[MS][clang] Add support for vector deleting destructors (#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 https://github.com/llvm/llvm-project/issues/19772

1 files changed, 38 insertions, 4 deletions

diff --git a/clang/lib/CodeGen/CGExprCXX.cpp b/clang/lib/CodeGen/CGExprCXX.cpp
index f71c18a8041b..d4e14f4574b8 100644
--- a/clang/lib/CodeGen/CGExprCXX.cpp
+++ b/clang/lib/CodeGen/CGExprCXX.cpp
@@ -1209,6 +1209,8 @@ void CodeGenFunction::EmitNewArrayInitializer(
     EmitCXXAggrConstructorCall(Ctor, NumElements, CurPtr, CCE,
                                /*NewPointerIsChecked*/true,
                                CCE->requiresZeroInitialization());
+    if (CGM.getCXXABI().hasVectorDeletingDtors())
+      CGM.requireVectorDestructorDefinition(Ctor->getParent());
     return;
   }
 
@@ -1912,10 +1914,8 @@ static void EmitDestroyingObjectDelete(CodeGenFunction &CGF,
 /// Emit the code for deleting a single object.
 /// \return \c true if we started emitting UnconditionalDeleteBlock, \c false
 /// if not.
-static bool EmitObjectDelete(CodeGenFunction &CGF,
-                             const CXXDeleteExpr *DE,
-                             Address Ptr,
-                             QualType ElementType,
+static bool EmitObjectDelete(CodeGenFunction &CGF, const CXXDeleteExpr *DE,
+                             Address Ptr, QualType ElementType,
                              llvm::BasicBlock *UnconditionalDeleteBlock) {
   // C++11 [expr.delete]p3:
   //   If the static type of the object to be deleted is different from its
@@ -2131,6 +2131,40 @@ void CodeGenFunction::EmitCXXDeleteExpr(const CXXDeleteExpr *E) {
 
   assert(ConvertTypeForMem(DeleteTy) == Ptr.getElementType());
 
+  if (E->isArrayForm() && CGM.getCXXABI().hasVectorDeletingDtors()) {
+    if (auto *RD = DeleteTy->getAsCXXRecordDecl()) {
+      auto *Dtor = RD->getDestructor();
+      if (Dtor && Dtor->isVirtual()) {
+        llvm::Value *NumElements = nullptr;
+        llvm::Value *AllocatedPtr = nullptr;
+        CharUnits CookieSize;
+        llvm::BasicBlock *bodyBB = createBasicBlock("vdtor.call");
+        llvm::BasicBlock *doneBB = createBasicBlock("vdtor.nocall");
+        // Check array cookie to see if the array has 0 length. Don't call
+        // the destructor in that case.
+        CGM.getCXXABI().ReadArrayCookie(*this, Ptr, E, DeleteTy, NumElements,
+                                        AllocatedPtr, CookieSize);
+
+        auto *CondTy = cast<llvm::IntegerType>(NumElements->getType());
+        llvm::Value *isEmpty = Builder.CreateICmpEQ(
+            NumElements, llvm::ConstantInt::get(CondTy, 0));
+        Builder.CreateCondBr(isEmpty, doneBB, bodyBB);
+
+        // Delete cookie for empty array.
+        const FunctionDecl *operatorDelete = E->getOperatorDelete();
+        EmitBlock(doneBB);
+        EmitDeleteCall(operatorDelete, AllocatedPtr, DeleteTy, NumElements,
+                       CookieSize);
+        EmitBranch(DeleteEnd);
+
+        EmitBlock(bodyBB);
+        if (!EmitObjectDelete(*this, E, Ptr, DeleteTy, DeleteEnd))
+          EmitBlock(DeleteEnd);
+        return;
+      }
+    }
+  }
+
   if (E->isArrayForm()) {
     EmitArrayDelete(*this, E, Ptr, DeleteTy);
     EmitBlock(DeleteEnd);