[happy_dino]

There is no need or reason to change or add any bytecode instructions to support proper tail calls.

Take standard class files and execute them on a runtime with proper tail calls. Done. Works.

[kragen]

Which JVMs support proper tail calls? Doesn't this violate requirements of the JRE?

[happy_dino]

For instance oss.readytalk.com/avian. Why should it?

[kragen]

Because the security manager needs to be able to introspect the stack. Avian isn't a JVM; it's "designed to provide a useful subset of Java's features" and can run some Java code.

[abecedarius]

It's actually possible to implement the stack inspection in a tail-call-friendly way (along the lines of Racket's continuation marks IIRC), though AFAIK nobody does it.

[happy_dino]

> Because the security manager needs to be able to introspect the stack.

Not allowing certain “optimizations” in security-sensitive contexts is perfectly fine. In fact, this is exactly what Avian, the CLR (and pretty much everyone else) is doing.

> Avian isn't a JVM; it's "designed to provide a useful subset of Java's features" and can run some Java code.

Now you're talking about legal aspects. Frankly, I'm not interested in discussing those.

Avian is a JVM for all practical purposes. If you disagree, please provide a test-case which runs on HotSpot but not on Avian.