Phases do moves by calling Move.doMove(), which always creates and returns an undo move. This is also true for undo moves – as part of doing an undo move, a secondary undo move (undo of undo) instance is created. But that is (most likely) completely useless.

Slow stepping algorithms that evaluate thousands and thousands of moves before making a step might benefit from not creating those useless undo-of-undo-move instances.

• Measure the performance gain. Start with an example that has a high score calculation speed, where the potential performance gain is greatest. Based on the result there either continue or kill this idea.
• Be careful not to break the contract of Move.doMove() when optimizing this. If the contract is significantly broken, the change must go into the next major version.