rc       <1> srefgen sK/1 ->rd
-           <1> ex-list lKRM ->rc
rb             <@> anonlist sKRM/1 ->rc
r7                <0> pushmark s ->r8
r8                <0> padsv[$tainted:50,end] l ->r9
ra                <1> backtick[t6] lK ->rb
-                    <0> ex-pushmark s ->r9
r9                   <$> const(PV "echo \"BAR\"") s ->ra