Auto merge of #78816 - SkiFire13:fix-slice-pointer-provenance, r=RalfJung

<[T]>::reverse: Fix pointer provenance rules Should fix #78749

Author: bors

library/core/src/slice/mod.rs

@@ -605,8 +605,9 @@ impl<T> [T] {
  // many bytes away from the end of `self`.
  // - Any initialized memory is valid `usize`.
  unsafe {
- let pa: *mut T = self.get_unchecked_mut(i);
- let pb: *mut T = self.get_unchecked_mut(ln - i - chunk);
+ let ptr = self.as_mut_ptr();
+ let pa = ptr.add(i);
+ let pb = ptr.add(ln - i - chunk);
  let va = ptr::read_unaligned(pa as *mut usize);
  let vb = ptr::read_unaligned(pb as *mut usize);
  ptr::write_unaligned(pa as *mut usize, vb.swap_bytes());
@@ -635,8 +636,9 @@ impl<T> [T] {
  // always respected, ensuring the `pb` pointer can be used
  // safely.
  unsafe {
- let pa: *mut T = self.get_unchecked_mut(i);
- let pb: *mut T = self.get_unchecked_mut(ln - i - chunk);
+ let ptr = self.as_mut_ptr();
+ let pa = ptr.add(i);
+ let pb = ptr.add(ln - i - chunk);
  let va = ptr::read_unaligned(pa as *mut u32);
  let vb = ptr::read_unaligned(pb as *mut u32);
  ptr::write_unaligned(pa as *mut u32, vb.rotate_left(16));
@@ -654,8 +656,9 @@ impl<T> [T] {
  // aligned, and can be read from and written to.
  unsafe {
  // Unsafe swap to avoid the bounds check in safe swap.
- let pa: *mut T = self.get_unchecked_mut(i);
- let pb: *mut T = self.get_unchecked_mut(ln - i - 1);
+ let ptr = self.as_mut_ptr();
+ let pa = ptr.add(i);
+ let pb = ptr.add(ln - i - 1);
  ptr::swap(pa, pb);
  }
  i += 1;