Address review comments.

Author: nnethercote

Diff for: compiler/rustc_data_structures/src/intern.rs

@@ -62,17 +62,13 @@ impl<'a, T> PartialEq for Interned<'a, T> {
 
 impl<'a, T> Eq for Interned<'a, T> {}
 
-impl<'a, T: PartialOrd> PartialOrd for Interned<'a, T> {
+// In practice you can't intern any `T` that doesn't implement `Eq`, because
+// that's needed for hashing. Therefore, we won't be interning any `T` that
+// implements `PartialOrd` without also implementing `Ord`. So we can have the
+// bound `T: Ord` here and avoid duplication with the `Ord` impl below.
+impl<'a, T: Ord> PartialOrd for Interned<'a, T> {
     fn partial_cmp(&self, other: &Interned<'a, T>) -> Option<Ordering> {
-        // Pointer equality implies equality, due to the uniqueness constraint,
-        // but the contents must be compared otherwise.
-        if ptr::eq(self.0, other.0) {
-            Some(Ordering::Equal)
-        } else {
-            let res = self.0.partial_cmp(&other.0);
-            debug_assert!(res != Some(Ordering::Equal));
-            res
-        }
+        Some(self.cmp(other))
     }
 }
 
@@ -84,7 +80,7 @@ impl<'a, T: Ord> Ord for Interned<'a, T> {
             Ordering::Equal
         } else {
             let res = self.0.cmp(&other.0);
-            debug_assert!(res != Ordering::Equal);
+            debug_assert_ne!(res, Ordering::Equal);
             res
         }
     }