/**
* In case the scrutinee:
*
* <ul>
* <li>is known to be null, an unconditional deopt is added.
* <li>is known to be non-null, the NullCheckNode is removed.
* <li>otherwise, the NullCheckNode is lowered to a FixedGuardNode which then allows using it as
* anchor for state-tracking.
* </ul>
*
* <p>Precondition: the input (ie, object) hasn't been deverbosified yet.
*/
private void visitNullCheckNode(NullCheckNode ncn) {
ValueNode object = ncn.getObject();
if (state.isNull(object)) {
postponedDeopts.addDeoptBefore(ncn, NullCheckException);
state.impossiblePath();
return;
}
if (state.isNonNull(object)) {
/*
* Redundant NullCheckNode. Unlike GuardingPiNode or FixedGuardNode, NullCheckNode-s
* aren't used as GuardingNode-s, thus in this case can be removed without further ado.
*/
assert FlowUtil.lacksUsages(ncn);
graph.removeFixed(ncn);
return;
}
/*
* Lower the NullCheckNode to a FixedGuardNode which then allows using it as anchor for
* state-tracking. TODO the assumption here is that the code emitted for the resulting
* FixedGuardNode is as efficient as for NullCheckNode.
*/
IsNullNode isNN = graph.unique(IsNullNode.create(object));
reasoner.added.add(isNN);
FixedGuardNode nullCheck =
graph.add(FixedGuardNode.create(isNN, UnreachedCode, InvalidateReprofile, true));
graph.replaceFixedWithFixed(ncn, nullCheck);
state.trackNN(object, nullCheck);
}
/**
* Similar to {@link #deverbosifyInputsInPlace(com.oracle.graal.nodes.ValueNode)}, except that not
* the parent but a fresh clone is updated upon any of its children changing.
*
* @return the original parent if no updated took place, a copy-on-write version of it otherwise.
*/
private MethodCallTargetNode deverbosifyInputsCopyOnWrite(MethodCallTargetNode parent) {
final CallTargetNode.InvokeKind ik = parent.invokeKind();
final boolean shouldTryDevirt =
(ik == CallTargetNode.InvokeKind.Interface || ik == CallTargetNode.InvokeKind.Virtual);
boolean shouldDowncastReceiver = shouldTryDevirt;
MethodCallTargetNode changed = null;
for (ValueNode i : FlowUtil.distinctValueAndConditionInputs(parent)) {
ValueNode j = (ValueNode) reasoner.deverbosify(i);
if (shouldDowncastReceiver) {
shouldDowncastReceiver = false;
j = reasoner.downcast(j);
}
if (i != j) {
assert j != parent;
if (changed == null) {
changed = (MethodCallTargetNode) parent.copyWithInputs();
reasoner.added.add(changed);
// copyWithInputs() implies graph.unique(changed)
assert changed.isAlive();
assert FlowUtil.lacksUsages(changed);
}
FlowUtil.replaceInPlace(changed, i, j);
}
}
if (changed == null) {
return parent;
}
FlowUtil.inferStampAndCheck(changed);
/*
* No need to rememberSubstitution() because not called from deverbosify(). In detail, it's
* only deverbosify() that skips visited nodes (thus we'd better have recorded any
* substitutions we want for them). Not this case.
*/
return changed;
}
/**
* This method performs two kinds of cleanup:
*
* <ol>
* <li>marking as unreachable certain code-paths, as described in {@link
* com.oracle.graal.phases.common.cfs.BaseReduction.PostponedDeopt}
* <li>Removing nodes not in use that were added during this phase, as described next.
* </ol>
*
* <p>Methods like {@link
* com.oracle.graal.phases.common.cfs.FlowUtil#replaceInPlace(com.oracle.graal.graph.Node,
* com.oracle.graal.graph.Node, com.oracle.graal.graph.Node)} may result in old inputs becoming
* disconnected from the graph. It's not advisable to {@link
* com.oracle.graal.nodes.util.GraphUtil#tryKillUnused(com.oracle.graal.graph.Node)} at that
* moment, because one of the inputs that might get killed is one of {@link #nullConstant}, {@link
* #falseConstant}, or {@link #trueConstant}; which thus could get killed too early, before
* another invocation of {@link
* com.oracle.graal.phases.common.cfs.EquationalReasoner#deverbosify(com.oracle.graal.graph.Node)}
* needs them. To recap, {@link
* com.oracle.graal.nodes.util.GraphUtil#tryKillUnused(com.oracle.graal.graph.Node)} also
* recursively visits the inputs of the its argument.
*
* <p>This method goes over all of the nodes that deverbosification might have added, which are
* either:
*
* <ul>
* <li>{@link com.oracle.graal.nodes.calc.FloatingNode}, added by {@link
* com.oracle.graal.phases.common.cfs.EquationalReasoner#deverbosifyFloatingNode(com.oracle.graal.nodes.calc.FloatingNode)}
* ; or
* <li>{@link com.oracle.graal.nodes.java.MethodCallTargetNode}, added by {@link
* #deverbosifyInputsCopyOnWrite(com.oracle.graal.nodes.java.MethodCallTargetNode)}
* </ul>
*
* Checking if they aren't in use, proceeding to remove them in that case.
*/
@Override
public void finished() {
if (!postponedDeopts.isEmpty()) {
for (PostponedDeopt postponed : postponedDeopts) {
postponed.doRewrite(falseConstant);
}
new DeadCodeEliminationPhase(Optional).apply(graph);
}
for (MethodCallTargetNode mcn : graph.getNodes().filter(MethodCallTargetNode.class)) {
if (mcn.isAlive() && FlowUtil.lacksUsages(mcn)) {
mcn.safeDelete();
}
}
for (Node n : graph.getNodes().filter(FloatingNode.class)) {
GraphUtil.tryKillUnused(n);
}
assert !isAliveWithoutUsages(trueConstant);
assert !isAliveWithoutUsages(falseConstant);
assert !isAliveWithoutUsages(nullConstant);
super.finished();
}
private static boolean isAliveWithoutUsages(FloatingNode node) {
return node.isAlive() && FlowUtil.lacksUsages(node);
}