diff --git a/llvm/include/llvm/Transforms/IPO/FunctionImport.h b/llvm/include/llvm/Transforms/IPO/FunctionImport.h
index c06d96bbe62e22..78932c12e76ff8 100644
--- a/llvm/include/llvm/Transforms/IPO/FunctionImport.h
+++ b/llvm/include/llvm/Transforms/IPO/FunctionImport.h
@@ -150,7 +150,24 @@ class FunctionImporter {
   };
 
   // A map from destination modules to lists of imports.
-  using ImportListsTy = DenseMap<StringRef, ImportMapTy>;
+  class ImportListsTy {
+  public:
+    ImportListsTy() = default;
+    ImportListsTy(size_t Size) : ListsImpl(Size) {}
+
+    ImportMapTy &operator[](StringRef DestMod) {
+      return ListsImpl.try_emplace(DestMod).first->second;
+    }
+
+    size_t size() const { return ListsImpl.size(); }
+
+    using const_iterator = DenseMap<StringRef, ImportMapTy>::const_iterator;
+    const_iterator begin() const { return ListsImpl.begin(); }
+    const_iterator end() const { return ListsImpl.end(); }
+
+  private:
+    DenseMap<StringRef, ImportMapTy> ListsImpl;
+  };
 
   /// The set contains an entry for every global value that the module exports.
   /// Depending on the user context, this container is allowed to contain