+/* Build the result of __builtin_offsetof. EXPR is a nested sequence of
+ component references, with an INDIRECT_REF at the bottom; much like
+ the traditional rendering of offsetof as a macro. Returns the folded
+ and properly cast result. */
+
+static tree
+fold_offsetof_1 (tree expr)
+{
+ enum tree_code code = PLUS_EXPR;
+ tree base, off, t;
+
+ switch (TREE_CODE (expr))
+ {
+ case ERROR_MARK:
+ return expr;
+
+ case INDIRECT_REF:
+ return size_zero_node;
+
+ case COMPONENT_REF:
+ base = fold_offsetof_1 (TREE_OPERAND (expr, 0));
+ if (base == error_mark_node)
+ return base;
+
+ t = TREE_OPERAND (expr, 1);
+ if (DECL_C_BIT_FIELD (t))
+ {
+ error ("attempt to take address of bit-field structure "
+ "member `%s'", IDENTIFIER_POINTER (DECL_NAME (t)));
+ return error_mark_node;
+ }
+ 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 ARRAY_REF:
+ base = fold_offsetof_1 (TREE_OPERAND (expr, 0));
+ 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:
+ gcc_unreachable ();
+ }
+
+ return size_binop (code, base, off);
+}
+
+tree
+fold_offsetof (tree expr)
+{
+ /* Convert back from the internal sizetype to size_t. */
+ return convert (size_type_node, fold_offsetof_1 (expr));
+}
+