[Clang][CodeGen] Fix CanSkipVTablePointerInitialization for dynamic classes with a trivial anonymous union

clang/lib/CodeGen/CGClass.cpp

@@ -1395,7 +1395,7 @@ FieldHasTrivialDestructorBody(ASTContext &Context,
 
   // The destructor for an implicit anonymous union member is never invoked.
   if (FieldClassDecl->isUnion() && FieldClassDecl->isAnonymousStructOrUnion())
-    return false;
+    return true;
 
   return HasTrivialDestructorBody(Context, FieldClassDecl, FieldClassDecl);
 }

clang/test/CodeGenCXX/skip-vtable-pointer-initialization.cpp

@@ -198,3 +198,65 @@ struct C : virtual B {
 C::~C() {}
 
 }
+
+namespace Test10 {
+
+// Check that we don't initialize the vtable pointer in A::~A(), since the class has an anonymous union which
+// never has its destructor invoked.
+struct A {
+    virtual void f();
+    ~A();
+
+    union
+    {
+        int i;
+        unsigned u;
+    };
+};
+
+// CHECK-LABEL: define{{.*}} void @_ZN6Test101AD2Ev
+// CHECK-NOT: store ptr getelementptr inbounds ({ [3 x ptr] }, ptr @_ZTVN6Test101AE, i32 0, inrange i32 0, i32 2), ptr
+A::~A() {
+}
+
+}
+
+namespace Test11 {
+
+// Check that we don't initialize the vtable pointer in A::~A(), even if the base class has a non trivial destructor.
+struct Field {
+    ~Field();
+};
+
+struct A : public Field {
+    virtual void f();
+    ~A();
+};
+
+// CHECK-LABEL: define{{.*}} void @_ZN6Test111AD2Ev
+// CHECK-NOT: store ptr getelementptr inbounds ({ [3 x ptr] }, ptr @_ZTVN6Test111AE, i32 0, inrange i32 0, i32 2), ptr
+A::~A() {
+}
+
+}
+
+namespace Test12 {
+
+// Check that we don't initialize the vtable pointer in A::~A(), since the class has an anonymous struct with trivial fields.
+struct A {
+    virtual void f();
+    ~A();
+
+    struct
+    {
+        int i;
+        unsigned u;
+    };
+};
+
+// CHECK-LABEL: define{{.*}} void @_ZN6Test121AD2Ev
+// CHECK-NOT: store ptr getelementptr inbounds ({ [3 x ptr] }, ptr @_ZTVN6Test121AE, i32 0, inrange i32 0, i32 2), ptr
+A::~A() {
+}
+
+}