On Thu, Jul 16, 2015 at 5:59 AM, Andrew Haley <aph@xxxxxxxxxx> wrote: > On 16/07/15 10:40, Jeffrey Walton wrote: >>>> Many folks try and cast ptr to volatile, but that's an abuse because >>>> GCC considers volatile something for memory mapped hardware. Volatile >>>> should not be used in an attempt to tame the optimizer. >>> >>> GCC does not consider volatile to be something for memory mapped >>> hardware. >> >> OK, this appears to be creating a moving definition (or the definition >> has changed since I took note of it). I took the last definition from >> Ian Lance Taylor. See http://www.airs.com/blog/archives/154 and, for >> example, https://gcc.gnu.org/ml/gcc-help/2012-03/msg00257.html. > > Well, reluctant as I am to argue with Ian, the definition of volatile > I used is a direct quote from the standard. There are problems with > volatile as defined, it's true: for example, nowhere is it specified > exactly what constitutes a memory access. And Ian is quite right to > say that the standard doesn't guarantee that a pointer-to-volatile > should be handled as though it pointed to a volatile object. But in > this case, with GCC, I think it's fine. > Yeah, it kind of crossed my wires for a moment. There's a handful of folks I always listen to when it comes to GCC, and you and Ian are two of them :o If you tell me the memory barrier works to tame the optimizer for a function, then that's what I will use. Jeff
