http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49413
Richard Guenther <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |INVALID
--- Comment #10 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-08-04
09:35:13 UTC ---
There are two camps of users, some want the compiler to treat *(double *)
as aligned because, damn, they said so (especially on targets where
accessing unaligned data is costly)! Others want the compiler to figure
out misalignment properly, thus, treat *(double *) as aligned only if
it knows (for sure?).
We can't serve both camps.
Consider
void foo (double *p, double *q, int n)
{
int i;
for (i = 0; i < n; ++i)
p[i] += q[i];
}
do you want the compiler to vectorize the above or not? The C standard
says we can assume *p and *q are properly aligned for what the ABI
says about doubles. But you say, well, I may als well call this function
with some misaligned data where I think the compiler should figure this
out for me.
Now, I say not so.
