Context reduction stack overflow can take very long

The following code, taken from the "Haskell Type Constraints Unleashed" paper:

{-# LANGUAGE TypeFamilies #-}

type family TF a :: *
type instance TF (a,b) = (TF a, TF b)

t :: (a ~ TF (a,Int)) => Int
t = undefined

fails almost immediately with Context reduction stack overflow on GHC 7.2, but seems to loop forever with 7.4.1-rc2. Setting -fcontext-stack to 20 results in near immediate termination with the same error. But #5395 (closed) raised the context stack size default to 200, which makes this code (that does not use -XUndecidableInstances) take "forever" to compile.

Trac metadata

Trac field	Value
Version	7.4.1-rc2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
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