https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88813
--- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> ---
To be safe, even though %s requires that the argument be a nul-terminated
string, the snprintf optimization would need to be predicated on knowing that
it, in fact, is one (to avoid buffer overflow if snprintf was called with a
non-string argument). The optimization opportunity is in the length of the
source string not needing to be known. When the source array is not guaranteed
to be a nul-terminated string then the memccpy optimization described in
pr88814 could take place instead.
So to clarify the example in comment #0, the array size optimization would only
be applicable if s was previously used as a string, such as in an argument to
some string function like in:
char d[8];
char s[8];
char *p;
void g (void)
{
p = __builtin_strchr (s, '/'); // s must be a nul-terminated string
...
__builtin_snprintf (d, sizeof d, "%s", s); // can be folded to strcpy
}
