RFR: 8335392: C2 MergeStores: enhanced pointer parsing [v18]

[Emanuel Peter]

On Thu, 7 Nov 2024 00:45:22 GMT, Shaojin Wen <swen at openjdk.org> wrote:

>> Emanuel Peter has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   more changes for Christian
>
> If it is not provided in the release image, users need to find the source code of the current version of JDK to build the fastdebug image to analyze whether the MergeStore optimization of a certain code works.
> 
> I can understand that MergeStore may still need to be improved, so it cannot be used as a product feature, but this is a useful optimization and I hope it can be provided in the product eventually.
> 
> I hope that TraceMergeStore can eventually be used in the release image like `PrintInlining` and become a tool for performance optimizers.

@wenshao I suppose we could consider making `TraceMergeStores` and `TraceAutoVectorization` available in product, but under the `-XX:+UnlockDiagnosticVMOptions` flag... I will discuss this with other VM engineers. That means it is available, but there is no promise of stability. Still, once people become dependent on it, maybe even tools become dependent, then it is harder to make changes without everybody complaining 😅

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PR Comment: https://git.openjdk.org/jdk/pull/19970#issuecomment-2461437763