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 * 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.api.replacements;

import java.lang.annotation.ElementType;

import java.lang.annotation.Retention;

import java.lang.annotation.RetentionPolicy;

import java.lang.annotation.Target;

import java.lang.reflect.Array;

import jdk.vm.ci.meta.Signature;

/**

 * Denotes a method whose body is used by a compiler as the substitute (or intrinsification) of

 * another method. The exact mechanism used to do the substitution is compiler dependent but every

 *

 * A compiler may support partial intrinsification where only a part of a method is implemented by

 * the compiler. The unsupported path is expressed by a call to either the original or substitute

 * method from within the substitute method. Such as call is a <i>partial intrinsic exit</i>.

 *

 * For example, here's a HotSpot specific intrinsic for {@link Array#newInstance(Class, int)} that

 * only handles the case where the VM representation of the array class to be instantiated already

 * exists:

 *

 * <pre>

 * @MethodSubstitution

 * public static Object newInstance(Class<?> componentType, int length) {

 *     if (componentType == null || loadKlassFromObject(componentType, arrayKlassOffset(INJECTED_VMCONFIG), CLASS_ARRAY_KLASS_LOCATION).isNull()) {

 *         // Array class not yet created - exit the intrinsic and call the original method

 *         return newInstance(componentType, length);

 *     }

 *     return DynamicNewArrayNode.newArray(GraalDirectives.guardingNonNull(componentType), length, JavaKind.Object);

 * }

 * </pre>

 *

 * Here's the same intrinsification where the exit is expressed as a call to the original method:

 *

 * <pre>

 * @MethodSubstitution

 * public static Object newInstance(Class<?> componentType, int length) {

 *     if (componentType == null || loadKlassFromObject(componentType, arrayKlassOffset(INJECTED_VMCONFIG), CLASS_ARRAY_KLASS_LOCATION).isNull()) {

 *         // Array class not yet created - exit the intrinsic and call the original method

 *         return java.lang.reflect.newInstance(componentType, length);

 *     }

 *     return DynamicNewArrayNode.newArray(GraalDirectives.guardingNonNull(componentType), length, JavaKind.Object);

 * }

 * </pre>

 *

 * A condition for a partial intrinsic exit is that it is uses the unmodified parameters of the

 * substitute as arguments to the partial intrinsic exit call. There must also be no side effecting

 * instruction between the start of the substitute method and the partial intrinsic exit.

 */

@Retention(RetentionPolicy.RUNTIME)

@Target(ElementType.METHOD)

public @interface MethodSubstitution {

    /**

     * Gets the name of the original method.

     * <p>

     * If the default value is specified for this element, then the name of the original method is

     * same as the substitute method.

     */

    String value() default "";

    /**

     * Determines if the original method is static.

     */

    boolean isStatic() default true;

    /**

     * Gets the {@linkplain Signature#toMethodDescriptor signature} of the original method.

     * <p>

     * If the default value is specified for this element, then the signature of the original method

     * is the same as the substitute method.

     */

    String signature() default "";

    /**

     * Determines if the substitution is for a method that may not be part of the runtime. For

     * example, a method introduced in a later JDK version. Substitutions for such methods are

     * omitted if the original method cannot be found.

     */

    boolean optional() default false;

}