SmallSet.h revision a5b4760cbd23d49b6d94bc56d85b5a499fa54802 
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 <set>
19
20namespace llvm {
21
22/// SmallSet - This maintains a set of unique values, optimizing for the case
23/// when the set is small (less than N).  In this case, the set can be
24/// maintained with no mallocs.  If the set gets large, we expand to using an
25/// std::set to maintain reasonable lookup times.
26///
27/// Note that this set does not provide a way to iterate over members in the
28/// set.
29template <typename T, unsigned N>
30class SmallSet {
31  /// Use a SmallVector to hold the elements here (even though it will never
32  /// reach it's 'large' stage) to avoid calling the default ctors of elements
33  /// we will never use.
34  SmallVector<T, N> Vector;
35  std::set<T> Set;
36  typedef typename SmallVector<T, N>::const_iterator VIterator;
37  typedef typename SmallVector<T, N>::iterator mutable_iterator;
38public:
39  SmallSet() {}
40
41  bool empty() const { return Vector.empty() && Set.empty(); }
42  unsigned size() const {
43    return isSmall() ? Vector.size() : Set.size();
44  }
45
46  /// count - Return true if the element is in the set.
47  bool count(const T &V) const {
48    if (isSmall()) {
49      // Since the collection is small, just do a linear search.
50      return vfind(V) != Vector.end();
51    } else {
52      return Set.count(V);
53    }
54  }
55
56  /// insert - Insert an element into the set if it isn't already there.
57  bool insert(const T &V) {
58    if (!isSmall())
59      return Set.insert(V).second;
60
61    VIterator I = vfind(V);
62    if (I != Vector.end())    // Don't reinsert if it already exists.
63      return false;
64    if (Vector.size() < N) {
65      Vector.push_back(V);
66      return true;
67    }
68
69    // Otherwise, grow from vector to set.
70    while (!Vector.empty()) {
71      Set.insert(Vector.back());
72      Vector.pop_back();
73    }
74    Set.insert(V);
75    return true;
76  }
77
78  bool erase(const T &V) {
79    if (!isSmall())
80      return Set.erase(V).second;
81    for (mutable_iterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
82      if (*I == V) {
83        Vector.erase(I);
84        return true;
85      }
86    return false;
87  }
88
89  void clear() {
90    Vector.clear();
91    Set.clear();
92  }
93private:
94  bool isSmall() const { return Set.empty(); }
95
96  VIterator vfind(const T &V) const {
97    for (VIterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
98      if (*I == V)
99        return I;
100    return Vector.end();
101  }
102};
103
104
105} // end namespace llvm
106
107#endif
108