A method generating a layout diagram includes: arranging the layout diagram into rows; configuring one or more of the rows as combination rows, the combination-row-configuring including relative to a second direction substantially perpendicular to the first direction, setting a height of each of the one or more combination rows to be substantially equal to a sum of a first height of a first cell and a second height of a second cell, the first cell being different than the second cell, and the first height being different than the second height; and populating each of the one or more combination rows including: stacking a first instance of the first cell on a first instance of the second cell, or stacking a second instance of the second cell on a second instance of the first cell.