Speeding up GC

[David S. Miller]

   From: Alexandre Oliva <aoliva@redhat.com>
   Date: 04 Jun 2002 15:41:10 -0300
   
   So how about going back to using obstacks for allocation and grouping
   of objects, and doing garbage collection on obstacks, instead of on
   individual objects?

I have a patch which essentially does that, but implemented within GGC
itself.  I create 3 GGC pools:

1	Obstack like GC allocation for long-term RTL
2	Obstack like GC allocation for short-term RTL
3	Obstack like GC allocation for Trees

I didn't enable usage of #3 in my changes.  This patch was deeply
a work in progress, and I'll get back to it after I finish up
with my "kill gen_sequence()" patch.