RFR: 8343689: AArch64: Optimize MulReduction implementation [v3]

[Mikhail Ablakatov]

On Tue, 1 Jul 2025 16:22:42 GMT, Mikhail Ablakatov <mablakatov at openjdk.org> wrote:

>> That would be the operations with partial vector size valid. For such cases, we will generate a mask in IR level, and a `VectorBlend` will be generated for this reduction case. Otherwise the result will be incorrect. So the vector size should be equal to MaxVectorSize theoretically.
>
> Thank you for elaborating on this :)

Done, thanks!

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PR Review Comment: https://git.openjdk.org/jdk/pull/23181#discussion_r2182576732