Undo June 11th change

[official-gcc.git] / gcc / gcse.c

/* Global common subexpression elimination
   and global constant/copy propagation for GNU compiler.
   Copyright (C) 1997 Free Software Foundation, Inc.

This file is part of GNU CC.

GNU CC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

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

You should have received a copy of the GNU General Public License
along with GNU CC; see the file COPYING.  If not, write to
the Free Software Foundation, 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */

/* 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.
   - memory aliasing support
   - ability to realloc sbitmap vectors would allow one initial computation
     of reg_set_in_block with only subsequent additions, rather than
     recomputing it for each pass

   NOTES
   - the classic gcse implementation is kept in for now for comparison
*/

/* References searched while implementing this.
   This list will eventually be deleted but I wanted to have a record of it
   for now.

   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

xxx
   Elimination Algorithms for Data Flow Analysis
   B.G. Ryder, M.C. Paull
   ACM Computing Surveys, Vol. 18, Num. 3, Sep. 1986

reread
   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

yyy
   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

   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

   People wishing to speed up the code here should read xxx, yyy.
   People wishing to do something different can find various possibilities
   in the above papers and elsewhere.
*/

#include "config.h"
/* Must precede rtl.h for FFS.  */
#include "system.h"

#include "rtl.h"
#include "regs.h"
#include "hard-reg-set.h"
#include "flags.h"
#include "real.h"
#include "insn-config.h"
#include "recog.h"
#include "basic-block.h"
#include "output.h"

#include "obstack.h"
#define obstack_chunk_alloc gmalloc
#define obstack_chunk_free free

/* Maximum number of passes to perform.  */
#define MAX_PASSES 1

/* Propagate flow information through back edges and thus enable PRE's
   moving loop invariant calculations out of loops.

   Originally this tended to create worse overall code, but several
   improvements during the development of PRE seem to have made following
   back edges generally a win.

   Note much of the loop invariant code motion done here would normally
   be done by loop.c, which has more heuristics for when to move invariants
   out of loops.  At some point we might need to move some of those
   heuristics into gcse.c.  */
#define FOLLOW_BACK_EDGES 1

/* We support two GCSE implementations: Classic GCSE (i.e. Dragon Book)
   and PRE (Partial Redundancy Elimination) GCSE (based on Fred Chow's thesis).
   The default is PRE.

   In either case we perform the following steps:

   1) Compute basic block information.

   2) Compute table of places where registers are set.

   3) Perform copy/constant propagation.

   4) Perform global cse.

   5) Perform another pass of copy/constant propagation [only if PRE].

   Two passes of copy/constant propagation are done because the first one
   enables more GCSE and the second one helps to clean up the copies that
   GCSE creates.  This is needed more for PRE than for Classic because Classic
   GCSE 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 Classic GCSE 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.

   PRE handles moving invariant expressions out of loops (by treating them as
   partially redundant).  This feature of PRE is disabled here (by not
   propagating dataflow information along back edges) because loop.c has more
   involved (and thus typically better) heuristics for what to move out of
   loops.

   Eventually it would be nice to replace cse.c/gcse.c with SSA (static single
   assignment) based GVN (global value numbering).  L. T. Simpson's paper
   (Rice University) on value numbering is a useful reference for this.

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

   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.

   PRE is quite expensive in complicated functions because the DFA can take
   awhile to converge.  Hence we only perform one pass.  Macro MAX_PASSES can
   be modified if one wants to experiment.

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

   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 seconds CSE 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.

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

   When -fclassic-gcse, we perform a classic global CSE pass.
   It is based on the algorithms in the Dragon book, and is based on code
   written by Devor Tevi at Intel.

   The steps for Classic GCSE are:

   1) Build the hash table of expressions we wish to GCSE (expr_hash_table).
      Also recorded are reaching definition "gen" statements (rd_gen)

   2) Compute the reaching definitions (reaching_defs).
      This is a bitmap for each basic block indexed by INSN_CUID that is 1
      for each statement containing a definition that reaches the block.

   3) Compute the available expressions (ae_in).
      This is a bitmap for each basic block indexed by expression number
      that is 1 for each expression that is available at the beginning of
      the block.

   4) Perform GCSE.
      This is done by scanning each instruction looking for sets of the form
      (set (pseudo-reg) (expression)) and checking if `expression' is in the
      hash table.  If it is, and if the expression is available, and if only
      one computation of the expression reaches the instruction, we substitute
      the expression for a register containing its value.  If there is no
      such register, but the expression is expensive enough we create an
      instruction to copy the result of the expression into and use that.

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

   A fair bit of simplicity is created by creating small functions for simple
   tasks, even when the function is only called in one place.  This may
   measurably slow things down [or may not] by creating more function call
   overhead than is necessary.  The source is laid out so that it's trivial
   to make the affected functions inline so that one can measure what speed
   up, if any, can be achieved, and maybe later when things settle things can
   be rearranged.

   Help stamp out big monolithic functions!  */
\f
/* GCSE global vars.  */

/* -dG dump file.  */
static FILE *gcse_file;

/* Bitmaps are normally not included in debugging dumps.
   However it's useful to be able to print them from GDB.
   We could create special functions for this, but it's simpler to
   just allow passing stderr to the dump_foo fns.  Since stderr can
   be a macro, we store a copy here.  */
static FILE *debug_stderr;

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

/* Non-zero for each mode that supports (set (reg) (reg)).
   This is trivially true for integer and floating point values.
   It may or may not be true for condition codes.  */
static char can_copy_p[(int) NUM_MACHINE_MODES];

/* Non-zero if can_copy_p has been initialized.  */
static int can_copy_init_p;

/* Element I is a list of I's predecessors/successors.  */
static int_list_ptr *s_preds;
static int_list_ptr *s_succs;

/* Element I is the number of predecessors/successors of basic block I.  */
static int *num_preds;
static int *num_succs;

/* Hash table of expressions.  */

struct expr
{
  /* The expression (SET_SRC for expressions, PATTERN for assignments).  */
  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 and the operands are not modified in the basic block prior
     to 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;
};

/* 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;
  /* Non-zero if this [anticipatable] occurrence has been deleted.  */
  char deleted_p;
  /* Non-zero 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;
};

/* Expression and copy propagation 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.
*/

/* Total size of the expression hash table, in elements.  */
static int expr_hash_table_size;
/* The table itself.
   This is an array of `expr_hash_table_size' elements.  */
static struct expr **expr_hash_table;

/* Total size of the copy propagation hash table, in elements.  */
static int set_hash_table_size;
/* The table itself.
   This is an array of `set_hash_table_size' elements.  */
static struct expr **set_hash_table;

/* Mapping of uids to cuids.
   Only real insns get cuids.  */
static int *uid_cuid;

/* Highest UID in UID_CUID.  */
static int max_uid;

/* Get the cuid of an insn.  */
#define INSN_CUID(INSN) (uid_cuid[INSN_UID (INSN)])

/* Number of cuids.  */
static int max_cuid;

/* Mapping of cuids to insns.  */
static rtx *cuid_insn;

/* Get insn from cuid.  */
#define CUID_INSN(CUID) (cuid_insn[CUID])

/* Maximum register number in function prior to doing gcse + 1.
   Registers created during this pass have regno >= max_gcse_regno.
   This is named with "gcse" to not collide with global of same name.  */
static int max_gcse_regno;

/* Maximum number of cse-able expressions found.  */
static int n_exprs;
/* Maximum number of assignments for copy propagation found.  */
static int n_sets;

/* Table of registers that are modified.
   For each register, each element is a list of places where the pseudo-reg
   is set.

   For simplicity, GCSE is done on sets of pseudo-regs only.  PRE GCSE only
   requires knowledge of which blocks kill which regs [and thus could use
   a bitmap instead of the lists `reg_set_table' uses].  The classic GCSE
   uses the information in lists.

   If the classic GCSE pass is deleted `reg_set_table' and could be turned
   into an array of bitmaps (num-bbs x num-regs)
   [however perhaps it may be useful to keep the data as is].
   One advantage of recording things this way is that `reg_set_table' is
   fairly sparse with respect to pseudo regs but for hard regs could be
   fairly dense [relatively speaking].
   And recording sets of pseudo-regs in lists speeds
   up functions like compute_transp since in the case of pseudo-regs we only
   need to iterate over the number of times a pseudo-reg is set, not over the
   number of basic blocks [clearly there is a bit of a slow down in the cases
   where a pseudo is set more than once in a block, however it is believed
   that the net effect is to speed things up].  This isn't done for hard-regs
   because recording call-clobbered hard-regs in `reg_set_table' at each
   function call can consume a fair bit of memory, and iterating over hard-regs
   stored this way in compute_transp will be more expensive.  */

typedef struct reg_set {
  /* The next setting of this register.  */
  struct reg_set *next;
  /* The insn where it was set.  */
  rtx insn;
} reg_set;
static reg_set **reg_set_table;
/* Size of `reg_set_table'.
   The table starts out at max_gcse_regno + slop, and is enlarged as
   necessary.  */
static int reg_set_table_size;
/* Amount to grow `reg_set_table' by when it's full.  */
#define REG_SET_TABLE_SLOP 100

/* 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 sbitmap reg_set_bitmap;

/* For each block, a bitmap of registers set in the block.
   This is used by expr_killed_p and compute_transp.
   It is computed during hash table computation and not by compute_sets
   as it includes registers added since the last pass (or between cprop and
   gcse) and it's currently not easy to realloc sbitmap vectors.  */
static sbitmap *reg_set_in_block;

/* For each block, non-zero if memory is set in that block.
   This is computed during hash table computation and is used by
   expr_killed_p and compute_transp.
   ??? Handling of memory is very simple, we don't make any attempt
   to optimize things (later).
   ??? This can be computed by compute_sets since the information
   doesn't change.  */
static char *mem_set_in_block;

/* 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;
/* Number of constants propagated.  */
static int const_prop_count;
/* Number of copys propagated.  */
static int copy_prop_count;

extern char *current_function_name;
extern int current_function_calls_setjmp;
extern int current_function_calls_longjmp;
\f
/* These variables are used by classic GCSE.
   Normally they'd be defined a bit later, but `rd_gen' needs to
   be declared sooner.  */

/* A bitmap of all ones for implementing the algorithm for available
   expressions and reaching definitions.  */
/* ??? Available expression bitmaps have a different size than reaching
   definition bitmaps.  This should be the larger of the two, however, it
   is not currently used for reaching definitions.  */
static sbitmap u_bitmap;

/* Each block has a bitmap of each type.
   The length of each blocks bitmap is:

       max_cuid  - for reaching definitions
       n_exprs - for available expressions

   Thus we view the bitmaps as 2 dimensional arrays.  i.e.
   rd_kill[block_num][cuid_num]
   ae_kill[block_num][expr_num]
*/

/* For reaching defs */
static sbitmap *rd_kill, *rd_gen, *reaching_defs, *rd_out;

/* for available exprs */
static sbitmap *ae_kill, *ae_gen, *ae_in, *ae_out;
\f
static void compute_can_copy          PROTO ((void));

static char *gmalloc                  PROTO ((unsigned int));
static char *grealloc                 PROTO ((char *, unsigned int));
static char *gcse_alloc               PROTO ((unsigned long));
static void alloc_gcse_mem            PROTO ((rtx));
static void free_gcse_mem             PROTO ((void));
extern void dump_cuid_table           PROTO ((FILE *));

static void alloc_reg_set_mem         PROTO ((int));
static void free_reg_set_mem          PROTO ((void));
static void record_one_set            PROTO ((int, rtx));
static void record_set_info           PROTO ((rtx, rtx));
static void compute_sets              PROTO ((rtx));

static void hash_scan_insn            PROTO ((rtx, int));
static void hash_scan_set             PROTO ((rtx, rtx, int));
static void hash_scan_clobber         PROTO ((rtx, rtx));
static void hash_scan_call            PROTO ((rtx, rtx));
static void maybe_set_rd_gen          PROTO ((int, rtx));
static int want_to_gcse_p             PROTO ((rtx));
static int oprs_unchanged_p           PROTO ((rtx, rtx, int));
static int oprs_anticipatable_p       PROTO ((rtx, rtx));
static int oprs_available_p           PROTO ((rtx, rtx));
static void insert_expr_in_table      PROTO ((rtx, enum machine_mode, rtx, int, int));
static void insert_set_in_table       PROTO ((rtx, rtx));
static unsigned int hash_expr         PROTO ((rtx, enum machine_mode, int *, int));
static unsigned int hash_expr_1       PROTO ((rtx, enum machine_mode, int *));
static unsigned int hash_set          PROTO ((int, int));
static int expr_equiv_p               PROTO ((rtx, rtx));
static void record_last_reg_set_info  PROTO ((rtx, int));
static void record_last_mem_set_info  PROTO ((rtx));
static void record_last_set_info      PROTO ((rtx, rtx));
static void compute_hash_table        PROTO ((rtx, int));
static void alloc_set_hash_table      PROTO ((int));
static void free_set_hash_table       PROTO ((void));
static void compute_set_hash_table    PROTO ((rtx));
static void alloc_expr_hash_table     PROTO ((int));
static void free_expr_hash_table      PROTO ((void));
static void compute_expr_hash_table   PROTO ((rtx));
static void dump_hash_table           PROTO ((FILE *, char *, struct expr **, int, int));
static struct expr *lookup_expr       PROTO ((rtx));
static struct expr *lookup_set        PROTO ((int, rtx));
static struct expr *next_set          PROTO ((int, struct expr *));
static void reset_opr_set_tables      PROTO ((void));
static int oprs_not_set_p             PROTO ((rtx, rtx));
static void mark_call                 PROTO ((rtx, rtx));
static void mark_set                  PROTO ((rtx, rtx));
static void mark_clobber              PROTO ((rtx, rtx));
static void mark_oprs_set             PROTO ((rtx));

static void alloc_rd_mem              PROTO ((int, int));
static void free_rd_mem               PROTO ((void));
static void compute_kill_rd           PROTO ((void));
static void handle_rd_kill_set        PROTO ((rtx, int, int));
static void compute_rd                PROTO ((void));
extern void dump_rd_table             PROTO ((FILE *, char *, sbitmap *));

static void alloc_avail_expr_mem      PROTO ((int, int));
static void free_avail_expr_mem       PROTO ((void));
static void compute_ae_gen            PROTO ((void));
static void compute_ae_kill           PROTO ((void));
static int expr_killed_p              PROTO ((rtx, int));
static void compute_available         PROTO ((void));

static int expr_reaches_here_p        PROTO ((struct occr *, struct expr *,
                                              int, int, char *));
static rtx computing_insn             PROTO ((struct expr *, rtx));
static int def_reaches_here_p         PROTO ((rtx, rtx));
static int can_disregard_other_sets   PROTO ((struct reg_set **, rtx, int));
static int handle_avail_expr          PROTO ((rtx, struct expr *));
static int classic_gcse               PROTO ((void));
static int one_classic_gcse_pass      PROTO ((rtx, int));

static void alloc_cprop_mem           PROTO ((int, int));
static void free_cprop_mem            PROTO ((void));
extern void dump_cprop_data           PROTO ((FILE *));
static void compute_transp            PROTO ((rtx, int, sbitmap *, int));
static void compute_cprop_local_properties PROTO ((void));
static void compute_cprop_avinout     PROTO ((void));
static void compute_cprop_data        PROTO ((void));
static void find_used_regs            PROTO ((rtx));
static int try_replace_reg            PROTO ((rtx, rtx, rtx));
static struct expr *find_avail_set    PROTO ((int, rtx));
static int cprop_insn                 PROTO ((rtx));
static int cprop                      PROTO ((void));
static int one_cprop_pass             PROTO ((rtx, int));

static void alloc_pre_mem             PROTO ((int, int));
static void free_pre_mem              PROTO ((void));
extern void dump_pre_data             PROTO ((FILE *));
static void compute_pre_local_properties PROTO ((void));
static void compute_pre_avinout       PROTO ((void));
static void compute_pre_antinout      PROTO ((void));
static void compute_pre_pavinout      PROTO ((void));
static void compute_pre_ppinout       PROTO ((void));
static void compute_pre_data          PROTO ((void));
static int pre_expr_reaches_here_p    PROTO ((struct occr *, struct expr *,
                                              int, char *));
static void pre_insert_insn           PROTO ((struct expr *, int));
static void pre_insert                PROTO ((struct expr **));
static void pre_insert_copy_insn      PROTO ((struct expr *, rtx));
static void pre_insert_copies         PROTO ((void));
static int pre_delete                 PROTO ((void));
static int pre_gcse                   PROTO ((void));
static int one_pre_gcse_pass          PROTO ((rtx, int));
\f
/* Entry point for global common subexpression elimination.
   F is the first instruction in the function.  */

void
gcse_main (f, file)
     rtx f;
     FILE *file;
{
  int changed, pass;
  /* Bytes used at start of pass.  */
  int initial_bytes_used;
  /* Maximum number of bytes used by a pass.  */
  int max_pass_bytes;
  /* Point to release obstack data from for each pass.  */
  char *gcse_obstack_bottom;

  /* It's impossible to construct a correct control flow graph in the
     presense of setjmp, so just punt to be safe.  */
  if (current_function_calls_setjmp)
    return;
   
  /* For calling dump_foo fns from gdb.  */
  debug_stderr = stderr;

  max_gcse_regno = max_reg_num ();
  find_basic_blocks (f, max_gcse_regno, file, 0);

  /* Return if there's nothing to do.  */
  if (n_basic_blocks <= 1)
    {
      /* Free storage allocated by find_basic_blocks.  */
      free_basic_block_vars (0);
      return;
    }

  /* See what modes support reg/reg copy operations.  */
  if (! can_copy_init_p)
    {
      compute_can_copy ();
      can_copy_init_p = 1;
    }

  gcc_obstack_init (&gcse_obstack);

  gcse_file = file;

  /* Allocate and compute predecessors/successors.  */

  s_preds = (int_list_ptr *) alloca (n_basic_blocks * sizeof (int_list_ptr));
  s_succs = (int_list_ptr *) alloca (n_basic_blocks * sizeof (int_list_ptr));
  num_preds = (int *) alloca (n_basic_blocks * sizeof (int));
  num_succs = (int *) alloca (n_basic_blocks * sizeof (int));
  bytes_used = 4 * n_basic_blocks * sizeof (int_list_ptr);
  compute_preds_succs (s_preds, s_succs, num_preds, num_succs);

  if (file)
    {
      dump_bb_data (file, s_preds, s_succs);
    }

  /* Record where pseudo-registers are set.
     This data is kept accurate during each pass.
     ??? We could also record hard-reg and memory information here
     [since it's unchanging], however it is currently done during
     hash table computation.  */

  alloc_reg_set_mem (max_gcse_regno);
  compute_sets (f);

  pass = 0;
  initial_bytes_used = bytes_used;
  max_pass_bytes = 0;
  gcse_obstack_bottom = gcse_alloc (1);
  changed = 1;
  while (changed && pass < MAX_PASSES)
    {
      changed = 0;
      if (file)
        fprintf (file, "GCSE pass %d\n\n", pass + 1);

      /* Initialize bytes_used to the space for the pred/succ lists,
         and the reg_set_table data.  */
      bytes_used = initial_bytes_used;

      /* Each pass may create new registers, so recalculate each time.  */
      max_gcse_regno = max_reg_num ();

      alloc_gcse_mem (f);

      changed = one_cprop_pass (f, pass + 1);

      if (optimize_size)
        changed |= one_classic_gcse_pass (f, pass + 1);
      else
        changed |= one_pre_gcse_pass (f, pass + 1);

      if (max_pass_bytes < bytes_used)
        max_pass_bytes = bytes_used;

      free_gcse_mem ();

      if (file)
        {
          fprintf (file, "\n");
          fflush (file);
        }
      obstack_free (&gcse_obstack, gcse_obstack_bottom);
      pass++;
    }

  /* If we're doing PRE, do one last pass of copy propagation.  */
  if (! optimize_size)
    {
      max_gcse_regno = max_reg_num ();
      alloc_gcse_mem (f);
      one_cprop_pass (f, pass + 1);
      free_gcse_mem ();
    }

  if (file)
    {
      fprintf (file, "GCSE of %s: %d basic blocks, ",
               current_function_name, n_basic_blocks);
      fprintf (file, "%d pass%s, %d bytes\n\n",
               pass, pass > 1 ? "es" : "", max_pass_bytes);
    }

  /* Free our obstack.  */
  obstack_free (&gcse_obstack, NULL_PTR);
  /* Free reg_set_table.  */
  free_reg_set_mem ();
  /* Free storage used to record predecessor/successor data.  */
  free_bb_mem ();
  /* Free storage allocated by find_basic_blocks.  */
  free_basic_block_vars (0);
}
\f
/* Misc. utilities.  */

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

static void
compute_can_copy ()
{
  int i;
#ifndef AVOID_CCMODE_COPIES
  rtx reg,insn;
#endif
  char *free_point = (char *) oballoc (1);

  bzero (can_copy_p, NUM_MACHINE_MODES);

  start_sequence ();
  for (i = 0; i < NUM_MACHINE_MODES; i++)
    {
      switch (GET_MODE_CLASS (i))
        {
        case MODE_CC :
#ifdef AVOID_CCMODE_COPIES
          can_copy_p[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_PTR) >= 0)
            can_copy_p[i] = 1;
#endif
          break;
        default :
          can_copy_p[i] = 1;
          break;
        }
    }
  end_sequence ();

  /* Free the objects we just allocated.  */
  obfree (free_point);
}
\f
/* Cover function to xmalloc to record bytes allocated.  */

static char *
gmalloc (size)
     unsigned int size;
{
  bytes_used += size;
  return xmalloc (size);
}

/* Cover function to xrealloc.
   We don't record the additional size since we don't know it.
   It won't affect memory usage stats much anyway.  */

static char *
grealloc (ptr, size)
     char *ptr;
     unsigned int size;
{
  return xrealloc (ptr, size);
}

/* Cover function to obstack_alloc.
   We don't need to record the bytes allocated here since
   obstack_chunk_alloc is set to gmalloc.  */

static char *
gcse_alloc (size)
     unsigned long size;
{
  return (char *) obstack_alloc (&gcse_obstack, size);
}

/* Allocate memory for the cuid mapping array,
   and reg/memory set tracking tables.

   This is called at the start of each pass.  */

static void
alloc_gcse_mem (f)
     rtx f;
{
  int i,n;
  rtx insn;

  /* Find the largest UID and create a mapping from UIDs to CUIDs.
     CUIDs are like UIDs except they increase monotonically, have no gaps,
     and only apply to real insns.  */

  max_uid = get_max_uid ();
  n = (max_uid + 1) * sizeof (int);
  uid_cuid = (int *) gmalloc (n);
  bzero ((char *) uid_cuid, n);
  for (insn = f, i = 0; insn; insn = NEXT_INSN (insn))
    {
      if (GET_RTX_CLASS (GET_CODE (insn)) == 'i')
        INSN_CUID (insn) = i++;
      else
        INSN_CUID (insn) = i;
    }

  /* Create a table mapping cuids to insns.  */

  max_cuid = i;
  n = (max_cuid + 1) * sizeof (rtx);
  cuid_insn = (rtx *) gmalloc (n);
  bzero ((char *) cuid_insn, n);
  for (insn = f, i = 0; insn; insn = NEXT_INSN (insn))
    {
      if (GET_RTX_CLASS (GET_CODE (insn)) == 'i')
        {
          CUID_INSN (i) = insn;
          i++;
        }
    }

  /* Allocate vars to track sets of regs.  */

  reg_set_bitmap = (sbitmap) sbitmap_alloc (max_gcse_regno);

  /* Allocate vars to track sets of regs, memory per block.  */

  reg_set_in_block = (sbitmap *) sbitmap_vector_alloc (n_basic_blocks,
                                                       max_gcse_regno);
  mem_set_in_block = (char *) gmalloc (n_basic_blocks);
}

/* Free memory allocated by alloc_gcse_mem.  */

static void
free_gcse_mem ()
{
  free (uid_cuid);
  free (cuid_insn);

  free (reg_set_bitmap);

  free (reg_set_in_block);
  free (mem_set_in_block);
}

void
dump_cuid_table (file)
     FILE *file;
{
  int i,n;

  fprintf (file, "CUID table\n");
  for (i = n = 0; i < max_cuid; i++)
    {
      rtx insn = CUID_INSN (i);
      if (n != 0 && n % 10 == 0)
        fprintf (file, "\n");
      if (insn != NULL)
        fprintf (file, " %d", INSN_UID (insn));
    }
  fprintf (file, "\n\n");
}
\f
/* Register set information.

   `reg_set_table' records where each register is set or otherwise
   modified.  */

static struct obstack reg_set_obstack;

static void
alloc_reg_set_mem (n_regs)
     int n_regs;
{
  int n;

  reg_set_table_size = n_regs + REG_SET_TABLE_SLOP;
  n = reg_set_table_size * sizeof (struct reg_set *);
  reg_set_table = (struct reg_set **) gmalloc (n);
  bzero ((char *) reg_set_table, n);

  gcc_obstack_init (&reg_set_obstack);
}

static void
free_reg_set_mem ()
{
  free (reg_set_table);
  obstack_free (&reg_set_obstack, NULL_PTR);
}

/* Record REGNO in the reg_set table.  */

static void
record_one_set (regno, insn)
     int regno;
     rtx insn;
{
  /* allocate a new reg_set element and link it onto the list */
  struct reg_set *new_reg_info, *reg_info_ptr1, *reg_info_ptr2;

  /* If the table isn't big enough, enlarge it.  */
  if (regno >= reg_set_table_size)
    {
      int new_size = regno + REG_SET_TABLE_SLOP;
      reg_set_table = (struct reg_set **)
        grealloc ((char *) reg_set_table,
                  new_size * sizeof (struct reg_set *));
      bzero ((char *) (reg_set_table + reg_set_table_size),
             (new_size - reg_set_table_size) * sizeof (struct reg_set *));
      reg_set_table_size = new_size;
    }

  new_reg_info = (struct reg_set *) obstack_alloc (&reg_set_obstack,
                                                   sizeof (struct reg_set));
  bytes_used += sizeof (struct reg_set);
  new_reg_info->insn = insn;
  new_reg_info->next = NULL;
  if (reg_set_table[regno] == NULL)
    reg_set_table[regno] = new_reg_info;
  else
    {
      reg_info_ptr1 = reg_info_ptr2 = reg_set_table[regno];
      /* ??? One could keep a "last" pointer to speed this up.  */
      while (reg_info_ptr1 != NULL)
        {
          reg_info_ptr2 = reg_info_ptr1;
          reg_info_ptr1 = reg_info_ptr1->next;
        }
      reg_info_ptr2->next = new_reg_info;
    }
}

/* For communication between next two functions (via note_stores).  */
static rtx record_set_insn;

/* Called from compute_sets via note_stores to handle one
   SET or CLOBBER in an insn.  */

static void
record_set_info (dest, setter)
     rtx dest, setter ATTRIBUTE_UNUSED;
{
  if (GET_CODE (dest) == SUBREG)
    dest = SUBREG_REG (dest);

  if (GET_CODE (dest) == REG)
    {
      if (REGNO (dest) >= FIRST_PSEUDO_REGISTER)
        record_one_set (REGNO (dest), record_set_insn);
    }
}

/* Scan the function and record each set of each pseudo-register.

   This is called once, at the start of the gcse pass.
   See the comments for `reg_set_table' for further docs.  */

static void
compute_sets (f)
     rtx f;
{
  rtx insn = f;

  while (insn)
    {
      if (GET_RTX_CLASS (GET_CODE (insn)) == 'i')
        {
          record_set_insn = insn;
          note_stores (PATTERN (insn), record_set_info);
        }
      insn = NEXT_INSN (insn);
    }
}
\f
/* Hash table support.  */

/* For each register, the cuid of the first/last insn in the block to set it,
   or zero if not set.  */
static int *reg_first_set;
static int *reg_last_set;

/* While computing "first/last set" info, this is the CUID of first/last insn
   to set memory or zero if not set.  `mem_last_set' is also used when
   performing GCSE to record whether memory has been set since the beginning
   of the block.
   Note that handling of memory is very simple, we don't make any attempt
   to optimize things (later).  */
static int mem_first_set;
static int mem_last_set;

/* Set the appropriate bit in `rd_gen' [the gen for reaching defs] if the
   register set in this insn is not set after this insn in this block.  */

static void
maybe_set_rd_gen (regno, insn)
     int regno;
     rtx insn;
{
  if (reg_last_set[regno] <= INSN_CUID (insn))
    SET_BIT (rd_gen[BLOCK_NUM (insn)], INSN_CUID (insn));
}

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

static int
want_to_gcse_p (x)
     rtx x;
{
  enum rtx_code code = GET_CODE (x);

  switch (code)
    {
    case REG:
    case SUBREG:
    case CONST_INT:
    case CONST_DOUBLE:
    case CALL:
      return 0;

    default:
      break;
    }

  return 1;
}

/* Return non-zero 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 (x, insn, avail_p)
     rtx x, insn;
     int avail_p;
{
  int i;
  enum rtx_code code;
  char *fmt;

  /* repeat is used to turn tail-recursion into iteration.  */
 repeat:

  if (x == 0)
    return 1;

  code = GET_CODE (x);
  switch (code)
    {
    case REG:
      if (avail_p)
        return (reg_last_set[REGNO (x)] == 0
                || reg_last_set[REGNO (x)] < INSN_CUID (insn));
      else
        return (reg_first_set[REGNO (x)] == 0
                || reg_first_set[REGNO (x)] >= INSN_CUID (insn));

    case MEM:
      if (avail_p)
        {
          if (mem_last_set != 0
              && mem_last_set >= INSN_CUID (insn))
            return 0;
        }
      else
        {
          if (mem_first_set != 0
              && mem_first_set < INSN_CUID (insn))
            return 0;
        }
      x = XEXP (x, 0);
      goto repeat;

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

    case PC:
    case CC0: /*FIXME*/
    case CONST:
    case CONST_INT:
    case CONST_DOUBLE:
    case SYMBOL_REF:
    case LABEL_REF:
    case ADDR_VEC:
    case ADDR_DIFF_VEC:
      return 1;

    default:
      break;
    }

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

          /* If we are about to do the last recursive call
             needed at this level, change it into iteration.
             This function is called enough to be worth it.  */
          if (i == 0)
            {
              x = tem;
              goto repeat;
            }
          if (! oprs_unchanged_p (tem, insn, avail_p))
            return 0;
        }
      else if (fmt[i] == 'E')
        {
          int j;
          for (j = 0; j < XVECLEN (x, i); j++)
            {
              if (! oprs_unchanged_p (XVECEXP (x, i, j), insn, avail_p))
                return 0;
            }
        }
    }

  return 1;
}

/* Return non-zero 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 (x, insn)
     rtx x, insn;
{
  return oprs_unchanged_p (x, insn, 0);
}

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

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

/* Hash expression X.
   MODE is only used if X is a CONST_INT.
   A boolean indicating if a volatile operand is found or if the expression
   contains something we don't want to insert in the table is stored in
   DO_NOT_RECORD_P.

   ??? One might want to merge this with canon_hash.  Later.  */

static unsigned int
hash_expr (x, mode, do_not_record_p, hash_table_size)
     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_expr_1 (x, mode, do_not_record_p);
  return hash % hash_table_size;
}

/* Subroutine of hash_expr to do the actual work.  */

static unsigned int
hash_expr_1 (x, mode, do_not_record_p)
     rtx x;
     enum machine_mode mode;
     int *do_not_record_p;
{
  int i, j;
  unsigned hash = 0;
  enum rtx_code code;
  char *fmt;

  /* repeat is used to turn tail-recursion into iteration.  */
 repeat:

  if (x == 0)
    return hash;

  code = GET_CODE (x);
  switch (code)
    {
    case REG:
      {
        register int regno = REGNO (x);
        hash += ((unsigned) REG << 7) + regno;
        return hash;
      }

    case CONST_INT:
      {
        unsigned HOST_WIDE_INT tem = INTVAL (x);
        hash += ((unsigned) CONST_INT << 7) + (unsigned) mode + tem;
        return hash;
      }

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

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

    case SYMBOL_REF:
      {
        /* Don't hash on the symbol's address to avoid bootstrap differences.
           Different hash values may cause expressions to be recorded in
           different orders and thus different registers to be used in the
           final assembler.  This also avoids differences in the dump files
           between various stages.  */
        unsigned int h = 0;
        unsigned char *p = (unsigned char *) XSTR (x, 0);
        while (*p)
          h += (h << 7) + *p++; /* ??? revisit */
        hash += ((unsigned) SYMBOL_REF << 7) + h;
        return hash;
      }

    case MEM:
      if (MEM_VOLATILE_P (x))
        {
          *do_not_record_p = 1;
          return 0;
        }
      hash += (unsigned) MEM;
      x = XEXP (x, 0);
      goto repeat;

    case PRE_DEC:
    case PRE_INC:
    case POST_DEC:
    case POST_INC:
    case PC:
    case CC0:
    case CALL:
    case UNSPEC_VOLATILE:
      *do_not_record_p = 1;
      return 0;

    case ASM_OPERANDS:
      if (MEM_VOLATILE_P (x))
        {
          *do_not_record_p = 1;
          return 0;
        }

    default:
      break;
    }

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

          /* If we are about to do the last recursive call
             needed at this level, change it into iteration.
             This function is called enough to be worth it.  */
          if (i == 0)
            {
              x = tem;
              goto repeat;
            }
          hash += hash_expr_1 (tem, 0, do_not_record_p);
          if (*do_not_record_p)
            return 0;
        }
      else if (fmt[i] == 'E')
        for (j = 0; j < XVECLEN (x, i); j++)
          {
            hash += hash_expr_1 (XVECEXP (x, i, j), 0, do_not_record_p);
            if (*do_not_record_p)
              return 0;
          }
      else if (fmt[i] == 's')
        {
          register unsigned char *p = (unsigned char *) XSTR (x, i);
          if (p)
            while (*p)
              hash += *p++;
        }
      else if (fmt[i] == 'i')
        {
          register unsigned tem = XINT (x, i);
          hash += tem;
        }
      else
        abort ();
    }

  return hash;
}

/* Hash a set of register REGNO.

   Sets are hashed on the register that is set.
   This simplifies the PRE copy propagation code.

   ??? May need to make things more elaborate.  Later, as necessary.  */

static unsigned int
hash_set (regno, hash_table_size)
     int regno;
     int hash_table_size;
{
  unsigned int hash;

  hash = regno;
  return hash % hash_table_size;
}

/* Return non-zero if exp1 is equivalent to exp2.
   ??? Borrowed from cse.c.  Might want to remerge with cse.c.  Later.  */

static int
expr_equiv_p (x, y)
     rtx x, y;
{
  register int i, j;
  register enum rtx_code code;
  register char *fmt;

  if (x == y)
    return 1;
  if (x == 0 || y == 0)
    return x == y;

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

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

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

    case CONST_INT:
      return INTVAL (x) == INTVAL (y);

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

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

    case REG:
      return REGNO (x) == REGNO (y);

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

    default:
      break;
    }

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

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

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

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

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

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

        case '0':
          break;

        default:
          abort ();
        }
      }

  return 1;
}

/* 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 non-zero if X is an anticipatable expression.
   AVAIL_P is non-zero if X is an available expression.  */

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

  hash = hash_expr (x, mode, &do_not_record_p, expr_hash_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 = expr_hash_table[hash];
  found = 0;

  while (cur_expr && ! (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 = (struct expr *) gcse_alloc (sizeof (struct expr));
      bytes_used += sizeof (struct expr);
      if (expr_hash_table[hash] == NULL)
        {
          /* This is the first pattern that hashed to this index.  */
          expr_hash_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 = n_exprs++;
      cur_expr->next_same_hash = NULL;
      cur_expr->antic_occr = NULL;
      cur_expr->avail_occr = NULL;
    }

  /* Now record the occurrence(s).  */

  if (antic_p)
    {
      antic_occr = cur_expr->antic_occr;

      /* Search for another occurrence in the same basic block.  */
      while (antic_occr && BLOCK_NUM (antic_occr->insn) != BLOCK_NUM (insn))
        {
          /* If an occurrence isn't found, save a pointer to the end of
             the list.  */
          last_occr = antic_occr;
          antic_occr = antic_occr->next;
        }

      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 = (struct occr *) gcse_alloc (sizeof (struct occr));
          bytes_used += sizeof (struct occr);
          /* First occurrence of this expression in any block?  */
          if (cur_expr->antic_occr == NULL)
            cur_expr->antic_occr = antic_occr;
          else
            last_occr->next = antic_occr;
          antic_occr->insn = insn;
          antic_occr->next = NULL;
        }
    }

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

      /* Search for another occurrence in the same basic block.  */
      while (avail_occr && BLOCK_NUM (avail_occr->insn) != BLOCK_NUM (insn))
        {
          /* If an occurrence isn't found, save a pointer to the end of
             the list.  */
          last_occr = avail_occr;
          avail_occr = avail_occr->next;
        }

      if (avail_occr)
        {
          /* 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 = (struct occr *) gcse_alloc (sizeof (struct occr));
          bytes_used += sizeof (struct occr);
          /* First occurrence of this expression in any block?  */
          if (cur_expr->avail_occr == NULL)
            cur_expr->avail_occr = avail_occr;
          else
            last_occr->next = avail_occr;
          avail_occr->insn = insn;
          avail_occr->next = NULL;
        }
    }
}

/* Insert pattern X in INSN in the hash table.
   X is a SET of a reg to either another reg or a constant.
   If it is already present, record it as the last occurrence in INSN's
   basic block.  */

static void
insert_set_in_table (x, insn)
     rtx x;
     rtx insn;
{
  int found;
  unsigned int hash;
  struct expr *cur_expr, *last_expr = NULL;
  struct occr *cur_occr, *last_occr = NULL;

  if (GET_CODE (x) != SET
      || GET_CODE (SET_DEST (x)) != REG)
    abort ();

  hash = hash_set (REGNO (SET_DEST (x)), set_hash_table_size);

  cur_expr = set_hash_table[hash];
  found = 0;

  while (cur_expr && ! (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 = (struct expr *) gcse_alloc (sizeof (struct expr));
      bytes_used += sizeof (struct expr);
      if (set_hash_table[hash] == NULL)
        {
          /* This is the first pattern that hashed to this index.  */
          set_hash_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.
         We must copy X because it can be modified when copy propagation is
         performed on its operands.  */
      /* ??? Should this go in a different obstack?  */
      cur_expr->expr = copy_rtx (x);
      cur_expr->bitmap_index = n_sets++;
      cur_expr->next_same_hash = NULL;
      cur_expr->antic_occr = NULL;
      cur_expr->avail_occr = NULL;
    }

  /* Now record the occurrence.  */

  cur_occr = cur_expr->avail_occr;

  /* Search for another occurrence in the same basic block.  */
  while (cur_occr && BLOCK_NUM (cur_occr->insn) != BLOCK_NUM (insn))
    {
      /* If an occurrence isn't found, save a pointer to the end of
         the list.  */
      last_occr = cur_occr;
      cur_occr = cur_occr->next;
    }

  if (cur_occr)
    {
      /* 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.  */
      cur_occr->insn = insn;
    }
  else
    {
      /* First occurrence of this expression in this basic block.  */
      cur_occr = (struct occr *) gcse_alloc (sizeof (struct occr));
      bytes_used += sizeof (struct occr);
      /* First occurrence of this expression in any block?  */
      if (cur_expr->avail_occr == NULL)
        cur_expr->avail_occr = cur_occr;
      else
        last_occr->next = cur_occr;
      cur_occr->insn = insn;
      cur_occr->next = NULL;
    }
}

/* Scan pattern PAT of INSN and add an entry to the hash table.
   If SET_P is non-zero, this is for the assignment hash table,
   otherwise it is for the expression hash table.  */

static void
hash_scan_set (pat, insn, set_p)
     rtx pat, insn;
     int set_p;
{
  rtx src = SET_SRC (pat);
  rtx dest = SET_DEST (pat);

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

  if (GET_CODE (dest) == REG)
    {
      int regno = REGNO (dest);
      rtx tmp;

      /* Only record sets of pseudo-regs in the hash table.  */
      if (! set_p
          && regno >= FIRST_PSEUDO_REGISTER
          /* Don't GCSE something if we can't do a reg/reg copy.  */
          && can_copy_p [GET_MODE (dest)]
          /* Is SET_SRC something we want to gcse?  */
          && want_to_gcse_p (src))
        {
          /* An expression is not anticipatable if its operands are
             modified before this insn.  */
          int antic_p = ! optimize_size && oprs_anticipatable_p (src, insn);
          /* An expression is not available if its operands are
             subsequently modified, including this insn.  */
          int avail_p = oprs_available_p (src, insn);
          insert_expr_in_table (src, GET_MODE (dest), insn, antic_p, avail_p);
        }
      /* Record sets for constant/copy propagation.  */
      else if (set_p
               && regno >= FIRST_PSEUDO_REGISTER
               && ((GET_CODE (src) == REG
                    && REGNO (src) >= FIRST_PSEUDO_REGISTER
                    && can_copy_p [GET_MODE (dest)])
                   /* ??? CONST_INT:wip */
                   || GET_CODE (src) == CONST_INT)
               /* A copy is not available if its src or dest is subsequently
                  modified.  Here we want to search from INSN+1 on, but
                  oprs_available_p searches from INSN on.  */
               && (insn == BLOCK_END (BLOCK_NUM (insn))
                   || ((tmp = next_nonnote_insn (insn)) != NULL_RTX
                       && oprs_available_p (pat, tmp))))
        insert_set_in_table (pat, insn);
    }

  /* Check if first/last set in this block for classic gcse,
     but not for copy/constant propagation.  */
  if (optimize_size && !set_p)
      
    {
      rtx dest = SET_DEST (pat);

      while (GET_CODE (dest) == SUBREG
             || GET_CODE (dest) == ZERO_EXTRACT
             || GET_CODE (dest) == SIGN_EXTRACT
             || GET_CODE (dest) == STRICT_LOW_PART)
        dest = XEXP (dest, 0);
      if (GET_CODE (dest) == REG)
        maybe_set_rd_gen (REGNO (dest), insn);
    }
}

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

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

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

   Only available expressions that set a single pseudo-reg are recorded.

   Single sets in a PARALLEL could be handled, but it's an extra complication
   that isn't dealt with right now.  The trick is handling the CLOBBERs that
   are also in the PARALLEL.  Later.

   If SET_P is non-zero, this is for the assignment hash table,
   otherwise it is for the expression hash table.  */

static void
hash_scan_insn (insn, set_p)
     rtx insn;
     int set_p;
{
  rtx pat = PATTERN (insn);

  /* 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, set_p);
  else if (GET_CODE (pat) == PARALLEL)
    {
      int i;

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

          if (GET_CODE (x) == SET)
            {
              if (GET_CODE (SET_SRC (x)) == CALL)
                hash_scan_call (SET_SRC (x), insn);

              /* Check if first/last set in this block for classic
                 gcse, but not for constant/copy propagation.  */
              if (optimize_size && !set_p)
                {
                  rtx dest = SET_DEST (x);

                  while (GET_CODE (dest) == SUBREG
                         || GET_CODE (dest) == ZERO_EXTRACT
                         || GET_CODE (dest) == SIGN_EXTRACT
                         || GET_CODE (dest) == STRICT_LOW_PART)
                    dest = XEXP (dest, 0);
                  if (GET_CODE (dest) == REG)
                    maybe_set_rd_gen (REGNO (dest), insn);
                }
            }
          else if (GET_CODE (x) == CLOBBER)
            hash_scan_clobber (x, insn);
          else if (GET_CODE (x) == CALL)
            hash_scan_call (x, insn);
        }
    }
  else if (GET_CODE (pat) == CLOBBER)
    hash_scan_clobber (pat, insn);
  else if (GET_CODE (pat) == CALL)
    hash_scan_call (pat, insn);
}

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

  bzero ((char *) flat_table, total_size * sizeof (struct expr *));
  for (i = 0; i < table_size; i++)
    {
      struct expr *expr;

      for (expr = 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, total_size);

  for (i = 0; i < total_size; i++)
    {
      struct expr *expr = flat_table[i];

      fprintf (file, "Index %d (hash value %d)\n  ",
               expr->bitmap_index, hash_val[i]);
      print_rtl (file, expr->expr);
      fprintf (file, "\n");
    }

  fprintf (file, "\n");
}

/* Record register first/last/block set information for REGNO in INSN.
   reg_first_set records the first place in the block where the register
   is set and is used to compute "anticipatability".
   reg_last_set records the last place in the block where the register
   is set and is used to compute "availability".
   reg_set_in_block records whether the register is set in the block
   and is used to compute "transparency".  */

static void
record_last_reg_set_info (insn, regno)
     rtx insn;
     int regno;
{
  if (reg_first_set[regno] == 0)
    reg_first_set[regno] = INSN_CUID (insn);
  reg_last_set[regno] = INSN_CUID (insn);
  SET_BIT (reg_set_in_block[BLOCK_NUM (insn)], regno);
}

/* Record memory first/last/block set information for INSN.  */

static void
record_last_mem_set_info (insn)
     rtx insn;
{
  if (mem_first_set == 0)
    mem_first_set = INSN_CUID (insn);
  mem_last_set = INSN_CUID (insn);
  mem_set_in_block[BLOCK_NUM (insn)] = 1;
}

/* Used for communicating between next two routines.  */
static rtx last_set_insn;

/* Called from compute_hash_table via note_stores to handle one
   SET or CLOBBER in an insn.  */

static void
record_last_set_info (dest, setter)
     rtx dest, setter ATTRIBUTE_UNUSED;
{
  if (GET_CODE (dest) == SUBREG)
    dest = SUBREG_REG (dest);

  if (GET_CODE (dest) == REG)
    record_last_reg_set_info (last_set_insn, REGNO (dest));
  else if (GET_CODE (dest) == MEM
           /* 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 or assignment 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

   Assignment entries are placed in the hash table if
   - they are of the form (set (pseudo-reg) src),
   - src is something we want to perform const/copy propagation on,
   - none of the operands or target are subsequently modified in the block
   Currently src must be a pseudo-reg or a const_int.

   F is the first insn.
   SET_P is non-zero for computing the assignment hash table.  */

static void
compute_hash_table (f, set_p)
     rtx f;
     int set_p;
{
  int bb;

  /* While we compute the hash table we also compute a bit array of which
     registers are set in which blocks.
     We also compute which blocks set memory, in the absence of aliasing
     support [which is TODO].
     ??? This isn't needed during const/copy propagation, but it's cheap to
     compute.  Later.  */
  sbitmap_vector_zero (reg_set_in_block, n_basic_blocks);
  bzero ((char *) mem_set_in_block, n_basic_blocks);

  /* Some working arrays used to track first and last set in each block.  */
  /* ??? One could use alloca here, but at some size a threshold is crossed
     beyond which one should use malloc.  Are we at that threshold here?  */
  reg_first_set = (int *) gmalloc (max_gcse_regno * sizeof (int));
  reg_last_set = (int *) gmalloc (max_gcse_regno * sizeof (int));

  for (bb = 0; bb < n_basic_blocks; bb++)
    {
      rtx insn;
      int regno;

      /* First pass over the instructions records information used to
         determine when registers and memory are first and last set.
         ??? The mem_set_in_block and hard-reg reg_set_in_block computation
         could be moved to compute_sets since they currently don't change.  */

      bzero ((char *) reg_first_set, max_gcse_regno * sizeof (int));
      bzero ((char *) reg_last_set, max_gcse_regno * sizeof (int));
      mem_first_set = 0;
      mem_last_set = 0;

      for (insn = basic_block_head[bb];
           insn && insn != NEXT_INSN (basic_block_end[bb]);
           insn = NEXT_INSN (insn))
        {
#ifdef NON_SAVING_SETJMP 
          if (NON_SAVING_SETJMP && GET_CODE (insn) == NOTE
              && NOTE_LINE_NUMBER (insn) == NOTE_INSN_SETJMP)
            {
              for (regno = 0; regno < FIRST_PSEUDO_REGISTER; regno++)
                record_last_reg_set_info (insn, regno);
              continue;
            }
#endif

          if (GET_RTX_CLASS (GET_CODE (insn)) != 'i')
            continue;

          if (GET_CODE (insn) == CALL_INSN)
            {
              for (regno = 0; regno < FIRST_PSEUDO_REGISTER; regno++)
                if (call_used_regs[regno])
                  record_last_reg_set_info (insn, regno);
              if (! CONST_CALL_P (insn))
                record_last_mem_set_info (insn);
            }

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

      /* The next pass builds the hash table.  */

      for (insn = basic_block_head[bb];
           insn && insn != NEXT_INSN (basic_block_end[bb]);
           insn = NEXT_INSN (insn))
        {
          if (GET_RTX_CLASS (GET_CODE (insn)) == 'i')
            hash_scan_insn (insn, set_p);
        }
    }

  free (reg_first_set);
  free (reg_last_set);
  /* Catch bugs early.  */
  reg_first_set = reg_last_set = 0;
}

/* Allocate space for the set hash table.
   N_INSNS is the number of instructions in the function.
   It is used to determine the number of buckets to use.  */

static void
alloc_set_hash_table (n_insns)
     int n_insns;
{
  int n;

  set_hash_table_size = n_insns / 4;
  if (set_hash_table_size < 11)
    set_hash_table_size = 11;
  /* Attempt to maintain efficient use of hash table.
     Making it an odd number is simplest for now.
     ??? Later take some measurements.  */
  set_hash_table_size |= 1;
  n = set_hash_table_size * sizeof (struct expr *);
  set_hash_table = (struct expr **) gmalloc (n);
}

/* Free things allocated by alloc_set_hash_table.  */

static void
free_set_hash_table ()
{
  free (set_hash_table);
}

/* Compute the hash table for doing copy/const propagation.  */

static void
compute_set_hash_table (f)
     rtx f;
{
  /* Initialize count of number of entries in hash table.  */
  n_sets = 0;
  bzero ((char *) set_hash_table, set_hash_table_size * sizeof (struct expr *));

  compute_hash_table (f, 1);
}

/* Allocate space for the expression hash table.
   N_INSNS is the number of instructions in the function.
   It is used to determine the number of buckets to use.  */

static void
alloc_expr_hash_table (n_insns)
     int n_insns;
{
  int n;

  expr_hash_table_size = n_insns / 2;
  /* Make sure the amount is usable.  */
  if (expr_hash_table_size < 11)
    expr_hash_table_size = 11;
  /* Attempt to maintain efficient use of hash table.
     Making it an odd number is simplest for now.
     ??? Later take some measurements.  */
  expr_hash_table_size |= 1;
  n = expr_hash_table_size * sizeof (struct expr *);
  expr_hash_table = (struct expr **) gmalloc (n);
}

/* Free things allocated by alloc_expr_hash_table.  */

static void
free_expr_hash_table ()
{
  free (expr_hash_table);
}

/* Compute the hash table for doing GCSE.  */

static void
compute_expr_hash_table (f)
     rtx f;
{
  /* Initialize count of number of entries in hash table.  */
  n_exprs = 0;
  bzero ((char *) expr_hash_table, expr_hash_table_size * sizeof (struct expr *));

  compute_hash_table (f, 0);
}
\f
/* Expression tracking support.  */

/* Lookup pattern PAT in the expression table.
   The result is a pointer to the table entry, or NULL if not found.  */

static struct expr *
lookup_expr (pat)
     rtx pat;
{
  int do_not_record_p;
  unsigned int hash = hash_expr (pat, GET_MODE (pat), &do_not_record_p,
                                 expr_hash_table_size);
  struct expr *expr;

  if (do_not_record_p)
    return NULL;

  expr = expr_hash_table[hash];

  while (expr && ! expr_equiv_p (expr->expr, pat))
    expr = expr->next_same_hash;

  return expr;
}

/* Lookup REGNO in the set table.
   If PAT is non-NULL look for the entry that matches it, otherwise return
   the first entry for REGNO.
   The result is a pointer to the table entry, or NULL if not found.  */

static struct expr *
lookup_set (regno, pat)
     int regno;
     rtx pat;
{
  unsigned int hash = hash_set (regno, set_hash_table_size);
  struct expr *expr;

  expr = set_hash_table[hash];

  if (pat)
    {
      while (expr && ! expr_equiv_p (expr->expr, pat))
        expr = expr->next_same_hash;
    }
  else
    {
      while (expr && REGNO (SET_DEST (expr->expr)) != regno)
        expr = expr->next_same_hash;
    }

  return expr;
}

/* Return the next entry for REGNO in list EXPR.  */

static struct expr *
next_set (regno, expr)
     int regno;
     struct expr *expr;
{
  do
    expr = expr->next_same_hash;
  while (expr && REGNO (SET_DEST (expr->expr)) != regno);
  return expr;
}

/* Reset tables used to keep track of what's still available [since the
   start of the block].  */

static void
reset_opr_set_tables ()
{
  /* Maintain a bitmap of which regs have been set since beginning of
     the block.  */
  sbitmap_zero (reg_set_bitmap);
  /* Also keep a record of the last instruction to modify memory.
     For now this is very trivial, we only record whether any memory
     location has been modified.  */
  mem_last_set = 0;
}

/* Return non-zero if the operands of X are not set before INSN in
   INSN's basic block.  */

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

  /* repeat is used to turn tail-recursion into iteration.  */
repeat:

  if (x == 0)
    return 1;

  code = GET_CODE (x);
  switch (code)
    {
    case PC:
    case CC0:
    case CONST:
    case CONST_INT:
    case CONST_DOUBLE:
    case SYMBOL_REF:
    case LABEL_REF:
    case ADDR_VEC:
    case ADDR_DIFF_VEC:
      return 1;

    case MEM:
      if (mem_last_set != 0)
        return 0;
      x = XEXP (x, 0);
      goto repeat;

    case REG:
      return ! TEST_BIT (reg_set_bitmap, REGNO (x));

    default:
      break;
    }

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      if (fmt[i] == 'e')
        {
          int not_set_p;
          /* 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, 0);
              goto repeat;
            }
          not_set_p = oprs_not_set_p (XEXP (x, i), insn);
          if (! not_set_p)
            return 0;
        }
      else if (fmt[i] == 'E')
        {
          int j;
          for (j = 0; j < XVECLEN (x, i); j++)
            {
              int not_set_p = oprs_not_set_p (XVECEXP (x, i, j), insn);
              if (! not_set_p)
                return 0;
            }
        }
    }

  return 1;
}

/* Mark things set by a CALL.  */

static void
mark_call (pat, insn)
     rtx pat ATTRIBUTE_UNUSED, insn;
{
  mem_last_set = INSN_CUID (insn);
}

/* Mark things set by a SET.  */

static void
mark_set (pat, insn)
     rtx pat, insn;
{
  rtx dest = SET_DEST (pat);

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

  if (GET_CODE (dest) == REG)
    SET_BIT (reg_set_bitmap, REGNO (dest));
  else if (GET_CODE (dest) == MEM)
    mem_last_set = INSN_CUID (insn);

  if (GET_CODE (SET_SRC (pat)) == CALL)
    mark_call (SET_SRC (pat), insn);
}

/* Record things set by a CLOBBER.  */

static void
mark_clobber (pat, insn)
     rtx pat, insn;
{
  rtx clob = XEXP (pat, 0);

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

  if (GET_CODE (clob) == REG)
    SET_BIT (reg_set_bitmap, REGNO (clob));
  else
    mem_last_set = INSN_CUID (insn);
}

/* Record things set by INSN.
   This data is used by oprs_not_set_p.  */

static void
mark_oprs_set (insn)
     rtx insn;
{
  rtx pat = PATTERN (insn);

  if (GET_CODE (pat) == SET)
    mark_set (pat, insn);
  else if (GET_CODE (pat) == PARALLEL)
    {
      int i;

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

          if (GET_CODE (x) == SET)
            mark_set (x, insn);
          else if (GET_CODE (x) == CLOBBER)
            mark_clobber (x, insn);
          else if (GET_CODE (x) == CALL)
            mark_call (x, insn);
        }
    }
  else if (GET_CODE (pat) == CLOBBER)
    mark_clobber (pat, insn);
  else if (GET_CODE (pat) == CALL)
    mark_call (pat, insn);
}
\f
/* Classic GCSE reaching definition support.  */

/* Allocate reaching def variables.  */

static void
alloc_rd_mem (n_blocks, n_insns)
     int n_blocks, n_insns;
{
  rd_kill = (sbitmap *) sbitmap_vector_alloc (n_blocks, n_insns);
  sbitmap_vector_zero (rd_kill, n_basic_blocks);

  rd_gen = (sbitmap *) sbitmap_vector_alloc (n_blocks, n_insns);
  sbitmap_vector_zero (rd_gen, n_basic_blocks);

  reaching_defs = (sbitmap *) sbitmap_vector_alloc (n_blocks, n_insns);
  sbitmap_vector_zero (reaching_defs, n_basic_blocks);

  rd_out = (sbitmap *) sbitmap_vector_alloc (n_blocks, n_insns);
  sbitmap_vector_zero (rd_out, n_basic_blocks);
}

/* Free reaching def variables.  */

static void
free_rd_mem ()
{
  free (rd_kill);
  free (rd_gen);
  free (reaching_defs);
  free (rd_out);
}

/* Add INSN to the kills of BB.
   REGNO, set in BB, is killed by INSN.  */

static void
handle_rd_kill_set (insn, regno, bb)
     rtx insn;
     int regno, bb;
{
  struct reg_set *this_reg = reg_set_table[regno];

  while (this_reg)
    {
      if (BLOCK_NUM (this_reg->insn) != BLOCK_NUM (insn))
        SET_BIT (rd_kill[bb], INSN_CUID (this_reg->insn));
      this_reg = this_reg->next;
    }
}

void
dump_rd_table (file, title, bmap)
     FILE *file;
     char *title;
     sbitmap *bmap;
{
  int bb,cuid,i,j,n;

  fprintf (file, "%s\n", title);
  for (bb = 0; bb < n_basic_blocks; bb++)
    {
      fprintf (file, "BB %d\n", bb);
      dump_sbitmap (file, bmap[bb]);
      for (i = n = cuid = 0; i < bmap[bb]->size; i++)
        {
          for (j = 0; j < SBITMAP_ELT_BITS; j++, cuid++)
            {
              if ((bmap[bb]->elms[i] & (1 << j)) != 0)
                {
                  if (n % 10 == 0)
                    fprintf (file, " ");
                  fprintf (file, " %d", INSN_UID (CUID_INSN (cuid)));
                  n++;
                }
            }
        }
      if (n != 0)
        fprintf (file, "\n");
    }
  fprintf (file, "\n");
}

/* Compute the set of kill's for reaching definitions.  */

static void
compute_kill_rd ()
{
  int bb,cuid;

  /* For each block
       For each set bit in `gen' of the block (i.e each insn which
           generates a definition in the block)
         Call the reg set by the insn corresponding to that bit regx
         Look at the linked list starting at reg_set_table[regx]
         For each setting of regx in the linked list, which is not in
             this block
           Set the bit in `kill' corresponding to that insn
    */

  for (bb = 0; bb < n_basic_blocks; bb++)
    {
      for (cuid = 0; cuid < max_cuid; cuid++)
        {
          if (TEST_BIT (rd_gen[bb], cuid))
            {
              rtx insn = CUID_INSN (cuid);
              rtx pat = PATTERN (insn);

              if (GET_CODE (insn) == CALL_INSN)
                {
                  int regno;

                  for (regno = 0; regno < FIRST_PSEUDO_REGISTER; regno++)
                    {
                      if (call_used_regs[regno])
                        handle_rd_kill_set (insn, regno, bb);
                    }
                }

              if (GET_CODE (pat) == PARALLEL)
                {
                  int i;

                  /* We work backwards because ... */
                  for (i = XVECLEN (pat, 0) - 1; i >= 0; i--)
                    {
                      enum rtx_code code = GET_CODE (XVECEXP (pat, 0, i));
                      if ((code == SET || code == CLOBBER)
                          && GET_CODE (XEXP (XVECEXP (pat, 0, i), 0)) == REG)
                        handle_rd_kill_set (insn,
                                            REGNO (XEXP (XVECEXP (pat, 0, i), 0)),
                                            bb);
                    }
                }
              else if (GET_CODE (pat) == SET)
                {
                  if (GET_CODE (SET_DEST (pat)) == REG)
                    {
                      /* Each setting of this register outside of this block
                         must be marked in the set of kills in this block.  */
                      handle_rd_kill_set (insn, REGNO (SET_DEST (pat)), bb);
                    }
                }
              /* FIXME: CLOBBER? */
            }
        }
    }
}

/* Compute the reaching definitions as in 
   Compilers Principles, Techniques, and Tools. Aho, Sethi, Ullman,
   Chapter 10.  It is the same algorithm as used for computing available
   expressions but applied to the gens and kills of reaching definitions.  */

static void
compute_rd ()
{
  int bb, changed, passes;

  for (bb = 0; bb < n_basic_blocks; bb++)
    sbitmap_copy (rd_out[bb] /*dst*/, rd_gen[bb] /*src*/);

  passes = 0;
  changed = 1;
  while (changed)
    {
      changed = 0;
      for (bb = 0; bb < n_basic_blocks; bb++)
        {
          sbitmap_union_of_predecessors (reaching_defs[bb], rd_out,
                                         bb, s_preds);
          changed |= sbitmap_union_of_diff (rd_out[bb], rd_gen[bb],
                                            reaching_defs[bb], rd_kill[bb]);
        }
      passes++;
    }

  if (gcse_file)
    fprintf (gcse_file, "reaching def computation: %d passes\n", passes);
}
\f
/* Classic GCSE available expression support.  */

/* Allocate memory for available expression computation.  */

static void
alloc_avail_expr_mem (n_blocks, n_exprs)
     int n_blocks, n_exprs;
{
  ae_kill = (sbitmap *) sbitmap_vector_alloc (n_blocks, n_exprs);
  sbitmap_vector_zero (ae_kill, n_basic_blocks);

  ae_gen = (sbitmap *) sbitmap_vector_alloc (n_blocks, n_exprs);
  sbitmap_vector_zero (ae_gen, n_basic_blocks);

  ae_in = (sbitmap *) sbitmap_vector_alloc (n_blocks, n_exprs);
  sbitmap_vector_zero (ae_in, n_basic_blocks);

  ae_out = (sbitmap *) sbitmap_vector_alloc (n_blocks, n_exprs);
  sbitmap_vector_zero (ae_out, n_basic_blocks);

  u_bitmap = (sbitmap) sbitmap_alloc (n_exprs);
  sbitmap_ones (u_bitmap);
}

static void
free_avail_expr_mem ()
{
  free (ae_kill);
  free (ae_gen);
  free (ae_in);
  free (ae_out);
  free (u_bitmap);
}

/* Compute the set of available expressions generated in each basic block.  */

static void
compute_ae_gen ()
{
  int i;

  /* For each recorded occurrence of each expression, set ae_gen[bb][expr].
     This is all we have to do because an expression is not recorded if it
     is not available, and the only expressions we want to work with are the
     ones that are recorded.  */

  for (i = 0; i < expr_hash_table_size; i++)
    {
      struct expr *expr = expr_hash_table[i];
      while (expr != NULL)
        {
          struct occr *occr = expr->avail_occr;
          while (occr != NULL)
            {
              SET_BIT (ae_gen[BLOCK_NUM (occr->insn)], expr->bitmap_index);
              occr = occr->next;
            }
          expr = expr->next_same_hash;
        }
    }
}

/* Return non-zero if expression X is killed in BB.  */

static int
expr_killed_p (x, bb)
     rtx x;
     int bb;
{
  int i;
  enum rtx_code code;
  char *fmt;

  /* repeat is used to turn tail-recursion into iteration.  */
 repeat:

  if (x == 0)
    return 1;

  code = GET_CODE (x);
  switch (code)
    {
    case REG:
      return TEST_BIT (reg_set_in_block[bb], REGNO (x));

    case MEM:
      if (mem_set_in_block[bb])
        return 1;
      x = XEXP (x, 0);
      goto repeat;

    case PC:
    case CC0: /*FIXME*/
    case CONST:
    case CONST_INT:
    case CONST_DOUBLE:
    case SYMBOL_REF:
    case LABEL_REF:
    case ADDR_VEC:
    case ADDR_DIFF_VEC:
      return 0;

    default:
      break;
    }

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

          /* If we are about to do the last recursive call
             needed at this level, change it into iteration.
             This function is called enough to be worth it.  */
          if (i == 0)
            {
              x = tem;
              goto repeat;
            }
          if (expr_killed_p (tem, bb))
            return 1;
        }
      else if (fmt[i] == 'E')
        {
          int j;
          for (j = 0; j < XVECLEN (x, i); j++)
            {
              if (expr_killed_p (XVECEXP (x, i, j), bb))
                return 1;
            }
        }
    }

  return 0;
}

/* Compute the set of available expressions killed in each basic block.  */

static void
compute_ae_kill ()
{
  int bb,i;

  for (bb = 0; bb < n_basic_blocks; bb++)
    {
      for (i = 0; i < expr_hash_table_size; i++)
        {
          struct expr *expr = expr_hash_table[i];

          for ( ; expr != NULL; expr = expr->next_same_hash)
            {
              /* Skip EXPR if generated in this block.  */
              if (TEST_BIT (ae_gen[bb], expr->bitmap_index))
                continue;

              if (expr_killed_p (expr->expr, bb))
                SET_BIT (ae_kill[bb], expr->bitmap_index);
            }
        }
    }
}

/* Compute available expressions.

   Implement the algorithm to find available expressions
   as given in the Aho Sethi Ullman book, pages 627-631.  */

static void
compute_available ()
{
  int bb, changed, passes;

  sbitmap_zero (ae_in[0]);

  sbitmap_copy (ae_out[0] /*dst*/, ae_gen[0] /*src*/);

  for (bb = 1; bb < n_basic_blocks; bb++)
    sbitmap_difference (ae_out[bb], u_bitmap, ae_kill[bb]);
    
  passes = 0;
  changed = 1;
  while (changed)
    {
      changed = 0;
      for (bb = 1; bb < n_basic_blocks; bb++)
        {
          sbitmap_intersect_of_predecessors (ae_in[bb], ae_out,
                                             bb, s_preds);
          changed |= sbitmap_union_of_diff (ae_out[bb], ae_gen[bb],
                                            ae_in[bb], ae_kill[bb]);
        }
      passes++;
    }

  if (gcse_file)
    fprintf (gcse_file, "avail expr computation: %d passes\n", passes);
}
\f
/* Actually perform the Classic GCSE optimizations.  */

/* Return non-zero if occurrence OCCR of expression EXPR reaches block BB.

   CHECK_SELF_LOOP is non-zero if we should consider a block reaching itself
   as a positive reach.  We want to do this when there are two computations
   of the expression in the block.

   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
expr_reaches_here_p (occr, expr, bb, check_self_loop, visited)
     struct occr *occr;
     struct expr *expr;
     int bb;
     int check_self_loop;
     char *visited;
{
  int_list_ptr pred;

  if (visited == NULL)
    {
      visited = (char *) alloca (n_basic_blocks);
      bzero (visited, n_basic_blocks);
    }

  for (pred = s_preds[bb]; pred != NULL; pred = pred->next)
    {
      int pred_bb = INT_LIST_VAL (pred);

      if (visited[pred_bb])
        {
          /* This predecessor has already been visited.
             Nothing to do.  */
          ;
        }
      else if (pred_bb == bb)
        {
          /* BB loops on itself.  */
          if (check_self_loop
              && TEST_BIT (ae_gen[pred_bb], expr->bitmap_index)
              && BLOCK_NUM (occr->insn) == pred_bb)
            return 1;
          visited[pred_bb] = 1;
        }
      /* Ignore this predecessor if it kills the expression.  */
      else if (TEST_BIT (ae_kill[pred_bb], expr->bitmap_index))
        visited[pred_bb] = 1;
      /* Does this predecessor generate this expression?  */
      else if (TEST_BIT (ae_gen[pred_bb], 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 (BLOCK_NUM (occr->insn) == pred_bb)
            return 1;
          visited[pred_bb] = 1;
        }
      /* Neither gen nor kill.  */
      else
        {
          visited[pred_bb] = 1;
          if (expr_reaches_here_p (occr, expr, pred_bb, check_self_loop, visited))
            return 1;
        }
    }

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

/* Return the instruction that computes EXPR that reaches INSN's basic block.
   If there is more than one such instruction, return NULL.

   Called only by handle_avail_expr.  */

static rtx
computing_insn (expr, insn)
     struct expr *expr;
     rtx insn;
{
  int bb = BLOCK_NUM (insn);

  if (expr->avail_occr->next == NULL)
    {    
      if (BLOCK_NUM (expr->avail_occr->insn) == bb)
        {
          /* The available expression is actually itself
             (i.e. a loop in the flow graph) so do nothing.  */
          return NULL;
        }
      /* (FIXME) Case that we found a pattern that was created by
         a substitution that took place.  */
      return expr->avail_occr->insn;
    }
  else
    {
      /* Pattern is computed more than once.
         Search backwards from this insn to see how many of these 
         computations actually reach this insn.  */
      struct occr *occr;
      rtx insn_computes_expr = NULL;
      int can_reach = 0;

      for (occr = expr->avail_occr; occr != NULL; occr = occr->next)
        {
          if (BLOCK_NUM (occr->insn) == bb)
            {
              /* The expression is generated in this block.
                 The only time we care about this is when the expression
                 is generated later in the block [and thus there's a loop].
                 We let the normal cse pass handle the other cases.  */
              if (INSN_CUID (insn) < INSN_CUID (occr->insn))
                {
                  if (expr_reaches_here_p (occr, expr, bb, 1, NULL))
                    {
                      can_reach++;
                      if (can_reach > 1)
                        return NULL;
                      insn_computes_expr = occr->insn;
                    }
                }
            }
          else /* Computation of the pattern outside this block.  */
            {
              if (expr_reaches_here_p (occr, expr, bb, 0, NULL))
                {
                  can_reach++;
                  if (can_reach > 1)
                    return NULL;
                  insn_computes_expr = occr->insn;
                }
            }
        }

      if (insn_computes_expr == NULL)
        abort ();
      return insn_computes_expr;
    }
}

/* Return non-zero if the definition in DEF_INSN can reach INSN.
   Only called by can_disregard_other_sets.  */

static int
def_reaches_here_p (insn, def_insn)
     rtx insn, def_insn;
{
  rtx reg;

  if (TEST_BIT (reaching_defs[BLOCK_NUM (insn)], INSN_CUID (def_insn)))
    return 1;

  if (BLOCK_NUM (insn) == BLOCK_NUM (def_insn))
    {
      if (INSN_CUID (def_insn) < INSN_CUID (insn))
        {
          if (GET_CODE (PATTERN (def_insn)) == PARALLEL)
            return 1;
          if (GET_CODE (PATTERN (def_insn)) == CLOBBER)
            reg = XEXP (PATTERN (def_insn), 0);
          else if (GET_CODE (PATTERN (def_insn)) == SET)
            reg = SET_DEST (PATTERN (def_insn));
          else
            abort ();
          return ! reg_set_between_p (reg, NEXT_INSN (def_insn), insn);
        }
      else
        return 0;
    }

  return 0;
}

/* Return non-zero if *ADDR_THIS_REG can only have one value at INSN.
   The value returned is the number of definitions that reach INSN.
   Returning a value of zero means that [maybe] more than one definition
   reaches INSN and the caller can't perform whatever optimization it is
   trying.  i.e. it is always safe to return zero.  */

static int
can_disregard_other_sets (addr_this_reg, insn, for_combine)
     struct reg_set **addr_this_reg;
     rtx insn;
     int for_combine;
{
  int number_of_reaching_defs = 0;
  struct reg_set *this_reg = *addr_this_reg;

  while (this_reg)
    {
      if (def_reaches_here_p (insn, this_reg->insn))
        {
          number_of_reaching_defs++;
          /* Ignore parallels for now.  */
          if (GET_CODE (PATTERN (this_reg->insn)) == PARALLEL)
            return 0;
          if (!for_combine
              && (GET_CODE (PATTERN (this_reg->insn)) == CLOBBER
                  || ! rtx_equal_p (SET_SRC (PATTERN (this_reg->insn)),
                                    SET_SRC (PATTERN (insn)))))
            {
              /* A setting of the reg to a different value reaches INSN.  */
              return 0;
            }
          if (number_of_reaching_defs > 1)
            {
              /* If in this setting the value the register is being
                 set to is equal to the previous value the register 
                 was set to and this setting reaches the insn we are
                 trying to do the substitution on then we are ok.  */

              if (GET_CODE (PATTERN (this_reg->insn)) == CLOBBER)
                return 0;
              if (! rtx_equal_p (SET_SRC (PATTERN (this_reg->insn)),
                                 SET_SRC (PATTERN (insn))))
                return 0;
            }
          *addr_this_reg = this_reg; 
        }

      /* prev_this_reg = this_reg; */
      this_reg = this_reg->next;
    }

  return number_of_reaching_defs;
}

/* Expression computed by insn is available and the substitution is legal,
   so try to perform the substitution.

   The result is non-zero if any changes were made.  */

static int
handle_avail_expr (insn, expr)
     rtx insn;
     struct expr *expr;
{
  rtx pat, insn_computes_expr;
  rtx to;
  struct reg_set *this_reg;
  int found_setting, use_src;
  int changed = 0;

  /* We only handle the case where one computation of the expression
     reaches this instruction.  */
  insn_computes_expr = computing_insn (expr, insn);
  if (insn_computes_expr == NULL)
    return 0;

  found_setting = 0;
  use_src = 0;

  /* At this point we know only one computation of EXPR outside of this
     block reaches this insn.  Now try to find a register that the
     expression is computed into.  */

  if (GET_CODE (SET_SRC (PATTERN (insn_computes_expr))) == REG)
    {
      /* This is the case when the available expression that reaches
         here has already been handled as an available expression.  */
      int regnum_for_replacing = REGNO (SET_SRC (PATTERN (insn_computes_expr)));
      /* If the register was created by GCSE we can't use `reg_set_table',
         however we know it's set only once.  */
      if (regnum_for_replacing >= max_gcse_regno
          /* If the register the expression is computed into is set only once,
             or only one set reaches this insn, we can use it.  */
          || (((this_reg = reg_set_table[regnum_for_replacing]),
               this_reg->next == NULL)
              || can_disregard_other_sets (&this_reg, insn, 0)))
       {
         use_src = 1;
         found_setting = 1;
       }
    }

  if (!found_setting)
    {
      int regnum_for_replacing = REGNO (SET_DEST (PATTERN (insn_computes_expr)));
      /* This shouldn't happen.  */
      if (regnum_for_replacing >= max_gcse_regno)
        abort ();
      this_reg = reg_set_table[regnum_for_replacing];
      /* If the register the expression is computed into is set only once,
         or only one set reaches this insn, use it.  */
      if (this_reg->next == NULL
          || can_disregard_other_sets (&this_reg, insn, 0))
        found_setting = 1;
    }

  if (found_setting)
    {
      pat = PATTERN (insn);
      if (use_src)
        to = SET_SRC (PATTERN (insn_computes_expr));
      else
        to = SET_DEST (PATTERN (insn_computes_expr));
      changed = validate_change (insn, &SET_SRC (pat), to, 0);

      /* We should be able to ignore the return code from validate_change but
         to play it safe we check.  */
      if (changed)
        {
          gcse_subst_count++;
          if (gcse_file != NULL)
            {
              fprintf (gcse_file, "GCSE: Replacing the source in insn %d with reg %d %s insn %d\n",
                       INSN_UID (insn), REGNO (to),
                       use_src ? "from" : "set in",
                       INSN_UID (insn_computes_expr));
            }

        }
    }
  /* The register that the expr is computed into is set more than once.  */
  else if (1 /*expensive_op(this_pattrn->op) && do_expensive_gcse)*/)
    {
      /* Insert an insn after insnx that copies the reg set in insnx
         into a new pseudo register call this new register REGN.
         From insnb until end of basic block or until REGB is set
         replace all uses of REGB with REGN.  */
      rtx new_insn;

      to = gen_reg_rtx (GET_MODE (SET_DEST (PATTERN (insn_computes_expr))));

      /* Generate the new insn.  */
      /* ??? If the change fails, we return 0, even though we created
         an insn.  I think this is ok.  */
      new_insn = emit_insn_after (gen_rtx (SET, VOIDmode, to,
                                           SET_DEST (PATTERN (insn_computes_expr))),
                                  insn_computes_expr);
      /* Keep block number table up to date.  */
      set_block_num (new_insn, BLOCK_NUM (insn_computes_expr));
      /* Keep register set table up to date.  */
      record_one_set (REGNO (to), new_insn);

      gcse_create_count++;
      if (gcse_file != NULL)
        {
          fprintf (gcse_file, "GCSE: Creating insn %d to copy value of reg %d, computed in insn %d,\n",
                   INSN_UID (NEXT_INSN (insn_computes_expr)),
                   REGNO (SET_SRC (PATTERN (NEXT_INSN (insn_computes_expr)))),
                   INSN_UID (insn_computes_expr));
          fprintf (gcse_file, "      into newly allocated reg %d\n", REGNO (to));
        }

      pat = PATTERN (insn);

      /* Do register replacement for INSN.  */
      changed = validate_change (insn, &SET_SRC (pat),
                                 SET_DEST (PATTERN (NEXT_INSN (insn_computes_expr))),
                                 0);

      /* We should be able to ignore the return code from validate_change but
         to play it safe we check.  */
      if (changed)
        {
          gcse_subst_count++;
          if (gcse_file != NULL)
            {
              fprintf (gcse_file, "GCSE: Replacing the source in insn %d with reg %d set in insn %d\n",
                       INSN_UID (insn),
                       REGNO (SET_DEST (PATTERN (NEXT_INSN (insn_computes_expr)))),
                       INSN_UID (insn_computes_expr)); 
            }

        }
    }

  return changed;
}

/* Perform classic GCSE.
   This is called by one_classic_gcse_pass after all the dataflow analysis
   has been done.

   The result is non-zero if a change was made.  */

static int
classic_gcse ()
{
  int bb, changed;
  rtx insn;

  /* Note we start at block 1.  */

  changed = 0;
  for (bb = 1; bb < n_basic_blocks; bb++)
    {
      /* Reset tables used to keep track of what's still valid [since the
         start of the block].  */
      reset_opr_set_tables ();

      for (insn = basic_block_head[bb];
           insn != NULL && insn != NEXT_INSN (basic_block_end[bb]);
           insn = NEXT_INSN (insn))
        {
          /* Is insn of form (set (pseudo-reg) ...)?  */

          if (GET_CODE (insn) == INSN
              && GET_CODE (PATTERN (insn)) == SET
              && GET_CODE (SET_DEST (PATTERN (insn))) == REG
              && REGNO (SET_DEST (PATTERN (insn))) >= FIRST_PSEUDO_REGISTER)
            {
              rtx pat = PATTERN (insn);
              rtx src = SET_SRC (pat);
              struct expr *expr;

              if (want_to_gcse_p (src)
                  /* Is the expression recorded?  */
                  && ((expr = lookup_expr (src)) != NULL)
                  /* Is the expression available [at the start of the
                     block]?  */
                  && TEST_BIT (ae_in[bb], expr->bitmap_index)
                  /* Are the operands unchanged since the start of the
                     block?  */
                  && oprs_not_set_p (src, insn))
                changed |= handle_avail_expr (insn, expr);
            }

          /* Keep track of everything modified by this insn.  */
          /* ??? Need to be careful w.r.t. mods done to INSN.  */
          if (GET_RTX_CLASS (GET_CODE (insn)) == 'i')
            mark_oprs_set (insn);
        }
    }

  return changed;
}

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

   Return non-zero if a change was made.  */

static int
one_classic_gcse_pass (f, pass)
     rtx f;
     int pass;
{
  int changed = 0;

  gcse_subst_count = 0;
  gcse_create_count = 0;

  alloc_expr_hash_table (max_cuid);
  alloc_rd_mem (n_basic_blocks, max_cuid);
  compute_expr_hash_table (f);
  if (gcse_file)
    dump_hash_table (gcse_file, "Expression", expr_hash_table,
                     expr_hash_table_size, n_exprs);
  if (n_exprs > 0)
    {
      compute_kill_rd ();
      compute_rd ();
      alloc_avail_expr_mem (n_basic_blocks, n_exprs);
      compute_ae_gen ();
      compute_ae_kill ();
      compute_available ();
      changed = classic_gcse ();
      free_avail_expr_mem ();
    }
  free_rd_mem ();
  free_expr_hash_table ();

  if (gcse_file)
    {
      fprintf (gcse_file, "\n");
      fprintf (gcse_file, "GCSE of %s, pass %d: %d bytes needed, %d substs, %d insns created\n",
               current_function_name, pass,
               bytes_used, gcse_subst_count, gcse_create_count);
    }

  return changed;
}
\f
/* Compute copy/constant propagation working variables.  */

/* Local properties of assignments.  */

static sbitmap *cprop_pavloc;
static sbitmap *cprop_absaltered;

/* Global properties of assignments (computed from the local properties).  */

static sbitmap *cprop_avin;
static sbitmap *cprop_avout;

/* Allocate vars used for copy/const propagation.
   N_BLOCKS is the number of basic blocks.
   N_SETS is the number of sets.  */

static void
alloc_cprop_mem (n_blocks, n_sets)
     int n_blocks, n_sets;
{
  cprop_pavloc = sbitmap_vector_alloc (n_blocks, n_sets);
  cprop_absaltered = sbitmap_vector_alloc (n_blocks, n_sets);

  cprop_avin = sbitmap_vector_alloc (n_blocks, n_sets);
  cprop_avout = sbitmap_vector_alloc (n_blocks, n_sets);
}

/* Free vars used by copy/const propagation.  */

static void
free_cprop_mem ()
{
  free (cprop_pavloc);
  free (cprop_absaltered);
  free (cprop_avin);
  free (cprop_avout);
}

/* Dump copy/const propagation data.  */

void
dump_cprop_data (file)
     FILE *file;
{
  dump_sbitmap_vector (file, "CPROP partially locally available sets", "BB",
                       cprop_pavloc, n_basic_blocks);
  dump_sbitmap_vector (file, "CPROP absolutely altered sets", "BB",
                       cprop_absaltered, n_basic_blocks);

  dump_sbitmap_vector (file, "CPROP available incoming sets", "BB",
                       cprop_avin, n_basic_blocks);
  dump_sbitmap_vector (file, "CPROP available outgoing sets", "BB",
                       cprop_avout, n_basic_blocks);
}

/* 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, set (SET_P == 1) or reset
   (SET_P == 0) the INDX bit in BMAP.  */

static void
compute_transp (x, indx, bmap, set_p)
     rtx x;
     int indx;
     sbitmap *bmap;
     int set_p;
{
  int bb,i;
  enum rtx_code code;
  char *fmt;

  /* repeat is used to turn tail-recursion into iteration.  */
 repeat:

  if (x == 0)
    return;

  code = GET_CODE (x);
  switch (code)
    {
    case REG:
      {
        reg_set *r;
        int regno = REGNO (x);

        if (set_p)
          {
            if (regno < FIRST_PSEUDO_REGISTER)
              {
                for (bb = 0; bb < n_basic_blocks; bb++)
                  if (TEST_BIT (reg_set_in_block[bb], regno))
                    SET_BIT (bmap[bb], indx);
              }
            else
              {
                for (r = reg_set_table[regno]; r != NULL; r = r->next)
                  {
                    bb = BLOCK_NUM (r->insn);
                    SET_BIT (bmap[bb], indx);
                  }
              }
          }
        else
          {
            if (regno < FIRST_PSEUDO_REGISTER)
              {
                for (bb = 0; bb < n_basic_blocks; bb++)
                  if (TEST_BIT (reg_set_in_block[bb], regno))
                    RESET_BIT (bmap[bb], indx);
              }
            else
              {
                for (r = reg_set_table[regno]; r != NULL; r = r->next)
                  {
                    bb = BLOCK_NUM (r->insn);
                    RESET_BIT (bmap[bb], indx);
                  }
              }
          }
        return;
      }

    case MEM:
      if (set_p)
        {
          for (bb = 0; bb < n_basic_blocks; bb++)
            if (mem_set_in_block[bb])
              SET_BIT (bmap[bb], indx);
        }
      else
        {
          for (bb = 0; bb < n_basic_blocks; bb++)
            if (mem_set_in_block[bb])
              RESET_BIT (bmap[bb], indx);
        }
      x = XEXP (x, 0);
      goto repeat;

    case PC:
    case CC0: /*FIXME*/
    case CONST:
    case CONST_INT:
    case CONST_DOUBLE:
    case SYMBOL_REF:
    case LABEL_REF:
    case ADDR_VEC:
    case ADDR_DIFF_VEC:
      return;

    default:
      break;
    }

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

          /* If we are about to do the last recursive call
             needed at this level, change it into iteration.
             This function is called enough to be worth it.  */
          if (i == 0)
            {
              x = tem;
              goto repeat;
            }
          compute_transp (tem, indx, bmap, set_p);
        }
      else if (fmt[i] == 'E')
        {
          int j;
          for (j = 0; j < XVECLEN (x, i); j++)
            compute_transp (XVECEXP (x, i, j), indx, bmap, set_p);
        }
    }
}

static void
compute_cprop_local_properties ()
{
  int i;

  sbitmap_vector_zero (cprop_absaltered, n_basic_blocks);
  sbitmap_vector_zero (cprop_pavloc, n_basic_blocks);

  for (i = 0; i < set_hash_table_size; i++)
    {
      struct expr *expr;

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

          /* The assignment is absolutely altered if any operand is modified
             by this block [excluding the assignment itself].
             We start by assuming all are transparent [none are killed], and
             then setting the bits for those that are.  */

          compute_transp (expr->expr, indx, cprop_absaltered, 1);

          /* The occurrences recorded in avail_occr are exactly those that
             we want to set to non-zero in PAVLOC.  */

          for (occr = expr->avail_occr; occr != NULL; occr = occr->next)
            {
              int bb = BLOCK_NUM (occr->insn);
              SET_BIT (cprop_pavloc[bb], indx);
            }
        }
    }
}

static void
compute_cprop_avinout ()
{
  int bb, changed, passes;

  sbitmap_zero (cprop_avin[0]);
  sbitmap_vector_ones (cprop_avout, n_basic_blocks);

  passes = 0;
  changed = 1;
  while (changed)
    {
      changed = 0;
      for (bb = 0; bb < n_basic_blocks; bb++)
        {
          if (bb != 0)
            sbitmap_intersect_of_predecessors (cprop_avin[bb], cprop_avout,
                                               bb, s_preds);
          changed |= sbitmap_union_of_diff (cprop_avout[bb],
                                            cprop_pavloc[bb],
                                            cprop_avin[bb],
                                            cprop_absaltered[bb]);
        }
      passes++;
    }

  if (gcse_file)
    fprintf (gcse_file, "cprop avail expr computation: %d passes\n", passes);
}

/* Top level routine to do the dataflow analysis needed by copy/const
   propagation.  */

static void
compute_cprop_data ()
{
  compute_cprop_local_properties ();
  compute_cprop_avinout ();
}
\f
/* Copy/constant propagation.  */

struct reg_use {
  rtx reg_rtx;
};

/* Maximum number of register uses in an insn that we handle.  */
#define MAX_USES 8

/* Table of uses found in an insn.
   Allocated statically to avoid alloc/free complexity and overhead.  */
static struct reg_use reg_use_table[MAX_USES];

/* Index into `reg_use_table' while building it.  */
static int reg_use_count;

/* Set up a list of register numbers used in INSN.
   The found uses are stored in `reg_use_table'.
   `reg_use_count' is initialized to zero before entry, and
   contains the number of uses in the table upon exit.

   ??? If a register appears multiple times we will record it multiple
   times.  This doesn't hurt anything but it will slow things down.  */

static void
find_used_regs (x)
     rtx x;
{
  int i;
  enum rtx_code code;
  char *fmt;

  /* repeat is used to turn tail-recursion into iteration.  */
 repeat:

  if (x == 0)
    return;

  code = GET_CODE (x);
  switch (code)
    {
    case REG:
      if (reg_use_count == MAX_USES)
        return;
      reg_use_table[reg_use_count].reg_rtx = x;
      reg_use_count++;
      return;

    case MEM:
      x = XEXP (x, 0);
      goto repeat;

    case PC:
    case CC0:
    case CONST:
    case CONST_INT:
    case CONST_DOUBLE:
    case SYMBOL_REF:
    case LABEL_REF:
    case CLOBBER:
    case ADDR_VEC:
    case ADDR_DIFF_VEC:
    case ASM_INPUT: /*FIXME*/
      return;

    case SET:
      if (GET_CODE (SET_DEST (x)) == MEM)
        find_used_regs (SET_DEST (x));
      x = SET_SRC (x);
      goto repeat;

    default:
      break;
    }

  /* Recursively scan the operands of this expression.  */

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; 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, 0);
              goto repeat;
            }
          find_used_regs (XEXP (x, i));
        }
      else if (fmt[i] == 'E')
        {
          int j;
          for (j = 0; j < XVECLEN (x, i); j++)
            find_used_regs (XVECEXP (x, i, j));
        }
    }
}

/* Try to replace all non-SET_DEST occurrences of FROM in INSN with TO.
   Returns non-zero is successful.  */

static int
try_replace_reg (from, to, insn)
     rtx from, to, insn;
{
  return validate_replace_src (from, to, insn);
}

/* Find a set of REGNO that is available on entry to INSN's block.
   Returns NULL if not found.  */

static struct expr *
find_avail_set (regno, insn)
     int regno;
     rtx insn;
{
  struct expr *set = lookup_set (regno, NULL_RTX);

  while (set)
    {
      if (TEST_BIT (cprop_avin[BLOCK_NUM (insn)], set->bitmap_index))
        break;
      set = next_set (regno, set);
    }

  return set;
}

/* Perform constant and copy propagation on INSN.
   The result is non-zero if a change was made.  */

static int
cprop_insn (insn)
     rtx insn;
{
  struct reg_use *reg_used;
  int changed = 0;

  /* ??? For now only propagate into SETs.  */
  if (GET_CODE (insn) != INSN
      || GET_CODE (PATTERN (insn)) != SET)
    return 0;

  reg_use_count = 0;
  find_used_regs (PATTERN (insn));

  reg_used = &reg_use_table[0];
  for ( ; reg_use_count > 0; reg_used++, reg_use_count--)
    {
      rtx pat, src;
      struct expr *set;
      int regno = REGNO (reg_used->reg_rtx);

      /* Ignore registers created by GCSE.
         We do this because ... */
      if (regno >= max_gcse_regno)
        continue;

      /* If the register has already been set in this block, there's
         nothing we can do.  */
      if (! oprs_not_set_p (reg_used->reg_rtx, insn))
        continue;

      /* Find an assignment that sets reg_used and is available
         at the start of the block.  */
      set = find_avail_set (regno, insn);
      if (! set)
        continue;
  
      pat = set->expr;
      /* ??? We might be able to handle PARALLELs.  Later.  */
      if (GET_CODE (pat) != SET)
        abort ();
      src = SET_SRC (pat);

      if (GET_CODE (src) == CONST_INT)
        {
          if (try_replace_reg (reg_used->reg_rtx, src, insn))
            {
              changed = 1;
              const_prop_count++;
              if (gcse_file != NULL)
                {
                  fprintf (gcse_file, "CONST-PROP: Replacing reg %d in insn %d with constant ",
                           regno, INSN_UID (insn));
                  fprintf (gcse_file, HOST_WIDE_INT_PRINT_DEC, INTVAL (src));
                  fprintf (gcse_file, "\n");
                }

              /* The original insn setting reg_used may or may not now be
                 deletable.  We leave the deletion to flow.  */
            }
        }
      else if (GET_CODE (src) == REG
               && REGNO (src) >= FIRST_PSEUDO_REGISTER
               && REGNO (src) != regno)
        {
          /* We know the set is available.
             Now check that SET_SRC is ANTLOC (i.e. none of the source operands
             have changed since the start of the block).  */
          if (oprs_not_set_p (src, insn))
            {
              if (try_replace_reg (reg_used->reg_rtx, src, insn))
                {
                  changed = 1;
                  copy_prop_count++;
                  if (gcse_file != NULL)
                    {
                      fprintf (gcse_file, "COPY-PROP: Replacing reg %d in insn %d with reg %d\n",
                               regno, INSN_UID (insn), REGNO (src));
                    }

                  /* The original insn setting reg_used may or may not now be
                     deletable.  We leave the deletion to flow.  */
                  /* FIXME: If it turns out that the insn isn't deletable,
                     then we may have unnecessarily extended register lifetimes
                     and made things worse.  */
                }
            }
        }
    }

  return changed;
}

/* Forward propagate copies.
   This includes copies and constants.
   Return non-zero if a change was made.  */

static int
cprop ()
{
  int bb, changed;
  rtx insn;

  /* Note we start at block 1.  */

  changed = 0;
  for (bb = 1; bb < n_basic_blocks; bb++)
    {
      /* Reset tables used to keep track of what's still valid [since the
         start of the block].  */
      reset_opr_set_tables ();

      for (insn = basic_block_head[bb];
           insn != NULL && insn != NEXT_INSN (basic_block_end[bb]);
           insn = NEXT_INSN (insn))
        {
          if (GET_RTX_CLASS (GET_CODE (insn)) == 'i')
            {
              changed |= cprop_insn (insn);

              /* Keep track of everything modified by this insn.  */
              /* ??? Need to be careful w.r.t. mods done to INSN.  */
              mark_oprs_set (insn);
            }
        }
    }

  if (gcse_file != NULL)
    fprintf (gcse_file, "\n");

  return changed;
}

/* Perform one copy/constant propagation pass.
   F is the first insn in the function.
   PASS is the pass count.  */

static int
one_cprop_pass (f, pass)
     rtx f;
     int pass;
{
  int changed = 0;

  const_prop_count = 0;
  copy_prop_count = 0;

  alloc_set_hash_table (max_cuid);
  compute_set_hash_table (f);
  if (gcse_file)
    dump_hash_table (gcse_file, "SET", set_hash_table, set_hash_table_size,
                     n_sets);
  if (n_sets > 0)
    {
      alloc_cprop_mem (n_basic_blocks, n_sets);
      compute_cprop_data ();
      changed = cprop ();
      free_cprop_mem ();
    }
  free_set_hash_table ();

  if (gcse_file)
    {
      fprintf (gcse_file, "CPROP of %s, pass %d: %d bytes needed, %d const props, %d copy props\n",
               current_function_name, pass,
               bytes_used, const_prop_count, copy_prop_count);
      fprintf (gcse_file, "\n");
    }

  return changed;
}
\f
/* Compute PRE working variables.  */

/* Local properties of expressions.  */
/* Nonzero for expressions that are transparent in the block.  */
static sbitmap *pre_transp;
/* Nonzero for expressions that are computed (available) in the block.  */
static sbitmap *pre_comp;
/* Nonzero for expressions that are locally anticipatable in the block.  */
static sbitmap *pre_antloc;

/* Global properties (computed from the expression local properties).  */
/* Nonzero for expressions that are available on block entry/exit.  */
static sbitmap *pre_avin;
static sbitmap *pre_avout;
/* Nonzero for expressions that are anticipatable on block entry/exit.  */
static sbitmap *pre_antin;
static sbitmap *pre_antout;
/* Nonzero for expressions that are partially available on block entry/exit.  */
static sbitmap *pre_pavin;
static sbitmap *pre_pavout;
/* Nonzero for expressions that are "placement possible" on block entry/exit.  */
static sbitmap *pre_ppin;
static sbitmap *pre_ppout;

/* Used while performing PRE to denote which insns are redundant.  */
static sbitmap pre_redundant;

/* Allocate vars used for PRE analysis.  */

static void
alloc_pre_mem (n_blocks, n_exprs)
     int n_blocks, n_exprs;
{
  pre_transp = sbitmap_vector_alloc (n_blocks, n_exprs);
  pre_comp = sbitmap_vector_alloc (n_blocks, n_exprs);
  pre_antloc = sbitmap_vector_alloc (n_blocks, n_exprs);

  pre_avin = sbitmap_vector_alloc (n_blocks, n_exprs);
  pre_avout = sbitmap_vector_alloc (n_blocks, n_exprs);
  pre_antin = sbitmap_vector_alloc (n_blocks, n_exprs);
  pre_antout = sbitmap_vector_alloc (n_blocks, n_exprs);

  pre_pavin = sbitmap_vector_alloc (n_blocks, n_exprs);
  pre_pavout = sbitmap_vector_alloc (n_blocks, n_exprs);
  pre_ppin = sbitmap_vector_alloc (n_blocks, n_exprs);
  pre_ppout = sbitmap_vector_alloc (n_blocks, n_exprs);
}

/* Free vars used for PRE analysis.  */

static void
free_pre_mem ()
{
  free (pre_transp);
  free (pre_comp);
  free (pre_antloc);

  free (pre_avin);
  free (pre_avout);
  free (pre_antin);
  free (pre_antout);

  free (pre_pavin);
  free (pre_pavout);
  free (pre_ppin);
  free (pre_ppout);
}

/* Dump PRE data.  */

void
dump_pre_data (file)
     FILE *file;
{
  dump_sbitmap_vector (file, "PRE locally transparent expressions", "BB",
                       pre_transp, n_basic_blocks);
  dump_sbitmap_vector (file, "PRE locally available expressions", "BB",
                       pre_comp, n_basic_blocks);
  dump_sbitmap_vector (file, "PRE locally anticipatable expressions", "BB",
                       pre_antloc, n_basic_blocks);

  dump_sbitmap_vector (file, "PRE available incoming expressions", "BB",
                       pre_avin, n_basic_blocks);
  dump_sbitmap_vector (file, "PRE available outgoing expressions", "BB",
                       pre_avout, n_basic_blocks);
  dump_sbitmap_vector (file, "PRE anticipatable incoming expressions", "BB",
                       pre_antin, n_basic_blocks);
  dump_sbitmap_vector (file, "PRE anticipatable outgoing expressions", "BB",
                       pre_antout, n_basic_blocks);

  dump_sbitmap_vector (file, "PRE partially available incoming expressions", "BB",
                       pre_pavin, n_basic_blocks);
  dump_sbitmap_vector (file, "PRE partially available outgoing expressions", "BB",
                       pre_pavout, n_basic_blocks);
  dump_sbitmap_vector (file, "PRE placement possible on incoming", "BB",
                       pre_ppin, n_basic_blocks);
  dump_sbitmap_vector (file, "PRE placement possible on outgoing", "BB",
                       pre_ppout, n_basic_blocks);
}

/* 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.  */

static void
compute_pre_local_properties ()
{
  int i;

  sbitmap_vector_ones (pre_transp, n_basic_blocks);
  sbitmap_vector_zero (pre_comp, n_basic_blocks);
  sbitmap_vector_zero (pre_antloc, n_basic_blocks);

  for (i = 0; i < expr_hash_table_size; i++)
    {
      struct expr *expr;

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

          /* 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.  */

          compute_transp (expr->expr, indx, pre_transp, 0);

          /* The occurrences recorded in antic_occr are exactly those that
             we want to set to non-zero in ANTLOC.  */

          for (occr = expr->antic_occr; occr != NULL; occr = occr->next)
            {
              int bb = BLOCK_NUM (occr->insn);
              SET_BIT (pre_antloc[bb], 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 non-zero in COMP.  */

          for (occr = expr->avail_occr; occr != NULL; occr = occr->next)
            {
              int bb = BLOCK_NUM (occr->insn);
              SET_BIT (pre_comp[bb], 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;
        }
    }
}

/* Compute expression availability at entrance and exit of each block.  */

static void
compute_pre_avinout ()
{
  int bb, changed, passes;

  sbitmap_zero (pre_avin[0]);
  sbitmap_vector_ones (pre_avout, n_basic_blocks);

  passes = 0;
  changed = 1;
  while (changed)
    {
      changed = 0;
      for (bb = 0; bb < n_basic_blocks; bb++)
        {
          if (bb != 0)
            sbitmap_intersect_of_predecessors (pre_avin[bb], pre_avout,
                                               bb, s_preds);
          changed |= sbitmap_a_or_b_and_c (pre_avout[bb], pre_comp[bb],
                                           pre_transp[bb], pre_avin[bb]);
        }
      passes++;
    }

  if (gcse_file)
    fprintf (gcse_file, "avail expr computation: %d passes\n", passes);
}

/* Compute expression anticipatability at entrance and exit of each block.  */

static void
compute_pre_antinout ()
{
  int bb, changed, passes;

  sbitmap_zero (pre_antout[n_basic_blocks - 1]);
  sbitmap_vector_ones (pre_antin, n_basic_blocks);

  passes = 0;
  changed = 1;
  while (changed)
    {
      changed = 0;
      /* We scan the blocks in the reverse order to speed up
         the convergence.  */
      for (bb = n_basic_blocks - 1; bb >= 0; bb--)
        {
          if (bb != n_basic_blocks - 1)
            sbitmap_intersect_of_successors (pre_antout[bb], pre_antin,
                                             bb, s_succs);
          changed |= sbitmap_a_or_b_and_c (pre_antin[bb], pre_antloc[bb],
                                           pre_transp[bb], pre_antout[bb]);
        }
      passes++;
    }

  if (gcse_file)
    fprintf (gcse_file, "antic expr computation: %d passes\n", passes);
}

/* Compute expression partial availability at entrance and exit of
   each block.  */

static void
compute_pre_pavinout ()
{
  int bb, changed, passes;

  sbitmap_zero (pre_pavin[0]);
  sbitmap_vector_zero (pre_pavout, n_basic_blocks);

  passes = 0;
  changed = 1;
  while (changed)
    {
      changed = 0;
      for (bb = 0; bb < n_basic_blocks; bb++)
        {
          if (bb != 0)
            sbitmap_union_of_predecessors (pre_pavin[bb], pre_pavout,
                                           bb, s_preds);
          changed |= sbitmap_a_or_b_and_c (pre_pavout[bb], pre_comp[bb],
                                           pre_transp[bb], pre_pavin[bb]);
        }
      passes++;
    }

  if (gcse_file)
    fprintf (gcse_file, "partially avail expr computation: %d passes\n", passes);
}

/* Compute "placement possible" information on entrance and exit of
   each block.

   From Fred Chow's Thesis:
   A computation `e' is PP at a point `p' if it is anticipated at `p' and
   all the anticipated e's can be rendered redundant by zero or more
   insertions at that point and some other points in the procedure, and
   these insertions satisfy the conditions that the insertions are always
   at points that `e' is anticipated and the first anticipated e's after the
   insertions are rendered redundant.  */

static void
compute_pre_ppinout ()
{
  int bb, i, changed, size, passes;

  sbitmap_vector_ones (pre_ppin, n_basic_blocks);
  /* ??? Inefficient as we set pre_ppin[0] twice, but simple.  */
  sbitmap_zero (pre_ppin[0]);

  sbitmap_vector_ones (pre_ppout, n_basic_blocks);
  /* ??? Inefficient as we set pre_ppout[n_basic_blocks-1] twice, but simple.  */
  sbitmap_zero (pre_ppout[n_basic_blocks - 1]);

  size = pre_ppin[0]->size;
  passes = 0;
  changed = 1;
  while (changed)
    {
      changed = 0;
      for (bb = 1; bb < n_basic_blocks; bb++)
        {
          sbitmap_ptr antin = pre_antin[bb]->elms;
          sbitmap_ptr pavin = pre_pavin[bb]->elms;
          sbitmap_ptr antloc = pre_antloc[bb]->elms;
          sbitmap_ptr transp = pre_transp[bb]->elms;
          sbitmap_ptr ppout = pre_ppout[bb]->elms;
          sbitmap_ptr ppin = pre_ppin[bb]->elms;

          for (i = 0; i < size; i++)
            {
              int_list_ptr pred;
              SBITMAP_ELT_TYPE tmp = *antin & *pavin & (*antloc | (*transp & *ppout));
              SBITMAP_ELT_TYPE pred_val = -1L;

              for (pred = s_preds[bb]; pred != NULL; pred = pred->next)
                {
                  int pred_bb = INT_LIST_VAL (pred);
                  sbitmap_ptr ppout_j,avout_j;

                  if (pred_bb == ENTRY_BLOCK)
                    continue;

                  /* If this is a back edge, propagate info along the back
                     edge to allow for loop invariant code motion.

                     See FOLLOW_BACK_EDGES at the top of this file for a longer
                     discussion about loop invariant code motion in pre.  */
                  if (! FOLLOW_BACK_EDGES
                      && (INSN_CUID (BLOCK_HEAD (bb))
                          < INSN_CUID (BLOCK_END (pred_bb))))
                    {
                      pred_val = 0;
                    }
                  else
                    {
                      ppout_j = pre_ppout[pred_bb]->elms + i;
                      avout_j = pre_avout[pred_bb]->elms + i;
                      pred_val &= *ppout_j | *avout_j;
                    }
                }
              tmp &= pred_val;
              *ppin = tmp;
              antin++; pavin++; antloc++; transp++; ppout++; ppin++;
            }
        }

      for (bb = 0; bb < n_basic_blocks - 1; bb++)
        {
          sbitmap_ptr ppout = pre_ppout[bb]->elms;

          for (i = 0; i < size; i++)
            {
              int_list_ptr succ;
              SBITMAP_ELT_TYPE tmp = -1L;

              for (succ = s_succs[bb]; succ != NULL; succ = succ->next)
                {
                  int succ_bb = INT_LIST_VAL (succ);
                  sbitmap_ptr ppin;

                  if (succ_bb == EXIT_BLOCK)
                    continue;

                  ppin = pre_ppin[succ_bb]->elms + i;
                  tmp &= *ppin;
                }
              if (*ppout != tmp)
                {
                  changed = 1;
                  *ppout++ = tmp;
                }
              else
                ppout++;
            }
        }

      passes++;
    }

  if (gcse_file)
    fprintf (gcse_file, "placement possible computation: %d passes\n", passes);
}

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

static void
compute_pre_data ()
{
  compute_pre_local_properties ();
  compute_pre_avinout ();
  compute_pre_antinout ();
  compute_pre_pavinout ();
  compute_pre_ppinout ();
  if (gcse_file)
    fprintf (gcse_file, "\n");
}
\f
/* PRE utilities */

/* Return non-zero if occurrence OCCR of expression EXPR reaches 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 (occr, expr, bb, visited)
     struct occr *occr;
     struct expr *expr;
     int bb;
     char *visited;
{
  int_list_ptr pred;

  if (visited == NULL)
    {
      visited = (char *) alloca (n_basic_blocks);
      bzero (visited, n_basic_blocks);
    }

  for (pred = s_preds[bb]; pred != NULL; pred = pred->next)
    {
      int pred_bb = INT_LIST_VAL (pred);

      if (pred_bb == ENTRY_BLOCK
          /* Has predecessor has already been visited?  */
          || visited[pred_bb])
        {
          /* Nothing to do.  */
        }
      /* Does this predecessor generate this expression?  */
      else if (TEST_BIT (pre_comp[pred_bb], 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 (BLOCK_NUM (occr->insn) == pred_bb)
            return 1;
          visited[pred_bb] = 1;
        }
      /* Ignore this predecessor if it kills the expression.  */
      else if (! TEST_BIT (pre_transp[pred_bb], expr->bitmap_index))
        visited[pred_bb] = 1;
      /* Neither gen nor kill.  */
      else
        {
          visited[pred_bb] = 1;
          if (pre_expr_reaches_here_p (occr, expr, pred_bb, visited))
            return 1;
        }
    }

  /* All paths have been checked.  */
  return 0;
}
\f
/* Add EXPR to the end of basic block BB.  */

static void
pre_insert_insn (expr, bb)
     struct expr *expr;
     int bb;
{
  rtx insn = BLOCK_END (bb);
  rtx new_insn;
  rtx reg = expr->reaching_reg;
  int regno = REGNO (reg);
  rtx pat;

  pat = gen_rtx (SET, VOIDmode, reg, copy_rtx (expr->expr));

  /* If the last insn is a jump, insert EXPR in front [taking care to
     handle cc0, etc. properly].  */

  if (GET_CODE (insn) == JUMP_INSN)
    {
#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_real_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
              && GET_RTX_CLASS (GET_CODE (maybe_cc0_setter)) == 'i'
              && 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 (pat, insn);
      if (BLOCK_HEAD (bb) == insn)
        BLOCK_HEAD (bb) = new_insn;
      /* Keep block number table up to date.  */
      set_block_num (new_insn, bb);
      /* Keep register set table up to date.  */
      record_one_set (regno, new_insn);
    }
  else
    {
      new_insn = emit_insn_after (pat, insn);
      BLOCK_END (bb) = new_insn;
      /* Keep block number table up to date.  */
      set_block_num (new_insn, bb);
      /* Keep register set table up to date.  */
      record_one_set (regno, new_insn);
    }

  gcse_create_count++;

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

/* Insert partially redundant expressions at the ends of appropriate basic
   blocks making them now redundant.  */

static void
pre_insert (index_map)
     struct expr **index_map;
{
  int bb, i, size;

  /* Compute INSERT = PPOUT & (~AVOUT) & (~PPIN | ~TRANSP) for each
     expression.  Where INSERT == TRUE, add the expression at the end of
     the basic block.  */

  size = pre_ppout[0]->size;
  for (bb = 0; bb < n_basic_blocks; bb++)
    {
      int indx;
      sbitmap_ptr ppout = pre_ppout[bb]->elms;
      sbitmap_ptr avout = pre_avout[bb]->elms;
      sbitmap_ptr ppin = pre_ppin[bb]->elms;
      sbitmap_ptr transp = pre_transp[bb]->elms;

      for (i = indx = 0;
           i < size;
           i++, indx += SBITMAP_ELT_BITS, ppout++, avout++, ppin++, transp++)
        {
          int j;
          SBITMAP_ELT_TYPE insert = *ppout & (~*avout) & (~*ppin | ~*transp);

          for (j = indx; insert != 0 && j < n_exprs; j++, insert >>= 1)
            {
              if ((insert & 1) != 0
                  /* 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.  */
                  && index_map[j]->reaching_reg != NULL)
                pre_insert_insn (index_map[j], bb);
            }
        }
    }
}

/* Copy the result of INSN to REG.
   INDX is the expression number.  */

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

  if (!set)
    abort ();
  new_insn = emit_insn_after (gen_rtx (SET, VOIDmode, reg, SET_DEST (set)),
                              insn);
  /* Keep block number table up to date.  */
  set_block_num (new_insn, BLOCK_NUM (insn));
  /* Keep register set table up to date.  */
  record_one_set (regno, new_insn);

  gcse_create_count++;

  if (gcse_file)
    {
      fprintf (gcse_file, "PRE: bb %d, insn %d, copying expression %d in insn %d to reg %d\n",
               BLOCK_NUM (insn), 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 ()
{
  int i;

  /* 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++)
    {
      struct expr *expr;

      for (expr = expr_hash_table[i]; expr != NULL; expr = expr->next_same_hash)
        {
          struct occr *occr;

          /* 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;

          for (occr = expr->antic_occr; occr != NULL; occr = occr->next)
            {
              struct occr *avail;

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

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

/* Delete redundant computations.
   These are ones that satisy ANTLOC & PPIN.
   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.

   Returns non-zero if a change is made.  */

static int
pre_delete ()
{
  int i, changed;

  changed = 0;
  for (i = 0; i < expr_hash_table_size; i++)
    {
      struct expr *expr;

      for (expr = expr_hash_table[i]; expr != NULL; expr = expr->next_same_hash)
        {
          struct occr *occr;
          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;
              int bb = BLOCK_NUM (insn);
              sbitmap ppin = pre_ppin[bb];

              if (TEST_BIT (ppin, indx))
                {
                  set = single_set (insn);
                  if (! set)
                    abort ();

                  /* 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 (GET_MODE (SET_DEST (set)));

                  /* In theory this should never fail since we're creating
                     a reg->reg copy.

                     However, on the x86 some of the movXX patterns actually
                     contain clobbers of scratch regs.  This may cause the
                     insn created by validate_change to not patch any pattern
                     and thus cause validate_change to fail.   */
                  if (validate_change (insn, &SET_SRC (set),
                                       expr->reaching_reg, 0))
                    {
                      occr->deleted_p = 1;
                      SET_BIT (pre_redundant, INSN_CUID (insn));
                      changed = 1;
                      gcse_subst_count++;
                    }

                  if (gcse_file)
                    {
                      fprintf (gcse_file, "PRE: redundant insn %d (expression %d) in bb %d, reaching reg is %d\n",
                               INSN_UID (insn), indx, bb, 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 and Fred Chow's thesis.

   The M-R paper uses "TRANSP" to describe an expression as being transparent
   in a block where as Chow's thesis uses "ALTERED".  We use TRANSP.

   ??? 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 ()
{
  int i;
  int changed;
  struct expr **index_map;

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

  index_map = (struct expr **) alloca (n_exprs * sizeof (struct expr *));
  bzero ((char *) index_map, n_exprs * sizeof (struct expr *));
  for (i = 0; i < expr_hash_table_size; i++)
    {
      struct expr *expr;

      for (expr = expr_hash_table[i]; expr != NULL; expr = expr->next_same_hash)
        index_map[expr->bitmap_index] = expr;
    }

  /* Reset bitmap used to track which insns are redundant.  */
  pre_redundant = sbitmap_alloc (max_cuid);
  sbitmap_zero (pre_redundant);

  /* 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 ();

  /* Insert insns in places that make partially redundant expressions
     fully redundant.  */
  pre_insert (index_map);

  /* In other places with reaching expressions, copy the expression to the
     specially allocated pseudo-reg that reaches the redundant expression.  */
  pre_insert_copies ();

  free (pre_redundant);

  return changed;
}

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

   Return non-zero if a change was made.  */

static int
one_pre_gcse_pass (f, pass)
     rtx f;
     int pass;
{
  int changed = 0;

  gcse_subst_count = 0;
  gcse_create_count = 0;

  alloc_expr_hash_table (max_cuid);
  compute_expr_hash_table (f);
  if (gcse_file)
    dump_hash_table (gcse_file, "Expression", expr_hash_table,
                     expr_hash_table_size, n_exprs);
  if (n_exprs > 0)
    {
      alloc_pre_mem (n_basic_blocks, n_exprs);
      compute_pre_data ();
      changed |= pre_gcse ();
      free_pre_mem ();
    }
  free_expr_hash_table ();

  if (gcse_file)
    {
      fprintf (gcse_file, "\n");
      fprintf (gcse_file, "PRE GCSE of %s, pass %d: %d bytes needed, %d substs, %d insns created\n",
               current_function_name, pass,
               bytes_used, gcse_subst_count, gcse_create_count);
    }

  return changed;
}