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286 lines
8.6 KiB
C++
286 lines
8.6 KiB
C++
//===- llvm/ADT/SmallSet.h - 'Normally small' sets --------------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the SmallSet class.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ADT_SMALLSET_H
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#define LLVM_ADT_SMALLSET_H
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#include "llvm/ADT/None.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/iterator.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/type_traits.h"
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#include <cstddef>
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#include <functional>
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#include <set>
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#include <type_traits>
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#include <utility>
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namespace llvm {
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/// SmallSetIterator - This class implements a const_iterator for SmallSet by
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/// delegating to the underlying SmallVector or Set iterators.
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template <typename T, unsigned N, typename C>
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class SmallSetIterator
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: public iterator_facade_base<SmallSetIterator<T, N, C>,
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std::forward_iterator_tag, T> {
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private:
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using SetIterTy = typename std::set<T, C>::const_iterator;
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using VecIterTy = typename SmallVector<T, N>::const_iterator;
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using SelfTy = SmallSetIterator<T, N, C>;
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/// Iterators to the parts of the SmallSet containing the data. They are set
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/// depending on isSmall.
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union {
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SetIterTy SetIter;
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VecIterTy VecIter;
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};
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bool isSmall;
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public:
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SmallSetIterator(SetIterTy SetIter) : SetIter(SetIter), isSmall(false) {}
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SmallSetIterator(VecIterTy VecIter) : VecIter(VecIter), isSmall(true) {}
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// Spell out destructor, copy/move constructor and assignment operators for
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// MSVC STL, where set<T>::const_iterator is not trivially copy constructible.
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~SmallSetIterator() {
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if (isSmall)
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VecIter.~VecIterTy();
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else
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SetIter.~SetIterTy();
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}
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SmallSetIterator(const SmallSetIterator &Other) : isSmall(Other.isSmall) {
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if (isSmall)
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VecIter = Other.VecIter;
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else
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// Use placement new, to make sure SetIter is properly constructed, even
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// if it is not trivially copy-able (e.g. in MSVC).
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new (&SetIter) SetIterTy(Other.SetIter);
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}
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SmallSetIterator(SmallSetIterator &&Other) : isSmall(Other.isSmall) {
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if (isSmall)
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VecIter = std::move(Other.VecIter);
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else
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// Use placement new, to make sure SetIter is properly constructed, even
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// if it is not trivially copy-able (e.g. in MSVC).
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new (&SetIter) SetIterTy(std::move(Other.SetIter));
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}
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SmallSetIterator& operator=(const SmallSetIterator& Other) {
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// Call destructor for SetIter, so it gets properly destroyed if it is
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// not trivially destructible in case we are setting VecIter.
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if (!isSmall)
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SetIter.~SetIterTy();
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isSmall = Other.isSmall;
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if (isSmall)
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VecIter = Other.VecIter;
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else
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new (&SetIter) SetIterTy(Other.SetIter);
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return *this;
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}
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SmallSetIterator& operator=(SmallSetIterator&& Other) {
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// Call destructor for SetIter, so it gets properly destroyed if it is
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// not trivially destructible in case we are setting VecIter.
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if (!isSmall)
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SetIter.~SetIterTy();
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isSmall = Other.isSmall;
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if (isSmall)
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VecIter = std::move(Other.VecIter);
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else
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new (&SetIter) SetIterTy(std::move(Other.SetIter));
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return *this;
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}
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bool operator==(const SmallSetIterator &RHS) const {
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if (isSmall != RHS.isSmall)
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return false;
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if (isSmall)
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return VecIter == RHS.VecIter;
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return SetIter == RHS.SetIter;
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}
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SmallSetIterator &operator++() { // Preincrement
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if (isSmall)
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VecIter++;
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else
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SetIter++;
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return *this;
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}
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const T &operator*() const { return isSmall ? *VecIter : *SetIter; }
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};
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/// SmallSet - This maintains a set of unique values, optimizing for the case
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/// when the set is small (less than N). In this case, the set can be
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/// maintained with no mallocs. If the set gets large, we expand to using an
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/// std::set to maintain reasonable lookup times.
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template <typename T, unsigned N, typename C = std::less<T>>
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class SmallSet {
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/// Use a SmallVector to hold the elements here (even though it will never
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/// reach its 'large' stage) to avoid calling the default ctors of elements
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/// we will never use.
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SmallVector<T, N> Vector;
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std::set<T, C> Set;
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using VIterator = typename SmallVector<T, N>::const_iterator;
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using mutable_iterator = typename SmallVector<T, N>::iterator;
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// In small mode SmallPtrSet uses linear search for the elements, so it is
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// not a good idea to choose this value too high. You may consider using a
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// DenseSet<> instead if you expect many elements in the set.
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static_assert(N <= 32, "N should be small");
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public:
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using size_type = size_t;
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using const_iterator = SmallSetIterator<T, N, C>;
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SmallSet() = default;
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LLVM_NODISCARD bool empty() const {
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return Vector.empty() && Set.empty();
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}
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size_type size() const {
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return isSmall() ? Vector.size() : Set.size();
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}
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/// count - Return 1 if the element is in the set, 0 otherwise.
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size_type count(const T &V) const {
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if (isSmall()) {
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// Since the collection is small, just do a linear search.
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return vfind(V) == Vector.end() ? 0 : 1;
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} else {
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return Set.count(V);
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}
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}
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/// insert - Insert an element into the set if it isn't already there.
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/// Returns true if the element is inserted (it was not in the set before).
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/// The first value of the returned pair is unused and provided for
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/// partial compatibility with the standard library self-associative container
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/// concept.
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// FIXME: Add iterators that abstract over the small and large form, and then
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// return those here.
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std::pair<NoneType, bool> insert(const T &V) {
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if (!isSmall())
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return std::make_pair(None, Set.insert(V).second);
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VIterator I = vfind(V);
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if (I != Vector.end()) // Don't reinsert if it already exists.
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return std::make_pair(None, false);
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if (Vector.size() < N) {
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Vector.push_back(V);
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return std::make_pair(None, true);
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}
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// Otherwise, grow from vector to set.
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while (!Vector.empty()) {
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Set.insert(Vector.back());
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Vector.pop_back();
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}
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Set.insert(V);
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return std::make_pair(None, true);
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}
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template <typename IterT>
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void insert(IterT I, IterT E) {
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for (; I != E; ++I)
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insert(*I);
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}
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bool erase(const T &V) {
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if (!isSmall())
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return Set.erase(V);
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for (mutable_iterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
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if (*I == V) {
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Vector.erase(I);
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return true;
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}
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return false;
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}
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void clear() {
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Vector.clear();
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Set.clear();
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}
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const_iterator begin() const {
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if (isSmall())
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return {Vector.begin()};
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return {Set.begin()};
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}
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const_iterator end() const {
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if (isSmall())
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return {Vector.end()};
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return {Set.end()};
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}
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/// Check if the SmallSet contains the given element.
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bool contains(const T &V) const {
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if (isSmall())
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return vfind(V) != Vector.end();
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return Set.find(V) != Set.end();
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}
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private:
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bool isSmall() const { return Set.empty(); }
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VIterator vfind(const T &V) const {
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for (VIterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
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if (*I == V)
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return I;
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return Vector.end();
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}
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};
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/// If this set is of pointer values, transparently switch over to using
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/// SmallPtrSet for performance.
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template <typename PointeeType, unsigned N>
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class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N> {};
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/// Equality comparison for SmallSet.
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///
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/// Iterates over elements of LHS confirming that each element is also a member
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/// of RHS, and that RHS contains no additional values.
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/// Equivalent to N calls to RHS.count.
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/// For small-set mode amortized complexity is O(N^2)
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/// For large-set mode amortized complexity is linear, worst case is O(N^2) (if
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/// every hash collides).
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template <typename T, unsigned LN, unsigned RN, typename C>
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bool operator==(const SmallSet<T, LN, C> &LHS, const SmallSet<T, RN, C> &RHS) {
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if (LHS.size() != RHS.size())
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return false;
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// All elements in LHS must also be in RHS
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return all_of(LHS, [&RHS](const T &E) { return RHS.count(E); });
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}
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/// Inequality comparison for SmallSet.
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///
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/// Equivalent to !(LHS == RHS). See operator== for performance notes.
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template <typename T, unsigned LN, unsigned RN, typename C>
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bool operator!=(const SmallSet<T, LN, C> &LHS, const SmallSet<T, RN, C> &RHS) {
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return !(LHS == RHS);
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}
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} // end namespace llvm
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#endif // LLVM_ADT_SMALLSET_H
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