[Serialization] Code cleanups and polish 83233

clang/include/clang/AST/DeclTemplate.h

@@ -256,8 +256,8 @@ class TemplateArgumentList final
   TemplateArgumentList(const TemplateArgumentList &) = delete;
   TemplateArgumentList &operator=(const TemplateArgumentList &) = delete;
 
-  /// Create hash for the given arguments.
-  static unsigned ComputeODRHash(ArrayRef<TemplateArgument> Args);
+  /// Create stable hash for the given arguments across compiler invocations.
+  static unsigned ComputeStableHash(ArrayRef<TemplateArgument> Args);
 
   /// Create a new template argument list that copies the given set of
   /// template arguments.
@@ -733,25 +733,6 @@ class RedeclarableTemplateDecl : public TemplateDecl,
   }
 
   void anchor() override;
-  struct LazySpecializationInfo {
-    uint32_t DeclID = ~0U;
-    unsigned ODRHash = ~0U;
-    bool IsPartial = false;
-    LazySpecializationInfo(uint32_t ID, unsigned Hash = ~0U,
-                           bool Partial = false)
-        : DeclID(ID), ODRHash(Hash), IsPartial(Partial) {}
-    LazySpecializationInfo() {}
-    bool operator<(const LazySpecializationInfo &Other) const {
-      return DeclID < Other.DeclID;
-    }
-    bool operator==(const LazySpecializationInfo &Other) const {
-      assert((DeclID != Other.DeclID || ODRHash == Other.ODRHash) &&
-             "Hashes differ!");
-      assert((DeclID != Other.DeclID || IsPartial == Other.IsPartial) &&
-             "Both must be the same kinds!");
-      return DeclID == Other.DeclID;
-    }
-  };
 
 protected:
   template <typename EntryType> struct SpecEntryTraits {
@@ -795,11 +776,9 @@ class RedeclarableTemplateDecl : public TemplateDecl,
 
   void loadLazySpecializationsImpl(bool OnlyPartial = false) const;
 
-  void loadLazySpecializationsImpl(llvm::ArrayRef<TemplateArgument> Args,
+  bool loadLazySpecializationsImpl(llvm::ArrayRef<TemplateArgument> Args,
                                    TemplateParameterList *TPL = nullptr) const;
 
-  Decl *loadLazySpecializationImpl(LazySpecializationInfo &LazySpecInfo) const;
-
   template <class EntryType, typename ...ProfileArguments>
   typename SpecEntryTraits<EntryType>::DeclType*
   findSpecializationImpl(llvm::FoldingSetVector<EntryType> &Specs,
@@ -820,13 +799,6 @@ class RedeclarableTemplateDecl : public TemplateDecl,
     llvm::PointerIntPair<RedeclarableTemplateDecl*, 1, bool>
       InstantiatedFromMember;
 
-    /// If non-null, points to an array of specializations (including
-    /// partial specializations) known only by their external declaration IDs.
-    ///
-    /// The first value in the array is the number of specializations/partial
-    /// specializations that follow.
-    LazySpecializationInfo *LazySpecializations = nullptr;
-
     /// The set of "injected" template arguments used within this
     /// template.
     ///

clang/include/clang/AST/ExternalASTSource.h

@@ -157,7 +157,9 @@ class ExternalASTSource : public RefCountedBase<ExternalASTSource> {
 
   /// Load all the specializations for the Decl \param D with the same template
   /// args specified by \param TemplateArgs.
-  virtual void
+  ///
+  /// Return true if any new specializations get loaded. Return false otherwise.
+  virtual bool
   LoadExternalSpecializations(const Decl *D,
                               ArrayRef<TemplateArgument> TemplateArgs);
 

clang/include/clang/Sema/MultiplexExternalSemaSource.h

@@ -99,7 +99,7 @@ class MultiplexExternalSemaSource : public ExternalSemaSource {
 
   void LoadExternalSpecializations(const Decl *D, bool OnlyPartial) override;
 
-  void
+  bool
   LoadExternalSpecializations(const Decl *D,
                               ArrayRef<TemplateArgument> TemplateArgs) override;
 

clang/include/clang/Serialization/ASTBitCodes.h

@@ -699,7 +699,7 @@ enum ASTRecordTypes {
   /// recorded in a preamble.
   PP_ASSUME_NONNULL_LOC = 67,
 
-  UPDATE_SPECIALIZATION = 68,
+  CXX_ADDED_TEMPLATE_SPECIALIZATION = 68,
 };
 
 /// Record types used within a source manager block.

clang/include/clang/Serialization/ASTReader.h

@@ -2006,7 +2006,7 @@ class ASTReader
 
   void LoadExternalSpecializations(const Decl *D, bool OnlyPartial) override;
 
-  void
+  bool
   LoadExternalSpecializations(const Decl *D,
                               ArrayRef<TemplateArgument> TemplateArgs) override;
 

clang/lib/AST/DeclTemplate.cpp

@@ -342,68 +342,50 @@ void RedeclarableTemplateDecl::loadLazySpecializationsImpl(
   ExternalSource->LoadExternalSpecializations(this->getCanonicalDecl(),
                                               OnlyPartial);
   return;
-
-  // Grab the most recent declaration to ensure we've loaded any lazy
-  // redeclarations of this template.
-  CommonBase *CommonBasePtr = getMostRecentDecl()->getCommonPtr();
-  if (auto *Specs = CommonBasePtr->LazySpecializations) {
-    if (!OnlyPartial)
-      CommonBasePtr->LazySpecializations = nullptr;
-    for (uint32_t I = 0, N = Specs[0].DeclID; I != N; ++I) {
-      // Skip over already loaded specializations.
-      if (!Specs[I + 1].ODRHash)
-        continue;
-      if (!OnlyPartial || Specs[I + 1].IsPartial)
-        (void)loadLazySpecializationImpl(Specs[I + 1]);
-    }
-  }
-}
-
-Decl *RedeclarableTemplateDecl::loadLazySpecializationImpl(
-    LazySpecializationInfo &LazySpecInfo) const {
-  llvm_unreachable("We don't use LazySpecializationInfo any more");
-
-  uint32_t ID = LazySpecInfo.DeclID;
-  assert(ID && "Loading already loaded specialization!");
-  // Note that we loaded the specialization.
-  LazySpecInfo.DeclID = LazySpecInfo.ODRHash = LazySpecInfo.IsPartial = 0;
-  return getASTContext().getExternalSource()->GetExternalDecl(ID);
 }
 
-void RedeclarableTemplateDecl::loadLazySpecializationsImpl(
+bool RedeclarableTemplateDecl::loadLazySpecializationsImpl(
     ArrayRef<TemplateArgument> Args, TemplateParameterList *TPL) const {
   auto *ExternalSource = getASTContext().getExternalSource();
   if (!ExternalSource)
-    return;
-
-  ExternalSource->LoadExternalSpecializations(this->getCanonicalDecl(), Args);
-  return;
+    return false;
 
-  CommonBase *CommonBasePtr = getMostRecentDecl()->getCommonPtr();
-  if (auto *Specs = CommonBasePtr->LazySpecializations) {
-    unsigned Hash = TemplateArgumentList::ComputeODRHash(Args);
-    for (uint32_t I = 0, N = Specs[0].DeclID; I != N; ++I)
-      if (Specs[I + 1].ODRHash && Specs[I + 1].ODRHash == Hash)
-        (void)loadLazySpecializationImpl(Specs[I + 1]);
-  }
+  return ExternalSource->LoadExternalSpecializations(this->getCanonicalDecl(), Args);
 }
 
 template<class EntryType, typename... ProfileArguments>
+static
 typename RedeclarableTemplateDecl::SpecEntryTraits<EntryType>::DeclType *
-RedeclarableTemplateDecl::findSpecializationImpl(
-    llvm::FoldingSetVector<EntryType> &Specs, void *&InsertPos,
+findSpecializationLocally(llvm::FoldingSetVector<EntryType> &Specs, void *&InsertPos,
+    ASTContext &Context,
     ProfileArguments&&... ProfileArgs) {
-  using SETraits = SpecEntryTraits<EntryType>;
-
-  loadLazySpecializationsImpl(std::forward<ProfileArguments>(ProfileArgs)...);
+  using SETraits = RedeclarableTemplateDecl::SpecEntryTraits<EntryType>;
 
   llvm::FoldingSetNodeID ID;
   EntryType::Profile(ID, std::forward<ProfileArguments>(ProfileArgs)...,
-                     getASTContext());
+                     Context);
   EntryType *Entry = Specs.FindNodeOrInsertPos(ID, InsertPos);
   return Entry ? SETraits::getDecl(Entry)->getMostRecentDecl() : nullptr;
 }
 
+
+template<class EntryType, typename... ProfileArguments>
+typename RedeclarableTemplateDecl::SpecEntryTraits<EntryType>::DeclType *
+RedeclarableTemplateDecl::findSpecializationImpl(
+    llvm::FoldingSetVector<EntryType> &Specs, void *&InsertPos,
+    ProfileArguments&&... ProfileArgs) {
+
+  if (auto *Found = findSpecializationLocally(Specs, InsertPos, getASTContext(),
+          std::forward<ProfileArguments>(ProfileArgs)...))
+    return Found;
+
+  if (!loadLazySpecializationsImpl(std::forward<ProfileArguments>(ProfileArgs)...))
+    return nullptr;
+
+  return findSpecializationLocally(Specs, InsertPos, getASTContext(),
+          std::forward<ProfileArguments>(ProfileArgs)...);
+}
+
 template<class Derived, class EntryType>
 void RedeclarableTemplateDecl::addSpecializationImpl(
     llvm::FoldingSetVector<EntryType> &Specializations, EntryType *Entry,
@@ -939,7 +921,20 @@ TemplateArgumentList::CreateCopy(ASTContext &Context,
   return new (Mem) TemplateArgumentList(Args);
 }
 
-unsigned TemplateArgumentList::ComputeODRHash(ArrayRef<TemplateArgument> Args) {
+unsigned
+TemplateArgumentList::ComputeStableHash(ArrayRef<TemplateArgument> Args) {
+  // FIXME: ODR hashing may not be the best mechanism to hash the template
+  // arguments. ODR hashing is (or perhaps, should be) about determining whether
+  // two things are spelled the same way and have the same meaning (as required
+  // by the C++ ODR), whereas what we want here is whether they have the same
+  // meaning regardless of spelling. Maybe we can get away with reusing ODR
+  // hashing anyway, on the basis that any canonical, non-dependent template
+  // argument should have the same (invented) spelling in every translation
+  // unit, but it is not sure that's true in all cases. There may still be cases
+  // where the canonical type includes some aspect of "whatever we saw first",
+  // in which case the ODR hash can differ across translation units for
+  // non-dependent, canonical template arguments that are spelled differently
+  // but have the same meaning. But it is not easy to raise examples.
   ODRHash Hasher;
   for (TemplateArgument TA : Args)
     Hasher.AddTemplateArgument(TA);

clang/lib/AST/ExternalASTSource.cpp

@@ -102,8 +102,8 @@ ExternalASTSource::FindExternalVisibleDeclsByName(const DeclContext *DC,
 
 void ExternalASTSource::LoadExternalSpecializations(const Decl *D, bool) {}
 
-void ExternalASTSource::LoadExternalSpecializations(
-    const Decl *D, ArrayRef<TemplateArgument>) {}
+bool ExternalASTSource::LoadExternalSpecializations(
+    const Decl *D, ArrayRef<TemplateArgument>) { return false; }
 
 void ExternalASTSource::completeVisibleDeclsMap(const DeclContext *DC) {}
 

clang/lib/Sema/MultiplexExternalSemaSource.cpp

@@ -121,10 +121,12 @@ void MultiplexExternalSemaSource::LoadExternalSpecializations(
     Sources[i]->LoadExternalSpecializations(D, OnlyPartial);
 }
 
-void MultiplexExternalSemaSource::LoadExternalSpecializations(
+bool MultiplexExternalSemaSource::LoadExternalSpecializations(
     const Decl *D, ArrayRef<TemplateArgument> TemplateArgs) {
+  bool AnyNewSpecsLoaded = false;
   for (size_t i = 0; i < Sources.size(); ++i)
-    Sources[i]->LoadExternalSpecializations(D, TemplateArgs);
+    AnyNewSpecsLoaded |= Sources[i]->LoadExternalSpecializations(D, TemplateArgs);
+  return AnyNewSpecsLoaded;
 }
 
 void MultiplexExternalSemaSource::completeVisibleDeclsMap(const DeclContext *DC){

clang/lib/Serialization/ASTCommon.h

@@ -23,7 +23,6 @@ namespace serialization {
 
 enum DeclUpdateKind {
   UPD_CXX_ADDED_IMPLICIT_MEMBER,
-  UPD_CXX_ADDED_TEMPLATE_SPECIALIZATION,
   UPD_CXX_ADDED_ANONYMOUS_NAMESPACE,
   UPD_CXX_ADDED_FUNCTION_DEFINITION,
   UPD_CXX_ADDED_VAR_DEFINITION,

clang/lib/Serialization/ASTReader.cpp

@@ -3499,7 +3499,7 @@ llvm::Error ASTReader::ReadASTBlock(ModuleFile &F,
       break;
     }
 
-    case UPDATE_SPECIALIZATION: {
+    case CXX_ADDED_TEMPLATE_SPECIALIZATION: {
       unsigned Idx = 0;
       serialization::DeclID ID = ReadDeclID(F, Record, Idx);
       auto *Data = (const unsigned char *)Blob.data();
@@ -7964,23 +7964,30 @@ void ASTReader::LoadExternalSpecializations(const Decl *D, bool OnlyPartial) {
       GetDecl(Info.ID);
 }
 
-void ASTReader::LoadExternalSpecializations(
+bool ASTReader::LoadExternalSpecializations(
     const Decl *D, ArrayRef<TemplateArgument> TemplateArgs) {
   assert(D);
 
   auto It = SpecializationsLookups.find(D);
   if (It == SpecializationsLookups.end())
-    return;
+    return false;
 
   Deserializing LookupResults(this);
-  auto HashValue = TemplateArgumentList::ComputeODRHash(TemplateArgs);
+  auto HashValue = TemplateArgumentList::ComputeStableHash(TemplateArgs);
 
   // Get Decl may violate the iterator from SpecializationsLookups
   llvm::SmallVector<serialization::reader::LazySpecializationInfo, 8> Infos =
       It->second.Table.find(HashValue);
 
-  for (auto &Info : Infos)
+  bool NewSpecsFound = false;
+  for (auto &Info : Infos) {
+    if (GetExistingDecl(Info.ID))
+      continue;
+    NewSpecsFound = true;
     GetDecl(Info.ID);
+  }
+
+  return NewSpecsFound;
 }
 
 void ASTReader::FindExternalLexicalDecls(