MS ABI: Generate default constructor closures

The MS ABI utilizes a compiler generated function called the "vector
constructor iterator" to construct arrays of objects with
non-trivial constructors/destructors.  For this to work, the constructor
must follow a specific calling convention.  A thunk must be created if
the default constructor has default arguments, is variadic or is
otherwise incompatible.  This thunk is called the default constructor
closure.

N.B.  Default constructor closures are only generated if the default
constructor is exported because clang itself does not utilize vector
constructor iterators.  Failing to export the default constructor
closure will result in link/load failure if a translation unit compiled
with MSVC is on the import side.

Differential Revision: http://reviews.llvm.org/D8331

llvm-svn: 232229

6 files changed, 103 insertions, 27 deletions

diff --git a/clang/lib/AST/MicrosoftMangle.cpp b/clang/lib/AST/MicrosoftMangle.cpp
index f56da26a09b..6a0ebda7b33 100644
--- a/clang/lib/AST/MicrosoftMangle.cpp
+++ b/clang/lib/AST/MicrosoftMangle.cpp
@@ -1640,10 +1640,11 @@ void MicrosoftCXXNameMangler::mangleFunctionType(const FunctionType *T,
                                    ->getPointeeType(),
                                /*SpelledAsLValue=*/true),
                            Range);
+        Out << '@';
       } else {
         llvm_unreachable("unexpected constructor closure!");
       }
-      Out << "@Z";
+      Out << 'Z';
       return;
     }
     Out << '@';
diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index 67849642118..3cb72bd1512 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -347,12 +347,16 @@ CodeGenTypes::arrangeMSMemberPointerThunk(const CXXMethodDecl *MD) {
 }
 
 const CGFunctionInfo &
-CodeGenTypes::arrangeMSCopyCtorClosure(const CXXConstructorDecl *CD) {
+CodeGenTypes::arrangeMSCtorClosure(const CXXConstructorDecl *CD,
+                                   CXXCtorType CT) {
+  assert(CT == Ctor_CopyingClosure || CT == Ctor_DefaultClosure);
+
   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 (CT == Ctor_CopyingClosure)
+    ArgTys.push_back(*FTP->param_type_begin());
   if (RD->getNumVBases() > 0)
     ArgTys.push_back(Context.IntTy);
   CallingConv CC = Context.getDefaultCallingConvention(
diff --git a/clang/lib/CodeGen/CodeGenTypes.h b/clang/lib/CodeGen/CodeGenTypes.h
index f9cd3837fe9..26d37f3c240 100644
--- a/clang/lib/CodeGen/CodeGenTypes.h
+++ b/clang/lib/CodeGen/CodeGenTypes.h
@@ -264,7 +264,8 @@ public:
                                              const FunctionProtoType *type,
                                              RequiredArgs required);
   const CGFunctionInfo &arrangeMSMemberPointerThunk(const CXXMethodDecl *MD);
-  const CGFunctionInfo &arrangeMSCopyCtorClosure(const CXXConstructorDecl *CD);
+  const CGFunctionInfo &arrangeMSCtorClosure(const CXXConstructorDecl *CD,
+                                                 CXXCtorType CT);
 
   const CGFunctionInfo &arrangeFreeFunctionType(CanQual<FunctionProtoType> Ty);
   const CGFunctionInfo &arrangeFreeFunctionType(CanQual<FunctionNoProtoType> Ty);
diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index 6b53359f28b..96fcb2f8dbe 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -635,7 +635,8 @@ public:
     return Fn;
   }
 
-  llvm::Function *getAddrOfCXXCopyCtorClosure(const CXXConstructorDecl *CD);
+  llvm::Function *getAddrOfCXXCtorClosure(const CXXConstructorDecl *CD,
+                                          CXXCtorType CT);
 
   llvm::Constant *getCatchableType(QualType T,
                                    uint32_t NVOffset = 0,
@@ -1060,9 +1061,29 @@ void MicrosoftCXXABI::initializeHiddenVirtualInheritanceMembers(
   }
 }
 
+static bool hasDefaultCXXMethodCC(ASTContext &Context,
+                                  const CXXMethodDecl *MD) {
+  CallingConv ExpectedCallingConv = Context.getDefaultCallingConvention(
+      /*IsVariadic=*/false, /*IsCXXMethod=*/true);
+  CallingConv ActualCallingConv =
+      MD->getType()->getAs<FunctionProtoType>()->getCallConv();
+  return ExpectedCallingConv == ActualCallingConv;
+}
+
 void MicrosoftCXXABI::EmitCXXConstructors(const CXXConstructorDecl *D) {
   // There's only one constructor type in this ABI.
   CGM.EmitGlobal(GlobalDecl(D, Ctor_Complete));
+
+  // Exported default constructors either have a simple call-site where they use
+  // the typical calling convention and have a single 'this' pointer for an
+  // argument -or- they get a wrapper function which appropriately thunks to the
+  // real default constructor.  This thunk is the default constructor closure.
+  if (D->hasAttr<DLLExportAttr>() && D->isDefaultConstructor())
+    if (!hasDefaultCXXMethodCC(getContext(), D) || D->getNumParams() != 0) {
+      llvm::Function *Fn = getAddrOfCXXCtorClosure(D, Ctor_DefaultClosure);
+      Fn->setLinkage(llvm::GlobalValue::WeakODRLinkage);
+      Fn->setDLLStorageClass(llvm::GlobalValue::DLLExportStorageClass);
+    }
 }
 
 void MicrosoftCXXABI::EmitVBPtrStores(CodeGenFunction &CGF,
@@ -3223,11 +3244,14 @@ void MicrosoftCXXABI::emitCXXStructor(const CXXMethodDecl *MD,
 }
 
 llvm::Function *
-MicrosoftCXXABI::getAddrOfCXXCopyCtorClosure(const CXXConstructorDecl *CD) {
+MicrosoftCXXABI::getAddrOfCXXCtorClosure(const CXXConstructorDecl *CD,
+                                         CXXCtorType CT) {
+  assert(CT == Ctor_CopyingClosure || CT == Ctor_DefaultClosure);
+
   // Calculate the mangled name.
   SmallString<256> ThunkName;
   llvm::raw_svector_ostream Out(ThunkName);
-  getMangleContext().mangleCXXCtor(CD, Ctor_CopyingClosure, Out);
+  getMangleContext().mangleCXXCtor(CD, CT, Out);
   Out.flush();
 
   // If the thunk has been generated previously, just return it.
@@ -3235,12 +3259,13 @@ MicrosoftCXXABI::getAddrOfCXXCopyCtorClosure(const CXXConstructorDecl *CD) {
     return cast<llvm::Function>(GV);
 
   // Create the llvm::Function.
-  const CGFunctionInfo &FnInfo = CGM.getTypes().arrangeMSCopyCtorClosure(CD);
+  const CGFunctionInfo &FnInfo = CGM.getTypes().arrangeMSCtorClosure(CD, CT);
   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());
+  bool IsCopy = CT == Ctor_CopyingClosure;
 
   // Start codegen.
   CodeGenFunction CGF(CGM);
@@ -3249,8 +3274,7 @@ MicrosoftCXXABI::getAddrOfCXXCopyCtorClosure(const CXXConstructorDecl *CD) {
   // Build FunctionArgs.
   FunctionArgList FunctionArgs;
 
-  // A copy constructor always starts with a 'this' pointer as its first
-  // argument.
+  // A 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
@@ -3259,11 +3283,12 @@ MicrosoftCXXABI::getAddrOfCXXCopyCtorClosure(const CXXConstructorDecl *CD) {
       getContext(), nullptr, SourceLocation(), &getContext().Idents.get("src"),
       getContext().getLValueReferenceType(RecordTy,
                                           /*SpelledAsLValue=*/true));
-  FunctionArgs.push_back(&SrcParam);
+  if (IsCopy)
+    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.
+  // 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);
@@ -3278,7 +3303,8 @@ MicrosoftCXXABI::getAddrOfCXXCopyCtorClosure(const CXXConstructorDecl *CD) {
   llvm::Value *This = getThisValue(CGF);
 
   llvm::Value *SrcVal =
-      CGF.Builder.CreateLoad(CGF.GetAddrOfLocalVar(&SrcParam), "src");
+      IsCopy ? CGF.Builder.CreateLoad(CGF.GetAddrOfLocalVar(&SrcParam), "src")
+             : nullptr;
 
   CallArgList Args;
 
@@ -3286,11 +3312,12 @@ MicrosoftCXXABI::getAddrOfCXXCopyCtorClosure(const CXXConstructorDecl *CD) {
   Args.add(RValue::get(This), CD->getThisType(getContext()));
 
   // Push the src ptr.
-  Args.add(RValue::get(SrcVal), SrcParam.getType());
+  if (SrcVal)
+    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)
+  for (unsigned I = IsCopy ? 1 : 0, E = CD->getNumParams(); I != E; ++I)
     ArgVec.push_back(getContext().getDefaultArgExprForConstructor(CD, I));
 
   CodeGenFunction::RunCleanupsScope Cleanups(CGF);
@@ -3298,7 +3325,7 @@ MicrosoftCXXABI::getAddrOfCXXCopyCtorClosure(const CXXConstructorDecl *CD) {
   const auto *FPT = CD->getType()->castAs<FunctionProtoType>();
   ConstExprIterator ArgBegin(ArgVec.data()),
       ArgEnd(ArgVec.data() + ArgVec.size());
-  CGF.EmitCallArgs(Args, FPT, ArgBegin, ArgEnd, CD, 1);
+  CGF.EmitCallArgs(Args, FPT, ArgBegin, ArgEnd, CD, IsCopy ? 1 : 0);
 
   // Insert any ABI-specific implicit constructor arguments.
   unsigned ExtraArgs = addImplicitConstructorArgs(CGF, CD, Ctor_Complete,
@@ -3330,14 +3357,9 @@ llvm::Constant *MicrosoftCXXABI::getCatchableType(QualType T,
   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()->getAs<FunctionProtoType>()->getCallConv();
-    if (ExpectedCallingConv != ActualCallingConv || CD->getNumParams() != 1)
+  if (CD)
+    if (!hasDefaultCXXMethodCC(getContext(), CD) || CD->getNumParams() != 1)
       CT = Ctor_CopyingClosure;
-  }
 
   uint32_t Size = getContext().getTypeSizeInChars(T).getQuantity();
   SmallString<256> MangledName;
@@ -3358,7 +3380,7 @@ llvm::Constant *MicrosoftCXXABI::getCatchableType(QualType T,
   llvm::Constant *CopyCtor;
   if (CD) {
     if (CT == Ctor_CopyingClosure)
-      CopyCtor = getAddrOfCXXCopyCtorClosure(CD);
+      CopyCtor = getAddrOfCXXCtorClosure(CD, Ctor_CopyingClosure);
     else
       CopyCtor = CGM.getAddrOfCXXStructor(CD, StructorType::Complete);
 
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 9c6f638119b..7a70cddf9d0 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -12064,6 +12064,24 @@ void Sema::ActOnStartCXXMemberDeclarations(Scope *S, Decl *TagD,
          "Broken injected-class-name");
 }
 
+static void getDefaultArgExprsForConstructors(Sema &S, CXXRecordDecl *Class) {
+  for (Decl *Member : Class->decls()) {
+    auto *CD = dyn_cast<CXXConstructorDecl>(Member);
+    if (!CD || !CD->isDefaultConstructor() || !CD->hasAttr<DLLExportAttr>())
+      continue;
+
+    for (unsigned I = 0, E = CD->getNumParams(); I != E; ++I) {
+      // Skip any default arguments that we've already instantiated.
+      if (S.Context.getDefaultArgExprForConstructor(CD, I))
+        continue;
+
+      Expr *DefaultArg = S.BuildCXXDefaultArgExpr(Class->getLocation(), CD,
+                                                  CD->getParamDecl(I)).get();
+      S.Context.addDefaultArgExprForConstructor(CD, I, DefaultArg);
+    }
+  }
+}
+
 void Sema::ActOnTagFinishDefinition(Scope *S, Decl *TagD,
                                     SourceLocation RBraceLoc) {
   AdjustDeclIfTemplate(TagD);
@@ -12077,9 +12095,17 @@ void Sema::ActOnTagFinishDefinition(Scope *S, Decl *TagD,
       RD->completeDefinition();
   }
 
-  if (isa<CXXRecordDecl>(Tag))
+  if (auto *Class = dyn_cast<CXXRecordDecl>(Tag)) {
     FieldCollector->FinishClass();
 
+    // Default constructors that are annotated with __declspec(dllexport) which
+    // have default arguments or don't use the standard calling convention are
+    // wrapped with a thunk called the default constructor closure.
+    if (!Class->getDescribedClassTemplate() &&
+        Context.getTargetInfo().getCXXABI().isMicrosoft())
+      getDefaultArgExprsForConstructors(*this, Class);
+  }
+
   // Exit this scope of this tag's definition.
   PopDeclContext();
 
diff --git a/clang/test/CodeGenCXX/dllexport.cpp b/clang/test/CodeGenCXX/dllexport.cpp
index 3b04c264c5d..60d37ef0a87 100644
--- a/clang/test/CodeGenCXX/dllexport.cpp
+++ b/clang/test/CodeGenCXX/dllexport.cpp
@@ -484,6 +484,28 @@ struct S {
   };
 };
 
+struct CtorWithClosure {
+  __declspec(dllexport) CtorWithClosure(...) {}
+// M32-DAG: define weak_odr dllexport void @"\01??_FCtorWithClosure@@QAEXXZ"
+// M32-DAG:   %[[this_addr:.*]] = alloca %struct.CtorWithClosure*, align 4
+// M32-DAG:   store %struct.CtorWithClosure* %this, %struct.CtorWithClosure** %[[this_addr]], align 4
+// M32-DAG:   %[[this:.*]] = load %struct.CtorWithClosure*, %struct.CtorWithClosure** %[[this_addr]]
+// M32-DAG:   call %struct.CtorWithClosure* (%struct.CtorWithClosure*, ...)* @"\01??0CtorWithClosure@@QAA@ZZ"(%struct.CtorWithClosure* %[[this]])
+// M32-DAG:   ret void
+};
+
+struct __declspec(dllexport) ClassWithClosure {
+  ClassWithClosure(ClassWithClosure &&) = delete;
+  ClassWithClosure(ClassWithClosure &) = delete;
+  ~ClassWithClosure() = delete;
+  ClassWithClosure(...) {}
+// M32-DAG: define weak_odr dllexport void @"\01??_FClassWithClosure@@QAEXXZ"
+// M32-DAG:   %[[this_addr:.*]] = alloca %struct.ClassWithClosure*, align 4
+// M32-DAG:   store %struct.ClassWithClosure* %this, %struct.ClassWithClosure** %[[this_addr]], align 4
+// M32-DAG:   %[[this:.*]] = load %struct.ClassWithClosure*, %struct.ClassWithClosure** %[[this_addr]]
+// M32-DAG:   call %struct.ClassWithClosure* (%struct.ClassWithClosure*, ...)* @"\01??0ClassWithClosure@@QAA@ZZ"(%struct.ClassWithClosure* %[[this]])
+// M32-DAG:   ret void
+};
 
 struct __declspec(dllexport) T {
   // Copy assignment operator: