While looking into bug 92666 I noticed the following false positive in C (it can be reproduced in C++ making the pointer non-const so it doesn't get folded).  By being implemented fully in the front-end the warning doesn't see that the nullptr variable is, in fact, a null pointer.

$ cat t.c && cat t.c && gcc -S -Wall t.c
void f (void)
{
  const char* const null = 0;

  __builtin_execl ("foo", "bar", null);
}
void f (void)
{
  const char* const null = 0;

  __builtin_execl ("foo", "bar", null);
}
t.c: In function ‘f’:
t.c:5:3: warning: missing sentinel in function call [-Wformat=]
    5 |   __builtin_execl ("foo", "bar", null);
      |   ^~~~~~~~~~~~~~~