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

[GHC]

#11172: Turning on optimisations produces SEGFAULT or Impossible case alternative
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        Reporter:  nh2               |                Owner:  bgamari
            Type:  bug               |               Status:  new
        Priority:  highest           |            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 jscholl):

 I tried to break down the input data and arrieved at the following program
 triggering this bug. I derived it by taking the core before the bad
 transformation and simplified it. It still fails with an impossible case
 alternative when compiled with optimizations, but works without themIt is
 a lot smaller than the original code, so hopefully this helps in tracking
 down this bug.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11172#comment:23>
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