[Bug middle-end/83404] bogus stringop-overflow warning

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83404

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=83412

--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
It should and does as long as the result is used (see below) and as long as
some GCC bug doesn't get in the way.  When <string.h> defines strncat as macro
like in Glibc 2.24 the warning doesn't trigger.  I opened bug 83412 for it. 
There's also bug 82944 that I thought was due to warnings being suppressed for
macros defined in system headers but maybe it's actually the same as bug 83412.
 Phew.

$ cat a.c && gcc -O2 -S -Wall a.c
extern char* strncpy (char*, const char*, __SIZE_TYPE__);
extern char* strncat (char*, const char*, __SIZE_TYPE__);

int main (void)
{
  char x[12];

  strncpy (x, "", 12);

  strncat (x, "aa", 1);

  __builtin_puts (x);
}
a.c: In function ‘main’:
a.c:10:3: warning: ‘strncat’ output truncated copying 1 byte from a string of
length 2 [-Wstringop-truncation]
   strncat (x, "aa", 1);
   ^~~~~~~~~~~~~~~~~~~~