RFR: 8370691: Add new Float16Vector type and enable intrinsification of vector operations supported by auto-vectorizer [v9]

[Fei Yang]

On Wed, 17 Dec 2025 12:56:01 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 23 commits:
> 
>  - Fix from Bhavana Kilambi for failing JTREG regressions on AARCH64
>  - Merge branch 'master' of http://github.com/openjdk/jdk into JDK-8370691
>  - Including test changes from Bhavana Kilambi (ARM)
>  - Merge branch 'master' of http://github.com/openjdk/jdk into JDK-8370691
>  - Optimizing tail handling
>  - Merge branch 'master' of http://github.com/openjdk/jdk into JDK-8370691
>  - Cleanups
>  - Fix failing jtreg test in CI
>  - Merge branch 'master' of http://github.com/openjdk/jdk into JDK-8370691
>  - Cleanups
>  - ... and 13 more: https://git.openjdk.org/jdk/compare/5e7ae281...703f313d

Hi, I have a minor question about the tests.

test/jdk/jdk/incubator/vector/Float16Vector64Tests.java line 1893:

> 1891:         VectorMask<Float16> m = three.compare(VectorOperators.LE, higher);
> 1892:         assert(m.allTrue());
> 1893:         m = higher.min((short)-1).test(VectorOperators.IS_NEGATIVE);

I find that `higher.min((short)-1)` produces a float16 vector of 4 NaNs. So are we testing for negative NaNs with `VectorOperators.IS_NEGATIVE`? Is it more reasonable to test `VectorOperators.IS_NAN` instead?

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PR Review: https://git.openjdk.org/jdk/pull/28002#pullrequestreview-3633583291
PR Review Comment: https://git.openjdk.org/jdk/pull/28002#discussion_r2667282723