Prajwal Suhas P wrote:
> Hi Dag,
>
> I am currently looking at the tickets.
>
> I was looking at this -
>
> cdef int i, n
> n = 10
> for i in range(n):
> if i == 5:
> n *= 2
> print i
>
>
> The generated c code for this is -
>
> __pyx_v_5test1_n = 10;
>
> for (__pyx_v_5test1_i = 0; __pyx_v_5test1_i < __pyx_v_5test1_n;
> __pyx_v_5test1_i+=1) {
>
> __pyx_1 = (__pyx_v_5test1_i == 5);
> if (__pyx_1) {
> __pyx_v_5test1_n *= 2;
> goto __pyx_L4;
> }
> __pyx_L4:;
> }
>
> Can the var 'n' be held in another temp variable?
>
> Something like this -
>
> __pyx_v_5test1_n = 10;
> __pyx_v_5test1_const_n = 10;
>
> for (__pyx_v_5test1_i = 0; __pyx_v_5test1_i < __pyx_v_5test1_const_n;
> __pyx_v_5test1_i+=1) {
>
> __pyx_1 = (__pyx_v_5test1_i == 5);
> if (__pyx_1) {
> __pyx_v_5test1_n *= 2;
> goto __pyx_L4;
> }
> __pyx_L4:;
> }
> i--;
>
> I haven't looked at the cython code which parses the loop and outputs
> the c code. I would really appreciate if you can give me a head start
> into this and correct me if I am wrong.
You are correct, this is what you need to do. Some suggestions:
a) Add a flag to ForFromStatNode in Nodes.py, say, "freeze_endpoints".
b) IterationTransform in Optimize.py is what takes a "for i in
range(...)" and turns it into a ForFromStatNode. Here you should turn
the freeze_endpoints flag on when the ForFromStatNode is constructed.
c) If this flag is set, then ForFromStatNode.generate_execution_code
must put the start or end points (or both, depending on the case) into
temporary variables.
d) You can get hold of a temporary variable to use (like __pyx_t2) by
calling code.funcstate.allocate_temp/release_temp. See Code.py for docs.
(Stefan: Yes, this can be done by temp handling nodes in the transform
as well, but since the canonical way of doing that is a bit unclear/a
mess at the moment I don't want to encourage that. This works as well,
and is likely less code in the end.)
Another for-loop bug was also fixed with a bit of assistance on the
mailing list, you may want to read through:
http://thread.gmane.org/gmane.comp.python.cython.devel/4195
Also please make sure you make a testcase in
tests/bugs/something_T203.pyx (then run this with python runtests.py
-T203 while developing).
--
Dag Sverre
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