[LLVMdev] JVM bytecode generation vs. LLVM

[Joachim Durchholz]

Sorry if I'm repeating something that was already said.

I was just thinking "why the heck do I seem headed for JVM generation if 
what I want to use is LLVM", and this is the result:

I'm coming from a Java background. I'm using Eclipse, I'm used to the 
syntax highlighting, cross referencing and refactoring support that 
Eclipse offers.
I know I will want to have the same infrastructure for my language, and 
I want it written in my language. I WILL need a JVM backend, no matter what.

Now, I'd still love to use LLVM. It has a lot to offer for the phases 
"above" code generation. I don't need register allocation, but I'd like 
to make use of common constant elimination, loop unrolling, inlining, or 
the pass management infrastructure; that's a whole lot of code I don't 
need to write.
And when it comes to generating raw machine code, I can confidently say: 
develop in Eclipse and run the stuff as JVM code, but deploy using the 
machine-code backend provided by LLVM.

So my conclusion is:
To make LLVM attractive for us Java-based language designers, we need 
the means to write a JVM backend.
The actual backend is easy, libraries for class file and JAR generation 
exist.
I'd need help for:
* Determining where exactly the line is drawn between "this LLVM 
component is useful for JVM bytecode generation" and "this LLVM 
component isnt". (Constant folding would be, register allocation would 
not, but there's a lot of gray areas between these two.)
* Not being a JNI or C++ expert, building the JNI infrastructure that 
would allow calling LLVM components from Java.
* Not being a true Eclipse expert, wrapping LLVM binaries as Eclipse 
plugins. Eclipse expects plugins to be available for download via HTTP, 
with some XML that describes dependencies. Setting this up would be 
easy, getting the details right would be work.

That's just my specific skillset, other language designers might have 
different ones, but I guess it is not very likely that the exact right 
combination will come up easily. There aren't many people around who're 
experts in C++, Java, and Eclipse.

Oh, and the question I'm having is: Is LLVM for me?

Regards,
Jo