RFR: 8307084: C2: Vectorized drain loop is not executed for some small trip counts

[Fei Gao]

On Wed, 3 Sep 2025 17:08:08 GMT, Fei Gao <fgao at openjdk.org> wrote:

>> I'm a little sick and don't feel very focused, so I'll have to look at the PR next week.
>> 
>> BTW: I just integrated https://github.com/openjdk/jdk/pull/24278 which may have silent merge conflicts, so it would be good if you merged and tested again. Once you do that I could also run some internal testing, if you like :)
>
>> BTW: I just integrated https://github.com/openjdk/jdk/pull/24278 which may have silent merge conflicts, so it would be good if you merged and tested again.
> 
> Hi @eme64 , I’ve rebased the patch onto the latest JDK, and all tier1 to tier3 tests have passed on my local AArch64 and x86 machines.
> 
>> It would be good if you re-ran the benchmarks. It seems the last ones you did in December of 2024.
> We should see that we have various benchmarks, both for array and MemorySegment.
> You could look at the array benchmarks from here: https://github.com/openjdk/jdk/pull/22070
> 
> I also re-verified the benchmark from [PR #22070](https://github.com/openjdk/jdk/pull/22070) on 128-bit, 256-bit, and 512-bit vector machines. The results show no significant regressions and performance changes are consistent with the previous round described in [perf results]( https://bugs.openjdk.org/browse/JDK-8307084?focusedId=14729524&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-14729524). 
> 
>> Once you do that I could also run some internal testing, if you like :)
> 
> I’d really appreciate it if you could run some internal testing at a time you think is suitable.
> Thanks :)

> @fg1417 Are you still working on this?

@eme64 Apologies for the delay. I’m still working on this and will push the updated changes soon. The update addresses your comments, resolves some test failures after rebasing to the latest JDK, and is currently being tested.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/22629#issuecomment-3421046488