Segfaults on levity-polymorphic type class

{-# Language FlexibleInstances, TypeFamilies, TypeInType, MagicHash #-}

import Data.Kind
import GHC.Exts

class Shw (a :: TYPE rep) where
  shw :: a -> String

instance Int# ~ a => Shw (a :: TYPE IntRep) where
  shw a = "I#" ++ show (I# a)

main = putStrLn (shw 3#)

induces a segfault

$ runghc --version
runghc 8.0.1
$ runghc test.hs
I#Segmentation fault

Trac metadata

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