[LLVMdev] Introducing myself, and Java project.

[Tanya Lattner]

On Feb 3, 2008, at 7:09 PM, Ramón García wrote:

> I have just worked with this code. The architecture is fine, and I
> think that this code should be reused,
> It needs updating, however, because it does not compile with LLVM 2.1
> (I prefer to use a stable version
> to focus my work, and port to LLVM 2.2 later).
>

LLVM 2.2 comes out in a week, I would recommend using that over 2.1  
if you must use a release. You can use the pre-releases to get  
started. However, if you are going to be actively developing you  
should use llvm svn.

-Tanya


> I have seen that one incompatibility is that this Java frontend
> requires C++ with exceptions, but LLVM is compiled with
> -fno-exceptions. For now, I am compiling with -fexceptions. Should
> exceptions be removed from the code of the Java frontend?
>
> Then, I have doubts about whether the changes for getting it built are
> correct or not. I will make more questions later.
>
> This could be a work plan:
>
> * Getting the java frontend built.
>
> * Implement exception handling (jsr/ret bytecodes)
>
> * Implement garbage collection.
>
> * Support JAR files.
>
> This should get an usable Java implementation. But there is still very
> hard work to be done. The difficult part is dynamic class loading,
> reflection and creation of classloaders. This would enable to use LLVM
> for Java server applications such as Tomcat or JBoss. I am not sure if
> this work is possible without funding a full time position. Just some
> questions to think about it. To what extent does LLVM support dynamic
> code loading? Is it posible to get code loaded at runtime? Could this
> break assumptions made by interprocedural optimization? (A function
> may be called in unexpected ways)
>
> Another difficult part is optimization. In order to get good
> performance, references should be converted to values whenever
> possible. Recent virtual machines support scape analysis, so that
> local references can be converted into values, and be stored and
> released in the stack. This should be generalized to references that
> are class members.
>
> Java code is particular hard to optimize because any function call is
> a virtual function call. Is inlining posible? Only if one makes
> assumptions about any code using some class, that no other class is
> going to override the called method. Programmers could declare methods
> final, but this is rarely done. Assumptions may be checked for all
> loaded classes, but, for classes not yet loaded (and which may be
> loaded dynamically), who nows?
>
> But this is for very long term feature. For now, let us have fun
> completing the doable parts.
>
> Best regards,
>
> Ramon
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