[ThinLTO] Optimize writeonly globals out

Differential revision: https://reviews.llvm.org/D63444


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@365040 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/ModuleSummaryIndex.h

@@ -162,7 +162,8 @@ using GlobalValueSummaryMapTy =
 /// Struct that holds a reference to a particular GUID in a global value
 /// summary.
 struct ValueInfo {
-  PointerIntPair<const GlobalValueSummaryMapTy::value_type *, 2, int>
+  enum Flags { HaveGV = 1, ReadOnly = 2, WriteOnly = 4 };
+  PointerIntPair<const GlobalValueSummaryMapTy::value_type *, 3, int>
       RefAndFlags;
 
   ValueInfo() = default;
@@ -188,9 +189,33 @@ struct ValueInfo {
                      : getRef()->second.U.Name;
   }
 
-  bool haveGVs() const { return RefAndFlags.getInt() & 0x1; }
-  bool isReadOnly() const { return RefAndFlags.getInt() & 0x2; }
-  void setReadOnly() { RefAndFlags.setInt(RefAndFlags.getInt() | 0x2); }
+  bool haveGVs() const { return RefAndFlags.getInt() & HaveGV; }
+  bool isReadOnly() const {
+    assert(isValidAccessSpecifier());
+    return RefAndFlags.getInt() & ReadOnly;
+  }
+  bool isWriteOnly() const {
+    assert(isValidAccessSpecifier());
+    return RefAndFlags.getInt() & WriteOnly;
+  }
+  unsigned getAccessSpecifier() const {
+    assert(isValidAccessSpecifier());
+    return RefAndFlags.getInt() & (ReadOnly | WriteOnly);
+  }
+  bool isValidAccessSpecifier() const {
+    unsigned BadAccessMask = ReadOnly | WriteOnly;
+    return (RefAndFlags.getInt() & BadAccessMask) != BadAccessMask;
+  }
+  void setReadOnly() {
+    // We expect ro/wo attribute to set only once during
+    // ValueInfo lifetime.
+    assert(getAccessSpecifier() == 0);   
+    RefAndFlags.setInt(RefAndFlags.getInt() | ReadOnly);
+  }
+  void setWriteOnly() {
+    assert(getAccessSpecifier() == 0);   
+    RefAndFlags.setInt(RefAndFlags.getInt() | WriteOnly);
+  }
 
   const GlobalValueSummaryMapTy::value_type *getRef() const {
     return RefAndFlags.getPointer();
@@ -584,8 +609,8 @@ public:
           std::move(TypeTestAssumeConstVCalls),
           std::move(TypeCheckedLoadConstVCalls)});
   }
-  // Gets the number of immutable refs in RefEdgeList
-  unsigned immutableRefCount() const;
+  // Gets the number of readonly and writeonly refs in RefEdgeList
+  std::pair<unsigned, unsigned> specialRefCounts() const;
 
   /// Check if this is a function summary.
   static bool classof(const GlobalValueSummary *GVS) {
@@ -713,9 +738,12 @@ using VTableFuncList = std::vector<VirtFuncOffset>;
 /// Global variable summary information to aid decisions and
 /// implementation of importing.
 ///
-/// Global variable summary has extra flag, telling if it is
-/// modified during the program run or not. This affects ThinLTO
-/// internalization
+/// Global variable summary has two extra flag, telling if it is
+/// readonly or writeonly. Both readonly and writeonly variables
+/// can be optimized in the backed: readonly variables can be
+/// const-folded, while writeonly vars can be completely eliminated
+/// together with corresponding stores. We let both things happen
+/// by means of internalizing such variables after ThinLTO import.
 class GlobalVarSummary : public GlobalValueSummary {
 private:
   /// For vtable definitions this holds the list of functions and
@@ -724,9 +752,14 @@ private:
 
 public:
   struct GVarFlags {
-    GVarFlags(bool ReadOnly = false) : ReadOnly(ReadOnly) {}
-
-    unsigned ReadOnly : 1;
+    GVarFlags(bool ReadOnly, bool WriteOnly)
+        : MaybeReadOnly(ReadOnly), MaybeWriteOnly(WriteOnly) {}
+
+    // In permodule summaries both MaybeReadOnly and MaybeWriteOnly
+    // bits are set, because attribute propagation occurs later on
+    // thin link phase.
+    unsigned MaybeReadOnly : 1;
+    unsigned MaybeWriteOnly : 1;
   } VarFlags;
 
   GlobalVarSummary(GVFlags Flags, GVarFlags VarFlags,
@@ -740,8 +773,10 @@ public:
   }
 
   GVarFlags varflags() const { return VarFlags; }
-  void setReadOnly(bool RO) { VarFlags.ReadOnly = RO; }
-  bool isReadOnly() const { return VarFlags.ReadOnly; }
+  void setReadOnly(bool RO) { VarFlags.MaybeReadOnly = RO; }
+  void setWriteOnly(bool WO) { VarFlags.MaybeWriteOnly = WO; }
+  bool maybeReadOnly() const { return VarFlags.MaybeReadOnly; }
+  bool maybeWriteOnly() const { return VarFlags.MaybeWriteOnly; }
 
   void setVTableFuncs(VTableFuncList Funcs) {
     assert(!VTableFuncs);
@@ -1312,7 +1347,7 @@ public:
   void dumpSCCs(raw_ostream &OS);
 
   /// Analyze index and detect unmodified globals
-  void propagateConstants(const DenseSet<GlobalValue::GUID> &PreservedSymbols);
+  void propagateAttributes(const DenseSet<GlobalValue::GUID> &PreservedSymbols);
 };
 
 /// GraphTraits definition to build SCC for the index

lib/Analysis/ModuleSummaryAnalysis.cpp

@@ -231,6 +231,13 @@ static bool isNonVolatileLoad(const Instruction *I) {
   return false;
 }
 
+static bool isNonVolatileStore(const Instruction *I) {
+  if (const auto *SI = dyn_cast<StoreInst>(I))
+    return !SI->isVolatile();
+
+  return false;
+}
+
 static void computeFunctionSummary(ModuleSummaryIndex &Index, const Module &M,
                                    const Function &F, BlockFrequencyInfo *BFI,
                                    ProfileSummaryInfo *PSI, DominatorTree &DT,
@@ -245,7 +252,7 @@ static void computeFunctionSummary(ModuleSummaryIndex &Index, const Module &M,
   // Map from callee ValueId to profile count. Used to accumulate profile
   // counts for all static calls to a given callee.
   MapVector<ValueInfo, CalleeInfo> CallGraphEdges;
-  SetVector<ValueInfo> RefEdges;
+  SetVector<ValueInfo> RefEdges, LoadRefEdges, StoreRefEdges;
   SetVector<GlobalValue::GUID> TypeTests;
   SetVector<FunctionSummary::VFuncId> TypeTestAssumeVCalls,
       TypeCheckedLoadVCalls;
@@ -258,6 +265,7 @@ static void computeFunctionSummary(ModuleSummaryIndex &Index, const Module &M,
   // list.
   findRefEdges(Index, &F, RefEdges, Visited);
   std::vector<const Instruction *> NonVolatileLoads;
+  std::vector<const Instruction *> NonVolatileStores;
 
   bool HasInlineAsmMaybeReferencingInternal = false;
   for (const BasicBlock &BB : F)
@@ -265,12 +273,34 @@ static void computeFunctionSummary(ModuleSummaryIndex &Index, const Module &M,
       if (isa<DbgInfoIntrinsic>(I))
         continue;
       ++NumInsts;
-      if (isNonVolatileLoad(&I)) {
-        // Postpone processing of non-volatile load instructions
-        // See comments below
-        Visited.insert(&I);
-        NonVolatileLoads.push_back(&I);
-        continue;
+      // Regular LTO module doesn't participate in ThinLTO import,
+      // so no reference from it can be read/writeonly, since this
+      // would require importing variable as local copy
+      if (IsThinLTO) {
+        if (isNonVolatileLoad(&I)) {
+          // Postpone processing of non-volatile load instructions
+          // See comments below
+          Visited.insert(&I);
+          NonVolatileLoads.push_back(&I);
+          continue;
+        } else if (isNonVolatileStore(&I)) {
+          Visited.insert(&I);
+          NonVolatileStores.push_back(&I);
+          // All references from second operand of store (destination address)
+          // can be considered write-only if they're not referenced by any
+          // non-store instruction. References from first operand of store 
+          // (stored value) can't be treated either as read- or as write-only
+          // so we add them to RefEdges as we do with all other instructions
+          // except non-volatile load.
+          Value *Stored = I.getOperand(0);
+          if (auto *GV = dyn_cast<GlobalValue>(Stored))
+            // findRefEdges will try to examine GV operands, so instead
+            // of calling it we should add GV to RefEdges directly.
+            RefEdges.insert(Index.getOrInsertValueInfo(GV));
+          else if (auto *U = dyn_cast<User>(Stored))
+            findRefEdges(Index, U, RefEdges, Visited);
+          continue;
+        }
       }
       findRefEdges(Index, &I, RefEdges, Visited);
       auto CS = ImmutableCallSite(&I);
@@ -361,24 +391,49 @@ static void computeFunctionSummary(ModuleSummaryIndex &Index, const Module &M,
       }
     }
 
-  // By now we processed all instructions in a function, except
-  // non-volatile loads. All new refs we add in a loop below
-  // are obviously constant. All constant refs are grouped in the
-  // end of RefEdges vector, so we can use a single integer value
-  // to identify them.
-  unsigned RefCnt = RefEdges.size();
-  for (const Instruction *I : NonVolatileLoads) {
-    Visited.erase(I);
-    findRefEdges(Index, I, RefEdges, Visited);
-  }
-  std::vector<ValueInfo> Refs = RefEdges.takeVector();
-  // Regular LTO module doesn't participate in ThinLTO import,
-  // so no reference from it can be readonly, since this would
-  // require importing variable as local copy
-  if (IsThinLTO)
-    for (; RefCnt < Refs.size(); ++RefCnt)
+  std::vector<ValueInfo> Refs;
+  if (IsThinLTO) {
+    auto AddRefEdges = [&](const std::vector<const Instruction *> &Instrs,
+                          SetVector<ValueInfo> &Edges) {
+      for (const auto *I : Instrs) {
+        Visited.erase(I);
+        findRefEdges(Index, I, Edges, Visited);
+      }
+    };
+
+    // By now we processed all instructions in a function, except
+    // non-volatile loads and non-volatile value stores. Let's find
+    // ref edges for both of instruction sets
+    AddRefEdges(NonVolatileLoads, LoadRefEdges);
+    AddRefEdges(NonVolatileStores, StoreRefEdges);
+
+    // If both load and store instruction reference the same variable
+    // we won't be able to optimize it. Add all such reference edges
+    // to RefEdges set.
+    for (auto &VI : StoreRefEdges)
+      if (LoadRefEdges.remove(VI))
+        RefEdges.insert(VI);
+
+    unsigned RefCnt = RefEdges.size();
+    // All new reference edges inserted in two loops below are either
+    // read or write only. They will be grouped in the end of RefEdges
+    // vector, so we can use a single integer value to identify them.
+    for (auto &VI : LoadRefEdges)
+      RefEdges.insert(VI);
+
+    unsigned FirstWORef = RefEdges.size();
+    for (auto &VI : StoreRefEdges)
+      RefEdges.insert(VI);
+
+    Refs = RefEdges.takeVector();
+    for (; RefCnt < FirstWORef; ++RefCnt)
       Refs[RefCnt].setReadOnly();
 
+    for (; RefCnt < Refs.size(); ++RefCnt)
+      Refs[RefCnt].setWriteOnly();
+  } else {
+    Refs = RefEdges.takeVector();
+  }
   // Explicit add hot edges to enforce importing for designated GUIDs for
   // sample PGO, to enable the same inlines as the profiled optimized binary.
   for (auto &I : F.getImportGUIDs())
@@ -526,10 +581,11 @@ static void computeVariableSummary(ModuleSummaryIndex &Index,
     }
   }
 
-  // Don't mark variables we won't be able to internalize as read-only.
-  GlobalVarSummary::GVarFlags VarFlags(
+  // Don't mark variables we won't be able to internalize as read/write-only.
+  bool CanBeInternalized =
       !V.hasComdat() && !V.hasAppendingLinkage() && !V.isInterposable() &&
-      !V.hasAvailableExternallyLinkage() && !V.hasDLLExportStorageClass());
+      !V.hasAvailableExternallyLinkage() && !V.hasDLLExportStorageClass();
+  GlobalVarSummary::GVarFlags VarFlags(CanBeInternalized, CanBeInternalized);
   auto GVarSummary = llvm::make_unique<GlobalVarSummary>(Flags, VarFlags,
                                                          RefEdges.takeVector());
   if (NonRenamableLocal)
@@ -647,7 +703,7 @@ ModuleSummaryIndex llvm::buildModuleSummaryIndex(
           } else {
             std::unique_ptr<GlobalVarSummary> Summary =
                 llvm::make_unique<GlobalVarSummary>(
-                    GVFlags, GlobalVarSummary::GVarFlags(),
+                    GVFlags, GlobalVarSummary::GVarFlags(false, false),
                     ArrayRef<ValueInfo>{});
             Index.addGlobalValueSummary(*GV, std::move(Summary));
           }

lib/AsmParser/LLParser.cpp

@@ -7849,9 +7849,13 @@ static const auto FwdVIRef = (GlobalValueSummaryMapTy::value_type *)-8;
 
 static void resolveFwdRef(ValueInfo *Fwd, ValueInfo &Resolved) {
   bool ReadOnly = Fwd->isReadOnly();
+  bool WriteOnly = Fwd->isWriteOnly();
+  assert(!(ReadOnly && WriteOnly));
   *Fwd = Resolved;
   if (ReadOnly)
     Fwd->setReadOnly();
+  if (WriteOnly)
+    Fwd->setWriteOnly();
 }
 
 /// Stores the given Name/GUID and associated summary into the Index.
@@ -8081,7 +8085,8 @@ bool LLParser::ParseVariableSummary(std::string Name, GlobalValue::GUID GUID,
   GlobalValueSummary::GVFlags GVFlags = GlobalValueSummary::GVFlags(
       /*Linkage=*/GlobalValue::ExternalLinkage, /*NotEligibleToImport=*/false,
       /*Live=*/false, /*IsLocal=*/false, /*CanAutoHide=*/false);
-  GlobalVarSummary::GVarFlags GVarFlags(/*ReadOnly*/ false);
+  GlobalVarSummary::GVarFlags GVarFlags(/*ReadOnly*/ false,
+                                        /* WriteOnly */ false);
   std::vector<ValueInfo> Refs;
   VTableFuncList VTableFuncs;
   if (ParseToken(lltok::colon, "expected ':' here") ||
@@ -8422,10 +8427,11 @@ bool LLParser::ParseOptionalRefs(std::vector<ValueInfo> &Refs) {
     VContexts.push_back(VC);
   } while (EatIfPresent(lltok::comma));
 
-  // Sort value contexts so that ones with readonly ValueInfo are at the end
-  // of VContexts vector. This is needed to match immutableRefCount() behavior.
+  // Sort value contexts so that ones with writeonly
+  // and readonly ValueInfo  are at the end of VContexts vector.
+  // See FunctionSummary::specialRefCounts()
   llvm::sort(VContexts, [](const ValueContext &VC1, const ValueContext &VC2) {
-    return VC1.VI.isReadOnly() < VC2.VI.isReadOnly();
+    return VC1.VI.getAccessSpecifier() < VC2.VI.getAccessSpecifier();
   });
 
   IdToIndexMapType IdToIndexMap;
@@ -8743,24 +8749,41 @@ bool LLParser::ParseGVFlags(GlobalValueSummary::GVFlags &GVFlags) {
 }
 
 /// GVarFlags
-///   ::= 'varFlags' ':' '(' 'readonly' ':' Flag ')'
+///   ::= 'varFlags' ':' '(' 'readonly' ':' Flag
+///                      ',' 'writeonly' ':' Flag ')'
 bool LLParser::ParseGVarFlags(GlobalVarSummary::GVarFlags &GVarFlags) {
   assert(Lex.getKind() == lltok::kw_varFlags);
   Lex.Lex();
 
-  unsigned Flag = 0;
   if (ParseToken(lltok::colon, "expected ':' here") ||
-      ParseToken(lltok::lparen, "expected '(' here") ||
-      ParseToken(lltok::kw_readonly, "expected 'readonly' here") ||
-      ParseToken(lltok::colon, "expected ':' here"))
+      ParseToken(lltok::lparen, "expected '(' here"))
     return true;
 
-  ParseFlag(Flag);
-  GVarFlags.ReadOnly = Flag;
+  auto ParseRest = [this](unsigned int &Val) {
+    Lex.Lex();
+    if (ParseToken(lltok::colon, "expected ':'"))
+      return true;
+    return ParseFlag(Val);
+  };
 
-  if (ParseToken(lltok::rparen, "expected ')' here"))
-    return true;
-  return false;
+  do {
+    unsigned Flag = 0;
+    switch (Lex.getKind()) {
+    case lltok::kw_readonly:
+      if (ParseRest(Flag))
+        return true;
+      GVarFlags.MaybeReadOnly = Flag;
+      break;
+    case lltok::kw_writeonly:
+      if (ParseRest(Flag))
+        return true;
+      GVarFlags.MaybeWriteOnly = Flag;
+      break;
+    default:
+      return Error(Lex.getLoc(), "expected gvar flag type");
+    }
+  } while (EatIfPresent(lltok::comma));
+  return ParseToken(lltok::rparen, "expected ')' here");
 }
 
 /// ModuleReference
@@ -8783,7 +8806,9 @@ bool LLParser::ParseModuleReference(StringRef &ModulePath) {
 /// GVReference
 ///   ::= SummaryID
 bool LLParser::ParseGVReference(ValueInfo &VI, unsigned &GVId) {
-  bool ReadOnly = EatIfPresent(lltok::kw_readonly);
+  bool WriteOnly = false, ReadOnly = EatIfPresent(lltok::kw_readonly);
+  if (!ReadOnly)
+    WriteOnly = EatIfPresent(lltok::kw_writeonly);
   if (ParseToken(lltok::SummaryID, "expected GV ID"))
     return true;
 
@@ -8798,5 +8823,7 @@ bool LLParser::ParseGVReference(ValueInfo &VI, unsigned &GVId) {
 
   if (ReadOnly)
     VI.setReadOnly();
+  if (WriteOnly)
+    VI.setWriteOnly();
   return false;
 }

lib/Bitcode/Reader/BitcodeReader.cpp

@@ -984,7 +984,8 @@ static GlobalValueSummary::GVFlags getDecodedGVSummaryFlags(uint64_t RawFlags,
 
 // Decode the flags for GlobalVariable in the summary
 static GlobalVarSummary::GVarFlags getDecodedGVarFlags(uint64_t RawFlags) {
-  return GlobalVarSummary::GVarFlags((RawFlags & 0x1) ? true : false);
+  return GlobalVarSummary::GVarFlags((RawFlags & 0x1) ? true : false,
+                                     (RawFlags & 0x2) ? true : false);
 }
 
 static GlobalValue::VisibilityTypes getDecodedVisibility(unsigned Val) {
@@ -5681,10 +5682,16 @@ void ModuleSummaryIndexBitcodeReader::parseTypeIdCompatibleVtableSummaryRecord(
     parseTypeIdCompatibleVtableInfo(Record, Slot, TypeId);
 }
 
-static void setImmutableRefs(std::vector<ValueInfo> &Refs, unsigned Count) {
-  // Read-only refs are in the end of the refs list.
-  for (unsigned RefNo = Refs.size() - Count; RefNo < Refs.size(); ++RefNo)
+static void setSpecialRefs(std::vector<ValueInfo> &Refs, unsigned ROCnt,
+                           unsigned WOCnt) {
+  // Readonly and writeonly refs are in the end of the refs list.
+  assert(ROCnt + WOCnt <= Refs.size());
+  unsigned FirstWORef = Refs.size() - WOCnt;
+  unsigned RefNo = FirstWORef - ROCnt;
+  for (; RefNo < FirstWORef; ++RefNo)
     Refs[RefNo].setReadOnly();
+  for (; RefNo < Refs.size(); ++RefNo)
+    Refs[RefNo].setWriteOnly();
 }
 
 // Eagerly parse the entire summary block. This populates the GlobalValueSummary
@@ -5711,9 +5718,9 @@ Error ModuleSummaryIndexBitcodeReader::parseEntireSummary(unsigned ID) {
   }
   const uint64_t Version = Record[0];
   const bool IsOldProfileFormat = Version == 1;
-  if (Version < 1 || Version > 6)
+  if (Version < 1 || Version > 7)
     return error("Invalid summary version " + Twine(Version) +
-                 ". Version should be in the range [1-6].");
+                 ". Version should be in the range [1-7].");
   Record.clear();
 
   // Keep around the last seen summary to be used when we see an optional
@@ -5812,15 +5819,19 @@ Error ModuleSummaryIndexBitcodeReader::parseEntireSummary(unsigned ID) {
       unsigned InstCount = Record[2];
       uint64_t RawFunFlags = 0;
       unsigned NumRefs = Record[3];
-      unsigned NumImmutableRefs = 0;
+      unsigned NumRORefs = 0, NumWORefs = 0;
       int RefListStartIndex = 4;
       if (Version >= 4) {
         RawFunFlags = Record[3];
         NumRefs = Record[4];
         RefListStartIndex = 5;
         if (Version >= 5) {
-          NumImmutableRefs = Record[5];
+          NumRORefs = Record[5];
           RefListStartIndex = 6;
+          if (Version >= 7) {
+            NumWORefs = Record[6];
+            RefListStartIndex = 7;
+          }
         }
       }
 
@@ -5840,7 +5851,7 @@ Error ModuleSummaryIndexBitcodeReader::parseEntireSummary(unsigned ID) {
       std::vector<FunctionSummary::EdgeTy> Calls = makeCallList(
           ArrayRef<uint64_t>(Record).slice(CallGraphEdgeStartIndex),
           IsOldProfileFormat, HasProfile, HasRelBF);
-      setImmutableRefs(Refs, NumImmutableRefs);
+      setSpecialRefs(Refs, NumRORefs, NumWORefs);
       auto FS = llvm::make_unique<FunctionSummary>(
           Flags, InstCount, getDecodedFFlags(RawFunFlags), /*EntryCount=*/0,
           std::move(Refs), std::move(Calls), std::move(PendingTypeTests),
@@ -5891,7 +5902,8 @@ Error ModuleSummaryIndexBitcodeReader::parseEntireSummary(unsigned ID) {
       unsigned ValueID = Record[0];
       uint64_t RawFlags = Record[1];
       unsigned RefArrayStart = 2;
-      GlobalVarSummary::GVarFlags GVF;
+      GlobalVarSummary::GVarFlags GVF(/* ReadOnly */ false,
+                                      /* WriteOnly */ false);
       auto Flags = getDecodedGVSummaryFlags(RawFlags, Version);
       if (Version >= 5) {
         GVF = getDecodedGVarFlags(Record[2]);
@@ -5948,7 +5960,7 @@ Error ModuleSummaryIndexBitcodeReader::parseEntireSummary(unsigned ID) {
       uint64_t RawFunFlags = 0;
       uint64_t EntryCount = 0;
       unsigned NumRefs = Record[4];
-      unsigned NumImmutableRefs = 0;
+      unsigned NumRORefs = 0, NumWORefs = 0;
       int RefListStartIndex = 5;
 
       if (Version >= 4) {
@@ -5956,13 +5968,19 @@ Error ModuleSummaryIndexBitcodeReader::parseEntireSummary(unsigned ID) {
         RefListStartIndex = 6;
         size_t NumRefsIndex = 5;
         if (Version >= 5) {
+          unsigned NumRORefsOffset = 1;
           RefListStartIndex = 7;
           if (Version >= 6) {
             NumRefsIndex = 6;
             EntryCount = Record[5];
             RefListStartIndex = 8;
+            if (Version >= 7) {
+              RefListStartIndex = 9;
+              NumWORefs = Record[8];
+              NumRORefsOffset = 2;
+            }
           }
-          NumImmutableRefs = Record[RefListStartIndex - 1];
+          NumRORefs = Record[RefListStartIndex - NumRORefsOffset];
         }
         NumRefs = Record[NumRefsIndex];
       }
@@ -5978,7 +5996,7 @@ Error ModuleSummaryIndexBitcodeReader::parseEntireSummary(unsigned ID) {
           ArrayRef<uint64_t>(Record).slice(CallGraphEdgeStartIndex),
           IsOldProfileFormat, HasProfile, false);
       ValueInfo VI = getValueInfoFromValueId(ValueID).first;
-      setImmutableRefs(Refs, NumImmutableRefs);
+      setSpecialRefs(Refs, NumRORefs, NumWORefs);
       auto FS = llvm::make_unique<FunctionSummary>(
           Flags, InstCount, getDecodedFFlags(RawFunFlags), EntryCount,
           std::move(Refs), std::move(Edges), std::move(PendingTypeTests),
@@ -6025,7 +6043,8 @@ Error ModuleSummaryIndexBitcodeReader::parseEntireSummary(unsigned ID) {
       uint64_t ModuleId = Record[1];
       uint64_t RawFlags = Record[2];
       unsigned RefArrayStart = 3;
-      GlobalVarSummary::GVarFlags GVF;
+      GlobalVarSummary::GVarFlags GVF(/* ReadOnly */ false,
+                                      /* WriteOnly */ false);
       auto Flags = getDecodedGVSummaryFlags(RawFlags, Version);
       if (Version >= 5) {
         GVF = getDecodedGVarFlags(Record[3]);

lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -1017,7 +1017,7 @@ static uint64_t getEncodedGVSummaryFlags(GlobalValueSummary::GVFlags Flags) {
 }
 
 static uint64_t getEncodedGVarFlags(GlobalVarSummary::GVarFlags Flags) {
-  uint64_t RawFlags = Flags.ReadOnly;
+  uint64_t RawFlags = Flags.MaybeReadOnly | (Flags.MaybeWriteOnly << 1);
   return RawFlags;
 }
 
@@ -3629,11 +3629,13 @@ void ModuleBitcodeWriterBase::writePerModuleFunctionSummaryRecord(
   FunctionSummary *FS = cast<FunctionSummary>(Summary);
   writeFunctionTypeMetadataRecords(Stream, FS);
 
+  auto SpecialRefCnts = FS->specialRefCounts();
   NameVals.push_back(getEncodedGVSummaryFlags(FS->flags()));
   NameVals.push_back(FS->instCount());
   NameVals.push_back(getEncodedFFlags(FS->fflags()));
   NameVals.push_back(FS->refs().size());
-  NameVals.push_back(FS->immutableRefCount());
+  NameVals.push_back(SpecialRefCnts.first);  // rorefcnt
+  NameVals.push_back(SpecialRefCnts.second); // worefcnt
 
   for (auto &RI : FS->refs())
     NameVals.push_back(VE.getValueID(RI.getValue()));
@@ -3707,7 +3709,7 @@ void ModuleBitcodeWriterBase::writeModuleLevelReferences(
 // Current version for the summary.
 // This is bumped whenever we introduce changes in the way some record are
 // interpreted, like flags for instance.
-static const uint64_t INDEX_VERSION = 6;
+static const uint64_t INDEX_VERSION = 7;
 
 /// Emit the per-module summary section alongside the rest of
 /// the module's bitcode.
@@ -3749,7 +3751,8 @@ void ModuleBitcodeWriterBase::writePerModuleGlobalValueSummary() {
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // instcount
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // fflags
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // numrefs
-  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // immutablerefcnt
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // rorefcnt
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // worefcnt
   // numrefs x valueid, n x (valueid, hotness)
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
@@ -3766,7 +3769,8 @@ void ModuleBitcodeWriterBase::writePerModuleGlobalValueSummary() {
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // instcount
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // fflags
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // numrefs
-  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // immutablerefcnt
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // rorefcnt
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // worefcnt
   // numrefs x valueid, n x (valueid [, rel_block_freq])
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
@@ -3898,7 +3902,8 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // fflags
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // entrycount
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // numrefs
-  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // immutablerefcnt
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // rorefcnt
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // worefcnt
   // numrefs x valueid, n x (valueid)
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
@@ -3914,7 +3919,8 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // fflags
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // entrycount
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // numrefs
-  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // immutablerefcnt
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // rorefcnt
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4));   // worefcnt
   // numrefs x valueid, n x (valueid, hotness)
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
@@ -4016,20 +4022,24 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
 
     // Fill in below
     NameVals.push_back(0); // numrefs
-    NameVals.push_back(0); // immutablerefcnt
+    NameVals.push_back(0); // rorefcnt
+    NameVals.push_back(0); // worefcnt
 
-    unsigned Count = 0, ImmutableRefCnt = 0;
+    unsigned Count = 0, RORefCnt = 0, WORefCnt = 0;
     for (auto &RI : FS->refs()) {
       auto RefValueId = getValueId(RI.getGUID());
       if (!RefValueId)
         continue;
       NameVals.push_back(*RefValueId);
       if (RI.isReadOnly())
-        ImmutableRefCnt++;
+        RORefCnt++;
+      else if (RI.isWriteOnly())
+        WORefCnt++;
       Count++;
     }
     NameVals[6] = Count;
-    NameVals[7] = ImmutableRefCnt;
+    NameVals[7] = RORefCnt;
+    NameVals[8] = WORefCnt;
 
     bool HasProfileData = false;
     for (auto &EI : FS->calls()) {

lib/IR/AsmWriter.cpp

@@ -2888,7 +2888,8 @@ void AssemblyWriter::printAliasSummary(const AliasSummary *AS) {
 }
 
 void AssemblyWriter::printGlobalVarSummary(const GlobalVarSummary *GS) {
-  Out << ", varFlags: (readonly: " << GS->VarFlags.ReadOnly << ")";
+  Out << ", varFlags: (readonly: " << GS->VarFlags.MaybeReadOnly << ", "
+      << "writeonly: " << GS->VarFlags.MaybeWriteOnly << ")";
 
   auto VTableFuncs = GS->vTableFuncs();
   if (!VTableFuncs.empty()) {
@@ -3098,6 +3099,8 @@ void AssemblyWriter::printSummary(const GlobalValueSummary &Summary) {
       Out << FS;
       if (Ref.isReadOnly())
         Out << "readonly ";
+      else if (Ref.isWriteOnly())
+        Out << "writeonly ";
       Out << "^" << Machine.getGUIDSlot(Ref.getGUID());
     }
     Out << ")";

lib/IR/ModuleSummaryIndex.cpp

@@ -23,6 +23,8 @@ using namespace llvm;
 
 STATISTIC(ReadOnlyLiveGVars,
           "Number of live global variables marked read only");
+STATISTIC(WriteOnlyLiveGVars,
+          "Number of live global variables marked write only");
 
 FunctionSummary FunctionSummary::ExternalNode =
     FunctionSummary::makeDummyFunctionSummary({});
@@ -45,15 +47,18 @@ bool ValueInfo::canAutoHide() const {
                       });
 }
 
-// Gets the number of immutable refs in RefEdgeList
-unsigned FunctionSummary::immutableRefCount() const {
-  // Here we take advantage of having all readonly references
+// Gets the number of readonly and writeonly refs in RefEdgeList
+std::pair<unsigned, unsigned> FunctionSummary::specialRefCounts() const {
+  // Here we take advantage of having all readonly and writeonly references
   // located in the end of the RefEdgeList.
   auto Refs = refs();
-  unsigned ImmutableRefCnt = 0;
-  for (int I = Refs.size() - 1; I >= 0 && Refs[I].isReadOnly(); --I)
-    ImmutableRefCnt++;
-  return ImmutableRefCnt;
+  unsigned RORefCnt = 0, WORefCnt = 0;
+  int I;
+  for (I = Refs.size() - 1; I >= 0 && Refs[I].isWriteOnly(); --I)
+    WORefCnt++;
+  for (; I >= 0 && Refs[I].isReadOnly(); --I)
+    RORefCnt++;
+  return {RORefCnt, WORefCnt};
 }
 
 // Collect for the given module the list of function it defines
@@ -99,48 +104,56 @@ bool ModuleSummaryIndex::isGUIDLive(GlobalValue::GUID GUID) const {
   return false;
 }
 
-static void propagateConstantsToRefs(GlobalValueSummary *S) {
-  // If reference is not readonly then referenced summary is not
-  // readonly either. Note that:
+static void propagateAttributesToRefs(GlobalValueSummary *S) {
+  // If reference is not readonly or writeonly then referenced summary is not
+  // read/writeonly either. Note that:
   // - All references from GlobalVarSummary are conservatively considered as
-  //   not readonly. Tracking them properly requires more complex analysis
-  //   then we have now.
+  //   not readonly or writeonly. Tracking them properly requires more complex
+  //   analysis then we have now.
   //
   // - AliasSummary objects have no refs at all so this function is a no-op
   //   for them.
   for (auto &VI : S->refs()) {
-    if (VI.isReadOnly()) {
-      // We only mark refs as readonly when computing function summaries on
-      // analysis phase.
-      assert(isa<FunctionSummary>(S));
-      continue;
-    }
+    assert(VI.getAccessSpecifier() == 0 || isa<FunctionSummary>(S));
     for (auto &Ref : VI.getSummaryList())
-      // If references to alias is not readonly then aliasee is not readonly
-      if (auto *GVS = dyn_cast<GlobalVarSummary>(Ref->getBaseObject()))
-        GVS->setReadOnly(false);
+      // If references to alias is not read/writeonly then aliasee
+      // is not read/writeonly
+      if (auto *GVS = dyn_cast<GlobalVarSummary>(Ref->getBaseObject())) {
+        if (!VI.isReadOnly())
+          GVS->setReadOnly(false);
+        if (!VI.isWriteOnly())
+          GVS->setWriteOnly(false);
+      }
   }
 }
 
-// Do the constant propagation in combined index.
-// The goal of constant propagation is internalization of readonly
-// variables. To determine which variables are readonly and which
-// are not we take following steps:
-// - During analysis we speculatively assign readonly attribute to
-//   all variables which can be internalized. When computing function
-//   summary we also assign readonly attribute to a reference if
-//   function doesn't modify referenced variable.
+// Do the access attribute propagation in combined index.
+// The goal of attribute propagation is internalization of readonly (RO)
+// or writeonly (WO) variables. To determine which variables are RO or WO
+// and which are not we take following steps:
+// - During analysis we speculatively assign readonly and writeonly
+//   attribute to all variables which can be internalized. When computing
+//   function summary we also assign readonly or writeonly attribute to a
+//   reference if function doesn't modify referenced variable (readonly)
+//   or doesn't read it (writeonly).
+//
+// - After computing dead symbols in combined index we do the attribute
+//   propagation. During this step we:
+//   a. clear RO and WO attributes from variables which are preserved or
+//      can't be imported
+//   b. clear RO and WO attributes from variables referenced by any global
+//      variable initializer
+//   c. clear RO attribute from variable referenced by a function when
+//      reference is not readonly
+//   d. clear WO attribute from variable referenced by a function when
+//      reference is not writeonly
 //
-// - After computing dead symbols in combined index we do the constant
-//   propagation. During this step we clear readonly attribute from
-//   all variables which:
-//   a. are preserved or can't be imported
-//   b. referenced by any global variable initializer
-//   c. referenced by a function and reference is not readonly
+//   Because of (c, d) we don't internalize variables read by function A
+//   and modified by function B.
 //
 // Internalization itself happens in the backend after import is finished
-// See internalizeImmutableGVs.
-void ModuleSummaryIndex::propagateConstants(
+// See internalizeGVsAfterImport.
+void ModuleSummaryIndex::propagateAttributes(
     const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols) {
   for (auto &P : *this)
     for (auto &S : P.second.SummaryList) {
@@ -148,29 +161,36 @@ void ModuleSummaryIndex::propagateConstants(
         // We don't examine references from dead objects
         continue;
 
-      // Global variable can't be marked read only if it is not eligible
-      // to import since we need to ensure that all external references
-      // get a local (imported) copy. It also can't be marked read only
-      // if it or any alias (since alias points to the same memory) are
-      // preserved or notEligibleToImport, since either of those means
-      // there could be writes that are not visible (because preserved
-      // means it could have external to DSO writes, and notEligibleToImport
-      // means it could have writes via inline assembly leading it to be
-      // in the @llvm.*used).
+      // Global variable can't be marked read/writeonly if it is not eligible
+      // to import since we need to ensure that all external references get
+      // a local (imported) copy. It also can't be marked read/writeonly if
+      // it or any alias (since alias points to the same memory) are preserved
+      // or notEligibleToImport, since either of those means there could be
+      // writes (or reads in case of writeonly) that are not visible (because
+      // preserved means it could have external to DSO writes or reads, and
+      // notEligibleToImport means it could have writes or reads via inline
+      // assembly leading it to be in the @llvm.*used).
       if (auto *GVS = dyn_cast<GlobalVarSummary>(S->getBaseObject()))
         // Here we intentionally pass S.get() not GVS, because S could be
         // an alias.
-        if (!canImportGlobalVar(S.get()) || GUIDPreservedSymbols.count(P.first))
+        if (!canImportGlobalVar(S.get()) ||
+            GUIDPreservedSymbols.count(P.first)) {
           GVS->setReadOnly(false);
-      propagateConstantsToRefs(S.get());
+          GVS->setWriteOnly(false);
+        }
+      propagateAttributesToRefs(S.get());
     }
   if (llvm::AreStatisticsEnabled())
     for (auto &P : *this)
       if (P.second.SummaryList.size())
         if (auto *GVS = dyn_cast<GlobalVarSummary>(
                 P.second.SummaryList[0]->getBaseObject()))
-          if (isGlobalValueLive(GVS) && GVS->isReadOnly())
-            ReadOnlyLiveGVars++;
+          if (isGlobalValueLive(GVS)) {
+            if (GVS->maybeReadOnly())
+              ReadOnlyLiveGVars++;
+            if (GVS->maybeWriteOnly())
+              WriteOnlyLiveGVars++;
+          }
 }
 
 // TODO: write a graphviz dumper for SCCs (see ModuleSummaryIndex::exportToDot)
@@ -333,7 +353,13 @@ static void defineExternalNode(raw_ostream &OS, const char *Pfx,
 
 static bool hasReadOnlyFlag(const GlobalValueSummary *S) {
   if (auto *GVS = dyn_cast<GlobalVarSummary>(S))
-    return GVS->isReadOnly();
+    return GVS->maybeReadOnly();
+  return false;
+}
+
+static bool hasWriteOnlyFlag(const GlobalValueSummary *S) {
+  if (auto *GVS = dyn_cast<GlobalVarSummary>(S))
+    return GVS->maybeWriteOnly();
   return false;
 }
 
@@ -358,12 +384,14 @@ void ModuleSummaryIndex::exportToDot(raw_ostream &OS) const {
     // 0 - alias
     // 1 - reference
     // 2 - constant reference
-    // Other value: (hotness - 3).
-    TypeOrHotness += 3;
+    // 3 - writeonly reference
+    // Other value: (hotness - 4).
+    TypeOrHotness += 4;
     static const char *EdgeAttrs[] = {
         " [style=dotted]; // alias",
         " [style=dashed]; // ref",
         " [style=dashed,color=forestgreen]; // const-ref",
+        " [style=dashed,color=violetred]; // writeOnly-ref",
         " // call (hotness : Unknown)",
         " [color=blue]; // call (hotness : Cold)",
         " // call (hotness : None)",
@@ -408,6 +436,8 @@ void ModuleSummaryIndex::exportToDot(raw_ostream &OS) const {
         A.add("shape", "Mrecord", "variable");
         if (Flags.Live && hasReadOnlyFlag(SummaryIt.second))
           A.addComment("immutable");
+        if (Flags.Live && hasWriteOnlyFlag(SummaryIt.second))
+          A.addComment("writeOnly");
       }
       if (Flags.DSOLocal)
         A.addComment("dsoLocal");
@@ -429,10 +459,11 @@ void ModuleSummaryIndex::exportToDot(raw_ostream &OS) const {
     for (auto &SummaryIt : GVSMap) {
       auto *GVS = SummaryIt.second;
       for (auto &R : GVS->refs())
-        Draw(SummaryIt.first, R.getGUID(), R.isReadOnly() ? -1 : -2);
+        Draw(SummaryIt.first, R.getGUID(),
+             R.isWriteOnly() ? -1 : (R.isReadOnly() ? -2 : -3));
 
       if (auto *AS = dyn_cast_or_null<AliasSummary>(SummaryIt.second)) {
-        Draw(SummaryIt.first, AS->getAliaseeGUID(), -3);
+        Draw(SummaryIt.first, AS->getAliaseeGUID(), -4);
         continue;
       }
 

lib/LTO/LTO.cpp

@@ -192,8 +192,10 @@ void llvm::computeLTOCacheKey(
       AddUnsigned(VI.isDSOLocal());
       AddUsedCfiGlobal(VI.getGUID());
     }
-    if (auto *GVS = dyn_cast<GlobalVarSummary>(GS))
-      AddUnsigned(GVS->isReadOnly());
+    if (auto *GVS = dyn_cast<GlobalVarSummary>(GS)) {
+      AddUnsigned(GVS->maybeReadOnly());
+      AddUnsigned(GVS->maybeWriteOnly());
+    }
     if (auto *FS = dyn_cast<FunctionSummary>(GS)) {
       for (auto &TT : FS->type_tests())
         UsedTypeIds.insert(TT);
@@ -371,9 +373,9 @@ void llvm::thinLTOResolvePrevailingInIndex(
                                  GUIDPreservedSymbols);
 }
 
-static bool isWeakWriteableObject(GlobalValueSummary *GVS) {
+static bool isWeakObjectWithRWAccess(GlobalValueSummary *GVS) {
   if (auto *VarSummary = dyn_cast<GlobalVarSummary>(GVS->getBaseObject()))
-    return !VarSummary->isReadOnly() &&
+    return !VarSummary->maybeReadOnly() && !VarSummary->maybeWriteOnly() &&
            (VarSummary->linkage() == GlobalValue::WeakODRLinkage ||
             VarSummary->linkage() == GlobalValue::LinkOnceODRLinkage);
   return false;
@@ -394,11 +396,12 @@ static void thinLTOInternalizeAndPromoteGUID(
                // We can't internalize available_externally globals because this
                // can break function pointer equality.
                S->linkage() != GlobalValue::AvailableExternallyLinkage &&
-               // Functions and read-only variables with linkonce_odr and weak_odr 
-               // linkage can be internalized. We can't internalize linkonce_odr
-               // and weak_odr variables which are modified somewhere in the
-               // program because reads and writes will become inconsistent.
-               !isWeakWriteableObject(S.get()))
+               // Functions and read-only variables with linkonce_odr and
+               // weak_odr linkage can be internalized. We can't internalize
+               // linkonce_odr and weak_odr variables which are both modified
+               // and read somewhere in the program because reads and writes
+               // will become inconsistent.
+               !isWeakObjectWithRWAccess(S.get()))
       S->setLinkage(GlobalValue::InternalLinkage);
   }
 }

lib/Transforms/IPO/FunctionImport.cpp

@@ -850,14 +850,16 @@ void llvm::computeDeadSymbolsWithConstProp(
     bool ImportEnabled) {
   computeDeadSymbols(Index, GUIDPreservedSymbols, isPrevailing);
   if (ImportEnabled) {
-    Index.propagateConstants(GUIDPreservedSymbols);
+    Index.propagateAttributes(GUIDPreservedSymbols);
   } else {
-    // If import is disabled we should drop read-only attribute
+    // If import is disabled we should drop read/write-only attribute
     // from all summaries to prevent internalization.
     for (auto &P : Index)
       for (auto &S : P.second.SummaryList)
-        if (auto *GVS = dyn_cast<GlobalVarSummary>(S.get()))
+        if (auto *GVS = dyn_cast<GlobalVarSummary>(S.get())) {
           GVS->setReadOnly(false);
+          GVS->setWriteOnly(false);
+        }
   }
 }
 
@@ -1064,7 +1066,7 @@ static Function *replaceAliasWithAliasee(Module *SrcModule, GlobalAlias *GA) {
 
 // Internalize values that we marked with specific attribute
 // in processGlobalForThinLTO.
-static void internalizeImmutableGVs(Module &M) {
+static void internalizeGVsAfterImport(Module &M) {
   for (auto &GV : M.globals())
     // Skip GVs which have been converted to declarations
     // by dropDeadSymbols.
@@ -1197,7 +1199,7 @@ Expected<bool> FunctionImporter::importFunctions(
     NumImportedModules++;
   }
 
-  internalizeImmutableGVs(DestModule);
+  internalizeGVsAfterImport(DestModule);
 
   NumImportedFunctions += (ImportedCount - ImportedGVCount);
   NumImportedGlobalVars += ImportedGVCount;

lib/Transforms/Utils/FunctionImportUtils.cpp

@@ -229,11 +229,11 @@ void FunctionImportGlobalProcessing::processGlobalForThinLTO(GlobalValue &GV) {
     }
   }
 
-  // Mark read-only variables which can be imported with specific attribute.
-  // We can't internalize them now because IRMover will fail to link variable
-  // definitions to their external declarations during ThinLTO import. We'll
-  // internalize read-only variables later, after import is finished.
-  // See internalizeImmutableGVs.
+  // Mark read/write-only variables which can be imported with specific
+  // attribute. We can't internalize them now because IRMover will fail
+  // to link variable definitions to their external declarations during
+  // ThinLTO import. We'll internalize read-only variables later, after
+  // import is finished. See internalizeGVsAfterImport.
   //
   // If global value dead stripping is not enabled in summary then
   // propagateConstants hasn't been run. We can't internalize GV
@@ -241,7 +241,8 @@ void FunctionImportGlobalProcessing::processGlobalForThinLTO(GlobalValue &GV) {
   if (!GV.isDeclaration() && VI && ImportIndex.withGlobalValueDeadStripping()) {
     const auto &SL = VI.getSummaryList();
     auto *GVS = SL.empty() ? nullptr : dyn_cast<GlobalVarSummary>(SL[0].get());
-    if (GVS && GVS->isReadOnly())
+    // At this stage "maybe" is "definitely"
+    if (GVS && (GVS->maybeReadOnly() || GVS->maybeWriteOnly()))
       cast<GlobalVariable>(&GV)->addAttribute("thinlto-internalize");
   }
 

test/Assembler/thinlto-summary.ll

@@ -9,7 +9,7 @@
 ; Check a function that makes several calls with various profile hotness, and a
 ; reference (also tests forward references to function and variables in calls
 ; and refs).
-^2 = gv: (guid: 1, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 10, calls: ((callee: ^15, hotness: hot), (callee: ^17, hotness: cold), (callee: ^16, hotness: none)), refs: (readonly ^13, ^14))))
+^2 = gv: (guid: 1, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 10, calls: ((callee: ^15, hotness: hot), (callee: ^17, hotness: cold), (callee: ^16, hotness: none)), refs: (writeonly ^14, readonly ^13, ^11))))
 
 ; Function with a call that has relative block frequency instead of profile
 ; hotness.
@@ -33,7 +33,7 @@
 ^13 = gv: (guid: 12, summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), varFlags: (readonly: 1))))
 
 ; Test a dsoLocal variable.
-^14 = gv: (guid: 13, summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 1), varFlags: (readonly: 0))))
+^14 = gv: (guid: 13, summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 1), varFlags: (writeonly: 0))))
 
 ; Functions with various flag combinations (notEligibleToImport, Live,
 ; combinations of optional function flags).
@@ -67,7 +67,7 @@
 ; Make sure we get back from llvm-dis essentially what we put in via llvm-as.
 ; CHECK: ^0 = module: (path: "thinlto-summary1.o", hash: (1369602428, 2747878711, 259090915, 2507395659, 1141468049))
 ; CHECK: ^1 = module: (path: "thinlto-summary2.o", hash: (2998369023, 4283347029, 1195487472, 2757298015, 1852134156))
-; CHECK: ^2 = gv: (guid: 1, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 10, calls: ((callee: ^15, hotness: hot), (callee: ^17, hotness: cold), (callee: ^16, hotness: none)), refs: (^14, readonly ^13))))
+; CHECK: ^2 = gv: (guid: 1, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 10, calls: ((callee: ^15, hotness: hot), (callee: ^17, hotness: cold), (callee: ^16, hotness: none)), refs: (^11, readonly ^13, writeonly ^14))))
 ; CHECK: ^3 = gv: (guid: 2, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 10, calls: ((callee: ^15)))))
 ; CHECK: ^4 = gv: (guid: 3, summaries: (function: (module: ^0, flags: (linkage: internal, notEligibleToImport: 0, live: 0, dsoLocal: 1, canAutoHide: 0), insts: 1)))
 ; CHECK: ^5 = gv: (guid: 4, summaries: (alias: (module: ^0, flags: (linkage: private, notEligibleToImport: 0, live: 0, dsoLocal: 1, canAutoHide: 0), aliasee: ^14)))
@@ -76,10 +76,10 @@
 ; CHECK: ^8 = gv: (guid: 7, summaries: (function: (module: ^0, flags: (linkage: linkonce_odr, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 1)))
 ; CHECK: ^9 = gv: (guid: 8, summaries: (function: (module: ^0, flags: (linkage: weak_odr, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 1), insts: 1)))
 ; CHECK: ^10 = gv: (guid: 9, summaries: (function: (module: ^0, flags: (linkage: weak, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 1)))
-; CHECK: ^11 = gv: (guid: 10, summaries: (variable: (module: ^0, flags: (linkage: common, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), varFlags: (readonly: 0))))
-; CHECK: ^12 = gv: (guid: 11, summaries: (variable: (module: ^0, flags: (linkage: appending, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), varFlags: (readonly: 0), refs: (^4))))
-; CHECK: ^13 = gv: (guid: 12, summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), varFlags: (readonly: 1))))
-; CHECK: ^14 = gv: (guid: 13, summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 1, canAutoHide: 0), varFlags: (readonly: 0))))
+; CHECK: ^11 = gv: (guid: 10, summaries: (variable: (module: ^0, flags: (linkage: common, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), varFlags: (readonly: 0, writeonly: 0))))
+; CHECK: ^12 = gv: (guid: 11, summaries: (variable: (module: ^0, flags: (linkage: appending, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), varFlags: (readonly: 0, writeonly: 0), refs: (^4))))
+; CHECK: ^13 = gv: (guid: 12, summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), varFlags: (readonly: 1, writeonly: 0))))
+; CHECK: ^14 = gv: (guid: 13, summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 1, canAutoHide: 0), varFlags: (readonly: 0, writeonly: 0))))
 ; CHECK: ^15 = gv: (guid: 14, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 1, live: 1, dsoLocal: 0, canAutoHide: 0), insts: 1)))
 ; CHECK: ^16 = gv: (guid: 15, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 1, funcFlags: (readNone: 1, readOnly: 0, noRecurse: 1, returnDoesNotAlias: 0, noInline: 0))))
 ; CHECK: ^17 = gv: (guid: 16, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 1, funcFlags: (readNone: 0, readOnly: 1, noRecurse: 0, returnDoesNotAlias: 1, noInline: 0), calls: ((callee: ^15)))))

test/Assembler/thinlto-vtable-summary.ll

@@ -29,9 +29,9 @@ declare i32 @_ZN1C1fEi(%struct.C*, i32)
 
 ^0 = module: (path: "<stdin>", hash: (0, 0, 0, 0, 0))
 ^1 = gv: (name: "_ZN1A1nEi") ; guid = 1621563287929432257
-^2 = gv: (name: "_ZTV1B", summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), varFlags: (readonly: 0), vTableFuncs: ((virtFunc: ^3, offset: 16), (virtFunc: ^1, offset: 24)), refs: (^3, ^1)))) ; guid = 5283576821522790367
+^2 = gv: (name: "_ZTV1B", summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), varFlags: (readonly: 0, writeonly: 0), vTableFuncs: ((virtFunc: ^3, offset: 16), (virtFunc: ^1, offset: 24)), refs: (^3, ^1)))) ; guid = 5283576821522790367
 ^3 = gv: (name: "_ZN1B1fEi") ; guid = 7162046368816414394
-^4 = gv: (name: "_ZTV1C", summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), varFlags: (readonly: 0), vTableFuncs: ((virtFunc: ^5, offset: 16), (virtFunc: ^1, offset: 24)), refs: (^1, ^5)))) ; guid = 13624023785555846296
+^4 = gv: (name: "_ZTV1C", summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), varFlags: (readonly: 0, writeonly: 0), vTableFuncs: ((virtFunc: ^5, offset: 16), (virtFunc: ^1, offset: 24)), refs: (^1, ^5)))) ; guid = 13624023785555846296
 ^5 = gv: (name: "_ZN1C1fEi") ; guid = 14876272565662207556
 ^6 = typeidCompatibleVTable: (name: "_ZTS1A", summary: ((offset: 16, ^2), (offset: 16, ^4))) ; guid = 7004155349499253778
 ^7 = typeidCompatibleVTable: (name: "_ZTS1B", summary: ((offset: 16, ^2))) ; guid = 6203814149063363976

test/Bitcode/summary_version.ll

@@ -2,7 +2,7 @@
 ; RUN: opt  -module-summary  %s -o - | llvm-bcanalyzer -dump | FileCheck %s
 
 ; CHECK: <GLOBALVAL_SUMMARY_BLOCK
-; CHECK: <VERSION op0=6/>
+; CHECK: <VERSION op0=7/>
 
 
 

test/Bitcode/thinlto-alias.ll

@@ -21,7 +21,7 @@
 ; CHECK-NEXT:    <FLAGS
 ; See if the call to func is registered.
 ; The value id 1 matches the second FUNCTION record above.
-; CHECK-NEXT:    <PERMODULE {{.*}} op6=1/>
+; CHECK-NEXT:    <PERMODULE {{.*}} op7=1/>
 ; CHECK-NEXT:  </GLOBALVAL_SUMMARY_BLOCK>
 
 ; CHECK: <STRTAB_BLOCK
@@ -34,7 +34,7 @@
 ; COMBINED-NEXT:    <VALUE_GUID op0=[[ALIASID:[0-9]+]] op1=-5751648690987223394/>
 ; COMBINED-NEXT:    <VALUE_GUID
 ; COMBINED-NEXT:    <VALUE_GUID op0=[[ALIASEEID:[0-9]+]] op1=-1039159065113703048/>
-; COMBINED-NEXT:    <COMBINED {{.*}} op8=[[ALIASID]]/>
+; COMBINED-NEXT:    <COMBINED {{.*}} op9=[[ALIASID]]/>
 ; COMBINED-NEXT:    <COMBINED {{.*}}
 ; COMBINED-NEXT:    <COMBINED_ALIAS  {{.*}} op3=[[ALIASEEID]]
 ; COMBINED-NEXT:  </GLOBALVAL_SUMMARY_BLOCK

test/Bitcode/thinlto-alias2.ll

@@ -5,7 +5,7 @@
 ; CHECK:       <GLOBALVAL_SUMMARY_BLOCK
 ; CHECK-NEXT:    <VERSION
 ; CHECK-NEXT:    <FLAGS
-; CHECK-NEXT:    <PERMODULE {{.*}} op4=0 op5=0 op6=[[ALIASID:[0-9]+]]/>
+; CHECK-NEXT:    <PERMODULE {{.*}} op4=0 op5=0 op6=0 op7=[[ALIASID:[0-9]+]]/>
 ; CHECK-NEXT:    <PERMODULE {{.*}} op0=[[ALIASEEID:[0-9]+]]
 ; CHECK-NEXT:    <ALIAS {{.*}} op0=[[ALIASID]] {{.*}} op2=[[ALIASEEID]]/>
 ; CHECK-NEXT:  </GLOBALVAL_SUMMARY_BLOCK>

test/Bitcode/thinlto-function-summary-callgraph-cast.ll

@@ -7,9 +7,9 @@
 ; CHECK-NEXT:    <VERSION
 ; CHECK-NEXT:    <FLAGS
 ; "op7" is a call to "callee" function.
-; CHECK-NEXT:    <PERMODULE {{.*}} op8=3 op9=[[ALIASID:[0-9]+]]/>
+; CHECK-NEXT:    <PERMODULE {{.*}} op9=3 op10=[[ALIASID:[0-9]+]]/>
 ; "another_caller" has only references but no calls.
-; CHECK-NEXT:    <PERMODULE {{.*}} op4=3 {{.*}} op8={{[0-9]+}}/>
+; CHECK-NEXT:    <PERMODULE {{.*}} op4=3 {{.*}} op9={{[0-9]+}}/>
 ; CHECK-NEXT:    <PERMODULE {{.*}} op0=[[ALIASEEID:[0-9]+]]
 ; CHECK-NEXT:    <ALIAS {{.*}} op0=[[ALIASID]] {{.*}} op2=[[ALIASEEID]]/>
 ; CHECK-NEXT:  </GLOBALVAL_SUMMARY_BLOCK>

test/Bitcode/thinlto-function-summary-callgraph-pgo.ll

@@ -18,7 +18,7 @@
 ; CHECK-NEXT:    <VERSION
 ; CHECK-NEXT:    <FLAGS
 ; See if the call to func is registered, using the expected hotness type.
-; CHECK-NEXT:    <PERMODULE_PROFILE {{.*}} op6=1 op7=2/>
+; CHECK-NEXT:    <PERMODULE_PROFILE {{.*}} op7=1 op8=2/>
 ; CHECK-NEXT:  </GLOBALVAL_SUMMARY_BLOCK>
 ; CHECK: <STRTAB_BLOCK
 ; CHECK-NEXT: blob data = 'mainfunc{{.*}}'
@@ -31,7 +31,7 @@
 ; COMBINED-NEXT:    <COMBINED
 ; See if the call to func is registered, using the expected hotness type.
 ; op6=2 which is hotnessType::None.
-; COMBINED-NEXT:    <COMBINED_PROFILE {{.*}} op8=[[FUNCID]] op9=2/>
+; COMBINED-NEXT:    <COMBINED_PROFILE {{.*}} op9=[[FUNCID]] op10=2/>
 ; COMBINED-NEXT:  </GLOBALVAL_SUMMARY_BLOCK>
 
 ; ModuleID = 'thinlto-function-summary-callgraph.ll'

test/Bitcode/thinlto-function-summary-callgraph-profile-summary.ll

@@ -49,7 +49,7 @@
 ; CHECK-NEXT:    <FLAGS
 ; CHECK-NEXT:    <VALUE_GUID op0=25 op1=123/>
 ; op4=hot1 op6=cold op8=hot2 op10=hot4 op12=none1 op14=hot3 op16=none2 op18=none3 op20=123
-; CHECK-NEXT:    <PERMODULE_PROFILE {{.*}} op6=1 op7=3 op8=5 op9=1 op10=2 op11=3 op12=4 op13=1 op14=6 op15=2 op16=3 op17=3 op18=7 op19=2 op20=8 op21=2 op22=25 op23=4/>
+; CHECK-NEXT:    <PERMODULE_PROFILE {{.*}} op7=1 op8=3 op9=5 op10=1 op11=2 op12=3 op13=4 op14=1 op15=6 op16=2 op17=3 op18=3 op19=7 op20=2 op21=8 op22=2 op23=25 op24=4/>
 ; CHECK-NEXT:  </GLOBALVAL_SUMMARY_BLOCK>
 
 ; CHECK: <STRTAB_BLOCK
@@ -72,7 +72,7 @@
 ; COMBINED-NEXT:    <COMBINED abbrevid=
 ; COMBINED-NEXT:    <COMBINED abbrevid=
 ; COMBINED-NEXT:    <COMBINED abbrevid=
-; COMBINED-NEXT:    <COMBINED_PROFILE {{.*}} op8=[[HOT1:.*]] op9=3 op10=[[COLD:.*]] op11=1 op12=[[HOT2:.*]] op13=3 op14=[[NONE1:.*]] op15=2 op16=[[HOT3:.*]] op17=3 op18=[[NONE2:.*]] op19=2 op20=[[NONE3:.*]] op21=2/>
+; COMBINED-NEXT:    <COMBINED_PROFILE {{.*}} op9=[[HOT1:.*]] op10=3 op11=[[COLD:.*]] op12=1 op13=[[HOT2:.*]] op14=3 op15=[[NONE1:.*]] op16=2 op17=[[HOT3:.*]] op18=3 op19=[[NONE2:.*]] op20=2 op21=[[NONE3:.*]] op22=2/>
 ; COMBINED_NEXT:    <COMBINED abbrevid=
 ; COMBINED_NEXT:  </GLOBALVAL_SUMMARY_BLOCK>
 

test/Bitcode/thinlto-function-summary-callgraph-relbf.ll

@@ -14,7 +14,7 @@
 ; CHECK-NEXT:    <VERSION
 ; CHECK-NEXT:    <FLAGS
 ; See if the call to func is registered.
-; CHECK-NEXT:    <PERMODULE_RELBF {{.*}} op4=1 {{.*}} op8=256
+; CHECK-NEXT:    <PERMODULE_RELBF {{.*}} op4=1 {{.*}} op9=256
 ; CHECK-NEXT:  </GLOBALVAL_SUMMARY_BLOCK>
 ; CHECK: <STRTAB_BLOCK
 ; CHECK-NEXT: blob data = 'undefinedglobmainfunc{{.*}}'

test/Bitcode/thinlto-function-summary-callgraph-sample-profile-summary.ll

@@ -32,7 +32,7 @@
 ; CHECK-NEXT:    <FLAGS
 ; CHECK-NEXT:    <VALUE_GUID op0=26 op1=123/>
 ; op4=none1 op6=hot1 op8=cold1 op10=none2 op12=hot2 op14=cold2 op16=none3 op18=hot3 op20=cold3 op22=123
-; CHECK-NEXT:    <PERMODULE_PROFILE {{.*}} op6=7 op7=0 op8=1 op9=3 op10=4 op11=1 op12=8 op13=0 op14=2 op15=3 op16=5 op17=1 op18=9 op19=0 op20=3 op21=3 op22=6 op23=1 op24=26 op25=4/>
+; CHECK-NEXT:    <PERMODULE_PROFILE {{.*}} op7=7 op8=0 op9=1 op10=3 op11=4 op12=1 op13=8 op14=0 op15=2 op16=3 op17=5 op18=1 op19=9 op20=0 op21=3 op22=3 op23=6 op24=1 op25=26 op26=4/>
 ; CHECK-NEXT:  </GLOBALVAL_SUMMARY_BLOCK>
 
 ; CHECK: <STRTAB_BLOCK
@@ -59,7 +59,7 @@
 ; COMBINED-NEXT:    <COMBINED abbrevid=
 ; COMBINED-NEXT:    <COMBINED abbrevid=
 ; COMBINED-NEXT:    <COMBINED abbrevid=
-; COMBINED-NEXT:    <COMBINED_PROFILE {{.*}} op8=[[NONE1:.*]] op9=0 op10=[[HOT1:.*]] op11=3 op12=[[COLD1:.*]] op13=1 op14=[[NONE2:.*]] op15=0 op16=[[HOT2:.*]] op17=3 op18=[[COLD2:.*]] op19=1 op20=[[NONE3:.*]] op21=0 op22=[[HOT3:.*]] op23=3 op24=[[COLD3:.*]] op25=1/>
+; COMBINED-NEXT:    <COMBINED_PROFILE {{.*}} op9=[[NONE1:.*]] op10=0 op11=[[HOT1:.*]] op12=3 op13=[[COLD1:.*]] op14=1 op15=[[NONE2:.*]] op16=0 op17=[[HOT2:.*]] op18=3 op19=[[COLD2:.*]] op20=1 op21=[[NONE3:.*]] op22=0 op23=[[HOT3:.*]] op24=3 op25=[[COLD3:.*]] op26=1/>
 ; COMBINED_NEXT:    <COMBINED abbrevid=
 ; COMBINED_NEXT:  </GLOBALVAL_SUMMARY_BLOCK>
 

test/Bitcode/thinlto-function-summary-callgraph.ll

@@ -34,7 +34,7 @@
 ; COMBINED-NEXT:    <VALUE_GUID
 ; COMBINED-NEXT:    <COMBINED
 ; See if the call to func is registered.
-; COMBINED-NEXT:    <COMBINED {{.*}} op8=[[FUNCID]]/>
+; COMBINED-NEXT:    <COMBINED {{.*}} op9=[[FUNCID]]/>
 ; COMBINED-NEXT:  </GLOBALVAL_SUMMARY_BLOCK>
 
 ; ModuleID = 'thinlto-function-summary-callgraph.ll'

test/Bitcode/thinlto-function-summary-refgraph.ll

@@ -41,27 +41,27 @@
 ; CHECK:       <GLOBALVAL_SUMMARY_BLOCK
 ; Function main contains call to func, as well as address reference to func:
 ; op0=main op4=func op5=func
-; CHECK-DAG:    <PERMODULE {{.*}} op0=11 op1=0 {{.*}} op4=1 op5=0 op6=2 op7=2/>
+; CHECK-DAG:    <PERMODULE {{.*}} op0=11 op1=0 {{.*}} op4=1 op5=0 op6=0 op7=2 op8=2/>
 ; Function W contains a call to func3 as well as a reference to globalvar:
 ; op0=W op4=globalvar op5=func3
-; CHECK-DAG:    <PERMODULE {{.*}} op0=6 op1=5 {{.*}} op4=1 op5=0 op6=1 op7=5/>
+; CHECK-DAG:    <PERMODULE {{.*}} op0=6 op1=5 {{.*}} op4=1 op5=0 op6=0 op7=1 op8=5/>
 ; Function X contains call to foo, as well as address reference to foo
 ; which is in the same instruction as the call:
 ; op0=X op4=foo op5=foo
-; CHECK-DAG:    <PERMODULE {{.*}} op0=7 op1=1 {{.*}} op4=1 op5=0 op6=4 op7=4/>
+; CHECK-DAG:    <PERMODULE {{.*}} op0=7 op1=1 {{.*}} op4=1 op5=0 op6=0 op7=4 op8=4/>
 ; Function Y contains call to func2, and ensures we don't incorrectly add
 ; a reference to it when reached while earlier analyzing the phi using its
 ; return value:
 ; op0=Y op4=func2
-; CHECK-DAG:    <PERMODULE {{.*}} op0=8 op1=72 {{.*}} op4=0 op5=0 op6=3/>
+; CHECK-DAG:    <PERMODULE {{.*}} op0=8 op1=72 {{.*}} op4=0 op5=0 op6=0 op7=3/>
 ; Function Z contains call to func2, and ensures we don't incorrectly add
 ; a reference to it when reached while analyzing subsequent use of its return
 ; value:
 ; op0=Z op4=func2
-; CHECK-DAG:    <PERMODULE {{.*}} op0=9 op1=3 {{.*}} op4=0 op5=0 op6=3/>
+; CHECK-DAG:    <PERMODULE {{.*}} op0=9 op1=3 {{.*}} op4=0 op5=0 op6=0 op7=3/>
 ; Variable bar initialization contains address reference to func:
 ; op0=bar op2=func
-; CHECK-DAG:    <PERMODULE_GLOBALVAR_INIT_REFS {{.*}} op0=0 op1=0 op2=1 op3=2/>
+; CHECK-DAG:    <PERMODULE_GLOBALVAR_INIT_REFS {{.*}} op0=0 op1=0 op2=3 op3=2/>
 ; CHECK:  </GLOBALVAL_SUMMARY_BLOCK>
 
 ; CHECK: <STRTAB_BLOCK
@@ -154,11 +154,11 @@ entry:
 ; DIS-DAG: = gv: (name: "foo") ; guid = 6699318081062747564
 ; DIS-DAG: = gv: (name: "func") ; guid = 7289175272376759421
 ; DIS-DAG: = gv: (name: "func3") ; guid = 11517462787082255043
-; DIS-DAG: = gv: (name: "globalvar", summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), varFlags: (readonly: 1)))) ; guid = 12887606300320728018
+; DIS-DAG: = gv: (name: "globalvar", summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), varFlags: (readonly: 1, writeonly: 1)))) ; guid = 12887606300320728018
 ; DIS-DAG: = gv: (name: "func2") ; guid = 14069196320850861797
 ; DIS-DAG: = gv: (name: "llvm.ctpop.i8") ; guid = 15254915475081819833
 ; DIS-DAG: = gv: (name: "main", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 9, calls: ((callee: ^{{.*}})), refs: (^{{.*}})))) ; guid = 15822663052811949562
-; DIS-DAG: = gv: (name: "bar", summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), varFlags: (readonly: 1),  refs: (^{{.*}})))) ; guid = 16434608426314478903
+; DIS-DAG: = gv: (name: "bar", summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), varFlags: (readonly: 1, writeonly: 1),  refs: (^{{.*}})))) ; guid = 16434608426314478903
 ; Don't try to match the exact GUID. Since it is private, the file path
 ; will get hashed, and that will be test dependent.
 ; DIS-DAG: = gv: (name: "Y", summaries: (function: (module: ^0, flags: (linkage: private, notEligibleToImport: 0, live: 0, dsoLocal: 1, canAutoHide: 0), insts: 14, calls: ((callee: ^{{.*}}))))) ; guid =

test/ThinLTO/X86/Inputs/dot-dumper2.ll

@@ -0,0 +1,4 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@A = local_unnamed_addr global i32 10, align 4

test/ThinLTO/X86/dot-dumper2.ll

@@ -0,0 +1,43 @@
+; Test writeOnly attribute
+; RUN: opt -module-summary %s -o %t1.bc
+; RUN: opt -module-summary %p/Inputs/dot-dumper2.ll -o %t2.bc
+; RUN: llvm-lto2 run -save-temps %t1.bc %t2.bc -o %t3 \
+; RUN:  -r=%t1.bc,main,px \
+; RUN:  -r=%t1.bc,A, \
+; RUN:  -r=%t2.bc,A,p
+
+; RUN: cat %t3.index.dot | FileCheck --check-prefix=COMBINED %s
+
+; COMBINED: digraph Summary {
+; COMBINED-NEXT:  // Module:
+; COMBINED-NEXT:  subgraph cluster_0 {
+; COMBINED-NEXT:    style = filled;
+; COMBINED-NEXT:    color = lightgrey;
+; COMBINED-NEXT:    label =
+; COMBINED-NEXT:    node [style=filled,fillcolor=lightblue];
+; COMBINED-NEXT:    M0_[[MAIN:[0-9]+]] [shape="record",label="main|extern (inst: 2, ffl: 00000)}"]; // function
+; COMBINED-NEXT:    // Edges:
+; COMBINED-NEXT:  }
+; COMBINED-NEXT:  // Module:
+; COMBINED-NEXT:  subgraph cluster_1 {
+; COMBINED-NEXT:    style = filled;
+; COMBINED-NEXT:    color = lightgrey;
+; COMBINED-NEXT:    label =
+; COMBINED-NEXT:    node [style=filled,fillcolor=lightblue];
+; COMBINED-NEXT:    M1_[[A:[0-9]+]] [shape="Mrecord",label="A|extern}"]; // variable, writeOnly
+; COMBINED-NEXT:    // Edges:
+; COMBINED-NEXT:  }
+; COMBINED-NEXT:  // Cross-module edges:
+; COMBINED-NEXT:  M0_[[MAIN]] -> M1_[[A]] [style=dashed,color=violetred]; // writeOnly-ref
+; COMBINED-NEXT: }
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@A = external local_unnamed_addr global i32, align 4
+
+; Function Attrs: nounwind uwtable
+define i32 @main() local_unnamed_addr {
+  store i32 42, i32* @A, align 4
+  ret i32 0
+}

test/ThinLTO/X86/index-const-prop2.ll

@@ -11,8 +11,10 @@
 ; RUN:  -r=%t2.bc,rand, \
 ; RUN:  -r=%t2.bc,gBar,pl \
 ; RUN:  -r=%t1.bc,main,plx \
+; RUN:  -r=%t1.bc,main2,pl \
 ; RUN:  -r=%t1.bc,foo, \
 ; RUN:  -r=%t1.bc,bar, \
+; RUN:  -r=%t1.bc,baz, \
 ; RUN:  -r=%t1.bc,gBar, \
 ; RUN:  -o %t3
 ; RUN: llvm-dis %t3.1.3.import.bc -o - | FileCheck %s --check-prefix=IMPORT
@@ -26,11 +28,32 @@
 ; RUN:  -r=%t2.bc,rand, \
 ; RUN:  -r=%t2.bc,gBar,plx \
 ; RUN:  -r=%t1.bc,main,plx \
+; RUN:  -r=%t1.bc,main2,pl \
 ; RUN:  -r=%t1.bc,foo, \
 ; RUN:  -r=%t1.bc,bar, \
+; RUN:  -r=%t1.bc,baz, \
 ; RUN:  -r=%t1.bc,gBar, \
-; RUN:  -o %t3
-; RUN: llvm-dis %t3.1.3.import.bc -o - | FileCheck %s --check-prefix=IMPORT2
+; RUN:  -o %t4
+; RUN: llvm-dis %t4.1.3.import.bc -o - | FileCheck %s --check-prefix=IMPORT2
+
+; RUN: llvm-lto2 run %t1.bc %t2.bc -save-temps \
+; RUN:  -r=%t2.bc,foo,pl \
+; RUN:  -r=%t2.bc,bar,pl \
+; RUN:  -r=%t2.bc,baz,pl \
+; RUN:  -r=%t2.bc,rand, \
+; RUN:  -r=%t2.bc,gBar,pl \
+; RUN:  -r=%t1.bc,main,pl \
+; RUN:  -r=%t1.bc,main2,plx \
+; RUN:  -r=%t1.bc,foo, \
+; RUN:  -r=%t1.bc,bar, \
+; RUN:  -r=%t1.bc,baz, \
+; RUN:  -r=%t1.bc,gBar, \
+; RUN:  -o %t5
+; RUN: llvm-dis %t5.1.3.import.bc -o - | FileCheck %s --check-prefix=IMPORT
+; RUN: llvm-dis %t5.1.5.precodegen.bc -o - | FileCheck %s --check-prefix=CODEGEN2
+; Check that gFoo and gBar were eliminated from source module together
+; with corresponsing stores
+; RUN: llvm-dis %t5.2.5.precodegen.bc -o - | FileCheck %s --check-prefix=CODEGEN2-SRC
 
 ; IMPORT:       @gFoo.llvm.0 = internal unnamed_addr global i32 1, align 4
 ; IMPORT-NEXT:  @gBar = internal local_unnamed_addr global i32 2, align 4
@@ -41,6 +64,16 @@
 
 ; IMPORT2: @gBar = available_externally dso_local local_unnamed_addr global i32 2, align 4
 
+; CODEGEN2:      i32 @main2
+; CODEGEN2-NEXT:   %1 = tail call i32 @rand()
+; CODEGEN2-NEXT:   %2 = tail call i32 @rand()
+; CODEGEN2-NEXT:   ret i32 0
+
+; CODEGEN2-SRC:       void @baz()
+; CODEGEN2-SRC-NEXT:    %1 = tail call i32 @rand()
+; CODEGEN2-SRC-NEXT:    %2 = tail call i32 @rand()
+; CODEGEN2-SRC-NEXT:    ret void
+
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-pc-linux-gnu"
 
@@ -54,6 +87,13 @@ define i32 @main() local_unnamed_addr {
   ret i32 %add
 }
 
+define i32 @main2() local_unnamed_addr {
+  tail call void @baz()
+  ret i32 0
+}
+
 declare i32 @foo(...) local_unnamed_addr
 
 declare i32 @bar(...) local_unnamed_addr
+
+declare void @baz() local_unnamed_addr

test/ThinLTO/X86/writeonly.ll

@@ -0,0 +1,41 @@
+; Checks that we optimize writeonly variables and corresponding stores using llvm-lto
+; -stats requires asserts
+; REQUIRES: asserts
+
+; RUN: opt -module-summary %s -o %t1.bc
+; RUN: opt -module-summary %p/Inputs/index-const-prop.ll -o %t2.bc
+; RUN: llvm-lto -thinlto-action=thinlink -o %t3.index.bc %t1.bc %t2.bc
+
+; Check that we optimize write-only variables
+; RUN: llvm-lto -thinlto-action=import -exported-symbol=main  %t1.bc -thinlto-index=%t3.index.bc -o %t1.imported.bc -stats 2>&1 | FileCheck %s --check-prefix=STATS
+; RUN: llvm-dis %t1.imported.bc -o - | FileCheck %s --check-prefix=IMPORT
+; RUN: llvm-lto -thinlto-action=optimize %t1.imported.bc -o - | llvm-dis - -o - | FileCheck %s --check-prefix=OPTIMIZE
+
+; IMPORT: @gFoo.llvm.0 = internal unnamed_addr global i32 1, align 4, !dbg !0
+; IMPORT-NEXT: @gBar = internal local_unnamed_addr global i32 2, align 4, !dbg !5
+; IMPORT: !DICompileUnit({{.*}})
+
+; STATS:  2 module-summary-index - Number of live global variables marked write only 
+
+; Check that we've optimized out variables and corresponding stores
+; OPTIMIZE-NOT:  gFoo
+; OPTIMIZE-NOT:  gBar
+; OPTIMIZE:      i32 @main
+; OPTIMIZE-NEXT:   %1 = tail call i32 @rand()
+; OPTIMIZE-NEXT:   %2 = tail call i32 @rand()
+; OPTIMIZE-NEXT:   ret i32 0
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-linux-gnu"
+
+@gBar = external global i32
+
+; Should not be counted in the stats of live write only variables since it is
+; dead and will be dropped anyway.
+@gDead = internal unnamed_addr global i32 1, align 4
+
+define i32 @main() local_unnamed_addr {
+  tail call void @baz()
+  ret i32 0
+}
+declare void @baz() local_unnamed_addr

test/ThinLTO/X86/writeonly2.ll

@@ -0,0 +1,50 @@
+; Check that we optimize out writeonly variables and corresponding stores.
+; This test uses llvm-lto2
+
+; RUN: opt -module-summary %s -o %t1.bc
+; RUN: opt -module-summary %p/Inputs/index-const-prop.ll -o %t2.bc
+; RUN: llvm-lto2 run %t1.bc %t2.bc -save-temps \
+; RUN:  -r=%t2.bc,foo,pl \
+; RUN:  -r=%t2.bc,bar,pl \
+; RUN:  -r=%t2.bc,baz,pl \
+; RUN:  -r=%t2.bc,rand, \
+; RUN:  -r=%t2.bc,gBar,pl \
+; RUN:  -r=%t1.bc,main,plx \
+; RUN:  -r=%t1.bc,baz, \
+; RUN:  -r=%t1.bc,gBar, \
+; RUN:  -o %t3
+; RUN: llvm-dis %t3.1.3.import.bc -o - | FileCheck %s --check-prefix=IMPORT
+; RUN: llvm-dis %t3.1.5.precodegen.bc -o - | FileCheck %s --check-prefix=CODEGEN
+; Check that gFoo and gBar were eliminated from source module together
+; with corresponsing stores
+; RUN: llvm-dis %t3.2.5.precodegen.bc -o - | FileCheck %s --check-prefix=CODEGEN-SRC
+
+; IMPORT:       @gFoo.llvm.0 = internal unnamed_addr global i32 1, align 4
+; IMPORT-NEXT:  @gBar = internal local_unnamed_addr global i32 2, align 4
+; IMPORT:       !DICompileUnit({{.*}})
+
+; CODEGEN-NOT:  gFoo
+; CODEGEN-NOT:  gBar
+; CODEGEN:      i32 @main
+; CODEGEN-NEXT:   %1 = tail call i32 @rand()
+; CODEGEN-NEXT:   %2 = tail call i32 @rand()
+; CODEGEN-NEXT:   ret i32 0
+
+; CODEGEN-SRC-NOT:   gFoo
+; CODEGEN-SRC-NOT:   gBar
+; CODEGEN-SRC:       void @baz()
+; CODEGEN-SRC-NEXT:    %1 = tail call i32 @rand()
+; CODEGEN-SRC-NEXT:    %2 = tail call i32 @rand()
+; CODEGEN-SRC-NEXT:    ret void
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-linux-gnu"
+
+; We should be able to link external definition of gBar to its declaration
+@gBar = external global i32
+
+define i32 @main() local_unnamed_addr {
+  tail call void @baz()
+  ret i32 0
+}
+declare void @baz() local_unnamed_addr