[pypy-dev] Dependence Graphs in Pypy?

[Tim Henderson]

On Wed, Aug 8, 2012 at 3:05 PM, Armin Rigo <arigo at tunes.org> wrote:

> Hi Tim,
>
> An additional remark: if you're looking for a tool that is able to
> extract a complete call graph from a random Python program, then it's
> impossible.  Only approximations can be done, like e.g. done in
> pylint, I believe.
>
> Such tools are pointless in PyPy but could be useful in other
> projects.  For example I can imagine a tool that would statically
> compile some version of a random Python program, including all
> necessary guards to check at run-time that the assumptions made are
> correct.  When these guards fail, it would fall back to a regular
> interpreter.
>
> The difference with PyPy is that the latter uses a tracing JIT
> compiler to do at run-time (partially) the same job as I describe
> above.  It does it by observation of the run-time behavior, which is a
> rather better estimator of the program's general behavior than a
> complex static analysis.  And it dispenses us from writing any such
> analysis.  This gives us a result that is not specific to a particular
> version of Python (or to Python at all).
>
>
> A bientôt,
>
> Armin.
>

Hi Armin,

Thanks for the lengthy reply.

Fortunately, I don't need a complete call graph. To get started I really
only need procedure level dependency graphs (with control and
data-dependencies). This graph is essentially a CFG with extra edges for
different types of data dependencies. Thanks to Alex's previous reply I am
taking a look at the CPython bytecode compiler to see if I can extract the
local CFG's it produces.

I could see a static approach potentially beating the dynamic approach
prior to the jit getting *hot* but after that it seems like the dynamic
approach would win in the long run. Luckily, I don't have to worry about
such things as I have no intention of writing a compiler (well for python
anyway you guys seem to have that under control), my main interest lies in
studying the evolution of the structure of the programs themselves.

Thanks for the pointers!

-Tim
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