RFR: 8347499: C2: Make `PhaseIdealLoop` eliminate more redundant safepoints in loops [v3]

[Qizheng Xing]

On Tue, 16 Sep 2025 06:11:15 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Qizheng Xing has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Improve documentation comments
>
> test/hotspot/jtreg/compiler/loopopts/TestRedundantSafepointElimination.java line 84:
> 
>> (failed to retrieve contents of file, check the PR for context)
> All of the cases here are only single loops, right? But is the algorithm not mostly dealing with nested loops, where we have to make sure that in some cases the `SafePoint` is not eliminated? Could you add some extra cases for that?

Updated IR test.

> test/micro/org/openjdk/bench/vm/compiler/LoopSafepoint.java line 76:
> 
>> 74:         }
>> 75:         return sum;
>> 76:     }
> 
> I think it would be nice if you made the examples in the JMH and the JTREG as similar as possible.

Updated microbenchmark to be in sync with the IR test.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23057#discussion_r2439005605
PR Review Comment: https://git.openjdk.org/jdk/pull/23057#discussion_r2439007562