branchinstr.java

用Java实现的编译器。把源代码编译成SPARC汇编程序

// $Id: BranchInstr.java,v 1.4 1999/10/06 03:39:42 deberg Exp $

package java6035.tools.IR;

/**
 * The BranchInstr class captures a branch statement. This class optionally
 * takes a Rhs value as the branch conditional.
 */

public class BranchInstr extends Instruction
{
    protected Rhs cond;
    protected LabelInstr target;

    /**
     * Creates a branch instruction to label.
     */
    public BranchInstr(LabelInstr label)
    {
	this(null, label);
    }

    /**
     * Creates a branch instruction with a conditional cond
     */
    public BranchInstr(Rhs cond, LabelInstr label)
    {
	this.cond = cond;
	this.target = label;

	if (this.target == null)
	    throw new IRException
		("BranchInstr: constructor: target null");
    }

    /**
     * Returns the type of the instruction.
     */
    protected int tnkind()
    {
	return BRANCH_INSTR;
    }

    /**
     * Returns the conditional, if branch is conditional.
     */
    public Rhs getConditional()
    {
	return cond;
    }

    /**
     * Sets the conditional.
     */
    public void setConditional(Rhs cond)
    {
	this.cond = cond;
    }

    /**
     * Returns the branch target.
     */
    public LabelInstr getTarget()
    {
	return target;
    }

    /**
     * Sets the branch target.
     */
    public void setTarget(LabelInstr target)
    {
	this.target = target;

	if (this.target == null)
	    throw new IRException
		("BranchInstr: setTarget: target null");
    }

    /**
     * Walkable: returns the name of the node.
     */
    public String getNodeName()
    {
	return "branch";
    }

    /**
     * Walkable: returns the number of neighbors from this node.
     */
    public int getNeighborCount()
    {
	if (cond != null) 
	    return 2;
	return 1;
    }

    /**
     * Walkable: returns a specific neighbor: 0, label instr; 1, conditional
     * value if there is one.
     */
    public Object getNeighbor(int index)
    {
	if (index == 0) 
	    return this.target;
	else if (cond != null && index == 1)
	    return this.cond;
	else 
	    return null;
    }

    public String PPrint(int indent, boolean recursive)
    {
        String output = new String();
        for(int i=0;i<indent;i++) output += " ";
        
        output += "(branch_instruction to " + this.target.getLabel() + "\n";

        if (recursive) {
            if (this.cond != null) {
                output += this.cond.PPrint(indent+2, recursive);
            }
        }

        for(int i=0;i<indent;i++) output += " ";
        output += ") /* branch to " + this.target.getLabel() + " */\n";

        return output;
    }
}