public CfgLoop(LoopPart header, IList <LoopPart> body, bool isMultiExit, int?mainExit)
{
Header = header;
Body = body;
IsMultiExit = isMultiExit;
MainExit = mainExit;
}
static ControlFlowGraph ReduceContinue(ControlFlowGraph graph, CfgLoop loop, LoopPart part)
{
// Func<string> vis = () => graph.ToVis().AddPointer("index", index).AddPointer("part", part.Index).ToString(); // For VS Code debug visualisation
// Outside entry = non-structured code, so give up
// Tail = the tail of a loop always continues by default, don't need a statement - the top-level loop reduction will handle it.
// Header = continuing header should be handled by simple loop rule
// !Continue = if it's not a jump back to the header, it's not a continue
// Break = shouldn't be both a continue and a break
if (part.OutsideEntry || part.Tail || part.Header || !part.Continue || part.Break)
{
return(graph);
}
var children = graph.Children(part.Index);
switch (children.Length)
{
case 1:
{
var seq = Emit.Seq(graph.Nodes[part.Index], Emit.Continue());
var tailIndex = loop.Body.First(x => x.Tail).Index;
return(graph
.ReplaceNode(part.Index, seq)
.RemoveEdge(part.Index, loop.Header.Index)
.AddEdge(part.Index, tailIndex, CfgEdge.True));
}
case 2:
return(ReplaceLoopBranch(graph, part.Index, loop.Header.Index, Emit.Continue()));
default:
throw new ControlFlowGraphException($"Continue at {part.Index} has unexpected child count ({children.Length})", graph);
}
}
static ControlFlowGraph ReduceBreak(ControlFlowGraph graph, CfgLoop loop, LoopPart part)
{
// Func<string> vis = () => graph.ToVis().AddPointer("part", part.Index).ToString(); // For VS Code debug visualisation
// Break = needs to exit the loop to be a break
if (!part.Break)
{
return(graph);
}
// Outside entry = non-structured code, so give up
if (part.OutsideEntry)
{
return(graph);
}
var children = graph.Children(part.Index);
if (children.Length != 2)
{
throw new ControlFlowGraphException($"Break at {part.Index} has unexpected child count ({children.Length})", graph);
}
bool isfirstChildInLoop = loop.Body.Any(x => x.Index == children[0]) || children[0] == loop.Header.Index;
var exitTarget = isfirstChildInLoop ? children[1] : children[0];
// Add LoopSuccessor edge if this is the last link to the MainExit.
var remainingLoopChildren = loop.Body
.Where(x => x.Index != part.Index)
.Aggregate(
(IEnumerable <int>)graph.Children(loop.Header.Index),
(current, x) => current.Union(graph.Children(x.Index)));
if (loop.MainExit.HasValue && !remainingLoopChildren.Contains(loop.MainExit.Value))
{
graph = graph.AddEdge(loop.Header.Index, loop.MainExit.Value, CfgEdge.LoopSuccessor);
}
if (exitTarget != loop.MainExit)
{
var targetChildren = graph.Children(exitTarget);
if (targetChildren.Length != 1 || targetChildren[0] != loop.MainExit)
{
return(graph);
}
var condition = graph.Nodes[part.Index];
if (graph.GetEdgeLabel(part.Index, exitTarget) == CfgEdge.False)
{
condition = Emit.Negation(condition);
}
var ifNode = Emit.If(condition, Emit.Seq(graph.Nodes[exitTarget], Emit.Break()));
return(graph
.RemoveNode(exitTarget)
.ReplaceNode(part.Index, ifNode));
}
return(ReplaceLoopBranch(graph, part.Index, exitTarget, Emit.Break()));
}
public CfgLoop(LoopPart header, ImmutableList <LoopPart> body, ImmutableList <int> exits, int?mainExit)
{
Header = header;
Body = body;
Exits = exits;
MainExit = mainExit;
}
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));
}
