[Bug c++/88815] [9 Regression] is_constexpr (based on narrowing conversion and expression SFINAE) broken

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88815

--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(My proof-of-concept patch to deal with narrowing in decltype fixed this PR as
a result.)