RFR: 8346280: C2: implement late barrier elision for G1 [v4]

[Amit Kumar]

On Fri, 7 Feb 2025 09:21:39 GMT, Roberto Castañeda Lozano <rcastanedalo at openjdk.org> wrote:

>> I see TestG1BarrierGeneration.java failure :( 
>> 
>> [TestG1BarrierGeneration_jtr.log](https://github.com/user-attachments/files/18676532/TestG1BarrierGeneration_jtr.log)
>
>> I see TestG1BarrierGeneration.java failure :(
>> 
>> [TestG1BarrierGeneration_jtr.log](https://github.com/user-attachments/files/18676532/TestG1BarrierGeneration_jtr.log)
> 
> @offamitkumar thanks for the report! Most likely the test failures are only due to missing optimizations (because of limitations in the barrier elision pattern matching analysis), but if you want me to confirm please send the entire jtreg log, without truncation. You can disable output truncation running the test like this:
> `make run-test TEST="compiler/gcbarriers/TestG1BarrierGeneration.java" JTREG="MAX_OUTPUT=999999999"`
> Please double-check that the output log file does not contain any `Output overflow` message.

@robcasloz Sure: 

I can spend time on it, maybe on weekend, for now I am overloaded with some other tasks.

[TestG1BarrierGeneration_jtr_no_overflow.log](https://github.com/user-attachments/files/18706090/TestG1BarrierGeneration_jtr_no_overflow.log)

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PR Comment: https://git.openjdk.org/jdk/pull/23235#issuecomment-2642733177