[Python-3000] Use Py_CLEAR only

[Walter Dörwald]

Greg Ewing wrote:

> Walter Dörwald wrote:
> 
>> The "checking for NULL" scenario looks somewhat like this:
>>
>> And the "clearing the reference" scenario should look ike this:
> 
> But only if the reference is a local to the function,

True Py_CLEAR(foo->bar->baz) probably won't be optimized.

> and it's used in a disciplined enough way, and the
> compiler is smart enough. None of those things are
> guaranteed true for all uses of Py_DECREF/Py_XDECREF.

I tried simply replacing all Py_DECREF()/Py_XDECREF() calls with
Py_CLEAR with the result that nothing works any more. ;)

Modules/posixmodule.c uses Py_DECREF(Py_None) which can't work with
Py_CLEAR, because Py_None is not an lvalue.

Python/import.c::PyImport_AddModule() returns m after doing a Py_DECREF,
so this would have to continue to use Py_DECREF() (or do a dance with a
second local variable).

Python/compile.c::makecode() must use Py_DECREF, because the variable is
still checked afterwards.

Python/symtable.c::symtable_new_tmpname() and
Python/compile.c::compiler_listcomp() (and probable many others)
use the same var name as the Py_CLEAR macro which doesn't work.

Objects/dictobject.c::insertdict() does a Py_DECREF(dummy), but that
probably shouldn't clear dummy.

And then I gave up.

If we would do this, IMHO it would only make sense to do it the other
way round: Replace Py_(X)DECREF with Py_CLEAR in selected spots. But
that's not much different from what has happened up to now.

Servus,
   Walter