On 9/9/07, Mark Mitchell <[EMAIL PROTECTED]> wrote:
> Richard Guenther wrote:
> > On 9/9/07, Mark Mitchell <[EMAIL PROTECTED]> wrote:
> >> But, I don't think that even the C meaning is safe in C++ for use with
> >> the library declaration of <new>. I'm also somewhat skeptical of the
> >> idea that we will never do any optimization on pointer comparisons.
> >> What design principle in the compiler is going to keep us from some day
> >> introducing the obvious idea that "if modifying *p cannot affect the
> >> value of *q, and p and q are of the same type, then p != q"?
> >
> > But that reasoning is not valid. Consider
> >
> > void foo(int *q, double *p)
> > {
> > if (q != p)
> > abort ();
> > }
> > int main()
> > {
> > int i;
> > foo (&i, &i);
> > }
>
> That doesn't type-check; did you want to have a cast somewhere? Note
> that my statement above depends on the pointers having the same type.
>
> What is an example program in that meets the requirements I gave above
> -- i.e., allows the compiler to prove that two same-typed pointers do
> not alias (whether by the compiler's cleverness, use of "restrict", or
> whatever), but where the compiler must still assume that the values of
> the pointers might be the same?
I see I misinterpreted your sentence. I don't think a testcase that
holds all your requirements can be constructed as they
contradict each other. Can you give one?
Richard.
