diff --git a/clippy_utils/src/lib.rs b/clippy_utils/src/lib.rs
index 886dde4b977..0ae0450cbe0 100644
--- a/clippy_utils/src/lib.rs
+++ b/clippy_utils/src/lib.rs
@@ -20,7 +20,6 @@ extern crate rustc_attr;
 extern crate rustc_data_structures;
 extern crate rustc_errors;
 extern crate rustc_hir;
-extern crate rustc_hir_pretty;
 extern crate rustc_infer;
 extern crate rustc_lexer;
 extern crate rustc_lint;
@@ -1333,7 +1332,7 @@ pub fn if_sequence<'tcx>(mut expr: &'tcx Expr<'tcx>) -> (Vec<&'tcx Expr<'tcx>>,
 }
 
 /// Checks if the given function kind is an async function.
-pub fn is_async_fn(kind: FnKind) -> bool {
+pub fn is_async_fn(kind: FnKind<'_>) -> bool {
     matches!(kind, FnKind::ItemFn(_, _, header, _) if header.asyncness == IsAsync::Async)
 }
 
diff --git a/clippy_utils/src/ty.rs b/clippy_utils/src/ty.rs
index e1f8aff3740..c36e215f184 100644
--- a/clippy_utils/src/ty.rs
+++ b/clippy_utils/src/ty.rs
@@ -2,9 +2,8 @@
 
 #![allow(clippy::module_name_repetitions)]
 
-use std::collections::HashMap;
-
 use rustc_ast::ast::Mutability;
+use rustc_data_structures::fx::FxHashMap;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_hir::{TyKind, Unsafety};
@@ -184,14 +183,14 @@ pub fn is_must_use_ty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
 /// Checks if `Ty` is normalizable. This function is useful
 /// to avoid crashes on `layout_of`.
 pub fn is_normalizable<'tcx>(cx: &LateContext<'tcx>, param_env: ty::ParamEnv<'tcx>, ty: Ty<'tcx>) -> bool {
-    is_normalizable_helper(cx, param_env, ty, &mut HashMap::new())
+    is_normalizable_helper(cx, param_env, ty, &mut FxHashMap::default())
 }
 
 fn is_normalizable_helper<'tcx>(
     cx: &LateContext<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     ty: Ty<'tcx>,
-    cache: &mut HashMap<Ty<'tcx>, bool>,
+    cache: &mut FxHashMap<Ty<'tcx>, bool>,
 ) -> bool {
     if let Some(&cached_result) = cache.get(ty) {
         return cached_result;