let preal_cmp op r1 r2 =
match op with
| Lt -> F.p_rcmp Formula.Clt r1 r2
| Gt -> F.p_rcmp Formula.Clt r2 r1
| Le -> F.p_rcmp Formula.Cleq r1 r2
| Ge -> F.p_rcmp Formula.Cleq r2 r1
| Eq -> F.p_rcmp Formula.Ceq r1 r2
| Ne -> F.p_rcmp Formula.Cneq r1 r2
| _ -> WpLog.fatal "[preal_cmp] non real relation"