[kragen]

The JVM also doesn't (I'm fairly sure) have an indirect JMP instruction, which means you can't compile a polymorphic source-language method call into a JMP inside of a single generated method. Instead you have to use a call to a method. That means that tail-calls to functions passed as parameters (rather than functions that can be statically bound at compile time) can't use JMP.

[happy_dino]

The “JVM” can use any instruction it wants to use.

If you want a runtime with proper tail calls, use a implementation which supports it.

[kragen]

I'm talking about the bytecode instructions standardized in the "JVM" specification. The "JVM" has to implement the semantics of the instructions found in your bytecode program, or your program won't run. Your bytecode program can only use bytecodes defined in the "JVM" specification, or it won't run on the "JVM".

[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.