yosys/tests/opt/opt_clean_init.ys

read_verilog << EOT
module top(...);

input [1:0] D;
input C;
output O;
reg [1:0] Q;

initial Q = 0;

always @(posedge C)
        Q <= D;

assign O = Q[1];

endmodule
EOT

synth
check -assert -initdrv

select -assert-count 1 a:init=2'b0x