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Rollup merge of #122601 - joboet:ptr_replace, r=workingjubilee

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Optimize `ptr::replace`

#83022 optimized `mem::replace` to reduce the number of `memcpy`s. `ptr::replace`, which is [documented to behave just like `mem::replace`](https://doc.rust-lang.org/nightly/std/ptr/fn.replace.html), was not optimized however, leading to [worse code](https://godbolt.org/z/T3hdEEdfe) and missed optimizations. This PR simply forwards `ptr::replace` to `mem::replace` to take advantage of the better implementation.
This commit is contained in:
León Orell Valerian Liehr 2024-03-16 23:28:49 +01:00 committed by GitHub
commit de0c2a4723
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1 changed files with 2 additions and 3 deletions
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library/core/src/ptr/mod.rs
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@ -1114,7 +1114,7 @@ const unsafe fn swap_nonoverlapping_simple_untyped<T>(x: *mut T, y: *mut T, coun
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_replace", issue = "83164")]
#[rustc_diagnostic_item = "ptr_replace"]
pub const unsafe fn replace<T>(dst: *mut T, mut src: T) -> T {
pub const unsafe fn replace<T>(dst: *mut T, src: T) -> T {
// SAFETY: the caller must guarantee that `dst` is valid to be
// cast to a mutable reference (valid for writes, aligned, initialized),
// and cannot overlap `src` since `dst` must point to a distinct
@ -1128,9 +1128,8 @@ pub const unsafe fn replace<T>(dst: *mut T, mut src: T) -> T {
align: usize = align_of::<T>(),
) => is_aligned_and_not_null(addr, align)
);
mem::swap(&mut *dst, &mut src); // cannot overlap
mem::replace(&mut *dst, src)
}
src
}
/// Reads the value from `src` without moving it. This leaves the