Example:
* *
* // Method to analyze
* public Object doSomething(int x) {
* Number n;
* if (x < 5) {
* n = new Double(0);
* } else {
* n = new Long(0);
* }
*
* return n;
* }
*
* // Which compiles to:
* // 0: iload_1
* // 1: iconst_5
* // 2: if_icmpge 17
* // 5: new #18; //class java/lang/Double
* // 8: dup
* // 9: dconst_0
* // 10: invokespecial #44; //Method java/lang/Double."":(D)V
* // 13: astore_2
* // 14: goto 26
* // 17: new #16; //class java/lang/Long
* // 20: dup
* // 21: lconst_1
* // 22: invokespecial #47; //Method java/lang/Long."":(J)V
* // 25: astore_2
* // 26: aload_2
* // 27: areturn
*
* public void analyzeIt(CtClass clazz, MethodInfo method) {
* Analyzer analyzer = new Analyzer();
* Frame[] frames = analyzer.analyze(clazz, method);
* frames[0].getLocal(0).getCtClass(); // returns clazz;
* frames[0].getLocal(1).getCtClass(); // returns java.lang.String
* frames[1].peek(); // returns Type.INTEGER
* frames[27].peek().getCtClass(); // returns java.lang.Number
* }
*
*
* @see FramePrinter
* @author Jason T. Greene
*/
public class Analyzer implements Opcode {
private final SubroutineScanner scanner = new SubroutineScanner();
private CtClass clazz;
private ExceptionInfo[] exceptions;
private Frame[] frames;
private Subroutine[] subroutines;
private static class ExceptionInfo {
private int end;
private int handler;
private int start;
private Type type;
private ExceptionInfo(int start, int end, int handler, Type type) {
this.start = start;
this.end = end;
this.handler = handler;
this.type = type;
}
}
/**
* Performs data-flow analysis on a method and returns an array, indexed by
* instruction position, containing the starting frame state of all reachable
* instructions. Non-reachable code, and illegal code offsets are represented
* as a null in the frame state array. This can be used to detect dead code.
*
* If the method does not contain code (it is either native or abstract), null
* is returned.
*
* @param clazz the declaring class of the method
* @param method the method to analyze
* @return an array, indexed by instruction position, of the starting frame state,
* or null if this method doesn't have code
* @throws BadBytecode if the bytecode does not comply with the JVM specification
*/
public Frame[] analyze(CtClass clazz, MethodInfo method) throws BadBytecode {
this.clazz = clazz;
CodeAttribute codeAttribute = method.getCodeAttribute();
// Native or Abstract
if (codeAttribute == null)
return null;
int maxLocals = codeAttribute.getMaxLocals();
int maxStack = codeAttribute.getMaxStack();
int codeLength = codeAttribute.getCodeLength();
CodeIterator iter = codeAttribute.iterator();
IntQueue queue = new IntQueue();
exceptions = buildExceptionInfo(method);
subroutines = scanner.scan(method);
Executor executor = new Executor(clazz.getClassPool(), method.getConstPool());
frames = new Frame[codeLength];
frames[iter.lookAhead()] = firstFrame(method, maxLocals, maxStack);
queue.add(iter.next());
while (!queue.isEmpty()) {
analyzeNextEntry(method, iter, queue, executor);
}
return frames;
}
/**
* Performs data-flow analysis on a method and returns an array, indexed by
* instruction position, containing the starting frame state of all reachable
* instructions. Non-reachable code, and illegal code offsets are represented
* as a null in the frame state array. This can be used to detect dead code.
*
* If the method does not contain code (it is either native or abstract), null
* is returned.
*
* @param method the method to analyze
* @return an array, indexed by instruction position, of the starting frame state,
* or null if this method doesn't have code
* @throws BadBytecode if the bytecode does not comply with the JVM specification
*/
public Frame[] analyze(CtMethod method) throws BadBytecode {
return analyze(method.getDeclaringClass(), method.getMethodInfo2());
}
private void analyzeNextEntry(MethodInfo method, CodeIterator iter,
IntQueue queue, Executor executor) throws BadBytecode {
int pos = queue.take();
iter.move(pos);
iter.next();
Frame frame = frames[pos].copy();
Subroutine subroutine = subroutines[pos];
try {
executor.execute(method, pos, iter, frame, subroutine);
} catch (RuntimeException e) {
throw new BadBytecode(e.getMessage() + "[pos = " + pos + "]", e);
}
int opcode = iter.byteAt(pos);
if (opcode == TABLESWITCH) {
mergeTableSwitch(queue, pos, iter, frame);
} else if (opcode == LOOKUPSWITCH) {
mergeLookupSwitch(queue, pos, iter, frame);
} else if (opcode == RET) {
mergeRet(queue, iter, pos, frame, subroutine);
} else if (Util.isJumpInstruction(opcode)) {
int target = Util.getJumpTarget(pos, iter);
if (Util.isJsr(opcode)) {
// Merge the state before the jsr into the next instruction
mergeJsr(queue, frames[pos], subroutines[target], pos, lookAhead(iter, pos));
} else if (! Util.isGoto(opcode)) {
merge(queue, frame, lookAhead(iter, pos));
}
merge(queue, frame, target);
} else if (opcode != ATHROW && ! Util.isReturn(opcode)) {
// Can advance to next instruction
merge(queue, frame, lookAhead(iter, pos));
}
// Merge all exceptions that are reachable from this instruction.
// The redundancy is intentional, since the state must be based
// on the current instruction frame.
mergeExceptionHandlers(queue, method, pos, frame);
}
private ExceptionInfo[] buildExceptionInfo(MethodInfo method) {
ConstPool constPool = method.getConstPool();
ClassPool classes = clazz.getClassPool();
ExceptionTable table = method.getCodeAttribute().getExceptionTable();
ExceptionInfo[] exceptions = new ExceptionInfo[table.size()];
for (int i = 0; i < table.size(); i++) {
int index = table.catchType(i);
Type type;
try {
type = index == 0 ? Type.THROWABLE : Type.get(classes.get(constPool.getClassInfo(index)));
} catch (NotFoundException e) {
throw new IllegalStateException(e.getMessage());
}
exceptions[i] = new ExceptionInfo(table.startPc(i), table.endPc(i), table.handlerPc(i), type);
}
return exceptions;
}
private Frame firstFrame(MethodInfo method, int maxLocals, int maxStack) {
int pos = 0;
Frame first = new Frame(maxLocals, maxStack);
if ((method.getAccessFlags() & AccessFlag.STATIC) == 0) {
first.setLocal(pos++, Type.get(clazz));
}
CtClass[] parameters;
try {
parameters = Descriptor.getParameterTypes(method.getDescriptor(), clazz.getClassPool());
} catch (NotFoundException e) {
throw new RuntimeException(e);
}
for (int i = 0; i < parameters.length; i++) {
Type type = zeroExtend(Type.get(parameters[i]));
first.setLocal(pos++, type);
if (type.getSize() == 2)
first.setLocal(pos++, Type.TOP);
}
return first;
}
private int getNext(CodeIterator iter, int of, int restore) throws BadBytecode {
iter.move(of);
iter.next();
int next = iter.lookAhead();
iter.move(restore);
iter.next();
return next;
}
private int lookAhead(CodeIterator iter, int pos) throws BadBytecode {
if (! iter.hasNext())
throw new BadBytecode("Execution falls off end! [pos = " + pos + "]");
return iter.lookAhead();
}
private void merge(IntQueue queue, Frame frame, int target) {
Frame old = frames[target];
boolean changed;
if (old == null) {
frames[target] = frame.copy();
changed = true;
} else {
changed = old.merge(frame);
}
if (changed) {
queue.add(target);
}
}
private void mergeExceptionHandlers(IntQueue queue, MethodInfo method, int pos, Frame frame) {
for (int i = 0; i < exceptions.length; i++) {
ExceptionInfo exception = exceptions[i];
// Start is inclusive, while end is exclusive!
if (pos >= exception.start && pos < exception.end) {
Frame newFrame = frame.copy();
newFrame.clearStack();
newFrame.push(exception.type);
merge(queue, newFrame, exception.handler);
}
}
}
private void mergeJsr(IntQueue queue, Frame frame, Subroutine sub, int pos, int next) throws BadBytecode {
if (sub == null)
throw new BadBytecode("No subroutine at jsr target! [pos = " + pos + "]");
Frame old = frames[next];
boolean changed = false;
if (old == null) {
old = frames[next] = frame.copy();
changed = true;
} else {
for (int i = 0; i < frame.localsLength(); i++) {
// Skip everything accessed by a subroutine, mergeRet must handle this
if (!sub.isAccessed(i)) {
Type oldType = old.getLocal(i);
Type newType = frame.getLocal(i);
if (oldType == null) {
old.setLocal(i, newType);
changed = true;
continue;
}
newType = oldType.merge(newType);
// Always set the type, in case a multi-type switched to a standard type.
old.setLocal(i, newType);
if (!newType.equals(oldType) || newType.popChanged())
changed = true;
}
}
}
if (! old.isJsrMerged()) {
old.setJsrMerged(true);
changed = true;
}
if (changed && old.isRetMerged())
queue.add(next);
}
private void mergeLookupSwitch(IntQueue queue, int pos, CodeIterator iter, Frame frame) throws BadBytecode {
int index = (pos & ~3) + 4;
// default
merge(queue, frame, pos + iter.s32bitAt(index));
int npairs = iter.s32bitAt(index += 4);
int end = npairs * 8 + (index += 4);
// skip "match"
for (index += 4; index < end; index += 8) {
int target = iter.s32bitAt(index) + pos;
merge(queue, frame, target);
}
}
private void mergeRet(IntQueue queue, CodeIterator iter, int pos, Frame frame, Subroutine subroutine) throws BadBytecode {
if (subroutine == null)
throw new BadBytecode("Ret on no subroutine! [pos = " + pos + "]");
Iterator callerIter = subroutine.callers().iterator();
while (callerIter.hasNext()) {
int caller = ((Integer) callerIter.next()).intValue();
int returnLoc = getNext(iter, caller, pos);
boolean changed = false;
Frame old = frames[returnLoc];
if (old == null) {
old = frames[returnLoc] = frame.copyStack();
changed = true;
} else {
changed = old.mergeStack(frame);
}
for (Iterator i = subroutine.accessed().iterator(); i.hasNext(); ) {
int index = ((Integer)i.next()).intValue();
Type oldType = old.getLocal(index);
Type newType = frame.getLocal(index);
if (oldType != newType) {
old.setLocal(index, newType);
changed = true;
}
}
if (! old.isRetMerged()) {
old.setRetMerged(true);
changed = true;
}
if (changed && old.isJsrMerged())
queue.add(returnLoc);
}
}
private void mergeTableSwitch(IntQueue queue, int pos, CodeIterator iter, Frame frame) throws BadBytecode {
// Skip 4 byte alignment padding
int index = (pos & ~3) + 4;
// default
merge(queue, frame, pos + iter.s32bitAt(index));
int low = iter.s32bitAt(index += 4);
int high = iter.s32bitAt(index += 4);
int end = (high - low + 1) * 4 + (index += 4);
// Offset table
for (; index < end; index += 4) {
int target = iter.s32bitAt(index) + pos;
merge(queue, frame, target);
}
}
private Type zeroExtend(Type type) {
if (type == Type.SHORT || type == Type.BYTE || type == Type.CHAR || type == Type.BOOLEAN)
return Type.INTEGER;
return type;
}
}