This is a new instruction that can be used by SILGen to perform a semantic move
in between two entities that are considered separate variables at the AST
level. I am going to use it to implement an experimental borrow checker.
This PR contains the following:
1. I define move_value, setup parsing, printing, serializing, deserializing,
cloning, and filled in all of the visitors as appropriate.
2. I added createMoveValue and emitMoveValueOperation SILBuilder
APIs. createMoveValue always creates a move and asserts is passed a trivial
type. emitMoveValueOperation in contrast, will short circuit if passed a
trivial value and just return the trivial value.
3. I added IRGen tests to show that we can push this through the entire system.
This is all just scaffolding for the instruction to live in SIL land and as of
this PR doesn't actually do anything.
Change the code generation patterns for `async let` bindings to use an ABI based on the following
functions:
- `swift_asyncLet_begin`, which starts an `async let` child task, but which additionally
now associates the `async let` with a caller-owned buffer to receive the result of the task.
This is intended to allow the task to emplace its result in caller-owned memory, allowing the
child task to be deallocated after completion without invalidating the result buffer.
- `swift_asyncLet_get[_throwing]`, which replaces `swift_asyncLet_wait[_throwing]`. Instead of
returning a copy of the value, this entry point concerns itself with populating the local buffer.
If the buffer hasn't been populated, then it awaits completion of the task and emplaces the
result in the buffer; otherwise, it simply returns. The caller can then read the result out of
its owned memory. These entry points are intended to be used before every read from the
`async let` binding, after which point the local buffer is guaranteed to contain an initialized
value.
- `swift_asyncLet_finish`, which replaces `swift_asyncLet_end`. Unlike `_end`, this variant
is async and will suspend the parent task after cancelling the child to ensure it finishes
before cleaning up. The local buffer will also be deinitialized if necessary. This is intended
to be used on exit from an `async let` scope, to handle cleaning up the local buffer if necessary
as well as cancelling, awaiting, and deallocating the child task.
- `swift_asyncLet_consume[_throwing]`, which combines `get` and `finish`. This will await completion
of the task, leaving the result value in the result buffer (or propagating the error, if it
throws), while destroying and deallocating the child task. This is intended as an optimization
for reading `async let` variables that are read exactly once by their parent task.
To avoid an epoch break with existing swiftinterfaces and ABI clients, the old builtins and entry
points are kept intact for now, but SILGen now only generates code using the new interface.
This new interface fixes several issues with the old async let codegen, including use-after-free
crashes if the `async let` was never awaited, and the inability to read from an `async let` variable
more than once.
rdar://77855176
Rather than using group task options constructed from the Swift parts
of the _Concurrency library and passed through `createAsyncTask`'s
options, introduce a separate builtin that always takes a group. Move
the responsibility for creating the options structure into IRGen, so
we don't need to expose the TaskGroupTaskOptionRecord type in Swift.
Introduce a builtin `createAsyncTask` that maps to `swift_task_create`,
and use that for the non-group task creation operations based on the
task-creation flags. `swift_task_create` and the thin function version
`swift_task_create_f` go through the dynamically-replaceable
`swift_task_create_common`, where all of the task creation logic is
present.
While here, move copying of task locals and the initial scheduling of
the task into `swift_task_create_common`, enabling by separate flags.
* [Distributed] Initial distributed checking
* [Distributed] initial types shapes and conform to DistributedActor
* [Distributed] Require Codable params and return types
* [Distributed] initial synthesis of fields and constructors
* [Distributed] Field and initializer synthesis
* [Distributed] Codable requirement on distributed funcs; also handle <T: Codable>
* [Distributed] handle generic type params which are Codable in dist func
[Distributed] conformsToProtocol after all
* [Distributed] Implement remote flag on actors
* Implement remote flag on actors
* add test
* actor initializer that sets remote flag
[Distributed] conformances getting there
* [Distributed] dont require async throws; cleanup compile tests
* [Distributed] do not synthesize default implicit init, only our special ones
* [Distributed] properly synth inits and properties; mark actorTransport as _distributedActorIndependent
Also:
- do not synthesize default init() initializer for dist actor
* [Distributed] init(transport:) designated and typechecking
* [Distributed] dist actor initializers MUST delegate to local-init
* [Distributed] check if any ctors in delegation call init(transport:)
* [Distributed] check init(transport:) delegation through many inits; ban invoking init(resolve:using:) explicitly
* [Distributed] disable IRGen test for now
* [Distributed] Rebase cleanups
* [Concurrent] transport and address are concurrent value
* [Distributed] introduce -enable-experimental-distributed flag
* rebase adjustments again
* rebase again...
* [Distributed] distributed functions are implicitly async+throws outside the actor
* [Distributed] implicitly throwing and async distributed funcs
* remove printlns
* add more checks to implicit function test
* [Distributed] resolve initializer now marks the isRemote actor flag
* [Distributed] distributedActor_destroy invoked instead, rather than before normal
* [Distributed] Generate distributed thunk for actors
* [distributed] typechecking for _remote_ functions existing, add tests for remote funcs
* adding one XFAIL'ed task & actor lifetime test
The `executor_deinit1` test fails 100% of the time
(from what I've seen) so I thought we could track
and see when/if someone happens to fix this bug.
Also, added extra coverage for #36298 via `executor_deinit2`
* Fix a memory issue with actors in the runtime system, by @phausler
* add new test that now passes because of patch by @phausler
See previous commit in this PR.
Test is based on one from rdar://74281361
* fix all tests that require the _remote_ function stubs
* Do not infer @actorIndependent onto `let` decls
* REVERT_ME: remove some tests that hacky workarounds will fail
* another flaky test, help build toolchain
* [Distributed] experimental distributed implies experimental concurrency
* [Distributed] Allow distributed function that are not marked async or throws
* [Distributed] make attrs SIMPLE to get serialization generated
* [Distributed] ActorAddress must be Hashable
* [Distributed] Implement transport.actorReady call in local init
* cleanup after rebase
* [Distributed] add availability attributes to all distributed actor code
* cleanup - this fixed some things
* fixing up
* fixing up
* [Distributed] introduce new Distributed module
* [Distributed] diagnose when missing 'import _Distributed'
* [Distributed] make all tests import the module
* more docs on address
* [Distributed] fixup merge issues
* cleanup: remove unnecessary code for now SIMPLE attribute
* fix: fix getActorIsolationOfContext
* [Distributed] cmake: depend on _concurrency module
* fixing tests...
* Revert "another flaky test, help build toolchain"
This reverts commit 83ae6654dd.
* remove xfail
* clenup some IR and SIL tests
* cleanup
* [Distributed] fix cmake test and ScanDependencies/can_import_with_map.swift
* [Distributed] fix flags/build tests
* cleanup: use isDistributed wherever possible
* [Distributed] don't import Dispatch in tests
* dont link distributed in stdlib unittest
* trying always append distributed module
* cleanups
* [Distributed] move all tests to Distributed/ directory
* [lit] try to fix lit test discovery
* [Distributed] update tests after diagnostics for implicit async changed
* [Distributed] Disable remote func tests on Windows for now
* Review cleanups
* [Distributed] fix typo, fixes Concurrency/actor_isolation_objc.swift
* [Distributed] attributes are DistributedOnly (only)
* cleanup
* [Distributed] cleanup: rely on DistributedOnly for guarding the keyword
* Update include/swift/AST/ActorIsolation.h
Co-authored-by: Doug Gregor <dgregor@apple.com>
* introduce isAnyThunk, minor cleanup
* wip
* [Distributed] move some type checking to TypeCheckDistributed.cpp
* [TypeCheckAttr] remove extra debug info
* [Distributed/AutoDiff] fix SILDeclRef creation which caused AutoDiff issue
* cleanups
* [lit] remove json import from lit test suite, not needed after all
* [Distributed] distributed functions only in DistributedActor protocols
* [Distributed] fix flag overlap & build setting
* [Distributed] Simplify noteIsolatedActorMember to not take bool distributed param
* [Distributed] make __isRemote not public
* [Distributed] Fix availability and remove actor class tests
* [actorIndependent] do not apply actorIndependent implicitly to values where it would be illegal to apply
* [Distributed] disable tests until issue fixed
Co-authored-by: Dario Rexin <drexin@apple.com>
Co-authored-by: Kavon Farvardin <kfarvardin@apple.com>
Co-authored-by: Doug Gregor <dgregor@apple.com>
* Revert "[Distributed] disable tests until issue fixed"
This reverts commit 0a04278920.
* Revert "[Distributed] Initial `distributed` actors and functions and new module (#37109)"
This reverts commit 814ede0cf3.
* [Distributed] Initial distributed checking
* [Distributed] initial types shapes and conform to DistributedActor
* [Distributed] Require Codable params and return types
* [Distributed] initial synthesis of fields and constructors
* [Distributed] Field and initializer synthesis
* [Distributed] Codable requirement on distributed funcs; also handle <T: Codable>
* [Distributed] handle generic type params which are Codable in dist func
[Distributed] conformsToProtocol after all
* [Distributed] Implement remote flag on actors
* Implement remote flag on actors
* add test
* actor initializer that sets remote flag
[Distributed] conformances getting there
* [Distributed] dont require async throws; cleanup compile tests
* [Distributed] do not synthesize default implicit init, only our special ones
* [Distributed] properly synth inits and properties; mark actorTransport as _distributedActorIndependent
Also:
- do not synthesize default init() initializer for dist actor
* [Distributed] init(transport:) designated and typechecking
* [Distributed] dist actor initializers MUST delegate to local-init
* [Distributed] check if any ctors in delegation call init(transport:)
* [Distributed] check init(transport:) delegation through many inits; ban invoking init(resolve:using:) explicitly
* [Distributed] disable IRGen test for now
* [Distributed] Rebase cleanups
* [Concurrent] transport and address are concurrent value
* [Distributed] introduce -enable-experimental-distributed flag
* rebase adjustments again
* rebase again...
* [Distributed] distributed functions are implicitly async+throws outside the actor
* [Distributed] implicitly throwing and async distributed funcs
* remove printlns
* add more checks to implicit function test
* [Distributed] resolve initializer now marks the isRemote actor flag
* [Distributed] distributedActor_destroy invoked instead, rather than before normal
* [Distributed] Generate distributed thunk for actors
* [distributed] typechecking for _remote_ functions existing, add tests for remote funcs
* adding one XFAIL'ed task & actor lifetime test
The `executor_deinit1` test fails 100% of the time
(from what I've seen) so I thought we could track
and see when/if someone happens to fix this bug.
Also, added extra coverage for #36298 via `executor_deinit2`
* Fix a memory issue with actors in the runtime system, by @phausler
* add new test that now passes because of patch by @phausler
See previous commit in this PR.
Test is based on one from rdar://74281361
* fix all tests that require the _remote_ function stubs
* Do not infer @actorIndependent onto `let` decls
* REVERT_ME: remove some tests that hacky workarounds will fail
* another flaky test, help build toolchain
* [Distributed] experimental distributed implies experimental concurrency
* [Distributed] Allow distributed function that are not marked async or throws
* [Distributed] make attrs SIMPLE to get serialization generated
* [Distributed] ActorAddress must be Hashable
* [Distributed] Implement transport.actorReady call in local init
* cleanup after rebase
* [Distributed] add availability attributes to all distributed actor code
* cleanup - this fixed some things
* fixing up
* fixing up
* [Distributed] introduce new Distributed module
* [Distributed] diagnose when missing 'import _Distributed'
* [Distributed] make all tests import the module
* more docs on address
* [Distributed] fixup merge issues
* cleanup: remove unnecessary code for now SIMPLE attribute
* fix: fix getActorIsolationOfContext
* [Distributed] cmake: depend on _concurrency module
* fixing tests...
* Revert "another flaky test, help build toolchain"
This reverts commit 83ae6654dd.
* remove xfail
* clenup some IR and SIL tests
* cleanup
* [Distributed] fix cmake test and ScanDependencies/can_import_with_map.swift
* [Distributed] fix flags/build tests
* cleanup: use isDistributed wherever possible
* [Distributed] don't import Dispatch in tests
* dont link distributed in stdlib unittest
* trying always append distributed module
* cleanups
* [Distributed] move all tests to Distributed/ directory
* [lit] try to fix lit test discovery
* [Distributed] update tests after diagnostics for implicit async changed
* [Distributed] Disable remote func tests on Windows for now
* Review cleanups
* [Distributed] fix typo, fixes Concurrency/actor_isolation_objc.swift
* [Distributed] attributes are DistributedOnly (only)
* cleanup
* [Distributed] cleanup: rely on DistributedOnly for guarding the keyword
* Update include/swift/AST/ActorIsolation.h
Co-authored-by: Doug Gregor <dgregor@apple.com>
* introduce isAnyThunk, minor cleanup
* wip
* [Distributed] move some type checking to TypeCheckDistributed.cpp
* [TypeCheckAttr] remove extra debug info
* [Distributed/AutoDiff] fix SILDeclRef creation which caused AutoDiff issue
* cleanups
* [lit] remove json import from lit test suite, not needed after all
* [Distributed] distributed functions only in DistributedActor protocols
* [Distributed] fix flag overlap & build setting
* [Distributed] Simplify noteIsolatedActorMember to not take bool distributed param
* [Distributed] make __isRemote not public
Co-authored-by: Dario Rexin <drexin@apple.com>
Co-authored-by: Kavon Farvardin <kfarvardin@apple.com>
Co-authored-by: Doug Gregor <dgregor@apple.com>
- Introduce an UnownedSerialExecutor type into the concurrency library.
- Create a SerialExecutor protocol which allows an executor type to
change how it executes jobs.
- Add an unownedExecutor requirement to the Actor protocol.
- Change the ABI for ExecutorRef so that it stores a SerialExecutor
witness table pointer in the implementation field. This effectively
makes ExecutorRef an `unowned(unsafe) SerialExecutor`, except that
default actors are represented without a witness table pointer (just
a bit-pattern).
- Synthesize the unownedExecutor method for default actors (i.e. actors
that don't provide an unownedExecutor property).
- Make synthesized unownedExecutor properties `final`, and give them
a semantics attribute specifying that they're for default actors.
- Split `Builtin.buildSerialExecutorRef` into a few more precise
builtins. We're not using the main-actor one yet, though.
Pitch thread:
https://forums.swift.org/t/support-custom-executors-in-swift-concurrency/44425
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.
- stop storing the parent task in the TaskGroup at the .swift level
- make sure that swift_taskGroup_isCancelled is implied by the parent
task being cancelled
- make the TaskGroup structs frozen
- make the withTaskGroup functions inlinable
- remove swift_taskGroup_create
- teach IRGen to allocate memory for the task group
- don't deallocate the task group in swift_taskGroup_destroy
To achieve the allocation change, introduce paired create/destroy builtins.
Furthermore, remove the _swiftRetain and _swiftRelease functions and
several calls to them. Replace them with uses of the appropriate builtins.
I should probably change the builtins to return retained, since they're
working with a managed type, but I'll do that in a separate commit.
This isn't _terribly_ useful as-is, because the only constant mask you can get at from Swift at present is the zeroinitializer, but even that is quite useful for optimizing the repeating: intializer on SIMD. At some future point we should wire up generating constant masks for the .even, .odd, .high and .low properties (and also eventually make shufflevector take non-constant masks in LLVM). But this is enough to be useful, so let's get it in.
The comment in LowerHopToActor explains the design here.
We want SILGen to emit hops to actors, ignoring executors,
because it's easier to fully optimize in a world where deriving
an executor is a non-trivial operation. But we also want something
prior to IRGen to lower the executor derivation because there are
useful static optimizations we can do, such as doing the derivation
exactly once on a dominance path and strength-reducing the derivation
(e.g. exploiting static knowledge that an actor is a default actor).
There are probably phase-ordering problems with doing this so late,
but hopefully they're restricted to situations like actors that
share an executor. We'll want to optimize that eventually, but
in the meantime, this unblocks the executor work.
The immediate desire is to minimize the set of ABI dependencies
on the layout of an ExecutorRef. In addition to that, however,
I wanted to generally reduce the code size impact of an unsafe
continuation since it now requires accessing thread-local state,
and I wanted resumption to not have to create unnecessary type
metadata for the value type just to do the initialization.
Therefore, I've introduced a swift_continuation_init function
which handles the default initialization of a continuation
and returns a reference to the current task. I've also moved
the initialization of the normal continuation result into the
caller (out of the runtime), and I've moved the resumption-side
cmpxchg into the runtime (and prior to the task being enqueued).
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
In their previous form, the non-`_f` variants of these entry points were unused, and IRGen
lowered the `createAsyncTask` builtins to use the `_f` variants with a large amount of caller-side
codegen to manually unpack closure values. Amid all this, it also failed to make anyone responsible
for releasing the closure context after the task completed, causing every task creation to leak.
Redo the `swift_task_create_*` entry points to accept the two words of an async closure value
directly, and unpack the closure to get its invocation entry point and initial context size
inside the runtime. (Also get rid of the non-future `swift_task_create` variant, since it's unused
and it's subtly different in a lot of hairy ways from the future forms. Better to add it later
when it's needed than to have a broken unexercised version now.)
The API for values is on the ValueBase. SILValue is supposed to be a
pointer-like wrapper class. Accessing a value's API is always done as
'value->api()'. The ValueBase subclasses, like SingleValueInstruction,
need to inherit the API.
I didn't have time to fix all the cases of value.isOwnershipKind()
throughout the code.
Otherwise the forwarding instruction will return a trivial value with
non-OwnershipKind::None ownership. This inevitably causes an ownership violation
since any place that we use that trivial value will expect the value to have
OwnershipKind::None, showing the inconsistency that this problem yields.
TLDR: This is just an NFC rename in preparation for changing
SILValue::getOwnershipKind() of any forwarding instructions to return
OwnershipKind::None if they have a trivial result despite forwarding ownership
that isn't OwnershipKind::None (consider an unchecked_enum_data of a trivial
payload from a non-trivial enum).
This ensures that one does not by mistake use this routine instead of
SILValue::getOwnershipKind(). The reason why these two things must be
distinguished is that the forwarding ownership kind of an instruction that
inherits from OwnershipForwardingMixin is explicitly not the ValueOwnershipKind
of the result of the instruction. Instead it is a separate piece of state that:
1. For certain forwarding instructions, defines the OwnershipConstraint of the
forwarding instruction.
2. Defines the ownership kind of the result of the value. If the result of the
value is non-trivial then it is exactly the set ownership kind. If the result is
trivial, we use OwnershipKind::None instead. As an example of this, consider an
unchecked_enum_data that extracts from a non-trivial enum a trivial payload:
```
enum Either {
case int(Int)
case obj(Klass)
}
%1 = load_borrow %0 : $*Either
%2 = unchecked_enum_data %1 : $Either, #Either.int!enumelt.1 // Int type
end_borrow %1 : $Either
```
If we were to identify the forwarding ownership kind (guaranteed) of
unchecked_enum_data with the value ownership kind of its result, we would
violate ownership since we would be passing a guaranteed value to the operand of
the unchecked_enum_data that will only accept values with
OwnershipKind::None. =><=.
It would be more abstractly correct if this got DI support so
that we destroy the member if the constructor terminates
abnormally, but we can get to that later.
Operationally it just means that in SILGlobalVariable blocks, all operands have
ownership constraint:
{OwnershipKind::Any, UseLifetimeConstraint::NonLifetimeEnding}
and all values yield an ownership kind of: OwnershipKind::None.
In derivatives of loops, no longer allocate boxes for indirect case payloads. Instead, use a custom pullback context in the runtime which contains a bump-pointer allocator.
When a function contains a differentiated loop, the closure context is a `Builtin.NativeObject`, which contains a `swift::AutoDiffLinearMapContext` and a tail-allocated top-level linear map struct (which represents the linear map struct that was previously directly partial-applied into the pullback). In branching trace enums, the payloads of previously indirect cases will be allocated by `swift::AutoDiffLinearMapContext::allocate` and stored as a `Builtin.RawPointer`.
Specifically, I made it so that assuming our instruction is inserted into a
block already that we:
1. Return a constraint of {OwnershipKind::Any, UseLifetimeConstraint::NonLifetimeEnding}.
2. Return OwnershipKind::None for all values.
Noticed above I said that if the instruction is already inserted into a block
then we do this. The reason why is that if this is called before an instruction
is inserted into a block, we can't get access to the SILFunction that has the
information on whether or not we are in OSSA form. The only time this can happen
is if one is using these APIs from within SILBuilder since SILBuilder is the
only place where we allow this to happen. In SILBuilder, we already know whether
or not our function is in ossa or not and already does different things as
appropriate (namely in non-ossa does not call getOwnershipKind()). So we know
that if these APIs are called in such a situation, we will only be calling it if
we are in OSSA already. Given that, we just assume we are in OSSA if we do not
have a function.
To make sure that no mistakes are made as a result of that assumption, I put in
a verifier check that all values when ownership is disabled return a
OwnershipKind::None from getOwnershipKind().
The main upside to this is this means that we can write code for both
OSSA/non-OSSA and write code for non-None ownership without needing to check if
ownership is enabled.
This makes it easier to understand conceptually why a ValueOwnershipKind with
Any ownership is invalid and also allowed me to explicitly document the lattice
that relates ownership constraints/value ownership kinds.
`Builtin.createAsyncTask` takes flags, an optional parent task, and an
async/throwing function to execute, and passes it along to the
`swift_task_create_f` entry point to create a new (potentially child)
task, returning the new task and its initial context.
Implement a new builtin, `cancelAsyncTask()`, to cancel the given
asynchronous task. This lowers down to a call into the runtime
operation `swift_task_cancel()`.
Use this builtin to implement Task.Handle.cancel().
Rather than produce an "unowned" result from `getCurrentAsyncTask()`,
take advantage of the fact that the task is effectively guaranteed in
the scope. Do so be returning it as "unowned", and push an
end_lifetime cleanup to end the lifetime. This eliminates unnecessary
ref-count traffic as well as introducing another use of unowned.
Approach is thanks to Michael Gottesman, bugs are mine.
This introduces a new builtin, `getCurrentAsyncTask()`, that produces a
reference to the current task. This builtin can only be used within
`async` functions, and IR generation merely grabs the task argument
and packages it up.
The type of this function is `() -> Builtin.NativeObject`, because we
don't currently have a Swift-level representation of tasks, and can
probably handle everything through builtins or runtime calls.
Treating a trivial type as having ownership seems only to confuse the ownership verifier.
The structural property we're trying to enforce here (that a continuation is always
consumed by an `await` locally) can be enforced by flow-sensitive verification without
ownership.
It can already only accept values with none ownership and the merging of
ownership around ownership phis ensure that if we phi this with a partial_apply
or the like, we get the appropriate ownership on any such ownership phi values.
We are now out of SILGen emitting fewer destroy_value unnecessarily on
thin_to_thick functions. This changed some codegen and also forced me to update
some tests/fix AutoDiff.
I also deleted the DebugInfo test mandatoryinlining-wrongdebugscope.swift since:
1. It was depending on these destroys being there.
2. Given the need to improve the test @aprantl suggested I just eliminate it
solving the test failure for me.
`get_async_continuation[_addr]` begins a suspend operation by accessing the continuation value that can resume
the task, which can then be used in a callback or event handler before executing `await_async_continuation` to
suspend the task.
Today unchecked_bitwise_cast returns a value with ObjCUnowned ownership. This is
important to do since the instruction can truncate memory meaning we want to
treat it as a new object that must be copied before use.
This means that in OSSA we do not have a purely ossa forwarding unchecked
layout-compatible assuming cast. This role is filled by unchecked_value_cast.
The ``base_addr_for_offset`` instruction creates a base address for offset calculations.
The result can be used by address projections, like ``struct_element_addr``, which themselves return the offset of the projected fields.
IR generation simply creates a null pointer for ``base_addr_for_offset``.
* a new [immutable] attribute on ref_element_addr and ref_tail_addr
* new instructions: begin_cow_mutation and end_cow_mutation
These new instructions are intended to be used for the stdlib's COW containers, e.g. Array.
They allow more aggressive optimizations, especially for Array.
Specifically, I split it into 3 initial categories: IR, Utils, Verifier. I just
did this quickly, we can always split it more later if we want.
I followed the model that we use in SILOptimizer: ./lib/SIL/CMakeLists.txt vends
a macro (sil_register_sources) to the sub-folders that register the sources of
the subdirectory with a global state variable that ./lib/SIL/CMakeLists.txt
defines. Then after including those subdirs, the parent cmake declares the SIL
library. So the output is the same, but we have the flexibility of having
subdirectories to categorize source files.
