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111 lines
3.6 KiB
C++
111 lines
3.6 KiB
C++
//===- llvm/Analysis/MaximumSpanningTree.h - Interface ----------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This module provides means for calculating a maximum spanning tree for a
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// given set of weighted edges. The type parameter T is the type of a node.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_LIB_TRANSFORMS_INSTRUMENTATION_MAXIMUMSPANNINGTREE_H
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#define LLVM_LIB_TRANSFORMS_INSTRUMENTATION_MAXIMUMSPANNINGTREE_H
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#include "llvm/ADT/EquivalenceClasses.h"
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#include "llvm/IR/BasicBlock.h"
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#include <algorithm>
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#include <vector>
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namespace llvm {
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/// MaximumSpanningTree - A MST implementation.
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/// The type parameter T determines the type of the nodes of the graph.
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template <typename T>
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class MaximumSpanningTree {
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public:
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typedef std::pair<const T*, const T*> Edge;
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typedef std::pair<Edge, double> EdgeWeight;
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typedef std::vector<EdgeWeight> EdgeWeights;
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protected:
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typedef std::vector<Edge> MaxSpanTree;
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MaxSpanTree MST;
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private:
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// A comparing class for comparing weighted edges.
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struct EdgeWeightCompare {
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static bool getBlockSize(const T *X) {
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const BasicBlock *BB = dyn_cast_or_null<BasicBlock>(X);
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return BB ? BB->size() : 0;
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}
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bool operator()(EdgeWeight X, EdgeWeight Y) const {
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if (X.second > Y.second) return true;
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if (X.second < Y.second) return false;
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// Equal edge weights: break ties by comparing block sizes.
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size_t XSizeA = getBlockSize(X.first.first);
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size_t YSizeA = getBlockSize(Y.first.first);
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if (XSizeA > YSizeA) return true;
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if (XSizeA < YSizeA) return false;
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size_t XSizeB = getBlockSize(X.first.second);
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size_t YSizeB = getBlockSize(Y.first.second);
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if (XSizeB > YSizeB) return true;
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if (XSizeB < YSizeB) return false;
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return false;
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}
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};
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public:
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static char ID; // Class identification, replacement for typeinfo
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/// MaximumSpanningTree() - Takes a vector of weighted edges and returns a
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/// spanning tree.
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MaximumSpanningTree(EdgeWeights &EdgeVector) {
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std::stable_sort(EdgeVector.begin(), EdgeVector.end(), EdgeWeightCompare());
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// Create spanning tree, Forest contains a special data structure
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// that makes checking if two nodes are already in a common (sub-)tree
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// fast and cheap.
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EquivalenceClasses<const T*> Forest;
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for (typename EdgeWeights::iterator EWi = EdgeVector.begin(),
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EWe = EdgeVector.end(); EWi != EWe; ++EWi) {
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Edge e = (*EWi).first;
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Forest.insert(e.first);
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Forest.insert(e.second);
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}
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// Iterate over the sorted edges, biggest first.
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for (typename EdgeWeights::iterator EWi = EdgeVector.begin(),
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EWe = EdgeVector.end(); EWi != EWe; ++EWi) {
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Edge e = (*EWi).first;
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if (Forest.findLeader(e.first) != Forest.findLeader(e.second)) {
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Forest.unionSets(e.first, e.second);
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// So we know now that the edge is not already in a subtree, so we push
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// the edge to the MST.
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MST.push_back(e);
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}
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}
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}
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typename MaxSpanTree::iterator begin() {
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return MST.begin();
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}
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typename MaxSpanTree::iterator end() {
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return MST.end();
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}
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};
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} // End llvm namespace
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#endif // LLVM_LIB_TRANSFORMS_INSTRUMENTATION_MAXIMUMSPANNINGTREE_H
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