It would be simpler to use the portable intrinsics from github.com/google/highway (disclosure: I am the main author). You include a header, and use the same functions on all platforms; the library provides wrapper functions which boil down to the platform's intrinsics.

Well, there is SIMD proposal for C++23 with kind-of-reference implementation. But I don't know how well it works for AVX0512

From what I have seen, this is unfortunately not very useful: it mainly only includes operations that the compiler is often able to autovectorize anyway (simple arithmetic). Support for anything more interesting such as swizzles seems nonexistent. Also, last I checked, this was only available on GCC 11+; has that changed?

I think proposed Vc lib is tested under clang as well.

Here is my source: https://github.com/VcDevel/std-simd

Ah, but this repo mentions that the GCC 11 implementation apparently also works with clang: https://github.com/VcDevel/Vc. Thanks!