MaximumSpanningTree.h revision 059a983531dd13618fc671c70a175bdb4e87ec47 
1//===- llvm/Analysis/MaximumSpanningTree.h - Interface ----------*- 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 module privides means for calculating a maximum spanning tree for a
11// given set of weighted edges. The type parameter T is the type of a node.
12//
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_ANALYSIS_MAXIMUMSPANNINGTREE_H
16#define LLVM_ANALYSIS_MAXIMUMSPANNINGTREE_H
17
18#include "llvm/BasicBlock.h"
19#include "llvm/ADT/EquivalenceClasses.h"
20#include <vector>
21#include <algorithm>
22
23namespace llvm {
24
25  /// MaximumSpanningTree - A MST implementation.
26  /// The type parameter T determines the type of the nodes of the graph.
27  template <typename T>
28  class MaximumSpanningTree {
29
30    // A comparing class for comparing weighted edges.
31    template <typename CT>
32    struct EdgeWeightCompare {
33      bool operator()(typename MaximumSpanningTree<CT>::EdgeWeight X,
34                      typename MaximumSpanningTree<CT>::EdgeWeight Y) const {
35        if (X.second > Y.second) return true;
36        if (X.second < Y.second) return false;
37        if (const BasicBlock *BBX = dyn_cast<BasicBlock>(X.first.first)) {
38          if (const BasicBlock *BBY = dyn_cast<BasicBlock>(Y.first.first)) {
39            if (BBX->size() > BBY->size()) return true;
40            if (BBX->size() < BBY->size()) return false;
41          }
42        }
43        if (const BasicBlock *BBX = dyn_cast<BasicBlock>(X.first.second)) {
44          if (const BasicBlock *BBY = dyn_cast<BasicBlock>(Y.first.second)) {
45            if (BBX->size() > BBY->size()) return true;
46            if (BBX->size() < BBY->size()) return false;
47          }
48        }
49        return false;
50      }
51    };
52
53  public:
54    typedef std::pair<const T*, const T*> Edge;
55    typedef std::pair<Edge, double> EdgeWeight;
56    typedef std::vector<EdgeWeight> EdgeWeights;
57  protected:
58    typedef std::vector<Edge> MaxSpanTree;
59
60    MaxSpanTree MST;
61
62  public:
63    static char ID; // Class identification, replacement for typeinfo
64
65    /// MaximumSpanningTree() - Takes a vector of weighted edges and returns a
66    /// spanning tree.
67    MaximumSpanningTree(EdgeWeights &EdgeVector) {
68
69      std::stable_sort(EdgeVector.begin(), EdgeVector.end(), EdgeWeightCompare<T>());
70
71      // Create spanning tree, Forest contains a special data structure
72      // that makes checking if two nodes are already in a common (sub-)tree
73      // fast and cheap.
74      EquivalenceClasses<const T*> Forest;
75      for (typename EdgeWeights::iterator EWi = EdgeVector.begin(),
76           EWe = EdgeVector.end(); EWi != EWe; ++EWi) {
77        Edge e = (*EWi).first;
78
79        Forest.insert(e.first);
80        Forest.insert(e.second);
81      }
82
83      // Iterate over the sorted edges, biggest first.
84      for (typename EdgeWeights::iterator EWi = EdgeVector.begin(),
85           EWe = EdgeVector.end(); EWi != EWe; ++EWi) {
86        Edge e = (*EWi).first;
87
88        if (Forest.findLeader(e.first) != Forest.findLeader(e.second)) {
89          Forest.unionSets(e.first, e.second);
90          // So we know now that the edge is not already in a subtree, so we push
91          // the edge to the MST.
92          MST.push_back(e);
93        }
94      }
95    }
96
97    typename MaxSpanTree::iterator begin() {
98      return MST.begin();
99    }
100
101    typename MaxSpanTree::iterator end() {
102      return MST.end();
103    }
104  };
105
106} // End llvm namespace
107
108#endif
109