extract_reduce - converts gate chains into $reduce_* cells

yosys> help extract_reduce

extract_reduce [options] [selection]

converts gate chains into $reduce_* cells

This command finds chains of $_AND_, $_OR_, and $_XOR_ cells and replaces them
with their corresponding $reduce_* cells. Because this command only operates on
these cell types, it is recommended to map the design to only these cell types
using the `abc -g` command. Note that, in some cases, it may be more effective
to map the design to only $_AND_ cells, run extract_reduce, map the remaining
parts of the design to AND/OR/XOR cells, and run extract_reduce a second time.

-allow-off-chain

Allows matching of cells that have loads outside the chain. These cells
will be replicated and folded into the $reduce_* cell, but the original
cell will remain, driving its original loads.