It's been a long time since I dealt with this aspect of porting, but
isn't it the case that most ports don't expose branch-on-carry-set
branch-on-carry-clear? It looks like the mn103 was recently changed to
not use cc0, which is definitely a good thing. I'm not sure offhand the
best way to recode this optimization in that new world.
It was removed there, but I would just use a new define_insn producing
more than one instruction, like
(define_insn "cbranch_si_ge0_clobber"
(set (pc)
(if_then_else
(ge [(match_operand:SI 0 "register_operand" "+dx")
(const_int 0)])
(label_ref (match_operand 1 ""))
(pc)))
(clobber (match_dup 0))
(clobber (reg:CC CC_REG))]
"add %0, %0\;bcc %1"
[(set_attr "cc", "clobber")])
and likewise for bcs. While not many, there are some instances of this
in the port.
Paolo
