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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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