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

[Qizheng Xing]

On Tue, 16 Sep 2025 06:09:33 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 66:
> 
>> (failed to retrieve contents of file, check the PR for context)
> So these do not end up being CountedLoop?

The first one is a counted loop. The second one is not, because it calls `empty` (not inlined) which may modify `loopCount`.

Both the two loops should have no safepoints, since the `empty` call always polls the safepoint.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23057#discussion_r2431669294