RFR: 8264945: Optimize the code-gen for Math.pow(x, 0.5) [v2]

[Vladimir Kozlov]

On Mon, 19 Apr 2021 15:10:55 GMT, Jie Fu <jiefu at openjdk.org> wrote:

>> Hi all,
>> 
>> I'd like to optimize the code-gen for Math.pow(x, 0.5).
>> And 7x ~ 14x performance improvement is observed by the jmh micro-benchmarks.
>> 
>> While I was optimizing a machine learning program, I found both Math.pow(x, 2) and Math.pow(x, 0.5) are used.
>> To my surprise, C2 just optimizes the case for Math.pow(x, 2) [1], but still not for Math.pow(x, 0.5) yet.
>> 
>> The patch just replace Math.pow(x, 0.5) with Math.sqrt(x).
>> 
>> Before:
>> 
>> Benchmark                     (seed)   Mode  Cnt      Score    Error   Units
>> MathBench.powDouble0Dot5           0  thrpt    8  45525.117 ? 11.686  ops/ms
>> MathBench.powDouble0Dot5Loop       0  thrpt    8      0.031 ?  0.001  ops/ms
>> 
>> Benchmark                     (seed)   Mode  Cnt      Score    Error   Units
>> MathBench.powDouble0Dot5           0  thrpt    8  45509.317 ?  6.581  ops/ms
>> MathBench.powDouble0Dot5Loop       0  thrpt    8      0.031 ?  0.001  ops/ms
>> 
>> 
>> After:
>> 
>> Benchmark                     (seed)   Mode  Cnt       Score     Error   Units
>> MathBench.powDouble0Dot5           0  thrpt    8  343354.892 ? 362.900  ops/ms
>> MathBench.powDouble0Dot5Loop       0  thrpt    8       0.457 ?   0.001  ops/mso
>> 
>> Benchmark                     (seed)   Mode  Cnt       Score    Error   Units
>> MathBench.powDouble0Dot5           0  thrpt    8  343421.559 ? 49.326  ops/ms
>> MathBench.powDouble0Dot5Loop       0  thrpt    8       0.457 ?  0.001  ops/ms
>> 
>> 
>> Testing:
>>   - tier1~3 on Linux/x64
>> 
>> Thanks,
>> Best regards,
>> Jie
>> 
>> [1] https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/library_call.cpp#L1680
>
> Jie Fu has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains four commits:
> 
>  - Optimize C2
>  - Merge branch 'master' into JDK-8264945
>  - Revert old changes
>  - 8264945: Optimize the code-gen for Math.pow(x, 0.5)

Good.

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Marked as reviewed by kvn (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/3404