[vm] Fix compiler crash when returning a value of uninitialized late variable from async function

This change fixes CompileType::CanBeFuture() which previously attempted
to use Class objects by class id without first checking if cid is internal.

Cid can be internal (SentinelCid) when CompileType::CanBeFuture() is
called for a return value of an async function when it is returning
a value of an uninitialized late local variable (such Return
instruction is unreachable).

TEST=runtime/tests/vm/dart/regress_flutter117892_test.dart
Fixes flutter/flutter#117892

Change-Id: I63f0ca32d6246487f5c33d983cef9bd22aaa2fb8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/278094
Reviewed-by: Slava Egorov <[email protected]>
Commit-Queue: Alexander Markov <[email protected]>

Author: alexmarkov

runtime/tests/vm/dart/regress_flutter117892_test.dart

@@ -0,0 +1,23 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Verifies that compiler doesn't crash when uninitialized late variable
+// (sentinel) is returned from an async function.
+// Regression test for https://github.com/flutter/flutter/issues/117892.
+
+import 'package:expect/expect.dart';
+
+foo() async {
+  late int x;
+  if (3 != 3) {
+    x = 42;
+  }
+  return x;
+}
+
+main() {
+  foo().then((_) {
+    Expect.fail("Exception should be thrown.");
+  }, onError: (_) {});
+}

runtime/vm/compiler/backend/type_propagator.cc

@@ -947,7 +947,8 @@ bool CompileType::CanBeFuture() {
   ObjectStore* object_store = isolate_group->object_store();
 
   if (cid_ != kIllegalCid && cid_ != kDynamicCid) {
-    if ((cid_ == kNullCid) || (cid_ == kNeverCid)) {
+    if ((cid_ == kNullCid) || (cid_ == kNeverCid) ||
+        IsInternalOnlyClassId(cid_) || cid_ == kTypeArgumentsCid) {
       return false;
     }
     const Class& cls = Class::Handle(isolate_group->class_table()->At(cid_));