Missing implementation of xsimd::kernel::detail::interleave for AVX2

[ni-eddiemond]

The function xsimd::kernel::detail::interleave does not seem to be implemented for AVX2. It is however present in the SSE4.1 header. It would be great if the AVX2 header would not depend on the SSE4.1 header to be included beforehand but to be self-sufficient instead.
I get a compilation error because of this. I'm using with MSVC 17.12.2

xsimd/include/xsimd/arch/xsimd_avx2.hpp

Line 744 in 0252ae7

constexpr int imask = detail::interleave(mask);

[serge-sans-paille]

Can you provide a reproducer ? xsimd is available on godbolt ;-)

[ni-eddiemond]

Unfortunately not because godbolt says 'Please note that Windows-based compilers currently do not support libraries. '

But as you can see in the xsimd_avx2 header, there is no interleave function defined in its detail namespace and there is no #include statement that would pull in a definition from somewhere else. So it's a conceptual issue.

[serge-sans-paille]

ack. avx2 implementation depends on avx for some parts, which itself depends on sse4 for some parts (basically for fallbacks). The dependency is implicit (and not enforced, but it basically should) through https://github.com/xtensor-stack/xsimd/blob/0252ae756f660c00ffaba4af67bd7d32e1b0a72c/include/xsimd/arch/xsimd_isa.hpp

Should we just error when this is not respected?

[ni-eddiemond]

Creating an explicit error (maybe a static_assert) is probably the best and easiest solution that can give users a hint at what's going wrong. It would have saved us some time knowing about that implicit dependency.