Always compute all the bits in ComputeMaskedBits.

This allows us to keep passing reduced masks to SimplifyDemandedBits, but
know about all the bits if SimplifyDemandedBits fails. This allows instcombine
to simplify cases like the one in the included testcase.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154011 91177308-0d34-0410-b5e6-96231b3b80d8

35 files changed, 265 insertions, 417 deletions

diff --git a/include/llvm/Analysis/ValueTracking.h b/include/llvm/Analysis/ValueTracking.h
index 68ea8a105d..f2f9db4ce4 100644
--- a/include/llvm/Analysis/ValueTracking.h
+++ b/include/llvm/Analysis/ValueTracking.h
@@ -36,11 +36,9 @@ namespace llvm {
   /// where V is a vector, the mask, known zero, and known one values are the
   /// same width as the vector element, and the bit is set only if it is true
   /// for all of the elements in the vector.
-  void ComputeMaskedBits(Value *V, const APInt &Mask, APInt &KnownZero,
-                         APInt &KnownOne, const TargetData *TD = 0,
-                         unsigned Depth = 0);
-  void computeMaskedBitsLoad(const MDNode &Ranges, const APInt &Mask,
-                             APInt &KnownZero);
+  void ComputeMaskedBits(Value *V,  APInt &KnownZero, APInt &KnownOne,
+                         const TargetData *TD = 0, unsigned Depth = 0);
+  void computeMaskedBitsLoad(const MDNode &Ranges, APInt &KnownZero);
 
   /// ComputeSignBit - Determine whether the sign bit is known to be zero or
   /// one.  Convenience wrapper around ComputeMaskedBits.
diff --git a/include/llvm/CodeGen/SelectionDAG.h b/include/llvm/CodeGen/SelectionDAG.h
index aae4ee182b..6a7a87e866 100644
--- a/include/llvm/CodeGen/SelectionDAG.h
+++ b/include/llvm/CodeGen/SelectionDAG.h
@@ -980,8 +980,8 @@ public:
   /// bitsets.  This code only analyzes bits in Mask, in order to short-circuit
   /// processing.  Targets can implement the computeMaskedBitsForTargetNode
   /// method in the TargetLowering class to allow target nodes to be understood.
-  void ComputeMaskedBits(SDValue Op, const APInt &Mask, APInt &KnownZero,
-                         APInt &KnownOne, unsigned Depth = 0) const;
+  void ComputeMaskedBits(SDValue Op, APInt &KnownZero, APInt &KnownOne,
+                         unsigned Depth = 0) const;
 
   /// 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
diff --git a/include/llvm/Target/TargetLowering.h b/include/llvm/Target/TargetLowering.h
index 153138f08a..5f44e0dd48 100644
--- a/include/llvm/Target/TargetLowering.h
+++ b/include/llvm/Target/TargetLowering.h
@@ -873,7 +873,6 @@ public:
   /// Mask are known to be either zero or one and return them in the
   /// KnownZero/KnownOne bitsets.
   virtual void computeMaskedBitsForTargetNode(const SDValue Op,
-                                              const APInt &Mask,
                                               APInt &KnownZero,
                                               APInt &KnownOne,
                                               const SelectionDAG &DAG,
diff --git a/lib/Analysis/Lint.cpp b/lib/Analysis/Lint.cpp
index 971065f8d4..83bdf5286a 100644
--- a/lib/Analysis/Lint.cpp
+++ b/lib/Analysis/Lint.cpp
@@ -416,9 +416,8 @@ void Lint::visitMemoryReference(Instruction &I,
 
     if (Align != 0) {
       unsigned BitWidth = TD->getTypeSizeInBits(Ptr->getType());
-      APInt Mask = APInt::getAllOnesValue(BitWidth),
-                   KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
-      ComputeMaskedBits(Ptr, Mask, KnownZero, KnownOne, TD);
+      APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
+      ComputeMaskedBits(Ptr, KnownZero, KnownOne, TD);
       Assert1(!(KnownOne & APInt::getLowBitsSet(BitWidth, Log2_32(Align))),
               "Undefined behavior: Memory reference address is misaligned", &I);
     }
@@ -476,9 +475,8 @@ static bool isZero(Value *V, TargetData *TD) {
   if (isa<UndefValue>(V)) return true;
 
   unsigned BitWidth = cast<IntegerType>(V->getType())->getBitWidth();
-  APInt Mask = APInt::getAllOnesValue(BitWidth),
-               KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
-  ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD);
+  APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
+  ComputeMaskedBits(V, KnownZero, KnownOne, TD);
   return KnownZero.isAllOnesValue();
 }
 
diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 8b5397946e..205227ca0b 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -3261,9 +3261,8 @@ ScalarEvolution::GetMinTrailingZeros(const SCEV *S) {
   if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
     // For a SCEVUnknown, ask ValueTracking.
     unsigned BitWidth = getTypeSizeInBits(U->getType());
-    APInt Mask = APInt::getAllOnesValue(BitWidth);
     APInt Zeros(BitWidth, 0), Ones(BitWidth, 0);
-    ComputeMaskedBits(U->getValue(), Mask, Zeros, Ones);
+    ComputeMaskedBits(U->getValue(), Zeros, Ones);
     return Zeros.countTrailingOnes();
   }
 
@@ -3401,9 +3400,8 @@ ScalarEvolution::getUnsignedRange(const SCEV *S) {
 
   if (const SCEVUnknown *U = dyn_cast<SCEVUnknown>(S)) {
     // For a SCEVUnknown, ask ValueTracking.
-    APInt Mask = APInt::getAllOnesValue(BitWidth);
     APInt Zeros(BitWidth, 0), Ones(BitWidth, 0);
-    ComputeMaskedBits(U->getValue(), Mask, Zeros, Ones, TD);
+    ComputeMaskedBits(U->getValue(), Zeros, Ones, TD);
     if (Ones == ~Zeros + 1)
       return setUnsignedRange(U, ConservativeResult);
     return setUnsignedRange(U,
@@ -3660,9 +3658,8 @@ const SCEV *ScalarEvolution::createSCEV(Value *V) {
       // knew about to reconstruct a low-bits mask value.
       unsigned LZ = A.countLeadingZeros();
       unsigned BitWidth = A.getBitWidth();
-      APInt AllOnes = APInt::getAllOnesValue(BitWidth);
       APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
-      ComputeMaskedBits(U->getOperand(0), AllOnes, KnownZero, KnownOne, TD);
+      ComputeMaskedBits(U->getOperand(0), KnownZero, KnownOne, TD);
 
       APInt EffectiveMask = APInt::getLowBitsSet(BitWidth, BitWidth - LZ);
 
diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 1784f008d5..c6b53a927d 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -44,7 +44,6 @@ static unsigned getBitWidth(Type *Ty, const TargetData *TD) {
 }
 
 static void ComputeMaskedBitsAddSub(bool Add, Value *Op0, Value *Op1, bool NSW,
-                                    const APInt &Mask,
                                     APInt &KnownZero, APInt &KnownOne,
                                     APInt &KnownZero2, APInt &KnownOne2,
                                     const TargetData *TD, unsigned Depth) {
@@ -54,11 +53,11 @@ static void ComputeMaskedBitsAddSub(bool Add, Value *Op0, Value *Op1, bool NSW,
       // 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 BitWidth = Mask.getBitWidth();
+        unsigned BitWidth = KnownZero.getBitWidth();
         unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros();
         // NLZ can't be BitWidth with no sign bit
         APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1);
-        llvm::ComputeMaskedBits(Op1, MaskV, KnownZero2, KnownOne2, TD, Depth+1);
+        llvm::ComputeMaskedBits(Op1, KnownZero2, KnownOne2, TD, 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
@@ -66,27 +65,25 @@ static void ComputeMaskedBitsAddSub(bool Add, Value *Op0, Value *Op1, bool NSW,
         if ((KnownZero2 & MaskV) == MaskV) {
           unsigned NLZ2 = CLHS->getValue().countLeadingZeros();
           // Top bits known zero.
-          KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2) & Mask;
+          KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2);
         }
       }
     }
   }
 
-  unsigned BitWidth = Mask.getBitWidth();
+  unsigned BitWidth = KnownZero.getBitWidth();
 
   // If one of the operands has trailing zeros, then the bits that the
   // other operand has in those bit positions will be preserved in the
   // result. For an add, this works with either operand. For a subtract,
   // this only works if the known zeros are in the right operand.
   APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
-  APInt Mask2 = APInt::getLowBitsSet(BitWidth,
-                                     BitWidth - Mask.countLeadingZeros());
-  llvm::ComputeMaskedBits(Op0, Mask2, LHSKnownZero, LHSKnownOne, TD, Depth+1);
+  llvm::ComputeMaskedBits(Op0, LHSKnownZero, LHSKnownOne, TD, Depth+1);
   assert((LHSKnownZero & LHSKnownOne) == 0 &&
          "Bits known to be one AND zero?");
   unsigned LHSKnownZeroOut = LHSKnownZero.countTrailingOnes();
 
-  llvm::ComputeMaskedBits(Op1, Mask2, KnownZero2, KnownOne2, TD, Depth+1);
+  llvm::ComputeMaskedBits(Op1, KnownZero2, KnownOne2, TD, Depth+1);
   assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
   unsigned RHSKnownZeroOut = KnownZero2.countTrailingOnes();
 
@@ -111,7 +108,7 @@ static void ComputeMaskedBitsAddSub(bool Add, Value *Op0, Value *Op1, bool NSW,
   }
 
   // Are we still trying to solve for the sign bit?
-  if (Mask.isNegative() && !KnownZero.isNegative() && !KnownOne.isNegative()) {
+  if (!KnownZero.isNegative() && !KnownOne.isNegative()) {
     if (NSW) {
       if (Add) {
         // Adding two positive numbers can't wrap into negative
@@ -133,21 +130,19 @@ static void ComputeMaskedBitsAddSub(bool Add, Value *Op0, Value *Op1, bool NSW,
 }
 
 static void ComputeMaskedBitsMul(Value *Op0, Value *Op1, bool NSW,
-                                 const APInt &Mask,
                                  APInt &KnownZero, APInt &KnownOne,
                                  APInt &KnownZero2, APInt &KnownOne2,
                                  const TargetData *TD, unsigned Depth) {
-  unsigned BitWidth = Mask.getBitWidth();
-  APInt Mask2 = APInt::getAllOnesValue(BitWidth);
-  ComputeMaskedBits(Op1, Mask2, KnownZero, KnownOne, TD, Depth+1);
-  ComputeMaskedBits(Op0, Mask2, KnownZero2, KnownOne2, TD, Depth+1);
+  unsigned BitWidth = KnownZero.getBitWidth();
+  ComputeMaskedBits(Op1, KnownZero, KnownOne, TD, Depth+1);
+  ComputeMaskedBits(Op0, KnownZero2, KnownOne2, TD, Depth+1);
   assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
   assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
 
   bool isKnownNegative = false;
   bool isKnownNonNegative = false;
   // If the multiplication is known not to overflow, compute the sign bit.
-  if (Mask.isNegative() && NSW) {
+  if (NSW) {
     if (Op0 == Op1) {
       // The product of a number with itself is non-negative.
       isKnownNonNegative = true;
@@ -184,7 +179,6 @@ static void ComputeMaskedBitsMul(Value *Op0, Value *Op1, bool NSW,
   LeadZ = std::min(LeadZ, BitWidth);
   KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) |
               APInt::getHighBitsSet(BitWidth, LeadZ);
-  KnownZero &= Mask;
 
   // Only make use of no-wrap flags if we failed to compute the sign bit
   // directly.  This matters if the multiplication always overflows, in
@@ -197,9 +191,8 @@ static void ComputeMaskedBitsMul(Value *Op0, Value *Op1, bool NSW,
     KnownOne.setBit(BitWidth - 1);
 }
 
-void llvm::computeMaskedBitsLoad(const MDNode &Ranges, const APInt &Mask,
-                                 APInt &KnownZero) {
-  unsigned BitWidth = Mask.getBitWidth();
+void llvm::computeMaskedBitsLoad(const MDNode &Ranges, APInt &KnownZero) {
+  unsigned BitWidth = KnownZero.getBitWidth();
   unsigned NumRanges = Ranges.getNumOperands() / 2;
   assert(NumRanges >= 1);
 
@@ -215,12 +208,11 @@ void llvm::computeMaskedBitsLoad(const MDNode &Ranges, const APInt &Mask,
     MinLeadingZeros = std::min(LeadingZeros, MinLeadingZeros);
   }
 
-  KnownZero = Mask & APInt::getHighBitsSet(BitWidth, MinLeadingZeros);
+  KnownZero = APInt::getHighBitsSet(BitWidth, MinLeadingZeros);
 }
-/// 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.
+/// ComputeMaskedBits - Determine which of the bits are known to be either zero
+/// or one and return them in the KnownZero/KnownOne bit sets.
+///
 /// 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
@@ -230,15 +222,15 @@ void llvm::computeMaskedBitsLoad(const MDNode &Ranges, const APInt &Mask,
 ///
 /// This function is defined on values with integer type, values with pointer
 /// type (but only if TD is non-null), and vectors of integers.  In the case
-/// where V is a vector, the mask, known zero, and known one values are the
+/// where V is a vector, known zero, and known one values are the
 /// same width as the vector element, and the bit is set only if it is true
 /// for all of the elements in the vector.
-void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
-                             APInt &KnownZero, APInt &KnownOne,
+void llvm::ComputeMaskedBits(Value *V, APInt &KnownZero, APInt &KnownOne,
                              const TargetData *TD, unsigned Depth) {
   assert(V && "No Value?");
   assert(Depth <= MaxDepth && "Limit Search Depth");
-  unsigned BitWidth = Mask.getBitWidth();
+  unsigned BitWidth = KnownZero.getBitWidth();
+
   assert((V->getType()->isIntOrIntVectorTy() ||
           V->getType()->getScalarType()->isPointerTy()) &&
          "Not integer or pointer type!");
@@ -252,15 +244,15 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
 
   if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
     // We know all of the bits for a constant!
-    KnownOne = CI->getValue() & Mask;
-    KnownZero = ~KnownOne & Mask;
+    KnownOne = CI->getValue();
+    KnownZero = ~KnownOne;
     return;
   }
   // Null and aggregate-zero are all-zeros.
   if (isa<ConstantPointerNull>(V) ||
       isa<ConstantAggregateZero>(V)) {
     KnownOne.clearAllBits();
-    KnownZero = Mask;
+    KnownZero = APInt::getAllOnesValue(BitWidth);
     return;
   }
   // Handle a constant vector by taking the intersection of the known bits of
@@ -297,8 +289,8 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
       }
     }
     if (Align > 0)
-      KnownZero = Mask & APInt::getLowBitsSet(BitWidth,
-                                              CountTrailingZeros_32(Align));
+      KnownZero = APInt::getLowBitsSet(BitWidth,
+                                       CountTrailingZeros_32(Align));
     else
       KnownZero.clearAllBits();
     KnownOne.clearAllBits();
@@ -310,8 +302,7 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
     if (GA->mayBeOverridden()) {
       KnownZero.clearAllBits(); KnownOne.clearAllBits();
     } else {
-      ComputeMaskedBits(GA->getAliasee(), Mask, KnownZero, KnownOne,
-                        TD, Depth+1);
+      ComputeMaskedBits(GA->getAliasee(), KnownZero, KnownOne, TD, Depth+1);
     }
     return;
   }
@@ -320,15 +311,15 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
     // Get alignment information off byval arguments if specified in the IR.
     if (A->hasByValAttr())
       if (unsigned Align = A->getParamAlignment())
-        KnownZero = Mask & APInt::getLowBitsSet(BitWidth,
-                                                CountTrailingZeros_32(Align));
+        KnownZero = APInt::getLowBitsSet(BitWidth,
+                                         CountTrailingZeros_32(Align));
     return;
   }
 
   // Start out not knowing anything.
   KnownZero.clearAllBits(); KnownOne.clearAllBits();
 
-  if (Depth == MaxDepth || Mask == 0)
+  if (Depth == MaxDepth)
     return;  // Limit search depth.
 
   Operator *I = dyn_cast<Operator>(V);
@@ -339,14 +330,12 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
   default: break;
   case Instruction::Load:
     if (MDNode *MD = cast<LoadInst>(I)->getMetadata(LLVMContext::MD_range))
-      computeMaskedBitsLoad(*MD, Mask, KnownZero);
+      computeMaskedBitsLoad(*MD, KnownZero);
     return;
   case Instruction::And: {
     // If either the LHS or the RHS are Zero, the result is zero.
-    ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);
-    APInt Mask2(Mask & ~KnownZero);
-    ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
-                      Depth+1);
+    ComputeMaskedBits(I->getOperand(1), KnownZero, KnownOne, TD, Depth+1);
+    ComputeMaskedBits(I->getOperand(0), KnownZero2, KnownOne2, TD, Depth+1);
     assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
     assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
     
@@ -357,10 +346,8 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
     return;
   }
   case Instruction::Or: {
-    ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);
-    APInt Mask2(Mask & ~KnownOne);
-    ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD,
-                      Depth+1);
+    ComputeMaskedBits(I->getOperand(1), KnownZero, KnownOne, TD, Depth+1);
+    ComputeMaskedBits(I->getOperand(0), KnownZero2, KnownOne2, TD, Depth+1);
     assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
     assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
     
@@ -371,9 +358,8 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
     return;
   }
   case Instruction::Xor: {
-    ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);
-    ComputeMaskedBits(I->getOperand(0), Mask, KnownZero2, KnownOne2, TD,
-                      Depth+1);
+    ComputeMaskedBits(I->getOperand(1), KnownZero, KnownOne, TD, Depth+1);
+    ComputeMaskedBits(I->getOperand(0), KnownZero2, KnownOne2, TD, Depth+1);
     assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
     assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
     
@@ -387,34 +373,30 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
   case Instruction::Mul: {
     bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
     ComputeMaskedBitsMul(I->getOperand(0), I->getOperand(1), NSW,
-                         Mask, KnownZero, KnownOne, KnownZero2, KnownOne2,
-                         TD, Depth);
+                         KnownZero, KnownOne, KnownZero2, KnownOne2, TD, Depth);
     break;
   }
   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, TD, Depth+1);
+    ComputeMaskedBits(I->getOperand(0), KnownZero2, KnownOne2, TD, Depth+1);
     unsigned LeadZ = KnownZero2.countLeadingOnes();
 
     KnownOne2.clearAllBits();
     KnownZero2.clearAllBits();
-    ComputeMaskedBits(I->getOperand(1),
-                      AllOnes, KnownZero2, KnownOne2, TD, Depth+1);
+    ComputeMaskedBits(I->getOperand(1), KnownZero2, KnownOne2, TD, Depth+1);
     unsigned RHSUnknownLeadingOnes = KnownOne2.countLeadingZeros();
     if (RHSUnknownLeadingOnes != BitWidth)
       LeadZ = std::min(BitWidth,
                        LeadZ + BitWidth - RHSUnknownLeadingOnes - 1);
 
-    KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ) & Mask;
+    KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ);
     return;
   }
   case Instruction::Select:
-    ComputeMaskedBits(I->getOperand(2), Mask, KnownZero, KnownOne, TD, Depth+1);
-    ComputeMaskedBits(I->getOperand(1), Mask, KnownZero2, KnownOne2, TD,
+    ComputeMaskedBits(I->getOperand(2), KnownZero, KnownOne, TD, Depth+1);
+    ComputeMaskedBits(I->getOperand(1), KnownZero2, KnownOne2, TD,
                       Depth+1);
     assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
     assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?"); 
@@ -447,11 +429,9 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
     else
       SrcBitWidth = SrcTy->getScalarSizeInBits();
     
-    APInt MaskIn = Mask.zextOrTrunc(SrcBitWidth);
     KnownZero = KnownZero.zextOrTrunc(SrcBitWidth);
     KnownOne = KnownOne.zextOrTrunc(SrcBitWidth);
-    ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, TD,
-                      Depth+1);
+    ComputeMaskedBits(I->getOperand(0), KnownZero, KnownOne, TD, Depth+1);
     KnownZero = KnownZero.zextOrTrunc(BitWidth);
     KnownOne = KnownOne.zextOrTrunc(BitWidth);
     // Any top bits are known to be zero.
@@ -465,8 +445,7 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
         // TODO: For now, not handling conversions like:
         // (bitcast i64 %x to <2 x i32>)
         !I->getType()->isVectorTy()) {
-      ComputeMaskedBits(I->getOperand(0), Mask, KnownZero, KnownOne, TD,
-                        Depth+1);
+      ComputeMaskedBits(I->getOperand(0), KnownZero, KnownOne, TD, Depth+1);
       return;
     }
     break;
@@ -475,11 +454,9 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
     // Compute the bits in the result that are not present in the input.
     unsigned SrcBitWidth = I->getOperand(0)->getType()->getScalarSizeInBits();
       
-    APInt MaskIn = Mask.trunc(SrcBitWidth);
     KnownZero = KnownZero.trunc(SrcBitWidth);
     KnownOne = KnownOne.trunc(SrcBitWidth);
-    ComputeMaskedBits(I->getOperand(0), MaskIn, KnownZero, KnownOne, TD,
-                      Depth+1);
+    ComputeMaskedBits(I->getOperand(0), KnownZero, KnownOne, TD, Depth+1);
     assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
     KnownZero = KnownZero.zext(BitWidth);
     KnownOne = KnownOne.zext(BitWidth);
@@ -496,9 +473,7 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
     // (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, TD,
-                        Depth+1);
+      ComputeMaskedBits(I->getOperand(0), KnownZero, KnownOne, TD, Depth+1);
       assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
       KnownZero <<= ShiftAmt;
       KnownOne  <<= ShiftAmt;
@@ -513,9 +488,7 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
       uint64_t ShiftAmt = SA->getLimitedValue(BitWidth);
       
       // Unsigned shift right.
-      APInt Mask2(Mask.shl(ShiftAmt));
-      ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero,KnownOne, TD,
-                        Depth+1);
+      ComputeMaskedBits(I->getOperand(0), KnownZero,KnownOne, TD, Depth+1);
       assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
       KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
       KnownOne  = APIntOps::lshr(KnownOne, ShiftAmt);
@@ -531,9 +504,7 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
       uint64_t ShiftAmt = SA->getLimitedValue(BitWidth-1);
       
       // Signed shift right.
-      APInt Mask2(Mask.shl(ShiftAmt));
-      ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero, KnownOne, TD,
-                        Depth+1);
+      ComputeMaskedBits(I->getOperand(0), KnownZero, KnownOne, TD, Depth+1);
       assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
       KnownZero = APIntOps::lshr(KnownZero, ShiftAmt);
       KnownOne  = APIntOps::lshr(KnownOne, ShiftAmt);
@@ -549,15 +520,15 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
   case Instruction::Sub: {
     bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
     ComputeMaskedBitsAddSub(false, I->getOperand(0), I->getOperand(1), NSW,
-                            Mask, KnownZero, KnownOne, KnownZero2, KnownOne2,
-                            TD, Depth);
+                            KnownZero, KnownOne, KnownZero2, KnownOne2, TD,
+                            Depth);
     break;
   }
   case Instruction::Add: {
     bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
     ComputeMaskedBitsAddSub(true, I->getOperand(0), I->getOperand(1), NSW,
-                            Mask, KnownZero, KnownOne, KnownZero2, KnownOne2,
-                            TD, Depth);
+                            KnownZero, KnownOne, KnownZero2, KnownOne2, TD,
+                            Depth);
     break;
   }
   case Instruction::SRem:
@@ -565,9 +536,7 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
       APInt RA = Rem->getValue().abs();
       if (RA.isPowerOf2()) {
         APInt LowBits = RA - 1;
-        APInt Mask2 = LowBits | APInt::getSignBit(BitWidth);
-        ComputeMaskedBits(I->getOperand(0), Mask2, KnownZero2, KnownOne2, TD, 
-                          Depth+1);
+        ComputeMaskedBits(I->getOperand(0), KnownZero2, KnownOne2, TD, Depth+1);
 
         // The low bits of the first operand are unchanged by the srem.
         KnownZero = KnownZero2 & LowBits;
@@ -583,19 +552,15 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
         if (KnownOne2[BitWidth-1] && ((KnownOne2 & LowBits) != 0))
           KnownOne |= ~LowBits;
 
-        KnownZero &= Mask;
-        KnownOne &= Mask;
-
         assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
       }
     }
 
     // The sign bit is the LHS's sign bit, except when the result of the
     // remainder is zero.
-    if (Mask.isNegative() && KnownZero.isNonNegative()) {
-      APInt Mask2 = APInt::getSignBit(BitWidth);
+    if (KnownZero.isNonNegative()) {
       APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
-      ComputeMaskedBits(I->getOperand(0), Mask2, LHSKnownZero, LHSKnownOne, TD,
+      ComputeMaskedBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, TD,
                         Depth+1);
       // If it's known zero, our sign bit is also zero.
       if (LHSKnownZero.isNegative())
@@ -608,27 +573,24 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
       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, TD,
+        ComputeMaskedBits(I->getOperand(0), KnownZero, KnownOne, TD,
                           Depth+1);
         assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
+        KnownZero |= ~LowBits;
+        KnownOne &= LowBits;
         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,
-                      TD, Depth+1);
-    ComputeMaskedBits(I->getOperand(1), AllOnes, KnownZero2, KnownOne2,
-                      TD, Depth+1);
+    ComputeMaskedBits(I->getOperand(0), KnownZero, KnownOne, TD, Depth+1);
+    ComputeMaskedBits(I->getOperand(1), KnownZero2, KnownOne2, TD, Depth+1);
 
     unsigned Leaders = std::max(KnownZero.countLeadingOnes(),
                                 KnownZero2.countLeadingOnes());
     KnownOne.clearAllBits();
-    KnownZero = APInt::getHighBitsSet(BitWidth, Leaders) & Mask;
+    KnownZero = APInt::getHighBitsSet(BitWidth, Leaders);
     break;
   }
 
@@ -639,17 +601,15 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
       Align = TD->getABITypeAlignment(AI->getType()->getElementType());
     
     if (Align > 0)
-      KnownZero = Mask & APInt::getLowBitsSet(BitWidth,
-                                              CountTrailingZeros_32(Align));
+      KnownZero = 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, TD, Depth+1);
+    ComputeMaskedBits(I->getOperand(0), LocalKnownZero, LocalKnownOne, TD,
+                      Depth+1);
     unsigned TrailZ = LocalKnownZero.countTrailingOnes();
 
     gep_type_iterator GTI = gep_type_begin(I);
@@ -669,17 +629,15 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
         if (!IndexedTy->isSized()) return;
         unsigned GEPOpiBits = Index->getType()->getScalarSizeInBits();
         uint64_t TypeSize = TD ? TD->getTypeAllocSize(IndexedTy) : 1;
-        LocalMask = APInt::getAllOnesValue(GEPOpiBits);
         LocalKnownZero = LocalKnownOne = APInt(GEPOpiBits, 0);
-        ComputeMaskedBits(Index, LocalMask,
-                          LocalKnownZero, LocalKnownOne, TD, Depth+1);
+        ComputeMaskedBits(Index, LocalKnownZero, LocalKnownOne, TD, Depth+1);
         TrailZ = std::min(TrailZ,
                           unsigned(CountTrailingZeros_64(TypeSize) +
                                    LocalKnownZero.countTrailingOnes()));
       }
     }
     
-    KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) & Mask;
+    KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ);
     break;
   }
   case Instruction::PHI: {
@@ -714,17 +672,13 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
             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, TD, Depth+1);
-          Mask2 = APInt::getLowBitsSet(BitWidth,
-                                       KnownZero2.countTrailingOnes());
+          ComputeMaskedBits(R, KnownZero2, KnownOne2, TD, Depth+1);
 
           // We need to take the minimum number of known bits
           APInt KnownZero3(KnownZero), KnownOne3(KnownOne);
-          ComputeMaskedBits(L, Mask2, KnownZero3, KnownOne3, TD, Depth+1);
+          ComputeMaskedBits(L, KnownZero3, KnownOne3, TD, Depth+1);
 
-          KnownZero = Mask &
-                      APInt::getLowBitsSet(BitWidth,
+          KnownZero = APInt::getLowBitsSet(BitWidth,
                                            std::min(KnownZero2.countTrailingOnes(),
                                                     KnownZero3.countTrailingOnes()));
           break;
@@ -743,8 +697,8 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
       if (P->hasConstantValue() == P)
         break;
 
-      KnownZero = Mask;
-      KnownOne = Mask;
+      KnownZero = APInt::getAllOnesValue(BitWidth);
+      KnownOne = APInt::getAllOnesValue(BitWidth);
       for (unsigned i = 0, e = P->getNumIncomingValues(); i != e; ++i) {
         // Skip direct self references.
         if (P->getIncomingValue(i) == P) continue;
@@ -753,8 +707,8 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
         KnownOne2 = APInt(BitWidth, 0);
         // Recurse, but cap the recursion to one level, because we don't
         // want to waste time spinning around in loops.
-        ComputeMaskedBits(P->getIncomingValue(i), KnownZero | KnownOne,
-                          KnownZero2, KnownOne2, TD, MaxDepth-1);
+        ComputeMaskedBits(P->getIncomingValue(i), KnownZero2, KnownOne2, TD,
+                          MaxDepth-1);
         KnownZero &= KnownZero2;
         KnownOne &= KnownOne2;
         // If all bits have been ruled out, there's no need to check
@@ -775,17 +729,17 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
         // If this call is undefined for 0, the result will be less than 2^n.
         if (II->getArgOperand(1) == ConstantInt::getTrue(II->getContext()))
           LowBits -= 1;
-        KnownZero = Mask & APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
+        KnownZero = APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
         break;
       }
       case Intrinsic::ctpop: {
         unsigned LowBits = Log2_32(BitWidth)+1;
-        KnownZero = Mask & APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
+        KnownZero = APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
         break;
       }
       case Intrinsic::x86_sse42_crc32_64_8:
       case Intrinsic::x86_sse42_crc32_64_64:
-        KnownZero = Mask & APInt::getHighBitsSet(64, 32);
+        KnownZero = APInt::getHighBitsSet(64, 32);
         break;
       }
     }
@@ -800,21 +754,19 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
         case Intrinsic::uadd_with_overflow:
         case Intrinsic::sadd_with_overflow:
           ComputeMaskedBitsAddSub(true, II->getArgOperand(0),
-                                  II->getArgOperand(1), false, Mask,
-                                  KnownZero, KnownOne, KnownZero2, KnownOne2,
-                                  TD, Depth);
+                                  II->getArgOperand(1), false, KnownZero,
+                                  KnownOne, KnownZero2, KnownOne2, TD, Depth);
           break;
         case Intrinsic::usub_with_overflow:
         case Intrinsic::ssub_with_overflow:
           ComputeMaskedBitsAddSub(false, II->getArgOperand(0),
-                                  II->getArgOperand(1), false, Mask,
-                                  KnownZero, KnownOne, KnownZero2, KnownOne2,
-                                  TD, Depth);
+                                  II->getArgOperand(1), false, KnownZero,
+                                  KnownOne, KnownZero2, KnownOne2, TD, Depth);
           break;
         case Intrinsic::umul_with_overflow:
         case Intrinsic::smul_with_overflow:
           ComputeMaskedBitsMul(II->getArgOperand(0), II->getArgOperand(1),
-                               false, Mask, KnownZero, KnownOne,
+                               false, KnownZero, KnownOne,
                                KnownZero2, KnownOne2, TD, Depth);
           break;
         }
@@ -835,8 +787,7 @@ void llvm::ComputeSignBit(Value *V, bool &KnownZero, bool &KnownOne,
   }
   APInt ZeroBits(BitWidth, 0);
   APInt OneBits(BitWidth, 0);
-  ComputeMaskedBits(V, APInt::getSignBit(BitWidth), ZeroBits, OneBits, TD,
-                    Depth);
+  ComputeMaskedBits(V, ZeroBits, OneBits, TD, Depth);
   KnownOne = OneBits[BitWidth - 1];
   KnownZero = ZeroBits[BitWidth - 1];
 }
@@ -944,7 +895,7 @@ bool llvm::isKnownNonZero(Value *V, const TargetData *TD, unsigned Depth) {
 
     APInt KnownZero(BitWidth, 0);
     APInt KnownOne(BitWidth, 0);
-    ComputeMaskedBits(X, APInt(BitWidth, 1), KnownZero, KnownOne, TD, Depth);
+    ComputeMaskedBits(X, KnownZero, KnownOne, TD, Depth);
     if (KnownOne[0])
       return true;
   }
@@ -986,12 +937,12 @@ bool llvm::isKnownNonZero(Value *V, const TargetData *TD, unsigned Depth) {
       APInt Mask = APInt::getSignedMaxValue(BitWidth);
       // The sign bit of X is set.  If some other bit is set then X is not equal
       // to INT_MIN.
-      ComputeMaskedBits(X, Mask, KnownZero, KnownOne, TD, Depth);
+      ComputeMaskedBits(X, KnownZero, KnownOne, TD, Depth);
       if ((KnownOne & Mask) != 0)
         return true;
       // The sign bit of Y is set.  If some other bit is set then Y is not equal
       // to INT_MIN.
-      ComputeMaskedBits(Y, Mask, KnownZero, KnownOne, TD, Depth);
+      ComputeMaskedBits(Y, KnownZero, KnownOne, TD, Depth);
       if ((KnownOne & Mask) != 0)
         return true;
     }
@@ -1021,8 +972,7 @@ bool llvm::isKnownNonZero(Value *V, const TargetData *TD, unsigned Depth) {
   if (!BitWidth) return false;
   APInt KnownZero(BitWidth, 0);
   APInt KnownOne(BitWidth, 0);
-  ComputeMaskedBits(V, APInt::getAllOnesValue(BitWidth), KnownZero, KnownOne,
-                    TD, Depth);
+  ComputeMaskedBits(V, KnownZero, KnownOne, TD, Depth);
   return KnownOne != 0;
 }
 
@@ -1038,7 +988,7 @@ bool llvm::isKnownNonZero(Value *V, const TargetData *TD, unsigned Depth) {
 bool llvm::MaskedValueIsZero(Value *V, const APInt &Mask,
                              const TargetData *TD, unsigned Depth) {
   APInt KnownZero(Mask.getBitWidth(), 0), KnownOne(Mask.getBitWidth(), 0);
-  ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD, Depth);
+  ComputeMaskedBits(V, KnownZero, KnownOne, TD, Depth);
   assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?"); 
   return (KnownZero & Mask) == Mask;
 }
@@ -1129,13 +1079,11 @@ unsigned llvm::ComputeNumSignBits(Value *V, const TargetData *TD,
     if (ConstantInt *CRHS = dyn_cast<ConstantInt>(U->getOperand(1)))
       if (CRHS->isAllOnesValue()) {
         APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
-        APInt Mask = APInt::getAllOnesValue(TyBits);
-        ComputeMaskedBits(U->getOperand(0), Mask, KnownZero, KnownOne, TD,
-                          Depth+1);
+        ComputeMaskedBits(U->getOperand(0), KnownZero, KnownOne, TD, 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)
+        if ((KnownZero | APInt(TyBits, 1)).isAllOnesValue())
           return TyBits;
         
         // If we are subtracting one from a positive number, there is no carry
@@ -1156,12 +1104,10 @@ unsigned llvm::ComputeNumSignBits(Value *V, const TargetData *TD,
     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, 
-                          TD, Depth+1);
+        ComputeMaskedBits(U->getOperand(1), KnownZero, KnownOne, TD, 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)
+        if ((KnownZero | APInt(TyBits, 1)).isAllOnesValue())
           return TyBits;
         
         // If the input is known to be positive (the sign bit is known clear),
@@ -1203,8 +1149,8 @@ unsigned llvm::ComputeNumSignBits(Value *V, const TargetData *TD,
   // 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, TD, Depth);
+  APInt Mask;
+  ComputeMaskedBits(V, KnownZero, KnownOne, TD, Depth);
   
   if (KnownZero.isNegative()) {        // sign bit is 0
     Mask = KnownZero;
@@ -1896,8 +1842,7 @@ bool llvm::isSafeToSpeculativelyExecute(const Value *V,
       return false;
     APInt KnownZero(BitWidth, 0);
     APInt KnownOne(BitWidth, 0);
-    ComputeMaskedBits(Op, APInt::getAllOnesValue(BitWidth),
-                      KnownZero, KnownOne, TD);
+    ComputeMaskedBits(Op, KnownZero, KnownOne, TD);
     return !!KnownZero;
   }
   case Instruction::Load: {
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index a71cf82cd5..e03668777d 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -1452,16 +1452,14 @@ SDValue DAGCombiner::visitADD(SDNode *N) {
   if (VT.isInteger() && !VT.isVector()) {
     APInt LHSZero, LHSOne;
     APInt RHSZero, RHSOne;
-    APInt Mask = APInt::getAllOnesValue(VT.getScalarType().getSizeInBits());
-    DAG.ComputeMaskedBits(N0, Mask, LHSZero, LHSOne);
+    DAG.ComputeMaskedBits(N0, LHSZero, LHSOne);
 
     if (LHSZero.getBoolValue()) {
-      DAG.ComputeMaskedBits(N1, Mask, RHSZero, RHSOne);
+      DAG.ComputeMaskedBits(N1, RHSZero, RHSOne);
 
       // If all possibly-set bits on the LHS are clear on the RHS, return an OR.
       // If all possibly-set bits on the RHS are clear on the LHS, return an OR.
-      if ((RHSZero & (~LHSZero & Mask)) == (~LHSZero & Mask) ||
-          (LHSZero & (~RHSZero & Mask)) == (~RHSZero & Mask))
+      if ((RHSZero & ~LHSZero) == ~LHSZero || (LHSZero & ~RHSZero) == ~RHSZero)
         return DAG.getNode(ISD::OR, N->getDebugLoc(), VT, N0, N1);
     }
   }
@@ -1547,16 +1545,14 @@ SDValue DAGCombiner::visitADDC(SDNode *N) {
   // fold (addc a, b) -> (or a, b), CARRY_FALSE iff a and b share no bits.
   APInt LHSZero, LHSOne;
   APInt RHSZero, RHSOne;
-  APInt Mask = APInt::getAllOnesValue(VT.getScalarType().getSizeInBits());
-  DAG.ComputeMaskedBits(N0, Mask, LHSZero, LHSOne);
+  DAG.ComputeMaskedBits(N0, LHSZero, LHSOne);
 
   if (LHSZero.getBoolValue()) {
-    DAG.ComputeMaskedBits(N1, Mask, RHSZero, RHSOne);
+    DAG.ComputeMaskedBits(N1, RHSZero, RHSOne);
 
     // If all possibly-set bits on the LHS are clear on the RHS, return an OR.
     // If all possibly-set bits on the RHS are clear on the LHS, return an OR.
-    if ((RHSZero & (~LHSZero & Mask)) == (~LHSZero & Mask) ||
-        (LHSZero & (~RHSZero & Mask)) == (~RHSZero & Mask))
+    if ((RHSZero & ~LHSZero) == ~LHSZero || (LHSZero & ~RHSZero) == ~RHSZero)
       return CombineTo(N, DAG.getNode(ISD::OR, N->getDebugLoc(), VT, N0, N1),
                        DAG.getNode(ISD::CARRY_FALSE,
                                    N->getDebugLoc(), MVT::Glue));
@@ -3835,8 +3831,7 @@ SDValue DAGCombiner::visitSRL(SDNode *N) {
   if (N1C && N0.getOpcode() == ISD::CTLZ &&
       N1C->getAPIntValue() == Log2_32(VT.getSizeInBits())) {
     APInt KnownZero, KnownOne;
-    APInt Mask = APInt::getAllOnesValue(VT.getScalarType().getSizeInBits());
-    DAG.ComputeMaskedBits(N0.getOperand(0), Mask, KnownZero, KnownOne);
+    DAG.ComputeMaskedBits(N0.getOperand(0), KnownZero, KnownOne);
 
     // If any of the input bits are KnownOne, then the input couldn't be all
     // zeros, thus the result of the srl will always be zero.
@@ -3844,7 +3839,7 @@ SDValue DAGCombiner::visitSRL(SDNode *N) {
 
     // If all of the bits input the to ctlz node are known to be zero, then
     // the result of the ctlz is "32" and the result of the shift is one.
-    APInt UnknownBits = ~KnownZero & Mask;
+    APInt UnknownBits = ~KnownZero;
     if (UnknownBits == 0) return DAG.getConstant(1, VT);
 
     // Otherwise, check to see if there is exactly one bit input to the ctlz.
@@ -4439,8 +4434,8 @@ SDValue DAGCombiner::visitZERO_EXTEND(SDNode *N) {
                           std::min(Op.getValueSizeInBits(),
                                    VT.getSizeInBits()));
     APInt KnownZero, KnownOne;
-    DAG.ComputeMaskedBits(Op, TruncatedBits, KnownZero, KnownOne);
-    if (TruncatedBits == KnownZero) {
+    DAG.ComputeMaskedBits(Op, KnownZero, KnownOne);
+    if (TruncatedBits == (KnownZero & TruncatedBits)) {
       if (VT.bitsGT(Op.getValueType()))
         return DAG.getNode(ISD::ZERO_EXTEND, N->getDebugLoc(), VT, Op);
       if (VT.bitsLT(Op.getValueType()))
diff --git a/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp b/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
index 41506d17b7..95ddb1e0f6 100644
--- a/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
+++ b/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
@@ -1362,7 +1362,7 @@ ExpandShiftWithKnownAmountBit(SDNode *N, SDValue &Lo, SDValue &Hi) {
 
   APInt HighBitMask = APInt::getHighBitsSet(ShBits, ShBits - Log2_32(NVTBits));
   APInt KnownZero, KnownOne;
-  DAG.ComputeMaskedBits(N->getOperand(1), HighBitMask, KnownZero, KnownOne);
+  DAG.ComputeMaskedBits(N->getOperand(1), KnownZero, KnownOne);
 
   // If we don't know anything about the high bits, exit.
   if (((KnownZero|KnownOne) & HighBitMask) == 0)
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 48f8f773be..305eee81cd 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -1627,7 +1627,7 @@ bool SelectionDAG::SignBitIsZero(SDValue Op, unsigned Depth) const {
 bool SelectionDAG::MaskedValueIsZero(SDValue Op, const APInt &Mask,
                                      unsigned Depth) const {
   APInt KnownZero, KnownOne;
-  ComputeMaskedBits(Op, Mask, KnownZero, KnownOne, Depth);
+  ComputeMaskedBits(Op, KnownZero, KnownOne, Depth);
   assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
   return (KnownZero & Mask) == Mask;
 }
@@ -1636,15 +1636,12 @@ bool SelectionDAG::MaskedValueIsZero(SDValue Op, const APInt &Mask,
 /// known to be either zero or one and return them in the KnownZero/KnownOne
 /// bitsets.  This code only analyzes bits in Mask, in order to short-circuit
 /// processing.
-void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
-                                     APInt &KnownZero, APInt &KnownOne,
-                                     unsigned Depth) const {
-  unsigned BitWidth = Mask.getBitWidth();
-  assert(BitWidth == Op.getValueType().getScalarType().getSizeInBits() &&
-         "Mask size mismatches value type size!");
+void SelectionDAG::ComputeMaskedBits(SDValue Op, APInt &KnownZero,
+                                     APInt &KnownOne, unsigned Depth) const {
+  unsigned BitWidth = Op.getValueType().getScalarType().getSizeInBits();
 
   KnownZero = KnownOne = APInt(BitWidth, 0);   // Don't know anything.
-  if (Depth == 6 || Mask == 0)
+  if (Depth == 6)
     return;  // Limit search depth.
 
   APInt KnownZero2, KnownOne2;
@@ -1652,14 +1649,13 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
   switch (Op.getOpcode()) {
   case ISD::Constant:
     // We know all of the bits for a constant!
-    KnownOne = cast<ConstantSDNode>(Op)->getAPIntValue() & Mask;
-    KnownZero = ~KnownOne & Mask;
+    KnownOne = cast<ConstantSDNode>(Op)->getAPIntValue();
+    KnownZero = ~KnownOne;
     return;
   case ISD::AND:
     // If either the LHS or the RHS are Zero, the result is zero.
-    ComputeMaskedBits(Op.getOperand(1), Mask, KnownZero, KnownOne, Depth+1);
-    ComputeMaskedBits(Op.getOperand(0), Mask & ~KnownZero,
-                      KnownZero2, KnownOne2, Depth+1);
+    ComputeMaskedBits(Op.getOperand(1), KnownZero, KnownOne, Depth+1);
+    ComputeMaskedBits(Op.getOperand(0), 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?");
 
@@ -1669,9 +1665,8 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
     KnownZero |= KnownZero2;
     return;
   case ISD::OR:
-    ComputeMaskedBits(Op.getOperand(1), Mask, KnownZero, KnownOne, Depth+1);
-    ComputeMaskedBits(Op.getOperand(0), Mask & ~KnownOne,
-                      KnownZero2, KnownOne2, Depth+1);
+    ComputeMaskedBits(Op.getOperand(1), KnownZero, KnownOne, Depth+1);
+    ComputeMaskedBits(Op.getOperand(0), 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?");
 
@@ -1681,8 +1676,8 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
     KnownOne |= KnownOne2;
     return;
   case ISD::XOR: {
-    ComputeMaskedBits(Op.getOperand(1), Mask, KnownZero, KnownOne, Depth+1);
-    ComputeMaskedBits(Op.getOperand(0), Mask, KnownZero2, KnownOne2, Depth+1);
+    ComputeMaskedBits(Op.getOperand(1), KnownZero, KnownOne, Depth+1);
+    ComputeMaskedBits(Op.getOperand(0), 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?");
 
@@ -1694,9 +1689,8 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
     return;
   }
   case ISD::MUL: {
-    APInt Mask2 = APInt::getAllOnesValue(BitWidth);
-    ComputeMaskedBits(Op.getOperand(1), Mask2, KnownZero, KnownOne, Depth+1);
-    ComputeMaskedBits(Op.getOperand(0), Mask2, KnownZero2, KnownOne2, Depth+1);
+    ComputeMaskedBits(Op.getOperand(1), KnownZero, KnownOne, Depth+1);
+    ComputeMaskedBits(Op.getOperand(0), 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?");
 
@@ -1715,33 +1709,29 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
     LeadZ = std::min(LeadZ, BitWidth);
     KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) |
                 APInt::getHighBitsSet(BitWidth, LeadZ);
-    KnownZero &= Mask;
     return;
   }
   case ISD::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(Op.getOperand(0),
-                      AllOnes, KnownZero2, KnownOne2, Depth+1);
+    ComputeMaskedBits(Op.getOperand(0), KnownZero2, KnownOne2, Depth+1);
     unsigned LeadZ = KnownZero2.countLeadingOnes();
 
     KnownOne2.clearAllBits();
     KnownZero2.clearAllBits();
-    ComputeMaskedBits(Op.getOperand(1),
-                      AllOnes, KnownZero2, KnownOne2, Depth+1);
+    ComputeMaskedBits(Op.getOperand(1), 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;
+    KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ);
     return;
   }
   case ISD::SELECT:
-    ComputeMaskedBits(Op.getOperand(2), Mask, KnownZero, KnownOne, Depth+1);
-    ComputeMaskedBits(Op.getOperand(1), Mask, KnownZero2, KnownOne2, Depth+1);
+    ComputeMaskedBits(Op.getOperand(2), KnownZero, KnownOne, Depth+1);
+    ComputeMaskedBits(Op.getOperand(1), 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?");
 
@@ -1750,8 +1740,8 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
     KnownZero &= KnownZero2;
     return;
   case ISD::SELECT_CC:
-    ComputeMaskedBits(Op.getOperand(3), Mask, KnownZero, KnownOne, Depth+1);
-    ComputeMaskedBits(Op.getOperand(2), Mask, KnownZero2, KnownOne2, Depth+1);
+    ComputeMaskedBits(Op.getOperand(3), KnownZero, KnownOne, Depth+1);
+    ComputeMaskedBits(Op.getOperand(2), 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?");
 
@@ -1783,8 +1773,7 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
       if (ShAmt >= BitWidth)
         return;
 
-      ComputeMaskedBits(Op.getOperand(0), Mask.lshr(ShAmt),
-                        KnownZero, KnownOne, Depth+1);
+      ComputeMaskedBits(Op.getOperand(0), KnownZero, KnownOne, Depth+1);
       assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
       KnownZero <<= ShAmt;
       KnownOne  <<= ShAmt;
@@ -1801,13 +1790,12 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
       if (ShAmt >= BitWidth)
         return;
 
-      ComputeMaskedBits(Op.getOperand(0), (Mask << ShAmt),
-                        KnownZero, KnownOne, Depth+1);
+      ComputeMaskedBits(Op.getOperand(0), KnownZero, KnownOne, Depth+1);
       assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
       KnownZero = KnownZero.lshr(ShAmt);
       KnownOne  = KnownOne.lshr(ShAmt);
 
-      APInt HighBits = APInt::getHighBitsSet(BitWidth, ShAmt) & Mask;
+      APInt HighBits = APInt::getHighBitsSet(BitWidth, ShAmt);
       KnownZero |= HighBits;  // High bits known zero.
     }
     return;
@@ -1819,15 +1807,11 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
       if (ShAmt >= BitWidth)
         return;
 
-      APInt InDemandedMask = (Mask << ShAmt);
       // If any of the demanded bits are produced by the sign extension, we also
       // demand the input sign bit.
-      APInt HighBits = APInt::getHighBitsSet(BitWidth, ShAmt) & Mask;
-      if (HighBits.getBoolValue())
-        InDemandedMask |= APInt::getSignBit(BitWidth);
+      APInt HighBits = APInt::getHighBitsSet(BitWidth, ShAmt);
 
-      ComputeMaskedBits(Op.getOperand(0), InDemandedMask, KnownZero, KnownOne,
-                        Depth+1);
+      ComputeMaskedBits(Op.getOperand(0), KnownZero, KnownOne, Depth+1);
       assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
       KnownZero = KnownZero.lshr(ShAmt);
       KnownOne  = KnownOne.lshr(ShAmt);
@@ -1849,10 +1833,10 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
 
     // Sign extension.  Compute the demanded bits in the result that are not
     // present in the input.
-    APInt NewBits = APInt::getHighBitsSet(BitWidth, BitWidth - EBits) & Mask;
+    APInt NewBits = APInt::getHighBitsSet(BitWidth, BitWidth - EBits);
 
     APInt InSignBit = APInt::getSignBit(EBits);
-    APInt InputDemandedBits = Mask & APInt::getLowBitsSet(BitWidth, EBits);
+    APInt InputDemandedBits = APInt::getLowBitsSet(BitWidth, EBits);
 
     // If the sign extended bits are demanded, we know that the sign
     // bit is demanded.
@@ -1860,8 +1844,9 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
     if (NewBits.getBoolValue())
       InputDemandedBits |= InSignBit;
 
-    ComputeMaskedBits(Op.getOperand(0), InputDemandedBits,
-                      KnownZero, KnownOne, Depth+1);
+    ComputeMaskedBits(Op.getOperand(0), KnownZero, KnownOne, Depth+1);
+    KnownOne &= InputDemandedBits;
+    KnownZero &= InputDemandedBits;
     assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
 
     // If the sign bit of the input is known set or clear, then we know the
@@ -1893,20 +1878,19 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
     if (ISD::isZEXTLoad(Op.getNode())) {
       EVT VT = LD->getMemoryVT();
       unsigned MemBits = VT.getScalarType().getSizeInBits();
-      KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - MemBits) & Mask;
+      KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - MemBits);
     } else if (const MDNode *Ranges = LD->getRanges()) {
-      computeMaskedBitsLoad(*Ranges, Mask, KnownZero);
+      computeMaskedBitsLoad(*Ranges, KnownZero);
     }
     return;
   }
   case ISD::ZERO_EXTEND: {
     EVT InVT = Op.getOperand(0).getValueType();
     unsigned InBits = InVT.getScalarType().getSizeInBits();
-    APInt NewBits   = APInt::getHighBitsSet(BitWidth, BitWidth - InBits) & Mask;
-    APInt InMask    = Mask.trunc(InBits);
+    APInt NewBits   = APInt::getHighBitsSet(BitWidth, BitWidth - InBits);
     KnownZero = KnownZero.trunc(InBits);
     KnownOne = KnownOne.trunc(InBits);
-    ComputeMaskedBits(Op.getOperand(0), InMask, KnownZero, KnownOne, Depth+1);
+    ComputeMaskedBits(Op.getOperand(0), KnownZero, KnownOne, Depth+1);
     KnownZero = KnownZero.zext(BitWidth);
     KnownOne = KnownOne.zext(BitWidth);
     KnownZero |= NewBits;
@@ -1916,17 +1900,11 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
     EVT InVT = Op.getOperand(0).getValueType();
     unsigned InBits = InVT.getScalarType().getSizeInBits();
     APInt InSignBit = APInt::getSignBit(InBits);
-    APInt NewBits   = APInt::getHighBitsSet(BitWidth, BitWidth - InBits) & Mask;
-    APInt InMask = Mask.trunc(InBits);
-
-    // If any of the sign extended bits are demanded, we know that the sign
-    // bit is demanded. Temporarily set this bit in the mask for our callee.
-    if (NewBits.getBoolValue())
-      InMask |= InSignBit;
+    APInt NewBits   = APInt::getHighBitsSet(BitWidth, BitWidth - InBits);
 
     KnownZero = KnownZero.trunc(InBits);
     KnownOne = KnownOne.trunc(InBits);
-    ComputeMaskedBits(Op.getOperand(0), InMask, KnownZero, KnownOne, Depth+1);
+    ComputeMaskedBits(Op.getOperand(0), KnownZero, KnownOne, Depth+1);
 
     // Note if the sign bit is known to be zero or one.
     bool SignBitKnownZero = KnownZero.isNegative();
@@ -1934,13 +1912,6 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
     assert(!(SignBitKnownZero && SignBitKnownOne) &&
            "Sign bit can't be known to be both zero and one!");
 
-    // If the sign bit wasn't actually demanded by our caller, we don't
-    // want it set in the KnownZero and KnownOne result values. Reset the
-    // mask and reapply it to the result values.
-    InMask = Mask.trunc(InBits);
-    KnownZero &= InMask;
-    KnownOne  &= InMask;
-
     KnownZero = KnownZero.zext(BitWidth);
     KnownOne = KnownOne.zext(BitWidth);
 
@@ -1954,10 +1925,9 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
   case ISD::ANY_EXTEND: {
     EVT InVT = Op.getOperand(0).getValueType();
     unsigned InBits = InVT.getScalarType().getSizeInBits();
-    APInt InMask = Mask.trunc(InBits);
     KnownZero = KnownZero.trunc(InBits);
     KnownOne = KnownOne.trunc(InBits);
-    ComputeMaskedBits(Op.getOperand(0), InMask, KnownZero, KnownOne, Depth+1);
+    ComputeMaskedBits(Op.getOperand(0), KnownZero, KnownOne, Depth+1);
     KnownZero = KnownZero.zext(BitWidth);
     KnownOne = KnownOne.zext(BitWidth);
     return;
@@ -1965,10 +1935,9 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
   case ISD::TRUNCATE: {
     EVT InVT = Op.getOperand(0).getValueType();
     unsigned InBits = InVT.getScalarType().getSizeInBits();
-    APInt InMask = Mask.zext(InBits);
     KnownZero = KnownZero.zext(InBits);
     KnownOne = KnownOne.zext(InBits);
-    ComputeMaskedBits(Op.getOperand(0), InMask, KnownZero, KnownOne, Depth+1);
+    ComputeMaskedBits(Op.getOperand(0), KnownZero, KnownOne, Depth+1);
     assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
     KnownZero = KnownZero.trunc(BitWidth);
     KnownOne = KnownOne.trunc(BitWidth);
@@ -1977,9 +1946,8 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
   case ISD::AssertZext: {
     EVT VT = cast<VTSDNode>(Op.getOperand(1))->getVT();
     APInt InMask = APInt::getLowBitsSet(BitWidth, VT.getSizeInBits());
-    ComputeMaskedBits(Op.getOperand(0), Mask & InMask, KnownZero,
-                      KnownOne, Depth+1);
-    KnownZero |= (~InMask) & Mask;
+    ComputeMaskedBits(Op.getOperand(0), KnownZero, KnownOne, Depth+1);
+    KnownZero |= (~InMask);
     return;
   }
   case ISD::FGETSIGN:
@@ -1996,8 +1964,7 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
         unsigned NLZ = (CLHS->getAPIntValue()+1).countLeadingZeros();
         // NLZ can't be BitWidth with no sign bit
         APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1);
-        ComputeMaskedBits(Op.getOperand(1), MaskV, KnownZero2, KnownOne2,
-                          Depth+1);
+        ComputeMaskedBits(Op.getOperand(1), 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
@@ -2005,7 +1972,7 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
         if ((KnownZero2 & MaskV) == MaskV) {
           unsigned NLZ2 = CLHS->getAPIntValue().countLeadingZeros();
           // Top bits known zero.
-          KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2) & Mask;
+          KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2);
         }
       }
     }
@@ -2016,13 +1983,11 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
     // 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,
-                                       BitWidth - Mask.countLeadingZeros());
-    ComputeMaskedBits(Op.getOperand(0), Mask2, KnownZero2, KnownOne2, Depth+1);
+    ComputeMaskedBits(Op.getOperand(0), KnownZero2, KnownOne2, Depth+1);
     assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
     unsigned KnownZeroOut = KnownZero2.countTrailingOnes();
 
-    ComputeMaskedBits(Op.getOperand(1), Mask2, KnownZero2, KnownOne2, Depth+1);
+    ComputeMaskedBits(Op.getOperand(1), KnownZero2, KnownOne2, Depth+1);
     assert((KnownZero2 & KnownOne2) == 0 && "Bits known to be one AND zero?");
     KnownZeroOut = std::min(KnownZeroOut,
                             KnownZero2.countTrailingOnes());
@@ -2046,7 +2011,7 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
       if (RA.isPowerOf2()) {
         APInt LowBits = RA - 1;
         APInt Mask2 = LowBits | APInt::getSignBit(BitWidth);
-        ComputeMaskedBits(Op.getOperand(0), Mask2,KnownZero2,KnownOne2,Depth+1);
+        ComputeMaskedBits(Op.getOperand(0), KnownZero2,KnownOne2,Depth+1);
 
         // The low bits of the first operand are unchanged by the srem.
         KnownZero = KnownZero2 & LowBits;
@@ -2061,10 +2026,6 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
         // the upper bits are all one.
         if (KnownOne2[BitWidth-1] && ((KnownOne2 & LowBits) != 0))
           KnownOne |= ~LowBits;
-
-        KnownZero &= Mask;
-        KnownOne &= Mask;
-
         assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?");
       }
     }
@@ -2074,9 +2035,8 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
       const APInt &RA = Rem->getAPIntValue();
       if (RA.isPowerOf2()) {
         APInt LowBits = (RA - 1);
-        APInt Mask2 = LowBits & Mask;
-        KnownZero |= ~LowBits & Mask;
-        ComputeMaskedBits(Op.getOperand(0), Mask2, KnownZero, KnownOne,Depth+1);
+        KnownZero |= ~LowBits;
+        ComputeMaskedBits(Op.getOperand(0), KnownZero, KnownOne,Depth+1);
         assert((KnownZero & KnownOne) == 0&&"Bits known to be one AND zero?");
         break;
       }
@@ -2084,16 +2044,13 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
 
     // 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(Op.getOperand(0), AllOnes, KnownZero, KnownOne,
-                      Depth+1);
-    ComputeMaskedBits(Op.getOperand(1), AllOnes, KnownZero2, KnownOne2,
-                      Depth+1);
+    ComputeMaskedBits(Op.getOperand(0), KnownZero, KnownOne, Depth+1);
+    ComputeMaskedBits(Op.getOperand(1), KnownZero2, KnownOne2, Depth+1);
 
     uint32_t Leaders = std::max(KnownZero.countLeadingOnes(),
                                 KnownZero2.countLeadingOnes());
     KnownOne.clearAllBits();
-    KnownZero = APInt::getHighBitsSet(BitWidth, Leaders) & Mask;
+    KnownZero = APInt::getHighBitsSet(BitWidth, Leaders);
     return;
   }
   case ISD::FrameIndex:
@@ -2113,8 +2070,7 @@ void SelectionDAG::ComputeMaskedBits(SDValue Op, const APInt &Mask,
   case ISD::INTRINSIC_W_CHAIN:
   case ISD::INTRINSIC_VOID:
     // Allow the target to implement this method for its nodes.
-    TLI.computeMaskedBitsForTargetNode(Op, Mask, KnownZero, KnownOne, *this,
-                                       Depth);
+    TLI.computeMaskedBitsForTargetNode(Op, KnownZero, KnownOne, *this, Depth);
     return;
   }
 }
@@ -2238,12 +2194,11 @@ unsigned SelectionDAG::ComputeNumSignBits(SDValue Op, unsigned Depth) const{
     if (ConstantSDNode *CRHS = dyn_cast<ConstantSDNode>(Op.getOperand(1)))
       if (CRHS->isAllOnesValue()) {
         APInt KnownZero, KnownOne;
-        APInt Mask = APInt::getAllOnesValue(VTBits);
-        ComputeMaskedBits(Op.getOperand(0), Mask, KnownZero, KnownOne, Depth+1);
+        ComputeMaskedBits(Op.getOperand(0), 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(VTBits, 1)) == Mask)
+        if ((KnownZero | APInt(VTBits, 1)).isAllOnesValue())
           return VTBits;
 
         // If we are subtracting one from a positive number, there is no carry
@@ -2264,11 +2219,10 @@ unsigned SelectionDAG::ComputeNumSignBits(SDValue Op, unsigned Depth) const{
     if (ConstantSDNode *CLHS = dyn_cast<ConstantSDNode>(Op.getOperand(0)))
       if (CLHS->isNullValue()) {
         APInt KnownZero, KnownOne;
-        APInt Mask = APInt::getAllOnesValue(VTBits);
-        ComputeMaskedBits(Op.getOperand(1), Mask, KnownZero, KnownOne, Depth+1);
+        ComputeMaskedBits(Op.getOperand(1), 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(VTBits, 1)) == Mask)
+        if ((KnownZero | APInt(VTBits, 1)).isAllOnesValue())
           return VTBits;
 
         // If the input is known to be positive (the sign bit is known clear),
@@ -2317,9 +2271,9 @@ unsigned SelectionDAG::ComputeNumSignBits(SDValue Op, unsigned Depth) const{
   // Finally, if we can prove that the top bits of the result are 0's or 1's,
   // use this information.
   APInt KnownZero, KnownOne;
-  APInt Mask = APInt::getAllOnesValue(VTBits);
-  ComputeMaskedBits(Op, Mask, KnownZero, KnownOne, Depth);
+  ComputeMaskedBits(Op, KnownZero, KnownOne, Depth);
 
+  APInt Mask;
   if (KnownZero.isNegative()) {        // sign bit is 0
     Mask = KnownZero;
   } else if (KnownOne.isNegative()) {  // sign bit is 1;
@@ -6040,10 +5994,9 @@ unsigned SelectionDAG::InferPtrAlignment(SDValue Ptr) const {
   int64_t GVOffset = 0;
   if (TLI.isGAPlusOffset(Ptr.getNode(), GV, GVOffset)) {
     unsigned PtrWidth = TLI.getPointerTy().getSizeInBits();
-    APInt AllOnes = APInt::getAllOnesValue(PtrWidth);
     APInt KnownZero(PtrWidth, 0), KnownOne(PtrWidth, 0);
-    llvm::ComputeMaskedBits(const_cast<GlobalValue*>(GV), AllOnes,
-                            KnownZero, KnownOne, TLI.getTargetData());
+    llvm::ComputeMaskedBits(const_cast<GlobalValue*>(GV), KnownZero, KnownOne,
+                            TLI.getTargetData());
     unsigned AlignBits = KnownZero.countTrailingOnes();
     unsigned Align = AlignBits ? 1 << std::min(31U, AlignBits) : 0;
     if (Align)
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index 8aabc02443..605509bd22 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -508,7 +508,6 @@ void SelectionDAGISel::ComputeLiveOutVRegInfo() {
 
   Worklist.push_back(CurDAG->getRoot().getNode());
 
-  APInt Mask;
   APInt KnownZero;
   APInt KnownOne;
 
@@ -539,8 +538,7 @@ void SelectionDAGISel::ComputeLiveOutVRegInfo() {
       continue;
 
     unsigned NumSignBits = CurDAG->ComputeNumSignBits(Src);
-    Mask = APInt::getAllOnesValue(SrcVT.getSizeInBits());
-    CurDAG->ComputeMaskedBits(Src, Mask, KnownZero, KnownOne);
+    CurDAG->ComputeMaskedBits(Src, KnownZero, KnownOne);
     FuncInfo->AddLiveOutRegInfo(DestReg, NumSignBits, KnownZero, KnownOne);
   } while (!Worklist.empty());
 }
@@ -1444,7 +1442,7 @@ bool SelectionDAGISel::CheckOrMask(SDValue LHS, ConstantSDNode *RHS,
   APInt NeededMask = DesiredMask & ~ActualMask;
 
   APInt KnownZero, KnownOne;
-  CurDAG->ComputeMaskedBits(LHS, NeededMask, KnownZero, KnownOne);
+  CurDAG->ComputeMaskedBits(LHS, KnownZero, KnownOne);
 
   // If all the missing bits in the or are already known to be set, match!
   if ((NeededMask & KnownOne) == NeededMask)
diff --git a/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index e4a0016435..eefb9e84b1 100644
--- a/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -1244,7 +1244,7 @@ bool TargetLowering::SimplifyDemandedBits(SDValue Op,
     if (Depth != 0) {
       // If not at the root, Just compute the KnownZero/KnownOne bits to
       // simplify things downstream.
-      TLO.DAG.ComputeMaskedBits(Op, DemandedMask, KnownZero, KnownOne, Depth);
+      TLO.DAG.ComputeMaskedBits(Op, KnownZero, KnownOne, Depth);
       return false;
     }
     // If this is the root being simplified, allow it to have multiple uses,
@@ -1263,8 +1263,8 @@ bool TargetLowering::SimplifyDemandedBits(SDValue Op,
   switch (Op.getOpcode()) {
   case ISD::Constant:
     // We know all of the bits for a constant!
-    KnownOne = cast<ConstantSDNode>(Op)->getAPIntValue() & NewMask;
-    KnownZero = ~KnownOne & NewMask;
+    KnownOne = cast<ConstantSDNode>(Op)->getAPIntValue();
+    KnownZero = ~KnownOne;
     return false;   // Don't fall through, will infinitely loop.
   case ISD::AND:
     // If the RHS is a constant, check to see if the LHS would be zero without
@@ -1274,8 +1274,7 @@ bool TargetLowering::SimplifyDemandedBits(SDValue Op,
     if (ConstantSDNode *RHSC = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
       APInt LHSZero, LHSOne;
       // Do not increment Depth here; that can cause an infinite loop.
-      TLO.DAG.ComputeMaskedBits(Op.getOperand(0), NewMask,
-                                LHSZero, LHSOne, Depth);
+      TLO.DAG.ComputeMaskedBits(Op.getOperand(0), LHSZero, LHSOne, Depth);
       // If the LHS already has zeros where RHSC does, this and is dead.
       if ((LHSZero & NewMask) == (~RHSC->getAPIntValue() & NewMask))
         return TLO.CombineTo(Op, Op.getOperand(0));
@@ -1725,11 +1724,11 @@ bool TargetLowering::SimplifyDemandedBits(SDValue Op,
 
     // If the sign bit is known one, the top bits match.
     if (KnownOne.intersects(InSignBit)) {
-      KnownOne  |= NewBits;
-      KnownZero &= ~NewBits;
+      KnownOne |= NewBits;
+      assert((KnownZero & NewBits) == 0);
     } else {   // Otherwise, top bits aren't known.
-      KnownOne  &= ~NewBits;
-      KnownZero &= ~NewBits;
+      assert((KnownOne & NewBits) == 0);
+      assert((KnownZero & NewBits) == 0);
     }
     break;
   }
@@ -1863,7 +1862,7 @@ bool TargetLowering::SimplifyDemandedBits(SDValue Op,
   // FALL THROUGH
   default:
     // Just use ComputeMaskedBits to compute output bits.
-    TLO.DAG.ComputeMaskedBits(Op, NewMask, KnownZero, KnownOne, Depth);
+    TLO.DAG.ComputeMaskedBits(Op, KnownZero, KnownOne, Depth);
     break;
   }
 
@@ -1879,7 +1878,6 @@ bool TargetLowering::SimplifyDemandedBits(SDValue Op,
 /// in Mask are known to be either zero or one and return them in the
 /// KnownZero/KnownOne bitsets.
 void TargetLowering::computeMaskedBitsForTargetNode(const SDValue Op,
-                                                    const APInt &Mask,
                                                     APInt &KnownZero,
                                                     APInt &KnownOne,
                                                     const SelectionDAG &DAG,
@@ -1890,7 +1888,7 @@ void TargetLowering::computeMaskedBitsForTargetNode(const SDValue Op,
           Op.getOpcode() == ISD::INTRINSIC_VOID) &&
          "Should use MaskedValueIsZero if you don't know whether Op"
          " is a target node!");
-  KnownZero = KnownOne = APInt(Mask.getBitWidth(), 0);
+  KnownZero = KnownOne = APInt(KnownOne.getBitWidth(), 0);
 }
 
 /// ComputeNumSignBitsForTargetNode - This method can be implemented by
@@ -1934,9 +1932,8 @@ static bool ValueHasExactlyOneBitSet(SDValue Val, const SelectionDAG &DAG) {
   // Fall back to ComputeMaskedBits to catch other known cases.
   EVT OpVT = Val.getValueType();
   unsigned BitWidth = OpVT.getScalarType().getSizeInBits();
-  APInt Mask = APInt::getAllOnesValue(BitWidth);
   APInt KnownZero, KnownOne;
-  DAG.ComputeMaskedBits(Val, Mask, KnownZero, KnownOne);
+  DAG.ComputeMaskedBits(Val, KnownZero, KnownOne);
   return (KnownZero.countPopulation() == BitWidth - 1) &&
          (KnownOne.countPopulation() == 1);
 }
diff --git a/lib/Target/ARM/ARMISelLowering.cpp b/lib/Target/ARM/ARMISelLowering.cpp
index d5c38d5e1b..fab3e24551 100644
--- a/lib/Target/ARM/ARMISelLowering.cpp
+++ b/lib/Target/ARM/ARMISelLowering.cpp
@@ -8288,8 +8288,7 @@ ARMTargetLowering::PerformCMOVCombine(SDNode *N, SelectionDAG &DAG) const {
 
   if (Res.getNode()) {
     APInt KnownZero, KnownOne;
-    APInt Mask = APInt::getAllOnesValue(VT.getScalarType().getSizeInBits());
-    DAG.ComputeMaskedBits(SDValue(N,0), Mask, KnownZero, KnownOne);
+    DAG.ComputeMaskedBits(SDValue(N,0), KnownZero, KnownOne);
     // Capture demanded bits information that would be otherwise lost.
     if (KnownZero == 0xfffffffe)
       Res = DAG.getNode(ISD::AssertZext, dl, MVT::i32, Res,
@@ -8805,22 +8804,20 @@ bool ARMTargetLowering::getPostIndexedAddressParts(SDNode *N, SDNode *Op,
 }
 
 void ARMTargetLowering::computeMaskedBitsForTargetNode(const SDValue Op,
-                                                       const APInt &Mask,
                                                        APInt &KnownZero,
                                                        APInt &KnownOne,
                                                        const SelectionDAG &DAG,
                                                        unsigned Depth) const {
-  KnownZero = KnownOne = APInt(Mask.getBitWidth(), 0);
+  KnownZero = KnownOne = APInt(KnownOne.getBitWidth(), 0);
   switch (Op.getOpcode()) {
   default: break;
   case ARMISD::CMOV: {
     // Bits are known zero/one if known on the LHS and RHS.
-    DAG.ComputeMaskedBits(Op.getOperand(0), Mask, KnownZero, KnownOne, Depth+1);
+    DAG.ComputeMaskedBits(Op.getOperand(0), KnownZero, KnownOne, Depth+1);
     if (KnownZero == 0 && KnownOne == 0) return;
 
     APInt KnownZeroRHS, KnownOneRHS;
-    DAG.ComputeMaskedBits(Op.getOperand(1), Mask,
-                          KnownZeroRHS, KnownOneRHS, Depth+1);
+    DAG.ComputeMaskedBits(Op.getOperand(1), KnownZeroRHS, KnownOneRHS, Depth+1);
     KnownZero &= KnownZeroRHS;
     KnownOne  &= KnownOneRHS;
     return;
diff --git a/lib/Target/ARM/ARMISelLowering.h b/lib/Target/ARM/ARMISelLowering.h
index a71b74e7af..80c5716bb0 100644
--- a/lib/Target/ARM/ARMISelLowering.h
+++ b/lib/Target/ARM/ARMISelLowering.h
@@ -315,7 +315,6 @@ namespace llvm {
                                             SelectionDAG &DAG) const;
 
     virtual void computeMaskedBitsForTargetNode(const SDValue Op,
-                                                const APInt &Mask,
                                                 APInt &KnownZero,
                                                 APInt &KnownOne,
                                                 const SelectionDAG &DAG,
diff --git a/lib/Target/CellSPU/SPUISelLowering.cpp b/lib/Target/CellSPU/SPUISelLowering.cpp
index d9072bd777..062374127e 100644
--- a/lib/Target/CellSPU/SPUISelLowering.cpp
+++ b/lib/Target/CellSPU/SPUISelLowering.cpp
@@ -3158,7 +3158,6 @@ SPUTargetLowering::getRegForInlineAsmConstraint(const std::string &Constraint,
 //! Compute used/known bits for a SPU operand
 void
 SPUTargetLowering::computeMaskedBitsForTargetNode(const SDValue Op,
-                                                  const APInt &Mask,
                                                   APInt &KnownZero,
                                                   APInt &KnownOne,
                                                   const SelectionDAG &DAG,
diff --git a/lib/Target/CellSPU/SPUISelLowering.h b/lib/Target/CellSPU/SPUISelLowering.h
index 25c5355095..e3db7b2f1f 100644
--- a/lib/Target/CellSPU/SPUISelLowering.h
+++ b/lib/Target/CellSPU/SPUISelLowering.h
@@ -121,7 +121,6 @@ namespace llvm {
     virtual SDValue PerformDAGCombine(SDNode *N, DAGCombinerInfo &DCI) const;
 
     virtual void computeMaskedBitsForTargetNode(const SDValue Op,
-                                                const APInt &Mask,
                                                 APInt &KnownZero,
                                                 APInt &KnownOne,
                                                 const SelectionDAG &DAG,
diff --git a/lib/Target/PowerPC/PPCISelDAGToDAG.cpp b/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
index 6651d141fb..5a04888dd4 100644
--- a/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ b/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -377,8 +377,8 @@ SDNode *PPCDAGToDAGISel::SelectBitfieldInsert(SDNode *N) {
   DebugLoc dl = N->getDebugLoc();
 
   APInt LKZ, LKO, RKZ, RKO;
-  CurDAG->ComputeMaskedBits(Op0, APInt::getAllOnesValue(32), LKZ, LKO);
-  CurDAG->ComputeMaskedBits(Op1, APInt::getAllOnesValue(32), RKZ, RKO);
+  CurDAG->ComputeMaskedBits(Op0, LKZ, LKO);
+  CurDAG->ComputeMaskedBits(Op1, RKZ, RKO);
 
   unsigned TargetMask = LKZ.getZExtValue();
   unsigned InsertMask = RKZ.getZExtValue();
diff --git a/lib/Target/PowerPC/PPCISelLowering.cpp b/lib/Target/PowerPC/PPCISelLowering.cpp
index 746fc23c21..3b24951d1d 100644
--- a/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -860,14 +860,10 @@ bool PPCTargetLowering::SelectAddressRegReg(SDValue N, SDValue &Base,
     APInt LHSKnownZero, LHSKnownOne;
     APInt RHSKnownZero, RHSKnownOne;
     DAG.ComputeMaskedBits(N.getOperand(0),
-                          APInt::getAllOnesValue(N.getOperand(0)
-                            .getValueSizeInBits()),
                           LHSKnownZero, LHSKnownOne);
 
     if (LHSKnownZero.getBoolValue()) {
       DAG.ComputeMaskedBits(N.getOperand(1),
-                            APInt::getAllOnesValue(N.getOperand(1)
-                              .getValueSizeInBits()),
                             RHSKnownZero, RHSKnownOne);
       // If all of the bits are known zero on the LHS or RHS, the add won't
       // carry.
@@ -922,10 +918,7 @@ bool PPCTargetLowering::SelectAddressRegImm(SDValue N, SDValue &Disp,
       // (for better address arithmetic) if the LHS and RHS of the OR are
       // provably disjoint.
       APInt LHSKnownZero, LHSKnownOne;
-      DAG.ComputeMaskedBits(N.getOperand(0),
-                            APInt::getAllOnesValue(N.getOperand(0)
-                                                   .getValueSizeInBits()),
-                            LHSKnownZero, LHSKnownOne);
+      DAG.ComputeMaskedBits(N.getOperand(0), LHSKnownZero, LHSKnownOne);
 
       if ((LHSKnownZero.getZExtValue()|~(uint64_t)imm) == ~0ULL) {
         // If all of the bits are known zero on the LHS or RHS, the add won't
@@ -1038,10 +1031,7 @@ bool PPCTargetLowering::SelectAddressRegImmShift(SDValue N, SDValue &Disp,
       // (for better address arithmetic) if the LHS and RHS of the OR are
       // provably disjoint.
       APInt LHSKnownZero, LHSKnownOne;
-      DAG.ComputeMaskedBits(N.getOperand(0),
-                            APInt::getAllOnesValue(N.getOperand(0)
-                                                   .getValueSizeInBits()),
-                            LHSKnownZero, LHSKnownOne);
+      DAG.ComputeMaskedBits(N.getOperand(0), LHSKnownZero, LHSKnownOne);
       if ((LHSKnownZero.getZExtValue()|~(uint64_t)imm) == ~0ULL) {
         // If all of the bits are known zero on the LHS or RHS, the add won't
         // carry.
@@ -5517,12 +5507,11 @@ SDValue PPCTargetLowering::PerformDAGCombine(SDNode *N,
 //===----------------------------------------------------------------------===//
 
 void PPCTargetLowering::computeMaskedBitsForTargetNode(const SDValue Op,
-                                                       const APInt &Mask,
                                                        APInt &KnownZero,
                                                        APInt &KnownOne,
                                                        const SelectionDAG &DAG,
                                                        unsigned Depth) const {
-  KnownZero = KnownOne = APInt(Mask.getBitWidth(), 0);
+  KnownZero = KnownOne = APInt(KnownZero.getBitWidth(), 0);
   switch (Op.getOpcode()) {
   default: break;
   case PPCISD::LBRX: {
diff --git a/lib/Target/PowerPC/PPCISelLowering.h b/lib/Target/PowerPC/PPCISelLowering.h
index 6a00989611..18eb072003 100644
--- a/lib/Target/PowerPC/PPCISelLowering.h
+++ b/lib/Target/PowerPC/PPCISelLowering.h
@@ -296,7 +296,6 @@ namespace llvm {
     virtual SDValue PerformDAGCombine(SDNode *N, DAGCombinerInfo &DCI) const;
 
     virtual void computeMaskedBitsForTargetNode(const SDValue Op,
-                                                const APInt &Mask,
                                                 APInt &KnownZero,
                                                 APInt &KnownOne,
                                                 const SelectionDAG &DAG,
diff --git a/lib/Target/Sparc/SparcISelLowering.cpp b/lib/Target/Sparc/SparcISelLowering.cpp
index ee12633130..c3e6f16067 100644
--- a/lib/Target/Sparc/SparcISelLowering.cpp
+++ b/lib/Target/Sparc/SparcISelLowering.cpp
@@ -832,22 +832,19 @@ const char *SparcTargetLowering::getTargetNodeName(unsigned Opcode) const {
 /// be zero. Op is expected to be a target specific node. Used by DAG
 /// combiner.
 void SparcTargetLowering::computeMaskedBitsForTargetNode(const SDValue Op,
-                                                         const APInt &Mask,
                                                          APInt &KnownZero,
                                                          APInt &KnownOne,
                                                          const SelectionDAG &DAG,
                                                          unsigned Depth) const {
   APInt KnownZero2, KnownOne2;
-  KnownZero = KnownOne = APInt(Mask.getBitWidth(), 0);   // Don't know anything.
+  KnownZero = KnownOne = APInt(KnownZero.getBitWidth(), 0);
 
   switch (Op.getOpcode()) {
   default: break;
   case SPISD::SELECT_ICC:
   case SPISD::SELECT_FCC:
-    DAG.ComputeMaskedBits(Op.getOperand(1), Mask, KnownZero, KnownOne,
-                          Depth+1);
-    DAG.ComputeMaskedBits(Op.getOperand(0), Mask, KnownZero2, KnownOne2,
-                          Depth+1);
+    DAG.ComputeMaskedBits(Op.getOperand(1), KnownZero, KnownOne, Depth+1);
+    DAG.ComputeMaskedBits(Op.getOperand(0), 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?");
 
diff --git a/lib/Target/Sparc/SparcISelLowering.h b/lib/Target/Sparc/SparcISelLowering.h
index f483c96d66..cf430485cf 100644
--- a/lib/Target/Sparc/SparcISelLowering.h
+++ b/lib/Target/Sparc/SparcISelLowering.h
@@ -50,7 +50,6 @@ namespace llvm {
     /// in Mask are known to be either zero or one and return them in the
     /// KnownZero/KnownOne bitsets.
     virtual void computeMaskedBitsForTargetNode(const SDValue Op,
-                                                const APInt &Mask,
                                                 APInt &KnownZero,
                                                 APInt &KnownOne,
                                                 const SelectionDAG &DAG,
diff --git a/lib/Target/X86/X86ISelDAGToDAG.cpp b/lib/Target/X86/X86ISelDAGToDAG.cpp
index 36861a5e28..ff89d70b1a 100644
--- a/lib/Target/X86/X86ISelDAGToDAG.cpp
+++ b/lib/Target/X86/X86ISelDAGToDAG.cpp
@@ -896,7 +896,7 @@ static bool FoldMaskAndShiftToScale(SelectionDAG &DAG, SDValue N,
   APInt MaskedHighBits = APInt::getHighBitsSet(X.getValueSizeInBits(),
                                                MaskLZ);
   APInt KnownZero, KnownOne;
-  DAG.ComputeMaskedBits(X, MaskedHighBits, KnownZero, KnownOne);
+  DAG.ComputeMaskedBits(X, KnownZero, KnownOne);
   if (MaskedHighBits != KnownZero) return true;
 
   // We've identified a pattern that can be transformed into a single shift
diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 69a6036131..e80bb87470 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -8099,8 +8099,8 @@ SDValue X86TargetLowering::LowerToBT(SDValue And, ISD::CondCode CC,
         unsigned BitWidth = Op0.getValueSizeInBits();
         unsigned AndBitWidth = And.getValueSizeInBits();
         if (BitWidth > AndBitWidth) {
-          APInt Mask = APInt::getAllOnesValue(BitWidth), Zeros, Ones;
-          DAG.ComputeMaskedBits(Op0, Mask, Zeros, Ones);
+          APInt Zeros, Ones;
+          DAG.ComputeMaskedBits(Op0, Zeros, Ones);
           if (Zeros.countLeadingOnes() < BitWidth - AndBitWidth)
             return SDValue();
         }
@@ -12620,11 +12620,11 @@ X86TargetLowering::EmitInstrWithCustomInserter(MachineInstr *MI,
 //===----------------------------------------------------------------------===//
 
 void X86TargetLowering::computeMaskedBitsForTargetNode(const SDValue Op,
-                                                       const APInt &Mask,
                                                        APInt &KnownZero,
                                                        APInt &KnownOne,
                                                        const SelectionDAG &DAG,
                                                        unsigned Depth) const {
+  unsigned BitWidth = KnownZero.getBitWidth();
   unsigned Opc = Op.getOpcode();
   assert((Opc >= ISD::BUILTIN_OP_END ||
           Opc == ISD::INTRINSIC_WO_CHAIN ||
@@ -12633,7 +12633,7 @@ void X86TargetLowering::computeMaskedBitsForTargetNode(const SDValue Op,
          "Should use MaskedValueIsZero if you don't know whether Op"
          " is a target node!");
 
-  KnownZero = KnownOne = APInt(Mask.getBitWidth(), 0);   // Don't know anything.
+  KnownZero = KnownOne = APInt(BitWidth, 0);   // Don't know anything.
   switch (Opc) {
   default: break;
   case X86ISD::ADD:
@@ -12652,8 +12652,7 @@ void X86TargetLowering::computeMaskedBitsForTargetNode(const SDValue Op,
       break;
     // Fallthrough
   case X86ISD::SETCC:
-    KnownZero |= APInt::getHighBitsSet(Mask.getBitWidth(),
-                                       Mask.getBitWidth() - 1);
+    KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - 1);
     break;
   case ISD::INTRINSIC_WO_CHAIN: {
     unsigned IntId = cast<ConstantSDNode>(Op.getOperand(0))->getZExtValue();
@@ -12678,8 +12677,7 @@ void X86TargetLowering::computeMaskedBitsForTargetNode(const SDValue Op,
         case Intrinsic::x86_sse2_pmovmskb_128:  NumLoBits = 16; break;
         case Intrinsic::x86_avx2_pmovmskb:      NumLoBits = 32; break;
       }
-      KnownZero = APInt::getHighBitsSet(Mask.getBitWidth(),
-                                        Mask.getBitWidth() - NumLoBits);
+      KnownZero = APInt::getHighBitsSet(BitWidth, BitWidth - NumLoBits);
       break;
     }
     }
diff --git a/lib/Target/X86/X86ISelLowering.h b/lib/Target/X86/X86ISelLowering.h
index 0327b1fc64..d11b4334a9 100644
--- a/lib/Target/X86/X86ISelLowering.h
+++ b/lib/Target/X86/X86ISelLowering.h
@@ -504,7 +504,6 @@ namespace llvm {
     /// in Mask are known to be either zero or one and return them in the
     /// KnownZero/KnownOne bitsets.
     virtual void computeMaskedBitsForTargetNode(const SDValue Op,
-                                                const APInt &Mask,
                                                 APInt &KnownZero,
                                                 APInt &KnownOne,
                                                 const SelectionDAG &DAG,
diff --git a/lib/Target/X86/X86InstrCompiler.td b/lib/Target/X86/X86InstrCompiler.td
index 03bb3ed6d8..6f9e849261 100644
--- a/lib/Target/X86/X86InstrCompiler.td
+++ b/lib/Target/X86/X86InstrCompiler.td
@@ -1167,12 +1167,10 @@ def or_is_add : PatFrag<(ops node:$lhs, node:$rhs), (or node:$lhs, node:$rhs),[{
   if (ConstantSDNode *CN = dyn_cast<ConstantSDNode>(N->getOperand(1)))
     return CurDAG->MaskedValueIsZero(N->getOperand(0), CN->getAPIntValue());
 
-  unsigned BitWidth = N->getValueType(0).getScalarType().getSizeInBits();
-  APInt Mask = APInt::getAllOnesValue(BitWidth);
   APInt KnownZero0, KnownOne0;
-  CurDAG->ComputeMaskedBits(N->getOperand(0), Mask, KnownZero0, KnownOne0, 0);
+  CurDAG->ComputeMaskedBits(N->getOperand(0), KnownZero0, KnownOne0, 0);
   APInt KnownZero1, KnownOne1;
-  CurDAG->ComputeMaskedBits(N->getOperand(1), Mask, KnownZero1, KnownOne1, 0);
+  CurDAG->ComputeMaskedBits(N->getOperand(1), KnownZero1, KnownOne1, 0);
   return (~KnownZero0 & ~KnownZero1) == 0;
 }]>;
 
diff --git a/lib/Target/XCore/XCoreISelLowering.cpp b/lib/Target/XCore/XCoreISelLowering.cpp
index 593cebcfd2..fdf2b78324 100644
--- a/lib/Target/XCore/XCoreISelLowering.cpp
+++ b/lib/Target/XCore/XCoreISelLowering.cpp
@@ -1363,8 +1363,8 @@ SDValue XCoreTargetLowering::PerformDAGCombine(SDNode *N,
       APInt KnownZero, KnownOne;
       APInt Mask = APInt::getHighBitsSet(VT.getSizeInBits(),
                                          VT.getSizeInBits() - 1);
-      DAG.ComputeMaskedBits(N2, Mask, KnownZero, KnownOne);
-      if (KnownZero == Mask) {
+      DAG.ComputeMaskedBits(N2, KnownZero, KnownOne);
+      if ((KnownZero & Mask) == Mask) {
         SDValue Carry = DAG.getConstant(0, VT);
         SDValue Result = DAG.getNode(ISD::ADD, dl, VT, N0, N2);
         SDValue Ops [] = { Carry, Result };
@@ -1386,8 +1386,8 @@ SDValue XCoreTargetLowering::PerformDAGCombine(SDNode *N,
       APInt KnownZero, KnownOne;
       APInt Mask = APInt::getHighBitsSet(VT.getSizeInBits(),
                                          VT.getSizeInBits() - 1);
-      DAG.ComputeMaskedBits(N2, Mask, KnownZero, KnownOne);
-      if (KnownZero == Mask) {
+      DAG.ComputeMaskedBits(N2, KnownZero, KnownOne);
+      if ((KnownZero & Mask) == Mask) {
         SDValue Borrow = N2;
         SDValue Result = DAG.getNode(ISD::SUB, dl, VT,
                                      DAG.getConstant(0, VT), N2);
@@ -1402,8 +1402,8 @@ SDValue XCoreTargetLowering::PerformDAGCombine(SDNode *N,
       APInt KnownZero, KnownOne;
       APInt Mask = APInt::getHighBitsSet(VT.getSizeInBits(),
                                          VT.getSizeInBits() - 1);
-      DAG.ComputeMaskedBits(N2, Mask, KnownZero, KnownOne);
-      if (KnownZero == Mask) {
+      DAG.ComputeMaskedBits(N2, KnownZero, KnownOne);
+      if ((KnownZero & Mask) == Mask) {
         SDValue Borrow = DAG.getConstant(0, VT);
         SDValue Result = DAG.getNode(ISD::SUB, dl, VT, N0, N2);
         SDValue Ops [] = { Borrow, Result };
@@ -1521,21 +1521,19 @@ SDValue XCoreTargetLowering::PerformDAGCombine(SDNode *N,
 }
 
 void XCoreTargetLowering::computeMaskedBitsForTargetNode(const SDValue Op,
-                                                         const APInt &Mask,
                                                          APInt &KnownZero,
                                                          APInt &KnownOne,
                                                          const SelectionDAG &DAG,
                                                          unsigned Depth) const {
-  KnownZero = KnownOne = APInt(Mask.getBitWidth(), 0);
+  KnownZero = KnownOne = APInt(KnownZero.getBitWidth(), 0);
   switch (Op.getOpcode()) {
   default: break;
   case XCoreISD::LADD:
   case XCoreISD::LSUB:
     if (Op.getResNo() == 0) {
       // Top bits of carry / borrow are clear.
-      KnownZero = APInt::getHighBitsSet(Mask.getBitWidth(),
-                                        Mask.getBitWidth() - 1);
-      KnownZero &= Mask;
+      KnownZero = APInt::getHighBitsSet(KnownZero.getBitWidth(),
+                                        KnownZero.getBitWidth() - 1);
     }
     break;
   }
diff --git a/lib/Target/XCore/XCoreISelLowering.h b/lib/Target/XCore/XCoreISelLowering.h
index 5cd3e672e0..0b63ecd0f7 100644
--- a/lib/Target/XCore/XCoreISelLowering.h
+++ b/lib/Target/XCore/XCoreISelLowering.h
@@ -160,7 +160,6 @@ namespace llvm {
     virtual SDValue PerformDAGCombine(SDNode *N, DAGCombinerInfo &DCI) const;
 
     virtual void computeMaskedBitsForTargetNode(const SDValue Op,
-                                                const APInt &Mask,
                                                 APInt &KnownZero,
                                                 APInt &KnownOne,
                                                 const SelectionDAG &DAG,
diff --git a/lib/Transforms/InstCombine/InstCombine.h b/lib/Transforms/InstCombine/InstCombine.h
index 464e9d0a61..199df519ce 100644
--- a/lib/Transforms/InstCombine/InstCombine.h
+++ b/lib/Transforms/InstCombine/InstCombine.h
@@ -291,9 +291,9 @@ public:
     return 0;  // Don't do anything with FI
   }
       
-  void ComputeMaskedBits(Value *V, const APInt &Mask, APInt &KnownZero,
+  void ComputeMaskedBits(Value *V, APInt &KnownZero,
                          APInt &KnownOne, unsigned Depth = 0) const {
-    return llvm::ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD, Depth);
+    return llvm::ComputeMaskedBits(V, KnownZero, KnownOne, TD, Depth);
   }
   
   bool MaskedValueIsZero(Value *V, const APInt &Mask, 
diff --git a/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 908038b35e..05e702fa43 100644
--- a/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -141,10 +141,9 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
       // a sub and fuse this add with it.
       if (LHS->hasOneUse() && (XorRHS->getValue()+1).isPowerOf2()) {
         IntegerType *IT = cast<IntegerType>(I.getType());
-        APInt Mask = APInt::getAllOnesValue(IT->getBitWidth());
         APInt LHSKnownOne(IT->getBitWidth(), 0);
         APInt LHSKnownZero(IT->getBitWidth(), 0);
-        ComputeMaskedBits(XorLHS, Mask, LHSKnownZero, LHSKnownOne);
+        ComputeMaskedBits(XorLHS, LHSKnownZero, LHSKnownOne);
         if ((XorRHS->getValue() | LHSKnownZero).isAllOnesValue())
           return BinaryOperator::CreateSub(ConstantExpr::getAdd(XorRHS, CI),
                                            XorLHS);
@@ -202,14 +201,13 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
 
   // A+B --> A|B iff A and B have no bits set in common.
   if (IntegerType *IT = dyn_cast<IntegerType>(I.getType())) {
-    APInt Mask = APInt::getAllOnesValue(IT->getBitWidth());
     APInt LHSKnownOne(IT->getBitWidth(), 0);
     APInt LHSKnownZero(IT->getBitWidth(), 0);
-    ComputeMaskedBits(LHS, Mask, LHSKnownZero, LHSKnownOne);
+    ComputeMaskedBits(LHS, LHSKnownZero, LHSKnownOne);
     if (LHSKnownZero != 0) {
       APInt RHSKnownOne(IT->getBitWidth(), 0);
       APInt RHSKnownZero(IT->getBitWidth(), 0);
-      ComputeMaskedBits(RHS, Mask, RHSKnownZero, RHSKnownOne);
+      ComputeMaskedBits(RHS, RHSKnownZero, RHSKnownOne);
       
       // No bits in common -> bitwise or.
       if ((LHSKnownZero|RHSKnownZero).isAllOnesValue())
diff --git a/lib/Transforms/InstCombine/InstCombineCalls.cpp b/lib/Transforms/InstCombine/InstCombineCalls.cpp
index b550fe83eb..77e4727100 100644
--- a/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -361,8 +361,7 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
     uint32_t BitWidth = IT->getBitWidth();
     APInt KnownZero(BitWidth, 0);
     APInt KnownOne(BitWidth, 0);
-    ComputeMaskedBits(II->getArgOperand(0), APInt::getAllOnesValue(BitWidth),
-                      KnownZero, KnownOne);
+    ComputeMaskedBits(II->getArgOperand(0), KnownZero, KnownOne);
     unsigned TrailingZeros = KnownOne.countTrailingZeros();
     APInt Mask(APInt::getLowBitsSet(BitWidth, TrailingZeros));
     if ((Mask & KnownZero) == Mask)
@@ -380,8 +379,7 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
     uint32_t BitWidth = IT->getBitWidth();
     APInt KnownZero(BitWidth, 0);
     APInt KnownOne(BitWidth, 0);
-    ComputeMaskedBits(II->getArgOperand(0), APInt::getAllOnesValue(BitWidth),
-                      KnownZero, KnownOne);
+    ComputeMaskedBits(II->getArgOperand(0), KnownZero, KnownOne);
     unsigned LeadingZeros = KnownOne.countLeadingZeros();
     APInt Mask(APInt::getHighBitsSet(BitWidth, LeadingZeros));
     if ((Mask & KnownZero) == Mask)
@@ -394,17 +392,16 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
     Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1);
     IntegerType *IT = cast<IntegerType>(II->getArgOperand(0)->getType());
     uint32_t BitWidth = IT->getBitWidth();
-    APInt Mask = APInt::getSignBit(BitWidth);
     APInt LHSKnownZero(BitWidth, 0);
     APInt LHSKnownOne(BitWidth, 0);
-    ComputeMaskedBits(LHS, Mask, LHSKnownZero, LHSKnownOne);
+    ComputeMaskedBits(LHS, LHSKnownZero, LHSKnownOne);
     bool LHSKnownNegative = LHSKnownOne[BitWidth - 1];
     bool LHSKnownPositive = LHSKnownZero[BitWidth - 1];
 
     if (LHSKnownNegative || LHSKnownPositive) {
       APInt RHSKnownZero(BitWidth, 0);
       APInt RHSKnownOne(BitWidth, 0);
-      ComputeMaskedBits(RHS, Mask, RHSKnownZero, RHSKnownOne);
+      ComputeMaskedBits(RHS, RHSKnownZero, RHSKnownOne);
       bool RHSKnownNegative = RHSKnownOne[BitWidth - 1];
       bool RHSKnownPositive = RHSKnownZero[BitWidth - 1];
       if (LHSKnownNegative && RHSKnownNegative) {
@@ -488,14 +485,13 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
   case Intrinsic::umul_with_overflow: {
     Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1);
     unsigned BitWidth = cast<IntegerType>(LHS->getType())->getBitWidth();
-    APInt Mask = APInt::getAllOnesValue(BitWidth);
 
     APInt LHSKnownZero(BitWidth, 0);
     APInt LHSKnownOne(BitWidth, 0);
-    ComputeMaskedBits(LHS, Mask, LHSKnownZero, LHSKnownOne);
+    ComputeMaskedBits(LHS, LHSKnownZero, LHSKnownOne);
     APInt RHSKnownZero(BitWidth, 0);
     APInt RHSKnownOne(BitWidth, 0);
-    ComputeMaskedBits(RHS, Mask, RHSKnownZero, RHSKnownOne);
+    ComputeMaskedBits(RHS, RHSKnownZero, RHSKnownOne);
 
     // Get the largest possible values for each operand.
     APInt LHSMax = ~LHSKnownZero;
diff --git a/lib/Transforms/InstCombine/InstCombineCasts.cpp b/lib/Transforms/InstCombine/InstCombineCasts.cpp
index c5ddb75dbf..39279f4372 100644
--- a/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -541,8 +541,7 @@ Instruction *InstCombiner::transformZExtICmp(ICmpInst *ICI, Instruction &CI,
       // 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);
+      ComputeMaskedBits(ICI->getOperand(0), KnownZero, KnownOne);
         
       APInt KnownZeroMask(~KnownZero);
       if (KnownZeroMask.isPowerOf2()) { // Exactly 1 possible 1?
@@ -590,9 +589,8 @@ Instruction *InstCombiner::transformZExtICmp(ICmpInst *ICI, Instruction &CI,
 
       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);
+      ComputeMaskedBits(LHS, KnownZeroLHS, KnownOneLHS);
+      ComputeMaskedBits(RHS, KnownZeroRHS, KnownOneRHS);
 
       if (KnownZeroLHS == KnownZeroRHS && KnownOneLHS == KnownOneRHS) {
         APInt KnownBits = KnownZeroLHS | KnownOneLHS;
@@ -911,8 +909,7 @@ Instruction *InstCombiner::transformSExtICmp(ICmpInst *ICI, Instruction &CI) {
         ICI->isEquality() && (Op1C->isZero() || Op1C->getValue().isPowerOf2())){
       unsigned BitWidth = Op1C->getType()->getBitWidth();
       APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
-      APInt TypeMask(APInt::getAllOnesValue(BitWidth));
-      ComputeMaskedBits(Op0, TypeMask, KnownZero, KnownOne);
+      ComputeMaskedBits(Op0, KnownZero, KnownOne);
 
       APInt KnownZeroMask(~KnownZero);
       if (KnownZeroMask.isPowerOf2()) {
diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 53089928c3..ab2987ff24 100644
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -1028,9 +1028,8 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
       // of the high bits truncated out of x are known.
       unsigned DstBits = LHSI->getType()->getPrimitiveSizeInBits(),
              SrcBits = LHSI->getOperand(0)->getType()->getPrimitiveSizeInBits();
-      APInt Mask(APInt::getHighBitsSet(SrcBits, SrcBits-DstBits));
       APInt KnownZero(SrcBits, 0), KnownOne(SrcBits, 0);
-      ComputeMaskedBits(LHSI->getOperand(0), Mask, KnownZero, KnownOne);
+      ComputeMaskedBits(LHSI->getOperand(0), KnownZero, KnownOne);
 
       // If all the high bits are known, we can do this xform.
       if ((KnownZero|KnownOne).countLeadingOnes() >= SrcBits-DstBits) {
diff --git a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 61a8e5b3bc..125c74a89a 100644
--- a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -142,7 +142,7 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
 
   Instruction *I = dyn_cast<Instruction>(V);
   if (!I) {
-    ComputeMaskedBits(V, DemandedMask, KnownZero, KnownOne, Depth);
+    ComputeMaskedBits(V, KnownZero, KnownOne, Depth);
     return 0;        // Only analyze instructions.
   }
 
@@ -156,10 +156,8 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
     // this instruction has a simpler value in that context.
     if (I->getOpcode() == Instruction::And) {
       // If either the LHS or the RHS are Zero, the result is zero.
-      ComputeMaskedBits(I->getOperand(1), DemandedMask,
-                        RHSKnownZero, RHSKnownOne, Depth+1);
-      ComputeMaskedBits(I->getOperand(0), DemandedMask & ~RHSKnownZero,
-                        LHSKnownZero, LHSKnownOne, Depth+1);
+      ComputeMaskedBits(I->getOperand(1), RHSKnownZero, RHSKnownOne, Depth+1);
+      ComputeMaskedBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, Depth+1);
       
       // If all of the demanded bits are known 1 on one side, return the other.
       // These bits cannot contribute to the result of the 'and' in this
@@ -180,10 +178,8 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
       // only bits from X or Y are demanded.
       
       // If either the LHS or the RHS are One, the result is One.
-      ComputeMaskedBits(I->getOperand(1), DemandedMask, 
-                        RHSKnownZero, RHSKnownOne, Depth+1);
-      ComputeMaskedBits(I->getOperand(0), DemandedMask & ~RHSKnownOne, 
-                        LHSKnownZero, LHSKnownOne, Depth+1);
+      ComputeMaskedBits(I->getOperand(1), RHSKnownZero, RHSKnownOne, Depth+1);
+      ComputeMaskedBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, Depth+1);
       
       // If all of the demanded bits are known zero on one side, return the
       // other.  These bits cannot contribute to the result of the 'or' in this
@@ -206,7 +202,7 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
     }
     
     // Compute the KnownZero/KnownOne bits to simplify things downstream.
-    ComputeMaskedBits(I, DemandedMask, KnownZero, KnownOne, Depth);
+    ComputeMaskedBits(I, KnownZero, KnownOne, Depth);
     return 0;
   }
   
@@ -219,7 +215,7 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
   
   switch (I->getOpcode()) {
   default:
-    ComputeMaskedBits(I, DemandedMask, KnownZero, KnownOne, Depth);
+    ComputeMaskedBits(I, KnownZero, KnownOne, Depth);
     break;
   case Instruction::And:
     // If either the LHS or the RHS are Zero, the result is zero.
@@ -570,7 +566,7 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
 
     // Otherwise just hand the sub off to ComputeMaskedBits to fill in
     // the known zeros and ones.
-    ComputeMaskedBits(V, DemandedMask, KnownZero, KnownOne, Depth);
+    ComputeMaskedBits(V, KnownZero, KnownOne, Depth);
 
     // Turn this into a xor if LHS is 2^n-1 and the remaining bits are known
     // zero.
@@ -729,10 +725,8 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
     // The sign bit is the LHS's sign bit, except when the result of the
     // remainder is zero.
     if (DemandedMask.isNegative() && KnownZero.isNonNegative()) {
-      APInt Mask2 = APInt::getSignBit(BitWidth);
       APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
-      ComputeMaskedBits(I->getOperand(0), Mask2, LHSKnownZero, LHSKnownOne,
-                        Depth+1);
+      ComputeMaskedBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, Depth+1);
       // If it's known zero, our sign bit is also zero.
       if (LHSKnownZero.isNegative())
         KnownZero |= LHSKnownZero;
@@ -795,7 +789,7 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
         return 0;
       }
     }
-    ComputeMaskedBits(V, DemandedMask, KnownZero, KnownOne, Depth);
+    ComputeMaskedBits(V, KnownZero, KnownOne, Depth);
     break;
   }
   
diff --git a/lib/Transforms/Utils/Local.cpp b/lib/Transforms/Utils/Local.cpp
index b51dd29b57..d1c4d59682 100644
--- a/lib/Transforms/Utils/Local.cpp
+++ b/lib/Transforms/Utils/Local.cpp
@@ -762,9 +762,8 @@ unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
   assert(V->getType()->isPointerTy() &&
          "getOrEnforceKnownAlignment expects a pointer!");
   unsigned BitWidth = TD ? TD->getPointerSizeInBits() : 64;
-  APInt Mask = APInt::getAllOnesValue(BitWidth);
   APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
-  ComputeMaskedBits(V, Mask, KnownZero, KnownOne, TD);
+  ComputeMaskedBits(V, KnownZero, KnownOne, TD);
   unsigned TrailZ = KnownZero.countTrailingOnes();
   
   // Avoid trouble with rediculously large TrailZ values, such as
diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index d53a46ee02..66dd2c954e 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2562,7 +2562,7 @@ static bool EliminateDeadSwitchCases(SwitchInst *SI) {
   Value *Cond = SI->getCondition();
   unsigned Bits = cast<IntegerType>(Cond->getType())->getBitWidth();
   APInt KnownZero(Bits, 0), KnownOne(Bits, 0);
-  ComputeMaskedBits(Cond, APInt::getAllOnesValue(Bits), KnownZero, KnownOne);
+  ComputeMaskedBits(Cond, KnownZero, KnownOne);
 
   // Gather dead cases.
   SmallVector<ConstantInt*, 8> DeadCases;
diff --git a/test/Transforms/InstCombine/pr12251.ll b/test/Transforms/InstCombine/pr12251.ll
new file mode 100644
index 0000000000..74a41eb7d2
--- /dev/null
+++ b/test/Transforms/InstCombine/pr12251.ll
@@ -0,0 +1,15 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+define zeroext i1 @_Z3fooPb(i8* nocapture %x) {
+entry:
+  %a = load i8* %x, align 1, !range !0
+  %b = and i8 %a, 1
+  %tobool = icmp ne i8 %b, 0
+  ret i1 %tobool
+}
+
+; CHECK: %a = load i8* %x, align 1, !range !0
+; CHECK-NEXT: %tobool = icmp ne i8 %a, 0
+; CHECK-NEXT: ret i1 %tobool
+
+!0 = metadata !{i8 0, i8 2}