Function impossible_clauses 

pub fn impossible_clauses<'tcx>(
    tcx: TyCtxt<'tcx>,
    clauses: Vec<Clause<'tcx>>,
) -> bool

Normalizes the clauses and checks whether they hold in an empty environment. If this returns true, then either normalize encountered an error or one of the predicates did not hold. Used when creating vtables to check for unsatisfiable methods. This should not be used during analysis.