[llvm-dev] A "Java Backend"

[David Chisnall via llvm-dev]

On 21 Jul 2016, at 09:31, Lorenzo Laneve <lore97drk at icloud.com> wrote:
> 
> I thought about something like that but I think it's not a good idea.
> Like writing an AST visitor on Clang for example would be cool but it isn't open to other frontends, and I think that this is a job for LLVM.
> What about java-* attributes that can be put on certain IR operations to indicate structures that are needed to know about the Java Bytecode structure, or operations that should be translated in a specific way for Java?
> These attributes can be added to the IR modules optionally like debug info

I’m not sure what problem you’re trying to solve.  Providing these attributes from the front end and ensuring that they’re correctly preserved by optimisers would likely be more effort than writing a Java bytecode back end (and a lot more for any language that has a simple mapping to the Java object model).  By the time code is in LLVM IR, it’s already got a lot of assumptions about things like calling conventions and data layout embedded in it.  You’d need to treat the Java back end as another target in your front end (and a particularly weird one, at that).

If I had a front end that I wanted to use to target the JVM then I would not go via LLVM IR to get there.  The same probably holds for the CLR, though it’s a little bit less clear cut.

David

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