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package com.oracle.truffle.sl.nodes.local;

import com.oracle.truffle.api.dsl.NodeField;
import com.oracle.truffle.api.dsl.Specialization;
import com.oracle.truffle.api.frame.FrameSlot;
import com.oracle.truffle.api.frame.FrameSlotTypeException;
import com.oracle.truffle.api.frame.VirtualFrame;
import com.oracle.truffle.api.source.SourceSection;
import com.oracle.truffle.sl.nodes.SLExpressionNode;

/**
 * Node to read a local variable from a function's {@link VirtualFrame frame}. The Truffle frame API
 * allows to store primitive values of all Java primitive types, and Object values. This means that
 * all SL types that are objects are handled by the {@link #readObject} method. When a local
 * variable changes its type, the frame access method throws an {@link FrameSlotTypeException},
 * which causes not rewriting. The rewriting code is generated by the Truffle DSL.
 */
@NodeField(name = "slot", type = FrameSlot.class)
public abstract class SLReadLocalVariableNode extends SLExpressionNode {

    public SLReadLocalVariableNode(SourceSection src) {
        super(src);
    }

    /**
     * Returns the descriptor of the accessed local variable. The implementation of this method is
     * created by the Truffle DSL based on the {@link NodeField} annotation on the class.
     */
    protected abstract FrameSlot getSlot();

    @Specialization(rewriteOn = FrameSlotTypeException.class)
    protected long readLong(VirtualFrame frame) throws FrameSlotTypeException {
        return frame.getLong(getSlot());
    }

    @Specialization(rewriteOn = FrameSlotTypeException.class)
    protected boolean readBoolean(VirtualFrame frame) throws FrameSlotTypeException {
        return frame.getBoolean(getSlot());
    }

    @Specialization(rewriteOn = FrameSlotTypeException.class)
    protected Object readObject(VirtualFrame frame) throws FrameSlotTypeException {
        return frame.getObject(getSlot());
    }

    /**
     * This is the generic case that always succeeds. Since we already have another specialization
     * with the same signature above, we need to order them explicitly with the order attribute.
     */
    @Specialization(contains = {"readLong", "readBoolean", "readObject"})
    protected Object read(VirtualFrame frame) {
        return frame.getValue(getSlot());
    }
}