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package jdk.vm.ci.meta;

import java.util.Map;
import java.util.function.Supplier;


Manages unique SpeculationReason objects that denote why a deoptimization occurred. Reasons are embedded in compiled code for a method. If the compiled code deoptimizes at a position associated with a SpeculationReason, the reason is added to a set of failed speculations associated with the method. A subsequent compilation of the method can query the failed speculations via a SpeculationLog to avoid making a speculation based on invalidated reasons. This avoids repeated deoptimizations. 
/**
 * Manages unique {@link SpeculationReason} objects that denote why a deoptimization occurred.
 * Reasons are embedded in compiled code for a method. If the compiled code deoptimizes at a
 * position associated with a {@link SpeculationReason}, the reason is added to a set of failed
 * speculations associated with the method. A subsequent compilation of the method can query the
 * failed speculations via a {@link SpeculationLog} to avoid making a speculation based on
 * invalidated reasons. This avoids repeated deoptimizations.
 */
public interface SpeculationLog {
    
The specific attributes of a speculation that a compiler uses to denote a speculation in a compiled method. Typical attributes of a speculation are a bytecode position, type information about a variable being speculated on and an enum denoting the type of operation to which the speculation applies. A SpeculationReason is used as a key in a Map and so it must implement Object.equals(Object) and Object.hashCode() in terms of its attributes. A JVMCI implementation may serialize speculations for storage off heap (e.g. in native memory associated with an nmethod). For this reason, the attributes of a SpeculationReason are restricted to those supported by the add... methods of SpeculationReasonEncoding. 
/**
     * The specific attributes of a speculation that a compiler uses to denote a speculation in a
     * compiled method. Typical attributes of a speculation are a bytecode position, type
     * information about a variable being speculated on and an enum denoting the type of operation
     * to which the speculation applies. A {@link SpeculationReason} is used as a key in a
     * {@link Map} and so it must implement {@link Object#equals(Object)} and
     * {@link Object#hashCode()} in terms of its attributes.
     *
     * A JVMCI implementation may serialize speculations for storage off heap (e.g. in native memory
     * associated with an nmethod). For this reason, the attributes of a {@link SpeculationReason}
     * are restricted to those supported by the {@code add...} methods of
     * {@link SpeculationReasonEncoding}.
     */
    public interface SpeculationReason {

        
Encodes the attributes of this reason using a SpeculationReasonEncoding. For efficiency, a SpeculationReason implementation should cache the returned value and return it for all subsequent calls to this method. This also underlines the requirement that the encoding for a specific reason instance should be stable. 
Params:
Returns:a SpeculationReasonEncoding that encodes all the attributes that uniquely identify this reason
/**
         * Encodes the attributes of this reason using a {@link SpeculationReasonEncoding}. For
         * efficiency, a {@link SpeculationReason} implementation should cache the returned value
         * and return it for all subsequent calls to this method. This also underlines the
         * requirement that the encoding for a specific reason instance should be stable.
         *
         * @param encodingSupplier source of a {@link SpeculationReasonEncoding}
         * @return a {@link SpeculationReasonEncoding} that encodes all the attributes that uniquely
         *         identify this reason
         */
        default SpeculationReasonEncoding encode(Supplier<SpeculationReasonEncoding> encodingSupplier) {
            return null;
        }
    }

    
Provides a facility for encoding the attributes of a SpeculationReason. The encoding format is determined by the implementation of this interface. 
/**
     * Provides a facility for encoding the attributes of a {@link SpeculationReason}. The encoding
     * format is determined by the implementation of this interface.
     */
    public interface SpeculationReasonEncoding {
        void addByte(int value);

        void addShort(int value);

        void addInt(int value);

        void addLong(long value);

        void addMethod(ResolvedJavaMethod method);

        void addType(ResolvedJavaType type);

        void addString(String value);

        default void addField(ResolvedJavaField field) {
            addType(field.getDeclaringClass());
            addInt(field.getModifiers());
            addInt(field.getOffset());
        }
    }

    
Marker class that indicates that a speculation has no reason.

/**
     * Marker class that indicates that a speculation has no reason.
     */
    final class NoSpeculationReason implements SpeculationReason {
    }

    class Speculation {
        private final SpeculationReason reason;

        public Speculation(SpeculationReason reason) {
            this.reason = reason;
        }

        public SpeculationReason getReason() {
            return reason;
        }

        @Override
        public String toString() {
            return reason.toString();
        }

        @Override
        public boolean equals(Object obj) {
            if (obj instanceof Speculation) {
                Speculation other = (Speculation) obj;
                return reason.equals(other.reason);
            }
            return false;
        }

        @Override
        public int hashCode() {
            return getReason().hashCode();
        }
    }

    Speculation NO_SPECULATION = new Speculation(new NoSpeculationReason());

    
Updates the set of failed speculations recorded in this log. This must be called before
compilation.

/**
     * Updates the set of failed speculations recorded in this log. This must be called before
     * compilation.
     */
    void collectFailedSpeculations();

    
If this method returns true, the compiler is allowed to speculate with the given reason. 
/**
     * If this method returns true, the compiler is allowed to {@link #speculate} with the given
     * reason.
     */
    boolean maySpeculate(SpeculationReason reason);

    
Registers a speculation performed by the compiler. The compiler must guard every call to this method for a specific reason with a call to maySpeculate(SpeculationReason). This API is subject to a benign race where a during the course of a compilation another thread might fail a speculation such that maySpeculate(SpeculationReason) will return false but an earlier call returned true. This method will still return a working Speculation in that case but the compile will eventually be invalidated and the compile attempted again without the now invalid speculation. 
Params:
  • reason – an object representing the reason for the speculation
Returns:a compiler constant encapsulating the provided reason. It is usually passed as an
        argument to the deoptimization function.
/**
     * Registers a speculation performed by the compiler. The compiler must guard every call to this
     * method for a specific reason with a call to {@link #maySpeculate(SpeculationReason)}.
     *
     * This API is subject to a benign race where a during the course of a compilation another
     * thread might fail a speculation such that {@link #maySpeculate(SpeculationReason)} will
     * return false but an earlier call returned true. This method will still return a working
     * {@link Speculation} in that case but the compile will eventually be invalidated and the
     * compile attempted again without the now invalid speculation.
     *
     * @param reason an object representing the reason for the speculation
     * @return a compiler constant encapsulating the provided reason. It is usually passed as an
     *         argument to the deoptimization function.
     */
    Speculation speculate(SpeculationReason reason);

    
Returns if this log has speculations.

Returns:true if there are speculations, false otherwise
/**
     * Returns if this log has speculations.
     *
     * @return true if there are speculations, false otherwise
     */
    boolean hasSpeculations();

    
Given a JavaConstant previously returned from MetaAccessProvider.encodeSpeculation(Speculation) return the original Speculation object. 
/**
     * Given a {@link JavaConstant} previously returned from
     * {@link MetaAccessProvider#encodeSpeculation(Speculation)} return the original
     * {@link Speculation} object.
     */
    Speculation lookupSpeculation(JavaConstant constant);
}