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//===- llvm/ADT/SmallPtrSet.h - 'Normally small' pointer set ----*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file defines the SmallPtrSet class. See the doxygen comment for
// SmallPtrSetImplBase for more details on the algorithm used.
#include "llvm/ADT/EpochTracker.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/ReverseIteration.h"
#include "llvm/Support/type_traits.h"
#include <cassert>
#include <cstddef>
#include <cstdlib>
#include <cstring>
#include <initializer_list>
#include <iterator>
#include <utility>
namespace llvm {
/// SmallPtrSetImplBase - This is the common code shared among all the
/// SmallPtrSet<>'s, which is almost everything. SmallPtrSet has two modes, one
/// for small and one for large sets.
/// Small sets use an array of pointers allocated in the SmallPtrSet object,
/// which is treated as a simple array of pointers. When a pointer is added to
/// the set, the array is scanned to see if the element already exists, if not
/// the element is 'pushed back' onto the array. If we run out of space in the
/// array, we grow into the 'large set' case. SmallSet should be used when the
/// sets are often small. In this case, no memory allocation is used, and only
/// light-weight and cache-efficient scanning is used.
/// Large sets use a classic exponentially-probed hash table. Empty buckets are
/// represented with an illegal pointer value (-1) to allow null pointers to be
/// inserted. Tombstones are represented with another illegal pointer value
/// (-2), to allow deletion. The hash table is resized when the table is 3/4 or
/// more. When this happens, the table is doubled in size.
class SmallPtrSetImplBase : public DebugEpochBase {
friend class SmallPtrSetIteratorImpl;
/// SmallArray - Points to a fixed size set of buckets, used in 'small mode'.
const void **SmallArray;
/// CurArray - This is the current set of buckets. If equal to SmallArray,
/// then the set is in 'small mode'.
const void **CurArray;
/// CurArraySize - The allocated size of CurArray, always a power of two.
unsigned CurArraySize;
/// Number of elements in CurArray that contain a value or are a tombstone.
/// If small, all these elements are at the beginning of CurArray and the rest
/// is uninitialized.
unsigned NumNonEmpty;
/// Number of tombstones in CurArray.
unsigned NumTombstones;
// Helpers to copy and move construct a SmallPtrSet.
SmallPtrSetImplBase(const void **SmallStorage,
const SmallPtrSetImplBase &that);
SmallPtrSetImplBase(const void **SmallStorage, unsigned SmallSize,
SmallPtrSetImplBase &&that);
explicit SmallPtrSetImplBase(const void **SmallStorage, unsigned SmallSize)
: SmallArray(SmallStorage), CurArray(SmallStorage),
CurArraySize(SmallSize), NumNonEmpty(0), NumTombstones(0) {
assert(SmallSize && (SmallSize & (SmallSize-1)) == 0 &&
"Initial size must be a power of two!");
~SmallPtrSetImplBase() {
if (!isSmall())
using size_type = unsigned;
SmallPtrSetImplBase &operator=(const SmallPtrSetImplBase &) = delete;
LLVM_NODISCARD bool empty() const { return size() == 0; }
size_type size() const { return NumNonEmpty - NumTombstones; }
void clear() {
// If the capacity of the array is huge, and the # elements used is small,
// shrink the array.
if (!isSmall()) {
if (size() * 4 < CurArraySize && CurArraySize > 32)
return shrink_and_clear();
// Fill the array with empty markers.
memset(CurArray, -1, CurArraySize * sizeof(void *));
NumNonEmpty = 0;
NumTombstones = 0;
static void *getTombstoneMarker() { return reinterpret_cast<void*>(-2); }
static void *getEmptyMarker() {
// Note that -1 is chosen to make clear() efficiently implementable with
// memset and because it's not a valid pointer value.
return reinterpret_cast<void*>(-1);
const void **EndPointer() const {
return isSmall() ? CurArray + NumNonEmpty : CurArray + CurArraySize;
/// insert_imp - This returns true if the pointer was new to the set, false if
/// it was already in the set. This is hidden from the client so that the
/// derived class can check that the right type of pointer is passed in.
std::pair<const void *const *, bool> insert_imp(const void *Ptr) {
if (isSmall()) {
// Check to see if it is already in the set.
const void **LastTombstone = nullptr;
for (const void **APtr = SmallArray, **E = SmallArray + NumNonEmpty;
APtr != E; ++APtr) {
const void *Value = *APtr;
if (Value == Ptr)
return std::make_pair(APtr, false);
if (Value == getTombstoneMarker())
LastTombstone = APtr;
// Did we find any tombstone marker?
if (LastTombstone != nullptr) {
*LastTombstone = Ptr;
return std::make_pair(LastTombstone, true);
// Nope, there isn't. If we stay small, just 'pushback' now.
if (NumNonEmpty < CurArraySize) {
SmallArray[NumNonEmpty++] = Ptr;
return std::make_pair(SmallArray + (NumNonEmpty - 1), true);
// Otherwise, hit the big set case, which will call grow.
return insert_imp_big(Ptr);
/// erase_imp - If the set contains the specified pointer, remove it and
/// return true, otherwise return false. This is hidden from the client so
/// that the derived class can check that the right type of pointer is passed
/// in.
bool erase_imp(const void * Ptr) {
const void *const *P = find_imp(Ptr);
if (P == EndPointer())
return false;
const void **Loc = const_cast<const void **>(P);
assert(*Loc == Ptr && "broken find!");
*Loc = getTombstoneMarker();
return true;
/// Returns the raw pointer needed to construct an iterator. If element not
/// found, this will be EndPointer. Otherwise, it will be a pointer to the
/// slot which stores Ptr;
const void *const * find_imp(const void * Ptr) const {
if (isSmall()) {
// Linear search for the item.
for (const void *const *APtr = SmallArray,
*const *E = SmallArray + NumNonEmpty; APtr != E; ++APtr)
if (*APtr == Ptr)
return APtr;
return EndPointer();
// Big set case.
auto *Bucket = FindBucketFor(Ptr);
if (*Bucket == Ptr)
return Bucket;
return EndPointer();
bool isSmall() const { return CurArray == SmallArray; }
std::pair<const void *const *, bool> insert_imp_big(const void *Ptr);
const void * const *FindBucketFor(const void *Ptr) const;
void shrink_and_clear();
/// Grow - Allocate a larger backing store for the buckets and move it over.
void Grow(unsigned NewSize);
/// swap - Swaps the elements of two sets.
/// Note: This method assumes that both sets have the same small size.
void swap(SmallPtrSetImplBase &RHS);
void CopyFrom(const SmallPtrSetImplBase &RHS);
void MoveFrom(unsigned SmallSize, SmallPtrSetImplBase &&RHS);
/// Code shared by MoveFrom() and move constructor.
void MoveHelper(unsigned SmallSize, SmallPtrSetImplBase &&RHS);
/// Code shared by CopyFrom() and copy constructor.
void CopyHelper(const SmallPtrSetImplBase &RHS);
/// SmallPtrSetIteratorImpl - This is the common base class shared between all
/// instances of SmallPtrSetIterator.
class SmallPtrSetIteratorImpl {
const void *const *Bucket;
const void *const *End;
explicit SmallPtrSetIteratorImpl(const void *const *BP, const void*const *E)
: Bucket(BP), End(E) {
if (shouldReverseIterate()) {
bool operator==(const SmallPtrSetIteratorImpl &RHS) const {
return Bucket == RHS.Bucket;
bool operator!=(const SmallPtrSetIteratorImpl &RHS) const {
return Bucket != RHS.Bucket;
/// AdvanceIfNotValid - If the current bucket isn't valid, advance to a bucket
/// that is. This is guaranteed to stop because the end() bucket is marked
/// valid.
void AdvanceIfNotValid() {
assert(Bucket <= End);
while (Bucket != End &&
(*Bucket == SmallPtrSetImplBase::getEmptyMarker() ||
*Bucket == SmallPtrSetImplBase::getTombstoneMarker()))
void RetreatIfNotValid() {
assert(Bucket >= End);
while (Bucket != End &&
(Bucket[-1] == SmallPtrSetImplBase::getEmptyMarker() ||
Bucket[-1] == SmallPtrSetImplBase::getTombstoneMarker())) {
/// SmallPtrSetIterator - This implements a const_iterator for SmallPtrSet.
template <typename PtrTy>
class SmallPtrSetIterator : public SmallPtrSetIteratorImpl,
DebugEpochBase::HandleBase {
using PtrTraits = PointerLikeTypeTraits<PtrTy>;
using value_type = PtrTy;
using reference = PtrTy;
using pointer = PtrTy;
using difference_type = std::ptrdiff_t;
using iterator_category = std::forward_iterator_tag;
explicit SmallPtrSetIterator(const void *const *BP, const void *const *E,
const DebugEpochBase &Epoch)
: SmallPtrSetIteratorImpl(BP, E), DebugEpochBase::HandleBase(&Epoch) {}
// Most methods provided by baseclass.
const PtrTy operator*() const {
assert(isHandleInSync() && "invalid iterator access!");
if (shouldReverseIterate()) {
assert(Bucket > End);
return PtrTraits::getFromVoidPointer(const_cast<void *>(Bucket[-1]));
assert(Bucket < End);
return PtrTraits::getFromVoidPointer(const_cast<void*>(*Bucket));
inline SmallPtrSetIterator& operator++() { // Preincrement
assert(isHandleInSync() && "invalid iterator access!");
if (shouldReverseIterate()) {
return *this;
return *this;
SmallPtrSetIterator operator++(int) { // Postincrement
SmallPtrSetIterator tmp = *this;
return tmp;
/// RoundUpToPowerOfTwo - This is a helper template that rounds N up to the next
/// power of two (which means N itself if N is already a power of two).
template<unsigned N>
struct RoundUpToPowerOfTwo;
/// RoundUpToPowerOfTwoH - If N is not a power of two, increase it. This is a
/// helper template used to implement RoundUpToPowerOfTwo.
template<unsigned N, bool isPowerTwo>
struct RoundUpToPowerOfTwoH {
enum { Val = N };
template<unsigned N>
struct RoundUpToPowerOfTwoH<N, false> {
enum {
// We could just use NextVal = N+1, but this converges faster. N|(N-1) sets
// the right-most zero bits to one all at once, e.g. 0b0011000 -> 0b0011111.
Val = RoundUpToPowerOfTwo<(N|(N-1)) + 1>::Val
template<unsigned N>
struct RoundUpToPowerOfTwo {
enum { Val = RoundUpToPowerOfTwoH<N, (N&(N-1)) == 0>::Val };
/// A templated base class for \c SmallPtrSet which provides the
/// typesafe interface that is common across all small sizes.
/// This is particularly useful for passing around between interface boundaries
/// to avoid encoding a particular small size in the interface boundary.
template <typename PtrType>
class SmallPtrSetImpl : public SmallPtrSetImplBase {
using ConstPtrType = typename add_const_past_pointer<PtrType>::type;
using PtrTraits = PointerLikeTypeTraits<PtrType>;
using ConstPtrTraits = PointerLikeTypeTraits<ConstPtrType>;
// Constructors that forward to the base.
SmallPtrSetImpl(const void **SmallStorage, const SmallPtrSetImpl &that)
: SmallPtrSetImplBase(SmallStorage, that) {}
SmallPtrSetImpl(const void **SmallStorage, unsigned SmallSize,
SmallPtrSetImpl &&that)
: SmallPtrSetImplBase(SmallStorage, SmallSize, std::move(that)) {}
explicit SmallPtrSetImpl(const void **SmallStorage, unsigned SmallSize)
: SmallPtrSetImplBase(SmallStorage, SmallSize) {}
using iterator = SmallPtrSetIterator<PtrType>;
using const_iterator = SmallPtrSetIterator<PtrType>;
using key_type = ConstPtrType;
using value_type = PtrType;
SmallPtrSetImpl(const SmallPtrSetImpl &) = delete;
/// Inserts Ptr if and only if there is no element in the container equal to
/// Ptr. The bool component of the returned pair is true if and only if the
/// insertion takes place, and the iterator component of the pair points to
/// the element equal to Ptr.
std::pair<iterator, bool> insert(PtrType Ptr) {
auto p = insert_imp(PtrTraits::getAsVoidPointer(Ptr));
return std::make_pair(makeIterator(p.first), p.second);
/// erase - If the set contains the specified pointer, remove it and return
/// true, otherwise return false.
bool erase(PtrType Ptr) {
return erase_imp(PtrTraits::getAsVoidPointer(Ptr));
/// count - Return 1 if the specified pointer is in the set, 0 otherwise.
size_type count(ConstPtrType Ptr) const { return find(Ptr) != end() ? 1 : 0; }
iterator find(ConstPtrType Ptr) const {
return makeIterator(find_imp(ConstPtrTraits::getAsVoidPointer(Ptr)));
template <typename IterT>
void insert(IterT I, IterT E) {
for (; I != E; ++I)
void insert(std::initializer_list<PtrType> IL) {
insert(IL.begin(), IL.end());
iterator begin() const {
if (shouldReverseIterate())
return makeIterator(EndPointer() - 1);
return makeIterator(CurArray);
iterator end() const { return makeIterator(EndPointer()); }
/// Create an iterator that dereferences to same place as the given pointer.
iterator makeIterator(const void *const *P) const {
if (shouldReverseIterate())
return iterator(P == EndPointer() ? CurArray : P + 1, CurArray, *this);
return iterator(P, EndPointer(), *this);
/// SmallPtrSet - This class implements a set which is optimized for holding
/// SmallSize or less elements. This internally rounds up SmallSize to the next
/// power of two if it is not already a power of two. See the comments above
/// SmallPtrSetImplBase for details of the algorithm.
template<class PtrType, unsigned SmallSize>
class SmallPtrSet : public SmallPtrSetImpl<PtrType> {
// In small mode SmallPtrSet uses linear search for the elements, so it is
// not a good idea to choose this value too high. You may consider using a
// DenseSet<> instead if you expect many elements in the set.
static_assert(SmallSize <= 32, "SmallSize should be small");
using BaseT = SmallPtrSetImpl<PtrType>;
// Make sure that SmallSize is a power of two, round up if not.
enum { SmallSizePowTwo = RoundUpToPowerOfTwo<SmallSize>::Val };
/// SmallStorage - Fixed size storage used in 'small mode'.
const void *SmallStorage[SmallSizePowTwo];
SmallPtrSet() : BaseT(SmallStorage, SmallSizePowTwo) {}
SmallPtrSet(const SmallPtrSet &that) : BaseT(SmallStorage, that) {}
SmallPtrSet(SmallPtrSet &&that)
: BaseT(SmallStorage, SmallSizePowTwo, std::move(that)) {}
template<typename It>
SmallPtrSet(It I, It E) : BaseT(SmallStorage, SmallSizePowTwo) {
this->insert(I, E);
SmallPtrSet(std::initializer_list<PtrType> IL)
: BaseT(SmallStorage, SmallSizePowTwo) {
this->insert(IL.begin(), IL.end());
SmallPtrSet<PtrType, SmallSize> &
operator=(const SmallPtrSet<PtrType, SmallSize> &RHS) {
if (&RHS != this)
return *this;
SmallPtrSet<PtrType, SmallSize> &
operator=(SmallPtrSet<PtrType, SmallSize> &&RHS) {
if (&RHS != this)
this->MoveFrom(SmallSizePowTwo, std::move(RHS));
return *this;
SmallPtrSet<PtrType, SmallSize> &
operator=(std::initializer_list<PtrType> IL) {
this->insert(IL.begin(), IL.end());
return *this;
/// swap - Swaps the elements of two sets.
void swap(SmallPtrSet<PtrType, SmallSize> &RHS) {
} // end namespace llvm
namespace std {
/// Implement std::swap in terms of SmallPtrSet swap.
template<class T, unsigned N>
inline void swap(llvm::SmallPtrSet<T, N> &LHS, llvm::SmallPtrSet<T, N> &RHS) {
} // end namespace std