backport: As described in http://gcc.gnu.org/ml/gcc/2012-08/msg00015.html...

[thirdparty/gcc.git] / gcc / gcse.c

/* Partial redundancy elimination / Hoisting for RTL.
   Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
   2006, 2007, 2008, 2009, 2010, 2011 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/>.  */

/* TODO
   - reordering of memory allocation and freeing to be more space efficient
   - do rough calc of how many regs are needed in each block, and a rough
     calc of how many regs are available in each class and use that to
     throttle back the code in cases where RTX_COST is minimal.
*/

/* References searched while implementing this.

   Compilers Principles, Techniques and Tools
   Aho, Sethi, Ullman
   Addison-Wesley, 1988

   Global Optimization by Suppression of Partial Redundancies
   E. Morel, C. Renvoise
   communications of the acm, Vol. 22, Num. 2, Feb. 1979

   A Portable Machine-Independent Global Optimizer - Design and Measurements
   Frederick Chow
   Stanford Ph.D. thesis, Dec. 1983

   A Fast Algorithm for Code Movement Optimization
   D.M. Dhamdhere
   SIGPLAN Notices, Vol. 23, Num. 10, Oct. 1988

   A Solution to a Problem with Morel and Renvoise's
   Global Optimization by Suppression of Partial Redundancies
   K-H Drechsler, M.P. Stadel
   ACM TOPLAS, Vol. 10, Num. 4, Oct. 1988

   Practical Adaptation of the Global Optimization
   Algorithm of Morel and Renvoise
   D.M. Dhamdhere
   ACM TOPLAS, Vol. 13, Num. 2. Apr. 1991

   Efficiently Computing Static Single Assignment Form and the Control
   Dependence Graph
   R. Cytron, J. Ferrante, B.K. Rosen, M.N. Wegman, and F.K. Zadeck
   ACM TOPLAS, Vol. 13, Num. 4, Oct. 1991

   Lazy Code Motion
   J. Knoop, O. Ruthing, B. Steffen
   ACM SIGPLAN Notices Vol. 27, Num. 7, Jul. 1992, '92 Conference on PLDI

   What's In a Region?  Or Computing Control Dependence Regions in Near-Linear
   Time for Reducible Flow Control
   Thomas Ball
   ACM Letters on Programming Languages and Systems,
   Vol. 2, Num. 1-4, Mar-Dec 1993

   An Efficient Representation for Sparse Sets
   Preston Briggs, Linda Torczon
   ACM Letters on Programming Languages and Systems,
   Vol. 2, Num. 1-4, Mar-Dec 1993

   A Variation of Knoop, Ruthing, and Steffen's Lazy Code Motion
   K-H Drechsler, M.P. Stadel
   ACM SIGPLAN Notices, Vol. 28, Num. 5, May 1993

   Partial Dead Code Elimination
   J. Knoop, O. Ruthing, B. Steffen
   ACM SIGPLAN Notices, Vol. 29, Num. 6, Jun. 1994

   Effective Partial Redundancy Elimination
   P. Briggs, K.D. Cooper
   ACM SIGPLAN Notices, Vol. 29, Num. 6, Jun. 1994

   The Program Structure Tree: Computing Control Regions in Linear Time
   R. Johnson, D. Pearson, K. Pingali
   ACM SIGPLAN Notices, Vol. 29, Num. 6, Jun. 1994

   Optimal Code Motion: Theory and Practice
   J. Knoop, O. Ruthing, B. Steffen
   ACM TOPLAS, Vol. 16, Num. 4, Jul. 1994

   The power of assignment motion
   J. Knoop, O. Ruthing, B. Steffen
   ACM SIGPLAN Notices Vol. 30, Num. 6, Jun. 1995, '95 Conference on PLDI

   Global code motion / global value numbering
   C. Click
   ACM SIGPLAN Notices Vol. 30, Num. 6, Jun. 1995, '95 Conference on PLDI

   Value Driven Redundancy Elimination
   L.T. Simpson
   Rice University Ph.D. thesis, Apr. 1996

   Value Numbering
   L.T. Simpson
   Massively Scalar Compiler Project, Rice University, Sep. 1996

   High Performance Compilers for Parallel Computing
   Michael Wolfe
   Addison-Wesley, 1996

   Advanced Compiler Design and Implementation
   Steven Muchnick
   Morgan Kaufmann, 1997

   Building an Optimizing Compiler
   Robert Morgan
   Digital Press, 1998

   People wishing to speed up the code here should read:
     Elimination Algorithms for Data Flow Analysis
     B.G. Ryder, M.C. Paull
     ACM Computing Surveys, Vol. 18, Num. 3, Sep. 1986

     How to Analyze Large Programs Efficiently and Informatively
     D.M. Dhamdhere, B.K. Rosen, F.K. Zadeck
     ACM SIGPLAN Notices Vol. 27, Num. 7, Jul. 1992, '92 Conference on PLDI

   People wishing to do something different can find various possibilities
   in the above papers and elsewhere.
*/

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "diagnostic-core.h"
#include "toplev.h"

#include "rtl.h"
#include "tree.h"
#include "tm_p.h"
#include "regs.h"
#include "hard-reg-set.h"
#include "flags.h"
#include "insn-config.h"
#include "recog.h"
#include "basic-block.h"
#include "function.h"
#include "expr.h"
#include "except.h"
#include "ggc.h"
#include "params.h"
#include "cselib.h"
#include "intl.h"
#include "obstack.h"
#include "tree-pass.h"
#include "hashtab.h"
#include "df.h"
#include "dbgcnt.h"
#include "target.h"
#include "gcse.h"

/* We support GCSE via Partial Redundancy Elimination.  PRE optimizations
   are a superset of those done by classic GCSE.

   Two passes of copy/constant propagation are done around PRE or hoisting
   because the first one enables more GCSE and the second one helps to clean
   up the copies that PRE and HOIST create.  This is needed more for PRE than
   for HOIST because code hoisting will try to use an existing register
   containing the common subexpression rather than create a new one.  This is
   harder to do for PRE because of the code motion (which HOIST doesn't do).

   Expressions we are interested in GCSE-ing are of the form
   (set (pseudo-reg) (expression)).
   Function want_to_gcse_p says what these are.

   In addition, expressions in REG_EQUAL notes are candidates for GCSE-ing.
   This allows PRE to hoist expressions that are expressed in multiple insns,
   such as complex address calculations (e.g. for PIC code, or loads with a
   high part and a low part).

   PRE handles moving invariant expressions out of loops (by treating them as
   partially redundant).

   **********************

   We used to support multiple passes but there are diminishing returns in
   doing so.  The first pass usually makes 90% of the changes that are doable.
   A second pass can make a few more changes made possible by the first pass.
   Experiments show any further passes don't make enough changes to justify
   the expense.

   A study of spec92 using an unlimited number of passes:
   [1 pass] = 1208 substitutions, [2] = 577, [3] = 202, [4] = 192, [5] = 83,
   [6] = 34, [7] = 17, [8] = 9, [9] = 4, [10] = 4, [11] = 2,
   [12] = 2, [13] = 1, [15] = 1, [16] = 2, [41] = 1

   It was found doing copy propagation between each pass enables further
   substitutions.

   This study was done before expressions in REG_EQUAL notes were added as
   candidate expressions for optimization, and before the GIMPLE optimizers
   were added.  Probably, multiple passes is even less efficient now than
   at the time when the study was conducted.

   PRE is quite expensive in complicated functions because the DFA can take
   a while to converge.  Hence we only perform one pass.

   **********************

   The steps for PRE are:

   1) Build the hash table of expressions we wish to GCSE (expr_hash_table).

   2) Perform the data flow analysis for PRE.

   3) Delete the redundant instructions

   4) Insert the required copies [if any] that make the partially
      redundant instructions fully redundant.

   5) For other reaching expressions, insert an instruction to copy the value
      to a newly created pseudo that will reach the redundant instruction.

   The deletion is done first so that when we do insertions we
   know which pseudo reg to use.

   Various papers have argued that PRE DFA is expensive (O(n^2)) and others
   argue it is not.  The number of iterations for the algorithm to converge
   is typically 2-4 so I don't view it as that expensive (relatively speaking).

   PRE GCSE depends heavily on the second CPROP pass to clean up the copies
   we create.  To make an expression reach the place where it's redundant,
   the result of the expression is copied to a new register, and the redundant
   expression is deleted by replacing it with this new register.  Classic GCSE
   doesn't have this problem as much as it computes the reaching defs of
   each register in each block and thus can try to use an existing
   register.  */
\f
/* GCSE global vars.  */

struct target_gcse default_target_gcse;
#if SWITCHABLE_TARGET
struct target_gcse *this_target_gcse = &default_target_gcse;
#endif

/* Set to non-zero if CSE should run after all GCSE optimizations are done.  */
int flag_rerun_cse_after_global_opts;

/* An obstack for our working variables.  */
static struct obstack gcse_obstack;

struct reg_use {rtx reg_rtx; };

/* Hash table of expressions.  */

struct expr
{
  /* The expression.  */
  rtx expr;
  /* Index in the available expression bitmaps.  */
  int bitmap_index;
  /* Next entry with the same hash.  */
  struct expr *next_same_hash;
  /* List of anticipatable occurrences in basic blocks in the function.
     An "anticipatable occurrence" is one that is the first occurrence in the
     basic block, the operands are not modified in the basic block prior
     to the occurrence and the output is not used between the start of
     the block and the occurrence.  */
  struct occr *antic_occr;
  /* List of available occurrence in basic blocks in the function.
     An "available occurrence" is one that is the last occurrence in the
     basic block and the operands are not modified by following statements in
     the basic block [including this insn].  */
  struct occr *avail_occr;
  /* Non-null if the computation is PRE redundant.
     The value is the newly created pseudo-reg to record a copy of the
     expression in all the places that reach the redundant copy.  */
  rtx reaching_reg;
  /* Maximum distance in instructions this expression can travel.
     We avoid moving simple expressions for more than a few instructions
     to keep register pressure under control.
     A value of "0" removes restrictions on how far the expression can
     travel.  */
  int max_distance;
};

/* Occurrence of an expression.
   There is one per basic block.  If a pattern appears more than once the
   last appearance is used [or first for anticipatable expressions].  */

struct occr
{
  /* Next occurrence of this expression.  */
  struct occr *next;
  /* The insn that computes the expression.  */
  rtx insn;
  /* Nonzero if this [anticipatable] occurrence has been deleted.  */
  char deleted_p;
  /* Nonzero if this [available] occurrence has been copied to
     reaching_reg.  */
  /* ??? This is mutually exclusive with deleted_p, so they could share
     the same byte.  */
  char copied_p;
};

typedef struct occr *occr_t;
DEF_VEC_P (occr_t);
DEF_VEC_ALLOC_P (occr_t, heap);

/* Expression hash tables.
   Each hash table is an array of buckets.
   ??? It is known that if it were an array of entries, structure elements
   `next_same_hash' and `bitmap_index' wouldn't be necessary.  However, it is
   not clear whether in the final analysis a sufficient amount of memory would
   be saved as the size of the available expression bitmaps would be larger
   [one could build a mapping table without holes afterwards though].
   Someday I'll perform the computation and figure it out.  */

struct hash_table_d
{
  /* The table itself.
     This is an array of `expr_hash_table_size' elements.  */
  struct expr **table;

  /* Size of the hash table, in elements.  */
  unsigned int size;

  /* Number of hash table elements.  */
  unsigned int n_elems;
};

/* Expression hash table.  */
static struct hash_table_d expr_hash_table;

/* This is a list of expressions which are MEMs and will be used by load
   or store motion.
   Load motion tracks MEMs which aren't killed by anything except itself,
   i.e. loads and stores to a single location.
   We can then allow movement of these MEM refs with a little special
   allowance. (all stores copy the same value to the reaching reg used
   for the loads).  This means all values used to store into memory must have
   no side effects so we can re-issue the setter value.  */

struct ls_expr
{
  struct expr * expr;           /* Gcse expression reference for LM.  */
  rtx pattern;                  /* Pattern of this mem.  */
  rtx pattern_regs;             /* List of registers mentioned by the mem.  */
  rtx loads;                    /* INSN list of loads seen.  */
  rtx stores;                   /* INSN list of stores seen.  */
  struct ls_expr * next;        /* Next in the list.  */
  int invalid;                  /* Invalid for some reason.  */
  int index;                    /* If it maps to a bitmap index.  */
  unsigned int hash_index;      /* Index when in a hash table.  */
  rtx reaching_reg;             /* Register to use when re-writing.  */
};

/* Head of the list of load/store memory refs.  */
static struct ls_expr * pre_ldst_mems = NULL;

/* Hashtable for the load/store memory refs.  */
static htab_t pre_ldst_table = NULL;

/* Bitmap containing one bit for each register in the program.
   Used when performing GCSE to track which registers have been set since
   the start of the basic block.  */
static regset reg_set_bitmap;

/* Array, indexed by basic block number for a list of insns which modify
   memory within that block.  */
static VEC (rtx,heap) **modify_mem_list;
static bitmap modify_mem_list_set;

typedef struct modify_pair_s
{
  rtx dest;                     /* A MEM.  */
  rtx dest_addr;                /* The canonical address of `dest'.  */
} modify_pair;

DEF_VEC_O(modify_pair);
DEF_VEC_ALLOC_O(modify_pair,heap);

/* This array parallels modify_mem_list, except that it stores MEMs
   being set and their canonicalized memory addresses.  */
static VEC (modify_pair,heap) **canon_modify_mem_list;

/* Bitmap indexed by block numbers to record which blocks contain
   function calls.  */
static bitmap blocks_with_calls;

/* Various variables for statistics gathering.  */

/* Memory used in a pass.
   This isn't intended to be absolutely precise.  Its intent is only
   to keep an eye on memory usage.  */
static int bytes_used;

/* GCSE substitutions made.  */
static int gcse_subst_count;
/* Number of copy instructions created.  */
static int gcse_create_count;
\f
/* Doing code hoisting.  */
static bool doing_code_hoisting_p = false;
\f
/* For available exprs */
static sbitmap *ae_kill;
\f
static void compute_can_copy (void);
static void *gmalloc (size_t) ATTRIBUTE_MALLOC;
static void *gcalloc (size_t, size_t) ATTRIBUTE_MALLOC;
static void *gcse_alloc (unsigned long);
static void alloc_gcse_mem (void);
static void free_gcse_mem (void);
static void hash_scan_insn (rtx, struct hash_table_d *);
static void hash_scan_set (rtx, rtx, struct hash_table_d *);
static void hash_scan_clobber (rtx, rtx, struct hash_table_d *);
static void hash_scan_call (rtx, rtx, struct hash_table_d *);
static int want_to_gcse_p (rtx, int *);
static int oprs_unchanged_p (const_rtx, const_rtx, int);
static int oprs_anticipatable_p (const_rtx, const_rtx);
static int oprs_available_p (const_rtx, const_rtx);
static void insert_expr_in_table (rtx, enum machine_mode, rtx, int, int, int,
                                  struct hash_table_d *);
static unsigned int hash_expr (const_rtx, enum machine_mode, int *, int);
static int expr_equiv_p (const_rtx, const_rtx);
static void record_last_reg_set_info (rtx, int);
static void record_last_mem_set_info (rtx);
static void record_last_set_info (rtx, const_rtx, void *);
static void compute_hash_table (struct hash_table_d *);
static void alloc_hash_table (struct hash_table_d *);
static void free_hash_table (struct hash_table_d *);
static void compute_hash_table_work (struct hash_table_d *);
static void dump_hash_table (FILE *, const char *, struct hash_table_d *);
static void compute_transp (const_rtx, int, sbitmap *);
static void compute_local_properties (sbitmap *, sbitmap *, sbitmap *,
                                      struct hash_table_d *);
static void mems_conflict_for_gcse_p (rtx, const_rtx, void *);
static int load_killed_in_block_p (const_basic_block, int, const_rtx, int);
static void canon_list_insert (rtx, const_rtx, void *);
static void alloc_pre_mem (int, int);
static void free_pre_mem (void);
static struct edge_list *compute_pre_data (void);
static int pre_expr_reaches_here_p (basic_block, struct expr *,
                                    basic_block);
static void insert_insn_end_basic_block (struct expr *, basic_block);
static void pre_insert_copy_insn (struct expr *, rtx);
static void pre_insert_copies (void);
static int pre_delete (void);
static int pre_gcse (struct edge_list *);
static int one_pre_gcse_pass (void);
static void add_label_notes (rtx, rtx);
static void alloc_code_hoist_mem (int, int);
static void free_code_hoist_mem (void);
static void compute_code_hoist_vbeinout (void);
static void compute_code_hoist_data (void);
static int hoist_expr_reaches_here_p (basic_block, int, basic_block, char *,
                                      int, int *);
static int hoist_code (void);
static int one_code_hoisting_pass (void);
static rtx process_insert_insn (struct expr *);
static int pre_edge_insert (struct edge_list *, struct expr **);
static int pre_expr_reaches_here_p_work (basic_block, struct expr *,
                                         basic_block, char *);
static struct ls_expr * ldst_entry (rtx);
static void free_ldst_entry (struct ls_expr *);
static void free_ld_motion_mems (void);
static void print_ldst_list (FILE *);
static struct ls_expr * find_rtx_in_ldst (rtx);
static int simple_mem (const_rtx);
static void invalidate_any_buried_refs (rtx);
static void compute_ld_motion_mems (void);
static void trim_ld_motion_mems (void);
static void update_ld_motion_stores (struct expr *);
static void clear_modify_mem_tables (void);
static void free_modify_mem_tables (void);
static rtx gcse_emit_move_after (rtx, rtx, rtx);
static bool is_too_expensive (const char *);

#define GNEW(T)                 ((T *) gmalloc (sizeof (T)))
#define GCNEW(T)                ((T *) gcalloc (1, sizeof (T)))

#define GNEWVEC(T, N)           ((T *) gmalloc (sizeof (T) * (N)))
#define GCNEWVEC(T, N)          ((T *) gcalloc ((N), sizeof (T)))

#define GNEWVAR(T, S)           ((T *) gmalloc ((S)))
#define GCNEWVAR(T, S)          ((T *) gcalloc (1, (S)))

#define GOBNEW(T)               ((T *) gcse_alloc (sizeof (T)))
#define GOBNEWVAR(T, S)         ((T *) gcse_alloc ((S)))
\f
/* Misc. utilities.  */

#define can_copy \
  (this_target_gcse->x_can_copy)
#define can_copy_init_p \
  (this_target_gcse->x_can_copy_init_p)

/* Compute which modes support reg/reg copy operations.  */

static void
compute_can_copy (void)
{
  int i;
#ifndef AVOID_CCMODE_COPIES
  rtx reg, insn;
#endif
  memset (can_copy, 0, NUM_MACHINE_MODES);

  start_sequence ();
  for (i = 0; i < NUM_MACHINE_MODES; i++)
    if (GET_MODE_CLASS (i) == MODE_CC)
      {
#ifdef AVOID_CCMODE_COPIES
        can_copy[i] = 0;
#else
        reg = gen_rtx_REG ((enum machine_mode) i, LAST_VIRTUAL_REGISTER + 1);
        insn = emit_insn (gen_rtx_SET (VOIDmode, reg, reg));
        if (recog (PATTERN (insn), insn, NULL) >= 0)
          can_copy[i] = 1;
#endif
      }
    else
      can_copy[i] = 1;

  end_sequence ();
}

/* Returns whether the mode supports reg/reg copy operations.  */

bool
can_copy_p (enum machine_mode mode)
{
  if (! can_copy_init_p)
    {
      compute_can_copy ();
      can_copy_init_p = true;
    }

  return can_copy[mode] != 0;
}
\f
/* Cover function to xmalloc to record bytes allocated.  */

static void *
gmalloc (size_t size)
{
  bytes_used += size;
  return xmalloc (size);
}

/* Cover function to xcalloc to record bytes allocated.  */

static void *
gcalloc (size_t nelem, size_t elsize)
{
  bytes_used += nelem * elsize;
  return xcalloc (nelem, elsize);
}

/* Cover function to obstack_alloc.  */

static void *
gcse_alloc (unsigned long size)
{
  bytes_used += size;
  return obstack_alloc (&gcse_obstack, size);
}

/* Allocate memory for the reg/memory set tracking tables.
   This is called at the start of each pass.  */

static void
alloc_gcse_mem (void)
{
  /* Allocate vars to track sets of regs.  */
  reg_set_bitmap = ALLOC_REG_SET (NULL);

  /* Allocate array to keep a list of insns which modify memory in each
     basic block.  */
  modify_mem_list = GCNEWVEC (VEC (rtx,heap) *, last_basic_block);
  canon_modify_mem_list = GCNEWVEC (VEC (modify_pair,heap) *,
                                    last_basic_block);
  modify_mem_list_set = BITMAP_ALLOC (NULL);
  blocks_with_calls = BITMAP_ALLOC (NULL);
}

/* Free memory allocated by alloc_gcse_mem.  */

static void
free_gcse_mem (void)
{
  FREE_REG_SET (reg_set_bitmap);

  free_modify_mem_tables ();
  BITMAP_FREE (modify_mem_list_set);
  BITMAP_FREE (blocks_with_calls);
}
\f
/* Compute the local properties of each recorded expression.

   Local properties are those that are defined by the block, irrespective of
   other blocks.

   An expression is transparent in a block if its operands are not modified
   in the block.

   An expression is computed (locally available) in a block if it is computed
   at least once and expression would contain the same value if the
   computation was moved to the end of the block.

   An expression is locally anticipatable in a block if it is computed at
   least once and expression would contain the same value if the computation
   was moved to the beginning of the block.

   We call this routine for pre and code hoisting.  They all compute
   basically the same information and thus can easily share this code.

   TRANSP, COMP, and ANTLOC are destination sbitmaps for recording local
   properties.  If NULL, then it is not necessary to compute or record that
   particular property.

   TABLE controls which hash table to look at.  */

static void
compute_local_properties (sbitmap *transp, sbitmap *comp, sbitmap *antloc,
                          struct hash_table_d *table)
{
  unsigned int i;

  /* Initialize any bitmaps that were passed in.  */
  if (transp)
    {
      sbitmap_vector_ones (transp, last_basic_block);
    }

  if (comp)
    sbitmap_vector_zero (comp, last_basic_block);
  if (antloc)
    sbitmap_vector_zero (antloc, last_basic_block);

  for (i = 0; i < table->size; i++)
    {
      struct expr *expr;

      for (expr = table->table[i]; expr != NULL; expr = expr->next_same_hash)
        {
          int indx = expr->bitmap_index;
          struct occr *occr;

          /* The expression is transparent in this block if it is not killed.
             We start by assuming all are transparent [none are killed], and
             then reset the bits for those that are.  */
          if (transp)
            compute_transp (expr->expr, indx, transp);

          /* The occurrences recorded in antic_occr are exactly those that
             we want to set to nonzero in ANTLOC.  */
          if (antloc)
            for (occr = expr->antic_occr; occr != NULL; occr = occr->next)
              {
                SET_BIT (antloc[BLOCK_FOR_INSN (occr->insn)->index], indx);

                /* While we're scanning the table, this is a good place to
                   initialize this.  */
                occr->deleted_p = 0;
              }

          /* The occurrences recorded in avail_occr are exactly those that
             we want to set to nonzero in COMP.  */
          if (comp)
            for (occr = expr->avail_occr; occr != NULL; occr = occr->next)
              {
                SET_BIT (comp[BLOCK_FOR_INSN (occr->insn)->index], indx);

                /* While we're scanning the table, this is a good place to
                   initialize this.  */
                occr->copied_p = 0;
              }

          /* While we're scanning the table, this is a good place to
             initialize this.  */
          expr->reaching_reg = 0;
        }
    }
}
\f
/* Hash table support.  */

struct reg_avail_info
{
  basic_block last_bb;
  int first_set;
  int last_set;
};

static struct reg_avail_info *reg_avail_info;
static basic_block current_bb;

/* See whether X, the source of a set, is something we want to consider for
   GCSE.  */

static int
want_to_gcse_p (rtx x, int *max_distance_ptr)
{
#ifdef STACK_REGS
  /* On register stack architectures, don't GCSE constants from the
     constant pool, as the benefits are often swamped by the overhead
     of shuffling the register stack between basic blocks.  */
  if (IS_STACK_MODE (GET_MODE (x)))
    x = avoid_constant_pool_reference (x);
#endif

  /* GCSE'ing constants:

     We do not specifically distinguish between constant and non-constant
     expressions in PRE and Hoist.  We use set_src_cost below to limit
     the maximum distance simple expressions can travel.

     Nevertheless, constants are much easier to GCSE, and, hence,
     it is easy to overdo the optimizations.  Usually, excessive PRE and
     Hoisting of constant leads to increased register pressure.

     RA can deal with this by rematerialing some of the constants.
     Therefore, it is important that the back-end generates sets of constants
     in a way that allows reload rematerialize them under high register
     pressure, i.e., a pseudo register with REG_EQUAL to constant
     is set only once.  Failing to do so will result in IRA/reload
     spilling such constants under high register pressure instead of
     rematerializing them.  */

  switch (GET_CODE (x))
    {
    case REG:
    case SUBREG:
    case CALL:
      return 0;

    case CONST_INT:
    case CONST_DOUBLE:
    case CONST_FIXED:
    case CONST_VECTOR:
      if (!doing_code_hoisting_p)
        /* Do not PRE constants.  */
        return 0;

      /* FALLTHRU */

    default:
      if (doing_code_hoisting_p)
        /* PRE doesn't implement max_distance restriction.  */
        {
          int cost;
          int max_distance;

          gcc_assert (!optimize_function_for_speed_p (cfun)
                      && optimize_function_for_size_p (cfun));
          cost = set_src_cost (x, 0);

          if (cost < COSTS_N_INSNS (GCSE_UNRESTRICTED_COST))
            {
              max_distance = (GCSE_COST_DISTANCE_RATIO * cost) / 10;
              if (max_distance == 0)
                return 0;

              gcc_assert (max_distance > 0);
            }
          else
            max_distance = 0;

          if (max_distance_ptr)
            *max_distance_ptr = max_distance;
        }

      return can_assign_to_reg_without_clobbers_p (x);
    }
}

/* Used internally by can_assign_to_reg_without_clobbers_p.  */

static GTY(()) rtx test_insn;

/* Return true if we can assign X to a pseudo register such that the
   resulting insn does not result in clobbering a hard register as a
   side-effect.

   Additionally, if the target requires it, check that the resulting insn
   can be copied.  If it cannot, this means that X is special and probably
   has hidden side-effects we don't want to mess with.

   This function is typically used by code motion passes, to verify
   that it is safe to insert an insn without worrying about clobbering
   maybe live hard regs.  */

bool
can_assign_to_reg_without_clobbers_p (rtx x)
{
  int num_clobbers = 0;
  int icode;

  /* If this is a valid operand, we are OK.  If it's VOIDmode, we aren't.  */
  if (general_operand (x, GET_MODE (x)))
    return 1;
  else if (GET_MODE (x) == VOIDmode)
    return 0;

  /* Otherwise, check if we can make a valid insn from it.  First initialize
     our test insn if we haven't already.  */
  if (test_insn == 0)
    {
      test_insn
        = make_insn_raw (gen_rtx_SET (VOIDmode,
                                      gen_rtx_REG (word_mode,
                                                   FIRST_PSEUDO_REGISTER * 2),
                                      const0_rtx));
      NEXT_INSN (test_insn) = PREV_INSN (test_insn) = 0;
    }

  /* Now make an insn like the one we would make when GCSE'ing and see if
     valid.  */
  PUT_MODE (SET_DEST (PATTERN (test_insn)), GET_MODE (x));
  SET_SRC (PATTERN (test_insn)) = x;

  icode = recog (PATTERN (test_insn), test_insn, &num_clobbers);
  if (icode < 0)
    return false;

  if (num_clobbers > 0 && added_clobbers_hard_reg_p (icode))
    return false;

  if (targetm.cannot_copy_insn_p && targetm.cannot_copy_insn_p (test_insn))
    return false;

  return true;
}

/* Return nonzero if the operands of expression X are unchanged from the
   start of INSN's basic block up to but not including INSN (if AVAIL_P == 0),
   or from INSN to the end of INSN's basic block (if AVAIL_P != 0).  */

static int
oprs_unchanged_p (const_rtx x, const_rtx insn, int avail_p)
{
  int i, j;
  enum rtx_code code;
  const char *fmt;

  if (x == 0)
    return 1;

  code = GET_CODE (x);
  switch (code)
    {
    case REG:
      {
        struct reg_avail_info *info = &reg_avail_info[REGNO (x)];

        if (info->last_bb != current_bb)
          return 1;
        if (avail_p)
          return info->last_set < DF_INSN_LUID (insn);
        else
          return info->first_set >= DF_INSN_LUID (insn);
      }

    case MEM:
      if (load_killed_in_block_p (current_bb, DF_INSN_LUID (insn),
                                  x, avail_p))
        return 0;
      else
        return oprs_unchanged_p (XEXP (x, 0), insn, avail_p);

    case PRE_DEC:
    case PRE_INC:
    case POST_DEC:
    case POST_INC:
    case PRE_MODIFY:
    case POST_MODIFY:
      return 0;

    case PC:
    case CC0: /*FIXME*/
    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 1;

    default:
      break;
    }

  for (i = GET_RTX_LENGTH (code) - 1, fmt = GET_RTX_FORMAT (code); i >= 0; i--)
    {
      if (fmt[i] == '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)
            return oprs_unchanged_p (XEXP (x, i), insn, avail_p);

          else if (! oprs_unchanged_p (XEXP (x, i), insn, avail_p))
            return 0;
        }
      else if (fmt[i] == 'E')
        for (j = 0; j < XVECLEN (x, i); j++)
          if (! oprs_unchanged_p (XVECEXP (x, i, j), insn, avail_p))
            return 0;
    }

  return 1;
}

/* Info passed from load_killed_in_block_p to mems_conflict_for_gcse_p.  */

struct mem_conflict_info
{
  /* A memory reference for a load instruction, mems_conflict_for_gcse_p will
     see if a memory store conflicts with this memory load.  */
  const_rtx mem;

  /* True if mems_conflict_for_gcse_p finds a conflict between two memory
     references.  */
  bool conflict;
};

/* DEST is the output of an instruction.  If it is a memory reference and
   possibly conflicts with the load found in DATA, then communicate this
   information back through DATA.  */

static void
mems_conflict_for_gcse_p (rtx dest, const_rtx setter ATTRIBUTE_UNUSED,
                          void *data)
{
  struct mem_conflict_info *mci = (struct mem_conflict_info *) data;

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

  /* If DEST is not a MEM, then it will not conflict with the load.  Note
     that function calls are assumed to clobber memory, but are handled
     elsewhere.  */
  if (! MEM_P (dest))
    return;

  /* If we are setting a MEM in our list of specially recognized MEMs,
     don't mark as killed this time.  */
  if (pre_ldst_mems != NULL && expr_equiv_p (dest, mci->mem))
    {
      if (!find_rtx_in_ldst (dest))
        mci->conflict = true;
      return;
    }

  if (true_dependence (dest, GET_MODE (dest), mci->mem))
    mci->conflict = true;
}

/* Return nonzero if the expression in X (a memory reference) is killed
   in block BB before or after the insn with the LUID in UID_LIMIT.
   AVAIL_P is nonzero for kills after UID_LIMIT, and zero for kills
   before UID_LIMIT.

   To check the entire block, set UID_LIMIT to max_uid + 1 and
   AVAIL_P to 0.  */

static int
load_killed_in_block_p (const_basic_block bb, int uid_limit, const_rtx x,
                        int avail_p)
{
  VEC (rtx,heap) *list = modify_mem_list[bb->index];
  rtx setter;
  unsigned ix;

  /* If this is a readonly then we aren't going to be changing it.  */
  if (MEM_READONLY_P (x))
    return 0;

  FOR_EACH_VEC_ELT_REVERSE (rtx, list, ix, setter)
    {
      struct mem_conflict_info mci;

      /* Ignore entries in the list that do not apply.  */
      if ((avail_p
           && DF_INSN_LUID (setter) < uid_limit)
          || (! avail_p
              && DF_INSN_LUID (setter) > uid_limit))
        continue;

      /* If SETTER is a call everything is clobbered.  Note that calls
         to pure functions are never put on the list, so we need not
         worry about them.  */
      if (CALL_P (setter))
        return 1;

      /* SETTER must be an INSN of some kind that sets memory.  Call
         note_stores to examine each hunk of memory that is modified.  */
      mci.mem = x;
      mci.conflict = false;
      note_stores (PATTERN (setter), mems_conflict_for_gcse_p, &mci);
      if (mci.conflict)
        return 1;
    }
  return 0;
}

/* Return nonzero if the operands of expression X are unchanged from
   the start of INSN's basic block up to but not including INSN.  */

static int
oprs_anticipatable_p (const_rtx x, const_rtx insn)
{
  return oprs_unchanged_p (x, insn, 0);
}

/* Return nonzero if the operands of expression X are unchanged from
   INSN to the end of INSN's basic block.  */

static int
oprs_available_p (const_rtx x, const_rtx insn)
{
  return oprs_unchanged_p (x, insn, 1);
}

/* Hash expression X.

   MODE is only used if X is a CONST_INT.  DO_NOT_RECORD_P is a boolean
   indicating if a volatile operand is found or if the expression contains
   something we don't want to insert in the table.  HASH_TABLE_SIZE is
   the current size of the hash table to be probed.  */

static unsigned int
hash_expr (const_rtx x, enum machine_mode mode, int *do_not_record_p,
           int hash_table_size)
{
  unsigned int hash;

  *do_not_record_p = 0;

  hash = hash_rtx (x, mode, do_not_record_p, NULL, /*have_reg_qty=*/false);
  return hash % hash_table_size;
}

/* Return nonzero if exp1 is equivalent to exp2.  */

static int
expr_equiv_p (const_rtx x, const_rtx y)
{
  return exp_equiv_p (x, y, 0, true);
}

/* Insert expression X in INSN in the hash TABLE.
   If it is already present, record it as the last occurrence in INSN's
   basic block.

   MODE is the mode of the value X is being stored into.
   It is only used if X is a CONST_INT.

   ANTIC_P is nonzero if X is an anticipatable expression.
   AVAIL_P is nonzero if X is an available expression.

   MAX_DISTANCE is the maximum distance in instructions this expression can
   be moved.  */

static void
insert_expr_in_table (rtx x, enum machine_mode mode, rtx insn, int antic_p,
                      int avail_p, int max_distance, struct hash_table_d *table)
{
  int found, do_not_record_p;
  unsigned int hash;
  struct expr *cur_expr, *last_expr = NULL;
  struct occr *antic_occr, *avail_occr;

  hash = hash_expr (x, mode, &do_not_record_p, table->size);

  /* Do not insert expression in table if it contains volatile operands,
     or if hash_expr determines the expression is something we don't want
     to or can't handle.  */
  if (do_not_record_p)
    return;

  cur_expr = table->table[hash];
  found = 0;

  while (cur_expr && 0 == (found = expr_equiv_p (cur_expr->expr, x)))
    {
      /* If the expression isn't found, save a pointer to the end of
         the list.  */
      last_expr = cur_expr;
      cur_expr = cur_expr->next_same_hash;
    }

  if (! found)
    {
      cur_expr = GOBNEW (struct expr);
      bytes_used += sizeof (struct expr);
      if (table->table[hash] == NULL)
        /* This is the first pattern that hashed to this index.  */
        table->table[hash] = cur_expr;
      else
        /* Add EXPR to end of this hash chain.  */
        last_expr->next_same_hash = cur_expr;

      /* Set the fields of the expr element.  */
      cur_expr->expr = x;
      cur_expr->bitmap_index = table->n_elems++;
      cur_expr->next_same_hash = NULL;
      cur_expr->antic_occr = NULL;
      cur_expr->avail_occr = NULL;
      gcc_assert (max_distance >= 0);
      cur_expr->max_distance = max_distance;
    }
  else
    gcc_assert (cur_expr->max_distance == max_distance);

  /* Now record the occurrence(s).  */
  if (antic_p)
    {
      antic_occr = cur_expr->antic_occr;

      if (antic_occr
          && BLOCK_FOR_INSN (antic_occr->insn) != BLOCK_FOR_INSN (insn))
        antic_occr = NULL;

      if (antic_occr)
        /* Found another instance of the expression in the same basic block.
           Prefer the currently recorded one.  We want the first one in the
           block and the block is scanned from start to end.  */
        ; /* nothing to do */
      else
        {
          /* First occurrence of this expression in this basic block.  */
          antic_occr = GOBNEW (struct occr);
          bytes_used += sizeof (struct occr);
          antic_occr->insn = insn;
          antic_occr->next = cur_expr->antic_occr;
          antic_occr->deleted_p = 0;
          cur_expr->antic_occr = antic_occr;
        }
    }

  if (avail_p)
    {
      avail_occr = cur_expr->avail_occr;

      if (avail_occr
          && BLOCK_FOR_INSN (avail_occr->insn) == BLOCK_FOR_INSN (insn))
        {
          /* Found another instance of the expression in the same basic block.
             Prefer this occurrence to the currently recorded one.  We want
             the last one in the block and the block is scanned from start
             to end.  */
          avail_occr->insn = insn;
        }
      else
        {
          /* First occurrence of this expression in this basic block.  */
          avail_occr = GOBNEW (struct occr);
          bytes_used += sizeof (struct occr);
          avail_occr->insn = insn;
          avail_occr->next = cur_expr->avail_occr;
          avail_occr->deleted_p = 0;
          cur_expr->avail_occr = avail_occr;
        }
    }
}

/* Scan SET present in INSN and add an entry to the hash TABLE.  */

static void
hash_scan_set (rtx set, rtx insn, struct hash_table_d *table)
{
  rtx src = SET_SRC (set);
  rtx dest = SET_DEST (set);
  rtx note;

  if (GET_CODE (src) == CALL)
    hash_scan_call (src, insn, table);

  else if (REG_P (dest))
    {
      unsigned int regno = REGNO (dest);
      int max_distance = 0;

      /* See if a REG_EQUAL note shows this equivalent to a simpler expression.

         This allows us to do a single GCSE pass and still eliminate
         redundant constants, addresses or other expressions that are
         constructed with multiple instructions.

         However, keep the original SRC if INSN is a simple reg-reg move.
         In this case, there will almost always be a REG_EQUAL note on the
         insn that sets SRC.  By recording the REG_EQUAL value here as SRC
         for INSN, we miss copy propagation opportunities and we perform the
         same PRE GCSE operation repeatedly on the same REG_EQUAL value if we
         do more than one PRE GCSE pass.

         Note that this does not impede profitable constant propagations.  We
         "look through" reg-reg sets in lookup_avail_set.  */
      note = find_reg_equal_equiv_note (insn);
      if (note != 0
          && REG_NOTE_KIND (note) == REG_EQUAL
          && !REG_P (src)
          && want_to_gcse_p (XEXP (note, 0), NULL))
        src = XEXP (note, 0), set = gen_rtx_SET (VOIDmode, dest, src);

      /* Only record sets of pseudo-regs in the hash table.  */
      if (regno >= FIRST_PSEUDO_REGISTER
          /* Don't GCSE something if we can't do a reg/reg copy.  */
          && can_copy_p (GET_MODE (dest))
          /* GCSE commonly inserts instruction after the insn.  We can't
             do that easily for EH edges so disable GCSE on these for now.  */
          /* ??? We can now easily create new EH landing pads at the
             gimple level, for splitting edges; there's no reason we
             can't do the same thing at the rtl level.  */
          && !can_throw_internal (insn)
          /* Is SET_SRC something we want to gcse?  */
          && want_to_gcse_p (src, &max_distance)
          /* Don't CSE a nop.  */
          && ! set_noop_p (set)
          /* Don't GCSE if it has attached REG_EQUIV note.
             At this point this only function parameters should have
             REG_EQUIV notes and if the argument slot is used somewhere
             explicitly, it means address of parameter has been taken,
             so we should not extend the lifetime of the pseudo.  */
          && (note == NULL_RTX || ! MEM_P (XEXP (note, 0))))
        {
          /* An expression is not anticipatable if its operands are
             modified before this insn or if this is not the only SET in
             this insn.  The latter condition does not have to mean that
             SRC itself is not anticipatable, but we just will not be
             able to handle code motion of insns with multiple sets.  */
          int antic_p = oprs_anticipatable_p (src, insn)
                        && !multiple_sets (insn);
          /* An expression is not available if its operands are
             subsequently modified, including this insn.  It's also not
             available if this is a branch, because we can't insert
             a set after the branch.  */
          int avail_p = (oprs_available_p (src, insn)
                         && ! JUMP_P (insn));

          insert_expr_in_table (src, GET_MODE (dest), insn, antic_p, avail_p,
                                max_distance, table);
        }
    }
  /* In case of store we want to consider the memory value as available in
     the REG stored in that memory. This makes it possible to remove
     redundant loads from due to stores to the same location.  */
  else if (flag_gcse_las && REG_P (src) && MEM_P (dest))
      {
        unsigned int regno = REGNO (src);
        int max_distance = 0;

        /* Only record sets of pseudo-regs in the hash table.  */
        if (regno >= FIRST_PSEUDO_REGISTER
           /* Don't GCSE something if we can't do a reg/reg copy.  */
           && can_copy_p (GET_MODE (src))
           /* GCSE commonly inserts instruction after the insn.  We can't
              do that easily for EH edges so disable GCSE on these for now.  */
           && !can_throw_internal (insn)
           /* Is SET_DEST something we want to gcse?  */
           && want_to_gcse_p (dest, &max_distance)
           /* Don't CSE a nop.  */
           && ! set_noop_p (set)
           /* Don't GCSE if it has attached REG_EQUIV note.
              At this point this only function parameters should have
              REG_EQUIV notes and if the argument slot is used somewhere
              explicitly, it means address of parameter has been taken,
              so we should not extend the lifetime of the pseudo.  */
           && ((note = find_reg_note (insn, REG_EQUIV, NULL_RTX)) == 0
               || ! MEM_P (XEXP (note, 0))))
             {
               /* Stores are never anticipatable.  */
               int antic_p = 0;
               /* An expression is not available if its operands are
                  subsequently modified, including this insn.  It's also not
                  available if this is a branch, because we can't insert
                  a set after the branch.  */
               int avail_p = oprs_available_p (dest, insn)
                             && ! JUMP_P (insn);

               /* Record the memory expression (DEST) in the hash table.  */
               insert_expr_in_table (dest, GET_MODE (dest), insn,
                                     antic_p, avail_p, max_distance, table);
             }
      }
}

static void
hash_scan_clobber (rtx x ATTRIBUTE_UNUSED, rtx insn ATTRIBUTE_UNUSED,
                   struct hash_table_d *table ATTRIBUTE_UNUSED)
{
  /* Currently nothing to do.  */
}

static void
hash_scan_call (rtx x ATTRIBUTE_UNUSED, rtx insn ATTRIBUTE_UNUSED,
                struct hash_table_d *table ATTRIBUTE_UNUSED)
{
  /* Currently nothing to do.  */
}

/* Process INSN and add hash table entries as appropriate.  */

static void
hash_scan_insn (rtx insn, struct hash_table_d *table)
{
  rtx pat = PATTERN (insn);
  int i;

  /* Pick out the sets of INSN and for other forms of instructions record
     what's been modified.  */

  if (GET_CODE (pat) == SET)
    hash_scan_set (pat, insn, table);

  else if (GET_CODE (pat) == CLOBBER)
    hash_scan_clobber (pat, insn, table);

  else if (GET_CODE (pat) == CALL)
    hash_scan_call (pat, insn, table);

  else if (GET_CODE (pat) == PARALLEL)
    for (i = 0; i < XVECLEN (pat, 0); i++)
      {
        rtx x = XVECEXP (pat, 0, i);

        if (GET_CODE (x) == SET)
          hash_scan_set (x, insn, table);
        else if (GET_CODE (x) == CLOBBER)
          hash_scan_clobber (x, insn, table);
        else if (GET_CODE (x) == CALL)
          hash_scan_call (x, insn, table);
      }
}

/* Dump the hash table TABLE to file FILE under the name NAME.  */

static void
dump_hash_table (FILE *file, const char *name, struct hash_table_d *table)
{
  int i;
  /* Flattened out table, so it's printed in proper order.  */
  struct expr **flat_table;
  unsigned int *hash_val;
  struct expr *expr;

  flat_table = XCNEWVEC (struct expr *, table->n_elems);
  hash_val = XNEWVEC (unsigned int, table->n_elems);

  for (i = 0; i < (int) table->size; i++)
    for (expr = table->table[i]; expr != NULL; expr = expr->next_same_hash)
      {
        flat_table[expr->bitmap_index] = expr;
        hash_val[expr->bitmap_index] = i;
      }

  fprintf (file, "%s hash table (%d buckets, %d entries)\n",
           name, table->size, table->n_elems);

  for (i = 0; i < (int) table->n_elems; i++)
    if (flat_table[i] != 0)
      {
        expr = flat_table[i];
        fprintf (file, "Index %d (hash value %d; max distance %d)\n  ",
                 expr->bitmap_index, hash_val[i], expr->max_distance);
        print_rtl (file, expr->expr);
        fprintf (file, "\n");
      }

  fprintf (file, "\n");

  free (flat_table);
  free (hash_val);
}

/* Record register first/last/block set information for REGNO in INSN.

   first_set records the first place in the block where the register
   is set and is used to compute "anticipatability".

   last_set records the last place in the block where the register
   is set and is used to compute "availability".

   last_bb records the block for which first_set and last_set are
   valid, as a quick test to invalidate them.  */

static void
record_last_reg_set_info (rtx insn, int regno)
{
  struct reg_avail_info *info = &reg_avail_info[regno];
  int luid = DF_INSN_LUID (insn);

  info->last_set = luid;
  if (info->last_bb != current_bb)
    {
      info->last_bb = current_bb;
      info->first_set = luid;
    }
}

/* Record all of the canonicalized MEMs of record_last_mem_set_info's insn.
   Note we store a pair of elements in the list, so they have to be
   taken off pairwise.  */

static void
canon_list_insert (rtx dest ATTRIBUTE_UNUSED, const_rtx x ATTRIBUTE_UNUSED,
                   void * v_insn)
{
  rtx dest_addr, insn;
  int bb;
  modify_pair *pair;

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

  /* If DEST is not a MEM, then it will not conflict with a load.  Note
     that function calls are assumed to clobber memory, but are handled
     elsewhere.  */

  if (! MEM_P (dest))
    return;

  dest_addr = get_addr (XEXP (dest, 0));
  dest_addr = canon_rtx (dest_addr);
  insn = (rtx) v_insn;
  bb = BLOCK_FOR_INSN (insn)->index;

  pair = VEC_safe_push (modify_pair, heap, canon_modify_mem_list[bb], NULL);
  pair->dest = dest;
  pair->dest_addr = dest_addr;
}

/* Record memory modification information for INSN.  We do not actually care
   about the memory location(s) that are set, or even how they are set (consider
   a CALL_INSN).  We merely need to record which insns modify memory.  */

static void
record_last_mem_set_info (rtx insn)
{
  int bb = BLOCK_FOR_INSN (insn)->index;

  /* load_killed_in_block_p will handle the case of calls clobbering
     everything.  */
  VEC_safe_push (rtx, heap, modify_mem_list[bb], insn);
  bitmap_set_bit (modify_mem_list_set, bb);

  if (CALL_P (insn))
    bitmap_set_bit (blocks_with_calls, bb);
  else
    note_stores (PATTERN (insn), canon_list_insert, (void*) insn);
}

/* Called from compute_hash_table via note_stores to handle one
   SET or CLOBBER in an insn.  DATA is really the instruction in which
   the SET is taking place.  */

static void
record_last_set_info (rtx dest, const_rtx setter ATTRIBUTE_UNUSED, void *data)
{
  rtx last_set_insn = (rtx) data;

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

  if (REG_P (dest))
    record_last_reg_set_info (last_set_insn, REGNO (dest));
  else if (MEM_P (dest)
           /* Ignore pushes, they clobber nothing.  */
           && ! push_operand (dest, GET_MODE (dest)))
    record_last_mem_set_info (last_set_insn);
}

/* Top level function to create an expression hash table.

   Expression entries are placed in the hash table if
   - they are of the form (set (pseudo-reg) src),
   - src is something we want to perform GCSE on,
   - none of the operands are subsequently modified in the block

   Currently src must be a pseudo-reg or a const_int.

   TABLE is the table computed.  */

static void
compute_hash_table_work (struct hash_table_d *table)
{
  int i;

  /* re-Cache any INSN_LIST nodes we have allocated.  */
  clear_modify_mem_tables ();
  /* Some working arrays used to track first and last set in each block.  */
  reg_avail_info = GNEWVEC (struct reg_avail_info, max_reg_num ());

  for (i = 0; i < max_reg_num (); ++i)
    reg_avail_info[i].last_bb = NULL;

  FOR_EACH_BB (current_bb)
    {
      rtx insn;
      unsigned int regno;

      /* First pass over the instructions records information used to
         determine when registers and memory are first and last set.  */
      FOR_BB_INSNS (current_bb, insn)
        {
          if (!NONDEBUG_INSN_P (insn))
            continue;

          if (CALL_P (insn))
            {
              for (regno = 0; regno < FIRST_PSEUDO_REGISTER; regno++)
                if (TEST_HARD_REG_BIT (regs_invalidated_by_call, regno))
                  record_last_reg_set_info (insn, regno);

              if (! RTL_CONST_OR_PURE_CALL_P (insn))
                record_last_mem_set_info (insn);
            }

          note_stores (PATTERN (insn), record_last_set_info, insn);
        }

      /* The next pass builds the hash table.  */
      FOR_BB_INSNS (current_bb, insn)
        if (NONDEBUG_INSN_P (insn))
          hash_scan_insn (insn, table);
    }

  free (reg_avail_info);
  reg_avail_info = NULL;
}

/* Allocate space for the set/expr hash TABLE.
   It is used to determine the number of buckets to use.  */

static void
alloc_hash_table (struct hash_table_d *table)
{
  int n;

  n = get_max_insn_count ();

  table->size = n / 4;
  if (table->size < 11)
    table->size = 11;

  /* Attempt to maintain efficient use of hash table.
     Making it an odd number is simplest for now.
     ??? Later take some measurements.  */
  table->size |= 1;
  n = table->size * sizeof (struct expr *);
  table->table = GNEWVAR (struct expr *, n);
}

/* Free things allocated by alloc_hash_table.  */

static void
free_hash_table (struct hash_table_d *table)
{
  free (table->table);
}

/* Compute the expression hash table TABLE.  */

static void
compute_hash_table (struct hash_table_d *table)
{
  /* Initialize count of number of entries in hash table.  */
  table->n_elems = 0;
  memset (table->table, 0, table->size * sizeof (struct expr *));

  compute_hash_table_work (table);
}
\f
/* Expression tracking support.  */

/* Clear canon_modify_mem_list and modify_mem_list tables.  */
static void
clear_modify_mem_tables (void)
{
  unsigned i;
  bitmap_iterator bi;

  EXECUTE_IF_SET_IN_BITMAP (modify_mem_list_set, 0, i, bi)
    {
      VEC_free (rtx, heap, modify_mem_list[i]);
      VEC_free (modify_pair, heap, canon_modify_mem_list[i]);
    }
  bitmap_clear (modify_mem_list_set);
  bitmap_clear (blocks_with_calls);
}

/* Release memory used by modify_mem_list_set.  */

static void
free_modify_mem_tables (void)
{
  clear_modify_mem_tables ();
  free (modify_mem_list);
  free (canon_modify_mem_list);
  modify_mem_list = 0;
  canon_modify_mem_list = 0;
}
\f
/* For each block, compute whether X is transparent.  X is either an
   expression or an assignment [though we don't care which, for this context
   an assignment is treated as an expression].  For each block where an
   element of X is modified, reset the INDX bit in BMAP.  */

static void
compute_transp (const_rtx x, int indx, sbitmap *bmap)
{
  int i, j;
  enum rtx_code code;
  const char *fmt;

  /* repeat is used to turn tail-recursion into iteration since GCC
     can't do it when there's no return value.  */
 repeat:

  if (x == 0)
    return;

  code = GET_CODE (x);
  switch (code)
    {
    case REG:
        {
          df_ref def;
          for (def = DF_REG_DEF_CHAIN (REGNO (x));
               def;
               def = DF_REF_NEXT_REG (def))
            RESET_BIT (bmap[DF_REF_BB (def)->index], indx);
        }

      return;

    case MEM:
      if (! MEM_READONLY_P (x))
        {
          bitmap_iterator bi;
          unsigned bb_index;

          /* First handle all the blocks with calls.  We don't need to
             do any list walking for them.  */
          EXECUTE_IF_SET_IN_BITMAP (blocks_with_calls, 0, bb_index, bi)
            {
              RESET_BIT (bmap[bb_index], indx);
            }

            /* Now iterate over the blocks which have memory modifications
               but which do not have any calls.  */
            EXECUTE_IF_AND_COMPL_IN_BITMAP (modify_mem_list_set,
                                            blocks_with_calls,
                                            0, bb_index, bi)
              {
                VEC (modify_pair,heap) *list
                  = canon_modify_mem_list[bb_index];
                modify_pair *pair;
                unsigned ix;

                FOR_EACH_VEC_ELT_REVERSE (modify_pair, list, ix, pair)
                  {
                    rtx dest = pair->dest;
                    rtx dest_addr = pair->dest_addr;

                    if (canon_true_dependence (dest, GET_MODE (dest),
                                               dest_addr, x, NULL_RTX))
                      RESET_BIT (bmap[bb_index], indx);
                  }
              }
        }

      x = XEXP (x, 0);
      goto repeat;

    case PC:
    case CC0: /*FIXME*/
    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;

    default:
      break;
    }

  for (i = GET_RTX_LENGTH (code) - 1, fmt = GET_RTX_FORMAT (code); i >= 0; i--)
    {
      if (fmt[i] == '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;
            }

          compute_transp (XEXP (x, i), indx, bmap);
        }
      else if (fmt[i] == 'E')
        for (j = 0; j < XVECLEN (x, i); j++)
          compute_transp (XVECEXP (x, i, j), indx, bmap);
    }
}
\f
/* Compute PRE+LCM working variables.  */

/* Local properties of expressions.  */

/* Nonzero for expressions that are transparent in the block.  */
static sbitmap *transp;

/* Nonzero for expressions that are computed (available) in the block.  */
static sbitmap *comp;

/* Nonzero for expressions that are locally anticipatable in the block.  */
static sbitmap *antloc;

/* Nonzero for expressions where this block is an optimal computation
   point.  */
static sbitmap *pre_optimal;

/* Nonzero for expressions which are redundant in a particular block.  */
static sbitmap *pre_redundant;

/* Nonzero for expressions which should be inserted on a specific edge.  */
static sbitmap *pre_insert_map;

/* Nonzero for expressions which should be deleted in a specific block.  */
static sbitmap *pre_delete_map;

/* Allocate vars used for PRE analysis.  */

static void
alloc_pre_mem (int n_blocks, int n_exprs)
{
  transp = sbitmap_vector_alloc (n_blocks, n_exprs);
  comp = sbitmap_vector_alloc (n_blocks, n_exprs);
  antloc = sbitmap_vector_alloc (n_blocks, n_exprs);

  pre_optimal = NULL;
  pre_redundant = NULL;
  pre_insert_map = NULL;
  pre_delete_map = NULL;
  ae_kill = sbitmap_vector_alloc (n_blocks, n_exprs);

  /* pre_insert and pre_delete are allocated later.  */
}

/* Free vars used for PRE analysis.  */

static void
free_pre_mem (void)
{
  sbitmap_vector_free (transp);
  sbitmap_vector_free (comp);

  /* ANTLOC and AE_KILL are freed just after pre_lcm finishes.  */

  if (pre_optimal)
    sbitmap_vector_free (pre_optimal);
  if (pre_redundant)
    sbitmap_vector_free (pre_redundant);
  if (pre_insert_map)
    sbitmap_vector_free (pre_insert_map);
  if (pre_delete_map)
    sbitmap_vector_free (pre_delete_map);

  transp = comp = NULL;
  pre_optimal = pre_redundant = pre_insert_map = pre_delete_map = NULL;
}

/* Remove certain expressions from anticipatable and transparent
   sets of basic blocks that have incoming abnormal edge.
   For PRE remove potentially trapping expressions to avoid placing
   them on abnormal edges.  For hoisting remove memory references that
   can be clobbered by calls.  */

static void
prune_expressions (bool pre_p)
{
  sbitmap prune_exprs;
  struct expr *expr;
  unsigned int ui;
  basic_block bb;

  prune_exprs = sbitmap_alloc (expr_hash_table.n_elems);
  sbitmap_zero (prune_exprs);
  for (ui = 0; ui < expr_hash_table.size; ui++)
    {
      for (expr = expr_hash_table.table[ui]; expr; expr = expr->next_same_hash)
        {
          /* Note potentially trapping expressions.  */
          if (may_trap_p (expr->expr))
            {
              SET_BIT (prune_exprs, expr->bitmap_index);
              continue;
            }

          if (!pre_p && MEM_P (expr->expr))
            /* Note memory references that can be clobbered by a call.
               We do not split abnormal edges in hoisting, so would
               a memory reference get hoisted along an abnormal edge,
               it would be placed /before/ the call.  Therefore, only
               constant memory references can be hoisted along abnormal
               edges.  */
            {
              if (GET_CODE (XEXP (expr->expr, 0)) == SYMBOL_REF
                  && CONSTANT_POOL_ADDRESS_P (XEXP (expr->expr, 0)))
                continue;

              if (MEM_READONLY_P (expr->expr)
                  && !MEM_VOLATILE_P (expr->expr)
                  && MEM_NOTRAP_P (expr->expr))
                /* Constant memory reference, e.g., a PIC address.  */
                continue;

              /* ??? Optimally, we would use interprocedural alias
                 analysis to determine if this mem is actually killed
                 by this call.  */

              SET_BIT (prune_exprs, expr->bitmap_index);
            }
        }
    }

  FOR_EACH_BB (bb)
    {
      edge e;
      edge_iterator ei;

      /* If the current block is the destination of an abnormal edge, we
         kill all trapping (for PRE) and memory (for hoist) expressions
         because we won't be able to properly place the instruction on
         the edge.  So make them neither anticipatable nor transparent.
         This is fairly conservative.

         ??? For hoisting it may be necessary to check for set-and-jump
         instructions here, not just for abnormal edges.  The general problem
         is that when an expression cannot not be placed right at the end of
         a basic block we should account for any side-effects of a subsequent
         jump instructions that could clobber the expression.  It would
         be best to implement this check along the lines of
         hoist_expr_reaches_here_p where the target block is already known
         and, hence, there's no need to conservatively prune expressions on
         "intermediate" set-and-jump instructions.  */
      FOR_EACH_EDGE (e, ei, bb->preds)
        if ((e->flags & EDGE_ABNORMAL)
            && (pre_p || CALL_P (BB_END (e->src))))
          {
            sbitmap_difference (antloc[bb->index],
                                antloc[bb->index], prune_exprs);
            sbitmap_difference (transp[bb->index],
                                transp[bb->index], prune_exprs);
            break;
          }
    }

  sbitmap_free (prune_exprs);
}

/* It may be necessary to insert a large number of insns on edges to
   make the existing occurrences of expressions fully redundant.  This
   routine examines the set of insertions and deletions and if the ratio
   of insertions to deletions is too high for a particular expression, then
   the expression is removed from the insertion/deletion sets. 

   N_ELEMS is the number of elements in the hash table.  */

static void
prune_insertions_deletions (int n_elems)
{
  sbitmap_iterator sbi;
  sbitmap prune_exprs;

  /* We always use I to iterate over blocks/edges and J to iterate over
     expressions.  */
  unsigned int i, j;

  /* Counts for the number of times an expression needs to be inserted and
     number of times an expression can be removed as a result.  */
  int *insertions = GCNEWVEC (int, n_elems);
  int *deletions = GCNEWVEC (int, n_elems);

  /* Set of expressions which require too many insertions relative to
     the number of deletions achieved.  We will prune these out of the
     insertion/deletion sets.  */
  prune_exprs = sbitmap_alloc (n_elems);
  sbitmap_zero (prune_exprs);

  /* Iterate over the edges counting the number of times each expression
     needs to be inserted.  */
  for (i = 0; i < (unsigned) n_edges; i++)
    {
      EXECUTE_IF_SET_IN_SBITMAP (pre_insert_map[i], 0, j, sbi)
        insertions[j]++;
    }

  /* Similarly for deletions, but those occur in blocks rather than on
     edges.  */
  for (i = 0; i < (unsigned) last_basic_block; i++)
    {
      EXECUTE_IF_SET_IN_SBITMAP (pre_delete_map[i], 0, j, sbi)
        deletions[j]++;
    }

  /* Now that we have accurate counts, iterate over the elements in the
     hash table and see if any need too many insertions relative to the
     number of evaluations that can be removed.  If so, mark them in
     PRUNE_EXPRS.  */
  for (j = 0; j < (unsigned) n_elems; j++)
    if (deletions[j]
        && ((unsigned) insertions[j] / deletions[j]) > MAX_GCSE_INSERTION_RATIO)
      SET_BIT (prune_exprs, j);

  /* Now prune PRE_INSERT_MAP and PRE_DELETE_MAP based on PRUNE_EXPRS.  */
  EXECUTE_IF_SET_IN_SBITMAP (prune_exprs, 0, j, sbi)
    {
      for (i = 0; i < (unsigned) n_edges; i++)
        RESET_BIT (pre_insert_map[i], j);

      for (i = 0; i < (unsigned) last_basic_block; i++)
        RESET_BIT (pre_delete_map[i], j);
    }

  sbitmap_free (prune_exprs);
  free (insertions);
  free (deletions);
}

/* Top level routine to do the dataflow analysis needed by PRE.  */

static struct edge_list *
compute_pre_data (void)
{
  struct edge_list *edge_list;
  basic_block bb;

  compute_local_properties (transp, comp, antloc, &expr_hash_table);
  prune_expressions (true);
  sbitmap_vector_zero (ae_kill, last_basic_block);

  /* Compute ae_kill for each basic block using:

     ~(TRANSP | COMP)
  */

  FOR_EACH_BB (bb)
    {
      sbitmap_a_or_b (ae_kill[bb->index], transp[bb->index], comp[bb->index]);
      sbitmap_not (ae_kill[bb->index], ae_kill[bb->index]);
    }

  edge_list = pre_edge_lcm (expr_hash_table.n_elems, transp, comp, antloc,
                            ae_kill, &pre_insert_map, &pre_delete_map);
  sbitmap_vector_free (antloc);
  antloc = NULL;
  sbitmap_vector_free (ae_kill);
  ae_kill = NULL;

  prune_insertions_deletions (expr_hash_table.n_elems);

  return edge_list;
}
\f
/* PRE utilities */

/* Return nonzero if an occurrence of expression EXPR in OCCR_BB would reach
   block BB.

   VISITED is a pointer to a working buffer for tracking which BB's have
   been visited.  It is NULL for the top-level call.

   We treat reaching expressions that go through blocks containing the same
   reaching expression as "not reaching".  E.g. if EXPR is generated in blocks
   2 and 3, INSN is in block 4, and 2->3->4, we treat the expression in block
   2 as not reaching.  The intent is to improve the probability of finding
   only one reaching expression and to reduce register lifetimes by picking
   the closest such expression.  */

static int
pre_expr_reaches_here_p_work (basic_block occr_bb, struct expr *expr,
                              basic_block bb, char *visited)
{
  edge pred;
  edge_iterator ei;

  FOR_EACH_EDGE (pred, ei, bb->preds)
    {
      basic_block pred_bb = pred->src;

      if (pred->src == ENTRY_BLOCK_PTR
          /* Has predecessor has already been visited?  */
          || visited[pred_bb->index])
        ;/* Nothing to do.  */

      /* Does this predecessor generate this expression?  */
      else if (TEST_BIT (comp[pred_bb->index], expr->bitmap_index))
        {
          /* Is this the occurrence we're looking for?
             Note that there's only one generating occurrence per block
             so we just need to check the block number.  */
          if (occr_bb == pred_bb)
            return 1;

          visited[pred_bb->index] = 1;
        }
      /* Ignore this predecessor if it kills the expression.  */
      else if (! TEST_BIT (transp[pred_bb->index], expr->bitmap_index))
        visited[pred_bb->index] = 1;

      /* Neither gen nor kill.  */
      else
        {
          visited[pred_bb->index] = 1;
          if (pre_expr_reaches_here_p_work (occr_bb, expr, pred_bb, visited))
            return 1;
        }
    }

  /* All paths have been checked.  */
  return 0;
}

/* The wrapper for pre_expr_reaches_here_work that ensures that any
   memory allocated for that function is returned.  */

static int
pre_expr_reaches_here_p (basic_block occr_bb, struct expr *expr, basic_block bb)
{
  int rval;
  char *visited = XCNEWVEC (char, last_basic_block);

  rval = pre_expr_reaches_here_p_work (occr_bb, expr, bb, visited);

  free (visited);
  return rval;
}
\f
/* Generate RTL to copy an EXPR to its `reaching_reg' and return it.  */

static rtx
process_insert_insn (struct expr *expr)
{
  rtx reg = expr->reaching_reg;
  /* Copy the expression to make sure we don't have any sharing issues.  */
  rtx exp = copy_rtx (expr->expr);
  rtx pat;

  start_sequence ();

  /* If the expression is something that's an operand, like a constant,
     just copy it to a register.  */
  if (general_operand (exp, GET_MODE (reg)))
    emit_move_insn (reg, exp);

  /* Otherwise, make a new insn to compute this expression and make sure the
     insn will be recognized (this also adds any needed CLOBBERs).  */
  else
    {
      rtx insn = emit_insn (gen_rtx_SET (VOIDmode, reg, exp));

      if (insn_invalid_p (insn, false))
        gcc_unreachable ();
    }

  pat = get_insns ();
  end_sequence ();

  return pat;
}

/* Add EXPR to the end of basic block BB.

   This is used by both the PRE and code hoisting.  */

static void
insert_insn_end_basic_block (struct expr *expr, basic_block bb)
{
  rtx insn = BB_END (bb);
  rtx new_insn;
  rtx reg = expr->reaching_reg;
  int regno = REGNO (reg);
  rtx pat, pat_end;

  pat = process_insert_insn (expr);
  gcc_assert (pat && INSN_P (pat));

  pat_end = pat;
  while (NEXT_INSN (pat_end) != NULL_RTX)
    pat_end = NEXT_INSN (pat_end);

  /* If the last insn is a jump, insert EXPR in front [taking care to
     handle cc0, etc. properly].  Similarly we need to care trapping
     instructions in presence of non-call exceptions.  */

  if (JUMP_P (insn)
      || (NONJUMP_INSN_P (insn)
          && (!single_succ_p (bb)
              || single_succ_edge (bb)->flags & EDGE_ABNORMAL)))
    {
#ifdef HAVE_cc0
      rtx note;
#endif

      /* If this is a jump table, then we can't insert stuff here.  Since
         we know the previous real insn must be the tablejump, we insert
         the new instruction just before the tablejump.  */
      if (GET_CODE (PATTERN (insn)) == ADDR_VEC
          || GET_CODE (PATTERN (insn)) == ADDR_DIFF_VEC)
        insn = prev_active_insn (insn);

#ifdef HAVE_cc0
      /* FIXME: 'twould be nice to call prev_cc0_setter here but it aborts
         if cc0 isn't set.  */
      note = find_reg_note (insn, REG_CC_SETTER, NULL_RTX);
      if (note)
        insn = XEXP (note, 0);
      else
        {
          rtx maybe_cc0_setter = prev_nonnote_insn (insn);
          if (maybe_cc0_setter
              && INSN_P (maybe_cc0_setter)
              && sets_cc0_p (PATTERN (maybe_cc0_setter)))
            insn = maybe_cc0_setter;
        }
#endif
      /* FIXME: What if something in cc0/jump uses value set in new insn?  */
      new_insn = emit_insn_before_noloc (pat, insn, bb);
    }

  /* Likewise if the last insn is a call, as will happen in the presence
     of exception handling.  */
  else if (CALL_P (insn)
           && (!single_succ_p (bb)
               || single_succ_edge (bb)->flags & EDGE_ABNORMAL))
    {
      /* Keeping in mind targets with small register classes and parameters
         in registers, we search backward and place the instructions before
         the first parameter is loaded.  Do this for everyone for consistency
         and a presumption that we'll get better code elsewhere as well.  */

      /* Since different machines initialize their parameter registers
         in different orders, assume nothing.  Collect the set of all
         parameter registers.  */
      insn = find_first_parameter_load (insn, BB_HEAD (bb));

      /* If we found all the parameter loads, then we want to insert
         before the first parameter load.

         If we did not find all the parameter loads, then we might have
         stopped on the head of the block, which could be a CODE_LABEL.
         If we inserted before the CODE_LABEL, then we would be putting
         the insn in the wrong basic block.  In that case, put the insn
         after the CODE_LABEL.  Also, respect NOTE_INSN_BASIC_BLOCK.  */
      while (LABEL_P (insn)
             || NOTE_INSN_BASIC_BLOCK_P (insn))
        insn = NEXT_INSN (insn);

      new_insn = emit_insn_before_noloc (pat, insn, bb);
    }
  else
    new_insn = emit_insn_after_noloc (pat, insn, bb);

  while (1)
    {
      if (INSN_P (pat))
        add_label_notes (PATTERN (pat), new_insn);
      if (pat == pat_end)
        break;
      pat = NEXT_INSN (pat);
    }

  gcse_create_count++;

  if (dump_file)
    {
      fprintf (dump_file, "PRE/HOIST: end of bb %d, insn %d, ",
               bb->index, INSN_UID (new_insn));
      fprintf (dump_file, "copying expression %d to reg %d\n",
               expr->bitmap_index, regno);
    }
}

/* Insert partially redundant expressions on edges in the CFG to make
   the expressions fully redundant.  */

static int
pre_edge_insert (struct edge_list *edge_list, struct expr **index_map)
{
  int e, i, j, num_edges, set_size, did_insert = 0;
  sbitmap *inserted;

  /* Where PRE_INSERT_MAP is nonzero, we add the expression on that edge
     if it reaches any of the deleted expressions.  */

  set_size = pre_insert_map[0]->size;
  num_edges = NUM_EDGES (edge_list);
  inserted = sbitmap_vector_alloc (num_edges, expr_hash_table.n_elems);
  sbitmap_vector_zero (inserted, num_edges);

  for (e = 0; e < num_edges; e++)
    {
      int indx;
      basic_block bb = INDEX_EDGE_PRED_BB (edge_list, e);

      for (i = indx = 0; i < set_size; i++, indx += SBITMAP_ELT_BITS)
        {
          SBITMAP_ELT_TYPE insert = pre_insert_map[e]->elms[i];

          for (j = indx;
               insert && j < (int) expr_hash_table.n_elems;
               j++, insert >>= 1)
            if ((insert & 1) != 0 && index_map[j]->reaching_reg != NULL_RTX)
              {
                struct expr *expr = index_map[j];
                struct occr *occr;

                /* Now look at each deleted occurrence of this expression.  */
                for (occr = expr->antic_occr; occr != NULL; occr = occr->next)
                  {
                    if (! occr->deleted_p)
                      continue;

                    /* Insert this expression on this edge if it would
                       reach the deleted occurrence in BB.  */
                    if (!TEST_BIT (inserted[e], j))
                      {
                        rtx insn;
                        edge eg = INDEX_EDGE (edge_list, e);

                        /* We can't insert anything on an abnormal and
                           critical edge, so we insert the insn at the end of
                           the previous block. There are several alternatives
                           detailed in Morgans book P277 (sec 10.5) for
                           handling this situation.  This one is easiest for
                           now.  */

                        if (eg->flags & EDGE_ABNORMAL)
                          insert_insn_end_basic_block (index_map[j], bb);
                        else
                          {
                            insn = process_insert_insn (index_map[j]);
                            insert_insn_on_edge (insn, eg);
                          }

                        if (dump_file)
                          {
                            fprintf (dump_file, "PRE: edge (%d,%d), ",
                                     bb->index,
                                     INDEX_EDGE_SUCC_BB (edge_list, e)->index);
                            fprintf (dump_file, "copy expression %d\n",
                                     expr->bitmap_index);
                          }

                        update_ld_motion_stores (expr);
                        SET_BIT (inserted[e], j);
                        did_insert = 1;
                        gcse_create_count++;
                      }
                  }
              }
        }
    }

  sbitmap_vector_free (inserted);
  return did_insert;
}

/* Copy the result of EXPR->EXPR generated by INSN to EXPR->REACHING_REG.
   Given "old_reg <- expr" (INSN), instead of adding after it
     reaching_reg <- old_reg
   it's better to do the following:
     reaching_reg <- expr
     old_reg      <- reaching_reg
   because this way copy propagation can discover additional PRE
   opportunities.  But if this fails, we try the old way.
   When "expr" is a store, i.e.
   given "MEM <- old_reg", instead of adding after it
     reaching_reg <- old_reg
   it's better to add it before as follows:
     reaching_reg <- old_reg
     MEM          <- reaching_reg.  */

static void
pre_insert_copy_insn (struct expr *expr, rtx insn)
{
  rtx reg = expr->reaching_reg;
  int regno = REGNO (reg);
  int indx = expr->bitmap_index;
  rtx pat = PATTERN (insn);
  rtx set, first_set, new_insn;
  rtx old_reg;
  int i;

  /* This block matches the logic in hash_scan_insn.  */
  switch (GET_CODE (pat))
    {
    case SET:
      set = pat;
      break;

    case PARALLEL:
      /* Search through the parallel looking for the set whose
         source was the expression that we're interested in.  */
      first_set = NULL_RTX;
      set = NULL_RTX;
      for (i = 0; i < XVECLEN (pat, 0); i++)
        {
          rtx x = XVECEXP (pat, 0, i);
          if (GET_CODE (x) == SET)
            {
              /* If the source was a REG_EQUAL or REG_EQUIV note, we
                 may not find an equivalent expression, but in this
                 case the PARALLEL will have a single set.  */
              if (first_set == NULL_RTX)
                first_set = x;
              if (expr_equiv_p (SET_SRC (x), expr->expr))
                {
                  set = x;
                  break;
                }
            }
        }

      gcc_assert (first_set);
      if (set == NULL_RTX)
        set = first_set;
      break;

    default:
      gcc_unreachable ();
    }

  if (REG_P (SET_DEST (set)))
    {
      old_reg = SET_DEST (set);
      /* Check if we can modify the set destination in the original insn.  */
      if (validate_change (insn, &SET_DEST (set), reg, 0))
        {
          new_insn = gen_move_insn (old_reg, reg);
          new_insn = emit_insn_after (new_insn, insn);
        }
      else
        {
          new_insn = gen_move_insn (reg, old_reg);
          new_insn = emit_insn_after (new_insn, insn);
        }
    }
  else /* This is possible only in case of a store to memory.  */
    {
      old_reg = SET_SRC (set);
      new_insn = gen_move_insn (reg, old_reg);

      /* Check if we can modify the set source in the original insn.  */
      if (validate_change (insn, &SET_SRC (set), reg, 0))
        new_insn = emit_insn_before (new_insn, insn);
      else
        new_insn = emit_insn_after (new_insn, insn);
    }

  gcse_create_count++;

  if (dump_file)
    fprintf (dump_file,
             "PRE: bb %d, insn %d, copy expression %d in insn %d to reg %d\n",
              BLOCK_FOR_INSN (insn)->index, INSN_UID (new_insn), indx,
              INSN_UID (insn), regno);
}

/* Copy available expressions that reach the redundant expression
   to `reaching_reg'.  */

static void
pre_insert_copies (void)
{
  unsigned int i, added_copy;
  struct expr *expr;
  struct occr *occr;
  struct occr *avail;

  /* For each available expression in the table, copy the result to
     `reaching_reg' if the expression reaches a deleted one.

     ??? The current algorithm is rather brute force.
     Need to do some profiling.  */

  for (i = 0; i < expr_hash_table.size; i++)
    for (expr = expr_hash_table.table[i]; expr; expr = expr->next_same_hash)
      {
        /* If the basic block isn't reachable, PPOUT will be TRUE.  However,
           we don't want to insert a copy here because the expression may not
           really be redundant.  So only insert an insn if the expression was
           deleted.  This test also avoids further processing if the
           expression wasn't deleted anywhere.  */
        if (expr->reaching_reg == NULL)
          continue;

        /* Set when we add a copy for that expression.  */
        added_copy = 0;

        for (occr = expr->antic_occr; occr != NULL; occr = occr->next)
          {
            if (! occr->deleted_p)
              continue;

            for (avail = expr->avail_occr; avail != NULL; avail = avail->next)
              {
                rtx insn = avail->insn;

                /* No need to handle this one if handled already.  */
                if (avail->copied_p)
                  continue;

                /* Don't handle this one if it's a redundant one.  */
                if (INSN_DELETED_P (insn))
                  continue;

                /* Or if the expression doesn't reach the deleted one.  */
                if (! pre_expr_reaches_here_p (BLOCK_FOR_INSN (avail->insn),
                                               expr,
                                               BLOCK_FOR_INSN (occr->insn)))
                  continue;

                added_copy = 1;

                /* Copy the result of avail to reaching_reg.  */
                pre_insert_copy_insn (expr, insn);
                avail->copied_p = 1;
              }
          }

          if (added_copy)
            update_ld_motion_stores (expr);
      }
}

/* Emit move from SRC to DEST noting the equivalence with expression computed
   in INSN.  */

static rtx
gcse_emit_move_after (rtx dest, rtx src, rtx insn)
{
  rtx new_rtx;
  rtx set = single_set (insn), set2;
  rtx note;
  rtx eqv;

  /* This should never fail since we're creating a reg->reg copy
     we've verified to be valid.  */

  new_rtx = emit_insn_after (gen_move_insn (dest, src), insn);

  /* Note the equivalence for local CSE pass.  */
  set2 = single_set (new_rtx);
  if (!set2 || !rtx_equal_p (SET_DEST (set2), dest))
    return new_rtx;
  if ((note = find_reg_equal_equiv_note (insn)))
    eqv = XEXP (note, 0);
  else
    eqv = SET_SRC (set);

  set_unique_reg_note (new_rtx, REG_EQUAL, copy_insn_1 (eqv));

  return new_rtx;
}

/* Delete redundant computations.
   Deletion is done by changing the insn to copy the `reaching_reg' of
   the expression into the result of the SET.  It is left to later passes
   (cprop, cse2, flow, combine, regmove) to propagate the copy or eliminate it.

   Return nonzero if a change is made.  */

static int
pre_delete (void)
{
  unsigned int i;
  int changed;
  struct expr *expr;
  struct occr *occr;

  changed = 0;
  for (i = 0; i < expr_hash_table.size; i++)
    for (expr = expr_hash_table.table[i]; expr; expr = expr->next_same_hash)
      {
        int indx = expr->bitmap_index;

        /* We only need to search antic_occr since we require ANTLOC != 0.  */
        for (occr = expr->antic_occr; occr != NULL; occr = occr->next)
          {
            rtx insn = occr->insn;
            rtx set;
            basic_block bb = BLOCK_FOR_INSN (insn);

            /* We only delete insns that have a single_set.  */
            if (TEST_BIT (pre_delete_map[bb->index], indx)
                && (set = single_set (insn)) != 0
                && dbg_cnt (pre_insn))
              {
                /* Create a pseudo-reg to store the result of reaching
                   expressions into.  Get the mode for the new pseudo from
                   the mode of the original destination pseudo.  */
                if (expr->reaching_reg == NULL)
                  expr->reaching_reg = gen_reg_rtx_and_attrs (SET_DEST (set));

                gcse_emit_move_after (SET_DEST (set), expr->reaching_reg, insn);
                delete_insn (insn);
                occr->deleted_p = 1;
                changed = 1;
                gcse_subst_count++;

                if (dump_file)
                  {
                    fprintf (dump_file,
                             "PRE: redundant insn %d (expression %d) in ",
                               INSN_UID (insn), indx);
                    fprintf (dump_file, "bb %d, reaching reg is %d\n",
                             bb->index, REGNO (expr->reaching_reg));
                  }
              }
          }
      }

  return changed;
}

/* Perform GCSE optimizations using PRE.
   This is called by one_pre_gcse_pass after all the dataflow analysis
   has been done.

   This is based on the original Morel-Renvoise paper Fred Chow's thesis, and
   lazy code motion from Knoop, Ruthing and Steffen as described in Advanced
   Compiler Design and Implementation.

   ??? A new pseudo reg is created to hold the reaching expression.  The nice
   thing about the classical approach is that it would try to use an existing
   reg.  If the register can't be adequately optimized [i.e. we introduce
   reload problems], one could add a pass here to propagate the new register
   through the block.

   ??? We don't handle single sets in PARALLELs because we're [currently] not
   able to copy the rest of the parallel when we insert copies to create full
   redundancies from partial redundancies.  However, there's no reason why we
   can't handle PARALLELs in the cases where there are no partial
   redundancies.  */

static int
pre_gcse (struct edge_list *edge_list)
{
  unsigned int i;
  int did_insert, changed;
  struct expr **index_map;
  struct expr *expr;

  /* Compute a mapping from expression number (`bitmap_index') to
     hash table entry.  */

  index_map = XCNEWVEC (struct expr *, expr_hash_table.n_elems);
  for (i = 0; i < expr_hash_table.size; i++)
    for (expr = expr_hash_table.table[i]; expr; expr = expr->next_same_hash)
      index_map[expr->bitmap_index] = expr;

  /* Delete the redundant insns first so that
     - we know what register to use for the new insns and for the other
       ones with reaching expressions
     - we know which insns are redundant when we go to create copies  */

  changed = pre_delete ();
  did_insert = pre_edge_insert (edge_list, index_map);

  /* In other places with reaching expressions, copy the expression to the
     specially allocated pseudo-reg that reaches the redundant expr.  */
  pre_insert_copies ();
  if (did_insert)
    {
      commit_edge_insertions ();
      changed = 1;
    }

  free (index_map);
  return changed;
}

/* Top level routine to perform one PRE GCSE pass.

   Return nonzero if a change was made.  */

static int
one_pre_gcse_pass (void)
{
  int changed = 0;

  gcse_subst_count = 0;
  gcse_create_count = 0;

  /* Return if there's nothing to do, or it is too expensive.  */
  if (n_basic_blocks <= NUM_FIXED_BLOCKS + 1
      || is_too_expensive (_("PRE disabled")))
    return 0;

  /* We need alias.  */
  init_alias_analysis ();

  bytes_used = 0;
  gcc_obstack_init (&gcse_obstack);
  alloc_gcse_mem ();

  alloc_hash_table (&expr_hash_table);
  add_noreturn_fake_exit_edges ();
  if (flag_gcse_lm)
    compute_ld_motion_mems ();

  compute_hash_table (&expr_hash_table);
  if (flag_gcse_lm)
    trim_ld_motion_mems ();
  if (dump_file)
    dump_hash_table (dump_file, "Expression", &expr_hash_table);

  if (expr_hash_table.n_elems > 0)
    {
      struct edge_list *edge_list;
      alloc_pre_mem (last_basic_block, expr_hash_table.n_elems);
      edge_list = compute_pre_data ();
      changed |= pre_gcse (edge_list);
      free_edge_list (edge_list);
      free_pre_mem ();
    }

  if (flag_gcse_lm)
    free_ld_motion_mems ();
  remove_fake_exit_edges ();
  free_hash_table (&expr_hash_table);

  free_gcse_mem ();
  obstack_free (&gcse_obstack, NULL);

  /* We are finished with alias.  */
  end_alias_analysis ();

  if (dump_file)
    {
      fprintf (dump_file, "PRE GCSE of %s, %d basic blocks, %d bytes needed, ",
               current_function_name (), n_basic_blocks, bytes_used);
      fprintf (dump_file, "%d substs, %d insns created\n",
               gcse_subst_count, gcse_create_count);
    }

  return changed;
}
\f
/* If X contains any LABEL_REF's, add REG_LABEL_OPERAND notes for them
   to INSN.  If such notes are added to an insn which references a
   CODE_LABEL, the LABEL_NUSES count is incremented.  We have to add
   that note, because the following loop optimization pass requires
   them.  */

/* ??? If there was a jump optimization pass after gcse and before loop,
   then we would not need to do this here, because jump would add the
   necessary REG_LABEL_OPERAND and REG_LABEL_TARGET notes.  */

static void
add_label_notes (rtx x, rtx insn)
{
  enum rtx_code code = GET_CODE (x);
  int i, j;
  const char *fmt;

  if (code == LABEL_REF && !LABEL_REF_NONLOCAL_P (x))
    {
      /* This code used to ignore labels that referred to dispatch tables to
         avoid flow generating (slightly) worse code.

         We no longer ignore such label references (see LABEL_REF handling in
         mark_jump_label for additional information).  */

      /* There's no reason for current users to emit jump-insns with
         such a LABEL_REF, so we don't have to handle REG_LABEL_TARGET
         notes.  */
      gcc_assert (!JUMP_P (insn));
      add_reg_note (insn, REG_LABEL_OPERAND, XEXP (x, 0));

      if (LABEL_P (XEXP (x, 0)))
        LABEL_NUSES (XEXP (x, 0))++;

      return;
    }

  for (i = GET_RTX_LENGTH (code) - 1, fmt = GET_RTX_FORMAT (code); i >= 0; i--)
    {
      if (fmt[i] == 'e')
        add_label_notes (XEXP (x, i), insn);
      else if (fmt[i] == 'E')
        for (j = XVECLEN (x, i) - 1; j >= 0; j--)
          add_label_notes (XVECEXP (x, i, j), insn);
    }
}

/* Code Hoisting variables and subroutines.  */

/* Very busy expressions.  */
static sbitmap *hoist_vbein;
static sbitmap *hoist_vbeout;

/* ??? We could compute post dominators and run this algorithm in
   reverse to perform tail merging, doing so would probably be
   more effective than the tail merging code in jump.c.

   It's unclear if tail merging could be run in parallel with
   code hoisting.  It would be nice.  */

/* Allocate vars used for code hoisting analysis.  */

static void
alloc_code_hoist_mem (int n_blocks, int n_exprs)
{
  antloc = sbitmap_vector_alloc (n_blocks, n_exprs);
  transp = sbitmap_vector_alloc (n_blocks, n_exprs);
  comp = sbitmap_vector_alloc (n_blocks, n_exprs);

  hoist_vbein = sbitmap_vector_alloc (n_blocks, n_exprs);
  hoist_vbeout = sbitmap_vector_alloc (n_blocks, n_exprs);
}

/* Free vars used for code hoisting analysis.  */

static void
free_code_hoist_mem (void)
{
  sbitmap_vector_free (antloc);
  sbitmap_vector_free (transp);
  sbitmap_vector_free (comp);

  sbitmap_vector_free (hoist_vbein);
  sbitmap_vector_free (hoist_vbeout);

  free_dominance_info (CDI_DOMINATORS);
}

/* Compute the very busy expressions at entry/exit from each block.

   An expression is very busy if all paths from a given point
   compute the expression.  */

static void
compute_code_hoist_vbeinout (void)
{
  int changed, passes;
  basic_block bb;

  sbitmap_vector_zero (hoist_vbeout, last_basic_block);
  sbitmap_vector_zero (hoist_vbein, last_basic_block);

  passes = 0;
  changed = 1;

  while (changed)
    {
      changed = 0;

      /* We scan the blocks in the reverse order to speed up
         the convergence.  */
      FOR_EACH_BB_REVERSE (bb)
        {
          if (bb->next_bb != EXIT_BLOCK_PTR)
            {
              sbitmap_intersection_of_succs (hoist_vbeout[bb->index],
                                             hoist_vbein, bb);

              /* Include expressions in VBEout that are calculated
                 in BB and available at its end.  */
              sbitmap_a_or_b (hoist_vbeout[bb->index],
                              hoist_vbeout[bb->index], comp[bb->index]);
            }

          changed |= sbitmap_a_or_b_and_c_cg (hoist_vbein[bb->index],
                                              antloc[bb->index],
                                              hoist_vbeout[bb->index],
                                              transp[bb->index]);
        }

      passes++;
    }

  if (dump_file)
    {
      fprintf (dump_file, "hoisting vbeinout computation: %d passes\n", passes);

      FOR_EACH_BB (bb)
        {
          fprintf (dump_file, "vbein (%d): ", bb->index);
          dump_sbitmap_file (dump_file, hoist_vbein[bb->index]);
          fprintf (dump_file, "vbeout(%d): ", bb->index);
          dump_sbitmap_file (dump_file, hoist_vbeout[bb->index]);
        }
    }
}

/* Top level routine to do the dataflow analysis needed by code hoisting.  */

static void
compute_code_hoist_data (void)
{
  compute_local_properties (transp, comp, antloc, &expr_hash_table);
  prune_expressions (false);
  compute_code_hoist_vbeinout ();
  calculate_dominance_info (CDI_DOMINATORS);
  if (dump_file)
    fprintf (dump_file, "\n");
}

/* Determine if the expression identified by EXPR_INDEX would
   reach BB unimpared if it was placed at the end of EXPR_BB.
   Stop the search if the expression would need to be moved more
   than DISTANCE instructions.

   It's unclear exactly what Muchnick meant by "unimpared".  It seems
   to me that the expression must either be computed or transparent in
   *every* block in the path(s) from EXPR_BB to BB.  Any other definition
   would allow the expression to be hoisted out of loops, even if
   the expression wasn't a loop invariant.

   Contrast this to reachability for PRE where an expression is
   considered reachable if *any* path reaches instead of *all*
   paths.  */

static int
hoist_expr_reaches_here_p (basic_block expr_bb, int expr_index, basic_block bb,
                           char *visited, int distance, int *bb_size)
{
  edge pred;
  edge_iterator ei;
  int visited_allocated_locally = 0;

  /* Terminate the search if distance, for which EXPR is allowed to move,
     is exhausted.  */
  if (distance > 0)
    {
      distance -= bb_size[bb->index];

      if (distance <= 0)
        return 0;
    }
  else
    gcc_assert (distance == 0);

  if (visited == NULL)
    {
      visited_allocated_locally = 1;
      visited = XCNEWVEC (char, last_basic_block);
    }

  FOR_EACH_EDGE (pred, ei, bb->preds)
    {
      basic_block pred_bb = pred->src;

      if (pred->src == ENTRY_BLOCK_PTR)
        break;
      else if (pred_bb == expr_bb)
        continue;
      else if (visited[pred_bb->index])
        continue;

      else if (! TEST_BIT (transp[pred_bb->index], expr_index))
        break;

      /* Not killed.  */
      else
        {
          visited[pred_bb->index] = 1;
          if (! hoist_expr_reaches_here_p (expr_bb, expr_index, pred_bb,
                                           visited, distance, bb_size))
            break;
        }
    }
  if (visited_allocated_locally)
    free (visited);

  return (pred == NULL);
}
\f
/* Find occurrence in BB.  */

static struct occr *
find_occr_in_bb (struct occr *occr, basic_block bb)
{
  /* Find the right occurrence of this expression.  */
  while (occr && BLOCK_FOR_INSN (occr->insn) != bb)
    occr = occr->next;

  return occr;
}

/* Actually perform code hoisting.  */

static int
hoist_code (void)
{
  basic_block bb, dominated;
  VEC (basic_block, heap) *dom_tree_walk;
  unsigned int dom_tree_walk_index;
  VEC (basic_block, heap) *domby;
  unsigned int i,j;
  struct expr **index_map;
  struct expr *expr;
  int *to_bb_head;
  int *bb_size;
  int changed = 0;

  /* Compute a mapping from expression number (`bitmap_index') to
     hash table entry.  */

  index_map = XCNEWVEC (struct expr *, expr_hash_table.n_elems);
  for (i = 0; i < expr_hash_table.size; i++)
    for (expr = expr_hash_table.table[i]; expr; expr = expr->next_same_hash)
      index_map[expr->bitmap_index] = expr;

  /* Calculate sizes of basic blocks and note how far
     each instruction is from the start of its block.  We then use this
     data to restrict distance an expression can travel.  */

  to_bb_head = XCNEWVEC (int, get_max_uid ());
  bb_size = XCNEWVEC (int, last_basic_block);

  FOR_EACH_BB (bb)
    {
      rtx insn;
      int to_head;

      to_head = 0;
      FOR_BB_INSNS (bb, insn)
        {
          /* Don't count debug instructions to avoid them affecting
             decision choices.  */
          if (NONDEBUG_INSN_P (insn))
            to_bb_head[INSN_UID (insn)] = to_head++;
        }

      bb_size[bb->index] = to_head;
    }

  gcc_assert (EDGE_COUNT (ENTRY_BLOCK_PTR->succs) == 1
              && (EDGE_SUCC (ENTRY_BLOCK_PTR, 0)->dest
                  == ENTRY_BLOCK_PTR->next_bb));

  dom_tree_walk = get_all_dominated_blocks (CDI_DOMINATORS,
                                            ENTRY_BLOCK_PTR->next_bb);

  /* Walk over each basic block looking for potentially hoistable
     expressions, nothing gets hoisted from the entry block.  */
  FOR_EACH_VEC_ELT (basic_block, dom_tree_walk, dom_tree_walk_index, bb)
    {
      domby = get_dominated_to_depth (CDI_DOMINATORS, bb, MAX_HOIST_DEPTH);

      if (VEC_length (basic_block, domby) == 0)
        continue;

      /* Examine each expression that is very busy at the exit of this
         block.  These are the potentially hoistable expressions.  */
      for (i = 0; i < SBITMAP_SIZE (hoist_vbeout[bb->index]); i++)
        {
          if (TEST_BIT (hoist_vbeout[bb->index], i))
            {
              /* Current expression.  */
              struct expr *expr = index_map[i];
              /* Number of occurrences of EXPR that can be hoisted to BB.  */
              int hoistable = 0;
              /* Basic blocks that have occurrences reachable from BB.  */
              bitmap_head _from_bbs, *from_bbs = &_from_bbs;
              /* Occurrences reachable from BB.  */
              VEC (occr_t, heap) *occrs_to_hoist = NULL;
              /* We want to insert the expression into BB only once, so
                 note when we've inserted it.  */
              int insn_inserted_p;
              occr_t occr;

              bitmap_initialize (from_bbs, 0);

              /* If an expression is computed in BB and is available at end of
                 BB, hoist all occurrences dominated by BB to BB.  */
              if (TEST_BIT (comp[bb->index], i))
                {
                  occr = find_occr_in_bb (expr->antic_occr, bb);

                  if (occr)
                    {
                      /* An occurrence might've been already deleted
                         while processing a dominator of BB.  */
                      if (!occr->deleted_p)
                        {
                          gcc_assert (NONDEBUG_INSN_P (occr->insn));
                          hoistable++;
                        }
                    }
                  else
                    hoistable++;
                }

              /* We've found a potentially hoistable expression, now
                 we look at every block BB dominates to see if it
                 computes the expression.  */
              FOR_EACH_VEC_ELT (basic_block, domby, j, dominated)
                {
                  int max_distance;

                  /* Ignore self dominance.  */
                  if (bb == dominated)
                    continue;
                  /* We've found a dominated block, now see if it computes
                     the busy expression and whether or not moving that
                     expression to the "beginning" of that block is safe.  */
                  if (!TEST_BIT (antloc[dominated->index], i))
                    continue;

                  occr = find_occr_in_bb (expr->antic_occr, dominated);
                  gcc_assert (occr);

                  /* An occurrence might've been already deleted
                     while processing a dominator of BB.  */
                  if (occr->deleted_p)
                    continue;
                  gcc_assert (NONDEBUG_INSN_P (occr->insn));

                  max_distance = expr->max_distance;
                  if (max_distance > 0)
                    /* Adjust MAX_DISTANCE to account for the fact that
                       OCCR won't have to travel all of DOMINATED, but
                       only part of it.  */
                    max_distance += (bb_size[dominated->index]
                                     - to_bb_head[INSN_UID (occr->insn)]);

                  /* Note if the expression would reach the dominated block
                     unimpared if it was placed at the end of BB.

                     Keep track of how many times this expression is hoistable
                     from a dominated block into BB.  */
                  if (hoist_expr_reaches_here_p (bb, i, dominated, NULL,
                                                 max_distance, bb_size))
                    {
                      hoistable++;
                      VEC_safe_push (occr_t, heap,
                                     occrs_to_hoist, occr);
                      bitmap_set_bit (from_bbs, dominated->index);
                    }
                }

              /* If we found more than one hoistable occurrence of this
                 expression, then note it in the vector of expressions to
                 hoist.  It makes no sense to hoist things which are computed
                 in only one BB, and doing so tends to pessimize register
                 allocation.  One could increase this value to try harder
                 to avoid any possible code expansion due to register
                 allocation issues; however experiments have shown that
                 the vast majority of hoistable expressions are only movable
                 from two successors, so raising this threshold is likely
                 to nullify any benefit we get from code hoisting.  */
              if (hoistable > 1 && dbg_cnt (hoist_insn))
                {
                  /* If (hoistable != VEC_length), then there is
                     an occurrence of EXPR in BB itself.  Don't waste
                     time looking for LCA in this case.  */
                  if ((unsigned) hoistable
                      == VEC_length (occr_t, occrs_to_hoist))
                    {
                      basic_block lca;

                      lca = nearest_common_dominator_for_set (CDI_DOMINATORS,
                                                              from_bbs);
                      if (lca != bb)
                        /* Punt, it's better to hoist these occurrences to
                           LCA.  */
                        VEC_free (occr_t, heap, occrs_to_hoist);
                    }
                }
              else
                /* Punt, no point hoisting a single occurence.  */
                VEC_free (occr_t, heap, occrs_to_hoist);

              insn_inserted_p = 0;

              /* Walk through occurrences of I'th expressions we want
                 to hoist to BB and make the transformations.  */
              FOR_EACH_VEC_ELT (occr_t, occrs_to_hoist, j, occr)
                {
                  rtx insn;
                  rtx set;

                  gcc_assert (!occr->deleted_p);

                  insn = occr->insn;
                  set = single_set (insn);
                  gcc_assert (set);

                  /* Create a pseudo-reg to store the result of reaching
                     expressions into.  Get the mode for the new pseudo
                     from the mode of the original destination pseudo.

                     It is important to use new pseudos whenever we
                     emit a set.  This will allow reload to use
                     rematerialization for such registers.  */
                  if (!insn_inserted_p)
                    expr->reaching_reg
                      = gen_reg_rtx_and_attrs (SET_DEST (set));

                  gcse_emit_move_after (SET_DEST (set), expr->reaching_reg,
                                        insn);
                  delete_insn (insn);
                  occr->deleted_p = 1;
                  changed = 1;
                  gcse_subst_count++;

                  if (!insn_inserted_p)
                    {
                      insert_insn_end_basic_block (expr, bb);
                      insn_inserted_p = 1;
                    }
                }

              VEC_free (occr_t, heap, occrs_to_hoist);
              bitmap_clear (from_bbs);
            }
        }
      VEC_free (basic_block, heap, domby);
    }

  VEC_free (basic_block, heap, dom_tree_walk);
  free (bb_size);
  free (to_bb_head);
  free (index_map);

  return changed;
}

/* Top level routine to perform one code hoisting (aka unification) pass

   Return nonzero if a change was made.  */

static int
one_code_hoisting_pass (void)
{
  int changed = 0;

  gcse_subst_count = 0;
  gcse_create_count = 0;

  /* Return if there's nothing to do, or it is too expensive.  */
  if (n_basic_blocks <= NUM_FIXED_BLOCKS + 1
      || is_too_expensive (_("GCSE disabled")))
    return 0;

  doing_code_hoisting_p = true;

  /* We need alias.  */
  init_alias_analysis ();

  bytes_used = 0;
  gcc_obstack_init (&gcse_obstack);
  alloc_gcse_mem ();

  alloc_hash_table (&expr_hash_table);
  compute_hash_table (&expr_hash_table);
  if (dump_file)
    dump_hash_table (dump_file, "Code Hosting Expressions", &expr_hash_table);

  if (expr_hash_table.n_elems > 0)
    {
      alloc_code_hoist_mem (last_basic_block, expr_hash_table.n_elems);
      compute_code_hoist_data ();
      changed = hoist_code ();
      free_code_hoist_mem ();
    }

  free_hash_table (&expr_hash_table);
  free_gcse_mem ();
  obstack_free (&gcse_obstack, NULL);

  /* We are finished with alias.  */
  end_alias_analysis ();

  if (dump_file)
    {
      fprintf (dump_file, "HOIST of %s, %d basic blocks, %d bytes needed, ",
               current_function_name (), n_basic_blocks, bytes_used);
      fprintf (dump_file, "%d substs, %d insns created\n",
               gcse_subst_count, gcse_create_count);
    }

  doing_code_hoisting_p = false;

  return changed;
}
\f
/*  Here we provide the things required to do store motion towards the exit.
    In order for this to be effective, gcse also needed to be taught how to
    move a load when it is killed only by a store to itself.

            int i;
            float a[10];

            void foo(float scale)
            {
              for (i=0; i<10; i++)
                a[i] *= scale;
            }

    'i' is both loaded and stored to in the loop. Normally, gcse cannot move
    the load out since its live around the loop, and stored at the bottom
    of the loop.

      The 'Load Motion' referred to and implemented in this file is
    an enhancement to gcse which when using edge based LCM, recognizes
    this situation and allows gcse to move the load out of the loop.

      Once gcse has hoisted the load, store motion can then push this
    load towards the exit, and we end up with no loads or stores of 'i'
    in the loop.  */

static hashval_t
pre_ldst_expr_hash (const void *p)
{
  int do_not_record_p = 0;
  const struct ls_expr *const x = (const struct ls_expr *) p;
  return
    hash_rtx (x->pattern, GET_MODE (x->pattern), &do_not_record_p, NULL, false);
}

static int
pre_ldst_expr_eq (const void *p1, const void *p2)
{
  const struct ls_expr *const ptr1 = (const struct ls_expr *) p1,
    *const ptr2 = (const struct ls_expr *) p2;
  return expr_equiv_p (ptr1->pattern, ptr2->pattern);
}

/* This will search the ldst list for a matching expression. If it
   doesn't find one, we create one and initialize it.  */

static struct ls_expr *
ldst_entry (rtx x)
{
  int do_not_record_p = 0;
  struct ls_expr * ptr;
  unsigned int hash;
  void **slot;
  struct ls_expr e;

  hash = hash_rtx (x, GET_MODE (x), &do_not_record_p,
                   NULL,  /*have_reg_qty=*/false);

  e.pattern = x;
  slot = htab_find_slot_with_hash (pre_ldst_table, &e, hash, INSERT);
  if (*slot)
    return (struct ls_expr *)*slot;

  ptr = XNEW (struct ls_expr);

  ptr->next         = pre_ldst_mems;
  ptr->expr         = NULL;
  ptr->pattern      = x;
  ptr->pattern_regs = NULL_RTX;
  ptr->loads        = NULL_RTX;
  ptr->stores       = NULL_RTX;
  ptr->reaching_reg = NULL_RTX;
  ptr->invalid      = 0;
  ptr->index        = 0;
  ptr->hash_index   = hash;
  pre_ldst_mems     = ptr;
  *slot = ptr;

  return ptr;
}

/* Free up an individual ldst entry.  */

static void
free_ldst_entry (struct ls_expr * ptr)
{
  free_INSN_LIST_list (& ptr->loads);
  free_INSN_LIST_list (& ptr->stores);

  free (ptr);
}

/* Free up all memory associated with the ldst list.  */

static void
free_ld_motion_mems (void)
{
  if (pre_ldst_table)
    htab_delete (pre_ldst_table);
  pre_ldst_table = NULL;

  while (pre_ldst_mems)
    {
      struct ls_expr * tmp = pre_ldst_mems;

      pre_ldst_mems = pre_ldst_mems->next;

      free_ldst_entry (tmp);
    }

  pre_ldst_mems = NULL;
}

/* Dump debugging info about the ldst list.  */

static void
print_ldst_list (FILE * file)
{
  struct ls_expr * ptr;

  fprintf (file, "LDST list: \n");

  for (ptr = pre_ldst_mems; ptr != NULL; ptr = ptr->next)
    {
      fprintf (file, "  Pattern (%3d): ", ptr->index);

      print_rtl (file, ptr->pattern);

      fprintf (file, "\n         Loads : ");

      if (ptr->loads)
        print_rtl (file, ptr->loads);
      else
        fprintf (file, "(nil)");

      fprintf (file, "\n        Stores : ");

      if (ptr->stores)
        print_rtl (file, ptr->stores);
      else
        fprintf (file, "(nil)");

      fprintf (file, "\n\n");
    }

  fprintf (file, "\n");
}

/* Returns 1 if X is in the list of ldst only expressions.  */

static struct ls_expr *
find_rtx_in_ldst (rtx x)
{
  struct ls_expr e;
  void **slot;
  if (!pre_ldst_table)
    return NULL;
  e.pattern = x;
  slot = htab_find_slot (pre_ldst_table, &e, NO_INSERT);
  if (!slot || ((struct ls_expr *)*slot)->invalid)
    return NULL;
  return (struct ls_expr *) *slot;
}
\f
/* Load Motion for loads which only kill themselves.  */

/* Return true if x, a MEM, is a simple access with no side effects.
   These are the types of loads we consider for the ld_motion list,
   otherwise we let the usual aliasing take care of it.  */

static int
simple_mem (const_rtx x)
{
  if (MEM_VOLATILE_P (x))
    return 0;

  if (GET_MODE (x) == BLKmode)
    return 0;

  /* If we are handling exceptions, we must be careful with memory references
     that may trap.  If we are not, the behavior is undefined, so we may just
     continue.  */
  if (cfun->can_throw_non_call_exceptions && may_trap_p (x))
    return 0;

  if (side_effects_p (x))
    return 0;

  /* Do not consider function arguments passed on stack.  */
  if (reg_mentioned_p (stack_pointer_rtx, x))
    return 0;

  if (flag_float_store && FLOAT_MODE_P (GET_MODE (x)))
    return 0;

  return 1;
}

/* Make sure there isn't a buried reference in this pattern anywhere.
   If there is, invalidate the entry for it since we're not capable
   of fixing it up just yet.. We have to be sure we know about ALL
   loads since the aliasing code will allow all entries in the
   ld_motion list to not-alias itself.  If we miss a load, we will get
   the wrong value since gcse might common it and we won't know to
   fix it up.  */

static void
invalidate_any_buried_refs (rtx x)
{
  const char * fmt;
  int i, j;
  struct ls_expr * ptr;

  /* Invalidate it in the list.  */
  if (MEM_P (x) && simple_mem (x))
    {
      ptr = ldst_entry (x);
      ptr->invalid = 1;
    }

  /* Recursively process the insn.  */
  fmt = GET_RTX_FORMAT (GET_CODE (x));

  for (i = GET_RTX_LENGTH (GET_CODE (x)) - 1; i >= 0; i--)
    {
      if (fmt[i] == 'e')
        invalidate_any_buried_refs (XEXP (x, i));
      else if (fmt[i] == 'E')
        for (j = XVECLEN (x, i) - 1; j >= 0; j--)
          invalidate_any_buried_refs (XVECEXP (x, i, j));
    }
}

/* Find all the 'simple' MEMs which are used in LOADs and STORES.  Simple
   being defined as MEM loads and stores to symbols, with no side effects
   and no registers in the expression.  For a MEM destination, we also
   check that the insn is still valid if we replace the destination with a
   REG, as is done in update_ld_motion_stores.  If there are any uses/defs
   which don't match this criteria, they are invalidated and trimmed out
   later.  */

static void
compute_ld_motion_mems (void)
{
  struct ls_expr * ptr;
  basic_block bb;
  rtx insn;

  pre_ldst_mems = NULL;
  pre_ldst_table
    = htab_create (13, pre_ldst_expr_hash, pre_ldst_expr_eq, NULL);

  FOR_EACH_BB (bb)
    {
      FOR_BB_INSNS (bb, insn)
        {
          if (NONDEBUG_INSN_P (insn))
            {
              if (GET_CODE (PATTERN (insn)) == SET)
                {
                  rtx src = SET_SRC (PATTERN (insn));
                  rtx dest = SET_DEST (PATTERN (insn));

                  /* Check for a simple LOAD...  */
                  if (MEM_P (src) && simple_mem (src))
                    {
                      ptr = ldst_entry (src);
                      if (REG_P (dest))
                        ptr->loads = alloc_INSN_LIST (insn, ptr->loads);
                      else
                        ptr->invalid = 1;
                    }
                  else
                    {
                      /* Make sure there isn't a buried load somewhere.  */
                      invalidate_any_buried_refs (src);
                    }

                  /* Check for stores. Don't worry about aliased ones, they
                     will block any movement we might do later. We only care
                     about this exact pattern since those are the only
                     circumstance that we will ignore the aliasing info.  */
                  if (MEM_P (dest) && simple_mem (dest))
                    {
                      ptr = ldst_entry (dest);

                      if (! MEM_P (src)
                          && GET_CODE (src) != ASM_OPERANDS
                          /* Check for REG manually since want_to_gcse_p
                             returns 0 for all REGs.  */
                          && can_assign_to_reg_without_clobbers_p (src))
                        ptr->stores = alloc_INSN_LIST (insn, ptr->stores);
                      else
                        ptr->invalid = 1;
                    }
                }
              else
                invalidate_any_buried_refs (PATTERN (insn));
            }
        }
    }
}

/* Remove any references that have been either invalidated or are not in the
   expression list for pre gcse.  */

static void
trim_ld_motion_mems (void)
{
  struct ls_expr * * last = & pre_ldst_mems;
  struct ls_expr * ptr = pre_ldst_mems;

  while (ptr != NULL)
    {
      struct expr * expr;

      /* Delete if entry has been made invalid.  */
      if (! ptr->invalid)
        {
          /* Delete if we cannot find this mem in the expression list.  */
          unsigned int hash = ptr->hash_index % expr_hash_table.size;

          for (expr = expr_hash_table.table[hash];
               expr != NULL;
               expr = expr->next_same_hash)
            if (expr_equiv_p (expr->expr, ptr->pattern))
              break;
        }
      else
        expr = (struct expr *) 0;

      if (expr)
        {
          /* Set the expression field if we are keeping it.  */
          ptr->expr = expr;
          last = & ptr->next;
          ptr = ptr->next;
        }
      else
        {
          *last = ptr->next;
          htab_remove_elt_with_hash (pre_ldst_table, ptr, ptr->hash_index);
          free_ldst_entry (ptr);
          ptr = * last;
        }
    }

  /* Show the world what we've found.  */
  if (dump_file && pre_ldst_mems != NULL)
    print_ldst_list (dump_file);
}

/* This routine will take an expression which we are replacing with
   a reaching register, and update any stores that are needed if
   that expression is in the ld_motion list.  Stores are updated by
   copying their SRC to the reaching register, and then storing
   the reaching register into the store location. These keeps the
   correct value in the reaching register for the loads.  */

static void
update_ld_motion_stores (struct expr * expr)
{
  struct ls_expr * mem_ptr;

  if ((mem_ptr = find_rtx_in_ldst (expr->expr)))
    {
      /* We can try to find just the REACHED stores, but is shouldn't
         matter to set the reaching reg everywhere...  some might be
         dead and should be eliminated later.  */

      /* We replace (set mem expr) with (set reg expr) (set mem reg)
         where reg is the reaching reg used in the load.  We checked in
         compute_ld_motion_mems that we can replace (set mem expr) with
         (set reg expr) in that insn.  */
      rtx list = mem_ptr->stores;

      for ( ; list != NULL_RTX; list = XEXP (list, 1))
        {
          rtx insn = XEXP (list, 0);
          rtx pat = PATTERN (insn);
          rtx src = SET_SRC (pat);
          rtx reg = expr->reaching_reg;
          rtx copy;

          /* If we've already copied it, continue.  */
          if (expr->reaching_reg == src)
            continue;

          if (dump_file)
            {
              fprintf (dump_file, "PRE:  store updated with reaching reg ");
              print_rtl (dump_file, reg);
              fprintf (dump_file, ":\n  ");
              print_inline_rtx (dump_file, insn, 8);
              fprintf (dump_file, "\n");
            }

          copy = gen_move_insn (reg, copy_rtx (SET_SRC (pat)));
          emit_insn_before (copy, insn);
          SET_SRC (pat) = reg;
          df_insn_rescan (insn);

          /* un-recognize this pattern since it's probably different now.  */
          INSN_CODE (insn) = -1;
          gcse_create_count++;
        }
    }
}
\f
/* Return true if the graph is too expensive to optimize. PASS is the
   optimization about to be performed.  */

static bool
is_too_expensive (const char *pass)
{
  /* Trying to perform global optimizations on flow graphs which have
     a high connectivity will take a long time and is unlikely to be
     particularly useful.

     In normal circumstances a cfg should have about twice as many
     edges as blocks.  But we do not want to punish small functions
     which have a couple switch statements.  Rather than simply
     threshold the number of blocks, uses something with a more
     graceful degradation.  */
  if (n_edges > 20000 + n_basic_blocks * 4)
    {
      warning (OPT_Wdisabled_optimization,
               "%s: %d basic blocks and %d edges/basic block",
               pass, n_basic_blocks, n_edges / n_basic_blocks);

      return true;
    }

  /* If allocating memory for the dataflow bitmaps would take up too much
     storage it's better just to disable the optimization.  */
  if ((n_basic_blocks
       * SBITMAP_SET_SIZE (max_reg_num ())
       * sizeof (SBITMAP_ELT_TYPE)) > MAX_GCSE_MEMORY)
    {
      warning (OPT_Wdisabled_optimization,
               "%s: %d basic blocks and %d registers",
               pass, n_basic_blocks, max_reg_num ());

      return true;
    }

  return false;
}
\f
/* All the passes implemented in this file.  Each pass has its
   own gate and execute function, and at the end of the file a
   pass definition for passes.c.

   We do not construct an accurate cfg in functions which call
   setjmp, so none of these passes runs if the function calls
   setjmp.
   FIXME: Should just handle setjmp via REG_SETJMP notes.  */

static bool
gate_rtl_pre (void)
{
  return optimize > 0 && flag_gcse
    && !cfun->calls_setjmp
    && optimize_function_for_speed_p (cfun)
    && dbg_cnt (pre);
}

static unsigned int
execute_rtl_pre (void)
{
  int changed;
  delete_unreachable_blocks ();
  df_analyze ();
  changed = one_pre_gcse_pass ();
  flag_rerun_cse_after_global_opts |= changed;
  if (changed)
    cleanup_cfg (0);
  return 0;
}

static bool
gate_rtl_hoist (void)
{
  return optimize > 0 && flag_gcse
    && !cfun->calls_setjmp
    /* It does not make sense to run code hoisting unless we are optimizing
       for code size -- it rarely makes programs faster, and can make then
       bigger if we did PRE (when optimizing for space, we don't run PRE).  */
    && optimize_function_for_size_p (cfun)
    && dbg_cnt (hoist);
}

static unsigned int
execute_rtl_hoist (void)
{
  int changed;
  delete_unreachable_blocks ();
  df_analyze ();
  changed = one_code_hoisting_pass ();
  flag_rerun_cse_after_global_opts |= changed;
  if (changed)
    cleanup_cfg (0);
  return 0;
}

struct rtl_opt_pass pass_rtl_pre =
{
 {
  RTL_PASS,
  "rtl pre",                            /* name */
  gate_rtl_pre,                         /* gate */
  execute_rtl_pre,                      /* execute */
  NULL,                                 /* sub */
  NULL,                                 /* next */
  0,                                    /* static_pass_number */
  TV_PRE,                               /* tv_id */
  PROP_cfglayout,                       /* properties_required */
  0,                                    /* properties_provided */
  0,                                    /* properties_destroyed */
  0,                                    /* todo_flags_start */
  TODO_df_finish | TODO_verify_rtl_sharing |
  TODO_verify_flow | TODO_ggc_collect   /* todo_flags_finish */
 }
};

struct rtl_opt_pass pass_rtl_hoist =
{
 {
  RTL_PASS,
  "hoist",                              /* name */
  gate_rtl_hoist,                       /* gate */
  execute_rtl_hoist,                    /* execute */
  NULL,                                 /* sub */
  NULL,                                 /* next */
  0,                                    /* static_pass_number */
  TV_HOIST,                             /* tv_id */
  PROP_cfglayout,                       /* properties_required */
  0,                                    /* properties_provided */
  0,                                    /* properties_destroyed */
  0,                                    /* todo_flags_start */
  TODO_df_finish | TODO_verify_rtl_sharing |
  TODO_verify_flow | TODO_ggc_collect   /* todo_flags_finish */
 }
};

#include "gt-gcse.h"