[modules] Stop performing PCM lookups for all identifiers when building with C++ modules. Instead, serialize a list of interesting identifiers and mark those ones out of date on module import. Avoiding the identifier lookups here gives a 20-30% speedup in builds with large numbers of modules. No functionality change intended.

llvm-svn: 242868

Author: zygoloid

clang/include/clang/Serialization/ASTBitCodes.h

@@ -543,7 +543,10 @@ namespace clang {
       /// macro definition.
       MACRO_OFFSET = 47,
 
-      // ID 48 used to be a table of macros.
+      /// \brief A list of "interesting" identifiers. Only used in C++ (where we
+      /// don't normally do lookups into the serialized identifier table). These
+      /// are eagerly deserialized.
+      INTERESTING_IDENTIFIERS = 48,
 
       /// \brief Record code for undefined but used functions and variables that
       /// need a definition in this TU.

clang/include/clang/Serialization/Module.h

@@ -270,6 +270,10 @@ class ModuleFile {
   /// IdentifierHashTable.
   void *IdentifierLookupTable;
 
+  /// \brief Offsets of identifiers that we're going to preload within
+  /// IdentifierTableData.
+  std::vector<unsigned> PreloadIdentifierOffsets;
+
   // === Macros ===
 
   /// \brief The cursor to the start of the preprocessor block, which stores

clang/include/clang/Serialization/ModuleManager.h

@@ -30,14 +30,19 @@ namespace serialization {
 
 /// \brief Manages the set of modules loaded by an AST reader.
 class ModuleManager {
-  /// \brief The chain of AST files. The first entry is the one named by the
-  /// user, the last one is the one that doesn't depend on anything further.
+  /// \brief The chain of AST files, in the order in which we started to load
+  /// them (this order isn't really useful for anything).
   SmallVector<ModuleFile *, 2> Chain;
 
+  /// \brief The chain of non-module PCH files. The first entry is the one named
+  /// by the user, the last one is the one that doesn't depend on anything
+  /// further.
+  SmallVector<ModuleFile *, 2> PCHChain;
+
   // \brief The roots of the dependency DAG of AST files. This is used
   // to implement short-circuiting logic when running DFS over the dependencies.
   SmallVector<ModuleFile *, 2> Roots;
-  
+
   /// \brief All loaded modules, indexed by name.
   llvm::DenseMap<const FileEntry *, ModuleFile *> Modules;
 
@@ -138,6 +143,11 @@ class ModuleManager {
   ModuleReverseIterator rbegin() { return Chain.rbegin(); }
   /// \brief Reverse iterator end-point to traverse all loaded modules.
   ModuleReverseIterator rend() { return Chain.rend(); }
+
+  /// \brief A range covering the PCH and preamble module files loaded.
+  llvm::iterator_range<ModuleConstIterator> pch_modules() const {
+    return llvm::make_range(PCHChain.begin(), PCHChain.end());
+  }
 
   /// \brief Returns the primary module associated with the manager, that is,
   /// the first module loaded

clang/lib/Sema/Sema.cpp

@@ -154,6 +154,9 @@ void Sema::Initialize() {
   // will not be able to merge any duplicate __va_list_tag decls correctly.
   VAListTagName = PP.getIdentifierInfo("__va_list_tag");
 
+  if (!TUScope)
+    return;
+
   // Initialize predefined 128-bit integer types, if needed.
   if (Context.getTargetInfo().hasInt128Type()) {
     // If either of the 128-bit integer types are unavailable to name lookup,

clang/lib/Serialization/ASTReader.cpp

@@ -2564,6 +2564,10 @@ ASTReader::ReadASTBlock(ModuleFile &F, unsigned ClientLoadCapabilities) {
       break;
     }
 
+    case INTERESTING_IDENTIFIERS:
+      F.PreloadIdentifierOffsets.assign(Record.begin(), Record.end());
+      break;
+
     case EAGERLY_DESERIALIZED_DECLS:
       // FIXME: Skip reading this record if our ASTConsumer doesn't care
       // about "interesting" decls (for instance, if we're building a module).
@@ -3410,6 +3414,18 @@ ASTReader::ASTReadResult ASTReader::ReadAST(const std::string &FileName,
       // SourceManager.
       SourceMgr.getLoadedSLocEntryByID(Index);
     }
+
+    // Preload all the pending interesting identifiers by marking them out of
+    // date.
+    for (auto Offset : F.PreloadIdentifierOffsets) {
+      const unsigned char *Data = reinterpret_cast<const unsigned char *>(
+          F.IdentifierTableData + Offset);
+
+      ASTIdentifierLookupTrait Trait(*this, F);
+      auto KeyDataLen = Trait.ReadKeyDataLength(Data);
+      auto Key = Trait.ReadKey(Data, KeyDataLen.first);
+      PP.getIdentifierTable().getOwn(Key).setOutOfDate(true);
+    }
   }
 
   // Setup the import locations and notify the module manager that we've
@@ -3430,13 +3446,20 @@ ASTReader::ASTReadResult ASTReader::ReadAST(const std::string &FileName,
                                        M->ImportLoc.getRawEncoding());
   }
 
-  // Mark all of the identifiers in the identifier table as being out of date,
-  // so that various accessors know to check the loaded modules when the
-  // identifier is used.
-  for (IdentifierTable::iterator Id = PP.getIdentifierTable().begin(),
-                              IdEnd = PP.getIdentifierTable().end();
-       Id != IdEnd; ++Id)
-    Id->second->setOutOfDate(true);
+  if (!Context.getLangOpts().CPlusPlus ||
+      (Type != MK_ImplicitModule && Type != MK_ExplicitModule)) {
+    // Mark all of the identifiers in the identifier table as being out of date,
+    // so that various accessors know to check the loaded modules when the
+    // identifier is used.
+    //
+    // For C++ modules, we don't need information on many identifiers (just
+    // those that provide macros or are poisoned), so we mark all of
+    // the interesting ones via PreloadIdentifierOffsets.
+    for (IdentifierTable::iterator Id = PP.getIdentifierTable().begin(),
+                                IdEnd = PP.getIdentifierTable().end();
+         Id != IdEnd; ++Id)
+      Id->second->setOutOfDate(true);
+  }
 
   // Resolve any unresolved module exports.
   for (unsigned I = 0, N = UnresolvedModuleRefs.size(); I != N; ++I) {
@@ -6827,19 +6850,32 @@ IdentifierInfo *ASTReader::get(StringRef Name) {
   // Note that we are loading an identifier.
   Deserializing AnIdentifier(this);
 
-  // If there is a global index, look there first to determine which modules
-  // provably do not have any results for this identifier.
-  GlobalModuleIndex::HitSet Hits;
-  GlobalModuleIndex::HitSet *HitsPtr = nullptr;
-  if (!loadGlobalIndex()) {
-    if (GlobalIndex->lookupIdentifier(Name, Hits)) {
-      HitsPtr = &Hits;
-    }
-  }
   IdentifierLookupVisitor Visitor(Name, /*PriorGeneration=*/0,
                                   NumIdentifierLookups,
                                   NumIdentifierLookupHits);
-  ModuleMgr.visit(IdentifierLookupVisitor::visit, &Visitor, HitsPtr);
+
+  // We don't need to do identifier table lookups in C++ modules (we preload
+  // all interesting declarations, and don't need to use the scope for name
+  // lookups). Perform the lookup in PCH files, though, since we don't build
+  // a complete initial identifier table if we're carrying on from a PCH.
+  if (Context.getLangOpts().CPlusPlus) {
+    for (auto F : ModuleMgr.pch_modules())
+      if (Visitor.visit(*F, &Visitor))
+        break;
+  } else {
+    // If there is a global index, look there first to determine which modules
+    // provably do not have any results for this identifier.
+    GlobalModuleIndex::HitSet Hits;
+    GlobalModuleIndex::HitSet *HitsPtr = nullptr;
+    if (!loadGlobalIndex()) {
+      if (GlobalIndex->lookupIdentifier(Name, Hits)) {
+        HitsPtr = &Hits;
+      }
+    }
+
+    ModuleMgr.visit(IdentifierLookupVisitor::visit, &Visitor, HitsPtr);
+  }
+
   IdentifierInfo *II = Visitor.getIdentifierInfo();
   markIdentifierUpToDate(II);
   return II;

clang/lib/Serialization/ASTWriter.cpp

@@ -3104,6 +3104,7 @@ class ASTIdentifierTableTrait {
   IdentifierResolver &IdResolver;
   bool IsModule;
   bool NeedDecls;
+  ASTWriter::RecordData *InterestingIdentifierOffsets;
 
   /// \brief Determines whether this is an "interesting" identifier that needs a
   /// full IdentifierInfo structure written into the hash table. Notably, this
@@ -3131,14 +3132,20 @@ class ASTIdentifierTableTrait {
   typedef unsigned offset_type;
 
   ASTIdentifierTableTrait(ASTWriter &Writer, Preprocessor &PP,
-                          IdentifierResolver &IdResolver, bool IsModule)
+                          IdentifierResolver &IdResolver, bool IsModule,
+                          ASTWriter::RecordData *InterestingIdentifierOffsets)
       : Writer(Writer), PP(PP), IdResolver(IdResolver), IsModule(IsModule),
-        NeedDecls(!IsModule || !Writer.getLangOpts().CPlusPlus) {}
+        NeedDecls(!IsModule || !Writer.getLangOpts().CPlusPlus),
+        InterestingIdentifierOffsets(InterestingIdentifierOffsets) {}
 
   static hash_value_type ComputeHash(const IdentifierInfo* II) {
     return llvm::HashString(II->getName());
   }
 
+  bool isInterestingIdentifier(const IdentifierInfo *II) {
+    auto MacroOffset = Writer.getMacroDirectivesOffset(II);
+    return isInterestingIdentifier(II, MacroOffset);
+  }
   bool isInterestingNonMacroIdentifier(const IdentifierInfo *II) {
     return isInterestingIdentifier(II, 0);
   }
@@ -3178,6 +3185,12 @@ class ASTIdentifierTableTrait {
     // Record the location of the key data.  This is used when generating
     // the mapping from persistent IDs to strings.
     Writer.SetIdentifierOffset(II, Out.tell());
+
+    // Emit the offset of the key/data length information to the interesting
+    // identifiers table if necessary.
+    if (InterestingIdentifierOffsets && isInterestingIdentifier(II))
+      InterestingIdentifierOffsets->push_back(Out.tell() - 4);
+
     Out.write(II->getNameStart(), KeyLen);
   }
 
@@ -3238,11 +3251,15 @@ void ASTWriter::WriteIdentifierTable(Preprocessor &PP,
                                      bool IsModule) {
   using namespace llvm;
 
+  RecordData InterestingIdents;
+
   // Create and write out the blob that contains the identifier
   // strings.
   {
     llvm::OnDiskChainedHashTableGenerator<ASTIdentifierTableTrait> Generator;
-    ASTIdentifierTableTrait Trait(*this, PP, IdResolver, IsModule);
+    ASTIdentifierTableTrait Trait(
+        *this, PP, IdResolver, IsModule,
+        (getLangOpts().CPlusPlus && IsModule) ? &InterestingIdents : nullptr);
 
     // Look for any identifiers that were named while processing the
     // headers, but are otherwise not needed. We add these to the hash
@@ -3316,6 +3333,11 @@ void ASTWriter::WriteIdentifierTable(Preprocessor &PP,
   Record.push_back(FirstIdentID - NUM_PREDEF_IDENT_IDS);
   Stream.EmitRecordWithBlob(IdentifierOffsetAbbrev, Record,
                             bytes(IdentifierOffsets));
+
+  // In C++, write the list of interesting identifiers (those that are
+  // defined as macros, poisoned, or similar unusual things).
+  if (!InterestingIdents.empty())
+    Stream.EmitRecord(INTERESTING_IDENTIFIERS, InterestingIdents);
 }
 
 //===----------------------------------------------------------------------===//

clang/lib/Serialization/ModuleManager.cpp

@@ -95,6 +95,8 @@ ModuleManager::addModule(StringRef FileName, ModuleKind Type,
     New->File = Entry;
     New->ImportLoc = ImportLoc;
     Chain.push_back(New);
+    if (!New->isModule())
+      PCHChain.push_back(New);
     if (!ImportedBy)
       Roots.push_back(New);
     NewModule = true;
@@ -159,6 +161,8 @@ ModuleManager::addModule(StringRef FileName, ModuleKind Type,
         Modules.erase(Entry);
         assert(Chain.back() == ModuleEntry);
         Chain.pop_back();
+        if (!ModuleEntry->isModule())
+          PCHChain.pop_back();
         if (Roots.back() == ModuleEntry)
           Roots.pop_back();
         else
@@ -225,6 +229,15 @@ void ModuleManager::removeModules(
 
   // Remove the modules from the chain.
   Chain.erase(first, last);
+
+  // Also remove them from the PCH chain.
+  for (auto I = first; I != last; ++I) {
+    if (!(*I)->isModule()) {
+      PCHChain.erase(std::find(PCHChain.begin(), PCHChain.end(), *I),
+                     PCHChain.end());
+      break;
+    }
+  }
 }
 
 void