MS ABI: Implement copy-ctor closures, finish implementing throw

[majnemer]

Summary

This adds support for copy-constructor closures. These are generated
when the C++ runtime has to call a copy-constructor with a particular
calling convention or with default arguments substituted in to the call.

Because the runtime has no mechanism to call the function with a
different calling convention or know-how to evaluate the default
arguments at run-time, we create a thunk which will do all the
appropriate work and package it in a way the runtime can use.

[rnk]

lib/AST/MicrosoftMangle.cpp

790

Keep the Ctor_Complete assertion to avoid decl mangling collisions?

lib/CodeGen/MicrosoftCXXABI.cpp

3332–3335

Surely this can be:

CD->getType()->getAs<FunctionType>()->getCallConv()?

Does the canonical unqualified type step matter in practice?

3336

Can you test the calling convention difference case and the variadic case?

lib/Sema/SemaExprCXX.cpp

829

I can see that you need to call BuildCXXDefautlArgExpr to do all the necessary semantic checking, but is it really necessary to maintain a map of all the CXXDefaultArgExprs, rather than simply calling ParmVarDecl::getDefaultArgExpr() during CodeGen?

[majnemer]

lib/AST/MicrosoftMangle.cpp

790

That assertion was never like because Structor was always null for constructors. This assertion is actually wrong in practice because Ctor_Base can happen and weakening the assertion doesn't seem very useful.

lib/CodeGen/MicrosoftCXXABI.cpp

3332–3335

Done.

3336

The different calling convention case is the variadic case.

A test for the variadic case has been added.

lib/Sema/SemaExprCXX.cpp

829

Yes because the we won't have an instantiated default argument at CodeGen-time, just the dependent one which won't be suitable.

[majnemer]

• Addressed review comments.

[rnk]

include/clang/Basic/ABI.h

27–28

I'm not super psyched about adding to this enum. What do you think about adding custom entry points to the MS C++ ABI that just tweak internal bools?

lib/AST/MicrosoftMangle.cpp

772–773

Oh dear, does isCopyConstructor() return false for the variadic test case?

[rnk]

lgtm

include/clang/Basic/ABI.h

27–28

Sure, if we think of this as just an enum of different constructor manglings, then I guess this is OK.

test/CodeGenCXX/microsoft-abi-throw.cpp

58

Maybe s/Bad/DoubleDefault/?

include/clang/AST/ASTContext.h

public:
   bool DeclMustBeEmitted(const Decl *D);
 
   const CXXConstructorDecl *
   getCopyConstructorForExceptionObject(CXXRecordDecl *RD);
 
   void addCopyConstructorForExceptionObject(CXXRecordDecl *RD,
                                             CXXConstructorDecl *CD);
 
+  void addDefaultArgExprForConstructor(const CXXConstructorDecl *CD,
+                                       unsigned ParmIdx, Expr *DAE);
+
+  Expr *getDefaultArgExprForConstructor(const CXXConstructorDecl *CD,
+                                        unsigned ParmIdx);
+
   void setManglingNumber(const NamedDecl *ND, unsigned Number);
   unsigned getManglingNumber(const NamedDecl *ND) const;
 
   void setStaticLocalNumber(const VarDecl *VD, unsigned Number);
   unsigned getStaticLocalNumber(const VarDecl *VD) const;
 
   /// \brief Retrieve the context for computing mangling numbers in the given
   /// DeclContext.

include/clang/AST/Mangle.h

public:
 
   virtual void mangleCXXThrowInfo(QualType T, bool IsConst, bool IsVolatile,
                                   uint32_t NumEntries, raw_ostream &Out) = 0;
 
   virtual void mangleCXXCatchableTypeArray(QualType T, uint32_t NumEntries,
                                            raw_ostream &Out) = 0;
 
   virtual void mangleCXXCatchableType(QualType T, const CXXConstructorDecl *CD,
-                                      uint32_t Size, uint32_t NVOffset,
-                                      int32_t VBPtrOffset, uint32_t VBIndex,
-                                      raw_ostream &Out) = 0;
+                                      CXXCtorType CT, uint32_t Size,
+                                      uint32_t NVOffset, int32_t VBPtrOffset,
+                                      uint32_t VBIndex, raw_ostream &Out) = 0;
 
   virtual void mangleCXXRTTIBaseClassDescriptor(
       const CXXRecordDecl *Derived, uint32_t NVOffset, int32_t VBPtrOffset,
       uint32_t VBTableOffset, uint32_t Flags, raw_ostream &Out) = 0;
 
   virtual void mangleCXXRTTIBaseClassArray(const CXXRecordDecl *Derived,
                                            raw_ostream &Out) = 0;
   virtual void

include/clang/Basic/ABI.h

 #define LLVM_CLANG_BASIC_ABI_H
 
 #include "llvm/Support/DataTypes.h"
 
 namespace clang {
 
 /// \brief C++ constructor types.
 enum CXXCtorType {
-    Ctor_Complete,          ///< Complete object ctor
-    Ctor_Base,              ///< Base object ctor
-    Ctor_Comdat             ///< The COMDAT used for ctors
+  Ctor_Complete, ///< Complete object ctor
+  Ctor_Base,     ///< Base object ctor
+  Ctor_Comdat,   ///< The COMDAT used for ctors
+  Ctor_Closure,  ///< Closure variant of a ctor
 };
 
 /// \brief C++ destructor types.
 enum CXXDtorType {
     Dtor_Deleting, ///< Deleting dtor
     Dtor_Complete, ///< Complete object dtor
     Dtor_Base,     ///< Base object dtor
     Dtor_Comdat    ///< The COMDAT used for dtors

lib/AST/ASTContext.cpp

 
 void ASTContext::addCopyConstructorForExceptionObject(CXXRecordDecl *RD,
                                                       CXXConstructorDecl *CD) {
   return ABI->addCopyConstructorForExceptionObject(
       cast<CXXRecordDecl>(RD->getFirstDecl()),
       cast<CXXConstructorDecl>(CD->getFirstDecl()));
 }
 
+void ASTContext::addDefaultArgExprForConstructor(const CXXConstructorDecl *CD,
+                                                 unsigned ParmIdx, Expr *DAE) {
+  ABI->addDefaultArgExprForConstructor(
+      cast<CXXConstructorDecl>(CD->getFirstDecl()), ParmIdx, DAE);
+}
+
+Expr *ASTContext::getDefaultArgExprForConstructor(const CXXConstructorDecl *CD,
+                                                  unsigned ParmIdx) {
+  return ABI->getDefaultArgExprForConstructor(
+      cast<CXXConstructorDecl>(CD->getFirstDecl()), ParmIdx);
+}
+
 void ASTContext::setParameterIndex(const ParmVarDecl *D, unsigned int index) {
   ParamIndices[D] = index;
 }
 
 unsigned ASTContext::getParameterIndex(const ParmVarDecl *D) const {
   ParameterIndexTable::const_iterator I = ParamIndices.find(D);
   assert(I != ParamIndices.end() && 
          "ParmIndices lacks entry set by ParmVarDecl");

lib/AST/CXXABI.h

 #define LLVM_CLANG_LIB_AST_CXXABI_H
 
 #include "clang/AST/Type.h"
 
 namespace clang {
 
 class ASTContext;
 class CXXConstructorDecl;
+class Expr;
 class MemberPointerType;
 class MangleNumberingContext;
 
 /// Implements C++ ABI-specific semantic analysis functions.
 class CXXABI {
 public:
   virtual ~CXXABI();
 
public:
 
   /// Adds a mapping from class to copy constructor for this C++ ABI.
   virtual void addCopyConstructorForExceptionObject(CXXRecordDecl *,
                                                     CXXConstructorDecl *) = 0;
 
   /// Retrieves the mapping from class to copy constructor for this C++ ABI.
   virtual const CXXConstructorDecl *
   getCopyConstructorForExceptionObject(CXXRecordDecl *) = 0;
+
+  virtual void addDefaultArgExprForConstructor(const CXXConstructorDecl *CD,
+                                               unsigned ParmIdx, Expr *DAE) = 0;
+
+  virtual Expr *getDefaultArgExprForConstructor(const CXXConstructorDecl *CD,
+                                                unsigned ParmIdx) = 0;
 };
 
 /// Creates an instance of a C++ ABI class.
 CXXABI *CreateItaniumCXXABI(ASTContext &Ctx);
 CXXABI *CreateMicrosoftCXXABI(ASTContext &Ctx);
 }
 
 #endif

lib/AST/ItaniumCXXABI.cpp

public:
   const CXXConstructorDecl *
   getCopyConstructorForExceptionObject(CXXRecordDecl *RD) override {
     return nullptr;
   }
 
   void addCopyConstructorForExceptionObject(CXXRecordDecl *RD,
                                             CXXConstructorDecl *CD) override {}
 
+  void addDefaultArgExprForConstructor(const CXXConstructorDecl *CD,
+                                       unsigned ParmIdx, Expr *DAE) override {}
+
+  Expr *getDefaultArgExprForConstructor(const CXXConstructorDecl *CD,
+                                        unsigned ParmIdx) override {
+    return nullptr;
+  }
+
   MangleNumberingContext *createMangleNumberingContext() const override {
     return new ItaniumNumberingContext();
   }
 };
 }
 
 CXXABI *clang::CreateItaniumCXXABI(ASTContext &Ctx) {
   return new ItaniumCXXABI(Ctx);
 }

lib/AST/ItaniumMangle.cpp

case Ctor_Complete:
     Out << "C1";
     break;
   case Ctor_Base:
     Out << "C2";
     break;
   case Ctor_Comdat:
     Out << "C5";
     break;
+  case Ctor_Closure:
+    llvm_unreachable("closure constructors don't exist for the Itanium ABI!");
   }
 }
 
 void CXXNameMangler::mangleCXXDtorType(CXXDtorType T) {
   // <ctor-dtor-name> ::= D0  # deleting destructor
   //                  ::= D1  # complete object destructor
   //                  ::= D2  # base object destructor
   //

lib/AST/MicrosoftCXXABI.cpp

unsigned getManglingNumber(const TagDecl *TD,
                              unsigned MSLocalManglingNumber) override {
     return MSLocalManglingNumber;
   }
 };
 
 class MicrosoftCXXABI : public CXXABI {
   ASTContext &Context;
   llvm::SmallDenseMap<CXXRecordDecl *, CXXConstructorDecl *> RecordToCopyCtor;
+  llvm::SmallDenseMap<std::pair<const CXXConstructorDecl *, unsigned>, Expr *>
+      CtorToDefaultArgExpr;
 
 public:
   MicrosoftCXXABI(ASTContext &Ctx) : Context(Ctx) { }
 
   std::pair<uint64_t, unsigned>
   getMemberPointerWidthAndAlign(const MemberPointerType *MPT) const override;
 
   CallingConv getDefaultMethodCallConv(bool isVariadic) const override {
bool isNearlyEmpty(const CXXRecordDecl *RD) const override {
 
     // In the Microsoft ABI, classes can have one or two vtable pointers.
     CharUnits PointerSize =
         Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(0));
     return Layout.getNonVirtualSize() == PointerSize ||
       Layout.getNonVirtualSize() == PointerSize * 2;
   }
 
+  void addDefaultArgExprForConstructor(const CXXConstructorDecl *CD,
+                                       unsigned ParmIdx, Expr *DAE) override {
+    CtorToDefaultArgExpr[std::make_pair(CD, ParmIdx)] = DAE;
+  }
+
+  Expr *getDefaultArgExprForConstructor(const CXXConstructorDecl *CD,
+                                        unsigned ParmIdx) override {
+    return CtorToDefaultArgExpr[std::make_pair(CD, ParmIdx)];
+  }
+
   const CXXConstructorDecl *
   getCopyConstructorForExceptionObject(CXXRecordDecl *RD) override {
     return RecordToCopyCtor[RD];
   }
 
   void
   addCopyConstructorForExceptionObject(CXXRecordDecl *RD,
                                        CXXConstructorDecl *CD) override {

lib/AST/MicrosoftMangle.cpp

public:
   void mangleCXXVBTable(const CXXRecordDecl *Derived,
                         ArrayRef<const CXXRecordDecl *> BasePath,
                         raw_ostream &Out) override;
   void mangleCXXThrowInfo(QualType T, bool IsConst, bool IsVolatile,
                           uint32_t NumEntries, raw_ostream &Out) override;
   void mangleCXXCatchableTypeArray(QualType T, uint32_t NumEntries,
                                    raw_ostream &Out) override;
   void mangleCXXCatchableType(QualType T, const CXXConstructorDecl *CD,
-                              uint32_t Size, uint32_t NVOffset,
+                              CXXCtorType CT, uint32_t Size, uint32_t NVOffset,
                               int32_t VBPtrOffset, uint32_t VBIndex,
                               raw_ostream &Out) override;
   void mangleCXXRTTI(QualType T, raw_ostream &Out) override;
   void mangleCXXRTTIName(QualType T, raw_ostream &Out) override;
   void mangleCXXRTTIBaseClassDescriptor(const CXXRecordDecl *Derived,
                                         uint32_t NVOffset, int32_t VBPtrOffset,
                                         uint32_t VBTableOffset, uint32_t Flags,
                                         raw_ostream &Out) override;
public:
   enum QualifierMangleMode { QMM_Drop, QMM_Mangle, QMM_Escape, QMM_Result };
 
   MicrosoftCXXNameMangler(MicrosoftMangleContextImpl &C, raw_ostream &Out_)
       : Context(C), Out(Out_), Structor(nullptr), StructorType(-1),
         PointersAre64Bit(C.getASTContext().getTargetInfo().getPointerWidth(0) ==
                          64) {}
 
   MicrosoftCXXNameMangler(MicrosoftMangleContextImpl &C, raw_ostream &Out_,
+                          const CXXConstructorDecl *D, CXXCtorType Type)
+      : Context(C), Out(Out_), Structor(getStructor(D)), StructorType(Type),
+        PointersAre64Bit(C.getASTContext().getTargetInfo().getPointerWidth(0) ==
+                         64) {}
+
+  MicrosoftCXXNameMangler(MicrosoftMangleContextImpl &C, raw_ostream &Out_,
                           const CXXDestructorDecl *D, CXXDtorType Type)
       : Context(C), Out(Out_), Structor(getStructor(D)), StructorType(Type),
         PointersAre64Bit(C.getASTContext().getTargetInfo().getPointerWidth(0) ==
                          64) {}
 
   raw_ostream &getStream() const { return Out; }
 
   void mangle(const NamedDecl *D, StringRef Prefix = "\01?");

 #undef ABSTRACT_TYPE
 #undef NON_CANONICAL_TYPE
 #undef TYPE
 
   void mangleType(const TagDecl *TD);
   void mangleDecayedArrayType(const ArrayType *T);
   void mangleArrayType(const ArrayType *T);
   void mangleFunctionClass(const FunctionDecl *FD);
+  void mangleCallingConvention(CallingConv CC);
   void mangleCallingConvention(const FunctionType *T);
   void mangleIntegerLiteral(const llvm::APSInt &Number, bool IsBoolean);
   void mangleExpression(const Expr *E);
   void mangleThrowSpecification(const FunctionProtoType *T);
 
   void mangleTemplateArgs(const TemplateDecl *TD,
                           const TemplateArgumentList &TemplateArgs);
   void mangleTemplateArg(const TemplateDecl *TD, const TemplateArgument &TA,
case DeclarationName::Identifier: {
       break;
     }
 
     case DeclarationName::ObjCZeroArgSelector:
     case DeclarationName::ObjCOneArgSelector:
     case DeclarationName::ObjCMultiArgSelector:
       llvm_unreachable("Can't mangle Objective-C selector names here!");
 
     case DeclarationName::CXXConstructorName:
-      if (ND == Structor) {
-        assert(StructorType == Ctor_Complete &&
-               "Should never be asked to mangle a ctor other than complete");
+      if (Structor == ND && StructorType == Ctor_Closure) {
+        const auto *CD = cast<CXXConstructorDecl>(ND);
+        if (CD->isDefaultConstructor()) {
+          Out << "?_F";
+        } else if (CD->isCopyConstructor()) {
+          Out << "?_O";
+        } else {
+          llvm_unreachable("unexpected constructor closure!");
         }
+      } else {
         Out << "?0";
+      }
       break;
 
     case DeclarationName::CXXDestructorName:
       if (ND == Structor)
         // If the named decl is the C++ destructor we're mangling,
         // use the type we were given.
         mangleCXXDtorType(static_cast<CXXDtorType>(StructorType));
       else
void MicrosoftCXXNameMangler::mangleFunctionType(const FunctionType *T,
                                                  bool ForceThisQuals) {
   // <function-type> ::= <this-cvr-qualifiers> <calling-convention>
   //                     <return-type> <argument-list> <throw-spec>
   const FunctionProtoType *Proto = cast<FunctionProtoType>(T);
 
   SourceRange Range;
   if (D) Range = D->getSourceRange();
 
-  bool IsStructor = false, HasThisQuals = ForceThisQuals;
+  bool IsStructor = false, HasThisQuals = ForceThisQuals, IsCtorClosure = false;
+  CallingConv CC = T->getCallConv();
   if (const CXXMethodDecl *MD = dyn_cast_or_null<CXXMethodDecl>(D)) {
     if (MD->isInstance())
       HasThisQuals = true;
-    if (isa<CXXConstructorDecl>(MD) || isa<CXXDestructorDecl>(MD))
+    if (isa<CXXDestructorDecl>(MD)) {
+      IsStructor = true;
+    } else if (isa<CXXConstructorDecl>(MD)) {
       IsStructor = true;
+      IsCtorClosure = MD == Structor && StructorType == Ctor_Closure;
+      if (IsCtorClosure)
+        CC = getASTContext().getDefaultCallingConvention(
+            /*IsVariadic=*/false, /*IsCXXMethod=*/true);
+    }
   }
 
   // If this is a C++ instance method, mangle the CVR qualifiers for the
   // this pointer.
   if (HasThisQuals) {
     Qualifiers Quals = Qualifiers::fromCVRMask(Proto->getTypeQuals());
     manglePointerExtQualifiers(Quals, /*PointeeType=*/nullptr);
     mangleRefQualifier(Proto->getRefQualifier());
     mangleQualifiers(Quals, /*IsMember=*/false);
   }
 
-  mangleCallingConvention(T);
+  mangleCallingConvention(CC);
 
   // <return-type> ::= <type>
   //               ::= @ # structors (they have no declared return type)
   if (IsStructor) {
     if (isa<CXXDestructorDecl>(D) && D == Structor &&
         StructorType == Dtor_Deleting) {
       // The scalar deleting destructor takes an extra int argument.
       // However, the FunctionType generated has 0 arguments.
       // FIXME: This is a temporary hack.
       // Maybe should fix the FunctionType creation instead?
       Out << (PointersAre64Bit ? "PEAXI@Z" : "PAXI@Z");
       return;
     }
+    if (IsCtorClosure) {
+      const auto *CD = cast<CXXConstructorDecl>(D);
+
+      // Default constructor closure and copy constructor closure both return
+      // void.
+      Out << 'X';
+
+      if (CD->isDefaultConstructor()) {
+        // Default constructor closure always has no arguments.
+        Out << 'X';
+      } else if (CD->isCopyConstructor()) {
+        // Copy constructor closure always takes an unqualified reference.
+        mangleArgumentType(getASTContext().getLValueReferenceType(
+                               Proto->getParamType(0)
+                                   ->getAs<LValueReferenceType>()
+                                   ->getPointeeType(),
+                               /*SpelledAsLValue=*/true),
+                           Range);
+      } else {
+        llvm_unreachable("unexpected constructor closure!");
+      }
+      Out << "@Z";
+      return;
+    }
     Out << '@';
   } else {
     QualType ResultType = Proto->getReturnType();
     if (const auto *AT =
             dyn_cast_or_null<AutoType>(ResultType->getContainedAutoType())) {
       Out << '?';
       mangleQualifiers(ResultType.getLocalQualifiers(), /*IsMember=*/false);
       Out << '?';
switch (MD->getAccess()) {
         else if (MD->isVirtual())
           Out << 'U';
         else
           Out << 'Q';
     }
   } else
     Out << 'Y';
 }
-void MicrosoftCXXNameMangler::mangleCallingConvention(const FunctionType *T) {
+void MicrosoftCXXNameMangler::mangleCallingConvention(CallingConv CC) {
   // <calling-convention> ::= A # __cdecl
   //                      ::= B # __export __cdecl
   //                      ::= C # __pascal
   //                      ::= D # __export __pascal
   //                      ::= E # __thiscall
   //                      ::= F # __export __thiscall
   //                      ::= G # __stdcall
   //                      ::= H # __export __stdcall
   //                      ::= I # __fastcall
   //                      ::= J # __export __fastcall
   //                      ::= Q # __vectorcall
   // The 'export' calling conventions are from a bygone era
   // (*cough*Win16*cough*) when functions were declared for export with
   // that keyword. (It didn't actually export them, it just made them so
   // that they could be in a DLL and somebody from another module could call
   // them.)
-  CallingConv CC = T->getCallConv();
+
   switch (CC) {
     default:
       llvm_unreachable("Unsupported CC for mangling");
     case CC_X86_64Win64:
     case CC_X86_64SysV:
     case CC_C: Out << 'A'; break;
     case CC_X86Pascal: Out << 'C'; break;
     case CC_X86ThisCall: Out << 'E'; break;
     case CC_X86StdCall: Out << 'G'; break;
     case CC_X86FastCall: Out << 'I'; break;
     case CC_X86VectorCall: Out << 'Q'; break;
   }
 }
+void MicrosoftCXXNameMangler::mangleCallingConvention(const FunctionType *T) {
+  mangleCallingConvention(T->getCallConv());
+}
 void MicrosoftCXXNameMangler::mangleThrowSpecification(
                                                 const FunctionProtoType *FT) {
   // <throw-spec> ::= Z # throw(...) (default)
   //              ::= @ # throw() or __declspec/__attribute__((nothrow))
   //              ::= <type>+
   // NOTE: Since the Microsoft compiler ignores throw specifications, they are
   // all actually mangled as 'Z'. (They're ignored because their associated
   // functionality isn't implemented, and probably never will be.)
void MicrosoftMangleContextImpl::mangleCXXCatchableTypeArray(
     QualType T, uint32_t NumEntries, raw_ostream &Out) {
   MicrosoftCXXNameMangler Mangler(*this, Out);
   Mangler.getStream() << "_CTA";
   Mangler.getStream() << NumEntries;
   Mangler.mangleType(T, SourceRange(), MicrosoftCXXNameMangler::QMM_Result);
 }
 
 void MicrosoftMangleContextImpl::mangleCXXCatchableType(
-    QualType T, const CXXConstructorDecl *CD, uint32_t Size, uint32_t NVOffset,
-    int32_t VBPtrOffset, uint32_t VBIndex, raw_ostream &Out) {
+    QualType T, const CXXConstructorDecl *CD, CXXCtorType CT, uint32_t Size,
+    uint32_t NVOffset, int32_t VBPtrOffset, uint32_t VBIndex,
+    raw_ostream &Out) {
   MicrosoftCXXNameMangler Mangler(*this, Out);
   Mangler.getStream() << "_CT";
 
   llvm::SmallString<64> RTTIMangling;
   {
     llvm::raw_svector_ostream Stream(RTTIMangling);
     mangleCXXRTTI(T, Stream);
   }
   Mangler.getStream() << RTTIMangling.substr(1);
 
   // VS2015 CTP6 omits the copy-constructor in the mangled name.  This name is,
   // in fact, superfluous but I'm not sure the change was made consciously.
   // TODO: Revisit this when VS2015 gets released.
   llvm::SmallString<64> CopyCtorMangling;
   if (CD) {
     llvm::raw_svector_ostream Stream(CopyCtorMangling);
-    mangleCXXCtor(CD, Ctor_Complete, Stream);
+    mangleCXXCtor(CD, CT, Stream);
   }
   Mangler.getStream() << CopyCtorMangling.substr(1);
 
   Mangler.getStream() << Size;
   if (VBPtrOffset == -1) {
     if (NVOffset) {
       Mangler.getStream() << NVOffset;
     }
void MicrosoftMangleContextImpl::mangleTypeName(QualType T, raw_ostream &Out) {
   MicrosoftCXXNameMangler Mangler(*this, Out);
   Mangler.getStream() << '?';
   Mangler.mangleType(T, SourceRange());
 }
 
 void MicrosoftMangleContextImpl::mangleCXXCtor(const CXXConstructorDecl *D,
                                                CXXCtorType Type,
                                                raw_ostream &Out) {
-  MicrosoftCXXNameMangler mangler(*this, Out);
+  MicrosoftCXXNameMangler mangler(*this, Out, D, Type);
   mangler.mangle(D);
 }
 
 void MicrosoftMangleContextImpl::mangleCXXDtor(const CXXDestructorDecl *D,
                                                CXXDtorType Type,
                                                raw_ostream &Out) {
   MicrosoftCXXNameMangler mangler(*this, Out, D, Type);
   mangler.mangle(D);

lib/CodeGen/CGCall.cpp

CodeGenTypes::arrangeMSMemberPointerThunk(const CXXMethodDecl *MD) {
   assert(MD->isVirtual() && "only virtual memptrs have thunks");
   CanQual<FunctionProtoType> FTP = GetFormalType(MD);
   CanQualType ArgTys[] = { GetThisType(Context, MD->getParent()) };
   return arrangeLLVMFunctionInfo(Context.VoidTy, /*instanceMethod=*/false,
                                  /*chainCall=*/false, ArgTys,
                                  FTP->getExtInfo(), RequiredArgs(1));
 }
 
+const CGFunctionInfo &
+CodeGenTypes::arrangeMSCopyCtorClosure(const CXXConstructorDecl *CD) {
+  CanQual<FunctionProtoType> FTP = GetFormalType(CD);
+  SmallVector<CanQualType, 2> ArgTys;
+  const CXXRecordDecl *RD = CD->getParent();
+  ArgTys.push_back(GetThisType(Context, RD));
+  ArgTys.push_back(*FTP->param_type_begin());
+  if (RD->getNumVBases() > 0)
+    ArgTys.push_back(Context.IntTy);
+  CallingConv CC = Context.getDefaultCallingConvention(
+      /*IsVariadic=*/false, /*IsCXXMethod=*/true);
+  return arrangeLLVMFunctionInfo(Context.VoidTy, /*instanceMethod=*/true,
+                                 /*chainCall=*/false, ArgTys,
+                                 FunctionType::ExtInfo(CC), RequiredArgs::All);
+}
+
 /// Arrange a call as unto a free function, except possibly with an
 /// additional number of formal parameters considered required.
 static const CGFunctionInfo &
 arrangeFreeFunctionLikeCall(CodeGenTypes &CGT,
                             CodeGenModule &CGM,
                             const CallArgList &args,
                             const FunctionType *fnType,
                             unsigned numExtraRequiredArgs,

lib/CodeGen/CodeGenTypes.h

 inline StructorType getFromCtorType(CXXCtorType T) {
   switch (T) {
   case Ctor_Complete:
     return StructorType::Complete;
   case Ctor_Base:
     return StructorType::Base;
   case Ctor_Comdat:
     llvm_unreachable("not expecting a COMDAT");
+  case Ctor_Closure:
+    llvm_unreachable("not expecting a closure");
   }
   llvm_unreachable("not a CXXCtorType");
 }
 
 inline CXXDtorType toCXXDtorType(StructorType T) {
   switch (T) {
   case StructorType::Complete:
     return Dtor_Complete;
const CGFunctionInfo &arrangeFreeFunctionCall(QualType ResTy,
                                                 RequiredArgs required);
   const CGFunctionInfo &arrangeBlockFunctionCall(const CallArgList &args,
                                                  const FunctionType *type);
 
   const CGFunctionInfo &arrangeCXXMethodCall(const CallArgList &args,
                                              const FunctionProtoType *type,
                                              RequiredArgs required);
   const CGFunctionInfo &arrangeMSMemberPointerThunk(const CXXMethodDecl *MD);
+  const CGFunctionInfo &arrangeMSCopyCtorClosure(const CXXConstructorDecl *CD);
 
   const CGFunctionInfo &arrangeFreeFunctionType(CanQual<FunctionProtoType> Ty);
   const CGFunctionInfo &arrangeFreeFunctionType(CanQual<FunctionNoProtoType> Ty);
   const CGFunctionInfo &arrangeCXXMethodType(const CXXRecordDecl *RD,
                                              const FunctionProtoType *FTP);
 
   /// "Arrange" the LLVM information for a call or type with the given
   /// signature.  This is largely an internal method; other clients

lib/CodeGen/MicrosoftCXXABI.cpp

llvm::Constant *getThrowFn() {
     auto *Fn = cast<llvm::Function>(
         CGM.CreateRuntimeFunction(FTy, "_CxxThrowException"));
     // _CxxThrowException is stdcall on 32-bit x86 platforms.
     if (CGM.getTarget().getTriple().getArch() == llvm::Triple::x86)
       Fn->setCallingConv(llvm::CallingConv::X86_StdCall);
     return Fn;
   }
 
+  llvm::Function *getAddrOfCXXCopyCtorClosure(const CXXConstructorDecl *CD);
+
   llvm::Constant *getCatchableType(QualType T,
                                    uint32_t NVOffset = 0,
                                    int32_t VBPtrOffset = -1,
                                    uint32_t VBIndex = 0);
 
   llvm::GlobalVariable *getCatchableTypeArray(QualType T);
 
   llvm::GlobalVariable *getThrowInfo(QualType T);
void MicrosoftCXXABI::emitCXXStructor(const CXXMethodDecl *MD,
                                       StructorType Type) {
   if (auto *CD = dyn_cast<CXXConstructorDecl>(MD)) {
     emitCXXConstructor(CGM, CD, Type);
     return;
   }
   emitCXXDestructor(CGM, cast<CXXDestructorDecl>(MD), Type);
 }
 
+llvm::Function *
+MicrosoftCXXABI::getAddrOfCXXCopyCtorClosure(const CXXConstructorDecl *CD) {
+  // Calculate the mangled name.
+  SmallString<256> ThunkName;
+  llvm::raw_svector_ostream Out(ThunkName);
+  getMangleContext().mangleCXXCtor(CD, Ctor_Closure, Out);
+  Out.flush();
+
+  // If the thunk has been generated previously, just return it.
+  if (llvm::GlobalValue *GV = CGM.getModule().getNamedValue(ThunkName))
+    return cast<llvm::Function>(GV);
+
+  // Create the llvm::Function.
+  const CGFunctionInfo &FnInfo = CGM.getTypes().arrangeMSCopyCtorClosure(CD);
+  llvm::FunctionType *ThunkTy = CGM.getTypes().GetFunctionType(FnInfo);
+  const CXXRecordDecl *RD = CD->getParent();
+  QualType RecordTy = getContext().getRecordType(RD);
+  llvm::Function *ThunkFn = llvm::Function::Create(
+      ThunkTy, getLinkageForRTTI(RecordTy), ThunkName.str(), &CGM.getModule());
+
+  // Start codegen.
+  CodeGenFunction CGF(CGM);
+  CGF.CurGD = GlobalDecl(CD, Ctor_Complete);
+
+  // Build FunctionArgs.
+  FunctionArgList FunctionArgs;
+
+  // A copy constructor always starts with a 'this' pointer as its first
+  // argument.
+  buildThisParam(CGF, FunctionArgs);
+
+  // Following the 'this' pointer is a reference to the source object that we
+  // are copying from.
+  ImplicitParamDecl SrcParam(
+      getContext(), nullptr, SourceLocation(), &getContext().Idents.get("src"),
+      getContext().getLValueReferenceType(RecordTy,
+                                          /*SpelledAsLValue=*/true));
+  FunctionArgs.push_back(&SrcParam);
+
+  // Copy constructors for classes which utilize virtual bases have an
+  // additional parameter which indicates whether or not it is being delegated
+  // to by a more derived constructor.
+  ImplicitParamDecl IsMostDerived(getContext(), nullptr, SourceLocation(),
+                                  &getContext().Idents.get("is_most_derived"),
+                                  getContext().IntTy);
+  // Only add the parameter to the list if thie class has virtual bases.
+  if (RD->getNumVBases() > 0)
+    FunctionArgs.push_back(&IsMostDerived);
+
+  // Start defining the function.
+  CGF.StartFunction(GlobalDecl(), FnInfo.getReturnType(), ThunkFn, FnInfo,
+                    FunctionArgs, CD->getLocation(), SourceLocation());
+  EmitThisParam(CGF);
+  llvm::Value *This = getThisValue(CGF);
+
+  llvm::Value *SrcVal =
+      CGF.Builder.CreateLoad(CGF.GetAddrOfLocalVar(&SrcParam), "src");
+
+  CallArgList Args;
+
+  // Push the this ptr.
+  Args.add(RValue::get(This), CD->getThisType(getContext()));
+
+  // Push the src ptr.
+  Args.add(RValue::get(SrcVal), SrcParam.getType());
+
+  // Add the rest of the default arguments.
+  std::vector<Stmt *> ArgVec;
+  for (unsigned I = 1, E = CD->getNumParams(); I != E; ++I)
+    ArgVec.push_back(getContext().getDefaultArgExprForConstructor(CD, I));
+
+  const auto *FPT = CD->getType()->castAs<FunctionProtoType>();
+  ConstExprIterator ArgBegin(ArgVec.data()), ArgEnd(&*ArgVec.end());
+  CGF.EmitCallArgs(Args, FPT, ArgBegin, ArgEnd, CD, 1);
+
+  // Insert any ABI-specific implicit constructor arguments.
+  unsigned ExtraArgs = addImplicitConstructorArgs(CGF, CD, Ctor_Complete,
+                                                  /*ForVirtualBase=*/false,
+                                                  /*Delegating=*/false, Args);
+
+  // Call the destructor with our arguments.
+  llvm::Value *CalleeFn = CGM.getAddrOfCXXStructor(CD, StructorType::Complete);
+  const CGFunctionInfo &CalleeInfo = CGM.getTypes().arrangeCXXConstructorCall(
+      Args, CD, Ctor_Complete, ExtraArgs);
+  CGF.EmitCall(CalleeInfo, CalleeFn, ReturnValueSlot(), Args, CD);
+
+  // Emit the ret instruction, remove any temporary instructions created for the
+  // aid of CodeGen.
+  CGF.FinishFunction(SourceLocation());
+
+  return ThunkFn;
+}
+
 llvm::Constant *MicrosoftCXXABI::getCatchableType(QualType T,
                                                   uint32_t NVOffset,
                                                   int32_t VBPtrOffset,
                                                   uint32_t VBIndex) {
   assert(!T->isReferenceType());
 
   CXXRecordDecl *RD = T->getAsCXXRecordDecl();
   const CXXConstructorDecl *CD =
       RD ? CGM.getContext().getCopyConstructorForExceptionObject(RD) : nullptr;
+  CXXCtorType CT = Ctor_Complete;
+  if (CD) {
+    CallingConv ExpectedCallingConv = getContext().getDefaultCallingConvention(
+        /*IsVariadic=*/false, /*IsCXXMethod=*/true);
+    CallingConv ActualCallingConv = CD->getType()
+                                        ->getCanonicalTypeUnqualified()
+                                        .getAs<FunctionProtoType>()
+                                        ->getExtInfo()
+                                        .getCC();
+    if (ExpectedCallingConv != ActualCallingConv || CD->getNumParams() != 1)
+      CT = Ctor_Closure;
+  }
+
   uint32_t Size = getContext().getTypeSizeInChars(T).getQuantity();
   SmallString<256> MangledName;
   {
     llvm::raw_svector_ostream Out(MangledName);
-    getMangleContext().mangleCXXCatchableType(T, CD, Size, NVOffset,
+    getMangleContext().mangleCXXCatchableType(T, CD, CT, Size, NVOffset,
                                               VBPtrOffset, VBIndex, Out);
   }
   if (llvm::GlobalVariable *GV = CGM.getModule().getNamedGlobal(MangledName))
     return getImageRelativeConstant(GV);
 
-  // The TypeDescriptor is used by the runtime to determine of a catch handler
+  // The TypeDescriptor is used by the runtime to determine if a catch handler
   // is appropriate for the exception object.
   llvm::Constant *TD = getImageRelativeConstant(getAddrOfRTTIDescriptor(T));
 
   // The runtime is responsible for calling the copy constructor if the
   // exception is caught by value.
-  llvm::Constant *CopyCtor =
-      CD ? llvm::ConstantExpr::getBitCast(
-               CGM.getAddrOfCXXStructor(CD, StructorType::Complete),
-               CGM.Int8PtrTy)
-         : llvm::Constant::getNullValue(CGM.Int8PtrTy);
+  llvm::Constant *CopyCtor;
+  if (CD) {
+    if (CT == Ctor_Closure)
+      CopyCtor = getAddrOfCXXCopyCtorClosure(CD);
+    else
+      CopyCtor = CGM.getAddrOfCXXStructor(CD, StructorType::Complete);
+
+    CopyCtor = llvm::ConstantExpr::getBitCast(CopyCtor, CGM.Int8PtrTy);
+  } else {
+    CopyCtor = llvm::Constant::getNullValue(CGM.Int8PtrTy);
+  }
   CopyCtor = getImageRelativeConstant(CopyCtor);
 
   bool IsScalar = !RD;
   bool HasVirtualBases = false;
   bool IsStdBadAlloc = false; // std::bad_alloc is special for some reason.
   QualType PointeeType = T;
   if (T->isPointerType())
     PointeeType = T->getPointeeType();

lib/Sema/SemaExprCXX.cpp

if (CXXDestructorDecl *Destructor = LookupDestructor(RD)) {
       MarkFunctionReferenced(E->getExprLoc(), Destructor);
       CheckDestructorAccess(E->getExprLoc(), Destructor,
                             PDiag(diag::err_access_dtor_exception) << Ty);
       if (DiagnoseUseOfDecl(Destructor, E->getExprLoc()))
         return ExprError();
     }
   }
 
+  // The MSVC ABI creates a list of all types which can catch the exception
+  // object.  This list also references the appropriate copy constructor to call
+  // if the object is caught by value and has a non-trivial copy constructor.
   if (Context.getTargetInfo().getCXXABI().isMicrosoft()) {
+    // We are only interested in the public, unambiguous bases contained within
+    // the exception object.  Bases which are ambiguous or otherwise
+    // inaccessible are not catchable types.
     llvm::SmallVector<CXXRecordDecl *, 2> UnambiguousPublicSubobjects;
     getUnambiguousPublicSubobjects(RD, UnambiguousPublicSubobjects);
+
     for (CXXRecordDecl *Subobject : UnambiguousPublicSubobjects) {
-      if (CXXConstructorDecl *CD = LookupCopyingConstructor(Subobject, 0)) {
-        MarkFunctionReferenced(E->getExprLoc(), CD);
-        if (!CD->isTrivial())
-          Context.addCopyConstructorForExceptionObject(Subobject, CD);
+      // Attempt to lookup the copy constructor.  Various pieces of machinery
+      // will spring into action, like template instantiation, which means this
+      // cannot be a simple walk of the class's decls.  Instead, we must perform
+      // lookup and overload resolution.
+      CXXConstructorDecl *CD = LookupCopyingConstructor(Subobject, 0);
+      if (!CD)
+        continue;
+
+      // Mark the constructor referenced as it is used by this throw expression.
+
+      // Skip this copy constructor if it is trivial, we don't need to record it
+      // in the catchable type data.
+      if (CD->isTrivial())
+        continue;
+
+      // The copy constructor is non-trivial, create a mapping from this class
+      // type to this constructor.
+      // N.B.  The selection of copy constructor is not sensitive to this
+      // particular throw-site.  Lookup will be performed at the catch-site to
+      // ensure that the copy constructor is, in fact, accessible (via
+      // friendship or any other means).
+
+      // We don't keep the instantiated default argument expressions around so
+      // we must rebuild them here.
+      for (unsigned I = 1, E = CD->getNumParams(); I != E; ++I) {
+        // Skip any default arguments that we've already instantiated.
+        if (Context.getDefaultArgExprForConstructor(CD, I))
+          continue;
+
+        Expr *DefaultArg =
+            BuildCXXDefaultArgExpr(ThrowLoc, CD, CD->getParamDecl(I)).get();
+        Context.addDefaultArgExprForConstructor(CD, I, DefaultArg);
       }
     }
   }
 
   return E;
 }
 
 QualType Sema::getCurrentThisType() {

test/CodeGenCXX/microsoft-abi-throw.cpp

 // RUN: %clang_cc1 -emit-llvm -o - -triple=i386-pc-win32 %s -fcxx-exceptions | FileCheck %s
 
 // CHECK-DAG: @"\01??_R0?AUY@@@8" = linkonce_odr global %rtti.TypeDescriptor7 { i8** @"\01??_7type_info@@6B@", i8* null, [8 x i8] c".?AUY@@\00" }, comdat
 // CHECK-DAG: @"_CT??_R0?AUY@@@8??0Y@@QAE@ABU0@@Z8" = linkonce_odr unnamed_addr constant %eh.CatchableType { i32 4, i8* bitcast (%rtti.TypeDescriptor7* @"\01??_R0?AUY@@@8" to i8*), i32 0, i32 -1, i32 0, i32 8, i8* bitcast (%struct.Y* (%struct.Y*, %struct.Y*, i32)* @"\01??0Y@@QAE@ABU0@@Z" to i8*) }, section ".xdata", comdat
 // CHECK-DAG: @"\01??_R0?AUZ@@@8" = linkonce_odr global %rtti.TypeDescriptor7 { i8** @"\01??_7type_info@@6B@", i8* null, [8 x i8] c".?AUZ@@\00" }, comdat
 // CHECK-DAG: @"_CT??_R0?AUZ@@@81" = linkonce_odr unnamed_addr constant %eh.CatchableType { i32 0, i8* bitcast (%rtti.TypeDescriptor7* @"\01??_R0?AUZ@@@8" to i8*), i32 0, i32 -1, i32 0, i32 1, i8* null }, section ".xdata", comdat
 // CHECK-DAG: @"\01??_R0?AUW@@@8" = linkonce_odr global %rtti.TypeDescriptor7 { i8** @"\01??_7type_info@@6B@", i8* null, [8 x i8] c".?AUW@@\00" }, comdat
 // CHECK-DAG: @"_CT??_R0?AUW@@@8??0W@@QAE@ABU0@@Z44" = linkonce_odr unnamed_addr constant %eh.CatchableType { i32 4, i8* bitcast (%rtti.TypeDescriptor7* @"\01??_R0?AUW@@@8" to i8*), i32 4, i32 -1, i32 0, i32 4, i8* bitcast (%struct.W* (%struct.W*, %struct.W*, i32)* @"\01??0W@@QAE@ABU0@@Z" to i8*) }, section ".xdata", comdat
 // CHECK-DAG: @"\01??_R0?AUM@@@8" = linkonce_odr global %rtti.TypeDescriptor7 { i8** @"\01??_7type_info@@6B@", i8* null, [8 x i8] c".?AUM@@\00" }, comdat
 // CHECK-DAG: @"_CT??_R0?AUM@@@818" = linkonce_odr unnamed_addr constant %eh.CatchableType { i32 0, i8* bitcast (%rtti.TypeDescriptor7* @"\01??_R0?AUM@@@8" to i8*), i32 8, i32 -1, i32 0, i32 1, i8* null }, section ".xdata", comdat
 // CHECK-DAG: @"\01??_R0?AUV@@@8" = linkonce_odr global %rtti.TypeDescriptor7 { i8** @"\01??_7type_info@@6B@", i8* null, [8 x i8] c".?AUV@@\00" }, comdat
 // CHECK-DAG: @"_CT??_R0?AUV@@@81044" = linkonce_odr unnamed_addr constant %eh.CatchableType { i32 0, i8* bitcast (%rtti.TypeDescriptor7* @"\01??_R0?AUV@@@8" to i8*), i32 0, i32 4, i32 4, i32 1, i8* null }, section ".xdata", comdat
 // CHECK-DAG: @"_CTA5?AUY@@" = linkonce_odr unnamed_addr constant %eh.CatchableTypeArray.5 { i32 5, [5 x %eh.CatchableType*] [%eh.CatchableType* @"_CT??_R0?AUY@@@8??0Y@@QAE@ABU0@@Z8", %eh.CatchableType* @"_CT??_R0?AUZ@@@81", %eh.CatchableType* @"_CT??_R0?AUW@@@8??0W@@QAE@ABU0@@Z44", %eh.CatchableType* @"_CT??_R0?AUM@@@818", %eh.CatchableType* @"_CT??_R0?AUV@@@81044"] }, section ".xdata", comdat
 // CHECK-DAG: @"_TI5?AUY@@" = linkonce_odr unnamed_addr constant %eh.ThrowInfo { i32 0, i8* bitcast (void (%struct.Y*)* @"\01??_DY@@QAE@XZ" to i8*), i8* null, i8* bitcast (%eh.CatchableTypeArray.5* @"_CTA5?AUY@@" to i8*) }, section ".xdata", comdat
+// CHECK-DAG: @"_CT??_R0?AUDefault@@@8??_ODefault@@QAEXAAU0@@Z1" = linkonce_odr unnamed_addr constant %eh.CatchableType { i32 0, i8* bitcast (%rtti.TypeDescriptor13* @"\01??_R0?AUDefault@@@8" to i8*), i32 0, i32 -1, i32 0, i32 1, i8* bitcast (void (%struct.Default*, %struct.Default*)* @"\01??_ODefault@@QAEXAAU0@@Z" to i8*) }, section ".xdata", comdat
 
 
 struct N { ~N(); };
 struct M : private N {};
 struct X {};
 struct Z {};
 struct V : private X {};
 struct W : M, virtual V {};
 struct Y : Z, W, virtual V {};
 
 void f(const Y &y) {
   // CHECK-LABEL: @"\01?f@@YAXABUY@@@Z"
   // CHECK: call x86_thiscallcc %struct.Y* @"\01??0Y@@QAE@ABU0@@Z"(%struct.Y* %[[mem:.*]], %struct.Y*
   // CHECK: %[[cast:.*]] = bitcast %struct.Y* %[[mem]] to i8*
   // CHECK: call void @_CxxThrowException(i8* %[[cast]], %eh.ThrowInfo* @"_TI5?AUY@@")
   throw y;
 }
 
 void g(const int *const *y) {
   // CHECK-LABEL: @"\01?g@@YAXPBQBH@Z"
   // CHECK: call void @_CxxThrowException(i8* %{{.*}}, %eh.ThrowInfo* @_TIC2PAPBH)
   throw y;
 }
+
+struct Default {
+  Default(Default &, int = 42);
+};
+
+// CHECK-LABEL: @"\01??_ODefault@@QAEXAAU0@@Z"
+// CHECK: %[[src_addr:.*]] = alloca
+// CHECK: %[[this_addr:.*]] = alloca
+// CHECK: store {{.*}} %src, {{.*}} %[[src_addr]], align 4
+// CHECK: store {{.*}} %this, {{.*}} %[[this_addr]], align 4
+// CHECK: %[[this:.*]] = load {{.*}} %[[this_addr]]
+// CHECK: %[[src:.*]] = load {{.*}} %[[src_addr]]
+// CHECK: call x86_thiscallcc {{.*}} @"\01??0Default@@QAE@AAU0@H@Z"({{.*}} %[[this]], {{.*}} %[[src]], i32 42)
+// CHECK: ret void
+
+void h(Default &d) {
+  throw d;
+}