SmallSet.h revision 7235928b45e6a353f6fcca8b9a40e83ab3420fb0 
1//===- llvm/ADT/SmallSet.h - 'Normally small' sets --------------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file was developed by Chris Lattner and is distributed under
6// the University of Illinois Open Source 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/SmallVector.h"
18#include "llvm/ADT/SmallPtrSet.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>
31class SmallSet {
32  /// Use a SmallVector to hold the elements here (even though it will never
33  /// reach it's 'large' stage) to avoid calling the default ctors of elements
34  /// we will never use.
35  SmallVector<T, N> Vector;
36  std::set<T> 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  bool insert(const T &V) {
59    if (!isSmall())
60      return Set.insert(V).second;
61
62    VIterator I = vfind(V);
63    if (I != Vector.end())    // Don't reinsert if it already exists.
64      return false;
65    if (Vector.size() < N) {
66      Vector.push_back(V);
67      return true;
68    }
69
70    // Otherwise, grow from vector to set.
71    while (!Vector.empty()) {
72      Set.insert(Vector.back());
73      Vector.pop_back();
74    }
75    Set.insert(V);
76    return true;
77  }
78
79  bool erase(const T &V) {
80    if (!isSmall())
81      return Set.erase(V);
82    for (mutable_iterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
83      if (*I == V) {
84        Vector.erase(I);
85        return true;
86      }
87    return false;
88  }
89
90  void clear() {
91    Vector.clear();
92    Set.clear();
93  }
94private:
95  bool isSmall() const { return Set.empty(); }
96
97  VIterator vfind(const T &V) const {
98    for (VIterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
99      if (*I == V)
100        return I;
101    return Vector.end();
102  }
103};
104
105/// If this set is of pointer values, transparently switch over to using
106/// SmallPtrSet for performance.
107template <typename PointeeType, unsigned N>
108class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N> {};
109
110} // end namespace llvm
111
112#endif
113