This inference context:

inferenceContext = (com.sun.tools.javac.comp.Infer$InferenceContext) Inference vars: T
Undet vars: inference var = T
UPPER = SOMETYPE

is the most common one during compilation and one expensive operation like propagation is a no-op, also the solution is to instantiate the variable to SOMETYPE. It should be interesting to measure if taking advantage of this can save some time during compilation. The difference should be noticeable for big chunks of code like jdk.