SmallSet.h revision cd81d94322a39503e4a3e87b6ee03d4fcb3465fb 
1//===- llvm/ADT/SmallSet.h - 'Normally small' sets --------------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file defines the SmallSet class.
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_ADT_SMALLSET_H
15#define LLVM_ADT_SMALLSET_H
16
17#include "llvm/ADT/SmallPtrSet.h"
18#include "llvm/ADT/SmallVector.h"
19#include <set>
20
21namespace llvm {
22
23/// SmallSet - This maintains a set of unique values, optimizing for the case
24/// when the set is small (less than N).  In this case, the set can be
25/// maintained with no mallocs.  If the set gets large, we expand to using an
26/// std::set to maintain reasonable lookup times.
27///
28/// Note that this set does not provide a way to iterate over members in the
29/// set.
30template <typename T, unsigned N,  typename C = std::less<T> >
31class SmallSet {
32  /// Use a SmallVector to hold the elements here (even though it will never
33  /// reach its 'large' stage) to avoid calling the default ctors of elements
34  /// we will never use.
35  SmallVector<T, N> Vector;
36  std::set<T, C> Set;
37  typedef typename SmallVector<T, N>::const_iterator VIterator;
38  typedef typename SmallVector<T, N>::iterator mutable_iterator;
39public:
40  typedef size_t size_type;
41  SmallSet() {}
42
43  bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const {
44    return Vector.empty() && Set.empty();
45  }
46
47  size_type size() const {
48    return isSmall() ? Vector.size() : Set.size();
49  }
50
51  /// count - Return 1 if the element is in the set, 0 otherwise.
52  size_type count(const T &V) const {
53    if (isSmall()) {
54      // Since the collection is small, just do a linear search.
55      return vfind(V) == Vector.end() ? 0 : 1;
56    } else {
57      return Set.count(V);
58    }
59  }
60
61  /// insert - Insert an element into the set if it isn't already there.
62  /// Returns true if the element is inserted (it was not in the set before).
63  bool insert(const T &V) {
64    if (!isSmall())
65      return Set.insert(V).second;
66
67    VIterator I = vfind(V);
68    if (I != Vector.end())    // Don't reinsert if it already exists.
69      return false;
70    if (Vector.size() < N) {
71      Vector.push_back(V);
72      return true;
73    }
74
75    // Otherwise, grow from vector to set.
76    while (!Vector.empty()) {
77      Set.insert(Vector.back());
78      Vector.pop_back();
79    }
80    Set.insert(V);
81    return true;
82  }
83
84  template <typename IterT>
85  void insert(IterT I, IterT E) {
86    for (; I != E; ++I)
87      insert(*I);
88  }
89
90  bool erase(const T &V) {
91    if (!isSmall())
92      return Set.erase(V);
93    for (mutable_iterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
94      if (*I == V) {
95        Vector.erase(I);
96        return true;
97      }
98    return false;
99  }
100
101  void clear() {
102    Vector.clear();
103    Set.clear();
104  }
105private:
106  bool isSmall() const { return Set.empty(); }
107
108  VIterator vfind(const T &V) const {
109    for (VIterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
110      if (*I == V)
111        return I;
112    return Vector.end();
113  }
114};
115
116/// If this set is of pointer values, transparently switch over to using
117/// SmallPtrSet for performance.
118template <typename PointeeType, unsigned N>
119class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N> {};
120
121} // end namespace llvm
122
123#endif
124