Your block of code can be (and absolutely is) optimized to output zero directly (in c, because the assembly is easier to read):
https://c.godbolt.org/z/qe3f4K
`*(&i+1)` dereferences the pointer "one past the end" which is UB.
https://c.godbolt.org/z/qe3f4K
`*(&i+1)` dereferences the pointer "one past the end" which is UB.
But then, why such a long article for a code whose second line is a UB ('p+1' is undefined)?
uintptr_t ip = (uintptr_t)(p+1);
So now I think it's the first optimization the one that is wrong. If you replace a variable with another, don't you need to keep information of the original variable?
I mean, if a==b and you do *a=1 you can replace it with *b=1, but then you need to keep the information that 'a' was written to, so other optimizations (the third one) don't think it wasn't. Or am I missing something else here?
Note that ip and iq are integers. If you can't replace integers freely, it makes it really hard to optimize arithmetic.
It constructs a pointer to the "one past the end" element, but that is fine, and the original program never dereferences that pointer. Again: there is no UB in the original program.