On Tue, 2014-02-18 at 23:48 +0000, Peter Sewell wrote: > On 18 February 2014 20:43, Torvald Riegel <triegel@xxxxxxxxxx> wrote: > > On Tue, 2014-02-18 at 12:12 +0000, Peter Sewell wrote: > >> Several of you have said that the standard and compiler should not > >> permit speculative writes of atomics, or (effectively) that the > >> compiler should preserve dependencies. In simple examples it's easy > >> to see what that means, but in general it's not so clear what the > >> language should guarantee, because dependencies may go via non-atomic > >> code in other compilation units, and we have to consider the extent to > >> which it's desirable to limit optimisation there. > > > > [...] > > > >> 2) otherwise, the language definition should prohibit it but the > >> compiler would have to preserve dependencies even in compilation > >> units that have no mention of atomics. It's unclear what the > >> (runtime and compiler development) cost of that would be in > >> practice - perhaps Torvald could comment? > > > > If I'm reading the standard correctly, it requires that data > > dependencies are preserved through loads and stores, including nonatomic > > ones. That sounds convenient because it allows programmers to use > > temporary storage. > > The standard only needs this for consume chains, That's right, and the runtime cost / implementation problems of mo_consume was what I was making statements about. Sorry if that wasn't clear. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
