private void LowerDecisionDagCore(BoundDecisionDag decisionDag)
{
ImmutableArray <BoundDecisionDagNode> sortedNodes = decisionDag.TopologicallySortedNodes;
var firstNode = sortedNodes[0];
switch (firstNode)
{
case BoundWhenDecisionDagNode _:
case BoundLeafDecisionDagNode _:
// If the first node is a leaf or when clause rather than the code for the
// lowered decision dag, jump there to start.
_loweredDecisionDag.Add(_factory.Goto(GetDagNodeLabel(firstNode)));
break;
}
// Code for each when clause goes in the separate code section for its switch section.
foreach (BoundDecisionDagNode node in sortedNodes)
{
if (node is BoundWhenDecisionDagNode w)
{
LowerWhenClause(w);
}
}
ImmutableArray <BoundDecisionDagNode> nodesToLower = sortedNodes.WhereAsArray(n => n.Kind != BoundKind.WhenDecisionDagNode && n.Kind != BoundKind.LeafDecisionDagNode);
var loweredNodes = PooledHashSet <BoundDecisionDagNode> .GetInstance();
for (int i = 0, length = nodesToLower.Length; i < length; i++)
{
BoundDecisionDagNode node = nodesToLower[i];
if (loweredNodes.Contains(node))
{
Debug.Assert(!_dagNodeLabels.TryGetValue(node, out _));
continue;
}
if (this._dagNodeLabels.TryGetValue(node, out LabelSymbol label))
{
_loweredDecisionDag.Add(_factory.Label(label));
}
// If we can generate an IL switch instruction, do so
if (GenerateSwitchDispatch(node, loweredNodes))
{
continue;
}
// If we can generate a type test and cast more efficiently as an `is` followed by a null check, do so
if (GenerateTypeTestAndCast(node, loweredNodes, nodesToLower, i))
{
continue;
}
// We pass the node that will follow so we can permit a test to fall through if appropriate
BoundDecisionDagNode nextNode = ((i + 1) < length) ? nodesToLower[i + 1] : null;
if (nextNode != null && loweredNodes.Contains(nextNode))
{
nextNode = null;
}
LowerDecisionDagNode(node, nextNode);
}
loweredNodes.Free();
}
