C++ APInt::isMinValue方法代码示例

ConstantRange::ConstantRange(const APInt &L, const APInt &U) :
  Lower(L), Upper(U) {
  assert(L.getBitWidth() == U.getBitWidth() &&
         "ConstantRange with unequal bit widths");
  assert((L != U || (L.isMaxValue() || L.isMinValue())) &&
         "Lower == Upper, but they aren't min or max value!");
}

ConstantRange
ConstantRange::binaryOr(const ConstantRange &Other) const {
  if (isEmptySet() || Other.isEmptySet())
    return ConstantRange(getBitWidth(), /*isFullSet=*/false);

  // TODO: replace this with something less conservative

  APInt umax = APIntOps::umax(getUnsignedMin(), Other.getUnsignedMin());
  if (umax.isMinValue())
    return ConstantRange(getBitWidth(), /*isFullSet=*/true);
  return ConstantRange(umax, APInt::getNullValue(getBitWidth()));
}

ConstantRange
ConstantRange::makeGuaranteedNoWrapRegion(Instruction::BinaryOps BinOp,
                                          const APInt &C, unsigned NoWrapKind) {
  typedef OverflowingBinaryOperator OBO;

  // Computes the intersection of CR0 and CR1.  It is different from
  // intersectWith in that the ConstantRange returned will only contain elements
  // in both CR0 and CR1 (i.e. SubsetIntersect(X, Y) is a *subset*, proper or
  // not, of both X and Y).
  auto SubsetIntersect =
      [](const ConstantRange &CR0, const ConstantRange &CR1) {
    return CR0.inverse().unionWith(CR1.inverse()).inverse();
  };

  assert(BinOp >= Instruction::BinaryOpsBegin &&
         BinOp < Instruction::BinaryOpsEnd && "Binary operators only!");

  assert((NoWrapKind == OBO::NoSignedWrap ||
          NoWrapKind == OBO::NoUnsignedWrap ||
          NoWrapKind == (OBO::NoUnsignedWrap | OBO::NoSignedWrap)) &&
         "NoWrapKind invalid!");

  unsigned BitWidth = C.getBitWidth();
  if (BinOp != Instruction::Add)
    // Conservative answer: empty set
    return ConstantRange(BitWidth, false);

  if (C.isMinValue())
    // Full set: nothing signed / unsigned wraps when added to 0.
    return ConstantRange(BitWidth);

  ConstantRange Result(BitWidth);

  if (NoWrapKind & OBO::NoUnsignedWrap)
    Result = SubsetIntersect(Result,
                             ConstantRange(APInt::getNullValue(BitWidth), -C));

  if (NoWrapKind & OBO::NoSignedWrap) {
    if (C.isStrictlyPositive())
      Result = SubsetIntersect(
          Result, ConstantRange(APInt::getSignedMinValue(BitWidth),
                                APInt::getSignedMinValue(BitWidth) - C));
    else
      Result = SubsetIntersect(
          Result, ConstantRange(APInt::getSignedMinValue(BitWidth) - C,
                                APInt::getSignedMinValue(BitWidth)));
  }

  return Result;
}

bool GuardWideningImpl::combineRangeChecks(
    SmallVectorImpl<GuardWideningImpl::RangeCheck> &Checks,
    SmallVectorImpl<GuardWideningImpl::RangeCheck> &RangeChecksOut) {
  unsigned OldCount = Checks.size();
  while (!Checks.empty()) {
    // Pick all of the range checks with a specific base and length, and try to
    // merge them.
    Value *CurrentBase = Checks.front().getBase();
    Value *CurrentLength = Checks.front().getLength();

    SmallVector<GuardWideningImpl::RangeCheck, 3> CurrentChecks;

    auto IsCurrentCheck = [&](GuardWideningImpl::RangeCheck &RC) {
      return RC.getBase() == CurrentBase && RC.getLength() == CurrentLength;
    };

    copy_if(Checks, std::back_inserter(CurrentChecks), IsCurrentCheck);
    Checks.erase(remove_if(Checks, IsCurrentCheck), Checks.end());

    assert(CurrentChecks.size() != 0 && "We know we have at least one!");

    if (CurrentChecks.size() < 3) {
      RangeChecksOut.insert(RangeChecksOut.end(), CurrentChecks.begin(),
                            CurrentChecks.end());
      continue;
    }

    // CurrentChecks.size() will typically be 3 here, but so far there has been
    // no need to hard-code that fact.

    std::sort(CurrentChecks.begin(), CurrentChecks.end(),
              [&](const GuardWideningImpl::RangeCheck &LHS,
                  const GuardWideningImpl::RangeCheck &RHS) {
      return LHS.getOffsetValue().slt(RHS.getOffsetValue());
    });

    // Note: std::sort should not invalidate the ChecksStart iterator.

    ConstantInt *MinOffset = CurrentChecks.front().getOffset(),
                *MaxOffset = CurrentChecks.back().getOffset();

    unsigned BitWidth = MaxOffset->getValue().getBitWidth();
    if ((MaxOffset->getValue() - MinOffset->getValue())
            .ugt(APInt::getSignedMinValue(BitWidth)))
      return false;

    APInt MaxDiff = MaxOffset->getValue() - MinOffset->getValue();
    const APInt &HighOffset = MaxOffset->getValue();
    auto OffsetOK = [&](const GuardWideningImpl::RangeCheck &RC) {
      return (HighOffset - RC.getOffsetValue()).ult(MaxDiff);
    };

    if (MaxDiff.isMinValue() ||
        !std::all_of(std::next(CurrentChecks.begin()), CurrentChecks.end(),
                     OffsetOK))
      return false;

    // We have a series of f+1 checks as:
    //
    //   I+k_0 u< L   ... Chk_0
    //   I_k_1 u< L   ... Chk_1
    //   ...
    //   I_k_f u< L   ... Chk_(f+1)
    //
    //     with forall i in [0,f): k_f-k_i u< k_f-k_0  ... Precond_0
    //          k_f-k_0 u< INT_MIN+k_f                 ... Precond_1
    //          k_f != k_0                             ... Precond_2
    //
    // Claim:
    //   Chk_0 AND Chk_(f+1)  implies all the other checks
    //
    // Informal proof sketch:
    //
    // We will show that the integer range [I+k_0,I+k_f] does not unsigned-wrap
    // (i.e. going from I+k_0 to I+k_f does not cross the -1,0 boundary) and
    // thus I+k_f is the greatest unsigned value in that range.
    //
    // This combined with Ckh_(f+1) shows that everything in that range is u< L.
    // Via Precond_0 we know that all of the indices in Chk_0 through Chk_(f+1)
    // lie in [I+k_0,I+k_f], this proving our claim.
    //
    // To see that [I+k_0,I+k_f] is not a wrapping range, note that there are
    // two possibilities: I+k_0 u< I+k_f or I+k_0 >u I+k_f (they can't be equal
    // since k_0 != k_f).  In the former case, [I+k_0,I+k_f] is not a wrapping
    // range by definition, and the latter case is impossible:
    //
    //   0-----I+k_f---I+k_0----L---INT_MAX,INT_MIN------------------(-1)
    //   xxxxxx             xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
    //
    // For Chk_0 to succeed, we'd have to have k_f-k_0 (the range highlighted
    // with 'x' above) to be at least >u INT_MIN.

    RangeChecksOut.emplace_back(CurrentChecks.front());
    RangeChecksOut.emplace_back(CurrentChecks.back());
  }

  assert(RangeChecksOut.size() <= OldCount && "We pessimized!");
  return RangeChecksOut.size() != OldCount;
}