We want SILGen to have a simplified view of its executor and know that whenever
one sees an Actor, it is an actual actor instead of a Builtin.Executor. This
just simplifies code. Also, we should eventually have an invariant that
Builtin.Executor should only be allowed in LoweredSIL after LowerHopToExecutor
has run. But that is a change for another day.
SILGen expects actor instance isolation to always come from captures,
we need to maintain that with implicit isolation capture performed by
`@_inheritActorContext(always)`.
`getLoweredLocalCaptures` seems the best place to do it because
during Sema there is a chicken and an egg situation where isolation
depends on captures and in this case captures depend on isolation.
Without this, the borrow of the hop_to_executor lasts after the apply. Beyond
being unnecessary this results in an OSSA violation if we are passing an actor
as an isolated parameter to an initializer since we hop_to_executor the actor
and then pass it as a +1 parameter to the initializer causing the actor to be
consumed before its borrow ends.
rdar://144994837
Type annotations for instruction operands are omitted, e.g.
```
%3 = struct $S(%1, %2)
```
Operand types are redundant anyway and were only used for sanity checking in the SIL parser.
But: operand types _are_ printed if the definition of the operand value was not printed yet.
This happens:
* if the block with the definition appears after the block where the operand's instruction is located
* if a block or instruction is printed in isolation, e.g. in a debugger
The old behavior can be restored with `-Xllvm -sil-print-types`.
This option is added to many existing test files which check for operand types in their check-lines.
Use the `%target-swift-5.1-abi-triple` substitution to compile the tests for
deployment to the minimum OS versions required for use of _Concurrency APIs,
instead of disabling availability checking.
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
Although nonescaping closures are representationally trivial pointers to their
on-stack context, it is useful to model them as borrowing their captures, which
allows for checking correct use of move-only values across the closure, and
lets us model the lifetime dependence between a closure and its captures without
an ad-hoc web of `mark_dependence` instructions.
During ownership elimination, We eliminate copy/destroy_value instructions and
end the partial_apply's lifetime with an explicit dealloc_stack as before,
for compatibility with existing IRGen and non-OSSA aware passes.
SE-0338 changed the execution of non-actor async functions
so that they always hop to the generic executor, but some
functions need a way to suppress this so that they inherit
the caller's executor.
The right way to implement this is to have the caller pass
down the target executor in some reliable way and then
switch to it in all the appropriate places in the caller.
We might reasonably be able to build this on top of isolated
parameters, using some sort of default argument, or we might
need a wholly novel mechanism.
But those things are all ABI-breaking absent some sort of
guarantee about switching that we probably don't want to make,
and unfortunately we have functions in the library which we
need to export that need to inherit executors. So in the
short term, we need some unsafe way of getting back to the
previous behavior.
For global-actor isolated async inits within an actor, we will have separate restrictions
on access to self's differently-isolated stored properties to prevent data races. But,
we also must be on the global actor while in such initializers. The problem was only
that the prologue was missing a hop because of a bad conditional check. Previously
the check assumed that actors cannot have global-actor isolated initializers, but they
can currently.
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.
Introduce the `@preconcurrency` attribute name for `@_predatesConcurrency`,
which has been the favored name in the pitch thread so far. Retain the
old name for now to help smooth migration.
The notion of "actor-isolated" currently exists at the declaration level.
For functions, it is going to be captured in the function type itself,
where 'self' is declared to be 'isolated'. Model isolation both
ways: the 'self' of a method that is isolated to an actor instance
will be 'isolated' as well.
We are still using declaration-based checking of actor isolation.
However, by mirroring this information we can move more incrementally
over to doing checking based on 'isolated' parameters.
Implement name mangling, type metadata, runtime demangling, etc. for
global-actor qualified function types. Ensure that the manglings
round-trip through the various subsystems.
Implements rdar://78269642.
For `async` function types, an actor constraint can be enforced by the callee by hopping executors,
unlike with `sync` functions, so doesn't need to influence the outward type of the function.
rdar://76248452
Through various means, it is possible for a synchronous actor-isolated
function to escape to another concurrency domain and be called from
outside the actor. The problem existed previously, but has become far
easier to trigger now that `@escaping` closures and local functions
can be actor-isolated.
Introduce runtime detection of such data races, where a synchronous
actor-isolated function ends up being called from the wrong executor.
Do this by emitting an executor check in actor-isolated synchronous
functions, where we query the executor in thread-local storage and
ensure that it is what we expect. If it isn't, the runtime complains.
The runtime's complaints can be controlled with the environment
variable `SWIFT_UNEXPECTED_EXECUTOR_LOG_LEVEL`:
0 - disable checking
1 - warn when a data race is detected
2 - error and abort when a data race is detected
At an implementation level, this introduces a new concurrency runtime
entry point `_checkExpectedExecutor` that checks the given executor
(on which the function should always have been called) against the
executor on which is called (which is in thread-local storage). There
is a special carve-out here for `@MainActor` code, where we check
against the OS's notion of "main thread" as well, so that `@MainActor`
code can be called via (e.g.) the Dispatch library's
`DispatchQueue.main.async`.
The new SIL instruction `extract_executor` performs the lowering of an
actor down to its executor, which is implicit in the `hop_to_executor`
instruction. Extend the LowerHopToExecutor pass to perform said
lowering.
Repurpose mangling operator `Y` as an umbrella operator that covers new attributes on function types. Free up operators `J`, `j`, and `k`.
```
async ::= 'Ya' // 'async' annotation on function types
sendable ::= 'Yb' // @Sendable on function types
throws ::= 'K' // 'throws' annotation on function types
differentiable ::= 'Yjf' // @differentiable(_forward) on function type
differentiable ::= 'Yjr' // @differentiable(reverse) on function type
differentiable ::= 'Yjd' // @differentiable on function type
differentiable ::= 'Yjl' // @differentiable(_linear) on function type
```
Resolves rdar://76299796.
Tasks shouldn't normally hog the actor context indefinitely after making a call that's bound to
that actor, since that prevents the actor from potentially taking on other jobs it needs to
be able to address. Set up SILGen so that it saves the current executor (using a new runtime
entry point) and hops back to it after every actor call, not only ones where the caller context
is also actor-bound.
The added executor hopping here also exposed a bug in the runtime implementation while processing
DefaultActor jobs, where if an actor job returned to the processing loop having already yielded
the thread back to a generic executor, we would still attempt to make the actor give up the thread
again, corrupting its state.
rdar://71905765
This patch updates the `actor class` spelling to `actor` in almost all
of the tests. There are places where I verify that we sanely handle
`actor` as an attribute though. These include:
- test/decl/class/actor/basic.swift
- test/decl/protocol/special/Actor.swift
- test/SourceKit/CursorInfo/cursor_info_concurrency.swift
- test/attr/attr_objc_async.swift
- test/ModuleInterface/actor_protocol.swift
The `try await` ordering is both easier to read and indicates the order
of operations better, because the suspension point occurs first and
then one can observe a thrown error.
implicitly-async calls are calls to synchronous
actor-isolated functions. Synchronous functions
cannot perform hop_to_executor, so implicitly
async calls have the convention that the caller
is responsible for switching to the right
executor prior to entering the actor-isolated
callee.
It follows naturally that the caller must then
switch back to the appropriate executor after
the implicitly-async call completed.
Now, if the caller is not isolated to a
_specific_ actor, then we are (currently)
_not_ emitting a hop to go back to the
caller's executor, because that caller's
executor is unspecified (and currently not
accessable in SIL). This behavior may change
in the future; tracked in rdar://71905765
