RFR: 8324751: C2 SuperWord: Aliasing Analysis runtime check [v10]

[Emanuel Peter]

On Thu, 14 Aug 2025 14:33:03 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Emanuel Peter has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Update src/hotspot/share/opto/c2_globals.hpp
>>    
>>    Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>
>>  - improve predicates.hpp documentation
>
> @chhagedorn Thanks for the drive-by comments about the Predicate documentation. Are you now satisfied? Maybe @rwestrel should have a look at it too, since I completed the missing documentation from the Short-Running-Long-Loop-Predicates as well.

> @eme64 did you measure how much C2 compilation time changed with these changes (all optimizations enabled)?

I did not. I don't think it would take much extra time in almost all cases. The extra analysis is not that costly compared to unrolling that we do in all cases already. What might cost more: if we deopt because of the runtime check, and recompile with multiversioning. That could essencially double C2 compile time for those cases.

Do you think it is worth it to benchmark now, or should be just rely on @robcasloz 's occasional benchmarking and address the issues if they come up?

If you want me to do C2 time benchmarking: should I just show a few specific micro-benchmarks, or do you want to have statistics collected on larger benchmark suites?

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PR Comment: https://git.openjdk.org/jdk/pull/24278#issuecomment-3195515822