[commit: ghc] master: Improve eta expansion (again) (802f4b8)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/802f4b89c1a823f7d530454d52bca80b13fb2f15/ghc

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

commit 802f4b89c1a823f7d530454d52bca80b13fb2f15
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Tue Nov 12 13:12:16 2013 +0000

    Improve eta expansion (again)
    
    The presenting issue was that we were never eta-expanding
    
        f (\x -> case x of (a,b) -> \s -> blah)
    
    and that meant we were allocating two lambdas instead of one.
    See Note [Eta expanding lambdas] in SimplUtils.
    
    However I didn't want to eta expand the lambda, and then try all over
    again for tryEtaExpandRhs.  Yet the latter is important in the context
    of a let-binding it can do simple arity analysis.  So I ended up
    refactoring CallCtxt so that it tells when we are on the RHS of a let.
    
    I also moved findRhsArity from SimplUtils to CoreArity.
    
    Performance increases nicely. Here are the ones where allocation improved
    by more than 0.5%. Notice the nice decrease in binary size too.
    
    --------------------------------------------------------------------------------
            Program           Size    Allocs   Runtime   Elapsed  TotalMem
    --------------------------------------------------------------------------------
               ansi          -2.3%     -0.9%      0.00      0.00     +0.0%
               bspt          -2.1%     -9.7%      0.01      0.01    -33.3%
              fasta          -1.8%    -11.7%     -3.4%     -3.6%     +0.0%
                fft          -1.9%     -1.3%      0.06      0.06    +11.1%
    reverse-complem          -1.9%    -18.1%     -1.9%     -2.8%     +0.0%
             sphere          -1.8%     -4.5%      0.09      0.09     +0.0%
          transform          -1.8%     -2.3%     -4.6%     -3.1%     +0.0%
    --------------------------------------------------------------------------------
                Min          -3.0%    -18.1%    -13.9%    -14.6%    -35.7%
                Max          -1.3%     +0.0%     +7.7%     +7.7%    +50.0%
     Geometric Mean          -1.9%     -0.6%     -2.1%     -2.1%     -0.2%


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

802f4b89c1a823f7d530454d52bca80b13fb2f15
 compiler/coreSyn/CoreArity.lhs    |  111 ++++++++++++++++++++++++----
 compiler/coreSyn/CoreUnfold.lhs   |   70 ++++++++++--------
 compiler/simplCore/SimplUtils.lhs |  144 ++++++++++++-------------------------
 compiler/simplCore/Simplify.lhs   |   21 +++---
 4 files changed, 198 insertions(+), 148 deletions(-)

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

    git diff-tree --root --patch-with-stat --no-color --find-copies-harder --ignore-space-at-eol --cc 802f4b89c1a823f7d530454d52bca80b13fb2f15