[MS ABI] Invent a mangling for reference temporaries

MSVC is non-conforming and doesn't have a mangling for these.  Invent
our own to unblock folks using clang.

This fixes PR25795.

llvm-svn: 256589

Author: majnemer

clang/lib/AST/MicrosoftMangle.cpp

@@ -2760,12 +2760,12 @@ void MicrosoftMangleContextImpl::mangleCXXDtor(const CXXDestructorDecl *D,
   mangler.mangle(D);
 }
 
-void MicrosoftMangleContextImpl::mangleReferenceTemporary(const VarDecl *VD,
-                                                          unsigned,
-                                                          raw_ostream &) {
-  unsigned DiagID = getDiags().getCustomDiagID(DiagnosticsEngine::Error,
-    "cannot mangle this reference temporary yet");
-  getDiags().Report(VD->getLocation(), DiagID);
+void MicrosoftMangleContextImpl::mangleReferenceTemporary(
+    const VarDecl *VD, unsigned ManglingNumber, raw_ostream &Out) {
+  MicrosoftCXXNameMangler Mangler(*this, Out);
+
+  Mangler.getStream() << "\01?$RT" << ManglingNumber << '@';
+  Mangler.mangle(VD, "");
 }
 
 void MicrosoftMangleContextImpl::mangleThreadSafeStaticGuardVariable(

clang/test/CodeGenCXX/mangle-ms.cpp

@@ -21,6 +21,10 @@ int _c(void) {return N::anonymous + c;}
 // CHECK-DAG: @"\01?_c@@YAHXZ"
 // X64-DAG:   @"\01?_c@@YAHXZ"
 
+const int &NeedsReferenceTemporary = 2;
+// CHECK-DAG: @"\01?NeedsReferenceTemporary@@3ABHB" = constant i32* @"\01?$RT1@NeedsReferenceTemporary@@3ABHB"
+// X64-DAG: @"\01?NeedsReferenceTemporary@@3AEBHEB" = constant i32* @"\01?$RT1@NeedsReferenceTemporary@@3AEBHEB"
+
 class foo {
   static const short d;
 // CHECK-DAG: @"\01?d@foo@@0FB"