RFR: 8353290: C2: Refactor PhaseIdealLoop::is_counted_loop() [v29]

[Christian Hagedorn]

On Wed, 14 Jan 2026 16:38:25 GMT, Kangcheng Xu <kxu at openjdk.org> wrote:

>> This PR refactors `PhaseIdealLoop::is_counted_loop()` into (mostly) `CountedLoopConverter::is_counted_loop()` and `CountedLoopConverter::convert()` to decouple the detection and conversion code. This enables us to try different loop configurations easily and finally convert once a counted loop is found. 
>> 
>> A nested `PhaseIdealLoop::CountedLoopConverter` class is created to handle the context, but I'm not if this is the best name or place for it. Please let me know what you think.
>> 
>> Blocks [JDK-8336759](https://bugs.openjdk.org/browse/JDK-8336759).
>
> Kangcheng Xu has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fix safepoint detection

Thanks for doing that! I've ran it on the old state up to tier7 which looked good. Unfortunately, there was some intermittent closed test failure again with the current non-DIFF-patch with latest mainline. I will investigate further and try to extract a reproducer.

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PR Comment: https://git.openjdk.org/jdk/pull/24458#issuecomment-3790777110