[GHC] #12562: GHC panic on rebuild (idInfo r_XsTP)

[GHC]

#12562: GHC panic on rebuild (idInfo r_XsTP)
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        Reporter:  cocreature        |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by mpickering):

 The instructions in the ticket are the right ones. I managed to reproduce
 the issue and there is no dependency on llvm. It looked like the problem
 was somewhere in `CorePrep` but this isn't an informed opinion, just by
 looking at the output of `-v5`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12562#comment:8>
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