Sharing the markword (aka Valhalla's markword use)

[Kennke, Roman]

> (Why not a fixed location, like offset=4?  Because you might overflow the narrow-klass field’s encoding range, when loading a subclass of a class which already uses the desirable offset=4 slot for a regular instance field.  You can get around this by using offset=-4, but that opens different cans of worms. Better to assume instance fields will compete for offsets with the injected full-klass field.)

Ah I just carefully re-read this. You are right, this would be a problem, indeed. Very good point. I also like the joint-bit encoding. However, we’d have to ensure that the relevant mode bit-pattern (e.g. upper 8 bits zero) would not happen in normal encoding. Currently, I think this is in-fact a very common situation.

Roman




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