[pypy-dev] Static bytecode instruction optimization and pypy (JIT?) optimization

[Rocky Bernstein]

On Tue, Jul 11, 2017 at 4:35 AM, William ML Leslie <
william.leslie.ttg at gmail.com> wrote:

> On 11 July 2017 at 18:22, Rocky Bernstein <rb at dustyfeet.com> wrote:
> > There's too much generalization and abstraction in the discussion at
> least
> > for me. So let me try to make this a little more concrete with real
> > examples. First note that, although Python, yes, does "optimize" "if 0:"
> > away, as soon as
> > you do something as simple as "debug = 0; if debug:" it is confounded.
> And
> > in my own experience I have done this.
> >
>
> Typically DEBUG is a global in the module, which means it can be set
> from /outside/ the module, so it's not constant as far as the runtime
> is concerned.  Within a function it's a bit wacky sure, and is only
> kept around for interactive debugging reasons afaict.
>

You presume to know much more about the programmer's intentions and
behavior than I would care to venture into, or how and why such things
could arise.



> Here's a possible type for `self.a` which illustrates why
> CSE/Store-Sinking on a STORE_ATTR is not valid for the example
> function `foo`.
>
> class A(object):
>     def set_b(self, value):
>         print value
>         self._b = value
>     b = property(set_b)
>
> class Example(object):
>     def __init__(self):
>         self.a = A()
>
>     def foo(self):
>         self.a.b = 5
>         x = 0
>         if x:
>             self.a.b = 2
>         else:
>             return
>
> Example().foo()
>


Absolutely one can create pathological cases like this. I hope though this
isn't your normal mode of coding though.

I suspect that this kind of thing doesn't occur often. You know, I
encountered something analogous when I first started using Python's code
coverage tool, coverage, and the Python style checker flake8. As per Mark
Pilgram's original version of Dive into Python I used:

if __name__ == '__main__':

And I was annoyed that older versions of code coverage dinged me because
that code was untested code unless I took special care to run it in
testing. (Which sometimes I would do).

And I suspect most people have run into *some* annoyance with flake8 and
the way it dictates formatting things.

So what people typically do *if *they choose to use coverage or flake8 is
add additional comments that clew the tool not to consider that section of
the code. As best as I can tell, it works out pretty well.


--
William Leslie

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