[Sablevm-user] JIT integration (was RE: bug report -- cannot run 'HelloWorld' test)

[Purtell, A. <And...@NA...>]

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> "Etienne M. Gagnon" wrote:

> You mean that the "re-implemented" version would be GPLed (+ JNI
> exception, like SableVM), right?

Yes.

> my requirement is that I do not have to change the structure
> of SableVM; the JIT has to adapt, and you get to do the work
> (I can help answering questions, though;-)

Yes, that is the idea.

> It's ok for additional per method data.  SableVM could even encode 
> JIT method calls using its own internal bytecodes (much like it
> does for native calls).

You mentioned that another individual has approached you about
integrating a JIT with SableVM. The only work required on the SableVM
side for supporting any JIT is the integration of a generic interface
that

1) allows the JIT a means for substituting native code for bytecodes,
e.g. a simple protocol for letting the interpreter know native code has
been generated from bytecode and a means for insuring that subsequent
method invocations transfer control to that native code

2) extends the runtime with a few native methods for accessing internal
state normally not exposed, such as the constant pool

Note that having a JIT implemented mostly in Java means that the JIT,
generated code, and associated state are first-class Java objects.

There would certainly be the expectation that this would be my work, and
at various milestones patches would be submitted for consideration. If
SourceForge CVS can be accessed by another protocol than pserver, then I
could instead check in the work under a branch. Unfortunately our
firewall blocks pserver, though rsh and ssh are allowed.

> [e.g. SableVM object instances can move in memory (copying 
> collection), so the JIT must cope with this]. 

> Will JIT compiled code use JNI local/global refs? (it should.  
> Even SableVM uses them internally)

I expect that JIT compiled code can adhere to the requirements of the
runtime environment, whatever they are. Whether or not there are
performance losses because of them depends on how clever the JIT
implementor is. :)

> What's the protocol for passing arguments and results back
> and forth?  (does it also require ffi?)

Presumably a JIT would use the same convention and glue that is in place
for invoking native methods. There is nothing that ties it to a
particular library or convention, so those can change as need be. I
develop on both the x86 and Alpha platforms. If this effort were to take
off, I would eventually like to see a SableVM/JIT combination running on
both.


Andrew Purtell
NAI Labs at Network Associates, Inc.
Los Angeles, CA
PGP Fingerprint: 5A21 10DB 92B0 CE20 80B4  90D7 A89C D464 AA0A A616

The difference between theory and practice in practice is larger 
than the difference between theory and practice in theory. -- Steve
Crocker


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