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

[Emanuel Peter]

On Mon, 15 Dec 2025 19:44:47 GMT, Chen Liang <liach at openjdk.org> wrote:

>> 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.

Right. Vladimir already argued against it. I forgot. I still believe it is best practice not to limit tests unless they are very expensive. But I'll accept the majority vote.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28589#discussion_r2730682963