RFR: 8265491: Math Signum optimization for x86

[Jie Fu]

On Mon, 19 Apr 2021 23:00:47 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 3.782 ? 0.019 ns/op
> Signum._2_overheadFloat avgt 5 3.309 ? 0.011 ns/op
> Signum._3_signumDoubleTest avgt 5 3.782 ? 0.017 ns/op
> Signum._4_overheadDouble avgt 5 3.310 ? 0.006 ns/op
> 
> Signed-off-by: Marcus G K Williams <marcus.williams at intel.com>

test/hotspot/jtreg/compiler/intrinsics/math/TestSignumIntrinsic.java line 28:

> 26:  * @test
> 27:  * @summary Test compiler intrinsics for signum
> 28:  * @requires os.arch=="aarch64" | os.arch=="x86" | os.arch=="amd64" | os.arch=="x86_64"

What about os.arch=="i386" ?

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