[llvm-dev] A "Java Backend"

[David Chisnall via llvm-dev]

On 19 Jul 2016, at 15:52, Sanjoy Das <sanjoy at playingwithpointers.com> wrote:
> 
> But you're right that it will still be difficult to naively
> inter-operate between Java and C++ objects.  Which is why it will be
> an interesting research project. :)

If that’s your goal, then you might have better luck doing source-to-source than going via LLVM IR.  In the past, I’ve managed to do most of Objective-C (not goto, pretty much everything else) -> JavaScript and Dart using clang AST visitors, with Objective-C classes being represented as native objects, with a bit of glue code to paper over the differences in the object models.  With C++, you would most likely want to implement subclassing as composition and make each C++ class a Java interface so that you could do all of the kinds of casts required for multiple inheritance.

There have been a few attempts at C to Java compilation, though I’m not sure of the current status of any of them.  gcj implements Java classes using the same ABI as C++ classes, effectively treating Java as a subset of C++ (plus garbage collection).  It might be interesting to start with the same subset of C++ that Microsoft has used for one of their various C++-on-the-CLR implementations and work from there.  I think Alp Toker had some parsing for MS managed C++ extensions and CLR code generation working a few years back, but I’m not sure what happened to his code.

David

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