Avoid generating wires for function args which are constant

tests/various/const_arg_loop.v

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+module top;
+	function automatic [31:0] operation1;
+		input [4:0] rounds;
+		input integer num;
+		integer i;
+		begin
+			begin : shadow
+				integer rounds;
+				rounds = 0;
+			end
+			for (i = 0; i < rounds; i = i + 1)
+				num = num * 2;
+			operation1 = num;
+		end
+	endfunction
+
+	function automatic [31:0] operation2;
+		input [4:0] var;
+		input integer num;
+		begin
+			var[0] = var[0] ^ 1;
+			operation2 = num * var;
+		end
+	endfunction
+
+	wire [31:0] a;
+	assign a = 2;
+
+	parameter A = 3;
+
+	wire [31:0] x1;
+	assign x1 = operation1(A, a);
+
+	wire [31:0] x2;
+	assign x2 = operation2(A, a);
+
+// `define VERIFY
+`ifdef VERIFY
+    assert property (a == 2);
+    assert property (A == 3);
+    assert property (x1 == 16);
+    assert property (x2 == 4);
+`endif
+endmodule

tests/various/const_arg_loop.ys

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+read_verilog const_arg_loop.v