Currently the G1ParCopyHelper inherits G1ParClosureSuper which in turn inherits ExtendedOopClosure. This is not needed because the G1ParCopyClosure (which inherits G1ParCopyHelper) is only used as an ordinary OopClosure.

Changing the G1ParCopyHelper to inherit directly from OopClosure will make it more obvious that this closure is not used with oop_iterate and thus does not rely on inheriting the implementation of apply_to_weak_ref_discovered_field() from G1ParClosureSuper.