For an isolated ObjC function that is not async, we
emit a hops around the call. But if that function
returns an autoreleased pointer, we need to ensure
we're retaining that pointer before hopping back
after the call. We weren't doing that in the case
of an autoreleased NSError:
```
%10 = alloc_stack $@sil_unmanaged Optional<NSError>
%19 = ... a bunch of steps to wrap up %10 ...
%20 = enum $Optional<AutoreleasingUnsafeMutablePointer<Optional<NSError>>>, #Optional.some!enumelt, %19 : $AutoreleasingUnsafeMutablePointer<Optional<NSError>>
hop_to_executor $MainActor
%26 = apply X(Y, %20) : $@convention(objc_method) (NSObject, Optional<AutoreleasingUnsafeMutablePointer<Optional<NSError>>>) -> @autoreleased Optional<NSString>
hop_to_executor $Optional<Builtin.Executor>
// retain the autoreleased pointer written-out.
%28 = load [trivial] %10 : $*@sil_unmanaged Optional<NSError>
%29 = unmanaged_to_ref %28 : $@sil_unmanaged Optional<NSError> to $Optional<NSError>
%30 = copy_value %29 : $Optional<NSError>
assign %31 to %7 : $*Optional<NSError>
```
This patch sinks the hop emission after the call
so it happens after doing that copy.
rdar://114049646
Async functions are now expected to set ExpectedExecutor in their
prologue (and, generally, immediately hop to it). I updated the
prologue code for a bunch of function emission, most of which was
uninteresting. Top-level code was not returning to the main
executor, which is now fixed; fortunately, we weren't assuming
that we were on the main executor yet.
We had some code that only kicked in when an ExpectedExecutor
wasn't set which made us capture the current executor before
a hop and then return to it later. This code has been removed;
there's no situation in which save-and-return is the semantically
correct thing to do given the possibility of hop optimization.
I suspect it could also have led to crashes if the current
executor is being kept alive only because it's currently running
code. If we ever add async functions that are supposed to inherit
their caller's executor, we should have the caller pass the right
executor down to it.
This is the first half of SE-0338; the second, sendability
enforcement, is much more complicated, and Doug has volunteered
to do it.
Fixes rdar://79284465, as well as some tests that were XFAILed
on Windows.
The concurrency runtime now deploys back to macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, which corresponds to the 5.1 release of the stdlib.
Adjust macro usages accordingly.
