let start_stmt_of_node v = match !v.kind with
| Vstart | Vtest (false, _, _) | VblkOut _ | VcallOut _ | VcallExit _
| VfctIn | VfctOut | Vend | Vexit -> None
| VblkIn (bk, _) -> bkind_stmt bk
| Vstmt s | Vtest (true, s, _) | Vloop (_, s) | Vswitch (s,_)
| VcallIn (s, _, _, _)
-> Some s