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 <set>
21 
22 namespace llvm {
23 
24 /// SmallSet - This maintains a set of unique values, optimizing for the case
25 /// when the set is small (less than N).  In this case, the set can be
26 /// maintained with no mallocs.  If the set gets large, we expand to using an
27 /// std::set to maintain reasonable lookup times.
28 ///
29 /// Note that this set does not provide a way to iterate over members in the
30 /// set.
31 template <typename T, unsigned N,  typename C = std::less<T> >
32 class SmallSet {
33   /// Use a SmallVector to hold the elements here (even though it will never
34   /// reach its 'large' stage) to avoid calling the default ctors of elements
35   /// we will never use.
36   SmallVector<T, N> Vector;
37   std::set<T, C> Set;
38   typedef typename SmallVector<T, N>::const_iterator VIterator;
39   typedef typename SmallVector<T, N>::iterator mutable_iterator;
40 
41 public:
42   typedef size_t size_type;
SmallSet()43   SmallSet() {}
44 
empty()45   bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const {
46     return Vector.empty() && Set.empty();
47   }
48 
size()49   size_type size() const {
50     return isSmall() ? Vector.size() : Set.size();
51   }
52 
53   /// count - Return 1 if the element is in the set, 0 otherwise.
count(const T & V)54   size_type count(const T &V) const {
55     if (isSmall()) {
56       // Since the collection is small, just do a linear search.
57       return vfind(V) == Vector.end() ? 0 : 1;
58     } else {
59       return Set.count(V);
60     }
61   }
62 
63   /// insert - Insert an element into the set if it isn't already there.
64   /// Returns true if the element is inserted (it was not in the set before).
65   /// The first value of the returned pair is unused and provided for
66   /// partial compatibility with the standard library self-associative container
67   /// concept.
68   // FIXME: Add iterators that abstract over the small and large form, and then
69   // return those here.
insert(const T & V)70   std::pair<NoneType, bool> insert(const T &V) {
71     if (!isSmall())
72       return std::make_pair(None, Set.insert(V).second);
73 
74     VIterator I = vfind(V);
75     if (I != Vector.end())    // Don't reinsert if it already exists.
76       return std::make_pair(None, false);
77     if (Vector.size() < N) {
78       Vector.push_back(V);
79       return std::make_pair(None, true);
80     }
81 
82     // Otherwise, grow from vector to set.
83     while (!Vector.empty()) {
84       Set.insert(Vector.back());
85       Vector.pop_back();
86     }
87     Set.insert(V);
88     return std::make_pair(None, true);
89   }
90 
91   template <typename IterT>
insert(IterT I,IterT E)92   void insert(IterT I, IterT E) {
93     for (; I != E; ++I)
94       insert(*I);
95   }
96 
erase(const T & V)97   bool erase(const T &V) {
98     if (!isSmall())
99       return Set.erase(V);
100     for (mutable_iterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
101       if (*I == V) {
102         Vector.erase(I);
103         return true;
104       }
105     return false;
106   }
107 
clear()108   void clear() {
109     Vector.clear();
110     Set.clear();
111   }
112 
113 private:
isSmall()114   bool isSmall() const { return Set.empty(); }
115 
vfind(const T & V)116   VIterator vfind(const T &V) const {
117     for (VIterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
118       if (*I == V)
119         return I;
120     return Vector.end();
121   }
122 };
123 
124 /// If this set is of pointer values, transparently switch over to using
125 /// SmallPtrSet for performance.
126 template <typename PointeeType, unsigned N>
127 class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N> {};
128 
129 } // end namespace llvm
130 
131 #endif
132