Debugging Dynamic Language Features in a Multi-Tier Virtual Machine
summary
Derir is a debugging and visualization tool for Ř (a JIT R runtime) that connects to the VM, shows bytecode, closures, stack, call graph and inspect and mutate feedback slots so users can force eager values and observe different compiled dispatch. Evaluation on real programs shows contextual specializations proliferate (many distinct compiled variants remain useful rather than one dominating), reveals redundant implicit returns that bloat bytecode, and confirms promises are costly for generated code.
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