Index: clang/lib/AST/ItaniumMangle.cpp
===================================================================
--- clang/lib/AST/ItaniumMangle.cpp
+++ clang/lib/AST/ItaniumMangle.cpp
@@ -2648,12 +2648,8 @@
   case CC_C:
     return "";
 
-  case CC_X86StdCall:
-  case CC_X86FastCall:
-  case CC_X86ThisCall:
   case CC_X86VectorCall:
   case CC_X86Pascal:
-  case CC_Win64:
   case CC_X86_64SysV:
   case CC_X86RegCall:
   case CC_AAPCS:
@@ -2667,6 +2663,14 @@
     // FIXME: we should be mangling all of the above.
     return "";
 
+  case CC_X86StdCall:
+    return "stdcall";
+  case CC_X86FastCall:
+    return "fastcall";
+  case CC_X86ThisCall:
+    return "thiscall";
+  case CC_Win64:
+    return "ms_abi";
   case CC_Swift:
     return "swiftcall";
   }
Index: clang/test/CodeGenCXX/mangle-win-ccs.cpp
===================================================================
--- /dev/null
+++ clang/test/CodeGenCXX/mangle-win-ccs.cpp
@@ -0,0 +1,34 @@
+// RUN: %clang_cc1 %s -emit-llvm -triple i686-windows-gnu -o - | FileCheck %s
+// RUN: %clang_cc1 %s -emit-llvm -triple i686-windows-itanium -o - | FileCheck %s
+
+// GCC 5.1 began mangling these Windows calling conventions into function
+// types, since they can be used for overloading. They've always been mangled
+// in the MS ABI, but they are new to the Itanium mangler. Note that the main
+// function definition does not use a calling convention. Only function types
+// that appear later use it.
+
+template <typename Fn> static __PTRDIFF_TYPE__ func_as_ptr(Fn fn) {
+  return __PTRDIFF_TYPE__(fn);
+}
+
+void f_cdecl(int, int);
+void __attribute__((stdcall)) f_stdcall(int, int);
+void __attribute__((fastcall)) f_fastcall(int, int);
+void __attribute__((thiscall)) f_thiscall(int, int);
+
+__PTRDIFF_TYPE__ as_cdecl() { return func_as_ptr(f_cdecl); }
+__PTRDIFF_TYPE__ as_stdcall() { return func_as_ptr(f_stdcall); }
+__PTRDIFF_TYPE__ as_fastcall() { return func_as_ptr(f_fastcall); }
+__PTRDIFF_TYPE__ as_thiscall() { return func_as_ptr(f_thiscall); }
+
+// CHECK: define dso_local i32 @_Z8as_cdeclv()
+// CHECK:   call i32 @_ZL11func_as_ptrIPFviiEEiT_(void (i32, i32)* @_Z7f_cdeclii)
+
+// CHECK: define dso_local i32 @_Z10as_stdcallv()
+// CHECK:   call i32 @_ZL11func_as_ptrIPU7stdcallFviiEEiT_(void (i32, i32)* @"\01__Z9f_stdcallii@8")
+
+// CHECK: define dso_local i32 @_Z11as_fastcallv()
+// CHECK:   call i32 @_ZL11func_as_ptrIPU8fastcallFviiEEiT_(void (i32, i32)* @"\01@_Z10f_fastcallii@8")
+
+// CHECK: define dso_local i32 @_Z11as_thiscallv()
+// CHECK:   call i32 @_ZL11func_as_ptrIPU8thiscallFviiEEiT_(void (i32, i32)* @_Z10f_thiscallii)