/*
* ProGuard -- shrinking, optimization, obfuscation, and preverification
* of Java bytecode.
*
* Copyright (c) 2002-2010 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.*;
import proguard.classfile.instruction.*;
import proguard.classfile.instruction.visitor.InstructionVisitor;
import proguard.classfile.util.SimplifiedVisitor;
/**
* This AttributeVisitor finds all instruction offsets, branch targets, and
* exception targets in the CodeAttribute objects that it visits.
*
* @author Eric Lafortune
*/
public class ReachableCodeMarker
extends SimplifiedVisitor
implements AttributeVisitor,
InstructionVisitor,
ExceptionInfoVisitor
{
private boolean[] isReachable = new boolean[ClassConstants.TYPICAL_CODE_LENGTH];
private boolean next;
private boolean evaluateExceptions;
/**
* Returns whether the instruction at the given offset is reachable in
* the CodeAttribute that was visited most recently.
*/
public boolean isReachable(int offset)
{
return isReachable[offset];
}
/**
* Returns whether any of the instructions at the given offsets are
* reachable in the CodeAttribute that was visited most recently.
*/
public boolean isReachable(int startOffset, int endOffset)
{
// Check if any of the instructions is reachable.
for (int offset = startOffset; offset < endOffset; offset++)
{
if (isReachable[offset])
{
return true;
}
}
return false;
}
// Implementations for AttributeVisitor.
public void visitAnyAttribute(Clazz clazz, Attribute attribute) {}
public void visitCodeAttribute(Clazz clazz, Method method, CodeAttribute codeAttribute)
{
// Make sure there is a sufficiently large array.
int codeLength = codeAttribute.u4codeLength;
if (isReachable.length < codeLength)
{
// Create a new array.
isReachable = new boolean[codeLength];
}
else
{
// Reset the array.
for (int index = 0; index < codeLength; index++)
{
isReachable[index] = false;
}
}
// Mark the code, starting at the entry point.
markCode(clazz, method, codeAttribute, 0);
// Mark the exception handlers, iterating as long as necessary.
do
{
evaluateExceptions = false;
codeAttribute.exceptionsAccept(clazz, method, this);
}
while (evaluateExceptions);
}
// Implementations for InstructionVisitor.
public void visitSimpleInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, SimpleInstruction simpleInstruction)
{
byte opcode = simpleInstruction.opcode;
if (opcode == InstructionConstants.OP_IRETURN ||
opcode == InstructionConstants.OP_LRETURN ||
opcode == InstructionConstants.OP_FRETURN ||
opcode == InstructionConstants.OP_DRETURN ||
opcode == InstructionConstants.OP_ARETURN ||
opcode == InstructionConstants.OP_RETURN ||
opcode == InstructionConstants.OP_ATHROW)
{
next = false;
}
}
public void visitConstantInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, ConstantInstruction constantInstruction)
{
}
public void visitVariableInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, VariableInstruction variableInstruction)
{
if (variableInstruction.opcode == InstructionConstants.OP_RET)
{
next = false;
}
}
public void visitBranchInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, BranchInstruction branchInstruction)
{
// Mark the branch target.
markBranchTarget(clazz,
method,
codeAttribute,
offset + branchInstruction.branchOffset);
byte opcode = branchInstruction.opcode;
if (opcode == InstructionConstants.OP_GOTO ||
opcode == InstructionConstants.OP_GOTO_W)
{
next = false;
}
}
public void visitAnySwitchInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, SwitchInstruction switchInstruction)
{
// Mark the branch targets of the default jump offset.
markBranchTarget(clazz,
method,
codeAttribute,
offset + switchInstruction.defaultOffset);
// Mark the branch targets of the jump offsets.
markBranchTargets(clazz,
method,
codeAttribute,
offset,
switchInstruction.jumpOffsets);
next = false;
}
// Implementations for ExceptionInfoVisitor.
public void visitExceptionInfo(Clazz clazz, Method method, CodeAttribute codeAttribute, ExceptionInfo exceptionInfo)
{
// Mark the exception handler if it's relevant.
if (!isReachable(exceptionInfo.u2handlerPC) &&
isReachable(exceptionInfo.u2startPC, exceptionInfo.u2endPC))
{
markCode(clazz, method, codeAttribute, exceptionInfo.u2handlerPC);
evaluateExceptions = true;
}
}
// Small utility methods.
/**
* Marks the branch targets of the given jump offsets for the instruction
* at the given offset.
*/
private void markBranchTargets(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, int[] jumpOffsets)
{
for (int index = 0; index < jumpOffsets.length; index++)
{
markCode(clazz, method, codeAttribute, offset + jumpOffsets[index]);
}
}
/**
* Marks the branch target at the given offset.
*/
private void markBranchTarget(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset)
{
boolean oldNext = next;
markCode(clazz, method, codeAttribute, offset);
next = oldNext;
}
/**
* Marks the code starting at the given offset.
*/
private void markCode(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset)
{
boolean oldNext = next;
byte[] code = codeAttribute.code;
// Continue with the current instruction as long as we haven't marked it
// yet.
while (!isReachable[offset])
{
// Get the current instruction.
Instruction instruction = InstructionFactory.create(code, offset);
// Mark it as reachable.
isReachable[offset] = true;
// By default, we'll assume we can continue with the next
// instruction in a moment.
next = true;
// Mark the branch targets, if any.
instruction.accept(clazz, method, codeAttribute, offset, this);
// Can we really continue with the next instruction?
if (!next)
{
break;
}
// Go to the next instruction.
offset += instruction.length(offset);
}
next = oldNext;
}
}