Lambda dropping in loops

Given a function like fill 0# mpa = return () fill i# mpa = do let i'# = i# -# 1# writeMP mpa (I# i'#) e fill i'# mpa it would be nice if GHC were to lambda drop it (on the core level) into fill i# mpa = fill' i# where fill' 0# = return () fill' i# = do let i'# = i# -# 1# writeMP mpa (I# i'#) e fill' i'# as this allows it to subsequently apply the new case liberation optimisation. By performing the lambda dropping manually, I have gotten much better code in some performance sensitive definitions. Cheers, Manuel