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Truffle is a multi-language framework for executing dynamic languages that achieves high performance when combined with Graal.
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/*
 * Copyright (c) 2012, 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.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * 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.truffle.api.nodes;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Specifies for a method that the loops with constant number of invocations should be fully
 * unrolled.
 *
 * @since 0.8 or earlier
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface ExplodeLoop {

    /**
     * Controls behavior of {@link ExplodeLoop} annotation.
     *
     * @since 0.15
     */
    enum LoopExplosionKind {
        /**
         * Fully unroll all loops. The loops must have a known finite number of iterations. If a
         * loop has multiple loop ends, they are merged so that the subsequent loop iteration is
         * processed only once. For example, a loop with 4 iterations and 2 loop ends leads to
         * 1+1+1+1 = 4 copies of the loop body.
         *
         * @since 0.15
         */
        FULL_UNROLL,
        /**
         * Fully explode all loops. The loops must have a known finite number of iterations. If a
         * loop has multiple loop ends, they are not merged so that subsequent loop iterations are
         * processed multiple times. For example, a loop with 4 iterations and 2 loop ends leads to
         * 1+2+4+8 = 15 copies of the loop body.
         *
         * @since 0.15
         */
        FULL_EXPLODE,
        /**
         * Like {@link #FULL_EXPLODE}, but in addition explosion does not stop at loop exits. Code
         * after the loop is duplicated for every loop exit of every loop iteration. For example, a
         * loop with 4 iterations and 2 loop exits leads to 4 * 2 = 8 copies of the code after the
         * loop.
         *
         * @since 0.15
         */
        FULL_EXPLODE_UNTIL_RETURN,
        /**
         * like {@link #FULL_EXPLODE}, but copies of the loop body that have the exact same state
         * (all local variables have the same value) are merged. This reduces the number of copies
         * necessary, but can introduce loops again. This kind is useful for bytecode interpreter
         * loops.
         *
         * @since 0.15
         */
        MERGE_EXPLODE
    }

    /**
     * The loop explosion kind.
     *
     * @since 0.15
     */
    LoopExplosionKind kind() default LoopExplosionKind.FULL_UNROLL;

    /**
     * @deprecated Use {@link #kind} = {@link LoopExplosionKind#MERGE_EXPLODE} instead of setting
     *             this property to true.
     * @since 0.8 or earlier
     */
    @Deprecated
    boolean merge() default false;
}