RWRoute and routethru-s

[eddieh-xlnx]

On the back of a question from #510: what does the routethru check here

RapidWright/src/com/xilinx/rapidwright/rwroute/RoutableNode.java

Lines 130 to 137 in bb3dc2b

	public int setChildren(int globalIndex, Map<Node, Routable> createdRoutable, Set<Node> reserved, RouteThruHelper routethruHelper){
	children = new ArrayList<>();
	List<Node> allDownHillNodes = node.getAllDownhillNodes();
	for(Node downhill : allDownHillNodes){
	if(reserved.contains(downhill)) continue;
	if(isExcluded(downhill, timingDriven)) continue;
	if(routethruHelper.isRouteThru(node, downhill)) continue;

do since it was broken since RWRoute's initial release and doesn't seem to have affected anything?

I think the answer is that this check eliminates the routethru nodes appearing in the graph at all.

The reason it doesn't have an effect is that routethru-s were actually being discarded later during RWRoute.exploreAndExpand() (which processes the child nodes gotten from the graph) for non-SLR crossings -- since in order to do a routethru one must pass through a PINFEED_I type node?

RapidWright/src/com/xilinx/rapidwright/rwroute/RWRoute.java

Lines 1459 to 1464 in bb3dc2b

	}else if(childRNode.getRoutableType() == RoutableType.PINFEED_I) {
	if(connection.isCrossSLR()) {
	evaluateCostAndPush(rnode, longParent, childRNode, connection, shareWeight, rnodeCostWeight,
	rnodeLengthWeight, rnodeEstWlWeight, rnodeDelayWeight, rnodeEstDlyWeight);
	}
	}

Thoughts @clavin-xlnx @pongstorn-xilinx @YunxZhou?