No doubt straight up ARC with refcounting bumps on every function call,etc. vs a good GC with same allocation paths...a good GC will smoke it. No question.
But that isn't how I read what Lattner said here, and I've been thinking similar things. Essentially with ARC the goal is to cheat (to be fair with tracing GC it is as well, just in different ways). And you cheat by implementing an ownership/borrow collector type system behind the scenes for getting rid of the need for RC on most of your objects. Once you do that, you have GC competing with stack allocation + some malloc/free scattered in. It becomes a much more interesting fight.
But that isn't how I read what Lattner said here, and I've been thinking similar things. Essentially with ARC the goal is to cheat (to be fair with tracing GC it is as well, just in different ways). And you cheat by implementing an ownership/borrow collector type system behind the scenes for getting rid of the need for RC on most of your objects. Once you do that, you have GC competing with stack allocation + some malloc/free scattered in. It becomes a much more interesting fight.