Re:TruffleC: A C implementation on top of JVM (2014)
by chrisseaton on Friday August 12, 2022 @06:32AM
(#32436573)
> 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.
Re:TruffleC: A C implementation on top of JVM (2014)
by chaosite on Friday August 12, 2022 @07:22AM
(#32436861)
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?
Re:TruffleC: A C implementation on top of JVM (2014)
by origin_path on Friday August 12, 2022 @07:30AM
(#32436915)
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.
Re:TruffleC: A C implementation on top of JVM (2014)
by chaosite on Friday August 12, 2022 @07:43AM
(#32437021)
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!
Re:TruffleC: A C implementation on top of JVM (2014)
by chrisseaton on Friday August 12, 2022 @07:46AM
(#32437039)
> 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.
Re:TruffleC: A C implementation on top of JVM (2014)
by rschatz on Friday August 12, 2022 @08:07AM
(#32437245)
Truffle and partial evaluation also works on native-image. You could say this is a VM where there are no bytecodes anymore.
Re:TruffleC: A C implementation on top of JVM (2014)
by chaosite on Friday August 12, 2022 @08:09AM
(#32437271)
Oh, of course, but native-image is still a Graal feature, and I was asking about Truffle without Graal.
Re:TruffleC: A C implementation on top of JVM (2014)
by entropicdrifter on Friday August 12, 2022 @03:33PM
(#32442958)
native-image was created as part of the Graal project but I think it's a separate JVM implementation from GraalVM
Re:TruffleC: A C implementation on top of JVM (2014)
by dzaima on Friday August 12, 2022 @06:20AM
(#32436495)
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.
Re:TruffleC: A C implementation on top of JVM (2014)
by rschatz on Friday August 12, 2022 @06:27AM
(#32436540)
You can still use pointers. It's a bit hidden, but there are things like `Unsafe.allocateMemory`, `Unsafe.getByte` and so on ;)
Re:TruffleC: A C implementation on top of JVM (2014)
by dzaima on Friday August 12, 2022 @06:32AM
(#32436575)
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.
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?