Scala types: reflect: How to find least upper bound of two types at runtime

I'm implementing some expressions using Scala type system. To determine the type of if-then-else expression I need to be able to implement the following function

def leastUpperBound(thenPartType: Type, elsePartType: Type): Type

Is there a function somewhere in scala.reflect._ to perform the evaluation? Or do I have to implement the search with those *TypeApi extractors?

Thanks in advance