A plan for eliminating cc0

[Richard Kenner]

    3) Write a new optimization pass enabled on targets which define
       NOTICE_UPDATE_CC.  I think this pass would be run just before
       machine dependent reorg, although perhaps there is a better place
       for it.  Walk through the instructions, calling NOTICE_UPDATE_CC on
       each one.  When we find an instruction which sets CC_REG, check the
       source of the set with the current CC status, just as
       final_scan_insn does now.  If the current CC status is the same,
       delete the instruction which sets CC_REG.

My gut feeling is that we shouldn't need to do this: the present
optimization passes should do this when we have an explicit register.