(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

8 files changed, 114 insertions, 103 deletions

diff --git a/include/llvm/IR/ModuleSummaryIndex.h b/include/llvm/IR/ModuleSummaryIndex.h
index c46c609609e..757ddf6cf46 100644
--- a/include/llvm/IR/ModuleSummaryIndex.h
+++ b/include/llvm/IR/ModuleSummaryIndex.h
@@ -134,16 +134,18 @@ public:
     /// 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 @@ private:
   /// 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 @@ public:
   /// 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 @@ private:
   /// 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 @@ public:
   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);
diff --git a/include/llvm/Transforms/IPO/FunctionImport.h b/include/llvm/Transforms/IPO/FunctionImport.h
index d66b6edc7a4..de35cdf052e 100644
--- a/include/llvm/Transforms/IPO/FunctionImport.h
+++ b/include/llvm/Transforms/IPO/FunctionImport.h
@@ -81,15 +81,11 @@ public:
 /// \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.
diff --git a/lib/Analysis/ModuleSummaryAnalysis.cpp b/lib/Analysis/ModuleSummaryAnalysis.cpp
index 26706f5509b..3253f27c010 100644
--- a/lib/Analysis/ModuleSummaryAnalysis.cpp
+++ b/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)) {
diff --git a/lib/Bitcode/Reader/BitcodeReader.cpp b/lib/Bitcode/Reader/BitcodeReader.cpp
index 686c9468766..fffa9045b2f 100644
--- a/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/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) {
diff --git a/lib/Bitcode/Writer/BitcodeWriter.cpp b/lib/Bitcode/Writer/BitcodeWriter.cpp
index a402b4ddd46..421dc261604 100644
--- a/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/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.
diff --git a/lib/LTO/LTO.cpp b/lib/LTO/LTO.cpp
index 9efc095f9fc..b8698c8a4f0 100644
--- a/lib/LTO/LTO.cpp
+++ b/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);
     }
 
diff --git a/lib/LTO/ThinLTOCodeGenerator.cpp b/lib/LTO/ThinLTOCodeGenerator.cpp
index ca3fc60f950..6b221a347c1 100644
--- a/lib/LTO/ThinLTOCodeGenerator.cpp
+++ b/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.
diff --git a/lib/Transforms/IPO/FunctionImport.cpp b/lib/Transforms/IPO/FunctionImport.cpp
index 231487923fa..6d34ab8b0d9 100644
--- a/lib/Transforms/IPO/FunctionImport.cpp
+++ b/lib/Transforms/IPO/FunctionImport.cpp
@@ -292,8 +292,7 @@ static void computeImportForFunction(
 static void ComputeImportForModule(
     const GVSummaryMapTy &DefinedGVSummaries, const ModuleSummaryIndex &Index,
     FunctionImporter::ImportMapTy &ImportList,
-    StringMap<FunctionImporter::ExportSetTy> *ExportLists = nullptr,
-    const DenseSet<GlobalValue::GUID> *DeadSymbols = nullptr) {
+    StringMap<FunctionImporter::ExportSetTy> *ExportLists = nullptr) {
   // Worklist contains the list of function imported in this module, for which
   // we will analyse the callees and may import further down the callgraph.
   SmallVector<EdgeInfo, 128> Worklist;
@@ -301,7 +300,7 @@ static void ComputeImportForModule(
   // Populate the worklist with the import for the functions in the current
   // module
   for (auto &GVSummary : DefinedGVSummaries) {
-    if (DeadSymbols && DeadSymbols->count(GVSummary.first)) {
+    if (!Index.isGlobalValueLive(GVSummary.second)) {
       DEBUG(dbgs() << "Ignores Dead GUID: " << GVSummary.first << "\n");
       continue;
     }
@@ -344,15 +343,14 @@ void llvm::ComputeCrossModuleImport(
     const ModuleSummaryIndex &Index,
     const StringMap<GVSummaryMapTy> &ModuleToDefinedGVSummaries,
     StringMap<FunctionImporter::ImportMapTy> &ImportLists,
-    StringMap<FunctionImporter::ExportSetTy> &ExportLists,
-    const DenseSet<GlobalValue::GUID> *DeadSymbols) {
+    StringMap<FunctionImporter::ExportSetTy> &ExportLists) {
   // For each module that has function defined, compute the import/export lists.
   for (auto &DefinedGVSummaries : ModuleToDefinedGVSummaries) {
     auto &ImportList = ImportLists[DefinedGVSummaries.first()];
     DEBUG(dbgs() << "Computing import for Module '"
                  << DefinedGVSummaries.first() << "'\n");
     ComputeImportForModule(DefinedGVSummaries.second, Index, ImportList,
-                           &ExportLists, DeadSymbols);
+                           &ExportLists);
   }
 
   // When computing imports we added all GUIDs referenced by anything
@@ -414,82 +412,71 @@ void llvm::ComputeCrossModuleImportForModule(
 #endif
 }
 
-DenseSet<GlobalValue::GUID> llvm::computeDeadSymbols(
-    const ModuleSummaryIndex &Index,
+void llvm::computeDeadSymbols(
+    ModuleSummaryIndex &Index,
     const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols) {
+  assert(!Index.withGlobalValueDeadStripping());
   if (!ComputeDead)
-    return DenseSet<GlobalValue::GUID>();
+    return;
   if (GUIDPreservedSymbols.empty())
     // Don't do anything when nothing is live, this is friendly with tests.
-    return DenseSet<GlobalValue::GUID>();
-  DenseSet<ValueInfo> LiveSymbols;
+    return;
+  unsigned LiveSymbols = 0;
   SmallVector<ValueInfo, 128> Worklist;
   Worklist.reserve(GUIDPreservedSymbols.size() * 2);
   for (auto GUID : GUIDPreservedSymbols) {
     ValueInfo VI = Index.getValueInfo(GUID);
     if (!VI)
       continue;
-    DEBUG(dbgs() << "Live root: " << VI.getGUID() << "\n");
-    LiveSymbols.insert(VI);
-    Worklist.push_back(VI);
+    for (auto &S : VI.getSummaryList())
+      S->setLive(true);
   }
+
   // Add values flagged in the index as live roots to the worklist.
-  for (const auto &Entry : Index) {
-    bool IsLiveRoot = llvm::any_of(
-        Entry.second.SummaryList,
-        [&](const std::unique_ptr<llvm::GlobalValueSummary> &Summary) {
-          return Summary->liveRoot();
-        });
-    if (!IsLiveRoot)
-      continue;
-    DEBUG(dbgs() << "Live root (summary): " << Entry.first << "\n");
-    Worklist.push_back(ValueInfo(&Entry));
-  }
+  for (const auto &Entry : Index)
+    for (auto &S : Entry.second.SummaryList)
+      if (S->isLive()) {
+        DEBUG(dbgs() << "Live root: " << Entry.first << "\n");
+        Worklist.push_back(ValueInfo(&Entry));
+        ++LiveSymbols;
+        break;
+      }
+
+  // Make value live and add it to the worklist if it was not live before.
+  // FIXME: we should only make the prevailing copy live here
+  auto visit = [&](ValueInfo VI) {
+    for (auto &S : VI.getSummaryList())
+      if (S->isLive())
+        return;
+    for (auto &S : VI.getSummaryList())
+      S->setLive(true);
+    ++LiveSymbols;
+    Worklist.push_back(VI);
+  };
 
   while (!Worklist.empty()) {
     auto VI = Worklist.pop_back_val();
-
-    // FIXME: we should only make the prevailing copy live here
     for (auto &Summary : VI.getSummaryList()) {
-      for (auto Ref : Summary->refs()) {
-        if (LiveSymbols.insert(Ref).second) {
-          DEBUG(dbgs() << "Marking live (ref): " << Ref.getGUID() << "\n");
-          Worklist.push_back(Ref);
-        }
-      }
-      if (auto *FS = dyn_cast<FunctionSummary>(Summary.get())) {
-        for (auto Call : FS->calls()) {
-          if (LiveSymbols.insert(Call.first).second) {
-            DEBUG(dbgs() << "Marking live (call): " << Call.first.getGUID()
-                         << "\n");
-            Worklist.push_back(Call.first);
-          }
-        }
-      }
+      for (auto Ref : Summary->refs())
+        visit(Ref);
+      if (auto *FS = dyn_cast<FunctionSummary>(Summary.get()))
+        for (auto Call : FS->calls())
+          visit(Call.first);
       if (auto *AS = dyn_cast<AliasSummary>(Summary.get())) {
         auto AliaseeGUID = AS->getAliasee().getOriginalName();
         ValueInfo AliaseeVI = Index.getValueInfo(AliaseeGUID);
-        if (AliaseeVI && LiveSymbols.insert(AliaseeVI).second) {
-          DEBUG(dbgs() << "Marking live (alias): " << AliaseeGUID << "\n");
-          Worklist.push_back(AliaseeVI);
-        }
+        if (AliaseeVI)
+          visit(AliaseeVI);
       }
     }
   }
-  DenseSet<GlobalValue::GUID> DeadSymbols;
-  DeadSymbols.reserve(
-      std::min(Index.size(), Index.size() - LiveSymbols.size()));
-  for (auto &Entry : Index) {
-    if (!LiveSymbols.count(ValueInfo(&Entry))) {
-      DEBUG(dbgs() << "Marking dead: " << Entry.first << "\n");
-      DeadSymbols.insert(Entry.first);
-    }
-  }
-  DEBUG(dbgs() << LiveSymbols.size() << " symbols Live, and "
-               << DeadSymbols.size() << " symbols Dead \n");
-  NumDeadSymbols += DeadSymbols.size();
-  NumLiveSymbols += LiveSymbols.size();
-  return DeadSymbols;
+  Index.setWithGlobalValueDeadStripping();
+
+  unsigned DeadSymbols = Index.size() - LiveSymbols;
+  DEBUG(dbgs() << LiveSymbols << " symbols Live, and " << DeadSymbols
+               << " symbols Dead \n");
+  NumDeadSymbols += DeadSymbols;
+  NumLiveSymbols += LiveSymbols;
 }
 
 /// Compute the set of summaries needed for a ThinLTO backend compilation of