Area Increase in Yosys 0.43 vs 0.37+64 on GCD Design (ORFS)

[rr667]

Hey everyone,

I'm seeing a big area difference between Yosys 0.37+64 and 0.43 (latest) in the ORFS GCD design with Nangate45 (and other designs as well).

With Yosys 0.37+64, I get 365 cells and an area of 523.754, but Yosys 0.43 gives me 503 cells and an area of 650.104 (same design and constraints, same ABC area script).

My goal is to synthesize the design and reduce the area as much as possible, such a cliché I know, but what are the knobs in yosys and ABC to do a synthesis exploration and reduce the area? I can't seem to find good docs for this.

Thanks a lot! 😄

Here's a quick comparison:

The newer Yosys seems to be replacing complex gates (MUX, XOR) with simpler ones (INV, NAND, AOI21), reducing critical path delay but increasing area.

Yosys 0.37+64 (git sha1 bbb8ad5)

Cells: 365
Area: 523.754
Critical Path Delay: 0.4598
Total Power: 2.30e-03

Yosys 0.43 (git sha1 ead4718)

Cells: 503
Area: 650.104
Critical Path Delay: 0.4223
Total Power: 3.15e-03

Link to the ORFS thread on slack