RFR: 8307084: C2: Vectorized drain loop is not executed for some small trip counts [v4]

[Emanuel Peter]

On Wed, 21 Jan 2026 10:34:03 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Fei Gao has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 13 commits:
>> 
>>  - Fix build failure after rebasing and address review comments
>>  - Merge branch 'master' into optimize-atomic-post
>>  - Fixed new test failures after rebasing and refined parts of the code to address review comments
>>  - Merge branch 'master' into optimize-atomic-post
>>  - Merge branch 'master' into optimize-atomic-post
>>  - Clean up comments for consistency and add spacing for readability
>>  - Fix some corner case failures and refined part of code
>>  - Merge branch 'master' into optimize-atomic-post
>>  - Refine ascii art, rename some variables and resolve conflicts
>>  - Merge branch 'master' into optimize-atomic-post
>>  - ... and 3 more: https://git.openjdk.org/jdk/compare/a8552243...ab1de504
>
> test/micro/org/openjdk/bench/vm/compiler/VectorThroughputForIterationCount.java line 136:
> 
>> 134:     // effects of this patch unobservable.
>> 135:     @Param({"true", "false"})
>> 136:     public static boolean ENABLE_LARGE_LOOP_WARMUP;
> 
> It would be nice to have some more comments here:
> - for which benchmarks would the effect of "this patch" not be observable? Also: referring to "this patch" will require a future reader to trace things back in the "git blame" history, that's a bit unfortunate.
> - Generally, it would now be nice to have a summary of which types of benchmarks show what kind of results, and why do we have all the variants.

I'm asking for more comments because I fear the benchmark is becoming harder to use, with all the extra options and benchmark variants.

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PR Review Comment: https://git.openjdk.org/jdk/pull/22629#discussion_r2711970327