In my company, it's common not to do any intermediate build to check how each feature/bugfix branch is merged in dev. There is only daily build, which always elicit a lot of test fails and build errors. I have been told that it's unreasonable to do build for each merge for over 1000 developers.
So I searched how CI is organized in companies that have that much developers or more (Microsoft, Facebook), and found nothing. Maybe, insiders can tell me then?