RFR: 8372978: [VectorAPI] Fix incorrect identity values in UMIN/UMAX reductions

[Eric Fang]

On Mon, 8 Dec 2025 23:29:33 GMT, Paul Sandoz <psandoz at openjdk.org> wrote:

>> Okay, I got your point. I think this might be to maintain consistency with `UMINReduceMasked`; for the masked version, if no element is selected, it returns the identity value. I'm okay with both approaches, maybe let’s hear what @PaulSandoz  thinks.
>
> For masking we need to start with the identity or otherwise use the identify when no mask bits are set. It would be better to declare as constants and refer to them e.g., `UMAX_VALUE`, `UMIN_VALUE`. There are also other cases where we use identity values for reduction and they follow the same pattern of declaration and use.

Okay, I understand, thank you for your insight! I'll wait for @PaulSandoz 's comment and see if we should add two **public** constants to this PR. Then I'll modify it accordingly.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28692#discussion_r2601593342