On Tue, Jan 12, 2021 at 9:18 AM Alexander Potapenko <glider@xxxxxxxxxx> wrote: > > On Tue, Jan 5, 2021 at 7:28 PM Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote: > > > > It might not be obvious to the compiler that the expression must be > > executed between writing and reading to fail_data. In this case, the > > compiler might reorder or optimize away some of the accesses, and > > the tests will fail. > > Have you seen this happen in practice? Yes. > Are these accesses to fail_data that are optimized (in which case we > could make it volatile)? Yes. AFAIU compiler doesn't expect expression to change fail_data fields, no those accesses and checks are optimized away. > Note that compiler barriers won't probably help against removing > memory accesses, they only prevent reordering. > > > + barrier(); \ > > expression; \ > > + barrier(); \ > > The need for barriers is not obvious to the reader, so a comment in > the code clarifying that would be nice. Will add a comment in v2, thanks!
