Polymorphize `array::IntoIter`'s iterator impl
Today we emit all the iterator methods for every different array width. That's wasteful since the actual array length never even comes into it -- the indices used are from the separate `alive: IndexRange` field, not even the `N` const param.
This PR switches things so that an `array::IntoIter<T, N>` stores a `PolymorphicIter<[MaybeUninit<T>; N]>`, which we *unsize* to `PolymorphicIter<[MaybeUninit<T>]>` and call methods on that non-`Sized` type for all the iterator methods.
That also necessarily makes the layout consistent between the different lengths of arrays, because of the unsizing. Compare that to today <https://rust.godbolt.org/z/Prb4xMPrb>, where different widths can't even be deduped because the offset to the indices is different for different array widths.
These gates are unnecessary now that unit tests for `core` are in a
separate package, `coretests`, instead of in the same files as the
source code. They previously prevented the two `core` versions from
conflicting with each other.
remove pointless allowed_through_unstable_modules on TryFromSliceError
This got added in https://github.com/rust-lang/rust/pull/132482 but the PR does not explain why. `@lukas-code` do you still remember? Also Cc `@Noratrieb` as reviewer of that PR.
If I understand the issue description correctly, all paths under which this type is exported are stable now: `core::array::TryFromSliceError` and `std::array::TryFromSliceError`. If that is the case, we shouldn't have the attribute; it's a terrible hack that should only be used when needed to maintain backward compatibility. Getting some historic information right is IMO *not* sufficient justification to risk accidentally exposing this type via more unstable paths today or in the future.
Mark `<[T; N]>::as_mut_slice` with the `const` specifier.
Tracking issue: #133333
`<[T; N]>::as_mut_slice` can have the `const` specifier without any changes to the function body.
get rid of a whole bunch of unnecessary rustc_const_unstable attributes
In general, when a `const fn` is still unstable, it doesn't need a `#[rustc_const_unstable]` attribute. The only exception is functions that internally use things that can't be used in stable const fn yet.
So this gets rid of a whole bunch of `#[rustc_const_unstable]` in libcore.
Added `#[inline]` to the `drop` method in the `Guard` implementation to ensure that the method is removed by the compiler at optimization level `opt-level=s` for `Copy` types. This change aims to align the method's behavior with optimization expectations and ensure it does not affect performance.
This is possible now that inline const blocks are stable; the idea was
even mentioned as an alternative when `uninit_array()` was added:
<https://github.com/rust-lang/rust/pull/65580#issuecomment-544200681>
> if it’s stabilized soon enough maybe it’s not worth having a
> standard library method that will be replaceable with
> `let buffer = [MaybeUninit::<T>::uninit(); $N];`
Const array repetition and inline const blocks are now stable (in the
next release), so that circumstance has come to pass, and we no longer
have reason to want `uninit_array()` other than convenience. Therefore,
let’s evaluate the inconvenience by not using `uninit_array()` in
the standard library, before potentially deleting it entirely.
People keep making fun of this signature for being so gnarly.
Associated type bounds lend it a much simpler scribbling.
ChangeOutputType can also come along for the ride.
stabilise array methods
Closes#76118
Stabilises the remaining array methods
FCP is yet to be carried out for this
There wasn't a clear consensus on the naming, but all the other alternatives had some flaws as discussed in the tracking issue and there was a silence on this issue for a year
Stabilize `slice_first_last_chunk`
This PR does a few different things based around stabilizing `slice_first_last_chunk`. They are split up so this PR can be by-commit reviewed, I can move parts to a separate PR if desired.
This feature provides a very elegant API to extract arrays from either end of a slice, such as for parsing integers from binary data.
## Stabilize `slice_first_last_chunk`
ACP: https://github.com/rust-lang/libs-team/issues/69
Implementation: https://github.com/rust-lang/rust/issues/90091
Tracking issue: https://github.com/rust-lang/rust/issues/111774
This stabilizes the functionality from https://github.com/rust-lang/rust/issues/111774:
```rust
impl [T] {
pub const fn first_chunk<const N: usize>(&self) -> Option<&[T; N]>;
pub fn first_chunk_mut<const N: usize>(&mut self) -> Option<&mut [T; N]>;
pub const fn last_chunk<const N: usize>(&self) -> Option<&[T; N]>;
pub fn last_chunk_mut<const N: usize>(&mut self) -> Option<&mut [T; N]>;
pub const fn split_first_chunk<const N: usize>(&self) -> Option<(&[T; N], &[T])>;
pub fn split_first_chunk_mut<const N: usize>(&mut self) -> Option<(&mut [T; N], &mut [T])>;
pub const fn split_last_chunk<const N: usize>(&self) -> Option<(&[T], &[T; N])>;
pub fn split_last_chunk_mut<const N: usize>(&mut self) -> Option<(&mut [T], &mut [T; N])>;
}
```
Const stabilization is included for all non-mut methods, which are blocked on `const_mut_refs`. This change includes marking the trivial function `slice_split_at_unchecked` const-stable for internal use (but not fully stable).
## Remove `split_array` slice methods
Tracking issue: https://github.com/rust-lang/rust/issues/90091
Implementation: https://github.com/rust-lang/rust/pull/83233#pullrequestreview-780315524
This PR also removes the following unstable methods from the `split_array` feature, https://github.com/rust-lang/rust/issues/90091:
```rust
impl<T> [T] {
pub fn split_array_ref<const N: usize>(&self) -> (&[T; N], &[T]);
pub fn split_array_mut<const N: usize>(&mut self) -> (&mut [T; N], &mut [T]);
pub fn rsplit_array_ref<const N: usize>(&self) -> (&[T], &[T; N]);
pub fn rsplit_array_mut<const N: usize>(&mut self) -> (&mut [T], &mut [T; N]);
}
```
This is done because discussion at #90091 and its implementation PR indicate a strong preference for nonpanicking APIs that return `Option`. The only difference between functions under the `split_array` and `slice_first_last_chunk` features is `Option` vs. panic, so remove the duplicates as part of this stabilization.
This does not affect the array methods from `split_array`. We will want to revisit these once `generic_const_exprs` is further along.
## Reverse order of return tuple for `split_last_chunk{,_mut}`
An unresolved question for #111774 is whether to return `(preceding_slice, last_chunk)` (`(&[T], &[T; N])`) or the reverse (`(&[T; N], &[T])`), from `split_last_chunk` and `split_last_chunk_mut`. It is currently implemented as `(last_chunk, preceding_slice)` which matches `split_last -> (&T, &[T])`. The first commit changes these to `(&[T], &[T; N])` for these reasons:
- More consistent with other splitting methods that return multiple values: `str::rsplit_once`, `slice::split_at{,_mut}`, `slice::align_to` all return tuples with the items in order
- More intuitive (arguably opinion, but it is consistent with other language elements like pattern matching `let [a, b, rest @ ..] ...`
- If we ever added a varidic way to obtain multiple chunks, it would likely return something in order: `.split_many_last::<(2, 4)>() -> (&[T], &[T; 2], &[T; 4])`
- It is the ordering used in the `rsplit_array` methods
I think the inconsistency with `split_last` could be acceptable in this case, since for `split_last` the scalar `&T` doesn't have any internal order to maintain with the other items.
## Unresolved questions
Do we want to reserve the same names on `[u8; N]` to avoid inference confusion? https://github.com/rust-lang/rust/pull/117561#issuecomment-1793388647
---
`slice_first_last_chunk` has only been around since early 2023, but `split_array` has been around since 2021.
`@rustbot` label -T-libs +T-libs-api -T-libs +needs-fcp
cc `@rust-lang/wg-const-eval,` `@scottmcm` who raised this topic, `@clarfonthey` implementer of `slice_first_last_chunk` `@jethrogb` implementer of `split_array`
Zulip discussion: https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/Stabilizing.20array-from-slice.20*something*.3FFixes: #111774
detects redundant imports that can be eliminated.
for #117772 :
In order to facilitate review and modification, split the checking code and
removing redundant imports code into two PR.
The functionality of these methods from `split_array` has been absorbed by the
`slice_first_last_chunk` feature. This only affects the methods on slices,
not those with the same name that are implemented on array types.
Also adjusts testing to reflect this change.
optimize zipping over array iterators
Fixes#115339 (somewhat)
the new assembly:
```asm
zip_arrays:
.cfi_startproc
vmovups (%rdx), %ymm0
leaq 32(%rsi), %rcx
vxorps %xmm1, %xmm1, %xmm1
vmovups %xmm1, -24(%rsp)
movq $0, -8(%rsp)
movq %rsi, -88(%rsp)
movq %rdi, %rax
movq %rcx, -80(%rsp)
vmovups %ymm0, -72(%rsp)
movq $0, -40(%rsp)
movq $32, -32(%rsp)
movq -24(%rsp), %rcx
vmovups (%rsi,%rcx), %ymm0
vorps -72(%rsp,%rcx), %ymm0, %ymm0
vmovups %ymm0, (%rsi,%rcx)
vmovups (%rsi), %ymm0
vmovups %ymm0, (%rdi)
vzeroupper
retq
```
This is still longer than the slice version given in the issue but at least it eliminates the terrible `vpextrb`/`orb` chain. I guess this is due to excessive memcpys again (haven't looked at the llvmir)?
The `TrustedLen` specialization is a drive-by change since I had to do something for the default impl anyway to be able to specialize the `TrustedRandomAccessNoCoerce` impl.
