GNU Java Compiler and Swarm

[Marcus G. Daniels]

With today's Swarm snapshot, it is possible to build models using the
(just released) native code GNU Java Compiler in GCC 3.0.  This is an
advantage for several reasons:

  1) It can facilitate development of faster models by removing the
     indirection of the Java virtual machine.  With GCC, there are
     many more options for controlling the optimization of code.

     GCC is a traditional static analysis compiler and thus it can do
     much deeper analysis of code than the common just-in-time compilers
     (JITs).

  2) It unifies debugging with GDB.  Current (snapshot) versions of GDB 
     available from sources.redhat.com have full Java support.  A crash,
     whether in Swarm or in a model are all handled in the same way.

  3) It provides a unified profiling environment.

  4) It provides a way to make C++ look like Java code and vice versa.

  5) It's just the right thing to do.  :-)

There is one extra step on the Swarm side, which is that you need
to make a shared library of the Java Swarm stubs.  You can do that
by making a build done in the usual way, and then, having your PATH
setup so that gcj from GCC 3.0 is available, run:

 $ cd /build/swarm-jdk # your Swarm build area
 $ cd java
 $ make gcjswarm.so

Then, in your model, add a rule like this:

model: $(SOURCES)
        CLASSPATH=/build/swarm-jdk/java gcj -O2 -g --main=StartModel -o model 
$(SOURCES) /build/swarm-jdk/java/gcjswarm.so

StartModel would be the class having the `main' you want to run.

I know this works on Intel Linux, but other architectures may have
problems.  E.g. I know of a bug in the GCJ compiler and the libffi library
that prevent it working on Sparc.  I can't say when I'll have time to
fix them.  (They aren't bugs in Swarm.)




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