//===- ConstantFPRange.cpp - ConstantFPRange implementation ---------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include "llvm/IR/ConstantFPRange.h"
#include "llvm/ADT/APFloat.h"
#include "llvm/ADT/FloatingPointMode.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>

using namespace llvm;

void ConstantFPRange::makeEmpty() {
  auto &Sem = Lower.getSemantics();
  Lower = APFloat::getInf(Sem, /*Negative=*/false);
  Upper = APFloat::getInf(Sem, /*Negative=*/true);
  MayBeQNaN = false;
  MayBeSNaN = false;
}

void ConstantFPRange::makeFull() {
  auto &Sem = Lower.getSemantics();
  Lower = APFloat::getInf(Sem, /*Negative=*/true);
  Upper = APFloat::getInf(Sem, /*Negative=*/false);
  MayBeQNaN = true;
  MayBeSNaN = true;
}

bool ConstantFPRange::isNaNOnly() const {
  return Lower.isPosInfinity() && Upper.isNegInfinity();
}

ConstantFPRange::ConstantFPRange(const fltSemantics &Sem, bool IsFullSet)
    : Lower(Sem, APFloat::uninitialized), Upper(Sem, APFloat::uninitialized) {
  Lower = APFloat::getInf(Sem, /*Negative=*/IsFullSet);
  Upper = APFloat::getInf(Sem, /*Negative=*/!IsFullSet);
  MayBeQNaN = IsFullSet;
  MayBeSNaN = IsFullSet;
}

ConstantFPRange::ConstantFPRange(const APFloat &Value)
    : Lower(Value.getSemantics(), APFloat::uninitialized),
      Upper(Value.getSemantics(), APFloat::uninitialized) {
  if (Value.isNaN()) {
    makeEmpty();
    bool IsSNaN = Value.isSignaling();
    MayBeQNaN = !IsSNaN;
    MayBeSNaN = IsSNaN;
  } else {
    Lower = Upper = Value;
    MayBeQNaN = MayBeSNaN = false;
  }
}

// We treat that -0 is less than 0 here.
static APFloat::cmpResult strictCompare(const APFloat &LHS,
                                        const APFloat &RHS) {
  assert(!LHS.isNaN() && !RHS.isNaN() && "Unordered compare");
  if (LHS.isZero() && RHS.isZero()) {
    if (LHS.isNegative() == RHS.isNegative())
      return APFloat::cmpEqual;
    return LHS.isNegative() ? APFloat::cmpLessThan : APFloat::cmpGreaterThan;
  }
  return LHS.compare(RHS);
}

static bool isNonCanonicalEmptySet(const APFloat &Lower, const APFloat &Upper) {
  return strictCompare(Lower, Upper) == APFloat::cmpGreaterThan &&
         !(Lower.isInfinity() && Upper.isInfinity());
}

static void canonicalizeRange(APFloat &Lower, APFloat &Upper) {
  if (isNonCanonicalEmptySet(Lower, Upper)) {
    Lower = APFloat::getInf(Lower.getSemantics(), /*Negative=*/false);
    Upper = APFloat::getInf(Upper.getSemantics(), /*Negative=*/true);
  }
}

ConstantFPRange::ConstantFPRange(APFloat LowerVal, APFloat UpperVal,
                                 bool MayBeQNaNVal, bool MayBeSNaNVal)
    : Lower(std::move(LowerVal)), Upper(std::move(UpperVal)),
      MayBeQNaN(MayBeQNaNVal), MayBeSNaN(MayBeSNaNVal) {
  assert(&Lower.getSemantics() == &Upper.getSemantics() &&
         "Should only use the same semantics");
  assert(!isNonCanonicalEmptySet(Lower, Upper) && "Non-canonical form");
}

ConstantFPRange ConstantFPRange::getFinite(const fltSemantics &Sem) {
  return ConstantFPRange(APFloat::getLargest(Sem, /*Negative=*/true),
                         APFloat::getLargest(Sem, /*Negative=*/false),
                         /*MayBeQNaN=*/false, /*MayBeSNaN=*/false);
}

ConstantFPRange ConstantFPRange::getNaNOnly(const fltSemantics &Sem,
                                            bool MayBeQNaN, bool MayBeSNaN) {
  return ConstantFPRange(APFloat::getInf(Sem, /*Negative=*/false),
                         APFloat::getInf(Sem, /*Negative=*/true), MayBeQNaN,
                         MayBeSNaN);
}

ConstantFPRange ConstantFPRange::getNonNaN(const fltSemantics &Sem) {
  return ConstantFPRange(APFloat::getInf(Sem, /*Negative=*/true),
                         APFloat::getInf(Sem, /*Negative=*/false),
                         /*MayBeQNaN=*/false, /*MayBeSNaN=*/false);
}

/// Return true for ULT/UGT/OLT/OGT
static bool fcmpPredExcludesEqual(FCmpInst::Predicate Pred) {
  return !(Pred & FCmpInst::FCMP_OEQ);
}

/// Return [-inf, V) or [-inf, V]
static ConstantFPRange makeLessThan(APFloat V, FCmpInst::Predicate Pred) {
  const fltSemantics &Sem = V.getSemantics();
  if (fcmpPredExcludesEqual(Pred)) {
    if (V.isNegInfinity())
      return ConstantFPRange::getEmpty(Sem);
    V.next(/*nextDown=*/true);
  }
  return ConstantFPRange::getNonNaN(APFloat::getInf(Sem, /*Negative=*/true),
                                    std::move(V));
}

/// Return (V, +inf] or [V, +inf]
static ConstantFPRange makeGreaterThan(APFloat V, FCmpInst::Predicate Pred) {
  const fltSemantics &Sem = V.getSemantics();
  if (fcmpPredExcludesEqual(Pred)) {
    if (V.isPosInfinity())
      return ConstantFPRange::getEmpty(Sem);
    V.next(/*nextDown=*/false);
  }
  return ConstantFPRange::getNonNaN(std::move(V),
                                    APFloat::getInf(Sem, /*Negative=*/false));
}

/// Make sure that +0/-0 are both included in the range.
static ConstantFPRange extendZeroIfEqual(const ConstantFPRange &CR,
                                         FCmpInst::Predicate Pred) {
  if (fcmpPredExcludesEqual(Pred))
    return CR;

  APFloat Lower = CR.getLower();
  APFloat Upper = CR.getUpper();
  if (Lower.isPosZero())
    Lower = APFloat::getZero(Lower.getSemantics(), /*Negative=*/true);
  if (Upper.isNegZero())
    Upper = APFloat::getZero(Upper.getSemantics(), /*Negative=*/false);
  return ConstantFPRange(std::move(Lower), std::move(Upper), CR.containsQNaN(),
                         CR.containsSNaN());
}

static ConstantFPRange setNaNField(const ConstantFPRange &CR,
                                   FCmpInst::Predicate Pred) {
  bool ContainsNaN = FCmpInst::isUnordered(Pred);
  return ConstantFPRange(CR.getLower(), CR.getUpper(),
                         /*MayBeQNaN=*/ContainsNaN, /*MayBeSNaN=*/ContainsNaN);
}

ConstantFPRange
ConstantFPRange::makeAllowedFCmpRegion(FCmpInst::Predicate Pred,
                                       const ConstantFPRange &Other) {
  if (Other.isEmptySet())
    return Other;
  if (Other.containsNaN() && FCmpInst::isUnordered(Pred))
    return getFull(Other.getSemantics());
  if (Other.isNaNOnly() && FCmpInst::isOrdered(Pred))
    return getEmpty(Other.getSemantics());

  switch (Pred) {
  case FCmpInst::FCMP_TRUE:
    return getFull(Other.getSemantics());
  case FCmpInst::FCMP_FALSE:
    return getEmpty(Other.getSemantics());
  case FCmpInst::FCMP_ORD:
    return getNonNaN(Other.getSemantics());
  case FCmpInst::FCMP_UNO:
    return getNaNOnly(Other.getSemantics(), /*MayBeQNaN=*/true,
                      /*MayBeSNaN=*/true);
  case FCmpInst::FCMP_OEQ:
  case FCmpInst::FCMP_UEQ:
    return setNaNField(extendZeroIfEqual(Other, Pred), Pred);
  case FCmpInst::FCMP_ONE:
  case FCmpInst::FCMP_UNE:
    if (const APFloat *SingleElement =
            Other.getSingleElement(/*ExcludesNaN=*/true)) {
      const fltSemantics &Sem = SingleElement->getSemantics();
      if (SingleElement->isPosInfinity())
        return setNaNField(
            getNonNaN(APFloat::getInf(Sem, /*Negative=*/true),
                      APFloat::getLargest(Sem, /*Negative=*/false)),
            Pred);
      if (SingleElement->isNegInfinity())
        return setNaNField(
            getNonNaN(APFloat::getLargest(Sem, /*Negative=*/true),
                      APFloat::getInf(Sem, /*Negative=*/false)),
            Pred);
    }
    return Pred == FCmpInst::FCMP_ONE ? getNonNaN(Other.getSemantics())
                                      : getFull(Other.getSemantics());
  case FCmpInst::FCMP_OLT:
  case FCmpInst::FCMP_OLE:
  case FCmpInst::FCMP_ULT:
  case FCmpInst::FCMP_ULE:
    return setNaNField(
        extendZeroIfEqual(makeLessThan(Other.getUpper(), Pred), Pred), Pred);
  case FCmpInst::FCMP_OGT:
  case FCmpInst::FCMP_OGE:
  case FCmpInst::FCMP_UGT:
  case FCmpInst::FCMP_UGE:
    return setNaNField(
        extendZeroIfEqual(makeGreaterThan(Other.getLower(), Pred), Pred), Pred);
  default:
    llvm_unreachable("Unexpected predicate");
  }
}

ConstantFPRange
ConstantFPRange::makeSatisfyingFCmpRegion(FCmpInst::Predicate Pred,
                                          const ConstantFPRange &Other) {
  if (Other.isEmptySet())
    return getFull(Other.getSemantics());
  if (Other.containsNaN() && FCmpInst::isOrdered(Pred))
    return getEmpty(Other.getSemantics());
  if (Other.isNaNOnly() && FCmpInst::isUnordered(Pred))
    return getFull(Other.getSemantics());

  switch (Pred) {
  case FCmpInst::FCMP_TRUE:
    return getFull(Other.getSemantics());
  case FCmpInst::FCMP_FALSE:
    return getEmpty(Other.getSemantics());
  case FCmpInst::FCMP_ORD:
    return getNonNaN(Other.getSemantics());
  case FCmpInst::FCMP_UNO:
    return getNaNOnly(Other.getSemantics(), /*MayBeQNaN=*/true,
                      /*MayBeSNaN=*/true);
  case FCmpInst::FCMP_OEQ:
  case FCmpInst::FCMP_UEQ:
    return setNaNField(Other.isSingleElement(/*ExcludesNaN=*/true) ||
                               ((Other.classify() & ~fcNan) == fcZero)
                           ? extendZeroIfEqual(Other, Pred)
                           : getEmpty(Other.getSemantics()),
                       Pred);
  case FCmpInst::FCMP_ONE:
  case FCmpInst::FCMP_UNE:
    return getEmpty(Other.getSemantics());
  case FCmpInst::FCMP_OLT:
  case FCmpInst::FCMP_OLE:
  case FCmpInst::FCMP_ULT:
  case FCmpInst::FCMP_ULE:
    return setNaNField(
        extendZeroIfEqual(makeLessThan(Other.getLower(), Pred), Pred), Pred);
  case FCmpInst::FCMP_OGT:
  case FCmpInst::FCMP_OGE:
  case FCmpInst::FCMP_UGT:
  case FCmpInst::FCMP_UGE:
    return setNaNField(
        extendZeroIfEqual(makeGreaterThan(Other.getUpper(), Pred), Pred), Pred);
  default:
    llvm_unreachable("Unexpected predicate");
  }
}

std::optional<ConstantFPRange>
ConstantFPRange::makeExactFCmpRegion(FCmpInst::Predicate Pred,
                                     const APFloat &Other) {
  if ((Pred == FCmpInst::FCMP_UNE || Pred == FCmpInst::FCMP_ONE) &&
      !Other.isNaN())
    return std::nullopt;
  return makeSatisfyingFCmpRegion(Pred, ConstantFPRange(Other));
}

bool ConstantFPRange::fcmp(FCmpInst::Predicate Pred,
                           const ConstantFPRange &Other) const {
  return makeSatisfyingFCmpRegion(Pred, Other).contains(*this);
}

bool ConstantFPRange::isFullSet() const {
  return Lower.isNegInfinity() && Upper.isPosInfinity() && MayBeQNaN &&
         MayBeSNaN;
}

bool ConstantFPRange::isEmptySet() const {
  return Lower.isPosInfinity() && Upper.isNegInfinity() && !MayBeQNaN &&
         !MayBeSNaN;
}

bool ConstantFPRange::contains(const APFloat &Val) const {
  assert(&getSemantics() == &Val.getSemantics() &&
         "Should only use the same semantics");

  if (Val.isNaN())
    return Val.isSignaling() ? MayBeSNaN : MayBeQNaN;
  return strictCompare(Lower, Val) != APFloat::cmpGreaterThan &&
         strictCompare(Val, Upper) != APFloat::cmpGreaterThan;
}

bool ConstantFPRange::contains(const ConstantFPRange &CR) const {
  assert(&getSemantics() == &CR.getSemantics() &&
         "Should only use the same semantics");

  if (CR.MayBeQNaN && !MayBeQNaN)
    return false;

  if (CR.MayBeSNaN && !MayBeSNaN)
    return false;

  return strictCompare(Lower, CR.Lower) != APFloat::cmpGreaterThan &&
         strictCompare(CR.Upper, Upper) != APFloat::cmpGreaterThan;
}

const APFloat *ConstantFPRange::getSingleElement(bool ExcludesNaN) const {
  if (!ExcludesNaN && (MayBeSNaN || MayBeQNaN))
    return nullptr;
  return Lower.bitwiseIsEqual(Upper) ? &Lower : nullptr;
}

std::optional<bool> ConstantFPRange::getSignBit() const {
  if (!MayBeSNaN && !MayBeQNaN && Lower.isNegative() == Upper.isNegative())
    return Lower.isNegative();
  return std::nullopt;
}

bool ConstantFPRange::operator==(const ConstantFPRange &CR) const {
  assert(&getSemantics() == &CR.getSemantics() &&
         "Should only use the same semantics");
  if (MayBeSNaN != CR.MayBeSNaN || MayBeQNaN != CR.MayBeQNaN)
    return false;
  return Lower.bitwiseIsEqual(CR.Lower) && Upper.bitwiseIsEqual(CR.Upper);
}

FPClassTest ConstantFPRange::classify() const {
  uint32_t Mask = fcNone;
  if (MayBeSNaN)
    Mask |= fcSNan;
  if (MayBeQNaN)
    Mask |= fcQNan;
  if (!isNaNOnly()) {
    FPClassTest LowerMask = Lower.classify();
    FPClassTest UpperMask = Upper.classify();
    assert(LowerMask <= UpperMask && "Range is nan-only.");
    // Set all bits from log2(LowerMask) to log2(UpperMask).
    Mask |= (UpperMask << 1) - LowerMask;
  }
  return static_cast<FPClassTest>(Mask);
}

void ConstantFPRange::print(raw_ostream &OS) const {
  if (isFullSet())
    OS << "full-set";
  else if (isEmptySet())
    OS << "empty-set";
  else {
    bool NaNOnly = isNaNOnly();
    if (!NaNOnly)
      OS << '[' << Lower << ", " << Upper << ']';

    if (MayBeSNaN || MayBeQNaN) {
      if (!NaNOnly)
        OS << " with ";
      if (MayBeSNaN && MayBeQNaN)
        OS << "NaN";
      else if (MayBeSNaN)
        OS << "SNaN";
      else if (MayBeQNaN)
        OS << "QNaN";
    }
  }
}

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
LLVM_DUMP_METHOD void ConstantFPRange::dump() const { print(dbgs()); }
#endif

ConstantFPRange
ConstantFPRange::intersectWith(const ConstantFPRange &CR) const {
  assert(&getSemantics() == &CR.getSemantics() &&
         "Should only use the same semantics");
  APFloat NewLower = maxnum(Lower, CR.Lower);
  APFloat NewUpper = minnum(Upper, CR.Upper);
  canonicalizeRange(NewLower, NewUpper);
  return ConstantFPRange(std::move(NewLower), std::move(NewUpper),
                         MayBeQNaN & CR.MayBeQNaN, MayBeSNaN & CR.MayBeSNaN);
}

ConstantFPRange ConstantFPRange::unionWith(const ConstantFPRange &CR) const {
  assert(&getSemantics() == &CR.getSemantics() &&
         "Should only use the same semantics");
  return ConstantFPRange(minnum(Lower, CR.Lower), maxnum(Upper, CR.Upper),
                         MayBeQNaN | CR.MayBeQNaN, MayBeSNaN | CR.MayBeSNaN);
}

ConstantFPRange ConstantFPRange::abs() const {
  if (isNaNOnly())
    return *this;
  // Check if the range is all non-negative or all non-positive.
  if (Lower.isNegative() == Upper.isNegative()) {
    if (Lower.isNegative())
      return negate();
    return *this;
  }
  // The range contains both positive and negative values.
  APFloat NewLower = APFloat::getZero(getSemantics());
  APFloat NewUpper = maxnum(-Lower, Upper);
  return ConstantFPRange(std::move(NewLower), std::move(NewUpper), MayBeQNaN,
                         MayBeSNaN);
}

ConstantFPRange ConstantFPRange::negate() const {
  return ConstantFPRange(-Upper, -Lower, MayBeQNaN, MayBeSNaN);
}

/// Return true if the finite part is not empty after removing infinities.
static bool removeInf(APFloat &Lower, APFloat &Upper, bool &HasPosInf,
                      bool &HasNegInf) {
  assert(strictCompare(Lower, Upper) != APFloat::cmpGreaterThan &&
         "Non-NaN part is empty.");
  auto &Sem = Lower.getSemantics();
  if (Lower.isNegInfinity()) {
    Lower = APFloat::getLargest(Sem, /*Negative=*/true);
    HasNegInf = true;
  }
  if (Upper.isPosInfinity()) {
    Upper = APFloat::getLargest(Sem, /*Negative=*/false);
    HasPosInf = true;
  }
  return strictCompare(Lower, Upper) != APFloat::cmpGreaterThan;
}

ConstantFPRange ConstantFPRange::getWithoutInf() const {
  if (isNaNOnly())
    return *this;
  APFloat NewLower = Lower;
  APFloat NewUpper = Upper;
  bool UnusedFlag;
  removeInf(NewLower, NewUpper, /*HasPosInf=*/UnusedFlag,
            /*HasNegInf=*/UnusedFlag);
  canonicalizeRange(NewLower, NewUpper);
  return ConstantFPRange(std::move(NewLower), std::move(NewUpper), MayBeQNaN,
                         MayBeSNaN);
}

ConstantFPRange ConstantFPRange::cast(const fltSemantics &DstSem,
                                      APFloat::roundingMode RM) const {
  bool LosesInfo;
  APFloat NewLower = Lower;
  APFloat NewUpper = Upper;
  // For conservative, return full range if conversion is invalid.
  if (NewLower.convert(DstSem, RM, &LosesInfo) == APFloat::opInvalidOp ||
      NewLower.isNaN())
    return getFull(DstSem);
  if (NewUpper.convert(DstSem, RM, &LosesInfo) == APFloat::opInvalidOp ||
      NewUpper.isNaN())
    return getFull(DstSem);
  return ConstantFPRange(std::move(NewLower), std::move(NewUpper),
                         /*MayBeQNaNVal=*/MayBeQNaN || MayBeSNaN,
                         /*MayBeSNaNVal=*/false);
}

ConstantFPRange ConstantFPRange::add(const ConstantFPRange &Other) const {
  bool ResMayBeQNaN = ((MayBeQNaN || MayBeSNaN) && !Other.isEmptySet()) ||
                      ((Other.MayBeQNaN || Other.MayBeSNaN) && !isEmptySet());
  if (isNaNOnly() || Other.isNaNOnly())
    return getNaNOnly(getSemantics(), /*MayBeQNaN=*/ResMayBeQNaN,
                      /*MayBeSNaN=*/false);
  bool LHSHasNegInf = false, LHSHasPosInf = false;
  APFloat LHSLower = Lower, LHSUpper = Upper;
  bool LHSFiniteIsNonEmpty =
      removeInf(LHSLower, LHSUpper, LHSHasPosInf, LHSHasNegInf);
  bool RHSHasNegInf = false, RHSHasPosInf = false;
  APFloat RHSLower = Other.Lower, RHSUpper = Other.Upper;
  bool RHSFiniteIsNonEmpty =
      removeInf(RHSLower, RHSUpper, RHSHasPosInf, RHSHasNegInf);
  // -inf + +inf = QNaN
  ResMayBeQNaN |=
      (LHSHasNegInf && RHSHasPosInf) || (LHSHasPosInf && RHSHasNegInf);
  // +inf + finite/+inf = +inf, -inf + finite/-inf = -inf
  bool HasNegInf = (LHSHasNegInf && (RHSFiniteIsNonEmpty || RHSHasNegInf)) ||
                   (RHSHasNegInf && (LHSFiniteIsNonEmpty || LHSHasNegInf));
  bool HasPosInf = (LHSHasPosInf && (RHSFiniteIsNonEmpty || RHSHasPosInf)) ||
                   (RHSHasPosInf && (LHSFiniteIsNonEmpty || LHSHasPosInf));
  if (LHSFiniteIsNonEmpty && RHSFiniteIsNonEmpty) {
    APFloat NewLower =
        HasNegInf ? APFloat::getInf(LHSLower.getSemantics(), /*Negative=*/true)
                  : LHSLower + RHSLower;
    APFloat NewUpper =
        HasPosInf ? APFloat::getInf(LHSUpper.getSemantics(), /*Negative=*/false)
                  : LHSUpper + RHSUpper;
    return ConstantFPRange(NewLower, NewUpper, ResMayBeQNaN,
                           /*MayBeSNaN=*/false);
  }
  // If both HasNegInf and HasPosInf are false, the non-NaN part is empty.
  // We just return the canonical form [+inf, -inf] for the empty non-NaN set.
  return ConstantFPRange(
      APFloat::getInf(Lower.getSemantics(), /*Negative=*/HasNegInf),
      APFloat::getInf(Upper.getSemantics(), /*Negative=*/!HasPosInf),
      ResMayBeQNaN,
      /*MayBeSNaN=*/false);
}

ConstantFPRange ConstantFPRange::sub(const ConstantFPRange &Other) const {
  // fsub X, Y = fadd X, (fneg Y)
  return add(Other.negate());
}

void ConstantFPRange::flushDenormals(DenormalMode::DenormalModeKind Mode) {
  if (Mode == DenormalMode::IEEE)
    return;
  FPClassTest Class = classify();
  if (!(Class & fcSubnormal))
    return;

  auto &Sem = getSemantics();
  // PreserveSign: PosSubnormal -> PosZero, NegSubnormal -> NegZero
  // PositiveZero: PosSubnormal -> PosZero, NegSubnormal -> PosZero
  // Dynamic:      PosSubnormal -> PosZero, NegSubnormal -> NegZero/PosZero
  bool ZeroLowerNegative =
      Mode != DenormalMode::PositiveZero && (Class & fcNegSubnormal);
  bool ZeroUpperNegative =
      Mode == DenormalMode::PreserveSign && !(Class & fcPosSubnormal);
  assert((ZeroLowerNegative || !ZeroUpperNegative) &&
         "ZeroLower is greater than ZeroUpper.");
  Lower = minnum(Lower, APFloat::getZero(Sem, ZeroLowerNegative));
  Upper = maxnum(Upper, APFloat::getZero(Sem, ZeroUpperNegative));
}

/// Represent a contiguous range of values sharing the same sign.
struct SameSignRange {
  bool HasZero;
  bool HasNonZero;
  bool HasInf;
  // The lower and upper bounds of the range (inclusive).
  // The sign is dropped and infinities are excluded.
  std::optional<std::pair<APFloat, APFloat>> FinitePart;

  explicit SameSignRange(const APFloat &Lower, const APFloat &Upper)
      : HasZero(Lower.isZero()), HasNonZero(!Upper.isZero()),
        HasInf(Upper.isInfinity()) {
    assert(!Lower.isNegative() && !Upper.isNegative() &&
           "The sign should be dropped.");
    assert(strictCompare(Lower, Upper) != APFloat::cmpGreaterThan &&
           "Empty set.");
    if (!Lower.isInfinity())
      FinitePart = {Lower,
                    HasInf ? APFloat::getLargest(Lower.getSemantics()) : Upper};
  }
};

/// Split the range into positive and negative components.
static void splitPosNeg(const APFloat &Lower, const APFloat &Upper,
                        std::optional<SameSignRange> &NegPart,
                        std::optional<SameSignRange> &PosPart) {
  assert(strictCompare(Lower, Upper) != APFloat::cmpGreaterThan &&
         "Non-NaN part is empty.");
  if (Lower.isNegative() == Upper.isNegative()) {
    if (Lower.isNegative())
      NegPart = SameSignRange{abs(Upper), abs(Lower)};
    else
      PosPart = SameSignRange{Lower, Upper};
    return;
  }
  auto &Sem = Lower.getSemantics();
  NegPart = SameSignRange{APFloat::getZero(Sem), abs(Lower)};
  PosPart = SameSignRange{APFloat::getZero(Sem), Upper};
}

ConstantFPRange ConstantFPRange::mul(const ConstantFPRange &Other) const {
  auto &Sem = getSemantics();
  bool ResMayBeQNaN = ((MayBeQNaN || MayBeSNaN) && !Other.isEmptySet()) ||
                      ((Other.MayBeQNaN || Other.MayBeSNaN) && !isEmptySet());
  if (isNaNOnly() || Other.isNaNOnly())
    return getNaNOnly(Sem, /*MayBeQNaN=*/ResMayBeQNaN,
                      /*MayBeSNaN=*/false);
  std::optional<SameSignRange> LHSNeg, LHSPos, RHSNeg, RHSPos;
  splitPosNeg(Lower, Upper, LHSNeg, LHSPos);
  splitPosNeg(Other.Lower, Other.Upper, RHSNeg, RHSPos);
  APFloat ResLower = APFloat::getInf(Sem, /*Negative=*/false);
  APFloat ResUpper = APFloat::getInf(Sem, /*Negative=*/true);
  auto Update = [&](std::optional<SameSignRange> &LHS,
                    std::optional<SameSignRange> &RHS, bool Negative) {
    if (!LHS || !RHS)
      return;
    // 0 * inf = QNaN
    ResMayBeQNaN |= LHS->HasZero && RHS->HasInf;
    ResMayBeQNaN |= RHS->HasZero && LHS->HasInf;
    // NonZero * inf = inf
    if ((LHS->HasInf && RHS->HasNonZero) || (RHS->HasInf && LHS->HasNonZero))
      (Negative ? ResLower : ResUpper) = APFloat::getInf(Sem, Negative);
    // Finite * Finite
    if (LHS->FinitePart && RHS->FinitePart) {
      APFloat NewLower = LHS->FinitePart->first * RHS->FinitePart->first;
      APFloat NewUpper = LHS->FinitePart->second * RHS->FinitePart->second;
      if (Negative) {
        ResLower = minnum(ResLower, -NewUpper);
        ResUpper = maxnum(ResUpper, -NewLower);
      } else {
        ResLower = minnum(ResLower, NewLower);
        ResUpper = maxnum(ResUpper, NewUpper);
      }
    }
  };
  Update(LHSNeg, RHSNeg, /*Negative=*/false);
  Update(LHSNeg, RHSPos, /*Negative=*/true);
  Update(LHSPos, RHSNeg, /*Negative=*/true);
  Update(LHSPos, RHSPos, /*Negative=*/false);
  return ConstantFPRange(ResLower, ResUpper, ResMayBeQNaN, /*MayBeSNaN=*/false);
}

ConstantFPRange ConstantFPRange::div(const ConstantFPRange &Other) const {
  auto &Sem = getSemantics();
  bool ResMayBeQNaN = ((MayBeQNaN || MayBeSNaN) && !Other.isEmptySet()) ||
                      ((Other.MayBeQNaN || Other.MayBeSNaN) && !isEmptySet());
  if (isNaNOnly() || Other.isNaNOnly())
    return getNaNOnly(Sem, /*MayBeQNaN=*/ResMayBeQNaN,
                      /*MayBeSNaN=*/false);
  std::optional<SameSignRange> LHSNeg, LHSPos, RHSNeg, RHSPos;
  splitPosNeg(Lower, Upper, LHSNeg, LHSPos);
  splitPosNeg(Other.Lower, Other.Upper, RHSNeg, RHSPos);
  APFloat ResLower = APFloat::getInf(Sem, /*Negative=*/false);
  APFloat ResUpper = APFloat::getInf(Sem, /*Negative=*/true);
  auto Update = [&](std::optional<SameSignRange> &LHS,
                    std::optional<SameSignRange> &RHS, bool Negative) {
    if (!LHS || !RHS)
      return;
    // inf / inf = QNaN 0 / 0 = QNaN
    ResMayBeQNaN |= LHS->HasInf && RHS->HasInf;
    ResMayBeQNaN |= LHS->HasZero && RHS->HasZero;
    // It is not straightforward to infer HasNonZeroFinite = HasFinite &&
    // HasNonZero. By definitions we have:
    //   HasFinite = HasNonZeroFinite || HasZero
    //   HasNonZero = HasNonZeroFinite || HasInf
    // Since the range is contiguous, if both HasFinite and HasNonZero are true,
    // HasNonZeroFinite must be true.
    bool LHSHasNonZeroFinite = LHS->FinitePart && LHS->HasNonZero;
    bool RHSHasNonZeroFinite = RHS->FinitePart && RHS->HasNonZero;
    // inf / Finite = inf FiniteNonZero / 0 = inf
    if ((LHS->HasInf && RHS->FinitePart) ||
        (LHSHasNonZeroFinite && RHS->HasZero))
      (Negative ? ResLower : ResUpper) = APFloat::getInf(Sem, Negative);
    // Finite / inf = 0
    if (LHS->FinitePart && RHS->HasInf) {
      APFloat Zero = APFloat::getZero(Sem, /*Negative=*/Negative);
      ResLower = minnum(ResLower, Zero);
      ResUpper = maxnum(ResUpper, Zero);
    }
    // Finite / FiniteNonZero
    if (LHS->FinitePart && RHSHasNonZeroFinite) {
      assert(!RHS->FinitePart->second.isZero() &&
             "Divisor should be non-zero.");
      APFloat NewLower = LHS->FinitePart->first / RHS->FinitePart->second;
      APFloat NewUpper = LHS->FinitePart->second /
                         (RHS->FinitePart->first.isZero()
                              ? APFloat::getSmallest(Sem, /*Negative=*/false)
                              : RHS->FinitePart->first);
      if (Negative) {
        ResLower = minnum(ResLower, -NewUpper);
        ResUpper = maxnum(ResUpper, -NewLower);
      } else {
        ResLower = minnum(ResLower, NewLower);
        ResUpper = maxnum(ResUpper, NewUpper);
      }
    }
  };
  Update(LHSNeg, RHSNeg, /*Negative=*/false);
  Update(LHSNeg, RHSPos, /*Negative=*/true);
  Update(LHSPos, RHSNeg, /*Negative=*/true);
  Update(LHSPos, RHSPos, /*Negative=*/false);
  return ConstantFPRange(ResLower, ResUpper, ResMayBeQNaN, /*MayBeSNaN=*/false);
}