Paul E. McKenney <paulmck@xxxxxxxxxx> wrote: > On Fri, Jul 15, 2022 at 09:27:26AM -0400, Alan Stern wrote: >> On Fri, Jul 15, 2022 at 02:27:28PM +0200, Paul Heidekrüger wrote: >>> I have just been thinking about how to word this patch; am I correct in >>> assuming that the LKMM does not deal with loop conditions? Or in other >>> words, there is no way for a loop condition to impose a ctrl dependency on >>> any WRITE_ONCE's in the loop body? It are only if and switch statements the >>> LKMM is concerned with in the case of ctrl dependencies? >> >> In theory, the LKMM does say that a loop condition imposes a control >> dependency on any memory accesses within the loop body. However, the >> herd7 tool has only very limited support for looping constructs, so in >> practice it's not possible to create suitable litmus tests with loops. > > And Alan isn't joking. The closest simulation that I know of is to > combine limited loop unrolling with the "filter" clause. The point of > the filter clause is to eliminate from consideration executions that > need the more iterations of the loop to be unrolled. > > And that means that as far as LKMM is concerned, loop-based control > dependencies are similar to those for nested "if" statements. > > Thanx, Paul Makes sense, thank you both! Paul
