[Cython] Bug in Cython producing incorrect C code

Dag Sverre Seljebotn d.s.seljebotn at astro.uio.no
Tue Jan 24 20:18:06 CET 2012

On 01/24/2012 08:05 PM, Vitja Makarov wrote:
> 2012/1/24 mark florisson<markflorisson88 at gmail.com>:
>> On 24 January 2012 18:30, Vitja Makarov<vitja.makarov at gmail.com>  wrote:
>>> 2012/1/24 Robert Bradshaw<robertwb at math.washington.edu>:
>>>> On Tue, Jan 24, 2012 at 6:09 AM, Vitja Makarov<vitja.makarov at gmail.com>  wrote:
>>>>> 2012/1/24 mark florisson<markflorisson88 at gmail.com>:
>>>>>> On 24 January 2012 11:37, Konrad Hinsen<konrad.hinsen at fastmail.net>  wrote:
>>>>>>> Compiling the attached Cython file produced the attached C file which
>>>>>>> has errors in lines 532-534:
>>>>>>>   __pyx_v_self->xx = None;
>>>>>>>   __pyx_v_self->yy = None;
>>>>>>>   __pyx_v_self->zz = None;
>>>>>>> There is no C symbol "None", so this doesn't compile.
>>>>>>> I first noticed the bug in Cython 0.15, but it's still in the latest
>>>>>>> revision from Github.
>>>>>>> Konrad.
>>>>>>> _______________________________________________
>>>>>>> cython-devel mailing list
>>>>>>> cython-devel at python.org
>>>>>>> http://mail.python.org/mailman/listinfo/cython-devel
>>>>>> Hm, it seems the problem is that the call to the builtin float results
>>>>>> in SimpleCallNode being replaced with PythonCApiNode, which then
>>>>>> generates the result code, but the list of coerced nodes are
>>>>>> CloneNodes of the original rhs, and CloneNode does not generate the
>>>>>> result code of the original rhs (i.e. allocate and assign to a temp),
>>>>>> which results in a None result.
>>>>>> Maybe CascadedAssignmentNode should replace CloneNode.arg with the
>>>>>> latest self.rhs in generate_assignment_code? I'm not entirely sure.
>>> Seems like a hack to me.
>>>>> May be it's better to run OptimizeBuiltinCalls before
>>>>> AnalyseExpressionsTransform?
>>>> Doesn't OptimizeBuiltinCalls take advantage of type information?
>>> Yes, it does :(
>>> So as Mark said the problem is CascadedAssignmentNode.coerced_rhs_list
>>> is created before rhs is updated.
>> I think deferring the CloneNode creation to code generation time works
>> (are there any known problem with doing type coercions at code
>> generation time?).
> Coercion errors at code generation time?

Apologies up front for raising my voice, as my knowledge of the 
internals are getting so rusty...take this with a grain of salt.

I'm +1 on working towards having the code generation phase be pure code 
generation. I did some refactorings to take mini-steps towards that once 
upon a time, moving some error conditions to before code generation.

My preferred approach would be to do away with CascadedAssignmentNode at 
the parse tree stage:

a = b = c = expr

goes to

tmp = expr
c = tmp
b = tmp
a = tmp

and so on. Of course it gets messier;

(expr1)[expr2] = (expr3).attr = expr4

But apart from getting the time of evaluating each expression right the 
transform should be straightforward. One of the tempnodes/"let"-nodes (I 
forgot which one, or if they've been consolidated) should be able to fix 

Takes some more work though than a quick hack though...


>> E.g. save 'env' during analyse_types and in
>> generate_assignment_code do
>>     rhs = CloneNode(self.rhs).coerce_to(lhs.type, self.env)
>>     rhs.generate_evaluation_code(code)
>>     lhs.generate_assignment_code(rhs, code)
>> Seems to work.
> Yeah, that's better.

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