It's not JavaScript bytecode, but regex bytecode. V8 parses regular expressions to regex ASTs, takes them through some more intermediate forms, then finally to a special regex bytecode. That bytecode is either interpreted, or JIT compiled (depending of some build options, I think). You can look at a list of bytecodes in [1], and at the x64 JIT in [2].

1 - http://code.google.com/p/v8/source/browse/trunk/src/bytecode...

2 - http://code.google.com/p/v8/source/browse/trunk/src/x64/rege...