[C++-sig] boost/python 1.33.1 breaks aliasing rules

[David Abrahams]

Philipp Thomas <pth at suse.de> writes:

>> Can Philipp explain why we should invest energy in trying to make
>> these warnings go away?
>
> gcc bases parts of its optimisations on the result of the
> strict-alias analysis. So for instance objects (still non-C++ sense)
> will be eliminated if gcc determines that they aren't accessed by a
> pointer of the allowed type. So an access via a type-punned pointer
> will return garbage in this case.

But we can't control it, can we?  Python is going to access that data,
and you can't use Python without that sort of punning.  If Python is
compiled with optimizations that take advantage of those aliasing
rules, everybody who uses it will have the same problem.  What
alternative do we have?

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com