAT_MODE_P (mode))
            {
              HOST_WIDE_INT coeff0 = 1, coeff1 = 1;
              rtx lhs = op0, rhs = op1;
              int had_mult = 0;

              if (GET_CODE (lhs) == NEG)
                coeff0 = -1, lhs = XEXP (lhs, 0);
              else if (GET_CODE (lhs) == MULT
                       && GET_CODE (XEXP (lhs, 1)) == CONST_INT)
                {
                  coeff0 = INTVAL (XEXP (lhs, 1)), lhs = XEXP (lhs, 0);
                  had_mult = 1;
                }
              else if (GET_CODE (lhs) == ASHIFT
                       && GET_CODE (XEXP (lhs, 1)) == CONST_INT
                       && INTVAL (XEXP (lhs, 1)) >= 0
                       && INTVAL (XEXP (lhs, 1)) < HOST_BITS_PER_WIDE_INT)
                {
                  coeff0 = ((HOST_WIDE_INT) 1) << INTVAL (XEXP (lhs, 1));
                  lhs = XEXP (lhs, 0);
                }

              if (GET_CODE (rhs) == NEG)
                coeff1 = - 1, rhs = XEXP (rhs, 0);
              else if (GET_CODE (rhs) == MULT
                       && GET_CODE (XEXP (rhs, 1)) == CONST_INT)
                {
                  coeff1 = INTVAL (XEXP (rhs, 1)), rhs = XEXP (rhs, 0);
                  had_mult = 1;
                }
              else if (GET_CODE (rhs) == ASHIFT
                       && GET_CODE (XEXP (rhs, 1)) == CONST_INT
                       && INTVAL (XEXP (rhs, 1)) >= 0
                       && INTVAL (XEXP (rhs, 1)) < HOST_BITS_PER_WIDE_INT)
                {
                  coeff1 = ((HOST_WIDE_INT) 1) << INTVAL (XEXP (rhs, 1));
                  rhs = XEXP (rhs, 0);
                }

              if (rtx_equal_p (lhs, rhs))
                {
                  tem = simplify_gen_binary (MULT, mode, lhs,
                                             GEN_INT (coeff0 - coeff1));
                  return (GET_CODE (tem) == MULT && ! had_mult) ? 0 : tem;
                }
            }

          /* (a - (-b)) -> (a + b).  */
          if (GET_CODE (op1) == NEG)
            return simplify_gen_binary (PLUS, mode, op0, XEXP (op1, 0));

          /* If one of the operands is a PLUS or a MINUS, see if we can
             simplify this by the associative law. 
             Don't use the associative law for floating point.
             The inaccuracy makes it nonassociative,
             and subtle programs can break if operations are associated.  */

          if (INTEGRAL_MODE_P (mode)
              && (GET_CODE (op0) == PLUS || GET_CODE (op0) == MINUS
                  || GET_CODE (op1) == PLUS || GET_CODE (op1) == MINUS)
              && (tem = simplify_plus_minus (code, mode, op0, op1)) != 0)
            return tem;

          /* Don't let a relocatable value get a negative coeff.  */
          if (GET_CODE (op1) == CONST_INT && GET_MODE (op0) != VOIDmode)
            return plus_constant (op0, - INTVAL (op1));

          /* (x - (x & y)) -> (x & ~y) */
          if (GET_CODE (op1) == AND)
            {
             if (rtx_equal_p (op0, XEXP (op1, 0)))
               return simplify_gen_binary (AND, mode, op0,
                                           gen_rtx_NOT (mode, XEXP (op1, 1)));
             if (rtx_equal_p (op0, XEXP (op1, 1)))
               return simplify_gen_binary (AND, mode, op0,
                                           gen_rtx_NOT (mode, XEXP (op1, 0)));
           }
          break;

        case MULT:
          if (op1 == constm1_rtx)
            {
              tem = simplify_unary_operation (NEG, mode, op0, mode);

              return tem ? tem : gen_rtx_NEG (mode, op0);
            }

          /* In IEEE floating point, x*0 is not always 0.  */
          if ((TARGET_FLOAT_FORMAT != IEEE_FLOAT_FORMAT
               || ! FLOAT_MODE_P (mode) || flag_fast_math)
              && op1 == CONST0_RTX (mode)
              && ! side_effects_p (op0))
            return op1;

          /* In IEEE floating point, x*1 is not equivalent to x for nans.
             However, ANSI says we can drop signals,
             so we can do this anyway.  */
          if (op1 == CONST1_RTX (mode))
            return op0;

          /* Convert multiply by constant power of two into shift unless
             we are still generating RTL.  This test is a kludge.  */
          if (GET_CODE (op1) == CONST_INT
              && (val = exact_log2 (INTVAL (op1))) >= 0
              /* If the mode is larger than the host word size, and the
                 uppermost bit is set, then this isn't a power of two due
                 to implicit sign extension.  */
              && (width <= HOST_BITS_PER_WIDE_INT
                  || val != HOST_BITS_PER_WIDE_INT - 1)
              && ! rtx_equal_function_value_matters)
            return gen_rtx_ASHIFT (mode, op0, GEN_INT (val));

          if (GET_CODE (op1) == CONST_DOUBLE
              && GET_MODE_CLASS (GET_MODE (op1)) == MODE_FLOAT)
            {
              REAL_VALUE_TYPE d;
              jmp_buf handler;
              int op1is2, op1ism1;

              if (setjmp (handler))
                return 0;

              set_float_handler (handler);
              REAL_VALUE_FROM_CONST_DOUBLE (d, op1);
              op1is2 = REAL_VALUES_EQUAL (d, dconst2);
              op1ism1 = REAL_VALUES_EQUAL (d, dconstm1);
              set_float_handler (NULL_PTR);

              /* x*2 is x+x and x*(-1) is -x */
              if (op1is2 && GET_MODE (op0) == mode)
                return gen_rtx_PLUS (mode, op0, copy_rtx (op0));

              else if (op1ism1 && GET_MODE (op0) == mode)
                return gen_rtx_NEG (mode, op0);
            }
          break;

        case IOR:
          if (op1 == const0_rtx)
            return op0;
          if (GET_CODE (op1) == CONST_INT
              && (INTVAL (op1) & GET_MODE_MASK (mode)) == GET_MODE_MASK (mode))
            return op1;
          if (rtx_equal_p (op0, op1) && ! side_effects_p (op0))
            return op0;
          /* A | (~A) -> -1 */
          if (((GET_CODE (op0) == NOT && rtx_equal_p (XEXP (op0, 0), op1))
               || (GET_CODE (op1) == NOT && rtx_equal_p (XEXP (op1, 0), op0)))
              && ! side_effects_p (op0)
              && GET_MODE_CLASS (mode) != MODE_CC)
            return constm1_rtx;
          break;

        case XOR:
          if (op1 == const0_rtx)
            return op0;
          if (GET_CODE (op1) == CONST_INT
              && (INTVAL (op1) & GET_MODE_MASK (mode)) == GET_MODE_MASK (mode))
            return gen_rtx_NOT (mode, op0);
          if (op0 == op1 && ! side_effects_p (op0)
              && GET_MODE_CLASS (mode) != MODE_CC)
            return const0_rtx;
          break;

        case AND:
          if (op1 == const0_rtx && ! side_effects_p (op0))
            return const0_rtx;
          if (GET_CODE (op1) == CONST_INT
              && (INTVAL (op1) & GET_MODE_MASK (mode)) == GET_MODE_MASK (mode))
            return op0;
          if (op0 == op1 && ! side_effects_p (op0)
              && GET_MODE_CLASS (mode) != MODE_CC)
            return op0;
          /* A & (~A) -> 0 */
          if (((GET_CODE (op0) == NOT && rtx_equal_p (XEXP (op0, 0), op1))
               || (GET_CODE (op1) == NOT && rtx_equal_p (XEXP (op1, 0), op0)))
              && ! side_effects_p (op0)
              && GET_MODE_CLASS (mode) != MODE_CC)
            return const0_rtx;
          break;

        case UDIV:
          /* Convert divide by power of two into shift (divide by 1 handled
             below).  */
          if (GET_CODE (op1) == CONST_INT
              && (arg1 = exact_log2 (INTVAL (op1))) > 0)
            return gen_rtx_LSHIFTRT (mode, op0, GEN_INT (arg1));

          /* ... fall through ...  */

        case DIV:
          if (op1 == CONST1_RTX (mode))
            return op0;

          /* In IEEE floating point, 0/x is not always 0.  */
          if ((TARGET_FLOAT_FORMAT != IEEE_FLOAT_FORMAT
               || ! FLOAT_MODE_P (mode) || flag_fast_math)
              && op0 == CONST0_RTX (mode)
              && ! side_effects_p (op1))
            return op0;

#if ! defined (REAL_IS_NOT_DOUBLE) || defined (REAL_ARITHMETIC)
          /* Change division by a constant into multiplication.  Only do
             this with -ffast-math until an expert says it is safe in
             general.  */
          else if (GET_CODE (op1) == CONST_DOUBLE
                   && GET_MODE_CLASS (GET_MODE (op1)) == MODE_FLOAT
                   && op1 != CONST0_RTX (mode)
                   && flag_fast_math)
            {
              REAL_VALUE_TYPE d;
              REAL_VALUE_FROM_CONST_DOUBLE (d, op1);

              if (! REAL_VALUES_EQUAL (d, dconst0))
                {
#if defined (REAL_ARITHMETIC)
                  REAL_ARITHMETIC (d, rtx_to_tree_code (DIV), dconst1, d);
                  return gen_rtx_MULT (mode, op0, 
                                       CONST_DOUBLE_FROM_REAL_VALUE (d, mode));
#else
                  return
                    gen_rtx_MULT (mode, op0, 
                                  CONST_DOUBLE_FROM_REAL_VALUE (1./d, mode));
#endif
                }
            }
#endif
          break;

        case UMOD:
          /* Handle modulus by power of two (mod with 1 handled below).  */
          if (GET_CODE (op1) == CONST_INT
              && exact_log2 (INTVAL (op1)) > 0)
            return gen_rtx_AND (mode, op0, GEN_INT (INTVAL (op1) - 1));

          /* ... fall through ...  */

        case MOD:
          if ((op0 == const0_rtx || op1 == const1_rtx)
              && ! side_effects_p (op0) && ! side_effects_p (op1))
            return const0_rtx;
          break;

        case ROTATERT:
        case ROTATE:
          /* Rotating ~0 always results in ~0.  */
          if (GET_CODE (op0) == CONST_INT && width <= HOST_BITS_PER_WIDE_INT
              && (unsigned HOST_WIDE_INT) INTVAL (op0) == GET_MODE_MASK (mode)
              && ! side_effects_p (op1))
            return op0;

          /* ... fall through ...  */

        case ASHIFT:
        case ASHIFTRT:
        case LSHIFTRT:
          if (op1 == const0_rtx)
            return op0;
          if (op0 == const0_rtx && ! side_effects_p (op1))
            return op0;
          break;

        case SMIN:
          if (width <= HOST_BITS_PER_WIDE_INT && GET_CODE (op1) == CONST_INT 
              && INTVAL (op1) == (HOST_WIDE_INT) 1 << (width -1)
              && ! side_effects_p (op0))
            return op1;
          else if (rtx_equal_p (op0, op1) && ! side_effects_p (op0))
            return op0;
          break;
           
        case SMAX:
          if (width <= HOST_BITS_PER_WIDE_INT && GET_CODE (op1) == CONST_INT
              && ((unsigned HOST_WIDE_INT) INTVAL (op1)
                  == (unsigned HOST_WIDE_INT) GET_MODE_MASK (mode) >> 1)
              && ! side_effects_p (op0))
            return op1;
          else if (rtx_equal_p (op0, op1) && ! side_effects_p (op0))
            return op0;
          break;

        case UMIN:
          if (op1 == const0_rtx && ! side_effects_p (op0))
            return op1;
          else if (rtx_equal_p (op0, op1) && ! side_effects_p (op0))
            return op0;
          break;
            
        case UMAX:
          if (op1 == constm1_rtx && ! side_effects_p (op0))
            return op1;
          else if (rtx_equal_p (op0, op1) && ! side_effects_p (op0))
            return op0;
          break;

        default:
          abort ();
        }
      
      return 0;
    }

  /* Get the integer argument values in two forms:
     zero-extended in ARG0, ARG1 and sign-extended in ARG0S, ARG1S.  */

  arg0 = INTVAL (op0);
  arg1 = INTVAL (op1);

  if (width < HOST_BITS_PER_WIDE_INT)
    {
      arg0 &= ((HOST_WIDE_INT) 1 << width) - 1;
      arg1 &= ((HOST_WIDE_INT) 1 << width) - 1;

      arg0s = arg0;
      if (arg0s & ((HOST_WIDE_INT) 1 << (width - 1)))
        arg0s |= ((HOST_WIDE_INT) (-1) << width);

      arg1s = arg1;
      if (arg1s & ((HOST_WIDE_INT) 1 << (width - 1)))
        arg1s |= ((HOST_WIDE_INT) (-1) << width);
    }
  else
    {
      arg0s = arg0;
      arg1s = arg1;
    }

  /* Compute the value of the arithmetic.  */

  switch (code)
    {
    case PLUS:
      val = arg0s + arg1s;
      break;

    case MINUS:
      val = arg0s - arg1s;
      break;

    case MULT:
      val = arg0s * arg1s;
      break;

    case DIV:
      if (arg1s == 0)
        return 0;
      val = arg0s / arg1s;
      break;

    case MOD:
      if (arg1s == 0)
        return 0;
      val = arg0s % arg1s;
      break;

    case UDIV:
      if (arg1 == 0)
        return 0;
      val = (unsigned HOST_WIDE_INT) arg0 / arg1;
      break;

    case UMOD:
      if (arg1 == 0)
        return 0;
      val = (unsigned HOST_WIDE_INT) arg0 % arg1;
      break;

    case AND:
      val = arg0 & arg1;
      break;

    case IOR:
      val = arg0 | arg1;
      break;

    case XOR:
      val = arg0 ^ arg1;
      break;

    case LSHIFTRT:
      /* If shift count is undefined, don't fold it; let the machine do
         what it wants.  But truncate it if the machine will do that.  */
      if (arg1 < 0)
        return 0;

#ifdef SHIFT_COUNT_TRUNCATED
      if (SHIFT_COUNT_TRUNCATED)
        arg1 %= width;
#endif

      val = ((unsigned HOST_WIDE_INT) arg0) >> arg1;
      break;

    case ASHIFT:
      if (arg1 < 0)
        return 0;

#ifdef SHIFT_COUNT_TRUNCATED
      if (SHIFT_COUNT_TRUNCATED)
        arg1 %= width;
#endif

      val = ((unsigned HOST_WIDE_INT) arg0) << arg1;
      break;

    case ASHIFTRT:
      if (arg1 < 0)
        return 0;

#ifdef SHIFT_COUNT_TRUNCATED
      if (SHIFT_COUNT_TRUNCATED)
        arg1 %= width;
#endif

      val = arg0s >> arg1;

      /* Bootstrap compiler may not have sign extended the right shift.
         Manually extend the sign to insure bootstrap cc matches gcc.  */
      if (arg0s < 0 && arg1 > 0)
        val |= ((HOST_WIDE_INT) -1) << (HOST_BITS_PER_WIDE_INT - arg1);

      break;

    case ROTATERT:
      if (arg1 < 0)
        return 0;

      arg1 %= width;
      val = ((((unsigned HOST_WIDE_INT) arg0) << (width - arg1))
             | (((unsigned HOST_WIDE_INT) arg0) >> arg1));
      break;

    case ROTATE:
      if (arg1 < 0)
        return 0;

      arg1 %= width;
      val = ((((unsigned HOST_WIDE_INT) arg0) << arg1)
             | (((unsigned HOST_WIDE_INT) arg0) >> (width - arg1)));
      break;

    case COMPARE:
      /* Do nothing here.  */
      return 0;

    case SMIN:
      val = arg0s <= arg1s ? arg0s : arg1s;
      break;

    case UMIN:
      val = ((unsigned HOST_WIDE_INT) arg0
             <= (unsigned HOST_WIDE_INT) arg1 ? arg0 : arg1);
      break;

    case SMAX:
      val = arg0s > arg1s ? arg0s : arg1s;
      break;

    case UMAX:
      val = ((unsigned HOST_WIDE_INT) arg0
             > (unsigned HOST_WIDE_INT) arg1 ? arg0 : arg1);
      break;

    default:
      abort ();
    }

  val = trunc_int_for_mode (val, mode);

  return GEN_INT (val);
}
\f
/* Simplify a PLUS or MINUS, at least one of whose operands may be another
   PLUS or MINUS.

   Rather than test for specific case, we do this by a brute-force method
   and do all possible simplifications until no more changes occur.  Then
   we rebuild the operation.  */

static rtx
simplify_plus_minus (code, mode, op0, op1)
     enum rtx_code code;
     enum machine_mode mode;
     rtx op0, op1;
{
  rtx ops[8];
  int negs[8];
  rtx result, tem;
  int n_ops = 2, input_ops = 2, input_consts = 0, n_consts = 0;
  int first = 1, negate = 0, changed;
  int i, j;

  bzero ((char *) ops, sizeof ops);
  
  /* Set up the two operands and then expand them until nothing has been
     changed.  If we run out of room in our array, give up; this should
     almost never happen.  */

  ops[0] = op0, ops[1] = op1, negs[0] = 0, negs[1] = (code == MINUS);

  changed = 1;
  while (changed)
    {
      changed = 0;

      for (i = 0; i < n_ops; i++)
        switch (GET_CODE (ops[i]))
          {
          case PLUS:
          case MINUS:
            if (n_ops == 7)
              return 0;

            ops[n_ops] = XEXP (ops[i], 1);
            negs[n_ops++] = GET_CODE (ops[i]) == MINUS ? !negs[i] : negs[i];
            ops[i] = XEXP (ops[i], 0);
            input_ops++;
            changed = 1;
            break;

          case NEG:
            ops[i] = XEXP (ops[i], 0);
            negs[i] = ! negs[i];
            changed = 1;
            break;

          case CONST:
            ops[i] = XEXP (ops[i], 0);
            input_consts++;
            changed = 1;
            break;

          case NOT:
            /* ~a -> (-a - 1) */
            if (n_ops != 7)
              {
                ops[n_ops] = constm1_rtx;
                negs[n_ops++] = negs[i];
                ops[i] = XEXP (ops[i], 0);
                negs[i] = ! negs[i];
                changed = 1;
              }
            break;

          case CONST_INT:
            if (negs[i])
              ops[i] = GEN_INT (- INTVAL (ops[i])), negs[i] = 0, changed = 1;
            break;

          default:
            break;
          }
    }

  /* If we only have two operands, we can't do anything.  */
  if (n_ops <= 2)
    return 0;

  /* Now simplify each pair of operands until nothing changes.  The first
     time through just simplify constants against each other.  */

  changed = 1;
  while (changed)
    {
      changed = first;

      for (i = 0; i < n_ops - 1; i++)
        for (j = i + 1; j < n_ops; j++)
          if (ops[i] != 0 && ops[j] != 0
              && (! first || (CONSTANT_P (ops[i]) && CONSTANT_P (ops[j]))))
            {
              rtx lhs = ops[i], rhs = ops[j];
              enum rtx_code ncode = PLUS;

              if (negs[i] && ! negs[j])
                lhs = ops[j], rhs = ops[i], ncode = MINUS;
              else if (! negs[i] && negs[j])
                ncode = MINUS;

              tem = simplify_binary_operation (ncode, mode, lhs, rhs);
              if (tem)
                {
                  ops[i] = tem, ops[j] = 0;
                  negs[i] = negs[i] && negs[j];
                  if (GET_CODE (tem) == NEG)
                    ops[i] = XEXP (tem, 0), negs[i] = ! negs[i];

                  if (GET_CODE (ops[i]) == CONST_INT && negs[i])
                    ops[i] = GEN_INT (- INTVAL (ops[i])), negs[i] = 0;
                  changed = 1;
                }
            }

      first = 0;
    }

  /* Pack all the operands to the lower-numbered entries and give up if
     we didn't reduce the number of operands we had.  Make sure we
     count a CONST as two operands.  If we have the same number of
     operands, but have made more CONSTs than we had, this is also
     an improvement, so accept it.  */

  for (i = 0, j = 0; j < n_ops; j++)
    if (ops[j] != 0)
      {
        ops[i] = ops[j], negs[i++] = negs[j];
        if (GET_CODE (ops[j]) == CONST)
          n_consts++;
      }

  if (i + n_consts > input_ops
      || (i + n_consts == input_ops && n_consts <= input_consts))
    return 0;

  n_ops = i;

  /* If we have a CONST_INT, put it last.  */
  for (i = 0; i < n_ops - 1; i++)
    if (GET_CODE (ops[i]) == CONST_INT)
      {
        tem = ops[n_ops - 1], ops[n_ops - 1] = ops[i] , ops[i] = tem;
        j = negs[n_ops - 1], negs[n_ops - 1] = negs[i], negs[i] = j;
      }

  /* Put a non-negated operand first.  If there aren't any, make all
     operands positive and negate the whole thing later.  */
  for (i = 0; i < n_ops && negs[i]; i++)
    ;

  if (i == n_ops)
    {
      for (i = 0; i < n_ops; i++)
        negs[i] = 0;
      negate = 1;
    }
  else if (i != 0)
    {
      tem = ops[0], ops[0] = ops[i], ops[i] = tem;
      j = negs[0], negs[0] = negs[i], negs[i] = j;
    }

  /* Now make the result by performing the requested operations.  */
  result = ops[0];
  for (i = 1; i < n_ops; i++)
    result = simplify_gen_binary (negs[i] ? MINUS : PLUS, mode, result, ops[i]);

  return negate ? gen_rtx_NEG (mode, result) : result;
}

struct cfc_args
{
  rtx op0, op1;                 /* Input */
  int equal, op0lt, op1lt;      /* Output */
};

static void
check_fold_consts (data)
  PTR data;
{
  struct cfc_args *args = (struct cfc_args *) data;
  REAL_VALUE_TYPE d0, d1;

  REAL_VALUE_FROM_CONST_DOUBLE (d0, args->op0);
  REAL_VALUE_FROM_CONST_DOUBLE (d1, args->op1);
  args->equal = REAL_VALUES_EQUAL (d0, d1);
  args->op0lt = REAL_VALUES_LESS (d0, d1);
  args->op1lt = REAL_VALUES_LESS (d1, d0);
}

/* Like simplify_binary_operation except used for relational operators.
   MODE is the mode of the operands, not that of the result.  If MODE
   is VOIDmode, both operands must also be VOIDmode and we compare the
   operands in "infinite precision".

   If no simplification is possible, this function returns zero.  Otherwise,
   it returns either const_true_rtx or const0_rtx.  */

rtx
simplify_relational_operation (code, mode, op0, op1)
     enum rtx_code code;
     enum machine_mode mode;
     rtx op0, op1;
{
  int equal, op0lt, op0ltu, op1lt, op1ltu;
  rtx tem;

  /* If op0 is a compare, extract the comparison arguments from it.  */
  if (GET_CODE (op0) == COMPARE && op1 == const0_rtx)
    op1 = XEXP (op0, 1), op0 = XEXP (op0, 0);

  /* We can't simplify MODE_CC values since we don't know what the
     actual comparison is.  */
  if (GET_MODE_CLASS (GET_MODE (op0)) == MODE_CC
#ifdef HAVE_cc0
      || op0 == cc0_rtx
#endif
      )
    return 0;

  /* Make sure the constant is second.  */
  if ((CONSTANT_P (op0) && ! CONSTANT_P (op1))
      || (GET_CODE (op0) == CONST_INT && GET_CODE (op1) != CONST_INT))
    {
      tem = op0, op0 = op1, op1 = tem;
      code = swap_condition (code);
    }

  /* For integer comparisons of A and B maybe we can simplify A - B and can
     then simplify a comparison of that with zero.  If A and B are both either
     a register or a CONST_INT, this can't help; testing for these cases will
     prevent infinite recursion here and speed things up.

     If CODE is an unsigned comparison, then we can never do this optimization,
     because it gives an incorrect result if the subtraction wraps around zero.
     ANSI C defines unsigned operations such that they never overflow, and
     thus such cases can not be ignored.  */

  if (INTEGRAL_MODE_P (mode) && op1 != const0_rtx
      && ! ((GET_CODE (op0) == REG || GET_CODE (op0) == CONST_INT)
            && (GET_CODE (op1) == REG || GET_CODE (op1) == CONST_INT))
      && 0 != (tem = simplify_binary_operation (MINUS, mode, op0, op1))
      && code != GTU && code != GEU && code != LTU && code != LEU)
    return simplify_relational_operation (signed_condition (code),
                                          mode, tem, const0_rtx);

  /* For non-IEEE floating-point, if the two operands are equal, we know the
     result.  */
  if (rtx_equal_p (op0, op1)
      && (TARGET_FLOAT_FORMAT != IEEE_FLOAT_FORMAT
          || ! FLOAT_MODE_P (GET_MODE (op0)) || flag_fast_math))
    equal = 1, op0lt = 0, op0ltu = 0, op1lt = 0, op1ltu = 0;

  /* If the operands are floating-point constants, see if we can fold
     the result.  */
#if ! defined (REAL_IS_NOT_DOUBLE) || defined (REAL_ARITHMETIC)
  else if (GET_CODE (op0) == CONST_DOUBLE && GET_CODE (op1) == CONST_DOUBLE
           && GET_MODE_CLASS (GET_MODE (op0)) == MODE_FLOAT)
    {
      struct cfc_args args;

      /* Setup input for check_fold_consts() */
      args.op0 = op0;
      args.op1 = op1;
      
      if (do_float_handler(check_fold_consts, (PTR) &args) == 0)
        /* We got an exception from check_fold_consts() */
        return 0;

      /* Receive output from check_fold_consts() */
      equal = args.equal;
      op0lt = op0ltu = args.op0lt;
      op1lt = op1ltu = args.op1lt;
    }
#endif  /* not REAL_IS_NOT_DOUBLE, or REAL_ARITHMETIC */

  /* Otherwise, see if the operands are both integers.  */
  else if ((GET_MODE_CLASS (mode) == MODE_INT || mode == VOIDmode)
           && (GET_CODE (op0) == CONST_DOUBLE || GET_CODE (op0) == CONST_INT)
           && (GET_CODE (op1) == CONST_DOUBLE || GET_CODE (op1) == CONST_INT))
    {
      int width = GET_MODE_BITSIZE (mode);
      HOST_WIDE_INT l0s, h0s, l1s, h1s;
      unsigned HOST_WIDE_INT l0u, h0u, l1u, h1u;

      /* Get the two words comprising each integer constant.  */
      if (GET_CODE (op0) == CONST_DOUBLE)
        {
          l0u = l0s = CONST_DOUBLE_LOW (op0);
          h0u = h0s = CONST_DOUBLE_HIGH (op0);
        }
      else
        {
          l0u = l0s = INTVAL (op0);
          h0u = h0s = l0s < 0 ? -1 : 0;
        }
          
      if (GET_CODE (op1) == CONST_DOUBLE)
        {
          l1u = l1s = CONST_DOUBLE_LOW (op1);
          h1u = h1s = CONST_DOUBLE_HIGH (op1);
        }
      else
        {
          l1u = l1s = INTVAL (op1);
          h1u = h1s = l1s < 0 ? -1 : 0;
        }

      /* If WIDTH is nonzero and smaller than HOST_BITS_PER_WIDE_INT,
         we have to sign or zero-extend the values.  */
      if (width != 0 && width <= HOST_BITS_PER_WIDE_INT)
        h0u = h1u = 0, h0s = l0s < 0 ? -1 : 0, h1s = l1s < 0 ? -1 : 0;

      if (width != 0 && width < HOST_BITS_PER_WIDE_INT)
        {
          l0u &= ((HOST_WIDE_INT) 1 << width) - 1;
          l1u &= ((HOST_WIDE_INT) 1 << width) - 1;

          if (l0s & ((HOST_WIDE_INT) 1 << (width - 1)))
            l0s |= ((HOST_WIDE_INT) (-1) << width);

          if (l1s & ((HOST_WIDE_INT) 1 << (width - 1)))
            l1s |= ((HOST_WIDE_INT) (-1) << width);
        }

      equal = (h0u == h1u && l0u == l1u);
      op0lt = (h0s < h1s || (h0s == h1s && l0s < l1s));
      op1lt = (h1s < h0s || (h1s == h0s && l1s < l0s));
      op0ltu = (h0u < h1u || (h0u == h1u && l0u < l1u));
      op1ltu = (h1u < h0u || (h1u == h0u && l1u < l0u));
    }

  /* Otherwise, there are some code-specific tests we can make.  */
  else
    {
      switch (code)
        {
        case EQ:
          /* References to the frame plus a constant or labels cannot
             be zero, but a SYMBOL_REF can due to #pragma weak.  */
          if (((NONZERO_BASE_PLUS_P (op0) && op1 == const0_rtx)
               || GET_CODE (op0) == LABEL_REF)
#if FRAME_POINTER_REGNUM != ARG_POINTER_REGNUM
              /* On some machines, the ap reg can be 0 sometimes.  */
              && op0 != arg_pointer_rtx
#endif
                )
            return const0_rtx;
          break;

        case NE:
          if (((NONZERO_BASE_PLUS_P (op0) && op1 == const0_rtx)
               || GET_CODE (op0) == LABEL_REF)
#if FRAME_POINTER_REGNUM != ARG_POINTER_REGNUM
              && op0 != arg_pointer_rtx
#endif
              )
            return const_true_rtx;
          break;

        case GEU:
          /* Unsigned values are never negative.  */
          if (op1 == const0_rtx)
            return const_true_rtx;
          break;

        case LTU:
          if (op1 == const0_rtx)
            return const0_rtx;
          break;

        case LEU:
          /* Unsigned values are never greater than the largest
             unsigned value.  */
          if (GET_CODE (op1) == CONST_INT
              && (unsigned HOST_WIDE_INT) INTVAL (op1) == GET_MODE_MASK (mode)
            && INTEGRAL_MODE_P (mode))
          return const_true_rtx;
          break;

        case GTU:
          if (GET_CODE (op1) == CONST_INT
              && (unsigned HOST_WIDE_INT) INTVAL (op1) == GET_MODE_MASK (mode)
              && INTEGRAL_MODE_P (mode))
            return const0_rtx;
          break;
          
        default:
          break;
        }

      return 0;
    }

  /* If we reach here, EQUAL, OP0LT, OP0LTU, OP1LT, and OP1LTU are set
     as appropriate.  */
  switch (code)
    {
    case EQ:
      return equal ? const_true_rtx : const0_rtx;
    case NE:
      return ! equal ? const_true_rtx : const0_rtx;
    case LT:
      return op0lt ? const_true_rtx : const0_rtx;
    case GT:
      return op1lt ? const_true_rtx : const0_rtx;
    case LTU:
      return op0ltu ? const_true_rtx : const0_rtx;
    case GTU:
      return op1ltu ? const_true_rtx : const0_rtx;
    case LE:
      return equal || op0lt ? const_true_rtx : const0_rtx;
    case GE:
      return equal || op1lt ? const_true_rtx : const0_rtx;
    case LEU:
      return equal || op0ltu ? const_true_rtx : const0_rtx;
    case GEU:
      return equal || op1ltu ? const_true_rtx : const0_rtx;
    default:
      abort ();
    }
}
\f
/* Simplify CODE, an operation with result mode MODE and three operands,
   OP0, OP1, and OP2.  OP0_MODE was the mode of OP0 before it became
   a constant.  Return 0 if no simplifications is possible.  */

rtx
simplify_ternary_operation (code, mode, op0_mode, op0, op1, op2)
     enum rtx_code code;
     enum machine_mode mode, op0_mode;
     rtx op0, op1, op2;
{
  unsigned int width = GET_MODE_BITSIZE (mode);

  /* VOIDmode means "infinite" precision.  */
  if (width == 0)
    width = HOST_BITS_PER_WIDE_INT;

  switch (code)
    {
    case SIGN_EXTRACT:
    case ZERO_EXTRACT:
      if (GET_CODE (op0) == CONST_INT
          && GET_CODE (op1) == CONST_INT
          && GET_CODE (op2) == CONST_INT
          && INTVAL (op1) + INTVAL (op2) <= GET_MODE_BITSIZE (op0_mode)
          && width <= (unsigned) HOST_BITS_PER_WIDE_INT)
        {
          /* Extracting a bit-field from a constant */
          HOST_WIDE_INT val = INTVAL (op0);

          if (BITS_BIG_ENDIAN)
            val >>= (GET_MODE_BITSIZE (op0_mode)
                     - INTVAL (op2) - INTVAL (op1));
          else
            val >>= INTVAL (op2);

          if (HOST_BITS_PER_WIDE_INT != INTVAL (op1))
            {
              /* First zero-extend.  */
              val &= ((HOST_WIDE_INT) 1 << INTVAL (op1)) - 1;
              /* If desired, propagate sign bit.  */
              if (code == SIGN_EXTRACT
                  && (val & ((HOST_WIDE_INT) 1 << (INTVAL (op1) - 1))))
                val |= ~ (((HOST_WIDE_INT) 1 << INTVAL (op1)) - 1);
            }

          /* Clear the bits that don't belong in our mode,
             unless they and our sign bit are all one.
             So we get either a reasonable negative value or a reasonable
             unsigned value for this mode.  */
          if (width < HOST_BITS_PER_WIDE_INT
              && ((val & ((HOST_WIDE_INT) (-1) << (width - 1)))
                  != ((HOST_WIDE_INT) (-1) << (width - 1))))
            val &= ((HOST_WIDE_INT) 1 << width) - 1;

          return GEN_INT (val);
        }
      break;

    case IF_THEN_ELSE:
      if (GET_CODE (op0) == CONST_INT)
        return op0 != const0_rtx ? op1 : op2;

      /* Convert a == b ? b : a to "a".  */
      if (GET_CODE (op0) == NE && ! side_effects_p (op0)
          && rtx_equal_p (XEXP (op0, 0), op1)
          && rtx_equal_p (XEXP (op0, 1), op2))
        return op1;
      else if (GET_CODE (op0) == EQ && ! side_effects_p (op0)
          && rtx_equal_p (XEXP (op0, 1), op1)
          && rtx_equal_p (XEXP (op0, 0), op2))
        return op2;
      else if (GET_RTX_CLASS (GET_CODE (op0)) == '<' && ! side_effects_p (op0))
        {
          rtx temp
             = simplify_relational_operation (GET_CODE (op0), op0_mode,
                                              XEXP (op0, 0), XEXP (op0, 1));

          /* See if any simplifications were possible.  */
          if (temp == const0_rtx)
            return op2;
          else if (temp == const1_rtx)
            return op1;
        }
      break;

    default:
      abort ();
    }

  return 0;
}

/* Simplify X, an rtx expression.

   Return the simplified expression or NULL if no simplifications
   were possible.

   This is the preferred entry point into the simplification routines;
   however, we still allow passes to call the more specific routines.

   Right now GCC has three (yes, three) major bodies of RTL simplficiation
   code that need to be unified.

        1. fold_rtx in cse.c.  This code uses various CSE specific
           information to aid in RTL simplification.

        2. simplify_rtx in combine.c.  Similar to fold_rtx, except that
           it uses combine specific information to aid in RTL
           simplification.

        3. The routines in this file.


   Long term we want to only have one body of simplification code; to
   get to that state I recommend the following steps:

        1. Pour over fold_rtx & simplify_rtx and move any simplifications
           which are not pass dependent state into these routines.

        2. As code is moved by #1, change fold_rtx & simplify_rtx to
           use this routine whenever possible.

        3. Allow for pass dependent state to be provided to these
           routines and add simplifications based on the pass dependent
           state.  Remove code from cse.c & combine.c that becomes
           redundant/dead.

    It will take time, but ultimately the compiler will be easier to
    maintain and improve.  It's totally silly that when we add a
    simplification that it needs to be added to 4 places (3 for RTL
    simplification and 1 for tree simplification.  */
           
rtx
simplify_rtx (x)
     rtx x;
{
  enum rtx_code code;
  enum machine_mode mode;

  mode = GET_MODE (x);
  code = GET_CODE (x);

  switch (GET_RTX_CLASS (code))
    {
    case '1':
      return simplify_unary_operation (code, mode,
                                       XEXP (x, 0), GET_MODE (XEXP (x, 0)));
    case '2':
    case 'c':
      return simplify_binary_operation (code, mode, XEXP (x, 0), XEXP (x, 1));

    case '3':
    case 'b':
      return simplify_ternary_operation (code, mode, GET_MODE (XEXP (x, 0)),
                                         XEXP (x, 0), XEXP (x, 1), XEXP (x, 2));

    case '<':
      return simplify_relational_operation (code, GET_MODE (XEXP (x, 0)),
                                            XEXP (x, 0), XEXP (x, 1));
    default:
      return NULL;
    }
}
\f

/* Allocate a struct elt_list and fill in its two elements with the
   arguments.  */

static struct elt_list *
new_elt_list (next, elt)
     struct elt_list *next;
     cselib_val *elt;
{
  struct elt_list *el = empty_elt_lists;

  if (el)
    empty_elt_lists = el->next;
  else
    el = (struct elt_list *) obstack_alloc (&cselib_obstack,
                                            sizeof (struct elt_list));
  el->next = next;
  el->elt = elt;
  return el;
}

/* Allocate a struct elt_loc_list and fill in its two elements with the
   arguments.  */

static struct elt_loc_list *
new_elt_loc_list (next, loc)
     struct elt_loc_list *next;
     rtx loc;
{
  struct elt_loc_list *el = empty_elt_loc_lists;

  if (el)
    empty_elt_loc_lists = el->next;
  else
    el = (struct elt_loc_list *) obstack_alloc (&cselib_obstack,
                                                sizeof (struct elt_loc_list));
  el->next = next;
  el->loc = loc;
  el->setting_insn = cselib_current_insn;
  return el;
}

/* The elt_list at *PL is no longer needed.  Unchain it and free its
   storage.  */

static void
unchain_one_elt_list (pl)
     struct elt_list **pl;
{
  struct elt_list *l = *pl;

  *pl = l->next;
  l->next = empty_elt_lists;
  empty_elt_lists = l;
}

/* Likewise for elt_loc_lists.  */

static void
unchain_one_elt_loc_list (pl)
     struct elt_loc_list **pl;
{
  struct elt_loc_list *l = *pl;

  *pl = l->next;
  l->next = empty_elt_loc_lists;
  empty_elt_loc_lists = l;
}

/* Likewise for cselib_vals.  This also frees the addr_list associated with
   V.  */

static void
unchain_one_value (v)
     cselib_val *v;
{
  while (v->addr_list)
    unchain_one_elt_list (&v->addr_list);

  v->u.next_free = empty_vals;
  empty_vals = v;
}

/* Remove all entries from the hash table.  Also used during
   initialization.  */

static void
clear_table ()
{
  unsigned int i;

  for (i = 0; i < cselib_nregs; i++)
    REG_VALUES (i) = 0;

  htab_empty (hash_table);
  obstack_free (&cselib_obstack, cselib_startobj);

  empty_vals = 0;
  empty_elt_lists = 0;
  empty_elt_loc_lists = 0;
  n_useless_values = 0;

  next_unknown_value = 0;
}

/* The equality test for our hash table.  The first argument ENTRY is a table
   element (i.e. a cselib_val), while the second arg X is an rtx.  */

static int
entry_and_rtx_equal_p (entry, x_arg)
     const void *entry, *x_arg;
{
  struct elt_loc_list *l;
  const cselib_val *v = (const cselib_val *) entry;
  rtx x = (rtx) x_arg;

  /* We don't guarantee that distinct rtx's have different hash values,
     so we need to do a comparison.  */
  for (l = v->locs; l; l = l->next)
    if (rtx_equal_for_cselib_p (l->loc, x))
      return 1;

  return 0;
}

/* The hash function for our hash table.  The value is always computed with
   hash_rtx when adding an element; this function just extracts the hash
   value from a cselib_val structure.  */

static unsigned int
get_value_hash (entry)
     const void *entry;
{
  const cselib_val *v = (const cselib_val *) entry;
  return v->value;
}

/* Return true if X contains a VALUE rtx.  If ONLY_USELESS is set, we
   only return true for values which point to a cselib_val whose value
   element has been set to zero, which implies the cselib_val will be
   removed.  */

int
references_value_p (x, only_useless)
     rtx x;
     int only_useless;
{
  enum rtx_code code = GET_CODE (x);
  const char *fmt = GET_RTX_FORMAT (code);
  int i, j;

  if (GET_CODE (x) == VALUE
      && (! only_useless || CSELIB_VAL_PTR (x)->locs == 0))
    return 1;

  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      if (fmt[i] == 'e' && references_value_p (XEXP (x, i), only_useless))
        return 1;
      else if (fmt[i] == 'E')
        for (j = 0; j < XVECLEN (x, i); j++)
          if (references_value_p (XVECEXP (x, i, j), only_useless))
            return 1;
    }

  return 0;
}

/* For all locations found in X, delete locations that reference useless
   values (i.e. values without any location).  Called through
   htab_traverse.  */

static int
discard_useless_locs (x, info)
     void **x;
     void *info ATTRIBUTE_UNUSED;
{
  cselib_val *v = (cselib_val *)*x;
  struct elt_loc_list **p = &v->locs;
  int had_locs = v->locs != 0;

  while (*p)
    {
      if (references_value_p ((*p)->loc, 1))
        unchain_one_elt_loc_list (p);
      else
        p = &(*p)->next;
    }

  if (had_locs && v->locs == 0)
    {
      n_useless_values++;
      values_became_useless = 1;
    }
  return 1;
}

/* If X is a value with no locations, remove it from the hashtable.  */

static int
discard_useless_values (x, info)
     void **x;
     void *info ATTRIBUTE_UNUSED;
{
  cselib_val *v = (cselib_val *)*x;

  if (v->locs == 0)
    {
      htab_clear_slot (hash_table, x);
      unchain_one_value (v);
      n_useless_values--;
    }

  return 1;
}

/* Clean out useless values (i.e. those which no longer have locations
   associated with them) from the hash table.  */

static void
remove_useless_values ()
{
  /* First pass: eliminate locations that reference the value.  That in
     turn can make more values useless.  */
  do
    {
      values_became_useless = 0;
      htab_traverse (hash_table, discard_useless_locs, 0);
    }
  while (values_became_useless);

  /* Second pass: actually remove the values.  */
  htab_traverse (hash_table, discard_useless_values, 0);

  if (n_useless_values != 0)
    abort ();
}

/* Return nonzero if we can prove that X and Y contain the same value, taking
   our gathered information into account.  */

int
rtx_equal_for_cselib_p (x, y)
     rtx x, y;
{
  enum rtx_code code;
  const char *fmt;
  int i;
  
  if (GET_CODE (x) == REG || GET_CODE (x) == MEM)
    {
      cselib_val *e = cselib_lookup (x, VOIDmode, 0);

      if (e)
        x = e->u.val_rtx;
    }

  if (GET_CODE (y) == REG || GET_CODE (y) == MEM)
    {
      cselib_val *e = cselib_lookup (y, VOIDmode, 0);

      if (e)
        y = e->u.val_rtx;
    }

  if (x == y)
    return 1;

  if (GET_CODE (x) == VALUE && GET_CODE (y) == VALUE)
    return CSELIB_VAL_PTR (x) == CSELIB_VAL_PTR (y);

  if (GET_CODE (x) == VALUE)
    {
      cselib_val *e = CSELIB_VAL_PTR (x);
      struct elt_loc_list *l;

      for (l = e->locs; l; l = l->next)
        {
          rtx t = l->loc;

          /* Avoid infinite recursion.  */
          if (GET_CODE (t) == REG || GET_CODE (t) == MEM)
            continue;
          else if (rtx_equal_for_cselib_p (t, y))
            return 1;
        }
      
      return 0;
    }

  if (GET_CODE (y) == VALUE)
    {
      cselib_val *e = CSELIB_VAL_PTR (y);
      struct elt_loc_list *l;

      for (l = e->locs; l; l = l->next)
        {
          rtx t = l->loc;

          if (GET_CODE (t) == REG || GET_CODE (t) == MEM)
            continue;
          else if (rtx_equal_for_cselib_p (x, t))
            return 1;
        }
      
      return 0;
    }

  if (GET_CODE (x) != GET_CODE (y) || GET_MODE (x) != GET_MODE (y))
    return 0;

  /* This won't be handled correctly by the code below.  */
  if (GET_CODE (x) == LABEL_REF)
    return XEXP (x, 0) == XEXP (y, 0);
  
  code = GET_CODE (x);
  fmt = GET_RTX_FORMAT (code);

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

      switch (fmt[i])
        {
        case 'w':
          if (XWINT (x, i) != XWINT (y, i))
            return 0;
          break;

        case 'n':
        case 'i':
          if (XINT (x, i) != XINT (y, i))
            return 0;
          break;

        case 'V':
        case 'E':
          /* Two vectors must have the same length.  */
          if (XVECLEN (x, i) != XVECLEN (y, i))
            return 0;

          /* And the corresponding elements must match.  */
          for (j = 0; j < XVECLEN (x, i); j++)
            if (! rtx_equal_for_cselib_p (XVECEXP (x, i, j),
                                          XVECEXP (y, i, j)))
              return 0;
          break;

        case 'e':
          if (! rtx_equal_for_cselib_p (XEXP (x, i), XEXP (y, i)))
            return 0;
          break;

        case 'S':
        case 's':
          if (strcmp (XSTR (x, i), XSTR (y, i)))
            return 0;
          break;

        case 'u':
          /* These are just backpointers, so they don't matter.  */
          break;

        case '0':
        case 't':
          break;

          /* It is believed that rtx's at this level will never
             contain anything but integers and other rtx's,
             except for within LABEL_REFs and SYMBOL_REFs.  */
        default:
          abort ();
        }
    }
  return 1;
}

/* Hash an rtx.  Return 0 if we couldn't hash the rtx.
   For registers and memory locations, we look up their cselib_val structure
   and return its VALUE element.
   Possible reasons for return 0 are: the object is volatile, or we couldn't
   find a register or memory location in the table and CREATE is zero.  If
   CREATE is nonzero, table elts are created for regs and mem.
   MODE is used in hashing for CONST_INTs only;
   otherwise the mode of X is used.  */

static unsigned int
hash_rtx (x, mode, create)
     rtx x;
     enum machine_mode mode;
     int create;
{
  cselib_val *e;
  int i, j;
  enum rtx_code code;
  const char *fmt;
  unsigned int hash = 0;

  /* repeat is used to turn tail-recursion into iteration.  */
 repeat:
  code = GET_CODE (x);
  hash += (unsigned) code + (unsigned) GET_MODE (x);

  switch (code)
    {
    case MEM:
    case REG:
      e = cselib_lookup (x, GET_MODE (x), create);
      if (! e)
        return 0;

      hash += e->value;
      return hash;

    case CONST_INT:
      hash += ((unsigned) CONST_INT << 7) + (unsigned) mode + INTVAL (x);
      return hash ? hash : CONST_INT;

    case CONST_DOUBLE:
      /* This is like the general case, except that it only counts
         the integers representing the constant.  */
      hash += (unsigned) code + (unsigned) GET_MODE (x);
      if (GET_MODE (x) != VOIDmode)
        for (i = 2; i < GET_RTX_LENGTH (CONST_DOUBLE); i++)
          hash += XWINT (x, i);
      else
        hash += ((unsigned) CONST_DOUBLE_LOW (x)
                 + (unsigned) CONST_DOUBLE_HIGH (x));
      return hash ? hash : CONST_DOUBLE;

      /* Assume there is only one rtx object for any given label.  */
    case LABEL_REF:
      hash
        += ((unsigned) LABEL_REF << 7) + (unsigned long) XEXP (x, 0);
      return hash ? hash : LABEL_REF;

    case SYMBOL_REF:
      hash
        += ((unsigned) SYMBOL_REF << 7) + (unsigned long) XSTR (x, 0);
      return hash ? hash : SYMBOL_REF;

    case PRE_DEC:
    case PRE_INC:
    case POST_DEC:
    case POST_INC:
    case PC:
    case CC0:
    case CALL:
    case UNSPEC_VOLATILE:
      return 0;

    case ASM_OPERANDS:
      if (MEM_VOLATILE_P (x))
        return 0;

      break;
      
    default:
      break;
    }

  i = GET_RTX_LENGTH (code) - 1;
  fmt = GET_RTX_FORMAT (code);
  for (; i >= 0; i--)
    {
      if (fmt[i] == 'e')
        {
          rtx tem = XEXP (x, i);
          unsigned int tem_hash;

          /* If we are about to do the last recursive call
             needed at this level, change it into iteration.
             This function  is called enough to be worth it.  */
          if (i == 0)
            {
              x = tem;
              goto repeat;
            }

          tem_hash = hash_rtx (tem, 0, create);
          if (tem_hash == 0)
            return 0;

          hash += tem_hash;
        }
      else if (fmt[i] == 'E')
        for (j = 0; j < XVECLEN (x, i); j++)
          {
            unsigned int tem_hash = hash_rtx (XVECEXP (x, i, j), 0, create);

            if (tem_hash == 0)
              return 0;

            hash += tem_hash;
          }
      else if (fmt[i] == 's')
        {
          const unsigned char *p = (const unsigned char *) XSTR (x, i);

          if (p)
            while (*p)
              hash += *p++;
        }
      else if (fmt[i] == 'i')
        hash += XINT (x, i);
      else if (fmt[i] == '0' || fmt[i] == 't')
        /* unused */;
      else
        abort ();
    }

  return hash ? hash : 1 + GET_CODE (x);
}

/* Create a new value structure for VALUE and initialize it.  The mode of the
   value is MODE.  */

static cselib_val *
new_cselib_val (value, mode)
     unsigned int value;
     enum machine_mode mode;
{
  cselib_val *e = empty_vals;

  if (e)
    empty_vals = e->u.next_free;
  else
    e = (cselib_val *) obstack_alloc (&cselib_obstack, sizeof (cselib_val));

  if (value == 0)
    abort ();

  e->value = value;
  e->u.val_rtx = gen_rtx_VALUE (mode);
  CSELIB_VAL_PTR (e->u.val_rtx) = e;
  e->addr_list = 0;
  e->locs = 0;
  return e;
}

/* ADDR_ELT is a value that is used as address.  MEM_ELT is the value that
   contains the data at this address.  X is a MEM that represents the
   value.  Update the two value structures to represent this situation.  */

static void
add_mem_for_addr (addr_elt, mem_elt, x)
     cselib_val *addr_elt, *mem_elt;
     rtx x;
{
  rtx new;
  struct elt_loc_list *l;

  /* Avoid duplicates.  */
  for (l = mem_elt->locs; l; l = l->next)
    if (GET_CODE (l->loc) == MEM
        && CSELIB_VAL_PTR (XEXP (l->loc, 0)) == addr_elt)
      return;

  new = gen_rtx_MEM (GET_MODE (x), addr_elt->u.val_rtx);
  MEM_COPY_ATTRIBUTES (new, x);

  addr_elt->addr_list = new_elt_list (addr_elt->addr_list, mem_elt);
  mem_elt->locs = new_elt_loc_list (mem_elt->locs, new);
}

/* Subroutine of cselib_lookup.  Return a value for X, which is a MEM rtx.
   If CREATE, make a new one if we haven't seen it before.  */

static cselib_val *
cselib_lookup_mem (x, create)
     rtx x;
     int create;
{
  void **slot;
  cselib_val *addr;
  cselib_val *mem_elt;
  struct elt_list *l;

  if (MEM_VOLATILE_P (x) || GET_MODE (x) == BLKmode
      || (FLOAT_MODE_P (GET_MODE (x)) && flag_float_store))
    return 0;

  /* Look up the value for the address.  */
  addr = cselib_lookup (XEXP (x, 0), GET_MODE (x), create);
  if (! addr)
    return 0;

  /* Find a value that describes a value of our mode at that address.  */
  for (l = addr->addr_list; l; l = l->next)
    if (GET_MODE (l->elt->u.val_rtx) == GET_MODE (x))
      return l->elt;

  if (! create)
    return 0;

  mem_elt = new_cselib_val (++next_unknown_value, GET_MODE (x));
  add_mem_for_addr (addr, mem_elt, x);
  slot = htab_find_slot_with_hash (hash_table, x, mem_elt->value, INSERT);
  *slot = mem_elt;
  return mem_elt;
}

/* Walk rtx X and replace all occurrences of REG and MEM subexpressions
   with VALUE expressions.  This way, it becomes independent of changes
   to registers and memory.
   X isn't actually modified; if modifications are needed, new rtl is
   allocated.  However, the return value can share rtl with X.  */

static rtx
cselib_subst_to_values (x)
     rtx x;
{
  enum rtx_code code = GET_CODE (x);
  const char *fmt = GET_RTX_FORMAT (code);
  cselib_val *e;
  struct elt_list *l;
  rtx copy = x;
  int i;

  switch (code)
    {
    case REG:
      for (l = REG_VALUES (REGNO (x)); l; l = l->next)
        if (GET_MODE (l->elt->u.val_rtx) == GET_MODE (x))
          return l->elt->u.val_rtx;

      abort ();

    case MEM:
      e = cselib_lookup_mem (x, 0);
      if (! e)
        abort ();
      return e->u.val_rtx;

      /* CONST_DOUBLEs must be special-cased here so that we won't try to
         look up the CONST_DOUBLE_MEM inside.  */
    case CONST_DOUBLE:
    case CONST_INT:
      return x;

    default:
      break;
    }

  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      if (fmt[i] == 'e')
        {
          rtx t = cselib_subst_to_values (XEXP (x, i));

          if (t != XEXP (x, i) && x == copy)
            copy = shallow_copy_rtx (x);

          XEXP (copy, i) = t;
        }
      else if (fmt[i] == 'E')
        {
          int j, k;

          for (j = 0; j < XVECLEN (x, i); j++)
            {
              rtx t = cselib_subst_to_values (XVECEXP (x, i, j));

              if (t != XVECEXP (x, i, j) && XVEC (x, i) == XVEC (copy, i))
                {
                  if (x == copy)
                    copy = shallow_copy_rtx (x);

                  XVEC (copy, i) = rtvec_alloc (XVECLEN (x, i));
                  for (k = 0; k < j; k++)
                    XVECEXP (copy, i, k) = XVECEXP (x, i, k);
                }

              XVECEXP (copy, i, j) = t;
            }
        }
    }

  return copy;
}

/* Look up the rtl expression X in our tables and return the value it has.
   If CREATE is zero, we return NULL if we don't know the value.  Otherwise,
   we create a new one if possible, using mode MODE if X doesn't have a mode
   (i.e. because it's a constant).  */

cselib_val *
cselib_lookup (x, mode, create)
     rtx x;
     enum machine_mode mode;
     int create;
{
  void **slot;
  cselib_val *e;
  unsigned int hashval;

  if (GET_MODE (x) != VOIDmode)
    mode = GET_MODE (x);

  if (GET_CODE (x) == VALUE)
    return CSELIB_VAL_PTR (x);

  if (GET_CODE (x) == REG)
    {
      struct elt_list *l;
      unsigned int i = REGNO (x);

      for (l = REG_VALUES (i); l; l = l->next)
        if (mode == GET_MODE (l->elt->u.val_rtx))
          return l->elt;

      if (! create)
        return 0;

      e = new_cselib_val (++next_unknown_value, GET_MODE (x));
      e->locs = new_elt_loc_list (e->locs, x);
      REG_VALUES (i) = new_elt_list (REG_VALUES (i), e);
      slot = htab_find_slot_with_hash (hash_table, x, e->value, INSERT);
      *slot = e;
      return e;
    }

  if (GET_CODE (x) == MEM)
    return cselib_lookup_mem (x, create);

  hashval = hash_rtx (x, mode, create);
  /* Can't even create if hashing is not possible.  */
  if (! hashval)
    return 0;

  slot = htab_find_slot_with_hash (hash_table, x, hashval,
                                   create ? INSERT : NO_INSERT);
  if (slot == 0)
    return 0;

  e = (cselib_val *) *slot;
  if (e)
    return e;

  e = new_cselib_val (hashval, mode);

  /* We have to fill the slot before calling cselib_subst_to_values:
     the hash table is inconsistent until we do so, and
     cselib_subst_to_values will need to do lookups.  */
  *slot = (void *) e;
  e->locs = new_elt_loc_list (e->locs, cselib_subst_to_values (x));
  return e;
}

/* Invalidate any entries in reg_values that overlap REGNO.  This is called
   if REGNO is changing.  MODE is the mode of the assignment to REGNO, which
   is used to determine how many hard registers are being changed.  If MODE
   is VOIDmode, then only REGNO is being changed; this is used when
   invalidating call clobbered registers across a call.  */

static void
cselib_invalidate_regno (regno, mode)
     unsigned int regno;
     enum machine_mode mode;
{
  unsigned int endregno;
  unsigned int i;

  /* If we see pseudos after reload, something is _wrong_.  */
  if (reload_completed && regno >= FIRST_PSEUDO_REGISTER
      && reg_renumber[regno] >= 0)
    abort ();

  /* Determine the range of registers that must be invalidated.  For
     pseudos, only REGNO is affected.  For hard regs, we must take MODE
     into account, and we must also invalidate lower register numbers
     if they contain values that overlap REGNO.  */
  endregno = regno + 1;
  if (regno < FIRST_PSEUDO_REGISTER && mode != VOIDmode) 
    endregno = regno + HARD_REGNO_NREGS (regno, mode);

  for (i = 0; i < endregno; i++)
    {
      struct elt_list **l = &REG_VALUES (i);

      /* Go through all known values for this reg; if it overlaps the range
         we're invalidating, remove the value.  */
      while (*l)
        {
          cselib_val *v = (*l)->elt;
          struct elt_loc_list **p;
          unsigned int this_last = i;

          if (i < FIRST_PSEUDO_REGISTER)
            this_last += HARD_REGNO_NREGS (i, GET_MODE (v->u.val_rtx)) - 1;

          if (this_last < regno)
            {
              l = &(*l)->next;
              continue;
            }

          /* We have an overlap.  */
          unchain_one_elt_list (l);

          /* Now, we clear the mapping from value to reg.  It must exist, so
             this code will crash intentionally if it doesn't.  */
          for (p = &v->locs; ; p = &(*p)->next)
            {
              rtx x = (*p)->loc;

              if (GET_CODE (x) == REG && REGNO (x) == i)
                {
                  unchain_one_elt_loc_list (p);
                  break;
                }
            }
          if (v->locs == 0)
            n_useless_values++;
        }
    }
}

/* The memory at address MEM_BASE is being changed.
   Return whether this change will invalidate VAL.  */

static int
cselib_mem_conflict_p (mem_base, val)
     rtx mem_base;
     rtx val;
{
  enum rtx_code code;
  const char *fmt;
  int i, j;

  code = GET_CODE (val);
  switch (code)
    {
      /* Get rid of a few simple cases quickly. */
    case REG:
    case PC:
    case CC0:
    case SCRATCH:
    case CONST:
    case CONST_INT:
    case CONST_DOUBLE:
    case SYMBOL_REF:
    case LABEL_REF:
      return 0;

    case MEM:
      if (GET_MODE (mem_base) == BLKmode
          || GET_MODE (val) == BLKmode
          || anti_dependence (val, mem_base))
        return 1;

      /* The address may contain nested MEMs.  */
      break;

    default:
      break;
    }

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      if (fmt[i] == 'e')
        {
          if (cselib_mem_conflict_p (mem_base, XEXP (val, i)))
            return 1;
        }
      else if (fmt[i] == 'E')
        for (j = 0; j < XVECLEN (val, i); j++)
          if (cselib_mem_conflict_p (mem_base, XVECEXP (val, i, j)))
            return 1;
    }

  return 0;
}

/* For the value found in SLOT, walk its locations to determine if any overlap
   INFO (which is a MEM rtx).  */

static int
cselib_invalidate_mem_1 (slot, info)
     void **slot;
     void *info;
{
  cselib_val *v = (cselib_val *) *slot;
  rtx mem_rtx = (rtx) info;
  struct elt_loc_list **p = &v->locs;
  int had_locs = v->locs != 0;

  while (*p)
    {
      rtx x = (*p)->loc;
      cselib_val *addr;
      struct elt_list **mem_chain;

      /* MEMs may occur in locations only at the top level; below
         that every MEM or REG is substituted by its VALUE.  */
      if (GET_CODE (x) != MEM
          || ! cselib_mem_conflict_p (mem_rtx, x))
        {
          p = &(*p)->next;
          continue;
        }

      /* This one overlaps.  */
      /* We must have a mapping from this MEM's address to the
         value (E).  Remove that, too.  */
      addr = cselib_lookup (XEXP (x, 0), VOIDmode, 0);
      mem_chain = &addr->addr_list;
      for (;;)
        {
          if ((*mem_chain)->elt == v)
            {
              unchain_one_elt_list (mem_chain);
              break;
            }

          mem_chain = &(*mem_chain)->next;
        }

      unchain_one_elt_loc_list (p);
    }

  if (had_locs && v->locs == 0)
    n_useless_values++;

  return 1;
}

/* Invalidate any locations in the table which are changed because of a
   store to MEM_RTX.  If this is called because of a non-const call
   instruction, MEM_RTX is (mem:BLK const0_rtx).  */

static void
cselib_invalidate_mem (mem_rtx)
     rtx mem_rtx;
{
  htab_traverse (hash_table, cselib_invalidate_mem_1, mem_rtx);
}

/* Invalidate DEST, which is being assigned to or clobbered.  The second and
   the third parameter exist so that this function can be passed to
   note_stores; they are ignored.  */

static void
cselib_invalidate_rtx (dest, ignore, data)
     rtx dest;
     rtx ignore ATTRIBUTE_UNUSED;
     void *data ATTRIBUTE_UNUSED;
{
  while (GET_CODE (dest) == STRICT_LOW_PART || GET_CODE (dest) == SIGN_EXTRACT
         || GET_CODE (dest) == ZERO_EXTRACT || GET_CODE (dest) == SUBREG)
    dest = XEXP (dest, 0);

  if (GET_CODE (dest) == REG)
    cselib_invalidate_regno (REGNO (dest), GET_MODE (dest));
  else if (GET_CODE (dest) == MEM)
    cselib_invalidate_mem (dest);

  /* Some machines don't define AUTO_INC_DEC, but they still use push
     instructions.  We need to catch that case here in order to
     invalidate the stack pointer correctly.  Note that invalidating
     the stack pointer is different from invalidating DEST.  */
  if (push_operand (dest, GET_MODE (dest)))
    cselib_invalidate_rtx (stack_pointer_rtx, NULL_RTX, NULL);
}

/* Record the result of a SET instruction.  DEST is being set; the source
   contains the value described by SRC_ELT.  If DEST is a MEM, DEST_ADDR_ELT
   describes its address.  */

static void
cselib_record_set (dest, src_elt, dest_addr_elt)
     rtx dest;
     cselib_val *src_elt, *dest_addr_elt;
{
  int dreg = GET_CODE (dest) == REG ? (int) REGNO (dest) : -1;

  if (src_elt == 0 || side_effects_p (dest))
    return;

  if (dreg >= 0)
    {
      REG_VALUES (dreg) = new_elt_list (REG_VALUES (dreg), src_elt);
      if (src_elt->locs == 0)
        n_useless_values--;
      src_elt->locs = new_elt_loc_list (src_elt->locs, dest);
    }
  else if (GET_CODE (dest) == MEM && dest_addr_elt != 0)
    {
      if (src_elt->locs == 0)
        n_useless_values--;
      add_mem_for_addr (dest_addr_elt, src_elt, dest);
    }
}

/* Describe a single set that is part of an insn.  */
struct set
{
  rtx src;
  rtx dest;
  cselib_val *src_elt;
  cselib_val *dest_addr_elt;
};

/* There is no good way to determine how many elements there can be
   in a PARALLEL.  Since it's fairly cheap, use a really large number.  */
#define MAX_SETS (FIRST_PSEUDO_REGISTER * 2)

/* Record the effects of any sets in INSN.  */
static void
cselib_record_sets (insn)
     rtx insn;
{
  int n_sets = 0;
  int i;
  struct set sets[MAX_SETS];
  rtx body = PATTERN (insn);

  body = PATTERN (insn);
  /* Find all sets.  */
  if (GET_CODE (body) == SET)
    {
      sets[0].src = SET_SRC (body);
      sets[0].dest = SET_DEST (body);
      n_sets = 1;
    }
  else if (GET_CODE (body) == PARALLEL)
    {
      /* Look through the PARALLEL and record the values being
         set, if possible.  Also handle any CLOBBERs.  */
      for (i = XVECLEN (body, 0) - 1; i >= 0; --i)
        {
          rtx x = XVECEXP (body, 0, i);

          if (GET_CODE (x) == SET)
            {
              sets[n_sets].src = SET_SRC (x);
              sets[n_sets].dest = SET_DEST (x);
              n_sets++;
            }
        }
    }

  /* Look up the values that are read.  Do this before invalidating the
     locations that are written.  */
  for (i = 0; i < n_sets; i++)
    {
      sets[i].src_elt = cselib_lookup (sets[i].src, GET_MODE (sets[i].dest),
                                       1);
      if (GET_CODE (sets[i].dest) == MEM)
        sets[i].dest_addr_elt = cselib_lookup (XEXP (sets[i].dest, 0), Pmode,
                                               1);
      else
        sets[i].dest_addr_elt = 0;
    }

  /* Invalidate all locations written by this insn.  Note that the elts we
     looked up in the previous loop aren't affected, just some of their
     locations may go away.  */
  note_stores (body, cselib_invalidate_rtx, NULL);

  /* Now enter the equivalences in our tables.  */
  for (i = 0; i < n_sets; i++)
    cselib_record_set (sets[i].dest, sets[i].src_elt, sets[i].dest_addr_elt);
}

/* Record the effects of INSN.  */

void
cselib_process_insn (insn)
     rtx insn;
{
  int i;
  rtx x;

  cselib_current_insn = insn;

  /* Forget everything at a CODE_LABEL, a volatile asm, or a setjmp.  */
  if (GET_CODE (insn) == CODE_LABEL
      || (GET_CODE (insn) == NOTE
          && NOTE_LINE_NUMBER (insn) == NOTE_INSN_SETJMP)
      || (GET_CODE (insn) == INSN
          && GET_CODE (PATTERN (insn)) == ASM_OPERANDS
          && MEM_VOLATILE_P (PATTERN (insn))))
    {
      clear_table ();
      return;
    }

  if (GET_RTX_CLASS (GET_CODE (insn)) != 'i')
    {
      cselib_current_insn = 0;
      return;
    }

  /* If this is a call instruction, forget anything stored in a
     call clobbered register, or, if this is not a const call, in
     memory.  */
  if (GET_CODE (insn) == CALL_INSN)
    {
      for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
        if (call_used_regs[i])
          cselib_invalidate_regno (i, VOIDmode);

      if (! CONST_CALL_P (insn))
        cselib_invalidate_mem (callmem);
    }

  cselib_record_sets (insn);

#ifdef AUTO_INC_DEC
  /* Clobber any registers which appear in REG_INC notes.  We
     could keep track of the changes to their values, but it is
     unlikely to help.  */
  for (x = REG_NOTES (insn); x; x = XEXP (x, 1))
    if (REG_NOTE_KIND (x) == REG_INC)
      cselib_invalidate_rtx (XEXP (x, 0), NULL_RTX, NULL);
#endif

  /* Look for any CLOBBERs in CALL_INSN_FUNCTION_USAGE, but only
     after we have processed the insn.  */
  if (GET_CODE (insn) == CALL_INSN)
    for (x = CALL_INSN_FUNCTION_USAGE (insn); x; x = XEXP (x, 1))
      if (GET_CODE (XEXP (x, 0)) == CLOBBER)
        cselib_invalidate_rtx (XEXP (XEXP (x, 0), 0), NULL_RTX, NULL);

  cselib_current_insn = 0;

  if (n_useless_values > MAX_USELESS_VALUES)
    remove_useless_values ();
}

/* Make sure our varrays are big enough.  Not called from any cselib routines;
   it must be called by the user if it allocated new registers.  */

void
cselib_update_varray_sizes ()
{
  unsigned int nregs = max_reg_num ();

  if (nregs == cselib_nregs)
    return;

  cselib_nregs = nregs;
  VARRAY_GROW (reg_values, nregs);
}

/* Initialize cselib for one pass.  The caller must also call
   init_alias_analysis.  */

void
cselib_init ()
{
  /* These are only created once.  */
  if (! callmem)
    {
      extern struct obstack permanent_obstack;

      gcc_obstack_init (&cselib_obstack);
      cselib_startobj = obstack_alloc (&cselib_obstack, 0);

      push_obstacks (&permanent_obstack, &permanent_obstack);
      callmem = gen_rtx_MEM (BLKmode, const0_rtx);
      pop_obstacks ();
      ggc_add_rtx_root (&callmem, 1);
    }

  cselib_nregs = max_reg_num ();
  VARRAY_ELT_LIST_INIT (reg_values, cselib_nregs, "reg_values");
  hash_table = htab_create (31, get_value_hash, entry_and_rtx_equal_p, NULL);
  clear_table ();
}

/* Called when the current user is done with cselib.  */

void
cselib_finish ()
{
  clear_table ();
  htab_delete (hash_table);
}