[GHC] #10538: Simpilifier produces empty case in core, segfaults at runtime.

[GHC]

#10538: Simpilifier produces empty case in core, segfaults at runtime.
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        Reporter:  sopvop            |                   Owner:  bgamari
            Type:  bug               |                  Status:  new
        Priority:  high              |               Milestone:  7.10.2
       Component:  Compiler          |                 Version:  7.10.2-rc1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Runtime crash     |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Comment (by int-e):

 Sorry, I meant to add a description to that file: It reproduces the same
 bug with a bit less code and a single file (note the strategically placed
 `NOINLINE`). Interestingly, the `Applicative` constraint on `reqField` is
 essential.

 I've looked a bit at the resulting traces, but I'm not sure what to look
 for. Here are two excerpts that I found interesting:
 http://lpaste.net/raw/2270642354903842816 looks like an inlining step
 going horribly wrong, and http://lpaste.net/6349604574378065920 shows how
 the odd duplicated `a1_X9lA` is introduced.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10538#comment:2>
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