/*

 * Copyright (c) 2011, 2018, 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

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 */

package org.graalvm.compiler.java;

import static org.graalvm.compiler.nodes.cfg.ControlFlowGraph.multiplyRelativeFrequencies;

import java.util.List;

import jdk.internal.vm.compiler.collections.EconomicMap;

import org.graalvm.compiler.nodes.AbstractBeginNode;

import org.graalvm.compiler.nodes.AbstractMergeNode;

import org.graalvm.compiler.nodes.ControlSplitNode;

import org.graalvm.compiler.nodes.FixedNode;

import org.graalvm.compiler.nodes.LoopBeginNode;

import org.graalvm.compiler.nodes.LoopExitNode;

import org.graalvm.compiler.nodes.StructuredGraph;

import org.graalvm.compiler.nodes.cfg.ControlFlowGraph;

import org.graalvm.compiler.phases.Phase;

import org.graalvm.compiler.phases.graph.ReentrantNodeIterator;

public final class ComputeLoopFrequenciesClosure extends ReentrantNodeIterator.NodeIteratorClosure<Double> {

    private static final ComputeLoopFrequenciesClosure INSTANCE = new ComputeLoopFrequenciesClosure();

    private ComputeLoopFrequenciesClosure() {

        // nothing to do

    }

    @Override

    protected Double processNode(FixedNode node, Double currentState) {

        // normal nodes never change the probability of a path

        return currentState;

    }

    @Override

    protected Double merge(AbstractMergeNode merge, List<Double> states) {

        // a merge has the sum of all predecessor probabilities

        double result = 0.0;

        for (double d : states) {

            result += d;

        }

        return result;

    }

    @Override

    protected Double afterSplit(AbstractBeginNode node, Double oldState) {

        // a control split splits up the probability

        ControlSplitNode split = (ControlSplitNode) node.predecessor();

        return oldState * split.probability(node);

    }

    @Override

    protected EconomicMap<LoopExitNode, Double> processLoop(LoopBeginNode loop, Double initialState) {

        EconomicMap<LoopExitNode, Double> exitStates = ReentrantNodeIterator.processLoop(this, loop, 1D).exitStates;

        double exitRelativeFrequency = 0.0;

        for (double d : exitStates.getValues()) {

            exitRelativeFrequency += d;

        }

        exitRelativeFrequency = Math.min(1.0, exitRelativeFrequency);

        exitRelativeFrequency = Math.max(ControlFlowGraph.MIN_RELATIVE_FREQUENCY, exitRelativeFrequency);

        double loopFrequency = 1.0 / exitRelativeFrequency;

        loop.setLoopFrequency(loopFrequency);

        double adjustmentFactor = initialState * loopFrequency;

        exitStates.replaceAll((exitNode, frequency) -> multiplyRelativeFrequencies(frequency, adjustmentFactor));

        return exitStates;

    }

    /**

     * Computes the frequencies of all loops in the given graph. This is done by performing a

     * reverse postorder iteration and computing the probability of all fixed nodes. The combined

     * probability of all exits of a loop can be used to compute the loop's expected frequency.

     */

    public static void compute(StructuredGraph graph) {

        if (graph.hasLoops()) {

            ReentrantNodeIterator.apply(INSTANCE, graph.start(), 1D);

        }

    }

    public static class ComputeLoopFrequencyPhase extends Phase {

        @Override

        protected void run(StructuredGraph graph) {

            compute(graph);

        }

    }

    public static final ComputeLoopFrequencyPhase PHASE_INSTANCE = new ComputeLoopFrequencyPhase();

}