[issue4715] optimize bytecode for conditional branches

[Antoine Pitrou]

Antoine Pitrou <pitrou at free.fr> added the comment:

> http://code.google.com/p/spitfire/. It's a template system designed
> for performance that I have some experience with.

6% faster on a template system simply by optimizing conditional jumps is
quite neat.
(the spitfire homepage itself is rather intriguing, they claim to be
faster than plain string joining...)

> I was mostly curious whether the POP_OR_JUMP and JUMP_OR_POP opcodes
> had a noticeable performance impact, ie, do they make things fast
> enough to warrant their inclusion over the old JUMP_IF_FALSE
> implementations.

Well, I don't remember really, although this is only a few weeks old.
POP_OR_JUMP / JUMP_OR_POP will be used when the "and" and "or" keywords
are involved. That's basically the only situation where you don't want
to pop the top of stack after a conditional jump.

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