IRGen: fix the LLVM struct definition of AsyncTask.

The object header was missing.

Author: eeckstein

lib/IRGen/IRGenFunction.cpp

@@ -634,7 +634,7 @@ void IRGenFunction::emitGetAsyncContinuation(SILType unsafeContinuationTy,
   // information.
   // currTask->ResumeTask = @llvm.coro.async.resume();
   assert(currTask->getType() == IGM.SwiftTaskPtrTy);
-  auto currTaskResumeTaskAddr = Builder.CreateStructGEP(currTask,3);
+  auto currTaskResumeTaskAddr = Builder.CreateStructGEP(currTask, 4);
   auto coroResume =
       Builder.CreateIntrinsicCall(llvm::Intrinsic::coro_async_resume, {});
 
@@ -645,7 +645,7 @@ void IRGenFunction::emitGetAsyncContinuation(SILType unsafeContinuationTy,
       Builder.CreateBitOrPointerCast(coroResume, IGM.FunctionPtrTy),
       Address(currTaskResumeTaskAddr, pointerAlignment));
   // currTask->ResumeContext = &continuation_context;
-  auto currTaskResumeCtxtAddr = Builder.CreateStructGEP(currTask, 4);
+  auto currTaskResumeCtxtAddr = Builder.CreateStructGEP(currTask, 5);
   Builder.CreateStore(
       Builder.CreateBitOrPointerCast(continuationContext.getAddress(),
                                      IGM.SwiftContextPtrTy),

lib/IRGen/IRGenModule.cpp

@@ -594,13 +594,17 @@ IRGenModule::IRGenModule(IRGenerator &irgen,
                                             {RelativeAddressTy, Int32Ty}, true);
   SwiftContextTy = createStructType(*this, "swift.context", {});
   auto *ContextPtrTy = llvm::PointerType::getUnqual(SwiftContextTy);
+
+  // This must match the definition of class AsyncTask in swift/ABI/Task.h.
   SwiftTaskTy = createStructType(*this, "swift.task", {
+    RefCountedStructTy,   // object header
     Int8PtrTy, Int8PtrTy, // Job.SchedulerPrivate
     Int64Ty,              // Job.Flags
     FunctionPtrTy,        // Job.RunJob/Job.ResumeTask
     ContextPtrTy,         // Task.ResumeContext
     Int64Ty               // Task.Status
   });
+
   SwiftExecutorTy = createStructType(*this, "swift.executor", {});
   AsyncFunctionPointerPtrTy = AsyncFunctionPointerTy->getPointerTo(DefaultAS);
   SwiftContextPtrTy = SwiftContextTy->getPointerTo(DefaultAS);

test/IRGen/async/get_async_continuation.sil

@@ -39,10 +39,10 @@ bb0:
 // CHECK:  [[exe:%.*]] = load %swift.executor*, %swift.executor** [[exe_addr]]
 // CHECK:  store %swift.executor* [[exe]], %swift.executor** [[exectuor_addr]]
 //   Initialize the async task with the continuation function and async continuation context.
-// CHECK: [[task_continuation_fn_addr:%.*]] = getelementptr inbounds %swift.task, %swift.task* [[tsk]], i32 0, i32 3
+// CHECK: [[task_continuation_fn_addr:%.*]] = getelementptr inbounds %swift.task, %swift.task* [[tsk]], i32 0, i32 4
 // CHECK: [[continuation_fn:%.*]] = call i8* @llvm.coro.async.resume()
 // CHECK: store i8* [[continuation_fn]], i8** [[task_continuation_fn_addr]]
-// CHECK: [[task_resume_context_addr:%.*]] = getelementptr inbounds %swift.task, %swift.task* [[tsk]], i32 0, i32 4
+// CHECK: [[task_resume_context_addr:%.*]] = getelementptr inbounds %swift.task, %swift.task* [[tsk]], i32 0, i32 5
 // CHECK: [[cont_context2:%.*]] = bitcast %swift.async_continuation_context* [[cont_context]] to %swift.context*
 // CHECK: store %swift.context* [[cont_context2]], %swift.context** [[task_resume_context_addr]]
 //  Initialize the synchronization variable.