Factors that can affect compile time improvement include:
- The amount of change in timing-critical areas. If critical path placement and routing cannot be reused, more effort is required to preserve timing. Also, if the small design changes introduce new timing problems that did not exist in the reference design, higher effort and compile time might be required, and the design might not meet timing.
- The initialization portion of the place and route runtime. In short place and route runs, the initialization overhead of the placer and router might eliminate any gain from the incremental place and route process. For designs with longer compile times, initialization becomes a small percentage of the runtime.