skip normalizing param env if it is already normalized

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -409,6 +409,9 @@ fn fold_const(&mut self, c: ty::Const<'tcx>) -> ty::Const<'tcx> {
     debug!("normalize_param_env_or_error: elaborated-predicates={:?}", predicates);
 
     let elaborated_env = ty::ParamEnv::new(tcx.mk_clauses(&predicates), unnormalized_env.reveal());
+    if !normalize::needs_normalization(&elaborated_env, unnormalized_env.reveal()) {
+        return elaborated_env;
+    }
 
     // HACK: we are trying to normalize the param-env inside *itself*. The problem is that
     // normalization expects its param-env to be already normalized, which means we have