Not all instantiated variable is odr-used. Do not mark non-odr-used variable template specializations as such.

llvm-svn: 214267

clang/lib/Sema/SemaExpr.cpp

@@ -12440,6 +12440,7 @@ static void DoMarkVarDeclReferenced(Sema &SemaRef, SourceLocation Loc,
   Var->setReferenced();
 
   TemplateSpecializationKind TSK = Var->getTemplateSpecializationKind();
+  bool MarkODRUsed = true;
 
   // If the context is not potentially evaluated, this is not an odr-use and
   // does not trigger instantiation.
@@ -12475,6 +12476,9 @@ static void DoMarkVarDeclReferenced(Sema &SemaRef, SourceLocation Loc,
 
     if (!isTemplateInstantiation(TSK))
     	return;
+
+    // Instantiate, but do not mark as odr-used, variable templates.
+    MarkODRUsed = false;
   }
 
   VarTemplateSpecializationDecl *VarSpec =
@@ -12525,6 +12529,8 @@ static void DoMarkVarDeclReferenced(Sema &SemaRef, SourceLocation Loc,
     }
   }
 
+  if(!MarkODRUsed) return;
+
   // Per C++11 [basic.def.odr], a variable is odr-used "unless it satisfies
   // the requirements for appearing in a constant expression (5.19) and, if
   // it is an object, the lvalue-to-rvalue conversion (4.1)

clang/test/SemaCXX/PR10177.cpp

@@ -1,4 +1,7 @@
 // RUN: %clang_cc1 -fsyntax-only -std=c++11 -verify %s
+// RUN: %clang_cc1 -fsyntax-only -std=c++1y -verify %s -DCXX1Y
+
+#ifndef CXX1Y
 
 template<typename T, typename U, U> using alias_ref = T;
 template<typename T, typename U, U> void func_ref() {}
@@ -21,6 +24,7 @@ void f() {
   (void)class_ref<int, int&, U<2>::a>(); // expected-note {{here}}
 };
 
+
 template<int N>
 void fi() {
   (void)alias_ref<int, int&, U<N>::a>(); // expected-note {{here}}
@@ -45,3 +49,11 @@ namespace N {
   int j = f<int>();
 }
 
+#else
+// expected-no-diagnostics
+
+namespace { template<typename> extern int n; }
+template<typename T> int g() { return n<int>; }
+
+#endif
+