1/*
2 * ProGuard -- shrinking, optimization, obfuscation, and preverification
3 *             of Java bytecode.
4 *
5 * Copyright (c) 2002-2009 Eric Lafortune (eric@graphics.cornell.edu)
6 *
7 * This program is free software; you can redistribute it and/or modify it
8 * under the terms of the GNU General Public License as published by the Free
9 * Software Foundation; either version 2 of the License, or (at your option)
10 * any later version.
11 *
12 * This program is distributed in the hope that it will be useful, but WITHOUT
13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
15 * more details.
16 *
17 * You should have received a copy of the GNU General Public License along
18 * with this program; if not, write to the Free Software Foundation, Inc.,
19 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
20 */
21package proguard.classfile.instruction;
22
23import proguard.classfile.*;
24import proguard.classfile.attribute.CodeAttribute;
25import proguard.classfile.constant.*;
26import proguard.classfile.constant.visitor.ConstantVisitor;
27import proguard.classfile.instruction.visitor.InstructionVisitor;
28import proguard.classfile.util.ClassUtil;
29
30/**
31 * This Instruction represents an instruction that refers to an entry in the
32 * constant pool.
33 *
34 * @author Eric Lafortune
35 */
36public class ConstantInstruction extends Instruction
37implements   ConstantVisitor
38{
39    public int constantIndex;
40    public int constant;
41
42
43    // Fields acting as return parameters for the ConstantVisitor methods.
44    private int parameterStackDelta;
45    private int typeStackDelta;
46
47
48    /**
49     * Creates an uninitialized ConstantInstruction.
50     */
51    public ConstantInstruction() {}
52
53
54    /**
55     * Creates a new ConstantInstruction with the given opcode and constant pool
56     * index.
57     */
58    public ConstantInstruction(byte opcode, int constantIndex)
59    {
60        this(opcode, constantIndex, 0);
61    }
62
63
64    /**
65     * Creates a new ConstantInstruction with the given opcode, constant pool
66     * index, and constant.
67     */
68    public ConstantInstruction(byte opcode, int constantIndex, int constant)
69    {
70        this.opcode        = opcode;
71        this.constantIndex = constantIndex;
72        this.constant      = constant;
73    }
74
75
76    /**
77     * Copies the given instruction into this instruction.
78     * @param constantInstruction the instruction to be copied.
79     * @return this instruction.
80     */
81    public ConstantInstruction copy(ConstantInstruction constantInstruction)
82    {
83        this.opcode        = constantInstruction.opcode;
84        this.constantIndex = constantInstruction.constantIndex;
85        this.constant      = constantInstruction.constant;
86
87        return this;
88    }
89
90
91    // Implementations for Instruction.
92
93    public byte canonicalOpcode()
94    {
95        // Remove the _w extension, if any.
96        switch (opcode)
97        {
98            case InstructionConstants.OP_LDC_W:
99            case InstructionConstants.OP_LDC2_W: return InstructionConstants.OP_LDC;
100
101            default: return opcode;
102        }
103    }
104
105    public Instruction shrink()
106    {
107        // Do we need a short index or a long index?
108        if (requiredConstantIndexSize() == 1)
109        {
110            // Can we replace the long instruction by a short instruction?
111            if (opcode == InstructionConstants.OP_LDC_W)
112            {
113                opcode = InstructionConstants.OP_LDC;
114            }
115        }
116        else
117        {
118            // Should we replace the short instruction by a long instruction?
119            if (opcode == InstructionConstants.OP_LDC)
120            {
121                opcode = InstructionConstants.OP_LDC_W;
122            }
123        }
124
125        return this;
126    }
127
128    protected void readInfo(byte[] code, int offset)
129    {
130        int constantIndexSize = constantIndexSize();
131        int constantSize      = constantSize();
132
133        constantIndex = readValue(code, offset, constantIndexSize);  offset += constantIndexSize;
134        constant      = readValue(code, offset, constantSize);
135    }
136
137
138    protected void writeInfo(byte[] code, int offset)
139    {
140        int constantIndexSize = constantIndexSize();
141        int constantSize      = constantSize();
142
143        if (requiredConstantIndexSize() > constantIndexSize)
144        {
145            throw new IllegalArgumentException("Instruction has invalid constant index size ("+this.toString(offset)+")");
146        }
147
148        writeValue(code, offset, constantIndex, constantIndexSize); offset += constantIndexSize;
149        writeValue(code, offset, constant,      constantSize);
150    }
151
152
153    public int length(int offset)
154    {
155        return 1 + constantIndexSize() + constantSize();
156    }
157
158
159    public void accept(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, InstructionVisitor instructionVisitor)
160    {
161        instructionVisitor.visitConstantInstruction(clazz, method, codeAttribute, offset, this);
162    }
163
164
165    public int stackPopCount(Clazz clazz)
166    {
167        int stackPopCount = super.stackPopCount(clazz);
168
169        // Some special cases.
170        switch (opcode)
171        {
172            case InstructionConstants.OP_MULTIANEWARRAY:
173                // For each dimension, an integer size is popped from the stack.
174                stackPopCount += constant;
175                break;
176
177            case InstructionConstants.OP_PUTSTATIC:
178            case InstructionConstants.OP_PUTFIELD:
179                // The field value is be popped from the stack.
180                clazz.constantPoolEntryAccept(constantIndex, this);
181                stackPopCount += typeStackDelta;
182                break;
183
184            case InstructionConstants.OP_INVOKEVIRTUAL:
185            case InstructionConstants.OP_INVOKESPECIAL:
186            case InstructionConstants.OP_INVOKESTATIC:
187            case InstructionConstants.OP_INVOKEINTERFACE:
188                // The some parameters may be popped from the stack.
189                clazz.constantPoolEntryAccept(constantIndex, this);
190                stackPopCount += parameterStackDelta;
191                break;
192        }
193
194        return stackPopCount;
195    }
196
197
198    public int stackPushCount(Clazz clazz)
199    {
200        int stackPushCount = super.stackPushCount(clazz);
201
202        // Some special cases.
203        switch (opcode)
204        {
205            case InstructionConstants.OP_GETSTATIC:
206            case InstructionConstants.OP_GETFIELD:
207            case InstructionConstants.OP_INVOKEVIRTUAL:
208            case InstructionConstants.OP_INVOKESPECIAL:
209            case InstructionConstants.OP_INVOKESTATIC:
210            case InstructionConstants.OP_INVOKEINTERFACE:
211                // The field value or a return value may be pushed onto the stack.
212                clazz.constantPoolEntryAccept(constantIndex, this);
213                stackPushCount += typeStackDelta;
214                break;
215        }
216
217        return stackPushCount;
218    }
219
220
221    // Implementations for ConstantVisitor.
222
223    public void visitIntegerConstant(Clazz clazz, IntegerConstant integerConstant) {}
224    public void visitLongConstant(Clazz clazz, LongConstant longConstant) {}
225    public void visitFloatConstant(Clazz clazz, FloatConstant floatConstant) {}
226    public void visitDoubleConstant(Clazz clazz, DoubleConstant doubleConstant) {}
227    public void visitStringConstant(Clazz clazz, StringConstant stringConstant) {}
228    public void visitUtf8Constant(Clazz clazz, Utf8Constant utf8Constant) {}
229    public void visitClassConstant(Clazz clazz, ClassConstant classConstant) {}
230    public void visitNameAndTypeConstant(Clazz clazz, NameAndTypeConstant nameAndTypeConstant) {}
231
232
233    public void visitFieldrefConstant(Clazz clazz, FieldrefConstant fieldrefConstant)
234    {
235        String type = fieldrefConstant.getType(clazz);
236
237        typeStackDelta = ClassUtil.internalTypeSize(ClassUtil.internalMethodReturnType(type));
238    }
239
240
241    public void visitInterfaceMethodrefConstant(Clazz clazz, InterfaceMethodrefConstant interfaceMethodrefConstant)
242    {
243        visitRefConstant(clazz, interfaceMethodrefConstant);
244    }
245
246
247    public void visitMethodrefConstant(Clazz clazz, MethodrefConstant methodrefConstant)
248    {
249        visitRefConstant(clazz, methodrefConstant);
250    }
251
252
253    private void visitRefConstant(Clazz clazz, RefConstant methodrefConstant)
254    {
255        String type = methodrefConstant.getType(clazz);
256
257        parameterStackDelta = ClassUtil.internalMethodParameterSize(type);
258        typeStackDelta      = ClassUtil.internalTypeSize(ClassUtil.internalMethodReturnType(type));
259    }
260
261
262    // Implementations for Object.
263
264    public String toString()
265    {
266        return getName()+" #"+constantIndex;
267    }
268
269
270    // Small utility methods.
271
272    /**
273     * Returns the constant pool index size for this instruction.
274     */
275    private int constantIndexSize()
276    {
277        return opcode == InstructionConstants.OP_LDC ? 1 :
278                                                       2;
279    }
280
281
282    /**
283     * Returns the constant size for this instruction.
284     */
285    private int constantSize()
286    {
287        return opcode == InstructionConstants.OP_MULTIANEWARRAY  ? 1 :
288               opcode == InstructionConstants.OP_INVOKEINTERFACE ? 2 :
289                                                                   0;
290    }
291
292
293    /**
294     * Computes the required constant pool index size for this instruction's
295     * constant pool index.
296     */
297    private int requiredConstantIndexSize()
298    {
299        return (constantIndex &   0xff) == constantIndex ? 1 :
300               (constantIndex & 0xffff) == constantIndex ? 2 :
301                                                           4;
302    }
303}
304