The way that field layout is computed has been changed, with more aggressive optimizations to avoid unused gaps in instances. These new optimizations can be disabled by using a new VM option `-XX:-UseEmptySlotsInSupers`.

For a limited time, it is possible to continue to use the old code to compute field layout with a new VM option `-XX:-UseNewFieldLayout`. However, this option has been deprecated in JDK 15 and the old code will be removed in a future release.