diff --git a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
index d4890e48032..2df039c766c 100644
--- a/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs
@@ -258,7 +258,7 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_callable<I: Intern
             if sig.skip_binder().is_fn_trait_compatible() && !tcx.has_target_features(def_id) {
                 Ok(Some(
                     sig.instantiate(tcx, args)
-                        .map_bound(|sig| (Ty::new_tup(tcx, &sig.inputs()), sig.output())),
+                        .map_bound(|sig| (Ty::new_tup(tcx, sig.inputs().as_slice()), sig.output())),
                 ))
             } else {
                 Err(NoSolution)
@@ -267,7 +267,9 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_callable<I: Intern
         // keep this in sync with assemble_fn_pointer_candidates until the old solver is removed.
         ty::FnPtr(sig) => {
             if sig.is_fn_trait_compatible() {
-                Ok(Some(sig.map_bound(|sig| (Ty::new_tup(tcx, &sig.inputs()), sig.output()))))
+                Ok(Some(
+                    sig.map_bound(|sig| (Ty::new_tup(tcx, sig.inputs().as_slice()), sig.output())),
+                ))
             } else {
                 Err(NoSolution)
             }
@@ -290,7 +292,9 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_callable<I: Intern
                     }
                 }
             }
-            Ok(Some(closure_args.sig().map_bound(|sig| (sig.inputs()[0], sig.output()))))
+            Ok(Some(
+                closure_args.sig().map_bound(|sig| (sig.inputs().get(0).unwrap(), sig.output())),
+            ))
         }
 
         // Coroutine-closures don't implement `Fn` traits the normal way.
@@ -468,7 +472,7 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_async_callable<I:
             let future_output_ty = Ty::new_projection(tcx, future_output_def_id, [sig.output()]);
             Ok((
                 bound_sig.rebind(AsyncCallableRelevantTypes {
-                    tupled_inputs_ty: Ty::new_tup(tcx, &sig.inputs()),
+                    tupled_inputs_ty: Ty::new_tup(tcx, sig.inputs().as_slice()),
                     output_coroutine_ty: sig.output(),
                     coroutine_return_ty: future_output_ty,
                 }),
@@ -519,7 +523,7 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_async_callable<I:
             let future_output_ty = Ty::new_projection(tcx, future_output_def_id, [sig.output()]);
             Ok((
                 bound_sig.rebind(AsyncCallableRelevantTypes {
-                    tupled_inputs_ty: sig.inputs()[0],
+                    tupled_inputs_ty: sig.inputs().get(0).unwrap(),
                     output_coroutine_ty: sig.output(),
                     coroutine_return_ty: future_output_ty,
                 }),
diff --git a/compiler/rustc_type_ir/src/interner.rs b/compiler/rustc_type_ir/src/interner.rs
index 3640a8dea54..b89ea30fc34 100644
--- a/compiler/rustc_type_ir/src/interner.rs
+++ b/compiler/rustc_type_ir/src/interner.rs
@@ -90,7 +90,7 @@ pub trait Interner:
     // Kinds of tys
     type Ty: Ty<Self>;
     type Tys: Tys<Self>;
-    type FnInputTys: Copy + Debug + Hash + Eq + Deref<Target = [Self::Ty]> + TypeVisitable<Self>;
+    type FnInputTys: Copy + Debug + Hash + Eq + SliceLike<Item = Self::Ty> + TypeVisitable<Self>;
     type ParamTy: Copy + Debug + Hash + Eq + ParamLike;
     type BoundTy: Copy + Debug + Hash + Eq + BoundVarLike<Self>;
     type PlaceholderTy: PlaceholderLike;
diff --git a/compiler/rustc_type_ir/src/predicate_kind.rs b/compiler/rustc_type_ir/src/predicate_kind.rs
index efe270ed608..b1d0f8d19b3 100644
--- a/compiler/rustc_type_ir/src/predicate_kind.rs
+++ b/compiler/rustc_type_ir/src/predicate_kind.rs
@@ -127,7 +127,6 @@ impl std::fmt::Display for AliasRelationDirection {
     }
 }
 
-// FIXME: Convert to DebugWithInfcx impl
 impl<I: Interner> fmt::Debug for ClauseKind<I> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
@@ -144,7 +143,6 @@ impl<I: Interner> fmt::Debug for ClauseKind<I> {
     }
 }
 
-// FIXME: Convert to DebugWithInfcx impl
 impl<I: Interner> fmt::Debug for PredicateKind<I> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
diff --git a/compiler/rustc_type_ir/src/relate.rs b/compiler/rustc_type_ir/src/relate.rs
index c803d7e1794..0439e7f857f 100644
--- a/compiler/rustc_type_ir/src/relate.rs
+++ b/compiler/rustc_type_ir/src/relate.rs
@@ -185,7 +185,7 @@ impl<I: Interner> Relate<I> for ty::FnSig<I> {
         }
 
         let inputs_and_output = iter::zip(a_inputs.iter(), b_inputs.iter())
-            .map(|(&a, &b)| ((a, b), false))
+            .map(|(a, b)| ((a, b), false))
             .chain(iter::once(((a.output(), b.output()), true)))
             .map(|((a, b), is_output)| {
                 if is_output {
diff --git a/compiler/rustc_type_ir/src/ty_kind.rs b/compiler/rustc_type_ir/src/ty_kind.rs
index 4782b8558d7..4ffebef9f1f 100644
--- a/compiler/rustc_type_ir/src/ty_kind.rs
+++ b/compiler/rustc_type_ir/src/ty_kind.rs
@@ -1005,7 +1005,7 @@ impl<I: Interner> ty::Binder<I, FnSig<I>> {
     #[inline]
     #[track_caller]
     pub fn input(self, index: usize) -> ty::Binder<I, I::Ty> {
-        self.map_bound(|fn_sig| fn_sig.inputs()[index])
+        self.map_bound(|fn_sig| fn_sig.inputs().get(index).unwrap())
     }
 
     pub fn inputs_and_output(self) -> ty::Binder<I, I::Tys> {
diff --git a/compiler/rustc_type_ir/src/ty_kind/closure.rs b/compiler/rustc_type_ir/src/ty_kind/closure.rs
index 04aadfdabb4..24a7c0c67e9 100644
--- a/compiler/rustc_type_ir/src/ty_kind/closure.rs
+++ b/compiler/rustc_type_ir/src/ty_kind/closure.rs
@@ -309,7 +309,7 @@ impl<I: Interner> CoroutineClosureArgs<I> {
         let interior = self.coroutine_witness_ty();
         let ty::FnPtr(sig) = self.signature_parts_ty().kind() else { panic!() };
         sig.map_bound(|sig| {
-            let [resume_ty, tupled_inputs_ty] = *sig.inputs() else {
+            let [resume_ty, tupled_inputs_ty] = *sig.inputs().as_slice() else {
                 panic!();
             };
             let [yield_ty, return_ty] = *sig.output().tuple_fields().as_slice() else { panic!() };