PR bootstrap/39454

[pf3gnuchains/gcc-fork.git] / gcc / cse.c

/* Common subexpression elimination for GNU compiler.
   Copyright (C) 1987, 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998
   1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
   Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 3, or (at your option) any later
version.

GCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

#include "config.h"
/* stdio.h must precede rtl.h for FFS.  */
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "rtl.h"
#include "tm_p.h"
#include "hard-reg-set.h"
#include "regs.h"
#include "basic-block.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 "timevar.h"
#include "except.h"
#include "target.h"
#include "params.h"
#include "rtlhooks-def.h"
#include "tree-pass.h"
#include "df.h"
#include "dbgcnt.h"

/* The basic idea of common subexpression elimination is to go
   through the code, keeping a record of expressions that would
   have the same value at the current scan point, and replacing
   expressions encountered with the cheapest equivalent expression.

   It is too complicated to keep track of the different possibilities
   when control paths merge in this code; so, at each label, we forget all
   that is known and start fresh.  This can be described as processing each
   extended basic block separately.  We have a separate pass to perform
   global CSE.

   Note CSE can turn a conditional or computed jump into a nop or
   an unconditional jump.  When this occurs we arrange to run the jump
   optimizer after CSE to delete the unreachable code.

   We use two data structures to record the equivalent expressions:
   a hash table for most expressions, and a vector of "quantity
   numbers" to record equivalent (pseudo) registers.

   The use of the special data structure for registers is desirable
   because it is faster.  It is possible because registers references
   contain a fairly small number, the register number, taken from
   a contiguously allocated series, and two register references are
   identical if they have the same number.  General expressions
   do not have any such thing, so the only way to retrieve the
   information recorded on an expression other than a register
   is to keep it in a hash table.

Registers and "quantity numbers":

   At the start of each basic block, all of the (hardware and pseudo)
   registers used in the function are given distinct quantity
   numbers to indicate their contents.  During scan, when the code
   copies one register into another, we copy the quantity number.
   When a register is loaded in any other way, we allocate a new
   quantity number to describe the value generated by this operation.
   `REG_QTY (N)' records what quantity register N is currently thought
   of as containing.

   All real quantity numbers are greater than or equal to zero.
   If register N has not been assigned a quantity, `REG_QTY (N)' will
   equal -N - 1, which is always negative.

   Quantity numbers below zero do not exist and none of the `qty_table'
   entries should be referenced with a negative index.

   We also maintain a bidirectional chain of registers for each
   quantity number.  The `qty_table` members `first_reg' and `last_reg',
   and `reg_eqv_table' members `next' and `prev' hold these chains.

   The first register in a chain is the one whose lifespan is least local.
   Among equals, it is the one that was seen first.
   We replace any equivalent register with that one.

   If two registers have the same quantity number, it must be true that
   REG expressions with qty_table `mode' must be in the hash table for both
   registers and must be in the same class.

   The converse is not true.  Since hard registers may be referenced in
   any mode, two REG expressions might be equivalent in the hash table
   but not have the same quantity number if the quantity number of one
   of the registers is not the same mode as those expressions.

Constants and quantity numbers

   When a quantity has a known constant value, that value is stored
   in the appropriate qty_table `const_rtx'.  This is in addition to
   putting the constant in the hash table as is usual for non-regs.

   Whether a reg or a constant is preferred is determined by the configuration
   macro CONST_COSTS and will often depend on the constant value.  In any
   event, expressions containing constants can be simplified, by fold_rtx.

   When a quantity has a known nearly constant value (such as an address
   of a stack slot), that value is stored in the appropriate qty_table
   `const_rtx'.

   Integer constants don't have a machine mode.  However, cse
   determines the intended machine mode from the destination
   of the instruction that moves the constant.  The machine mode
   is recorded in the hash table along with the actual RTL
   constant expression so that different modes are kept separate.

Other expressions:

   To record known equivalences among expressions in general
   we use a hash table called `table'.  It has a fixed number of buckets
   that contain chains of `struct table_elt' elements for expressions.
   These chains connect the elements whose expressions have the same
   hash codes.

   Other chains through the same elements connect the elements which
   currently have equivalent values.

   Register references in an expression are canonicalized before hashing
   the expression.  This is done using `reg_qty' and qty_table `first_reg'.
   The hash code of a register reference is computed using the quantity
   number, not the register number.

   When the value of an expression changes, it is necessary to remove from the
   hash table not just that expression but all expressions whose values
   could be different as a result.

     1. If the value changing is in memory, except in special cases
     ANYTHING referring to memory could be changed.  That is because
     nobody knows where a pointer does not point.
     The function `invalidate_memory' removes what is necessary.

     The special cases are when the address is constant or is
     a constant plus a fixed register such as the frame pointer
     or a static chain pointer.  When such addresses are stored in,
     we can tell exactly which other such addresses must be invalidated
     due to overlap.  `invalidate' does this.
     All expressions that refer to non-constant
     memory addresses are also invalidated.  `invalidate_memory' does this.

     2. If the value changing is a register, all expressions
     containing references to that register, and only those,
     must be removed.

   Because searching the entire hash table for expressions that contain
   a register is very slow, we try to figure out when it isn't necessary.
   Precisely, this is necessary only when expressions have been
   entered in the hash table using this register, and then the value has
   changed, and then another expression wants to be added to refer to
   the register's new value.  This sequence of circumstances is rare
   within any one basic block.

   `REG_TICK' and `REG_IN_TABLE', accessors for members of
   cse_reg_info, are used to detect this case.  REG_TICK (i) is
   incremented whenever a value is stored in register i.
   REG_IN_TABLE (i) holds -1 if no references to register i have been
   entered in the table; otherwise, it contains the value REG_TICK (i)
   had when the references were entered.  If we want to enter a
   reference and REG_IN_TABLE (i) != REG_TICK (i), we must scan and
   remove old references.  Until we want to enter a new entry, the
   mere fact that the two vectors don't match makes the entries be
   ignored if anyone tries to match them.

   Registers themselves are entered in the hash table as well as in
   the equivalent-register chains.  However, `REG_TICK' and
   `REG_IN_TABLE' do not apply to expressions which are simple
   register references.  These expressions are removed from the table
   immediately when they become invalid, and this can be done even if
   we do not immediately search for all the expressions that refer to
   the register.

   A CLOBBER rtx in an instruction invalidates its operand for further
   reuse.  A CLOBBER or SET rtx whose operand is a MEM:BLK
   invalidates everything that resides in memory.

Related expressions:

   Constant expressions that differ only by an additive integer
   are called related.  When a constant expression is put in
   the table, the related expression with no constant term
   is also entered.  These are made to point at each other
   so that it is possible to find out if there exists any
   register equivalent to an expression related to a given expression.  */

/* Length of qty_table vector.  We know in advance we will not need
   a quantity number this big.  */

static int max_qty;

/* Next quantity number to be allocated.
   This is 1 + the largest number needed so far.  */

static int next_qty;

/* Per-qty information tracking.

   `first_reg' and `last_reg' track the head and tail of the
   chain of registers which currently contain this quantity.

   `mode' contains the machine mode of this quantity.

   `const_rtx' holds the rtx of the constant value of this
   quantity, if known.  A summations of the frame/arg pointer
   and a constant can also be entered here.  When this holds
   a known value, `const_insn' is the insn which stored the
   constant value.

   `comparison_{code,const,qty}' are used to track when a
   comparison between a quantity and some constant or register has
   been passed.  In such a case, we know the results of the comparison
   in case we see it again.  These members record a comparison that
   is known to be true.  `comparison_code' holds the rtx code of such
   a comparison, else it is set to UNKNOWN and the other two
   comparison members are undefined.  `comparison_const' holds
   the constant being compared against, or zero if the comparison
   is not against a constant.  `comparison_qty' holds the quantity
   being compared against when the result is known.  If the comparison
   is not with a register, `comparison_qty' is -1.  */

struct qty_table_elem
{
  rtx const_rtx;
  rtx const_insn;
  rtx comparison_const;
  int comparison_qty;
  unsigned int first_reg, last_reg;
  /* The sizes of these fields should match the sizes of the
     code and mode fields of struct rtx_def (see rtl.h).  */
  ENUM_BITFIELD(rtx_code) comparison_code : 16;
  ENUM_BITFIELD(machine_mode) mode : 8;
};

/* The table of all qtys, indexed by qty number.  */
static struct qty_table_elem *qty_table;

/* Structure used to pass arguments via for_each_rtx to function
   cse_change_cc_mode.  */
struct change_cc_mode_args
{
  rtx insn;
  rtx newreg;
};

#ifdef HAVE_cc0
/* For machines that have a CC0, we do not record its value in the hash
   table since its use is guaranteed to be the insn immediately following
   its definition and any other insn is presumed to invalidate it.

   Instead, we store below the current and last value assigned to CC0.
   If it should happen to be a constant, it is stored in preference
   to the actual assigned value.  In case it is a constant, we store
   the mode in which the constant should be interpreted.  */

static rtx this_insn_cc0, prev_insn_cc0;
static enum machine_mode this_insn_cc0_mode, prev_insn_cc0_mode;
#endif

/* Insn being scanned.  */

static rtx this_insn;
static bool optimize_this_for_speed_p;

/* Index by register number, gives the number of the next (or
   previous) register in the chain of registers sharing the same
   value.

   Or -1 if this register is at the end of the chain.

   If REG_QTY (N) == -N - 1, reg_eqv_table[N].next is undefined.  */

/* Per-register equivalence chain.  */
struct reg_eqv_elem
{
  int next, prev;
};

/* The table of all register equivalence chains.  */
static struct reg_eqv_elem *reg_eqv_table;

struct cse_reg_info
{
  /* The timestamp at which this register is initialized.  */
  unsigned int timestamp;

  /* The quantity number of the register's current contents.  */
  int reg_qty;

  /* The number of times the register has been altered in the current
     basic block.  */
  int reg_tick;

  /* The REG_TICK value at which rtx's containing this register are
     valid in the hash table.  If this does not equal the current
     reg_tick value, such expressions existing in the hash table are
     invalid.  */
  int reg_in_table;

  /* The SUBREG that was set when REG_TICK was last incremented.  Set
     to -1 if the last store was to the whole register, not a subreg.  */
  unsigned int subreg_ticked;
};

/* A table of cse_reg_info indexed by register numbers.  */
static struct cse_reg_info *cse_reg_info_table;

/* The size of the above table.  */
static unsigned int cse_reg_info_table_size;

/* The index of the first entry that has not been initialized.  */
static unsigned int cse_reg_info_table_first_uninitialized;

/* The timestamp at the beginning of the current run of
   cse_extended_basic_block.  We increment this variable at the beginning of
   the current run of cse_extended_basic_block.  The timestamp field of a
   cse_reg_info entry matches the value of this variable if and only
   if the entry has been initialized during the current run of
   cse_extended_basic_block.  */
static unsigned int cse_reg_info_timestamp;

/* A HARD_REG_SET containing all the hard registers for which there is
   currently a REG expression in the hash table.  Note the difference
   from the above variables, which indicate if the REG is mentioned in some
   expression in the table.  */

static HARD_REG_SET hard_regs_in_table;

/* True if CSE has altered the CFG.  */
static bool cse_cfg_altered;

/* True if CSE has altered conditional jump insns in such a way
   that jump optimization should be redone.  */
static bool cse_jumps_altered;

/* True if we put a LABEL_REF into the hash table for an INSN
   without a REG_LABEL_OPERAND, we have to rerun jump after CSE
   to put in the note.  */
static bool recorded_label_ref;

/* canon_hash stores 1 in do_not_record
   if it notices a reference to CC0, PC, or some other volatile
   subexpression.  */

static int do_not_record;

/* canon_hash stores 1 in hash_arg_in_memory
   if it notices a reference to memory within the expression being hashed.  */

static int hash_arg_in_memory;

/* The hash table contains buckets which are chains of `struct table_elt's,
   each recording one expression's information.
   That expression is in the `exp' field.

   The canon_exp field contains a canonical (from the point of view of
   alias analysis) version of the `exp' field.

   Those elements with the same hash code are chained in both directions
   through the `next_same_hash' and `prev_same_hash' fields.

   Each set of expressions with equivalent values
   are on a two-way chain through the `next_same_value'
   and `prev_same_value' fields, and all point with
   the `first_same_value' field at the first element in
   that chain.  The chain is in order of increasing cost.
   Each element's cost value is in its `cost' field.

   The `in_memory' field is nonzero for elements that
   involve any reference to memory.  These elements are removed
   whenever a write is done to an unidentified location in memory.
   To be safe, we assume that a memory address is unidentified unless
   the address is either a symbol constant or a constant plus
   the frame pointer or argument pointer.

   The `related_value' field is used to connect related expressions
   (that differ by adding an integer).
   The related expressions are chained in a circular fashion.
   `related_value' is zero for expressions for which this
   chain is not useful.

   The `cost' field stores the cost of this element's expression.
   The `regcost' field stores the value returned by approx_reg_cost for
   this element's expression.

   The `is_const' flag is set if the element is a constant (including
   a fixed address).

   The `flag' field is used as a temporary during some search routines.

   The `mode' field is usually the same as GET_MODE (`exp'), but
   if `exp' is a CONST_INT and has no machine mode then the `mode'
   field is the mode it was being used as.  Each constant is
   recorded separately for each mode it is used with.  */

struct table_elt
{
  rtx exp;
  rtx canon_exp;
  struct table_elt *next_same_hash;
  struct table_elt *prev_same_hash;
  struct table_elt *next_same_value;
  struct table_elt *prev_same_value;
  struct table_elt *first_same_value;
  struct table_elt *related_value;
  int cost;
  int regcost;
  /* The size of this field should match the size
     of the mode field of struct rtx_def (see rtl.h).  */
  ENUM_BITFIELD(machine_mode) mode : 8;
  char in_memory;
  char is_const;
  char flag;
};

/* We don't want a lot of buckets, because we rarely have very many
   things stored in the hash table, and a lot of buckets slows
   down a lot of loops that happen frequently.  */
#define HASH_SHIFT      5
#define HASH_SIZE       (1 << HASH_SHIFT)
#define HASH_MASK       (HASH_SIZE - 1)

/* Compute hash code of X in mode M.  Special-case case where X is a pseudo
   register (hard registers may require `do_not_record' to be set).  */

#define HASH(X, M)      \
 ((REG_P (X) && REGNO (X) >= FIRST_PSEUDO_REGISTER      \
  ? (((unsigned) REG << 7) + (unsigned) REG_QTY (REGNO (X)))    \
  : canon_hash (X, M)) & HASH_MASK)

/* Like HASH, but without side-effects.  */
#define SAFE_HASH(X, M) \
 ((REG_P (X) && REGNO (X) >= FIRST_PSEUDO_REGISTER      \
  ? (((unsigned) REG << 7) + (unsigned) REG_QTY (REGNO (X)))    \
  : safe_hash (X, M)) & HASH_MASK)

/* Determine whether register number N is considered a fixed register for the
   purpose of approximating register costs.
   It is desirable to replace other regs with fixed regs, to reduce need for
   non-fixed hard regs.
   A reg wins if it is either the frame pointer or designated as fixed.  */
#define FIXED_REGNO_P(N)  \
  ((N) == FRAME_POINTER_REGNUM || (N) == HARD_FRAME_POINTER_REGNUM \
   || fixed_regs[N] || global_regs[N])

/* Compute cost of X, as stored in the `cost' field of a table_elt.  Fixed
   hard registers and pointers into the frame are the cheapest with a cost
   of 0.  Next come pseudos with a cost of one and other hard registers with
   a cost of 2.  Aside from these special cases, call `rtx_cost'.  */

#define CHEAP_REGNO(N)                                                  \
  (REGNO_PTR_FRAME_P(N)                                                 \
   || (HARD_REGISTER_NUM_P (N)                                          \
       && FIXED_REGNO_P (N) && REGNO_REG_CLASS (N) != NO_REGS))

#define COST(X) (REG_P (X) ? 0 : notreg_cost (X, SET))
#define COST_IN(X,OUTER) (REG_P (X) ? 0 : notreg_cost (X, OUTER))

/* Get the number of times this register has been updated in this
   basic block.  */

#define REG_TICK(N) (get_cse_reg_info (N)->reg_tick)

/* Get the point at which REG was recorded in the table.  */

#define REG_IN_TABLE(N) (get_cse_reg_info (N)->reg_in_table)

/* Get the SUBREG set at the last increment to REG_TICK (-1 if not a
   SUBREG).  */

#define SUBREG_TICKED(N) (get_cse_reg_info (N)->subreg_ticked)

/* Get the quantity number for REG.  */

#define REG_QTY(N) (get_cse_reg_info (N)->reg_qty)

/* Determine if the quantity number for register X represents a valid index
   into the qty_table.  */

#define REGNO_QTY_VALID_P(N) (REG_QTY (N) >= 0)

static struct table_elt *table[HASH_SIZE];

/* Chain of `struct table_elt's made so far for this function
   but currently removed from the table.  */

static struct table_elt *free_element_chain;

/* Set to the cost of a constant pool reference if one was found for a
   symbolic constant.  If this was found, it means we should try to
   convert constants into constant pool entries if they don't fit in
   the insn.  */

static int constant_pool_entries_cost;
static int constant_pool_entries_regcost;

/* This data describes a block that will be processed by
   cse_extended_basic_block.  */

struct cse_basic_block_data
{
  /* Total number of SETs in block.  */
  int nsets;
  /* Size of current branch path, if any.  */
  int path_size;
  /* Current path, indicating which basic_blocks will be processed.  */
  struct branch_path
    {
      /* The basic block for this path entry.  */
      basic_block bb;
    } *path;
};


/* Pointers to the live in/live out bitmaps for the boundaries of the
   current EBB.  */
static bitmap cse_ebb_live_in, cse_ebb_live_out;

/* A simple bitmap to track which basic blocks have been visited
   already as part of an already processed extended basic block.  */
static sbitmap cse_visited_basic_blocks;

static bool fixed_base_plus_p (rtx x);
static int notreg_cost (rtx, enum rtx_code);
static int approx_reg_cost_1 (rtx *, void *);
static int approx_reg_cost (rtx);
static int preferable (int, int, int, int);
static void new_basic_block (void);
static void make_new_qty (unsigned int, enum machine_mode);
static void make_regs_eqv (unsigned int, unsigned int);
static void delete_reg_equiv (unsigned int);
static int mention_regs (rtx);
static int insert_regs (rtx, struct table_elt *, int);
static void remove_from_table (struct table_elt *, unsigned);
static void remove_pseudo_from_table (rtx, unsigned);
static struct table_elt *lookup (rtx, unsigned, enum machine_mode);
static struct table_elt *lookup_for_remove (rtx, unsigned, enum machine_mode);
static rtx lookup_as_function (rtx, enum rtx_code);
static struct table_elt *insert (rtx, struct table_elt *, unsigned,
                                 enum machine_mode);
static void merge_equiv_classes (struct table_elt *, struct table_elt *);
static void invalidate (rtx, enum machine_mode);
static bool cse_rtx_varies_p (const_rtx, bool);
static void remove_invalid_refs (unsigned int);
static void remove_invalid_subreg_refs (unsigned int, unsigned int,
                                        enum machine_mode);
static void rehash_using_reg (rtx);
static void invalidate_memory (void);
static void invalidate_for_call (void);
static rtx use_related_value (rtx, struct table_elt *);

static inline unsigned canon_hash (rtx, enum machine_mode);
static inline unsigned safe_hash (rtx, enum machine_mode);
static inline unsigned hash_rtx_string (const char *);

static rtx canon_reg (rtx, rtx);
static enum rtx_code find_comparison_args (enum rtx_code, rtx *, rtx *,
                                           enum machine_mode *,
                                           enum machine_mode *);
static rtx fold_rtx (rtx, rtx);
static rtx equiv_constant (rtx);
static void record_jump_equiv (rtx, bool);
static void record_jump_cond (enum rtx_code, enum machine_mode, rtx, rtx,
                              int);
static void cse_insn (rtx);
static void cse_prescan_path (struct cse_basic_block_data *);
static void invalidate_from_clobbers (rtx);
static rtx cse_process_notes (rtx, rtx, bool *);
static void cse_extended_basic_block (struct cse_basic_block_data *);
static void count_reg_usage (rtx, int *, rtx, int);
static int check_for_label_ref (rtx *, void *);
extern void dump_class (struct table_elt*);
static void get_cse_reg_info_1 (unsigned int regno);
static struct cse_reg_info * get_cse_reg_info (unsigned int regno);
static int check_dependence (rtx *, void *);

static void flush_hash_table (void);
static bool insn_live_p (rtx, int *);
static bool set_live_p (rtx, rtx, int *);
static int cse_change_cc_mode (rtx *, void *);
static void cse_change_cc_mode_insn (rtx, rtx);
static void cse_change_cc_mode_insns (rtx, rtx, rtx);
static enum machine_mode cse_cc_succs (basic_block, basic_block, rtx, rtx,
                                       bool);
\f

#undef RTL_HOOKS_GEN_LOWPART
#define RTL_HOOKS_GEN_LOWPART           gen_lowpart_if_possible

static const struct rtl_hooks cse_rtl_hooks = RTL_HOOKS_INITIALIZER;
\f
/* 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.  */

static bool
fixed_base_plus_p (rtx x)
{
  switch (GET_CODE (x))
    {
    case REG:
      if (x == frame_pointer_rtx || x == hard_frame_pointer_rtx)
        return true;
      if (x == arg_pointer_rtx && fixed_regs[ARG_POINTER_REGNUM])
        return true;
      if (REGNO (x) >= FIRST_VIRTUAL_REGISTER
          && REGNO (x) <= LAST_VIRTUAL_REGISTER)
        return true;
      return false;

    case PLUS:
      if (GET_CODE (XEXP (x, 1)) != CONST_INT)
        return false;
      return fixed_base_plus_p (XEXP (x, 0));

    default:
      return false;
    }
}

/* Dump the expressions in the equivalence class indicated by CLASSP.
   This function is used only for debugging.  */
void
dump_class (struct table_elt *classp)
{
  struct table_elt *elt;

  fprintf (stderr, "Equivalence chain for ");
  print_rtl (stderr, classp->exp);
  fprintf (stderr, ": \n");

  for (elt = classp->first_same_value; elt; elt = elt->next_same_value)
    {
      print_rtl (stderr, elt->exp);
      fprintf (stderr, "\n");
    }
}

/* Subroutine of approx_reg_cost; called through for_each_rtx.  */

static int
approx_reg_cost_1 (rtx *xp, void *data)
{
  rtx x = *xp;
  int *cost_p = (int *) data;

  if (x && REG_P (x))
    {
      unsigned int regno = REGNO (x);

      if (! CHEAP_REGNO (regno))
        {
          if (regno < FIRST_PSEUDO_REGISTER)
            {
              if (SMALL_REGISTER_CLASSES)
                return 1;
              *cost_p += 2;
            }
          else
            *cost_p += 1;
        }
    }

  return 0;
}

/* Return an estimate of the cost of the registers used in an rtx.
   This is mostly the number of different REG expressions in the rtx;
   however for some exceptions like fixed registers we use a cost of
   0.  If any other hard register reference occurs, return MAX_COST.  */

static int
approx_reg_cost (rtx x)
{
  int cost = 0;

  if (for_each_rtx (&x, approx_reg_cost_1, (void *) &cost))
    return MAX_COST;

  return cost;
}

/* Return a negative value if an rtx A, whose costs are given by COST_A
   and REGCOST_A, is more desirable than an rtx B.
   Return a positive value if A is less desirable, or 0 if the two are
   equally good.  */
static int
preferable (int cost_a, int regcost_a, int cost_b, int regcost_b)
{
  /* First, get rid of cases involving expressions that are entirely
     unwanted.  */
  if (cost_a != cost_b)
    {
      if (cost_a == MAX_COST)
        return 1;
      if (cost_b == MAX_COST)
        return -1;
    }

  /* Avoid extending lifetimes of hardregs.  */
  if (regcost_a != regcost_b)
    {
      if (regcost_a == MAX_COST)
        return 1;
      if (regcost_b == MAX_COST)
        return -1;
    }

  /* Normal operation costs take precedence.  */
  if (cost_a != cost_b)
    return cost_a - cost_b;
  /* Only if these are identical consider effects on register pressure.  */
  if (regcost_a != regcost_b)
    return regcost_a - regcost_b;
  return 0;
}

/* Internal function, to compute cost when X is not a register; called
   from COST macro to keep it simple.  */

static int
notreg_cost (rtx x, enum rtx_code outer)
{
  return ((GET_CODE (x) == SUBREG
           && REG_P (SUBREG_REG (x))
           && GET_MODE_CLASS (GET_MODE (x)) == MODE_INT
           && GET_MODE_CLASS (GET_MODE (SUBREG_REG (x))) == MODE_INT
           && (GET_MODE_SIZE (GET_MODE (x))
               < GET_MODE_SIZE (GET_MODE (SUBREG_REG (x))))
           && subreg_lowpart_p (x)
           && TRULY_NOOP_TRUNCATION (GET_MODE_BITSIZE (GET_MODE (x)),
                                     GET_MODE_BITSIZE (GET_MODE (SUBREG_REG (x)))))
          ? 0
          : rtx_cost (x, outer, optimize_this_for_speed_p) * 2);
}

\f
/* Initialize CSE_REG_INFO_TABLE.  */

static void
init_cse_reg_info (unsigned int nregs)
{
  /* Do we need to grow the table?  */
  if (nregs > cse_reg_info_table_size)
    {
      unsigned int new_size;

      if (cse_reg_info_table_size < 2048)
        {
          /* Compute a new size that is a power of 2 and no smaller
             than the large of NREGS and 64.  */
          new_size = (cse_reg_info_table_size
                      ? cse_reg_info_table_size : 64);

          while (new_size < nregs)
            new_size *= 2;
        }
      else
        {
          /* If we need a big table, allocate just enough to hold
             NREGS registers.  */
          new_size = nregs;
        }

      /* Reallocate the table with NEW_SIZE entries.  */
      if (cse_reg_info_table)
        free (cse_reg_info_table);
      cse_reg_info_table = XNEWVEC (struct cse_reg_info, new_size);
      cse_reg_info_table_size = new_size;
      cse_reg_info_table_first_uninitialized = 0;
    }

  /* Do we have all of the first NREGS entries initialized?  */
  if (cse_reg_info_table_first_uninitialized < nregs)
    {
      unsigned int old_timestamp = cse_reg_info_timestamp - 1;
      unsigned int i;

      /* Put the old timestamp on newly allocated entries so that they
         will all be considered out of date.  We do not touch those
         entries beyond the first NREGS entries to be nice to the
         virtual memory.  */
      for (i = cse_reg_info_table_first_uninitialized; i < nregs; i++)
        cse_reg_info_table[i].timestamp = old_timestamp;

      cse_reg_info_table_first_uninitialized = nregs;
    }
}

/* Given REGNO, initialize the cse_reg_info entry for REGNO.  */

static void
get_cse_reg_info_1 (unsigned int regno)
{
  /* Set TIMESTAMP field to CSE_REG_INFO_TIMESTAMP so that this
     entry will be considered to have been initialized.  */
  cse_reg_info_table[regno].timestamp = cse_reg_info_timestamp;

  /* Initialize the rest of the entry.  */
  cse_reg_info_table[regno].reg_tick = 1;
  cse_reg_info_table[regno].reg_in_table = -1;
  cse_reg_info_table[regno].subreg_ticked = -1;
  cse_reg_info_table[regno].reg_qty = -regno - 1;
}

/* Find a cse_reg_info entry for REGNO.  */

static inline struct cse_reg_info *
get_cse_reg_info (unsigned int regno)
{
  struct cse_reg_info *p = &cse_reg_info_table[regno];

  /* If this entry has not been initialized, go ahead and initialize
     it.  */
  if (p->timestamp != cse_reg_info_timestamp)
    get_cse_reg_info_1 (regno);

  return p;
}

/* Clear the hash table and initialize each register with its own quantity,
   for a new basic block.  */

static void
new_basic_block (void)
{
  int i;

  next_qty = 0;

  /* Invalidate cse_reg_info_table.  */
  cse_reg_info_timestamp++;

  /* Clear out hash table state for this pass.  */
  CLEAR_HARD_REG_SET (hard_regs_in_table);

  /* The per-quantity values used to be initialized here, but it is
     much faster to initialize each as it is made in `make_new_qty'.  */

  for (i = 0; i < HASH_SIZE; i++)
    {
      struct table_elt *first;

      first = table[i];
      if (first != NULL)
        {
          struct table_elt *last = first;

          table[i] = NULL;

          while (last->next_same_hash != NULL)
            last = last->next_same_hash;

          /* Now relink this hash entire chain into
             the free element list.  */

          last->next_same_hash = free_element_chain;
          free_element_chain = first;
        }
    }

#ifdef HAVE_cc0
  prev_insn_cc0 = 0;
#endif
}

/* Say that register REG contains a quantity in mode MODE not in any
   register before and initialize that quantity.  */

static void
make_new_qty (unsigned int reg, enum machine_mode mode)
{
  int q;
  struct qty_table_elem *ent;
  struct reg_eqv_elem *eqv;

  gcc_assert (next_qty < max_qty);

  q = REG_QTY (reg) = next_qty++;
  ent = &qty_table[q];
  ent->first_reg = reg;
  ent->last_reg = reg;
  ent->mode = mode;
  ent->const_rtx = ent->const_insn = NULL_RTX;
  ent->comparison_code = UNKNOWN;

  eqv = &reg_eqv_table[reg];
  eqv->next = eqv->prev = -1;
}

/* Make reg NEW equivalent to reg OLD.
   OLD is not changing; NEW is.  */

static void
make_regs_eqv (unsigned int new_reg, unsigned int old_reg)
{
  unsigned int lastr, firstr;
  int q = REG_QTY (old_reg);
  struct qty_table_elem *ent;

  ent = &qty_table[q];

  /* Nothing should become eqv until it has a "non-invalid" qty number.  */
  gcc_assert (REGNO_QTY_VALID_P (old_reg));

  REG_QTY (new_reg) = q;
  firstr = ent->first_reg;
  lastr = ent->last_reg;

  /* Prefer fixed hard registers to anything.  Prefer pseudo regs to other
     hard regs.  Among pseudos, if NEW will live longer than any other reg
     of the same qty, and that is beyond the current basic block,
     make it the new canonical replacement for this qty.  */
  if (! (firstr < FIRST_PSEUDO_REGISTER && FIXED_REGNO_P (firstr))
      /* Certain fixed registers might be of the class NO_REGS.  This means
         that not only can they not be allocated by the compiler, but
         they cannot be used in substitutions or canonicalizations
         either.  */
      && (new_reg >= FIRST_PSEUDO_REGISTER || REGNO_REG_CLASS (new_reg) != NO_REGS)
      && ((new_reg < FIRST_PSEUDO_REGISTER && FIXED_REGNO_P (new_reg))
          || (new_reg >= FIRST_PSEUDO_REGISTER
              && (firstr < FIRST_PSEUDO_REGISTER
                  || (bitmap_bit_p (cse_ebb_live_out, new_reg)
                      && !bitmap_bit_p (cse_ebb_live_out, firstr))
                  || (bitmap_bit_p (cse_ebb_live_in, new_reg)
                      && !bitmap_bit_p (cse_ebb_live_in, firstr))))))
    {
      reg_eqv_table[firstr].prev = new_reg;
      reg_eqv_table[new_reg].next = firstr;
      reg_eqv_table[new_reg].prev = -1;
      ent->first_reg = new_reg;
    }
  else
    {
      /* If NEW is a hard reg (known to be non-fixed), insert at end.
         Otherwise, insert before any non-fixed hard regs that are at the
         end.  Registers of class NO_REGS cannot be used as an
         equivalent for anything.  */
      while (lastr < FIRST_PSEUDO_REGISTER && reg_eqv_table[lastr].prev >= 0
             && (REGNO_REG_CLASS (lastr) == NO_REGS || ! FIXED_REGNO_P (lastr))
             && new_reg >= FIRST_PSEUDO_REGISTER)
        lastr = reg_eqv_table[lastr].prev;
      reg_eqv_table[new_reg].next = reg_eqv_table[lastr].next;
      if (reg_eqv_table[lastr].next >= 0)
        reg_eqv_table[reg_eqv_table[lastr].next].prev = new_reg;
      else
        qty_table[q].last_reg = new_reg;
      reg_eqv_table[lastr].next = new_reg;
      reg_eqv_table[new_reg].prev = lastr;
    }
}

/* Remove REG from its equivalence class.  */

static void
delete_reg_equiv (unsigned int reg)
{
  struct qty_table_elem *ent;
  int q = REG_QTY (reg);
  int p, n;

  /* If invalid, do nothing.  */
  if (! REGNO_QTY_VALID_P (reg))
    return;

  ent = &qty_table[q];

  p = reg_eqv_table[reg].prev;
  n = reg_eqv_table[reg].next;

  if (n != -1)
    reg_eqv_table[n].prev = p;
  else
    ent->last_reg = p;
  if (p != -1)
    reg_eqv_table[p].next = n;
  else
    ent->first_reg = n;

  REG_QTY (reg) = -reg - 1;
}

/* Remove any invalid expressions from the hash table
   that refer to any of the registers contained in expression X.

   Make sure that newly inserted references to those registers
   as subexpressions will be considered valid.

   mention_regs is not called when a register itself
   is being stored in the table.

   Return 1 if we have done something that may have changed the hash code
   of X.  */

static int
mention_regs (rtx x)
{
  enum rtx_code code;
  int i, j;
  const char *fmt;
  int changed = 0;

  if (x == 0)
    return 0;

  code = GET_CODE (x);
  if (code == REG)
    {
      unsigned int regno = REGNO (x);
      unsigned int endregno = END_REGNO (x);
      unsigned int i;

      for (i = regno; i < endregno; i++)
        {
          if (REG_IN_TABLE (i) >= 0 && REG_IN_TABLE (i) != REG_TICK (i))
            remove_invalid_refs (i);

          REG_IN_TABLE (i) = REG_TICK (i);
          SUBREG_TICKED (i) = -1;
        }

      return 0;
    }

  /* If this is a SUBREG, we don't want to discard other SUBREGs of the same
     pseudo if they don't use overlapping words.  We handle only pseudos
     here for simplicity.  */
  if (code == SUBREG && REG_P (SUBREG_REG (x))
      && REGNO (SUBREG_REG (x)) >= FIRST_PSEUDO_REGISTER)
    {
      unsigned int i = REGNO (SUBREG_REG (x));

      if (REG_IN_TABLE (i) >= 0 && REG_IN_TABLE (i) != REG_TICK (i))
        {
          /* If REG_IN_TABLE (i) differs from REG_TICK (i) by one, and
             the last store to this register really stored into this
             subreg, then remove the memory of this subreg.
             Otherwise, remove any memory of the entire register and
             all its subregs from the table.  */
          if (REG_TICK (i) - REG_IN_TABLE (i) > 1
              || SUBREG_TICKED (i) != REGNO (SUBREG_REG (x)))
            remove_invalid_refs (i);
          else
            remove_invalid_subreg_refs (i, SUBREG_BYTE (x), GET_MODE (x));
        }

      REG_IN_TABLE (i) = REG_TICK (i);
      SUBREG_TICKED (i) = REGNO (SUBREG_REG (x));
      return 0;
    }

  /* If X is a comparison or a COMPARE and either operand is a register
     that does not have a quantity, give it one.  This is so that a later
     call to record_jump_equiv won't cause X to be assigned a different
     hash code and not found in the table after that call.

     It is not necessary to do this here, since rehash_using_reg can
     fix up the table later, but doing this here eliminates the need to
     call that expensive function in the most common case where the only
     use of the register is in the comparison.  */

  if (code == COMPARE || COMPARISON_P (x))
    {
      if (REG_P (XEXP (x, 0))
          && ! REGNO_QTY_VALID_P (REGNO (XEXP (x, 0))))
        if (insert_regs (XEXP (x, 0), NULL, 0))
          {
            rehash_using_reg (XEXP (x, 0));
            changed = 1;
          }

      if (REG_P (XEXP (x, 1))
          && ! REGNO_QTY_VALID_P (REGNO (XEXP (x, 1))))
        if (insert_regs (XEXP (x, 1), NULL, 0))
          {
            rehash_using_reg (XEXP (x, 1));
            changed = 1;
          }
    }

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    if (fmt[i] == 'e')
      changed |= mention_regs (XEXP (x, i));
    else if (fmt[i] == 'E')
      for (j = 0; j < XVECLEN (x, i); j++)
        changed |= mention_regs (XVECEXP (x, i, j));

  return changed;
}

/* Update the register quantities for inserting X into the hash table
   with a value equivalent to CLASSP.
   (If the class does not contain a REG, it is irrelevant.)
   If MODIFIED is nonzero, X is a destination; it is being modified.
   Note that delete_reg_equiv should be called on a register
   before insert_regs is done on that register with MODIFIED != 0.

   Nonzero value means that elements of reg_qty have changed
   so X's hash code may be different.  */

static int
insert_regs (rtx x, struct table_elt *classp, int modified)
{
  if (REG_P (x))
    {
      unsigned int regno = REGNO (x);
      int qty_valid;

      /* If REGNO is in the equivalence table already but is of the
         wrong mode for that equivalence, don't do anything here.  */

      qty_valid = REGNO_QTY_VALID_P (regno);
      if (qty_valid)
        {
          struct qty_table_elem *ent = &qty_table[REG_QTY (regno)];

          if (ent->mode != GET_MODE (x))
            return 0;
        }

      if (modified || ! qty_valid)
        {
          if (classp)
            for (classp = classp->first_same_value;
                 classp != 0;
                 classp = classp->next_same_value)
              if (REG_P (classp->exp)
                  && GET_MODE (classp->exp) == GET_MODE (x))
                {
                  unsigned c_regno = REGNO (classp->exp);

                  gcc_assert (REGNO_QTY_VALID_P (c_regno));

                  /* Suppose that 5 is hard reg and 100 and 101 are
                     pseudos.  Consider

                     (set (reg:si 100) (reg:si 5))
                     (set (reg:si 5) (reg:si 100))
                     (set (reg:di 101) (reg:di 5))

                     We would now set REG_QTY (101) = REG_QTY (5), but the
                     entry for 5 is in SImode.  When we use this later in
                     copy propagation, we get the register in wrong mode.  */
                  if (qty_table[REG_QTY (c_regno)].mode != GET_MODE (x))
                    continue;

                  make_regs_eqv (regno, c_regno);
                  return 1;
                }

          /* Mention_regs for a SUBREG checks if REG_TICK is exactly one larger
             than REG_IN_TABLE to find out if there was only a single preceding
             invalidation - for the SUBREG - or another one, which would be
             for the full register.  However, if we find here that REG_TICK
             indicates that the register is invalid, it means that it has
             been invalidated in a separate operation.  The SUBREG might be used
             now (then this is a recursive call), or we might use the full REG
             now and a SUBREG of it later.  So bump up REG_TICK so that
             mention_regs will do the right thing.  */
          if (! modified
              && REG_IN_TABLE (regno) >= 0
              && REG_TICK (regno) == REG_IN_TABLE (regno) + 1)
            REG_TICK (regno)++;
          make_new_qty (regno, GET_MODE (x));
          return 1;
        }

      return 0;
    }

  /* If X is a SUBREG, we will likely be inserting the inner register in the
     table.  If that register doesn't have an assigned quantity number at
     this point but does later, the insertion that we will be doing now will
     not be accessible because its hash code will have changed.  So assign
     a quantity number now.  */

  else if (GET_CODE (x) == SUBREG && REG_P (SUBREG_REG (x))
           && ! REGNO_QTY_VALID_P (REGNO (SUBREG_REG (x))))
    {
      insert_regs (SUBREG_REG (x), NULL, 0);
      mention_regs (x);
      return 1;
    }
  else
    return mention_regs (x);
}
\f
/* Look in or update the hash table.  */

/* Remove table element ELT from use in the table.
   HASH is its hash code, made using the HASH macro.
   It's an argument because often that is known in advance
   and we save much time not recomputing it.  */

static void
remove_from_table (struct table_elt *elt, unsigned int hash)
{
  if (elt == 0)
    return;

  /* Mark this element as removed.  See cse_insn.  */
  elt->first_same_value = 0;

  /* Remove the table element from its equivalence class.  */

  {
    struct table_elt *prev = elt->prev_same_value;
    struct table_elt *next = elt->next_same_value;

    if (next)
      next->prev_same_value = prev;

    if (prev)
      prev->next_same_value = next;
    else
      {
        struct table_elt *newfirst = next;
        while (next)
          {
            next->first_same_value = newfirst;
            next = next->next_same_value;
          }
      }
  }

  /* Remove the table element from its hash bucket.  */

  {
    struct table_elt *prev = elt->prev_same_hash;
    struct table_elt *next = elt->next_same_hash;

    if (next)
      next->prev_same_hash = prev;

    if (prev)
      prev->next_same_hash = next;
    else if (table[hash] == elt)
      table[hash] = next;
    else
      {
        /* This entry is not in the proper hash bucket.  This can happen
           when two classes were merged by `merge_equiv_classes'.  Search
           for the hash bucket that it heads.  This happens only very
           rarely, so the cost is acceptable.  */
        for (hash = 0; hash < HASH_SIZE; hash++)
          if (table[hash] == elt)
            table[hash] = next;
      }
  }

  /* Remove the table element from its related-value circular chain.  */

  if (elt->related_value != 0 && elt->related_value != elt)
    {
      struct table_elt *p = elt->related_value;

      while (p->related_value != elt)
        p = p->related_value;
      p->related_value = elt->related_value;
      if (p->related_value == p)
        p->related_value = 0;
    }

  /* Now add it to the free element chain.  */
  elt->next_same_hash = free_element_chain;
  free_element_chain = elt;
}

/* Same as above, but X is a pseudo-register.  */

static void
remove_pseudo_from_table (rtx x, unsigned int hash)
{
  struct table_elt *elt;

  /* Because a pseudo-register can be referenced in more than one
     mode, we might have to remove more than one table entry.  */
  while ((elt = lookup_for_remove (x, hash, VOIDmode)))
    remove_from_table (elt, hash);
}

/* Look up X in the hash table and return its table element,
   or 0 if X is not in the table.

   MODE is the machine-mode of X, or if X is an integer constant
   with VOIDmode then MODE is the mode with which X will be used.

   Here we are satisfied to find an expression whose tree structure
   looks like X.  */

static struct table_elt *
lookup (rtx x, unsigned int hash, enum machine_mode mode)
{
  struct table_elt *p;

  for (p = table[hash]; p; p = p->next_same_hash)
    if (mode == p->mode && ((x == p->exp && REG_P (x))
                            || exp_equiv_p (x, p->exp, !REG_P (x), false)))
      return p;

  return 0;
}

/* Like `lookup' but don't care whether the table element uses invalid regs.
   Also ignore discrepancies in the machine mode of a register.  */

static struct table_elt *
lookup_for_remove (rtx x, unsigned int hash, enum machine_mode mode)
{
  struct table_elt *p;

  if (REG_P (x))
    {
      unsigned int regno = REGNO (x);

      /* Don't check the machine mode when comparing registers;
         invalidating (REG:SI 0) also invalidates (REG:DF 0).  */
      for (p = table[hash]; p; p = p->next_same_hash)
        if (REG_P (p->exp)
            && REGNO (p->exp) == regno)
          return p;
    }
  else
    {
      for (p = table[hash]; p; p = p->next_same_hash)
        if (mode == p->mode
            && (x == p->exp || exp_equiv_p (x, p->exp, 0, false)))
          return p;
    }

  return 0;
}

/* Look for an expression equivalent to X and with code CODE.
   If one is found, return that expression.  */

static rtx
lookup_as_function (rtx x, enum rtx_code code)
{
  struct table_elt *p
    = lookup (x, SAFE_HASH (x, VOIDmode), GET_MODE (x));

  if (p == 0)
    return 0;

  for (p = p->first_same_value; p; p = p->next_same_value)
    if (GET_CODE (p->exp) == code
        /* Make sure this is a valid entry in the table.  */
        && exp_equiv_p (p->exp, p->exp, 1, false))
      return p->exp;

  return 0;
}

/* Insert X in the hash table, assuming HASH is its hash code
   and CLASSP is an element of the class it should go in
   (or 0 if a new class should be made).
   It is inserted at the proper position to keep the class in
   the order cheapest first.

   MODE is the machine-mode of X, or if X is an integer constant
   with VOIDmode then MODE is the mode with which X will be used.

   For elements of equal cheapness, the most recent one
   goes in front, except that the first element in the list
   remains first unless a cheaper element is added.  The order of
   pseudo-registers does not matter, as canon_reg will be called to
   find the cheapest when a register is retrieved from the table.

   The in_memory field in the hash table element is set to 0.
   The caller must set it nonzero if appropriate.

   You should call insert_regs (X, CLASSP, MODIFY) before calling here,
   and if insert_regs returns a nonzero value
   you must then recompute its hash code before calling here.

   If necessary, update table showing constant values of quantities.  */

#define CHEAPER(X, Y) \
 (preferable ((X)->cost, (X)->regcost, (Y)->cost, (Y)->regcost) < 0)

static struct table_elt *
insert (rtx x, struct table_elt *classp, unsigned int hash, enum machine_mode mode)
{
  struct table_elt *elt;

  /* If X is a register and we haven't made a quantity for it,
     something is wrong.  */
  gcc_assert (!REG_P (x) || REGNO_QTY_VALID_P (REGNO (x)));

  /* If X is a hard register, show it is being put in the table.  */
  if (REG_P (x) && REGNO (x) < FIRST_PSEUDO_REGISTER)
    add_to_hard_reg_set (&hard_regs_in_table, GET_MODE (x), REGNO (x));

  /* Put an element for X into the right hash bucket.  */

  elt = free_element_chain;
  if (elt)
    free_element_chain = elt->next_same_hash;
  else
    elt = XNEW (struct table_elt);

  elt->exp = x;
  elt->canon_exp = NULL_RTX;
  elt->cost = COST (x);
  elt->regcost = approx_reg_cost (x);
  elt->next_same_value = 0;
  elt->prev_same_value = 0;
  elt->next_same_hash = table[hash];
  elt->prev_same_hash = 0;
  elt->related_value = 0;
  elt->in_memory = 0;
  elt->mode = mode;
  elt->is_const = (CONSTANT_P (x) || fixed_base_plus_p (x));

  if (table[hash])
    table[hash]->prev_same_hash = elt;
  table[hash] = elt;

  /* Put it into the proper value-class.  */
  if (classp)
    {
      classp = classp->first_same_value;
      if (CHEAPER (elt, classp))
        /* Insert at the head of the class.  */
        {
          struct table_elt *p;
          elt->next_same_value = classp;
          classp->prev_same_value = elt;
          elt->first_same_value = elt;

          for (p = classp; p; p = p->next_same_value)
            p->first_same_value = elt;
        }
      else
        {
          /* Insert not at head of the class.  */
          /* Put it after the last element cheaper than X.  */
          struct table_elt *p, *next;

          for (p = classp; (next = p->next_same_value) && CHEAPER (next, elt);
               p = next);

          /* Put it after P and before NEXT.  */
          elt->next_same_value = next;
          if (next)
            next->prev_same_value = elt;

          elt->prev_same_value = p;
          p->next_same_value = elt;
          elt->first_same_value = classp;
        }
    }
  else
    elt->first_same_value = elt;

  /* If this is a constant being set equivalent to a register or a register
     being set equivalent to a constant, note the constant equivalence.

     If this is a constant, it cannot be equivalent to a different constant,
     and a constant is the only thing that can be cheaper than a register.  So
     we know the register is the head of the class (before the constant was
     inserted).

     If this is a register that is not already known equivalent to a
     constant, we must check the entire class.

     If this is a register that is already known equivalent to an insn,
     update the qtys `const_insn' to show that `this_insn' is the latest
     insn making that quantity equivalent to the constant.  */

  if (elt->is_const && classp && REG_P (classp->exp)
      && !REG_P (x))
    {
      int exp_q = REG_QTY (REGNO (classp->exp));
      struct qty_table_elem *exp_ent = &qty_table[exp_q];

      exp_ent->const_rtx = gen_lowpart (exp_ent->mode, x);
      exp_ent->const_insn = this_insn;
    }

  else if (REG_P (x)
           && classp
           && ! qty_table[REG_QTY (REGNO (x))].const_rtx
           && ! elt->is_const)
    {
      struct table_elt *p;

      for (p = classp; p != 0; p = p->next_same_value)
        {
          if (p->is_const && !REG_P (p->exp))
            {
              int x_q = REG_QTY (REGNO (x));
              struct qty_table_elem *x_ent = &qty_table[x_q];

              x_ent->const_rtx
                = gen_lowpart (GET_MODE (x), p->exp);
              x_ent->const_insn = this_insn;
              break;
            }
        }
    }

  else if (REG_P (x)
           && qty_table[REG_QTY (REGNO (x))].const_rtx
           && GET_MODE (x) == qty_table[REG_QTY (REGNO (x))].mode)
    qty_table[REG_QTY (REGNO (x))].const_insn = this_insn;

  /* If this is a constant with symbolic value,
     and it has a term with an explicit integer value,
     link it up with related expressions.  */
  if (GET_CODE (x) == CONST)
    {
      rtx subexp = get_related_value (x);
      unsigned subhash;
      struct table_elt *subelt, *subelt_prev;

      if (subexp != 0)
        {
          /* Get the integer-free subexpression in the hash table.  */
          subhash = SAFE_HASH (subexp, mode);
          subelt = lookup (subexp, subhash, mode);
          if (subelt == 0)
            subelt = insert (subexp, NULL, subhash, mode);
          /* Initialize SUBELT's circular chain if it has none.  */
          if (subelt->related_value == 0)
            subelt->related_value = subelt;
          /* Find the element in the circular chain that precedes SUBELT.  */
          subelt_prev = subelt;
          while (subelt_prev->related_value != subelt)
            subelt_prev = subelt_prev->related_value;
          /* Put new ELT into SUBELT's circular chain just before SUBELT.
             This way the element that follows SUBELT is the oldest one.  */
          elt->related_value = subelt_prev->related_value;
          subelt_prev->related_value = elt;
        }
    }

  return elt;
}
\f
/* Given two equivalence classes, CLASS1 and CLASS2, put all the entries from
   CLASS2 into CLASS1.  This is done when we have reached an insn which makes
   the two classes equivalent.

   CLASS1 will be the surviving class; CLASS2 should not be used after this
   call.

   Any invalid entries in CLASS2 will not be copied.  */

static void
merge_equiv_classes (struct table_elt *class1, struct table_elt *class2)
{
  struct table_elt *elt, *next, *new_elt;

  /* Ensure we start with the head of the classes.  */
  class1 = class1->first_same_value;
  class2 = class2->first_same_value;

  /* If they were already equal, forget it.  */
  if (class1 == class2)
    return;

  for (elt = class2; elt; elt = next)
    {
      unsigned int hash;
      rtx exp = elt->exp;
      enum machine_mode mode = elt->mode;

      next = elt->next_same_value;

      /* Remove old entry, make a new one in CLASS1's class.
         Don't do this for invalid entries as we cannot find their
         hash code (it also isn't necessary).  */
      if (REG_P (exp) || exp_equiv_p (exp, exp, 1, false))
        {
          bool need_rehash = false;

          hash_arg_in_memory = 0;
          hash = HASH (exp, mode);

          if (REG_P (exp))
            {
              need_rehash = REGNO_QTY_VALID_P (REGNO (exp));
              delete_reg_equiv (REGNO (exp));
            }

          if (REG_P (exp) && REGNO (exp) >= FIRST_PSEUDO_REGISTER)
            remove_pseudo_from_table (exp, hash);
          else
            remove_from_table (elt, hash);

          if (insert_regs (exp, class1, 0) || need_rehash)
            {
              rehash_using_reg (exp);
              hash = HASH (exp, mode);
            }
          new_elt = insert (exp, class1, hash, mode);
          new_elt->in_memory = hash_arg_in_memory;
        }
    }
}
\f
/* Flush the entire hash table.  */

static void
flush_hash_table (void)
{
  int i;
  struct table_elt *p;

  for (i = 0; i < HASH_SIZE; i++)
    for (p = table[i]; p; p = table[i])
      {
        /* Note that invalidate can remove elements
           after P in the current hash chain.  */
        if (REG_P (p->exp))
          invalidate (p->exp, VOIDmode);
        else
          remove_from_table (p, i);
      }
}
\f
/* Function called for each rtx to check whether true dependence exist.  */
struct check_dependence_data
{
  enum machine_mode mode;
  rtx exp;
  rtx addr;
};

static int
check_dependence (rtx *x, void *data)
{
  struct check_dependence_data *d = (struct check_dependence_data *) data;
  if (*x && MEM_P (*x))
    return canon_true_dependence (d->exp, d->mode, d->addr, *x,
                                  cse_rtx_varies_p);
  else
    return 0;
}
\f
/* Remove from the hash table, or mark as invalid, all expressions whose
   values could be altered by storing in X.  X is a register, a subreg, or
   a memory reference with nonvarying address (because, when a memory
   reference with a varying address is stored in, all memory references are
   removed by invalidate_memory so specific invalidation is superfluous).
   FULL_MODE, if not VOIDmode, indicates that this much should be
   invalidated instead of just the amount indicated by the mode of X.  This
   is only used for bitfield stores into memory.

   A nonvarying address may be just a register or just a symbol reference,
   or it may be either of those plus a numeric offset.  */

static void
invalidate (rtx x, enum machine_mode full_mode)
{
  int i;
  struct table_elt *p;
  rtx addr;

  switch (GET_CODE (x))
    {
    case REG:
      {
        /* If X is a register, dependencies on its contents are recorded
           through the qty number mechanism.  Just change the qty number of
           the register, mark it as invalid for expressions that refer to it,
           and remove it itself.  */
        unsigned int regno = REGNO (x);
        unsigned int hash = HASH (x, GET_MODE (x));

        /* Remove REGNO from any quantity list it might be on and indicate
           that its value might have changed.  If it is a pseudo, remove its
           entry from the hash table.

           For a hard register, we do the first two actions above for any
           additional hard registers corresponding to X.  Then, if any of these
           registers are in the table, we must remove any REG entries that
           overlap these registers.  */

        delete_reg_equiv (regno);
        REG_TICK (regno)++;
        SUBREG_TICKED (regno) = -1;

        if (regno >= FIRST_PSEUDO_REGISTER)
          remove_pseudo_from_table (x, hash);
        else
          {
            HOST_WIDE_INT in_table
              = TEST_HARD_REG_BIT (hard_regs_in_table, regno);
            unsigned int endregno = END_HARD_REGNO (x);
            unsigned int tregno, tendregno, rn;
            struct table_elt *p, *next;

            CLEAR_HARD_REG_BIT (hard_regs_in_table, regno);

            for (rn = regno + 1; rn < endregno; rn++)
              {
                in_table |= TEST_HARD_REG_BIT (hard_regs_in_table, rn);
                CLEAR_HARD_REG_BIT (hard_regs_in_table, rn);
                delete_reg_equiv (rn);
                REG_TICK (rn)++;
                SUBREG_TICKED (rn) = -1;
              }

            if (in_table)
              for (hash = 0; hash < HASH_SIZE; hash++)
                for (p = table[hash]; p; p = next)
                  {
                    next = p->next_same_hash;

                    if (!REG_P (p->exp)
                        || REGNO (p->exp) >= FIRST_PSEUDO_REGISTER)
                      continue;

                    tregno = REGNO (p->exp);
                    tendregno = END_HARD_REGNO (p->exp);
                    if (tendregno > regno && tregno < endregno)
                      remove_from_table (p, hash);
                  }
          }
      }
      return;

    case SUBREG:
      invalidate (SUBREG_REG (x), VOIDmode);
      return;

    case PARALLEL:
      for (i = XVECLEN (x, 0) - 1; i >= 0; --i)
        invalidate (XVECEXP (x, 0, i), VOIDmode);
      return;

    case EXPR_LIST:
      /* This is part of a disjoint return value; extract the location in
         question ignoring the offset.  */
      invalidate (XEXP (x, 0), VOIDmode);
      return;

    case MEM:
      addr = canon_rtx (get_addr (XEXP (x, 0)));
      /* Calculate the canonical version of X here so that
         true_dependence doesn't generate new RTL for X on each call.  */
      x = canon_rtx (x);

      /* Remove all hash table elements that refer to overlapping pieces of
         memory.  */
      if (full_mode == VOIDmode)
        full_mode = GET_MODE (x);

      for (i = 0; i < HASH_SIZE; i++)
        {
          struct table_elt *next;

          for (p = table[i]; p; p = next)
            {
              next = p->next_same_hash;
              if (p->in_memory)
                {
                  struct check_dependence_data d;

                  /* Just canonicalize the expression once;
                     otherwise each time we call invalidate
                     true_dependence will canonicalize the
                     expression again.  */
                  if (!p->canon_exp)
                    p->canon_exp = canon_rtx (p->exp);
                  d.exp = x;
                  d.addr = addr;
                  d.mode = full_mode;
                  if (for_each_rtx (&p->canon_exp, check_dependence, &d))
                    remove_from_table (p, i);
                }
            }
        }
      return;

    default:
      gcc_unreachable ();
    }
}
\f
/* Remove all expressions that refer to register REGNO,
   since they are already invalid, and we are about to
   mark that register valid again and don't want the old
   expressions to reappear as valid.  */

static void
remove_invalid_refs (unsigned int regno)
{
  unsigned int i;
  struct table_elt *p, *next;

  for (i = 0; i < HASH_SIZE; i++)
    for (p = table[i]; p; p = next)
      {
        next = p->next_same_hash;
        if (!REG_P (p->exp)
            && refers_to_regno_p (regno, regno + 1, p->exp, (rtx *) 0))
          remove_from_table (p, i);
      }
}

/* Likewise for a subreg with subreg_reg REGNO, subreg_byte OFFSET,
   and mode MODE.  */
static void
remove_invalid_subreg_refs (unsigned int regno, unsigned int offset,
                            enum machine_mode mode)
{
  unsigned int i;
  struct table_elt *p, *next;
  unsigned int end = offset + (GET_MODE_SIZE (mode) - 1);

  for (i = 0; i < HASH_SIZE; i++)
    for (p = table[i]; p; p = next)
      {
        rtx exp = p->exp;
        next = p->next_same_hash;

        if (!REG_P (exp)
            && (GET_CODE (exp) != SUBREG
                || !REG_P (SUBREG_REG (exp))
                || REGNO (SUBREG_REG (exp)) != regno
                || (((SUBREG_BYTE (exp)
                      + (GET_MODE_SIZE (GET_MODE (exp)) - 1)) >= offset)
                    && SUBREG_BYTE (exp) <= end))
            && refers_to_regno_p (regno, regno + 1, p->exp, (rtx *) 0))
          remove_from_table (p, i);
      }
}
\f
/* Recompute the hash codes of any valid entries in the hash table that
   reference X, if X is a register, or SUBREG_REG (X) if X is a SUBREG.

   This is called when we make a jump equivalence.  */

static void
rehash_using_reg (rtx x)
{
  unsigned int i;
  struct table_elt *p, *next;
  unsigned hash;

  if (GET_CODE (x) == SUBREG)
    x = SUBREG_REG (x);

  /* If X is not a register or if the register is known not to be in any
     valid entries in the table, we have no work to do.  */

  if (!REG_P (x)
      || REG_IN_TABLE (REGNO (x)) < 0
      || REG_IN_TABLE (REGNO (x)) != REG_TICK (REGNO (x)))
    return;

  /* Scan all hash chains looking for valid entries that mention X.
     If we find one and it is in the wrong hash chain, move it.  */

  for (i = 0; i < HASH_SIZE; i++)
    for (p = table[i]; p; p = next)
      {
        next = p->next_same_hash;
        if (reg_mentioned_p (x, p->exp)
            && exp_equiv_p (p->exp, p->exp, 1, false)
            && i != (hash = SAFE_HASH (p->exp, p->mode)))
          {
            if (p->next_same_hash)
              p->next_same_hash->prev_same_hash = p->prev_same_hash;

            if (p->prev_same_hash)
              p->prev_same_hash->next_same_hash = p->next_same_hash;
            else
              table[i] = p->next_same_hash;

            p->next_same_hash = table[hash];
            p->prev_same_hash = 0;
            if (table[hash])
              table[hash]->prev_same_hash = p;
            table[hash] = p;
          }
      }
}
\f
/* Remove from the hash table any expression that is a call-clobbered
   register.  Also update their TICK values.  */

static void
invalidate_for_call (void)
{
  unsigned int regno, endregno;
  unsigned int i;
  unsigned hash;
  struct table_elt *p, *next;
  int in_table = 0;

  /* Go through all the hard registers.  For each that is clobbered in
     a CALL_INSN, remove the register from quantity chains and update
     reg_tick if defined.  Also see if any of these registers is currently
     in the table.  */

  for (regno = 0; regno < FIRST_PSEUDO_REGISTER; regno++)
    if (TEST_HARD_REG_BIT (regs_invalidated_by_call, regno))
      {
        delete_reg_equiv (regno);
        if (REG_TICK (regno) >= 0)
          {
            REG_TICK (regno)++;
            SUBREG_TICKED (regno) = -1;
          }

        in_table |= (TEST_HARD_REG_BIT (hard_regs_in_table, regno) != 0);
      }

  /* In the case where we have no call-clobbered hard registers in the
     table, we are done.  Otherwise, scan the table and remove any
     entry that overlaps a call-clobbered register.  */

  if (in_table)
    for (hash = 0; hash < HASH_SIZE; hash++)
      for (p = table[hash]; p; p = next)
        {
          next = p->next_same_hash;

          if (!REG_P (p->exp)
              || REGNO (p->exp) >= FIRST_PSEUDO_REGISTER)
            continue;

          regno = REGNO (p->exp);
          endregno = END_HARD_REGNO (p->exp);

          for (i = regno; i < endregno; i++)
            if (TEST_HARD_REG_BIT (regs_invalidated_by_call, i))
              {
                remove_from_table (p, hash);
                break;
              }
        }
}
\f
/* Given an expression X of type CONST,
   and ELT which is its table entry (or 0 if it
   is not in the hash table),
   return an alternate expression for X as a register plus integer.
   If none can be found, return 0.  */

static rtx
use_related_value (rtx x, struct table_elt *elt)
{
  struct table_elt *relt = 0;
  struct table_elt *p, *q;
  HOST_WIDE_INT offset;

  /* First, is there anything related known?
     If we have a table element, we can tell from that.
     Otherwise, must look it up.  */

  if (elt != 0 && elt->related_value != 0)
    relt = elt;
  else if (elt == 0 && GET_CODE (x) == CONST)
    {
      rtx subexp = get_related_value (x);
      if (subexp != 0)
        relt = lookup (subexp,
                       SAFE_HASH (subexp, GET_MODE (subexp)),
                       GET_MODE (subexp));
    }

  if (relt == 0)
    return 0;

  /* Search all related table entries for one that has an
     equivalent register.  */

  p = relt;
  while (1)
    {
      /* This loop is strange in that it is executed in two different cases.
         The first is when X is already in the table.  Then it is searching
         the RELATED_VALUE list of X's class (RELT).  The second case is when
         X is not in the table.  Then RELT points to a class for the related
         value.

         Ensure that, whatever case we are in, that we ignore classes that have
         the same value as X.  */

      if (rtx_equal_p (x, p->exp))
        q = 0;
      else
        for (q = p->first_same_value; q; q = q->next_same_value)
          if (REG_P (q->exp))
            break;

      if (q)
        break;

      p = p->related_value;

      /* We went all the way around, so there is nothing to be found.
         Alternatively, perhaps RELT was in the table for some other reason
         and it has no related values recorded.  */
      if (p == relt || p == 0)
        break;
    }

  if (q == 0)
    return 0;

  offset = (get_integer_term (x) - get_integer_term (p->exp));
  /* Note: OFFSET may be 0 if P->xexp and X are related by commutativity.  */
  return plus_constant (q->exp, offset);
}
\f

/* Hash a string.  Just add its bytes up.  */
static inline unsigned
hash_rtx_string (const char *ps)
{
  unsigned hash = 0;
  const unsigned char *p = (const unsigned char *) ps;

  if (p)
    while (*p)
      hash += *p++;

  return hash;
}

/* Same as hash_rtx, but call CB on each rtx if it is not NULL.  
   When the callback returns true, we continue with the new rtx.  */

unsigned
hash_rtx_cb (const_rtx x, enum machine_mode mode,
             int *do_not_record_p, int *hash_arg_in_memory_p,
             bool have_reg_qty, hash_rtx_callback_function cb)
{
  int i, j;
  unsigned hash = 0;
  enum rtx_code code;
  const char *fmt;
  enum machine_mode newmode;
  rtx newx;

  /* Used to turn recursion into iteration.  We can't rely on GCC's
     tail-recursion elimination since we need to keep accumulating values
     in HASH.  */
 repeat:
  if (x == 0)
    return hash;

  /* Invoke the callback first.  */
  if (cb != NULL 
      && ((*cb) (x, mode, &newx, &newmode)))
    {
      hash += hash_rtx_cb (newx, newmode, do_not_record_p,
                           hash_arg_in_memory_p, have_reg_qty, cb);
      return hash;
    }

  code = GET_CODE (x);
  switch (code)
    {
    case REG:
      {
        unsigned int regno = REGNO (x);

        if (do_not_record_p && !reload_completed)
          {
            /* On some machines, we can't record any non-fixed hard register,
               because extending its life will cause reload problems.  We
               consider ap, fp, sp, gp to be fixed for this purpose.

               We also consider CCmode registers to be fixed for this purpose;
               failure to do so leads to failure to simplify 0<100 type of
               conditionals.

               On all machines, we can't record any global registers.
               Nor should we record any register that is in a small
               class, as defined by CLASS_LIKELY_SPILLED_P.  */
            bool record;

            if (regno >= FIRST_PSEUDO_REGISTER)
              record = true;
            else if (x == frame_pointer_rtx
                     || x == hard_frame_pointer_rtx
                     || x == arg_pointer_rtx
                     || x == stack_pointer_rtx
                     || x == pic_offset_table_rtx)
              record = true;
            else if (global_regs[regno])
              record = false;
            else if (fixed_regs[regno])
              record = true;
            else if (GET_MODE_CLASS (GET_MODE (x)) == MODE_CC)
              record = true;
            else if (SMALL_REGISTER_CLASSES)
              record = false;
            else if (CLASS_LIKELY_SPILLED_P (REGNO_REG_CLASS (regno)))
              record = false;
            else
              record = true;

            if (!record)
              {
                *do_not_record_p = 1;
                return 0;
              }
          }

        hash += ((unsigned int) REG << 7);
        hash += (have_reg_qty ? (unsigned) REG_QTY (regno) : regno);
        return hash;
      }

    /* We handle SUBREG of a REG specially because the underlying
       reg changes its hash value with every value change; we don't
       want to have to forget unrelated subregs when one subreg changes.  */
    case SUBREG:
      {
        if (REG_P (SUBREG_REG (x)))
          {
            hash += (((unsigned int) SUBREG << 7)
                     + REGNO (SUBREG_REG (x))
                     + (SUBREG_BYTE (x) / UNITS_PER_WORD));
            return hash;
          }
        break;
      }

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

    case CONST_DOUBLE:
      /* This is like the general case, except that it only counts
         the integers representing the constant.  */
      hash += (unsigned int) code + (unsigned int) GET_MODE (x);
      if (GET_MODE (x) != VOIDmode)
        hash += real_hash (CONST_DOUBLE_REAL_VALUE (x));
      else
        hash += ((unsigned int) CONST_DOUBLE_LOW (x)
                 + (unsigned int) CONST_DOUBLE_HIGH (x));
      return hash;

    case CONST_FIXED:
      hash += (unsigned int) code + (unsigned int) GET_MODE (x);
      hash += fixed_hash (CONST_FIXED_VALUE (x));
      return hash;

    case CONST_VECTOR:
      {
        int units;
        rtx elt;

        units = CONST_VECTOR_NUNITS (x);

        for (i = 0; i < units; ++i)
          {
            elt = CONST_VECTOR_ELT (x, i);
            hash += hash_rtx_cb (elt, GET_MODE (elt),
                                 do_not_record_p, hash_arg_in_memory_p, 
                                 have_reg_qty, cb);
          }

        return hash;
      }

      /* Assume there is only one rtx object for any given label.  */
    case LABEL_REF:
      /* We don't hash on the address of the CODE_LABEL to avoid bootstrap
         differences and differences between each stage's debugging dumps.  */
         hash += (((unsigned int) LABEL_REF << 7)
                  + CODE_LABEL_NUMBER (XEXP (x, 0)));
      return hash;

    case SYMBOL_REF:
      {
        /* Don't hash on the symbol's address to avoid bootstrap differences.
           Different hash values may cause expressions to be recorded in
           different orders and thus different registers to be used in the
           final assembler.  This also avoids differences in the dump files
           between various stages.  */
        unsigned int h = 0;
        const unsigned char *p = (const unsigned char *) XSTR (x, 0);

        while (*p)
          h += (h << 7) + *p++; /* ??? revisit */

        hash += ((unsigned int) SYMBOL_REF << 7) + h;
        return hash;
      }

    case MEM:
      /* We don't record if marked volatile or if BLKmode since we don't
         know the size of the move.  */
      if (do_not_record_p && (MEM_VOLATILE_P (x) || GET_MODE (x) == BLKmode))
        {
          *do_not_record_p = 1;
          return 0;
        }
      if (hash_arg_in_memory_p && !MEM_READONLY_P (x))
        *hash_arg_in_memory_p = 1;

      /* Now that we have already found this special case,
         might as well speed it up as much as possible.  */
      hash += (unsigned) MEM;
      x = XEXP (x, 0);
      goto repeat;

    case USE:
      /* A USE that mentions non-volatile memory needs special
         handling since the MEM may be BLKmode which normally
         prevents an entry from being made.  Pure calls are
         marked by a USE which mentions BLKmode memory.
         See calls.c:emit_call_1.  */
      if (MEM_P (XEXP (x, 0))
          && ! MEM_VOLATILE_P (XEXP (x, 0)))
        {
          hash += (unsigned) USE;
          x = XEXP (x, 0);

          if (hash_arg_in_memory_p && !MEM_READONLY_P (x))
            *hash_arg_in_memory_p = 1;

          /* Now that we have already found this special case,
             might as well speed it up as much as possible.  */
          hash += (unsigned) MEM;
          x = XEXP (x, 0);
          goto repeat;
        }
      break;

    case PRE_DEC:
    case PRE_INC:
    case POST_DEC:
    case POST_INC:
    case PRE_MODIFY:
    case POST_MODIFY:
    case PC:
    case CC0:
    case CALL:
    case UNSPEC_VOLATILE:
      if (do_not_record_p) {
        *do_not_record_p = 1;
        return 0;
      }
      else
        return hash;
      break;

    case ASM_OPERANDS:
      if (do_not_record_p && MEM_VOLATILE_P (x))
        {
          *do_not_record_p = 1;
          return 0;
        }
      else
        {
          /* We don't want to take the filename and line into account.  */
          hash += (unsigned) code + (unsigned) GET_MODE (x)
            + hash_rtx_string (ASM_OPERANDS_TEMPLATE (x))
            + hash_rtx_string (ASM_OPERANDS_OUTPUT_CONSTRAINT (x))
            + (unsigned) ASM_OPERANDS_OUTPUT_IDX (x);

          if (ASM_OPERANDS_INPUT_LENGTH (x))
            {
              for (i = 1; i < ASM_OPERANDS_INPUT_LENGTH (x); i++)
                {
                  hash += (hash_rtx_cb (ASM_OPERANDS_INPUT (x, i),
                                        GET_MODE (ASM_OPERANDS_INPUT (x, i)),
                                        do_not_record_p, hash_arg_in_memory_p,
                                        have_reg_qty, cb)
                           + hash_rtx_string
                           (ASM_OPERANDS_INPUT_CONSTRAINT (x, i)));
                }

              hash += hash_rtx_string (ASM_OPERANDS_INPUT_CONSTRAINT (x, 0));
              x = ASM_OPERANDS_INPUT (x, 0);
              mode = GET_MODE (x);
              goto repeat;
            }

          return hash;
        }
      break;

    default:
      break;
    }

  i = GET_RTX_LENGTH (code) - 1;
  hash += (unsigned) code + (unsigned) GET_MODE (x);
  fmt = GET_RTX_FORMAT (code);
  for (; i >= 0; i--)
    {
      switch (fmt[i])
        {
        case 'e':
          /* 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 = XEXP (x, i);
              goto repeat;
            }
          
          hash += hash_rtx_cb (XEXP (x, i), 0, do_not_record_p,
                               hash_arg_in_memory_p,
                               have_reg_qty, cb);
          break;

        case 'E':
          for (j = 0; j < XVECLEN (x, i); j++)
            hash += hash_rtx_cb (XVECEXP (x, i, j), 0, do_not_record_p,
                                 hash_arg_in_memory_p,
                                 have_reg_qty, cb);
          break;

        case 's':
          hash += hash_rtx_string (XSTR (x, i));
          break;

        case 'i':
          hash += (unsigned int) XINT (x, i);
          break;

        case '0': case 't':
          /* Unused.  */
          break;

        default:
          gcc_unreachable ();
        }
    }

  return hash;
}

/* Hash an rtx.  We are careful to make sure the value is never negative.
   Equivalent registers hash identically.
   MODE is used in hashing for CONST_INTs only;
   otherwise the mode of X is used.

   Store 1 in DO_NOT_RECORD_P if any subexpression is volatile.

   If HASH_ARG_IN_MEMORY_P is not NULL, store 1 in it if X contains
   a MEM rtx which does not have the RTX_UNCHANGING_P bit set.

   Note that cse_insn knows that the hash code of a MEM expression
   is just (int) MEM plus the hash code of the address.  */

unsigned
hash_rtx (const_rtx x, enum machine_mode mode, int *do_not_record_p,
          int *hash_arg_in_memory_p, bool have_reg_qty)
{
  return hash_rtx_cb (x, mode, do_not_record_p,
                      hash_arg_in_memory_p, have_reg_qty, NULL);
}

/* Hash an rtx X for cse via hash_rtx.
   Stores 1 in do_not_record if any subexpression is volatile.
   Stores 1 in hash_arg_in_memory if X contains a mem rtx which
   does not have the RTX_UNCHANGING_P bit set.  */

static inline unsigned
canon_hash (rtx x, enum machine_mode mode)
{
  return hash_rtx (x, mode, &do_not_record, &hash_arg_in_memory, true);
}

/* Like canon_hash but with no side effects, i.e. do_not_record
   and hash_arg_in_memory are not changed.  */

static inline unsigned
safe_hash (rtx x, enum machine_mode mode)
{
  int dummy_do_not_record;
  return hash_rtx (x, mode, &dummy_do_not_record, NULL, true);
}
\f
/* Return 1 iff X and Y would canonicalize into the same thing,
   without actually constructing the canonicalization of either one.
   If VALIDATE is nonzero,
   we assume X is an expression being processed from the rtl
   and Y was found in the hash table.  We check register refs
   in Y for being marked as valid.

   If FOR_GCSE is true, we compare X and Y for equivalence for GCSE.  */

int
exp_equiv_p (const_rtx x, const_rtx y, int validate, bool for_gcse)
{
  int i, j;
  enum rtx_code code;
  const char *fmt;

  /* Note: it is incorrect to assume an expression is equivalent to itself
     if VALIDATE is nonzero.  */
  if (x == y && !validate)
    return 1;

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

  code = GET_CODE (x);
  if (code != GET_CODE (y))
    return 0;

  /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent.  */
  if (GET_MODE (x) != GET_MODE (y))
    return 0;

  switch (code)
    {
    case PC:
    case CC0:
    case CONST_INT:
    case CONST_DOUBLE:
    case CONST_FIXED:
      return x == y;

    case LABEL_REF:
      return XEXP (x, 0) == XEXP (y, 0);

    case SYMBOL_REF:
      return XSTR (x, 0) == XSTR (y, 0);

    case REG:
      if (for_gcse)
        return REGNO (x) == REGNO (y);
      else
        {
          unsigned int regno = REGNO (y);
          unsigned int i;
          unsigned int endregno = END_REGNO (y);

          /* If the quantities are not the same, the expressions are not
             equivalent.  If there are and we are not to validate, they
             are equivalent.  Otherwise, ensure all regs are up-to-date.  */

          if (REG_QTY (REGNO (x)) != REG_QTY (regno))
            return 0;

          if (! validate)
            return 1;

          for (i = regno; i < endregno; i++)
            if (REG_IN_TABLE (i) != REG_TICK (i))
              return 0;

          return 1;
        }

    case MEM:
      if (for_gcse)
        {
          /* A volatile mem should not be considered equivalent to any
             other.  */
          if (MEM_VOLATILE_P (x) || MEM_VOLATILE_P (y))
            return 0;

          /* Can't merge two expressions in different alias sets, since we
             can decide that the expression is transparent in a block when
             it isn't, due to it being set with the different alias set.

             Also, can't merge two expressions with different MEM_ATTRS.
             They could e.g. be two different entities allocated into the
             same space on the stack (see e.g. PR25130).  In that case, the
             MEM addresses can be the same, even though the two MEMs are
             absolutely not equivalent.  
   
             But because really all MEM attributes should be the same for
             equivalent MEMs, we just use the invariant that MEMs that have
             the same attributes share the same mem_attrs data structure.  */
          if (MEM_ATTRS (x) != MEM_ATTRS (y))
            return 0;
        }
      break;

    /*  For commutative operations, check both orders.  */
    case PLUS:
    case MULT:
    case AND:
    case IOR:
    case XOR:
    case NE:
    case EQ:
      return ((exp_equiv_p (XEXP (x, 0), XEXP (y, 0),
                             validate, for_gcse)
               && exp_equiv_p (XEXP (x, 1), XEXP (y, 1),
                                validate, for_gcse))
              || (exp_equiv_p (XEXP (x, 0), XEXP (y, 1),
                                validate, for_gcse)
                  && exp_equiv_p (XEXP (x, 1), XEXP (y, 0),
                                   validate, for_gcse)));

    case ASM_OPERANDS:
      /* We don't use the generic code below because we want to
         disregard filename and line numbers.  */

      /* A volatile asm isn't equivalent to any other.  */
      if (MEM_VOLATILE_P (x) || MEM_VOLATILE_P (y))
        return 0;

      if (GET_MODE (x) != GET_MODE (y)
          || strcmp (ASM_OPERANDS_TEMPLATE (x), ASM_OPERANDS_TEMPLATE (y))
          || strcmp (ASM_OPERANDS_OUTPUT_CONSTRAINT (x),
                     ASM_OPERANDS_OUTPUT_CONSTRAINT (y))
          || ASM_OPERANDS_OUTPUT_IDX (x) != ASM_OPERANDS_OUTPUT_IDX (y)
          || ASM_OPERANDS_INPUT_LENGTH (x) != ASM_OPERANDS_INPUT_LENGTH (y))
        return 0;

      if (ASM_OPERANDS_INPUT_LENGTH (x))
        {
          for (i = ASM_OPERANDS_INPUT_LENGTH (x) - 1; i >= 0; i--)
            if (! exp_equiv_p (ASM_OPERANDS_INPUT (x, i),
                               ASM_OPERANDS_INPUT (y, i),
                               validate, for_gcse)
                || strcmp (ASM_OPERANDS_INPUT_CONSTRAINT (x, i),
                           ASM_OPERANDS_INPUT_CONSTRAINT (y, i)))
              return 0;
        }

      return 1;

    default:
      break;
    }

  /* Compare the elements.  If any pair of corresponding elements
     fail to match, return 0 for the whole thing.  */

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      switch (fmt[i])
        {
        case 'e':
          if (! exp_equiv_p (XEXP (x, i), XEXP (y, i),
                              validate, for_gcse))
            return 0;
          break;

        case 'E':
          if (XVECLEN (x, i) != XVECLEN (y, i))
            return 0;
          for (j = 0; j < XVECLEN (x, i); j++)
            if (! exp_equiv_p (XVECEXP (x, i, j), XVECEXP (y, i, j),
                                validate, for_gcse))
              return 0;
          break;

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

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

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

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

        default:
          gcc_unreachable ();
        }
    }

  return 1;
}
\f
/* Return 1 if X has a value that can vary even between two
   executions of the program.  0 means X can be compared reliably
   against certain constants or near-constants.  */

static bool
cse_rtx_varies_p (const_rtx x, bool from_alias)
{
  /* We need not check for X and the equivalence class being of the same
     mode because if X is equivalent to a constant in some mode, it
     doesn't vary in any mode.  */

  if (REG_P (x)
      && REGNO_QTY_VALID_P (REGNO (x)))
    {
      int x_q = REG_QTY (REGNO (x));
      struct qty_table_elem *x_ent = &qty_table[x_q];

      if (GET_MODE (x) == x_ent->mode
          && x_ent->const_rtx != NULL_RTX)
        return 0;
    }

  if (GET_CODE (x) == PLUS
      && GET_CODE (XEXP (x, 1)) == CONST_INT
      && REG_P (XEXP (x, 0))
      && REGNO_QTY_VALID_P (REGNO (XEXP (x, 0))))
    {
      int x0_q = REG_QTY (REGNO (XEXP (x, 0)));
      struct qty_table_elem *x0_ent = &qty_table[x0_q];

      if ((GET_MODE (XEXP (x, 0)) == x0_ent->mode)
          && x0_ent->const_rtx != NULL_RTX)
        return 0;
    }

  /* This can happen as the result of virtual register instantiation, if
     the initial constant is too large to be a valid address.  This gives
     us a three instruction sequence, load large offset into a register,
     load fp minus a constant into a register, then a MEM which is the
     sum of the two `constant' registers.  */
  if (GET_CODE (x) == PLUS
      && REG_P (XEXP (x, 0))
      && REG_P (XEXP (x, 1))
      && REGNO_QTY_VALID_P (REGNO (XEXP (x, 0)))
      && REGNO_QTY_VALID_P (REGNO (XEXP (x, 1))))
    {
      int x0_q = REG_QTY (REGNO (XEXP (x, 0)));
      int x1_q = REG_QTY (REGNO (XEXP (x, 1)));
      struct qty_table_elem *x0_ent = &qty_table[x0_q];
      struct qty_table_elem *x1_ent = &qty_table[x1_q];

      if ((GET_MODE (XEXP (x, 0)) == x0_ent->mode)
          && x0_ent->const_rtx != NULL_RTX
          && (GET_MODE (XEXP (x, 1)) == x1_ent->mode)
          && x1_ent->const_rtx != NULL_RTX)
        return 0;
    }

  return rtx_varies_p (x, from_alias);
}
\f
/* Subroutine of canon_reg.  Pass *XLOC through canon_reg, and validate
   the result if necessary.  INSN is as for canon_reg.  */

static void
validate_canon_reg (rtx *xloc, rtx insn)
{
  if (*xloc)
    {
      rtx new_rtx = canon_reg (*xloc, insn);

      /* If replacing pseudo with hard reg or vice versa, ensure the
         insn remains valid.  Likewise if the insn has MATCH_DUPs.  */
      gcc_assert (insn && new_rtx);
      validate_change (insn, xloc, new_rtx, 1);
    }
}

/* Canonicalize an expression:
   replace each register reference inside it
   with the "oldest" equivalent register.

   If INSN is nonzero validate_change is used to ensure that INSN remains valid
   after we make our substitution.  The calls are made with IN_GROUP nonzero
   so apply_change_group must be called upon the outermost return from this
   function (unless INSN is zero).  The result of apply_change_group can
   generally be discarded since the changes we are making are optional.  */

static rtx
canon_reg (rtx x, rtx insn)
{
  int i;
  enum rtx_code code;
  const char *fmt;

  if (x == 0)
    return x;

  code = GET_CODE (x);
  switch (code)
    {
    case PC:
    case CC0:
    case CONST:
    case CONST_INT:
    case CONST_DOUBLE:
    case CONST_FIXED:
    case CONST_VECTOR:
    case SYMBOL_REF:
    case LABEL_REF:
    case ADDR_VEC:
    case ADDR_DIFF_VEC:
      return x;

    case REG:
      {
        int first;
        int q;
        struct qty_table_elem *ent;

        /* Never replace a hard reg, because hard regs can appear
           in more than one machine mode, and we must preserve the mode
           of each occurrence.  Also, some hard regs appear in
           MEMs that are shared and mustn't be altered.  Don't try to
           replace any reg that maps to a reg of class NO_REGS.  */
        if (REGNO (x) < FIRST_PSEUDO_REGISTER
            || ! REGNO_QTY_VALID_P (REGNO (x)))
          return x;

        q = REG_QTY (REGNO (x));
        ent = &qty_table[q];
        first = ent->first_reg;
        return (first >= FIRST_PSEUDO_REGISTER ? regno_reg_rtx[first]
                : REGNO_REG_CLASS (first) == NO_REGS ? x
                : gen_rtx_REG (ent->mode, first));
      }

    default:
      break;
    }

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

      if (fmt[i] == 'e')
        validate_canon_reg (&XEXP (x, i), insn);
      else if (fmt[i] == 'E')
        for (j = 0; j < XVECLEN (x, i); j++)
          validate_canon_reg (&XVECEXP (x, i, j), insn);
    }

  return x;
}
\f
/* Given an operation (CODE, *PARG1, *PARG2), where code is a comparison
   operation (EQ, NE, GT, etc.), follow it back through the hash table and
   what values are being compared.

   *PARG1 and *PARG2 are updated to contain the rtx representing the values
   actually being compared.  For example, if *PARG1 was (cc0) and *PARG2
   was (const_int 0), *PARG1 and *PARG2 will be set to the objects that were
   compared to produce cc0.

   The return value is the comparison operator and is either the code of
   A or the code corresponding to the inverse of the comparison.  */

static enum rtx_code
find_comparison_args (enum rtx_code code, rtx *parg1, rtx *parg2,
                      enum machine_mode *pmode1, enum machine_mode *pmode2)
{
  rtx arg1, arg2;

  arg1 = *parg1, arg2 = *parg2;

  /* If ARG2 is const0_rtx, see what ARG1 is equivalent to.  */

  while (arg2 == CONST0_RTX (GET_MODE (arg1)))
    {
      /* Set nonzero when we find something of interest.  */
      rtx x = 0;
      int reverse_code = 0;
      struct table_elt *p = 0;

      /* If arg1 is a COMPARE, extract the comparison arguments from it.
         On machines with CC0, this is the only case that can occur, since
         fold_rtx will return the COMPARE or item being compared with zero
         when given CC0.  */

      if (GET_CODE (arg1) == COMPARE && arg2 == const0_rtx)
        x = arg1;

      /* If ARG1 is a comparison operator and CODE is testing for
         STORE_FLAG_VALUE, get the inner arguments.  */

      else if (COMPARISON_P (arg1))
        {
#ifdef FLOAT_STORE_FLAG_VALUE
          REAL_VALUE_TYPE fsfv;
#endif

          if (code == NE
              || (GET_MODE_CLASS (GET_MODE (arg1)) == MODE_INT
                  && code == LT && STORE_FLAG_VALUE == -1)
#ifdef FLOAT_STORE_FLAG_VALUE
              || (SCALAR_FLOAT_MODE_P (GET_MODE (arg1))
                  && (fsfv = FLOAT_STORE_FLAG_VALUE (GET_MODE (arg1)),
                      REAL_VALUE_NEGATIVE (fsfv)))
#endif
              )
            x = arg1;
          else if (code == EQ
                   || (GET_MODE_CLASS (GET_MODE (arg1)) == MODE_INT
                       && code == GE && STORE_FLAG_VALUE == -1)
#ifdef FLOAT_STORE_FLAG_VALUE
                   || (SCALAR_FLOAT_MODE_P (GET_MODE (arg1))
                       && (fsfv = FLOAT_STORE_FLAG_VALUE (GET_MODE (arg1)),
                           REAL_VALUE_NEGATIVE (fsfv)))
#endif
                   )
            x = arg1, reverse_code = 1;
        }

      /* ??? We could also check for

         (ne (and (eq (...) (const_int 1))) (const_int 0))

         and related forms, but let's wait until we see them occurring.  */

      if (x == 0)
        /* Look up ARG1 in the hash table and see if it has an equivalence
           that lets us see what is being compared.  */
        p = lookup (arg1, SAFE_HASH (arg1, GET_MODE (arg1)), GET_MODE (arg1));
      if (p)
        {
          p = p->first_same_value;

          /* If what we compare is already known to be constant, that is as
             good as it gets.
             We need to break the loop in this case, because otherwise we
             can have an infinite loop when looking at a reg that is known
             to be a constant which is the same as a comparison of a reg
             against zero which appears later in the insn stream, which in
             turn is constant and the same as the comparison of the first reg
             against zero...  */
          if (p->is_const)
            break;
        }

      for (; p; p = p->next_same_value)
        {
          enum machine_mode inner_mode = GET_MODE (p->exp);
#ifdef FLOAT_STORE_FLAG_VALUE
          REAL_VALUE_TYPE fsfv;
#endif

          /* If the entry isn't valid, skip it.  */
          if (! exp_equiv_p (p->exp, p->exp, 1, false))
            continue;

          if (GET_CODE (p->exp) == COMPARE
              /* Another possibility is that this machine has a compare insn
                 that includes the comparison code.  In that case, ARG1 would
                 be equivalent to a comparison operation that would set ARG1 to
                 either STORE_FLAG_VALUE or zero.  If this is an NE operation,
                 ORIG_CODE is the actual comparison being done; if it is an EQ,
                 we must reverse ORIG_CODE.  On machine with a negative value
                 for STORE_FLAG_VALUE, also look at LT and GE operations.  */
              || ((code == NE
                   || (code == LT
                       && GET_MODE_CLASS (inner_mode) == MODE_INT
                       && (GET_MODE_BITSIZE (inner_mode)
                           <= HOST_BITS_PER_WIDE_INT)
                       && (STORE_FLAG_VALUE
                           & ((HOST_WIDE_INT) 1
                              << (GET_MODE_BITSIZE (inner_mode) - 1))))
#ifdef FLOAT_STORE_FLAG_VALUE
                   || (code == LT
                       && SCALAR_FLOAT_MODE_P (inner_mode)
                       && (fsfv = FLOAT_STORE_FLAG_VALUE (GET_MODE (arg1)),
                           REAL_VALUE_NEGATIVE (fsfv)))
#endif
                   )
                  && COMPARISON_P (p->exp)))
            {
              x = p->exp;
              break;
            }
          else if ((code == EQ
                    || (code == GE
                        && GET_MODE_CLASS (inner_mode) == MODE_INT
                        && (GET_MODE_BITSIZE (inner_mode)
                            <= HOST_BITS_PER_WIDE_INT)
                        && (STORE_FLAG_VALUE
                            & ((HOST_WIDE_INT) 1
                               << (GET_MODE_BITSIZE (inner_mode) - 1))))
#ifdef FLOAT_STORE_FLAG_VALUE
                    || (code == GE
                        && SCALAR_FLOAT_MODE_P (inner_mode)
                        && (fsfv = FLOAT_STORE_FLAG_VALUE (GET_MODE (arg1)),
                            REAL_VALUE_NEGATIVE (fsfv)))
#endif
                    )
                   && COMPARISON_P (p->exp))
            {
              reverse_code = 1;
              x = p->exp;
              break;
            }

          /* If this non-trapping address, e.g. fp + constant, the
             equivalent is a better operand since it may let us predict
             the value of the comparison.  */
          else if (!rtx_addr_can_trap_p (p->exp))
            {
              arg1 = p->exp;
              continue;
            }
        }

      /* If we didn't find a useful equivalence for ARG1, we are done.
         Otherwise, set up for the next iteration.  */
      if (x == 0)
        break;

      /* If we need to reverse the comparison, make sure that that is
         possible -- we can't necessarily infer the value of GE from LT
         with floating-point operands.  */
      if (reverse_code)
        {
          enum rtx_code reversed = reversed_comparison_code (x, NULL_RTX);
          if (reversed == UNKNOWN)
            break;
          else
            code = reversed;
        }
      else if (COMPARISON_P (x))
        code = GET_CODE (x);
      arg1 = XEXP (x, 0), arg2 = XEXP (x, 1);
    }

  /* Return our results.  Return the modes from before fold_rtx
     because fold_rtx might produce const_int, and then it's too late.  */
  *pmode1 = GET_MODE (arg1), *pmode2 = GET_MODE (arg2);
  *parg1 = fold_rtx (arg1, 0), *parg2 = fold_rtx (arg2, 0);

  return code;
}
\f
/* If X is a nontrivial arithmetic operation on an argument for which
   a constant value can be determined, return the result of operating
   on that value, as a constant.  Otherwise, return X, possibly with
   one or more operands changed to a forward-propagated constant.

   If X is a register whose contents are known, we do NOT return
   those contents here; equiv_constant is called to perform that task.
   For SUBREGs and MEMs, we do that both here and in equiv_constant.

   INSN is the insn that we may be modifying.  If it is 0, make a copy
   of X before modifying it.  */

static rtx
fold_rtx (rtx x, rtx insn)
{
  enum rtx_code code;
  enum machine_mode mode;
  const char *fmt;
  int i;
  rtx new_rtx = 0;
  int changed = 0;

  /* Operands of X.  */
  rtx folded_arg0;
  rtx folded_arg1;

  /* Constant equivalents of first three operands of X;
     0 when no such equivalent is known.  */
  rtx const_arg0;
  rtx const_arg1;
  rtx const_arg2;

  /* The mode of the first operand of X.  We need this for sign and zero
     extends.  */
  enum machine_mode mode_arg0;

  if (x == 0)
    return x;

  /* Try to perform some initial simplifications on X.  */
  code = GET_CODE (x);
  switch (code)
    {
    case MEM:
    case SUBREG:
      if ((new_rtx = equiv_constant (x)) != NULL_RTX)
        return new_rtx;
      return x;

    case CONST:
    case CONST_INT:
    case CONST_DOUBLE:
    case CONST_FIXED:
    case CONST_VECTOR:
    case SYMBOL_REF:
    case LABEL_REF:
    case REG:
    case PC:
      /* No use simplifying an EXPR_LIST
         since they are used only for lists of args
         in a function call's REG_EQUAL note.  */
    case EXPR_LIST:
      return x;

#ifdef HAVE_cc0
    case CC0:
      return prev_insn_cc0;
#endif

    case ASM_OPERANDS:
      if (insn)
        {
          for (i = ASM_OPERANDS_INPUT_LENGTH (x) - 1; i >= 0; i--)
            validate_change (insn, &ASM_OPERANDS_INPUT (x, i),
                             fold_rtx (ASM_OPERANDS_INPUT (x, i), insn), 0);
        }
      return x;

#ifdef NO_FUNCTION_CSE
    case CALL:
      if (CONSTANT_P (XEXP (XEXP (x, 0), 0)))
        return x;
      break;
#endif

    /* Anything else goes through the loop below.  */
    default:
      break;
    }

  mode = GET_MODE (x);
  const_arg0 = 0;
  const_arg1 = 0;
  const_arg2 = 0;
  mode_arg0 = VOIDmode;

  /* Try folding our operands.
     Then see which ones have constant values known.  */

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    if (fmt[i] == 'e')
      {
        rtx folded_arg = XEXP (x, i), const_arg;
        enum machine_mode mode_arg = GET_MODE (folded_arg);

        switch (GET_CODE (folded_arg))
          {
          case MEM:
          case REG:
          case SUBREG:
            const_arg = equiv_constant (folded_arg);
            break;

          case CONST:
          case CONST_INT:
          case SYMBOL_REF:
          case LABEL_REF:
          case CONST_DOUBLE:
          case CONST_FIXED:
          case CONST_VECTOR:
            const_arg = folded_arg;
            break;

#ifdef HAVE_cc0
          case CC0:
            folded_arg = prev_insn_cc0;
            mode_arg = prev_insn_cc0_mode;
            const_arg = equiv_constant (folded_arg);
            break;
#endif

          default:
            folded_arg = fold_rtx (folded_arg, insn);
            const_arg = equiv_constant (folded_arg);
            break;
          }

        /* For the first three operands, see if the operand
           is constant or equivalent to a constant.  */
        switch (i)
          {
          case 0:
            folded_arg0 = folded_arg;
            const_arg0 = const_arg;
            mode_arg0 = mode_arg;
            break;
          case 1:
            folded_arg1 = folded_arg;
            const_arg1 = const_arg;
            break;
          case 2:
            const_arg2 = const_arg;
            break;
          }

        /* Pick the least expensive of the argument and an equivalent constant
           argument.  */
        if (const_arg != 0
            && const_arg != folded_arg
            && COST_IN (const_arg, code) <= COST_IN (folded_arg, code)

            /* It's not safe to substitute the operand of a conversion
               operator with a constant, as the conversion's identity
               depends upon the mode of its operand.  This optimization
               is handled by the call to simplify_unary_operation.  */
            && (GET_RTX_CLASS (code) != RTX_UNARY
                || GET_MODE (const_arg) == mode_arg0
                || (code != ZERO_EXTEND
                    && code != SIGN_EXTEND
                    && code != TRUNCATE
                    && code != FLOAT_TRUNCATE
                    && code != FLOAT_EXTEND
                    && code != FLOAT
                    && code != FIX
                    && code != UNSIGNED_FLOAT
                    && code != UNSIGNED_FIX)))
          folded_arg = const_arg;

        if (folded_arg == XEXP (x, i))
          continue;

        if (insn == NULL_RTX && !changed)
          x = copy_rtx (x);
        changed = 1;
        validate_unshare_change (insn, &XEXP (x, i), folded_arg, 1);
      }

  if (changed)
    {
      /* Canonicalize X if necessary, and keep const_argN and folded_argN
         consistent with the order in X.  */
      if (canonicalize_change_group (insn, x))
        {
          rtx tem;
          tem = const_arg0, const_arg0 = const_arg1, const_arg1 = tem;
          tem = folded_arg0, folded_arg0 = folded_arg1, folded_arg1 = tem;
        }

      apply_change_group ();
    }

  /* If X is an arithmetic operation, see if we can simplify it.  */

  switch (GET_RTX_CLASS (code))
    {
    case RTX_UNARY:
      {
        /* We can't simplify extension ops unless we know the
           original mode.  */
        if ((code == ZERO_EXTEND || code == SIGN_EXTEND)
            && mode_arg0 == VOIDmode)
          break;

        new_rtx = simplify_unary_operation (code, mode,
                                        const_arg0 ? const_arg0 : folded_arg0,
                                        mode_arg0);
      }
      break;

    case RTX_COMPARE:
    case RTX_COMM_COMPARE:
      /* See what items are actually being compared and set FOLDED_ARG[01]
         to those values and CODE to the actual comparison code.  If any are
         constant, set CONST_ARG0 and CONST_ARG1 appropriately.  We needn't
         do anything if both operands are already known to be constant.  */

      /* ??? Vector mode comparisons are not supported yet.  */
      if (VECTOR_MODE_P (mode))
        break;

      if (const_arg0 == 0 || const_arg1 == 0)
        {
          struct table_elt *p0, *p1;
          rtx true_rtx, false_rtx;
          enum machine_mode mode_arg1;

          if (SCALAR_FLOAT_MODE_P (mode))
            {
#ifdef FLOAT_STORE_FLAG_VALUE
              true_rtx = (CONST_DOUBLE_FROM_REAL_VALUE
                          (FLOAT_STORE_FLAG_VALUE (mode), mode));
#else
              true_rtx = NULL_RTX;
#endif
              false_rtx = CONST0_RTX (mode);
            }
          else
            {
              true_rtx = const_true_rtx;
              false_rtx = const0_rtx;
            }

          code = find_comparison_args (code, &folded_arg0, &folded_arg1,
                                       &mode_arg0, &mode_arg1);

          /* If the mode is VOIDmode or a MODE_CC mode, we don't know
             what kinds of things are being compared, so we can't do
             anything with this comparison.  */

          if (mode_arg0 == VOIDmode || GET_MODE_CLASS (mode_arg0) == MODE_CC)
            break;

          const_arg0 = equiv_constant (folded_arg0);
          const_arg1 = equiv_constant (folded_arg1);

          /* If we do not now have two constants being compared, see
             if we can nevertheless deduce some things about the
             comparison.  */
          if (const_arg0 == 0 || const_arg1 == 0)
            {
              if (const_arg1 != NULL)
                {
                  rtx cheapest_simplification;
                  int cheapest_cost;
                  rtx simp_result;
                  struct table_elt *p;

                  /* See if we can find an equivalent of folded_arg0
                     that gets us a cheaper expression, possibly a
                     constant through simplifications.  */
                  p = lookup (folded_arg0, SAFE_HASH (folded_arg0, mode_arg0),
                              mode_arg0);
                  
                  if (p != NULL)
                    {
                      cheapest_simplification = x;
                      cheapest_cost = COST (x);

                      for (p = p->first_same_value; p != NULL; p = p->next_same_value)
                        {
                          int cost;

                          /* If the entry isn't valid, skip it.  */
                          if (! exp_equiv_p (p->exp, p->exp, 1, false))
                            continue;

                          /* Try to simplify using this equivalence.  */
                          simp_result
                            = simplify_relational_operation (code, mode,
                                                             mode_arg0,
                                                             p->exp,
                                                             const_arg1);

                          if (simp_result == NULL)
                            continue;

                          cost = COST (simp_result);
                          if (cost < cheapest_cost)
                            {
                              cheapest_cost = cost;
                              cheapest_simplification = simp_result;
                            }
                        }

                      /* If we have a cheaper expression now, use that
                         and try folding it further, from the top.  */
                      if (cheapest_simplification != x)
                        return fold_rtx (copy_rtx (cheapest_simplification),
                                         insn);
                    }
                }

              /* See if the two operands are the same.  */

              if ((REG_P (folded_arg0)
                   && REG_P (folded_arg1)
                   && (REG_QTY (REGNO (folded_arg0))
                       == REG_QTY (REGNO (folded_arg1))))
                  || ((p0 = lookup (folded_arg0,
                                    SAFE_HASH (folded_arg0, mode_arg0),
                                    mode_arg0))
                      && (p1 = lookup (folded_arg1,
                                       SAFE_HASH (folded_arg1, mode_arg0),
                                       mode_arg0))
                      && p0->first_same_value == p1->first_same_value))
                folded_arg1 = folded_arg0;

              /* If FOLDED_ARG0 is a register, see if the comparison we are
                 doing now is either the same as we did before or the reverse
                 (we only check the reverse if not floating-point).  */
              else if (REG_P (folded_arg0))
                {
                  int qty = REG_QTY (REGNO (folded_arg0));

                  if (REGNO_QTY_VALID_P (REGNO (folded_arg0)))
                    {
                      struct qty_table_elem *ent = &qty_table[qty];

                      if ((comparison_dominates_p (ent->comparison_code, code)
                           || (! FLOAT_MODE_P (mode_arg0)
                               && comparison_dominates_p (ent->comparison_code,
                                                          reverse_condition (code))))
                          && (rtx_equal_p (ent->comparison_const, folded_arg1)
                              || (const_arg1
                                  && rtx_equal_p (ent->comparison_const,
                                                  const_arg1))
                              || (REG_P (folded_arg1)
                                  && (REG_QTY (REGNO (folded_arg1)) == ent->comparison_qty))))
                        {
                          if (comparison_dominates_p (ent->comparison_code, code))
                            {
                              if (true_rtx)
                                return true_rtx;
                              else
                                break;
                            }
                          else
                            return false_rtx;
                        }
                    }
                }
            }
        }

      /* If we are comparing against zero, see if the first operand is
         equivalent to an IOR with a constant.  If so, we may be able to
         determine the result of this comparison.  */
      if (const_arg1 == const0_rtx && !const_arg0)
        {
          rtx y = lookup_as_function (folded_arg0, IOR);
          rtx inner_const;

          if (y != 0
              && (inner_const = equiv_constant (XEXP (y, 1))) != 0
              && GET_CODE (inner_const) == CONST_INT
              && INTVAL (inner_const) != 0)
            folded_arg0 = gen_rtx_IOR (mode_arg0, XEXP (y, 0), inner_const);
        }

      {
        rtx op0 = const_arg0 ? const_arg0 : folded_arg0;
        rtx op1 = const_arg1 ? const_arg1 : folded_arg1;
        new_rtx = simplify_relational_operation (code, mode, mode_arg0, op0, op1);
      }
      break;

    case RTX_BIN_ARITH:
    case RTX_COMM_ARITH:
      switch (code)
        {
        case PLUS:
          /* If the second operand is a LABEL_REF, see if the first is a MINUS
             with that LABEL_REF as its second operand.  If so, the result is
             the first operand of that MINUS.  This handles switches with an
             ADDR_DIFF_VEC table.  */
          if (const_arg1 && GET_CODE (const_arg1) == LABEL_REF)
            {
              rtx y
                = GET_CODE (folded_arg0) == MINUS ? folded_arg0
                : lookup_as_function (folded_arg0, MINUS);

              if (y != 0 && GET_CODE (XEXP (y, 1)) == LABEL_REF
                  && XEXP (XEXP (y, 1), 0) == XEXP (const_arg1, 0))
                return XEXP (y, 0);

              /* Now try for a CONST of a MINUS like the above.  */
              if ((y = (GET_CODE (folded_arg0) == CONST ? folded_arg0
                        : lookup_as_function (folded_arg0, CONST))) != 0
                  && GET_CODE (XEXP (y, 0)) == MINUS
                  && GET_CODE (XEXP (XEXP (y, 0), 1)) == LABEL_REF
                  && XEXP (XEXP (XEXP (y, 0), 1), 0) == XEXP (const_arg1, 0))
                return XEXP (XEXP (y, 0), 0);
            }

          /* Likewise if the operands are in the other order.  */
          if (const_arg0 && GET_CODE (const_arg0) == LABEL_REF)
            {
              rtx y
                = GET_CODE (folded_arg1) == MINUS ? folded_arg1
                : lookup_as_function (folded_arg1, MINUS);

              if (y != 0 && GET_CODE (XEXP (y, 1)) == LABEL_REF
                  && XEXP (XEXP (y, 1), 0) == XEXP (const_arg0, 0))
                return XEXP (y, 0);

              /* Now try for a CONST of a MINUS like the above.  */
              if ((y = (GET_CODE (folded_arg1) == CONST ? folded_arg1
                        : lookup_as_function (folded_arg1, CONST))) != 0
                  && GET_CODE (XEXP (y, 0)) == MINUS
                  && GET_CODE (XEXP (XEXP (y, 0), 1)) == LABEL_REF
                  && XEXP (XEXP (XEXP (y, 0), 1), 0) == XEXP (const_arg0, 0))
                return XEXP (XEXP (y, 0), 0);
            }

          /* If second operand is a register equivalent to a negative
             CONST_INT, see if we can find a register equivalent to the
             positive constant.  Make a MINUS if so.  Don't do this for
             a non-negative constant since we might then alternate between
             choosing positive and negative constants.  Having the positive
             constant previously-used is the more common case.  Be sure
             the resulting constant is non-negative; if const_arg1 were
             the smallest negative number this would overflow: depending
             on the mode, this would either just be the same value (and
             hence not save anything) or be incorrect.  */
          if (const_arg1 != 0 && GET_CODE (const_arg1) == CONST_INT
              && INTVAL (const_arg1) < 0
              /* This used to test

                 -INTVAL (const_arg1) >= 0

                 But The Sun V5.0 compilers mis-compiled that test.  So
                 instead we test for the problematic value in a more direct
                 manner and hope the Sun compilers get it correct.  */
              && INTVAL (const_arg1) !=
                ((HOST_WIDE_INT) 1 << (HOST_BITS_PER_WIDE_INT - 1))
              && REG_P (folded_arg1))
            {
              rtx new_const = GEN_INT (-INTVAL (const_arg1));
              struct table_elt *p
                = lookup (new_const, SAFE_HASH (new_const, mode), mode);

              if (p)
                for (p = p->first_same_value; p; p = p->next_same_value)
                  if (REG_P (p->exp))
                    return simplify_gen_binary (MINUS, mode, folded_arg0,
                                                canon_reg (p->exp, NULL_RTX));
            }
          goto from_plus;

        case MINUS:
          /* If we have (MINUS Y C), see if Y is known to be (PLUS Z C2).
             If so, produce (PLUS Z C2-C).  */
          if (const_arg1 != 0 && GET_CODE (const_arg1) == CONST_INT)
            {
              rtx y = lookup_as_function (XEXP (x, 0), PLUS);
              if (y && GET_CODE (XEXP (y, 1)) == CONST_INT)
                return fold_rtx (plus_constant (copy_rtx (y),
                                                -INTVAL (const_arg1)),
                                 NULL_RTX);
            }

          /* Fall through.  */

        from_plus:
        case SMIN:    case SMAX:      case UMIN:    case UMAX:
        case IOR:     case AND:       case XOR:
        case MULT:
        case ASHIFT:  case LSHIFTRT:  case ASHIFTRT:
          /* If we have (<op> <reg> <const_int>) for an associative OP and REG
             is known to be of similar form, we may be able to replace the
             operation with a combined operation.  This may eliminate the
             intermediate operation if every use is simplified in this way.
             Note that the similar optimization done by combine.c only works
             if the intermediate operation's result has only one reference.  */

          if (REG_P (folded_arg0)
              && const_arg1 && GET_CODE (const_arg1) == CONST_INT)
            {
              int is_shift
                = (code == ASHIFT || code == ASHIFTRT || code == LSHIFTRT);
              rtx y, inner_const, new_const;
              rtx canon_const_arg1 = const_arg1;
              enum rtx_code associate_code;

              if (is_shift
                  && (INTVAL (const_arg1) >= GET_MODE_BITSIZE (mode)
                      || INTVAL (const_arg1) < 0))
                {
                  if (SHIFT_COUNT_TRUNCATED)
                    canon_const_arg1 = GEN_INT (INTVAL (const_arg1)
                                                & (GET_MODE_BITSIZE (mode)
                                                   - 1));
                  else
                    break;
                }

              y = lookup_as_function (folded_arg0, code);
              if (y == 0)
                break;

              /* If we have compiled a statement like
                 "if (x == (x & mask1))", and now are looking at
                 "x & mask2", we will have a case where the first operand
                 of Y is the same as our first operand.  Unless we detect
                 this case, an infinite loop will result.  */
              if (XEXP (y, 0) == folded_arg0)
                break;

              inner_const = equiv_constant (fold_rtx (XEXP (y, 1), 0));
              if (!inner_const || GET_CODE (inner_const) != CONST_INT)
                break;

              /* Don't associate these operations if they are a PLUS with the
                 same constant and it is a power of two.  These might be doable
                 with a pre- or post-increment.  Similarly for two subtracts of
                 identical powers of two with post decrement.  */

              if (code == PLUS && const_arg1 == inner_const
                  && ((HAVE_PRE_INCREMENT
                          && exact_log2 (INTVAL (const_arg1)) >= 0)
                      || (HAVE_POST_INCREMENT
                          && exact_log2 (INTVAL (const_arg1)) >= 0)
                      || (HAVE_PRE_DECREMENT
                          && exact_log2 (- INTVAL (const_arg1)) >= 0)
                      || (HAVE_POST_DECREMENT
                          && exact_log2 (- INTVAL (const_arg1)) >= 0)))
                break;