RFC -- update_equiv_regs and friends

[Jeffrey A Law]

  In message <Pine.LNX.4.30.0102281118330.1311-100000@host140.cambridge.redhat.
com>you write:
  > On Tue, 27 Feb 2001, Jeffrey A Law wrote:
  > Shouldn't the equivalences be restricted to function invariant expressions?
  > That should rule out pseudos.
Generally they are.  In this particular case we do not kick out the
lo_sum due to code which special cases the first argument of a lo_sum
(because we know it's the high part of the expression and is constant).


  > It seems that the problem may be the special handling of LO_SUM in
  > rtx_varies_p.  Maybe we want to change the equivalence to be
  > (mem (symbol_ref)) if we detect this case.
  > 
  > >   F. Don't consider the first argument of a LO_SUM as special in
  > >      rtx_varies_p.
  > 
  > Or maybe do that.
:-)

jeff