Drop instruction `recurse`

[jan-ferdinand]

Even though it is a beautiful instruction, dropping recurse might lead to a simpler design and better overall performance.

Pro recurse

• proper tail recursion, i.e., no new entry to the jump stack

Contra recurse

• requires columns “jump destination” jsd in both the Processor Table and the Jump Stack Table
• (slight) complexity increase in the AIR to take proper care of jsd, also in both tables
• instruction deselectors for the Processor Table might have higher degree[^deselect]

[^deselect]: Since instructions are deselected based on the decomposition of their opcode, the corresponding deselectors do probably not change in degree when dropping recurse.

[sshine]

recurse delivers some convenience wrt. not pushing the same jump address to the stack repeatedly, since call-return pops it. Let's assess this removal when we write a big enough program to understand the cost of the inconvenience. It may be that it's not worth its own constraint polynomials.

[jan-ferdinand]

This is stale – closing.