#7596: Opportunity to improve CSE
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Reporter: simonpj | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.6.1
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: None/Unknown
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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Comment(by simonpj@…):
commit 0831a12ea2fc73c33652eeec1adc79fa19700578
{{{
Author: Simon Peyton Jones
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 | 1229
+++++++++++++++++++++++++++++-------
compiler/basicTypes/Id.lhs | 65 +-
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 | 11 +-
compiler/coreSyn/PprCore.lhs | 12 +-
compiler/iface/BinIface.hs | 100 +---
compiler/iface/IfaceSyn.lhs | 22 +-
compiler/iface/MkIface.lhs | 8 +-
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 | 30 +-
compiler/stranal/DmdAnal.lhs | 1077 ++++++++++---------------------
compiler/stranal/WorkWrap.lhs | 58 +--
compiler/stranal/WwLib.lhs | 131 +++--
24 files changed, 1658 insertions(+), 1344 deletions(-)
}}}
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7596#comment:1
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