From 8bfc1e118169229960b90a4ef8761ee0eb296755 Mon Sep 17 00:00:00 2001
From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Sun, 13 Oct 2013 23:50:45 +0000
Subject: [PATCH] Merge common pointers for redeclarations of the same template
 across modules.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@192560 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Serialization/ASTReaderDecl.cpp   | 5 +++++
 test/Modules/Inputs/cxx-templates-a.h | 3 +++
 test/Modules/Inputs/cxx-templates-b.h | 3 +++
 test/Modules/cxx-templates.cpp        | 2 ++
 4 files changed, 13 insertions(+)

diff --git a/lib/Serialization/ASTReaderDecl.cpp b/lib/Serialization/ASTReaderDecl.cpp
index 341f8eb068..2a1ac11ec0 100644
--- a/lib/Serialization/ASTReaderDecl.cpp
+++ b/lib/Serialization/ASTReaderDecl.cpp
@@ -1429,6 +1429,11 @@ ASTDeclReader::VisitRedeclarableTemplateDecl(RedeclarableTemplateDecl *D) {
 
   mergeRedeclarable(D, Redecl);
 
+  // If we merged the template with a prior declaration chain, merge the common
+  // pointer.
+  // FIXME: Actually merge here, don't just overwrite.
+  D->Common = D->getCanonicalDecl()->Common;
+
   return Redecl;
 }
 
diff --git a/test/Modules/Inputs/cxx-templates-a.h b/test/Modules/Inputs/cxx-templates-a.h
index 37e3426fc0..d2261f6a29 100644
--- a/test/Modules/Inputs/cxx-templates-a.h
+++ b/test/Modules/Inputs/cxx-templates-a.h
@@ -30,3 +30,6 @@ void use_some_template_a() {
   SomeTemplate<char[1]> b, c;
   b = c;
 }
+
+template<int> struct MergeTemplates;
+MergeTemplates<0> *merge_templates_a;
diff --git a/test/Modules/Inputs/cxx-templates-b.h b/test/Modules/Inputs/cxx-templates-b.h
index c495074a93..6cc951b0ee 100644
--- a/test/Modules/Inputs/cxx-templates-b.h
+++ b/test/Modules/Inputs/cxx-templates-b.h
@@ -17,6 +17,9 @@ typedef SomeTemplate<int&> SomeTemplateIntRef;
 
 extern DefinedInCommon &defined_in_common;
 
+template<int> struct MergeTemplates;
+MergeTemplates<0> *merge_templates_b;
+
 @import cxx_templates_b_impl;
 
 template<typename T, typename> struct Identity { typedef T type; };
diff --git a/test/Modules/cxx-templates.cpp b/test/Modules/cxx-templates.cpp
index f34a2bdaa7..911f953a5c 100644
--- a/test/Modules/cxx-templates.cpp
+++ b/test/Modules/cxx-templates.cpp
@@ -69,6 +69,8 @@ void g() {
   // expected-error@Inputs/cxx-templates-a.h:19 {{definition of 'DefinedInBImpl' must be imported}}
   // expected-note@Inputs/cxx-templates-b-impl.h:1 {{definition is here}}
   PerformDelayedLookup(defined_in_b_impl); // expected-note {{in instantiation of}}
+
+  merge_templates_a = merge_templates_b; // ok, same type
 }
 
 RedeclaredAsFriend<int> raf1;
-- 
2.40.0