diff --git a/cl/_testdata/async/in.go b/cl/_testdata/async/in.go
new file mode 100644
index 00000000..259b98b2
--- /dev/null
+++ b/cl/_testdata/async/in.go
@@ -0,0 +1,37 @@
+package async_compile
+
+import (
+	"fmt"
+
+	"github.com/goplus/llgo/x/async"
+)
+
+func GenInts() (co *async.Promise[int]) {
+	co.Yield(1)
+	co.Yield(2)
+	co.Yield(3)
+	return
+}
+
+func WrapGenInts() *async.Promise[int] {
+	return GenInts()
+}
+
+func UseGenInts() int {
+	co := WrapGenInts()
+	r := 0
+	for !co.Done() {
+		r += co.Next()
+	}
+	return r
+}
+
+func GenIntsWithDefer() (co *async.Promise[int]) {
+	defer func() {
+		if r := recover(); r != nil {
+			fmt.Println("panic:", r)
+		}
+	}()
+	co.Yield(1)
+	panic("GenIntsWithDefer")
+}
diff --git a/cl/_testdata/async/out.ll b/cl/_testdata/async/out.ll
new file mode 100644
index 00000000..3306d581
--- /dev/null
+++ b/cl/_testdata/async/out.ll
@@ -0,0 +1,372 @@
+; ModuleID = 'github.com/goplus/llgo/cl/_testdata/async'
+source_filename = "github.com/goplus/llgo/cl/_testdata/async"
+
+%"github.com/goplus/llgo/internal/runtime.Defer" = type { ptr, i64, ptr, ptr }
+%"github.com/goplus/llgo/internal/runtime.String" = type { ptr, i64 }
+%"github.com/goplus/llgo/internal/runtime.eface" = type { ptr, ptr }
+%"github.com/goplus/llgo/internal/runtime.Slice" = type { ptr, i64, i64 }
+%"github.com/goplus/llgo/internal/runtime.iface" = type { ptr, ptr }
+%"github.com/goplus/llgo/x/async.Promise[int]" = type { ptr, i64 }
+
+@"github.com/goplus/llgo/cl/_testdata/async.init$guard" = global i1 false, align 1
+@__llgo_defer = linkonce global i32 0, align 4
+@0 = private unnamed_addr constant [16 x i8] c"GenIntsWithDefer", align 1
+@_llgo_string = linkonce global ptr null, align 8
+@1 = private unnamed_addr constant [6 x i8] c"panic:", align 1
+
+define ptr @"github.com/goplus/llgo/cl/_testdata/async.GenInts"() #0 {
+entry:
+  %promise = call ptr @"github.com/goplus/llgo/internal/runtime.AllocZ"(i64 16)
+  %id = call token @llvm.coro.id(i32 0, ptr null, ptr null, ptr null)
+  %need.dyn.alloc = call i1 @llvm.coro.alloc(token %id)
+  br i1 %need.dyn.alloc, label %alloc, label %_llgo_4
+
+alloc:                                            ; preds = %entry
+  %frame.size = call i64 @llvm.coro.size.i64()
+  %frame = call ptr @"github.com/goplus/llgo/internal/runtime.AllocZ"(i64 %frame.size)
+  br label %_llgo_4
+
+clean:                                            ; preds = %_llgo_7, %_llgo_6, %_llgo_5, %_llgo_4
+  %0 = call ptr @llvm.coro.free(token %id, ptr %hdl)
+  br label %suspend
+
+suspend:                                          ; preds = %_llgo_6, %_llgo_5, %_llgo_4, %clean
+  %1 = call i1 @llvm.coro.end(ptr %hdl, i1 false, token none)
+  ret ptr %promise
+
+_llgo_4:                                          ; preds = %alloc, %entry
+  %frame1 = phi ptr [ null, %entry ], [ %frame, %alloc ]
+  %hdl = call ptr @llvm.coro.begin(token %id, ptr %frame1)
+  store ptr %hdl, ptr %promise, align 8
+  call void @"github.com/goplus/llgo/x/async.(*Promise).setValue[int]"(ptr %promise, i64 1)
+  %2 = call i8 @llvm.coro.suspend(token %id, i1 false)
+  switch i8 %2, label %suspend [
+    i8 0, label %_llgo_5
+    i8 1, label %clean
+  ]
+
+_llgo_5:                                          ; preds = %_llgo_4
+  call void @"github.com/goplus/llgo/x/async.(*Promise).setValue[int]"(ptr %promise, i64 2)
+  %3 = call i8 @llvm.coro.suspend(token %id, i1 false)
+  switch i8 %3, label %suspend [
+    i8 0, label %_llgo_6
+    i8 1, label %clean
+  ]
+
+_llgo_6:                                          ; preds = %_llgo_5
+  call void @"github.com/goplus/llgo/x/async.(*Promise).setValue[int]"(ptr %promise, i64 3)
+  %4 = call i8 @llvm.coro.suspend(token %id, i1 false)
+  switch i8 %4, label %suspend [
+    i8 0, label %_llgo_7
+    i8 1, label %clean
+  ]
+
+_llgo_7:                                          ; preds = %_llgo_6
+  br label %clean
+}
+
+define ptr @"github.com/goplus/llgo/cl/_testdata/async.GenIntsWithDefer"() #0 {
+entry:
+  %promise = call ptr @"github.com/goplus/llgo/internal/runtime.AllocZ"(i64 16)
+  %id = call token @llvm.coro.id(i32 0, ptr null, ptr null, ptr null)
+  %need.dyn.alloc = call i1 @llvm.coro.alloc(token %id)
+  br i1 %need.dyn.alloc, label %alloc, label %_llgo_4
+
+alloc:                                            ; preds = %entry
+  %frame.size = call i64 @llvm.coro.size.i64()
+  %frame = call ptr @"github.com/goplus/llgo/internal/runtime.AllocZ"(i64 %frame.size)
+  br label %_llgo_4
+
+clean:                                            ; preds = %_llgo_5, %_llgo_8
+  %0 = call ptr @llvm.coro.free(token %id, ptr %hdl)
+  br label %suspend
+
+suspend:                                          ; preds = %_llgo_8, %clean
+  %1 = call i1 @llvm.coro.end(ptr %hdl, i1 false, token none)
+  ret ptr %promise
+
+_llgo_4:                                          ; preds = %alloc, %entry
+  %frame1 = phi ptr [ null, %entry ], [ %frame, %alloc ]
+  %hdl = call ptr @llvm.coro.begin(token %id, ptr %frame1)
+  store ptr %hdl, ptr %promise, align 8
+  %2 = alloca ptr, align 8
+  %3 = call ptr @"github.com/goplus/llgo/internal/runtime.Zeroinit"(ptr %2, i64 8)
+  %4 = load i32, ptr @__llgo_defer, align 4
+  %5 = call ptr @pthread_getspecific(i32 %4)
+  %6 = alloca i8, i64 196, align 1
+  %7 = alloca i8, i64 32, align 1
+  %8 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.Defer", ptr %7, i32 0, i32 0
+  store ptr %6, ptr %8, align 8
+  %9 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.Defer", ptr %7, i32 0, i32 1
+  store i64 0, ptr %9, align 4
+  %10 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.Defer", ptr %7, i32 0, i32 2
+  store ptr %5, ptr %10, align 8
+  %11 = call i32 @pthread_setspecific(i32 %4, ptr %7)
+  %12 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.Defer", ptr %7, i32 0, i32 1
+  %13 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.Defer", ptr %7, i32 0, i32 3
+  %14 = call i32 @sigsetjmp(ptr %6, i32 0)
+  %15 = icmp eq i32 %14, 0
+  br i1 %15, label %_llgo_8, label %_llgo_9
+
+_llgo_5:                                          ; preds = %_llgo_8, %_llgo_7
+  %16 = alloca %"github.com/goplus/llgo/internal/runtime.String", align 8
+  %17 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.String", ptr %16, i32 0, i32 0
+  store ptr @0, ptr %17, align 8
+  %18 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.String", ptr %16, i32 0, i32 1
+  store i64 16, ptr %18, align 4
+  %19 = load %"github.com/goplus/llgo/internal/runtime.String", ptr %16, align 8
+  %20 = load ptr, ptr @_llgo_string, align 8
+  %21 = call ptr @"github.com/goplus/llgo/internal/runtime.AllocU"(i64 16)
+  store %"github.com/goplus/llgo/internal/runtime.String" %19, ptr %21, align 8
+  %22 = alloca %"github.com/goplus/llgo/internal/runtime.eface", align 8
+  %23 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.eface", ptr %22, i32 0, i32 0
+  store ptr %20, ptr %23, align 8
+  %24 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.eface", ptr %22, i32 0, i32 1
+  store ptr %21, ptr %24, align 8
+  %25 = load %"github.com/goplus/llgo/internal/runtime.eface", ptr %22, align 8
+  call void @"github.com/goplus/llgo/internal/runtime.Panic"(%"github.com/goplus/llgo/internal/runtime.eface" %25)
+  unreachable
+  %26 = load ptr, ptr %3, align 8
+  br label %clean
+
+_llgo_6:                                          ; preds = %_llgo_9
+  %27 = load i64, ptr %12, align 4
+  call void @"github.com/goplus/llgo/cl/_testdata/async.GenIntsWithDefer$1"()
+  %28 = load %"github.com/goplus/llgo/internal/runtime.Defer", ptr %7, align 8
+  %29 = extractvalue %"github.com/goplus/llgo/internal/runtime.Defer" %28, 2
+  %30 = call i32 @pthread_setspecific(i32 %4, ptr %29)
+  %31 = load ptr, ptr %13, align 8
+  indirectbr ptr %31, [label %_llgo_7]
+
+_llgo_7:                                          ; preds = %_llgo_6
+  call void @"github.com/goplus/llgo/internal/runtime.Rethrow"(ptr %5)
+  br label %_llgo_5
+
+_llgo_8:                                          ; preds = %_llgo_4
+  %32 = load ptr, ptr %3, align 8
+  call void @"github.com/goplus/llgo/x/async.(*Promise).setValue[int]"(ptr %promise, i64 1)
+  %33 = call i8 @llvm.coro.suspend(token %id, i1 false)
+  switch i8 %33, label %suspend [
+    i8 0, label %_llgo_5
+    i8 1, label %clean
+  ]
+
+_llgo_9:                                          ; preds = %_llgo_4
+  store ptr blockaddress(@"github.com/goplus/llgo/cl/_testdata/async.GenIntsWithDefer", %_llgo_7), ptr %13, align 8
+  br label %_llgo_6
+
+_llgo_10:                                         ; No predecessors!
+}
+
+define void @"github.com/goplus/llgo/cl/_testdata/async.GenIntsWithDefer$1"() {
+_llgo_0:
+  %0 = call %"github.com/goplus/llgo/internal/runtime.eface" @"github.com/goplus/llgo/internal/runtime.Recover"()
+  %1 = call i1 @"github.com/goplus/llgo/internal/runtime.EfaceEqual"(%"github.com/goplus/llgo/internal/runtime.eface" %0, %"github.com/goplus/llgo/internal/runtime.eface" zeroinitializer)
+  %2 = xor i1 %1, true
+  br i1 %2, label %_llgo_1, label %_llgo_2
+
+_llgo_1:                                          ; preds = %_llgo_0
+  %3 = call ptr @"github.com/goplus/llgo/internal/runtime.AllocZ"(i64 32)
+  %4 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.eface", ptr %3, i64 0
+  %5 = alloca %"github.com/goplus/llgo/internal/runtime.String", align 8
+  %6 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.String", ptr %5, i32 0, i32 0
+  store ptr @1, ptr %6, align 8
+  %7 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.String", ptr %5, i32 0, i32 1
+  store i64 6, ptr %7, align 4
+  %8 = load %"github.com/goplus/llgo/internal/runtime.String", ptr %5, align 8
+  %9 = load ptr, ptr @_llgo_string, align 8
+  %10 = call ptr @"github.com/goplus/llgo/internal/runtime.AllocU"(i64 16)
+  store %"github.com/goplus/llgo/internal/runtime.String" %8, ptr %10, align 8
+  %11 = alloca %"github.com/goplus/llgo/internal/runtime.eface", align 8
+  %12 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.eface", ptr %11, i32 0, i32 0
+  store ptr %9, ptr %12, align 8
+  %13 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.eface", ptr %11, i32 0, i32 1
+  store ptr %10, ptr %13, align 8
+  %14 = load %"github.com/goplus/llgo/internal/runtime.eface", ptr %11, align 8
+  store %"github.com/goplus/llgo/internal/runtime.eface" %14, ptr %4, align 8
+  %15 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.eface", ptr %3, i64 1
+  store %"github.com/goplus/llgo/internal/runtime.eface" %0, ptr %15, align 8
+  %16 = alloca %"github.com/goplus/llgo/internal/runtime.Slice", align 8
+  %17 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.Slice", ptr %16, i32 0, i32 0
+  store ptr %3, ptr %17, align 8
+  %18 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.Slice", ptr %16, i32 0, i32 1
+  store i64 2, ptr %18, align 4
+  %19 = getelementptr inbounds %"github.com/goplus/llgo/internal/runtime.Slice", ptr %16, i32 0, i32 2
+  store i64 2, ptr %19, align 4
+  %20 = load %"github.com/goplus/llgo/internal/runtime.Slice", ptr %16, align 8
+  %21 = call { i64, %"github.com/goplus/llgo/internal/runtime.iface" } @fmt.Println(%"github.com/goplus/llgo/internal/runtime.Slice" %20)
+  br label %_llgo_2
+
+_llgo_2:                                          ; preds = %_llgo_1, %_llgo_0
+  ret void
+}
+
+define i64 @"github.com/goplus/llgo/cl/_testdata/async.UseGenInts"() {
+_llgo_0:
+  %0 = call ptr @"github.com/goplus/llgo/cl/_testdata/async.WrapGenInts"()
+  br label %_llgo_3
+
+_llgo_1:                                          ; preds = %_llgo_3
+  %1 = call i64 @"github.com/goplus/llgo/x/async.(*Promise).Next[int]"(ptr %0)
+  %2 = add i64 %3, %1
+  br label %_llgo_3
+
+_llgo_2:                                          ; preds = %_llgo_3
+  ret i64 %3
+
+_llgo_3:                                          ; preds = %_llgo_1, %_llgo_0
+  %3 = phi i64 [ 0, %_llgo_0 ], [ %2, %_llgo_1 ]
+  %4 = call i1 @"github.com/goplus/llgo/x/async.(*Promise).Done[int]"(ptr %0)
+  br i1 %4, label %_llgo_2, label %_llgo_1
+}
+
+define ptr @"github.com/goplus/llgo/cl/_testdata/async.WrapGenInts"() #0 {
+entry:
+  %promise = call ptr @"github.com/goplus/llgo/internal/runtime.AllocZ"(i64 16)
+  %id = call token @llvm.coro.id(i32 0, ptr null, ptr null, ptr null)
+  %need.dyn.alloc = call i1 @llvm.coro.alloc(token %id)
+  br i1 %need.dyn.alloc, label %alloc, label %_llgo_4
+
+alloc:                                            ; preds = %entry
+  %frame.size = call i64 @llvm.coro.size.i64()
+  %frame = call ptr @"github.com/goplus/llgo/internal/runtime.AllocZ"(i64 %frame.size)
+  br label %_llgo_4
+
+clean:                                            ; preds = %_llgo_4
+  %0 = call ptr @llvm.coro.free(token %id, ptr %hdl)
+  br label %suspend
+
+suspend:                                          ; preds = %clean
+  %1 = call i1 @llvm.coro.end(ptr %hdl, i1 false, token none)
+  ret ptr %promise
+
+_llgo_4:                                          ; preds = %alloc, %entry
+  %frame1 = phi ptr [ null, %entry ], [ %frame, %alloc ]
+  %hdl = call ptr @llvm.coro.begin(token %id, ptr %frame1)
+  store ptr %hdl, ptr %promise, align 8
+  %2 = call ptr @"github.com/goplus/llgo/cl/_testdata/async.GenInts"()
+  br label %clean
+}
+
+define void @"github.com/goplus/llgo/cl/_testdata/async.init"() {
+_llgo_0:
+  %0 = load i1, ptr @"github.com/goplus/llgo/cl/_testdata/async.init$guard", align 1
+  br i1 %0, label %_llgo_2, label %_llgo_1
+
+_llgo_1:                                          ; preds = %_llgo_0
+  store i1 true, ptr @"github.com/goplus/llgo/cl/_testdata/async.init$guard", align 1
+  call void @fmt.init()
+  call void @"github.com/goplus/llgo/cl/_testdata/async.init$after"()
+  br label %_llgo_2
+
+_llgo_2:                                          ; preds = %_llgo_1, %_llgo_0
+  ret void
+}
+
+declare ptr @"github.com/goplus/llgo/internal/runtime.AllocZ"(i64)
+
+; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: read)
+declare token @llvm.coro.id(i32, ptr readnone, ptr nocapture readonly, ptr) #1
+
+; Function Attrs: nounwind
+declare i1 @llvm.coro.alloc(token) #2
+
+; Function Attrs: nounwind memory(none)
+declare i64 @llvm.coro.size.i64() #3
+
+; Function Attrs: nounwind
+declare ptr @llvm.coro.begin(token, ptr writeonly) #2
+
+; Function Attrs: nounwind memory(argmem: read)
+declare ptr @llvm.coro.free(token, ptr nocapture readonly) #4
+
+; Function Attrs: nounwind
+declare i1 @llvm.coro.end(ptr, i1, token) #2
+
+declare void @"github.com/goplus/llgo/x/async.(*Promise).setValue[int]"(ptr, i64)
+
+; Function Attrs: nounwind
+declare i8 @llvm.coro.suspend(token, i1) #2
+
+declare ptr @"github.com/goplus/llgo/internal/runtime.Zeroinit"(ptr, i64)
+
+declare ptr @pthread_getspecific(i32)
+
+declare i32 @pthread_setspecific(i32, ptr)
+
+declare i32 @sigsetjmp(ptr, i32)
+
+declare void @"github.com/goplus/llgo/internal/runtime.Rethrow"(ptr)
+
+define void @"github.com/goplus/llgo/cl/_testdata/async.init$after"() {
+_llgo_0:
+  %0 = load ptr, ptr @_llgo_string, align 8
+  %1 = icmp eq ptr %0, null
+  br i1 %1, label %_llgo_1, label %_llgo_2
+
+_llgo_1:                                          ; preds = %_llgo_0
+  %2 = call ptr @"github.com/goplus/llgo/internal/runtime.Basic"(i64 24)
+  store ptr %2, ptr @_llgo_string, align 8
+  br label %_llgo_2
+
+_llgo_2:                                          ; preds = %_llgo_1, %_llgo_0
+  %3 = load i32, ptr @__llgo_defer, align 4
+  %4 = icmp eq i32 %3, 0
+  br i1 %4, label %_llgo_3, label %_llgo_4
+
+_llgo_3:                                          ; preds = %_llgo_2
+  %5 = call i32 @pthread_key_create(ptr @__llgo_defer, ptr null)
+  br label %_llgo_4
+
+_llgo_4:                                          ; preds = %_llgo_3, %_llgo_2
+  ret void
+}
+
+declare ptr @"github.com/goplus/llgo/internal/runtime.Basic"(i64)
+
+declare ptr @"github.com/goplus/llgo/internal/runtime.AllocU"(i64)
+
+declare void @"github.com/goplus/llgo/internal/runtime.Panic"(%"github.com/goplus/llgo/internal/runtime.eface")
+
+declare %"github.com/goplus/llgo/internal/runtime.eface" @"github.com/goplus/llgo/internal/runtime.Recover"()
+
+declare i1 @"github.com/goplus/llgo/internal/runtime.EfaceEqual"(%"github.com/goplus/llgo/internal/runtime.eface", %"github.com/goplus/llgo/internal/runtime.eface")
+
+declare { i64, %"github.com/goplus/llgo/internal/runtime.iface" } @fmt.Println(%"github.com/goplus/llgo/internal/runtime.Slice")
+
+define i1 @"github.com/goplus/llgo/x/async.(*Promise).Done[int]"(ptr %0) {
+_llgo_0:
+  %1 = getelementptr inbounds %"github.com/goplus/llgo/x/async.Promise[int]", ptr %0, i32 0, i32 0
+  %2 = load ptr, ptr %1, align 8
+  %3 = call i1 @llvm.coro.done(ptr %2)
+  %4 = zext i1 %3 to i64
+  %5 = trunc i64 %4 to i8
+  %6 = icmp ne i8 %5, 0
+  ret i1 %6
+}
+
+define i64 @"github.com/goplus/llgo/x/async.(*Promise).Next[int]"(ptr %0) {
+_llgo_0:
+  %1 = getelementptr inbounds %"github.com/goplus/llgo/x/async.Promise[int]", ptr %0, i32 0, i32 0
+  %2 = load ptr, ptr %1, align 8
+  call void @llvm.coro.resume(ptr %2)
+  %3 = getelementptr inbounds %"github.com/goplus/llgo/x/async.Promise[int]", ptr %0, i32 0, i32 1
+  %4 = load i64, ptr %3, align 4
+  ret i64 %4
+}
+
+declare void @fmt.init()
+
+; Function Attrs: nounwind memory(argmem: readwrite)
+declare i1 @llvm.coro.done(ptr nocapture readonly) #5
+
+declare void @llvm.coro.resume(ptr)
+
+declare i32 @pthread_key_create(ptr, ptr)
+
+attributes #0 = { "presplitcoroutine" }
+attributes #1 = { nocallback nofree nosync nounwind willreturn memory(argmem: read) }
+attributes #2 = { nounwind }
+attributes #3 = { nounwind memory(none) }
+attributes #4 = { nounwind memory(argmem: read) }
+attributes #5 = { nounwind memory(argmem: readwrite) }
diff --git a/cl/async.go b/cl/async.go
new file mode 100644
index 00000000..217f80ae
--- /dev/null
+++ b/cl/async.go
@@ -0,0 +1,119 @@
+/*
+ * Copyright (c) 2024 The GoPlus Authors (goplus.org). All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package cl
+
+import (
+	"go/types"
+	"strings"
+
+	llssa "github.com/goplus/llgo/ssa"
+	"golang.org/x/tools/go/ssa"
+)
+
+// TODO(lijie): need more generics, shouldn't limit to async.Promise
+func promiseType(ty types.Type) (types.Type, bool) {
+	// ty is a generic type, so we need to check the package path and type name
+	if ptrTy, ok := ty.(*types.Pointer); ok {
+		ty = ptrTy.Elem()
+		if ty, ok := ty.(*types.Named); ok {
+			if ty.Obj().Pkg() == nil {
+				return nil, false
+			}
+			if ty.Obj().Pkg().Path() == "github.com/goplus/llgo/x/async" && ty.Obj().Name() == "Promise" {
+				return ty, true
+			}
+		}
+	}
+	return nil, false
+}
+
+// check function return async.Promise[T]
+// TODO(lijie): make it generic
+func isAsyncFunc(sig *types.Signature) bool {
+	r := sig.Results()
+	if r.Len() != 1 {
+		return false
+	}
+	ty := r.At(0).Type()
+	_, ok := promiseType(ty)
+	return ok
+}
+
+func (p *context) coAwait(b llssa.Builder, args []ssa.Value) llssa.Expr {
+	if !isAsyncFunc(b.Func.RawType().(*types.Signature)) {
+		panic("coAwait(promise *T) T: invalid context")
+	}
+	if len(args) == 1 {
+		// promise := p.compileValue(b, args[0])
+		b.Unreachable()
+		// return b.CoroutineAwait(promise)
+	}
+	panic("coAwait(promise *T) T: invalid arguments")
+}
+
+func (p *context) coSuspend(b llssa.Builder, final llssa.Expr) {
+	b.CoSuspend(b.AsyncToken(), final)
+}
+
+func (p *context) coDone(b llssa.Builder, args []ssa.Value) llssa.Expr {
+	if len(args) != 1 {
+		panic("coDone(promise *T): invalid arguments")
+	}
+	hdl := p.compileValue(b, args[0])
+	return b.CoDone(hdl)
+}
+
+func (p *context) coResume(b llssa.Builder, args []ssa.Value) {
+	if len(args) == 1 {
+		hdl := p.compileValue(b, args[0])
+		b.CoResume(hdl)
+	}
+}
+
+func (p *context) coReturn(b llssa.Builder, args []ssa.Value) {
+	cargs := make([]llssa.Expr, len(args))
+	for i, arg := range args {
+		cargs[i] = p.compileValue(b, arg)
+	}
+	b.CoReturn(cargs...)
+}
+
+func (p *context) coYield(b llssa.Builder, fn *ssa.Function, args []ssa.Value) {
+	typ := fn.Signature.Recv().Type()
+	mthds := p.goProg.MethodSets.MethodSet(typ)
+	// TODO(lijie): make llgo instruction callable (e.g. llgo.yield)
+	var setValue *ssa.Function
+	for i := 0; i < mthds.Len(); i++ {
+		m := mthds.At(i)
+		if ssaMthd := p.goProg.MethodValue(m); ssaMthd != nil {
+			if ssaMthd.Name() == "setValue" || strings.HasPrefix(ssaMthd.Name(), "setValue[") {
+				setValue = ssaMthd
+				break
+			}
+		}
+	}
+	if setValue == nil {
+		panic("coYield(): not found method setValue")
+	}
+	value := p.compileValue(b, args[1])
+	setValueFn, _, _ := p.funcOf(setValue)
+	b.CoYield(setValueFn, value)
+}
+
+func (p *context) coRun(b llssa.Builder, args []ssa.Value) {
+	panic("coRun(): not implemented")
+}
diff --git a/cl/compile.go b/cl/compile.go
index cadc8a8d..e36e838a 100644
--- a/cl/compile.go
+++ b/cl/compile.go
@@ -214,6 +214,7 @@ func (p *context) compileFuncDecl(pkg llssa.Package, f *ssa.Function) (llssa.Fun
 			log.Println("==> NewFunc", name, "type:", sig.Recv(), sig, "ftype:", ftype)
 		}
 	}
+	async := isAsyncFunc(f.Signature)
 	if fn == nil {
 		if name == "main" {
 			argc := types.NewParam(token.NoPos, pkgTypes, "", types.Typ[types.Int32])
@@ -223,13 +224,20 @@ func (p *context) compileFuncDecl(pkg llssa.Package, f *ssa.Function) (llssa.Fun
 			results := types.NewTuple(ret)
 			sig = types.NewSignatureType(nil, nil, nil, params, results, false)
 		}
-		fn = pkg.NewFuncEx(name, sig, llssa.Background(ftype), hasCtx)
+		fn = pkg.NewFuncEx(name, sig, llssa.Background(ftype), hasCtx, async)
 	}
-
+	nBlkOff := 0
 	if nblk := len(f.Blocks); nblk > 0 {
+		if async {
+			nBlkOff = 4
+			fn.MakeBlock("entry")
+			fn.MakeBlock("alloc")
+			fn.MakeBlock("clean")
+			fn.MakeBlock("suspend")
+		}
 		fn.MakeBlocks(nblk)   // to set fn.HasBody() = true
 		if f.Recover != nil { // set recover block
-			fn.SetRecover(fn.Block(f.Recover.Index))
+			fn.SetRecover(fn.Block(f.Recover.Index + nBlkOff))
 		}
 		p.inits = append(p.inits, func() {
 			p.fn = fn
@@ -245,6 +253,10 @@ func (p *context) compileFuncDecl(pkg llssa.Package, f *ssa.Function) (llssa.Fun
 				log.Println("==> FuncBody", name)
 			}
 			b := fn.NewBuilder()
+			b.SetBlockOffset(nBlkOff)
+			if async {
+				b.BeginAsync(fn)
+			}
 			p.bvals = make(map[ssa.Value]llssa.Expr)
 			off := make([]int, len(f.Blocks))
 			for i, block := range f.Blocks {
@@ -280,7 +292,7 @@ func (p *context) compileBlock(b llssa.Builder, block *ssa.BasicBlock, n int, do
 	var pkg = p.pkg
 	var fn = p.fn
 	var instrs = block.Instrs[n:]
-	var ret = fn.Block(block.Index)
+	var ret = fn.Block(block.Index + b.BlockOffset())
 	b.SetBlock(ret)
 	if doModInit {
 		if pyModInit = p.pyMod != ""; pyModInit {
@@ -650,7 +662,11 @@ func (p *context) compileInstr(b llssa.Builder, instr ssa.Instruction) {
 			results = make([]llssa.Expr, 1)
 			results[0] = p.prog.IntVal(0, p.prog.CInt())
 		}
-		b.Return(results...)
+		if b.Async() {
+			b.EndAsync()
+		} else {
+			b.Return(results...)
+		}
 	case *ssa.If:
 		fn := p.fn
 		cond := p.compileValue(b, v.Cond)
diff --git a/cl/import.go b/cl/import.go
index 5d9b8b25..d723f3a8 100644
--- a/cl/import.go
+++ b/cl/import.go
@@ -412,7 +412,16 @@ const (
 	llgoAtomicUMax = llgoAtomicOpBase + llssa.OpUMax
 	llgoAtomicUMin = llgoAtomicOpBase + llssa.OpUMin
 
-	llgoAtomicOpLast = llgoAtomicOpBase + int(llssa.OpUMin)
+	llgoCoBase    = llgoInstrBase + 0x30
+	llgoCoAwait   = llgoCoBase + 0
+	llgoCoSuspend = llgoCoBase + 1
+	llgoCoDone    = llgoCoBase + 2
+	llgoCoResume  = llgoCoBase + 3
+	llgoCoReturn  = llgoCoBase + 4
+	llgoCoYield   = llgoCoBase + 5
+	llgoCoRun     = llgoCoBase + 6
+
+	llgoAtomicOpLast = llgoCoRun
 )
 
 func (p *context) funcName(fn *ssa.Function, ignore bool) (*types.Package, string, int) {
diff --git a/cl/instr.go b/cl/instr.go
index 83837ad0..9a65ba8e 100644
--- a/cl/instr.go
+++ b/cl/instr.go
@@ -237,6 +237,14 @@ var llgoInstrs = map[string]int{
 	"atomicMin":  int(llgoAtomicMin),
 	"atomicUMax": int(llgoAtomicUMax),
 	"atomicUMin": int(llgoAtomicUMin),
+
+	"coAwait":   int(llgoCoAwait),
+	"coResume":  int(llgoCoResume),
+	"coSuspend": int(llgoCoSuspend),
+	"coDone":    int(llgoCoDone),
+	"coReturn":  int(llgoCoReturn),
+	"coYield":   int(llgoCoYield),
+	"coRun":     int(llgoCoRun),
 }
 
 // funcOf returns a function by name and set ftype = goFunc, cFunc, etc.
@@ -265,7 +273,8 @@ func (p *context) funcOf(fn *ssa.Function) (aFn llssa.Function, pyFn llssa.PyObj
 				return nil, nil, ignoredFunc
 			}
 			sig := fn.Signature
-			aFn = pkg.NewFuncEx(name, sig, llssa.Background(ftype), false)
+			async := isAsyncFunc(sig)
+			aFn = pkg.NewFuncEx(name, sig, llssa.Background(ftype), false, async)
 		}
 	}
 	return
@@ -390,6 +399,20 @@ func (p *context) call(b llssa.Builder, act llssa.DoAction, call *ssa.CallCommon
 			ret = p.funcAddr(b, args)
 		case llgoUnreachable: // func unreachable()
 			b.Unreachable()
+		case llgoCoAwait:
+			ret = p.coAwait(b, args)
+		case llgoCoSuspend:
+			p.coSuspend(b, p.prog.BoolVal(false))
+		case llgoCoDone:
+			return p.coDone(b, args)
+		case llgoCoResume:
+			p.coResume(b, args)
+		case llgoCoReturn:
+			p.coReturn(b, args)
+		case llgoCoYield:
+			p.coYield(b, cv, args)
+		case llgoCoRun:
+			p.coRun(b, args)
 		default:
 			if ftype >= llgoAtomicOpBase && ftype <= llgoAtomicOpLast {
 				ret = p.atomic(b, llssa.AtomicOp(ftype-llgoAtomicOpBase), args)
diff --git a/ssa/coro.go b/ssa/coro.go
index d6183f93..e765332c 100644
--- a/ssa/coro.go
+++ b/ssa/coro.go
@@ -17,11 +17,46 @@
 package ssa
 
 import (
+	"fmt"
+	"go/constant"
 	"go/token"
 	"go/types"
+	"log"
 )
 
-// declare void @llvm.coro.destroy(i8*)
+// declare void @llvm.coro.destroy(ptr <handle>)
+// declare void @llvm.coro.resume(ptr <handle>)
+// declare i1 @llvm.coro.done(ptr <handle>)
+// declare ptr @llvm.coro.promise(ptr <ptr>, i32 <alignment>, i1 <from>)
+// declare i32 @llvm.coro.size.i32()
+// declare i32 @llvm.coro.size.i64()
+// declare i32 @llvm.coro.align.i32()
+// declare i64 @llvm.coro.align.i64()
+// declare ptr @llvm.coro.begin(token <id>, ptr <mem>)
+// declare ptr @llvm.coro.free(token %id, ptr <frame>)
+// declare i1 @llvm.coro.alloc(token <id>)
+// declare ptr @llvm.coro.noop()
+// declare ptr @llvm.coro.frame()
+// declare token @llvm.coro.id(i32 <align>, ptr <promise>, ptr <coroaddr>, ptr <fnaddrs>)
+// declare token @llvm.coro.id.async(i32 <context size>, i32 <align>, ptr <context arg>, ptr <async function pointer>)
+// declare token @llvm.coro.id.retcon(i32 <size>, i32 <align>, ptr <buffer>, ptr <continuation prototype>, ptr <alloc>, ptr <dealloc>)
+// declare token @llvm.coro.id.retcon.once(i32 <size>, i32 <align>, ptr <buffer>, ptr <prototype>, ptr <alloc>, ptr <dealloc>)
+// declare i1 @llvm.coro.end(ptr <handle>, i1 <unwind>, token <result.token>)
+// declare token @llvm.coro.end.results(...)
+// declare i1 @llvm.coro.end.async(ptr <handle>, i1 <unwind>, ...)
+// declare i8 @llvm.coro.suspend(token <save>, i1 <final>)
+// declare token @llvm.coro.save(ptr <handle>)
+// declare {ptr, ptr, ptr} @llvm.coro.suspend.async(ptr <resume function>, ptr <context projection function>, ... <function to call> ... <arguments to function>)
+// declare ptr @llvm.coro.prepare.async(ptr <coroutine function>)
+// declare i1 @llvm.coro.suspend.retcon(...)
+// declare void @await_suspend_function(ptr %awaiter, ptr %hdl)
+// declare void @llvm.coro.await.suspend.void(ptr <awaiter>, ptr <handle>, ptr <await_suspend_function>)
+// declare i1 @llvm.coro.await.suspend.bool(ptr <awaiter>, ptr <handle>, ptr <await_suspend_function>)
+// declare void @llvm.coro.await.suspend.handle(ptr <awaiter>, ptr <handle>, ptr <await_suspend_function>)
+
+// -----------------------------------------------------------------------------
+
+// declare void @llvm.coro.destroy(ptr <handle>)
 func (p Program) tyCoDestroy() *types.Signature {
 	if p.coDestroyTy == nil {
 		i8Ptr := types.NewParam(token.NoPos, nil, "", p.VoidPtr().raw.Type)
@@ -31,7 +66,7 @@ func (p Program) tyCoDestroy() *types.Signature {
 	return p.coDestroyTy
 }
 
-// declare void @llvm.coro.resume(i8*)
+// declare void @llvm.coro.resume(ptr <handle>)
 func (p Program) tyCoResume() *types.Signature {
 	if p.coResumeTy == nil {
 		i8Ptr := types.NewParam(token.NoPos, nil, "", p.VoidPtr().raw.Type)
@@ -101,7 +136,7 @@ func (p Program) tyCoAlignI64() *types.Signature {
 	return p.coAlignI64Ty
 }
 
-// declare i8* @llvm.coro.begin(token, i8*)
+// declare ptr @llvm.coro.begin(token <id>, ptr <mem>)
 func (p Program) tyCoBegin() *types.Signature {
 	if p.coBeginTy == nil {
 		tokenParam := types.NewParam(token.NoPos, nil, "", p.Token().raw.Type)
@@ -113,7 +148,7 @@ func (p Program) tyCoBegin() *types.Signature {
 	return p.coBeginTy
 }
 
-// declare i8* @llvm.coro.free(token, i8*)
+// declare ptr @llvm.coro.free(token %id, ptr <frame>)
 func (p Program) tyCoFree() *types.Signature {
 	if p.coFreeTy == nil {
 		tokenParam := types.NewParam(token.NoPos, nil, "", p.Token().raw.Type)
@@ -125,7 +160,7 @@ func (p Program) tyCoFree() *types.Signature {
 	return p.coFreeTy
 }
 
-// declare i1 @llvm.coro.alloc(token)
+// declare i1 @llvm.coro.alloc(token <id>)
 func (p Program) tyCoAlloc() *types.Signature {
 	if p.coAllocTy == nil {
 		tokenParam := types.NewParam(token.NoPos, nil, "", p.Token().raw.Type)
@@ -155,7 +190,7 @@ func (p Program) tyCoFrame() *types.Signature {
 	return p.coFrameTy
 }
 
-// declare token @llvm.coro.id(i32, i8*, i8*, i8*)
+// declare token @llvm.coro.id(i32 <align>, ptr <promise>, ptr <coroaddr>, ptr <fnaddrs>)
 func (p Program) tyCoID() *types.Signature {
 	if p.coIDTy == nil {
 		i32 := types.NewParam(token.NoPos, nil, "", p.Int32().raw.Type)
@@ -207,7 +242,7 @@ func (p Program) tyCoIDRetconOnce() *types.Signature {
 	return p.coIDRetconOnceTy
 }
 
-// declare i1 @llvm.coro.end(i8*, i1, token)
+// declare i1 @llvm.coro.end(ptr <handle>, i1 <unwind>, token <result.token>)
 func (p Program) tyCoEnd() *types.Signature {
 	if p.coEndTy == nil {
 		i8Ptr := types.NewParam(token.NoPos, nil, "", p.VoidPtr().raw.Type)
@@ -322,6 +357,112 @@ func (p Program) tyCoAwaitSuspendHandle() *types.Signature {
 
 // -----------------------------------------------------------------------------
 
+func (b Builder) SetBlockOffset(offset int) {
+	b.blkOffset = offset
+}
+
+func (b Builder) BlockOffset() int {
+	return b.blkOffset
+}
+
+func (b Builder) Async() bool {
+	return b.async
+}
+
+func (b Builder) AsyncToken() Expr {
+	return b.asyncToken
+}
+
+func (b Builder) SetAsyncToken(token Expr) {
+	b.asyncToken = token
+}
+
+func (b Builder) EndAsync() {
+	_, _, cleanBlk := b.onSuspBlk(b.blk)
+	b.Jump(cleanBlk)
+}
+
+func promiseImplType(ty types.Type) types.Type {
+	ty = ty.Underlying().(*types.Struct).Field(0).Type()
+	if ptrTy, ok := ty.(*types.Pointer); ok {
+		return ptrTy.Elem()
+	}
+	panic(fmt.Sprintf("unexpected promise impl type: %v", ty))
+}
+
+/*
+id := @llvm.coro.id(0, null, null, null)
+frameSize := @llvm.coro.size.i64()
+needAlloc := @llvm.coro.alloc(id)
+; Allocate memory for return type and coroutine frame
+frame := null
+
+	if needAlloc {
+		frame := malloc(frameSize)
+	}
+
+hdl := @llvm.coro.begin(id, frame)
+*retPtr = hdl
+*/
+func (b Builder) BeginAsync(fn Function) {
+	ty := fn.Type.RawType().(*types.Signature).Results().At(0).Type()
+	ptrTy, ok := ty.(*types.Pointer)
+	if !ok {
+		panic("async function must return a *async.Promise")
+	}
+	promiseTy := b.Prog.Type(ptrTy.Elem(), InGo)
+
+	b.async = true
+	entryBlk := fn.Block(0)
+	allocBlk := fn.Block(1)
+	cleanBlk := fn.Block(2)
+	suspdBlk := fn.Block(3)
+	beginBlk := fn.Block(4)
+
+	b.SetBlock(entryBlk)
+	promiseSize := b.Const(constant.MakeUint64(b.Prog.SizeOf(promiseTy)), b.Prog.Int64()).SetName("promise.size")
+	promise := b.AllocZ(promiseSize).SetName("promise")
+	promise.Type = b.Prog.Pointer(promiseTy)
+	b.promise = promise
+	log.Printf("promise ptr: %v", promise.RawType())
+	align := b.Const(constant.MakeInt64(0), b.Prog.CInt()).SetName("align")
+	null := b.Const(nil, b.Prog.CIntPtr())
+	id := b.CoID(align, null, null, null).SetName("id")
+	b.asyncToken = id
+	needAlloc := b.CoAlloc(id).SetName("need.dyn.alloc")
+	b.If(needAlloc, allocBlk, beginBlk)
+	b.SetBlock(allocBlk)
+	frameSize := b.CoSizeI64().SetName("frame.size")
+	frame := b.AllocZ(frameSize).SetName("frame")
+	b.Jump(beginBlk)
+	b.SetBlock(beginBlk)
+	phi := b.Phi(b.Prog.VoidPtr())
+	phi.SetName("frame")
+	phi.AddIncoming(b, []BasicBlock{entryBlk, allocBlk}, func(i int, blk BasicBlock) Expr {
+		if i == 0 {
+			return null
+		}
+		return frame
+	})
+	hdl := b.CoBegin(id, phi.Expr)
+	hdl.SetName("hdl")
+	b.Store(promise, hdl)
+
+	b.SetBlock(cleanBlk)
+	b.CoFree(id, hdl)
+	b.Jump(suspdBlk)
+
+	b.SetBlock(suspdBlk)
+	b.CoEnd(hdl, b.Prog.BoolVal(false), b.Prog.TokenNone())
+	b.Return(promise)
+
+	b.onSuspBlk = func(nextBlk BasicBlock) (BasicBlock, BasicBlock, BasicBlock) {
+		return suspdBlk, nextBlk, cleanBlk
+	}
+}
+
+// -----------------------------------------------------------------------------
+
 // declare void @llvm.coro.destroy(ptr <handle>)
 func (b Builder) CoDestroy(hdl Expr) {
 	fn := b.Pkg.cFunc("llvm.coro.destroy", b.Prog.tyCoDestroy())
@@ -335,11 +476,20 @@ func (b Builder) CoResume(hdl Expr) {
 }
 
 // declare i1 @llvm.coro.done(ptr <handle>)
-func (b Builder) CoDone(hdl Expr) Expr {
+func (b Builder) coDone(hdl Expr) Expr {
 	fn := b.Pkg.cFunc("llvm.coro.done", b.Prog.tyCoDone())
 	return b.Call(fn, hdl)
 }
 
+// return c.Char
+func (b Builder) CoDone(hdl Expr) Expr {
+	bvar := b.coDone(hdl)
+	// TODO(lijie): inefficient
+	// %6 = zext i1 %5 to i64
+	// %7 = trunc i64 %6 to i8
+	return b.valFromData(b.Prog.Byte(), bvar.impl)
+}
+
 // declare ptr @llvm.coro.promise(ptr <ptr>, i32 <alignment>, i1 <from>)
 func (b Builder) CoPromise(ptr, align, from Expr) Expr {
 	fn := b.Pkg.cFunc("llvm.coro.promise", b.Prog.tyCoPromise())
@@ -402,12 +552,21 @@ func (b Builder) CoFrame() Expr {
 
 // declare token @llvm.coro.id(i32 <align>, ptr <promise>, ptr <coroaddr>, ptr <fnaddrs>)
 func (b Builder) CoID(align Expr, promise, coroAddr, fnAddrs Expr) Expr {
+	if align.Type != b.Prog.Int32() {
+		panic("align must be i32")
+	}
 	fn := b.Pkg.cFunc("llvm.coro.id", b.Prog.tyCoID())
 	return b.Call(fn, align, promise, coroAddr, fnAddrs)
 }
 
 // declare token @llvm.coro.id.async(i32 <context size>, i32 <align>, ptr <context arg>, ptr <async function pointer>)
 func (b Builder) CoIDAsync(contextSize, align, contextArg, asyncFnPtr Expr) Expr {
+	if contextSize.Type != b.Prog.Int32() {
+		panic("contextSize must be i32")
+	}
+	if align.Type != b.Prog.Int32() {
+		panic("align must be i32")
+	}
 	fn := b.Pkg.cFunc("llvm.coro.id.async", b.Prog.tyCoIDAsync())
 	return b.Call(fn, contextSize, align, contextArg, asyncFnPtr)
 }
@@ -439,16 +598,44 @@ func (b Builder) CoEndResults(args []Expr) Expr {
 // declare i1 @llvm.coro.end.async(ptr <handle>, i1 <unwind>, ...)
 func (b Builder) CoEndAsync(handle, unwind Expr, args ...Expr) Expr {
 	fn := b.Pkg.cFunc("llvm.coro.end.async", b.Prog.tyCoEndAsync())
-	args = append([]Expr{handle, unwind}, args...)
-	return b.Call(fn, args...)
+	vargs := append([]Expr{handle, unwind}, args...)
+	return b.Call(fn, vargs...)
 }
 
 // declare i8 @llvm.coro.suspend(token <save>, i1 <final>)
-func (b Builder) CoSuspend(save, final Expr) Expr {
+func (b Builder) coSuspend(save, final Expr) Expr {
 	fn := b.Pkg.cFunc("llvm.coro.suspend", b.Prog.tyCoSuspend())
 	return b.Call(fn, save, final)
 }
 
+func (b Builder) CoSuspend(save, final Expr) {
+	if !b.async {
+		panic(fmt.Errorf("suspend %v not in async block", b.Func.Name()))
+	}
+	ret := b.coSuspend(save, final)
+	// add resume block
+	b.Func.MakeBlock("")
+	nextBlk := b.Func.Block(b.blk.idx + 1)
+	susp, next, clean := b.onSuspBlk(nextBlk)
+	swt := b.Switch(ret, susp)
+	swt.Case(b.Const(constant.MakeInt64(0), b.Prog.Byte()), next)
+	swt.Case(b.Const(constant.MakeInt64(1), b.Prog.Byte()), clean)
+	swt.End(b)
+	b.SetBlock(nextBlk)
+}
+
+func (b Builder) CoReturn(args ...Expr) {
+	if !b.async {
+		panic(fmt.Errorf("return %v not in async block", b.Func.Name()))
+	}
+
+	b.Func.MakeBlock("")
+	nextBlk := b.Func.Block(b.blk.idx + 1)
+	_, _, cleanBlk := b.onSuspBlk(nextBlk)
+	b.Jump(cleanBlk)
+	b.SetBlock(nextBlk)
+}
+
 // declare token @llvm.coro.save(ptr <handle>)
 func (b Builder) CoSave(hdl Expr) Expr {
 	fn := b.Pkg.cFunc("llvm.coro.save", b.Prog.tyCoSave())
@@ -484,3 +671,11 @@ func (b Builder) CoAwaitSuspendHandle(awaiter, handle, f Expr) {
 	fn := b.Pkg.cFunc("llvm.coro.await.suspend.handle", b.Prog.tyCoAwaitSuspendHandle())
 	b.Call(fn, awaiter, handle, f)
 }
+
+func (b Builder) CoYield(setValueFn Function, value Expr) {
+	if !b.async {
+		panic(fmt.Errorf("yield %v not in async block", b.Func.Name()))
+	}
+	b.Call(setValueFn.Expr, b.promise, value)
+	b.CoSuspend(b.AsyncToken(), b.Prog.BoolVal(false))
+}
diff --git a/ssa/decl.go b/ssa/decl.go
index 6bdde0fd..ceae3e72 100644
--- a/ssa/decl.go
+++ b/ssa/decl.go
@@ -180,11 +180,11 @@ type Function = *aFunction
 
 // NewFunc creates a new function.
 func (p Package) NewFunc(name string, sig *types.Signature, bg Background) Function {
-	return p.NewFuncEx(name, sig, bg, false)
+	return p.NewFuncEx(name, sig, bg, false, false)
 }
 
 // NewFuncEx creates a new function.
-func (p Package) NewFuncEx(name string, sig *types.Signature, bg Background, hasFreeVars bool) Function {
+func (p Package) NewFuncEx(name string, sig *types.Signature, bg Background, hasFreeVars, async bool) Function {
 	if v, ok := p.fns[name]; ok {
 		return v
 	}
@@ -193,6 +193,9 @@ func (p Package) NewFuncEx(name string, sig *types.Signature, bg Background, has
 		log.Println("NewFunc", name, t.raw.Type, "hasFreeVars:", hasFreeVars)
 	}
 	fn := llvm.AddFunction(p.mod, name, t.ll)
+	if async {
+		fn.AddFunctionAttr(p.Prog.ctx.CreateStringAttribute("presplitcoroutine", ""))
+	}
 	ret := newFunction(fn, t, p, p.Prog, hasFreeVars)
 	p.fns[name] = ret
 	return ret
@@ -268,7 +271,7 @@ func (p Function) NewBuilder() Builder {
 	b := prog.ctx.NewBuilder()
 	// TODO(xsw): Finalize may cause panic, so comment it.
 	// b.Finalize()
-	return &aBuilder{b, nil, p, p.Pkg, prog}
+	return &aBuilder{impl: b, blk: nil, Func: p, Pkg: p.Pkg, Prog: prog}
 }
 
 // HasBody reports whether the function has a body.
diff --git a/ssa/memory.go b/ssa/memory.go
index d14fd71b..3f49be6c 100644
--- a/ssa/memory.go
+++ b/ssa/memory.go
@@ -232,6 +232,13 @@ func (b Builder) ArrayAlloca(telem Type, n Expr) (ret Expr) {
 	return
 }
 
+func (b Builder) OffsetPtr(ptr, offset Expr) Expr {
+	if debugInstr {
+		log.Printf("OffsetPtr %v, %v\n", ptr.impl, offset.impl)
+	}
+	return Expr{llvm.CreateGEP(b.impl, ptr.Type.ll, ptr.impl, []llvm.Value{offset.impl}), ptr.Type}
+}
+
 /* TODO(xsw):
 // ArrayAlloc allocates zero initialized space for an array of n elements of type telem.
 func (b Builder) ArrayAlloc(telem Type, n Expr) (ret Expr) {
diff --git a/ssa/package.go b/ssa/package.go
index 7be6d901..9ce5f227 100644
--- a/ssa/package.go
+++ b/ssa/package.go
@@ -481,6 +481,11 @@ func (p Program) Token() Type {
 	return p.tokenTy
 }
 
+func (p Program) TokenNone() Expr {
+	impl := llvm.ConstNull(p.Token().ll)
+	return Expr{impl: impl, Type: p.Token()}
+}
+
 /*
 // Eface returns the empty interface type.
 // It is equivalent to Any.
diff --git a/ssa/stmt_builder.go b/ssa/stmt_builder.go
index 15546ccc..c2b7cff4 100644
--- a/ssa/stmt_builder.go
+++ b/ssa/stmt_builder.go
@@ -63,6 +63,12 @@ type aBuilder struct {
 	Func Function
 	Pkg  Package
 	Prog Program
+
+	async      bool
+	asyncToken Expr
+	promise    Expr
+	onSuspBlk  func(blk BasicBlock) (susp BasicBlock, next BasicBlock, clean BasicBlock)
+	blkOffset  int
 }
 
 // Builder represents a builder for creating instructions in a function.
@@ -288,7 +294,7 @@ func (b Builder) Times(n Expr, loop func(i Expr)) {
 }
 
 // -----------------------------------------------------------------------------
-/*
+
 type caseStmt struct {
 	v   llvm.Value
 	blk llvm.BasicBlock
@@ -326,7 +332,7 @@ func (b Builder) Switch(v Expr, defb BasicBlock) Switch {
 	}
 	return &aSwitch{v.impl, defb.first, nil}
 }
-*/
+
 // -----------------------------------------------------------------------------
 
 // Phi represents a phi node.
diff --git a/x/async/_demo/asyncdemo/async.go b/x/async/_demo/asyncdemo/async.go
deleted file mode 100644
index a0d49fd9..00000000
--- a/x/async/_demo/asyncdemo/async.go
+++ /dev/null
@@ -1,623 +0,0 @@
-package main
-
-import (
-	"encoding/json"
-	"fmt"
-	"log"
-	"strings"
-	"time"
-
-	"github.com/goplus/llgo/x/async"
-	"github.com/goplus/llgo/x/async/naive"
-	"github.com/goplus/llgo/x/tuple"
-)
-
-// -----------------------------------------------------------------------------
-
-func http(method string, url string, callback func(resp *Response, err error)) {
-	go func() {
-		body := ""
-		if strings.HasPrefix(url, "http://example.com/user/") {
-			name := url[len("http://example.com/user/"):]
-			body = `{"name":"` + name + `"}`
-		} else if strings.HasPrefix(url, "http://example.com/score/") {
-			body = "99.5"
-		}
-		time.Sleep(200 * time.Millisecond)
-		resp := &Response{StatusCode: 200, Body: body}
-		callback(resp, nil)
-	}()
-}
-
-// -----------------------------------------------------------------------------
-
-type Response struct {
-	StatusCode int
-
-	Body string
-}
-
-func (r *Response) Text() (co *async.Promise[tuple.Tuple2[string, error]]) {
-	co.Return(tuple.Tuple2[string, error]{V1: r.Body, V2: nil})
-	return
-}
-
-func (r *Response) TextCompiled() *naive.PromiseImpl[tuple.Tuple2[string, error]] {
-	co := &naive.PromiseImpl[tuple.Tuple2[string, error]]{}
-	co.Debug = "Text"
-	co.Func = func() {
-		switch co.Next {
-		case 0:
-			co.Next = -1
-			co.Return(tuple.Tuple2[string, error]{V1: r.Body, V2: nil})
-			return
-		default:
-			panic("Promise already done")
-		}
-	}
-	return co
-}
-
-//	async AsyncHttpGet(url string) (resp *Response, err error) {
-//	  http("GET", url, func(resp *Response, err error) {
-//	    return resp, err
-//	  })
-//	}
-func AsyncHttpGet(url string) *async.Promise[tuple.Tuple2[*Response, error]] {
-	co := &async.Promise[tuple.Tuple2[*Response, error]]{}
-	http("GET", url, func(resp *Response, err error) {
-		co.Return(tuple.Tuple2[*Response, error]{V1: resp, V2: nil})
-	})
-	co.Suspend()
-	return co
-}
-
-func AsyncHttpGetCompiled(url string) *naive.PromiseImpl[tuple.Tuple2[*Response, error]] {
-	co := &naive.PromiseImpl[tuple.Tuple2[*Response, error]]{}
-	co.Debug = "HttpGet"
-	co.Func = func() {
-		switch co.Next {
-		case 0:
-			co.Next = -1
-			http("GET", url, func(resp *Response, err error) {
-				co.Return(tuple.Tuple2[*Response, error]{V1: resp, V2: nil})
-			})
-			co.Suspend()
-			return
-		default:
-			panic("Promise already done")
-		}
-	}
-	return co
-}
-
-func AsyncHttpPost(url string) *async.Promise[tuple.Tuple2[*Response, error]] {
-	co := &async.Promise[tuple.Tuple2[*Response, error]]{}
-	http("POST", url, func(resp *Response, err error) {
-		co.Return(tuple.Tuple2[*Response, error]{V1: resp, V2: nil})
-	})
-	co.Suspend()
-	return co
-}
-
-func AsyncHttpPostCompiled(url string) *naive.PromiseImpl[tuple.Tuple2[*Response, error]] {
-	P := &naive.PromiseImpl[tuple.Tuple2[*Response, error]]{}
-	P.Debug = "HttpPost"
-	P.Func = func() {
-		switch P.Next {
-		case 0:
-			P.Next = -1
-			http("POST", url, func(resp *Response, err error) {
-				P.Return(tuple.Tuple2[*Response, error]{V1: resp, V2: nil})
-			})
-			return
-		default:
-			panic("Promise already done")
-		}
-	}
-	return P
-}
-
-// -----------------------------------------------------------------------------
-
-type User struct {
-	Name string
-}
-
-func GetUser(name string) (co *naive.PromiseImpl[tuple.Tuple2[User, error]]) {
-	resp, err := AsyncHttpGet("http://example.com/user/" + name).Await().Values()
-	if err != nil {
-		// return User{}, err
-		co.Return(tuple.Tuple2[User, error]{V1: User{}, V2: err})
-		return
-	}
-
-	if resp.StatusCode != 200 {
-		// return User{}, fmt.Errorf("http status code: %d", resp.StatusCode)
-		co.Return(tuple.Tuple2[User, error]{V1: User{}, V2: fmt.Errorf("http status code: %d", resp.StatusCode)})
-		return
-	}
-
-	body, err := resp.Text().Await().Values()
-	if err != nil {
-		// return User{}, err
-		co.Return(tuple.Tuple2[User, error]{V1: User{}, V2: err})
-		return
-	}
-	user := User{}
-	if err := json.Unmarshal([]byte(body), &user); err != nil {
-		// return User{}, err
-		co.Return(tuple.Tuple2[User, error]{V1: User{}, V2: err})
-		return
-	}
-
-	// return user, nil
-	co.Return(tuple.Tuple2[User, error]{V1: user, V2: nil})
-	return
-}
-
-func GetUserCompiled(name string) (co *naive.PromiseImpl[tuple.Tuple2[User, error]]) {
-	var state1 *naive.PromiseImpl[tuple.Tuple2[*Response, error]]
-	var state2 *naive.PromiseImpl[tuple.Tuple2[string, error]]
-
-	co = &naive.PromiseImpl[tuple.Tuple2[User, error]]{}
-	co.Debug = "GetUser"
-	co.Func = func() {
-		switch co.Next {
-		case 0:
-			co.Next = 1
-			state1 = AsyncHttpGetCompiled("http://example.com/user/" + name)
-			state1.Exec = co.Exec
-			state1.Parent = co
-			state1.Call()
-			return
-		case 1:
-			co.Next = 2
-			resp, err := state1.Value().Values()
-			log.Printf("resp: %v, err: %v\n", resp, err)
-			if err != nil {
-				co.Return(tuple.Tuple2[User, error]{V1: User{}, V2: err})
-				return
-			}
-
-			if resp.StatusCode != 200 {
-				co.Return(tuple.Tuple2[User, error]{V1: User{}, V2: fmt.Errorf("http status code: %d", resp.StatusCode)})
-				return
-			}
-
-			state2 = resp.TextCompiled()
-			state2.Exec = co.Exec
-			state2.Parent = co
-			state2.Call()
-			return
-		case 2:
-			co.Next = -1
-			body, err := state2.Value().Values()
-			if err != nil {
-				co.Return(tuple.Tuple2[User, error]{V1: User{}, V2: err})
-				return
-			}
-			user := User{}
-			log.Printf("body: %v\n", body)
-			if err := json.Unmarshal([]byte(body), &user); err != nil {
-				co.Return(tuple.Tuple2[User, error]{V1: User{}, V2: err})
-				return
-			}
-
-			log.Printf("resolve user: %+v\n", user)
-			co.Return(tuple.Tuple2[User, error]{V1: user, V2: nil})
-			return
-		default:
-			panic(fmt.Errorf("Promise already done, %+v", co))
-		}
-	}
-	return
-}
-
-func GetScore() (co *naive.PromiseImpl[tuple.Tuple2[float64, error]]) {
-	resp, err := AsyncHttpGet("http://example.com/score/").Await().Values()
-	if err != nil {
-		co.Return(tuple.Tuple2[float64, error]{V1: 0, V2: err})
-		return
-	}
-
-	if resp.StatusCode != 200 {
-		// return 0, fmt.Errorf("http status code: %d", resp.StatusCode)
-		co.Return(tuple.Tuple2[float64, error]{V1: 0, V2: fmt.Errorf("http status code: %d", resp.StatusCode)})
-		return
-	}
-
-	body, err := resp.Text().Await().Values()
-	if err != nil {
-		// return 0, err
-		co.Return(tuple.Tuple2[float64, error]{V1: 0, V2: err})
-		return
-	}
-
-	score := 0.0
-	if _, err := fmt.Sscanf(body, "%f", &score); err != nil {
-		// return 0, err
-		co.Return(tuple.Tuple2[float64, error]{V1: 0, V2: err})
-		return
-	}
-
-	// return score, nil
-	co.Return(tuple.Tuple2[float64, error]{V1: score, V2: nil})
-	return
-}
-
-func GetScoreCompiled() *naive.PromiseImpl[tuple.Tuple2[float64, error]] {
-	var state1 *naive.PromiseImpl[tuple.Tuple2[*Response, error]]
-	var state2 *naive.PromiseImpl[tuple.Tuple2[string, error]]
-
-	co := &naive.PromiseImpl[tuple.Tuple2[float64, error]]{}
-	co.Debug = "GetScore"
-	co.Func = func() {
-		switch co.Next {
-		case 0:
-			co.Next = 1
-			state1 = AsyncHttpGetCompiled("http://example.com/score/")
-			state1.Exec = co.Exec
-			state1.Parent = co
-			state1.Call()
-			return
-		case 1:
-			co.Next = 2
-
-			resp, err := state1.Value().Values()
-			if err != nil {
-				co.Return(tuple.Tuple2[float64, error]{V1: 0, V2: err})
-				return
-			}
-
-			if resp.StatusCode != 200 {
-				co.Return(tuple.Tuple2[float64, error]{V1: 0, V2: fmt.Errorf("http status code: %d", resp.StatusCode)})
-				return
-			}
-
-			state2 = resp.TextCompiled()
-			state2.Exec = co.Exec
-			state2.Parent = co
-			state2.Call()
-
-			return
-		case 2:
-			co.Next = -1
-			body, err := state2.Value().Values()
-			if err != nil {
-				co.Return(tuple.Tuple2[float64, error]{V1: 0, V2: err})
-				return
-			}
-
-			score := 0.0
-			if _, err := fmt.Sscanf(body, "%f", &score); err != nil {
-				co.Return(tuple.Tuple2[float64, error]{V1: 0, V2: err})
-				return
-			}
-			co.Return(tuple.Tuple2[float64, error]{V1: score, V2: nil})
-			return
-		default:
-			panic("Promise already done")
-		}
-	}
-	return co
-}
-
-func DoUpdate(op string) (co *naive.PromiseImpl[error]) {
-	resp, err := AsyncHttpPost("http://example.com/update/" + op).Await().Values()
-	if err != nil {
-		co.Return(err)
-		return
-	}
-
-	if resp.StatusCode != 200 {
-		co.Return(fmt.Errorf("http status code: %d", resp.StatusCode))
-	}
-
-	co.Return(nil)
-	return
-}
-
-func DoUpdateCompiled(op string) *naive.PromiseImpl[error] {
-	var state1 *naive.PromiseImpl[tuple.Tuple2[*Response, error]]
-
-	co := &naive.PromiseImpl[error]{}
-	co.Debug = "DoUpdate"
-	co.Func = func() {
-		switch co.Next {
-		case 0:
-			co.Next = 1
-			state1 = AsyncHttpPostCompiled("http://example.com/update/" + op)
-			state1.Exec = co.Exec
-			state1.Parent = co
-			state1.Call()
-			return
-		case 1:
-			co.Next = -1
-			resp, err := state1.Value().Values()
-			if err != nil {
-				co.Return(err)
-				return
-			}
-
-			if resp.StatusCode != 200 {
-				co.Return(fmt.Errorf("http status code: %d", resp.StatusCode))
-				return
-			}
-
-			co.Return(nil)
-			return
-		default:
-			panic("Promise already done")
-		}
-	}
-	return co
-}
-
-func GenInts() (co *naive.PromiseImpl[int]) {
-	co.Yield(3)
-	co.Yield(2)
-	co.Yield(5)
-	return
-}
-
-func GenIntsCompiled() *naive.PromiseImpl[int] {
-	co := &naive.PromiseImpl[int]{}
-	co.Debug = "GenInts"
-	co.Func = func() {
-		switch co.Next {
-		case 0:
-			co.Next = 1
-			co.Yield(3)
-			return
-		case 1:
-			co.Next = 2
-			co.Yield(2)
-			return
-		case 2:
-			co.Next = 3
-			co.Yield(5)
-			return
-		case 3:
-			co.Next = -1
-		default:
-			panic("Generator already done")
-		}
-	}
-	return co
-}
-
-// Generator with async calls and panic
-func GenUsers() (co *naive.PromiseImpl[User]) {
-	u, err := GetUser("Alice").Await().Values()
-	if err != nil {
-		panic(err)
-	}
-	co.Yield(u)
-	u, err = GetUser("Bob").Await().Values()
-	if err != nil {
-		panic(err)
-	}
-	co.Yield(u)
-	u, err = GetUser("Cindy").Await().Values()
-	if err != nil {
-		panic(err)
-	}
-	co.Yield(u)
-	log.Printf("genUsers done\n")
-	return
-}
-
-func GenUsersCompiled() (resolve *naive.PromiseImpl[User]) {
-	var state1, state2, state3 *naive.PromiseImpl[tuple.Tuple2[User, error]]
-
-	co := &naive.PromiseImpl[User]{}
-	co.Debug = "GenUsers"
-	co.Func = func() {
-		switch co.Next {
-		case 0:
-			co.Next = 1
-			state1 = GetUserCompiled("Alice")
-			state1.Exec = co.Exec
-			state1.Parent = co
-			state1.Call()
-			return
-		case 1:
-			co.Next = 2
-			u, err := state1.Value().Values()
-			if err != nil {
-				panic(err)
-			} else {
-				co.Yield(u)
-			}
-			return
-		case 2:
-			co.Next = 3
-			state2 = GetUserCompiled("Bob")
-			state2.Exec = co.Exec
-			state2.Parent = co
-			state2.Call()
-			return
-		case 3:
-			co.Next = 4
-			u, err := state2.Value().Values()
-			if err != nil {
-				panic(err)
-			} else {
-				co.Yield(u)
-			}
-			return
-		case 4:
-			co.Next = 5
-			state3 = GetUserCompiled("Cindy")
-			state3.Exec = co.Exec
-			state3.Parent = co
-			state3.Call()
-			return
-		case 5:
-			co.Next = 6
-			u, err := state3.Value().Values()
-			if err != nil {
-				panic(err)
-			} else {
-				co.Yield(u)
-			}
-			return
-		case 6:
-			co.Next = -1
-		default:
-			panic("Generator already done")
-		}
-	}
-	return co
-}
-
-func Demo() (co *async.Promise[async.Void]) {
-	user, err := GetUser("1").Await().Values()
-	log.Println(user, err)
-
-	user, err = naive.Race[tuple.Tuple2[User, error]](GetUser("2"), GetUser("3"), GetUser("4")).Value().Values()
-	log.Println(user, err)
-
-	users := naive.All[tuple.Tuple2[User, error]]([]naive.AsyncCall[tuple.Tuple2[User, error]]{GetUser("5"), GetUser("6"), GetUser("7")}).Value()
-	log.Println(users, err)
-
-	user, score, _ := naive.Await3Compiled[User, float64, async.Void](GetUser("8"), GetScore(), DoUpdate("update sth.")).Value().Values()
-	log.Println(user, score, err)
-
-	// for loop with generator
-	g := GenInts()
-	for {
-		g.Call()
-		if g.Done() {
-			break
-		}
-		log.Println("genInt:", g.Value(), g.Done())
-	}
-
-	// for loop with async generator
-	// for u, err := range GenUsers() {...}
-	g1 := GenUsers()
-	for {
-		g1.Call()
-		u := g1.Await()
-		if g1.Done() {
-			break
-		}
-		log.Println("genUser:", u, err)
-	}
-
-	// TODO(lijie): select from multiple promises without channel
-	// select {
-	// case user := <-GetUser("123").Chan():
-	// 	log.Println("user:", user)
-	// case score := <-GetScore().Chan():
-	// 	log.Println("score:", score)
-	// case <-async.Timeout(5 * time.Second).Chan():
-	// 	log.Println("timeout")
-	// }
-
-	log.Println("Demo done")
-	co.Return(async.Void{})
-	return
-}
-
-func DemoCompiled() *naive.PromiseImpl[async.Void] {
-	var state1 *naive.PromiseImpl[tuple.Tuple2[User, error]]
-	var state2 *naive.PromiseImpl[tuple.Tuple2[User, error]]
-	var state3 *naive.PromiseImpl[[]tuple.Tuple2[User, error]]
-	var state4 *naive.PromiseImpl[tuple.Tuple3[tuple.Tuple2[User, error], tuple.Tuple2[float64, error], error]]
-	var g1 *naive.PromiseImpl[int]
-	var g2 *naive.PromiseImpl[User]
-
-	P := &naive.PromiseImpl[async.Void]{}
-	P.Debug = "Demo"
-	P.Func = func() {
-		switch P.Next {
-		case 0:
-			P.Next = 1
-			state1 = GetUserCompiled("1")
-			state1.Exec = P.Exec
-			state1.Parent = P
-			state1.Call()
-			return
-		case 1:
-			P.Next = 2
-			user, err := state1.Value().Values()
-			log.Printf("user: %+v, err: %v\n", user, err)
-
-			state2 = naive.Race[tuple.Tuple2[User, error]](GetUserCompiled("2"), GetUserCompiled("3"), GetUserCompiled("4"))
-			state2.Exec = P.Exec
-			state2.Parent = P
-			state2.Call()
-			return
-		case 2:
-			P.Next = 3
-			user, err := state2.Value().Values()
-			log.Printf("race user: %+v, err: %v\n", user, err)
-
-			state3 = naive.All[tuple.Tuple2[User, error]]([]naive.AsyncCall[tuple.Tuple2[User, error]]{GetUserCompiled("5"), GetUserCompiled("6"), GetUserCompiled("7")})
-			state3.Exec = P.Exec
-			state3.Parent = P
-			state3.Call()
-			return
-		case 3:
-
-			P.Next = 4
-			users := state3.Value()
-			log.Println(users)
-
-			state4 = naive.Await3Compiled[tuple.Tuple2[User, error], tuple.Tuple2[float64, error], error](GetUserCompiled("8"), GetScoreCompiled(), DoUpdateCompiled("update sth."))
-			state4.Exec = P.Exec
-			state4.Parent = P
-			state4.Call()
-			return
-		case 4:
-			P.Next = 5
-			user, score, _ := state4.Value().Values()
-			log.Println(user, score)
-
-			g1 = GenIntsCompiled()
-			for {
-				g1.Call()
-				if g1.Done() {
-					break
-				}
-
-				log.Printf("genInt: %+v, done: %v\n", g1.Value(), g1.Done())
-			}
-
-			g2 = GenUsersCompiled()
-			g2.Exec = P.Exec
-			g2.Parent = P
-			g2.Call()
-			return
-		case 5:
-			g2.Call()
-			if g2.Done() {
-				P.Next = -1
-				log.Printf("Demo done\n")
-				P.Return(async.Void{})
-				return
-			}
-			log.Printf("genUser: %+v, done: %v\n", g2.Value(), g2.Done())
-			return
-		default:
-			panic("Promise already done")
-		}
-	}
-	return P
-}
-
-func main() {
-	log.SetFlags(log.Lshortfile | log.LstdFlags)
-	log.Printf("=========== Run Naive Demo ===========\n")
-	v := naive.RunImpl[async.Void](DemoCompiled())
-	log.Println(v)
-	log.Printf("=========== Run Naive Demo finished ===========\n")
-
-	log.Printf("=========== Run Demo ===========\n")
-	v1 := Demo()
-	log.Println(v1)
-	log.Printf("=========== Run Demo finished ===========\n")
-}
diff --git a/x/async/_demo/asyncdemo/asyncdemo.go b/x/async/_demo/asyncdemo/asyncdemo.go
new file mode 100644
index 00000000..45e0f959
--- /dev/null
+++ b/x/async/_demo/asyncdemo/asyncdemo.go
@@ -0,0 +1,229 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"log"
+	"strings"
+	"time"
+
+	"github.com/goplus/llgo/x/async"
+	"github.com/goplus/llgo/x/tuple"
+)
+
+// -----------------------------------------------------------------------------
+
+func http(method string, url string, callback func(resp *Response, err error)) {
+	go func() {
+		body := ""
+		if strings.HasPrefix(url, "http://example.com/user/") {
+			name := url[len("http://example.com/user/"):]
+			body = `{"name":"` + name + `"}`
+		} else if strings.HasPrefix(url, "http://example.com/score/") {
+			body = "99.5"
+		}
+		time.Sleep(200 * time.Millisecond)
+		resp := &Response{StatusCode: 200, Body: body}
+		callback(resp, nil)
+	}()
+}
+
+// -----------------------------------------------------------------------------
+
+type Response struct {
+	StatusCode int
+
+	Body string
+}
+
+func (r *Response) Text() (co async.Promise[tuple.Tuple2[string, error]]) {
+	co.Return(tuple.Tuple2[string, error]{V1: r.Body, V2: nil})
+	return
+}
+
+//	async AsyncHttpGet(url string) (resp *Response, err error) {
+//	  http("GET", url, func(resp *Response, err error) {
+//	    return resp, err
+//	  })
+//	}
+func AsyncHttpGet(url string) (co async.Promise[tuple.Tuple2[*Response, error]]) {
+	return co.Async(func(resolve func(tuple.Tuple2[*Response, error])) {
+		http("GET", url, func(resp *Response, err error) {
+			resolve(tuple.Tuple2[*Response, error]{V1: resp, V2: nil})
+		})
+	})
+}
+
+func AsyncHttpPost(url string) (co async.Promise[tuple.Tuple2[*Response, error]]) {
+	http("POST", url, func(resp *Response, err error) {
+		// co.Return(tuple.Tuple2[*Response, error]{V1: resp, V2: nil})
+	})
+	co.Suspend()
+	return
+}
+
+// -----------------------------------------------------------------------------
+
+type User struct {
+	Name string
+}
+
+func GetUser(name string) (co async.Promise[tuple.Tuple2[User, error]]) {
+	resp, err := AsyncHttpGet("http://example.com/user/" + name).Await().Values()
+	if err != nil {
+		// return User{}, err
+		co.Return(tuple.Tuple2[User, error]{V1: User{}, V2: err})
+		return
+	}
+
+	if resp.StatusCode != 200 {
+		// return User{}, fmt.Errorf("http status code: %d", resp.StatusCode)
+		co.Return(tuple.Tuple2[User, error]{V1: User{}, V2: fmt.Errorf("http status code: %d", resp.StatusCode)})
+		return
+	}
+
+	body, err := resp.Text().Await().Values()
+	if err != nil {
+		// return User{}, err
+		co.Return(tuple.Tuple2[User, error]{V1: User{}, V2: err})
+		return
+	}
+	user := User{}
+	if err := json.Unmarshal([]byte(body), &user); err != nil {
+		// return User{}, err
+		co.Return(tuple.Tuple2[User, error]{V1: User{}, V2: err})
+		return
+	}
+
+	// return user, nil
+	co.Return(tuple.Tuple2[User, error]{V1: user, V2: nil})
+	return
+}
+
+func GetScore() (co *async.Promise[tuple.Tuple2[float64, error]]) {
+	resp, err := AsyncHttpGet("http://example.com/score/").Await().Values()
+	if err != nil {
+		co.Return(tuple.Tuple2[float64, error]{V1: 0, V2: err})
+		return
+	}
+
+	if resp.StatusCode != 200 {
+		// return 0, fmt.Errorf("http status code: %d", resp.StatusCode)
+		co.Return(tuple.Tuple2[float64, error]{V1: 0, V2: fmt.Errorf("http status code: %d", resp.StatusCode)})
+		return
+	}
+
+	body, err := resp.Text().Await().Values()
+	if err != nil {
+		// return 0, err
+		co.Return(tuple.Tuple2[float64, error]{V1: 0, V2: err})
+		return
+	}
+
+	score := 0.0
+	if _, err := fmt.Sscanf(body, "%f", &score); err != nil {
+		// return 0, err
+		co.Return(tuple.Tuple2[float64, error]{V1: 0, V2: err})
+		return
+	}
+
+	// return score, nil
+	co.Return(tuple.Tuple2[float64, error]{V1: score, V2: nil})
+	return
+}
+
+func DoUpdate(op string) (co *async.Promise[error]) {
+	resp, err := AsyncHttpPost("http://example.com/update/" + op).Await().Values()
+	if err != nil {
+		co.Return(err)
+		return
+	}
+
+	if resp.StatusCode != 200 {
+		co.Return(fmt.Errorf("http status code: %d", resp.StatusCode))
+	}
+
+	co.Return(nil)
+	return
+}
+
+func GenInts() (co *async.Promise[int]) {
+	co.Yield(3)
+	co.Yield(2)
+	co.Yield(5)
+	return
+}
+
+// Generator with async calls and panic
+func GenUsers() (co *async.Promise[User]) {
+	u, err := GetUser("Alice").Await().Values()
+	if err != nil {
+		panic(err)
+	}
+	co.Yield(u)
+	u, err = GetUser("Bob").Await().Values()
+	if err != nil {
+		panic(err)
+	}
+	co.Yield(u)
+	u, err = GetUser("Cindy").Await().Values()
+	if err != nil {
+		panic(err)
+	}
+	co.Yield(u)
+	log.Printf("genUsers done\n")
+	return
+}
+
+func Demo() (co *async.Promise[async.Void]) {
+	user, err := GetUser("1").Await().Values()
+	log.Println(user, err)
+
+	// user, err = naive.Race[tuple.Tuple2[User, error]](GetUser("2"), GetUser("3"), GetUser("4")).Value().Values()
+	// log.Println(user, err)
+
+	// users := naive.All[tuple.Tuple2[User, error]]([]naive.AsyncCall[tuple.Tuple2[User, error]]{GetUser("5"), GetUser("6"), GetUser("7")}).Value()
+	// log.Println(users, err)
+
+	// user, score, _ := naive.Await3Compiled[User, float64, async.Void](GetUser("8"), GetScore(), DoUpdate("update sth.")).Value().Values()
+	// log.Println(user, score, err)
+
+	// for loop with generator
+	g := GenInts()
+	for !g.Done() {
+		log.Println("genInt:", g.Value(), g.Done())
+		g.Resume()
+	}
+
+	// for loop with async generator
+	// for u, err := range GenUsers() {...}
+	g1 := GenUsers()
+	for !g1.Done() {
+		u := g1.Value()
+		log.Println("genUser:", u)
+		g1.Resume()
+	}
+
+	// TODO(lijie): select from multiple promises without channel
+	// select {
+	// case user := <-GetUser("123").Chan():
+	// 	log.Println("user:", user)
+	// case score := <-GetScore().Chan():
+	// 	log.Println("score:", score)
+	// case <-async.Timeout(5 * time.Second).Chan():
+	// 	log.Println("timeout")
+	// }
+
+	log.Println("Demo done")
+	co.Return(async.Void{})
+	return
+}
+
+func main() {
+	log.SetFlags(log.Lshortfile | log.LstdFlags)
+
+	log.Printf("=========== Run Demo ===========\n")
+	v1 := Demo()
+	log.Println(v1)
+	log.Printf("=========== Run Demo finished ===========\n")
+}
diff --git a/x/async/_demo/gendemo/gendemo.go b/x/async/_demo/gendemo/gendemo.go
new file mode 100644
index 00000000..b58b3e27
--- /dev/null
+++ b/x/async/_demo/gendemo/gendemo.go
@@ -0,0 +1,21 @@
+package main
+
+import "github.com/goplus/llgo/x/async"
+
+func GenInts() (co *async.Promise[int]) {
+	print("1")
+	co.Yield(1)
+	print("2")
+	co.Yield(2)
+	print("3")
+	co.Yield(3)
+	print("4")
+	return
+}
+
+func main() {
+	co := GenInts()
+	for !co.Done() {
+		print(co.Next())
+	}
+}
diff --git a/x/async/async.go b/x/async/async.go
index 83b4af40..0060a959 100644
--- a/x/async/async.go
+++ b/x/async/async.go
@@ -25,12 +25,8 @@ const (
 	LLGoPackage = "decl"
 )
 
-const debugAsync = false
-
 type Void = [0]byte
 
-type AsyncCall[TOut any] interface{}
-
 // -----------------------------------------------------------------------------
 
 type Promise[TOut any] struct {
@@ -38,36 +34,45 @@ type Promise[TOut any] struct {
 	value TOut
 }
 
-// llgo:link PromiseImpl llgo.coAwait
+// // llgo:link (*Promise).Await llgo.coAwait
 func (p *Promise[TOut]) Await() TOut {
 	panic("should not executed")
 }
 
-// llgo:link Return llgo.coReturn
 func (p *Promise[TOut]) Return(v TOut) {
-	panic("should not executed")
+	p.value = v
+	coReturn(p.hdl)
 }
 
-// llgo:link Yield llgo.coYield
-func (p *Promise[TOut]) Yield(v TOut) {
-	panic("should not executed")
-}
+// llgo:link (*Promise).Yield llgo.coYield
+func (p *Promise[TOut]) Yield(v TOut) {}
 
-// llgo:link Suspend llgo.coSuspend
-func (p *Promise[TOut]) Suspend() {
-	panic("should not executed")
-}
+// llgo:link (*Promise).Suspend llgo.coSuspend
+func (p *Promise[TOut]) Suspend() {}
 
-// llgo:link Resume llgo.coResume
 func (p *Promise[TOut]) Resume() {
-	panic("should not executed")
+	coResume(p.hdl)
+}
+
+func (p *Promise[TOut]) Next() TOut {
+	coResume(p.hdl)
+	return p.value
+}
+
+// TODO(lijie): should merge to Yield()
+// call by llgo.coYield
+func (p *Promise[TOut]) setValue(v TOut) {
+	p.value = v
 }
 
 func (p *Promise[TOut]) Value() TOut {
 	return p.value
 }
 
-// llgo:link Run llgo.coRun
+func (p *Promise[TOut]) Done() bool {
+	return coDone(p.hdl) != 0
+}
+
 func Run[TOut any](f func() TOut) TOut {
 	panic("should not executed")
 }
diff --git a/x/async/coro.go b/x/async/coro.go
new file mode 100644
index 00000000..62393d4e
--- /dev/null
+++ b/x/async/coro.go
@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) 2024 The GoPlus Authors (goplus.org). All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package async
+
+import (
+	"unsafe"
+	_ "unsafe"
+
+	"github.com/goplus/llgo/c"
+)
+
+// llgo:link coDone llgo.coDone
+func coDone(hdl unsafe.Pointer) c.Char {
+	panic("should not executed")
+}
+
+// llgo:link coResume llgo.coResume
+func coResume(hdl unsafe.Pointer) {
+	panic("should not executed")
+}
+
+// llgo:link coReturn llgo.coReturn
+func coReturn(hdl unsafe.Pointer) {
+	panic("should not executed")
+}
diff --git a/x/async/naive/extra.go b/x/async/naive/extra.go
deleted file mode 100644
index 21c00af3..00000000
--- a/x/async/naive/extra.go
+++ /dev/null
@@ -1,285 +0,0 @@
-/*
- * Copyright (c) 2024 The GoPlus Authors (goplus.org). All rights reserved.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package naive
-
-import (
-	"log"
-	"sync"
-	"time"
-	_ "unsafe"
-
-	"github.com/goplus/llgo/x/async"
-	"github.com/goplus/llgo/x/tuple"
-)
-
-// -----------------------------------------------------------------------------
-
-func TimeoutCompiled(d time.Duration) *PromiseImpl[async.Void] {
-	P := &PromiseImpl[async.Void]{}
-	P.Debug = "Timeout"
-	P.Func = func() {
-		go func() {
-			time.Sleep(d)
-			P.Return(async.Void{})
-		}()
-	}
-	return P
-}
-
-type Result[T any] struct {
-	V   T
-	Err error
-}
-
-func Race[OutT any](acs ...AsyncCall[OutT]) *PromiseImpl[OutT] {
-	if len(acs) == 0 {
-		panic("race: no promise")
-	}
-	ps := make([]*PromiseImpl[OutT], len(acs))
-	for idx, ac := range acs {
-		ps[idx] = ac.(*PromiseImpl[OutT])
-	}
-	remaining := len(acs)
-	returned := false
-	P := &PromiseImpl[OutT]{}
-	P.Debug = "Race"
-	P.Func = func() {
-		switch P.Next {
-		case 0:
-			P.Next = 1
-			for _, p := range ps {
-				p.Exec = P.Exec
-				p.Parent = P
-				p.Call()
-			}
-			return
-		case 1:
-			remaining--
-			if remaining < 0 {
-				log.Fatalf("race: remaining < 0: %+v\n", remaining)
-			}
-			if returned {
-				return
-			}
-
-			for _, p := range ps {
-				if p.Done() {
-					if debugAsync {
-						log.Printf("async.Race done: %+v won the race\n", p)
-					}
-					returned = true
-					P.Return(p.value)
-					return
-				}
-			}
-			log.Fatalf("no promise done: %+v\n", ps)
-			return
-		default:
-			panic("unreachable")
-		}
-	}
-	return P
-}
-
-func All[OutT any](acs []AsyncCall[OutT]) *PromiseImpl[[]OutT] {
-	ps := make([]*PromiseImpl[OutT], len(acs))
-	for idx, ac := range acs {
-		ps[idx] = ac.(*PromiseImpl[OutT])
-	}
-	done := 0
-	P := &PromiseImpl[[]OutT]{}
-	P.Debug = "All"
-	P.Func = func() {
-		switch P.Next {
-		case 0:
-			P.Next = 1
-			for _, p := range ps {
-				p.Exec = P.Exec
-				p.Parent = P
-				p.Call()
-			}
-			return
-		case 1:
-			done++
-			if done < len(acs) {
-				return
-			}
-			P.Next = -1
-
-			for _, p := range ps {
-				if !p.Done() {
-					log.Fatalf("async.All: not done: %+v\n", p)
-				}
-			}
-
-			ret := make([]OutT, len(acs))
-			for idx, p := range ps {
-				ret[idx] = p.value
-			}
-			if debugAsync {
-				log.Printf("async.All done: %+v\n", ret)
-			}
-			P.Return(ret)
-			return
-		default:
-			panic("unreachable")
-		}
-	}
-	return P
-}
-
-// llgo:link Await2 llgo.await
-func Await2Compiled[OutT1, OutT2 any](
-	ac1 AsyncCall[OutT1], ac2 AsyncCall[OutT2],
-	timeout ...time.Duration) (ret *PromiseImpl[tuple.Tuple3[OutT1, OutT2, error]]) {
-	p1 := ac1.(*PromiseImpl[OutT1])
-	p2 := ac2.(*PromiseImpl[OutT2])
-	remaining := 2
-	P := &PromiseImpl[tuple.Tuple3[OutT1, OutT2, error]]{}
-	P.Debug = "Await2"
-	P.Func = func() {
-		switch P.Next {
-		case 0:
-			P.Next = 1
-			p1.Exec = P.Exec
-			p1.Parent = P
-			p1.Call()
-
-			p2.Exec = P.Exec
-			p2.Parent = P
-			p2.Call()
-			return
-		case 1:
-			remaining--
-			if remaining > 0 {
-				return
-			}
-			P.Next = -1
-			if !p1.Done() || !p2.Done() {
-				log.Fatalf("async.Await2: not done: %+v, %+v\n", p1, p2)
-			}
-
-			P.Return(tuple.Tuple3[OutT1, OutT2, error]{
-				V1: p1.value,
-				V2: p2.value,
-				V3: nil,
-			})
-			return
-		default:
-			panic("unreachable")
-		}
-	}
-	return P
-}
-
-// llgo:link Await2 llgo.await
-func Await3Compiled[OutT1, OutT2, OutT3 any](
-	ac1 AsyncCall[OutT1], ac2 AsyncCall[OutT2], ac3 AsyncCall[OutT3],
-	timeout ...time.Duration) *PromiseImpl[tuple.Tuple3[OutT1, OutT2, OutT3]] {
-	p1 := ac1.(*PromiseImpl[OutT1])
-	p2 := ac2.(*PromiseImpl[OutT2])
-	p3 := ac3.(*PromiseImpl[OutT3])
-	remaining := 3
-	P := &PromiseImpl[tuple.Tuple3[OutT1, OutT2, OutT3]]{}
-	P.Debug = "Await3"
-	P.Func = func() {
-		switch P.Next {
-		case 0:
-			P.Next = 1
-			p1.Exec = P.Exec
-			p1.Parent = P
-			p1.Call()
-
-			p2.Exec = P.Exec
-			p2.Parent = P
-			p2.Call()
-
-			p3.Exec = P.Exec
-			p3.Parent = P
-			p3.Call()
-			return
-		case 1:
-			remaining--
-			if remaining > 0 {
-				return
-			}
-			P.Next = -1
-			// TODO(lijie): return every error?
-			if !p1.Done() || !p2.Done() || !p3.Done() {
-				log.Fatalf("async.Await3: not done: %+v, %+v, %+v\n", p1, p2, p3)
-			}
-
-			P.Return(tuple.Tuple3[OutT1, OutT2, OutT3]{
-				V1: p1.value,
-				V2: p2.value,
-				V3: p3.value,
-			})
-			return
-		default:
-			panic("unreachable")
-		}
-	}
-	return P
-}
-
-func PAllCompiled[OutT any](acs ...AsyncCall[OutT]) *PromiseImpl[[]OutT] {
-	P := &PromiseImpl[[]OutT]{}
-	P.Debug = "Parallel"
-	P.Func = func() {
-		ret := make([]OutT, len(acs))
-		wg := sync.WaitGroup{}
-		for idx, ac := range acs {
-			idx := idx
-			ac := ac
-			wg.Add(1)
-			go func(ac AsyncCall[OutT]) {
-				v := RunImpl[OutT](ac)
-				ret[idx] = v
-				wg.Done()
-			}(ac)
-		}
-		wg.Wait()
-		P.Return(ret)
-	}
-	return P
-}
-
-func PAwait3Compiled[OutT1, OutT2, OutT3 any](
-	ac1 AsyncCall[OutT1], ac2 AsyncCall[OutT2], ac3 AsyncCall[OutT3]) *PromiseImpl[tuple.Tuple4[OutT1, OutT2, OutT3, error]] {
-	P := &PromiseImpl[tuple.Tuple4[OutT1, OutT2, OutT3, error]]{}
-	P.Debug = "PAwait3"
-	P.Func = func() {
-		ret := tuple.Tuple4[OutT1, OutT2, OutT3, error]{}
-		wg := sync.WaitGroup{}
-		wg.Add(3)
-		go func() {
-			ret.V1 = RunImpl[OutT1](ac1)
-			wg.Done()
-		}()
-		go func() {
-			ret.V2 = RunImpl[OutT2](ac2)
-			wg.Done()
-		}()
-		go func() {
-			ret.V3 = RunImpl[OutT3](ac3)
-			wg.Done()
-		}()
-		wg.Wait()
-		P.Return(ret)
-	}
-	return P
-}
diff --git a/x/async/naive/naive.go b/x/async/naive/naive.go
deleted file mode 100644
index a8de2bd9..00000000
--- a/x/async/naive/naive.go
+++ /dev/null
@@ -1,154 +0,0 @@
-/*
- * Copyright (c) 2024 The GoPlus Authors (goplus.org). All rights reserved.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package naive
-
-import (
-	"log"
-	"sync"
-)
-
-const debugAsync = false
-
-// -----------------------------------------------------------------------------
-
-type asyncCall interface {
-	parent() asyncCall
-	Resume()
-	Call()
-	Done() bool
-}
-
-type AsyncCall[OutT any] interface {
-	Resume()
-}
-
-type executor struct {
-	acs  []asyncCall
-	mu   sync.Mutex
-	cond *sync.Cond
-}
-
-func newExecutor() *executor {
-	e := &executor{}
-	e.cond = sync.NewCond(&e.mu)
-	return e
-}
-
-func (e *executor) schedule(ac asyncCall) {
-	e.mu.Lock()
-	e.acs = append(e.acs, ac)
-	e.mu.Unlock()
-	e.cond.Signal()
-}
-
-func RunImpl[OutT any](ac AsyncCall[OutT]) OutT {
-	e := newExecutor()
-	p := ac.(*PromiseImpl[OutT])
-	p.Exec = e
-	var rootAc asyncCall = p
-	e.schedule(rootAc)
-
-	for {
-		e.mu.Lock()
-		for len(e.acs) == 0 {
-			e.cond.Wait()
-		}
-		e.mu.Unlock()
-		ac := e.acs[0]
-		e.acs = e.acs[1:]
-		ac.Call()
-		if ac.Done() && ac == rootAc {
-			return p.value
-		}
-	}
-}
-
-// -----------------------------------------------------------------------------
-
-type PromiseImpl[TOut any] struct {
-	Debug  string
-	Next   int
-	Exec   *executor
-	Parent asyncCall
-
-	Func  func()
-	value TOut
-	c     chan TOut
-}
-
-func (p *PromiseImpl[TOut]) parent() asyncCall {
-	return p.Parent
-}
-
-func (p *PromiseImpl[TOut]) Resume() {
-	if debugAsync {
-		log.Printf("Resume task: %+v\n", p)
-	}
-	p.Exec.schedule(p)
-}
-
-func (p *PromiseImpl[TOut]) Done() bool {
-	return p.Next == -1
-}
-
-func (p *PromiseImpl[TOut]) Call() {
-	p.Func()
-}
-
-func (p *PromiseImpl[TOut]) Suspend() {
-
-}
-
-func (p *PromiseImpl[TOut]) Return(v TOut) {
-	// TODO(lijie): panic if already resolved
-	p.value = v
-	if p.c != nil {
-		p.c <- v
-	}
-	if debugAsync {
-		log.Printf("Return task: %+v\n", p)
-	}
-	if p.Parent != nil {
-		p.Parent.Resume()
-	}
-}
-
-func (p *PromiseImpl[TOut]) Yield(v TOut) {
-	p.value = v
-	if debugAsync {
-		log.Printf("Yield task: %+v\n", p)
-	}
-	if p.Parent != nil {
-		p.Parent.Resume()
-	}
-}
-
-func (p *PromiseImpl[TOut]) Value() TOut {
-	return p.value
-}
-
-func (p *PromiseImpl[TOut]) Chan() <-chan TOut {
-	if p.c == nil {
-		p.c = make(chan TOut, 1)
-		p.Func()
-	}
-	return p.c
-}
-
-func (p *PromiseImpl[TOut]) Await() (ret TOut) {
-	panic("should not called")
-}