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by kaba0 1511 days ago
With Truffle you have to map your language’s semantics to java ones. I am unfortunately out of my depth on the details, but my guess would be that LLVM operates here with this in mind in a completely safe way (I guess pointers to the stack are not safe) so presumably it should work for these as well.
1 comments
mike_hearn 1511 days ago
Not exactly, no. That's the whole point of Truffle and why it's such a big leap forward. You do not map your language's semantics to Java semantics. You can implement them on top of the JVM but bypassing Java bytecode. Your language doesn't even have to be garbage collected, and LLVM bitcode isn't (unless you use the enterprise version which adds support for automatically converting C/C++ to memory safe GCd code!).

So - C code running on the JVM via Sulong keeps C/C++ semantics. That probably means you can build pointers into the stack, and then I don't know what Loom would do. Right now they aren't integrated so I guess that's a research question.

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kaba0 1511 days ago
Perhaps I wasn’t clear. I do know that Truffle works by writing an AST interpreter for another language, but to achieve the best performance you have to map/reuse existing java constructs. E.g. I have read that perhaps Ruby uses java exceptions in a not too idiomatic way, but this is what Graal can later optimize to very good code.

My way out of depth idea with Sulong is that it uses small heap-allocated regions for every manual memory usage (it even has a Managed mode in Enterprise).

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mike_hearn 1511 days ago
You use Java constructs to implement the interpreter, but that doesn't mean the language itself has to be mapped to Java constructs, any more than writing an interpreter in C means your language has to be mapped to C semantics.

Sulong uses a standard C-style heap in the open source version. In EE they (can) trap malloc/free and re-point it towards the GCd heap. They also do bounds checking on pointer de-references. It's actually amazingly cool but unfortunately, EE is expensive enough in dollar terms that it gets ignored. I don't know of anything that uses it for real.

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