Support for experimental SIMD types?

[orlp]

Could the types__m128bh, __m256bh, __m512, __m512bh, __m512d, __m512i be added to bytemuck under an experimental feature flag (or multiple, one for AVX-512 and one for the bh types)?

[Lokathor]

I suppose. I'm not familiar with those but if they're basically normalish simd types that sounds fine.

[reinerp]

I'd also request the portable_simd types when compiling under nightly: impl Pod for std::simd::Simd<T, LANES> where T: Pod. Something for std::simd::Mask too, but the requirements there are more subtle, and I'm not yet confident of what they should be.

[Lokathor]

I can agree with Simd<T> where T: Pod, but Mask is kinda dodgy, yeah.

Let's add each of these under a bytemuck cargo flag named after the rustc feature that lets you use them. So, portable_simd, and then whatever the avx-512 stuff is called.

Someone who isn't me do the PR, then I'll approve the PR and do a patch release of the provisional support.