The compiler can only reorder when that would be ok in the absence of UB. What can be reordered before the write through the pointer can't read the pointer, and

The compiler can only reorder when that would be ok in the absence of UB. What can be reordered before the write through the pointer can't read the pointer, and can't really do any damage. Syscalls and library calls (in particular if dynamically linked) can't be reordered before the write because the compiler can't see what the do. Most of the UB FUD are contrived examples that hardly happen in practice. What I'm saying is not that you should write bugs, but that bugs (especially segfaults) will immediately turn up in practice.