RFR: 8343689: AArch64: Optimize MulReduction implementation [v11]

[Xiaohong Gong]

On Fri, 31 Oct 2025 02:18:29 GMT, Xiaohong Gong <xgong at openjdk.org> wrote:

> > > Do you intend to ignore ops with >32B vector size? May I ask the reason?
> > 
> > 
> > The reason is the lack of relevant hardware. The only publicly available platform that implements 512b SVE I'm aware of is Fujitsu A64FX. I used to have access to that platform but no longer which makes it difficult to test and benchmark changes for 512b SVE. Stripping that functionality and keeping the implementation in bounds of 256b SVE reduces complexity of this patch.
> 
> The 512-bit SVE cases can be tested with QEMU. I'm fine with this PR. I will trigger a test with my AArch64 environment which support 512-bit SVE. I assume you'v verified the correctness on other SVE machines?

The tests pass on my side.

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PR Comment: https://git.openjdk.org/jdk/pull/23181#issuecomment-3471533386