[jdk24u] Integrated: 8350483: AArch64: turn on signum intrinsics by default on Ampere CPUs

[Patrick Zhang]

On Tue, 4 Mar 2025 04:12:12 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 problem solving in a manner, which can be a point to support this backport request too.
> 
> The backporting is of low risk as the patch is limited to Ampere CPUs only and well verified on Ampere-1A with related jmh and jtreg tier1 tests.

This pull request has now been integrated.

Changeset: 23389d08
Author:    Patrick Zhang <qpzhang at openjdk.org>
Committer: Paul Hohensee <phh at openjdk.org>
URL:       https://git.openjdk.org/jdk24u/commit/23389d08a2b5c0840d2b18fb2e74d2d112b3192d
Stats:     3 lines in 1 file changed: 3 ins; 0 del; 0 mod

8350483: AArch64: turn on signum intrinsics by default on Ampere CPUs

Backport-of: f529bf712d8946584999dfc98abea60c22c97167

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PR: https://git.openjdk.org/jdk24u/pull/101