[llvm-dev] RFC: Switching to the new pass manager by default

Wed Oct 25 10:14:15 PDT 2017

On 10/25/2017 12:10 PM, Evgeny Astigeevich via llvm-dev wrote:
>
> Hi Chandler,
>
> I ran the LNT benchmarks and SPEC2k6.train on AArch64 Cortex-A57. I 
> used revisions: Clang 316561, LLVM 316563.
>
> Options: -O3 -mcpu=cortex-a57 -fomit-frame-pointer 
> -fexperimental-new-pass-manager
>
> Regressions: execution time increase
>
> LNT
>
> MultiSource/Benchmarks/FreeBench/fourinarow/fourinarow 1018.58%
>

How real is this?

  -Hal

> MultiSource/Benchmarks/Fhourstones/fhourstones 
>                                 9.06%
>
> MultiSource/Benchmarks/Ptrdist/yacr2/yacr2 
>                                 7.23%
>
> MultiSource/Benchmarks/Olden/perimeter/perimeter 
>                                 6.87%
>
> MultiSource/Benchmarks/MiBench/consumer-typeset/consumer-typeset 6.02%
>
> MultiSource/Benchmarks/Trimaran/enc-pc1/enc-pc1 
>                                 5.59%
>
> MultiSource/Benchmarks/ASC_Sequoia/AMGmk/AMGmk                 
>                 5.03%
>
> SPEC2k6
>
> 453.povray 17.11%
>
> 482.sphinx3 3.44%
>
> 444.namd 2.89%
>
> Improvements: execution time decrease
>
> LNT
>
> MultiSource/Benchmarks/BitBench/uudecode/uudecode                 -50.90%
>
> SingleSource/Benchmarks/Adobe-C++/loop_unroll 
>                                 -27.75%
>
> SingleSource/Benchmarks/Misc/perlin 
>                                                 -21.35%
>
> MultiSource/Benchmarks/Olden/em3d/em3d                                 
> -19.12%
>
> MultiSource/Benchmarks/tramp3d-v4/tramp3d-v4 
>                                 -8.58%
>
> SingleSource/Benchmarks/McGill/chomp 
>                                                 -6.33%
>
> MultiSource/Benchmarks/sim/sim 
>                                                                 -5.41%
>
> MultiSource/Applications/ClamAV/clamscan 
>                                 -3.11%
>
> MultiSource/Benchmarks/TSVC/Symbolics-dbl/Symbolics-dbl 
>                 -2.81%
>
> SPEC2k6
>
> 429.mcf -5.18%
>
> 473.astar -2.65%
>
> 400.perlbench -1.90%
>
> There are also code sizes increases/decreases. The maximum increase is 
> 18.98%. The maximum decrease is 25.65%.
>
> Thanks,
>
> Evgeny Astigeevich
>
> *From: *llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of 
> Chandler Carruth via llvm-dev <llvm-dev at lists.llvm.org>
> *Reply-To: *Chandler Carruth <chandlerc at gmail.com>
> *Date: *Wednesday, 18 October 2017 at 07:51
> *To: *llvm-dev <llvm-dev at lists.llvm.org>
> *Subject: *[llvm-dev] RFC: Switching to the new pass manager by default
>
> Greetings everyone!
>
> The new pass manager is getting extremely close to the point where I'm 
> not aware of any significant outstanding work needed, and I'd like to 
> see what else would be needed to enable it by default. Here are the 
> current functionality I'm aware of outstanding:
>
> 1) Does not do non-trivial loop unswitching. Majority of this is in 
> https://reviews.llvm.org/D34200 but will need one or two small follow-ups.
>
> 2) Currently, sanitizers don't work correctly with it. Thanks to the 
> work of others, the missing infrastructure has been added and I'll 
> send a patch to wire this up this week.
>
> 3) Missing support for 'optnone'. I've been working on this, but the 
> existing testing wasn't as thorough as I wanted, so it is going 
> slowly. I've got about 1/4 of this implemented and should have patches 
> this week or next.
>
> 4) Missing opt-bisect (or similar) facility. This looks pretty trivial 
> to add, but I've not even started. If anyone is interested in it, go 
> for it. We might even be able to do something simpler using the 
> generic debug counters and get equivalent functionality.
>
> ... that's it?
>
> Optimization quality / run-time performance:
>
> - We've been using it at Google extensively and are very happy with 
> the optimization quality. Benchmarks look *very* good here.
>
> - More data from other users would be important.
>
> - You can try it out with `-fexperimental-new-pass-manager` to Clang
>
> Compile-time performance:
>
> - Sometimes *much* better due to cached analyses.
>
> - Sometimes worse, typically due to more / different inlining in turn 
> running main pipeline (GVN + InstCombine) more times or over more code.
>
> - Overall somewhat a wash, but the increased compile times typically 
> due to the optimizer "trying" harder, so not too concerning on our end.
>
> - Again, more feedback from other users good: 
> `-fexperimental-new-pass-manager` to Clang
>
> Once the four missing things land, I'll also happily work on 
> collecting some of the basics on the test-suite and CTMark. But I 
> suspect more "in the wild" data would really be useful here given the 
> significance of the change.
>
> Thoughts? What else (beyond the four items above and feedback on 
> run-time and compile-time) would folks like to see?
>
> Once this happens, I'll also be preparing some batch, mechanical 
> updates to the test suite to primarily use the new pass manager. Also 
> there is lots of documentation updates that will be needed here.
>
> -Chandler
>
> PS: I'll be sending a note to cfe-dev as a "heads up" about this 
> discussion as in some ways, the default flip is mostly a Clang default 
> flip. But hopefully our doc updates will trigger this being 
> "perceived" as the default for other frontends, and I'll try to reach 
> out to other major frontends as well (Swift and Rust are on my radar, 
> and I've already started talking with Philip Reames about their Falcon 
> JIT).
>
>
>
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-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory

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