Subversion Repositories QNX 8.QNX8 LLVM/Clang compiler suite

//===- llvm/ADT/SparseBitVector.h - Efficient Sparse BitVector --*- C++ -*-===//

//

// 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

//

//===----------------------------------------------------------------------===//

///

/// \file

/// This file defines the SparseBitVector class.  See the doxygen comment for

/// SparseBitVector for more details on the algorithm used.

///

//===----------------------------------------------------------------------===//

#ifndef LLVM_ADT_SPARSEBITVECTOR_H

#define LLVM_ADT_SPARSEBITVECTOR_H

#include "llvm/Support/ErrorHandling.h"

#include "llvm/Support/MathExtras.h"

#include "llvm/Support/raw_ostream.h"

#include <cassert>

#include <climits>

#include <cstring>

#include <iterator>

#include <list>

namespace llvm {

/// SparseBitVector is an implementation of a bitvector that is sparse by only

/// storing the elements that have non-zero bits set.  In order to make this

/// fast for the most common cases, SparseBitVector is implemented as a linked

/// list of SparseBitVectorElements.  We maintain a pointer to the last

/// SparseBitVectorElement accessed (in the form of a list iterator), in order

/// to make multiple in-order test/set constant time after the first one is

/// executed.  Note that using vectors to store SparseBitVectorElement's does

/// not work out very well because it causes insertion in the middle to take

/// enormous amounts of time with a large amount of bits.  Other structures that

/// have better worst cases for insertion in the middle (various balanced trees,

/// etc) do not perform as well in practice as a linked list with this iterator

/// kept up to date.  They are also significantly more memory intensive.

template <unsigned ElementSize = 128> struct SparseBitVectorElement {

public:

  using BitWord = unsigned long;

  using size_type = unsigned;

  enum {

    BITWORD_SIZE = sizeof(BitWord) * CHAR_BIT,

    BITWORDS_PER_ELEMENT = (ElementSize + BITWORD_SIZE - 1) / BITWORD_SIZE,

    BITS_PER_ELEMENT = ElementSize

  };

private:

  // Index of Element in terms of where first bit starts.

  unsigned ElementIndex;

  BitWord Bits[BITWORDS_PER_ELEMENT];

  SparseBitVectorElement() {

    ElementIndex = ~0U;

    memset(&Bits[0], 0, sizeof (BitWord) * BITWORDS_PER_ELEMENT);

  }

public:

  explicit SparseBitVectorElement(unsigned Idx) {

    ElementIndex = Idx;

    memset(&Bits[0], 0, sizeof (BitWord) * BITWORDS_PER_ELEMENT);

  }

  // Comparison.

  bool operator==(const SparseBitVectorElement &RHS) const {

    if (ElementIndex != RHS.ElementIndex)

      return false;

    for (unsigned i = 0; i < BITWORDS_PER_ELEMENT; ++i)

      if (Bits[i] != RHS.Bits[i])

        return false;

    return true;

  }

  bool operator!=(const SparseBitVectorElement &RHS) const {

    return !(*this == RHS);

  }

  // Return the bits that make up word Idx in our element.

  BitWord word(unsigned Idx) const {

    assert(Idx < BITWORDS_PER_ELEMENT);

    return Bits[Idx];

  }

  unsigned index() const {

    return ElementIndex;

  }

  bool empty() const {

    for (unsigned i = 0; i < BITWORDS_PER_ELEMENT; ++i)

      if (Bits[i])

        return false;

    return true;

  }

  void set(unsigned Idx) {

    Bits[Idx / BITWORD_SIZE] |= 1L << (Idx % BITWORD_SIZE);

  }

  bool test_and_set(unsigned Idx) {

    bool old = test(Idx);

    if (!old) {

      set(Idx);

      return true;

    }

    return false;

  }

  void reset(unsigned Idx) {

    Bits[Idx / BITWORD_SIZE] &= ~(1L << (Idx % BITWORD_SIZE));

  }

  bool test(unsigned Idx) const {

    return Bits[Idx / BITWORD_SIZE] & (1L << (Idx % BITWORD_SIZE));

  }

  size_type count() const {

    unsigned NumBits = 0;

    for (unsigned i = 0; i < BITWORDS_PER_ELEMENT; ++i)

      NumBits += llvm::popcount(Bits[i]);

    return NumBits;

  }

  /// find_first - Returns the index of the first set bit.

  int find_first() const {

    for (unsigned i = 0; i < BITWORDS_PER_ELEMENT; ++i)

      if (Bits[i] != 0)

        return i * BITWORD_SIZE + countTrailingZeros(Bits[i]);

    llvm_unreachable("Illegal empty element");

  }

  /// find_last - Returns the index of the last set bit.

  int find_last() const {

    for (unsigned I = 0; I < BITWORDS_PER_ELEMENT; ++I) {

      unsigned Idx = BITWORDS_PER_ELEMENT - I - 1;

      if (Bits[Idx] != 0)

        return Idx * BITWORD_SIZE + BITWORD_SIZE -

               countLeadingZeros(Bits[Idx]) - 1;

    }

    llvm_unreachable("Illegal empty element");

  }

  /// find_next - Returns the index of the next set bit starting from the

  /// "Curr" bit. Returns -1 if the next set bit is not found.

  int find_next(unsigned Curr) const {

    if (Curr >= BITS_PER_ELEMENT)

      return -1;

    unsigned WordPos = Curr / BITWORD_SIZE;

    unsigned BitPos = Curr % BITWORD_SIZE;

    BitWord Copy = Bits[WordPos];

    assert(WordPos <= BITWORDS_PER_ELEMENT

           && "Word Position outside of element");

    // Mask off previous bits.

    Copy &= ~0UL << BitPos;

    if (Copy != 0)

      return WordPos * BITWORD_SIZE + countTrailingZeros(Copy);

    // Check subsequent words.

    for (unsigned i = WordPos+1; i < BITWORDS_PER_ELEMENT; ++i)

      if (Bits[i] != 0)

        return i * BITWORD_SIZE + countTrailingZeros(Bits[i]);

    return -1;

  }

  // Union this element with RHS and return true if this one changed.

  bool unionWith(const SparseBitVectorElement &RHS) {

    bool changed = false;

    for (unsigned i = 0; i < BITWORDS_PER_ELEMENT; ++i) {

      BitWord old = changed ? 0 : Bits[i];

      Bits[i] |= RHS.Bits[i];

      if (!changed && old != Bits[i])

        changed = true;

    }

    return changed;

  }

  // Return true if we have any bits in common with RHS

  bool intersects(const SparseBitVectorElement &RHS) const {

    for (unsigned i = 0; i < BITWORDS_PER_ELEMENT; ++i) {

      if (RHS.Bits[i] & Bits[i])

        return true;

    }

    return false;

  }

  // Intersect this Element with RHS and return true if this one changed.

  // BecameZero is set to true if this element became all-zero bits.

  bool intersectWith(const SparseBitVectorElement &RHS,

                     bool &BecameZero) {

    bool changed = false;

    bool allzero = true;

    BecameZero = false;

    for (unsigned i = 0; i < BITWORDS_PER_ELEMENT; ++i) {

      BitWord old = changed ? 0 : Bits[i];

      Bits[i] &= RHS.Bits[i];

      if (Bits[i] != 0)

        allzero = false;

      if (!changed && old != Bits[i])

        changed = true;

    }

    BecameZero = allzero;

    return changed;

  }

  // Intersect this Element with the complement of RHS and return true if this

  // one changed.  BecameZero is set to true if this element became all-zero

  // bits.

  bool intersectWithComplement(const SparseBitVectorElement &RHS,

                               bool &BecameZero) {

    bool changed = false;

    bool allzero = true;

    BecameZero = false;

    for (unsigned i = 0; i < BITWORDS_PER_ELEMENT; ++i) {

      BitWord old = changed ? 0 : Bits[i];

      Bits[i] &= ~RHS.Bits[i];

      if (Bits[i] != 0)

        allzero = false;

      if (!changed && old != Bits[i])

        changed = true;

    }

    BecameZero = allzero;

    return changed;

  }

  // Three argument version of intersectWithComplement that intersects

  // RHS1 & ~RHS2 into this element

  void intersectWithComplement(const SparseBitVectorElement &RHS1,

                               const SparseBitVectorElement &RHS2,

                               bool &BecameZero) {

    bool allzero = true;

    BecameZero = false;

    for (unsigned i = 0; i < BITWORDS_PER_ELEMENT; ++i) {

      Bits[i] = RHS1.Bits[i] & ~RHS2.Bits[i];

      if (Bits[i] != 0)

        allzero = false;

    }

    BecameZero = allzero;

  }

};

template <unsigned ElementSize = 128>

class SparseBitVector {

  using ElementList = std::list<SparseBitVectorElement<ElementSize>>;

  using ElementListIter = typename ElementList::iterator;

  using ElementListConstIter = typename ElementList::const_iterator;

  enum {

    BITWORD_SIZE = SparseBitVectorElement<ElementSize>::BITWORD_SIZE

  };

  ElementList Elements;

  // Pointer to our current Element. This has no visible effect on the external

  // state of a SparseBitVector, it's just used to improve performance in the

  // common case of testing/modifying bits with similar indices.

  mutable ElementListIter CurrElementIter;

  // This is like std::lower_bound, except we do linear searching from the

  // current position.

  ElementListIter FindLowerBoundImpl(unsigned ElementIndex) const {

    // We cache a non-const iterator so we're forced to resort to const_cast to

    // get the begin/end in the case where 'this' is const. To avoid duplication

    // of code with the only difference being whether the const cast is present

    // 'this' is always const in this particular function and we sort out the

    // difference in FindLowerBound and FindLowerBoundConst.

    ElementListIter Begin =

        const_cast<SparseBitVector<ElementSize> *>(this)->Elements.begin();

    ElementListIter End =

        const_cast<SparseBitVector<ElementSize> *>(this)->Elements.end();

    if (Elements.empty()) {

      CurrElementIter = Begin;

      return CurrElementIter;

    }

    // Make sure our current iterator is valid.

    if (CurrElementIter == End)

      --CurrElementIter;

    // Search from our current iterator, either backwards or forwards,

    // depending on what element we are looking for.

    ElementListIter ElementIter = CurrElementIter;

    if (CurrElementIter->index() == ElementIndex) {

      return ElementIter;

    } else if (CurrElementIter->index() > ElementIndex) {

      while (ElementIter != Begin

             && ElementIter->index() > ElementIndex)

        --ElementIter;

    } else {

      while (ElementIter != End &&

             ElementIter->index() < ElementIndex)

        ++ElementIter;

    }

    CurrElementIter = ElementIter;

    return ElementIter;

  }

  ElementListConstIter FindLowerBoundConst(unsigned ElementIndex) const {

    return FindLowerBoundImpl(ElementIndex);

  }

  ElementListIter FindLowerBound(unsigned ElementIndex) {

    return FindLowerBoundImpl(ElementIndex);

  }

  // Iterator to walk set bits in the bitmap.  This iterator is a lot uglier

  // than it would be, in order to be efficient.

  class SparseBitVectorIterator {

  private:

    bool AtEnd;

    const SparseBitVector<ElementSize> *BitVector = nullptr;

    // Current element inside of bitmap.

    ElementListConstIter Iter;

    // Current bit number inside of our bitmap.

    unsigned BitNumber;

    // Current word number inside of our element.

    unsigned WordNumber;

    // Current bits from the element.

    typename SparseBitVectorElement<ElementSize>::BitWord Bits;

    // Move our iterator to the first non-zero bit in the bitmap.

    void AdvanceToFirstNonZero() {

      if (AtEnd)

        return;

      if (BitVector->Elements.empty()) {

        AtEnd = true;

        return;

      }

      Iter = BitVector->Elements.begin();

      BitNumber = Iter->index() * ElementSize;

      unsigned BitPos = Iter->find_first();

      BitNumber += BitPos;

      WordNumber = (BitNumber % ElementSize) / BITWORD_SIZE;

      Bits = Iter->word(WordNumber);

      Bits >>= BitPos % BITWORD_SIZE;

    }

    // Move our iterator to the next non-zero bit.

    void AdvanceToNextNonZero() {

      if (AtEnd)

        return;

      while (Bits && !(Bits & 1)) {

        Bits >>= 1;

        BitNumber += 1;

      }

      // See if we ran out of Bits in this word.

      if (!Bits) {

        int NextSetBitNumber = Iter->find_next(BitNumber % ElementSize) ;

        // If we ran out of set bits in this element, move to next element.

        if (NextSetBitNumber == -1 || (BitNumber % ElementSize == 0)) {

          ++Iter;

          WordNumber = 0;

          // We may run out of elements in the bitmap.

          if (Iter == BitVector->Elements.end()) {

            AtEnd = true;

            return;

          }

          // Set up for next non-zero word in bitmap.

          BitNumber = Iter->index() * ElementSize;

          NextSetBitNumber = Iter->find_first();

          BitNumber += NextSetBitNumber;

          WordNumber = (BitNumber % ElementSize) / BITWORD_SIZE;

          Bits = Iter->word(WordNumber);

          Bits >>= NextSetBitNumber % BITWORD_SIZE;

        } else {

          WordNumber = (NextSetBitNumber % ElementSize) / BITWORD_SIZE;

          Bits = Iter->word(WordNumber);

          Bits >>= NextSetBitNumber % BITWORD_SIZE;

          BitNumber = Iter->index() * ElementSize;

          BitNumber += NextSetBitNumber;

        }

      }

    }

  public:

    SparseBitVectorIterator() = default;

    SparseBitVectorIterator(const SparseBitVector<ElementSize> *RHS,

                            bool end = false):BitVector(RHS) {

      Iter = BitVector->Elements.begin();

      BitNumber = 0;

      Bits = 0;

      WordNumber = ~0;

      AtEnd = end;

      AdvanceToFirstNonZero();

    }

    // Preincrement.

    inline SparseBitVectorIterator& operator++() {

      ++BitNumber;

      Bits >>= 1;

      AdvanceToNextNonZero();

      return *this;

    }

    // Postincrement.

    inline SparseBitVectorIterator operator++(int) {

      SparseBitVectorIterator tmp = *this;

      ++*this;

      return tmp;

    }

    // Return the current set bit number.

    unsigned operator*() const {

      return BitNumber;

    }

    bool operator==(const SparseBitVectorIterator &RHS) const {

      // If they are both at the end, ignore the rest of the fields.

      if (AtEnd && RHS.AtEnd)

        return true;

      // Otherwise they are the same if they have the same bit number and

      // bitmap.

      return AtEnd == RHS.AtEnd && RHS.BitNumber == BitNumber;

    }

    bool operator!=(const SparseBitVectorIterator &RHS) const {

      return !(*this == RHS);

    }

  };

public:

  using iterator = SparseBitVectorIterator;

  SparseBitVector() : Elements(), CurrElementIter(Elements.begin()) {}

  SparseBitVector(const SparseBitVector &RHS)

      : Elements(RHS.Elements), CurrElementIter(Elements.begin()) {}

  SparseBitVector(SparseBitVector &&RHS)

      : Elements(std::move(RHS.Elements)), CurrElementIter(Elements.begin()) {}

  // Clear.

  void clear() {

    Elements.clear();

  }

  // Assignment

  SparseBitVector& operator=(const SparseBitVector& RHS) {

    if (this == &RHS)

      return *this;

    Elements = RHS.Elements;

    CurrElementIter = Elements.begin();

    return *this;

  }

  SparseBitVector &operator=(SparseBitVector &&RHS) {

    Elements = std::move(RHS.Elements);

    CurrElementIter = Elements.begin();

    return *this;

  }

  // Test, Reset, and Set a bit in the bitmap.

  bool test(unsigned Idx) const {

    if (Elements.empty())

      return false;

    unsigned ElementIndex = Idx / ElementSize;

    ElementListConstIter ElementIter = FindLowerBoundConst(ElementIndex);

    // If we can't find an element that is supposed to contain this bit, there

    // is nothing more to do.

    if (ElementIter == Elements.end() ||

        ElementIter->index() != ElementIndex)

      return false;

    return ElementIter->test(Idx % ElementSize);

  }

  void reset(unsigned Idx) {

    if (Elements.empty())

      return;

    unsigned ElementIndex = Idx / ElementSize;

    ElementListIter ElementIter = FindLowerBound(ElementIndex);

    // If we can't find an element that is supposed to contain this bit, there

    // is nothing more to do.

    if (ElementIter == Elements.end() ||

        ElementIter->index() != ElementIndex)

      return;

    ElementIter->reset(Idx % ElementSize);

    // When the element is zeroed out, delete it.

    if (ElementIter->empty()) {

      ++CurrElementIter;

      Elements.erase(ElementIter);

    }

  }

  void set(unsigned Idx) {

    unsigned ElementIndex = Idx / ElementSize;

    ElementListIter ElementIter;

    if (Elements.empty()) {

      ElementIter = Elements.emplace(Elements.end(), ElementIndex);

    } else {

      ElementIter = FindLowerBound(ElementIndex);

      if (ElementIter == Elements.end() ||

          ElementIter->index() != ElementIndex) {

        // We may have hit the beginning of our SparseBitVector, in which case,

        // we may need to insert right after this element, which requires moving

        // the current iterator forward one, because insert does insert before.

        if (ElementIter != Elements.end() &&

            ElementIter->index() < ElementIndex)

          ++ElementIter;

        ElementIter = Elements.emplace(ElementIter, ElementIndex);

      }

    }

    CurrElementIter = ElementIter;

    ElementIter->set(Idx % ElementSize);

  }

  bool test_and_set(unsigned Idx) {

    bool old = test(Idx);

    if (!old) {

      set(Idx);

      return true;

    }

    return false;

  }

  bool operator!=(const SparseBitVector &RHS) const {

    return !(*this == RHS);

  }

  bool operator==(const SparseBitVector &RHS) const {

    ElementListConstIter Iter1 = Elements.begin();

    ElementListConstIter Iter2 = RHS.Elements.begin();

    for (; Iter1 != Elements.end() && Iter2 != RHS.Elements.end();

         ++Iter1, ++Iter2) {

      if (*Iter1 != *Iter2)

        return false;

    }

    return Iter1 == Elements.end() && Iter2 == RHS.Elements.end();

  }

  // Union our bitmap with the RHS and return true if we changed.

  bool operator|=(const SparseBitVector &RHS) {

    if (this == &RHS)

      return false;

    bool changed = false;

    ElementListIter Iter1 = Elements.begin();

    ElementListConstIter Iter2 = RHS.Elements.begin();

    // If RHS is empty, we are done

    if (RHS.Elements.empty())

      return false;

    while (Iter2 != RHS.Elements.end()) {

      if (Iter1 == Elements.end() || Iter1->index() > Iter2->index()) {

        Elements.insert(Iter1, *Iter2);

        ++Iter2;

        changed = true;

      } else if (Iter1->index() == Iter2->index()) {

        changed |= Iter1->unionWith(*Iter2);

        ++Iter1;

        ++Iter2;

      } else {

        ++Iter1;

      }

    }

    CurrElementIter = Elements.begin();

    return changed;

  }

  // Intersect our bitmap with the RHS and return true if ours changed.

  bool operator&=(const SparseBitVector &RHS) {

    if (this == &RHS)

      return false;

    bool changed = false;

    ElementListIter Iter1 = Elements.begin();

    ElementListConstIter Iter2 = RHS.Elements.begin();

    // Check if both bitmaps are empty.

    if (Elements.empty() && RHS.Elements.empty())

      return false;

    // Loop through, intersecting as we go, erasing elements when necessary.

    while (Iter2 != RHS.Elements.end()) {

      if (Iter1 == Elements.end()) {

        CurrElementIter = Elements.begin();

        return changed;

      }

      if (Iter1->index() > Iter2->index()) {

        ++Iter2;

      } else if (Iter1->index() == Iter2->index()) {

        bool BecameZero;

        changed |= Iter1->intersectWith(*Iter2, BecameZero);

        if (BecameZero) {

          ElementListIter IterTmp = Iter1;

          ++Iter1;

          Elements.erase(IterTmp);

        } else {

          ++Iter1;

        }

        ++Iter2;

      } else {

        ElementListIter IterTmp = Iter1;

        ++Iter1;

        Elements.erase(IterTmp);

        changed = true;

      }

    }

    if (Iter1 != Elements.end()) {

      Elements.erase(Iter1, Elements.end());

      changed = true;

    }

    CurrElementIter = Elements.begin();

    return changed;

  }

  // Intersect our bitmap with the complement of the RHS and return true

  // if ours changed.

  bool intersectWithComplement(const SparseBitVector &RHS) {

    if (this == &RHS) {

      if (!empty()) {

        clear();

        return true;

      }

      return false;

    }

    bool changed = false;

    ElementListIter Iter1 = Elements.begin();

    ElementListConstIter Iter2 = RHS.Elements.begin();

    // If either our bitmap or RHS is empty, we are done

    if (Elements.empty() || RHS.Elements.empty())

      return false;

    // Loop through, intersecting as we go, erasing elements when necessary.

    while (Iter2 != RHS.Elements.end()) {

      if (Iter1 == Elements.end()) {

        CurrElementIter = Elements.begin();

        return changed;

      }

      if (Iter1->index() > Iter2->index()) {

        ++Iter2;

      } else if (Iter1->index() == Iter2->index()) {

        bool BecameZero;

        changed |= Iter1->intersectWithComplement(*Iter2, BecameZero);

        if (BecameZero) {

          ElementListIter IterTmp = Iter1;

          ++Iter1;

          Elements.erase(IterTmp);

        } else {

          ++Iter1;

        }

        ++Iter2;

      } else {

        ++Iter1;

      }

    }

    CurrElementIter = Elements.begin();

    return changed;

  }

  bool intersectWithComplement(const SparseBitVector<ElementSize> *RHS) const {

    return intersectWithComplement(*RHS);

  }

  //  Three argument version of intersectWithComplement.

  //  Result of RHS1 & ~RHS2 is stored into this bitmap.

  void intersectWithComplement(const SparseBitVector<ElementSize> &RHS1,

                               const SparseBitVector<ElementSize> &RHS2)

  {

    if (this == &RHS1) {

      intersectWithComplement(RHS2);

      return;

    } else if (this == &RHS2) {

      SparseBitVector RHS2Copy(RHS2);

      intersectWithComplement(RHS1, RHS2Copy);

      return;

    }

    Elements.clear();

    CurrElementIter = Elements.begin();

    ElementListConstIter Iter1 = RHS1.Elements.begin();

    ElementListConstIter Iter2 = RHS2.Elements.begin();

    // If RHS1 is empty, we are done

    // If RHS2 is empty, we still have to copy RHS1

    if (RHS1.Elements.empty())

      return;

    // Loop through, intersecting as we go, erasing elements when necessary.

    while (Iter2 != RHS2.Elements.end()) {

      if (Iter1 == RHS1.Elements.end())

        return;

      if (Iter1->index() > Iter2->index()) {

        ++Iter2;

      } else if (Iter1->index() == Iter2->index()) {

        bool BecameZero = false;

        Elements.emplace_back(Iter1->index());

        Elements.back().intersectWithComplement(*Iter1, *Iter2, BecameZero);

        if (BecameZero)

          Elements.pop_back();

        ++Iter1;

        ++Iter2;

      } else {

        Elements.push_back(*Iter1++);

      }

    }

    // copy the remaining elements

    std::copy(Iter1, RHS1.Elements.end(), std::back_inserter(Elements));

  }

  void intersectWithComplement(const SparseBitVector<ElementSize> *RHS1,

                               const SparseBitVector<ElementSize> *RHS2) {

    intersectWithComplement(*RHS1, *RHS2);

  }

  bool intersects(const SparseBitVector<ElementSize> *RHS) const {

    return intersects(*RHS);

  }

  // Return true if we share any bits in common with RHS

  bool intersects(const SparseBitVector<ElementSize> &RHS) const {

    ElementListConstIter Iter1 = Elements.begin();

    ElementListConstIter Iter2 = RHS.Elements.begin();

    // Check if both bitmaps are empty.

    if (Elements.empty() && RHS.Elements.empty())

      return false;

    // Loop through, intersecting stopping when we hit bits in common.

    while (Iter2 != RHS.Elements.end()) {

      if (Iter1 == Elements.end())

        return false;

      if (Iter1->index() > Iter2->index()) {

        ++Iter2;

      } else if (Iter1->index() == Iter2->index()) {

        if (Iter1->intersects(*Iter2))