RFR: 8343689: AArch64: Optimize MulReduction implementation [v4]

Tue Jul 1 06:27:44 UTC 2025

On Mon, 30 Jun 2025 12:20:19 GMT, Mikhail Ablakatov <mablakatov at openjdk.org> wrote:

>> I have the same concern about the order issue with @eme64.
>> Should we only enable this only for VectorAPI case, which doesn't require strict-order?
>
> FP reductions have been disabled for auto-vectorization, please see the following comment: https://github.com/openjdk/jdk/pull/23181/files#diff-edf6d70f65d81dc12a483088e0610f4e059bd40697f242aedfed5c2da7475f1aR130 . You can also check https://github.com/openjdk/jdk/pull/23181#issuecomment-3018988067 to see how the patch affects auto-vectorization performance. The only benchmarks that saw a performance uplift on a 256b SVE platform is `VectorReduction2.WithSuperword.intMulBig` (which is fine since it's an integer benchmark).

Yes, these operations are disabled for SLP. But maybe we could add an assertion to check the restrict flag in the match rules.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23181#discussion_r2176528442