[Bug c/92667] New: spurious missing sentinel in function call with a local sentinel variable

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92667

            Bug ID: 92667
           Summary: spurious missing sentinel in function call with a
                    local sentinel variable
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

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);
      |   ^~~~~~~~~~~~~~~