[GHC] #12899: ghc panics at random places with -jX

[GHC]

#12899: ghc panics at random places with -jX
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        Reporter:  pacak             |                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 pacak):

 After recompilation in devel2 mode, one of the panics:


 {{{


 <no location info>: error:
     ghc: panic! (the 'impossible' happened)
   (GHC version 8.1.20161206 for x86_64-unknown-linux):
         applyTypeToArgs
   Expression: $fDataFixity_$cgmapQ
                 @ (Exchange ByteString ByteString)
                 @ Identity
                 ($fProfunctorExchange @ ByteString @ ByteString)
                 $fFunctorIdentity
   Type: forall u. (forall d. Data d => d -> u) -> Fixity -> [u]
   Args: [TYPE: Exchange ByteString ByteString, TYPE: Identity,
          $fProfunctorExchange @ ByteString @ ByteString,
 $fFunctorIdentity]
   Call stack:
       CallStack (from HasCallStack):
         prettyCurrentCallStack, called at
 compiler/utils/Outputable.hs:1114:58 in ghc:Outputable
         callStackDoc, called at compiler/utils/Outputable.hs:1118:37 in
 ghc:Outputable
         pprPanic, called at compiler/coreSyn/CoreUtils.hs:181:14 in
 ghc:CoreUtils

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12899#comment:3>
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