RFR: 8370691: Add new Float16Vector type and enable intrinsification of vector operations supported by auto-vectorizer [v17]

[Emanuel Peter]

On Mon, 26 Jan 2026 12:17:02 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> Add a new  Float16lVector type and corresponding concrete vector classes, in addition to existing primitive vector types, maintaining operation parity with the FloatVector type.
>> - Add necessary inline expander support.
>>    - Enable intrinsification for a few vector operations, namely ADD/SUB/MUL/DIV/MAX/MIN/FMA.
>> - Use existing Float16 vector IR and backend support.
>> - Extended the existing VectorAPI JTREG test suite for the newly added Float16Vector operations.
>>  
>> The idea here is to first be at par with Float16 auto-vectorization support before intrinsifying new operations (conversions, reduction, etc).
>> 
>> The following are the performance numbers for some of the selected Float16Vector benchmarking kernels compared to equivalent auto-vectorized Float16OperationsBenchmark kernels.
>> 
>> <img width="1344" height="532" alt="image" src="https://github.com/user-attachments/assets/c8157c3c-22b0-4bc1-9de9-7a68cadb7b2a" />
>> 
>> Initial RFP[1] was floated on the panama-dev mailing list.
>> 
>> Kindly review the draft PR and share your feedback.
>> 
>> Best Regards,
>> Jatin
>> 
>> [1] https://mail.openjdk.org/pipermail/panama-dev/2025-August/021100.html
>
> Jatin Bhateja has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 34 commits:
> 
>  - Merge branch 'master' of http://github.com/openjdk/jdk into JDK-8370691
>  - Clanups
>  - Refactoring vectorIntrinsics
>  - Refactoring and cleanups
>  - Refactoring and cleanups
>  - Review comments resolutions
>  - Merge branch 'master' of http://github.com/openjdk/jdk into JDK-8370691
>  - Adding testpoint for JDK-8373574
>  - Review comments resolutions
>  - Merge branch 'master' of http://github.com/openjdk/jdk into JDK-8370691
>  - ... and 24 more: https://git.openjdk.org/jdk/compare/0f1b96a5...ce5768fa

I asked some people internally, and they seem to be _very_ opposed to a new BasicType. Because it goes across the JVM, as I can also see in your patch. Apparently, they wanted to avoid the use of new BasicTypes, mostly managed except for the new `T_FLAT_ELEMENT`. Using `T_SHORT` for `Float16` would be strongly preferred.

I think it may be good to ask @fparain @rose00 @iwanowww @vnkozlov  if they have opinions.

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PR Comment: https://git.openjdk.org/jdk/pull/28002#issuecomment-3800525049