PhiExpr


1   /* Soot - a J*va Optimization Framework
2    * Copyright (C) 2003 Navindra Umanee <navindra@cs.mcgill.ca>
3    *
4    * This library is free software; you can redistribute it and/or
5    * modify it under the terms of the GNU Lesser General Public
6    * License as published by the Free Software Foundation; either
7    * version 2.1 of the License, or (at your option) any later version.
8    *
9    * This library is distributed in the hope that it will be useful,
10   * but WITHOUT ANY WARRANTY; without even the implied warranty of
11   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
12   * Lesser General Public License for more details.
13   *
14   * You should have received a copy of the GNU Lesser General Public
15   * License along with this library; if not, write to the
16   * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
17   * Boston, MA 02111-1307, USA.
18   */
19  
20  package soot.shimple;
21  
22  import soot.*;
23  import soot.util.*;
24  import java.util.*;
25  import soot.jimple.*;
26  import soot.toolkits.scalar.*;
27  import soot.toolkits.graph.*;
28  
29  /**
30   * A fully defined PhiExpr usually consists of a list of Values for
31   * the arguments alongst with the corresponding control flow
32   * predecessor for each argument.  This may be provided either as a
33   * Soot CFG Block or more directly as the Unit at the end of the
34   * corresponding CFG block.
35   *
36   * <p> As much as possible we try to conform to the semantics as
37   * described by Cytron et al., TOPLAS Oct. 91.  A Phi node such as
38   * "x_1 = Phi(x_2, x_3)" is eliminated by respectively adding the
39   * statements "x_1 = x_2" and "x_1 = x_3" at the end of the
40   * corresponding control flow predecessor.
41   *
42   * <p> However, due to the fact that each argument is explicitly
43   * associated with the control flow predecessor, there may be some
44   * subtle differences.  We tried to make the behaviour as robust and
45   * transparent as possible by handling the common cases of Unit chain
46   * manipulations in the Shimple internal implementation of
47   * PatchingChain.
48   *
49   * @author Navindra Umanee
50   * @see
51   <a
52   * HREF="http://citeseer.nj.nec.com/cytron91efficiently.html">Efficiently
53   * Computing Static Single Assignment Form and the Control Dependence
54   * Graph</a>
55   * @see Shimple#newPhiExpr(List, List)
56   * @see Shimple#newPhiExpr(Local, List)
57   **/
58  public interface PhiExpr extends ShimpleExpr
59  {
60      /**
61       * Returns an unmodifiable, backed view of the arguments to this PhiExpr.
62       * Each argument is a ValueUnitPair.
63       *
64       * @see soot.toolkits.scalar.ValueUnitPair
65       **/
66      public List getArgs();
67  
68      /**
69       * Returns a list of the values used by this PhiExpr.
70       **/
71      public List getValues();
72  
73      /**
74       * Returns a list of the control flow predecessor Units being
75       * tracked by this PhiExpr
76       **/
77      public List getPreds();
78  
79      /**
80       * Returns the number of arguments in this PhiExpr.
81       **/
82      public int getArgCount();
83  
84      /**
85       * Returns the argument pair for the given index.  Null if
86       * out-of-bounds.
87       **/
88      public ValueUnitPair getArgBox(int index);
89  
90      /**
91       * Returns the value for the given index into the PhiExpr.  Null
92       * if out-of-bounds.
93       **/
94      public Value getValue(int index);
95  
96      /**
97       * Returns the control flow predecessor Unit for the given index
98       * into the PhiExpr.  Null if out-of-bounds.
99       **/
100     public Unit getPred(int index);
101 
102     /**
103      * Returns the index of the argument associated with the given
104      * control flow predecessor Unit.  Returns -1 if not found.
105      **/
106     public int getArgIndex(Unit predTailUnit);
107 
108     /**
109      * Returns the argument pair corresponding to the given CFG
110      * predecessor.  Returns null if not found.
111      **/
112     public ValueUnitPair getArgBox(Unit predTailUnit);
113     
114     /**
115      * Get the PhiExpr argument corresponding to the given control
116      * flow predecessor, returns null if not available.
117      **/
118     public Value getValue(Unit predTailUnit);
119     
120     /**
121      * Returns the index of the argument associated with the given
122      * control flow predecessor.  Returns -1 if not found.
123      **/
124     public int getArgIndex(Block pred);
125 
126     /**
127      * Returns the argument pair corresponding to the given CFG
128      * predecessor.  Returns null if not found.
129      **/
130     public ValueUnitPair getArgBox(Block pred);
131     
132     /**
133      * Get the PhiExpr argument corresponding to the given control flow
134      * predecessor, returns null if not available.
135      **/
136     public Value getValue(Block pred);
137 
138     /**
139      * Modify the PhiExpr argument at the given index with the given
140      * information.  Returns false on failure.
141      **/
142     public boolean setArg(int index, Value arg, Unit predTailUnit);
143 
144     /**
145      * Modify the PhiExpr argument at the given index with the given
146      * information.  Returns false on failure.
147      **/
148     public boolean setArg(int index, Value arg, Block pred);
149 
150     /**
151      * Set the value at the given index into the PhiExpr.  Returns
152      * false on failure.
153      **/
154     public boolean setValue(int index, Value arg);
155 
156     /**
157      * Locate the argument assocatiated with the given CFG predecessor unit
158      * and set the value.  Returns false on failure.
159      **/
160     public boolean setValue(Unit predTailUnit, Value arg);
161 
162     /**
163      * Locate the argument assocatiated with the given CFG predecessor
164      * and set the value.  Returns false on failure.
165      **/
166     public boolean setValue(Block pred, Value arg);
167     
168     /**
169      * Update the CFG predecessor associated with the PhiExpr
170      * argument at the given index.  Returns false on failure.
171      **/
172     public boolean setPred(int index, Unit predTailUnit);
173 
174     /**
175      * Update the CFG predecessor associated with the PhiExpr
176      * argument at the given index.  Returns false on failure.
177      **/
178     public boolean setPred(int index, Block pred);
179 
180     /**
181      * Remove the argument at the given index.  Returns false on
182      * failure.
183      **/
184     public boolean removeArg(int index);
185 
186     /**
187      * Remove the argument corresponding to the given CFG predecessor.
188      * Returns false on failure.
189      **/
190     public boolean removeArg(Unit predTailUnit);
191 
192     /**
193      * Remove the argument corresponding to the given CFG predecessor.
194      * Returns false on failure.
195      **/
196     public boolean removeArg(Block pred);
197 
198     /**
199      * Remove the given argument.  Returns false on failure.
200      **/
201     public boolean removeArg(ValueUnitPair arg);
202 
203     /**
204      * Add the given argument associated with the given CFG
205      * predecessor.  Returns false on failure.
206      **/
207     public boolean addArg(Value arg, Block pred);
208 
209     /**
210      * Add the given argument associated with the given CFG
211      * predecessor.  Returns false on failure.
212      **/
213     public boolean addArg(Value arg, Unit predTailUnit);
214         
215     /**
216      * Set the block number of the Phi node.
217      **/
218     public void setBlockId(int blockId);
219      
220     /**
221      * Returns the id number of the block from which the Phi node
222      * originated from.
223      **/
224     public int getBlockId();
225 
226     /**
227      * The type of the PhiExpr is usually the same as the type of its
228      * arguments.
229      **/
230     public Type getType();
231 
232     public void apply(Switch sw);
233 }
234
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