Class member functions not substituted for MultiParamTypeClasses

When the following code is compiled with "-O2 -ddump-rule-firings" the rule is not fired: presumably because the simplifier does not recognize that (+++) = ex_or.

{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies #-}
class Ex2 a b c | a b -> c where
  (+++) :: a -> b -> c

instance Ex2 Bool Bool Bool where
  (+++) = ex_or

{-# INLINE [2] ex_or #-}
ex_or = (||)

{-# RULES
"force-inline" forall a b . ex_or a b = a || b
 #-}

main = print (True +++ True)

Trac metadata

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