Index: lib/AST/MicrosoftMangle.cpp
===================================================================
--- lib/AST/MicrosoftMangle.cpp
+++ lib/AST/MicrosoftMangle.cpp
@@ -2451,9 +2451,36 @@

 void MicrosoftCXXNameMangler::mangleType(const ObjCObjectType *T, Qualifiers,
                                          SourceRange Range) {
-  // We don't allow overloading by different protocol qualification,
-  // so mangling them isn't necessary.
-  mangleType(T->getBaseType(), Range, QMM_Drop);
+  if (T->qual_empty())
+    return mangleType(T->getBaseType(), Range, QMM_Drop);
+
+  ArgBackRefMap OuterArgsContext;
+  BackRefVec OuterTemplateContext;
+
+  TypeBackReferences.swap(OuterArgsContext);
+  NameBackReferences.swap(OuterTemplateContext);
+
+  mangleTagTypeKind(TTK_Struct);
+
+  Out << "?$";
+  if (T->isObjCId())
+    mangleSourceName("objc_object");
+  else if (T->isObjCClass())
+    mangleSourceName("objc_class");
+  else
+    mangleSourceName(T->getInterface()->getName());
+
+  for (const auto &Q : T->quals()) {
+    Out << 'Y'; // cointerface
+    mangleSourceName(Q->getName());
+    Out << '@';
+  }
+  Out << '@';
+
+  Out << '@';
+
+  TypeBackReferences.swap(OuterArgsContext);
+  NameBackReferences.swap(OuterTemplateContext);
 }

 void MicrosoftCXXNameMangler::mangleType(const BlockPointerType *T,
Index: test/CodeGenObjCXX/msabi-protocol-conformance.mm
===================================================================
--- /dev/null
+++ test/CodeGenObjCXX/msabi-protocol-conformance.mm
@@ -0,0 +1,31 @@
+// RUN: %clang_cc1 -triple thumbv7-windows-msvc -fobjc-runtime=ios-6.0 -o - -emit-llvm %s | FileCheck %s
+
+@protocol P;
+@protocol Q;
+
+@class I;
+
+void f(id, id<P>, id<P>, id) {}
+// CHECK-LABEL: "\01?f@@YAXPAUobjc_object@@PAU?$objc_object@YP@@@@10@Z"
+
+void f(id<P>, id<P>) {}
+// CHECK-LABEL: "\01?f@@YAXPAU?$objc_object@YP@@@@0@Z"
+
+void f(id<P>) {}
+// CHECK-LABEL: "\01?f@@YAXPAU?$objc_object@YP@@@@@Z"
+
+void f(id<P, Q>) {}
+// CHECK-LABEL: "\01?f@@YAXPAU?$objc_object@YP@@YQ@@@@@Z"
+
+void f(Class<P>) {}
+// CHECK-LABEL: "\01?f@@YAXPAU?$objc_class@YP@@@@@Z"
+
+void f(Class<P, Q>) {}
+// CHECK-LABEL: "\01?f@@YAXPAU?$objc_class@YP@@YQ@@@@@Z"
+
+void f(I<P> *) {}
+// CHECK-LABEL: "\01?f@@YAXPAU?$I@YP@@@@@Z"
+
+void f(I<P, Q> *) {}
+// CHECK-LABEL: "\01?f@@YAXPAU?$I@YP@@YQ@@@@@Z"
+