Reinstate "Load lazily the template specialization in multi-module setups."

It was reverted in r305460 but the issue appears to only break our self-host
libcxx modules bot. Reapplying it will give us a chance to get a reproducer and
fix the issue.

llvm-svn: 306903

clang/lib/Serialization/ASTReaderDecl.cpp

@@ -219,6 +219,30 @@ namespace clang {
           TypedefNameForLinkage(nullptr), HasPendingBody(false),
           IsDeclMarkedUsed(false) {}
 
+    template <typename T> static
+    void AddLazySpecializations(T *D,
+                                SmallVectorImpl<serialization::DeclID>& IDs) {
+      if (IDs.empty())
+        return;
+
+      // FIXME: We should avoid this pattern of getting the ASTContext.
+      ASTContext &C = D->getASTContext();
+
+      auto *&LazySpecializations = D->getCommonPtr()->LazySpecializations;
+
+      if (auto &Old = LazySpecializations) {
+        IDs.insert(IDs.end(), Old + 1, Old + 1 + Old[0]);
+        std::sort(IDs.begin(), IDs.end());
+        IDs.erase(std::unique(IDs.begin(), IDs.end()), IDs.end());
+      }
+
+      auto *Result = new (C) serialization::DeclID[1 + IDs.size()];
+      *Result = IDs.size();
+      std::copy(IDs.begin(), IDs.end(), Result + 1);
+
+      LazySpecializations = Result;
+    }
+
     template <typename DeclT>
     static Decl *getMostRecentDeclImpl(Redeclarable<DeclT> *D);
     static Decl *getMostRecentDeclImpl(...);
@@ -247,7 +271,7 @@ namespace clang {
     void ReadFunctionDefinition(FunctionDecl *FD);
     void Visit(Decl *D);
 
-    void UpdateDecl(Decl *D);
+    void UpdateDecl(Decl *D, llvm::SmallVectorImpl<serialization::DeclID>&);
 
     static void setNextObjCCategory(ObjCCategoryDecl *Cat,
                                     ObjCCategoryDecl *Next) {
@@ -1971,21 +1995,6 @@ ASTDeclReader::VisitRedeclarableTemplateDecl(RedeclarableTemplateDecl *D) {
   return Redecl;
 }
 
-static DeclID *newDeclIDList(ASTContext &Context, DeclID *Old,
-                             SmallVectorImpl<DeclID> &IDs) {
-  assert(!IDs.empty() && "no IDs to add to list");
-  if (Old) {
-    IDs.insert(IDs.end(), Old + 1, Old + 1 + Old[0]);
-    std::sort(IDs.begin(), IDs.end());
-    IDs.erase(std::unique(IDs.begin(), IDs.end()), IDs.end());
-  }
-
-  auto *Result = new (Context) DeclID[1 + IDs.size()];
-  *Result = IDs.size();
-  std::copy(IDs.begin(), IDs.end(), Result + 1);
-  return Result;
-}
-
 void ASTDeclReader::VisitClassTemplateDecl(ClassTemplateDecl *D) {
   RedeclarableResult Redecl = VisitRedeclarableTemplateDecl(D);
 
@@ -1994,12 +2003,7 @@ void ASTDeclReader::VisitClassTemplateDecl(ClassTemplateDecl *D) {
     // the specializations.
     SmallVector<serialization::DeclID, 32> SpecIDs;
     ReadDeclIDList(SpecIDs);
-
-    if (!SpecIDs.empty()) {
-      auto *CommonPtr = D->getCommonPtr();
-      CommonPtr->LazySpecializations = newDeclIDList(
-          Reader.getContext(), CommonPtr->LazySpecializations, SpecIDs);
-    }
+    ASTDeclReader::AddLazySpecializations(D, SpecIDs);
   }
 
   if (D->getTemplatedDecl()->TemplateOrInstantiation) {
@@ -2026,12 +2030,7 @@ void ASTDeclReader::VisitVarTemplateDecl(VarTemplateDecl *D) {
     // the specializations.
     SmallVector<serialization::DeclID, 32> SpecIDs;
     ReadDeclIDList(SpecIDs);
-
-    if (!SpecIDs.empty()) {
-      auto *CommonPtr = D->getCommonPtr();
-      CommonPtr->LazySpecializations = newDeclIDList(
-          Reader.getContext(), CommonPtr->LazySpecializations, SpecIDs);
-    }
+    ASTDeclReader::AddLazySpecializations(D, SpecIDs);
   }
 }
 
@@ -2137,12 +2136,7 @@ void ASTDeclReader::VisitFunctionTemplateDecl(FunctionTemplateDecl *D) {
     // This FunctionTemplateDecl owns a CommonPtr; read it.
     SmallVector<serialization::DeclID, 32> SpecIDs;
     ReadDeclIDList(SpecIDs);
-
-    if (!SpecIDs.empty()) {
-      auto *CommonPtr = D->getCommonPtr();
-      CommonPtr->LazySpecializations = newDeclIDList(
-          Reader.getContext(), CommonPtr->LazySpecializations, SpecIDs);
-    }
+    ASTDeclReader::AddLazySpecializations(D, SpecIDs);
   }
 }
 
@@ -3688,6 +3682,9 @@ void ASTReader::loadDeclUpdateRecords(PendingUpdateRecord &Record) {
   Decl *D = Record.D;
   ProcessingUpdatesRAIIObj ProcessingUpdates(*this);
   DeclUpdateOffsetsMap::iterator UpdI = DeclUpdateOffsets.find(ID);
+
+  llvm::SmallVector<serialization::DeclID, 8> PendingLazySpecializationIDs;
+
   if (UpdI != DeclUpdateOffsets.end()) {
     auto UpdateOffsets = std::move(UpdI->second);
     DeclUpdateOffsets.erase(UpdI);
@@ -3712,7 +3709,7 @@ void ASTReader::loadDeclUpdateRecords(PendingUpdateRecord &Record) {
 
       ASTDeclReader Reader(*this, Record, RecordLocation(F, Offset), ID,
                            SourceLocation());
-      Reader.UpdateDecl(D);
+      Reader.UpdateDecl(D, PendingLazySpecializationIDs);
 
       // We might have made this declaration interesting. If so, remember that
       // we need to hand it off to the consumer.
@@ -3724,6 +3721,17 @@ void ASTReader::loadDeclUpdateRecords(PendingUpdateRecord &Record) {
       }
     }
   }
+  // Add the lazy specializations to the template.
+  assert((PendingLazySpecializationIDs.empty() || isa<ClassTemplateDecl>(D) ||
+          isa<FunctionTemplateDecl>(D) || isa<VarTemplateDecl>(D)) &&
+         "Must not have pending specializations");
+  if (auto *CTD = dyn_cast<ClassTemplateDecl>(D))
+    ASTDeclReader::AddLazySpecializations(CTD, PendingLazySpecializationIDs);
+  else if (auto *FTD = dyn_cast<FunctionTemplateDecl>(D))
+    ASTDeclReader::AddLazySpecializations(FTD, PendingLazySpecializationIDs);
+  else if (auto *VTD = dyn_cast<VarTemplateDecl>(D))
+    ASTDeclReader::AddLazySpecializations(VTD, PendingLazySpecializationIDs);
+  PendingLazySpecializationIDs.clear();
 
   // Load the pending visible updates for this decl context, if it has any.
   auto I = PendingVisibleUpdates.find(ID);
@@ -3920,7 +3928,8 @@ static void forAllLaterRedecls(DeclT *D, Fn F) {
   }
 }
 
-void ASTDeclReader::UpdateDecl(Decl *D) {
+void ASTDeclReader::UpdateDecl(Decl *D,
+   llvm::SmallVectorImpl<serialization::DeclID> &PendingLazySpecializationIDs) {
   while (Record.getIdx() < Record.size()) {
     switch ((DeclUpdateKind)Record.readInt()) {
     case UPD_CXX_ADDED_IMPLICIT_MEMBER: {
@@ -3936,8 +3945,8 @@ void ASTDeclReader::UpdateDecl(Decl *D) {
     }
 
     case UPD_CXX_ADDED_TEMPLATE_SPECIALIZATION:
-      // It will be added to the template's specializations set when loaded.
-      (void)Record.readDecl();
+      // It will be added to the template's lazy specialization set.
+      PendingLazySpecializationIDs.push_back(ReadDeclID());
       break;
 
     case UPD_CXX_ADDED_ANONYMOUS_NAMESPACE: {