RFR: 8324751: C2 SuperWord: Aliasing Analysis runtime check [v9]

[Emanuel Peter]

On Thu, 14 Aug 2025 11:17:57 GMT, Manuel Hässig <mhaessig at openjdk.org> wrote:

>> Emanuel Peter has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   moved swapping up, suggested by Manuel
>
> Thank you for addressing my feedback! This looks good to me now.

@mhaessig @vnkozlov 
Update: I also had to fix the `TestAliasingFuzzer.java`: I can no longer assert that there is no `multiversioning` because there are some edge-cases where we have issues. I filed bugs for those, and already integrated an IR test for each.
https://bugs.openjdk.org/browse/JDK-8359688
https://bugs.openjdk.org/browse/JDK-8360204
https://bugs.openjdk.org/browse/JDK-8365982

So if anybody accidentally, or intentionally fixes those, we should come back to `TestAliasingFuzzer.java` and tighten the IR rules.

Asserting that there is no `multiversioning` in the IR rules makes sure that we made the runtime check as exact as possible, and do not fail in cases where it would have been safe to keep the predicate, rather than deoptimizing and compiling with multiversioning (more compile time, more code -> just worse).

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PR Comment: https://git.openjdk.org/jdk/pull/24278#issuecomment-3214406740