1 files changed, 731 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/contrib/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
new file mode 100644
index 0000000..4d2c89e
--- /dev/null
+++ b/contrib/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -0,0 +1,731 @@
+//===- InstCombineAddSub.cpp ----------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the visit functions for add, fadd, sub, and fsub.
+//
+//===----------------------------------------------------------------------===//
+
+#include "InstCombine.h"
+#include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Target/TargetData.h"
+#include "llvm/Support/GetElementPtrTypeIterator.h"
+#include "llvm/Support/PatternMatch.h"
+using namespace llvm;
+using namespace PatternMatch;
+
+/// AddOne - Add one to a ConstantInt.
+static Constant *AddOne(Constant *C) {
+  return ConstantExpr::getAdd(C, ConstantInt::get(C->getType(), 1));
+}
+/// SubOne - Subtract one from a ConstantInt.
+static Constant *SubOne(ConstantInt *C) {
+  return ConstantInt::get(C->getContext(), C->getValue()-1);
+}
+
+
+// dyn_castFoldableMul - If this value is a multiply that can be folded into
+// other computations (because it has a constant operand), return the
+// non-constant operand of the multiply, and set CST to point to the multiplier.
+// Otherwise, return null.
+//
+static inline Value *dyn_castFoldableMul(Value *V, ConstantInt *&CST) {
+  if (!V->hasOneUse() || !V->getType()->isIntegerTy())
+    return 0;
+  
+  Instruction *I = dyn_cast<Instruction>(V);
+  if (I == 0) return 0;
+  
+  if (I->getOpcode() == Instruction::Mul)
+    if ((CST = dyn_cast<ConstantInt>(I->getOperand(1))))
+      return I->getOperand(0);
+  if (I->getOpcode() == Instruction::Shl)
+    if ((CST = dyn_cast<ConstantInt>(I->getOperand(1)))) {
+      // The multiplier is really 1 << CST.
+      uint32_t BitWidth = cast<IntegerType>(V->getType())->getBitWidth();
+      uint32_t CSTVal = CST->getLimitedValue(BitWidth);
+      CST = ConstantInt::get(V->getType()->getContext(),
+                             APInt(BitWidth, 1).shl(CSTVal));
+      return I->getOperand(0);
+    }
+  return 0;
+}
+
+
+/// WillNotOverflowSignedAdd - Return true if we can prove that:
+///    (sext (add LHS, RHS))  === (add (sext LHS), (sext RHS))
+/// This basically requires proving that the add in the original type would not
+/// overflow to change the sign bit or have a carry out.
+bool InstCombiner::WillNotOverflowSignedAdd(Value *LHS, Value *RHS) {
+  // There are different heuristics we can use for this.  Here are some simple
+  // ones.
+  
+  // Add has the property that adding any two 2's complement numbers can only 
+  // have one carry bit which can change a sign.  As such, if LHS and RHS each
+  // have at least two sign bits, we know that the addition of the two values
+  // will sign extend fine.
+  if (ComputeNumSignBits(LHS) > 1 && ComputeNumSignBits(RHS) > 1)
+    return true;
+  
+  
+  // If one of the operands only has one non-zero bit, and if the other operand
+  // has a known-zero bit in a more significant place than it (not including the
+  // sign bit) the ripple may go up to and fill the zero, but won't change the
+  // sign.  For example, (X & ~4) + 1.
+  
+  // TODO: Implement.
+  
+  return false;
+}
+
+Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
+  bool Changed = SimplifyCommutative(I);
+  Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
+
+  if (Value *V = SimplifyAddInst(LHS, RHS, I.hasNoSignedWrap(),
+                                 I.hasNoUnsignedWrap(), TD))
+    return ReplaceInstUsesWith(I, V);
+
+  
+  if (Constant *RHSC = dyn_cast<Constant>(RHS)) {
+    if (ConstantInt *CI = dyn_cast<ConstantInt>(RHSC)) {
+      // X + (signbit) --> X ^ signbit
+      const APInt& Val = CI->getValue();
+      uint32_t BitWidth = Val.getBitWidth();
+      if (Val == APInt::getSignBit(BitWidth))
+        return BinaryOperator::CreateXor(LHS, RHS);
+      
+      // See if SimplifyDemandedBits can simplify this.  This handles stuff like
+      // (X & 254)+1 -> (X&254)|1
+      if (SimplifyDemandedInstructionBits(I))
+        return &I;
+
+      // zext(bool) + C -> bool ? C + 1 : C
+      if (ZExtInst *ZI = dyn_cast<ZExtInst>(LHS))
+        if (ZI->getSrcTy() == Type::getInt1Ty(I.getContext()))
+          return SelectInst::Create(ZI->getOperand(0), AddOne(CI), CI);
+    }
+
+    if (isa<PHINode>(LHS))
+      if (Instruction *NV = FoldOpIntoPhi(I))
+        return NV;
+    
+    ConstantInt *XorRHS = 0;
+    Value *XorLHS = 0;
+    if (isa<ConstantInt>(RHSC) &&
+        match(LHS, m_Xor(m_Value(XorLHS), m_ConstantInt(XorRHS)))) {
+      uint32_t TySizeBits = I.getType()->getScalarSizeInBits();
+      const APInt& RHSVal = cast<ConstantInt>(RHSC)->getValue();
+      unsigned ExtendAmt = 0;
+      // If we have ADD(XOR(AND(X, 0xFF), 0x80), 0xF..F80), it's a sext.
+      // If we have ADD(XOR(AND(X, 0xFF), 0xF..F80), 0x80), it's a sext.
+      if (XorRHS->getValue() == -RHSVal) {
+        if (RHSVal.isPowerOf2())
+          ExtendAmt = TySizeBits - RHSVal.logBase2() - 1;
+        else if (XorRHS->getValue().isPowerOf2())
+          ExtendAmt = TySizeBits - XorRHS->getValue().logBase2() - 1;
+      }
+
+      if (ExtendAmt) {
+        APInt Mask = APInt::getHighBitsSet(TySizeBits, ExtendAmt);
+        if (!MaskedValueIsZero(XorLHS, Mask))
+          ExtendAmt = 0;
+      }
+
+      if (ExtendAmt) {
+        Constant *ShAmt = ConstantInt::get(I.getType(), ExtendAmt);
+        Value *NewShl = Builder->CreateShl(XorLHS, ShAmt, "sext");
+        return BinaryOperator::CreateAShr(NewShl, ShAmt);
+      }
+    }
+  }
+
+  if (I.getType()->isIntegerTy(1))
+    return BinaryOperator::CreateXor(LHS, RHS);
+
+  if (I.getType()->isIntegerTy()) {
+    // X + X --> X << 1
+    if (LHS == RHS)
+      return BinaryOperator::CreateShl(LHS, ConstantInt::get(I.getType(), 1));
+
+    if (Instruction *RHSI = dyn_cast<Instruction>(RHS)) {
+      if (RHSI->getOpcode() == Instruction::Sub)
+        if (LHS == RHSI->getOperand(1))                   // A + (B - A) --> B
+          return ReplaceInstUsesWith(I, RHSI->getOperand(0));
+    }
+    if (Instruction *LHSI = dyn_cast<Instruction>(LHS)) {
+      if (LHSI->getOpcode() == Instruction::Sub)
+        if (RHS == LHSI->getOperand(1))                   // (B - A) + A --> B
+          return ReplaceInstUsesWith(I, LHSI->getOperand(0));
+    }
+  }
+
+  // -A + B  -->  B - A
+  // -A + -B  -->  -(A + B)
+  if (Value *LHSV = dyn_castNegVal(LHS)) {
+    if (LHS->getType()->isIntOrIntVectorTy()) {
+      if (Value *RHSV = dyn_castNegVal(RHS)) {
+        Value *NewAdd = Builder->CreateAdd(LHSV, RHSV, "sum");
+        return BinaryOperator::CreateNeg(NewAdd);
+      }
+    }
+    
+    return BinaryOperator::CreateSub(RHS, LHSV);
+  }
+
+  // A + -B  -->  A - B
+  if (!isa<Constant>(RHS))
+    if (Value *V = dyn_castNegVal(RHS))
+      return BinaryOperator::CreateSub(LHS, V);
+
+
+  ConstantInt *C2;
+  if (Value *X = dyn_castFoldableMul(LHS, C2)) {
+    if (X == RHS)   // X*C + X --> X * (C+1)
+      return BinaryOperator::CreateMul(RHS, AddOne(C2));
+
+    // X*C1 + X*C2 --> X * (C1+C2)
+    ConstantInt *C1;
+    if (X == dyn_castFoldableMul(RHS, C1))
+      return BinaryOperator::CreateMul(X, ConstantExpr::getAdd(C1, C2));
+  }
+
+  // X + X*C --> X * (C+1)
+  if (dyn_castFoldableMul(RHS, C2) == LHS)
+    return BinaryOperator::CreateMul(LHS, AddOne(C2));
+
+  // X + ~X --> -1   since   ~X = -X-1
+  if (match(LHS, m_Not(m_Specific(RHS))) ||
+      match(RHS, m_Not(m_Specific(LHS))))
+    return ReplaceInstUsesWith(I, Constant::getAllOnesValue(I.getType()));
+
+  // A+B --> A|B iff A and B have no bits set in common.
+  if (const 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);
+    if (LHSKnownZero != 0) {
+      APInt RHSKnownOne(IT->getBitWidth(), 0);
+      APInt RHSKnownZero(IT->getBitWidth(), 0);
+      ComputeMaskedBits(RHS, Mask, RHSKnownZero, RHSKnownOne);
+      
+      // No bits in common -> bitwise or.
+      if ((LHSKnownZero|RHSKnownZero).isAllOnesValue())
+        return BinaryOperator::CreateOr(LHS, RHS);
+    }
+  }
+
+  // W*X + Y*Z --> W * (X+Z)  iff W == Y
+  if (I.getType()->isIntOrIntVectorTy()) {
+    Value *W, *X, *Y, *Z;
+    if (match(LHS, m_Mul(m_Value(W), m_Value(X))) &&
+        match(RHS, m_Mul(m_Value(Y), m_Value(Z)))) {
+      if (W != Y) {
+        if (W == Z) {
+          std::swap(Y, Z);
+        } else if (Y == X) {
+          std::swap(W, X);
+        } else if (X == Z) {
+          std::swap(Y, Z);
+          std::swap(W, X);
+        }
+      }
+
+      if (W == Y) {
+        Value *NewAdd = Builder->CreateAdd(X, Z, LHS->getName());
+        return BinaryOperator::CreateMul(W, NewAdd);
+      }
+    }
+  }
+
+  if (ConstantInt *CRHS = dyn_cast<ConstantInt>(RHS)) {
+    Value *X = 0;
+    if (match(LHS, m_Not(m_Value(X))))    // ~X + C --> (C-1) - X
+      return BinaryOperator::CreateSub(SubOne(CRHS), X);
+
+    // (X & FF00) + xx00  -> (X+xx00) & FF00
+    if (LHS->hasOneUse() &&
+        match(LHS, m_And(m_Value(X), m_ConstantInt(C2)))) {
+      Constant *Anded = ConstantExpr::getAnd(CRHS, C2);
+      if (Anded == CRHS) {
+        // See if all bits from the first bit set in the Add RHS up are included
+        // in the mask.  First, get the rightmost bit.
+        const APInt &AddRHSV = CRHS->getValue();
+
+        // Form a mask of all bits from the lowest bit added through the top.
+        APInt AddRHSHighBits(~((AddRHSV & -AddRHSV)-1));
+
+        // See if the and mask includes all of these bits.
+        APInt AddRHSHighBitsAnd(AddRHSHighBits & C2->getValue());
+
+        if (AddRHSHighBits == AddRHSHighBitsAnd) {
+          // Okay, the xform is safe.  Insert the new add pronto.
+          Value *NewAdd = Builder->CreateAdd(X, CRHS, LHS->getName());
+          return BinaryOperator::CreateAnd(NewAdd, C2);
+        }
+      }
+    }
+
+    // Try to fold constant add into select arguments.
+    if (SelectInst *SI = dyn_cast<SelectInst>(LHS))
+      if (Instruction *R = FoldOpIntoSelect(I, SI))
+        return R;
+  }
+
+  // add (select X 0 (sub n A)) A  -->  select X A n
+  {
+    SelectInst *SI = dyn_cast<SelectInst>(LHS);
+    Value *A = RHS;
+    if (!SI) {
+      SI = dyn_cast<SelectInst>(RHS);
+      A = LHS;
+    }
+    if (SI && SI->hasOneUse()) {
+      Value *TV = SI->getTrueValue();
+      Value *FV = SI->getFalseValue();
+      Value *N;
+
+      // Can we fold the add into the argument of the select?
+      // We check both true and false select arguments for a matching subtract.
+      if (match(FV, m_Zero()) &&
+          match(TV, m_Sub(m_Value(N), m_Specific(A))))
+        // Fold the add into the true select value.
+        return SelectInst::Create(SI->getCondition(), N, A);
+      if (match(TV, m_Zero()) &&
+          match(FV, m_Sub(m_Value(N), m_Specific(A))))
+        // Fold the add into the false select value.
+        return SelectInst::Create(SI->getCondition(), A, N);
+    }
+  }
+
+  // Check for (add (sext x), y), see if we can merge this into an
+  // integer add followed by a sext.
+  if (SExtInst *LHSConv = dyn_cast<SExtInst>(LHS)) {
+    // (add (sext x), cst) --> (sext (add x, cst'))
+    if (ConstantInt *RHSC = dyn_cast<ConstantInt>(RHS)) {
+      Constant *CI = 
+        ConstantExpr::getTrunc(RHSC, LHSConv->getOperand(0)->getType());
+      if (LHSConv->hasOneUse() &&
+          ConstantExpr::getSExt(CI, I.getType()) == RHSC &&
+          WillNotOverflowSignedAdd(LHSConv->getOperand(0), CI)) {
+        // Insert the new, smaller add.
+        Value *NewAdd = Builder->CreateNSWAdd(LHSConv->getOperand(0), 
+                                              CI, "addconv");
+        return new SExtInst(NewAdd, I.getType());
+      }
+    }
+    
+    // (add (sext x), (sext y)) --> (sext (add int x, y))
+    if (SExtInst *RHSConv = dyn_cast<SExtInst>(RHS)) {
+      // Only do this if x/y have the same type, if at last one of them has a
+      // single use (so we don't increase the number of sexts), and if the
+      // integer add will not overflow.
+      if (LHSConv->getOperand(0)->getType()==RHSConv->getOperand(0)->getType()&&
+          (LHSConv->hasOneUse() || RHSConv->hasOneUse()) &&
+          WillNotOverflowSignedAdd(LHSConv->getOperand(0),
+                                   RHSConv->getOperand(0))) {
+        // Insert the new integer add.
+        Value *NewAdd = Builder->CreateNSWAdd(LHSConv->getOperand(0), 
+                                             RHSConv->getOperand(0), "addconv");
+        return new SExtInst(NewAdd, I.getType());
+      }
+    }
+  }
+
+  return Changed ? &I : 0;
+}
+
+Instruction *InstCombiner::visitFAdd(BinaryOperator &I) {
+  bool Changed = SimplifyCommutative(I);
+  Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
+
+  if (Constant *RHSC = dyn_cast<Constant>(RHS)) {
+    // X + 0 --> X
+    if (ConstantFP *CFP = dyn_cast<ConstantFP>(RHSC)) {
+      if (CFP->isExactlyValue(ConstantFP::getNegativeZero
+                              (I.getType())->getValueAPF()))
+        return ReplaceInstUsesWith(I, LHS);
+    }
+
+    if (isa<PHINode>(LHS))
+      if (Instruction *NV = FoldOpIntoPhi(I))
+        return NV;
+  }
+
+  // -A + B  -->  B - A
+  // -A + -B  -->  -(A + B)
+  if (Value *LHSV = dyn_castFNegVal(LHS))
+    return BinaryOperator::CreateFSub(RHS, LHSV);
+
+  // A + -B  -->  A - B
+  if (!isa<Constant>(RHS))
+    if (Value *V = dyn_castFNegVal(RHS))
+      return BinaryOperator::CreateFSub(LHS, V);
+
+  // Check for X+0.0.  Simplify it to X if we know X is not -0.0.
+  if (ConstantFP *CFP = dyn_cast<ConstantFP>(RHS))
+    if (CFP->getValueAPF().isPosZero() && CannotBeNegativeZero(LHS))
+      return ReplaceInstUsesWith(I, LHS);
+
+  // Check for (fadd double (sitofp x), y), see if we can merge this into an
+  // integer add followed by a promotion.
+  if (SIToFPInst *LHSConv = dyn_cast<SIToFPInst>(LHS)) {
+    // (fadd double (sitofp x), fpcst) --> (sitofp (add int x, intcst))
+    // ... if the constant fits in the integer value.  This is useful for things
+    // like (double)(x & 1234) + 4.0 -> (double)((X & 1234)+4) which no longer
+    // requires a constant pool load, and generally allows the add to be better
+    // instcombined.
+    if (ConstantFP *CFP = dyn_cast<ConstantFP>(RHS)) {
+      Constant *CI = 
+      ConstantExpr::getFPToSI(CFP, LHSConv->getOperand(0)->getType());
+      if (LHSConv->hasOneUse() &&
+          ConstantExpr::getSIToFP(CI, I.getType()) == CFP &&
+          WillNotOverflowSignedAdd(LHSConv->getOperand(0), CI)) {
+        // Insert the new integer add.
+        Value *NewAdd = Builder->CreateNSWAdd(LHSConv->getOperand(0),
+                                              CI, "addconv");
+        return new SIToFPInst(NewAdd, I.getType());
+      }
+    }
+    
+    // (fadd double (sitofp x), (sitofp y)) --> (sitofp (add int x, y))
+    if (SIToFPInst *RHSConv = dyn_cast<SIToFPInst>(RHS)) {
+      // Only do this if x/y have the same type, if at last one of them has a
+      // single use (so we don't increase the number of int->fp conversions),
+      // and if the integer add will not overflow.
+      if (LHSConv->getOperand(0)->getType()==RHSConv->getOperand(0)->getType()&&
+          (LHSConv->hasOneUse() || RHSConv->hasOneUse()) &&
+          WillNotOverflowSignedAdd(LHSConv->getOperand(0),
+                                   RHSConv->getOperand(0))) {
+        // Insert the new integer add.
+        Value *NewAdd = Builder->CreateNSWAdd(LHSConv->getOperand(0), 
+                                              RHSConv->getOperand(0),"addconv");
+        return new SIToFPInst(NewAdd, I.getType());
+      }
+    }
+  }
+  
+  return Changed ? &I : 0;
+}
+
+
+/// EmitGEPOffset - Given a getelementptr instruction/constantexpr, emit the
+/// code necessary to compute the offset from the base pointer (without adding
+/// in the base pointer).  Return the result as a signed integer of intptr size.
+Value *InstCombiner::EmitGEPOffset(User *GEP) {
+  TargetData &TD = *getTargetData();
+  gep_type_iterator GTI = gep_type_begin(GEP);
+  const Type *IntPtrTy = TD.getIntPtrType(GEP->getContext());
+  Value *Result = Constant::getNullValue(IntPtrTy);
+
+  // Build a mask for high order bits.
+  unsigned IntPtrWidth = TD.getPointerSizeInBits();
+  uint64_t PtrSizeMask = ~0ULL >> (64-IntPtrWidth);
+
+  for (User::op_iterator i = GEP->op_begin() + 1, e = GEP->op_end(); i != e;
+       ++i, ++GTI) {
+    Value *Op = *i;
+    uint64_t Size = TD.getTypeAllocSize(GTI.getIndexedType()) & PtrSizeMask;
+    if (ConstantInt *OpC = dyn_cast<ConstantInt>(Op)) {
+      if (OpC->isZero()) continue;
+      
+      // Handle a struct index, which adds its field offset to the pointer.
+      if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
+        Size = TD.getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
+        
+        Result = Builder->CreateAdd(Result,
+                                    ConstantInt::get(IntPtrTy, Size),
+                                    GEP->getName()+".offs");
+        continue;
+      }
+      
+      Constant *Scale = ConstantInt::get(IntPtrTy, Size);
+      Constant *OC =
+              ConstantExpr::getIntegerCast(OpC, IntPtrTy, true /*SExt*/);
+      Scale = ConstantExpr::getMul(OC, Scale);
+      // Emit an add instruction.
+      Result = Builder->CreateAdd(Result, Scale, GEP->getName()+".offs");
+      continue;
+    }
+    // Convert to correct type.
+    if (Op->getType() != IntPtrTy)
+      Op = Builder->CreateIntCast(Op, IntPtrTy, true, Op->getName()+".c");
+    if (Size != 1) {
+      Constant *Scale = ConstantInt::get(IntPtrTy, Size);
+      // We'll let instcombine(mul) convert this to a shl if possible.
+      Op = Builder->CreateMul(Op, Scale, GEP->getName()+".idx");
+    }
+
+    // Emit an add instruction.
+    Result = Builder->CreateAdd(Op, Result, GEP->getName()+".offs");
+  }
+  return Result;
+}
+
+
+
+
+/// Optimize pointer differences into the same array into a size.  Consider:
+///  &A[10] - &A[0]: we should compile this to "10".  LHS/RHS are the pointer
+/// operands to the ptrtoint instructions for the LHS/RHS of the subtract.
+///
+Value *InstCombiner::OptimizePointerDifference(Value *LHS, Value *RHS,
+                                               const Type *Ty) {
+  assert(TD && "Must have target data info for this");
+  
+  // If LHS is a gep based on RHS or RHS is a gep based on LHS, we can optimize
+  // this.
+  bool Swapped = false;
+  GetElementPtrInst *GEP = 0;
+  ConstantExpr *CstGEP = 0;
+  
+  // TODO: Could also optimize &A[i] - &A[j] -> "i-j", and "&A.foo[i] - &A.foo".
+  // For now we require one side to be the base pointer "A" or a constant
+  // expression derived from it.
+  if (GetElementPtrInst *LHSGEP = dyn_cast<GetElementPtrInst>(LHS)) {
+    // (gep X, ...) - X
+    if (LHSGEP->getOperand(0) == RHS) {
+      GEP = LHSGEP;
+      Swapped = false;
+    } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(RHS)) {
+      // (gep X, ...) - (ce_gep X, ...)
+      if (CE->getOpcode() == Instruction::GetElementPtr &&
+          LHSGEP->getOperand(0) == CE->getOperand(0)) {
+        CstGEP = CE;
+        GEP = LHSGEP;
+        Swapped = false;
+      }
+    }
+  }
+  
+  if (GetElementPtrInst *RHSGEP = dyn_cast<GetElementPtrInst>(RHS)) {
+    // X - (gep X, ...)
+    if (RHSGEP->getOperand(0) == LHS) {
+      GEP = RHSGEP;
+      Swapped = true;
+    } else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(LHS)) {
+      // (ce_gep X, ...) - (gep X, ...)
+      if (CE->getOpcode() == Instruction::GetElementPtr &&
+          RHSGEP->getOperand(0) == CE->getOperand(0)) {
+        CstGEP = CE;
+        GEP = RHSGEP;
+        Swapped = true;
+      }
+    }
+  }
+  
+  if (GEP == 0)
+    return 0;
+  
+  // Emit the offset of the GEP and an intptr_t.
+  Value *Result = EmitGEPOffset(GEP);
+  
+  // If we had a constant expression GEP on the other side offsetting the
+  // pointer, subtract it from the offset we have.
+  if (CstGEP) {
+    Value *CstOffset = EmitGEPOffset(CstGEP);
+    Result = Builder->CreateSub(Result, CstOffset);
+  }
+  
+
+  // If we have p - gep(p, ...)  then we have to negate the result.
+  if (Swapped)
+    Result = Builder->CreateNeg(Result, "diff.neg");
+
+  return Builder->CreateIntCast(Result, Ty, true);
+}
+
+
+Instruction *InstCombiner::visitSub(BinaryOperator &I) {
+  Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
+
+  if (Op0 == Op1)                        // sub X, X  -> 0
+    return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
+
+  // If this is a 'B = x-(-A)', change to B = x+A.  This preserves NSW/NUW.
+  if (Value *V = dyn_castNegVal(Op1)) {
+    BinaryOperator *Res = BinaryOperator::CreateAdd(Op0, V);
+    Res->setHasNoSignedWrap(I.hasNoSignedWrap());
+    Res->setHasNoUnsignedWrap(I.hasNoUnsignedWrap());
+    return Res;
+  }
+
+  if (isa<UndefValue>(Op0))
+    return ReplaceInstUsesWith(I, Op0);    // undef - X -> undef
+  if (isa<UndefValue>(Op1))
+    return ReplaceInstUsesWith(I, Op1);    // X - undef -> undef
+  if (I.getType()->isIntegerTy(1))
+    return BinaryOperator::CreateXor(Op0, Op1);
+  
+  if (ConstantInt *C = dyn_cast<ConstantInt>(Op0)) {
+    // Replace (-1 - A) with (~A).
+    if (C->isAllOnesValue())
+      return BinaryOperator::CreateNot(Op1);
+
+    // C - ~X == X + (1+C)
+    Value *X = 0;
+    if (match(Op1, m_Not(m_Value(X))))
+      return BinaryOperator::CreateAdd(X, AddOne(C));
+
+    // -(X >>u 31) -> (X >>s 31)
+    // -(X >>s 31) -> (X >>u 31)
+    if (C->isZero()) {
+      if (BinaryOperator *SI = dyn_cast<BinaryOperator>(Op1)) {
+        if (SI->getOpcode() == Instruction::LShr) {
+          if (ConstantInt *CU = dyn_cast<ConstantInt>(SI->getOperand(1))) {
+            // Check to see if we are shifting out everything but the sign bit.
+            if (CU->getLimitedValue(SI->getType()->getPrimitiveSizeInBits()) ==
+                SI->getType()->getPrimitiveSizeInBits()-1) {
+              // Ok, the transformation is safe.  Insert AShr.
+              return BinaryOperator::Create(Instruction::AShr, 
+                                          SI->getOperand(0), CU, SI->getName());
+            }
+          }
+        } else if (SI->getOpcode() == Instruction::AShr) {
+          if (ConstantInt *CU = dyn_cast<ConstantInt>(SI->getOperand(1))) {
+            // Check to see if we are shifting out everything but the sign bit.
+            if (CU->getLimitedValue(SI->getType()->getPrimitiveSizeInBits()) ==
+                SI->getType()->getPrimitiveSizeInBits()-1) {
+              // Ok, the transformation is safe.  Insert LShr. 
+              return BinaryOperator::CreateLShr(
+                                          SI->getOperand(0), CU, SI->getName());
+            }
+          }
+        }
+      }
+    }
+
+    // Try to fold constant sub into select arguments.
+    if (SelectInst *SI = dyn_cast<SelectInst>(Op1))
+      if (Instruction *R = FoldOpIntoSelect(I, SI))
+        return R;
+
+    // C - zext(bool) -> bool ? C - 1 : C
+    if (ZExtInst *ZI = dyn_cast<ZExtInst>(Op1))
+      if (ZI->getSrcTy() == Type::getInt1Ty(I.getContext()))
+        return SelectInst::Create(ZI->getOperand(0), SubOne(C), C);
+  }
+
+  if (BinaryOperator *Op1I = dyn_cast<BinaryOperator>(Op1)) {
+    if (Op1I->getOpcode() == Instruction::Add) {
+      if (Op1I->getOperand(0) == Op0)              // X-(X+Y) == -Y
+        return BinaryOperator::CreateNeg(Op1I->getOperand(1),
+                                         I.getName());
+      else if (Op1I->getOperand(1) == Op0)         // X-(Y+X) == -Y
+        return BinaryOperator::CreateNeg(Op1I->getOperand(0),
+                                         I.getName());
+      else if (ConstantInt *CI1 = dyn_cast<ConstantInt>(I.getOperand(0))) {
+        if (ConstantInt *CI2 = dyn_cast<ConstantInt>(Op1I->getOperand(1)))
+          // C1-(X+C2) --> (C1-C2)-X
+          return BinaryOperator::CreateSub(
+            ConstantExpr::getSub(CI1, CI2), Op1I->getOperand(0));
+      }
+    }
+
+    if (Op1I->hasOneUse()) {
+      // Replace (x - (y - z)) with (x + (z - y)) if the (y - z) subexpression
+      // is not used by anyone else...
+      //
+      if (Op1I->getOpcode() == Instruction::Sub) {
+        // Swap the two operands of the subexpr...
+        Value *IIOp0 = Op1I->getOperand(0), *IIOp1 = Op1I->getOperand(1);
+        Op1I->setOperand(0, IIOp1);
+        Op1I->setOperand(1, IIOp0);
+
+        // Create the new top level add instruction...
+        return BinaryOperator::CreateAdd(Op0, Op1);
+      }
+
+      // Replace (A - (A & B)) with (A & ~B) if this is the only use of (A&B)...
+      //
+      if (Op1I->getOpcode() == Instruction::And &&
+          (Op1I->getOperand(0) == Op0 || Op1I->getOperand(1) == Op0)) {
+        Value *OtherOp = Op1I->getOperand(Op1I->getOperand(0) == Op0);
+
+        Value *NewNot = Builder->CreateNot(OtherOp, "B.not");
+        return BinaryOperator::CreateAnd(Op0, NewNot);
+      }
+
+      // 0 - (X sdiv C)  -> (X sdiv -C)
+      if (Op1I->getOpcode() == Instruction::SDiv)
+        if (ConstantInt *CSI = dyn_cast<ConstantInt>(Op0))
+          if (CSI->isZero())
+            if (Constant *DivRHS = dyn_cast<Constant>(Op1I->getOperand(1)))
+              return BinaryOperator::CreateSDiv(Op1I->getOperand(0),
+                                          ConstantExpr::getNeg(DivRHS));
+
+      // 0 - (C << X)  -> (-C << X)
+      if (Op1I->getOpcode() == Instruction::Shl)
+        if (ConstantInt *CSI = dyn_cast<ConstantInt>(Op0))
+          if (CSI->isZero())
+            if (Value *ShlLHSNeg = dyn_castNegVal(Op1I->getOperand(0)))
+              return BinaryOperator::CreateShl(ShlLHSNeg, Op1I->getOperand(1));
+
+      // X - X*C --> X * (1-C)
+      ConstantInt *C2 = 0;
+      if (dyn_castFoldableMul(Op1I, C2) == Op0) {
+        Constant *CP1 = 
+          ConstantExpr::getSub(ConstantInt::get(I.getType(), 1),
+                                             C2);
+        return BinaryOperator::CreateMul(Op0, CP1);
+      }
+    }
+  }
+
+  if (BinaryOperator *Op0I = dyn_cast<BinaryOperator>(Op0)) {
+    if (Op0I->getOpcode() == Instruction::Add) {
+      if (Op0I->getOperand(0) == Op1)             // (Y+X)-Y == X
+        return ReplaceInstUsesWith(I, Op0I->getOperand(1));
+      else if (Op0I->getOperand(1) == Op1)        // (X+Y)-Y == X
+        return ReplaceInstUsesWith(I, Op0I->getOperand(0));
+    } else if (Op0I->getOpcode() == Instruction::Sub) {
+      if (Op0I->getOperand(0) == Op1)             // (X-Y)-X == -Y
+        return BinaryOperator::CreateNeg(Op0I->getOperand(1),
+                                         I.getName());
+    }
+  }
+
+  ConstantInt *C1;
+  if (Value *X = dyn_castFoldableMul(Op0, C1)) {
+    if (X == Op1)  // X*C - X --> X * (C-1)
+      return BinaryOperator::CreateMul(Op1, SubOne(C1));
+
+    ConstantInt *C2;   // X*C1 - X*C2 -> X * (C1-C2)
+    if (X == dyn_castFoldableMul(Op1, C2))
+      return BinaryOperator::CreateMul(X, ConstantExpr::getSub(C1, C2));
+  }
+  
+  // Optimize pointer differences into the same array into a size.  Consider:
+  //  &A[10] - &A[0]: we should compile this to "10".
+  if (TD) {
+    Value *LHSOp, *RHSOp;
+    if (match(Op0, m_PtrToInt(m_Value(LHSOp))) &&
+        match(Op1, m_PtrToInt(m_Value(RHSOp))))
+      if (Value *Res = OptimizePointerDifference(LHSOp, RHSOp, I.getType()))
+        return ReplaceInstUsesWith(I, Res);
+    
+    // trunc(p)-trunc(q) -> trunc(p-q)
+    if (match(Op0, m_Trunc(m_PtrToInt(m_Value(LHSOp)))) &&
+        match(Op1, m_Trunc(m_PtrToInt(m_Value(RHSOp)))))
+      if (Value *Res = OptimizePointerDifference(LHSOp, RHSOp, I.getType()))
+        return ReplaceInstUsesWith(I, Res);
+  }
+  
+  return 0;
+}
+
+Instruction *InstCombiner::visitFSub(BinaryOperator &I) {
+  Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
+
+  // If this is a 'B = x-(-A)', change to B = x+A...
+  if (Value *V = dyn_castFNegVal(Op1))
+    return BinaryOperator::CreateFAdd(Op0, V);
+
+  return 0;
+}