public static CfgLoop GetLoopInformation(ControlFlowGraph graph, List <int> nodes)
{
if (nodes == null)
{
throw new ArgumentNullException(nameof(nodes));
}
if (nodes.Count == 0)
{
throw new ArgumentException("Empty loop provided to GetLoopInformation", nameof(nodes));
}
var body = new List <LoopPart>();
var header = new LoopPart(nodes[0], true);
var exits = new HashSet <int>();
// Determine if header can break out of the loop
foreach (int child in graph.Children(nodes[0]))
{
if (nodes.Contains(child))
{
continue;
}
CfgEdge edgeLabel = graph.GetEdgeLabel(nodes[0], child);
if (edgeLabel == CfgEdge.LoopSuccessor) // Loop successor pseudo-edges don't count for break-detection
{
continue;
}
header = new LoopPart(header.Index, true, Break: true, Negated: edgeLabel == CfgEdge.True);
exits.Add(child);
}
for (int i = 1; i < nodes.Count; i++)
{
var node = nodes[i];
bool isContinue = false;
bool isBreak = false;
bool isTail = true;
bool negated = false;
foreach (int child in graph.Children(node))
{
// Func<string> vis = () => ToVis().AddPointer("i", node).AddPointer("child", child).ToString(); // For VS Code debug visualisation
if (child == header.Index) // Jump to header = possible continue
{
isContinue = true;
}
else if (nodes.Contains(child))
{
isTail = false;
}
else
{
negated = graph.GetEdgeLabel(node, child) == CfgEdge.False;
isBreak = true;
exits.Add(child);
}
}
bool hasOutsideEntry = Enumerable.Any(graph.Parents(node), x => !nodes.Contains(x));
body.Add(new LoopPart(node, false, isTail, isBreak, isContinue, hasOutsideEntry, negated));
}
var postDom = graph.GetPostDominatorTree();
int?mainExit = postDom.ImmediateDominator(header.Index);
while (mainExit.HasValue && body.Any(x => !postDom.Dominates(mainExit.Value, x.Index)))
{
mainExit = postDom.ImmediateDominator(mainExit.Value);
}
if (body.Count(x => x.Tail) > 1) // Only allow one tail, pick one of the nodes with the longest path from the header.
{
var longestPaths = new Dictionary <int, int>();
for (int i = 0; i < body.Count; i++)
{
var part = body[i];
if (!part.Tail)
{
continue;
}
var paths = graph.GetAllReachingPaths(header.Index, part.Index);
longestPaths[i] = paths.Select(x => x.Count).Max();
}
var longestDistance = longestPaths.Values.Max();
var winner = longestPaths.First(x => x.Value == longestDistance).Key;
foreach (var kvp in longestPaths)
{
if (kvp.Key == winner)
{
continue;
}
var part = body[kvp.Key];
body[kvp.Key] = new LoopPart(part.Index, part.Header, false, part.Break, part.Continue, part.OutsideEntry, part.Negated);
}
}
return(new CfgLoop(header, body.ToImmutableList(), exits.ToImmutableList(), mainExit));
}
