Yosys CSA tree - demo

[Goubermouche]

This PR aims to evaluate QoR of YosysHQ/yosys#5753, which introduces a new CSA pass, potentially improving critical path length. Note that the CSA pass runs before the wrapped operator flow (SWAP_ARITH_OPERATORS). The CSA pass consumes $alu/$macc chains, which may reduce the cells available for the wrapped operator flow, so hopefully this doesn't break things.

cc @maliberty @QuantamHD

[maliberty]

Please summarize the benefit you see

[widlarizer]

CSA_TREE isn't getting run in CI for some reason. Probably the yosys is not the one we set in the submodule, I can't rule it out since it reports Yosys 0.63+post (git sha1 UNKNOWN-dirty. I'm seeing in the logs that a docker image foss-fpga-tools-ext-openroad gets used. Does that mean we no longer can just bump the submodule to whatever experimental yosys version we'd like to try out then?

[maliberty]

Submodules point at a specific commit which I don't see updated here. You just changed repo path and are still getting the same commit