2 files changed, 30 insertions, 3 deletions
diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index 65c9cccaf1..6327ee71db 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -443,9 +443,15 @@ ExprResult Sema::DefaultArgumentPromotion(Expr *E) {
   if (Ty->isSpecificBuiltinType(BuiltinType::Float))
     E = ImpCastExprToType(E, Context.DoubleTy, CK_FloatingCast).take();
 
-  // C++ includes lvalue-to-rvalue conversion as a default argument
-  // promotion.  If we have a gl-value, initialize a temporary.
-  if (getLangOptions().CPlusPlus && E->isGLValue()) {
+  // C++ performs lvalue-to-rvalue conversion as a default argument
+  // promotion.  If we still have a gl-value after usual unary
+  // conversion, we must have an l-value of class type, so we need to
+  // initialize a temporary.  For compatibility reasons, however, we
+  // don't want to do this in unevaluated contexts; otherwise we
+  // reject metaprograms which work by passing uncopyable l-values to
+  // variadic functions.
+  if (getLangOptions().CPlusPlus && E->isGLValue() && 
+      ExprEvalContexts.back().Context != Unevaluated) {
     ExprResult Temp = PerformCopyInitialization(
                        InitializedEntity::InitializeTemporary(E->getType()),
                                                 E->getExprLoc(),
diff --git a/test/CXX/special/class.temporary/p1.cpp b/test/CXX/special/class.temporary/p1.cpp
index e3b8f9ce66..07890eb297 100644
--- a/test/CXX/special/class.temporary/p1.cpp
+++ b/test/CXX/special/class.temporary/p1.cpp
@@ -35,3 +35,24 @@ namespace test1 {
     foo(a); // expected-error {{calling a private constructor of class 'test1::A'}} expected-error {{cannot pass object of non-trivial type 'test1::A' through variadic function}}
   }
 }
+
+// Don't enforce this in an unevaluated context.
+namespace test2 {
+  struct A {
+    A(const A&) = delete; // expected-note {{marked deleted here}}
+  };
+
+  typedef char one[1];
+  typedef char two[2];
+
+  one &meta(bool);
+  two &meta(...);
+
+  void a(A &a) {
+    char check[sizeof(meta(a)) == 2 ? 1 : -1];
+  }
+
+  void b(A &a) {
+    meta(a); // expected-error {{call to deleted constructor}}
+  }
+}