RFR: 8357568: IGV: Show NULL and numbers up to 4 characters in "Condense graph" filter [v2]

[Marc Chevalier]

On Thu, 22 May 2025 14:44:07 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
>
> Christian Hagedorn has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Increase number of parameters as suggested by Manuel

I like it.

src/hotspot/share/opto/idealGraphPrinter.cpp line 657:

> 655: 
> 656:         // Only use up to 4 chars and fall back to a generic "L" to keep it short.
> 657:         if (value >= -999 && value <= 9999) {

Just for the sake of saying something, can we somewhat factor this test? And ideally, it could be marginally nicer, if I want to see 6 chars, to just replace a 4 into a 6 and it'd work magically. But I don't really see a way beside length(to_string(value)) <= max_length, and it's not really efficient so... If you have a brilliant idea, good. Otherwise, feel free to ignore: changing it as it is now is easy too.

-------------

Marked as reviewed by mchevalier (Committer).

PR Review: https://git.openjdk.org/jdk/pull/25393#pullrequestreview-2863481391
PR Review Comment: https://git.openjdk.org/jdk/pull/25393#discussion_r2103989707