If it was hard to write, it should be hard to understand. /s

Oftentimes if you have some hairy code, the best option is to use a goto, make a commit or leave a note, and then clean it up later, in a separate commit. It's more bisectable and leaves a more readable diff. I'm pretty sure I've had occasion to jump into the middle of a loop as the point of entry. Duff's device is a case of this.

I'd say all the rules about code complexity are like this.

Recommended function/class/file size, when to abstract vs when to copy, even size/names of function arguments.

There are "rules" about all of these, but the best codebases have tons and tons of violations. Not because they are bad, but because the devs working on it know when to break those rules, and know that they are mostly guidelines.