[Bug tree-optimization/22000] [4.0 Regression] Read from volatile member of struct is optimized away

[schlie at comcast dot net]

------- Additional Comments From schlie at comcast dot net  2005-06-13 11:17 -------
(In reply to comment #0)
> I think that the C standard says C that the "name" of variable 
> becomes an rvalue (the actual value) thus requires that the variable 
> is accessed.

It actually says that accessing a volatile qualified object through a nonvolatile
qualified lvalue (as would be the case if referenced via a non-volatile qualified
cast expression) is implementation defined.

Personally, it seems more consistent to abide by the semantics specified
by a programmer's explicit cast expression, thereby if given:

int x, y;
const int *z;

x = (volatile int)y; // specifies a reference to a volatile int object.

z = &(const int)x;   // specifies a reference to a const int object.

And correspondingly:

int x;
volatile int y;
const int z;

x = (int)y; // cast's away volatile (therefore may be optimized away),
            // therefore if not desired, shouldn't be "cast away".

(int)z = x; // cast's away const (although may generate a run-time
            // exception if referencing a READONLY allocated object),
            // therefore if not desired, shouldn't be "cast away".


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22000