Index: cfe/trunk/lib/Sema/SemaTemplate.cpp
===================================================================
--- cfe/trunk/lib/Sema/SemaTemplate.cpp
+++ cfe/trunk/lib/Sema/SemaTemplate.cpp
@@ -974,7 +974,7 @@
 QualType Sema::CheckNonTypeTemplateParameterType(TypeSourceInfo *&TSI,
                                                  SourceLocation Loc) {
   if (TSI->getType()->isUndeducedType()) {
-    // C++1z [temp.dep.expr]p3:
+    // C++17 [temp.dep.expr]p3:
     //   An id-expression is type-dependent if it contains
     //    - an identifier associated by name lookup with a non-type
     //      template-parameter declared with a type that contains a
@@ -9866,6 +9866,15 @@
     if (!NewTSI)
       return true;
 
+    if (NewTSI->getType()->isUndeducedType()) {
+      // C++17 [temp.dep.expr]p3:
+      //   An id-expression is type-dependent if it contains
+      //    - an identifier associated by name lookup with a non-type
+      //      template-parameter declared with a type that contains a
+      //      placeholder type (7.1.7.4),
+      NewTSI = SubstAutoTypeSourceInfo(NewTSI, Context.DependentTy);
+    }
+
     if (NewTSI != NTTP->getTypeSourceInfo()) {
       NTTP->setTypeSourceInfo(NewTSI);
       NTTP->setType(NewTSI->getType());
Index: cfe/trunk/test/SemaTemplate/temp_arg_nontype_cxx1z.cpp
===================================================================
--- cfe/trunk/test/SemaTemplate/temp_arg_nontype_cxx1z.cpp
+++ cfe/trunk/test/SemaTemplate/temp_arg_nontype_cxx1z.cpp
@@ -335,3 +335,46 @@
   void g(int, int);
   using Int = A<int>::B<&g>::param2;
 }
+
+namespace rdar41852459 {
+template <auto V> struct G {};
+
+template <class T> struct S {
+  template <auto V> void f() {
+    G<V> x;
+  }
+  template <auto *PV> void f2() {
+    G<PV> x;
+  }
+  template <decltype(auto) V> void f3() {
+    G<V> x;
+  }
+};
+
+template <auto *PV> struct I {};
+
+template <class T> struct K {
+  template <auto *PV> void f() {
+    I<PV> x;
+  }
+  template <auto V> void f2() {
+    I<V> x;
+  }
+  template <decltype(auto) V> void f3() {
+    I<V> x;
+  }
+};
+
+template <decltype(auto)> struct L {};
+template <class T> struct M {
+  template <auto *PV> void f() {
+    L<PV> x;
+  }
+  template <auto V> void f() {
+    L<V> x;
+  }
+  template <decltype(auto) V> void f() {
+    L<V> x;
+  }
+};
+}