[Bug middle-end/78917] missing -Wnonnull passing null to a nonnull function

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78917

--- Comment #2 from Martin Sebor <msebor at gcc dot gnu.org> ---
Another test case:

$ cat f.c && gcc -O2 -S -Wall -Wextra f.c
int f (int i)
{
  const char * p = __builtin_strchr (i ? "123" : "456", '2');
  return __builtin_strlen (p);
}

The strlen argument is a phi with a null operand so that should make it easy to
detect:

  # prephitmp_11 = PHI <_10(3), 0B(2)>
  _1 = __builtin_strlen (prephitmp_11);