https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63707
--- Comment #13 from Jakub Jelinek <jakub at gcc dot gnu.org> --- At least for #c5 the important difference between that testcase and // ~Child (); which is accepted is I think since r0-113052-ge2df21bfc6c81b4bc410a42002c8427454ffa628 in the cp/init.c (perform_member_init) code: 888 /* A FIELD_DECL doesn't really have a suitable lifetime, but 889 make_temporary_var_for_ref_to_temp will treat it as automatic and 890 set_up_extended_ref_temp wants to use the decl in a warning. */ 891 init = extend_ref_init_temps (member, init, &cleanups); 892 if (TREE_CODE (type) == ARRAY_TYPE 893 && TYPE_HAS_NONTRIVIAL_DESTRUCTOR (TREE_TYPE (type))) 894 init = build_vec_init_expr (type, init, tf_warning_or_error); If it has trivial destructor, nothing calls build_vec_init_expr and the copy ctor isn't needed, but when it is called, it is needed. I think in this case extend_ref_init_temps doesn't do anything at all, so it is unclear if build_vec_init_expr is needed too or not.
