On Tue, Oct 04, 2011 at 11:01:27AM +0200, Richard Guenther wrote:
> > > > void foo (int *p)
> > > > {
> > > > int * __restrict p1 = p;
> > > > int * __restrict p2 = p + 32;
> > > > int *q;
> > > > int i;
> > > > for (i = 0; i < 32; ++i)
> > > > p1[i] = p2[i];
> > > > p = p1;
> > > > q = p2 - 31;
> > > > for (i = 0; i < 32; ++i)
> > > > p[i] = q[i];
> > > > }
> > > >
> In the above first loop the restrict pointers p1 and p2 access
> distinct object pieces. The second loop uses non-restrict qualified
> pointers p and q (that are based on the restrict variants p1 and p2
> though) to access overlapping pieces. Is the second loop invalid
> because p and q are based on p1 and p2 even though they are not
> restrict qualified?
IMHO yes. The standard doesn't seem to talk about the accesses being done
through the restricted pointer, but about accesses that are based on
the restricted pointer, and as soon as you access in the associated block
(here the foo function) some object through an lvalue whose address is
based on some restricted pointer and the value is modified by any means,
then all accesses to that object need to be done through something
based on that restricted pointer.
Jakub
