[GHC] #10858: Smaller generated Ord instances

[GHC]

#10858: Smaller generated Ord instances
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        Reporter:  nomeata           |                   Owner:
            Type:  task              |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.10.2
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:  #9557             |  Differential Revisions:
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Comment (by nomeata):

 With some of the ideas in #10858 implemented, the number of terms reported
 in `-ddump-ds` for `Language.Haskell.Exts.Annotated.Syntax` goes down from
 207,936 to 202,252. An improvement, but I was hoping for more.

 Using the overloaded `(<>)` on `Ordering` incurs a cost; lots of code just
 to call `<>` with the right instance. It might be worth monomorphizing
 that to `thenCmp`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10858#comment:6>
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