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Diffstat (limited to 'src/proguard/optimize/peephole/GotoCommonCodeReplacer.java')
| -rw-r--r-- | src/proguard/optimize/peephole/GotoCommonCodeReplacer.java | 266 |
1 files changed, 266 insertions, 0 deletions
diff --git a/src/proguard/optimize/peephole/GotoCommonCodeReplacer.java b/src/proguard/optimize/peephole/GotoCommonCodeReplacer.java new file mode 100644 index 0000000..4833275 --- /dev/null +++ b/src/proguard/optimize/peephole/GotoCommonCodeReplacer.java @@ -0,0 +1,266 @@ +/* + * ProGuard -- shrinking, optimization, obfuscation, and preverification + * of Java bytecode. + * + * Copyright (c) 2002-2009 Eric Lafortune (eric@graphics.cornell.edu) + * + * This program is free software; you can redistribute it and/or modify it + * under the terms of the GNU General Public License as published by the Free + * Software Foundation; either version 2 of the License, or (at your option) + * any later version. + * + * This program is distributed in the hope that it will be useful, but WITHOUT + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for + * more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + */ +package proguard.optimize.peephole; + +import proguard.classfile.*; +import proguard.classfile.attribute.*; +import proguard.classfile.attribute.visitor.AttributeVisitor; +import proguard.classfile.editor.CodeAttributeEditor; +import proguard.classfile.instruction.*; +import proguard.classfile.instruction.visitor.InstructionVisitor; +import proguard.classfile.util.SimplifiedVisitor; + +/** + * This AttributeVisitor redirects unconditional branches so any common code + * is shared, and the code preceding the branch can be removed, in the code + * attributes that it visits. + * + * @author Eric Lafortune + */ +public class GotoCommonCodeReplacer +extends SimplifiedVisitor +implements AttributeVisitor, + InstructionVisitor +{ + //* + private static final boolean DEBUG = false; + /*/ + private static boolean DEBUG = true; + //*/ + + + private final InstructionVisitor extraInstructionVisitor; + + private final BranchTargetFinder branchTargetFinder = new BranchTargetFinder(); + private final CodeAttributeEditor codeAttributeEditor = new CodeAttributeEditor(); + + + /** + * Creates a new GotoCommonCodeReplacer. + * @param extraInstructionVisitor an optional extra visitor for all replaced + * goto instructions. + */ + public GotoCommonCodeReplacer(InstructionVisitor extraInstructionVisitor) + { + this.extraInstructionVisitor = extraInstructionVisitor; + } + + + // Implementations for AttributeVisitor. + + public void visitAnyAttribute(Clazz clazz, Attribute attribute) {} + + + public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute) + { +// DEBUG = +// clazz.getName().equals("abc/Def") && +// method.getName(clazz).equals("abc"); + + // Mark all branch targets. + branchTargetFinder.visitCodeAttribute(clazz, method, codeAttribute); + + // Reset the code attribute editor. + codeAttributeEditor.reset(codeAttribute.u4codeLength); + + // Remap the variables of the instructions. + codeAttribute.instructionsAccept(clazz, method, this); + + // Apply the code atribute editor. + codeAttributeEditor.visitCodeAttribute(clazz, method, codeAttribute); + } + + + // Implementations for InstructionVisitor. + + public void visitAnyInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, Instruction instruction) {} + + + public void visitBranchInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, BranchInstruction branchInstruction) + { + // Check if the instruction is an unconditional goto instruction that + // isn't the target of a branch itself. + byte opcode = branchInstruction.opcode; + if ((opcode == InstructionConstants.OP_GOTO || + opcode == InstructionConstants.OP_GOTO_W) && + !branchTargetFinder.isBranchTarget(offset)) + { + int branchOffset = branchInstruction.branchOffset; + int targetOffset = offset + branchOffset; + + // Get the number of common bytes. + int commonCount = commonByteCodeCount(codeAttribute, offset, targetOffset); + + if (commonCount > 0 && + !exceptionBoundary(codeAttribute, offset, targetOffset)) + { + if (DEBUG) + { + System.out.println("GotoCommonCodeReplacer: "+clazz.getName()+"."+method.getName(clazz)+" (["+(offset-commonCount)+"] - "+branchInstruction.toString(offset)+" -> "+targetOffset+")"); + } + + // Delete the common instructions. + for (int delta = 0; delta <= commonCount; delta++) + { + int deleteOffset = offset - delta; + if (branchTargetFinder.isInstruction(deleteOffset)) + { + codeAttributeEditor.replaceInstruction( deleteOffset, (Instruction)null); + codeAttributeEditor.insertBeforeInstruction(deleteOffset, (Instruction)null); + codeAttributeEditor.insertAfterInstruction( deleteOffset, (Instruction)null); + + codeAttributeEditor.deleteInstruction(deleteOffset); + } + } + + // Redirect the goto instruction, if it is still necessary. + int newBranchOffset = branchOffset - commonCount; + if (newBranchOffset != branchInstruction.length(offset)) + { + Instruction newGotoInstruction = + new BranchInstruction(opcode, newBranchOffset); + codeAttributeEditor.replaceInstruction(offset, + newGotoInstruction); + } + + // Visit the instruction, if required. + if (extraInstructionVisitor != null) + { + extraInstructionVisitor.visitBranchInstruction(clazz, method, codeAttribute, offset, branchInstruction); + } + } + } + } + + + // Small utility methods. + + /** + * Returns the number of common bytes preceding the given offsets, + * avoiding branches and exception blocks. + */ + private int commonByteCodeCount(CodeAttribute codeAttribute, int offset1, int offset2) + { + // Find the block of common instructions preceding it. + byte[] code = codeAttribute.code; + + int successfulDelta = 0; + + for (int delta = 1; + delta <= offset1 && + delta <= offset2 && + offset2 - delta != offset1; + delta++) + { + int newOffset1 = offset1 - delta; + int newOffset2 = offset2 - delta; + + // Is the code identical at both offsets? + if (code[newOffset1] != code[newOffset2]) + { + break; + } + + // Are there instructions at either offset but not both? + if (branchTargetFinder.isInstruction(newOffset1) ^ + branchTargetFinder.isInstruction(newOffset2)) + { + break; + } + + // Are there instructions at both offsets? + if (branchTargetFinder.isInstruction(newOffset1) && + branchTargetFinder.isInstruction(newOffset2)) + { + // Are the offsets involved in some branches? + // Note that the preverifier doesn't like initializer + // invocations to be moved around. + // Also note that the preverifier doesn't like pop instructions + // that work on different operands. + if (branchTargetFinder.isBranchOrigin(newOffset1) || + branchTargetFinder.isBranchTarget(newOffset1) || + branchTargetFinder.isExceptionStart(newOffset1) || + branchTargetFinder.isExceptionEnd(newOffset1) || + branchTargetFinder.isInitializer(newOffset1) || + branchTargetFinder.isExceptionStart(newOffset2) || + branchTargetFinder.isExceptionEnd(newOffset2) || + isPop(code[newOffset1])) + { + break; + } + + // Make sure the new branch target was a branch target before, + // in order not to introduce new entries in the stack map table. + if (branchTargetFinder.isBranchTarget(newOffset2)) + { + successfulDelta = delta; + } + + if (branchTargetFinder.isBranchTarget(newOffset1)) + { + break; + } + } + } + + return successfulDelta; + } + + + /** + * Returns whether the given opcode represents a pop instruction that must + * get a consistent type (pop, pop2, arraylength). + */ + private boolean isPop(byte opcode) + { + return opcode == InstructionConstants.OP_POP || + opcode == InstructionConstants.OP_POP2 || + opcode == InstructionConstants.OP_ARRAYLENGTH; + } + + + /** + * Returns the whether there is a boundary of an exception block between + * the given offsets (including both). + */ + private boolean exceptionBoundary(CodeAttribute codeAttribute, int offset1, int offset2) + { + // Swap the offsets if the second one is smaller than the first one. + if (offset2 < offset1) + { + int offset = offset1; + offset1 = offset2; + offset2 = offset; + } + + // Check if there is a boundary of an exception block. + for (int offset = offset1; offset <= offset2; offset++) + { + if (branchTargetFinder.isExceptionStart(offset) || + branchTargetFinder.isExceptionEnd(offset)) + { + return true; + } + } + + return false; + } +} |