1 files changed, 1274 insertions, 0 deletions

diff --git a/lib/Transforms/InstCombine/InstructionCombining.cpp b/lib/Transforms/InstCombine/InstructionCombining.cpp
new file mode 100644
index 000000000000..93b196126b20
--- /dev/null
+++ b/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -0,0 +1,1274 @@
+//===- InstructionCombining.cpp - Combine multiple instructions -----------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// InstructionCombining - Combine instructions to form fewer, simple
+// instructions.  This pass does not modify the CFG.  This pass is where
+// algebraic simplification happens.
+//
+// This pass combines things like:
+//    %Y = add i32 %X, 1
+//    %Z = add i32 %Y, 1
+// into:
+//    %Z = add i32 %X, 2
+//
+// This is a simple worklist driven algorithm.
+//
+// This pass guarantees that the following canonicalizations are performed on
+// the program:
+//    1. If a binary operator has a constant operand, it is moved to the RHS
+//    2. Bitwise operators with constant operands are always grouped so that
+//       shifts are performed first, then or's, then and's, then xor's.
+//    3. Compare instructions are converted from <,>,<=,>= to ==,!= if possible
+//    4. All cmp instructions on boolean values are replaced with logical ops
+//    5. add X, X is represented as (X*2) => (X << 1)
+//    6. Multiplies with a power-of-two constant argument are transformed into
+//       shifts.
+//   ... etc.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "instcombine"
+#include "llvm/Transforms/Scalar.h"
+#include "InstCombine.h"
+#include "llvm/IntrinsicInst.h"
+#include "llvm/Analysis/ConstantFolding.h"
+#include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Analysis/MemoryBuiltins.h"
+#include "llvm/Target/TargetData.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/GetElementPtrTypeIterator.h"
+#include "llvm/Support/PatternMatch.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/Statistic.h"
+#include <algorithm>
+#include <climits>
+using namespace llvm;
+using namespace llvm::PatternMatch;
+
+STATISTIC(NumCombined , "Number of insts combined");
+STATISTIC(NumConstProp, "Number of constant folds");
+STATISTIC(NumDeadInst , "Number of dead inst eliminated");
+STATISTIC(NumSunkInst , "Number of instructions sunk");
+
+
+char InstCombiner::ID = 0;
+static RegisterPass<InstCombiner>
+X("instcombine", "Combine redundant instructions");
+
+void InstCombiner::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.addPreservedID(LCSSAID);
+  AU.setPreservesCFG();
+}
+
+
+/// ShouldChangeType - Return true if it is desirable to convert a computation
+/// from 'From' to 'To'.  We don't want to convert from a legal to an illegal
+/// type for example, or from a smaller to a larger illegal type.
+bool InstCombiner::ShouldChangeType(const Type *From, const Type *To) const {
+  assert(isa<IntegerType>(From) && isa<IntegerType>(To));
+  
+  // If we don't have TD, we don't know if the source/dest are legal.
+  if (!TD) return false;
+  
+  unsigned FromWidth = From->getPrimitiveSizeInBits();
+  unsigned ToWidth = To->getPrimitiveSizeInBits();
+  bool FromLegal = TD->isLegalInteger(FromWidth);
+  bool ToLegal = TD->isLegalInteger(ToWidth);
+  
+  // If this is a legal integer from type, and the result would be an illegal
+  // type, don't do the transformation.
+  if (FromLegal && !ToLegal)
+    return false;
+  
+  // Otherwise, if both are illegal, do not increase the size of the result. We
+  // do allow things like i160 -> i64, but not i64 -> i160.
+  if (!FromLegal && !ToLegal && ToWidth > FromWidth)
+    return false;
+  
+  return true;
+}
+
+
+// SimplifyCommutative - This performs a few simplifications for commutative
+// operators:
+//
+//  1. Order operands such that they are listed from right (least complex) to
+//     left (most complex).  This puts constants before unary operators before
+//     binary operators.
+//
+//  2. Transform: (op (op V, C1), C2) ==> (op V, (op C1, C2))
+//  3. Transform: (op (op V1, C1), (op V2, C2)) ==> (op (op V1, V2), (op C1,C2))
+//
+bool InstCombiner::SimplifyCommutative(BinaryOperator &I) {
+  bool Changed = false;
+  if (getComplexity(I.getOperand(0)) < getComplexity(I.getOperand(1)))
+    Changed = !I.swapOperands();
+
+  if (!I.isAssociative()) return Changed;
+  
+  Instruction::BinaryOps Opcode = I.getOpcode();
+  if (BinaryOperator *Op = dyn_cast<BinaryOperator>(I.getOperand(0)))
+    if (Op->getOpcode() == Opcode && isa<Constant>(Op->getOperand(1))) {
+      if (isa<Constant>(I.getOperand(1))) {
+        Constant *Folded = ConstantExpr::get(I.getOpcode(),
+                                             cast<Constant>(I.getOperand(1)),
+                                             cast<Constant>(Op->getOperand(1)));
+        I.setOperand(0, Op->getOperand(0));
+        I.setOperand(1, Folded);
+        return true;
+      }
+      
+      if (BinaryOperator *Op1 = dyn_cast<BinaryOperator>(I.getOperand(1)))
+        if (Op1->getOpcode() == Opcode && isa<Constant>(Op1->getOperand(1)) &&
+            Op->hasOneUse() && Op1->hasOneUse()) {
+          Constant *C1 = cast<Constant>(Op->getOperand(1));
+          Constant *C2 = cast<Constant>(Op1->getOperand(1));
+
+          // Fold (op (op V1, C1), (op V2, C2)) ==> (op (op V1, V2), (op C1,C2))
+          Constant *Folded = ConstantExpr::get(I.getOpcode(), C1, C2);
+          Instruction *New = BinaryOperator::Create(Opcode, Op->getOperand(0),
+                                                    Op1->getOperand(0),
+                                                    Op1->getName(), &I);
+          Worklist.Add(New);
+          I.setOperand(0, New);
+          I.setOperand(1, Folded);
+          return true;
+        }
+    }
+  return Changed;
+}
+
+// dyn_castNegVal - Given a 'sub' instruction, return the RHS of the instruction
+// if the LHS is a constant zero (which is the 'negate' form).
+//
+Value *InstCombiner::dyn_castNegVal(Value *V) const {
+  if (BinaryOperator::isNeg(V))
+    return BinaryOperator::getNegArgument(V);
+
+  // Constants can be considered to be negated values if they can be folded.
+  if (ConstantInt *C = dyn_cast<ConstantInt>(V))
+    return ConstantExpr::getNeg(C);
+
+  if (ConstantVector *C = dyn_cast<ConstantVector>(V))
+    if (C->getType()->getElementType()->isInteger())
+      return ConstantExpr::getNeg(C);
+
+  return 0;
+}
+
+// dyn_castFNegVal - Given a 'fsub' instruction, return the RHS of the
+// instruction if the LHS is a constant negative zero (which is the 'negate'
+// form).
+//
+Value *InstCombiner::dyn_castFNegVal(Value *V) const {
+  if (BinaryOperator::isFNeg(V))
+    return BinaryOperator::getFNegArgument(V);
+
+  // Constants can be considered to be negated values if they can be folded.
+  if (ConstantFP *C = dyn_cast<ConstantFP>(V))
+    return ConstantExpr::getFNeg(C);
+
+  if (ConstantVector *C = dyn_cast<ConstantVector>(V))
+    if (C->getType()->getElementType()->isFloatingPoint())
+      return ConstantExpr::getFNeg(C);
+
+  return 0;
+}
+
+static Value *FoldOperationIntoSelectOperand(Instruction &I, Value *SO,
+                                             InstCombiner *IC) {
+  if (CastInst *CI = dyn_cast<CastInst>(&I))
+    return IC->Builder->CreateCast(CI->getOpcode(), SO, I.getType());
+
+  // Figure out if the constant is the left or the right argument.
+  bool ConstIsRHS = isa<Constant>(I.getOperand(1));
+  Constant *ConstOperand = cast<Constant>(I.getOperand(ConstIsRHS));
+
+  if (Constant *SOC = dyn_cast<Constant>(SO)) {
+    if (ConstIsRHS)
+      return ConstantExpr::get(I.getOpcode(), SOC, ConstOperand);
+    return ConstantExpr::get(I.getOpcode(), ConstOperand, SOC);
+  }
+
+  Value *Op0 = SO, *Op1 = ConstOperand;
+  if (!ConstIsRHS)
+    std::swap(Op0, Op1);
+  
+  if (BinaryOperator *BO = dyn_cast<BinaryOperator>(&I))
+    return IC->Builder->CreateBinOp(BO->getOpcode(), Op0, Op1,
+                                    SO->getName()+".op");
+  if (ICmpInst *CI = dyn_cast<ICmpInst>(&I))
+    return IC->Builder->CreateICmp(CI->getPredicate(), Op0, Op1,
+                                   SO->getName()+".cmp");
+  if (FCmpInst *CI = dyn_cast<FCmpInst>(&I))
+    return IC->Builder->CreateICmp(CI->getPredicate(), Op0, Op1,
+                                   SO->getName()+".cmp");
+  llvm_unreachable("Unknown binary instruction type!");
+}
+
+// FoldOpIntoSelect - Given an instruction with a select as one operand and a
+// constant as the other operand, try to fold the binary operator into the
+// select arguments.  This also works for Cast instructions, which obviously do
+// not have a second operand.
+Instruction *InstCombiner::FoldOpIntoSelect(Instruction &Op, SelectInst *SI) {
+  // Don't modify shared select instructions
+  if (!SI->hasOneUse()) return 0;
+  Value *TV = SI->getOperand(1);
+  Value *FV = SI->getOperand(2);
+
+  if (isa<Constant>(TV) || isa<Constant>(FV)) {
+    // Bool selects with constant operands can be folded to logical ops.
+    if (SI->getType()->isInteger(1)) return 0;
+
+    Value *SelectTrueVal = FoldOperationIntoSelectOperand(Op, TV, this);
+    Value *SelectFalseVal = FoldOperationIntoSelectOperand(Op, FV, this);
+
+    return SelectInst::Create(SI->getCondition(), SelectTrueVal,
+                              SelectFalseVal);
+  }
+  return 0;
+}
+
+
+/// FoldOpIntoPhi - Given a binary operator, cast instruction, or select which
+/// has a PHI node as operand #0, see if we can fold the instruction into the
+/// PHI (which is only possible if all operands to the PHI are constants).
+///
+/// If AllowAggressive is true, FoldOpIntoPhi will allow certain transforms
+/// that would normally be unprofitable because they strongly encourage jump
+/// threading.
+Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I,
+                                         bool AllowAggressive) {
+  AllowAggressive = false;
+  PHINode *PN = cast<PHINode>(I.getOperand(0));
+  unsigned NumPHIValues = PN->getNumIncomingValues();
+  if (NumPHIValues == 0 ||
+      // We normally only transform phis with a single use, unless we're trying
+      // hard to make jump threading happen.
+      (!PN->hasOneUse() && !AllowAggressive))
+    return 0;
+  
+  
+  // Check to see if all of the operands of the PHI are simple constants
+  // (constantint/constantfp/undef).  If there is one non-constant value,
+  // remember the BB it is in.  If there is more than one or if *it* is a PHI,
+  // bail out.  We don't do arbitrary constant expressions here because moving
+  // their computation can be expensive without a cost model.
+  BasicBlock *NonConstBB = 0;
+  for (unsigned i = 0; i != NumPHIValues; ++i)
+    if (!isa<Constant>(PN->getIncomingValue(i)) ||
+        isa<ConstantExpr>(PN->getIncomingValue(i))) {
+      if (NonConstBB) return 0;  // More than one non-const value.
+      if (isa<PHINode>(PN->getIncomingValue(i))) return 0;  // Itself a phi.
+      NonConstBB = PN->getIncomingBlock(i);
+      
+      // If the incoming non-constant value is in I's block, we have an infinite
+      // loop.
+      if (NonConstBB == I.getParent())
+        return 0;
+    }
+  
+  // If there is exactly one non-constant value, we can insert a copy of the
+  // operation in that block.  However, if this is a critical edge, we would be
+  // inserting the computation one some other paths (e.g. inside a loop).  Only
+  // do this if the pred block is unconditionally branching into the phi block.
+  if (NonConstBB != 0 && !AllowAggressive) {
+    BranchInst *BI = dyn_cast<BranchInst>(NonConstBB->getTerminator());
+    if (!BI || !BI->isUnconditional()) return 0;
+  }
+
+  // Okay, we can do the transformation: create the new PHI node.
+  PHINode *NewPN = PHINode::Create(I.getType(), "");
+  NewPN->reserveOperandSpace(PN->getNumOperands()/2);
+  InsertNewInstBefore(NewPN, *PN);
+  NewPN->takeName(PN);
+
+  // Next, add all of the operands to the PHI.
+  if (SelectInst *SI = dyn_cast<SelectInst>(&I)) {
+    // We only currently try to fold the condition of a select when it is a phi,
+    // not the true/false values.
+    Value *TrueV = SI->getTrueValue();
+    Value *FalseV = SI->getFalseValue();
+    BasicBlock *PhiTransBB = PN->getParent();
+    for (unsigned i = 0; i != NumPHIValues; ++i) {
+      BasicBlock *ThisBB = PN->getIncomingBlock(i);
+      Value *TrueVInPred = TrueV->DoPHITranslation(PhiTransBB, ThisBB);
+      Value *FalseVInPred = FalseV->DoPHITranslation(PhiTransBB, ThisBB);
+      Value *InV = 0;
+      if (Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i))) {
+        InV = InC->isNullValue() ? FalseVInPred : TrueVInPred;
+      } else {
+        assert(PN->getIncomingBlock(i) == NonConstBB);
+        InV = SelectInst::Create(PN->getIncomingValue(i), TrueVInPred,
+                                 FalseVInPred,
+                                 "phitmp", NonConstBB->getTerminator());
+        Worklist.Add(cast<Instruction>(InV));
+      }
+      NewPN->addIncoming(InV, ThisBB);
+    }
+  } else if (I.getNumOperands() == 2) {
+    Constant *C = cast<Constant>(I.getOperand(1));
+    for (unsigned i = 0; i != NumPHIValues; ++i) {
+      Value *InV = 0;
+      if (Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i))) {
+        if (CmpInst *CI = dyn_cast<CmpInst>(&I))
+          InV = ConstantExpr::getCompare(CI->getPredicate(), InC, C);
+        else
+          InV = ConstantExpr::get(I.getOpcode(), InC, C);
+      } else {
+        assert(PN->getIncomingBlock(i) == NonConstBB);
+        if (BinaryOperator *BO = dyn_cast<BinaryOperator>(&I)) 
+          InV = BinaryOperator::Create(BO->getOpcode(),
+                                       PN->getIncomingValue(i), C, "phitmp",
+                                       NonConstBB->getTerminator());
+        else if (CmpInst *CI = dyn_cast<CmpInst>(&I))
+          InV = CmpInst::Create(CI->getOpcode(),
+                                CI->getPredicate(),
+                                PN->getIncomingValue(i), C, "phitmp",
+                                NonConstBB->getTerminator());
+        else
+          llvm_unreachable("Unknown binop!");
+        
+        Worklist.Add(cast<Instruction>(InV));
+      }
+      NewPN->addIncoming(InV, PN->getIncomingBlock(i));
+    }
+  } else { 
+    CastInst *CI = cast<CastInst>(&I);
+    const Type *RetTy = CI->getType();
+    for (unsigned i = 0; i != NumPHIValues; ++i) {
+      Value *InV;
+      if (Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i))) {
+        InV = ConstantExpr::getCast(CI->getOpcode(), InC, RetTy);
+      } else {
+        assert(PN->getIncomingBlock(i) == NonConstBB);
+        InV = CastInst::Create(CI->getOpcode(), PN->getIncomingValue(i), 
+                               I.getType(), "phitmp", 
+                               NonConstBB->getTerminator());
+        Worklist.Add(cast<Instruction>(InV));
+      }
+      NewPN->addIncoming(InV, PN->getIncomingBlock(i));
+    }
+  }
+  return ReplaceInstUsesWith(I, NewPN);
+}
+
+/// FindElementAtOffset - Given a type and a constant offset, determine whether
+/// or not there is a sequence of GEP indices into the type that will land us at
+/// the specified offset.  If so, fill them into NewIndices and return the
+/// resultant element type, otherwise return null.
+const Type *InstCombiner::FindElementAtOffset(const Type *Ty, int64_t Offset, 
+                                          SmallVectorImpl<Value*> &NewIndices) {
+  if (!TD) return 0;
+  if (!Ty->isSized()) return 0;
+  
+  // Start with the index over the outer type.  Note that the type size
+  // might be zero (even if the offset isn't zero) if the indexed type
+  // is something like [0 x {int, int}]
+  const Type *IntPtrTy = TD->getIntPtrType(Ty->getContext());
+  int64_t FirstIdx = 0;
+  if (int64_t TySize = TD->getTypeAllocSize(Ty)) {
+    FirstIdx = Offset/TySize;
+    Offset -= FirstIdx*TySize;
+    
+    // Handle hosts where % returns negative instead of values [0..TySize).
+    if (Offset < 0) {
+      --FirstIdx;
+      Offset += TySize;
+      assert(Offset >= 0);
+    }
+    assert((uint64_t)Offset < (uint64_t)TySize && "Out of range offset");
+  }
+  
+  NewIndices.push_back(ConstantInt::get(IntPtrTy, FirstIdx));
+    
+  // Index into the types.  If we fail, set OrigBase to null.
+  while (Offset) {
+    // Indexing into tail padding between struct/array elements.
+    if (uint64_t(Offset*8) >= TD->getTypeSizeInBits(Ty))
+      return 0;
+    
+    if (const StructType *STy = dyn_cast<StructType>(Ty)) {
+      const StructLayout *SL = TD->getStructLayout(STy);
+      assert(Offset < (int64_t)SL->getSizeInBytes() &&
+             "Offset must stay within the indexed type");
+      
+      unsigned Elt = SL->getElementContainingOffset(Offset);
+      NewIndices.push_back(ConstantInt::get(Type::getInt32Ty(Ty->getContext()),
+                                            Elt));
+      
+      Offset -= SL->getElementOffset(Elt);
+      Ty = STy->getElementType(Elt);
+    } else if (const ArrayType *AT = dyn_cast<ArrayType>(Ty)) {
+      uint64_t EltSize = TD->getTypeAllocSize(AT->getElementType());
+      assert(EltSize && "Cannot index into a zero-sized array");
+      NewIndices.push_back(ConstantInt::get(IntPtrTy,Offset/EltSize));
+      Offset %= EltSize;
+      Ty = AT->getElementType();
+    } else {
+      // Otherwise, we can't index into the middle of this atomic type, bail.
+      return 0;
+    }
+  }
+  
+  return Ty;
+}
+
+
+
+Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
+  SmallVector<Value*, 8> Ops(GEP.op_begin(), GEP.op_end());
+
+  if (Value *V = SimplifyGEPInst(&Ops[0], Ops.size(), TD))
+    return ReplaceInstUsesWith(GEP, V);
+
+  Value *PtrOp = GEP.getOperand(0);
+
+  if (isa<UndefValue>(GEP.getOperand(0)))
+    return ReplaceInstUsesWith(GEP, UndefValue::get(GEP.getType()));
+
+  // Eliminate unneeded casts for indices.
+  if (TD) {
+    bool MadeChange = false;
+    unsigned PtrSize = TD->getPointerSizeInBits();
+    
+    gep_type_iterator GTI = gep_type_begin(GEP);
+    for (User::op_iterator I = GEP.op_begin() + 1, E = GEP.op_end();
+         I != E; ++I, ++GTI) {
+      if (!isa<SequentialType>(*GTI)) continue;
+      
+      // If we are using a wider index than needed for this platform, shrink it
+      // to what we need.  If narrower, sign-extend it to what we need.  This
+      // explicit cast can make subsequent optimizations more obvious.
+      unsigned OpBits = cast<IntegerType>((*I)->getType())->getBitWidth();
+      if (OpBits == PtrSize)
+        continue;
+      
+      *I = Builder->CreateIntCast(*I, TD->getIntPtrType(GEP.getContext()),true);
+      MadeChange = true;
+    }
+    if (MadeChange) return &GEP;
+  }
+
+  // Combine Indices - If the source pointer to this getelementptr instruction
+  // is a getelementptr instruction, combine the indices of the two
+  // getelementptr instructions into a single instruction.
+  //
+  if (GEPOperator *Src = dyn_cast<GEPOperator>(PtrOp)) {
+    // Note that if our source is a gep chain itself that we wait for that
+    // chain to be resolved before we perform this transformation.  This
+    // avoids us creating a TON of code in some cases.
+    //
+    if (GetElementPtrInst *SrcGEP =
+          dyn_cast<GetElementPtrInst>(Src->getOperand(0)))
+      if (SrcGEP->getNumOperands() == 2)
+        return 0;   // Wait until our source is folded to completion.
+
+    SmallVector<Value*, 8> Indices;
+
+    // Find out whether the last index in the source GEP is a sequential idx.
+    bool EndsWithSequential = false;
+    for (gep_type_iterator I = gep_type_begin(*Src), E = gep_type_end(*Src);
+         I != E; ++I)
+      EndsWithSequential = !isa<StructType>(*I);
+
+    // Can we combine the two pointer arithmetics offsets?
+    if (EndsWithSequential) {
+      // Replace: gep (gep %P, long B), long A, ...
+      // With:    T = long A+B; gep %P, T, ...
+      //
+      Value *Sum;
+      Value *SO1 = Src->getOperand(Src->getNumOperands()-1);
+      Value *GO1 = GEP.getOperand(1);
+      if (SO1 == Constant::getNullValue(SO1->getType())) {
+        Sum = GO1;
+      } else if (GO1 == Constant::getNullValue(GO1->getType())) {
+        Sum = SO1;
+      } else {
+        // If they aren't the same type, then the input hasn't been processed
+        // by the loop above yet (which canonicalizes sequential index types to
+        // intptr_t).  Just avoid transforming this until the input has been
+        // normalized.
+        if (SO1->getType() != GO1->getType())
+          return 0;
+        Sum = Builder->CreateAdd(SO1, GO1, PtrOp->getName()+".sum");
+      }
+
+      // Update the GEP in place if possible.
+      if (Src->getNumOperands() == 2) {
+        GEP.setOperand(0, Src->getOperand(0));
+        GEP.setOperand(1, Sum);
+        return &GEP;
+      }
+      Indices.append(Src->op_begin()+1, Src->op_end()-1);
+      Indices.push_back(Sum);
+      Indices.append(GEP.op_begin()+2, GEP.op_end());
+    } else if (isa<Constant>(*GEP.idx_begin()) &&
+               cast<Constant>(*GEP.idx_begin())->isNullValue() &&
+               Src->getNumOperands() != 1) {
+      // Otherwise we can do the fold if the first index of the GEP is a zero
+      Indices.append(Src->op_begin()+1, Src->op_end());
+      Indices.append(GEP.idx_begin()+1, GEP.idx_end());
+    }
+
+    if (!Indices.empty())
+      return (GEP.isInBounds() && Src->isInBounds()) ?
+        GetElementPtrInst::CreateInBounds(Src->getOperand(0), Indices.begin(),
+                                          Indices.end(), GEP.getName()) :
+        GetElementPtrInst::Create(Src->getOperand(0), Indices.begin(),
+                                  Indices.end(), GEP.getName());
+  }
+  
+  // Handle gep(bitcast x) and gep(gep x, 0, 0, 0).
+  Value *StrippedPtr = PtrOp->stripPointerCasts();
+  if (StrippedPtr != PtrOp) {
+    const PointerType *StrippedPtrTy =cast<PointerType>(StrippedPtr->getType());
+
+    bool HasZeroPointerIndex = false;
+    if (ConstantInt *C = dyn_cast<ConstantInt>(GEP.getOperand(1)))
+      HasZeroPointerIndex = C->isZero();
+    
+    // Transform: GEP (bitcast [10 x i8]* X to [0 x i8]*), i32 0, ...
+    // into     : GEP [10 x i8]* X, i32 0, ...
+    //
+    // Likewise, transform: GEP (bitcast i8* X to [0 x i8]*), i32 0, ...
+    //           into     : GEP i8* X, ...
+    // 
+    // This occurs when the program declares an array extern like "int X[];"
+    if (HasZeroPointerIndex) {
+      const PointerType *CPTy = cast<PointerType>(PtrOp->getType());
+      if (const ArrayType *CATy =
+          dyn_cast<ArrayType>(CPTy->getElementType())) {
+        // GEP (bitcast i8* X to [0 x i8]*), i32 0, ... ?
+        if (CATy->getElementType() == StrippedPtrTy->getElementType()) {
+          // -> GEP i8* X, ...
+          SmallVector<Value*, 8> Idx(GEP.idx_begin()+1, GEP.idx_end());
+          GetElementPtrInst *Res =
+            GetElementPtrInst::Create(StrippedPtr, Idx.begin(),
+                                      Idx.end(), GEP.getName());
+          Res->setIsInBounds(GEP.isInBounds());
+          return Res;
+        }
+        
+        if (const ArrayType *XATy =
+              dyn_cast<ArrayType>(StrippedPtrTy->getElementType())){
+          // GEP (bitcast [10 x i8]* X to [0 x i8]*), i32 0, ... ?
+          if (CATy->getElementType() == XATy->getElementType()) {
+            // -> GEP [10 x i8]* X, i32 0, ...
+            // At this point, we know that the cast source type is a pointer
+            // to an array of the same type as the destination pointer
+            // array.  Because the array type is never stepped over (there
+            // is a leading zero) we can fold the cast into this GEP.
+            GEP.setOperand(0, StrippedPtr);
+            return &GEP;
+          }
+        }
+      }
+    } else if (GEP.getNumOperands() == 2) {
+      // Transform things like:
+      // %t = getelementptr i32* bitcast ([2 x i32]* %str to i32*), i32 %V
+      // into:  %t1 = getelementptr [2 x i32]* %str, i32 0, i32 %V; bitcast
+      const Type *SrcElTy = StrippedPtrTy->getElementType();
+      const Type *ResElTy=cast<PointerType>(PtrOp->getType())->getElementType();
+      if (TD && isa<ArrayType>(SrcElTy) &&
+          TD->getTypeAllocSize(cast<ArrayType>(SrcElTy)->getElementType()) ==
+          TD->getTypeAllocSize(ResElTy)) {
+        Value *Idx[2];
+        Idx[0] = Constant::getNullValue(Type::getInt32Ty(GEP.getContext()));
+        Idx[1] = GEP.getOperand(1);
+        Value *NewGEP = GEP.isInBounds() ?
+          Builder->CreateInBoundsGEP(StrippedPtr, Idx, Idx + 2, GEP.getName()) :
+          Builder->CreateGEP(StrippedPtr, Idx, Idx + 2, GEP.getName());
+        // V and GEP are both pointer types --> BitCast
+        return new BitCastInst(NewGEP, GEP.getType());
+      }
+      
+      // Transform things like:
+      // getelementptr i8* bitcast ([100 x double]* X to i8*), i32 %tmp
+      //   (where tmp = 8*tmp2) into:
+      // getelementptr [100 x double]* %arr, i32 0, i32 %tmp2; bitcast
+      
+      if (TD && isa<ArrayType>(SrcElTy) && ResElTy->isInteger(8)) {
+        uint64_t ArrayEltSize =
+            TD->getTypeAllocSize(cast<ArrayType>(SrcElTy)->getElementType());
+        
+        // Check to see if "tmp" is a scale by a multiple of ArrayEltSize.  We
+        // allow either a mul, shift, or constant here.
+        Value *NewIdx = 0;
+        ConstantInt *Scale = 0;
+        if (ArrayEltSize == 1) {
+          NewIdx = GEP.getOperand(1);
+          Scale = ConstantInt::get(cast<IntegerType>(NewIdx->getType()), 1);
+        } else if (ConstantInt *CI = dyn_cast<ConstantInt>(GEP.getOperand(1))) {
+          NewIdx = ConstantInt::get(CI->getType(), 1);
+          Scale = CI;
+        } else if (Instruction *Inst =dyn_cast<Instruction>(GEP.getOperand(1))){
+          if (Inst->getOpcode() == Instruction::Shl &&
+              isa<ConstantInt>(Inst->getOperand(1))) {
+            ConstantInt *ShAmt = cast<ConstantInt>(Inst->getOperand(1));
+            uint32_t ShAmtVal = ShAmt->getLimitedValue(64);
+            Scale = ConstantInt::get(cast<IntegerType>(Inst->getType()),
+                                     1ULL << ShAmtVal);
+            NewIdx = Inst->getOperand(0);
+          } else if (Inst->getOpcode() == Instruction::Mul &&
+                     isa<ConstantInt>(Inst->getOperand(1))) {
+            Scale = cast<ConstantInt>(Inst->getOperand(1));
+            NewIdx = Inst->getOperand(0);
+          }
+        }
+        
+        // If the index will be to exactly the right offset with the scale taken
+        // out, perform the transformation. Note, we don't know whether Scale is
+        // signed or not. We'll use unsigned version of division/modulo
+        // operation after making sure Scale doesn't have the sign bit set.
+        if (ArrayEltSize && Scale && Scale->getSExtValue() >= 0LL &&
+            Scale->getZExtValue() % ArrayEltSize == 0) {
+          Scale = ConstantInt::get(Scale->getType(),
+                                   Scale->getZExtValue() / ArrayEltSize);
+          if (Scale->getZExtValue() != 1) {
+            Constant *C = ConstantExpr::getIntegerCast(Scale, NewIdx->getType(),
+                                                       false /*ZExt*/);
+            NewIdx = Builder->CreateMul(NewIdx, C, "idxscale");
+          }
+
+          // Insert the new GEP instruction.
+          Value *Idx[2];
+          Idx[0] = Constant::getNullValue(Type::getInt32Ty(GEP.getContext()));
+          Idx[1] = NewIdx;
+          Value *NewGEP = GEP.isInBounds() ?
+            Builder->CreateInBoundsGEP(StrippedPtr, Idx, Idx + 2,GEP.getName()):
+            Builder->CreateGEP(StrippedPtr, Idx, Idx + 2, GEP.getName());
+          // The NewGEP must be pointer typed, so must the old one -> BitCast
+          return new BitCastInst(NewGEP, GEP.getType());
+        }
+      }
+    }
+  }
+  
+  /// See if we can simplify:
+  ///   X = bitcast A* to B*
+  ///   Y = gep X, <...constant indices...>
+  /// into a gep of the original struct.  This is important for SROA and alias
+  /// analysis of unions.  If "A" is also a bitcast, wait for A/X to be merged.
+  if (BitCastInst *BCI = dyn_cast<BitCastInst>(PtrOp)) {
+    if (TD &&
+        !isa<BitCastInst>(BCI->getOperand(0)) && GEP.hasAllConstantIndices()) {
+      // Determine how much the GEP moves the pointer.  We are guaranteed to get
+      // a constant back from EmitGEPOffset.
+      ConstantInt *OffsetV = cast<ConstantInt>(EmitGEPOffset(&GEP));
+      int64_t Offset = OffsetV->getSExtValue();
+      
+      // If this GEP instruction doesn't move the pointer, just replace the GEP
+      // with a bitcast of the real input to the dest type.
+      if (Offset == 0) {
+        // If the bitcast is of an allocation, and the allocation will be
+        // converted to match the type of the cast, don't touch this.
+        if (isa<AllocaInst>(BCI->getOperand(0)) ||
+            isMalloc(BCI->getOperand(0))) {
+          // See if the bitcast simplifies, if so, don't nuke this GEP yet.
+          if (Instruction *I = visitBitCast(*BCI)) {
+            if (I != BCI) {
+              I->takeName(BCI);
+              BCI->getParent()->getInstList().insert(BCI, I);
+              ReplaceInstUsesWith(*BCI, I);
+            }
+            return &GEP;
+          }
+        }
+        return new BitCastInst(BCI->getOperand(0), GEP.getType());
+      }
+      
+      // Otherwise, if the offset is non-zero, we need to find out if there is a
+      // field at Offset in 'A's type.  If so, we can pull the cast through the
+      // GEP.
+      SmallVector<Value*, 8> NewIndices;
+      const Type *InTy =
+        cast<PointerType>(BCI->getOperand(0)->getType())->getElementType();
+      if (FindElementAtOffset(InTy, Offset, NewIndices)) {
+        Value *NGEP = GEP.isInBounds() ?
+          Builder->CreateInBoundsGEP(BCI->getOperand(0), NewIndices.begin(),
+                                     NewIndices.end()) :
+          Builder->CreateGEP(BCI->getOperand(0), NewIndices.begin(),
+                             NewIndices.end());
+        
+        if (NGEP->getType() == GEP.getType())
+          return ReplaceInstUsesWith(GEP, NGEP);
+        NGEP->takeName(&GEP);
+        return new BitCastInst(NGEP, GEP.getType());
+      }
+    }
+  }    
+    
+  return 0;
+}
+
+Instruction *InstCombiner::visitFree(Instruction &FI) {
+  Value *Op = FI.getOperand(1);
+
+  // free undef -> unreachable.
+  if (isa<UndefValue>(Op)) {
+    // Insert a new store to null because we cannot modify the CFG here.
+    new StoreInst(ConstantInt::getTrue(FI.getContext()),
+           UndefValue::get(Type::getInt1PtrTy(FI.getContext())), &FI);
+    return EraseInstFromFunction(FI);
+  }
+  
+  // If we have 'free null' delete the instruction.  This can happen in stl code
+  // when lots of inlining happens.
+  if (isa<ConstantPointerNull>(Op))
+    return EraseInstFromFunction(FI);
+
+  // If we have a malloc call whose only use is a free call, delete both.
+  if (isMalloc(Op)) {
+    if (CallInst* CI = extractMallocCallFromBitCast(Op)) {
+      if (Op->hasOneUse() && CI->hasOneUse()) {
+        EraseInstFromFunction(FI);
+        EraseInstFromFunction(*CI);
+        return EraseInstFromFunction(*cast<Instruction>(Op));
+      }
+    } else {
+      // Op is a call to malloc
+      if (Op->hasOneUse()) {
+        EraseInstFromFunction(FI);
+        return EraseInstFromFunction(*cast<Instruction>(Op));
+      }
+    }
+  }
+
+  return 0;
+}
+
+
+
+Instruction *InstCombiner::visitBranchInst(BranchInst &BI) {
+  // Change br (not X), label True, label False to: br X, label False, True
+  Value *X = 0;
+  BasicBlock *TrueDest;
+  BasicBlock *FalseDest;
+  if (match(&BI, m_Br(m_Not(m_Value(X)), TrueDest, FalseDest)) &&
+      !isa<Constant>(X)) {
+    // Swap Destinations and condition...
+    BI.setCondition(X);
+    BI.setSuccessor(0, FalseDest);
+    BI.setSuccessor(1, TrueDest);
+    return &BI;
+  }
+
+  // Cannonicalize fcmp_one -> fcmp_oeq
+  FCmpInst::Predicate FPred; Value *Y;
+  if (match(&BI, m_Br(m_FCmp(FPred, m_Value(X), m_Value(Y)), 
+                             TrueDest, FalseDest)) &&
+      BI.getCondition()->hasOneUse())
+    if (FPred == FCmpInst::FCMP_ONE || FPred == FCmpInst::FCMP_OLE ||
+        FPred == FCmpInst::FCMP_OGE) {
+      FCmpInst *Cond = cast<FCmpInst>(BI.getCondition());
+      Cond->setPredicate(FCmpInst::getInversePredicate(FPred));
+      
+      // Swap Destinations and condition.
+      BI.setSuccessor(0, FalseDest);
+      BI.setSuccessor(1, TrueDest);
+      Worklist.Add(Cond);
+      return &BI;
+    }
+
+  // Cannonicalize icmp_ne -> icmp_eq
+  ICmpInst::Predicate IPred;
+  if (match(&BI, m_Br(m_ICmp(IPred, m_Value(X), m_Value(Y)),
+                      TrueDest, FalseDest)) &&
+      BI.getCondition()->hasOneUse())
+    if (IPred == ICmpInst::ICMP_NE  || IPred == ICmpInst::ICMP_ULE ||
+        IPred == ICmpInst::ICMP_SLE || IPred == ICmpInst::ICMP_UGE ||
+        IPred == ICmpInst::ICMP_SGE) {
+      ICmpInst *Cond = cast<ICmpInst>(BI.getCondition());
+      Cond->setPredicate(ICmpInst::getInversePredicate(IPred));
+      // Swap Destinations and condition.
+      BI.setSuccessor(0, FalseDest);
+      BI.setSuccessor(1, TrueDest);
+      Worklist.Add(Cond);
+      return &BI;
+    }
+
+  return 0;
+}
+
+Instruction *InstCombiner::visitSwitchInst(SwitchInst &SI) {
+  Value *Cond = SI.getCondition();
+  if (Instruction *I = dyn_cast<Instruction>(Cond)) {
+    if (I->getOpcode() == Instruction::Add)
+      if (ConstantInt *AddRHS = dyn_cast<ConstantInt>(I->getOperand(1))) {
+        // change 'switch (X+4) case 1:' into 'switch (X) case -3'
+        for (unsigned i = 2, e = SI.getNumOperands(); i != e; i += 2)
+          SI.setOperand(i,
+                   ConstantExpr::getSub(cast<Constant>(SI.getOperand(i)),
+                                                AddRHS));
+        SI.setOperand(0, I->getOperand(0));
+        Worklist.Add(I);
+        return &SI;
+      }
+  }
+  return 0;
+}
+
+Instruction *InstCombiner::visitExtractValueInst(ExtractValueInst &EV) {
+  Value *Agg = EV.getAggregateOperand();
+
+  if (!EV.hasIndices())
+    return ReplaceInstUsesWith(EV, Agg);
+
+  if (Constant *C = dyn_cast<Constant>(Agg)) {
+    if (isa<UndefValue>(C))
+      return ReplaceInstUsesWith(EV, UndefValue::get(EV.getType()));
+      
+    if (isa<ConstantAggregateZero>(C))
+      return ReplaceInstUsesWith(EV, Constant::getNullValue(EV.getType()));
+
+    if (isa<ConstantArray>(C) || isa<ConstantStruct>(C)) {
+      // Extract the element indexed by the first index out of the constant
+      Value *V = C->getOperand(*EV.idx_begin());
+      if (EV.getNumIndices() > 1)
+        // Extract the remaining indices out of the constant indexed by the
+        // first index
+        return ExtractValueInst::Create(V, EV.idx_begin() + 1, EV.idx_end());
+      else
+        return ReplaceInstUsesWith(EV, V);
+    }
+    return 0; // Can't handle other constants
+  } 
+  if (InsertValueInst *IV = dyn_cast<InsertValueInst>(Agg)) {
+    // We're extracting from an insertvalue instruction, compare the indices
+    const unsigned *exti, *exte, *insi, *inse;
+    for (exti = EV.idx_begin(), insi = IV->idx_begin(),
+         exte = EV.idx_end(), inse = IV->idx_end();
+         exti != exte && insi != inse;
+         ++exti, ++insi) {
+      if (*insi != *exti)
+        // The insert and extract both reference distinctly different elements.
+        // This means the extract is not influenced by the insert, and we can
+        // replace the aggregate operand of the extract with the aggregate
+        // operand of the insert. i.e., replace
+        // %I = insertvalue { i32, { i32 } } %A, { i32 } { i32 42 }, 1
+        // %E = extractvalue { i32, { i32 } } %I, 0
+        // with
+        // %E = extractvalue { i32, { i32 } } %A, 0
+        return ExtractValueInst::Create(IV->getAggregateOperand(),
+                                        EV.idx_begin(), EV.idx_end());
+    }
+    if (exti == exte && insi == inse)
+      // Both iterators are at the end: Index lists are identical. Replace
+      // %B = insertvalue { i32, { i32 } } %A, i32 42, 1, 0
+      // %C = extractvalue { i32, { i32 } } %B, 1, 0
+      // with "i32 42"
+      return ReplaceInstUsesWith(EV, IV->getInsertedValueOperand());
+    if (exti == exte) {
+      // The extract list is a prefix of the insert list. i.e. replace
+      // %I = insertvalue { i32, { i32 } } %A, i32 42, 1, 0
+      // %E = extractvalue { i32, { i32 } } %I, 1
+      // with
+      // %X = extractvalue { i32, { i32 } } %A, 1
+      // %E = insertvalue { i32 } %X, i32 42, 0
+      // by switching the order of the insert and extract (though the
+      // insertvalue should be left in, since it may have other uses).
+      Value *NewEV = Builder->CreateExtractValue(IV->getAggregateOperand(),
+                                                 EV.idx_begin(), EV.idx_end());
+      return InsertValueInst::Create(NewEV, IV->getInsertedValueOperand(),
+                                     insi, inse);
+    }
+    if (insi == inse)
+      // The insert list is a prefix of the extract list
+      // We can simply remove the common indices from the extract and make it
+      // operate on the inserted value instead of the insertvalue result.
+      // i.e., replace
+      // %I = insertvalue { i32, { i32 } } %A, { i32 } { i32 42 }, 1
+      // %E = extractvalue { i32, { i32 } } %I, 1, 0
+      // with
+      // %E extractvalue { i32 } { i32 42 }, 0
+      return ExtractValueInst::Create(IV->getInsertedValueOperand(), 
+                                      exti, exte);
+  }
+  if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Agg)) {
+    // We're extracting from an intrinsic, see if we're the only user, which
+    // allows us to simplify multiple result intrinsics to simpler things that
+    // just get one value..
+    if (II->hasOneUse()) {
+      // Check if we're grabbing the overflow bit or the result of a 'with
+      // overflow' intrinsic.  If it's the latter we can remove the intrinsic
+      // and replace it with a traditional binary instruction.
+      switch (II->getIntrinsicID()) {
+      case Intrinsic::uadd_with_overflow:
+      case Intrinsic::sadd_with_overflow:
+        if (*EV.idx_begin() == 0) {  // Normal result.
+          Value *LHS = II->getOperand(1), *RHS = II->getOperand(2);
+          II->replaceAllUsesWith(UndefValue::get(II->getType()));
+          EraseInstFromFunction(*II);
+          return BinaryOperator::CreateAdd(LHS, RHS);
+        }
+        break;
+      case Intrinsic::usub_with_overflow:
+      case Intrinsic::ssub_with_overflow:
+        if (*EV.idx_begin() == 0) {  // Normal result.
+          Value *LHS = II->getOperand(1), *RHS = II->getOperand(2);
+          II->replaceAllUsesWith(UndefValue::get(II->getType()));
+          EraseInstFromFunction(*II);
+          return BinaryOperator::CreateSub(LHS, RHS);
+        }
+        break;
+      case Intrinsic::umul_with_overflow:
+      case Intrinsic::smul_with_overflow:
+        if (*EV.idx_begin() == 0) {  // Normal result.
+          Value *LHS = II->getOperand(1), *RHS = II->getOperand(2);
+          II->replaceAllUsesWith(UndefValue::get(II->getType()));
+          EraseInstFromFunction(*II);
+          return BinaryOperator::CreateMul(LHS, RHS);
+        }
+        break;
+      default:
+        break;
+      }
+    }
+  }
+  // Can't simplify extracts from other values. Note that nested extracts are
+  // already simplified implicitely by the above (extract ( extract (insert) )
+  // will be translated into extract ( insert ( extract ) ) first and then just
+  // the value inserted, if appropriate).
+  return 0;
+}
+
+
+
+
+/// TryToSinkInstruction - Try to move the specified instruction from its
+/// current block into the beginning of DestBlock, which can only happen if it's
+/// safe to move the instruction past all of the instructions between it and the
+/// end of its block.
+static bool TryToSinkInstruction(Instruction *I, BasicBlock *DestBlock) {
+  assert(I->hasOneUse() && "Invariants didn't hold!");
+
+  // Cannot move control-flow-involving, volatile loads, vaarg, etc.
+  if (isa<PHINode>(I) || I->mayHaveSideEffects() || isa<TerminatorInst>(I))
+    return false;
+
+  // Do not sink alloca instructions out of the entry block.
+  if (isa<AllocaInst>(I) && I->getParent() ==
+        &DestBlock->getParent()->getEntryBlock())
+    return false;
+
+  // We can only sink load instructions if there is nothing between the load and
+  // the end of block that could change the value.
+  if (I->mayReadFromMemory()) {
+    for (BasicBlock::iterator Scan = I, E = I->getParent()->end();
+         Scan != E; ++Scan)
+      if (Scan->mayWriteToMemory())
+        return false;
+  }
+
+  BasicBlock::iterator InsertPos = DestBlock->getFirstNonPHI();
+
+  I->moveBefore(InsertPos);
+  ++NumSunkInst;
+  return true;
+}
+
+
+/// AddReachableCodeToWorklist - Walk the function in depth-first order, adding
+/// all reachable code to the worklist.
+///
+/// This has a couple of tricks to make the code faster and more powerful.  In
+/// particular, we constant fold and DCE instructions as we go, to avoid adding
+/// them to the worklist (this significantly speeds up instcombine on code where
+/// many instructions are dead or constant).  Additionally, if we find a branch
+/// whose condition is a known constant, we only visit the reachable successors.
+///
+static bool AddReachableCodeToWorklist(BasicBlock *BB, 
+                                       SmallPtrSet<BasicBlock*, 64> &Visited,
+                                       InstCombiner &IC,
+                                       const TargetData *TD) {
+  bool MadeIRChange = false;
+  SmallVector<BasicBlock*, 256> Worklist;
+  Worklist.push_back(BB);
+  
+  std::vector<Instruction*> InstrsForInstCombineWorklist;
+  InstrsForInstCombineWorklist.reserve(128);
+
+  SmallPtrSet<ConstantExpr*, 64> FoldedConstants;
+  
+  do {
+    BB = Worklist.pop_back_val();
+    
+    // We have now visited this block!  If we've already been here, ignore it.
+    if (!Visited.insert(BB)) continue;
+
+    for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E; ) {
+      Instruction *Inst = BBI++;
+      
+      // DCE instruction if trivially dead.
+      if (isInstructionTriviallyDead(Inst)) {
+        ++NumDeadInst;
+        DEBUG(errs() << "IC: DCE: " << *Inst << '\n');
+        Inst->eraseFromParent();
+        continue;
+      }
+      
+      // ConstantProp instruction if trivially constant.
+      if (!Inst->use_empty() && isa<Constant>(Inst->getOperand(0)))
+        if (Constant *C = ConstantFoldInstruction(Inst, TD)) {
+          DEBUG(errs() << "IC: ConstFold to: " << *C << " from: "
+                       << *Inst << '\n');
+          Inst->replaceAllUsesWith(C);
+          ++NumConstProp;
+          Inst->eraseFromParent();
+          continue;
+        }
+      
+      if (TD) {
+        // See if we can constant fold its operands.
+        for (User::op_iterator i = Inst->op_begin(), e = Inst->op_end();
+             i != e; ++i) {
+          ConstantExpr *CE = dyn_cast<ConstantExpr>(i);
+          if (CE == 0) continue;
+          
+          // If we already folded this constant, don't try again.
+          if (!FoldedConstants.insert(CE))
+            continue;
+          
+          Constant *NewC = ConstantFoldConstantExpression(CE, TD);
+          if (NewC && NewC != CE) {
+            *i = NewC;
+            MadeIRChange = true;
+          }
+        }
+      }
+
+      InstrsForInstCombineWorklist.push_back(Inst);
+    }
+
+    // Recursively visit successors.  If this is a branch or switch on a
+    // constant, only visit the reachable successor.
+    TerminatorInst *TI = BB->getTerminator();
+    if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
+      if (BI->isConditional() && isa<ConstantInt>(BI->getCondition())) {
+        bool CondVal = cast<ConstantInt>(BI->getCondition())->getZExtValue();
+        BasicBlock *ReachableBB = BI->getSuccessor(!CondVal);
+        Worklist.push_back(ReachableBB);
+        continue;
+      }
+    } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
+      if (ConstantInt *Cond = dyn_cast<ConstantInt>(SI->getCondition())) {
+        // See if this is an explicit destination.
+        for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i)
+          if (SI->getCaseValue(i) == Cond) {
+            BasicBlock *ReachableBB = SI->getSuccessor(i);
+            Worklist.push_back(ReachableBB);
+            continue;
+          }
+        
+        // Otherwise it is the default destination.
+        Worklist.push_back(SI->getSuccessor(0));
+        continue;
+      }
+    }
+    
+    for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
+      Worklist.push_back(TI->getSuccessor(i));
+  } while (!Worklist.empty());
+  
+  // Once we've found all of the instructions to add to instcombine's worklist,
+  // add them in reverse order.  This way instcombine will visit from the top
+  // of the function down.  This jives well with the way that it adds all uses
+  // of instructions to the worklist after doing a transformation, thus avoiding
+  // some N^2 behavior in pathological cases.
+  IC.Worklist.AddInitialGroup(&InstrsForInstCombineWorklist[0],
+                              InstrsForInstCombineWorklist.size());
+  
+  return MadeIRChange;
+}
+
+bool InstCombiner::DoOneIteration(Function &F, unsigned Iteration) {
+  MadeIRChange = false;
+  
+  DEBUG(errs() << "\n\nINSTCOMBINE ITERATION #" << Iteration << " on "
+        << F.getNameStr() << "\n");
+
+  {
+    // Do a depth-first traversal of the function, populate the worklist with
+    // the reachable instructions.  Ignore blocks that are not reachable.  Keep
+    // track of which blocks we visit.
+    SmallPtrSet<BasicBlock*, 64> Visited;
+    MadeIRChange |= AddReachableCodeToWorklist(F.begin(), Visited, *this, TD);
+
+    // Do a quick scan over the function.  If we find any blocks that are
+    // unreachable, remove any instructions inside of them.  This prevents
+    // the instcombine code from having to deal with some bad special cases.
+    for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
+      if (!Visited.count(BB)) {
+        Instruction *Term = BB->getTerminator();
+        while (Term != BB->begin()) {   // Remove instrs bottom-up
+          BasicBlock::iterator I = Term; --I;
+
+          DEBUG(errs() << "IC: DCE: " << *I << '\n');
+          // A debug intrinsic shouldn't force another iteration if we weren't
+          // going to do one without it.
+          if (!isa<DbgInfoIntrinsic>(I)) {
+            ++NumDeadInst;
+            MadeIRChange = true;
+          }
+
+          // If I is not void type then replaceAllUsesWith undef.
+          // This allows ValueHandlers and custom metadata to adjust itself.
+          if (!I->getType()->isVoidTy())
+            I->replaceAllUsesWith(UndefValue::get(I->getType()));
+          I->eraseFromParent();
+        }
+      }
+  }
+
+  while (!Worklist.isEmpty()) {
+    Instruction *I = Worklist.RemoveOne();
+    if (I == 0) continue;  // skip null values.
+
+    // Check to see if we can DCE the instruction.
+    if (isInstructionTriviallyDead(I)) {
+      DEBUG(errs() << "IC: DCE: " << *I << '\n');
+      EraseInstFromFunction(*I);
+      ++NumDeadInst;
+      MadeIRChange = true;
+      continue;
+    }
+
+    // Instruction isn't dead, see if we can constant propagate it.
+    if (!I->use_empty() && isa<Constant>(I->getOperand(0)))
+      if (Constant *C = ConstantFoldInstruction(I, TD)) {
+        DEBUG(errs() << "IC: ConstFold to: " << *C << " from: " << *I << '\n');
+
+        // Add operands to the worklist.
+        ReplaceInstUsesWith(*I, C);
+        ++NumConstProp;
+        EraseInstFromFunction(*I);
+        MadeIRChange = true;
+        continue;
+      }
+
+    // See if we can trivially sink this instruction to a successor basic block.
+    if (I->hasOneUse()) {
+      BasicBlock *BB = I->getParent();
+      Instruction *UserInst = cast<Instruction>(I->use_back());
+      BasicBlock *UserParent;
+      
+      // Get the block the use occurs in.
+      if (PHINode *PN = dyn_cast<PHINode>(UserInst))
+        UserParent = PN->getIncomingBlock(I->use_begin().getUse());
+      else
+        UserParent = UserInst->getParent();
+      
+      if (UserParent != BB) {
+        bool UserIsSuccessor = false;
+        // See if the user is one of our successors.
+        for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
+          if (*SI == UserParent) {
+            UserIsSuccessor = true;
+            break;
+          }
+
+        // If the user is one of our immediate successors, and if that successor
+        // only has us as a predecessors (we'd have to split the critical edge
+        // otherwise), we can keep going.
+        if (UserIsSuccessor && UserParent->getSinglePredecessor())
+          // Okay, the CFG is simple enough, try to sink this instruction.
+          MadeIRChange |= TryToSinkInstruction(I, UserParent);
+      }
+    }
+
+    // Now that we have an instruction, try combining it to simplify it.
+    Builder->SetInsertPoint(I->getParent(), I);
+    
+#ifndef NDEBUG
+    std::string OrigI;
+#endif
+    DEBUG(raw_string_ostream SS(OrigI); I->print(SS); OrigI = SS.str(););
+    DEBUG(errs() << "IC: Visiting: " << OrigI << '\n');
+
+    if (Instruction *Result = visit(*I)) {
+      ++NumCombined;
+      // Should we replace the old instruction with a new one?
+      if (Result != I) {
+        DEBUG(errs() << "IC: Old = " << *I << '\n'
+                     << "    New = " << *Result << '\n');
+
+        // Everything uses the new instruction now.
+        I->replaceAllUsesWith(Result);
+
+        // Push the new instruction and any users onto the worklist.
+        Worklist.Add(Result);
+        Worklist.AddUsersToWorkList(*Result);
+
+        // Move the name to the new instruction first.
+        Result->takeName(I);
+
+        // Insert the new instruction into the basic block...
+        BasicBlock *InstParent = I->getParent();
+        BasicBlock::iterator InsertPos = I;
+
+        if (!isa<PHINode>(Result))        // If combining a PHI, don't insert
+          while (isa<PHINode>(InsertPos)) // middle of a block of PHIs.
+            ++InsertPos;
+
+        InstParent->getInstList().insert(InsertPos, Result);
+
+        EraseInstFromFunction(*I);
+      } else {
+#ifndef NDEBUG
+        DEBUG(errs() << "IC: Mod = " << OrigI << '\n'
+                     << "    New = " << *I << '\n');
+#endif
+
+        // If the instruction was modified, it's possible that it is now dead.
+        // if so, remove it.
+        if (isInstructionTriviallyDead(I)) {
+          EraseInstFromFunction(*I);
+        } else {
+          Worklist.Add(I);
+          Worklist.AddUsersToWorkList(*I);
+        }
+      }
+      MadeIRChange = true;
+    }
+  }
+
+  Worklist.Zap();
+  return MadeIRChange;
+}
+
+
+bool InstCombiner::runOnFunction(Function &F) {
+  MustPreserveLCSSA = mustPreserveAnalysisID(LCSSAID);
+  TD = getAnalysisIfAvailable<TargetData>();
+
+  
+  /// Builder - This is an IRBuilder that automatically inserts new
+  /// instructions into the worklist when they are created.
+  IRBuilder<true, TargetFolder, InstCombineIRInserter> 
+    TheBuilder(F.getContext(), TargetFolder(TD),
+               InstCombineIRInserter(Worklist));
+  Builder = &TheBuilder;
+  
+  bool EverMadeChange = false;
+
+  // Iterate while there is work to do.
+  unsigned Iteration = 0;
+  while (DoOneIteration(F, Iteration++))
+    EverMadeChange = true;
+  
+  Builder = 0;
+  return EverMadeChange;
+}
+
+FunctionPass *llvm::createInstructionCombiningPass() {
+  return new InstCombiner();
+}