volatile semantics

[Dale Johannesen]

On May 3, 2005, at 7:41 AM, Nathan Sidwell wrote:
> Mike Stump wrote:
>> int avail;
>> int main() {
>>   while (*(volatile int *)&avail == 0)
>>     continue;
>>   return 0;
>> }
>> Ok, so, the question is, should gcc produce code that infinitely  
>> loops, or should it be obligated to actually fetch from memory?   
>> Hint, 3.3 fetched.
>
> I beleive the compiler is so licensed. [5.1.2.3/2] talks about 
> accessing
> a volatile object.  If the compiled can determine the actual object
> being accessed through a series of pointer and volatile cast 
> conversions,
> then I see nothing in the std saying it must behave as-if the object
> were volatile when it is not.

This is correct; the standard consistently talks about the type of the 
object,
not the type of the lvalue, when describing volatile.

However, as a QOI issue, I believe the compiler should treat the 
reference as
volatile if either the object or the lvalue is volatile.  That is 
obviously the
user's intent.