From 4e32604f60c03c71c81f3f30fb31b1b0734e467d Mon Sep 17 00:00:00 2001
From: Reid Kleckner <reid@kleckner.net>
Date: Wed, 16 Jul 2014 00:30:59 +0000
Subject: [PATCH] Avoid referencing the vtable when calling the ctor without
 emitting it

This fixes compilation errors about incomplete types used with WebKit's
RefPtr template.  Simply calling an out of line constructor should not
instantiate all inline and defaulted virtual methods.

Tested by building and testing several big piles of code on Linux.

Reviewers: rsmith

Differential Revision: http://reviews.llvm.org/D4429

llvm-svn: 213109
---
 clang/lib/Sema/SemaExpr.cpp                   |  2 -
 .../SemaTemplate/virtual-member-functions.cpp | 54 ++++++++++++++++++-
 2 files changed, 52 insertions(+), 4 deletions(-)

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 8db782a7e206..1db903675e50 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -11445,8 +11445,6 @@ void Sema::MarkFunctionReferenced(SourceLocation Loc, FunctionDecl *Func) {
     } else if (Constructor->getInheritedConstructor()) {
       DefineInheritingConstructor(Loc, Constructor);
     }
-
-    MarkVTableUsed(Loc, Constructor->getParent());
   } else if (CXXDestructorDecl *Destructor =
                  dyn_cast<CXXDestructorDecl>(Func)) {
     Destructor = cast<CXXDestructorDecl>(Destructor->getFirstDecl());
diff --git a/clang/test/SemaTemplate/virtual-member-functions.cpp b/clang/test/SemaTemplate/virtual-member-functions.cpp
index 1a018084a53a..a23bf4e3ee5e 100644
--- a/clang/test/SemaTemplate/virtual-member-functions.cpp
+++ b/clang/test/SemaTemplate/virtual-member-functions.cpp
@@ -44,7 +44,7 @@ template struct Derived<int>; // expected-note {{in instantiation of member func
 
 template<typename T>
 struct HasOutOfLineKey {
-  HasOutOfLineKey() { } 
+  HasOutOfLineKey() { } // expected-note{{in instantiation of member function 'HasOutOfLineKey<int>::f' requested here}}
   virtual T *f(float *fp);
 };
 
@@ -53,7 +53,7 @@ T *HasOutOfLineKey<T>::f(float *fp) {
   return fp; // expected-error{{cannot initialize return object of type 'int *' with an lvalue of type 'float *'}}
 }
 
-HasOutOfLineKey<int> out_of_line; // expected-note{{in instantiation of member function 'HasOutOfLineKey<int>::f' requested here}}
+HasOutOfLineKey<int> out_of_line; // expected-note{{in instantiation of member function 'HasOutOfLineKey<int>::HasOutOfLineKey' requested here}}
 
 namespace std {
   class type_info;
@@ -102,3 +102,53 @@ namespace DynamicCast {
   Y* f(X<void>* x) { return dynamic_cast<Y*>(x); } // expected-note {{in instantiation of member function 'DynamicCast::X<void>::foo' requested here}}
   Y* f2(X<void>* x) { return dynamic_cast<Y*>(x); }
 }
+
+namespace avoid_using_vtable {
+// We shouldn't emit the vtable for this code, in any ABI.  If we emit the
+// vtable, we emit an implicit virtual dtor, which calls ~RefPtr, which requires
+// a complete type for DeclaredOnly.
+//
+// Previously we would reference the vtable in the MS C++ ABI, even though we
+// don't need to emit either the ctor or the dtor.  In the Itanium C++ ABI, the
+// 'trace' method is the key function, so even though we use the vtable, we
+// don't emit it.
+
+template <typename T>
+struct RefPtr {
+  T *m_ptr;
+  ~RefPtr() { m_ptr->deref(); }
+};
+struct DeclaredOnly;
+struct Base {
+  virtual ~Base();
+};
+
+struct AvoidVTable : Base {
+  RefPtr<DeclaredOnly> m_insertionStyle;
+  virtual void trace();
+  AvoidVTable();
+};
+// Don't call the dtor, because that will emit an implicit dtor, and require a
+// complete type for DeclaredOnly.
+void foo() { new AvoidVTable; }
+}
+
+namespace vtable_uses_incomplete {
+// Opposite of the previous test that avoids a vtable, this one tests that we
+// use the vtable when the ctor is defined inline.
+template <typename T>
+struct RefPtr {
+  T *m_ptr;
+  ~RefPtr() { m_ptr->deref(); }  // expected-error {{member access into incomplete type 'vtable_uses_incomplete::DeclaredOnly'}}
+};
+struct DeclaredOnly; // expected-note {{forward declaration of 'vtable_uses_incomplete::DeclaredOnly'}}
+struct Base {
+  virtual ~Base();
+};
+
+struct UsesVTable : Base {
+  RefPtr<DeclaredOnly> m_insertionStyle;
+  virtual void trace();
+  UsesVTable() {} // expected-note {{in instantiation of member function 'vtable_uses_incomplete::RefPtr<vtable_uses_incomplete::DeclaredOnly>::~RefPtr' requested here}}
+};
+}