https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65327
--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> --- Presumably started with r166013. Note that in constexpr volatile int a = 42; constexpr int b = a; the initialization of b should be rejected, but it is not. This is a related problem though, my patch doesn't change it.