Rework how UuidAttr, CXXUuidofExpr, and GUID template arguments and constants are represented.

[rsmith]

Summary

Previously, we treated CXXUuidofExpr as quite a special case: it was the
only kind of expression that could be a canonical template argument, it
could be a constant lvalue base object, and so on. In addition, we
represented the UUID value as a string, whose source form we did not
preserve faithfully, and that we partially parsed in multiple different
places.

With this patch, we create an MSGuidDecl object to represent the
implicit object of type 'struct _GUID' created by a UuidAttr. Each
UuidAttr holds a pointer to its 'struct _GUID' and its original
(as-written) UUID string. A non-value-dependent CXXUuidofExpr behaves
like a DeclRefExpr denoting that MSGuidDecl object. We cache an APValue
representation of the GUID on the MSGuidDecl and use it from constant
evaluation where needed.

This allows removing a lot of the special-case logic to handle these
expressions. Unfortunately, many parts of Clang assume there are only
a couple of interesting kinds of ValueDecl, so the total amount of
special-case logic is not really reduced very much.

This fixes a few bugs and issues:

• PR38490: we now support reading from GUID objects returned from __uuidof during constant evaluation.
• Our Itanium mangling for a non-instantiation-dependent template argument involving __uuidof no longer depends on which CXXUuidofExpr template argument we happened to see first.
• We now predeclare ::_GUID, and permit use of uuidof without any header inclusion, better matching MSVC's behavior. We do not predefine ::s_GUID, though; that seems like a step too far.
• Our IR representation for GUID constants now uses the correct IR type wherever possible. We will still fall back to using the {i32, i16, i16, [8 x i8]} layout if a definition of struct _GUID is not available. This is not ideal: in principle the two layouts could have different padding.

[rsmith]

There are a few cleanups I made along the way here that I'll be factoring out and committing separately.

[rnk]

lgtm

There's a lot of stuff going on here, and I didn't review that deeply. Let me know if you want a closer reading of the code.

clang/include/clang/AST/TemplateBase.h

85–86

I think this is worth doing just to remove this special case.

clang/lib/AST/Decl.cpp

897–898

I suppose the answer is yes, it can be hidden. One cannot write a Windows app that expects &__uuidof(Foo) to be the same across DSOs. Hopefully we don't have to aim for compatibility to some compiler that targets ELF and supports uuids.

clang/lib/Sema/SemaExpr.cpp

3278

Weird things in the compiler never cease to surprise me.

[rsmith]

clang/lib/AST/Decl.cpp

897–898

I've not made this change for now. The patch as-is matches our former behavior, and it's far from obvious to me whether

template<const GUID&> void f() {}
f<__uuidof(x)>();

... should create a template instantiation with hidden visibility. For what it's worth, the variables we create for these GUID objects are dso_local and linkonce_odr but not hidden, which seems a little fishy to me. (We expose the symbol to other DSOs but never consume the symbol from other DSOs.) We could probably argue that that's "morally hidden"?

This is certainly easy to change if we think using default visibility is wrong.

clang/include/clang/AST/ASTContext.h

 class Expr;
 class FixedPointSemantics;
 class GlobalDecl;
 class MangleContext;
 class MangleNumberingContext;
 class MaterializeTemporaryExpr;
 class MemberSpecializationInfo;
 class Module;
+struct MSGuidDeclParts;
 class ObjCCategoryDecl;
 class ObjCCategoryImplDecl;
 class ObjCContainerDecl;
 class ObjCImplDecl;
 class ObjCImplementationDecl;
 class ObjCInterfaceDecl;
 class ObjCIvarDecl;
 class ObjCMethodDecl;
class ASTContext : public RefCountedBase<ASTContext> {
 
   /// Mapping from ObjCMethod to its duplicate declaration in the same
   /// interface.
   llvm::DenseMap<const ObjCMethodDecl*,const ObjCMethodDecl*> ObjCMethodRedecls;
 
   /// Mapping from __block VarDecls to BlockVarCopyInit.
   llvm::DenseMap<const VarDecl *, BlockVarCopyInit> BlockVarCopyInits;
 
+  /// Mapping from GUIDs to the corresponding MSGuidDecl.
+  mutable llvm::FoldingSet<MSGuidDecl> MSGuidDecls;
+
   /// Used to cleanups APValues stored in the AST.
   mutable llvm::SmallVector<APValue *, 0> APValueCleanups;
 
   /// A cache mapping a string value to a StringLiteral object with the same
   /// value.
   ///
   /// This is lazily created.  This is intentionally not serialized.
   mutable llvm::StringMap<StringLiteral *> StringLiteralCache;

 #include "clang/Basic/AArch64SVEACLETypes.def"
 
   // Types for deductions in C++0x [stmt.ranged]'s desugaring. Built on demand.
   mutable QualType AutoDeductTy;     // Deduction against 'auto'.
   mutable QualType AutoRRefDeductTy; // Deduction against 'auto &&'.
 
   // Decl used to help define __builtin_va_list for some targets.
   // The decl is built when constructing 'BuiltinVaListDecl'.
-  mutable Decl *VaListTagDecl;
+  mutable Decl *VaListTagDecl = nullptr;
+
+  // Implicitly-declared type 'struct _GUID'.
+  mutable TagDecl *MSGuidTagDecl = nullptr;
 
   ASTContext(LangOptions &LOpts, SourceManager &SM, IdentifierTable &idents,
              SelectorTable &sels, Builtin::Context &builtins);
   ASTContext(const ASTContext &) = delete;
   ASTContext &operator=(const ASTContext &) = delete;
   ~ASTContext();
 
   /// Attach an external AST source to the AST context.
public:
   /// \c __builtin_ms_va_list type.
   TypedefDecl *getBuiltinMSVaListDecl() const;
 
   /// Retrieve the type of the \c __builtin_ms_va_list type.
   QualType getBuiltinMSVaListType() const {
     return getTypeDeclType(getBuiltinMSVaListDecl());
   }
 
+  /// Retrieve the implicitly-predeclared 'struct _GUID' declaration.
+  TagDecl *getMSGuidTagDecl() const { return MSGuidTagDecl; }
+
+  /// Retrieve the implicitly-predeclared 'struct _GUID' type.
+  QualType getMSGuidType() const {
+    assert(MSGuidTagDecl && "asked for GUID type but MS extensions disabled");
+    return getTagDeclType(MSGuidTagDecl);
+  }
+
   /// Return whether a declaration to a builtin is allowed to be
   /// overloaded/redeclared.
   bool canBuiltinBeRedeclared(const FunctionDecl *) const;
 
   /// Return a type with additional \c const, \c volatile, or
   /// \c restrict qualifiers.
   QualType getCVRQualifiedType(QualType T, unsigned CVR) const {
     return getQualifiedType(T, Qualifiers::fromCVRMask(CVR));
public:
   /// index of the parameter when it exceeds the size of the normal bitfield.
   unsigned getParameterIndex(const ParmVarDecl *D) const;
 
   /// Return a string representing the human readable name for the specified
   /// function declaration or file name. Used by SourceLocExpr and
   /// PredefinedExpr to cache evaluated results.
   StringLiteral *getPredefinedStringLiteralFromCache(StringRef Key) const;
 
+  /// Return a declaration for the global GUID object representing the given
+  /// GUID value.
+  MSGuidDecl *getMSGuidDecl(MSGuidDeclParts Parts) const;
+
   /// Parses the target attributes passed in, and returns only the ones that are
   /// valid feature names.
   ParsedTargetAttr filterFunctionTargetAttrs(const TargetAttr *TD) const;
 
   void getFunctionFeatureMap(llvm::StringMap<bool> &FeatureMap,
                              const FunctionDecl *) const;
   void getFunctionFeatureMap(llvm::StringMap<bool> &FeatureMap,
                              GlobalDecl GD) const;

clang/include/clang/AST/DeclCXX.h

public:
   static bool classof(const Decl *D) { return D->getKind() == MSProperty; }
 
   bool hasGetter() const { return GetterId != nullptr; }
   IdentifierInfo* getGetterId() const { return GetterId; }
   bool hasSetter() const { return SetterId != nullptr; }
   IdentifierInfo* getSetterId() const { return SetterId; }
 };
 
+/// Parts of a decomposed MSGuidDecl. Factored out to avoid unnecessary
+/// dependencies on DeclCXX.h.
+struct MSGuidDeclParts {
+  /// {01234567-...
+  uint32_t Part1;
+  /// ...-89ab-...
+  uint16_t Part2;
+  /// ...-cdef-...
+  uint16_t Part3;
+  /// ...-0123-456789abcdef}
+  uint8_t Part4And5[8];
+
+  uint64_t getPart4And5AsUint64() const {
+    uint64_t Val;
+    memcpy(&Val, &Part4And5, sizeof(Part4And5));
+    return Val;
+  }
+};
+
+/// A global _GUID constant. These are implicitly created by UuidAttrs.
+///
+///   struct _declspec(uuid("01234567-89ab-cdef-0123-456789abcdef")) X{};
+///
+/// X is a CXXRecordDecl that contains a UuidAttr that references the (unique)
+/// MSGuidDecl for the specified UUID.
+class MSGuidDecl : public ValueDecl,
+                   public Mergeable<MSGuidDecl>,
+                   public llvm::FoldingSetNode {
+public:
+  using Parts = MSGuidDeclParts;
+
+private:
+  /// The decomposed form of the UUID.
+  Parts PartVal;
+
+  /// The resolved value of the UUID as an APValue. Computed on demand and
+  /// cached.
+  mutable APValue APVal;
+
+  void anchor() override;
+
+  MSGuidDecl(DeclContext *DC, QualType T, Parts P);
+
+  static MSGuidDecl *Create(const ASTContext &C, QualType T, Parts P);
+  static MSGuidDecl *CreateDeserialized(ASTContext &C, unsigned ID);
+
+  // Only ASTContext::getMSGuidDecl and deserialization create these.
+  friend class ASTContext;
+  friend class ASTReader;
+  friend class ASTDeclReader;
+
+public:
+  /// Print this UUID in a human-readable format.
+  void printName(llvm::raw_ostream &OS) const override;
+
+  /// Get the decomposed parts of this declaration.
+  Parts getParts() const { return PartVal; }
+
+  /// Get the value of this MSGuidDecl as an APValue. This may fail and return
+  /// an absent APValue if the type of the declaration is not of the expected
+  /// shape.
+  APValue &getAsAPValue() const;
+
+  static void Profile(llvm::FoldingSetNodeID &ID, Parts P) {
+    ID.AddInteger(P.Part1);
+    ID.AddInteger(P.Part2);
+    ID.AddInteger(P.Part3);
+    ID.AddInteger(P.getPart4And5AsUint64());
+  }
+  void Profile(llvm::FoldingSetNodeID &ID) { Profile(ID, PartVal); }
+
+  static bool classof(const Decl *D) { return classofKind(D->getKind()); }
+  static bool classofKind(Kind K) { return K == Decl::MSGuid; }
+};
+
 /// Insertion operator for diagnostics.  This allows sending an AccessSpecifier
 /// into a diagnostic with <<.
 const DiagnosticBuilder &operator<<(const DiagnosticBuilder &DB,
                                     AccessSpecifier AS);
 
 const PartialDiagnostic &operator<<(const PartialDiagnostic &DB,
                                     AccessSpecifier AS);
 
 } // namespace clang
 
 #endif // LLVM_CLANG_AST_DECLCXX_H

clang/include/clang/AST/ExprCXX.h

 /// the _GUID that corresponds to the supplied type or expression.
 ///
 /// This represents code like @c __uuidof(COMTYPE) or @c __uuidof(*comPtr)
 class CXXUuidofExpr : public Expr {
   friend class ASTStmtReader;
 
 private:
   llvm::PointerUnion<Stmt *, TypeSourceInfo *> Operand;
-  StringRef UuidStr;
+  MSGuidDecl *Guid;
   SourceRange Range;
 
 public:
-  CXXUuidofExpr(QualType Ty, TypeSourceInfo *Operand, StringRef UuidStr,
+  CXXUuidofExpr(QualType Ty, TypeSourceInfo *Operand, MSGuidDecl *Guid,
                 SourceRange R)
       : Expr(CXXUuidofExprClass, Ty, VK_LValue, OK_Ordinary), Operand(Operand),
-        UuidStr(UuidStr), Range(R) {
+        Guid(Guid), Range(R) {
     setDependence(computeDependence(this));
   }
 
-  CXXUuidofExpr(QualType Ty, Expr *Operand, StringRef UuidStr, SourceRange R)
+  CXXUuidofExpr(QualType Ty, Expr *Operand, MSGuidDecl *Guid, SourceRange R)
       : Expr(CXXUuidofExprClass, Ty, VK_LValue, OK_Ordinary), Operand(Operand),
-        UuidStr(UuidStr), Range(R) {
+        Guid(Guid), Range(R) {
     setDependence(computeDependence(this));
   }
 
   CXXUuidofExpr(EmptyShell Empty, bool isExpr)
     : Expr(CXXUuidofExprClass, Empty) {
     if (isExpr)
       Operand = (Expr*)nullptr;
     else
TypeSourceInfo *getTypeOperandSourceInfo() const {
     assert(isTypeOperand() && "Cannot call getTypeOperand for __uuidof(expr)");
     return Operand.get<TypeSourceInfo *>();
   }
   Expr *getExprOperand() const {
     assert(!isTypeOperand() && "Cannot call getExprOperand for __uuidof(type)");
     return static_cast<Expr*>(Operand.get<Stmt *>());
   }
 
-  void setUuidStr(StringRef US) { UuidStr = US; }
-  StringRef getUuidStr() const { return UuidStr; }
+  MSGuidDecl *getGuidDecl() const { return Guid; }
 
   SourceLocation getBeginLoc() const LLVM_READONLY { return Range.getBegin(); }
   SourceLocation getEndLoc() const LLVM_READONLY { return Range.getEnd(); }
   SourceRange getSourceRange() const LLVM_READONLY { return Range; }
   void setSourceRange(SourceRange R) { Range = R; }
 
   static bool classof(const Stmt *T) {
     return T->getStmtClass() == CXXUuidofExprClass;

clang/include/clang/AST/Mangle.h

virtual void mangleCXXDtorThunk(const CXXDestructorDecl *DD, CXXDtorType Type,
                                   const ThisAdjustment &ThisAdjustment,
                                   raw_ostream &) = 0;
   virtual void mangleReferenceTemporary(const VarDecl *D,
                                         unsigned ManglingNumber,
                                         raw_ostream &) = 0;
   virtual void mangleCXXRTTI(QualType T, raw_ostream &) = 0;
   virtual void mangleCXXRTTIName(QualType T, raw_ostream &) = 0;
   virtual void mangleStringLiteral(const StringLiteral *SL, raw_ostream &) = 0;
+  virtual void mangleMSGuidDecl(const MSGuidDecl *GD, raw_ostream&);
 
   void mangleGlobalBlock(const BlockDecl *BD,
                          const NamedDecl *ID,
                          raw_ostream &Out);
   void mangleCtorBlock(const CXXConstructorDecl *CD, CXXCtorType CT,
                        const BlockDecl *BD, raw_ostream &Out);
   void mangleDtorBlock(const CXXDestructorDecl *CD, CXXDtorType DT,
                        const BlockDecl *BD, raw_ostream &Out);

clang/include/clang/AST/RecursiveASTVisitor.h

 
 DEF_TRAVERSE_DECL(BindingDecl, {
   if (getDerived().shouldVisitImplicitCode())
     TRY_TO(TraverseStmt(D->getBinding()));
 })
 
 DEF_TRAVERSE_DECL(MSPropertyDecl, { TRY_TO(TraverseDeclaratorHelper(D)); })
 
+DEF_TRAVERSE_DECL(MSGuidDecl, {});
+
 DEF_TRAVERSE_DECL(FieldDecl, {
   TRY_TO(TraverseDeclaratorHelper(D));
   if (D->isBitField())
     TRY_TO(TraverseStmt(D->getBitWidth()));
   else if (D->hasInClassInitializer())
     TRY_TO(TraverseStmt(D->getInClassInitializer()));
 })
 

clang/include/clang/AST/TemplateBase.h

enum ArgKind {
 
     /// The template argument is a pack expansion of a template name that was
     /// provided for a template template parameter.
     TemplateExpansion,
 
     /// The template argument is an expression, and we've not resolved it to one
     /// of the other forms yet, either because it's dependent or because we're
     /// representing a non-canonical template argument (for instance, in a
-    /// TemplateSpecializationType). Also used to represent a non-dependent
-    /// __uuidof expression (a Microsoft extension).
+    /// TemplateSpecializationType).
     Expression,
 
     /// The template argument is actually a parameter pack. Arguments are stored
     /// in the Args struct.
     Pack
   };
 
 private:

clang/include/clang/Basic/Attr.td

def Used : InheritableAttr {
   let Spellings = [GCC<"used">];
   let Subjects = SubjectList<[NonLocalVar, Function, ObjCMethod]>;
   let Documentation = [Undocumented];
   let SimpleHandler = 1;
 }
 
 def Uuid : InheritableAttr {
   let Spellings = [Declspec<"uuid">, Microsoft<"uuid">];
-  let Args = [StringArgument<"Guid">];
+  let Args = [StringArgument<"Guid">,
+              DeclArgument<MSGuid, "GuidDecl", 0, /*fake=*/1>];
   let Subjects = SubjectList<[Record, Enum]>;
   // FIXME: Allow expressing logical AND for LangOpts. Our condition should be:
   // CPlusPlus && (MicrosoftExt || Borland)
   let LangOpts = [MicrosoftExt, Borland];
   let Documentation = [Undocumented];
 }
 
 def VectorSize : TypeAttr {

clang/include/clang/Basic/DeclNodes.td

def Type : DeclNode<Named, "types", 1>;
     def TemplateTypeParm : DeclNode<Type>;
   def Value : DeclNode<Named, "value declarations", 1>;
     def EnumConstant : DeclNode<Value, "enumerators">;
     def UnresolvedUsingValue : DeclNode<Value>;
     def IndirectField : DeclNode<Value>;
     def Binding : DeclNode<Value>;
     def OMPDeclareReduction : DeclNode<Value>, DeclContext;
     def OMPDeclareMapper : DeclNode<Value>, DeclContext;
+    def MSGuid : DeclNode<Value>;
     def Declarator : DeclNode<Value, "declarators", 1>;
       def Field : DeclNode<Declarator, "non-static data members">;
         def ObjCIvar : DeclNode<Field>;
         def ObjCAtDefsField : DeclNode<Field>;
       def MSProperty : DeclNode<Declarator>;
       def Function : DeclNode<Declarator, "functions">, DeclContext;
         def CXXDeductionGuide : DeclNode<Function>;
         def CXXMethod : DeclNode<Function>;

clang/include/clang/Basic/DiagnosticASTKinds.td

def note_constexpr_delete_subobject : Note<
   "delete of pointer%select{ to subobject|}1 '%0' "
   "%select{|that does not point to complete object}1">;
 def note_constexpr_delete_base_nonvirt_dtor : Note<
   "delete of object with dynamic type %1 through pointer to "
   "base class type %0 with non-virtual destructor">;
 def note_constexpr_memory_leak : Note<
   "allocation performed here was not deallocated"
   "%plural{0:|: (along with %0 other memory leak%s0)}0">;
+def note_constexpr_unsupported_layout : Note<
+  "type %0 has unexpected layout">;
 def err_experimental_clang_interp_failed : Error<
   "the experimental clang interpreter failed to evaluate an expression">;
 
 def warn_integer_constant_overflow : Warning<
   "overflow in expression; result is %0 with type %1">,
   InGroup<DiagGroup<"integer-overflow">>;
 
 // This is a temporary diagnostic, and shall be removed once our

clang/include/clang/Sema/Sema.h

mergeAvailabilityAttr(NamedDecl *D, const AttributeCommonInfo &CI,
                         StringRef Message, bool IsStrict, StringRef Replacement,
                         AvailabilityMergeKind AMK, int Priority);
   TypeVisibilityAttr *
   mergeTypeVisibilityAttr(Decl *D, const AttributeCommonInfo &CI,
                           TypeVisibilityAttr::VisibilityType Vis);
   VisibilityAttr *mergeVisibilityAttr(Decl *D, const AttributeCommonInfo &CI,
                                       VisibilityAttr::VisibilityType Vis);
   UuidAttr *mergeUuidAttr(Decl *D, const AttributeCommonInfo &CI,
-                          StringRef Uuid);
+                          StringRef UuidAsWritten, MSGuidDecl *GuidDecl);
   DLLImportAttr *mergeDLLImportAttr(Decl *D, const AttributeCommonInfo &CI);
   DLLExportAttr *mergeDLLExportAttr(Decl *D, const AttributeCommonInfo &CI);
   MSInheritanceAttr *mergeMSInheritanceAttr(Decl *D,
                                             const AttributeCommonInfo &CI,
                                             bool BestCase,
                                             MSInheritanceModel Model);
   FormatAttr *mergeFormatAttr(Decl *D, const AttributeCommonInfo &CI,
                               IdentifierInfo *Format, int FormatIdx,

clang/include/clang/Serialization/ASTBitCodes.h

enum PredefinedDeclIDs {
       PREDEF_DECL_BUILTIN_VA_LIST_ID = 9,
 
       /// The internal '__va_list_tag' struct, if any.
       PREDEF_DECL_VA_LIST_TAG = 10,
 
       /// The internal '__builtin_ms_va_list' typedef.
       PREDEF_DECL_BUILTIN_MS_VA_LIST_ID = 11,
 
+      /// The predeclared '_GUID' struct.
+      PREDEF_DECL_BUILTIN_MS_GUID_ID = 12,
+
       /// The extern "C" context.
-      PREDEF_DECL_EXTERN_C_CONTEXT_ID = 12,
+      PREDEF_DECL_EXTERN_C_CONTEXT_ID = 13,
 
       /// The internal '__make_integer_seq' template.
-      PREDEF_DECL_MAKE_INTEGER_SEQ_ID = 13,
+      PREDEF_DECL_MAKE_INTEGER_SEQ_ID = 14,
 
       /// The internal '__NSConstantString' typedef.
-      PREDEF_DECL_CF_CONSTANT_STRING_ID = 14,
+      PREDEF_DECL_CF_CONSTANT_STRING_ID = 15,
 
       /// The internal '__NSConstantString' tag type.
-      PREDEF_DECL_CF_CONSTANT_STRING_TAG_ID = 15,
+      PREDEF_DECL_CF_CONSTANT_STRING_TAG_ID = 16,
 
       /// The internal '__type_pack_element' template.
-      PREDEF_DECL_TYPE_PACK_ELEMENT_ID = 16,
+      PREDEF_DECL_TYPE_PACK_ELEMENT_ID = 17,
     };
 
     /// The number of declaration IDs that are predefined.
     ///
     /// For more information about predefined declarations, see the
     /// \c PredefinedDeclIDs type and the PREDEF_DECL_*_ID constants.
-    const unsigned int NUM_PREDEF_DECL_IDS = 17;
+    const unsigned int NUM_PREDEF_DECL_IDS = 18;
 
     /// Record of updates for a declaration that was modified after
     /// being deserialized. This can occur within DECLTYPES_BLOCK_ID.
     const unsigned int DECL_UPDATES = 49;
 
     /// Record code for a list of local redeclarations of a declaration.
     /// This can occur within DECLTYPES_BLOCK_ID.
     const unsigned int LOCAL_REDECLARATIONS = 50;
enum DeclCode {
       DECL_OBJC_PROPERTY_IMPL,
 
       /// A FieldDecl record.
       DECL_FIELD,
 
       /// A MSPropertyDecl record.
       DECL_MS_PROPERTY,
 
+      /// A MSGuidDecl record.
+      DECL_MS_GUID,
+
       /// A VarDecl record.
       DECL_VAR,
 
       /// An ImplicitParamDecl record.
       DECL_IMPLICIT_PARAM,
 
       /// A ParmVarDecl record.
       DECL_PARM_VAR,

clang/lib/AST/ASTContext.cpp

#include "clang/Basic/AArch64SVEACLETypes.def"
   // nullptr type (C++0x 2.14.7)
   InitBuiltinType(NullPtrTy,           BuiltinType::NullPtr);
 
   // half type (OpenCL 6.1.1.1) / ARM NEON __fp16
   InitBuiltinType(HalfTy, BuiltinType::Half);
 
   // Builtin type used to help define __builtin_va_list.
   VaListTagDecl = nullptr;
+
+  // MSVC predeclares struct _GUID, and we need it to create MSGuidDecls.
+  if (LangOpts.MicrosoftExt || LangOpts.Borland) {
+    MSGuidTagDecl = buildImplicitRecord("_GUID");
+    TUDecl->addDecl(MSGuidTagDecl);
+  }
 }
 
 DiagnosticsEngine &ASTContext::getDiagnostics() const {
   return SourceMgr.getDiagnostics();
 }
 
 AttrVec& ASTContext::getDeclAttrs(const Decl *D) {
   AttrVec *&Result = DeclAttrs[D];
ASTContext::getPredefinedStringLiteralFromCache(StringRef Key) const {
   if (!Result)
     Result = StringLiteral::Create(
         *this, Key, StringLiteral::Ascii,
         /*Pascal*/ false, getStringLiteralArrayType(CharTy, Key.size()),
         SourceLocation());
   return Result;
 }
 
+MSGuidDecl *
+ASTContext::getMSGuidDecl(MSGuidDecl::Parts Parts) const {
+  assert(MSGuidTagDecl && "building MS GUID without MS extensions?");
+
+  llvm::FoldingSetNodeID ID;
+  MSGuidDecl::Profile(ID, Parts);
+
+  void *InsertPos;
+  if (MSGuidDecl *Existing = MSGuidDecls.FindNodeOrInsertPos(ID, InsertPos))
+    return Existing;
+
+  QualType GUIDType = getMSGuidType().withConst();
+  MSGuidDecl *New = MSGuidDecl::Create(*this, GUIDType, Parts);
+  MSGuidDecls.InsertNode(New, InsertPos);
+  return New;
+}
+
 bool ASTContext::AtomicUsesUnsupportedLibcall(const AtomicExpr *E) const {
   const llvm::Triple &T = getTargetInfo().getTriple();
   if (!T.isOSDarwin())
     return false;
 
   if (!(T.isiOS() && T.isOSVersionLT(7)) &&
       !(T.isMacOSX() && T.isOSVersionLT(10, 9)))
     return false;

clang/lib/AST/Decl.cpp

// interfaces.
     // fallout
 
   } else if (auto *TD = dyn_cast<TypedefNameDecl>(D)) {
     // A typedef declaration has linkage if it gives a type a name for
     // linkage purposes.
     if (!TD->getAnonDeclWithTypedefName(/*AnyRedecl*/true))
       return LinkageInfo::none();
 
+  } else if (isa<MSGuidDecl>(D)) {
+    // A GUID behaves like an inline variable with external linkage. Fall
+    // through.
+
   // Everything not covered here has no linkage.
   } else {
     return LinkageInfo::none();
   }
 
   // If we ended up with non-externally-visible linkage, visibility should
   // always be default.
   if (!isExternallyVisible(LV.getLinkage()))

clang/lib/AST/DeclBase.cpp

switch (DeclKind) {
     case ObjCPropertyImpl:
     case PragmaComment:
     case PragmaDetectMismatch:
     case Block:
     case Captured:
     case TranslationUnit:
     case ExternCContext:
     case Decomposition:
+    case MSGuid:
 
     case UsingDirective:
     case BuiltinTemplate:
     case ClassTemplateSpecialization:
     case ClassTemplatePartialSpecialization:
     case ClassScopeFunctionSpecialization:
     case VarTemplateSpecialization:
     case VarTemplatePartialSpecialization:

clang/lib/AST/DeclCXX.cpp

 #include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/Specifiers.h"
 #include "llvm/ADT/None.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/Format.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 #include <cassert>
 #include <cstddef>
 #include <cstdint>
 
 using namespace clang;
 

 
 MSPropertyDecl *MSPropertyDecl::CreateDeserialized(ASTContext &C,
                                                    unsigned ID) {
   return new (C, ID) MSPropertyDecl(nullptr, SourceLocation(),
                                     DeclarationName(), QualType(), nullptr,
                                     SourceLocation(), nullptr, nullptr);
 }
 
+void MSGuidDecl::anchor() {}
+
+MSGuidDecl::MSGuidDecl(DeclContext *DC, QualType T, Parts P)
+    : ValueDecl(Decl::MSGuid, DC, SourceLocation(), DeclarationName(), T),
+      PartVal(P), APVal() {}
+
+MSGuidDecl *MSGuidDecl::Create(const ASTContext &C, QualType T, Parts P) {
+  DeclContext *DC = C.getTranslationUnitDecl();
+  return new (C, DC) MSGuidDecl(DC, T, P);
+}
+
+MSGuidDecl *MSGuidDecl::CreateDeserialized(ASTContext &C, unsigned ID) {
+  return new (C, ID) MSGuidDecl(nullptr, QualType(), Parts());
+}
+
+void MSGuidDecl::printName(llvm::raw_ostream &OS) const {
+  OS << llvm::format("GUID{%08" PRIx32 "-%04" PRIx16 "-%04" PRIx16 "-",
+                     PartVal.Part1, PartVal.Part2, PartVal.Part3);
+  unsigned I = 0;
+  for (uint8_t Byte : PartVal.Part4And5) {
+    OS << llvm::format("%02" PRIx8, Byte);
+    if (++I == 2)
+      OS << '-';
+  }
+  OS << '}';
+}
+
+/// Determine if T is a valid 'struct _GUID' of the shape that we expect.
+static bool isValidStructGUID(ASTContext &Ctx, QualType T) {
+  // FIXME: We only need to check this once, not once each time we compute a
+  // GUID APValue.
+  using MatcherRef = llvm::function_ref<bool(QualType)>;
+
+  auto IsInt = [&Ctx](unsigned N) {
+    return [&Ctx, N](QualType T) {
+      return T->isUnsignedIntegerOrEnumerationType() &&
+             Ctx.getIntWidth(T) == N;
+    };
+  };
+
+  auto IsArray = [&Ctx](MatcherRef Elem, unsigned N) {
+    return [&Ctx, Elem, N](QualType T) {
+      const ConstantArrayType *CAT = Ctx.getAsConstantArrayType(T);
+      return CAT && CAT->getSize() == N && Elem(CAT->getElementType());
+    };
+  };
+
+  auto IsStruct = [](std::initializer_list<MatcherRef> Fields) {
+    return [Fields](QualType T) {
+      const RecordDecl *RD = T->getAsRecordDecl();
+      if (!RD || RD->isUnion())
+        return false;
+      RD = RD->getDefinition();
+      if (!RD)
+        return false;
+      if (auto *CXXRD = dyn_cast<CXXRecordDecl>(RD))
+        if (CXXRD->getNumBases())
+          return false;
+      auto MatcherIt = Fields.begin();
+      for (const FieldDecl *FD : RD->fields()) {
+        if (FD->isUnnamedBitfield()) continue;
+        if (FD->isBitField() || MatcherIt == Fields.end() ||
+            !(*MatcherIt)(FD->getType()))
+          return false;
+        ++MatcherIt;
+      }
+      return MatcherIt == Fields.end();
+    };
+  };
+
+  // We expect an {i32, i16, i16, [8 x i8]}.
+  return IsStruct({IsInt(32), IsInt(16), IsInt(16), IsArray(IsInt(8), 8)})(T);
+}
+
+APValue &MSGuidDecl::getAsAPValue() const {
+  if (APVal.isAbsent() && isValidStructGUID(getASTContext(), getType())) {
+    using llvm::APInt;
+    using llvm::APSInt;
+    APVal = APValue(APValue::UninitStruct(), 0, 4);
+    APVal.getStructField(0) = APValue(APSInt(APInt(32, PartVal.Part1), true));
+    APVal.getStructField(1) = APValue(APSInt(APInt(16, PartVal.Part2), true));
+    APVal.getStructField(2) = APValue(APSInt(APInt(16, PartVal.Part3), true));
+    APValue &Arr = APVal.getStructField(3) =
+        APValue(APValue::UninitArray(), 8, 8);
+    for (unsigned I = 0; I != 8; ++I) {
+      Arr.getArrayInitializedElt(I) =
+          APValue(APSInt(APInt(8, PartVal.Part4And5[I]), true));
+    }
+  }
+
+  return APVal;
+}
+
 static const char *getAccessName(AccessSpecifier AS) {
   switch (AS) {
     case AS_none:
       llvm_unreachable("Invalid access specifier!");
     case AS_public:
       return "public";
     case AS_private:
       return "private";

clang/lib/AST/ExprClassification.cpp

#include "clang/AST/StmtNodes.inc"
   case Expr::ObjCEncodeExprClass:
     // __func__ and friends are too.
   case Expr::PredefinedExprClass:
     // Property references are lvalues
   case Expr::ObjCSubscriptRefExprClass:
   case Expr::ObjCPropertyRefExprClass:
     // C++ [expr.typeid]p1: The result of a typeid expression is an lvalue of...
   case Expr::CXXTypeidExprClass:
+  case Expr::CXXUuidofExprClass:
     // Unresolved lookups and uncorrected typos get classified as lvalues.
     // FIXME: Is this wise? Should they get their own kind?
   case Expr::UnresolvedLookupExprClass:
   case Expr::UnresolvedMemberExprClass:
   case Expr::TypoExprClass:
   case Expr::RecoveryExprClass:
   case Expr::DependentCoawaitExprClass:
   case Expr::CXXDependentScopeMemberExprClass:
#include "clang/AST/StmtNodes.inc"
 
   case Expr::StmtExprClass: {
     const CompoundStmt *S = cast<StmtExpr>(E)->getSubStmt();
     if (const auto *LastExpr = dyn_cast_or_null<Expr>(S->body_back()))
       return ClassifyUnnamed(Ctx, LastExpr->getType());
     return Cl::CL_PRValue;
   }
 
-  case Expr::CXXUuidofExprClass:
-    return Cl::CL_LValue;
-
   case Expr::PackExpansionExprClass:
     return ClassifyInternal(Ctx, cast<PackExpansionExpr>(E)->getPattern());
 
   case Expr::MaterializeTemporaryExprClass:
     return cast<MaterializeTemporaryExpr>(E)->isBoundToLvalueReference()
               ? Cl::CL_LValue
               : Cl::CL_XValue;
 
static Cl::Kinds ClassifyDecl(ASTContext &Ctx, const Decl *D) {
 
   bool islvalue;
   if (const auto *NTTParm = dyn_cast<NonTypeTemplateParmDecl>(D))
     islvalue = NTTParm->getType()->isReferenceType();
   else
     islvalue = isa<VarDecl>(D) || isa<FieldDecl>(D) ||
                isa<IndirectFieldDecl>(D) ||
                isa<BindingDecl>(D) ||
+               isa<MSGuidDecl>(D) ||
                (Ctx.getLangOpts().CPlusPlus &&
                 (isa<FunctionDecl>(D) || isa<MSPropertyDecl>(D) ||
                  isa<FunctionTemplateDecl>(D)));
 
   return islvalue ? Cl::CL_LValue : Cl::CL_PRValue;
 }
 
 /// ClassifyUnnamed - Return the classification of an expression yielding an

clang/lib/AST/ExprConstant.cpp

static bool IsGlobalLValue(APValue::LValueBase B) {
   // std::nullptr_t.
   if (!B) return true;
 
   if (const ValueDecl *D = B.dyn_cast<const ValueDecl*>()) {
     // ... the address of an object with static storage duration,
     if (const VarDecl *VD = dyn_cast<VarDecl>(D))
       return VD->hasGlobalStorage();
     // ... the address of a function,
-    return isa<FunctionDecl>(D);
+    // ... the address of a GUID [MS extension],
+    return isa<FunctionDecl>(D) || isa<MSGuidDecl>(D);
   }
 
   if (B.is<TypeInfoLValue>() || B.is<DynamicAllocLValue>())
     return true;
 
   const Expr *E = B.get<const Expr*>();
   switch (E->getStmtClass()) {
   default:
     return false;
   case Expr::CompoundLiteralExprClass: {
     const CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
     return CLE->isFileScope() && CLE->isLValue();
   }
   case Expr::MaterializeTemporaryExprClass:
     // A materialized temporary might have been lifetime-extended to static
     // storage duration.
     return cast<MaterializeTemporaryExpr>(E)->getStorageDuration() == SD_Static;
   // A string literal has static storage duration.
   case Expr::StringLiteralClass:
   case Expr::PredefinedExprClass:
   case Expr::ObjCStringLiteralClass:
   case Expr::ObjCEncodeExprClass:
-  case Expr::CXXUuidofExprClass:
     return true;
   case Expr::ObjCBoxedExprClass:
     return cast<ObjCBoxedExpr>(E)->isExpressibleAsConstantInitializer();
   case Expr::CallExprClass:
     return IsStringLiteralCall(cast<CallExpr>(E));
   // For GCC compatibility, &&label has static storage duration.
   case Expr::AddrLabelExprClass:
     return true;
static CompleteObject findCompleteObject(EvalInfo &Info, const Expr *E,
   if (const ConstantExpr *CE =
           dyn_cast_or_null<ConstantExpr>(LVal.Base.dyn_cast<const Expr *>())) {
     /// Nested immediate invocation have been previously removed so if we found
     /// a ConstantExpr it can only be the EvaluatingDecl.
     assert(CE->isImmediateInvocation() && CE == Info.EvaluatingDecl);
     (void)CE;
     BaseVal = Info.EvaluatingDeclValue;
   } else if (const ValueDecl *D = LVal.Base.dyn_cast<const ValueDecl *>()) {
+    // Allow reading from a GUID declaration.
+    if (auto *GD = dyn_cast<MSGuidDecl>(D)) {
+      if (isModification(AK)) {
+        // All the remaining cases do not permit modification of the object.
+        Info.FFDiag(E, diag::note_constexpr_modify_global);
+        return CompleteObject();
+      }
+      APValue &V = GD->getAsAPValue();
+      if (V.isAbsent()) {
+        Info.FFDiag(E, diag::note_constexpr_unsupported_layout)
+            << GD->getType();
+        return CompleteObject();
+      }
+      return CompleteObject(LVal.Base, &V, GD->getType());
+    }
+
     // In C++98, const, non-volatile integers initialized with ICEs are ICEs.
     // In C++11, constexpr, non-volatile variables initialized with constant
     // expressions are constant expressions too. Inside constexpr functions,
     // parameters are constant expressions even if they're non-const.
     // In C++1y, objects local to a constant expression (those with a Frame) are
     // both readable and writable inside constant expressions.
     // In C, such things can also be folded, although they are not ICEs.
     const VarDecl *VD = dyn_cast<VarDecl>(D);

 
 bool LValueExprEvaluator::VisitDeclRefExpr(const DeclRefExpr *E) {
   if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(E->getDecl()))
     return Success(FD);
   if (const VarDecl *VD = dyn_cast<VarDecl>(E->getDecl()))
     return VisitVarDecl(E, VD);
   if (const BindingDecl *BD = dyn_cast<BindingDecl>(E->getDecl()))
     return Visit(BD->getBinding());
+  if (const MSGuidDecl *GD = dyn_cast<MSGuidDecl>(E->getDecl()))
+    return Success(GD);
   return Error(E);
 }
 
 
 bool LValueExprEvaluator::VisitVarDecl(const Expr *E, const VarDecl *VD) {
 
   // If we are within a lambda's call operator, check whether the 'VD' referred
   // to within 'E' actually represents a lambda-capture that maps to a
if (!E->isPotentiallyEvaluated()) {
     TypeInfo =
         TypeInfoLValue(Info.Ctx.getRecordType(DynType->Type).getTypePtr());
   }
 
   return Success(APValue::LValueBase::getTypeInfo(TypeInfo, E->getType()));
 }
 
 bool LValueExprEvaluator::VisitCXXUuidofExpr(const CXXUuidofExpr *E) {
-  return Success(E);
+  return Success(E->getGuidDecl());
 }
 
 bool LValueExprEvaluator::VisitMemberExpr(const MemberExpr *E) {
   // Handle static data members.
   if (const VarDecl *VD = dyn_cast<VarDecl>(E->getMemberDecl())) {
     VisitIgnoredBaseExpression(E->getBase());
     return VisitVarDecl(E, VD);
   }

clang/lib/AST/ItaniumMangle.cpp

void CXXNameMangler::mangle(GlobalDecl GD) {
   Out << "_Z";
   if (isa<FunctionDecl>(GD.getDecl()))
     mangleFunctionEncoding(GD);
   else if (const VarDecl *VD = dyn_cast<VarDecl>(GD.getDecl()))
     mangleName(VD);
   else if (const IndirectFieldDecl *IFD =
                dyn_cast<IndirectFieldDecl>(GD.getDecl()))
     mangleName(IFD->getAnonField());
+  else if (const FieldDecl *FD = dyn_cast<FieldDecl>(GD.getDecl()))
+    mangleName(FD);
+  else if (const MSGuidDecl *GuidD = dyn_cast<MSGuidDecl>(GD.getDecl()))
+    mangleName(GuidD);
   else
-    mangleName(cast<FieldDecl>(GD.getDecl()));
+    llvm_unreachable("unexpected kind of global decl");
 }
 
 void CXXNameMangler::mangleFunctionEncoding(GlobalDecl GD) {
   const FunctionDecl *FD = cast<FunctionDecl>(GD.getDecl());
   // <encoding> ::= <function name> <bare-function-type>
 
   // Don't mangle in the type if this isn't a decl we should typically mangle.
   if (!Context.shouldMangleDeclName(FD)) {
if (auto *DD = dyn_cast<DecompositionDecl>(ND)) {
       Out << "DC";
       for (auto *BD : DD->bindings())
         mangleSourceName(BD->getDeclName().getAsIdentifierInfo());
       Out << 'E';
       writeAbiTags(ND, AdditionalAbiTags);
       break;
     }
 
+    if (auto *GD = dyn_cast<MSGuidDecl>(ND)) {
+      // We follow MSVC in mangling GUID declarations as if they were variables
+      // with a particular reserved name. Continue the pretense here.
+      SmallString<sizeof("_GUID_12345678_1234_1234_1234_1234567890ab")> GUID;
+      llvm::raw_svector_ostream GUIDOS(GUID);
+      Context.mangleMSGuidDecl(GD, GUIDOS);
+      Out << GUID.size() << GUID;
+      break;
+    }
+
     if (II) {
       // Match GCC's naming convention for internal linkage symbols, for
       // symbols that are not actually visible outside of this TU. GCC
       // distinguishes between internal and external linkage symbols in
       // its mangling, to support cases like this that were valid C++ prior
       // to DR426:
       //
       //   void test() { extern void foo(); }

clang/lib/AST/Mangle.cpp

enum CCMangling {
   CCM_Vector,
   CCM_Std,
   CCM_WasmMainArgcArgv
 };
 
 static bool isExternC(const NamedDecl *ND) {
   if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(ND))
     return FD->isExternC();
-  return cast<VarDecl>(ND)->isExternC();
+  if (const VarDecl *VD = dyn_cast<VarDecl>(ND))
+    return VD->isExternC();
+  return false;
 }
 
 static CCMangling getCallingConvMangling(const ASTContext &Context,
                                          const NamedDecl *ND) {
   const TargetInfo &TI = Context.getTargetInfo();
   const llvm::Triple &Triple = TI.getTriple();
 
   // On wasm, the argc/argv form of "main" is renamed so that the startup code
bool MangleContext::shouldMangleDeclName(const NamedDecl *D) {
   if (!getASTContext().getLangOpts().CPlusPlus && !D->hasAttrs())
     return false;
 
   // Any decl can be declared with __asm("foo") on it, and this takes precedence
   // over all other naming in the .o file.
   if (D->hasAttr<AsmLabelAttr>())
     return true;
 
+  // Declarations that don't have identifier names always need to be mangled.
+  if (isa<MSGuidDecl>(D))
+    return true;
+
   return shouldMangleCXXName(D);
 }
 
 void MangleContext::mangleName(GlobalDecl GD, raw_ostream &Out) {
   const NamedDecl *D = cast<NamedDecl>(GD.getDecl());
   // Any decl can be declared with __asm("foo") on it, and this takes precedence
   // over all other naming in the .o file.
   if (const AsmLabelAttr *ALA = D->getAttr<AsmLabelAttr>()) {
char GlobalPrefix =
         getASTContext().getTargetInfo().getDataLayout().getGlobalPrefix();
     if (GlobalPrefix)
       Out << '\01'; // LLVM IR Marker for __asm("foo")
 
     Out << ALA->getLabel();
     return;
   }
 
+  if (auto *GD = dyn_cast<MSGuidDecl>(D))
+    return mangleMSGuidDecl(GD, Out);
+
   const ASTContext &ASTContext = getASTContext();
   CCMangling CC = getCallingConvMangling(ASTContext, D);
 
   if (CC == CCM_WasmMainArgcArgv) {
     Out << "__main_argc_argv";
     return;
   }
 
void MangleContext::mangleName(GlobalDecl GD, raw_ostream &Out) {
   for (const auto &AT : Proto->param_types())
     // Size should be aligned to pointer size.
     ArgWords +=
         llvm::alignTo(ASTContext.getTypeSize(AT), TI.getPointerWidth(0)) /
         TI.getPointerWidth(0);
   Out << ((TI.getPointerWidth(0) / 8) * ArgWords);
 }
 
+void MangleContext::mangleMSGuidDecl(const MSGuidDecl *GD, raw_ostream &Out) {
+  // For now, follow the MSVC naming convention for GUID objects on all
+  // targets.
+  MSGuidDecl::Parts P = GD->getParts();
+  Out << llvm::format("_GUID_%08" PRIx32 "_%04" PRIx32 "_%04" PRIx32 "_",
+                      P.Part1, P.Part2, P.Part3);
+  unsigned I = 0;
+  for (uint8_t C : P.Part4And5) {
+    Out << llvm::format("%02" PRIx8, C);
+    if (++I == 2)
+      Out << "_";
+  }
+}
+
 void MangleContext::mangleGlobalBlock(const BlockDecl *BD,
                                       const NamedDecl *ID,
                                       raw_ostream &Out) {
   unsigned discriminator = getBlockId(BD, false);
   if (ID) {
     if (shouldMangleDeclName(ID))
       mangleName(ID, Out);
     else {

clang/lib/AST/MicrosoftMangle.cpp

if (!getASTContext().getLangOpts().CPlusPlus)
     return false;
 
   const VarDecl *VD = dyn_cast<VarDecl>(D);
   if (VD && !isa<DecompositionDecl>(D)) {
     // C variables are not mangled.
     if (VD->isExternC())
       return false;
 
-    // Variables at global scope with non-internal linkage are not mangled.
+    // Variables at global scope with internal linkage are not mangled.
     const DeclContext *DC = getEffectiveDeclContext(D);
     // Check for extern variable declared locally.
     if (DC->isFunctionOrMethod() && D->hasLinkage())
       while (!DC->isNamespace() && !DC->isTranslationUnit())
         DC = getEffectiveParentContext(DC);
 
     if (DC->isTranslationUnit() && D->getFormalLinkage() == InternalLinkage &&
         !isa<VarTemplateSpecializationDecl>(D) &&
void MicrosoftCXXNameMangler::mangle(const NamedDecl *D, StringRef Prefix) {
 
   // <mangled-name> ::= ? <name> <type-encoding>
   Out << Prefix;
   mangleName(D);
   if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D))
     mangleFunctionEncoding(FD, Context.shouldMangleDeclName(FD));
   else if (const VarDecl *VD = dyn_cast<VarDecl>(D))
     mangleVariableEncoding(VD);
+  else if (isa<MSGuidDecl>(D))
+    // MSVC appears to mangle GUIDs as if they were variables of type
+    // 'const struct __s_GUID'.
+    Out << "3U__s_GUID@@B";
   else
     llvm_unreachable("Tried to mangle unexpected NamedDecl!");
 }
 
 void MicrosoftCXXNameMangler::mangleFunctionEncoding(const FunctionDecl *FD,
                                                      bool ShouldMangle) {
   // <type-encoding> ::= <function-class> <function-type>
 
case DeclarationName::Identifier: {
         // a $S prefix.
         llvm::SmallString<64> Name("$S");
         // Get a unique id for the anonymous struct.
         Name += llvm::utostr(Context.getAnonymousStructId(RD) + 1);
         mangleSourceName(Name.str());
         break;
       }
 
+      if (const MSGuidDecl *GD = dyn_cast<MSGuidDecl>(ND)) {
+        // Mangle a GUID object as if it were a variable with the corresponding
+        // mangled name.
+        SmallString<sizeof("_GUID_12345678_1234_1234_1234_1234567890ab")> GUID;
+        llvm::raw_svector_ostream GUIDOS(GUID);
+        Context.mangleMSGuidDecl(GD, GUIDOS);
+        mangleSourceName(GUID);
+        break;
+      }
+
       // We must have an anonymous struct.
       const TagDecl *TD = cast<TagDecl>(ND);
       if (const TypedefNameDecl *D = TD->getTypedefNameForAnonDecl()) {
         assert(TD->getDeclContext() == D->getDeclContext() &&
                "Typedef should not be in another decl context!");
         assert(D->getDeclName().getAsIdentifierInfo() &&
                "Typedef was not named!");
         mangleSourceName(D->getDeclName().getAsIdentifierInfo()->getName());

 void MicrosoftCXXNameMangler::mangleExpression(const Expr *E) {
   // See if this is a constant expression.
   llvm::APSInt Value;
   if (E->isIntegerConstantExpr(Value, Context.getASTContext())) {
     mangleIntegerLiteral(Value, E->getType()->isBooleanType());
     return;
   }
 
-  // Look through no-op casts like template parameter substitutions.
-  E = E->IgnoreParenNoopCasts(Context.getASTContext());
-
-  const CXXUuidofExpr *UE = nullptr;
-  if (const UnaryOperator *UO = dyn_cast<UnaryOperator>(E)) {
-    if (UO->getOpcode() == UO_AddrOf)
-      UE = dyn_cast<CXXUuidofExpr>(UO->getSubExpr());
-  } else
-    UE = dyn_cast<CXXUuidofExpr>(E);
-
-  if (UE) {
-    // If we had to peek through an address-of operator, treat this like we are
-    // dealing with a pointer type.  Otherwise, treat it like a const reference.
-    //
-    // N.B. This matches up with the handling of TemplateArgument::Declaration
-    // in mangleTemplateArg
-    if (UE == E)
-      Out << "$E?";
-    else
-      Out << "$1?";
-
-    // This CXXUuidofExpr is mangled as-if it were actually a VarDecl from
-    // const __s_GUID _GUID_{lower case UUID with underscores}
-    StringRef Uuid = UE->getUuidStr();
-    std::string Name = "_GUID_" + Uuid.lower();
-    std::replace(Name.begin(), Name.end(), '-', '_');
-
-    mangleSourceName(Name);
-    // Terminate the whole name with an '@'.
-    Out << '@';
-    // It's a global variable.
-    Out << '3';
-    // It's a struct called __s_GUID.
-    mangleArtificialTagType(TTK_Struct, "__s_GUID");
-    // It's const.
-    Out << 'B';
-    return;
-  }
-
   // As bad as this diagnostic is, it's better than crashing.
   DiagnosticsEngine &Diags = Context.getDiags();
   unsigned DiagID = Diags.getCustomDiagID(
       DiagnosticsEngine::Error, "cannot yet mangle expression type %0");
   Diags.Report(E->getExprLoc(), DiagID) << E->getStmtClassName()
                                         << E->getSourceRange();
 }
 

clang/lib/CodeGen/CGDebugInfo.cpp

case TemplateArgument::Declaration: {
                      dyn_cast<MemberPointerType>(T.getTypePtr())) {
           // These five lines (& possibly the above member function pointer
           // handling) might be able to be refactored to use similar code in
           // CodeGenModule::getMemberPointerConstant
           uint64_t fieldOffset = CGM.getContext().getFieldOffset(D);
           CharUnits chars =
               CGM.getContext().toCharUnitsFromBits((int64_t)fieldOffset);
           V = CGM.getCXXABI().EmitMemberDataPointer(MPT, chars);
+        } else if (const auto *GD = dyn_cast<MSGuidDecl>(D)) {
+          V = CGM.GetAddrOfMSGuidDecl(GD).getPointer();
         }
         assert(V && "Failed to find template parameter pointer");
         V = V->stripPointerCasts();
       }
       TemplateParams.push_back(DBuilder.createTemplateValueParameter(
           TheCU, Name, TTy, defaultParameter, cast_or_null<llvm::Constant>(V)));
     } break;
     case TemplateArgument::NullPtr: {

clang/lib/CodeGen/CGDecl.cpp

void CodeGenFunction::EmitDecl(const Decl &D) {
   case Decl::Function:  // void X();
   case Decl::Record:    // struct/union/class X;
   case Decl::Enum:      // enum X;
   case Decl::EnumConstant: // enum ? { X = ? }
   case Decl::CXXRecord: // struct/union/class X; [C++]
   case Decl::StaticAssert: // static_assert(X, ""); [C++0x]
   case Decl::Label:        // __label__ x;
   case Decl::Import:
+  case Decl::MSGuid:    // __declspec(uuid("..."))
   case Decl::OMPThreadPrivate:
   case Decl::OMPAllocate:
   case Decl::OMPCapturedExpr:
   case Decl::OMPRequires:
   case Decl::Empty:
   case Decl::Concept:
   case Decl::LifetimeExtendedTemporary:
   case Decl::RequiresExprBody:

clang/lib/CodeGen/CGExpr.cpp

if (const auto *FD = dyn_cast<FunctionDecl>(ND))
     return EmitFunctionDeclLValue(*this, E, FD);
 
   // FIXME: While we're emitting a binding from an enclosing scope, all other
   // DeclRefExprs we see should be implicitly treated as if they also refer to
   // an enclosing scope.
   if (const auto *BD = dyn_cast<BindingDecl>(ND))
     return EmitLValue(BD->getBinding());
 
+  // We can form DeclRefExprs naming GUID declarations when reconstituting
+  // non-type template parameters into expressions.
+  if (const auto *GD = dyn_cast<MSGuidDecl>(ND))
+    return MakeAddrLValue(CGM.GetAddrOfMSGuidDecl(GD), T,
+                          AlignmentSource::Decl);
+
   llvm_unreachable("Unhandled DeclRefExpr");
 }
 
 LValue CodeGenFunction::EmitUnaryOpLValue(const UnaryOperator *E) {
   // __extension__ doesn't affect lvalue-ness.
   if (E->getOpcode() == UO_Extension)
     return EmitLValue(E->getSubExpr());
 

 }
 
 LValue
 CodeGenFunction::EmitCXXTypeidLValue(const CXXTypeidExpr *E) {
   return MakeNaturalAlignAddrLValue(EmitCXXTypeidExpr(E), E->getType());
 }
 
 Address CodeGenFunction::EmitCXXUuidofExpr(const CXXUuidofExpr *E) {
-  return Builder.CreateElementBitCast(CGM.GetAddrOfUuidDescriptor(E),
+  return Builder.CreateElementBitCast(CGM.GetAddrOfMSGuidDecl(E->getGuidDecl()),
                                       ConvertType(E->getType()));
 }
 
 LValue CodeGenFunction::EmitCXXUuidofLValue(const CXXUuidofExpr *E) {
   return MakeAddrLValue(EmitCXXUuidofExpr(E), E->getType(),
                         AlignmentSource::Decl);
 }
 

clang/lib/CodeGen/CGExprConstant.cpp

private:
   ConstantLValue VisitObjCBoxedExpr(const ObjCBoxedExpr *E);
   ConstantLValue VisitObjCEncodeExpr(const ObjCEncodeExpr *E);
   ConstantLValue VisitObjCStringLiteral(const ObjCStringLiteral *E);
   ConstantLValue VisitPredefinedExpr(const PredefinedExpr *E);
   ConstantLValue VisitAddrLabelExpr(const AddrLabelExpr *E);
   ConstantLValue VisitCallExpr(const CallExpr *E);
   ConstantLValue VisitBlockExpr(const BlockExpr *E);
   ConstantLValue VisitCXXTypeidExpr(const CXXTypeidExpr *E);
-  ConstantLValue VisitCXXUuidofExpr(const CXXUuidofExpr *E);
   ConstantLValue VisitMaterializeTemporaryExpr(
                                          const MaterializeTemporaryExpr *E);
 
   bool hasNonZeroOffset() const {
     return !Value.getLValueOffset().isZero();
   }
 
   /// Return the value offset.
if (auto VD = dyn_cast<VarDecl>(D)) {
 
         if (VD->isLocalVarDecl()) {
           return CGM.getOrCreateStaticVarDecl(
               *VD, CGM.getLLVMLinkageVarDefinition(VD, /*IsConstant=*/false));
         }
       }
     }
 
+    if (auto *GD = dyn_cast<MSGuidDecl>(D))
+      return CGM.GetAddrOfMSGuidDecl(GD);
+
     return nullptr;
   }
 
   // Handle typeid(T).
   if (TypeInfoLValue TI = base.dyn_cast<TypeInfoLValue>()) {
     llvm::Type *StdTypeInfoPtrTy =
         CGM.getTypes().ConvertType(base.getTypeInfoType())->getPointerTo();
     llvm::Constant *TypeInfo =
ConstantLValueEmitter::VisitCXXTypeidExpr(const CXXTypeidExpr *E) {
   if (E->isTypeOperand())
     T = E->getTypeOperand(CGM.getContext());
   else
     T = E->getExprOperand()->getType();
   return CGM.GetAddrOfRTTIDescriptor(T);
 }
 
 ConstantLValue
-ConstantLValueEmitter::VisitCXXUuidofExpr(const CXXUuidofExpr *E) {
-  return CGM.GetAddrOfUuidDescriptor(E);
-}
-
-ConstantLValue
 ConstantLValueEmitter::VisitMaterializeTemporaryExpr(
                                             const MaterializeTemporaryExpr *E) {
   assert(E->getStorageDuration() == SD_Static);
   SmallVector<const Expr *, 2> CommaLHSs;
   SmallVector<SubobjectAdjustment, 2> Adjustments;
   const Expr *Inner =
       E->getSubExpr()->skipRValueSubobjectAdjustments(CommaLHSs, Adjustments);
   return CGM.GetAddrOfGlobalTemporary(E, Inner);

clang/lib/CodeGen/CodeGenModule.h

llvm::Constant *GetAddrOfFunction(GlobalDecl GD, llvm::Type *Ty = nullptr,
                                     bool ForVTable = false,
                                     bool DontDefer = false,
                                     ForDefinition_t IsForDefinition
                                       = NotForDefinition);
 
   /// Get the address of the RTTI descriptor for the given type.
   llvm::Constant *GetAddrOfRTTIDescriptor(QualType Ty, bool ForEH = false);
 
-  /// Get the address of a uuid descriptor .
-  ConstantAddress GetAddrOfUuidDescriptor(const CXXUuidofExpr* E);
+  /// Get the address of a GUID.
+  ConstantAddress GetAddrOfMSGuidDecl(const MSGuidDecl *GD);
 
   /// Get the address of the thunk for the given global decl.
   llvm::Constant *GetAddrOfThunk(StringRef Name, llvm::Type *FnTy,
                                  GlobalDecl GD);
 
   /// Get a reference to the target of VD.
   ConstantAddress GetWeakRefReference(const ValueDecl *VD);
 
private:
 
   /// Emits OpenCL specific Metadata e.g. OpenCL version.
   void EmitOpenCLMetadata();
 
   /// Emit the llvm.gcov metadata used to tell LLVM where to emit the .gcno and
   /// .gcda files in a way that persists in .bc files.
   void EmitCoverageFile();
 
-  /// Emits the initializer for a uuidof string.
-  llvm::Constant *EmitUuidofInitializer(StringRef uuidstr);
-
   /// Determine whether the definition must be emitted; if this returns \c
   /// false, the definition can be emitted lazily if it's used.
   bool MustBeEmitted(const ValueDecl *D);
 
   /// Determine whether the definition can be emitted eagerly, or should be
   /// delayed until the end of the translation unit. This is relevant for
   /// definitions whose linkage can change, e.g. implicit function instantions
   /// which may later be explicitly instantiated.

clang/lib/CodeGen/CodeGenModule.cpp

if (LangOpts.OpenMP && LangOpts.OpenMPUseTLS &&
       getContext().getTargetInfo().isTLSSupported() && isa<VarDecl>(Global) &&
       !isTypeConstant(Global->getType(), false) &&
       !OMPDeclareTargetDeclAttr::isDeclareTargetDeclaration(Global))
     return false;
 
   return true;
 }
 
-ConstantAddress CodeGenModule::GetAddrOfUuidDescriptor(
-    const CXXUuidofExpr* E) {
-  // Sema has verified that IIDSource has a __declspec(uuid()), and that its
-  // well-formed.
-  StringRef Uuid = E->getUuidStr();
-  std::string Name = "_GUID_" + Uuid.lower();
-  std::replace(Name.begin(), Name.end(), '-', '_');
+ConstantAddress CodeGenModule::GetAddrOfMSGuidDecl(const MSGuidDecl *GD) {
+  StringRef Name = getMangledName(GD);
 
   // The UUID descriptor should be pointer aligned.
   CharUnits Alignment = CharUnits::fromQuantity(PointerAlignInBytes);
 
   // Look for an existing global.
   if (llvm::GlobalVariable *GV = getModule().getNamedGlobal(Name))
     return ConstantAddress(GV, Alignment);
 
-  llvm::Constant *Init = EmitUuidofInitializer(Uuid);
-  assert(Init && "failed to initialize as constant");
+  ConstantEmitter Emitter(*this);
+  llvm::Constant *Init;
+
+  APValue &V = GD->getAsAPValue();
+  if (!V.isAbsent()) {
+    // If possible, emit the APValue version of the initializer. In particular,
+    // this gets the type of the constant right.
+    Init = Emitter.emitForInitializer(
+        GD->getAsAPValue(), GD->getType().getAddressSpace(), GD->getType());
+  } else {
+    // As a fallback, directly construct the constant.
+    // FIXME: This may get padding wrong under esoteric struct layout rules.
+    // MSVC appears to create a complete type 'struct __s_GUID' that it
+    // presumably uses to represent these constants.
+    MSGuidDecl::Parts Parts = GD->getParts();
+    llvm::Constant *Fields[4] = {
+        llvm::ConstantInt::get(Int32Ty, Parts.Part1),
+        llvm::ConstantInt::get(Int16Ty, Parts.Part2),
+        llvm::ConstantInt::get(Int16Ty, Parts.Part3),
+        llvm::ConstantDataArray::getRaw(
+            StringRef(reinterpret_cast<char *>(Parts.Part4And5), 8), 8,
+            Int8Ty)};
+    Init = llvm::ConstantStruct::getAnon(Fields);
+  }
 
   auto *GV = new llvm::GlobalVariable(
       getModule(), Init->getType(),
       /*isConstant=*/true, llvm::GlobalValue::LinkOnceODRLinkage, Init, Name);
   if (supportsCOMDAT())
     GV->setComdat(TheModule.getOrInsertComdat(GV->getName()));
   setDSOLocal(GV);
-  return ConstantAddress(GV, Alignment);
+
+  llvm::Constant *Addr = GV;
+  if (!V.isAbsent()) {
+    Emitter.finalize(GV);
+  } else {
+    llvm::Type *Ty = getTypes().ConvertTypeForMem(GD->getType());
+    Addr = llvm::ConstantExpr::getBitCast(
+        GV, Ty->getPointerTo(GV->getAddressSpace()));
+  }
+  return ConstantAddress(Addr, Alignment);
 }
 
 ConstantAddress CodeGenModule::GetWeakRefReference(const ValueDecl *VD) {
   const AliasAttr *AA = VD->getAttr<AliasAttr>();
   assert(AA && "No alias?");
 
   CharUnits Alignment = getContext().getDeclAlign(VD);
   llvm::Type *DeclTy = getTypes().ConvertTypeForMem(VD->getType());
auto *CoverageNotesFile =
       llvm::MDString::get(Ctx, getCodeGenOpts().CoverageNotesFile);
   for (int i = 0, e = CUNode->getNumOperands(); i != e; ++i) {
     llvm::MDNode *CU = CUNode->getOperand(i);
     llvm::Metadata *Elts[] = {CoverageNotesFile, CoverageDataFile, CU};
     GCov->addOperand(llvm::MDNode::get(Ctx, Elts));
   }
 }
 
-llvm::Constant *CodeGenModule::EmitUuidofInitializer(StringRef Uuid) {
-  // Sema has checked that all uuid strings are of the form
-  // "12345678-1234-1234-1234-1234567890ab".
-  assert(Uuid.size() == 36);
-  for (unsigned i = 0; i < 36; ++i) {
-    if (i == 8 || i == 13 || i == 18 || i == 23) assert(Uuid[i] == '-');
-    else                                         assert(isHexDigit(Uuid[i]));
-  }
-
-  // The starts of all bytes of Field3 in Uuid. Field 3 is "1234-1234567890ab".
-  const unsigned Field3ValueOffsets[8] = { 19, 21, 24, 26, 28, 30, 32, 34 };
-
-  llvm::Constant *Field3[8];
-  for (unsigned Idx = 0; Idx < 8; ++Idx)
-    Field3[Idx] = llvm::ConstantInt::get(
-        Int8Ty, Uuid.substr(Field3ValueOffsets[Idx], 2), 16);
-
-  llvm::Constant *Fields[4] = {
-    llvm::ConstantInt::get(Int32Ty, Uuid.substr(0,  8), 16),
-    llvm::ConstantInt::get(Int16Ty, Uuid.substr(9,  4), 16),
-    llvm::ConstantInt::get(Int16Ty, Uuid.substr(14, 4), 16),
-    llvm::ConstantArray::get(llvm::ArrayType::get(Int8Ty, 8), Field3)
-  };
-
-  return llvm::ConstantStruct::getAnon(Fields);
-}
-
 llvm::Constant *CodeGenModule::GetAddrOfRTTIDescriptor(QualType Ty,
                                                        bool ForEH) {
   // Return a bogus pointer if RTTI is disabled, unless it's for EH.
   // FIXME: should we even be calling this method if RTTI is disabled
   // and it's not for EH?
   if ((!ForEH && !getLangOpts().RTTI) || getLangOpts().CUDAIsDevice ||
       (getLangOpts().OpenMP && getLangOpts().OpenMPIsDevice &&
        getTriple().isNVPTX()))

clang/lib/Sema/SemaDecl.cpp

else if (isa<AlignedAttr>(Attr))
     // AlignedAttrs are handled separately, because we need to handle all
     // such attributes on a declaration at the same time.
     NewAttr = nullptr;
   else if ((isa<DeprecatedAttr>(Attr) || isa<UnavailableAttr>(Attr)) &&
            (AMK == Sema::AMK_Override ||
             AMK == Sema::AMK_ProtocolImplementation))
     NewAttr = nullptr;
   else if (const auto *UA = dyn_cast<UuidAttr>(Attr))
-    NewAttr = S.mergeUuidAttr(D, *UA, UA->getGuid());
+    NewAttr = S.mergeUuidAttr(D, *UA, UA->getGuid(), UA->getGuidDecl());
   else if (const auto *SLHA = dyn_cast<SpeculativeLoadHardeningAttr>(Attr))
     NewAttr = S.mergeSpeculativeLoadHardeningAttr(D, *SLHA);
   else if (const auto *SLHA = dyn_cast<NoSpeculativeLoadHardeningAttr>(Attr))
     NewAttr = S.mergeNoSpeculativeLoadHardeningAttr(D, *SLHA);
   else if (Attr->shouldInheritEvenIfAlreadyPresent() || !DeclHasAttr(D, Attr))
     NewAttr = cast<InheritableAttr>(Attr->clone(S.Context));
 
   if (NewAttr) {

clang/lib/Sema/SemaDeclAttr.cpp

static void handleObjCPreciseLifetimeAttr(Sema &S, Decl *D,
   D->addAttr(::new (S.Context) ObjCPreciseLifetimeAttr(S.Context, AL));
 }
 
 //===----------------------------------------------------------------------===//
 // Microsoft specific attribute handlers.
 //===----------------------------------------------------------------------===//
 
 UuidAttr *Sema::mergeUuidAttr(Decl *D, const AttributeCommonInfo &CI,
-                              StringRef Uuid) {
+                              StringRef UuidAsWritten, MSGuidDecl *GuidDecl) {
   if (const auto *UA = D->getAttr<UuidAttr>()) {
-    if (UA->getGuid().equals_lower(Uuid))
+    if (declaresSameEntity(UA->getGuidDecl(), GuidDecl))
       return nullptr;
     if (!UA->getGuid().empty()) {
       Diag(UA->getLocation(), diag::err_mismatched_uuid);
       Diag(CI.getLoc(), diag::note_previous_uuid);
       D->dropAttr<UuidAttr>();
     }
   }
 
-  return ::new (Context) UuidAttr(Context, CI, Uuid);
+  return ::new (Context) UuidAttr(Context, CI, UuidAsWritten, GuidDecl);
 }
 
 static void handleUuidAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
   if (!S.LangOpts.CPlusPlus) {
     S.Diag(AL.getLoc(), diag::err_attribute_not_supported_in_lang)
         << AL << AttributeLangSupport::C;
     return;
   }
 
-  StringRef StrRef;
+  StringRef OrigStrRef;
   SourceLocation LiteralLoc;
-  if (!S.checkStringLiteralArgumentAttr(AL, 0, StrRef, &LiteralLoc))
+  if (!S.checkStringLiteralArgumentAttr(AL, 0, OrigStrRef, &LiteralLoc))
     return;
 
   // GUID format is "XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX" or
   // "{XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX}", normalize to the former.
+  StringRef StrRef = OrigStrRef;
   if (StrRef.size() == 38 && StrRef.front() == '{' && StrRef.back() == '}')
     StrRef = StrRef.drop_front().drop_back();
 
   // Validate GUID length.
   if (StrRef.size() != 36) {
     S.Diag(LiteralLoc, diag::err_attribute_uuid_malformed_guid);
     return;
   }
 
   for (unsigned i = 0; i < 36; ++i) {
     if (i == 8 || i == 13 || i == 18 || i == 23) {
       if (StrRef[i] != '-') {
         S.Diag(LiteralLoc, diag::err_attribute_uuid_malformed_guid);
         return;
       }
     } else if (!isHexDigit(StrRef[i])) {
       S.Diag(LiteralLoc, diag::err_attribute_uuid_malformed_guid);
       return;
     }
   }
 
+  // Convert to our parsed format and canonicalize.
+  MSGuidDecl::Parts Parsed;
+  StrRef.substr(0, 8).getAsInteger(16, Parsed.Part1);
+  StrRef.substr(9, 4).getAsInteger(16, Parsed.Part2);
+  StrRef.substr(14, 4).getAsInteger(16, Parsed.Part3);
+  for (unsigned i = 0; i != 8; ++i)
+    StrRef.substr(19 + 2 * i + (i >= 2 ? 1 : 0), 2)
+        .getAsInteger(16, Parsed.Part4And5[i]);
+  MSGuidDecl *Guid = S.Context.getMSGuidDecl(Parsed);
+
   // FIXME: It'd be nice to also emit a fixit removing uuid(...) (and, if it's
   // the only thing in the [] list, the [] too), and add an insertion of
   // __declspec(uuid(...)).  But sadly, neither the SourceLocs of the commas
   // separating attributes nor of the [ and the ] are in the AST.
   // Cf "SourceLocations of attribute list delimiters - [[ ... , ... ]] etc"
   // on cfe-dev.
   if (AL.isMicrosoftAttribute()) // Check for [uuid(...)] spelling.
     S.Diag(AL.getLoc(), diag::warn_atl_uuid_deprecated);
 
-  UuidAttr *UA = S.mergeUuidAttr(D, AL, StrRef);
+  UuidAttr *UA = S.mergeUuidAttr(D, AL, OrigStrRef, Guid);
   if (UA)
     D->addAttr(UA);
 }
 
 static void handleMSInheritanceAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
   if (!S.LangOpts.CPlusPlus) {
     S.Diag(AL.getLoc(), diag::err_attribute_not_supported_in_lang)
         << AL << AttributeLangSupport::C;

clang/lib/Sema/SemaExpr.cpp

case Decl::Function: {
       valueKind = VK_RValue;
       break;
     }
 
     case Decl::CXXDeductionGuide:
       llvm_unreachable("building reference to deduction guide");
 
     case Decl::MSProperty:
+    case Decl::MSGuid:
+      // FIXME: Should MSGuidDecl be subject to capture in OpenMP,
+      // or duplicated between host and device?
       valueKind = VK_LValue;
       break;
 
     case Decl::CXXMethod:
       // If we're referring to a method with an __unknown_anytype
       // result type, make the entire expression __unknown_anytype.
       // This should only be possible with a type written directly.
       if (const FunctionProtoType *proto

 /// or is an lvalue. Here are some examples:
 ///  - &(x) => x
 ///  - &*****f => f for f a function designator.
 ///  - &s.xx => s
 ///  - &s.zz[1].yy -> s, if zz is an array
 ///  - *(x + 1) -> x, if x is an array
 ///  - &"123"[2] -> 0
 ///  - & __real__ x -> x
+///
+/// FIXME: We don't recurse to the RHS of a comma, nor handle pointers to
+/// members.
 static ValueDecl *getPrimaryDecl(Expr *E) {
   switch (E->getStmtClass()) {
   case Stmt::DeclRefExprClass:
     return cast<DeclRefExpr>(E)->getDecl();
   case Stmt::MemberExprClass:
     // If this is an arrow operator, the address is an offset from
     // the base's value, so the object the base refers to is
     // irrelevant.
case Stmt::UnaryOperatorClass: {
     }
   }
   case Stmt::ParenExprClass:
     return getPrimaryDecl(cast<ParenExpr>(E)->getSubExpr());
   case Stmt::ImplicitCastExprClass:
     // If the result of an implicit cast is an l-value, we care about
     // the sub-expression; otherwise, the result here doesn't matter.
     return getPrimaryDecl(cast<ImplicitCastExpr>(E)->getSubExpr());
+  case Stmt::CXXUuidofExprClass:
+    return cast<CXXUuidofExpr>(E)->getGuidDecl();
   default:
     return nullptr;
   }
 }
 
 namespace {
   enum {
     AO_Bit_Field = 0,
if (const VarDecl *vd = dyn_cast<VarDecl>(dcl)) {
               Context.getTypeDeclType(cast<RecordDecl>(Ctx)).getTypePtr());
           // Under the MS ABI, lock down the inheritance model now.
           if (Context.getTargetInfo().getCXXABI().isMicrosoft())
             (void)isCompleteType(OpLoc, MPTy);
           return MPTy;
         }
       }
     } else if (!isa<FunctionDecl>(dcl) && !isa<NonTypeTemplateParmDecl>(dcl) &&
-               !isa<BindingDecl>(dcl))
+               !isa<BindingDecl>(dcl) && !isa<MSGuidDecl>(dcl))
       llvm_unreachable("Unknown/unexpected decl type");
   }
 
   if (AddressOfError != AO_No_Error) {
     diagnoseAddressOfInvalidType(*this, OpLoc, op, AddressOfError);
     return QualType();
   }
 

clang/lib/Sema/SemaExprCXX.cpp

for (const TemplateArgument &TA : TAL.asArray()) {
 
       if (UuidForTA)
         UuidAttrs.insert(UuidForTA);
     }
   }
 }
 
 /// Build a Microsoft __uuidof expression with a type operand.
-ExprResult Sema::BuildCXXUuidof(QualType TypeInfoType,
+ExprResult Sema::BuildCXXUuidof(QualType Type,
                                 SourceLocation TypeidLoc,
                                 TypeSourceInfo *Operand,
                                 SourceLocation RParenLoc) {
-  StringRef UuidStr;
+  MSGuidDecl *Guid = nullptr;
   if (!Operand->getType()->isDependentType()) {
     llvm::SmallSetVector<const UuidAttr *, 1> UuidAttrs;
     getUuidAttrOfType(*this, Operand->getType(), UuidAttrs);
     if (UuidAttrs.empty())
       return ExprError(Diag(TypeidLoc, diag::err_uuidof_without_guid));
     if (UuidAttrs.size() > 1)
       return ExprError(Diag(TypeidLoc, diag::err_uuidof_with_multiple_guids));
-    UuidStr = UuidAttrs.back()->getGuid();
+    Guid = UuidAttrs.back()->getGuidDecl();
   }
 
-  return new (Context) CXXUuidofExpr(TypeInfoType.withConst(), Operand, UuidStr,
-                                     SourceRange(TypeidLoc, RParenLoc));
+  return new (Context)
+      CXXUuidofExpr(Type, Operand, Guid, SourceRange(TypeidLoc, RParenLoc));
 }
 
 /// Build a Microsoft __uuidof expression with an expression operand.
-ExprResult Sema::BuildCXXUuidof(QualType TypeInfoType,
-                                SourceLocation TypeidLoc,
-                                Expr *E,
-                                SourceLocation RParenLoc) {
-  StringRef UuidStr;
+ExprResult Sema::BuildCXXUuidof(QualType Type, SourceLocation TypeidLoc,
+                                Expr *E, SourceLocation RParenLoc) {
+  MSGuidDecl *Guid = nullptr;
   if (!E->getType()->isDependentType()) {
     if (E->isNullPointerConstant(Context, Expr::NPC_ValueDependentIsNull)) {
-      UuidStr = "00000000-0000-0000-0000-000000000000";
+      // A null pointer results in {00000000-0000-0000-0000-000000000000}.
+      Guid = Context.getMSGuidDecl(MSGuidDecl::Parts{});
     } else {
       llvm::SmallSetVector<const UuidAttr *, 1> UuidAttrs;
       getUuidAttrOfType(*this, E->getType(), UuidAttrs);
       if (UuidAttrs.empty())
         return ExprError(Diag(TypeidLoc, diag::err_uuidof_without_guid));
       if (UuidAttrs.size() > 1)
         return ExprError(Diag(TypeidLoc, diag::err_uuidof_with_multiple_guids));
-      UuidStr = UuidAttrs.back()->getGuid();
+      Guid = UuidAttrs.back()->getGuidDecl();
     }
   }
 
-  return new (Context) CXXUuidofExpr(TypeInfoType.withConst(), E, UuidStr,
-                                     SourceRange(TypeidLoc, RParenLoc));
+  return new (Context)
+      CXXUuidofExpr(Type, E, Guid, SourceRange(TypeidLoc, RParenLoc));
 }
 
 /// ActOnCXXUuidof - Parse __uuidof( type-id ) or __uuidof (expression);
 ExprResult
 Sema::ActOnCXXUuidof(SourceLocation OpLoc, SourceLocation LParenLoc,
                      bool isType, void *TyOrExpr, SourceLocation RParenLoc) {
-  // If MSVCGuidDecl has not been cached, do the lookup.
-  if (!MSVCGuidDecl) {
-    IdentifierInfo *GuidII = &PP.getIdentifierTable().get("_GUID");
-    LookupResult R(*this, GuidII, SourceLocation(), LookupTagName);
-    LookupQualifiedName(R, Context.getTranslationUnitDecl());
-    MSVCGuidDecl = R.getAsSingle<RecordDecl>();
-    if (!MSVCGuidDecl)
-      return ExprError(Diag(OpLoc, diag::err_need_header_before_ms_uuidof));
-  }
-
-  QualType GuidType = Context.getTypeDeclType(MSVCGuidDecl);
+  QualType GuidType = Context.getMSGuidType();
+  GuidType.addConst();
 
   if (isType) {
     // The operand is a type; handle it as such.
     TypeSourceInfo *TInfo = nullptr;
     QualType T = GetTypeFromParser(ParsedType::getFromOpaquePtr(TyOrExpr),
                                    &TInfo);
     if (T.isNull())
       return ExprError();

clang/lib/Sema/SemaTemplate.cpp

if (UnaryOperator *UnOp = dyn_cast<UnaryOperator>(Arg)) {
       }
     }
 
     while (SubstNonTypeTemplateParmExpr *subst =
                dyn_cast<SubstNonTypeTemplateParmExpr>(Arg))
       Arg = subst->getReplacement()->IgnoreImpCasts();
   }
 
-  DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(Arg);
-  ValueDecl *Entity = DRE ? DRE->getDecl() : nullptr;
+  ValueDecl *Entity = nullptr;
+  if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(Arg))
+    Entity = DRE->getDecl();
+  else if (CXXUuidofExpr *CUE = dyn_cast<CXXUuidofExpr>(Arg))
+    Entity = CUE->getGuidDecl();
 
   // If our parameter has pointer type, check for a null template value.
   if (ParamType->isPointerType() || ParamType->isNullPtrType()) {
     switch (isNullPointerValueTemplateArgument(S, Param, ParamType, ArgIn,
                                                Entity)) {
     case NPV_NullPointer:
       S.Diag(Arg->getExprLoc(), diag::warn_cxx98_compat_template_arg_null);
       Converted = TemplateArgument(S.Context.getCanonicalType(ParamType),
CheckTemplateArgumentAddressOfObjectOrFunction(Sema &S,
 
   // Stop checking the precise nature of the argument if it is value dependent,
   // it should be checked when instantiated.
   if (Arg->isValueDependent()) {
     Converted = TemplateArgument(ArgIn);
     return false;
   }
 
-  if (isa<CXXUuidofExpr>(Arg)) {
-    if (CheckTemplateArgumentIsCompatibleWithParameter(S, Param, ParamType,
-                                                       ArgIn, Arg, ArgType))
-      return true;
-
-    Converted = TemplateArgument(ArgIn);
-    return false;
-  }
-
-  if (!DRE) {
+  if (!Entity) {
     S.Diag(Arg->getBeginLoc(), diag::err_template_arg_not_decl_ref)
         << Arg->getSourceRange();
     S.Diag(Param->getLocation(), diag::note_template_param_here);
     return true;
   }
 
   // Cannot refer to non-static data members
   if (isa<FieldDecl>(Entity) || isa<IndirectFieldDecl>(Entity)) {
if (!Method->isStatic()) {
           << Method << Arg->getSourceRange();
       S.Diag(Param->getLocation(), diag::note_template_param_here);
       return true;
     }
   }
 
   FunctionDecl *Func = dyn_cast<FunctionDecl>(Entity);
   VarDecl *Var = dyn_cast<VarDecl>(Entity);
+  MSGuidDecl *Guid = dyn_cast<MSGuidDecl>(Entity);
 
   // A non-type template argument must refer to an object or function.
-  if (!Func && !Var) {
+  if (!Func && !Var && !Guid) {
     // We found something, but we don't know specifically what it is.
     S.Diag(Arg->getBeginLoc(), diag::err_template_arg_not_object_or_func)
         << Arg->getSourceRange();
-    S.Diag(DRE->getDecl()->getLocation(), diag::note_template_arg_refers_here);
+    S.Diag(Entity->getLocation(), diag::note_template_arg_refers_here);
     return true;
   }
 
   // Address / reference template args must have external linkage in C++98.
   if (Entity->getFormalLinkage() == InternalLinkage) {
     S.Diag(Arg->getBeginLoc(),
            S.getLangOpts().CPlusPlus11
                ? diag::warn_cxx98_compat_template_arg_object_internal
                : diag::ext_template_arg_object_internal)
         << !Func << Entity << Arg->getSourceRange();
     S.Diag(Entity->getLocation(), diag::note_template_arg_internal_object)
       << !Func;
   } else if (!Entity->hasLinkage()) {
     S.Diag(Arg->getBeginLoc(), diag::err_template_arg_object_no_linkage)
         << !Func << Entity << Arg->getSourceRange();
     S.Diag(Entity->getLocation(), diag::note_template_arg_internal_object)
       << !Func;
     return true;
   }
 
-  if (Func) {
-    // If the template parameter has pointer type, the function decays.
-    if (ParamType->isPointerType() && !AddressTaken)
-      ArgType = S.Context.getPointerType(Func->getType());
-    else if (AddressTaken && ParamType->isReferenceType()) {
-      // If we originally had an address-of operator, but the
-      // parameter has reference type, complain and (if things look
-      // like they will work) drop the address-of operator.
-      if (!S.Context.hasSameUnqualifiedType(Func->getType(),
-                                            ParamType.getNonReferenceType())) {
-        S.Diag(AddrOpLoc, diag::err_template_arg_address_of_non_pointer)
-          << ParamType;
-        S.Diag(Param->getLocation(), diag::note_template_param_here);
-        return true;
-      }
-
-      S.Diag(AddrOpLoc, diag::err_template_arg_address_of_non_pointer)
-        << ParamType
-        << FixItHint::CreateRemoval(AddrOpLoc);
-      S.Diag(Param->getLocation(), diag::note_template_param_here);
-
-      ArgType = Func->getType();
-    }
-  } else {
+  if (Var) {
     // A value of reference type is not an object.
     if (Var->getType()->isReferenceType()) {
       S.Diag(Arg->getBeginLoc(), diag::err_template_arg_reference_var)
           << Var->getType() << Arg->getSourceRange();
       S.Diag(Param->getLocation(), diag::note_template_param_here);
       return true;
     }
 
     // A template argument must have static storage duration.
     if (Var->getTLSKind()) {
       S.Diag(Arg->getBeginLoc(), diag::err_template_arg_thread_local)
           << Arg->getSourceRange();
       S.Diag(Var->getLocation(), diag::note_template_arg_refers_here);
       return true;
     }
+  }
 
-    // If the template parameter has pointer type, we must have taken
-    // the address of this object.
-    if (ParamType->isReferenceType()) {
-      if (AddressTaken) {
-        // If we originally had an address-of operator, but the
-        // parameter has reference type, complain and (if things look
-        // like they will work) drop the address-of operator.
-        if (!S.Context.hasSameUnqualifiedType(Var->getType(),
-                                            ParamType.getNonReferenceType())) {
-          S.Diag(AddrOpLoc, diag::err_template_arg_address_of_non_pointer)
-            << ParamType;
-          S.Diag(Param->getLocation(), diag::note_template_param_here);
-          return true;
-        }
+  if (AddressTaken && ParamType->isReferenceType()) {
+    if (!S.Context.hasSameUnqualifiedType(Entity->getType(),
 
-        S.Diag(AddrOpLoc, diag::err_template_arg_address_of_non_pointer)
-          << ParamType
-          << FixItHint::CreateRemoval(AddrOpLoc);
-        S.Diag(Param->getLocation(), diag::note_template_param_here);
 
-        ArgType = Var->getType();
-      }
-    } else if (!AddressTaken && ParamType->isPointerType()) {
-      if (Var->getType()->isArrayType()) {
-        // Array-to-pointer decay.
-        ArgType = S.Context.getArrayDecayedType(Var->getType());
-      } else {
-        // If the template parameter has pointer type but the address of
-        // this object was not taken, complain and (possibly) recover by
-        // taking the address of the entity.
-        ArgType = S.Context.getPointerType(Var->getType());
-        if (!S.Context.hasSameUnqualifiedType(ArgType, ParamType)) {
-          S.Diag(Arg->getBeginLoc(), diag::err_template_arg_not_address_of)
-              << ParamType;
-          S.Diag(Param->getLocation(), diag::note_template_param_here);
-          return true;
-        }
+    ArgType = Entity->getType();
+
+  // If the template parameter has pointer type, either we must have taken the
+  // address or the argument must decay to a pointer.
+  if (!AddressTaken && ParamType->isPointerType()) {
+    if (Func) {
+      // Function-to-pointer decay.
+      ArgType = S.Context.getPointerType(Func->getType());
+    } else if (Entity->getType()->isArrayType()) {
+      ArgType = S.Context.getArrayDecayedType(Entity->getType());
+      ArgType = S.Context.getPointerType(Entity->getType());
 
-        S.Diag(Arg->getBeginLoc(), diag::err_template_arg_not_address_of)
-            << ParamType << FixItHint::CreateInsertion(Arg->getBeginLoc(), "&");
 
-        S.Diag(Param->getLocation(), diag::note_template_param_here);
-      }
-    }
-  }
 
   if (CheckTemplateArgumentIsCompatibleWithParameter(S, Param, ParamType, ArgIn,
                                                      Arg, ArgType))
     return true;
 
   // Create the template argument.
   Converted =
       TemplateArgument(cast<ValueDecl>(Entity->getCanonicalDecl()), ParamType);
case APValue::LValue: {
              ParamType->isNullPtrType());
       // -- a temporary object
       // -- a string literal
       // -- the result of a typeid expression, or
       // -- a predefined __func__ variable
       APValue::LValueBase Base = Value.getLValueBase();
       auto *VD = const_cast<ValueDecl *>(Base.dyn_cast<const ValueDecl *>());
       if (Base && (!VD || isa<LifetimeExtendedTemporaryDecl>(VD))) {
-        auto *E = Base.dyn_cast<const Expr *>();
-        if (E && isa<CXXUuidofExpr>(E)) {
-          Converted = TemplateArgument(ArgResult.get()->IgnoreImpCasts());
-          break;
-        }
         Diag(Arg->getBeginLoc(), diag::err_template_arg_not_decl_ref)
             << Arg->getSourceRange();
         return ExprError();
       }
       // -- a subobject
       if (Value.hasLValuePath() && Value.getLValuePath().size() == 1 &&
           VD && VD->getType()->isArrayType() &&
           Value.getLValuePath()[0].getAsArrayIndex() == 0 &&

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

Decl *TemplateDeclInstantiator::VisitPragmaDetectMismatchDecl(
   llvm_unreachable("pragma comment cannot be instantiated");
 }
 
 Decl *
 TemplateDeclInstantiator::VisitExternCContextDecl(ExternCContextDecl *D) {
   llvm_unreachable("extern \"C\" context cannot be instantiated");
 }
 
+Decl *TemplateDeclInstantiator::VisitMSGuidDecl(MSGuidDecl *D) {
+  llvm_unreachable("GUID declaration cannot be instantiated");
+}
+
 Decl *
 TemplateDeclInstantiator::VisitLabelDecl(LabelDecl *D) {
   LabelDecl *Inst = LabelDecl::Create(SemaRef.Context, Owner, D->getLocation(),
                                       D->getIdentifier());
   Owner->addDecl(Inst);
   return Inst;
 }
 

clang/lib/Sema/SemaType.cpp

bool Sema::RequireCompleteTypeImpl(SourceLocation Loc, QualType T,
 
   if (!Diagnoser)
     return true;
 
   Diagnoser->diagnose(*this, Loc, T);
 
   // If the type was a forward declaration of a class/struct/union
   // type, produce a note.
-  if (Tag && !Tag->isInvalidDecl())
+  if (Tag && !Tag->isInvalidDecl() && !Tag->getLocation().isInvalid())
     Diag(Tag->getLocation(),
          Tag->isBeingDefined() ? diag::note_type_being_defined
                                : diag::note_forward_declaration)
       << Context.getTagDeclType(Tag);
 
   // If the Objective-C class was a forward declaration, produce a note.
-  if (IFace && !IFace->isInvalidDecl())
+  if (IFace && !IFace->isInvalidDecl() && !IFace->getLocation().isInvalid())
     Diag(IFace->getLocation(), diag::note_forward_class);
 
   // If we have external information that we can use to suggest a fix,
   // produce a note.
   if (ExternalSource)
     ExternalSource->MaybeDiagnoseMissingCompleteType(Loc, T);
 
   return true;

clang/lib/Sema/TreeTransform.h

ExprResult RebuildCXXTypeidExpr(QualType TypeInfoType,
     return getSema().BuildCXXTypeId(TypeInfoType, TypeidLoc, Operand,
                                     RParenLoc);
   }
 
   /// Build a new C++ __uuidof(type) expression.
   ///
   /// By default, performs semantic analysis to build the new expression.
   /// Subclasses may override this routine to provide different behavior.
-  ExprResult RebuildCXXUuidofExpr(QualType TypeInfoType,
-                                        SourceLocation TypeidLoc,
-                                        TypeSourceInfo *Operand,
-                                        SourceLocation RParenLoc) {
-    return getSema().BuildCXXUuidof(TypeInfoType, TypeidLoc, Operand,
-                                    RParenLoc);
+  ExprResult RebuildCXXUuidofExpr(QualType Type, SourceLocation TypeidLoc,
+    return getSema().BuildCXXUuidof(Type, TypeidLoc, Operand, RParenLoc);
   }
 
   /// Build a new C++ __uuidof(expr) expression.
   ///
   /// By default, performs semantic analysis to build the new expression.
   /// Subclasses may override this routine to provide different behavior.
-  ExprResult RebuildCXXUuidofExpr(QualType TypeInfoType,
-                                        SourceLocation TypeidLoc,
-                                        Expr *Operand,
-                                        SourceLocation RParenLoc) {
-    return getSema().BuildCXXUuidof(TypeInfoType, TypeidLoc, Operand,
-                                    RParenLoc);
+  ExprResult RebuildCXXUuidofExpr(QualType Type, SourceLocation TypeidLoc,
+                                  Expr *Operand, SourceLocation RParenLoc) {
+    return getSema().BuildCXXUuidof(Type, TypeidLoc, Operand, RParenLoc);
   }
 
   /// Build a new C++ "this" expression.
   ///
   /// By default, builds a new "this" expression without performing any
   /// semantic analysis. Subclasses may override this routine to provide
   /// different behavior.
   ExprResult RebuildCXXThisExpr(SourceLocation ThisLoc,

clang/lib/Serialization/ASTCommon.cpp

bool serialization::isRedeclarableDeclKind(unsigned Kind) {
   case Decl::Label:
   case Decl::UnresolvedUsingTypename:
   case Decl::TemplateTypeParm:
   case Decl::EnumConstant:
   case Decl::UnresolvedUsingValue:
   case Decl::IndirectField:
   case Decl::Field:
   case Decl::MSProperty:
+  case Decl::MSGuid:
   case Decl::ObjCIvar:
   case Decl::ObjCAtDefsField:
   case Decl::NonTypeTemplateParm:
   case Decl::TemplateTemplateParm:
   case Decl::Using:
   case Decl::UsingPack:
   case Decl::ObjCMethod:
   case Decl::ObjCCategory:

clang/lib/Serialization/ASTReader.cpp

case PREDEF_DECL_BUILTIN_VA_LIST_ID:
     return Context.getBuiltinVaListDecl();
 
   case PREDEF_DECL_VA_LIST_TAG:
     return Context.getVaListTagDecl();
 
   case PREDEF_DECL_BUILTIN_MS_VA_LIST_ID:
     return Context.getBuiltinMSVaListDecl();
 
+  case PREDEF_DECL_BUILTIN_MS_GUID_ID:
+    return Context.getMSGuidTagDecl();
+
   case PREDEF_DECL_EXTERN_C_CONTEXT_ID:
     return Context.getExternCContextDecl();
 
   case PREDEF_DECL_MAKE_INTEGER_SEQ_ID:
     return Context.getMakeIntegerSeqDecl();
 
   case PREDEF_DECL_CF_CONSTANT_STRING_ID:
     return Context.getCFConstantStringDecl();

clang/lib/Serialization/ASTReaderDecl.cpp

public:
     void VisitFunctionDecl(FunctionDecl *FD);
     void VisitCXXDeductionGuideDecl(CXXDeductionGuideDecl *GD);
     void VisitCXXMethodDecl(CXXMethodDecl *D);
     void VisitCXXConstructorDecl(CXXConstructorDecl *D);
     void VisitCXXDestructorDecl(CXXDestructorDecl *D);
     void VisitCXXConversionDecl(CXXConversionDecl *D);
     void VisitFieldDecl(FieldDecl *FD);
     void VisitMSPropertyDecl(MSPropertyDecl *FD);
+    void VisitMSGuidDecl(MSGuidDecl *D);
     void VisitIndirectFieldDecl(IndirectFieldDecl *FD);
     RedeclarableResult VisitVarDeclImpl(VarDecl *D);
     void VisitVarDecl(VarDecl *VD) { VisitVarDeclImpl(VD); }
     void VisitImplicitParamDecl(ImplicitParamDecl *PD);
     void VisitParmVarDecl(ParmVarDecl *PD);
     void VisitDecompositionDecl(DecompositionDecl *DD);
     void VisitBindingDecl(BindingDecl *BD);
     void VisitNonTypeTemplateParmDecl(NonTypeTemplateParmDecl *D);

 }
 
 void ASTDeclReader::VisitMSPropertyDecl(MSPropertyDecl *PD) {
   VisitDeclaratorDecl(PD);
   PD->GetterId = Record.readIdentifier();
   PD->SetterId = Record.readIdentifier();
 }
 
+void ASTDeclReader::VisitMSGuidDecl(MSGuidDecl *D) {
+  VisitValueDecl(D);
+  D->PartVal.Part1 = Record.readInt();
+  D->PartVal.Part2 = Record.readInt();
+  D->PartVal.Part3 = Record.readInt();
+  for (auto &C : D->PartVal.Part4And5)
+    C = Record.readInt();
+
+  // Add this GUID to the AST context's lookup structure, and merge if needed.
+  if (MSGuidDecl *Existing = Reader.getContext().MSGuidDecls.GetOrInsertNode(D))
+    Reader.getContext().setPrimaryMergedDecl(D, Existing->getCanonicalDecl());
+}
+
 void ASTDeclReader::VisitIndirectFieldDecl(IndirectFieldDecl *FD) {
   VisitValueDecl(FD);
 
   FD->ChainingSize = Record.readInt();
   assert(FD->ChainingSize >= 2 && "Anonymous chaining must be >= 2");
   FD->Chaining = new (Reader.getContext())NamedDecl*[FD->ChainingSize];
 
   for (unsigned I = 0; I != FD->ChainingSize; ++I)
case DECL_FILE_SCOPE_ASM:
     D = FileScopeAsmDecl::CreateDeserialized(Context, ID);
     break;
   case DECL_BLOCK:
     D = BlockDecl::CreateDeserialized(Context, ID);
     break;
   case DECL_MS_PROPERTY:
     D = MSPropertyDecl::CreateDeserialized(Context, ID);
     break;
+  case DECL_MS_GUID:
+    D = MSGuidDecl::CreateDeserialized(Context, ID);
+    break;
   case DECL_CAPTURED:
     D = CapturedDecl::CreateDeserialized(Context, ID, Record.readInt());
     break;
   case DECL_CXX_BASE_SPECIFIERS:
     Error("attempt to read a C++ base-specifier record as a declaration");
     return nullptr;
   case DECL_CXX_CTOR_INITIALIZERS:
     Error("attempt to read a C++ ctor initializer record as a declaration");

clang/lib/Serialization/ASTReaderStmt.cpp

void ASTStmtReader::VisitMSPropertySubscriptExpr(MSPropertySubscriptExpr *E) {
   E->setBase(Record.readSubExpr());
   E->setIdx(Record.readSubExpr());
   E->setRBracketLoc(readSourceLocation());
 }
 
 void ASTStmtReader::VisitCXXUuidofExpr(CXXUuidofExpr *E) {
   VisitExpr(E);
   E->setSourceRange(readSourceRange());
-  std::string UuidStr = readString();
-  E->setUuidStr(StringRef(UuidStr).copy(Record.getContext()));
+  E->Guid = readDeclAs<MSGuidDecl>();
   if (E->isTypeOperand())
     E->Operand = readTypeSourceInfo();
   else
     E->Operand = Record.readSubExpr();
 }
 
 void ASTStmtReader::VisitSEHLeaveStmt(SEHLeaveStmt *S) {
   VisitStmt(S);

clang/lib/Serialization/ASTWriter.cpp

ASTFileSignature ASTWriter::WriteASTCore(Sema &SemaRef, StringRef isysroot,
   RegisterPredefDecl(Context.Int128Decl, PREDEF_DECL_INT_128_ID);
   RegisterPredefDecl(Context.UInt128Decl, PREDEF_DECL_UNSIGNED_INT_128_ID);
   RegisterPredefDecl(Context.ObjCInstanceTypeDecl,
                      PREDEF_DECL_OBJC_INSTANCETYPE_ID);
   RegisterPredefDecl(Context.BuiltinVaListDecl, PREDEF_DECL_BUILTIN_VA_LIST_ID);
   RegisterPredefDecl(Context.VaListTagDecl, PREDEF_DECL_VA_LIST_TAG);
   RegisterPredefDecl(Context.BuiltinMSVaListDecl,
                      PREDEF_DECL_BUILTIN_MS_VA_LIST_ID);
+  RegisterPredefDecl(Context.MSGuidTagDecl,
+                     PREDEF_DECL_BUILTIN_MS_GUID_ID);
   RegisterPredefDecl(Context.ExternCContext, PREDEF_DECL_EXTERN_C_CONTEXT_ID);
   RegisterPredefDecl(Context.MakeIntegerSeqDecl,
                      PREDEF_DECL_MAKE_INTEGER_SEQ_ID);
   RegisterPredefDecl(Context.CFConstantStringTypeDecl,
                      PREDEF_DECL_CF_CONSTANT_STRING_ID);
   RegisterPredefDecl(Context.CFConstantStringTagDecl,
                      PREDEF_DECL_CF_CONSTANT_STRING_TAG_ID);
   RegisterPredefDecl(Context.TypePackElementDecl,

clang/lib/Serialization/ASTWriterDecl.cpp

public:
     void VisitFunctionDecl(FunctionDecl *D);
     void VisitCXXDeductionGuideDecl(CXXDeductionGuideDecl *D);
     void VisitCXXMethodDecl(CXXMethodDecl *D);
     void VisitCXXConstructorDecl(CXXConstructorDecl *D);
     void VisitCXXDestructorDecl(CXXDestructorDecl *D);
     void VisitCXXConversionDecl(CXXConversionDecl *D);
     void VisitFieldDecl(FieldDecl *D);
     void VisitMSPropertyDecl(MSPropertyDecl *D);
+    void VisitMSGuidDecl(MSGuidDecl *D);
     void VisitIndirectFieldDecl(IndirectFieldDecl *D);
     void VisitVarDecl(VarDecl *D);
     void VisitImplicitParamDecl(ImplicitParamDecl *D);
     void VisitParmVarDecl(ParmVarDecl *D);
     void VisitDecompositionDecl(DecompositionDecl *D);
     void VisitBindingDecl(BindingDecl *D);
     void VisitNonTypeTemplateParmDecl(NonTypeTemplateParmDecl *D);
     void VisitTemplateDecl(TemplateDecl *D);

 
 void ASTDeclWriter::VisitMSPropertyDecl(MSPropertyDecl *D) {
   VisitDeclaratorDecl(D);
   Record.AddIdentifierRef(D->getGetterId());
   Record.AddIdentifierRef(D->getSetterId());
   Code = serialization::DECL_MS_PROPERTY;
 }
 
+void ASTDeclWriter::VisitMSGuidDecl(MSGuidDecl *D) {
+  VisitValueDecl(D);
+  MSGuidDecl::Parts Parts = D->getParts();
+  Record.push_back(Parts.Part1);
+  Record.push_back(Parts.Part2);
+  Record.push_back(Parts.Part3);
+  for (auto C : Parts.Part4And5)
+    Record.push_back(C);
+  Code = serialization::DECL_MS_GUID;
+}
+
 void ASTDeclWriter::VisitIndirectFieldDecl(IndirectFieldDecl *D) {
   VisitValueDecl(D);
   Record.push_back(D->getChainingSize());
 
   for (const auto *P : D->chain())
     Record.AddDeclRef(P);
   Code = serialization::DECL_INDIRECTFIELD;
 }

clang/lib/Serialization/ASTWriterStmt.cpp

void ASTStmtWriter::VisitMSPropertySubscriptExpr(MSPropertySubscriptExpr *E) {
   Record.AddStmt(E->getIdx());
   Record.AddSourceLocation(E->getRBracketLoc());
   Code = serialization::EXPR_CXX_PROPERTY_SUBSCRIPT_EXPR;
 }
 
 void ASTStmtWriter::VisitCXXUuidofExpr(CXXUuidofExpr *E) {
   VisitExpr(E);
   Record.AddSourceRange(E->getSourceRange());
-  Record.AddString(E->getUuidStr());
+  Record.AddDeclRef(E->getGuidDecl());
   if (E->isTypeOperand()) {
     Record.AddTypeSourceInfo(E->getTypeOperandSourceInfo());
     Code = serialization::EXPR_CXX_UUIDOF_TYPE;
   } else {
     Record.AddStmt(E->getExprOperand());
     Code = serialization::EXPR_CXX_UUIDOF_EXPR;
   }
 }

clang/test/CodeGenCXX/debug-info-uuid.cpp

 // RUN: %clang_cc1 -emit-llvm -fms-extensions -triple=x86_64-pc-win32 -debug-info-kind=limited %s -o - -std=c++11 | FileCheck %s
 // RUN: %clang_cc1 -emit-llvm -fms-extensions -triple=x86_64-unknown-unknown -debug-info-kind=limited %s -o - -std=c++11 2>&1 | FileCheck %s --check-prefix=CHECK-ITANIUM
 
-// CHECK: !DICompositeType(tag: DW_TAG_structure_type, name: "tmpl_guid2<__uuidof(uuid)>"
+// CHECK: !DICompositeType(tag: DW_TAG_structure_type, name: "tmpl_guid2<GUID{12345678-1234-1234-1234-1234567890ab}>"
 // CHECK-SAME:             templateParams: [[TGI2ARGS:![0-9]*]]
 // CHECK: [[TGI2ARGS]] = !{[[TGI2ARG1:![0-9]*]]}
 // CHECK: [[TGI2ARG1]] = !DITemplateValueParameter(
 // CHECK-SAME:                                     type: [[CONST_GUID_REF:![0-9]*]]
-// CHECK-SAME:                                     value: { i32, i16, i16, [8 x i8] }* @_GUID_12345678_1234_1234_1234_1234567890ab
+// CHECK-SAME:                                     value: %struct._GUID* @_GUID_12345678_1234_1234_1234_1234567890ab
 // CHECK: [[CONST_GUID_REF]] = !DIDerivedType(tag: DW_TAG_reference_type,
 // CHECK-SAME:                                baseType: [[CONST_GUID:![0-9]*]]
 // CHECK: [[CONST_GUID]] = !DIDerivedType(tag: DW_TAG_const_type
 // CHECK-SAME:                            baseType: [[GUID:![0-9]*]]
 // CHECK: [[GUID]] = !DICompositeType(tag: DW_TAG_structure_type, name: "_GUID"
 
-// CHECK: !DICompositeType(tag: DW_TAG_structure_type, name: "tmpl_guid<&__uuidof(uuid)>"
+// CHECK: !DICompositeType(tag: DW_TAG_structure_type, name: "tmpl_guid<&GUID{12345678-1234-1234-1234-1234567890ab}>"
 // CHECK-SAME:             templateParams: [[TGIARGS:![0-9]*]]
 // CHECK: [[TGIARGS]] = !{[[TGIARG1:![0-9]*]]}
 // CHECK: [[TGIARG1]] = !DITemplateValueParameter(
 // CHECK-SAME:                                    type: [[CONST_GUID_PTR:![0-9]*]]
-// CHECK-SAME:                                    value: { i32, i16, i16, [8 x i8] }* @_GUID_12345678_1234_1234_1234_1234567890ab
+// CHECK-SAME:                                    value: %struct._GUID* @_GUID_12345678_1234_1234_1234_1234567890ab
 // CHECK: [[CONST_GUID_PTR]] = !DIDerivedType(tag: DW_TAG_pointer_type
 // CHECK-SAME:                                baseType: [[CONST_GUID:![0-9]*]]
 // CHECK-SAME:                                size: 64
 
-// CHECK-ITANIUM: !DICompositeType(tag: DW_TAG_structure_type, name: "tmpl_guid2<__uuidof(uuid)>"
-// CHECK-ITANIUM-SAME:             identifier: "_ZTS10tmpl_guid2IXu8__uuidoft4uuidEE"
-// CHECK-ITANIUM: !DICompositeType(tag: DW_TAG_structure_type, name: "tmpl_guid<&__uuidof(uuid)>"
-// CHECK-ITANIUM-SAME:             identifier: "_ZTS9tmpl_guidIXadu8__uuidoft4uuidEE"
+// CHECK-ITANIUM: !DICompositeType(tag: DW_TAG_structure_type, name: "tmpl_guid2<GUID{12345678-1234-1234-1234-1234567890ab}>"
+// CHECK-ITANIUM-SAME:             identifier: "_ZTS10tmpl_guid2IL_Z42_GUID_12345678_1234_1234_1234_1234567890abEE"
+// CHECK-ITANIUM: !DICompositeType(tag: DW_TAG_structure_type, name: "tmpl_guid<&GUID{12345678-1234-1234-1234-1234567890ab}>"
+// CHECK-ITANIUM-SAME:             identifier: "_ZTS9tmpl_guidIXadL_Z42_GUID_12345678_1234_1234_1234_1234567890abEEE"
 
-struct _GUID;
+struct _GUID {
+  __UINT32_TYPE__ a; __UINT16_TYPE__ b, c; __UINT8_TYPE__ d[8];
+};
 template <const _GUID *>
 struct tmpl_guid {
 };
 
 struct __declspec(uuid("{12345678-1234-1234-1234-1234567890ab}")) uuid;
 tmpl_guid<&__uuidof(uuid)> tgi;
 
 template <const _GUID &>
 struct tmpl_guid2 {};
 tmpl_guid2<__uuidof(uuid)> tgi2;

clang/test/CodeGenCXX/microsoft-templ-uuidof.cpp

 // RUN: %clang_cc1 -emit-llvm %s -o - -DDEFINE_GUID -triple=i386-pc-win32 -fms-extensions | FileCheck %s
 
-struct _GUID;
+struct _GUID {
+  __UINT32_TYPE__ a;
+  __UINT16_TYPE__ b, c;
+  __UINT8_TYPE__ d[8];
+};
 
 template <typename>
 struct X {
 };
 
 struct __declspec(uuid("{AAAAAAAA-AAAA-AAAA-AAAA-AAAAAAAAAAAA}")) A {};
 
 struct B {};

clang/test/CodeGenCXX/microsoft-uuidof-mangling.cpp

public:
   UUIDTest() { }
 };
 
 struct __declspec(uuid("EAFA1952-66F8-438B-8FBA-AF1BBAE42191")) TestStruct
 {
   int foo;
 };
 
+struct __declspec(uuid("EAFA1952-66F8-438B-8FBA-AF1BBAE42191")) OtherStruct {};
+
 template <class T> void test_uuidofType(void *arg[sizeof(__uuidof(T))] = 0) {}
 
 template <class T> void test_uuidofExpr(void *arg[sizeof(__uuidof(typename T::member))] = 0) {}
 
 struct HasMember { typedef TestStruct member; };
 
+template<const GUID&> struct UUIDTestTwo { UUIDTestTwo(); };
+
 int main(int argc, const char * argv[])
 {
-
     UUIDTest<TestStruct> uuidof_test;
+    // Note that these variables have the same type, so the mangling of that
+    // type had better not mention TestStruct or OtherStruct!
+    UUIDTestTwo<__uuidof(TestStruct)> uuidof_test2;
+    UUIDTestTwo<__uuidof(OtherStruct)> uuidof_test3;
     test_uuidofType<TestStruct>();
     test_uuidofExpr<HasMember>();
     return 0;
 }
 
 // CHECK: define i32 @main
-// CHECK: call void @_ZN8UUIDTestI10TestStructXu8__uuidoftS0_EEC1Ev
+// CHECK: call void @_ZN8UUIDTestI10TestStructL_Z42_GUID_eafa1952_66f8_438b_8fba_af1bbae42191EEC1Ev
+// CHECK: call void @_ZN11UUIDTestTwoIL_Z42_GUID_eafa1952_66f8_438b_8fba_af1bbae42191EEC1Ev
+// CHECK: call void @_ZN11UUIDTestTwoIL_Z42_GUID_eafa1952_66f8_438b_8fba_af1bbae42191EEC1Ev
 // CHECK: call void @_Z15test_uuidofTypeI10TestStructEvPPv(i8** null)
 // CHECK: call void @_Z15test_uuidofExprI9HasMemberEvPPv(i8** null)
 
-// CHECK: define linkonce_odr void @_ZN8UUIDTestI10TestStructXu8__uuidoftS0_EEC1Ev
+// CHECK: define linkonce_odr void @_ZN8UUIDTestI10TestStructL_Z42_GUID_eafa1952_66f8_438b_8fba_af1bbae42191EEC1Ev
 // CHECK: define linkonce_odr void @_Z15test_uuidofTypeI10TestStructEvPPv
 // CHECK: define linkonce_odr void @_Z15test_uuidofExprI9HasMemberEvPPv
-// CHECK: define linkonce_odr void @_ZN8UUIDTestI10TestStructXu8__uuidoftS0_EEC2Ev
+// CHECK: define linkonce_odr void @_ZN8UUIDTestI10TestStructL_Z42_GUID_eafa1952_66f8_438b_8fba_af1bbae42191EEC2Ev

clang/test/CodeGenCXX/microsoft-uuidof.cpp

 [uuid({12345678-1234-1234-1234-1234567890ac})] struct Curly;
 #else
 struct __declspec(uuid("12345678-1234-1234-1234-1234567890aB")) S1 { } s1;
 struct __declspec(uuid("87654321-4321-4321-4321-ba0987654321")) S2 { };
 struct __declspec(uuid("{12345678-1234-1234-1234-1234567890ac}")) Curly;
 struct __declspec(uuid("{12345678-1234-1234-1234-1234567890ac}")) Curly;
 #endif
 
+void side_effect();
+
 #ifdef DEFINE_GUID
 // Make sure we can properly generate code when the UUID has curly braces on it.
-GUID thing = __uuidof(Curly);
+GUID thing = (side_effect(), __uuidof(Curly));
 // CHECK-DEFINE-GUID: @thing = global %struct._GUID zeroinitializer, align 4
 // CHECK-DEFINE-WRONG-GUID: @thing = global %struct._GUID zeroinitializer, align 4
 
 // This gets initialized in a static initializer.
 // CHECK-DEFINE-GUID: @g = global %struct._GUID zeroinitializer, align 4
 // CHECK-DEFINE-WRONG-GUID: @g = global %struct._GUID zeroinitializer, align 4
-GUID g = __uuidof(S1);
+GUID g = (side_effect(), __uuidof(S1));
+
+// CHECK-DEFINE-GUID: @const_init = global %struct._GUID { i32 305419896, i16 4660, i16 4660, [8 x i8] c"\124\124Vx\90\AC" }
+// CHECK-DEFINE-WRONG-GUID: @const_init = global %struct._GUID zeroinitializer
+GUID const_init = __uuidof(Curly);
 #endif
 
 // First global use of __uuidof(S1) forces the creation of the global.
 // CHECK: @_GUID_12345678_1234_1234_1234_1234567890ab = linkonce_odr constant { i32, i16, i16, [8 x i8] } { i32 305419896, i16 4660, i16 4660, [8 x i8] c"\124\124Vx\90\AB" }, comdat
 // CHECK: @gr = constant %struct._GUID* bitcast ({ i32, i16, i16, [8 x i8] }* @_GUID_12345678_1234_1234_1234_1234567890ab to %struct._GUID*), align 4
 // CHECK-64: @gr = constant %struct._GUID* bitcast ({ i32, i16, i16, [8 x i8] }* @_GUID_12345678_1234_1234_1234_1234567890ab to %struct._GUID*), align 8
 const GUID& gr = __uuidof(S1);
 
 // CHECK: @gp = global %struct._GUID* bitcast ({ i32, i16, i16, [8 x i8] }* @_GUID_12345678_1234_1234_1234_1234567890ab to %struct._GUID*), align 4
 const GUID* gp = &__uuidof(S1);
 
 // CHECK: @cp = global %struct._GUID* bitcast ({ i32, i16, i16, [8 x i8] }* @_GUID_12345678_1234_1234_1234_1234567890ac to %struct._GUID*), align 4
 const GUID* cp = &__uuidof(Curly);
 
 // Special case: _uuidof(0)
 // CHECK: @zeroiid = constant %struct._GUID* bitcast ({ i32, i16, i16, [8 x i8] }* @_GUID_00000000_0000_0000_0000_000000000000 to %struct._GUID*), align 4
 const GUID& zeroiid = __uuidof(0);
 
 // __uuidof(S2) hasn't been used globally yet, so it's emitted when it's used
 // in a function and is emitted at the end of the globals section.
 // CHECK: @_GUID_87654321_4321_4321_4321_ba0987654321 = linkonce_odr constant { i32, i16, i16, [8 x i8] } { i32 -2023406815, i16 17185, i16 17185, [8 x i8] c"C!\BA\09\87eC!" }, comdat
 
 // The static initializer for thing.
-// CHECK-DEFINE-GUID: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 bitcast (%struct._GUID* @thing to i8*), i8* align 4 bitcast ({ i32, i16, i16, [8 x i8] }* @_GUID_12345678_1234_1234_1234_1234567890ac to i8*), i32 16, i1 false)
+// CHECK-DEFINE-GUID: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 bitcast (%struct._GUID* @thing to i8*), i8* align 4 bitcast (%struct._GUID* @_GUID_12345678_1234_1234_1234_1234567890ac to i8*), i32 16, i1 false)
 // CHECK-DEFINE-WRONG-GUID: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 bitcast (%struct._GUID* @thing to i8*), i8* align 4 bitcast ({ i32, i16, i16, [8 x i8] }* @_GUID_12345678_1234_1234_1234_1234567890ac to i8*), i32 4, i1 false)
 
 // The static initializer for g.
-// CHECK-DEFINE-GUID: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 bitcast (%struct._GUID* @g to i8*), i8* align 4 bitcast ({ i32, i16, i16, [8 x i8] }* @_GUID_12345678_1234_1234_1234_1234567890ab to i8*), i32 16, i1 false)
+// CHECK-DEFINE-GUID: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 bitcast (%struct._GUID* @g to i8*), i8* align 4 bitcast (%struct._GUID* @_GUID_12345678_1234_1234_1234_1234567890ab to i8*), i32 16, i1 false)
 // CHECK-DEFINE-WRONG-GUID: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 bitcast (%struct._GUID* @g to i8*), i8* align 4 bitcast ({ i32, i16, i16, [8 x i8] }* @_GUID_12345678_1234_1234_1234_1234567890ab to i8*), i32 4, i1 false)
 
+// We don't constant-initialize const_init if the definition of _GUID is dodgy.
+// CHECK-DEFINE-GUID-NOT: @const_init
+// CHECK-DEFINE-WRONG-GUID: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 bitcast (%struct._GUID* @const_init to i8*), i8* align 4 bitcast ({ i32, i16, i16, [8 x i8] }* @_GUID_12345678_1234_1234_1234_1234567890ac to i8*), i32 4, i1 false)
+
 #ifdef DEFINE_GUID
 void fun() {
   // CHECK-DEFINE-GUID: %s1_1 = alloca %struct._GUID, align 4
   // CHECK-DEFINE-WRONG-GUID: %s1_1 = alloca %struct._GUID, align 4
   // CHECK-DEFINE-GUID: %s1_2 = alloca %struct._GUID, align 4
   // CHECK-DEFINE-WRONG-GUID: %s1_2 = alloca %struct._GUID, align 4
   // CHECK-DEFINE-GUID: %s1_3 = alloca %struct._GUID, align 4
   // CHECK-DEFINE-WRONG-GUID: %s1_3 = alloca %struct._GUID, align 4
 
   // CHECK-DEFINE-GUID: [[U1:%.+]] = bitcast %struct._GUID* %s1_1 to i8*
   // CHECK-DEFINE-WRONG-GUID: [[U1:%.+]] = bitcast %struct._GUID* %s1_1 to i8*
-  // CHECK-DEFINE-GUID: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 [[U1]], i8* align 4 bitcast ({ i32, i16, i16, [8 x i8] }* @_GUID_12345678_1234_1234_1234_1234567890ab to i8*), i32 16, i1 false)
+  // CHECK-DEFINE-GUID: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 [[U1]], i8* align 4 bitcast (%struct._GUID* @_GUID_12345678_1234_1234_1234_1234567890ab to i8*), i32 16, i1 false)
   // CHECK-DEFINE-WRONG-GUID: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 [[U1]], i8* align 4 bitcast ({ i32, i16, i16, [8 x i8] }* @_GUID_12345678_1234_1234_1234_1234567890ab to i8*), i32 4, i1 false)
-  GUID s1_1 = __uuidof(S1);
+  GUID s1_1 = (side_effect(), __uuidof(S1));
 
   // CHECK-DEFINE-GUID: [[U2:%.+]] = bitcast %struct._GUID* %s1_2 to i8*
   // CHECK-DEFINE-WRONG-GUID: [[U2:%.+]] = bitcast %struct._GUID* %s1_2 to i8*
-  // CHECK-DEFINE-GUID: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 [[U2]], i8* align 4 bitcast ({ i32, i16, i16, [8 x i8] }* @_GUID_12345678_1234_1234_1234_1234567890ab to i8*), i32 16, i1 false)
+  // CHECK-DEFINE-GUID: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 [[U2]], i8* align 4 bitcast (%struct._GUID* @_GUID_12345678_1234_1234_1234_1234567890ab to i8*), i32 16, i1 false)
   // CHECK-DEFINE-WRONG-GUID: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 [[U2]], i8* align 4 bitcast ({ i32, i16, i16, [8 x i8] }* @_GUID_12345678_1234_1234_1234_1234567890ab to i8*), i32 4, i1 false)
-  GUID s1_2 = __uuidof(S1);
+  GUID s1_2 = (side_effect(), __uuidof(S1));
 
   // CHECK-DEFINE-GUID: [[U3:%.+]] = bitcast %struct._GUID* %s1_3 to i8*
   // CHECK-DEFINE-WRONG-GUID: [[U3:%.+]] = bitcast %struct._GUID* %s1_3 to i8*
-  // CHECK-DEFINE-GUID: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 [[U3]], i8* align 4 bitcast ({ i32, i16, i16, [8 x i8] }* @_GUID_12345678_1234_1234_1234_1234567890ab to i8*), i32 16, i1 false)
+  // CHECK-DEFINE-GUID: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 [[U3]], i8* align 4 bitcast (%struct._GUID* @_GUID_12345678_1234_1234_1234_1234567890ab to i8*), i32 16, i1 false)
   // CHECK-DEFINE-WRONG-GUID: call void @llvm.memcpy.p0i8.p0i8.i32(i8* align 4 [[U3]], i8* align 4 bitcast ({ i32, i16, i16, [8 x i8] }* @_GUID_12345678_1234_1234_1234_1234567890ab to i8*), i32 4, i1 false)
-  GUID s1_3 = __uuidof(s1);
+  GUID s1_3 = (side_effect(), __uuidof(s1));
 }
 #endif
 
 void gun() {
 #ifdef DEFINE_GUID
   // CHECK-DEFINE-GUID: %s2_1 = alloca %struct._GUID, align 4
   // CHECK-DEFINE-WRONG-GUID: %s2_1 = alloca %struct._GUID, align 4
   // CHECK-DEFINE-GUID: %s2_2 = alloca %struct._GUID, align 4
#endif
   const GUID& r = __uuidof(S2);
   // CHECK: store %struct._GUID* bitcast ({ i32, i16, i16, [8 x i8] }* @_GUID_87654321_4321_4321_4321_ba0987654321 to %struct._GUID*), %struct._GUID** %p, align 4
   const GUID* p = &__uuidof(S2);
 
   // Special case _uuidof(0), local scope version.
   // CHECK: store %struct._GUID* bitcast ({ i32, i16, i16, [8 x i8] }* @_GUID_00000000_0000_0000_0000_000000000000 to %struct._GUID*), %struct._GUID** %zeroiid, align 4
   const GUID& zeroiid = __uuidof(0);
 }
+
+namespace DeclRefExprNamingGUID {
+  template<const _GUID &g> const _GUID &f() { return g; }
+  struct __declspec(uuid("12345678-1234-1234-1234-123412341234")) S {};
+  auto &r = f<__uuidof(S)>();
+}

clang/test/Parser/MicrosoftExtensions.cpp

public:
   {
   }
 };
 
 
 
 void uuidof_test1()
 {
-  __uuidof(0);  // expected-error {{you need to include <guiddef.h> before using the '__uuidof' operator}}
+  __uuidof(0);
 }
 
 typedef struct _GUID
 {
     unsigned long  Data1;
     unsigned short Data2;
     unsigned short Data3;
     unsigned char  Data4[8];
typedef COM_CLASS_TEMPLATE_REF<struct_with_uuid, __uuidof(struct_with_uuid)> COM_TYPE_REF;
   template<typename T>
   void test_late_defined_uuid() {
     __uuidof(late_defined_uuid);
   }
   struct __declspec(uuid("000000A0-0000-0000-C000-000000000049")) late_defined_uuid;
 
 COM_CLASS_TEMPLATE_REF<int, __uuidof(struct_with_uuid)> good_template_arg;
 
-COM_CLASS_TEMPLATE<int, __uuidof(struct_with_uuid)> bad_template_arg; // expected-error {{non-type template argument of type 'const _GUID' is not a constant expression}}
-// expected-note@-1 {{read of object '__uuidof(struct_with_uuid)' whose value is not known}}
-// expected-note@-2 {{temporary created here}}
+COM_CLASS_TEMPLATE<int, __uuidof(struct_with_uuid)> bad_template_arg; // expected-error {{non-type template argument for template parameter of pointer type 'const GUID *' (aka 'const _GUID *') must have its address taken}}
 
 namespace PR16911 {
 struct __declspec(uuid("{12345678-1234-1234-1234-1234567890aB}")) uuid;
 struct __declspec(uuid("{12345678-1234-1234-1234-1234567890aB}")) uuid2;
 
 template <typename T, typename T2>
 struct thing {
 };

clang/test/SemaCXX/ms-uuid.cpp

 // RUN: %clang_cc1 -fsyntax-only -verify -fms-extensions %s -Wno-deprecated-declarations
 // RUN: %clang_cc1 -fsyntax-only -std=c++17 -verify -fms-extensions %s -Wno-deprecated-declarations
 
 typedef struct _GUID {
-  unsigned long Data1;
-  unsigned short Data2;
-  unsigned short Data3;
-  unsigned char Data4[8];
+  __UINT32_TYPE__ Data1;
+  __UINT16_TYPE__ Data2;
+  __UINT16_TYPE__ Data3;
+  __UINT8_TYPE__ Data4[8];
 } GUID;
 
 namespace {
 // cl.exe's behavior with merging uuid attributes is a bit erratic:
 // * In []-style attributes, a single [] list must not list a duplicate uuid
 //   (even if it's the same uuid), and only a single declaration of a class
 //   must have a uuid else the compiler errors out (even if two declarations of
 //   a class have the same uuid).

 }
 
 }
 
 // Test class/struct redeclaration where the subsequent
 // declaration has a uuid attribute
 struct X{};
 
-struct __declspec(uuid("00000000-0000-0000-0000-000000000000")) X;
+struct __declspec(uuid("00000000-0000-0000-0000-000000000000")) X;
+
+namespace ConstantEvaluation {
+  class __declspec(uuid("1babb1ed-feed-c01d-1ced-decafc0ffee5")) Request;
+  constexpr GUID a = __uuidof(Request);
+  static_assert(a.Data1 == 0x1babb1ed, "");
+  static_assert(__uuidof(Request).Data1 == 0x1babb1ed, "");
+  static_assert(a.Data2 == 0xfeed, "");
+  static_assert(__uuidof(Request).Data2 == 0xfeed, "");
+  static_assert(a.Data3 == 0xc01d, "");
+  static_assert(__uuidof(Request).Data3 == 0xc01d, "");
+  static_assert(a.Data4[0] == 0x1c, "");
+  static_assert(__uuidof(Request).Data4[0] == 0x1c, "");
+  static_assert(a.Data4[1] == 0xed, "");
+  static_assert(__uuidof(Request).Data4[1] == 0xed, "");
+  static_assert(a.Data4[2] == 0xde, "");
+  static_assert(__uuidof(Request).Data4[2] == 0xde, "");
+  static_assert(a.Data4[7] == 0xe5, "");
+  static_assert(__uuidof(Request).Data4[7] == 0xe5, "");
+  constexpr int k = __uuidof(Request).Data4[8]; // expected-error {{constant expression}} expected-note {{past-the-end}}
+}

clang/tools/libclang/CIndex.cpp

CXCursor clang_getCursorDefinition(CXCursor C) {
   case Decl::Typedef:
   case Decl::TypeAlias:
   case Decl::TypeAliasTemplate:
   case Decl::TemplateTypeParm:
   case Decl::EnumConstant:
   case Decl::Field:
   case Decl::Binding:
   case Decl::MSProperty:
+  case Decl::MSGuid:
   case Decl::IndirectField:
   case Decl::ObjCIvar:
   case Decl::ObjCAtDefsField:
   case Decl::ImplicitParam:
   case Decl::ParmVar:
   case Decl::NonTypeTemplateParm:
   case Decl::TemplateTemplateParm:
   case Decl::ObjCCategoryImpl: