@@ -7909,7 +7909,7 @@ build_over_call (struct z_candidate *cand, int flags, tsubst_flags_t complain)
arg2 = TYPE_SIZE_UNIT (as_base);
arg0 = cp_build_addr_expr (to, complain);
- array_type = build_array_type (char_type_node,
+ array_type = build_array_type (unsigned_char_type_node,
build_index_type
(size_binop (MINUS_EXPR,
arg2, size_int (1))));
@@ -3206,6 +3206,26 @@ var_in_maybe_constexpr_fn (tree t)
return var_in_constexpr_fn (t);
}
+/* We're assigning INIT to TARGET. In do_build_copy_constructor and
+ build_over_call we implement trivial copy of a class with tail padding using
+ assignment of character arrays, which is valid in normal code, but not in
+ constexpr evaluation. We don't need to worry about clobbering tail padding
+ in constexpr evaluation, so strip the type punning. */
+
+static void
+maybe_simplify_trivial_copy (tree &target, tree &init)
+{
+ if (TREE_CODE (target) == MEM_REF
+ && TREE_CODE (init) == MEM_REF
+ && TREE_TYPE (target) == TREE_TYPE (init)
+ && TREE_CODE (TREE_TYPE (target)) == ARRAY_TYPE
+ && TREE_TYPE (TREE_TYPE (target)) == unsigned_char_type_node)
+ {
+ target = build_fold_indirect_ref (TREE_OPERAND (target, 0));
+ init = build_fold_indirect_ref (TREE_OPERAND (init, 0));
+ }
+}
+
/* Evaluate an INIT_EXPR or MODIFY_EXPR. */
static tree
@@ -3222,6 +3242,9 @@ cxx_eval_store_expression (const constexpr_ctx *ctx, tree t,
/* First we figure out where we're storing to. */
tree target = TREE_OPERAND (t, 0);
+
+ maybe_simplify_trivial_copy (target, init);
+
tree type = TREE_TYPE (target);
target = cxx_eval_constant_expression (ctx, target,
true,
new file mode 100644
@@ -0,0 +1,14 @@
+// PR c++/77945
+// { dg-do compile { target c++11 } }
+
+struct T
+{
+ int x = 0;
+ bool y = 0;
+ constexpr T() {}
+};
+
+int main()
+{
+ constexpr T t = (T{} = T{});
+}