The following input (a reduction of an example of dot syntax on wikipedia) causes dot to hang indefinitely (or... at least for 3 or 4 minutes now, which is effectively forever!) on my dual-core machine. By removing any element from the sample input, dot will process the file in less than a second.

```
```digraph g {
A1 -> B1
A2 -> B2
A3 -> B3
A2 -> A3
B1 -> B3 [label="xyz" tailport=s headport=s]
B2 -> B3
{ rank=same; B1 B2 B3 } }

[erg] The base problem is that the spline router produces an incorrect route, which goes wildly outside the given boxes. The code recognizes something has gone wrong. This is usually a case where increased sampling helps but since a line segment is involved, finer sampling doesn't help.