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

1 files changed, 44 insertions, 22 deletions

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);