[C++20] [Modules] Support module level lookup (#122887)

clang/docs/ReleaseNotes.rst

@@ -316,6 +316,8 @@ C++23 Feature Support
 C++20 Feature Support
 ^^^^^^^^^^^^^^^^^^^^^
 
+- Implemented module level lookup for C++20 modules. (#GH90154)
+
 
 Resolutions to C++ Defect Reports
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/include/clang/AST/DeclBase.h

@@ -836,6 +836,10 @@ class alignas(8) Decl {
     return isFromASTFile() ? getImportedOwningModule() : getLocalOwningModule();
   }
 
+  /// Get the top level owning named module that owns this declaration if any.
+  /// \returns nullptr if the declaration is not owned by a named module.
+  Module *getTopLevelOwningNamedModule() const;
+
   /// Get the module that owns this declaration for linkage purposes.
   /// There only ever is such a standard C++ module.
   Module *getOwningModuleForLinkage() const;

clang/include/clang/Serialization/ASTBitCodes.h

@@ -738,6 +738,8 @@ enum ASTRecordTypes {
   CXX_ADDED_TEMPLATE_SPECIALIZATION = 74,
 
   CXX_ADDED_TEMPLATE_PARTIAL_SPECIALIZATION = 75,
+
+  UPDATE_MODULE_LOCAL_VISIBLE = 76,
 };
 
 /// Record types used within a source manager block.
@@ -1334,6 +1336,10 @@ enum DeclCode {
   /// into a DeclContext via DeclContext::lookup.
   DECL_CONTEXT_VISIBLE,
 
+  /// A record containing the set of declarations that are
+  /// only visible from DeclContext in the same module.
+  DECL_CONTEXT_MODULE_LOCAL_VISIBLE,
+
   /// A LabelDecl record.
   DECL_LABEL,
 

clang/include/clang/Serialization/ASTReader.h

@@ -353,6 +353,7 @@ class ASTIdentifierLookupTrait;
 
 /// The on-disk hash table(s) used for DeclContext name lookup.
 struct DeclContextLookupTable;
+struct ModuleLocalLookupTable;
 
 /// The on-disk hash table(s) used for specialization decls.
 struct LazySpecializationInfoLookupTable;
@@ -523,9 +524,14 @@ class ASTReader
   /// in the chain.
   DeclUpdateOffsetsMap DeclUpdateOffsets;
 
+  struct LookupBlockOffsets {
+    uint64_t LexicalOffset;
+    uint64_t VisibleOffset;
+    uint64_t ModuleLocalOffset;
+  };
+
   using DelayedNamespaceOffsetMapTy =
-      llvm::DenseMap<GlobalDeclID, std::pair</*LexicalOffset*/ uint64_t,
-                                             /*VisibleOffset*/ uint64_t>>;
+      llvm::DenseMap<GlobalDeclID, LookupBlockOffsets>;
 
   /// Mapping from global declaration IDs to the lexical and visible block
   /// offset for delayed namespace in reduced BMI.
@@ -631,6 +637,9 @@ class ASTReader
   /// Map from a DeclContext to its lookup tables.
   llvm::DenseMap<const DeclContext *,
                  serialization::reader::DeclContextLookupTable> Lookups;
+  llvm::DenseMap<const DeclContext *,
+                 serialization::reader::ModuleLocalLookupTable>
+      ModuleLocalLookups;
 
   using SpecLookupTableTy =
       llvm::DenseMap<const Decl *,
@@ -659,6 +668,8 @@ class ASTReader
   /// Updates to the visible declarations of declaration contexts that
   /// haven't been loaded yet.
   llvm::DenseMap<GlobalDeclID, DeclContextVisibleUpdates> PendingVisibleUpdates;
+  llvm::DenseMap<GlobalDeclID, DeclContextVisibleUpdates>
+      PendingModuleLocalVisibleUpdates;
 
   using SpecializationsUpdate = SmallVector<UpdateData, 1>;
   using SpecializationsUpdateMap =
@@ -696,7 +707,8 @@ class ASTReader
   /// Read the record that describes the visible contents of a DC.
   bool ReadVisibleDeclContextStorage(ModuleFile &M,
                                      llvm::BitstreamCursor &Cursor,
-                                     uint64_t Offset, GlobalDeclID ID);
+                                     uint64_t Offset, GlobalDeclID ID,
+                                     bool IsModuleLocal);
 
   bool ReadSpecializations(ModuleFile &M, llvm::BitstreamCursor &Cursor,
                            uint64_t Offset, Decl *D, bool IsPartial);
@@ -1132,6 +1144,10 @@ class ASTReader
   /// Number of visible decl contexts read/total.
   unsigned NumVisibleDeclContextsRead = 0, TotalVisibleDeclContexts = 0;
 
+  /// Number of module local visible decl contexts read/total.
+  unsigned NumModuleLocalVisibleDeclContexts = 0,
+           TotalModuleLocalVisibleDeclContexts = 0;
+
   /// Total size of modules, in bits, currently loaded
   uint64_t TotalModulesSizeInBits = 0;
 
@@ -1444,6 +1460,9 @@ class ASTReader
   const serialization::reader::DeclContextLookupTable *
   getLoadedLookupTables(DeclContext *Primary) const;
 
+  const serialization::reader::ModuleLocalLookupTable *
+  getModuleLocalLookupTables(DeclContext *Primary) const;
+
   /// Get the loaded specializations lookup tables for \p D,
   /// if any.
   serialization::reader::LazySpecializationInfoLookupTable *
@@ -2608,6 +2627,10 @@ inline bool shouldSkipCheckingODR(const Decl *D) {
          (D->isFromGlobalModule() || D->isFromHeaderUnit());
 }
 
+/// Calculate a hash value for the primary module name of the given module.
+/// \returns std::nullopt if M is not a C++ standard module.
+std::optional<unsigned> getPrimaryModuleHash(const Module *M);
+
 } // namespace clang
 
 #endif // LLVM_CLANG_SERIALIZATION_ASTREADER_H

clang/include/clang/Serialization/ASTWriter.h

@@ -492,6 +492,10 @@ class ASTWriter : public ASTDeserializationListener,
   /// file.
   unsigned NumVisibleDeclContexts = 0;
 
+  /// The number of module local visible declcontexts written to the AST
+  /// file.
+  unsigned NumModuleLocalDeclContexts = 0;
+
   /// A mapping from each known submodule to its ID number, which will
   /// be a positive integer.
   llvm::DenseMap<const Module *, unsigned> SubmoduleIDs;
@@ -587,11 +591,15 @@ class ASTWriter : public ASTDeserializationListener,
   uint64_t WriteSpecializationInfoLookupTable(
       const NamedDecl *D, llvm::SmallVectorImpl<const Decl *> &Specializations,
       bool IsPartial);
-  void GenerateNameLookupTable(ASTContext &Context, const DeclContext *DC,
-                               llvm::SmallVectorImpl<char> &LookupTable);
+  void
+  GenerateNameLookupTable(ASTContext &Context, const DeclContext *DC,
+                          llvm::SmallVectorImpl<char> &LookupTable,
+                          llvm::SmallVectorImpl<char> &ModuleLocalLookupTable);
   uint64_t WriteDeclContextLexicalBlock(ASTContext &Context,
                                         const DeclContext *DC);
-  uint64_t WriteDeclContextVisibleBlock(ASTContext &Context, DeclContext *DC);
+  void WriteDeclContextVisibleBlock(ASTContext &Context, DeclContext *DC,
+                                    uint64_t &VisibleBlockOffset,
+                                    uint64_t &ModuleLocalBlockOffset);
   void WriteTypeDeclOffsets();
   void WriteFileDeclIDsMap();
   void WriteComments(ASTContext &Context);
@@ -624,7 +632,9 @@ class ASTWriter : public ASTDeserializationListener,
   unsigned DeclParmVarAbbrev = 0;
   unsigned DeclContextLexicalAbbrev = 0;
   unsigned DeclContextVisibleLookupAbbrev = 0;
+  unsigned DeclModuleLocalVisibleLookupAbbrev = 0;
   unsigned UpdateVisibleAbbrev = 0;
+  unsigned ModuleLocalUpdateVisibleAbbrev = 0;
   unsigned DeclRecordAbbrev = 0;
   unsigned DeclTypedefAbbrev = 0;
   unsigned DeclVarAbbrev = 0;

clang/lib/AST/DeclBase.cpp

@@ -130,6 +130,14 @@ void Decl::setOwningModuleID(unsigned ID) {
   *IDAddress |= (uint64_t)ID << 48;
 }
 
+Module *Decl::getTopLevelOwningNamedModule() const {
+  if (getOwningModule() &&
+      getOwningModule()->getTopLevelModule()->isNamedModule())
+    return getOwningModule()->getTopLevelModule();
+
+  return nullptr;
+}
+
 Module *Decl::getOwningModuleSlow() const {
   assert(isFromASTFile() && "Not from AST file?");
   return getASTContext().getExternalSource()->getModule(getOwningModuleID());