RFR: 8366444: Add support for add/mul reduction operations for Float16

[Bhavana Kilambi]

On Tue, 7 Oct 2025 01:33:05 GMT, Xiaohong Gong <xgong at openjdk.org> wrote:

>> Hi @XiaohongGong, yes `length_in_bytes < 8` is also not supported and currently we support only for vector lengths of 8B and 16B.
>> IRs with 32-bit vector size might exist but we do not have an optimized implementation for 32B vector lengths and thus I have disabled it. Instead of that, it generates the 16B scalarized Neon instruction sequence for a 32B vector length. Is this what you were asking?
>
> I mean do we need to check the length_in_bytes < 8, such as:
> Suggestion:
> 
>         if (length_in_bytes < 8 || length_in_bytes > 16 || !is_feat_fp16_supported()) {
>           return false;
>         }

Yes, I understood that part (and I already made that change in my patch interally) but not this - 

> the IRs with 32-bit vector size might exist

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PR Review Comment: https://git.openjdk.org/jdk/pull/27526#discussion_r2409685656