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make ptr::rotate smaller when using optimize_for_size #125720

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Jun 17, 2024
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make ptr::rotate smaller when using optimize_for_size #125720

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8 changes: 6 additions & 2 deletions library/core/src/slice/rotate.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -71,7 +71,9 @@ pub unsafe fn ptr_rotate<T>(mut left: usize, mut mid: *mut T, mut right: usize)
if (right == 0) || (left == 0) {
return;
}
if (left + right < 24) || (mem::size_of::<T>() > mem::size_of::<[usize; 4]>()) {
if !cfg!(feature = "optimize_for_size")
&& ((left + right < 24) || (mem::size_of::<T>() > mem::size_of::<[usize; 4]>()))
{
// Algorithm 1
// Microbenchmarks indicate that the average performance for random shifts is better all
// the way until about `left + right == 32`, but the worst case performance breaks even
Expand Down Expand Up @@ -158,7 +160,9 @@ pub unsafe fn ptr_rotate<T>(mut left: usize, mut mid: *mut T, mut right: usize)
}
return;
// `T` is not a zero-sized type, so it's okay to divide by its size.
} else if cmp::min(left, right) <= mem::size_of::<BufType>() / mem::size_of::<T>() {
} else if !cfg!(feature = "optimize_for_size")
&& cmp::min(left, right) <= mem::size_of::<BufType>() / mem::size_of::<T>()
{
// Algorithm 2
// The `[T; 0]` here is to ensure this is appropriately aligned for T
let mut rawarray = MaybeUninit::<(BufType, [T; 0])>::uninit();
Expand Down
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