On Tue, 4 Oct 2011, Richard Guenther wrote:
> On Tue, 4 Oct 2011, Jakub Jelinek wrote:
>
> > On Tue, Oct 04, 2011 at 12:17:30PM +0200, Richard Guenther wrote:
> > > int *x;
> > >
> > > > void foo (int *p)
> > > > {
> > > > int * __restrict p1 = p;
> > > > int * __restrict p2 = p + 32;
> > > > int *q;
> > > > int i;
> > > x = p2;
> > > > q = p + 32;
> > > q = q - 31;
> > > > for (i = 0; i < 32; ++i)
> > > > p[i] = q[i];
> > > > }
> >
> > Yes, this is valid and so is a modified version of the earlier
> > testcase where all accesses in the first loop are biased
> > (bar below, assuming y > 32 or y <= -32).
> >
> > int *x;
> >
> > void
> > foo (int *p)
> > {
> > int *__restrict p1 = p;
> > int *__restrict p2 = p + 32;
> > int *q;
> > int i;
> > x = p2;
> > q = p + 32;
> > q = q - 31;
> > for (i = 0; i < 32; ++i)
> > p[i] = q[i];
> > }
> >
> > void
> > bar (int *p, int y)
> > {
> > int *__restrict p1 = p;
> > int *__restrict p2 = p + 32;
> > int *q;
> > int i;
> > for (i = 0; i < 32; ++i)
> > p1[i + y] = p2[i + y];
> > q = (p + 32) - 31;
> > for (i = 0; i < 32; ++i)
> > p[i] = q[i];
> > }
> >
> > >
> > > would be valid and we'd rely on CSE not to replace q = p + 32
> > > with q = p2 (ignoring the fact that for a miscompile we need
> > > similar tricks for p1). It doesn't do that at the moment
> > > because we fold int * __restrict p2 = p + 32 to
> > > ((int * __restrict)p) + 32 and thus see
> > >
> > > p.0_4 = (int * restrict) p_2(D);
> > > p2_5 = p.0_4 + 128;
> > >
> > > vs.
> > >
> > > q_6 = p_2(D) + 128;
> > >
> > > but you are going to change that ;)
> >
> > But even with the "Restrict fixes" patch I've just checked in
> > and with the TYPE_RESTRICT check removal patch I don't see anything
> > wrong in the IL, the only thing that is PT (restr) is the stmt
> > computing p2, which is just stored into x and nothing else, and
> > in the second function only the first loop.
>
> But that's by pure luck and not by design, no?
Well, updating my tree and playing with it a bit the above case
looks safe.
So, I think the patch removing the TYPE_RESTRICT checks is ok.
We can revert it again when issues show up.
Thanks,
Richard.
