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So if something kicked in at 75% stack usage (via a guard page?) and forced analysis, wouldn't that work? It'd be like the plethora of JVM options now: another configurable switch.

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How much of the stack are you willing to look at when you hit a guard page? The non-tail call might not be right near the top, depending on the structure of the code. I'm not saying it's impossible, but I think the approach of having the higher-level language add the annotations is probably more practical.

If the tail-call-needing function isn't found rather quickly (say, in the first 100? frames), then isn't it unlikely that the tail call will help? That seems like a much rarer case. Is the cost of going 1000 functions deep that expensive? Most threads aren't gonna hit a high % of stack without having some sort of problem anyways.

Of course it'd be better for the JVM to support this in bytecode, just like generics, stack allocation, and pointers. But it seems to me that if there was a real solid need for TCO then a JVM could implement it with tunable heuristics (most Java code doesn't need TCO, so if your code really depends on it in complex scenarios, you can always pass a -XXTcoInspectionDepth argument.)

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