On Fri, 22 Aug 2014, Marc Glisse wrote:
On Fri, 22 Aug 2014, Jason Merrill wrote:
On 08/22/2014 03:24 PM, Marc Glisse wrote:
Note that there is a patch waiting for a review that makes us accept !v
for vector v:
Ah, indeed. I still think we might as well treat vectors the same as other
types here.
Ok, now that it is a conscious choice, it feels much safer :-)
Though depending on where exactly this is called, it would be funny if we
warned for !v==-1 but not for !v==true, when the possible values for the
elements of !v are actually {-1,0}. I guess I'll have to test after Marek
commits.
Sadly, this is exactly what is happening. With my patch,
typedef int veci __attribute__ ((vector_size (4 * sizeof (int))));
void f (veci *a)
{
*a = !*a == -1;
}
warning: logical not is only applied to the left hand side of comparison
I also get the warning if I replace -1 with 0 or with a vector, but not
with true. This seems like the reverse of what is desirable.
I don't see how to change that, the warning is super-early (it warns for
templates that are not instantiated) and we may not know yet if the lhs is
a vector.
I guess people using vectors in such a strange construct can just always
add parentheses, and it should be rare that anyone writes !vec==true and
thus misses a useful warning.
--
Marc Glisse
