swift234

[g-arc-opts] Refactor out bottomup dataflow instruction initialization into a new visitor class BottomUpDataflowRCStateVisitor.

This allows for the state transition kind caused by an instruction to change how
we process it. It also decouples this effect from the actual CFG visiting code.

This will give us the flexibility to teach the ARC optimizer in a clean way
about many more types of instructions.

Swift SVN r26901