Sign extend port connections where necessary

- Signed cell outputs are sign extended when bound to larger wires
- Signed connections are sign extended when bound to larger cell inputs
- Sign extension is performed in hierarchy and flatten phases
- genrtlil indirects signed constants through signed wires
- Other phases producing RTLIL may need to be updated to preserve
  signedness information
- Resolves #1418
- Resolves #2265

tests/various/port_sign_extend.v

@@ -0,0 +1,76 @@
+module GeneratorSigned1(out);
+	output wire signed out;
+	assign out = 1;
+endmodule
+
+module GeneratorUnsigned1(out);
+	output wire out;
+	assign out = 1;
+endmodule
+
+module GeneratorSigned2(out);
+	output wire signed [1:0] out;
+	assign out = 2;
+endmodule
+
+module GeneratorUnsigned2(out);
+	output wire [1:0] out;
+	assign out = 2;
+endmodule
+
+module PassThrough(a, b);
+	input wire [3:0] a;
+	output wire [3:0] b;
+	assign b = a;
+endmodule
+
+module act(o1, o2, o3, o4, o5, yay1, nay1, yay2, nay2);
+	output wire [3:0] o1, o2, o3, o4, o5;
+
+	// unsigned constant
+	PassThrough pt1(1'b1, o1);
+
+	// unsigned wire
+	wire tmp2;
+	assign tmp2 = 1'sb1;
+	PassThrough pt2(tmp2, o2);
+
+	// signed constant
+	PassThrough pt3(1'sb1, o3);
+
+	// signed wire
+	wire signed tmp4;
+	assign tmp4 = 1'sb1;
+	PassThrough pt4(tmp4, o4);
+
+	// signed expressions
+	wire signed [1:0] tmp5a = 2'b11;
+	wire signed [1:0] tmp5b = 2'b01;
+	PassThrough pt5(tmp5a ^ tmp5b, o5);
+
+	output wire [2:0] yay1, nay1;
+	GeneratorSigned1   os1(yay1);
+	GeneratorUnsigned1 ou1(nay1);
+
+	output wire [2:0] yay2, nay2;
+	GeneratorSigned2   os2(yay2);
+	GeneratorUnsigned2 ou2(nay2);
+endmodule
+
+module ref(o1, o2, o3, o4, o5, yay1, nay1, yay2, nay2);
+	output wire [3:0] o1, o2, o3, o4, o5;
+
+	assign o1 = 4'b0001;
+	assign o2 = 4'b0001;
+	assign o3 = 4'b1111;
+	assign o4 = 4'b1111;
+	assign o5 = 4'b1110;
+
+	output wire [2:0] yay1, nay1;
+	assign yay1 = 3'b111;
+	assign nay1 = 3'b001;
+
+	output wire [2:0] yay2, nay2;
+	assign yay2 = 3'b110;
+	assign nay2 = 3'b010;
+endmodule

tests/various/port_sign_extend.ys

@@ -0,0 +1,22 @@
+read_verilog port_sign_extend.v
+hierarchy
+flatten
+equiv_make ref act equiv
+equiv_simple
+equiv_status -assert
+
+delete
+
+read_verilog port_sign_extend.v
+flatten
+equiv_make ref act equiv
+equiv_simple
+equiv_status -assert
+
+delete
+
+read_verilog port_sign_extend.v
+hierarchy
+equiv_make ref act equiv
+prep -flatten -top equiv
+equiv_status -assert