http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60165
--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
How can the compiler know that fn2 never returns 0, without inlining (not in
this case), some attribute (not provided, gcc right now has returns_nonnull
attribute but that is only for pointers) or some interprocedural analysis)?
Of course, if you want zero false positives, the uninitialized warnings could
not exist, even if you do:
int
foo (void)
{
int c;
return c;
}
you could say that warning here is a false positive, because you might actually
never call that function.
For -O2 we don't warn, because then the compiler does see an opaque call that
might be initializing what the arguments points to, might not, but warning in
that case would just mean too many false positives as I've said before.
While for -O3, when it is inlined a few times, the compiler clearly sees code
paths where the value is uninitialized, and has nothing that would hint such
code paths are impossible.
Of course, if fn2 is guaranteed to return non-NULL, why do you even write if
(fn2 (a, 0)) *p1 = b; rather than just
fn2 (a, 0); *p1 = b; ?
