RFR: 8348638: Performance regression in Math.tanh [v8]

[Emanuel Peter]

On Fri, 25 Apr 2025 12:07:28 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> Mohamed Issa has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Switch to constant double fields with separate micro-benchmarks
>
> Over all the patch looks good to me now apart from concerns around benchmark, existing Java implementation handles special cases upfront, thereby compromising the performance of most common cases. Java implementation scores above intrinsic in two outlier ranges < 2^-55 and > 22. While intrinsic implementation is performant for a meaty generic range ie. > 2^-55 and < 22.0
> We get around 30% performance uplift from intrinsic implementation over java implementation for the bulky generic input range.
> For ranges above 22.0, we now see better performance in comparison to the earlier intrinsic implementation. 
> 
> New benchmark shows clear gain for the value range [A][B][C] this patch optimizes. 
> 
> 
> Baseline:
> =========
> Benchmark                                       (tanhRangeIndex)   Mode  Cnt       Score   Error   Units
> TanhPerf.TanhPerfConstant.tanhConstDouble1                   N/A  thrpt    2  117588.175          ops/ms
> TanhPerf.TanhPerfConstant.tanhConstDouble21                  N/A  thrpt    2  117550.954          ops/ms
> TanhPerf.TanhPerfConstant.tanhConstDoubleLarge               N/A  thrpt    2  117580.385          ops/ms  => A
> TanhPerf.TanhPerfConstant.tanhConstDoubleSmall               N/A  thrpt    2  403652.485          ops/ms
> TanhPerf.TanhPerfConstant.tanhConstDoubleTiny                N/A  thrpt    2  408909.294          ops/ms
> TanhPerf.TanhPerfRanges.tanhNegRangeDouble                     0  thrpt    2  397200.032          ops/ms
> TanhPerf.TanhPerfRanges.tanhNegRangeDouble                     1  thrpt    2  116082.297          ops/ms
> TanhPerf.TanhPerfRanges.tanhNegRangeDouble                     2  thrpt    2  112213.540          ops/ms
> TanhPerf.TanhPerfRanges.tanhNegRangeDouble                     3  thrpt    2  433899.459          ops/ms  => B
> TanhPerf.TanhPerfRanges.tanhPosDoubleRange                     0  thrpt    2  396818.181          ops/ms   
> TanhPerf.TanhPerfRanges.tanhPosDoubleRange                     1  thrpt    2  115886.117          ops/ms
> TanhPerf.TanhPerfRanges.tanhPosDoubleRange                     2  thrpt    2  112048.023          ops/ms
> TanhPerf.TanhPerfRanges.tanhPosDoubleRange                     3  thrpt    2  440250.930          ops/ms  => C
> 
> WithOpt:
> ========
> Benchmark                                       (tanhRangeIndex)   Mode  Cnt       Score   Error   Units
> TanhPerf.TanhPerfConstant.tanhConstDouble1                   N/A  thrpt    2  116459.753          ops/ms
> TanhPerf.TanhPerfConstant.tanhConstDouble21                  N/...

@jatin-bhateja @missa-prime Is https://bugs.openjdk.org/browse/JDK-8355238 related to this bug here?

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PR Comment: https://git.openjdk.org/jdk/pull/23889#issuecomment-2846434350