Bug 1585921 - Remove GCPtrHasher which is invalid, and replace with HeapPtrHasher r=sfink

Differential Revision: https://phabricator.services.mozilla.com/D48544

--HG--
extra : moz-landing-system : lando

js/src/gc/Barrier.h

@@ -933,10 +933,10 @@ struct MovableCellHasher<WeakHeapPtr<T>> {
   static void rekey(Key& k, const Key& newKey) { k.unsafeSet(newKey); }
 };
 
-/* Useful for hashtables with a GCPtr as key. */
+/* Useful for hashtables with a HeapPtr as key. */
 template <class T>
-struct GCPtrHasher {
-  typedef GCPtr<T> Key;
+struct HeapPtrHasher {
+  typedef HeapPtr<T> Key;
   typedef T Lookup;
 
   static HashNumber hash(Lookup obj) { return DefaultHasher<T>::hash(obj); }
@@ -986,14 +986,18 @@ class MOZ_STACK_CLASS StackGCCellPtr {
 
 namespace mozilla {
 
-/* Specialized hashing policy for GCPtrs. */
 template <class T>
-struct DefaultHasher<js::GCPtr<T>> : js::GCPtrHasher<T> {};
+struct DefaultHasher<js::HeapPtr<T>> : js::HeapPtrHasher<T> {};
+
+template <class T>
+struct DefaultHasher<js::GCPtr<T>> {
+  // Not implemented. GCPtr can't be used as a hash table key because it has a
+  // post barrier but doesn't support relocation.
+};
 
 template <class T>
 struct DefaultHasher<js::PreBarriered<T>> : js::PreBarrieredHasher<T> {};
 
-/* Specialized hashing policy for WeakHeapPtrs. */
 template <class T>
 struct DefaultHasher<js::WeakHeapPtr<T>> : js::WeakHeapPtrHasher<T> {};