[Cython] Control flow graph

Stefan Behnel stefan_ml at behnel.de
Tue Feb 15 08:38:22 CET 2011

Robert Bradshaw, 15.02.2011 08:21:
> On Mon, Feb 14, 2011 at 9:49 PM, Vitja Makarov wrote:
>> 2011/2/15 Robert Bradshaw:
>>> On Sun, Feb 13, 2011 at 11:40 PM, Vitja Makarov wrote:
>>>> Hi!
>>>> In order to implement "reaching definitions" algorithm.
>>>> I'm now working on control-flow (or data-flow) graph.
>>>> Here is funny picture made with graphviz ;)
>>>> http://piccy.info/view3/1099337/ca29d7054d09bd0503cefa25f5f49420/1200/
>>> Cool. Any plans on handling exceptions?
>> Sure, but I don't have much time for this :(
>> Linear block inside try...except body should be split by assignments
>> and each subblock should point to exception handling entry point.
> Would every possible failing sub-expression have to point to the
> exception handling point(s)?

Well, in most cases (especially the interesting ones), this will be the 
function exit point, so it'll be easy. And in some cases, we may be able to 
infer that a specific exception that an expression (e.g. arithmetics or a 
'raise' statement) can raise will not get caught by a given except clause 
(although that's certainly a tricky optimisation).

But in general, I think any subexpression that potentially raises an 
exception must point to the next exception handling point.

> I suppose it depends on whether you'll be handling more than assignment
> tracking.

We *may* get away with a statement-level graph in that case, but I somehow 
doubt it already. For example, list comprehensions leak their variable in 
Py2 code, so it's important to know if they are executed or not, and they 
may appear in any kind of expression.


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