Since the introduction of the specialized loop opcodes, op_jless is not used in any significant way (and not at all on SunSpider). Of course, life is never easy in Machine.cpp, so removing it with r34883 is a 1.5% regression. I guess we'll have to wait until it's not a performance regression.
Wow, I made this bug twice. *** This bug has been marked as a duplicate of 20419 ***