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

[Goetz Lindenmaier]

On Thu, 27 Feb 2025 06:58:37 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 @cnqpzhang ,
can you please backport to 24 and 21 first?  Removing the label in the meantime. Performance optimizations are not necessarily good candidates for backport to a rather old release.

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PR Comment: https://git.openjdk.org/jdk17u-dev/pull/3300#issuecomment-2693726779