Metal-only vs all-layer decision

Metal-only vs all-layer decision. With the base (transistor) layers already on silicon, a change is cheap only when it can be done by re-wiring metal and vias: reusing a pre-placed spare cell or moving connections. A change that needs new transistors (a stronger cell, a new flip-flop, a whole new block) forces new base-layer masks: an all-layer respin, which is slow and costly.

For each proposed change, decide the class it falls into, given the spare cells on hand. The dividing question is always the same: does this need a new transistor, or just new wire to a spare that already exists?

Classify every row as metal-only or all-layer, then Submit calls.