[jdk21u-dev] RFR: 8350483: AArch64: turn on signum intrinsics by default on Ampere CPUs

[duke]

On Tue, 8 Apr 2025 08:57:04 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*. In the worst test cases, run speed is 1~2% of the expected (patched) and functions got severely impacted. So, the fix can be regarded not only a performance fix but also a function **defect** fixing in a manner, which can be a point to support this backport request too. 
> 
> The commit is in jdk mainline and got successfully merged to jdk24u. It is of low risk as the patch is limited to Ampere CPUs only and well tested on Ampere-1A with related jmh and jtreg tier1 tests.

@cnqpzhang 
Your change (at version 7ee518d6977f17d1f927d9b68968d475d0b291c5) is now ready to be sponsored by a Committer.

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PR Comment: https://git.openjdk.org/jdk21u-dev/pull/1606#issuecomment-2786747507