RFR: 8351623: VectorAPI: Add SVE implementation of subword gather load operation [v6]

[Xiaohong Gong]

On Wed, 12 Nov 2025 20:22:45 GMT, Paul Sandoz <psandoz at openjdk.org> wrote:

> > Yes, converting mask to vector will be the way to resolve. Do you think it's better that defining a private VectorMask function for the slice operation? The function could be implemented with corresponding vector slice APIs. Although this function is not friendly to SVE performance, it wins on unifying the implementation.
> 
> If it helps just add a utility method that does the slice/rearrange mask<->vector conversion, but given your use case i expect it only to be used in one location, so perhaps keep it close to there. It maybe you don't need full slice functionality, since you only care about a part of the mask elements that was rearranged to the start of the vector and therefore don't need to zero out the remaining parts that are not relevant. (The same happens for conversion by parts.) Since we don't yet have any slice intrinsic i think that would be OK and we could revisit later. Ideally we should able to optimize rearrange of vectors using constant shuffles with recognizable patterns.

Make sense to me. Thanks for all your inputs! I will create a PR for the java-level refactor and X86 modifications first. We can have more discussion then.

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PR Comment: https://git.openjdk.org/jdk/pull/26236#issuecomment-3524804695