001    /*
002     *  This file is part of the Jikes RVM project (http://jikesrvm.org).
003     *
004     *  This file is licensed to You under the Eclipse Public License (EPL);
005     *  You may not use this file except in compliance with the License. You
006     *  may obtain a copy of the License at
007     *
008     *      http://www.opensource.org/licenses/eclipse-1.0.php
009     *
010     *  See the COPYRIGHT.txt file distributed with this work for information
011     *  regarding copyright ownership.
012     */
013    package org.jikesrvm.compilers.opt.ssa;
014    
015    import org.jikesrvm.compilers.opt.ir.Instruction;
016    import org.jikesrvm.compilers.opt.ir.operand.ConstantOperand;
017    import org.jikesrvm.compilers.opt.util.SpaceEffGraphNode;
018    
019    /**
020     * This class implements a vertex in the value graph used in global
021     * value numbering
022     * ala Alpern, Wegman and Zadeck.  See Muchnick p.348 for a nice
023     * discussion.
024     */
025    final class ValueGraphVertex extends SpaceEffGraphNode {
026      /** the name of the variable defined by this node */
027      private final Object name;
028      /** the name of the operator that does the definition */
029      private Object label;
030      /** operand vertices, in order */
031      private ValueGraphVertex[] targets;
032      /** integer value number */
033      private int valueNumber;
034      /** number of operands needed */
035      private int arity;
036    
037      ValueGraphVertex(Object name) {
038        this.name = name;
039      }
040    
041      /**
042       * Set up properties of this vertex identically to another vertex
043       */
044      void copyVertex(ValueGraphVertex v) {
045        this.label = v.label;
046        this.valueNumber = v.valueNumber;
047        this.arity = v.arity;
048        this.targets = new ValueGraphVertex[v.targets.length];
049        for (int i = 0; i < targets.length; i++) {
050          this.targets[i] = v.targets[i];
051        }
052      }
053    
054      /**
055       * Does this vertex represent an incoming parameter?
056       */
057      boolean representsParameter() {
058        return (label instanceof ValueGraphParamLabel);
059      }
060    
061      /**
062       * Set the label for this vertex.
063       *
064       * @param label the label (an operator of some type)
065       * @param arity the number of operands needed
066       */
067      void setLabel(Object label, int arity) {
068        this.label = label;
069        this.arity = arity;
070        targets = new ValueGraphVertex[arity];
071      }
072    
073      Object getLabel() {
074        return label;
075      }
076    
077      Object getName() {
078        return name;
079      }
080    
081      int getValueNumber() {
082        return valueNumber;
083      }
084    
085      void setValueNumber(int number) {
086        valueNumber = number;
087      }
088    
089      boolean isConstant() {
090        return (label instanceof ConstantOperand);
091      }
092    
093      // is the def for this node an allocation instruction?
094      boolean isBornAtAllocation() {
095        return (label instanceof Instruction);
096      }
097    
098      /**
099       * return the target of the ith operand of this node
100       */
101      public ValueGraphVertex getTarget(int i) {
102        return targets[i];
103      }
104    
105      public void addTarget(ValueGraphVertex target, int pos) {
106        targets[pos] = target;
107      }
108    
109      public int getArity() {
110        return arity;
111      }
112    
113      public String toString() {
114        StringBuilder s = new StringBuilder("Vertex: " + name + " " + label);
115        s.append(" Targets: ");
116        for (int i = 0; i < arity; i++) {
117          if (targets[i] == null) {
118            s.append("null  ");
119          } else {
120            s.append(targets[i].getName()).append("  ");
121          }
122        }
123        return s.toString();
124      }
125    }
126    
127    
128