:q
Index: lib/AST/ItaniumMangle.cpp
===================================================================
--- lib/AST/ItaniumMangle.cpp	(revision 218249)
+++ lib/AST/ItaniumMangle.cpp	(working copy)
@@ -2643,7 +2643,6 @@
   case Expr::ArrayTypeTraitExprClass:
   case Expr::ExpressionTraitExprClass:
   case Expr::VAArgExprClass:
-  case Expr::CXXUuidofExprClass:
   case Expr::CUDAKernelCallExprClass:
   case Expr::AsTypeExprClass:
   case Expr::PseudoObjectExprClass:
@@ -2658,6 +2657,26 @@
     break;
   }
 
+  case Expr::CXXUuidofExprClass: {
+    if (!getASTContext().getLangOpts().MicrosoftExt) {
+      DiagnosticsEngine &Diags = Context.getDiags();
+        unsigned DiagID = Diags.getCustomDiagID(DiagnosticsEngine::Error,
+                                    "cannot yet mangle __uuidof expression");
+        Diags.Report(E->getExprLoc(), DiagID)
+        << E->getStmtClassName() << E->getSourceRange();
+    } else {
+        const CXXUuidofExpr *UE = cast<CXXUuidofExpr>(E);
+        // This CXXUuidofExpr is mangled as-if it were actually a VarDecl from
+        // const __s_GUID _GUID_{lower case UUID with underscores}
+        StringRef Uuid = UE->getUuidAsStringRef(Context.getASTContext());
+        std::string Name = "_GUID_" + Uuid.lower();
+        std::replace(Name.begin(), Name.end(), '-', '_');
+        Out << "$E?";
+        Out << Name << "@@3U__s_GUID@@B";
+    }
+    break;
+  }
+
   // Even gcc-4.5 doesn't mangle this.
   case Expr::BinaryConditionalOperatorClass: {
     DiagnosticsEngine &Diags = Context.getDiags();
Index: test/CodeGenCXX/debug-info-uuid.cpp
===================================================================
--- test/CodeGenCXX/debug-info-uuid.cpp	(revision 218283)
+++ test/CodeGenCXX/debug-info-uuid.cpp	(working copy)
@@ -1,5 +1,5 @@
 // RUN: %clang_cc1 -emit-llvm -fms-extensions -triple=x86_64-pc-win32 -g %s -o - -std=c++11 | FileCheck %s
-// RUN: not %clang_cc1 -emit-llvm -fms-extensions -triple=x86_64-unknown-unknown -g %s -o - -std=c++11 2>&1 | FileCheck %s --check-prefix=CHECK-ITANIUM
+// RUN: %clang_cc1 -emit-llvm -fms-extensions -triple=x86_64-unknown-unknown -g %s -o - -std=c++11 2>&1 | FileCheck %s --check-prefix=CHECK-ITANIUM
 
 // CHECK: metadata [[TGIARGS:![0-9]*]], null} ; [ DW_TAG_structure_type ] [tmpl_guid<&__uuidof(uuid)>]
 // CHECK: [[TGIARGS]] = metadata !{metadata [[TGIARG1:![0-9]*]]}
@@ -8,7 +8,7 @@
 // CHECK: [[CONST_GUID]] = {{.*}}, metadata [[GUID:![0-9]*]]} ; [ DW_TAG_const_type ] [line 0, size 0, align 0, offset 0] [from _GUID]
 // CHECK: [[GUID]] = {{.*}} ; [ DW_TAG_structure_type ] [_GUID]
 
-// CHECK-ITANIUM: error: cannot yet mangle expression type CXXUuidofExpr
+// CHECK-ITANIUM: metadata !"_ZTS9tmpl_guidIXad$E?_GUID_12345678_1234_1234_1234_1234567890ab@@3U__s_GUID@@BEE"} ; [ DW_TAG_structure_type ] [tmpl_guid<&__uuidof(uuid)>]
 
 struct _GUID;
 template <const _GUID *>
Index: test/CodeGenCXX/microsoft-uuidof-mangling.cpp
===================================================================
--- test/CodeGenCXX/microsoft-uuidof-mangling.cpp	(revision 0)
+++ test/CodeGenCXX/microsoft-uuidof-mangling.cpp	(working copy)
@@ -0,0 +1,36 @@
+// RUN: %clang_cc1 -emit-llvm %s -o - -triple x86_64-unknown-unknown -fms-extensions | FileCheck %s
+// rdar://17784718
+
+typedef struct _GUID
+{
+    unsigned int  Data1;
+    unsigned short Data2;
+    unsigned short Data3;
+    unsigned char  Data4[ 8 ];
+} GUID;
+
+
+template < typename T, const GUID & T_iid = __uuidof(T)>
+class UUIDTest
+{
+public:
+	UUIDTest() { }
+};
+
+struct __declspec(uuid("EAFA1952-66F8-438B-8FBA-AF1BBAE42191")) TestStruct
+{
+	int foo;
+};
+
+int main(int argc, const char * argv[])
+{
+
+    UUIDTest<TestStruct> uuidof_test;
+    return 0;
+}
+
+// CHECK: define i32 @main
+// CHECK: call void @"_ZN8UUIDTestI10TestStructX$E?_GUID_eafa1952_66f8_438b_8fba_af1bbae42191@@3U__s_GUID@@BEEC1Ev"
+// CHECK: define linkonce_odr void @"_ZN8UUIDTestI10TestStructX$E?_GUID_eafa1952_66f8_438b_8fba_af1bbae42191@@3U__s_GUID@@BEEC1Ev"
+// CHECK: call void @"_ZN8UUIDTestI10TestStructX$E?_GUID_eafa1952_66f8_438b_8fba_af1bbae42191@@3U__s_GUID@@BEEC2Ev"
+// CHECK: define linkonce_odr void @"_ZN8UUIDTestI10TestStructX$E?_GUID_eafa1952_66f8_438b_8fba_af1bbae42191@@3U__s_GUID@@BEEC2Ev"