Reimplementing pgcc's -frisc

[Jeffrey A Law]

  In message <Pine.GSO.4.02A.9810061609140.9758-100000@quincy.informatik.rwth-a
achen.de>you write:
  > I have thought of a way to implement this properly (the pgcc implemention is
  > rather complicated), and I'd like to describe it here so people can stop me
  > if the idea isn't so hot.
  > 
  > First of all, the transformation should not be done before reload, since it
  > requires additional registers, and increasing register pressure is likely
  > to lose all the benefits we gain from the transformation.
Right.


  > The actual splitting can be done in sched2 via a define_split.
Yup.

  > The only
  > problem that remains is to allocate a scratch register _after_ reload has
  > run.
Yup.

  > I suggest adding a small hard register life analysis pass (I've posted
  > an early version of such a pass last Friday to egcs-patches), which is
  > useful for a variety of reasons, not just for implementing -frisc.
This is precisely how I recommended we reimplement -frisc :-)  I think Stan
Cox even has some code.  Stan, want to post it to egcs-patches so that people
can start hacking on it?

jeff