Removing AVX-512 code from the headers.

[lemire]

This is an attempt at fixing our illegal-instruction issue with the recent versions of Visual Studio.

We think it is a bug in Visual Studio whereas if a function might use AVX-512 in one code path, then all code paths get to use AVX-512 instructions... This means that routines such as...

if(avx512_is_supported) {
// run AVX-512 code
} else {
// run other code
}

are broken...

See RoaringBitmap/croaring-rs#128

cc @Dr-Emann

[lemire]

Ok. I am going to try to disable AVX-512 under visual studio.

[Dr-Emann]

I still don't think that will help: in this godbolt, we use only avx2 intrinsics, and configure the compiler with /arch:AVX2. There are no avx512 intrinsics in other code paths, there are no avx512 intrinsics at all, but the compiler outputs a vpxord instruction, which is AVX512 only. The bug sure seems like it's:

If AVX2 instructions are used, the compiler is incorrectly assuming that AVX512 is also allowed, and sometimes optimizations produce AVX512-only instructions.

I really believe the only solution is either disable AVX2 with this specific compiler version, or fiddle around with the code and inspect the assembly output, and see if we can find an incantation that accidentally avoids any optimization attempts the compiler thinks it can use avx512 for.

[lemire]

Closing.