[GHC] #16058: GHC built on macOS Mojave nondeterministically segfaults

[GHC]

#16058: GHC built on macOS Mojave nondeterministically segfaults
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           Reporter:  bgamari        |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  highest        |         Milestone:  8.8.1
          Component:  Compiler       |           Version:  8.6.3
           Keywords:                 |  Operating System:  MacOS X
       Architecture:  x86_64         |   Type of failure:  Building GHC
  (amd64)                            |  failed
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 I am seeing perhaps a quarter of GHC builds on the GitLab Darwin builder
 (running Mojave) fail with a segfault in `ghc-stage1`. Unfortunately I've
 been entirely unable to reproduce this in a debugger (which isn't
 surprising given the low probability of the crash manifesting).

 Given that we haven't seen this in any Darwin builds until now I'm
 suspicious of either the XCode toolchain or Mojave itself.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16058>
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