[GHC] #9630: compile-time performance regression (probably due to Generics)

[GHC]

#9630: compile-time performance regression (probably due to Generics)
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        Reporter:  hvr               |                Owner:  dfeuer
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  7.9
      Resolution:                    |             Keywords:  deriving-
                                     |  perf, Generics
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #9583, #10293,    |  Differential Rev(s):  Phab:D3656
  #13059, #10818                     |
       Wiki Page:                    |
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Changes (by dfeuer):

 * differential:   => Phab:D3656


Comment:

 I've added a test demonstrating improvement from the specializer change.
 It's not as precise as I'd like. A variation (moving the definition of `T`
 into the `T9630a` module while leaving the specialization in `T9630`) has
 more dramatic effects, with simplifier tick exhaustion in the older GHC.
 But as mentioned, a similar modification of Edward's test case does
 ''not'' see any improvement.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9630#comment:64>
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