Some embodiments provide a method for processing a packet for a pipeline of a hardware switch. The pipeline, in some embodiments, includes several different stages that match against packet header fields and modify packet header fields. The method receives a packet that includes a set of packet headers. The method then populates, for each packet header in the set of packet headers, (i) a first set of registers with packet header field values of the packet header that are used in the pipeline, and (ii) a second set of registers with packet header field values of the packet header that are not used in the pipeline.