[NFC] [Serialization] Unify how LocalDeclID can be created

Now we can create a LocalDeclID directly with an integer without
verifying. It may be hard to refactor if we want to change the way we
serialize DeclIDs (See #95897).
Also it is hard for us to debug if someday someone construct a
LocalDeclID with an incorrect value.

So in this patch, I tried to unify the way we can construct a
LocalDeclID in ASTReader, where we will construct the LocalDeclID from
the serialized data. Also, now we can verify the constructed LocalDeclID
sooner in the new interface.

clang/include/clang/AST/ASTUnresolvedSet.h

@@ -58,7 +58,7 @@ class ASTUnresolvedSet {
   }
 
   void addLazyDecl(ASTContext &C, GlobalDeclID ID, AccessSpecifier AS) {
-    Decls.push_back(DeclAccessPair::makeLazy(ID.get(), AS), C);
+    Decls.push_back(DeclAccessPair::makeLazy(ID.getRawValue(), AS), C);
   }
 
   /// Replaces the given declaration with the new one, once.

clang/include/clang/AST/DeclID.h

@@ -116,12 +116,8 @@ class DeclIDBase {
   DeclIDBase() : ID(PREDEF_DECL_NULL_ID) {}
   explicit DeclIDBase(DeclID ID) : ID(ID) {}
 
-  explicit DeclIDBase(unsigned LocalID, unsigned ModuleFileIndex) {
-    ID = (DeclID)LocalID | ((DeclID)ModuleFileIndex << 32);
-  }
-
 public:
-  DeclID get() const { return ID; }
+  DeclID getRawValue() const { return ID; }
 
   explicit operator DeclID() const { return ID; }
 
@@ -135,12 +131,33 @@ class DeclIDBase {
 
   unsigned getLocalDeclIndex() const;
 
+  // The DeclID may be compared with predefined decl ID.
+  friend bool operator==(const DeclIDBase &LHS, const DeclID &RHS) {
+    return LHS.ID == RHS;
+  }
+  friend bool operator!=(const DeclIDBase &LHS, const DeclID &RHS) {
+    return !operator==(LHS, RHS);
+  }
+  friend bool operator<(const DeclIDBase &LHS, const DeclID &RHS) {
+    return LHS.ID < RHS;
+  }
+  friend bool operator<=(const DeclIDBase &LHS, const DeclID &RHS) {
+    return LHS.ID <= RHS;
+  }
+  friend bool operator>(const DeclIDBase &LHS, const DeclID &RHS) {
+    return LHS.ID > RHS;
+  }
+  friend bool operator>=(const DeclIDBase &LHS, const DeclID &RHS) {
+    return LHS.ID >= RHS;
+  }
+
   friend bool operator==(const DeclIDBase &LHS, const DeclIDBase &RHS) {
     return LHS.ID == RHS.ID;
   }
   friend bool operator!=(const DeclIDBase &LHS, const DeclIDBase &RHS) {
     return LHS.ID != RHS.ID;
   }
+
   // We may sort the decl ID.
   friend bool operator<(const DeclIDBase &LHS, const DeclIDBase &RHS) {
     return LHS.ID < RHS.ID;
@@ -159,16 +176,27 @@ class DeclIDBase {
   DeclID ID;
 };
 
+class ASTWriter;
+class ASTReader;
+namespace serialization {
+class ModuleFile;
+} // namespace serialization
+
 class LocalDeclID : public DeclIDBase {
   using Base = DeclIDBase;
 
-public:
-  LocalDeclID() : Base() {}
   LocalDeclID(PredefinedDeclIDs ID) : Base(ID) {}
   explicit LocalDeclID(DeclID ID) : Base(ID) {}
 
-  explicit LocalDeclID(unsigned LocalID, unsigned ModuleFileIndex)
-      : Base(LocalID, ModuleFileIndex) {}
+  // Every Decl ID is a local decl ID to the module being writing in ASTWriter.
+  friend class ASTWriter;
+  friend class GlobalDeclID;
+
+public:
+  LocalDeclID() : Base() {}
+
+  static LocalDeclID get(ASTReader &Reader, serialization::ModuleFile &MF,
+                         DeclID ID);
 
   LocalDeclID &operator++() {
     ++ID;
@@ -189,8 +217,8 @@ class GlobalDeclID : public DeclIDBase {
   GlobalDeclID() : Base() {}
   explicit GlobalDeclID(DeclID ID) : Base(ID) {}
 
-  explicit GlobalDeclID(unsigned LocalID, unsigned ModuleFileIndex)
-      : Base(LocalID, ModuleFileIndex) {}
+  explicit GlobalDeclID(unsigned ModuleFileIndex, unsigned LocalID)
+      : Base((DeclID)ModuleFileIndex << 32 | (DeclID)LocalID) {}
 
   // For DeclIDIterator<GlobalDeclID> to be able to convert a GlobalDeclID
   // to a LocalDeclID.
@@ -235,7 +263,7 @@ template <> struct DenseMapInfo<clang::GlobalDeclID> {
     // In GlobalDeclID's case, it is pretty common that the lower 32 bits can
     // be same.
     // FIXME: Remove this when we fix the underlying issue.
-    return llvm::hash_value(Key.get());
+    return llvm::hash_value(Key.getRawValue());
   }
 
   static bool isEqual(const GlobalDeclID &L, const GlobalDeclID &R) {

clang/include/clang/Serialization/ASTBitCodes.h

@@ -2004,9 +2004,9 @@ struct ObjCCategoriesInfo {
 
   ObjCCategoriesInfo() = default;
   ObjCCategoriesInfo(LocalDeclID ID, unsigned Offset)
-      : DefinitionID(ID.get()), Offset(Offset) {}
+      : DefinitionID(ID.getRawValue()), Offset(Offset) {}
 
-  LocalDeclID getDefinitionID() const { return LocalDeclID(DefinitionID); }
+  DeclID getDefinitionID() const { return DefinitionID; }
 
   friend bool operator<(const ObjCCategoriesInfo &X,
                         const ObjCCategoriesInfo &Y) {

clang/include/clang/Serialization/ASTReader.h

@@ -375,6 +375,7 @@ class ASTReader
   friend class serialization::reader::ASTIdentifierLookupTrait;
   friend class serialization::ReadMethodPoolVisitor;
   friend class TypeLocReader;
+  friend class LocalDeclID;
 
   using RecordData = SmallVector<uint64_t, 64>;
   using RecordDataImpl = SmallVectorImpl<uint64_t>;
@@ -1501,7 +1502,8 @@ class ASTReader
         : iterator_adaptor_base(Pos), Reader(Reader), Mod(Mod) {}
 
     value_type operator*() const {
-      return Reader->GetDecl(Reader->getGlobalDeclID(*Mod, (LocalDeclID)*I));
+      LocalDeclID ID = LocalDeclID::get(*Reader, *Mod, *I);
+      return Reader->GetDecl(Reader->getGlobalDeclID(*Mod, ID));
     }
 
     value_type operator->() const { return **this; }
@@ -1955,12 +1957,12 @@ class ASTReader
   /// given module.
   ///
   /// \returns The declaration ID read from the record, adjusted to a global ID.
-  GlobalDeclID ReadDeclID(ModuleFile &F, const RecordData &Record,
+  GlobalDeclID ReadDeclID(ModuleFile &F, const RecordDataImpl &Record,
                           unsigned &Idx);
 
   /// Reads a declaration from the given position in a record in the
   /// given module.
-  Decl *ReadDecl(ModuleFile &F, const RecordData &R, unsigned &I) {
+  Decl *ReadDecl(ModuleFile &F, const RecordDataImpl &R, unsigned &I) {
     return GetDecl(ReadDeclID(F, R, I));
   }
 
@@ -1969,8 +1971,8 @@ class ASTReader
   ///
   /// \returns The declaration read from this location, casted to the given
   /// result type.
-  template<typename T>
-  T *ReadDeclAs(ModuleFile &F, const RecordData &R, unsigned &I) {
+  template <typename T>
+  T *ReadDeclAs(ModuleFile &F, const RecordDataImpl &R, unsigned &I) {
     return cast_or_null<T>(GetDecl(ReadDeclID(F, R, I)));
   }
 

clang/include/clang/Serialization/ASTWriter.h

@@ -729,8 +729,7 @@ class ASTWriter : public ASTDeserializationListener,
     if (D->isFromASTFile())
       return false;
     auto I = DeclIDs.find(D);
-    return (I == DeclIDs.end() ||
-            I->second.get() >= clang::NUM_PREDEF_DECL_IDS);
+    return (I == DeclIDs.end() || I->second >= clang::NUM_PREDEF_DECL_IDS);
   };
 
   /// Emit a reference to a declaration.

clang/lib/AST/DeclBase.cpp

@@ -80,7 +80,7 @@ void *Decl::operator new(std::size_t Size, const ASTContext &Context,
 
   uint64_t *PrefixPtr = (uint64_t *)Result - 1;
 
-  *PrefixPtr = ID.get();
+  *PrefixPtr = ID.getRawValue();
 
   // We leave the upper 16 bits to store the module IDs. 48 bits should be
   // sufficient to store a declaration ID.

clang/lib/AST/DeclTemplate.cpp

@@ -339,7 +339,7 @@ void RedeclarableTemplateDecl::loadLazySpecializationsImpl() const {
     ASTContext &Context = getASTContext();
     GlobalDeclID *Specs = CommonBasePtr->LazySpecializations;
     CommonBasePtr->LazySpecializations = nullptr;
-    unsigned SpecSize = (*Specs++).get();
+    unsigned SpecSize = (*Specs++).getRawValue();
     for (unsigned I = 0; I != SpecSize; ++I)
       (void)Context.getExternalSource()->GetExternalDecl(Specs[I]);
   }

clang/lib/Frontend/ASTUnit.cpp

@@ -1473,7 +1473,7 @@ void ASTUnit::RealizeTopLevelDeclsFromPreamble() {
   for (const auto TopLevelDecl : TopLevelDeclsInPreamble) {
     // Resolve the declaration ID to an actual declaration, possibly
     // deserializing the declaration in the process.
-    if (Decl *D = Reader->GetDecl(Reader->getGlobalDeclID(MF, TopLevelDecl)))
+    if (Decl *D = Reader->GetLocalDecl(MF, TopLevelDecl))
       Resolved.push_back(D);
   }
   TopLevelDeclsInPreamble.clear();