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

[Eric Fang]

On Tue, 9 Dec 2025 08:01:07 GMT, Quan Anh Mai <qamai at openjdk.org> wrote:

>> @merykitty I apologize for not being clear. Actually, It's `SUADDReduce` that doesn't allow starting with `a[idx]` because that would result in `a[idx]` being added twice.
>> 
>> Specifically, this happens as follows: `gen_saturating_reduction_op` (used to generate `SUADDReduce`) and `gen_reduction_op_func` (used to generate `umin/umax, etc.`) both use the `Unit-Reduction-Scalar-op.template` template. When we modify it, `SUADDReduce` is also affected. Therefore, a new template needs to be defined.
>
> But then the loop can start from `idx + 1` instead of `idx`, right?

What I really wanted to talk about was code consistency and maintainability. There are many ways to handle this problem if we want to. I just think the current code style might be more maintainable, since the masked version is written this way too. The code looks more consistent.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28692#discussion_r2601545153