Merge common pointers for redeclarations of the same template across modules.

llvm-svn: 192560

clang/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;
 }
 

clang/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;

clang/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; };

clang/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;