text: //===- GlobalOpt.cpp - Optimize Global Variables --------------------------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This pass transforms simple global variables that never have their address
  // taken.  If obviously true, it marks read/write globals as constant, deletes
  // variables only stored to, etc.
  //
  //===----------------------------------------------------------------------===//
  
  #define DEBUG_TYPE "globalopt"
  #include "llvm/Transforms/IPO.h"
  #include "llvm/CallingConv.h"
  #include "llvm/Constants.h"
  #include "llvm/DerivedTypes.h"
  #include "llvm/Instructions.h"
  #include "llvm/IntrinsicInst.h"
  #include "llvm/Module.h"
  #include "llvm/Pass.h"
  #include "llvm/Analysis/ConstantFolding.h"
  #include "llvm/Analysis/MemoryBuiltins.h"
  #include "llvm/Target/TargetData.h"
  #include "llvm/Support/CallSite.h"
  #include "llvm/Support/Debug.h"
  #include "llvm/Support/ErrorHandling.h"
  #include "llvm/Support/GetElementPtrTypeIterator.h"
  #include "llvm/Support/MathExtras.h"
  #include "llvm/Support/raw_ostream.h"
  #include "llvm/ADT/DenseMap.h"
  #include "llvm/ADT/SmallPtrSet.h"
  #include "llvm/ADT/SmallVector.h"
  #include "llvm/ADT/Statistic.h"
  #include "llvm/ADT/STLExtras.h"
  #include <algorithm>
  using namespace llvm;
  
  STATISTIC(NumMarked    , "Number of globals marked constant");
  STATISTIC(NumUnnamed   , "Number of globals marked unnamed_addr");
  STATISTIC(NumSRA       , "Number of aggregate globals broken into scalars");
  STATISTIC(NumHeapSRA   , "Number of heap objects SRA'd");
  STATISTIC(NumSubstitute,"Number of globals with initializers stored into them");
  STATISTIC(NumDeleted   , "Number of globals deleted");
  STATISTIC(NumFnDeleted , "Number of functions deleted");
  STATISTIC(NumGlobUses  , "Number of global uses devirtualized");
  STATISTIC(NumLocalized , "Number of globals localized");
  STATISTIC(NumShrunkToBool  , "Number of global vars shrunk to booleans");
  STATISTIC(NumFastCallFns   , "Number of functions converted to fastcc");
  STATISTIC(NumCtorsEvaluated, "Number of static ctors evaluated");
  STATISTIC(NumNestRemoved   , "Number of nest attributes removed");
  STATISTIC(NumAliasesResolved, "Number of global aliases resolved");
  STATISTIC(NumAliasesRemoved, "Number of global aliases eliminated");
  
  namespace {
    struct GlobalStatus;
    struct GlobalOpt : public ModulePass {
      virtual void getAnalysisUsage(AnalysisUsage &AU) const {
      }
      static char ID; // Pass identification, replacement for typeid
      GlobalOpt() : ModulePass(ID) {
        initializeGlobalOptPass(*PassRegistry::getPassRegistry());
      }
  
      bool runOnModule(Module &M);
  
    private:
      GlobalVariable *FindGlobalCtors(Module &M);
      bool OptimizeFunctions(Module &M);
      bool OptimizeGlobalVars(Module &M);
      bool OptimizeGlobalAliases(Module &M);
      bool OptimizeGlobalCtorsList(GlobalVariable *&GCL);
      bool ProcessGlobal(GlobalVariable *GV,Module::global_iterator &GVI);
      bool ProcessInternalGlobal(GlobalVariable *GV,Module::global_iterator &GVI,
                                 const SmallPtrSet<const PHINode*, 16> &PHIUsers,
                                 const GlobalStatus &GS);
    };
  }
  
  char GlobalOpt::ID = 0;
  INITIALIZE_PASS(GlobalOpt, "globalopt",
                  "Global Variable Optimizer", false, false)
  
  ModulePass *llvm::createGlobalOptimizerPass() { return new GlobalOpt(); }
  
  namespace {
  
  /// GlobalStatus - As we analyze each global, keep track of some information
  /// about it.  If we find out that the address of the global is taken, none of
  /// this info will be accurate.
  struct GlobalStatus {
    /// isCompared - True if the global's address is used in a comparison.
    bool isCompared;
  
    /// isLoaded - True if the global is ever loaded.  If the global isn't ever
    /// loaded it can be deleted.
    bool isLoaded;
  
    /// StoredType - Keep track of what stores to the global look like.
    ///
    enum StoredType {
      /// NotStored - There is no store to this global.  It can thus be marked
      /// constant.
      NotStored,
  
      /// isInitializerStored - This global is stored to, but the only thing
      /// stored is the constant it was initialized with.  This is only tracked
      /// for scalar globals.
      isInitializerStored,
  
      /// isStoredOnce - This global is stored to, but only its initializer and
      /// one other value is ever stored to it.  If this global isStoredOnce, we
      /// track the value stored to it in StoredOnceValue below.  This is only
      /// tracked for scalar globals.
      isStoredOnce,
  
      /// isStored - This global is stored to by multiple values or something else
      /// that we cannot track.
      isStored
    } StoredType;
  
    /// StoredOnceValue - If only one value (besides the initializer constant) is
    /// ever stored to this global, keep track of what value it is.
    Value *StoredOnceValue;
  
    /// AccessingFunction/HasMultipleAccessingFunctions - These start out
    /// null/false.  When the first accessing function is noticed, it is recorded.
    /// When a second different accessing function is noticed,
    /// HasMultipleAccessingFunctions is set to true.
    const Function *AccessingFunction;
    bool HasMultipleAccessingFunctions;
  
    /// HasNonInstructionUser - Set to true if this global has a user that is not
    /// an instruction (e.g. a constant expr or GV initializer).
    bool HasNonInstructionUser;
  
    /// HasPHIUser - Set to true if this global has a user that is a PHI node.
    bool HasPHIUser;
  
    GlobalStatus() : isCompared(false), isLoaded(false), StoredType(NotStored),
                     StoredOnceValue(0), AccessingFunction(0),
                     HasMultipleAccessingFunctions(false), HasNonInstructionUser(false),
                     HasPHIUser(false) {}
  };
  
  }
  
  // SafeToDestroyConstant - It is safe to destroy a constant iff it is only used
  // by constants itself.  Note that constants cannot be cyclic, so this test is
  // pretty easy to implement recursively.
  //
  static bool SafeToDestroyConstant(const Constant *C) {
    if (isa<GlobalValue>(C)) return false;
  
    for (Value::const_use_iterator UI = C->use_begin(), E = C->use_end(); UI != E;
         ++UI)
      if (const Constant *CU = dyn_cast<Constant>(*UI)) {
        if (!SafeToDestroyConstant(CU)) return false;
      } else
        return false;
    return true;
  }
  
  
  /// AnalyzeGlobal - Look at all uses of the global and fill in the GlobalStatus
  /// structure.  If the global has its address taken, return true to indicate we
  /// can't do anything with it.
  ///
  static bool AnalyzeGlobal(const Value *V, GlobalStatus &GS,
                            SmallPtrSet<const PHINode*, 16> &PHIUsers) {
    for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
         ++UI) {
      const User *U = *UI;
      if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
        GS.HasNonInstructionUser = true;
        
        // If the result of the constantexpr isn't pointer type, then we won't
        // know to expect it in various places.  Just reject early.
        if (!isa<PointerType>(CE->getType())) return true;
        
        if (AnalyzeGlobal(CE, GS, PHIUsers)) return true;
      } else if (const Instruction *I = dyn_cast<Instruction>(U)) {
        if (!GS.HasMultipleAccessingFunctions) {
          const Function *F = I->getParent()->getParent();
          if (GS.AccessingFunction == 0)
            GS.AccessingFunction = F;
          else if (GS.AccessingFunction != F)
            GS.HasMultipleAccessingFunctions = true;
        }
        if (const LoadInst *LI = dyn_cast<LoadInst>(I)) {
          GS.isLoaded = true;
          if (LI->isVolatile()) return true;  // Don't hack on volatile loads.
        } else if (const StoreInst *SI = dyn_cast<StoreInst>(I)) {
          // Don't allow a store OF the address, only stores TO the address.
          if (SI->getOperand(0) == V) return true;
  
          if (SI->isVolatile()) return true;  // Don't hack on volatile stores.
  
          // If this is a direct store to the global (i.e., the global is a scalar
          // value, not an aggregate), keep more specific information about
          // stores.
          if (GS.StoredType != GlobalStatus::isStored) {
            if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(
                                                             SI->getOperand(1))) {
              Value *StoredVal = SI->getOperand(0);
              if (StoredVal == GV->getInitializer()) {
                if (GS.StoredType < GlobalStatus::isInitializerStored)
                  GS.StoredType = GlobalStatus::isInitializerStored;
              } else if (isa<LoadInst>(StoredVal) &&
                         cast<LoadInst>(StoredVal)->getOperand(0) == GV) {
                if (GS.StoredType < GlobalStatus::isInitializerStored)
                  GS.StoredType = GlobalStatus::isInitializerStored;
              } else if (GS.StoredType < GlobalStatus::isStoredOnce) {
                GS.StoredType = GlobalStatus::isStoredOnce;
                GS.StoredOnceValue = StoredVal;
              } else if (GS.StoredType == GlobalStatus::isStoredOnce &&
                         GS.StoredOnceValue == StoredVal) {
                // noop.
              } else {
                GS.StoredType = GlobalStatus::isStored;
              }
            } else {
              GS.StoredType = GlobalStatus::isStored;
            }
          }
        } else if (isa<GetElementPtrInst>(I)) {
          if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
        } else if (isa<SelectInst>(I)) {
          if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
        } else if (const PHINode *PN = dyn_cast<PHINode>(I)) {
          // PHI nodes we can check just like select or GEP instructions, but we
          // have to be careful about infinite recursion.
          if (PHIUsers.insert(PN))  // Not already visited.
            if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
          GS.HasPHIUser = true;
        } else if (isa<CmpInst>(I)) {
          GS.isCompared = true;
        } else if (isa<MemTransferInst>(I)) {
          const MemTransferInst *MTI = cast<MemTransferInst>(I);
          if (MTI->getArgOperand(0) == V)
            GS.StoredType = GlobalStatus::isStored;
          if (MTI->getArgOperand(1) == V)
            GS.isLoaded = true;
        } else if (isa<MemSetInst>(I)) {
          assert(cast<MemSetInst>(I)->getArgOperand(0) == V &&
                 "Memset only takes one pointer!");
          GS.StoredType = GlobalStatus::isStored;
        } else {
          return true;  // Any other non-load instruction might take address!
        }
      } else if (const Constant *C = dyn_cast<Constant>(U)) {
        GS.HasNonInstructionUser = true;
        // We might have a dead and dangling constant hanging off of here.
        if (!SafeToDestroyConstant(C))
          return true;
      } else {
        GS.HasNonInstructionUser = true;
        // Otherwise must be some other user.
        return true;
      }
    }
  
    return false;
  }
  
  static Constant *getAggregateConstantElement(Constant *Agg, Constant *Idx) {
    ConstantInt *CI = dyn_cast<ConstantInt>(Idx);
    if (!CI) return 0;
    unsigned IdxV = CI->getZExtValue();
  
    if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Agg)) {
      if (IdxV < CS->getNumOperands()) return CS->getOperand(IdxV);
    } else if (ConstantArray *CA = dyn_cast<ConstantArray>(Agg)) {
      if (IdxV < CA->getNumOperands()) return CA->getOperand(IdxV);
    } else if (ConstantVector *CP = dyn_cast<ConstantVector>(Agg)) {
      if (IdxV < CP->getNumOperands()) return CP->getOperand(IdxV);
    } else if (isa<ConstantAggregateZero>(Agg)) {
      if (const StructType *STy = dyn_cast<StructType>(Agg->getType())) {
        if (IdxV < STy->getNumElements())
          return Constant::getNullValue(STy->getElementType(IdxV));
      } else if (const SequentialType *STy =
                 dyn_cast<SequentialType>(Agg->getType())) {
        return Constant::getNullValue(STy->getElementType());
      }
    } else if (isa<UndefValue>(Agg)) {
      if (const StructType *STy = dyn_cast<StructType>(Agg->getType())) {
        if (IdxV < STy->getNumElements())
          return UndefValue::get(STy->getElementType(IdxV));
      } else if (const SequentialType *STy =
                 dyn_cast<SequentialType>(Agg->getType())) {
        return UndefValue::get(STy->getElementType());
      }
    }
    return 0;
  }
  
  
  /// CleanupConstantGlobalUsers - We just marked GV constant.  Loop over all
  /// users of the global, cleaning up the obvious ones.  This is largely just a
  /// quick scan over the use list to clean up the easy and obvious cruft.  This
  /// returns true if it made a change.
  static bool CleanupConstantGlobalUsers(Value *V, Constant *Init) {
    bool Changed = false;
    for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;) {
      User *U = *UI++;
  
      if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
        if (Init) {
          // Replace the load with the initializer.
          LI->replaceAllUsesWith(Init);
          LI->eraseFromParent();
          Changed = true;
        }
      } else if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
        // Store must be unreachable or storing Init into the global.
        SI->eraseFromParent();
        Changed = true;
      } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
        if (CE->getOpcode() == Instruction::GetElementPtr) {
          Constant *SubInit = 0;
          if (Init)
            SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
          Changed |= CleanupConstantGlobalUsers(CE, SubInit);
        } else if (CE->getOpcode() == Instruction::BitCast &&
                   CE->getType()->isPointerTy()) {
          // Pointer cast, delete any stores and memsets to the global.
          Changed |= CleanupConstantGlobalUsers(CE, 0);
        }
  
        if (CE->use_empty()) {
          CE->destroyConstant();
          Changed = true;
        }
      } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
        // Do not transform "gepinst (gep constexpr (GV))" here, because forming
        // "gepconstexpr (gep constexpr (GV))" will cause the two gep's to fold
        // and will invalidate our notion of what Init is.
        Constant *SubInit = 0;
        if (!isa<ConstantExpr>(GEP->getOperand(0))) {
          ConstantExpr *CE =
            dyn_cast_or_null<ConstantExpr>(ConstantFoldInstruction(GEP));
          if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr)
            SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
        }
        Changed |= CleanupConstantGlobalUsers(GEP, SubInit);
  
        if (GEP->use_empty()) {
          GEP->eraseFromParent();
          Changed = true;
        }
      } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U)) { // memset/cpy/mv
        if (MI->getRawDest() == V) {
          MI->eraseFromParent();
          Changed = true;
        }
  
      } else if (Constant *C = dyn_cast<Constant>(U)) {
        // If we have a chain of dead constantexprs or other things dangling from
        // us, and if they are all dead, nuke them without remorse.
        if (SafeToDestroyConstant(C)) {
          C->destroyConstant();
          // This could have invalidated UI, start over from scratch.
          CleanupConstantGlobalUsers(V, Init);
          return true;
        }
      }
    }
    return Changed;
  }
  
  /// isSafeSROAElementUse - Return true if the specified instruction is a safe
  /// user of a derived expression from a global that we want to SROA.
  static bool isSafeSROAElementUse(Value *V) {
    // We might have a dead and dangling constant hanging off of here.
    if (Constant *C = dyn_cast<Constant>(V))
      return SafeToDestroyConstant(C);
  
    Instruction *I = dyn_cast<Instruction>(V);
    if (!I) return false;
  
    // Loads are ok.
    if (isa<LoadInst>(I)) return true;
  
    // Stores *to* the pointer are ok.
    if (StoreInst *SI = dyn_cast<StoreInst>(I))
      return SI->getOperand(0) != V;
  
    // Otherwise, it must be a GEP.
    GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I);
    if (GEPI == 0) return false;
  
    if (GEPI->getNumOperands() < 3 || !isa<Constant>(GEPI->getOperand(1)) ||
        !cast<Constant>(GEPI->getOperand(1))->isNullValue())
      return false;
  
    for (Value::use_iterator I = GEPI->use_begin(), E = GEPI->use_end();
         I != E; ++I)
      if (!isSafeSROAElementUse(*I))
        return false;
    return true;
  }
  
  
  /// IsUserOfGlobalSafeForSRA - U is a direct user of the specified global value.
  /// Look at it and its uses and decide whether it is safe to SROA this global.
  ///
  static bool IsUserOfGlobalSafeForSRA(User *U, GlobalValue *GV) {
    // The user of the global must be a GEP Inst or a ConstantExpr GEP.
    if (!isa<GetElementPtrInst>(U) &&
        (!isa<ConstantExpr>(U) ||
         cast<ConstantExpr>(U)->getOpcode() != Instruction::GetElementPtr))
      return false;
  
    // Check to see if this ConstantExpr GEP is SRA'able.  In particular, we
    // don't like < 3 operand CE's, and we don't like non-constant integer
    // indices.  This enforces that all uses are 'gep GV, 0, C, ...' for some
    // value of C.
    if (U->getNumOperands() < 3 || !isa<Constant>(U->getOperand(1)) ||
        !cast<Constant>(U->getOperand(1))->isNullValue() ||
        !isa<ConstantInt>(U->getOperand(2)))
      return false;
  
    gep_type_iterator GEPI = gep_type_begin(U), E = gep_type_end(U);
    ++GEPI;  // Skip over the pointer index.
  
    // If this is a use of an array allocation, do a bit more checking for sanity.
    if (const ArrayType *AT = dyn_cast<ArrayType>(*GEPI)) {
      uint64_t NumElements = AT->getNumElements();
      ConstantInt *Idx = cast<ConstantInt>(U->getOperand(2));
  
      // Check to make sure that index falls within the array.  If not,
      // something funny is going on, so we won't do the optimization.
      //
      if (Idx->getZExtValue() >= NumElements)
        return false;
  
      // We cannot scalar repl this level of the array unless any array
      // sub-indices are in-range constants.  In particular, consider:
      // A[0][i].  We cannot know that the user isn't doing invalid things like
      // allowing i to index an out-of-range subscript that accesses A[1].
      //
      // Scalar replacing *just* the outer index of the array is probably not
      // going to be a win anyway, so just give up.
      for (++GEPI; // Skip array index.
           GEPI != E;
           ++GEPI) {
        uint64_t NumElements;
        if (const ArrayType *SubArrayTy = dyn_cast<ArrayType>(*GEPI))
          NumElements = SubArrayTy->getNumElements();
        else if (const VectorType *SubVectorTy = dyn_cast<VectorType>(*GEPI))
          NumElements = SubVectorTy->getNumElements();
        else {
          assert((*GEPI)->isStructTy() &&
                 "Indexed GEP type is not array, vector, or struct!");
          continue;
        }
  
        ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPI.getOperand());
        if (!IdxVal || IdxVal->getZExtValue() >= NumElements)
          return false;
      }
    }
  
    for (Value::use_iterator I = U->use_begin(), E = U->use_end(); I != E; ++I)
      if (!isSafeSROAElementUse(*I))
        return false;
    return true;
  }
  
  /// GlobalUsersSafeToSRA - Look at all uses of the global and decide whether it
  /// is safe for us to perform this transformation.
  ///
  static bool GlobalUsersSafeToSRA(GlobalValue *GV) {
    for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end();
         UI != E; ++UI) {
      if (!IsUserOfGlobalSafeForSRA(*UI, GV))
        return false;
    }
    return true;
  }
  
  
  /// SRAGlobal - Perform scalar replacement of aggregates on the specified global
  /// variable.  This opens the door for other optimizations by exposing the
  /// behavior of the program in a more fine-grained way.  We have determined that
  /// this transformation is safe already.  We return the first global variable we
  /// insert so that the caller can reprocess it.
  static GlobalVariable *SRAGlobal(GlobalVariable *GV, const TargetData &TD) {
    // Make sure this global only has simple uses that we can SRA.
    if (!GlobalUsersSafeToSRA(GV))
      return 0;
  
    assert(GV->hasLocalLinkage() && !GV->isConstant());
    Constant *Init = GV->getInitializer();
    const Type *Ty = Init->getType();
  
    std::vector<GlobalVariable*> NewGlobals;
    Module::GlobalListType &Globals = GV->getParent()->getGlobalList();
  
    // Get the alignment of the global, either explicit or target-specific.
    unsigned StartAlignment = GV->getAlignment();
    if (StartAlignment == 0)
      StartAlignment = TD.getABITypeAlignment(GV->getType());
  
    if (const StructType *STy = dyn_cast<StructType>(Ty)) {
      NewGlobals.reserve(STy->getNumElements());
      const StructLayout &Layout = *TD.getStructLayout(STy);
      for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
        Constant *In = getAggregateConstantElement(Init,
                      ConstantInt::get(Type::getInt32Ty(STy->getContext()), i));
        assert(In && "Couldn't get element of initializer?");
        GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false,
                                                 GlobalVariable::InternalLinkage,
                                                 In, GV->getName()+"."+Twine(i),
                                                 GV->isThreadLocal(),
                                                GV->getType()->getAddressSpace());
        Globals.insert(GV, NGV);
        NewGlobals.push_back(NGV);
  
        // Calculate the known alignment of the field.  If the original aggregate
        // had 256 byte alignment for example, something might depend on that:
        // propagate info to each field.
        uint64_t FieldOffset = Layout.getElementOffset(i);
        unsigned NewAlign = (unsigned)MinAlign(StartAlignment, FieldOffset);
        if (NewAlign > TD.getABITypeAlignment(STy->getElementType(i)))
          NGV->setAlignment(NewAlign);
      }
    } else if (const SequentialType *STy = dyn_cast<SequentialType>(Ty)) {
      unsigned NumElements = 0;
      if (const ArrayType *ATy = dyn_cast<ArrayType>(STy))
        NumElements = ATy->getNumElements();
      else
        NumElements = cast<VectorType>(STy)->getNumElements();
  
      if (NumElements > 16 && GV->hasNUsesOrMore(16))
        return 0; // It's not worth it.
      NewGlobals.reserve(NumElements);
  
      uint64_t EltSize = TD.getTypeAllocSize(STy->getElementType());
      unsigned EltAlign = TD.getABITypeAlignment(STy->getElementType());
      for (unsigned i = 0, e = NumElements; i != e; ++i) {
        Constant *In = getAggregateConstantElement(Init,
                      ConstantInt::get(Type::getInt32Ty(Init->getContext()), i));
        assert(In && "Couldn't get element of initializer?");
  
        GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false,
                                                 GlobalVariable::InternalLinkage,
                                                 In, GV->getName()+"."+Twine(i),
                                                 GV->isThreadLocal(),
                                                GV->getType()->getAddressSpace());
        Globals.insert(GV, NGV);
        NewGlobals.push_back(NGV);
  
        // Calculate the known alignment of the field.  If the original aggregate
        // had 256 byte alignment for example, something might depend on that:
        // propagate info to each field.
        unsigned NewAlign = (unsigned)MinAlign(StartAlignment, EltSize*i);
        if (NewAlign > EltAlign)
          NGV->setAlignment(NewAlign);
      }
    }
  
    if (NewGlobals.empty())
      return 0;
  
    DEBUG(dbgs() << "PERFORMING GLOBAL SRA ON: " << *GV);
  
    Constant *NullInt =Constant::getNullValue(Type::getInt32Ty(GV->getContext()));
  
    // Loop over all of the uses of the global, replacing the constantexpr geps,
    // with smaller constantexpr geps or direct references.
    while (!GV->use_empty()) {
      User *GEP = GV->use_back();
      assert(((isa<ConstantExpr>(GEP) &&
               cast<ConstantExpr>(GEP)->getOpcode()==Instruction::GetElementPtr)||
              isa<GetElementPtrInst>(GEP)) && "NonGEP CE's are not SRAable!");
  
      // Ignore the 1th operand, which has to be zero or else the program is quite
      // broken (undefined).  Get the 2nd operand, which is the structure or array
      // index.
      unsigned Val = cast<ConstantInt>(GEP->getOperand(2))->getZExtValue();
      if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access.
  
      Value *NewPtr = NewGlobals[Val];
  
      // Form a shorter GEP if needed.
      if (GEP->getNumOperands() > 3) {
        if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEP)) {
          SmallVector<Constant*, 8> Idxs;
          Idxs.push_back(NullInt);
          for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i)
            Idxs.push_back(CE->getOperand(i));
          NewPtr = ConstantExpr::getGetElementPtr(cast<Constant>(NewPtr),
                                                  &Idxs[0], Idxs.size());
        } else {
          GetElementPtrInst *GEPI = cast<GetElementPtrInst>(GEP);
          SmallVector<Value*, 8> Idxs;
          Idxs.push_back(NullInt);
          for (unsigned i = 3, e = GEPI->getNumOperands(); i != e; ++i)
            Idxs.push_back(GEPI->getOperand(i));
          NewPtr = GetElementPtrInst::Create(NewPtr, Idxs.begin(), Idxs.end(),
                                             GEPI->getName()+"."+Twine(Val),GEPI);
        }
      }
      GEP->replaceAllUsesWith(NewPtr);
  
      if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(GEP))
        GEPI->eraseFromParent();
      else
        cast<ConstantExpr>(GEP)->destroyConstant();
    }
  
    // Delete the old global, now that it is dead.
    Globals.erase(GV);
    ++NumSRA;
  
    // Loop over the new globals array deleting any globals that are obviously
    // dead.  This can arise due to scalarization of a structure or an array that
    // has elements that are dead.
    unsigned FirstGlobal = 0;
    for (unsigned i = 0, e = NewGlobals.size(); i != e; ++i)
      if (NewGlobals[i]->use_empty()) {
        Globals.erase(NewGlobals[i]);
        if (FirstGlobal == i) ++FirstGlobal;
      }
  
    return FirstGlobal != NewGlobals.size() ? NewGlobals[FirstGlobal] : 0;
  }
  
  /// AllUsesOfValueWillTrapIfNull - Return true if all users of the specified
  /// value will trap if the value is dynamically null.  PHIs keeps track of any
  /// phi nodes we've seen to avoid reprocessing them.
  static bool AllUsesOfValueWillTrapIfNull(const Value *V,
                                           SmallPtrSet<const PHINode*, 8> &PHIs) {
    for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
         ++UI) {
      const User *U = *UI;
  
      if (isa<LoadInst>(U)) {
        // Will trap.
      } else if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
        if (SI->getOperand(0) == V) {
          //cerr << "NONTRAPPING USE: " << *U;
          return false;  // Storing the value.
        }
      } else if (const CallInst *CI = dyn_cast<CallInst>(U)) {
        if (CI->getCalledValue() != V) {
          //cerr << "NONTRAPPING USE: " << *U;
          return false;  // Not calling the ptr
        }
      } else if (const InvokeInst *II = dyn_cast<InvokeInst>(U)) {
        if (II->getCalledValue() != V) {
          //cerr << "NONTRAPPING USE: " << *U;
          return false;  // Not calling the ptr
        }
      } else if (const BitCastInst *CI = dyn_cast<BitCastInst>(U)) {
        if (!AllUsesOfValueWillTrapIfNull(CI, PHIs)) return false;
      } else if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
        if (!AllUsesOfValueWillTrapIfNull(GEPI, PHIs)) return false;
      } else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
        // If we've already seen this phi node, ignore it, it has already been
        // checked.
        if (PHIs.insert(PN) && !AllUsesOfValueWillTrapIfNull(PN, PHIs))
          return false;
      } else if (isa<ICmpInst>(U) &&
                 isa<ConstantPointerNull>(UI->getOperand(1))) {
        // Ignore icmp X, null
      } else {
        //cerr << "NONTRAPPING USE: " << *U;
        return false;
      }
    }
    return true;
  }
  
  /// AllUsesOfLoadedValueWillTrapIfNull - Return true if all uses of any loads
  /// from GV will trap if the loaded value is null.  Note that this also permits
  /// comparisons of the loaded value against null, as a special case.
  static bool AllUsesOfLoadedValueWillTrapIfNull(const GlobalVariable *GV) {
    for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end();
         UI != E; ++UI) {
      const User *U = *UI;
  
      if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {
        SmallPtrSet<const PHINode*, 8> PHIs;
        if (!AllUsesOfValueWillTrapIfNull(LI, PHIs))
          return false;
      } else if (isa<StoreInst>(U)) {
        // Ignore stores to the global.
      } else {
        // We don't know or understand this user, bail out.
        //cerr << "UNKNOWN USER OF GLOBAL!: " << *U;
        return false;
      }
    }
    return true;
  }
  
  static bool OptimizeAwayTrappingUsesOfValue(Value *V, Constant *NewV) {
    bool Changed = false;
    for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ) {
      Instruction *I = cast<Instruction>(*UI++);
      if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
        LI->setOperand(0, NewV);
        Changed = true;
      } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
        if (SI->getOperand(1) == V) {
          SI->setOperand(1, NewV);
          Changed = true;
        }
      } else if (isa<CallInst>(I) || isa<InvokeInst>(I)) {
        CallSite CS(I);
        if (CS.getCalledValue() == V) {
          // Calling through the pointer!  Turn into a direct call, but be careful
          // that the pointer is not also being passed as an argument.
          CS.setCalledFunction(NewV);
          Changed = true;
          bool PassedAsArg = false;
          for (unsigned i = 0, e = CS.arg_size(); i != e; ++i)
            if (CS.getArgument(i) == V) {
              PassedAsArg = true;
              CS.setArgument(i, NewV);
            }
  
          if (PassedAsArg) {
            // Being passed as an argument also.  Be careful to not invalidate UI!
            UI = V->use_begin();
          }
        }
      } else if (CastInst *CI = dyn_cast<CastInst>(I)) {
        Changed |= OptimizeAwayTrappingUsesOfValue(CI,
                                  ConstantExpr::getCast(CI->getOpcode(),
                                                        NewV, CI->getType()));
        if (CI->use_empty()) {
          Changed = true;
          CI->eraseFromParent();
        }
      } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
        // Should handle GEP here.
        SmallVector<Constant*, 8> Idxs;
        Idxs.reserve(GEPI->getNumOperands()-1);
        for (User::op_iterator i = GEPI->op_begin() + 1, e = GEPI->op_end();
             i != e; ++i)
          if (Constant *C = dyn_cast<Constant>(*i))
            Idxs.push_back(C);
          else
            break;
        if (Idxs.size() == GEPI->getNumOperands()-1)
          Changed |= OptimizeAwayTrappingUsesOfValue(GEPI,
                            ConstantExpr::getGetElementPtr(NewV, &Idxs[0],
                                                          Idxs.size()));
        if (GEPI->use_empty()) {
          Changed = true;
          GEPI->eraseFromParent();
        }
      }
    }
  
    return Changed;
  }
  
  
  /// OptimizeAwayTrappingUsesOfLoads - The specified global has only one non-null
  /// value stored into it.  If there are uses of the loaded value that would trap
  /// if the loaded value is dynamically null, then we know that they cannot be
  /// reachable with a null optimize away the load.
  static bool OptimizeAwayTrappingUsesOfLoads(GlobalVariable *GV, Constant *LV) {
    bool Changed = false;
  
    // Keep track of whether we are able to remove all the uses of the global
    // other than the store that defines it.
    bool AllNonStoreUsesGone = true;
  
    // Replace all uses of loads with uses of uses of the stored value.
    for (Value::use_iterator GUI = GV->use_begin(), E = GV->use_end(); GUI != E;){
      User *GlobalUser = *GUI++;
      if (LoadInst *LI = dyn_cast<LoadInst>(GlobalUser)) {
        Changed |= OptimizeAwayTrappingUsesOfValue(LI, LV);
        // If we were able to delete all uses of the loads
        if (LI->use_empty()) {
          LI->eraseFromParent();
          Changed = true;
        } else {
          AllNonStoreUsesGone = false;
        }
      } else if (isa<StoreInst>(GlobalUser)) {
        // Ignore the store that stores "LV" to the global.
        assert(GlobalUser->getOperand(1) == GV &&
               "Must be storing *to* the global");
      } else {
        AllNonStoreUsesGone = false;
  
        // If we get here we could have other crazy uses that are transitively
        // loaded.
        assert((isa<PHINode>(GlobalUser) || isa<SelectInst>(GlobalUser) ||
                isa<ConstantExpr>(GlobalUser)) && "Only expect load and stores!");
      }
    }
  
    if (Changed) {
      DEBUG(dbgs() << "OPTIMIZED LOADS FROM STORED ONCE POINTER: " << *GV);
      ++NumGlobUses;
    }
  
    // If we nuked all of the loads, then none of the stores are needed either,
    // nor is the global.
    if (AllNonStoreUsesGone) {
      DEBUG(dbgs() << "  *** GLOBAL NOW DEAD!\n");
      CleanupConstantGlobalUsers(GV, 0);
      if (GV->use_empty()) {
        GV->eraseFromParent();
        ++NumDeleted;
      }
      Changed = true;
    }
    return Changed;
  }
  
  /// ConstantPropUsersOf - Walk the use list of V, constant folding all of the
  /// instructions that are foldable.
  static void ConstantPropUsersOf(Value *V) {
    for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; )
      if (Instruction *I = dyn_cast<Instruction>(*UI++))
        if (Constant *NewC = ConstantFoldInstruction(I)) {
          I->replaceAllUsesWith(NewC);
  
          // Advance UI to the next non-I use to avoid invalidating it!
          // Instructions could multiply use V.
          while (UI != E && *UI == I)
            ++UI;
          I->eraseFromParent();
        }
  }
  
  /// OptimizeGlobalAddressOfMalloc - This function takes the specified global
  /// variable, and transforms the program as if it always contained the result of
  /// the specified malloc.  Because it is always the result of the specified
  /// malloc, there is no reason to actually DO the malloc.  Instead, turn the
  /// malloc into a global, and any loads of GV as uses of the new global.
  static GlobalVariable *OptimizeGlobalAddressOfMalloc(GlobalVariable *GV,
                                                       CallInst *CI,
                                                       const Type *AllocTy,
                                                       ConstantInt *NElements,
                                                       TargetData* TD) {
    DEBUG(errs() << "PROMOTING GLOBAL: " << *GV << "  CALL = " << *CI << '\n');
  
    const Type *GlobalType;
    if (NElements->getZExtValue() == 1)
      GlobalType = AllocTy;
    else
      // If we have an array allocation, the global variable is of an array.
      GlobalType = ArrayType::get(AllocTy, NElements->getZExtValue());
  
    // Create the new global variable.  The contents of the malloc'd memory is
    // undefined, so initialize with an undef value.
    GlobalVariable *NewGV = new GlobalVariable(*GV->getParent(),
                                               GlobalType, false,
                                               GlobalValue::InternalLinkage,
                                               UndefValue::get(GlobalType),
                                               GV->getName()+".body",
                                               GV,
                                               GV->isThreadLocal());
  
    // If there are bitcast users of the malloc (which is typical, usually we have
    // a malloc + bitcast) then replace them with uses of the new global.  Update
    // other users to use the global as well.
    BitCastInst *TheBC = 0;
    while (!CI->use_empty()) {
      Instruction *User = cast<Instruction>(CI->use_back());
      if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) {
        if (BCI->getType() == NewGV->getType()) {
          BCI->replaceAllUsesWith(NewGV);
          BCI->eraseFromParent();
        } else {
          BCI->setOperand(0, NewGV);
        }
      } else {
        if (TheBC == 0)
          TheBC = new BitCastInst(NewGV, CI->getType(), "newgv", CI);
        User->replaceUsesOfWith(CI, TheBC);
      }
    }
  
    Constant *RepValue = NewGV;
    if (NewGV->getType() != GV->getType()->getElementType())
      RepValue = ConstantExpr::getBitCast(RepValue,
                                          GV->getType()->getElementType());
  
    // If there is a comparison against null, we will insert a global bool to
    // keep track of whether the global was initialized yet or not.
    GlobalVariable *InitBool =
      new GlobalVariable(Type::getInt1Ty(GV->getContext()), false,
                         GlobalValue::InternalLinkage,
                         ConstantInt::getFalse(GV->getContext()),
                         GV->getName()+".init", GV->isThreadLocal());
    bool InitBoolUsed = false;
  
    // Loop over all uses of GV, processing them in turn.
    while (!GV->use_empty()) {
      if (StoreInst *SI = dyn_cast<StoreInst>(GV->use_back())) {
        // The global is initialized when the store to it occurs.
        new StoreInst(ConstantInt::getTrue(GV->getContext()), InitBool, SI);
        SI->eraseFromParent();
        continue;
      }
  
      LoadInst *LI = cast<LoadInst>(GV->use_back());
      while (!LI->use_empty()) {
        Use &LoadUse = LI->use_begin().getUse();
        if (!isa<ICmpInst>(LoadUse.getUser())) {
          LoadUse = RepValue;
          continue;
        }
  
        ICmpInst *ICI = cast<ICmpInst>(LoadUse.getUser());
        // Replace the cmp X, 0 with a use of the bool value.
        Value *LV = new LoadInst(InitBool, InitBool->getName()+".val", ICI);
        InitBoolUsed = true;
        switch (ICI->getPredicate()) {
        default: llvm_unreachable("Unknown ICmp Predicate!");
        case ICmpInst::ICMP_ULT:
        case ICmpInst::ICMP_SLT:   // X < null -> always false
          LV = ConstantInt::getFalse(GV->getContext());
          break;
        case ICmpInst::ICMP_ULE:
        case ICmpInst::ICMP_SLE:
        case ICmpInst::ICMP_EQ:
          LV = BinaryOperator::CreateNot(LV, "notinit", ICI);
          break;
        case ICmpInst::ICMP_NE:
        case ICmpInst::ICMP_UGE:
        case ICmpInst::ICMP_SGE:
        case ICmpInst::ICMP_UGT:
        case ICmpInst::ICMP_SGT:
          break;  // no change.
        }
        ICI->replaceAllUsesWith(LV);
        ICI->eraseFromParent();
      }
      LI->eraseFromParent();
    }
  
    // If the initialization boolean was used, insert it, otherwise delete it.
    if (!InitBoolUsed) {
      while (!InitBool->use_empty())  // Delete initializations
        cast<StoreInst>(InitBool->use_back())->eraseFromParent();
      delete InitBool;
    } else
      GV->getParent()->getGlobalList().insert(GV, InitBool);
  
    // Now the GV is dead, nuke it and the malloc..
    GV->eraseFromParent();
    CI->eraseFromParent();
  
    // To further other optimizations, loop over all users of NewGV and try to
    // constant prop them.  This will promote GEP instructions with constant
    // indices into GEP constant-exprs, which will allow global-opt to hack on it.
    ConstantPropUsersOf(NewGV);
    if (RepValue != NewGV)
      ConstantPropUsersOf(RepValue);
  
    return NewGV;
  }
  
  /// ValueIsOnlyUsedLocallyOrStoredToOneGlobal - Scan the use-list of V checking
  /// to make sure that there are no complex uses of V.  We permit simple things
  /// like dereferencing the pointer, but not storing through the address, unless
  /// it is to the specified global.
  static bool ValueIsOnlyUsedLocallyOrStoredToOneGlobal(const Instruction *V,
                                                        const GlobalVariable *GV,
                                           SmallPtrSet<const PHINode*, 8> &PHIs) {
    for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end();
         UI != E; ++UI) {
      const Instruction *Inst = cast<Instruction>(*UI);
  
      if (isa<LoadInst>(Inst) || isa<CmpInst>(Inst)) {
        continue; // Fine, ignore.
      }
  
      if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
        if (SI->getOperand(0) == V && SI->getOperand(1) != GV)
          return false;  // Storing the pointer itself... bad.
        continue; // Otherwise, storing through it, or storing into GV... fine.
      }
  
      // Must index into the array and into the struct.
      if (isa<GetElementPtrInst>(Inst) && Inst->getNumOperands() >= 3) {
        if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(Inst, GV, PHIs))
          return false;
        continue;
      }
  
      if (const PHINode *PN = dyn_cast<PHINode>(Inst)) {
        // PHIs are ok if all uses are ok.  Don't infinitely recurse through PHI
        // cycles.
        if (PHIs.insert(PN))
          if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(PN, GV, PHIs))
            return false;
        continue;
      }
  
      if (const BitCastInst *BCI = dyn_cast<BitCastInst>(Inst)) {
        if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(BCI, GV, PHIs))
          return false;
        continue;
      }
  
      return false;
    }
    return true;
  }
  
  /// ReplaceUsesOfMallocWithGlobal - The Alloc pointer is stored into GV
  /// somewhere.  Transform all uses of the allocation into loads from the
  /// global and uses of the resultant pointer.  Further, delete the store into
  /// GV.  This assumes that these value pass the
  /// 'ValueIsOnlyUsedLocallyOrStoredToOneGlobal' predicate.
  static void ReplaceUsesOfMallocWithGlobal(Instruction *Alloc,
                                            GlobalVariable *GV) {
    while (!Alloc->use_empty()) {
      Instruction *U = cast<Instruction>(*Alloc->use_begin());
      Instruction *InsertPt = U;
      if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
        // If this is the store of the allocation into the global, remove it.
        if (SI->getOperand(1) == GV) {
          SI->eraseFromParent();
          continue;
        }
      } else if (PHINode *PN = dyn_cast<PHINode>(U)) {
        // Insert the load in the corresponding predecessor, not right before the
        // PHI.
        InsertPt = PN->getIncomingBlock(Alloc->use_begin())->getTerminator();
      } else if (isa<BitCastInst>(U)) {
        // Must be bitcast between the malloc and store to initialize the global.
        ReplaceUsesOfMallocWithGlobal(U, GV);
        U->eraseFromParent();
        continue;
      } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U)) {
        // If this is a "GEP bitcast" and the user is a store to the global, then
        // just process it as a bitcast.
        if (GEPI->hasAllZeroIndices() && GEPI->hasOneUse())
          if (StoreInst *SI = dyn_cast<StoreInst>(GEPI->use_back()))
            if (SI->getOperand(1) == GV) {
              // Must be bitcast GEP between the malloc and store to initialize
              // the global.
              ReplaceUsesOfMallocWithGlobal(GEPI, GV);
              GEPI->eraseFromParent();
              continue;
            }
      }
  
      // Insert a load from the global, and use it instead of the malloc.
      Value *NL = new LoadInst(GV, GV->getName()+".val", InsertPt);
      U->replaceUsesOfWith(Alloc, NL);
    }
  }
  
  /// LoadUsesSimpleEnoughForHeapSRA - Verify that all uses of V (a load, or a phi
  /// of a load) are simple enough to perform heap SRA on.  This permits GEP's
  /// that index through the array and struct field, icmps of null, and PHIs.
  static bool LoadUsesSimpleEnoughForHeapSRA(const Value *V,
                          SmallPtrSet<const PHINode*, 32> &LoadUsingPHIs,
                          SmallPtrSet<const PHINode*, 32> &LoadUsingPHIsPerLoad) {
    // We permit two users of the load: setcc comparing against the null
    // pointer, and a getelementptr of a specific form.
    for (Value::const_use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;
         ++UI) {
      const Instruction *User = cast<Instruction>(*UI);
  
      // Comparison against null is ok.
      if (const ICmpInst *ICI = dyn_cast<ICmpInst>(User)) {
        if (!isa<ConstantPointerNull>(ICI->getOperand(1)))
          return false;
        continue;
      }
  
      // getelementptr is also ok, but only a simple form.
      if (const GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
        // Must index into the array and into the struct.
        if (GEPI->getNumOperands() < 3)
          return false;
  
        // Otherwise the GEP is ok.
        continue;
      }
  
      if (const PHINode *PN = dyn_cast<PHINode>(User)) {
        if (!LoadUsingPHIsPerLoad.insert(PN))
          // This means some phi nodes are dependent on each other.
          // Avoid infinite looping!
          return false;
        if (!LoadUsingPHIs.insert(PN))
          // If we have already analyzed this PHI, then it is safe.
          continue;
  
        // Make sure all uses of the PHI are simple enough to transform.
        if (!LoadUsesSimpleEnoughForHeapSRA(PN,
                                            LoadUsingPHIs, LoadUsingPHIsPerLoad))
          return false;
  
        continue;
      }
  
      // Otherwise we don't know what this is, not ok.
      return false;
    }
  
    return true;
  }
  
  
  /// AllGlobalLoadUsesSimpleEnoughForHeapSRA - If all users of values loaded from
  /// GV are simple enough to perform HeapSRA, return true.
  static bool AllGlobalLoadUsesSimpleEnoughForHeapSRA(const GlobalVariable *GV,
                                                      Instruction *StoredVal) {
    SmallPtrSet<const PHINode*, 32> LoadUsingPHIs;
    SmallPtrSet<const PHINode*, 32> LoadUsingPHIsPerLoad;
    for (Value::const_use_iterator UI = GV->use_begin(), E = GV->use_end();
         UI != E; ++UI)
      if (const LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
        if (!LoadUsesSimpleEnoughForHeapSRA(LI, LoadUsingPHIs,
                                            LoadUsingPHIsPerLoad))
          return false;
        LoadUsingPHIsPerLoad.clear();
      }
  
    // If we reach here, we know that all uses of the loads and transitive uses
    // (through PHI nodes) are simple enough to transform.  However, we don't know
    // that all inputs the to the PHI nodes are in the same equivalence sets.
    // Check to verify that all operands of the PHIs are either PHIS that can be
    // transformed, loads from GV, or MI itself.
    for (SmallPtrSet<const PHINode*, 32>::const_iterator I = LoadUsingPHIs.begin()
         , E = LoadUsingPHIs.end(); I != E; ++I) {
      const PHINode *PN = *I;
      for (unsigned op = 0, e = PN->getNumIncomingValues(); op != e; ++op) {
        Value *InVal = PN->getIncomingValue(op);
  
        // PHI of the stored value itself is ok.
        if (InVal == StoredVal) continue;
  
        if (const PHINode *InPN = dyn_cast<PHINode>(InVal)) {
          // One of the PHIs in our set is (optimistically) ok.
          if (LoadUsingPHIs.count(InPN))
            continue;
          return false;
        }
  
        // Load from GV is ok.
        if (const LoadInst *LI = dyn_cast<LoadInst>(InVal))
          if (LI->getOperand(0) == GV)
            continue;
  
        // UNDEF? NULL?
  
        // Anything else is rejected.
        return false;
      }
    }
  
    return true;
  }
  
  static Value *GetHeapSROAValue(Value *V, unsigned FieldNo,
                 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
                     std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
    std::vector<Value*> &FieldVals = InsertedScalarizedValues[V];
  
    if (FieldNo >= FieldVals.size())
      FieldVals.resize(FieldNo+1);
  
    // If we already have this value, just reuse the previously scalarized
    // version.
    if (Value *FieldVal = FieldVals[FieldNo])
      return FieldVal;
  
    // Depending on what instruction this is, we have several cases.
    Value *Result;
    if (LoadInst *LI = dyn_cast<LoadInst>(V)) {
      // This is a scalarized version of the load from the global.  Just create
      // a new Load of the scalarized global.
      Result = new LoadInst(GetHeapSROAValue(LI->getOperand(0), FieldNo,
                                             InsertedScalarizedValues,
                                             PHIsToRewrite),
                            LI->getName()+".f"+Twine(FieldNo), LI);
    } else if (PHINode *PN = dyn_cast<PHINode>(V)) {
      // PN's type is pointer to struct.  Make a new PHI of pointer to struct
      // field.
      const StructType *ST =
        cast<StructType>(cast<PointerType>(PN->getType())->getElementType());
  
      Result =
       PHINode::Create(PointerType::getUnqual(ST->getElementType(FieldNo)),
                       PN->getName()+".f"+Twine(FieldNo), PN);
      PHIsToRewrite.push_back(std::make_pair(PN, FieldNo));
    } else {
      llvm_unreachable("Unknown usable value");
      Result = 0;
    }
  
    return FieldVals[FieldNo] = Result;
  }
  
  /// RewriteHeapSROALoadUser - Given a load instruction and a value derived from
  /// the load, rewrite the derived value to use the HeapSRoA'd load.
  static void RewriteHeapSROALoadUser(Instruction *LoadUser,
               DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
                     std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
    // If this is a comparison against null, handle it.
    if (ICmpInst *SCI = dyn_cast<ICmpInst>(LoadUser)) {
      assert(isa<ConstantPointerNull>(SCI->getOperand(1)));
      // If we have a setcc of the loaded pointer, we can use a setcc of any
      // field.
      Value *NPtr = GetHeapSROAValue(SCI->getOperand(0), 0,
                                     InsertedScalarizedValues, PHIsToRewrite);
  
      Value *New = new ICmpInst(SCI, SCI->getPredicate(), NPtr,
                                Constant::getNullValue(NPtr->getType()),
                                SCI->getName());
      SCI->replaceAllUsesWith(New);
      SCI->eraseFromParent();
      return;
    }
  
    // Handle 'getelementptr Ptr, Idx, i32 FieldNo ...'
    if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(LoadUser)) {
      assert(GEPI->getNumOperands() >= 3 && isa<ConstantInt>(GEPI->getOperand(2))
             && "Unexpected GEPI!");
  
      // Load the pointer for this field.
      unsigned FieldNo = cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue();
      Value *NewPtr = GetHeapSROAValue(GEPI->getOperand(0), FieldNo,
                                       InsertedScalarizedValues, PHIsToRewrite);
  
      // Create the new GEP idx vector.
      SmallVector<Value*, 8> GEPIdx;
      GEPIdx.push_back(GEPI->getOperand(1));
      GEPIdx.append(GEPI->op_begin()+3, GEPI->op_end());
  
      Value *NGEPI = GetElementPtrInst::Create(NewPtr,
                                               GEPIdx.begin(), GEPIdx.end(),
                                               GEPI->getName(), GEPI);
      GEPI->replaceAllUsesWith(NGEPI);
      GEPI->eraseFromParent();
      return;
    }
  
    // Recursively transform the users of PHI nodes.  This will lazily create the
    // PHIs that are needed for individual elements.  Keep track of what PHIs we
    // see in InsertedScalarizedValues so that we don't get infinite loops (very
    // antisocial).  If the PHI is already in InsertedScalarizedValues, it has
    // already been seen first by another load, so its uses have already been
    // processed.
    PHINode *PN = cast<PHINode>(LoadUser);
    bool Inserted;
    DenseMap<Value*, std::vector<Value*> >::iterator InsertPos;
    tie(InsertPos, Inserted) =
      InsertedScalarizedValues.insert(std::make_pair(PN, std::vector<Value*>()));
    if (!Inserted) return;
  
    // If this is the first time we've seen this PHI, recursively process all
    // users.
    for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E; ) {
      Instruction *User = cast<Instruction>(*UI++);
      RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
    }
  }
  
  /// RewriteUsesOfLoadForHeapSRoA - We are performing Heap SRoA on a global.  Ptr
  /// is a value loaded from the global.  Eliminate all uses of Ptr, making them
  /// use FieldGlobals instead.  All uses of loaded values satisfy
  /// AllGlobalLoadUsesSimpleEnoughForHeapSRA.
  static void RewriteUsesOfLoadForHeapSRoA(LoadInst *Load,
                 DenseMap<Value*, std::vector<Value*> > &InsertedScalarizedValues,
                     std::vector<std::pair<PHINode*, unsigned> > &PHIsToRewrite) {
    for (Value::use_iterator UI = Load->use_begin(), E = Load->use_end();
         UI != E; ) {
      Instruction *User = cast<Instruction>(*UI++);
      RewriteHeapSROALoadUser(User, InsertedScalarizedValues, PHIsToRewrite);
    }
  
    if (Load->use_empty()) {
      Load->eraseFromParent();
      InsertedScalarizedValues.erase(Load);
    }
  }
  
  /// PerformHeapAllocSRoA - CI is an allocation of an array of structures.  Break
  /// it up into multiple allocations of arrays of the fields.
  static GlobalVariable *PerformHeapAllocSRoA(GlobalVariable *GV, CallInst *CI,
                                              Value* NElems, TargetData *TD) {
    DEBUG(dbgs() << "SROA HEAP ALLOC: " << *GV << "  MALLOC = " << *CI << '\n');
    const Type* MAT = getMallocAllocatedType(CI);
    const StructType *STy = cast<StructType>(MAT);
  
    // There is guaranteed to be at least one use of the malloc (storing
    // it into GV).  If there are other uses, change them to be uses of
    // the global to simplify later code.  This also deletes the store
    // into GV.
    ReplaceUsesOfMallocWithGlobal(CI, GV);
  
    // Okay, at this point, there are no users of the malloc.  Insert N
    // new mallocs at the same place as CI, and N globals.
    std::vector<Value*> FieldGlobals;
    std::vector<Value*> FieldMallocs;
  
    for (unsigned FieldNo = 0, e = STy->getNumElements(); FieldNo != e;++FieldNo){
      const Type *FieldTy = STy->getElementType(FieldNo);
      const PointerType *PFieldTy = PointerType::getUnqual(FieldTy);
  
      GlobalVariable *NGV =
        new GlobalVariable(*GV->getParent(),
                           PFieldTy, false, GlobalValue::InternalLinkage,
                           Constant::getNullValue(PFieldTy),
                           GV->getName() + ".f" + Twine(FieldNo), GV,
                           GV->isThreadLocal());
      FieldGlobals.push_back(NGV);
  
      unsigned TypeSize = TD->getTypeAllocSize(FieldTy);
      if (const StructType *ST = dyn_cast<StructType>(FieldTy))
        TypeSize = TD->getStructLayout(ST)->getSizeInBytes();
      const Type *IntPtrTy = TD->getIntPtrType(CI->getContext());
      Value *NMI = CallInst::CreateMalloc(CI, IntPtrTy, FieldTy,
                                          ConstantInt::get(IntPtrTy, TypeSize),
                                          NElems, 0,
                                          CI->getName() + ".f" + Twine(FieldNo));
      FieldMallocs.push_back(NMI);
      new StoreInst(NMI, NGV, CI);
    }
  
    // The tricky aspect of this transformation is handling the case when malloc
    // fails.  In the original code, malloc failing would set the result pointer
    // of malloc to null.  In this case, some mallocs could succeed and others
    // could fail.  As such, we emit code that looks like this:
    //    F0 = malloc(field0)
    //    F1 = malloc(field1)
    //    F2 = malloc(field2)
    //    if (F0 == 0 || F1 == 0 || F2 == 0) {
    //      if (F0) { free(F0); F0 = 0; }
    //      if (F1) { free(F1); F1 = 0; }
    //      if (F2) { free(F2); F2 = 0; }
    //    }
    // The malloc can also fail if its argument is too large.
    Constant *ConstantZero = ConstantInt::get(CI->getArgOperand(0)->getType(), 0);
    Value *RunningOr = new ICmpInst(CI, ICmpInst::ICMP_SLT, CI->getArgOperand(0),
                                    ConstantZero, "isneg");
    for (unsigned i = 0, e = FieldMallocs.size(); i != e; ++i) {
      Value *Cond = new ICmpInst(CI, ICmpInst::ICMP_EQ, FieldMallocs[i],
                               Constant::getNullValue(FieldMallocs[i]->getType()),
                                 "isnull");
      RunningOr = BinaryOperator::CreateOr(RunningOr, Cond, "tmp", CI);
    }
  
    // Split the basic block at the old malloc.
    BasicBlock *OrigBB = CI->getParent();
    BasicBlock *ContBB = OrigBB->splitBasicBlock(CI, "malloc_cont");
  
    // Create the block to check the first condition.  Put all these blocks at the
    // end of the function as they are unlikely to be executed.
    BasicBlock *NullPtrBlock = BasicBlock::Create(OrigBB->getContext(),
                                                  "malloc_ret_null",
                                                  OrigBB->getParent());
  
    // Remove the uncond branch from OrigBB to ContBB, turning it into a cond
    // branch on RunningOr.
    OrigBB->getTerminator()->eraseFromParent();
    BranchInst::Create(NullPtrBlock, ContBB, RunningOr, OrigBB);
  
    // Within the NullPtrBlock, we need to emit a comparison and branch for each
    // pointer, because some may be null while others are not.
    for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
      Value *GVVal = new LoadInst(FieldGlobals[i], "tmp", NullPtrBlock);
      Value *Cmp = new ICmpInst(*NullPtrBlock, ICmpInst::ICMP_NE, GVVal,
                                Constant::getNullValue(GVVal->getType()),
                                "tmp");
      BasicBlock *FreeBlock = BasicBlock::Create(Cmp->getContext(), "free_it",
                                                 OrigBB->getParent());
      BasicBlock *NextBlock = BasicBlock::Create(Cmp->getContext(), "next",
                                                 OrigBB->getParent());
      Instruction *BI = BranchInst::Create(FreeBlock, NextBlock,
                                           Cmp, NullPtrBlock);
  
      // Fill in FreeBlock.
      CallInst::CreateFree(GVVal, BI);
      new StoreInst(Constant::getNullValue(GVVal->getType()), FieldGlobals[i],
                    FreeBlock);
      BranchInst::Create(NextBlock, FreeBlock);
  
      NullPtrBlock = NextBlock;
    }
  
    BranchInst::Create(ContBB, NullPtrBlock);
  
    // CI is no longer needed, remove it.
    CI->eraseFromParent();
  
    /// InsertedScalarizedLoads - As we process loads, if we can't immediately
    /// update all uses of the load, keep track of what scalarized loads are
    /// inserted for a given load.
    DenseMap<Value*, std::vector<Value*> > InsertedScalarizedValues;
    InsertedScalarizedValues[GV] = FieldGlobals;
  
    std::vector<std::pair<PHINode*, unsigned> > PHIsToRewrite;
  
    // Okay, the malloc site is completely handled.  All of the uses of GV are now
    // loads, and all uses of those loads are simple.  Rewrite them to use loads
    // of the per-field globals instead.
    for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI != E;) {
      Instruction *User = cast<Instruction>(*UI++);
  
      if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
        RewriteUsesOfLoadForHeapSRoA(LI, InsertedScalarizedValues, PHIsToRewrite);
        continue;
      }
  
      // Must be a store of null.
      StoreInst *SI = cast<StoreInst>(User);
      assert(isa<ConstantPointerNull>(SI->getOperand(0)) &&
             "Unexpected heap-sra user!");
  
      // Insert a store of null into each global.
      for (unsigned i = 0, e = FieldGlobals.size(); i != e; ++i) {
        const PointerType *PT = cast<PointerType>(FieldGlobals[i]->getType());
        Constant *Null = Constant::getNullValue(PT->getElementType());
        new StoreInst(Null, FieldGlobals[i], SI);
      }
      // Erase the original store.
      SI->eraseFromParent();
    }
  
    // While we have PHIs that are interesting to rewrite, do it.
    while (!PHIsToRewrite.empty()) {
      PHINode *PN = PHIsToRewrite.back().first;
      unsigned FieldNo = PHIsToRewrite.back().second;
      PHIsToRewrite.pop_back();
      PHINode *FieldPN = cast<PHINode>(InsertedScalarizedValues[PN][FieldNo]);
      assert(FieldPN->getNumIncomingValues() == 0 &&"Already processed this phi");
  
      // Add all the incoming values.  This can materialize more phis.
      for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
        Value *InVal = PN->getIncomingValue(i);
        InVal = GetHeapSROAValue(InVal, FieldNo, InsertedScalarizedValues,
                                 PHIsToRewrite);
        FieldPN->addIncoming(InVal, PN->getIncomingBlock(i));
      }
    }
  
    // Drop all inter-phi links and any loads that made it this far.
    for (DenseMap<Value*, std::vector<Value*> >::iterator
         I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end();
         I != E; ++I) {
      if (PHINode *PN = dyn_cast<PHINode>(I->first))
        PN->dropAllReferences();
      else if (LoadInst *LI = dyn_cast<LoadInst>(I->first))
        LI->dropAllReferences();
    }
  
    // Delete all the phis and loads now that inter-references are dead.
    for (DenseMap<Value*, std::vector<Value*> >::iterator
         I = InsertedScalarizedValues.begin(), E = InsertedScalarizedValues.end();
         I != E; ++I) {
      if (PHINode *PN = dyn_cast<PHINode>(I->first))
        PN->eraseFromParent();
      else if (LoadInst *LI = dyn_cast<LoadInst>(I->first))
        LI->eraseFromParent();
    }
  
    // The old global is now dead, remove it.
    GV->eraseFromParent();
  
    ++NumHeapSRA;
    return cast<GlobalVariable>(FieldGlobals[0]);
  }
  
  /// TryToOptimizeStoreOfMallocToGlobal - This function is called when we see a
  /// pointer global variable with a single value stored it that is a malloc or
  /// cast of malloc.
  static bool TryToOptimizeStoreOfMallocToGlobal(GlobalVariable *GV,
                                                 CallInst *CI,
                                                 const Type *AllocTy,
                                                 Module::global_iterator &GVI,
                                                 TargetData *TD) {
    if (!TD)
      return false;
  
    // If this is a malloc of an abstract type, don't touch it.
    if (!AllocTy->isSized())
      return false;
  
    // We can't optimize this global unless all uses of it are *known* to be
    // of the malloc value, not of the null initializer value (consider a use
    // that compares the global's value against zero to see if the malloc has
    // been reached).  To do this, we check to see if all uses of the global
    // would trap if the global were null: this proves that they must all
    // happen after the malloc.
    if (!AllUsesOfLoadedValueWillTrapIfNull(GV))
      return false;
  
    // We can't optimize this if the malloc itself is used in a complex way,
    // for example, being stored into multiple globals.  This allows the
    // malloc to be stored into the specified global, loaded setcc'd, and
    // GEP'd.  These are all things we could transform to using the global
    // for.
    SmallPtrSet<const PHINode*, 8> PHIs;
    if (!ValueIsOnlyUsedLocallyOrStoredToOneGlobal(CI, GV, PHIs))
      return false;
  
    // If we have a global that is only initialized with a fixed size malloc,
    // transform the program to use global memory instead of malloc'd memory.
    // This eliminates dynamic allocation, avoids an indirection accessing the
    // data, and exposes the resultant global to further GlobalOpt.
    // We cannot optimize the malloc if we cannot determine malloc array size.
    Value *NElems = getMallocArraySize(CI, TD, true);
    if (!NElems)
      return false;
  
    if (ConstantInt *NElements = dyn_cast<ConstantInt>(NElems))
      // Restrict this transformation to only working on small allocations
      // (2048 bytes currently), as we don't want to introduce a 16M global or
      // something.
      if (NElements->getZExtValue() * TD->getTypeAllocSize(AllocTy) < 2048) {
        GVI = OptimizeGlobalAddressOfMalloc(GV, CI, AllocTy, NElements, TD);
        return true;
      }
  
    // If the allocation is an array of structures, consider transforming this
    // into multiple malloc'd arrays, one for each field.  This is basically
    // SRoA for malloc'd memory.
  
    // If this is an allocation of a fixed size array of structs, analyze as a
    // variable size array.  malloc [100 x struct],1 -> malloc struct, 100
    if (NElems == ConstantInt::get(CI->getArgOperand(0)->getType(), 1))
      if (const ArrayType *AT = dyn_cast<ArrayType>(AllocTy))
        AllocTy = AT->getElementType();
  
    const StructType *AllocSTy = dyn_cast<StructType>(AllocTy);
    if (!AllocSTy)
      return false;
  
    // This the structure has an unreasonable number of fields, leave it
    // alone.
    if (AllocSTy->getNumElements() <= 16 && AllocSTy->getNumElements() != 0 &&
        AllGlobalLoadUsesSimpleEnoughForHeapSRA(GV, CI)) {
  
      // If this is a fixed size array, transform the Malloc to be an alloc of
      // structs.  malloc [100 x struct],1 -> malloc struct, 100
      if (const ArrayType *AT = dyn_cast<ArrayType>(getMallocAllocatedType(CI))) {
        const Type *IntPtrTy = TD->getIntPtrType(CI->getContext());
        unsigned TypeSize = TD->getStructLayout(AllocSTy)->getSizeInBytes();
        Value *AllocSize = ConstantInt::get(IntPtrTy, TypeSize);
        Value *NumElements = ConstantInt::get(IntPtrTy, AT->getNumElements());
        Instruction *Malloc = CallInst::CreateMalloc(CI, IntPtrTy, AllocSTy,
                                                     AllocSize, NumElements,
                                                     0, CI->getName());
        Instruction *Cast = new BitCastInst(Malloc, CI->getType(), "tmp", CI);
        CI->replaceAllUsesWith(Cast);
        CI->eraseFromParent();
        CI = dyn_cast<BitCastInst>(Malloc) ?
          extractMallocCallFromBitCast(Malloc) : cast<CallInst>(Malloc);
      }
  
      GVI = PerformHeapAllocSRoA(GV, CI, getMallocArraySize(CI, TD, true),TD);
      return true;
    }
  
    return false;
  }
  
  // OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge
  // that only one value (besides its initializer) is ever stored to the global.
  static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal,
                                       Module::global_iterator &GVI,
                                       TargetData *TD) {
    // Ignore no-op GEPs and bitcasts.
    StoredOnceVal = StoredOnceVal->stripPointerCasts();
  
    // If we are dealing with a pointer global that is initialized to null and
    // only has one (non-null) value stored into it, then we can optimize any
    // users of the loaded value (often calls and loads) that would trap if the
    // value was null.
    if (GV->getInitializer()->getType()->isPointerTy() &&
        GV->getInitializer()->isNullValue()) {
      if (Constant *SOVC = dyn_cast<Constant>(StoredOnceVal)) {
        if (GV->getInitializer()->getType() != SOVC->getType())
          SOVC =
           ConstantExpr::getBitCast(SOVC, GV->getInitializer()->getType());
  
        // Optimize away any trapping uses of the loaded value.
        if (OptimizeAwayTrappingUsesOfLoads(GV, SOVC))
          return true;
      } else if (CallInst *CI = extractMallocCall(StoredOnceVal)) {
        const Type* MallocType = getMallocAllocatedType(CI);
        if (MallocType && TryToOptimizeStoreOfMallocToGlobal(GV, CI, MallocType,
                                                             GVI, TD))
          return true;
      }
    }
  
    return false;
  }
  
  /// TryToShrinkGlobalToBoolean - At this point, we have learned that the only
  /// two values ever stored into GV are its initializer and OtherVal.  See if we
  /// can shrink the global into a boolean and select between the two values
  /// whenever it is used.  This exposes the values to other scalar optimizations.
  static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) {
    const Type *GVElType = GV->getType()->getElementType();
  
    // If GVElType is already i1, it is already shrunk.  If the type of the GV is
    // an FP value, pointer or vector, don't do this optimization because a select
    // between them is very expensive and unlikely to lead to later
    // simplification.  In these cases, we typically end up with "cond ? v1 : v2"
    // where v1 and v2 both require constant pool loads, a big loss.
    if (GVElType == Type::getInt1Ty(GV->getContext()) ||
        GVElType->isFloatingPointTy() ||
        GVElType->isPointerTy() || GVElType->isVectorTy())
      return false;
  
    // Walk the use list of the global seeing if all the uses are load or store.
    // If there is anything else, bail out.
    for (Value::use_iterator I = GV->use_begin(), E = GV->use_end(); I != E; ++I){
      User *U = *I;
      if (!isa<LoadInst>(U) && !isa<StoreInst>(U))
        return false;
    }
  
    DEBUG(dbgs() << "   *** SHRINKING TO BOOL: " << *GV);
  
    // Create the new global, initializing it to false.
    GlobalVariable *NewGV = new GlobalVariable(Type::getInt1Ty(GV->getContext()),
                                               false,
                                               GlobalValue::InternalLinkage,
                                          ConstantInt::getFalse(GV->getContext()),
                                               GV->getName()+".b",
                                               GV->isThreadLocal());
    GV->getParent()->getGlobalList().insert(GV, NewGV);
  
    Constant *InitVal = GV->getInitializer();
    assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) &&
           "No reason to shrink to bool!");
  
    // If initialized to zero and storing one into the global, we can use a cast
    // instead of a select to synthesize the desired value.
    bool IsOneZero = false;
    if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal))
      IsOneZero = InitVal->isNullValue() && CI->isOne();
  
    while (!GV->use_empty()) {
      Instruction *UI = cast<Instruction>(GV->use_back());
      if (StoreInst *SI = dyn_cast<StoreInst>(UI)) {
        // Change the store into a boolean store.
        bool StoringOther = SI->getOperand(0) == OtherVal;
        // Only do this if we weren't storing a loaded value.
        Value *StoreVal;
        if (StoringOther || SI->getOperand(0) == InitVal)
          StoreVal = ConstantInt::get(Type::getInt1Ty(GV->getContext()),
                                      StoringOther);
        else {
          // Otherwise, we are storing a previously loaded copy.  To do this,
          // change the copy from copying the original value to just copying the
          // bool.
          Instruction *StoredVal = cast<Instruction>(SI->getOperand(0));
  
          // If we've already replaced the input, StoredVal will be a cast or
          // select instruction.  If not, it will be a load of the original
          // global.
          if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
            assert(LI->getOperand(0) == GV && "Not a copy!");
            // Insert a new load, to preserve the saved value.
            StoreVal = new LoadInst(NewGV, LI->getName()+".b", LI);
          } else {
            assert((isa<CastInst>(StoredVal) || isa<SelectInst>(StoredVal)) &&
                   "This is not a form that we understand!");
            StoreVal = StoredVal->getOperand(0);
            assert(isa<LoadInst>(StoreVal) && "Not a load of NewGV!");
          }
        }
        new StoreInst(StoreVal, NewGV, SI);
      } else {
        // Change the load into a load of bool then a select.
        LoadInst *LI = cast<LoadInst>(UI);
        LoadInst *NLI = new LoadInst(NewGV, LI->getName()+".b", LI);
        Value *NSI;
        if (IsOneZero)
          NSI = new ZExtInst(NLI, LI->getType(), "", LI);
        else
          NSI = SelectInst::Create(NLI, OtherVal, InitVal, "", LI);
        NSI->takeName(LI);
        LI->replaceAllUsesWith(NSI);
      }
      UI->eraseFromParent();
    }
  
    GV->eraseFromParent();
    return true;
  }
  
  
  /// ProcessInternalGlobal - Analyze the specified global variable and optimize
  /// it if possible.  If we make a change, return true.
  bool GlobalOpt::ProcessGlobal(GlobalVariable *GV,
                                Module::global_iterator &GVI) {
    if (!GV->hasLocalLinkage())
      return false;
  
    // Do more involved optimizations if the global is internal.
    GV->removeDeadConstantUsers();
  
    if (GV->use_empty()) {
      DEBUG(dbgs() << "GLOBAL DEAD: " << *GV);
      GV->eraseFromParent();
      ++NumDeleted;
      return true;
    }
  
    SmallPtrSet<const PHINode*, 16> PHIUsers;
    GlobalStatus GS;
  
    if (AnalyzeGlobal(GV, GS, PHIUsers))
      return false;
  
    if (!GS.isCompared && !GV->hasUnnamedAddr()) {
      GV->setUnnamedAddr(true);
      NumUnnamed++;
    }
  
    if (GV->isConstant() || !GV->hasInitializer())
      return false;
  
    return ProcessInternalGlobal(GV, GVI, PHIUsers, GS);
  }
  
  /// ProcessInternalGlobal - Analyze the specified global variable and optimize
  /// it if possible.  If we make a change, return true.
  bool GlobalOpt::ProcessInternalGlobal(GlobalVariable *GV,
                                        Module::global_iterator &GVI,
                                        const SmallPtrSet<const PHINode*, 16> &PHIUsers,
                                        const GlobalStatus &GS) {
    // If this is a first class global and has only one accessing function
    // and this function is main (which we know is not recursive we can make
    // this global a local variable) we replace the global with a local alloca
    // in this function.
    //
    // NOTE: It doesn't make sense to promote non single-value types since we
    // are just replacing static memory to stack memory.
    //
    // If the global is in different address space, don't bring it to stack.
    if (!GS.HasMultipleAccessingFunctions &&
        GS.AccessingFunction && !GS.HasNonInstructionUser &&
        GV->getType()->getElementType()->isSingleValueType() &&
        GS.AccessingFunction->getName() == "main" &&
        GS.AccessingFunction->hasExternalLinkage() &&
        GV->getType()->getAddressSpace() == 0) {
      DEBUG(dbgs() << "LOCALIZING GLOBAL: " << *GV);
      Instruction& FirstI = const_cast<Instruction&>(*GS.AccessingFunction
                                                     ->getEntryBlock().begin());
      const Type* ElemTy = GV->getType()->getElementType();
      // FIXME: Pass Global's alignment when globals have alignment
      AllocaInst* Alloca = new AllocaInst(ElemTy, NULL, GV->getName(), &FirstI);
      if (!isa<UndefValue>(GV->getInitializer()))
        new StoreInst(GV->getInitializer(), Alloca, &FirstI);
  
      GV->replaceAllUsesWith(Alloca);
      GV->eraseFromParent();
      ++NumLocalized;
      return true;
    }
  
    // If the global is never loaded (but may be stored to), it is dead.
    // Delete it now.
    if (!GS.isLoaded) {
      DEBUG(dbgs() << "GLOBAL NEVER LOADED: " << *GV);
  
      // Delete any stores we can find to the global.  We may not be able to
      // make it completely dead though.
      bool Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer());
  
      // If the global is dead now, delete it.
      if (GV->use_empty()) {
        GV->eraseFromParent();
        ++NumDeleted;
        Changed = true;
      }
      return Changed;
  
    } else if (GS.StoredType <= GlobalStatus::isInitializerStored) {
      DEBUG(dbgs() << "MARKING CONSTANT: " << *GV);
      GV->setConstant(true);
  
      // Clean up any obviously simplifiable users now.
      CleanupConstantGlobalUsers(GV, GV->getInitializer());
  
      // If the global is dead now, just nuke it.
      if (GV->use_empty()) {
        DEBUG(dbgs() << "   *** Marking constant allowed us to simplify "
              << "all users and delete global!\n");
        GV->eraseFromParent();
        ++NumDeleted;
      }
  
      ++NumMarked;
      return true;
    } else if (!GV->getInitializer()->getType()->isSingleValueType()) {
      if (TargetData *TD = getAnalysisIfAvailable<TargetData>())
        if (GlobalVariable *FirstNewGV = SRAGlobal(GV, *TD)) {
          GVI = FirstNewGV;  // Don't skip the newly produced globals!
          return true;
        }
    } else if (GS.StoredType == GlobalStatus::isStoredOnce) {
      // If the initial value for the global was an undef value, and if only
      // one other value was stored into it, we can just change the
      // initializer to be the stored value, then delete all stores to the
      // global.  This allows us to mark it constant.
      if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
        if (isa<UndefValue>(GV->getInitializer())) {
          // Change the initial value here.
          GV->setInitializer(SOVConstant);
  
          // Clean up any obviously simplifiable users now.
          CleanupConstantGlobalUsers(GV, GV->getInitializer());
  
          if (GV->use_empty()) {
            DEBUG(dbgs() << "   *** Substituting initializer allowed us to "
                  << "simplify all users and delete global!\n");
            GV->eraseFromParent();
            ++NumDeleted;
          } else {
            GVI = GV;
          }
          ++NumSubstitute;
          return true;
        }
  
      // Try to optimize globals based on the knowledge that only one value
      // (besides its initializer) is ever stored to the global.
      if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue, GVI,
                                   getAnalysisIfAvailable<TargetData>()))
        return true;
  
      // Otherwise, if the global was not a boolean, we can shrink it to be a
      // boolean.
      if (Constant *SOVConstant = dyn_cast<Constant>(GS.StoredOnceValue))
        if (TryToShrinkGlobalToBoolean(GV, SOVConstant)) {
          ++NumShrunkToBool;
          return true;
        }
    }
  
    return false;
  }
  
  /// ChangeCalleesToFastCall - Walk all of the direct calls of the specified
  /// function, changing them to FastCC.
  static void ChangeCalleesToFastCall(Function *F) {
    for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){
      CallSite User(cast<Instruction>(*UI));
      User.setCallingConv(CallingConv::Fast);
    }
  }
  
  static AttrListPtr StripNest(const AttrListPtr &Attrs) {
    for (unsigned i = 0, e = Attrs.getNumSlots(); i != e; ++i) {
      if ((Attrs.getSlot(i).Attrs & Attribute::Nest) == 0)
        continue;
  
      // There can be only one.
      return Attrs.removeAttr(Attrs.getSlot(i).Index, Attribute::Nest);
    }
  
    return Attrs;
  }
  
  static void RemoveNestAttribute(Function *F) {
    F->setAttributes(StripNest(F->getAttributes()));
    for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); UI != E;++UI){
      CallSite User(cast<Instruction>(*UI));
      User.setAttributes(StripNest(User.getAttributes()));
    }
  }
  
  bool GlobalOpt::OptimizeFunctions(Module &M) {
    bool Changed = false;
    // Optimize functions.
    for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) {
      Function *F = FI++;
      // Functions without names cannot be referenced outside this module.
      if (!F->hasName() && !F->isDeclaration())
        F->setLinkage(GlobalValue::InternalLinkage);
      F->removeDeadConstantUsers();
      if (F->use_empty() && (F->hasLocalLinkage() || F->hasLinkOnceLinkage())) {
        F->eraseFromParent();
        Changed = true;
        ++NumFnDeleted;
      } else if (F->hasLocalLinkage()) {
        if (F->getCallingConv() == CallingConv::C && !F->isVarArg() &&
            !F->hasAddressTaken()) {
          // If this function has C calling conventions, is not a varargs
          // function, and is only called directly, promote it to use the Fast
          // calling convention.
          F->setCallingConv(CallingConv::Fast);
          ChangeCalleesToFastCall(F);
          ++NumFastCallFns;
          Changed = true;
        }
  
        if (F->getAttributes().hasAttrSomewhere(Attribute::Nest) &&
            !F->hasAddressTaken()) {
          // The function is not used by a trampoline intrinsic, so it is safe
          // to remove the 'nest' attribute.
          RemoveNestAttribute(F);
          ++NumNestRemoved;
          Changed = true;
        }
      }
    }
    return Changed;
  }
  
  bool GlobalOpt::OptimizeGlobalVars(Module &M) {
    bool Changed = false;
    for (Module::global_iterator GVI = M.global_begin(), E = M.global_end();
         GVI != E; ) {
      GlobalVariable *GV = GVI++;
      // Global variables without names cannot be referenced outside this module.
      if (!GV->hasName() && !GV->isDeclaration())
        GV->setLinkage(GlobalValue::InternalLinkage);
      // Simplify the initializer.
      if (GV->hasInitializer())
        if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GV->getInitializer())) {
          TargetData *TD = getAnalysisIfAvailable<TargetData>();
          Constant *New = ConstantFoldConstantExpression(CE, TD);
          if (New && New != CE)
            GV->setInitializer(New);
        }
  
      Changed |= ProcessGlobal(GV, GVI);
    }
    return Changed;
  }
  
  /// FindGlobalCtors - Find the llvm.globalctors list, verifying that all
  /// initializers have an init priority of 65535.
  GlobalVariable *GlobalOpt::FindGlobalCtors(Module &M) {
    GlobalVariable *GV = M.getGlobalVariable("llvm.global_ctors");
    if (GV == 0) return 0;
    
    // Found it, verify it's an array of { int, void()* }.
    const ArrayType *ATy =dyn_cast<ArrayType>(GV->getType()->getElementType());
    if (!ATy) return 0;
    const StructType *STy = dyn_cast<StructType>(ATy->getElementType());
    if (!STy || STy->getNumElements() != 2 ||
        !STy->getElementType(0)->isIntegerTy(32)) return 0;
    const PointerType *PFTy = dyn_cast<PointerType>(STy->getElementType(1));
    if (!PFTy) return 0;
    const FunctionType *FTy = dyn_cast<FunctionType>(PFTy->getElementType());
    if (!FTy || !FTy->getReturnType()->isVoidTy() ||
        FTy->isVarArg() || FTy->getNumParams() != 0)
      return 0;
  
    // Verify that the initializer is simple enough for us to handle. We are
    // only allowed to optimize the initializer if it is unique.
    if (!GV->hasUniqueInitializer()) return 0;
    
    ConstantArray *CA = dyn_cast<ConstantArray>(GV->getInitializer());
    if (!CA) return 0;
    
    for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) {
      ConstantStruct *CS = dyn_cast<ConstantStruct>(*i);
      if (CS == 0) return 0;
      
      if (isa<ConstantPointerNull>(CS->getOperand(1)))
        continue;
  
      // Must have a function or null ptr.
      if (!isa<Function>(CS->getOperand(1)))
        return 0;
  
      // Init priority must be standard.
      ConstantInt *CI = dyn_cast<ConstantInt>(CS->getOperand(0));
      if (!CI || CI->getZExtValue() != 65535)
        return 0;
    }
  
    return GV;
  }
  
  /// ParseGlobalCtors - Given a llvm.global_ctors list that we can understand,
  /// return a list of the functions and null terminator as a vector.
  static std::vector<Function*> ParseGlobalCtors(GlobalVariable *GV) {
    ConstantArray *CA = cast<ConstantArray>(GV->getInitializer());
    std::vector<Function*> Result;
    Result.reserve(CA->getNumOperands());
    for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i) {
      ConstantStruct *CS = cast<ConstantStruct>(*i);
      Result.push_back(dyn_cast<Function>(CS->getOperand(1)));
    }
    return Result;
  }
  
  /// InstallGlobalCtors - Given a specified llvm.global_ctors list, install the
  /// specified array, returning the new global to use.
  static GlobalVariable *InstallGlobalCtors(GlobalVariable *GCL,
                                            const std::vector<Function*> &Ctors) {
    // If we made a change, reassemble the initializer list.
    std::vector<Constant*> CSVals;
    CSVals.push_back(ConstantInt::get(Type::getInt32Ty(GCL->getContext()),65535));
    CSVals.push_back(0);
  
    // Create the new init list.
    std::vector<Constant*> CAList;
    for (unsigned i = 0, e = Ctors.size(); i != e; ++i) {
      if (Ctors[i]) {
        CSVals[1] = Ctors[i];
      } else {
        const Type *FTy = FunctionType::get(Type::getVoidTy(GCL->getContext()),
                                            false);
        const PointerType *PFTy = PointerType::getUnqual(FTy);
        CSVals[1] = Constant::getNullValue(PFTy);
        CSVals[0] = ConstantInt::get(Type::getInt32Ty(GCL->getContext()),
                                     2147483647);
      }
      CAList.push_back(ConstantStruct::get(GCL->getContext(), CSVals, false));
    }
  
    // Create the array initializer.
    const Type *StructTy =
        cast<ArrayType>(GCL->getType()->getElementType())->getElementType();
    Constant *CA = ConstantArray::get(ArrayType::get(StructTy,
                                                     CAList.size()), CAList);
  
    // If we didn't change the number of elements, don't create a new GV.
    if (CA->getType() == GCL->getInitializer()->getType()) {
      GCL->setInitializer(CA);
      return GCL;
    }
  
    // Create the new global and insert it next to the existing list.
    GlobalVariable *NGV = new GlobalVariable(CA->getType(), GCL->isConstant(),
                                             GCL->getLinkage(), CA, "",
                                             GCL->isThreadLocal());
    GCL->getParent()->getGlobalList().insert(GCL, NGV);
    NGV->takeName(GCL);
  
    // Nuke the old list, replacing any uses with the new one.
    if (!GCL->use_empty()) {
      Constant *V = NGV;
      if (V->getType() != GCL->getType())
        V = ConstantExpr::getBitCast(V, GCL->getType());
      GCL->replaceAllUsesWith(V);
    }
    GCL->eraseFromParent();
  
    if (Ctors.size())
      return NGV;
    else
      return 0;
  }
  
  
  static Constant *getVal(DenseMap<Value*, Constant*> &ComputedValues, Value *V) {
    if (Constant *CV = dyn_cast<Constant>(V)) return CV;
    Constant *R = ComputedValues[V];
    assert(R && "Reference to an uncomputed value!");
    return R;
  }
  
  static inline bool 
  isSimpleEnoughValueToCommit(Constant *C,
                              SmallPtrSet<Constant*, 8> &SimpleConstants);
  
  
  /// isSimpleEnoughValueToCommit - Return true if the specified constant can be
  /// handled by the code generator.  We don't want to generate something like:
  ///   void *X = &X/42;
  /// because the code generator doesn't have a relocation that can handle that.
  ///
  /// This function should be called if C was not found (but just got inserted)
  /// in SimpleConstants to avoid having to rescan the same constants all the
  /// time.
  static bool isSimpleEnoughValueToCommitHelper(Constant *C,
                                     SmallPtrSet<Constant*, 8> &SimpleConstants) {
    // Simple integer, undef, constant aggregate zero, global addresses, etc are
    // all supported.
    if (C->getNumOperands() == 0 || isa<BlockAddress>(C) ||
        isa<GlobalValue>(C))
      return true;
    
    // Aggregate values are safe if all their elements are.
    if (isa<ConstantArray>(C) || isa<ConstantStruct>(C) ||
        isa<ConstantVector>(C)) {
      for (unsigned i = 0, e = C->getNumOperands(); i != e; ++i) {
        Constant *Op = cast<Constant>(C->getOperand(i));
        if (!isSimpleEnoughValueToCommit(Op, SimpleConstants))
          return false;
      }
      return true;
    }
    
    // We don't know exactly what relocations are allowed in constant expressions,
    // so we allow &global+constantoffset, which is safe and uniformly supported
    // across targets.
    ConstantExpr *CE = cast<ConstantExpr>(C);
    switch (CE->getOpcode()) {
    case Instruction::BitCast:
    case Instruction::IntToPtr:
    case Instruction::PtrToInt:
      // These casts are always fine if the casted value is.
      return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants);
        
    // GEP is fine if it is simple + constant offset.
    case Instruction::GetElementPtr:
      for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i)
        if (!isa<ConstantInt>(CE->getOperand(i)))
          return false;
      return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants);
        
    case Instruction::Add:
      // We allow simple+cst.
      if (!isa<ConstantInt>(CE->getOperand(1)))
        return false;
      return isSimpleEnoughValueToCommit(CE->getOperand(0), SimpleConstants);
    }
    return false;
  }
  
  static inline bool 
  isSimpleEnoughValueToCommit(Constant *C,
                              SmallPtrSet<Constant*, 8> &SimpleConstants) {
    // If we already checked this constant, we win.
    if (!SimpleConstants.insert(C)) return true;
    // Check the constant.
    return isSimpleEnoughValueToCommitHelper(C, SimpleConstants);
  }
  
  
  /// isSimpleEnoughPointerToCommit - Return true if this constant is simple
  /// enough for us to understand.  In particular, if it is a cast to anything
  /// other than from one pointer type to another pointer type, we punt.
  /// We basically just support direct accesses to globals and GEP's of
  /// globals.  This should be kept up to date with CommitValueTo.
  static bool isSimpleEnoughPointerToCommit(Constant *C) {
    // Conservatively, avoid aggregate types. This is because we don't
    // want to worry about them partially overlapping other stores.
    if (!cast<PointerType>(C->getType())->getElementType()->isSingleValueType())
      return false;
  
    if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C))
      // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
      // external globals.
      return GV->hasUniqueInitializer();
  
    if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
      // Handle a constantexpr gep.
      if (CE->getOpcode() == Instruction::GetElementPtr &&
          isa<GlobalVariable>(CE->getOperand(0)) &&
          cast<GEPOperator>(CE)->isInBounds()) {
        GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
        // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
        // external globals.
        if (!GV->hasUniqueInitializer())
          return false;
  
        // The first index must be zero.
        ConstantInt *CI = dyn_cast<ConstantInt>(*llvm::next(CE->op_begin()));
        if (!CI || !CI->isZero()) return false;
  
        // The remaining indices must be compile-time known integers within the
        // notional bounds of the corresponding static array types.
        if (!CE->isGEPWithNoNotionalOverIndexing())
          return false;
  
        return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
      
      // A constantexpr bitcast from a pointer to another pointer is a no-op,
      // and we know how to evaluate it by moving the bitcast from the pointer
      // operand to the value operand.
      } else if (CE->getOpcode() == Instruction::BitCast &&
                 isa<GlobalVariable>(CE->getOperand(0))) {
        // Do not allow weak/*_odr/linkonce/dllimport/dllexport linkage or
        // external globals.
        return cast<GlobalVariable>(CE->getOperand(0))->hasUniqueInitializer();
      }
    }
    
    return false;
  }
  
  /// EvaluateStoreInto - Evaluate a piece of a constantexpr store into a global
  /// initializer.  This returns 'Init' modified to reflect 'Val' stored into it.
  /// At this point, the GEP operands of Addr [0, OpNo) have been stepped into.
  static Constant *EvaluateStoreInto(Constant *Init, Constant *Val,
                                     ConstantExpr *Addr, unsigned OpNo) {
    // Base case of the recursion.
    if (OpNo == Addr->getNumOperands()) {
      assert(Val->getType() == Init->getType() && "Type mismatch!");
      return Val;
    }
  
    std::vector<Constant*> Elts;
    if (const StructType *STy = dyn_cast<StructType>(Init->getType())) {
  
      // Break up the constant into its elements.
      if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Init)) {
        for (User::op_iterator i = CS->op_begin(), e = CS->op_end(); i != e; ++i)
          Elts.push_back(cast<Constant>(*i));
      } else if (isa<ConstantAggregateZero>(Init)) {
        for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
          Elts.push_back(Constant::getNullValue(STy->getElementType(i)));
      } else if (isa<UndefValue>(Init)) {
        for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
          Elts.push_back(UndefValue::get(STy->getElementType(i)));
      } else {
        llvm_unreachable("This code is out of sync with "
               " ConstantFoldLoadThroughGEPConstantExpr");
      }
  
      // Replace the element that we are supposed to.
      ConstantInt *CU = cast<ConstantInt>(Addr->getOperand(OpNo));
      unsigned Idx = CU->getZExtValue();
      assert(Idx < STy->getNumElements() && "Struct index out of range!");
      Elts[Idx] = EvaluateStoreInto(Elts[Idx], Val, Addr, OpNo+1);
  
      // Return the modified struct.
      return ConstantStruct::get(Init->getContext(), &Elts[0], Elts.size(),
                                 STy->isPacked());
    } else {
      ConstantInt *CI = cast<ConstantInt>(Addr->getOperand(OpNo));
      const SequentialType *InitTy = cast<SequentialType>(Init->getType());
  
      uint64_t NumElts;
      if (const ArrayType *ATy = dyn_cast<ArrayType>(InitTy))
        NumElts = ATy->getNumElements();
      else
        NumElts = cast<VectorType>(InitTy)->getNumElements();
  
  
      // Break up the array into elements.
      if (ConstantArray *CA = dyn_cast<ConstantArray>(Init)) {
        for (User::op_iterator i = CA->op_begin(), e = CA->op_end(); i != e; ++i)
          Elts.push_back(cast<Constant>(*i));
      } else if (ConstantVector *CV = dyn_cast<ConstantVector>(Init)) {
        for (User::op_iterator i = CV->op_begin(), e = CV->op_end(); i != e; ++i)
          Elts.push_back(cast<Constant>(*i));
      } else if (isa<ConstantAggregateZero>(Init)) {
        Elts.assign(NumElts, Constant::getNullValue(InitTy->getElementType()));
      } else {
        assert(isa<UndefValue>(Init) && "This code is out of sync with "
               " ConstantFoldLoadThroughGEPConstantExpr");
        Elts.assign(NumElts, UndefValue::get(InitTy->getElementType()));
      }
  
      assert(CI->getZExtValue() < NumElts);
      Elts[CI->getZExtValue()] =
        EvaluateStoreInto(Elts[CI->getZExtValue()], Val, Addr, OpNo+1);
  
      if (Init->getType()->isArrayTy())
        return ConstantArray::get(cast<ArrayType>(InitTy), Elts);
      return ConstantVector::get(Elts);
    }
  }
  
  /// CommitValueTo - We have decided that Addr (which satisfies the predicate
  /// isSimpleEnoughPointerToCommit) should get Val as its value.  Make it happen.
  static void CommitValueTo(Constant *Val, Constant *Addr) {
    if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Addr)) {
      assert(GV->hasInitializer());
      GV->setInitializer(Val);
      return;
    }
  
    ConstantExpr *CE = cast<ConstantExpr>(Addr);
    GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
    GV->setInitializer(EvaluateStoreInto(GV->getInitializer(), Val, CE, 2));
  }
  
  /// ComputeLoadResult - Return the value that would be computed by a load from
  /// P after the stores reflected by 'memory' have been performed.  If we can't
  /// decide, return null.
  static Constant *ComputeLoadResult(Constant *P,
                                  const DenseMap<Constant*, Constant*> &Memory) {
    // If this memory location has been recently stored, use the stored value: it
    // is the most up-to-date.
    DenseMap<Constant*, Constant*>::const_iterator I = Memory.find(P);
    if (I != Memory.end()) return I->second;
  
    // Access it.
    if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) {
      if (GV->hasDefinitiveInitializer())
        return GV->getInitializer();
      return 0;
    }
  
    // Handle a constantexpr getelementptr.
    if (ConstantExpr *CE = dyn_cast<ConstantExpr>(P))
      if (CE->getOpcode() == Instruction::GetElementPtr &&
          isa<GlobalVariable>(CE->getOperand(0))) {
        GlobalVariable *GV = cast<GlobalVariable>(CE->getOperand(0));
        if (GV->hasDefinitiveInitializer())
          return ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE);
      }
  
    return 0;  // don't know how to evaluate.
  }
  
  /// EvaluateFunction - Evaluate a call to function F, returning true if
  /// successful, false if we can't evaluate it.  ActualArgs contains the formal
  /// arguments for the function.
  static bool EvaluateFunction(Function *F, Constant *&RetVal,
                               const SmallVectorImpl<Constant*> &ActualArgs,
                               std::vector<Function*> &CallStack,
                               DenseMap<Constant*, Constant*> &MutatedMemory,
                               std::vector<GlobalVariable*> &AllocaTmps,
                               SmallPtrSet<Constant*, 8> &SimpleConstants,
                               const TargetData *TD) {
    // Check to see if this function is already executing (recursion).  If so,
    // bail out.  TODO: we might want to accept limited recursion.
    if (std::find(CallStack.begin(), CallStack.end(), F) != CallStack.end())
      return false;
  
    CallStack.push_back(F);
  
    /// Values - As we compute SSA register values, we store their contents here.
    DenseMap<Value*, Constant*> Values;
  
    // Initialize arguments to the incoming values specified.
    unsigned ArgNo = 0;
    for (Function::arg_iterator AI = F->arg_begin(), E = F->arg_end(); AI != E;
         ++AI, ++ArgNo)
      Values[AI] = ActualArgs[ArgNo];
  
    /// ExecutedBlocks - We only handle non-looping, non-recursive code.  As such,
    /// we can only evaluate any one basic block at most once.  This set keeps
    /// track of what we have executed so we can detect recursive cases etc.
    SmallPtrSet<BasicBlock*, 32> ExecutedBlocks;
  
    // CurInst - The current instruction we're evaluating.
    BasicBlock::iterator CurInst = F->begin()->begin();
  
    // This is the main evaluation loop.
    while (1) {
      Constant *InstResult = 0;
  
      if (StoreInst *SI = dyn_cast<StoreInst>(CurInst)) {
        if (SI->isVolatile()) return false;  // no volatile accesses.
        Constant *Ptr = getVal(Values, SI->getOperand(1));
        if (!isSimpleEnoughPointerToCommit(Ptr))
          // If this is too complex for us to commit, reject it.
          return false;
        
        Constant *Val = getVal(Values, SI->getOperand(0));
  
        // If this might be too difficult for the backend to handle (e.g. the addr
        // of one global variable divided by another) then we can't commit it.
        if (!isSimpleEnoughValueToCommit(Val, SimpleConstants))
          return false;
          
        if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
          if (CE->getOpcode() == Instruction::BitCast) {
            // If we're evaluating a store through a bitcast, then we need
            // to pull the bitcast off the pointer type and push it onto the
            // stored value.
            Ptr = CE->getOperand(0);
            
            const Type *NewTy=cast<PointerType>(Ptr->getType())->getElementType();
            
            // In order to push the bitcast onto the stored value, a bitcast
            // from NewTy to Val's type must be legal.  If it's not, we can try
            // introspecting NewTy to find a legal conversion.
            while (!Val->getType()->canLosslesslyBitCastTo(NewTy)) {
              // If NewTy is a struct, we can convert the pointer to the struct
              // into a pointer to its first member.
              // FIXME: This could be extended to support arrays as well.
              if (const StructType *STy = dyn_cast<StructType>(NewTy)) {
                NewTy = STy->getTypeAtIndex(0U);
  
                const IntegerType *IdxTy =IntegerType::get(NewTy->getContext(), 32);
                Constant *IdxZero = ConstantInt::get(IdxTy, 0, false);
                Constant * const IdxList[] = {IdxZero, IdxZero};
  
                Ptr = ConstantExpr::getGetElementPtr(Ptr, IdxList, 2);
              
              // If we can't improve the situation by introspecting NewTy,
              // we have to give up.
              } else {
                return 0;
              }
            }
            
            // If we found compatible types, go ahead and push the bitcast
            // onto the stored value.
            Val = ConstantExpr::getBitCast(Val, NewTy);
          }
            
        MutatedMemory[Ptr] = Val;
      } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(CurInst)) {
        InstResult = ConstantExpr::get(BO->getOpcode(),
                                       getVal(Values, BO->getOperand(0)),
                                       getVal(Values, BO->getOperand(1)));
      } else if (CmpInst *CI = dyn_cast<CmpInst>(CurInst)) {
        InstResult = ConstantExpr::getCompare(CI->getPredicate(),
                                              getVal(Values, CI->getOperand(0)),
                                              getVal(Values, CI->getOperand(1)));
      } else if (CastInst *CI = dyn_cast<CastInst>(CurInst)) {
        InstResult = ConstantExpr::getCast(CI->getOpcode(),
                                           getVal(Values, CI->getOperand(0)),
                                           CI->getType());
      } else if (SelectInst *SI = dyn_cast<SelectInst>(CurInst)) {
        InstResult = ConstantExpr::getSelect(getVal(Values, SI->getOperand(0)),
                                             getVal(Values, SI->getOperand(1)),
                                             getVal(Values, SI->getOperand(2)));
      } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurInst)) {
        Constant *P = getVal(Values, GEP->getOperand(0));
        SmallVector<Constant*, 8> GEPOps;
        for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end();
             i != e; ++i)
          GEPOps.push_back(getVal(Values, *i));
        InstResult = cast<GEPOperator>(GEP)->isInBounds() ?
            ConstantExpr::getInBoundsGetElementPtr(P, &GEPOps[0], GEPOps.size()) :
            ConstantExpr::getGetElementPtr(P, &GEPOps[0], GEPOps.size());
      } else if (LoadInst *LI = dyn_cast<LoadInst>(CurInst)) {
        if (LI->isVolatile()) return false;  // no volatile accesses.
        InstResult = ComputeLoadResult(getVal(Values, LI->getOperand(0)),
                                       MutatedMemory);
        if (InstResult == 0) return false; // Could not evaluate load.
      } else if (AllocaInst *AI = dyn_cast<AllocaInst>(CurInst)) {
        if (AI->isArrayAllocation()) return false;  // Cannot handle array allocs.
        const Type *Ty = AI->getType()->getElementType();
        AllocaTmps.push_back(new GlobalVariable(Ty, false,
                                                GlobalValue::InternalLinkage,
                                                UndefValue::get(Ty),
                                                AI->getName()));
        InstResult = AllocaTmps.back();
      } else if (CallInst *CI = dyn_cast<CallInst>(CurInst)) {
  
        // Debug info can safely be ignored here.
        if (isa<DbgInfoIntrinsic>(CI)) {
          ++CurInst;
          continue;
        }
  
        // Cannot handle inline asm.
        if (isa<InlineAsm>(CI->getCalledValue())) return false;
  
        // Resolve function pointers.
        Function *Callee = dyn_cast<Function>(getVal(Values,
                                                     CI->getCalledValue()));
        if (!Callee) return false;  // Cannot resolve.
  
        SmallVector<Constant*, 8> Formals;
        CallSite CS(CI);
        for (User::op_iterator i = CS.arg_begin(), e = CS.arg_end();
             i != e; ++i)
          Formals.push_back(getVal(Values, *i));
  
        if (Callee->isDeclaration()) {
          // If this is a function we can constant fold, do it.
          if (Constant *C = ConstantFoldCall(Callee, Formals.data(),
                                             Formals.size())) {
            InstResult = C;
          } else {
            return false;
          }
        } else {
          if (Callee->getFunctionType()->isVarArg())
            return false;
  
          Constant *RetVal;
          // Execute the call, if successful, use the return value.
          if (!EvaluateFunction(Callee, RetVal, Formals, CallStack,
                                MutatedMemory, AllocaTmps, SimpleConstants, TD))
            return false;
          InstResult = RetVal;
        }
      } else if (isa<TerminatorInst>(CurInst)) {
        BasicBlock *NewBB = 0;
        if (BranchInst *BI = dyn_cast<BranchInst>(CurInst)) {
          if (BI->isUnconditional()) {
            NewBB = BI->getSuccessor(0);
          } else {
            ConstantInt *Cond =
              dyn_cast<ConstantInt>(getVal(Values, BI->getCondition()));
            if (!Cond) return false;  // Cannot determine.
  
            NewBB = BI->getSuccessor(!Cond->getZExtValue());
          }
        } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurInst)) {
          ConstantInt *Val =
            dyn_cast<ConstantInt>(getVal(Values, SI->getCondition()));
          if (!Val) return false;  // Cannot determine.
          NewBB = SI->getSuccessor(SI->findCaseValue(Val));
        } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(CurInst)) {
          Value *Val = getVal(Values, IBI->getAddress())->stripPointerCasts();
          if (BlockAddress *BA = dyn_cast<BlockAddress>(Val))
            NewBB = BA->getBasicBlock();
          else
            return false;  // Cannot determine.
        } else if (ReturnInst *RI = dyn_cast<ReturnInst>(CurInst)) {
          if (RI->getNumOperands())
            RetVal = getVal(Values, RI->getOperand(0));
  
          CallStack.pop_back();  // return from fn.
          return true;  // We succeeded at evaluating this ctor!
        } else {
          // invoke, unwind, unreachable.
          return false;  // Cannot handle this terminator.
        }
  
        // Okay, we succeeded in evaluating this control flow.  See if we have
        // executed the new block before.  If so, we have a looping function,
        // which we cannot evaluate in reasonable time.
        if (!ExecutedBlocks.insert(NewBB))
          return false;  // looped!
  
        // Okay, we have never been in this block before.  Check to see if there
        // are any PHI nodes.  If so, evaluate them with information about where
        // we came from.
        BasicBlock *OldBB = CurInst->getParent();
        CurInst = NewBB->begin();
        PHINode *PN;
        for (; (PN = dyn_cast<PHINode>(CurInst)); ++CurInst)
          Values[PN] = getVal(Values, PN->getIncomingValueForBlock(OldBB));
  
        // Do NOT increment CurInst.  We know that the terminator had no value.
        continue;
      } else {
        // Did not know how to evaluate this!
        return false;
      }
  
      if (!CurInst->use_empty()) {
        if (ConstantExpr *CE = dyn_cast<ConstantExpr>(InstResult))
          InstResult = ConstantFoldConstantExpression(CE, TD);
        
        Values[CurInst] = InstResult;
      }
  
      // Advance program counter.
      ++CurInst;
    }
  }
  
  /// EvaluateStaticConstructor - Evaluate static constructors in the function, if
  /// we can.  Return true if we can, false otherwise.
  static bool EvaluateStaticConstructor(Function *F, const TargetData *TD) {
    /// MutatedMemory - For each store we execute, we update this map.  Loads
    /// check this to get the most up-to-date value.  If evaluation is successful,
    /// this state is committed to the process.
    DenseMap<Constant*, Constant*> MutatedMemory;
  
    /// AllocaTmps - To 'execute' an alloca, we create a temporary global variable
    /// to represent its body.  This vector is needed so we can delete the
    /// temporary globals when we are done.
    std::vector<GlobalVariable*> AllocaTmps;
  
    /// CallStack - This is used to detect recursion.  In pathological situations
    /// we could hit exponential behavior, but at least there is nothing
    /// unbounded.
    std::vector<Function*> CallStack;
  
    /// SimpleConstants - These are constants we have checked and know to be
    /// simple enough to live in a static initializer of a global.
    SmallPtrSet<Constant*, 8> SimpleConstants;
    
    // Call the function.
    Constant *RetValDummy;
    bool EvalSuccess = EvaluateFunction(F, RetValDummy,
                                        SmallVector<Constant*, 0>(), CallStack,
                                        MutatedMemory, AllocaTmps,
                                        SimpleConstants, TD);
    
    if (EvalSuccess) {
      // We succeeded at evaluation: commit the result.
      DEBUG(dbgs() << "FULLY EVALUATED GLOBAL CTOR FUNCTION '"
            << F->getName() << "' to " << MutatedMemory.size()
            << " stores.\n");
      for (DenseMap<Constant*, Constant*>::iterator I = MutatedMemory.begin(),
           E = MutatedMemory.end(); I != E; ++I)
        CommitValueTo(I->second, I->first);
    }
  
    // At this point, we are done interpreting.  If we created any 'alloca'
    // temporaries, release them now.
    while (!AllocaTmps.empty()) {
      GlobalVariable *Tmp = AllocaTmps.back();
      AllocaTmps.pop_back();
  
      // If there are still users of the alloca, the program is doing something
      // silly, e.g. storing the address of the alloca somewhere and using it
      // later.  Since this is undefined, we'll just make it be null.
      if (!Tmp->use_empty())
        Tmp->replaceAllUsesWith(Constant::getNullValue(Tmp->getType()));
      delete Tmp;
    }
  
    return EvalSuccess;
  }
  
  
  
  /// OptimizeGlobalCtorsList - Simplify and evaluation global ctors if possible.
  /// Return true if anything changed.
  bool GlobalOpt::OptimizeGlobalCtorsList(GlobalVariable *&GCL) {
    std::vector<Function*> Ctors = ParseGlobalCtors(GCL);
    bool MadeChange = false;
    if (Ctors.empty()) return false;
  
    const TargetData *TD = getAnalysisIfAvailable<TargetData>();
    // Loop over global ctors, optimizing them when we can.
    for (unsigned i = 0; i != Ctors.size(); ++i) {
      Function *F = Ctors[i];
      // Found a null terminator in the middle of the list, prune off the rest of
      // the list.
      if (F == 0) {
        if (i != Ctors.size()-1) {
          Ctors.resize(i+1);
          MadeChange = true;
        }
        break;
      }
  
      // We cannot simplify external ctor functions.
      if (F->empty()) continue;
  
      // If we can evaluate the ctor at compile time, do.
      if (EvaluateStaticConstructor(F, TD)) {
        Ctors.erase(Ctors.begin()+i);
        MadeChange = true;
        --i;
        ++NumCtorsEvaluated;
        continue;
      }
    }
  
    if (!MadeChange) return false;
  
    GCL = InstallGlobalCtors(GCL, Ctors);
    return true;
  }
  
  bool GlobalOpt::OptimizeGlobalAliases(Module &M) {
    bool Changed = false;
  
    for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end();
         I != E;) {
      Module::alias_iterator J = I++;
      // Aliases without names cannot be referenced outside this module.
      if (!J->hasName() && !J->isDeclaration())
        J->setLinkage(GlobalValue::InternalLinkage);
      // If the aliasee may change at link time, nothing can be done - bail out.
      if (J->mayBeOverridden())
        continue;
  
      Constant *Aliasee = J->getAliasee();
      GlobalValue *Target = cast<GlobalValue>(Aliasee->stripPointerCasts());
      Target->removeDeadConstantUsers();
      bool hasOneUse = Target->hasOneUse() && Aliasee->hasOneUse();
  
      // Make all users of the alias use the aliasee instead.
      if (!J->use_empty()) {
        J->replaceAllUsesWith(Aliasee);
        ++NumAliasesResolved;
        Changed = true;
      }
  
      // If the alias is externally visible, we may still be able to simplify it.
      if (!J->hasLocalLinkage()) {
        // If the aliasee has internal linkage, give it the name and linkage
        // of the alias, and delete the alias.  This turns:
        //   define internal ... @f(...)
        //   @a = alias ... @f
        // into:
        //   define ... @a(...)
        if (!Target->hasLocalLinkage())
          continue;
  
        // Do not perform the transform if multiple aliases potentially target the
        // aliasee. This check also ensures that it is safe to replace the section
        // and other attributes of the aliasee with those of the alias.
        if (!hasOneUse)
          continue;
  
        // Give the aliasee the name, linkage and other attributes of the alias.
        Target->takeName(J);
        Target->setLinkage(J->getLinkage());
        Target->GlobalValue::copyAttributesFrom(J);
      }
  
      // Delete the alias.
      M.getAliasList().erase(J);
      ++NumAliasesRemoved;
      Changed = true;
    }
  
    return Changed;
  }
  
  bool GlobalOpt::runOnModule(Module &M) {
    bool Changed = false;
  
    // Try to find the llvm.globalctors list.
    GlobalVariable *GlobalCtors = FindGlobalCtors(M);
  
    bool LocalChange = true;
    while (LocalChange) {
      LocalChange = false;
  
      // Delete functions that are trivially dead, ccc -> fastcc
      LocalChange |= OptimizeFunctions(M);
  
      // Optimize global_ctors list.
      if (GlobalCtors)
        LocalChange |= OptimizeGlobalCtorsList(GlobalCtors);
  
      // Optimize non-address-taken globals.
      LocalChange |= OptimizeGlobalVars(M);
  
      // Resolve aliases, when possible.
      LocalChange |= OptimizeGlobalAliases(M);
      Changed |= LocalChange;
    }
  
    // TODO: Move all global ctors functions to the end of the module for code
    // layout.
  
    return Changed;
  }
  