Hi, On Mon, 8 Oct 2018, Alexander Monakov wrote:
> > Only if you somewhere visibly add accesses to *i and *j. Without them > > you only have the "accesses" via memcpy, and as Richi says, those > > don't imply any alignment requirements. The i and j pointers might > > validly be char* pointers in disguise and hence be in fact only > > 1-aligned. I.e. there's nothing in your small example program from > > which GCC can infer that those two global pointers are in fact > > 2-aligned. > > Well, it's not that simple. C11 6.3.2.3 p7 makes it undefined to form an > 'int *' value that is not suitably aligned: > > So in addition to what you said, we should probably say that GCC decides > not to exploit this UB in order to allow code to round-trip pointer values > via arbitrary pointer types? That's correct, I was explaining from the middle-end perspective. There we are consciously more lenient as we have to support the real world and other languages than C. This is one of the cases. Ciao, Michael.
