split 943 lines of instcombine out to a new InstCombineCasts.cpp

file.  InstructionCombining.cpp is now down to a svelte 9300 lines :)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92468 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 943 insertions, 0 deletions

diff --git a/lib/Transforms/InstCombine/InstCombineCasts.cpp b/lib/Transforms/InstCombine/InstCombineCasts.cpp
new file mode 100644
index 0000000000..c5ad10feed
--- /dev/null
+++ b/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -0,0 +1,943 @@
+//===- 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;
+
+// FIXME: InstCombiner::EvaluateInDifferentType!
+
+
+/// 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;
+}
+
+/// @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))) {
+      if (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);
+}
+
+/// commonIntCastTransforms - This function implements the common transforms
+/// for trunc, zext, and sext.
+Instruction *InstCombiner::commonIntCastTransforms(CastInst &CI) {
+  if (Instruction *Result = commonCastTransforms(CI))
+    return Result;
+
+  Value *Src = CI.getOperand(0);
+  const Type *SrcTy = Src->getType();
+  const Type *DestTy = CI.getType();
+  uint32_t SrcBitSize = SrcTy->getScalarSizeInBits();
+  uint32_t DestBitSize = DestTy->getScalarSizeInBits();
+
+  // See if we can simplify any instructions used by the LHS whose sole 
+  // purpose is to compute bits we don't care about.
+  if (SimplifyDemandedInstructionBits(CI))
+    return &CI;
+
+  // If the source isn't an instruction or has more than one use then we
+  // can't do anything more. 
+  Instruction *SrcI = dyn_cast<Instruction>(Src);
+  if (!SrcI || !Src->hasOneUse())
+    return 0;
+
+  // Attempt to propagate the cast into the instruction for int->int casts.
+  int NumCastsRemoved = 0;
+  // 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(SrcI->getType(), DestTy)) &&
+      CanEvaluateInDifferentType(SrcI, DestTy,
+                                 CI.getOpcode(), NumCastsRemoved)) {
+    // If this cast is a truncate, evaluting in a different type always
+    // eliminates the cast, so it is always a win.  If this is a zero-extension,
+    // we need to do an AND to maintain the clear top-part of the computation,
+    // so we require that the input have eliminated at least one cast.  If this
+    // is a sign extension, we insert two new casts (to do the extension) so we
+    // require that two casts have been eliminated.
+    bool DoXForm = false;
+    bool JustReplace = false;
+    switch (CI.getOpcode()) {
+    default:
+      // All the others use floating point so we shouldn't actually 
+      // get here because of the check above.
+      llvm_unreachable("Unknown cast type");
+    case Instruction::Trunc:
+      DoXForm = true;
+      break;
+    case Instruction::ZExt: {
+      DoXForm = NumCastsRemoved >= 1;
+      
+      if (!DoXForm && 0) {
+        // If it's unnecessary to issue an AND to clear the high bits, it's
+        // always profitable to do this xform.
+        Value *TryRes = EvaluateInDifferentType(SrcI, DestTy, false);
+        APInt Mask(APInt::getBitsSet(DestBitSize, SrcBitSize, DestBitSize));
+        if (MaskedValueIsZero(TryRes, Mask))
+          return ReplaceInstUsesWith(CI, TryRes);
+        
+        if (Instruction *TryI = dyn_cast<Instruction>(TryRes))
+          if (TryI->use_empty())
+            EraseInstFromFunction(*TryI);
+      }
+      break;
+    }
+    case Instruction::SExt: {
+      DoXForm = NumCastsRemoved >= 2;
+      if (!DoXForm && !isa<TruncInst>(SrcI) && 0) {
+        // If we do not have to emit the truncate + sext pair, then it's always
+        // profitable to do this xform.
+        //
+        // It's not safe to eliminate the trunc + sext pair if one of the
+        // eliminated cast is a truncate. e.g.
+        // t2 = trunc i32 t1 to i16
+        // t3 = sext i16 t2 to i32
+        // !=
+        // i32 t1
+        Value *TryRes = EvaluateInDifferentType(SrcI, DestTy, true);
+        unsigned NumSignBits = ComputeNumSignBits(TryRes);
+        if (NumSignBits > (DestBitSize - SrcBitSize))
+          return ReplaceInstUsesWith(CI, TryRes);
+        
+        if (Instruction *TryI = dyn_cast<Instruction>(TryRes))
+          if (TryI->use_empty())
+            EraseInstFromFunction(*TryI);
+      }
+      break;
+    }
+    }
+    
+    if (DoXForm) {
+      DEBUG(errs() << "ICE: EvaluateInDifferentType converting expression type"
+            " to avoid cast: " << CI);
+      Value *Res = EvaluateInDifferentType(SrcI, DestTy, 
+                                           CI.getOpcode() == Instruction::SExt);
+      if (JustReplace)
+        // Just replace this cast with the result.
+        return ReplaceInstUsesWith(CI, Res);
+
+      assert(Res->getType() == DestTy);
+      switch (CI.getOpcode()) {
+      default: llvm_unreachable("Unknown cast type!");
+      case Instruction::Trunc:
+        // Just replace this cast with the result.
+        return ReplaceInstUsesWith(CI, Res);
+      case Instruction::ZExt: {
+        assert(SrcBitSize < DestBitSize && "Not a zext?");
+
+        // If the high bits are already zero, just replace this cast with the
+        // result.
+        APInt Mask(APInt::getBitsSet(DestBitSize, SrcBitSize, DestBitSize));
+        if (MaskedValueIsZero(Res, Mask))
+          return ReplaceInstUsesWith(CI, Res);
+
+        // We need to emit an AND to clear the high bits.
+        Constant *C = ConstantInt::get(CI.getContext(), 
+                                 APInt::getLowBitsSet(DestBitSize, SrcBitSize));
+        return BinaryOperator::CreateAnd(Res, C);
+      }
+      case Instruction::SExt: {
+        // If the high bits are already filled with sign bit, just replace this
+        // cast with the result.
+        unsigned NumSignBits = ComputeNumSignBits(Res);
+        if (NumSignBits > (DestBitSize - SrcBitSize))
+          return ReplaceInstUsesWith(CI, Res);
+
+        // We need to emit a cast to truncate, then a cast to sext.
+        return new SExtInst(Builder->CreateTrunc(Res, Src->getType()), DestTy);
+      }
+      }
+    }
+  }
+  
+  Value *Op0 = SrcI->getNumOperands() > 0 ? SrcI->getOperand(0) : 0;
+  Value *Op1 = SrcI->getNumOperands() > 1 ? SrcI->getOperand(1) : 0;
+
+  switch (SrcI->getOpcode()) {
+  case Instruction::Add:
+  case Instruction::Mul:
+  case Instruction::And:
+  case Instruction::Or:
+  case Instruction::Xor:
+    // If we are discarding information, rewrite.
+    if (DestBitSize < SrcBitSize && DestBitSize != 1) {
+      // Don't insert two casts unless at least one can be eliminated.
+      if (!ValueRequiresCast(CI.getOpcode(), Op1, DestTy) ||
+          !ValueRequiresCast(CI.getOpcode(), Op0, DestTy)) {
+        Value *Op0c = Builder->CreateTrunc(Op0, DestTy, Op0->getName());
+        Value *Op1c = Builder->CreateTrunc(Op1, DestTy, Op1->getName());
+        return BinaryOperator::Create(
+            cast<BinaryOperator>(SrcI)->getOpcode(), Op0c, Op1c);
+      }
+    }
+
+    // cast (xor bool X, true) to int  --> xor (cast bool X to int), 1
+    if (isa<ZExtInst>(CI) && SrcBitSize == 1 && 
+        SrcI->getOpcode() == Instruction::Xor &&
+        Op1 == ConstantInt::getTrue(CI.getContext()) &&
+        (!Op0->hasOneUse() || !isa<CmpInst>(Op0))) {
+      Value *New = Builder->CreateZExt(Op0, DestTy, Op0->getName());
+      return BinaryOperator::CreateXor(New,
+                                      ConstantInt::get(CI.getType(), 1));
+    }
+    break;
+
+  case Instruction::Shl: {
+    // Canonicalize trunc inside shl, if we can.
+    ConstantInt *CI = dyn_cast<ConstantInt>(Op1);
+    if (CI && DestBitSize < SrcBitSize &&
+        CI->getLimitedValue(DestBitSize) < DestBitSize) {
+      Value *Op0c = Builder->CreateTrunc(Op0, DestTy, Op0->getName());
+      Value *Op1c = Builder->CreateTrunc(Op1, DestTy, Op1->getName());
+      return BinaryOperator::CreateShl(Op0c, Op1c);
+    }
+    break;
+  }
+  }
+  return 0;
+}
+
+
+Instruction *InstCombiner::visitTrunc(TruncInst &CI) {
+  if (Instruction *Result = commonIntCastTransforms(CI))
+    return Result;
+  
+  Value *Src = CI.getOperand(0);
+  const Type *Ty = CI.getType();
+  uint32_t DestBitWidth = Ty->getScalarSizeInBits();
+  uint32_t SrcBitWidth = Src->getType()->getScalarSizeInBits();
+
+  // Canonicalize trunc x to i1 -> (icmp ne (and x, 1), 0)
+  if (DestBitWidth == 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);
+  }
+
+  // Optimize trunc(lshr(), c) to pull the shift through the truncate.
+  ConstantInt *ShAmtV = 0;
+  Value *ShiftOp = 0;
+  if (Src->hasOneUse() &&
+      match(Src, m_LShr(m_Value(ShiftOp), m_ConstantInt(ShAmtV)))) {
+    uint32_t ShAmt = ShAmtV->getLimitedValue(SrcBitWidth);
+    
+    // Get a mask for the bits shifting in.
+    APInt Mask(APInt::getLowBitsSet(SrcBitWidth, ShAmt).shl(DestBitWidth));
+    if (MaskedValueIsZero(ShiftOp, Mask)) {
+      if (ShAmt >= DestBitWidth)        // All zeros.
+        return ReplaceInstUsesWith(CI, Constant::getNullValue(Ty));
+      
+      // Okay, we can shrink this.  Truncate the input, then return a new
+      // shift.
+      Value *V1 = Builder->CreateTrunc(ShiftOp, Ty, ShiftOp->getName());
+      Value *V2 = ConstantExpr::getTrunc(ShAmtV, Ty);
+      return BinaryOperator::CreateLShr(V1, V2);
+    }
+  }
+ 
+  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;
+}
+
+Instruction *InstCombiner::visitZExt(ZExtInst &CI) {
+  // If one of the common conversion will work, do it.
+  if (Instruction *Result = commonIntCastTransforms(CI))
+    return Result;
+
+  Value *Src = CI.getOperand(0);
+
+  // 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
+    // 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);
+            }
+          }
+
+  return 0;
+}
+
+Instruction *InstCombiner::visitSExt(SExtInst &CI) {
+  if (Instruction *I = commonIntCastTransforms(CI))
+    return I;
+  
+  Value *Src = CI.getOperand(0);
+  
+  // Canonicalize sign-extend from i1 to a select.
+  if (Src->getType() == Type::getInt1Ty(CI.getContext()))
+    return SelectInst::Create(Src,
+                              Constant::getAllOnesValue(CI.getType()),
+                              Constant::getNullValue(CI.getType()));
+
+  // See if the value being truncated is already sign extended.  If so, just
+  // eliminate the trunc/sext pair.
+  if (Operator::getOpcode(Src) == Instruction::Trunc) {
+    Value *Op = cast<User>(Src)->getOperand(0);
+    unsigned OpBits   = Op->getType()->getScalarSizeInBits();
+    unsigned MidBits  = Src->getType()->getScalarSizeInBits();
+    unsigned DestBits = CI.getType()->getScalarSizeInBits();
+    unsigned NumSignBits = ComputeNumSignBits(Op);
+
+    if (OpBits == DestBits) {
+      // Op is i32, Mid is i8, and Dest is i32.  If Op has more than 24 sign
+      // bits, it is already ready.
+      if (NumSignBits > DestBits-MidBits)
+        return ReplaceInstUsesWith(CI, Op);
+    } else if (OpBits < DestBits) {
+      // Op is i32, Mid is i8, and Dest is i64.  If Op has more than 24 sign
+      // bits, just sext from i32.
+      if (NumSignBits > OpBits-MidBits)
+        return new SExtInst(Op, CI.getType(), "tmp");
+    } else {
+      // Op is i64, Mid is i8, and Dest is i32.  If Op has more than 56 sign
+      // bits, just truncate to i32.
+      if (NumSignBits > OpBits-MidBits)
+        return new TruncInst(Op, CI.getType(), "tmp");
+    }
+  }
+
+  // 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;
+  ConstantInt *BA = 0, *CA = 0;
+  if (match(Src, m_AShr(m_Shl(m_Value(A), m_ConstantInt(BA)),
+                        m_ConstantInt(CA))) &&
+      BA == CA && isa<TruncInst>(A)) {
+    Value *I = cast<TruncInst>(A)->getOperand(0);
+    if (I->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);
+      I = Builder->CreateShl(I, ShAmtV, CI.getName());
+      return BinaryOperator::CreateAShr(I, 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() == Type::getDoubleTy(V->getContext()))
+      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::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::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;
+}
+
+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();
+
+  if (isa<PointerType>(SrcTy)) {
+    if (Instruction *I = commonPointerCastTransforms(CI))
+      return I;
+  } else {
+    if (Instruction *Result = commonCastTransforms(CI))
+      return Result;
+  }
+
+
+  // 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();
+    
+