Import LLVM, at r72732.

1 files changed, 1820 insertions, 0 deletions

diff --git a/lib/Transforms/Scalar/ScalarReplAggregates.cpp b/lib/Transforms/Scalar/ScalarReplAggregates.cpp
new file mode 100644
index 0000000..9935f12
--- /dev/null
+++ b/lib/Transforms/Scalar/ScalarReplAggregates.cpp
@@ -0,0 +1,1820 @@
+//===- ScalarReplAggregates.cpp - Scalar Replacement of Aggregates --------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This transformation implements the well known scalar replacement of
+// aggregates transformation.  This xform breaks up alloca instructions of
+// aggregate type (structure or array) into individual alloca instructions for
+// each member (if possible).  Then, if possible, it transforms the individual
+// alloca instructions into nice clean scalar SSA form.
+//
+// This combines a simple SRoA algorithm with the Mem2Reg algorithm because
+// often interact, especially for C++ programs.  As such, iterating between
+// SRoA, then Mem2Reg until we run out of things to promote works well.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "scalarrepl"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Constants.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/Function.h"
+#include "llvm/GlobalVariable.h"
+#include "llvm/Instructions.h"
+#include "llvm/IntrinsicInst.h"
+#include "llvm/Pass.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Target/TargetData.h"
+#include "llvm/Transforms/Utils/PromoteMemToReg.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/GetElementPtrTypeIterator.h"
+#include "llvm/Support/IRBuilder.h"
+#include "llvm/Support/MathExtras.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/StringExtras.h"
+using namespace llvm;
+
+STATISTIC(NumReplaced,  "Number of allocas broken up");
+STATISTIC(NumPromoted,  "Number of allocas promoted");
+STATISTIC(NumConverted, "Number of aggregates converted to scalar");
+STATISTIC(NumGlobals,   "Number of allocas copied from constant global");
+
+namespace {
+  struct VISIBILITY_HIDDEN SROA : public FunctionPass {
+    static char ID; // Pass identification, replacement for typeid
+    explicit SROA(signed T = -1) : FunctionPass(&ID) {
+      if (T == -1)
+        SRThreshold = 128;
+      else
+        SRThreshold = T;
+    }
+
+    bool runOnFunction(Function &F);
+
+    bool performScalarRepl(Function &F);
+    bool performPromotion(Function &F);
+
+    // getAnalysisUsage - This pass does not require any passes, but we know it
+    // will not alter the CFG, so say so.
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.addRequired<DominatorTree>();
+      AU.addRequired<DominanceFrontier>();
+      AU.addRequired<TargetData>();
+      AU.setPreservesCFG();
+    }
+
+  private:
+    TargetData *TD;
+    
+    /// AllocaInfo - When analyzing uses of an alloca instruction, this captures
+    /// information about the uses.  All these fields are initialized to false
+    /// and set to true when something is learned.
+    struct AllocaInfo {
+      /// isUnsafe - This is set to true if the alloca cannot be SROA'd.
+      bool isUnsafe : 1;
+      
+      /// needsCleanup - This is set to true if there is some use of the alloca
+      /// that requires cleanup.
+      bool needsCleanup : 1;
+      
+      /// isMemCpySrc - This is true if this aggregate is memcpy'd from.
+      bool isMemCpySrc : 1;
+
+      /// isMemCpyDst - This is true if this aggregate is memcpy'd into.
+      bool isMemCpyDst : 1;
+
+      AllocaInfo()
+        : isUnsafe(false), needsCleanup(false), 
+          isMemCpySrc(false), isMemCpyDst(false) {}
+    };
+    
+    unsigned SRThreshold;
+
+    void MarkUnsafe(AllocaInfo &I) { I.isUnsafe = true; }
+
+    int isSafeAllocaToScalarRepl(AllocationInst *AI);
+
+    void isSafeUseOfAllocation(Instruction *User, AllocationInst *AI,
+                               AllocaInfo &Info);
+    void isSafeElementUse(Value *Ptr, bool isFirstElt, AllocationInst *AI,
+                         AllocaInfo &Info);
+    void isSafeMemIntrinsicOnAllocation(MemIntrinsic *MI, AllocationInst *AI,
+                                        unsigned OpNo, AllocaInfo &Info);
+    void isSafeUseOfBitCastedAllocation(BitCastInst *User, AllocationInst *AI,
+                                        AllocaInfo &Info);
+    
+    void DoScalarReplacement(AllocationInst *AI, 
+                             std::vector<AllocationInst*> &WorkList);
+    void CleanupGEP(GetElementPtrInst *GEP);
+    void CleanupAllocaUsers(AllocationInst *AI);
+    AllocaInst *AddNewAlloca(Function &F, const Type *Ty, AllocationInst *Base);
+    
+    void RewriteBitCastUserOfAlloca(Instruction *BCInst, AllocationInst *AI,
+                                    SmallVector<AllocaInst*, 32> &NewElts);
+    
+    void RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *BCInst,
+                                      AllocationInst *AI,
+                                      SmallVector<AllocaInst*, 32> &NewElts);
+    void RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocationInst *AI,
+                                       SmallVector<AllocaInst*, 32> &NewElts);
+    void RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocationInst *AI,
+                                      SmallVector<AllocaInst*, 32> &NewElts);
+    
+    bool CanConvertToScalar(Value *V, bool &IsNotTrivial, const Type *&VecTy,
+                            bool &SawVec, uint64_t Offset, unsigned AllocaSize);
+    void ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset);
+    Value *ConvertScalar_ExtractValue(Value *NV, const Type *ToType,
+                                     uint64_t Offset, IRBuilder<> &Builder);
+    Value *ConvertScalar_InsertValue(Value *StoredVal, Value *ExistingVal,
+                                     uint64_t Offset, IRBuilder<> &Builder);
+    static Instruction *isOnlyCopiedFromConstantGlobal(AllocationInst *AI);
+  };
+}
+
+char SROA::ID = 0;
+static RegisterPass<SROA> X("scalarrepl", "Scalar Replacement of Aggregates");
+
+// Public interface to the ScalarReplAggregates pass
+FunctionPass *llvm::createScalarReplAggregatesPass(signed int Threshold) { 
+  return new SROA(Threshold);
+}
+
+
+bool SROA::runOnFunction(Function &F) {
+  TD = &getAnalysis<TargetData>();
+  
+  bool Changed = performPromotion(F);
+  while (1) {
+    bool LocalChange = performScalarRepl(F);
+    if (!LocalChange) break;   // No need to repromote if no scalarrepl
+    Changed = true;
+    LocalChange = performPromotion(F);
+    if (!LocalChange) break;   // No need to re-scalarrepl if no promotion
+  }
+
+  return Changed;
+}
+
+
+bool SROA::performPromotion(Function &F) {
+  std::vector<AllocaInst*> Allocas;
+  DominatorTree         &DT = getAnalysis<DominatorTree>();
+  DominanceFrontier &DF = getAnalysis<DominanceFrontier>();
+
+  BasicBlock &BB = F.getEntryBlock();  // Get the entry node for the function
+
+  bool Changed = false;
+
+  while (1) {
+    Allocas.clear();
+
+    // Find allocas that are safe to promote, by looking at all instructions in
+    // the entry node
+    for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
+      if (AllocaInst *AI = dyn_cast<AllocaInst>(I))       // Is it an alloca?
+        if (isAllocaPromotable(AI))
+          Allocas.push_back(AI);
+
+    if (Allocas.empty()) break;
+
+    PromoteMemToReg(Allocas, DT, DF);
+    NumPromoted += Allocas.size();
+    Changed = true;
+  }
+
+  return Changed;
+}
+
+/// getNumSAElements - Return the number of elements in the specific struct or
+/// array.
+static uint64_t getNumSAElements(const Type *T) {
+  if (const StructType *ST = dyn_cast<StructType>(T))
+    return ST->getNumElements();
+  return cast<ArrayType>(T)->getNumElements();
+}
+
+// performScalarRepl - This algorithm is a simple worklist driven algorithm,
+// which runs on all of the malloc/alloca instructions in the function, removing
+// them if they are only used by getelementptr instructions.
+//
+bool SROA::performScalarRepl(Function &F) {
+  std::vector<AllocationInst*> WorkList;
+
+  // Scan the entry basic block, adding any alloca's and mallocs to the worklist
+  BasicBlock &BB = F.getEntryBlock();
+  for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I)
+    if (AllocationInst *A = dyn_cast<AllocationInst>(I))
+      WorkList.push_back(A);
+
+  // Process the worklist
+  bool Changed = false;
+  while (!WorkList.empty()) {
+    AllocationInst *AI = WorkList.back();
+    WorkList.pop_back();
+    
+    // Handle dead allocas trivially.  These can be formed by SROA'ing arrays
+    // with unused elements.
+    if (AI->use_empty()) {
+      AI->eraseFromParent();
+      continue;
+    }
+
+    // If this alloca is impossible for us to promote, reject it early.
+    if (AI->isArrayAllocation() || !AI->getAllocatedType()->isSized())
+      continue;
+    
+    // Check to see if this allocation is only modified by a memcpy/memmove from
+    // a constant global.  If this is the case, we can change all users to use
+    // the constant global instead.  This is commonly produced by the CFE by
+    // constructs like "void foo() { int A[] = {1,2,3,4,5,6,7,8,9...}; }" if 'A'
+    // is only subsequently read.
+    if (Instruction *TheCopy = isOnlyCopiedFromConstantGlobal(AI)) {
+      DOUT << "Found alloca equal to global: " << *AI;
+      DOUT << "  memcpy = " << *TheCopy;
+      Constant *TheSrc = cast<Constant>(TheCopy->getOperand(2));
+      AI->replaceAllUsesWith(ConstantExpr::getBitCast(TheSrc, AI->getType()));
+      TheCopy->eraseFromParent();  // Don't mutate the global.
+      AI->eraseFromParent();
+      ++NumGlobals;
+      Changed = true;
+      continue;
+    }
+    
+    // Check to see if we can perform the core SROA transformation.  We cannot
+    // transform the allocation instruction if it is an array allocation
+    // (allocations OF arrays are ok though), and an allocation of a scalar
+    // value cannot be decomposed at all.
+    uint64_t AllocaSize = TD->getTypeAllocSize(AI->getAllocatedType());
+
+    // Do not promote any struct whose size is too big.
+    if (AllocaSize > SRThreshold) continue;
+        
+    if ((isa<StructType>(AI->getAllocatedType()) ||
+         isa<ArrayType>(AI->getAllocatedType())) &&
+        // Do not promote any struct into more than "32" separate vars.
+        getNumSAElements(AI->getAllocatedType()) <= SRThreshold/4) {
+      // Check that all of the users of the allocation are capable of being
+      // transformed.
+      switch (isSafeAllocaToScalarRepl(AI)) {
+      default: assert(0 && "Unexpected value!");
+      case 0:  // Not safe to scalar replace.
+        break;
+      case 1:  // Safe, but requires cleanup/canonicalizations first
+        CleanupAllocaUsers(AI);
+        // FALL THROUGH.
+      case 3:  // Safe to scalar replace.
+        DoScalarReplacement(AI, WorkList);
+        Changed = true;
+        continue;
+      }
+    }
+
+    // If we can turn this aggregate value (potentially with casts) into a
+    // simple scalar value that can be mem2reg'd into a register value.
+    // IsNotTrivial tracks whether this is something that mem2reg could have
+    // promoted itself.  If so, we don't want to transform it needlessly.  Note
+    // that we can't just check based on the type: the alloca may be of an i32
+    // but that has pointer arithmetic to set byte 3 of it or something.
+    bool IsNotTrivial = false;
+    const Type *VectorTy = 0;
+    bool HadAVector = false;
+    if (CanConvertToScalar(AI, IsNotTrivial, VectorTy, HadAVector, 
+                           0, unsigned(AllocaSize)) && IsNotTrivial) {
+      AllocaInst *NewAI;
+      // If we were able to find a vector type that can handle this with
+      // insert/extract elements, and if there was at least one use that had
+      // a vector type, promote this to a vector.  We don't want to promote
+      // random stuff that doesn't use vectors (e.g. <9 x double>) because then
+      // we just get a lot of insert/extracts.  If at least one vector is
+      // involved, then we probably really do have a union of vector/array.
+      if (VectorTy && isa<VectorType>(VectorTy) && HadAVector) {
+        DOUT << "CONVERT TO VECTOR: " << *AI << "  TYPE = " << *VectorTy <<"\n";
+        
+        // Create and insert the vector alloca.
+        NewAI = new AllocaInst(VectorTy, 0, "", AI->getParent()->begin());
+        ConvertUsesToScalar(AI, NewAI, 0);
+      } else {
+        DOUT << "CONVERT TO SCALAR INTEGER: " << *AI << "\n";
+        
+        // Create and insert the integer alloca.
+        const Type *NewTy = IntegerType::get(AllocaSize*8);
+        NewAI = new AllocaInst(NewTy, 0, "", AI->getParent()->begin());
+        ConvertUsesToScalar(AI, NewAI, 0);
+      }
+      NewAI->takeName(AI);
+      AI->eraseFromParent();
+      ++NumConverted;
+      Changed = true;
+      continue;
+    }
+    
+    // Otherwise, couldn't process this alloca.
+  }
+
+  return Changed;
+}
+
+/// DoScalarReplacement - This alloca satisfied the isSafeAllocaToScalarRepl
+/// predicate, do SROA now.
+void SROA::DoScalarReplacement(AllocationInst *AI, 
+                               std::vector<AllocationInst*> &WorkList) {
+  DOUT << "Found inst to SROA: " << *AI;
+  SmallVector<AllocaInst*, 32> ElementAllocas;
+  if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) {
+    ElementAllocas.reserve(ST->getNumContainedTypes());
+    for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) {
+      AllocaInst *NA = new AllocaInst(ST->getContainedType(i), 0, 
+                                      AI->getAlignment(),
+                                      AI->getName() + "." + utostr(i), AI);
+      ElementAllocas.push_back(NA);
+      WorkList.push_back(NA);  // Add to worklist for recursive processing
+    }
+  } else {
+    const ArrayType *AT = cast<ArrayType>(AI->getAllocatedType());
+    ElementAllocas.reserve(AT->getNumElements());
+    const Type *ElTy = AT->getElementType();
+    for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
+      AllocaInst *NA = new AllocaInst(ElTy, 0, AI->getAlignment(),
+                                      AI->getName() + "." + utostr(i), AI);
+      ElementAllocas.push_back(NA);
+      WorkList.push_back(NA);  // Add to worklist for recursive processing
+    }
+  }
+
+  // Now that we have created the alloca instructions that we want to use,
+  // expand the getelementptr instructions to use them.
+  //
+  while (!AI->use_empty()) {
+    Instruction *User = cast<Instruction>(AI->use_back());
+    if (BitCastInst *BCInst = dyn_cast<BitCastInst>(User)) {
+      RewriteBitCastUserOfAlloca(BCInst, AI, ElementAllocas);
+      BCInst->eraseFromParent();
+      continue;
+    }
+    
+    // Replace:
+    //   %res = load { i32, i32 }* %alloc
+    // with:
+    //   %load.0 = load i32* %alloc.0
+    //   %insert.0 insertvalue { i32, i32 } zeroinitializer, i32 %load.0, 0 
+    //   %load.1 = load i32* %alloc.1
+    //   %insert = insertvalue { i32, i32 } %insert.0, i32 %load.1, 1 
+    // (Also works for arrays instead of structs)
+    if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
+      Value *Insert = UndefValue::get(LI->getType());
+      for (unsigned i = 0, e = ElementAllocas.size(); i != e; ++i) {
+        Value *Load = new LoadInst(ElementAllocas[i], "load", LI);
+        Insert = InsertValueInst::Create(Insert, Load, i, "insert", LI);
+      }
+      LI->replaceAllUsesWith(Insert);
+      LI->eraseFromParent();
+      continue;
+    }
+
+    // Replace:
+    //   store { i32, i32 } %val, { i32, i32 }* %alloc
+    // with:
+    //   %val.0 = extractvalue { i32, i32 } %val, 0 
+    //   store i32 %val.0, i32* %alloc.0
+    //   %val.1 = extractvalue { i32, i32 } %val, 1 
+    //   store i32 %val.1, i32* %alloc.1
+    // (Also works for arrays instead of structs)
+    if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
+      Value *Val = SI->getOperand(0);
+      for (unsigned i = 0, e = ElementAllocas.size(); i != e; ++i) {
+        Value *Extract = ExtractValueInst::Create(Val, i, Val->getName(), SI);
+        new StoreInst(Extract, ElementAllocas[i], SI);
+      }
+      SI->eraseFromParent();
+      continue;
+    }
+    
+    GetElementPtrInst *GEPI = cast<GetElementPtrInst>(User);
+    // We now know that the GEP is of the form: GEP <ptr>, 0, <cst>
+    unsigned Idx =
+       (unsigned)cast<ConstantInt>(GEPI->getOperand(2))->getZExtValue();
+
+    assert(Idx < ElementAllocas.size() && "Index out of range?");
+    AllocaInst *AllocaToUse = ElementAllocas[Idx];
+
+    Value *RepValue;
+    if (GEPI->getNumOperands() == 3) {
+      // Do not insert a new getelementptr instruction with zero indices, only
+      // to have it optimized out later.
+      RepValue = AllocaToUse;
+    } else {
+      // We are indexing deeply into the structure, so we still need a
+      // getelement ptr instruction to finish the indexing.  This may be
+      // expanded itself once the worklist is rerun.
+      //
+      SmallVector<Value*, 8> NewArgs;
+      NewArgs.push_back(Constant::getNullValue(Type::Int32Ty));
+      NewArgs.append(GEPI->op_begin()+3, GEPI->op_end());
+      RepValue = GetElementPtrInst::Create(AllocaToUse, NewArgs.begin(),
+                                           NewArgs.end(), "", GEPI);
+      RepValue->takeName(GEPI);
+    }
+    
+    // If this GEP is to the start of the aggregate, check for memcpys.
+    if (Idx == 0 && GEPI->hasAllZeroIndices())
+      RewriteBitCastUserOfAlloca(GEPI, AI, ElementAllocas);
+
+    // Move all of the users over to the new GEP.
+    GEPI->replaceAllUsesWith(RepValue);
+    // Delete the old GEP
+    GEPI->eraseFromParent();
+  }
+
+  // Finally, delete the Alloca instruction
+  AI->eraseFromParent();
+  NumReplaced++;
+}
+
+
+/// isSafeElementUse - Check to see if this use is an allowed use for a
+/// getelementptr instruction of an array aggregate allocation.  isFirstElt
+/// indicates whether Ptr is known to the start of the aggregate.
+///
+void SROA::isSafeElementUse(Value *Ptr, bool isFirstElt, AllocationInst *AI,
+                            AllocaInfo &Info) {
+  for (Value::use_iterator I = Ptr->use_begin(), E = Ptr->use_end();
+       I != E; ++I) {
+    Instruction *User = cast<Instruction>(*I);
+    switch (User->getOpcode()) {
+    case Instruction::Load:  break;
+    case Instruction::Store:
+      // Store is ok if storing INTO the pointer, not storing the pointer
+      if (User->getOperand(0) == Ptr) return MarkUnsafe(Info);
+      break;
+    case Instruction::GetElementPtr: {
+      GetElementPtrInst *GEP = cast<GetElementPtrInst>(User);
+      bool AreAllZeroIndices = isFirstElt;
+      if (GEP->getNumOperands() > 1) {
+        if (!isa<ConstantInt>(GEP->getOperand(1)) ||
+            !cast<ConstantInt>(GEP->getOperand(1))->isZero())
+          // Using pointer arithmetic to navigate the array.
+          return MarkUnsafe(Info);
+       
+        if (AreAllZeroIndices)
+          AreAllZeroIndices = GEP->hasAllZeroIndices();
+      }
+      isSafeElementUse(GEP, AreAllZeroIndices, AI, Info);
+      if (Info.isUnsafe) return;
+      break;
+    }
+    case Instruction::BitCast:
+      if (isFirstElt) {
+        isSafeUseOfBitCastedAllocation(cast<BitCastInst>(User), AI, Info);
+        if (Info.isUnsafe) return;
+        break;
+      }
+      DOUT << "  Transformation preventing inst: " << *User;
+      return MarkUnsafe(Info);
+    case Instruction::Call:
+      if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) {
+        if (isFirstElt) {
+          isSafeMemIntrinsicOnAllocation(MI, AI, I.getOperandNo(), Info);
+          if (Info.isUnsafe) return;
+          break;
+        }
+      }
+      DOUT << "  Transformation preventing inst: " << *User;
+      return MarkUnsafe(Info);
+    default:
+      DOUT << "  Transformation preventing inst: " << *User;
+      return MarkUnsafe(Info);
+    }
+  }
+  return;  // All users look ok :)
+}
+
+/// AllUsersAreLoads - Return true if all users of this value are loads.
+static bool AllUsersAreLoads(Value *Ptr) {
+  for (Value::use_iterator I = Ptr->use_begin(), E = Ptr->use_end();
+       I != E; ++I)
+    if (cast<Instruction>(*I)->getOpcode() != Instruction::Load)
+      return false;
+  return true;
+}
+
+/// isSafeUseOfAllocation - Check to see if this user is an allowed use for an
+/// aggregate allocation.
+///
+void SROA::isSafeUseOfAllocation(Instruction *User, AllocationInst *AI,
+                                 AllocaInfo &Info) {
+  if (BitCastInst *C = dyn_cast<BitCastInst>(User))
+    return isSafeUseOfBitCastedAllocation(C, AI, Info);
+
+  if (LoadInst *LI = dyn_cast<LoadInst>(User))
+    if (!LI->isVolatile())
+      return;// Loads (returning a first class aggregrate) are always rewritable
+
+  if (StoreInst *SI = dyn_cast<StoreInst>(User))
+    if (!SI->isVolatile() && SI->getOperand(0) != AI)
+      return;// Store is ok if storing INTO the pointer, not storing the pointer
+ 
+  GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User);
+  if (GEPI == 0)
+    return MarkUnsafe(Info);
+
+  gep_type_iterator I = gep_type_begin(GEPI), E = gep_type_end(GEPI);
+
+  // The GEP is not safe to transform if not of the form "GEP <ptr>, 0, <cst>".
+  if (I == E ||
+      I.getOperand() != Constant::getNullValue(I.getOperand()->getType())) {
+    return MarkUnsafe(Info);
+  }
+
+  ++I;
+  if (I == E) return MarkUnsafe(Info);  // ran out of GEP indices??
+
+  bool IsAllZeroIndices = true;
+  
+  // If the first index is a non-constant index into an array, see if we can
+  // handle it as a special case.
+  if (const ArrayType *AT = dyn_cast<ArrayType>(*I)) {
+    if (!isa<ConstantInt>(I.getOperand())) {
+      IsAllZeroIndices = 0;
+      uint64_t NumElements = AT->getNumElements();
+      
+      // If this is an array index and the index is not constant, we cannot
+      // promote... that is unless the array has exactly one or two elements in
+      // it, in which case we CAN promote it, but we have to canonicalize this
+      // out if this is the only problem.
+      if ((NumElements == 1 || NumElements == 2) &&
+          AllUsersAreLoads(GEPI)) {
+        Info.needsCleanup = true;
+        return;  // Canonicalization required!
+      }
+      return MarkUnsafe(Info);
+    }
+  }
+ 
+  // Walk through the GEP type indices, checking the types that this indexes
+  // into.
+  for (; I != E; ++I) {
+    // Ignore struct elements, no extra checking needed for these.
+    if (isa<StructType>(*I))
+      continue;
+    
+    ConstantInt *IdxVal = dyn_cast<ConstantInt>(I.getOperand());
+    if (!IdxVal) return MarkUnsafe(Info);
+
+    // Are all indices still zero?
+    IsAllZeroIndices &= IdxVal->isZero();
+    
+    if (const ArrayType *AT = dyn_cast<ArrayType>(*I)) {
+      // This GEP indexes an array.  Verify that this is an in-range constant
+      // integer. Specifically, 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].  Because of this, we have to reject SROA
+      // of any accesses into structs where any of the components are variables. 
+      if (IdxVal->getZExtValue() >= AT->getNumElements())
+        return MarkUnsafe(Info);
+    } else if (const VectorType *VT = dyn_cast<VectorType>(*I)) {
+      if (IdxVal->getZExtValue() >= VT->getNumElements())
+        return MarkUnsafe(Info);
+    }
+  }
+  
+  // If there are any non-simple uses of this getelementptr, make sure to reject
+  // them.
+  return isSafeElementUse(GEPI, IsAllZeroIndices, AI, Info);
+}
+
+/// isSafeMemIntrinsicOnAllocation - Return true if the specified memory
+/// intrinsic can be promoted by SROA.  At this point, we know that the operand
+/// of the memintrinsic is a pointer to the beginning of the allocation.
+void SROA::isSafeMemIntrinsicOnAllocation(MemIntrinsic *MI, AllocationInst *AI,
+                                          unsigned OpNo, AllocaInfo &Info) {
+  // If not constant length, give up.
+  ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength());
+  if (!Length) return MarkUnsafe(Info);
+  
+  // If not the whole aggregate, give up.
+  if (Length->getZExtValue() !=
+      TD->getTypeAllocSize(AI->getType()->getElementType()))
+    return MarkUnsafe(Info);
+  
+  // We only know about memcpy/memset/memmove.
+  if (!isa<MemIntrinsic>(MI))
+    return MarkUnsafe(Info);
+  
+  // Otherwise, we can transform it.  Determine whether this is a memcpy/set
+  // into or out of the aggregate.
+  if (OpNo == 1)
+    Info.isMemCpyDst = true;
+  else {
+    assert(OpNo == 2);
+    Info.isMemCpySrc = true;
+  }
+}
+
+/// isSafeUseOfBitCastedAllocation - Return true if all users of this bitcast
+/// are 
+void SROA::isSafeUseOfBitCastedAllocation(BitCastInst *BC, AllocationInst *AI,
+                                          AllocaInfo &Info) {
+  for (Value::use_iterator UI = BC->use_begin(), E = BC->use_end();
+       UI != E; ++UI) {
+    if (BitCastInst *BCU = dyn_cast<BitCastInst>(UI)) {
+      isSafeUseOfBitCastedAllocation(BCU, AI, Info);
+    } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(UI)) {
+      isSafeMemIntrinsicOnAllocation(MI, AI, UI.getOperandNo(), Info);
+    } else if (StoreInst *SI = dyn_cast<StoreInst>(UI)) {
+      if (SI->isVolatile())
+        return MarkUnsafe(Info);
+      
+      // If storing the entire alloca in one chunk through a bitcasted pointer
+      // to integer, we can transform it.  This happens (for example) when you
+      // cast a {i32,i32}* to i64* and store through it.  This is similar to the
+      // memcpy case and occurs in various "byval" cases and emulated memcpys.
+      if (isa<IntegerType>(SI->getOperand(0)->getType()) &&
+          TD->getTypeAllocSize(SI->getOperand(0)->getType()) ==
+          TD->getTypeAllocSize(AI->getType()->getElementType())) {
+        Info.isMemCpyDst = true;
+        continue;
+      }
+      return MarkUnsafe(Info);
+    } else if (LoadInst *LI = dyn_cast<LoadInst>(UI)) {
+      if (LI->isVolatile())
+        return MarkUnsafe(Info);
+
+      // If loading the entire alloca in one chunk through a bitcasted pointer
+      // to integer, we can transform it.  This happens (for example) when you
+      // cast a {i32,i32}* to i64* and load through it.  This is similar to the
+      // memcpy case and occurs in various "byval" cases and emulated memcpys.
+      if (isa<IntegerType>(LI->getType()) &&
+          TD->getTypeAllocSize(LI->getType()) ==
+          TD->getTypeAllocSize(AI->getType()->getElementType())) {
+        Info.isMemCpySrc = true;
+        continue;
+      }
+      return MarkUnsafe(Info);
+    } else if (isa<DbgInfoIntrinsic>(UI)) {
+      // If one user is DbgInfoIntrinsic then check if all users are
+      // DbgInfoIntrinsics.
+      if (OnlyUsedByDbgInfoIntrinsics(BC)) {
+        Info.needsCleanup = true;
+        return;
+      }
+      else
+        MarkUnsafe(Info);
+    }
+    else {
+      return MarkUnsafe(Info);
+    }
+    if (Info.isUnsafe) return;
+  }
+}
+
+/// RewriteBitCastUserOfAlloca - BCInst (transitively) bitcasts AI, or indexes
+/// to its first element.  Transform users of the cast to use the new values
+/// instead.
+void SROA::RewriteBitCastUserOfAlloca(Instruction *BCInst, AllocationInst *AI,
+                                      SmallVector<AllocaInst*, 32> &NewElts) {
+  Value::use_iterator UI = BCInst->use_begin(), UE = BCInst->use_end();
+  while (UI != UE) {
+    Instruction *User = cast<Instruction>(*UI++);
+    if (BitCastInst *BCU = dyn_cast<BitCastInst>(User)) {
+      RewriteBitCastUserOfAlloca(BCU, AI, NewElts);
+      if (BCU->use_empty()) BCU->eraseFromParent();
+      continue;
+    }
+
+    if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) {
+      // This must be memcpy/memmove/memset of the entire aggregate.
+      // Split into one per element.
+      RewriteMemIntrinUserOfAlloca(MI, BCInst, AI, NewElts);
+      continue;
+    }
+      
+    if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
+      // If this is a store of the entire alloca from an integer, rewrite it.
+      RewriteStoreUserOfWholeAlloca(SI, AI, NewElts);
+      continue;
+    }
+
+    if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
+      // If this is a load of the entire alloca to an integer, rewrite it.
+      RewriteLoadUserOfWholeAlloca(LI, AI, NewElts);
+      continue;
+    }
+    
+    // Otherwise it must be some other user of a gep of the first pointer.  Just
+    // leave these alone.
+    continue;
+  }
+}
+
+/// RewriteMemIntrinUserOfAlloca - MI is a memcpy/memset/memmove from or to AI.
+/// Rewrite it to copy or set the elements of the scalarized memory.
+void SROA::RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *BCInst,
+                                        AllocationInst *AI,
+                                        SmallVector<AllocaInst*, 32> &NewElts) {
+  
+  // If this is a memcpy/memmove, construct the other pointer as the
+  // appropriate type.  The "Other" pointer is the pointer that goes to memory
+  // that doesn't have anything to do with the alloca that we are promoting. For
+  // memset, this Value* stays null.
+  Value *OtherPtr = 0;
+  unsigned MemAlignment = MI->getAlignment();
+  if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) { // memmove/memcopy
+    if (BCInst == MTI->getRawDest())
+      OtherPtr = MTI->getRawSource();
+    else {
+      assert(BCInst == MTI->getRawSource());
+      OtherPtr = MTI->getRawDest();
+    }
+  }
+  
+  // If there is an other pointer, we want to convert it to the same pointer
+  // type as AI has, so we can GEP through it safely.
+  if (OtherPtr) {
+    // It is likely that OtherPtr is a bitcast, if so, remove it.
+    if (BitCastInst *BC = dyn_cast<BitCastInst>(OtherPtr))
+      OtherPtr = BC->getOperand(0);
+    // All zero GEPs are effectively bitcasts.
+    if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(OtherPtr))
+      if (GEP->hasAllZeroIndices())
+        OtherPtr = GEP->getOperand(0);
+    
+    if (ConstantExpr *BCE = dyn_cast<ConstantExpr>(OtherPtr))
+      if (BCE->getOpcode() == Instruction::BitCast)
+        OtherPtr = BCE->getOperand(0);
+    
+    // If the pointer is not the right type, insert a bitcast to the right
+    // type.
+    if (OtherPtr->getType() != AI->getType())
+      OtherPtr = new BitCastInst(OtherPtr, AI->getType(), OtherPtr->getName(),
+                                 MI);
+  }
+  
+  // Process each element of the aggregate.
+  Value *TheFn = MI->getOperand(0);
+  const Type *BytePtrTy = MI->getRawDest()->getType();
+  bool SROADest = MI->getRawDest() == BCInst;
+  
+  Constant *Zero = Constant::getNullValue(Type::Int32Ty);
+
+  for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
+    // If this is a memcpy/memmove, emit a GEP of the other element address.
+    Value *OtherElt = 0;
+    unsigned OtherEltAlign = MemAlignment;
+    
+    if (OtherPtr) {
+      Value *Idx[2] = { Zero, ConstantInt::get(Type::Int32Ty, i) };
+      OtherElt = GetElementPtrInst::Create(OtherPtr, Idx, Idx + 2,
+                                           OtherPtr->getNameStr()+"."+utostr(i),
+                                           MI);
+      uint64_t EltOffset;
+      const PointerType *OtherPtrTy = cast<PointerType>(OtherPtr->getType());
+      if (const StructType *ST =
+            dyn_cast<StructType>(OtherPtrTy->getElementType())) {
+        EltOffset = TD->getStructLayout(ST)->getElementOffset(i);
+      } else {
+        const Type *EltTy =
+          cast<SequentialType>(OtherPtr->getType())->getElementType();
+        EltOffset = TD->getTypeAllocSize(EltTy)*i;
+      }
+      
+      // The alignment of the other pointer is the guaranteed alignment of the
+      // element, which is affected by both the known alignment of the whole
+      // mem intrinsic and the alignment of the element.  If the alignment of
+      // the memcpy (f.e.) is 32 but the element is at a 4-byte offset, then the
+      // known alignment is just 4 bytes.
+      OtherEltAlign = (unsigned)MinAlign(OtherEltAlign, EltOffset);
+    }
+    
+    Value *EltPtr = NewElts[i];
+    const Type *EltTy = cast<PointerType>(EltPtr->getType())->getElementType();
+    
+    // If we got down to a scalar, insert a load or store as appropriate.
+    if (EltTy->isSingleValueType()) {
+      if (isa<MemTransferInst>(MI)) {
+        if (SROADest) {
+          // From Other to Alloca.
+          Value *Elt = new LoadInst(OtherElt, "tmp", false, OtherEltAlign, MI);
+          new StoreInst(Elt, EltPtr, MI);
+        } else {
+          // From Alloca to Other.
+          Value *Elt = new LoadInst(EltPtr, "tmp", MI);
+          new StoreInst(Elt, OtherElt, false, OtherEltAlign, MI);
+        }
+        continue;
+      }
+      assert(isa<MemSetInst>(MI));
+      
+      // If the stored element is zero (common case), just store a null
+      // constant.
+      Constant *StoreVal;
+      if (ConstantInt *CI = dyn_cast<ConstantInt>(MI->getOperand(2))) {
+        if (CI->isZero()) {
+          StoreVal = Constant::getNullValue(EltTy);  // 0.0, null, 0, <0,0>
+        } else {
+          // If EltTy is a vector type, get the element type.
+          const Type *ValTy = EltTy;
+          if (const VectorType *VTy = dyn_cast<VectorType>(ValTy))
+            ValTy = VTy->getElementType();
+          
+          // Construct an integer with the right value.
+          unsigned EltSize = TD->getTypeSizeInBits(ValTy);
+          APInt OneVal(EltSize, CI->getZExtValue());
+          APInt TotalVal(OneVal);
+          // Set each byte.
+          for (unsigned i = 0; 8*i < EltSize; ++i) {
+            TotalVal = TotalVal.shl(8);
+            TotalVal |= OneVal;
+          }
+          
+          // Convert the integer value to the appropriate type.
+          StoreVal = ConstantInt::get(TotalVal);
+          if (isa<PointerType>(ValTy))
+            StoreVal = ConstantExpr::getIntToPtr(StoreVal, ValTy);
+          else if (ValTy->isFloatingPoint())
+            StoreVal = ConstantExpr::getBitCast(StoreVal, ValTy);
+          assert(StoreVal->getType() == ValTy && "Type mismatch!");
+          
+          // If the requested value was a vector constant, create it.
+          if (EltTy != ValTy) {
+            unsigned NumElts = cast<VectorType>(ValTy)->getNumElements();
+            SmallVector<Constant*, 16> Elts(NumElts, StoreVal);
+            StoreVal = ConstantVector::get(&Elts[0], NumElts);
+          }
+        }
+        new StoreInst(StoreVal, EltPtr, MI);
+        continue;
+      }
+      // Otherwise, if we're storing a byte variable, use a memset call for
+      // this element.
+    }
+    
+    // Cast the element pointer to BytePtrTy.
+    if (EltPtr->getType() != BytePtrTy)
+      EltPtr = new BitCastInst(EltPtr, BytePtrTy, EltPtr->getNameStr(), MI);
+    
+    // Cast the other pointer (if we have one) to BytePtrTy. 
+    if (OtherElt && OtherElt->getType() != BytePtrTy)
+      OtherElt = new BitCastInst(OtherElt, BytePtrTy,OtherElt->getNameStr(),
+                                 MI);
+    
+    unsigned EltSize = TD->getTypeAllocSize(EltTy);
+    
+    // Finally, insert the meminst for this element.
+    if (isa<MemTransferInst>(MI)) {
+      Value *Ops[] = {
+        SROADest ? EltPtr : OtherElt,  // Dest ptr
+        SROADest ? OtherElt : EltPtr,  // Src ptr
+        ConstantInt::get(MI->getOperand(3)->getType(), EltSize), // Size
+        ConstantInt::get(Type::Int32Ty, OtherEltAlign)  // Align
+      };
+      CallInst::Create(TheFn, Ops, Ops + 4, "", MI);
+    } else {
+      assert(isa<MemSetInst>(MI));
+      Value *Ops[] = {
+        EltPtr, MI->getOperand(2),  // Dest, Value,
+        ConstantInt::get(MI->getOperand(3)->getType(), EltSize), // Size
+        Zero  // Align
+      };
+      CallInst::Create(TheFn, Ops, Ops + 4, "", MI);
+    }
+  }
+  MI->eraseFromParent();
+}
+
+/// RewriteStoreUserOfWholeAlloca - We found an store of an integer that
+/// overwrites the entire allocation.  Extract out the pieces of the stored
+/// integer and store them individually.
+void SROA::RewriteStoreUserOfWholeAlloca(StoreInst *SI,
+                                         AllocationInst *AI,
+                                         SmallVector<AllocaInst*, 32> &NewElts){
+  // Extract each element out of the integer according to its structure offset
+  // and store the element value to the individual alloca.
+  Value *SrcVal = SI->getOperand(0);
+  const Type *AllocaEltTy = AI->getType()->getElementType();
+  uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy);
+  
+  // If this isn't a store of an integer to the whole alloca, it may be a store
+  // to the first element.  Just ignore the store in this case and normal SROA
+  // will handle it.
+  if (!isa<IntegerType>(SrcVal->getType()) ||
+      TD->getTypeAllocSizeInBits(SrcVal->getType()) != AllocaSizeBits)
+    return;
+  // Handle tail padding by extending the operand
+  if (TD->getTypeSizeInBits(SrcVal->getType()) != AllocaSizeBits)
+    SrcVal = new ZExtInst(SrcVal, IntegerType::get(AllocaSizeBits), "", SI);
+
+  DOUT << "PROMOTING STORE TO WHOLE ALLOCA: " << *AI << *SI;
+
+  // There are two forms here: AI could be an array or struct.  Both cases
+  // have different ways to compute the element offset.
+  if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) {
+    const StructLayout *Layout = TD->getStructLayout(EltSTy);
+    
+    for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
+      // Get the number of bits to shift SrcVal to get the value.
+      const Type *FieldTy = EltSTy->getElementType(i);
+      uint64_t Shift = Layout->getElementOffsetInBits(i);
+      
+      if (TD->isBigEndian())
+        Shift = AllocaSizeBits-Shift-TD->getTypeAllocSizeInBits(FieldTy);
+      
+      Value *EltVal = SrcVal;
+      if (Shift) {
+        Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift);
+        EltVal = BinaryOperator::CreateLShr(EltVal, ShiftVal,
+                                            "sroa.store.elt", SI);
+      }
+      
+      // Truncate down to an integer of the right size.
+      uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy);
+      
+      // Ignore zero sized fields like {}, they obviously contain no data.
+      if (FieldSizeBits == 0) continue;
+      
+      if (FieldSizeBits != AllocaSizeBits)
+        EltVal = new TruncInst(EltVal, IntegerType::get(FieldSizeBits), "", SI);
+      Value *DestField = NewElts[i];
+      if (EltVal->getType() == FieldTy) {
+        // Storing to an integer field of this size, just do it.
+      } else if (FieldTy->isFloatingPoint() || isa<VectorType>(FieldTy)) {
+        // Bitcast to the right element type (for fp/vector values).
+        EltVal = new BitCastInst(EltVal, FieldTy, "", SI);
+      } else {
+        // Otherwise, bitcast the dest pointer (for aggregates).
+        DestField = new BitCastInst(DestField,
+                                    PointerType::getUnqual(EltVal->getType()),
+                                    "", SI);
+      }
+      new StoreInst(EltVal, DestField, SI);
+    }
+    
+  } else {
+    const ArrayType *ATy = cast<ArrayType>(AllocaEltTy);
+    const Type *ArrayEltTy = ATy->getElementType();
+    uint64_t ElementOffset = TD->getTypeAllocSizeInBits(ArrayEltTy);
+    uint64_t ElementSizeBits = TD->getTypeSizeInBits(ArrayEltTy);
+
+    uint64_t Shift;
+    
+    if (TD->isBigEndian())
+      Shift = AllocaSizeBits-ElementOffset;
+    else 
+      Shift = 0;
+    
+    for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
+      // Ignore zero sized fields like {}, they obviously contain no data.
+      if (ElementSizeBits == 0) continue;
+      
+      Value *EltVal = SrcVal;
+      if (Shift) {
+        Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift);
+        EltVal = BinaryOperator::CreateLShr(EltVal, ShiftVal,
+                                            "sroa.store.elt", SI);
+      }
+      
+      // Truncate down to an integer of the right size.
+      if (ElementSizeBits != AllocaSizeBits)
+        EltVal = new TruncInst(EltVal, IntegerType::get(ElementSizeBits),"",SI);
+      Value *DestField = NewElts[i];
+      if (EltVal->getType() == ArrayEltTy) {
+        // Storing to an integer field of this size, just do it.
+      } else if (ArrayEltTy->isFloatingPoint() || isa<VectorType>(ArrayEltTy)) {
+        // Bitcast to the right element type (for fp/vector values).
+        EltVal = new BitCastInst(EltVal, ArrayEltTy, "", SI);
+      } else {
+        // Otherwise, bitcast the dest pointer (for aggregates).
+        DestField = new BitCastInst(DestField,
+                                    PointerType::getUnqual(EltVal->getType()),
+                                    "", SI);
+      }
+      new StoreInst(EltVal, DestField, SI);
+      
+      if (TD->isBigEndian())
+        Shift -= ElementOffset;
+      else 
+        Shift += ElementOffset;
+    }
+  }
+  
+  SI->eraseFromParent();
+}
+
+/// RewriteLoadUserOfWholeAlloca - We found an load of the entire allocation to
+/// an integer.  Load the individual pieces to form the aggregate value.
+void SROA::RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocationInst *AI,
+                                        SmallVector<AllocaInst*, 32> &NewElts) {
+  // Extract each element out of the NewElts according to its structure offset
+  // and form the result value.
+  const Type *AllocaEltTy = AI->getType()->getElementType();
+  uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy);
+  
+  // If this isn't a load of the whole alloca to an integer, it may be a load
+  // of the first element.  Just ignore the load in this case and normal SROA
+  // will handle it.
+  if (!isa<IntegerType>(LI->getType()) ||
+      TD->getTypeAllocSizeInBits(LI->getType()) != AllocaSizeBits)
+    return;
+  
+  DOUT << "PROMOTING LOAD OF WHOLE ALLOCA: " << *AI << *LI;
+  
+  // There are two forms here: AI could be an array or struct.  Both cases
+  // have different ways to compute the element offset.
+  const StructLayout *Layout = 0;
+  uint64_t ArrayEltBitOffset = 0;
+  if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) {
+    Layout = TD->getStructLayout(EltSTy);
+  } else {
+    const Type *ArrayEltTy = cast<ArrayType>(AllocaEltTy)->getElementType();
+    ArrayEltBitOffset = TD->getTypeAllocSizeInBits(ArrayEltTy);
+  }    
+    
+  Value *ResultVal = Constant::getNullValue(IntegerType::get(AllocaSizeBits));
+  
+  for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
+    // Load the value from the alloca.  If the NewElt is an aggregate, cast
+    // the pointer to an integer of the same size before doing the load.
+    Value *SrcField = NewElts[i];
+    const Type *FieldTy =
+      cast<PointerType>(SrcField->getType())->getElementType();
+    uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy);
+    
+    // Ignore zero sized fields like {}, they obviously contain no data.
+    if (FieldSizeBits == 0) continue;
+    
+    const IntegerType *FieldIntTy = IntegerType::get(FieldSizeBits);
+    if (!isa<IntegerType>(FieldTy) && !FieldTy->isFloatingPoint() &&
+        !isa<VectorType>(FieldTy))
+      SrcField = new BitCastInst(SrcField, PointerType::getUnqual(FieldIntTy),
+                                 "", LI);
+    SrcField = new LoadInst(SrcField, "sroa.load.elt", LI);
+
+    // If SrcField is a fp or vector of the right size but that isn't an
+    // integer type, bitcast to an integer so we can shift it.
+    if (SrcField->getType() != FieldIntTy)
+      SrcField = new BitCastInst(SrcField, FieldIntTy, "", LI);
+
+    // Zero extend the field to be the same size as the final alloca so that
+    // we can shift and insert it.
+    if (SrcField->getType() != ResultVal->getType())
+      SrcField = new ZExtInst(SrcField, ResultVal->getType(), "", LI);
+    
+    // Determine the number of bits to shift SrcField.
+    uint64_t Shift;
+    if (Layout) // Struct case.
+      Shift = Layout->getElementOffsetInBits(i);
+    else  // Array case.
+      Shift = i*ArrayEltBitOffset;
+    
+    if (TD->isBigEndian())
+      Shift = AllocaSizeBits-Shift-FieldIntTy->getBitWidth();
+    
+    if (Shift) {
+      Value *ShiftVal = ConstantInt::get(SrcField->getType(), Shift);
+      SrcField = BinaryOperator::CreateShl(SrcField, ShiftVal, "", LI);
+    }
+
+    ResultVal = BinaryOperator::CreateOr(SrcField, ResultVal, "", LI);
+  }
+
+  // Handle tail padding by truncating the result
+  if (TD->getTypeSizeInBits(LI->getType()) != AllocaSizeBits)
+    ResultVal = new TruncInst(ResultVal, LI->getType(), "", LI);
+
+  LI->replaceAllUsesWith(ResultVal);
+  LI->eraseFromParent();
+}
+
+
+/// HasPadding - Return true if the specified type has any structure or
+/// alignment padding, false otherwise.
+static bool HasPadding(const Type *Ty, const TargetData &TD) {
+  if (const StructType *STy = dyn_cast<StructType>(Ty)) {
+    const StructLayout *SL = TD.getStructLayout(STy);
+    unsigned PrevFieldBitOffset = 0;
+    for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
+      unsigned FieldBitOffset = SL->getElementOffsetInBits(i);
+
+      // Padding in sub-elements?
+      if (HasPadding(STy->getElementType(i), TD))
+        return true;
+
+      // Check to see if there is any padding between this element and the
+      // previous one.
+      if (i) {
+        unsigned PrevFieldEnd =
+        PrevFieldBitOffset+TD.getTypeSizeInBits(STy->getElementType(i-1));
+        if (PrevFieldEnd < FieldBitOffset)
+          return true;
+      }
+
+      PrevFieldBitOffset = FieldBitOffset;
+    }
+
+    //  Check for tail padding.
+    if (unsigned EltCount = STy->getNumElements()) {
+      unsigned PrevFieldEnd = PrevFieldBitOffset +
+                   TD.getTypeSizeInBits(STy->getElementType(EltCount-1));
+      if (PrevFieldEnd < SL->getSizeInBits())
+        return true;
+    }
+
+  } else if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
+    return HasPadding(ATy->getElementType(), TD);
+  } else if (const VectorType *VTy = dyn_cast<VectorType>(Ty)) {
+    return HasPadding(VTy->getElementType(), TD);
+  }
+  return TD.getTypeSizeInBits(Ty) != TD.getTypeAllocSizeInBits(Ty);
+}
+
+/// isSafeStructAllocaToScalarRepl - Check to see if the specified allocation of
+/// an aggregate can be broken down into elements.  Return 0 if not, 3 if safe,
+/// or 1 if safe after canonicalization has been performed.
+///
+int SROA::isSafeAllocaToScalarRepl(AllocationInst *AI) {
+  // Loop over the use list of the alloca.  We can only transform it if all of
+  // the users are safe to transform.
+  AllocaInfo Info;
+  
+  for (Value::use_iterator I = AI->use_begin(), E = AI->use_end();
+       I != E; ++I) {
+    isSafeUseOfAllocation(cast<Instruction>(*I), AI, Info);
+    if (Info.isUnsafe) {
+      DOUT << "Cannot transform: " << *AI << "  due to user: " << **I;
+      return 0;
+    }
+  }
+  
+  // Okay, we know all the users are promotable.  If the aggregate is a memcpy
+  // source and destination, we have to be careful.  In particular, the memcpy
+  // could be moving around elements that live in structure padding of the LLVM
+  // types, but may actually be used.  In these cases, we refuse to promote the
+  // struct.
+  if (Info.isMemCpySrc && Info.isMemCpyDst &&
+      HasPadding(AI->getType()->getElementType(), *TD))
+    return 0;
+
+  // If we require cleanup, return 1, otherwise return 3.
+  return Info.needsCleanup ? 1 : 3;
+}
+
+/// CleanupGEP - GEP is used by an Alloca, which can be prompted after the GEP
+/// is canonicalized here.
+void SROA::CleanupGEP(GetElementPtrInst *GEPI) {
+  gep_type_iterator I = gep_type_begin(GEPI);
+  ++I;
+  
+  const ArrayType *AT = dyn_cast<ArrayType>(*I);
+  if (!AT) 
+    return;
+
+  uint64_t NumElements = AT->getNumElements();
+  
+  if (isa<ConstantInt>(I.getOperand()))
+    return;
+
+  if (NumElements == 1) {
+    GEPI->setOperand(2, Constant::getNullValue(Type::Int32Ty));
+    return;
+  } 
+    
+  assert(NumElements == 2 && "Unhandled case!");
+  // All users of the GEP must be loads.  At each use of the GEP, insert
+  // two loads of the appropriate indexed GEP and select between them.
+  Value *IsOne = new ICmpInst(ICmpInst::ICMP_NE, I.getOperand(), 
+                              Constant::getNullValue(I.getOperand()->getType()),
+                              "isone", GEPI);
+  // Insert the new GEP instructions, which are properly indexed.
+  SmallVector<Value*, 8> Indices(GEPI->op_begin()+1, GEPI->op_end());
+  Indices[1] = Constant::getNullValue(Type::Int32Ty);
+  Value *ZeroIdx = GetElementPtrInst::Create(GEPI->getOperand(0),
+                                             Indices.begin(),
+                                             Indices.end(),
+                                             GEPI->getName()+".0", GEPI);
+  Indices[1] = ConstantInt::get(Type::Int32Ty, 1);
+  Value *OneIdx = GetElementPtrInst::Create(GEPI->getOperand(0),
+                                            Indices.begin(),
+                                            Indices.end(),
+                                            GEPI->getName()+".1", GEPI);
+  // Replace all loads of the variable index GEP with loads from both
+  // indexes and a select.
+  while (!GEPI->use_empty()) {
+    LoadInst *LI = cast<LoadInst>(GEPI->use_back());
+    Value *Zero = new LoadInst(ZeroIdx, LI->getName()+".0", LI);
+    Value *One  = new LoadInst(OneIdx , LI->getName()+".1", LI);
+    Value *R = SelectInst::Create(IsOne, One, Zero, LI->getName(), LI);
+    LI->replaceAllUsesWith(R);
+    LI->eraseFromParent();
+  }
+  GEPI->eraseFromParent();
+}
+
+
+/// CleanupAllocaUsers - If SROA reported that it can promote the specified
+/// allocation, but only if cleaned up, perform the cleanups required.
+void SROA::CleanupAllocaUsers(AllocationInst *AI) {
+  // At this point, we know that the end result will be SROA'd and promoted, so
+  // we can insert ugly code if required so long as sroa+mem2reg will clean it
+  // up.
+  for (Value::use_iterator UI = AI->use_begin(), E = AI->use_end();
+       UI != E; ) {
+    User *U = *UI++;
+    if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(U))
+      CleanupGEP(GEPI);
+    else if (Instruction *I = dyn_cast<Instruction>(U)) {
+      SmallVector<DbgInfoIntrinsic *, 2> DbgInUses;
+      if (!isa<StoreInst>(I) && OnlyUsedByDbgInfoIntrinsics(I, &DbgInUses)) {
+        // Safe to remove debug info uses.
+        while (!DbgInUses.empty()) {
+          DbgInfoIntrinsic *DI = DbgInUses.back(); DbgInUses.pop_back();
+          DI->eraseFromParent();
+        }
+        I->eraseFromParent();
+      }
+    }
+  }
+}
+
+/// MergeInType - Add the 'In' type to the accumulated type (Accum) so far at
+/// the offset specified by Offset (which is specified in bytes).
+///
+/// There are two cases we handle here:
+///   1) A union of vector types of the same size and potentially its elements.
+///      Here we turn element accesses into insert/extract element operations.
+///      This promotes a <4 x float> with a store of float to the third element
+///      into a <4 x float> that uses insert element.
+///   2) A fully general blob of memory, which we turn into some (potentially
+///      large) integer type with extract and insert operations where the loads
+///      and stores would mutate the memory.
+static void MergeInType(const Type *In, uint64_t Offset, const Type *&VecTy,
+                        unsigned AllocaSize, const TargetData &TD) {
+  // If this could be contributing to a vector, analyze it.
+  if (VecTy != Type::VoidTy) { // either null or a vector type.
+
+    // If the In type is a vector that is the same size as the alloca, see if it
+    // matches the existing VecTy.
+    if (const VectorType *VInTy = dyn_cast<VectorType>(In)) {
+      if (VInTy->getBitWidth()/8 == AllocaSize && Offset == 0) {
+        // If we're storing/loading a vector of the right size, allow it as a
+        // vector.  If this the first vector we see, remember the type so that
+        // we know the element size.
+        if (VecTy == 0)
+          VecTy = VInTy;
+        return;
+      }
+    } else if (In == Type::FloatTy || In == Type::DoubleTy ||
+               (isa<IntegerType>(In) && In->getPrimitiveSizeInBits() >= 8 &&
+                isPowerOf2_32(In->getPrimitiveSizeInBits()))) {
+      // If we're accessing something that could be an element of a vector, see
+      // if the implied vector agrees with what we already have and if Offset is
+      // compatible with it.
+      unsigned EltSize = In->getPrimitiveSizeInBits()/8;
+      if (Offset % EltSize == 0 &&
+          AllocaSize % EltSize == 0 &&
+          (VecTy == 0 || 
+           cast<VectorType>(VecTy)->getElementType()
+                 ->getPrimitiveSizeInBits()/8 == EltSize)) {
+        if (VecTy == 0)
+          VecTy = VectorType::get(In, AllocaSize/EltSize);
+        return;
+      }
+    }
+  }
+  
+  // Otherwise, we have a case that we can't handle with an optimized vector
+  // form.  We can still turn this into a large integer.
+  VecTy = Type::VoidTy;
+}
+
+/// CanConvertToScalar - V is a pointer.  If we can convert the pointee and all
+/// its accesses to use a to single vector type, return true, and set VecTy to
+/// the new type.  If we could convert the alloca into a single promotable
+/// integer, return true but set VecTy to VoidTy.  Further, if the use is not a
+/// completely trivial use that mem2reg could promote, set IsNotTrivial.  Offset
+/// is the current offset from the base of the alloca being analyzed.
+///
+/// If we see at least one access to the value that is as a vector type, set the
+/// SawVec flag.
+///
+bool SROA::CanConvertToScalar(Value *V, bool &IsNotTrivial, const Type *&VecTy,
+                              bool &SawVec, uint64_t Offset,
+                              unsigned AllocaSize) {
+  for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) {
+    Instruction *User = cast<Instruction>(*UI);
+    
+    if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
+      // Don't break volatile loads.
+      if (LI->isVolatile())
+        return false;
+      MergeInType(LI->getType(), Offset, VecTy, AllocaSize, *TD);
+      SawVec |= isa<VectorType>(LI->getType());
+      continue;
+    }
+    
+    if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
+      // Storing the pointer, not into the value?
+      if (SI->getOperand(0) == V || SI->isVolatile()) return 0;
+      MergeInType(SI->getOperand(0)->getType(), Offset, VecTy, AllocaSize, *TD);
+      SawVec |= isa<VectorType>(SI->getOperand(0)->getType());
+      continue;
+    }
+    
+    if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) {
+      if (!CanConvertToScalar(BCI, IsNotTrivial, VecTy, SawVec, Offset,
+                              AllocaSize))
+        return false;
+      IsNotTrivial = true;
+      continue;
+    }
+
+    if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) {
+      // If this is a GEP with a variable indices, we can't handle it.
+      if (!GEP->hasAllConstantIndices())
+        return false;
+      
+      // Compute the offset that this GEP adds to the pointer.
+      SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end());
+      uint64_t GEPOffset = TD->getIndexedOffset(GEP->getOperand(0)->getType(),
+                                                &Indices[0], Indices.size());
+      // See if all uses can be converted.
+      if (!CanConvertToScalar(GEP, IsNotTrivial, VecTy, SawVec,Offset+GEPOffset,
+                              AllocaSize))
+        return false;
+      IsNotTrivial = true;
+      continue;
+    }
+
+    // If this is a constant sized memset of a constant value (e.g. 0) we can
+    // handle it.
+    if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) {
+      // Store of constant value and constant size.
+      if (isa<ConstantInt>(MSI->getValue()) &&
+          isa<ConstantInt>(MSI->getLength())) {
+        IsNotTrivial = true;
+        continue;
+      }
+    }
+
+    // If this is a memcpy or memmove into or out of the whole allocation, we
+    // can handle it like a load or store of the scalar type.
+    if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) {
+      if (ConstantInt *Len = dyn_cast<ConstantInt>(MTI->getLength()))
+        if (Len->getZExtValue() == AllocaSize && Offset == 0) {
+          IsNotTrivial = true;
+          continue;
+        }
+    }
+    
+    // Ignore dbg intrinsic.
+    if (isa<DbgInfoIntrinsic>(User))
+      continue;
+
+    // Otherwise, we cannot handle this!
+    return false;
+  }
+  
+  return true;
+}
+
+
+/// ConvertUsesToScalar - Convert all of the users of Ptr to use the new alloca
+/// directly.  This happens when we are converting an "integer union" to a
+/// single integer scalar, or when we are converting a "vector union" to a
+/// vector with insert/extractelement instructions.
+///
+/// Offset is an offset from the original alloca, in bits that need to be
+/// shifted to the right.  By the end of this, there should be no uses of Ptr.
+void SROA::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset) {
+  while (!Ptr->use_empty()) {
+    Instruction *User = cast<Instruction>(Ptr->use_back());
+
+    if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) {
+      ConvertUsesToScalar(CI, NewAI, Offset);
+      CI->eraseFromParent();
+      continue;
+    }
+
+    if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) {
+      // Compute the offset that this GEP adds to the pointer.
+      SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end());
+      uint64_t GEPOffset = TD->getIndexedOffset(GEP->getOperand(0)->getType(),
+                                                &Indices[0], Indices.size());
+      ConvertUsesToScalar(GEP, NewAI, Offset+GEPOffset*8);
+      GEP->eraseFromParent();
+      continue;
+    }
+    
+    IRBuilder<> Builder(User->getParent(), User);
+    
+    if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
+      // The load is a bit extract from NewAI shifted right by Offset bits.
+      Value *LoadedVal = Builder.CreateLoad(NewAI, "tmp");
+      Value *NewLoadVal
+        = ConvertScalar_ExtractValue(LoadedVal, LI->getType(), Offset, Builder);
+      LI->replaceAllUsesWith(NewLoadVal);
+      LI->eraseFromParent();
+      continue;
+    }
+    
+    if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
+      assert(SI->getOperand(0) != Ptr && "Consistency error!");
+      Value *Old = Builder.CreateLoad(NewAI, (NewAI->getName()+".in").c_str());
+      Value *New = ConvertScalar_InsertValue(SI->getOperand(0), Old, Offset,
+                                             Builder);
+      Builder.CreateStore(New, NewAI);
+      SI->eraseFromParent();
+      continue;
+    }
+    
+    // If this is a constant sized memset of a constant value (e.g. 0) we can
+    // transform it into a store of the expanded constant value.
+    if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) {
+      assert(MSI->getRawDest() == Ptr && "Consistency error!");
+      unsigned NumBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue();
+      if (NumBytes != 0) {
+        unsigned Val = cast<ConstantInt>(MSI->getValue())->getZExtValue();
+        
+        // Compute the value replicated the right number of times.
+        APInt APVal(NumBytes*8, Val);
+
+        // Splat the value if non-zero.
+        if (Val)
+          for (unsigned i = 1; i != NumBytes; ++i)
+            APVal |= APVal << 8;
+        
+        Value *Old = Builder.CreateLoad(NewAI, (NewAI->getName()+".in").c_str());
+        Value *New = ConvertScalar_InsertValue(ConstantInt::get(APVal), Old,
+                                               Offset, Builder);
+        Builder.CreateStore(New, NewAI);
+      }
+      MSI->eraseFromParent();
+      continue;
+    }
+
+    // If this is a memcpy or memmove into or out of the whole allocation, we
+    // can handle it like a load or store of the scalar type.
+    if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) {
+      assert(Offset == 0 && "must be store to start of alloca");
+      
+      // If the source and destination are both to the same alloca, then this is
+      // a noop copy-to-self, just delete it.  Otherwise, emit a load and store
+      // as appropriate.
+      AllocaInst *OrigAI = cast<AllocaInst>(Ptr->getUnderlyingObject());
+      
+      if (MTI->getSource()->getUnderlyingObject() != OrigAI) {
+        // Dest must be OrigAI, change this to be a load from the original
+        // pointer (bitcasted), then a store to our new alloca.
+        assert(MTI->getRawDest() == Ptr && "Neither use is of pointer?");
+        Value *SrcPtr = MTI->getSource();
+        SrcPtr = Builder.CreateBitCast(SrcPtr, NewAI->getType());
+        
+        LoadInst *SrcVal = Builder.CreateLoad(SrcPtr, "srcval");
+        SrcVal->setAlignment(MTI->getAlignment());
+        Builder.CreateStore(SrcVal, NewAI);
+      } else if (MTI->getDest()->getUnderlyingObject() != OrigAI) {
+        // Src must be OrigAI, change this to be a load from NewAI then a store
+        // through the original dest pointer (bitcasted).
+        assert(MTI->getRawSource() == Ptr && "Neither use is of pointer?");
+        LoadInst *SrcVal = Builder.CreateLoad(NewAI, "srcval");
+
+        Value *DstPtr = Builder.CreateBitCast(MTI->getDest(), NewAI->getType());
+        StoreInst *NewStore = Builder.CreateStore(SrcVal, DstPtr);
+        NewStore->setAlignment(MTI->getAlignment());
+      } else {
+        // Noop transfer. Src == Dst
+      }
+          
+
+      MTI->eraseFromParent();
+      continue;
+    }
+    
+    // If user is a dbg info intrinsic then it is safe to remove it.
+    if (isa<DbgInfoIntrinsic>(User)) {
+      User->eraseFromParent();
+      continue;
+    }
+
+    assert(0 && "Unsupported operation!");
+    abort();
+  }
+}
+
+/// ConvertScalar_ExtractValue - Extract a value of type ToType from an integer
+/// or vector value FromVal, extracting the bits from the offset specified by
+/// Offset.  This returns the value, which is of type ToType.
+///
+/// This happens when we are converting an "integer union" to a single
+/// integer scalar, or when we are converting a "vector union" to a vector with
+/// insert/extractelement instructions.
+///
+/// Offset is an offset from the original alloca, in bits that need to be
+/// shifted to the right.
+Value *SROA::ConvertScalar_ExtractValue(Value *FromVal, const Type *ToType,
+                                        uint64_t Offset, IRBuilder<> &Builder) {
+  // If the load is of the whole new alloca, no conversion is needed.
+  if (FromVal->getType() == ToType && Offset == 0)
+    return FromVal;
+
+  // If the result alloca is a vector type, this is either an element
+  // access or a bitcast to another vector type of the same size.
+  if (const VectorType *VTy = dyn_cast<VectorType>(FromVal->getType())) {
+    if (isa<VectorType>(ToType))
+      return Builder.CreateBitCast(FromVal, ToType, "tmp");
+
+    // Otherwise it must be an element access.
+    unsigned Elt = 0;
+    if (Offset) {
+      unsigned EltSize = TD->getTypeAllocSizeInBits(VTy->getElementType());
+      Elt = Offset/EltSize;
+      assert(EltSize*Elt == Offset && "Invalid modulus in validity checking");
+    }
+    // Return the element extracted out of it.
+    Value *V = Builder.CreateExtractElement(FromVal,
+                                            ConstantInt::get(Type::Int32Ty,Elt),
+                                            "tmp");
+    if (V->getType() != ToType)
+      V = Builder.CreateBitCast(V, ToType, "tmp");
+    return V;
+  }
+  
+  // If ToType is a first class aggregate, extract out each of the pieces and
+  // use insertvalue's to form the FCA.
+  if (const StructType *ST = dyn_cast<StructType>(ToType)) {
+    const StructLayout &Layout = *TD->getStructLayout(ST);
+    Value *Res = UndefValue::get(ST);
+    for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) {
+      Value *Elt = ConvertScalar_ExtractValue(FromVal, ST->getElementType(i),
+                                        Offset+Layout.getElementOffsetInBits(i),
+                                              Builder);
+      Res = Builder.CreateInsertValue(Res, Elt, i, "tmp");
+    }
+    return Res;
+  }
+  
+  if (const ArrayType *AT = dyn_cast<ArrayType>(ToType)) {
+    uint64_t EltSize = TD->getTypeAllocSizeInBits(AT->getElementType());
+    Value *Res = UndefValue::get(AT);
+    for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
+      Value *Elt = ConvertScalar_ExtractValue(FromVal, AT->getElementType(),
+                                              Offset+i*EltSize, Builder);
+      Res = Builder.CreateInsertValue(Res, Elt, i, "tmp");
+    }
+    return Res;
+  }
+
+  // Otherwise, this must be a union that was converted to an integer value.
+  const IntegerType *NTy = cast<IntegerType>(FromVal->getType());
+
+  // If this is a big-endian system and the load is narrower than the
+  // full alloca type, we need to do a shift to get the right bits.
+  int ShAmt = 0;
+  if (TD->isBigEndian()) {
+    // On big-endian machines, the lowest bit is stored at the bit offset
+    // from the pointer given by getTypeStoreSizeInBits.  This matters for
+    // integers with a bitwidth that is not a multiple of 8.
+    ShAmt = TD->getTypeStoreSizeInBits(NTy) -
+            TD->getTypeStoreSizeInBits(ToType) - Offset;
+  } else {
+    ShAmt = Offset;
+  }
+
+  // Note: we support negative bitwidths (with shl) which are not defined.
+  // We do this to support (f.e.) loads off the end of a structure where
+  // only some bits are used.
+  if (ShAmt > 0 && (unsigned)ShAmt < NTy->getBitWidth())
+    FromVal = Builder.CreateLShr(FromVal, ConstantInt::get(FromVal->getType(),
+                                                           ShAmt), "tmp");
+  else if (ShAmt < 0 && (unsigned)-ShAmt < NTy->getBitWidth())
+    FromVal = Builder.CreateShl(FromVal, ConstantInt::get(FromVal->getType(),
+                                                          -ShAmt), "tmp");
+
+  // Finally, unconditionally truncate the integer to the right width.
+  unsigned LIBitWidth = TD->getTypeSizeInBits(ToType);
+  if (LIBitWidth < NTy->getBitWidth())
+    FromVal = Builder.CreateTrunc(FromVal, IntegerType::get(LIBitWidth), "tmp");
+  else if (LIBitWidth > NTy->getBitWidth())
+    FromVal = Builder.CreateZExt(FromVal, IntegerType::get(LIBitWidth), "tmp");
+
+  // If the result is an integer, this is a trunc or bitcast.
+  if (isa<IntegerType>(ToType)) {
+    // Should be done.
+  } else if (ToType->isFloatingPoint() || isa<VectorType>(ToType)) {
+    // Just do a bitcast, we know the sizes match up.
+    FromVal = Builder.CreateBitCast(FromVal, ToType, "tmp");
+  } else {
+    // Otherwise must be a pointer.
+    FromVal = Builder.CreateIntToPtr(FromVal, ToType, "tmp");
+  }
+  assert(FromVal->getType() == ToType && "Didn't convert right?");
+  return FromVal;
+}
+
+
+/// ConvertScalar_InsertValue - Insert the value "SV" into the existing integer
+/// or vector value "Old" at the offset specified by Offset.
+///
+/// This happens when we are converting an "integer union" to a
+/// single integer scalar, or when we are converting a "vector union" to a
+/// vector with insert/extractelement instructions.
+///
+/// Offset is an offset from the original alloca, in bits that need to be
+/// shifted to the right.
+Value *SROA::ConvertScalar_InsertValue(Value *SV, Value *Old,
+                                       uint64_t Offset, IRBuilder<> &Builder) {
+
+  // Convert the stored type to the actual type, shift it left to insert
+  // then 'or' into place.
+  const Type *AllocaType = Old->getType();
+
+  if (const VectorType *VTy = dyn_cast<VectorType>(AllocaType)) {
+    uint64_t VecSize = TD->getTypeAllocSizeInBits(VTy);
+    uint64_t ValSize = TD->getTypeAllocSizeInBits(SV->getType());
+    
+    // Changing the whole vector with memset or with an access of a different
+    // vector type?
+    if (ValSize == VecSize)
+      return Builder.CreateBitCast(SV, AllocaType, "tmp");
+
+    uint64_t EltSize = TD->getTypeAllocSizeInBits(VTy->getElementType());
+
+    // Must be an element insertion.
+    unsigned Elt = Offset/EltSize;
+    
+    if (SV->getType() != VTy->getElementType())
+      SV = Builder.CreateBitCast(SV, VTy->getElementType(), "tmp");
+    
+    SV = Builder.CreateInsertElement(Old, SV, 
+                                     ConstantInt::get(Type::Int32Ty, Elt),
+                                     "tmp");
+    return SV;
+  }
+  
+  // If SV is a first-class aggregate value, insert each value recursively.
+  if (const StructType *ST = dyn_cast<StructType>(SV->getType())) {
+    const StructLayout &Layout = *TD->getStructLayout(ST);
+    for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) {
+      Value *Elt = Builder.CreateExtractValue(SV, i, "tmp");
+      Old = ConvertScalar_InsertValue(Elt, Old, 
+                                      Offset+Layout.getElementOffsetInBits(i),
+                                      Builder);
+    }
+    return Old;
+  }
+  
+  if (const ArrayType *AT = dyn_cast<ArrayType>(SV->getType())) {
+    uint64_t EltSize = TD->getTypeAllocSizeInBits(AT->getElementType());
+    for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
+      Value *Elt = Builder.CreateExtractValue(SV, i, "tmp");
+      Old = ConvertScalar_InsertValue(Elt, Old, Offset+i*EltSize, Builder);
+    }
+    return Old;
+  }
+
+  // If SV is a float, convert it to the appropriate integer type.
+  // If it is a pointer, do the same.
+  unsigned SrcWidth = TD->getTypeSizeInBits(SV->getType());
+  unsigned DestWidth = TD->getTypeSizeInBits(AllocaType);
+  unsigned SrcStoreWidth = TD->getTypeStoreSizeInBits(SV->getType());
+  unsigned DestStoreWidth = TD->getTypeStoreSizeInBits(AllocaType);
+  if (SV->getType()->isFloatingPoint() || isa<VectorType>(SV->getType()))
+    SV = Builder.CreateBitCast(SV, IntegerType::get(SrcWidth), "tmp");
+  else if (isa<PointerType>(SV->getType()))
+    SV = Builder.CreatePtrToInt(SV, TD->getIntPtrType(), "tmp");
+
+  // Zero extend or truncate the value if needed.
+  if (SV->getType() != AllocaType) {
+    if (SV->getType()->getPrimitiveSizeInBits() <
+             AllocaType->getPrimitiveSizeInBits())
+      SV = Builder.CreateZExt(SV, AllocaType, "tmp");
+    else {
+      // Truncation may be needed if storing more than the alloca can hold
+      // (undefined behavior).
+      SV = Builder.CreateTrunc(SV, AllocaType, "tmp");
+      SrcWidth = DestWidth;
+      SrcStoreWidth = DestStoreWidth;
+    }
+  }
+
+  // If this is a big-endian system and the store is narrower than the
+  // full alloca type, we need to do a shift to get the right bits.
+  int ShAmt = 0;
+  if (TD->isBigEndian()) {
+    // On big-endian machines, the lowest bit is stored at the bit offset
+    // from the pointer given by getTypeStoreSizeInBits.  This matters for
+    // integers with a bitwidth that is not a multiple of 8.
+    ShAmt = DestStoreWidth - SrcStoreWidth - Offset;
+  } else {
+    ShAmt = Offset;
+  }
+
+  // Note: we support negative bitwidths (with shr) which are not defined.
+  // We do this to support (f.e.) stores off the end of a structure where
+  // only some bits in the structure are set.
+  APInt Mask(APInt::getLowBitsSet(DestWidth, SrcWidth));
+  if (ShAmt > 0 && (unsigned)ShAmt < DestWidth) {
+    SV = Builder.CreateShl(SV, ConstantInt::get(SV->getType(), ShAmt), "tmp");
+    Mask <<= ShAmt;
+  } else if (ShAmt < 0 && (unsigned)-ShAmt < DestWidth) {
+    SV = Builder.CreateLShr(SV, ConstantInt::get(SV->getType(), -ShAmt), "tmp");
+    Mask = Mask.lshr(-ShAmt);
+  }
+
+  // Mask out the bits we are about to insert from the old value, and or
+  // in the new bits.
+  if (SrcWidth != DestWidth) {
+    assert(DestWidth > SrcWidth);
+    Old = Builder.CreateAnd(Old, ConstantInt::get(~Mask), "mask");
+    SV = Builder.CreateOr(Old, SV, "ins");
+  }
+  return SV;
+}
+
+
+
+/// PointsToConstantGlobal - Return true if V (possibly indirectly) points to
+/// some part of a constant global variable.  This intentionally only accepts
+/// constant expressions because we don't can't rewrite arbitrary instructions.
+static bool PointsToConstantGlobal(Value *V) {
+  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
+    return GV->isConstant();
+  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
+    if (CE->getOpcode() == Instruction::BitCast || 
+        CE->getOpcode() == Instruction::GetElementPtr)
+      return PointsToConstantGlobal(CE->getOperand(0));
+  return false;
+}
+
+/// isOnlyCopiedFromConstantGlobal - Recursively walk the uses of a (derived)
+/// pointer to an alloca.  Ignore any reads of the pointer, return false if we
+/// see any stores or other unknown uses.  If we see pointer arithmetic, keep
+/// track of whether it moves the pointer (with isOffset) but otherwise traverse
+/// the uses.  If we see a memcpy/memmove that targets an unoffseted pointer to
+/// the alloca, and if the source pointer is a pointer to a constant  global, we
+/// can optimize this.
+static bool isOnlyCopiedFromConstantGlobal(Value *V, Instruction *&TheCopy,
+                                           bool isOffset) {
+  for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) {
+    if (LoadInst *LI = dyn_cast<LoadInst>(*UI))
+      // Ignore non-volatile loads, they are always ok.
+      if (!LI->isVolatile())
+        continue;
+    
+    if (BitCastInst *BCI = dyn_cast<BitCastInst>(*UI)) {
+      // If uses of the bitcast are ok, we are ok.
+      if (!isOnlyCopiedFromConstantGlobal(BCI, TheCopy, isOffset))
+        return false;
+      continue;
+    }
+    if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) {
+      // If the GEP has all zero indices, it doesn't offset the pointer.  If it
+      // doesn't, it does.
+      if (!isOnlyCopiedFromConstantGlobal(GEP, TheCopy,
+                                         isOffset || !GEP->hasAllZeroIndices()))
+        return false;
+      continue;
+    }
+    
+    // If this is isn't our memcpy/memmove, reject it as something we can't
+    // handle.
+    if (!isa<MemTransferInst>(*UI))
+      return false;
+
+    // If we already have seen a copy, reject the second one.
+    if (TheCopy) return false;
+    
+    // If the pointer has been offset from the start of the alloca, we can't
+    // safely handle this.
+    if (isOffset) return false;
+
+    // If the memintrinsic isn't using the alloca as the dest, reject it.
+    if (UI.getOperandNo() != 1) return false;
+    
+    MemIntrinsic *MI = cast<MemIntrinsic>(*UI);
+    
+    // If the source of the memcpy/move is not a constant global, reject it.
+    if (!PointsToConstantGlobal(MI->getOperand(2)))
+      return false;
+    
+    // Otherwise, the transform is safe.  Remember the copy instruction.
+    TheCopy = MI;
+  }
+  return true;
+}
+
+/// isOnlyCopiedFromConstantGlobal - Return true if the specified alloca is only
+/// modified by a copy from a constant global.  If we can prove this, we can
+/// replace any uses of the alloca with uses of the global directly.
+Instruction *SROA::isOnlyCopiedFromConstantGlobal(AllocationInst *AI) {
+  Instruction *TheCopy = 0;
+  if (::isOnlyCopiedFromConstantGlobal(AI, TheCopy, false))
+    return TheCopy;
+  return 0;
+}