This seems fine to me… at a high level! -Andy > On Oct 14, 2016, at 2:44 PM, Michael Gottesman via swift-dev > <swift-dev@swift.org> wrote: > > Attached below is a final version of the proposal. I am going to commit it to > the repo if there are no further questions/changes/etc. > >> https://gottesmm.github.io/proposals/high-level-arc-memory-operations.html >> <https://gottesmm.github.io/proposals/high-level-arc-memory-operations.html> > Michael > > ---- > > # Summary > > This document proposes: > > 1. adding the following ownership qualifiers to `load`: `[take]`, `[copy]`, > `[trivial]`. > 2. adding the following ownership qualifiers to `store`: `[init]`, `[assign]`, > `[trivial]`. > 3. adding the `load_borrow` instruction and the `end_borrow` instruction. > 3. requiring all `load` and `store` operations to have ownership qualifiers. > 4. banning the use of `load [trivial]`, `store [trivial]` on memory locations > of > `non-trivial` type. > > This will allow for: > > 1. eliminating optimizer miscompiles that occur due to releases being moved > into > the region in between a `load`/`retain`, `load`/`release`, > `store`/`release`. (For a specific example, see the appendix). > 2. explicitly modeling `load [trivial]`/`store [trivial]` as having `unsafe > unowned` ownership semantics. This will be enforced via the verifier. > 3. more aggressive ARC code motion. > > # Definitions > > ## ownership qualified load > > We propose three different ownership qualifiers for load. Define `load > [trivial]` > as: > > %x = load [trivial] %x_ptr : $*Int > > => > > %x = load %x_ptr : $*Int > > A `load [trivial]` can not be used to load values of non-trivial type. Define > `load [copy]` as: > > %x = load [copy] %x_ptr : $*C > > => > > %x = load %x_ptr : $*C > retain_value %x : $C > > Then define `load [take]` as: > > %x = load [take] %x_ptr : $*Builtin.NativeObject > > => > > %x = load %x_ptr : $*Builtin.NativeObject > > **NOTE** `load [take]` implies that the loaded from memory location no longer > owns the result object (i.e. a take is a move). Loading from the memory > location > again without reinitialization is illegal. > > ## load_borrow and end_borrow > > Next we provide `load_borrow` and `end_borrow`: > > %x = load_borrow %x_ptr : $*Builtin.NativeObject > ... > end_borrow %x, %x_ptr : $*Builtin.NativeObject > > => > > %x = load %x_ptr : $*Builtin.NativeObject > ... > endLifetime %x : $Builtin.NativeObject > fixLifetime %x_ptr : $*Builtin.NativeObject > > `load [borrow]` implies that in the region between the `load` and the > `end_borrow`, the loaded object must semantically remain alive. The > `end_borrow` > communicates to the optimizer: > > 1. that the value in `%x_ptr` should not be destroyed before endBorrow. > 2. uses of `%x` should not be sunk past endBorrow since `%x` is only a shallow > copy of the value in `%x_ptr` and past that point `%x_ptr` may not remain > alive. > > An example of where this construct is useful is when one has a let binding to > a > class instance `c` that contains a let field `f`. In that case `c`'s lifetime > guarantees `f`'s lifetime meaning that returning `f` over the function call > boundary is safe. > > *NOTE* since the SILOwnershipModelEliminator will not process these > instructions, endLifetime is just a strawman instruction that will not be > implemented. In practice though, IRGen will need to create a suitable barrier > to > ensure that LLVM does not move any uses of `%x` past the `fixLifetime` > instruction of `%x_ptr` once we begin creating such instructions as a result > of > ARC optimization. > > ## ownership qualified store > > First define a `store [trivial]` as: > > store %x to [trivial] %x_ptr : $*Int > > => > > store %x to %x_ptr : $*Int > > The verifier will prevent this instruction from being used on types with > non-trivial ownership. Define a `store [assign]` as follows: > > store %x to [assign] %x_ptr : $*C > > => > > %old_x = load %x_ptr : $*C > store %new_x to %x_ptr : $*C > release_value %old_x : $C > > *NOTE* `store` is defined as a consuming operation. We also provide > `store [init]` in the case where we know statically that there is no > previous value in the memory location: > > store %x to [init] %x_ptr : $*C > > => > > store %new_x to %x_ptr : $*C > > # Implementation > > ## Goals > > Our implementation strategy goals are: > > 1. zero impact on other compiler developers until the feature is fully > developed. This implies all work will be done behind a flag. > 2. separation of feature implementation from updating passes. > > Goal 2 will be implemented via a pass that transforms ownership qualified > `load`/`store` instructions into unqualified `load`/`store` right after > SILGen. > > ## Plan > > We begin by adding initial infrastructure for our development. This means: > > 1. Adding to SILOptions a disabled by default flag called > "EnableSILOwnershipModel". This flag will be set by a false by default > frontend > option called "-enable-sil-ownership-mode". > > 2. Bots will be brought up to test the compiler with > "-enable-sil-ownership-model" set to true. The specific bots are: > > * RA-OSX+simulators > * RA-Device > * RA-Linux. > > The bots will run once a day until the feature is close to completion. > Then a > polling model will be followed. > > Now that change isolation is borrow, we develop building blocks for the > optimization: > > 1. Two enums will be defined: `LoadInstOwnershipQualifier`, > `StoreInstOwnershipQualifier`. The exact definition of these enums are as > follows: > > enum class LoadOwnershipQualifier { > Unqualified, Take, Copy, Trivial > }; > enum class StoreOwnershipQualifier { > Unqualified, Init, Assign, Trivial > }; > > *NOTE* `LoadOwnershipQualifier::Unqualified` and > `StoreOwnershipQualifier::Unqualified` are only needed for staging > purposes. > > 2. Creating a `LoadInst`, `StoreInst` will be changed to require an ownership > qualifier. At this stage, this argument will default to `Unqualified`. "Bare" > `load`, `store` when parsed via textual SIL will be considered to be > unqualified. This implies that the rest of the compiler will not have to be > changed as a result of this step. > > 3. Support will be added to SIL, IRGen, Serialization, SIL Printing, and SIL > Parsing for the rest of the qualifiers. SILGen will not be modified at this > stage. > > 4. The `load_borrow` and `end_borrow` instructions will be implemented in SIL, > IRGen, Serialization, SIL Printing, and SIL Parsing. They will not be used > immediately. > > 4. A pass called the "OwnershipModelEliminator" will be implemented. It will > blow up all `load`, `store` instructions with non `*::Unqualified` > ownership > into their constituant ARC operations and `*::Unqualified` `load`, `store` > insts. It will not process `load_borrow` and `end_borrow` since currently > it > is not expected for SILGen to emit such instructions. > > 5. An option called "EnforceSILOwnershipMode" will be added to the verifier. > If > the option is set, the verifier will assert if: > > a. `load`, `store` operations with trivial ownership are applied to memory > locations with non-trivial type. > > b. `load`, `store` operation with unqualified ownership type are present in > the IR. > > c. `load_borrow` or `end_borrow` are present in the IR. This is because > currently we do not support SIL containing such instructions in SIL > Ownership Mode. Once we have the ability to verify borrowing scopes, this > will no longer be the case, but this is a different proposal. > > Finally, we wire up the building blocks: > > 1. If SILOption.EnableSILOwnershipModel is true, then the after SILGen SIL > verification will be performed with EnforceSILOwnershipModel set to true. > 2. If SILOption.EnableSILOwnershipModel is true, then the pass manager will > run > the OwnershipModelEliminator pass right after SILGen before the normal pass > pipeline starts. > 3. SILGen will be changed to emit non-unqualified ownership qualifiers on > load, > store instructions when the EnableSILOwnershipModel flag is set. We will > use > the verifier throwing to guarantee that we are not missing any specific > cases. > > Then once all of the bots are green, we change > SILOption.EnableSILOwnershipModel > to be true by default. After a cooling off period, we move all of the code > behind the SILOwnershipModel flag in front of the flag. We do this so we can > reuse that flag for further SILOwnershipModel changes. > > ## Optimizer Changes > > Since the SILOwnershipModel eliminator will eliminate the ownership qualifiers > on load, store instructions right after ownership verification, there will be > no > immediate effects on the optimizer and thus the optimizer changes can be done > in > parallel with the rest of the ARC optimization work. > > But, in the long run, we want to enforce these ownership invariants all > throughout the SIL pipeline implying these ownership qualified `load`, `store` > instructions must be processed by IRGen, not eliminated by the > SILOwnershipModel > eliminator. Thus we will need to update passes to handle these new > instructions > and also will need to implement the `load_borrow`, `end_borrow` instruction. > > The main optimizer changes can be separated into the following areas: memory > forwarding, dead stores, ARC optimization. In all of these cases, the > necessary > changes are relatively trivial to respond to. We give a quick taste of two of > them: store->load forwarding and ARC Code Motion. > > ### store->load forwarding > > Currently we perform store->load forwarding as follows: > > store %x to %x_ptr : $C > ... NO SIDE EFFECTS THAT TOUCH X_PTR ... > %y = load %x_ptr : $C > use(%y) > > => > > store %x to %x_ptr : $C > ... NO SIDE EFFECTS THAT TOUCH X_PTR ... > use(%x) > > In a world, where we are using ownership qualified load, store, we have to > also > consider the ownership implications. *NOTE* Since we are not modifying the > store, `store [assign]` and `store [init]` are treated the same. Thus without > any loss of generality, lets consider solely `store`. > > store %x to [assign] %x_ptr : $C > ... NO SIDE EFFECTS THAT TOUCH X_PTR ... > %y = load [copy] %x_ptr : $C > use(%y) > > => > > store %x to [assign] %x_ptr : $C > ... NO SIDE EFFECTS THAT TOUCH X_PTR ... > strong_retain %x > use(%x) > > ### ARC Code Motion > > If ARC Code Motion wishes to move the ARC semantics of ownership qualified > `load`, `store` instructions, it must now consider read/write effects. On the > other hand, we can perform more aggressive ARC code motion of ownership > qualified loads and stores in the face of deinits. This is because we no > longer > need to worry about our code motion causing a deinit to fire in between > (without > any loss of generality) the load/retain. > > ### Normal Code Motion > > Normal code motion will lose some effectiveness since many of the load/store > operations that it used to be able to move now must consider ARC information. > We > may need to consider running ARC code motion earlier in the pipeline where we > normally run Normal Code Motion to ensure that we are able to handle these > cases. > > ### ARC Optimization > > The main implication for ARC optimization is that instead of eliminating just > retains, releases, it must be able to recognize ownership qualified `load`, > `store` and set their flags as appropriate. Also in general ARC optimization > and > memory behavior will need to recognize the `end_borrow` instruction as a code > motion barrier. > > ### Function Signature Optimization > > Semantic ARC affects function signature optimization in the context of the > owned > to borrow optimization. Specifically: > > 1. A `store [assign]` must be recognized as a release of the old value that is > being overridden. In such a case, we can move the `release` of the old > value > into the caller and change the `store [assign]` into a `store [init]`. > 2. A `load [copy]` must be recognized as a retain in the callee. Then function > signature optimization will transform the `load [copy]` into a > `load_borrow`. This would require the addition of a new `@borrow` return > value convention. > > # Appendix > > ## Partial Initialization of Loadable References in SIL > > In SIL, a value of non-trivial loadable type is loaded from a memory location > as > follows: > > %x = load %x_ptr : $*S > ... > retain_value %x_ptr : $S > > At first glance, this looks reasonable, but in truth there is a hidden > drawback: > the partially initialized zone in between the load and the retain > operation. This zone creates a period of time when an "evil optimizer" could > insert an instruction that causes x to be deallocated before the copy is > finished being initialized. Similar issues come up when trying to perform a > store of a non-trival value into a memory location. > > Since this sort of partial initialization is allowed in SIL, the optimizer is > forced to be overly conservative when attempting to move releases passed > retains > lest the release triggers a deinit that destroys a value like `%x`. Lets look > at > two concrete examples that show how semantically providing ownership qualified > load, store instructions eliminate this problem. > > **NOTE** Without any loss of generality, we will speak of values with > reference > semantics instead of non-trivial values. > > ## Case Study: Partial Initialization and load [copy] > > ### The Problem > > Consider the following swift program: > > func opaque_call() > > final class C { > var int: Int = 0 > deinit { > opaque_call() > } > } > > final class D { > var int: Int = 0 > } > > var GLOBAL_C : C? = nil > var GLOBAL_D : D? = nil > > func useC(_ c: C) > func useD(_ d: D) > > func run() { > let c = C() > GLOBAL_C = c > let d = D() > GLOBAL_D = d > useC(c) > useD(d) > } > > Notice that both `C` and `D` have fixed layouts and separate class > hierarchies, > but `C`'s deinit has a call to the function `opaque_call` which may write to > `GLOBAL_D` or `GLOBAL_C`. Additionally assume that both `useC` and `useD` are > known to the compiler to not have any affects on instances of type `D`, `C` > respectively and useC assigns `nil` to `GLOBAL_C`. Now consider the following > valid SIL lowering for `run`: > > sil_global GLOBAL_D : $D > sil_global GLOBAL_C : $C > > final class C { > var x: Int > deinit > } > > final class D { > var x: Int > } > > sil @useC : $@convention(thin) () -> () > sil @useD : $@convention(thin) () -> () > > sil @run : $@convention(thin) () -> () { > bb0: > %c = alloc_ref $C > %global_c = global_addr @GLOBAL_C : $*C > strong_retain %c : $C > store %c to %global_c : $*C > (1) > > %d = alloc_ref $D > %global_d = global_addr @GLOBAL_D : $*D > strong_retain %d : $D > store %d to %global_d : $*D > (2) > > %c2 = load %global_c : $*C > (3) > strong_retain %c2 : $C > (4) > %d2 = load %global_d : $*D > (5) > strong_retain %d2 : $D > (6) > > %useC_func = function_ref @useC : $@convention(thin) (@owned C) -> () > apply %useC_func(%c2) : $@convention(thin) (@owned C) -> () > (7) > > %useD_func = function_ref @useD : $@convention(thin) (@owned D) -> () > apply %useD_func(%d2) : $@convention(thin) (@owned D) -> () > (8) > > strong_release %d : $D > (9) > strong_release %c : $C > (10) > } > > Lets optimize this function! First we perform the following operations: > > 1. Since `(2)` is storing to an identified object that can not be `GLOBAL_C`, > we > can store to load forward `(1)` to `(3)`. > 2. Since a retain does not block store to load forwarding, we can forward > `(2)` > to `(5)`. But lets for the sake of argument, assume that the optimizer > keeps > such information as an analysis and does not perform the actual load->store > forwarding. > 3. Even though we do not foward `(2)` to `(5)`, we can still move `(4)` over > `(6)` so that `(4)` is right before `(7)`. > > This yields (using the ' marker to designate that a register has had > load-store > forwarding applied to it): > > sil @run : $@convention(thin) () -> () { > bb0: > %c = alloc_ref $C > %global_c = global_addr @GLOBAL_C : $*C > strong_retain %c : $C > store %c to %global_c : $*C > (1) > > %d = alloc_ref $D > %global_d = global_addr @GLOBAL_D : $*D > strong_retain %d : $D > store %d to %global_d : $*D > (2) > > strong_retain %c : $C > (4') > %d2 = load %global_d : $*D > (5) > strong_retain %d2 : $D > (6) > > %useC_func = function_ref @useC : $@convention(thin) (@owned C) -> () > apply %useC_func(%c) : $@convention(thin) (@owned C) -> () > (7') > > %useD_func = function_ref @useD : $@convention(thin) (@owned D) -> () > apply %useD_func(%d2) : $@convention(thin) (@owned D) -> () > (8) > > strong_release %d : $D > (9) > strong_release %c : $C > (10) > } > > Then by assumption, we know that `%useC` does not perform any releases of any > instances of class `D`. Thus `(6)` can be moved past `(7')` and we can then > pair > and eliminate `(6)` and `(9)` via the rules of ARC optimization using the > analysis information that `%d2` and `%d` are th same due to the possibility of > performing store->load forwarding. After performing such transformations, > `run` > looks as follows: > > sil @run : $@convention(thin) () -> () { > bb0: > %c = alloc_ref $C > %global_c = global_addr @GLOBAL_C : $*C > strong_retain %c : $C > store %c to %global_c : $*C > (1) > > %d = alloc_ref $D > %global_d = global_addr @GLOBAL_D : $*D > strong_retain %d : $D > store %d to %global_d : $*D > > %d2 = load %global_d : $*D > (5) > strong_retain %c : $C > (4') > %useC_func = function_ref @useC : $@convention(thin) (@owned C) -> () > apply %useC_func(%c) : $@convention(thin) (@owned C) -> () > (7') > > %useD_func = function_ref @useD : $@convention(thin) (@owned D) -> () > apply %useD_func(%d2) : $@convention(thin) (@owned D) -> () > (8) > > strong_release %c : $C > (10) > } > > Now by assumption, we know that `%useD_func` does not touch any instances of > class `C` and `%c` does not contain any ivars of type `D` and is final so none > can be added. At first glance, this seems to suggest that we can move `(10)` > before `(8')` and then pair/eliminate `(4')` and `(10)`. But is this a safe > optimization perform? Absolutely Not! Why? Remember that since `useC_func` > assigns `nil` to `GLOBAL_C`, after `(7')`, `%c` could have a reference count > of 1. Thus `(10)` _may_ invoke the destructor of `C`. Since this destructor > calls an opaque function that _could_ potentially write to `GLOBAL_D`, we may > be > be passing `%d2`, an already deallocated object to `%useD_func`, an illegal > optimization! > > Lets think a bit more about this example and consider this example at the > language level. Remember that while Swift's deinit are not asychronous, we do > not allow for user level code to create dependencies from the body of the > destructor into the normal control flow that has called it. This means that > there are two valid results of this code: > > - Operation Sequence 1: No optimization is performed and `%d2` is passed to > `%useD_func`. > - Operation Sequence 2: We shorten the lifetime of `%c` before `%useD_func` > and > a different instance of `$D` is passed into `%useD_func`. > > The fact that 1 occurs without optimization is just as a result of an > implementation detail of SILGen. 2 is also a valid sequence of operations. > > Given that: > > 1. As a principle, the optimizer does not consider such dependencies to avoid > being overly conservative. > 2. We provide constructs to ensure appropriate lifetimes via the usage of > constructs such as fix_lifetime. > > We need to figure out how to express our optimization such that 2 > happens. Remember that one of the optimizations that we performed at the > beginning was to move `(6)` over `(7')`, i.e., transform this: > > %d = alloc_ref $D > %global_d_addr = global_addr GLOBAL_D : $D > %d = load %global_d_addr : $*D (5) > strong_retain %d : $D (6) > > // Call the user functions passing in the instances that we loaded from > the globals. > %useC_func = function_ref @useC : $@convention(thin) (@owned C) -> () > apply %useC_func(%c) : $@convention(thin) (@owned C) -> () > (7') > > into: > > %global_d_addr = global_addr GLOBAL_D : $D > %d2 = load %global_d_addr : $*D (5) > > // Call the user functions passing in the instances that we loaded from > the globals. > %useC_func = function_ref @useC : $@convention(thin) (@owned C) -> () > apply %useC_func(%c) : $@convention(thin) (@owned C) -> () > (7') > strong_retain %d2 : $D (6) > > This transformation in Swift corresponds to transforming: > > let d = GLOBAL_D > useC(c) > > to: > > let d_raw = load_d_value(GLOBAL_D) > useC(c) > let d = take_ownership_of_d(d_raw) > > This is clearly an instance where we have moved a side-effect in between the > loading of the data and the taking ownership of such data, that is before the > `let` is fully initialized. What if instead of just moving the retain, we > moved > the entire let statement? This would then result in the following swift code: > > useC(c) > let d = GLOBAL_D > > and would correspond to the following SIL snippet: > > %global_d_addr = global_addr GLOBAL_D : $D > > // Call the user functions passing in the instances that we loaded from > the globals. > %useC_func = function_ref @useC : $@convention(thin) (@owned C) -> () > apply %useC_func(%c) : $@convention(thin) (@owned C) -> () > (7') > %d2 = load %global_d_addr : $*D > (5) > strong_retain %d2 : $D > (6) > > Moving the load with the strong_retain to ensure that the full initialization > is > performed even after code motion causes our SIL to look as follows: > > sil @run : $@convention(thin) () -> () { > bb0: > %c = alloc_ref $C > %global_c = global_addr @GLOBAL_C : $*C > strong_retain %c : $C > store %c to %global_c : $*C > (1) > > %d = alloc_ref $D > %global_d = global_addr @GLOBAL_D : $*D > strong_retain %d : $D > store %d to %global_d : $*D > > strong_retain %c : $C > (4') > %useC_func = function_ref @useC : $@convention(thin) (@owned C) -> () > apply %useC_func(%c) : $@convention(thin) (@owned C) -> () > (7') > > %d2 = load %global_d : $*D > (5) > %useD_func = function_ref @useD : $@convention(thin) (@owned D) -> () > apply %useD_func(%d2) : $@convention(thin) (@owned D) -> () > (8) > > strong_release %c : $C > (10) > } > > Giving us the exact result that we want: Operation Sequence 2! > > ### Defining load [copy] > > Given that we wish the load, store to be tightly coupled together, it is > natural > to express this operation as a `load [copy]` instruction. Lets define the > `load > [copy]` instruction as follows: > > %1 = load [copy] %0 : $*C > > => > > %1 = load %0 : $*C > retain_value %1 : $C > > Now lets transform our initial example to use this instruction: > > Notice how now if we move `(7)` over `(3)` and `(6)` now, we get the > following SIL: > > sil @run : $@convention(thin) () -> () { > bb0: > %c = alloc_ref $C > %global_c = global_addr @GLOBAL_C : $*C > strong_retain %c : $C > store %c to %global_c : $*C > (1) > > %d = alloc_ref $D > %global_d = global_addr @GLOBAL_D : $*D > strong_retain %d : $D > store %d to %global_d : $*D > (2) > > %c2 = load [copy] %global_c : $*C > (3) > %d2 = load [copy] %global_d : $*D > (5) > > %useC_func = function_ref @useC : $@convention(thin) (@owned C) -> () > apply %useC_func(%c2) : $@convention(thin) (@owned C) -> () > (7) > > %useD_func = function_ref @useD : $@convention(thin) (@owned D) -> () > apply %useD_func(%d2) : $@convention(thin) (@owned D) -> () > (8) > > strong_release %d : $D > (9) > strong_release %c : $C > (10) > } > > We then perform the previous code motion: > > sil @run : $@convention(thin) () -> () { > bb0: > %c = alloc_ref $C > %global_c = global_addr @GLOBAL_C : $*C > strong_retain %c : $C > store %c to %global_c : $*C > (1) > > %d = alloc_ref $D > %global_d = global_addr @GLOBAL_D : $*D > strong_retain %d : $D > store %d to %global_d : $*D > (2) > > %c2 = load [copy] %global_c : $*C > (3) > %useC_func = function_ref @useC : $@convention(thin) (@owned C) -> () > apply %useC_func(%c2) : $@convention(thin) (@owned C) -> () > (7) > strong_release %d : $D > (9) > > %d2 = load [copy] %global_d : $*D > (5) > %useD_func = function_ref @useD : $@convention(thin) (@owned D) -> () > apply %useD_func(%d2) : $@convention(thin) (@owned D) -> () > (8) > strong_release %c : $C > (10) > } > > We then would like to eliminate `(9)` and `(10)` by pairing them with `(3)` > and > `(8)`. Can we still do so? One way we could do this is by introducing the > `[take]` flag. The `[take]` flag on a `load [take]` says that one is > semantically loading a value from a memory location and are taking ownership > of > the value thus eliding the retain. In terms of SIL this flag is defined as: > > %x = load [take] %x_ptr : $*C > > => > > %x = load %x_ptr : $*C > > Why do we care about having such a `load [take]` instruction when we could > just > use a `load`? The reason why is that a normal `load` has unsafe unowned > ownership (i.e. it has no implications on ownership). We would like for memory > that has non-trivial type to only be able to be loaded via instructions that > maintain said ownership. We will allow for casting to trivial types as usual > to > provide such access if it is required. > > Thus we have achieved the desired result: > > sil @run : $@convention(thin) () -> () { > bb0: > %c = alloc_ref $C > %global_c = global_addr @GLOBAL_C : $*C > strong_retain %c : $C > store %c to %global_c : $*C > (1) > > %d = alloc_ref $D > %global_d = global_addr @GLOBAL_D : $*D > strong_retain %d : $D > store %d to %global_d : $*D > (2) > > %c2 = load [take] %global_c : $*C > (3) > %useC_func = function_ref @useC : $@convention(thin) (@owned C) -> () > apply %useC_func(%c2) : $@convention(thin) (@owned C) -> () > (7) > > %d2 = load [take] %global_d : $*D > (5) > %useD_func = function_ref @useD : $@convention(thin) (@owned D) -> () > apply %useD_func(%d2) : $@convention(thin) (@owned D) -> () > (8) > } > > ---- > > _______________________________________________ > swift-dev mailing list > swift-dev@swift.org > https://lists.swift.org/mailman/listinfo/swift-dev
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