New zeroed slice

[amosonn]

Add to #63291 the methods

impl<T>Box<[T]>{pubfnnew_zeroed_slice(len:usize) -> Box<[MaybeUninit<T>]>{…}}impl<T>Rc<[T]>{pubfnnew_zeroed_slice(len:usize) -> Rc<[MaybeUninit<T>]>{…}}impl<T>Arc<[T]>{pubfnnew_zeroed_slice(len:usize) -> Arc<[MaybeUninit<T>]>{…}}

as suggested in #63291 (comment) .

Also optimize {Rc, Arc}::new_zeroed to use alloc_zeroed, otherwise they are no more efficient than using new_uninit and zeroing the memory manually (which was the original implementation).

[rust-highfive]

r? @sfackler

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[amosonn]

r? @SimonSapin

[bors]

@amosonn: 🔑 Insufficient privileges: not in try users

[bors]

@amosonn: 🔑 Insufficient privileges: not in try users

[bors]

☔ The latest upstream changes (presumably #75174) made this pull request unmergeable. Please resolve the merge conflicts.

[Dylan-DPC-zz]

r? @Amanieu

[Amanieu]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion

[bors]

⌛ Trying commit ab204c5 with merge c7bc9915d37800e60ddf1d2cc573758c724395c3...

[Amanieu]

@bors try

[bors]

⌛ Trying commit 5aba816 with merge f3a9871a4972d9c4fe07f70e3e5aa63d6bdb6577...

[bors]

☀️ Try build successful - checks-actions, checks-azure
Build commit: f3a9871a4972d9c4fe07f70e3e5aa63d6bdb6577 (f3a9871a4972d9c4fe07f70e3e5aa63d6bdb6577)

[rust-timer]

Queued f3a9871a4972d9c4fe07f70e3e5aa63d6bdb6577 with parent de521cb, future comparison URL.

[rust-timer]

Finished benchmarking try commit (f3a9871a4972d9c4fe07f70e3e5aa63d6bdb6577): comparison url.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. Please note that if the perf results are neutral, you should likely undo the rollup=never given below by specifying rollup- to bors.

Importantly, though, if the results of this run are non-neutral do not roll this PR up -- it will mask other regressions or improvements in the roll up.

@bors rollup=never

[Amanieu]

@bors r+ rollup-

[bors]

📌 Commit 5aba816 has been approved by Amanieu

[bors]

⌛ Testing commit 5aba816 with merge 663d2f5...

[bors]

☀️ Test successful - checks-actions, checks-azure
Approved by: Amanieu
Pushing 663d2f5 to master...