[6.8.1 regression] 6.8.2 panics in nameModule with -O2

The attached file makes GHC 6.8.2 panic:

$ ghc-6.8.2 -fforce-recomp -O2 -c PPrCF.hs 
ghc-6.8.2: panic! (the 'impossible' happened)
  (GHC version 6.8.2 for i386-apple-darwin):
        nameModule $wprCFTree{v sdg}

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

It only happens with -O2:

$ ghc-6.8.2 -fforce-recomp -O1 -c PPrCF.hs 

And only with 6.8.2:

$ ghc-6.8.1 -fforce-recomp -O2 -c PPrCF.hs
$ ghc-6.6.1 -fforce-recomp -O2 -c PPrCF.hs

-dcore-lint gives no additional information.

Adding a NOINLINE pragma for prCFTree makes the panic go away.

This problem and the NOINLINE work-around was found by Jean-Philippe Bernardy in GF.

Trac metadata

Trac field	Value
Version	6.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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