Backward insn combination?

[Jeffrey A Law]

  In message < 199906301104.MAA22454@sun52.NIS.cambridge >you write:
  > 
  > law@cygnus.com said:
  > > What you may need is multiple iterations of the combiner at higher
  > > optimization levels.  Though I have no idea how safe that would be and
  > > how many new combinations later passes would find. Probably worth some
  > > experiments.
  > 
  > 
  > Rather than doing multiple passes, each time you do make a successful 
  > combination you could restart at the insn after the one deleted (or when 
  > three are combined after the earliest insn deleted).
That does not work in the case Michael is talking about.  For his case to
work you have to back up to an unknown point *before* the insn you delete.

A
B
C
D

Assume we can't combine A & C because of B.  But we can combine B & D and
delete B.  To then be able to combine A & C you have to restart at A, not
after B.


jeff