On Mon, Feb 10, 2014 at 11:49:29AM +0000, Will Deacon wrote:
> On Mon, Feb 10, 2014 at 11:48:13AM +0000, Peter Zijlstra wrote:
> > On Fri, Feb 07, 2014 at 10:02:16AM -0800, Paul E. McKenney wrote:
> > > As near as I can tell, compiler writers hate the idea of prohibiting
> > > speculative-store optimizations because it requires them to introduce
> > > both control and data dependency tracking into their compilers. Many of
> > > them seem to hate dependency tracking with a purple passion. At least,
> > > such a hatred would go a long way towards explaining the incomplete
> > > and high-overhead implementations of memory_order_consume, the long
> > > and successful use of idioms based on the memory_order_consume pattern
> > > notwithstanding [*]. ;-)
> >
> > Just tell them that because the hardware provides control dependencies
> > we actually use and rely on them.
>
> s/control/address/ ?
Both are important, but as Peter's reply noted, it was control
dependencies under discussion. Data dependencies (which include the
ARM/PowerPC notion of address dependencies) are called out by the standard
already, but control dependencies are not. I am not all that satisified
by current implementations of data dependencies, admittedly. Should
be an interesting discussion. ;-)
Thanx, Paul
