RFR: 8265491: Math Signum optimization for x86 [v4]

[Marcus G K Williams]

On Wed, 21 Apr 2021 17:47:12 GMT, Marcus G K Williams <github.com+168222+mgkwill at openjdk.org> wrote:

>> x86 Math.Signum() uses two floating point compares and a copy sign operation involving data movement to gpr and XMM.
>> 
>> We can optimize to one floating point compare and sign computation in XMM. We observe ~25% performance improvement with this optimization.
>> 
>> Base:
>> 
>> Benchmark                       Mode Cnt Score Error Units
>> Signum._1_signumFloatTest avgt 5 4.660 ? 0.040 ns/op
>> Signum._2_overheadFloat avgt 5 3.314 ? 0.023 ns/op
>> Signum._3_signumDoubleTest avgt 5 4.809 ? 0.043 ns/op
>> Signum._4_overheadDouble avgt 5 3.313 ? 0.015 ns/op
>> 
>>  
>> Optimized:
>> signum intrinsic patch
>> 
>> Benchmark                       Mode  Cnt  Score   Error  Units
>> Signum._1_signumFloatTest       avgt    5  3.769 ? 0.015  ns/op
>> Signum._2_overheadFloat         avgt    5  3.312 ? 0.025  ns/op
>> Signum._3_signumDoubleTest      avgt    5  3.765 ? 0.005  ns/op
>> Signum._4_overheadDouble        avgt    5  3.309 ? 0.010  ns/op
>> 
>> 
>> Signed-off-by: Marcus G K Williams <marcus.williams at intel.com>
>
> Marcus G K Williams has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix predicate
>   
>   Signed-off-by: Marcus G K Williams <marcus.williams at intel.com>

Updated benchmarks from patch updated from comments of @DamonFool:

Benchmark                       Mode  Cnt  Score   Error  Units
Signum._1_signumFloatTest       avgt    5  3.769 ? 0.015  ns/op
Signum._2_overheadFloat         avgt    5  3.312 ? 0.025  ns/op
Signum._3_signumDoubleTest      avgt    5  3.765 ? 0.005  ns/op
Signum._4_overheadDouble        avgt    5  3.309 ? 0.010  ns/op


Updated Summary.

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PR: https://git.openjdk.java.net/jdk/pull/3581