Segmentation fault, runtime representation polymorphism

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

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

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

instance P.Num a => Num a where
  (+) = (P.+)
  fromInteger = P.fromInteger

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

u :: Bool
u = isTrue# v_ where
  v_ :: forall rep (a :: TYPE rep). Num a => a
  v_ = fromInteger 10

segfaults

$ ./bin/repo/ghc4/inplace/bin/ghc-stage2 --interactive -ignore-dot-ghci /tmp/tMjN.hs
GHCi, version 8.1.20160930: http://www.haskell.org/ghc/  :? for help
[1 of 1] Compiling Main             ( /tmp/tMjN.hs, interpreted )
Ok, modules loaded: Main.
*Main> u
True
*Main> Segmentation fault (core dumped)
$ 

Trac metadata

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