[GHC] #9557: Deriving instances is slow

[GHC]

#9557: Deriving instances is slow
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              Reporter:  Feuerbach   |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.8.3
            Resolution:              |         Keywords:
      Operating System:              |     Architecture:  Unknown/Multiple
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:              |       Blocked By:
  None/Unknown                       |  Related Tickets:  #8731
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by nomeata):

 Obviously, people have considered my second suggest before, see `Note [Do
 not rely on compare]` in
 [source:ghc/compiler/typecheck/TcGenDeriv.lhs#L300]...

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9557#comment:11>
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