Make sure that explicitly instantiated functions get the right linkage.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@91069 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/CodeGenModule.cpp

@@ -256,9 +256,18 @@ GetLinkageForFunction(ASTContext &Context, const FunctionDecl *FD,
   // The kind of external linkage this function will have, if it is not
   // inline or static.
   CodeGenModule::GVALinkage External = CodeGenModule::GVA_StrongExternal;
-  if (Context.getLangOptions().CPlusPlus &&
+  if (Context.getLangOptions().CPlusPlus) {
-      FD->getTemplateSpecializationKind() == TSK_ImplicitInstantiation)
+    TemplateSpecializationKind TSK = FD->getTemplateSpecializationKind();
+    
+    if (TSK == TSK_ExplicitInstantiationDefinition) {
+      // If a function has been explicitly instantiated, then it should
+      // always have strong external linkage.
+      return CodeGenModule::GVA_StrongExternal;
+    } 
+    
+    if (TSK == TSK_ImplicitInstantiation)
       External = CodeGenModule::GVA_TemplateInstantiation;
+  }
 
   if (!FD->isInlined())
     return External;

test/CodeGenCXX/template-linkage.cpp

@@ -0,0 +1,24 @@
+// RUN: clang-cc %s -triple=x86_64-apple-darwin10 -emit-llvm -o - | FileCheck %s
+template<typename T> struct A {
+  virtual void f(T) { }
+  inline void g() { } 
+};
+
+// Explicit instantiations have external linkage.
+
+// CHECK: define void @_ZN1AIiE1gEv(
+template void A<int>::g();
+
+// CHECK: define void @_ZN1AIfE1fEf(
+// CHECK: define void @_ZN1AIfE1gEv(
+// FIXME: This should also emit the vtable.
+template struct A<float>;
+
+// CHECK: define void @_Z1fIiEvT_
+template <typename T> void f(T) { }
+template void f<int>(int);
+
+// CHECK: define void @_Z1gIiEvT_
+template <typename T> inline void g(T) { }
+template void g<int>(int);
+