optimisation of overflowing integers

[Davide Mancusi]

Hi all,

I posted a question on stackoverflow concerning the way gfortran
optimises integer arithmetics relying on variable overflow. I would
appreciate if you guys could give it a look.

http://stackoverflow.com/questions/22455956/gfortran-optimisation-of-overflowing-integers

I was mildly shocked by the result of gfortran's optimisation. I was wondering:
1. does gfortran's aggressive optimisation qualify as a bug?
2. wouldn't gfortran's unexpected behaviour warrant at least a
warning? Note that no warning is generated, even with -Wall -Wextra
-pedantic.

Thank you in advance for your time.

Regards,
Davide