[issue2183] optimize list comprehensions

[Antoine Pitrou]

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

> I presume it has been tested with nested and conditional variants? 

The whole test suite runs fine. test_iter and test_grammar seem to cover
all possible cases.

As for performance, the new benches in #4677 show a moderate improvement
(~ 10%).

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue2183>
_______________________________________