Update LLVM to 93512.

1 files changed, 1301 insertions, 0 deletions

diff --git a/lib/Transforms/InstCombine/InstCombineCasts.cpp b/lib/Transforms/InstCombine/InstCombineCasts.cpp
new file mode 100644
index 000000000000..e018b351082a
--- /dev/null
+++ b/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -0,0 +1,1301 @@
+//===- InstCombineCasts.cpp -----------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the visit functions for cast operations.
+//
+//===----------------------------------------------------------------------===//
+
+#include "InstCombine.h"
+#include "llvm/Target/TargetData.h"
+#include "llvm/Support/PatternMatch.h"
+using namespace llvm;
+using namespace PatternMatch;
+
+/// DecomposeSimpleLinearExpr - Analyze 'Val', seeing if it is a simple linear
+/// expression.  If so, decompose it, returning some value X, such that Val is
+/// X*Scale+Offset.
+///
+static Value *DecomposeSimpleLinearExpr(Value *Val, unsigned &Scale,
+                                        int &Offset) {
+  assert(Val->getType()->isInteger(32) && "Unexpected allocation size type!");
+  if (ConstantInt *CI = dyn_cast<ConstantInt>(Val)) {
+    Offset = CI->getZExtValue();
+    Scale  = 0;
+    return ConstantInt::get(Type::getInt32Ty(Val->getContext()), 0);
+  }
+  
+  if (BinaryOperator *I = dyn_cast<BinaryOperator>(Val)) {
+    if (ConstantInt *RHS = dyn_cast<ConstantInt>(I->getOperand(1))) {
+      if (I->getOpcode() == Instruction::Shl) {
+        // This is a value scaled by '1 << the shift amt'.
+        Scale = 1U << RHS->getZExtValue();
+        Offset = 0;
+        return I->getOperand(0);
+      }
+      
+      if (I->getOpcode() == Instruction::Mul) {
+        // This value is scaled by 'RHS'.
+        Scale = RHS->getZExtValue();
+        Offset = 0;
+        return I->getOperand(0);
+      }
+      
+      if (I->getOpcode() == Instruction::Add) {
+        // We have X+C.  Check to see if we really have (X*C2)+C1, 
+        // where C1 is divisible by C2.
+        unsigned SubScale;
+        Value *SubVal = 
+          DecomposeSimpleLinearExpr(I->getOperand(0), SubScale, Offset);
+        Offset += RHS->getZExtValue();
+        Scale = SubScale;
+        return SubVal;
+      }
+    }
+  }
+
+  // Otherwise, we can't look past this.
+  Scale = 1;
+  Offset = 0;
+  return Val;
+}
+
+/// PromoteCastOfAllocation - If we find a cast of an allocation instruction,
+/// try to eliminate the cast by moving the type information into the alloc.
+Instruction *InstCombiner::PromoteCastOfAllocation(BitCastInst &CI,
+                                                   AllocaInst &AI) {
+  // This requires TargetData to get the alloca alignment and size information.
+  if (!TD) return 0;
+
+  const PointerType *PTy = cast<PointerType>(CI.getType());
+  
+  BuilderTy AllocaBuilder(*Builder);
+  AllocaBuilder.SetInsertPoint(AI.getParent(), &AI);
+
+  // Get the type really allocated and the type casted to.
+  const Type *AllocElTy = AI.getAllocatedType();
+  const Type *CastElTy = PTy->getElementType();
+  if (!AllocElTy->isSized() || !CastElTy->isSized()) return 0;
+
+  unsigned AllocElTyAlign = TD->getABITypeAlignment(AllocElTy);
+  unsigned CastElTyAlign = TD->getABITypeAlignment(CastElTy);
+  if (CastElTyAlign < AllocElTyAlign) return 0;
+
+  // If the allocation has multiple uses, only promote it if we are strictly
+  // increasing the alignment of the resultant allocation.  If we keep it the
+  // same, we open the door to infinite loops of various kinds.  (A reference
+  // from a dbg.declare doesn't count as a use for this purpose.)
+  if (!AI.hasOneUse() && !hasOneUsePlusDeclare(&AI) &&
+      CastElTyAlign == AllocElTyAlign) return 0;
+
+  uint64_t AllocElTySize = TD->getTypeAllocSize(AllocElTy);
+  uint64_t CastElTySize = TD->getTypeAllocSize(CastElTy);
+  if (CastElTySize == 0 || AllocElTySize == 0) return 0;
+
+  // See if we can satisfy the modulus by pulling a scale out of the array
+  // size argument.
+  unsigned ArraySizeScale;
+  int ArrayOffset;
+  Value *NumElements = // See if the array size is a decomposable linear expr.
+    DecomposeSimpleLinearExpr(AI.getOperand(0), ArraySizeScale, ArrayOffset);
+ 
+  // If we can now satisfy the modulus, by using a non-1 scale, we really can
+  // do the xform.
+  if ((AllocElTySize*ArraySizeScale) % CastElTySize != 0 ||
+      (AllocElTySize*ArrayOffset   ) % CastElTySize != 0) return 0;
+
+  unsigned Scale = (AllocElTySize*ArraySizeScale)/CastElTySize;
+  Value *Amt = 0;
+  if (Scale == 1) {
+    Amt = NumElements;
+  } else {
+    Amt = ConstantInt::get(Type::getInt32Ty(CI.getContext()), Scale);
+    // Insert before the alloca, not before the cast.
+    Amt = AllocaBuilder.CreateMul(Amt, NumElements, "tmp");
+  }
+  
+  if (int Offset = (AllocElTySize*ArrayOffset)/CastElTySize) {
+    Value *Off = ConstantInt::get(Type::getInt32Ty(CI.getContext()),
+                                  Offset, true);
+    Amt = AllocaBuilder.CreateAdd(Amt, Off, "tmp");
+  }
+  
+  AllocaInst *New = AllocaBuilder.CreateAlloca(CastElTy, Amt);
+  New->setAlignment(AI.getAlignment());
+  New->takeName(&AI);
+  
+  // If the allocation has one real use plus a dbg.declare, just remove the
+  // declare.
+  if (DbgDeclareInst *DI = hasOneUsePlusDeclare(&AI)) {
+    EraseInstFromFunction(*(Instruction*)DI);
+  }
+  // If the allocation has multiple real uses, insert a cast and change all
+  // things that used it to use the new cast.  This will also hack on CI, but it
+  // will die soon.
+  else if (!AI.hasOneUse()) {
+    // New is the allocation instruction, pointer typed. AI is the original
+    // allocation instruction, also pointer typed. Thus, cast to use is BitCast.
+    Value *NewCast = AllocaBuilder.CreateBitCast(New, AI.getType(), "tmpcast");
+    AI.replaceAllUsesWith(NewCast);
+  }
+  return ReplaceInstUsesWith(CI, New);
+}
+
+
+
+/// EvaluateInDifferentType - Given an expression that 
+/// CanEvaluateTruncated or CanEvaluateSExtd returns true for, actually
+/// insert the code to evaluate the expression.
+Value *InstCombiner::EvaluateInDifferentType(Value *V, const Type *Ty, 
+                                             bool isSigned) {
+  if (Constant *C = dyn_cast<Constant>(V)) {
+    C = ConstantExpr::getIntegerCast(C, Ty, isSigned /*Sext or ZExt*/);
+    // If we got a constantexpr back, try to simplify it with TD info.
+    if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C))
+      C = ConstantFoldConstantExpression(CE, TD);
+    return C;
+  }
+
+  // Otherwise, it must be an instruction.
+  Instruction *I = cast<Instruction>(V);
+  Instruction *Res = 0;
+  unsigned Opc = I->getOpcode();
+  switch (Opc) {
+  case Instruction::Add:
+  case Instruction::Sub:
+  case Instruction::Mul:
+  case Instruction::And:
+  case Instruction::Or:
+  case Instruction::Xor:
+  case Instruction::AShr:
+  case Instruction::LShr:
+  case Instruction::Shl:
+  case Instruction::UDiv:
+  case Instruction::URem: {
+    Value *LHS = EvaluateInDifferentType(I->getOperand(0), Ty, isSigned);
+    Value *RHS = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned);
+    Res = BinaryOperator::Create((Instruction::BinaryOps)Opc, LHS, RHS);
+    break;
+  }    
+  case Instruction::Trunc:
+  case Instruction::ZExt:
+  case Instruction::SExt:
+    // If the source type of the cast is the type we're trying for then we can
+    // just return the source.  There's no need to insert it because it is not
+    // new.
+    if (I->getOperand(0)->getType() == Ty)
+      return I->getOperand(0);
+    
+    // Otherwise, must be the same type of cast, so just reinsert a new one.
+    // This also handles the case of zext(trunc(x)) -> zext(x).
+    Res = CastInst::CreateIntegerCast(I->getOperand(0), Ty,
+                                      Opc == Instruction::SExt);
+    break;
+  case Instruction::Select: {
+    Value *True = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned);
+    Value *False = EvaluateInDifferentType(I->getOperand(2), Ty, isSigned);
+    Res = SelectInst::Create(I->getOperand(0), True, False);
+    break;
+  }
+  case Instruction::PHI: {
+    PHINode *OPN = cast<PHINode>(I);
+    PHINode *NPN = PHINode::Create(Ty);
+    for (unsigned i = 0, e = OPN->getNumIncomingValues(); i != e; ++i) {
+      Value *V =EvaluateInDifferentType(OPN->getIncomingValue(i), Ty, isSigned);
+      NPN->addIncoming(V, OPN->getIncomingBlock(i));
+    }
+    Res = NPN;
+    break;
+  }
+  default: 
+    // TODO: Can handle more cases here.
+    llvm_unreachable("Unreachable!");
+    break;
+  }
+  
+  Res->takeName(I);
+  return InsertNewInstBefore(Res, *I);
+}
+
+
+/// This function is a wrapper around CastInst::isEliminableCastPair. It
+/// simply extracts arguments and returns what that function returns.
+static Instruction::CastOps 
+isEliminableCastPair(
+  const CastInst *CI, ///< The first cast instruction
+  unsigned opcode,       ///< The opcode of the second cast instruction
+  const Type *DstTy,     ///< The target type for the second cast instruction
+  TargetData *TD         ///< The target data for pointer size
+) {
+
+  const Type *SrcTy = CI->getOperand(0)->getType();   // A from above
+  const Type *MidTy = CI->getType();                  // B from above
+
+  // Get the opcodes of the two Cast instructions
+  Instruction::CastOps firstOp = Instruction::CastOps(CI->getOpcode());
+  Instruction::CastOps secondOp = Instruction::CastOps(opcode);
+
+  unsigned Res = CastInst::isEliminableCastPair(firstOp, secondOp, SrcTy, MidTy,
+                                                DstTy,
+                                  TD ? TD->getIntPtrType(CI->getContext()) : 0);
+  
+  // We don't want to form an inttoptr or ptrtoint that converts to an integer
+  // type that differs from the pointer size.
+  if ((Res == Instruction::IntToPtr &&
+          (!TD || SrcTy != TD->getIntPtrType(CI->getContext()))) ||
+      (Res == Instruction::PtrToInt &&
+          (!TD || DstTy != TD->getIntPtrType(CI->getContext()))))
+    Res = 0;
+  
+  return Instruction::CastOps(Res);
+}
+
+/// ValueRequiresCast - Return true if the cast from "V to Ty" actually results
+/// in any code being generated.  It does not require codegen if V is simple
+/// enough or if the cast can be folded into other casts.
+bool InstCombiner::ValueRequiresCast(Instruction::CastOps opcode,const Value *V,
+                                     const Type *Ty) {
+  if (V->getType() == Ty || isa<Constant>(V)) return false;
+  
+  // If this is another cast that can be eliminated, it isn't codegen either.
+  if (const CastInst *CI = dyn_cast<CastInst>(V))
+    if (isEliminableCastPair(CI, opcode, Ty, TD))
+      return false;
+  return true;
+}
+
+
+/// @brief Implement the transforms common to all CastInst visitors.
+Instruction *InstCombiner::commonCastTransforms(CastInst &CI) {
+  Value *Src = CI.getOperand(0);
+
+  // Many cases of "cast of a cast" are eliminable. If it's eliminable we just
+  // eliminate it now.
+  if (CastInst *CSrc = dyn_cast<CastInst>(Src)) {   // A->B->C cast
+    if (Instruction::CastOps opc = 
+        isEliminableCastPair(CSrc, CI.getOpcode(), CI.getType(), TD)) {
+      // The first cast (CSrc) is eliminable so we need to fix up or replace
+      // the second cast (CI). CSrc will then have a good chance of being dead.
+      return CastInst::Create(opc, CSrc->getOperand(0), CI.getType());
+    }
+  }
+
+  // If we are casting a select then fold the cast into the select
+  if (SelectInst *SI = dyn_cast<SelectInst>(Src))
+    if (Instruction *NV = FoldOpIntoSelect(CI, SI))
+      return NV;
+
+  // If we are casting a PHI then fold the cast into the PHI
+  if (isa<PHINode>(Src)) {
+    // We don't do this if this would create a PHI node with an illegal type if
+    // it is currently legal.
+    if (!isa<IntegerType>(Src->getType()) ||
+        !isa<IntegerType>(CI.getType()) ||
+        ShouldChangeType(CI.getType(), Src->getType()))
+      if (Instruction *NV = FoldOpIntoPhi(CI))
+        return NV;
+  }
+  
+  return 0;
+}
+
+/// CanEvaluateTruncated - Return true if we can evaluate the specified
+/// expression tree as type Ty instead of its larger type, and arrive with the
+/// same value.  This is used by code that tries to eliminate truncates.
+///
+/// Ty will always be a type smaller than V.  We should return true if trunc(V)
+/// can be computed by computing V in the smaller type.  If V is an instruction,
+/// then trunc(inst(x,y)) can be computed as inst(trunc(x),trunc(y)), which only
+/// makes sense if x and y can be efficiently truncated.
+///
+/// This function works on both vectors and scalars.
+///
+static bool CanEvaluateTruncated(Value *V, const Type *Ty) {
+  // We can always evaluate constants in another type.
+  if (isa<Constant>(V))
+    return true;
+  
+  Instruction *I = dyn_cast<Instruction>(V);
+  if (!I) return false;
+  
+  const Type *OrigTy = V->getType();
+  
+  // If this is an extension from the dest type, we can eliminate it, even if it
+  // has multiple uses.
+  if ((isa<ZExtInst>(I) || isa<SExtInst>(I)) && 
+      I->getOperand(0)->getType() == Ty)
+    return true;
+
+  // We can't extend or shrink something that has multiple uses: doing so would
+  // require duplicating the instruction in general, which isn't profitable.
+  if (!I->hasOneUse()) return false;
+
+  unsigned Opc = I->getOpcode();
+  switch (Opc) {
+  case Instruction::Add:
+  case Instruction::Sub:
+  case Instruction::Mul:
+  case Instruction::And:
+  case Instruction::Or:
+  case Instruction::Xor:
+    // These operators can all arbitrarily be extended or truncated.
+    return CanEvaluateTruncated(I->getOperand(0), Ty) &&
+           CanEvaluateTruncated(I->getOperand(1), Ty);
+
+  case Instruction::UDiv:
+  case Instruction::URem: {
+    // UDiv and URem can be truncated if all the truncated bits are zero.
+    uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
+    uint32_t BitWidth = Ty->getScalarSizeInBits();
+    if (BitWidth < OrigBitWidth) {
+      APInt Mask = APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth);
+      if (MaskedValueIsZero(I->getOperand(0), Mask) &&
+          MaskedValueIsZero(I->getOperand(1), Mask)) {
+        return CanEvaluateTruncated(I->getOperand(0), Ty) &&
+               CanEvaluateTruncated(I->getOperand(1), Ty);
+      }
+    }
+    break;
+  }
+  case Instruction::Shl:
+    // If we are truncating the result of this SHL, and if it's a shift of a
+    // constant amount, we can always perform a SHL in a smaller type.
+    if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) {
+      uint32_t BitWidth = Ty->getScalarSizeInBits();
+      if (CI->getLimitedValue(BitWidth) < BitWidth)
+        return CanEvaluateTruncated(I->getOperand(0), Ty);
+    }
+    break;
+  case Instruction::LShr:
+    // If this is a truncate of a logical shr, we can truncate it to a smaller
+    // lshr iff we know that the bits we would otherwise be shifting in are
+    // already zeros.
+    if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) {
+      uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
+      uint32_t BitWidth = Ty->getScalarSizeInBits();
+      if (MaskedValueIsZero(I->getOperand(0),
+            APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth)) &&
+          CI->getLimitedValue(BitWidth) < BitWidth) {
+        return CanEvaluateTruncated(I->getOperand(0), Ty);
+      }
+    }
+    break;
+  case Instruction::Trunc:
+    // trunc(trunc(x)) -> trunc(x)
+    return true;
+  case Instruction::Select: {
+    SelectInst *SI = cast<SelectInst>(I);
+    return CanEvaluateTruncated(SI->getTrueValue(), Ty) &&
+           CanEvaluateTruncated(SI->getFalseValue(), Ty);
+  }
+  case Instruction::PHI: {
+    // We can change a phi if we can change all operands.  Note that we never
+    // get into trouble with cyclic PHIs here because we only consider
+    // instructions with a single use.
+    PHINode *PN = cast<PHINode>(I);
+    for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+      if (!CanEvaluateTruncated(PN->getIncomingValue(i), Ty))
+        return false;
+    return true;
+  }
+  default:
+    // TODO: Can handle more cases here.
+    break;
+  }
+  
+  return false;
+}
+
+Instruction *InstCombiner::visitTrunc(TruncInst &CI) {
+  if (Instruction *Result = commonCastTransforms(CI))
+    return Result;
+  
+  // See if we can simplify any instructions used by the input whose sole 
+  // purpose is to compute bits we don't care about.
+  if (SimplifyDemandedInstructionBits(CI))
+    return &CI;
+  
+  Value *Src = CI.getOperand(0);
+  const Type *DestTy = CI.getType(), *SrcTy = Src->getType();
+  
+  // Attempt to truncate the entire input expression tree to the destination
+  // type.   Only do this if the dest type is a simple type, don't convert the
+  // expression tree to something weird like i93 unless the source is also
+  // strange.
+  if ((isa<VectorType>(DestTy) || ShouldChangeType(SrcTy, DestTy)) &&
+      CanEvaluateTruncated(Src, DestTy)) {
+      
+    // If this cast is a truncate, evaluting in a different type always
+    // eliminates the cast, so it is always a win.
+    DEBUG(dbgs() << "ICE: EvaluateInDifferentType converting expression type"
+          " to avoid cast: " << CI);
+    Value *Res = EvaluateInDifferentType(Src, DestTy, false);
+    assert(Res->getType() == DestTy);
+    return ReplaceInstUsesWith(CI, Res);
+  }
+
+  // Canonicalize trunc x to i1 -> (icmp ne (and x, 1), 0), likewise for vector.
+  if (DestTy->getScalarSizeInBits() == 1) {
+    Constant *One = ConstantInt::get(Src->getType(), 1);
+    Src = Builder->CreateAnd(Src, One, "tmp");
+    Value *Zero = Constant::getNullValue(Src->getType());
+    return new ICmpInst(ICmpInst::ICMP_NE, Src, Zero);
+  }
+
+  return 0;
+}
+
+/// transformZExtICmp - Transform (zext icmp) to bitwise / integer operations
+/// in order to eliminate the icmp.
+Instruction *InstCombiner::transformZExtICmp(ICmpInst *ICI, Instruction &CI,
+                                             bool DoXform) {
+  // If we are just checking for a icmp eq of a single bit and zext'ing it
+  // to an integer, then shift the bit to the appropriate place and then
+  // cast to integer to avoid the comparison.
+  if (ConstantInt *Op1C = dyn_cast<ConstantInt>(ICI->getOperand(1))) {
+    const APInt &Op1CV = Op1C->getValue();
+      
+    // zext (x <s  0) to i32 --> x>>u31      true if signbit set.
+    // zext (x >s -1) to i32 --> (x>>u31)^1  true if signbit clear.
+    if ((ICI->getPredicate() == ICmpInst::ICMP_SLT && Op1CV == 0) ||
+        (ICI->getPredicate() == ICmpInst::ICMP_SGT &&Op1CV.isAllOnesValue())) {
+      if (!DoXform) return ICI;
+
+      Value *In = ICI->getOperand(0);
+      Value *Sh = ConstantInt::get(In->getType(),
+                                   In->getType()->getScalarSizeInBits()-1);
+      In = Builder->CreateLShr(In, Sh, In->getName()+".lobit");
+      if (In->getType() != CI.getType())
+        In = Builder->CreateIntCast(In, CI.getType(), false/*ZExt*/, "tmp");
+
+      if (ICI->getPredicate() == ICmpInst::ICMP_SGT) {
+        Constant *One = ConstantInt::get(In->getType(), 1);
+        In = Builder->CreateXor(In, One, In->getName()+".not");
+      }
+
+      return ReplaceInstUsesWith(CI, In);
+    }
+      
+      
+      
+    // zext (X == 0) to i32 --> X^1      iff X has only the low bit set.
+    // zext (X == 0) to i32 --> (X>>1)^1 iff X has only the 2nd bit set.
+    // zext (X == 1) to i32 --> X        iff X has only the low bit set.
+    // zext (X == 2) to i32 --> X>>1     iff X has only the 2nd bit set.
+    // zext (X != 0) to i32 --> X        iff X has only the low bit set.
+    // zext (X != 0) to i32 --> X>>1     iff X has only the 2nd bit set.
+    // zext (X != 1) to i32 --> X^1      iff X has only the low bit set.
+    // zext (X != 2) to i32 --> (X>>1)^1 iff X has only the 2nd bit set.
+    if ((Op1CV == 0 || Op1CV.isPowerOf2()) && 
+        // This only works for EQ and NE
+        ICI->isEquality()) {
+      // If Op1C some other power of two, convert:
+      uint32_t BitWidth = Op1C->getType()->getBitWidth();
+      APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
+      APInt TypeMask(APInt::getAllOnesValue(BitWidth));
+      ComputeMaskedBits(ICI->getOperand(0), TypeMask, KnownZero, KnownOne);
+        
+      APInt KnownZeroMask(~KnownZero);
+      if (KnownZeroMask.isPowerOf2()) { // Exactly 1 possible 1?
+        if (!DoXform) return ICI;
+
+        bool isNE = ICI->getPredicate() == ICmpInst::ICMP_NE;
+        if (Op1CV != 0 && (Op1CV != KnownZeroMask)) {
+          // (X&4) == 2 --> false
+          // (X&4) != 2 --> true
+          Constant *Res = ConstantInt::get(Type::getInt1Ty(CI.getContext()),
+                                           isNE);
+          Res = ConstantExpr::getZExt(Res, CI.getType());
+          return ReplaceInstUsesWith(CI, Res);
+        }
+          
+        uint32_t ShiftAmt = KnownZeroMask.logBase2();
+        Value *In = ICI->getOperand(0);
+        if (ShiftAmt) {
+          // Perform a logical shr by shiftamt.
+          // Insert the shift to put the result in the low bit.
+          In = Builder->CreateLShr(In, ConstantInt::get(In->getType(),ShiftAmt),
+                                   In->getName()+".lobit");
+        }
+          
+        if ((Op1CV != 0) == isNE) { // Toggle the low bit.
+          Constant *One = ConstantInt::get(In->getType(), 1);
+          In = Builder->CreateXor(In, One, "tmp");
+        }
+          
+        if (CI.getType() == In->getType())
+          return ReplaceInstUsesWith(CI, In);
+        else
+          return CastInst::CreateIntegerCast(In, CI.getType(), false/*ZExt*/);
+      }
+    }
+  }
+
+  // icmp ne A, B is equal to xor A, B when A and B only really have one bit.
+  // It is also profitable to transform icmp eq into not(xor(A, B)) because that
+  // may lead to additional simplifications.
+  if (ICI->isEquality() && CI.getType() == ICI->getOperand(0)->getType()) {
+    if (const IntegerType *ITy = dyn_cast<IntegerType>(CI.getType())) {
+      uint32_t BitWidth = ITy->getBitWidth();
+      Value *LHS = ICI->getOperand(0);
+      Value *RHS = ICI->getOperand(1);
+
+      APInt KnownZeroLHS(BitWidth, 0), KnownOneLHS(BitWidth, 0);
+      APInt KnownZeroRHS(BitWidth, 0), KnownOneRHS(BitWidth, 0);
+      APInt TypeMask(APInt::getAllOnesValue(BitWidth));
+      ComputeMaskedBits(LHS, TypeMask, KnownZeroLHS, KnownOneLHS);
+      ComputeMaskedBits(RHS, TypeMask, KnownZeroRHS, KnownOneRHS);
+
+      if (KnownZeroLHS == KnownZeroRHS && KnownOneLHS == KnownOneRHS) {
+        APInt KnownBits = KnownZeroLHS | KnownOneLHS;
+        APInt UnknownBit = ~KnownBits;
+        if (UnknownBit.countPopulation() == 1) {
+          if (!DoXform) return ICI;
+
+          Value *Result = Builder->CreateXor(LHS, RHS);
+
+          // Mask off any bits that are set and won't be shifted away.
+          if (KnownOneLHS.uge(UnknownBit))
+            Result = Builder->CreateAnd(Result,
+                                        ConstantInt::get(ITy, UnknownBit));
+
+          // Shift the bit we're testing down to the lsb.
+          Result = Builder->CreateLShr(
+               Result, ConstantInt::get(ITy, UnknownBit.countTrailingZeros()));
+
+          if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
+            Result = Builder->CreateXor(Result, ConstantInt::get(ITy, 1));
+          Result->takeName(ICI);
+          return ReplaceInstUsesWith(CI, Result);
+        }
+      }
+    }
+  }
+
+  return 0;
+}
+
+/// CanEvaluateZExtd - Determine if the specified value can be computed in the
+/// specified wider type and produce the same low bits.  If not, return false.
+///
+/// If this function returns true, it can also return a non-zero number of bits
+/// (in BitsToClear) which indicates that the value it computes is correct for
+/// the zero extend, but that the additional BitsToClear bits need to be zero'd
+/// out.  For example, to promote something like:
+///
+///   %B = trunc i64 %A to i32
+///   %C = lshr i32 %B, 8
+///   %E = zext i32 %C to i64
+///
+/// CanEvaluateZExtd for the 'lshr' will return true, and BitsToClear will be
+/// set to 8 to indicate that the promoted value needs to have bits 24-31
+/// cleared in addition to bits 32-63.  Since an 'and' will be generated to
+/// clear the top bits anyway, doing this has no extra cost.
+///
+/// This function works on both vectors and scalars.
+static bool CanEvaluateZExtd(Value *V, const Type *Ty, unsigned &BitsToClear) {
+  BitsToClear = 0;
+  if (isa<Constant>(V))
+    return true;
+  
+  Instruction *I = dyn_cast<Instruction>(V);
+  if (!I) return false;
+  
+  // If the input is a truncate from the destination type, we can trivially
+  // eliminate it, even if it has multiple uses.
+  // FIXME: This is currently disabled until codegen can handle this without
+  // pessimizing code, PR5997.
+  if (0 && isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty)
+    return true;
+  
+  // We can't extend or shrink something that has multiple uses: doing so would
+  // require duplicating the instruction in general, which isn't profitable.
+  if (!I->hasOneUse()) return false;
+  
+  unsigned Opc = I->getOpcode(), Tmp;
+  switch (Opc) {
+  case Instruction::ZExt:  // zext(zext(x)) -> zext(x).
+  case Instruction::SExt:  // zext(sext(x)) -> sext(x).
+  case Instruction::Trunc: // zext(trunc(x)) -> trunc(x) or zext(x)
+    return true;
+  case Instruction::And:
+  case Instruction::Or:
+  case Instruction::Xor:
+  case Instruction::Add:
+  case Instruction::Sub:
+  case Instruction::Mul:
+  case Instruction::Shl:
+    if (!CanEvaluateZExtd(I->getOperand(0), Ty, BitsToClear) ||
+        !CanEvaluateZExtd(I->getOperand(1), Ty, Tmp))
+      return false;
+    // These can all be promoted if neither operand has 'bits to clear'.
+    if (BitsToClear == 0 && Tmp == 0)
+      return true;
+      
+    // If the operation is an AND/OR/XOR and the bits to clear are zero in the
+    // other side, BitsToClear is ok.
+    if (Tmp == 0 &&
+        (Opc == Instruction::And || Opc == Instruction::Or ||
+         Opc == Instruction::Xor)) {
+      // We use MaskedValueIsZero here for generality, but the case we care
+      // about the most is constant RHS.
+      unsigned VSize = V->getType()->getScalarSizeInBits();
+      if (MaskedValueIsZero(I->getOperand(1),
+                            APInt::getHighBitsSet(VSize, BitsToClear)))
+        return true;
+    }
+      
+    // Otherwise, we don't know how to analyze this BitsToClear case yet.
+    return false;
+      
+  case Instruction::LShr:
+    // We can promote lshr(x, cst) if we can promote x.  This requires the
+    // ultimate 'and' to clear out the high zero bits we're clearing out though.
+    if (ConstantInt *Amt = dyn_cast<ConstantInt>(I->getOperand(1))) {
+      if (!CanEvaluateZExtd(I->getOperand(0), Ty, BitsToClear))
+        return false;
+      BitsToClear += Amt->getZExtValue();
+      if (BitsToClear > V->getType()->getScalarSizeInBits())
+        BitsToClear = V->getType()->getScalarSizeInBits();
+      return true;
+    }
+    // Cannot promote variable LSHR.
+    return false;
+  case Instruction::Select:
+    if (!CanEvaluateZExtd(I->getOperand(1), Ty, Tmp) ||
+        !CanEvaluateZExtd(I->getOperand(2), Ty, BitsToClear) ||
+        // TODO: If important, we could handle the case when the BitsToClear are
+        // known zero in the disagreeing side.
+        Tmp != BitsToClear)
+      return false;
+    return true;
+      
+  case Instruction::PHI: {
+    // We can change a phi if we can change all operands.  Note that we never
+    // get into trouble with cyclic PHIs here because we only consider
+    // instructions with a single use.
+    PHINode *PN = cast<PHINode>(I);
+    if (!CanEvaluateZExtd(PN->getIncomingValue(0), Ty, BitsToClear))
+      return false;
+    for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i)
+      if (!CanEvaluateZExtd(PN->getIncomingValue(i), Ty, Tmp) ||
+          // TODO: If important, we could handle the case when the BitsToClear
+          // are known zero in the disagreeing input.
+          Tmp != BitsToClear)
+        return false;
+    return true;
+  }
+  default:
+    // TODO: Can handle more cases here.
+    return false;
+  }
+}
+
+Instruction *InstCombiner::visitZExt(ZExtInst &CI) {
+  // If this zero extend is only used by a truncate, let the truncate by
+  // eliminated before we try to optimize this zext.
+  if (CI.hasOneUse() && isa<TruncInst>(CI.use_back()))
+    return 0;
+  
+  // If one of the common conversion will work, do it.
+  if (Instruction *Result = commonCastTransforms(CI))
+    return Result;
+
+  // See if we can simplify any instructions used by the input whose sole 
+  // purpose is to compute bits we don't care about.
+  if (SimplifyDemandedInstructionBits(CI))
+    return &CI;
+  
+  Value *Src = CI.getOperand(0);
+  const Type *SrcTy = Src->getType(), *DestTy = CI.getType();
+  
+  // Attempt to extend the entire input expression tree to the destination
+  // type.   Only do this if the dest type is a simple type, don't convert the
+  // expression tree to something weird like i93 unless the source is also
+  // strange.
+  unsigned BitsToClear;
+  if ((isa<VectorType>(DestTy) || ShouldChangeType(SrcTy, DestTy)) &&
+      CanEvaluateZExtd(Src, DestTy, BitsToClear)) { 
+    assert(BitsToClear < SrcTy->getScalarSizeInBits() &&
+           "Unreasonable BitsToClear");
+    
+    // Okay, we can transform this!  Insert the new expression now.
+    DEBUG(dbgs() << "ICE: EvaluateInDifferentType converting expression type"
+          " to avoid zero extend: " << CI);
+    Value *Res = EvaluateInDifferentType(Src, DestTy, false);
+    assert(Res->getType() == DestTy);
+    
+    uint32_t SrcBitsKept = SrcTy->getScalarSizeInBits()-BitsToClear;
+    uint32_t DestBitSize = DestTy->getScalarSizeInBits();
+    
+    // If the high bits are already filled with zeros, just replace this
+    // cast with the result.
+    if (MaskedValueIsZero(Res, APInt::getHighBitsSet(DestBitSize,
+                                                     DestBitSize-SrcBitsKept)))
+      return ReplaceInstUsesWith(CI, Res);
+    
+    // We need to emit an AND to clear the high bits.
+    Constant *C = ConstantInt::get(Res->getType(),
+                               APInt::getLowBitsSet(DestBitSize, SrcBitsKept));
+    return BinaryOperator::CreateAnd(Res, C);
+  }
+
+  // If this is a TRUNC followed by a ZEXT then we are dealing with integral
+  // types and if the sizes are just right we can convert this into a logical
+  // 'and' which will be much cheaper than the pair of casts.
+  if (TruncInst *CSrc = dyn_cast<TruncInst>(Src)) {   // A->B->C cast
+    // TODO: Subsume this into EvaluateInDifferentType.
+    
+    // Get the sizes of the types involved.  We know that the intermediate type
+    // will be smaller than A or C, but don't know the relation between A and C.
+    Value *A = CSrc->getOperand(0);
+    unsigned SrcSize = A->getType()->getScalarSizeInBits();
+    unsigned MidSize = CSrc->getType()->getScalarSizeInBits();
+    unsigned DstSize = CI.getType()->getScalarSizeInBits();
+    // If we're actually extending zero bits, then if
+    // SrcSize <  DstSize: zext(a & mask)
+    // SrcSize == DstSize: a & mask
+    // SrcSize  > DstSize: trunc(a) & mask
+    if (SrcSize < DstSize) {
+      APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize));
+      Constant *AndConst = ConstantInt::get(A->getType(), AndValue);
+      Value *And = Builder->CreateAnd(A, AndConst, CSrc->getName()+".mask");
+      return new ZExtInst(And, CI.getType());
+    }
+    
+    if (SrcSize == DstSize) {
+      APInt AndValue(APInt::getLowBitsSet(SrcSize, MidSize));
+      return BinaryOperator::CreateAnd(A, ConstantInt::get(A->getType(),
+                                                           AndValue));
+    }
+    if (SrcSize > DstSize) {
+      Value *Trunc = Builder->CreateTrunc(A, CI.getType(), "tmp");
+      APInt AndValue(APInt::getLowBitsSet(DstSize, MidSize));
+      return BinaryOperator::CreateAnd(Trunc, 
+                                       ConstantInt::get(Trunc->getType(),
+                                                        AndValue));
+    }
+  }
+
+  if (ICmpInst *ICI = dyn_cast<ICmpInst>(Src))
+    return transformZExtICmp(ICI, CI);
+
+  BinaryOperator *SrcI = dyn_cast<BinaryOperator>(Src);
+  if (SrcI && SrcI->getOpcode() == Instruction::Or) {
+    // zext (or icmp, icmp) --> or (zext icmp), (zext icmp) if at least one
+    // of the (zext icmp) will be transformed.
+    ICmpInst *LHS = dyn_cast<ICmpInst>(SrcI->getOperand(0));
+    ICmpInst *RHS = dyn_cast<ICmpInst>(SrcI->getOperand(1));
+    if (LHS && RHS && LHS->hasOneUse() && RHS->hasOneUse() &&
+        (transformZExtICmp(LHS, CI, false) ||
+         transformZExtICmp(RHS, CI, false))) {
+      Value *LCast = Builder->CreateZExt(LHS, CI.getType(), LHS->getName());
+      Value *RCast = Builder->CreateZExt(RHS, CI.getType(), RHS->getName());
+      return BinaryOperator::Create(Instruction::Or, LCast, RCast);
+    }
+  }
+
+  // zext(trunc(t) & C) -> (t & zext(C)).
+  if (SrcI && SrcI->getOpcode() == Instruction::And && SrcI->hasOneUse())
+    if (ConstantInt *C = dyn_cast<ConstantInt>(SrcI->getOperand(1)))
+      if (TruncInst *TI = dyn_cast<TruncInst>(SrcI->getOperand(0))) {
+        Value *TI0 = TI->getOperand(0);
+        if (TI0->getType() == CI.getType())
+          return
+            BinaryOperator::CreateAnd(TI0,
+                                ConstantExpr::getZExt(C, CI.getType()));
+      }
+
+  // zext((trunc(t) & C) ^ C) -> ((t & zext(C)) ^ zext(C)).
+  if (SrcI && SrcI->getOpcode() == Instruction::Xor && SrcI->hasOneUse())
+    if (ConstantInt *C = dyn_cast<ConstantInt>(SrcI->getOperand(1)))
+      if (BinaryOperator *And = dyn_cast<BinaryOperator>(SrcI->getOperand(0)))
+        if (And->getOpcode() == Instruction::And && And->hasOneUse() &&
+            And->getOperand(1) == C)
+          if (TruncInst *TI = dyn_cast<TruncInst>(And->getOperand(0))) {
+            Value *TI0 = TI->getOperand(0);
+            if (TI0->getType() == CI.getType()) {
+              Constant *ZC = ConstantExpr::getZExt(C, CI.getType());
+              Value *NewAnd = Builder->CreateAnd(TI0, ZC, "tmp");
+              return BinaryOperator::CreateXor(NewAnd, ZC);
+            }
+          }
+
+  // zext (xor i1 X, true) to i32  --> xor (zext i1 X to i32), 1
+  Value *X;
+  if (SrcI && SrcI->hasOneUse() && SrcI->getType()->isInteger(1) &&
+      match(SrcI, m_Not(m_Value(X))) &&
+      (!X->hasOneUse() || !isa<CmpInst>(X))) {
+    Value *New = Builder->CreateZExt(X, CI.getType());
+    return BinaryOperator::CreateXor(New, ConstantInt::get(CI.getType(), 1));
+  }
+  
+  return 0;
+}
+
+/// CanEvaluateSExtd - Return true if we can take the specified value
+/// and return it as type Ty without inserting any new casts and without
+/// changing the value of the common low bits.  This is used by code that tries
+/// to promote integer operations to a wider types will allow us to eliminate
+/// the extension.
+///
+/// This function works on both vectors and scalars.
+///
+static bool CanEvaluateSExtd(Value *V, const Type *Ty) {
+  assert(V->getType()->getScalarSizeInBits() < Ty->getScalarSizeInBits() &&
+         "Can't sign extend type to a smaller type");
+  // If this is a constant, it can be trivially promoted.
+  if (isa<Constant>(V))
+    return true;
+  
+  Instruction *I = dyn_cast<Instruction>(V);
+  if (!I) return false;
+  
+  // If this is a truncate from the dest type, we can trivially eliminate it,
+  // even if it has multiple uses.
+  // FIXME: This is currently disabled until codegen can handle this without
+  // pessimizing code, PR5997.
+  if (0 && isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty)
+    return true;
+  
+  // We can't extend or shrink something that has multiple uses: doing so would
+  // require duplicating the instruction in general, which isn't profitable.
+  if (!I->hasOneUse()) return false;
+
+  switch (I->getOpcode()) {
+  case Instruction::SExt:  // sext(sext(x)) -> sext(x)
+  case Instruction::ZExt:  // sext(zext(x)) -> zext(x)
+  case Instruction::Trunc: // sext(trunc(x)) -> trunc(x) or sext(x)
+    return true;
+  case Instruction::And:
+  case Instruction::Or:
+  case Instruction::Xor:
+  case Instruction::Add:
+  case Instruction::Sub:
+  case Instruction::Mul:
+    // These operators can all arbitrarily be extended if their inputs can.
+    return CanEvaluateSExtd(I->getOperand(0), Ty) &&
+           CanEvaluateSExtd(I->getOperand(1), Ty);
+      
+  //case Instruction::Shl:   TODO
+  //case Instruction::LShr:  TODO
+      
+  case Instruction::Select:
+    return CanEvaluateSExtd(I->getOperand(1), Ty) &&
+           CanEvaluateSExtd(I->getOperand(2), Ty);
+      
+  case Instruction::PHI: {
+    // We can change a phi if we can change all operands.  Note that we never
+    // get into trouble with cyclic PHIs here because we only consider
+    // instructions with a single use.
+    PHINode *PN = cast<PHINode>(I);
+    for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+      if (!CanEvaluateSExtd(PN->getIncomingValue(i), Ty)) return false;
+    return true;
+  }
+  default:
+    // TODO: Can handle more cases here.
+    break;
+  }
+  
+  return false;
+}
+
+Instruction *InstCombiner::visitSExt(SExtInst &CI) {
+  // If this sign extend is only used by a truncate, let the truncate by
+  // eliminated before we try to optimize this zext.
+  if (CI.hasOneUse() && isa<TruncInst>(CI.use_back()))
+    return 0;
+  
+  if (Instruction *I = commonCastTransforms(CI))
+    return I;
+  
+  // See if we can simplify any instructions used by the input whose sole 
+  // purpose is to compute bits we don't care about.
+  if (SimplifyDemandedInstructionBits(CI))
+    return &CI;
+  
+  Value *Src = CI.getOperand(0);
+  const Type *SrcTy = Src->getType(), *DestTy = CI.getType();
+
+  // Canonicalize sign-extend from i1 to a select.
+  if (Src->getType()->isInteger(1))
+    return SelectInst::Create(Src,
+                              Constant::getAllOnesValue(CI.getType()),
+                              Constant::getNullValue(CI.getType()));
+  
+  // Attempt to extend the entire input expression tree to the destination
+  // type.   Only do this if the dest type is a simple type, don't convert the
+  // expression tree to something weird like i93 unless the source is also
+  // strange.
+  if ((isa<VectorType>(DestTy) || ShouldChangeType(SrcTy, DestTy)) &&
+      CanEvaluateSExtd(Src, DestTy)) {
+    // Okay, we can transform this!  Insert the new expression now.
+    DEBUG(dbgs() << "ICE: EvaluateInDifferentType converting expression type"
+          " to avoid sign extend: " << CI);
+    Value *Res = EvaluateInDifferentType(Src, DestTy, true);
+    assert(Res->getType() == DestTy);
+
+    uint32_t SrcBitSize = SrcTy->getScalarSizeInBits();
+    uint32_t DestBitSize = DestTy->getScalarSizeInBits();
+
+    // If the high bits are already filled with sign bit, just replace this
+    // cast with the result.
+    if (ComputeNumSignBits(Res) > DestBitSize - SrcBitSize)
+      return ReplaceInstUsesWith(CI, Res);
+    
+    // We need to emit a shl + ashr to do the sign extend.
+    Value *ShAmt = ConstantInt::get(DestTy, DestBitSize-SrcBitSize);
+    return BinaryOperator::CreateAShr(Builder->CreateShl(Res, ShAmt, "sext"),
+                                      ShAmt);
+  }
+
+  // If the input is a shl/ashr pair of a same constant, then this is a sign
+  // extension from a smaller value.  If we could trust arbitrary bitwidth
+  // integers, we could turn this into a truncate to the smaller bit and then
+  // use a sext for the whole extension.  Since we don't, look deeper and check
+  // for a truncate.  If the source and dest are the same type, eliminate the
+  // trunc and extend and just do shifts.  For example, turn:
+  //   %a = trunc i32 %i to i8
+  //   %b = shl i8 %a, 6
+  //   %c = ashr i8 %b, 6
+  //   %d = sext i8 %c to i32
+  // into:
+  //   %a = shl i32 %i, 30
+  //   %d = ashr i32 %a, 30
+  Value *A = 0;
+  // TODO: Eventually this could be subsumed by EvaluateInDifferentType.
+  ConstantInt *BA = 0, *CA = 0;
+  if (match(Src, m_AShr(m_Shl(m_Trunc(m_Value(A)), m_ConstantInt(BA)),
+                        m_ConstantInt(CA))) &&
+      BA == CA && A->getType() == CI.getType()) {
+    unsigned MidSize = Src->getType()->getScalarSizeInBits();
+    unsigned SrcDstSize = CI.getType()->getScalarSizeInBits();
+    unsigned ShAmt = CA->getZExtValue()+SrcDstSize-MidSize;
+    Constant *ShAmtV = ConstantInt::get(CI.getType(), ShAmt);
+    A = Builder->CreateShl(A, ShAmtV, CI.getName());
+    return BinaryOperator::CreateAShr(A, ShAmtV);
+  }
+  
+  return 0;
+}
+
+
+/// FitsInFPType - Return a Constant* for the specified FP constant if it fits
+/// in the specified FP type without changing its value.
+static Constant *FitsInFPType(ConstantFP *CFP, const fltSemantics &Sem) {
+  bool losesInfo;
+  APFloat F = CFP->getValueAPF();
+  (void)F.convert(Sem, APFloat::rmNearestTiesToEven, &losesInfo);
+  if (!losesInfo)
+    return ConstantFP::get(CFP->getContext(), F);
+  return 0;
+}
+
+/// LookThroughFPExtensions - If this is an fp extension instruction, look
+/// through it until we get the source value.
+static Value *LookThroughFPExtensions(Value *V) {
+  if (Instruction *I = dyn_cast<Instruction>(V))
+    if (I->getOpcode() == Instruction::FPExt)
+      return LookThroughFPExtensions(I->getOperand(0));
+  
+  // If this value is a constant, return the constant in the smallest FP type
+  // that can accurately represent it.  This allows us to turn
+  // (float)((double)X+2.0) into x+2.0f.
+  if (ConstantFP *CFP = dyn_cast<ConstantFP>(V)) {
+    if (CFP->getType() == Type::getPPC_FP128Ty(V->getContext()))
+      return V;  // No constant folding of this.
+    // See if the value can be truncated to float and then reextended.
+    if (Value *V = FitsInFPType(CFP, APFloat::IEEEsingle))
+      return V;
+    if (CFP->getType()->isDoubleTy())
+      return V;  // Won't shrink.
+    if (Value *V = FitsInFPType(CFP, APFloat::IEEEdouble))
+      return V;
+    // Don't try to shrink to various long double types.
+  }
+  
+  return V;
+}
+
+Instruction *InstCombiner::visitFPTrunc(FPTruncInst &CI) {
+  if (Instruction *I = commonCastTransforms(CI))
+    return I;
+  
+  // If we have fptrunc(fadd (fpextend x), (fpextend y)), where x and y are
+  // smaller than the destination type, we can eliminate the truncate by doing
+  // the add as the smaller type.  This applies to fadd/fsub/fmul/fdiv as well
+  // as many builtins (sqrt, etc).
+  BinaryOperator *OpI = dyn_cast<BinaryOperator>(CI.getOperand(0));
+  if (OpI && OpI->hasOneUse()) {
+    switch (OpI->getOpcode()) {
+    default: break;
+    case Instruction::FAdd:
+    case Instruction::FSub:
+    case Instruction::FMul:
+    case Instruction::FDiv:
+    case Instruction::FRem:
+      const Type *SrcTy = OpI->getType();
+      Value *LHSTrunc = LookThroughFPExtensions(OpI->getOperand(0));
+      Value *RHSTrunc = LookThroughFPExtensions(OpI->getOperand(1));
+      if (LHSTrunc->getType() != SrcTy && 
+          RHSTrunc->getType() != SrcTy) {
+        unsigned DstSize = CI.getType()->getScalarSizeInBits();
+        // If the source types were both smaller than the destination type of
+        // the cast, do this xform.
+        if (LHSTrunc->getType()->getScalarSizeInBits() <= DstSize &&
+            RHSTrunc->getType()->getScalarSizeInBits() <= DstSize) {
+          LHSTrunc = Builder->CreateFPExt(LHSTrunc, CI.getType());
+          RHSTrunc = Builder->CreateFPExt(RHSTrunc, CI.getType());
+          return BinaryOperator::Create(OpI->getOpcode(), LHSTrunc, RHSTrunc);
+        }
+      }
+      break;  
+    }
+  }
+  return 0;
+}
+
+Instruction *InstCombiner::visitFPExt(CastInst &CI) {
+  return commonCastTransforms(CI);
+}
+
+Instruction *InstCombiner::visitFPToUI(FPToUIInst &FI) {
+  Instruction *OpI = dyn_cast<Instruction>(FI.getOperand(0));
+  if (OpI == 0)
+    return commonCastTransforms(FI);
+
+  // fptoui(uitofp(X)) --> X
+  // fptoui(sitofp(X)) --> X
+  // This is safe if the intermediate type has enough bits in its mantissa to
+  // accurately represent all values of X.  For example, do not do this with
+  // i64->float->i64.  This is also safe for sitofp case, because any negative
+  // 'X' value would cause an undefined result for the fptoui. 
+  if ((isa<UIToFPInst>(OpI) || isa<SIToFPInst>(OpI)) &&
+      OpI->getOperand(0)->getType() == FI.getType() &&
+      (int)FI.getType()->getScalarSizeInBits() < /*extra bit for sign */
+                    OpI->getType()->getFPMantissaWidth())
+    return ReplaceInstUsesWith(FI, OpI->getOperand(0));
+
+  return commonCastTransforms(FI);
+}
+
+Instruction *InstCombiner::visitFPToSI(FPToSIInst &FI) {
+  Instruction *OpI = dyn_cast<Instruction>(FI.getOperand(0));
+  if (OpI == 0)
+    return commonCastTransforms(FI);
+  
+  // fptosi(sitofp(X)) --> X
+  // fptosi(uitofp(X)) --> X
+  // This is safe if the intermediate type has enough bits in its mantissa to
+  // accurately represent all values of X.  For example, do not do this with
+  // i64->float->i64.  This is also safe for sitofp case, because any negative
+  // 'X' value would cause an undefined result for the fptoui. 
+  if ((isa<UIToFPInst>(OpI) || isa<SIToFPInst>(OpI)) &&
+      OpI->getOperand(0)->getType() == FI.getType() &&
+      (int)FI.getType()->getScalarSizeInBits() <=
+                    OpI->getType()->getFPMantissaWidth())
+    return ReplaceInstUsesWith(FI, OpI->getOperand(0));
+  
+  return commonCastTransforms(FI);
+}
+
+Instruction *InstCombiner::visitUIToFP(CastInst &CI) {
+  return commonCastTransforms(CI);
+}
+
+Instruction *InstCombiner::visitSIToFP(CastInst &CI) {
+  return commonCastTransforms(CI);
+}
+
+Instruction *InstCombiner::visitIntToPtr(IntToPtrInst &CI) {
+  // If the source integer type is larger than the intptr_t type for
+  // this target, do a trunc to the intptr_t type, then inttoptr of it.  This
+  // allows the trunc to be exposed to other transforms.  Don't do this for
+  // extending inttoptr's, because we don't know if the target sign or zero
+  // extends to pointers.
+  if (TD && CI.getOperand(0)->getType()->getScalarSizeInBits() >
+      TD->getPointerSizeInBits()) {
+    Value *P = Builder->CreateTrunc(CI.getOperand(0),
+                                    TD->getIntPtrType(CI.getContext()), "tmp");
+    return new IntToPtrInst(P, CI.getType());
+  }
+  
+  if (Instruction *I = commonCastTransforms(CI))
+    return I;
+
+  return 0;
+}
+
+/// @brief Implement the transforms for cast of pointer (bitcast/ptrtoint)
+Instruction *InstCombiner::commonPointerCastTransforms(CastInst &CI) {
+  Value *Src = CI.getOperand(0);
+  
+  if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Src)) {
+    // If casting the result of a getelementptr instruction with no offset, turn
+    // this into a cast of the original pointer!
+    if (GEP->hasAllZeroIndices()) {
+      // Changing the cast operand is usually not a good idea but it is safe
+      // here because the pointer operand is being replaced with another 
+      // pointer operand so the opcode doesn't need to change.
+      Worklist.Add(GEP);
+      CI.setOperand(0, GEP->getOperand(0));
+      return &CI;
+    }
+    
+    // If the GEP has a single use, and the base pointer is a bitcast, and the
+    // GEP computes a constant offset, see if we can convert these three
+    // instructions into fewer.  This typically happens with unions and other
+    // non-type-safe code.
+    if (TD && GEP->hasOneUse() && isa<BitCastInst>(GEP->getOperand(0)) &&
+        GEP->hasAllConstantIndices()) {
+      // We are guaranteed to get a constant from EmitGEPOffset.
+      ConstantInt *OffsetV = cast<ConstantInt>(EmitGEPOffset(GEP));
+      int64_t Offset = OffsetV->getSExtValue();
+      
+      // Get the base pointer input of the bitcast, and the type it points to.
+      Value *OrigBase = cast<BitCastInst>(GEP->getOperand(0))->getOperand(0);
+      const Type *GEPIdxTy =
+      cast<PointerType>(OrigBase->getType())->getElementType();
+      SmallVector<Value*, 8> NewIndices;
+      if (FindElementAtOffset(GEPIdxTy, Offset, NewIndices)) {
+        // If we were able to index down into an element, create the GEP
+        // and bitcast the result.  This eliminates one bitcast, potentially
+        // two.
+        Value *NGEP = cast<GEPOperator>(GEP)->isInBounds() ?
+        Builder->CreateInBoundsGEP(OrigBase,
+                                   NewIndices.begin(), NewIndices.end()) :
+        Builder->CreateGEP(OrigBase, NewIndices.begin(), NewIndices.end());
+        NGEP->takeName(GEP);
+        
+        if (isa<BitCastInst>(CI))
+          return new BitCastInst(NGEP, CI.getType());
+        assert(isa<PtrToIntInst>(CI));
+        return new PtrToIntInst(NGEP, CI.getType());
+      }      
+    }
+  }
+  
+  return commonCastTransforms(CI);
+}
+
+Instruction *InstCombiner::visitPtrToInt(PtrToIntInst &CI) {
+  // If the destination integer type is smaller than the intptr_t type for
+  // this target, do a ptrtoint to intptr_t then do a trunc.  This allows the
+  // trunc to be exposed to other transforms.  Don't do this for extending
+  // ptrtoint's, because we don't know if the target sign or zero extends its
+  // pointers.
+  if (TD &&
+      CI.getType()->getScalarSizeInBits() < TD->getPointerSizeInBits()) {
+    Value *P = Builder->CreatePtrToInt(CI.getOperand(0),
+                                       TD->getIntPtrType(CI.getContext()),
+                                       "tmp");
+    return new TruncInst(P, CI.getType());
+  }
+  
+  return commonPointerCastTransforms(CI);
+}
+
+Instruction *InstCombiner::visitBitCast(BitCastInst &CI) {
+  // If the operands are integer typed then apply the integer transforms,
+  // otherwise just apply the common ones.
+  Value *Src = CI.getOperand(0);
+  const Type *SrcTy = Src->getType();
+  const Type *DestTy = CI.getType();
+
+  // Get rid of casts from one type to the same type. These are useless and can
+  // be replaced by the operand.
+  if (DestTy == Src->getType())
+    return ReplaceInstUsesWith(CI, Src);
+
+  if (const PointerType *DstPTy = dyn_cast<PointerType>(DestTy)) {
+    const PointerType *SrcPTy = cast<PointerType>(SrcTy);
+    const Type *DstElTy = DstPTy->getElementType();
+    const Type *SrcElTy = SrcPTy->getElementType();
+    
+    // If the address spaces don't match, don't eliminate the bitcast, which is
+    // required for changing types.
+    if (SrcPTy->getAddressSpace() != DstPTy->getAddressSpace())
+      return 0;
+    
+    // If we are casting a alloca to a pointer to a type of the same
+    // size, rewrite the allocation instruction to allocate the "right" type.
+    // There is no need to modify malloc calls because it is their bitcast that
+    // needs to be cleaned up.
+    if (AllocaInst *AI = dyn_cast<AllocaInst>(Src))
+      if (Instruction *V = PromoteCastOfAllocation(CI, *AI))
+        return V;
+    
+    // If the source and destination are pointers, and this cast is equivalent
+    // to a getelementptr X, 0, 0, 0...  turn it into the appropriate gep.
+    // This can enhance SROA and other transforms that want type-safe pointers.
+    Constant *ZeroUInt =
+      Constant::getNullValue(Type::getInt32Ty(CI.getContext()));
+    unsigned NumZeros = 0;
+    while (SrcElTy != DstElTy && 
+           isa<CompositeType>(SrcElTy) && !isa<PointerType>(SrcElTy) &&
+           SrcElTy->getNumContainedTypes() /* not "{}" */) {
+      SrcElTy = cast<CompositeType>(SrcElTy)->getTypeAtIndex(ZeroUInt);
+      ++NumZeros;
+    }
+
+    // If we found a path from the src to dest, create the getelementptr now.
+    if (SrcElTy == DstElTy) {
+      SmallVector<Value*, 8> Idxs(NumZeros+1, ZeroUInt);
+      return GetElementPtrInst::CreateInBounds(Src, Idxs.begin(), Idxs.end(),"",
+                                               ((Instruction*)NULL));
+    }
+  }
+
+  if (const VectorType *DestVTy = dyn_cast<VectorType>(DestTy)) {
+    if (DestVTy->getNumElements() == 1 && !isa<VectorType>(SrcTy)) {
+      Value *Elem = Builder->CreateBitCast(Src, DestVTy->getElementType());
+      return InsertElementInst::Create(UndefValue::get(DestTy), Elem,
+                     Constant::getNullValue(Type::getInt32Ty(CI.getContext())));
+      // FIXME: Canonicalize bitcast(insertelement) -> insertelement(bitcast)
+    }
+  }
+
+  if (const VectorType *SrcVTy = dyn_cast<VectorType>(SrcTy)) {
+    if (SrcVTy->getNumElements() == 1 && !isa<VectorType>(DestTy)) {
+      Value *Elem = 
+        Builder->CreateExtractElement(Src,
+                   Constant::getNullValue(Type::getInt32Ty(CI.getContext())));
+      return CastInst::Create(Instruction::BitCast, Elem, DestTy);
+    }
+  }
+
+  if (ShuffleVectorInst *SVI = dyn_cast<ShuffleVectorInst>(Src)) {
+    // Okay, we have (bitcast (shuffle ..)).  Check to see if this is
+    // a bitconvert to a vector with the same # elts.
+    if (SVI->hasOneUse() && isa<VectorType>(DestTy) && 
+        cast<VectorType>(DestTy)->getNumElements() ==
+              SVI->getType()->getNumElements() &&
+        SVI->getType()->getNumElements() ==
+          cast<VectorType>(SVI->getOperand(0)->getType())->getNumElements()) {
+      BitCastInst *Tmp;
+      // If either of the operands is a cast from CI.getType(), then
+      // evaluating the shuffle in the casted destination's type will allow
+      // us to eliminate at least one cast.
+      if (((Tmp = dyn_cast<BitCastInst>(SVI->getOperand(0))) && 
+           Tmp->getOperand(0)->getType() == DestTy) ||
+          ((Tmp = dyn_cast<BitCastInst>(SVI->getOperand(1))) && 
+           Tmp->getOperand(0)->getType() == DestTy)) {
+        Value *LHS = Builder->CreateBitCast(SVI->getOperand(0), DestTy);
+        Value *RHS = Builder->CreateBitCast(SVI->getOperand(1), DestTy);
+        // Return a new shuffle vector.  Use the same element ID's, as we
+        // know the vector types match #elts.
+        return new ShuffleVectorInst(LHS, RHS, SVI->getOperand(2));
+      }
+    }
+  }
+  
+  if (isa<PointerType>(SrcTy))
+    return commonPointerCastTransforms(CI);
+  return commonCastTransforms(CI);
+}