Function bench_startup 

pub(crate) fn bench_startup(
    iterations: u32,
    backend: Backend,
) -> Result<StartupReport, String>

The startup a --backend vm process pays is the one this measures, which is the point of measuring it here rather than in-process: the lowering is part of what a vm run costs before it does any work, and a process is where every such cost is paid at once.