/*
 * Copyright (c) 2011, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code 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 General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
package com.oracle.graal.phases.common;

import java.util.*;

import com.oracle.graal.debug.*;
import com.oracle.graal.graph.*;
import com.oracle.graal.nodes.*;
import com.oracle.graal.nodes.util.*;
import com.oracle.graal.phases.*;

/**
 * This phase will find branches which always end with a {@link DeoptimizeNode} and replace their
 * {@link ControlSplitNode ControlSplitNodes} with {@link FixedGuardNode FixedGuardNodes}.
 * 
 * This is currently only done for branches that start from a {@link IfNode}. If it encounters a
 * branch starting at an other kind of {@link ControlSplitNode}, it will only bring the
 * {@link DeoptimizeNode} as close to the {@link ControlSplitNode} as possible.
 * 
 */
public class ConvertDeoptimizeToGuardPhase extends Phase {

    private static AbstractBeginNode findBeginNode(Node startNode) {
        Node n = startNode;
        while (true) {
            if (n instanceof AbstractBeginNode) {
                return (AbstractBeginNode) n;
            } else {
                n = n.predecessor();
            }
        }
    }

    @Override
    protected void run(final StructuredGraph graph) {
        if (graph.getNodes(DeoptimizeNode.class).isEmpty()) {
            return;
        }

        for (DeoptimizeNode d : graph.getNodes(DeoptimizeNode.class)) {
            assert d.isAlive();
            visitDeoptBegin(findBeginNode(d), d, graph);
        }

        new DeadCodeEliminationPhase().apply(graph);
    }

    private void visitDeoptBegin(AbstractBeginNode deoptBegin, DeoptimizeNode deopt, StructuredGraph graph) {
        if (deoptBegin instanceof MergeNode) {
            MergeNode mergeNode = (MergeNode) deoptBegin;
            Debug.log("Visiting %s followed by %s", mergeNode, deopt);
            List<AbstractBeginNode> begins = new ArrayList<>();
            for (AbstractEndNode end : mergeNode.forwardEnds()) {
                AbstractBeginNode newBeginNode = findBeginNode(end);
                assert !begins.contains(newBeginNode);
                begins.add(newBeginNode);
            }
            for (AbstractBeginNode begin : begins) {
                assert !begin.isDeleted();
                visitDeoptBegin(begin, deopt, graph);
            }
            assert mergeNode.isDeleted();
            return;
        } else if (deoptBegin.predecessor() instanceof IfNode) {
            IfNode ifNode = (IfNode) deoptBegin.predecessor();
            AbstractBeginNode otherBegin = ifNode.trueSuccessor();
            LogicNode conditionNode = ifNode.condition();
            FixedGuardNode guard = graph.add(new FixedGuardNode(conditionNode, deopt.reason(), deopt.action(), deoptBegin == ifNode.trueSuccessor()));
            FixedWithNextNode pred = (FixedWithNextNode) ifNode.predecessor();
            AbstractBeginNode survivingSuccessor;
            if (deoptBegin == ifNode.trueSuccessor()) {
                survivingSuccessor = ifNode.falseSuccessor();
            } else {
                survivingSuccessor = ifNode.trueSuccessor();
            }
            graph.removeSplitPropagate(ifNode, survivingSuccessor);
            ProxyNode proxyGuard = null;
            for (Node n : survivingSuccessor.usages().snapshot()) {
                if (n instanceof GuardNode || n instanceof ProxyNode) {
                    // Keep wired to the begin node.
                } else {
                    // Rewire to the fixed guard.
                    if (survivingSuccessor instanceof LoopExitNode) {
                        if (proxyGuard == null) {
                            proxyGuard = ProxyNode.forGuard(guard, survivingSuccessor, graph);
                        }
                        n.replaceFirstInput(survivingSuccessor, proxyGuard);
                    } else {
                        n.replaceFirstInput(survivingSuccessor, guard);
                    }
                }
            }
            Debug.log("Converting %s on %-5s branch of %s to guard for remaining branch %s.", deopt, deoptBegin == ifNode.trueSuccessor() ? "true" : "false", ifNode, otherBegin);
            FixedNode next = pred.next();
            pred.setNext(guard);
            guard.setNext(next);
            return;
        }

        // We could not convert the control split - at least cut off control flow after the split.
        FixedWithNextNode deoptPred = deoptBegin;
        FixedNode next = deoptPred.next();

        if (next != deopt) {
            DeoptimizeNode newDeoptNode = (DeoptimizeNode) deopt.clone(graph);
            deoptPred.setNext(newDeoptNode);
            assert deoptPred == newDeoptNode.predecessor();
            GraphUtil.killCFG(next);
        }
    }
}