RFR: 8352075: Perf regression accessing fields [v4]

[Radim Vansa]

On Mon, 12 May 2025 12:38:43 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> One test that it failed on is trying to load a class where the number of fields of a class is equal to 65535. It's a JCK test. Do you have JCK tests or you could write this one?

You mean replicating the JCK testing logic into regular testsuite? I could do that, which test is that for reference? I wonder how that fails when the fields are only reordered, nothing is added.

However, while [class format](https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.1) technically supports up to 65535 fields, I believe that we are also limited by the constant pool holding no more than 65535 entries, where some space would be occupied by the type field type, there's the dummy index 0 and there might be further records so we won't get as high. I think that normally `javac` does not de-duplicate the signature record, so this might require some handcrafting. Maybe the JCK test reuses some names to form a different combo (which could be valid from JVMS POV but not JLS?) to max it out at 65535 fields?

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PR Comment: https://git.openjdk.org/jdk/pull/24847#issuecomment-2872968852