[GHC] #7258: Compiling DynFlags is jolly slow

[GHC]

#7258: Compiling DynFlags is jolly slow
-------------------------------------+-------------------------------------
        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:                    |
-------------------------------------+-------------------------------------

Comment (by tdammers):

 Replying to [comment:49 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?

 Hmm, maybe `-O` vs. `-O2`? I'll run a few trials myself.

 Other thought, though probably not really an explanation: the t-10-XXXX
 examples are maybe too small to produce useful metrics, the performance
 differences only start to get dramatic past 100 fields or so.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7258#comment:51>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler