core: rearrange ptr::swap_nonoverlapping_one's cases (no functional…

… changes).

library/core/src/ptr/mod.rs

@@ -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);
  }
 }