template <class>
_INLINE_VAR constexpr bool test = false;

template <>
_INLINE_VAR constexpr bool test<char> = true;

in two different cpp files gives fatal error LNK1169: one or more multiply defined symbols found with clang-cl and C++14.

Fortunately, there is no code like this in the STL.

Ordinary constexpr variables or constexpr templates variables without explicit specialization work fine.

Do we need remove_cv_t<_Ty> like there?:

The type traits for the "primary type categories" like is_integral_v are required to ignore top-level cv-qualifiers (WG21-N4910 [meta.unary.cat]/2). Our internal type traits don't always remove_cv_t, but we need to keep this in mind whenever we're using them, as this is a potential source of bugs.

(_Is_any_of_v itself should not remove_cv_t as it is a generalized is_same which must care about cv-qualifiers; it's things like the "is it safe to activate the memmeow() optimization" helpers that sometimes expect usage to have already removed cv.)

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

Thanks for this major performance improvement! 🚀 🐇 🏎️