diff --git a/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs b/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs
index f4703b22ecb..55c9b4d9ba1 100644
--- a/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs
+++ b/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs
@@ -90,7 +90,7 @@ macro call_intrinsic_match {
         match $intrinsic {
             $(
                 sym::$name => {
-                    assert!($substs.is_noop());
+                    assert!($substs.is_empty());
                     if let [$(ref $arg),*] = *$args {
                         let ($($arg,)*) = (
                             $(codegen_operand($fx, $arg),)*
diff --git a/compiler/rustc_middle/src/ty/subst.rs b/compiler/rustc_middle/src/ty/subst.rs
index ab33fbcca15..63e9b58584c 100644
--- a/compiler/rustc_middle/src/ty/subst.rs
+++ b/compiler/rustc_middle/src/ty/subst.rs
@@ -275,10 +275,6 @@ impl<'a, 'tcx> InternalSubsts<'tcx> {
         }
     }
 
-    pub fn is_noop(&self) -> bool {
-        self.is_empty()
-    }
-
     #[inline]
     pub fn types(&'a self) -> impl DoubleEndedIterator<Item = Ty<'tcx>> + 'a {
         self.iter()
diff --git a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
index cd2e0f18e0c..195a4a4a653 100644
--- a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
@@ -484,7 +484,7 @@ crate fn to_pretty_impl_header(tcx: TyCtxt<'_>, impl_def_id: DefId) -> Option<St
     let mut types_without_default_bounds = FxHashSet::default();
     let sized_trait = tcx.lang_items().sized_trait();
 
-    if !substs.is_noop() {
+    if !substs.is_empty() {
         types_without_default_bounds.extend(substs.types());
         w.push('<');
         w.push_str(
diff --git a/compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs b/compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs
index a031f802b6d..f01b8267817 100644
--- a/compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs
+++ b/compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs
@@ -182,7 +182,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // `foo.bar::<u32>(...)` -- the `Self` type here will be the
         // type of `foo` (possibly adjusted), but we don't want to
         // include that. We want just the `[_, u32]` part.
-        if !method.substs.is_noop() {
+        if !method.substs.is_empty() {
             let method_generics = self.tcx.generics_of(method.def_id);
             if !method_generics.params.is_empty() {
                 let user_type_annotation = self.infcx.probe(|_| {
@@ -211,7 +211,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     }
 
     pub fn write_substs(&self, node_id: hir::HirId, substs: SubstsRef<'tcx>) {
-        if !substs.is_noop() {
+        if !substs.is_empty() {
             debug!("write_substs({:?}, {:?}) in fcx {}", node_id, substs, self.tag());
 
             self.typeck_results.borrow_mut().node_substs_mut().insert(node_id, substs);