move ComputeMaskedBits, MaskedValueIsZero, and ComputeNumSignBits

out of instcombine into a new file in libanalysis.  This also teaches
ComputeNumSignBits about the number of sign bits in a constantint.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51863 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 14 insertions, 651 deletions

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index bb15e3504c..05d935e1a9 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -40,6 +40,7 @@
 #include "llvm/DerivedTypes.h"
 #include "llvm/GlobalVariable.h"
 #include "llvm/Analysis/ConstantFolding.h"
+#include "llvm/Analysis/ValueTracking.h"
 #include "llvm/Target/TargetData.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/Local.h"
@@ -323,6 +324,19 @@ namespace {
       I.eraseFromParent();
       return 0;  // Don't do anything with FI
     }
+        
+    void ComputeMaskedBits(Value *V, const APInt &Mask, APInt &KnownZero,
+                           APInt &KnownOne, unsigned Depth = 0) const {
+      return llvm::ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD, Depth);
+    }
+    
+    bool MaskedValueIsZero(Value *V, const APInt &Mask, 
+                           unsigned Depth = 0) const {
+      return llvm::MaskedValueIsZero(V, Mask, TD, Depth);
+    }
+    unsigned ComputeNumSignBits(Value *Op, unsigned Depth = 0) const {
+      return llvm::ComputeNumSignBits(Op, TD, Depth);
+    }
 
   private:
     /// InsertOperandCastBefore - This inserts a cast of V to DestTy before the
@@ -378,10 +392,6 @@ namespace {
 
     Value *EvaluateInDifferentType(Value *V, const Type *Ty, bool isSigned);
 
-    void ComputeMaskedBits(Value *V, const APInt &Mask, APInt& KnownZero,
-                           APInt& KnownOne, unsigned Depth = 0) const;
-    bool MaskedValueIsZero(Value *V, const APInt& Mask, unsigned Depth = 0);
-    unsigned ComputeNumSignBits(Value *Op, unsigned Depth = 0) const;
     bool CanEvaluateInDifferentType(Value *V, const IntegerType *Ty,
                                     unsigned CastOpc,
                                     int &NumCastsRemoved);
@@ -661,506 +671,6 @@ static bool MultiplyOverflows(ConstantInt *C1, ConstantInt *C2, bool sign) {
     return MulExt.ugt(APInt::getLowBitsSet(W * 2, W));
 }
 
-/// ComputeMaskedBits - Determine which of the bits specified in Mask are
-/// known to be either zero or one and return them in the KnownZero/KnownOne
-/// bit sets.  This code only analyzes bits in Mask, in order to short-circuit
-/// processing.
-/// NOTE: we cannot consider 'undef' to be "IsZero" here.  The problem is that
-/// we cannot optimize based on the assumption that it is zero without changing
-/// it to be an explicit zero.  If we don't change it to zero, other code could
-/// optimized based on the contradictory assumption that it is non-zero.
-/// Because instcombine aggressively folds operations with undef args anyway,
-/// this won't lose us code quality.
-void InstCombiner::ComputeMaskedBits(Value *V, const APInt &Mask,
-                                     APInt& KnownZero, APInt& KnownOne,
-                                     unsigned Depth) const {
-  assert(V && "No Value?");
-  assert(Depth <= 6 && "Limit Search Depth");
-  uint32_t BitWidth = Mask.getBitWidth();
-  assert((V->getType()->isInteger() || isa<PointerType>(V->getType())) &&
-         "Not integer or pointer type!");
-  assert((!TD || TD->getTypeSizeInBits(V->getType()) == BitWidth) &&
-         (!isa<IntegerType>(V->getType()) ||
-          V->getType()->getPrimitiveSizeInBits() == BitWidth) &&
-         KnownZero.getBitWidth() == BitWidth && 
-         KnownOne.getBitWidth() == BitWidth &&
-         "V, Mask, KnownOne and KnownZero should have same BitWidth");
-
-  if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
-    // We know all of the bits for a constant!
-    KnownOne = CI->getValue() & Mask;
-    KnownZero = ~KnownOne & Mask;
-    return;
-  }
-  // Null is all-zeros.
-  if (isa<ConstantPointerNull>(V)) {
-    KnownOne.clear();
-    KnownZero = Mask;
-    return;
-  }
-  // The address of an aligned GlobalValue has trailing zeros.
-  if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
-    unsigned Align = GV->getAlignment();
-    if (Align == 0 && TD && GV->getType()->getElementType()->isSized()) 
-      Align = TD->getPrefTypeAlignment(GV->getType()->getElementType());
-    if (Align > 0)
-      KnownZero = Mask & APInt::getLowBitsSet(BitWidth,
-                                              CountTrailingZeros_32(Align));
-    else
-      KnownZero.clear();
-    KnownOne.clear();
-    return;
-  }
-
-  KnownZero.clear(); KnownOne.clear();   // Start out not knowing anything.
-
-  if (Depth == 6 || Mask == 0)
-    return;  // Limit search depth.
-
-  User *I = dyn_cast<User>(V);
-  if (!I) return;
-
-  APInt KnownZero2(KnownZero), KnownOne2(KnownOne);
-  switch (getOpcode(I)) {
-  default: break;
-  case Instruction::And: {
-    // If either the LHS or the RHS are Zero, the result is zero.
-    ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, Depth+1);
-    APInt Mask2(Mask & ~KnownZero);
-    ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, Depth+1);
-    assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
-    assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
-    
-    // Output known-1 bits are only known if set in both the LHS & RHS.
-    KnownOne &= KnownOne2;
-    // Output known-0 are known to be clear if zero in either the LHS | RHS.
-    KnownZero |= KnownZero2;
-    return;
-  }
-  case Instruction::Or: {
-    ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, Depth+1);
-    APInt Mask2(Mask & ~KnownOne);
-    ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, Depth+1);
-    assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
-    assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
-    
-    // Output known-0 bits are only known if clear in both the LHS & RHS.
-    KnownZero &= KnownZero2;
-    // Output known-1 are known to be set if set in either the LHS | RHS.
-    KnownOne |= KnownOne2;
-    return;
-  }
-  case Instruction::Xor: {
-    ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, Depth+1);
-    ComputeMaskedBits(I->getOperand(0), Mask, KnownZero2, KnownOne2, Depth+1);
-    assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
-    assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
-    
-    // Output known-0 bits are known if clear or set in both the LHS & RHS.
-    APInt KnownZeroOut = (KnownZero & KnownZero2) | (KnownOne & KnownOne2);
-    // Output known-1 are known to be set if set in only one of the LHS, RHS.
-    KnownOne = (KnownZero & KnownOne2) | (KnownOne & KnownZero2);
-    KnownZero = KnownZeroOut;
-    return;
-  }
-  case Instruction::Mul: {
-    APInt Mask2 = APInt::getAllOnesValue(BitWidth);
-    ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero, KnownOne, Depth+1);
-    ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, Depth+1);
-    assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
-    assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
-    
-    // If low bits are zero in either operand, output low known-0 bits.
-    // Also compute a conserative estimate for high known-0 bits.
-    // More trickiness is possible, but this is sufficient for the
-    // interesting case of alignment computation.
-    KnownOne.clear();
-    unsigned TrailZ = KnownZero.countTrailingOnes() +
-                      KnownZero2.countTrailingOnes();
-    unsigned LeadZ =  std::max(KnownZero.countLeadingOnes() +
-                               KnownZero2.countLeadingOnes(),
-                               BitWidth) - BitWidth;
-
-    TrailZ = std::min(TrailZ, BitWidth);
-    LeadZ = std::min(LeadZ, BitWidth);
-    KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) |
-                APInt::getHighBitsSet(BitWidth, LeadZ);
-    KnownZero &= Mask;
-    return;
-  }
-  case Instruction::UDiv: {
-    // For the purposes of computing leading zeros we can conservatively
-    // treat a udiv as a logical right shift by the power of 2 known to
-    // be less than the denominator.
-    APInt AllOnes = APInt::getAllOnesValue(BitWidth);
-    ComputeMaskedBits(I->getOperand(0),
-                      AllOnes, KnownZero2, KnownOne2, Depth+1);
-    unsigned LeadZ = KnownZero2.countLeadingOnes();
-
-    KnownOne2.clear();
-    KnownZero2.clear();
-    ComputeMaskedBits(I->getOperand(1),
-                      AllOnes, KnownZero2, KnownOne2, Depth+1);
-    unsigned RHSUnknownLeadingOnes = KnownOne2.countLeadingZeros();
-    if (RHSUnknownLeadingOnes != BitWidth)
-      LeadZ = std::min(BitWidth,
-                       LeadZ + BitWidth - RHSUnknownLeadingOnes - 1);
-
-    KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ) & Mask;
-    return;
-  }
-  case Instruction::Select:
-    ComputeMaskedBits(I->getOperand(2), Mask, KnownZero, KnownOne, Depth+1);
-    ComputeMaskedBits(I->getOperand(1), Mask, KnownZero2, KnownOne2, Depth+1);
-    assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
-    assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
-
-    // Only known if known in both the LHS and RHS.
-    KnownOne &= KnownOne2;
-    KnownZero &= KnownZero2;
-    return;
-  case Instruction::FPTrunc:
-  case Instruction::FPExt:
-  case Instruction::FPToUI:
-  case Instruction::FPToSI:
-  case Instruction::SIToFP:
-  case Instruction::UIToFP:
-    return; // Can't work with floating point.
-  case Instruction::PtrToInt:
-  case Instruction::IntToPtr:
-    // We can't handle these if we don't know the pointer size.
-    if (!TD) return;
-    // FALL THROUGH and handle them the same as zext/trunc.
-  case Instruction::ZExt:
-  case Instruction::Trunc: {
-    // Note that we handle pointer operands here because of inttoptr/ptrtoint
-    // which fall through here.
-    const Type *SrcTy = I->getOperand(0)->getType();
-    uint32_t SrcBitWidth = TD ?
-      TD->getTypeSizeInBits(SrcTy) :
-      SrcTy->getPrimitiveSizeInBits();
-    APInt MaskIn(Mask);
-    MaskIn.zextOrTrunc(SrcBitWidth);
-    KnownZero.zextOrTrunc(SrcBitWidth);
-    KnownOne.zextOrTrunc(SrcBitWidth);
-    ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, Depth+1);
-    KnownZero.zextOrTrunc(BitWidth);
-    KnownOne.zextOrTrunc(BitWidth);
-    // Any top bits are known to be zero.
-    if (BitWidth > SrcBitWidth)
-      KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
-    return;
-  }
-  case Instruction::BitCast: {
-    const Type *SrcTy = I->getOperand(0)->getType();
-    if (SrcTy->isInteger() || isa<PointerType>(SrcTy)) {
-      ComputeMaskedBits(I->getOperand(0), Mask, KnownZero, KnownOne, Depth+1);
-      return;
-    }
-    break;
-  }
-  case Instruction::SExt: {
-    // Compute the bits in the result that are not present in the input.
-    const IntegerType *SrcTy = cast<IntegerType>(I->getOperand(0)->getType());
-    uint32_t SrcBitWidth = SrcTy->getBitWidth();
-      
-    APInt MaskIn(Mask); 
-    MaskIn.trunc(SrcBitWidth);
-    KnownZero.trunc(SrcBitWidth);
-    KnownOne.trunc(SrcBitWidth);
-    ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, Depth+1);
-    assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
-    KnownZero.zext(BitWidth);
-    KnownOne.zext(BitWidth);
-
-    // If the sign bit of the input is known set or clear, then we know the
-    // top bits of the result.
-    if (KnownZero[SrcBitWidth-1])             // Input sign bit known zero
-      KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
-    else if (KnownOne[SrcBitWidth-1])           // Input sign bit known set
-      KnownOne |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
-    return;
-  }
-  case Instruction::Shl:
-    // (shl X, C1) & C2 == 0   iff   (X & C2 >>u C1) == 0
-    if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
-      uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
-      APInt Mask2(Mask.lshr(ShiftAmt));
-      ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, Depth+1);
-      assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
-      KnownZero <<= ShiftAmt;
-      KnownOne  <<= ShiftAmt;
-      KnownZero |= APInt::getLowBitsSet(BitWidth, ShiftAmt); // low bits known 0
-      return;
-    }
-    break;
-  case Instruction::LShr:
-    // (ushr X, C1) & C2 == 0   iff  (-1 >> C1) & C2 == 0
-    if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
-      // Compute the new bits that are at the top now.
-      uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
-      
-      // Unsigned shift right.
-      APInt Mask2(Mask.shl(ShiftAmt));
-      ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero,KnownOne,Depth+1);
-      assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?"); 
-      KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
-      KnownOne  = APIntOps::lshr(KnownOne, ShiftAmt);
-      // high bits known zero.
-      KnownZero |= APInt::getHighBitsSet(BitWidth, ShiftAmt);
-      return;
-    }
-    break;
-  case Instruction::AShr:
-    // (ashr X, C1) & C2 == 0   iff  (-1 >> C1) & C2 == 0
-    if (ConstantInt *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
-      // Compute the new bits that are at the top now.
-      uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
-      
-      // Signed shift right.
-      APInt Mask2(Mask.shl(ShiftAmt));
-      ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero,KnownOne,Depth+1);
-      assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?"); 
-      KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
-      KnownOne  = APIntOps::lshr(KnownOne, ShiftAmt);
-        
-      APInt HighBits(APInt::getHighBitsSet(BitWidth, ShiftAmt));
-      if (KnownZero[BitWidth-ShiftAmt-1])    // New bits are known zero.
-        KnownZero |= HighBits;
-      else if (KnownOne[BitWidth-ShiftAmt-1])  // New bits are known one.
-        KnownOne |= HighBits;
-      return;
-    }
-    break;
-  case Instruction::Sub: {
-    if (ConstantInt *CLHS = dyn_cast<ConstantInt>(I->getOperand(0))) {
-      // We know that the top bits of C-X are clear if X contains less bits
-      // than C (i.e. no wrap-around can happen).  For example, 20-X is
-      // positive if we can prove that X is >= 0 and < 16.
-      if (!CLHS->getValue().isNegative()) {
-        unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros();
-        // NLZ can't be BitWidth with no sign bit
-        APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1);
-        ComputeMaskedBits(I->getOperand(1), MaskV, KnownZero2, KnownOne2,
-                          Depth+1);
-    
-        // If all of the MaskV bits are known to be zero, then we know the
-        // output top bits are zero, because we now know that the output is
-        // from [0-C].
-        if ((KnownZero2 & MaskV) == MaskV) {
-          unsigned NLZ2 = CLHS->getValue().countLeadingZeros();
-          // Top bits known zero.
-          KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2) & Mask;
-        }
-      }        
-    }
-  }
-  // fall through
-  case Instruction::Add: {
-    // Output known-0 bits are known if clear or set in both the low clear bits
-    // common to both LHS & RHS.  For example, 8+(X<<3) is known to have the
-    // low 3 bits clear.
-    APInt Mask2 = APInt::getLowBitsSet(BitWidth, Mask.countTrailingOnes());
-    ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, Depth+1);
-    assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
-    unsigned KnownZeroOut = KnownZero2.countTrailingOnes();
-
-    ComputeMaskedBits(I->getOperand(1), Mask2, KnownZero2, KnownOne2, Depth+1);
-    assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
-    KnownZeroOut = std::min(KnownZeroOut, 
-                            KnownZero2.countTrailingOnes());
-
-    KnownZero |= APInt::getLowBitsSet(BitWidth, KnownZeroOut);
-    return;
-  }
-  case Instruction::SRem:
-    if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
-      APInt RA = Rem->getValue();
-      if (RA.isPowerOf2() || (-RA).isPowerOf2()) {
-        APInt LowBits = RA.isStrictlyPositive() ? (RA - 1) : ~RA;
-        APInt Mask2 = LowBits | APInt::getSignBit(BitWidth);
-        ComputeMaskedBits(I->getOperand(0), Mask2,KnownZero2,KnownOne2,Depth+1);
-
-        // The sign of a remainder is equal to the sign of the first
-        // operand (zero being positive).
-        if (KnownZero2[BitWidth-1] || ((KnownZero2 & LowBits) == LowBits))
-          KnownZero2 |= ~LowBits;
-        else if (KnownOne2[BitWidth-1])
-          KnownOne2 |= ~LowBits;
-
-        KnownZero |= KnownZero2 & Mask;
-        KnownOne |= KnownOne2 & Mask;
-
-        assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?"); 
-      }
-    }
-    break;
-  case Instruction::URem: {
-    if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
-      APInt RA = Rem->getValue();
-      if (RA.isPowerOf2()) {
-        APInt LowBits = (RA - 1);
-        APInt Mask2 = LowBits & Mask;
-        KnownZero |= ~LowBits & Mask;
-        ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne,Depth+1);
-        assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?");
-        break;
-      }
-    }
-
-    // Since the result is less than or equal to either operand, any leading
-    // zero bits in either operand must also exist in the result.
-    APInt AllOnes = APInt::getAllOnesValue(BitWidth);
-    ComputeMaskedBits(I->getOperand(0), AllOnes, KnownZero, KnownOne,
-                      Depth+1);
-    ComputeMaskedBits(I->getOperand(1), AllOnes, KnownZero2, KnownOne2,
-                      Depth+1);
-
-    uint32_t Leaders = std::max(KnownZero.countLeadingOnes(),
-                                KnownZero2.countLeadingOnes());
-    KnownOne.clear();
-    KnownZero = APInt::getHighBitsSet(BitWidth, Leaders) & Mask;
-    break;
-  }
-
-  case Instruction::Alloca:
-  case Instruction::Malloc: {
-    AllocationInst *AI = cast<AllocationInst>(V);
-    unsigned Align = AI->getAlignment();
-    if (Align == 0 && TD) {
-      if (isa<AllocaInst>(AI))
-        Align = TD->getPrefTypeAlignment(AI->getType()->getElementType());
-      else if (isa<MallocInst>(AI)) {
-        // Malloc returns maximally aligned memory.
-        Align = TD->getABITypeAlignment(AI->getType()->getElementType());
-        Align =
-          std::max(Align,
-                   (unsigned)TD->getABITypeAlignment(Type::DoubleTy));
-        Align =
-          std::max(Align,
-                   (unsigned)TD->getABITypeAlignment(Type::Int64Ty));
-      }
-    }
-    
-    if (Align > 0)
-      KnownZero = Mask & APInt::getLowBitsSet(BitWidth,
-                                              CountTrailingZeros_32(Align));
-    break;
-  }
-  case Instruction::GetElementPtr: {
-    // Analyze all of the subscripts of this getelementptr instruction
-    // to determine if we can prove known low zero bits.
-    APInt LocalMask = APInt::getAllOnesValue(BitWidth);
-    APInt LocalKnownZero(BitWidth, 0), LocalKnownOne(BitWidth, 0);
-    ComputeMaskedBits(I->getOperand(0), LocalMask,
-                      LocalKnownZero, LocalKnownOne, Depth+1);
-    unsigned TrailZ = LocalKnownZero.countTrailingOnes();
-
-    gep_type_iterator GTI = gep_type_begin(I);
-    for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i, ++GTI) {
-      Value *Index = I->getOperand(i);
-      if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
-        // Handle struct member offset arithmetic.
-        if (!TD) return;
-        const StructLayout *SL = TD->getStructLayout(STy);
-        unsigned Idx = cast<ConstantInt>(Index)->getZExtValue();
-        uint64_t Offset = SL->getElementOffset(Idx);
-        TrailZ = std::min(TrailZ,
-                          CountTrailingZeros_64(Offset));
-      } else {
-        // Handle array index arithmetic.
-        const Type *IndexedTy = GTI.getIndexedType();
-        if (!IndexedTy->isSized()) return;
-        unsigned GEPOpiBits = Index->getType()->getPrimitiveSizeInBits();
-        uint64_t TypeSize = TD ? TD->getABITypeSize(IndexedTy) : 1;
-        LocalMask = APInt::getAllOnesValue(GEPOpiBits);
-        LocalKnownZero = LocalKnownOne = APInt(GEPOpiBits, 0);
-        ComputeMaskedBits(Index, LocalMask,
-                          LocalKnownZero, LocalKnownOne, Depth+1);
-        TrailZ = std::min(TrailZ,
-                          CountTrailingZeros_64(TypeSize) +
-                            LocalKnownZero.countTrailingOnes());
-      }
-    }
-    
-    KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) & Mask;
-    break;
-  }
-  case Instruction::PHI: {
-    PHINode *P = cast<PHINode>(I);
-    // Handle the case of a simple two-predecessor recurrence PHI.
-    // There's a lot more that could theoretically be done here, but
-    // this is sufficient to catch some interesting cases.
-    if (P->getNumIncomingValues() == 2) {
-      for (unsigned i = 0; i != 2; ++i) {
-        Value *L = P->getIncomingValue(i);
-        Value *R = P->getIncomingValue(!i);
-        User *LU = dyn_cast<User>(L);
-        if (!LU)
-          continue;
-        unsigned Opcode = getOpcode(LU);
-        // Check for operations that have the property that if
-        // both their operands have low zero bits, the result
-        // will have low zero bits.
-        if (Opcode == Instruction::Add ||
-            Opcode == Instruction::Sub ||
-            Opcode == Instruction::And ||
-            Opcode == Instruction::Or ||
-            Opcode == Instruction::Mul) {
-          Value *LL = LU->getOperand(0);
-          Value *LR = LU->getOperand(1);
-          // Find a recurrence.
-          if (LL == I)
-            L = LR;
-          else if (LR == I)
-            L = LL;
-          else
-            break;
-          // Ok, we have a PHI of the form L op= R. Check for low
-          // zero bits.
-          APInt Mask2 = APInt::getAllOnesValue(BitWidth);
-          ComputeMaskedBits(R, Mask2, KnownZero2, KnownOne2, Depth+1);
-          Mask2 = APInt::getLowBitsSet(BitWidth,
-                                       KnownZero2.countTrailingOnes());
-          KnownOne2.clear();
-          KnownZero2.clear();
-          ComputeMaskedBits(L, Mask2, KnownZero2, KnownOne2, Depth+1);
-          KnownZero = Mask &
-                      APInt::getLowBitsSet(BitWidth,
-                                           KnownZero2.countTrailingOnes());
-          break;
-        }
-      }
-    }
-    break;
-  }
-  case Instruction::Call:
-    if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
-      switch (II->getIntrinsicID()) {
-      default: break;
-      case Intrinsic::ctpop:
-      case Intrinsic::ctlz:
-      case Intrinsic::cttz: {
-        unsigned LowBits = Log2_32(BitWidth)+1;
-        KnownZero = APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
-        break;
-      }
-      }
-    }
-    break;
-  }
-}
-
-/// MaskedValueIsZero - Return true if 'V & Mask' is known to be zero.  We use
-/// this predicate to simplify operations downstream.  Mask is known to be zero
-/// for bits that V cannot have.
-bool InstCombiner::MaskedValueIsZero(Value *V, const APInt& Mask,
-                                     unsigned Depth) {
-  APInt KnownZero(Mask.getBitWidth(), 0), KnownOne(Mask.getBitWidth(), 0);
-  ComputeMaskedBits(V, Mask, KnownZero, KnownOne, Depth);
-  assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
-  return (KnownZero & Mask) == Mask;
-}
 
 /// ShrinkDemandedConstant - Check to see if the specified operand of the 
 /// specified instruction is a constant integer.  If so, check to see if there
@@ -2069,153 +1579,6 @@ Value *InstCombiner::SimplifyDemandedVectorElts(Value *V, uint64_t DemandedElts,
   return MadeChange ? I : 0;
 }
 
-/// ComputeNumSignBits - Return the number of times the sign bit of the
-/// register is replicated into the other bits.  We know that at least 1 bit
-/// is always equal to the sign bit (itself), but other cases can give us
-/// information.  For example, immediately after an "ashr X, 2", we know that
-/// the top 3 bits are all equal to each other, so we return 3.
-///
-unsigned InstCombiner::ComputeNumSignBits(Value *V, unsigned Depth) const{
-  const IntegerType *Ty = cast<IntegerType>(V->getType());
-  unsigned TyBits = Ty->getBitWidth();
-  unsigned Tmp, Tmp2;
-  unsigned FirstAnswer = 1;
-
-  if (Depth == 6)
-    return 1;  // Limit search depth.
-
-  User *U = dyn_cast<User>(V);
-  switch (getOpcode(V)) {
-  default: break;
-  case Instruction::SExt:
-    Tmp = TyBits-cast<IntegerType>(U->getOperand(0)->getType())->getBitWidth();
-    return ComputeNumSignBits(U->getOperand(0), Depth+1) + Tmp;
-    
-  case Instruction::AShr:
-    Tmp = ComputeNumSignBits(U->getOperand(0), Depth+1);
-    // ashr X, C   -> adds C sign bits.
-    if (ConstantInt *C = dyn_cast<ConstantInt>(U->getOperand(1))) {
-      Tmp += C->getZExtValue();
-      if (Tmp > TyBits) Tmp = TyBits;
-    }
-    return Tmp;
-  case Instruction::Shl:
-    if (ConstantInt *C = dyn_cast<ConstantInt>(U->getOperand(1))) {
-      // shl destroys sign bits.
-      Tmp = ComputeNumSignBits(U->getOperand(0), Depth+1);
-      if (C->getZExtValue() >= TyBits ||      // Bad shift.
-          C->getZExtValue() >= Tmp) break;    // Shifted all sign bits out.
-      return Tmp - C->getZExtValue();
-    }
-    break;
-  case Instruction::And:
-  case Instruction::Or:
-  case Instruction::Xor:    // NOT is handled here.
-    // Logical binary ops preserve the number of sign bits at the worst.
-    Tmp = ComputeNumSignBits(U->getOperand(0), Depth+1);
-    if (Tmp != 1) {
-      Tmp2 = ComputeNumSignBits(U->getOperand(1), Depth+1);
-      FirstAnswer = std::min(Tmp, Tmp2);
-      // We computed what we know about the sign bits as our first
-      // answer. Now proceed to the generic code that uses
-      // ComputeMaskedBits, and pick whichever answer is better.
-    }
-    break;
-
-  case Instruction::Select:
-    Tmp = ComputeNumSignBits(U->getOperand(1), Depth+1);
-    if (Tmp == 1) return 1;  // Early out.
-    Tmp2 = ComputeNumSignBits(U->getOperand(2), Depth+1);
-    return std::min(Tmp, Tmp2);
-    
-  case Instruction::Add:
-    // Add can have at most one carry bit.  Thus we know that the output
-    // is, at worst, one more bit than the inputs.
-    Tmp = ComputeNumSignBits(U->getOperand(0), Depth+1);
-    if (Tmp == 1) return 1;  // Early out.
-      
-    // Special case decrementing a value (ADD X, -1):
-    if (ConstantInt *CRHS = dyn_cast<ConstantInt>(U->getOperand(0)))
-      if (CRHS->isAllOnesValue()) {
-        APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
-        APInt Mask = APInt::getAllOnesValue(TyBits);
-        ComputeMaskedBits(U->getOperand(0), Mask, KnownZero, KnownOne, Depth+1);
-        
-        // If the input is known to be 0 or 1, the output is 0/-1, which is all
-        // sign bits set.
-        if ((KnownZero | APInt(TyBits, 1)) == Mask)
-          return TyBits;
-        
-        // If we are subtracting one from a positive number, there is no carry
-        // out of the result.
-        if (KnownZero.isNegative())
-          return Tmp;
-      }
-      
-    Tmp2 = ComputeNumSignBits(U->getOperand(1), Depth+1);
-    if (Tmp2 == 1) return 1;
-      return std::min(Tmp, Tmp2)-1;
-    break;
-    
-  case Instruction::Sub:
-    Tmp2 = ComputeNumSignBits(U->getOperand(1), Depth+1);
-    if (Tmp2 == 1) return 1;
-      
-    // Handle NEG.
-    if (ConstantInt *CLHS = dyn_cast<ConstantInt>(U->getOperand(0)))
-      if (CLHS->isNullValue()) {
-        APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
-        APInt Mask = APInt::getAllOnesValue(TyBits);
-        ComputeMaskedBits(U->getOperand(1), Mask, KnownZero, KnownOne, Depth+1);
-        // If the input is known to be 0 or 1, the output is 0/-1, which is all
-        // sign bits set.
-        if ((KnownZero | APInt(TyBits, 1)) == Mask)
-          return TyBits;
-        
-        // If the input is known to be positive (the sign bit is known clear),
-        // the output of the NEG has the same number of sign bits as the input.
-        if (KnownZero.isNegative())
-          return Tmp2;
-        
-        // Otherwise, we treat this like a SUB.
-      }
-    
-    // Sub can have at most one carry bit.  Thus we know that the output
-    // is, at worst, one more bit than the inputs.
-    Tmp = ComputeNumSignBits(U->getOperand(0), Depth+1);
-    if (Tmp == 1) return 1;  // Early out.
-      return std::min(Tmp, Tmp2)-1;
-    break;
-  case Instruction::Trunc:
-    // FIXME: it's tricky to do anything useful for this, but it is an important
-    // case for targets like X86.
-    break;
-  }
-  
-  // Finally, if we can prove that the top bits of the result are 0's or 1's,
-  // use this information.
-  APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
-  APInt Mask = APInt::getAllOnesValue(TyBits);
-  ComputeMaskedBits(V, Mask, KnownZero, KnownOne, Depth);
-  
-  if (KnownZero.isNegative()) {        // sign bit is 0
-    Mask = KnownZero;
-  } else if (KnownOne.isNegative()) {  // sign bit is 1;
-    Mask = KnownOne;
-  } else {
-    // Nothing known.
-    return FirstAnswer;
-  }
-  
-  // Okay, we know that the sign bit in Mask is set.  Use CLZ to determine
-  // the number of identical bits in the top of the input value.
-  Mask = ~Mask;
-  Mask <<= Mask.getBitWidth()-TyBits;
-  // Return # leading zeros.  We use 'min' here in case Val was zero before
-  // shifting.  We don't want to return '64' as for an i32 "0".
-  return std::max(FirstAnswer, std::min(TyBits, Mask.countLeadingZeros()));
-}
-
 
 /// AssociativeOpt - Perform an optimization on an associative operator.  This
 /// function is designed to check a chain of associative operators for a