c – 轻松或严格的指针安全？

我想澄清关于严格指针安全概念的以下事项.有一个引用(第3.7.4.3/4节)：

Alternatively,an implementation may have strict pointer safety,in
which case a pointer value referring to an object with dynamic storage
duration that is not a safely-derived pointer value is an invalid
pointer value unless the referenced complete object has previously
been declared reachable (20.7.4).

这个限制对我来说完全不清楚.此外,我尝试用cplusplus.com example进行实验

// declare_reachable / undeclare_reachable example
#include <iostream>
#include <memory>
#include <cstdint>

int main() {
  int * p = new int (1);    // dynamic object

  std::declare_reachable(p);

  p = (int*)((std::uintptr_t)p ^ UINTPTR_MAX);  // scrambling p

  // dynamic object not reachable by any live safely-derived pointer

  p = std::undeclare_reachable((int*)((std::uintptr_t)p ^ UINTPTR_MAX));
  // p is back again a safely-derived pointer to the dynamic object

  std::cout << "p: " << *p << 'n';
  delete p;

  return 0;
}

代码甚至无法编译.

demo