Initial Task Executor implementation Task(on:), addTask(on:) etc. (#68793)

Co-authored-by: John McCall <rjmccall@gmail.com>

lib/IRGen/IRGenModule.cpp

@@ -674,7 +674,8 @@ IRGenModule::IRGenModule(IRGenerator &irgen,
   SwiftAsyncLetPtrTy = Int8PtrTy; // we pass it opaquely (AsyncLet*)
   SwiftTaskOptionRecordPtrTy = SizeTy; // Builtin.RawPointer? that we get as (TaskOptionRecord*)
   SwiftTaskGroupPtrTy = Int8PtrTy; // we pass it opaquely (TaskGroup*)
-  SwiftTaskOptionRecordTy = createStructType(*this, "swift.task_option", {
+  SwiftTaskOptionRecordTy = createStructType(
+      *this, "swift.task_option", {
     SizeTy,                     // Flags
     SwiftTaskOptionRecordPtrTy, // Parent
   });
@@ -698,6 +699,11 @@ IRGenModule::IRGenModule(IRGenerator &irgen,
     ExecutorFirstTy,      // identity
     ExecutorSecondTy,     // implementation
   });
+  SwiftInitialTaskExecutorPreferenceTaskOptionRecordTy =
+      createStructType(*this, "swift.task_executor_task_option", {
+    SwiftTaskOptionRecordTy, // Base option record
+    SwiftExecutorTy,         // Executor
+  });
   SwiftJobTy = createStructType(*this, "swift.job", {
     RefCountedStructTy,   // object header
     Int8PtrTy, Int8PtrTy, // SchedulerPrivate
@@ -881,6 +887,14 @@ namespace RuntimeConstants {
     return RuntimeAvailability::AlwaysAvailable;
   }
 
+  RuntimeAvailability TaskExecutorAvailability(ASTContext &context) {
+    auto featureAvailability = context.getTaskExecutorAvailability();
+    if (!isDeploymentAvailabilityContainedIn(context, featureAvailability)) {
+      return RuntimeAvailability::ConditionallyAvailable;
+    }
+    return RuntimeAvailability::AlwaysAvailable;
+  }
+
   RuntimeAvailability ConcurrencyDiscardingTaskGroupAvailability(ASTContext &context) {
     auto featureAvailability =
         context.getConcurrencyDiscardingTaskGroupAvailability();