------- Additional Comments From gdr at integrable-solutions dot net
2005-07-03 04:43 -------
Subject: Re: gcc -O2 discards cast to volatile
"gcc2eran at tromer dot org" <[EMAIL PROTECTED]> writes:
| (In reply to comment #30)
| > | OK. Then the volatile-stripping direction can be handled arbitrarily.
| >
| > I do not understand that comment.
|
| I meant that we were mostly concerned about what the standard says about the
| effect of casting (say) int* into volatile int*, but the other directly is
| simply undefined.
That is what I do not understand. Could you point me to the relevant
passage of the C standard?
| Still, consider the following variant:
|
| void quux(int *bar) {
| *(volatile int*)bar = 42;
| }
|
| volatile int foo;
| quux((int*)&foo);
|
| This time there is no "attempt [...] to refer to an object defined with a
| volatile-qualified type through use of an lvalue with non-volatile-qualified
| type".
Really? What does quux() does to the object defined through foo then?
| So why does gcc 4.0.0 -O3 still optimize away the assignment? And how
| would you fix that with an approach that construes the standard to require
| following the type of the "real" object?
|
| Could the standard intend something so convoluted, when the interpretation in
| comment 23 makes things perfectly sensible, well-defined and (in principle)
easy
| to implement?
My understanding is that you have gotten everything backwards.
-- Gaby
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22278
