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 * Copyright (c) 2014, 2019, 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 jdk.vm.ci.hotspot;

import static jdk.vm.ci.hotspot.CompilerToVM.compilerToVM;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.Formatter;

import java.util.List;

import jdk.vm.ci.code.BailoutException;

import jdk.vm.ci.meta.JavaConstant;

import jdk.vm.ci.meta.SpeculationLog;

/**

 * Implements a {@link SpeculationLog} that can be used to:

 * <ul>

 * <li>Query failed speculations recorded in a native linked list of {@code FailedSpeculation}s (see

 * methodData.hpp).</li>

 * <li>Make speculations during compilation and record them in compiled code. This must only be done

 * on compilation-local {@link HotSpotSpeculationLog} objects.</li>

 * </ul>

 *

 * The choice of constructor determines whether the native failed speculations list is

 * {@linkplain #managesFailedSpeculations() managed} by a {@link HotSpotSpeculationLog} object.

 */

public class HotSpotSpeculationLog implements SpeculationLog {

    private static final byte[] NO_FLATTENED_SPECULATIONS = {};

    /**

     * Creates a speculation log that manages a failed speculation list. That is, when this object

     * dies, the native resources of the list are freed.

     *

     * @see #managesFailedSpeculations()

     * @see #getFailedSpeculationsAddress()

     */

    public HotSpotSpeculationLog() {

        managesFailedSpeculations = true;

    }

    /**

     * Creates a speculation log that reads from an externally managed failed speculation list. That

     * is, the lifetime of the list is independent of this object.

     *

     * @param failedSpeculationsAddress an address in native memory at which the pointer to the

     *            externally managed sailed speculation list resides

     */

    public HotSpotSpeculationLog(long failedSpeculationsAddress) {

        if (failedSpeculationsAddress == 0) {

            throw new IllegalArgumentException("failedSpeculationsAddress cannot be 0");

        }

        this.failedSpeculationsAddress = failedSpeculationsAddress;

        managesFailedSpeculations = false;

    }

    /**

     * Gets the address of the pointer to the native failed speculations list.

     *

     * @see #managesFailedSpeculations()

     */

    public long getFailedSpeculationsAddress() {

        if (managesFailedSpeculations) {

            synchronized (this) {

                if (failedSpeculationsAddress == 0L) {

                    failedSpeculationsAddress = UnsafeAccess.UNSAFE.allocateMemory(HotSpotJVMCIRuntime.getHostWordKind().getByteCount());

                    UnsafeAccess.UNSAFE.putAddress(failedSpeculationsAddress, 0L);

                    LogCleaner c = new LogCleaner(this, failedSpeculationsAddress);

                    assert c.address == failedSpeculationsAddress;

                }

            }

        }

        return failedSpeculationsAddress;

    }

    /**

     * Adds {@code speculation} to the native list of failed speculations. To update this object's

     * view of the failed speculations, {@link #collectFailedSpeculations()} must be called after

     * this method returns.

     *

     * This method exists primarily for testing purposes. Speculations are normally only added to

     * the list by HotSpot during deoptimization.

     *

     * @return {@code false} if the speculation could not be appended to the list

     */

    public boolean addFailedSpeculation(Speculation speculation) {

        return compilerToVM().addFailedSpeculation(getFailedSpeculationsAddress(), ((HotSpotSpeculation) speculation).encoding);

    }

    /**

     * Returns {@code true} if the value returned by {@link #getFailedSpeculationsAddress()} is only

     * valid only as long as this object is alive, {@code false} otherwise.

     */

    public boolean managesFailedSpeculations() {

        return managesFailedSpeculations;

    }

    public static final class HotSpotSpeculation extends Speculation {

        /**

         * A speculation id is a long encoding an offset (high 32 bits) and a length (low 32 bts).

         * Combined, the index and length denote where the {@linkplain #encoding encoded

         * speculation} is in a {@linkplain HotSpotSpeculationLog#getFlattenedSpeculations

         * flattened} speculations array.

         */

        private final JavaConstant id;

        private final byte[] encoding;

        HotSpotSpeculation(SpeculationReason reason, JavaConstant id, byte[] encoding) {

            super(reason);

            this.id = id;

            this.encoding = encoding;

        }

        public JavaConstant getEncoding() {

            return id;

        }

        @Override

        public String toString() {

            long indexAndLength = id.asLong();

            int index = decodeIndex(indexAndLength);

            int length = decodeLength(indexAndLength);

            return String.format("{0x%016x[index: %d, len: %d, hash: 0x%x]: %s}", indexAndLength, index, length, Arrays.hashCode(encoding), getReason());

        }

    }

    /**

     * Address of a pointer to a set of failed speculations. The address is recorded in the nmethod

     * compiled with this speculation log such that when it fails a speculation, the speculation is

     * added to the list.

     */

    private long failedSpeculationsAddress;

    private final boolean managesFailedSpeculations;

    /**

     * The list of failed speculations read from native memory via

     * {@link CompilerToVM#getFailedSpeculations}.

     */

    private byte[][] failedSpeculations;

    /**

     * Speculations made during the compilation associated with this log.

     */

    private List<byte[]> speculations;

    private List<SpeculationReason> speculationReasons;

    @Override

    public void collectFailedSpeculations() {

        if (failedSpeculationsAddress != 0 && UnsafeAccess.UNSAFE.getLong(failedSpeculationsAddress) != 0) {

            failedSpeculations = compilerToVM().getFailedSpeculations(failedSpeculationsAddress, failedSpeculations);

            assert failedSpeculations.getClass() == byte[][].class;

        }

    }

    byte[] getFlattenedSpeculations(boolean validate) {

        if (speculations == null) {

            return NO_FLATTENED_SPECULATIONS;

        }

        if (validate) {

            int newFailuresStart = failedSpeculations == null ? 0 : failedSpeculations.length;

            collectFailedSpeculations();

            if (failedSpeculations != null && failedSpeculations.length != newFailuresStart) {

                for (SpeculationReason reason : speculationReasons) {

                    byte[] encoding = encode(reason);

                    // Only check against new failures

                    if (contains(failedSpeculations, newFailuresStart, encoding)) {

                        throw new BailoutException(false, "Speculation failed: " + reason);

                    }

                }

            }

        }

        int size = 0;

        for (byte[] s : speculations) {

            size += s.length;

        }

        byte[] result = new byte[size];

        size = 0;

        for (byte[] s : speculations) {

            System.arraycopy(s, 0, result, size, s.length);

            size += s.length;

        }

        return result;

    }

    @Override

    public boolean maySpeculate(SpeculationReason reason) {

        if (failedSpeculations == null) {

            collectFailedSpeculations();

        }

        if (failedSpeculations != null && failedSpeculations.length != 0) {

            byte[] encoding = encode(reason);

            return !contains(failedSpeculations, 0, encoding);

        }

        return true;

    }

    /**

     * @return {@code true} if {@code needle} is in {@code haystack[fromIndex..haystack.length-1]}

     */

    private static boolean contains(byte[][] haystack, int fromIndex, byte[] needle) {

        for (int i = fromIndex; i < haystack.length; i++) {

            byte[] fs = haystack[i];

            if (Arrays.equals(fs, needle)) {

                return true;

            }

        }

        return false;

    }

    private static long encodeIndexAndLength(int index, int length) {

        return ((long) index) << 32 | length;

    }

    private static int decodeIndex(long indexAndLength) {

        return (int) (indexAndLength >>> 32);

    }

    private static int decodeLength(long indexAndLength) {

        return (int) indexAndLength & 0xFFFFFFFF;

    }

    @Override

    public Speculation speculate(SpeculationReason reason) {

        byte[] encoding = encode(reason);

        JavaConstant id;

        if (speculations == null) {

            speculations = new ArrayList<>();

            speculationReasons = new ArrayList<>();

            id = JavaConstant.forLong(encodeIndexAndLength(0, encoding.length));

            speculations.add(encoding);

            speculationReasons.add(reason);

        } else {

            id = null;

            int flattenedIndex = 0;

            for (byte[] fs : speculations) {

                if (Arrays.equals(fs, encoding)) {

                    id = JavaConstant.forLong(encodeIndexAndLength(flattenedIndex, fs.length));

                    break;

                }

                flattenedIndex += fs.length;

            }

            if (id == null) {

                id = JavaConstant.forLong(encodeIndexAndLength(flattenedIndex, encoding.length));

                speculations.add(encoding);

                speculationReasons.add(reason);

            }

        }

        return new HotSpotSpeculation(reason, id, encoding);

    }

    private static byte[] encode(SpeculationReason reason) {

        HotSpotSpeculationEncoding encoding = (HotSpotSpeculationEncoding) reason.encode(HotSpotSpeculationEncoding::new);

        byte[] result = encoding == null ? null : encoding.getByteArray();

        if (result == null) {

            throw new IllegalArgumentException(HotSpotSpeculationLog.class.getName() + " expects " + reason.getClass().getName() + ".encode() to return a non-empty encoding");

        }

        return result;

    }

    @Override

    public boolean hasSpeculations() {

        return speculations != null;

    }

    @Override

    public Speculation lookupSpeculation(JavaConstant constant) {

        if (constant.isDefaultForKind()) {

            return NO_SPECULATION;

        }

        int flattenedIndex = decodeIndex(constant.asLong());

        int index = 0;

        for (byte[] s : speculations) {

            if (flattenedIndex == 0) {

                SpeculationReason reason = speculationReasons.get(index);

                return new HotSpotSpeculation(reason, constant, s);

            }

            index++;

            flattenedIndex -= s.length;

        }

        throw new IllegalArgumentException("Unknown encoded speculation: " + constant);

    }

    @Override

    public String toString() {

        Formatter buf = new Formatter();

        buf.format("{managed:%s, failedSpeculationsAddress:0x%x, failedSpeculations:[", managesFailedSpeculations, failedSpeculationsAddress);

        String sep = "";

        if (failedSpeculations != null) {

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

                buf.format("%s{len:%d, hash:0x%x}", sep, failedSpeculations[i].length, Arrays.hashCode(failedSpeculations[i]));

                sep = ", ";

            }

        }

        buf.format("], speculations:[");

        int size = 0;

        if (speculations != null) {

            sep = "";

            for (int i = 0; i < speculations.size(); i++) {

                byte[] s = speculations.get(i);

                size += s.length;

                buf.format("%s{len:%d, hash:0x%x, reason:{%s}}", sep, s.length, Arrays.hashCode(s), speculationReasons.get(i));

                sep = ", ";

            }

        }

        buf.format("], len:%d, hash:0x%x}", size, Arrays.hashCode(getFlattenedSpeculations(false)));

        return buf.toString();

    }

    /**

     * Frees the native memory resources associated with {@link HotSpotSpeculationLog}s once they

     * become reclaimable.

     */

    private static final class LogCleaner extends Cleaner {

        LogCleaner(HotSpotSpeculationLog referent, long address) {

            super(referent);

            this.address = address;

        }

        @Override

        void doCleanup() {

            long pointer = UnsafeAccess.UNSAFE.getAddress(address);

            if (pointer != 0) {

                compilerToVM().releaseFailedSpeculations(address);

            }

            UnsafeAccess.UNSAFE.freeMemory(address);

        }

        final long address;

    }

}