Faster compilation speed

[David S. Miller]

   From: kenner@vlsi1.ultra.nyu.edu (Richard Kenner)
   Date: Wed, 21 Aug 02 09:58:57 EDT
   
   True if you only walk *one* SET, but normally you walk a whole bunch,
   each of which have MEM and REG objects.  So I disagree this adds to
   the working set size.
   
In the obstack days, it was not uncommon to walk several full
consequetive INSNs (including traversing into their contents) and stay
on the same system page.  Today this never happens, it is in fact
guarenteed NOT to happen.