Re: Why doesn't combine like volatiles? (volatile_ok again, sorry!)

[Paolo Bonzini <paolo dot bonzini at lu dot unisi dot ch>]

Robert Dewar wrote:
> Richard Earnshaw wrote:
>
> > Possibly, but I think the more interesting observation is listed in
> > parenthesis: Can a volatile access ever alias a non-volatile access?
>
> I think the answer is no, Certainly Ada has compile time rules
> carefully written to make this impossible.

Usually I try to avoid the realm of "hypotetical targets" and 
hypotetical optimizations, but I can imagine a target where one bit of a 
register needs to be accessed in a volatile way and the others need not.

Then, I don't know if it would be legal to optimize

  struct r {
    unsigned int x : 7;
    volatile unsigned int y : 1;
  };

  struct r my_reg;

So that my_reg.x is accessed with a non-volatile mem, and my_reg.y is 
accessed with a volatile one.  Would such an optimization be possible 
within the Ada compile-time rules?

Paolo