[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 cocreature):

 The only changes I made to the instructions are changing the url and the
 branch which now point to the one linked by mpickering where I tried to
 remove as much code as possible and stub things with undefined while still
 being able to reproduce this. I also removed the requirement to install
 LLVM from the instructions since this is no longer necessary.

 Also it is now only a single cabal project so it is easy to just use a
 normal `cabal build` rather than `cabal new-build` and you can reproduce
 the issue that way too (I tried this).

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12562#comment:11>
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