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.BasicBlock;
016    import org.jikesrvm.compilers.opt.ir.IR;
017    import org.jikesrvm.util.BitVector;
018    
019    /**
020     * An HeapVariable represents a heap variable for heap array SSA form
021     */
022    public class HeapVariable<T> {
023      /**
024       * a unique identifier for this heap variable among all heap variables
025       * with this type.
026       */
027      private final int number;
028      /**
029       * a bit vector representing the basic blocks that write to this
030       * variable
031       */
032      private final BitVector definedIn;
033      /**
034       * The type of this heap variable.  Must be either a
035       * TypeReference, FieldReference, RVMField or a String
036       */
037      private final T type;
038    
039      /**
040       * Create a new Heap variable of a given type, with a given number.
041       *
042       * @param type a FieldReference or TypeReference object, naming the type of this
043       *              heap
044       * @param number second part of the name of this heap variable
045       * @param ir the governing IR
046       */
047      public HeapVariable(T type, int number, IR ir) {
048        this.type = type;
049        this.number = number;
050        definedIn = new BitVector(ir.getMaxBasicBlockNumber() + 1);
051      }
052    
053      /**
054       * Return a number that uniquely identifies this heap variable, among
055       * all the heap variables with the same type.
056       * @return the number
057       */
058      public int getNumber() {
059        return number;
060      }
061    
062      /**
063       * Return the type representing this heap object.
064       * @return either a TypeReference, FieldReference, RVMField or
065       * String object
066       */
067      public T getHeapType() {
068        return type;
069      }
070    
071      /**
072       * Is the this the exception heap type?
073       * @return true if the heap represents exceptions
074       */
075      public boolean isExceptionHeapType() {
076        return type == SSADictionary.exceptionState;
077      }
078    
079      /**
080       * Return a bit vector that represents the basic blocks that define
081       * this heap variable.
082       * @return a bit vector that represents the basic blocks that define
083       * this heap variable.
084       */
085      public BitVector getDefBlocks() {
086        return definedIn;
087      }
088    
089      /**
090       * Note that this heap variable is defined in a given basic block.
091       * @param b a basic block that defines this heap variable
092       */
093      public void registerDef(BasicBlock b) {
094        definedIn.set(b.getNumber());
095      }
096    
097      /**
098       * Return a String representation of this variable
099       * @return a String representation of this variable
100       */
101      public String toString() {
102        return "HEAP<" + type + ">" + number;
103      }
104    
105      /**
106       * Is this heap variable exposed on procedure entry?
107       * <p> Equivalently: is the number = zero?
108       * @return true or false
109       */
110      public boolean isExposedOnEntry() {
111        return (number == 0);
112      }
113    }