Re: Volatile qualification on pointer and data

[David Brown <david at westcontrol dot com>]

On 21/09/2011 10:21, Paulo J. Matos wrote:
> On 21/09/11 08:03, David Brown wrote:
> > Asking to read it by a volatile read does not
> > change the nature of "foo" - the compiler can still implement it as a
> > compile-time constant.
>
> But since I am accessing the data through the pointer and the pointer
> qualifies the data as volatile, shouldn't the compiler avoid this kind
> of optimization for reads through the pointer?

My thought is that the nature of "foo" is independent of how it is 
accessed.  On the other hand, some uses of a variable will affect its 
implementation - if you take the address of "foo" and pass that on to an 
external function or data, then the compiler would have to generate 
"foo" in memory (but in read-only memory, and it can still assume its 
value does not change).  So I am not sure what the "correct" behaviour 
is here - I merely ask the question.

Fortunately, this situation is not going to occur in real code.

> It still is a regression from GCC45, however it might be considered a
> feature instead of a bug as I already mentioned to Ian.