[MS][clang] Add support for vector deleting destructors (llvm#126240)

Whereas it is UB in terms of the standard to delete an array of objects
via pointer whose static type doesn't match its dynamic type, MSVC
supports an extension allowing to do it.
Aside from array deletion not working correctly in the mentioned case,
currently not having this extension implemented causes clang to generate
code that is not compatible with the code generated by MSVC, because
clang always puts scalar deleting destructor to the vftable. This PR
aims to resolve these problems.

Fixes llvm#19772

Author: Fznamznon

clang/docs/ReleaseNotes.rst

@@ -308,6 +308,8 @@ Android Support
 Windows Support
 ^^^^^^^^^^^^^^^
 
+- Clang now supports MSVC vector deleting destructors (GH19772).
+
 LoongArch Support
 ^^^^^^^^^^^^^^^^^
 

clang/include/clang/AST/VTableBuilder.h

@@ -150,7 +150,7 @@ class VTableComponent {
 
   bool isRTTIKind() const { return isRTTIKind(getKind()); }
 
-  GlobalDecl getGlobalDecl() const {
+  GlobalDecl getGlobalDecl(bool HasVectorDeletingDtors) const {
     assert(isUsedFunctionPointerKind() &&
            "GlobalDecl can be created only from virtual function");
 
@@ -161,7 +161,9 @@ class VTableComponent {
     case CK_CompleteDtorPointer:
       return GlobalDecl(DtorDecl, CXXDtorType::Dtor_Complete);
     case CK_DeletingDtorPointer:
-      return GlobalDecl(DtorDecl, CXXDtorType::Dtor_Deleting);
+      return GlobalDecl(DtorDecl, (HasVectorDeletingDtors)
+                                      ? CXXDtorType::Dtor_VectorDeleting
+                                      : CXXDtorType::Dtor_Deleting);
     case CK_VCallOffset:
     case CK_VBaseOffset:
     case CK_OffsetToTop:

clang/include/clang/Basic/ABI.h

@@ -31,10 +31,11 @@ enum CXXCtorType {
 
 /// 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
+  Dtor_Deleting,      ///< Deleting dtor
+  Dtor_Complete,      ///< Complete object dtor
+  Dtor_Base,          ///< Base object dtor
+  Dtor_Comdat,        ///< The COMDAT used for dtors
+  Dtor_VectorDeleting ///< Vector deleting dtor
 };
 
 } // end namespace clang

clang/lib/AST/ItaniumMangle.cpp

@@ -6014,6 +6014,8 @@ void CXXNameMangler::mangleCXXDtorType(CXXDtorType T) {
   case Dtor_Comdat:
     Out << "D5";
     break;
+  case Dtor_VectorDeleting:
+    llvm_unreachable("Itanium ABI does not use vector deleting dtors");
   }
 }
 

clang/lib/AST/MicrosoftMangle.cpp

@@ -1484,8 +1484,9 @@ void MicrosoftCXXNameMangler::mangleCXXDtorType(CXXDtorType T) {
   // <operator-name> ::= ?_G # scalar deleting destructor
   case Dtor_Deleting: Out << "?_G"; return;
   // <operator-name> ::= ?_E # vector deleting destructor
-  // FIXME: Add a vector deleting dtor type.  It goes in the vtable, so we need
-  // it.
+  case Dtor_VectorDeleting:
+    Out << "?_E";
+    return;
   case Dtor_Comdat:
     llvm_unreachable("not expecting a COMDAT");
   }
@@ -2886,9 +2887,12 @@ void MicrosoftCXXNameMangler::mangleFunctionType(const FunctionType *T,
   //               ::= @ # structors (they have no declared return type)
   if (IsStructor) {
     if (isa<CXXDestructorDecl>(D) && isStructorDecl(D)) {
-      // The scalar deleting destructor takes an extra int argument which is not
-      // reflected in the AST.
-      if (StructorType == Dtor_Deleting) {
+      // The deleting destructors take an extra argument of type int that
+      // indicates whether the storage for the object should be deleted and
+      // whether a single object or an array of objects is being destroyed. This
+      // extra argument is not reflected in the AST.
+      if (StructorType == Dtor_Deleting ||
+          StructorType == Dtor_VectorDeleting) {
         Out << (PointersAre64Bit ? "PEAXI@Z" : "PAXI@Z");
         return;
       }
@@ -3861,10 +3865,10 @@ void MicrosoftMangleContextImpl::mangleCXXDtorThunk(const CXXDestructorDecl *DD,
                                                     const ThunkInfo &Thunk,
                                                     bool /*ElideOverrideInfo*/,
                                                     raw_ostream &Out) {
-  // FIXME: Actually, the dtor thunk should be emitted for vector deleting
-  // dtors rather than scalar deleting dtors. Just use the vector deleting dtor
-  // mangling manually until we support both deleting dtor types.
-  assert(Type == Dtor_Deleting);
+  // The dtor thunk should use vector deleting dtor mangling, however as an
+  // optimization we may end up emitting only scalar deleting dtor body, so just
+  // use the vector deleting dtor mangling manually.
+  assert(Type == Dtor_Deleting || Type == Dtor_VectorDeleting);
   msvc_hashing_ostream MHO(Out);
   MicrosoftCXXNameMangler Mangler(*this, MHO, DD, Type);
   Mangler.getStream() << "??_E";

clang/lib/AST/VTableBuilder.cpp

@@ -1735,8 +1735,8 @@ void ItaniumVTableBuilder::LayoutPrimaryAndSecondaryVTables(
       const CXXMethodDecl *MD = I.first;
       const MethodInfo &MI = I.second;
       if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD)) {
-        MethodVTableIndices[GlobalDecl(DD, Dtor_Complete)]
-            = MI.VTableIndex - AddressPoint;
+        MethodVTableIndices[GlobalDecl(DD, Dtor_Complete)] =
+            MI.VTableIndex - AddressPoint;
         MethodVTableIndices[GlobalDecl(DD, Dtor_Deleting)]
             = MI.VTableIndex + 1 - AddressPoint;
       } else {
@@ -2657,7 +2657,11 @@ class VFTableBuilder {
       MethodVFTableLocation Loc(MI.VBTableIndex, WhichVFPtr.getVBaseWithVPtr(),
                                 WhichVFPtr.NonVirtualOffset, MI.VFTableIndex);
       if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD)) {
-        MethodVFTableLocations[GlobalDecl(DD, Dtor_Deleting)] = Loc;
+        // In Microsoft ABI vftable always references vector deleting dtor.
+        CXXDtorType DtorTy = Context.getTargetInfo().getCXXABI().isMicrosoft()
+                                 ? Dtor_VectorDeleting
+                                 : Dtor_Deleting;
+        MethodVFTableLocations[GlobalDecl(DD, DtorTy)] = Loc;
       } else {
         MethodVFTableLocations[MD] = Loc;
       }
@@ -3287,7 +3291,10 @@ void VFTableBuilder::dumpLayout(raw_ostream &Out) {
       const CXXDestructorDecl *DD = Component.getDestructorDecl();
 
       DD->printQualifiedName(Out);
-      Out << "() [scalar deleting]";
+      if (Context.getTargetInfo().getCXXABI().isMicrosoft())
+        Out << "() [vector deleting]";
+      else
+        Out << "() [scalar deleting]";
 
       if (DD->isPureVirtual())
         Out << " [pure]";
@@ -3758,7 +3765,7 @@ void MicrosoftVTableContext::dumpMethodLocations(
         PredefinedIdentKind::PrettyFunctionNoVirtual, MD);
 
     if (isa<CXXDestructorDecl>(MD)) {
-      IndicesMap[I.second] = MethodName + " [scalar deleting]";
+      IndicesMap[I.second] = MethodName + " [vector deleting]";
     } else {
       IndicesMap[I.second] = MethodName;
     }
@@ -3875,7 +3882,7 @@ MicrosoftVTableContext::getMethodVFTableLocation(GlobalDecl GD) {
   assert(hasVtableSlot(cast<CXXMethodDecl>(GD.getDecl())) &&
          "Only use this method for virtual methods or dtors");
   if (isa<CXXDestructorDecl>(GD.getDecl()))
-    assert(GD.getDtorType() == Dtor_Deleting);
+    assert(GD.getDtorType() == Dtor_VectorDeleting);
 
   GD = GD.getCanonicalDecl();
 

clang/lib/CodeGen/CGCXX.cpp

@@ -175,7 +175,6 @@ bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
   // requires explicit comdat support in the IL.
   if (llvm::GlobalValue::isWeakForLinker(TargetLinkage))
     return true;
-
   // Create the alias with no name.
   auto *Alias = llvm::GlobalAlias::create(AliasValueType, 0, Linkage, "",
                                           Aliasee, &getModule());
@@ -201,6 +200,42 @@ bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
   return false;
 }
 
+/// Emit a definition as a global alias for another definition, unconditionally.
+void CodeGenModule::EmitDefinitionAsAlias(GlobalDecl AliasDecl,
+                                          GlobalDecl TargetDecl) {
+
+  llvm::Type *AliasValueType = getTypes().GetFunctionType(AliasDecl);
+
+  StringRef MangledName = getMangledName(AliasDecl);
+  llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
+  if (Entry && !Entry->isDeclaration())
+    return;
+  auto *Aliasee = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));
+
+  // Determine the linkage type for the alias.
+  llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl);
+
+  // Create the alias with no name.
+  auto *Alias = llvm::GlobalAlias::create(AliasValueType, 0, Linkage, "",
+                                          Aliasee, &getModule());
+  // Destructors are always unnamed_addr.
+  Alias->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
+
+  if (Entry) {
+    assert(Entry->getValueType() == AliasValueType &&
+           Entry->getAddressSpace() == Alias->getAddressSpace() &&
+           "declaration exists with different type");
+    Alias->takeName(Entry);
+    Entry->replaceAllUsesWith(Alias);
+    Entry->eraseFromParent();
+  } else {
+    Alias->setName(MangledName);
+  }
+
+  // Set any additional necessary attributes for the alias.
+  SetCommonAttributes(AliasDecl, Alias);
+}
+
 llvm::Function *CodeGenModule::codegenCXXStructor(GlobalDecl GD) {
   const CGFunctionInfo &FnInfo = getTypes().arrangeCXXStructorDeclaration(GD);
   auto *Fn = cast<llvm::Function>(

clang/lib/CodeGen/CGCXXABI.cpp

@@ -273,6 +273,20 @@ void CGCXXABI::ReadArrayCookie(CodeGenFunction &CGF, Address ptr,
   numElements = readArrayCookieImpl(CGF, allocAddr, cookieSize);
 }
 
+void CGCXXABI::ReadArrayCookie(CodeGenFunction &CGF, Address ptr,
+                               QualType eltTy, llvm::Value *&numElements,
+                               llvm::Value *&allocPtr, CharUnits &cookieSize) {
+  assert(eltTy.isDestructedType());
+
+  // Derive a char* in the same address space as the pointer.
+  ptr = ptr.withElementType(CGF.Int8Ty);
+
+  cookieSize = getArrayCookieSizeImpl(eltTy);
+  Address allocAddr = CGF.Builder.CreateConstInBoundsByteGEP(ptr, -cookieSize);
+  allocPtr = allocAddr.emitRawPointer(CGF);
+  numElements = readArrayCookieImpl(CGF, allocAddr, cookieSize);
+}
+
 llvm::Value *CGCXXABI::readArrayCookieImpl(CodeGenFunction &CGF,
                                            Address ptr,
                                            CharUnits cookieSize) {

clang/lib/CodeGen/CGCXXABI.h

@@ -275,6 +275,7 @@ class CGCXXABI {
   virtual CatchTypeInfo getCatchAllTypeInfo();
 
   virtual bool shouldTypeidBeNullChecked(QualType SrcRecordTy) = 0;
+  virtual bool hasVectorDeletingDtors() = 0;
   virtual void EmitBadTypeidCall(CodeGenFunction &CGF) = 0;
   virtual llvm::Value *EmitTypeid(CodeGenFunction &CGF, QualType SrcRecordTy,
                                   Address ThisPtr,
@@ -575,6 +576,12 @@ class CGCXXABI {
                                QualType ElementType, llvm::Value *&NumElements,
                                llvm::Value *&AllocPtr, CharUnits &CookieSize);
 
+  /// Reads the array cookie associated with the given pointer,
+  /// that should have one.
+  void ReadArrayCookie(CodeGenFunction &CGF, Address Ptr, QualType ElementType,
+                       llvm::Value *&NumElements, llvm::Value *&AllocPtr,
+                       CharUnits &CookieSize);
+
   /// Return whether the given global decl needs a VTT parameter.
   virtual bool NeedsVTTParameter(GlobalDecl GD);
 

clang/lib/CodeGen/CGClass.cpp

@@ -1433,6 +1433,70 @@ static bool CanSkipVTablePointerInitialization(CodeGenFunction &CGF,
   return true;
 }
 
+static void EmitConditionalArrayDtorCall(const CXXDestructorDecl *DD,
+                                         CodeGenFunction &CGF,
+                                         llvm::Value *ShouldDeleteCondition) {
+  Address ThisPtr = CGF.LoadCXXThisAddress();
+  llvm::BasicBlock *ScalarBB = CGF.createBasicBlock("dtor.scalar");
+  llvm::BasicBlock *callDeleteBB =
+      CGF.createBasicBlock("dtor.call_delete_after_array_destroy");
+  llvm::BasicBlock *VectorBB = CGF.createBasicBlock("dtor.vector");
+  auto *CondTy = cast<llvm::IntegerType>(ShouldDeleteCondition->getType());
+  llvm::Value *CheckTheBitForArrayDestroy = CGF.Builder.CreateAnd(
+      ShouldDeleteCondition, llvm::ConstantInt::get(CondTy, 2));
+  llvm::Value *ShouldDestroyArray =
+      CGF.Builder.CreateIsNull(CheckTheBitForArrayDestroy);
+  CGF.Builder.CreateCondBr(ShouldDestroyArray, ScalarBB, VectorBB);
+
+  CGF.EmitBlock(VectorBB);
+
+  llvm::Value *numElements = nullptr;
+  llvm::Value *allocatedPtr = nullptr;
+  CharUnits cookieSize;
+  QualType EltTy = DD->getThisType()->getPointeeType();
+  CGF.CGM.getCXXABI().ReadArrayCookie(CGF, ThisPtr, EltTy, numElements,
+                                      allocatedPtr, cookieSize);
+
+  // Destroy the elements.
+  QualType::DestructionKind dtorKind = EltTy.isDestructedType();
+
+  assert(dtorKind);
+  assert(numElements && "no element count for a type with a destructor!");
+
+  CharUnits elementSize = CGF.getContext().getTypeSizeInChars(EltTy);
+  CharUnits elementAlign =
+      ThisPtr.getAlignment().alignmentOfArrayElement(elementSize);
+
+  llvm::Value *arrayBegin = ThisPtr.emitRawPointer(CGF);
+  llvm::Value *arrayEnd = CGF.Builder.CreateInBoundsGEP(
+      ThisPtr.getElementType(), arrayBegin, numElements, "delete.end");
+
+  // We already checked that the array is not 0-length before entering vector
+  // deleting dtor.
+  CGF.emitArrayDestroy(arrayBegin, arrayEnd, EltTy, elementAlign,
+                       CGF.getDestroyer(dtorKind),
+                       /*checkZeroLength*/ false, CGF.needsEHCleanup(dtorKind));
+
+  llvm::BasicBlock *VectorBBCont = CGF.createBasicBlock("dtor.vector.cont");
+  CGF.EmitBlock(VectorBBCont);
+
+  llvm::Value *CheckTheBitForDeleteCall = CGF.Builder.CreateAnd(
+      ShouldDeleteCondition, llvm::ConstantInt::get(CondTy, 1));
+
+  llvm::Value *ShouldCallDelete =
+      CGF.Builder.CreateIsNull(CheckTheBitForDeleteCall);
+  CGF.Builder.CreateCondBr(ShouldCallDelete, CGF.ReturnBlock.getBlock(),
+                           callDeleteBB);
+  CGF.EmitBlock(callDeleteBB);
+  const CXXDestructorDecl *Dtor = cast<CXXDestructorDecl>(CGF.CurCodeDecl);
+  const CXXRecordDecl *ClassDecl = Dtor->getParent();
+  CGF.EmitDeleteCall(Dtor->getOperatorDelete(), allocatedPtr,
+                     CGF.getContext().getTagDeclType(ClassDecl));
+
+  CGF.EmitBranchThroughCleanup(CGF.ReturnBlock);
+  CGF.EmitBlock(ScalarBB);
+}
+
 /// EmitDestructorBody - Emits the body of the current destructor.
 void CodeGenFunction::EmitDestructorBody(FunctionArgList &Args) {
   const CXXDestructorDecl *Dtor = cast<CXXDestructorDecl>(CurGD.getDecl());
@@ -1462,7 +1526,9 @@ void CodeGenFunction::EmitDestructorBody(FunctionArgList &Args) {
   // outside of the function-try-block, which means it's always
   // possible to delegate the destructor body to the complete
   // destructor.  Do so.
-  if (DtorType == Dtor_Deleting) {
+  if (DtorType == Dtor_Deleting || DtorType == Dtor_VectorDeleting) {
+    if (CXXStructorImplicitParamValue && DtorType == Dtor_VectorDeleting)
+      EmitConditionalArrayDtorCall(Dtor, *this, CXXStructorImplicitParamValue);
     RunCleanupsScope DtorEpilogue(*this);
     EnterDtorCleanups(Dtor, Dtor_Deleting);
     if (HaveInsertPoint()) {
@@ -1491,6 +1557,8 @@ void CodeGenFunction::EmitDestructorBody(FunctionArgList &Args) {
   switch (DtorType) {
   case Dtor_Comdat: llvm_unreachable("not expecting a COMDAT");
   case Dtor_Deleting: llvm_unreachable("already handled deleting case");
+  case Dtor_VectorDeleting:
+    llvm_unreachable("already handled vector deleting case");
 
   case Dtor_Complete:
     assert((Body || getTarget().getCXXABI().isMicrosoft()) &&
@@ -1573,7 +1641,6 @@ namespace {
       return CGF.EmitScalarExpr(ThisArg);
     return CGF.LoadCXXThis();
   }
-
   /// Call the operator delete associated with the current destructor.
   struct CallDtorDelete final : EHScopeStack::Cleanup {
     CallDtorDelete() {}
@@ -1592,8 +1659,10 @@ namespace {
                                      bool ReturnAfterDelete) {
     llvm::BasicBlock *callDeleteBB = CGF.createBasicBlock("dtor.call_delete");
     llvm::BasicBlock *continueBB = CGF.createBasicBlock("dtor.continue");
-    llvm::Value *ShouldCallDelete
-      = CGF.Builder.CreateIsNull(ShouldDeleteCondition);
+    auto *CondTy = cast<llvm::IntegerType>(ShouldDeleteCondition->getType());
+    llvm::Value *CheckTheBit = CGF.Builder.CreateAnd(
+        ShouldDeleteCondition, llvm::ConstantInt::get(CondTy, 1));
+    llvm::Value *ShouldCallDelete = CGF.Builder.CreateIsNull(CheckTheBit);
     CGF.Builder.CreateCondBr(ShouldCallDelete, continueBB, callDeleteBB);
 
     CGF.EmitBlock(callDeleteBB);

clang/lib/CodeGen/CGDebugInfo.cpp

@@ -2119,7 +2119,8 @@ llvm::DISubprogram *CGDebugInfo::CreateCXXMemberFunction(
       // Emit MS ABI vftable information.  There is only one entry for the
       // deleting dtor.
       const auto *DD = dyn_cast<CXXDestructorDecl>(Method);
-      GlobalDecl GD = DD ? GlobalDecl(DD, Dtor_Deleting) : GlobalDecl(Method);
+      GlobalDecl GD =
+          DD ? GlobalDecl(DD, Dtor_VectorDeleting) : GlobalDecl(Method);
       MethodVFTableLocation ML =
           CGM.getMicrosoftVTableContext().getMethodVFTableLocation(GD);
       VIndex = ML.Index;