LLVM  6.0.0svn
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;
42 
43  using VIterator = typename SmallVector<T, N>::const_iterator;
44  using mutable_iterator = typename SmallVector<T, N>::iterator;
45 
46  // In small mode SmallPtrSet uses linear search for the elements, so it is
47  // not a good idea to choose this value too high. You may consider using a
48  // DenseSet<> instead if you expect many elements in the set.
49  static_assert(N <= 32, "N should be small");
50 
51 public:
52  using size_type = size_t;
53 
54  SmallSet() = default;
55 
56  LLVM_NODISCARD bool empty() const {
57  return Vector.empty() && Set.empty();
58  }
59 
60  size_type size() const {
61  return isSmall() ? Vector.size() : Set.size();
62  }
63 
64  /// count - Return 1 if the element is in the set, 0 otherwise.
65  size_type count(const T &V) const {
66  if (isSmall()) {
67  // Since the collection is small, just do a linear search.
68  return vfind(V) == Vector.end() ? 0 : 1;
69  } else {
70  return Set.count(V);
71  }
72  }
73 
74  /// insert - Insert an element into the set if it isn't already there.
75  /// Returns true if the element is inserted (it was not in the set before).
76  /// The first value of the returned pair is unused and provided for
77  /// partial compatibility with the standard library self-associative container
78  /// concept.
79  // FIXME: Add iterators that abstract over the small and large form, and then
80  // return those here.
81  std::pair<NoneType, bool> insert(const T &V) {
82  if (!isSmall())
83  return std::make_pair(None, Set.insert(V).second);
84 
85  VIterator I = vfind(V);
86  if (I != Vector.end()) // Don't reinsert if it already exists.
87  return std::make_pair(None, false);
88  if (Vector.size() < N) {
89  Vector.push_back(V);
90  return std::make_pair(None, true);
91  }
92 
93  // Otherwise, grow from vector to set.
94  while (!Vector.empty()) {
95  Set.insert(Vector.back());
96  Vector.pop_back();
97  }
98  Set.insert(V);
99  return std::make_pair(None, true);
100  }
101 
102  template <typename IterT>
103  void insert(IterT I, IterT E) {
104  for (; I != E; ++I)
105  insert(*I);
106  }
107 
108  bool erase(const T &V) {
109  if (!isSmall())
110  return Set.erase(V);
111  for (mutable_iterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
112  if (*I == V) {
113  Vector.erase(I);
114  return true;
115  }
116  return false;
117  }
118 
119  void clear() {
120  Vector.clear();
121  Set.clear();
122  }
123 
124 private:
125  bool isSmall() const { return Set.empty(); }
126 
127  VIterator vfind(const T &V) const {
128  for (VIterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
129  if (*I == V)
130  return I;
131  return Vector.end();
132  }
133 };
134 
135 /// If this set is of pointer values, transparently switch over to using
136 /// SmallPtrSet for performance.
137 template <typename PointeeType, unsigned N>
138 class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N> {};
139 
140 } // end namespace llvm
141 
142 #endif // LLVM_ADT_SMALLSET_H
typename SuperClass::const_iterator const_iterator
Definition: SmallVector.h:329
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
LLVM_ATTRIBUTE_ALWAYS_INLINE size_type size() const
Definition: SmallVector.h:136
bool erase(const T &V)
Definition: SmallSet.h:108
LLVM_NODISCARD bool empty() const
Definition: SmallSet.h:56
void clear()
Definition: SmallSet.h:119
void insert(IterT I, IterT E)
Definition: SmallSet.h:103
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
LLVM_ATTRIBUTE_ALWAYS_INLINE iterator begin()
Definition: SmallVector.h:116
SmallSet - This maintains a set of unique values, optimizing for the case when the set is small (less...
Definition: SmallSet.h:36
size_type size() const
Definition: SmallSet.h:60
std::pair< NoneType, bool > insert(const T &V)
insert - Insert an element into the set if it isn&#39;t already there.
Definition: SmallSet.h:81
iterator erase(const_iterator CI)
Definition: SmallVector.h:449
This is a &#39;vector&#39; (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:864
typename SuperClass::iterator iterator
Definition: SmallVector.h:328
LLVM_ATTRIBUTE_ALWAYS_INLINE iterator end()
Definition: SmallVector.h:120
LLVM_NODISCARD bool empty() const
Definition: SmallVector.h:61
#define I(x, y, z)
Definition: MD5.cpp:58
#define N
SmallSet()=default
#define LLVM_NODISCARD
LLVM_NODISCARD - Warn if a type or return value is discarded.
Definition: Compiler.h:126
size_type count(const T &V) const
count - Return 1 if the element is in the set, 0 otherwise.
Definition: SmallSet.h:65