On Sun, Mar 05, 2017 at 05:58:37PM +0100, Gabriel Paubert wrote: > > > Erk sorry. One of the static checkers spotted it, but I hadn't got > > > around to fixing it because it seemed to not actually blow up, guess > > > not. > > > > The PowerPC divw etc. instructions do not trap by themselves, but recent > > GCC inserts trap instructions on code paths that are always undefined > > behaviour (like, dividing by zero). > > Is it systematic or does it depend from, e.g., optimization levels?
In this case it needs -fisolate-erroneous-paths-dereference which is default at -O2 and higher. > Is there anything in the standards about this feature? The compiler can do whatever it likes with code that has undefined behaviour. With this optimisation it a) can compile the conforming code to something better; and b) undefined behaviour will trap instead of doing something random (which often is exploitable). Segher
