https://openjdk.java.net/ 
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 * Copyright (c) 2010, 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.code;

import java.util.Collections;
import java.util.IdentityHashMap;
import java.util.Set;

import jdk.vm.ci.common.JVMCIError;
import jdk.vm.ci.meta.JavaKind;
import jdk.vm.ci.meta.JavaValue;
import jdk.vm.ci.meta.ResolvedJavaField;
import jdk.vm.ci.meta.ResolvedJavaType;


An instance of this class represents an object whose allocation was removed by escape analysis. The information stored in the VirtualObject is used during deoptimization to recreate the object. 
/**
 * An instance of this class represents an object whose allocation was removed by escape analysis.
 * The information stored in the {@link VirtualObject} is used during deoptimization to recreate the
 * object.
 */
public final class VirtualObject implements JavaValue {

    private final ResolvedJavaType type;
    private JavaValue[] values;
    private JavaKind[] slotKinds;
    private final int id;
    private boolean isAutoBox;

    
Creates a new VirtualObject for the given type, with the given fields. If type is an instance class then values provides the values for the fields returned by getInstanceFields(true). If type is an array then the length of the values array determines the reallocated array length. 
Params:
  • type – the type of the object whose allocation was removed during compilation. This can
           be either an instance of an array type.
  • id – a unique id that identifies the object within the debug information for one
           position in the compiled code.
Returns:a new VirtualObject instance.
/**
     * Creates a new {@link VirtualObject} for the given type, with the given fields. If
     * {@code type} is an instance class then {@code values} provides the values for the fields
     * returned by {@link ResolvedJavaType#getInstanceFields(boolean) getInstanceFields(true)}. If
     * {@code type} is an array then the length of the values array determines the reallocated array
     * length.
     *
     * @param type the type of the object whose allocation was removed during compilation. This can
     *            be either an instance of an array type.
     * @param id a unique id that identifies the object within the debug information for one
     *            position in the compiled code.
     * @return a new {@link VirtualObject} instance.
     */
    public static VirtualObject get(ResolvedJavaType type, int id) {
        return new VirtualObject(type, id, false);
    }

    
Creates a new VirtualObject for the given type, with the given fields. If type is an instance class then values provides the values for the fields returned by getInstanceFields(true). If type is an array then the length of the values array determines the reallocated array length. 
Params:
  • type – the type of the object whose allocation was removed during compilation. This can
           be either an instance of an array type.
  • id – a unique id that identifies the object within the debug information for one
           position in the compiled code.
  • isAutoBox – a flag that tells the runtime that the object may be a boxed primitive and
           that it possibly needs to be obtained for the box cache instead of creating a new
           instance.
Returns:a new VirtualObject instance.
/**
     * Creates a new {@link VirtualObject} for the given type, with the given fields. If
     * {@code type} is an instance class then {@code values} provides the values for the fields
     * returned by {@link ResolvedJavaType#getInstanceFields(boolean) getInstanceFields(true)}. If
     * {@code type} is an array then the length of the values array determines the reallocated array
     * length.
     *
     * @param type the type of the object whose allocation was removed during compilation. This can
     *            be either an instance of an array type.
     * @param id a unique id that identifies the object within the debug information for one
     *            position in the compiled code.
     * @param isAutoBox a flag that tells the runtime that the object may be a boxed primitive and
     *            that it possibly needs to be obtained for the box cache instead of creating a new
     *            instance.
     * @return a new {@link VirtualObject} instance.
     */
    public static VirtualObject get(ResolvedJavaType type, int id, boolean isAutoBox) {
        return new VirtualObject(type, id, isAutoBox);
    }

    private VirtualObject(ResolvedJavaType type, int id, boolean isAutoBox) {
        this.type = type;
        this.id = id;
        this.isAutoBox = isAutoBox;
    }

    private static StringBuilder appendValue(StringBuilder buf, JavaValue value, Set<VirtualObject> visited) {
        if (value instanceof VirtualObject) {
            VirtualObject vo = (VirtualObject) value;
            buf.append("vobject:").append(vo.type.toJavaName(false)).append(':').append(vo.id);
            if (!visited.contains(vo)) {
                visited.add(vo);
                buf.append('{');
                if (vo.values == null) {
                    buf.append("<uninitialized>");
                } else {
                    if (vo.type.isArray()) {
                        for (int i = 0; i < vo.values.length; i++) {
                            if (i != 0) {
                                buf.append(',');
                            }
                            buf.append(i).append('=');
                            appendValue(buf, vo.values[i], visited);
                        }
                    } else {
                        ResolvedJavaField[] fields = vo.type.getInstanceFields(true);
                        int fieldIndex = 0;
                        for (int i = 0; i < vo.values.length; i++, fieldIndex++) {
                            if (i != 0) {
                                buf.append(',');
                            }
                            if (fieldIndex >= fields.length) {
                                buf.append("<missing field>");
                            } else {
                                ResolvedJavaField field = fields[fieldIndex];
                                buf.append(field.getName());
                                if (vo.slotKinds[i].getSlotCount() == 2 && field.getType().getJavaKind().getSlotCount() == 1) {
                                    if (fieldIndex + 1 >= fields.length) {
                                        buf.append("/<missing field>");
                                    } else {
                                        ResolvedJavaField field2 = fields[++fieldIndex];
                                        buf.append('/').append(field2.getName());
                                    }
                                }
                            }
                            buf.append('=');
                            appendValue(buf, vo.values[i], visited);
                        }
                        // Extra fields
                        for (; fieldIndex < fields.length; fieldIndex++) {
                            buf.append(fields[fieldIndex].getName()).append("=<missing value>");
                        }
                    }
                }
                buf.append('}');
            }
        } else {
            buf.append(value);
        }
        return buf;
    }

    public interface LayoutVerifier {
        int getOffset(ResolvedJavaField field);

        default JavaKind getStorageKind(ResolvedJavaField field) {
            return field.getType().getJavaKind();
        }
    }

    public void verifyLayout(LayoutVerifier verifier) {
        if (!type.isArray()) {
            ResolvedJavaField[] fields = type.getInstanceFields(true);
            int fieldIndex = 0;
            for (int i = 0; i < values.length; i++, fieldIndex++) {
                JavaKind slotKind = slotKinds[i];
                if (fieldIndex >= fields.length) {
                    throw new JVMCIError("Not enough fields for the values provided for %s", toString());
                } else {
                    ResolvedJavaField field = fields[fieldIndex];
                    JavaKind fieldKind = verifier.getStorageKind(field);
                    if (slotKind.getSlotCount() == 2 && fieldKind == JavaKind.Int) {
                        int offset = verifier.getOffset(field);
                        if (offset % 8 != 0) {
                            throw new JVMCIError("Double word value stored across two ints must be aligned %s", toString());
                        }

                        if (fieldIndex + 1 >= fields.length) {
                            throw new JVMCIError("Missing second field for double word value stored in two ints %s", toString());
                        }
                        ResolvedJavaField field2 = fields[fieldIndex + 1];
                        if (field2.getType().getJavaKind() != JavaKind.Int) {
                            throw new JVMCIError("Second field for double word value stored in two ints must be int but got %s in %s", field2.getType().getJavaKind(), toString());
                        }
                        int offset2 = verifier.getOffset(field2);
                        if (offset + 4 != offset2) {
                            throw new JVMCIError("Double word value stored across two ints must be sequential %s", toString());
                        }
                        fieldIndex++;
                    } else if (fieldKind.getStackKind() != slotKind.getStackKind()) {
                        throw new JVMCIError("Expected value of kind %s but got %s for field %s in %s", fieldKind, slotKind, field, toString());
                    }
                }
            }
            // Extra fields
            if (fieldIndex < fields.length) {
                throw new JVMCIError("Not enough values provided for fields in %s", this);
            }
        }
    }

    @Override
    public String toString() {
        Set<VirtualObject> visited = Collections.newSetFromMap(new IdentityHashMap<VirtualObject, Boolean>());
        return appendValue(new StringBuilder(), this, visited).toString();
    }

    
Returns the type of the object whose allocation was removed during compilation. This can be
either an instance of an array type.

/**
     * Returns the type of the object whose allocation was removed during compilation. This can be
     * either an instance of an array type.
     */
    public ResolvedJavaType getType() {
        return type;
    }

    
Returns the array containing all the values to be stored into the object when it is
recreated. This field is intentional exposed as a mutable array that a compiler may modify
(e.g. during register allocation).

/**
     * Returns the array containing all the values to be stored into the object when it is
     * recreated. This field is intentional exposed as a mutable array that a compiler may modify
     * (e.g. during register allocation).
     */
    @SuppressFBWarnings(value = "EI_EXPOSE_REP", justification = "`values` is intentional mutable")//
    public JavaValue[] getValues() {
        return values;
    }

    
Returns the kind of the value at index. 
/**
     * Returns the kind of the value at {@code index}.
     */
    public JavaKind getSlotKind(int index) {
        return slotKinds[index];
    }

    
Returns the unique id that identifies the object within the debug information for one
position in the compiled code.

/**
     * Returns the unique id that identifies the object within the debug information for one
     * position in the compiled code.
     */
    public int getId() {
        return id;
    }

    
Returns true if the object is a box. For boxes the deoptimization would check if the value of
the box is in the cache range and try to return a cached object.

/**
     * Returns true if the object is a box. For boxes the deoptimization would check if the value of
     * the box is in the cache range and try to return a cached object.
     */
    public boolean isAutoBox() {
        return isAutoBox;
    }

    
Sets the value of the box flag.

Params:
  • isAutoBox – a flag that tells the runtime that the object may be a boxed primitive and
           that it possibly needs to be obtained for the box cache instead of creating a new
           instance.
/**
     * Sets the value of the box flag.
     *
     * @param isAutoBox a flag that tells the runtime that the object may be a boxed primitive and
     *            that it possibly needs to be obtained for the box cache instead of creating a new
     *            instance.
     */
    public void setIsAutoBox(boolean isAutoBox) {
        this.isAutoBox = isAutoBox;
    }

    
Overwrites the current set of values with a new one.

Params:
  • values – an array containing all the values to be stored into the object when it is
           recreated.
  • slotKinds – an array containing the Java kinds of the values. This must have the same length as values. This array is now owned by this object and must not be mutated by the caller.
/**
     * Overwrites the current set of values with a new one.
     *
     * @param values an array containing all the values to be stored into the object when it is
     *            recreated.
     * @param slotKinds an array containing the Java kinds of the values. This must have the same
     *            length as {@code values}. This array is now owned by this object and must not be
     *            mutated by the caller.
     */
    @SuppressFBWarnings(value = "EI_EXPOSE_REP2", justification = "caller transfers ownership of `slotKinds`")
    public void setValues(JavaValue[] values, JavaKind[] slotKinds) {
        assert values.length == slotKinds.length;
        this.values = values;
        this.slotKinds = slotKinds;
    }

    @Override
    public int hashCode() {
        return 42 + type.hashCode();
    }

    @Override
    public boolean equals(Object o) {
        if (o == this) {
            return true;
        }
        if (o instanceof VirtualObject) {
            VirtualObject l = (VirtualObject) o;
            if (!l.type.equals(type) || l.values.length != values.length) {
                return false;
            }
            for (int i = 0; i < values.length; i++) {
                /*
                 * Virtual objects can form cycles. Calling equals() could therefore lead to
                 * infinite recursion.
                 */
                if (!same(values[i], l.values[i])) {
                    return false;
                }
            }
            return true;
        }
        return false;
    }

    private static boolean same(Object o1, Object o2) {
        return o1 == o2;
    }
}