Function render 

pub fn render(
    file: &str,
    report: &Report,
    names: &Interner,
    wants: Wants,
) -> String

Renders the remarks a run produced, as the lines -fopt-info prints.

In the order the passes ran, then the order the module holds its functions, then the order each pass recorded its events. That is the order the work happened in, which is the order somebody reading down the output is reconstructing.

A function a pass had nothing to say about produces no lines. The record for it still exists, and --print-pass-stats is where a pass that fires on nothing becomes visible. Printing a line per silent pass per function here would bury the ones that spoke.