diff --git a/compiler/rustc_privacy/src/lib.rs b/compiler/rustc_privacy/src/lib.rs
index 9c376c6c93e2e..e424a51d01c97 100644
--- a/compiler/rustc_privacy/src/lib.rs
+++ b/compiler/rustc_privacy/src/lib.rs
@@ -23,7 +23,7 @@ use rustc_middle::mir::abstract_const::Node as ACNode;
 use rustc_middle::span_bug;
 use rustc_middle::ty::fold::TypeVisitor;
 use rustc_middle::ty::query::Providers;
-use rustc_middle::ty::subst::{InternalSubsts, Subst};
+use rustc_middle::ty::subst::InternalSubsts;
 use rustc_middle::ty::{self, Const, GenericParamDefKind, TraitRef, Ty, TyCtxt, TypeFoldable};
 use rustc_session::lint;
 use rustc_span::hygiene::Transparency;
@@ -153,11 +153,8 @@ where
         tcx: TyCtxt<'tcx>,
         ct: AbstractConst<'tcx>,
     ) -> ControlFlow<V::BreakTy> {
-        const_evaluatable::walk_abstract_const(tcx, ct, |node| match node.root() {
-            ACNode::Leaf(leaf) => {
-                let leaf = leaf.subst(tcx, ct.substs);
-                self.visit_const(leaf)
-            }
+        const_evaluatable::walk_abstract_const(tcx, ct, |node| match node.root(tcx) {
+            ACNode::Leaf(leaf) => self.visit_const(leaf),
             ACNode::Cast(_, _, ty) => self.visit_ty(ty),
             ACNode::Binop(..) | ACNode::UnaryOp(..) | ACNode::FunctionCall(_, _) => {
                 ControlFlow::CONTINUE
diff --git a/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs b/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
index ddabe5967d79c..076597587f510 100644
--- a/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
+++ b/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
@@ -80,9 +80,8 @@ pub fn is_const_evaluatable<'cx, 'tcx>(
                     Concrete,
                 }
                 let mut failure_kind = FailureKind::Concrete;
-                walk_abstract_const::<!, _>(tcx, ct, |node| match node.root() {
+                walk_abstract_const::<!, _>(tcx, ct, |node| match node.root(tcx) {
                     Node::Leaf(leaf) => {
-                        let leaf = leaf.subst(tcx, ct.substs);
                         if leaf.has_infer_types_or_consts() {
                             failure_kind = FailureKind::MentionsInfer;
                         } else if leaf.definitely_has_param_types_or_consts(tcx) {
@@ -92,7 +91,6 @@ pub fn is_const_evaluatable<'cx, 'tcx>(
                         ControlFlow::CONTINUE
                     }
                     Node::Cast(_, _, ty) => {
-                        let ty = ty.subst(tcx, ct.substs);
                         if ty.has_infer_types_or_consts() {
                             failure_kind = FailureKind::MentionsInfer;
                         } else if ty.definitely_has_param_types_or_consts(tcx) {
@@ -187,8 +185,8 @@ pub fn is_const_evaluatable<'cx, 'tcx>(
 pub struct AbstractConst<'tcx> {
     // FIXME: Consider adding something like `IndexSlice`
     // and use this here.
-    pub inner: &'tcx [Node<'tcx>],
-    pub substs: SubstsRef<'tcx>,
+    inner: &'tcx [Node<'tcx>],
+    substs: SubstsRef<'tcx>,
 }
 
 impl<'tcx> AbstractConst<'tcx> {
@@ -218,8 +216,14 @@ impl<'tcx> AbstractConst<'tcx> {
     }
 
     #[inline]
-    pub fn root(self) -> Node<'tcx> {
-        self.inner.last().copied().unwrap()
+    pub fn root(self, tcx: TyCtxt<'tcx>) -> Node<'tcx> {
+        let node = self.inner.last().copied().unwrap();
+        match node {
+            Node::Leaf(leaf) => Node::Leaf(leaf.subst(tcx, self.substs)),
+            Node::Cast(kind, operand, ty) => Node::Cast(kind, operand, ty.subst(tcx, self.substs)),
+            // Don't perform substitution on the following as they can't directly contain generic params
+            Node::Binop(_, _, _) | Node::UnaryOp(_, _) | Node::FunctionCall(_, _) => node,
+        }
     }
 }
 
@@ -587,7 +591,7 @@ where
         f: &mut dyn FnMut(AbstractConst<'tcx>) -> ControlFlow<R>,
     ) -> ControlFlow<R> {
         f(ct)?;
-        let root = ct.root();
+        let root = ct.root(tcx);
         match root {
             Node::Leaf(_) => ControlFlow::CONTINUE,
             Node::Binop(_, l, r) => {
@@ -615,16 +619,14 @@ pub(super) fn try_unify<'tcx>(
     // We substitute generics repeatedly to allow AbstractConsts to unify where a
     // ConstKind::Unevalated could be turned into an AbstractConst that would unify e.g.
     // Param(N) should unify with Param(T), substs: [Unevaluated("T2", [Unevaluated("T3", [Param(N)])])]
-    while let Node::Leaf(a_ct) = a.root() {
-        let a_ct = a_ct.subst(tcx, a.substs);
+    while let Node::Leaf(a_ct) = a.root(tcx) {
         match AbstractConst::from_const(tcx, a_ct) {
             Ok(Some(a_act)) => a = a_act,
             Ok(None) => break,
             Err(_) => return true,
         }
     }
-    while let Node::Leaf(b_ct) = b.root() {
-        let b_ct = b_ct.subst(tcx, b.substs);
+    while let Node::Leaf(b_ct) = b.root(tcx) {
         match AbstractConst::from_const(tcx, b_ct) {
             Ok(Some(b_act)) => b = b_act,
             Ok(None) => break,
@@ -632,10 +634,8 @@ pub(super) fn try_unify<'tcx>(
         }
     }
 
-    match (a.root(), b.root()) {
+    match (a.root(tcx), b.root(tcx)) {
         (Node::Leaf(a_ct), Node::Leaf(b_ct)) => {
-            let a_ct = a_ct.subst(tcx, a.substs);
-            let b_ct = b_ct.subst(tcx, b.substs);
             if a_ct.ty != b_ct.ty {
                 return false;
             }
diff --git a/compiler/rustc_trait_selection/src/traits/object_safety.rs b/compiler/rustc_trait_selection/src/traits/object_safety.rs
index 57b8a84300ff9..4eaa3ea47325f 100644
--- a/compiler/rustc_trait_selection/src/traits/object_safety.rs
+++ b/compiler/rustc_trait_selection/src/traits/object_safety.rs
@@ -838,14 +838,13 @@ fn contains_illegal_self_type_reference<'tcx, T: TypeFoldable<'tcx>>(
             // constants which are not considered const evaluatable.
             use rustc_middle::mir::abstract_const::Node;
             if let Ok(Some(ct)) = AbstractConst::new(self.tcx, uv.shrink()) {
-                const_evaluatable::walk_abstract_const(self.tcx, ct, |node| match node.root() {
-                    Node::Leaf(leaf) => {
-                        let leaf = leaf.subst(self.tcx, ct.substs);
-                        self.visit_const(leaf)
-                    }
-                    Node::Cast(_, _, ty) => self.visit_ty(ty),
-                    Node::Binop(..) | Node::UnaryOp(..) | Node::FunctionCall(_, _) => {
-                        ControlFlow::CONTINUE
+                const_evaluatable::walk_abstract_const(self.tcx, ct, |node| {
+                    match node.root(self.tcx) {
+                        Node::Leaf(leaf) => self.visit_const(leaf),
+                        Node::Cast(_, _, ty) => self.visit_ty(ty),
+                        Node::Binop(..) | Node::UnaryOp(..) | Node::FunctionCall(_, _) => {
+                            ControlFlow::CONTINUE
+                        }
                     }
                 })
             } else {