diff --git a/clang/include/clang/Basic/Module.h b/clang/include/clang/Basic/Module.h
--- a/clang/include/clang/Basic/Module.h
+++ b/clang/include/clang/Basic/Module.h
@@ -457,8 +457,12 @@
   /// Determine whether this module is a submodule.
   bool isSubModule() const { return Parent != nullptr; }
 
-  /// Determine whether this module is a submodule of the given other
-  /// module.
+  /// Check if this module is a (possibly transitive) submodule of \p Other.
+  ///
+  /// The 'A is a submodule of B' relation is a partial order based on the
+  /// the parent-child relationship between individual modules.
+  ///
+  /// Returns \c false if \p Other is \c nullptr.
   bool isSubModuleOf(const Module *Other) const;
 
   /// Determine whether this module is a part of a framework,
diff --git a/clang/lib/Basic/Module.cpp b/clang/lib/Basic/Module.cpp
--- a/clang/lib/Basic/Module.cpp
+++ b/clang/lib/Basic/Module.cpp
@@ -173,14 +173,10 @@
 }
 
 bool Module::isSubModuleOf(const Module *Other) const {
-  const Module *This = this;
-  do {
+  for (const Module *This = this; This != nullptr; This = This->Parent) {
     if (This == Other)
       return true;
-
-    This = This->Parent;
-  } while (This);
-
+  }
   return false;
 }