The Cliffs of Inanity

Thu, 13 Apr 2006

libjit and gcj

Last weekend I wrote a JIT for libgcj using libjit. Well, 90% of a JIT anyway.

libjit is remarkably simple to use. It took me about a day to write a functioning (if not completely debugged) JIT for java bytecode. On some microbenchmarks it was between 2 and 6 times faster than the existing bytecode interpreter.

I've checked it in to the old gcjx repository... but you won't be able to see it; I heard that sourceforge has stopped updating its anonymous CVS. Email me if you want a copy. The repository includes a patch for libgcj, the needed modifications there are very minor.

Note that exception handling doesn't work. This is somewhat hard to do, since it requires modifying the JIT and also (probably) patching libgcc. And...

Unfortunately libjit is pure GPL, so I doubt we'll be including this in libgcj, or even finishing it. Instead I think I'll investigate rewriting this JIT using LLVM instead. I've been thinking of generalizing my existing patch to libgcj to make it possible to dynamically load a JIT. That would make it easier to experiment here.

posted at: 19:05 | path: /software | permanent link to this entry