aggregate aliasing losage

[Richard Henderson]

On Thu, Jun 01, 2000 at 03:42:55PM -0400, Richard Kenner wrote:
> I'm wondering if this means that in Fortran, the alias set of an array
> has to be the same as the alias set of its component.

I don't think this issue is limited to Fortran.  Consider 

   struct s1 { double d; };
   struct s2 { double d; };
   
   double f(struct s1 *a, struct s2 *b)
   {
     a->d = 1.0;
     return b->d + 1.0;
   }
   
   int main()
   {
     struct s1 a;
     a.d = 0.0;
     if (f (&a, (struct s2 *)&a) != 2.0)
       abort ();
     return 0;
   }

The way I read c99's 6.5/7

] 7    An object shall have its stored value accessed only by an lvalue
]      expression that has one of the following types:
]      - a type compatible with the effective type of the object,

the type of `b->d' is certainly compatible with the type of `a->d',
which is the object being referenced.

It is true that the structures themselves are not compatible, due to
having different structure tags, but I don't necessarily agree that's
relevant.


r~