read_techlib -icells -formal <<EOT
module top(input CI, I0, output [1:0] CO, output O);
    wire A = 1'b0, B = 1'b0;
	\$__ICE40_CARRY_WRAPPER #(
		//    A[0]: 1010 1010 1010 1010
		//    A[1]: 1100 1100 1100 1100
		//    A[2]: 1111 0000 1111 0000
		//    A[3]: 1111 1111 0000 0000
		.LUT(~16'b 0110_1001_1001_0110),
		.I3_IS_CI(1'b1)
	) u0 (
		.A(A),
		.B(B),
		.CI(CI),
		.I0(I0),
		.I3(1'bx),
		.CO(CO[0]),
		.O(O)
	);
    SB_CARRY u1 (.I0(~A), .I1(~B), .CI(CI), .CO(CO[1]));
endmodule
EOT

read_techlib -icells -lib +/ice40/abc9_model.v +/ice40/cells_sim.v
equiv_opt -assert -map +/ice40/abc9_model.v -map +/ice40/cells_sim.v ice40_opt
design -load postopt
select -assert-count 1 t:*
select -assert-count 1 t:$lut

# https://github.com/YosysHQ/yosys/issues/1543
design -reset
read_verilog <<EOT
module delay_element (input wire clk, input wire reset, input wire enable,
                      input wire chainin,  output wire chainout, output reg latch);


   reg                           const_zero = 0;
   reg                           const_one = 1;

    wire                         delay_tap;


   //carry logic
   (* keep *) SB_CARRY carry ( .CO(chainout), .I0(const_zero),
                    .I1(const_one), .CI(chainin));


   //flip flop latch
   (* keep *) SB_DFFER flipflop( .Q(latch), .C(clk), .E(enable),
                      .D(delay_tap), .R(reset));


   //LUT table
   // the LUT should just echo the carry in (I3)
   // carry I0 = LUT I1
   // carry I1 = LUT I2
   // carry in = LUT I3
   // LUT_INIT[0] = 0
   // LUT_INIT[1] = 0
   // LUT_INIT[2] = 0
   // LUT_INIT[3] = 0
   // LUT_INIT[4] = 0
   // LUT_INIT[5] = 0
   // LUT_INIT[6] = 0
   // LUT_INIT[7] = 0
   // LUT_INIT[8] = 1
   // LUT_INIT[9] = 1
   // LUT_INIT[10] = 1
   // LUT_INIT[11] = 1
   // LUT_INIT[12] = 1
   // LUT_INIT[13] = 1
   // LUT_INIT[14] = 1
   // LUT_INIT[15] = 1

   (* keep *) SB_LUT4 lut( .O(delay_tap), .I0(const_zero), .I1(const_zero),
                .I2(const_one), .I3(chainin));

   //TODO: is this the right way round??
   defparam lut.LUT_INIT=16'hFF00;


endmodule // delay_element
EOT

synth_ice40
select -assert-count 1 t:SB_LUT4
select -assert-count 1 t:SB_CARRY
select -assert-count 1 t:SB_CARRY a:keep %i
select -assert-count 1 t:SB_CARRY c:carry %i


design -reset
read_techlib -icells <<EOT
module top(input I3, I2, I1, I0, output O, O2);
	SB_LUT4 #(
		.LUT_INIT(8'b 1001_0110)
	) u0 (
		.I0(I0),
		.I1(I1),
		.I2(I2),
		.I3(),
		.O(O)
	);
	wire CO;
	\$__ICE40_CARRY_WRAPPER #(
		.LUT(~8'b 1001_0110),
		.I3_IS_CI(1'b0)
	) u1 (
		.A(1'b0),
		.B(1'b0),
		.CI(1'b0),
		.I0(),
		.I3(),
		.CO(CO),
		.O(O2)
	);
endmodule
EOT
ice40_opt