[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, 46 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 3caa79b..cec8f12 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -7927,3 +7927,49 @@ void CodeGenModule::moveLazyEmissionStates(CodeGenModule *NewBuilder) {
 
   NewBuilder->ABI->MangleCtx = std::move(ABI->MangleCtx);
 }
+
+bool CodeGenModule::classNeedsVectorDestructor(const CXXRecordDecl *RD) {
+  CXXDestructorDecl *Dtor = RD->getDestructor();
+  // The compiler can't know if new[]/delete[] will be used outside of the DLL,
+  // so just force vector deleting destructor emission if dllexport is present.
+  // This matches MSVC behavior.
+  if (Dtor && Dtor->isVirtual() && Dtor->isDefined() &&
+      Dtor->hasAttr<DLLExportAttr>())
+    return true;
+
+  assert(getCXXABI().hasVectorDeletingDtors());
+  return RequireVectorDeletingDtor.count(RD);
+}
+
+void CodeGenModule::requireVectorDestructorDefinition(const CXXRecordDecl *RD) {
+  assert(getCXXABI().hasVectorDeletingDtors());
+  RequireVectorDeletingDtor.insert(RD);
+
+  // To reduce code size in general case we lazily emit scalar deleting
+  // destructor definition and an alias from vector deleting destructor to
+  // scalar deleting destructor. It may happen that we first emitted the scalar
+  // deleting destructor definition and the alias and then discovered that the
+  // definition of the vector deleting destructor is required. Then we need to
+  // remove the alias and the scalar deleting destructor and queue vector
+  // deleting destructor body for emission. Check if that is the case.
+  CXXDestructorDecl *DtorD = RD->getDestructor();
+  GlobalDecl ScalarDtorGD(DtorD, Dtor_Deleting);
+  StringRef MangledName = getMangledName(ScalarDtorGD);
+  llvm::GlobalValue *Entry = GetGlobalValue(MangledName);
+  if (Entry && !Entry->isDeclaration()) {
+    GlobalDecl VectorDtorGD(DtorD, Dtor_VectorDeleting);
+    StringRef VDName = getMangledName(VectorDtorGD);
+    llvm::GlobalValue *VDEntry = GetGlobalValue(VDName);
+    // It exists and it should be an alias.
+    assert(VDEntry && isa<llvm::GlobalAlias>(VDEntry));
+    auto *NewFn = llvm::Function::Create(
+        cast<llvm::FunctionType>(VDEntry->getValueType()),
+        llvm::Function::ExternalLinkage, VDName, &getModule());
+    NewFn->takeName(VDEntry);
+    VDEntry->replaceAllUsesWith(NewFn);
+    VDEntry->eraseFromParent();
+    Entry->replaceAllUsesWith(NewFn);
+    Entry->eraseFromParent();
+    addDeferredDeclToEmit(VectorDtorGD);
+  }
+}