The tool partitions the design during a reference synthesis run performed. During the reference synthesis run, the tool partitions the design. When an incremental run starts, it compares the elaborated design with the reference run to find the changed modules. It then applies the same partitioning from the reference run, marks partitions containing the changes and those affected by them, and re-synthesizes only these marked partitions. Details about which parts were re-synthesized are available in the log file after the incremental run.
This information is in the Incremental Synthesis Report Summary. The following is an example of the report.
This section has information on which sections of the design changed and needed to be re-synthesized. In addition, it also has information on how much of the design changed from reference run to incremental run.