volatile semantics

[Nathan Sidwell]

Dale Johannesen wrote:

> 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.

I'm not disagreeing with you, but I wonder at gcc's ability to make
good on such a promise.  A cast introducing a volatile qualifier
will be a NOP_EXPR, and gcc tends to strip those at every opportunity.

Also, I wonder about the following example

int const avail = <something>

int main() {
   while (*(int *)&avail == Foo ())
     do_something();
   return 0;
}

Seeing through the const-stripping cast is a useful optimization. We'd
have to have one rule for adding volatile and a different one for removing
const.

A further pathelogical case would be,

int main() {
   while (*(int *)(volatile int *)&avail)
     do_something ();
   return 0;
}

What should this do, treat the volatile qualifier as sticky?


nathan

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