Stabilize LoongArch64 SIMD Intrinsics

[heiher]

Tracking issue: rust-lang/rust#162508

LoongArch64 SIMD intrinsics are already used by rustc itself and by a number of downstream projects. Experience from these real-world uses indicates that the API is ready for stabilization. Stabilizing the intrinsics would remove the nightly requirement for applications that currently depend on them.

API surface

• core::arch::loongarch64::lsx_*
• core::arch::loongarch64::lasx_*

Note for subtree update

Remove this line: https://github.com/rust-lang/rust/blob/1edd55dcfcd573872c727fa3e086369a71661ee0/compiler/rustc_span/src/lib.rs#L20

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[tgross35]

What's the reason for changing the feature name?

View changes since the review

[heiher]

What's the reason for changing the feature name?

There are also some unstable APIs gated by stdarch_loongarch. Having both stable and unstable APIs gated by the same feature name causes the following error:

error[E0711]: feature `stdarch_loongarch` is declared stable, but was previously declared unstable

Also, putting the SIMD intrinsics under stdarch_loongarch_simd makes the categorization more explicit, similar to stdarch_loongarch_crc.

[tgross35]

Note that this stabilizes more cases of rustc_legacy_const_generics, which was discussed at rust-lang/rust#149654. Cc @rust-lang/lang

Nominating since that's probably worth clarifying, and also this is a lot of surface area with potential sharp edges.

@rustbot label +I-libs-nominated

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[heiher]

Note that this stabilizes more cases of rustc_legacy_const_generics, which was discussed at rust-lang/rust#149654.

Thanks for pointing this out. As far as I know, no projects currently depend on the LoongArch SIMD API signatures using the rustc_legacy_const_generics form, so there are no legacy compatibility concerns here. If adding new instances of rustc_legacy_const_generics is not desirable, we can simply remove it.

[heiher]

rustc_legacy_const_generics has been removed from LoongArch64 SIMD in v2.