Do less generous pointer globbing in alias.c

[Jan Hubicka]

> Yes, so is
> 
> struct foo {struct bar a;};
> 
>   a.a = ...
>   ... = a;
> 
> and
> 
>   a = ...
>   ... = a.a;
> 
> this is why conflict is symmetrization of the subset relation.


OK the statement above is true, but subsets alone are not quite right for use
in aliasing_component_refs_p

 void *a;
 char **ptr=&a;
 *ptr = ....

is defined for us, but the structure-substructure equivalent is not.
I will implement the variant with extra flag after teaching and send updated
patch.

Thanks,
Honza