Changed altivec.rs to new intrinsic declaration

[BLANKatGITHUB]

No description provided.

[rustbot]

r? @Amanieu

rustbot has assigned @Amanieu.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[eduardosm]

It think you can call crate::intrinsics::copy_nonoverlapping directly to avoid declaring the intrinsic.

[BLANKatGITHUB]

Well in rust-lang/rust#132735 the pr said to migrate it to the same style like in compiler and standard library , I will change it if its not ok

[eduardosm]

The goal is to avoid having an extern "rust-intrinsic" block, which can also be achieved by not needing to declare the intrinsic.

[folkertdev]

The code does note that the intrinsic declaration is there to

// Workaround ptr::copy_nonoverlapping not being inlined

there are some issues around target features preventing inlining, so it may be related to that. That problem also may have been fixed in the meantime (by more aggressively inlining on the rust side), but it's something to check for.

[folkertdev]

Looks like that is no longer a problem (in this case) https://godbolt.org/z/vYzxKMdeo, and both versions generate the same assembly. So just using core::ptr::copy_nonoverlapping should be fine. (I don't even see a reason to prefer the intrinsic from core::intrinsics, but maybe there is one?)

[RalfJung]

Note that the rustc_intrinsic_must_be_overridden attribute is being removed, please do not use it any more. The new new way to declare an intrinsic is:

#[rustc_intrinsic]
unsafe fn unreachable() -> !;

[RalfJung]

We used to do something similar in core::ptr where we sometimes called the intrinsic directly to avoid the extra debug checks that exist in core::intrinsics::copy_nonoverlapping. But we no longer seem to do that so I agree we shouldn't have to do it here either -- just call core::ptr::copy_nonoverlapping.

[RalfJung]

You can then also remove this line; stdarch no longer should declare any intrinsics itself:

https://github.com/rust-lang/stdarch//blob/f32eeffb47d783a703017851b1cf6bdecf1601c0/crates/core_arch/src/lib.rs#L16

[BLANKatGITHUB]

You can then also remove this line; stdarch no longer should declare any intrinsics itself:

https://github.com/rust-lang/stdarch//blob/f32eeffb47d783a703017851b1cf6bdecf1601c0/crates/core_arch/src/lib.rs#L16

wont it potentially break some of the functionality?

[folkertdev]

No, you've removed all usages of rust-intrinsic, so this feature is no longer needed (and in fact we'd want adding a new rustc-intrinsic to fail). Also CI would catch it if something did break, so there is no risk.

[RalfJung]

This crate has a sumewhat funny import structure due to how it is integrated with libcore. Everything else uses crate::ptr, not core::ptr, so just to be sure let's also use that here.

[RalfJung]

Suggested change

	core::ptr::copy_nonoverlapping(
	crate::ptr::copy_nonoverlapping(

[RalfJung]

Suggested change

	core::ptr::copy_nonoverlapping(
	crate::ptr::copy_nonoverlapping(

[RalfJung]

LGTM, thanks!
(But I can't land changes in this repo.)