RFR: 8264945: Optimize the code-gen for Math.pow(x, 0.5)
Nils Eliasson
neliasso at openjdk.java.net
Fri Apr 9 12:00:14 UTC 2021
On Fri, 9 Apr 2021 02:19:10 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
Looks good.
-------------
Marked as reviewed by neliasso (Reviewer).
PR: https://git.openjdk.java.net/jdk/pull/3404
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