[GHC] #11172: Turning on optimisations produces Impossible case alternative

[GHC]

#11172: Turning on optimisations produces Impossible case alternative
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        Reporter:  nh2               |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  Runtime crash     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by rwbarton):

 > First thing I'd appreciate is somebody to tell me: Is this a real bug or
 something GHC allows itself to do? Since for most other run-time errors,
 GHC asks me to report a bug, but it doesn't do so for `Impossible case
 alternative`.

 It is a GHC bug. Are you sure you have seen GHC ask you to report a bug
 when running a program compiled by GHC (other than GHC itself)? I don't
 think that ever happens.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11172#comment:1>
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