Efficient detection of signed overflow?

[Florian Weimer]

* Andrew Haley:

>> I wouldn't rule it out.  Just use -fwrapv (perhaps after benchmarking
>> to make sure that it doesn't make a difference).  Other compilers will
>> have similar switches.
>
> This is bad advice.  -fwrapv suppresses loop optimizations.

Some loop optimizations perhaps, which are likely not to be relevant
for the code base in the question.

> Given that it's not difficult to detect overflow with perfectly
> compliant code, there's no point.

The fully compliant solution has an additional performance overhead
compared to the one that assumes -fwrapv.  Instead of -fwrapv, you can
rely on additional guarantees from the documentation, but for someone
that ships code to be compiled with unknown GCC versions, this might
not be the best solution.