Why does ";;" in the script remove redundant buffers?

[gatk555]

Please excuse any ignorance; I am new at this. I am using 0.32 with scripts like this (no code blocks, as they seem not to work today):

read_verilog minimal.v
read_verilog -lib prim_cells.v

proc; memory; techmap

dfflibmap -liberty prim_cells.lib
abc -liberty prim_cells.lib;;

write_verilog minimal_syn.v
write_spice -neg d_low -pos d_high -buf BUF minimal.subckt

With this input:

module my_nand(a, b, c);
input wire a, b;
output wire c;
assign c = ~(a & b);
endmodule // my_and

I get the expected:

.SUBCKT my_nand a b c
X0 a b 1 NAND
.ENDS my_nand

However, if I remove a semicolon from the "abc" line in the script the output becomes:

.SUBCKT my_nand a b c
X0 a b 1 NAND
X1 a 2 BUF
X2 b 3 BUF
X3 1 c BUF
.ENDS my_nand

If I compare the logging output, it gets weirder. The only significant difference is that with the semicolons:

Removed 0 unused cells and 1 unused wires.

appears in the proc pass. Can anyone explain this?

[whitequark]

;; is equivalent to clean (and ;;; is equivalent to clean -purge). See help opt_clean.

[gatk555]

So undocumented magic?

Edit: actually not undocumented as "help clean" describes it. The documentation is just hidden behind a door labelled "Beware of the leopard".

Thanks.

[whitequark]

It's documented in several places; aside from the one I gave you, here and here.