Peter Dimov wrote:
Ben Hutchings wrote:
Peter Dimov <pdimov@mmltd.net> wrote:
Alexander Terekhov wrote:
C'mon, volatile is brain-dead.
Nobody's arguing otherwise. ;-) But a nop it isn't.
I think Alexander is arguing that without a clear definition of what it means for a memory access to be "observable",
A memory access is observable if and only if the variable is volatile. 1.9/6.
Yes, I understand what is observable (extensional definition). Yet the real meaning of "observable" (intensional definition) is vague (and understandably so).
the fact that volatile memory accesses are "observable behaviour" doesn't prevent them from being optimised away under the as-if rule.
A compiler is not allowed to alter the observable behavior under the "as if" rule. 1.9/1.
Yet there is no statement of *how* the observable behaviour can be observed. Observation is outside the program and outside the standard and so practically implementation-defined. However, I do feel that Alexander's interpretation of volatile memory access is perverse. Ben.