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

[msebor at gcc dot gnu.org]

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

            Bug ID: 78917
           Summary: missing -Wnonnull passing null to a nonnull function
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

While experimenting with the enhanced -Wnonnull warning added in GCC 7.0 (bug
17308) I noticed that it fails to detect the following trivial case of  passing
a null pointer to a function declared nonnull.  This is different from bug
78914 where the null pointer is being dereferenced directly.

$ cat z.c && gcc -O2 -S -Wall -Wextra -Wpedantic
-fdump-tree-optimized=/dev/stdout z.c
int g (int i, int j)
{
  char *p = i <= 0 ? (char*)0 : "123";
  char *q = 0 != i ? (char*)0 : "4567";
  char *r = i ? q : p;

  return __builtin_strlen (r);
}

z.c: In function ‘g’:
z.c:1:19: warning: unused parameter ‘j’ [-Wunused-parameter]
 int g (int i, int j)
                   ^

;; Function g (g, funcdef_no=0, decl_uid=1796, cgraph_uid=0, symbol_order=0)

g (int i, int j)
{
  long unsigned int _1;
  int _7;

  <bb 2> [100.00%]:
  _1 = __builtin_strlen (0B);
  _7 = (int) _1;
  return _7;

}