Re: Canonical type nodes, or, comptypes considered harmful

[Dale Johannesen <dalej at apple dot com>]

On Nov 9, 2006, at 4:54 PM, Mike Stump wrote:

> On Nov 8, 2006, at 7:14 AM, Ian Lance Taylor wrote:
> > The way to canonicalize them is to have all equivalent types point to
> > a single canonical type for the equivalence set.  The comparison is
> > one memory dereference and one pointer comparison, not the current
> > procedure of checking for structural equivalence.
>
> Once not equal addresses might mean equal types, you have to do a  
> structure walk to compare types, and you're right back were we  
> started.  The only way to save yourself, is to be able to say,  
> different addresses, _must_ be different types.

I had in mind something like

   if (p1 == p2)
          equal
   else if (p1->ptr_equality_suffices_for_this_type || p2- 
>ptr_equality_suffices_for_this_type)
          not equal
   else
          tree walk

Don't know how workable that is.