[Bug middle-end/79310] -Wnonnull false positive on strlen after strstr

["msebor at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79310

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization

--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
A similar case and optimization opportunity (and also a possible source of
false positives) exists with strchr.

$ cat t.c && gcc -O2 -S -Wall -fdump-tree-optimized=/dev/stdout t.c
void foo (const char *s, int x)
{
  if (!__builtin_strchr (s, '\0'))
    __builtin_abort ();
}

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

foo (const char * s, int x)
{
  char * _1;
  long unsigned int _4;

  <bb 2> [100.00%]:
  _4 = __builtin_strlen (s_3(D));
  _1 = s_3(D) + _4;
  if (_1 == 0B)
    goto <bb 3>; [0.04%]
  else
    goto <bb 4>; [99.96%]

  <bb 3> [0.04%]:
  __builtin_abort ();

  <bb 4> [99.96%]:
  return;

}