[Cython] Generators & closure optimization

[Stefan Behnel]

Stefan Behnel, 21.12.2011 21:17:
> Vitja Makarov, 21.12.2011 19:48:
>> Some time ago we were talking about generators optimization by copying
>> local variables from closure into local scope.
>
> Yes, I think that will make it easier for the C compiler to make optimistic
> assumptions about external values.
>
>> Now I think that should be a good idea to implement this for both
>> generators and regular closure functions. So local var will be used
>> for reference and assignment should be made to both copies. Of course
>> there are some variables that shouldn't be copied: non-local vars,
>> arrays, C++ classes and structures.
>
> Basically, anything that external code can modify. That makes it a bit
> tricky to do it also for 'normal' closure functions - the whole idea is
> that there is more than one function that can refer to a variable.
>
>> Also it may be a good idea to move outer scope pointer into local variable.
>>
>> So I'm wondering what is a good test to measure actual speedup?
>
> http://blog.behnel.de/index.php?p=163
>
> Just take the plain Python versions of the iterparse functions and compare
> them before and after the change. The raw C implementation in CPython gives
> a good baseline.
>
> Actually, it would be generally interesting to run the Cython versions
> through callgrind to see where the time is actually being spent.

Another useful test is the "nqueens" benchmark from the CPython test suite. 
It's regularly run on Jenkins in Py2.7 and 3.3.

https://sage.math.washington.edu:8091/hudson/view/bench/

Note that it mostly uses generator expressions, which could easily benefit 
from a couple of further optimisations by specialising them, e.g. by 
providing a length hint.

http://trac.cython.org/cython_trac/ticket/756

Stefan