RFR: 8347273: C2: VerifyIterativeGVN for Ideal and Identity [v3]

[Emanuel Peter]

On Tue, 10 Jun 2025 12:46:48 GMT, Christian Hagedorn <chagedorn at openjdk.org> wrote:

>> It would allow us to extend it further with a most significant bit of `E`, so that the order is `EDCBA`. If I do it in alphabetical order, then I would have to rename them. What do you think?
>
> Okay, I only looked at it from a user-perspective that you might mismatch the description to the value passed to the flag. What could help here is reversing the order you mention the modes: first D:, then C: etc.

@chhagedorn If I mention `D` on the same line as `=DCBA, with `, then we have to change 2 lines next time.

But I suppose we will have to change all lines anyway because the indentation would change...

What I would really want to avoid is to have to change the parsing. So the lowest significant bits have to stay where they are, but I can rename them.

Why don't you make a suggestion how you would like it to look, and then I can apply it :)

>> Having the whole conversation in a single JBS issue sounds a bit tricky... it is more like 100 different issues each with their own conversation.
>> 
>> And I don't yet know which nodes have to be fixed together, and which nodes have multiple problems.
>> 
>> I would also prefer if the comments were in the code - it's not that bad to create a JBS issue and commit the comments. That way, everything is in the code, and not spread over multiple JBS issues and GitHub conversations.
>> 
>> My suggestion is this:
>> - Use the umbrella issue: [JDK-8359103](https://bugs.openjdk.org/browse/JDK-8359103)
>> C2 VerifyIterativeGVN: Umbrella for extending Ideal and Identity verification (JDK-8347273)
>> - There, we can do some basic triaging, and then file subtasks.
>> - In the end, everything interesting to know needs to be committed back. Including text and pictures (ASCII).
>> 
>> @chhagedorn Would that work for you?
>
> I'm honestly not sure what the best way is. Currently, it feels a bit too verbose when also mentioning reproducers with command line options and failing tests which sounds more like things to keep track of in JBS. But I also see your point that having everything in the comments is quite handy and keeps everything in one part. Maybe we can find some middle ground when you move the "how to reproduce" to the umbrella JBS? The rest you can keep in the comments, I'm fine with that and see its benefit.

@chhagedorn And how do we link from code <-> JBS issue? How do we make sure that this stays up to date when the code changes around? Because I predict that this will all move a lot over the next months.

Personally, I prefer the verbose character here. I spent a lot of time finding reproducers, and if we put them in JBS, they will most likely just get lost. That would be sad.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/22970#discussion_r2137865665
PR Review Comment: https://git.openjdk.org/jdk/pull/22970#discussion_r2137879139