Firefox engine outraces self after Jäger shot
SpiderMonkey amps up
"JägerMonkey has crossed the streams," developer David Anderson said in a Tuesday blog post , boasting that the JägerMonkey performance line had passed TraceMonkey's when running the V8 benchmark suite. "It’s not by a lot, but this gap will continue to widen, and it’s an exciting milestone."
JagerMonkey (black) v TraceMonkey (orange) running the V8 benchmark
Since unveiling the JägerMonkey project  in late February, Anderson says, Mozilla has rewritten the extension from scratch. Anderson and team decided to retool the entire platform in early May, and by June they were ready to start optimizing again. The new version is now faster than the old.
At this point, the developers have yet to actually integrate JägerMonkey and TraceMonkey, and, well, they're not quite sure how this will work. "What about tracer integration? This is a tough one to answer, and people are really curious! The bad news is we’re pretty curious too — we just don’t know what will happen yet. One thing is sure: if not carefully and properly tuned, the tracer will negatively dominate the method JIT’s performance," Anderson writes.
"The goal of JägerMonkey is to be as fast or faster than the competition, whether or not tracing is enabled. We have to integrate the two in a way that gives us a competitive edge. We didn’t do this in the first iteration [of JägerMonkey, before it was rewritten]."
TraceMonkey speeds performance by detecting code loops and converting them into assembly language, a trick that Mozilla's competitors have yet to adopt. But there are times when such "tracing" doesn't work. "Loops can throw curveballs that cause tracing to stop," Anderson said in announcing JägerMonkey, aka JäegerMonkey and JagerMonkey and JaegerMonkey. "Especially with recursion, or lots of nesting, it can be very difficult to build good traces on complex code."
JägerMonkey borrows the Nitro assembler from WebKit
Anderson says the team hopes to have JägerMonkey ready by September 1. Firefox 4.0 is already in beta, and the official release is due in November. By September, Anderson says, "Integration with the tracing JIT must work, without degrading method JIT performance." ®