- /* If the Lhs loads do load from zeropage, we have to include
- ** them into UsedRegs registers used. The Rhs loads have already
- ** been tracked.
+ /* Check if the lhs loads from zeropage. If this is true, these
+ ** zero page locations have to be added to ZPUsage, because
+ ** they cannot be used for intermediate storage. In addition,
+ ** if one of these zero page locations is destroyed between
+ ** pushing the lhs and the actual operation, we cannot use the
+ ** original zero page locations for the final op, but must
+ ** use another ZP location to save them.