panic on negative literal in case on Word

module Case where
f :: Word -> Word
f n = case n of
       -1 -> 2
       _ -> 3

ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 8.1.20170119 for x86_64-unknown-linux):
	ASSERT failed!
  -1
  Call stack:
      CallStack (from HasCallStack):
        prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1133:58 in ghc:Outputable
        callStackDoc, called at compiler/utils/Outputable.hs:1182:22 in ghc:Outputable
        assertPprPanic, called at compiler/basicTypes/Literal.hs:223:75 in ghc:Literal
  Call stack:
      CallStack (from HasCallStack):
        prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1133:58 in ghc:Outputable
        callStackDoc, called at compiler/utils/Outputable.hs:1137:37 in ghc:Outputable
        pprPanic, called at compiler/utils/Outputable.hs:1180:5 in ghc:Outputable
        assertPprPanic, called at compiler/basicTypes/Literal.hs:223:75 in ghc:Literal

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

Doesn't happen in 8.0.1.

Trac metadata

Trac field	Value
Version	8.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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