[GHC] #7258: Compiling DynFlags is jolly slow

[GHC]

#7258: Compiling DynFlags is jolly slow
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        Reporter:  simonpj           |                Owner:  simonpj
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.6.1
      Resolution:                    |             Keywords:  deriving-perf
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Here's a mystery.

 * I took `t-10-getline.hs` and `t-10-getine-appl.hs` from `examples.zip`
 just before comment:44

 * I compiled both with `-O -dshow-passes -ddump-simpl`.

 * Both produced ''identical'' Core.  In the early stages `getline-appl` is
 a little bigger, but they become identical after the first run of the
 simplifier following specialise/float-out.  (I.e. early)

 I am at a loss for how to reconcile these results with the dramatically
 worse compile times for `getline` compared with `getline-appl` reported in
 the graph plot in comment:43.

 Tobias, any ideas?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7258#comment:49>
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