/*

 * Copyright (c) 2009, 2015, 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 org.graalvm.compiler.nodes.extended;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.Comparator;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

import org.graalvm.compiler.core.common.spi.ConstantFieldProvider;

import org.graalvm.compiler.core.common.type.IntegerStamp;

import org.graalvm.compiler.core.common.type.PrimitiveStamp;

import org.graalvm.compiler.core.common.type.Stamp;

import org.graalvm.compiler.core.common.type.StampFactory;

import org.graalvm.compiler.graph.NodeClass;

import org.graalvm.compiler.graph.spi.Simplifiable;

import org.graalvm.compiler.graph.spi.SimplifierTool;

import org.graalvm.compiler.nodeinfo.NodeInfo;

import org.graalvm.compiler.nodes.AbstractBeginNode;

import org.graalvm.compiler.nodes.ConstantNode;

import org.graalvm.compiler.nodes.FixedGuardNode;

import org.graalvm.compiler.nodes.FixedWithNextNode;

import org.graalvm.compiler.nodes.LogicNode;

import org.graalvm.compiler.nodes.NodeView;

import org.graalvm.compiler.nodes.ValueNode;

import org.graalvm.compiler.nodes.calc.IntegerBelowNode;

import org.graalvm.compiler.nodes.java.LoadIndexedNode;

import org.graalvm.compiler.nodes.spi.LIRLowerable;

import org.graalvm.compiler.nodes.spi.NodeLIRBuilderTool;

import org.graalvm.compiler.nodes.util.GraphUtil;

import jdk.vm.ci.meta.DeoptimizationAction;

import jdk.vm.ci.meta.DeoptimizationReason;

import jdk.vm.ci.meta.JavaConstant;

import jdk.vm.ci.meta.JavaKind;

/**

 * The {@code IntegerSwitchNode} represents a switch on integer keys, with a sorted array of key

 * values. The actual implementation of the switch will be decided by the backend.

 */

@NodeInfo

public final class IntegerSwitchNode extends SwitchNode implements LIRLowerable, Simplifiable {

    public static final NodeClass<IntegerSwitchNode> TYPE = NodeClass.create(IntegerSwitchNode.class);

    protected final int[] keys;

    public IntegerSwitchNode(ValueNode value, AbstractBeginNode[] successors, int[] keys, double[] keyProbabilities, int[] keySuccessors) {

        super(TYPE, value, successors, keySuccessors, keyProbabilities);

        assert keySuccessors.length == keys.length + 1;

        assert keySuccessors.length == keyProbabilities.length;

        this.keys = keys;

        assert value.stamp(NodeView.DEFAULT) instanceof PrimitiveStamp && value.stamp(NodeView.DEFAULT).getStackKind().isNumericInteger();

        assert assertSorted();

    }

    private boolean assertSorted() {

        for (int i = 1; i < keys.length; i++) {

            assert keys[i - 1] < keys[i];

        }

        return true;

    }

    public IntegerSwitchNode(ValueNode value, int successorCount, int[] keys, double[] keyProbabilities, int[] keySuccessors) {

        this(value, new AbstractBeginNode[successorCount], keys, keyProbabilities, keySuccessors);

    }

    @Override

    public boolean isSorted() {

        return true;

    }

    /**

     * Gets the key at the specified index.

     *

     * @param i the index

     * @return the key at that index

     */

    @Override

    public JavaConstant keyAt(int i) {

        return JavaConstant.forInt(keys[i]);

    }

    @Override

    public int keyCount() {

        return keys.length;

    }

    @Override

    public boolean equalKeys(SwitchNode switchNode) {

        if (!(switchNode instanceof IntegerSwitchNode)) {

            return false;

        }

        IntegerSwitchNode other = (IntegerSwitchNode) switchNode;

        return Arrays.equals(keys, other.keys);

    }

    @Override

    public void generate(NodeLIRBuilderTool gen) {

        gen.emitSwitch(this);

    }

    public AbstractBeginNode successorAtKey(int key) {

        return blockSuccessor(successorIndexAtKey(key));

    }

    public int successorIndexAtKey(int key) {

        for (int i = 0; i < keyCount(); i++) {

            if (keys[i] == key) {

                return keySuccessorIndex(i);

            }

        }

        return keySuccessorIndex(keyCount());

    }

    @Override

    public void simplify(SimplifierTool tool) {

        NodeView view = NodeView.from(tool);

        if (blockSuccessorCount() == 1) {

            tool.addToWorkList(defaultSuccessor());

            graph().removeSplitPropagate(this, defaultSuccessor());

        } else if (value() instanceof ConstantNode) {

            killOtherSuccessors(tool, successorIndexAtKey(value().asJavaConstant().asInt()));

        } else if (tryOptimizeEnumSwitch(tool)) {

            return;

        } else if (tryRemoveUnreachableKeys(tool, value().stamp(view))) {

            return;

        }

    }

    static final class KeyData {

        final int key;

        final double keyProbability;

        final int keySuccessor;

        KeyData(int key, double keyProbability, int keySuccessor) {

            this.key = key;

            this.keyProbability = keyProbability;

            this.keySuccessor = keySuccessor;

        }

    }

    /**

     * Remove unreachable keys from the switch based on the stamp of the value, i.e., based on the

     * known range of the switch value.

     */

    public boolean tryRemoveUnreachableKeys(SimplifierTool tool, Stamp valueStamp) {

        if (!(valueStamp instanceof IntegerStamp)) {

            return false;

        }

        IntegerStamp integerStamp = (IntegerStamp) valueStamp;

        if (integerStamp.isUnrestricted()) {

            return false;

        }

        List<KeyData> newKeyDatas = new ArrayList<>(keys.length);

        ArrayList<AbstractBeginNode> newSuccessors = new ArrayList<>(blockSuccessorCount());

        for (int i = 0; i < keys.length; i++) {

            if (integerStamp.contains(keys[i]) && keySuccessor(i) != defaultSuccessor()) {

                newKeyDatas.add(new KeyData(keys[i], keyProbabilities[i], addNewSuccessor(keySuccessor(i), newSuccessors)));

            }

        }

        if (newKeyDatas.size() == keys.length) {

            /* All keys are reachable. */

            return false;

        } else if (newKeyDatas.size() == 0) {

            if (tool != null) {

                tool.addToWorkList(defaultSuccessor());

            }

            graph().removeSplitPropagate(this, defaultSuccessor());

            return true;

        } else {

            int newDefaultSuccessor = addNewSuccessor(defaultSuccessor(), newSuccessors);

            double newDefaultProbability = keyProbabilities[keyProbabilities.length - 1];

            doReplace(value(), newKeyDatas, newSuccessors, newDefaultSuccessor, newDefaultProbability);

            return true;

        }

    }

    /**

     * For switch statements on enum values, the Java compiler has to generate complicated code:

     * because {@link Enum#ordinal()} can change when recompiling an enum, it cannot be used

     * directly as the value that is switched on. An intermediate int[] array, which is initialized

     * once at run time based on the actual {@link Enum#ordinal()} values, is used.

     *

     * The {@link ConstantFieldProvider} of Graal already detects the int[] arrays and marks them as

     * {@link ConstantNode#isDefaultStable() stable}, i.e., the array elements are constant. The

     * code in this method detects array loads from such a stable array and re-wires the switch to

     * use the keys from the array elements, so that the array load is unnecessary.

     */

    private boolean tryOptimizeEnumSwitch(SimplifierTool tool) {

        if (!(value() instanceof LoadIndexedNode)) {

            /* Not the switch pattern we are looking for. */

            return false;

        }

        LoadIndexedNode loadIndexed = (LoadIndexedNode) value();

        if (loadIndexed.usages().count() > 1) {

            /*

             * The array load is necessary for other reasons too, so there is no benefit optimizing

             * the switch.

             */

            return false;

        }

        assert loadIndexed.usages().first() == this;

        ValueNode newValue = loadIndexed.index();

        JavaConstant arrayConstant = loadIndexed.array().asJavaConstant();

        if (arrayConstant == null || ((ConstantNode) loadIndexed.array()).getStableDimension() != 1 || !((ConstantNode) loadIndexed.array()).isDefaultStable()) {

            /*

             * The array is a constant that we can optimize. We require the array elements to be

             * constant too, since we put them as literal constants into the switch keys.

             */

            return false;

        }

        Integer optionalArrayLength = tool.getConstantReflection().readArrayLength(arrayConstant);

        if (optionalArrayLength == null) {

            /* Loading a constant value can be denied by the VM. */

            return false;

        }

        int arrayLength = optionalArrayLength;

        Map<Integer, List<Integer>> reverseArrayMapping = new HashMap<>();

        for (int i = 0; i < arrayLength; i++) {

            JavaConstant elementConstant = tool.getConstantReflection().readArrayElement(arrayConstant, i);

            if (elementConstant == null || elementConstant.getJavaKind() != JavaKind.Int) {

                /* Loading a constant value can be denied by the VM. */

                return false;

            }

            int element = elementConstant.asInt();

            /*

             * The value loaded from the array is the old switch key, the index into the array is

             * the new switch key. We build a mapping from the old switch key to new keys.

             */

            reverseArrayMapping.computeIfAbsent(element, e -> new ArrayList<>()).add(i);

        }

        /* Build high-level representation of new switch keys. */

        List<KeyData> newKeyDatas = new ArrayList<>(arrayLength);

        ArrayList<AbstractBeginNode> newSuccessors = new ArrayList<>(blockSuccessorCount());

        for (int i = 0; i < keys.length; i++) {

            List<Integer> newKeys = reverseArrayMapping.get(keys[i]);

            if (newKeys == null || newKeys.size() == 0) {

                /* The switch case is unreachable, we can ignore it. */

                continue;

            }

            /*

             * We do not have detailed profiling information about the individual new keys, so we

             * have to assume they split the probability of the old key.

             */

            double newKeyProbability = keyProbabilities[i] / newKeys.size();

            int newKeySuccessor = addNewSuccessor(keySuccessor(i), newSuccessors);

            for (int newKey : newKeys) {

                newKeyDatas.add(new KeyData(newKey, newKeyProbability, newKeySuccessor));

            }

        }

        int newDefaultSuccessor = addNewSuccessor(defaultSuccessor(), newSuccessors);

        double newDefaultProbability = keyProbabilities[keyProbabilities.length - 1];

        /*

         * We remove the array load, but we still need to preserve exception semantics by keeping

         * the bounds check. Fortunately the array length is a constant.

         */

        LogicNode boundsCheck = graph().unique(new IntegerBelowNode(newValue, ConstantNode.forInt(arrayLength, graph())));

        graph().addBeforeFixed(this, graph().add(new FixedGuardNode(boundsCheck, DeoptimizationReason.BoundsCheckException, DeoptimizationAction.InvalidateReprofile)));

        /*

         * Build the low-level representation of the new switch keys and replace ourself with a new

         * node.

         */

        doReplace(newValue, newKeyDatas, newSuccessors, newDefaultSuccessor, newDefaultProbability);

        /* The array load is now unnecessary. */

        assert loadIndexed.hasNoUsages();

        GraphUtil.removeFixedWithUnusedInputs(loadIndexed);

        return true;

    }

    private static int addNewSuccessor(AbstractBeginNode newSuccessor, ArrayList<AbstractBeginNode> newSuccessors) {

        int index = newSuccessors.indexOf(newSuccessor);

        if (index == -1) {

            index = newSuccessors.size();

            newSuccessors.add(newSuccessor);

        }

        return index;

    }

    private void doReplace(ValueNode newValue, List<KeyData> newKeyDatas, ArrayList<AbstractBeginNode> newSuccessors, int newDefaultSuccessor, double newDefaultProbability) {

        /* Sort the new keys (invariant of the IntegerSwitchNode). */

        newKeyDatas.sort(Comparator.comparingInt(k -> k.key));

        /* Create the final data arrays. */

        int newKeyCount = newKeyDatas.size();

        int[] newKeys = new int[newKeyCount];

        double[] newKeyProbabilities = new double[newKeyCount + 1];

        int[] newKeySuccessors = new int[newKeyCount + 1];

        for (int i = 0; i < newKeyCount; i++) {

            KeyData keyData = newKeyDatas.get(i);

            newKeys[i] = keyData.key;

            newKeyProbabilities[i] = keyData.keyProbability;

            newKeySuccessors[i] = keyData.keySuccessor;

        }

        newKeySuccessors[newKeyCount] = newDefaultSuccessor;

        newKeyProbabilities[newKeyCount] = newDefaultProbability;

        /* Normalize new probabilities so that they sum up to 1. */

        double totalProbability = 0;

        for (double probability : newKeyProbabilities) {

            totalProbability += probability;

        }

        if (totalProbability > 0) {

            for (int i = 0; i < newKeyProbabilities.length; i++) {

                newKeyProbabilities[i] /= totalProbability;

            }

        } else {

            for (int i = 0; i < newKeyProbabilities.length; i++) {

                newKeyProbabilities[i] = 1.0 / newKeyProbabilities.length;

            }

        }

        /*

         * Collect dead successors. Successors have to be cleaned before adding the new node to the

         * graph.

         */

        List<AbstractBeginNode> deadSuccessors = successors.filter(s -> !newSuccessors.contains(s)).snapshot();

        successors.clear();

        /*

         * Create the new switch node. This is done before removing dead successors as `killCFG`

         * could edit some of the inputs (e.g., if `newValue` is a loop-phi of the loop that dies

         * while removing successors).

         */

        AbstractBeginNode[] successorsArray = newSuccessors.toArray(new AbstractBeginNode[newSuccessors.size()]);

        SwitchNode newSwitch = graph().add(new IntegerSwitchNode(newValue, successorsArray, newKeys, newKeyProbabilities, newKeySuccessors));

        /* Remove dead successors. */

        for (AbstractBeginNode successor : deadSuccessors) {

            GraphUtil.killCFG(successor);

        }

        /* Replace ourselves with the new switch */

        ((FixedWithNextNode) predecessor()).setNext(newSwitch);

        GraphUtil.killWithUnusedFloatingInputs(this);

    }

    @Override

    public Stamp getValueStampForSuccessor(AbstractBeginNode beginNode) {

        Stamp result = null;

        if (beginNode != this.defaultSuccessor()) {

            for (int i = 0; i < keyCount(); i++) {

                if (keySuccessor(i) == beginNode) {

                    if (result == null) {

                        result = StampFactory.forConstant(keyAt(i));

                    } else {

                        result = result.meet(StampFactory.forConstant(keyAt(i)));

                    }

                }

            }

        }

        return result;

    }

}