diff --git a/clang/lib/AST/ItaniumMangle.cpp b/clang/lib/AST/ItaniumMangle.cpp
--- a/clang/lib/AST/ItaniumMangle.cpp
+++ b/clang/lib/AST/ItaniumMangle.cpp
@@ -546,8 +546,8 @@
                         unsigned knownArity);
   void mangleCastExpression(const Expr *E, StringRef CastEncoding);
   void mangleInitListElements(const InitListExpr *InitList);
-  void mangleDeclRefExpr(const NamedDecl *D);
-  void mangleExpression(const Expr *E, unsigned Arity = UnknownArity);
+  void mangleExpression(const Expr *E, unsigned Arity = UnknownArity,
+                        bool AsTemplateArg = false);
   void mangleCXXCtorType(CXXCtorType T, const CXXRecordDecl *InheritedFrom);
   void mangleCXXDtorType(CXXDtorType T);
 
@@ -3872,33 +3872,8 @@
     mangleExpression(InitList->getInit(i));
 }
 
-void CXXNameMangler::mangleDeclRefExpr(const NamedDecl *D) {
-  switch (D->getKind()) {
-  default:
-    //  <expr-primary> ::= L <mangled-name> E # external name
-    Out << 'L';
-    mangle(D);
-    Out << 'E';
-    break;
-
-  case Decl::ParmVar:
-    mangleFunctionParam(cast<ParmVarDecl>(D));
-    break;
-
-  case Decl::EnumConstant: {
-    const EnumConstantDecl *ED = cast<EnumConstantDecl>(D);
-    mangleIntegerLiteral(ED->getType(), ED->getInitVal());
-    break;
-  }
-
-  case Decl::NonTypeTemplateParm:
-    const NonTypeTemplateParmDecl *PD = cast<NonTypeTemplateParmDecl>(D);
-    mangleTemplateParameter(PD->getDepth(), PD->getIndex());
-    break;
-  }
-}
-
-void CXXNameMangler::mangleExpression(const Expr *E, unsigned Arity) {
+void CXXNameMangler::mangleExpression(const Expr *E, unsigned Arity,
+                                      bool AsTemplateArg) {
   // <expression> ::= <unary operator-name> <expression>
   //              ::= <binary operator-name> <expression> <expression>
   //              ::= <trinary operator-name> <expression> <expression> <expression>
@@ -3912,6 +3887,7 @@
   //              ::= at <type>                      # alignof (a type)
   //              ::= <template-param>
   //              ::= <function-param>
+  //              ::= fpT                            # 'this' expression (part of <function-param>)
   //              ::= sr <type> <unqualified-name>                   # dependent name
   //              ::= sr <type> <unqualified-name> <template-args>   # dependent template-id
   //              ::= ds <expression> <expression>                   # expr.*expr
@@ -3920,11 +3896,55 @@
   //              ::= u <source-name> <template-arg>* E # vendor extended expression
   //              ::= <expr-primary>
   // <expr-primary> ::= L <type> <value number> E    # integer literal
-  //                ::= L <type <value float> E      # floating literal
+  //                ::= L <type> <value float> E     # floating literal
+  //                ::= L <type> <string type> E     # string literal
+  //                ::= L <nullptr type> E           # nullptr literal "LDnE"
+  //                ::= L <pointer type> 0 E         # null pointer template argument
+  //                ::= L <type> <real-part float> _ <imag-part float> E    # complex floating point literal (C99); not used by clang
   //                ::= L <mangled-name> E           # external name
-  //                ::= fpT                          # 'this' expression
   QualType ImplicitlyConvertedToType;
 
+  // A top-level expression that's not <expr-primary> needs to be wrapped in
+  // X...E in a template arg.
+  bool IsPrimaryExpr = true;
+  auto NotPrimaryExpr = [&] {
+    if (AsTemplateArg && IsPrimaryExpr)
+      Out << 'X';
+    IsPrimaryExpr = false;
+  };
+
+  auto MangleDeclRefExpr = [&](const NamedDecl *D) {
+    switch (D->getKind()) {
+    default:
+      //  <expr-primary> ::= L <mangled-name> E # external name
+      Out << 'L';
+      mangle(D);
+      Out << 'E';
+      break;
+
+    case Decl::ParmVar:
+      NotPrimaryExpr();
+      mangleFunctionParam(cast<ParmVarDecl>(D));
+      break;
+
+    case Decl::EnumConstant: {
+      // <expr-primary>
+      const EnumConstantDecl *ED = cast<EnumConstantDecl>(D);
+      mangleIntegerLiteral(ED->getType(), ED->getInitVal());
+      break;
+    }
+
+    case Decl::NonTypeTemplateParm:
+      NotPrimaryExpr();
+      const NonTypeTemplateParmDecl *PD = cast<NonTypeTemplateParmDecl>(D);
+      mangleTemplateParameter(PD->getDepth(), PD->getIndex());
+      break;
+    }
+  };
+
+  // 'goto recurse' is used when handling a simple "unwrapping" node which
+  // produces no output, where ImplicitlyConvertedToType and AsTemplateArg need
+  // to be preserved.
 recurse:
   switch (E->getStmtClass()) {
   case Expr::NoStmtClass:
@@ -3996,6 +4016,7 @@
   case Expr::SourceLocExprClass:
   case Expr::BuiltinBitCastExprClass:
   {
+    NotPrimaryExpr();
     if (!NullOut) {
       // As bad as this diagnostic is, it's better than crashing.
       DiagnosticsEngine &Diags = Context.getDiags();
@@ -4003,11 +4024,13 @@
                                        "cannot yet mangle expression type %0");
       Diags.Report(E->getExprLoc(), DiagID)
         << E->getStmtClassName() << E->getSourceRange();
+      return;
     }
     break;
   }
 
   case Expr::CXXUuidofExprClass: {
+    NotPrimaryExpr();
     const CXXUuidofExpr *UE = cast<CXXUuidofExpr>(E);
     // As of clang 12, uuidof uses the vendor extended expression
     // mangling. Previously, it used a special-cased nonstandard extension.
@@ -4027,7 +4050,7 @@
       } else {
         Expr *UuidExp = UE->getExprOperand();
         Out << "u8__uuidofz";
-        mangleExpression(UuidExp, Arity);
+        mangleExpression(UuidExp);
       }
     }
     break;
@@ -4035,13 +4058,14 @@
 
   // Even gcc-4.5 doesn't mangle this.
   case Expr::BinaryConditionalOperatorClass: {
+    NotPrimaryExpr();
     DiagnosticsEngine &Diags = Context.getDiags();
     unsigned DiagID =
       Diags.getCustomDiagID(DiagnosticsEngine::Error,
                 "?: operator with omitted middle operand cannot be mangled");
     Diags.Report(E->getExprLoc(), DiagID)
       << E->getStmtClassName() << E->getSourceRange();
-    break;
+    return;
   }
 
   // These are used for internal purposes and cannot be meaningfully mangled.
@@ -4049,6 +4073,7 @@
     llvm_unreachable("cannot mangle opaque value; mangling wrong thing?");
 
   case Expr::InitListExprClass: {
+    NotPrimaryExpr();
     Out << "il";
     mangleInitListElements(cast<InitListExpr>(E));
     Out << "E";
@@ -4056,6 +4081,7 @@
   }
 
   case Expr::DesignatedInitExprClass: {
+    NotPrimaryExpr();
     auto *DIE = cast<DesignatedInitExpr>(E);
     for (const auto &Designator : DIE->designators()) {
       if (Designator.isFieldDesignator()) {
@@ -4077,27 +4103,27 @@
   }
 
   case Expr::CXXDefaultArgExprClass:
-    mangleExpression(cast<CXXDefaultArgExpr>(E)->getExpr(), Arity);
-    break;
+    E = cast<CXXDefaultArgExpr>(E)->getExpr();
+    goto recurse;
 
   case Expr::CXXDefaultInitExprClass:
-    mangleExpression(cast<CXXDefaultInitExpr>(E)->getExpr(), Arity);
-    break;
+    E = cast<CXXDefaultInitExpr>(E)->getExpr();
+    goto recurse;
 
   case Expr::CXXStdInitializerListExprClass:
-    mangleExpression(cast<CXXStdInitializerListExpr>(E)->getSubExpr(), Arity);
-    break;
+    E = cast<CXXStdInitializerListExpr>(E)->getSubExpr();
+    goto recurse;
 
   case Expr::SubstNonTypeTemplateParmExprClass:
-    mangleExpression(cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement(),
-                     Arity);
-    break;
+    E = cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement();
+    goto recurse;
 
   case Expr::UserDefinedLiteralClass:
     // We follow g++'s approach of mangling a UDL as a call to the literal
     // operator.
   case Expr::CXXMemberCallExprClass: // fallthrough
   case Expr::CallExprClass: {
+    NotPrimaryExpr();
     const CallExpr *CE = cast<CallExpr>(E);
 
     // <expression> ::= cp <simple-id> <expression>* E
@@ -4128,6 +4154,7 @@
   }
 
   case Expr::CXXNewExprClass: {
+    NotPrimaryExpr();
     const CXXNewExpr *New = cast<CXXNewExpr>(E);
     if (New->isGlobalNew()) Out << "gs";
     Out << (New->isArray() ? "na" : "nw");
@@ -4163,6 +4190,7 @@
   }
 
   case Expr::CXXPseudoDestructorExprClass: {
+    NotPrimaryExpr();
     const auto *PDE = cast<CXXPseudoDestructorExpr>(E);
     if (const Expr *Base = PDE->getBase())
       mangleMemberExprBase(Base, PDE->isArrow());
@@ -4189,6 +4217,7 @@
   }
 
   case Expr::MemberExprClass: {
+    NotPrimaryExpr();
     const MemberExpr *ME = cast<MemberExpr>(E);
     mangleMemberExpr(ME->getBase(), ME->isArrow(),
                      ME->getQualifier(), nullptr,
@@ -4199,6 +4228,7 @@
   }
 
   case Expr::UnresolvedMemberExprClass: {
+    NotPrimaryExpr();
     const UnresolvedMemberExpr *ME = cast<UnresolvedMemberExpr>(E);
     mangleMemberExpr(ME->isImplicitAccess() ? nullptr : ME->getBase(),
                      ME->isArrow(), ME->getQualifier(), nullptr,
@@ -4209,6 +4239,7 @@
   }
 
   case Expr::CXXDependentScopeMemberExprClass: {
+    NotPrimaryExpr();
     const CXXDependentScopeMemberExpr *ME
       = cast<CXXDependentScopeMemberExpr>(E);
     mangleMemberExpr(ME->isImplicitAccess() ? nullptr : ME->getBase(),
@@ -4221,6 +4252,7 @@
   }
 
   case Expr::UnresolvedLookupExprClass: {
+    NotPrimaryExpr();
     const UnresolvedLookupExpr *ULE = cast<UnresolvedLookupExpr>(E);
     mangleUnresolvedName(ULE->getQualifier(), ULE->getName(),
                          ULE->getTemplateArgs(), ULE->getNumTemplateArgs(),
@@ -4229,6 +4261,7 @@
   }
 
   case Expr::CXXUnresolvedConstructExprClass: {
+    NotPrimaryExpr();
     const CXXUnresolvedConstructExpr *CE = cast<CXXUnresolvedConstructExpr>(E);
     unsigned N = CE->getNumArgs();
 
@@ -4239,7 +4272,7 @@
       mangleType(CE->getType());
       mangleInitListElements(IL);
       Out << "E";
-      return;
+      break;
     }
 
     Out << "cv";
@@ -4251,14 +4284,17 @@
   }
 
   case Expr::CXXConstructExprClass: {
+    // An implicit cast is silent, thus may contain <expr-primary>.
     const auto *CE = cast<CXXConstructExpr>(E);
     if (!CE->isListInitialization() || CE->isStdInitListInitialization()) {
       assert(
           CE->getNumArgs() >= 1 &&
           (CE->getNumArgs() == 1 || isa<CXXDefaultArgExpr>(CE->getArg(1))) &&
           "implicit CXXConstructExpr must have one argument");
-      return mangleExpression(cast<CXXConstructExpr>(E)->getArg(0));
+      E = cast<CXXConstructExpr>(E)->getArg(0);
+      goto recurse;
     }
+    NotPrimaryExpr();
     Out << "il";
     for (auto *E : CE->arguments())
       mangleExpression(E);
@@ -4267,6 +4303,7 @@
   }
 
   case Expr::CXXTemporaryObjectExprClass: {
+    NotPrimaryExpr();
     const auto *CE = cast<CXXTemporaryObjectExpr>(E);
     unsigned N = CE->getNumArgs();
     bool List = CE->isListInitialization();
@@ -4296,17 +4333,20 @@
   }
 
   case Expr::CXXScalarValueInitExprClass:
+    NotPrimaryExpr();
     Out << "cv";
     mangleType(E->getType());
     Out << "_E";
     break;
 
   case Expr::CXXNoexceptExprClass:
+    NotPrimaryExpr();
     Out << "nx";
     mangleExpression(cast<CXXNoexceptExpr>(E)->getOperand());
     break;
 
   case Expr::UnaryExprOrTypeTraitExprClass: {
+    // Non-instantiation-dependent traits are an <expr-primary> integer literal.
     const UnaryExprOrTypeTraitExpr *SAE = cast<UnaryExprOrTypeTraitExpr>(E);
 
     if (!SAE->isInstantiationDependent()) {
@@ -4326,6 +4366,8 @@
       break;
     }
 
+    NotPrimaryExpr(); // But otherwise, they are not.
+
     auto MangleAlignofSizeofArg = [&] {
       if (SAE->isArgumentType()) {
         Out << 't';
@@ -4380,6 +4422,7 @@
   }
 
   case Expr::CXXThrowExprClass: {
+    NotPrimaryExpr();
     const CXXThrowExpr *TE = cast<CXXThrowExpr>(E);
     //  <expression> ::= tw <expression>  # throw expression
     //               ::= tr               # rethrow
@@ -4393,6 +4436,7 @@
   }
 
   case Expr::CXXTypeidExprClass: {
+    NotPrimaryExpr();
     const CXXTypeidExpr *TIE = cast<CXXTypeidExpr>(E);
     //  <expression> ::= ti <type>        # typeid (type)
     //               ::= te <expression>  # typeid (expression)
@@ -4407,6 +4451,7 @@
   }
 
   case Expr::CXXDeleteExprClass: {
+    NotPrimaryExpr();
     const CXXDeleteExpr *DE = cast<CXXDeleteExpr>(E);
     //  <expression> ::= [gs] dl <expression>  # [::] delete expr
     //               ::= [gs] da <expression>  # [::] delete [] expr
@@ -4417,6 +4462,7 @@
   }
 
   case Expr::UnaryOperatorClass: {
+    NotPrimaryExpr();
     const UnaryOperator *UO = cast<UnaryOperator>(E);
     mangleOperatorName(UnaryOperator::getOverloadedOperator(UO->getOpcode()),
                        /*Arity=*/1);
@@ -4425,6 +4471,7 @@
   }
 
   case Expr::ArraySubscriptExprClass: {
+    NotPrimaryExpr();
     const ArraySubscriptExpr *AE = cast<ArraySubscriptExpr>(E);
 
     // Array subscript is treated as a syntactically weird form of
@@ -4436,6 +4483,7 @@
   }
 
   case Expr::MatrixSubscriptExprClass: {
+    NotPrimaryExpr();
     const MatrixSubscriptExpr *ME = cast<MatrixSubscriptExpr>(E);
     Out << "ixix";
     mangleExpression(ME->getBase());
@@ -4446,6 +4494,7 @@
 
   case Expr::CompoundAssignOperatorClass: // fallthrough
   case Expr::BinaryOperatorClass: {
+    NotPrimaryExpr();
     const BinaryOperator *BO = cast<BinaryOperator>(E);
     if (BO->getOpcode() == BO_PtrMemD)
       Out << "ds";
@@ -4458,6 +4507,7 @@
   }
 
   case Expr::CXXRewrittenBinaryOperatorClass: {
+    NotPrimaryExpr();
     // The mangled form represents the original syntax.
     CXXRewrittenBinaryOperator::DecomposedForm Decomposed =
         cast<CXXRewrittenBinaryOperator>(E)->getDecomposedForm();
@@ -4469,6 +4519,7 @@
   }
 
   case Expr::ConditionalOperatorClass: {
+    NotPrimaryExpr();
     const ConditionalOperator *CO = cast<ConditionalOperator>(E);
     mangleOperatorName(OO_Conditional, /*Arity=*/3);
     mangleExpression(CO->getCond());
@@ -4484,19 +4535,22 @@
   }
 
   case Expr::ObjCBridgedCastExprClass: {
+    NotPrimaryExpr();
     // Mangle ownership casts as a vendor extended operator __bridge,
     // __bridge_transfer, or __bridge_retain.
     StringRef Kind = cast<ObjCBridgedCastExpr>(E)->getBridgeKindName();
     Out << "v1U" << Kind.size() << Kind;
+    mangleCastExpression(E, "cv");
+    break;
   }
-  // Fall through to mangle the cast itself.
-  LLVM_FALLTHROUGH;
 
   case Expr::CStyleCastExprClass:
+    NotPrimaryExpr();
     mangleCastExpression(E, "cv");
     break;
 
   case Expr::CXXFunctionalCastExprClass: {
+    NotPrimaryExpr();
     auto *Sub = cast<ExplicitCastExpr>(E)->getSubExpr()->IgnoreImplicit();
     // FIXME: Add isImplicit to CXXConstructExpr.
     if (auto *CCE = dyn_cast<CXXConstructExpr>(Sub))
@@ -4516,22 +4570,28 @@
   }
 
   case Expr::CXXStaticCastExprClass:
+    NotPrimaryExpr();
     mangleCastExpression(E, "sc");
     break;
   case Expr::CXXDynamicCastExprClass:
+    NotPrimaryExpr();
     mangleCastExpression(E, "dc");
     break;
   case Expr::CXXReinterpretCastExprClass:
+    NotPrimaryExpr();
     mangleCastExpression(E, "rc");
     break;
   case Expr::CXXConstCastExprClass:
+    NotPrimaryExpr();
     mangleCastExpression(E, "cc");
     break;
   case Expr::CXXAddrspaceCastExprClass:
+    NotPrimaryExpr();
     mangleCastExpression(E, "ac");
     break;
 
   case Expr::CXXOperatorCallExprClass: {
+    NotPrimaryExpr();
     const CXXOperatorCallExpr *CE = cast<CXXOperatorCallExpr>(E);
     unsigned NumArgs = CE->getNumArgs();
     // A CXXOperatorCallExpr for OO_Arrow models only semantics, not syntax
@@ -4545,9 +4605,8 @@
   }
 
   case Expr::ParenExprClass:
-    mangleExpression(cast<ParenExpr>(E)->getSubExpr(), Arity);
-    break;
-
+    E = cast<ParenExpr>(E)->getSubExpr();
+    goto recurse;
 
   case Expr::ConceptSpecializationExprClass: {
     //  <expr-primary> ::= L <mangled-name> E # external name
@@ -4561,10 +4620,12 @@
   }
 
   case Expr::DeclRefExprClass:
-    mangleDeclRefExpr(cast<DeclRefExpr>(E)->getDecl());
+    // MangleDeclRefExpr helper handles primary-vs-nonprimary
+    MangleDeclRefExpr(cast<DeclRefExpr>(E)->getDecl());
     break;
 
   case Expr::SubstNonTypeTemplateParmPackExprClass:
+    NotPrimaryExpr();
     // FIXME: not clear how to mangle this!
     // template <unsigned N...> class A {
     //   template <class U...> void foo(U (&x)[N]...);
@@ -4573,14 +4634,16 @@
     break;
 
   case Expr::FunctionParmPackExprClass: {
+    NotPrimaryExpr();
     // FIXME: not clear how to mangle this!
     const FunctionParmPackExpr *FPPE = cast<FunctionParmPackExpr>(E);
     Out << "v110_SUBSTPACK";
-    mangleDeclRefExpr(FPPE->getParameterPack());
+    MangleDeclRefExpr(FPPE->getParameterPack());
     break;
   }
 
   case Expr::DependentScopeDeclRefExprClass: {
+    NotPrimaryExpr();
     const DependentScopeDeclRefExpr *DRE = cast<DependentScopeDeclRefExpr>(E);
     mangleUnresolvedName(DRE->getQualifier(), DRE->getDeclName(),
                          DRE->getTemplateArgs(), DRE->getNumTemplateArgs(),
@@ -4589,24 +4652,27 @@
   }
 
   case Expr::CXXBindTemporaryExprClass:
-    mangleExpression(cast<CXXBindTemporaryExpr>(E)->getSubExpr());
-    break;
+    E = cast<CXXBindTemporaryExpr>(E)->getSubExpr();
+    goto recurse;
 
   case Expr::ExprWithCleanupsClass:
-    mangleExpression(cast<ExprWithCleanups>(E)->getSubExpr(), Arity);
-    break;
+    E = cast<ExprWithCleanups>(E)->getSubExpr();
+    goto recurse;
 
   case Expr::FloatingLiteralClass: {
+    // <expr-primary>
     const FloatingLiteral *FL = cast<FloatingLiteral>(E);
     mangleFloatLiteral(FL->getType(), FL->getValue());
     break;
   }
 
   case Expr::FixedPointLiteralClass:
+    // Currently unimplemented -- might be <expr-primary> in future?
     mangleFixedPointLiteral();
     break;
 
   case Expr::CharacterLiteralClass:
+    // <expr-primary>
     Out << 'L';
     mangleType(E->getType());
     Out << cast<CharacterLiteral>(E)->getValue();
@@ -4615,18 +4681,21 @@
 
   // FIXME. __objc_yes/__objc_no are mangled same as true/false
   case Expr::ObjCBoolLiteralExprClass:
+    // <expr-primary>
     Out << "Lb";
     Out << (cast<ObjCBoolLiteralExpr>(E)->getValue() ? '1' : '0');
     Out << 'E';
     break;
 
   case Expr::CXXBoolLiteralExprClass:
+    // <expr-primary>
     Out << "Lb";
     Out << (cast<CXXBoolLiteralExpr>(E)->getValue() ? '1' : '0');
     Out << 'E';
     break;
 
   case Expr::IntegerLiteralClass: {
+    // <expr-primary>
     llvm::APSInt Value(cast<IntegerLiteral>(E)->getValue());
     if (E->getType()->isSignedIntegerType())
       Value.setIsSigned(true);
@@ -4635,6 +4704,7 @@
   }
 
   case Expr::ImaginaryLiteralClass: {
+    // <expr-primary>
     const ImaginaryLiteral *IE = cast<ImaginaryLiteral>(E);
     // Mangle as if a complex literal.
     // Proposal from David Vandevoorde, 2010.06.30.
@@ -4658,6 +4728,7 @@
   }
 
   case Expr::StringLiteralClass: {
+    // <expr-primary>
     // Revised proposal from David Vandervoorde, 2010.07.15.
     Out << 'L';
     assert(isa<ConstantArrayType>(E->getType()));
@@ -4667,21 +4738,25 @@
   }
 
   case Expr::GNUNullExprClass:
+    // <expr-primary>
     // Mangle as if an integer literal 0.
     mangleIntegerLiteral(E->getType(), llvm::APSInt(32));
     break;
 
   case Expr::CXXNullPtrLiteralExprClass: {
+    // <expr-primary>
     Out << "LDnE";
     break;
   }
 
   case Expr::PackExpansionExprClass:
+    NotPrimaryExpr();
     Out << "sp";
     mangleExpression(cast<PackExpansionExpr>(E)->getPattern());
     break;
 
   case Expr::SizeOfPackExprClass: {
+    NotPrimaryExpr();
     auto *SPE = cast<SizeOfPackExpr>(E);
     if (SPE->isPartiallySubstituted()) {
       Out << "sP";
@@ -4706,12 +4781,12 @@
     break;
   }
 
-  case Expr::MaterializeTemporaryExprClass: {
-    mangleExpression(cast<MaterializeTemporaryExpr>(E)->getSubExpr());
-    break;
-  }
+  case Expr::MaterializeTemporaryExprClass:
+    E = cast<MaterializeTemporaryExpr>(E)->getSubExpr();
+    goto recurse;
 
   case Expr::CXXFoldExprClass: {
+    NotPrimaryExpr();
     auto *FE = cast<CXXFoldExpr>(E);
     if (FE->isLeftFold())
       Out << (FE->getInit() ? "fL" : "fl");
@@ -4733,27 +4808,34 @@
   }
 
   case Expr::CXXThisExprClass:
+    NotPrimaryExpr();
     Out << "fpT";
     break;
 
   case Expr::CoawaitExprClass:
     // FIXME: Propose a non-vendor mangling.
+    NotPrimaryExpr();
     Out << "v18co_await";
     mangleExpression(cast<CoawaitExpr>(E)->getOperand());
     break;
 
   case Expr::DependentCoawaitExprClass:
     // FIXME: Propose a non-vendor mangling.
+    NotPrimaryExpr();
     Out << "v18co_await";
     mangleExpression(cast<DependentCoawaitExpr>(E)->getOperand());
     break;
 
   case Expr::CoyieldExprClass:
     // FIXME: Propose a non-vendor mangling.
+    NotPrimaryExpr();
     Out << "v18co_yield";
     mangleExpression(cast<CoawaitExpr>(E)->getOperand());
     break;
   }
+
+  if (AsTemplateArg && !IsPrimaryExpr)
+    Out << 'E';
 }
 
 /// Mangle an expression which refers to a parameter variable.
@@ -5003,10 +5085,9 @@
     Out << "Dp";
     mangleType(A.getAsTemplateOrTemplatePattern());
     break;
-  case TemplateArgument::Expression: {
+  case TemplateArgument::Expression:
     mangleTemplateArgExpr(A.getAsExpr());
     break;
-  }
   case TemplateArgument::Integral:
     mangleIntegerLiteral(A.getIntegralType(), A.getAsIntegral());
     break;
@@ -5062,9 +5143,22 @@
 }
 
 void CXXNameMangler::mangleTemplateArgExpr(const Expr *E) {
-  // It's possible to end up with a DeclRefExpr here in certain
-  // dependent cases, in which case we should mangle as a
-  // declaration.
+  ASTContext &Ctx = Context.getASTContext();
+  if (Ctx.getLangOpts().getClangABICompat() > LangOptions::ClangABI::Ver11) {
+    mangleExpression(E, UnknownArity, /*AsTemplateArg=*/true);
+    return;
+  }
+
+  // Prior to Clang 12, we didn't omit the X .. E around <expr-primary>
+  // correctly in cases where the template argument was
+  // constructed from an expression rather than an already-evaluated
+  // literal. In such a case, we would then e.g. emit 'XLi0EE' instead of
+  // 'Li0E'.
+  //
+  // We did special-case DeclRefExpr to attempt to DTRT for that one
+  // expression-kind, but while doing so, unfortunately handled ParmVarDecl
+  // (subtype of VarDecl) _incorrectly_, and emitted 'L_Z .. E' instead of
+  // the proper 'Xfp_E'.
   E = E->IgnoreParenImpCasts();
   if (const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E)) {
     const ValueDecl *D = DRE->getDecl();
@@ -5075,7 +5169,6 @@
       return;
     }
   }
-
   Out << 'X';
   mangleExpression(E);
   Out << 'E';
diff --git a/clang/test/CodeGenCXX/clang-abi-compat.cpp b/clang/test/CodeGenCXX/clang-abi-compat.cpp
--- a/clang/test/CodeGenCXX/clang-abi-compat.cpp
+++ b/clang/test/CodeGenCXX/clang-abi-compat.cpp
@@ -1,12 +1,23 @@
-// RUN: %clang_cc1 -std=c++98 -triple x86_64-linux-gnu -fclang-abi-compat=3.0 %s -emit-llvm -o -    | FileCheck --check-prefixes=CHECK,PRE39,PRE5,PRE12 %s
-// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fclang-abi-compat=3.0 %s -emit-llvm -o -    | FileCheck --check-prefixes=CHECK,PRE39,PRE5,PRE12 %s
-// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fclang-abi-compat=3.8 %s -emit-llvm -o -    | FileCheck --check-prefixes=CHECK,PRE39,PRE5,PRE12 %s
-// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fclang-abi-compat=3.9 %s -emit-llvm -o -    | FileCheck --check-prefixes=CHECK,V39,PRE5,PRE12 %s
-// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fclang-abi-compat=4.0 %s -emit-llvm -o -    | FileCheck --check-prefixes=CHECK,V39,PRE5,PRE12 %s
-// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fclang-abi-compat=5 %s -emit-llvm -o -      | FileCheck --check-prefixes=CHECK,V39,V5,PRE12,PRE12-CXX17 %s
-// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fclang-abi-compat=11 %s -emit-llvm -o -     | FileCheck --check-prefixes=CHECK,V39,V5,PRE12,PRE12-CXX17 %s
-// RUN: %clang_cc1 -std=c++98 -triple x86_64-linux-gnu -fclang-abi-compat=latest %s -emit-llvm -o - | FileCheck --check-prefixes=CHECK,V39,V5,V12 %s
-// RUN: %clang_cc1 -std=c++20 -triple x86_64-linux-gnu -fclang-abi-compat=latest %s -emit-llvm -o - | FileCheck --check-prefixes=CHECK,V39,V5,V12,V12-CXX17 %s
+// RUN: %clang_cc1 -std=c++98 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=3.0 %s -emit-llvm -o - -Wno-c++11-extensions \
+// RUN:     | FileCheck --check-prefixes=CHECK,PRE39,PRE5,PRE12 %s
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=3.0 %s -emit-llvm -o - \
+// RUN:     | FileCheck --check-prefixes=CHECK,PRE39,PRE5,PRE12 %s
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=3.8 %s -emit-llvm -o - \
+// RUN:     | FileCheck --check-prefixes=CHECK,PRE39,PRE5,PRE12 %s
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=3.9 %s -emit-llvm -o - \
+// RUN:     | FileCheck --check-prefixes=CHECK,V39,PRE5,PRE12 %s
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=4.0 %s -emit-llvm -o - \
+// RUN:     | FileCheck --check-prefixes=CHECK,V39,PRE5,PRE12 %s
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=5 %s -emit-llvm -o - \
+// RUN:     | FileCheck --check-prefixes=CHECK,V39,V5,PRE12,PRE12-CXX17 %s
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=11 %s -emit-llvm -o - \
+// RUN:     | FileCheck --check-prefixes=CHECK,V39,V5,PRE12,PRE12-CXX17 %s
+// RUN: %clang_cc1 -std=c++20 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=11 %s -emit-llvm -o - \
+// RUN:     | FileCheck --check-prefixes=CHECK,V39,V5,PRE12,PRE12-CXX17,PRE12-CXX20 %s
+// RUN: %clang_cc1 -std=c++98 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=latest %s -emit-llvm -o - -Wno-c++11-extensions \
+// RUN:     | FileCheck --check-prefixes=CHECK,V39,V5,V12 %s
+// RUN: %clang_cc1 -std=c++20 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=latest %s -emit-llvm -o - \
+// RUN:     | FileCheck --check-prefixes=CHECK,V39,V5,V12,V12-CXX17,V12-CXX20 %s
 
 typedef __attribute__((vector_size(8))) long long v1xi64;
 void clang39(v1xi64) {}
@@ -55,3 +66,68 @@
 // CHECK: @_Z9clang12_cIXadL_Z3arrEEEvv
 template<const char (*)[6]> void clang12_c() {}
 template void clang12_c<&arr>();
+
+
+/// Tests for <template-arg> <expr-primary> changes in clang12:
+namespace expr_primary {
+struct A {
+  template<int N> struct Int {};
+  template<int& N> struct Ref {};
+};
+
+/// Check various DeclRefExpr manglings
+
+// PRE12: @_ZN12expr_primary5test1INS_1AEEEvNT_3IntIXLi1EEEE
+// V12:   @_ZN12expr_primary5test1INS_1AEEEvNT_3IntILi1EEE
+template <typename T> void test1(typename T::template Int<1> a) {}
+template void test1<A>(typename A::template Int<1> a);
+
+enum Enum { EnumVal = 4 };
+int Global;
+
+// PRE12: @_ZN12expr_primary5test2INS_1AEEEvNT_3IntIXLNS_4EnumE4EEEE
+// V12:   @_ZN12expr_primary5test2INS_1AEEEvNT_3IntILNS_4EnumE4EEE
+template <typename T> void test2(typename T::template Int<EnumVal> a) {}
+template void test2<A>(typename A::template Int<4> a);
+
+// CHECK: @_ZN12expr_primary5test3ILi3EEEvNS_1A3IntIXT_EEE
+template <int X> void test3(typename A::template Int<X> a) {}
+template void test3<3>(A::Int<3> a);
+
+#if __cplusplus >= 202002L
+// CHECK-CXX20: @_ZN12expr_primary5test4INS_1AEEEvNT_3RefIL_ZNS_6GlobalEEEE
+template <typename T> void test4(typename T::template Ref<(Global)> a) {}
+template void test4<A>(typename A::template Ref<Global> a);
+
+struct B {
+  struct X {
+    constexpr X(double) {}
+    constexpr X(int&) {}
+  };
+  template<X> struct Y {};
+};
+
+// PRE12-CXX20: _ZN12expr_primary5test5INS_1BEEEvNT_1YIXLd3ff0000000000000EEEE
+// V12-CXX20: _ZN12expr_primary5test5INS_1BEEEvNT_1YILd3ff0000000000000EEE
+template<typename T> void test5(typename T::template Y<1.0>) { }
+template void test5<B>(typename B::Y<1.0>);
+
+// PRE12-CXX20: @_ZN12expr_primary5test6INS_1BEEENT_1YIL_ZZNS_5test6EiE1bEEEi
+// V12-CXX20:   @_ZN12expr_primary5test6INS_1BEEENT_1YIXfp_EEEi
+template<typename T> auto test6(int b) -> typename T::template Y<b> { return {}; }
+template auto test6<B>(int b) -> B::Y<b>;
+#endif
+
+/// Verify non-dependent type-traits within a dependent template arg.
+
+// PRE12: @_ZN12expr_primary5test7INS_1AEEEvNT_3IntIXLm1EEEE
+// V12:   @_ZN12expr_primary5test7INS_1AEEEvNT_3IntILm1EEE
+template <class T> void test7(typename T::template Int<sizeof(char)> a) {}
+template void test7<A>(A::Int<1>);
+
+// PRE12: @_ZN12expr_primary5test8ILi2EEEvu11matrix_typeIXLi1EEXT_EiE
+// V12:   @_ZN12expr_primary5test8ILi2EEEvu11matrix_typeILi1EXT_EiE
+template<int N> using matrix1xN = int __attribute__((matrix_type(1, N)));
+template<int N> void test8(matrix1xN<N> a) {}
+template void test8<2>(matrix1xN<2> a);
+}
diff --git a/clang/test/CodeGenCXX/mangle-abi-tag.cpp b/clang/test/CodeGenCXX/mangle-abi-tag.cpp
--- a/clang/test/CodeGenCXX/mangle-abi-tag.cpp
+++ b/clang/test/CodeGenCXX/mangle-abi-tag.cpp
@@ -225,7 +225,7 @@
 template<class F> void g(F);
 template<class ...A> auto h(A ...a)->decltype (g (0, g < a > (a) ...)) {
 }
-// CHECK-DAG: define {{.*}} @_ZN7pr304401hIJEEEDTcl1gLi0Espcl1gIL_ZZNS_1hEDpT_E1aEEfp_EEES2_(
+// CHECK-DAG: define {{.*}} @_ZN7pr304401hIJEEEDTcl1gLi0Espcl1gIXfp_EEfp_EEEDpT_(
 
 void pr30440_test () {
   h();
diff --git a/clang/test/CodeGenCXX/mangle-concept.cpp b/clang/test/CodeGenCXX/mangle-concept.cpp
--- a/clang/test/CodeGenCXX/mangle-concept.cpp
+++ b/clang/test/CodeGenCXX/mangle-concept.cpp
@@ -6,11 +6,11 @@
 template <typename> concept C = true;
 template <typename T = int> S<C<T>> f0() { return S<C<T>>{}; }
 template S<C<int>> f0<>();
-// CHECK: @_ZN5test12f0IiEENS_1SIXL_ZNS_1CIT_EEEEEEv(
+// CHECK: @_ZN5test12f0IiEENS_1SIL_ZNS_1CIT_EEEEEv(
 }
 
 template <bool> struct S {};
 template <typename> concept C = true;
 template <typename T = int> S<C<T>> f0() { return S<C<T>>{}; }
 template S<C<int>> f0<>();
-// CHECK: @_Z2f0IiE1SIXL_Z1CIT_EEEEv(
+// CHECK: @_Z2f0IiE1SIL_Z1CIT_EEEv(
diff --git a/clang/test/CodeGenCXX/mangle-template.cpp b/clang/test/CodeGenCXX/mangle-template.cpp
--- a/clang/test/CodeGenCXX/mangle-template.cpp
+++ b/clang/test/CodeGenCXX/mangle-template.cpp
@@ -270,7 +270,7 @@
   // Note: there is no J...E here, because we can't form a pack argument, and
   // the 5u and 6u are mangled with the original type 'j' (unsigned int) not
   // with the resolved type 'i' (signed int).
-  // CHECK: define {{.*}} @_ZN6test171hILi4EJLi1ELi2ELi3EEEEvNS_1XIXspT0_EXLj5EEXT_EXLj6EEEE
+  // CHECK: define {{.*}} @_ZN6test171hILi4EJLi1ELi2ELi3EEEEvNS_1XIXspT0_ELj5EXT_ELj6EEE
   template<int D, int ...C> void h(X<C..., 5u, D, 6u>) {}
   void i() { h<4, 1, 2, 3>({}); }
 
@@ -323,7 +323,7 @@
     // callee is unresolved, the rest mangle the converted argument Lj0E
     // because the callee is resolved.
     void h() {
-      // CHECK: @_ZN33partially_dependent_template_args5test22g1INS0_1XEEEvDTcl1fIXLi0EEEcvT__EEE
+      // CHECK: @_ZN33partially_dependent_template_args5test22g1INS0_1XEEEvDTcl1fILi0EEcvT__EEE
       g1<X>({});
       // CHECK: @_ZN33partially_dependent_template_args5test22g2IiEEvDTplclL_ZNS0_1fILj0EEEiNS0_1XEEilEEcvT__EE
       g2<int>({});
diff --git a/clang/test/CodeGenCXX/mangle.cpp b/clang/test/CodeGenCXX/mangle.cpp
--- a/clang/test/CodeGenCXX/mangle.cpp
+++ b/clang/test/CodeGenCXX/mangle.cpp
@@ -1123,7 +1123,7 @@
 namespace test57 {
   struct X { template <int N> int f(); } x;
   template<int N> void f(decltype(x.f<0>() + N)) {}
-  // CHECK-LABEL: @_ZN6test571fILi0EEEvDTplcldtL_ZNS_1xEE1fIXLi0EEEET_E
+  // CHECK-LABEL: @_ZN6test571fILi0EEEvDTplcldtL_ZNS_1xEE1fILi0EEET_E
   template void f<0>(int);
 }
 
diff --git a/clang/test/CodeGenCXX/matrix-type.cpp b/clang/test/CodeGenCXX/matrix-type.cpp
--- a/clang/test/CodeGenCXX/matrix-type.cpp
+++ b/clang/test/CodeGenCXX/matrix-type.cpp
@@ -215,14 +215,14 @@
   // CHECK-NEXT:    %m4 = alloca [144 x float], align 4
   // CHECK-NEXT:    %v = alloca %struct.selector.3, align 1
   // CHECK-NEXT:    %undef.agg.tmp4 = alloca %struct.selector.3, align 1
-  // CHECK-NEXT:    call void @_Z10use_matrixIiLm12EE8selectorILi3EERu11matrix_typeIXLm10EEXT0_ET_E([120 x i32]* nonnull align 4 dereferenceable(480) %m0)
+  // CHECK-NEXT:    call void @_Z10use_matrixIiLm12EE8selectorILi3EERu11matrix_typeILm10EXT0_ET_E([120 x i32]* nonnull align 4 dereferenceable(480) %m0)
   // CHECK-NEXT:    call void @_Z10use_matrixIiE8selectorILi2EERu11matrix_typeILm10ELm10ET_E([100 x i32]* nonnull align 4 dereferenceable(400) %m1)
-  // CHECK-NEXT:    call void @_Z10use_matrixIiLm12EE8selectorILi1EERu11matrix_typeIXT0_EXLm10EET_E([120 x i32]* nonnull align 4 dereferenceable(480) %m2)
+  // CHECK-NEXT:    call void @_Z10use_matrixIiLm12EE8selectorILi1EERu11matrix_typeIXT0_ELm10ET_E([120 x i32]* nonnull align 4 dereferenceable(480) %m2)
   // CHECK-NEXT:    call void @_Z10use_matrixIiLm12ELm12EE8selectorILi0EERu11matrix_typeIXT0_EXT1_ET_E([144 x i32]* nonnull align 4 dereferenceable(576) %m3)
   // CHECK-NEXT:    call void @_Z10use_matrixILm12ELm12EE8selectorILi4EERu11matrix_typeIXT_EXT0_EfE([144 x float]* nonnull align 4 dereferenceable(576) %m4)
   // CHECK-NEXT:    ret void
 
-  // CHECK-LABEL: define linkonce_odr void @_Z10use_matrixIiLm12EE8selectorILi3EERu11matrix_typeIXLm10EEXT0_ET_E([120 x i32]* nonnull align 4 dereferenceable(480) %m)
+  // CHECK-LABEL: define linkonce_odr void @_Z10use_matrixIiLm12EE8selectorILi3EERu11matrix_typeILm10EXT0_ET_E([120 x i32]* nonnull align 4 dereferenceable(480) %m)
   // CHECK-NEXT:  entry:
   // CHECK-NEXT:    %m.addr = alloca [120 x i32]*, align 8
   // CHECK-NEXT:    store [120 x i32]* %m, [120 x i32]** %m.addr, align 8
@@ -236,7 +236,7 @@
   // CHECK-NEXT:    call void @llvm.trap()
   // CHECK-NEXT:    unreachable
 
-  // CHECK-LABEL: define linkonce_odr void @_Z10use_matrixIiLm12EE8selectorILi1EERu11matrix_typeIXT0_EXLm10EET_E([120 x i32]* nonnull align 4 dereferenceable(480) %m)
+  // CHECK-LABEL: define linkonce_odr void @_Z10use_matrixIiLm12EE8selectorILi1EERu11matrix_typeIXT0_ELm10ET_E([120 x i32]* nonnull align 4 dereferenceable(480) %m)
   // CHECK-NEXT:  entry:
   // CHECK-NEXT:    %m.addr = alloca [120 x i32]*, align 8
   // CHECK-NEXT:    store [120 x i32]* %m, [120 x i32]** %m.addr, align 8
@@ -277,10 +277,10 @@
   // CHECK-LABEL: define{{.*}} void @_Z11test_auto_tv()
   // CHECK-NEXT:  entry:
   // CHECK-NEXT:    %m = alloca [130 x i32], align 4
-  // CHECK-NEXT:    call void @_Z3fooILm13EEvRu11matrix_typeIXT_EXLm10EEiE([130 x i32]* nonnull align 4 dereferenceable(520) %m)
+  // CHECK-NEXT:    call void @_Z3fooILm13EEvRu11matrix_typeIXT_ELm10EiE([130 x i32]* nonnull align 4 dereferenceable(520) %m)
   // CHECK-NEXT:    ret void
 
-  // CHECK-LABEL: define linkonce_odr void @_Z3fooILm13EEvRu11matrix_typeIXT_EXLm10EEiE([130 x i32]* nonnull align 4 dereferenceable(520) %m)
+  // CHECK-LABEL: define linkonce_odr void @_Z3fooILm13EEvRu11matrix_typeIXT_ELm10EiE([130 x i32]* nonnull align 4 dereferenceable(520) %m)
   // CHECK-NEXT:  entry:
   // CHECK-NEXT:    %m.addr = alloca [130 x i32]*, align 8
   // CHECK-NEXT:    store [130 x i32]* %m, [130 x i32]** %m.addr, align 8
@@ -326,7 +326,7 @@
   // CHECK-NEXT:    store <40 x float> %call, <40 x float>* %0, align 4
   // CHECK-NEXT:    call void @_Z12use_matrix_2ILm2ELm12EE8selectorILi0EERu11matrix_typeIXplT_Li2EEXdvT0_Li2EEiERu11matrix_typeIXT_EXT0_EfE([24 x i32]* nonnull align 4 dereferenceable(96) %m1, [24 x float]* nonnull align 4 dereferenceable(96) %m2)
   // CHECK-NEXT:    call void @_Z12use_matrix_2ILm5ELm8EE8selectorILi1EERu11matrix_typeIXplT_T0_EXT0_EiERu11matrix_typeIXT_EXmiT0_T_EfE([104 x i32]* nonnull align 4 dereferenceable(416) %m3, [15 x float]* nonnull align 4 dereferenceable(60) %m4)
-  // CHECK-NEXT:    %call2 = call <20 x float> @_Z12use_matrix_2ILm5EEu11matrix_typeIXplT_T_EXmiT_Li3EEfERu11matrix_typeIXT_EXLm10EEiE([50 x i32]* nonnull align 4 dereferenceable(200) %m5)
+  // CHECK-NEXT:    %call2 = call <20 x float> @_Z12use_matrix_2ILm5EEu11matrix_typeIXplT_T_EXmiT_Li3EEfERu11matrix_typeIXT_ELm10EiE([50 x i32]* nonnull align 4 dereferenceable(200) %m5)
   // CHECK-NEXT:    %1 = bitcast [20 x float]* %r4 to <20 x float>*
   // CHECK-NEXT:    store <20 x float> %call2, <20 x float>* %1, align 4
   // CHECK-NEXT:    call void @_Z12use_matrix_3ILm6EE8selectorILi2EERu11matrix_typeIXmiT_Li2EEXT_EiE([24 x i32]* nonnull align 4 dereferenceable(96) %m1)
@@ -357,7 +357,7 @@
   // CHECK-NEXT:    call void @llvm.trap()
   // CHECK-NEXT:    unreachable
 
-  // CHECK-LABEL: define linkonce_odr <20 x float> @_Z12use_matrix_2ILm5EEu11matrix_typeIXplT_T_EXmiT_Li3EEfERu11matrix_typeIXT_EXLm10EEiE([50 x i32]* nonnull align 4 dereferenceable(200) %m1)
+  // CHECK-LABEL: define linkonce_odr <20 x float> @_Z12use_matrix_2ILm5EEu11matrix_typeIXplT_T_EXmiT_Li3EEfERu11matrix_typeIXT_ELm10EiE([50 x i32]* nonnull align 4 dereferenceable(200) %m1)
   // CHECK-NEXT:  entry:
   // CHECK-NEXT:    %m1.addr = alloca [50 x i32]*, align 8
   // CHECK-NEXT:    store [50 x i32]* %m1, [50 x i32]** %m1.addr, align 8
diff --git a/clang/test/CodeGenCXX/microsoft-uuidof-mangling.cpp b/clang/test/CodeGenCXX/microsoft-uuidof-mangling.cpp
--- a/clang/test/CodeGenCXX/microsoft-uuidof-mangling.cpp
+++ b/clang/test/CodeGenCXX/microsoft-uuidof-mangling.cpp
@@ -60,14 +60,12 @@
 // CHECK-V11: call void @_Z15test_uuidofExprI9HasMemberEvDTu8__uuidofzsrT_6memberE(
 // CHECK-V12: call void @_Z15test_uuidofExprI9HasMemberEvDTu8__uuidofXsrT_6memberEEE(
 // CHECK-V11: call void @_Z16test_uuidofExpr2I10TestStructEvDTcmtlT_Eu8__uuidofzL_ZN9HasMember6memberEEE(
-// CHECK-V12: call void @_Z16test_uuidofExpr2I10TestStructEvDTcmtlT_Eu8__uuidofXL_ZN9HasMember6memberEEEEE(
-//    TODO: the above mangling is wrong -- the X/E shouldn't be emitted:       ^                     ^
+// CHECK-V12: call void @_Z16test_uuidofExpr2I10TestStructEvDTcmtlT_Eu8__uuidofL_ZN9HasMember6memberEEEE(
 // CHECK: define linkonce_odr void @_ZN8UUIDTestI10TestStructL_Z42_GUID_eafa1952_66f8_438b_8fba_af1bbae42191EEC1Ev
 // CHECK-V11: define linkonce_odr void @_Z15test_uuidofTypeI10TestStructEvDTu8__uuidoftT_E(
 // CHECK-V12: define linkonce_odr void @_Z15test_uuidofTypeI10TestStructEvDTu8__uuidofT_EE(
 // CHECK-V11: define linkonce_odr void @_Z15test_uuidofExprI9HasMemberEvDTu8__uuidofzsrT_6memberE(
 // CHECK-V12: define linkonce_odr void @_Z15test_uuidofExprI9HasMemberEvDTu8__uuidofXsrT_6memberEEE(
 // CHECK-V11: define linkonce_odr void @_Z16test_uuidofExpr2I10TestStructEvDTcmtlT_Eu8__uuidofzL_ZN9HasMember6memberEEE(
-// CHECK-V12: define linkonce_odr void @_Z16test_uuidofExpr2I10TestStructEvDTcmtlT_Eu8__uuidofXL_ZN9HasMember6memberEEEEE(
-//    TODO: the above mangling is wrong -- the X/E shouldn't be emitted:                      ^                     ^
+// CHECK-V12: define linkonce_odr void @_Z16test_uuidofExpr2I10TestStructEvDTcmtlT_Eu8__uuidofL_ZN9HasMember6memberEEEE(
 // CHECK: define linkonce_odr void @_ZN8UUIDTestI10TestStructL_Z42_GUID_eafa1952_66f8_438b_8fba_af1bbae42191EEC2Ev