Tracking issue for hint::spin_loop (renamed sync::atomic::spin_loop_hint)

[clarfonthey]

Now that we have at least one thing in std::hint it makes sense to move this to std::hint::spin_loop.

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EDIT (@KodrAus)

Before stabilisation:

• Decide on new function name (hint::spin_loop or spin_loop_hint)

Stabilisation/deprecation:

• Stabilise renamed_spin_loop feature [Stabilize hint::spin_loop #76097]
• Deprecate the sync::atomic::spin_loop_hint function

[gnzlbg]

spin_loop currently invokes undefined behavior on x86 and x86_64 targets without SSE2. One of those targets is tier-1: i686-apple-darwin.

[hanna-kruppe]

Are you sure? The target spec for that sets the cpu to Yonah, which has SSE2.

[gnzlbg]

@rkruppe if that was fixed we should close: #53423

[gnzlbg]

@rkruppe indeed, that's fixed, I've closed that issue.

[clarfonthey]

Note that this isn't a tracking issue for the function itself; it's already stable and any bugs/qualms are reported separately. This is just for the renaming of it.

[zopsicle]

If this routine is moved to std::hint then the documentation of std::hint should be updated as well. It currently reads:

Hints to compiler that affects how code should be emitted or optimized.

Pause instruction is a hint to the CPU, not to the compiler.