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core: rearrange ptr::swap_nonoverlapping_one's cases (no functional changes).

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Eduard-Mihai Burtescu 2021-03-11 14:39:37 +02:00
parent 5b0ab79116
commit 3c3d3ddde9
1 changed files with 13 additions and 11 deletions
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24
library/core/src/ptr/mod.rs
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@ -473,19 +473,21 @@ pub const fn slice_from_raw_parts_mut<T>(data: *mut T, len: usize) -> *mut [T] {
#[inline]
#[rustc_const_unstable(feature = "const_swap", issue = "83163")]
pub(crate) const unsafe fn swap_nonoverlapping_one<T>(x: *mut T, y: *mut T) {
// For types smaller than the block optimization below,
// just swap directly to avoid pessimizing codegen.
if mem::size_of::<T>() < 32 {
// SAFETY: the caller must guarantee that `x` and `y` are valid
// for writes, properly aligned, and non-overlapping.
unsafe {
let z = read(x);
copy_nonoverlapping(y, x, 1);
write(y, z);
}
} else {
// Only apply the block optimization in `swap_nonoverlapping_bytes` for types
// at least as large as the block size, to avoid pessimizing codegen.
if mem::size_of::<T>() >= 32 {
// SAFETY: the caller must uphold the safety contract for `swap_nonoverlapping`.
unsafe { swap_nonoverlapping(x, y, 1) };
return;
}
// Direct swapping, for the cases not going through the block optimization.
// SAFETY: the caller must guarantee that `x` and `y` are valid
// for writes, properly aligned, and non-overlapping.
unsafe {
let z = read(x);
copy_nonoverlapping(y, x, 1);
write(y, z);
}
}