[GHC] #14364: Reduce repetition in derived Read instances

[GHC]

#14364: Reduce repetition in derived Read instances
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        Reporter:  bgamari           |                Owner:  (none)
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:  deriving
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #10980 #7258      |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 Quite a difference indeed. It's not every day you see a 40% reduction in
 compile time. Can you put the patch up for review?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14364#comment:7>
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