[Concurrency] Implement a builtin createAsyncTask() to create a new task.

`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.

include/swift/AST/Builtins.def

@@ -728,6 +728,13 @@ BUILTIN_MISC_OPERATION_WITH_SILGEN(GetCurrentAsyncTask, "getCurrentAsyncTask", "
 /// Cancel the given asynchronous task.
 BUILTIN_MISC_OPERATION_WITH_SILGEN(CancelAsyncTask, "cancelAsyncTask", "", Special)
 
+/// createAsyncTask(): (
+///     Int, Builtin.NativeObject?, @escaping () async throws -> Void
+/// ) -> Builtin.NativeObject
+///
+/// Create a new asynchronous task, given flags, an (optional) parent task, and
+/// a function to execute.
+BUILTIN_MISC_OPERATION_WITH_SILGEN(CreateAsyncTask, "createAsyncTask", "", Special)
 
 /// globalStringTablePointer has type String -> Builtin.RawPointer.
 /// It returns an immortal, global string table pointer for strings constructed

include/swift/AST/Builtins.h

@@ -135,6 +135,11 @@ llvm::AtomicOrdering decodeLLVMAtomicOrdering(StringRef O);
 /// Returns true if the builtin with ID \p ID has a defined static overload for
 /// the type \p Ty.
 bool canBuiltinBeOverloadedForType(BuiltinValueKind ID, Type Ty);
+
+/// Retrieve the AST-level AsyncTaskAndContext type, used for the
+/// createAsyncTask builtin.
+Type getAsyncTaskAndContextType(ASTContext &ctx);
+
 }
 
 #endif

include/swift/Runtime/RuntimeFunctions.def

@@ -1489,7 +1489,7 @@ FUNCTION(TaskDealloc,
          ARGS(SwiftTaskPtrTy, Int8PtrTy),
          ATTRS(NoUnwind, ArgMemOnly))
 
-// void swift_task_dealloc(AsyncTask *task, void *ptr);
+// void swift_task_cancel(AsyncTask *task);
 FUNCTION(TaskCancel,
          swift_task_cancel, SwiftCC,
          ConcurrencyAvailability,
@@ -1497,6 +1497,16 @@ FUNCTION(TaskCancel,
          ARGS(SwiftTaskPtrTy),
          ATTRS(NoUnwind, ArgMemOnly))
 
+// AsyncTaskAndContext swift_task_create_f(
+//     size_t flags, AsyncTask *task, AsyncFunctionType<void()> *function,
+//     size_t initialContextSize);
+FUNCTION(TaskCreateFunc,
+         swift_task_create_f, SwiftCC,
+         ConcurrencyAvailability,
+         RETURNS(AsyncTaskAndContextTy),
+         ARGS(SizeTy, SwiftTaskPtrTy, TaskContinuationFunctionPtrTy, SizeTy),
+         ATTRS(NoUnwind, ArgMemOnly))
+
 #undef RETURNS
 #undef ARGS
 #undef ATTRS

lib/AST/Builtins.cpp

@@ -1350,6 +1350,25 @@ static ValueDecl *getCancelAsyncTask(ASTContext &ctx, Identifier id) {
       id, { ctx.TheNativeObjectType }, ctx.TheEmptyTupleType);
 }
 
+Type swift::getAsyncTaskAndContextType(ASTContext &ctx) {
+  TupleTypeElt resultTupleElements[2] = {
+    ctx.TheNativeObjectType, // task,
+    ctx.TheRawPointerType    // initial context
+  };
+
+  return TupleType::get(resultTupleElements, ctx);
+}
+
+static ValueDecl *getCreateAsyncTask(ASTContext &ctx, Identifier id) {
+  auto extInfo = ASTExtInfoBuilder().withAsync().withThrows().build();
+  return getBuiltinFunction(
+      id,
+      { ctx.getIntDecl()->getDeclaredInterfaceType(),
+        OptionalType::get(ctx.TheNativeObjectType),
+        FunctionType::get({ }, ctx.TheEmptyTupleType, extInfo) },
+      getAsyncTaskAndContextType(ctx));
+}
+
 static ValueDecl *getPoundAssert(ASTContext &Context, Identifier Id) {
   auto int1Type = BuiltinIntegerType::get(1, Context);
   auto optionalRawPointerType = BoundGenericEnumType::get(
@@ -2482,6 +2501,9 @@ ValueDecl *swift::getBuiltinValueDecl(ASTContext &Context, Identifier Id) {
   case BuiltinValueKind::CancelAsyncTask:
     return getCancelAsyncTask(Context, Id);
 
+  case BuiltinValueKind::CreateAsyncTask:
+    return getCreateAsyncTask(Context, Id);
+
   case BuiltinValueKind::PoundAssert:
     return getPoundAssert(Context, Id);
 

lib/IRGen/GenBuiltin.cpp

@@ -225,6 +225,24 @@ void irgen::emitBuiltinCall(IRGenFunction &IGF, const BuiltinInfo &Builtin,
     return;
   }
 
+  if (Builtin.ID == BuiltinValueKind::CreateAsyncTask) {
+    auto flags = args.claimNext();
+    auto parentTask = args.claimNext();
+    auto taskFunction = args.claimNext();
+    auto taskContext = args.claimNext();
+    auto newTaskAndContext = emitTaskCreate(
+        IGF, flags, parentTask, taskFunction, taskContext);
+
+    // Cast back to NativeObject/RawPointer.
+    auto newTask = IGF.Builder.CreateExtractValue(newTaskAndContext, { 0 });
+    newTask = IGF.Builder.CreateBitCast(newTask, IGF.IGM.RefCountedPtrTy);
+    auto newContext = IGF.Builder.CreateExtractValue(newTaskAndContext, { 1 });
+    newContext = IGF.Builder.CreateBitCast(newContext, IGF.IGM.Int8PtrTy);
+    out.add(newTask);
+    out.add(newContext);
+    return;
+  }
+
   // If this is an LLVM IR intrinsic, lower it to an intrinsic call.
   const IntrinsicInfo &IInfo = IGF.getSILModule().getIntrinsicInfo(FnId);
   llvm::Intrinsic::ID IID = IInfo.ID;

lib/IRGen/GenCall.cpp

@@ -3466,8 +3466,52 @@ void irgen::emitTaskCancel(IRGenFunction &IGF, llvm::Value *task) {
   auto *call = IGF.Builder.CreateCall(IGF.IGM.getTaskCancelFn(), {task});
   call->setDoesNotThrow();
   call->setCallingConv(IGF.IGM.SwiftCC);
-  call->addAttribute(llvm::AttributeList::FunctionIndex,
-                     llvm::Attribute::ReadNone);
+}
+
+llvm::Value *irgen::emitTaskCreate(
+    IRGenFunction &IGF, llvm::Value *flags, llvm::Value *parentTask,
+    llvm::Value *taskFunction, llvm::Value *localContextInfo) {
+  parentTask = IGF.Builder.CreateBitOrPointerCast(
+      parentTask, IGF.IGM.SwiftTaskPtrTy);
+  taskFunction = IGF.Builder.CreateBitOrPointerCast(
+      taskFunction, IGF.IGM.TaskContinuationFunctionPtrTy);
+
+  // Determine the size of the async context for the closure.
+  // FIXME: If the task function comes in as an AsyncFunctionPointer, we might
+  // want to use swift_task_create instead of swift_task_create_f.
+  ASTContext &ctx = IGF.IGM.IRGen.SIL.getASTContext();
+  auto extInfo = ASTExtInfoBuilder().withAsync().withThrows().build();
+  auto taskFunctionType = FunctionType::get(
+    { }, ctx.TheEmptyTupleType, extInfo);
+  CanSILFunctionType taskFunctionCanSILType =
+      IGF.IGM.getLoweredType(taskFunctionType).castTo<SILFunctionType>();
+  auto layout = getAsyncContextLayout(
+      IGF.IGM, taskFunctionCanSILType, taskFunctionCanSILType,
+      SubstitutionMap());
+  auto layoutSize = getAsyncContextSize(layout);
+  auto layoutSizeVal = llvm::ConstantInt::get(
+      IGF.IGM.SizeTy, layoutSize.getValue());
+
+  // Call the function.
+  auto *result = IGF.Builder.CreateCall(
+      IGF.IGM.getTaskCreateFuncFn(),
+      { flags, parentTask, taskFunction, layoutSizeVal });
+  result->setDoesNotThrow();
+  result->setCallingConv(IGF.IGM.SwiftCC);
+
+  // Write the local context information into the initial context for the task.
+  if (layout.hasLocalContext()) {
+    // Dig out the initial context returned from task creation.
+    auto initialContext = IGF.Builder.CreateExtractValue(result, { 1 });
+    Address initialContextAddr = layout.emitCastTo(IGF, initialContext);
+
+    auto localContextLayout = layout.getLocalContextLayout();
+    auto localContextAddr = localContextLayout.project(
+        IGF, initialContextAddr, llvm::None);
+    IGF.Builder.CreateStore(localContextInfo, localContextAddr);
+  }
+
+  return result;
 }
 
 std::pair<Address, Size> irgen::emitAllocAsyncContext(IRGenFunction &IGF,

lib/IRGen/GenCall.h

@@ -390,6 +390,12 @@ namespace irgen {
   void emitTaskDealloc(IRGenFunction &IGF, Address address, llvm::Value *size);
   void emitTaskCancel(IRGenFunction &IGF, llvm::Value *task);
 
+  /// Emit a class to swift_task_create[_f] with the given flags, parent task,
+  /// and task function.
+  llvm::Value *emitTaskCreate(
+    IRGenFunction &IGF, llvm::Value *flags, llvm::Value *parentTask,
+    llvm::Value *taskFunction, llvm::Value *localContextInfo);
+
   /// Allocate task local storage for the specified layout but using the
   /// provided dynamic size.  Allowing the size to be specified dynamically is
   /// necessary for applies of thick functions the sizes of whose async contexts

lib/IRGen/IRGenModule.cpp

@@ -602,6 +602,10 @@ IRGenModule::IRGenModule(IRGenerator &irgen,
       /*isVarArg*/ false);
   TaskContinuationFunctionPtrTy = TaskContinuationFunctionTy->getPointerTo();
 
+  AsyncTaskAndContextTy = createStructType(
+      *this, "swift.async_task_and_context",
+      { SwiftTaskPtrTy, SwiftContextPtrTy });
+
   DifferentiabilityWitnessTy = createStructType(
       *this, "swift.differentiability_witness", {Int8PtrTy, Int8PtrTy});
 }

lib/IRGen/IRGenModule.h

@@ -731,7 +731,7 @@ public:
   llvm::PointerType *SwiftExecutorPtrTy;
   llvm::FunctionType *TaskContinuationFunctionTy;
   llvm::PointerType *TaskContinuationFunctionPtrTy;
-
+  llvm::StructType *AsyncTaskAndContextTy;
   llvm::StructType *DifferentiabilityWitnessTy; // { i8*, i8* }
 
   llvm::GlobalVariable *TheTrivialPropertyDescriptor = nullptr;

lib/SIL/IR/OperandOwnership.cpp

@@ -1020,6 +1020,7 @@ ANY_OWNERSHIP_BUILTIN(IntInstrprofIncrement)
 CONSTANT_OWNERSHIP_BUILTIN(Owned, MustBeInvalidated, COWBufferForReading)
 CONSTANT_OWNERSHIP_BUILTIN(Owned, MustBeInvalidated, UnsafeGuaranteed)
 CONSTANT_OWNERSHIP_BUILTIN(Guaranteed, MustBeLive, CancelAsyncTask)
+CONSTANT_OWNERSHIP_BUILTIN(Guaranteed, MustBeLive, CreateAsyncTask)
 
 #undef CONSTANT_OWNERSHIP_BUILTIN
 

lib/SIL/IR/ValueOwnership.cpp

@@ -543,6 +543,7 @@ CONSTANT_OWNERSHIP_BUILTIN(None, IntInstrprofIncrement)
 CONSTANT_OWNERSHIP_BUILTIN(None, GlobalStringTablePointer)
 CONSTANT_OWNERSHIP_BUILTIN(Owned, GetCurrentAsyncTask)
 CONSTANT_OWNERSHIP_BUILTIN(None, CancelAsyncTask)
+CONSTANT_OWNERSHIP_BUILTIN(Owned, CreateAsyncTask)
 
 #undef CONSTANT_OWNERSHIP_BUILTIN
 

lib/SIL/Utils/MemAccessUtils.cpp

@@ -1800,6 +1800,7 @@ static void visitBuiltinAddress(BuiltinInst *builtin,
     case BuiltinValueKind::IntInstrprofIncrement:
     case BuiltinValueKind::TSanInoutAccess:
     case BuiltinValueKind::CancelAsyncTask:
+    case BuiltinValueKind::CreateAsyncTask:
       return;
 
     // General memory access to a pointer in first operand position.

lib/SILGen/SILGenBuiltin.cpp

@@ -1405,7 +1405,7 @@ static ManagedValue emitBuiltinGetCurrentAsyncTask(
   return SGF.emitManagedRValueWithEndLifetimeCleanup(apply);
 }
 
-// Emit SIL for the named builtin: getCurrentAsyncTask.
+// Emit SIL for the named builtin: cancelAsyncTask.
 static ManagedValue emitBuiltinCancelAsyncTask(
     SILGenFunction &SGF, SILLocation loc, SubstitutionMap subs,
     ArrayRef<ManagedValue> args, SGFContext C) {
@@ -1419,6 +1419,22 @@ static ManagedValue emitBuiltinCancelAsyncTask(
   return ManagedValue::forUnmanaged(apply);
 }
 
+// Emit SIL for the named builtin: createAsyncTask.
+static ManagedValue emitBuiltinCreateAsyncTask(
+    SILGenFunction &SGF, SILLocation loc, SubstitutionMap subs,
+    ArrayRef<ManagedValue> args, SGFContext C) {
+  ASTContext &ctx = SGF.getASTContext();
+  auto flags = args[0].forward(SGF);
+  auto parentTask = args[1].borrow(SGF, loc).forward(SGF);
+  auto function = args[2].borrow(SGF, loc).forward(SGF);
+  auto apply = SGF.B.createBuiltin(
+      loc,
+      ctx.getIdentifier(getBuiltinName(BuiltinValueKind::CreateAsyncTask)),
+      SGF.getLoweredType(getAsyncTaskAndContextType(ctx)), SubstitutionMap(),
+      { flags, parentTask, function });
+  return SGF.emitManagedRValueWithCleanup(apply);
+}
+
 Optional<SpecializedEmitter>
 SpecializedEmitter::forDecl(SILGenModule &SGM, SILDeclRef function) {
   // Only consider standalone declarations in the Builtin module.

lib/SILOptimizer/Transforms/AccessEnforcementReleaseSinking.cpp

@@ -166,6 +166,7 @@ static bool isBarrier(SILInstruction *inst) {
     case BuiltinValueKind::UnsafeGuaranteed:
     case BuiltinValueKind::UnsafeGuaranteedEnd:
     case BuiltinValueKind::CancelAsyncTask:
+    case BuiltinValueKind::CreateAsyncTask:
       return true;
     }
   }

test/IRGen/async/builtins.sil

@@ -6,6 +6,7 @@
 sil_stage canonical
 
 import Builtin
+import Swift
 
 // CHECK-LABEL: define hidden swiftcc void @get_task(%swift.task* %0, %swift.executor* %1, %swift.context* %2)
 sil hidden [ossa] @get_task : $@async @convention(thin) () -> @owned Builtin.NativeObject {
@@ -21,10 +22,25 @@ bb0:
 // CHECK-LABEL: define hidden swiftcc void @cancel_task(%swift.refcounted* %0)
 // CHECK: [[TASK:%.*]] = bitcast %swift.refcounted* %0 to %swift.task*
 // CHECK-NEXT:  call swiftcc void @swift_task_cancel(%swift.task* [[TASK]])
-
 sil hidden [ossa] @cancel_task : $@convention(method) (@guaranteed Builtin.NativeObject) -> () {
 bb0(%0 : @guaranteed $Builtin.NativeObject):
   %4 = builtin "cancelAsyncTask"(%0 : $Builtin.NativeObject) : $()
   %5 = tuple ()
   return %5 : $()
 }
+
+// CHECK-LABEL: define hidden swiftcc void @launch_task
+sil hidden [ossa] @launch_task : $@convention(method) @async (Int, Optional<Builtin.NativeObject>, @guaranteed @async @callee_guaranteed () -> (@error Error)) -> () {
+bb0(%0 : $Int, %1: @unowned $Optional<Builtin.NativeObject>, %2: @guaranteed $@async @callee_guaranteed () -> (@error Error)):
+  %3 = begin_borrow %1 : $Optional<Builtin.NativeObject>
+  // CHECK: [[NEW_TASK_AND_CONTEXT:%.*]] = call swiftcc %swift.async_task_and_context @swift_task_create_f
+  // CHECK-NEXT: [[NEW_CONTEXT_RAW:%.*]] = extractvalue %swift.async_task_and_context [[NEW_TASK_AND_CONTEXT]], 1
+  // CHECK-NEXT: [[NEW_CONTEXT:%.*]] = bitcast %swift.context* [[NEW_CONTEXT_RAW]] to
+  // CHECK-NEXT: [[CONTEXT_INFO_LOC:%.*]] = getelementptr inbounds <{{.*}}>* [[NEW_CONTEXT]]
+  // CHECK-NEXT: store %swift.refcounted* %{{.*}}, %swift.refcounted** [[CONTEXT_INFO_LOC]]
+  %20 = builtin "createAsyncTask"(%0 : $Int, %3 : $Optional<Builtin.NativeObject>, %2 : $@async @callee_guaranteed () -> (@error Error)) : $(Builtin.NativeObject, Builtin.RawPointer)
+  end_borrow %3 : $Optional<Builtin.NativeObject>
+  destroy_value %20 : $(Builtin.NativeObject, Builtin.RawPointer)
+  %21 = tuple ()
+  return %21 : $()
+}

test/SILGen/async_builtins.swift

@@ -1,7 +1,9 @@
 // RUN: %target-swift-frontend -emit-silgen %s -module-name test -swift-version 5 -enable-experimental-concurrency -parse-stdlib -sil-verify-all | %FileCheck %s
 // REQUIRES: concurrency
 
-struct X {
+import Swift
+
+public struct X {
   // CHECK-LABEL: sil hidden [ossa] @$s4test1XV14getCurrentTaskBoyYF
   func getCurrentTask() async -> Builtin.NativeObject {
     // CHECK: builtin "getCurrentAsyncTask"() : $Builtin.NativeObject
@@ -13,4 +15,14 @@ struct X {
     // CHECK: builtin "cancelAsyncTask"(%0 : $Builtin.NativeObject) : $()
     Builtin.cancelAsyncTask(task)
   }
+
+  // CHECK-LABEL: sil hidden [ossa] @$s4test1XV10launchTaskyyYF : $@convention(method) @async (X) -> ()
+  func launchTask() async {
+    // CHECK: builtin "createAsyncTask"([[FLAGS:%.*]] : $Int, [[PARENT:%.*]] : $Optional<Builtin.NativeObject>, [[FN:%.*]] : $@async @callee_guaranteed () -> @error Error) : $(Builtin.NativeObject, Builtin.RawPointer)
+    let task = Builtin.getCurrentAsyncTask()
+    let childTask = Builtin.createAsyncTask(0, task) {
+      await launchTask()
+      print("child is done")
+    }
+  }
 }