add tbaa metadata to vtable pointer loads/stores

llvm-svn: 153447

clang/lib/CodeGen/CGClass.cpp

@@ -1514,7 +1514,8 @@ CodeGenFunction::InitializeVTablePointer(BaseSubobject Base,
   llvm::Type *AddressPointPtrTy =
     VTableAddressPoint->getType()->getPointerTo();
   VTableField = Builder.CreateBitCast(VTableField, AddressPointPtrTy);
-  Builder.CreateStore(VTableAddressPoint, VTableField);
+  llvm::StoreInst *Store = Builder.CreateStore(VTableAddressPoint, VTableField);
+  CGM.DecorateInstruction(Store, CGM.getTBAAInfoForVTablePtr());
 }
 
 void
@@ -1597,7 +1598,9 @@ void CodeGenFunction::InitializeVTablePointers(const CXXRecordDecl *RD) {
 llvm::Value *CodeGenFunction::GetVTablePtr(llvm::Value *This,
                                            llvm::Type *Ty) {
   llvm::Value *VTablePtrSrc = Builder.CreateBitCast(This, Ty->getPointerTo());
-  return Builder.CreateLoad(VTablePtrSrc, "vtable");
+  llvm::Instruction *VTable = Builder.CreateLoad(VTablePtrSrc, "vtable");
+  CGM.DecorateInstruction(VTable, CGM.getTBAAInfoForVTablePtr());
+  return VTable;
 }
 
 static const CXXRecordDecl *getMostDerivedClassDecl(const Expr *Base) {

clang/lib/CodeGen/CodeGenModule.cpp

@@ -182,6 +182,12 @@ llvm::MDNode *CodeGenModule::getTBAAInfo(QualType QTy) {
   return TBAA->getTBAAInfo(QTy);
 }
 
+llvm::MDNode *CodeGenModule::getTBAAInfoForVTablePtr() {
+  if (!TBAA)
+    return 0;
+  return TBAA->getTBAAInfoForVTablePtr();
+}
+
 void CodeGenModule::DecorateInstruction(llvm::Instruction *Inst,
                                         llvm::MDNode *TBAAInfo) {
   Inst->setMetadata(llvm::LLVMContext::MD_tbaa, TBAAInfo);

clang/lib/CodeGen/CodeGenModule.h

@@ -448,6 +448,7 @@ public:
   bool shouldUseTBAA() const { return TBAA != 0; }
 
   llvm::MDNode *getTBAAInfo(QualType QTy);
+  llvm::MDNode *getTBAAInfoForVTablePtr();
 
   bool isTypeConstant(QualType QTy, bool ExcludeCtorDtor);
 

clang/lib/CodeGen/CodeGenTBAA.cpp

@@ -179,3 +179,7 @@ CodeGenTBAA::getTBAAInfo(QualType QTy) {
   // For now, handle any other kind of type conservatively.
   return MetadataCache[Ty] = getChar();
 }
+
+llvm::MDNode *CodeGenTBAA::getTBAAInfoForVTablePtr() {
+  return getTBAAInfoForNamedType("vtable pointer", getRoot());
+}

clang/lib/CodeGen/CodeGenTBAA.h

@@ -68,6 +68,10 @@ public:
   /// getTBAAInfo - Get the TBAA MDNode to be used for a dereference
   /// of the given type.
   llvm::MDNode *getTBAAInfo(QualType QTy);
+
+  /// getTBAAInfoForVTablePtr - Get the TBAA MDNode to be used for a
+  /// dereference of a vtable pointer.
+  llvm::MDNode *getTBAAInfoForVTablePtr();
 };
 
 }  // end namespace CodeGen

clang/test/CodeGen/tbaa-for-vptr.cpp

@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -emit-llvm -o - -O1 %s | FileCheck %s
+// Check that we generate TBAA for vtable pointer loads and stores.
+struct A {
+  virtual int foo() const ;
+  virtual ~A();
+};
+
+void CreateA() {
+  new A;
+}
+
+void CallFoo(A *a) {
+  a->foo();
+}
+
+// CHECK: %vtable = load {{.*}} !tbaa !0
+// CHECK: store {{.*}} !tbaa !0
+// CHECK: !0 = metadata !{metadata !"vtable pointer", metadata !1}
+// CHECK: !1 = metadata !{metadata !"Simple C/C++ TBAA", null}