slice: make swap delegate to swap_unchecked

library/core/src/slice/mod.rs

@@ -906,16 +906,12 @@ impl<T> [T] {
     #[inline]
     #[track_caller]
     pub const fn swap(&mut self, a: usize, b: usize) {
-        // FIXME: use swap_unchecked here (https://github.com/rust-lang/rust/pull/88540#issuecomment-944344343)
-        // Can't take two mutable loans from one vector, so instead use raw pointers.
-        let pa = &raw mut self[a];
-        let pb = &raw mut self[b];
-        // SAFETY: `pa` and `pb` have been created from safe mutable references and refer
-        // to elements in the slice and therefore are guaranteed to be valid and aligned.
-        // Note that accessing the elements behind `a` and `b` is checked and will
-        // panic when out of bounds.
+        // Bounds checks that panic exactly like indexing would.
+        let _ = &self[a];
+        let _ = &self[b];
+        // SAFETY: `a` and `b` were checked to be in bounds above.
         unsafe {
-            ptr::swap(pa, pb);
+            self.swap_unchecked(a, b);
         }
     }