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/* Forward propagation of expressions for single use variables.

   Copyright (C) 2004, 2005, 2007, 2008, 2009 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 "ggc.h"

#include "tree.h"

#include "rtl.h"

#include "tm_p.h"

#include "basic-block.h"

#include "timevar.h"

#include "diagnostic.h"

#include "tree-flow.h"

#include "tree-pass.h"

#include "tree-dump.h"

#include "langhooks.h"

#include "flags.h"

#include "gimple.h"

/* This pass propagates the RHS of assignment statements into use

   sites of the LHS of the assignment.  It's basically a specialized

   form of tree combination.   It is hoped all of this can disappear

   when we have a generalized tree combiner.

   One class of common cases we handle is forward propagating a single use

   variable into a COND_EXPR.

     bb0:

       x = a COND b;

       if (x) goto ... else goto ...

   Will be transformed into:

     bb0:

       if (a COND b) goto ... else goto ...

   Similarly for the tests (x == 0), (x != 0), (x == 1) and (x != 1).

   Or (assuming c1 and c2 are constants):

     bb0:

       x = a + c1;

       if (x EQ/NEQ c2) goto ... else goto ...

   Will be transformed into:

     bb0:

        if (a EQ/NEQ (c2 - c1)) goto ... else goto ...

   Similarly for x = a - c1.

   Or

     bb0:

       x = !a

       if (x) goto ... else goto ...

   Will be transformed into:

     bb0:

        if (a == 0) goto ... else goto ...

   Similarly for the tests (x == 0), (x != 0), (x == 1) and (x != 1).

   For these cases, we propagate A into all, possibly more than one,

   COND_EXPRs that use X.

   Or

     bb0:

       x = (typecast) a

       if (x) goto ... else goto ...

   Will be transformed into:

     bb0:

        if (a != 0) goto ... else goto ...

   (Assuming a is an integral type and x is a boolean or x is an

    integral and a is a boolean.)

   Similarly for the tests (x == 0), (x != 0), (x == 1) and (x != 1).

   For these cases, we propagate A into all, possibly more than one,

   COND_EXPRs that use X.

   In addition to eliminating the variable and the statement which assigns

   a value to the variable, we may be able to later thread the jump without

   adding insane complexity in the dominator optimizer.

   Also note these transformations can cascade.  We handle this by having

   a worklist of COND_EXPR statements to examine.  As we make a change to

   a statement, we put it back on the worklist to examine on the next

   iteration of the main loop.

   A second class of propagation opportunities arises for ADDR_EXPR

   nodes.

     ptr = &x->y->z;

     res = *ptr;

   Will get turned into

     res = x->y->z;

   Or

     ptr = (type1*)&type2var;

     res = *ptr

   Will get turned into (if type1 and type2 are the same size

   and neither have volatile on them):

     res = VIEW_CONVERT_EXPR<type1>(type2var)

   Or

     ptr = &x[0];

     ptr2 = ptr + <constant>;

   Will get turned into

     ptr2 = &x[constant/elementsize];

  Or

     ptr = &x[0];

     offset = index * element_size;

     offset_p = (pointer) offset;

     ptr2 = ptr + offset_p

  Will get turned into:

     ptr2 = &x[index];

  Or

    ssa = (int) decl

    res = ssa & 1

  Provided that decl has known alignment >= 2, will get turned into

    res = 0

  We also propagate casts into SWITCH_EXPR and COND_EXPR conditions to

  allow us to remove the cast and {NOT_EXPR,NEG_EXPR} into a subsequent

  {NOT_EXPR,NEG_EXPR}.

   This will (of course) be extended as other needs arise.  */

static bool forward_propagate_addr_expr (tree name, tree rhs);

/* Set to true if we delete EH edges during the optimization.  */

static bool cfg_changed;

static tree rhs_to_tree (tree type, gimple stmt);

/* Get the next statement we can propagate NAME's value into skipping

   trivial copies.  Returns the statement that is suitable as a

   propagation destination or NULL_TREE if there is no such one.

   This only returns destinations in a single-use chain.  FINAL_NAME_P

   if non-NULL is written to the ssa name that represents the use.  */

static gimple

get_prop_dest_stmt (tree name, tree *final_name_p)

{

  use_operand_p use;

  gimple use_stmt;

  do {

    /* If name has multiple uses, bail out.  */

    if (!single_imm_use (name, &use, &use_stmt))

      return NULL;

    /* If this is not a trivial copy, we found it.  */

    if (!gimple_assign_ssa_name_copy_p (use_stmt)

        || gimple_assign_rhs1 (use_stmt) != name)

      break;

    /* Continue searching uses of the copy destination.  */

    name = gimple_assign_lhs (use_stmt);

  } while (1);

  if (final_name_p)

    *final_name_p = name;

  return use_stmt;

}

/* Get the statement we can propagate from into NAME skipping

   trivial copies.  Returns the statement which defines the

   propagation source or NULL_TREE if there is no such one.

   If SINGLE_USE_ONLY is set considers only sources which have

   a single use chain up to NAME.  If SINGLE_USE_P is non-null,

   it is set to whether the chain to NAME is a single use chain

   or not.  SINGLE_USE_P is not written to if SINGLE_USE_ONLY is set.  */

static gimple

get_prop_source_stmt (tree name, bool single_use_only, bool *single_use_p)

{

  bool single_use = true;

  do {

    gimple def_stmt = SSA_NAME_DEF_STMT (name);

    if (!has_single_use (name))

      {

        single_use = false;

        if (single_use_only)

          return NULL;

      }

    /* If name is defined by a PHI node or is the default def, bail out.  */

    if (!is_gimple_assign (def_stmt))

      return NULL;

    /* If def_stmt is not a simple copy, we possibly found it.  */

    if (!gimple_assign_ssa_name_copy_p (def_stmt))

      {

        tree rhs;

        if (!single_use_only && single_use_p)

          *single_use_p = single_use;

        /* We can look through pointer conversions in the search

           for a useful stmt for the comparison folding.  */

        rhs = gimple_assign_rhs1 (def_stmt);

        if (CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (def_stmt))

            && TREE_CODE (rhs) == SSA_NAME

            && POINTER_TYPE_P (TREE_TYPE (gimple_assign_lhs (def_stmt)))

            && POINTER_TYPE_P (TREE_TYPE (rhs)))

          name = rhs;

        else

          return def_stmt;

      }

    else

      {

        /* Continue searching the def of the copy source name.  */

        name = gimple_assign_rhs1 (def_stmt);

      }

  } while (1);

}

/* Checks if the destination ssa name in DEF_STMT can be used as

   propagation source.  Returns true if so, otherwise false.  */

static bool

can_propagate_from (gimple def_stmt)

{

  use_operand_p use_p;

  ssa_op_iter iter;

  gcc_assert (is_gimple_assign (def_stmt));

  /* If the rhs has side-effects we cannot propagate from it.  */

  if (gimple_has_volatile_ops (def_stmt))

    return false;

  /* If the rhs is a load we cannot propagate from it.  */

  if (TREE_CODE_CLASS (gimple_assign_rhs_code (def_stmt)) == tcc_reference

      || TREE_CODE_CLASS (gimple_assign_rhs_code (def_stmt)) == tcc_declaration)

    return false;

  /* Constants can be always propagated.  */

  if (gimple_assign_single_p (def_stmt)

      && is_gimple_min_invariant (gimple_assign_rhs1 (def_stmt)))

    return true;

  /* We cannot propagate ssa names that occur in abnormal phi nodes.  */

  FOR_EACH_SSA_USE_OPERAND (use_p, def_stmt, iter, SSA_OP_USE)

    if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (USE_FROM_PTR (use_p)))

      return false;

  /* If the definition is a conversion of a pointer to a function type,

     then we can not apply optimizations as some targets require

     function pointers to be canonicalized and in this case this

     optimization could eliminate a necessary canonicalization.  */

  if (CONVERT_EXPR_CODE_P (gimple_assign_rhs_code (def_stmt)))

    {

      tree rhs = gimple_assign_rhs1 (def_stmt);

      if (POINTER_TYPE_P (TREE_TYPE (rhs))

          && TREE_CODE (TREE_TYPE (TREE_TYPE (rhs))) == FUNCTION_TYPE)

        return false;

    }

  return true;

}

/* Remove a copy chain ending in NAME along the defs but not

   further or including UP_TO_STMT.  If NAME was replaced in

   its only use then this function can be used to clean up

   dead stmts.  Returns true if UP_TO_STMT can be removed

   as well, otherwise false.  */

static bool

remove_prop_source_from_use (tree name, gimple up_to_stmt)

{

  gimple_stmt_iterator gsi;

  gimple stmt;

  do {

    if (!has_zero_uses (name))

      return false;

    stmt = SSA_NAME_DEF_STMT (name);

    if (stmt == up_to_stmt)

      return true;

    gsi = gsi_for_stmt (stmt);

    release_defs (stmt);

    gsi_remove (&gsi, true);

    name = (gimple_assign_copy_p (stmt)) ? gimple_assign_rhs1 (stmt) : NULL;

  } while (name && TREE_CODE (name) == SSA_NAME);

  return false;

}

/* Return the rhs of a gimple_assign STMT in a form of a single tree,

   converted to type TYPE.

   This should disappear, but is needed so we can combine expressions and use

   the fold() interfaces. Long term, we need to develop folding and combine

   routines that deal with gimple exclusively . */

static tree

rhs_to_tree (tree type, gimple stmt)

{

  location_t loc = gimple_location (stmt);

  enum tree_code code = gimple_assign_rhs_code (stmt);

  if (get_gimple_rhs_class (code) == GIMPLE_BINARY_RHS)

    return fold_build2_loc (loc, code, type, gimple_assign_rhs1 (stmt),

                        gimple_assign_rhs2 (stmt));

  else if (get_gimple_rhs_class (code) == GIMPLE_UNARY_RHS)

    return build1 (code, type, gimple_assign_rhs1 (stmt));

  else if (get_gimple_rhs_class (code) == GIMPLE_SINGLE_RHS)

    return gimple_assign_rhs1 (stmt);

  else

    gcc_unreachable ();

}

/* Combine OP0 CODE OP1 in the context of a COND_EXPR.  Returns

   the folded result in a form suitable for COND_EXPR_COND or

   NULL_TREE, if there is no suitable simplified form.  If

   INVARIANT_ONLY is true only gimple_min_invariant results are

   considered simplified.  */

static tree

combine_cond_expr_cond (location_t loc, enum tree_code code, tree type,

                        tree op0, tree op1, bool invariant_only)

{

  tree t;

  gcc_assert (TREE_CODE_CLASS (code) == tcc_comparison);

  t = fold_binary_loc (loc, code, type, op0, op1);

  if (!t)

    return NULL_TREE;

  /* Require that we got a boolean type out if we put one in.  */

  gcc_assert (TREE_CODE (TREE_TYPE (t)) == TREE_CODE (type));

  /* Canonicalize the combined condition for use in a COND_EXPR.  */

  t = canonicalize_cond_expr_cond (t);

  /* Bail out if we required an invariant but didn't get one.  */

  if (!t || (invariant_only && !is_gimple_min_invariant (t)))

    return NULL_TREE;

  return t;

}

/* Propagate from the ssa name definition statements of COND_EXPR

   in GIMPLE_COND statement STMT into the conditional if that simplifies it.

   Returns zero if no statement was changed, one if there were

   changes and two if cfg_cleanup needs to run.

   This must be kept in sync with forward_propagate_into_cond.  */

static int

forward_propagate_into_gimple_cond (gimple stmt)

{

  int did_something = 0;

  location_t loc = gimple_location (stmt);

  do {

    tree tmp = NULL_TREE;

    tree name, rhs0 = NULL_TREE, rhs1 = NULL_TREE;

    gimple def_stmt;

    bool single_use0_p = false, single_use1_p = false;

    enum tree_code code = gimple_cond_code (stmt);

    /* We can do tree combining on SSA_NAME and comparison expressions.  */

    if (TREE_CODE_CLASS (gimple_cond_code (stmt)) == tcc_comparison

        && TREE_CODE (gimple_cond_lhs (stmt)) == SSA_NAME)

      {

        /* For comparisons use the first operand, that is likely to

           simplify comparisons against constants.  */

        name = gimple_cond_lhs (stmt);

        def_stmt = get_prop_source_stmt (name, false, &single_use0_p);

        if (def_stmt && can_propagate_from (def_stmt))

          {

            tree op1 = gimple_cond_rhs (stmt);

            rhs0 = rhs_to_tree (TREE_TYPE (op1), def_stmt);

            tmp = combine_cond_expr_cond (loc, code, boolean_type_node, rhs0,

                                          op1, !single_use0_p);

          }

        /* If that wasn't successful, try the second operand.  */

        if (tmp == NULL_TREE

            && TREE_CODE (gimple_cond_rhs (stmt)) == SSA_NAME)

          {

            tree op0 = gimple_cond_lhs (stmt);

            name = gimple_cond_rhs (stmt);

            def_stmt = get_prop_source_stmt (name, false, &single_use1_p);

            if (!def_stmt || !can_propagate_from (def_stmt))

              return did_something;

            rhs1 = rhs_to_tree (TREE_TYPE (op0), def_stmt);

            tmp = combine_cond_expr_cond (loc, code, boolean_type_node, op0,

                                          rhs1, !single_use1_p);

          }

        /* If that wasn't successful either, try both operands.  */

        if (tmp == NULL_TREE

            && rhs0 != NULL_TREE

            && rhs1 != NULL_TREE)

          tmp = combine_cond_expr_cond (loc, code, boolean_type_node, rhs0,

                                        fold_convert_loc (loc,

                                                          TREE_TYPE (rhs0),

                                                          rhs1),

                                        !(single_use0_p && single_use1_p));

      }

    if (tmp)

      {

        if (dump_file && tmp)

          {

            tree cond = build2 (gimple_cond_code (stmt),

                                boolean_type_node,

                                gimple_cond_lhs (stmt),

                                gimple_cond_rhs (stmt));

            fprintf (dump_file, "  Replaced '");

            print_generic_expr (dump_file, cond, 0);

            fprintf (dump_file, "' with '");

            print_generic_expr (dump_file, tmp, 0);

            fprintf (dump_file, "'\n");

          }

        gimple_cond_set_condition_from_tree (stmt, unshare_expr (tmp));

        update_stmt (stmt);

        /* Remove defining statements.  */

        remove_prop_source_from_use (name, NULL);

        if (is_gimple_min_invariant (tmp))

          did_something = 2;

        else if (did_something == 0)

          did_something = 1;

        /* Continue combining.  */

        continue;

      }

    break;

  } while (1);

  return did_something;

}

/* Propagate from the ssa name definition statements of COND_EXPR

   in the rhs of statement STMT into the conditional if that simplifies it.

   Returns zero if no statement was changed, one if there were

   changes and two if cfg_cleanup needs to run.

   This must be kept in sync with forward_propagate_into_gimple_cond.  */

static int

forward_propagate_into_cond (gimple_stmt_iterator *gsi_p)

{

  gimple stmt = gsi_stmt (*gsi_p);

  location_t loc = gimple_location (stmt);

  int did_something = 0;

  do {

    tree tmp = NULL_TREE;

    tree cond = gimple_assign_rhs1 (stmt);

    tree name, rhs0 = NULL_TREE, rhs1 = NULL_TREE;

    gimple def_stmt;

    bool single_use0_p = false, single_use1_p = false;

    /* We can do tree combining on SSA_NAME and comparison expressions.  */

    if (COMPARISON_CLASS_P (cond)

        && TREE_CODE (TREE_OPERAND (cond, 0)) == SSA_NAME)

      {

        /* For comparisons use the first operand, that is likely to

           simplify comparisons against constants.  */

        name = TREE_OPERAND (cond, 0);

        def_stmt = get_prop_source_stmt (name, false, &single_use0_p);

        if (def_stmt && can_propagate_from (def_stmt))

          {

            tree op1 = TREE_OPERAND (cond, 1);

            rhs0 = rhs_to_tree (TREE_TYPE (op1), def_stmt);

            tmp = combine_cond_expr_cond (loc, TREE_CODE (cond),

                                          boolean_type_node,

                                          rhs0, op1, !single_use0_p);

          }

        /* If that wasn't successful, try the second operand.  */

        if (tmp == NULL_TREE

            && TREE_CODE (TREE_OPERAND (cond, 1)) == SSA_NAME)

          {

            tree op0 = TREE_OPERAND (cond, 0);

            name = TREE_OPERAND (cond, 1);

            def_stmt = get_prop_source_stmt (name, false, &single_use1_p);

            if (!def_stmt || !can_propagate_from (def_stmt))

              return did_something;

            rhs1 = rhs_to_tree (TREE_TYPE (op0), def_stmt);

            tmp = combine_cond_expr_cond (loc, TREE_CODE (cond),

                                          boolean_type_node,

                                          op0, rhs1, !single_use1_p);

          }

        /* If that wasn't successful either, try both operands.  */

        if (tmp == NULL_TREE

            && rhs0 != NULL_TREE

            && rhs1 != NULL_TREE)

          tmp = combine_cond_expr_cond (loc, TREE_CODE (cond),

                                        boolean_type_node,

                                        rhs0,

                                        fold_convert_loc (loc,

                                                          TREE_TYPE (rhs0),

                                                          rhs1),

                                        !(single_use0_p && single_use1_p));

      }

    else if (TREE_CODE (cond) == SSA_NAME)

      {

        name = cond;

        def_stmt = get_prop_source_stmt (name, true, NULL);

        if (def_stmt || !can_propagate_from (def_stmt))

          return did_something;

        rhs0 = gimple_assign_rhs1 (def_stmt);

        tmp = combine_cond_expr_cond (loc, NE_EXPR, boolean_type_node, rhs0,

                                      build_int_cst (TREE_TYPE (rhs0), 0),

                                      false);

      }

    if (tmp)

      {

        if (dump_file && tmp)

          {

            fprintf (dump_file, "  Replaced '");

            print_generic_expr (dump_file, cond, 0);

            fprintf (dump_file, "' with '");

            print_generic_expr (dump_file, tmp, 0);

            fprintf (dump_file, "'\n");

          }

        gimple_assign_set_rhs_from_tree (gsi_p, unshare_expr (tmp));

        stmt = gsi_stmt (*gsi_p);

        update_stmt (stmt);

        /* Remove defining statements.  */

        remove_prop_source_from_use (name, NULL);

        if (is_gimple_min_invariant (tmp))

          did_something = 2;

        else if (did_something == 0)

          did_something = 1;

        /* Continue combining.  */

        continue;

      }

    break;

  } while (1);

  return did_something;

}

/* We've just substituted an ADDR_EXPR into stmt.  Update all the

   relevant data structures to match.  */

static void

tidy_after_forward_propagate_addr (gimple stmt)

{

  /* We may have turned a trapping insn into a non-trapping insn.  */

  if (maybe_clean_or_replace_eh_stmt (stmt, stmt)

      && gimple_purge_dead_eh_edges (gimple_bb (stmt)))

    cfg_changed = true;

  if (TREE_CODE (gimple_assign_rhs1 (stmt)) == ADDR_EXPR)

     recompute_tree_invariant_for_addr_expr (gimple_assign_rhs1 (stmt));

}

/* DEF_RHS contains the address of the 0th element in an array.

   USE_STMT uses type of DEF_RHS to compute the address of an

   arbitrary element within the array.  The (variable) byte offset

   of the element is contained in OFFSET.

   We walk back through the use-def chains of OFFSET to verify that

   it is indeed computing the offset of an element within the array

   and extract the index corresponding to the given byte offset.

   We then try to fold the entire address expression into a form

   &array[index].

   If we are successful, we replace the right hand side of USE_STMT

   with the new address computation.  */

static bool

forward_propagate_addr_into_variable_array_index (tree offset,

                                                  tree def_rhs,

                                                  gimple_stmt_iterator *use_stmt_gsi)

{

  tree index, tunit;

  gimple offset_def, use_stmt = gsi_stmt (*use_stmt_gsi);

  tree tmp;

  tunit = TYPE_SIZE_UNIT (TREE_TYPE (TREE_TYPE (def_rhs)));

  if (!host_integerp (tunit, 1))

    return false;

  /* Get the offset's defining statement.  */

  offset_def = SSA_NAME_DEF_STMT (offset);

  /* Try to find an expression for a proper index.  This is either a

     multiplication expression by the element size or just the ssa name we came

     along in case the element size is one. In that case, however, we do not

     allow multiplications because they can be computing index to a higher

     level dimension (PR 37861). */

  if (integer_onep (tunit))

    {

      if (is_gimple_assign (offset_def)

          && gimple_assign_rhs_code (offset_def) == MULT_EXPR)

        return false;

      index = offset;

    }

  else

    {

      /* The statement which defines OFFSET before type conversion

         must be a simple GIMPLE_ASSIGN.  */

      if (!is_gimple_assign (offset_def))

        return false;

      /* The RHS of the statement which defines OFFSET must be a

         multiplication of an object by the size of the array elements.

         This implicitly verifies that the size of the array elements

         is constant.  */

     if (gimple_assign_rhs_code (offset_def) == MULT_EXPR

         && TREE_CODE (gimple_assign_rhs2 (offset_def)) == INTEGER_CST

         && tree_int_cst_equal (gimple_assign_rhs2 (offset_def), tunit))

       {

         /* The first operand to the MULT_EXPR is the desired index.  */

         index = gimple_assign_rhs1 (offset_def);

       }

     /* If we have idx * tunit + CST * tunit re-associate that.  */

     else if ((gimple_assign_rhs_code (offset_def) == PLUS_EXPR

               || gimple_assign_rhs_code (offset_def) == MINUS_EXPR)

              && TREE_CODE (gimple_assign_rhs1 (offset_def)) == SSA_NAME

              && TREE_CODE (gimple_assign_rhs2 (offset_def)) == INTEGER_CST

              && (tmp = div_if_zero_remainder (EXACT_DIV_EXPR,

                                               gimple_assign_rhs2 (offset_def),

                                               tunit)) != NULL_TREE)

       {

         gimple offset_def2 = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (offset_def));

         if (is_gimple_assign (offset_def2)

             && gimple_assign_rhs_code (offset_def2) == MULT_EXPR

             && TREE_CODE (gimple_assign_rhs2 (offset_def2)) == INTEGER_CST

             && tree_int_cst_equal (gimple_assign_rhs2 (offset_def2), tunit))

           {

             index = fold_build2 (gimple_assign_rhs_code (offset_def),

                                  TREE_TYPE (offset),

                                  gimple_assign_rhs1 (offset_def2), tmp);

           }

         else

           return false;

       }

     else

        return false;

    }

  /* Replace the pointer addition with array indexing.  */

  index = force_gimple_operand_gsi (use_stmt_gsi, index, true, NULL_TREE,

                                    true, GSI_SAME_STMT);

  gimple_assign_set_rhs_from_tree (use_stmt_gsi, unshare_expr (def_rhs));

  use_stmt = gsi_stmt (*use_stmt_gsi);

  TREE_OPERAND (TREE_OPERAND (gimple_assign_rhs1 (use_stmt), 0), 1)

    = index;

  /* That should have created gimple, so there is no need to

     record information to undo the propagation.  */

  fold_stmt_inplace (use_stmt);

  tidy_after_forward_propagate_addr (use_stmt);

  return true;

}

/* NAME is a SSA_NAME representing DEF_RHS which is of the form

   ADDR_EXPR <whatever>.

   Try to forward propagate the ADDR_EXPR into the use USE_STMT.

   Often this will allow for removal of an ADDR_EXPR and INDIRECT_REF

   node or for recovery of array indexing from pointer arithmetic.

   Return true if the propagation was successful (the propagation can

   be not totally successful, yet things may have been changed).  */

static bool

forward_propagate_addr_expr_1 (tree name, tree def_rhs,

                               gimple_stmt_iterator *use_stmt_gsi,

                               bool single_use_p)

{

  tree lhs, rhs, rhs2, array_ref;

  tree *rhsp, *lhsp;

  gimple use_stmt = gsi_stmt (*use_stmt_gsi);

  enum tree_code rhs_code;

  bool res = true;

  bool addr_p = false;

  gcc_assert (TREE_CODE (def_rhs) == ADDR_EXPR);

  lhs = gimple_assign_lhs (use_stmt);