Support Intel IceLake ISAs through target_feature

[elalfer]

Working on CPUID based dispatch for Vector AES code for https://crates.io/crates/crypto_pimitives library.

Based on https://doc.rust-lang.org/reference/attributes/codegen.html#x86-or-x86_64 Rust doesn't support any AVX512 targets.

[workingjubilee]

The reference is outdated only concerned with stable here, there is partial AVX512 support in core::arch and the compiler on nightly, as can be seen here: https://doc.rust-lang.org/core/arch/x86_64/index.html

As there is quite a lot to support it has not been finished (nor stabilized) however: rust-lang/stdarch#310
So I believe it does not yet include the specifics of the AVX512 VAES extension you want, either.

[DevJPM]

I have looked into implementing this (for nightly at least over on rust-lang/stdarch) however it appears that support is blocked by the compiler not being willing to accept the VAES (and vaguely related VPCLMULQDQ) feature flags for enabling the relevant LLVM intrinsics. And I would be willing to make a PR for the compiler to add that flag, but I'm not sure if there's more to it than "just" adding the "vaes" string here and here. Though the feature seems to be supported in std::detect already though it is named avx512vaes there.

[workingjubilee]

In #78361, a large amount of support for AVX512 features was added to the compiler, including all the ones (afaict) that IceLake included, resolving this issue for the Rust compiler, and many intrinsics have been added to std::arch since.