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ProGuardCORE is a free library to read, analyze, modify, and write Java class files.
/*
* ProGuardCORE -- library to process Java bytecode.
*
* Copyright (c) 2002-2020 Guardsquare NV
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package proguard.evaluation;
import proguard.classfile.*;
import proguard.classfile.attribute.*;
import proguard.classfile.attribute.visitor.*;
import proguard.classfile.editor.ClassEstimates;
import proguard.classfile.instruction.*;
import proguard.classfile.instruction.visitor.InstructionVisitor;
import proguard.evaluation.value.*;
import proguard.util.ArrayUtil;
/**
* This {@link AttributeVisitor} analyzes the liveness of the variables in the code
* attributes that it visits, based on partial evaluation.
*
* @author Eric Lafortune
*/
public class LivenessAnalyzer
implements AttributeVisitor,
InstructionVisitor,
ExceptionInfoVisitor
{
//*
private static final boolean DEBUG = false;
/*/
private static boolean DEBUG = System.getProperty("la") != null;
//*/
private static final int MAX_VARIABLES_SIZE = 64;
private final PartialEvaluator partialEvaluator;
private final boolean runPartialEvaluator;
private final InitializationFinder initializationFinder;
private final boolean runInitializationFinder;
private long[] isAliveBefore = new long[ClassEstimates.TYPICAL_CODE_LENGTH];
private long[] isAliveAfter = new long[ClassEstimates.TYPICAL_CODE_LENGTH];
private long[] isCategory2 = new long[ClassEstimates.TYPICAL_CODE_LENGTH];
// Fields acting as global temporary variables.
private boolean checkAgain;
private long alive;
/**
* Creates a new LivenessAnalyzer.
*/
public LivenessAnalyzer()
{
this(new ReferenceTracingValueFactory(new BasicValueFactory()));
}
/**
* Creates a new LivenessAnalyzer. This private constructor gets around
* the constraint that it's not allowed to add statements before calling
* 'this'.
*/
private LivenessAnalyzer(ReferenceTracingValueFactory referenceTracingValueFactory)
{
this(new PartialEvaluator(referenceTracingValueFactory,
new ReferenceTracingInvocationUnit(new BasicInvocationUnit(referenceTracingValueFactory)),
true,
referenceTracingValueFactory),
true);
}
/**
* Creates a new LivenessAnalyzer. This private constructor gets around
* the constraint that it's not allowed to add statements before calling
* 'this'.
*/
private LivenessAnalyzer(PartialEvaluator partialEvaluator,
boolean runPartialEvaluator)
{
this(partialEvaluator,
runPartialEvaluator,
new InitializationFinder(partialEvaluator, false),
true);
}
/**
* Creates a new LivenessAnalyzer that will use the given partial evaluator
* and initialization finder.
* @param partialEvaluator the evaluator to be used for the analysis.
* @param runPartialEvaluator specifies whether to run this evaluator on
* every code attribute that is visited.
* @param initializationFinder the initialization finder to be used for
* the analysis.
* @param runInitializationFinder specifies whether to run this
* initialization finder on every code
* attribute that is visited.
*/
public LivenessAnalyzer(PartialEvaluator partialEvaluator,
boolean runPartialEvaluator,
InitializationFinder initializationFinder,
boolean runInitializationFinder)
{
this.partialEvaluator = partialEvaluator;
this.runPartialEvaluator = runPartialEvaluator;
this.initializationFinder = initializationFinder;
this.runInitializationFinder = runInitializationFinder;
}
/**
* Returns whether the instruction at the given offset has ever been
* executed during the partial evaluation.
*/
public boolean isTraced(int instructionOffset)
{
return partialEvaluator.isTraced(instructionOffset);
}
/**
* Returns whether the specified variable is alive before the instruction
* at the given offset.
*/
public boolean isAliveBefore(int instructionOffset, int variableIndex)
{
return variableIndex >= MAX_VARIABLES_SIZE ?
partialEvaluator.getVariablesBefore(instructionOffset).getValue(variableIndex) != null :
(isAliveBefore[instructionOffset] & (1L << variableIndex)) != 0;
}
/**
* Sets whether the specified variable is alive before the instruction
* at the given offset.
*/
public void setAliveBefore(int instructionOffset, int variableIndex, boolean alive)
{
if (variableIndex < MAX_VARIABLES_SIZE)
{
if (alive)
{
isAliveBefore[instructionOffset] |= 1L << variableIndex;
}
else
{
isAliveBefore[instructionOffset] &= ~(1L << variableIndex);
}
}
}
/**
* Returns whether the specified variable is alive after the instruction
* at the given offset.
*/
public boolean isAliveAfter(int instructionOffset, int variableIndex)
{
return variableIndex >= MAX_VARIABLES_SIZE ?
partialEvaluator.getVariablesAfter(instructionOffset).getValue(variableIndex) != null :
(isAliveAfter[instructionOffset] & (1L << variableIndex)) != 0;
}
/**
* Sets whether the specified variable is alive after the instruction
* at the given offset.
*/
public void setAliveAfter(int instructionOffset, int variableIndex, boolean alive)
{
if (variableIndex < MAX_VARIABLES_SIZE)
{
if (alive)
{
isAliveAfter[instructionOffset] |= 1L << variableIndex;
}
else
{
isAliveAfter[instructionOffset] &= ~(1L << variableIndex);
}
}
}
/**
* Returns whether the specified variable takes up two entries after the
* instruction at the given offset.
*/
public boolean isCategory2(int instructionOffset, int variableIndex)
{
return variableIndex >= MAX_VARIABLES_SIZE ?
partialEvaluator.getVariablesBefore(instructionOffset).getValue(variableIndex) != null &&
partialEvaluator.getVariablesBefore(instructionOffset).getValue(variableIndex).isCategory2() :
(isCategory2[instructionOffset] & (1L << variableIndex)) != 0;
}
/**
* Sets whether the specified variable takes up two entries after the
* instruction at the given offset.
*/
public void setCategory2(int instructionOffset, int variableIndex, boolean category2)
{
if (variableIndex < MAX_VARIABLES_SIZE)
{
if (category2)
{
isCategory2[instructionOffset] |= 1L << variableIndex;
}
else
{
isCategory2[instructionOffset] &= ~(1L << variableIndex);
}
}
}
// 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");
if (DEBUG)
{
System.out.println();
System.out.println("Liveness analysis: "+clazz.getName()+"."+method.getName(clazz)+method.getDescriptor(clazz));
}
int codeLength = codeAttribute.u4codeLength;
int variablesSize = codeAttribute.u2maxLocals;
// Initialize the global arrays.
isAliveBefore = ArrayUtil.ensureArraySize(isAliveBefore, codeLength, 0L);
isAliveAfter = ArrayUtil.ensureArraySize(isAliveAfter, codeLength, 0L);
isCategory2 = ArrayUtil.ensureArraySize(isCategory2, codeLength, 0L);
// Evaluate the method.
if (runPartialEvaluator)
{
partialEvaluator.visitCodeAttribute(clazz, method, codeAttribute);
}
if (runInitializationFinder)
{
initializationFinder.visitCodeAttribute(clazz, method, codeAttribute);
}
// We'll only really analyze the first 64 variables.
if (variablesSize > MAX_VARIABLES_SIZE)
{
variablesSize = MAX_VARIABLES_SIZE;
}
// Mark liveness blocks, as many times as necessary.
do
{
checkAgain = false;
alive = 0L;
// Loop over all traced instructions, backward.
for (int offset = codeLength - 1; offset >= 0; offset--)
{
if (partialEvaluator.isTraced(offset))
{
// Update the liveness based on the branch targets.
InstructionOffsetValue branchTargets = partialEvaluator.branchTargets(offset);
if (branchTargets != null)
{
// Update the liveness right after the branch instruction.
alive = combinedLiveness(branchTargets);
}
// Merge the current liveness.
alive |= isAliveAfter[offset];
// Update the liveness after the instruction.
isAliveAfter[offset] = alive;
// Update the current liveness based on the instruction.
codeAttribute.instructionAccept(clazz, method, offset, this);
// Merge the current liveness.
alive |= isAliveBefore[offset];
// Update the liveness before the instruction.
if ((~isAliveBefore[offset] & alive) != 0L)
{
isAliveBefore[offset] = alive;
// Do we have to check again after this loop?
InstructionOffsetValue branchOrigins = partialEvaluator.branchOrigins(offset);
if (branchOrigins != null &&
offset < branchOrigins.maximumValue())
{
checkAgain = true;
}
}
}
}
// Account for the liveness at the start of the exception handlers.
codeAttribute.exceptionsAccept(clazz, method, this);
}
while (checkAgain);
// Loop over all instructions, to mark variables that take up two entries.
for (int offset = 0; offset < codeLength; offset++)
{
if (partialEvaluator.isTraced(offset))
{
// Loop over all variables.
for (int variableIndex = 0; variableIndex < variablesSize; variableIndex++)
{
// Is the variable alive and a category 2 type?
if (isAliveBefore(offset, variableIndex))
{
Value value = partialEvaluator.getVariablesBefore(offset).getValue(variableIndex);
if (value != null && value.isCategory2())
{
// Mark it as such.
setCategory2(offset, variableIndex, true);
// Mark the next variable as well.
setAliveBefore(offset, variableIndex + 1, true);
setCategory2( offset, variableIndex + 1, true);
}
}
// Is the variable alive and a category 2 type?
if (isAliveAfter(offset, variableIndex))
{
Value value = partialEvaluator.getVariablesAfter(offset).getValue(variableIndex);
if (value != null && value.isCategory2())
{
// Mark it as such.
setCategory2(offset, variableIndex, true);
// Mark the next variable as well.
setAliveAfter(offset, variableIndex + 1, true);
setCategory2( offset, variableIndex + 1, true);
}
}
}
}
}
if (DEBUG)
{
// Loop over all instructions.
for (int offset = 0; offset < codeLength; offset++)
{
if (partialEvaluator.isTraced(offset))
{
long aliveBefore = isAliveBefore[offset];
long aliveAfter = isAliveAfter[offset];
long category2 = isCategory2[offset];
// Print out the liveness of all variables before the instruction.
for (int variableIndex = 0; variableIndex < variablesSize; variableIndex++)
{
long variableMask = (1L << variableIndex);
System.out.print((aliveBefore & variableMask) == 0L ? '.' :
(category2 & variableMask) == 0L ? 'x' :
'*');
}
// Print out the instruction itself.
System.out.println(" "+ InstructionFactory.create(codeAttribute.code, offset).toString(offset));
// Print out the liveness of all variables after the instruction.
for (int variableIndex = 0; variableIndex < variablesSize; variableIndex++)
{
long variableMask = (1L << variableIndex);
System.out.print((aliveAfter & variableMask) == 0L ? '.' :
(category2 & variableMask) == 0L ? 'x' :
'=');
}
System.out.println();
}
}
}
}
// Implementations for InstructionVisitor.
public void visitAnyInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, Instruction instruction) {}
public void visitVariableInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, VariableInstruction variableInstruction)
{
int variableIndex = variableInstruction.variableIndex;
if (variableIndex < MAX_VARIABLES_SIZE)
{
long livenessMask = 1L << variableIndex;
// Is it a load instruction or a store instruction?
if (variableInstruction.isLoad())
{
// Start marking the variable before the load instruction.
alive |= livenessMask;
}
else
{
// Stop marking the variable before the store instruction.
alive &= ~livenessMask;
// But do mark the variable right after the store instruction.
isAliveAfter[offset] |= livenessMask;
}
}
}
public void visitConstantInstruction(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, ConstantInstruction constantInstruction)
{
// Special case: variable 0 ('this') in an initializer has to be alive
// as long as it hasn't been initialized.
if (offset == initializationFinder.superInitializationOffset())
{
alive |= 1L;
}
}
// Implementations for ExceptionInfoVisitor.
public void visitExceptionInfo(Clazz clazz, Method method, CodeAttribute codeAttribute, ExceptionInfo exceptionInfo)
{
// Are any variables alive at the start of the handler?
long alive = isAliveBefore[exceptionInfo.u2handlerPC];
if (alive != 0L)
{
// Set the same liveness flags for the entire try block.
int startOffset = exceptionInfo.u2startPC;
int endOffset = exceptionInfo.u2endPC;
for (int offset = startOffset; offset < endOffset; offset++)
{
if (partialEvaluator.isTraced(offset))
{
if ((~(isAliveBefore[offset] & isAliveAfter[offset]) & alive) != 0L)
{
isAliveBefore[offset] |= alive;
isAliveAfter[offset] |= alive;
// Check again after having marked this try block.
checkAgain = true;
}
}
}
}
}
// Small utility methods.
/**
* Returns the combined liveness mask of the variables right before the
* specified instruction offsets.
*/
private long combinedLiveness(InstructionOffsetValue instructionOffsetValue)
{
long alive = 0L;
int count = instructionOffsetValue.instructionOffsetCount();
for (int index = 0; index < count; index++)
{
alive |= isAliveBefore[instructionOffsetValue.instructionOffset(index)];
}
return alive;
}
}
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