Simplify globals in PNaCl wire format based on normalized constants.

Generates simple global variable records, followed by list of records defining
byte initialization and relocations.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=3504
R=mseaborn@chromium.org

Review URL: https://codereview.chromium.org/18111002

5 files changed, 434 insertions, 173 deletions

diff --git a/lib/Bitcode/NaCl/Reader/NaClBitcodeReader.cpp b/lib/Bitcode/NaCl/Reader/NaClBitcodeReader.cpp
index 9f36a73654..5f14a639ba 100644
--- a/lib/Bitcode/NaCl/Reader/NaClBitcodeReader.cpp
+++ b/lib/Bitcode/NaCl/Reader/NaClBitcodeReader.cpp
@@ -101,17 +101,6 @@ static GlobalValue::VisibilityTypes GetDecodedVisibility(unsigned Val) {
   }
 }
 
-static GlobalVariable::ThreadLocalMode GetDecodedThreadLocalMode(unsigned Val) {
-  switch (Val) {
-    case 0: return GlobalVariable::NotThreadLocal;
-    default: // Map unknown non-zero value to general dynamic.
-    case 1: return GlobalVariable::GeneralDynamicTLSModel;
-    case 2: return GlobalVariable::LocalDynamicTLSModel;
-    case 3: return GlobalVariable::InitialExecTLSModel;
-    case 4: return GlobalVariable::LocalExecTLSModel;
-  }
-}
-
 static int GetDecodedCastOpcode(unsigned Val) {
   switch (Val) {
   default: return -1;
@@ -236,6 +225,7 @@ struct OperandTraits<ConstantPlaceHolder> :
 
 
 void NaClBitcodeReaderValueList::AssignValue(Value *V, unsigned Idx) {
+  assert(V);
   if (Idx == size()) {
     push_back(V);
     return;
@@ -263,9 +253,35 @@ void NaClBitcodeReaderValueList::AssignValue(Value *V, unsigned Idx) {
   }
 }
 
+void NaClBitcodeReaderValueList::AssignGlobalVar(GlobalVariable *GV,
+                                                 unsigned Idx) {
+  assert(GV);
+
+  if (Idx == size()) {
+    push_back(GV);
+    return;
+  }
+
+  if (Idx >= size())
+    resize(Idx+1);
+
+  WeakVH &OldV = ValuePtrs[Idx];
+  if (OldV == 0) {
+    OldV = GV;
+    return;
+  }
+
+  // If there was a forward reference to this value, replace it.
+  Value *PrevVal = OldV;
+  GlobalVariable *Placeholder = cast<GlobalVariable>(PrevVal);
+  Placeholder->replaceAllUsesWith(
+      ConstantExpr::getBitCast(GV, Placeholder->getType()));
+  Placeholder->eraseFromParent();
+  ValuePtrs[Idx] = GV;
+}
 
 Constant *NaClBitcodeReaderValueList::getConstantFwdRef(unsigned Idx,
-                                                    Type *Ty) {
+                                                        Type *Ty) {
   if (Idx >= size())
     resize(Idx + 1);
 
@@ -307,6 +323,26 @@ bool NaClBitcodeReaderValueList::createValueFwdRef(unsigned Idx, Type *Ty) {
   return false;
 }
 
+Constant *NaClBitcodeReaderValueList::getOrCreateGlobalVarRef(
+    unsigned Idx, Module *M) {
+  // First make sure the element for Idx is defined.
+  if (Idx >= size())
+    resize(Idx + 1);
+
+  // Now get its value (if applicable).
+  if (Value *V = ValuePtrs[Idx])
+    return dyn_cast<Constant>(V);
+
+  // Create a placeholder, which will later be RAUW'd.
+  Type *PlaceholderType = Type::getInt8Ty(Context);
+
+  Constant *C =
+      new GlobalVariable(*M, PlaceholderType, false,
+                         GlobalValue::ExternalLinkage, 0);
+  ValuePtrs[Idx] = C;
+  return C;
+}
+
 /// ResolveConstantForwardRefs - Once all constants are read, this method bulk
 /// resolves any forward references.  The idea behind this is that we sometimes
 /// get constants (such as large arrays) which reference *many* forward ref
@@ -635,6 +671,147 @@ bool NaClBitcodeReader::ParseTypeTableBody() {
   }
 }
 
+bool NaClBitcodeReader::ParseGlobalVars() {
+  if (Stream.EnterSubBlock(naclbitc::GLOBALVAR_BLOCK_ID))
+    return Error("Malformed block record");
+
+  SmallVector<uint64_t, 64> Record;
+
+  // True when processing a global variable. Stays true until all records
+  // are processed, and the global variable is created.
+  bool ProcessingGlobal = false;
+  // The alignment value defined for the global variable.
+  unsigned VarAlignment = 0;
+  // True if the variable is read-only.
+  bool VarIsConstant = false;
+  // The initializer for the global variable.
+  SmallVector<Constant *, 10> VarInit;
+  // The number of initializers needed for the global variable.
+  unsigned VarInitializersNeeded = 0;
+  unsigned FirstValueNo = ValueList.size();
+  // The index of the next global variable.
+  unsigned NextValueNo = FirstValueNo;
+  // The number of expected global variable definitions.
+  unsigned NumGlobals = 0;
+
+  // Read all global variable records.
+  while (1) {
+    NaClBitstreamEntry Entry = Stream.advanceSkippingSubblocks();
+    switch (Entry.Kind) {
+    case NaClBitstreamEntry::SubBlock:
+    case NaClBitstreamEntry::Error:
+      return Error("Error in the global vars block");
+    case NaClBitstreamEntry::EndBlock:
+      if (ProcessingGlobal || NumGlobals != (NextValueNo - FirstValueNo))
+        return Error("Error in the global vars block");
+      return false;
+    case NaClBitstreamEntry::Record:
+      // The interesting case.
+      break;
+    }
+
+    // Read a record.
+    Record.clear();
+    unsigned Bitcode = Stream.readRecord(Entry.ID, Record);
+    switch (Bitcode) {
+    default: return Error("Unknown global variable entry");
+    case naclbitc::GLOBALVAR_VAR:
+      // Start the definition of a global variable.
+      if (ProcessingGlobal || Record.size() != 2)
+        return Error("Bad GLOBALVAR_VAR record");
+      ProcessingGlobal = true;
+      VarAlignment = (1 << Record[0]) >> 1;
+      VarIsConstant = Record[1] != 0;
+      // Assume (by default) there is a single initializer.
+      VarInitializersNeeded = 1;
+      break;
+    case naclbitc::GLOBALVAR_COMPOUND:
+      // Global variable has multiple initializers. Changes the
+      // default number of initializers to the given value in
+      // Record[0].
+      if (!ProcessingGlobal || !VarInit.empty() ||
+          VarInitializersNeeded != 1 || Record.size() != 1)
+        return Error("Bad GLOBALVAR_COMPOUND record");
+      VarInitializersNeeded = Record[0];
+      break;
+    case naclbitc::GLOBALVAR_ZEROFILL: {
+      // Define an initializer that defines a sequence of zero-filled bytes.
+      if (!ProcessingGlobal || Record.size() != 1)
+        return Error("Bad GLOBALVAR_ZEROFILL record");
+      Type *Ty = ArrayType::get(Type::getInt8Ty(Context), Record[0]);
+      Constant *Zero = ConstantAggregateZero::get(Ty);
+      VarInit.push_back(Zero);
+      break;
+    }
+    case naclbitc::GLOBALVAR_DATA: {
+      // Defines an initializer defined by a sequence of byte values.
+      if (!ProcessingGlobal || Record.size() < 1)
+        return Error("Bad GLOBALVAR_DATA record");
+      unsigned Size = Record.size();
+      uint8_t *Buf = new uint8_t[Size];
+      assert(Buf);
+      for (unsigned i = 0; i < Size; ++i)
+        Buf[i] = Record[i];
+      Constant *Init = ConstantDataArray::get(
+          Context, ArrayRef<uint8_t>(Buf, Buf + Size));
+      VarInit.push_back(Init);
+      delete[] Buf;
+      break;
+    }
+    case naclbitc::GLOBALVAR_RELOC: {
+      // Define a relocation initializer.
+      if (!ProcessingGlobal || Record.size() < 1 || Record.size() > 2)
+        return Error("Bad GLOBALVAR_RELOC record");
+      Constant *BaseVal =
+          ValueList.getOrCreateGlobalVarRef(Record[0], TheModule);
+      if (BaseVal == 0)
+        return Error("Bad base value in GLOBALVAR_RELOC record");
+      Type *IntPtrType = IntegerType::get(Context, 32);
+      Constant *Val = ConstantExpr::getPtrToInt(BaseVal, IntPtrType);
+      if (Record.size() == 2) {
+        uint32_t Addend = Record[1];
+        Val = ConstantExpr::getAdd(Val, ConstantInt::get(IntPtrType,
+                                                         Addend));
+      }
+      VarInit.push_back(Val);
+      break;
+    }
+    case naclbitc::GLOBALVAR_COUNT:
+      if (Record.size() != 1 || NumGlobals != 0)
+        return Error("Invalid global count record");
+      NumGlobals = Record[0];
+      break;
+    }
+
+    // If more initializers needed for global variable, continue processing.
+    if (!ProcessingGlobal || VarInit.size() < VarInitializersNeeded)
+      continue;
+
+    Constant *Init = 0;
+    switch (VarInit.size()) {
+    case 0:
+      return Error("No initializer for global variable in global vars block");
+    case 1:
+      Init = VarInit[0];
+      break;
+    default:
+      Init = ConstantStruct::getAnon(Context, VarInit, true);
+      break;
+    }
+    GlobalVariable *GV = new GlobalVariable(
+        *TheModule, Init->getType(), VarIsConstant,
+        GlobalValue::InternalLinkage, Init, "");
+    GV->setAlignment(VarAlignment);
+    ValueList.AssignGlobalVar(GV, NextValueNo);
+    ++NextValueNo;
+    ProcessingGlobal = false;
+    VarAlignment = 0;
+    VarIsConstant = false;
+    VarInitializersNeeded = 0;
+    VarInit.clear();
+  }
+}
+
 bool NaClBitcodeReader::ParseValueSymbolTable() {
   DEBUG(dbgs() << "-> ParseValueSymbolTable\n");
   if (Stream.EnterSubBlock(naclbitc::VALUE_SYMTAB_BLOCK_ID))
@@ -691,29 +868,12 @@ bool NaClBitcodeReader::ParseValueSymbolTable() {
   }
 }
 
-/// ResolveGlobalAndAliasInits - Resolve all of the initializers for global
-/// values and aliases that we can.
-bool NaClBitcodeReader::ResolveGlobalAndAliasInits() {
-  std::vector<std::pair<GlobalVariable*, unsigned> > GlobalInitWorklist;
+/// ResolveAliasInits - Resolve all of the initializers for aliases that we can.
+bool NaClBitcodeReader::ResolveAliasInits() {
   std::vector<std::pair<GlobalAlias*, unsigned> > AliasInitWorklist;
 
-  GlobalInitWorklist.swap(GlobalInits);
   AliasInitWorklist.swap(AliasInits);
 
-  while (!GlobalInitWorklist.empty()) {
-    unsigned ValID = GlobalInitWorklist.back().second;
-    if (ValID >= ValueList.size()) {
-      // Not ready to resolve this yet, it requires something later in the file.
-      GlobalInits.push_back(GlobalInitWorklist.back());
-    } else {
-      if (Constant *C = dyn_cast<Constant>(ValueList[ValID]))
-        GlobalInitWorklist.back().first->setInitializer(C);
-      else
-        return Error("Global variable initializer is not a constant!");
-    }
-    GlobalInitWorklist.pop_back();
-  }
-
   while (!AliasInitWorklist.empty()) {
     unsigned ValID = AliasInitWorklist.back().second;
     if (ValID >= ValueList.size()) {
@@ -1199,9 +1359,10 @@ bool NaClBitcodeReader::RememberAndSkipFunctionBody() {
 
 bool NaClBitcodeReader::GlobalCleanup() {
   // Patch the initializers for globals and aliases up.
-  ResolveGlobalAndAliasInits();
-  if (!GlobalInits.empty() || !AliasInits.empty())
-    return Error("Malformed global initializer set");
+  ResolveAliasInits();
+
+  if (!AliasInits.empty())
+    return Error("Malformed Alias Initializer");
 
   // Look for intrinsic functions which need to be upgraded at some point
   for (Module::iterator FI = TheModule->begin(), FE = TheModule->end();
@@ -1216,9 +1377,6 @@ bool NaClBitcodeReader::GlobalCleanup() {
          GI = TheModule->global_begin(), GE = TheModule->global_end();
        GI != GE; ++GI)
     UpgradeGlobalVariable(GI);
-  // Force deallocation of memory for these vectors to favor the client that
-  // want lazy deserialization.
-  std::vector<std::pair<GlobalVariable*, unsigned> >().swap(GlobalInits);
   std::vector<std::pair<GlobalAlias*, unsigned> >().swap(AliasInits);
   return false;
 }
@@ -1261,13 +1419,17 @@ bool NaClBitcodeReader::ParseModule(bool Resume) {
         if (ParseTypeTable())
           return true;
         break;
+      case naclbitc::GLOBALVAR_BLOCK_ID:
+        if (ParseGlobalVars())
+          return true;
+        break;
       case naclbitc::VALUE_SYMTAB_BLOCK_ID:
         if (ParseValueSymbolTable())
           return true;
         SeenValueSymbolTable = true;
         break;
       case naclbitc::CONSTANTS_BLOCK_ID:
-        if (ParseConstants() || ResolveGlobalAndAliasInits())
+        if (ParseConstants() || ResolveAliasInits())
           return true;
         break;
       case naclbitc::FUNCTION_BLOCK_ID:
@@ -1359,57 +1521,8 @@ bool NaClBitcodeReader::ParseModule(bool Resume) {
     // GLOBALVAR: [pointer type, isconst, initid,
     //             linkage, alignment, section, visibility, threadlocal,
     //             unnamed_addr]
-    case naclbitc::MODULE_CODE_GLOBALVAR: {
-      if (Record.size() < 6)
-        return Error("Invalid MODULE_CODE_GLOBALVAR record");
-      Type *Ty = getTypeByID(Record[0]);
-      if (!Ty) return Error("Invalid MODULE_CODE_GLOBALVAR record");
-      if (!Ty->isPointerTy())
-        return Error("Global not a pointer type!");
-      unsigned AddressSpace = cast<PointerType>(Ty)->getAddressSpace();
-      Ty = cast<PointerType>(Ty)->getElementType();
-
-      bool isConstant = Record[1];
-      GlobalValue::LinkageTypes Linkage = GetDecodedLinkage(Record[3]);
-      unsigned Alignment = (1 << Record[4]) >> 1;
-      std::string Section;
-      if (Record[5]) {
-        if (Record[5]-1 >= SectionTable.size())
-          return Error("Invalid section ID");
-        Section = SectionTable[Record[5]-1];
-      }
-      GlobalValue::VisibilityTypes Visibility = GlobalValue::DefaultVisibility;
-      if (Record.size() > 6)
-        Visibility = GetDecodedVisibility(Record[6]);
-
-      GlobalVariable::ThreadLocalMode TLM = GlobalVariable::NotThreadLocal;
-      if (Record.size() > 7)
-        TLM = GetDecodedThreadLocalMode(Record[7]);
-
-      bool UnnamedAddr = false;
-      if (Record.size() > 8)
-        UnnamedAddr = Record[8];
-
-      bool ExternallyInitialized = false;
-      if (Record.size() > 9)
-        ExternallyInitialized = Record[9];
-
-      GlobalVariable *NewGV =
-        new GlobalVariable(*TheModule, Ty, isConstant, Linkage, 0, "", 0,
-                           TLM, AddressSpace, ExternallyInitialized);
-      NewGV->setAlignment(Alignment);
-      if (!Section.empty())
-        NewGV->setSection(Section);
-      NewGV->setVisibility(Visibility);
-      NewGV->setUnnamedAddr(UnnamedAddr);
-
-      ValueList.push_back(NewGV);
-
-      // Remember which value to use for the global initializer.
-      if (unsigned InitID = Record[2])
-        GlobalInits.push_back(std::make_pair(NewGV, InitID-1));
-      break;
-    }
+    case naclbitc::MODULE_CODE_GLOBALVAR:
+      return Error("Invalid MODULE_CODE_GLOBALVAR record");
     // FUNCTION:  [type, callingconv, isproto, linkage]
     case naclbitc::MODULE_CODE_FUNCTION: {
       if (Record.size() < 4)
diff --git a/lib/Bitcode/NaCl/Reader/NaClBitcodeReader.h b/lib/Bitcode/NaCl/Reader/NaClBitcodeReader.h
index 9320de92ea..454875796a 100644
--- a/lib/Bitcode/NaCl/Reader/NaClBitcodeReader.h
+++ b/lib/Bitcode/NaCl/Reader/NaClBitcodeReader.h
@@ -82,13 +82,32 @@ public:
   // already been declared.
   bool createValueFwdRef(unsigned Idx, Type *Ty);
 
+  // Declares the type of the forward-referenced constant Idx. Returns
+  // 0 if an error occurred.
+  // TODO(kschimpf) Convert these to be like createValueFwdRef and
+  // getValueFwdRef.
   Constant *getConstantFwdRef(unsigned Idx, Type *Ty);
 
   // Gets the forward reference value for Idx.
   Value *getValueFwdRef(unsigned Idx);
 
+  // Gets the corresponding constant defining the address of the
+  // corresponding global variable defined by Idx, if already defined.
+  // Otherwise, creates a forward reference for Idx, and returns the
+  // placeholder constant for the address of the corresponding global
+  // variable defined by Idx.
+  Constant *getOrCreateGlobalVarRef(unsigned Idx, Module* M);
+
+  // Assigns Idx to the given value (if new), or assigns V to Idx (if Idx
+  // was forward referenced).
   void AssignValue(Value *V, unsigned Idx);
 
+  // Assigns Idx to the given global variable. If the Idx currently has
+  // a forward reference (built by createGlobalVarFwdRef(unsigned Idx)),
+  // replaces uses of the global variable forward reference with the
+  // value GV.
+  void AssignGlobalVar(GlobalVariable *GV, unsigned Idx);
+
   /// ResolveConstantForwardRefs - Once all constants are read, this method bulk
   /// resolves any forward references.
   void ResolveConstantForwardRefs();
@@ -114,7 +133,6 @@ class NaClBitcodeReader : public GVMaterializer {
   SmallVector<Instruction *, 64> InstructionList;
   SmallVector<SmallVector<uint64_t, 64>, 64> UseListRecords;
 
-  std::vector<std::pair<GlobalVariable*, unsigned> > GlobalInits;
   std::vector<std::pair<GlobalAlias*, unsigned> > AliasInits;
 
   /// FunctionBBs - While parsing a function body, this is a list of the basic
@@ -259,13 +277,13 @@ private:
   bool ParseModule(bool Resume);
   bool ParseTypeTable();
   bool ParseTypeTableBody();
-
+  bool ParseGlobalVars();
   bool ParseValueSymbolTable();
   bool ParseConstants();
   bool RememberAndSkipFunctionBody();
   bool ParseFunctionBody(Function *F);
   bool GlobalCleanup();
-  bool ResolveGlobalAndAliasInits();
+  bool ResolveAliasInits();
   bool ParseUseLists();
   bool InitStream();
   bool InitStreamFromBuffer();
diff --git a/lib/Bitcode/NaCl/Writer/NaClBitcodeWriter.cpp b/lib/Bitcode/NaCl/Writer/NaClBitcodeWriter.cpp
index be75af1e40..44aaeb3f0e 100644
--- a/lib/Bitcode/NaCl/Writer/NaClBitcodeWriter.cpp
+++ b/lib/Bitcode/NaCl/Writer/NaClBitcodeWriter.cpp
@@ -69,6 +69,15 @@ enum {
   CST_CONSTANTS_CSTRING_6_ABBREV,
   CST_CONSTANTS_MAX_ABBREV = CST_CONSTANTS_CSTRING_6_ABBREV,
 
+  // GLOBALVAR BLOCK abbrev id's.
+  GLOBALVAR_VAR_ABBREV = naclbitc::FIRST_APPLICATION_ABBREV,
+  GLOBALVAR_COMPOUND_ABBREV,
+  GLOBALVAR_ZEROFILL_ABBREV,
+  GLOBALVAR_DATA_ABBREV,
+  GLOBALVAR_RELOC_ABBREV,
+  GLOBALVAR_RELOC_WITH_ADDEND_ABBREV,
+  GLOBALVAR_MAX_ABBREV = GLOBALVAR_RELOC_WITH_ADDEND_ABBREV,
+
   // FUNCTION_BLOCK abbrev id's.
   FUNCTION_INST_LOAD_ABBREV = naclbitc::FIRST_APPLICATION_ABBREV,
   FUNCTION_INST_BINOP_ABBREV,
@@ -89,10 +98,6 @@ enum {
   TYPE_ARRAY_ABBREV,
   TYPE_MAX_ABBREV = TYPE_ARRAY_ABBREV,
 
-  // MODULE_BLOCK abbrev id's.
-  MODULE_GLOBALVAR_ABBREV = naclbitc::FIRST_APPLICATION_ABBREV,
-  MODULE_MAX_ABBREV = MODULE_GLOBALVAR_ABBREV,
-
   // SwitchInst Magic
   SWITCH_INST_MAGIC = 0x4B5 // May 2012 => 1205 => Hex
 };
@@ -409,15 +414,124 @@ static unsigned getEncodedVisibility(const GlobalValue *GV) {
   llvm_unreachable("Invalid visibility");
 }
 
-static unsigned getEncodedThreadLocalMode(const GlobalVariable *GV) {
-  switch (GV->getThreadLocalMode()) {
-    case GlobalVariable::NotThreadLocal:         return 0;
-    case GlobalVariable::GeneralDynamicTLSModel: return 1;
-    case GlobalVariable::LocalDynamicTLSModel:   return 2;
-    case GlobalVariable::InitialExecTLSModel:    return 3;
-    case GlobalVariable::LocalExecTLSModel:      return 4;
+/// \brief Function to convert constant initializers for global
+/// variables into corresponding bitcode. Takes advantage that these
+/// global variable initializations are normalized (see
+/// lib/Transforms/NaCl/FlattenGlobals.cpp).
+void WriteGlobalInit(const Constant *C, unsigned GlobalVarID,
+                     SmallVectorImpl<uint32_t> &Vals,
+                     const NaClValueEnumerator &VE,
+                     NaClBitstreamWriter &Stream) {
+  if (ArrayType *Ty = dyn_cast<ArrayType>(C->getType())) {
+    if (!Ty->getElementType()->isIntegerTy(8))
+      report_fatal_error("Global array initializer not i8");
+    uint32_t Size = Ty->getNumElements();
+    if (isa<ConstantAggregateZero>(C)) {
+      Vals.push_back(Size);
+      Stream.EmitRecord(naclbitc::GLOBALVAR_ZEROFILL, Vals,
+                        GLOBALVAR_ZEROFILL_ABBREV);
+      Vals.clear();
+    } else {
+      const ConstantDataSequential *CD = cast<ConstantDataSequential>(C);
+      StringRef Data = CD->getRawDataValues();
+      for (size_t i = 0; i < Size; ++i) {
+        Vals.push_back(Data[i] & 0xFF);
+      }
+      Stream.EmitRecord(naclbitc::GLOBALVAR_DATA, Vals,
+                        GLOBALVAR_DATA_ABBREV);
+      Vals.clear();
+    }
+    return;
+  }
+  if (C->getType()->isIntegerTy(32)) {
+    // This constant defines a relocation. Start by verifying the
+    // relocation is of the right form.
+    const ConstantExpr *CE = dyn_cast<ConstantExpr>(C);
+    if (CE == 0)
+      report_fatal_error("Global i32 initializer not constant");
+    assert(CE);
+    int32_t Addend = 0;
+    if (CE->getOpcode() == Instruction::Add) {
+      const ConstantInt *AddendConst = dyn_cast<ConstantInt>(CE->getOperand(1));
+      if (AddendConst == 0)
+        report_fatal_error("Malformed addend in global relocation initializer");
+      Addend = AddendConst->getSExtValue();
+      CE = dyn_cast<ConstantExpr>(CE->getOperand(0));
+      if (CE == 0)
+        report_fatal_error(
+            "Base of global relocation initializer not constant");
+    }
+    if (CE->getOpcode() != Instruction::PtrToInt)
+      report_fatal_error("Global relocation base doesn't contain ptrtoint");
+    GlobalValue *GV = dyn_cast<GlobalValue>(CE->getOperand(0));
+    if (GV == 0)
+      report_fatal_error(
+          "Argument of ptrtoint in global relocation no global value");
+
+    // Now generate the corresponding relocation record.
+    unsigned RelocID = VE.getValueID(GV);
+    // This is a value index.
+    unsigned AbbrevToUse = GLOBALVAR_RELOC_ABBREV;
+    Vals.push_back(RelocID);
+    if (Addend) {
+      Vals.push_back(Addend);
+      AbbrevToUse = GLOBALVAR_RELOC_WITH_ADDEND_ABBREV;
+    }
+    Stream.EmitRecord(naclbitc::GLOBALVAR_RELOC, Vals, AbbrevToUse);
+    Vals.clear();
+    return;
+  }
+  report_fatal_error("Global initializer is not a SimpleElement");
+}
+
+// Emit global variables.
+static void WriteGlobalVars(const Module *M,
+                            const NaClValueEnumerator &VE,
+                            NaClBitstreamWriter &Stream) {
+  Stream.EnterSubblock(naclbitc::GLOBALVAR_BLOCK_ID);
+  SmallVector<uint32_t, 32> Vals;
+  unsigned GlobalVarID = VE.getFirstGlobalVarID();
+
+  // Emit the number of global variables.
+
+  Vals.push_back(M->getGlobalList().size());
+  Stream.EmitRecord(naclbitc::GLOBALVAR_COUNT, Vals);
+  Vals.clear();
+
+  // Now emit each global variable.
+  for (Module::const_global_iterator
+           GV = M->global_begin(), E = M->global_end();
+       GV != E; ++GV, ++GlobalVarID) {
+    // Define the global variable.
+    Vals.push_back(Log2_32(GV->getAlignment()) + 1);
+    Vals.push_back(GV->isConstant());
+    Stream.EmitRecord(naclbitc::GLOBALVAR_VAR, Vals, GLOBALVAR_VAR_ABBREV);
+    Vals.clear();
+
+    // Add the field(s).
+    const Constant *C = GV->getInitializer();
+    if (C == 0)
+      report_fatal_error("Global variable initializer not a constant");
+    if (const ConstantStruct *CS = dyn_cast<ConstantStruct>(C)) {
+      if (!CS->getType()->isPacked())
+        report_fatal_error("Global variable type not packed");
+      if (CS->getType()->hasName())
+        report_fatal_error("Global variable type is named");
+      Vals.push_back(CS->getNumOperands());
+      Stream.EmitRecord(naclbitc::GLOBALVAR_COMPOUND, Vals,
+                        GLOBALVAR_COMPOUND_ABBREV);
+      Vals.clear();
+      for (unsigned I = 0; I < CS->getNumOperands(); ++I) {
+        WriteGlobalInit(dyn_cast<Constant>(CS->getOperand(I)), GlobalVarID,
+                        Vals, VE, Stream);
+      }
+    } else {
+      WriteGlobalInit(C, GlobalVarID, Vals, VE, Stream);
+    }
   }
-  llvm_unreachable("Invalid TLS model");
+
+  assert(GlobalVarID == VE.getFirstGlobalVarID() + VE.getNumGlobalVarIDs());
+  Stream.ExitBlock();
 }
 
 // Emit top-level description of module, including inline asm,
@@ -472,65 +586,10 @@ static void WriteModuleInfo(const Module *M, const NaClValueEnumerator &VE,
     }
   }
 
-  // Emit abbrev for globals, now that we know # sections and max alignment.
-  // Add an abbrev for common globals with no visibility or thread localness.
-  // Don't bother emitting vis + thread local abbreviation.
-  {
-    NaClBitCodeAbbrev *Abbv = new NaClBitCodeAbbrev();
-    Abbv->Add(NaClBitCodeAbbrevOp(naclbitc::MODULE_CODE_GLOBALVAR));
-    Abbv->Add(NaClBitCodeAbbrevOp(
-        NaClBitCodeAbbrevOp::Fixed, NaClBitsNeededForValue(MaxGlobalType)));
-    Abbv->Add(NaClBitCodeAbbrevOp(NaClBitCodeAbbrevOp::Fixed, 1)); // Constant.
-    Abbv->Add(NaClBitCodeAbbrevOp(NaClBitCodeAbbrevOp::VBR, 6));   // Initializer.
-    Abbv->Add(NaClBitCodeAbbrevOp(NaClBitCodeAbbrevOp::Fixed, 4)); // Linkage.
-    if (MaxAlignment == 0)                                         // Alignment.
-      Abbv->Add(NaClBitCodeAbbrevOp(0));
-    else {
-      unsigned MaxEncAlignment = Log2_32(MaxAlignment)+1;
-      Abbv->Add(NaClBitCodeAbbrevOp(NaClBitCodeAbbrevOp::Fixed,
-                                    NaClBitsNeededForValue(MaxEncAlignment)));
-    }
-    if (SectionMap.empty())                                    // Section.
-      Abbv->Add(NaClBitCodeAbbrevOp(0));
-    else
-      Abbv->Add(NaClBitCodeAbbrevOp(NaClBitCodeAbbrevOp::Fixed,
-                                    NaClBitsNeededForValue(SectionMap.size())));
-    if (MODULE_GLOBALVAR_ABBREV != Stream.EmitAbbrev(Abbv))
-      llvm_unreachable("Unexpected abbrev ordering!");
-  }
-
-  // Emit the global variable information.
+  // Emit the function proto information. Note: We do this before
+  // global variables, so that global variable initializations can
+  // refer to the functions without a forward reference.
   SmallVector<unsigned, 64> Vals;
-  for (Module::const_global_iterator GV = M->global_begin(),E = M->global_end();
-       GV != E; ++GV) {
-    unsigned AbbrevToUse = 0;
-
-    // GLOBALVAR: [type, isconst, initid,
-    //             linkage, alignment, section, visibility, threadlocal,
-    //             unnamed_addr]
-    Vals.push_back(VE.getTypeID(GV->getType()));
-    Vals.push_back(GV->isConstant());
-    Vals.push_back(GV->isDeclaration() ? 0 :
-                   (VE.getValueID(GV->getInitializer()) + 1));
-    Vals.push_back(getEncodedLinkage(GV));
-    Vals.push_back(Log2_32(GV->getAlignment())+1);
-    Vals.push_back(GV->hasSection() ? SectionMap[GV->getSection()] : 0);
-    if (GV->isThreadLocal() ||
-        GV->getVisibility() != GlobalValue::DefaultVisibility ||
-        GV->hasUnnamedAddr() || GV->isExternallyInitialized()) {
-      Vals.push_back(getEncodedVisibility(GV));
-      Vals.push_back(getEncodedThreadLocalMode(GV));
-      Vals.push_back(GV->hasUnnamedAddr());
-      Vals.push_back(GV->isExternallyInitialized());
-    } else {
-      AbbrevToUse = MODULE_GLOBALVAR_ABBREV;
-    }
-
-    Stream.EmitRecord(naclbitc::MODULE_CODE_GLOBALVAR, Vals, AbbrevToUse);
-    Vals.clear();
-  }
-
-  // Emit the function proto information.
   for (Module::const_iterator F = M->begin(), E = M->end(); F != E; ++F) {
     // FUNCTION:  [type, callingconv, isproto, linkage]
     Vals.push_back(VE.getTypeID(F->getType()));
@@ -543,6 +602,9 @@ static void WriteModuleInfo(const Module *M, const NaClValueEnumerator &VE,
     Vals.clear();
   }
 
+  // Emit the global variable information.
+  WriteGlobalVars(M, VE, Stream);
+
   // Emit the alias information.
   for (Module::const_alias_iterator AI = M->alias_begin(), E = M->alias_end();
        AI != E; ++AI) {
@@ -1561,13 +1623,66 @@ static void WriteBlockInfo(const NaClValueEnumerator &VE,
       llvm_unreachable("Unexpected abbrev ordering!");
   }
 
+  { // VAR abbrev for GLOBALVAR_BLOCK.
+    NaClBitCodeAbbrev *Abbv = new NaClBitCodeAbbrev();
+    Abbv->Add(NaClBitCodeAbbrevOp(naclbitc::GLOBALVAR_VAR));
+    Abbv->Add(NaClBitCodeAbbrevOp(NaClBitCodeAbbrevOp::VBR, 6));
+    Abbv->Add(NaClBitCodeAbbrevOp(NaClBitCodeAbbrevOp::Fixed, 1));
+    if (Stream.EmitBlockInfoAbbrev(naclbitc::GLOBALVAR_BLOCK_ID,
+                                   Abbv) != GLOBALVAR_VAR_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+  { // COMPOUND abbrev for GLOBALVAR_BLOCK.
+    NaClBitCodeAbbrev *Abbv = new NaClBitCodeAbbrev();
+    Abbv->Add(NaClBitCodeAbbrevOp(naclbitc::GLOBALVAR_COMPOUND));
+    Abbv->Add(NaClBitCodeAbbrevOp(NaClBitCodeAbbrevOp::VBR, 8));
+    if (Stream.EmitBlockInfoAbbrev(naclbitc::GLOBALVAR_BLOCK_ID,
+                                   Abbv) != GLOBALVAR_COMPOUND_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+  { // ZEROFILL abbrev for GLOBALVAR_BLOCK.
+    NaClBitCodeAbbrev *Abbv = new NaClBitCodeAbbrev();
+    Abbv->Add(NaClBitCodeAbbrevOp(naclbitc::GLOBALVAR_ZEROFILL));
+    Abbv->Add(NaClBitCodeAbbrevOp(NaClBitCodeAbbrevOp::VBR, 8));
+    if (Stream.EmitBlockInfoAbbrev(naclbitc::GLOBALVAR_BLOCK_ID,
+                                   Abbv) != GLOBALVAR_ZEROFILL_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+  { // DATA abbrev for GLOBALVAR_BLOCK.
+    NaClBitCodeAbbrev *Abbv = new NaClBitCodeAbbrev();
+    Abbv->Add(NaClBitCodeAbbrevOp(naclbitc::GLOBALVAR_DATA));
+    Abbv->Add(NaClBitCodeAbbrevOp(NaClBitCodeAbbrevOp::Array));
+    Abbv->Add(NaClBitCodeAbbrevOp(NaClBitCodeAbbrevOp::Fixed, 8));
+    if (Stream.EmitBlockInfoAbbrev(naclbitc::GLOBALVAR_BLOCK_ID,
+                                   Abbv) != GLOBALVAR_DATA_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+  { // RELOC abbrev for GLOBALVAR_BLOCK.
+    NaClBitCodeAbbrev *Abbv = new NaClBitCodeAbbrev();
+    Abbv->Add(NaClBitCodeAbbrevOp(naclbitc::GLOBALVAR_RELOC));
+    Abbv->Add(NaClBitCodeAbbrevOp(NaClBitCodeAbbrevOp::VBR, 6));
+    if (Stream.EmitBlockInfoAbbrev(naclbitc::GLOBALVAR_BLOCK_ID,
+                                   Abbv) != GLOBALVAR_RELOC_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+  { // RELOC_WITH_ADDEND_ABBREV abbrev for GLOBALVAR_BLOCK.
+    NaClBitCodeAbbrev *Abbv = new NaClBitCodeAbbrev();
+    Abbv->Add(NaClBitCodeAbbrevOp(naclbitc::GLOBALVAR_RELOC));
+    Abbv->Add(NaClBitCodeAbbrevOp(NaClBitCodeAbbrevOp::VBR, 6));
+    Abbv->Add(NaClBitCodeAbbrevOp(NaClBitCodeAbbrevOp::VBR, 6));
+    if (Stream.EmitBlockInfoAbbrev(
+            naclbitc::GLOBALVAR_BLOCK_ID,
+            Abbv) != GLOBALVAR_RELOC_WITH_ADDEND_ABBREV)
+      llvm_unreachable("Unexpected abbrev ordering!");
+  }
+
   Stream.ExitBlock();
 }
 
 /// WriteModule - Emit the specified module to the bitstream.
 static void WriteModule(const Module *M, NaClBitstreamWriter &Stream) {
   DEBUG(dbgs() << "-> WriteModule\n");
-  Stream.EnterSubblock(naclbitc::MODULE_BLOCK_ID, MODULE_MAX_ABBREV);
+  Stream.EnterSubblock(naclbitc::MODULE_BLOCK_ID);
 
   SmallVector<unsigned, 1> Vals;
   unsigned CurVersion = 1;
diff --git a/lib/Bitcode/NaCl/Writer/NaClValueEnumerator.cpp b/lib/Bitcode/NaCl/Writer/NaClValueEnumerator.cpp
index feb14cdb0c..393c5bc934 100644
--- a/lib/Bitcode/NaCl/Writer/NaClValueEnumerator.cpp
+++ b/lib/Bitcode/NaCl/Writer/NaClValueEnumerator.cpp
@@ -42,16 +42,21 @@ NaClValueEnumerator::NaClValueEnumerator(const Module *M) {
   // constructor completes.
   TypeCountMapType count_map;
   TypeCountMap = &count_map;
-  // Enumerate the global variables.
-  for (Module::const_global_iterator I = M->global_begin(),
-         E = M->global_end(); I != E; ++I)
-    EnumerateValue(I);
 
-  // Enumerate the functions.
+  // Enumerate the functions. Note: We do this before global
+  // variables, so that global variable initializations can refer to
+  // the functions without a forward reference.
   for (Module::const_iterator I = M->begin(), E = M->end(); I != E; ++I) {
     EnumerateValue(I);
   }
 
+  // Enumerate the global variables.
+  FirstGlobalVarID = Values.size();
+  for (Module::const_global_iterator I = M->global_begin(),
+         E = M->global_end(); I != E; ++I)
+    EnumerateValue(I);
+  NumGlobalVarIDs = Values.size() - FirstGlobalVarID;
+
   // Enumerate the aliases.
   for (Module::const_alias_iterator I = M->alias_begin(), E = M->alias_end();
        I != E; ++I)
@@ -60,11 +65,8 @@ NaClValueEnumerator::NaClValueEnumerator(const Module *M) {
   // Remember what is the cutoff between globalvalue's and other constants.
   unsigned FirstConstant = Values.size();
 
-  // Enumerate the global variable initializers.
-  for (Module::const_global_iterator I = M->global_begin(),
-         E = M->global_end(); I != E; ++I)
-    if (I->hasInitializer())
-      EnumerateValue(I->getInitializer());
+  // Skip global variable initializers since they are handled within
+  // WriteGlobalVars of file NaClBitcodeWriter.cpp.
 
   // Enumerate the aliasees.
   for (Module::const_alias_iterator I = M->alias_begin(), E = M->alias_end();
diff --git a/lib/Bitcode/NaCl/Writer/NaClValueEnumerator.h b/lib/Bitcode/NaCl/Writer/NaClValueEnumerator.h
index 90946551f5..e98a091ba8 100644
--- a/lib/Bitcode/NaCl/Writer/NaClValueEnumerator.h
+++ b/lib/Bitcode/NaCl/Writer/NaClValueEnumerator.h
@@ -79,6 +79,11 @@ private:
   /// than necessary.
   SmallSet<unsigned, 32> FnForwardTypeRefs;
 
+  // The index of the first global variable ID in the bitcode file.
+  unsigned FirstGlobalVarID;
+  // The number of global variable IDs defined in the bitcode file.
+  unsigned NumGlobalVarIDs;
+
   NaClValueEnumerator(const NaClValueEnumerator &) LLVM_DELETED_FUNCTION;
   void operator=(const NaClValueEnumerator &) LLVM_DELETED_FUNCTION;
 public:
@@ -87,6 +92,14 @@ public:
   void dump() const;
   void print(raw_ostream &OS, const ValueMapType &Map, const char *Name) const;
 
+  unsigned getFirstGlobalVarID() const {
+    return FirstGlobalVarID;
+  }
+
+  unsigned getNumGlobalVarIDs() const {
+    return NumGlobalVarIDs;
+  }
+
   unsigned getValueID(const Value *V) const;
 
   unsigned getTypeID(Type *T) const {