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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78359 91177308-0d34-0410-b5e6-96231b3b80d8
111 lines
2.8 KiB
C++
111 lines
2.8 KiB
C++
//===-- ExhaustiveSolver.h - Brute Force PBQP Solver -----------*- C++ --*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// Uses a trivial brute force algorithm to solve a PBQP problem.
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// PBQP is NP-HARD - This solver should only be used for debugging small
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// problems.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_CODEGEN_PBQP_EXHAUSTIVESOLVER_H
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#define LLVM_CODEGEN_PBQP_EXHAUSTIVESOLVER_H
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#include "Solver.h"
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namespace PBQP {
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/// A brute force PBQP solver. This solver takes exponential time. It should
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/// only be used for debugging purposes.
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class ExhaustiveSolverImpl {
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private:
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const SimpleGraph &g;
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PBQPNum getSolutionCost(const Solution &solution) const {
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PBQPNum cost = 0.0;
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for (SimpleGraph::ConstNodeIterator
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nodeItr = g.nodesBegin(), nodeEnd = g.nodesEnd();
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nodeItr != nodeEnd; ++nodeItr) {
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unsigned nodeId = g.getNodeID(nodeItr);
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cost += g.getNodeCosts(nodeItr)[solution.getSelection(nodeId)];
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}
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for (SimpleGraph::ConstEdgeIterator
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edgeItr = g.edgesBegin(), edgeEnd = g.edgesEnd();
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edgeItr != edgeEnd; ++edgeItr) {
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SimpleGraph::ConstNodeIterator n1 = g.getEdgeNode1Itr(edgeItr),
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n2 = g.getEdgeNode2Itr(edgeItr);
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unsigned sol1 = solution.getSelection(g.getNodeID(n1)),
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sol2 = solution.getSelection(g.getNodeID(n2));
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cost += g.getEdgeCosts(edgeItr)[sol1][sol2];
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}
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return cost;
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}
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public:
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ExhaustiveSolverImpl(const SimpleGraph &g) : g(g) {}
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Solution solve() const {
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Solution current(g.getNumNodes(), true), optimal(current);
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PBQPNum bestCost = std::numeric_limits<PBQPNum>::infinity();
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bool finished = false;
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while (!finished) {
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PBQPNum currentCost = getSolutionCost(current);
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if (currentCost < bestCost) {
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optimal = current;
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bestCost = currentCost;
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}
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// assume we're done.
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finished = true;
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for (unsigned i = 0; i < g.getNumNodes(); ++i) {
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if (current.getSelection(i) ==
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(g.getNodeCosts(g.getNodeItr(i)).getLength() - 1)) {
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current.setSelection(i, 0);
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}
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else {
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current.setSelection(i, current.getSelection(i) + 1);
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finished = false;
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break;
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}
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}
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}
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optimal.setSolutionCost(bestCost);
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return optimal;
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}
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};
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class ExhaustiveSolver : public Solver {
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public:
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~ExhaustiveSolver() {}
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Solution solve(const SimpleGraph &g) const {
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ExhaustiveSolverImpl solver(g);
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return solver.solve();
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}
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};
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}
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#endif // LLVM_CODGEN_PBQP_EXHAUSTIVESOLVER_HPP
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