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Comment by PDoyle | Hacker News Reader

IBM's Java jit compiler already has this "partial escape analysis". EA basically still never made much difference in real apps. It also fundamentally can't solve the problem you want it to solve, because what happens if your value objects do escape? I really think the compiler is the wrong tool for the job here.

Java has two fundamentally different kinds of types: objects and primitives. Value types are user-defined primitives. Seems pretty straightforward, from a language design perspective. I'm not sure why we're trying so hard to avoid this.

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> It also fundamentally can't solve the problem you want it to solve, because what happens if your value objects do escape? I really think the compiler is the wrong tool for the job here.

You'd need to generalize stacks to full-fledged region analysis to see any real benefits, but only MLKit has taken it this far IIRC.

Ok, so you analyze "regions". Then what? Modify the data structures to use some kind of efficient headerless representation? Then stop the world and rewrite the whole heap if a new class gets loaded that violates an assumption? Or if existing code tries to use reflection to look at these things?

Nothing's impossible I guess, but this kind of global datastructure reshaping is definitely far beyond the state of the art in Java JIT compilers.

Combining Region Inference and Garbage Collection, http://www.elsman.com/pdf/pldi2002.pdf

Cool, thanks for the link.

My mistake--I thought "regions" meant some sort of interprocedural "code regions".

I suspect the state of the art in GC has moved in the last 15 years since this paper was written, and they might have trouble beating modern techniques, but that's speculation.

It's hard to beat regions in time overhead, since every operation is constant time; space overhead is where they suffer, and that's where GC enters the picture.

Escape analysis is a degenerate region analysis, and many of the cases where it fails because it's not general enough would be handled quite well by regions.

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