[commit: ghc] master: Major patch to implement the new Demand Analyser (0831a12)

Simon Peyton Jones simonpj at microsoft.com
Thu Jan 17 14:57:53 CET 2013


Repository : ssh://darcs.haskell.org//srv/darcs/ghc

On branch  : master

http://hackage.haskell.org/trac/ghc/changeset/0831a12ea2fc73c33652eeec1adc79fa19700578

>---------------------------------------------------------------

commit 0831a12ea2fc73c33652eeec1adc79fa19700578
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Thu Jan 17 10:54:07 2013 +0000

    Major patch to implement the new Demand Analyser
    
    This patch is the result of Ilya Sergey's internship at MSR.  It
    constitutes a thorough overhaul and simplification of the demand
    analyser.  It makes a solid foundation on which we can now build.
    Main changes are
    
    * Instead of having one combined type for Demand, a Demand is
       now a pair (JointDmd) of
          - a StrDmd and
          - an AbsDmd.
       This allows strictness and absence to be though about quite
       orthogonally, and greatly reduces brain melt-down.
    
    * Similarly in the DmdResult type, it's a pair of
         - a PureResult (indicating only divergence/non-divergence)
         - a CPRResult (which deals only with the CPR property
    
    * In IdInfo, the
        strictnessInfo field contains a StrictSig, not a Maybe StrictSig
        demandInfo     field contains a Demand, not a Maybe Demand
      We don't need Nothing (to indicate no strictness/demand info)
      any more; topSig/topDmd will do.
    
    * Remove "boxity" analysis entirely.  This was an attempt to
      avoid "reboxing", but it added complexity, is extremely
      ad-hoc, and makes very little difference in practice.
    
    * Remove the "unboxing strategy" computation. This was an an
      attempt to ensure that a worker didn't get zillions of
      arguments by unboxing big tuples.  But in fact removing it
      DRAMATICALLY reduces allocation in an inner loop of the
      I/O library (where the threshold argument-count had been
      set just too low).  It's exceptional to have a zillion arguments
      and I don't think it's worth the complexity, especially since
      it turned out to have a serious performance hit.
    
    * Remove quite a bit of ad-hoc cruft
    
    * Move worthSplittingFun, worthSplittingThunk from WorkWrap to
      Demand. This allows JointDmd to be fully abstract, examined
      only inside Demand.
    
    Everything else really follows from these changes.
    
    All of this is really just refactoring, so we don't expect
    big performance changes, but acutally the numbers look quite
    good.  Here is a full nofib run with some highlights identified:
    
            Program           Size    Allocs   Runtime   Elapsed  TotalMem
    --------------------------------------------------------------------------------
             expert          -2.6%    -15.5%      0.00      0.00     +0.0%
              fluid          -2.4%     -7.1%      0.01      0.01     +0.0%
                 gg          -2.5%    -28.9%      0.02      0.02    -33.3%
          integrate          -2.6%     +3.2%     +2.6%     +2.6%     +0.0%
            mandel2          -2.6%     +4.2%      0.01      0.01     +0.0%
           nucleic2          -2.0%    -16.3%      0.11      0.11     +0.0%
               para          -2.6%    -20.0%    -11.8%    -11.7%     +0.0%
             parser          -2.5%    -17.9%      0.05      0.05     +0.0%
             prolog          -2.6%    -13.0%      0.00      0.00     +0.0%
             puzzle          -2.6%     +2.2%     +0.8%     +0.8%     +0.0%
            sorting          -2.6%    -35.9%      0.00      0.00     +0.0%
           treejoin          -2.6%    -52.2%     -9.8%     -9.9%     +0.0%
    --------------------------------------------------------------------------------
                Min          -2.7%    -52.2%    -11.8%    -11.7%    -33.3%
                Max          -1.8%     +4.2%    +10.5%    +10.5%     +7.7%
     Geometric Mean          -2.5%     -2.8%     -0.4%     -0.5%     -0.4%
    
    Things to note
    
    * Binary sizes are smaller. I don't know why, but it's good.
    
    * Allocation is sometiemes a *lot* smaller. I believe that all the big numbers
      (I checked treejoin, gg, sorting) arise from one place, namely a function
      GHC.IO.Encoding.UTF8.utf8_decode, which is strict in two Buffers both of
      which have several arugments.  Not w/w'ing both arguments (which is what
      we did before) has a big effect.  So the big win in actually somewhat
      accidental, gained by removing the "unboxing strategy" code.
    
    * A couple of benchmarks allocate slightly more.  This turns out
      to be due to reboxing (integrate).  But the biggest increase is
      mandel2, and *that* turned out also to be a somewhat accidental
      loss of CSE, and pointed the way to doing better CSE: see Trac
      #7596.
    
    * Runtimes are never very reliable, but seem to improve very slightly.
    
    All in all, a good piece of work.  Thank you Ilya!

 compiler/basicTypes/Demand.lhs     | 1215 +++++++++++++++++++++++++++++-------
 compiler/basicTypes/Id.lhs         |   55 +-
 compiler/basicTypes/IdInfo.lhs     |   54 +-
 compiler/basicTypes/MkId.lhs       |   45 +-
 compiler/coreSyn/CoreArity.lhs     |    8 +-
 compiler/coreSyn/CoreLint.lhs      |    7 +-
 compiler/coreSyn/CorePrep.lhs      |   24 +-
 compiler/coreSyn/CoreTidy.lhs      |    4 +-
 compiler/coreSyn/MkCore.lhs        |    9 +-
 compiler/coreSyn/PprCore.lhs       |   12 +-
 compiler/iface/BinIface.hs         |  100 +---
 compiler/iface/IfaceSyn.lhs        |   22 +-
 compiler/iface/MkIface.lhs         |    6 +-
 compiler/iface/TcIface.lhs         |   22 +-
 compiler/main/TidyPgm.lhs          |   28 +-
 compiler/prelude/primops.txt.pp    |   10 +-
 compiler/simplCore/FloatOut.lhs    |    8 +-
 compiler/simplCore/SetLevels.lhs   |   23 +-
 compiler/simplCore/SimplCore.lhs   |   21 +-
 compiler/simplCore/Simplify.lhs    |    5 +-
 compiler/specialise/SpecConstr.lhs |   22 +-
 compiler/stranal/DmdAnal.lhs       | 1077 +++++++++++---------------------
 compiler/stranal/WorkWrap.lhs      |   58 +--
 compiler/stranal/WwLib.lhs         |  131 +++--
 24 files changed, 1640 insertions(+), 1326 deletions(-)


Diff suppressed because of size. To see it, use:

    git show 0831a12ea2fc73c33652eeec1adc79fa19700578



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