scala-js/scala-js — pull request #873 by sjrd (2014-07-25 15:15:56+00:00)
Title: Add RefinedType to track types more accurately.

In particular, we track whether:
* the type is exact, i.e., the value is of that particular class, not any of its subclasses
* the type is nullable.

The former is mostly useful for determining the target of
a dynamic call: if the type is exact, we can perform the
lookup as if it were a static call, which always gives 1
target, which means more inlining is possible.