Panic with DeriveAnyClass

With the code

{-# LANGUAGE DefaultSignatures, DeriveAnyClass #-}
class Eq1 f where
  (==#) :: Eq a => f a -> f a -> Bool
  default (==#) :: Eq (f a) => f a -> f a -> Bool
  (==#) = (==)

data Foo a = Foo (Either a a)
    deriving (Eq, Eq1)

GHC 8.0.1 and 7.10.3 both panic:

ghc: panic! (the 'impossible' happened)
  (GHC version 8.0.1 for x86_64-apple-darwin):
	in other argument

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

Trac metadata

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