Consider:

    {-# LANGUAGE DeriveGeneric #-}
    module A where
    import Data.Binary
    import GHC.Generics
    data T = T
     () () () () () () () () () ()
     () () () () () () () () () ()
     () () () () () () () () () ()
     () () () () () () () () () ()
     () () () () () () () () () ()
     () () () () () () () () () ()
     () () () () () () () () () ()
     () () () () () () () () () ()
     () () () () () () () () () ()
     () () () () () () () () () ()
     deriving Generic
    instance Binary T

Without this patch, on GHC 7.10.2, building this -O2 takes 6.7s.  With
this patch, it takes 1.7s.  Amazing.  (There are modest improvements
with other versions of GHC too.)

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>