[suprjami]

I don't think this is how it works.

The JVM is a specification which describes a pretend computer and its instruction set.

This TruffleC doesn't translate C to Java and run a Java program. This compiles C to bytecode which operates on the JVM.

Whatever Java does or doesn't support is irrelevant to this compiler. TruffleC has nothing to do with the Java programming language at all.

Just like you can compile C and get a memory address of a stack or heap location on any physical computer supported by a C compiler, likewise you can compile C with TruffleC and get a memory address within the stack or heap of the pretend computer called the JVM.

This must be how it works, unless the JVM itself has no concept of memory addresses, which seems very unlikely to me. Let me know if I am wrong?

[chrisseaton]

> This compiles C to bytecode which operates on the JVM.

No, it compiles C to an AST, which it then interprets. The AST, which is also the interpreter in the Truffle design, are then partially evaluated to produce machine code. No bytecode is generated at any point, and in fact you can run it on a JVM that doesn't use byteocde, and then there is no bytecode anywhere.

[chaosite]

I learned most of what I know about Truffle and Graal from your blog posts, so you obviously know more about this than me. However, I was under the impression that Truffle is quite closely integrated into GraalVM, that is, you can't use Truffle on a different JVM. Is that not true?

[origin_path]

Not so. Truffle is just a Java library like any other. You can therefore run Truffle languages on any JVM. However, they will run slow as they are just interpreters, then. To get the speedups you need to use Graal, which recognizes Truffle as a library and treats it specially.

[chaosite]

Well, OK, sure, but Truffle without partial evaluation is just an interpreter written in a very particular way...

I see what you mean though, thanks!

[chrisseaton]

> Well, OK, sure, but Truffle without partial evaluation is just an interpreter written in a very particular way..

That's what it was to start with. Partial evaluation came later.

[rschatz]

Truffle and partial evaluation also works on native-image. You could say this is a VM where there are no bytecodes anymore.

[chaosite]

Oh, of course, but native-image is still a Graal feature, and I was asking about Truffle without Graal.

[entropicdrifter]

native-image was created as part of the Graal project but I think it's a separate JVM implementation from GraalVM

[dzaima]

the JVM bytecode does not have any memory address type. Just various width integers & floats, and references to managed heap objects. Arbitrary pointers would have to be done with 'long's one way or another.

[rschatz]

You can still use pointers. It's a bit hidden, but there are things like `Unsafe.allocateMemory`, `Unsafe.getByte` and so on ;)

[dzaima]

right; at which point the subset of jvm you're using is a subset of any other IR/VM, the 'j' in 'jvm' being only useful as an implementation/runtime.

[chaosite]

Sure, but don't discount all of the JIT optimizations that were implemented in the JVM and the huge number of engineer years invested in that particular implementation/runtime...