Generating available_externally vtables for outline virtual functions

Generating available_externally vtables for optimizations purposes.
Unfortunatelly ItaniumABI doesn't guarantee that we will be able to
refer to virtual inline method by name.
But when we don't have any inline virtual methods, and key function is
not defined in this TU, we can generate that there will be vtable and
mark it as available_externally.

This is patch will help devirtualize better.
Differential Revision: http://reviews.llvm.org/D11441

llvm-svn: 243090

2 files changed, 144 insertions, 6 deletions

diff --git a/clang/test/CodeGenCXX/vtable-available-externally.cpp b/clang/test/CodeGenCXX/vtable-available-externally.cpp
index e07d48463f4..ab090936cbd 100644
--- a/clang/test/CodeGenCXX/vtable-available-externally.cpp
+++ b/clang/test/CodeGenCXX/vtable-available-externally.cpp
@@ -1,7 +1,12 @@
-// RUN: %clang_cc1 %s -I%S -triple=x86_64-apple-darwin10 -emit-llvm -o %t 
+// RUN: %clang_cc1 %s -I%S -triple=x86_64-apple-darwin10 -emit-llvm -o %t
+// RUN: %clang_cc1 %s -I%S -triple=x86_64-apple-darwin10 -O2 -disable-llvm-optzns -emit-llvm -o %t.opt
 // RUN: FileCheck --check-prefix=CHECK-TEST1 %s < %t
 // RUN: FileCheck --check-prefix=CHECK-TEST2 %s < %t
 // RUN: FileCheck --check-prefix=CHECK-TEST5 %s < %t
+// RUN: FileCheck --check-prefix=CHECK-TEST8 %s < %t.opt
+// RUN: FileCheck --check-prefix=CHECK-TEST9 %s < %t.opt
+// RUN: FileCheck --check-prefix=CHECK-TEST10 %s < %t.opt
+// RUN: FileCheck --check-prefix=CHECK-TEST11 %s < %t.opt
 
 #include <typeinfo>
 
@@ -152,3 +157,135 @@ struct c28 : virtual c11{
   void f6 ();
 };
 }
+
+namespace Test8 {
+// CHECK-TEST8: @_ZTVN5Test81YE = available_externally unnamed_addr constant
+// vtable for X is not generated because there are no stores here
+struct X {
+  X();
+  virtual void foo();
+};
+struct Y : X {
+  void foo();
+};
+
+void g(X* p) { p->foo(); }
+void f() {
+  Y y;
+  g(&y);
+  X x;
+  g(&x);
+}
+
+}  // Test8
+
+namespace Test9 {
+// all virtual functions are outline, so we can assume that it will
+// be generated in translation unit where foo is defined
+// CHECK-TEST9: @_ZTVN5Test91AE = available_externally unnamed_addr constant
+// CHECK-TEST9: @_ZTVN5Test91BE = available_externally unnamed_addr constant
+struct A {
+  virtual void foo();
+  virtual void bar();
+};
+void A::bar() {}
+
+struct B : A {
+  void foo();
+};
+
+void g() {
+  A a;
+  a.foo();
+  B b;
+  b.foo();
+}
+
+}  // Test9
+
+namespace Test10 {
+
+// because A's key function is defined here, vtable is generated in this TU
+// CHECK-TEST10: @_ZTVN6Test101AE = unnamed_addr constant
+struct A {
+  virtual void foo();
+  virtual void bar();
+};
+void A::foo() {}
+
+// Because key function is inline we will generate vtable as linkonce_odr
+// CHECK-TEST10: @_ZTVN6Test101DE = linkonce_odr unnamed_addr constant
+struct D : A {
+  void bar();
+};
+inline void D::bar() {}
+
+// because B has outline key function then we can refer to
+// CHECK-TEST10: @_ZTVN6Test101BE = available_externally unnamed_addr constant
+struct B : A {
+  void foo();
+  void bar();
+};
+
+// C's key function (car) is outline, but C has inline virtual function so we
+// can't guarantee that we will be able to refer to bar from name
+// so (at the moment) we can't emit vtable available_externally
+// CHECK-TEST10: @_ZTVN6Test101CE = external unnamed_addr constant
+struct C : A {
+  void bar() {}               // defined in body - not key function
+  virtual inline void gar();  // inline in body - not key function
+  virtual void car();
+};
+
+// no key function, vtable will be generated everywhere it will be used
+// CHECK-TEST10: @_ZTVN6Test101EE = linkonce_odr unnamed_addr constant
+struct E : A {};
+
+void g(A& a) {
+  a.foo();
+  a.bar();
+}
+
+void f() {
+  A a;
+  g(a);
+  B b;
+  g(b);
+  C c;
+  g(c);
+  D d;
+  g(d);
+  E e;
+  g(e);
+}
+
+}  // Test10
+
+namespace Test11 {
+struct D;
+// Can emit C's vtable available_externally.
+// CHECK-TEST11: @_ZTVN6Test111CE = available_externally unnamed_addr constant
+struct C {
+  virtual D& operator=(const D&);
+};
+
+// Cannot emit B's vtable available_externally, because we cannot create
+// a reference to the inline virtual B::operator= function.
+// CHECK-TEST11: @_ZTVN6Test111DE = external unnamed_addr constant
+struct D : C {
+  virtual void key();
+};
+D f();
+
+void g(D& a) {
+  C c;
+  c = a;
+  a.key();
+  a.key();
+}
+void g() {
+  D d;
+  d = f();
+  g(d);
+}
+}  // Test 11
diff --git a/clang/test/CodeGenCXX/vtable-linkage.cpp b/clang/test/CodeGenCXX/vtable-linkage.cpp
index 5cbd3897a1f..ff398ffa61d 100644
--- a/clang/test/CodeGenCXX/vtable-linkage.cpp
+++ b/clang/test/CodeGenCXX/vtable-linkage.cpp
@@ -139,10 +139,11 @@ void use_F() {
 // CHECK-OPT-DAG: @_ZTV1FIiE = external unnamed_addr constant
 
 // E<int> is an explicit template instantiation declaration. It has a
-// key function that is not instantiated, so we should only reference
-// its vtable, not define it.
+// key function is not instantiated, so we know that vtable definition
+// will be generated in TU where key function will be defined
+// so we can mark it as available_externally (only with optimizations)
 // CHECK-DAG: @_ZTV1EIiE = external unnamed_addr constant
-// CHECK-OPT-DAG: @_ZTV1EIiE = external unnamed_addr constant
+// CHECK-OPT-DAG: @_ZTV1EIiE = available_externally unnamed_addr constant
 
 // The anonymous struct for e has no linkage, so the vtable should have
 // internal linkage.
@@ -196,8 +197,8 @@ void use_H() {
 // CHECK-DAG: @_ZTT1IIiE = external unnamed_addr constant
 // CHECK-NOT: @_ZTC1IIiE
 //
-// CHECK-OPT-DAG: @_ZTV1IIiE = external unnamed_addr constant
-// CHECK-OPT-DAG: @_ZTT1IIiE = external unnamed_addr constant
+// CHECK-OPT-DAG: @_ZTV1IIiE = available_externally unnamed_addr constant
+// CHECK-OPT-DAG: @_ZTT1IIiE = available_externally unnamed_addr constant
 struct VBase1 { virtual void f(); }; struct VBase2 : virtual VBase1 {};
 template<typename T>
 struct I : VBase2 {};