[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 simonpj):

 OK thanks to jscholl the bug is fixed.

 But I am still eager to know why this could give a **seg-fault**.  An
 "impossible alternative" message perhaps; but a seg-fault is more
 worrying.

 Ben describes how to elicit the seg-fault in comment:17. (NB: you need the
 `segfault` branch of his repo.)

 jscholl: if you could repeat your amazing work on this variant, to make a
 much smaller seg-faulting test case, that would be amazing.

 (Of course it is always possible that there are two bugs, and I have only
 fixed one; another reason to investigate the seg-fault variant.)

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11172#comment:28>
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