Expensive wire to node mapping

[acomodi]

It is quite expensive, in terms of run-time, to build the Wire --> Node mapping: it takes ~10 seconds for a xc7a35t device, not a huge problem, but it may become one for bigger devices.

The Wire --> Node mapping is useful for lookups, specifically when trying to access all the other wires connected to a particular node for a given wire.

It might make sense to add a nodeIdx field to the wires, but I am unsure on the drawbacks of adding such a field.

[gatecat]

Long term, this might tie into routing graph folding too, there are efficient ways of folding routing graphs that get a fast bidirectional mapping without ever needing to flatten the graph.