[GHC] #15186: ghc 8.4.2 panic in profiling build

[GHC]

#15186: ghc 8.4.2 panic in profiling build
-------------------------------------+-------------------------------------
        Reporter:  kquick            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Profiling         |              Version:  8.4.2
      Resolution:                    |             Keywords:
Operating System:  Linux             |         Architecture:  x86_64
 Type of failure:  Compile-time      |  (amd64)
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 The problem appears to be caused by the matcher for `PointerExpr`, which
 is levity polymorphic:
 {{{#!hs
 Bar.$mPointerExpr
   :: forall (r :: TYPE rep) (tp :: CrucibleType).
      Expr tp -> (GHC.Prim.Void# -> r) -> (GHC.Prim.Void# -> r) -> r
 }}}
 This particular form of levity polymorphism should be perfectly fine.
 However, it seems that the worker-wrapper pass somehow stumbles on to
 this:
 {{{
 ghc-stage2: panic! (the 'impossible' happened)
   (GHC version 8.4.1 for x86_64-unknown-linux):
         isUnliftedType
   r_a32N :: TYPE rep_a32M
   Call stack:
       CallStack (from HasCallStack):
         callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in
 ghc:Outputable
         pprPanic, called at compiler/types/Type.hs:1951:10 in ghc:Type
 CallStack (from -prof):
   WorkWrap.splitFun (compiler/stranal/WorkWrap.hs:(470,1)-(566,42))
   WorkWrap.tryWW (compiler/stranal/WorkWrap.hs:(397,1)-(424,65))
   WorkWrap.wwBind (compiler/stranal/WorkWrap.hs:(86,1)-(97,76))
   WorkWrap.wwTopBinds (compiler/stranal/WorkWrap.hs:(63,1)-(66,30))
   SimplCore.WorkWrap (compiler/simplCore/SimplCore.hs:491:40-59)
   HscMain.Core2Core (compiler/main/HscMain.hs:1212:7-55)
   HscMain.hscSimplify' (compiler/main/HscMain.hs:(1206,1)-(1212,55))
   HscMain.finish (compiler/main/HscMain.hs:(728,1)-(768,70))
   HscMain.hscIncrementalCompile
 (compiler/main/HscMain.hs:(671,1)-(717,52))
   GhcMake.upsweep_mod.compile_it
 (compiler/main/GhcMake.hs:(1457,13)-(1459,66))
   GhcMake.upsweep_mod (compiler/main/GhcMake.hs:(1403,1)-(1559,49))
   GhcMake.upsweep.upsweep' (compiler/main/GhcMake.hs:(1272,3)-(1371,91))
   GhcMake.upsweep (compiler/main/GhcMake.hs:(1254,1)-(1371,91))
   GhcMake.load'.upsweep_fn (compiler/main/GhcMake.hs:(393,9)-(394,41))
   GhcMake.load'.checkHowMuch (compiler/main/GhcMake.hs:(270,9)-(272,27))
   GhcMake.load' (compiler/main/GhcMake.hs:(246,1)-(494,38))
   GhcMake.load (compiler/main/GhcMake.hs:(238,1)-(240,44))
   GHC.withCleanupSession (compiler/main/GHC.hs:(466,1)-(475,37))
   GHC.runGhc (compiler/main/GHC.hs:(441,1)-(446,26))
   GHC.defaultErrorHandler (compiler/main/GHC.hs:(381,1)-(413,7))
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15186#comment:3>
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