I'm not sure what would constitute a good reference given the breadth of applications of graph theory in integrated circuit design.
You could glance at the floorplanning, placement and routing chapters of Smith's "Application specific integrated circuits" to get a feel for what is involved. It is an old book (1997) but gives a decent, fairly concise overview.
However, the term 'optimal' is hard to characterize in terms of cpu design, there are many conflicting objectives that need to be addressed. The old adage was "power, speed, area - pick two". Design (in the broad sense) has become considerably more complicated since those relatively simple days.