Reland [MS][clang] Add support for vector deleting destructors (#165598)

MSVC supports an extension allowing to delete an array of objects via
pointer whose static type doesn't match its dynamic type. This is done
via generation of special destructors - vector deleting destructors.
MSVC's virtual tables always contain a pointer to the vector deleting
destructor for classes with virtual destructors, so not having this
extension implemented causes clang to generate code that is not
compatible with the code generated by MSVC, because clang always puts a
pointer to a scalar deleting destructor to the vtable. As a bonus the
deletion of an array of polymorphic object will work just like it does
with MSVC - no memory leaks and correct destructors are called.

This patch will cause clang to emit code that is compatible with code
produced by MSVC but not compatible with code produced with clang of
older versions, so the new behavior can be disabled via passing
-fclang-abi-compat=21 (or lower).

This is yet another attempt to land vector deleting destructors support
originally implemented by
https://github.com/llvm/llvm-project/pull/133451.

This PR contains fixes for issues reported in the original PR as well as
fixes for issues related to operator delete[] search reported in several
issues like

https://github.com/llvm/llvm-project/pull/133950#issuecomment-2787510484
https://github.com/llvm/llvm-project/issues/134265

Fixes https://github.com/llvm/llvm-project/issues/19772

1 files changed, 50 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 08c66bdbbb9f..3eeb1718e455 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -8288,3 +8288,53 @@ void CodeGenModule::moveLazyEmissionStates(CodeGenModule *NewBuilder) {
 
   NewBuilder->ABI->MangleCtx = std::move(ABI->MangleCtx);
 }
+
+bool CodeGenModule::classNeedsVectorDestructor(const CXXRecordDecl *RD) {
+  if (!Context.getTargetInfo().emitVectorDeletingDtors(Context.getLangOpts()))
+    return false;
+  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;
+
+  return RequireVectorDeletingDtor.count(RD);
+}
+
+void CodeGenModule::requireVectorDestructorDefinition(const CXXRecordDecl *RD) {
+  if (!Context.getTargetInfo().emitVectorDeletingDtors(Context.getLangOpts()))
+    return;
+  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());
+    SetFunctionAttributes(VectorDtorGD, NewFn, /*IsIncompleteFunction*/ false,
+                          /*IsThunk*/ false);
+    NewFn->takeName(VDEntry);
+    VDEntry->replaceAllUsesWith(NewFn);
+    VDEntry->eraseFromParent();
+    Entry->replaceAllUsesWith(NewFn);
+    Entry->eraseFromParent();
+    addDeferredDeclToEmit(VectorDtorGD);
+  }
+}