Speeding up ggc-simple on stage1

[Jeffrey A Law]

  In message < or7lhctraf.fsf@garnize.lsd.ic.unicamp.br >you write:
  > > Yea, you're thrashing.  The only aspect of this change that might help
  > > that is a smaller call chain within the garbage collector.
  > 
  > Which, by some of those amazing coincidences that happen just once in
  > a millenium, is exactly what the patch is trying to accomplish :-) :-)
I'd still be rather surprised.  Even at 1k levels deep in the collector you're
probably burning less than 256k of stack space unless the rs6000 port is
particularly wasteful of stack space.    Which is relatively small if
you're thrashing as badly as it seems.

  > I had expected gcc -O2 would perform tail recursion optimization in
  > all those places.  Shouldn't it?
The current tail recursion opts won't work if the function's return type
is null.  And it only works when the tail recursion is of the form
"return self (args)".  It's fairly lame.

jeff