>perl -MO=Concise,f -e"sub f { return $x }"
main::f:
5  <1> leavesub[1 ref] K/REFC,1 ->(end)
-     <@> lineseq KP ->5
1        <;> nextstate(main 1 -e:1) v ->2
4        <@> return K ->5
2           <0> pushmark s ->3
-           <1> ex-rv2sv sK/1 ->4
3              <#> gvsv[*x] s ->4
-e syntax OK