diff --git a/compiler/rustc_type_ir/src/flags.rs b/compiler/rustc_type_ir/src/flags.rs
index 50c30f4252703..19c59df0604c3 100644
--- a/compiler/rustc_type_ir/src/flags.rs
+++ b/compiler/rustc_type_ir/src/flags.rs
@@ -118,6 +118,11 @@ bitflags::bitflags! {
         /// Does this have any `ReErased` regions?
         const HAS_RE_ERASED               = 1 << 21;
 
+        /// Does this have any regions of any kind?
+        const HAS_REGIONS                 = TypeFlags::HAS_FREE_REGIONS.bits()
+                                          | TypeFlags::HAS_RE_BOUND.bits()
+                                          | TypeFlags::HAS_RE_ERASED.bits();
+
         /// Does this value have parameters/placeholders/inference variables which could be
         /// replaced later, in a way that would change the results of `impl` specialization?
         const STILL_FURTHER_SPECIALIZABLE = TypeFlags::HAS_TY_PARAM.bits()
@@ -139,7 +144,7 @@ bitflags::bitflags! {
         /// Does this type have any coroutines in it?
         const HAS_TY_CORO                 = 1 << 25;
 
-        /// Does this have have a `Bound(BoundVarIndexKind::Canonical, _)`?
+        /// Does this have a `Bound(BoundVarIndexKind::Canonical, _)`?
         const HAS_CANONICAL_BOUND         = 1 << 26;
     }
 }
@@ -192,7 +197,7 @@ impl<I: Interner> FlagComputation<I> {
     }
 
     fn add_flags(&mut self, flags: TypeFlags) {
-        self.flags = self.flags | flags;
+        self.flags |= flags;
     }
 
     /// indicates that `self` refers to something at binding level `binder`
diff --git a/compiler/rustc_type_ir/src/fold.rs b/compiler/rustc_type_ir/src/fold.rs
index d1a50599e8b9c..0fe68b5256691 100644
--- a/compiler/rustc_type_ir/src/fold.rs
+++ b/compiler/rustc_type_ir/src/fold.rs
@@ -55,7 +55,7 @@ use tracing::{debug, instrument};
 
 use crate::inherent::*;
 use crate::visit::{TypeVisitable, TypeVisitableExt as _};
-use crate::{self as ty, BoundVarIndexKind, Interner, TypeFlags};
+use crate::{self as ty, BoundVarIndexKind, Interner};
 
 /// This trait is implemented for every type that can be folded,
 /// providing the skeleton of the traversal.
@@ -121,10 +121,6 @@ pub trait TypeSuperFoldable<I: Interner>: TypeFoldable<I> {
 /// default that does an "identity" fold. Implementations of these methods
 /// often fall back to a `super_fold_with` method if the primary argument
 /// doesn't satisfy a particular condition.
-///
-/// A blanket implementation of [`FallibleTypeFolder`] will defer to
-/// the infallible methods of this trait to ensure that the two APIs
-/// are coherent.
 pub trait TypeFolder<I: Interner>: Sized {
     fn cx(&self) -> I;
 
@@ -437,6 +433,10 @@ impl<I: Interner> TypeFolder<I> for Shifter<I> {
     fn fold_predicate(&mut self, p: I::Predicate) -> I::Predicate {
         if p.has_vars_bound_at_or_above(self.current_index) { p.super_fold_with(self) } else { p }
     }
+
+    fn fold_clauses(&mut self, c: I::Clauses) -> I::Clauses {
+        if c.has_vars_bound_at_or_above(self.current_index) { c.super_fold_with(self) } else { c }
+    }
 }
 
 pub fn shift_region<I: Interner>(cx: I, region: I::Region, amount: u32) -> I::Region {
@@ -477,10 +477,10 @@ where
 /// Folds over the substructure of a type, visiting its component
 /// types and all regions that occur *free* within it.
 ///
-/// That is, function pointer types and trait object can introduce
-/// new bound regions which are not visited by this visitors as
+/// That is, function pointer types and trait objects can introduce
+/// new bound regions which are not visited by this visitor as
 /// they are not free; only regions that occur free will be
-/// visited by `fld_r`.
+/// visited by `fold_region_fn`.
 pub struct RegionFolder<I, F> {
     cx: I,
 
@@ -489,7 +489,7 @@ pub struct RegionFolder<I, F> {
     /// binder, it is incremented (via `shift_in`).
     current_index: ty::DebruijnIndex,
 
-    /// Callback invokes for each free region. The `DebruijnIndex`
+    /// Callback invoked for each free region. The `DebruijnIndex`
     /// points to the binder *just outside* the ones we have passed
     /// through.
     fold_region_fn: F,
@@ -539,32 +539,18 @@ where
     }
 
     fn fold_ty(&mut self, t: I::Ty) -> I::Ty {
-        if t.has_type_flags(
-            TypeFlags::HAS_FREE_REGIONS | TypeFlags::HAS_RE_BOUND | TypeFlags::HAS_RE_ERASED,
-        ) {
-            t.super_fold_with(self)
-        } else {
-            t
-        }
+        if t.has_regions() { t.super_fold_with(self) } else { t }
     }
 
     fn fold_const(&mut self, ct: I::Const) -> I::Const {
-        if ct.has_type_flags(
-            TypeFlags::HAS_FREE_REGIONS | TypeFlags::HAS_RE_BOUND | TypeFlags::HAS_RE_ERASED,
-        ) {
-            ct.super_fold_with(self)
-        } else {
-            ct
-        }
+        if ct.has_regions() { ct.super_fold_with(self) } else { ct }
     }
 
     fn fold_predicate(&mut self, p: I::Predicate) -> I::Predicate {
-        if p.has_type_flags(
-            TypeFlags::HAS_FREE_REGIONS | TypeFlags::HAS_RE_BOUND | TypeFlags::HAS_RE_ERASED,
-        ) {
-            p.super_fold_with(self)
-        } else {
-            p
-        }
+        if p.has_regions() { p.super_fold_with(self) } else { p }
+    }
+
+    fn fold_clauses(&mut self, c: I::Clauses) -> I::Clauses {
+        if c.has_regions() { c.super_fold_with(self) } else { c }
     }
 }
diff --git a/compiler/rustc_type_ir/src/visit.rs b/compiler/rustc_type_ir/src/visit.rs
index a078b860be774..492c37481298b 100644
--- a/compiler/rustc_type_ir/src/visit.rs
+++ b/compiler/rustc_type_ir/src/visit.rs
@@ -67,7 +67,7 @@ pub trait TypeVisitable<I: Interner>: fmt::Debug {
     /// each field/element.
     ///
     /// For types of interest (such as `Ty`), the implementation of this method
-    /// that calls a visitor method specifically for that type (such as
+    /// calls a visitor method specifically for that type (such as
     /// `V::visit_ty`). This is where control transfers from `TypeVisitable` to
     /// `TypeVisitor`.
     fn visit_with<V: TypeVisitor<I>>(&self, visitor: &mut V) -> V::Result;
@@ -102,8 +102,8 @@ pub trait TypeVisitor<I: Interner>: Sized {
         t.super_visit_with(self)
     }
 
-    // The default region visitor is a no-op because `Region` is non-recursive
-    // and has no `super_visit_with` method to call.
+    // `Region` is non-recursive so the default region visitor has no
+    // `super_visit_with` method to call.
     fn visit_region(&mut self, r: I::Region) -> Self::Result {
         if let ty::ReError(guar) = r.kind() {
             self.visit_error(guar)
@@ -251,10 +251,10 @@ pub trait TypeVisitableExt<I: Interner>: TypeVisitable<I> {
         self.has_vars_bound_at_or_above(binder.shifted_in(1))
     }
 
-    /// Return `true` if this type has regions that are not a part of the type.
-    /// For example, `for<'a> fn(&'a i32)` return `false`, while `fn(&'a i32)`
-    /// would return `true`. The latter can occur when traversing through the
-    /// former.
+    /// Returns `true` if this type has regions that are not a part of the
+    /// type. For example, given a `for<'a> fn(&'a i32)` this function returns
+    /// `false`, while given a `fn(&'a i32)` it returns `true`. The latter can
+    /// occur when traversing through the former.
     ///
     /// See [`HasEscapingVarsVisitor`] for more information.
     fn has_escaping_bound_vars(&self) -> bool {
@@ -285,6 +285,10 @@ pub trait TypeVisitableExt<I: Interner>: TypeVisitable<I> {
         self.has_type_flags(TypeFlags::HAS_PARAM - TypeFlags::HAS_RE_PARAM)
     }
 
+    fn has_regions(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_REGIONS)
+    }
+
     fn has_infer_regions(&self) -> bool {
         self.has_type_flags(TypeFlags::HAS_RE_INFER)
     }
@@ -363,13 +367,12 @@ pub trait TypeVisitableExt<I: Interner>: TypeVisitable<I> {
 
 impl<I: Interner, T: TypeVisitable<I>> TypeVisitableExt<I> for T {
     fn has_type_flags(&self, flags: TypeFlags) -> bool {
-        let res =
-            self.visit_with(&mut HasTypeFlagsVisitor { flags }) == ControlFlow::Break(FoundFlags);
-        res
+        self.visit_with(&mut HasTypeFlagsVisitor { flags }) == ControlFlow::Break(FoundFlags)
     }
 
     fn has_vars_bound_at_or_above(&self, binder: ty::DebruijnIndex) -> bool {
-        self.visit_with(&mut HasEscapingVarsVisitor { outer_index: binder }).is_break()
+        self.visit_with(&mut HasEscapingVarsVisitor { outer_index: binder })
+            == ControlFlow::Break(FoundEscapingVars)
     }
 
     fn error_reported(&self) -> Result<(), I::ErrorGuaranteed> {
@@ -438,8 +441,7 @@ impl<I: Interner> TypeVisitor<I> for HasTypeFlagsVisitor {
     #[inline]
     fn visit_ty(&mut self, t: I::Ty) -> Self::Result {
         // Note: no `super_visit_with` call.
-        let flags = t.flags();
-        if flags.intersects(self.flags) {
+        if t.flags().intersects(self.flags) {
             ControlFlow::Break(FoundFlags)
         } else {
             ControlFlow::Continue(())
@@ -449,8 +451,7 @@ impl<I: Interner> TypeVisitor<I> for HasTypeFlagsVisitor {
     #[inline]
     fn visit_region(&mut self, r: I::Region) -> Self::Result {
         // Note: no `super_visit_with` call, as usual for `Region`.
-        let flags = r.flags();
-        if flags.intersects(self.flags) {
+        if r.flags().intersects(self.flags) {
             ControlFlow::Break(FoundFlags)
         } else {
             ControlFlow::Continue(())
@@ -571,7 +572,7 @@ impl<I: Interner> TypeVisitor<I> for HasEscapingVarsVisitor {
         // `outer_index`, that means that `ct` contains some content
         // bound at `outer_index` or above (because
         // `outer_exclusive_binder` is always 1 higher than the
-        // content in `t`). Therefore, `t` has some escaping vars.
+        // content in `ct`). Therefore, `ct` has some escaping vars.
         if ct.outer_exclusive_binder() > self.outer_index {
             ControlFlow::Break(FoundEscapingVars)
         } else {