(NFC) Track global summary liveness in GVFlags.

Replace GVFlags::LiveRoot with GVFlags::Live and use that instead of
all the DeadSymbols sets. This is refactoring in order to make
liveness information available in the RegularLTO pipeline.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@304466 91177308-0d34-0410-b5e6-96231b3b80d8

Author: eugenis

include/llvm/IR/ModuleSummaryIndex.h

@@ -134,16 +134,18 @@ class GlobalValueSummary {
     /// be renamed or references something that can't be renamed).
     unsigned NotEligibleToImport : 1;
 
-    /// Indicate that the global value must be considered a live root for
-    /// index-based liveness analysis. Used for special LLVM values such as
-    /// llvm.global_ctors that the linker does not know about.
-    unsigned LiveRoot : 1;
+    /// In per-module summary, indicate that the global value must be considered
+    /// a live root for index-based liveness analysis. Used for special LLVM
+    /// values such as llvm.global_ctors that the linker does not know about.
+    ///
+    /// In combined summary, indicate that the global value is live.
+    unsigned Live : 1;
 
     /// Convenience Constructors
     explicit GVFlags(GlobalValue::LinkageTypes Linkage,
-                     bool NotEligibleToImport, bool LiveRoot)
+                     bool NotEligibleToImport, bool Live)
         : Linkage(Linkage), NotEligibleToImport(NotEligibleToImport),
-          LiveRoot(LiveRoot) {}
+          Live(Live) {}
   };
 
 private:
@@ -172,6 +174,8 @@ class GlobalValueSummary {
   /// are listed in the derived FunctionSummary object.
   std::vector<ValueInfo> RefEdgeList;
 
+  bool isLive() const { return Flags.Live; }
+
 protected:
   GlobalValueSummary(SummaryKind K, GVFlags Flags, std::vector<ValueInfo> Refs)
       : Kind(K), Flags(Flags), RefEdgeList(std::move(Refs)) {}
@@ -213,19 +217,17 @@ class GlobalValueSummary {
   /// Return true if this global value can't be imported.
   bool notEligibleToImport() const { return Flags.NotEligibleToImport; }
 
-  /// Return true if this global value must be considered a root for live
-  /// value analysis on the index.
-  bool liveRoot() const { return Flags.LiveRoot; }
-
-  /// Flag that this global value must be considered a root for live
-  /// value analysis on the index.
-  void setLiveRoot() { Flags.LiveRoot = true; }
+  void setLive(bool Live) { Flags.Live = Live; }
 
   /// Flag that this global value cannot be imported.
   void setNotEligibleToImport() { Flags.NotEligibleToImport = true; }
 
   /// Return the list of values referenced by this global value definition.
   ArrayRef<ValueInfo> refs() const { return RefEdgeList; }
+
+  friend class ModuleSummaryIndex;
+  friend void computeDeadSymbols(class ModuleSummaryIndex &,
+                                 const DenseSet<GlobalValue::GUID> &);
 };
 
 /// \brief Alias summary information.
@@ -535,6 +537,11 @@ class ModuleSummaryIndex {
   /// GUIDs, it will be mapped to 0.
   std::map<GlobalValue::GUID, GlobalValue::GUID> OidGuidMap;
 
+  /// Indicates that summary-based GlobalValue GC has run, and values with
+  /// GVFlags::Live==false are really dead. Otherwise, all values must be
+  /// considered live.
+  bool WithGlobalValueDeadStripping = false;
+
   // YAML I/O support.
   friend yaml::MappingTraits<ModuleSummaryIndex>;
 
@@ -550,6 +557,17 @@ class ModuleSummaryIndex {
   const_gvsummary_iterator end() const { return GlobalValueMap.end(); }
   size_t size() const { return GlobalValueMap.size(); }
 
+  bool withGlobalValueDeadStripping() const {
+    return WithGlobalValueDeadStripping;
+  }
+  void setWithGlobalValueDeadStripping() {
+    WithGlobalValueDeadStripping = true;
+  }
+
+  bool isGlobalValueLive(const GlobalValueSummary *GVS) const {
+    return !WithGlobalValueDeadStripping || GVS->isLive();
+  }
+
   /// Return a ValueInfo for GUID if it exists, otherwise return ValueInfo().
   ValueInfo getValueInfo(GlobalValue::GUID GUID) const {
     auto I = GlobalValueMap.find(GUID);

include/llvm/Transforms/IPO/FunctionImport.h

@@ -81,15 +81,11 @@ class FunctionImportPass : public PassInfoMixin<FunctionImportPass> {
 /// \p ExportLists contains for each Module the set of globals (GUID) that will
 /// be imported by another module, or referenced by such a function. I.e. this
 /// is the set of globals that need to be promoted/renamed appropriately.
-///
-/// \p DeadSymbols (optional) contains a list of GUID that are deemed "dead" and
-/// will be ignored for the purpose of importing.
 void ComputeCrossModuleImport(
     const ModuleSummaryIndex &Index,
     const StringMap<GVSummaryMapTy> &ModuleToDefinedGVSummaries,
     StringMap<FunctionImporter::ImportMapTy> &ImportLists,
-    StringMap<FunctionImporter::ExportSetTy> &ExportLists,
-    const DenseSet<GlobalValue::GUID> *DeadSymbols = nullptr);
+    StringMap<FunctionImporter::ExportSetTy> &ExportLists);
 
 /// Compute all the imports for the given module using the Index.
 ///
@@ -102,9 +98,9 @@ void ComputeCrossModuleImportForModule(
 /// Compute all the symbols that are "dead": i.e these that can't be reached
 /// in the graph from any of the given symbols listed in
 /// \p GUIDPreservedSymbols.
-DenseSet<GlobalValue::GUID>
-computeDeadSymbols(const ModuleSummaryIndex &Index,
-                   const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols);
+void computeDeadSymbols(
+    ModuleSummaryIndex &Index,
+    const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols);
 
 /// Compute the set of summaries needed for a ThinLTO backend compilation of
 /// \p ModulePath.

lib/Analysis/ModuleSummaryAnalysis.cpp

@@ -275,7 +275,7 @@ computeFunctionSummary(ModuleSummaryIndex &Index, const Module &M,
       // FIXME: refactor this to use the same code that inliner is using.
       F.isVarArg();
   GlobalValueSummary::GVFlags Flags(F.getLinkage(), NotEligibleForImport,
-                                    /* LiveRoot = */ false);
+                                    /* Live = */ false);
   auto FuncSummary = llvm::make_unique<FunctionSummary>(
       Flags, NumInsts, RefEdges.takeVector(), CallGraphEdges.takeVector(),
       TypeTests.takeVector(), TypeTestAssumeVCalls.takeVector(),
@@ -295,7 +295,7 @@ computeVariableSummary(ModuleSummaryIndex &Index, const GlobalVariable &V,
   findRefEdges(Index, &V, RefEdges, Visited);
   bool NonRenamableLocal = isNonRenamableLocal(V);
   GlobalValueSummary::GVFlags Flags(V.getLinkage(), NonRenamableLocal,
-                                    /* LiveRoot = */ false);
+                                    /* Live = */ false);
   auto GVarSummary =
       llvm::make_unique<GlobalVarSummary>(Flags, RefEdges.takeVector());
   if (NonRenamableLocal)
@@ -308,7 +308,7 @@ computeAliasSummary(ModuleSummaryIndex &Index, const GlobalAlias &A,
                     DenseSet<GlobalValue::GUID> &CantBePromoted) {
   bool NonRenamableLocal = isNonRenamableLocal(A);
   GlobalValueSummary::GVFlags Flags(A.getLinkage(), NonRenamableLocal,
-                                    /* LiveRoot = */ false);
+                                    /* Live = */ false);
   auto AS = llvm::make_unique<AliasSummary>(Flags, ArrayRef<ValueInfo>{});
   auto *Aliasee = A.getBaseObject();
   auto *AliaseeSummary = Index.getGlobalValueSummary(*Aliasee);
@@ -323,7 +323,7 @@ computeAliasSummary(ModuleSummaryIndex &Index, const GlobalAlias &A,
 static void setLiveRoot(ModuleSummaryIndex &Index, StringRef Name) {
   if (ValueInfo VI = Index.getValueInfo(GlobalValue::getGUID(Name)))
     for (auto &Summary : VI.getSummaryList())
-      Summary->setLiveRoot();
+      Summary->setLive(true);
 }
 
 ModuleSummaryIndex llvm::buildModuleSummaryIndex(
@@ -423,8 +423,8 @@ ModuleSummaryIndex llvm::buildModuleSummaryIndex(
             return;
           assert(GV->isDeclaration() && "Def in module asm already has definition");
           GlobalValueSummary::GVFlags GVFlags(GlobalValue::InternalLinkage,
-                                              /* NotEligibleToImport */ true,
-                                              /* LiveRoot */ true);
+                                              /* NotEligibleToImport = */ true,
+                                              /* Live = */ true);
           CantBePromoted.insert(GlobalValue::getGUID(Name));
           // Create the appropriate summary type.
           if (isa<Function>(GV)) {

lib/Bitcode/Reader/BitcodeReader.cpp

@@ -865,11 +865,11 @@ static GlobalValueSummary::GVFlags getDecodedGVSummaryFlags(uint64_t RawFlags,
   auto Linkage = GlobalValue::LinkageTypes(RawFlags & 0xF); // 4 bits
   RawFlags = RawFlags >> 4;
   bool NotEligibleToImport = (RawFlags & 0x1) || Version < 3;
-  // The LiveRoot flag wasn't introduced until version 3. For dead stripping
+  // The Live flag wasn't introduced until version 3. For dead stripping
   // to work correctly on earlier versions, we must conservatively treat all
   // values as live.
-  bool LiveRoot = (RawFlags & 0x2) || Version < 3;
-  return GlobalValueSummary::GVFlags(Linkage, NotEligibleToImport, LiveRoot);
+  bool Live = (RawFlags & 0x2) || Version < 3;
+  return GlobalValueSummary::GVFlags(Linkage, NotEligibleToImport, Live);
 }
 
 static GlobalValue::VisibilityTypes getDecodedVisibility(unsigned Val) {

lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -864,7 +864,7 @@ static uint64_t getEncodedGVSummaryFlags(GlobalValueSummary::GVFlags Flags) {
   uint64_t RawFlags = 0;
 
   RawFlags |= Flags.NotEligibleToImport; // bool
-  RawFlags |= (Flags.LiveRoot << 1);
+  RawFlags |= (Flags.Live << 1);
   // Linkage don't need to be remapped at that time for the summary. Any future
   // change to the getEncodedLinkage() function will need to be taken into
   // account here as well.

lib/LTO/LTO.cpp

@@ -930,6 +930,17 @@ ThinBackend lto::createWriteIndexesThinBackend(std::string OldPrefix,
   };
 }
 
+static bool IsLiveByGUID(const ModuleSummaryIndex &Index,
+                         GlobalValue::GUID GUID) {
+  auto VI = Index.getValueInfo(GUID);
+  if (!VI)
+    return false;
+  for (auto &I : VI.getSummaryList())
+    if (Index.isGlobalValueLive(I.get()))
+      return true;
+  return false;
+}
+
 Error LTO::runThinLTO(AddStreamFn AddStream, NativeObjectCache Cache,
                       bool HasRegularLTO) {
   if (ThinLTO.ModuleMap.empty())
@@ -973,11 +984,10 @@ Error LTO::runThinLTO(AddStreamFn AddStream, NativeObjectCache Cache,
             GlobalValue::dropLLVMManglingEscape(Res.second.IRName)));
     }
 
-    auto DeadSymbols =
-        computeDeadSymbols(ThinLTO.CombinedIndex, GUIDPreservedSymbols);
+    computeDeadSymbols(ThinLTO.CombinedIndex, GUIDPreservedSymbols);
 
     ComputeCrossModuleImport(ThinLTO.CombinedIndex, ModuleToDefinedGVSummaries,
-                             ImportLists, ExportLists, &DeadSymbols);
+                             ImportLists, ExportLists);
 
     std::set<GlobalValue::GUID> ExportedGUIDs;
     for (auto &Res : GlobalResolutions) {
@@ -992,7 +1002,7 @@ Error LTO::runThinLTO(AddStreamFn AddStream, NativeObjectCache Cache,
       auto GUID = GlobalValue::getGUID(
           GlobalValue::dropLLVMManglingEscape(Res.second.IRName));
       // Mark exported unless index-based analysis determined it to be dead.
-      if (!DeadSymbols.count(GUID))
+      if (IsLiveByGUID(ThinLTO.CombinedIndex, GUID))
         ExportedGUIDs.insert(GUID);
     }
 

lib/LTO/ThinLTOCodeGenerator.cpp

@@ -628,13 +628,13 @@ void ThinLTOCodeGenerator::promote(Module &TheModule,
       PreservedSymbols, Triple(TheModule.getTargetTriple()));
 
   // Compute "dead" symbols, we don't want to import/export these!
-  auto DeadSymbols = computeDeadSymbols(Index, GUIDPreservedSymbols);
+  computeDeadSymbols(Index, GUIDPreservedSymbols);
 
   // Generate import/export list
   StringMap<FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
   StringMap<FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
   ComputeCrossModuleImport(Index, ModuleToDefinedGVSummaries, ImportLists,
-                           ExportLists, &DeadSymbols);
+                           ExportLists);
 
   // Resolve LinkOnce/Weak symbols.
   StringMap<std::map<GlobalValue::GUID, GlobalValue::LinkageTypes>> ResolvedODR;
@@ -673,13 +673,13 @@ void ThinLTOCodeGenerator::crossModuleImport(Module &TheModule,
       PreservedSymbols, Triple(TheModule.getTargetTriple()));
 
   // Compute "dead" symbols, we don't want to import/export these!
-  auto DeadSymbols = computeDeadSymbols(Index, GUIDPreservedSymbols);
+  computeDeadSymbols(Index, GUIDPreservedSymbols);
 
   // Generate import/export list
   StringMap<FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
   StringMap<FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
   ComputeCrossModuleImport(Index, ModuleToDefinedGVSummaries, ImportLists,
-                           ExportLists, &DeadSymbols);
+                           ExportLists);
   auto &ImportList = ImportLists[TheModule.getModuleIdentifier()];
 
   crossImportIntoModule(TheModule, Index, ModuleMap, ImportList);
@@ -750,13 +750,13 @@ void ThinLTOCodeGenerator::internalize(Module &TheModule,
   Index.collectDefinedGVSummariesPerModule(ModuleToDefinedGVSummaries);
 
   // Compute "dead" symbols, we don't want to import/export these!
-  auto DeadSymbols = computeDeadSymbols(Index, GUIDPreservedSymbols);
+  computeDeadSymbols(Index, GUIDPreservedSymbols);
 
   // Generate import/export list
   StringMap<FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
   StringMap<FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
   ComputeCrossModuleImport(Index, ModuleToDefinedGVSummaries, ImportLists,
-                           ExportLists, &DeadSymbols);
+                           ExportLists);
   auto &ExportList = ExportLists[ModuleIdentifier];
 
   // Be friendly and don't nuke totally the module when the client didn't
@@ -902,14 +902,14 @@ void ThinLTOCodeGenerator::run() {
       computeGUIDPreservedSymbols(PreservedSymbols, TMBuilder.TheTriple);
 
   // Compute "dead" symbols, we don't want to import/export these!
-  auto DeadSymbols = computeDeadSymbols(*Index, GUIDPreservedSymbols);
+  computeDeadSymbols(*Index, GUIDPreservedSymbols);
 
   // Collect the import/export lists for all modules from the call-graph in the
   // combined index.
   StringMap<FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
   StringMap<FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
   ComputeCrossModuleImport(*Index, ModuleToDefinedGVSummaries, ImportLists,
-                           ExportLists, &DeadSymbols);
+                           ExportLists);
 
   // We use a std::map here to be able to have a defined ordering when
   // producing a hash for the cache entry.