Can someone with more knowledge chip in? If I define

  void bar(int* const p, int n) {
    for (int i=0; i<n; ++i) {
      int m = *p
      // other code (without UB)
    }
  }

it might get optimized via loop-invariant code motion to

  void bar(int* const p, int n) {
    int m = *p
    for (int i=0; i<n; ++i) {
      // other code (without UB)
    }
  }

so it could still be UB when called with p=NULL and n=0, right?

Edit: Oops, in the previous version I used a write instead of a read on *p, making the optimization invalid.