/**
* Determine whether dataflow should be propagated on given edge.
*
* @param edge the edge
* @return true if dataflow should be propagated on the edge, false otherwise
*/
private boolean isExceptionEdge(Edge edge) {
boolean isExceptionEdge = edge.isExceptionEdge();
if (isExceptionEdge) {
if (DEBUG) {
System.out.println("NOT Ignoring " + edge);
}
return true; // false
}
if (edge.getType() != EdgeTypes.FALL_THROUGH_EDGE) {
return false;
}
InstructionHandle h = edge.getSource().getLastInstruction();
if (h != null
&& h.getInstruction() instanceof IFNONNULL
&& isNullCheck(h, methodGen.getConstantPool())) {
return true;
}
return false;
}
/**
* Clear deref sets of values if this edge is the non-null branch of an if comparison.
*
* @param fact a datflow fact
* @param edge edge to check
* @return possibly-modified dataflow fact
*/
private @CheckForNull ValueNumber findValueKnownNonnullOnBranch(
UnconditionalValueDerefSet fact, Edge edge) {
IsNullValueFrame invFrame = invDataflow.getResultFact(edge.getSource());
if (!invFrame.isValid()) {
return null;
}
IsNullConditionDecision decision = invFrame.getDecision();
if (decision == null) {
return null;
}
IsNullValue inv = decision.getDecision(edge.getType());
if (inv == null || !inv.isDefinitelyNotNull()) {
return null;
}
ValueNumber value = decision.getValue();
if (DEBUG) {
System.out.println("Value number " + value + " is known nonnull on " + edge);
}
return value;
}
/**
* Find out if any VNs in the source block contribute to unconditionally dereferenced VNs in the
* target block. If so, the VN in the source block is also unconditionally dereferenced, and we
* must propagate the target VN's dereferences.
*
* @param fact a dataflow value
* @param edge edge to check for merge input values
* @return possibly-modified dataflow value
*/
private UnconditionalValueDerefSet propagateDerefSetsToMergeInputValues(
UnconditionalValueDerefSet fact, Edge edge) {
ValueNumberFrame blockValueNumberFrame = vnaDataflow.getResultFact(edge.getSource());
ValueNumberFrame targetValueNumberFrame = vnaDataflow.getStartFact(edge.getTarget());
UnconditionalValueDerefSet originalFact = fact;
fact = duplicateFact(fact);
if (blockValueNumberFrame.isValid() && targetValueNumberFrame.isValid()) {
int slots = 0;
if (targetValueNumberFrame.getNumSlots() == blockValueNumberFrame.getNumSlots()) {
slots = targetValueNumberFrame.getNumSlots();
} else if (targetValueNumberFrame.getNumLocals() == blockValueNumberFrame.getNumLocals()) {
slots = targetValueNumberFrame.getNumLocals();
}
if (slots > 0) {
if (DEBUG) {
System.out.println("** Valid VNA frames for " + edge);
System.out.println("** Block : " + blockValueNumberFrame);
System.out.println("** Target: " + targetValueNumberFrame);
}
for (int i = 0; i < slots; i++) {
ValueNumber blockVN = blockValueNumberFrame.getValue(i);
ValueNumber targetVN = targetValueNumberFrame.getValue(i);
if (blockVN.equals(targetVN)) {
continue;
}
fact.clearDerefSet(blockVN);
if (originalFact.isUnconditionallyDereferenced(targetVN)) {
fact.setDerefSet(blockVN, originalFact.getUnconditionalDerefLocationSet(targetVN));
}
} // for all slots
for (ValueNumber blockVN : blockValueNumberFrame.valueNumbersForLoads()) {
AvailableLoad load = blockValueNumberFrame.getLoad(blockVN);
if (load == null) {
continue;
}
ValueNumber[] targetVNs = targetValueNumberFrame.getAvailableLoad(load);
if (targetVNs != null) {
for (ValueNumber targetVN : targetVNs) {
if (targetVN.hasFlag(ValueNumber.PHI_NODE)
&& fact.isUnconditionallyDereferenced(targetVN)
&& !fact.isUnconditionallyDereferenced(blockVN)) {
// Block VN is also dereferenced
// unconditionally.
AvailableLoad targetLoad = targetValueNumberFrame.getLoad(targetVN);
if (!load.equals(targetLoad)) {
continue;
}
if (DEBUG) {
System.out.println(
"** Copy vn derefs for " + load + " from " + targetVN + " --> " + blockVN);
System.out.println(
"** block phi for "
+ System.identityHashCode(blockValueNumberFrame)
+ " is "
+ blockValueNumberFrame.phiNodeForLoads);
System.out.println(
"** target phi for "
+ System.identityHashCode(targetValueNumberFrame)
+ " is "
+ targetValueNumberFrame.phiNodeForLoads);
}
fact.setDerefSet(blockVN, fact.getUnconditionalDerefLocationSet(targetVN));
}
}
}
}
}
}
if (DEBUG) {
System.out.println("Target VNF: " + targetValueNumberFrame);
System.out.println("Block VNF: " + blockValueNumberFrame);
System.out.println("fact: " + fact);
}
fact.cleanDerefSet(null, blockValueNumberFrame);
return fact;
}
public void meetInto(
UnconditionalValueDerefSet fact,
Edge edge,
UnconditionalValueDerefSet result,
boolean onlyEdge) {
if (isExceptionEdge(edge) && !onlyEdge) {
if (DEBUG) {
System.out.println("Skipping exception edge");
}
return;
}
ValueNumber knownNonnullOnBranch = null;
// Edge transfer function
if (isFactValid(fact)) {
fact = propagateDerefSetsToMergeInputValues(fact, edge);
if (invDataflow != null) {
knownNonnullOnBranch = findValueKnownNonnullOnBranch(fact, edge);
if (knownNonnullOnBranch != null) {
fact = duplicateFact(fact);
fact.clearDerefSet(knownNonnullOnBranch);
}
}
}
boolean isBackEdge = edge.isBackwardInBytecode();
Set<Integer> loopExitBranches = ClassContext.getLoopExitBranches(method, methodGen);
assert loopExitBranches != null;
boolean sourceIsTopOfLoop = edge.sourceIsTopOfLoop(loopExitBranches);
if (sourceIsTopOfLoop && edge.getType() == EdgeTypes.FALL_THROUGH_EDGE) {
isBackEdge = true;
}
/*
if (false && (edge.getType() == EdgeTypes.IFCMP_EDGE || sourceIsTopOfLoop)) {
System.out.println("Meet into " + edge);
System.out.println(" foo2: " + sourceIsTopOfLoop);
System.out.println(" getType: " + edge.getType());
System.out.println(" Backedge according to bytecode: " + isBackEdge);
System.out.println(" Fact hashCode: " + System.identityHashCode(result));
System.out.println(" Initial fact: " + result);
System.out.println(" Edge fact: " + fact);
}
*/
if (result.isTop() || fact.isBottom()) {
// Make result identical to other fact
copy(fact, result);
if (ASSUME_NONZERO_TRIP_LOOPS && isBackEdge && !fact.isTop()) {
result.resultsFromBackEdge = true;
}
} else if (ASSUME_NONZERO_TRIP_LOOPS && isBackEdge && !fact.isTop()) {
result.unionWith(fact, vnaDataflow.getAnalysis().getFactory());
result.resultsFromBackEdge = true;
if (DEBUG) {
System.out.println(
"\n Forcing union of " + System.identityHashCode(result) + " due to backedge info");
System.out.println(" result: " + result);
}
} else if (result.isBottom() || fact.isTop()) {
// No change in result fact
} else {
// Dataflow merge
// (intersection of unconditional deref values)
if (ASSUME_NONZERO_TRIP_LOOPS && result.resultsFromBackEdge) {
result.backEdgeUpdateCount++;
if (result.backEdgeUpdateCount < 10) {
if (DEBUG) {
System.out.println(
"\n Union update of " + System.identityHashCode(result) + " due to backedge info");
}
result.unionWith(fact, vnaDataflow.getAnalysis().getFactory());
return;
}
}
result.mergeWith(fact, knownNonnullOnBranch, vnaDataflow.getAnalysis().getFactory());
if (DEBUG) {
System.out.println(" updated: " + System.identityHashCode(result));
System.out.println(" result: " + result);
}
}
if (DEBUG && isBackEdge && edge.getType() == EdgeTypes.IFCMP_EDGE) {
System.out.println(" result: " + result);
}
}
