I feel like another optimization that rust code can exploit is uninhabited types.
When combined with generics and sum types these can lead to entire branches being unreachable at the type level. Like Option<!> or Result<T, !>, rust hasn't stablized !, but you can declare them other ways such as an empty enum with no variants.
Sure, in the Result case, less in the option case. I didn't mention it because Infallible is documented and named specifically as an Error "The error type for errors that can never happen". The use of uninhabited types as an unreachable code optimization is useful beyond errors though.
