> There is, of course, no reason to believe that they will necessarily be functionally identical, but it is what developers take for granted every day, and if o

> There is, of course, no reason to believe that they will necessarily be functionally identical, but it is what developers take for granted every day, and if otherwise would be considered a bug somewhere in the package. Yes, the only possible differences result from either a compiler bug or a program bug that depends on undefined behaviour, in which case "anything can happen" as they say. As others have noted, parallel compilation depends on non-deterministic thread-scheduling, so this non-determinism can't be solved unless you restrict all compilation to be single-threaded. It's still not the only possible source of non-determinism though.