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Auto merge of #94342 - ibraheemdev:swap-regression, r=Dylan-DPC

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Revert implementation of `slice::swap`

Due to the perf regressions noticed here, possible due to inlining? https://github.com/rust-lang/rust/pull/88540#issuecomment-944344343

r? `@kennytm`
This commit is contained in:
bors 2022-02-25 23:47:00 +00:00
commit d973b358c6
1 changed files with 11 additions and 5 deletions
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16
library/core/src/slice/mod.rs
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@ -587,11 +587,17 @@ impl<T> [T] {
#[inline]
#[track_caller]
pub const fn swap(&mut self, a: usize, b: usize) {
let _ = &self[a];
let _ = &self[b];
// SAFETY: we just checked that both `a` and `b` are in bounds
unsafe { self.swap_unchecked(a, b) }
// FIXME: use swap_unchecked here (https://github.com/rust-lang/rust/pull/88540#issuecomment-944344343)
// Can't take two mutable loans from one vector, so instead use raw pointers.
let pa = ptr::addr_of_mut!(self[a]);
let pb = ptr::addr_of_mut!(self[b]);
// SAFETY: `pa` and `pb` have been created from safe mutable references and refer
// to elements in the slice and therefore are guaranteed to be valid and aligned.
// Note that accessing the elements behind `a` and `b` is checked and will
// panic when out of bounds.
unsafe {
ptr::swap(pa, pb);
}
}
/// Swaps two elements in the slice, without doing bounds checking.