[issue2459] speedup for / while / if with better bytecode

[Collin Winter]

Collin Winter <collinw at gmail.com> added the comment:

I don't see the changes to the lnotab format being a roadblock; just
mention it in NEWS. Likewise, the pure-Python compiler package shouldn't
be a high priority; your changes to that package look good enough.

I'm seeing encouraging speed-ups out of this (with gcc 4.3.1 x86_64,
compiling Python as 64-bit):
Django templates (render a 150x150 table 100 times):
Min: 0.595 -> 0.589: 0.94% faster
Avg: 0.599 -> 0.591: 1.30% faster

Spitfire templates (render a 1000x1000 table 100 times):
Min: 0.751 -> 0.729: 2.98% faster
Avg: 0.753 -> 0.730: 3.09% faster

None of the apps I've benchmarked are negatively impacted. I only have
two minor comments. Please commit this.


Review comments:
- The changes to Python/compile.c:compiler_if(), compiler_for(),
compiler_while() have some indentation issues (tabs and such).
- Functions like
def foo():
  while True:
    pass
have a useless JUMP_FORWARD 0 instruction, but I don't think it's worth
teaching the peepholer to remove them since it doesn't happen in other
circumstances (that I can tell).

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue2459>
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