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/* Copy propagation and SSA_NAME replacement support routines.

   Copyright (C) 2004, 2005, 2006, 2007, 2008, 2010

   Free Software Foundation, Inc.

This file is part of GCC.

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

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

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

any later version.

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

but WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

GNU General Public License for more details.

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

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

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

#include "config.h"

#include "system.h"

#include "coretypes.h"

#include "tm.h"

#include "tree.h"

#include "flags.h"

#include "rtl.h"

#include "tm_p.h"

#include "ggc.h"

#include "basic-block.h"

#include "output.h"

#include "expr.h"

#include "function.h"

#include "diagnostic.h"

#include "timevar.h"

#include "tree-dump.h"

#include "tree-flow.h"

#include "tree-pass.h"

#include "tree-ssa-propagate.h"

#include "langhooks.h"

#include "cfgloop.h"

/* This file implements the copy propagation pass and provides a

   handful of interfaces for performing const/copy propagation and

   simple expression replacement which keep variable annotations

   up-to-date.

   We require that for any copy operation where the RHS and LHS have

   a non-null memory tag the memory tag be the same.   It is OK

   for one or both of the memory tags to be NULL.

   We also require tracking if a variable is dereferenced in a load or

   store operation.

   We enforce these requirements by having all copy propagation and

   replacements of one SSA_NAME with a different SSA_NAME to use the

   APIs defined in this file.  */

/* Return true if we may propagate ORIG into DEST, false otherwise.  */

bool

may_propagate_copy (tree dest, tree orig)

{

  tree type_d = TREE_TYPE (dest);

  tree type_o = TREE_TYPE (orig);

  /* If ORIG flows in from an abnormal edge, it cannot be propagated.  */

  if (TREE_CODE (orig) == SSA_NAME

      && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (orig))

    return false;

  /* If DEST is an SSA_NAME that flows from an abnormal edge, then it

     cannot be replaced.  */

  if (TREE_CODE (dest) == SSA_NAME

      && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (dest))

    return false;

  /* Do not copy between types for which we *do* need a conversion.  */

  if (!useless_type_conversion_p (type_d, type_o))

    return false;

  /* Propagating virtual operands is always ok.  */

  if (TREE_CODE (dest) == SSA_NAME && !is_gimple_reg (dest))

    {

      /* But only between virtual operands.  */

      gcc_assert (TREE_CODE (orig) == SSA_NAME && !is_gimple_reg (orig));

      return true;

    }

  /* Anything else is OK.  */

  return true;

}

/* Like may_propagate_copy, but use as the destination expression

   the principal expression (typically, the RHS) contained in

   statement DEST.  This is more efficient when working with the

   gimple tuples representation.  */

bool

may_propagate_copy_into_stmt (gimple dest, tree orig)

{

  tree type_d;

  tree type_o;

  /* If the statement is a switch or a single-rhs assignment,

     then the expression to be replaced by the propagation may

     be an SSA_NAME.  Fortunately, there is an explicit tree

     for the expression, so we delegate to may_propagate_copy.  */

  if (gimple_assign_single_p (dest))

    return may_propagate_copy (gimple_assign_rhs1 (dest), orig);

  else if (gimple_code (dest) == GIMPLE_SWITCH)

    return may_propagate_copy (gimple_switch_index (dest), orig);

  /* In other cases, the expression is not materialized, so there

     is no destination to pass to may_propagate_copy.  On the other

     hand, the expression cannot be an SSA_NAME, so the analysis

     is much simpler.  */

  if (TREE_CODE (orig) == SSA_NAME

      && SSA_NAME_OCCURS_IN_ABNORMAL_PHI (orig))

    return false;

  if (is_gimple_assign (dest))

    type_d = TREE_TYPE (gimple_assign_lhs (dest));

  else if (gimple_code (dest) == GIMPLE_COND)

    type_d = boolean_type_node;

  else if (is_gimple_call (dest)

           && gimple_call_lhs (dest) != NULL_TREE)

    type_d = TREE_TYPE (gimple_call_lhs (dest));

  else

    gcc_unreachable ();

  type_o = TREE_TYPE (orig);

  if (!useless_type_conversion_p (type_d, type_o))

    return false;

  return true;

}

/* Similarly, but we know that we're propagating into an ASM_EXPR.  */

bool

may_propagate_copy_into_asm (tree dest)

{

  /* Hard register operands of asms are special.  Do not bypass.  */

  return !(TREE_CODE (dest) == SSA_NAME

           && TREE_CODE (SSA_NAME_VAR (dest)) == VAR_DECL

           && DECL_HARD_REGISTER (SSA_NAME_VAR (dest)));

}

/* Common code for propagate_value and replace_exp.

   Replace use operand OP_P with VAL.  FOR_PROPAGATION indicates if the

   replacement is done to propagate a value or not.  */

static void

replace_exp_1 (use_operand_p op_p, tree val,

               bool for_propagation ATTRIBUTE_UNUSED)

{

#if defined ENABLE_CHECKING

  tree op = USE_FROM_PTR (op_p);

  gcc_assert (!(for_propagation

                && TREE_CODE (op) == SSA_NAME

                && TREE_CODE (val) == SSA_NAME

                && !may_propagate_copy (op, val)));

#endif

  if (TREE_CODE (val) == SSA_NAME)

    SET_USE (op_p, val);

  else

    SET_USE (op_p, unsave_expr_now (val));

}

/* Propagate the value VAL (assumed to be a constant or another SSA_NAME)

   into the operand pointed to by OP_P.

   Use this version for const/copy propagation as it will perform additional

   checks to ensure validity of the const/copy propagation.  */

void

propagate_value (use_operand_p op_p, tree val)

{

  replace_exp_1 (op_p, val, true);

}

/* Replace *OP_P with value VAL (assumed to be a constant or another SSA_NAME).

   Use this version when not const/copy propagating values.  For example,

   PRE uses this version when building expressions as they would appear

   in specific blocks taking into account actions of PHI nodes.  */

void

replace_exp (use_operand_p op_p, tree val)

{

  replace_exp_1 (op_p, val, false);

}

/* Propagate the value VAL (assumed to be a constant or another SSA_NAME)

   into the tree pointed to by OP_P.

   Use this version for const/copy propagation when SSA operands are not

   available.  It will perform the additional checks to ensure validity of

   the const/copy propagation, but will not update any operand information.

   Be sure to mark the stmt as modified.  */

void

propagate_tree_value (tree *op_p, tree val)

{

#if defined ENABLE_CHECKING

  gcc_assert (!(TREE_CODE (val) == SSA_NAME

                && *op_p

                && TREE_CODE (*op_p) == SSA_NAME

                && !may_propagate_copy (*op_p, val)));

#endif

  if (TREE_CODE (val) == SSA_NAME)

    *op_p = val;

  else

    *op_p = unsave_expr_now (val);

}

/* Like propagate_tree_value, but use as the operand to replace

   the principal expression (typically, the RHS) contained in the

   statement referenced by iterator GSI.  Note that it is not

   always possible to update the statement in-place, so a new

   statement may be created to replace the original.  */

void

propagate_tree_value_into_stmt (gimple_stmt_iterator *gsi, tree val)

{

  gimple stmt = gsi_stmt (*gsi);

  if (is_gimple_assign (stmt))

    {

      tree expr = NULL_TREE;

      if (gimple_assign_single_p (stmt))

        expr = gimple_assign_rhs1 (stmt);

      propagate_tree_value (&expr, val);

      gimple_assign_set_rhs_from_tree (gsi, expr);

      stmt = gsi_stmt (*gsi);

    }

  else if (gimple_code (stmt) == GIMPLE_COND)

    {

      tree lhs = NULL_TREE;

      tree rhs = fold_convert (TREE_TYPE (val), integer_zero_node);

      propagate_tree_value (&lhs, val);

      gimple_cond_set_code (stmt, NE_EXPR);

      gimple_cond_set_lhs (stmt, lhs);

      gimple_cond_set_rhs (stmt, rhs);

    }

  else if (is_gimple_call (stmt)

           && gimple_call_lhs (stmt) != NULL_TREE)

    {

      gimple new_stmt;

      tree expr = NULL_TREE;

      propagate_tree_value (&expr, val);

      new_stmt = gimple_build_assign (gimple_call_lhs (stmt), expr);

      move_ssa_defining_stmt_for_defs (new_stmt, stmt);

      gsi_replace (gsi, new_stmt, false);

    }

  else if (gimple_code (stmt) == GIMPLE_SWITCH)

    propagate_tree_value (gimple_switch_index_ptr (stmt), val);

  else

    gcc_unreachable ();

}

/*---------------------------------------------------------------------------

                                Copy propagation

---------------------------------------------------------------------------*/

/* During propagation, we keep chains of variables that are copies of

   one another.  If variable X_i is a copy of X_j and X_j is a copy of

   X_k, COPY_OF will contain:

        COPY_OF[i].VALUE = X_j

        COPY_OF[j].VALUE = X_k

        COPY_OF[k].VALUE = X_k

   After propagation, the copy-of value for each variable X_i is

   converted into the final value by walking the copy-of chains and

   updating COPY_OF[i].VALUE to be the last element of the chain.  */

static prop_value_t *copy_of;

/* Used in set_copy_of_val to determine if the last link of a copy-of

   chain has changed.  */

static tree *cached_last_copy_of;

/* Return true if this statement may generate a useful copy.  */

static bool

stmt_may_generate_copy (gimple stmt)

{

  if (gimple_code (stmt) == GIMPLE_PHI)

    return !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (gimple_phi_result (stmt));

  if (gimple_code (stmt) != GIMPLE_ASSIGN)

    return false;

  /* If the statement has volatile operands, it won't generate a

     useful copy.  */

  if (gimple_has_volatile_ops (stmt))

    return false;

  /* Statements with loads and/or stores will never generate a useful copy.  */

  if (gimple_vuse (stmt))

    return false;

  /* Otherwise, the only statements that generate useful copies are

     assignments whose RHS is just an SSA name that doesn't flow

     through abnormal edges.  */

  return (gimple_assign_rhs_code (stmt) == SSA_NAME

          && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (gimple_assign_rhs1 (stmt)));

}

/* Return the copy-of value for VAR.  */

static inline prop_value_t *

get_copy_of_val (tree var)

{

  prop_value_t *val = &copy_of[SSA_NAME_VERSION (var)];

  if (val->value == NULL_TREE

      && !stmt_may_generate_copy (SSA_NAME_DEF_STMT (var)))

    {

      /* If the variable will never generate a useful copy relation,

         make it its own copy.  */

      val->value = var;

    }

  return val;

}

/* Return last link in the copy-of chain for VAR.  */

static tree

get_last_copy_of (tree var)

{

  tree last;

  int i;

  /* Traverse COPY_OF starting at VAR until we get to the last

     link in the chain.  Since it is possible to have cycles in PHI

     nodes, the copy-of chain may also contain cycles.

     To avoid infinite loops and to avoid traversing lengthy copy-of

     chains, we artificially limit the maximum number of chains we are

     willing to traverse.

     The value 5 was taken from a compiler and runtime library

     bootstrap and a mixture of C and C++ code from various sources.

     More than 82% of all copy-of chains were shorter than 5 links.  */

#define LIMIT   5

  last = var;

  for (i = 0; i < LIMIT; i++)

    {

      tree copy = copy_of[SSA_NAME_VERSION (last)].value;

      if (copy == NULL_TREE || copy == last)

        break;

      last = copy;

    }

  /* If we have reached the limit, then we are either in a copy-of

     cycle or the copy-of chain is too long.  In this case, just

     return VAR so that it is not considered a copy of anything.  */

  return (i < LIMIT ? last : var);

}

/* Set FIRST to be the first variable in the copy-of chain for DEST.

   If DEST's copy-of value or its copy-of chain has changed, return

   true.

   MEM_REF is the memory reference where FIRST is stored.  This is

   used when DEST is a non-register and we are copy propagating loads

   and stores.  */

static inline bool

set_copy_of_val (tree dest, tree first)

{

  unsigned int dest_ver = SSA_NAME_VERSION (dest);

  tree old_first, old_last, new_last;

  /* Set FIRST to be the first link in COPY_OF[DEST].  If that

     changed, return true.  */

  old_first = copy_of[dest_ver].value;

  copy_of[dest_ver].value = first;

  if (old_first != first)

    return true;

  /* If FIRST and OLD_FIRST are the same, we need to check whether the

     copy-of chain starting at FIRST ends in a different variable.  If

     the copy-of chain starting at FIRST ends up in a different

     variable than the last cached value we had for DEST, then return

     true because DEST is now a copy of a different variable.

     This test is necessary because even though the first link in the

     copy-of chain may not have changed, if any of the variables in

     the copy-of chain changed its final value, DEST will now be the

     copy of a different variable, so we have to do another round of

     propagation for everything that depends on DEST.  */

  old_last = cached_last_copy_of[dest_ver];

  new_last = get_last_copy_of (dest);

  cached_last_copy_of[dest_ver] = new_last;

  return (old_last != new_last);

}

/* Dump the copy-of value for variable VAR to FILE.  */

static void

dump_copy_of (FILE *file, tree var)

{

  tree val;

  sbitmap visited;

  print_generic_expr (file, var, dump_flags);

  if (TREE_CODE (var) != SSA_NAME)

    return;

  visited = sbitmap_alloc (num_ssa_names);

  sbitmap_zero (visited);

  SET_BIT (visited, SSA_NAME_VERSION (var));

  fprintf (file, " copy-of chain: ");

  val = var;

  print_generic_expr (file, val, 0);

  fprintf (file, " ");

  while (copy_of[SSA_NAME_VERSION (val)].value)

    {

      fprintf (file, "-> ");

      val = copy_of[SSA_NAME_VERSION (val)].value;

      print_generic_expr (file, val, 0);

      fprintf (file, " ");

      if (TEST_BIT (visited, SSA_NAME_VERSION (val)))

        break;

      SET_BIT (visited, SSA_NAME_VERSION (val));

    }

  val = get_copy_of_val (var)->value;

  if (val == NULL_TREE)

    fprintf (file, "[UNDEFINED]");

  else if (val != var)

    fprintf (file, "[COPY]");

  else

    fprintf (file, "[NOT A COPY]");

  sbitmap_free (visited);

}

/* Evaluate the RHS of STMT.  If it produces a valid copy, set the LHS

   value and store the LHS into *RESULT_P.  If STMT generates more

   than one name (i.e., STMT is an aliased store), it is enough to

   store the first name in the VDEF list into *RESULT_P.  After

   all, the names generated will be VUSEd in the same statements.  */

static enum ssa_prop_result

copy_prop_visit_assignment (gimple stmt, tree *result_p)

{

  tree lhs, rhs;

  prop_value_t *rhs_val;

  lhs = gimple_assign_lhs (stmt);

  rhs = gimple_assign_rhs1 (stmt);

  gcc_assert (gimple_assign_rhs_code (stmt) == SSA_NAME);

  rhs_val = get_copy_of_val (rhs);

  if (TREE_CODE (lhs) == SSA_NAME)

    {

      /* Straight copy between two SSA names.  First, make sure that

         we can propagate the RHS into uses of LHS.  */

      if (!may_propagate_copy (lhs, rhs))

        return SSA_PROP_VARYING;

      /* Notice that in the case of assignments, we make the LHS be a

         copy of RHS's value, not of RHS itself.  This avoids keeping

         unnecessary copy-of chains (assignments cannot be in a cycle

         like PHI nodes), speeding up the propagation process.

         This is different from what we do in copy_prop_visit_phi_node.

         In those cases, we are interested in the copy-of chains.  */

      *result_p = lhs;

      if (set_copy_of_val (*result_p, rhs_val->value))

        return SSA_PROP_INTERESTING;

      else

        return SSA_PROP_NOT_INTERESTING;

    }

  return SSA_PROP_VARYING;

}

/* Visit the GIMPLE_COND STMT.  Return SSA_PROP_INTERESTING

   if it can determine which edge will be taken.  Otherwise, return

   SSA_PROP_VARYING.  */

static enum ssa_prop_result

copy_prop_visit_cond_stmt (gimple stmt, edge *taken_edge_p)

{

  enum ssa_prop_result retval = SSA_PROP_VARYING;

  location_t loc = gimple_location (stmt);

  tree op0 = gimple_cond_lhs (stmt);

  tree op1 = gimple_cond_rhs (stmt);

  /* The only conditionals that we may be able to compute statically

     are predicates involving two SSA_NAMEs.  */

  if (TREE_CODE (op0) == SSA_NAME && TREE_CODE (op1) == SSA_NAME)

    {

      op0 = get_last_copy_of (op0);

      op1 = get_last_copy_of (op1);

      /* See if we can determine the predicate's value.  */

      if (dump_file && (dump_flags & TDF_DETAILS))

        {

          fprintf (dump_file, "Trying to determine truth value of ");

          fprintf (dump_file, "predicate ");

          print_gimple_stmt (dump_file, stmt, 0, 0);

        }

      /* We can fold COND and get a useful result only when we have

         the same SSA_NAME on both sides of a comparison operator.  */

      if (op0 == op1)

        {

          tree folded_cond = fold_binary_loc (loc, gimple_cond_code (stmt),

                                          boolean_type_node, op0, op1);

          if (folded_cond)

            {

              basic_block bb = gimple_bb (stmt);

              *taken_edge_p = find_taken_edge (bb, folded_cond);

              if (*taken_edge_p)

                retval = SSA_PROP_INTERESTING;

            }

        }

    }

  if (dump_file && (dump_flags & TDF_DETAILS) && *taken_edge_p)

    fprintf (dump_file, "\nConditional will always take edge %d->%d\n",

             (*taken_edge_p)->src->index, (*taken_edge_p)->dest->index);

  return retval;

}

/* Evaluate statement STMT.  If the statement produces a new output

   value, return SSA_PROP_INTERESTING and store the SSA_NAME holding

   the new value in *RESULT_P.

   If STMT is a conditional branch and we can determine its truth

   value, set *TAKEN_EDGE_P accordingly.

   If the new value produced by STMT is varying, return

   SSA_PROP_VARYING.  */

static enum ssa_prop_result

copy_prop_visit_stmt (gimple stmt, edge *taken_edge_p, tree *result_p)

{

  enum ssa_prop_result retval;

  if (dump_file && (dump_flags & TDF_DETAILS))

    {

      fprintf (dump_file, "\nVisiting statement:\n");

      print_gimple_stmt (dump_file, stmt, 0, dump_flags);

      fprintf (dump_file, "\n");

    }

  if (gimple_assign_single_p (stmt)

      && TREE_CODE (gimple_assign_lhs (stmt)) == SSA_NAME

      && TREE_CODE (gimple_assign_rhs1 (stmt)) == SSA_NAME)

    {

      /* If the statement is a copy assignment, evaluate its RHS to

         see if the lattice value of its output has changed.  */

      retval = copy_prop_visit_assignment (stmt, result_p);

    }

  else if (gimple_code (stmt) == GIMPLE_COND)

    {

      /* See if we can determine which edge goes out of a conditional

         jump.  */

      retval = copy_prop_visit_cond_stmt (stmt, taken_edge_p);

    }

  else

    retval = SSA_PROP_VARYING;

  if (retval == SSA_PROP_VARYING)

    {

      tree def;

      ssa_op_iter i;

      /* Any other kind of statement is not interesting for constant

         propagation and, therefore, not worth simulating.  */

      if (dump_file && (dump_flags & TDF_DETAILS))

        fprintf (dump_file, "No interesting values produced.\n");

      /* The assignment is not a copy operation.  Don't visit this

         statement again and mark all the definitions in the statement

         to be copies of nothing.  */

      FOR_EACH_SSA_TREE_OPERAND (def, stmt, i, SSA_OP_ALL_DEFS)

        set_copy_of_val (def, def);

    }

  return retval;

}

/* Visit PHI node PHI.  If all the arguments produce the same value,

   set it to be the value of the LHS of PHI.  */

static enum ssa_prop_result

copy_prop_visit_phi_node (gimple phi)

{

  enum ssa_prop_result retval;

  unsigned i;

  prop_value_t phi_val = { 0, NULL_TREE };

  tree lhs = gimple_phi_result (phi);

  if (dump_file && (dump_flags & TDF_DETAILS))

    {

      fprintf (dump_file, "\nVisiting PHI node: ");

      print_gimple_stmt (dump_file, phi, 0, dump_flags);

      fprintf (dump_file, "\n\n");

    }

  for (i = 0; i < gimple_phi_num_args (phi); i++)

    {

      prop_value_t *arg_val;

      tree arg = gimple_phi_arg_def (phi, i);

      edge e = gimple_phi_arg_edge (phi, i);

      /* We don't care about values flowing through non-executable

         edges.  */

      if (!(e->flags & EDGE_EXECUTABLE))

        continue;

      /* Constants in the argument list never generate a useful copy.

         Similarly, names that flow through abnormal edges cannot be

         used to derive copies.  */

      if (TREE_CODE (arg) != SSA_NAME || SSA_NAME_OCCURS_IN_ABNORMAL_PHI (arg))

        {

          phi_val.value = lhs;

          break;

        }

      /* Avoid copy propagation from an inner into an outer loop.

         Otherwise, this may move loop variant variables outside of

         their loops and prevent coalescing opportunities.  If the

         value was loop invariant, it will be hoisted by LICM and

         exposed for copy propagation.  Not a problem for virtual

         operands though.  */

      if (is_gimple_reg (lhs)

          && loop_depth_of_name (arg) > loop_depth_of_name (lhs))

        {

          phi_val.value = lhs;

          break;

        }

      /* If the LHS appears in the argument list, ignore it.  It is

         irrelevant as a copy.  */

      if (arg == lhs || get_last_copy_of (arg) == lhs)

        continue;

      if (dump_file && (dump_flags & TDF_DETAILS))

        {

          fprintf (dump_file, "\tArgument #%d: ", i);

          dump_copy_of (dump_file, arg);

          fprintf (dump_file, "\n");

        }

      arg_val = get_copy_of_val (arg);

      /* If the LHS didn't have a value yet, make it a copy of the

         first argument we find.  Notice that while we make the LHS be

         a copy of the argument itself, we take the memory reference

         from the argument's value so that we can compare it to the

         memory reference of all the other arguments.  */

      if (phi_val.value == NULL_TREE)

        {

          phi_val.value = arg_val->value ? arg_val->value : arg;

          continue;

        }

      /* If PHI_VAL and ARG don't have a common copy-of chain, then

         this PHI node cannot be a copy operation.  Also, if we are

         copy propagating stores and these two arguments came from

         different memory references, they cannot be considered

         copies.  */

      if (get_last_copy_of (phi_val.value) != get_last_copy_of (arg))

        {

          phi_val.value = lhs;

          break;

        }

    }

  if (phi_val.value &&  may_propagate_copy (lhs, phi_val.value)

      && set_copy_of_val (lhs, phi_val.value))

    retval = (phi_val.value != lhs) ? SSA_PROP_INTERESTING : SSA_PROP_VARYING;

  else

    retval = SSA_PROP_NOT_INTERESTING;

  if (dump_file && (dump_flags & TDF_DETAILS))

    {

      fprintf (dump_file, "\nPHI node ");

      dump_copy_of (dump_file, lhs);

      fprintf (dump_file, "\nTelling the propagator to ");

      if (retval == SSA_PROP_INTERESTING)

        fprintf (dump_file, "add SSA edges out of this PHI and continue.");

      else if (retval == SSA_PROP_VARYING)

        fprintf (dump_file, "add SSA edges out of this PHI and never visit again.");

      else

        fprintf (dump_file, "do nothing with SSA edges and keep iterating.");

      fprintf (dump_file, "\n\n");

    }

  return retval;

}