Compiler and hardware interactions to reuse register fields in the data plane of a network forwarding element

A non-transitory computer readable medium storing a program for configuring a physical hardware forwarding element comprising a message processing pipeline comprising a plurality of message processing stages for processing header fields of messages, the program executable by a processing unit, the program comprising sets of instructions for:

• identifying a first message processing stage that starts processing a first header field of a message and a second message processing stage that is a last message processing stage that processes the first header field;
• configuring a field of a packet header container in a data plane of the physical hardware forwarding element to store the first header field for a duration from a beginning of the first message processing stage;
• identifying a second header field used in a third message processing stage after the second message processing stage in the message processing pipeline;
• configuring a set of hardware circuitries in the data plane to initialize the field of the packet header container after an end of the second message processing stage and before a start of the third message processing stage;
• and
• configuring the field of the packet header container to overwrite the first header field and store the second header field of the message after the end of the second message processing stage and before the start of the third message processing stage and based on the second message processing stage having completed use of the first header field, wherein the third message processing stage processes the second header field stored in the field of the packet header container.