From b353ee18086227b3a4192a970cdbced5358003f5 Mon Sep 17 00:00:00 2001
From: Dmitri Gribenko <gribozavr@gmail.com>
Date: Thu, 19 Dec 2013 02:05:20 +0000
Subject: [PATCH] PCH: fix a crash caused by a circular deserialization
 dependency

We started by trying to deserialize decltype(func-param) in a trailing return
type, which causes the function parameter decl to be deserialized, which pulls
in the function decl, which pulls the function type, which pulls the same
decltype() in the return type, and then we crashed.

llvm-svn: 197644
---
 clang/lib/Serialization/ASTReaderDecl.cpp | 11 ++++--
 clang/test/PCH/cxx-templates.h            | 47 +++++++++++++++++++++++
 2 files changed, 54 insertions(+), 4 deletions(-)

diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 70fb062b2c59..c2e286814bca 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 992f478e33e6..c4a844727691 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);
+  }
+}
+