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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/SmallVector.h"
     18 #include "llvm/ADT/SmallPtrSet.h"
     19 #include <set>
     20 
     21 namespace 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.
     30 template <typename T, unsigned N>
     31 class SmallSet {
     32   /// Use a SmallVector to hold the elements here (even though it will never
     33   /// reach its '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;
     39 public:
     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   template <typename IterT>
     80   void insert(IterT I, IterT E) {
     81     for (; I != E; ++I)
     82       insert(*I);
     83   }
     84 
     85   bool erase(const T &V) {
     86     if (!isSmall())
     87       return Set.erase(V);
     88     for (mutable_iterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
     89       if (*I == V) {
     90         Vector.erase(I);
     91         return true;
     92       }
     93     return false;
     94   }
     95 
     96   void clear() {
     97     Vector.clear();
     98     Set.clear();
     99   }
    100 private:
    101   bool isSmall() const { return Set.empty(); }
    102 
    103   VIterator vfind(const T &V) const {
    104     for (VIterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
    105       if (*I == V)
    106         return I;
    107     return Vector.end();
    108   }
    109 };
    110 
    111 /// If this set is of pointer values, transparently switch over to using
    112 /// SmallPtrSet for performance.
    113 template <typename PointeeType, unsigned N>
    114 class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N> {};
    115 
    116 } // end namespace llvm
    117 
    118 #endif
    119