/// <summary>
/// Replaces nodes with an error statement and an error edge with an empty node and a continue edge
/// </summary>
/// <param name="cfg"></param>
/// <returns></returns>
public static IControlFlowGraph NormalizeErrors(this IControlFlowGraph cfg)
{
var todo = new HashSet <IBasicBlock>();
// Remove the error statements and save blocks to remove edges from
cfg = cfg.Modify((a, b) => {
if (!a.Statements.Any())
{
return;
}
var toCopy = a.Statements;
if ((a.Statements.Last() is ErrorStatement) && a.Outgoing.Count() == 1 && a.Outgoing.Single().Type == EdgeType.RuntimeError)
{
toCopy = a.Statements.Take(a.Statements.Count() - 1);
todo.Add(b);
}
foreach (var stmt in toCopy)
{
b.Add(stmt);
}
});
// Copy graph, replacing edges as necessary
return(cfg.Modify((e, c) => {
c(e.Start, e.End, todo.Contains(e.Start) ? EdgeType.Continue : e.Type);
}));
}
/// <summary>
/// Merge together basic blocks on the same line connected only by a continue edge
/// </summary>
/// <param name="cfg"></param>
/// <returns></returns>
public static IControlFlowGraph MergeAdjacentBasicBlocks(this IControlFlowGraph cfg)
{
// This keeps looping until it finds no work to do
while (true)
{
// Find all candidates for merging
var candidates = (from vertex in cfg.Vertices
where vertex.Type == BasicBlockType.Basic
where vertex.Outgoing.Count() == 1
let outgoing = vertex.Outgoing.Single()
where outgoing.Type == EdgeType.Continue
where outgoing.End.LineNumber == vertex.LineNumber
where outgoing.End.Type == BasicBlockType.Basic
where outgoing.End.Incoming.Count() == 1
select(vertex, outgoing.End));
// Select a single candidate pair (A -> B), if there is no work then exit now
var work = candidates.FirstOrDefault();
if (work == default)
{
return(cfg);
}
// Move all the items from the A into B, leaving A empty
cfg = cfg.Modify((a, b) => {
if (a.ID == work.End.ID)
{
work.vertex.CopyTo(b);
a.CopyTo(b);
}
else if (a.ID != work.vertex.ID)
{
a.CopyTo(b);
}
});
// Remove all empty blocks
cfg = cfg.RemoveEmptyBlocks();
}
}