From b0769101ac05792ccc539bc7359b1927b3fd4aca Mon Sep 17 00:00:00 2001
From: Douglas Gregor <dgregor@apple.com>
Date: Thu, 6 May 2010 23:13:35 +0000
Subject: [PATCH] Do not give implicitly-defined virtual members functions
 available_externally linkage, since they may not have been given a strong
 definition in another translation unit. Without this patch, the following
 test case fails to link with a GCC-compiled libstdc++:

  #include <sstream>
  int main() { std::basic_stringbuf<char> bs; }

Fixes the last problem with the Boost.IO library.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@103208 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/CodeGenModule.cpp        |  4 ++--
 test/CodeGenCXX/template-linkage.cpp | 20 ++++++++++++++++++++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/lib/CodeGen/CodeGenModule.cpp b/lib/CodeGen/CodeGenModule.cpp
index 9c84bcec05..6cbc3f67c2 100644
--- a/lib/CodeGen/CodeGenModule.cpp
+++ b/lib/CodeGen/CodeGenModule.cpp
@@ -322,8 +322,8 @@ GetLinkageForFunction(ASTContext &Context, const FunctionDecl *FD,
   // only for inlining and analysis. This is the semantics of c99 inline.
   if (const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(FD)) {
     const CXXRecordDecl *RD = MD->getParent();
-    if (MD->isVirtual() &&
-	CodeGenVTables::isKeyFunctionInAnotherTU(Context, RD))
+    if (MD->isVirtual() && !MD->isImplicit() &&
+        CodeGenVTables::isKeyFunctionInAnotherTU(Context, RD))
       return CodeGenModule::GVA_C99Inline;
   }  
 
diff --git a/test/CodeGenCXX/template-linkage.cpp b/test/CodeGenCXX/template-linkage.cpp
index ccd61a7bbe..63a5c09cd7 100644
--- a/test/CodeGenCXX/template-linkage.cpp
+++ b/test/CodeGenCXX/template-linkage.cpp
@@ -22,3 +22,23 @@ template void f<int>(int);
 template <typename T> inline void g(T) { }
 template void g<int>(int);
 
+template<typename T>
+struct X0 {
+  virtual ~X0() { }
+};
+
+template<typename T>
+struct X1 : X0<T> {
+  virtual void blarg();
+};
+
+template<typename T> void X1<T>::blarg() { }
+
+extern template struct X0<char>;
+extern template struct X1<char>;
+
+// CHECK: define linkonce_odr void @_ZN2X1IcED1Ev(
+void test_X1() {
+  X1<char> i1c;
+}
+
-- 
2.40.0