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core: disable ptr::swap_nonoverlapping_one's block optimization on SPIR-V. #83019

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Merged
merged 2 commits into from
Apr 5, 2021
Merged

core: disable ptr::swap_nonoverlapping_one's block optimization on SPIR-V. #83019

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3c3d3dd
core: rearrange `ptr::swap_nonoverlapping_one`'s cases (no functional…
eddyb Mar 11, 2021
bc6af97
core: disable `ptr::swap_nonoverlapping_one`'s block optimization on …
eddyb Mar 11, 2021
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core: rearrange ptr::swap_nonoverlapping_one's cases (no functional… 
… changes).
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@eddyb
eddyb committed Apr 4, 2021
commit 3c3d3ddde967f66938966d6d557a3a4fe4d267ff
24 changes: 13 additions & 11 deletions library/core/src/ptr/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -473,19 +473,21 @@ pub const unsafe fn swap_nonoverlapping<T>(x: *mut T, y: *mut T, count: usize) {
#[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);
}
}

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