[GHC] #13171: panic on negative literal in case on Word

[GHC]

#13171: panic on negative literal in case on Word
-------------------------------------+-------------------------------------
           Reporter:  rwbarton       |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 {{{#!hs
 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.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13171>
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