[Cython] local variable handling in generators

[Vitja Makarov]

2011/5/24 Stefan Behnel <stefan_ml at behnel.de>:
> Vitja Makarov, 23.05.2011 21:33:
>>
>> 2011/5/23 Stefan Behnel:
>>>
>>> However, once we really know which values change between yield calls,
>>> i.e.
>>> which ones need to be stored away, it will actually be less expensive in
>>> most cases. We currently pay the indirection penalty for each access,
>>> even
>>> read access, whereas the C compiler can then keep important variables in
>>> registers and only write them back once per yield.
>>>
>>
>> I think that all not NULL variables should be saved/restored inside yield.
>> I can not really track changes only assignments.
>
> I mean "assignments" when I write "changes". When a variable is being
> assigned to, we should assume that its value changed. Users can be expected
> to be smart enough to avoid unnecessary assignments in most cases, there's
> no need to put work into optimising them away automatically.
>
>
>> for i in a:
>>     yield i  # j is NULL here
>> for j in b:
>>     yield j # a, b, i ,j should be saved/restored
>
> Right. However, in general, we can expect that most variables will have been
> initialised on a yield.
>
> We can still avoid storing away C typed variables that are not being used
> later on, because they are not reference counted.
>
> And if the user sets 'a' and 'i' to None between the loops, they won't need
> to be saved on the second yield either. But that's an optimisation, not a
> requirement.
>

What about copying C++ structs and objects with constructor (and/or
overloaded = method)?
That wouldn't work well.

-- 
vitja.