SmallSet.h revision 252723 
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  SmallSet() {}
41
42  bool empty() const { return Vector.empty() && Set.empty(); }
43  unsigned size() const {
44    return isSmall() ? Vector.size() : Set.size();
45  }
46
47  /// count - Return true if the element is in the set.
48  bool count(const T &V) const {
49    if (isSmall()) {
50      // Since the collection is small, just do a linear search.
51      return vfind(V) != Vector.end();
52    } else {
53      return Set.count(V);
54    }
55  }
56
57  /// insert - Insert an element into the set if it isn't already there.
58  /// Returns true if the element is inserted (it was not in the set before).
59  bool insert(const T &V) {
60    if (!isSmall())
61      return Set.insert(V).second;
62
63    VIterator I = vfind(V);
64    if (I != Vector.end())    // Don't reinsert if it already exists.
65      return false;
66    if (Vector.size() < N) {
67      Vector.push_back(V);
68      return true;
69    }
70
71    // Otherwise, grow from vector to set.
72    while (!Vector.empty()) {
73      Set.insert(Vector.back());
74      Vector.pop_back();
75    }
76    Set.insert(V);
77    return true;
78  }
79
80  template <typename IterT>
81  void insert(IterT I, IterT E) {
82    for (; I != E; ++I)
83      insert(*I);
84  }
85
86  bool erase(const T &V) {
87    if (!isSmall())
88      return Set.erase(V);
89    for (mutable_iterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
90      if (*I == V) {
91        Vector.erase(I);
92        return true;
93      }
94    return false;
95  }
96
97  void clear() {
98    Vector.clear();
99    Set.clear();
100  }
101private:
102  bool isSmall() const { return Set.empty(); }
103
104  VIterator vfind(const T &V) const {
105    for (VIterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
106      if (*I == V)
107        return I;
108    return Vector.end();
109  }
110};
111
112/// If this set is of pointer values, transparently switch over to using
113/// SmallPtrSet for performance.
114template <typename PointeeType, unsigned N>
115class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N> {};
116
117} // end namespace llvm
118
119#endif
120