> On Feb 6, 2017, at 10:05 AM, Joe Groff <jgr...@apple.com> wrote:
>
>
>> On Feb 6, 2017, at 10:02 AM, Jordan Rose via swift-dev <swift-dev@swift.org>
>> wrote:
>>
>> I’ve said this Michael in person, but I’ll put it on the thread for others
>> to see:
>>
>> I don’t think modeling this is worth the increase in complexity. There’s a
>> partial workaround for anyone who notices this being a problem, which is to
>> put any expensive work in a ‘do’ block. And actually emitting cleanups
>> before a call to, e.g., dispatch_main would be a change in semantics, which
>> could both break existing programs and makes the language a bit harder to
>> reason about. The current rule that “defers happen at the close brace,
>> releases may happen sooner” is simple. (We certainly would not want to make
>> ‘defer’s happen before calling dispatch_main, though perhaps we should warn
>> that they will never be executed.)
>
> And we should keep that rule. The optimizer can't move `defer`s no matter
> what, since they're semantically fixed to happen at end of scope, so they
> would always "leak" in a case like `defer { doSomething() }; abort()`. It's
> only value lifetimes that could be shortened, and shortening lifetimes before
> a noreturn call wouldn't be a change to the existing model.
As long as we are clear with users that we are making this assumption that
no-returns and (semantically at the SIL level) unreachables are leaking, I am
happy. I can deal with that no problem. We should probably document that though.
>
> -Joe
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