LLVM  4.0.0
SmallSet.h
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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/None.h"
18 #include "llvm/ADT/SmallPtrSet.h"
19 #include "llvm/ADT/SmallVector.h"
20 #include "llvm/Support/Compiler.h"
21 #include <cstddef>
22 #include <functional>
23 #include <set>
24 #include <utility>
25 
26 namespace llvm {
27 
28 /// SmallSet - This maintains a set of unique values, optimizing for the case
29 /// when the set is small (less than N). In this case, the set can be
30 /// maintained with no mallocs. If the set gets large, we expand to using an
31 /// std::set to maintain reasonable lookup times.
32 ///
33 /// Note that this set does not provide a way to iterate over members in the
34 /// set.
35 template <typename T, unsigned N, typename C = std::less<T>>
36 class SmallSet {
37  /// Use a SmallVector to hold the elements here (even though it will never
38  /// reach its 'large' stage) to avoid calling the default ctors of elements
39  /// we will never use.
40  SmallVector<T, N> Vector;
41  std::set<T, C> Set;
44 
45  // In small mode SmallPtrSet uses linear search for the elements, so it is
46  // not a good idea to choose this value too high. You may consider using a
47  // DenseSet<> instead if you expect many elements in the set.
48  static_assert(N <= 32, "N should be small");
49 
50 public:
51  typedef size_t size_type;
52 
53  SmallSet() = default;
54 
55  LLVM_NODISCARD bool empty() const {
56  return Vector.empty() && Set.empty();
57  }
58 
59  size_type size() const {
60  return isSmall() ? Vector.size() : Set.size();
61  }
62 
63  /// count - Return 1 if the element is in the set, 0 otherwise.
64  size_type count(const T &V) const {
65  if (isSmall()) {
66  // Since the collection is small, just do a linear search.
67  return vfind(V) == Vector.end() ? 0 : 1;
68  } else {
69  return Set.count(V);
70  }
71  }
72 
73  /// insert - Insert an element into the set if it isn't already there.
74  /// Returns true if the element is inserted (it was not in the set before).
75  /// The first value of the returned pair is unused and provided for
76  /// partial compatibility with the standard library self-associative container
77  /// concept.
78  // FIXME: Add iterators that abstract over the small and large form, and then
79  // return those here.
80  std::pair<NoneType, bool> insert(const T &V) {
81  if (!isSmall())
82  return std::make_pair(None, Set.insert(V).second);
83 
84  VIterator I = vfind(V);
85  if (I != Vector.end()) // Don't reinsert if it already exists.
86  return std::make_pair(None, false);
87  if (Vector.size() < N) {
88  Vector.push_back(V);
89  return std::make_pair(None, true);
90  }
91 
92  // Otherwise, grow from vector to set.
93  while (!Vector.empty()) {
94  Set.insert(Vector.back());
95  Vector.pop_back();
96  }
97  Set.insert(V);
98  return std::make_pair(None, true);
99  }
100 
101  template <typename IterT>
102  void insert(IterT I, IterT E) {
103  for (; I != E; ++I)
104  insert(*I);
105  }
106 
107  bool erase(const T &V) {
108  if (!isSmall())
109  return Set.erase(V);
110  for (mutable_iterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
111  if (*I == V) {
112  Vector.erase(I);
113  return true;
114  }
115  return false;
116  }
117 
118  void clear() {
119  Vector.clear();
120  Set.clear();
121  }
122 
123 private:
124  bool isSmall() const { return Set.empty(); }
125 
126  VIterator vfind(const T &V) const {
127  for (VIterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
128  if (*I == V)
129  return I;
130  return Vector.end();
131  }
132 };
133 
134 /// If this set is of pointer values, transparently switch over to using
135 /// SmallPtrSet for performance.
136 template <typename PointeeType, unsigned N>
137 class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N> {};
138 
139 } // end namespace llvm
140 
141 #endif // LLVM_ADT_SMALLSET_H
bool erase(const T &V)
Definition: SmallSet.h:107
LLVM_NODISCARD bool empty() const
Definition: SmallSet.h:55
size_type size() const
Definition: SmallSet.h:59
void clear()
Definition: SmallSet.h:118
void insert(IterT I, IterT E)
Definition: SmallSet.h:102
static GCRegistry::Add< CoreCLRGC > E("coreclr","CoreCLR-compatible GC")
SmallSet - This maintains a set of unique values, optimizing for the case when the set is small (less...
Definition: SmallSet.h:36
std::pair< NoneType, bool > insert(const T &V)
insert - Insert an element into the set if it isn't already there.
Definition: SmallSet.h:80
size_type count(const T &V) const
count - Return 1 if the element is in the set, 0 otherwise.
Definition: SmallSet.h:64
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:843
size_t size_type
Definition: SmallSet.h:48
#define I(x, y, z)
Definition: MD5.cpp:54
#define N
SmallSet()=default
#define LLVM_NODISCARD
LLVM_NODISCARD - Warn if a type or return value is discarded.
Definition: Compiler.h:132