Subversion Repositories openrisc

/* Alias analysis for trees.

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

   Free Software Foundation, Inc.

   Contributed by Diego Novillo <dnovillo@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 "tm_p.h"

#include "target.h"

#include "basic-block.h"

#include "timevar.h"

#include "ggc.h"

#include "langhooks.h"

#include "flags.h"

#include "function.h"

#include "tree-pretty-print.h"

#include "tree-dump.h"

#include "gimple.h"

#include "tree-flow.h"

#include "tree-inline.h"

#include "tree-pass.h"

#include "convert.h"

#include "params.h"

#include "vec.h"

#include "bitmap.h"

#include "vecprim.h"

#include "pointer-set.h"

#include "alloc-pool.h"

#include "tree-ssa-alias.h"

/* Broad overview of how alias analysis on gimple works:

   Statements clobbering or using memory are linked through the

   virtual operand factored use-def chain.  The virtual operand

   is unique per function, its symbol is accessible via gimple_vop (cfun).

   Virtual operands are used for efficiently walking memory statements

   in the gimple IL and are useful for things like value-numbering as

   a generation count for memory references.

   SSA_NAME pointers may have associated points-to information

   accessible via the SSA_NAME_PTR_INFO macro.  Flow-insensitive

   points-to information is (re-)computed by the TODO_rebuild_alias

   pass manager todo.  Points-to information is also used for more

   precise tracking of call-clobbered and call-used variables and

   related disambiguations.

   This file contains functions for disambiguating memory references,

   the so called alias-oracle and tools for walking of the gimple IL.

   The main alias-oracle entry-points are

   bool stmt_may_clobber_ref_p (gimple, tree)

     This function queries if a statement may invalidate (parts of)

     the memory designated by the reference tree argument.

   bool ref_maybe_used_by_stmt_p (gimple, tree)

     This function queries if a statement may need (parts of) the

     memory designated by the reference tree argument.

   There are variants of these functions that only handle the call

   part of a statement, call_may_clobber_ref_p and ref_maybe_used_by_call_p.

   Note that these do not disambiguate against a possible call lhs.

   bool refs_may_alias_p (tree, tree)

     This function tries to disambiguate two reference trees.

   bool ptr_deref_may_alias_global_p (tree)

     This function queries if dereferencing a pointer variable may

     alias global memory.

   More low-level disambiguators are available and documented in

   this file.  Low-level disambiguators dealing with points-to

   information are in tree-ssa-structalias.c.  */

/* Query statistics for the different low-level disambiguators.

   A high-level query may trigger multiple of them.  */

static struct {

  unsigned HOST_WIDE_INT refs_may_alias_p_may_alias;

  unsigned HOST_WIDE_INT refs_may_alias_p_no_alias;

  unsigned HOST_WIDE_INT ref_maybe_used_by_call_p_may_alias;

  unsigned HOST_WIDE_INT ref_maybe_used_by_call_p_no_alias;

  unsigned HOST_WIDE_INT call_may_clobber_ref_p_may_alias;

  unsigned HOST_WIDE_INT call_may_clobber_ref_p_no_alias;

} alias_stats;

void

dump_alias_stats (FILE *s)

{

  fprintf (s, "\nAlias oracle query stats:\n");

  fprintf (s, "  refs_may_alias_p: "

           HOST_WIDE_INT_PRINT_DEC" disambiguations, "

           HOST_WIDE_INT_PRINT_DEC" queries\n",

           alias_stats.refs_may_alias_p_no_alias,

           alias_stats.refs_may_alias_p_no_alias

           + alias_stats.refs_may_alias_p_may_alias);

  fprintf (s, "  ref_maybe_used_by_call_p: "

           HOST_WIDE_INT_PRINT_DEC" disambiguations, "

           HOST_WIDE_INT_PRINT_DEC" queries\n",

           alias_stats.ref_maybe_used_by_call_p_no_alias,

           alias_stats.refs_may_alias_p_no_alias

           + alias_stats.ref_maybe_used_by_call_p_may_alias);

  fprintf (s, "  call_may_clobber_ref_p: "

           HOST_WIDE_INT_PRINT_DEC" disambiguations, "

           HOST_WIDE_INT_PRINT_DEC" queries\n",

           alias_stats.call_may_clobber_ref_p_no_alias,

           alias_stats.call_may_clobber_ref_p_no_alias

           + alias_stats.call_may_clobber_ref_p_may_alias);

}

/* Return true, if dereferencing PTR may alias with a global variable.  */

bool

ptr_deref_may_alias_global_p (tree ptr)

{

  struct ptr_info_def *pi;

  /* If we end up with a pointer constant here that may point

     to global memory.  */

  if (TREE_CODE (ptr) != SSA_NAME)

    return true;

  pi = SSA_NAME_PTR_INFO (ptr);

  /* If we do not have points-to information for this variable,

     we have to punt.  */

  if (!pi)

    return true;

  /* ???  This does not use TBAA to prune globals ptr may not access.  */

  return pt_solution_includes_global (&pi->pt);

}

/* Return true if dereferencing PTR may alias DECL.

   The caller is responsible for applying TBAA to see if PTR

   may access DECL at all.  */

static bool

ptr_deref_may_alias_decl_p (tree ptr, tree decl)

{

  struct ptr_info_def *pi;

  /* Conversions are irrelevant for points-to information and

     data-dependence analysis can feed us those.  */

  STRIP_NOPS (ptr);

  /* Anything we do not explicilty handle aliases.  */

  if ((TREE_CODE (ptr) != SSA_NAME

       && TREE_CODE (ptr) != ADDR_EXPR

       && TREE_CODE (ptr) != POINTER_PLUS_EXPR)

      || !POINTER_TYPE_P (TREE_TYPE (ptr))

      || (TREE_CODE (decl) != VAR_DECL

          && TREE_CODE (decl) != PARM_DECL

          && TREE_CODE (decl) != RESULT_DECL))

    return true;

  /* Disregard pointer offsetting.  */

  if (TREE_CODE (ptr) == POINTER_PLUS_EXPR)

    {

      do

        {

          ptr = TREE_OPERAND (ptr, 0);

        }

      while (TREE_CODE (ptr) == POINTER_PLUS_EXPR);

      return ptr_deref_may_alias_decl_p (ptr, decl);

    }

  /* ADDR_EXPR pointers either just offset another pointer or directly

     specify the pointed-to set.  */

  if (TREE_CODE (ptr) == ADDR_EXPR)

    {

      tree base = get_base_address (TREE_OPERAND (ptr, 0));

      if (base

          && (TREE_CODE (base) == MEM_REF

              || TREE_CODE (base) == TARGET_MEM_REF))

        ptr = TREE_OPERAND (base, 0);

      else if (base

               && DECL_P (base))

        return base == decl;

      else if (base

               && CONSTANT_CLASS_P (base))

        return false;

      else

        return true;

    }

  /* Non-aliased variables can not be pointed to.  */

  if (!may_be_aliased (decl))

    return false;

  /* If we do not have useful points-to information for this pointer

     we cannot disambiguate anything else.  */

  pi = SSA_NAME_PTR_INFO (ptr);

  if (!pi)

    return true;

  return pt_solution_includes (&pi->pt, decl);

}

/* Return true if dereferenced PTR1 and PTR2 may alias.

   The caller is responsible for applying TBAA to see if accesses

   through PTR1 and PTR2 may conflict at all.  */

bool

ptr_derefs_may_alias_p (tree ptr1, tree ptr2)

{

  struct ptr_info_def *pi1, *pi2;

  /* Conversions are irrelevant for points-to information and

     data-dependence analysis can feed us those.  */

  STRIP_NOPS (ptr1);

  STRIP_NOPS (ptr2);

  /* Anything we do not explicilty handle aliases.  */

  if ((TREE_CODE (ptr1) != SSA_NAME

       && TREE_CODE (ptr1) != ADDR_EXPR

       && TREE_CODE (ptr1) != POINTER_PLUS_EXPR)

      || (TREE_CODE (ptr2) != SSA_NAME

          && TREE_CODE (ptr2) != ADDR_EXPR

          && TREE_CODE (ptr2) != POINTER_PLUS_EXPR)

      || !POINTER_TYPE_P (TREE_TYPE (ptr1))

      || !POINTER_TYPE_P (TREE_TYPE (ptr2)))

    return true;

  /* Disregard pointer offsetting.  */

  if (TREE_CODE (ptr1) == POINTER_PLUS_EXPR)

    {

      do

        {

          ptr1 = TREE_OPERAND (ptr1, 0);

        }

      while (TREE_CODE (ptr1) == POINTER_PLUS_EXPR);

      return ptr_derefs_may_alias_p (ptr1, ptr2);

    }

  if (TREE_CODE (ptr2) == POINTER_PLUS_EXPR)

    {

      do

        {

          ptr2 = TREE_OPERAND (ptr2, 0);

        }

      while (TREE_CODE (ptr2) == POINTER_PLUS_EXPR);

      return ptr_derefs_may_alias_p (ptr1, ptr2);

    }

  /* ADDR_EXPR pointers either just offset another pointer or directly

     specify the pointed-to set.  */

  if (TREE_CODE (ptr1) == ADDR_EXPR)

    {

      tree base = get_base_address (TREE_OPERAND (ptr1, 0));

      if (base

          && (TREE_CODE (base) == MEM_REF

              || TREE_CODE (base) == TARGET_MEM_REF))

        ptr1 = TREE_OPERAND (base, 0);

      else if (base

               && DECL_P (base))

        return ptr_deref_may_alias_decl_p (ptr2, base);

      else

        return true;

    }

  if (TREE_CODE (ptr2) == ADDR_EXPR)

    {

      tree base = get_base_address (TREE_OPERAND (ptr2, 0));

      if (base

          && (TREE_CODE (base) == MEM_REF

              || TREE_CODE (base) == TARGET_MEM_REF))

        ptr2 = TREE_OPERAND (base, 0);

      else if (base

               && DECL_P (base))

        return ptr_deref_may_alias_decl_p (ptr1, base);

      else

        return true;

    }

  /* We may end up with two empty points-to solutions for two same pointers.

     In this case we still want to say both pointers alias, so shortcut

     that here.  */

  if (ptr1 == ptr2)

    return true;

  /* If we do not have useful points-to information for either pointer

     we cannot disambiguate anything else.  */

  pi1 = SSA_NAME_PTR_INFO (ptr1);

  pi2 = SSA_NAME_PTR_INFO (ptr2);

  if (!pi1 || !pi2)

    return true;

  /* ???  This does not use TBAA to prune decls from the intersection

     that not both pointers may access.  */

  return pt_solutions_intersect (&pi1->pt, &pi2->pt);

}

/* Return true if dereferencing PTR may alias *REF.

   The caller is responsible for applying TBAA to see if PTR

   may access *REF at all.  */

static bool

ptr_deref_may_alias_ref_p_1 (tree ptr, ao_ref *ref)

{

  tree base = ao_ref_base (ref);

  if (TREE_CODE (base) == MEM_REF

      || TREE_CODE (base) == TARGET_MEM_REF)

    return ptr_derefs_may_alias_p (ptr, TREE_OPERAND (base, 0));

  else if (DECL_P (base))

    return ptr_deref_may_alias_decl_p (ptr, base);

  return true;

}

/* Dump alias information on FILE.  */

void

dump_alias_info (FILE *file)

{

  size_t i;

  const char *funcname

    = lang_hooks.decl_printable_name (current_function_decl, 2);

  referenced_var_iterator rvi;

  tree var;

  fprintf (file, "\n\nAlias information for %s\n\n", funcname);

  fprintf (file, "Aliased symbols\n\n");

  FOR_EACH_REFERENCED_VAR (cfun, var, rvi)

    {

      if (may_be_aliased (var))

        dump_variable (file, var);

    }

  fprintf (file, "\nCall clobber information\n");

  fprintf (file, "\nESCAPED");

  dump_points_to_solution (file, &cfun->gimple_df->escaped);

  fprintf (file, "\n\nFlow-insensitive points-to information\n\n");

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

    {

      tree ptr = ssa_name (i);

      struct ptr_info_def *pi;

      if (ptr == NULL_TREE

          || SSA_NAME_IN_FREE_LIST (ptr))

        continue;

      pi = SSA_NAME_PTR_INFO (ptr);

      if (pi)

        dump_points_to_info_for (file, ptr);

    }

  fprintf (file, "\n");

}

/* Dump alias information on stderr.  */

DEBUG_FUNCTION void

debug_alias_info (void)

{

  dump_alias_info (stderr);

}

/* Dump the points-to set *PT into FILE.  */

void

dump_points_to_solution (FILE *file, struct pt_solution *pt)

{

  if (pt->anything)

    fprintf (file, ", points-to anything");

  if (pt->nonlocal)

    fprintf (file, ", points-to non-local");

  if (pt->escaped)

    fprintf (file, ", points-to escaped");

  if (pt->ipa_escaped)

    fprintf (file, ", points-to unit escaped");

  if (pt->null)

    fprintf (file, ", points-to NULL");

  if (pt->vars)

    {

      fprintf (file, ", points-to vars: ");

      dump_decl_set (file, pt->vars);

      if (pt->vars_contains_global)

        fprintf (file, " (includes global vars)");

    }

}

/* Dump points-to information for SSA_NAME PTR into FILE.  */

void

dump_points_to_info_for (FILE *file, tree ptr)

{

  struct ptr_info_def *pi = SSA_NAME_PTR_INFO (ptr);

  print_generic_expr (file, ptr, dump_flags);

  if (pi)

    dump_points_to_solution (file, &pi->pt);

  else

    fprintf (file, ", points-to anything");

  fprintf (file, "\n");

}

/* Dump points-to information for VAR into stderr.  */

DEBUG_FUNCTION void

debug_points_to_info_for (tree var)

{

  dump_points_to_info_for (stderr, var);

}

/* Initializes the alias-oracle reference representation *R from REF.  */

void

ao_ref_init (ao_ref *r, tree ref)

{

  r->ref = ref;

  r->base = NULL_TREE;

  r->offset = 0;

  r->size = -1;

  r->max_size = -1;

  r->ref_alias_set = -1;

  r->base_alias_set = -1;

  r->volatile_p = ref ? TREE_THIS_VOLATILE (ref) : false;

}

/* Returns the base object of the memory reference *REF.  */

tree

ao_ref_base (ao_ref *ref)

{

  if (ref->base)

    return ref->base;

  ref->base = get_ref_base_and_extent (ref->ref, &ref->offset, &ref->size,

                                       &ref->max_size);

  return ref->base;

}

/* Returns the base object alias set of the memory reference *REF.  */

static alias_set_type

ao_ref_base_alias_set (ao_ref *ref)

{

  tree base_ref;

  if (ref->base_alias_set != -1)

    return ref->base_alias_set;

  if (!ref->ref)

    return 0;

  base_ref = ref->ref;

  while (handled_component_p (base_ref))

    base_ref = TREE_OPERAND (base_ref, 0);

  ref->base_alias_set = get_alias_set (base_ref);

  return ref->base_alias_set;

}

/* Returns the reference alias set of the memory reference *REF.  */

alias_set_type

ao_ref_alias_set (ao_ref *ref)

{

  if (ref->ref_alias_set != -1)

    return ref->ref_alias_set;

  ref->ref_alias_set = get_alias_set (ref->ref);

  return ref->ref_alias_set;

}

/* Init an alias-oracle reference representation from a gimple pointer

   PTR and a gimple size SIZE in bytes.  If SIZE is NULL_TREE the the

   size is assumed to be unknown.  The access is assumed to be only

   to or after of the pointer target, not before it.  */

void

ao_ref_init_from_ptr_and_size (ao_ref *ref, tree ptr, tree size)

{

  HOST_WIDE_INT t1, t2;

  ref->ref = NULL_TREE;

  if (TREE_CODE (ptr) == ADDR_EXPR)

    ref->base = get_ref_base_and_extent (TREE_OPERAND (ptr, 0),

                                         &ref->offset, &t1, &t2);

  else

    {

      ref->base = build2 (MEM_REF, char_type_node,

                          ptr, null_pointer_node);

      ref->offset = 0;

    }

  if (size

      && host_integerp (size, 0)

      && TREE_INT_CST_LOW (size) * 8 / 8 == TREE_INT_CST_LOW (size))

    ref->max_size = ref->size = TREE_INT_CST_LOW (size) * 8;

  else

    ref->max_size = ref->size = -1;

  ref->ref_alias_set = 0;

  ref->base_alias_set = 0;

  ref->volatile_p = false;

}

/* Return 1 if TYPE1 and TYPE2 are to be considered equivalent for the

   purpose of TBAA.  Return 0 if they are distinct and -1 if we cannot

   decide.  */

static inline int

same_type_for_tbaa (tree type1, tree type2)

{

  type1 = TYPE_MAIN_VARIANT (type1);

  type2 = TYPE_MAIN_VARIANT (type2);

  /* If we would have to do structural comparison bail out.  */

  if (TYPE_STRUCTURAL_EQUALITY_P (type1)

      || TYPE_STRUCTURAL_EQUALITY_P (type2))

    return -1;

  /* Compare the canonical types.  */

  if (TYPE_CANONICAL (type1) == TYPE_CANONICAL (type2))

    return 1;

  /* ??? Array types are not properly unified in all cases as we have

     spurious changes in the index types for example.  Removing this

     causes all sorts of problems with the Fortran frontend.  */

  if (TREE_CODE (type1) == ARRAY_TYPE

      && TREE_CODE (type2) == ARRAY_TYPE)

    return -1;

  /* ??? In Ada, an lvalue of an unconstrained type can be used to access an

     object of one of its constrained subtypes, e.g. when a function with an

     unconstrained parameter passed by reference is called on an object and

     inlined.  But, even in the case of a fixed size, type and subtypes are

     not equivalent enough as to share the same TYPE_CANONICAL, since this

     would mean that conversions between them are useless, whereas they are

     not (e.g. type and subtypes can have different modes).  So, in the end,

     they are only guaranteed to have the same alias set.  */

  if (get_alias_set (type1) == get_alias_set (type2))

    return -1;

  /* The types are known to be not equal.  */

  return 0;

}

/* Determine if the two component references REF1 and REF2 which are

   based on access types TYPE1 and TYPE2 and of which at least one is based

   on an indirect reference may alias.  REF2 is the only one that can

   be a decl in which case REF2_IS_DECL is true.

   REF1_ALIAS_SET, BASE1_ALIAS_SET, REF2_ALIAS_SET and BASE2_ALIAS_SET

   are the respective alias sets.  */

static bool

aliasing_component_refs_p (tree ref1,

                           alias_set_type ref1_alias_set,

                           alias_set_type base1_alias_set,

                           HOST_WIDE_INT offset1, HOST_WIDE_INT max_size1,

                           tree ref2,

                           alias_set_type ref2_alias_set,

                           alias_set_type base2_alias_set,

                           HOST_WIDE_INT offset2, HOST_WIDE_INT max_size2,

                           bool ref2_is_decl)

{

  /* If one reference is a component references through pointers try to find a

     common base and apply offset based disambiguation.  This handles

     for example

       struct A { int i; int j; } *q;

       struct B { struct A a; int k; } *p;

     disambiguating q->i and p->a.j.  */

  tree base1, base2;

  tree type1, type2;

  tree *refp;

  int same_p;

  /* Choose bases and base types to search for.  */

  base1 = ref1;

  while (handled_component_p (base1))

    base1 = TREE_OPERAND (base1, 0);

  type1 = TREE_TYPE (base1);

  base2 = ref2;

  while (handled_component_p (base2))

    base2 = TREE_OPERAND (base2, 0);

  type2 = TREE_TYPE (base2);

  /* Now search for the type1 in the access path of ref2.  This

     would be a common base for doing offset based disambiguation on.  */

  refp = &ref2;

  while (handled_component_p (*refp)

         && same_type_for_tbaa (TREE_TYPE (*refp), type1) == 0)

    refp = &TREE_OPERAND (*refp, 0);

  same_p = same_type_for_tbaa (TREE_TYPE (*refp), type1);

  /* If we couldn't compare types we have to bail out.  */

  if (same_p == -1)

    return true;

  else if (same_p == 1)

    {

      HOST_WIDE_INT offadj, sztmp, msztmp;

      get_ref_base_and_extent (*refp, &offadj, &sztmp, &msztmp);

      offset2 -= offadj;

      get_ref_base_and_extent (base1, &offadj, &sztmp, &msztmp);

      offset1 -= offadj;

      return ranges_overlap_p (offset1, max_size1, offset2, max_size2);

    }

  /* If we didn't find a common base, try the other way around.  */

  refp = &ref1;

  while (handled_component_p (*refp)

         && same_type_for_tbaa (TREE_TYPE (*refp), type2) == 0)

    refp = &TREE_OPERAND (*refp, 0);

  same_p = same_type_for_tbaa (TREE_TYPE (*refp), type2);

  /* If we couldn't compare types we have to bail out.  */

  if (same_p == -1)

    return true;

  else if (same_p == 1)

    {

      HOST_WIDE_INT offadj, sztmp, msztmp;

      get_ref_base_and_extent (*refp, &offadj, &sztmp, &msztmp);

      offset1 -= offadj;

      get_ref_base_and_extent (base2, &offadj, &sztmp, &msztmp);

      offset2 -= offadj;

      return ranges_overlap_p (offset1, max_size1, offset2, max_size2);

    }

  /* If we have two type access paths B1.path1 and B2.path2 they may

     only alias if either B1 is in B2.path2 or B2 is in B1.path1.

     But we can still have a path that goes B1.path1...B2.path2 with

     a part that we do not see.  So we can only disambiguate now

     if there is no B2 in the tail of path1 and no B1 on the

     tail of path2.  */

  if (base1_alias_set == ref2_alias_set

      || alias_set_subset_of (base1_alias_set, ref2_alias_set))

    return true;

  /* If this is ptr vs. decl then we know there is no ptr ... decl path.  */

  if (!ref2_is_decl)

    return (base2_alias_set == ref1_alias_set

            || alias_set_subset_of (base2_alias_set, ref1_alias_set));

  return false;

}

/* Return true if two memory references based on the variables BASE1

   and BASE2 constrained to [OFFSET1, OFFSET1 + MAX_SIZE1) and

   [OFFSET2, OFFSET2 + MAX_SIZE2) may alias.  */

static bool

decl_refs_may_alias_p (tree base1,

                       HOST_WIDE_INT offset1, HOST_WIDE_INT max_size1,

                       tree base2,

                       HOST_WIDE_INT offset2, HOST_WIDE_INT max_size2)

{

  gcc_checking_assert (DECL_P (base1) && DECL_P (base2));

  /* If both references are based on different variables, they cannot alias.  */

  if (base1 != base2)

    return false;

  /* If both references are based on the same variable, they cannot alias if

     the accesses do not overlap.  */

  return ranges_overlap_p (offset1, max_size1, offset2, max_size2);

}

/* Return true if an indirect reference based on *PTR1 constrained

   to [OFFSET1, OFFSET1 + MAX_SIZE1) may alias a variable based on BASE2

   constrained to [OFFSET2, OFFSET2 + MAX_SIZE2).  *PTR1 and BASE2 have

   the alias sets BASE1_ALIAS_SET and BASE2_ALIAS_SET which can be -1

   in which case they are computed on-demand.  REF1 and REF2

   if non-NULL are the complete memory reference trees.  */

static bool

indirect_ref_may_alias_decl_p (tree ref1 ATTRIBUTE_UNUSED, tree base1,

                               HOST_WIDE_INT offset1,

                               HOST_WIDE_INT max_size1 ATTRIBUTE_UNUSED,

                               alias_set_type ref1_alias_set,

                               alias_set_type base1_alias_set,

                               tree ref2 ATTRIBUTE_UNUSED, tree base2,

                               HOST_WIDE_INT offset2, HOST_WIDE_INT max_size2,

                               alias_set_type ref2_alias_set,

                               alias_set_type base2_alias_set, bool tbaa_p)

{

  tree ptr1;

  tree ptrtype1, dbase2;

  HOST_WIDE_INT offset1p = offset1, offset2p = offset2;

  HOST_WIDE_INT doffset1, doffset2;

  double_int moff;

  gcc_checking_assert ((TREE_CODE (base1) == MEM_REF

                        || TREE_CODE (base1) == TARGET_MEM_REF)

                       && DECL_P (base2));

  ptr1 = TREE_OPERAND (base1, 0);

  /* The offset embedded in MEM_REFs can be negative.  Bias them