Index: lib/AST/MicrosoftMangle.cpp
===================================================================
--- lib/AST/MicrosoftMangle.cpp
+++ lib/AST/MicrosoftMangle.cpp
@@ -238,6 +238,7 @@
   void mangleNestedName(const NamedDecl *ND);
 
 private:
+  void mangleBackReference(StringRef Name, StringRef Suffix = "");
   void mangleUnqualifiedName(const NamedDecl *ND) {
     mangleUnqualifiedName(ND, ND->getDeclName());
   }
@@ -607,6 +608,27 @@
   }
 }
 
+void MicrosoftCXXNameMangler::mangleBackReference(StringRef Name,
+                                                  StringRef Suffix) {
+  if (NameBackReferences.size() < 10) {
+    size_t Size = NameBackReferences.size();
+    BackRefMap::MapEntryTy &Entry =
+        NameBackReferences.GetOrCreateValue(Name, Size);
+    if (Entry.second == Size) {
+      Out << Name << Suffix;
+    } else {
+      Out << Entry.second;
+    }
+  } else {
+    BackRefMap::iterator Found = NameBackReferences.find(Name);
+    if (Found == NameBackReferences.end()) {
+      Out << Name << Suffix;
+    } else {
+      Out << Found->second;
+    }
+  }
+}
+
 static const TemplateDecl *
 isTemplate(const NamedDecl *ND, const TemplateArgumentList *&TemplateArgs) {
   // Check if we have a function template.
@@ -668,22 +690,13 @@
     // the mangled type name as a key to check the mangling of different types
     // for aliasing.
 
-    std::string TemplateMangling;
-    llvm::raw_string_ostream Stream(TemplateMangling);
+    llvm::SmallString<64> TemplateMangling;
+    llvm::raw_svector_ostream Stream(TemplateMangling);
     MicrosoftCXXNameMangler Extra(Context, Stream);
     Extra.mangleTemplateInstantiationName(TD, *TemplateArgs);
     Stream.flush();
 
-    BackRefMap::iterator Found = NameBackReferences.find(TemplateMangling);
-    if (Found == NameBackReferences.end()) {
-      Out << TemplateMangling;
-      if (NameBackReferences.size() < 10) {
-        size_t Size = NameBackReferences.size();
-        NameBackReferences[TemplateMangling] = Size;
-      }
-    } else {
-      Out << Found->second;
-    }
+    mangleBackReference(TemplateMangling);
     return;
   }
 
@@ -1002,16 +1015,7 @@
 
 void MicrosoftCXXNameMangler::mangleSourceName(StringRef Name) {
   // <source name> ::= <identifier> @
-  BackRefMap::iterator Found = NameBackReferences.find(Name);
-  if (Found == NameBackReferences.end()) {
-    Out << Name << '@';
-    if (NameBackReferences.size() < 10) {
-      size_t Size = NameBackReferences.size();
-      NameBackReferences[Name] = Size;
-    }
-  } else {
-    Out << Found->second;
-  }
+  mangleBackReference(Name, "@");
 }
 
 void MicrosoftCXXNameMangler::mangleObjCMethodName(const ObjCMethodDecl *MD) {