Indeed I don't think C cares about how the pointers you mark as "restrict" were constructed, it just cares about how you actually use the pointers and in the example code they are never used in an "overlapping" way.
I just checked cppreference and it says: "if some object that is accessible through P [marked restrict] (directly or indirectly) is modified, by any means, then all accesses to that object (both reads and writes) in that block must occur through P (directly or indirectly), otherwise the behavior is undefined"
The only accesses I can see are "*x = 0;", "*ptr = 1;" and "return *x;". "*ptr" is an indirect access through "x" by way of an integer round trip. If the orignal program is indeed UB that would mean that pointers built from an integer round trip are not considered (indirect) accesses through the original pointer.
The author assumes that it is an indirect access: "However, the only possibly suspicious part of the original program is a pointer-integer-pointer round-trip – and if casting integers to pointers is allowed, surely that must work. I will, for the rest of this post, assume that replacing x by (int*)(uintptr_t)x is always allowed."
I just checked cppreference and it says: "if some object that is accessible through P [marked restrict] (directly or indirectly) is modified, by any means, then all accesses to that object (both reads and writes) in that block must occur through P (directly or indirectly), otherwise the behavior is undefined"
The only accesses I can see are "*x = 0;", "*ptr = 1;" and "return *x;". "*ptr" is an indirect access through "x" by way of an integer round trip. If the orignal program is indeed UB that would mean that pointers built from an integer round trip are not considered (indirect) accesses through the original pointer.
The author assumes that it is an indirect access: "However, the only possibly suspicious part of the original program is a pointer-integer-pointer round-trip – and if casting integers to pointers is allowed, surely that must work. I will, for the rest of this post, assume that replacing x by (int*)(uintptr_t)x is always allowed."