On Mon, Oct 05, 2020 at 12:18:01PM -0700, Paul E. McKenney wrote:
> Aside from naming and comment, how about my adding the following?
>
> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> C crypto-control-data-1
Let's call it something more along the lines of
dependencies-in-nested-expressions. Maybe you can think of something a
little more succinct, but that's the general idea of the test.
> (*
> * LB plus crypto-mb-data plus data.
The actual pattern is LB+mb+data.
> *
> * Result: Never
> *
> * This is an example of OOTA and we would like it to be forbidden.
> * If you want herd7 to get the right answer, you must use herdtools
> * 0f3f8188a326 (" [herd] Fix dependency definition") or later.
Versions of herd7 prior to commit 0f3f8188a326 ("[herd] Fix dependency
definition") recognize data dependencies only when they flow through an
intermediate local variable. Since the dependency in P1 doesn't, those
versions get the wrong answer for this test.
> *)
>
> {}
>
> P0(int *x, int *y)
> {
> int r1;
>
> r1 = READ_ONCE(*x);
> smp_mb();
> WRITE_ONCE(*y, r1);
> }
>
> P1(int *x, int *y)
> {
> int r2;
No need for r2.
>
> WRITE_ONCE(*x, READ_ONCE(*y));
> }
>
> exists (0:r1=1)
Alan
