include/llvm/ADT/SmallBitVector.h - llvm-project/llvm - Git at Google

 //===- llvm/ADT/SmallBitVector.h - 'Normally small' bit vectors -*- 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 implements the SmallBitVector class.
 ///
 //===----------------------------------------------------------------------===//

 #ifndef LLVM_ADT_SMALLBITVECTOR_H
 #define LLVM_ADT_SMALLBITVECTOR_H

 #include "llvm/ADT/BitVector.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/Support/MathExtras.h"
 #include <algorithm>
 #include <cassert>
 #include <climits>
 #include <cstddef>
 #include <cstdint>
 #include <limits>
 #include <utility>

 namespace llvm {

 /// This is a 'bitvector' (really, a variable-sized bit array), optimized for
 /// the case when the array is small. It contains one pointer-sized field, which
 /// is directly used as a plain collection of bits when possible, or as a
 /// pointer to a larger heap-allocated array when necessary. This allows normal
 /// "small" cases to be fast without losing generality for large inputs.
 class SmallBitVector {
   // TODO: In "large" mode, a pointer to a BitVector is used, leading to an
   // unnecessary level of indirection. It would be more efficient to use a
   // pointer to memory containing size, allocation size, and the array of bits.
   uintptr_t X = 1;

   enum {
     // The number of bits in this class.
     NumBaseBits = sizeof(uintptr_t) * CHAR_BIT,

     // One bit is used to discriminate between small and large mode. The
     // remaining bits are used for the small-mode representation.
     SmallNumRawBits = NumBaseBits - 1,

     // A few more bits are used to store the size of the bit set in small mode.
     // Theoretically this is a ceil-log2. These bits are encoded in the most
     // significant bits of the raw bits.
     SmallNumSizeBits = (NumBaseBits == 32 ? 5 :
                         NumBaseBits == 64 ? 6 :
                         SmallNumRawBits),

     // The remaining bits are used to store the actual set in small mode.
     SmallNumDataBits = SmallNumRawBits - SmallNumSizeBits
   };

   static_assert(NumBaseBits == 64 || NumBaseBits == 32,
                 "Unsupported word size");

 public:
   using size_type = uintptr_t;

   // Encapsulation of a single bit.
   class reference {
     SmallBitVector &TheVector;
     unsigned BitPos;

   public:
     reference(SmallBitVector &b, unsigned Idx) : TheVector(b), BitPos(Idx) {}

     reference(const reference&) = default;

     reference& operator=(reference t) {
       *this = bool(t);
       return *this;
     }

     reference& operator=(bool t) {
       if (t)
         TheVector.set(BitPos);
       else
         TheVector.reset(BitPos);
       return *this;
     }

     operator bool() const {
       return const_cast<const SmallBitVector &>(TheVector).operator[](BitPos);
     }
   };

 private:
   BitVector *getPointer() const {
     assert(!isSmall());
     return reinterpret_cast<BitVector *>(X);
   }

   void switchToSmall(uintptr_t NewSmallBits, size_type NewSize) {
     X = 1;
     setSmallSize(NewSize);
     setSmallBits(NewSmallBits);
   }

   void switchToLarge(BitVector *BV) {
     X = reinterpret_cast<uintptr_t>(BV);
     assert(!isSmall() && "Tried to use an unaligned pointer");
   }

   // Return all the bits used for the "small" representation; this includes
   // bits for the size as well as the element bits.
   uintptr_t getSmallRawBits() const {
     assert(isSmall());
     return X >> 1;
   }

   void setSmallRawBits(uintptr_t NewRawBits) {
     assert(isSmall());
     X = (NewRawBits << 1) | uintptr_t(1);
   }

   // Return the size.
   size_type getSmallSize() const {
     return getSmallRawBits() >> SmallNumDataBits;
   }

   void setSmallSize(size_type Size) {
     setSmallRawBits(getSmallBits() | (Size << SmallNumDataBits));
   }

   // Return the element bits.
   uintptr_t getSmallBits() const {
     return getSmallRawBits() & ~(~uintptr_t(0) << getSmallSize());
   }

   void setSmallBits(uintptr_t NewBits) {
     setSmallRawBits((NewBits & ~(~uintptr_t(0) << getSmallSize())) |
                     (getSmallSize() << SmallNumDataBits));
   }

 public:
   /// Creates an empty bitvector.
   SmallBitVector() = default;

   /// Creates a bitvector of specified number of bits. All bits are initialized
   /// to the specified value.
   explicit SmallBitVector(unsigned s, bool t = false) {
     if (s <= SmallNumDataBits)
       switchToSmall(t ? ~uintptr_t(0) : 0, s);
     else
       switchToLarge(new BitVector(s, t));
   }

   /// SmallBitVector copy ctor.
   SmallBitVector(const SmallBitVector &RHS) {
     if (RHS.isSmall())
       X = RHS.X;
     else
       switchToLarge(new BitVector(*RHS.getPointer()));
   }

   SmallBitVector(SmallBitVector &&RHS) : X(RHS.X) {
     RHS.X = 1;
   }

   ~SmallBitVector() {
     if (!isSmall())
       delete getPointer();
   }

   using const_set_bits_iterator = const_set_bits_iterator_impl<SmallBitVector>;
   using set_iterator = const_set_bits_iterator;

   const_set_bits_iterator set_bits_begin() const {
     return const_set_bits_iterator(*this);
   }

   const_set_bits_iterator set_bits_end() const {
     return const_set_bits_iterator(*this, -1);
   }

   iterator_range<const_set_bits_iterator> set_bits() const {
     return make_range(set_bits_begin(), set_bits_end());
   }

   bool isSmall() const { return X & uintptr_t(1); }

   /// Tests whether there are no bits in this bitvector.
   bool empty() const {
     return isSmall() ? getSmallSize() == 0 : getPointer()->empty();
   }

   /// Returns the number of bits in this bitvector.
   size_type size() const {
     return isSmall() ? getSmallSize() : getPointer()->size();
   }

   /// Returns the number of bits which are set.
   size_type count() const {
     if (isSmall()) {
       uintptr_t Bits = getSmallBits();
       return llvm::popcount(Bits);
     }
     return getPointer()->count();
   }

   /// Returns true if any bit is set.
   bool any() const {
     if (isSmall())
       return getSmallBits() != 0;
     return getPointer()->any();
   }

   /// Returns true if all bits are set.
   bool all() const {
     if (isSmall())
       return getSmallBits() == (uintptr_t(1) << getSmallSize()) - 1;
     return getPointer()->all();
   }

   /// Returns true if none of the bits are set.
   bool none() const {
     if (isSmall())
       return getSmallBits() == 0;
     return getPointer()->none();
   }

   /// Returns the index of the first set bit, -1 if none of the bits are set.
   int find_first() const {
     if (isSmall()) {
       uintptr_t Bits = getSmallBits();
       if (Bits == 0)
         return -1;
       return llvm::countr_zero(Bits);
     }
     return getPointer()->find_first();
   }

   int find_last() const {
     if (isSmall()) {
       uintptr_t Bits = getSmallBits();
       if (Bits == 0)
         return -1;
       return NumBaseBits - llvm::countl_zero(Bits) - 1;
     }
     return getPointer()->find_last();
   }

   /// Returns the index of the first unset bit, -1 if all of the bits are set.
   int find_first_unset() const {
     if (isSmall()) {
       if (count() == getSmallSize())
         return -1;

       uintptr_t Bits = getSmallBits();
       return llvm::countr_one(Bits);
     }
     return getPointer()->find_first_unset();
   }

   int find_last_unset() const {
     if (isSmall()) {
       if (count() == getSmallSize())
         return -1;

       uintptr_t Bits = getSmallBits();
       // Set unused bits.
       Bits |= ~uintptr_t(0) << getSmallSize();
       return NumBaseBits - llvm::countl_one(Bits) - 1;
     }
     return getPointer()->find_last_unset();
   }

   /// Returns the index of the next set bit following the "Prev" bit.
   /// Returns -1 if the next set bit is not found.
   int find_next(unsigned Prev) const {
     if (isSmall()) {
       uintptr_t Bits = getSmallBits();
       // Mask off previous bits.
       Bits &= ~uintptr_t(0) << (Prev + 1);
       if (Bits == 0 || Prev + 1 >= getSmallSize())
         return -1;
       return llvm::countr_zero(Bits);
     }
     return getPointer()->find_next(Prev);
   }

   /// Returns the index of the next unset bit following the "Prev" bit.
   /// Returns -1 if the next unset bit is not found.
   int find_next_unset(unsigned Prev) const {
     if (isSmall()) {
       uintptr_t Bits = getSmallBits();
       // Mask in previous bits.
       Bits |= (uintptr_t(1) << (Prev + 1)) - 1;
       // Mask in unused bits.
       Bits |= ~uintptr_t(0) << getSmallSize();

       if (Bits == ~uintptr_t(0) || Prev + 1 >= getSmallSize())
         return -1;
       return llvm::countr_one(Bits);
     }
     return getPointer()->find_next_unset(Prev);
   }

   /// find_prev - Returns the index of the first set bit that precedes the
   /// the bit at \p PriorTo.  Returns -1 if all previous bits are unset.
   int find_prev(unsigned PriorTo) const {
     if (isSmall()) {
       if (PriorTo == 0)
         return -1;

       --PriorTo;
       uintptr_t Bits = getSmallBits();
       Bits &= maskTrailingOnes<uintptr_t>(PriorTo + 1);
       if (Bits == 0)
         return -1;

       return NumBaseBits - llvm::countl_zero(Bits) - 1;
     }
     return getPointer()->find_prev(PriorTo);
   }

   /// Clear all bits.
   void clear() {
     if (!isSmall())
       delete getPointer();
     switchToSmall(0, 0);
   }

   /// Grow or shrink the bitvector.
   void resize(unsigned N, bool t = false) {
     if (!isSmall()) {
       getPointer()->resize(N, t);
     } else if (SmallNumDataBits >= N) {
       uintptr_t NewBits = t ? ~uintptr_t(0) << getSmallSize() : 0;
       setSmallSize(N);
       setSmallBits(NewBits | getSmallBits());
     } else {
       BitVector *BV = new BitVector(N, t);
       uintptr_t OldBits = getSmallBits();
       for (size_type I = 0, E = getSmallSize(); I != E; ++I)
         (*BV)[I] = (OldBits >> I) & 1;
       switchToLarge(BV);
     }
   }

   void reserve(unsigned N) {
     if (isSmall()) {
       if (N > SmallNumDataBits) {
         uintptr_t OldBits = getSmallRawBits();
         size_type SmallSize = getSmallSize();
         BitVector *BV = new BitVector(SmallSize);
         for (size_type I = 0; I < SmallSize; ++I)
           if ((OldBits >> I) & 1)
             BV->set(I);
         BV->reserve(N);
         switchToLarge(BV);
       }
     } else {
       getPointer()->reserve(N);
     }
   }

   // Set, reset, flip
   SmallBitVector &set() {
     if (isSmall())
       setSmallBits(~uintptr_t(0));
     else
       getPointer()->set();
     return *this;
   }

   SmallBitVector &set(unsigned Idx) {
     if (isSmall()) {
       assert(Idx <= static_cast<unsigned>(
                         std::numeric_limits<uintptr_t>::digits) &&
              "undefined behavior");
       setSmallBits(getSmallBits() | (uintptr_t(1) << Idx));
     }
     else
       getPointer()->set(Idx);
     return *this;
   }

   /// Efficiently set a range of bits in [I, E)
   SmallBitVector &set(unsigned I, unsigned E) {
     assert(I <= E && "Attempted to set backwards range!");
     assert(E <= size() && "Attempted to set out-of-bounds range!");
     if (I == E) return *this;
     if (isSmall()) {
       uintptr_t EMask = ((uintptr_t)1) << E;
       uintptr_t IMask = ((uintptr_t)1) << I;
       uintptr_t Mask = EMask - IMask;
       setSmallBits(getSmallBits() | Mask);
     } else
       getPointer()->set(I, E);
     return *this;
   }

   SmallBitVector &reset() {
     if (isSmall())
       setSmallBits(0);
     else
       getPointer()->reset();
     return *this;
   }

   SmallBitVector &reset(unsigned Idx) {
     if (isSmall())
       setSmallBits(getSmallBits() & ~(uintptr_t(1) << Idx));
     else
       getPointer()->reset(Idx);
     return *this;
   }

   /// Efficiently reset a range of bits in [I, E)
   SmallBitVector &reset(unsigned I, unsigned E) {
     assert(I <= E && "Attempted to reset backwards range!");
     assert(E <= size() && "Attempted to reset out-of-bounds range!");
     if (I == E) return *this;
     if (isSmall()) {
       uintptr_t EMask = ((uintptr_t)1) << E;
       uintptr_t IMask = ((uintptr_t)1) << I;
       uintptr_t Mask = EMask - IMask;
       setSmallBits(getSmallBits() & ~Mask);
     } else
       getPointer()->reset(I, E);
     return *this;
   }

   SmallBitVector &flip() {
     if (isSmall())
       setSmallBits(~getSmallBits());
     else
       getPointer()->flip();
     return *this;
   }

   SmallBitVector &flip(unsigned Idx) {
     if (isSmall())
       setSmallBits(getSmallBits() ^ (uintptr_t(1) << Idx));
     else
       getPointer()->flip(Idx);
     return *this;
   }

   // No argument flip.
   SmallBitVector operator~() const {
     return SmallBitVector(*this).flip();
   }

   // Indexing.
   reference operator[](unsigned Idx) {
     assert(Idx < size() && "Out-of-bounds Bit access.");
     return reference(*this, Idx);
   }

   bool operator[](unsigned Idx) const {
     assert(Idx < size() && "Out-of-bounds Bit access.");
     if (isSmall())
       return ((getSmallBits() >> Idx) & 1) != 0;
     return getPointer()->operator[](Idx);
   }

   /// Return the last element in the vector.
   bool back() const {
     assert(!empty() && "Getting last element of empty vector.");
     return (*this)[size() - 1];
   }

   bool test(unsigned Idx) const {
     return (*this)[Idx];
   }

   // Push single bit to end of vector.
   void push_back(bool Val) {
     resize(size() + 1, Val);
   }

   /// Pop one bit from the end of the vector.
   void pop_back() {
     assert(!empty() && "Empty vector has no element to pop.");
     resize(size() - 1);
   }

   /// Test if any common bits are set.
   bool anyCommon(const SmallBitVector &RHS) const {
     if (isSmall() && RHS.isSmall())
       return (getSmallBits() & RHS.getSmallBits()) != 0;
     if (!isSmall() && !RHS.isSmall())
       return getPointer()->anyCommon(*RHS.getPointer());

     for (unsigned i = 0, e = std::min(size(), RHS.size()); i != e; ++i)
       if (test(i) && RHS.test(i))
         return true;
     return false;
   }

   // Comparison operators.
   bool operator==(const SmallBitVector &RHS) const {
     if (size() != RHS.size())
       return false;
     if (isSmall() && RHS.isSmall())
       return getSmallBits() == RHS.getSmallBits();
     else if (!isSmall() && !RHS.isSmall())
       return *getPointer() == *RHS.getPointer();
     else {
       for (size_type I = 0, E = size(); I != E; ++I) {
         if ((*this)[I] != RHS[I])
           return false;
       }
       return true;
     }
   }

   bool operator!=(const SmallBitVector &RHS) const {
     return !(*this == RHS);
   }

   // Intersection, union, disjoint union.
   // FIXME BitVector::operator&= does not resize the LHS but this does
   SmallBitVector &operator&=(const SmallBitVector &RHS) {
     resize(std::max(size(), RHS.size()));
     if (isSmall() && RHS.isSmall())
       setSmallBits(getSmallBits() & RHS.getSmallBits());
     else if (!isSmall() && !RHS.isSmall())
       getPointer()->operator&=(*RHS.getPointer());
     else {
       size_type I, E;
       for (I = 0, E = std::min(size(), RHS.size()); I != E; ++I)
         (*this)[I] = test(I) && RHS.test(I);
       for (E = size(); I != E; ++I)
         reset(I);
     }
     return *this;
   }

   /// Reset bits that are set in RHS. Same as *this &= ~RHS.
   SmallBitVector &reset(const SmallBitVector &RHS) {
     if (isSmall() && RHS.isSmall())
       setSmallBits(getSmallBits() & ~RHS.getSmallBits());
     else if (!isSmall() && !RHS.isSmall())
       getPointer()->reset(*RHS.getPointer());
     else
       for (unsigned i = 0, e = std::min(size(), RHS.size()); i != e; ++i)
         if (RHS.test(i))
           reset(i);

     return *this;
   }

   /// Check if (This - RHS) is zero. This is the same as reset(RHS) and any().
   bool test(const SmallBitVector &RHS) const {
     if (isSmall() && RHS.isSmall())
       return (getSmallBits() & ~RHS.getSmallBits()) != 0;
     if (!isSmall() && !RHS.isSmall())
       return getPointer()->test(*RHS.getPointer());

     unsigned i, e;
     for (i = 0, e = std::min(size(), RHS.size()); i != e; ++i)
       if (test(i) && !RHS.test(i))
         return true;

     for (e = size(); i != e; ++i)
       if (test(i))
         return true;

     return false;
   }

   SmallBitVector &operator|=(const SmallBitVector &RHS) {
     resize(std::max(size(), RHS.size()));
     if (isSmall() && RHS.isSmall())
       setSmallBits(getSmallBits() | RHS.getSmallBits());
     else if (!isSmall() && !RHS.isSmall())
       getPointer()->operator|=(*RHS.getPointer());
     else {
       for (size_type I = 0, E = RHS.size(); I != E; ++I)
         (*this)[I] = test(I) || RHS.test(I);
     }
     return *this;
   }

   SmallBitVector &operator^=(const SmallBitVector &RHS) {
     resize(std::max(size(), RHS.size()));
     if (isSmall() && RHS.isSmall())
       setSmallBits(getSmallBits() ^ RHS.getSmallBits());
     else if (!isSmall() && !RHS.isSmall())
       getPointer()->operator^=(*RHS.getPointer());
     else {
       for (size_type I = 0, E = RHS.size(); I != E; ++I)
         (*this)[I] = test(I) != RHS.test(I);
     }
     return *this;
   }

   SmallBitVector &operator<<=(unsigned N) {
     if (isSmall())
       setSmallBits(getSmallBits() << N);
     else
       getPointer()->operator<<=(N);
     return *this;
   }

   SmallBitVector &operator>>=(unsigned N) {
     if (isSmall())
       setSmallBits(getSmallBits() >> N);
     else
       getPointer()->operator>>=(N);
     return *this;
   }

   // Assignment operator.
   const SmallBitVector &operator=(const SmallBitVector &RHS) {
     if (isSmall()) {
       if (RHS.isSmall())
         X = RHS.X;
       else
         switchToLarge(new BitVector(*RHS.getPointer()));
     } else {
       if (!RHS.isSmall())
         *getPointer() = *RHS.getPointer();
       else {
         delete getPointer();
         X = RHS.X;
       }
     }
     return *this;
   }

   const SmallBitVector &operator=(SmallBitVector &&RHS) {
     if (this != &RHS) {
       clear();
       swap(RHS);
     }
     return *this;
   }

   void swap(SmallBitVector &RHS) {
     std::swap(X, RHS.X);
   }

   /// Add '1' bits from Mask to this vector. Don't resize.
   /// This computes "*this |= Mask".
   void setBitsInMask(const uint32_t *Mask, unsigned MaskWords = ~0u) {
     if (isSmall())
       applyMask<true, false>(Mask, MaskWords);
     else
       getPointer()->setBitsInMask(Mask, MaskWords);
   }

   /// Clear any bits in this vector that are set in Mask. Don't resize.
   /// This computes "*this &= ~Mask".
   void clearBitsInMask(const uint32_t *Mask, unsigned MaskWords = ~0u) {
     if (isSmall())
       applyMask<false, false>(Mask, MaskWords);
     else
       getPointer()->clearBitsInMask(Mask, MaskWords);
   }

   /// Add a bit to this vector for every '0' bit in Mask. Don't resize.
   /// This computes "*this |= ~Mask".
   void setBitsNotInMask(const uint32_t *Mask, unsigned MaskWords = ~0u) {
     if (isSmall())
       applyMask<true, true>(Mask, MaskWords);
     else
       getPointer()->setBitsNotInMask(Mask, MaskWords);
   }

   /// Clear a bit in this vector for every '0' bit in Mask. Don't resize.
   /// This computes "*this &= Mask".
   void clearBitsNotInMask(const uint32_t *Mask, unsigned MaskWords = ~0u) {
     if (isSmall())
       applyMask<false, true>(Mask, MaskWords);
     else
       getPointer()->clearBitsNotInMask(Mask, MaskWords);
   }

   void invalid() {
     assert(empty());
     X = (uintptr_t)-1;
   }
   bool isInvalid() const { return X == (uintptr_t)-1; }

   ArrayRef<uintptr_t> getData(uintptr_t &Store) const {
     if (!isSmall())
       return getPointer()->getData();
     Store = getSmallBits();
     return Store;
   }

 private:
   template <bool AddBits, bool InvertMask>
   void applyMask(const uint32_t *Mask, unsigned MaskWords) {
     assert(MaskWords <= sizeof(uintptr_t) && "Mask is larger than base!");
     uintptr_t M = Mask[0];
     if (NumBaseBits == 64)
       M |= uint64_t(Mask[1]) << 32;
     if (InvertMask)
       M = ~M;
     if (AddBits)
       setSmallBits(getSmallBits() | M);
     else
       setSmallBits(getSmallBits() & ~M);
   }
 };

 inline SmallBitVector
 operator&(const SmallBitVector &LHS, const SmallBitVector &RHS) {
   SmallBitVector Result(LHS);
   Result &= RHS;
   return Result;
 }

 inline SmallBitVector
 operator|(const SmallBitVector &LHS, const SmallBitVector &RHS) {
   SmallBitVector Result(LHS);
   Result |= RHS;
   return Result;
 }

 inline SmallBitVector
 operator^(const SmallBitVector &LHS, const SmallBitVector &RHS) {
   SmallBitVector Result(LHS);
   Result ^= RHS;
   return Result;
 }

 template <> struct DenseMapInfo<SmallBitVector> {
   static inline SmallBitVector getEmptyKey() { return SmallBitVector(); }
   static inline SmallBitVector getTombstoneKey() {
     SmallBitVector V;
     V.invalid();
     return V;
   }
   static unsigned getHashValue(const SmallBitVector &V) {
     uintptr_t Store;
     return DenseMapInfo<
         std::pair<SmallBitVector::size_type, ArrayRef<uintptr_t>>>::
         getHashValue(std::make_pair(V.size(), V.getData(Store)));
   }
   static bool isEqual(const SmallBitVector &LHS, const SmallBitVector &RHS) {
     if (LHS.isInvalid() || RHS.isInvalid())
       return LHS.isInvalid() == RHS.isInvalid();
     return LHS == RHS;
   }
 };
 } // end namespace llvm

 namespace std {

 /// Implement std::swap in terms of BitVector swap.
 inline void
 swap(llvm::SmallBitVector &LHS, llvm::SmallBitVector &RHS) {
   LHS.swap(RHS);
 }

 } // end namespace std

 #endif // LLVM_ADT_SMALLBITVECTOR_H
	//===- llvm/ADT/SmallBitVector.h - 'Normally small' bit vectors -- 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 implements the SmallBitVector class.
	///
	//===----------------------------------------------------------------------===//

	#ifndef LLVM_ADT_SMALLBITVECTOR_H
	#define LLVM_ADT_SMALLBITVECTOR_H

	#include "llvm/ADT/BitVector.h"
	#include "llvm/ADT/iterator_range.h"
	#include "llvm/Support/MathExtras.h"
	#include <algorithm>
	#include <cassert>
	#include <climits>
	#include <cstddef>
	#include <cstdint>
	#include <limits>
	#include <utility>

	namespace llvm {

	/// This is a 'bitvector' (really, a variable-sized bit array), optimized for
	/// the case when the array is small. It contains one pointer-sized field, which
	/// is directly used as a plain collection of bits when possible, or as a
	/// pointer to a larger heap-allocated array when necessary. This allows normal
	/// "small" cases to be fast without losing generality for large inputs.
	class SmallBitVector {
	// TODO: In "large" mode, a pointer to a BitVector is used, leading to an
	// unnecessary level of indirection. It would be more efficient to use a
	// pointer to memory containing size, allocation size, and the array of bits.
	uintptr_t X = 1;

	enum {
	// The number of bits in this class.
	NumBaseBits = sizeof(uintptr_t) * CHAR_BIT,

	// One bit is used to discriminate between small and large mode. The
	// remaining bits are used for the small-mode representation.
	SmallNumRawBits = NumBaseBits - 1,

	// A few more bits are used to store the size of the bit set in small mode.
	// Theoretically this is a ceil-log2. These bits are encoded in the most
	// significant bits of the raw bits.
	SmallNumSizeBits = (NumBaseBits == 32 ? 5 :
	NumBaseBits == 64 ? 6 :
	SmallNumRawBits),

	// The remaining bits are used to store the actual set in small mode.
	SmallNumDataBits = SmallNumRawBits - SmallNumSizeBits
	};

	static_assert(NumBaseBits == 64 \|\| NumBaseBits == 32,
	"Unsupported word size");

	public:
	using size_type = uintptr_t;

	// Encapsulation of a single bit.
	class reference {
	SmallBitVector &TheVector;
	unsigned BitPos;

	public:
	reference(SmallBitVector &b, unsigned Idx) : TheVector(b), BitPos(Idx) {}

	reference(const reference&) = default;

	reference& operator=(reference t) {
	*this = bool(t);
	return *this;
	}

	reference& operator=(bool t) {
	if (t)
	TheVector.set(BitPos);
	else
	TheVector.reset(BitPos);
	return *this;
	}

	operator bool() const {
	return const_cast<const SmallBitVector &>(TheVector).operator[](BitPos);
	}
	};

	private:
	BitVector *getPointer() const {
	assert(!isSmall());
	return reinterpret_cast<BitVector *>(X);
	}

	void switchToSmall(uintptr_t NewSmallBits, size_type NewSize) {
	X = 1;
	setSmallSize(NewSize);
	setSmallBits(NewSmallBits);
	}

	void switchToLarge(BitVector *BV) {
	X = reinterpret_cast<uintptr_t>(BV);
	assert(!isSmall() && "Tried to use an unaligned pointer");
	}

	// Return all the bits used for the "small" representation; this includes
	// bits for the size as well as the element bits.
	uintptr_t getSmallRawBits() const {
	assert(isSmall());
	return X >> 1;
	}

	void setSmallRawBits(uintptr_t NewRawBits) {
	assert(isSmall());
	X = (NewRawBits << 1) \| uintptr_t(1);
	}

	// Return the size.
	size_type getSmallSize() const {
	return getSmallRawBits() >> SmallNumDataBits;
	}

	void setSmallSize(size_type Size) {
	setSmallRawBits(getSmallBits() \| (Size << SmallNumDataBits));
	}

	// Return the element bits.
	uintptr_t getSmallBits() const {
	return getSmallRawBits() & ~(~uintptr_t(0) << getSmallSize());
	}

	void setSmallBits(uintptr_t NewBits) {
	setSmallRawBits((NewBits & ~(~uintptr_t(0) << getSmallSize())) \|
	(getSmallSize() << SmallNumDataBits));
	}

	public:
	/// Creates an empty bitvector.
	SmallBitVector() = default;

	/// Creates a bitvector of specified number of bits. All bits are initialized
	/// to the specified value.
	explicit SmallBitVector(unsigned s, bool t = false) {
	if (s <= SmallNumDataBits)
	switchToSmall(t ? ~uintptr_t(0) : 0, s);
	else
	switchToLarge(new BitVector(s, t));
	}

	/// SmallBitVector copy ctor.
	SmallBitVector(const SmallBitVector &RHS) {
	if (RHS.isSmall())
	X = RHS.X;
	else
	switchToLarge(new BitVector(*RHS.getPointer()));
	}

	SmallBitVector(SmallBitVector &&RHS) : X(RHS.X) {
	RHS.X = 1;
	}

	~SmallBitVector() {
	if (!isSmall())
	delete getPointer();
	}

	using const_set_bits_iterator = const_set_bits_iterator_impl<SmallBitVector>;
	using set_iterator = const_set_bits_iterator;

	const_set_bits_iterator set_bits_begin() const {
	return const_set_bits_iterator(*this);
	}

	const_set_bits_iterator set_bits_end() const {
	return const_set_bits_iterator(*this, -1);
	}

	iterator_range<const_set_bits_iterator> set_bits() const {
	return make_range(set_bits_begin(), set_bits_end());
	}

	bool isSmall() const { return X & uintptr_t(1); }

	/// Tests whether there are no bits in this bitvector.
	bool empty() const {
	return isSmall() ? getSmallSize() == 0 : getPointer()->empty();
	}

	/// Returns the number of bits in this bitvector.
	size_type size() const {
	return isSmall() ? getSmallSize() : getPointer()->size();
	}

	/// Returns the number of bits which are set.
	size_type count() const {
	if (isSmall()) {
	uintptr_t Bits = getSmallBits();
	return llvm::popcount(Bits);
	}
	return getPointer()->count();
	}

	/// Returns true if any bit is set.
	bool any() const {
	if (isSmall())
	return getSmallBits() != 0;
	return getPointer()->any();
	}

	/// Returns true if all bits are set.
	bool all() const {
	if (isSmall())
	return getSmallBits() == (uintptr_t(1) << getSmallSize()) - 1;
	return getPointer()->all();
	}

	/// Returns true if none of the bits are set.
	bool none() const {
	if (isSmall())
	return getSmallBits() == 0;
	return getPointer()->none();
	}

	/// Returns the index of the first set bit, -1 if none of the bits are set.
	int find_first() const {
	if (isSmall()) {
	uintptr_t Bits = getSmallBits();
	if (Bits == 0)
	return -1;
	return llvm::countr_zero(Bits);
	}
	return getPointer()->find_first();
	}

	int find_last() const {
	if (isSmall()) {
	uintptr_t Bits = getSmallBits();
	if (Bits == 0)
	return -1;
	return NumBaseBits - llvm::countl_zero(Bits) - 1;
	}
	return getPointer()->find_last();
	}

	/// Returns the index of the first unset bit, -1 if all of the bits are set.
	int find_first_unset() const {
	if (isSmall()) {
	if (count() == getSmallSize())
	return -1;

	uintptr_t Bits = getSmallBits();
	return llvm::countr_one(Bits);
	}
	return getPointer()->find_first_unset();
	}

	int find_last_unset() const {
	if (isSmall()) {
	if (count() == getSmallSize())
	return -1;

	uintptr_t Bits = getSmallBits();
	// Set unused bits.
	Bits \|= ~uintptr_t(0) << getSmallSize();
	return NumBaseBits - llvm::countl_one(Bits) - 1;
	}
	return getPointer()->find_last_unset();
	}

	/// Returns the index of the next set bit following the "Prev" bit.
	/// Returns -1 if the next set bit is not found.
	int find_next(unsigned Prev) const {
	if (isSmall()) {
	uintptr_t Bits = getSmallBits();
	// Mask off previous bits.
	Bits &= ~uintptr_t(0) << (Prev + 1);
	if (Bits == 0 \|\| Prev + 1 >= getSmallSize())
	return -1;
	return llvm::countr_zero(Bits);
	}
	return getPointer()->find_next(Prev);
	}

	/// Returns the index of the next unset bit following the "Prev" bit.
	/// Returns -1 if the next unset bit is not found.
	int find_next_unset(unsigned Prev) const {
	if (isSmall()) {
	uintptr_t Bits = getSmallBits();
	// Mask in previous bits.
	Bits \|= (uintptr_t(1) << (Prev + 1)) - 1;
	// Mask in unused bits.
	Bits \|= ~uintptr_t(0) << getSmallSize();

	if (Bits == ~uintptr_t(0) \|\| Prev + 1 >= getSmallSize())
	return -1;
	return llvm::countr_one(Bits);
	}
	return getPointer()->find_next_unset(Prev);
	}

	/// find_prev - Returns the index of the first set bit that precedes the
	/// the bit at \p PriorTo. Returns -1 if all previous bits are unset.
	int find_prev(unsigned PriorTo) const {
	if (isSmall()) {
	if (PriorTo == 0)
	return -1;

	--PriorTo;
	uintptr_t Bits = getSmallBits();
	Bits &= maskTrailingOnes<uintptr_t>(PriorTo + 1);
	if (Bits == 0)
	return -1;

	return NumBaseBits - llvm::countl_zero(Bits) - 1;
	}
	return getPointer()->find_prev(PriorTo);
	}

	/// Clear all bits.
	void clear() {
	if (!isSmall())
	delete getPointer();
	switchToSmall(0, 0);
	}

	/// Grow or shrink the bitvector.
	void resize(unsigned N, bool t = false) {
	if (!isSmall()) {
	getPointer()->resize(N, t);
	} else if (SmallNumDataBits >= N) {
	uintptr_t NewBits = t ? ~uintptr_t(0) << getSmallSize() : 0;
	setSmallSize(N);
	setSmallBits(NewBits \| getSmallBits());
	} else {
	BitVector *BV = new BitVector(N, t);
	uintptr_t OldBits = getSmallBits();
	for (size_type I = 0, E = getSmallSize(); I != E; ++I)
	(*BV)[I] = (OldBits >> I) & 1;
	switchToLarge(BV);
	}
	}

	void reserve(unsigned N) {
	if (isSmall()) {
	if (N > SmallNumDataBits) {
	uintptr_t OldBits = getSmallRawBits();
	size_type SmallSize = getSmallSize();
	BitVector *BV = new BitVector(SmallSize);
	for (size_type I = 0; I < SmallSize; ++I)
	if ((OldBits >> I) & 1)
	BV->set(I);
	BV->reserve(N);
	switchToLarge(BV);
	}
	} else {
	getPointer()->reserve(N);
	}
	}

	// Set, reset, flip
	SmallBitVector &set() {
	if (isSmall())
	setSmallBits(~uintptr_t(0));
	else
	getPointer()->set();
	return *this;
	}

	SmallBitVector &set(unsigned Idx) {
	if (isSmall()) {
	assert(Idx <= static_cast<unsigned>(
	std::numeric_limits<uintptr_t>::digits) &&
	"undefined behavior");
	setSmallBits(getSmallBits() \| (uintptr_t(1) << Idx));
	}
	else
	getPointer()->set(Idx);
	return *this;
	}

	/// Efficiently set a range of bits in [I, E)
	SmallBitVector &set(unsigned I, unsigned E) {
	assert(I <= E && "Attempted to set backwards range!");
	assert(E <= size() && "Attempted to set out-of-bounds range!");
	if (I == E) return *this;
	if (isSmall()) {
	uintptr_t EMask = ((uintptr_t)1) << E;
	uintptr_t IMask = ((uintptr_t)1) << I;
	uintptr_t Mask = EMask - IMask;
	setSmallBits(getSmallBits() \| Mask);
	} else
	getPointer()->set(I, E);
	return *this;
	}

	SmallBitVector &reset() {
	if (isSmall())
	setSmallBits(0);
	else
	getPointer()->reset();
	return *this;
	}

	SmallBitVector &reset(unsigned Idx) {
	if (isSmall())
	setSmallBits(getSmallBits() & ~(uintptr_t(1) << Idx));
	else
	getPointer()->reset(Idx);
	return *this;
	}

	/// Efficiently reset a range of bits in [I, E)
	SmallBitVector &reset(unsigned I, unsigned E) {
	assert(I <= E && "Attempted to reset backwards range!");
	assert(E <= size() && "Attempted to reset out-of-bounds range!");
	if (I == E) return *this;
	if (isSmall()) {
	uintptr_t EMask = ((uintptr_t)1) << E;
	uintptr_t IMask = ((uintptr_t)1) << I;
	uintptr_t Mask = EMask - IMask;
	setSmallBits(getSmallBits() & ~Mask);
	} else
	getPointer()->reset(I, E);
	return *this;
	}

	SmallBitVector &flip() {
	if (isSmall())
	setSmallBits(~getSmallBits());
	else
	getPointer()->flip();
	return *this;
	}

	SmallBitVector &flip(unsigned Idx) {
	if (isSmall())
	setSmallBits(getSmallBits() ^ (uintptr_t(1) << Idx));
	else
	getPointer()->flip(Idx);
	return *this;
	}

	// No argument flip.
	SmallBitVector operator~() const {
	return SmallBitVector(*this).flip();
	}

	// Indexing.
	reference operator[](unsigned Idx) {
	assert(Idx < size() && "Out-of-bounds Bit access.");
	return reference(*this, Idx);
	}

	bool operator[](unsigned Idx) const {
	assert(Idx < size() && "Out-of-bounds Bit access.");
	if (isSmall())
	return ((getSmallBits() >> Idx) & 1) != 0;
	return getPointer()->operator[](Idx);
	}

	/// Return the last element in the vector.
	bool back() const {
	assert(!empty() && "Getting last element of empty vector.");
	return (*this)[size() - 1];
	}

	bool test(unsigned Idx) const {
	return (*this)[Idx];
	}

	// Push single bit to end of vector.
	void push_back(bool Val) {
	resize(size() + 1, Val);
	}

	/// Pop one bit from the end of the vector.
	void pop_back() {
	assert(!empty() && "Empty vector has no element to pop.");
	resize(size() - 1);
	}

	/// Test if any common bits are set.
	bool anyCommon(const SmallBitVector &RHS) const {
	if (isSmall() && RHS.isSmall())
	return (getSmallBits() & RHS.getSmallBits()) != 0;
	if (!isSmall() && !RHS.isSmall())
	return getPointer()->anyCommon(*RHS.getPointer());

	for (unsigned i = 0, e = std::min(size(), RHS.size()); i != e; ++i)
	if (test(i) && RHS.test(i))
	return true;
	return false;
	}

	// Comparison operators.
	bool operator==(const SmallBitVector &RHS) const {
	if (size() != RHS.size())
	return false;
	if (isSmall() && RHS.isSmall())
	return getSmallBits() == RHS.getSmallBits();
	else if (!isSmall() && !RHS.isSmall())
	return getPointer() == RHS.getPointer();
	else {
	for (size_type I = 0, E = size(); I != E; ++I) {
	if ((*this)[I] != RHS[I])
	return false;
	}
	return true;
	}
	}

	bool operator!=(const SmallBitVector &RHS) const {
	return !(*this == RHS);
	}

	// Intersection, union, disjoint union.
	// FIXME BitVector::operator&= does not resize the LHS but this does
	SmallBitVector &operator&=(const SmallBitVector &RHS) {
	resize(std::max(size(), RHS.size()));
	if (isSmall() && RHS.isSmall())
	setSmallBits(getSmallBits() & RHS.getSmallBits());
	else if (!isSmall() && !RHS.isSmall())
	getPointer()->operator&=(*RHS.getPointer());
	else {
	size_type I, E;
	for (I = 0, E = std::min(size(), RHS.size()); I != E; ++I)
	(*this)[I] = test(I) && RHS.test(I);
	for (E = size(); I != E; ++I)
	reset(I);
	}
	return *this;
	}

	/// Reset bits that are set in RHS. Same as *this &= ~RHS.
	SmallBitVector &reset(const SmallBitVector &RHS) {
	if (isSmall() && RHS.isSmall())
	setSmallBits(getSmallBits() & ~RHS.getSmallBits());
	else if (!isSmall() && !RHS.isSmall())
	getPointer()->reset(*RHS.getPointer());
	else
	for (unsigned i = 0, e = std::min(size(), RHS.size()); i != e; ++i)
	if (RHS.test(i))
	reset(i);

	return *this;
	}

	/// Check if (This - RHS) is zero. This is the same as reset(RHS) and any().
	bool test(const SmallBitVector &RHS) const {
	if (isSmall() && RHS.isSmall())
	return (getSmallBits() & ~RHS.getSmallBits()) != 0;
	if (!isSmall() && !RHS.isSmall())
	return getPointer()->test(*RHS.getPointer());

	unsigned i, e;
	for (i = 0, e = std::min(size(), RHS.size()); i != e; ++i)
	if (test(i) && !RHS.test(i))
	return true;

	for (e = size(); i != e; ++i)
	if (test(i))
	return true;

	return false;
	}

	SmallBitVector &operator\|=(const SmallBitVector &RHS) {
	resize(std::max(size(), RHS.size()));
	if (isSmall() && RHS.isSmall())
	setSmallBits(getSmallBits() \| RHS.getSmallBits());
	else if (!isSmall() && !RHS.isSmall())
	getPointer()->operator\|=(*RHS.getPointer());
	else {
	for (size_type I = 0, E = RHS.size(); I != E; ++I)
	(*this)[I] = test(I) \|\| RHS.test(I);
	}
	return *this;
	}

	SmallBitVector &operator^=(const SmallBitVector &RHS) {
	resize(std::max(size(), RHS.size()));
	if (isSmall() && RHS.isSmall())
	setSmallBits(getSmallBits() ^ RHS.getSmallBits());
	else if (!isSmall() && !RHS.isSmall())
	getPointer()->operator^=(*RHS.getPointer());
	else {
	for (size_type I = 0, E = RHS.size(); I != E; ++I)
	(*this)[I] = test(I) != RHS.test(I);
	}
	return *this;
	}

	SmallBitVector &operator<<=(unsigned N) {
	if (isSmall())
	setSmallBits(getSmallBits() << N);
	else
	getPointer()->operator<<=(N);
	return *this;
	}

	SmallBitVector &operator>>=(unsigned N) {
	if (isSmall())
	setSmallBits(getSmallBits() >> N);
	else
	getPointer()->operator>>=(N);
	return *this;
	}

	// Assignment operator.
	const SmallBitVector &operator=(const SmallBitVector &RHS) {
	if (isSmall()) {
	if (RHS.isSmall())
	X = RHS.X;
	else
	switchToLarge(new BitVector(*RHS.getPointer()));
	} else {
	if (!RHS.isSmall())
	getPointer() = RHS.getPointer();
	else {
	delete getPointer();
	X = RHS.X;
	}
	}
	return *this;
	}

	const SmallBitVector &operator=(SmallBitVector &&RHS) {
	if (this != &RHS) {
	clear();
	swap(RHS);
	}
	return *this;
	}

	void swap(SmallBitVector &RHS) {
	std::swap(X, RHS.X);
	}

	/// Add '1' bits from Mask to this vector. Don't resize.
	/// This computes "*this \|= Mask".
	void setBitsInMask(const uint32_t *Mask, unsigned MaskWords = ~0u) {
	if (isSmall())
	applyMask<true, false>(Mask, MaskWords);
	else
	getPointer()->setBitsInMask(Mask, MaskWords);
	}

	/// Clear any bits in this vector that are set in Mask. Don't resize.
	/// This computes "*this &= ~Mask".
	void clearBitsInMask(const uint32_t *Mask, unsigned MaskWords = ~0u) {
	if (isSmall())
	applyMask<false, false>(Mask, MaskWords);
	else
	getPointer()->clearBitsInMask(Mask, MaskWords);
	}

	/// Add a bit to this vector for every '0' bit in Mask. Don't resize.
	/// This computes "*this \|= ~Mask".
	void setBitsNotInMask(const uint32_t *Mask, unsigned MaskWords = ~0u) {
	if (isSmall())
	applyMask<true, true>(Mask, MaskWords);
	else
	getPointer()->setBitsNotInMask(Mask, MaskWords);
	}

	/// Clear a bit in this vector for every '0' bit in Mask. Don't resize.
	/// This computes "*this &= Mask".
	void clearBitsNotInMask(const uint32_t *Mask, unsigned MaskWords = ~0u) {
	if (isSmall())
	applyMask<false, true>(Mask, MaskWords);
	else
	getPointer()->clearBitsNotInMask(Mask, MaskWords);
	}

	void invalid() {
	assert(empty());
	X = (uintptr_t)-1;
	}
	bool isInvalid() const { return X == (uintptr_t)-1; }

	ArrayRef<uintptr_t> getData(uintptr_t &Store) const {
	if (!isSmall())
	return getPointer()->getData();
	Store = getSmallBits();
	return Store;
	}

	private:
	template <bool AddBits, bool InvertMask>
	void applyMask(const uint32_t *Mask, unsigned MaskWords) {
	assert(MaskWords <= sizeof(uintptr_t) && "Mask is larger than base!");
	uintptr_t M = Mask[0];
	if (NumBaseBits == 64)
	M \|= uint64_t(Mask[1]) << 32;
	if (InvertMask)
	M = ~M;
	if (AddBits)
	setSmallBits(getSmallBits() \| M);
	else
	setSmallBits(getSmallBits() & ~M);
	}
	};

	inline SmallBitVector
	operator&(const SmallBitVector &LHS, const SmallBitVector &RHS) {
	SmallBitVector Result(LHS);
	Result &= RHS;
	return Result;
	}

	inline SmallBitVector
	operator\|(const SmallBitVector &LHS, const SmallBitVector &RHS) {
	SmallBitVector Result(LHS);
	Result \|= RHS;
	return Result;
	}

	inline SmallBitVector
	operator^(const SmallBitVector &LHS, const SmallBitVector &RHS) {
	SmallBitVector Result(LHS);
	Result ^= RHS;
	return Result;
	}

	template <> struct DenseMapInfo<SmallBitVector> {
	static inline SmallBitVector getEmptyKey() { return SmallBitVector(); }
	static inline SmallBitVector getTombstoneKey() {
	SmallBitVector V;
	V.invalid();
	return V;
	}
	static unsigned getHashValue(const SmallBitVector &V) {
	uintptr_t Store;
	return DenseMapInfo<
	std::pair<SmallBitVector::size_type, ArrayRef<uintptr_t>>>::
	getHashValue(std::make_pair(V.size(), V.getData(Store)));
	}
	static bool isEqual(const SmallBitVector &LHS, const SmallBitVector &RHS) {
	if (LHS.isInvalid() \|\| RHS.isInvalid())
	return LHS.isInvalid() == RHS.isInvalid();
	return LHS == RHS;
	}
	};
	} // end namespace llvm

	namespace std {

	/// Implement std::swap in terms of BitVector swap.
	inline void
	swap(llvm::SmallBitVector &LHS, llvm::SmallBitVector &RHS) {
	LHS.swap(RHS);
	}

	} // end namespace std

	#endif // LLVM_ADT_SMALLBITVECTOR_H