Add execution-time loops

[jafingerhut]

For 2024-Dec-09 language design work group meeting, the only topic I propose for discussion should be quick: try to recruit one or two volunteers to review PR #1315, even though it has already been merged into the spec. Why? Because it had one author and one reviewer before it was approved, and it would be good to have at least a little more careful review before we forget about it.

Personnel

• Owner: @ChrisDodd
• Supporters: @jafingerhut

Design

• Document:

Implementation

• p4-spec: For-loop additions #1315
• p4c: Fix loop unrolling bugs related to issue4739 p4c#4783 and several other PRs to fix small issues

Process

• LDWG discussed: Discussed basic idea and corner cases at 3 or 4 monthly LDWG meetings in 2024. Have not yet discussed the proposed spec PR.
• LDWG approved:
• Merged into p4-spec: PR For-loop additions #1315 was merged into the spec with only one approval. It would be good to get a wider review by one or two other people, though.
• Merged into p4c:

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Note: This issue is only tracking the progress of adding "execution loops" or "run-time loops" to P4.

Issue #1326 tracks compile-time / macro loops.