iverilog/ivtest/gold/pr1792108.gold

                   0 y1 = x, y2 = x, y3 = x, a = x
                   1 y1 = 1, y2 = 1, y3 = 1, a = 1
                   2 y1 = 0, y2 = 0, y3 = 0, a = 0