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

[GHC]

#11172: Turning on optimisations produces SEGFAULT or 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 nh2):

 I managed to reproduce the `segmentation fault` now!

 See branch `segfault`, https://github.com/fpco/impossible-case-
 alternative-repro/tree/segfault

 (Note that that branch is only for GHC <= 7.10, I'd have to make the same
 adjustments as for the other repro to make it work on GHC 8 HEAD, if that
 is desired.)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11172#comment:11>
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