[GHC] #8834: 64-bit windows cabal.exe segfaults in GC

[GHC]

#8834: 64-bit windows cabal.exe segfaults in GC
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        Reporter:  awson          |            Owner:
            Type:  bug            |           Status:  patch
        Priority:  highest        |        Milestone:  7.8.1
       Component:  Compiler       |          Version:  7.8.1-rc2
      Resolution:                 |         Keywords:
Operating System:  Windows        |     Architecture:  x86_64 (amd64)
 Type of failure:  Runtime crash  |       Difficulty:  Unknown
       Test Case:                 |       Blocked By:
        Blocking:                 |  Related Tickets:
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Comment (by jstolarek):

 > Also I checked this bug is not triggered if relevant modules from
 `bytestring` package are compiled with `-O` flag instead of `-O2`

 That's interesting. Looking at `DynFlags.lhs` I see two optimisations that
 are enabled only with `-O2`: liberate case and SpecConstr. I admit have no
 idea what they do. Suggestions please?

 >  Also I think this bug is triggered near foreign `memchr` call in
 function `elemIndex` from `Data.ByteString` module in bytestring package,
 which is inlined down to lines function from `Data.ByteString.Char8`.

 It would be great if we had a test case that does not depend on any
 library code. This way we could eyeball the problem by looking at Cmm. Do
 you think you would be able to create such a test case.

 I got my hands on 64-bit Windows, I'm building GHC at the moment so I'll
 try to look into this one.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8834#comment:24>
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