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. Andrew.
