llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

//===- InstCombineCompares.cpp --------------------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the visitICmp and visitFCmp functions.
//
//===----------------------------------------------------------------------===//

#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"

using namespace llvm;
using namespace PatternMatch;

#define DEBUG_TYPE "instcombine"

// How many times is a select replaced by one of its operands?
STATISTIC(NumSel, "Number of select opts");

// Initialization Routines

static ConstantInt *getOne(Constant *C) {
  return ConstantInt::get(cast<IntegerType>(C->getType()), 1);
}

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, ConstantInt *RHS,
                           bool &TrueIfSigned) {
  switch (Pred) {
  case ICmpInst::ICMP_SLT:   // True if LHS s< 0
    TrueIfSigned = true;
    return RHS->isZero();
  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->isMaxValue(true);
  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->getValue().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.
static bool isSignTest(ICmpInst::Predicate &Pred, const ConstantInt *RHS) {
  if (!ICmpInst::isSigned(Pred))
    return false;

  if (RHS->isZero())
    return ICmpInst::isRelational(Pred);

  if (RHS->isOne()) {
    if (Pred == ICmpInst::ICMP_SLT) {
      Pred = ICmpInst::ICMP_SLE;
      return true;
    }
  } else if (RHS->isAllOnesValue()) {
    if (Pred == ICmpInst::ICMP_SGT) {
      Pred = ICmpInst::ICMP_SGE;
      return true;
    }
  }

  return false;
}

/// Return true if the constant is of the form 1+0+. This is the same as
/// lowones(~X).
static bool isHighOnes(const ConstantInt *CI) {
  return (~CI->getValue() + 1).isPowerOf2();
}

/// 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) {
  assert(KnownZero.getBitWidth() == KnownOne.getBitWidth() &&
         KnownZero.getBitWidth() == Min.getBitWidth() &&
         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) {
  assert(KnownZero.getBitWidth() == KnownOne.getBitWidth() &&
         KnownZero.getBitWidth() == Min.getBitWidth() &&
         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) {
    assert(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) {
    assert(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 = dyn_cast<StructType>(*GTI)) {
        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 = dyn_cast<StructType>(*GTI)) {
      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<GEPOperator>(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.
  assert(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;

    llvm_unreachable("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;

  Value *PtrBase, *Index;
  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, AllocaInst *Alloca,
                                         Value *Other) {
  assert(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<Use *, 32> Worklist;
  for (Use &U : Alloca->uses()) {
    if (Worklist.size() >= MaxIter)
      return nullptr;
    Worklist.push_back(&U);
  }

  unsigned NumCmps = 0;
  while (!Worklist.empty()) {
    assert(Worklist.size() <= MaxIter);
    Use *U = Worklist.pop_back_val();
    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 (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 (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 (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

  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));
}

/// Fold "icmp pred, ([su]div X, DivRHS), CmpRHS" where DivRHS and CmpRHS are
/// both known to be integer constants.
Instruction *InstCombiner::foldICmpDivConst(ICmpInst &ICI, BinaryOperator *DivI,
                                            ConstantInt *DivRHS) {
  ConstantInt *CmpRHS = cast<ConstantInt>(ICI.getOperand(1));
  const APInt &CmpRHSV = CmpRHS->getValue();

  // 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 C1) <s C2  produces different
  // results than (x /s C1) <u C2 or (x /u C1) <s C2 or even
  // (x /u C1) <u C2.  Simply casting the operands and result won't
  // work. :(  The if statement below tests that condition and bails
  // if it finds it.
  bool DivIsSigned = DivI->getOpcode() == Instruction::SDiv;
  if (!ICI.isEquality() && DivIsSigned != ICI.isSigned())
    return nullptr;
  if (DivRHS->isZero())
    return nullptr; // The ProdOV computation fails on divide by zero.
  if (DivIsSigned && DivRHS->isAllOnesValue())
    return nullptr; // The overflow computation also screws up here
  if (DivRHS->isOne()) {
    // This eliminates some funny cases with INT_MIN.
    ICI.setOperand(0, DivI->getOperand(0));   // X/1 == X.
    return &ICI;
  }

  // Compute Prod = CI * DivRHS. We are essentially solving an equation
  // of form X/C1=C2. We solve for X by multiplying C1 (DivRHS) and
  // C2 (CI). 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;

  // Get the ICmp opcode
  ICmpInst::Predicate Pred = ICI.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.
  ConstantInt *RangeSize = DivI->isExact() ? getOne(Prod) : 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 (DivRHS->getValue().isStrictlyPositive()) { // Divisor is > 0.
    if (CmpRHSV == 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 (CmpRHSV.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) {
        ConstantInt *DivNeg =cast<ConstantInt>(ConstantExpr::getNeg(RangeSize));
        LoOverflow = AddWithOverflow(LoBound, HiBound, DivNeg, true) ? -1 : 0;
      }
    }
  } else if (DivRHS->isNegative()) { // Divisor is < 0.
    if (DivI->isExact())
      RangeSize = cast<ConstantInt>(ConstantExpr::getNeg(RangeSize));
    if (CmpRHSV == 0) {       // (X / neg) op 0
      // e.g. X/-5 op 0  --> [-4, 5)
      LoBound = AddOne(RangeSize);
      HiBound = cast<ConstantInt>(ConstantExpr::getNeg(RangeSize));
      if (HiBound == DivRHS) {     // -INTMIN = INTMIN
        HiOverflow = 1;            // [INTMIN+1, overflow)
        HiBound = nullptr;         // e.g. X/INTMIN = 0 --> X > INTMIN
      }
    } else if (CmpRHSV.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 = DivI->getOperand(0);
  switch (Pred) {
  default: llvm_unreachable("Unhandled icmp opcode!");
  case ICmpInst::ICMP_EQ:
    if (LoOverflow && HiOverflow)
      return replaceInstUsesWith(ICI, 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(ICI, InsertRangeTest(X, LoBound, HiBound,
                                                    DivIsSigned, true));
  case ICmpInst::ICMP_NE:
    if (LoOverflow && HiOverflow)
      return replaceInstUsesWith(ICI, 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(ICI, InsertRangeTest(X, LoBound, HiBound,
                                                    DivIsSigned, false));
  case ICmpInst::ICMP_ULT:
  case ICmpInst::ICMP_SLT:
    if (LoOverflow == +1)   // Low bound is greater than input range.
      return replaceInstUsesWith(ICI, Builder->getTrue());
    if (LoOverflow == -1)   // Low bound is less than input range.
      return replaceInstUsesWith(ICI, 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(ICI, Builder->getFalse());
    if (HiOverflow == -1)       // High bound less than input range.
      return replaceInstUsesWith(ICI, Builder->getTrue());
    if (Pred == ICmpInst::ICMP_UGT)
      return new ICmpInst(ICmpInst::ICMP_UGE, X, HiBound);
    return new ICmpInst(ICmpInst::ICMP_SGE, X, HiBound);
  }
}

/// Handle "icmp(([al]shr X, cst1), cst2)".
Instruction *InstCombiner::foldICmpShrConst(ICmpInst &ICI, BinaryOperator *Shr,
                                            ConstantInt *ShAmt) {
  const APInt &CmpRHSV = cast<ConstantInt>(ICI.getOperand(1))->getValue();

  // Check that the shift amount is in range.  If not, don't perform
  // undefined shifts.  When the shift is visited it will be
  // simplified.
  uint32_t TypeBits = CmpRHSV.getBitWidth();
  uint32_t ShAmtVal = (uint32_t)ShAmt->getLimitedValue(TypeBits);
  if (ShAmtVal >= TypeBits || ShAmtVal == 0)
    return nullptr;

  if (!ICI.isEquality()) {
    // If we have an unsigned comparison and an ashr, we can't simplify this.
    // Similarly for signed comparisons with lshr.
    if (ICI.isSigned() != (Shr->getOpcode() == Instruction::AShr))
      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 (Shr->getOpcode() == Instruction::AShr &&
        (!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 =
      Shr->getOpcode() == Instruction::AShr ?
      Builder->CreateSDiv(Shr->getOperand(0), DivCst, "", Shr->isExact()) :
      Builder->CreateUDiv(Shr->getOperand(0), DivCst, "", Shr->isExact());

    ICI.setOperand(0, Tmp);

    // If the builder folded the binop, just return it.
    BinaryOperator *TheDiv = dyn_cast<BinaryOperator>(Tmp);
    if (!TheDiv)
      return &ICI;

    // Otherwise, fold this div/compare.
    assert(TheDiv->getOpcode() == Instruction::SDiv ||
           TheDiv->getOpcode() == Instruction::UDiv);

    Instruction *Res = foldICmpDivConst(ICI, TheDiv, cast<ConstantInt>(DivCst));
    assert(Res && "This div/cst should have folded!");
    return Res;
  }

  // If we are comparing against bits always shifted out, the
  // comparison cannot succeed.
  APInt Comp = CmpRHSV << ShAmtVal;
  ConstantInt *ShiftedCmpRHS = Builder->getInt(Comp);
  if (Shr->getOpcode() == Instruction::LShr)
    Comp = Comp.lshr(ShAmtVal);
  else
    Comp = Comp.ashr(ShAmtVal);

  if (Comp != CmpRHSV) { // Comparing against a bit that we know is zero.
    bool IsICMP_NE = ICI.getPredicate() == ICmpInst::ICMP_NE;
    Constant *Cst = Builder->getInt1(IsICMP_NE);
    return replaceInstUsesWith(ICI, Cst);
  }

  // Otherwise, check to see 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.
  if (Shr->hasOneUse() && Shr->isExact())
    return new ICmpInst(ICI.getPredicate(), Shr->getOperand(0), ShiftedCmpRHS);

  if (Shr->hasOneUse()) {
    // Otherwise strength reduce the shift into an and.
    APInt Val(APInt::getHighBitsSet(TypeBits, TypeBits - ShAmtVal));
    Constant *Mask = Builder->getInt(Val);

    Value *And = Builder->CreateAnd(Shr->getOperand(0),
                                    Mask, Shr->getName()+".mask");
    return new ICmpInst(ICI.getPredicate(), And, ShiftedCmpRHS);
  }
  return nullptr;
}

/// Handle "(icmp eq/ne (ashr/lshr const2, A), const1)" ->
/// (icmp eq/ne A, Log2(const2/const1)) ->
/// (icmp eq/ne A, Log2(const2) - Log2(const1)).
Instruction *InstCombiner::foldICmpCstShrConst(ICmpInst &I, Value *Op, Value *A,
                                             ConstantInt *CI1,
                                             ConstantInt *CI2) {
  assert(I.isEquality() && "Cannot fold icmp gt/lt");

  auto getConstant = [&I, this](bool IsTrue) {
    if (I.getPredicate() == I.ICMP_NE)
      IsTrue = !IsTrue;
    return replaceInstUsesWith(I, ConstantInt::get(I.getType(), IsTrue));
  };

  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);
  };

  const APInt &AP1 = CI1->getValue();
  const APInt &AP2 = CI2->getValue();

  // Don't bother doing any work for cases which InstSimplify handles.
  if (AP2 == 0)
    return nullptr;
  bool IsAShr = isa<AShrOperator>(Op);
  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.
  return getConstant(false);
}

/// Handle "(icmp eq/ne (shl const2, A), const1)" ->
/// (icmp eq/ne A, TrailingZeros(const1) - TrailingZeros(const2)).
Instruction *InstCombiner::foldICmpCstShlConst(ICmpInst &I, Value *Op, Value *A,
                                               ConstantInt *CI1,
                                               ConstantInt *CI2) {
  assert(I.isEquality() && "Cannot fold icmp gt/lt");

  auto getConstant = [&I, this](bool IsTrue) {
    if (I.getPredicate() == I.ICMP_NE)
      IsTrue = !IsTrue;
    return replaceInstUsesWith(I, ConstantInt::get(I.getType(), IsTrue));
  };

  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);
  };

  const APInt &AP1 = CI1->getValue();
  const APInt &AP2 = CI2->getValue();

  // 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.
  return getConstant(false);
}

/// Handle "icmp (instr, intcst)".
Instruction *InstCombiner::foldICmpWithConstant(ICmpInst &ICI,
                                                Instruction *LHSI,
                                                ConstantInt *RHS) {
  const APInt &RHSV = RHS->getValue();

  switch (LHSI->getOpcode()) {
  case Instruction::Trunc:
    if (RHS->isOne() && RHSV.getBitWidth() > 1) {
      // icmp slt trunc(signum(V)) 1 --> icmp slt V, 1
      Value *V = nullptr;
      if (ICI.getPredicate() == ICmpInst::ICMP_SLT &&
          match(LHSI->getOperand(0), m_Signum(m_Value(V))))
        return new ICmpInst(ICmpInst::ICMP_SLT, V,
                            ConstantInt::get(V->getType(), 1));
    }
    if (ICI.isEquality() && LHSI->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 = LHSI->getType()->getPrimitiveSizeInBits(),
             SrcBits = LHSI->getOperand(0)->getType()->getPrimitiveSizeInBits();
      APInt KnownZero(SrcBits, 0), KnownOne(SrcBits, 0);
      computeKnownBits(LHSI->getOperand(0), KnownZero, KnownOne, 0, &ICI);

      // 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 = RHS->getValue().zext(SrcBits);
        NewRHS |= KnownOne & APInt::getHighBitsSet(SrcBits, SrcBits-DstBits);
        return new ICmpInst(ICI.getPredicate(), LHSI->getOperand(0),
                            Builder->getInt(NewRHS));
      }
    }
    break;

  case Instruction::Xor:         // (icmp pred (xor X, XorCst), CI)
    if (ConstantInt *XorCst = dyn_cast<ConstantInt>(LHSI->getOperand(1))) {
      // If this is a comparison that tests the signbit (X < 0) or (x > -1),
      // fold the xor.
      if ((ICI.getPredicate() == ICmpInst::ICMP_SLT && RHSV == 0) ||
          (ICI.getPredicate() == ICmpInst::ICMP_SGT && RHSV.isAllOnesValue())) {
        Value *CompareVal = LHSI->getOperand(0);

        // If the sign bit of the XorCst is not set, there is no change to
        // the operation, just stop using the Xor.
        if (!XorCst->isNegative()) {
          ICI.setOperand(0, CompareVal);
          Worklist.Add(LHSI);
          return &ICI;
        }

        // Was the old condition true if the operand is positive?
        bool isTrueIfPositive = ICI.getPredicate() == ICmpInst::ICMP_SGT;

        // If so, the new one isn't.
        isTrueIfPositive ^= true;

        if (isTrueIfPositive)
          return new ICmpInst(ICmpInst::ICMP_SGT, CompareVal,
                              SubOne(RHS));
        else
          return new ICmpInst(ICmpInst::ICMP_SLT, CompareVal,
                              AddOne(RHS));
      }

      if (LHSI->hasOneUse()) {
        // (icmp u/s (xor A SignBit), C) -> (icmp s/u A, (xor C SignBit))
        if (!ICI.isEquality() && XorCst->getValue().isSignBit()) {
          const APInt &SignBit = XorCst->getValue();
          ICmpInst::Predicate Pred = ICI.isSigned()
                                         ? ICI.getUnsignedPredicate()
                                         : ICI.getSignedPredicate();
          return new ICmpInst(Pred, LHSI->getOperand(0),
                              Builder->getInt(RHSV ^ SignBit));
        }

        // (icmp u/s (xor A ~SignBit), C) -> (icmp s/u (xor C ~SignBit), A)
        if (!ICI.isEquality() && XorCst->isMaxValue(true)) {
          const APInt &NotSignBit = XorCst->getValue();
          ICmpInst::Predicate Pred = ICI.isSigned()
                                         ? ICI.getUnsignedPredicate()
                                         : ICI.getSignedPredicate();
          Pred = ICI.getSwappedPredicate(Pred);
          return new ICmpInst(Pred, LHSI->getOperand(0),
                              Builder->getInt(RHSV ^ NotSignBit));
        }
      }

      // (icmp ugt (xor X, C), ~C) -> (icmp ult X, C)
      //   iff -C is a power of 2
      if (ICI.getPredicate() == ICmpInst::ICMP_UGT &&
          XorCst->getValue() == ~RHSV && (RHSV + 1).isPowerOf2())
        return new ICmpInst(ICmpInst::ICMP_ULT, LHSI->getOperand(0), XorCst);

      // (icmp ult (xor X, C), -C) -> (icmp uge X, C)
      //   iff -C is a power of 2
      if (ICI.getPredicate() == ICmpInst::ICMP_ULT &&
          XorCst->getValue() == -RHSV && RHSV.isPowerOf2())
        return new ICmpInst(ICmpInst::ICMP_UGE, LHSI->getOperand(0), XorCst);
    }
    break;
  case Instruction::And:         // (icmp pred (and X, AndCst), RHS)
    if (LHSI->hasOneUse() && isa<ConstantInt>(LHSI->getOperand(1)) &&
        LHSI->getOperand(0)->hasOneUse()) {
      ConstantInt *AndCst = cast<ConstantInt>(LHSI->getOperand(1));

      // If the LHS is an AND of a truncating cast, we can widen the
      // and/compare to be the input width without changing the value
      // produced, eliminating a cast.
      if (TruncInst *Cast = dyn_cast<TruncInst>(LHSI->getOperand(0))) {
        // We can do this transformation if either the AND constant does not
        // have its sign bit set or if it is an equality comparison.
        // Extending a relational comparison when we're checking the sign
        // bit would not work.
        if (ICI.isEquality() ||
            (!AndCst->isNegative() && RHSV.isNonNegative())) {
          Value *NewAnd =
            Builder->CreateAnd(Cast->getOperand(0),
                               ConstantExpr::getZExt(AndCst, Cast->getSrcTy()));
          NewAnd->takeName(LHSI);
          return new ICmpInst(ICI.getPredicate(), NewAnd,
                              ConstantExpr::getZExt(RHS, Cast->getSrcTy()));
        }
      }

      // If the LHS is an AND of a zext, and we have an equality compare, we can
      // shrink the and/compare to the smaller type, eliminating the cast.
      if (ZExtInst *Cast = dyn_cast<ZExtInst>(LHSI->getOperand(0))) {
        IntegerType *Ty = cast<IntegerType>(Cast->getSrcTy());
        // Make sure we don't compare the upper bits, SimplifyDemandedBits
        // should fold the icmp to true/false in that case.
        if (ICI.isEquality() && RHSV.getActiveBits() <= Ty->getBitWidth()) {
          Value *NewAnd =
            Builder->CreateAnd(Cast->getOperand(0),
                               ConstantExpr::getTrunc(AndCst, Ty));
          NewAnd->takeName(LHSI);
          return new ICmpInst(ICI.getPredicate(), NewAnd,
                              ConstantExpr::getTrunc(RHS, Ty));
        }
      }

      // If this is: (X >> C1) & C2 != C3 (where any shift and any compare
      // could exist), turn it into (X & (C2 << C1)) != (C3 << C1).  This
      // happens a LOT in code produced by the C front-end, for bitfield
      // access.
      BinaryOperator *Shift = dyn_cast<BinaryOperator>(LHSI->getOperand(0));
      if (Shift && !Shift->isShift())
        Shift = nullptr;

      ConstantInt *ShAmt;
      ShAmt = Shift ? dyn_cast<ConstantInt>(Shift->getOperand(1)) : nullptr;

      // This seemingly simple opportunity to fold away a shift turns out to
      // be rather complicated. See PR17827
      // ( http://llvm.org/bugs/show_bug.cgi?id=17827 ) for details.
      if (ShAmt) {
        bool CanFold = false;
        unsigned ShiftOpcode = Shift->getOpcode();
        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 (!ICI.isSigned() || (!AndCst->isNegative() && !RHS->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 (!ICI.isSigned())
            CanFold = true;
          else {
            ConstantInt *ShiftedAndCst =
              cast<ConstantInt>(ConstantExpr::getShl(AndCst, ShAmt));
            ConstantInt *ShiftedRHSCst =
              cast<ConstantInt>(ConstantExpr::getShl(RHS, ShAmt));
            
            if (!ShiftedAndCst->isNegative() && !ShiftedRHSCst->isNegative())
              CanFold = true;
          }
        }

        if (CanFold) {
          Constant *NewCst;
          if (ShiftOpcode == Instruction::Shl)
            NewCst = ConstantExpr::getLShr(RHS, ShAmt);
          else
            NewCst = ConstantExpr::getShl(RHS, ShAmt);

          // Check to see if we are shifting out any of the bits being
          // compared.
          if (ConstantExpr::get(ShiftOpcode, NewCst, ShAmt) != RHS) {
            // 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 (ICI.getPredicate() == ICmpInst::ICMP_EQ)
              return replaceInstUsesWith(ICI, Builder->getFalse());
            if (ICI.getPredicate() == ICmpInst::ICMP_NE)
              return replaceInstUsesWith(ICI, Builder->getTrue());
          } else {
            ICI.setOperand(1, NewCst);
            Constant *NewAndCst;
            if (ShiftOpcode == Instruction::Shl)
              NewAndCst = ConstantExpr::getLShr(AndCst, ShAmt);
            else
              NewAndCst = ConstantExpr::getShl(AndCst, ShAmt);
            LHSI->setOperand(1, NewAndCst);
            LHSI->setOperand(0, Shift->getOperand(0));
            Worklist.Add(Shift); // Shift is dead.
            return &ICI;
          }
        }
      }

      // Turn ((X >> Y) & C) == 0  into  (X & (C << Y)) == 0.  The later is
      // preferable because it allows the C<<Y expression to be hoisted out
      // of a loop if Y is invariant and X is not.
      if (Shift && Shift->hasOneUse() && RHSV == 0 &&
          ICI.isEquality() && !Shift->isArithmeticShift() &&
          !isa<Constant>(Shift->getOperand(0))) {
        // Compute C << Y.
        Value *NS;
        if (Shift->getOpcode() == Instruction::LShr) {
          NS = Builder->CreateShl(AndCst, Shift->getOperand(1));
        } else {
          // Insert a logical shift.
          NS = Builder->CreateLShr(AndCst, Shift->getOperand(1));
        }

        // Compute X & (C << Y).
        Value *NewAnd =
          Builder->CreateAnd(Shift->getOperand(0), NS, LHSI->getName());

        ICI.setOperand(0, NewAnd);
        return &ICI;
      }

      // (icmp pred (and (or (lshr X, Y), X), 1), 0) -->
      //    (icmp pred (and X, (or (shl 1, Y), 1), 0))
      //
      // iff pred isn't signed
      {
        Value *X, *Y, *LShr;
        if (!ICI.isSigned() && RHSV == 0) {
          if (match(LHSI->getOperand(1), m_One())) {
            Constant *One = cast<Constant>(LHSI->getOperand(1));
            Value *Or = LHSI->getOperand(0);
            if (match(Or, m_Or(m_Value(LShr), m_Value(X))) &&
                match(LShr, m_LShr(m_Specific(X), m_Value(Y)))) {
              unsigned UsesRemoved = 0;
              if (LHSI->hasOneUse())
                ++UsesRemoved;
              if (Or->hasOneUse())
                ++UsesRemoved;
              if (LShr->hasOneUse())
                ++UsesRemoved;
              Value *NewOr = nullptr;
              // Compute X & ((1 << Y) | 1)
              if (auto *C = dyn_cast<Constant>(Y)) {
                if (UsesRemoved >= 1)
                  NewOr =
                      ConstantExpr::getOr(ConstantExpr::getNUWShl(One, C), One);
              } else {
                if (UsesRemoved >= 3)
                  NewOr = Builder->CreateOr(Builder->CreateShl(One, Y,
                                                               LShr->getName(),
                                                               /*HasNUW=*/true),
                                            One, Or->getName());
              }
              if (NewOr) {
                Value *NewAnd = Builder->CreateAnd(X, NewOr, LHSI->getName());
                ICI.setOperand(0, NewAnd);
                return &ICI;
              }
            }
          }
        }
      }

      // Replace ((X & AndCst) > RHSV) with ((X & AndCst) != 0), if any
      // bit set in (X & AndCst) will produce a result greater than RHSV.
      if (ICI.getPredicate() == ICmpInst::ICMP_UGT) {
        unsigned NTZ = AndCst->getValue().countTrailingZeros();
        if ((NTZ < AndCst->getBitWidth()) &&
            APInt::getOneBitSet(AndCst->getBitWidth(), NTZ).ugt(RHSV))
          return new ICmpInst(ICmpInst::ICMP_NE, LHSI,
                              Constant::getNullValue(RHS->getType()));
      }
    }

    // Try to optimize things like "A[i]&42 == 0" to index computations.
    if (LoadInst *LI = dyn_cast<LoadInst>(LHSI->getOperand(0))) {
      if (GetElementPtrInst *GEP =
          dyn_cast<GetElementPtrInst>(LI->getOperand(0)))
        if (GlobalVariable *GV = dyn_cast<GlobalVariable>(GEP->getOperand(0)))
          if (GV->isConstant() && GV->hasDefinitiveInitializer() &&
              !LI->isVolatile() && isa<ConstantInt>(LHSI->getOperand(1))) {
            ConstantInt *C = cast<ConstantInt>(LHSI->getOperand(1));
            if (Instruction *Res = foldCmpLoadFromIndexedGlobal(GEP, GV,ICI, C))
              return Res;
          }
    }

    // X & -C == -C -> X >  u ~C
    // X & -C != -C -> X <= u ~C
    //   iff C is a power of 2
    if (ICI.isEquality() && RHS == LHSI->getOperand(1) && (-RHSV).isPowerOf2())
      return new ICmpInst(
          ICI.getPredicate() == ICmpInst::ICMP_EQ ? ICmpInst::ICMP_UGT
                                                  : ICmpInst::ICMP_ULE,
          LHSI->getOperand(0), SubOne(RHS));

    // (icmp eq (and %A, C), 0) -> (icmp sgt (trunc %A), -1)
    //   iff C is a power of 2
    if (ICI.isEquality() && LHSI->hasOneUse() && match(RHS, m_Zero())) {
      if (auto *CI = dyn_cast<ConstantInt>(LHSI->getOperand(1))) {
        const APInt &AI = CI->getValue();
        int32_t ExactLogBase2 = AI.exactLogBase2();
        if (ExactLogBase2 != -1 && DL.isLegalInteger(ExactLogBase2 + 1)) {
          Type *NTy = IntegerType::get(ICI.getContext(), ExactLogBase2 + 1);
          Value *Trunc = Builder->CreateTrunc(LHSI->getOperand(0), NTy);
          return new ICmpInst(ICI.getPredicate() == ICmpInst::ICMP_EQ
                                  ? ICmpInst::ICMP_SGE
                                  : ICmpInst::ICMP_SLT,
                              Trunc, Constant::getNullValue(NTy));
        }
      }
    }
    break;

  case Instruction::Or: {
    if (RHS->isOne()) {
      // icmp slt signum(V) 1 --> icmp slt V, 1
      Value *V = nullptr;
      if (ICI.getPredicate() == ICmpInst::ICMP_SLT &&
          match(LHSI, m_Signum(m_Value(V))))
        return new ICmpInst(ICmpInst::ICMP_SLT, V,
                            ConstantInt::get(V->getType(), 1));
    }

    if (!ICI.isEquality() || !RHS->isNullValue() || !LHSI->hasOneUse())
      break;
    Value *P, *Q;
    if (match(LHSI, 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 *ICIP = Builder->CreateICmp(ICI.getPredicate(), P,
                                        Constant::getNullValue(P->getType()));
      Value *ICIQ = Builder->CreateICmp(ICI.getPredicate(), Q,
                                        Constant::getNullValue(Q->getType()));
      Instruction *Op;
      if (ICI.getPredicate() == ICmpInst::ICMP_EQ)
        Op = BinaryOperator::CreateAnd(ICIP, ICIQ);
      else
        Op = BinaryOperator::CreateOr(ICIP, ICIQ);
      return Op;
    }
    break;
  }

  case Instruction::Mul: {       // (icmp pred (mul X, Val), CI)
    ConstantInt *Val = dyn_cast<ConstantInt>(LHSI->getOperand(1));
    if (!Val) break;

    // If this is a signed comparison to 0 and the mul is sign preserving,
    // use the mul LHS operand instead.
    ICmpInst::Predicate pred = ICI.getPredicate();
    if (isSignTest(pred, RHS) && !Val->isZero() &&
        cast<BinaryOperator>(LHSI)->hasNoSignedWrap())
      return new ICmpInst(Val->isNegative() ?
                          ICmpInst::getSwappedPredicate(pred) : pred,
                          LHSI->getOperand(0),
                          Constant::getNullValue(RHS->getType()));

    break;
  }

  case Instruction::Shl: {       // (icmp pred (shl X, ShAmt), CI)
    uint32_t TypeBits = RHSV.getBitWidth();
    ConstantInt *ShAmt = dyn_cast<ConstantInt>(LHSI->getOperand(1));
    if (!ShAmt) {
      Value *X;
      // (1 << X) pred P2 -> X pred Log2(P2)
      if (match(LHSI, m_Shl(m_One(), m_Value(X)))) {
        bool RHSVIsPowerOf2 = RHSV.isPowerOf2();
        ICmpInst::Predicate Pred = ICI.getPredicate();
        if (ICI.isUnsigned()) {
          if (!RHSVIsPowerOf2) {
            // (1 << X) <  30 -> X <= 4
            // (1 << X) <= 30 -> X <= 4
            // (1 << X) >= 30 -> X >  4
            // (1 << X) >  30 -> X >  4
            if (Pred == ICmpInst::ICMP_ULT)
              Pred = ICmpInst::ICMP_ULE;
            else if (Pred == ICmpInst::ICMP_UGE)
              Pred = ICmpInst::ICMP_UGT;
          }
          unsigned RHSLog2 = RHSV.logBase2();

          // (1 << X) >= 2147483648 -> X >= 31 -> X == 31
          // (1 << X) <  2147483648 -> X <  31 -> X != 31
          if (RHSLog2 == 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, X,
                              ConstantInt::get(RHS->getType(), RHSLog2));
        } else if (ICI.isSigned()) {
          if (RHSV.isAllOnesValue()) {
            // (1 << X) <= -1 -> X == 31
            if (Pred == ICmpInst::ICMP_SLE)
              return new ICmpInst(ICmpInst::ICMP_EQ, X,
                                  ConstantInt::get(RHS->getType(), TypeBits-1));

            // (1 << X) >  -1 -> X != 31
            if (Pred == ICmpInst::ICMP_SGT)
              return new ICmpInst(ICmpInst::ICMP_NE, X,
                                  ConstantInt::get(RHS->getType(), TypeBits-1));
          } else if (!RHSV) {
            // (1 << X) <  0 -> X == 31
            // (1 << X) <= 0 -> X == 31
            if (Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SLE)
              return new ICmpInst(ICmpInst::ICMP_EQ, X,
                                  ConstantInt::get(RHS->getType(), TypeBits-1));

            // (1 << X) >= 0 -> X != 31
            // (1 << X) >  0 -> X != 31
            if (Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_SGE)
              return new ICmpInst(ICmpInst::ICMP_NE, X,
                                  ConstantInt::get(RHS->getType(), TypeBits-1));
          }
        } else if (ICI.isEquality()) {
          if (RHSVIsPowerOf2)
            return new ICmpInst(
                Pred, X, ConstantInt::get(RHS->getType(), RHSV.logBase2()));
        }
      }
      break;
    }

    // Check that the shift amount is in range.  If not, don't perform
    // undefined shifts.  When the shift is visited it will be
    // simplified.
    if (ShAmt->uge(TypeBits))
      break;

    if (ICI.isEquality()) {
      // If we are comparing against bits always shifted out, the
      // comparison cannot succeed.
      Constant *Comp =
        ConstantExpr::getShl(ConstantExpr::getLShr(RHS, ShAmt),
                                                                 ShAmt);
      if (Comp != RHS) {// Comparing against a bit that we know is zero.
        bool IsICMP_NE = ICI.getPredicate() == ICmpInst::ICMP_NE;
        Constant *Cst = Builder->getInt1(IsICMP_NE);
        return replaceInstUsesWith(ICI, Cst);
      }

      // If the shift is NUW, then it is just shifting out zeros, no need for an
      // AND.
      if (cast<BinaryOperator>(LHSI)->hasNoUnsignedWrap())
        return new ICmpInst(ICI.getPredicate(), LHSI->getOperand(0),
                            ConstantExpr::getLShr(RHS, ShAmt));

      // 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 (cast<BinaryOperator>(LHSI)->hasNoSignedWrap() && RHSV == 0)
        return new ICmpInst(ICI.getPredicate(), LHSI->getOperand(0),
                            ConstantExpr::getLShr(RHS, ShAmt));

      if (LHSI->hasOneUse()) {
        // Otherwise strength reduce the shift into an and.
        uint32_t ShAmtVal = (uint32_t)ShAmt->getLimitedValue(TypeBits);
        Constant *Mask = Builder->getInt(APInt::getLowBitsSet(TypeBits,
                                                          TypeBits - ShAmtVal));

        Value *And =
          Builder->CreateAnd(LHSI->getOperand(0),Mask, LHSI->getName()+".mask");
        return new ICmpInst(ICI.getPredicate(), And,
                            ConstantExpr::getLShr(RHS, ShAmt));
      }
    }

    // If this is a signed comparison to 0 and the shift is sign preserving,
    // use the shift LHS operand instead.
    ICmpInst::Predicate pred = ICI.getPredicate();
    if (isSignTest(pred, RHS) &&
        cast<BinaryOperator>(LHSI)->hasNoSignedWrap())
      return new ICmpInst(pred,
                          LHSI->getOperand(0),
                          Constant::getNullValue(RHS->getType()));

    // Otherwise, if this is a comparison of the sign bit, simplify to and/test.
    bool TrueIfSigned = false;
    if (LHSI->hasOneUse() &&
        isSignBitCheck(ICI.getPredicate(), RHS, TrueIfSigned)) {
      // (X << 31) <s 0  --> (X&1) != 0
      Constant *Mask = ConstantInt::get(LHSI->getOperand(0)->getType(),
                                        APInt::getOneBitSet(TypeBits,
                                            TypeBits-ShAmt->getZExtValue()-1));
      Value *And =
        Builder->CreateAnd(LHSI->getOperand(0), Mask, LHSI->getName()+".mask");
      return new ICmpInst(TrueIfSigned ? ICmpInst::ICMP_NE : ICmpInst::ICMP_EQ,
                          And, Constant::getNullValue(And->getType()));
    }

    // Transform (icmp pred iM (shl iM %v, N), CI)
    // -> (icmp pred i(M-N) (trunc %v iM to i(M-N)), (trunc (CI>>N))
    // Transform the shl to a trunc if (trunc (CI>>N)) has no loss and M-N.
    // This enables to get rid of the shift in favor of a trunc which can be
    // free on the target. It has the additional benefit of comparing to a
    // smaller constant, which will be target friendly.
    unsigned Amt = ShAmt->getLimitedValue(TypeBits-1);
    if (LHSI->hasOneUse() &&
        Amt != 0 && RHSV.countTrailingZeros() >= Amt) {
      Type *NTy = IntegerType::get(ICI.getContext(), TypeBits - Amt);
      Constant *NCI = ConstantExpr::getTrunc(
                        ConstantExpr::getAShr(RHS,
                          ConstantInt::get(RHS->getType(), Amt)),
                        NTy);
      return new ICmpInst(ICI.getPredicate(),
                          Builder->CreateTrunc(LHSI->getOperand(0), NTy),
                          NCI);
    }

    break;
  }

  case Instruction::LShr:         // (icmp pred (shr X, ShAmt), CI)
  case Instruction::AShr: {
    // Handle equality comparisons of shift-by-constant.
    BinaryOperator *BO = cast<BinaryOperator>(LHSI);
    if (ConstantInt *ShAmt = dyn_cast<ConstantInt>(LHSI->getOperand(1))) {
      if (Instruction *Res = foldICmpShrConst(ICI, BO, ShAmt))
        return Res;
    }

    // Handle exact shr's.
    if (ICI.isEquality() && BO->isExact() && BO->hasOneUse()) {
      if (RHSV.isMinValue())
        return new ICmpInst(ICI.getPredicate(), BO->getOperand(0), RHS);
    }
    break;
  }

  case Instruction::UDiv:
    if (ConstantInt *DivLHS = dyn_cast<ConstantInt>(LHSI->getOperand(0))) {
      Value *X = LHSI->getOperand(1);
      const APInt &C1 = RHS->getValue();
      const APInt &C2 = DivLHS->getValue();
      assert(C2 != 0 && "udiv 0, X should have been simplified already.");
      // (icmp ugt (udiv C2, X), C1) -> (icmp ule X, C2/(C1+1))
      if (ICI.getPredicate() == ICmpInst::ICMP_UGT) {
        assert(!C1.isMaxValue() &&
               "icmp ugt X, UINT_MAX should have been simplified already.");
        return new ICmpInst(ICmpInst::ICMP_ULE, X,
                            ConstantInt::get(X->getType(), C2.udiv(C1 + 1)));
      }
      // (icmp ult (udiv C2, X), C1) -> (icmp ugt X, C2/C1)
      if (ICI.getPredicate() == ICmpInst::ICMP_ULT) {
        assert(C1 != 0 && "icmp ult X, 0 should have been simplified already.");
        return new ICmpInst(ICmpInst::ICMP_UGT, X,
                            ConstantInt::get(X->getType(), C2.udiv(C1)));
      }
    }
  // fall-through
  case Instruction::SDiv:
    // Fold: icmp pred ([us]div X, C1), C2 -> 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.
    if (ConstantInt *DivRHS = dyn_cast<ConstantInt>(LHSI->getOperand(1)))
      if (Instruction *R = foldICmpDivConst(ICI, cast<BinaryOperator>(LHSI),
                                          DivRHS))
        return R;
    break;

  case Instruction::Sub: {
    ConstantInt *LHSC = dyn_cast<ConstantInt>(LHSI->getOperand(0));
    if (!LHSC) break;
    const APInt &LHSV = LHSC->getValue();

    // C1-X <u C2 -> (X|(C2-1)) == C1
    //   iff C1 & (C2-1) == C2-1
    //       C2 is a power of 2
    if (ICI.getPredicate() == ICmpInst::ICMP_ULT && LHSI->hasOneUse() &&
        RHSV.isPowerOf2() && (LHSV & (RHSV - 1)) == (RHSV - 1))
      return new ICmpInst(ICmpInst::ICMP_EQ,
                          Builder->CreateOr(LHSI->getOperand(1), RHSV - 1),
                          LHSC);

    // C1-X >u C2 -> (X|C2) != C1
    //   iff C1 & C2 == C2
    //       C2+1 is a power of 2
    if (ICI.getPredicate() == ICmpInst::ICMP_UGT && LHSI->hasOneUse() &&
        (RHSV + 1).isPowerOf2() && (LHSV & RHSV) == RHSV)
      return new ICmpInst(ICmpInst::ICMP_NE,
                          Builder->CreateOr(LHSI->getOperand(1), RHSV), LHSC);
    break;
  }

  case Instruction::Add:
    // Fold: icmp pred (add X, C1), C2
    if (!ICI.isEquality()) {
      ConstantInt *LHSC = dyn_cast<ConstantInt>(LHSI->getOperand(1));
      if (!LHSC) break;
      const APInt &LHSV = LHSC->getValue();

      ConstantRange CR = ICI.makeConstantRange(ICI.getPredicate(), RHSV)
                            .subtract(LHSV);

      if (ICI.isSigned()) {
        if (CR.getLower().isSignBit()) {
          return new ICmpInst(ICmpInst::ICMP_SLT, LHSI->getOperand(0),
                              Builder->getInt(CR.getUpper()));
        } else if (CR.getUpper().isSignBit()) {
          return new ICmpInst(ICmpInst::ICMP_SGE, LHSI->getOperand(0),
                              Builder->getInt(CR.getLower()));
        }
      } else {
        if (CR.getLower().isMinValue()) {
          return new ICmpInst(ICmpInst::ICMP_ULT, LHSI->getOperand(0),
                              Builder->getInt(CR.getUpper()));
        } else if (CR.getUpper().isMinValue()) {
          return new ICmpInst(ICmpInst::ICMP_UGE, LHSI->getOperand(0),
                              Builder->getInt(CR.getLower()));
        }
      }

      // X-C1 <u C2 -> (X & -C2) == C1
      //   iff C1 & (C2-1) == 0
      //       C2 is a power of 2
      if (ICI.getPredicate() == ICmpInst::ICMP_ULT && LHSI->hasOneUse() &&
          RHSV.isPowerOf2() && (LHSV & (RHSV - 1)) == 0)
        return new ICmpInst(ICmpInst::ICMP_EQ,
                            Builder->CreateAnd(LHSI->getOperand(0), -RHSV),
                            ConstantExpr::getNeg(LHSC));

      // X-C1 >u C2 -> (X & ~C2) != C1
      //   iff C1 & C2 == 0
      //       C2+1 is a power of 2
      if (ICI.getPredicate() == ICmpInst::ICMP_UGT && LHSI->hasOneUse() &&
          (RHSV + 1).isPowerOf2() && (LHSV & RHSV) == 0)
        return new ICmpInst(ICmpInst::ICMP_NE,
                            Builder->CreateAnd(LHSI->getOperand(0), ~RHSV),
                            ConstantExpr::getNeg(LHSC));
    }
    break;
  }

  return nullptr;
}

/// Simplify icmp_eq and icmp_ne instructions with binary operator LHS and
/// integer constant RHS.
Instruction *InstCombiner::foldICmpEqualityWithConstant(ICmpInst &ICI) {
  BinaryOperator *BO;
  const APInt *RHSV;
  // FIXME: Some of these folds could work with arbitrary constants, but this
  // match is limited to scalars and vector splat constants.
  if (!ICI.isEquality() || !match(ICI.getOperand(0), m_BinOp(BO)) ||
      !match(ICI.getOperand(1), m_APInt(RHSV)))
    return nullptr;

  Constant *RHS = cast<Constant>(ICI.getOperand(1));
  bool isICMP_NE = ICI.getPredicate() == ICmpInst::ICMP_NE;
  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 (*RHSV == 0 && BO->hasOneUse()) {
      const APInt *BOC;
      if (match(BOp1, m_APInt(BOC)) && BOC->sgt(1) && BOC->isPowerOf2()) {
        Value *NewRem = Builder->CreateURem(BOp0, BOp1, BO->getName());
        return new ICmpInst(ICI.getPredicate(), 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;
    if (match(BOp1, m_APInt(BOC))) {
      if (BO->hasOneUse()) {
        Constant *SubC = ConstantExpr::getSub(RHS, cast<Constant>(BOp1));
        return new ICmpInst(ICI.getPredicate(), BOp0, SubC);
      }
    } else if (*RHSV == 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(ICI.getPredicate(), BOp0, NegVal);
      if (Value *NegVal = dyn_castNegVal(BOp0))
        return new ICmpInst(ICI.getPredicate(), NegVal, BOp1);
      if (BO->hasOneUse()) {
        Value *Neg = Builder->CreateNeg(BOp1);
        Neg->takeName(BO);
        return new ICmpInst(ICI.getPredicate(), 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(ICI.getPredicate(), BOp0,
                            ConstantExpr::getXor(RHS, BOC));
      } else if (*RHSV == 0) {
        // Replace ((xor A, B) != 0) with (A != B)
        return new ICmpInst(ICI.getPredicate(), BOp0, BOp1);
      }
    }
    break;
  case Instruction::Sub:
    if (BO->hasOneUse()) {
      const APInt *BOC;
      if (match(BOp0, m_APInt(BOC))) {
        // Replace ((sub A, B) != C) with (B != A-C) if A & C are constants.
        Constant *SubC = ConstantExpr::getSub(cast<Constant>(BOp0), RHS);
        return new ICmpInst(ICI.getPredicate(), BOp1, SubC);
      } else if (*RHSV == 0) {
        // Replace ((sub A, B) != 0) with (A != B)
        return new ICmpInst(ICI.getPredicate(), BOp0, BOp1);
      }
    }
    break;
  case Instruction::Or:
    // FIXME: Vectors are excluded by ConstantInt.
    if (ConstantInt *BOC = dyn_cast<ConstantInt>(BOp1)) {
      // Comparing if all bits outside of a constant mask are set?
      // Replace (X | C) == -1 with (X & ~C) == ~C.
      // This removes the -1 constant.
      if (BO->hasOneUse() && RHS->isAllOnesValue()) {
        Constant *NotBOC = ConstantExpr::getNot(BOC);
        Value *And = Builder->CreateAnd(BOp0, NotBOC);
        return new ICmpInst(ICI.getPredicate(), And, NotBOC);
      }
    }
    break;

  case Instruction::And:
    // FIXME: Vectors are excluded by ConstantInt.
    if (ConstantInt *BOC = dyn_cast<ConstantInt>(BOp1)) {
      // If we have ((X & C) == C), turn it into ((X & C) != 0).
      if (RHS == BOC && RHSV->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->getValue().isSignBit()) {
        Constant *Zero = Constant::getNullValue(BOp0->getType());
        ICmpInst::Predicate Pred =
            isICMP_NE ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_SGE;
        return new ICmpInst(Pred, BOp0, Zero);
      }

      // ((X & ~7) == 0) --> X < 8
      if (*RHSV == 0 && isHighOnes(BOC)) {
        Constant *NegX = ConstantExpr::getNeg(BOC);
        ICmpInst::Predicate Pred =
            isICMP_NE ? ICmpInst::ICMP_UGE : ICmpInst::ICMP_ULT;
        return new ICmpInst(Pred, BOp0, NegX);
      }
    }
    break;
  case Instruction::Mul:
    if (*RHSV == 0 && BO->hasNoSignedWrap()) {
      // FIXME: Vectors are excluded by ConstantInt.
      if (ConstantInt *BOC = dyn_cast<ConstantInt>(BOp1)) {
        // 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
        if (!BOC->isZero())
          return new ICmpInst(ICI.getPredicate(), BOp0,
                              Constant::getNullValue(RHS->getType()));
      }
    }
    break;
  case Instruction::UDiv:
    if (*RHSV == 0) {
      // (icmp eq/ne (udiv A, B), 0) -> (icmp ugt/ule i32 B, A)
      ICmpInst::Predicate Pred =
          isICMP_NE ? ICmpInst::ICMP_ULE : ICmpInst::ICMP_UGT;
      return new ICmpInst(Pred, BOp1, BOp0);
    }
    break;
  default:
    break;
  }
  return nullptr;
}

Instruction *InstCombiner::foldICmpIntrinsicWithConstant(ICmpInst &ICI) {
  IntrinsicInst *II = dyn_cast<IntrinsicInst>(ICI.getOperand(0));
  const APInt *Op1C;
  if (!II || !ICI.isEquality() || !match(ICI.getOperand(1), m_APInt(Op1C)))
    return nullptr;

  // Handle icmp {eq|ne} <intrinsic>, intcst.
  switch (II->getIntrinsicID()) {
  case Intrinsic::bswap:
    Worklist.Add(II);
    ICI.setOperand(0, II->getArgOperand(0));
    ICI.setOperand(1, Builder->getInt(Op1C->byteSwap()));
    return &ICI;
  case Intrinsic::ctlz:
  case Intrinsic::cttz:
    // ctz(A) == bitwidth(A)  ->  A == 0 and likewise for !=
    if (*Op1C == Op1C->getBitWidth()) {
      Worklist.Add(II);
      ICI.setOperand(0, II->getArgOperand(0));
      ICI.setOperand(1, ConstantInt::getNullValue(II->getType()));
      return &ICI;
    }
    break;
  case Intrinsic::ctpop: {
    // popcount(A) == 0  ->  A == 0 and likewise for !=
    // popcount(A) == bitwidth(A)  ->  A == -1 and likewise for !=
    bool IsZero = *Op1C == 0;
    if (IsZero || *Op1C == Op1C->getBitWidth()) {
      Worklist.Add(II);
      ICI.setOperand(0, II->getArgOperand(0));
      auto *NewOp = IsZero
        ? ConstantInt::getNullValue(II->getType())
        : ConstantInt::getAllOnesValue(II->getType());
      ICI.setOperand(1, NewOp);
      return &ICI;
    }
    }
    break;
  default:
    break;
  }
  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;

  // 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);

  assert(ICmp.getPredicate() == ICmpInst::ICMP_UGT && "ICmp should be folded!");
  return BinaryOperator::CreateNot(Result);
}

/// 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");
}

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:
    llvm_unreachable("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
  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);
  } // FALL THROUGH
  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;

  assert(I.getOperand(0) == MulVal || I.getOperand(1) == MulVal);
  assert(I.getOperand(0) == OtherVal || I.getOperand(1) == OtherVal);
  auto *MulInstr = dyn_cast<Instruction>(MulVal);
  if (!MulInstr)
    return nullptr;
  assert(MulInstr->getOpcode() == Instruction::Mul);

  auto *LHS = cast<ZExtOperator>(MulInstr->getOperand(0)),
       *RHS = cast<ZExtOperator>(MulInstr->getOperand(1));
  assert(LHS->getOpcode() == Instruction::ZExt);
  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;
    Value *ValToMask;
    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)) {
        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 {
        llvm_unreachable("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:
    llvm_unreachable("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 DemandedBitsLHSMask(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 {
  assert(DI && 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;
  // DominatorTree available?
  if (!DT)
    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) {
  assert((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;
}

/// 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 assert 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
    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, *SelectTrue, *SelectFalse;
    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: llvm_unreachable("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
      // FALL THROUGH
    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
      // FALL THROUGH
    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
      // FALL THROUGH
    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
      // FALL THROUGH
    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;

  unsigned BitWidth = 0;
  if (Ty->isIntOrIntVectorTy())
    BitWidth = Ty->getScalarSizeInBits();
  else // Get pointer size.
    BitWidth = DL.getTypeSizeInBits(Ty->getScalarType());

  bool isSignBit = false;

  // See if we are doing a comparison with a constant.
  if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
    Value *A = nullptr, *B = nullptr;

    // Match the following pattern, which is a common idiom when writing
    // overflow-safe integer arithmetic function.  The source performs an
    // addition in wider type, and explicitly checks for overflow using
    // comparisons against INT_MIN and INT_MAX.  Simplify this 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;    // I = icmp ugt (add (add A, B), CI2), CI
    if (I.getPredicate() == ICmpInst::ICMP_UGT &&
        match(Op0, m_Add(m_Add(m_Value(A), m_Value(B)), m_ConstantInt(CI2))))
      if (Instruction *Res = ProcessUGT_ADDCST_ADD(I, A, B, CI2, CI, *this))
        return Res;
    }

    // (icmp sgt smin(PosA, B) 0) -> (icmp sgt B 0)
    if (CI->isZero() && I.getPredicate() == ICmpInst::ICMP_SGT)
      if (auto *SI = dyn_cast<SelectInst>(Op0)) {
        SelectPatternResult SPR = matchSelectPattern(SI, A, B);
        if (SPR.Flavor == SPF_SMIN) {
          if (isKnownPositive(A, DL))
            return new ICmpInst(I.getPredicate(), B, CI);
          if (isKnownPositive(B, DL))
            return new ICmpInst(I.getPredicate(), A, CI);
        }
      }
    

    // The following transforms are only 'worth it' if the only user of the
    // subtraction is the icmp.
    if (Op0->hasOneUse()) {
      // (icmp ne/eq (sub A B) 0) -> (icmp ne/eq A, B)
      if (I.isEquality() && CI->isZero() &&
          match(Op0, m_Sub(m_Value(A), m_Value(B))))
        return new ICmpInst(I.getPredicate(), A, B);

      // (icmp sgt (sub nsw A B), -1) -> (icmp sge A, B)
      if (I.getPredicate() == ICmpInst::ICMP_SGT && CI->isAllOnesValue() &&
          match(Op0, m_NSWSub(m_Value(A), m_Value(B))))
        return new ICmpInst(ICmpInst::ICMP_SGE, A, B);

      // (icmp sgt (sub nsw A B), 0) -> (icmp sgt A, B)
      if (I.getPredicate() == ICmpInst::ICMP_SGT && CI->isZero() &&
          match(Op0, m_NSWSub(m_Value(A), m_Value(B))))
        return new ICmpInst(ICmpInst::ICMP_SGT, A, B);

      // (icmp slt (sub nsw A B), 0) -> (icmp slt A, B)
      if (I.getPredicate() == ICmpInst::ICMP_SLT && CI->isZero() &&
          match(Op0, m_NSWSub(m_Value(A), m_Value(B))))
        return new ICmpInst(ICmpInst::ICMP_SLT, A, B);

      // (icmp slt (sub nsw A B), 1) -> (icmp sle A, B)
      if (I.getPredicate() == ICmpInst::ICMP_SLT && CI->isOne() &&
          match(Op0, m_NSWSub(m_Value(A), m_Value(B))))
        return new ICmpInst(ICmpInst::ICMP_SLE, A, B);
    }

    if (I.isEquality()) {
      ConstantInt *CI2;
      if (match(Op0, m_AShr(m_ConstantInt(CI2), m_Value(A))) ||
          match(Op0, m_LShr(m_ConstantInt(CI2), m_Value(A)))) {
        // (icmp eq/ne (ashr/lshr const2, A), const1)
        if (Instruction *Inst = foldICmpCstShrConst(I, Op0, A, CI, CI2))
          return Inst;
      }
      if (match(Op0, m_Shl(m_ConstantInt(CI2), m_Value(A)))) {
        // (icmp eq/ne (shl const2, A), const1)
        if (Instruction *Inst = foldICmpCstShlConst(I, Op0, A, CI, CI2))
          return Inst;
      }
    }

    // If this comparison is a normal comparison, it demands all
    // bits, if it is a sign bit comparison, it only demands the sign bit.
    bool UnusedBit;
    isSignBit = isSignBitCheck(I.getPredicate(), CI, UnusedBit);

    // Canonicalize icmp instructions based on dominating conditions.
    BasicBlock *Parent = I.getParent();
    BasicBlock *Dom = Parent->getSinglePredecessor();
    auto *BI = Dom ? dyn_cast<BranchInst>(Dom->getTerminator()) : nullptr;
    ICmpInst::Predicate Pred;
    BasicBlock *TrueBB, *FalseBB;
    ConstantInt *CI2;
    if (BI && match(BI, m_Br(m_ICmp(Pred, m_Specific(Op0), m_ConstantInt(CI2)),
                             TrueBB, FalseBB)) &&
        TrueBB != FalseBB) {
      ConstantRange CR = ConstantRange::makeAllowedICmpRegion(I.getPredicate(),
                                                              CI->getValue());
      ConstantRange DominatingCR =
          (Parent == TrueBB)
              ? ConstantRange::makeExactICmpRegion(Pred, CI2->getValue())
              : ConstantRange::makeExactICmpRegion(
                    CmpInst::getInversePredicate(Pred), CI2->getValue());
      ConstantRange Intersection = DominatingCR.intersectWith(CR);
      ConstantRange Difference = DominatingCR.difference(CR);
      if (Intersection.isEmptySet())
        return replaceInstUsesWith(I, Builder->getFalse());
      if (Difference.isEmptySet())
        return replaceInstUsesWith(I, Builder->getTrue());
      // 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(I, isSignBit) && !I.isEquality()) {
        if (auto *AI = Intersection.getSingleElement())
          return new ICmpInst(ICmpInst::ICMP_EQ, Op0, Builder->getInt(*AI));
        if (auto *AD = Difference.getSingleElement())
          return new ICmpInst(ICmpInst::ICMP_NE, Op0, Builder->getInt(*AD));
      }
    }
  }

  // See if we can fold the comparison based on range information we can get
  // by checking whether bits are known to be zero or one in the input.
  if (BitWidth != 0) {
    APInt Op0KnownZero(BitWidth, 0), Op0KnownOne(BitWidth, 0);
    APInt Op1KnownZero(BitWidth, 0), Op1KnownOne(BitWidth, 0);

    if (SimplifyDemandedBits(I.getOperandUse(0),
                             DemandedBitsLHSMask(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.  Just constant fold this now so
    // that code below can assume that Min != Max.
    if (!isa<Constant>(Op0) && Op0Min == Op0Max)
      return new ICmpInst(I.getPredicate(),
                          ConstantInt::get(Op0->getType(), Op0Min), Op1);
    if (!isa<Constant>(Op1) && Op1Min == Op1Max)
      return new ICmpInst(I.getPredicate(), 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 (I.getPredicate()) {
    default: llvm_unreachable("Unknown icmp opcode!");
    case ICmpInst::ICMP_EQ: {
      if (Op0Max.ult(Op1Min) || Op0Min.ugt(Op1Max))
        return replaceInstUsesWith(I, ConstantInt::getFalse(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;
        ConstantInt *LHSC = nullptr;
        if (!match(Op0, m_And(m_Value(LHS), m_ConstantInt(LHSC))) ||
            LHSC->getValue() != Op0KnownZeroInverted)
          LHS = Op0;

        // If the LHS is 1 << x, and we know the result is a power of 2 like 8,
        // then turn "((1 << x)&8) == 0" into "x != 3".
        // or turn "((1 << x)&7) == 0" into "x > 2".
        Value *X = nullptr;
        if (match(LHS, m_Shl(m_One(), m_Value(X)))) {
          APInt ValToCheck = Op0KnownZeroInverted;
          if (ValToCheck.isPowerOf2()) {
            unsigned CmpVal = ValToCheck.countTrailingZeros();
            return new ICmpInst(ICmpInst::ICMP_NE, X,
                                ConstantInt::get(X->getType(), CmpVal));
          } else if ((++ValToCheck).isPowerOf2()) {
            unsigned CmpVal = ValToCheck.countTrailingZeros() - 1;
            return new ICmpInst(ICmpInst::ICMP_UGT, X,
                                ConstantInt::get(X->getType(), CmpVal));
          }
        }

        // If the LHS is 8 >>u x, and we know the result is a power of 2 like 1,
        // then turn "((8 >>u x)&1) == 0" into "x != 3".
        const APInt *CI;
        if (Op0KnownZeroInverted == 1 &&
            match(LHS, m_LShr(m_Power2(CI), m_Value(X))))
          return new ICmpInst(ICmpInst::ICMP_NE, X,
                              ConstantInt::get(X->getType(),
                                               CI->countTrailingZeros()));
      }
      break;
    }
    case ICmpInst::ICMP_NE: {
      if (Op0Max.ult(Op1Min) || Op0Min.ugt(Op1Max))
        return 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;
        ConstantInt *LHSC = nullptr;
        if (!match(Op0, m_And(m_Value(LHS), m_ConstantInt(LHSC))) ||
            LHSC->getValue() != Op0KnownZeroInverted)
          LHS = Op0;

        // If the LHS is 1 << x, and we know the result is a power of 2 like 8,
        // then turn "((1 << x)&8) != 0" into "x == 3".
        // or turn "((1 << x)&7) != 0" into "x < 3".
        Value *X = nullptr;
        if (match(LHS, m_Shl(m_One(), m_Value(X)))) {
          APInt ValToCheck = Op0KnownZeroInverted;
          if (ValToCheck.isPowerOf2()) {
            unsigned CmpVal = ValToCheck.countTrailingZeros();
            return new ICmpInst(ICmpInst::ICMP_EQ, X,
                                ConstantInt::get(X->getType(), CmpVal));
          } else if ((++ValToCheck).isPowerOf2()) {
            unsigned CmpVal = ValToCheck.countTrailingZeros();
            return new ICmpInst(ICmpInst::ICMP_ULT, X,
                                ConstantInt::get(X->getType(), CmpVal));
          }
        }

        // If the LHS is 8 >>u x, and we know the result is a power of 2 like 1,
        // then turn "((8 >>u x)&1) != 0" into "x == 3".
        const APInt *CI;
        if (Op0KnownZeroInverted == 1 &&
            match(LHS, m_LShr(m_Power2(CI), m_Value(X))))
          return new ICmpInst(ICmpInst::ICMP_EQ, X,
                              ConstantInt::get(X->getType(),
                                               CI->countTrailingZeros()));
      }
      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);
      if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
        if (Op1Max == Op0Min+1)        // A <u C -> A == C-1 if min(A)+1 == C
          return new ICmpInst(ICmpInst::ICMP_EQ, Op0,
                              Builder->getInt(CI->getValue()-1));

        // (x <u 2147483648) -> (x >s -1)  -> true if sign bit clear
        if (CI->isMinValue(true))
          return new ICmpInst(ICmpInst::ICMP_SGT, Op0,
                           Constant::getAllOnesValue(Op0->getType()));
      }
      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);
      if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
        if (Op1Min == Op0Max-1)        // A >u C -> A == C+1 if max(a)-1 == C
          return new ICmpInst(ICmpInst::ICMP_EQ, Op0,
                              Builder->getInt(CI->getValue()+1));

        // (x >u 2147483647) -> (x <s 0)  -> true if sign bit set
        if (CI->isMaxValue(true))
          return new ICmpInst(ICmpInst::ICMP_SLT, Op0,
                              Constant::getNullValue(Op0->getType()));
      }
      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:
      assert(!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:
      assert(!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:
      assert(!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:
      assert(!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);
  }

  // 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;

  // See if we are doing a comparison between a constant and an instruction that
  // can be folded into the comparison.

  // FIXME: Use m_APInt instead of dyn_cast<ConstantInt> to allow these
  // transforms for vectors.

  if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
    // Since the RHS is a ConstantInt (CI), if the left hand side is an
    // instruction, see if that instruction also has constants so that the
    // instruction can be folded into the icmp
    if (Instruction *LHSI = dyn_cast<Instruction>(Op0))
      if (Instruction *Res = foldICmpWithConstant(I, LHSI, CI))
        return Res;
  }

  if (Instruction *Res = foldICmpEqualityWithConstant(I))
    return Res;

  if (Instruction *Res = foldICmpIntrinsicWithConstant(I))
    return Res;

  // Handle icmp with constant (but not simple integer constant) RHS
  if (Constant *RHSC = dyn_cast<Constant>(Op1)) {
    if (Instruction *LHSI = dyn_cast<Instruction>(Op0))
      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;
      }
  }

  // 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()) {
    assert(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;
  }

  // Special logic for binary operators.
  BinaryOperator *BO0 = dyn_cast<BinaryOperator>(Op0);
  BinaryOperator *BO1 = dyn_cast<BinaryOperator>(Op1);
  if (BO0 || BO1) {
    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 {
        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;
        // fall-through
      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);
      }
    }
  }

  { 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 (I.isEquality()) {
    Value *A, *B, *C, *D;

    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, *C2;
        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;
    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));
      }
    }
  }

  // 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());

        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).
  assert(!RHS.isNaN() && "NaN comparison not already folded!");

  ICmpInst::Predicate Pred;
  switch (I.getPredicate()) {
  default: llvm_unreachable("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: llvm_unreachable("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: llvm_unreachable("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;
        // 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;
        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:
          llvm_unreachable("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, *Y;
  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;
}