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/* Routines for performing Temporary Expression Replacement (TER) in SSA trees.

   Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011

   Free Software Foundation, Inc.

   Contributed by Andrew MacLeod  <amacleod@redhat.com>

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

the Free Software Foundation; either version 3, or (at your option)

any later version.

GCC is distributed in the hope that it will be useful,

but WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

GNU General Public License for more details.

You should have received a copy of the GNU General Public License

along with GCC; see the file COPYING3.  If not see

<http://www.gnu.org/licenses/>.  */

#include "config.h"

#include "system.h"

#include "coretypes.h"

#include "tm.h"

#include "tree.h"

#include "tree-pretty-print.h"

#include "gimple-pretty-print.h"

#include "bitmap.h"

#include "tree-flow.h"

#include "tree-dump.h"

#include "tree-ssa-live.h"

#include "flags.h"

/* Temporary Expression Replacement (TER)

   Replace SSA version variables during out-of-ssa with their defining

   expression if there is only one use of the variable.

   This pass is required in order for the RTL expansion pass to see larger

   chunks of code.  This allows it to make better choices on RTL pattern

   selection.  When expand is rewritten and merged with out-of-ssa, and

   understands SSA, this should be eliminated.

   A pass is made through the function, one block at a time.  No cross block

   information is tracked.

   Variables which only have one use, and whose defining stmt is considered

   a replaceable expression (see is_replaceable_p) are tracked to see whether

   they can be replaced at their use location.

   n_12 = C * 10

   a_2 = b_5 + 6

   v_9 = a_2 * n_12

   if there are the only use of n_12 and a_2, TER will substitute in their

   expressions in v_9, and end up with:

   v_9 = (b_5 + 6) * (C * 10)

   which will then have the ssa_name assigned to regular variables, and the

   resulting code which will be passed to the expander looks something like:

   v = (b + 6) * (C * 10)

   This requires ensuring that none of the variables used by the expression

   change between the def point and where it is used.  Furthermore, if any

   of the ssa_names used in this expression are themselves replaceable, we

   have to ensure none of that expressions' arguments change either.

   Although SSA_NAMES themselves don't change, this pass is performed after

   coalescing has coalesced different SSA_NAMES together, so there could be a

   definition of an SSA_NAME which is coalesced with a use that causes a

   problem, i.e.,

   PHI b_5 = <b_8(2), b_14(1)>

   <...>

   a_2 = b_5 + 6

   b_8 = c_4 + 4

   v_9 = a_2 * n_12

   <...>

   If b_5, b_8 and b_14 are all coalesced together...

   The expression b_5 + 6 CANNOT replace the use in the statement defining v_9

   because b_8 is in fact killing the value of b_5 since they share a partition

   and will be assigned the same memory or register location.

   TER implements this but stepping through the instructions in a block and

   tracking potential expressions for replacement, and the partitions they are

   dependent on.  Expressions are represented by the SSA_NAME_VERSION of the

   DEF on the LHS of a GIMPLE_ASSIGN and the expression is the RHS.

   When a stmt is determined to be a possible replacement expression, the

   following steps are taken:

   EXPR_DECL_UID bitmap is allocated and set to the base variable UID of the

   def and any uses in the expression.  non-NULL means the expression is being

   tracked.  The UID's themselves are used to prevent TER substitution into

   accumulating sequences, i.e.,

   x = x + y

   x = x + z

   x = x + w

   etc.

   this can result in very large expressions which don't accomplish anything

   see PR tree-optimization/17549.

   PARTITION_DEPENDENCIES is another bitmap array, and it has a bit set for any

   partition which is used in the expression.  This is primarily used to remove

   an expression from the partition kill lists when a decision is made whether

   to replace it or not.  This is indexed by ssa version number as well, and

   indicates a partition number.  virtual operands are not tracked individually,

   but they are summarized by an artificial partition called VIRTUAL_PARTITION.

   This means a MAY or MUST def will kill *ALL* expressions that are dependent

   on a virtual operand.

   Note that the EXPR_DECL_UID and this bitmap represent very similar

   information, but the info in one is not easy to obtain from the other.

   KILL_LIST is yet another bitmap array, this time it is indexed by partition

   number, and represents a list of active expressions which will will no

   longer be valid if a definition into this partition takes place.

   PARTITION_IN_USE is simply a bitmap which is used to track which partitions

   currently have something in their kill list.  This is used at the end of

   a block to clear out the KILL_LIST bitmaps at the end of each block.

   NEW_REPLACEABLE_DEPENDENCIES is used as a temporary place to store

   dependencies which will be reused by the current definition. All the uses

   on an expression are processed before anything else is done. If a use is

   determined to be a replaceable expression AND the current stmt is also going

   to be replaceable, all the dependencies of this replaceable use will be

   picked up by the current stmt's expression. Rather than recreate them, they

   are simply copied here and then copied into the new expression when it is

   processed.

   a_2 = b_5 + 6

   v_8 = a_2 + c_4

   a_2's expression 'b_5 + 6' is determined to be replaceable at the use

   location. It is dependent on the partition 'b_5' is in. This is cached into

   the NEW_REPLACEABLE_DEPENDENCIES bitmap, and when v_8 is examined for

   replaceability, it is a candidate, and it is dependent on the partition

   b_5 is in *NOT* a_2, as well as c_4's partition.

   if v_8 is also replaceable:

   x_9 = v_8 * 5

   x_9 is dependent on partitions b_5, and c_4

   if a statement is found which has either of those partitions written to

   before x_9 is used, then x_9 itself is NOT replaceable.  */

/* Temporary Expression Replacement (TER) table information.  */

typedef struct temp_expr_table_d

{

  var_map map;

  bitmap *partition_dependencies;       /* Partitions expr is dependent on.  */

  bitmap replaceable_expressions;       /* Replacement expression table.  */

  bitmap *expr_decl_uids;               /* Base uids of exprs.  */

  bitmap *kill_list;                    /* Expr's killed by a partition.  */

  int virtual_partition;                /* Pseudo partition for virtual ops.  */

  bitmap partition_in_use;              /* Partitions with kill entries.  */

  bitmap new_replaceable_dependencies;  /* Holding place for pending dep's.  */

  int *num_in_part;                     /* # of ssa_names in a partition.  */

  int *call_cnt;                        /* Call count at definition.  */

} *temp_expr_table_p;

/* Used to indicate a dependency on VDEFs.  */

#define VIRTUAL_PARTITION(table)        (table->virtual_partition)

#ifdef ENABLE_CHECKING

extern void debug_ter (FILE *, temp_expr_table_p);

#endif

/* Create a new TER table for MAP.  */

static temp_expr_table_p

new_temp_expr_table (var_map map)

{

  temp_expr_table_p t;

  unsigned x;

  t = XNEW (struct temp_expr_table_d);

  t->map = map;

  t->partition_dependencies = XCNEWVEC (bitmap, num_ssa_names + 1);

  t->expr_decl_uids = XCNEWVEC (bitmap, num_ssa_names + 1);

  t->kill_list = XCNEWVEC (bitmap, num_var_partitions (map) + 1);

  t->partition_in_use = BITMAP_ALLOC (NULL);

  t->virtual_partition = num_var_partitions (map);

  t->new_replaceable_dependencies = BITMAP_ALLOC (NULL);

  t->replaceable_expressions = NULL;

  t->num_in_part = XCNEWVEC (int, num_var_partitions (map));

  for (x = 1; x < num_ssa_names; x++)

    {

      int p;

      tree name = ssa_name (x);

      if (!name)

        continue;

      p = var_to_partition (map, name);

      if (p != NO_PARTITION)

        t->num_in_part[p]++;

    }

  t->call_cnt = XCNEWVEC (int, num_ssa_names + 1);

  return t;

}

/* Free TER table T.  If there are valid replacements, return the expression

   vector.  */

static bitmap

free_temp_expr_table (temp_expr_table_p t)

{

  bitmap ret = NULL;

#ifdef ENABLE_CHECKING

  unsigned x;

  for (x = 0; x <= num_var_partitions (t->map); x++)

    gcc_assert (!t->kill_list[x]);

  for (x = 0; x < num_ssa_names; x++)

    {

      gcc_assert (t->expr_decl_uids[x] == NULL);

      gcc_assert (t->partition_dependencies[x] == NULL);

    }

#endif

  BITMAP_FREE (t->partition_in_use);

  BITMAP_FREE (t->new_replaceable_dependencies);

  free (t->expr_decl_uids);

  free (t->kill_list);

  free (t->partition_dependencies);

  free (t->num_in_part);

  free (t->call_cnt);

  if (t->replaceable_expressions)

    ret = t->replaceable_expressions;

  free (t);

  return ret;

}

/* Return TRUE if VERSION is to be replaced by an expression in TAB.  */

static inline bool

version_to_be_replaced_p (temp_expr_table_p tab, int version)

{

  if (!tab->replaceable_expressions)

    return false;

  return bitmap_bit_p (tab->replaceable_expressions, version);

}

/* Add partition P to the list if partitions VERSION is dependent on.  TAB is

   the expression table */

static inline void

make_dependent_on_partition (temp_expr_table_p tab, int version, int p)

{

  if (!tab->partition_dependencies[version])

    tab->partition_dependencies[version] = BITMAP_ALLOC (NULL);

  bitmap_set_bit (tab->partition_dependencies[version], p);

}

/* Add VER to the kill list for P.  TAB is the expression table */

static inline void

add_to_partition_kill_list (temp_expr_table_p tab, int p, int ver)

{

  if (!tab->kill_list[p])

    {

      tab->kill_list[p] = BITMAP_ALLOC (NULL);

      bitmap_set_bit (tab->partition_in_use, p);

    }

  bitmap_set_bit (tab->kill_list[p], ver);

}

/* Remove VER from the partition kill list for P.  TAB is the expression

   table.  */

static inline void

remove_from_partition_kill_list (temp_expr_table_p tab, int p, int version)

{

  gcc_checking_assert (tab->kill_list[p]);

  bitmap_clear_bit (tab->kill_list[p], version);

  if (bitmap_empty_p (tab->kill_list[p]))

    {

      bitmap_clear_bit (tab->partition_in_use, p);

      BITMAP_FREE (tab->kill_list[p]);

    }

}

/* Add a dependency between the def of ssa VERSION and VAR.  If VAR is

   replaceable by an expression, add a dependence each of the elements of the

   expression.  These are contained in the new_replaceable list.  TAB is the

   expression table.  */

static void

add_dependence (temp_expr_table_p tab, int version, tree var)

{

  int i;

  bitmap_iterator bi;

  unsigned x;

  i = SSA_NAME_VERSION (var);

  if (version_to_be_replaced_p (tab, i))

    {

      if (!bitmap_empty_p (tab->new_replaceable_dependencies))

        {

          /* Version will now be killed by a write to any partition the

             substituted expression would have been killed by.  */

          EXECUTE_IF_SET_IN_BITMAP (tab->new_replaceable_dependencies, 0, x, bi)

            add_to_partition_kill_list (tab, x, version);

          /* Rather than set partition_dependencies and in_use lists bit by

             bit, simply OR in the new_replaceable_dependencies bits.  */

          if (!tab->partition_dependencies[version])

            tab->partition_dependencies[version] = BITMAP_ALLOC (NULL);

          bitmap_ior_into (tab->partition_dependencies[version],

                           tab->new_replaceable_dependencies);

          bitmap_ior_into (tab->partition_in_use,

                           tab->new_replaceable_dependencies);

          /* It is only necessary to add these once.  */

          bitmap_clear (tab->new_replaceable_dependencies);

        }

    }

  else

    {

      i = var_to_partition (tab->map, var);

      gcc_checking_assert (i != NO_PARTITION);

      gcc_checking_assert (tab->num_in_part[i] != 0);

      /* Only dependencies on ssa_names which are coalesced with something need

         to be tracked.  Partitions with containing only a single SSA_NAME

         *cannot* have their value changed.  */

      if (tab->num_in_part[i] > 1)

        {

          add_to_partition_kill_list (tab, i, version);

          make_dependent_on_partition (tab, version, i);

        }

    }

}

/* Return TRUE if expression STMT is suitable for replacement.

   TER is true if is_replaceable_p is called from within TER, false

   when used from within stmt_is_replaceable_p, i.e. EXPAND_INITIALIZER

   expansion.  The differences are that with !TER some tests are skipped

   to make it more aggressive (doesn't require the same bb, or for -O0

   same locus and same BLOCK), on the other side never considers memory

   loads as replaceable, because those don't ever lead into constant

   expressions.  */

static inline bool

is_replaceable_p (gimple stmt, bool ter)

{

  use_operand_p use_p;

  tree def;

  gimple use_stmt;

  location_t locus1, locus2;

  tree block1, block2;

  /* Only consider modify stmts.  */

  if (!is_gimple_assign (stmt))

    return false;

  /* If the statement may throw an exception, it cannot be replaced.  */

  if (stmt_could_throw_p (stmt))

    return false;

  /* Punt if there is more than 1 def.  */

  def = SINGLE_SSA_TREE_OPERAND (stmt, SSA_OP_DEF);

  if (!def)

    return false;

  /* Only consider definitions which have a single use.  */

  if (!single_imm_use (def, &use_p, &use_stmt))

    return false;

  /* If the use isn't in this block, it wont be replaced either.  */

  if (ter && gimple_bb (use_stmt) != gimple_bb (stmt))

    return false;

  locus1 = gimple_location (stmt);

  block1 = gimple_block (stmt);

  if (gimple_code (use_stmt) == GIMPLE_PHI)

    {

      locus2 = 0;

      block2 = NULL_TREE;

    }

  else

    {

      locus2 = gimple_location (use_stmt);

      block2 = gimple_block (use_stmt);

    }

  if (!optimize

      && ter

      && ((locus1 && locus1 != locus2) || (block1 && block1 != block2)))

    return false;

  /* Used in this block, but at the TOP of the block, not the end.  */

  if (gimple_code (use_stmt) == GIMPLE_PHI)

    return false;

  /* There must be no VDEFs.  */

  if (gimple_vdef (stmt))

    return false;

  /* Without alias info we can't move around loads.  */

  if ((!optimize || !ter)

      && gimple_assign_single_p (stmt)

      && !is_gimple_val (gimple_assign_rhs1 (stmt)))

    return false;

  /* Float expressions must go through memory if float-store is on.  */

  if (flag_float_store

      && FLOAT_TYPE_P (gimple_expr_type (stmt)))

    return false;

  /* An assignment with a register variable on the RHS is not

     replaceable.  */

  if (gimple_assign_rhs_code (stmt) == VAR_DECL

      && DECL_HARD_REGISTER (gimple_assign_rhs1 (stmt)))

    return false;

  /* No function calls can be replaced.  */

  if (is_gimple_call (stmt))

    return false;

  /* Leave any stmt with volatile operands alone as well.  */

  if (gimple_has_volatile_ops (stmt))

    return false;

  return true;

}

/* Variant of is_replaceable_p test for use in EXPAND_INITIALIZER

   expansion.  */

bool

stmt_is_replaceable_p (gimple stmt)

{

  return is_replaceable_p (stmt, false);

}

/* This function will remove the expression for VERSION from replacement

   consideration in table TAB.  If FREE_EXPR is true, then remove the

   expression from consideration as well by freeing the decl uid bitmap.  */

static void

finished_with_expr (temp_expr_table_p tab, int version, bool free_expr)

{

  unsigned i;

  bitmap_iterator bi;

  /* Remove this expression from its dependent lists.  The partition dependence

     list is retained and transfered later to whomever uses this version.  */

  if (tab->partition_dependencies[version])

    {

      EXECUTE_IF_SET_IN_BITMAP (tab->partition_dependencies[version], 0, i, bi)

        remove_from_partition_kill_list (tab, i, version);

      BITMAP_FREE (tab->partition_dependencies[version]);

    }

  if (free_expr)

    BITMAP_FREE (tab->expr_decl_uids[version]);

}

/* Create an expression entry for a replaceable expression.  */

static void

process_replaceable (temp_expr_table_p tab, gimple stmt, int call_cnt)

{

  tree var, def, basevar;

  int version;

  ssa_op_iter iter;

  bitmap def_vars, use_vars;

  gcc_checking_assert (is_replaceable_p (stmt, true));

  def = SINGLE_SSA_TREE_OPERAND (stmt, SSA_OP_DEF);

  version = SSA_NAME_VERSION (def);

  basevar = SSA_NAME_VAR (def);

  def_vars = BITMAP_ALLOC (NULL);

  bitmap_set_bit (def_vars, DECL_UID (basevar));

  /* Add this expression to the dependency list for each use partition.  */

  FOR_EACH_SSA_TREE_OPERAND (var, stmt, iter, SSA_OP_USE)

    {

      int var_version = SSA_NAME_VERSION (var);

      use_vars = tab->expr_decl_uids[var_version];

      add_dependence (tab, version, var);

      if (use_vars)

        {

          bitmap_ior_into (def_vars, use_vars);

          BITMAP_FREE (tab->expr_decl_uids[var_version]);

        }

      else

        bitmap_set_bit (def_vars, DECL_UID (SSA_NAME_VAR (var)));

    }

  tab->expr_decl_uids[version] = def_vars;

  /* If there are VUSES, add a dependence on virtual defs.  */

  if (gimple_vuse (stmt))

    {

      make_dependent_on_partition (tab, version, VIRTUAL_PARTITION (tab));

      add_to_partition_kill_list (tab, VIRTUAL_PARTITION (tab), version);

    }

  tab->call_cnt[version] = call_cnt;

}

/* This function removes any expression in TAB which is dependent on PARTITION

   from consideration, making it not replaceable.  */

static inline void

kill_expr (temp_expr_table_p tab, int partition)

{

  unsigned version;

  /* Mark every active expr dependent on this var as not replaceable.

     finished_with_expr can modify the bitmap, so we can't execute over it.  */

  while (tab->kill_list[partition])

    {

      version = bitmap_first_set_bit (tab->kill_list[partition]);

      finished_with_expr (tab, version, true);

    }

  gcc_checking_assert (!tab->kill_list[partition]);

}

/* This function kills all expressions in TAB which are dependent on virtual

   partitions.  */

static inline void

kill_virtual_exprs (temp_expr_table_p tab)

{

  kill_expr (tab, VIRTUAL_PARTITION (tab));

}

/* Mark the expression associated with VAR as replaceable, and enter

   the defining stmt into the partition_dependencies table TAB.  If

   MORE_REPLACING is true, accumulate the pending partition dependencies.  */

static void

mark_replaceable (temp_expr_table_p tab, tree var, bool more_replacing)

{

  int version = SSA_NAME_VERSION (var);

  /* Move the dependence list to the pending listpending.  */

  if (more_replacing && tab->partition_dependencies[version])

    bitmap_ior_into (tab->new_replaceable_dependencies,

                     tab->partition_dependencies[version]);

  finished_with_expr (tab, version, !more_replacing);

  /* Set the replaceable expression.  */

  if (!tab->replaceable_expressions)

    tab->replaceable_expressions = BITMAP_ALLOC (NULL);

  bitmap_set_bit (tab->replaceable_expressions, version);

}

/* This function processes basic block BB, and looks for variables which can

   be replaced by their expressions.  Results are stored in the table TAB.  */

static void

find_replaceable_in_bb (temp_expr_table_p tab, basic_block bb)

{

  gimple_stmt_iterator bsi;

  gimple stmt;

  tree def, use, fndecl;

  int partition;

  var_map map = tab->map;

  ssa_op_iter iter;

  bool stmt_replaceable;

  int cur_call_cnt = 0;

  for (bsi = gsi_start_bb (bb); !gsi_end_p (bsi); gsi_next (&bsi))

    {

      stmt = gsi_stmt (bsi);

      if (is_gimple_debug (stmt))

        continue;

      stmt_replaceable = is_replaceable_p (stmt, true);

      /* Determine if this stmt finishes an existing expression.  */

      FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)

        {

          unsigned ver = SSA_NAME_VERSION (use);

          /* If this use is a potential replacement variable, process it.  */

          if (tab->expr_decl_uids[ver])

            {

              bool same_root_var = false;

              ssa_op_iter iter2;

              bitmap vars = tab->expr_decl_uids[ver];

              /* See if the root variables are the same.  If they are, we

                 do not want to do the replacement to avoid problems with

                 code size, see PR tree-optimization/17549.  */

              if (!bitmap_empty_p (vars))

                FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter2, SSA_OP_DEF)

                  {

                    if (bitmap_bit_p (vars, DECL_UID (SSA_NAME_VAR (def))))

                      {

                        same_root_var = true;

                        break;

                      }

                  }

              /* If the stmt does a memory store and the replacement

                 is a load aliasing it avoid creating overlapping

                 assignments which we cannot expand correctly.  */

              if (gimple_vdef (stmt)

                  && gimple_assign_single_p (stmt))

                {

                  gimple def_stmt = SSA_NAME_DEF_STMT (use);

                  while (is_gimple_assign (def_stmt)

                         && gimple_assign_rhs_code (def_stmt) == SSA_NAME)

                    def_stmt

                      = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (def_stmt));

                  if (gimple_vuse (def_stmt)

                      && gimple_assign_single_p (def_stmt)

                      && refs_may_alias_p (gimple_assign_lhs (stmt),

                                           gimple_assign_rhs1 (def_stmt)))

                    same_root_var = true;

                }

              /* Mark expression as replaceable unless stmt is volatile, or the

                 def variable has the same root variable as something in the

                 substitution list, or the def and use span a call such that

                 we'll expand lifetimes across a call.  */

              if (gimple_has_volatile_ops (stmt) || same_root_var

                  || (tab->call_cnt[ver] != cur_call_cnt

                      && SINGLE_SSA_USE_OPERAND (SSA_NAME_DEF_STMT (use), SSA_OP_USE)

                         == NULL_USE_OPERAND_P))

                finished_with_expr (tab, ver, true);

              else

                mark_replaceable (tab, use, stmt_replaceable);

            }

        }

      /* Next, see if this stmt kills off an active expression.  */

      FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_DEF)

        {

          partition = var_to_partition (map, def);

          if (partition != NO_PARTITION && tab->kill_list[partition])

            kill_expr (tab, partition);

        }

      /* Increment counter if this is a non BUILT_IN call. We allow

         replacement over BUILT_IN calls since many will expand to inline

         insns instead of a true call.  */

      if (is_gimple_call (stmt)

          && !((fndecl = gimple_call_fndecl (stmt))

               && DECL_BUILT_IN (fndecl)))

        cur_call_cnt++;

      /* Now see if we are creating a new expression or not.  */

      if (stmt_replaceable)

        process_replaceable (tab, stmt, cur_call_cnt);

      /* Free any unused dependency lists.  */

      bitmap_clear (tab->new_replaceable_dependencies);

      /* A V_{MAY,MUST}_DEF kills any expression using a virtual operand,

         including the current stmt.  */

      if (gimple_vdef (stmt))

        kill_virtual_exprs (tab);

    }

}

/* This function is the driver routine for replacement of temporary expressions

   in the SSA->normal phase, operating on MAP.  If there are replaceable

   expressions, a table is returned which maps SSA versions to the

   expressions they should be replaced with.  A NULL_TREE indicates no

   replacement should take place.  If there are no replacements at all,

   NULL is returned by the function, otherwise an expression vector indexed

   by SSA_NAME version numbers.  */

extern bitmap

find_replaceable_exprs (var_map map)

{

  basic_block bb;

  temp_expr_table_p table;

  bitmap ret;

  table = new_temp_expr_table (map);

  FOR_EACH_BB (bb)

    {

      find_replaceable_in_bb (table, bb);

      gcc_checking_assert (bitmap_empty_p (table->partition_in_use));

    }

  ret = free_temp_expr_table (table);

  return ret;

}

/* Dump TER expression table EXPR to file F.  */

void

dump_replaceable_exprs (FILE *f, bitmap expr)

{

  tree var;

  unsigned x;

  fprintf (f, "\nReplacing Expressions\n");

  for (x = 0; x < num_ssa_names; x++)

    if (bitmap_bit_p (expr, x))

      {

        var = ssa_name (x);