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Generate right-shaped object subclasses #5171
We have been running with the reified instance variable logic for some time, which picks from among a fixed set of "right-shaped" object subtypes that use Java fields instead of instance variables for the first N ivars. However we want to improve and expand this logic as follows:
This work should proceed in tandem with explorations into Graal JIT's partial escape analysis, which will work better if we can avoid the extra indirection through the instance variable table.
The first part of this has been implemented for 188.8.131.52: all reified variable classes are now generated at runtime, allowing us to scale them to any size. None are pre-generated yet, but that may come later; the cost is rather low, since early execution will generate only a handful of classes and reuse them for many objects.