Revert "[vm] Avoid type parameter check of _Future._asyncComplete() when caller knows its safe"

This reverts commit 8e0feb9.

Reason for revert: breaks tests in Google3, see b/217919095

Original change's description:
> [vm] Avoid type parameter check of _Future._asyncComplete() when caller knows its safe
>
> Currently we have to do a runtime `as FutureOr<T>` check for the
> parameter to `_Future<T>.asyncComplete(FutureOr<T> value)`. Although
> needed for general cases, for the particular usage in the VM's
> async/await transformer, we know that the test is going to suceed.
>
> This CL adds two VM-specific methods on `_Future` that take `dynamic`
> and downcast via `unsafeCast<>()` to avoid this rather large runtime
> type checking overhead.
>
> Issue #48226
>
> TEST=ci
>
> Change-Id: Ieeffae3ac8e2960f849512cf22c51d41cadb1ecf
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/230261
> Reviewed-by: Slava Egorov <[email protected]>
> Reviewed-by: Lasse Nielsen <[email protected]>
> Commit-Queue: Martin Kustermann <[email protected]>

[email protected],[email protected],[email protected]

Change-Id: I37a07cbb6fb37620e5305dfe1b759b0de1c37653
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/231703
Reviewed-by: Ilya Yanok <[email protected]>
Commit-Queue: Ilya Yanok <[email protected]>

Author: Ilya Yanok

pkg/vm/testcases/transformations/type_flow/transformer/enum_from_lib_used_as_type.dart.expect

@@ -22,6 +22,6 @@ class Class extends core::Object {
   synthetic constructor •() → self::Class
     : super core::Object::•()
     ;
-[@vm.procedure-attributes.metadata=methodOrSetterCalledDynamically:false,getterCalledDynamically:false,hasThisUses:false,hasTearOffUses:false,methodOrSetterSelectorId:3397,getterSelectorId:3398]  method method([@vm.inferred-type.metadata=dart.core::Null? (value: null)] self::Enum e) → core::int
+[@vm.procedure-attributes.metadata=methodOrSetterCalledDynamically:false,getterCalledDynamically:false,hasThisUses:false,hasTearOffUses:false,methodOrSetterSelectorId:3395,getterSelectorId:3396]  method method([@vm.inferred-type.metadata=dart.core::Null? (value: null)] self::Enum e) → core::int
     return [@vm.inferred-type.metadata=!] e.{core::_Enum::index}{core::int};
 }

pkg/vm/testcases/transformations/type_flow/transformer/tree_shake_enum_from_lib.dart.expect

@@ -51,6 +51,6 @@ class ConstClass extends core::Object {
   synthetic constructor •() → self::ConstClass
     : super core::Object::•()
     ;
-[@vm.procedure-attributes.metadata=methodOrSetterCalledDynamically:false,getterCalledDynamically:false,hasThisUses:false,hasTearOffUses:false,methodOrSetterSelectorId:3401,getterSelectorId:3402]  method method([@vm.inferred-type.metadata=dart.core::Null? (value: null)] self::ConstEnum e) → core::int
+[@vm.procedure-attributes.metadata=methodOrSetterCalledDynamically:false,getterCalledDynamically:false,hasThisUses:false,hasTearOffUses:false,methodOrSetterSelectorId:3399,getterSelectorId:3400]  method method([@vm.inferred-type.metadata=dart.core::Null? (value: null)] self::ConstEnum e) → core::int
     return [@vm.inferred-type.metadata=!] e.{core::_Enum::index}{core::int};
 }

sdk/lib/_internal/vm/lib/async_patch.dart

@@ -257,7 +257,7 @@ void _completeOnAsyncReturn(_Future _future, Object? value, bool is_sync) {
   // allow then and error handlers to be attached.
   // async_jump_var=0 is prior to first await, =1 is first await.
   if (!is_sync || value is Future) {
-    _future._asyncCompleteUnchecked(value);
+    _future._asyncComplete(value);
   } else {
     _future._completeWithValue(value);
   }

sdk/lib/async/future_impl.dart

@@ -598,26 +598,6 @@ class _Future<T> implements Future<T> {
     _asyncCompleteWithValue(value as dynamic); // Value promoted to T.
   }
 
-  /// Internal helper function used by the implementation of `async` functions.
-  ///
-  /// Like [_asyncComplete], but avoids type checks that are guaranteed to
-  /// succeed by the way the function is called.
-  /// Should be used judiciously.
-  void _asyncCompleteUnchecked(/*FutureOr<T>*/ dynamic value) {
-    assert(value is T || value is Future<T>);
-    final typedValue = unsafeCast<FutureOr<T>>(value);
-
-    // Doing just "is Future" is not sufficient.
-    // If `T` is Object` and `value` is `Future<Object?>.value(null)`,
-    // then value is a `Future`, but not a `Future<T>`, and going through the
-    // `_chainFuture` branch would end up assigning `null` to `Object`.
-    if (typedValue is Future<T>) {
-      _chainFuture(typedValue);
-      return;
-    }
-    _asyncCompleteWithValue(unsafeCast<T>(typedValue));
-  }
-
   void _asyncCompleteWithValue(T value) {
     _setPendingComplete();
     _zone.scheduleMicrotask(() {