text: /*========================== begin_copyright_notice ============================
  
  Copyright (C) 2018-2021 Intel Corporation
  
  SPDX-License-Identifier: MIT
  
  ============================= end_copyright_notice ===========================*/
  
  /*========================== begin_copyright_notice ============================
  
  This file is distributed under the University of Illinois Open Source License.
  See LICENSE.TXT for details.
  
  ============================= end_copyright_notice ===========================*/
  
  // This file implements the visitICmp and visitFCmp functions.
  
  #include "common/LLVMWarningsPush.hpp"
  #include "InstCombineInternal.h"
  #include "llvm/ADT/APSInt.h"
  #include "llvm/ADT/SetVector.h"
  #include "llvm/ADT/Statistic.h"
  #include "llvm/Analysis/ConstantFolding.h"
  #include "llvm/Analysis/InstructionSimplify.h"
  #include "llvm/Analysis/MemoryBuiltins.h"
  #include "llvm/Analysis/TargetLibraryInfo.h"
  #include "llvm/Analysis/VectorUtils.h"
  #include "llvm/IR/ConstantRange.h"
  #include "llvm/IR/DataLayout.h"
  #include "llvm/IR/GetElementPtrTypeIterator.h"
  #include "llvm/IR/IntrinsicInst.h"
  #include "llvm/IR/PatternMatch.h"
  #include "llvm/Support/Debug.h"
  #include "Probe/Assertion.h"
  
  using namespace llvm;
  using namespace PatternMatch;
  using namespace IGCombiner;
  
  #define DEBUG_TYPE "instcombine"
  
  // How many times is a select replaced by one of its operands?
  STATISTIC(NumSel, "Number of select opts");
  
  
  static ConstantInt *extractElement(Constant *V, Constant *Idx) {
    return cast<ConstantInt>(ConstantExpr::getExtractElement(V, Idx));
  }
  
  static bool hasAddOverflow(ConstantInt *Result,
                             ConstantInt *In1, ConstantInt *In2,
                             bool IsSigned) {
    if (!IsSigned)
      return Result->getValue().ult(In1->getValue());
  
    if (In2->isNegative())
      return Result->getValue().sgt(In1->getValue());
    return Result->getValue().slt(In1->getValue());
  }
  
  /// Compute Result = In1+In2, returning true if the result overflowed for this
  /// type.
  static bool addWithOverflow(Constant *&Result, Constant *In1,
                              Constant *In2, bool IsSigned = false) {
    Result = ConstantExpr::getAdd(In1, In2);
  
    if (VectorType *VTy = dyn_cast<VectorType>(In1->getType())) {
      for (unsigned i = 0, e = VTy->getNumElements(); i != e; ++i) {
        Constant *Idx = ConstantInt::get(Type::getInt32Ty(In1->getContext()), i);
        if (hasAddOverflow(extractElement(Result, Idx),
                           extractElement(In1, Idx),
                           extractElement(In2, Idx),
                           IsSigned))
          return true;
      }
      return false;
    }
  
    return hasAddOverflow(cast<ConstantInt>(Result),
                          cast<ConstantInt>(In1), cast<ConstantInt>(In2),
                          IsSigned);
  }
  
  static bool hasSubOverflow(ConstantInt *Result,
                             ConstantInt *In1, ConstantInt *In2,
                             bool IsSigned) {
    if (!IsSigned)
      return Result->getValue().ugt(In1->getValue());
  
    if (In2->isNegative())
      return Result->getValue().slt(In1->getValue());
  
    return Result->getValue().sgt(In1->getValue());
  }
  
  /// Compute Result = In1-In2, returning true if the result overflowed for this
  /// type.
  static bool subWithOverflow(Constant *&Result, Constant *In1,
                              Constant *In2, bool IsSigned = false) {
    Result = ConstantExpr::getSub(In1, In2);
  
    if (VectorType *VTy = dyn_cast<VectorType>(In1->getType())) {
      for (unsigned i = 0, e = VTy->getNumElements(); i != e; ++i) {
        Constant *Idx = ConstantInt::get(Type::getInt32Ty(In1->getContext()), i);
        if (hasSubOverflow(extractElement(Result, Idx),
                           extractElement(In1, Idx),
                           extractElement(In2, Idx),
                           IsSigned))
          return true;
      }
      return false;
    }
  
    return hasSubOverflow(cast<ConstantInt>(Result),
                          cast<ConstantInt>(In1), cast<ConstantInt>(In2),
                          IsSigned);
  }
  
  /// Given an icmp instruction, return true if any use of this comparison is a
  /// branch on sign bit comparison.
  static bool isBranchOnSignBitCheck(ICmpInst &I, bool isSignBit) {
    for (auto *U : I.users())
      if (isa<BranchInst>(U))
        return isSignBit;
    return false;
  }
  
  /// Given an exploded icmp instruction, return true if the comparison only
  /// checks the sign bit. If it only checks the sign bit, set TrueIfSigned if the
  /// result of the comparison is true when the input value is signed.
  static bool isSignBitCheck(ICmpInst::Predicate Pred, const APInt &RHS,
                             bool &TrueIfSigned) {
    switch (Pred) {
    case ICmpInst::ICMP_SLT:   // True if LHS s< 0
      TrueIfSigned = true;
      return RHS == 0;
    case ICmpInst::ICMP_SLE:   // True if LHS s<= RHS and RHS == -1
      TrueIfSigned = true;
      return RHS.isAllOnesValue();
    case ICmpInst::ICMP_SGT:   // True if LHS s> -1
      TrueIfSigned = false;
      return RHS.isAllOnesValue();
    case ICmpInst::ICMP_UGT:
      // True if LHS u> RHS and RHS == high-bit-mask - 1
      TrueIfSigned = true;
      return RHS.isMaxSignedValue();
    case ICmpInst::ICMP_UGE:
      // True if LHS u>= RHS and RHS == high-bit-mask (2^7, 2^15, 2^31, etc)
      TrueIfSigned = true;
      return RHS.isSignBit();
    default:
      return false;
    }
  }
  
  /// Returns true if the exploded icmp can be expressed as a signed comparison
  /// to zero and updates the predicate accordingly.
  /// The signedness of the comparison is preserved.
  /// TODO: Refactor with decomposeBitTestICmp()?
  static bool isSignTest(ICmpInst::Predicate &Pred, const APInt &C) {
    if (!ICmpInst::isSigned(Pred))
      return false;
  
    if (C == 0)
      return ICmpInst::isRelational(Pred);
  
    if (C == 1) {
      if (Pred == ICmpInst::ICMP_SLT) {
        Pred = ICmpInst::ICMP_SLE;
        return true;
      }
    } else if (C.isAllOnesValue()) {
      if (Pred == ICmpInst::ICMP_SGT) {
        Pred = ICmpInst::ICMP_SGE;
        return true;
      }
    }
  
    return false;
  }
  
  /// Given a signed integer type and a set of known zero and one bits, compute
  /// the maximum and minimum values that could have the specified known zero and
  /// known one bits, returning them in Min/Max.
  static void computeSignedMinMaxValuesFromKnownBits(const APInt &KnownZero,
                                                     const APInt &KnownOne,
                                                     APInt &Min, APInt &Max) {
    IGC_ASSERT_MESSAGE(KnownZero.getBitWidth() == KnownOne.getBitWidth(), "KnownZero, KnownOne and Min, Max must have equal bitwidth.");
    IGC_ASSERT_MESSAGE(KnownZero.getBitWidth() == Min.getBitWidth(), "KnownZero, KnownOne and Min, Max must have equal bitwidth.");
    IGC_ASSERT_MESSAGE(KnownZero.getBitWidth() == Max.getBitWidth(), "KnownZero, KnownOne and Min, Max must have equal bitwidth.");
  
    APInt UnknownBits = ~(KnownZero|KnownOne);
  
    // The minimum value is when all unknown bits are zeros, EXCEPT for the sign
    // bit if it is unknown.
    Min = KnownOne;
    Max = KnownOne|UnknownBits;
  
    if (UnknownBits.isNegative()) { // Sign bit is unknown
      Min.setBit(Min.getBitWidth()-1);
      Max.clearBit(Max.getBitWidth()-1);
    }
  }
  
  /// Given an unsigned integer type and a set of known zero and one bits, compute
  /// the maximum and minimum values that could have the specified known zero and
  /// known one bits, returning them in Min/Max.
  static void computeUnsignedMinMaxValuesFromKnownBits(const APInt &KnownZero,
                                                       const APInt &KnownOne,
                                                       APInt &Min, APInt &Max) {
    IGC_ASSERT_MESSAGE(KnownZero.getBitWidth() == KnownOne.getBitWidth(), "Ty, KnownZero, KnownOne and Min, Max must have equal bitwidth.");
    IGC_ASSERT_MESSAGE(KnownZero.getBitWidth() == Min.getBitWidth(), "Ty, KnownZero, KnownOne and Min, Max must have equal bitwidth.");
    IGC_ASSERT_MESSAGE(KnownZero.getBitWidth() == Max.getBitWidth(), "Ty, KnownZero, KnownOne and Min, Max must have equal bitwidth.");
  
    APInt UnknownBits = ~(KnownZero|KnownOne);
  
    // The minimum value is when the unknown bits are all zeros.
    Min = KnownOne;
    // The maximum value is when the unknown bits are all ones.
    Max = KnownOne|UnknownBits;
  }
  
  /// This is called when we see this pattern:
  ///   cmp pred (load (gep GV, ...)), cmpcst
  /// where GV is a global variable with a constant initializer. Try to simplify
  /// this into some simple computation that does not need the load. For example
  /// we can optimize "icmp eq (load (gep "foo", 0, i)), 0" into "icmp eq i, 3".
  ///
  /// If AndCst is non-null, then the loaded value is masked with that constant
  /// before doing the comparison. This handles cases like "A[i]&4 == 0".
  Instruction *InstCombiner::foldCmpLoadFromIndexedGlobal(GetElementPtrInst *GEP,
                                                          GlobalVariable *GV,
                                                          CmpInst &ICI,
                                                          ConstantInt *AndCst) {
    Constant *Init = GV->getInitializer();
    if (!isa<ConstantArray>(Init) && !isa<ConstantDataArray>(Init))
      return nullptr;
  
    uint64_t ArrayElementCount = Init->getType()->getArrayNumElements();
    if (ArrayElementCount > 1024) return nullptr; // Don't blow up on huge arrays.
  
    // There are many forms of this optimization we can handle, for now, just do
    // the simple index into a single-dimensional array.
    //
    // Require: GEP GV, 0, i {{, constant indices}}
    if (GEP->getNumOperands() < 3 ||
        !isa<ConstantInt>(GEP->getOperand(1)) ||
        !cast<ConstantInt>(GEP->getOperand(1))->isZero() ||
        isa<Constant>(GEP->getOperand(2)))
      return nullptr;
  
    // Check that indices after the variable are constants and in-range for the
    // type they index.  Collect the indices.  This is typically for arrays of
    // structs.
    SmallVector<unsigned, 4> LaterIndices;
  
    Type *EltTy = Init->getType()->getArrayElementType();
    for (unsigned i = 3, e = GEP->getNumOperands(); i != e; ++i) {
      ConstantInt *Idx = dyn_cast<ConstantInt>(GEP->getOperand(i));
      if (!Idx) return nullptr;  // Variable index.
  
      uint64_t IdxVal = Idx->getZExtValue();
      if ((unsigned)IdxVal != IdxVal) return nullptr; // Too large array index.
  
      if (StructType *STy = dyn_cast<StructType>(EltTy))
        EltTy = STy->getElementType(IdxVal);
      else if (ArrayType *ATy = dyn_cast<ArrayType>(EltTy)) {
        if (IdxVal >= ATy->getNumElements()) return nullptr;
        EltTy = ATy->getElementType();
      } else {
        return nullptr; // Unknown type.
      }
  
      LaterIndices.push_back(IdxVal);
    }
  
    enum { Overdefined = -3, Undefined = -2 };
  
    // Variables for our state machines.
  
    // FirstTrueElement/SecondTrueElement - Used to emit a comparison of the form
    // "i == 47 | i == 87", where 47 is the first index the condition is true for,
    // and 87 is the second (and last) index.  FirstTrueElement is -2 when
    // undefined, otherwise set to the first true element.  SecondTrueElement is
    // -2 when undefined, -3 when overdefined and >= 0 when that index is true.
    int FirstTrueElement = Undefined, SecondTrueElement = Undefined;
  
    // FirstFalseElement/SecondFalseElement - Used to emit a comparison of the
    // form "i != 47 & i != 87".  Same state transitions as for true elements.
    int FirstFalseElement = Undefined, SecondFalseElement = Undefined;
  
    /// TrueRangeEnd/FalseRangeEnd - In conjunction with First*Element, these
    /// define a state machine that triggers for ranges of values that the index
    /// is true or false for.  This triggers on things like "abbbbc"[i] == 'b'.
    /// This is -2 when undefined, -3 when overdefined, and otherwise the last
    /// index in the range (inclusive).  We use -2 for undefined here because we
    /// use relative comparisons and don't want 0-1 to match -1.
    int TrueRangeEnd = Undefined, FalseRangeEnd = Undefined;
  
    // MagicBitvector - This is a magic bitvector where we set a bit if the
    // comparison is true for element 'i'.  If there are 64 elements or less in
    // the array, this will fully represent all the comparison results.
    uint64_t MagicBitvector = 0;
  
    // Scan the array and see if one of our patterns matches.
    Constant *CompareRHS = cast<Constant>(ICI.getOperand(1));
    for (unsigned i = 0, e = ArrayElementCount; i != e; ++i) {
      Constant *Elt = Init->getAggregateElement(i);
      if (!Elt) return nullptr;
  
      // If this is indexing an array of structures, get the structure element.
      if (!LaterIndices.empty())
        Elt = ConstantExpr::getExtractValue(Elt, LaterIndices);
  
      // If the element is masked, handle it.
      if (AndCst) Elt = ConstantExpr::getAnd(Elt, AndCst);
  
      // Find out if the comparison would be true or false for the i'th element.
      Constant *C = ConstantFoldCompareInstOperands(ICI.getPredicate(), Elt,
                                                    CompareRHS, DL, &TLI);
      // If the result is undef for this element, ignore it.
      if (isa<UndefValue>(C)) {
        // Extend range state machines to cover this element in case there is an
        // undef in the middle of the range.
        if (TrueRangeEnd == (int)i-1)
          TrueRangeEnd = i;
        if (FalseRangeEnd == (int)i-1)
          FalseRangeEnd = i;
        continue;
      }
  
      // If we can't compute the result for any of the elements, we have to give
      // up evaluating the entire conditional.
      if (!isa<ConstantInt>(C)) return nullptr;
  
      // Otherwise, we know if the comparison is true or false for this element,
      // update our state machines.
      bool IsTrueForElt = !cast<ConstantInt>(C)->isZero();
  
      // State machine for single/double/range index comparison.
      if (IsTrueForElt) {
        // Update the TrueElement state machine.
        if (FirstTrueElement == Undefined)
          FirstTrueElement = TrueRangeEnd = i;  // First true element.
        else {
          // Update double-compare state machine.
          if (SecondTrueElement == Undefined)
            SecondTrueElement = i;
          else
            SecondTrueElement = Overdefined;
  
          // Update range state machine.
          if (TrueRangeEnd == (int)i-1)
            TrueRangeEnd = i;
          else
            TrueRangeEnd = Overdefined;
        }
      } else {
        // Update the FalseElement state machine.
        if (FirstFalseElement == Undefined)
          FirstFalseElement = FalseRangeEnd = i; // First false element.
        else {
          // Update double-compare state machine.
          if (SecondFalseElement == Undefined)
            SecondFalseElement = i;
          else
            SecondFalseElement = Overdefined;
  
          // Update range state machine.
          if (FalseRangeEnd == (int)i-1)
            FalseRangeEnd = i;
          else
            FalseRangeEnd = Overdefined;
        }
      }
  
      // If this element is in range, update our magic bitvector.
      if (i < 64 && IsTrueForElt)
        MagicBitvector |= 1ULL << i;
  
      // If all of our states become overdefined, bail out early.  Since the
      // predicate is expensive, only check it every 8 elements.  This is only
      // really useful for really huge arrays.
      if ((i & 8) == 0 && i >= 64 && SecondTrueElement == Overdefined &&
          SecondFalseElement == Overdefined && TrueRangeEnd == Overdefined &&
          FalseRangeEnd == Overdefined)
        return nullptr;
    }
  
    // Now that we've scanned the entire array, emit our new comparison(s).  We
    // order the state machines in complexity of the generated code.
    Value *Idx = GEP->getOperand(2);
  
    // If the index is larger than the pointer size of the target, truncate the
    // index down like the GEP would do implicitly.  We don't have to do this for
    // an inbounds GEP because the index can't be out of range.
    if (!GEP->isInBounds()) {
      Type *IntPtrTy = DL.getIntPtrType(GEP->getType());
      unsigned PtrSize = IntPtrTy->getIntegerBitWidth();
      if (Idx->getType()->getPrimitiveSizeInBits() > PtrSize)
        Idx = Builder->CreateTrunc(Idx, IntPtrTy);
    }
  
    // If the comparison is only true for one or two elements, emit direct
    // comparisons.
    if (SecondTrueElement != Overdefined) {
      // None true -> false.
      if (FirstTrueElement == Undefined)
        return replaceInstUsesWith(ICI, Builder->getFalse());
  
      Value *FirstTrueIdx = ConstantInt::get(Idx->getType(), FirstTrueElement);
  
      // True for one element -> 'i == 47'.
      if (SecondTrueElement == Undefined)
        return new ICmpInst(ICmpInst::ICMP_EQ, Idx, FirstTrueIdx);
  
      // True for two elements -> 'i == 47 | i == 72'.
      Value *C1 = Builder->CreateICmpEQ(Idx, FirstTrueIdx);
      Value *SecondTrueIdx = ConstantInt::get(Idx->getType(), SecondTrueElement);
      Value *C2 = Builder->CreateICmpEQ(Idx, SecondTrueIdx);
      return BinaryOperator::CreateOr(C1, C2);
    }
  
    // If the comparison is only false for one or two elements, emit direct
    // comparisons.
    if (SecondFalseElement != Overdefined) {
      // None false -> true.
      if (FirstFalseElement == Undefined)
        return replaceInstUsesWith(ICI, Builder->getTrue());
  
      Value *FirstFalseIdx = ConstantInt::get(Idx->getType(), FirstFalseElement);
  
      // False for one element -> 'i != 47'.
      if (SecondFalseElement == Undefined)
        return new ICmpInst(ICmpInst::ICMP_NE, Idx, FirstFalseIdx);
  
      // False for two elements -> 'i != 47 & i != 72'.
      Value *C1 = Builder->CreateICmpNE(Idx, FirstFalseIdx);
      Value *SecondFalseIdx = ConstantInt::get(Idx->getType(),SecondFalseElement);
      Value *C2 = Builder->CreateICmpNE(Idx, SecondFalseIdx);
      return BinaryOperator::CreateAnd(C1, C2);
    }
  
    // If the comparison can be replaced with a range comparison for the elements
    // where it is true, emit the range check.
    if (TrueRangeEnd != Overdefined) {
      IGC_ASSERT_MESSAGE(TrueRangeEnd != FirstTrueElement, "Should emit single compare");
  
      // Generate (i-FirstTrue) <u (TrueRangeEnd-FirstTrue+1).
      if (FirstTrueElement) {
        Value *Offs = ConstantInt::get(Idx->getType(), -FirstTrueElement);
        Idx = Builder->CreateAdd(Idx, Offs);
      }
  
      Value *End = ConstantInt::get(Idx->getType(),
                                    TrueRangeEnd-FirstTrueElement+1);
      return new ICmpInst(ICmpInst::ICMP_ULT, Idx, End);
    }
  
    // False range check.
    if (FalseRangeEnd != Overdefined) {
      IGC_ASSERT_MESSAGE(FalseRangeEnd != FirstFalseElement, "Should emit single compare");
      // Generate (i-FirstFalse) >u (FalseRangeEnd-FirstFalse).
      if (FirstFalseElement) {
        Value *Offs = ConstantInt::get(Idx->getType(), -FirstFalseElement);
        Idx = Builder->CreateAdd(Idx, Offs);
      }
  
      Value *End = ConstantInt::get(Idx->getType(),
                                    FalseRangeEnd-FirstFalseElement);
      return new ICmpInst(ICmpInst::ICMP_UGT, Idx, End);
    }
  
    // If a magic bitvector captures the entire comparison state
    // of this load, replace it with computation that does:
    //   ((magic_cst >> i) & 1) != 0
    {
      Type *Ty = nullptr;
  
      // Look for an appropriate type:
      // - The type of Idx if the magic fits
      // - The smallest fitting legal type if we have a DataLayout
      // - Default to i32
      if (ArrayElementCount <= Idx->getType()->getIntegerBitWidth())
        Ty = Idx->getType();
      else
        Ty = DL.getSmallestLegalIntType(Init->getContext(), ArrayElementCount);
  
      if (Ty) {
        Value *V = Builder->CreateIntCast(Idx, Ty, false);
        V = Builder->CreateLShr(ConstantInt::get(Ty, MagicBitvector), V);
        V = Builder->CreateAnd(ConstantInt::get(Ty, 1), V);
        return new ICmpInst(ICmpInst::ICMP_NE, V, ConstantInt::get(Ty, 0));
      }
    }
  
    return nullptr;
  }
  
  /// Return a value that can be used to compare the *offset* implied by a GEP to
  /// zero. For example, if we have &A[i], we want to return 'i' for
  /// "icmp ne i, 0". Note that, in general, indices can be complex, and scales
  /// are involved. The above expression would also be legal to codegen as
  /// "icmp ne (i*4), 0" (assuming A is a pointer to i32).
  /// This latter form is less amenable to optimization though, and we are allowed
  /// to generate the first by knowing that pointer arithmetic doesn't overflow.
  ///
  /// If we can't emit an optimized form for this expression, this returns null.
  ///
  static Value *evaluateGEPOffsetExpression(User *GEP, InstCombiner &IC,
                                            const DataLayout &DL) {
    gep_type_iterator GTI = gep_type_begin(GEP);
  
    // Check to see if this gep only has a single variable index.  If so, and if
    // any constant indices are a multiple of its scale, then we can compute this
    // in terms of the scale of the variable index.  For example, if the GEP
    // implies an offset of "12 + i*4", then we can codegen this as "3 + i",
    // because the expression will cross zero at the same point.
    unsigned i, e = GEP->getNumOperands();
    int64_t Offset = 0;
    for (i = 1; i != e; ++i, ++GTI) {
      if (ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(i))) {
        // Compute the aggregate offset of constant indices.
        if (CI->isZero()) continue;
  
        // Handle a struct index, which adds its field offset to the pointer.
        if (StructType *STy = GTI.getStructTypeOrNull()) {
          Offset += DL.getStructLayout(STy)->getElementOffset(CI->getZExtValue());
        } else {
          uint64_t Size = DL.getTypeAllocSize(GTI.getIndexedType());
          Offset += Size*CI->getSExtValue();
        }
      } else {
        // Found our variable index.
        break;
      }
    }
  
    // If there are no variable indices, we must have a constant offset, just
    // evaluate it the general way.
    if (i == e) return nullptr;
  
    Value *VariableIdx = GEP->getOperand(i);
    // Determine the scale factor of the variable element.  For example, this is
    // 4 if the variable index is into an array of i32.
    uint64_t VariableScale = DL.getTypeAllocSize(GTI.getIndexedType());
  
    // Verify that there are no other variable indices.  If so, emit the hard way.
    for (++i, ++GTI; i != e; ++i, ++GTI) {
      ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(i));
      if (!CI) return nullptr;
  
      // Compute the aggregate offset of constant indices.
      if (CI->isZero()) continue;
  
      // Handle a struct index, which adds its field offset to the pointer.
      if (StructType *STy = GTI.getStructTypeOrNull()) {
        Offset += DL.getStructLayout(STy)->getElementOffset(CI->getZExtValue());
      } else {
        uint64_t Size = DL.getTypeAllocSize(GTI.getIndexedType());
        Offset += Size*CI->getSExtValue();
      }
    }
  
    // Okay, we know we have a single variable index, which must be a
    // pointer/array/vector index.  If there is no offset, life is simple, return
    // the index.
    Type *IntPtrTy = DL.getIntPtrType(GEP->getOperand(0)->getType());
    unsigned IntPtrWidth = IntPtrTy->getIntegerBitWidth();
    if (Offset == 0) {
      // Cast to intptrty in case a truncation occurs.  If an extension is needed,
      // we don't need to bother extending: the extension won't affect where the
      // computation crosses zero.
      if (VariableIdx->getType()->getPrimitiveSizeInBits() > IntPtrWidth) {
        VariableIdx = IC.Builder->CreateTrunc(VariableIdx, IntPtrTy);
      }
      return VariableIdx;
    }
  
    // Otherwise, there is an index.  The computation we will do will be modulo
    // the pointer size, so get it.
    uint64_t PtrSizeMask = ~0ULL >> (64-IntPtrWidth);
  
    Offset &= PtrSizeMask;
    VariableScale &= PtrSizeMask;
  
    // To do this transformation, any constant index must be a multiple of the
    // variable scale factor.  For example, we can evaluate "12 + 4*i" as "3 + i",
    // but we can't evaluate "10 + 3*i" in terms of i.  Check that the offset is a
    // multiple of the variable scale.
    int64_t NewOffs = Offset / (int64_t)VariableScale;
    if (Offset != NewOffs*(int64_t)VariableScale)
      return nullptr;
  
    // Okay, we can do this evaluation.  Start by converting the index to intptr.
    if (VariableIdx->getType() != IntPtrTy)
      VariableIdx = IC.Builder->CreateIntCast(VariableIdx, IntPtrTy,
                                              true /*Signed*/);
    Constant *OffsetVal = ConstantInt::get(IntPtrTy, NewOffs);
    return IC.Builder->CreateAdd(VariableIdx, OffsetVal, "offset");
  }
  
  /// Returns true if we can rewrite Start as a GEP with pointer Base
  /// and some integer offset. The nodes that need to be re-written
  /// for this transformation will be added to Explored.
  static bool canRewriteGEPAsOffset(Value *Start, Value *Base,
                                    const DataLayout &DL,
                                    SetVector<Value *> &Explored) {
    SmallVector<Value *, 16> WorkList(1, Start);
    Explored.insert(Base);
  
    // The following traversal gives us an order which can be used
    // when doing the final transformation. Since in the final
    // transformation we create the PHI replacement instructions first,
    // we don't have to get them in any particular order.
    //
    // However, for other instructions we will have to traverse the
    // operands of an instruction first, which means that we have to
    // do a post-order traversal.
    while (!WorkList.empty()) {
      SetVector<PHINode *> PHIs;
  
      while (!WorkList.empty()) {
        if (Explored.size() >= 100)
          return false;
  
        Value *V = WorkList.back();
  
        if (Explored.count(V) != 0) {
          WorkList.pop_back();
          continue;
        }
  
        if (!isa<IntToPtrInst>(V) && !isa<PtrToIntInst>(V) &&
            !isa<GetElementPtrInst>(V) && !isa<PHINode>(V))
          // We've found some value that we can't explore which is different from
          // the base. Therefore we can't do this transformation.
          return false;
  
        if (isa<IntToPtrInst>(V) || isa<PtrToIntInst>(V)) {
          auto *CI = dyn_cast<CastInst>(V);
          if (!CI->isNoopCast(DL))
            return false;
  
          if (Explored.count(CI->getOperand(0)) == 0)
            WorkList.push_back(CI->getOperand(0));
        }
  
        if (auto *GEP = dyn_cast<GEPOperator>(V)) {
          // We're limiting the GEP to having one index. This will preserve
          // the original pointer type. We could handle more cases in the
          // future.
          if (GEP->getNumIndices() != 1 || !GEP->isInBounds() ||
              GEP->getType() != Start->getType())
            return false;
  
          if (Explored.count(GEP->getOperand(0)) == 0)
            WorkList.push_back(GEP->getOperand(0));
        }
  
        if (WorkList.back() == V) {
          WorkList.pop_back();
          // We've finished visiting this node, mark it as such.
          Explored.insert(V);
        }
  
        if (auto *PN = dyn_cast<PHINode>(V)) {
          // We cannot transform PHIs on unsplittable basic blocks.
          if (isa<CatchSwitchInst>(PN->getParent()->getTerminator()))
            return false;
          Explored.insert(PN);
          PHIs.insert(PN);
        }
      }
  
      // Explore the PHI nodes further.
      for (auto *PN : PHIs)
        for (Value *Op : PN->incoming_values())
          if (Explored.count(Op) == 0)
            WorkList.push_back(Op);
    }
  
    // Make sure that we can do this. Since we can't insert GEPs in a basic
    // block before a PHI node, we can't easily do this transformation if
    // we have PHI node users of transformed instructions.
    for (Value *Val : Explored) {
      for (Value *Use : Val->uses()) {
  
        auto *PHI = dyn_cast<PHINode>(Use);
        auto *Inst = dyn_cast<Instruction>(Val);
  
        if (Inst == Base || Inst == PHI || !Inst || !PHI ||
            Explored.count(PHI) == 0)
          continue;
  
        if (PHI->getParent() == Inst->getParent())
          return false;
      }
    }
    return true;
  }
  
  // Sets the appropriate insert point on Builder where we can add
  // a replacement Instruction for V (if that is possible).
  static void setInsertionPoint(IRBuilder<> &Builder, Value *V,
                                bool Before = true) {
    if (auto *PHI = dyn_cast<PHINode>(V)) {
      Builder.SetInsertPoint(&*PHI->getParent()->getFirstInsertionPt());
      return;
    }
    if (auto *I = dyn_cast<Instruction>(V)) {
      if (!Before)
        I = &*std::next(I->getIterator());
      Builder.SetInsertPoint(I);
      return;
    }
    if (auto *A = dyn_cast<Argument>(V)) {
      // Set the insertion point in the entry block.
      BasicBlock &Entry = A->getParent()->getEntryBlock();
      Builder.SetInsertPoint(&*Entry.getFirstInsertionPt());
      return;
    }
    // Otherwise, this is a constant and we don't need to set a new
    // insertion point.
    IGC_ASSERT_MESSAGE(isa<Constant>(V), "Setting insertion point for unknown value!");
  }
  
  /// Returns a re-written value of Start as an indexed GEP using Base as a
  /// pointer.
  static Value *rewriteGEPAsOffset(Value *Start, Value *Base,
                                   const DataLayout &DL,
                                   SetVector<Value *> &Explored) {
    // Perform all the substitutions. This is a bit tricky because we can
    // have cycles in our use-def chains.
    // 1. Create the PHI nodes without any incoming values.
    // 2. Create all the other values.
    // 3. Add the edges for the PHI nodes.
    // 4. Emit GEPs to get the original pointers.
    // 5. Remove the original instructions.
    Type *IndexType = IntegerType::get(
        Base->getContext(), DL.getPointerTypeSizeInBits(Start->getType()));
  
    DenseMap<Value *, Value *> NewInsts;
    NewInsts[Base] = ConstantInt::getNullValue(IndexType);
  
    // Create the new PHI nodes, without adding any incoming values.
    for (Value *Val : Explored) {
      if (Val == Base)
        continue;
      // Create empty phi nodes. This avoids cyclic dependencies when creating
      // the remaining instructions.
      if (auto *PHI = dyn_cast<PHINode>(Val))
        NewInsts[PHI] = PHINode::Create(IndexType, PHI->getNumIncomingValues(),
                                        PHI->getName() + ".idx", PHI);
    }
    IRBuilder<> Builder(Base->getContext());
  
    // Create all the other instructions.
    for (Value *Val : Explored) {
  
      if (NewInsts.find(Val) != NewInsts.end())
        continue;
  
      if (auto *CI = dyn_cast<CastInst>(Val)) {
        NewInsts[CI] = NewInsts[CI->getOperand(0)];
        continue;
      }
      if (auto *GEP = dyn_cast<GEPOperator>(Val)) {
        Value *Index = NewInsts[GEP->getOperand(1)] ? NewInsts[GEP->getOperand(1)]
                                                    : GEP->getOperand(1);
        setInsertionPoint(Builder, GEP);
        // Indices might need to be sign extended. GEPs will magically do
        // this, but we need to do it ourselves here.
        if (Index->getType()->getScalarSizeInBits() !=
            NewInsts[GEP->getOperand(0)]->getType()->getScalarSizeInBits()) {
          Index = Builder.CreateSExtOrTrunc(
              Index, NewInsts[GEP->getOperand(0)]->getType(),
              GEP->getOperand(0)->getName() + ".sext");
        }
  
        auto *Op = NewInsts[GEP->getOperand(0)];
        if (isa<ConstantInt>(Op) && dyn_cast<ConstantInt>(Op)->isZero())
          NewInsts[GEP] = Index;
        else
          NewInsts[GEP] = Builder.CreateNSWAdd(
              Op, Index, GEP->getOperand(0)->getName() + ".add");
        continue;
      }
      if (isa<PHINode>(Val))
        continue;
  
      IGC_ASSERT_EXIT_MESSAGE(0, "Unexpected instruction type");
    }
  
    // Add the incoming values to the PHI nodes.
    for (Value *Val : Explored) {
      if (Val == Base)
        continue;
      // All the instructions have been created, we can now add edges to the
      // phi nodes.
      if (auto *PHI = dyn_cast<PHINode>(Val)) {
        PHINode *NewPhi = static_cast<PHINode *>(NewInsts[PHI]);
        for (unsigned I = 0, E = PHI->getNumIncomingValues(); I < E; ++I) {
          Value *NewIncoming = PHI->getIncomingValue(I);
  
          if (NewInsts.find(NewIncoming) != NewInsts.end())
            NewIncoming = NewInsts[NewIncoming];
  
          NewPhi->addIncoming(NewIncoming, PHI->getIncomingBlock(I));
        }
      }
    }
  
    for (Value *Val : Explored) {
      if (Val == Base)
        continue;
  
      // Depending on the type, for external users we have to emit
      // a GEP or a GEP + ptrtoint.
      setInsertionPoint(Builder, Val, false);
  
      // If required, create an inttoptr instruction for Base.
      Value *NewBase = Base;
      if (!Base->getType()->isPointerTy())
        NewBase = Builder.CreateBitOrPointerCast(Base, Start->getType(),
                                                 Start->getName() + "to.ptr");
  
      Value *GEP = Builder.CreateInBoundsGEP(
          Start->getType()->getPointerElementType(), NewBase,
          makeArrayRef(NewInsts[Val]), Val->getName() + ".ptr");
  
      if (!Val->getType()->isPointerTy()) {
        Value *Cast = Builder.CreatePointerCast(GEP, Val->getType(),
                                                Val->getName() + ".conv");
        GEP = Cast;
      }
      Val->replaceAllUsesWith(GEP);
    }
  
    return NewInsts[Start];
  }
  
  /// Looks through GEPs, IntToPtrInsts and PtrToIntInsts in order to express
  /// the input Value as a constant indexed GEP. Returns a pair containing
  /// the GEPs Pointer and Index.
  static std::pair<Value *, Value *>
  getAsConstantIndexedAddress(Value *V, const DataLayout &DL) {
    Type *IndexType = IntegerType::get(V->getContext(),
                                       DL.getPointerTypeSizeInBits(V->getType()));
  
    Constant *Index = ConstantInt::getNullValue(IndexType);
    while (true) {
      if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
        // We accept only inbouds GEPs here to exclude the possibility of
        // overflow.
        if (!GEP->isInBounds())
          break;
        if (GEP->hasAllConstantIndices() && GEP->getNumIndices() == 1 &&
            GEP->getType() == V->getType()) {
          V = GEP->getOperand(0);
          Constant *GEPIndex = static_cast<Constant *>(GEP->getOperand(1));
          Index = ConstantExpr::getAdd(
              Index, ConstantExpr::getSExtOrBitCast(GEPIndex, IndexType));
          continue;
        }
        break;
      }
      if (auto *CI = dyn_cast<IntToPtrInst>(V)) {
        if (!CI->isNoopCast(DL))
          break;
        V = CI->getOperand(0);
        continue;
      }
      if (auto *CI = dyn_cast<PtrToIntInst>(V)) {
        if (!CI->isNoopCast(DL))
          break;
        V = CI->getOperand(0);
        continue;
      }
      break;
    }
    return {V, Index};
  }
  
  /// Converts (CMP GEPLHS, RHS) if this change would make RHS a constant.
  /// We can look through PHIs, GEPs and casts in order to determine a common base
  /// between GEPLHS and RHS.
  static Instruction *transformToIndexedCompare(GEPOperator *GEPLHS, Value *RHS,
                                                ICmpInst::Predicate Cond,
                                                const DataLayout &DL) {
    if (!GEPLHS->hasAllConstantIndices())
      return nullptr;
  
    // Make sure the pointers have the same type.
    if (GEPLHS->getType() != RHS->getType())
      return nullptr;
  
    Value *PtrBase = nullptr, *Index = nullptr;
    std::tie(PtrBase, Index) = getAsConstantIndexedAddress(GEPLHS, DL);
  
    // The set of nodes that will take part in this transformation.
    SetVector<Value *> Nodes;
  
    if (!canRewriteGEPAsOffset(RHS, PtrBase, DL, Nodes))
      return nullptr;
  
    // We know we can re-write this as
    //  ((gep Ptr, OFFSET1) cmp (gep Ptr, OFFSET2)
    // Since we've only looked through inbouds GEPs we know that we
    // can't have overflow on either side. We can therefore re-write
    // this as:
    //   OFFSET1 cmp OFFSET2
    Value *NewRHS = rewriteGEPAsOffset(RHS, PtrBase, DL, Nodes);
  
    // RewriteGEPAsOffset has replaced RHS and all of its uses with a re-written
    // GEP having PtrBase as the pointer base, and has returned in NewRHS the
    // offset. Since Index is the offset of LHS to the base pointer, we will now
    // compare the offsets instead of comparing the pointers.
    return new ICmpInst(ICmpInst::getSignedPredicate(Cond), Index, NewRHS);
  }
  
  /// Fold comparisons between a GEP instruction and something else. At this point
  /// we know that the GEP is on the LHS of the comparison.
  Instruction *InstCombiner::foldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
                                         ICmpInst::Predicate Cond,
                                         Instruction &I) {
    // Don't transform signed compares of GEPs into index compares. Even if the
    // GEP is inbounds, the final add of the base pointer can have signed overflow
    // and would change the result of the icmp.
    // e.g. "&foo[0] <s &foo[1]" can't be folded to "true" because "foo" could be
    // the maximum signed value for the pointer type.
    if (ICmpInst::isSigned(Cond))
      return nullptr;
  
    // Look through bitcasts and addrspacecasts. We do not however want to remove
    // 0 GEPs.
    if (!isa<GetElementPtrInst>(RHS))
      RHS = RHS->stripPointerCasts();
  
    Value *PtrBase = GEPLHS->getOperand(0);
    if (PtrBase == RHS && GEPLHS->isInBounds()) {
      // ((gep Ptr, OFFSET) cmp Ptr)   ---> (OFFSET cmp 0).
      // This transformation (ignoring the base and scales) is valid because we
      // know pointers can't overflow since the gep is inbounds.  See if we can
      // output an optimized form.
      Value *Offset = evaluateGEPOffsetExpression(GEPLHS, *this, DL);
  
      // If not, synthesize the offset the hard way.
      if (!Offset)
        Offset = EmitGEPOffset(GEPLHS);
      return new ICmpInst(ICmpInst::getSignedPredicate(Cond), Offset,
                          Constant::getNullValue(Offset->getType()));
    } else if (GEPOperator *GEPRHS = dyn_cast<GEPOperator>(RHS)) {
      // If the base pointers are different, but the indices are the same, just
      // compare the base pointer.
      if (PtrBase != GEPRHS->getOperand(0)) {
        bool IndicesTheSame = GEPLHS->getNumOperands()==GEPRHS->getNumOperands();
        IndicesTheSame &= GEPLHS->getOperand(0)->getType() ==
                          GEPRHS->getOperand(0)->getType();
        if (IndicesTheSame)
          for (unsigned i = 1, e = GEPLHS->getNumOperands(); i != e; ++i)
            if (GEPLHS->getOperand(i) != GEPRHS->getOperand(i)) {
              IndicesTheSame = false;
              break;
            }
  
        // If all indices are the same, just compare the base pointers.
        if (IndicesTheSame)
          return new ICmpInst(Cond, GEPLHS->getOperand(0), GEPRHS->getOperand(0));
  
        // If we're comparing GEPs with two base pointers that only differ in type
        // and both GEPs have only constant indices or just one use, then fold
        // the compare with the adjusted indices.
        if (GEPLHS->isInBounds() && GEPRHS->isInBounds() &&
            (GEPLHS->hasAllConstantIndices() || GEPLHS->hasOneUse()) &&
            (GEPRHS->hasAllConstantIndices() || GEPRHS->hasOneUse()) &&
            PtrBase->stripPointerCasts() ==
                GEPRHS->getOperand(0)->stripPointerCasts()) {
          Value *LOffset = EmitGEPOffset(GEPLHS);
          Value *ROffset = EmitGEPOffset(GEPRHS);
  
          // If we looked through an addrspacecast between different sized address
          // spaces, the LHS and RHS pointers are different sized
          // integers. Truncate to the smaller one.
          Type *LHSIndexTy = LOffset->getType();
          Type *RHSIndexTy = ROffset->getType();
          if (LHSIndexTy != RHSIndexTy) {
            if (LHSIndexTy->getPrimitiveSizeInBits() <
                RHSIndexTy->getPrimitiveSizeInBits()) {
              ROffset = Builder->CreateTrunc(ROffset, LHSIndexTy);
            } else
              LOffset = Builder->CreateTrunc(LOffset, RHSIndexTy);
          }
  
          Value *Cmp = Builder->CreateICmp(ICmpInst::getSignedPredicate(Cond),
                                           LOffset, ROffset);
          return replaceInstUsesWith(I, Cmp);
        }
  
        // Otherwise, the base pointers are different and the indices are
        // different. Try convert this to an indexed compare by looking through
        // PHIs/casts.
        return transformToIndexedCompare(GEPLHS, RHS, Cond, DL);
      }
  
      // If one of the GEPs has all zero indices, recurse.
      if (GEPLHS->hasAllZeroIndices())
        return foldGEPICmp(GEPRHS, GEPLHS->getOperand(0),
                           ICmpInst::getSwappedPredicate(Cond), I);
  
      // If the other GEP has all zero indices, recurse.
      if (GEPRHS->hasAllZeroIndices())
        return foldGEPICmp(GEPLHS, GEPRHS->getOperand(0), Cond, I);
  
      bool GEPsInBounds = GEPLHS->isInBounds() && GEPRHS->isInBounds();
      if (GEPLHS->getNumOperands() == GEPRHS->getNumOperands()) {
        // If the GEPs only differ by one index, compare it.
        unsigned NumDifferences = 0;  // Keep track of # differences.
        unsigned DiffOperand = 0;     // The operand that differs.
        for (unsigned i = 1, e = GEPRHS->getNumOperands(); i != e; ++i)
          if (GEPLHS->getOperand(i) != GEPRHS->getOperand(i)) {
            if (GEPLHS->getOperand(i)->getType()->getPrimitiveSizeInBits() !=
                     GEPRHS->getOperand(i)->getType()->getPrimitiveSizeInBits()) {
              // Irreconcilable differences.
              NumDifferences = 2;
              break;
            } else {
              if (NumDifferences++) break;
              DiffOperand = i;
            }
          }
  
        if (NumDifferences == 0)   // SAME GEP?
          return replaceInstUsesWith(I, // No comparison is needed here.
                               Builder->getInt1(ICmpInst::isTrueWhenEqual(Cond)));
  
        else if (NumDifferences == 1 && GEPsInBounds) {
          Value *LHSV = GEPLHS->getOperand(DiffOperand);
          Value *RHSV = GEPRHS->getOperand(DiffOperand);
          // Make sure we do a signed comparison here.
          return new ICmpInst(ICmpInst::getSignedPredicate(Cond), LHSV, RHSV);
        }
      }
  
      // Only lower this if the icmp is the only user of the GEP or if we expect
      // the result to fold to a constant!
      if (GEPsInBounds && (isa<ConstantExpr>(GEPLHS) || GEPLHS->hasOneUse()) &&
          (isa<ConstantExpr>(GEPRHS) || GEPRHS->hasOneUse())) {
        // ((gep Ptr, OFFSET1) cmp (gep Ptr, OFFSET2)  --->  (OFFSET1 cmp OFFSET2)
        Value *L = EmitGEPOffset(GEPLHS);
        Value *R = EmitGEPOffset(GEPRHS);
        return new ICmpInst(ICmpInst::getSignedPredicate(Cond), L, R);
      }
    }
  
    // Try convert this to an indexed compare by looking through PHIs/casts as a
    // last resort.
    return transformToIndexedCompare(GEPLHS, RHS, Cond, DL);
  }
  
  Instruction *InstCombiner::foldAllocaCmp(ICmpInst &ICI,
                                           const AllocaInst *Alloca,
                                           const Value *Other) {
    IGC_ASSERT_MESSAGE(ICI.isEquality(), "Cannot fold non-equality comparison.");
  
    // It would be tempting to fold away comparisons between allocas and any
    // pointer not based on that alloca (e.g. an argument). However, even
    // though such pointers cannot alias, they can still compare equal.
    //
    // But LLVM doesn't specify where allocas get their memory, so if the alloca
    // doesn't escape we can argue that it's impossible to guess its value, and we
    // can therefore act as if any such guesses are wrong.
    //
    // The code below checks that the alloca doesn't escape, and that it's only
    // used in a comparison once (the current instruction). The
    // single-comparison-use condition ensures that we're trivially folding all
    // comparisons against the alloca consistently, and avoids the risk of
    // erroneously folding a comparison of the pointer with itself.
  
    unsigned MaxIter = 32; // Break cycles and bound to constant-time.
  
    SmallVector<const Use *, 32> Worklist;
    for (const Use &U : Alloca->uses()) {
      if (Worklist.size() >= MaxIter)
        return nullptr;
      Worklist.push_back(&U);
    }
  
    unsigned NumCmps = 0;
    while (!Worklist.empty()) {
      IGC_ASSERT(Worklist.size() <= MaxIter);
      const Use *U = Worklist.pop_back_val();
      const Value *V = U->getUser();
      --MaxIter;
  
      if (isa<BitCastInst>(V) || isa<GetElementPtrInst>(V) || isa<PHINode>(V) ||
          isa<SelectInst>(V)) {
        // Track the uses.
      } else if (isa<LoadInst>(V)) {
        // Loading from the pointer doesn't escape it.
        continue;
      } else if (const auto *SI = dyn_cast<StoreInst>(V)) {
        // Storing *to* the pointer is fine, but storing the pointer escapes it.
        if (SI->getValueOperand() == U->get())
          return nullptr;
        continue;
      } else if (isa<ICmpInst>(V)) {
        if (NumCmps++)
          return nullptr; // Found more than one cmp.
        continue;
      } else if (const auto *Intrin = dyn_cast<IntrinsicInst>(V)) {
        switch (Intrin->getIntrinsicID()) {
          // These intrinsics don't escape or compare the pointer. Memset is safe
          // because we don't allow ptrtoint. Memcpy and memmove are safe because
          // we don't allow stores, so src cannot point to V.
          case Intrinsic::lifetime_start: case Intrinsic::lifetime_end:
          case Intrinsic::dbg_declare: case Intrinsic::dbg_value:
          case Intrinsic::memcpy: case Intrinsic::memmove: case Intrinsic::memset:
            continue;
          default:
            return nullptr;
        }
      } else {
        return nullptr;
      }
      for (const Use &U : V->uses()) {
        if (Worklist.size() >= MaxIter)
          return nullptr;
        Worklist.push_back(&U);
      }
    }
  
    Type *CmpTy = CmpInst::makeCmpResultType(Other->getType());
    return replaceInstUsesWith(
        ICI,
        ConstantInt::get(CmpTy, !CmpInst::isTrueWhenEqual(ICI.getPredicate())));
  }
  
  /// Fold "icmp pred (X+CI), X".
  Instruction *InstCombiner::foldICmpAddOpConst(Instruction &ICI,
                                                Value *X, ConstantInt *CI,
                                                ICmpInst::Predicate Pred) {
    // From this point on, we know that (X+C <= X) --> (X+C < X) because C != 0,
    // so the values can never be equal.  Similarly for all other "or equals"
    // operators.
  
    // (X+1) <u X        --> X >u (MAXUINT-1)        --> X == 255
    // (X+2) <u X        --> X >u (MAXUINT-2)        --> X > 253
    // (X+MAXUINT) <u X  --> X >u (MAXUINT-MAXUINT)  --> X != 0
    if (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_ULE) {
      Value *R =
        ConstantExpr::getSub(ConstantInt::getAllOnesValue(CI->getType()), CI);
      return new ICmpInst(ICmpInst::ICMP_UGT, X, R);
    }
  
    // (X+1) >u X        --> X <u (0-1)        --> X != 255
    // (X+2) >u X        --> X <u (0-2)        --> X <u 254
    // (X+MAXUINT) >u X  --> X <u (0-MAXUINT)  --> X <u 1  --> X == 0
    if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_UGE)
      return new ICmpInst(ICmpInst::ICMP_ULT, X, ConstantExpr::getNeg(CI));
  
    unsigned BitWidth = CI->getType()->getPrimitiveSizeInBits();
    ConstantInt *SMax = ConstantInt::get(X->getContext(),
                                         APInt::getSignedMaxValue(BitWidth));
  
    // (X+ 1) <s X       --> X >s (MAXSINT-1)          --> X == 127
    // (X+ 2) <s X       --> X >s (MAXSINT-2)          --> X >s 125
    // (X+MAXSINT) <s X  --> X >s (MAXSINT-MAXSINT)    --> X >s 0
    // (X+MINSINT) <s X  --> X >s (MAXSINT-MINSINT)    --> X >s -1
    // (X+ -2) <s X      --> X >s (MAXSINT- -2)        --> X >s 126
    // (X+ -1) <s X      --> X >s (MAXSINT- -1)        --> X != 127
    if (Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SLE)
      return new ICmpInst(ICmpInst::ICMP_SGT, X, ConstantExpr::getSub(SMax, CI));
  
    // (X+ 1) >s X       --> X <s (MAXSINT-(1-1))       --> X != 127
    // (X+ 2) >s X       --> X <s (MAXSINT-(2-1))       --> X <s 126
    // (X+MAXSINT) >s X  --> X <s (MAXSINT-(MAXSINT-1)) --> X <s 1
    // (X+MINSINT) >s X  --> X <s (MAXSINT-(MINSINT-1)) --> X <s -2
    // (X+ -2) >s X      --> X <s (MAXSINT-(-2-1))      --> X <s -126
    // (X+ -1) >s X      --> X <s (MAXSINT-(-1-1))      --> X == -128
  
    IGC_ASSERT(Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_SGE);
    Constant *C = Builder->getInt(CI->getValue()-1);
    return new ICmpInst(ICmpInst::ICMP_SLT, X, ConstantExpr::getSub(SMax, C));
  }
  
  /// Handle "(icmp eq/ne (ashr/lshr AP2, A), AP1)" ->
  /// (icmp eq/ne A, Log2(AP2/AP1)) ->
  /// (icmp eq/ne A, Log2(AP2) - Log2(AP1)).
  Instruction *InstCombiner::foldICmpShrConstConst(ICmpInst &I, Value *A,
                                                   const APInt &AP1,
                                                   const APInt &AP2) {
    IGC_ASSERT_MESSAGE(I.isEquality(), "Cannot fold icmp gt/lt");
  
    auto getICmp = [&I](CmpInst::Predicate Pred, Value *LHS, Value *RHS) {
      if (I.getPredicate() == I.ICMP_NE)
        Pred = CmpInst::getInversePredicate(Pred);
      return new ICmpInst(Pred, LHS, RHS);
    };
  
    // Don't bother doing any work for cases which InstSimplify handles.
    if (AP2 == 0)
      return nullptr;
  
    bool IsAShr = isa<AShrOperator>(I.getOperand(0));
    if (IsAShr) {
      if (AP2.isAllOnesValue())
        return nullptr;
      if (AP2.isNegative() != AP1.isNegative())
        return nullptr;
      if (AP2.sgt(AP1))
        return nullptr;
    }
  
    if (!AP1)
      // 'A' must be large enough to shift out the highest set bit.
      return getICmp(I.ICMP_UGT, A,
                     ConstantInt::get(A->getType(), AP2.logBase2()));
  
    if (AP1 == AP2)
      return getICmp(I.ICMP_EQ, A, ConstantInt::getNullValue(A->getType()));
  
    int Shift;
    if (IsAShr && AP1.isNegative())
      Shift = AP1.countLeadingOnes() - AP2.countLeadingOnes();
    else
      Shift = AP1.countLeadingZeros() - AP2.countLeadingZeros();
  
    if (Shift > 0) {
      if (IsAShr && AP1 == AP2.ashr(Shift)) {
        // There are multiple solutions if we are comparing against -1 and the LHS
        // of the ashr is not a power of two.
        if (AP1.isAllOnesValue() && !AP2.isPowerOf2())
          return getICmp(I.ICMP_UGE, A, ConstantInt::get(A->getType(), Shift));
        return getICmp(I.ICMP_EQ, A, ConstantInt::get(A->getType(), Shift));
      } else if (AP1 == AP2.lshr(Shift)) {
        return getICmp(I.ICMP_EQ, A, ConstantInt::get(A->getType(), Shift));
      }
    }
  
    // Shifting const2 will never be equal to const1.
    // FIXME: This should always be handled by InstSimplify?
    auto *TorF = ConstantInt::get(I.getType(), I.getPredicate() == I.ICMP_NE);
    return replaceInstUsesWith(I, TorF);
  }
  
  /// Handle "(icmp eq/ne (shl AP2, A), AP1)" ->
  /// (icmp eq/ne A, TrailingZeros(AP1) - TrailingZeros(AP2)).
  Instruction *InstCombiner::foldICmpShlConstConst(ICmpInst &I, Value *A,
                                                   const APInt &AP1,
                                                   const APInt &AP2) {
    IGC_ASSERT_MESSAGE(I.isEquality(), "Cannot fold icmp gt/lt");
  
    auto getICmp = [&I](CmpInst::Predicate Pred, Value *LHS, Value *RHS) {
      if (I.getPredicate() == I.ICMP_NE)
        Pred = CmpInst::getInversePredicate(Pred);
      return new ICmpInst(Pred, LHS, RHS);
    };
  
    // Don't bother doing any work for cases which InstSimplify handles.
    if (AP2 == 0)
      return nullptr;
  
    unsigned AP2TrailingZeros = AP2.countTrailingZeros();
  
    if (!AP1 && AP2TrailingZeros != 0)
      return getICmp(
          I.ICMP_UGE, A,
          ConstantInt::get(A->getType(), AP2.getBitWidth() - AP2TrailingZeros));
  
    if (AP1 == AP2)
      return getICmp(I.ICMP_EQ, A, ConstantInt::getNullValue(A->getType()));
  
    // Get the distance between the lowest bits that are set.
    int Shift = AP1.countTrailingZeros() - AP2TrailingZeros;
  
    if (Shift > 0 && AP2.shl(Shift) == AP1)
      return getICmp(I.ICMP_EQ, A, ConstantInt::get(A->getType(), Shift));
  
    // Shifting const2 will never be equal to const1.
    // FIXME: This should always be handled by InstSimplify?
    auto *TorF = ConstantInt::get(I.getType(), I.getPredicate() == I.ICMP_NE);
    return replaceInstUsesWith(I, TorF);
  }
  
  /// The caller has matched a pattern of the form:
  ///   I = icmp ugt (add (add A, B), CI2), CI1
  /// If this is of the form:
  ///   sum = a + b
  ///   if (sum+128 >u 255)
  /// Then replace it with llvm.sadd.with.overflow.i8.
  ///
  static Instruction *processUGT_ADDCST_ADD(ICmpInst &I, Value *A, Value *B,
                                            ConstantInt *CI2, ConstantInt *CI1,
                                            InstCombiner &IC) {
    // The transformation we're trying to do here is to transform this into an
    // llvm.sadd.with.overflow.  To do this, we have to replace the original add
    // with a narrower add, and discard the add-with-constant that is part of the
    // range check (if we can't eliminate it, this isn't profitable).
  
    // In order to eliminate the add-with-constant, the compare can be its only
    // use.
    Instruction *AddWithCst = cast<Instruction>(I.getOperand(0));
    if (!AddWithCst->hasOneUse())
      return nullptr;
  
    // If CI2 is 2^7, 2^15, 2^31, then it might be an sadd.with.overflow.
    if (!CI2->getValue().isPowerOf2())
      return nullptr;
    unsigned NewWidth = CI2->getValue().countTrailingZeros();
    if (NewWidth != 7 && NewWidth != 15 && NewWidth != 31)
      return nullptr;
  
    // The width of the new add formed is 1 more than the bias.
    ++NewWidth;
  
    // Check to see that CI1 is an all-ones value with NewWidth bits.
    if (CI1->getBitWidth() == NewWidth ||
        CI1->getValue() != APInt::getLowBitsSet(CI1->getBitWidth(), NewWidth))
      return nullptr;
  
    // This is only really a signed overflow check if the inputs have been
    // sign-extended; check for that condition. For example, if CI2 is 2^31 and
    // the operands of the add are 64 bits wide, we need at least 33 sign bits.
    unsigned NeededSignBits = CI1->getBitWidth() - NewWidth + 1;
    if (IC.ComputeNumSignBits(A, 0, &I) < NeededSignBits ||
        IC.ComputeNumSignBits(B, 0, &I) < NeededSignBits)
      return nullptr;
  
    // In order to replace the original add with a narrower
    // llvm.sadd.with.overflow, the only uses allowed are the add-with-constant
    // and truncates that discard the high bits of the add.  Verify that this is
    // the case.
    Instruction *OrigAdd = cast<Instruction>(AddWithCst->getOperand(0));
    for (User *U : OrigAdd->users()) {
      if (U == AddWithCst)
        continue;
  
      // Only accept truncates for now.  We would really like a nice recursive
      // predicate like SimplifyDemandedBits, but which goes downwards the use-def
      // chain to see which bits of a value are actually demanded.  If the
      // original add had another add which was then immediately truncated, we
      // could still do the transformation.
      TruncInst *TI = dyn_cast<TruncInst>(U);
      if (!TI || TI->getType()->getPrimitiveSizeInBits() > NewWidth)
        return nullptr;
    }
  
    // If the pattern matches, truncate the inputs to the narrower type and
    // use the sadd_with_overflow intrinsic to efficiently compute both the
    // result and the overflow bit.
    Type *NewType = IntegerType::get(OrigAdd->getContext(), NewWidth);
    Value *F = Intrinsic::getDeclaration(I.getModule(),
                                         Intrinsic::sadd_with_overflow, NewType);
  
    InstCombiner::BuilderTy *Builder = IC.Builder;
  
    // Put the new code above the original add, in case there are any uses of the
    // add between the add and the compare.
    Builder->SetInsertPoint(OrigAdd);
  
    Value *TruncA = Builder->CreateTrunc(A, NewType, A->getName() + ".trunc");
    Value *TruncB = Builder->CreateTrunc(B, NewType, B->getName() + ".trunc");
    CallInst *Call = Builder->CreateCall(F, {TruncA, TruncB}, "sadd");
    Value *Add = Builder->CreateExtractValue(Call, 0, "sadd.result");
    Value *ZExt = Builder->CreateZExt(Add, OrigAdd->getType());
  
    // The inner add was the result of the narrow add, zero extended to the
    // wider type.  Replace it with the result computed by the intrinsic.
    IC.replaceInstUsesWith(*OrigAdd, ZExt);
  
    // The original icmp gets replaced with the overflow value.
    return ExtractValueInst::Create(Call, 1, "sadd.overflow");
  }
  
  // Fold icmp Pred X, C.
  Instruction *InstCombiner::foldICmpWithConstant(ICmpInst &Cmp) {
    CmpInst::Predicate Pred = Cmp.getPredicate();
    Value *X = Cmp.getOperand(0);
  
    const APInt *C = nullptr;
    if (!match(Cmp.getOperand(1), m_APInt(C)))
      return nullptr;
  
    Value *A = nullptr, *B = nullptr;
  
    // Match the following pattern, which is a common idiom when writing
    // overflow-safe integer arithmetic functions. The source performs an addition
    // in wider type and explicitly checks for overflow using comparisons against
    // INT_MIN and INT_MAX. Simplify by using the sadd_with_overflow intrinsic.
    //
    // TODO: This could probably be generalized to handle other overflow-safe
    // operations if we worked out the formulas to compute the appropriate magic
    // constants.
    //
    // sum = a + b
    // if (sum+128 >u 255)  ...  -> llvm.sadd.with.overflow.i8
    {
      ConstantInt *CI2 = nullptr; // I = icmp ugt (add (add A, B), CI2), CI
      if (Pred == ICmpInst::ICMP_UGT &&
          match(X, m_Add(m_Add(m_Value(A), m_Value(B)), m_ConstantInt(CI2))))
        if (Instruction *Res = processUGT_ADDCST_ADD(
                Cmp, A, B, CI2, cast<ConstantInt>(Cmp.getOperand(1)), *this))
          return Res;
    }
  
    // (icmp sgt smin(PosA, B) 0) -> (icmp sgt B 0)
    if (*C == 0 && Pred == ICmpInst::ICMP_SGT) {
      SelectPatternResult SPR = matchSelectPattern(X, A, B);
      if (SPR.Flavor == SPF_SMIN) {
        if (isKnownPositive(A, DL))
          return new ICmpInst(Pred, B, Cmp.getOperand(1));
        if (isKnownPositive(B, DL))
          return new ICmpInst(Pred, A, Cmp.getOperand(1));
      }
    }
  
    // FIXME: Use m_APInt to allow folds for splat constants.
    ConstantInt *CI = dyn_cast<ConstantInt>(Cmp.getOperand(1));
    if (!CI)
      return nullptr;
  
    // Canonicalize icmp instructions based on dominating conditions.
    BasicBlock *Parent = Cmp.getParent();
    BasicBlock *Dom = Parent->getSinglePredecessor();
    auto *BI = Dom ? dyn_cast<BranchInst>(Dom->getTerminator()) : nullptr;
    ICmpInst::Predicate Pred2 = ICmpInst::Predicate::BAD_ICMP_PREDICATE;
    BasicBlock *TrueBB = nullptr, *FalseBB = nullptr;
    ConstantInt *CI2 = nullptr;
    if (BI && match(BI, m_Br(m_ICmp(Pred2, m_Specific(X), m_ConstantInt(CI2)),
                             TrueBB, FalseBB)) &&
        TrueBB != FalseBB) {
      ConstantRange CR =
          ConstantRange::makeAllowedICmpRegion(Pred, CI->getValue());
      ConstantRange DominatingCR =
          (Parent == TrueBB)
              ? ConstantRange::makeExactICmpRegion(Pred2, CI2->getValue())
              : ConstantRange::makeExactICmpRegion(
                    CmpInst::getInversePredicate(Pred2), CI2->getValue());
      ConstantRange Intersection = DominatingCR.intersectWith(CR);
      ConstantRange Difference = DominatingCR.difference(CR);
      if (Intersection.isEmptySet())
        return replaceInstUsesWith(Cmp, Builder->getFalse());
      if (Difference.isEmptySet())
        return replaceInstUsesWith(Cmp, Builder->getTrue());
  
      // If this is a normal comparison, it demands all bits. If it is a sign
      // bit comparison, it only demands the sign bit.
      bool UnusedBit = false;
      bool IsSignBit = isSignBitCheck(Pred, CI->getValue(), UnusedBit);
  
      // Canonicalizing a sign bit comparison that gets used in a branch,
      // pessimizes codegen by generating branch on zero instruction instead
      // of a test and branch. So we avoid canonicalizing in such situations
      // because test and branch instruction has better branch displacement
      // than compare and branch instruction.
      if (!isBranchOnSignBitCheck(Cmp, IsSignBit) && !Cmp.isEquality()) {
        if (auto *AI = Intersection.getSingleElement())
          return new ICmpInst(ICmpInst::ICMP_EQ, X, Builder->getInt(*AI));
        if (auto *AD = Difference.getSingleElement())
          return new ICmpInst(ICmpInst::ICMP_NE, X, Builder->getInt(*AD));
      }
    }
  
    return nullptr;
  }
  
  /// Fold icmp (trunc X, Y), C.
  Instruction *InstCombiner::foldICmpTruncConstant(ICmpInst &Cmp,
                                                   Instruction *Trunc,
                                                   const APInt *C) {
    ICmpInst::Predicate Pred = Cmp.getPredicate();
    Value *X = Trunc->getOperand(0);
    if (*C == 1 && C->getBitWidth() > 1) {
      // icmp slt trunc(signum(V)) 1 --> icmp slt V, 1
      Value *V = nullptr;
      if (Pred == ICmpInst::ICMP_SLT && match(X, m_Signum(m_Value(V))))
        return new ICmpInst(ICmpInst::ICMP_SLT, V,
                            ConstantInt::get(V->getType(), 1));
    }
  
    if (Cmp.isEquality() && Trunc->hasOneUse()) {
      // Simplify icmp eq (trunc x to i8), 42 -> icmp eq x, 42|highbits if all
      // of the high bits truncated out of x are known.
      unsigned DstBits = Trunc->getType()->getScalarSizeInBits(),
               SrcBits = X->getType()->getScalarSizeInBits();
      APInt KnownZero(SrcBits, 0), KnownOne(SrcBits, 0);
      computeKnownBits(X, KnownZero, KnownOne, 0, &Cmp);
  
      // If all the high bits are known, we can do this xform.
      if ((KnownZero | KnownOne).countLeadingOnes() >= SrcBits - DstBits) {
        // Pull in the high bits from known-ones set.
        APInt NewRHS = C->zext(SrcBits);
        NewRHS |= KnownOne & APInt::getHighBitsSet(SrcBits, SrcBits - DstBits);
        return new ICmpInst(Pred, X, ConstantInt::get(X->getType(), NewRHS));
      }
    }
  
    return nullptr;
  }
  
  /// Fold icmp (xor X, Y), C.
  Instruction *InstCombiner::foldICmpXorConstant(ICmpInst &Cmp,
                                                 BinaryOperator *Xor,
                                                 const APInt *C) {
    Value *X = Xor->getOperand(0);
    Value *Y = Xor->getOperand(1);
    const APInt *XorC = nullptr;
    if (!match(Y, m_APInt(XorC)))
      return nullptr;
  
    // If this is a comparison that tests the signbit (X < 0) or (x > -1),
    // fold the xor.
    ICmpInst::Predicate Pred = Cmp.getPredicate();
    if ((Pred == ICmpInst::ICMP_SLT && *C == 0) ||
        (Pred == ICmpInst::ICMP_SGT && C->isAllOnesValue())) {
  
      // If the sign bit of the XorCst is not set, there is no change to
      // the operation, just stop using the Xor.
      if (!XorC->isNegative()) {
        Cmp.setOperand(0, X);
        Worklist.Add(Xor);
        return &Cmp;
      }
  
      // Was the old condition true if the operand is positive?
      bool isTrueIfPositive = Pred == ICmpInst::ICMP_SGT;
  
      // If so, the new one isn't.
      isTrueIfPositive ^= true;
  
      Constant *CmpConstant = cast<Constant>(Cmp.getOperand(1));
      if (isTrueIfPositive)
        return new ICmpInst(ICmpInst::ICMP_SGT, X, SubOne(CmpConstant));
      else
        return new ICmpInst(ICmpInst::ICMP_SLT, X, AddOne(CmpConstant));
    }
  
    if (Xor->hasOneUse()) {
      // (icmp u/s (xor X SignBit), C) -> (icmp s/u X, (xor C SignBit))
      if (!Cmp.isEquality() && XorC->isSignBit()) {
        Pred = Cmp.isSigned() ? Cmp.getUnsignedPredicate()
                              : Cmp.getSignedPredicate();
        return new ICmpInst(Pred, X, ConstantInt::get(X->getType(), *C ^ *XorC));
      }
  
      // (icmp u/s (xor X ~SignBit), C) -> (icmp s/u X, (xor C ~SignBit))
      if (!Cmp.isEquality() && XorC->isMaxSignedValue()) {
        Pred = Cmp.isSigned() ? Cmp.getUnsignedPredicate()
                              : Cmp.getSignedPredicate();
        Pred = Cmp.getSwappedPredicate(Pred);
        return new ICmpInst(Pred, X, ConstantInt::get(X->getType(), *C ^ *XorC));
      }
    }
  
    // (icmp ugt (xor X, C), ~C) -> (icmp ult X, C)
    //   iff -C is a power of 2
    if (Pred == ICmpInst::ICMP_UGT && *XorC == ~(*C) && (*C + 1).isPowerOf2())
      return new ICmpInst(ICmpInst::ICMP_ULT, X, Y);
  
    // (icmp ult (xor X, C), -C) -> (icmp uge X, C)
    //   iff -C is a power of 2
    if (Pred == ICmpInst::ICMP_ULT && *XorC == -(*C) && C->isPowerOf2())
      return new ICmpInst(ICmpInst::ICMP_UGE, X, Y);
  
    return nullptr;
  }
  
  /// Fold icmp (and (sh X, Y), C2), C1.
  Instruction *InstCombiner::foldICmpAndShift(ICmpInst &Cmp, BinaryOperator *And,
                                              const APInt *C1, const APInt *C2) {
    BinaryOperator *Shift = dyn_cast<BinaryOperator>(And->getOperand(0));
    if (!Shift || !Shift->isShift())
      return nullptr;
  
    // If this is: (X >> C3) & C2 != C1 (where any shift and any compare could
    // exist), turn it into (X & (C2 << C3)) != (C1 << C3). This happens a LOT in
    // code produced by the clang front-end, for bitfield access.
    // This seemingly simple opportunity to fold away a shift turns out to be
    // rather complicated. See PR17827 for details.
    unsigned ShiftOpcode = Shift->getOpcode();
    bool IsShl = ShiftOpcode == Instruction::Shl;
    const APInt *C3 = nullptr;
    if (match(Shift->getOperand(1), m_APInt(C3))) {
      bool CanFold = false;
      if (ShiftOpcode == Instruction::AShr) {
        // There may be some constraints that make this possible, but nothing
        // simple has been discovered yet.
        CanFold = false;
      } else if (ShiftOpcode == Instruction::Shl) {
        // For a left shift, we can fold if the comparison is not signed. We can
        // also fold a signed comparison if the mask value and comparison value
        // are not negative. These constraints may not be obvious, but we can
        // prove that they are correct using an SMT solver.
        if (!Cmp.isSigned() || (!C2->isNegative() && !C1->isNegative()))
          CanFold = true;
      } else if (ShiftOpcode == Instruction::LShr) {
        // For a logical right shift, we can fold if the comparison is not signed.
        // We can also fold a signed comparison if the shifted mask value and the
        // shifted comparison value are not negative. These constraints may not be
        // obvious, but we can prove that they are correct using an SMT solver.
        if (!Cmp.isSigned() ||
            (!C2->shl(*C3).isNegative() && !C1->shl(*C3).isNegative()))
          CanFold = true;
      }
  
      if (CanFold) {
        APInt NewCst = IsShl ? C1->lshr(*C3) : C1->shl(*C3);
        APInt SameAsC1 = IsShl ? NewCst.shl(*C3) : NewCst.lshr(*C3);
        // Check to see if we are shifting out any of the bits being compared.
        if (SameAsC1 != *C1) {
          // If we shifted bits out, the fold is not going to work out. As a
          // special case, check to see if this means that the result is always
          // true or false now.
          if (Cmp.getPredicate() == ICmpInst::ICMP_EQ)
            return replaceInstUsesWith(Cmp, ConstantInt::getFalse(Cmp.getType()));
          if (Cmp.getPredicate() == ICmpInst::ICMP_NE)
            return replaceInstUsesWith(Cmp, ConstantInt::getTrue(Cmp.getType()));
        } else {
          Cmp.setOperand(1, ConstantInt::get(And->getType(), NewCst));
          APInt NewAndCst = IsShl ? C2->lshr(*C3) : C2->shl(*C3);
          And->setOperand(1, ConstantInt::get(And->getType(), NewAndCst));
          And->setOperand(0, Shift->getOperand(0));
          Worklist.Add(Shift); // Shift is dead.
          return &Cmp;
        }
      }
    }
  
    // Turn ((X >> Y) & C2) == 0  into  (X & (C2 << Y)) == 0.  The latter is
    // preferable because it allows the C2 << Y expression to be hoisted out of a
    // loop if Y is invariant and X is not.
    if (Shift->hasOneUse() && *C1 == 0 && Cmp.isEquality() &&
        !Shift->isArithmeticShift() && !isa<Constant>(Shift->getOperand(0))) {
      // Compute C2 << Y.
      Value *NewShift =
          IsShl ? Builder->CreateLShr(And->getOperand(1), Shift->getOperand(1))
                : Builder->CreateShl(And->getOperand(1), Shift->getOperand(1));
  
      // Compute X & (C2 << Y).
      Value *NewAnd = Builder->CreateAnd(Shift->getOperand(0), NewShift);
      Cmp.setOperand(0, NewAnd);
      return &Cmp;
    }
  
    return nullptr;
  }
  
  /// Fold icmp (and X, C2), C1.
  Instruction *InstCombiner::foldICmpAndConstConst(ICmpInst &Cmp,
                                                   BinaryOperator *And,
                                                   const APInt *C1) {
    const APInt *C2 = nullptr;
    if (!match(And->getOperand(1), m_APInt(C2)))
      return nullptr;
  
    if (!And->hasOneUse() || !And->getOperand(0)->hasOneUse())
      return nullptr;
  
    // If the LHS is an 'and' of a truncate and we can widen the and/compare to
    // the input width without changing the value produced, eliminate the cast:
    //
    // icmp (and (trunc W), C2), C1 -> icmp (and W, C2'), C1'
    //
    // We can do this transformation if the constants do not have their sign bits
    // set or if it is an equality comparison. Extending a relational comparison
    // when we're checking the sign bit would not work.
    Value *W = nullptr;
    if (match(And->getOperand(0), m_Trunc(m_Value(W))) &&
        (Cmp.isEquality() || (!C1->isNegative() && !C2->isNegative()))) {
      // TODO: Is this a good transform for vectors? Wider types may reduce
      // throughput. Should this transform be limited (even for scalars) by using
      // ShouldChangeType()?
      if (!Cmp.getType()->isVectorTy()) {
        Type *WideType = W->getType();
        unsigned WideScalarBits = WideType->getScalarSizeInBits();
        Constant *ZextC1 = ConstantInt::get(WideType, C1->zext(WideScalarBits));
        Constant *ZextC2 = ConstantInt::get(WideType, C2->zext(WideScalarBits));
        Value *NewAnd = Builder->CreateAnd(W, ZextC2, And->getName());
        return new ICmpInst(Cmp.getPredicate(), NewAnd, ZextC1);
      }
    }
  
    if (Instruction *I = foldICmpAndShift(Cmp, And, C1, C2))
      return I;
  
    // (icmp pred (and (or (lshr A, B), A), 1), 0) -->
    // (icmp pred (and A, (or (shl 1, B), 1), 0))
    //
    // iff pred isn't signed
    if (!Cmp.isSigned() && *C1 == 0 && match(And->getOperand(1), m_One())) {
      Constant *One = cast<Constant>(And->getOperand(1));
      Value *Or = And->getOperand(0);
      Value *A = nullptr, *B = nullptr, *LShr = nullptr;
      if (match(Or, m_Or(m_Value(LShr), m_Value(A))) &&
          match(LShr, m_LShr(m_Specific(A), m_Value(B)))) {
        unsigned UsesRemoved = 0;
        if (And->hasOneUse())
          ++UsesRemoved;
        if (Or->hasOneUse())
          ++UsesRemoved;
        if (LShr->hasOneUse())
          ++UsesRemoved;
  
        // Compute A & ((1 << B) | 1)
        Value *NewOr = nullptr;
        if (auto *C = dyn_cast<Constant>(B)) {
          if (UsesRemoved >= 1)
            NewOr = ConstantExpr::getOr(ConstantExpr::getNUWShl(One, C), One);
        } else {
          if (UsesRemoved >= 3)
            NewOr = Builder->CreateOr(Builder->CreateShl(One, B, LShr->getName(),
                                                         /*HasNUW=*/true),
                                      One, Or->getName());
        }
        if (NewOr) {
          Value *NewAnd = Builder->CreateAnd(A, NewOr, And->getName());
          Cmp.setOperand(0, NewAnd);
          return &Cmp;
        }
      }
    }
  
    // (X & C2) > C1 --> (X & C2) != 0, if any bit set in (X & C2) will produce a
    // result greater than C1.
    unsigned NumTZ = C2->countTrailingZeros();
    if (Cmp.getPredicate() == ICmpInst::ICMP_UGT && NumTZ < C2->getBitWidth() &&
        APInt::getOneBitSet(C2->getBitWidth(), NumTZ).ugt(*C1)) {
      Constant *Zero = Constant::getNullValue(And->getType());
      return new ICmpInst(ICmpInst::ICMP_NE, And, Zero);
    }
  
    return nullptr;
  }
  
  /// Fold icmp (and X, Y), C.
  Instruction *InstCombiner::foldICmpAndConstant(ICmpInst &Cmp,
                                                 BinaryOperator *And,
                                                 const APInt *C) {
    if (Instruction *I = foldICmpAndConstConst(Cmp, And, C))
      return I;
  
    // TODO: These all require that Y is constant too, so refactor with the above.
  
    // Try to optimize things like "A[i] & 42 == 0" to index computations.
    Value *X = And->getOperand(0);
    Value *Y = And->getOperand(1);
    if (auto *LI = dyn_cast<LoadInst>(X))
      if (auto *GEP = dyn_cast<GetElementPtrInst>(LI->getOperand(0)))
        if (auto *GV = dyn_cast<GlobalVariable>(GEP->getOperand(0)))
          if (GV->isConstant() && GV->hasDefinitiveInitializer() &&
              !LI->isVolatile() && isa<ConstantInt>(Y)) {
            ConstantInt *C2 = cast<ConstantInt>(Y);
            if (Instruction *Res = foldCmpLoadFromIndexedGlobal(GEP, GV, Cmp, C2))
              return Res;
          }
  
    if (!Cmp.isEquality())
      return nullptr;
  
    // X & -C == -C -> X >  u ~C
    // X & -C != -C -> X <= u ~C
    //   iff C is a power of 2
    if (Cmp.getOperand(1) == Y && (-(*C)).isPowerOf2()) {
      auto NewPred = Cmp.getPredicate() == CmpInst::ICMP_EQ ? CmpInst::ICMP_UGT
                                                            : CmpInst::ICMP_ULE;
      return new ICmpInst(NewPred, X, SubOne(cast<Constant>(Cmp.getOperand(1))));
    }
  
    // (X & C2) == 0 -> (trunc X) >= 0
    // (X & C2) != 0 -> (trunc X) <  0
    //   iff C2 is a power of 2 and it masks the sign bit of a legal integer type.
    const APInt *C2 = nullptr;
    if (And->hasOneUse() && *C == 0 && match(Y, m_APInt(C2))) {
      int32_t ExactLogBase2 = C2->exactLogBase2();
      if (ExactLogBase2 != -1 && DL.isLegalInteger(ExactLogBase2 + 1)) {
        Type *NTy = IntegerType::get(Cmp.getContext(), ExactLogBase2 + 1);
        if (And->getType()->isVectorTy())
          NTy = VectorType::get(NTy, And->getType()->getVectorNumElements());
        Value *Trunc = Builder->CreateTrunc(X, NTy);
        auto NewPred = Cmp.getPredicate() == CmpInst::ICMP_EQ ? CmpInst::ICMP_SGE
                                                              : CmpInst::ICMP_SLT;
        return new ICmpInst(NewPred, Trunc, Constant::getNullValue(NTy));
      }
    }
  
    return nullptr;
  }
  
  /// Fold icmp (or X, Y), C.
  Instruction *InstCombiner::foldICmpOrConstant(ICmpInst &Cmp, BinaryOperator *Or,
                                                const APInt *C) {
    ICmpInst::Predicate Pred = Cmp.getPredicate();
    if (*C == 1) {
      // icmp slt signum(V) 1 --> icmp slt V, 1
      Value *V = nullptr;
      if (Pred == ICmpInst::ICMP_SLT && match(Or, m_Signum(m_Value(V))))
        return new ICmpInst(ICmpInst::ICMP_SLT, V,
                            ConstantInt::get(V->getType(), 1));
    }
  
    if (!Cmp.isEquality() || *C != 0 || !Or->hasOneUse())
      return nullptr;
  
    Value *P = nullptr, *Q = nullptr;
    if (match(Or, m_Or(m_PtrToInt(m_Value(P)), m_PtrToInt(m_Value(Q))))) {
      // Simplify icmp eq (or (ptrtoint P), (ptrtoint Q)), 0
      // -> and (icmp eq P, null), (icmp eq Q, null).
      Value *CmpP =
          Builder->CreateICmp(Pred, P, ConstantInt::getNullValue(P->getType()));
      Value *CmpQ =
          Builder->CreateICmp(Pred, Q, ConstantInt::getNullValue(Q->getType()));
      auto LogicOpc = Pred == ICmpInst::Predicate::ICMP_EQ ? Instruction::And
                                                           : Instruction::Or;
      return BinaryOperator::Create(LogicOpc, CmpP, CmpQ);
    }
  
    return nullptr;
  }
  
  /// Fold icmp (mul X, Y), C.
  Instruction *InstCombiner::foldICmpMulConstant(ICmpInst &Cmp,
                                                 BinaryOperator *Mul,
                                                 const APInt *C) {
    const APInt *MulC = nullptr;
    if (!match(Mul->getOperand(1), m_APInt(MulC)))
      return nullptr;
  
    // If this is a test of the sign bit and the multiply is sign-preserving with
    // a constant operand, use the multiply LHS operand instead.
    ICmpInst::Predicate Pred = Cmp.getPredicate();
    if (isSignTest(Pred, *C) && Mul->hasNoSignedWrap()) {
      if (MulC->isNegative())
        Pred = ICmpInst::getSwappedPredicate(Pred);
      return new ICmpInst(Pred, Mul->getOperand(0),
                          Constant::getNullValue(Mul->getType()));
    }
  
    return nullptr;
  }
  
  /// Fold icmp (shl 1, Y), C.
  static Instruction *foldICmpShlOne(ICmpInst &Cmp, Instruction *Shl,
                                     const APInt *C) {
    Value *Y = nullptr;
    if (!match(Shl, m_Shl(m_One(), m_Value(Y))))
      return nullptr;
  
    Type *ShiftType = Shl->getType();
    uint32_t TypeBits = C->getBitWidth();
    bool CIsPowerOf2 = C->isPowerOf2();
    ICmpInst::Predicate Pred = Cmp.getPredicate();
    if (Cmp.isUnsigned()) {
      // (1 << Y) pred C -> Y pred Log2(C)
      if (!CIsPowerOf2) {
        // (1 << Y) <  30 -> Y <= 4
        // (1 << Y) <= 30 -> Y <= 4
        // (1 << Y) >= 30 -> Y >  4
        // (1 << Y) >  30 -> Y >  4
        if (Pred == ICmpInst::ICMP_ULT)
          Pred = ICmpInst::ICMP_ULE;
        else if (Pred == ICmpInst::ICMP_UGE)
          Pred = ICmpInst::ICMP_UGT;
      }
  
      // (1 << Y) >= 2147483648 -> Y >= 31 -> Y == 31
      // (1 << Y) <  2147483648 -> Y <  31 -> Y != 31
      unsigned CLog2 = C->logBase2();
      if (CLog2 == TypeBits - 1) {
        if (Pred == ICmpInst::ICMP_UGE)
          Pred = ICmpInst::ICMP_EQ;
        else if (Pred == ICmpInst::ICMP_ULT)
          Pred = ICmpInst::ICMP_NE;
      }
      return new ICmpInst(Pred, Y, ConstantInt::get(ShiftType, CLog2));
    } else if (Cmp.isSigned()) {
      Constant *BitWidthMinusOne = ConstantInt::get(ShiftType, TypeBits - 1);
      if (C->isAllOnesValue()) {
        // (1 << Y) <= -1 -> Y == 31
        if (Pred == ICmpInst::ICMP_SLE)
          return new ICmpInst(ICmpInst::ICMP_EQ, Y, BitWidthMinusOne);
  
        // (1 << Y) >  -1 -> Y != 31
        if (Pred == ICmpInst::ICMP_SGT)
          return new ICmpInst(ICmpInst::ICMP_NE, Y, BitWidthMinusOne);
      } else if (!(*C)) {
        // (1 << Y) <  0 -> Y == 31
        // (1 << Y) <= 0 -> Y == 31
        if (Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SLE)
          return new ICmpInst(ICmpInst::ICMP_EQ, Y, BitWidthMinusOne);
  
        // (1 << Y) >= 0 -> Y != 31
        // (1 << Y) >  0 -> Y != 31
        if (Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_SGE)
          return new ICmpInst(ICmpInst::ICMP_NE, Y, BitWidthMinusOne);
      }
    } else if (Cmp.isEquality() && CIsPowerOf2) {
      return new ICmpInst(Pred, Y, ConstantInt::get(ShiftType, C->logBase2()));
    }
  
    return nullptr;
  }
  
  /// Fold icmp (shl X, Y), C.
  Instruction *InstCombiner::foldICmpShlConstant(ICmpInst &Cmp,
                                                 BinaryOperator *Shl,
                                                 const APInt *C) {
    const APInt *ShiftVal = nullptr;
    if (Cmp.isEquality() && match(Shl->getOperand(0), m_APInt(ShiftVal)))
      return foldICmpShlConstConst(Cmp, Shl->getOperand(1), *C, *ShiftVal);
  
    const APInt *ShiftAmt = nullptr;
    if (!match(Shl->getOperand(1), m_APInt(ShiftAmt)))
      return foldICmpShlOne(Cmp, Shl, C);
  
    // Check that the shift amount is in range. If not, don't perform undefined
    // shifts. When the shift is visited, it will be simplified.
    unsigned TypeBits = C->getBitWidth();
    if (ShiftAmt->uge(TypeBits))
      return nullptr;
  
    ICmpInst::Predicate Pred = Cmp.getPredicate();
    Value *X = Shl->getOperand(0);
    if (Cmp.isEquality()) {
      // If the shift is NUW, then it is just shifting out zeros, no need for an
      // AND.
      Constant *LShrC = ConstantInt::get(Shl->getType(), C->lshr(*ShiftAmt));
      if (Shl->hasNoUnsignedWrap())
        return new ICmpInst(Pred, X, LShrC);
  
      // If the shift is NSW and we compare to 0, then it is just shifting out
      // sign bits, no need for an AND either.
      if (Shl->hasNoSignedWrap() && *C == 0)
        return new ICmpInst(Pred, X, LShrC);
  
      if (Shl->hasOneUse()) {
        // Otherwise, strength reduce the shift into an and.
        Constant *Mask = ConstantInt::get(Shl->getType(),
            APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt->getZExtValue()));
  
        Value *And = Builder->CreateAnd(X, Mask, Shl->getName() + ".mask");
        return new ICmpInst(Pred, And, LShrC);
      }
    }
  
    // If this is a signed comparison to 0 and the shift is sign preserving,
    // use the shift LHS operand instead; isSignTest may change 'Pred', so only
    // do that if we're sure to not continue on in this function.
    if (Shl->hasNoSignedWrap() && isSignTest(Pred, *C))
      return new ICmpInst(Pred, X, Constant::getNullValue(X->getType()));
  
    // Otherwise, if this is a comparison of the sign bit, simplify to and/test.
    bool TrueIfSigned = false;
    if (Shl->hasOneUse() && isSignBitCheck(Pred, *C, TrueIfSigned)) {
      // (X << 31) <s 0  --> (X & 1) != 0
      Constant *Mask = ConstantInt::get(
          X->getType(),
          APInt::getOneBitSet(TypeBits, TypeBits - ShiftAmt->getZExtValue() - 1));
      Value *And = Builder->CreateAnd(X, Mask, Shl->getName() + ".mask");
      return new ICmpInst(TrueIfSigned ? ICmpInst::ICMP_NE : ICmpInst::ICMP_EQ,
                          And, Constant::getNullValue(And->getType()));
    }
  
    // When the shift is nuw and pred is >u or <=u, comparison only really happens
    // in the pre-shifted bits. Since InstSimplify canonicalizes <=u into <u, the
    // <=u case can be further converted to match <u (see below).
    if (Shl->hasNoUnsignedWrap() &&
        (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_ULT)) {
      // Derivation for the ult case:
      // (X << S) <=u C is equiv to X <=u (C >> S) for all C
      // (X << S) <u (C + 1) is equiv to X <u (C >> S) + 1 if C <u ~0u
      // (X << S) <u C is equiv to X <u ((C - 1) >> S) + 1 if C >u 0
      IGC_ASSERT_MESSAGE((Pred != ICmpInst::ICMP_ULT || C->ugt(0)), "Encountered `ult 0` that should have been eliminated by InstSimplify.");
      APInt ShiftedC = Pred == ICmpInst::ICMP_ULT ? (*C - 1).lshr(*ShiftAmt) + 1
                                                  : C->lshr(*ShiftAmt);
      return new ICmpInst(Pred, X, ConstantInt::get(X->getType(), ShiftedC));
    }
  
    // Transform (icmp pred iM (shl iM %v, N), C)
    // -> (icmp pred i(M-N) (trunc %v iM to i(M-N)), (trunc (C>>N))
    // Transform the shl to a trunc if (trunc (C>>N)) has no loss and M-N.
    // This enables us to get rid of the shift in favor of a trunc that may be
    // free on the target. It has the additional benefit of comparing to a
    // smaller constant that may be more target-friendly.
    unsigned Amt = ShiftAmt->getLimitedValue(TypeBits - 1);
    if (Shl->hasOneUse() && Amt != 0 && C->countTrailingZeros() >= Amt &&
        DL.isLegalInteger(TypeBits - Amt)) {
      Type *TruncTy = IntegerType::get(Cmp.getContext(), TypeBits - Amt);
      if (X->getType()->isVectorTy())
        TruncTy = VectorType::get(TruncTy, X->getType()->getVectorNumElements());
      Constant *NewC =
          ConstantInt::get(TruncTy, C->ashr(*ShiftAmt).trunc(TypeBits - Amt));
      return new ICmpInst(Pred, Builder->CreateTrunc(X, TruncTy), NewC);
    }
  
    return nullptr;
  }
  
  /// Fold icmp ({al}shr X, Y), C.
  Instruction *InstCombiner::foldICmpShrConstant(ICmpInst &Cmp,
                                                 BinaryOperator *Shr,
                                                 const APInt *C) {
    // An exact shr only shifts out zero bits, so:
    // icmp eq/ne (shr X, Y), 0 --> icmp eq/ne X, 0
    Value *X = Shr->getOperand(0);
    CmpInst::Predicate Pred = Cmp.getPredicate();
    if (Cmp.isEquality() && Shr->isExact() && Shr->hasOneUse() && *C == 0)
      return new ICmpInst(Pred, X, Cmp.getOperand(1));
  
    const APInt *ShiftVal;
    if (Cmp.isEquality() && match(Shr->getOperand(0), m_APInt(ShiftVal)))
      return foldICmpShrConstConst(Cmp, Shr->getOperand(1), *C, *ShiftVal);
  
    const APInt *ShiftAmt;
    if (!match(Shr->getOperand(1), m_APInt(ShiftAmt)))
      return nullptr;
  
    // Check that the shift amount is in range. If not, don't perform undefined
    // shifts. When the shift is visited it will be simplified.
    unsigned TypeBits = C->getBitWidth();
    unsigned ShAmtVal = ShiftAmt->getLimitedValue(TypeBits);
    if (ShAmtVal >= TypeBits || ShAmtVal == 0)
      return nullptr;
  
    bool IsAShr = Shr->getOpcode() == Instruction::AShr;
    if (!Cmp.isEquality()) {
      // If we have an unsigned comparison and an ashr, we can't simplify this.
      // Similarly for signed comparisons with lshr.
      if (Cmp.isSigned() != IsAShr)
        return nullptr;
  
      // Otherwise, all lshr and most exact ashr's are equivalent to a udiv/sdiv
      // by a power of 2.  Since we already have logic to simplify these,
      // transform to div and then simplify the resultant comparison.
      if (IsAShr && (!Shr->isExact() || ShAmtVal == TypeBits - 1))
        return nullptr;
  
      // Revisit the shift (to delete it).
      Worklist.Add(Shr);
  
      Constant *DivCst = ConstantInt::get(
          Shr->getType(), APInt::getOneBitSet(TypeBits, ShAmtVal));
  
      Value *Tmp = IsAShr ? Builder->CreateSDiv(X, DivCst, "", Shr->isExact())
                          : Builder->CreateUDiv(X, DivCst, "", Shr->isExact());
  
      Cmp.setOperand(0, Tmp);
  
      // If the builder folded the binop, just return it.
      BinaryOperator *TheDiv = dyn_cast<BinaryOperator>(Tmp);
      if (!TheDiv)
        return &Cmp;
  
      // Otherwise, fold this div/compare.
      IGC_ASSERT(TheDiv->getOpcode() == Instruction::SDiv || TheDiv->getOpcode() == Instruction::UDiv);
  
      Instruction *Res = foldICmpDivConstant(Cmp, TheDiv, C);
      IGC_ASSERT_MESSAGE(Res, "This div/cst should have folded!");
      return Res;
    }
  
    // Handle equality comparisons of shift-by-constant.
  
    // If the comparison constant changes with the shift, the comparison cannot
    // succeed (bits of the comparison constant cannot match the shifted value).
    // This should be known by InstSimplify and already be folded to true/false.
    IGC_ASSERT_MESSAGE(((IsAShr && C->shl(ShAmtVal).ashr(ShAmtVal) == *C) || (!IsAShr && C->shl(ShAmtVal).lshr(ShAmtVal) == *C)), "Expected icmp+shr simplify did not occur.");
  
    // Check if the bits shifted out are known to be zero. If so, we can compare
    // against the unshifted value:
    //  (X & 4) >> 1 == 2  --> (X & 4) == 4.
    Constant *ShiftedCmpRHS = ConstantInt::get(Shr->getType(), *C << ShAmtVal);
    if (Shr->hasOneUse()) {
      if (Shr->isExact())
        return new ICmpInst(Pred, X, ShiftedCmpRHS);
  
      // Otherwise strength reduce the shift into an 'and'.
      APInt Val(APInt::getHighBitsSet(TypeBits, TypeBits - ShAmtVal));
      Constant *Mask = ConstantInt::get(Shr->getType(), Val);
      Value *And = Builder->CreateAnd(X, Mask, Shr->getName() + ".mask");
      return new ICmpInst(Pred, And, ShiftedCmpRHS);
    }
  
    return nullptr;
  }
  
  /// Fold icmp (udiv X, Y), C.
  Instruction *InstCombiner::foldICmpUDivConstant(ICmpInst &Cmp,
                                                  BinaryOperator *UDiv,
                                                  const APInt *C) {
    const APInt *C2 = nullptr;
    if (!match(UDiv->getOperand(0), m_APInt(C2)))
      return nullptr;
  
    IGC_ASSERT_MESSAGE(C2 != 0, "udiv 0, X should have been simplified already.");
  
    // (icmp ugt (udiv C2, Y), C) -> (icmp ule Y, C2/(C+1))
    Value *Y = UDiv->getOperand(1);
    if (Cmp.getPredicate() == ICmpInst::ICMP_UGT) {
      IGC_ASSERT_MESSAGE(!C->isMaxValue(), "icmp ugt X, UINT_MAX should have been simplified already.");
      return new ICmpInst(ICmpInst::ICMP_ULE, Y,
                          ConstantInt::get(Y->getType(), C2->udiv(*C + 1)));
    }
  
    // (icmp ult (udiv C2, Y), C) -> (icmp ugt Y, C2/C)
    if (Cmp.getPredicate() == ICmpInst::ICMP_ULT) {
      IGC_ASSERT_MESSAGE(C != 0, "icmp ult X, 0 should have been simplified already.");
      return new ICmpInst(ICmpInst::ICMP_UGT, Y,
                          ConstantInt::get(Y->getType(), C2->udiv(*C)));
    }
  
    return nullptr;
  }
  
  /// Fold icmp ({su}div X, Y), C.
  Instruction *InstCombiner::foldICmpDivConstant(ICmpInst &Cmp,
                                                 BinaryOperator *Div,
                                                 const APInt *C) {
    // Fold: icmp pred ([us]div X, C2), C -> range test
    // Fold this div into the comparison, producing a range check.
    // Determine, based on the divide type, what the range is being
    // checked.  If there is an overflow on the low or high side, remember
    // it, otherwise compute the range [low, hi) bounding the new value.
    // See: InsertRangeTest above for the kinds of replacements possible.
    const APInt *C2;
    if (!match(Div->getOperand(1), m_APInt(C2)))
      return nullptr;
  
    // FIXME: If the operand types don't match the type of the divide
    // then don't attempt this transform. The code below doesn't have the
    // logic to deal with a signed divide and an unsigned compare (and
    // vice versa). This is because (x /s C2) <s C  produces different
    // results than (x /s C2) <u C or (x /u C2) <s C or even
    // (x /u C2) <u C.  Simply casting the operands and result won't
    // work. :(  The if statement below tests that condition and bails
    // if it finds it.
    bool DivIsSigned = Div->getOpcode() == Instruction::SDiv;
    if (!Cmp.isEquality() && DivIsSigned != Cmp.isSigned())
      return nullptr;
  
    // The ProdOV computation fails on divide by 0 and divide by -1. Cases with
    // INT_MIN will also fail if the divisor is 1. Although folds of all these
    // division-by-constant cases should be present, we can not assertion test that they
    // have happened before we reach this icmp instruction.
    if (*C2 == 0 || *C2 == 1 || (DivIsSigned && C2->isAllOnesValue()))
      return nullptr;
  
    // TODO: We could do all of the computations below using APInt.
    Constant *CmpRHS = cast<Constant>(Cmp.getOperand(1));
    Constant *DivRHS = cast<Constant>(Div->getOperand(1));
  
    // Compute Prod = CmpRHS * DivRHS. We are essentially solving an equation of
    // form X / C2 = C. We solve for X by multiplying C2 (DivRHS) and C (CmpRHS).
    // By solving for X, we can turn this into a range check instead of computing
    // a divide.
    Constant *Prod = ConstantExpr::getMul(CmpRHS, DivRHS);
  
    // Determine if the product overflows by seeing if the product is not equal to
    // the divide. Make sure we do the same kind of divide as in the LHS
    // instruction that we're folding.
    bool ProdOV = (DivIsSigned ? ConstantExpr::getSDiv(Prod, DivRHS)
                               : ConstantExpr::getUDiv(Prod, DivRHS)) != CmpRHS;
  
    ICmpInst::Predicate Pred = Cmp.getPredicate();
  
    // If the division is known to be exact, then there is no remainder from the
    // divide, so the covered range size is unit, otherwise it is the divisor.
    Constant *RangeSize =
        Div->isExact() ? ConstantInt::get(Div->getType(), 1) : DivRHS;
  
    // Figure out the interval that is being checked.  For example, a comparison
    // like "X /u 5 == 0" is really checking that X is in the interval [0, 5).
    // Compute this interval based on the constants involved and the signedness of
    // the compare/divide.  This computes a half-open interval, keeping track of
    // whether either value in the interval overflows.  After analysis each
    // overflow variable is set to 0 if it's corresponding bound variable is valid
    // -1 if overflowed off the bottom end, or +1 if overflowed off the top end.
    int LoOverflow = 0, HiOverflow = 0;
    Constant *LoBound = nullptr, *HiBound = nullptr;
  
    if (!DivIsSigned) {  // udiv
      // e.g. X/5 op 3  --> [15, 20)
      LoBound = Prod;
      HiOverflow = LoOverflow = ProdOV;
      if (!HiOverflow) {
        // If this is not an exact divide, then many values in the range collapse
        // to the same result value.
        HiOverflow = addWithOverflow(HiBound, LoBound, RangeSize, false);
      }
    } else if (C2->isStrictlyPositive()) { // Divisor is > 0.
      if (*C == 0) {       // (X / pos) op 0
        // Can't overflow.  e.g.  X/2 op 0 --> [-1, 2)
        LoBound = ConstantExpr::getNeg(SubOne(RangeSize));
        HiBound = RangeSize;
      } else if (C->isStrictlyPositive()) {   // (X / pos) op pos
        LoBound = Prod;     // e.g.   X/5 op 3 --> [15, 20)
        HiOverflow = LoOverflow = ProdOV;
        if (!HiOverflow)
          HiOverflow = addWithOverflow(HiBound, Prod, RangeSize, true);
      } else {                       // (X / pos) op neg
        // e.g. X/5 op -3  --> [-15-4, -15+1) --> [-19, -14)
        HiBound = AddOne(Prod);
        LoOverflow = HiOverflow = ProdOV ? -1 : 0;
        if (!LoOverflow) {
          Constant *DivNeg = ConstantExpr::getNeg(RangeSize);
          LoOverflow = addWithOverflow(LoBound, HiBound, DivNeg, true) ? -1 : 0;
        }
      }
    } else if (C2->isNegative()) { // Divisor is < 0.
      if (Div->isExact())
        RangeSize = ConstantExpr::getNeg(RangeSize);
      if (*C == 0) {       // (X / neg) op 0
        // e.g. X/-5 op 0  --> [-4, 5)
        LoBound = AddOne(RangeSize);
        HiBound = ConstantExpr::getNeg(RangeSize);
        if (HiBound == DivRHS) {     // -INTMIN = INTMIN
          HiOverflow = 1;            // [INTMIN+1, overflow)
          HiBound = nullptr;         // e.g. X/INTMIN = 0 --> X > INTMIN
        }
      } else if (C->isStrictlyPositive()) {   // (X / neg) op pos
        // e.g. X/-5 op 3  --> [-19, -14)
        HiBound = AddOne(Prod);
        HiOverflow = LoOverflow = ProdOV ? -1 : 0;
        if (!LoOverflow)
          LoOverflow = addWithOverflow(LoBound, HiBound, RangeSize, true) ? -1:0;
      } else {                       // (X / neg) op neg
        LoBound = Prod;       // e.g. X/-5 op -3  --> [15, 20)
        LoOverflow = HiOverflow = ProdOV;
        if (!HiOverflow)
          HiOverflow = subWithOverflow(HiBound, Prod, RangeSize, true);
      }
  
      // Dividing by a negative swaps the condition.  LT <-> GT
      Pred = ICmpInst::getSwappedPredicate(Pred);
    }
  
    Value *X = Div->getOperand(0);
    switch (Pred) {
      default: IGC_ASSERT_EXIT_MESSAGE(0, "Unhandled icmp opcode!");
      case ICmpInst::ICMP_EQ:
        if (LoOverflow && HiOverflow)
          return replaceInstUsesWith(Cmp, Builder->getFalse());
        if (HiOverflow)
          return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SGE :
                              ICmpInst::ICMP_UGE, X, LoBound);
        if (LoOverflow)
          return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SLT :
                              ICmpInst::ICMP_ULT, X, HiBound);
        return replaceInstUsesWith(
            Cmp, insertRangeTest(X, LoBound->getUniqueInteger(),
                                 HiBound->getUniqueInteger(), DivIsSigned, true));
      case ICmpInst::ICMP_NE:
        if (LoOverflow && HiOverflow)
          return replaceInstUsesWith(Cmp, Builder->getTrue());
        if (HiOverflow)
          return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SLT :
                              ICmpInst::ICMP_ULT, X, LoBound);
        if (LoOverflow)
          return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SGE :
                              ICmpInst::ICMP_UGE, X, HiBound);
        return replaceInstUsesWith(Cmp,
                                   insertRangeTest(X, LoBound->getUniqueInteger(),
                                                   HiBound->getUniqueInteger(),
                                                   DivIsSigned, false));
      case ICmpInst::ICMP_ULT:
      case ICmpInst::ICMP_SLT:
        if (LoOverflow == +1)   // Low bound is greater than input range.
          return replaceInstUsesWith(Cmp, Builder->getTrue());
        if (LoOverflow == -1)   // Low bound is less than input range.
          return replaceInstUsesWith(Cmp, Builder->getFalse());
        return new ICmpInst(Pred, X, LoBound);
      case ICmpInst::ICMP_UGT:
      case ICmpInst::ICMP_SGT:
        if (HiOverflow == +1)       // High bound greater than input range.
          return replaceInstUsesWith(Cmp, Builder->getFalse());
        if (HiOverflow == -1)       // High bound less than input range.
          return replaceInstUsesWith(Cmp, Builder->getTrue());
        if (Pred == ICmpInst::ICMP_UGT)
          return new ICmpInst(ICmpInst::ICMP_UGE, X, HiBound);
        return new ICmpInst(ICmpInst::ICMP_SGE, X, HiBound);
    }
  
    return nullptr;
  }
  
  /// Fold icmp (sub X, Y), C.
  Instruction *InstCombiner::foldICmpSubConstant(ICmpInst &Cmp,
                                                 BinaryOperator *Sub,
                                                 const APInt *C) {
    Value *X = Sub->getOperand(0), *Y = Sub->getOperand(1);
    ICmpInst::Predicate Pred = Cmp.getPredicate();
  
    // The following transforms are only worth it if the only user of the subtract
    // is the icmp.
    if (!Sub->hasOneUse())
      return nullptr;
  
    if (Sub->hasNoSignedWrap()) {
      // (icmp sgt (sub nsw X, Y), -1) -> (icmp sge X, Y)
      if (Pred == ICmpInst::ICMP_SGT && C->isAllOnesValue())
        return new ICmpInst(ICmpInst::ICMP_SGE, X, Y);
  
      // (icmp sgt (sub nsw X, Y), 0) -> (icmp sgt X, Y)
      if (Pred == ICmpInst::ICMP_SGT && *C == 0)
        return new ICmpInst(ICmpInst::ICMP_SGT, X, Y);
  
      // (icmp slt (sub nsw X, Y), 0) -> (icmp slt X, Y)
      if (Pred == ICmpInst::ICMP_SLT && *C == 0)
        return new ICmpInst(ICmpInst::ICMP_SLT, X, Y);
  
      // (icmp slt (sub nsw X, Y), 1) -> (icmp sle X, Y)
      if (Pred == ICmpInst::ICMP_SLT && *C == 1)
        return new ICmpInst(ICmpInst::ICMP_SLE, X, Y);
    }
  
    const APInt *C2;
    if (!match(X, m_APInt(C2)))
      return nullptr;
  
    // C2 - Y <u C -> (Y | (C - 1)) == C2
    //   iff (C2 & (C - 1)) == C - 1 and C is a power of 2
    if (Pred == ICmpInst::ICMP_ULT && C->isPowerOf2() &&
        (*C2 & (*C - 1)) == (*C - 1))
      return new ICmpInst(ICmpInst::ICMP_EQ, Builder->CreateOr(Y, *C - 1), X);
  
    // C2 - Y >u C -> (Y | C) != C2
    //   iff C2 & C == C and C + 1 is a power of 2
    if (Pred == ICmpInst::ICMP_UGT && (*C + 1).isPowerOf2() && (*C2 & *C) == *C)
      return new ICmpInst(ICmpInst::ICMP_NE, Builder->CreateOr(Y, *C), X);
  
    return nullptr;
  }
  
  /// Fold icmp (add X, Y), C.
  Instruction *InstCombiner::foldICmpAddConstant(ICmpInst &Cmp,
                                                 BinaryOperator *Add,
                                                 const APInt *C) {
    Value *Y = Add->getOperand(1);
    const APInt *C2 = nullptr;
    if (Cmp.isEquality() || !match(Y, m_APInt(C2)))
      return nullptr;
  
    // Fold icmp pred (add X, C2), C.
    Value *X = Add->getOperand(0);
    Type *Ty = Add->getType();
    auto CR =
        ConstantRange::makeExactICmpRegion(Cmp.getPredicate(), *C).subtract(*C2);
    const APInt &Upper = CR.getUpper();
    const APInt &Lower = CR.getLower();
    if (Cmp.isSigned()) {
      if (Lower.isSignBit())
        return new ICmpInst(ICmpInst::ICMP_SLT, X, ConstantInt::get(Ty, Upper));
      if (Upper.isSignBit())
        return new ICmpInst(ICmpInst::ICMP_SGE, X, ConstantInt::get(Ty, Lower));
    } else {
      if (Lower.isMinValue())
        return new ICmpInst(ICmpInst::ICMP_ULT, X, ConstantInt::get(Ty, Upper));
      if (Upper.isMinValue())
        return new ICmpInst(ICmpInst::ICMP_UGE, X, ConstantInt::get(Ty, Lower));
    }
  
    if (!Add->hasOneUse())
      return nullptr;
  
    // X+C <u C2 -> (X & -C2) == C
    //   iff C & (C2-1) == 0
    //       C2 is a power of 2
    if (Cmp.getPredicate() == ICmpInst::ICMP_ULT && C->isPowerOf2() &&
        (*C2 & (*C - 1)) == 0)
      return new ICmpInst(ICmpInst::ICMP_EQ, Builder->CreateAnd(X, -(*C)),
                          ConstantExpr::getNeg(cast<Constant>(Y)));
  
    // X+C >u C2 -> (X & ~C2) != C
    //   iff C & C2 == 0
    //       C2+1 is a power of 2
    if (Cmp.getPredicate() == ICmpInst::ICMP_UGT && (*C + 1).isPowerOf2() &&
        (*C2 & *C) == 0)
      return new ICmpInst(ICmpInst::ICMP_NE, Builder->CreateAnd(X, ~(*C)),
                          ConstantExpr::getNeg(cast<Constant>(Y)));
  
    return nullptr;
  }
  
  /// Try to fold integer comparisons with a constant operand: icmp Pred X, C
  /// where X is some kind of instruction.
  Instruction *InstCombiner::foldICmpInstWithConstant(ICmpInst &Cmp) {
    const APInt *C;
    if (!match(Cmp.getOperand(1), m_APInt(C)))
      return nullptr;
  
    BinaryOperator *BO;
    if (match(Cmp.getOperand(0), m_BinOp(BO))) {
      switch (BO->getOpcode()) {
      case Instruction::Xor:
        if (Instruction *I = foldICmpXorConstant(Cmp, BO, C))
          return I;
        break;
      case Instruction::And:
        if (Instruction *I = foldICmpAndConstant(Cmp, BO, C))
          return I;
        break;
      case Instruction::Or:
        if (Instruction *I = foldICmpOrConstant(Cmp, BO, C))
          return I;
        break;
      case Instruction::Mul:
        if (Instruction *I = foldICmpMulConstant(Cmp, BO, C))
          return I;
        break;
      case Instruction::Shl:
        if (Instruction *I = foldICmpShlConstant(Cmp, BO, C))
          return I;
        break;
      case Instruction::LShr:
      case Instruction::AShr:
        if (Instruction *I = foldICmpShrConstant(Cmp, BO, C))
          return I;
        break;
      case Instruction::UDiv:
        if (Instruction *I = foldICmpUDivConstant(Cmp, BO, C))
          return I;
        LLVM_FALLTHROUGH;
      case Instruction::SDiv:
        if (Instruction *I = foldICmpDivConstant(Cmp, BO, C))
          return I;
        break;
      case Instruction::Sub:
        if (Instruction *I = foldICmpSubConstant(Cmp, BO, C))
          return I;
        break;
      case Instruction::Add:
        if (Instruction *I = foldICmpAddConstant(Cmp, BO, C))
          return I;
        break;
      default:
        break;
      }
      // TODO: These folds could be refactored to be part of the above calls.
      if (Instruction *I = foldICmpBinOpEqualityWithConstant(Cmp, BO, C))
        return I;
    }
  
    Instruction *LHSI;
    if (match(Cmp.getOperand(0), m_Instruction(LHSI)) &&
        LHSI->getOpcode() == Instruction::Trunc)
      if (Instruction *I = foldICmpTruncConstant(Cmp, LHSI, C))
        return I;
  
    if (Instruction *I = foldICmpIntrinsicWithConstant(Cmp, C))
      return I;
  
    return nullptr;
  }
  
  /// Fold an icmp equality instruction with binary operator LHS and constant RHS:
  /// icmp eq/ne BO, C.
  Instruction *InstCombiner::foldICmpBinOpEqualityWithConstant(ICmpInst &Cmp,
                                                               BinaryOperator *BO,
                                                               const APInt *C) {
    // TODO: Some of these folds could work with arbitrary constants, but this
    // function is limited to scalar and vector splat constants.
    if (!Cmp.isEquality())
      return nullptr;
  
    ICmpInst::Predicate Pred = Cmp.getPredicate();
    bool isICMP_NE = Pred == ICmpInst::ICMP_NE;
    Constant *RHS = cast<Constant>(Cmp.getOperand(1));
    Value *BOp0 = BO->getOperand(0), *BOp1 = BO->getOperand(1);
  
    switch (BO->getOpcode()) {
    case Instruction::SRem:
      // If we have a signed (X % (2^c)) == 0, turn it into an unsigned one.
      if (*C == 0 && BO->hasOneUse()) {
        const APInt *BOC = nullptr;
        if (match(BOp1, m_APInt(BOC)) && BOC->sgt(1) && BOC->isPowerOf2()) {
          Value *NewRem = Builder->CreateURem(BOp0, BOp1, BO->getName());
          return new ICmpInst(Pred, NewRem,
                              Constant::getNullValue(BO->getType()));
        }
      }
      break;
    case Instruction::Add: {
      // Replace ((add A, B) != C) with (A != C-B) if B & C are constants.
      const APInt *BOC = nullptr;
      if (match(BOp1, m_APInt(BOC))) {
        if (BO->hasOneUse()) {
          Constant *SubC = ConstantExpr::getSub(RHS, cast<Constant>(BOp1));
          return new ICmpInst(Pred, BOp0, SubC);
        }
      } else if (*C == 0) {
        // Replace ((add A, B) != 0) with (A != -B) if A or B is
        // efficiently invertible, or if the add has just this one use.
        if (Value *NegVal = dyn_castNegVal(BOp1))
          return new ICmpInst(Pred, BOp0, NegVal);
        if (Value *NegVal = dyn_castNegVal(BOp0))
          return new ICmpInst(Pred, NegVal, BOp1);
        if (BO->hasOneUse()) {
          Value *Neg = Builder->CreateNeg(BOp1);
          Neg->takeName(BO);
          return new ICmpInst(Pred, BOp0, Neg);
        }
      }
      break;
    }
    case Instruction::Xor:
      if (BO->hasOneUse()) {
        if (Constant *BOC = dyn_cast<Constant>(BOp1)) {
          // For the xor case, we can xor two constants together, eliminating
          // the explicit xor.
          return new ICmpInst(Pred, BOp0, ConstantExpr::getXor(RHS, BOC));
        } else if (*C == 0) {
          // Replace ((xor A, B) != 0) with (A != B)
          return new ICmpInst(Pred, BOp0, BOp1);
        }
      }
      break;
    case Instruction::Sub:
      if (BO->hasOneUse()) {
        const APInt *BOC = nullptr;
        if (match(BOp0, m_APInt(BOC))) {
          // Replace ((sub BOC, B) != C) with (B != BOC-C).
          Constant *SubC = ConstantExpr::getSub(cast<Constant>(BOp0), RHS);
          return new ICmpInst(Pred, BOp1, SubC);
        } else if (*C == 0) {
          // Replace ((sub A, B) != 0) with (A != B).
          return new ICmpInst(Pred, BOp0, BOp1);
        }
      }
      break;
    case Instruction::Or: {
      const APInt *BOC = nullptr;
      if (match(BOp1, m_APInt(BOC)) && BO->hasOneUse() && RHS->isAllOnesValue()) {
        // Comparing if all bits outside of a constant mask are set?
        // Replace (X | C) == -1 with (X & ~C) == ~C.
        // This removes the -1 constant.
        Constant *NotBOC = ConstantExpr::getNot(cast<Constant>(BOp1));
        Value *And = Builder->CreateAnd(BOp0, NotBOC);
        return new ICmpInst(Pred, And, NotBOC);
      }
      break;
    }
    case Instruction::And: {
      const APInt *BOC = nullptr;
      if (match(BOp1, m_APInt(BOC))) {
        // If we have ((X & C) == C), turn it into ((X & C) != 0).
        if (C == BOC && C->isPowerOf2())
          return new ICmpInst(isICMP_NE ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE,
                              BO, Constant::getNullValue(RHS->getType()));
  
        // Don't perform the following transforms if the AND has multiple uses
        if (!BO->hasOneUse())
          break;
  
        // Replace (and X, (1 << size(X)-1) != 0) with x s< 0
        if (BOC->isSignBit()) {
          Constant *Zero = Constant::getNullValue(BOp0->getType());
          auto NewPred = isICMP_NE ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_SGE;
          return new ICmpInst(NewPred, BOp0, Zero);
        }
  
        // ((X & ~7) == 0) --> X < 8
        if (*C == 0 && (~(*BOC) + 1).isPowerOf2()) {
          Constant *NegBOC = ConstantExpr::getNeg(cast<Constant>(BOp1));
          auto NewPred = isICMP_NE ? ICmpInst::ICMP_UGE : ICmpInst::ICMP_ULT;
          return new ICmpInst(NewPred, BOp0, NegBOC);
        }
      }
      break;
    }
    case Instruction::Mul:
      if (*C == 0 && BO->hasNoSignedWrap()) {
        const APInt *BOC = nullptr;
        if (match(BOp1, m_APInt(BOC)) && *BOC != 0) {
          // The trivial case (mul X, 0) is handled by InstSimplify.
          // General case : (mul X, C) != 0 iff X != 0
          //                (mul X, C) == 0 iff X == 0
          return new ICmpInst(Pred, BOp0, Constant::getNullValue(RHS->getType()));
        }
      }
      break;
    case Instruction::UDiv:
      if (*C == 0) {
        // (icmp eq/ne (udiv A, B), 0) -> (icmp ugt/ule i32 B, A)
        auto NewPred = isICMP_NE ? ICmpInst::ICMP_ULE : ICmpInst::ICMP_UGT;
        return new ICmpInst(NewPred, BOp1, BOp0);
      }
      break;
    default:
      break;
    }
    return nullptr;
  }
  
  /// Fold an icmp with LLVM intrinsic and constant operand: icmp Pred II, C.
  Instruction *InstCombiner::foldICmpIntrinsicWithConstant(ICmpInst &Cmp,
                                                           const APInt *C) {
    IntrinsicInst *II = dyn_cast<IntrinsicInst>(Cmp.getOperand(0));
    if (!II || !Cmp.isEquality())
      return nullptr;
  
    // Handle icmp {eq|ne} <intrinsic>, intcst.
    switch (II->getIntrinsicID()) {
    case Intrinsic::bswap:
      Worklist.Add(II);
      Cmp.setOperand(0, II->getArgOperand(0));
      Cmp.setOperand(1, Builder->getInt(C->byteSwap()));
      return &Cmp;
    case Intrinsic::ctlz:
    case Intrinsic::cttz:
      // ctz(A) == bitwidth(A)  ->  A == 0 and likewise for !=
      if (*C == C->getBitWidth()) {
        Worklist.Add(II);
        Cmp.setOperand(0, II->getArgOperand(0));
        Cmp.setOperand(1, ConstantInt::getNullValue(II->getType()));
        return &Cmp;
      }
      break;
    case Intrinsic::ctpop: {
      // popcount(A) == 0  ->  A == 0 and likewise for !=
      // popcount(A) == bitwidth(A)  ->  A == -1 and likewise for !=
      bool IsZero = *C == 0;
      if (IsZero || *C == C->getBitWidth()) {
        Worklist.Add(II);
        Cmp.setOperand(0, II->getArgOperand(0));
        auto *NewOp = IsZero ? Constant::getNullValue(II->getType())
                             : Constant::getAllOnesValue(II->getType());
        Cmp.setOperand(1, NewOp);
        return &Cmp;
      }
      break;
    }
    default:
      break;
    }
    return nullptr;
  }
  
  /// Handle icmp with constant (but not simple integer constant) RHS.
  Instruction *InstCombiner::foldICmpInstWithConstantNotInt(ICmpInst &I) {
    Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
    Constant *RHSC = dyn_cast<Constant>(Op1);
    Instruction *LHSI = dyn_cast<Instruction>(Op0);
    if (!RHSC || !LHSI)
      return nullptr;
  
    switch (LHSI->getOpcode()) {
    case Instruction::GetElementPtr:
      // icmp pred GEP (P, int 0, int 0, int 0), null -> icmp pred P, null
      if (RHSC->isNullValue() &&
          cast<GetElementPtrInst>(LHSI)->hasAllZeroIndices())
        return new ICmpInst(
            I.getPredicate(), LHSI->getOperand(0),
            Constant::getNullValue(LHSI->getOperand(0)->getType()));
      break;
    case Instruction::PHI:
      // Only fold icmp into the PHI if the phi and icmp are in the same
      // block.  If in the same block, we're encouraging jump threading.  If
      // not, we are just pessimizing the code by making an i1 phi.
      if (LHSI->getParent() == I.getParent())
        if (Instruction *NV = FoldOpIntoPhi(I))
          return NV;
      break;
    case Instruction::Select: {
      // If either operand of the select is a constant, we can fold the
      // comparison into the select arms, which will cause one to be
      // constant folded and the select turned into a bitwise or.
      Value *Op1 = nullptr, *Op2 = nullptr;
      ConstantInt *CI = nullptr;
      if (Constant *C = dyn_cast<Constant>(LHSI->getOperand(1))) {
        Op1 = ConstantExpr::getICmp(I.getPredicate(), C, RHSC);
        CI = dyn_cast<ConstantInt>(Op1);
      }
      if (Constant *C = dyn_cast<Constant>(LHSI->getOperand(2))) {
        Op2 = ConstantExpr::getICmp(I.getPredicate(), C, RHSC);
        CI = dyn_cast<ConstantInt>(Op2);
      }
  
      // We only want to perform this transformation if it will not lead to
      // additional code. This is true if either both sides of the select
      // fold to a constant (in which case the icmp is replaced with a select
      // which will usually simplify) or this is the only user of the
      // select (in which case we are trading a select+icmp for a simpler
      // select+icmp) or all uses of the select can be replaced based on
      // dominance information ("Global cases").
      bool Transform = false;
      if (Op1 && Op2)
        Transform = true;
      else if (Op1 || Op2) {
        // Local case
        if (LHSI->hasOneUse())
          Transform = true;
        // Global cases
        else if (CI && !CI->isZero())
          // When Op1 is constant try replacing select with second operand.
          // Otherwise Op2 is constant and try replacing select with first
          // operand.
          Transform =
              replacedSelectWithOperand(cast<SelectInst>(LHSI), &I, Op1 ? 2 : 1);
      }
      if (Transform) {
        if (!Op1)
          Op1 = Builder->CreateICmp(I.getPredicate(), LHSI->getOperand(1), RHSC,
                                    I.getName());
        if (!Op2)
          Op2 = Builder->CreateICmp(I.getPredicate(), LHSI->getOperand(2), RHSC,
                                    I.getName());
        return SelectInst::Create(LHSI->getOperand(0), Op1, Op2);
      }
      break;
    }
    case Instruction::IntToPtr:
      // icmp pred inttoptr(X), null -> icmp pred X, 0
      if (RHSC->isNullValue() &&
          DL.getIntPtrType(RHSC->getType()) == LHSI->getOperand(0)->getType())
        return new ICmpInst(
            I.getPredicate(), LHSI->getOperand(0),
            Constant::getNullValue(LHSI->getOperand(0)->getType()));
      break;
  
    case Instruction::Load:
      // Try to optimize things like "A[i] > 4" to index computations.
      if (GetElementPtrInst *GEP =
              dyn_cast<GetElementPtrInst>(LHSI->getOperand(0))) {
        if (GlobalVariable *GV = dyn_cast<GlobalVariable>(GEP->getOperand(0)))
          if (GV->isConstant() && GV->hasDefinitiveInitializer() &&
              !cast<LoadInst>(LHSI)->isVolatile())
            if (Instruction *Res = foldCmpLoadFromIndexedGlobal(GEP, GV, I))
              return Res;
      }
      break;
    }
  
    return nullptr;
  }
  
  /// Try to fold icmp (binop), X or icmp X, (binop).
  Instruction *InstCombiner::foldICmpBinOp(ICmpInst &I) {
    Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
  
    // Special logic for binary operators.
    BinaryOperator *BO0 = dyn_cast<BinaryOperator>(Op0);
    BinaryOperator *BO1 = dyn_cast<BinaryOperator>(Op1);
    if (!BO0 && !BO1)
      return nullptr;
  
    CmpInst::Predicate Pred = I.getPredicate();
    bool NoOp0WrapProblem = false, NoOp1WrapProblem = false;
    if (BO0 && isa<OverflowingBinaryOperator>(BO0))
      NoOp0WrapProblem =
          ICmpInst::isEquality(Pred) ||
          (CmpInst::isUnsigned(Pred) && BO0->hasNoUnsignedWrap()) ||
          (CmpInst::isSigned(Pred) && BO0->hasNoSignedWrap());
    if (BO1 && isa<OverflowingBinaryOperator>(BO1))
      NoOp1WrapProblem =
          ICmpInst::isEquality(Pred) ||
          (CmpInst::isUnsigned(Pred) && BO1->hasNoUnsignedWrap()) ||
          (CmpInst::isSigned(Pred) && BO1->hasNoSignedWrap());
  
    // Analyze the case when either Op0 or Op1 is an add instruction.
    // Op0 = A + B (or A and B are null); Op1 = C + D (or C and D are null).
    Value *A = nullptr, *B = nullptr, *C = nullptr, *D = nullptr;
    if (BO0 && BO0->getOpcode() == Instruction::Add) {
      A = BO0->getOperand(0);
      B = BO0->getOperand(1);
    }
    if (BO1 && BO1->getOpcode() == Instruction::Add) {
      C = BO1->getOperand(0);
      D = BO1->getOperand(1);
    }
  
    // icmp (X+cst) < 0 --> X < -cst
    if (NoOp0WrapProblem && ICmpInst::isSigned(Pred) && match(Op1, m_Zero()))
      if (ConstantInt *RHSC = dyn_cast_or_null<ConstantInt>(B))
        if (!RHSC->isMinValue(/*isSigned=*/true))
          return new ICmpInst(Pred, A, ConstantExpr::getNeg(RHSC));
  
    // icmp (X+Y), X -> icmp Y, 0 for equalities or if there is no overflow.
    if ((A == Op1 || B == Op1) && NoOp0WrapProblem)
      return new ICmpInst(Pred, A == Op1 ? B : A,
                          Constant::getNullValue(Op1->getType()));
  
    // icmp X, (X+Y) -> icmp 0, Y for equalities or if there is no overflow.
    if ((C == Op0 || D == Op0) && NoOp1WrapProblem)
      return new ICmpInst(Pred, Constant::getNullValue(Op0->getType()),
                          C == Op0 ? D : C);
  
    // icmp (X+Y), (X+Z) -> icmp Y, Z for equalities or if there is no overflow.
    if (A && C && (A == C || A == D || B == C || B == D) && NoOp0WrapProblem &&
        NoOp1WrapProblem &&
        // Try not to increase register pressure.
        BO0->hasOneUse() && BO1->hasOneUse()) {
      // Determine Y and Z in the form icmp (X+Y), (X+Z).
      Value *Y, *Z;
      if (A == C) {
        // C + B == C + D  ->  B == D
        Y = B;
        Z = D;
      } else if (A == D) {
        // D + B == C + D  ->  B == C
        Y = B;
        Z = C;
      } else if (B == C) {
        // A + C == C + D  ->  A == D
        Y = A;
        Z = D;
      } else {
        IGC_ASSERT(B == D);
        // A + D == C + D  ->  A == C
        Y = A;
        Z = C;
      }
      return new ICmpInst(Pred, Y, Z);
    }
  
    // icmp slt (X + -1), Y -> icmp sle X, Y
    if (A && NoOp0WrapProblem && Pred == CmpInst::ICMP_SLT &&
        match(B, m_AllOnes()))
      return new ICmpInst(CmpInst::ICMP_SLE, A, Op1);
  
    // icmp sge (X + -1), Y -> icmp sgt X, Y
    if (A && NoOp0WrapProblem && Pred == CmpInst::ICMP_SGE &&
        match(B, m_AllOnes()))
      return new ICmpInst(CmpInst::ICMP_SGT, A, Op1);
  
    // icmp sle (X + 1), Y -> icmp slt X, Y
    if (A && NoOp0WrapProblem && Pred == CmpInst::ICMP_SLE && match(B, m_One()))
      return new ICmpInst(CmpInst::ICMP_SLT, A, Op1);
  
    // icmp sgt (X + 1), Y -> icmp sge X, Y
    if (A && NoOp0WrapProblem && Pred == CmpInst::ICMP_SGT && match(B, m_One()))
      return new ICmpInst(CmpInst::ICMP_SGE, A, Op1);
  
    // icmp sgt X, (Y + -1) -> icmp sge X, Y
    if (C && NoOp1WrapProblem && Pred == CmpInst::ICMP_SGT &&
        match(D, m_AllOnes()))
      return new ICmpInst(CmpInst::ICMP_SGE, Op0, C);
  
    // icmp sle X, (Y + -1) -> icmp slt X, Y
    if (C && NoOp1WrapProblem && Pred == CmpInst::ICMP_SLE &&
        match(D, m_AllOnes()))
      return new ICmpInst(CmpInst::ICMP_SLT, Op0, C);
  
    // icmp sge X, (Y + 1) -> icmp sgt X, Y
    if (C && NoOp1WrapProblem && Pred == CmpInst::ICMP_SGE && match(D, m_One()))
      return new ICmpInst(CmpInst::ICMP_SGT, Op0, C);
  
    // icmp slt X, (Y + 1) -> icmp sle X, Y
    if (C && NoOp1WrapProblem && Pred == CmpInst::ICMP_SLT && match(D, m_One()))
      return new ICmpInst(CmpInst::ICMP_SLE, Op0, C);
  
    // if C1 has greater magnitude than C2:
    //  icmp (X + C1), (Y + C2) -> icmp (X + C3), Y
    //  s.t. C3 = C1 - C2
    //
    // if C2 has greater magnitude than C1:
    //  icmp (X + C1), (Y + C2) -> icmp X, (Y + C3)
    //  s.t. C3 = C2 - C1
    if (A && C && NoOp0WrapProblem && NoOp1WrapProblem &&
        (BO0->hasOneUse() || BO1->hasOneUse()) && !I.isUnsigned())
      if (ConstantInt *C1 = dyn_cast<ConstantInt>(B))
        if (ConstantInt *C2 = dyn_cast<ConstantInt>(D)) {
          const APInt &AP1 = C1->getValue();
          const APInt &AP2 = C2->getValue();
          if (AP1.isNegative() == AP2.isNegative()) {
            APInt AP1Abs = C1->getValue().abs();
            APInt AP2Abs = C2->getValue().abs();
            if (AP1Abs.uge(AP2Abs)) {
              ConstantInt *C3 = Builder->getInt(AP1 - AP2);
              Value *NewAdd = Builder->CreateNSWAdd(A, C3);
              return new ICmpInst(Pred, NewAdd, C);
            } else {
              ConstantInt *C3 = Builder->getInt(AP2 - AP1);
              Value *NewAdd = Builder->CreateNSWAdd(C, C3);
              return new ICmpInst(Pred, A, NewAdd);
            }
          }
        }
  
    // Analyze the case when either Op0 or Op1 is a sub instruction.
    // Op0 = A - B (or A and B are null); Op1 = C - D (or C and D are null).
    A = nullptr;
    B = nullptr;
    C = nullptr;
    D = nullptr;
    if (BO0 && BO0->getOpcode() == Instruction::Sub) {
      A = BO0->getOperand(0);
      B = BO0->getOperand(1);
    }
    if (BO1 && BO1->getOpcode() == Instruction::Sub) {
      C = BO1->getOperand(0);
      D = BO1->getOperand(1);
    }
  
    // icmp (X-Y), X -> icmp 0, Y for equalities or if there is no overflow.
    if (A == Op1 && NoOp0WrapProblem)
      return new ICmpInst(Pred, Constant::getNullValue(Op1->getType()), B);
  
    // icmp X, (X-Y) -> icmp Y, 0 for equalities or if there is no overflow.
    if (C == Op0 && NoOp1WrapProblem)
      return new ICmpInst(Pred, D, Constant::getNullValue(Op0->getType()));
  
    // icmp (Y-X), (Z-X) -> icmp Y, Z for equalities or if there is no overflow.
    if (B && D && B == D && NoOp0WrapProblem && NoOp1WrapProblem &&
        // Try not to increase register pressure.
        BO0->hasOneUse() && BO1->hasOneUse())
      return new ICmpInst(Pred, A, C);
  
    // icmp (X-Y), (X-Z) -> icmp Z, Y for equalities or if there is no overflow.
    if (A && C && A == C && NoOp0WrapProblem && NoOp1WrapProblem &&
        // Try not to increase register pressure.
        BO0->hasOneUse() && BO1->hasOneUse())
      return new ICmpInst(Pred, D, B);
  
    // icmp (0-X) < cst --> x > -cst
    if (NoOp0WrapProblem && ICmpInst::isSigned(Pred)) {
      Value *X;
      if (match(BO0, m_Neg(m_Value(X))))
        if (ConstantInt *RHSC = dyn_cast<ConstantInt>(Op1))
          if (!RHSC->isMinValue(/*isSigned=*/true))
            return new ICmpInst(I.getSwappedPredicate(), X,
                                ConstantExpr::getNeg(RHSC));
    }
  
    BinaryOperator *SRem = nullptr;
    // icmp (srem X, Y), Y
    if (BO0 && BO0->getOpcode() == Instruction::SRem && Op1 == BO0->getOperand(1))
      SRem = BO0;
    // icmp Y, (srem X, Y)
    else if (BO1 && BO1->getOpcode() == Instruction::SRem &&
             Op0 == BO1->getOperand(1))
      SRem = BO1;
    if (SRem) {
      // We don't check hasOneUse to avoid increasing register pressure because
      // the value we use is the same value this instruction was already using.
      switch (SRem == BO0 ? ICmpInst::getSwappedPredicate(Pred) : Pred) {
      default:
        break;
      case ICmpInst::ICMP_EQ:
        return replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()));
      case ICmpInst::ICMP_NE:
        return replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
      case ICmpInst::ICMP_SGT:
      case ICmpInst::ICMP_SGE:
        return new ICmpInst(ICmpInst::ICMP_SGT, SRem->getOperand(1),
                            Constant::getAllOnesValue(SRem->getType()));
      case ICmpInst::ICMP_SLT:
      case ICmpInst::ICMP_SLE:
        return new ICmpInst(ICmpInst::ICMP_SLT, SRem->getOperand(1),
                            Constant::getNullValue(SRem->getType()));
      }
    }
  
    if (BO0 && BO1 && BO0->getOpcode() == BO1->getOpcode() && BO0->hasOneUse() &&
        BO1->hasOneUse() && BO0->getOperand(1) == BO1->getOperand(1)) {
      switch (BO0->getOpcode()) {
      default:
        break;
      case Instruction::Add:
      case Instruction::Sub:
      case Instruction::Xor:
        if (I.isEquality()) // a+x icmp eq/ne b+x --> a icmp b
          return new ICmpInst(I.getPredicate(), BO0->getOperand(0),
                              BO1->getOperand(0));
        // icmp u/s (a ^ signbit), (b ^ signbit) --> icmp s/u a, b
        if (ConstantInt *CI = dyn_cast<ConstantInt>(BO0->getOperand(1))) {
          if (CI->getValue().isSignBit()) {
            ICmpInst::Predicate Pred =
                I.isSigned() ? I.getUnsignedPredicate() : I.getSignedPredicate();
            return new ICmpInst(Pred, BO0->getOperand(0), BO1->getOperand(0));
          }
  
          if (BO0->getOpcode() == Instruction::Xor && CI->isMaxValue(true)) {
            ICmpInst::Predicate Pred =
                I.isSigned() ? I.getUnsignedPredicate() : I.getSignedPredicate();
            Pred = I.getSwappedPredicate(Pred);
            return new ICmpInst(Pred, BO0->getOperand(0), BO1->getOperand(0));
          }
        }
        break;
      case Instruction::Mul:
        if (!I.isEquality())
          break;
  
        if (ConstantInt *CI = dyn_cast<ConstantInt>(BO0->getOperand(1))) {
          // a * Cst icmp eq/ne b * Cst --> a & Mask icmp b & Mask
          // Mask = -1 >> count-trailing-zeros(Cst).
          if (!CI->isZero() && !CI->isOne()) {
            const APInt &AP = CI->getValue();
            ConstantInt *Mask = ConstantInt::get(
                I.getContext(),
                APInt::getLowBitsSet(AP.getBitWidth(),
                                     AP.getBitWidth() - AP.countTrailingZeros()));
            Value *And1 = Builder->CreateAnd(BO0->getOperand(0), Mask);
            Value *And2 = Builder->CreateAnd(BO1->getOperand(0), Mask);
            return new ICmpInst(I.getPredicate(), And1, And2);
          }
        }
        break;
      case Instruction::UDiv:
      case Instruction::LShr:
        if (I.isSigned())
          break;
        LLVM_FALLTHROUGH;
      case Instruction::SDiv:
      case Instruction::AShr:
        if (!BO0->isExact() || !BO1->isExact())
          break;
        return new ICmpInst(I.getPredicate(), BO0->getOperand(0),
                            BO1->getOperand(0));
      case Instruction::Shl: {
        bool NUW = BO0->hasNoUnsignedWrap() && BO1->hasNoUnsignedWrap();
        bool NSW = BO0->hasNoSignedWrap() && BO1->hasNoSignedWrap();
        if (!NUW && !NSW)
          break;
        if (!NSW && I.isSigned())
          break;
        return new ICmpInst(I.getPredicate(), BO0->getOperand(0),
                            BO1->getOperand(0));
      }
      }
    }
  
    if (BO0) {
      // Transform  A & (L - 1) `ult` L --> L != 0
      auto LSubOne = m_Add(m_Specific(Op1), m_AllOnes());
      auto BitwiseAnd =
          m_CombineOr(m_And(m_Value(), LSubOne), m_And(LSubOne, m_Value()));
  
      if (match(BO0, BitwiseAnd) && I.getPredicate() == ICmpInst::ICMP_ULT) {
        auto *Zero = Constant::getNullValue(BO0->getType());
        return new ICmpInst(ICmpInst::ICMP_NE, Op1, Zero);
      }
    }
  
    return nullptr;
  }
  
  /// Fold icmp Pred min|max(X, Y), X.
  static Instruction *foldICmpWithMinMax(ICmpInst &Cmp) {
    ICmpInst::Predicate Pred = Cmp.getPredicate();
    Value *Op0 = Cmp.getOperand(0);
    Value *X = Cmp.getOperand(1);
  
    // Canonicalize minimum or maximum operand to LHS of the icmp.
    if (match(X, m_c_SMin(m_Specific(Op0), m_Value())) ||
        match(X, m_c_SMax(m_Specific(Op0), m_Value())) ||
        match(X, m_c_UMin(m_Specific(Op0), m_Value())) ||
        match(X, m_c_UMax(m_Specific(Op0), m_Value()))) {
      std::swap(Op0, X);
      Pred = Cmp.getSwappedPredicate();
    }
  
    Value *Y = nullptr;
    if (match(Op0, m_c_SMin(m_Specific(X), m_Value(Y)))) {
      // smin(X, Y)  == X --> X s<= Y
      // smin(X, Y) s>= X --> X s<= Y
      if (Pred == CmpInst::ICMP_EQ || Pred == CmpInst::ICMP_SGE)
        return new ICmpInst(ICmpInst::ICMP_SLE, X, Y);
  
      // smin(X, Y) != X --> X s> Y
      // smin(X, Y) s< X --> X s> Y
      if (Pred == CmpInst::ICMP_NE || Pred == CmpInst::ICMP_SLT)
        return new ICmpInst(ICmpInst::ICMP_SGT, X, Y);
  
      // These cases should be handled in InstSimplify:
      // smin(X, Y) s<= X --> true
      // smin(X, Y) s> X --> false
      return nullptr;
    }
  
    if (match(Op0, m_c_SMax(m_Specific(X), m_Value(Y)))) {
      // smax(X, Y)  == X --> X s>= Y
      // smax(X, Y) s<= X --> X s>= Y
      if (Pred == CmpInst::ICMP_EQ || Pred == CmpInst::ICMP_SLE)
        return new ICmpInst(ICmpInst::ICMP_SGE, X, Y);
  
      // smax(X, Y) != X --> X s< Y
      // smax(X, Y) s> X --> X s< Y
      if (Pred == CmpInst::ICMP_NE || Pred == CmpInst::ICMP_SGT)
        return new ICmpInst(ICmpInst::ICMP_SLT, X, Y);
  
      // These cases should be handled in InstSimplify:
      // smax(X, Y) s>= X --> true
      // smax(X, Y) s< X --> false
      return nullptr;
    }
  
    if (match(Op0, m_c_UMin(m_Specific(X), m_Value(Y)))) {
      // umin(X, Y)  == X --> X u<= Y
      // umin(X, Y) u>= X --> X u<= Y
      if (Pred == CmpInst::ICMP_EQ || Pred == CmpInst::ICMP_UGE)
        return new ICmpInst(ICmpInst::ICMP_ULE, X, Y);
  
      // umin(X, Y) != X --> X u> Y
      // umin(X, Y) u< X --> X u> Y
      if (Pred == CmpInst::ICMP_NE || Pred == CmpInst::ICMP_ULT)
        return new ICmpInst(ICmpInst::ICMP_UGT, X, Y);
  
      // These cases should be handled in InstSimplify:
      // umin(X, Y) u<= X --> true
      // umin(X, Y) u> X --> false
      return nullptr;
    }
  
    if (match(Op0, m_c_UMax(m_Specific(X), m_Value(Y)))) {
      // umax(X, Y)  == X --> X u>= Y
      // umax(X, Y) u<= X --> X u>= Y
      if (Pred == CmpInst::ICMP_EQ || Pred == CmpInst::ICMP_ULE)
        return new ICmpInst(ICmpInst::ICMP_UGE, X, Y);
  
      // umax(X, Y) != X --> X u< Y
      // umax(X, Y) u> X --> X u< Y
      if (Pred == CmpInst::ICMP_NE || Pred == CmpInst::ICMP_UGT)
        return new ICmpInst(ICmpInst::ICMP_ULT, X, Y);
  
      // These cases should be handled in InstSimplify:
      // umax(X, Y) u>= X --> true
      // umax(X, Y) u< X --> false
      return nullptr;
    }
  
    return nullptr;
  }
  
  Instruction *InstCombiner::foldICmpEquality(ICmpInst &I) {
    if (!I.isEquality())
      return nullptr;
  
    Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
    Value *A = nullptr, *B = nullptr, *C = nullptr, *D = nullptr;
    if (match(Op0, m_Xor(m_Value(A), m_Value(B)))) {
      if (A == Op1 || B == Op1) { // (A^B) == A  ->  B == 0
        Value *OtherVal = A == Op1 ? B : A;
        return new ICmpInst(I.getPredicate(), OtherVal,
                            Constant::getNullValue(A->getType()));
      }
  
      if (match(Op1, m_Xor(m_Value(C), m_Value(D)))) {
        // A^c1 == C^c2 --> A == C^(c1^c2)
        ConstantInt *C1 = nullptr, *C2 = nullptr;
        if (match(B, m_ConstantInt(C1)) && match(D, m_ConstantInt(C2)) &&
            Op1->hasOneUse()) {
          Constant *NC = Builder->getInt(C1->getValue() ^ C2->getValue());
          Value *Xor = Builder->CreateXor(C, NC);
          return new ICmpInst(I.getPredicate(), A, Xor);
        }
  
        // A^B == A^D -> B == D
        if (A == C)
          return new ICmpInst(I.getPredicate(), B, D);
        if (A == D)
          return new ICmpInst(I.getPredicate(), B, C);
        if (B == C)
          return new ICmpInst(I.getPredicate(), A, D);
        if (B == D)
          return new ICmpInst(I.getPredicate(), A, C);
      }
    }
  
    if (match(Op1, m_Xor(m_Value(A), m_Value(B))) && (A == Op0 || B == Op0)) {
      // A == (A^B)  ->  B == 0
      Value *OtherVal = A == Op0 ? B : A;
      return new ICmpInst(I.getPredicate(), OtherVal,
                          Constant::getNullValue(A->getType()));
    }
  
    // (X&Z) == (Y&Z) -> (X^Y) & Z == 0
    if (match(Op0, m_OneUse(m_And(m_Value(A), m_Value(B)))) &&
        match(Op1, m_OneUse(m_And(m_Value(C), m_Value(D))))) {
      Value *X = nullptr, *Y = nullptr, *Z = nullptr;
  
      if (A == C) {
        X = B;
        Y = D;
        Z = A;
      } else if (A == D) {
        X = B;
        Y = C;
        Z = A;
      } else if (B == C) {
        X = A;
        Y = D;
        Z = B;
      } else if (B == D) {
        X = A;
        Y = C;
        Z = B;
      }
  
      if (X) { // Build (X^Y) & Z
        Op1 = Builder->CreateXor(X, Y);
        Op1 = Builder->CreateAnd(Op1, Z);
        I.setOperand(0, Op1);
        I.setOperand(1, Constant::getNullValue(Op1->getType()));
        return &I;
      }
    }
  
    // Transform (zext A) == (B & (1<<X)-1) --> A == (trunc B)
    // and       (B & (1<<X)-1) == (zext A) --> A == (trunc B)
    ConstantInt *Cst1 = nullptr;
    if ((Op0->hasOneUse() && match(Op0, m_ZExt(m_Value(A))) &&
         match(Op1, m_And(m_Value(B), m_ConstantInt(Cst1)))) ||
        (Op1->hasOneUse() && match(Op0, m_And(m_Value(B), m_ConstantInt(Cst1))) &&
         match(Op1, m_ZExt(m_Value(A))))) {
      APInt Pow2 = Cst1->getValue() + 1;
      if (Pow2.isPowerOf2() && isa<IntegerType>(A->getType()) &&
          Pow2.logBase2() == cast<IntegerType>(A->getType())->getBitWidth())
        return new ICmpInst(I.getPredicate(), A,
                            Builder->CreateTrunc(B, A->getType()));
    }
  
    // (A >> C) == (B >> C) --> (A^B) u< (1 << C)
    // For lshr and ashr pairs.
    if ((match(Op0, m_OneUse(m_LShr(m_Value(A), m_ConstantInt(Cst1)))) &&
         match(Op1, m_OneUse(m_LShr(m_Value(B), m_Specific(Cst1))))) ||
        (match(Op0, m_OneUse(m_AShr(m_Value(A), m_ConstantInt(Cst1)))) &&
         match(Op1, m_OneUse(m_AShr(m_Value(B), m_Specific(Cst1)))))) {
      unsigned TypeBits = Cst1->getBitWidth();
      unsigned ShAmt = (unsigned)Cst1->getLimitedValue(TypeBits);
      if (ShAmt < TypeBits && ShAmt != 0) {
        ICmpInst::Predicate Pred = I.getPredicate() == ICmpInst::ICMP_NE
                                       ? ICmpInst::ICMP_UGE
                                       : ICmpInst::ICMP_ULT;
        Value *Xor = Builder->CreateXor(A, B, I.getName() + ".unshifted");
        APInt CmpVal = APInt::getOneBitSet(TypeBits, ShAmt);
        return new ICmpInst(Pred, Xor, Builder->getInt(CmpVal));
      }
    }
  
    // (A << C) == (B << C) --> ((A^B) & (~0U >> C)) == 0
    if (match(Op0, m_OneUse(m_Shl(m_Value(A), m_ConstantInt(Cst1)))) &&
        match(Op1, m_OneUse(m_Shl(m_Value(B), m_Specific(Cst1))))) {
      unsigned TypeBits = Cst1->getBitWidth();
      unsigned ShAmt = (unsigned)Cst1->getLimitedValue(TypeBits);
      if (ShAmt < TypeBits && ShAmt != 0) {
        Value *Xor = Builder->CreateXor(A, B, I.getName() + ".unshifted");
        APInt AndVal = APInt::getLowBitsSet(TypeBits, TypeBits - ShAmt);
        Value *And = Builder->CreateAnd(Xor, Builder->getInt(AndVal),
                                        I.getName() + ".mask");
        return new ICmpInst(I.getPredicate(), And,
                            Constant::getNullValue(Cst1->getType()));
      }
    }
  
    // Transform "icmp eq (trunc (lshr(X, cst1)), cst" to
    // "icmp (and X, mask), cst"
    uint64_t ShAmt = 0;
    if (Op0->hasOneUse() &&
        match(Op0, m_Trunc(m_OneUse(m_LShr(m_Value(A), m_ConstantInt(ShAmt))))) &&
        match(Op1, m_ConstantInt(Cst1)) &&
        // Only do this when A has multiple uses.  This is most important to do
        // when it exposes other optimizations.
        !A->hasOneUse()) {
      unsigned ASize = cast<IntegerType>(A->getType())->getPrimitiveSizeInBits();
  
      if (ShAmt < ASize) {
        APInt MaskV =
            APInt::getLowBitsSet(ASize, Op0->getType()->getPrimitiveSizeInBits());
        MaskV <<= ShAmt;
  
        APInt CmpV = Cst1->getValue().zext(ASize);
        CmpV <<= ShAmt;
  
        Value *Mask = Builder->CreateAnd(A, Builder->getInt(MaskV));
        return new ICmpInst(I.getPredicate(), Mask, Builder->getInt(CmpV));
      }
    }
  
    return nullptr;
  }
  
  /// Handle icmp (cast x to y), (cast/cst). We only handle extending casts so
  /// far.
  Instruction *InstCombiner::foldICmpWithCastAndCast(ICmpInst &ICmp) {
    const CastInst *LHSCI = cast<CastInst>(ICmp.getOperand(0));
    Value *LHSCIOp        = LHSCI->getOperand(0);
    Type *SrcTy     = LHSCIOp->getType();
    Type *DestTy    = LHSCI->getType();
    Value *RHSCIOp = nullptr;
  
    // Turn icmp (ptrtoint x), (ptrtoint/c) into a compare of the input if the
    // integer type is the same size as the pointer type.
    if (LHSCI->getOpcode() == Instruction::PtrToInt &&
        DL.getPointerTypeSizeInBits(SrcTy) == DestTy->getIntegerBitWidth()) {
      Value *RHSOp = nullptr;
      if (auto *RHSC = dyn_cast<PtrToIntOperator>(ICmp.getOperand(1))) {
        Value *RHSCIOp = RHSC->getOperand(0);
        if (RHSCIOp->getType()->getPointerAddressSpace() ==
            LHSCIOp->getType()->getPointerAddressSpace()) {
          RHSOp = RHSC->getOperand(0);
          // If the pointer types don't match, insert a bitcast.
          if (LHSCIOp->getType() != RHSOp->getType())
            RHSOp = Builder->CreateBitCast(RHSOp, LHSCIOp->getType());
        }
      } else if (auto *RHSC = dyn_cast<Constant>(ICmp.getOperand(1))) {
        RHSOp = ConstantExpr::getIntToPtr(RHSC, SrcTy);
      }
  
      if (RHSOp)
        return new ICmpInst(ICmp.getPredicate(), LHSCIOp, RHSOp);
    }
  
    // The code below only handles extension cast instructions, so far.
    // Enforce this.
    if (LHSCI->getOpcode() != Instruction::ZExt &&
        LHSCI->getOpcode() != Instruction::SExt)
      return nullptr;
  
    bool isSignedExt = LHSCI->getOpcode() == Instruction::SExt;
    bool isSignedCmp = ICmp.isSigned();
  
    if (auto *CI = dyn_cast<CastInst>(ICmp.getOperand(1))) {
      // Not an extension from the same type?
      RHSCIOp = CI->getOperand(0);
      if (RHSCIOp->getType() != LHSCIOp->getType())
        return nullptr;
  
      // If the signedness of the two casts doesn't agree (i.e. one is a sext
      // and the other is a zext), then we can't handle this.
      if (CI->getOpcode() != LHSCI->getOpcode())
        return nullptr;
  
      // Deal with equality cases early.
      if (ICmp.isEquality())
        return new ICmpInst(ICmp.getPredicate(), LHSCIOp, RHSCIOp);
  
      // A signed comparison of sign extended values simplifies into a
      // signed comparison.
      if (isSignedCmp && isSignedExt)
        return new ICmpInst(ICmp.getPredicate(), LHSCIOp, RHSCIOp);
  
      // The other three cases all fold into an unsigned comparison.
      return new ICmpInst(ICmp.getUnsignedPredicate(), LHSCIOp, RHSCIOp);
    }
  
    // If we aren't dealing with a constant on the RHS, exit early.
    auto *C = dyn_cast<Constant>(ICmp.getOperand(1));
    if (!C)
      return nullptr;
  
    // Compute the constant that would happen if we truncated to SrcTy then
    // re-extended to DestTy.
    Constant *Res1 = ConstantExpr::getTrunc(C, SrcTy);
    Constant *Res2 = ConstantExpr::getCast(LHSCI->getOpcode(), Res1, DestTy);
  
    // If the re-extended constant didn't change...
    if (Res2 == C) {
      // Deal with equality cases early.
      if (ICmp.isEquality())
        return new ICmpInst(ICmp.getPredicate(), LHSCIOp, Res1);
  
      // A signed comparison of sign extended values simplifies into a
      // signed comparison.
      if (isSignedExt && isSignedCmp)
        return new ICmpInst(ICmp.getPredicate(), LHSCIOp, Res1);
  
      // The other three cases all fold into an unsigned comparison.
      return new ICmpInst(ICmp.getUnsignedPredicate(), LHSCIOp, Res1);
    }
  
    // The re-extended constant changed, partly changed (in the case of a vector),
    // or could not be determined to be equal (in the case of a constant
    // expression), so the constant cannot be represented in the shorter type.
    // Consequently, we cannot emit a simple comparison.
    // All the cases that fold to true or false will have already been handled
    // by SimplifyICmpInst, so only deal with the tricky case.
  
    if (isSignedCmp || !isSignedExt || !isa<ConstantInt>(C))
      return nullptr;
  
    // Evaluate the comparison for LT (we invert for GT below). LE and GE cases
    // should have been folded away previously and not enter in here.
  
    // We're performing an unsigned comp with a sign extended value.
    // This is true if the input is >= 0. [aka >s -1]
    Constant *NegOne = Constant::getAllOnesValue(SrcTy);
    Value *Result = Builder->CreateICmpSGT(LHSCIOp, NegOne, ICmp.getName());
  
    // Finally, return the value computed.
    if (ICmp.getPredicate() == ICmpInst::ICMP_ULT)
      return replaceInstUsesWith(ICmp, Result);
  
    IGC_ASSERT_MESSAGE(ICmp.getPredicate() == ICmpInst::ICMP_UGT, "ICmp should be folded!");
    return BinaryOperator::CreateNot(Result);
  }
  
  bool InstCombiner::OptimizeOverflowCheck(OverflowCheckFlavor OCF, Value *LHS,
                                           Value *RHS, Instruction &OrigI,
                                           Value *&Result, Constant *&Overflow) {
    if (OrigI.isCommutative() && isa<Constant>(LHS) && !isa<Constant>(RHS))
      std::swap(LHS, RHS);
  
    auto SetResult = [&](Value *OpResult, Constant *OverflowVal, bool ReuseName) {
      Result = OpResult;
      Overflow = OverflowVal;
      if (ReuseName)
        Result->takeName(&OrigI);
      return true;
    };
  
    // If the overflow check was an add followed by a compare, the insertion point
    // may be pointing to the compare.  We want to insert the new instructions
    // before the add in case there are uses of the add between the add and the
    // compare.
    Builder->SetInsertPoint(&OrigI);
  
    switch (OCF) {
    case OCF_INVALID:
      IGC_ASSERT_EXIT_MESSAGE(0, "bad overflow check kind!");
  
    case OCF_UNSIGNED_ADD: {
      OverflowResult OR = computeOverflowForUnsignedAdd(LHS, RHS, &OrigI);
      if (OR == OverflowResult::NeverOverflows)
        return SetResult(Builder->CreateNUWAdd(LHS, RHS), Builder->getFalse(),
                         true);
  
      if (OR == OverflowResult::AlwaysOverflows)
        return SetResult(Builder->CreateAdd(LHS, RHS), Builder->getTrue(), true);
  
      // Fall through uadd into sadd
      LLVM_FALLTHROUGH;
    }
    case OCF_SIGNED_ADD: {
      // X + 0 -> {X, false}
      if (match(RHS, m_Zero()))
        return SetResult(LHS, Builder->getFalse(), false);
  
      // We can strength reduce this signed add into a regular add if we can prove
      // that it will never overflow.
      if (OCF == OCF_SIGNED_ADD)
        if (WillNotOverflowSignedAdd(LHS, RHS, OrigI))
          return SetResult(Builder->CreateNSWAdd(LHS, RHS), Builder->getFalse(),
                           true);
      break;
    }
  
    case OCF_UNSIGNED_SUB:
    case OCF_SIGNED_SUB: {
      // X - 0 -> {X, false}
      if (match(RHS, m_Zero()))
        return SetResult(LHS, Builder->getFalse(), false);
  
      if (OCF == OCF_SIGNED_SUB) {
        if (WillNotOverflowSignedSub(LHS, RHS, OrigI))
          return SetResult(Builder->CreateNSWSub(LHS, RHS), Builder->getFalse(),
                           true);
      } else {
        if (WillNotOverflowUnsignedSub(LHS, RHS, OrigI))
          return SetResult(Builder->CreateNUWSub(LHS, RHS), Builder->getFalse(),
                           true);
      }
      break;
    }
  
    case OCF_UNSIGNED_MUL: {
      OverflowResult OR = computeOverflowForUnsignedMul(LHS, RHS, &OrigI);
      if (OR == OverflowResult::NeverOverflows)
        return SetResult(Builder->CreateNUWMul(LHS, RHS), Builder->getFalse(),
                         true);
      if (OR == OverflowResult::AlwaysOverflows)
        return SetResult(Builder->CreateMul(LHS, RHS), Builder->getTrue(), true);
      LLVM_FALLTHROUGH;
    }
    case OCF_SIGNED_MUL:
      // X * undef -> undef
      if (isa<UndefValue>(RHS))
        return SetResult(RHS, UndefValue::get(Builder->getInt1Ty()), false);
  
      // X * 0 -> {0, false}
      if (match(RHS, m_Zero()))
        return SetResult(RHS, Builder->getFalse(), false);
  
      // X * 1 -> {X, false}
      if (match(RHS, m_One()))
        return SetResult(LHS, Builder->getFalse(), false);
  
      if (OCF == OCF_SIGNED_MUL)
        if (WillNotOverflowSignedMul(LHS, RHS, OrigI))
          return SetResult(Builder->CreateNSWMul(LHS, RHS), Builder->getFalse(),
                           true);
      break;
    }
  
    return false;
  }
  
  /// \brief Recognize and process idiom involving test for multiplication
  /// overflow.
  ///
  /// The caller has matched a pattern of the form:
  ///   I = cmp u (mul(zext A, zext B), V
  /// The function checks if this is a test for overflow and if so replaces
  /// multiplication with call to 'mul.with.overflow' intrinsic.
  ///
  /// \param I Compare instruction.
  /// \param MulVal Result of 'mult' instruction.  It is one of the arguments of
  ///               the compare instruction.  Must be of integer type.
  /// \param OtherVal The other argument of compare instruction.
  /// \returns Instruction which must replace the compare instruction, NULL if no
  ///          replacement required.
  static Instruction *processUMulZExtIdiom(ICmpInst &I, Value *MulVal,
                                           Value *OtherVal, InstCombiner &IC) {
    // Don't bother doing this transformation for pointers, don't do it for
    // vectors.
    if (!isa<IntegerType>(MulVal->getType()))
      return nullptr;
  
    IGC_ASSERT(I.getOperand(0) == MulVal || I.getOperand(1) == MulVal);
    IGC_ASSERT(I.getOperand(0) == OtherVal || I.getOperand(1) == OtherVal);
    auto *MulInstr = dyn_cast<Instruction>(MulVal);
    if (!MulInstr)
      return nullptr;
    IGC_ASSERT(MulInstr->getOpcode() == Instruction::Mul);
  
    auto *LHS = cast<ZExtOperator>(MulInstr->getOperand(0)),
         *RHS = cast<ZExtOperator>(MulInstr->getOperand(1));
    IGC_ASSERT(LHS->getOpcode() == Instruction::ZExt);
    IGC_ASSERT(RHS->getOpcode() == Instruction::ZExt);
    Value *A = LHS->getOperand(0), *B = RHS->getOperand(0);
  
    // Calculate type and width of the result produced by mul.with.overflow.
    Type *TyA = A->getType(), *TyB = B->getType();
    unsigned WidthA = TyA->getPrimitiveSizeInBits(),
             WidthB = TyB->getPrimitiveSizeInBits();
    unsigned MulWidth;
    Type *MulType;
    if (WidthB > WidthA) {
      MulWidth = WidthB;
      MulType = TyB;
    } else {
      MulWidth = WidthA;
      MulType = TyA;
    }
  
    // In order to replace the original mul with a narrower mul.with.overflow,
    // all uses must ignore upper bits of the product.  The number of used low
    // bits must be not greater than the width of mul.with.overflow.
    if (MulVal->hasNUsesOrMore(2))
      for (User *U : MulVal->users()) {
        if (U == &I)
          continue;
        if (TruncInst *TI = dyn_cast<TruncInst>(U)) {
          // Check if truncation ignores bits above MulWidth.
          unsigned TruncWidth = TI->getType()->getPrimitiveSizeInBits();
          if (TruncWidth > MulWidth)
            return nullptr;
        } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U)) {
          // Check if AND ignores bits above MulWidth.
          if (BO->getOpcode() != Instruction::And)
            return nullptr;
          if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->getOperand(1))) {
            const APInt &CVal = CI->getValue();
            if (CVal.getBitWidth() - CVal.countLeadingZeros() > MulWidth)
              return nullptr;
          }
        } else {
          // Other uses prohibit this transformation.
          return nullptr;
        }
      }
  
    // Recognize patterns
    switch (I.getPredicate()) {
    case ICmpInst::ICMP_EQ:
    case ICmpInst::ICMP_NE:
    {
        // Recognize pattern:
        //   mulval = mul(zext A, zext B)
        //   cmp eq/neq mulval, zext trunc mulval
        if (ZExtInst *Zext = dyn_cast<ZExtInst>(OtherVal))
            if (Zext->hasOneUse()) {
                Value *ZextArg = Zext->getOperand(0);
                if (TruncInst *Trunc = dyn_cast<TruncInst>(ZextArg))
                    if (Trunc->getType()->getPrimitiveSizeInBits() == MulWidth)
                        break; //Recognized
            }
  
        // Recognize pattern:
        //   mulval = mul(zext A, zext B)
        //   cmp eq/neq mulval, and(mulval, mask), mask selects low MulWidth bits.
        ConstantInt *CI = nullptr;
        Value *ValToMask = nullptr;
        if (match(OtherVal, m_And(m_Value(ValToMask), m_ConstantInt(CI)))) {
            if (ValToMask != MulVal)
                return nullptr;
            const APInt &CVal = CI->getValue() + 1;
            if (CVal.isPowerOf2()) {
                unsigned MaskWidth = CVal.logBase2();
                if (MaskWidth == MulWidth)
                    break; // Recognized
            }
        }
        return nullptr;
    }
    case ICmpInst::ICMP_UGT:
      // Recognize pattern:
      //   mulval = mul(zext A, zext B)
      //   cmp ugt mulval, max
      if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)) {
        APInt MaxVal = APInt::getMaxValue(MulWidth);
        MaxVal = MaxVal.zext(CI->getBitWidth());
        if (MaxVal.eq(CI->getValue()))
          break; // Recognized
      }
      return nullptr;
  
    case ICmpInst::ICMP_UGE:
      // Recognize pattern:
      //   mulval = mul(zext A, zext B)
      //   cmp uge mulval, max+1
      if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)) {
        APInt MaxVal = APInt::getOneBitSet(CI->getBitWidth(), MulWidth);
        if (MaxVal.eq(CI->getValue()))
          break; // Recognized
      }
      return nullptr;
  
    case ICmpInst::ICMP_ULE:
      // Recognize pattern:
      //   mulval = mul(zext A, zext B)
      //   cmp ule mulval, max
      if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)) {
        APInt MaxVal = APInt::getMaxValue(MulWidth);
        MaxVal = MaxVal.zext(CI->getBitWidth());
        if (MaxVal.eq(CI->getValue()))
          break; // Recognized
      }
      return nullptr;
  
    case ICmpInst::ICMP_ULT:
      // Recognize pattern:
      //   mulval = mul(zext A, zext B)
      //   cmp ule mulval, max + 1
      if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)) {
        APInt MaxVal = APInt::getOneBitSet(CI->getBitWidth(), MulWidth);
        if (MaxVal.eq(CI->getValue()))
          break; // Recognized
      }
      return nullptr;
  
    default:
      return nullptr;
    }
  
    InstCombiner::BuilderTy *Builder = IC.Builder;
    Builder->SetInsertPoint(MulInstr);
  
    // Replace: mul(zext A, zext B) --> mul.with.overflow(A, B)
    Value *MulA = A, *MulB = B;
    if (WidthA < MulWidth)
      MulA = Builder->CreateZExt(A, MulType);
    if (WidthB < MulWidth)
      MulB = Builder->CreateZExt(B, MulType);
    Value *F = Intrinsic::getDeclaration(I.getModule(),
                                         Intrinsic::umul_with_overflow, MulType);
    CallInst *Call = Builder->CreateCall(F, {MulA, MulB}, "umul");
    IC.Worklist.Add(MulInstr);
  
    // If there are uses of mul result other than the comparison, we know that
    // they are truncation or binary AND. Change them to use result of
    // mul.with.overflow and adjust properly mask/size.
    if (MulVal->hasNUsesOrMore(2)) {
      Value *Mul = Builder->CreateExtractValue(Call, 0, "umul.value");
      for (User *U : MulVal->users()) {
        if (U == &I || U == OtherVal)
          continue;
        if (TruncInst *TI = dyn_cast<TruncInst>(U)) {
          if (TI->getType()->getPrimitiveSizeInBits() == MulWidth)
            IC.replaceInstUsesWith(*TI, Mul);
          else
            TI->setOperand(0, Mul);
        } else if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U)) {
          IGC_ASSERT(BO->getOpcode() == Instruction::And);
          // Replace (mul & mask) --> zext (mul.with.overflow & short_mask)
          ConstantInt *CI = cast<ConstantInt>(BO->getOperand(1));
          APInt ShortMask = CI->getValue().trunc(MulWidth);
          Value *ShortAnd = Builder->CreateAnd(Mul, ShortMask);
          Instruction *Zext =
              cast<Instruction>(Builder->CreateZExt(ShortAnd, BO->getType()));
          IC.Worklist.Add(Zext);
          IC.replaceInstUsesWith(*BO, Zext);
        } else {
          IGC_ASSERT_EXIT_MESSAGE(0, "Unexpected Binary operation");
        }
        IC.Worklist.Add(cast<Instruction>(U));
      }
    }
    if (isa<Instruction>(OtherVal))
      IC.Worklist.Add(cast<Instruction>(OtherVal));
  
    // The original icmp gets replaced with the overflow value, maybe inverted
    // depending on predicate.
    bool Inverse = false;
    switch (I.getPredicate()) {
    case ICmpInst::ICMP_NE:
      break;
    case ICmpInst::ICMP_EQ:
      Inverse = true;
      break;
    case ICmpInst::ICMP_UGT:
    case ICmpInst::ICMP_UGE:
      if (I.getOperand(0) == MulVal)
        break;
      Inverse = true;
      break;
    case ICmpInst::ICMP_ULT:
    case ICmpInst::ICMP_ULE:
      if (I.getOperand(1) == MulVal)
        break;
      Inverse = true;
      break;
    default:
      IGC_ASSERT_EXIT_MESSAGE(0, "Unexpected predicate");
    }
    if (Inverse) {
      Value *Res = Builder->CreateExtractValue(Call, 1);
      return BinaryOperator::CreateNot(Res);
    }
  
    return ExtractValueInst::Create(Call, 1);
  }
  
  /// When performing a comparison against a constant, it is possible that not all
  /// the bits in the LHS are demanded. This helper method computes the mask that
  /// IS demanded.
  static APInt getDemandedBitsLHSMask(ICmpInst &I, unsigned BitWidth,
                                      bool isSignCheck) {
    if (isSignCheck)
      return APInt::getSignBit(BitWidth);
  
    ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand(1));
    if (!CI) return APInt::getAllOnesValue(BitWidth);
    const APInt &RHS = CI->getValue();
  
    switch (I.getPredicate()) {
    // For a UGT comparison, we don't care about any bits that
    // correspond to the trailing ones of the comparand.  The value of these
    // bits doesn't impact the outcome of the comparison, because any value
    // greater than the RHS must differ in a bit higher than these due to carry.
    case ICmpInst::ICMP_UGT: {
      unsigned trailingOnes = RHS.countTrailingOnes();
      APInt lowBitsSet = APInt::getLowBitsSet(BitWidth, trailingOnes);
      return ~lowBitsSet;
    }
  
    // Similarly, for a ULT comparison, we don't care about the trailing zeros.
    // Any value less than the RHS must differ in a higher bit because of carries.
    case ICmpInst::ICMP_ULT: {
      unsigned trailingZeros = RHS.countTrailingZeros();
      APInt lowBitsSet = APInt::getLowBitsSet(BitWidth, trailingZeros);
      return ~lowBitsSet;
    }
  
    default:
      return APInt::getAllOnesValue(BitWidth);
    }
  }
  
  /// \brief Check if the order of \p Op0 and \p Op1 as operand in an ICmpInst
  /// should be swapped.
  /// The decision is based on how many times these two operands are reused
  /// as subtract operands and their positions in those instructions.
  /// The rational is that several architectures use the same instruction for
  /// both subtract and cmp, thus it is better if the order of those operands
  /// match.
  /// \return true if Op0 and Op1 should be swapped.
  static bool swapMayExposeCSEOpportunities(const Value * Op0,
                                            const Value * Op1) {
    // Filter out pointer value as those cannot appears directly in subtract.
    // FIXME: we may want to go through inttoptrs or bitcasts.
    if (Op0->getType()->isPointerTy())
      return false;
    // Count every uses of both Op0 and Op1 in a subtract.
    // Each time Op0 is the first operand, count -1: swapping is bad, the
    // subtract has already the same layout as the compare.
    // Each time Op0 is the second operand, count +1: swapping is good, the
    // subtract has a different layout as the compare.
    // At the end, if the benefit is greater than 0, Op0 should come second to
    // expose more CSE opportunities.
    int GlobalSwapBenefits = 0;
    for (const User *U : Op0->users()) {
      const BinaryOperator *BinOp = dyn_cast<BinaryOperator>(U);
      if (!BinOp || BinOp->getOpcode() != Instruction::Sub)
        continue;
      // If Op0 is the first argument, this is not beneficial to swap the
      // arguments.
      int LocalSwapBenefits = -1;
      unsigned Op1Idx = 1;
      if (BinOp->getOperand(Op1Idx) == Op0) {
        Op1Idx = 0;
        LocalSwapBenefits = 1;
      }
      if (BinOp->getOperand(Op1Idx) != Op1)
        continue;
      GlobalSwapBenefits += LocalSwapBenefits;
    }
    return GlobalSwapBenefits > 0;
  }
  
  /// \brief Check that one use is in the same block as the definition and all
  /// other uses are in blocks dominated by a given block.
  ///
  /// \param DI Definition
  /// \param UI Use
  /// \param DB Block that must dominate all uses of \p DI outside
  ///           the parent block
  /// \return true when \p UI is the only use of \p DI in the parent block
  /// and all other uses of \p DI are in blocks dominated by \p DB.
  ///
  bool InstCombiner::dominatesAllUses(const Instruction *DI,
                                      const Instruction *UI,
                                      const BasicBlock *DB) const {
    IGC_ASSERT_MESSAGE(nullptr != DI, "Instruction not defined\n");
    IGC_ASSERT_MESSAGE(nullptr != UI, "Instruction not defined\n");
    // Ignore incomplete definitions.
    if (!DI->getParent())
      return false;
    // DI and UI must be in the same block.
    if (DI->getParent() != UI->getParent())
      return false;
    // Protect from self-referencing blocks.
    if (DI->getParent() == DB)
      return false;
    for (const User *U : DI->users()) {
      auto *Usr = cast<Instruction>(U);
      if (Usr != UI && !DT.dominates(DB, Usr->getParent()))
        return false;
    }
    return true;
  }
  
  /// Return true when the instruction sequence within a block is select-cmp-br.
  static bool isChainSelectCmpBranch(const SelectInst *SI) {
    const BasicBlock *BB = SI->getParent();
    if (!BB)
      return false;
    auto *BI = dyn_cast_or_null<BranchInst>(BB->getTerminator());
    if (!BI || BI->getNumSuccessors() != 2)
      return false;
    auto *IC = dyn_cast<ICmpInst>(BI->getCondition());
    if (!IC || (IC->getOperand(0) != SI && IC->getOperand(1) != SI))
      return false;
    return true;
  }
  
  /// \brief True when a select result is replaced by one of its operands
  /// in select-icmp sequence. This will eventually result in the elimination
  /// of the select.
  ///
  /// \param SI    Select instruction
  /// \param Icmp  Compare instruction
  /// \param SIOpd Operand that replaces the select
  ///
  /// Notes:
  /// - The replacement is global and requires dominator information
  /// - The caller is responsible for the actual replacement
  ///
  /// Example:
  ///
  /// entry:
  ///  %4 = select i1 %3, %C* %0, %C* null
  ///  %5 = icmp eq %C* %4, null
  ///  br i1 %5, label %9, label %7
  ///  ...
  ///  ; <label>:7                                       ; preds = %entry
  ///  %8 = getelementptr inbounds %C* %4, i64 0, i32 0
  ///  ...
  ///
  /// can be transformed to
  ///
  ///  %5 = icmp eq %C* %0, null
  ///  %6 = select i1 %3, i1 %5, i1 true
  ///  br i1 %6, label %9, label %7
  ///  ...
  ///  ; <label>:7                                       ; preds = %entry
  ///  %8 = getelementptr inbounds %C* %0, i64 0, i32 0  // replace by %0!
  ///
  /// Similar when the first operand of the select is a constant or/and
  /// the compare is for not equal rather than equal.
  ///
  /// NOTE: The function is only called when the select and compare constants
  /// are equal, the optimization can work only for EQ predicates. This is not a
  /// major restriction since a NE compare should be 'normalized' to an equal
  /// compare, which usually happens in the combiner and test case
  /// select-cmp-br.ll checks for it.
  bool InstCombiner::replacedSelectWithOperand(SelectInst *SI,
                                               const ICmpInst *Icmp,
                                               const unsigned SIOpd) {
    IGC_ASSERT_MESSAGE((SIOpd == 1 || SIOpd == 2), "Invalid select operand!");
    if (isChainSelectCmpBranch(SI) && Icmp->getPredicate() == ICmpInst::ICMP_EQ) {
      BasicBlock *Succ = SI->getParent()->getTerminator()->getSuccessor(1);
      // The check for the unique predecessor is not the best that can be
      // done. But it protects efficiently against cases like when SI's
      // home block has two successors, Succ and Succ1, and Succ1 predecessor
      // of Succ. Then SI can't be replaced by SIOpd because the use that gets
      // replaced can be reached on either path. So the uniqueness check
      // guarantees that the path all uses of SI (outside SI's parent) are on
      // is disjoint from all other paths out of SI. But that information
      // is more expensive to compute, and the trade-off here is in favor
      // of compile-time.
      if (Succ->getUniquePredecessor() && dominatesAllUses(SI, Icmp, Succ)) {
        NumSel++;
        SI->replaceUsesOutsideBlock(SI->getOperand(SIOpd), SI->getParent());
        return true;
      }
    }
    return false;
  }
  
  /// Try to fold the comparison based on range information we can get by checking
  /// whether bits are known to be zero or one in the inputs.
  Instruction *InstCombiner::foldICmpUsingKnownBits(ICmpInst &I) {
    Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
    Type *Ty = Op0->getType();
    ICmpInst::Predicate Pred = I.getPredicate();
  
    // Get scalar or pointer size.
    unsigned BitWidth = Ty->isIntOrIntVectorTy()
                            ? Ty->getScalarSizeInBits()
                            : DL.getTypeSizeInBits(Ty->getScalarType());
  
    if (!BitWidth)
      return nullptr;
  
    // If this is a normal comparison, it demands all bits. If it is a sign bit
    // comparison, it only demands the sign bit.
    bool IsSignBit = false;
    const APInt *CmpC = nullptr;
    if (match(Op1, m_APInt(CmpC))) {
      bool UnusedBit = false;
      IsSignBit = isSignBitCheck(Pred, *CmpC, UnusedBit);
    }
  
    APInt Op0KnownZero(BitWidth, 0), Op0KnownOne(BitWidth, 0);
    APInt Op1KnownZero(BitWidth, 0), Op1KnownOne(BitWidth, 0);
  
    if (SimplifyDemandedBits(I.getOperandUse(0),
                             getDemandedBitsLHSMask(I, BitWidth, IsSignBit),
                             Op0KnownZero, Op0KnownOne, 0))
      return &I;
  
    if (SimplifyDemandedBits(I.getOperandUse(1), APInt::getAllOnesValue(BitWidth),
                             Op1KnownZero, Op1KnownOne, 0))
      return &I;
  
    // Given the known and unknown bits, compute a range that the LHS could be
    // in.  Compute the Min, Max and RHS values based on the known bits. For the
    // EQ and NE we use unsigned values.
    APInt Op0Min(BitWidth, 0), Op0Max(BitWidth, 0);
    APInt Op1Min(BitWidth, 0), Op1Max(BitWidth, 0);
    if (I.isSigned()) {
      computeSignedMinMaxValuesFromKnownBits(Op0KnownZero, Op0KnownOne, Op0Min,
                                             Op0Max);
      computeSignedMinMaxValuesFromKnownBits(Op1KnownZero, Op1KnownOne, Op1Min,
                                             Op1Max);
    } else {
      computeUnsignedMinMaxValuesFromKnownBits(Op0KnownZero, Op0KnownOne, Op0Min,
                                               Op0Max);
      computeUnsignedMinMaxValuesFromKnownBits(Op1KnownZero, Op1KnownOne, Op1Min,
                                               Op1Max);
    }
  
    // If Min and Max are known to be the same, then SimplifyDemandedBits
    // figured out that the LHS is a constant. Constant fold this now, so that
    // code below can assume that Min != Max.
    if (!isa<Constant>(Op0) && Op0Min == Op0Max)
      return new ICmpInst(Pred, ConstantInt::get(Op0->getType(), Op0Min), Op1);
    if (!isa<Constant>(Op1) && Op1Min == Op1Max)
      return new ICmpInst(Pred, Op0, ConstantInt::get(Op1->getType(), Op1Min));
  
    // Based on the range information we know about the LHS, see if we can
    // simplify this comparison.  For example, (x&4) < 8 is always true.
    switch (Pred) {
    default:
      IGC_ASSERT_EXIT_MESSAGE(0, "Unknown icmp opcode!");
    case ICmpInst::ICMP_EQ:
    case ICmpInst::ICMP_NE: {
      if (Op0Max.ult(Op1Min) || Op0Min.ugt(Op1Max)) {
        return Pred == CmpInst::ICMP_EQ
                   ? replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()))
                   : replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
      }
  
      // If all bits are known zero except for one, then we know at most one bit
      // is set. If the comparison is against zero, then this is a check to see if
      // *that* bit is set.
      APInt Op0KnownZeroInverted = ~Op0KnownZero;
      if (~Op1KnownZero == 0) {
        // If the LHS is an AND with the same constant, look through it.
        Value *LHS = nullptr;
        const APInt *LHSC = nullptr;
        if (!match(Op0, m_And(m_Value(LHS), m_APInt(LHSC))) ||
            *LHSC != Op0KnownZeroInverted)
          LHS = Op0;
  
        Value *X;
        if (match(LHS, m_Shl(m_One(), m_Value(X)))) {
          APInt ValToCheck = Op0KnownZeroInverted;
          Type *XTy = X->getType();
          if (ValToCheck.isPowerOf2()) {
            // ((1 << X) & 8) == 0 -> X != 3
            // ((1 << X) & 8) != 0 -> X == 3
            auto *CmpC = ConstantInt::get(XTy, ValToCheck.countTrailingZeros());
            auto NewPred = ICmpInst::getInversePredicate(Pred);
            return new ICmpInst(NewPred, X, CmpC);
          } else if ((++ValToCheck).isPowerOf2()) {
            // ((1 << X) & 7) == 0 -> X >= 3
            // ((1 << X) & 7) != 0 -> X  < 3
            auto *CmpC = ConstantInt::get(XTy, ValToCheck.countTrailingZeros());
            auto NewPred =
                Pred == CmpInst::ICMP_EQ ? CmpInst::ICMP_UGE : CmpInst::ICMP_ULT;
            return new ICmpInst(NewPred, X, CmpC);
          }
        }
  
        // Check if the LHS is 8 >>u x and the result is a power of 2 like 1.
        const APInt *CI = nullptr;
        if (Op0KnownZeroInverted == 1 &&
            match(LHS, m_LShr(m_Power2(CI), m_Value(X)))) {
          // ((8 >>u X) & 1) == 0 -> X != 3
          // ((8 >>u X) & 1) != 0 -> X == 3
          unsigned CmpVal = CI->countTrailingZeros();
          auto NewPred = ICmpInst::getInversePredicate(Pred);
          return new ICmpInst(NewPred, X, ConstantInt::get(X->getType(), CmpVal));
        }
      }
      break;
    }
    case ICmpInst::ICMP_ULT: {
      if (Op0Max.ult(Op1Min)) // A <u B -> true if max(A) < min(B)
        return replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
      if (Op0Min.uge(Op1Max)) // A <u B -> false if min(A) >= max(B)
        return replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()));
      if (Op1Min == Op0Max) // A <u B -> A != B if max(A) == min(B)
        return new ICmpInst(ICmpInst::ICMP_NE, Op0, Op1);
  
      const APInt *CmpC = nullptr;
      if (match(Op1, m_APInt(CmpC))) {
        // A <u C -> A == C-1 if min(A)+1 == C
        if (Op1Max == Op0Min + 1) {
          Constant *CMinus1 = ConstantInt::get(Op0->getType(), *CmpC - 1);
          return new ICmpInst(ICmpInst::ICMP_EQ, Op0, CMinus1);
        }
      }
      break;
    }
    case ICmpInst::ICMP_UGT: {
      if (Op0Min.ugt(Op1Max)) // A >u B -> true if min(A) > max(B)
        return replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
  
      if (Op0Max.ule(Op1Min)) // A >u B -> false if max(A) <= max(B)
        return replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()));
  
      if (Op1Max == Op0Min) // A >u B -> A != B if min(A) == max(B)
        return new ICmpInst(ICmpInst::ICMP_NE, Op0, Op1);
  
      const APInt *CmpC = nullptr;
      if (match(Op1, m_APInt(CmpC))) {
        // A >u C -> A == C+1 if max(a)-1 == C
        if (*CmpC == Op0Max - 1)
          return new ICmpInst(ICmpInst::ICMP_EQ, Op0,
                              ConstantInt::get(Op1->getType(), *CmpC + 1));
      }
      break;
    }
    case ICmpInst::ICMP_SLT:
      if (Op0Max.slt(Op1Min)) // A <s B -> true if max(A) < min(C)
        return replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
      if (Op0Min.sge(Op1Max)) // A <s B -> false if min(A) >= max(C)
        return replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()));
      if (Op1Min == Op0Max) // A <s B -> A != B if max(A) == min(B)
        return new ICmpInst(ICmpInst::ICMP_NE, Op0, Op1);
      if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
        if (Op1Max == Op0Min + 1) // A <s C -> A == C-1 if min(A)+1 == C
          return new ICmpInst(ICmpInst::ICMP_EQ, Op0,
                              Builder->getInt(CI->getValue() - 1));
      }
      break;
    case ICmpInst::ICMP_SGT:
      if (Op0Min.sgt(Op1Max)) // A >s B -> true if min(A) > max(B)
        return replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
      if (Op0Max.sle(Op1Min)) // A >s B -> false if max(A) <= min(B)
        return replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()));
  
      if (Op1Max == Op0Min) // A >s B -> A != B if min(A) == max(B)
        return new ICmpInst(ICmpInst::ICMP_NE, Op0, Op1);
      if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
        if (Op1Min == Op0Max - 1) // A >s C -> A == C+1 if max(A)-1 == C
          return new ICmpInst(ICmpInst::ICMP_EQ, Op0,
                              Builder->getInt(CI->getValue() + 1));
      }
      break;
    case ICmpInst::ICMP_SGE:
      IGC_ASSERT_MESSAGE(!isa<ConstantInt>(Op1), "ICMP_SGE with ConstantInt not folded!");
      if (Op0Min.sge(Op1Max)) // A >=s B -> true if min(A) >= max(B)
        return replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
      if (Op0Max.slt(Op1Min)) // A >=s B -> false if max(A) < min(B)
        return replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()));
      break;
    case ICmpInst::ICMP_SLE:
      IGC_ASSERT_MESSAGE(!isa<ConstantInt>(Op1), "ICMP_SLE with ConstantInt not folded!");
      if (Op0Max.sle(Op1Min)) // A <=s B -> true if max(A) <= min(B)
        return replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
      if (Op0Min.sgt(Op1Max)) // A <=s B -> false if min(A) > max(B)
        return replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()));
      break;
    case ICmpInst::ICMP_UGE:
      IGC_ASSERT_MESSAGE(!isa<ConstantInt>(Op1), "ICMP_UGE with ConstantInt not folded!");
      if (Op0Min.uge(Op1Max)) // A >=u B -> true if min(A) >= max(B)
        return replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
      if (Op0Max.ult(Op1Min)) // A >=u B -> false if max(A) < min(B)
        return replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()));
      break;
    case ICmpInst::ICMP_ULE:
      IGC_ASSERT_MESSAGE(!isa<ConstantInt>(Op1), "ICMP_ULE with ConstantInt not folded!");
      if (Op0Max.ule(Op1Min)) // A <=u B -> true if max(A) <= min(B)
        return replaceInstUsesWith(I, ConstantInt::getTrue(I.getType()));
      if (Op0Min.ugt(Op1Max)) // A <=u B -> false if min(A) > max(B)
        return replaceInstUsesWith(I, ConstantInt::getFalse(I.getType()));
      break;
    }
  
    // Turn a signed comparison into an unsigned one if both operands are known to
    // have the same sign.
    if (I.isSigned() &&
        ((Op0KnownZero.isNegative() && Op1KnownZero.isNegative()) ||
         (Op0KnownOne.isNegative() && Op1KnownOne.isNegative())))
      return new ICmpInst(I.getUnsignedPredicate(), Op0, Op1);
  
    return nullptr;
  }
  
  /// If we have an icmp le or icmp ge instruction with a constant operand, turn
  /// it into the appropriate icmp lt or icmp gt instruction. This transform
  /// allows them to be folded in visitICmpInst.
  static ICmpInst *canonicalizeCmpWithConstant(ICmpInst &I) {
    ICmpInst::Predicate Pred = I.getPredicate();
    if (Pred != ICmpInst::ICMP_SLE && Pred != ICmpInst::ICMP_SGE &&
        Pred != ICmpInst::ICMP_ULE && Pred != ICmpInst::ICMP_UGE)
      return nullptr;
  
    Value *Op0 = I.getOperand(0);
    Value *Op1 = I.getOperand(1);
    auto *Op1C = dyn_cast<Constant>(Op1);
    if (!Op1C)
      return nullptr;
  
    // Check if the constant operand can be safely incremented/decremented without
    // overflowing/underflowing. For scalars, SimplifyICmpInst has already handled
    // the edge cases for us, so we just assertion test on them. For vectors, we must
    // handle the edge cases.
    Type *Op1Type = Op1->getType();
    bool IsSigned = I.isSigned();
    bool IsLE = (Pred == ICmpInst::ICMP_SLE || Pred == ICmpInst::ICMP_ULE);
    auto *CI = dyn_cast<ConstantInt>(Op1C);
    if (CI) {
      // A <= MAX -> TRUE ; A >= MIN -> TRUE
      IGC_ASSERT(IsLE ? !CI->isMaxValue(IsSigned) : !CI->isMinValue(IsSigned));
    } else if (Op1Type->isVectorTy()) {
      // TODO? If the edge cases for vectors were guaranteed to be handled as they
      // are for scalar, we could remove the min/max checks. However, to do that,
      // we would have to use insertelement/shufflevector to replace edge values.
      unsigned NumElts = Op1Type->getVectorNumElements();
      for (unsigned i = 0; i != NumElts; ++i) {
        Constant *Elt = Op1C->getAggregateElement(i);
        if (!Elt)
          return nullptr;
  
        if (isa<UndefValue>(Elt))
          continue;
  
        // Bail out if we can't determine if this constant is min/max or if we
        // know that this constant is min/max.
        auto *CI = dyn_cast<ConstantInt>(Elt);
        if (!CI || (IsLE ? CI->isMaxValue(IsSigned) : CI->isMinValue(IsSigned)))
          return nullptr;
      }
    } else {
      // ConstantExpr?
      return nullptr;
    }
  
    // Increment or decrement the constant and set the new comparison predicate:
    // ULE -> ULT ; UGE -> UGT ; SLE -> SLT ; SGE -> SGT
    Constant *OneOrNegOne = ConstantInt::get(Op1Type, IsLE ? 1 : -1, true);
    CmpInst::Predicate NewPred = IsLE ? ICmpInst::ICMP_ULT: ICmpInst::ICMP_UGT;
    NewPred = IsSigned ? ICmpInst::getSignedPredicate(NewPred) : NewPred;
    return new ICmpInst(NewPred, Op0, ConstantExpr::getAdd(Op1C, OneOrNegOne));
  }
  
  Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
    bool Changed = false;
    Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
    unsigned Op0Cplxity = getComplexity(Op0);
    unsigned Op1Cplxity = getComplexity(Op1);
  
    /// Orders the operands of the compare so that they are listed from most
    /// complex to least complex.  This puts constants before unary operators,
    /// before binary operators.
    if (Op0Cplxity < Op1Cplxity ||
        (Op0Cplxity == Op1Cplxity && swapMayExposeCSEOpportunities(Op0, Op1))) {
      I.swapOperands();
      std::swap(Op0, Op1);
      Changed = true;
    }
  
    if (Value *V =
            SimplifyICmpInst(I.getPredicate(), Op0, Op1, DL, &TLI, &DT, &AC, &I))
      return replaceInstUsesWith(I, V);
  
    // comparing -val or val with non-zero is the same as just comparing val
    // ie, abs(val) != 0 -> val != 0
    if (I.getPredicate() == ICmpInst::ICMP_NE && match(Op1, m_Zero())) {
      Value *Cond = nullptr, *SelectTrue = nullptr, *SelectFalse = nullptr;
      if (match(Op0, m_Select(m_Value(Cond), m_Value(SelectTrue),
                              m_Value(SelectFalse)))) {
        if (Value *V = dyn_castNegVal(SelectTrue)) {
          if (V == SelectFalse)
            return CmpInst::Create(Instruction::ICmp, I.getPredicate(), V, Op1);
        }
        else if (Value *V = dyn_castNegVal(SelectFalse)) {
          if (V == SelectTrue)
            return CmpInst::Create(Instruction::ICmp, I.getPredicate(), V, Op1);
        }
      }
    }
  
    Type *Ty = Op0->getType();
  
    // icmp's with boolean values can always be turned into bitwise operations
    if (Ty->getScalarType()->isIntegerTy(1)) {
      switch (I.getPredicate()) {
      default: IGC_ASSERT_EXIT_MESSAGE(0, "Invalid icmp instruction!");
      case ICmpInst::ICMP_EQ: {                // icmp eq i1 A, B -> ~(A^B)
        Value *Xor = Builder->CreateXor(Op0, Op1, I.getName() + "tmp");
        return BinaryOperator::CreateNot(Xor);
      }
      case ICmpInst::ICMP_NE:                  // icmp ne i1 A, B -> A^B
        return BinaryOperator::CreateXor(Op0, Op1);
  
      case ICmpInst::ICMP_UGT:
        std::swap(Op0, Op1);                   // Change icmp ugt -> icmp ult
        LLVM_FALLTHROUGH;
      case ICmpInst::ICMP_ULT:{                // icmp ult i1 A, B -> ~A & B
        Value *Not = Builder->CreateNot(Op0, I.getName() + "tmp");
        return BinaryOperator::CreateAnd(Not, Op1);
      }
      case ICmpInst::ICMP_SGT:
        std::swap(Op0, Op1);                   // Change icmp sgt -> icmp slt
        LLVM_FALLTHROUGH;
      case ICmpInst::ICMP_SLT: {               // icmp slt i1 A, B -> A & ~B
        Value *Not = Builder->CreateNot(Op1, I.getName() + "tmp");
        return BinaryOperator::CreateAnd(Not, Op0);
      }
      case ICmpInst::ICMP_UGE:
        std::swap(Op0, Op1);                   // Change icmp uge -> icmp ule
        LLVM_FALLTHROUGH;
      case ICmpInst::ICMP_ULE: {               // icmp ule i1 A, B -> ~A | B
        Value *Not = Builder->CreateNot(Op0, I.getName() + "tmp");
        return BinaryOperator::CreateOr(Not, Op1);
      }
      case ICmpInst::ICMP_SGE:
        std::swap(Op0, Op1);                   // Change icmp sge -> icmp sle
        LLVM_FALLTHROUGH;
      case ICmpInst::ICMP_SLE: {               // icmp sle i1 A, B -> A | ~B
        Value *Not = Builder->CreateNot(Op1, I.getName() + "tmp");
        return BinaryOperator::CreateOr(Not, Op0);
      }
      }
    }
  
    if (ICmpInst *NewICmp = canonicalizeCmpWithConstant(I))
      return NewICmp;
  
    if (Instruction *Res = foldICmpWithConstant(I))
      return Res;
  
    if (Instruction *Res = foldICmpUsingKnownBits(I))
      return Res;
  
    // Test if the ICmpInst instruction is used exclusively by a select as
    // part of a minimum or maximum operation. If so, refrain from doing
    // any other folding. This helps out other analyses which understand
    // non-obfuscated minimum and maximum idioms, such as ScalarEvolution
    // and CodeGen. And in this case, at least one of the comparison
    // operands has at least one user besides the compare (the select),
    // which would often largely negate the benefit of folding anyway.
    if (I.hasOneUse())
      if (SelectInst *SI = dyn_cast<SelectInst>(*I.user_begin()))
        if ((SI->getOperand(1) == Op0 && SI->getOperand(2) == Op1) ||
            (SI->getOperand(2) == Op0 && SI->getOperand(1) == Op1))
          return nullptr;
  
    // FIXME: We only do this after checking for min/max to prevent infinite
    // looping caused by a reverse canonicalization of these patterns for min/max.
    // FIXME: The organization of folds is a mess. These would naturally go into
    // canonicalizeCmpWithConstant(), but we can't move all of the above folds
    // down here after the min/max restriction.
    ICmpInst::Predicate Pred = I.getPredicate();
    const APInt *C = nullptr;
    if (match(Op1, m_APInt(C))) {
      // For i32: x >u 2147483647 -> x <s 0  -> true if sign bit set
      if (Pred == ICmpInst::ICMP_UGT && C->isMaxSignedValue()) {
        Constant *Zero = Constant::getNullValue(Op0->getType());
        return new ICmpInst(ICmpInst::ICMP_SLT, Op0, Zero);
      }
  
      // For i32: x <u 2147483648 -> x >s -1  -> true if sign bit clear
      if (Pred == ICmpInst::ICMP_ULT && C->isMinSignedValue()) {
        Constant *AllOnes = Constant::getAllOnesValue(Op0->getType());
        return new ICmpInst(ICmpInst::ICMP_SGT, Op0, AllOnes);
      }
    }
  
    if (Instruction *Res = foldICmpInstWithConstant(I))
      return Res;
  
    if (Instruction *Res = foldICmpInstWithConstantNotInt(I))
      return Res;
  
    // If we can optimize a 'icmp GEP, P' or 'icmp P, GEP', do so now.
    if (GEPOperator *GEP = dyn_cast<GEPOperator>(Op0))
      if (Instruction *NI = foldGEPICmp(GEP, Op1, I.getPredicate(), I))
        return NI;
    if (GEPOperator *GEP = dyn_cast<GEPOperator>(Op1))
      if (Instruction *NI = foldGEPICmp(GEP, Op0,
                             ICmpInst::getSwappedPredicate(I.getPredicate()), I))
        return NI;
  
    // Try to optimize equality comparisons against alloca-based pointers.
    if (Op0->getType()->isPointerTy() && I.isEquality()) {
      IGC_ASSERT_MESSAGE(Op1->getType()->isPointerTy(), "Comparing pointer with non-pointer?");
      if (auto *Alloca = dyn_cast<AllocaInst>(GetUnderlyingObject(Op0, DL)))
        if (Instruction *New = foldAllocaCmp(I, Alloca, Op1))
          return New;
      if (auto *Alloca = dyn_cast<AllocaInst>(GetUnderlyingObject(Op1, DL)))
        if (Instruction *New = foldAllocaCmp(I, Alloca, Op0))
          return New;
    }
  
    // Test to see if the operands of the icmp are casted versions of other
    // values.  If the ptr->ptr cast can be stripped off both arguments, we do so
    // now.
    if (BitCastInst *CI = dyn_cast<BitCastInst>(Op0)) {
      if (Op0->getType()->isPointerTy() &&
          (isa<Constant>(Op1) || isa<BitCastInst>(Op1))) {
        // We keep moving the cast from the left operand over to the right
        // operand, where it can often be eliminated completely.
        Op0 = CI->getOperand(0);
  
        // If operand #1 is a bitcast instruction, it must also be a ptr->ptr cast
        // so eliminate it as well.
        if (BitCastInst *CI2 = dyn_cast<BitCastInst>(Op1))
          Op1 = CI2->getOperand(0);
  
        // If Op1 is a constant, we can fold the cast into the constant.
        if (Op0->getType() != Op1->getType()) {
          if (Constant *Op1C = dyn_cast<Constant>(Op1)) {
            Op1 = ConstantExpr::getBitCast(Op1C, Op0->getType());
          } else {
            // Otherwise, cast the RHS right before the icmp
            Op1 = Builder->CreateBitCast(Op1, Op0->getType());
          }
        }
        return new ICmpInst(I.getPredicate(), Op0, Op1);
      }
    }
  
    if (isa<CastInst>(Op0)) {
      // Handle the special case of: icmp (cast bool to X), <cst>
      // This comes up when you have code like
      //   int X = A < B;
      //   if (X) ...
      // For generality, we handle any zero-extension of any operand comparison
      // with a constant or another cast from the same type.
      if (isa<Constant>(Op1) || isa<CastInst>(Op1))
        if (Instruction *R = foldICmpWithCastAndCast(I))
          return R;
    }
  
    if (Instruction *Res = foldICmpBinOp(I))
      return Res;
  
    if (Instruction *Res = foldICmpWithMinMax(I))
      return Res;
  
    {
      Value *A, *B;
      // Transform (A & ~B) == 0 --> (A & B) != 0
      // and       (A & ~B) != 0 --> (A & B) == 0
      // if A is a power of 2.
      if (match(Op0, m_And(m_Value(A), m_Not(m_Value(B)))) &&
          match(Op1, m_Zero()) &&
          isKnownToBeAPowerOfTwo(A, DL, false, 0, &AC, &I, &DT) && I.isEquality())
        return new ICmpInst(I.getInversePredicate(),
                            Builder->CreateAnd(A, B),
                            Op1);
  
      // ~x < ~y --> y < x
      // ~x < cst --> ~cst < x
      if (match(Op0, m_Not(m_Value(A)))) {
        if (match(Op1, m_Not(m_Value(B))))
          return new ICmpInst(I.getPredicate(), B, A);
        if (ConstantInt *RHSC = dyn_cast<ConstantInt>(Op1))
          return new ICmpInst(I.getPredicate(), ConstantExpr::getNot(RHSC), A);
      }
  
      Instruction *AddI = nullptr;
      if (match(&I, m_UAddWithOverflow(m_Value(A), m_Value(B),
                                       m_Instruction(AddI))) &&
          isa<IntegerType>(A->getType())) {
        Value *Result;
        Constant *Overflow;
        if (OptimizeOverflowCheck(OCF_UNSIGNED_ADD, A, B, *AddI, Result,
                                  Overflow)) {
          replaceInstUsesWith(*AddI, Result);
          return replaceInstUsesWith(I, Overflow);
        }
      }
  
      // (zext a) * (zext b)  --> llvm.umul.with.overflow.
      if (match(Op0, m_Mul(m_ZExt(m_Value(A)), m_ZExt(m_Value(B))))) {
        if (Instruction *R = processUMulZExtIdiom(I, Op0, Op1, *this))
          return R;
      }
      if (match(Op1, m_Mul(m_ZExt(m_Value(A)), m_ZExt(m_Value(B))))) {
        if (Instruction *R = processUMulZExtIdiom(I, Op1, Op0, *this))
          return R;
      }
    }
  
    if (Instruction *Res = foldICmpEquality(I))
      return Res;
  
    // The 'cmpxchg' instruction returns an aggregate containing the old value and
    // an i1 which indicates whether or not we successfully did the swap.
    //
    // Replace comparisons between the old value and the expected value with the
    // indicator that 'cmpxchg' returns.
    //
    // N.B.  This transform is only valid when the 'cmpxchg' is not permitted to
    // spuriously fail.  In those cases, the old value may equal the expected
    // value but it is possible for the swap to not occur.
    if (I.getPredicate() == ICmpInst::ICMP_EQ)
      if (auto *EVI = dyn_cast<ExtractValueInst>(Op0))
        if (auto *ACXI = dyn_cast<AtomicCmpXchgInst>(EVI->getAggregateOperand()))
          if (EVI->getIndices()[0] == 0 && ACXI->getCompareOperand() == Op1 &&
              !ACXI->isWeak())
            return ExtractValueInst::Create(ACXI, 1);
  
    {
      Value *X; ConstantInt *Cst;
      // icmp X+Cst, X
      if (match(Op0, m_Add(m_Value(X), m_ConstantInt(Cst))) && Op1 == X)
        return foldICmpAddOpConst(I, X, Cst, I.getPredicate());
  
      // icmp X, X+Cst
      if (match(Op1, m_Add(m_Value(X), m_ConstantInt(Cst))) && Op0 == X)
        return foldICmpAddOpConst(I, X, Cst, I.getSwappedPredicate());
    }
    return Changed ? &I : nullptr;
  }
  
  /// Fold fcmp ([us]itofp x, cst) if possible.
  Instruction *InstCombiner::foldFCmpIntToFPConst(FCmpInst &I, Instruction *LHSI,
                                                  Constant *RHSC) {
    if (!isa<ConstantFP>(RHSC)) return nullptr;
    const APFloat &RHS = cast<ConstantFP>(RHSC)->getValueAPF();
  
    // Get the width of the mantissa.  We don't want to hack on conversions that
    // might lose information from the integer, e.g. "i64 -> float"
    int MantissaWidth = LHSI->getType()->getFPMantissaWidth();
    if (MantissaWidth == -1) return nullptr;  // Unknown.
  
    IntegerType *IntTy = cast<IntegerType>(LHSI->getOperand(0)->getType());
  
    bool LHSUnsigned = isa<UIToFPInst>(LHSI);
  
    if (I.isEquality()) {
      FCmpInst::Predicate P = I.getPredicate();
      bool IsExact = false;
      APSInt RHSCvt(IntTy->getBitWidth(), LHSUnsigned);
      RHS.convertToInteger(RHSCvt, APFloat::rmNearestTiesToEven, &IsExact);
  
      // If the floating point constant isn't an integer value, we know if we will
      // ever compare equal / not equal to it.
      if (!IsExact) {
        // TODO: Can never be -0.0 and other non-representable values
        APFloat RHSRoundInt(RHS);
        RHSRoundInt.roundToIntegral(APFloat::rmNearestTiesToEven);
        if (RHS.compare(RHSRoundInt) != APFloat::cmpEqual) {
          if (P == FCmpInst::FCMP_OEQ || P == FCmpInst::FCMP_UEQ)
            return replaceInstUsesWith(I, Builder->getFalse());
  
          IGC_ASSERT(P == FCmpInst::FCMP_ONE || P == FCmpInst::FCMP_UNE);
          return replaceInstUsesWith(I, Builder->getTrue());
        }
      }
  
      // TODO: If the constant is exactly representable, is it always OK to do
      // equality compares as integer?
    }
  
    // Check to see that the input is converted from an integer type that is small
    // enough that preserves all bits.  TODO: check here for "known" sign bits.
    // This would allow us to handle (fptosi (x >>s 62) to float) if x is i64 f.e.
    unsigned InputSize = IntTy->getScalarSizeInBits();
  
    // Following test does NOT adjust InputSize downwards for signed inputs,
    // because the most negative value still requires all the mantissa bits
    // to distinguish it from one less than that value.
    if ((int)InputSize > MantissaWidth) {
      // Conversion would lose accuracy. Check if loss can impact comparison.
      int Exp = ilogb(RHS);
      if (Exp == APFloat::IEK_Inf) {
        int MaxExponent = ilogb(APFloat::getLargest(RHS.getSemantics()));
        if (MaxExponent < (int)InputSize - !LHSUnsigned)
          // Conversion could create infinity.
          return nullptr;
      } else {
        // Note that if RHS is zero or NaN, then Exp is negative
        // and first condition is trivially false.
        if (MantissaWidth <= Exp && Exp <= (int)InputSize - !LHSUnsigned)
          // Conversion could affect comparison.
          return nullptr;
      }
    }
  
    // Otherwise, we can potentially simplify the comparison.  We know that it
    // will always come through as an integer value and we know the constant is
    // not a NAN (it would have been previously simplified).
    IGC_ASSERT_MESSAGE(!RHS.isNaN(), "NaN comparison not already folded!");
  
    ICmpInst::Predicate Pred;
    switch (I.getPredicate()) {
    default: IGC_ASSERT_EXIT_MESSAGE(0, "Unexpected predicate!");
    case FCmpInst::FCMP_UEQ:
    case FCmpInst::FCMP_OEQ:
      Pred = ICmpInst::ICMP_EQ;
      break;
    case FCmpInst::FCMP_UGT:
    case FCmpInst::FCMP_OGT:
      Pred = LHSUnsigned ? ICmpInst::ICMP_UGT : ICmpInst::ICMP_SGT;
      break;
    case FCmpInst::FCMP_UGE:
    case FCmpInst::FCMP_OGE:
      Pred = LHSUnsigned ? ICmpInst::ICMP_UGE : ICmpInst::ICMP_SGE;
      break;
    case FCmpInst::FCMP_ULT:
    case FCmpInst::FCMP_OLT:
      Pred = LHSUnsigned ? ICmpInst::ICMP_ULT : ICmpInst::ICMP_SLT;
      break;
    case FCmpInst::FCMP_ULE:
    case FCmpInst::FCMP_OLE:
      Pred = LHSUnsigned ? ICmpInst::ICMP_ULE : ICmpInst::ICMP_SLE;
      break;
    case FCmpInst::FCMP_UNE:
    case FCmpInst::FCMP_ONE:
      Pred = ICmpInst::ICMP_NE;
      break;
    case FCmpInst::FCMP_ORD:
      return replaceInstUsesWith(I, Builder->getTrue());
    case FCmpInst::FCMP_UNO:
      return replaceInstUsesWith(I, Builder->getFalse());
    }
  
    // Now we know that the APFloat is a normal number, zero or inf.
  
    // See if the FP constant is too large for the integer.  For example,
    // comparing an i8 to 300.0.
    unsigned IntWidth = IntTy->getScalarSizeInBits();
  
    if (!LHSUnsigned) {
      // If the RHS value is > SignedMax, fold the comparison.  This handles +INF
      // and large values.
      APFloat SMax(RHS.getSemantics());
      SMax.convertFromAPInt(APInt::getSignedMaxValue(IntWidth), true,
                            APFloat::rmNearestTiesToEven);
      if (SMax.compare(RHS) == APFloat::cmpLessThan) {  // smax < 13123.0
        if (Pred == ICmpInst::ICMP_NE  || Pred == ICmpInst::ICMP_SLT ||
            Pred == ICmpInst::ICMP_SLE)
          return replaceInstUsesWith(I, Builder->getTrue());
        return replaceInstUsesWith(I, Builder->getFalse());
      }
    } else {
      // If the RHS value is > UnsignedMax, fold the comparison. This handles
      // +INF and large values.
      APFloat UMax(RHS.getSemantics());
      UMax.convertFromAPInt(APInt::getMaxValue(IntWidth), false,
                            APFloat::rmNearestTiesToEven);
      if (UMax.compare(RHS) == APFloat::cmpLessThan) {  // umax < 13123.0
        if (Pred == ICmpInst::ICMP_NE  || Pred == ICmpInst::ICMP_ULT ||
            Pred == ICmpInst::ICMP_ULE)
          return replaceInstUsesWith(I, Builder->getTrue());
        return replaceInstUsesWith(I, Builder->getFalse());
      }
    }
  
    if (!LHSUnsigned) {
      // See if the RHS value is < SignedMin.
      APFloat SMin(RHS.getSemantics());
      SMin.convertFromAPInt(APInt::getSignedMinValue(IntWidth), true,
                            APFloat::rmNearestTiesToEven);
      if (SMin.compare(RHS) == APFloat::cmpGreaterThan) { // smin > 12312.0
        if (Pred == ICmpInst::ICMP_NE || Pred == ICmpInst::ICMP_SGT ||
            Pred == ICmpInst::ICMP_SGE)
          return replaceInstUsesWith(I, Builder->getTrue());
        return replaceInstUsesWith(I, Builder->getFalse());
      }
    } else {
      // See if the RHS value is < UnsignedMin.
      APFloat SMin(RHS.getSemantics());
      SMin.convertFromAPInt(APInt::getMinValue(IntWidth), true,
                            APFloat::rmNearestTiesToEven);
      if (SMin.compare(RHS) == APFloat::cmpGreaterThan) { // umin > 12312.0
        if (Pred == ICmpInst::ICMP_NE || Pred == ICmpInst::ICMP_UGT ||
            Pred == ICmpInst::ICMP_UGE)
          return replaceInstUsesWith(I, Builder->getTrue());
        return replaceInstUsesWith(I, Builder->getFalse());
      }
    }
  
    // Okay, now we know that the FP constant fits in the range [SMIN, SMAX] or
    // [0, UMAX], but it may still be fractional.  See if it is fractional by
    // casting the FP value to the integer value and back, checking for equality.
    // Don't do this for zero, because -0.0 is not fractional.
    Constant *RHSInt = LHSUnsigned
      ? ConstantExpr::getFPToUI(RHSC, IntTy)
      : ConstantExpr::getFPToSI(RHSC, IntTy);
    if (!RHS.isZero()) {
      bool Equal = LHSUnsigned
        ? ConstantExpr::getUIToFP(RHSInt, RHSC->getType()) == RHSC
        : ConstantExpr::getSIToFP(RHSInt, RHSC->getType()) == RHSC;
      if (!Equal) {
        // If we had a comparison against a fractional value, we have to adjust
        // the compare predicate and sometimes the value.  RHSC is rounded towards
        // zero at this point.
        switch (Pred) {
        default: IGC_ASSERT_EXIT_MESSAGE(0, "Unexpected integer comparison!");
        case ICmpInst::ICMP_NE:  // (float)int != 4.4   --> true
          return replaceInstUsesWith(I, Builder->getTrue());
        case ICmpInst::ICMP_EQ:  // (float)int == 4.4   --> false
          return replaceInstUsesWith(I, Builder->getFalse());
        case ICmpInst::ICMP_ULE:
          // (float)int <= 4.4   --> int <= 4
          // (float)int <= -4.4  --> false
          if (RHS.isNegative())
            return replaceInstUsesWith(I, Builder->getFalse());
          break;
        case ICmpInst::ICMP_SLE:
          // (float)int <= 4.4   --> int <= 4
          // (float)int <= -4.4  --> int < -4
          if (RHS.isNegative())
            Pred = ICmpInst::ICMP_SLT;
          break;
        case ICmpInst::ICMP_ULT:
          // (float)int < -4.4   --> false
          // (float)int < 4.4    --> int <= 4
          if (RHS.isNegative())
            return replaceInstUsesWith(I, Builder->getFalse());
          Pred = ICmpInst::ICMP_ULE;
          break;
        case ICmpInst::ICMP_SLT:
          // (float)int < -4.4   --> int < -4
          // (float)int < 4.4    --> int <= 4
          if (!RHS.isNegative())
            Pred = ICmpInst::ICMP_SLE;
          break;
        case ICmpInst::ICMP_UGT:
          // (float)int > 4.4    --> int > 4
          // (float)int > -4.4   --> true
          if (RHS.isNegative())
            return replaceInstUsesWith(I, Builder->getTrue());
          break;
        case ICmpInst::ICMP_SGT:
          // (float)int > 4.4    --> int > 4
          // (float)int > -4.4   --> int >= -4
          if (RHS.isNegative())
            Pred = ICmpInst::ICMP_SGE;
          break;
        case ICmpInst::ICMP_UGE:
          // (float)int >= -4.4   --> true
          // (float)int >= 4.4    --> int > 4
          if (RHS.isNegative())
            return replaceInstUsesWith(I, Builder->getTrue());
          Pred = ICmpInst::ICMP_UGT;
          break;
        case ICmpInst::ICMP_SGE:
          // (float)int >= -4.4   --> int >= -4
          // (float)int >= 4.4    --> int > 4
          if (!RHS.isNegative())
            Pred = ICmpInst::ICMP_SGT;
          break;
        }
      }
    }
  
    // Lower this FP comparison into an appropriate integer version of the
    // comparison.
    return new ICmpInst(Pred, LHSI->getOperand(0), RHSInt);
  }
  
  Instruction *InstCombiner::visitFCmpInst(FCmpInst &I) {
    bool Changed = false;
  
    /// Orders the operands of the compare so that they are listed from most
    /// complex to least complex.  This puts constants before unary operators,
    /// before binary operators.
    if (getComplexity(I.getOperand(0)) < getComplexity(I.getOperand(1))) {
      I.swapOperands();
      Changed = true;
    }
  
    Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
  
    if (Value *V = SimplifyFCmpInst(I.getPredicate(), Op0, Op1,
                                    I.getFastMathFlags(), DL, &TLI, &DT, &AC, &I))
      return replaceInstUsesWith(I, V);
  
    // Simplify 'fcmp pred X, X'
    if (Op0 == Op1) {
      switch (I.getPredicate()) {
      default: IGC_ASSERT_EXIT_MESSAGE(0, "Unknown predicate!");
      case FCmpInst::FCMP_UNO:    // True if unordered: isnan(X) | isnan(Y)
      case FCmpInst::FCMP_ULT:    // True if unordered or less than
      case FCmpInst::FCMP_UGT:    // True if unordered or greater than
      case FCmpInst::FCMP_UNE:    // True if unordered or not equal
        // Canonicalize these to be 'fcmp uno %X, 0.0'.
        I.setPredicate(FCmpInst::FCMP_UNO);
        I.setOperand(1, Constant::getNullValue(Op0->getType()));
        return &I;
  
      case FCmpInst::FCMP_ORD:    // True if ordered (no nans)
      case FCmpInst::FCMP_OEQ:    // True if ordered and equal
      case FCmpInst::FCMP_OGE:    // True if ordered and greater than or equal
      case FCmpInst::FCMP_OLE:    // True if ordered and less than or equal
        // Canonicalize these to be 'fcmp ord %X, 0.0'.
        I.setPredicate(FCmpInst::FCMP_ORD);
        I.setOperand(1, Constant::getNullValue(Op0->getType()));
        return &I;
      }
    }
  
    // Test if the FCmpInst instruction is used exclusively by a select as
    // part of a minimum or maximum operation. If so, refrain from doing
    // any other folding. This helps out other analyses which understand
    // non-obfuscated minimum and maximum idioms, such as ScalarEvolution
    // and CodeGen. And in this case, at least one of the comparison
    // operands has at least one user besides the compare (the select),
    // which would often largely negate the benefit of folding anyway.
    if (I.hasOneUse())
      if (SelectInst *SI = dyn_cast<SelectInst>(*I.user_begin()))
        if ((SI->getOperand(1) == Op0 && SI->getOperand(2) == Op1) ||
            (SI->getOperand(2) == Op0 && SI->getOperand(1) == Op1))
          return nullptr;
  
    // Handle fcmp with constant RHS
    if (Constant *RHSC = dyn_cast<Constant>(Op1)) {
      if (Instruction *LHSI = dyn_cast<Instruction>(Op0))
        switch (LHSI->getOpcode()) {
        case Instruction::FPExt: {
          // fcmp (fpext x), C -> fcmp x, (fptrunc C) if fptrunc is lossless
          FPExtInst *LHSExt = cast<FPExtInst>(LHSI);
          ConstantFP *RHSF = dyn_cast<ConstantFP>(RHSC);
          if (!RHSF)
            break;
  
          const fltSemantics *Sem = nullptr;
          // FIXME: This shouldn't be here.
          if (LHSExt->getSrcTy()->isHalfTy())
            Sem = &APFloat::IEEEhalf();
          else if (LHSExt->getSrcTy()->isFloatTy())
            Sem = &APFloat::IEEEsingle();
          else if (LHSExt->getSrcTy()->isDoubleTy())
            Sem = &APFloat::IEEEdouble();
          else if (LHSExt->getSrcTy()->isFP128Ty())
            Sem = &APFloat::IEEEquad();
          else if (LHSExt->getSrcTy()->isX86_FP80Ty())
            Sem = &APFloat::x87DoubleExtended();
          else if (LHSExt->getSrcTy()->isPPC_FP128Ty())
            Sem = &APFloat::PPCDoubleDouble();
          else
            break;
  
          bool Lossy = false;
          APFloat F = RHSF->getValueAPF();
          F.convert(*Sem, APFloat::rmNearestTiesToEven, &Lossy);
  
          // Avoid lossy conversions and denormals. Zero is a special case
          // that's OK to convert.
          APFloat Fabs = F;
          Fabs.clearSign();
          if (!Lossy &&
              ((Fabs.compare(APFloat::getSmallestNormalized(*Sem)) !=
                   APFloat::cmpLessThan) || Fabs.isZero()))
  
            return new FCmpInst(I.getPredicate(), LHSExt->getOperand(0),
                                ConstantFP::get(RHSC->getContext(), F));
          break;
        }
        case Instruction::PHI:
          // Only fold fcmp into the PHI if the phi and fcmp are in the same
          // block.  If in the same block, we're encouraging jump threading.  If
          // not, we are just pessimizing the code by making an i1 phi.
          if (LHSI->getParent() == I.getParent())
            if (Instruction *NV = FoldOpIntoPhi(I))
              return NV;
          break;
        case Instruction::SIToFP:
        case Instruction::UIToFP:
          if (Instruction *NV = foldFCmpIntToFPConst(I, LHSI, RHSC))
            return NV;
          break;
        case Instruction::FSub: {
          // fcmp pred (fneg x), C -> fcmp swap(pred) x, -C
          Value *Op;
          if (match(LHSI, m_FNeg(m_Value(Op))))
            return new FCmpInst(I.getSwappedPredicate(), Op,
                                ConstantExpr::getFNeg(RHSC));
          break;
        }
        case Instruction::Load:
          if (GetElementPtrInst *GEP =
              dyn_cast<GetElementPtrInst>(LHSI->getOperand(0))) {
            if (GlobalVariable *GV = dyn_cast<GlobalVariable>(GEP->getOperand(0)))
              if (GV->isConstant() && GV->hasDefinitiveInitializer() &&
                  !cast<LoadInst>(LHSI)->isVolatile())
                if (Instruction *Res = foldCmpLoadFromIndexedGlobal(GEP, GV, I))
                  return Res;
          }
          break;
        case Instruction::Call: {
          if (!RHSC->isNullValue())
            break;
  
          CallInst *CI = cast<CallInst>(LHSI);
          Intrinsic::ID IID = getIntrinsicForCallSite(CI, &TLI);
          if (IID != Intrinsic::fabs)
            break;
  
          // Various optimization for fabs compared with zero.
          switch (I.getPredicate()) {
          default:
            break;
          // fabs(x) < 0 --> false
          case FCmpInst::FCMP_OLT:
            IGC_ASSERT_EXIT_MESSAGE(0, "handled by SimplifyFCmpInst");
          // fabs(x) > 0 --> x != 0
          case FCmpInst::FCMP_OGT:
            return new FCmpInst(FCmpInst::FCMP_ONE, CI->getArgOperand(0), RHSC);
          // fabs(x) <= 0 --> x == 0
          case FCmpInst::FCMP_OLE:
            return new FCmpInst(FCmpInst::FCMP_OEQ, CI->getArgOperand(0), RHSC);
          // fabs(x) >= 0 --> !isnan(x)
          case FCmpInst::FCMP_OGE:
            return new FCmpInst(FCmpInst::FCMP_ORD, CI->getArgOperand(0), RHSC);
          // fabs(x) == 0 --> x == 0
          // fabs(x) != 0 --> x != 0
          case FCmpInst::FCMP_OEQ:
          case FCmpInst::FCMP_UEQ:
          case FCmpInst::FCMP_ONE:
          case FCmpInst::FCMP_UNE:
            return new FCmpInst(I.getPredicate(), CI->getArgOperand(0), RHSC);
          }
        }
        }
    }
  
    // fcmp pred (fneg x), (fneg y) -> fcmp swap(pred) x, y
    Value *X = nullptr, *Y = nullptr;
    if (match(Op0, m_FNeg(m_Value(X))) && match(Op1, m_FNeg(m_Value(Y))))
      return new FCmpInst(I.getSwappedPredicate(), X, Y);
  
    // fcmp (fpext x), (fpext y) -> fcmp x, y
    if (FPExtInst *LHSExt = dyn_cast<FPExtInst>(Op0))
      if (FPExtInst *RHSExt = dyn_cast<FPExtInst>(Op1))
        if (LHSExt->getSrcTy() == RHSExt->getSrcTy())
          return new FCmpInst(I.getPredicate(), LHSExt->getOperand(0),
                              RHSExt->getOperand(0));
  
    return Changed ? &I : nullptr;
  }
  #include "common/LLVMWarningsPop.hpp"
  