Actually, there might not be any harm in updating sigmap...

passes/techmap/shregmap.cc

@@ -304,11 +304,9 @@ struct ShregmapWorker
 						// so that it can be identified as another chain
 						// (omitting this common flop)
 						// Link: https://github.com/YosysHQ/yosys/pull/1085
-						// NB: This relies on us not updating sigmap with this
-						//     alias otherwise it would think they are the same
-						//     wire
 						Wire *wire = module->addWire(NEW_ID);
 						module->connect(wire, d_bit);
+						sigmap.add(wire, d_bit);
 						sigbit_chain_next.insert(std::make_pair(wire, cell));
 					}