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package jdk.vm.ci.meta;

Manages unique deoptimization reasons. Reasons are embedded in compiled code and can be
invalidated at run time. Subsequent compilations then should not speculate again on such
invalidated reasons to avoid repeated deoptimization.
All methods of this interface are called by the compiler. There is no need for API to register
failed speculations during deoptimization, since every VM has different needs there.
/**
 * Manages unique deoptimization reasons. Reasons are embedded in compiled code and can be
 * invalidated at run time. Subsequent compilations then should not speculate again on such
 * invalidated reasons to avoid repeated deoptimization.
 *
 * All methods of this interface are called by the compiler. There is no need for API to register
 * failed speculations during deoptimization, since every VM has different needs there.
 */
public interface SpeculationLog {
    
Marker interface for speculation objects that can be added to the speculation log.
/**
     * Marker interface for speculation objects that can be added to the speculation log.
     */
    public interface SpeculationReason {
    }

    
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 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());

    
Must be called before compilation, i.e., before a compiler calls maySpeculate. /**
     * Must be called before compilation, i.e., before a compiler calls {@link #maySpeculate}.
     */
    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);
}