/* * ProGuard -- shrinking, optimization, obfuscation, and preverification * of Java bytecode. * * Copyright (c) 2002-2014 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(true, false); /** * 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.clearModifications(deleteOffset); 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).shrink(); 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; } }