@Override
protected boolean checkMidTierGraph(StructuredGraph graph) {
int count = 0;
for (IsNullNode isNull : graph.getNodes().filter(IsNullNode.class).snapshot()) {
ValueNode value = isNull.getValue();
if (value instanceof CompressionNode) {
count++;
isNull.replaceFirstInput(value, ((CompressionNode) value).getValue());
}
}
Assert.assertEquals("graph should contain exactly one IsNullNode", 1, count);
return super.checkMidTierGraph(graph);
}
/**
* 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);
}