Last week's r276603 has introduced a bug into the count_nonzero_bytes function that leads to a false positive -Wstringop-overflow in glibc's timezone/zic.c.  The test case below reproduces the bogus warning.

$ cat zic.i && gcc -S -O2 -Wall zic.i
struct
{
  char *s1, *s2;
  char c;
} z;


void f (char **a, int i, int j)
{
  char * cp = __builtin_strchr (a[i], '%');

  if (cp && *++cp != 's')
    return;

  z.s1 = __builtin_strdup (a[i]);
  if (!z.s1) __builtin_abort ();

  z.s2 = __builtin_strdup (a[j]);
  if (!z.s2) __builtin_abort ();

  z.c = cp ? *cp : '\0';
}
zic.i: In function ‘f’:
zic.i:21:7: warning: writing 8 bytes into a region of size 1 [-Wstringop-overflow=]
   21 |   z.c = cp ? *cp : '\0';
      |   ~~~~^~~~~~~~~~~~~~~~~
zic.i:4:8: note: destination object declared here
    4 |   char c;
      |        ^