RFR: 8372845: C2: Fold identity hash code if object is constant [v3]

[Chen Liang]

On Sat, 13 Dec 2025 00:57:52 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> You can always do more than just C2 IR verification. For example, we could also do result verification. That would give us coverage for C1 for example. I think it is just good practice not to have a restriction if it is not absolutely necessary.
>
> I don't argue that there's always a chance to catch a bug, but unit tests on C2 IR are mostly trivial, so the actual chance to spot a unique problem is quite low. And the price is execution time.

I kept the C2 limit (note this is a build restriction instead of a flag restriction), but  updated to use test.main.class.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28589#discussion_r2620621537