(define_expand "cbranchsi4"
[(parallel [(set (cc0)
(compare (match_operand:SI 1 "register_operand" "")
(match_operand:SI 2 "nonmemory_operand" "")))
(clobber (match_scratch:QI 4 ""))])
(set (pc)
(if_then_else
(match_operator 0 "ordered_comparison_operator" [(cc0)
(const_int 0)])
(label_ref (match_operand 3 "" ""))
(pc)))]
"")
[...] the second pattern of the PARALLEL is just a CLOBBER.
The USE of CC0 happens in a completely separate second INSN that is
emitted by this define_expand. (Note that as opposed to define_insn,
define_expand can emit more than a single insn.)