Index: lib/AST/MicrosoftMangle.cpp
===================================================================
--- lib/AST/MicrosoftMangle.cpp
+++ lib/AST/MicrosoftMangle.cpp
@@ -2056,6 +2056,7 @@
   //                      ::= J # __export __fastcall
   //                      ::= Q # __vectorcall
   //                      ::= w # __regcall
+  //                      ::= __swift::swift_cc:: # __swiftcall (will change when Microsoft adds this to their scheme)
   // The 'export' calling conventions are from a bygone era
   // (*cough*Win16*cough*) when functions were declared for export with
   // that keyword. (It didn't actually export them, it just made them so
@@ -2074,6 +2075,7 @@
     case CC_X86FastCall: Out << 'I'; break;
     case CC_X86VectorCall: Out << 'Q'; break;
     case CC_X86RegCall: Out << 'w'; break;
+    case CC_Swift: Out << "__swift::swift_cc::"; break;
   }
 }
 void MicrosoftCXXNameMangler::mangleCallingConvention(const FunctionType *T) {