[Bug c++/80841] Fails to match template specialization with polymorphic non-type template argument

[cipherjason at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80841

--- Comment #2 from Jason Bell <cipherjason at hotmail dot com> ---
Thanks that's a good reduced example.  I've changed it slightly so it works
with constexpr input.

//#########################################
template <class T, T X>
struct A {};

template <class T, class U>
struct B {};

template <class T, T X>
struct B<T, A<T, X>> 
{
  using result = T;
};

static constexpr double input = 1.;

int main() {
  using result1 = typename B<int, A<int, 15>>::result; // OK
  using result2 = typename B<const double*, A<const double*, &input>>::result;
// OK
  using result3 = typename B<const double&, A<const double&, input>>::result;
// Error
}
//#########################################

I've noticed that it works in Clang if using --std=c++14 but not with
--std=c++1z (same as my previous example).