Starting with GHC 8.2 (rc1 -- head) I noticed that the SpecConstr pass does not always optimize completely with SpecConstr-heavy code. Setting -fmax-worker-args=100 leads to complete specialization again.

However, given that code annotated with SPEC should be optimized until no more SPEC arguments are alive, shouldn't callToNewPats in compiler/specialise/SpecConstr.hs specialize *irrespective* of the size of the worker argument list?

Code that actually fails to specialize is fairly large, hence no test case -- though I have some files with core output showing insufficient specialization.

(I'd be willing to write a patch for this)