RFR: 8367292: VectorAPI: Optimize VectorMask.fromLong/toLong() for SVE [v2]

[Emanuel Peter]

On Fri, 24 Oct 2025 07:17:08 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>>> Hence, these two APIs are a part of VectorMask.fromArray()/intoArray() relatively. Although they really do not any memory access operation. If we have a better name for these two IRs, I think that would be another topic that we can revisit with a separate thread. WDYT?
>> 
>> Sure, we can do it in a future RFE. It is just that bad naming makes it harder for me to review your PR, and so I'm a bit annoying for you probably. I'm sorry for that. Thanks for your patience and explaining things :)
>
>> Hi @eme64 , I updated a commit with renaming the matcher function to mask_op_uses_packed_vector. Is this fine to you? The main concern here is that only the specified vector mask ops [(VectorMaskOpNode)](https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/vectornode.hpp#L1343) need the packed vector mask. Name vector_mask_must_be_packed might extend the scope to all vector/mask operations.
> 
> Sounds, good. I'll have a look at the code. More precise names are always preferable. And some code comments can help refine the definition further: what are the guarantees if you return true or false?

Maybe @PaulSandoz has a good idea for a better naming of `VectorLoadMask` and `VectorStoreMask`?

@XiaohongGong Is there any good place where we already document the different kinds of masks, and how they can be converted, and how they are used? If not: it would be really great if we could add that to `vectornode.hpp`. I also see that `TypeVectMask` has no class comment. We really should improve things there. It would make reviewing Vector API code so much easier.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27481#discussion_r2459181885