https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70449
--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
I think the problem is that when we see
enum E { a = f<0> () };
we try to instantiate_decl "f", but at that time the "return 0;" wasn't seen
yet, so check_return_expr wasn't yet called thus current_function_returns_value
is not set when instantiating f.
