RFR: 8305895: Implement JEP 450: Compact Object Headers (Experimental) [v15]

[Roberto Castañeda Lozano]

On Thu, 19 Sep 2024 11:42:04 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

> > > I agree that this is the simplest and least intrusive way of getting klass loading working in C2 for this experimental version of the feature. However, the approach seems brittle and error-prone, and it may be hard to maintain in the long run. Therefore, I think that a more principled and robust modeling will be needed, after this PR is integrated, in preparation for the non-experimental version.
> > 
> > 
> > What do you think about this @rkennke? Do you agree on an alternative modeling of klass loading in C2 (without any reliance on `oopDesc::klass_offset_in_bytes()`) being a pre-condition for a future, non-experimental version of compact headers?
> 
> Yes, that sounds like a good improvement! It'd also clean up C2 considerably - right now there are many places in C2 that rely on klass_offset_in_bytes(). Getting rid of them all would be great, but also seems like a major effort. Could you file an issue to track that future work?

Done: https://bugs.openjdk.org/browse/JDK-8340453.

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PR Comment: https://git.openjdk.org/jdk/pull/20677#issuecomment-2360945827