StackSlot.java

/*
 * Copyright (c) 2010, 2016, 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
package jdk.vm.ci.code;

import jdk.vm.ci.meta.AllocatableValue;
import jdk.vm.ci.meta.ValueKind;

/**
 * Represents a compiler spill slot or an outgoing stack-based argument in a method's frame or an
 * incoming stack-based argument in a method's {@linkplain #isInCallerFrame() caller's frame}.
 */
public final class StackSlot extends AllocatableValue {

    private final int offset;
    private final boolean addFrameSize;

    /**
     * Gets a {@link StackSlot} instance representing a stack slot at a given index holding a value
     * of a given kind.
     *
     * @param kind The kind of the value stored in the stack slot.
     * @param offset The offset of the stack slot (in bytes)
     * @param addFrameSize Specifies if the offset is relative to the stack pointer, or the
     *            beginning of the frame (stack pointer + total frame size).
     */
    public static StackSlot get(ValueKind<?> kind, int offset, boolean addFrameSize) {
        assert addFrameSize || offset >= 0;
        return new StackSlot(kind, offset, addFrameSize);
    }

    /**
     * Private constructor to enforce use of {@link #get(ValueKind, int, boolean)} so that a cache
     * can be used.
     */
    private StackSlot(ValueKind<?> kind, int offset, boolean addFrameSize) {
        super(kind);
        this.offset = offset;
        this.addFrameSize = addFrameSize;
    }

    /**
     * Gets the offset of this stack slot, relative to the stack pointer.
     *
     * @return The offset of this slot (in bytes).
     */
    public int getOffset(int totalFrameSize) {
        assert totalFrameSize > 0 || !addFrameSize;
        int result = offset + (addFrameSize ? totalFrameSize : 0);
        assert result >= 0;
        return result;
    }

    public boolean isInCallerFrame() {
        return addFrameSize && offset >= 0;
    }

    public int getRawOffset() {
        return offset;
    }

    public boolean getRawAddFrameSize() {
        return addFrameSize;
    }

    @Override
    public String toString() {
        if (!addFrameSize) {
            return "out:" + offset + getKindSuffix();
        } else if (offset >= 0) {
            return "in:" + offset + getKindSuffix();
        } else {
            return "stack:" + (-offset) + getKindSuffix();
        }
    }

    /**
     * Gets this stack slot used to pass an argument from the perspective of a caller.
     */
    public StackSlot asOutArg() {
        assert offset >= 0;
        if (addFrameSize) {
            return get(getValueKind(), offset, false);
        }
        return this;
    }

    /**
     * Gets this stack slot used to pass an argument from the perspective of a callee.
     */
    public StackSlot asInArg() {
        assert offset >= 0;
        if (!addFrameSize) {
            return get(getValueKind(), offset, true);
        }
        return this;
    }

    @Override
    public int hashCode() {
        final int prime = 37;
        int result = super.hashCode();
        result = prime * result + (addFrameSize ? 1231 : 1237);
        result = prime * result + offset;
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (obj instanceof StackSlot) {
            StackSlot other = (StackSlot) obj;
            return super.equals(obj) && addFrameSize == other.addFrameSize && offset == other.offset;
        }
        return false;
    }
}