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

[Patrick Zhang]

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.

This pull request has now been integrated.

Changeset: 3c0c998e
Author:    Patrick Zhang <qpzhang at openjdk.org>
Committer: Andrew Haley <aph at openjdk.org>
URL:       https://git.openjdk.org/jdk21u-dev/commit/3c0c998e732140eef878c57e1c76d9e76eee3e46
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: 23389d08a2b5c0840d2b18fb2e74d2d112b3192d

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PR: https://git.openjdk.org/jdk21u-dev/pull/1606