[jdk17u-dev] RFR: 8350483: AArch64: turn on signum intrinsics by default on Ampere CPUs

[Goetz Lindenmaier]

On Sat, 28 Jun 2025 10:00:44 GMT, Patrick Zhang <qpzhang at openjdk.org> wrote:

>> Backport the commit to set -XX:+UseSignumIntrinsic by default for Ampere CPUs. It is to fix performance problem observed on JMH cases `vm.compiler.Signum|java.lang.*MathBench.sig[nN]um*`.  For example, `vm.compiler.Signum._1_signumFloatTest` thrpt score becomes 30x better on both jdk mainline and jdk17u-dev. The backporting can be very safe as it is limited to Ampere CPUs only and well verified on Ampere-1A with related jmh and jtreg tier1 tests.
>
> Hi, May I ask for any committer's help to push this approved PR? It’s been in the queue for about a week. Thanks so much in advance!

Hi @cnqpzhang 
Can you find someone with expertise on aarch to sponsor this?
It's the idea of sponsorship that a third person get's involved, if
the backportee hasn't the necessary roles.

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PR Comment: https://git.openjdk.org/jdk17u-dev/pull/3300#issuecomment-3015212600