Source Code Cross Referenced for PushPopRemover.java in  » Development » proguard » proguard » optimize » peephole » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Development » proguard » proguard.optimize.peephole 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:         * ProGuard -- shrinking, optimization, obfuscation, and preverification
003:         *             of Java bytecode.
004:         *
005:         * Copyright (c) 2002-2007 Eric Lafortune (eric@graphics.cornell.edu)
006:         *
007:         * This program is free software; you can redistribute it and/or modify it
008:         * under the terms of the GNU General Public License as published by the Free
009:         * Software Foundation; either version 2 of the License, or (at your option)
010:         * any later version.
011:         *
012:         * This program is distributed in the hope that it will be useful, but WITHOUT
013:         * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
014:         * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
015:         * more details.
016:         *
017:         * You should have received a copy of the GNU General Public License along
018:         * with this program; if not, write to the Free Software Foundation, Inc.,
019:         * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
020:         */
021:        package proguard.optimize.peephole;
022:
023:        import proguard.classfile.*;
024:        import proguard.classfile.attribute.CodeAttribute;
025:        import proguard.classfile.editor.CodeAttributeEditor;
026:        import proguard.classfile.instruction.*;
027:        import proguard.classfile.instruction.visitor.InstructionVisitor;
028:        import proguard.classfile.util.SimplifiedVisitor;
029:
030:        /**
031:         * This InstructionVisitor deletes all push/pop instruction pairs. In this
032:         * context, push instructions are instructions that push values onto the stack,
033:         * like dup and load instructions.
034:         *
035:         * @author Eric Lafortune
036:         */
037:        public class PushPopRemover extends SimplifiedVisitor implements 
038:                InstructionVisitor {
039:            private final BranchTargetFinder branchTargetFinder;
040:            private final CodeAttributeEditor codeAttributeEditor;
041:            private final InstructionVisitor extraInstructionVisitor;
042:
043:            /**
044:             * Creates a new PushPopRemover.
045:             * @param branchTargetFinder    a branch target finder that has been
046:             *                              initialized to indicate branch targets
047:             *                              in the visited code.
048:             * @param codeAttributeEditor   a code editor that can be used for
049:             *                              accumulating changes to the code.
050:             */
051:            public PushPopRemover(BranchTargetFinder branchTargetFinder,
052:                    CodeAttributeEditor codeAttributeEditor) {
053:                this (branchTargetFinder, codeAttributeEditor, null);
054:            }
055:
056:            /**
057:             * Creates a new PushPopRemover.
058:             * @param branchTargetFinder      a branch target finder that has been
059:             *                                initialized to indicate branch targets
060:             *                                in the visited code.
061:             * @param codeAttributeEditor     a code editor that can be used for
062:             *                                accumulating changes to the code.
063:             * @param extraInstructionVisitor an optional extra visitor for all deleted
064:             *                                push instructions.
065:             */
066:            public PushPopRemover(BranchTargetFinder branchTargetFinder,
067:                    CodeAttributeEditor codeAttributeEditor,
068:                    InstructionVisitor extraInstructionVisitor) {
069:                this .branchTargetFinder = branchTargetFinder;
070:                this .codeAttributeEditor = codeAttributeEditor;
071:                this .extraInstructionVisitor = extraInstructionVisitor;
072:            }
073:
074:            // Implementations for InstructionVisitor.
075:
076:            public void visitAnyInstruction(Clazz clazz, Method method,
077:                    CodeAttribute codeAttribute, int offset,
078:                    Instruction instruction) {
079:            }
080:
081:            public void visitSimpleInstruction(Clazz clazz, Method method,
082:                    CodeAttribute codeAttribute, int offset,
083:                    SimpleInstruction simpleInstruction) {
084:                switch (simpleInstruction.opcode) {
085:                case InstructionConstants.OP_ICONST_M1:
086:                case InstructionConstants.OP_ICONST_0:
087:                case InstructionConstants.OP_ICONST_1:
088:                case InstructionConstants.OP_ICONST_2:
089:                case InstructionConstants.OP_ICONST_3:
090:                case InstructionConstants.OP_ICONST_4:
091:                case InstructionConstants.OP_ICONST_5:
092:                case InstructionConstants.OP_LCONST_0:
093:                case InstructionConstants.OP_LCONST_1:
094:                case InstructionConstants.OP_FCONST_0:
095:                case InstructionConstants.OP_FCONST_1:
096:                case InstructionConstants.OP_FCONST_2:
097:                case InstructionConstants.OP_DCONST_0:
098:                case InstructionConstants.OP_DCONST_1:
099:
100:                case InstructionConstants.OP_DUP:
101:                case InstructionConstants.OP_DUP2:
102:                case InstructionConstants.OP_BIPUSH:
103:                case InstructionConstants.OP_SIPUSH:
104:                case InstructionConstants.OP_LDC:
105:                case InstructionConstants.OP_LDC_W:
106:                case InstructionConstants.OP_LDC2_W:
107:                    // All these simple instructions are pushing instructions.
108:                    deleteWithSubsequentPop(clazz, method, codeAttribute,
109:                            offset, simpleInstruction);
110:                    break;
111:                }
112:            }
113:
114:            public void visitVariableInstruction(Clazz clazz, Method method,
115:                    CodeAttribute codeAttribute, int offset,
116:                    VariableInstruction variableInstruction) {
117:                if (variableInstruction.isLoad()
118:                        && variableInstruction.opcode != InstructionConstants.OP_RET) {
119:                    // All load instructions are pushing instructions.
120:                    deleteWithSubsequentPop(clazz, method, codeAttribute,
121:                            offset, variableInstruction);
122:                }
123:            }
124:
125:            // Small utility methods.
126:
127:            /**
128:             * Deletes the given instruction and its subsequent compatible pop instruction,
129:             * if any, and if the latter is not a branch target.
130:             */
131:            private void deleteWithSubsequentPop(Clazz clazz, Method method,
132:                    CodeAttribute codeAttribute, int offset,
133:                    Instruction instruction) {
134:                boolean isCategory2 = instruction.isCategory2();
135:
136:                int nextOffset = offset + instruction.length(offset);
137:
138:                if (!codeAttributeEditor.isModified(offset)
139:                        && !codeAttributeEditor.isModified(nextOffset)
140:                        && !branchTargetFinder.isTarget(nextOffset)) {
141:                    Instruction nextInstruction = InstructionFactory.create(
142:                            codeAttribute.code, nextOffset);
143:                    int nextOpcode = nextInstruction.opcode;
144:                    if ((nextOpcode == InstructionConstants.OP_POP || nextOpcode == InstructionConstants.OP_POP2)
145:                            && nextInstruction.isCategory2() == isCategory2) {
146:                        // Delete the pushing instruction and the pop instruction.
147:                        codeAttributeEditor.deleteInstruction(offset);
148:                        codeAttributeEditor.deleteInstruction(nextOffset);
149:
150:                        // Visit the instruction, if required.
151:                        if (extraInstructionVisitor != null) {
152:                            instruction.accept(clazz, method, codeAttribute,
153:                                    offset, extraInstructionVisitor);
154:                        }
155:                    }
156:                }
157:            }
158:        }
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