An Output contains optimization info for an output port of the original node:
- If passthrough is set (non-negative), then this is the index of an input port of the original node whose value shall be taken over directly for the output port. For example this can be used for an Add node where one operand is known to be zero.
- Otherwise if value is non-null this is the compile-time constant value for the port.
- Otherwise there is no optimization info for the port, so the node substitution has to be used.