2 files changed, 54 insertions, 4 deletions
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 70fb062b2c5..c2e286814bc 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -356,11 +356,14 @@ void ASTDeclReader::Visit(Decl *D) {
 }
 
 void ASTDeclReader::VisitDecl(Decl *D) {
-  if (D->isTemplateParameter()) {
+  if (D->isTemplateParameter() || D->isTemplateParameterPack() ||
+      isa<ParmVarDecl>(D)) {
     // We don't want to deserialize the DeclContext of a template
-    // parameter immediately, because the template parameter might be
-    // used in the formulation of its DeclContext. Use the translation
-    // unit DeclContext as a placeholder.
+    // parameter or of a parameter of a function template immediately.   These
+    // entities might be used in the formulation of its DeclContext (for
+    // example, a function parameter can be used in decltype() in trailing
+    // return type of the function).  Use the translation unit DeclContext as a
+    // placeholder.
     GlobalDeclID SemaDCIDForTemplateParmDecl = ReadDeclID(Record, Idx);
     GlobalDeclID LexicalDCIDForTemplateParmDecl = ReadDeclID(Record, Idx);
     Reader.addPendingDeclContextInfo(D,
diff --git a/clang/test/PCH/cxx-templates.h b/clang/test/PCH/cxx-templates.h
index 992f478e33e..c4a84472769 100644
--- a/clang/test/PCH/cxx-templates.h
+++ b/clang/test/PCH/cxx-templates.h
@@ -311,3 +311,50 @@ namespace local_extern {
     return sizeof(arr);
   }
 }
+
+namespace rdar15468709a {
+  template<typename> struct decay {};
+
+  template<typename FooParamTy> auto foo(FooParamTy fooParam) -> decltype(fooParam);
+  template<typename BarParamTy> auto bar(BarParamTy barParam) -> decay<decltype(barParam)>;
+
+  struct B {};
+
+  void crash() {
+    B some;
+    bar(some);
+  }
+}
+
+namespace rdar15468709b {
+  template<typename> struct decay {};
+
+  template<typename... Foos> int returnsInt(Foos... foos);
+
+  template<typename... FooParamTy> auto foo(FooParamTy... fooParam) -> decltype(returnsInt(fooParam...));
+  template<typename... BarParamTy> auto bar(BarParamTy... barParam) -> decay<decltype(returnsInt(barParam...))>;
+
+  struct B {};
+
+  void crash() {
+    B some;
+    bar(some);
+  }
+}
+
+namespace rdar15468709c {
+  template<typename> struct decay {};
+
+  template<class... Foos> int returnsInt(Foos... foos);
+
+  template<typename FooParamTy> void foo(FooParamTy fooParam) { decltype(fooParam) a; }
+  template<typename BarParamTy> auto bar(BarParamTy barParam) -> decay<decltype(barParam)>;
+
+  struct B {};
+
+  void crash() {
+    B some;
+    bar(some);
+  }
+}
+