When emitting the destructor for a class with a vtable, if we can determine

that the destructor body is trivial and that all member variables also have either
trivial destructors or trivial destructor bodies, we don't need to initialize the
vtable pointers since no virtual member functions will be called on the destructor.

Fixes PR9181.

llvm-svn: 131368

2 files changed, 107 insertions, 1 deletions

diff --git a/clang/test/CodeGenCXX/mangle-subst-std.cpp b/clang/test/CodeGenCXX/mangle-subst-std.cpp
index fea3582d321..c54d3e5297f 100644
--- a/clang/test/CodeGenCXX/mangle-subst-std.cpp
+++ b/clang/test/CodeGenCXX/mangle-subst-std.cpp
@@ -8,8 +8,8 @@
 // CHECK: @_ZTCSd0_Si = linkonce_odr unnamed_addr constant 
 // CHECK: @_ZTCSd16_So = linkonce_odr unnamed_addr constant
 // CHECK: @_ZTTSo = linkonce_odr unnamed_addr constant
-// CHECK: @_ZTVSo = linkonce_odr unnamed_addr constant
 // CHECK: @_ZTTSi = linkonce_odr unnamed_addr constant
+// CHECK: @_ZTVSo = linkonce_odr unnamed_addr constant
 // CHECK: @_ZTVSi = linkonce_odr unnamed_addr constant
 namespace std {
   struct A { A(); };
diff --git a/clang/test/CodeGenCXX/skip-vtable-pointer-initialization.cpp b/clang/test/CodeGenCXX/skip-vtable-pointer-initialization.cpp
new file mode 100644
index 00000000000..f992bd339df
--- /dev/null
+++ b/clang/test/CodeGenCXX/skip-vtable-pointer-initialization.cpp
@@ -0,0 +1,106 @@
+// RUN: %clang_cc1 %s -triple=x86_64-apple-darwin10 -emit-llvm -o - | FileCheck %s
+
+namespace Test1 {
+
+// Check that we don't initialize the vtable pointer in A::~A(), since the destructor body is trivial.
+struct A {
+  virtual void f();
+  ~A();
+};
+
+// CHECK: define void @_ZN5Test11AD2Ev
+// CHECK-NOT: store i8** getelementptr inbounds ([3 x i8*]* @_ZTVN5Test11AE, i64 0, i64 2), i8***
+A::~A() 
+{
+}
+
+}
+
+namespace Test2 {
+
+// Check that we do initialize the vtable pointer in A::~A() since the destructor body isn't trivial.
+struct A {
+  virtual void f();
+  ~A();
+};
+
+// CHECK: define void @_ZN5Test21AD2Ev
+// CHECK: store i8** getelementptr inbounds ([3 x i8*]* @_ZTVN5Test21AE, i64 0, i64 2), i8***
+A::~A() {
+  f();
+}
+
+}
+
+namespace Test3 {
+
+// Check that we don't initialize the vtable pointer in A::~A(), since the destructor body is trivial
+// and Field's destructor body is also trivial.
+struct Field {
+  ~Field() { }
+};
+
+struct A {
+  virtual void f();
+  ~A();
+
+  Field field;
+};
+
+// CHECK: define void @_ZN5Test31AD2Ev
+// CHECK-NOT: store i8** getelementptr inbounds ([3 x i8*]* @_ZTVN5Test31AE, i64 0, i64 2), i8***
+A::~A() {
+  
+}
+
+}
+
+namespace Test4 {
+
+// Check that we do initialize the vtable pointer in A::~A(), since Field's destructor body
+// isn't trivial.
+
+void f();
+
+struct Field {
+  ~Field() { f(); }
+};
+
+struct A {
+  virtual void f();
+  ~A();
+
+  Field field;
+};
+
+// CHECK: define void @_ZN5Test41AD2Ev
+// CHECK: store i8** getelementptr inbounds ([3 x i8*]* @_ZTVN5Test41AE, i64 0, i64 2), i8***
+A::~A()
+{
+}
+
+}
+
+namespace Test5 {
+
+// Check that we do initialize the vtable pointer in A::~A(), since Field's destructor isn't
+// available in this translation unit.
+
+struct Field {
+  ~Field();
+};
+
+struct A {
+  virtual void f();
+  ~A();
+
+  Field field;
+};
+
+// CHECK: define void @_ZN5Test51AD2Ev
+// CHECK: store i8** getelementptr inbounds ([3 x i8*]* @_ZTVN5Test51AE, i64 0, i64 2), i8***
+A::~A()
+{
+}
+
+}
\ No newline at end of file