Tracking Issue for `clflushopt_target_feature`

[jlpetz]

This is a tracking issue for the clflushopt x86 target feature, used to gate the _mm_clflushopt intrinsic (#![feature(clflushopt_target_feature)]).

Requested in rust-lang/stdarch#1456. CLFLUSHOPT is a standalone x86 CPUID feature (Intel Skylake+ / AMD Excavator+, ~2015) for weakly-ordered cache-line flushing. Today stdarch exposes only the SSE2 _mm_clflush; there is no way to emit clflushopt from an intrinsic.

Steps

• Add the clflushopt target feature to the compiler (this issue).
• Add the _mm_clflushopt intrinsic in stdarch (see rust-lang/stdarch#1456).
• Stabilization PR.

[jlpetz]

Compiler PR opened: #157098 (adds the clflushopt target feature).

The stdarch intrinsic (_mm_clflushopt, rust-lang/stdarch#1456) is the follow-up and is blocked on #157098 merging + syncing into stdarch's pinned toolchain.