private static ImmutableArray <BoundDecisionDagNode> ShortestPathToNode(
ImmutableArray <BoundDecisionDagNode> nodes,
BoundDecisionDagNode node,
bool nullPaths,
out bool requiresFalseWhenClause)
{
// compute the distance from each node to the endpoint.
var dist = PooledDictionary <BoundDecisionDagNode, (int distance, BoundDecisionDagNode next)> .GetInstance();
int nodeCount = nodes.Length;
int infinity = 2 * nodeCount + 2;
int distance(BoundDecisionDagNode x)
{
if (x == null)
{
return(infinity);
}
if (dist.TryGetValue(x, out var v))
{
return(v.distance);
}
Debug.Assert(!nodes.Contains(x));
return(infinity);
}
for (int i = nodeCount - 1; i >= 0; i--)
{
var n = nodes[i];
dist.Add(n, n switch
{
BoundEvaluationDecisionDagNode e => (distance(e.Next), e.Next),
BoundTestDecisionDagNode {
Test: BoundDagNonNullTest _
} t when !nullPaths => (1 + distance(t.WhenTrue), t.WhenTrue),
BoundTestDecisionDagNode {
Test: BoundDagExplicitNullTest _
} t when !nullPaths => (1 + distance(t.WhenFalse), t.WhenFalse),
BoundTestDecisionDagNode t when distance(t.WhenTrue) is var trueDist1 && distance(t.WhenFalse) is var falseDist1 =>
(trueDist1 <= falseDist1) ? (1 + trueDist1, t.WhenTrue) : (1 + falseDist1, t.WhenFalse),
BoundWhenDecisionDagNode w when distance(w.WhenTrue) is var trueDist2 && distance(w.WhenFalse) is var falseDist2 =>
// add nodeCount to the distance if we need to flag that the path requires failure of a when clause
(trueDist2 <= falseDist2) ? (1 + trueDist2, w.WhenTrue) : (1 + (falseDist2 < nodeCount ? nodeCount : 0) + falseDist2, w.WhenFalse),
// treat the endpoint as distance 1.
// treat other nodes as not on the path to the endpoint
_ => ((n == node) ? 1 : infinity, null),
});
/// <summary>
/// Find the shortest path from the root node to the node of interest.
/// </summary>
/// <param name="nodes">The set of nodes in topological order.</param>
/// <param name="node">The node of interest.</param>
/// <param name="nullPaths">Whether to permit following paths that test for null.</param>
/// <returns>The shortest path, excluding the node of interest.</returns>
private static ImmutableArray <BoundDecisionDagNode> ShortestPathToNode(
ImmutableArray <BoundDecisionDagNode> nodes,
BoundDecisionDagNode node,
bool nullPaths)
{
// compute the distance from each node to the endpoint.
var dist = PooledDictionary <BoundDecisionDagNode, (int distance, BoundDecisionDagNode next)> .GetInstance();
int nodeCount = nodes.Length;
int distance(BoundDecisionDagNode x)
{
if (x == null)
{
return(nodeCount + 2);
}
if (dist.TryGetValue(x, out var v))
{
return(v.distance);
}
Debug.Assert(!nodes.Contains(x));
return(nodeCount + 2);
}
for (int i = nodeCount - 1; i >= 0; i--)
{
var n = nodes[i];
dist.Add(n, n switch
{
BoundEvaluationDecisionDagNode e => (distance(e.Next), e.Next),
BoundTestDecisionDagNode {
Test: BoundDagNonNullTest _
} t when !nullPaths => (1 + distance(t.WhenTrue), t.WhenTrue),
BoundTestDecisionDagNode {
Test: BoundDagExplicitNullTest _
} t when !nullPaths => (1 + distance(t.WhenFalse), t.WhenFalse),
BoundTestDecisionDagNode t when distance(t.WhenTrue) is var trueDist && distance(t.WhenFalse) is var falseDist =>
(trueDist <= falseDist) ? (1 + trueDist, t.WhenTrue) : (1 + falseDist, t.WhenFalse),
BoundWhenDecisionDagNode w when distance(w.WhenTrue) is var trueDist && distance(w.WhenFalse) is var falseDist =>
(trueDist <= falseDist) ? (1 + trueDist, w.WhenTrue) : (1 + falseDist, w.WhenFalse),
// treat the endpoint as distance 1.
// treat other nodes as not on the path to the endpoint
_ => ((n == node) ? 1 : nodeCount + 2, null),
});
