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()));
}
