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/*
 * Tai-e: A Static Analysis Framework for Java
 *
 * Copyright (C) 2022 Tian Tan 
 * Copyright (C) 2022 Yue Li 
 *
 * This file is part of Tai-e.
 *
 * Tai-e is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation, either version 3
 * of the License, or (at your option) any later version.
 *
 * Tai-e is distributed in the hope that it will be useful,but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General
 * Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with Tai-e. If not, see .
 */

package pascal.taie.analysis.dataflow.solver;

import pascal.taie.analysis.dataflow.analysis.DataflowAnalysis;
import pascal.taie.analysis.dataflow.fact.DataflowResult;
import pascal.taie.analysis.graph.cfg.CFG;
import pascal.taie.analysis.graph.cfg.CFGEdge;
import pascal.taie.util.collection.CollectionUtils;
import pascal.taie.util.collection.Sets;

import java.util.Comparator;
import java.util.NavigableSet;

/**
 * Work-list solver with optimization.
 */
class WorkListSolver extends AbstractSolver {

    @Override
    protected void initializeForward(DataflowAnalysis analysis,
                                     DataflowResult result) {
        CFG cfg = analysis.getCFG();
        // initialize entry
        Node entry = cfg.getEntry();
        Fact entryFact = analysis.newBoundaryFact();
        result.setInFact(entry, entryFact);
        result.setOutFact(entry, entryFact);
        cfg.forEach(node -> {
            // skip entry which has been initialized
            if (cfg.isEntry(node)) {
                return;
            }
            // initialize in fact
            if (cfg.getInDegreeOf(node) == 1) {
                cfg.getInEdgesOf(node).forEach(edge -> {
                    if (!analysis.needTransferEdge(edge)) {
                        result.setInFact(node,
                                getOrNewOutFact(result, analysis, edge.source()));
                    }
                });
            } else {
                result.setInFact(node, analysis.newInitialFact());
            }
            // initialize out fact
            getOrNewOutFact(result, analysis, node);
        });
    }

    private Fact getOrNewOutFact(DataflowResult result,
                                 DataflowAnalysis analysis,
                                 Node node) {
        Fact fact = result.getOutFact(node);
        if (fact == null) {
            fact = analysis.newInitialFact();
            result.setOutFact(node, fact);
        }
        return fact;
    }

    @Override
    protected void doSolveForward(DataflowAnalysis analysis,
                                  DataflowResult result) {
        CFG cfg = analysis.getCFG();
        NavigableSet workList = Sets.newOrderedSet(
                Comparator.comparingInt(cfg::getIndex));
        cfg.forEach(node -> {
            if (!cfg.isEntry(node)) {
                workList.add(node);
            }
        });
        while (!workList.isEmpty()) {
            Node node = workList.pollFirst();
            // meet incoming facts
            Fact in;
            int inDegree = cfg.getInDegreeOf(node);
            if (inDegree > 1) {
                in = result.getInFact(node);
                cfg.getInEdgesOf(node).forEach(inEdge -> {
                    Fact fact = result.getOutFact(inEdge.source());
                    if (analysis.needTransferEdge(inEdge)) {
                        fact = analysis.transferEdge(inEdge, fact);
                    }
                    analysis.meetInto(fact, in);
                });
            } else if (inDegree == 1) {
                CFGEdge inEdge = CollectionUtils.getOne(cfg.getInEdgesOf(node));
                if (analysis.needTransferEdge(inEdge)) {
                    in = analysis.transferEdge(inEdge,
                            result.getOutFact(inEdge.source()));
                    result.setInFact(node, in);
                } else {
                    in = result.getInFact(node);
                }
            } else {
                in = result.getInFact(node);
            }
            // apply node transfer function
            Fact out = result.getOutFact(node);
            boolean changed = analysis.transferNode(node, in, out);
            if (changed) {
                workList.addAll(cfg.getSuccsOf(node));
            }
        }
    }

    @Override
    protected void initializeBackward(DataflowAnalysis analysis,
                                      DataflowResult result) {
        CFG cfg = analysis.getCFG();
        // initialize exit
        Node exit = cfg.getExit();
        Fact exitFact = analysis.newBoundaryFact();
        result.setInFact(exit, exitFact);
        result.setOutFact(exit, exitFact);
        cfg.forEach(node -> {
            // skip exit which has been initialized
            if (cfg.isExit(node)) {
                return;
            }
            // initialize out fact
            if (cfg.getOutDegreeOf(node) == 1) {
                cfg.getOutEdgesOf(node).forEach(edge -> {
                    if (!analysis.needTransferEdge(edge)) {
                        result.setOutFact(node,
                                getOrNewInFact(result, analysis, edge.target()));
                    }
                });
            } else {
                result.setOutFact(node, analysis.newInitialFact());
            }
            // initialize in fact
            getOrNewInFact(result, analysis, node);
        });
    }

    private Fact getOrNewInFact(DataflowResult result,
                                DataflowAnalysis analysis,
                                Node node) {
        Fact fact = result.getInFact(node);
        if (fact == null) {
            fact = analysis.newInitialFact();
            result.setInFact(node, fact);
        }
        return fact;
    }

    @Override
    protected void doSolveBackward(DataflowAnalysis analysis,
                                   DataflowResult result) {
        CFG cfg = analysis.getCFG();
        NavigableSet workList = Sets.newOrderedSet(
                Comparator.comparingInt(n -> -cfg.getIndex(n)));
        cfg.forEach(node -> {
            if (!cfg.isExit(node)) {
                workList.add(node);
            }
        });
        while (!workList.isEmpty()) {
            Node node = workList.pollFirst();
            // meet incoming facts
            Fact out;
            int outDegree = cfg.getOutDegreeOf(node);
            if (outDegree > 1) {
                out = result.getOutFact(node);
                cfg.getOutEdgesOf(node).forEach(outEdge -> {
                    Fact fact = result.getInFact(outEdge.target());
                    if (analysis.needTransferEdge(outEdge)) {
                        fact = analysis.transferEdge(outEdge, fact);
                    }
                    analysis.meetInto(fact, out);
                });
            } else if (outDegree == 1) {
                CFGEdge outEdge = CollectionUtils.getOne(cfg.getOutEdgesOf(node));
                if (analysis.needTransferEdge(outEdge)) {
                    out = analysis.transferEdge(outEdge,
                            result.getInFact(outEdge.target()));
                    result.setOutFact(node, out);
                } else {
                    out = result.getOutFact(node);
                }
            } else {
                out = result.getOutFact(node);
            }
            // apply node transfer function
            Fact in = result.getInFact(node);
            boolean changed = analysis.transferNode(node, in, out);
            if (changed) {
                workList.addAll(cfg.getPredsOf(node));
            }
        }
    }
}