These are different things. UnsafeCell<T> is for shared mutable data. *mut T is for data that you assert will never be mutated while it's being shared with some other reference, but you can't rely on the compiler to prove this fact for you.
If I have a &mut T, what pointer type do I convert it into (and create multiple copies of), to allow shared mutation scoped within the lifetime of the source &mut T?
