RFR: 8342095: Add autovectorizer support for subword vector casts [v15]

[Jasmine Karthikeyan]

On Fri, 23 Jan 2026 09:19:52 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Jasmine Karthikeyan has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 19 commits:
>> 
>>  - Fix whitespace
>>  - Update tests after merge, apply changes from review
>>  - Merge from master
>>  - Update tests, cleanup logic
>>  - Merge branch 'master' into vectorize-subword
>>  - Check for AVX2 for byte/long conversions
>>  - Whitespace and benchmark tweak
>>  - Address more comments, make test and benchmark more exhaustive
>>  - Merge from master
>>  - Fix copyright after merge
>>  - ... and 9 more: https://git.openjdk.org/jdk/compare/de6f35ef...13378368
>
> Ok, I filed this as another follow-up:
> [JDK-8376179](https://bugs.openjdk.org/browse/JDK-8376179): C2 SuperWord: improve subword vectorization, avoid cast to-and-from int

Hi @eme64, thanks a lot for the review! I've pushed an update that should address the review comments and update the bug annotations and copyright years. About the cast to and from int, the only places where that should be required is when the node doesn't support truncation. Right now it looks like reductions also cast to int even when they're not required, such as with `AndReduction`. I can do some further investigation in a followup patch to see where the int vectors are generated.

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PR Comment: https://git.openjdk.org/jdk/pull/23413#issuecomment-3802833523