swift234

[sil-devirtualizer] Refinements of speculative devirtualization

- Take into account all subclasses, not only the direct subclasses of a static type of the instance.
- Emit exact type checks in the breadth-first order.
- If the number of alternatives in above the threshold N, try to speculatively devirtualize the first N alternatives.

rdar://22656904

Swift SVN r31956