C++ DECL_FIELD_OFFSET函数代码示例

static void
build_field (segment_info *h, tree union_type, record_layout_info rli)
{
  tree field;
  tree name;
  HOST_WIDE_INT offset = h->offset;
  unsigned HOST_WIDE_INT desired_align, known_align;

  name = get_identifier (h->sym->name);
  field = build_decl (FIELD_DECL, name, h->field);
  gfc_set_decl_location (field, &h->sym->declared_at);
  known_align = (offset & -offset) * BITS_PER_UNIT;
  if (known_align == 0 || known_align > BIGGEST_ALIGNMENT)
    known_align = BIGGEST_ALIGNMENT;

  desired_align = update_alignment_for_field (rli, field, known_align);
  if (desired_align > known_align)
    DECL_PACKED (field) = 1;

  DECL_FIELD_CONTEXT (field) = union_type;
  DECL_FIELD_OFFSET (field) = size_int (offset);
  DECL_FIELD_BIT_OFFSET (field) = bitsize_zero_node;
  SET_DECL_OFFSET_ALIGN (field, known_align);

  rli->offset = size_binop (MAX_EXPR, rli->offset,
                            size_binop (PLUS_EXPR,
                                        DECL_FIELD_OFFSET (field),
                                        DECL_SIZE_UNIT (field)));
  h->field = field;
}

void     field_DECL_FIELD_OFFSET(tree t)
{
  if (DECL_FIELD_OFFSET(t)) {
    //fprintf( code_outputfile,"DECL_BIT_FIELD %d\n",DECL_FIELD_OFFSET(t));
    fprintf( code_outputfile,"DECL_BIT_FIELD\n"); // tree
  }
}

struct FieldInfo* createFieldInfo(const tree field_decl)
{
  struct FieldInfo* fi = (struct FieldInfo*) xcalloc(1, sizeof(struct FieldInfo));
  fi->isSpecial = DECL_ARTIFICIAL(field_decl);
  fi->isBitField = DECL_BIT_FIELD(field_decl);

  const char* fieldName;
  if (fi->isSpecial)
    fieldName = fieldNames[FIELD_BASE];
  else if (DECL_NAME(field_decl))
    fieldName = IDENTIFIER_POINTER(DECL_NAME(field_decl));
  else
    fieldName = fieldNames[FIELD_NONAME];

  fi->name = xstrdup(fieldName);

  fi->size = TREE_INT_CST_LOW(DECL_SIZE(field_decl));

  // Offset calculation is a little bit wierd. According to GCC docs:
  // "... DECL_FIELD_OFFSET is position, counting in bytes, of the
  // DECL_OFFSET_ALIGN-bit sized word ..." and ".. DECL_FIELD_BIT_OFFSET is the
  // bit offset of the first bit of the field within this word"
  fi->offset = TREE_INT_CST_LOW(DECL_FIELD_OFFSET(field_decl)) * BITS_PER_UNIT +
    TREE_INT_CST_LOW(DECL_FIELD_BIT_OFFSET(field_decl));

  fi->align = DECL_ALIGN(field_decl);

  return fi;
}

static tree
compute_object_offset (tree expr, tree var)
{
  enum tree_code code = PLUS_EXPR;
  tree base, off, t;

  if (expr == var)
    return size_zero_node;

  switch (TREE_CODE (expr))
    {
    case COMPONENT_REF:
      base = compute_object_offset (TREE_OPERAND (expr, 0), var);
      if (base == error_mark_node)
	return base;

      t = TREE_OPERAND (expr, 1);
      off = size_binop (PLUS_EXPR, DECL_FIELD_OFFSET (t),
			size_int (tree_low_cst (DECL_FIELD_BIT_OFFSET (t), 1)
				  / BITS_PER_UNIT));
      break;

    case REALPART_EXPR:
    case NOP_EXPR:
    case CONVERT_EXPR:
    case VIEW_CONVERT_EXPR:
    case NON_LVALUE_EXPR:
      return compute_object_offset (TREE_OPERAND (expr, 0), var);

    case IMAGPART_EXPR:
      base = compute_object_offset (TREE_OPERAND (expr, 0), var);
      if (base == error_mark_node)
	return base;

      off = TYPE_SIZE_UNIT (TREE_TYPE (expr));
      break;

    case ARRAY_REF:
      base = compute_object_offset (TREE_OPERAND (expr, 0), var);
      if (base == error_mark_node)
	return base;

      t = TREE_OPERAND (expr, 1);
      if (TREE_CODE (t) == INTEGER_CST && tree_int_cst_sgn (t) < 0)
	{
	  code = MINUS_EXPR;
	  t = fold_build1 (NEGATE_EXPR, TREE_TYPE (t), t);
	}
      t = convert (sizetype, t);
      off = size_binop (MULT_EXPR, TYPE_SIZE_UNIT (TREE_TYPE (expr)), t);
      break;

    default:
      return error_mark_node;
    }

  return size_binop (code, base, off);
}

static void
lto_input_ts_field_decl_tree_pointers (struct lto_input_block *ib,
				       struct data_in *data_in, tree expr)
{
  DECL_FIELD_OFFSET (expr) = stream_read_tree (ib, data_in);
  DECL_BIT_FIELD_TYPE (expr) = stream_read_tree (ib, data_in);
  /* Do not stream DECL_QUALIFIER, it is useless after gimplification.  */
  DECL_FIELD_BIT_OFFSET (expr) = stream_read_tree (ib, data_in);
  DECL_FCONTEXT (expr) = stream_read_tree (ib, data_in);
}

static void
write_ts_field_decl_tree_pointers (struct output_block *ob, tree expr,
				   bool ref_p)
{
  stream_write_tree (ob, DECL_FIELD_OFFSET (expr), ref_p);
  stream_write_tree (ob, DECL_BIT_FIELD_TYPE (expr), ref_p);
  stream_write_tree (ob, DECL_BIT_FIELD_REPRESENTATIVE (expr), ref_p);
  stream_write_tree (ob, DECL_FIELD_BIT_OFFSET (expr), ref_p);
  stream_write_tree (ob, DECL_FCONTEXT (expr), ref_p);
}

static void
lto_input_ts_field_decl_tree_pointers (struct lto_input_block *ib,
				       struct data_in *data_in, tree expr)
{
  DECL_FIELD_OFFSET (expr) = stream_read_tree (ib, data_in);
  DECL_BIT_FIELD_TYPE (expr) = stream_read_tree (ib, data_in);
  DECL_BIT_FIELD_REPRESENTATIVE (expr) = stream_read_tree (ib, data_in);
  DECL_FIELD_BIT_OFFSET (expr) = stream_read_tree (ib, data_in);
  DECL_FCONTEXT (expr) = stream_read_tree (ib, data_in);
}

static void
write_ts_field_decl_tree_pointers (struct output_block *ob, tree expr,
				   bool ref_p)
{
  stream_write_tree (ob, DECL_FIELD_OFFSET (expr), ref_p);
  stream_write_tree (ob, DECL_BIT_FIELD_TYPE (expr), ref_p);
  stream_write_tree (ob, DECL_QUALIFIER (expr), ref_p);
  stream_write_tree (ob, DECL_FIELD_BIT_OFFSET (expr), ref_p);
  stream_write_tree (ob, DECL_FCONTEXT (expr), ref_p);
  streamer_write_chain (ob, TREE_CHAIN (expr), ref_p);
}

//.........这里部分代码省略.........
	    TB_WF;
	  break;

	case TB_ABSTRACT_ORIGIN:
	  if (head && DECL_P (head))
	    TB_SET_HEAD (DECL_ABSTRACT_ORIGIN (head));
	  else if (head && TREE_CODE (head) == BLOCK)
	    TB_SET_HEAD (BLOCK_ABSTRACT_ORIGIN (head));
	  else
	    TB_WF;
	  break;

	case TB_ATTRIBUTES:
	  if (head && DECL_P (head))
	    TB_SET_HEAD (DECL_ATTRIBUTES (head));
	  else if (head && TYPE_P (head))
	    TB_SET_HEAD (TYPE_ATTRIBUTES (head));
	  else
	    TB_WF;
	  break;

	case TB_CONTEXT:
	  if (head && DECL_P (head))
	    TB_SET_HEAD (DECL_CONTEXT (head));
	  else if (head && TYPE_P (head)
		   && TYPE_CONTEXT (head))
	    TB_SET_HEAD (TYPE_CONTEXT (head));
	  else
	    TB_WF;
	  break;

	case TB_OFFSET:
	  if (head && TREE_CODE (head) == FIELD_DECL)
	    TB_SET_HEAD (DECL_FIELD_OFFSET (head));
	  else
	    TB_WF;
	  break;

	case TB_BIT_OFFSET:
	  if (head && TREE_CODE (head) == FIELD_DECL)
	    TB_SET_HEAD (DECL_FIELD_BIT_OFFSET (head));
	  else
	    TB_WF;
          break;

	case TB_UNIT_SIZE:
	  if (head && DECL_P (head))
	    TB_SET_HEAD (DECL_SIZE_UNIT (head));
	  else if (head && TYPE_P (head))
	    TB_SET_HEAD (TYPE_SIZE_UNIT (head));
	  else
	    TB_WF;
	  break;

	case TB_SIZE:
	  if (head && DECL_P (head))
	    TB_SET_HEAD (DECL_SIZE (head));
	  else if (head && TYPE_P (head))
	    TB_SET_HEAD (TYPE_SIZE (head));
	  else
	    TB_WF;
	  break;

	case TB_TYPE:
	  if (head && TREE_TYPE (head))
	    TB_SET_HEAD (TREE_TYPE (head));

//.........这里部分代码省略.........

        xloc = expand_location (DECL_SOURCE_LOCATION (node));
        fprintf (file, " file %s line %d col %d", xloc.file, xloc.line,
                 xloc.column);

        if (CODE_CONTAINS_STRUCT (code, TS_DECL_COMMON))
        {
            print_node (file, "size", DECL_SIZE (node), indent + 4);
            print_node (file, "unit size", DECL_SIZE_UNIT (node), indent + 4);

            if (code != FUNCTION_DECL || DECL_BUILT_IN (node))
                indent_to (file, indent + 3);

            if (DECL_USER_ALIGN (node))
                fprintf (file, " user");

            fprintf (file, " align %d", DECL_ALIGN (node));
            if (code == FIELD_DECL)
                fprintf (file, " offset_align " HOST_WIDE_INT_PRINT_UNSIGNED,
                         DECL_OFFSET_ALIGN (node));

            if (code == FUNCTION_DECL && DECL_BUILT_IN (node))
            {
                if (DECL_BUILT_IN_CLASS (node) == BUILT_IN_MD)
                    fprintf (file, " built-in BUILT_IN_MD %d", DECL_FUNCTION_CODE (node));
                else
                    fprintf (file, " built-in %s:%s",
                             built_in_class_names[(int) DECL_BUILT_IN_CLASS (node)],
                             built_in_names[(int) DECL_FUNCTION_CODE (node)]);
            }
        }
        if (code == FIELD_DECL)
        {
            print_node (file, "offset", DECL_FIELD_OFFSET (node), indent + 4);
            print_node (file, "bit offset", DECL_FIELD_BIT_OFFSET (node),
                        indent + 4);
            if (DECL_BIT_FIELD_TYPE (node))
                print_node (file, "bit_field_type", DECL_BIT_FIELD_TYPE (node),
                            indent + 4);
        }

        print_node_brief (file, "context", DECL_CONTEXT (node), indent + 4);

        if (CODE_CONTAINS_STRUCT (code, TS_DECL_COMMON))
        {
            print_node_brief (file, "attributes",
                              DECL_ATTRIBUTES (node), indent + 4);
            if (code != PARM_DECL)
                print_node_brief (file, "initial", DECL_INITIAL (node),
                                  indent + 4);
        }
        if (CODE_CONTAINS_STRUCT (code, TS_DECL_WRTL))
        {
            print_node_brief (file, "abstract_origin",
                              DECL_ABSTRACT_ORIGIN (node), indent + 4);
        }
        if (CODE_CONTAINS_STRUCT (code, TS_DECL_NON_COMMON))
        {
            print_node (file, "result", DECL_RESULT_FLD (node), indent + 4);
        }

        lang_hooks.print_decl (file, node, indent);

        if (DECL_RTL_SET_P (node))
        {
            indent_to (file, indent + 4);

//.........这里部分代码省略.........
    case UNION_TYPE:
      if (TREE_CODE (t) == RECORD_TYPE)
	dump_string_field (di, "tag", "struct");
      else
	dump_string_field (di, "tag", "union");

      dump_child ("flds", TYPE_FIELDS (t));
      dump_child ("fncs", TYPE_METHODS (t));
      queue_and_dump_index (di, "binf", TYPE_BINFO (t),
			    DUMP_BINFO);
      break;

    case CONST_DECL:
      dump_child ("cnst", DECL_INITIAL (t));
      break;

    case DEBUG_EXPR_DECL:
      dump_int (di, "-uid", DEBUG_TEMP_UID (t));
      /* Fall through.  */

    case VAR_DECL:
    case PARM_DECL:
    case FIELD_DECL:
    case RESULT_DECL:
      if (TREE_CODE (t) == PARM_DECL)
	dump_child ("argt", DECL_ARG_TYPE (t));
      else
	dump_child ("init", DECL_INITIAL (t));
      dump_child ("size", DECL_SIZE (t));
      dump_int (di, "algn", DECL_ALIGN (t));

      if (TREE_CODE (t) == FIELD_DECL)
	{
	  if (DECL_FIELD_OFFSET (t))
	    dump_child ("bpos", bit_position (t));
	}
      else if (TREE_CODE (t) == VAR_DECL
	       || TREE_CODE (t) == PARM_DECL)
	{
	  dump_int (di, "used", TREE_USED (t));
	  if (DECL_REGISTER (t))
	    dump_string_field (di, "spec", "register");
	}
      break;

    case FUNCTION_DECL:
      dump_child ("args", DECL_ARGUMENTS (t));
      if (DECL_EXTERNAL (t))
	dump_string_field (di, "body", "undefined");
      if (TREE_PUBLIC (t))
	dump_string_field (di, "link", "extern");
      else
	dump_string_field (di, "link", "static");
      if (DECL_SAVED_TREE (t) && !dump_flag (di, TDF_SLIM, t))
	dump_child ("body", DECL_SAVED_TREE (t));
      break;

    case INTEGER_CST:
      if (TREE_INT_CST_HIGH (t))
	dump_int (di, "high", TREE_INT_CST_HIGH (t));
      dump_int (di, "low", TREE_INT_CST_LOW (t));
      break;

    case STRING_CST:
      fprintf (di->stream, "strg: %-7s ", TREE_STRING_POINTER (t));
      dump_int (di, "lngt", TREE_STRING_LENGTH (t));

int
gfc_interpret_derived (unsigned char *buffer, size_t buffer_size, gfc_expr *result)
{
  gfc_component *cmp;
  gfc_constructor *head = NULL, *tail = NULL;
  int ptr;
  tree type;

  /* The attributes of the derived type need to be bolted to the floor.  */
  result->expr_type = EXPR_STRUCTURE;

  type = gfc_typenode_for_spec (&result->ts);
  cmp = result->ts.u.derived->components;

  /* Run through the derived type components.  */
  for (;cmp; cmp = cmp->next)
    {
      if (head == NULL)
	head = tail = gfc_get_constructor ();
      else
	{
	  tail->next = gfc_get_constructor ();
	  tail = tail->next;
	}

      /* The constructor points to the component.  */
      tail->n.component = cmp;

      tail->expr = gfc_constant_result (cmp->ts.type, cmp->ts.kind,
					&result->where);
      tail->expr->ts = cmp->ts;

      /* Copy shape, if needed.  */
      if (cmp->as && cmp->as->rank)
	{
	  int n;

	  tail->expr->expr_type = EXPR_ARRAY;
	  tail->expr->rank = cmp->as->rank;

	  tail->expr->shape = gfc_get_shape (tail->expr->rank);
	  for (n = 0; n < tail->expr->rank; n++)
	     {
	       mpz_init_set_ui (tail->expr->shape[n], 1);
	       mpz_add (tail->expr->shape[n], tail->expr->shape[n],
			cmp->as->upper[n]->value.integer);
	       mpz_sub (tail->expr->shape[n], tail->expr->shape[n],
			cmp->as->lower[n]->value.integer);
	     }
	}

      /* Calculate the offset, which consists of the the FIELD_OFFSET in
	 bytes, which appears in multiples of DECL_OFFSET_ALIGN-bit-sized,
	 and additional bits of FIELD_BIT_OFFSET. The code assumes that all
	 sizes of the components are multiples of BITS_PER_UNIT,
	 i.e. there are, e.g., no bit fields.  */

      ptr = TREE_INT_CST_LOW (DECL_FIELD_BIT_OFFSET (cmp->backend_decl));
      gcc_assert (ptr % 8 == 0);
      ptr = ptr/8 + TREE_INT_CST_LOW (DECL_FIELD_OFFSET (cmp->backend_decl));

      gfc_target_interpret_expr (&buffer[ptr], buffer_size - ptr,
				 tail->expr);

      result->value.constructor = head;
    }
    
  return int_size_in_bytes (type);
}

void
expand_builtin_cilk_detach (tree exp)
{
  rtx_insn *insn;
  tree fptr = get_frame_arg (exp);

  if (fptr == NULL_TREE)
    return;

  tree parent = cilk_dot (fptr, CILK_TI_FRAME_PARENT, 0);
  tree worker = cilk_dot (fptr, CILK_TI_FRAME_WORKER, 0);
  tree tail = cilk_arrow (worker, CILK_TI_WORKER_TAIL, 1);

  rtx wreg = expand_expr (worker, NULL_RTX, Pmode, EXPAND_NORMAL);
  if (GET_CODE (wreg) != REG)
    wreg = copy_to_reg (wreg);
  rtx preg = expand_expr (parent, NULL_RTX, Pmode, EXPAND_NORMAL);

  /* TMP <- WORKER.TAIL
    *TMP <- PARENT
     TMP <- TMP + 1
     WORKER.TAIL <- TMP   */

  HOST_WIDE_INT worker_tail_offset =
    tree_to_shwi (DECL_FIELD_OFFSET (cilk_trees[CILK_TI_WORKER_TAIL])) +
    tree_to_shwi (DECL_FIELD_BIT_OFFSET (cilk_trees[CILK_TI_WORKER_TAIL])) /
    BITS_PER_UNIT;
  rtx tmem0 = gen_rtx_MEM (Pmode,
			   plus_constant (Pmode, wreg, worker_tail_offset));
  set_mem_attributes (tmem0, tail, 0);
  MEM_NOTRAP_P (tmem0) = 1;
  gcc_assert (MEM_VOLATILE_P (tmem0));
  rtx treg = copy_to_mode_reg (Pmode, tmem0);
  rtx tmem1 = gen_rtx_MEM (Pmode, treg);
  set_mem_attributes (tmem1, TREE_TYPE (TREE_TYPE (tail)), 0);
  MEM_NOTRAP_P (tmem1) = 1;
  emit_move_insn (tmem1, preg);
  emit_move_insn (treg, plus_constant (Pmode, treg, GET_MODE_SIZE (Pmode)));

  /* There is a release barrier (st8.rel, membar #StoreStore,
     sfence, lwsync, etc.) between the two stores.  On x86
     normal volatile stores have proper semantics; the sfence
     would only be needed for nontemporal stores (which we
     could generate using the storent optab, for no benefit
     in this case).

     The predicate may return false even for a REG if this is
     the limited release operation that only stores 0.  */
  enum insn_code icode = direct_optab_handler (sync_lock_release_optab, Pmode); 
  if (icode != CODE_FOR_nothing
      && insn_data[icode].operand[1].predicate (treg, Pmode)
      && (insn = GEN_FCN (icode) (tmem0, treg)) != NULL_RTX)
    emit_insn (insn);
  else
    emit_move_insn (tmem0, treg);

  /* The memory barrier inserted above should not prevent
     the load of flags from being moved before the stores,
     but in practice it does because it is implemented with
     unspec_volatile.  In-order RISC machines should
     explicitly load flags earlier.  */

  tree flags = cilk_dot (fptr, CILK_TI_FRAME_FLAGS, 0);
  expand_expr (build2 (MODIFY_EXPR, void_type_node, flags,
		       build2 (BIT_IOR_EXPR, TREE_TYPE (flags), flags,
			       build_int_cst (TREE_TYPE (flags),
					      CILK_FRAME_DETACHED))),
	       const0_rtx, VOIDmode, EXPAND_NORMAL);
}

static tree
get_init_field (segment_info *head, tree union_type, tree *field_init,
		record_layout_info rli)
{
  segment_info *s;
  HOST_WIDE_INT length = 0;
  HOST_WIDE_INT offset = 0;
  unsigned HOST_WIDE_INT known_align, desired_align;
  bool overlap = false;
  tree tmp, field;
  tree init;
  unsigned char *data, *chk;
  VEC(constructor_elt,gc) *v = NULL;

  tree type = unsigned_char_type_node;
  int i;

  /* Obtain the size of the union and check if there are any overlapping
     initializers.  */
  for (s = head; s; s = s->next)
    {
      HOST_WIDE_INT slen = s->offset + s->length;
      if (s->sym->value)
	{
	  if (s->offset < offset)
            overlap = true;
	  offset = slen;
	}
      length = length < slen ? slen : length;
    }

  if (!overlap)
    return NULL_TREE;

  /* Now absorb all the initializer data into a single vector,
     whilst checking for overlapping, unequal values.  */
  data = XCNEWVEC (unsigned char, (size_t)length);
  chk = XCNEWVEC (unsigned char, (size_t)length);

  /* TODO - change this when default initialization is implemented.  */
  memset (data, '\0', (size_t)length);
  memset (chk, '\0', (size_t)length);
  for (s = head; s; s = s->next)
    if (s->sym->value)
      gfc_merge_initializers (s->sym->ts, s->sym->value,
			      &data[s->offset],
			      &chk[s->offset],
			     (size_t)s->length);
  
  for (i = 0; i < length; i++)
    CONSTRUCTOR_APPEND_ELT (v, NULL, build_int_cst (type, data[i]));

  free (data);
  free (chk);

  /* Build a char[length] array to hold the initializers.  Much of what
     follows is borrowed from build_field, above.  */

  tmp = build_int_cst (gfc_array_index_type, length - 1);
  tmp = build_range_type (gfc_array_index_type,
			  gfc_index_zero_node, tmp);
  tmp = build_array_type (type, tmp);
  field = build_decl (gfc_current_locus.lb->location,
		      FIELD_DECL, NULL_TREE, tmp);

  known_align = BIGGEST_ALIGNMENT;

  desired_align = update_alignment_for_field (rli, field, known_align);
  if (desired_align > known_align)
    DECL_PACKED (field) = 1;

  DECL_FIELD_CONTEXT (field) = union_type;
  DECL_FIELD_OFFSET (field) = size_int (0);
  DECL_FIELD_BIT_OFFSET (field) = bitsize_zero_node;
  SET_DECL_OFFSET_ALIGN (field, known_align);

  rli->offset = size_binop (MAX_EXPR, rli->offset,
                            size_binop (PLUS_EXPR,
                                        DECL_FIELD_OFFSET (field),
                                        DECL_SIZE_UNIT (field)));

  init = build_constructor (TREE_TYPE (field), v);
  TREE_CONSTANT (init) = 1;

  *field_init = init;

  for (s = head; s; s = s->next)
    {
      if (s->sym->value == NULL)
	continue;

      gfc_free_expr (s->sym->value);
      s->sym->value = NULL;
    }

  return field;
}

static tree
compute_object_offset (const_tree expr, const_tree var)
{
  enum tree_code code = PLUS_EXPR;
  tree base, off, t;

  if (expr == var)
    return size_zero_node;

  switch (TREE_CODE (expr))
    {
    case COMPONENT_REF:
      base = compute_object_offset (TREE_OPERAND (expr, 0), var);
      if (base == error_mark_node)
	return base;

      t = TREE_OPERAND (expr, 1);
      off = size_binop (PLUS_EXPR, DECL_FIELD_OFFSET (t),
			size_int (tree_to_uhwi (DECL_FIELD_BIT_OFFSET (t))
				  / BITS_PER_UNIT));
      break;

    case REALPART_EXPR:
    CASE_CONVERT:
    case VIEW_CONVERT_EXPR:
    case NON_LVALUE_EXPR:
      return compute_object_offset (TREE_OPERAND (expr, 0), var);

    case IMAGPART_EXPR:
      base = compute_object_offset (TREE_OPERAND (expr, 0), var);
      if (base == error_mark_node)
	return base;

      off = TYPE_SIZE_UNIT (TREE_TYPE (expr));
      break;

    case ARRAY_REF:
      base = compute_object_offset (TREE_OPERAND (expr, 0), var);
      if (base == error_mark_node)
	return base;

      t = TREE_OPERAND (expr, 1);
      tree low_bound, unit_size;
      low_bound = array_ref_low_bound (CONST_CAST_TREE (expr));
      unit_size = array_ref_element_size (CONST_CAST_TREE (expr));
      if (! integer_zerop (low_bound))
	t = fold_build2 (MINUS_EXPR, TREE_TYPE (t), t, low_bound);
      if (TREE_CODE (t) == INTEGER_CST && tree_int_cst_sgn (t) < 0)
	{
	  code = MINUS_EXPR;
	  t = fold_build1 (NEGATE_EXPR, TREE_TYPE (t), t);
	}
      t = fold_convert (sizetype, t);
      off = size_binop (MULT_EXPR, unit_size, t);
      break;

    case MEM_REF:
      gcc_assert (TREE_CODE (TREE_OPERAND (expr, 0)) == ADDR_EXPR);
      return wide_int_to_tree (sizetype, mem_ref_offset (expr));

    default:
      return error_mark_node;
    }

  return size_binop (code, base, off);
}