From fd051a0a2ed4f53faac695be9efd2a2aabd4e7c3 Mon Sep 17 00:00:00 2001
From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Wed, 11 Mar 2015 01:44:51 +0000
Subject: [PATCH] [modules] Avoid accidentally completing the redeclaration
 chain when updating all the existing declarations of a record-like entity
 with a pointer to its definition.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@231901 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/clang/Serialization/ASTReader.h |  6 +++++
 lib/Serialization/ASTReader.cpp         | 34 ++++++++++++++-----------
 lib/Serialization/ASTReaderDecl.cpp     |  4 +++
 3 files changed, 29 insertions(+), 15 deletions(-)

diff --git a/include/clang/Serialization/ASTReader.h b/include/clang/Serialization/ASTReader.h
index 1037160ab2..951a21016f 100644
--- a/include/clang/Serialization/ASTReader.h
+++ b/include/clang/Serialization/ASTReader.h
@@ -1159,6 +1159,12 @@ private:
   void LoadedDecl(unsigned Index, Decl *D);
   Decl *ReadDeclRecord(serialization::DeclID ID);
   void markIncompleteDeclChain(Decl *Canon);
+
+  /// \brief Returns the most recent declaration of a declaration (which must be
+  /// of a redeclarable kind) that is either local or has already been loaded
+  /// merged into its redecl chain.
+  Decl *getMostRecentExistingDecl(Decl *D);
+
   RecordLocation DeclCursorForID(serialization::DeclID ID,
                                  unsigned &RawLocation);
   void loadDeclUpdateRecords(serialization::DeclID ID, Decl *D);
diff --git a/lib/Serialization/ASTReader.cpp b/lib/Serialization/ASTReader.cpp
index 7e3a779b07..da5a0e68e9 100644
--- a/lib/Serialization/ASTReader.cpp
+++ b/lib/Serialization/ASTReader.cpp
@@ -8369,10 +8369,12 @@ void ASTReader::finishPendingActions() {
         // Make sure that the TagType points at the definition.
         const_cast<TagType*>(TagT)->decl = TD;
       }
-      
+
       if (auto RD = dyn_cast<CXXRecordDecl>(D)) {
-        for (auto R : RD->redecls()) {
-          assert((R == D) == R->isThisDeclarationADefinition() &&
+        for (auto *R = getMostRecentExistingDecl(RD); R;
+             R = R->getPreviousDecl()) {
+          assert((R == D) ==
+                     cast<CXXRecordDecl>(R)->isThisDeclarationADefinition() &&
                  "declaration thinks it's the definition but it isn't");
           cast<CXXRecordDecl>(R)->DefinitionData = RD->DefinitionData;
         }
@@ -8380,34 +8382,36 @@ void ASTReader::finishPendingActions() {
 
       continue;
     }
-    
+
     if (auto ID = dyn_cast<ObjCInterfaceDecl>(D)) {
       // Make sure that the ObjCInterfaceType points at the definition.
       const_cast<ObjCInterfaceType *>(cast<ObjCInterfaceType>(ID->TypeForDecl))
         ->Decl = ID;
-      
-      for (auto R : ID->redecls())
-        R->Data = ID->Data;
-      
+
+      for (auto *R = getMostRecentExistingDecl(ID); R; R = R->getPreviousDecl())
+        cast<ObjCInterfaceDecl>(R)->Data = ID->Data;
+
       continue;
     }
-    
+
     if (auto PD = dyn_cast<ObjCProtocolDecl>(D)) {
-      for (auto R : PD->redecls())
-        R->Data = PD->Data;
-      
+      for (auto *R = getMostRecentExistingDecl(PD); R; R = R->getPreviousDecl())
+        cast<ObjCProtocolDecl>(R)->Data = PD->Data;
+
       continue;
     }
-    
+
     auto RTD = cast<RedeclarableTemplateDecl>(D)->getCanonicalDecl();
-    for (auto R : RTD->redecls())
-      R->Common = RTD->Common;
+    for (auto *R = getMostRecentExistingDecl(RTD); R; R = R->getPreviousDecl())
+      cast<RedeclarableTemplateDecl>(R)->Common = RTD->Common;
   }
   PendingDefinitions.clear();
 
   // Load the bodies of any functions or methods we've encountered. We do
   // this now (delayed) so that we can be sure that the declaration chains
   // have been fully wired up.
+  // FIXME: There seems to be no point in delaying this, it does not depend
+  // on the redecl chains having been wired up.
   for (PendingBodiesMap::iterator PB = PendingBodies.begin(),
                                PBEnd = PendingBodies.end();
        PB != PBEnd; ++PB) {
diff --git a/lib/Serialization/ASTReaderDecl.cpp b/lib/Serialization/ASTReaderDecl.cpp
index 0789ba5e3e..565f33ecba 100644
--- a/lib/Serialization/ASTReaderDecl.cpp
+++ b/lib/Serialization/ASTReaderDecl.cpp
@@ -2799,6 +2799,10 @@ Decl *ASTDeclReader::getMostRecentDecl(Decl *D) {
   llvm_unreachable("unknown decl kind");
 }
 
+Decl *ASTReader::getMostRecentExistingDecl(Decl *D) {
+  return ASTDeclReader::getMostRecentDecl(D->getCanonicalDecl());
+}
+
 template<typename DeclT>
 void ASTDeclReader::attachPreviousDeclImpl(ASTReader &Reader,
                                            Redeclarable<DeclT> *D,
-- 
2.40.0