[llvm-dev] Enable vectorizer-maximize-bandwidth by default?

[Dehao Chen via llvm-dev]

Yes, we do see performance benefits for this change on some google internal
benchmarks.

Dehao

On Fri, May 19, 2017 at 6:18 AM, 陳韋任 <chenwj.cs97g at g2.nctu.edu.tw> wrote:

> Besides speccpu, any other real-world applications benefit from this
> option?
>
> Regards,
> chenwj
>
> 2017-05-19 6:30 GMT+08:00 Dehao Chen via llvm-dev <llvm-dev at lists.llvm.org
> >:
>
>> Hi,
>>
>> I'm proposing to make vectorizer-maximize-bandwidth on by default for
>> loop vectorizer because it should generally help performance.
>>
>> I've tested the performance impact on Intel sandybridge machine with
>> speccpu benchmarks:
>>
>>            Benchmark             Base:Reference   (1)
>> -------------------------------------------------------
>> spec/2006/fp/C++/444.namd                 26.84  -0.31%
>> spec/2006/fp/C++/447.dealII               46.19  +0.89%
>> spec/2006/fp/C++/450.soplex               42.92  -0.44%
>> spec/2006/fp/C++/453.povray               38.57  -2.25%
>> spec/2006/fp/C/433.milc                   24.54  -0.76%
>> spec/2006/fp/C/470.lbm                    41.08  +0.26%
>> spec/2006/fp/C/482.sphinx3                47.58  -0.99%
>> spec/2006/int/C++/471.omnetpp             22.06  +1.87%
>> spec/2006/int/C++/473.astar               22.65  -0.12%
>> spec/2006/int/C++/483.xalancbmk           33.69  +4.97%
>> spec/2006/int/C/400.perlbench             33.43  +1.70%
>> spec/2006/int/C/401.bzip2                 23.02  -0.19%
>> spec/2006/int/C/403.gcc                   32.57  -0.43%
>> spec/2006/int/C/429.mcf                   40.35  +0.27%
>> spec/2006/int/C/445.gobmk                 26.96  +0.06%
>> spec/2006/int/C/456.hmmer                  24.4  +0.19%
>> spec/2006/int/C/458.sjeng                 27.91  -0.08%
>> spec/2006/int/C/462.libquantum            57.47  -0.20%
>> spec/2006/int/C/464.h264ref               46.52  +1.35%
>>
>> geometric mean                                   +0.29%
>>
>>   Scores are benchmark specific.
>>
>> We do have regression on 453.povray, but it's due to secondary effects as
>> all hot functions are the same. I've also tested the code size impact, it
>> does not change for tested speccpu benchmarks.
>>
>> I've prepared https://reviews.llvm.org/D33341 to do this.
>>
>> I really appreciate if the community can help test the performance impact
>> of this change on other architectures so that we can decide if this should
>> go target-dependent.
>>
>> Any comments/concerns?
>>
>> Thanks,
>> Dehao
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>
>
> --
> Wei-Ren Chen (陳韋任)
> Homepage: https://people.cs.nctu.edu.tw/~chenwj
>
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