swift234

Merge the dense maps for the representative of a type variable and the
fixed type bound to a type variable.

Since one can have a representative or a fixed type, but not a fixed
type that is different from the representatives, we can eliminate a
number of extra DenseMap lookups involving type variables by
collapsing the two dense maps into one. Improves Debug performance on
swift.swift by ~5%.


Swift SVN r3116