On Wed, Oct 02, 2024 at 03:24:45PM +0000, David Laight wrote: > I think I know what you are trying to do, and you just fail. > Whether something can work is another matter, but that code > can't ever work. > > Inside if (a == b) the compiler will always use the same register > for references to a and b - because it knows they have the same value. According to the other people in this discussion who have actually tried using this code, it _does_ work (at least some of the time). However, I'm not one of those people and so I leave it up to them to decide how to respond to this critique. Alan > Possibly something like: > c = b; > OPTIMISER_HIDE_VAR(c); > if (a == c) { > *b > will ensure that there isn't a speculative load from *a. > You'll get at least one register-register move - but they are safe. > Otherwise you'll need to put the condition inside an asm block. > > David