Re: Correctness question

[Richard Guenther <richard dot guenther at gmail dot com>]

On Tue, 8 Feb 2005 15:40:10 -0000, Dave Korn <dave.korn@artimi.com> wrote:
> > -----Original Message-----
> > From: gcc-owner On Behalf Of Richard Guenther
> > Sent: 08 February 2005 14:34
> 
> > On Tue, 8 Feb 2005, Florian Weimer wrote:
> >
> > > * Richard Guenther:
> > >
> > > > Is it correct for the middle-end to transform
> > > >
> > > > void foo(int i)
> > > > {
> > > >   int a[4];
> > > >   if (&a[i] == &a[2147483648U])
> > > >      abort();
> > > >   if (i == 2147483648U)
> > > >      abort();
> > > > }
> > >
> > > Is this valid C?  I doubt that even a + 5 is a valid
> > expression (a + 4 is okay, though).
> >
> > Do you mean (char *)&a + 5?
> 
>   No, he's referring to the fact that it is illegal to index more than one
> element past the end of an array.  You can take &a[4], but not dereference it
> legally, but you aren't even allowed to calculate &a[5] or greater.

Ah yes, I remember that.  It probably makes it undefined or
implementation defined.

But I guess the question for the middle-end is wether
ADDR_EXPR(ARRAY_REF(base, offset))
is equivalent to ADDR_EXPR(base) + offset.  So I guess the middle-end
doesn't care
about wether offset is greater than the size of the array.

Richard.