check_overlap panic (7.1 regression)

The attached program is rightfully rejected by GHC 7.0.4 (with "Could not deduce (HMapClass f l) ...") but makes GHC HEAD panic:

$ ghc-7.3.20110713 Overlap.hs 
[1 of 1] Compiling Overlap          ( Overlap.hs, Overlap.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 7.3.20110713 for x86_64-unknown-linux):
	check_overlap
    main:Overlap.HDropClass{tc raS}
      main:Overlap.PZero{tc raZ}
      (main:Overlap.HMap{tc raN} f{tv adi} [sk] l{tv adk} [sk])

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

Both versions are built with the devel2 BuildFlavour.

Trac metadata

Trac field	Value
Version	7.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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