RFR: 8357568: IGV: Show NULL and numbers up to 4 characters in "Condense graph" filter

[Christian Hagedorn]

On Thu, 22 May 2025 13:46:39 GMT, Christian Hagedorn <chagedorn at openjdk.org> wrote:

> When using the "Condense graph" filter in IGV, it would be useful to show `NULL` and numbers wider than 2 characters instead of `P` and `I/L` (fallback for larger numbers), respectively. There is a comment in `idealGrapPrinter.cpp` which says that maximally 2 chars are allowed for numbers:
> https://github.com/openjdk/jdk/blob/428d33ef3ca0af34d8f164fe9d9b722e81e866a7/src/hotspot/share/opto/idealGraphPrinter.cpp#L646
> 
> But we already allow larger entries today:
> ![image](https://github.com/user-attachments/assets/e90d0518-148f-4a33-a9e8-0bdca14aa017)
> 
> I there propose to use `NULL` and allow up to 4 characters for numbers which could be a good trade-off between shortness and expressiveness. This allows us to quickly see null checks and larger constants.
> 
> Without patch:
> ![image](https://github.com/user-attachments/assets/e450f1d2-503c-4b84-8137-25892f8ab7f9)
> 
> 
> With patch:
> ![image](https://github.com/user-attachments/assets/81371a53-be7e-4acd-afbf-e5613e96815a)
> 
> Thanks,
> Christian

Thanks Manuel for your review! As suggested, I also removed the limit for parameters which cannot exceed 255 which is more than 4 characters (e.g. `P123`).

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PR Comment: https://git.openjdk.org/jdk/pull/25393#issuecomment-2901490441