GHC panic

I get

$ ./ghc-stage2 -ignore-dot-ghci --interactive /tmp/tEZm.hs
GHCi, version 8.1.20160930: http://www.haskell.org/ghc/  :? for help
[1 of 1] Compiling Main             ( /tmp/tEZm.hs, interpreted )
ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 8.1.20160930 for x86_64-unknown-linux):
        kindPrimRep.go
  rep_a13E
  Call stack:
      CallStack (from HasCallStack):
        prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1076:58 in ghc:Outputable
        callStackDoc, called at compiler/utils/Outputable.hs:1080:37 in ghc:Outputable
        pprPanic, called at compiler/simplStg/RepType.hs:369:9 in ghc:RepType
        kindPrimRep, called at compiler/simplStg/RepType.hs:337:18 in ghc:RepType
        typePrimRep, called at compiler/ghci/ByteCodeGen.hs:1541:15 in ghc:ByteCodeGen

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

> 

running

{-# Language MagicHash, PolyKinds, ViewPatterns, TypeInType, RebindableSyntax, NoImplicitPrelude #-}

import GHC.Types
import Prelude hiding (Num (..))
import qualified Prelude as P
import GHC.Prim

data BoxUnbox = BUB Int Int#

class Num (a :: TYPE rep) where
  (+) :: a -> a -> a

  fromInteger :: Integer -> a

instance Num Int where
  (+) = (P.+)
  fromInteger = P.fromInteger

instance Num Int# where
  (+) = (+#)
  fromInteger (fromInteger -> I# n) = n

a :: BoxUnbox
a = let u :: Num (a :: TYPE rep) => a
        u = 1 + 2 + 3 + 4
     in
        BUB u u

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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