//===- llvm/ADT/SmallSet.h - 'Normally small' sets --------------*- 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 SmallSet class.
///
//===----------------------------------------------------------------------===//
#ifndef LLVM_ADT_SMALLSET_H
#define LLVM_ADT_SMALLSET_H
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/iterator.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/type_traits.h"
#include <cstddef>
#include <functional>
#include <set>
#include <type_traits>
#include <utility>
namespace llvm {
/// SmallSetIterator - This class implements a const_iterator for SmallSet by
/// delegating to the underlying SmallVector or Set iterators.
template <typename T, unsigned N, typename C>
class SmallSetIterator
: public iterator_facade_base<SmallSetIterator<T, N, C>,
std::forward_iterator_tag, T> {
private:
using SetIterTy = typename std::set<T, C>::const_iterator;
using VecIterTy = typename SmallVector<T, N>::const_iterator;
using SelfTy = SmallSetIterator<T, N, C>;
/// Iterators to the parts of the SmallSet containing the data. They are set
/// depending on isSmall.
union {
SetIterTy SetIter;
VecIterTy VecIter;
};
bool isSmall;
public:
SmallSetIterator(SetIterTy SetIter) : SetIter(SetIter), isSmall(false) {}
SmallSetIterator(VecIterTy VecIter) : VecIter(VecIter), isSmall(true) {}
// Spell out destructor, copy/move constructor and assignment operators for
// MSVC STL, where set<T>::const_iterator is not trivially copy constructible.
~SmallSetIterator() {
if (isSmall)
VecIter.~VecIterTy();
else
SetIter.~SetIterTy();
}
SmallSetIterator(const SmallSetIterator &Other) : isSmall(Other.isSmall) {
if (isSmall)
VecIter = Other.VecIter;
else
// Use placement new, to make sure SetIter is properly constructed, even
// if it is not trivially copy-able (e.g. in MSVC).
new (&SetIter) SetIterTy(Other.SetIter);
}
SmallSetIterator(SmallSetIterator &&Other) : isSmall(Other.isSmall) {
if (isSmall)
VecIter = std::move(Other.VecIter);
else
// Use placement new, to make sure SetIter is properly constructed, even
// if it is not trivially copy-able (e.g. in MSVC).
new (&SetIter) SetIterTy(std::move(Other.SetIter));
}
SmallSetIterator& operator=(const SmallSetIterator& Other) {
// Call destructor for SetIter, so it gets properly destroyed if it is
// not trivially destructible in case we are setting VecIter.
if (!isSmall)
SetIter.~SetIterTy();
isSmall = Other.isSmall;
if (isSmall)
VecIter = Other.VecIter;
else
new (&SetIter) SetIterTy(Other.SetIter);
return *this;
}
SmallSetIterator& operator=(SmallSetIterator&& Other) {
// Call destructor for SetIter, so it gets properly destroyed if it is
// not trivially destructible in case we are setting VecIter.
if (!isSmall)
SetIter.~SetIterTy();
isSmall = Other.isSmall;
if (isSmall)
VecIter = std::move(Other.VecIter);
else
new (&SetIter) SetIterTy(std::move(Other.SetIter));
return *this;
}
bool operator==(const SmallSetIterator &RHS) const {
if (isSmall != RHS.isSmall)
return false;
if (isSmall)
return VecIter == RHS.VecIter;
return SetIter == RHS.SetIter;
}
SmallSetIterator &operator++() { // Preincrement
if (isSmall)
VecIter++;
else
SetIter++;
return *this;
}
const T &operator*() const { return isSmall ? *VecIter : *SetIter; }
};
/// SmallSet - This maintains a set of unique values, optimizing for the case
/// when the set is small (less than N). In this case, the set can be
/// maintained with no mallocs. If the set gets large, we expand to using an
/// std::set to maintain reasonable lookup times.
template <typename T, unsigned N, typename C = std::less<T>>
class SmallSet {
/// Use a SmallVector to hold the elements here (even though it will never
/// reach its 'large' stage) to avoid calling the default ctors of elements
/// we will never use.
SmallVector<T, N> Vector;
std::set<T, C> Set;
using VIterator = typename SmallVector<T, N>::const_iterator;
using SIterator = typename std::set<T, C>::const_iterator;
using mutable_iterator = typename SmallVector<T, N>::iterator;
// 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(N <= 32, "N should be small");
public:
using size_type = size_t;
using const_iterator = SmallSetIterator<T, N, C>;
SmallSet() = default;
[[nodiscard]] bool empty() const { return Vector.empty() && Set.empty(); }
size_type size() const {
return isSmall() ? Vector.size() : Set.size();
}
/// count - Return 1 if the element is in the set, 0 otherwise.
size_type count(const T &V) const {
if (isSmall()) {
// Since the collection is small, just do a linear search.
return vfind(V) == Vector.end() ? 0 : 1;
} else {
return Set.count(V);
}
}
/// insert - Insert an element into the set if it isn't already there.
/// Returns a pair. The first value of it is an iterator to the inserted
/// element or the existing element in the set. The second value is true
/// if the element is inserted (it was not in the set before).
std::pair<const_iterator, bool> insert(const T &V) {
if (!isSmall()) {
auto [I, Inserted] = Set.insert(V);
return std::make_pair(const_iterator(I), Inserted);
}
VIterator I = vfind(V);
if (I != Vector.end()) // Don't reinsert if it already exists.
return std::make_pair(const_iterator(I), false);
if (Vector.size() < N) {
Vector.push_back(V);
return std::make_pair(const_iterator(std::prev(Vector.end())), true);
}
// Otherwise, grow from vector to set.
while (!Vector.empty()) {
Set.insert(Vector.back());
Vector.pop_back();
}
return std::make_pair(const_iterator(Set.insert(V).first), true);
}
template <typename IterT>
void insert(IterT I, IterT E) {
for (; I != E; ++I)
insert(*I);
}
bool erase(const T &V) {
if (!isSmall())
return Set.erase(V);
for (mutable_iterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
if (*I == V) {
Vector.erase(I);
return true;
}
return false;
}
void clear() {
Vector.clear();
Set.clear();
}
const_iterator begin() const {
if (isSmall())
return {Vector.begin()};
return {Set.begin()};
}
const_iterator end() const {
if (isSmall())
return {Vector.end()};
return {Set.end()};
}
/// Check if the SmallSet contains the given element.
bool contains(const T &V) const {
if (isSmall())
return vfind(V) != Vector.end();
return Set.find(V) != Set.end();
}
private:
bool isSmall() const { return Set.empty(); }
VIterator vfind(const T &V) const {
for (VIterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
if (*I == V)
return I;
return Vector.end();
}
};
/// If this set is of pointer values, transparently switch over to using
/// SmallPtrSet for performance.
template <typename PointeeType, unsigned N>
class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N> {};
/// Equality comparison for SmallSet.
///
/// Iterates over elements of LHS confirming that each element is also a member
/// of RHS, and that RHS contains no additional values.
/// Equivalent to N calls to RHS.count.
/// For small-set mode amortized complexity is O(N^2)
/// For large-set mode amortized complexity is linear, worst case is O(N^2) (if
/// every hash collides).
template <typename T, unsigned LN, unsigned RN, typename C>
bool operator==(const SmallSet<T, LN, C> &LHS, const SmallSet<T, RN, C> &RHS) {
if (LHS.size() != RHS.size())
return false;
// All elements in LHS must also be in RHS
return all_of(LHS, [&RHS](const T &E) { return RHS.count(E); });
}
/// Inequality comparison for SmallSet.
///
/// Equivalent to !(LHS == RHS). See operator== for performance notes.
template <typename T, unsigned LN, unsigned RN, typename C>
bool operator!=(const SmallSet<T, LN, C> &LHS, const SmallSet<T, RN, C> &RHS) {
return !(LHS == RHS);
}
} // end namespace llvm
#endif // LLVM_ADT_SMALLSET_H