llvm · ChuanqiXu9 · Dec 5, 2025
diff --git a/clang/include/clang/AST/Decl.h b/clang/include/clang/AST/Decl.h
@@ -108,6 +108,9 @@ class TranslationUnitDecl : public Decl,
   TranslationUnitDecl *getNextRedeclarationImpl() override {
     return getNextRedeclaration();
   }
+  TranslationUnitDecl *getNextRedeclarationNoUpdateImpl() override {
+    return getNextRedeclarationNoUpdate();
+  }
 
   TranslationUnitDecl *getPreviousDeclImpl() override {
     return getPreviousDecl();
@@ -607,6 +610,7 @@ class NamespaceDecl : public NamespaceBaseDecl,
   using redeclarable_base = Redeclarable<NamespaceDecl>;
 
   NamespaceDecl *getNextRedeclarationImpl() override;
+  NamespaceDecl *getNextRedeclarationNoUpdateImpl() override;
   NamespaceDecl *getPreviousDeclImpl() override;
   NamespaceDecl *getMostRecentDeclImpl() override;
 
@@ -1135,6 +1139,10 @@ class VarDecl : public DeclaratorDecl, public Redeclarable<VarDecl> {
     return getNextRedeclaration();
   }
 
+  VarDecl *getNextRedeclarationNoUpdateImpl() override {
+    return getNextRedeclarationNoUpdate();
+  }
+
   VarDecl *getPreviousDeclImpl() override {
     return getPreviousDecl();
   }
@@ -2163,6 +2171,10 @@ class FunctionDecl : public DeclaratorDecl,
     return getNextRedeclaration();
   }
 
+  FunctionDecl *getNextRedeclarationNoUpdateImpl() override {
+    return getNextRedeclarationNoUpdate();
+  }
+
   FunctionDecl *getPreviousDeclImpl() override {
     return getPreviousDecl();
   }
@@ -3586,6 +3598,10 @@ class TypedefNameDecl : public TypeDecl, public Redeclarable<TypedefNameDecl> {
     return getNextRedeclaration();
   }
 
+  TypedefNameDecl *getNextRedeclarationNoUpdateImpl() override {
+    return getNextRedeclarationNoUpdate();
+  }
+
   TypedefNameDecl *getPreviousDeclImpl() override {
     return getPreviousDecl();
   }
@@ -3755,6 +3771,10 @@ class TagDecl : public TypeDecl,
     return getNextRedeclaration();
   }
 
+  TagDecl *getNextRedeclarationNoUpdateImpl() override {
+    return getNextRedeclarationNoUpdate();
+  }
+
   TagDecl *getPreviousDeclImpl() override {
     return getPreviousDecl();
   }

diff --git a/clang/include/clang/AST/DeclBase.h b/clang/include/clang/AST/DeclBase.h
@@ -989,6 +989,10 @@ class alignas(8) Decl {
   /// Decl subclasses that can be redeclared should override this method so that
   /// Decl::redecl_iterator can iterate over them.
   virtual Decl *getNextRedeclarationImpl() { return this; }
+  /// Returns the next redeclaration without loading.
+  /// FIXME: We may be able to erase such unneccesary virtual function call by
+  /// introduce CRTP.
+  virtual Decl *getNextRedeclarationNoUpdateImpl() { return this; }
 
   /// Implementation of getPreviousDecl(), to be overridden by any
   /// subclass that has a redeclaration chain.
@@ -1000,7 +1004,8 @@ class alignas(8) Decl {
 
 public:
   /// Iterates through all the redeclarations of the same decl.
-  class redecl_iterator {
+  template <bool Update = true>
+  class redecl_iterator_impl {
     /// Current - The current declaration.
     Decl *Current = nullptr;
     Decl *Starter;
@@ -1012,36 +1017,37 @@ class alignas(8) Decl {
     using iterator_category = std::forward_iterator_tag;
     using difference_type = std::ptrdiff_t;
 
-    redecl_iterator() = default;
-    explicit redecl_iterator(Decl *C) : Current(C), Starter(C) {}
+    redecl_iterator_impl() = default;
+    explicit redecl_iterator_impl(Decl *C) : Current(C), Starter(C) {}
 
     reference operator*() const { return Current; }
     value_type operator->() const { return Current; }
 
-    redecl_iterator& operator++() {
+    redecl_iterator_impl& operator++() {
       assert(Current && "Advancing while iterator has reached end");
       // Get either previous decl or latest decl.
-      Decl *Next = Current->getNextRedeclarationImpl();
+      Decl *Next = Update ? Current->getNextRedeclarationImpl() : Current->getNextRedeclarationNoUpdateImpl(); 
       assert(Next && "Should return next redeclaration or itself, never null!");
       Current = (Next != Starter) ? Next : nullptr;
       return *this;
     }
 
-    redecl_iterator operator++(int) {
+    redecl_iterator_impl operator++(int) {
       redecl_iterator tmp(*this);
       ++(*this);
       return tmp;
     }
 
-    friend bool operator==(redecl_iterator x, redecl_iterator y) {
+    friend bool operator==(redecl_iterator_impl x, redecl_iterator_impl y) {
       return x.Current == y.Current;
     }
 
-    friend bool operator!=(redecl_iterator x, redecl_iterator y) {
+    friend bool operator!=(redecl_iterator_impl x, redecl_iterator_impl y) {
       return x.Current != y.Current;
     }
   };
 
+  using redecl_iterator = redecl_iterator_impl</*update=*/true>;
   using redecl_range = llvm::iterator_range<redecl_iterator>;
 
   /// Returns an iterator range for all the redeclarations of the same
@@ -1056,6 +1062,19 @@ class alignas(8) Decl {
 
   redecl_iterator redecls_end() const { return redecl_iterator(); }
 
+  using noload_redecl_iterator = redecl_iterator_impl</*update=*/false>;
+  using noload_redecl_range = llvm::iterator_range<noload_redecl_iterator>;
+
+  noload_redecl_range noload_redecls() const {
+    return noload_redecl_range(noload_redecls_begin(), noload_redecls_end());
+  }
+
+  noload_redecl_iterator noload_redecls_begin() const {
+    return noload_redecl_iterator(const_cast<Decl *>(this));
+  }
+
+  noload_redecl_iterator noload_redecls_end() const { return noload_redecl_iterator(); }
+
   /// Retrieve the previous declaration that declares the same entity
   /// as this declaration, or NULL if there is no previous declaration.
   Decl *getPreviousDecl() { return getPreviousDeclImpl(); }

diff --git a/clang/include/clang/AST/DeclCXX.h b/clang/include/clang/AST/DeclCXX.h
@@ -3229,6 +3229,7 @@ class NamespaceAliasDecl : public NamespaceBaseDecl,
   using redeclarable_base = Redeclarable<NamespaceAliasDecl>;
 
   NamespaceAliasDecl *getNextRedeclarationImpl() override;
+  NamespaceAliasDecl *getNextRedeclarationNoUpdateImpl() override;
   NamespaceAliasDecl *getPreviousDeclImpl() override;
   NamespaceAliasDecl *getMostRecentDeclImpl() override;
 
@@ -3414,6 +3415,10 @@ class UsingShadowDecl : public NamedDecl, public Redeclarable<UsingShadowDecl> {
     return getNextRedeclaration();
   }
 
+  UsingShadowDecl *getNextRedeclarationNoUpdateImpl() override {
+    return getNextRedeclarationNoUpdate();
+  }
+
   UsingShadowDecl *getPreviousDeclImpl() override {
     return getPreviousDecl();
   }

diff --git a/clang/include/clang/AST/DeclObjC.h b/clang/include/clang/AST/DeclObjC.h
@@ -221,6 +221,7 @@ class ObjCMethodDecl : public NamedDecl, public DeclContext {
   /// An interface declaration will return its definition.
   /// Otherwise it will return itself.
   ObjCMethodDecl *getNextRedeclarationImpl() override;
+  ObjCMethodDecl *getNextRedeclarationNoUpdateImpl() override;
 
 public:
   friend class ASTDeclReader;
@@ -1265,6 +1266,9 @@ class ObjCInterfaceDecl : public ObjCContainerDecl
   ObjCInterfaceDecl *getNextRedeclarationImpl() override {
     return getNextRedeclaration();
   }
+  ObjCInterfaceDecl *getNextRedeclarationNoUpdateImpl() override {
+    return getNextRedeclarationNoUpdate();
+  }
 
   ObjCInterfaceDecl *getPreviousDeclImpl() override {
     return getPreviousDecl();
@@ -2122,6 +2126,9 @@ class ObjCProtocolDecl : public ObjCContainerDecl,
   ObjCProtocolDecl *getNextRedeclarationImpl() override {
     return getNextRedeclaration();
   }
+  ObjCProtocolDecl *getNextRedeclarationNoUpdateImpl() override {
+    return getNextRedeclarationNoUpdate();
+  }
 
   ObjCProtocolDecl *getPreviousDeclImpl() override {
     return getPreviousDecl();

diff --git a/clang/include/clang/AST/DeclTemplate.h b/clang/include/clang/AST/DeclTemplate.h
@@ -718,6 +718,9 @@ class RedeclarableTemplateDecl : public TemplateDecl,
   RedeclarableTemplateDecl *getNextRedeclarationImpl() override {
     return getNextRedeclaration();
   }
+  RedeclarableTemplateDecl *getNextRedeclarationNoUpdateImpl() override {
+    return getNextRedeclarationNoUpdate();
+  }
 
   RedeclarableTemplateDecl *getPreviousDeclImpl() override {
     return getPreviousDecl();

diff --git a/clang/include/clang/AST/Redeclarable.h b/clang/include/clang/AST/Redeclarable.h
@@ -117,6 +117,7 @@ class Redeclarable {
              isa<UninitializedLatest>(cast<NotKnownLatest>(Link));
     }
 
+    template <bool Update = true>
     decl_type *getPrevious(const decl_type *D) const {
       if (NotKnownLatest NKL = dyn_cast<NotKnownLatest>(Link)) {
         if (auto *Prev = dyn_cast<Previous>(NKL))
@@ -128,7 +129,8 @@ class Redeclarable {
                            const_cast<decl_type *>(D));
       }
 
-      return static_cast<decl_type *>(cast<KnownLatest>(Link).get(D));
+      return Update ? static_cast<decl_type *>(cast<KnownLatest>(Link).get(D))
+        : static_cast<decl_type *>(cast<KnownLatest>(Link).getNotUpdated());
     }
 
     void setPrevious(decl_type *D) {
@@ -183,7 +185,11 @@ class Redeclarable {
   decl_type *First;
 
   decl_type *getNextRedeclaration() const {
-    return RedeclLink.getPrevious(static_cast<const decl_type *>(this));
+    return RedeclLink.template getPrevious</*update=*/true>(static_cast<const decl_type *>(this));
+  }
+
+  decl_type *getNextRedeclarationNoUpdate() const {
+    return RedeclLink.template getPrevious</*update=*/false>(static_cast<const decl_type *>(this));
   }
 
 public:

diff --git a/clang/include/clang/Serialization/ASTReader.h b/clang/include/clang/Serialization/ASTReader.h
@@ -2078,6 +2078,8 @@ class ASTReader
     return static_cast<unsigned>(DeclsLoaded.size());
   }
 
+  unsigned getNumDeclsLoaded() const;
+
   /// Returns the number of submodules known.
   unsigned getTotalNumSubmodules() const {
     return static_cast<unsigned>(SubmodulesLoaded.size());

diff --git a/clang/lib/AST/DeclCXX.cpp b/clang/lib/AST/DeclCXX.cpp
@@ -3276,6 +3276,10 @@ NamespaceDecl *NamespaceDecl::getNextRedeclarationImpl() {
   return getNextRedeclaration();
 }
 
+NamespaceDecl *NamespaceDecl::getNextRedeclarationNoUpdateImpl() {
+  return getNextRedeclarationNoUpdate();
+}
+
 NamespaceDecl *NamespaceDecl::getPreviousDeclImpl() {
   return getPreviousDecl();
 }
@@ -3290,6 +3294,10 @@ NamespaceAliasDecl *NamespaceAliasDecl::getNextRedeclarationImpl() {
   return getNextRedeclaration();
 }
 
+NamespaceAliasDecl *NamespaceAliasDecl::getNextRedeclarationNoUpdateImpl() {
+  return getNextRedeclarationNoUpdate();
+}
+
 NamespaceAliasDecl *NamespaceAliasDecl::getPreviousDeclImpl() {
   return getPreviousDecl();
 }

diff --git a/clang/lib/AST/DeclObjC.cpp b/clang/lib/AST/DeclObjC.cpp
@@ -1006,6 +1006,11 @@ ObjCMethodDecl *ObjCMethodDecl::getNextRedeclarationImpl() {
   return Redecl ? Redecl : this;
 }
 
+// FIXME: make sure ObjCMethodDecl::getNextRedeclarationImpl wont't load.
+ObjCMethodDecl *ObjCMethodDecl::getNextRedeclarationNoUpdateImpl() {
+  return getNextRedeclarationImpl();
+}
+
 ObjCMethodDecl *ObjCMethodDecl::getCanonicalDecl() {
   auto *CtxD = cast<Decl>(getDeclContext());
   const auto &Sel = getSelector();

diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
@@ -8847,14 +8847,17 @@ void ASTReader::StartTranslationUnit(ASTConsumer *Consumer) {
     DeserializationListener->ReaderInitialized(this);
 }
 
+unsigned ASTReader::getNumDeclsLoaded() const {
+  return DeclsLoaded.size() -
+  llvm::count(DeclsLoaded.materialized(), (Decl *)nullptr);
+}
+
 void ASTReader::PrintStats() {
   std::fprintf(stderr, "*** AST File Statistics:\n");
 
   unsigned NumTypesLoaded =
       TypesLoaded.size() - llvm::count(TypesLoaded.materialized(), QualType());
-  unsigned NumDeclsLoaded =
-      DeclsLoaded.size() -
-      llvm::count(DeclsLoaded.materialized(), (Decl *)nullptr);
+  unsigned NumDeclsLoaded = getNumDeclsLoaded();
   unsigned NumIdentifiersLoaded =
       IdentifiersLoaded.size() -
       llvm::count(IdentifiersLoaded, (IdentifierInfo *)nullptr);

diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -2107,8 +2107,18 @@ void ASTDeclMerger::MergeDefinitionData(
     auto *Def = DD.Definition;
     DD = std::move(MergeDD);
     DD.Definition = Def;
-    for (auto *D : Def->redecls())
-      cast<CXXRecordDecl>(D)->DefinitionData = &DD;
+
+#ifndef NDEBUG
+    unsigned OldLoadedSize = Reader.getNumDeclsLoaded();
+#endif
+
+    for (auto *RD : Def->noload_redecls())
+      cast<CXXRecordDecl>(RD)->DefinitionData = &DD;
+
+#ifndef NDEBUG
+    assert(Reader.getNumDeclsLoaded() == OldLoadedSize && "We shouldn't load new decls during merge definition data for class");
+#endif
+
     return;
   }