Re: [RFC] LKMM: Add volatile_if()

Peter Zijlstra
2021-06-04T15:22:16Z

On Fri, Jun 04, 2021 at 04:13:57PM +0100, Will Deacon wrote:

> In fact, maybe it's actually necessary to bundle the load and branch
> together. I looked at some of the examples of compilers breaking control
> dependencies from memory-barriers.txt and the "boolean short-circuit"
> example seems to defeat volatile_if:
>
> void foo(int *x, int *y)
> {
> volatile_if (READ_ONCE(*x) || 1 > 0)
> WRITE_ONCE(*y, 42);
> }

Yeah, I'm not too bothered about this. Broken is broken.

If this were a compiler feature, the above would be a compile error. But
alas, we're not there yet :/ and the best we get to say at this point
is: don't do that then.