swift234

IRGen: Implement class-bounded existential containers.

Provide TypeInfo for class-bounded existentials, which represents them as an explosion comprising one witness table per subscribed protocol and then the class instance pointer as an ObjC-refcounted pointer. Provide lowerings for the SIL instructions that manipulate class-bounded existentials (except for existential-to-existential erasures, which aren't critical to getting basic operations working and will need some abstraction remapping to deal with class-bounded-to-opaque upcasts aside from the representation change).

Swift SVN r5579