[llvm-dev] Enabling Loop Distribution Pass as default in the pipeline of new pass manager
Sjoerd Meijer via llvm-dev
llvm-dev at lists.llvm.org
Mon Jun 21 06:35:46 PDT 2021
> Based on this data, I think we could say the pass is usually beneficial without causing major regression.
I think we need to look at compile-times too before we can draw that conclusion, i.e. we need to justify it's worth spending extra compile-time for optimising a few cases. Hopefully loop distribution is a cheap pass to run (also when it is running but not triggering), but that's something that needs to be checked I think.
From: Jingu Kang <Jingu.Kang at arm.com>
Sent: 21 June 2021 14:27
To: Michael Kruse <llvmdev at meinersbur.de>; Kyrylo Tkachov <Kyrylo.Tkachov at arm.com>; Sjoerd Meijer <Sjoerd.Meijer at arm.com>
Cc: llvm-dev at lists.llvm.org <llvm-dev at lists.llvm.org>
Subject: RE: [llvm-dev] Enabling Loop Distribution Pass as default in the pipeline of new pass manager
For considering the LoopDistribute pass as a canonicalization with the profitability heuristic of LoopFuse pass, it looks the LoopFuse pass does not also have proper profitability function.
If possible, I would like to enable the LoopDistribute pass based on the performance data.
As you can see on the previous email, the Geomean difference from llvm-test-suite is -0.0%. From spec benchmarks, we can see 43% performance improvement on 456.hmmer of SPEC2006. Based on this data, I think we could say the pass is usually beneficial without causing major regression.
How do you think about it?
> -----Original Message-----
> From: Jingu Kang
> Sent: 18 June 2021 13:13
> To: Michael Kruse <llvmdev at meinersbur.de>; Kyrylo Tkachov
> <Kyrylo.Tkachov at arm.com>; Sjoerd Meijer <Sjoerd.Meijer at arm.com>
> Cc: llvm-dev at lists.llvm.org
> Subject: RE: [llvm-dev] Enabling Loop Distribution Pass as default in the pipeline
> of new pass manager
> I appreciate your replies. I have seen below performance data.
> For AArch64, the performance data from llvm-test-suite is as below.
> Metric: exec_time
> Program results_base results_loop_dist diff
> test-suite...ications/JM/lencod/lencod.test 3.95 4.29 8.8%
> test-suite...emCmp<5, GreaterThanZero, Mid> 1456.09 1574.29 8.1%
> test-suite...st:BM_BAND_LIN_EQ_LAMBDA/44217 22.83 24.50 7.3%
> test-suite....test:BM_BAND_LIN_EQ_RAW/44217 23.00 24.17 5.1%
> test-suite...st:BM_INT_PREDICT_LAMBDA/44217 589.54 616.70 4.6%
> test-suite...t:BENCHMARK_asin_novec_double_ 330.25 342.17 3.6%
> test-suite...ow-dbl/GlobalDataFlow-dbl.test 2.58 2.67 3.3%
> test-suite...da.test:BM_PIC_2D_LAMBDA/44217 781.30 806.36 3.2%
> test-suite...est:BM_ENERGY_CALC_LAMBDA/5001 63.02 64.93 3.0%
> test-suite...gebra/kernels/syr2k/syr2k.test 6.53 6.73 3.0%
> test-suite...t/StatementReordering-flt.test 2.33 2.40 2.8%
> test-suite...sCRaw.test:BM_PIC_2D_RAW/44217 789.90 810.05 2.6%
> test-suite...s/gramschmidt/gramschmidt.test 1.44 1.48 2.5%
> test-suite...Raw.test:BM_HYDRO_1D_RAW/44217 38.42 39.37 2.5%
> test-suite....test:BM_INT_PREDICT_RAW/44217 597.73 612.34 2.4%
> Geomean difference -0.0%
> results_base results_loop_dist diff
> count 584.000000 584.000000 584.000000
> mean 2761.681991 2759.451499 -0.000020
> std 30145.555650 30124.858004 0.011093
> min 0.608782 0.608729 -0.116286
> 25% 3.125425 3.106625 -0.000461
> 50% 130.212207 130.582658 0.000004
> 75% 602.708659 612.931769 0.000438
> max 511340.880000 511059.980000 0.087630
> For AArch64, the performance data from SPEC benchmark is as below.
> Benchmark Improvement(%)
> 400.perlbench -1.786911228
> 401.bzip2 -3.174199894
> 403.gcc 0.717990522
> 429.mcf 2.053027806
> 445.gobmk 0.775388165
> 456.hmmer 43.39308377
> 458.sjeng 0.133933093
> 462.libquantum 4.647923489
> 464.h264ref -0.059568786
> 471.omnetpp 1.352515266
> 473.astar 0.362752409
> 483.xalancbmk 0.746580249
> Benchmark Improvement(%)
> 500.perlbench_r 0.415424516
> 502.gcc_r -0.112915812
> 505.mcf_r 0.238633706
> 520.omnetpp_r 0.114830748
> 523.xalancbmk_r 0.460107636
> 525.x264_r -0.401915964
> 531.deepsjeng_r 0.010064227
> 541.leela_r 0.394797504
> 557.xz_r 0.111781366
> JinGu Kang
> > -----Original Message-----
> > From: Michael Kruse <llvmdev at meinersbur.de>
> > Sent: 17 June 2021 19:13
> > To: Jingu Kang <Jingu.Kang at arm.com>
> > Cc: llvm-dev at lists.llvm.org
> > Subject: Re: [llvm-dev] Enabling Loop Distribution Pass as default in
> > the pipeline of new pass manager
> > The LoopDistribute pass doesn't do anything unless it sees
> > llvm.loop.distribute.enable (`#pragma clang loop distribute(enable)`)
> > because it does not have a profitability heuristic. It cannot say
> > whether loop distribution is good for performance or not. What makes
> > it improve hmmer is that the distributed loops can be vectoried.
> > However, LoopDistribute is located before the vectorizer and cannot
> > say in advance whether a distributed loop will be vectorized or not.
> > If not, then it potentially only increased loop overhead.
> > To make -enable-loop-distribute on by default would mean that we could
> > consider loop distribution to be usually beneficial without causing
> > major regressions. We need a lot more data to support that conclusion.
> > Alternatively, we could consider loop-distribution a canonicalization.
> > A later LoopFuse would do the profitability heuristic to re-fuse loops
> > again if loop distribution did not gain anything.
> > Michael
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