I'm wondering if the max fanout default = 5 setting is considered at all. For example, the default regression output of the zipdiv design shows fanouts > 10 (for all synthesis results): Report: _2003_: 65 Report: _1968_: 68 Report: _0081_: 32 Report: pre_sign: 68 Report: r_busy: 65 Eventually the reason for the slow design performance. I see similar problems on other designs.

Its initial run. During resizer design those high fanout values will be optimized as per given value.

So zipdiv.synthesis_preroute.v is not the golden netlist after abc fanout optimization ?

Please file a GitHub issue with source files and logs