/*
 * $Id$
 *
 * Copyright (C) 2003-2015 JNode.org
 *
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published
 * by the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * This library 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 Lesser General Public 
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library; If not, write to the Free Software Foundation, Inc., 
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
 
package org.jnode.vm.compiler.ir.quad;

import java.util.Collection;
import java.util.List;
import org.jnode.vm.compiler.ir.IRBasicBlock;
import org.jnode.vm.compiler.ir.Operand;
import org.jnode.vm.compiler.ir.Variable;

/**
 * @author Madhu Siddalingaiah
 */
public abstract class AssignQuad<T> extends Quad<T> {
    /**
     * Left hand side of assignment
     */
    private Variable<T> lhs;

    public AssignQuad(int address, IRBasicBlock<T> block, Variable<T> lhs) {
        super(address, block);
        setLHS(lhs);
    }

    public AssignQuad(int address, int byteCodeAddress, IRBasicBlock<T> block, Variable<T> lhs) {
        super(address, byteCodeAddress, block);
        setLHS(lhs);
    }

    public AssignQuad(int address, IRBasicBlock<T> block, int lhsIndex) {
        this(address, block, (Variable<T>) block.getVariables()[lhsIndex].clone());
    }

    /**
     * @see org.jnode.vm.compiler.ir.quad.Quad#getDefinedOp()
     */
    public Operand<T> getDefinedOp() {
        return lhs;
    }

    public Variable<T> getLHS() {
        return lhs;
    }

    /**
     * Simplifies this operation by propagating the right hand side (RHS)
     * For example, constant assignments can be simplified to return the
     * RHS constant. Binary operations can be constant folded if the RHS
     * contains only constants.
     * <p/>
     * If simplification is not possible, this method should return the
     * argument operand.
     *
     * @param operand
     * @return simplifed result of this operation, or operand
     */
    public abstract Operand<T> propagate(Variable<T> operand);

    /**
     * Returns the address where the left hand side (LHS) of this quad
     * is live. In general, this address is simply this.getAddress() + 1.
     * In the case of CPUs that support only two address operations,
     * e.g. x86, there are conditions where the LHS will interfere
     * with the RHS. The obvious example is any non-commutative binary
     * operation:
     * <p/>
     * a = b / c
     * <p/>
     * Variables a and c cannot occupy the same location for two address
     * machines.
     * <p/>
     * For these cases, this method must return this.getAddress() so that
     * register allocators can accommodate the interference.
     *
     * @return the address where the left hand side variable is live
     */
    public abstract int getLHSLiveAddress();

    /**
     * @param lhs
     */
    public void setLHS(Variable<T> lhs) {
        this.lhs = lhs;
        lhs.setAssignQuad(this);
    }

    @Override
    public void doPass3(Collection<Variable<T>> values) {
        if (!values.contains(lhs)) {
            setDeadCode(true);
        }
    }

    @Override
    public void computeLiveness(List<Variable<?>> liveVariables) {
        super.computeLiveness(liveVariables);
        if (lhs.getLastUseAddress() < getAddress()) {
            lhs.setLastUseAddress(getAddress());
        }
        if (!liveVariables.contains(lhs)) {
            liveVariables.add(lhs);
        }
    }
}