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1   /*
2    * Copyright (c) 1997, 2003, Oracle and/or its affiliates. All rights reserved.
3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4    *
5    * This code is free software; you can redistribute it and/or modify it
6    * under the terms of the GNU General Public License version 2 only, as
7    * published by the Free Software Foundation.  Oracle designates this
8    * particular file as subject to the "Classpath" exception as provided
9    * by Oracle in the LICENSE file that accompanied this code.
10   *
11   * This code is distributed in the hope that it will be useful, but WITHOUT
12   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14   * version 2 for more details (a copy is included in the LICENSE file that
15   * accompanied this code).
16   *
17   * You should have received a copy of the GNU General Public License version
18   * 2 along with this work; if not, write to the Free Software Foundation,
19   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20   *
21   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22   * or visit www.oracle.com if you need additional information or have any
23   * questions.
24   */
25  
26  package sun.tools.tree;
27  
28  import sun.tools.java.*;
29  import sun.tools.asm.Assembler;
30  import java.io.PrintStream;
31  
32  /**
33   * This class encapsulates the information required to generate an update to a private
34   * field referenced from another class, e.g., an inner class.  An expression denoting a
35   * reference to the object to which the field belongs is associated with getter and
36   * setter methods.
37   * <p>
38   * We use this class only for assignment, increment, and decrement operators, in which
39   * the old value is first retrieved and then a new value is computed and stored.
40   * Simple assignment expressions in which a value is copied without modification are
41   * handled by another mechanism.
42   *
43   * WARNING: The contents of this source file are not part of any
44   * supported API.  Code that depends on them does so at its own risk:
45   * they are subject to change or removal without notice.
46   */
47  
48  class FieldUpdater implements Constants {
49  
50      // Location for reporting errors.
51      // Errors will always indicate compiler failure, but these will be easier to diagnose
52      // if the bogus error is localized to the offending assignment.
53      private long where;
54  
55      // The field to which this updater applies.
56      // It would be easy to eliminate the need to store the field here, but we retain it for
57      // diagnostic  purposes.
58      private MemberDefinition field;
59  
60      // Expression denoting the object to which the getter and setter are applied.
61      // If the field is static, 'base' may be null, but need not be, as a static field
62      // may be selected from an object reference. Even though the value of the object
63      // reference will be ignored, it may have side-effects.
64      private Expression base;
65  
66      // The getter and setter methods, generated by 'getAccessMember' and 'getUpdateMember'.
67      private MemberDefinition getter;
68      private MemberDefinition setter;
69  
70      // The number of words occupied on the stack by the object reference.
71      // For static fields, this is zero.
72      private int depth;
73  
74      /**
75       * Constructor.
76       */
77  
78      public FieldUpdater(long where, MemberDefinition field,
79                          Expression base, MemberDefinition getter, MemberDefinition setter) {
80          this.where = where;
81          this.field = field;
82          this.base = base;
83          this.getter = getter;
84          this.setter = setter;
85      }
86  
87  
88      /**
89       * Since the object reference expression may be captured before it has been inlined,
90       * we must inline it later.  A <code>FieldUpdater</code> is inlined essentially as if
91       * it were a child of the assignment node to which it belongs.
92       */
93  
94      public FieldUpdater inline(Environment env, Context ctx) {
95          if (base != null) {
96              if (field.isStatic()) {
97                  base = base.inline(env, ctx);
98              } else {
99                  base = base.inlineValue(env, ctx);
100             }
101         }
102         return this;
103     }
104 
105     public FieldUpdater copyInline(Context ctx) {
106         return new FieldUpdater(where, field, base.copyInline(ctx), getter, setter);
107     }
108 
109     public int costInline(int thresh, Environment env, Context ctx, boolean needGet) {
110         // Size of 'invokestatic' call for access method is 3 bytes.
111         int cost = needGet ? 7 : 3;  // getter needs extra invokestatic + dup
112         // Size of expression to compute 'this' arg if needed.
113         if (!field.isStatic() && base != null) {
114             cost += base.costInline(thresh, env, ctx);
115         }
116         // We ignore the cost of duplicating value in value-needed context.
117         return cost;
118     }
119 
120     /**
121      * Duplicate <code>items</code> words from the top of the stack, locating them
122      * below the topmost <code>depth</code> words on the stack.
123      */
124 
125     // This code was cribbed from 'Expression.java'.  We cannot reuse that code here,
126     // because we do not inherit from class 'Expression'.
127 
128     private void codeDup(Assembler asm, int items, int depth) {
129         switch (items) {
130           case 0:
131             return;
132           case 1:
133             switch (depth) {
134               case 0:
135                 asm.add(where, opc_dup);
136                 return;
137               case 1:
138                 asm.add(where, opc_dup_x1);
139                 return;
140               case 2:
141                 asm.add(where, opc_dup_x2);
142                 return;
143 
144             }
145             break;
146           case 2:
147             switch (depth) {
148               case 0:
149                 asm.add(where, opc_dup2);
150                 return;
151               case 1:
152                 asm.add(where, opc_dup2_x1);
153                 return;
154               case 2:
155                 asm.add(where, opc_dup2_x2);
156                 return;
157 
158             }
159             break;
160         }
161         throw new CompilerError("can't dup: " + items + ", " + depth);
162     }
163 
164     /**
165      * Begin a field update by an assignment, increment, or decrement operator.
166      * The current value of the field is left at the top of the stack.
167      * If <code>valNeeded</code> is true, we arrange for the initial value to remain
168      * on the stack after the update.
169      */
170 
171     public void startUpdate(Environment env, Context ctx, Assembler asm, boolean valNeeded) {
172         if (!(getter.isStatic() && setter.isStatic())) {
173             throw new CompilerError("startUpdate isStatic");
174         }
175         if (!field.isStatic()) {
176             // Provide explicit 'this' argument.
177             base.codeValue(env, ctx, asm);
178             depth = 1;
179         } else {
180             // May need to evaluate 'base' for effect.
181             // If 'base' was a type expression, it should have previously been inlined away.
182             if (base != null) {
183                 base.code(env, ctx, asm);
184             }
185             depth = 0;
186         }
187         codeDup(asm, depth, 0);
188         asm.add(where, opc_invokestatic, getter);
189         if (valNeeded) {
190             codeDup(asm, field.getType().stackSize(), depth);
191         }
192     }
193 
194     /**
195      * Complete a field update by an assignment, increment, or decrement operator.
196      * The original value of the field left on the stack by <code>startUpdate</code>
197      * must have been replaced with the updated value, with no other stack alterations.
198      * If <code>valNeeded</code> is true, we arrange for the updated value to remain
199      * on the stack after the update.  The <code>valNeeded</code> argument must not be
200      * true in both <code>startUpdate</code> and <code>finishUpdate</code>.
201      */
202 
203     public void finishUpdate(Environment env, Context ctx, Assembler asm, boolean valNeeded) {
204         if (valNeeded) {
205             codeDup(asm, field.getType().stackSize(), depth);
206         }
207         asm.add(where, opc_invokestatic, setter);
208     }
209 
210     /**
211      * Like above, but used when assigning a new value independent of the
212      * old, as in a simple assignment expression.  After 'startAssign',
213      * code must be emitted to leave one additional value on the stack without
214      * altering any others, followed by 'finishAssign'.
215      */
216 
217     public void startAssign(Environment env, Context ctx, Assembler asm) {
218         if (!setter.isStatic()) {
219             throw new CompilerError("startAssign isStatic");
220         }
221         if (!field.isStatic()) {
222             // Provide explicit 'this' argument.
223             base.codeValue(env, ctx, asm);
224             depth = 1;
225         } else {
226             // May need to evaluate 'base' for effect.
227             // If 'base' was a type expression, it should have previously been inlined away.
228             if (base != null) {
229                 base.code(env, ctx, asm);
230             }
231             depth = 0;
232         }
233     }
234 
235     public void finishAssign(Environment env, Context ctx, Assembler asm, boolean valNeeded) {
236         if (valNeeded) {
237             codeDup(asm, field.getType().stackSize(), depth);
238         }
239         asm.add(where, opc_invokestatic, setter);
240     }
241 
242 }