The aarch64 Address class has a number of subclasses for various kinds of literal addresses: RuntimeAddress, ExternalAddress, OopAddress, InternalAddress.

OopAddress appears to be unused, so can be deleted.

The others are all subject to slicing, since the Address dtor/copy/assign are all public.  And indeed they get sliced, since (almost) all uses of these subclasses are just to construct an argument to be passed by value to a function taking an Address object. So a slicing copy, with the derived type being of no real importance. While it works, it's icky and unnecessary.

A better approach (that avoids copy-slicing) would be to replace those subclasses with static functions with the names of those subclasses, with each function returning an appropriately initialized Address object.

There are a couple places where one of these derived types is used as a local variable's type.  Those can be changed to Address without any loss of functionality or readability.