[GHC] #13929: GHC panic with levity polymorphism

[GHC]

#13929: GHC panic with levity polymorphism
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        Reporter:  vagarenko     |                Owner:  (none)
            Type:  bug           |               Status:  new
        Priority:  high          |            Milestone:  8.2.1
       Component:  Compiler      |              Version:  8.2.1-rc2
      Resolution:                |             Keywords:  TypeInType
Operating System:  Windows       |         Architecture:  x86_64 (amd64)
 Type of failure:  None/Unknown  |            Test Case:
      Blocked By:                |             Blocking:
 Related Tickets:                |  Differential Rev(s):
       Wiki Page:                |
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Comment (by bgamari):

 For the record, a more complete callstack is,
 {{{
 ghc-stage2: panic! (the 'impossible' happened)
   (GHC version 8.2.0.20170704 for x86_64-unknown-linux):
         isUnliftedType
   GUnboxed g_a20x rg_a20y :: TYPE rg_a20y
   Call stack:
       CallStack (from HasCallStack):
         prettyCurrentCallStack, called at
 compiler/utils/Outputable.hs:1133:58 in ghc:Outputable
         callStackDoc, called at compiler/utils/Outputable.hs:1137:37 in
 ghc:Outputable
         pprPanic, called at compiler/types/Type.hs:1954:10 in ghc:Type
         isUnliftedType, called at compiler/coreSyn/CoreUtils.hs:487:27 in
 ghc:CoreUtils
         needsCaseBinding, called at compiler/coreSyn/MkCore.hs:162:10 in
 ghc:MkCore
         mk_val_app, called at compiler/coreSyn/MkCore.hs:146:42 in
 ghc:MkCore
         mkCoreApps, called at compiler/coreSyn/MkCore.hs:154:26 in
 ghc:MkCore
         mkCoreConApps, called at compiler/coreSyn/MkCore.hs:364:5 in
 ghc:MkCore
         mkCoreUbxTup, called at compiler/coreSyn/MkCore.hs:370:32 in
 ghc:MkCore
         mkCoreTupBoxity, called at compiler/deSugar/DsExpr.hs:382:19 in
 ghc:DsExpr

 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/13929#comment:4>
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