diff --git a/pkg/_js_interop_checks/lib/js_interop_checks.dart b/pkg/_js_interop_checks/lib/js_interop_checks.dart
index e3f0978..b936c44 100644
--- a/pkg/_js_interop_checks/lib/js_interop_checks.dart
+++ b/pkg/_js_interop_checks/lib/js_interop_checks.dart
@@ -30,6 +30,9 @@
   bool _classHasAnonymousAnnotation = false;
   bool _libraryHasJSAnnotation = false;
   bool _libraryIsGlobalNamespace = false;
+  // TODO(srujzs): This currently disables this check always. This check should
+  // instead only be disabled up until a given language version.
+  bool _disableJSNativeClassConflict = true;
 
   JsInteropChecks(
       this._coreTypes, this._diagnosticsReporter, this._nativeClasses);
@@ -83,7 +86,8 @@
             cls.location.file);
       }
     }
-    if (_classHasJSAnnotation &&
+    if (!_disableJSNativeClassConflict &&
+        _classHasJSAnnotation &&
         !_classHasAnonymousAnnotation &&
         _libraryIsGlobalNamespace) {
       var jsClass = getJSName(cls);
diff --git a/pkg/analysis_server/lib/src/services/correction/fix/data_driven/modify_parameters.dart b/pkg/analysis_server/lib/src/services/correction/fix/data_driven/modify_parameters.dart
index 32d0b8e..3c49589 100644
--- a/pkg/analysis_server/lib/src/services/correction/fix/data_driven/modify_parameters.dart
+++ b/pkg/analysis_server/lib/src/services/correction/fix/data_driven/modify_parameters.dart
@@ -60,7 +60,7 @@
     var arguments = argumentList.arguments;
     var argumentCount = arguments.length;
     var templateContext = TemplateContext(argumentList.parent, fix.utils);
-    var newNamed = <AddParameter>[];
+
     var indexToNewArgumentMap = <int, AddParameter>{};
     var argumentsToInsert = <int>[];
     var argumentsToDelete = <int>[];
@@ -69,16 +69,14 @@
       if (modification is AddParameter) {
         var index = modification.index;
         indexToNewArgumentMap[index] = modification;
-        if (modification.isPositional) {
+        if (modification.isPositional || modification.isRequired) {
           argumentsToInsert.add(index);
-        } else if (modification.isRequired) {
-          newNamed.add(modification);
         } else {
           var requiredIfCondition =
               modification.argumentValue?.requiredIfCondition;
           if (requiredIfCondition != null &&
               requiredIfCondition.evaluateIn(templateContext)) {
-            newNamed.add(modification);
+            argumentsToInsert.add(index);
           }
         }
       } else if (modification is RemoveParameter) {
@@ -94,7 +92,6 @@
       }
     }
     argumentsToInsert.sort();
-    newNamed.sort((first, second) => first.name.compareTo(second.name));
 
     /// Write to the [builder] the argument associated with a single
     /// [parameter].
@@ -185,39 +182,21 @@
         var insertionRange = insertionRanges[nextInsertionRange];
         var lower = insertionRange.lower;
         var upper = insertionRange.upper;
-        while (upper >= lower && !indexToNewArgumentMap[upper].isRequired) {
+        var parameter = indexToNewArgumentMap[upper];
+        while (upper >= lower &&
+            (parameter.isPositional && !parameter.isRequired)) {
           upper--;
         }
         if (upper >= lower) {
           builder.addInsertion(offset, (builder) {
-            writeInsertionRange(builder, _IndexRange(lower, upper), true);
+            writeInsertionRange(builder, _IndexRange(lower, upper),
+                nextRemaining > 0 || insertionCount > 0);
           });
         }
         nextInsertionRange++;
       }
     }
     //
-    // Insert arguments for required named parameters.
-    //
-    if (newNamed.isNotEmpty) {
-      int offset;
-      var needsInitialComma = false;
-      if (remainingArguments.isEmpty && argumentsToInsert.isEmpty) {
-        offset = argumentList.rightParenthesis.offset;
-      } else {
-        offset = arguments[arguments.length - 1].end;
-        needsInitialComma = true;
-      }
-      builder.addInsertion(offset, (builder) {
-        for (var i = 0; i < newNamed.length; i++) {
-          if (i > 0 || needsInitialComma) {
-            builder.write(', ');
-          }
-          writeArgument(builder, newNamed[i]);
-        }
-      });
-    }
-    //
     // The remaining deletion ranges are now ready to be removed.
     //
     for (var subRange in deletionRanges) {
diff --git a/pkg/analysis_server/lib/src/services/refactoring/extract_widget.dart b/pkg/analysis_server/lib/src/services/refactoring/extract_widget.dart
index 389b739..9570680 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/extract_widget.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/extract_widget.dart
@@ -428,8 +428,12 @@
               // Add parameters for fields, local, and method parameters.
               for (var parameter in _parameters) {
                 builder.write('    ');
-                builder.write('@');
-                builder.writeReference(accessorRequired);
+                if (_isNonNullable) {
+                  builder.write('required');
+                } else {
+                  builder.write('@');
+                  builder.writeReference(accessorRequired);
+                }
                 builder.write(' ');
                 if (parameter.constructorName != parameter.name) {
                   builder.writeType(parameter.type);
diff --git a/pkg/analysis_server/test/services/refactoring/abstract_refactoring.dart b/pkg/analysis_server/test/services/refactoring/abstract_refactoring.dart
index 2338885..82eca0f 100644
--- a/pkg/analysis_server/test/services/refactoring/abstract_refactoring.dart
+++ b/pkg/analysis_server/test/services/refactoring/abstract_refactoring.dart
@@ -12,6 +12,7 @@
     show RefactoringProblemSeverity, SourceChange, SourceEdit;
 import 'package:test/test.dart';
 
+import '../../abstract_context.dart';
 import '../../abstract_single_unit.dart';
 
 int findIdentifierLength(String search) {
@@ -29,7 +30,8 @@
 }
 
 /// The base class for all [Refactoring] tests.
-abstract class RefactoringTest extends AbstractSingleUnitTest {
+abstract class RefactoringTest extends AbstractSingleUnitTest
+    with WithNonFunctionTypeAliasesMixin {
   SearchEngine searchEngine;
 
   SourceChange refactoringChange;
diff --git a/pkg/analysis_server/test/services/refactoring/convert_getter_to_method_test.dart b/pkg/analysis_server/test/services/refactoring/convert_getter_to_method_test.dart
index aa6c028..17c7103 100644
--- a/pkg/analysis_server/test/services/refactoring/convert_getter_to_method_test.dart
+++ b/pkg/analysis_server/test/services/refactoring/convert_getter_to_method_test.dart
@@ -56,7 +56,7 @@
 class D extends A {
   int get test => 4;
 }
-main(A a, B b, C c, D d) {
+void f(A a, B b, C c, D d) {
   var va = a.test;
   var vb = b.test;
   var vc = c.test;
@@ -79,7 +79,7 @@
 class D extends A {
   int test() => 4;
 }
-main(A a, B b, C c, D d) {
+void f(A a, B b, C c, D d) {
   var va = a.test();
   var vb = b.test();
   var vc = c.test();
@@ -99,7 +99,7 @@
 class B extends A {
   int get test => 2;
 }
-main(A a, B b) {
+void f(A a, B b) {
   a.test;
   b.test;
 }
@@ -112,7 +112,7 @@
 class B extends A {
   int test() => 2;
 }
-main(A a, B b) {
+void f(A a, B b) {
   a.test();
   b.test();
 }
diff --git a/pkg/analysis_server/test/services/refactoring/convert_method_to_getter_test.dart b/pkg/analysis_server/test/services/refactoring/convert_method_to_getter_test.dart
index 95e8ed2..7afbb5d 100644
--- a/pkg/analysis_server/test/services/refactoring/convert_method_to_getter_test.dart
+++ b/pkg/analysis_server/test/services/refactoring/convert_method_to_getter_test.dart
@@ -55,7 +55,7 @@
 class D extends A {
   int test() => 4;
 }
-main(A a, B b, C c, D d) {
+void f(A a, B b, C c, D d) {
   var va = a.test();
   var vb = b.test();
   var vc = c.test();
@@ -78,7 +78,7 @@
 class D extends A {
   int get test => 4;
 }
-main(A a, B b, C c, D d) {
+void f(A a, B b, C c, D d) {
   var va = a.test;
   var vb = b.test;
   var vc = c.test;
@@ -98,7 +98,7 @@
 class B extends A {
   int test() => 2;
 }
-main(A a, B b) {
+void f(A a, B b) {
   a.test();
   b.test();
 }
@@ -111,7 +111,7 @@
 class B extends A {
   int get test => 2;
 }
-main(A a, B b) {
+void f(A a, B b) {
   a.test;
   b.test;
 }
diff --git a/pkg/analysis_server/test/services/refactoring/extract_local_test.dart b/pkg/analysis_server/test/services/refactoring/extract_local_test.dart
index 4ffad65..4d5d5bf 100644
--- a/pkg/analysis_server/test/services/refactoring/extract_local_test.dart
+++ b/pkg/analysis_server/test/services/refactoring/extract_local_test.dart
@@ -245,7 +245,7 @@
     await indexTestUnit('''
 main() {
   int a = 1 + 2;
-  Res b = null;
+  Res? b = null;
 }
 
 class Res {}
@@ -698,7 +698,7 @@
   Future<void> test_guessNames_singleExpression() async {
     await indexTestUnit('''
 class TreeItem {}
-TreeItem getSelectedItem() => null;
+TreeItem? getSelectedItem() => null;
 process(my) {}
 main() {
   process(getSelectedItem()); // marker
@@ -760,21 +760,21 @@
 
   Future<void> test_occurrences_differentName_samePrefix() async {
     await indexTestUnit('''
-void main(A a) {
+void f(A a) {
   if (a.foo != 1) {
   } else if (a.foo2 != 2) {
   }
 }
 
 class A {
-  int foo;
-  int foo2;
+  int? foo;
+  int? foo2;
 }
 ''');
     _createRefactoringWithSuffix('a.foo', ' != 1');
     // apply refactoring
     await _assertSuccessfulRefactoring('''
-void main(A a) {
+void f(A a) {
   var res = a.foo;
   if (res != 1) {
   } else if (a.foo2 != 2) {
@@ -782,8 +782,8 @@
 }
 
 class A {
-  int foo;
-  int foo2;
+  int? foo;
+  int? foo2;
 }
 ''');
   }
@@ -1068,7 +1068,7 @@
   Future<void> test_singleExpression_inExpressionBody_ofFunction() async {
     await indexTestUnit('''
 foo(Point p) => p.x * p.x + p.y * p.y;
-class Point {int x; int y;}
+class Point {int x = 0; int y = 0;}
 ''');
     _createRefactoringForString('p.x');
     // apply refactoring
@@ -1077,7 +1077,7 @@
   var res = p.x;
   return res * res + p.y * p.y;
 }
-class Point {int x; int y;}
+class Point {int x = 0; int y = 0;}
 ''');
     _assertSingleLinkedEditGroup(
         length: 3, offsets: [21, 41, 47], names: ['x', 'i']);
@@ -1088,7 +1088,7 @@
 class A {
   foo(Point p) => p.x * p.x + p.y * p.y;
 }
-class Point {int x; int y;}
+class Point {int x = 0; int y = 0;}
 ''');
     _createRefactoringForString('p.x');
     // apply refactoring
@@ -1099,7 +1099,7 @@
     return res * res + p.y * p.y;
   }
 }
-class Point {int x; int y;}
+class Point {int x = 0; int y = 0;}
 ''');
     _assertSingleLinkedEditGroup(
         length: 3, offsets: [35, 57, 63], names: ['x', 'i']);
@@ -1107,7 +1107,7 @@
 
   Future<void> test_singleExpression_inIfElseIf() async {
     await indexTestUnit('''
-main(int p) {
+void f(int p) {
   if (p == 1) {
     print(1);
   } else if (p == 2) {
@@ -1118,7 +1118,7 @@
     _createRefactoringForString('2');
     // apply refactoring
     return _assertSuccessfulRefactoring('''
-main(int p) {
+void f(int p) {
   var res = 2;
   if (p == 1) {
     print(1);
diff --git a/pkg/analysis_server/test/services/refactoring/extract_method_test.dart b/pkg/analysis_server/test/services/refactoring/extract_method_test.dart
index ff277f5..2396564 100644
--- a/pkg/analysis_server/test/services/refactoring/extract_method_test.dart
+++ b/pkg/analysis_server/test/services/refactoring/extract_method_test.dart
@@ -318,8 +318,8 @@
 class A {
   var fff;
 }
-main() {
-  A a;
+
+void f(A a) {
   a.fff = 1;
 }
 ''');
@@ -471,7 +471,7 @@
 
   Future<void> test_bad_statements_exit_notAllExecutionFlows() async {
     await indexTestUnit('''
-main(int p) {
+void f(int p) {
 // start
   if (p == 0) {
     return;
@@ -704,7 +704,7 @@
 
   Future<void> test_canExtractGetter_false_hasParameters() async {
     await indexTestUnit('''
-main(int p) {
+void f(int p) {
   int a = p + 1;
 }
 ''');
@@ -718,7 +718,7 @@
   Future<void> test_canExtractGetter_false_returnNotUsed_assignment() async {
     await indexTestUnit('''
 var topVar = 0;
-f(int p) {
+void f(int p) {
   topVar = 5;
 }
 ''');
@@ -897,7 +897,7 @@
 
   Future<void> test_closure_atArgumentName() async {
     await indexTestUnit('''
-void process({int fff(int x)}) {}
+void process({int fff(int x)?}) {}
 class C {
   main() {
     process(fff: (int x) => x * 2);
@@ -907,7 +907,7 @@
     _createRefactoring(findOffset('ff: (int x)'), 0);
     // apply refactoring
     return _assertSuccessfulRefactoring('''
-void process({int fff(int x)}) {}
+void process({int fff(int x)?}) {}
 class C {
   main() {
     process(fff: res);
@@ -960,7 +960,7 @@
   Future<void> test_closure_bad_referencesParameter() async {
     await indexTestUnit('''
 process(f(x)) {}
-main(int k) {
+void f(int k) {
   process((x) => x * k);
 }
 ''');
@@ -1114,7 +1114,7 @@
   Future<void> test_names_singleExpression() async {
     await indexTestUnit('''
 class TreeItem {}
-TreeItem getSelectedItem() => null;
+TreeItem getSelectedItem() => throw 0;
 process(my) {}
 main() {
   process(getSelectedItem()); // marker
@@ -1203,7 +1203,7 @@
 
   Future<void> test_returnType_statements_nullMix() async {
     await indexTestUnit('''
-main(bool p) {
+f(bool p) {
 // start
   if (p) {
     return 42;
@@ -1291,7 +1291,7 @@
 
   Future<void> test_singleExpression_coveringExpression() async {
     await indexTestUnit('''
-main(int n) {
+void f(int n) {
   var v = new FooBar(n);
 }
 
@@ -1301,7 +1301,7 @@
 ''');
     _createRefactoringForStringOffset('Bar(n);');
     return _assertSuccessfulRefactoring('''
-main(int n) {
+void f(int n) {
   var v = res(n);
 }
 
@@ -1535,7 +1535,7 @@
   Future<void> test_singleExpression_parameter_functionTypeAlias() async {
     await indexTestUnit('''
 typedef R Foo<S, R>(S s);
-void main(Foo<String, int> foo, String s) {
+void f(Foo<String, int> foo, String s) {
   int a = foo(s);
 }
 ''');
@@ -1543,7 +1543,7 @@
     // apply refactoring
     return _assertSuccessfulRefactoring('''
 typedef R Foo<S, R>(S s);
-void main(Foo<String, int> foo, String s) {
+void f(Foo<String, int> foo, String s) {
   int a = res(foo, s);
 }
 
@@ -2298,7 +2298,7 @@
 
   Future<void> test_statements_exit_throws() async {
     await indexTestUnit('''
-main(int p) {
+void f(int p) {
 // start
   if (p == 0) {
     return;
@@ -2376,7 +2376,7 @@
   Future<void> test_statements_hasAwait_forEach() async {
     await indexTestUnit('''
 import 'dart:async';
-Stream<int> getValueStream() => null;
+Stream<int> getValueStream() => throw 0;
 main() async {
 // start
   int sum = 0;
@@ -2391,7 +2391,7 @@
     // apply refactoring
     return _assertSuccessfulRefactoring('''
 import 'dart:async';
-Stream<int> getValueStream() => null;
+Stream<int> getValueStream() => throw 0;
 main() async {
 // start
   int sum = await res();
@@ -2672,7 +2672,7 @@
 
   Future<void> test_statements_return_multiple_ifElse() async {
     await indexTestUnit('''
-num main(bool b) {
+num f(bool b) {
 // start
   if (b) {
     return 1;
@@ -2685,7 +2685,7 @@
     _createRefactoringForStartEndComments();
     // apply refactoring
     return _assertSuccessfulRefactoring('''
-num main(bool b) {
+num f(bool b) {
 // start
   return res(b);
 // end
@@ -2703,7 +2703,7 @@
 
   Future<void> test_statements_return_multiple_ifThen() async {
     await indexTestUnit('''
-num main(bool b) {
+num f(bool b) {
 // start
   if (b) {
     return 1;
@@ -2715,7 +2715,7 @@
     _createRefactoringForStartEndComments();
     // apply refactoring
     return _assertSuccessfulRefactoring('''
-num main(bool b) {
+num f(bool b) {
 // start
   return res(b);
 // end
@@ -2761,7 +2761,7 @@
 
   Future<void> test_statements_return_multiple_interfaceFunction() async {
     await indexTestUnit('''
-main(bool b) {
+f(bool b) {
 // start
   if (b) {
     return 1;
@@ -2773,7 +2773,7 @@
     _createRefactoringForStartEndComments();
     // apply refactoring
     return _assertSuccessfulRefactoring('''
-main(bool b) {
+f(bool b) {
 // start
   return res(b);
 // end
@@ -2791,7 +2791,7 @@
   Future<void>
       test_statements_return_multiple_sameElementDifferentTypeArgs() async {
     await indexTestUnit('''
-main(bool b) {
+f(bool b) {
 // start
   if (b) {
     print(true);
@@ -2806,7 +2806,7 @@
     _createRefactoringForStartEndComments();
     // apply refactoring
     return _assertSuccessfulRefactoring('''
-main(bool b) {
+f(bool b) {
 // start
   return res(b);
 // end
diff --git a/pkg/analysis_server/test/services/refactoring/extract_widget_test.dart b/pkg/analysis_server/test/services/refactoring/extract_widget_test.dart
index be25023..23d0d92 100644
--- a/pkg/analysis_server/test/services/refactoring/extract_widget_test.dart
+++ b/pkg/analysis_server/test/services/refactoring/extract_widget_test.dart
@@ -133,7 +133,7 @@
 
 class Test extends StatelessWidget {
   const Test({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override
@@ -184,7 +184,7 @@
 
 class Test extends StatelessWidget {
   const Test({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override
@@ -220,7 +220,7 @@
 
 class Test extends StatelessWidget {
   const Test({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override
@@ -253,7 +253,7 @@
 
 class Test extends StatelessWidget {
   const Test({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override
@@ -307,7 +307,7 @@
 
 class Test extends StatelessWidget {
   const Test({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override
@@ -410,8 +410,8 @@
 
 class Test extends StatelessWidget {
   const Test({
-    Key key,
-    @required this.c,
+    Key? key,
+    required this.c,
   }) : super(key: key);
 
   final C c;
@@ -462,7 +462,7 @@
 
 class Test extends StatelessWidget {
   const Test({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override
@@ -482,7 +482,7 @@
 import 'package:flutter/material.dart';
 
 class MyWidget extends StatelessWidget {
-  String foo;
+  String foo = '';
 
   @override
   Widget build(BuildContext context) {
@@ -510,7 +510,7 @@
 import 'package:flutter/material.dart';
 
 class MyWidget extends StatelessWidget {
-  String foo;
+  String foo = '';
 
   @override
   Widget build(BuildContext context) {
@@ -526,10 +526,10 @@
 
 class Test extends StatelessWidget {
   const Test({
-    Key key,
-    @required this.foo,
-    @required this.p1,
-    @required this.p2,
+    Key? key,
+    required this.foo,
+    required this.p1,
+    required this.p2,
   }) : super(key: key);
 
   final String foo;
@@ -548,12 +548,14 @@
 ''');
   }
 
-  Future<void> test_method_parameters_named() async {
+  Future<void> test_method_parameters_namedRequired() async {
     await indexTestUnit(r'''
 import 'package:flutter/material.dart';
 
 class MyWidget extends StatelessWidget {
-  String foo;
+  final String foo;
+  
+  MyWidget(this.foo);
 
   @override
   Widget build(BuildContext context) {
@@ -566,7 +568,7 @@
     );
   }
 
-  Widget createColumn({String p1, int p2}) {
+  Widget createColumn({required String p1, required int p2}) {
     var a = new Text('$foo $p1');
     var b = new Text('$p2');
     return new Column(
@@ -575,13 +577,15 @@
   }
 }
 ''');
-    _createRefactoringForStringOffset('createColumn({String');
+    _createRefactoringForStringOffset('createColumn({');
 
     await _assertSuccessfulRefactoring(r'''
 import 'package:flutter/material.dart';
 
 class MyWidget extends StatelessWidget {
-  String foo;
+  final String foo;
+  
+  MyWidget(this.foo);
 
   @override
   Widget build(BuildContext context) {
@@ -597,10 +601,10 @@
 
 class Test extends StatelessWidget {
   const Test({
-    Key key,
-    @required this.foo,
-    @required this.p1,
-    @required this.p2,
+    Key? key,
+    required this.foo,
+    required this.p1,
+    required this.p2,
   }) : super(key: key);
 
   final String foo;
@@ -624,7 +628,9 @@
 import 'package:flutter/material.dart';
 
 class MyWidget extends StatelessWidget {
-  String field;
+  final String field;
+  
+  MyWidget(this.field);
 
   @override
   Widget build(BuildContext context) {
@@ -638,7 +644,9 @@
 import 'package:flutter/material.dart';
 
 class MyWidget extends StatelessWidget {
-  String field;
+  final String field;
+  
+  MyWidget(this.field);
 
   @override
   Widget build(BuildContext context) {
@@ -648,8 +656,8 @@
 
 class Test extends StatelessWidget {
   const Test({
-    Key key,
-    @required this.field,
+    Key? key,
+    required this.field,
   }) : super(key: key);
 
   final String field;
@@ -667,7 +675,7 @@
 import 'package:flutter/material.dart';
 
 class C {
-  String field;
+  String field = '';
 }
 
 class MyWidget extends StatelessWidget {
@@ -685,7 +693,7 @@
 import 'package:flutter/material.dart';
 
 class C {
-  String field;
+  String field = '';
 }
 
 class MyWidget extends StatelessWidget {
@@ -699,8 +707,8 @@
 
 class Test extends StatelessWidget {
   const Test({
-    Key key,
-    @required this.c,
+    Key? key,
+    required this.c,
   }) : super(key: key);
 
   final C c;
@@ -717,7 +725,7 @@
     await indexTestUnit(r'''
 import 'package:flutter/material.dart';
 
-String field;
+String field = '';
 
 class MyWidget extends StatelessWidget {
   @override
@@ -731,7 +739,7 @@
     await _assertSuccessfulRefactoring('''
 import 'package:flutter/material.dart';
 
-String field;
+String field = '';
 
 class MyWidget extends StatelessWidget {
   @override
@@ -742,7 +750,7 @@
 
 class Test extends StatelessWidget {
   const Test({
-    Key key,
+    Key? key,
   }) : super(key: key);
 
   @override
@@ -759,6 +767,8 @@
 
 class MyWidget extends StatelessWidget {
   String field;
+  
+  MyWidget(this.field);
 
   @override
   Widget build(BuildContext context) {
@@ -782,7 +792,7 @@
 import 'package:flutter/material.dart';
 
 abstract class MySuperWidget extends StatelessWidget {
-  String field;
+  String field = '';
 }
 
 class MyWidget extends MySuperWidget {
@@ -808,7 +818,7 @@
 import 'package:flutter/material.dart';
 
 class C {
-  String field;
+  String field = '';
 }
 
 class MyWidget extends StatelessWidget {
@@ -831,7 +841,7 @@
 import 'package:flutter/material.dart';
 
 class C {
-  String field;
+  String field = '';
 }
 
 class MyWidget extends StatelessWidget {
@@ -845,8 +855,8 @@
 
 class Test extends StatelessWidget {
   const Test({
-    Key key,
-    @required this.c,
+    Key? key,
+    required this.c,
   }) : super(key: key);
 
   final C c;
@@ -871,7 +881,7 @@
 class MyWidget extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
-    String key;
+    String key = '';
     return new Text('$key $key');
   }
 }
@@ -889,7 +899,7 @@
 class MyWidget extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
-    String local;
+    String local = '';
     return new Text('$local $local');
   }
 }
@@ -902,15 +912,15 @@
 class MyWidget extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
-    String local;
+    String local = '';
     return Test(local: local);
   }
 }
 
 class Test extends StatelessWidget {
   const Test({
-    Key key,
-    @required this.local,
+    Key? key,
+    required this.local,
   }) : super(key: key);
 
   final String local;
@@ -951,7 +961,9 @@
 import 'package:flutter/material.dart';
 
 class MyWidget extends StatelessWidget {
-  String _field;
+  final String _field;
+  
+  MyWidget(this._field);
 
   @override
   Widget build(BuildContext context) {
@@ -965,7 +977,9 @@
 import 'package:flutter/material.dart';
 
 class MyWidget extends StatelessWidget {
-  String _field;
+  final String _field;
+  
+  MyWidget(this._field);
 
   @override
   Widget build(BuildContext context) {
@@ -975,8 +989,8 @@
 
 class Test extends StatelessWidget {
   const Test({
-    Key key,
-    @required String field,
+    Key? key,
+    required String field,
   }) : _field = field, super(key: key);
 
   final String _field;
@@ -994,8 +1008,10 @@
 import 'package:flutter/material.dart';
 
 class MyWidget extends StatelessWidget {
-  int field;
-  String _field;
+  final int field;
+  final String _field;
+  
+  MyWidget(this.field, this._field);
 
   @override
   Widget build(BuildContext context) {
@@ -1009,8 +1025,10 @@
 import 'package:flutter/material.dart';
 
 class MyWidget extends StatelessWidget {
-  int field;
-  String _field;
+  final int field;
+  final String _field;
+  
+  MyWidget(this.field, this._field);
 
   @override
   Widget build(BuildContext context) {
@@ -1020,9 +1038,9 @@
 
 class Test extends StatelessWidget {
   const Test({
-    Key key,
-    @required this.field,
-    @required String field2,
+    Key? key,
+    required this.field,
+    required String field2,
   }) : _field = field2, super(key: key);
 
   final int field;
@@ -1041,11 +1059,13 @@
 import 'package:flutter/material.dart';
 
 class MyWidget extends StatelessWidget {
-  String field;
+  final String field;
+  
+  MyWidget(this.field);
 
   @override
   Widget build(BuildContext context) {
-    String local;
+    String local = '';
     return new Column(
       children: <Widget>[
         new Text(field),
@@ -1061,20 +1081,22 @@
 import 'package:flutter/material.dart';
 
 class MyWidget extends StatelessWidget {
-  String field;
+  final String field;
+  
+  MyWidget(this.field);
 
   @override
   Widget build(BuildContext context) {
-    String local;
+    String local = '';
     return Test(field: field, local: local);
   }
 }
 
 class Test extends StatelessWidget {
   const Test({
-    Key key,
-    @required this.field,
-    @required this.local,
+    Key? key,
+    required this.field,
+    required this.local,
   }) : super(key: key);
 
   final String field;
@@ -1141,9 +1163,9 @@
 
 class Test extends StatelessWidget {
   const Test({
-    Key key,
-    @required this.index,
-    @required this.a,
+    Key? key,
+    required this.index,
+    required this.a,
   }) : super(key: key);
 
   final int index;
diff --git a/pkg/analysis_server/test/services/refactoring/inline_local_test.dart b/pkg/analysis_server/test/services/refactoring/inline_local_test.dart
index e60b02b..6409980 100644
--- a/pkg/analysis_server/test/services/refactoring/inline_local_test.dart
+++ b/pkg/analysis_server/test/services/refactoring/inline_local_test.dart
@@ -50,7 +50,7 @@
 
   Future<void> test_bad_selectionParameter() async {
     await indexTestUnit(r'''
-main(int test) {
+void f(int test) {
 }
 ''');
     _createRefactoring('test) {');
@@ -157,7 +157,7 @@
 
   Future<void> test_OK_inSwitchCase() async {
     await indexTestUnit('''
-main(int p) {
+void f(int p) {
   switch (p) {
     case 0:
       int test = 42;
@@ -169,7 +169,7 @@
     _createRefactoring('test =');
     // validate change
     return assertSuccessfulRefactoring('''
-main(int p) {
+void f(int p) {
   switch (p) {
     case 0:
       print(42);
diff --git a/pkg/analysis_server/test/services/refactoring/inline_method_test.dart b/pkg/analysis_server/test/services/refactoring/inline_method_test.dart
index 04f61a5..0f5d160 100644
--- a/pkg/analysis_server/test/services/refactoring/inline_method_test.dart
+++ b/pkg/analysis_server/test/services/refactoring/inline_method_test.dart
@@ -203,10 +203,10 @@
   Future<void> test_bad_propertyAccessor_synthetic() async {
     await indexTestUnit(r'''
 class A {
-  int fff;
+  int fff = 0;
 }
 
-main(A a) {
+void f(A a) {
   print(a.fff);
 }
 ''');
@@ -252,12 +252,12 @@
   Future<void> test_cascadeInCascade() async {
     await indexTestUnit(r'''
 class Inner {
-  String a;
-  String b;
+  String a = '';
+  String b = '';
 }
 
 class Outer {
-  Inner inner;
+  Inner inner = Inner();
 }
 
 void main() {
@@ -273,12 +273,12 @@
     // validate change
     return _assertSuccessfulRefactoring(r'''
 class Inner {
-  String a;
-  String b;
+  String a = '';
+  String b = '';
 }
 
 class Outer {
-  Inner inner;
+  Inner inner = Inner();
 }
 
 void main() {
@@ -923,10 +923,10 @@
   Future<void> test_getter_classMember_instance() async {
     await indexTestUnit(r'''
 class A {
-  int f;
+  int f = 0;
   int get result => f + 1;
 }
-main(A a) {
+void f(A a) {
   print(a.result);
 }
 ''');
@@ -934,9 +934,9 @@
     // validate change
     return _assertSuccessfulRefactoring(r'''
 class A {
-  int f;
+  int f = 0;
 }
-main(A a) {
+void f(A a) {
   print(a.f + 1);
 }
 ''');
@@ -1063,7 +1063,7 @@
 abstract class A {
   test();
 }
-main(A a) {
+void f(A a) {
   print(a.test());
 }
 ''');
@@ -1182,7 +1182,7 @@
   }
   mb() {}
 }
-main(B b) {
+void f(B b) {
   b.test();
 }
 ''');
@@ -1199,7 +1199,7 @@
   }
   mb() {}
 }
-main(B b) {
+void f(B b) {
   b.ma();
   b.mb();
 }
@@ -1219,7 +1219,7 @@
     B.mb();
   }
 }
-main(B b) {
+void f(B b) {
   b.test();
 }
 ''');
@@ -1237,7 +1237,7 @@
     B.mb();
   }
 }
-main(B b) {
+void f(B b) {
   B.mb();
   A.ma();
   B.mb();
@@ -1559,12 +1559,12 @@
   Future<void> test_setter_classMember_instance() async {
     await indexTestUnit(r'''
 class A {
-  int f;
+  int f = 0;
   void set result(x) {
     f = x + 1;
   }
 }
-main(A a) {
+void f(A a) {
   a.result = 5;
 }
 ''');
@@ -1572,9 +1572,9 @@
     // validate change
     return _assertSuccessfulRefactoring(r'''
 class A {
-  int f;
+  int f = 0;
 }
-main(A a) {
+void f(A a) {
   a.f = 5 + 1;
 }
 ''');
@@ -1725,7 +1725,7 @@
 test(bool a, bool b) {
   return a || b;
 }
-main(bool p, bool p2, bool p3) {
+void f(bool p, bool p2, bool p3) {
   var res1 = p && test(p2, p3);
   var res2 = p || test(p2, p3);
 }
@@ -1733,7 +1733,7 @@
     _createRefactoring('test(bool a, bool b)');
     // validate change
     return _assertSuccessfulRefactoring(r'''
-main(bool p, bool p2, bool p3) {
+void f(bool p, bool p2, bool p3) {
   var res1 = p && (p2 || p3);
   var res2 = p || p2 || p3;
 }
diff --git a/pkg/analysis_server/test/services/refactoring/rename_class_member_test.dart b/pkg/analysis_server/test/services/refactoring/rename_class_member_test.dart
index 97731a6..24223d8 100644
--- a/pkg/analysis_server/test/services/refactoring/rename_class_member_test.dart
+++ b/pkg/analysis_server/test/services/refactoring/rename_class_member_test.dart
@@ -107,7 +107,7 @@
   Future<void> test_checkFinalConditions_OK_noShadow() async {
     await indexTestUnit('''
 class A {
-  int newName;
+  int newName = 0;
 }
 class B {
   test() {}
@@ -128,7 +128,7 @@
   Future<void> test_checkFinalConditions_OK_noShadow_nullVisibleRange() async {
     await indexTestUnit('''
 class A {
-  int foo;
+  int foo = 0;
 
   A(this.foo);
 }
@@ -161,7 +161,7 @@
 library my.lib;
 import 'test.dart';
 
-main(A a) {
+void f(A a) {
   a.test();
 }
 ''');
@@ -184,7 +184,7 @@
     await indexUnit('/home/test/lib/lib.dart', '''
 import 'test.dart';
 
-main(A a) {
+void f(A a) {
   print(a.foo);
 }
 ''');
@@ -342,7 +342,7 @@
   Future<void> test_checkFinalConditions_shadowsSuper_FieldElement() async {
     await indexTestUnit('''
 class A {
-  int newName; // marker
+  int newName = 0; // marker
 }
 class B extends A {
   test() {}
@@ -359,7 +359,7 @@
     var status = await refactoring.checkFinalConditions();
     assertRefactoringStatus(status, RefactoringProblemSeverity.ERROR,
         expectedMessage: "Renamed method will shadow field 'A.newName'.",
-        expectedContextSearch: 'newName; // marker');
+        expectedContextSearch: 'newName = 0; // marker');
   }
 
   Future<void> test_checkFinalConditions_shadowsSuper_MethodElement() async {
@@ -435,10 +435,10 @@
   Future<void> test_checkNewName_FieldElement() async {
     await indexTestUnit('''
 class A {
-  int test;
+  int test = 0;
 }
 ''');
-    createRenameRefactoringAtString('test;');
+    createRenameRefactoringAtString('test = 0;');
     // null
     refactoring.newName = null;
     assertRefactoringStatus(
@@ -480,7 +480,7 @@
   Future<void> test_createChange_FieldElement() async {
     await indexTestUnit('''
 class A {
-  int test; // marker
+  int test = 0; // marker
   main() {
     print(test);
     test = 1;
@@ -507,7 +507,7 @@
 }
 ''');
     // configure refactoring
-    createRenameRefactoringAtString('test; // marker');
+    createRenameRefactoringAtString('test = 0; // marker');
     expect(refactoring.refactoringName, 'Rename Field');
     expect(refactoring.elementKindName, 'field');
     expect(refactoring.oldName, 'test');
@@ -515,7 +515,7 @@
     // validate change
     return assertSuccessfulRefactoring('''
 class A {
-  int newName; // marker
+  int newName = 0; // marker
   main() {
     print(newName);
     newName = 1;
@@ -618,13 +618,13 @@
     await indexTestUnit('''
 typedef F(a);
 class A {
-  F test;
+  final F test;
+  A(this.test);
   main() {
     test(1);
   }
 }
-main() {
-  A a = new A();
+void f(A a) {
   a.test(2);
 }
 ''');
@@ -637,13 +637,13 @@
     return assertSuccessfulRefactoring('''
 typedef F(a);
 class A {
-  F newName;
+  final F newName;
+  A(this.newName);
   main() {
     newName(1);
   }
 }
-main() {
-  A a = new A();
+void f(A a) {
   a.newName(2);
 }
 ''');
@@ -850,7 +850,7 @@
   void test() {}
 }
 
-main(A a, B b) {
+void f(A a, B b) {
   a.test();
   b.test();
 }
@@ -865,7 +865,7 @@
   void newName() {}
 }
 
-main(A a, B b) {
+void f(A a, B b) {
   a.newName();
   b.newName();
 }
@@ -896,7 +896,7 @@
   void test() {}
 }
 
-main(A a) {
+void f(A a) {
   a.test();
 }
 ''');
@@ -912,7 +912,7 @@
   void newName() {}
 }
 
-main(A a) {
+void f(A a) {
   a.newName();
 }
 ''');
@@ -1035,8 +1035,9 @@
     await indexTestUnit('''
 class A<Test> {
   Test field;
-  List<Test> items;
-  Test method(Test p) => null;
+  List<Test> items = [];
+  A(this.field);
+  Test method(Test p) => field;
 }
 ''');
     // configure refactoring
@@ -1049,8 +1050,9 @@
     return assertSuccessfulRefactoring('''
 class A<NewName> {
   NewName field;
-  List<NewName> items;
-  NewName method(NewName p) => null;
+  List<NewName> items = [];
+  A(this.field);
+  NewName method(NewName p) => field;
 }
 ''');
   }
diff --git a/pkg/analysis_server/test/services/refactoring/rename_extension_member_test.dart b/pkg/analysis_server/test/services/refactoring/rename_extension_member_test.dart
index ddff7c5..8490802 100644
--- a/pkg/analysis_server/test/services/refactoring/rename_extension_member_test.dart
+++ b/pkg/analysis_server/test/services/refactoring/rename_extension_member_test.dart
@@ -312,9 +312,9 @@
   Future<void> test_createChange_named_TypeParameterElement() async {
     await indexTestUnit('''
 extension E<Test> on int {
-  Test get g1 => null;
-  List<Test> get g2 => null;
-  Test m(Test p) => null;
+  Test get g1 => throw 0;
+  List<Test> get g2 => throw 0;
+  Test m(Test p) => throw 0;
 }
 ''');
     // configure refactoring
@@ -326,9 +326,9 @@
     // validate change
     return assertSuccessfulRefactoring('''
 extension E<NewName> on int {
-  NewName get g1 => null;
-  List<NewName> get g2 => null;
-  NewName m(NewName p) => null;
+  NewName get g1 => throw 0;
+  List<NewName> get g2 => throw 0;
+  NewName m(NewName p) => throw 0;
 }
 ''');
   }
diff --git a/pkg/analysis_server/test/services/refactoring/rename_local_test.dart b/pkg/analysis_server/test/services/refactoring/rename_local_test.dart
index e13ea89..0e6b663 100644
--- a/pkg/analysis_server/test/services/refactoring/rename_local_test.dart
+++ b/pkg/analysis_server/test/services/refactoring/rename_local_test.dart
@@ -420,7 +420,7 @@
 
   Future<void> test_createChange_parameter_named() async {
     await indexTestUnit('''
-myFunction({int test}) {
+myFunction({required int test}) {
   test = 1;
   test += 2;
   print(test);
@@ -436,7 +436,7 @@
     refactoring.newName = 'newName';
     // validate change
     return assertSuccessfulRefactoring('''
-myFunction({int newName}) {
+myFunction({required int newName}) {
   newName = 1;
   newName += 2;
   print(newName);
@@ -490,7 +490,7 @@
       test_createChange_parameter_named_ofConstructor_genericClass() async {
     await indexTestUnit('''
 class A<T> {
-  A({T test});
+  A({required T test});
 }
 
 main() {
@@ -505,7 +505,7 @@
     // validate change
     return assertSuccessfulRefactoring('''
 class A<T> {
-  A({T newName});
+  A({required T newName});
 }
 
 main() {
@@ -517,10 +517,10 @@
   Future<void> test_createChange_parameter_named_ofMethod_genericClass() async {
     await indexTestUnit('''
 class A<T> {
-  void foo({T test}) {}
+  void foo({required T test}) {}
 }
 
-main(A<int> a) {
+void f(A<int> a) {
   a.foo(test: 0);
 }
 ''');
@@ -532,10 +532,10 @@
     // validate change
     return assertSuccessfulRefactoring('''
 class A<T> {
-  void foo({T newName}) {}
+  void foo({required T newName}) {}
 }
 
-main(A<int> a) {
+void f(A<int> a) {
   a.foo(newName: 0);
 }
 ''');
@@ -545,12 +545,12 @@
     await indexUnit('/home/test/lib/test2.dart', '''
 library test2;
 class A {
-  void foo({int test}) {
+  void foo({int? test}) {
     print(test);
   }
 }
 class B extends A {
-  void foo({int test}) {
+  void foo({int? test}) {
     print(test);
   }
 }
@@ -563,7 +563,7 @@
   new C().foo(test: 30);
 }
 class C extends A {
-  void foo({int test}) {
+  void foo({int? test}) {
     print(test);
   }
 }
@@ -581,7 +581,7 @@
   new C().foo(newName: 30);
 }
 class C extends A {
-  void foo({int newName}) {
+  void foo({int? newName}) {
     print(newName);
   }
 }
@@ -589,12 +589,12 @@
     assertFileChangeResult('/home/test/lib/test2.dart', '''
 library test2;
 class A {
-  void foo({int newName}) {
+  void foo({int? newName}) {
     print(newName);
   }
 }
 class B extends A {
-  void foo({int newName}) {
+  void foo({int? newName}) {
     print(newName);
   }
 }
@@ -603,7 +603,7 @@
 
   Future<void> test_createChange_parameter_optionalPositional() async {
     await indexTestUnit('''
-myFunction([int test]) {
+myFunction([int? test]) {
   test = 1;
   test += 2;
   print(test);
@@ -619,7 +619,7 @@
     refactoring.newName = 'newName';
     // validate change
     return assertSuccessfulRefactoring('''
-myFunction([int newName]) {
+myFunction([int? newName]) {
   newName = 1;
   newName += 2;
   print(newName);
diff --git a/pkg/analysis_server/test/src/services/correction/fix/data_driven/flutter_use_case_test.dart b/pkg/analysis_server/test/src/services/correction/fix/data_driven/flutter_use_case_test.dart
index f6359cd..ee6c688 100644
--- a/pkg/analysis_server/test/src/services/correction/fix/data_driven/flutter_use_case_test.dart
+++ b/pkg/analysis_server/test/src/services/correction/fix/data_driven/flutter_use_case_test.dart
@@ -2526,6 +2526,152 @@
 ''');
   }
 
+  Future<void> test_widgets_Stack_overflow_clip() async {
+    setPackageContent('''
+class Stack {
+  const Stack({
+    @deprecated Overflow overflow: Overflow.clip,
+    Clip clipBehavior: Clip.hardEdge,
+    List<Widget> children: const <Widget>[]});
+}
+class Overflow {
+  static const Overflow clip = Overflow();
+  static const Overflow visible = Overflow();
+  const Overflow();
+}
+class Clip {
+  static const Clip hardEdge = Clip();
+  static const Clip none = Clip();
+  const Clip();
+}
+class Widget {}
+''');
+    addPackageDataFile('''
+version: 1
+transforms:
+  - title: "Migrate to 'clipBehavior'"
+    date: 2020-09-22
+    element:
+      uris: ['$importUri']
+      constructor: ''
+      inClass: 'Stack'
+    oneOf:
+      - if: "overflow == 'Overflow.clip'"
+        changes:
+          - kind: 'addParameter'
+            index: 0
+            name: 'clipBehavior'
+            style: optional_named
+            argumentValue:
+              expression: 'Clip.hardEdge'
+              requiredIf: "overflow == 'Overflow.clip'"
+          - kind: 'removeParameter'
+            name: 'overflow'
+      - if: "overflow == 'Overflow.visible'"
+        changes:
+          - kind: 'addParameter'
+            index: 0
+            name: 'clipBehavior'
+            style: optional_named
+            argumentValue:
+              expression: 'Clip.none'
+              requiredIf: "overflow == 'Overflow.visible'"
+          - kind: 'removeParameter'
+            name: 'overflow'
+    variables:
+      overflow:
+        kind: 'fragment'
+        value: 'arguments[overflow]'
+''');
+    await resolveTestCode('''
+import '$importUri';
+
+void f() {
+  const Stack(overflow: Overflow.clip, children: []);
+}
+''');
+    await assertHasFix('''
+import '$importUri';
+
+void f() {
+  const Stack(clipBehavior: Clip.hardEdge, children: []);
+}
+''');
+  }
+
+  Future<void> test_widgets_Stack_overflow_visible() async {
+    setPackageContent('''
+class Stack {
+  const Stack({
+    @deprecated Overflow overflow: Overflow.clip,
+    Clip clipBehavior: Clip.hardEdge,
+    List<Widget> children: const <Widget>[]});
+}
+class Overflow {
+  static const Overflow clip = Overflow();
+  static const Overflow visible = Overflow();
+  const Overflow();
+}
+class Clip {
+  static const Clip hardEdge = Clip();
+  static const Clip none = Clip();
+  const Clip();
+}
+class Widget {}
+''');
+    addPackageDataFile('''
+version: 1
+transforms:
+  - title: "Migrate to 'clipBehavior'"
+    date: 2020-09-22
+    element:
+      uris: ['$importUri']
+      constructor: ''
+      inClass: 'Stack'
+    oneOf:
+      - if: "overflow == 'Overflow.clip'"
+        changes:
+          - kind: 'addParameter'
+            index: 0
+            name: 'clipBehavior'
+            style: optional_named
+            argumentValue:
+              expression: 'Clip.hardEdge'
+              requiredIf: "overflow == 'Overflow.clip'"
+          - kind: 'removeParameter'
+            name: 'overflow'
+      - if: "overflow == 'Overflow.visible'"
+        changes:
+          - kind: 'addParameter'
+            index: 0
+            name: 'clipBehavior'
+            style: optional_named
+            argumentValue:
+              expression: 'Clip.none'
+              requiredIf: "overflow == 'Overflow.visible'"
+          - kind: 'removeParameter'
+            name: 'overflow'
+    variables:
+      overflow:
+        kind: 'fragment'
+        value: 'arguments[overflow]'
+''');
+    await resolveTestCode('''
+import '$importUri';
+
+void f() {
+  const Stack(overflow: Overflow.visible, children: []);
+}
+''');
+    await assertHasFix('''
+import '$importUri';
+
+void f() {
+  const Stack(clipBehavior: Clip.none, children: []);
+}
+''');
+  }
+
   Future<void>
       test_widgets_StatefulElement_inheritFromElement_deprecated() async {
     setPackageContent('''
diff --git a/pkg/analysis_server/test/src/services/correction/fix/data_driven/modify_parameters_test.dart b/pkg/analysis_server/test/src/services/correction/fix/data_driven/modify_parameters_test.dart
index d67d30e..77e7e1f 100644
--- a/pkg/analysis_server/test/src/services/correction/fix/data_driven/modify_parameters_test.dart
+++ b/pkg/analysis_server/test/src/services/correction/fix/data_driven/modify_parameters_test.dart
@@ -101,7 +101,7 @@
 import '$importUri';
 
 void f(C c) {
-  c.m2(b: 1, a: 0);
+  c.m2(a: 0, b: 1);
 }
 ''');
   }
diff --git a/pkg/analyzer/lib/src/generated/ffi_verifier.dart b/pkg/analyzer/lib/src/generated/ffi_verifier.dart
index 8a32c10..7693984 100644
--- a/pkg/analyzer/lib/src/generated/ffi_verifier.dart
+++ b/pkg/analyzer/lib/src/generated/ffi_verifier.dart
@@ -775,7 +775,7 @@
   }
 
   void _validateRefIndexed(IndexExpression node) {
-    DartType targetType = node.target?.staticType;
+    DartType targetType = node.realTarget?.staticType;
     if (!_isValidFfiNativeType(targetType, false, true)) {
       final AstNode errorNode = node;
       _errorReporter.reportErrorForNode(
@@ -795,7 +795,7 @@
   }
 
   void _validateRefPropertyAccess(PropertyAccess node) {
-    DartType targetType = node.target?.staticType;
+    DartType targetType = node.realTarget?.staticType;
     if (!_isValidFfiNativeType(targetType, false, true)) {
       final AstNode errorNode = node;
       _errorReporter.reportErrorForNode(
diff --git a/pkg/analyzer/lib/src/test_utilities/mock_sdk.dart b/pkg/analyzer/lib/src/test_utilities/mock_sdk.dart
index 36be56b..16f0bcd 100644
--- a/pkg/analyzer/lib/src/test_utilities/mock_sdk.dart
+++ b/pkg/analyzer/lib/src/test_utilities/mock_sdk.dart
@@ -661,6 +661,8 @@
 }
 
 class Pointer<T extends NativeType> extends NativeType {
+  external factory Pointer.fromAddress(int ptr);
+
   static Pointer<NativeFunction<T>> fromFunction<T extends Function>(
       @DartRepresentationOf("T") Function f,
       [Object exceptionalReturn]) {}
@@ -685,6 +687,12 @@
 class DartRepresentationOf {
   const DartRepresentationOf(String nativeType);
 }
+
+extension StructPointer<T extends Struct> on Pointer<T> {
+  external T get ref;
+
+  external T operator [](int index);
+}
 ''',
   )
 ]);
diff --git a/pkg/analyzer/test/src/diagnostics/non_constant_type_argument_test.dart b/pkg/analyzer/test/src/diagnostics/non_constant_type_argument_test.dart
index eee33d4..f783c71 100644
--- a/pkg/analyzer/test/src/diagnostics/non_constant_type_argument_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/non_constant_type_argument_test.dart
@@ -9,11 +9,53 @@
 
 main() {
   defineReflectiveSuite(() {
+    defineReflectiveTests(NonConstantTypeArgumentNoWarningTest);
+    defineReflectiveTests(NonConstantTypeArgumentNoWarningTest2);
     defineReflectiveTests(NonConstantTypeArgumentTest);
+    defineReflectiveTests(NonConstantTypeArgumentWarningTest);
   });
 }
 
 @reflectiveTest
+class NonConstantTypeArgumentNoWarningTest extends PubPackageResolutionTest {
+  test_asFunction_R() async {
+    await assertNoErrorsInCode(r'''
+import 'dart:ffi';
+
+class MyStruct extends Struct {
+  @Uint8()
+  int myField;
+}
+
+void main(){
+  final pointer = Pointer<MyStruct>.fromAddress(0);
+  pointer.ref.myField = 1;
+}
+''');
+  }
+}
+
+@reflectiveTest
+class NonConstantTypeArgumentNoWarningTest2 extends PubPackageResolutionTest {
+  test_asFunction_R() async {
+    await assertNoErrorsInCode(r'''
+import 'dart:ffi';
+
+class MyStruct extends Struct {
+  @Uint8()
+  int myField;
+}
+
+void main(){
+  final pointer = Pointer<MyStruct>.fromAddress(0)
+    ..ref.myField = 1;
+  print(pointer);
+}
+''');
+  }
+}
+
+@reflectiveTest
 class NonConstantTypeArgumentTest extends PubPackageResolutionTest {
   test_asFunction_R() async {
     await assertErrorsInCode(r'''
@@ -29,3 +71,15 @@
     ]);
   }
 }
+
+@reflectiveTest
+class NonConstantTypeArgumentWarningTest extends PubPackageResolutionTest {
+  test_asFunction_R() async {
+    await assertErrorsInCode(r'''
+import 'dart:ffi';
+
+T genericRef<T extends Struct>(Pointer<T> p) =>
+    p.ref;
+''', [error(FfiCode.NON_CONSTANT_TYPE_ARGUMENT_WARNING, 72, 5)]);
+  }
+}
diff --git a/pkg/analyzer/test/src/diagnostics/subtype_of_ffi_class_test.dart b/pkg/analyzer/test/src/diagnostics/subtype_of_ffi_class_test.dart
index 7073a39..85129db 100644
--- a/pkg/analyzer/test/src/diagnostics/subtype_of_ffi_class_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/subtype_of_ffi_class_test.dart
@@ -75,7 +75,9 @@
   test_Pointer() async {
     await assertErrorsInCode(r'''
 import 'dart:ffi';
-class C extends Pointer {}
+class C extends Pointer {
+  external factory C();
+}
 ''', [
       error(FfiCode.SUBTYPE_OF_FFI_CLASS_IN_EXTENDS, 35, 7),
     ]);
diff --git a/pkg/dev_compiler/lib/src/kernel/compiler.dart b/pkg/dev_compiler/lib/src/kernel/compiler.dart
index db638dc..1fee87e 100644
--- a/pkg/dev_compiler/lib/src/kernel/compiler.dart
+++ b/pkg/dev_compiler/lib/src/kernel/compiler.dart
@@ -3316,10 +3316,15 @@
     // In the body of an `async`, `await` is generated simply as `yield`.
     var gen = emitGeneratorFn((_) => []);
     // Return type of an async body is `Future<flatten(T)>`, where T is the
-    // declared return type.
-    var returnType = _types.flatten(function
+    // declared return type, unless T is Object. In that case the Object refers
+    // to a return type of `Future<Object?>`.
+    // TODO(nshahan) Use the Future type value when available on a FunctionNode.
+    var declaredReturnType = function
         .computeThisFunctionType(_currentLibrary.nonNullable)
-        .returnType);
+        .returnType;
+    var returnType = _coreTypes.isObject(declaredReturnType)
+        ? _coreTypes.objectNullableRawType
+        : _types.flatten(declaredReturnType);
     return js.call('#.async(#, #)',
         [emitLibraryName(_coreTypes.asyncLibrary), _emitType(returnType), gen]);
   }
diff --git a/pkg/front_end/lib/src/fasta/type_inference/closure_context.dart b/pkg/front_end/lib/src/fasta/type_inference/closure_context.dart
index 4029c5c..78dc0c5 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/closure_context.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/closure_context.dart
@@ -546,75 +546,30 @@
               statement.expression.fileOffset,
               noLength)
             ..parent = statement;
-        } else {
-          DartType futureOrType =
-              inferrer.computeGreatestClosure2(_returnContext);
-          if (flattenedExpressionType is! VoidType &&
-              !inferrer.typeSchemaEnvironment
-                  .performNullabilityAwareSubtypeCheck(
-                      flattenedExpressionType, futureValueType)
-                  .isSubtypeWhenUsingNullabilities()) {
-            // It is a compile-time error if s is `return e;`, flatten(S) is not
-            // void, S is not assignable to T_v, and flatten(S) is not a subtype
-            // of T_v.
-            statement.expression = inferrer.ensureAssignable(
-                futureValueType, expressionType, statement.expression,
-                fileOffset: statement.expression.fileOffset,
-                runtimeCheckedType: futureOrType,
-                declaredContextType: returnType,
-                isVoidAllowed: false,
-                errorTemplate: templateInvalidReturnAsync,
-                nullabilityErrorTemplate: templateInvalidReturnAsyncNullability,
-                nullabilityPartErrorTemplate:
-                    templateInvalidReturnAsyncPartNullability,
-                nullabilityNullErrorTemplate:
-                    templateInvalidReturnAsyncNullabilityNull,
-                nullabilityNullTypeErrorTemplate:
-                    templateInvalidReturnAsyncNullabilityNullType)
-              ..parent = statement;
-          }
-          // For `return e`:
-          // When `f` is an asynchronous non-generator with future value type
-          // T_v, evaluation proceeds as follows:
-          //
-          //    The expression `e` is evaluated to an object `o`.
-          //      If the run-time type of `o` is a subtype of `Future<T_v>`,
-          //         let `v` be a fresh variable bound to `o` and
-          //         evaluate `await v` to an object `r`;
-          //         otherwise let `r` be `o`.
-          //    A dynamic error occurs unless the dynamic type of `r`
-          //      is a subtype of the actual value of T_v.
-          //    Then the return statement `s` completes returning `r`.
-          DartType futureType = new InterfaceType(
-              inferrer.coreTypes.futureClass,
-              Nullability.nonNullable,
-              [futureValueType]);
-          VariableDeclaration variable;
-          Expression isOperand;
-          Expression awaitOperand;
-          Expression resultExpression;
-          if (isPureExpression(statement.expression)) {
-            isOperand = clonePureExpression(statement.expression);
-            awaitOperand = clonePureExpression(statement.expression);
-            resultExpression = statement.expression;
-          } else {
-            variable = createVariable(statement.expression, expressionType);
-            isOperand = createVariableGet(variable);
-            awaitOperand = createVariableGet(variable);
-            resultExpression = createVariableGet(variable);
-          }
-          Expression replacement = new ConditionalExpression(
-              new IsExpression(isOperand, futureType)
-                ..fileOffset = statement.fileOffset,
-              new AwaitExpression(awaitOperand)
-                ..fileOffset = statement.fileOffset,
-              resultExpression,
-              futureOrType)
-            ..fileOffset = statement.fileOffset;
-          if (variable != null) {
-            replacement = createLet(variable, replacement);
-          }
-          statement.expression = replacement..parent = statement;
+        } else if (flattenedExpressionType is! VoidType &&
+            !inferrer.typeSchemaEnvironment
+                .performNullabilityAwareSubtypeCheck(
+                    flattenedExpressionType, futureValueType)
+                .isSubtypeWhenUsingNullabilities()) {
+          // It is a compile-time error if s is `return e;`, flatten(S) is not
+          // void, S is not assignable to T_v, and flatten(S) is not a subtype
+          // of T_v.
+          statement.expression = inferrer.ensureAssignable(
+              futureValueType, expressionType, statement.expression,
+              fileOffset: statement.expression.fileOffset,
+              runtimeCheckedType:
+                  inferrer.computeGreatestClosure2(_returnContext),
+              declaredContextType: returnType,
+              isVoidAllowed: false,
+              errorTemplate: templateInvalidReturnAsync,
+              nullabilityErrorTemplate: templateInvalidReturnAsyncNullability,
+              nullabilityPartErrorTemplate:
+                  templateInvalidReturnAsyncPartNullability,
+              nullabilityNullErrorTemplate:
+                  templateInvalidReturnAsyncNullabilityNull,
+              nullabilityNullTypeErrorTemplate:
+                  templateInvalidReturnAsyncNullabilityNullType)
+            ..parent = statement;
         }
       }
     } else {
diff --git a/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart b/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
index 4dd7287..0b50fbb 100644
--- a/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
+++ b/pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart
@@ -2514,13 +2514,16 @@
     // `void` if `B’` contains no `yield` expressions.  Otherwise, let `M` be
     // the least upper bound of the types of the `return` expressions in `B’`,
     // or `void` if `B’` contains no `return` expressions.
+    DartType inferredReturnType;
     if (needToSetReturnType) {
-      DartType inferredReturnType = closureContext.inferReturnType(this,
+      inferredReturnType = closureContext.inferReturnType(this,
           hasImplicitReturn: flowAnalysis.isReachable);
+    }
 
-      // Then the result of inference is `<T0, ..., Tn>(R0 x0, ..., Rn xn) B`
-      // with type `<T0, ..., Tn>(R0, ..., Rn) -> M'` (with some of the `Ri` and
-      // `xi` denoted as optional or named parameters, if appropriate).
+    // Then the result of inference is `<T0, ..., Tn>(R0 x0, ..., Rn xn) B` with
+    // type `<T0, ..., Tn>(R0, ..., Rn) -> M’` (with some of the `Ri` and `xi`
+    // denoted as optional or named parameters, if appropriate).
+    if (needToSetReturnType) {
       instrumentation?.record(uriForInstrumentation, fileOffset, 'returnType',
           new InstrumentationValueForType(inferredReturnType));
       function.returnType = inferredReturnType;
diff --git a/pkg/front_end/test/spell_checking_list_code.txt b/pkg/front_end/test/spell_checking_list_code.txt
index e422e9d..572493d 100644
--- a/pkg/front_end/test/spell_checking_list_code.txt
+++ b/pkg/front_end/test/spell_checking_list_code.txt
@@ -868,7 +868,6 @@
 printf
 println
 proc
-proceeds
 producers
 product
 progresses
diff --git a/pkg/front_end/test/spell_checking_list_tests.txt b/pkg/front_end/test/spell_checking_list_tests.txt
index d3bc3e1a..55be1a1 100644
--- a/pkg/front_end/test/spell_checking_list_tests.txt
+++ b/pkg/front_end/test/spell_checking_list_tests.txt
@@ -737,7 +737,6 @@
 unassignment
 unawaited
 unbreak
-uncaught
 unconverted
 uncover
 uncovers
diff --git a/pkg/front_end/test/text_representation/data/expressions.dart b/pkg/front_end/test/text_representation/data/expressions.dart
index 4d70d21..bf8c23c 100644
--- a/pkg/front_end/test/text_representation/data/expressions.dart
+++ b/pkg/front_end/test/text_representation/data/expressions.dart
@@ -382,9 +382,7 @@
 exprMap() => {0: "foo", 1: "bar"};
 
 /*member: exprAwait:await o*/
-exprAwait(o) async {
-  await o;
-}
+exprAwait(o) async => await o;
 
 /*member: exprLoadLibrary:prefix.loadLibrary()*/
 exprLoadLibrary() => prefix.loadLibrary();
diff --git a/pkg/front_end/test/text_representation/text_representation_test.dart b/pkg/front_end/test/text_representation/text_representation_test.dart
index d9019d0..f804385 100644
--- a/pkg/front_end/test/text_representation/text_representation_test.dart
+++ b/pkg/front_end/test/text_representation/text_representation_test.dart
@@ -156,16 +156,14 @@
 
   @override
   String computeMemberValue(Id id, Member node) {
+    if (node.name.text == 'stmtVariableDeclarationMulti') {
+      print(node);
+    }
     if (node.name.text.startsWith(expressionMarker)) {
       if (node is Procedure) {
         Statement body = node.function.body;
         if (body is ReturnStatement) {
           return body.expression.toText(strategy);
-        } else if (body is Block &&
-            body.statements.isNotEmpty &&
-            body.statements.first is ExpressionStatement) {
-          ExpressionStatement statement = body.statements.first;
-          return statement.expression.toText(strategy);
         }
       } else if (node is Field && node.initializer != null) {
         return node.initializer.toText(strategy);
diff --git a/pkg/front_end/testcases/late_lowering/later.dart.strong.expect b/pkg/front_end/testcases/late_lowering/later.dart.strong.expect
index 74694bf..0b84933 100644
--- a/pkg/front_end/testcases/late_lowering/later.dart.strong.expect
+++ b/pkg/front_end/testcases/late_lowering/later.dart.strong.expect
@@ -134,28 +134,28 @@
   await for (core::String s in asy::Stream::fromIterable<core::String>(<core::String>["hest"])) {
     core::print(s);
   }
-  return let final core::String #t8 = "hest" in #t8 is asy::Future<dynamic> ?{FutureOr<dynamic>} await #t8 : #t8;
+  return "hest";
 }
 static method fisk() → dynamic async {
   lowered core::String? #s1;
   function #s1#get() → core::String
-    return let final core::String? #t9 = #s1 in #t9.==(null) ?{core::String} #s1 = invalid-expression "pkg/front_end/testcases/late_lowering/later.dart:40:20: Error: `await` expressions are not supported in late local initializers.
+    return let final core::String? #t8 = #s1 in #t8.==(null) ?{core::String} #s1 = invalid-expression "pkg/front_end/testcases/late_lowering/later.dart:40:20: Error: `await` expressions are not supported in late local initializers.
   late String s1 = await hest(); // Error.
-                   ^^^^^" as{TypeError,ForDynamic,ForNonNullableByDefault} core::String : #t9{core::String};
-  function #s1#set(core::String #t10) → dynamic
-    return #s1 = #t10;
+                   ^^^^^" as{TypeError,ForDynamic,ForNonNullableByDefault} core::String : #t8{core::String};
+  function #s1#set(core::String #t9) → dynamic
+    return #s1 = #t9;
   lowered core::String? #s2;
   function #s2#get() → core::String
-    return let final core::String? #t11 = #s2 in #t11.==(null) ?{core::String} #s2 = "${#C1}${invalid-expression "pkg/front_end/testcases/late_lowering/later.dart:41:30: Error: `await` expressions are not supported in late local initializers.
+    return let final core::String? #t10 = #s2 in #t10.==(null) ?{core::String} #s2 = "${#C1}${invalid-expression "pkg/front_end/testcases/late_lowering/later.dart:41:30: Error: `await` expressions are not supported in late local initializers.
   late String s2 = '\${fisk}\${await hest()}\${fisk}'; // Error.
-                             ^^^^^"}${#C1}" : #t11{core::String};
-  function #s2#set(core::String #t12) → dynamic
-    return #s2 = #t12;
+                             ^^^^^"}${#C1}" : #t10{core::String};
+  function #s2#set(core::String #t11) → dynamic
+    return #s2 = #t11;
   lowered core::Function? #f;
   function #f#get() → core::Function
-    return let final core::Function? #t13 = #f in #t13.==(null) ?{core::Function} #f = () → asy::Future<dynamic> async => let final dynamic #t14 = await self::hest() in #t14 is asy::Future<dynamic> ?{FutureOr<dynamic>} await #t14 : #t14 : #t13{core::Function};
-  function #f#set(core::Function #t15) → dynamic
-    return #f = #t15;
+    return let final core::Function? #t12 = #f in #t12.==(null) ?{core::Function} #f = () → asy::Future<dynamic> async => await self::hest() : #t12{core::Function};
+  function #f#set(core::Function #t13) → dynamic
+    return #f = #t13;
 }
 static method main() → dynamic {}
 
diff --git a/pkg/front_end/testcases/late_lowering/later.dart.strong.transformed.expect b/pkg/front_end/testcases/late_lowering/later.dart.strong.transformed.expect
index 09236c4..12f0ed3 100644
--- a/pkg/front_end/testcases/late_lowering/later.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/late_lowering/later.dart.strong.transformed.expect
@@ -148,8 +148,6 @@
   dynamic :saved_try_context_var1;
   dynamic :exception0;
   dynamic :stack_trace0;
-  FutureOr<dynamic>:async_temporary_0;
-  FutureOr<dynamic>:async_temporary_1;
   function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
     try {
       #L1:
@@ -177,15 +175,7 @@
               :result;
             }
         }
-        final core::String #t11 = "hest";
-        if(#t11 is asy::Future<dynamic>) {
-          [yield] let dynamic #t12 = asy::_awaitHelper(#t11, :async_op_then, :async_op_error, :async_op) in null;
-          :async_temporary_1 = _in::unsafeCast<core::String>(:result);
-        }
-        else {
-          :async_temporary_1 = #t11;
-        }
-        :return_value = :async_temporary_1;
+        :return_value = "hest";
         break #L1;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -214,21 +204,21 @@
       {
         lowered core::String? #s1;
         function #s1#get() → core::String
-          return let final core::String? #t13 = #s1 in #t13.==(null) ?{core::String} #s1 = invalid-expression "pkg/front_end/testcases/late_lowering/later.dart:40:20: Error: `await` expressions are not supported in late local initializers.
+          return let final core::String? #t11 = #s1 in #t11.==(null) ?{core::String} #s1 = invalid-expression "pkg/front_end/testcases/late_lowering/later.dart:40:20: Error: `await` expressions are not supported in late local initializers.
   late String s1 = await hest(); // Error.
-                   ^^^^^" : #t13{core::String};
-        function #s1#set(core::String #t14) → dynamic
-          return #s1 = #t14;
+                   ^^^^^" : #t11{core::String};
+        function #s1#set(core::String #t12) → dynamic
+          return #s1 = #t12;
         lowered core::String? #s2;
         function #s2#get() → core::String
-          return let final core::String? #t15 = #s2 in #t15.==(null) ?{core::String} #s2 = "${#C1}${invalid-expression "pkg/front_end/testcases/late_lowering/later.dart:41:30: Error: `await` expressions are not supported in late local initializers.
+          return let final core::String? #t13 = #s2 in #t13.==(null) ?{core::String} #s2 = "${#C1}${invalid-expression "pkg/front_end/testcases/late_lowering/later.dart:41:30: Error: `await` expressions are not supported in late local initializers.
   late String s2 = '\${fisk}\${await hest()}\${fisk}'; // Error.
-                             ^^^^^"}${#C1}" : #t15{core::String};
-        function #s2#set(core::String #t16) → dynamic
-          return #s2 = #t16;
+                             ^^^^^"}${#C1}" : #t13{core::String};
+        function #s2#set(core::String #t14) → dynamic
+          return #s2 = #t14;
         lowered core::Function? #f;
         function #f#get() → core::Function
-          return let final core::Function? #t17 = #f in #t17.==(null) ?{core::Function} #f = () → asy::Future<dynamic> /* originally async */ {
+          return let final core::Function? #t15 = #f in #t15.==(null) ?{core::Function} #f = () → asy::Future<dynamic> /* originally async */ {
             final asy::_Future<dynamic> :async_future = new asy::_Future::•<dynamic>();
             core::bool* :is_sync = false;
             FutureOr<dynamic>? :return_value;
@@ -237,21 +227,12 @@
             core::int :await_jump_var = 0;
             dynamic :await_ctx_var;
             dynamic :saved_try_context_var0;
-            FutureOr<dynamic>:async_temporary_0;
             function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
               try {
                 #L4:
                 {
-                  [yield] let dynamic #t18 = asy::_awaitHelper(self::hest(), :async_op_then, :async_op_error, :async_op) in null;
-                  final dynamic #t19 = :result;
-                  if(#t19 is asy::Future<dynamic>) {
-                    [yield] let dynamic #t20 = asy::_awaitHelper(#t19, :async_op_then, :async_op_error, :async_op) in null;
-                    :async_temporary_0 = :result;
-                  }
-                  else {
-                    :async_temporary_0 = #t19;
-                  }
-                  :return_value = :async_temporary_0;
+                  [yield] let dynamic #t16 = asy::_awaitHelper(self::hest(), :async_op_then, :async_op_error, :async_op) in null;
+                  :return_value = :result;
                   break #L4;
                 }
                 asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -265,9 +246,9 @@
             :async_op.call();
             :is_sync = true;
             return :async_future;
-          } : #t17{core::Function};
-        function #f#set(core::Function #t21) → dynamic
-          return #f = #t21;
+          } : #t15{core::Function};
+        function #f#set(core::Function #t17) → dynamic
+          return #f = #t17;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
       return;
@@ -289,4 +270,4 @@
 
 Extra constant evaluation status:
 Evaluated: VariableGet @ org-dartlang-testcase:///later.dart:46:18 -> IntConstant(42)
-Extra constant evaluation: evaluated: 234, effectively constant: 1
+Extra constant evaluation: evaluated: 207, effectively constant: 1
diff --git a/pkg/front_end/testcases/late_lowering/later.dart.weak.expect b/pkg/front_end/testcases/late_lowering/later.dart.weak.expect
index 0d0243b..7123dd80 100644
--- a/pkg/front_end/testcases/late_lowering/later.dart.weak.expect
+++ b/pkg/front_end/testcases/late_lowering/later.dart.weak.expect
@@ -154,7 +154,7 @@
   await for (core::String s in asy::Stream::fromIterable<core::String>(<core::String>["hest"])) {
     core::print(s);
   }
-  return let final core::String #t8 = "hest" in #t8 is asy::Future<dynamic> ?{FutureOr<dynamic>} await #t8 : #t8;
+  return "hest";
 }
 static method fisk() → dynamic async {
   lowered core::String? #s1;
@@ -168,9 +168,9 @@
     }
     return #s1{core::String};
   }
-  function #s1#set(core::String #t9) → dynamic {
+  function #s1#set(core::String #t8) → dynamic {
     #s1#isSet = true;
-    return #s1 = #t9;
+    return #s1 = #t8;
   }
   lowered core::String? #s2;
   lowered core::bool #s2#isSet = false;
@@ -183,22 +183,22 @@
     }
     return #s2{core::String};
   }
-  function #s2#set(core::String #t10) → dynamic {
+  function #s2#set(core::String #t9) → dynamic {
     #s2#isSet = true;
-    return #s2 = #t10;
+    return #s2 = #t9;
   }
   lowered core::Function? #f;
   lowered core::bool #f#isSet = false;
   function #f#get() → core::Function {
     if(!#f#isSet) {
-      #f = () → asy::Future<dynamic> async => let final dynamic #t11 = await self::hest() in #t11 is asy::Future<dynamic> ?{FutureOr<dynamic>} await #t11 : #t11;
+      #f = () → asy::Future<dynamic> async => await self::hest();
       #f#isSet = true;
     }
     return #f{core::Function};
   }
-  function #f#set(core::Function #t12) → dynamic {
+  function #f#set(core::Function #t10) → dynamic {
     #f#isSet = true;
-    return #f = #t12;
+    return #f = #t10;
   }
 }
 static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/late_lowering/later.dart.weak.transformed.expect b/pkg/front_end/testcases/late_lowering/later.dart.weak.transformed.expect
index 7fe5b1b..3bcf2b7 100644
--- a/pkg/front_end/testcases/late_lowering/later.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/late_lowering/later.dart.weak.transformed.expect
@@ -168,8 +168,6 @@
   dynamic :saved_try_context_var1;
   dynamic :exception0;
   dynamic :stack_trace0;
-  FutureOr<dynamic>:async_temporary_0;
-  FutureOr<dynamic>:async_temporary_1;
   function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
     try {
       #L1:
@@ -197,15 +195,7 @@
               :result;
             }
         }
-        final core::String #t11 = "hest";
-        if(#t11 is asy::Future<dynamic>) {
-          [yield] let dynamic #t12 = asy::_awaitHelper(#t11, :async_op_then, :async_op_error, :async_op) in null;
-          :async_temporary_1 = _in::unsafeCast<core::String>(:result);
-        }
-        else {
-          :async_temporary_1 = #t11;
-        }
-        :return_value = :async_temporary_1;
+        :return_value = "hest";
         break #L1;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -243,9 +233,9 @@
           }
           return #s1{core::String};
         }
-        function #s1#set(core::String #t13) → dynamic {
+        function #s1#set(core::String #t11) → dynamic {
           #s1#isSet = true;
-          return #s1 = #t13;
+          return #s1 = #t11;
         }
         lowered core::String? #s2;
         lowered core::bool #s2#isSet = false;
@@ -258,9 +248,9 @@
           }
           return #s2{core::String};
         }
-        function #s2#set(core::String #t14) → dynamic {
+        function #s2#set(core::String #t12) → dynamic {
           #s2#isSet = true;
-          return #s2 = #t14;
+          return #s2 = #t12;
         }
         lowered core::Function? #f;
         lowered core::bool #f#isSet = false;
@@ -275,21 +265,12 @@
               core::int :await_jump_var = 0;
               dynamic :await_ctx_var;
               dynamic :saved_try_context_var0;
-              FutureOr<dynamic>:async_temporary_0;
               function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
                 try {
                   #L4:
                   {
-                    [yield] let dynamic #t15 = asy::_awaitHelper(self::hest(), :async_op_then, :async_op_error, :async_op) in null;
-                    final dynamic #t16 = :result;
-                    if(#t16 is asy::Future<dynamic>) {
-                      [yield] let dynamic #t17 = asy::_awaitHelper(#t16, :async_op_then, :async_op_error, :async_op) in null;
-                      :async_temporary_0 = :result;
-                    }
-                    else {
-                      :async_temporary_0 = #t16;
-                    }
-                    :return_value = :async_temporary_0;
+                    [yield] let dynamic #t13 = asy::_awaitHelper(self::hest(), :async_op_then, :async_op_error, :async_op) in null;
+                    :return_value = :result;
                     break #L4;
                   }
                   asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -308,9 +289,9 @@
           }
           return #f{core::Function};
         }
-        function #f#set(core::Function #t18) → dynamic {
+        function #f#set(core::Function #t14) → dynamic {
           #f#isSet = true;
-          return #f = #t18;
+          return #f = #t14;
         }
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
diff --git a/pkg/front_end/testcases/nnbd/assignability_error_messages.dart.strong.expect b/pkg/front_end/testcases/nnbd/assignability_error_messages.dart.strong.expect
index 6769397..0e66be9 100644
--- a/pkg/front_end/testcases/nnbd/assignability_error_messages.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/assignability_error_messages.dart.strong.expect
@@ -263,35 +263,35 @@
   }
   function local() → FutureOr<self::A> async {
     if(true) {
-      return let final self::B? #t6 = let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:43:14: Error: A value of type 'B?' can't be returned from an async function with return type 'FutureOr<A>' because 'B?' is nullable and 'FutureOr<A>' isn't.
+      return let final<BottomType> #t6 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:43:14: Error: A value of type 'B?' can't be returned from an async function with return type 'FutureOr<A>' because 'B?' is nullable and 'FutureOr<A>' isn't.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
       return x; // Error.
-             ^" in x as{TypeError,ForNonNullableByDefault} self::A in #t6 is asy::Future<self::A> ?{FutureOr<self::A>} await #t6 : #t6;
+             ^" in x as{TypeError,ForNonNullableByDefault} self::A;
     }
     else {
-      return let final asy::Future<self::B?> #t8 = let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:45:18: Error: A value of type 'Future<B?>' can't be returned from an async function with return type 'FutureOr<A>'.
+      return let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:45:18: Error: A value of type 'Future<B?>' can't be returned from an async function with return type 'FutureOr<A>'.
  - 'Future' is from 'dart:async'.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
       return new Future<B?>.value(x); // Error.
-                 ^" in asy::Future::value<self::B?>(x) as{TypeError,ForNonNullableByDefault} self::A in #t8 is asy::Future<self::A> ?{FutureOr<self::A>} await #t8 : #t8;
+                 ^" in asy::Future::value<self::B?>(x) as{TypeError,ForNonNullableByDefault} self::A;
     }
   }
-  return let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:49:10: Error: A value of type 'B?' can't be returned from a function with return type 'A' because 'B?' is nullable and 'A' isn't.
+  return let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:49:10: Error: A value of type 'B?' can't be returned from a function with return type 'A' because 'B?' is nullable and 'A' isn't.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   return x; // Error.
          ^" in x as{TypeError,ForNonNullableByDefault} self::A;
 }
 static method bar(core::List<self::B?> x, core::List<core::List<self::B?>> l, core::Map<core::List<self::B?>, core::List<self::B?>> m) → core::List<self::A> {
-  self::barContext(let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:53:14: Error: The argument type 'List<B?>' can't be assigned to the parameter type 'List<A>' because 'B?' is nullable and 'A' isn't.
+  self::barContext(let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:53:14: Error: The argument type 'List<B?>' can't be assigned to the parameter type 'List<A>' because 'B?' is nullable and 'A' isn't.
  - 'List' is from 'dart:core'.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   barContext(x); // Error.
              ^" in x as{TypeError,ForNonNullableByDefault} core::List<self::A>);
-  core::List<self::A> y = let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:54:15: Error: A value of type 'List<B?>' can't be assigned to a variable of type 'List<A>' because 'B?' is nullable and 'A' isn't.
+  core::List<self::A> y = let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:54:15: Error: A value of type 'List<B?>' can't be assigned to a variable of type 'List<A>' because 'B?' is nullable and 'A' isn't.
  - 'List' is from 'dart:core'.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
@@ -314,16 +314,16 @@
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   <List<A>, List<A>>{...m}; // Error.
                         ^"};
-  for (final core::List<self::B?> #t13 in l) {
-    core::List<self::A> y = let final<BottomType> #t14 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:57:16: Error: A value of type 'List<B?>' can't be assigned to a variable of type 'List<A>' because 'B?' is nullable and 'A' isn't.
+  for (final core::List<self::B?> #t11 in l) {
+    core::List<self::A> y = let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:57:16: Error: A value of type 'List<B?>' can't be assigned to a variable of type 'List<A>' because 'B?' is nullable and 'A' isn't.
  - 'List' is from 'dart:core'.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
 Try changing the type of the variable.
   for (List<A> y in l) {} // Error.
-               ^" in #t13 as{TypeError,ForNonNullableByDefault} core::List<self::A>;
+               ^" in #t11 as{TypeError,ForNonNullableByDefault} core::List<self::A>;
   }
-  return let final<BottomType> #t15 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:58:10: Error: A value of type 'List<B?>' can't be returned from a function with return type 'List<A>' because 'B?' is nullable and 'A' isn't.
+  return let final<BottomType> #t13 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:58:10: Error: A value of type 'List<B?>' can't be returned from a function with return type 'List<A>' because 'B?' is nullable and 'A' isn't.
  - 'List' is from 'dart:core'.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
@@ -331,52 +331,52 @@
          ^" in x as{TypeError,ForNonNullableByDefault} core::List<self::A>;
 }
 static method baz(self::C c) → void {
-  self::bazContext(let final<BottomType> #t16 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:62:14: Error: The argument type 'num? Function()' can't be assigned to the parameter type 'num Function()' because 'num?' is nullable and 'num' isn't.
+  self::bazContext(let final<BottomType> #t14 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:62:14: Error: The argument type 'num? Function()' can't be assigned to the parameter type 'num Function()' because 'num?' is nullable and 'num' isn't.
   bazContext(c);
-             ^" in (let final self::C #t17 = c in #t17.==(null) ?{() → core::num?} null : #t17.{self::C::call}) as{TypeError,ForNonNullableByDefault} () → core::num);
+             ^" in (let final self::C #t15 = c in #t15.==(null) ?{() → core::num?} null : #t15.{self::C::call}) as{TypeError,ForNonNullableByDefault} () → core::num);
 }
 static method boz(Null x) → self::A {
-  self::fooContext(let final<BottomType> #t18 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:66:14: Error: The argument type 'Null' can't be assigned to the parameter type 'A' because 'A' is not nullable.
+  self::fooContext(let final<BottomType> #t16 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:66:14: Error: The argument type 'Null' can't be assigned to the parameter type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   fooContext(x); // Error.
              ^" in x as{TypeError,ForNonNullableByDefault} self::A);
-  self::fooContext(let final<BottomType> #t19 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:67:14: Error: The value 'null' can't be assigned to the parameter type 'A' because 'A' is not nullable.
+  self::fooContext(let final<BottomType> #t17 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:67:14: Error: The value 'null' can't be assigned to the parameter type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   fooContext(null); // Error.
              ^" in null as{TypeError,ForNonNullableByDefault} self::A);
-  self::A a1 = let final<BottomType> #t20 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:68:10: Error: A value of type 'Null' can't be assigned to a variable of type 'A' because 'A' is not nullable.
+  self::A a1 = let final<BottomType> #t18 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:68:10: Error: A value of type 'Null' can't be assigned to a variable of type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   A a1 = x; // Error.
          ^" in x as{TypeError,ForNonNullableByDefault} self::A;
-  self::A a2 = let final<BottomType> #t21 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:69:10: Error: The value 'null' can't be assigned to a variable of type 'A' because 'A' is not nullable.
+  self::A a2 = let final<BottomType> #t19 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:69:10: Error: The value 'null' can't be assigned to a variable of type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   A a2 = null; // Error.
          ^" in null as{TypeError,ForNonNullableByDefault} self::A;
   if(true) {
-    return let final<BottomType> #t22 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:71:12: Error: A value of type 'Null' can't be returned from a function with return type 'A' because 'A' is not nullable.
+    return let final<BottomType> #t20 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:71:12: Error: A value of type 'Null' can't be returned from a function with return type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
     return x; // Error.
            ^" in x as{TypeError,ForNonNullableByDefault} self::A;
   }
   else {
-    return let final<BottomType> #t23 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:73:12: Error: The value 'null' can't be returned from a function with return type 'A' because 'A' is not nullable.
+    return let final<BottomType> #t21 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:73:12: Error: The value 'null' can't be returned from a function with return type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
     return null; // Error.
            ^" in null as{TypeError,ForNonNullableByDefault} self::A;
   }
   function local() → FutureOr<self::A> async {
     if(true) {
-      return let final Null #t24 = let final<BottomType> #t25 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:77:14: Error: The value 'null' can't be returned from an async function with return type 'FutureOr<A>' because 'FutureOr<A>' is not nullable.
+      return let final<BottomType> #t22 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:77:14: Error: The value 'null' can't be returned from an async function with return type 'FutureOr<A>' because 'FutureOr<A>' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
       return null; // Error.
-             ^" in null as{TypeError,ForNonNullableByDefault} self::A in #t24 is asy::Future<self::A> ?{FutureOr<self::A>} await #t24 : #t24;
+             ^" in null as{TypeError,ForNonNullableByDefault} self::A;
     }
     else {
-      return let final asy::Future<Null> #t26 = let final<BottomType> #t27 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:79:18: Error: A value of type 'Future<Null>' can't be returned from an async function with return type 'FutureOr<A>'.
+      return let final<BottomType> #t23 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:79:18: Error: A value of type 'Future<Null>' can't be returned from an async function with return type 'FutureOr<A>'.
  - 'Future' is from 'dart:async'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
       return new Future<Null>.value(null); // Error.
-                 ^" in asy::Future::value<Null>(null) as{TypeError,ForNonNullableByDefault} self::A in #t26 is asy::Future<self::A> ?{FutureOr<self::A>} await #t26 : #t26;
+                 ^" in asy::Future::value<Null>(null) as{TypeError,ForNonNullableByDefault} self::A;
     }
   }
 }
diff --git a/pkg/front_end/testcases/nnbd/assignability_error_messages.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/assignability_error_messages.dart.strong.transformed.expect
index c855781..bdd60d8 100644
--- a/pkg/front_end/testcases/nnbd/assignability_error_messages.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/assignability_error_messages.dart.strong.transformed.expect
@@ -180,7 +180,6 @@
 import self as self;
 import "dart:core" as core;
 import "dart:async" as asy;
-import "dart:_internal" as _in;
 
 import "dart:async";
 
@@ -281,45 +280,25 @@
     (core::Object, core::StackTrace) → dynamic :async_op_error;
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
-    dynamic :saved_try_context_var0;
-    FutureOr<self::A>:async_temporary_0;
-    FutureOr<self::A>:async_temporary_1;
-    FutureOr<self::A>:async_temporary_2;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L4:
         {
           if(true) {
-            final self::B? #t10 = let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:43:14: Error: A value of type 'B?' can't be returned from an async function with return type 'FutureOr<A>' because 'B?' is nullable and 'FutureOr<A>' isn't.
+            :return_value = let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:43:14: Error: A value of type 'B?' can't be returned from an async function with return type 'FutureOr<A>' because 'B?' is nullable and 'FutureOr<A>' isn't.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
       return x; // Error.
-             ^" in let self::B? #t12 = x in #t12.==(null) ?{self::A} #t12 as{TypeError,ForNonNullableByDefault} self::A : #t12{self::A};
-            if(#t10 is asy::Future<self::A>) {
-              [yield] let dynamic #t13 = asy::_awaitHelper(#t10, :async_op_then, :async_op_error, :async_op) in null;
-              :async_temporary_0 = _in::unsafeCast<self::B?>(:result);
-            }
-            else {
-              :async_temporary_0 = #t10;
-            }
-            :return_value = :async_temporary_0;
+             ^" in let self::B? #t11 = x in #t11.==(null) ?{self::A} #t11 as{TypeError,ForNonNullableByDefault} self::A : #t11{self::A};
             break #L4;
           }
           else {
-            final asy::Future<self::B?> #t14 = let final<BottomType> #t15 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:45:18: Error: A value of type 'Future<B?>' can't be returned from an async function with return type 'FutureOr<A>'.
+            :return_value = let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:45:18: Error: A value of type 'Future<B?>' can't be returned from an async function with return type 'FutureOr<A>'.
  - 'Future' is from 'dart:async'.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
       return new Future<B?>.value(x); // Error.
                  ^" in asy::Future::value<self::B?>(x) as{TypeError,ForNonNullableByDefault} self::A;
-            if(#t14 is asy::Future<self::A>) {
-              [yield] let dynamic #t16 = asy::_awaitHelper(#t14, :async_op_then, :async_op_error, :async_op) in null;
-              :async_temporary_2 = _in::unsafeCast<self::B?>(:result);
-            }
-            else {
-              :async_temporary_2 = #t14;
-            }
-            :return_value = :async_temporary_2;
             break #L4;
           }
         }
@@ -335,20 +314,20 @@
     :is_sync = true;
     return :async_future;
   }
-  return let final<BottomType> #t17 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:49:10: Error: A value of type 'B?' can't be returned from a function with return type 'A' because 'B?' is nullable and 'A' isn't.
+  return let final<BottomType> #t13 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:49:10: Error: A value of type 'B?' can't be returned from a function with return type 'A' because 'B?' is nullable and 'A' isn't.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   return x; // Error.
-         ^" in let self::B? #t18 = x in #t18.==(null) ?{self::A} #t18 as{TypeError,ForNonNullableByDefault} self::A : #t18{self::A};
+         ^" in let self::B? #t14 = x in #t14.==(null) ?{self::A} #t14 as{TypeError,ForNonNullableByDefault} self::A : #t14{self::A};
 }
 static method bar(core::List<self::B?> x, core::List<core::List<self::B?>> l, core::Map<core::List<self::B?>, core::List<self::B?>> m) → core::List<self::A> {
-  self::barContext(let final<BottomType> #t19 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:53:14: Error: The argument type 'List<B?>' can't be assigned to the parameter type 'List<A>' because 'B?' is nullable and 'A' isn't.
+  self::barContext(let final<BottomType> #t15 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:53:14: Error: The argument type 'List<B?>' can't be assigned to the parameter type 'List<A>' because 'B?' is nullable and 'A' isn't.
  - 'List' is from 'dart:core'.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   barContext(x); // Error.
              ^" in x as{TypeError,ForNonNullableByDefault} core::List<self::A>);
-  core::List<self::A> y = let final<BottomType> #t20 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:54:15: Error: A value of type 'List<B?>' can't be assigned to a variable of type 'List<A>' because 'B?' is nullable and 'A' isn't.
+  core::List<self::A> y = let final<BottomType> #t16 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:54:15: Error: A value of type 'List<B?>' can't be assigned to a variable of type 'List<A>' because 'B?' is nullable and 'A' isn't.
  - 'List' is from 'dart:core'.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
@@ -374,19 +353,19 @@
   {
     core::Iterator<core::List<self::B?>> :sync-for-iterator = l.{core::Iterable::iterator};
     for (; :sync-for-iterator.{core::Iterator::moveNext}(); ) {
-      final core::List<self::B?> #t21 = :sync-for-iterator.{core::Iterator::current};
+      final core::List<self::B?> #t17 = :sync-for-iterator.{core::Iterator::current};
       {
-        core::List<self::A> y = let final<BottomType> #t22 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:57:16: Error: A value of type 'List<B?>' can't be assigned to a variable of type 'List<A>' because 'B?' is nullable and 'A' isn't.
+        core::List<self::A> y = let final<BottomType> #t18 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:57:16: Error: A value of type 'List<B?>' can't be assigned to a variable of type 'List<A>' because 'B?' is nullable and 'A' isn't.
  - 'List' is from 'dart:core'.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
 Try changing the type of the variable.
   for (List<A> y in l) {} // Error.
-               ^" in #t21 as{TypeError,ForNonNullableByDefault} core::List<self::A>;
+               ^" in #t17 as{TypeError,ForNonNullableByDefault} core::List<self::A>;
       }
     }
   }
-  return let final<BottomType> #t23 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:58:10: Error: A value of type 'List<B?>' can't be returned from a function with return type 'List<A>' because 'B?' is nullable and 'A' isn't.
+  return let final<BottomType> #t19 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:58:10: Error: A value of type 'List<B?>' can't be returned from a function with return type 'List<A>' because 'B?' is nullable and 'A' isn't.
  - 'List' is from 'dart:core'.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
@@ -394,38 +373,38 @@
          ^" in x as{TypeError,ForNonNullableByDefault} core::List<self::A>;
 }
 static method baz(self::C c) → void {
-  self::bazContext(let final<BottomType> #t24 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:62:14: Error: The argument type 'num? Function()' can't be assigned to the parameter type 'num Function()' because 'num?' is nullable and 'num' isn't.
+  self::bazContext(let final<BottomType> #t20 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:62:14: Error: The argument type 'num? Function()' can't be assigned to the parameter type 'num Function()' because 'num?' is nullable and 'num' isn't.
   bazContext(c);
-             ^" in (let final self::C #t25 = c in #t25.==(null) ?{() → core::num?} null : #t25.{self::C::call}) as{TypeError,ForNonNullableByDefault} () → core::num);
+             ^" in (let final self::C #t21 = c in #t21.==(null) ?{() → core::num?} null : #t21.{self::C::call}) as{TypeError,ForNonNullableByDefault} () → core::num);
 }
 static method boz(Null x) → self::A {
-  self::fooContext(let final<BottomType> #t26 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:66:14: Error: The argument type 'Null' can't be assigned to the parameter type 'A' because 'A' is not nullable.
+  self::fooContext(let final<BottomType> #t22 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:66:14: Error: The argument type 'Null' can't be assigned to the parameter type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   fooContext(x); // Error.
-             ^" in let Null #t27 = x in #t27.==(null) ?{self::A} #t27 as{TypeError,ForNonNullableByDefault} self::A : #t27{self::A});
-  self::fooContext(let final<BottomType> #t28 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:67:14: Error: The value 'null' can't be assigned to the parameter type 'A' because 'A' is not nullable.
+             ^" in let Null #t23 = x in #t23.==(null) ?{self::A} #t23 as{TypeError,ForNonNullableByDefault} self::A : #t23{self::A});
+  self::fooContext(let final<BottomType> #t24 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:67:14: Error: The value 'null' can't be assigned to the parameter type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   fooContext(null); // Error.
-             ^" in let Null #t29 = null in #t29.==(null) ?{self::A} #t29 as{TypeError,ForNonNullableByDefault} self::A : #t29{self::A});
-  self::A a1 = let final<BottomType> #t30 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:68:10: Error: A value of type 'Null' can't be assigned to a variable of type 'A' because 'A' is not nullable.
+             ^" in let Null #t25 = null in #t25.==(null) ?{self::A} #t25 as{TypeError,ForNonNullableByDefault} self::A : #t25{self::A});
+  self::A a1 = let final<BottomType> #t26 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:68:10: Error: A value of type 'Null' can't be assigned to a variable of type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   A a1 = x; // Error.
-         ^" in let Null #t31 = x in #t31.==(null) ?{self::A} #t31 as{TypeError,ForNonNullableByDefault} self::A : #t31{self::A};
-  self::A a2 = let final<BottomType> #t32 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:69:10: Error: The value 'null' can't be assigned to a variable of type 'A' because 'A' is not nullable.
+         ^" in let Null #t27 = x in #t27.==(null) ?{self::A} #t27 as{TypeError,ForNonNullableByDefault} self::A : #t27{self::A};
+  self::A a2 = let final<BottomType> #t28 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:69:10: Error: The value 'null' can't be assigned to a variable of type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   A a2 = null; // Error.
-         ^" in let Null #t33 = null in #t33.==(null) ?{self::A} #t33 as{TypeError,ForNonNullableByDefault} self::A : #t33{self::A};
+         ^" in let Null #t29 = null in #t29.==(null) ?{self::A} #t29 as{TypeError,ForNonNullableByDefault} self::A : #t29{self::A};
   if(true) {
-    return let final<BottomType> #t34 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:71:12: Error: A value of type 'Null' can't be returned from a function with return type 'A' because 'A' is not nullable.
+    return let final<BottomType> #t30 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:71:12: Error: A value of type 'Null' can't be returned from a function with return type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
     return x; // Error.
-           ^" in let Null #t35 = x in #t35.==(null) ?{self::A} #t35 as{TypeError,ForNonNullableByDefault} self::A : #t35{self::A};
+           ^" in let Null #t31 = x in #t31.==(null) ?{self::A} #t31 as{TypeError,ForNonNullableByDefault} self::A : #t31{self::A};
   }
   else {
-    return let final<BottomType> #t36 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:73:12: Error: The value 'null' can't be returned from a function with return type 'A' because 'A' is not nullable.
+    return let final<BottomType> #t32 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:73:12: Error: The value 'null' can't be returned from a function with return type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
     return null; // Error.
-           ^" in let Null #t37 = null in #t37.==(null) ?{self::A} #t37 as{TypeError,ForNonNullableByDefault} self::A : #t37{self::A};
+           ^" in let Null #t33 = null in #t33.==(null) ?{self::A} #t33 as{TypeError,ForNonNullableByDefault} self::A : #t33{self::A};
   }
   function local() → FutureOr<self::A> /* originally async */ {
     final asy::_Future<self::A> :async_future = new asy::_Future::•<self::A>();
@@ -435,43 +414,23 @@
     (core::Object, core::StackTrace) → dynamic :async_op_error;
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
-    dynamic :saved_try_context_var0;
-    FutureOr<self::A>:async_temporary_0;
-    FutureOr<self::A>:async_temporary_1;
-    FutureOr<self::A>:async_temporary_2;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L5:
         {
           if(true) {
-            final Null #t38 = let final<BottomType> #t39 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:77:14: Error: The value 'null' can't be returned from an async function with return type 'FutureOr<A>' because 'FutureOr<A>' is not nullable.
+            :return_value = let final<BottomType> #t34 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:77:14: Error: The value 'null' can't be returned from an async function with return type 'FutureOr<A>' because 'FutureOr<A>' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
       return null; // Error.
-             ^" in let Null #t40 = null in #t40.==(null) ?{self::A} #t40 as{TypeError,ForNonNullableByDefault} self::A : #t40{self::A};
-            if(#t38 is asy::Future<self::A>) {
-              [yield] let dynamic #t41 = asy::_awaitHelper(#t38, :async_op_then, :async_op_error, :async_op) in null;
-              :async_temporary_0 = _in::unsafeCast<Null>(:result);
-            }
-            else {
-              :async_temporary_0 = #t38;
-            }
-            :return_value = :async_temporary_0;
+             ^" in let Null #t35 = null in #t35.==(null) ?{self::A} #t35 as{TypeError,ForNonNullableByDefault} self::A : #t35{self::A};
             break #L5;
           }
           else {
-            final asy::Future<Null> #t42 = let final<BottomType> #t43 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:79:18: Error: A value of type 'Future<Null>' can't be returned from an async function with return type 'FutureOr<A>'.
+            :return_value = let final<BottomType> #t36 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:79:18: Error: A value of type 'Future<Null>' can't be returned from an async function with return type 'FutureOr<A>'.
  - 'Future' is from 'dart:async'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
       return new Future<Null>.value(null); // Error.
                  ^" in asy::Future::value<Null>(null) as{TypeError,ForNonNullableByDefault} self::A;
-            if(#t42 is asy::Future<self::A>) {
-              [yield] let dynamic #t44 = asy::_awaitHelper(#t42, :async_op_then, :async_op_error, :async_op) in null;
-              :async_temporary_2 = _in::unsafeCast<Null>(:result);
-            }
-            else {
-              :async_temporary_2 = #t42;
-            }
-            :return_value = :async_temporary_2;
             break #L5;
           }
         }
@@ -507,7 +466,7 @@
 Evaluated: MethodInvocation @ org-dartlang-testcase:///assignability_error_messages.dart:77:14 -> BoolConstant(true)
 Evaluated: VariableGet @ org-dartlang-testcase:///assignability_error_messages.dart:77:14 -> NullConstant(null)
 Evaluated: VariableGet @ org-dartlang-testcase:///assignability_error_messages.dart:77:14 -> NullConstant(null)
-Extra constant evaluation: evaluated: 266, effectively constant: 12
+Extra constant evaluation: evaluated: 210, effectively constant: 12
 
 
 Constructor coverage from constants:
diff --git a/pkg/front_end/testcases/nnbd/assignability_error_messages.dart.weak.expect b/pkg/front_end/testcases/nnbd/assignability_error_messages.dart.weak.expect
index 6769397..0e66be9 100644
--- a/pkg/front_end/testcases/nnbd/assignability_error_messages.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/assignability_error_messages.dart.weak.expect
@@ -263,35 +263,35 @@
   }
   function local() → FutureOr<self::A> async {
     if(true) {
-      return let final self::B? #t6 = let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:43:14: Error: A value of type 'B?' can't be returned from an async function with return type 'FutureOr<A>' because 'B?' is nullable and 'FutureOr<A>' isn't.
+      return let final<BottomType> #t6 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:43:14: Error: A value of type 'B?' can't be returned from an async function with return type 'FutureOr<A>' because 'B?' is nullable and 'FutureOr<A>' isn't.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
       return x; // Error.
-             ^" in x as{TypeError,ForNonNullableByDefault} self::A in #t6 is asy::Future<self::A> ?{FutureOr<self::A>} await #t6 : #t6;
+             ^" in x as{TypeError,ForNonNullableByDefault} self::A;
     }
     else {
-      return let final asy::Future<self::B?> #t8 = let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:45:18: Error: A value of type 'Future<B?>' can't be returned from an async function with return type 'FutureOr<A>'.
+      return let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:45:18: Error: A value of type 'Future<B?>' can't be returned from an async function with return type 'FutureOr<A>'.
  - 'Future' is from 'dart:async'.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
       return new Future<B?>.value(x); // Error.
-                 ^" in asy::Future::value<self::B?>(x) as{TypeError,ForNonNullableByDefault} self::A in #t8 is asy::Future<self::A> ?{FutureOr<self::A>} await #t8 : #t8;
+                 ^" in asy::Future::value<self::B?>(x) as{TypeError,ForNonNullableByDefault} self::A;
     }
   }
-  return let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:49:10: Error: A value of type 'B?' can't be returned from a function with return type 'A' because 'B?' is nullable and 'A' isn't.
+  return let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:49:10: Error: A value of type 'B?' can't be returned from a function with return type 'A' because 'B?' is nullable and 'A' isn't.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   return x; // Error.
          ^" in x as{TypeError,ForNonNullableByDefault} self::A;
 }
 static method bar(core::List<self::B?> x, core::List<core::List<self::B?>> l, core::Map<core::List<self::B?>, core::List<self::B?>> m) → core::List<self::A> {
-  self::barContext(let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:53:14: Error: The argument type 'List<B?>' can't be assigned to the parameter type 'List<A>' because 'B?' is nullable and 'A' isn't.
+  self::barContext(let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:53:14: Error: The argument type 'List<B?>' can't be assigned to the parameter type 'List<A>' because 'B?' is nullable and 'A' isn't.
  - 'List' is from 'dart:core'.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   barContext(x); // Error.
              ^" in x as{TypeError,ForNonNullableByDefault} core::List<self::A>);
-  core::List<self::A> y = let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:54:15: Error: A value of type 'List<B?>' can't be assigned to a variable of type 'List<A>' because 'B?' is nullable and 'A' isn't.
+  core::List<self::A> y = let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:54:15: Error: A value of type 'List<B?>' can't be assigned to a variable of type 'List<A>' because 'B?' is nullable and 'A' isn't.
  - 'List' is from 'dart:core'.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
@@ -314,16 +314,16 @@
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   <List<A>, List<A>>{...m}; // Error.
                         ^"};
-  for (final core::List<self::B?> #t13 in l) {
-    core::List<self::A> y = let final<BottomType> #t14 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:57:16: Error: A value of type 'List<B?>' can't be assigned to a variable of type 'List<A>' because 'B?' is nullable and 'A' isn't.
+  for (final core::List<self::B?> #t11 in l) {
+    core::List<self::A> y = let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:57:16: Error: A value of type 'List<B?>' can't be assigned to a variable of type 'List<A>' because 'B?' is nullable and 'A' isn't.
  - 'List' is from 'dart:core'.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
 Try changing the type of the variable.
   for (List<A> y in l) {} // Error.
-               ^" in #t13 as{TypeError,ForNonNullableByDefault} core::List<self::A>;
+               ^" in #t11 as{TypeError,ForNonNullableByDefault} core::List<self::A>;
   }
-  return let final<BottomType> #t15 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:58:10: Error: A value of type 'List<B?>' can't be returned from a function with return type 'List<A>' because 'B?' is nullable and 'A' isn't.
+  return let final<BottomType> #t13 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:58:10: Error: A value of type 'List<B?>' can't be returned from a function with return type 'List<A>' because 'B?' is nullable and 'A' isn't.
  - 'List' is from 'dart:core'.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
@@ -331,52 +331,52 @@
          ^" in x as{TypeError,ForNonNullableByDefault} core::List<self::A>;
 }
 static method baz(self::C c) → void {
-  self::bazContext(let final<BottomType> #t16 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:62:14: Error: The argument type 'num? Function()' can't be assigned to the parameter type 'num Function()' because 'num?' is nullable and 'num' isn't.
+  self::bazContext(let final<BottomType> #t14 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:62:14: Error: The argument type 'num? Function()' can't be assigned to the parameter type 'num Function()' because 'num?' is nullable and 'num' isn't.
   bazContext(c);
-             ^" in (let final self::C #t17 = c in #t17.==(null) ?{() → core::num?} null : #t17.{self::C::call}) as{TypeError,ForNonNullableByDefault} () → core::num);
+             ^" in (let final self::C #t15 = c in #t15.==(null) ?{() → core::num?} null : #t15.{self::C::call}) as{TypeError,ForNonNullableByDefault} () → core::num);
 }
 static method boz(Null x) → self::A {
-  self::fooContext(let final<BottomType> #t18 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:66:14: Error: The argument type 'Null' can't be assigned to the parameter type 'A' because 'A' is not nullable.
+  self::fooContext(let final<BottomType> #t16 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:66:14: Error: The argument type 'Null' can't be assigned to the parameter type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   fooContext(x); // Error.
              ^" in x as{TypeError,ForNonNullableByDefault} self::A);
-  self::fooContext(let final<BottomType> #t19 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:67:14: Error: The value 'null' can't be assigned to the parameter type 'A' because 'A' is not nullable.
+  self::fooContext(let final<BottomType> #t17 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:67:14: Error: The value 'null' can't be assigned to the parameter type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   fooContext(null); // Error.
              ^" in null as{TypeError,ForNonNullableByDefault} self::A);
-  self::A a1 = let final<BottomType> #t20 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:68:10: Error: A value of type 'Null' can't be assigned to a variable of type 'A' because 'A' is not nullable.
+  self::A a1 = let final<BottomType> #t18 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:68:10: Error: A value of type 'Null' can't be assigned to a variable of type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   A a1 = x; // Error.
          ^" in x as{TypeError,ForNonNullableByDefault} self::A;
-  self::A a2 = let final<BottomType> #t21 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:69:10: Error: The value 'null' can't be assigned to a variable of type 'A' because 'A' is not nullable.
+  self::A a2 = let final<BottomType> #t19 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:69:10: Error: The value 'null' can't be assigned to a variable of type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   A a2 = null; // Error.
          ^" in null as{TypeError,ForNonNullableByDefault} self::A;
   if(true) {
-    return let final<BottomType> #t22 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:71:12: Error: A value of type 'Null' can't be returned from a function with return type 'A' because 'A' is not nullable.
+    return let final<BottomType> #t20 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:71:12: Error: A value of type 'Null' can't be returned from a function with return type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
     return x; // Error.
            ^" in x as{TypeError,ForNonNullableByDefault} self::A;
   }
   else {
-    return let final<BottomType> #t23 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:73:12: Error: The value 'null' can't be returned from a function with return type 'A' because 'A' is not nullable.
+    return let final<BottomType> #t21 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:73:12: Error: The value 'null' can't be returned from a function with return type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
     return null; // Error.
            ^" in null as{TypeError,ForNonNullableByDefault} self::A;
   }
   function local() → FutureOr<self::A> async {
     if(true) {
-      return let final Null #t24 = let final<BottomType> #t25 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:77:14: Error: The value 'null' can't be returned from an async function with return type 'FutureOr<A>' because 'FutureOr<A>' is not nullable.
+      return let final<BottomType> #t22 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:77:14: Error: The value 'null' can't be returned from an async function with return type 'FutureOr<A>' because 'FutureOr<A>' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
       return null; // Error.
-             ^" in null as{TypeError,ForNonNullableByDefault} self::A in #t24 is asy::Future<self::A> ?{FutureOr<self::A>} await #t24 : #t24;
+             ^" in null as{TypeError,ForNonNullableByDefault} self::A;
     }
     else {
-      return let final asy::Future<Null> #t26 = let final<BottomType> #t27 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:79:18: Error: A value of type 'Future<Null>' can't be returned from an async function with return type 'FutureOr<A>'.
+      return let final<BottomType> #t23 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:79:18: Error: A value of type 'Future<Null>' can't be returned from an async function with return type 'FutureOr<A>'.
  - 'Future' is from 'dart:async'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
       return new Future<Null>.value(null); // Error.
-                 ^" in asy::Future::value<Null>(null) as{TypeError,ForNonNullableByDefault} self::A in #t26 is asy::Future<self::A> ?{FutureOr<self::A>} await #t26 : #t26;
+                 ^" in asy::Future::value<Null>(null) as{TypeError,ForNonNullableByDefault} self::A;
     }
   }
 }
diff --git a/pkg/front_end/testcases/nnbd/assignability_error_messages.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/assignability_error_messages.dart.weak.transformed.expect
index 242b2b4..4ba3fa1 100644
--- a/pkg/front_end/testcases/nnbd/assignability_error_messages.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/assignability_error_messages.dart.weak.transformed.expect
@@ -180,7 +180,6 @@
 import self as self;
 import "dart:core" as core;
 import "dart:async" as asy;
-import "dart:_internal" as _in;
 
 import "dart:async";
 
@@ -281,45 +280,25 @@
     (core::Object, core::StackTrace) → dynamic :async_op_error;
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
-    dynamic :saved_try_context_var0;
-    FutureOr<self::A>:async_temporary_0;
-    FutureOr<self::A>:async_temporary_1;
-    FutureOr<self::A>:async_temporary_2;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L4:
         {
           if(true) {
-            final self::B? #t6 = let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:43:14: Error: A value of type 'B?' can't be returned from an async function with return type 'FutureOr<A>' because 'B?' is nullable and 'FutureOr<A>' isn't.
+            :return_value = let final<BottomType> #t6 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:43:14: Error: A value of type 'B?' can't be returned from an async function with return type 'FutureOr<A>' because 'B?' is nullable and 'FutureOr<A>' isn't.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
       return x; // Error.
              ^" in x;
-            if(#t6 is asy::Future<self::A>) {
-              [yield] let dynamic #t8 = asy::_awaitHelper(#t6, :async_op_then, :async_op_error, :async_op) in null;
-              :async_temporary_0 = _in::unsafeCast<self::B?>(:result);
-            }
-            else {
-              :async_temporary_0 = #t6;
-            }
-            :return_value = :async_temporary_0;
             break #L4;
           }
           else {
-            final asy::Future<self::B?> #t9 = let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:45:18: Error: A value of type 'Future<B?>' can't be returned from an async function with return type 'FutureOr<A>'.
+            :return_value = let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:45:18: Error: A value of type 'Future<B?>' can't be returned from an async function with return type 'FutureOr<A>'.
  - 'Future' is from 'dart:async'.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
       return new Future<B?>.value(x); // Error.
                  ^" in asy::Future::value<self::B?>(x) as{TypeError,ForNonNullableByDefault} self::A;
-            if(#t9 is asy::Future<self::A>) {
-              [yield] let dynamic #t11 = asy::_awaitHelper(#t9, :async_op_then, :async_op_error, :async_op) in null;
-              :async_temporary_2 = _in::unsafeCast<self::B?>(:result);
-            }
-            else {
-              :async_temporary_2 = #t9;
-            }
-            :return_value = :async_temporary_2;
             break #L4;
           }
         }
@@ -335,20 +314,20 @@
     :is_sync = true;
     return :async_future;
   }
-  return let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:49:10: Error: A value of type 'B?' can't be returned from a function with return type 'A' because 'B?' is nullable and 'A' isn't.
+  return let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:49:10: Error: A value of type 'B?' can't be returned from a function with return type 'A' because 'B?' is nullable and 'A' isn't.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   return x; // Error.
          ^" in x;
 }
 static method bar(core::List<self::B?> x, core::List<core::List<self::B?>> l, core::Map<core::List<self::B?>, core::List<self::B?>> m) → core::List<self::A> {
-  self::barContext(let final<BottomType> #t13 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:53:14: Error: The argument type 'List<B?>' can't be assigned to the parameter type 'List<A>' because 'B?' is nullable and 'A' isn't.
+  self::barContext(let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:53:14: Error: The argument type 'List<B?>' can't be assigned to the parameter type 'List<A>' because 'B?' is nullable and 'A' isn't.
  - 'List' is from 'dart:core'.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   barContext(x); // Error.
              ^" in x);
-  core::List<self::A> y = let final<BottomType> #t14 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:54:15: Error: A value of type 'List<B?>' can't be assigned to a variable of type 'List<A>' because 'B?' is nullable and 'A' isn't.
+  core::List<self::A> y = let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:54:15: Error: A value of type 'List<B?>' can't be assigned to a variable of type 'List<A>' because 'B?' is nullable and 'A' isn't.
  - 'List' is from 'dart:core'.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
@@ -374,19 +353,19 @@
   {
     core::Iterator<core::List<self::B?>> :sync-for-iterator = l.{core::Iterable::iterator};
     for (; :sync-for-iterator.{core::Iterator::moveNext}(); ) {
-      final core::List<self::B?> #t15 = :sync-for-iterator.{core::Iterator::current};
+      final core::List<self::B?> #t11 = :sync-for-iterator.{core::Iterator::current};
       {
-        core::List<self::A> y = let final<BottomType> #t16 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:57:16: Error: A value of type 'List<B?>' can't be assigned to a variable of type 'List<A>' because 'B?' is nullable and 'A' isn't.
+        core::List<self::A> y = let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:57:16: Error: A value of type 'List<B?>' can't be assigned to a variable of type 'List<A>' because 'B?' is nullable and 'A' isn't.
  - 'List' is from 'dart:core'.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
 Try changing the type of the variable.
   for (List<A> y in l) {} // Error.
-               ^" in #t15;
+               ^" in #t11;
       }
     }
   }
-  return let final<BottomType> #t17 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:58:10: Error: A value of type 'List<B?>' can't be returned from a function with return type 'List<A>' because 'B?' is nullable and 'A' isn't.
+  return let final<BottomType> #t13 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:58:10: Error: A value of type 'List<B?>' can't be returned from a function with return type 'List<A>' because 'B?' is nullable and 'A' isn't.
  - 'List' is from 'dart:core'.
  - 'B' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
@@ -394,35 +373,35 @@
          ^" in x;
 }
 static method baz(self::C c) → void {
-  self::bazContext(let final<BottomType> #t18 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:62:14: Error: The argument type 'num? Function()' can't be assigned to the parameter type 'num Function()' because 'num?' is nullable and 'num' isn't.
+  self::bazContext(let final<BottomType> #t14 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:62:14: Error: The argument type 'num? Function()' can't be assigned to the parameter type 'num Function()' because 'num?' is nullable and 'num' isn't.
   bazContext(c);
-             ^" in let final self::C #t19 = c in #t19.==(null) ?{() → core::num?} null : #t19.{self::C::call});
+             ^" in let final self::C #t15 = c in #t15.==(null) ?{() → core::num?} null : #t15.{self::C::call});
 }
 static method boz(Null x) → self::A {
-  self::fooContext(let final<BottomType> #t20 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:66:14: Error: The argument type 'Null' can't be assigned to the parameter type 'A' because 'A' is not nullable.
+  self::fooContext(let final<BottomType> #t16 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:66:14: Error: The argument type 'Null' can't be assigned to the parameter type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   fooContext(x); // Error.
              ^" in x);
-  self::fooContext(let final<BottomType> #t21 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:67:14: Error: The value 'null' can't be assigned to the parameter type 'A' because 'A' is not nullable.
+  self::fooContext(let final<BottomType> #t17 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:67:14: Error: The value 'null' can't be assigned to the parameter type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   fooContext(null); // Error.
              ^" in null);
-  self::A a1 = let final<BottomType> #t22 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:68:10: Error: A value of type 'Null' can't be assigned to a variable of type 'A' because 'A' is not nullable.
+  self::A a1 = let final<BottomType> #t18 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:68:10: Error: A value of type 'Null' can't be assigned to a variable of type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   A a1 = x; // Error.
          ^" in x;
-  self::A a2 = let final<BottomType> #t23 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:69:10: Error: The value 'null' can't be assigned to a variable of type 'A' because 'A' is not nullable.
+  self::A a2 = let final<BottomType> #t19 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:69:10: Error: The value 'null' can't be assigned to a variable of type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
   A a2 = null; // Error.
          ^" in null;
   if(true) {
-    return let final<BottomType> #t24 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:71:12: Error: A value of type 'Null' can't be returned from a function with return type 'A' because 'A' is not nullable.
+    return let final<BottomType> #t20 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:71:12: Error: A value of type 'Null' can't be returned from a function with return type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
     return x; // Error.
            ^" in x;
   }
   else {
-    return let final<BottomType> #t25 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:73:12: Error: The value 'null' can't be returned from a function with return type 'A' because 'A' is not nullable.
+    return let final<BottomType> #t21 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:73:12: Error: The value 'null' can't be returned from a function with return type 'A' because 'A' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
     return null; // Error.
            ^" in null;
@@ -435,43 +414,23 @@
     (core::Object, core::StackTrace) → dynamic :async_op_error;
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
-    dynamic :saved_try_context_var0;
-    FutureOr<self::A>:async_temporary_0;
-    FutureOr<self::A>:async_temporary_1;
-    FutureOr<self::A>:async_temporary_2;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L5:
         {
           if(true) {
-            final Null #t26 = let final<BottomType> #t27 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:77:14: Error: The value 'null' can't be returned from an async function with return type 'FutureOr<A>' because 'FutureOr<A>' is not nullable.
+            :return_value = let final<BottomType> #t22 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:77:14: Error: The value 'null' can't be returned from an async function with return type 'FutureOr<A>' because 'FutureOr<A>' is not nullable.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
       return null; // Error.
              ^" in null;
-            if(#t26 is asy::Future<self::A>) {
-              [yield] let dynamic #t28 = asy::_awaitHelper(#t26, :async_op_then, :async_op_error, :async_op) in null;
-              :async_temporary_0 = _in::unsafeCast<Null>(:result);
-            }
-            else {
-              :async_temporary_0 = #t26;
-            }
-            :return_value = :async_temporary_0;
             break #L5;
           }
           else {
-            final asy::Future<Null> #t29 = let final<BottomType> #t30 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:79:18: Error: A value of type 'Future<Null>' can't be returned from an async function with return type 'FutureOr<A>'.
+            :return_value = let final<BottomType> #t23 = invalid-expression "pkg/front_end/testcases/nnbd/assignability_error_messages.dart:79:18: Error: A value of type 'Future<Null>' can't be returned from an async function with return type 'FutureOr<A>'.
  - 'Future' is from 'dart:async'.
  - 'A' is from 'pkg/front_end/testcases/nnbd/assignability_error_messages.dart'.
       return new Future<Null>.value(null); // Error.
                  ^" in asy::Future::value<Null>(null) as{TypeError,ForNonNullableByDefault} self::A;
-            if(#t29 is asy::Future<self::A>) {
-              [yield] let dynamic #t31 = asy::_awaitHelper(#t29, :async_op_then, :async_op_error, :async_op) in null;
-              :async_temporary_2 = _in::unsafeCast<Null>(:result);
-            }
-            else {
-              :async_temporary_2 = #t29;
-            }
-            :return_value = :async_temporary_2;
             break #L5;
           }
         }
diff --git a/pkg/front_end/testcases/nnbd/flutter_issue64155.dart.strong.expect b/pkg/front_end/testcases/nnbd/flutter_issue64155.dart.strong.expect
index bda20dd..f39bdfbd 100644
--- a/pkg/front_end/testcases/nnbd/flutter_issue64155.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/flutter_issue64155.dart.strong.expect
@@ -21,7 +21,7 @@
         else {
           throw core::Exception::•("Invalid response type");
         }
-    return let final self::TestMixin::T% #t1 = result in #t1 is asy::Future<self::TestMixin::T%> ?{FutureOr<self::TestMixin::T%>} await #t1 : #t1;
+    return result;
   }
 }
 class PagingResponse<T extends core::Object? = dynamic> extends core::Object {
diff --git a/pkg/front_end/testcases/nnbd/flutter_issue64155.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/flutter_issue64155.dart.strong.transformed.expect
index e23e8dd..76b3473 100644
--- a/pkg/front_end/testcases/nnbd/flutter_issue64155.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/flutter_issue64155.dart.strong.transformed.expect
@@ -14,7 +14,6 @@
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
     dynamic :saved_try_context_var0;
-    FutureOr<self::TestMixin::T%>:async_temporary_0;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L1:
@@ -36,15 +35,7 @@
               else {
                 throw core::Exception::•("Invalid response type");
               }
-          final self::TestMixin::T% #t2 = result;
-          if(#t2 is asy::Future<self::TestMixin::T%>) {
-            [yield] let dynamic #t3 = asy::_awaitHelper(#t2, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<self::TestMixin::T%>(:result);
-          }
-          else {
-            :async_temporary_0 = #t2;
-          }
-          :return_value = :async_temporary_0;
+          :return_value = result;
           break #L1;
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -91,12 +82,11 @@
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
     dynamic :saved_try_context_var0;
-    FutureOr<core::String>:async_temporary_0;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L2:
         {
-          [yield] let dynamic #t4 = asy::_awaitHelper(fetch, :async_op_then, :async_op_error, :async_op) in null;
+          [yield] let dynamic #t2 = asy::_awaitHelper(fetch, :async_op_then, :async_op_error, :async_op) in null;
           final self::Response<core::String> response = _in::unsafeCast<self::Response<core::String>>(:result);
           core::String result;
           if(response is{ForNonNullableByDefault} self::Response<dynamic>) {
@@ -113,15 +103,7 @@
               else {
                 throw core::Exception::•("Invalid response type");
               }
-          final core::String #t5 = result;
-          if(#t5 is asy::Future<core::String>) {
-            [yield] let dynamic #t6 = asy::_awaitHelper(#t5, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::String>(:result);
-          }
-          else {
-            :async_temporary_0 = #t5;
-          }
-          :return_value = :async_temporary_0;
+          :return_value = result;
           break #L2;
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -159,12 +141,11 @@
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
     dynamic :saved_try_context_var0;
-    FutureOr<core::String>:async_temporary_0;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L3:
         {
-          [yield] let dynamic #t7 = asy::_awaitHelper(fetch, :async_op_then, :async_op_error, :async_op) in null;
+          [yield] let dynamic #t3 = asy::_awaitHelper(fetch, :async_op_then, :async_op_error, :async_op) in null;
           final self::PagingResponse<core::String> response = _in::unsafeCast<self::PagingResponse<core::String>>(:result);
           core::String result;
           if(response is{ForNonNullableByDefault} self::Response<dynamic>) {
@@ -181,15 +162,7 @@
               else {
                 throw core::Exception::•("Invalid response type");
               }
-          final core::String #t8 = result;
-          if(#t8 is asy::Future<core::String>) {
-            [yield] let dynamic #t9 = asy::_awaitHelper(#t8, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::String>(:result);
-          }
-          else {
-            :async_temporary_0 = #t8;
-          }
-          :return_value = :async_temporary_0;
+          :return_value = result;
           break #L3;
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
diff --git a/pkg/front_end/testcases/nnbd/flutter_issue64155.dart.weak.expect b/pkg/front_end/testcases/nnbd/flutter_issue64155.dart.weak.expect
index bda20dd..f39bdfbd 100644
--- a/pkg/front_end/testcases/nnbd/flutter_issue64155.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/flutter_issue64155.dart.weak.expect
@@ -21,7 +21,7 @@
         else {
           throw core::Exception::•("Invalid response type");
         }
-    return let final self::TestMixin::T% #t1 = result in #t1 is asy::Future<self::TestMixin::T%> ?{FutureOr<self::TestMixin::T%>} await #t1 : #t1;
+    return result;
   }
 }
 class PagingResponse<T extends core::Object? = dynamic> extends core::Object {
diff --git a/pkg/front_end/testcases/nnbd/flutter_issue64155.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/flutter_issue64155.dart.weak.transformed.expect
index e23e8dd..76b3473 100644
--- a/pkg/front_end/testcases/nnbd/flutter_issue64155.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/flutter_issue64155.dart.weak.transformed.expect
@@ -14,7 +14,6 @@
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
     dynamic :saved_try_context_var0;
-    FutureOr<self::TestMixin::T%>:async_temporary_0;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L1:
@@ -36,15 +35,7 @@
               else {
                 throw core::Exception::•("Invalid response type");
               }
-          final self::TestMixin::T% #t2 = result;
-          if(#t2 is asy::Future<self::TestMixin::T%>) {
-            [yield] let dynamic #t3 = asy::_awaitHelper(#t2, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<self::TestMixin::T%>(:result);
-          }
-          else {
-            :async_temporary_0 = #t2;
-          }
-          :return_value = :async_temporary_0;
+          :return_value = result;
           break #L1;
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -91,12 +82,11 @@
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
     dynamic :saved_try_context_var0;
-    FutureOr<core::String>:async_temporary_0;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L2:
         {
-          [yield] let dynamic #t4 = asy::_awaitHelper(fetch, :async_op_then, :async_op_error, :async_op) in null;
+          [yield] let dynamic #t2 = asy::_awaitHelper(fetch, :async_op_then, :async_op_error, :async_op) in null;
           final self::Response<core::String> response = _in::unsafeCast<self::Response<core::String>>(:result);
           core::String result;
           if(response is{ForNonNullableByDefault} self::Response<dynamic>) {
@@ -113,15 +103,7 @@
               else {
                 throw core::Exception::•("Invalid response type");
               }
-          final core::String #t5 = result;
-          if(#t5 is asy::Future<core::String>) {
-            [yield] let dynamic #t6 = asy::_awaitHelper(#t5, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::String>(:result);
-          }
-          else {
-            :async_temporary_0 = #t5;
-          }
-          :return_value = :async_temporary_0;
+          :return_value = result;
           break #L2;
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -159,12 +141,11 @@
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
     dynamic :saved_try_context_var0;
-    FutureOr<core::String>:async_temporary_0;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L3:
         {
-          [yield] let dynamic #t7 = asy::_awaitHelper(fetch, :async_op_then, :async_op_error, :async_op) in null;
+          [yield] let dynamic #t3 = asy::_awaitHelper(fetch, :async_op_then, :async_op_error, :async_op) in null;
           final self::PagingResponse<core::String> response = _in::unsafeCast<self::PagingResponse<core::String>>(:result);
           core::String result;
           if(response is{ForNonNullableByDefault} self::Response<dynamic>) {
@@ -181,15 +162,7 @@
               else {
                 throw core::Exception::•("Invalid response type");
               }
-          final core::String #t8 = result;
-          if(#t8 is asy::Future<core::String>) {
-            [yield] let dynamic #t9 = asy::_awaitHelper(#t8, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::String>(:result);
-          }
-          else {
-            :async_temporary_0 = #t8;
-          }
-          :return_value = :async_temporary_0;
+          :return_value = result;
           break #L3;
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
diff --git a/pkg/front_end/testcases/nnbd/issue41156.dart.strong.expect b/pkg/front_end/testcases/nnbd/issue41156.dart.strong.expect
index ca6b488..11217a1 100644
--- a/pkg/front_end/testcases/nnbd/issue41156.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/issue41156.dart.strong.expect
@@ -55,19 +55,19 @@
   (core::int) → core::String x6 = (core::int v) → Never {
     return self::throwing();
   };
-  (core::int) → asy::Future<core::String> y1 = (core::int v) → asy::Future<Never> async => let final Never #t1 = throw v in #t1 is asy::Future<Never> ?{FutureOr<core::String>} await #t1 : #t1;
+  (core::int) → asy::Future<core::String> y1 = (core::int v) → asy::Future<Never> async => throw v;
   (core::int) → asy::Future<core::String> y2 = (core::int v) → asy::Future<Never> async {
     throw v;
   };
   (core::int) → asy::Future<core::String> y3 = (core::int v) → asy::Future<Never> async {
-    return let final Never #t2 = throw v in #t2 is asy::Future<Never> ?{FutureOr<core::String>} await #t2 : #t2;
+    return throw v;
   };
-  (core::int) → asy::Future<core::String> y4 = (core::int v) → asy::Future<Never> async => let final Never #t3 = self::throwing() in #t3 is asy::Future<Never> ?{FutureOr<core::String>} await #t3 : #t3;
+  (core::int) → asy::Future<core::String> y4 = (core::int v) → asy::Future<Never> async => self::throwing();
   (core::int) → asy::Future<core::String> y5 = (core::int v) → asy::Future<Never> async {
     self::throwing();
   };
   (core::int) → asy::Future<core::String> y6 = (core::int v) → asy::Future<Never> async {
-    return let final Never #t4 = self::throwing() in #t4 is asy::Future<Never> ?{FutureOr<core::String>} await #t4 : #t4;
+    return self::throwing();
   };
 }
 static method errors() → void async {
@@ -77,7 +77,7 @@
     }
     on core::Object catch(final core::Object _) {
     }
-    return let final<BottomType> #t5 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:39:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t1 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:39:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String Function(int) x2 = (int v) /* error */ {
                             ^" in null;
   };
@@ -87,7 +87,7 @@
     }
     on core::Object catch(final core::Object _) {
     }
-    return let final<BottomType> #t6 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:44:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t2 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:44:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String Function(int) x3 = (int v) /* error */ {
                             ^" in null;
   };
@@ -97,7 +97,7 @@
     }
     on core::Object catch(final core::Object _) {
     }
-    return let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:49:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:49:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String Function(int) x5 = (int v) /* error */ {
                             ^" in null;
   };
@@ -107,7 +107,7 @@
     }
     on core::Object catch(final core::Object _) {
     }
-    return let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:54:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t4 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:54:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String Function(int) x6 = (int v) /* error */ {
                             ^" in null;
   };
@@ -117,17 +117,17 @@
     }
     on core::Object catch(final core::Object _) {
     }
-    return let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:59:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t5 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:59:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   Future<String> Function(int) y2 = (int v) async /* error */ {
                                     ^" in null;
   };
   (core::int) → asy::Future<core::String> y3 = (core::int v) → asy::Future<core::String> async {
     try {
-      return let final Never #t10 = throw v in #t10 is asy::Future<core::String> ?{FutureOr<core::String>} await #t10 : #t10;
+      return throw v;
     }
     on core::Object catch(final core::Object _) {
     }
-    return let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:64:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t6 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:64:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   Future<String> Function(int) y3 = (int v) async /* error */ {
                                     ^" in null;
   };
@@ -137,17 +137,17 @@
     }
     on core::Object catch(final core::Object _) {
     }
-    return let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:69:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:69:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   Future<String> Function(int) y5 = (int v) async /* error */ {
                                     ^" in null;
   };
   (core::int) → asy::Future<core::String> y6 = (core::int v) → asy::Future<core::String> async {
     try {
-      return let final Never #t13 = self::throwing() in #t13 is asy::Future<core::String> ?{FutureOr<core::String>} await #t13 : #t13;
+      return self::throwing();
     }
     on core::Object catch(final core::Object _) {
     }
-    return let final<BottomType> #t14 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:74:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:74:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   Future<String> Function(int) y6 = (int v) async /* error */ {
                                     ^" in null;
   };
diff --git a/pkg/front_end/testcases/nnbd/issue41156.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/issue41156.dart.strong.transformed.expect
index 515ceec..3e9bef1 100644
--- a/pkg/front_end/testcases/nnbd/issue41156.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/issue41156.dart.strong.transformed.expect
@@ -37,7 +37,6 @@
 import self as self;
 import "dart:core" as core;
 import "dart:async" as asy;
-import "dart:_internal" as _in;
 
 static method throwing() → Never
   return throw "";
@@ -64,21 +63,11 @@
     (core::Object, core::StackTrace) → dynamic :async_op_error;
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
-    dynamic :saved_try_context_var0;
-    FutureOr<core::String>:async_temporary_0;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L1:
         {
-          final Never #t1 = throw v;
-          if(#t1 is asy::Future<Never>) {
-            [yield] let dynamic #t2 = asy::_awaitHelper(#t1, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<Never>(:result);
-          }
-          else {
-            :async_temporary_0 = #t1;
-          }
-          :return_value = :async_temporary_0;
+          :return_value = throw v;
           break #L1;
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -127,21 +116,11 @@
     (core::Object, core::StackTrace) → dynamic :async_op_error;
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
-    dynamic :saved_try_context_var0;
-    FutureOr<core::String>:async_temporary_0;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L3:
         {
-          final Never #t3 = throw v;
-          if(#t3 is asy::Future<Never>) {
-            [yield] let dynamic #t4 = asy::_awaitHelper(#t3, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<Never>(:result);
-          }
-          else {
-            :async_temporary_0 = #t3;
-          }
-          :return_value = :async_temporary_0;
+          :return_value = throw v;
           break #L3;
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -164,21 +143,11 @@
     (core::Object, core::StackTrace) → dynamic :async_op_error;
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
-    dynamic :saved_try_context_var0;
-    FutureOr<core::String>:async_temporary_0;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L4:
         {
-          final Never #t5 = self::throwing();
-          if(#t5 is asy::Future<Never>) {
-            [yield] let dynamic #t6 = asy::_awaitHelper(#t5, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<Never>(:result);
-          }
-          else {
-            :async_temporary_0 = #t5;
-          }
-          :return_value = :async_temporary_0;
+          :return_value = self::throwing();
           break #L4;
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -227,21 +196,11 @@
     (core::Object, core::StackTrace) → dynamic :async_op_error;
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
-    dynamic :saved_try_context_var0;
-    FutureOr<core::String>:async_temporary_0;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L6:
         {
-          final Never #t7 = self::throwing();
-          if(#t7 is asy::Future<Never>) {
-            [yield] let dynamic #t8 = asy::_awaitHelper(#t7, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<Never>(:result);
-          }
-          else {
-            :async_temporary_0 = #t7;
-          }
-          :return_value = :async_temporary_0;
+          :return_value = self::throwing();
           break #L6;
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -275,7 +234,7 @@
           }
           on core::Object catch(final core::Object _) {
           }
-          return let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:39:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+          return let final<BottomType> #t1 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:39:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String Function(int) x2 = (int v) /* error */ {
                             ^" in null;
         };
@@ -285,7 +244,7 @@
           }
           on core::Object catch(final core::Object _) {
           }
-          return let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:44:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+          return let final<BottomType> #t2 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:44:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String Function(int) x3 = (int v) /* error */ {
                             ^" in null;
         };
@@ -295,7 +254,7 @@
           }
           on core::Object catch(final core::Object _) {
           }
-          return let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:49:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+          return let final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:49:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String Function(int) x5 = (int v) /* error */ {
                             ^" in null;
         };
@@ -305,7 +264,7 @@
           }
           on core::Object catch(final core::Object _) {
           }
-          return let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:54:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+          return let final<BottomType> #t4 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:54:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String Function(int) x6 = (int v) /* error */ {
                             ^" in null;
         };
@@ -326,7 +285,7 @@
                 }
                 on core::Object catch(final core::Object _) {
                 }
-                :return_value = let final<BottomType> #t13 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:59:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+                :return_value = let final<BottomType> #t5 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:59:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   Future<String> Function(int) y2 = (int v) async /* error */ {
                                     ^" in null;
                 break #L8;
@@ -351,28 +310,17 @@
           (core::Object, core::StackTrace) → dynamic :async_op_error;
           core::int :await_jump_var = 0;
           dynamic :await_ctx_var;
-          dynamic :saved_try_context_var0;
-          dynamic :saved_try_context_var1;
-          FutureOr<core::String>:async_temporary_0;
           function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
             try {
               #L9:
               {
                 try {
-                  final Never #t14 = throw v;
-                  if(#t14 is asy::Future<core::String>) {
-                    [yield] let dynamic #t15 = asy::_awaitHelper(#t14, :async_op_then, :async_op_error, :async_op) in null;
-                    :async_temporary_0 = _in::unsafeCast<Never>(:result);
-                  }
-                  else {
-                    :async_temporary_0 = #t14;
-                  }
-                  :return_value = :async_temporary_0;
+                  :return_value = throw v;
                   break #L9;
                 }
                 on core::Object catch(final core::Object _) {
                 }
-                :return_value = let final<BottomType> #t16 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:64:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+                :return_value = let final<BottomType> #t6 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:64:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   Future<String> Function(int) y3 = (int v) async /* error */ {
                                     ^" in null;
                 break #L9;
@@ -406,7 +354,7 @@
                 }
                 on core::Object catch(final core::Object _) {
                 }
-                :return_value = let final<BottomType> #t17 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:69:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+                :return_value = let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:69:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   Future<String> Function(int) y5 = (int v) async /* error */ {
                                     ^" in null;
                 break #L10;
@@ -431,28 +379,17 @@
           (core::Object, core::StackTrace) → dynamic :async_op_error;
           core::int :await_jump_var = 0;
           dynamic :await_ctx_var;
-          dynamic :saved_try_context_var0;
-          dynamic :saved_try_context_var1;
-          FutureOr<core::String>:async_temporary_0;
           function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
             try {
               #L11:
               {
                 try {
-                  final Never #t18 = self::throwing();
-                  if(#t18 is asy::Future<core::String>) {
-                    [yield] let dynamic #t19 = asy::_awaitHelper(#t18, :async_op_then, :async_op_error, :async_op) in null;
-                    :async_temporary_0 = _in::unsafeCast<Never>(:result);
-                  }
-                  else {
-                    :async_temporary_0 = #t18;
-                  }
-                  :return_value = :async_temporary_0;
+                  :return_value = self::throwing();
                   break #L11;
                 }
                 on core::Object catch(final core::Object _) {
                 }
-                :return_value = let final<BottomType> #t20 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:74:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+                :return_value = let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:74:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   Future<String> Function(int) y6 = (int v) async /* error */ {
                                     ^" in null;
                 break #L11;
diff --git a/pkg/front_end/testcases/nnbd/issue41156.dart.weak.expect b/pkg/front_end/testcases/nnbd/issue41156.dart.weak.expect
index 344471e..3ced126 100644
--- a/pkg/front_end/testcases/nnbd/issue41156.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/issue41156.dart.weak.expect
@@ -56,19 +56,19 @@
   (core::int) → core::String x6 = (core::int v) → Never {
     return let final Never #t3 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
   };
-  (core::int) → asy::Future<core::String> y1 = (core::int v) → asy::Future<Never> async => let final Never #t4 = throw v in #t4 is asy::Future<Never> ?{FutureOr<core::String>} await #t4 : #t4;
+  (core::int) → asy::Future<core::String> y1 = (core::int v) → asy::Future<Never> async => throw v;
   (core::int) → asy::Future<core::String> y2 = (core::int v) → asy::Future<Never> async {
     throw v;
   };
   (core::int) → asy::Future<core::String> y3 = (core::int v) → asy::Future<Never> async {
-    return let final Never #t5 = throw v in #t5 is asy::Future<Never> ?{FutureOr<core::String>} await #t5 : #t5;
+    return throw v;
   };
-  (core::int) → asy::Future<core::String> y4 = (core::int v) → asy::Future<Never> async => let final Never #t6 = let final Never #t7 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.") in #t6 is asy::Future<Never> ?{FutureOr<core::String>} await #t6 : #t6;
+  (core::int) → asy::Future<core::String> y4 = (core::int v) → asy::Future<Never> async => let final Never #t4 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
   (core::int) → asy::Future<core::String> y5 = (core::int v) → asy::Future<Never> async {
-    let final Never #t8 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
+    let final Never #t5 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
   };
   (core::int) → asy::Future<core::String> y6 = (core::int v) → asy::Future<Never> async {
-    return let final Never #t9 = let final Never #t10 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.") in #t9 is asy::Future<Never> ?{FutureOr<core::String>} await #t9 : #t9;
+    return let final Never #t6 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
   };
 }
 static method errors() → void async {
@@ -78,7 +78,7 @@
     }
     on core::Object catch(final core::Object _) {
     }
-    return let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:39:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:39:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String Function(int) x2 = (int v) /* error */ {
                             ^" in null;
   };
@@ -88,27 +88,27 @@
     }
     on core::Object catch(final core::Object _) {
     }
-    return let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:44:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:44:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String Function(int) x3 = (int v) /* error */ {
                             ^" in null;
   };
   (core::int) → core::String x5 = (core::int v) → core::String {
     try {
-      let final Never #t13 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
+      let final Never #t9 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
     }
     on core::Object catch(final core::Object _) {
     }
-    return let final<BottomType> #t14 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:49:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:49:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String Function(int) x5 = (int v) /* error */ {
                             ^" in null;
   };
   (core::int) → core::String x6 = (core::int v) → core::String {
     try {
-      return let final Never #t15 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
+      return let final Never #t11 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
     }
     on core::Object catch(final core::Object _) {
     }
-    return let final<BottomType> #t16 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:54:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:54:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String Function(int) x6 = (int v) /* error */ {
                             ^" in null;
   };
@@ -118,37 +118,37 @@
     }
     on core::Object catch(final core::Object _) {
     }
-    return let final<BottomType> #t17 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:59:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t13 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:59:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   Future<String> Function(int) y2 = (int v) async /* error */ {
                                     ^" in null;
   };
   (core::int) → asy::Future<core::String> y3 = (core::int v) → asy::Future<core::String> async {
     try {
-      return let final Never #t18 = throw v in #t18 is asy::Future<core::String> ?{FutureOr<core::String>} await #t18 : #t18;
+      return throw v;
     }
     on core::Object catch(final core::Object _) {
     }
-    return let final<BottomType> #t19 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:64:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t14 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:64:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   Future<String> Function(int) y3 = (int v) async /* error */ {
                                     ^" in null;
   };
   (core::int) → asy::Future<core::String> y5 = (core::int v) → asy::Future<core::String> async {
     try {
-      let final Never #t20 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
+      let final Never #t15 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
     }
     on core::Object catch(final core::Object _) {
     }
-    return let final<BottomType> #t21 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:69:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t16 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:69:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   Future<String> Function(int) y5 = (int v) async /* error */ {
                                     ^" in null;
   };
   (core::int) → asy::Future<core::String> y6 = (core::int v) → asy::Future<core::String> async {
     try {
-      return let final Never #t22 = let final Never #t23 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.") in #t22 is asy::Future<core::String> ?{FutureOr<core::String>} await #t22 : #t22;
+      return let final Never #t17 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
     }
     on core::Object catch(final core::Object _) {
     }
-    return let final<BottomType> #t24 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:74:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t18 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:74:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   Future<String> Function(int) y6 = (int v) async /* error */ {
                                     ^" in null;
   };
diff --git a/pkg/front_end/testcases/nnbd/issue41156.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/issue41156.dart.weak.transformed.expect
index 5ebb180..e3ff8f7 100644
--- a/pkg/front_end/testcases/nnbd/issue41156.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/issue41156.dart.weak.transformed.expect
@@ -64,21 +64,11 @@
     (core::Object, core::StackTrace) → dynamic :async_op_error;
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
-    dynamic :saved_try_context_var0;
-    FutureOr<core::String>:async_temporary_0;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L1:
         {
-          final Never #t4 = throw v;
-          if(#t4 is asy::Future<Never>) {
-            [yield] let dynamic #t5 = asy::_awaitHelper(#t4, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<Never>(:result);
-          }
-          else {
-            :async_temporary_0 = #t4;
-          }
-          :return_value = :async_temporary_0;
+          :return_value = throw v;
           break #L1;
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -127,21 +117,11 @@
     (core::Object, core::StackTrace) → dynamic :async_op_error;
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
-    dynamic :saved_try_context_var0;
-    FutureOr<core::String>:async_temporary_0;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L3:
         {
-          final Never #t6 = throw v;
-          if(#t6 is asy::Future<Never>) {
-            [yield] let dynamic #t7 = asy::_awaitHelper(#t6, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<Never>(:result);
-          }
-          else {
-            :async_temporary_0 = #t6;
-          }
-          :return_value = :async_temporary_0;
+          :return_value = throw v;
           break #L3;
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -164,21 +144,11 @@
     (core::Object, core::StackTrace) → dynamic :async_op_error;
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
-    dynamic :saved_try_context_var0;
-    FutureOr<core::String>:async_temporary_0;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L4:
         {
-          final Never #t8 = let final Never #t9 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
-          if(#t8 is asy::Future<Never>) {
-            [yield] let dynamic #t10 = asy::_awaitHelper(#t8, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<Never>(:result);
-          }
-          else {
-            :async_temporary_0 = #t8;
-          }
-          :return_value = :async_temporary_0;
+          :return_value = let final Never #t4 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
           break #L4;
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -205,7 +175,7 @@
       try {
         #L5:
         {
-          let final Never #t11 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
+          let final Never #t5 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
         return;
@@ -227,21 +197,11 @@
     (core::Object, core::StackTrace) → dynamic :async_op_error;
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
-    dynamic :saved_try_context_var0;
-    FutureOr<core::String>:async_temporary_0;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L6:
         {
-          final Never #t12 = let final Never #t13 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
-          if(#t12 is asy::Future<Never>) {
-            [yield] let dynamic #t14 = asy::_awaitHelper(#t12, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<Never>(:result);
-          }
-          else {
-            :async_temporary_0 = #t12;
-          }
-          :return_value = :async_temporary_0;
+          :return_value = let final Never #t6 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
           break #L6;
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -275,7 +235,7 @@
           }
           on core::Object catch(final core::Object _) {
           }
-          return let final<BottomType> #t15 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:39:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+          return let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:39:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String Function(int) x2 = (int v) /* error */ {
                             ^" in null;
         };
@@ -285,27 +245,27 @@
           }
           on core::Object catch(final core::Object _) {
           }
-          return let final<BottomType> #t16 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:44:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+          return let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:44:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String Function(int) x3 = (int v) /* error */ {
                             ^" in null;
         };
         (core::int) → core::String x5 = (core::int v) → core::String {
           try {
-            let final Never #t17 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
+            let final Never #t9 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
           }
           on core::Object catch(final core::Object _) {
           }
-          return let final<BottomType> #t18 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:49:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+          return let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:49:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String Function(int) x5 = (int v) /* error */ {
                             ^" in null;
         };
         (core::int) → core::String x6 = (core::int v) → core::String {
           try {
-            return let final Never #t19 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
+            return let final Never #t11 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
           }
           on core::Object catch(final core::Object _) {
           }
-          return let final<BottomType> #t20 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:54:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+          return let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:54:29: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String Function(int) x6 = (int v) /* error */ {
                             ^" in null;
         };
@@ -326,7 +286,7 @@
                 }
                 on core::Object catch(final core::Object _) {
                 }
-                :return_value = let final<BottomType> #t21 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:59:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+                :return_value = let final<BottomType> #t13 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:59:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   Future<String> Function(int) y2 = (int v) async /* error */ {
                                     ^" in null;
                 break #L8;
@@ -351,28 +311,17 @@
           (core::Object, core::StackTrace) → dynamic :async_op_error;
           core::int :await_jump_var = 0;
           dynamic :await_ctx_var;
-          dynamic :saved_try_context_var0;
-          dynamic :saved_try_context_var1;
-          FutureOr<core::String>:async_temporary_0;
           function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
             try {
               #L9:
               {
                 try {
-                  final Never #t22 = throw v;
-                  if(#t22 is asy::Future<core::String>) {
-                    [yield] let dynamic #t23 = asy::_awaitHelper(#t22, :async_op_then, :async_op_error, :async_op) in null;
-                    :async_temporary_0 = _in::unsafeCast<Never>(:result);
-                  }
-                  else {
-                    :async_temporary_0 = #t22;
-                  }
-                  :return_value = :async_temporary_0;
+                  :return_value = throw v;
                   break #L9;
                 }
                 on core::Object catch(final core::Object _) {
                 }
-                :return_value = let final<BottomType> #t24 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:64:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+                :return_value = let final<BottomType> #t14 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:64:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   Future<String> Function(int) y3 = (int v) async /* error */ {
                                     ^" in null;
                 break #L9;
@@ -402,11 +351,11 @@
               #L10:
               {
                 try {
-                  let final Never #t25 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
+                  let final Never #t15 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
                 }
                 on core::Object catch(final core::Object _) {
                 }
-                :return_value = let final<BottomType> #t26 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:69:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+                :return_value = let final<BottomType> #t16 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:69:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   Future<String> Function(int) y5 = (int v) async /* error */ {
                                     ^" in null;
                 break #L10;
@@ -431,28 +380,17 @@
           (core::Object, core::StackTrace) → dynamic :async_op_error;
           core::int :await_jump_var = 0;
           dynamic :await_ctx_var;
-          dynamic :saved_try_context_var0;
-          dynamic :saved_try_context_var1;
-          FutureOr<core::String>:async_temporary_0;
           function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
             try {
               #L11:
               {
                 try {
-                  final Never #t27 = let final Never #t28 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
-                  if(#t27 is asy::Future<core::String>) {
-                    [yield] let dynamic #t29 = asy::_awaitHelper(#t27, :async_op_then, :async_op_error, :async_op) in null;
-                    :async_temporary_0 = _in::unsafeCast<Never>(:result);
-                  }
-                  else {
-                    :async_temporary_0 = #t27;
-                  }
-                  :return_value = :async_temporary_0;
+                  :return_value = let final Never #t17 = self::throwing() in throw new _in::ReachabilityError::•("`null` encountered as the result from expression with type `Never`.");
                   break #L11;
                 }
                 on core::Object catch(final core::Object _) {
                 }
-                :return_value = let final<BottomType> #t30 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:74:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+                :return_value = let final<BottomType> #t18 = invalid-expression "pkg/front_end/testcases/nnbd/issue41156.dart:74:37: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   Future<String> Function(int) y6 = (int v) async /* error */ {
                                     ^" in null;
                 break #L11;
diff --git a/pkg/front_end/testcases/nnbd/issue41437a.dart.strong.expect b/pkg/front_end/testcases/nnbd/issue41437a.dart.strong.expect
index d7881ae..fbcd99e 100644
--- a/pkg/front_end/testcases/nnbd/issue41437a.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/issue41437a.dart.strong.expect
@@ -34,61 +34,61 @@
 static method getNull() → dynamic
   return null;
 static method getFutureNull() → asy::Future<dynamic> async {
-  return let final Null #t1 = null in #t1 is asy::Future<dynamic> ?{FutureOr<dynamic>} await #t1 : #t1;
+  return null;
 }
 static method getFutureBool() → asy::Future<core::bool> async {
-  return let final core::bool #t2 = true in #t2 is asy::Future<core::bool> ?{FutureOr<core::bool>} await #t2 : #t2;
+  return true;
 }
 static method test1() → asy::Future<core::bool> async 
-  return let final dynamic #t3 = await self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool> in #t3 is asy::Future<core::bool> ?{FutureOr<core::bool>} await #t3 : #t3;
+  return await self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
 static method test2() → asy::Future<core::bool>
   return self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} asy::Future<core::bool>;
 static method test3() → core::bool
   return self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} core::bool;
 static method test4() → asy::Future<core::bool> async 
-  return let final dynamic #t4 = await self::getFutureNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool> in #t4 is asy::Future<core::bool> ?{FutureOr<core::bool>} await #t4 : #t4;
+  return await self::getFutureNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
 static method test5() → asy::Future<core::bool>
-  return let final<BottomType> #t5 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:18:25: Error: A value of type 'Future<dynamic>' can't be returned from a function with return type 'Future<bool>'.
+  return let final<BottomType> #t1 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:18:25: Error: A value of type 'Future<dynamic>' can't be returned from a function with return type 'Future<bool>'.
  - 'Future' is from 'dart:async'.
 Future<bool> test5() => getFutureNull(); // error
                         ^" in self::getFutureNull() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
 static method test6() → asy::Future<core::bool>
   return self::getFutureBool();
 static method test7() → asy::Future<core::bool> async 
-  return let final asy::Future<core::bool> #t6 = self::getFutureBool() in #t6 is asy::Future<core::bool> ?{FutureOr<core::bool>} await #t6 : #t6;
+  return self::getFutureBool();
 static method test() → dynamic async {
   function test1() → asy::Future<core::bool> async 
-    return let final dynamic #t7 = await self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool> in #t7 is asy::Future<core::bool> ?{FutureOr<core::bool>} await #t7 : #t7;
+    return await self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
   function test2() → asy::Future<core::bool>
     return self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} asy::Future<core::bool>;
   function test3() → core::bool
     return self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} core::bool;
   function test4() → asy::Future<core::bool> async 
-    return let final dynamic #t8 = await self::getFutureNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool> in #t8 is asy::Future<core::bool> ?{FutureOr<core::bool>} await #t8 : #t8;
+    return await self::getFutureNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
   function test5() → asy::Future<core::bool>
-    return let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:27:27: Error: A value of type 'Future<dynamic>' can't be returned from a function with return type 'Future<bool>'.
+    return let final<BottomType> #t2 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:27:27: Error: A value of type 'Future<dynamic>' can't be returned from a function with return type 'Future<bool>'.
  - 'Future' is from 'dart:async'.
   Future<bool> test5() => getFutureNull(); // error
                           ^" in self::getFutureNull() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
   function test6() → asy::Future<core::bool>
     return self::getFutureBool();
   function test7() → asy::Future<core::bool> async 
-    return let final asy::Future<core::bool> #t10 = self::getFutureBool() in #t10 is asy::Future<core::bool> ?{FutureOr<core::bool>} await #t10 : #t10;
-  asy::Future<core::bool> var1 = let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:31:52: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
+    return self::getFutureBool();
+  asy::Future<core::bool> var1 = let final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:31:52: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
  - 'Future' is from 'dart:async'.
   Future<bool> var1 = (() async => await getNull())(); // error
-                                                   ^" in (() → asy::Future<dynamic> async => let final dynamic #t12 = await self::getNull() in #t12 is asy::Future<dynamic> ?{FutureOr<dynamic>} await #t12 : #t12).call() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
+                                                   ^" in (() → asy::Future<dynamic> async => await self::getNull()).call() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
   asy::Future<core::bool> var2 = (() → dynamic => self::getNull()).call() as{TypeError,ForDynamic,ForNonNullableByDefault} asy::Future<core::bool>;
   core::bool var3 = (() → dynamic => self::getNull()).call() as{TypeError,ForDynamic,ForNonNullableByDefault} core::bool;
-  asy::Future<core::bool> var4 = let final<BottomType> #t13 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:34:58: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
+  asy::Future<core::bool> var4 = let final<BottomType> #t4 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:34:58: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
  - 'Future' is from 'dart:async'.
   Future<bool> var4 = (() async => await getFutureNull())(); // error
-                                                         ^" in (() → asy::Future<dynamic> async => let final dynamic #t14 = await self::getFutureNull() in #t14 is asy::Future<dynamic> ?{FutureOr<dynamic>} await #t14 : #t14).call() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
-  asy::Future<core::bool> var5 = let final<BottomType> #t15 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:35:46: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
+                                                         ^" in (() → asy::Future<dynamic> async => await self::getFutureNull()).call() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
+  asy::Future<core::bool> var5 = let final<BottomType> #t5 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:35:46: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
  - 'Future' is from 'dart:async'.
   Future<bool> var5 = (() => getFutureNull())(); // error
                                              ^" in (() → asy::Future<dynamic> => self::getFutureNull()).call() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
   asy::Future<core::bool> var6 = (() → asy::Future<core::bool> => self::getFutureBool()).call();
-  asy::Future<core::bool> var7 = (() → asy::Future<core::bool> async => let final asy::Future<core::bool> #t16 = self::getFutureBool() in #t16 is asy::Future<core::bool> ?{FutureOr<dynamic>} await #t16 : #t16).call();
+  asy::Future<core::bool> var7 = (() → asy::Future<core::bool> async => self::getFutureBool()).call();
 }
 static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/nnbd/issue41437a.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/issue41437a.dart.strong.transformed.expect
index 2b35c4f..b4ab7d2 100644
--- a/pkg/front_end/testcases/nnbd/issue41437a.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/issue41437a.dart.strong.transformed.expect
@@ -30,7 +30,6 @@
 import self as self;
 import "dart:async" as asy;
 import "dart:core" as core;
-import "dart:_internal" as _in;
 
 static method getNull() → dynamic
   return null;
@@ -42,21 +41,11 @@
   (core::Object, core::StackTrace) → dynamic :async_op_error;
   core::int :await_jump_var = 0;
   dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  FutureOr<dynamic>:async_temporary_0;
   function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
     try {
       #L1:
       {
-        final Null #t1 = null;
-        if(#t1 is asy::Future<dynamic>) {
-          [yield] let dynamic #t2 = asy::_awaitHelper(#t1, :async_op_then, :async_op_error, :async_op) in null;
-          :async_temporary_0 = _in::unsafeCast<Null>(:result);
-        }
-        else {
-          :async_temporary_0 = #t1;
-        }
-        :return_value = :async_temporary_0;
+        :return_value = null;
         break #L1;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -79,21 +68,11 @@
   (core::Object, core::StackTrace) → dynamic :async_op_error;
   core::int :await_jump_var = 0;
   dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  FutureOr<core::bool>:async_temporary_0;
   function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
     try {
       #L2:
       {
-        final core::bool #t3 = true;
-        if(#t3 is asy::Future<core::bool>) {
-          [yield] let dynamic #t4 = asy::_awaitHelper(#t3, :async_op_then, :async_op_error, :async_op) in null;
-          :async_temporary_0 = _in::unsafeCast<core::bool>(:result);
-        }
-        else {
-          :async_temporary_0 = #t3;
-        }
-        :return_value = :async_temporary_0;
+        :return_value = true;
         break #L2;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -117,21 +96,12 @@
   core::int :await_jump_var = 0;
   dynamic :await_ctx_var;
   dynamic :saved_try_context_var0;
-  FutureOr<core::bool>:async_temporary_0;
   function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
     try {
       #L3:
       {
-        [yield] let dynamic #t5 = asy::_awaitHelper(self::getNull(), :async_op_then, :async_op_error, :async_op) in null;
-        final FutureOr<core::bool>#t6 = :result as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
-        if(#t6 is asy::Future<core::bool>) {
-          [yield] let dynamic #t7 = asy::_awaitHelper(#t6, :async_op_then, :async_op_error, :async_op) in null;
-          :async_temporary_0 = _in::unsafeCast<core::bool>(:result);
-        }
-        else {
-          :async_temporary_0 = #t6;
-        }
-        :return_value = :async_temporary_0;
+        [yield] let dynamic #t1 = asy::_awaitHelper(self::getNull(), :async_op_then, :async_op_error, :async_op) in null;
+        :return_value = :result as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
         break #L3;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -159,21 +129,12 @@
   core::int :await_jump_var = 0;
   dynamic :await_ctx_var;
   dynamic :saved_try_context_var0;
-  FutureOr<core::bool>:async_temporary_0;
   function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
     try {
       #L4:
       {
-        [yield] let dynamic #t8 = asy::_awaitHelper(self::getFutureNull(), :async_op_then, :async_op_error, :async_op) in null;
-        final FutureOr<core::bool>#t9 = :result as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
-        if(#t9 is asy::Future<core::bool>) {
-          [yield] let dynamic #t10 = asy::_awaitHelper(#t9, :async_op_then, :async_op_error, :async_op) in null;
-          :async_temporary_0 = _in::unsafeCast<core::bool>(:result);
-        }
-        else {
-          :async_temporary_0 = #t9;
-        }
-        :return_value = :async_temporary_0;
+        [yield] let dynamic #t2 = asy::_awaitHelper(self::getFutureNull(), :async_op_then, :async_op_error, :async_op) in null;
+        :return_value = :result as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
         break #L4;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -189,7 +150,7 @@
   return :async_future;
 }
 static method test5() → asy::Future<core::bool>
-  return let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:18:25: Error: A value of type 'Future<dynamic>' can't be returned from a function with return type 'Future<bool>'.
+  return let final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:18:25: Error: A value of type 'Future<dynamic>' can't be returned from a function with return type 'Future<bool>'.
  - 'Future' is from 'dart:async'.
 Future<bool> test5() => getFutureNull(); // error
                         ^" in self::getFutureNull() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
@@ -203,21 +164,11 @@
   (core::Object, core::StackTrace) → dynamic :async_op_error;
   core::int :await_jump_var = 0;
   dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  FutureOr<core::bool>:async_temporary_0;
   function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
     try {
       #L5:
       {
-        final asy::Future<core::bool> #t12 = self::getFutureBool();
-        if(#t12 is asy::Future<core::bool>) {
-          [yield] let dynamic #t13 = asy::_awaitHelper(#t12, :async_op_then, :async_op_error, :async_op) in null;
-          :async_temporary_0 = _in::unsafeCast<core::bool>(:result);
-        }
-        else {
-          :async_temporary_0 = #t12;
-        }
-        :return_value = :async_temporary_0;
+        :return_value = self::getFutureBool();
         break #L5;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -253,21 +204,12 @@
           core::int :await_jump_var = 0;
           dynamic :await_ctx_var;
           dynamic :saved_try_context_var0;
-          FutureOr<core::bool>:async_temporary_0;
           function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
             try {
               #L7:
               {
-                [yield] let dynamic #t14 = asy::_awaitHelper(self::getNull(), :async_op_then, :async_op_error, :async_op) in null;
-                final FutureOr<core::bool>#t15 = :result as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
-                if(#t15 is asy::Future<core::bool>) {
-                  [yield] let dynamic #t16 = asy::_awaitHelper(#t15, :async_op_then, :async_op_error, :async_op) in null;
-                  :async_temporary_0 = _in::unsafeCast<core::bool>(:result);
-                }
-                else {
-                  :async_temporary_0 = #t15;
-                }
-                :return_value = :async_temporary_0;
+                [yield] let dynamic #t4 = asy::_awaitHelper(self::getNull(), :async_op_then, :async_op_error, :async_op) in null;
+                :return_value = :result as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
                 break #L7;
               }
               asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -295,21 +237,12 @@
           core::int :await_jump_var = 0;
           dynamic :await_ctx_var;
           dynamic :saved_try_context_var0;
-          FutureOr<core::bool>:async_temporary_0;
           function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
             try {
               #L8:
               {
-                [yield] let dynamic #t17 = asy::_awaitHelper(self::getFutureNull(), :async_op_then, :async_op_error, :async_op) in null;
-                final FutureOr<core::bool>#t18 = :result as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
-                if(#t18 is asy::Future<core::bool>) {
-                  [yield] let dynamic #t19 = asy::_awaitHelper(#t18, :async_op_then, :async_op_error, :async_op) in null;
-                  :async_temporary_0 = _in::unsafeCast<core::bool>(:result);
-                }
-                else {
-                  :async_temporary_0 = #t18;
-                }
-                :return_value = :async_temporary_0;
+                [yield] let dynamic #t5 = asy::_awaitHelper(self::getFutureNull(), :async_op_then, :async_op_error, :async_op) in null;
+                :return_value = :result as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
                 break #L8;
               }
               asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -325,7 +258,7 @@
           return :async_future;
         }
         function test5() → asy::Future<core::bool>
-          return let final<BottomType> #t20 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:27:27: Error: A value of type 'Future<dynamic>' can't be returned from a function with return type 'Future<bool>'.
+          return let final<BottomType> #t6 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:27:27: Error: A value of type 'Future<dynamic>' can't be returned from a function with return type 'Future<bool>'.
  - 'Future' is from 'dart:async'.
   Future<bool> test5() => getFutureNull(); // error
                           ^" in self::getFutureNull() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
@@ -339,21 +272,11 @@
           (core::Object, core::StackTrace) → dynamic :async_op_error;
           core::int :await_jump_var = 0;
           dynamic :await_ctx_var;
-          dynamic :saved_try_context_var0;
-          FutureOr<core::bool>:async_temporary_0;
           function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
             try {
               #L9:
               {
-                final asy::Future<core::bool> #t21 = self::getFutureBool();
-                if(#t21 is asy::Future<core::bool>) {
-                  [yield] let dynamic #t22 = asy::_awaitHelper(#t21, :async_op_then, :async_op_error, :async_op) in null;
-                  :async_temporary_0 = _in::unsafeCast<core::bool>(:result);
-                }
-                else {
-                  :async_temporary_0 = #t21;
-                }
-                :return_value = :async_temporary_0;
+                :return_value = self::getFutureBool();
                 break #L9;
               }
               asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -368,7 +291,7 @@
           :is_sync = true;
           return :async_future;
         }
-        asy::Future<core::bool> var1 = let final<BottomType> #t23 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:31:52: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
+        asy::Future<core::bool> var1 = let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:31:52: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
  - 'Future' is from 'dart:async'.
   Future<bool> var1 = (() async => await getNull())(); // error
                                                    ^" in (() → asy::Future<dynamic> /* originally async */ {
@@ -380,21 +303,12 @@
           core::int :await_jump_var = 0;
           dynamic :await_ctx_var;
           dynamic :saved_try_context_var0;
-          FutureOr<dynamic>:async_temporary_0;
           function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
             try {
               #L10:
               {
-                [yield] let dynamic #t24 = asy::_awaitHelper(self::getNull(), :async_op_then, :async_op_error, :async_op) in null;
-                final dynamic #t25 = :result;
-                if(#t25 is asy::Future<dynamic>) {
-                  [yield] let dynamic #t26 = asy::_awaitHelper(#t25, :async_op_then, :async_op_error, :async_op) in null;
-                  :async_temporary_0 = :result;
-                }
-                else {
-                  :async_temporary_0 = #t25;
-                }
-                :return_value = :async_temporary_0;
+                [yield] let dynamic #t8 = asy::_awaitHelper(self::getNull(), :async_op_then, :async_op_error, :async_op) in null;
+                :return_value = :result;
                 break #L10;
               }
               asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -411,7 +325,7 @@
         }).call() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
         asy::Future<core::bool> var2 = (() → dynamic => self::getNull()).call() as{TypeError,ForDynamic,ForNonNullableByDefault} asy::Future<core::bool>;
         core::bool var3 = (() → dynamic => self::getNull()).call() as{TypeError,ForDynamic,ForNonNullableByDefault} core::bool;
-        asy::Future<core::bool> var4 = let final<BottomType> #t27 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:34:58: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
+        asy::Future<core::bool> var4 = let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:34:58: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
  - 'Future' is from 'dart:async'.
   Future<bool> var4 = (() async => await getFutureNull())(); // error
                                                          ^" in (() → asy::Future<dynamic> /* originally async */ {
@@ -423,21 +337,12 @@
           core::int :await_jump_var = 0;
           dynamic :await_ctx_var;
           dynamic :saved_try_context_var0;
-          FutureOr<dynamic>:async_temporary_0;
           function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
             try {
               #L11:
               {
-                [yield] let dynamic #t28 = asy::_awaitHelper(self::getFutureNull(), :async_op_then, :async_op_error, :async_op) in null;
-                final dynamic #t29 = :result;
-                if(#t29 is asy::Future<dynamic>) {
-                  [yield] let dynamic #t30 = asy::_awaitHelper(#t29, :async_op_then, :async_op_error, :async_op) in null;
-                  :async_temporary_0 = :result;
-                }
-                else {
-                  :async_temporary_0 = #t29;
-                }
-                :return_value = :async_temporary_0;
+                [yield] let dynamic #t10 = asy::_awaitHelper(self::getFutureNull(), :async_op_then, :async_op_error, :async_op) in null;
+                :return_value = :result;
                 break #L11;
               }
               asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -452,7 +357,7 @@
           :is_sync = true;
           return :async_future;
         }).call() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
-        asy::Future<core::bool> var5 = let final<BottomType> #t31 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:35:46: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
+        asy::Future<core::bool> var5 = let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:35:46: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
  - 'Future' is from 'dart:async'.
   Future<bool> var5 = (() => getFutureNull())(); // error
                                              ^" in (() → asy::Future<dynamic> => self::getFutureNull()).call() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
@@ -465,21 +370,11 @@
           (core::Object, core::StackTrace) → dynamic :async_op_error;
           core::int :await_jump_var = 0;
           dynamic :await_ctx_var;
-          dynamic :saved_try_context_var0;
-          FutureOr<dynamic>:async_temporary_0;
           function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
             try {
               #L12:
               {
-                final asy::Future<core::bool> #t32 = self::getFutureBool();
-                if(#t32 is asy::Future<core::bool>) {
-                  [yield] let dynamic #t33 = asy::_awaitHelper(#t32, :async_op_then, :async_op_error, :async_op) in null;
-                  :async_temporary_0 = _in::unsafeCast<core::bool>(:result);
-                }
-                else {
-                  :async_temporary_0 = #t32;
-                }
-                :return_value = :async_temporary_0;
+                :return_value = self::getFutureBool();
                 break #L12;
               }
               asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
diff --git a/pkg/front_end/testcases/nnbd/issue41437a.dart.weak.expect b/pkg/front_end/testcases/nnbd/issue41437a.dart.weak.expect
index d7881ae..fbcd99e 100644
--- a/pkg/front_end/testcases/nnbd/issue41437a.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/issue41437a.dart.weak.expect
@@ -34,61 +34,61 @@
 static method getNull() → dynamic
   return null;
 static method getFutureNull() → asy::Future<dynamic> async {
-  return let final Null #t1 = null in #t1 is asy::Future<dynamic> ?{FutureOr<dynamic>} await #t1 : #t1;
+  return null;
 }
 static method getFutureBool() → asy::Future<core::bool> async {
-  return let final core::bool #t2 = true in #t2 is asy::Future<core::bool> ?{FutureOr<core::bool>} await #t2 : #t2;
+  return true;
 }
 static method test1() → asy::Future<core::bool> async 
-  return let final dynamic #t3 = await self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool> in #t3 is asy::Future<core::bool> ?{FutureOr<core::bool>} await #t3 : #t3;
+  return await self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
 static method test2() → asy::Future<core::bool>
   return self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} asy::Future<core::bool>;
 static method test3() → core::bool
   return self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} core::bool;
 static method test4() → asy::Future<core::bool> async 
-  return let final dynamic #t4 = await self::getFutureNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool> in #t4 is asy::Future<core::bool> ?{FutureOr<core::bool>} await #t4 : #t4;
+  return await self::getFutureNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
 static method test5() → asy::Future<core::bool>
-  return let final<BottomType> #t5 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:18:25: Error: A value of type 'Future<dynamic>' can't be returned from a function with return type 'Future<bool>'.
+  return let final<BottomType> #t1 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:18:25: Error: A value of type 'Future<dynamic>' can't be returned from a function with return type 'Future<bool>'.
  - 'Future' is from 'dart:async'.
 Future<bool> test5() => getFutureNull(); // error
                         ^" in self::getFutureNull() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
 static method test6() → asy::Future<core::bool>
   return self::getFutureBool();
 static method test7() → asy::Future<core::bool> async 
-  return let final asy::Future<core::bool> #t6 = self::getFutureBool() in #t6 is asy::Future<core::bool> ?{FutureOr<core::bool>} await #t6 : #t6;
+  return self::getFutureBool();
 static method test() → dynamic async {
   function test1() → asy::Future<core::bool> async 
-    return let final dynamic #t7 = await self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool> in #t7 is asy::Future<core::bool> ?{FutureOr<core::bool>} await #t7 : #t7;
+    return await self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
   function test2() → asy::Future<core::bool>
     return self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} asy::Future<core::bool>;
   function test3() → core::bool
     return self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} core::bool;
   function test4() → asy::Future<core::bool> async 
-    return let final dynamic #t8 = await self::getFutureNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool> in #t8 is asy::Future<core::bool> ?{FutureOr<core::bool>} await #t8 : #t8;
+    return await self::getFutureNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
   function test5() → asy::Future<core::bool>
-    return let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:27:27: Error: A value of type 'Future<dynamic>' can't be returned from a function with return type 'Future<bool>'.
+    return let final<BottomType> #t2 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:27:27: Error: A value of type 'Future<dynamic>' can't be returned from a function with return type 'Future<bool>'.
  - 'Future' is from 'dart:async'.
   Future<bool> test5() => getFutureNull(); // error
                           ^" in self::getFutureNull() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
   function test6() → asy::Future<core::bool>
     return self::getFutureBool();
   function test7() → asy::Future<core::bool> async 
-    return let final asy::Future<core::bool> #t10 = self::getFutureBool() in #t10 is asy::Future<core::bool> ?{FutureOr<core::bool>} await #t10 : #t10;
-  asy::Future<core::bool> var1 = let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:31:52: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
+    return self::getFutureBool();
+  asy::Future<core::bool> var1 = let final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:31:52: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
  - 'Future' is from 'dart:async'.
   Future<bool> var1 = (() async => await getNull())(); // error
-                                                   ^" in (() → asy::Future<dynamic> async => let final dynamic #t12 = await self::getNull() in #t12 is asy::Future<dynamic> ?{FutureOr<dynamic>} await #t12 : #t12).call() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
+                                                   ^" in (() → asy::Future<dynamic> async => await self::getNull()).call() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
   asy::Future<core::bool> var2 = (() → dynamic => self::getNull()).call() as{TypeError,ForDynamic,ForNonNullableByDefault} asy::Future<core::bool>;
   core::bool var3 = (() → dynamic => self::getNull()).call() as{TypeError,ForDynamic,ForNonNullableByDefault} core::bool;
-  asy::Future<core::bool> var4 = let final<BottomType> #t13 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:34:58: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
+  asy::Future<core::bool> var4 = let final<BottomType> #t4 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:34:58: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
  - 'Future' is from 'dart:async'.
   Future<bool> var4 = (() async => await getFutureNull())(); // error
-                                                         ^" in (() → asy::Future<dynamic> async => let final dynamic #t14 = await self::getFutureNull() in #t14 is asy::Future<dynamic> ?{FutureOr<dynamic>} await #t14 : #t14).call() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
-  asy::Future<core::bool> var5 = let final<BottomType> #t15 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:35:46: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
+                                                         ^" in (() → asy::Future<dynamic> async => await self::getFutureNull()).call() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
+  asy::Future<core::bool> var5 = let final<BottomType> #t5 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:35:46: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
  - 'Future' is from 'dart:async'.
   Future<bool> var5 = (() => getFutureNull())(); // error
                                              ^" in (() → asy::Future<dynamic> => self::getFutureNull()).call() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
   asy::Future<core::bool> var6 = (() → asy::Future<core::bool> => self::getFutureBool()).call();
-  asy::Future<core::bool> var7 = (() → asy::Future<core::bool> async => let final asy::Future<core::bool> #t16 = self::getFutureBool() in #t16 is asy::Future<core::bool> ?{FutureOr<dynamic>} await #t16 : #t16).call();
+  asy::Future<core::bool> var7 = (() → asy::Future<core::bool> async => self::getFutureBool()).call();
 }
 static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/nnbd/issue41437a.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/issue41437a.dart.weak.transformed.expect
index 2b35c4f..b4ab7d2 100644
--- a/pkg/front_end/testcases/nnbd/issue41437a.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/issue41437a.dart.weak.transformed.expect
@@ -30,7 +30,6 @@
 import self as self;
 import "dart:async" as asy;
 import "dart:core" as core;
-import "dart:_internal" as _in;
 
 static method getNull() → dynamic
   return null;
@@ -42,21 +41,11 @@
   (core::Object, core::StackTrace) → dynamic :async_op_error;
   core::int :await_jump_var = 0;
   dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  FutureOr<dynamic>:async_temporary_0;
   function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
     try {
       #L1:
       {
-        final Null #t1 = null;
-        if(#t1 is asy::Future<dynamic>) {
-          [yield] let dynamic #t2 = asy::_awaitHelper(#t1, :async_op_then, :async_op_error, :async_op) in null;
-          :async_temporary_0 = _in::unsafeCast<Null>(:result);
-        }
-        else {
-          :async_temporary_0 = #t1;
-        }
-        :return_value = :async_temporary_0;
+        :return_value = null;
         break #L1;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -79,21 +68,11 @@
   (core::Object, core::StackTrace) → dynamic :async_op_error;
   core::int :await_jump_var = 0;
   dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  FutureOr<core::bool>:async_temporary_0;
   function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
     try {
       #L2:
       {
-        final core::bool #t3 = true;
-        if(#t3 is asy::Future<core::bool>) {
-          [yield] let dynamic #t4 = asy::_awaitHelper(#t3, :async_op_then, :async_op_error, :async_op) in null;
-          :async_temporary_0 = _in::unsafeCast<core::bool>(:result);
-        }
-        else {
-          :async_temporary_0 = #t3;
-        }
-        :return_value = :async_temporary_0;
+        :return_value = true;
         break #L2;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -117,21 +96,12 @@
   core::int :await_jump_var = 0;
   dynamic :await_ctx_var;
   dynamic :saved_try_context_var0;
-  FutureOr<core::bool>:async_temporary_0;
   function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
     try {
       #L3:
       {
-        [yield] let dynamic #t5 = asy::_awaitHelper(self::getNull(), :async_op_then, :async_op_error, :async_op) in null;
-        final FutureOr<core::bool>#t6 = :result as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
-        if(#t6 is asy::Future<core::bool>) {
-          [yield] let dynamic #t7 = asy::_awaitHelper(#t6, :async_op_then, :async_op_error, :async_op) in null;
-          :async_temporary_0 = _in::unsafeCast<core::bool>(:result);
-        }
-        else {
-          :async_temporary_0 = #t6;
-        }
-        :return_value = :async_temporary_0;
+        [yield] let dynamic #t1 = asy::_awaitHelper(self::getNull(), :async_op_then, :async_op_error, :async_op) in null;
+        :return_value = :result as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
         break #L3;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -159,21 +129,12 @@
   core::int :await_jump_var = 0;
   dynamic :await_ctx_var;
   dynamic :saved_try_context_var0;
-  FutureOr<core::bool>:async_temporary_0;
   function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
     try {
       #L4:
       {
-        [yield] let dynamic #t8 = asy::_awaitHelper(self::getFutureNull(), :async_op_then, :async_op_error, :async_op) in null;
-        final FutureOr<core::bool>#t9 = :result as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
-        if(#t9 is asy::Future<core::bool>) {
-          [yield] let dynamic #t10 = asy::_awaitHelper(#t9, :async_op_then, :async_op_error, :async_op) in null;
-          :async_temporary_0 = _in::unsafeCast<core::bool>(:result);
-        }
-        else {
-          :async_temporary_0 = #t9;
-        }
-        :return_value = :async_temporary_0;
+        [yield] let dynamic #t2 = asy::_awaitHelper(self::getFutureNull(), :async_op_then, :async_op_error, :async_op) in null;
+        :return_value = :result as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
         break #L4;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -189,7 +150,7 @@
   return :async_future;
 }
 static method test5() → asy::Future<core::bool>
-  return let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:18:25: Error: A value of type 'Future<dynamic>' can't be returned from a function with return type 'Future<bool>'.
+  return let final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:18:25: Error: A value of type 'Future<dynamic>' can't be returned from a function with return type 'Future<bool>'.
  - 'Future' is from 'dart:async'.
 Future<bool> test5() => getFutureNull(); // error
                         ^" in self::getFutureNull() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
@@ -203,21 +164,11 @@
   (core::Object, core::StackTrace) → dynamic :async_op_error;
   core::int :await_jump_var = 0;
   dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  FutureOr<core::bool>:async_temporary_0;
   function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
     try {
       #L5:
       {
-        final asy::Future<core::bool> #t12 = self::getFutureBool();
-        if(#t12 is asy::Future<core::bool>) {
-          [yield] let dynamic #t13 = asy::_awaitHelper(#t12, :async_op_then, :async_op_error, :async_op) in null;
-          :async_temporary_0 = _in::unsafeCast<core::bool>(:result);
-        }
-        else {
-          :async_temporary_0 = #t12;
-        }
-        :return_value = :async_temporary_0;
+        :return_value = self::getFutureBool();
         break #L5;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -253,21 +204,12 @@
           core::int :await_jump_var = 0;
           dynamic :await_ctx_var;
           dynamic :saved_try_context_var0;
-          FutureOr<core::bool>:async_temporary_0;
           function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
             try {
               #L7:
               {
-                [yield] let dynamic #t14 = asy::_awaitHelper(self::getNull(), :async_op_then, :async_op_error, :async_op) in null;
-                final FutureOr<core::bool>#t15 = :result as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
-                if(#t15 is asy::Future<core::bool>) {
-                  [yield] let dynamic #t16 = asy::_awaitHelper(#t15, :async_op_then, :async_op_error, :async_op) in null;
-                  :async_temporary_0 = _in::unsafeCast<core::bool>(:result);
-                }
-                else {
-                  :async_temporary_0 = #t15;
-                }
-                :return_value = :async_temporary_0;
+                [yield] let dynamic #t4 = asy::_awaitHelper(self::getNull(), :async_op_then, :async_op_error, :async_op) in null;
+                :return_value = :result as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
                 break #L7;
               }
               asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -295,21 +237,12 @@
           core::int :await_jump_var = 0;
           dynamic :await_ctx_var;
           dynamic :saved_try_context_var0;
-          FutureOr<core::bool>:async_temporary_0;
           function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
             try {
               #L8:
               {
-                [yield] let dynamic #t17 = asy::_awaitHelper(self::getFutureNull(), :async_op_then, :async_op_error, :async_op) in null;
-                final FutureOr<core::bool>#t18 = :result as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
-                if(#t18 is asy::Future<core::bool>) {
-                  [yield] let dynamic #t19 = asy::_awaitHelper(#t18, :async_op_then, :async_op_error, :async_op) in null;
-                  :async_temporary_0 = _in::unsafeCast<core::bool>(:result);
-                }
-                else {
-                  :async_temporary_0 = #t18;
-                }
-                :return_value = :async_temporary_0;
+                [yield] let dynamic #t5 = asy::_awaitHelper(self::getFutureNull(), :async_op_then, :async_op_error, :async_op) in null;
+                :return_value = :result as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::bool>;
                 break #L8;
               }
               asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -325,7 +258,7 @@
           return :async_future;
         }
         function test5() → asy::Future<core::bool>
-          return let final<BottomType> #t20 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:27:27: Error: A value of type 'Future<dynamic>' can't be returned from a function with return type 'Future<bool>'.
+          return let final<BottomType> #t6 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:27:27: Error: A value of type 'Future<dynamic>' can't be returned from a function with return type 'Future<bool>'.
  - 'Future' is from 'dart:async'.
   Future<bool> test5() => getFutureNull(); // error
                           ^" in self::getFutureNull() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
@@ -339,21 +272,11 @@
           (core::Object, core::StackTrace) → dynamic :async_op_error;
           core::int :await_jump_var = 0;
           dynamic :await_ctx_var;
-          dynamic :saved_try_context_var0;
-          FutureOr<core::bool>:async_temporary_0;
           function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
             try {
               #L9:
               {
-                final asy::Future<core::bool> #t21 = self::getFutureBool();
-                if(#t21 is asy::Future<core::bool>) {
-                  [yield] let dynamic #t22 = asy::_awaitHelper(#t21, :async_op_then, :async_op_error, :async_op) in null;
-                  :async_temporary_0 = _in::unsafeCast<core::bool>(:result);
-                }
-                else {
-                  :async_temporary_0 = #t21;
-                }
-                :return_value = :async_temporary_0;
+                :return_value = self::getFutureBool();
                 break #L9;
               }
               asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -368,7 +291,7 @@
           :is_sync = true;
           return :async_future;
         }
-        asy::Future<core::bool> var1 = let final<BottomType> #t23 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:31:52: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
+        asy::Future<core::bool> var1 = let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:31:52: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
  - 'Future' is from 'dart:async'.
   Future<bool> var1 = (() async => await getNull())(); // error
                                                    ^" in (() → asy::Future<dynamic> /* originally async */ {
@@ -380,21 +303,12 @@
           core::int :await_jump_var = 0;
           dynamic :await_ctx_var;
           dynamic :saved_try_context_var0;
-          FutureOr<dynamic>:async_temporary_0;
           function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
             try {
               #L10:
               {
-                [yield] let dynamic #t24 = asy::_awaitHelper(self::getNull(), :async_op_then, :async_op_error, :async_op) in null;
-                final dynamic #t25 = :result;
-                if(#t25 is asy::Future<dynamic>) {
-                  [yield] let dynamic #t26 = asy::_awaitHelper(#t25, :async_op_then, :async_op_error, :async_op) in null;
-                  :async_temporary_0 = :result;
-                }
-                else {
-                  :async_temporary_0 = #t25;
-                }
-                :return_value = :async_temporary_0;
+                [yield] let dynamic #t8 = asy::_awaitHelper(self::getNull(), :async_op_then, :async_op_error, :async_op) in null;
+                :return_value = :result;
                 break #L10;
               }
               asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -411,7 +325,7 @@
         }).call() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
         asy::Future<core::bool> var2 = (() → dynamic => self::getNull()).call() as{TypeError,ForDynamic,ForNonNullableByDefault} asy::Future<core::bool>;
         core::bool var3 = (() → dynamic => self::getNull()).call() as{TypeError,ForDynamic,ForNonNullableByDefault} core::bool;
-        asy::Future<core::bool> var4 = let final<BottomType> #t27 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:34:58: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
+        asy::Future<core::bool> var4 = let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:34:58: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
  - 'Future' is from 'dart:async'.
   Future<bool> var4 = (() async => await getFutureNull())(); // error
                                                          ^" in (() → asy::Future<dynamic> /* originally async */ {
@@ -423,21 +337,12 @@
           core::int :await_jump_var = 0;
           dynamic :await_ctx_var;
           dynamic :saved_try_context_var0;
-          FutureOr<dynamic>:async_temporary_0;
           function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
             try {
               #L11:
               {
-                [yield] let dynamic #t28 = asy::_awaitHelper(self::getFutureNull(), :async_op_then, :async_op_error, :async_op) in null;
-                final dynamic #t29 = :result;
-                if(#t29 is asy::Future<dynamic>) {
-                  [yield] let dynamic #t30 = asy::_awaitHelper(#t29, :async_op_then, :async_op_error, :async_op) in null;
-                  :async_temporary_0 = :result;
-                }
-                else {
-                  :async_temporary_0 = #t29;
-                }
-                :return_value = :async_temporary_0;
+                [yield] let dynamic #t10 = asy::_awaitHelper(self::getFutureNull(), :async_op_then, :async_op_error, :async_op) in null;
+                :return_value = :result;
                 break #L11;
               }
               asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -452,7 +357,7 @@
           :is_sync = true;
           return :async_future;
         }).call() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
-        asy::Future<core::bool> var5 = let final<BottomType> #t31 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:35:46: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
+        asy::Future<core::bool> var5 = let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/issue41437a.dart:35:46: Error: A value of type 'Future<dynamic>' can't be assigned to a variable of type 'Future<bool>'.
  - 'Future' is from 'dart:async'.
   Future<bool> var5 = (() => getFutureNull())(); // error
                                              ^" in (() → asy::Future<dynamic> => self::getFutureNull()).call() as{TypeError,ForNonNullableByDefault} asy::Future<core::bool>;
@@ -465,21 +370,11 @@
           (core::Object, core::StackTrace) → dynamic :async_op_error;
           core::int :await_jump_var = 0;
           dynamic :await_ctx_var;
-          dynamic :saved_try_context_var0;
-          FutureOr<dynamic>:async_temporary_0;
           function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
             try {
               #L12:
               {
-                final asy::Future<core::bool> #t32 = self::getFutureBool();
-                if(#t32 is asy::Future<core::bool>) {
-                  [yield] let dynamic #t33 = asy::_awaitHelper(#t32, :async_op_then, :async_op_error, :async_op) in null;
-                  :async_temporary_0 = _in::unsafeCast<core::bool>(:result);
-                }
-                else {
-                  :async_temporary_0 = #t32;
-                }
-                :return_value = :async_temporary_0;
+                :return_value = self::getFutureBool();
                 break #L12;
               }
               asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
diff --git a/pkg/front_end/testcases/nnbd/issue41697.dart.strong.expect b/pkg/front_end/testcases/nnbd/issue41697.dart.strong.expect
index 58eebef..f0b15fb 100644
--- a/pkg/front_end/testcases/nnbd/issue41697.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/issue41697.dart.strong.expect
@@ -34,23 +34,23 @@
     return s.{core::num::+}(1);
   };
   <S extends FutureOr<core::num> = FutureOr<core::num>>(S, FutureOr<core::num>) → asy::Future<core::num> f2 = c.{self::C::field2} = <S extends FutureOr<core::num> = FutureOr<core::num>>(S s, FutureOr<core::num>t) → asy::Future<core::num> async {
-    return let final core::num #t1 = (await t).{core::num::+}(1) in #t1 is asy::Future<core::num> ?{FutureOr<dynamic>} await #t1 : #t1;
+    return (await t).{core::num::+}(1);
   };
 }
 static method test2(self::C<core::num?> c) → dynamic {
   <S extends core::num? = core::num?>(S%) → core::num f1 = c.{self::C::field1} = <S extends core::num? = core::num?>(S% s) → core::num {
-    return let final<BottomType> #t2 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:33:14: Error: Operator '+' cannot be called on 'S' because it is potentially null.
+    return let final<BottomType> #t1 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:33:14: Error: Operator '+' cannot be called on 'S' because it is potentially null.
     return s + 1; // error
              ^" in s.{core::num::+}(1);
   };
   <S extends FutureOr<core::num?> = FutureOr<core::num?>>(S%, FutureOr<core::num?>) → asy::Future<core::num> f2 = c.{self::C::field2} = <S extends FutureOr<core::num?> = FutureOr<core::num?>>(S% s, FutureOr<core::num?>t) → asy::Future<core::num> async {
-    return let final core::num #t3 = let final<BottomType> #t4 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:36:22: Error: Operator '+' cannot be called on 'num?' because it is potentially null.
+    return let final<BottomType> #t2 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:36:22: Error: Operator '+' cannot be called on 'num?' because it is potentially null.
     return (await t) + 1; // error
-                     ^" in (await t).{core::num::+}(1) in #t3 is asy::Future<core::num> ?{FutureOr<dynamic>} await #t3 : #t3;
+                     ^" in (await t).{core::num::+}(1);
   };
 }
 static method test3<S extends core::num? = core::num?>(self::test3::S% s) → dynamic
-  return let final<BottomType> #t5 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:40:33: Error: Operator '+' cannot be called on 'S' because it is potentially null.
+  return let final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:40:33: Error: Operator '+' cannot be called on 'S' because it is potentially null.
 test3<S extends num?>(S s) => s + 1; // error
                                 ^" in s.{core::num::+}(1);
 static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/nnbd/issue41697.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/issue41697.dart.strong.transformed.expect
index b08be8f..b287a57 100644
--- a/pkg/front_end/testcases/nnbd/issue41697.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/issue41697.dart.strong.transformed.expect
@@ -43,21 +43,12 @@
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
     dynamic :saved_try_context_var0;
-    FutureOr<dynamic>:async_temporary_0;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L1:
         {
           [yield] let dynamic #t1 = asy::_awaitHelper(t, :async_op_then, :async_op_error, :async_op) in null;
-          final core::num #t2 = _in::unsafeCast<core::num>(:result).{core::num::+}(1);
-          if(#t2 is asy::Future<core::num>) {
-            [yield] let dynamic #t3 = asy::_awaitHelper(#t2, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::num>(:result);
-          }
-          else {
-            :async_temporary_0 = #t2;
-          }
-          :return_value = :async_temporary_0;
+          :return_value = _in::unsafeCast<core::num>(:result).{core::num::+}(1);
           break #L1;
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -75,7 +66,7 @@
 }
 static method test2(self::C<core::num?> c) → dynamic {
   <S extends core::num? = core::num?>(S%) → core::num f1 = c.{self::C::field1} = <S extends core::num? = core::num?>(S% s) → core::num {
-    return let final<BottomType> #t4 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:33:14: Error: Operator '+' cannot be called on 'S' because it is potentially null.
+    return let final<BottomType> #t2 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:33:14: Error: Operator '+' cannot be called on 'S' because it is potentially null.
     return s + 1; // error
              ^" in s.{core::num::+}(1);
   };
@@ -88,24 +79,15 @@
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
     dynamic :saved_try_context_var0;
-    FutureOr<dynamic>:async_temporary_0;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L2:
         {
-          final<BottomType> #t5 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:36:22: Error: Operator '+' cannot be called on 'num?' because it is potentially null.
+          final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:36:22: Error: Operator '+' cannot be called on 'num?' because it is potentially null.
     return (await t) + 1; // error
                      ^";
-          [yield] let dynamic #t6 = asy::_awaitHelper(t, :async_op_then, :async_op_error, :async_op) in null;
-          final core::num #t7 = _in::unsafeCast<core::num?>(:result).{core::num::+}(1);
-          if(#t7 is asy::Future<core::num>) {
-            [yield] let dynamic #t8 = asy::_awaitHelper(#t7, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::num>(:result);
-          }
-          else {
-            :async_temporary_0 = #t7;
-          }
-          :return_value = :async_temporary_0;
+          [yield] let dynamic #t4 = asy::_awaitHelper(t, :async_op_then, :async_op_error, :async_op) in null;
+          :return_value = _in::unsafeCast<core::num?>(:result).{core::num::+}(1);
           break #L2;
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -122,7 +104,7 @@
   };
 }
 static method test3<S extends core::num? = core::num?>(self::test3::S% s) → dynamic
-  return let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:40:33: Error: Operator '+' cannot be called on 'S' because it is potentially null.
+  return let final<BottomType> #t5 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:40:33: Error: Operator '+' cannot be called on 'S' because it is potentially null.
 test3<S extends num?>(S s) => s + 1; // error
                                 ^" in s.{core::num::+}(1);
 static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/nnbd/issue41697.dart.weak.expect b/pkg/front_end/testcases/nnbd/issue41697.dart.weak.expect
index 58eebef..f0b15fb 100644
--- a/pkg/front_end/testcases/nnbd/issue41697.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/issue41697.dart.weak.expect
@@ -34,23 +34,23 @@
     return s.{core::num::+}(1);
   };
   <S extends FutureOr<core::num> = FutureOr<core::num>>(S, FutureOr<core::num>) → asy::Future<core::num> f2 = c.{self::C::field2} = <S extends FutureOr<core::num> = FutureOr<core::num>>(S s, FutureOr<core::num>t) → asy::Future<core::num> async {
-    return let final core::num #t1 = (await t).{core::num::+}(1) in #t1 is asy::Future<core::num> ?{FutureOr<dynamic>} await #t1 : #t1;
+    return (await t).{core::num::+}(1);
   };
 }
 static method test2(self::C<core::num?> c) → dynamic {
   <S extends core::num? = core::num?>(S%) → core::num f1 = c.{self::C::field1} = <S extends core::num? = core::num?>(S% s) → core::num {
-    return let final<BottomType> #t2 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:33:14: Error: Operator '+' cannot be called on 'S' because it is potentially null.
+    return let final<BottomType> #t1 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:33:14: Error: Operator '+' cannot be called on 'S' because it is potentially null.
     return s + 1; // error
              ^" in s.{core::num::+}(1);
   };
   <S extends FutureOr<core::num?> = FutureOr<core::num?>>(S%, FutureOr<core::num?>) → asy::Future<core::num> f2 = c.{self::C::field2} = <S extends FutureOr<core::num?> = FutureOr<core::num?>>(S% s, FutureOr<core::num?>t) → asy::Future<core::num> async {
-    return let final core::num #t3 = let final<BottomType> #t4 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:36:22: Error: Operator '+' cannot be called on 'num?' because it is potentially null.
+    return let final<BottomType> #t2 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:36:22: Error: Operator '+' cannot be called on 'num?' because it is potentially null.
     return (await t) + 1; // error
-                     ^" in (await t).{core::num::+}(1) in #t3 is asy::Future<core::num> ?{FutureOr<dynamic>} await #t3 : #t3;
+                     ^" in (await t).{core::num::+}(1);
   };
 }
 static method test3<S extends core::num? = core::num?>(self::test3::S% s) → dynamic
-  return let final<BottomType> #t5 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:40:33: Error: Operator '+' cannot be called on 'S' because it is potentially null.
+  return let final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:40:33: Error: Operator '+' cannot be called on 'S' because it is potentially null.
 test3<S extends num?>(S s) => s + 1; // error
                                 ^" in s.{core::num::+}(1);
 static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/nnbd/issue41697.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/issue41697.dart.weak.transformed.expect
index b08be8f..b287a57 100644
--- a/pkg/front_end/testcases/nnbd/issue41697.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/issue41697.dart.weak.transformed.expect
@@ -43,21 +43,12 @@
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
     dynamic :saved_try_context_var0;
-    FutureOr<dynamic>:async_temporary_0;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L1:
         {
           [yield] let dynamic #t1 = asy::_awaitHelper(t, :async_op_then, :async_op_error, :async_op) in null;
-          final core::num #t2 = _in::unsafeCast<core::num>(:result).{core::num::+}(1);
-          if(#t2 is asy::Future<core::num>) {
-            [yield] let dynamic #t3 = asy::_awaitHelper(#t2, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::num>(:result);
-          }
-          else {
-            :async_temporary_0 = #t2;
-          }
-          :return_value = :async_temporary_0;
+          :return_value = _in::unsafeCast<core::num>(:result).{core::num::+}(1);
           break #L1;
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -75,7 +66,7 @@
 }
 static method test2(self::C<core::num?> c) → dynamic {
   <S extends core::num? = core::num?>(S%) → core::num f1 = c.{self::C::field1} = <S extends core::num? = core::num?>(S% s) → core::num {
-    return let final<BottomType> #t4 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:33:14: Error: Operator '+' cannot be called on 'S' because it is potentially null.
+    return let final<BottomType> #t2 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:33:14: Error: Operator '+' cannot be called on 'S' because it is potentially null.
     return s + 1; // error
              ^" in s.{core::num::+}(1);
   };
@@ -88,24 +79,15 @@
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
     dynamic :saved_try_context_var0;
-    FutureOr<dynamic>:async_temporary_0;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L2:
         {
-          final<BottomType> #t5 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:36:22: Error: Operator '+' cannot be called on 'num?' because it is potentially null.
+          final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:36:22: Error: Operator '+' cannot be called on 'num?' because it is potentially null.
     return (await t) + 1; // error
                      ^";
-          [yield] let dynamic #t6 = asy::_awaitHelper(t, :async_op_then, :async_op_error, :async_op) in null;
-          final core::num #t7 = _in::unsafeCast<core::num?>(:result).{core::num::+}(1);
-          if(#t7 is asy::Future<core::num>) {
-            [yield] let dynamic #t8 = asy::_awaitHelper(#t7, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::num>(:result);
-          }
-          else {
-            :async_temporary_0 = #t7;
-          }
-          :return_value = :async_temporary_0;
+          [yield] let dynamic #t4 = asy::_awaitHelper(t, :async_op_then, :async_op_error, :async_op) in null;
+          :return_value = _in::unsafeCast<core::num?>(:result).{core::num::+}(1);
           break #L2;
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -122,7 +104,7 @@
   };
 }
 static method test3<S extends core::num? = core::num?>(self::test3::S% s) → dynamic
-  return let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:40:33: Error: Operator '+' cannot be called on 'S' because it is potentially null.
+  return let final<BottomType> #t5 = invalid-expression "pkg/front_end/testcases/nnbd/issue41697.dart:40:33: Error: Operator '+' cannot be called on 'S' because it is potentially null.
 test3<S extends num?>(S s) => s + 1; // error
                                 ^" in s.{core::num::+}(1);
 static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/nnbd/issue42540.dart.strong.expect b/pkg/front_end/testcases/nnbd/issue42540.dart.strong.expect
index c1d787d..aaf931d 100644
--- a/pkg/front_end/testcases/nnbd/issue42540.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/issue42540.dart.strong.expect
@@ -7,6 +7,6 @@
   return null;
 static method fn() → asy::Future<core::Object> async {
   core::Object o = await self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} core::Object;
-  return let final dynamic #t1 = await self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::Object> in #t1 is asy::Future<core::Object> ?{FutureOr<core::Object>} await #t1 : #t1;
+  return await self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::Object>;
 }
 static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/nnbd/issue42540.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/issue42540.dart.strong.transformed.expect
index b5edde0..4e127a6 100644
--- a/pkg/front_end/testcases/nnbd/issue42540.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/issue42540.dart.strong.transformed.expect
@@ -2,7 +2,6 @@
 import self as self;
 import "dart:async" as asy;
 import "dart:core" as core;
-import "dart:_internal" as _in;
 
 static method getNull() → dynamic
   return null;
@@ -15,7 +14,6 @@
   core::int :await_jump_var = 0;
   dynamic :await_ctx_var;
   dynamic :saved_try_context_var0;
-  FutureOr<core::Object>:async_temporary_0;
   function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
     try {
       #L1:
@@ -23,15 +21,7 @@
         [yield] let dynamic #t1 = asy::_awaitHelper(self::getNull(), :async_op_then, :async_op_error, :async_op) in null;
         core::Object o = let dynamic #t2 = :result in #t2.==(null) ?{core::Object} #t2 as{TypeError,ForDynamic,ForNonNullableByDefault} core::Object : #t2{core::Object};
         [yield] let dynamic #t3 = asy::_awaitHelper(self::getNull(), :async_op_then, :async_op_error, :async_op) in null;
-        final FutureOr<core::Object>#t4 = let dynamic #t5 = :result in #t5.==(null) ?{FutureOr<core::Object>} #t5 as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::Object> : #t5{FutureOr<core::Object>};
-        if(#t4 is asy::Future<core::Object>) {
-          [yield] let dynamic #t6 = asy::_awaitHelper(#t4, :async_op_then, :async_op_error, :async_op) in null;
-          :async_temporary_0 = _in::unsafeCast<core::Object>(:result);
-        }
-        else {
-          :async_temporary_0 = #t4;
-        }
-        :return_value = :async_temporary_0;
+        :return_value = let dynamic #t4 = :result in #t4.==(null) ?{FutureOr<core::Object>} #t4 as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::Object> : #t4{FutureOr<core::Object>};
         break #L1;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
diff --git a/pkg/front_end/testcases/nnbd/issue42540.dart.weak.expect b/pkg/front_end/testcases/nnbd/issue42540.dart.weak.expect
index c1d787d..aaf931d 100644
--- a/pkg/front_end/testcases/nnbd/issue42540.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/issue42540.dart.weak.expect
@@ -7,6 +7,6 @@
   return null;
 static method fn() → asy::Future<core::Object> async {
   core::Object o = await self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} core::Object;
-  return let final dynamic #t1 = await self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::Object> in #t1 is asy::Future<core::Object> ?{FutureOr<core::Object>} await #t1 : #t1;
+  return await self::getNull() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::Object>;
 }
 static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/nnbd/issue42540.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/issue42540.dart.weak.transformed.expect
index 36497a3..e61b30d 100644
--- a/pkg/front_end/testcases/nnbd/issue42540.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/issue42540.dart.weak.transformed.expect
@@ -2,7 +2,6 @@
 import self as self;
 import "dart:async" as asy;
 import "dart:core" as core;
-import "dart:_internal" as _in;
 
 static method getNull() → dynamic
   return null;
@@ -15,7 +14,6 @@
   core::int :await_jump_var = 0;
   dynamic :await_ctx_var;
   dynamic :saved_try_context_var0;
-  FutureOr<core::Object>:async_temporary_0;
   function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
     try {
       #L1:
@@ -23,15 +21,7 @@
         [yield] let dynamic #t1 = asy::_awaitHelper(self::getNull(), :async_op_then, :async_op_error, :async_op) in null;
         core::Object o = :result;
         [yield] let dynamic #t2 = asy::_awaitHelper(self::getNull(), :async_op_then, :async_op_error, :async_op) in null;
-        final FutureOr<core::Object>#t3 = :result;
-        if(#t3 is asy::Future<core::Object>) {
-          [yield] let dynamic #t4 = asy::_awaitHelper(#t3, :async_op_then, :async_op_error, :async_op) in null;
-          :async_temporary_0 = _in::unsafeCast<core::Object>(:result);
-        }
-        else {
-          :async_temporary_0 = #t3;
-        }
-        :return_value = :async_temporary_0;
+        :return_value = :result;
         break #L1;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
diff --git a/pkg/front_end/testcases/nnbd/issue42546.dart.strong.expect b/pkg/front_end/testcases/nnbd/issue42546.dart.strong.expect
index e446f7c..e5372a7 100644
--- a/pkg/front_end/testcases/nnbd/issue42546.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/issue42546.dart.strong.expect
@@ -42,11 +42,11 @@
  - 'Future' is from 'dart:async'.
  - 'Divergent' is from 'pkg/front_end/testcases/nnbd/issue42546.dart'.
   Future<Divergent<Divergent<int>>> x = (() async => new Divergent<int>())();
-                                                                          ^" in (() → asy::Future<self::Divergent<self::Divergent<self::Divergent<core::int>>>> async => let final self::Divergent<core::int> #t2 = let final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/nnbd/issue42546.dart:14:58: Error: A value of type 'Divergent<int>' can't be returned from an async function with return type 'Future<Divergent<Divergent<Divergent<int>>>>'.
+                                                                          ^" in (() → asy::Future<self::Divergent<self::Divergent<self::Divergent<core::int>>>> async => let final<BottomType> #t2 = invalid-expression "pkg/front_end/testcases/nnbd/issue42546.dart:14:58: Error: A value of type 'Divergent<int>' can't be returned from an async function with return type 'Future<Divergent<Divergent<Divergent<int>>>>'.
  - 'Divergent' is from 'pkg/front_end/testcases/nnbd/issue42546.dart'.
  - 'Future' is from 'dart:async'.
   Future<Divergent<Divergent<int>>> x = (() async => new Divergent<int>())();
-                                                         ^" in new self::Divergent::•<core::int>() as{TypeError,ForNonNullableByDefault} self::Divergent<self::Divergent<self::Divergent<core::int>>> in #t2 is asy::Future<self::Divergent<self::Divergent<self::Divergent<core::int>>>> ?{FutureOr<dynamic>} await #t2 : #t2).call() as{TypeError,ForNonNullableByDefault} asy::Future<self::Divergent<self::Divergent<core::int>>>;
+                                                         ^" in new self::Divergent::•<core::int>() as{TypeError,ForNonNullableByDefault} self::Divergent<self::Divergent<self::Divergent<core::int>>>).call() as{TypeError,ForNonNullableByDefault} asy::Future<self::Divergent<self::Divergent<core::int>>>;
 }
 static method main() → dynamic {}
 
diff --git a/pkg/front_end/testcases/nnbd/issue42546.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/issue42546.dart.strong.transformed.expect
deleted file mode 100644
index 5ae2bec..0000000
--- a/pkg/front_end/testcases/nnbd/issue42546.dart.strong.transformed.expect
+++ /dev/null
@@ -1,126 +0,0 @@
-library /*isNonNullableByDefault*/;
-//
-// Problems in library:
-//
-// pkg/front_end/testcases/nnbd/issue42546.dart:14:58: Error: A value of type 'Divergent<int>' can't be returned from an async function with return type 'Future<Divergent<Divergent<Divergent<int>>>>'.
-//  - 'Divergent' is from 'pkg/front_end/testcases/nnbd/issue42546.dart'.
-//  - 'Future' is from 'dart:async'.
-//   Future<Divergent<Divergent<int>>> x = (() async => new Divergent<int>())();
-//                                                          ^
-//
-// pkg/front_end/testcases/nnbd/issue42546.dart:14:75: Error: A value of type 'Future<Divergent<Divergent<Divergent<int>>>>' can't be assigned to a variable of type 'Future<Divergent<Divergent<int>>>'.
-//  - 'Future' is from 'dart:async'.
-//  - 'Divergent' is from 'pkg/front_end/testcases/nnbd/issue42546.dart'.
-//   Future<Divergent<Divergent<int>>> x = (() async => new Divergent<int>())();
-//                                                                           ^
-//
-import self as self;
-import "dart:core" as core;
-import "dart:async" as asy;
-import "dart:_internal" as _in;
-
-import "dart:async";
-
-class Divergent<T extends core::Object? = dynamic> extends core::Object implements asy::Future<self::Divergent<self::Divergent<self::Divergent::T%>>> {
-  synthetic constructor •() → self::Divergent<self::Divergent::T%>
-    : super core::Object::•()
-    ;
-  method noSuchMethod(core::Invocation invocation) → dynamic
-    return super.{core::Object::noSuchMethod}(invocation);
-  no-such-method-forwarder method /* from org-dartlang-sdk:///sdk/lib/async/future.dart */ catchError(core::Function onError, {(core::Object) →? core::bool test = #C1}) → asy::Future<self::Divergent<self::Divergent<self::Divergent::T%>>>
-    return this.{self::Divergent::noSuchMethod}(new core::_InvocationMirror::_withType(#C2, 0, #C3, core::List::unmodifiable<dynamic>(core::_GrowableList::_literal1<dynamic>(onError)), core::Map::unmodifiable<core::Symbol*, dynamic>(<core::Symbol*, dynamic>{#C4: test}))) as{TypeError,ForDynamic,ForNonNullableByDefault} asy::Future<self::Divergent<self::Divergent<self::Divergent::T%>>>;
-  no-such-method-forwarder method /* from org-dartlang-sdk:///sdk/lib/async/future.dart */ whenComplete(() → FutureOr<void>action) → asy::Future<self::Divergent<self::Divergent<self::Divergent::T%>>>
-    return this.{self::Divergent::noSuchMethod}(new core::_InvocationMirror::_withType(#C5, 0, #C3, core::List::unmodifiable<dynamic>(core::_GrowableList::_literal1<dynamic>(action)), core::Map::unmodifiable<core::Symbol*, dynamic>(#C7))) as{TypeError,ForDynamic,ForNonNullableByDefault} asy::Future<self::Divergent<self::Divergent<self::Divergent::T%>>>;
-  no-such-method-forwarder method /* from org-dartlang-sdk:///sdk/lib/async/future.dart */ timeout(core::Duration timeLimit, {generic-covariant-impl () →? FutureOr<self::Divergent<self::Divergent<self::Divergent::T%>>>onTimeout = #C1}) → asy::Future<self::Divergent<self::Divergent<self::Divergent::T%>>>
-    return this.{self::Divergent::noSuchMethod}(new core::_InvocationMirror::_withType(#C8, 0, #C3, core::List::unmodifiable<dynamic>(core::_GrowableList::_literal1<dynamic>(timeLimit)), core::Map::unmodifiable<core::Symbol*, dynamic>(<core::Symbol*, dynamic>{#C9: onTimeout}))) as{TypeError,ForDynamic,ForNonNullableByDefault} asy::Future<self::Divergent<self::Divergent<self::Divergent::T%>>>;
-  no-such-method-forwarder method /* from org-dartlang-sdk:///sdk/lib/async/future.dart */ then<R extends core::Object? = dynamic>((self::Divergent<self::Divergent<self::Divergent::T%>>) → FutureOr<self::Divergent::then::R%>onValue, {core::Function? onError = #C1}) → asy::Future<self::Divergent::then::R%>
-    return this.{self::Divergent::noSuchMethod}(new core::_InvocationMirror::_withType(#C10, 0, core::List::unmodifiable<core::Type*>(core::_GrowableList::_literal1<core::Type*>(self::Divergent::then::R%)), core::List::unmodifiable<dynamic>(core::_GrowableList::_literal1<dynamic>(onValue)), core::Map::unmodifiable<core::Symbol*, dynamic>(<core::Symbol*, dynamic>{#C11: onError}))) as{TypeError,ForDynamic,ForNonNullableByDefault} asy::Future<self::Divergent::then::R%>;
-  no-such-method-forwarder method /* from org-dartlang-sdk:///sdk/lib/async/future.dart */ asStream() → asy::Stream<self::Divergent<self::Divergent<self::Divergent::T%>>>
-    return this.{self::Divergent::noSuchMethod}(new core::_InvocationMirror::_withType(#C12, 0, #C3, #C6, core::Map::unmodifiable<core::Symbol*, dynamic>(#C7))) as{TypeError,ForDynamic,ForNonNullableByDefault} asy::Stream<self::Divergent<self::Divergent<self::Divergent::T%>>>;
-}
-static method test() → dynamic /* originally async */ {
-  final asy::_Future<dynamic> :async_future = new asy::_Future::•<dynamic>();
-  core::bool* :is_sync = false;
-  FutureOr<dynamic>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L1:
-      {
-        asy::Future<self::Divergent<self::Divergent<core::int>>> x = let final<BottomType> #t1 = invalid-expression "pkg/front_end/testcases/nnbd/issue42546.dart:14:75: Error: A value of type 'Future<Divergent<Divergent<Divergent<int>>>>' can't be assigned to a variable of type 'Future<Divergent<Divergent<int>>>'.
- - 'Future' is from 'dart:async'.
- - 'Divergent' is from 'pkg/front_end/testcases/nnbd/issue42546.dart'.
-  Future<Divergent<Divergent<int>>> x = (() async => new Divergent<int>())();
-                                                                          ^" in (() → asy::Future<self::Divergent<self::Divergent<self::Divergent<core::int>>>> /* originally async */ {
-          final asy::_Future<self::Divergent<self::Divergent<self::Divergent<core::int>>>> :async_future = new asy::_Future::•<self::Divergent<self::Divergent<self::Divergent<core::int>>>>();
-          core::bool* :is_sync = false;
-          FutureOr<self::Divergent<self::Divergent<self::Divergent<core::int>>>>? :return_value;
-          (dynamic) → dynamic :async_op_then;
-          (core::Object, core::StackTrace) → dynamic :async_op_error;
-          core::int :await_jump_var = 0;
-          dynamic :await_ctx_var;
-          dynamic :saved_try_context_var0;
-          FutureOr<dynamic>:async_temporary_0;
-          function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-            try {
-              #L2:
-              {
-                final self::Divergent<core::int> #t2 = let final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/nnbd/issue42546.dart:14:58: Error: A value of type 'Divergent<int>' can't be returned from an async function with return type 'Future<Divergent<Divergent<Divergent<int>>>>'.
- - 'Divergent' is from 'pkg/front_end/testcases/nnbd/issue42546.dart'.
- - 'Future' is from 'dart:async'.
-  Future<Divergent<Divergent<int>>> x = (() async => new Divergent<int>())();
-                                                         ^" in new self::Divergent::•<core::int>() as{TypeError,ForNonNullableByDefault} self::Divergent<self::Divergent<self::Divergent<core::int>>>;
-                if(#t2 is asy::Future<self::Divergent<self::Divergent<self::Divergent<core::int>>>>) {
-                  [yield] let dynamic #t4 = asy::_awaitHelper(#t2, :async_op_then, :async_op_error, :async_op) in null;
-                  :async_temporary_0 = _in::unsafeCast<self::Divergent<self::Divergent<core::int>>>(:result);
-                }
-                else {
-                  :async_temporary_0 = #t2;
-                }
-                :return_value = :async_temporary_0;
-                break #L2;
-              }
-              asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-              return;
-            }
-            on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-              asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-            }
-          :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-          :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-          :async_op.call();
-          :is_sync = true;
-          return :async_future;
-        }).call() as{TypeError,ForNonNullableByDefault} asy::Future<self::Divergent<self::Divergent<core::int>>>;
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method main() → dynamic {}
-
-constants  {
-  #C1 = null
-  #C2 = #catchError
-  #C3 = <core::Type*>[]
-  #C4 = #test
-  #C5 = #whenComplete
-  #C6 = <dynamic>[]
-  #C7 = core::_ImmutableMap<core::Symbol*, dynamic> {_kvPairs:#C6}
-  #C8 = #timeout
-  #C9 = #onTimeout
-  #C10 = #then
-  #C11 = #onError
-  #C12 = #asStream
-}
diff --git a/pkg/front_end/testcases/nnbd/issue42546.dart.weak.expect b/pkg/front_end/testcases/nnbd/issue42546.dart.weak.expect
index e446f7c..e5372a7 100644
--- a/pkg/front_end/testcases/nnbd/issue42546.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/issue42546.dart.weak.expect
@@ -42,11 +42,11 @@
  - 'Future' is from 'dart:async'.
  - 'Divergent' is from 'pkg/front_end/testcases/nnbd/issue42546.dart'.
   Future<Divergent<Divergent<int>>> x = (() async => new Divergent<int>())();
-                                                                          ^" in (() → asy::Future<self::Divergent<self::Divergent<self::Divergent<core::int>>>> async => let final self::Divergent<core::int> #t2 = let final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/nnbd/issue42546.dart:14:58: Error: A value of type 'Divergent<int>' can't be returned from an async function with return type 'Future<Divergent<Divergent<Divergent<int>>>>'.
+                                                                          ^" in (() → asy::Future<self::Divergent<self::Divergent<self::Divergent<core::int>>>> async => let final<BottomType> #t2 = invalid-expression "pkg/front_end/testcases/nnbd/issue42546.dart:14:58: Error: A value of type 'Divergent<int>' can't be returned from an async function with return type 'Future<Divergent<Divergent<Divergent<int>>>>'.
  - 'Divergent' is from 'pkg/front_end/testcases/nnbd/issue42546.dart'.
  - 'Future' is from 'dart:async'.
   Future<Divergent<Divergent<int>>> x = (() async => new Divergent<int>())();
-                                                         ^" in new self::Divergent::•<core::int>() as{TypeError,ForNonNullableByDefault} self::Divergent<self::Divergent<self::Divergent<core::int>>> in #t2 is asy::Future<self::Divergent<self::Divergent<self::Divergent<core::int>>>> ?{FutureOr<dynamic>} await #t2 : #t2).call() as{TypeError,ForNonNullableByDefault} asy::Future<self::Divergent<self::Divergent<core::int>>>;
+                                                         ^" in new self::Divergent::•<core::int>() as{TypeError,ForNonNullableByDefault} self::Divergent<self::Divergent<self::Divergent<core::int>>>).call() as{TypeError,ForNonNullableByDefault} asy::Future<self::Divergent<self::Divergent<core::int>>>;
 }
 static method main() → dynamic {}
 
diff --git a/pkg/front_end/testcases/nnbd/issue42546.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/issue42546.dart.weak.transformed.expect
deleted file mode 100644
index 5ae2bec..0000000
--- a/pkg/front_end/testcases/nnbd/issue42546.dart.weak.transformed.expect
+++ /dev/null
@@ -1,126 +0,0 @@
-library /*isNonNullableByDefault*/;
-//
-// Problems in library:
-//
-// pkg/front_end/testcases/nnbd/issue42546.dart:14:58: Error: A value of type 'Divergent<int>' can't be returned from an async function with return type 'Future<Divergent<Divergent<Divergent<int>>>>'.
-//  - 'Divergent' is from 'pkg/front_end/testcases/nnbd/issue42546.dart'.
-//  - 'Future' is from 'dart:async'.
-//   Future<Divergent<Divergent<int>>> x = (() async => new Divergent<int>())();
-//                                                          ^
-//
-// pkg/front_end/testcases/nnbd/issue42546.dart:14:75: Error: A value of type 'Future<Divergent<Divergent<Divergent<int>>>>' can't be assigned to a variable of type 'Future<Divergent<Divergent<int>>>'.
-//  - 'Future' is from 'dart:async'.
-//  - 'Divergent' is from 'pkg/front_end/testcases/nnbd/issue42546.dart'.
-//   Future<Divergent<Divergent<int>>> x = (() async => new Divergent<int>())();
-//                                                                           ^
-//
-import self as self;
-import "dart:core" as core;
-import "dart:async" as asy;
-import "dart:_internal" as _in;
-
-import "dart:async";
-
-class Divergent<T extends core::Object? = dynamic> extends core::Object implements asy::Future<self::Divergent<self::Divergent<self::Divergent::T%>>> {
-  synthetic constructor •() → self::Divergent<self::Divergent::T%>
-    : super core::Object::•()
-    ;
-  method noSuchMethod(core::Invocation invocation) → dynamic
-    return super.{core::Object::noSuchMethod}(invocation);
-  no-such-method-forwarder method /* from org-dartlang-sdk:///sdk/lib/async/future.dart */ catchError(core::Function onError, {(core::Object) →? core::bool test = #C1}) → asy::Future<self::Divergent<self::Divergent<self::Divergent::T%>>>
-    return this.{self::Divergent::noSuchMethod}(new core::_InvocationMirror::_withType(#C2, 0, #C3, core::List::unmodifiable<dynamic>(core::_GrowableList::_literal1<dynamic>(onError)), core::Map::unmodifiable<core::Symbol*, dynamic>(<core::Symbol*, dynamic>{#C4: test}))) as{TypeError,ForDynamic,ForNonNullableByDefault} asy::Future<self::Divergent<self::Divergent<self::Divergent::T%>>>;
-  no-such-method-forwarder method /* from org-dartlang-sdk:///sdk/lib/async/future.dart */ whenComplete(() → FutureOr<void>action) → asy::Future<self::Divergent<self::Divergent<self::Divergent::T%>>>
-    return this.{self::Divergent::noSuchMethod}(new core::_InvocationMirror::_withType(#C5, 0, #C3, core::List::unmodifiable<dynamic>(core::_GrowableList::_literal1<dynamic>(action)), core::Map::unmodifiable<core::Symbol*, dynamic>(#C7))) as{TypeError,ForDynamic,ForNonNullableByDefault} asy::Future<self::Divergent<self::Divergent<self::Divergent::T%>>>;
-  no-such-method-forwarder method /* from org-dartlang-sdk:///sdk/lib/async/future.dart */ timeout(core::Duration timeLimit, {generic-covariant-impl () →? FutureOr<self::Divergent<self::Divergent<self::Divergent::T%>>>onTimeout = #C1}) → asy::Future<self::Divergent<self::Divergent<self::Divergent::T%>>>
-    return this.{self::Divergent::noSuchMethod}(new core::_InvocationMirror::_withType(#C8, 0, #C3, core::List::unmodifiable<dynamic>(core::_GrowableList::_literal1<dynamic>(timeLimit)), core::Map::unmodifiable<core::Symbol*, dynamic>(<core::Symbol*, dynamic>{#C9: onTimeout}))) as{TypeError,ForDynamic,ForNonNullableByDefault} asy::Future<self::Divergent<self::Divergent<self::Divergent::T%>>>;
-  no-such-method-forwarder method /* from org-dartlang-sdk:///sdk/lib/async/future.dart */ then<R extends core::Object? = dynamic>((self::Divergent<self::Divergent<self::Divergent::T%>>) → FutureOr<self::Divergent::then::R%>onValue, {core::Function? onError = #C1}) → asy::Future<self::Divergent::then::R%>
-    return this.{self::Divergent::noSuchMethod}(new core::_InvocationMirror::_withType(#C10, 0, core::List::unmodifiable<core::Type*>(core::_GrowableList::_literal1<core::Type*>(self::Divergent::then::R%)), core::List::unmodifiable<dynamic>(core::_GrowableList::_literal1<dynamic>(onValue)), core::Map::unmodifiable<core::Symbol*, dynamic>(<core::Symbol*, dynamic>{#C11: onError}))) as{TypeError,ForDynamic,ForNonNullableByDefault} asy::Future<self::Divergent::then::R%>;
-  no-such-method-forwarder method /* from org-dartlang-sdk:///sdk/lib/async/future.dart */ asStream() → asy::Stream<self::Divergent<self::Divergent<self::Divergent::T%>>>
-    return this.{self::Divergent::noSuchMethod}(new core::_InvocationMirror::_withType(#C12, 0, #C3, #C6, core::Map::unmodifiable<core::Symbol*, dynamic>(#C7))) as{TypeError,ForDynamic,ForNonNullableByDefault} asy::Stream<self::Divergent<self::Divergent<self::Divergent::T%>>>;
-}
-static method test() → dynamic /* originally async */ {
-  final asy::_Future<dynamic> :async_future = new asy::_Future::•<dynamic>();
-  core::bool* :is_sync = false;
-  FutureOr<dynamic>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L1:
-      {
-        asy::Future<self::Divergent<self::Divergent<core::int>>> x = let final<BottomType> #t1 = invalid-expression "pkg/front_end/testcases/nnbd/issue42546.dart:14:75: Error: A value of type 'Future<Divergent<Divergent<Divergent<int>>>>' can't be assigned to a variable of type 'Future<Divergent<Divergent<int>>>'.
- - 'Future' is from 'dart:async'.
- - 'Divergent' is from 'pkg/front_end/testcases/nnbd/issue42546.dart'.
-  Future<Divergent<Divergent<int>>> x = (() async => new Divergent<int>())();
-                                                                          ^" in (() → asy::Future<self::Divergent<self::Divergent<self::Divergent<core::int>>>> /* originally async */ {
-          final asy::_Future<self::Divergent<self::Divergent<self::Divergent<core::int>>>> :async_future = new asy::_Future::•<self::Divergent<self::Divergent<self::Divergent<core::int>>>>();
-          core::bool* :is_sync = false;
-          FutureOr<self::Divergent<self::Divergent<self::Divergent<core::int>>>>? :return_value;
-          (dynamic) → dynamic :async_op_then;
-          (core::Object, core::StackTrace) → dynamic :async_op_error;
-          core::int :await_jump_var = 0;
-          dynamic :await_ctx_var;
-          dynamic :saved_try_context_var0;
-          FutureOr<dynamic>:async_temporary_0;
-          function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-            try {
-              #L2:
-              {
-                final self::Divergent<core::int> #t2 = let final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/nnbd/issue42546.dart:14:58: Error: A value of type 'Divergent<int>' can't be returned from an async function with return type 'Future<Divergent<Divergent<Divergent<int>>>>'.
- - 'Divergent' is from 'pkg/front_end/testcases/nnbd/issue42546.dart'.
- - 'Future' is from 'dart:async'.
-  Future<Divergent<Divergent<int>>> x = (() async => new Divergent<int>())();
-                                                         ^" in new self::Divergent::•<core::int>() as{TypeError,ForNonNullableByDefault} self::Divergent<self::Divergent<self::Divergent<core::int>>>;
-                if(#t2 is asy::Future<self::Divergent<self::Divergent<self::Divergent<core::int>>>>) {
-                  [yield] let dynamic #t4 = asy::_awaitHelper(#t2, :async_op_then, :async_op_error, :async_op) in null;
-                  :async_temporary_0 = _in::unsafeCast<self::Divergent<self::Divergent<core::int>>>(:result);
-                }
-                else {
-                  :async_temporary_0 = #t2;
-                }
-                :return_value = :async_temporary_0;
-                break #L2;
-              }
-              asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-              return;
-            }
-            on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-              asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-            }
-          :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-          :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-          :async_op.call();
-          :is_sync = true;
-          return :async_future;
-        }).call() as{TypeError,ForNonNullableByDefault} asy::Future<self::Divergent<self::Divergent<core::int>>>;
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method main() → dynamic {}
-
-constants  {
-  #C1 = null
-  #C2 = #catchError
-  #C3 = <core::Type*>[]
-  #C4 = #test
-  #C5 = #whenComplete
-  #C6 = <dynamic>[]
-  #C7 = core::_ImmutableMap<core::Symbol*, dynamic> {_kvPairs:#C6}
-  #C8 = #timeout
-  #C9 = #onTimeout
-  #C10 = #then
-  #C11 = #onError
-  #C12 = #asStream
-}
diff --git a/pkg/front_end/testcases/nnbd/issue42743.dart.strong.expect b/pkg/front_end/testcases/nnbd/issue42743.dart.strong.expect
index eaaabba4..1d21b07 100644
--- a/pkg/front_end/testcases/nnbd/issue42743.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/issue42743.dart.strong.expect
@@ -11,6 +11,6 @@
   };
   (dynamic _) → asy::Future<core::int?> async {
     if(b)
-      return let final core::int #t1 = 42 in #t1 is asy::Future<core::int?> ?{FutureOr<dynamic>} await #t1 : #t1;
+      return 42;
   };
 }
diff --git a/pkg/front_end/testcases/nnbd/issue42743.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/issue42743.dart.strong.transformed.expect
index 1509333..0ab4a75 100644
--- a/pkg/front_end/testcases/nnbd/issue42743.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/issue42743.dart.strong.transformed.expect
@@ -2,7 +2,6 @@
 import self as self;
 import "dart:async" as asy;
 import "dart:core" as core;
-import "dart:_internal" as _in;
 
 static method main() → dynamic /* originally async */ {
   final asy::_Future<dynamic> :async_future = new asy::_Future::•<dynamic>();
@@ -29,22 +28,12 @@
           (core::Object, core::StackTrace) → dynamic :async_op_error;
           core::int :await_jump_var = 0;
           dynamic :await_ctx_var;
-          dynamic :saved_try_context_var0;
-          FutureOr<dynamic>:async_temporary_0;
           function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
             try {
               #L2:
               {
                 if(b) {
-                  final core::int #t1 = 42;
-                  if(#t1 is asy::Future<core::int?>) {
-                    [yield] let dynamic #t2 = asy::_awaitHelper(#t1, :async_op_then, :async_op_error, :async_op) in null;
-                    :async_temporary_0 = _in::unsafeCast<core::int>(:result);
-                  }
-                  else {
-                    :async_temporary_0 = #t1;
-                  }
-                  :return_value = :async_temporary_0;
+                  :return_value = 42;
                   break #L2;
                 }
               }
diff --git a/pkg/front_end/testcases/nnbd/issue42743.dart.weak.expect b/pkg/front_end/testcases/nnbd/issue42743.dart.weak.expect
index eaaabba4..1d21b07 100644
--- a/pkg/front_end/testcases/nnbd/issue42743.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/issue42743.dart.weak.expect
@@ -11,6 +11,6 @@
   };
   (dynamic _) → asy::Future<core::int?> async {
     if(b)
-      return let final core::int #t1 = 42 in #t1 is asy::Future<core::int?> ?{FutureOr<dynamic>} await #t1 : #t1;
+      return 42;
   };
 }
diff --git a/pkg/front_end/testcases/nnbd/issue42743.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/issue42743.dart.weak.transformed.expect
index 1509333..0ab4a75 100644
--- a/pkg/front_end/testcases/nnbd/issue42743.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/issue42743.dart.weak.transformed.expect
@@ -2,7 +2,6 @@
 import self as self;
 import "dart:async" as asy;
 import "dart:core" as core;
-import "dart:_internal" as _in;
 
 static method main() → dynamic /* originally async */ {
   final asy::_Future<dynamic> :async_future = new asy::_Future::•<dynamic>();
@@ -29,22 +28,12 @@
           (core::Object, core::StackTrace) → dynamic :async_op_error;
           core::int :await_jump_var = 0;
           dynamic :await_ctx_var;
-          dynamic :saved_try_context_var0;
-          FutureOr<dynamic>:async_temporary_0;
           function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
             try {
               #L2:
               {
                 if(b) {
-                  final core::int #t1 = 42;
-                  if(#t1 is asy::Future<core::int?>) {
-                    [yield] let dynamic #t2 = asy::_awaitHelper(#t1, :async_op_then, :async_op_error, :async_op) in null;
-                    :async_temporary_0 = _in::unsafeCast<core::int>(:result);
-                  }
-                  else {
-                    :async_temporary_0 = #t1;
-                  }
-                  :return_value = :async_temporary_0;
+                  :return_value = 42;
                   break #L2;
                 }
               }
diff --git a/pkg/front_end/testcases/nnbd/later.dart.strong.expect b/pkg/front_end/testcases/nnbd/later.dart.strong.expect
index 17dcee5..df47af6 100644
--- a/pkg/front_end/testcases/nnbd/later.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/later.dart.strong.expect
@@ -120,7 +120,7 @@
   await for (core::String s in asy::Stream::fromIterable<core::String>(<core::String>["hest"])) {
     core::print(s);
   }
-  return let final core::String #t2 = "hest" in #t2 is asy::Future<dynamic> ?{FutureOr<dynamic>} await #t2 : #t2;
+  return "hest";
 }
 static method fisk() → dynamic async {
   late core::String s1 = invalid-expression "pkg/front_end/testcases/nnbd/later.dart:38:20: Error: `await` expressions are not supported in late local initializers.
@@ -129,7 +129,7 @@
   late core::String s2 = "${#C1}${invalid-expression "pkg/front_end/testcases/nnbd/later.dart:39:30: Error: `await` expressions are not supported in late local initializers.
   late String s2 = '\${fisk}\${await hest()}\${fisk}';
                              ^^^^^"}${#C1}";
-  late core::Function f = () → asy::Future<dynamic> async => let final dynamic #t3 = await self::hest() in #t3 is asy::Future<dynamic> ?{FutureOr<dynamic>} await #t3 : #t3;
+  late core::Function f = () → asy::Future<dynamic> async => await self::hest();
 }
 static method main() → dynamic {}
 
diff --git a/pkg/front_end/testcases/nnbd/later.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/later.dart.strong.transformed.expect
index 53a4028..2aba575 100644
--- a/pkg/front_end/testcases/nnbd/later.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/later.dart.strong.transformed.expect
@@ -135,8 +135,6 @@
   dynamic :saved_try_context_var1;
   dynamic :exception0;
   dynamic :stack_trace0;
-  FutureOr<dynamic>:async_temporary_0;
-  FutureOr<dynamic>:async_temporary_1;
   function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
     try {
       #L1:
@@ -164,15 +162,7 @@
               :result;
             }
         }
-        final core::String #t5 = "hest";
-        if(#t5 is asy::Future<dynamic>) {
-          [yield] let dynamic #t6 = asy::_awaitHelper(#t5, :async_op_then, :async_op_error, :async_op) in null;
-          :async_temporary_1 = _in::unsafeCast<core::String>(:result);
-        }
-        else {
-          :async_temporary_1 = #t5;
-        }
-        :return_value = :async_temporary_1;
+        :return_value = "hest";
         break #L1;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -219,21 +209,12 @@
             core::int :await_jump_var = 0;
             dynamic :await_ctx_var;
             dynamic :saved_try_context_var0;
-            FutureOr<dynamic>:async_temporary_0;
             function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
               try {
                 #L4:
                 {
-                  [yield] let dynamic #t7 = asy::_awaitHelper(self::hest(), :async_op_then, :async_op_error, :async_op) in null;
-                  final dynamic #t8 = :result;
-                  if(#t8 is asy::Future<dynamic>) {
-                    [yield] let dynamic #t9 = asy::_awaitHelper(#t8, :async_op_then, :async_op_error, :async_op) in null;
-                    :async_temporary_0 = :result;
-                  }
-                  else {
-                    :async_temporary_0 = #t8;
-                  }
-                  :return_value = :async_temporary_0;
+                  [yield] let dynamic #t5 = asy::_awaitHelper(self::hest(), :async_op_then, :async_op_error, :async_op) in null;
+                  :return_value = :result;
                   break #L4;
                 }
                 asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
diff --git a/pkg/front_end/testcases/nnbd/later.dart.weak.expect b/pkg/front_end/testcases/nnbd/later.dart.weak.expect
index 17dcee5..df47af6 100644
--- a/pkg/front_end/testcases/nnbd/later.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/later.dart.weak.expect
@@ -120,7 +120,7 @@
   await for (core::String s in asy::Stream::fromIterable<core::String>(<core::String>["hest"])) {
     core::print(s);
   }
-  return let final core::String #t2 = "hest" in #t2 is asy::Future<dynamic> ?{FutureOr<dynamic>} await #t2 : #t2;
+  return "hest";
 }
 static method fisk() → dynamic async {
   late core::String s1 = invalid-expression "pkg/front_end/testcases/nnbd/later.dart:38:20: Error: `await` expressions are not supported in late local initializers.
@@ -129,7 +129,7 @@
   late core::String s2 = "${#C1}${invalid-expression "pkg/front_end/testcases/nnbd/later.dart:39:30: Error: `await` expressions are not supported in late local initializers.
   late String s2 = '\${fisk}\${await hest()}\${fisk}';
                              ^^^^^"}${#C1}";
-  late core::Function f = () → asy::Future<dynamic> async => let final dynamic #t3 = await self::hest() in #t3 is asy::Future<dynamic> ?{FutureOr<dynamic>} await #t3 : #t3;
+  late core::Function f = () → asy::Future<dynamic> async => await self::hest();
 }
 static method main() → dynamic {}
 
diff --git a/pkg/front_end/testcases/nnbd/later.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/later.dart.weak.transformed.expect
index 53a4028..2aba575 100644
--- a/pkg/front_end/testcases/nnbd/later.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/later.dart.weak.transformed.expect
@@ -135,8 +135,6 @@
   dynamic :saved_try_context_var1;
   dynamic :exception0;
   dynamic :stack_trace0;
-  FutureOr<dynamic>:async_temporary_0;
-  FutureOr<dynamic>:async_temporary_1;
   function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
     try {
       #L1:
@@ -164,15 +162,7 @@
               :result;
             }
         }
-        final core::String #t5 = "hest";
-        if(#t5 is asy::Future<dynamic>) {
-          [yield] let dynamic #t6 = asy::_awaitHelper(#t5, :async_op_then, :async_op_error, :async_op) in null;
-          :async_temporary_1 = _in::unsafeCast<core::String>(:result);
-        }
-        else {
-          :async_temporary_1 = #t5;
-        }
-        :return_value = :async_temporary_1;
+        :return_value = "hest";
         break #L1;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -219,21 +209,12 @@
             core::int :await_jump_var = 0;
             dynamic :await_ctx_var;
             dynamic :saved_try_context_var0;
-            FutureOr<dynamic>:async_temporary_0;
             function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
               try {
                 #L4:
                 {
-                  [yield] let dynamic #t7 = asy::_awaitHelper(self::hest(), :async_op_then, :async_op_error, :async_op) in null;
-                  final dynamic #t8 = :result;
-                  if(#t8 is asy::Future<dynamic>) {
-                    [yield] let dynamic #t9 = asy::_awaitHelper(#t8, :async_op_then, :async_op_error, :async_op) in null;
-                    :async_temporary_0 = :result;
-                  }
-                  else {
-                    :async_temporary_0 = #t8;
-                  }
-                  :return_value = :async_temporary_0;
+                  [yield] let dynamic #t5 = asy::_awaitHelper(self::hest(), :async_op_then, :async_op_error, :async_op) in null;
+                  :return_value = :result;
                   break #L4;
                 }
                 asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
diff --git a/pkg/front_end/testcases/nnbd/return_async.dart.strong.expect b/pkg/front_end/testcases/nnbd/return_async.dart.strong.expect
index 7fe1ab7..2c50b42 100644
--- a/pkg/front_end/testcases/nnbd/return_async.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/return_async.dart.strong.expect
@@ -28,6 +28,6 @@
   }, (core::Object e, core::StackTrace s) → void {
     completer.{asy::Completer::completeError}(e, s);
   });
-  return let final asy::Future<void> #t1 = completer.{asy::Completer::future} in #t1 is asy::Future<void> ?{FutureOr<void>} await #t1 : #t1;
+  return completer.{asy::Completer::future};
 }
 static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/nnbd/return_async.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/return_async.dart.strong.transformed.expect
index d88bd46..b9094ae 100644
--- a/pkg/front_end/testcases/nnbd/return_async.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/return_async.dart.strong.transformed.expect
@@ -106,8 +106,6 @@
   (core::Object, core::StackTrace) → dynamic :async_op_error;
   core::int :await_jump_var = 0;
   dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  FutureOr<void>:async_temporary_0;
   function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
     try {
       #L4:
@@ -144,15 +142,7 @@
         }, (core::Object e, core::StackTrace s) → void {
           completer.{asy::Completer::completeError}(e, s);
         });
-        final asy::Future<void> #t7 = completer.{asy::Completer::future};
-        if(#t7 is asy::Future<void>) {
-          [yield] let dynamic #t8 = asy::_awaitHelper(#t7, :async_op_then, :async_op_error, :async_op) in null;
-          :async_temporary_0 = _in::unsafeCast<void>(:result);
-        }
-        else {
-          :async_temporary_0 = #t7;
-        }
-        :return_value = :async_temporary_0;
+        :return_value = completer.{asy::Completer::future};
         break #L4;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
diff --git a/pkg/front_end/testcases/nnbd/return_async.dart.weak.expect b/pkg/front_end/testcases/nnbd/return_async.dart.weak.expect
index 7fe1ab7..2c50b42 100644
--- a/pkg/front_end/testcases/nnbd/return_async.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/return_async.dart.weak.expect
@@ -28,6 +28,6 @@
   }, (core::Object e, core::StackTrace s) → void {
     completer.{asy::Completer::completeError}(e, s);
   });
-  return let final asy::Future<void> #t1 = completer.{asy::Completer::future} in #t1 is asy::Future<void> ?{FutureOr<void>} await #t1 : #t1;
+  return completer.{asy::Completer::future};
 }
 static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/nnbd/return_async.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/return_async.dart.weak.transformed.expect
index d88bd46..b9094ae 100644
--- a/pkg/front_end/testcases/nnbd/return_async.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/return_async.dart.weak.transformed.expect
@@ -106,8 +106,6 @@
   (core::Object, core::StackTrace) → dynamic :async_op_error;
   core::int :await_jump_var = 0;
   dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  FutureOr<void>:async_temporary_0;
   function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
     try {
       #L4:
@@ -144,15 +142,7 @@
         }, (core::Object e, core::StackTrace s) → void {
           completer.{asy::Completer::completeError}(e, s);
         });
-        final asy::Future<void> #t7 = completer.{asy::Completer::future};
-        if(#t7 is asy::Future<void>) {
-          [yield] let dynamic #t8 = asy::_awaitHelper(#t7, :async_op_then, :async_op_error, :async_op) in null;
-          :async_temporary_0 = _in::unsafeCast<void>(:result);
-        }
-        else {
-          :async_temporary_0 = #t7;
-        }
-        :return_value = :async_temporary_0;
+        :return_value = completer.{asy::Completer::future};
         break #L4;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
diff --git a/pkg/front_end/testcases/nnbd/return_from_async.dart b/pkg/front_end/testcases/nnbd/return_from_async.dart
deleted file mode 100644
index 93e646e..0000000
--- a/pkg/front_end/testcases/nnbd/return_from_async.dart
+++ /dev/null
@@ -1,98 +0,0 @@
-// Copyright (c) 2020, 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.
-
-import 'dart:async';
-
-bool caughtFutureOrInt = false;
-
-FutureOr<int> throwFutureOrInt() async {
-  throw 'FutureOr<int>';
-}
-
-Future<int> callFutureOrInt() async {
-  try {
-    return throwFutureOrInt();
-  } catch (e) {
-    print('Caught "$e"');
-    caughtFutureOrInt = true;
-    return 0;
-  }
-}
-
-bool caughtInt = false;
-
-int throwInt() {
-  throw 'int';
-}
-
-Future<int> callInt() async {
-  try {
-    return throwInt();
-  } catch (e) {
-    print('Caught "$e"');
-    caughtInt = true;
-    return 0;
-  }
-}
-
-bool caughtFutureInt = false;
-
-Future<int> throwFutureInt() async {
-  throw 'Future<int>';
-}
-
-Future<int> callFutureInt() async {
-  try {
-    return throwFutureInt();
-  } catch (e) {
-    print('Caught "$e"');
-    caughtFutureInt = true;
-    return 0;
-  }
-}
-
-bool caughtDynamic = false;
-
-dynamic throwDynamic() {
-  throw 'dynamic';
-}
-
-Future<int> callDynamic() async {
-  try {
-    return throwDynamic();
-  } catch (e) {
-    print('Caught "$e"');
-    caughtDynamic = true;
-    return 0;
-  }
-}
-
-bool caughtFutureNum = false;
-
-Future<int> throwFutureNum() async {
-  throw 'Future<num>';
-}
-
-Future<num> callFutureNum() async {
-  try {
-    return throwFutureNum();
-  } catch (e) {
-    print('Caught "$e"');
-    caughtFutureNum = true;
-    return 0;
-  }
-}
-
-void main() async {
-  await callFutureOrInt();
-  if (!caughtFutureOrInt) throw 'Uncaught async return';
-  await callInt();
-  if (!caughtInt) throw 'Uncaught async return';
-  await callFutureInt();
-  if (!caughtFutureInt) throw 'Uncaught async return';
-  await callDynamic();
-  if (!caughtDynamic) throw 'Uncaught async return';
-  await callFutureNum();
-  if (!caughtFutureNum) throw 'Uncaught async return';
-}
diff --git a/pkg/front_end/testcases/nnbd/return_from_async.dart.outline.expect b/pkg/front_end/testcases/nnbd/return_from_async.dart.outline.expect
deleted file mode 100644
index fce58f8..0000000
--- a/pkg/front_end/testcases/nnbd/return_from_async.dart.outline.expect
+++ /dev/null
@@ -1,34 +0,0 @@
-library /*isNonNullableByDefault*/;
-import self as self;
-import "dart:core" as core;
-import "dart:async" as asy;
-
-import "dart:async";
-
-static field core::bool caughtFutureOrInt;
-static field core::bool caughtInt;
-static field core::bool caughtFutureInt;
-static field core::bool caughtDynamic;
-static field core::bool caughtFutureNum;
-static method throwFutureOrInt() → FutureOr<core::int> async 
-  ;
-static method callFutureOrInt() → asy::Future<core::int> async 
-  ;
-static method throwInt() → core::int
-  ;
-static method callInt() → asy::Future<core::int> async 
-  ;
-static method throwFutureInt() → asy::Future<core::int> async 
-  ;
-static method callFutureInt() → asy::Future<core::int> async 
-  ;
-static method throwDynamic() → dynamic
-  ;
-static method callDynamic() → asy::Future<core::int> async 
-  ;
-static method throwFutureNum() → asy::Future<core::int> async 
-  ;
-static method callFutureNum() → asy::Future<core::num> async 
-  ;
-static method main() → void async 
-  ;
diff --git a/pkg/front_end/testcases/nnbd/return_from_async.dart.strong.expect b/pkg/front_end/testcases/nnbd/return_from_async.dart.strong.expect
deleted file mode 100644
index 07f9c6e..0000000
--- a/pkg/front_end/testcases/nnbd/return_from_async.dart.strong.expect
+++ /dev/null
@@ -1,94 +0,0 @@
-library /*isNonNullableByDefault*/;
-import self as self;
-import "dart:core" as core;
-import "dart:async" as asy;
-
-import "dart:async";
-
-static field core::bool caughtFutureOrInt = false;
-static field core::bool caughtInt = false;
-static field core::bool caughtFutureInt = false;
-static field core::bool caughtDynamic = false;
-static field core::bool caughtFutureNum = false;
-static method throwFutureOrInt() → FutureOr<core::int> async {
-  throw "FutureOr<int>";
-}
-static method callFutureOrInt() → asy::Future<core::int> async {
-  try {
-    return let final FutureOr<core::int>#t1 = self::throwFutureOrInt() in #t1 is asy::Future<core::int> ?{FutureOr<core::int>} await #t1 : #t1;
-  }
-  on core::Object catch(final core::Object e) {
-    core::print("Caught \"${e}\"");
-    self::caughtFutureOrInt = true;
-    return let final core::int #t2 = 0 in #t2 is asy::Future<core::int> ?{FutureOr<core::int>} await #t2 : #t2;
-  }
-}
-static method throwInt() → core::int {
-  throw "int";
-}
-static method callInt() → asy::Future<core::int> async {
-  try {
-    return let final core::int #t3 = self::throwInt() in #t3 is asy::Future<core::int> ?{FutureOr<core::int>} await #t3 : #t3;
-  }
-  on core::Object catch(final core::Object e) {
-    core::print("Caught \"${e}\"");
-    self::caughtInt = true;
-    return let final core::int #t4 = 0 in #t4 is asy::Future<core::int> ?{FutureOr<core::int>} await #t4 : #t4;
-  }
-}
-static method throwFutureInt() → asy::Future<core::int> async {
-  throw "Future<int>";
-}
-static method callFutureInt() → asy::Future<core::int> async {
-  try {
-    return let final asy::Future<core::int> #t5 = self::throwFutureInt() in #t5 is asy::Future<core::int> ?{FutureOr<core::int>} await #t5 : #t5;
-  }
-  on core::Object catch(final core::Object e) {
-    core::print("Caught \"${e}\"");
-    self::caughtFutureInt = true;
-    return let final core::int #t6 = 0 in #t6 is asy::Future<core::int> ?{FutureOr<core::int>} await #t6 : #t6;
-  }
-}
-static method throwDynamic() → dynamic {
-  throw "dynamic";
-}
-static method callDynamic() → asy::Future<core::int> async {
-  try {
-    return let final dynamic #t7 = self::throwDynamic() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::int> in #t7 is asy::Future<core::int> ?{FutureOr<core::int>} await #t7 : #t7;
-  }
-  on core::Object catch(final core::Object e) {
-    core::print("Caught \"${e}\"");
-    self::caughtDynamic = true;
-    return let final core::int #t8 = 0 in #t8 is asy::Future<core::int> ?{FutureOr<core::int>} await #t8 : #t8;
-  }
-}
-static method throwFutureNum() → asy::Future<core::int> async {
-  throw "Future<num>";
-}
-static method callFutureNum() → asy::Future<core::num> async {
-  try {
-    return let final asy::Future<core::int> #t9 = self::throwFutureNum() in #t9 is asy::Future<core::num> ?{FutureOr<core::num>} await #t9 : #t9;
-  }
-  on core::Object catch(final core::Object e) {
-    core::print("Caught \"${e}\"");
-    self::caughtFutureNum = true;
-    return let final core::int #t10 = 0 in #t10 is asy::Future<core::num> ?{FutureOr<core::num>} await #t10 : #t10;
-  }
-}
-static method main() → void async {
-  await self::callFutureOrInt();
-  if(!self::caughtFutureOrInt)
-    throw "Uncaught async return";
-  await self::callInt();
-  if(!self::caughtInt)
-    throw "Uncaught async return";
-  await self::callFutureInt();
-  if(!self::caughtFutureInt)
-    throw "Uncaught async return";
-  await self::callDynamic();
-  if(!self::caughtDynamic)
-    throw "Uncaught async return";
-  await self::callFutureNum();
-  if(!self::caughtFutureNum)
-    throw "Uncaught async return";
-}
diff --git a/pkg/front_end/testcases/nnbd/return_from_async.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/return_from_async.dart.strong.transformed.expect
deleted file mode 100644
index 5bd5d9f..0000000
--- a/pkg/front_end/testcases/nnbd/return_from_async.dart.strong.transformed.expect
+++ /dev/null
@@ -1,433 +0,0 @@
-library /*isNonNullableByDefault*/;
-import self as self;
-import "dart:core" as core;
-import "dart:async" as asy;
-import "dart:_internal" as _in;
-
-import "dart:async";
-
-static field core::bool caughtFutureOrInt = false;
-static field core::bool caughtInt = false;
-static field core::bool caughtFutureInt = false;
-static field core::bool caughtDynamic = false;
-static field core::bool caughtFutureNum = false;
-static method throwFutureOrInt() → FutureOr<core::int> /* originally async */ {
-  final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
-  core::bool* :is_sync = false;
-  FutureOr<core::int>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L1:
-      {
-        throw "FutureOr<int>";
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method callFutureOrInt() → asy::Future<core::int> /* originally async */ {
-  final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
-  core::bool* :is_sync = false;
-  FutureOr<core::int>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  dynamic :saved_try_context_var1;
-  dynamic :exception0;
-  dynamic :stack_trace0;
-  FutureOr<core::int>:async_temporary_0;
-  FutureOr<core::int>:async_temporary_1;
-  FutureOr<core::int>:async_temporary_2;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L2:
-      {
-        try {
-          final FutureOr<core::int>#t1 = self::throwFutureOrInt();
-          if(#t1 is asy::Future<core::int>) {
-            [yield] let dynamic #t2 = asy::_awaitHelper(#t1, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_0 = #t1;
-          }
-          :return_value = :async_temporary_0;
-          break #L2;
-        }
-        on core::Object catch(final core::Object e) {
-          core::print("Caught \"${e}\"");
-          self::caughtFutureOrInt = true;
-          final core::int #t3 = 0;
-          if(#t3 is asy::Future<core::int>) {
-            [yield] let dynamic #t4 = asy::_awaitHelper(#t3, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_2 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_2 = #t3;
-          }
-          :return_value = :async_temporary_2;
-          break #L2;
-        }
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method throwInt() → core::int {
-  throw "int";
-}
-static method callInt() → asy::Future<core::int> /* originally async */ {
-  final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
-  core::bool* :is_sync = false;
-  FutureOr<core::int>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  dynamic :saved_try_context_var1;
-  dynamic :exception0;
-  dynamic :stack_trace0;
-  FutureOr<core::int>:async_temporary_0;
-  FutureOr<core::int>:async_temporary_1;
-  FutureOr<core::int>:async_temporary_2;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L3:
-      {
-        try {
-          final core::int #t5 = self::throwInt();
-          if(#t5 is asy::Future<core::int>) {
-            [yield] let dynamic #t6 = asy::_awaitHelper(#t5, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_0 = #t5;
-          }
-          :return_value = :async_temporary_0;
-          break #L3;
-        }
-        on core::Object catch(final core::Object e) {
-          core::print("Caught \"${e}\"");
-          self::caughtInt = true;
-          final core::int #t7 = 0;
-          if(#t7 is asy::Future<core::int>) {
-            [yield] let dynamic #t8 = asy::_awaitHelper(#t7, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_2 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_2 = #t7;
-          }
-          :return_value = :async_temporary_2;
-          break #L3;
-        }
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method throwFutureInt() → asy::Future<core::int> /* originally async */ {
-  final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
-  core::bool* :is_sync = false;
-  FutureOr<core::int>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L4:
-      {
-        throw "Future<int>";
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method callFutureInt() → asy::Future<core::int> /* originally async */ {
-  final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
-  core::bool* :is_sync = false;
-  FutureOr<core::int>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  dynamic :saved_try_context_var1;
-  dynamic :exception0;
-  dynamic :stack_trace0;
-  FutureOr<core::int>:async_temporary_0;
-  FutureOr<core::int>:async_temporary_1;
-  FutureOr<core::int>:async_temporary_2;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L5:
-      {
-        try {
-          final asy::Future<core::int> #t9 = self::throwFutureInt();
-          if(#t9 is asy::Future<core::int>) {
-            [yield] let dynamic #t10 = asy::_awaitHelper(#t9, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_0 = #t9;
-          }
-          :return_value = :async_temporary_0;
-          break #L5;
-        }
-        on core::Object catch(final core::Object e) {
-          core::print("Caught \"${e}\"");
-          self::caughtFutureInt = true;
-          final core::int #t11 = 0;
-          if(#t11 is asy::Future<core::int>) {
-            [yield] let dynamic #t12 = asy::_awaitHelper(#t11, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_2 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_2 = #t11;
-          }
-          :return_value = :async_temporary_2;
-          break #L5;
-        }
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method throwDynamic() → dynamic {
-  throw "dynamic";
-}
-static method callDynamic() → asy::Future<core::int> /* originally async */ {
-  final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
-  core::bool* :is_sync = false;
-  FutureOr<core::int>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  dynamic :saved_try_context_var1;
-  dynamic :exception0;
-  dynamic :stack_trace0;
-  FutureOr<core::int>:async_temporary_0;
-  FutureOr<core::int>:async_temporary_1;
-  FutureOr<core::int>:async_temporary_2;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L6:
-      {
-        try {
-          final FutureOr<core::int>#t13 = self::throwDynamic() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::int>;
-          if(#t13 is asy::Future<core::int>) {
-            [yield] let dynamic #t14 = asy::_awaitHelper(#t13, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_0 = #t13;
-          }
-          :return_value = :async_temporary_0;
-          break #L6;
-        }
-        on core::Object catch(final core::Object e) {
-          core::print("Caught \"${e}\"");
-          self::caughtDynamic = true;
-          final core::int #t15 = 0;
-          if(#t15 is asy::Future<core::int>) {
-            [yield] let dynamic #t16 = asy::_awaitHelper(#t15, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_2 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_2 = #t15;
-          }
-          :return_value = :async_temporary_2;
-          break #L6;
-        }
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method throwFutureNum() → asy::Future<core::int> /* originally async */ {
-  final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
-  core::bool* :is_sync = false;
-  FutureOr<core::int>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L7:
-      {
-        throw "Future<num>";
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method callFutureNum() → asy::Future<core::num> /* originally async */ {
-  final asy::_Future<core::num> :async_future = new asy::_Future::•<core::num>();
-  core::bool* :is_sync = false;
-  FutureOr<core::num>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  dynamic :saved_try_context_var1;
-  dynamic :exception0;
-  dynamic :stack_trace0;
-  FutureOr<core::num>:async_temporary_0;
-  FutureOr<core::num>:async_temporary_1;
-  FutureOr<core::num>:async_temporary_2;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L8:
-      {
-        try {
-          final asy::Future<core::int> #t17 = self::throwFutureNum();
-          if(#t17 is asy::Future<core::num>) {
-            [yield] let dynamic #t18 = asy::_awaitHelper(#t17, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_0 = #t17;
-          }
-          :return_value = :async_temporary_0;
-          break #L8;
-        }
-        on core::Object catch(final core::Object e) {
-          core::print("Caught \"${e}\"");
-          self::caughtFutureNum = true;
-          final core::int #t19 = 0;
-          if(#t19 is asy::Future<core::num>) {
-            [yield] let dynamic #t20 = asy::_awaitHelper(#t19, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_2 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_2 = #t19;
-          }
-          :return_value = :async_temporary_2;
-          break #L8;
-        }
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method main() → void /* originally async */ {
-  final asy::_Future<dynamic> :async_future = new asy::_Future::•<dynamic>();
-  core::bool* :is_sync = false;
-  FutureOr<dynamic>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L9:
-      {
-        [yield] let dynamic #t21 = asy::_awaitHelper(self::callFutureOrInt(), :async_op_then, :async_op_error, :async_op) in null;
-        _in::unsafeCast<core::int>(:result);
-        if(!self::caughtFutureOrInt)
-          throw "Uncaught async return";
-        [yield] let dynamic #t22 = asy::_awaitHelper(self::callInt(), :async_op_then, :async_op_error, :async_op) in null;
-        _in::unsafeCast<core::int>(:result);
-        if(!self::caughtInt)
-          throw "Uncaught async return";
-        [yield] let dynamic #t23 = asy::_awaitHelper(self::callFutureInt(), :async_op_then, :async_op_error, :async_op) in null;
-        _in::unsafeCast<core::int>(:result);
-        if(!self::caughtFutureInt)
-          throw "Uncaught async return";
-        [yield] let dynamic #t24 = asy::_awaitHelper(self::callDynamic(), :async_op_then, :async_op_error, :async_op) in null;
-        _in::unsafeCast<core::int>(:result);
-        if(!self::caughtDynamic)
-          throw "Uncaught async return";
-        [yield] let dynamic #t25 = asy::_awaitHelper(self::callFutureNum(), :async_op_then, :async_op_error, :async_op) in null;
-        _in::unsafeCast<core::num>(:result);
-        if(!self::caughtFutureNum)
-          throw "Uncaught async return";
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
diff --git a/pkg/front_end/testcases/nnbd/return_from_async.dart.textual_outline.expect b/pkg/front_end/testcases/nnbd/return_from_async.dart.textual_outline.expect
deleted file mode 100644
index bc32d23..0000000
--- a/pkg/front_end/testcases/nnbd/return_from_async.dart.textual_outline.expect
+++ /dev/null
@@ -1,18 +0,0 @@
-import 'dart:async';
-
-bool caughtFutureOrInt = false;
-FutureOr<int> throwFutureOrInt() async {}
-Future<int> callFutureOrInt() async {}
-bool caughtInt = false;
-int throwInt() {}
-Future<int> callInt() async {}
-bool caughtFutureInt = false;
-Future<int> throwFutureInt() async {}
-Future<int> callFutureInt() async {}
-bool caughtDynamic = false;
-dynamic throwDynamic() {}
-Future<int> callDynamic() async {}
-bool caughtFutureNum = false;
-Future<int> throwFutureNum() async {}
-Future<num> callFutureNum() async {}
-void main() async {}
diff --git a/pkg/front_end/testcases/nnbd/return_from_async.dart.textual_outline_modelled.expect b/pkg/front_end/testcases/nnbd/return_from_async.dart.textual_outline_modelled.expect
deleted file mode 100644
index 7a7e905..0000000
--- a/pkg/front_end/testcases/nnbd/return_from_async.dart.textual_outline_modelled.expect
+++ /dev/null
@@ -1,18 +0,0 @@
-import 'dart:async';
-
-Future<int> callDynamic() async {}
-Future<int> callFutureInt() async {}
-Future<int> callFutureOrInt() async {}
-Future<int> callInt() async {}
-Future<int> throwFutureInt() async {}
-Future<int> throwFutureNum() async {}
-Future<num> callFutureNum() async {}
-FutureOr<int> throwFutureOrInt() async {}
-bool caughtDynamic = false;
-bool caughtFutureInt = false;
-bool caughtFutureNum = false;
-bool caughtFutureOrInt = false;
-bool caughtInt = false;
-dynamic throwDynamic() {}
-int throwInt() {}
-void main() async {}
diff --git a/pkg/front_end/testcases/nnbd/return_from_async.dart.weak.expect b/pkg/front_end/testcases/nnbd/return_from_async.dart.weak.expect
deleted file mode 100644
index 07f9c6e..0000000
--- a/pkg/front_end/testcases/nnbd/return_from_async.dart.weak.expect
+++ /dev/null
@@ -1,94 +0,0 @@
-library /*isNonNullableByDefault*/;
-import self as self;
-import "dart:core" as core;
-import "dart:async" as asy;
-
-import "dart:async";
-
-static field core::bool caughtFutureOrInt = false;
-static field core::bool caughtInt = false;
-static field core::bool caughtFutureInt = false;
-static field core::bool caughtDynamic = false;
-static field core::bool caughtFutureNum = false;
-static method throwFutureOrInt() → FutureOr<core::int> async {
-  throw "FutureOr<int>";
-}
-static method callFutureOrInt() → asy::Future<core::int> async {
-  try {
-    return let final FutureOr<core::int>#t1 = self::throwFutureOrInt() in #t1 is asy::Future<core::int> ?{FutureOr<core::int>} await #t1 : #t1;
-  }
-  on core::Object catch(final core::Object e) {
-    core::print("Caught \"${e}\"");
-    self::caughtFutureOrInt = true;
-    return let final core::int #t2 = 0 in #t2 is asy::Future<core::int> ?{FutureOr<core::int>} await #t2 : #t2;
-  }
-}
-static method throwInt() → core::int {
-  throw "int";
-}
-static method callInt() → asy::Future<core::int> async {
-  try {
-    return let final core::int #t3 = self::throwInt() in #t3 is asy::Future<core::int> ?{FutureOr<core::int>} await #t3 : #t3;
-  }
-  on core::Object catch(final core::Object e) {
-    core::print("Caught \"${e}\"");
-    self::caughtInt = true;
-    return let final core::int #t4 = 0 in #t4 is asy::Future<core::int> ?{FutureOr<core::int>} await #t4 : #t4;
-  }
-}
-static method throwFutureInt() → asy::Future<core::int> async {
-  throw "Future<int>";
-}
-static method callFutureInt() → asy::Future<core::int> async {
-  try {
-    return let final asy::Future<core::int> #t5 = self::throwFutureInt() in #t5 is asy::Future<core::int> ?{FutureOr<core::int>} await #t5 : #t5;
-  }
-  on core::Object catch(final core::Object e) {
-    core::print("Caught \"${e}\"");
-    self::caughtFutureInt = true;
-    return let final core::int #t6 = 0 in #t6 is asy::Future<core::int> ?{FutureOr<core::int>} await #t6 : #t6;
-  }
-}
-static method throwDynamic() → dynamic {
-  throw "dynamic";
-}
-static method callDynamic() → asy::Future<core::int> async {
-  try {
-    return let final dynamic #t7 = self::throwDynamic() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::int> in #t7 is asy::Future<core::int> ?{FutureOr<core::int>} await #t7 : #t7;
-  }
-  on core::Object catch(final core::Object e) {
-    core::print("Caught \"${e}\"");
-    self::caughtDynamic = true;
-    return let final core::int #t8 = 0 in #t8 is asy::Future<core::int> ?{FutureOr<core::int>} await #t8 : #t8;
-  }
-}
-static method throwFutureNum() → asy::Future<core::int> async {
-  throw "Future<num>";
-}
-static method callFutureNum() → asy::Future<core::num> async {
-  try {
-    return let final asy::Future<core::int> #t9 = self::throwFutureNum() in #t9 is asy::Future<core::num> ?{FutureOr<core::num>} await #t9 : #t9;
-  }
-  on core::Object catch(final core::Object e) {
-    core::print("Caught \"${e}\"");
-    self::caughtFutureNum = true;
-    return let final core::int #t10 = 0 in #t10 is asy::Future<core::num> ?{FutureOr<core::num>} await #t10 : #t10;
-  }
-}
-static method main() → void async {
-  await self::callFutureOrInt();
-  if(!self::caughtFutureOrInt)
-    throw "Uncaught async return";
-  await self::callInt();
-  if(!self::caughtInt)
-    throw "Uncaught async return";
-  await self::callFutureInt();
-  if(!self::caughtFutureInt)
-    throw "Uncaught async return";
-  await self::callDynamic();
-  if(!self::caughtDynamic)
-    throw "Uncaught async return";
-  await self::callFutureNum();
-  if(!self::caughtFutureNum)
-    throw "Uncaught async return";
-}
diff --git a/pkg/front_end/testcases/nnbd/return_from_async.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/return_from_async.dart.weak.transformed.expect
deleted file mode 100644
index 5bd5d9f..0000000
--- a/pkg/front_end/testcases/nnbd/return_from_async.dart.weak.transformed.expect
+++ /dev/null
@@ -1,433 +0,0 @@
-library /*isNonNullableByDefault*/;
-import self as self;
-import "dart:core" as core;
-import "dart:async" as asy;
-import "dart:_internal" as _in;
-
-import "dart:async";
-
-static field core::bool caughtFutureOrInt = false;
-static field core::bool caughtInt = false;
-static field core::bool caughtFutureInt = false;
-static field core::bool caughtDynamic = false;
-static field core::bool caughtFutureNum = false;
-static method throwFutureOrInt() → FutureOr<core::int> /* originally async */ {
-  final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
-  core::bool* :is_sync = false;
-  FutureOr<core::int>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L1:
-      {
-        throw "FutureOr<int>";
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method callFutureOrInt() → asy::Future<core::int> /* originally async */ {
-  final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
-  core::bool* :is_sync = false;
-  FutureOr<core::int>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  dynamic :saved_try_context_var1;
-  dynamic :exception0;
-  dynamic :stack_trace0;
-  FutureOr<core::int>:async_temporary_0;
-  FutureOr<core::int>:async_temporary_1;
-  FutureOr<core::int>:async_temporary_2;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L2:
-      {
-        try {
-          final FutureOr<core::int>#t1 = self::throwFutureOrInt();
-          if(#t1 is asy::Future<core::int>) {
-            [yield] let dynamic #t2 = asy::_awaitHelper(#t1, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_0 = #t1;
-          }
-          :return_value = :async_temporary_0;
-          break #L2;
-        }
-        on core::Object catch(final core::Object e) {
-          core::print("Caught \"${e}\"");
-          self::caughtFutureOrInt = true;
-          final core::int #t3 = 0;
-          if(#t3 is asy::Future<core::int>) {
-            [yield] let dynamic #t4 = asy::_awaitHelper(#t3, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_2 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_2 = #t3;
-          }
-          :return_value = :async_temporary_2;
-          break #L2;
-        }
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method throwInt() → core::int {
-  throw "int";
-}
-static method callInt() → asy::Future<core::int> /* originally async */ {
-  final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
-  core::bool* :is_sync = false;
-  FutureOr<core::int>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  dynamic :saved_try_context_var1;
-  dynamic :exception0;
-  dynamic :stack_trace0;
-  FutureOr<core::int>:async_temporary_0;
-  FutureOr<core::int>:async_temporary_1;
-  FutureOr<core::int>:async_temporary_2;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L3:
-      {
-        try {
-          final core::int #t5 = self::throwInt();
-          if(#t5 is asy::Future<core::int>) {
-            [yield] let dynamic #t6 = asy::_awaitHelper(#t5, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_0 = #t5;
-          }
-          :return_value = :async_temporary_0;
-          break #L3;
-        }
-        on core::Object catch(final core::Object e) {
-          core::print("Caught \"${e}\"");
-          self::caughtInt = true;
-          final core::int #t7 = 0;
-          if(#t7 is asy::Future<core::int>) {
-            [yield] let dynamic #t8 = asy::_awaitHelper(#t7, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_2 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_2 = #t7;
-          }
-          :return_value = :async_temporary_2;
-          break #L3;
-        }
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method throwFutureInt() → asy::Future<core::int> /* originally async */ {
-  final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
-  core::bool* :is_sync = false;
-  FutureOr<core::int>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L4:
-      {
-        throw "Future<int>";
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method callFutureInt() → asy::Future<core::int> /* originally async */ {
-  final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
-  core::bool* :is_sync = false;
-  FutureOr<core::int>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  dynamic :saved_try_context_var1;
-  dynamic :exception0;
-  dynamic :stack_trace0;
-  FutureOr<core::int>:async_temporary_0;
-  FutureOr<core::int>:async_temporary_1;
-  FutureOr<core::int>:async_temporary_2;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L5:
-      {
-        try {
-          final asy::Future<core::int> #t9 = self::throwFutureInt();
-          if(#t9 is asy::Future<core::int>) {
-            [yield] let dynamic #t10 = asy::_awaitHelper(#t9, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_0 = #t9;
-          }
-          :return_value = :async_temporary_0;
-          break #L5;
-        }
-        on core::Object catch(final core::Object e) {
-          core::print("Caught \"${e}\"");
-          self::caughtFutureInt = true;
-          final core::int #t11 = 0;
-          if(#t11 is asy::Future<core::int>) {
-            [yield] let dynamic #t12 = asy::_awaitHelper(#t11, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_2 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_2 = #t11;
-          }
-          :return_value = :async_temporary_2;
-          break #L5;
-        }
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method throwDynamic() → dynamic {
-  throw "dynamic";
-}
-static method callDynamic() → asy::Future<core::int> /* originally async */ {
-  final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
-  core::bool* :is_sync = false;
-  FutureOr<core::int>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  dynamic :saved_try_context_var1;
-  dynamic :exception0;
-  dynamic :stack_trace0;
-  FutureOr<core::int>:async_temporary_0;
-  FutureOr<core::int>:async_temporary_1;
-  FutureOr<core::int>:async_temporary_2;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L6:
-      {
-        try {
-          final FutureOr<core::int>#t13 = self::throwDynamic() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::int>;
-          if(#t13 is asy::Future<core::int>) {
-            [yield] let dynamic #t14 = asy::_awaitHelper(#t13, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_0 = #t13;
-          }
-          :return_value = :async_temporary_0;
-          break #L6;
-        }
-        on core::Object catch(final core::Object e) {
-          core::print("Caught \"${e}\"");
-          self::caughtDynamic = true;
-          final core::int #t15 = 0;
-          if(#t15 is asy::Future<core::int>) {
-            [yield] let dynamic #t16 = asy::_awaitHelper(#t15, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_2 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_2 = #t15;
-          }
-          :return_value = :async_temporary_2;
-          break #L6;
-        }
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method throwFutureNum() → asy::Future<core::int> /* originally async */ {
-  final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
-  core::bool* :is_sync = false;
-  FutureOr<core::int>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L7:
-      {
-        throw "Future<num>";
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method callFutureNum() → asy::Future<core::num> /* originally async */ {
-  final asy::_Future<core::num> :async_future = new asy::_Future::•<core::num>();
-  core::bool* :is_sync = false;
-  FutureOr<core::num>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  dynamic :saved_try_context_var1;
-  dynamic :exception0;
-  dynamic :stack_trace0;
-  FutureOr<core::num>:async_temporary_0;
-  FutureOr<core::num>:async_temporary_1;
-  FutureOr<core::num>:async_temporary_2;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L8:
-      {
-        try {
-          final asy::Future<core::int> #t17 = self::throwFutureNum();
-          if(#t17 is asy::Future<core::num>) {
-            [yield] let dynamic #t18 = asy::_awaitHelper(#t17, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_0 = #t17;
-          }
-          :return_value = :async_temporary_0;
-          break #L8;
-        }
-        on core::Object catch(final core::Object e) {
-          core::print("Caught \"${e}\"");
-          self::caughtFutureNum = true;
-          final core::int #t19 = 0;
-          if(#t19 is asy::Future<core::num>) {
-            [yield] let dynamic #t20 = asy::_awaitHelper(#t19, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_2 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_2 = #t19;
-          }
-          :return_value = :async_temporary_2;
-          break #L8;
-        }
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method main() → void /* originally async */ {
-  final asy::_Future<dynamic> :async_future = new asy::_Future::•<dynamic>();
-  core::bool* :is_sync = false;
-  FutureOr<dynamic>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L9:
-      {
-        [yield] let dynamic #t21 = asy::_awaitHelper(self::callFutureOrInt(), :async_op_then, :async_op_error, :async_op) in null;
-        _in::unsafeCast<core::int>(:result);
-        if(!self::caughtFutureOrInt)
-          throw "Uncaught async return";
-        [yield] let dynamic #t22 = asy::_awaitHelper(self::callInt(), :async_op_then, :async_op_error, :async_op) in null;
-        _in::unsafeCast<core::int>(:result);
-        if(!self::caughtInt)
-          throw "Uncaught async return";
-        [yield] let dynamic #t23 = asy::_awaitHelper(self::callFutureInt(), :async_op_then, :async_op_error, :async_op) in null;
-        _in::unsafeCast<core::int>(:result);
-        if(!self::caughtFutureInt)
-          throw "Uncaught async return";
-        [yield] let dynamic #t24 = asy::_awaitHelper(self::callDynamic(), :async_op_then, :async_op_error, :async_op) in null;
-        _in::unsafeCast<core::int>(:result);
-        if(!self::caughtDynamic)
-          throw "Uncaught async return";
-        [yield] let dynamic #t25 = asy::_awaitHelper(self::callFutureNum(), :async_op_then, :async_op_error, :async_op) in null;
-        _in::unsafeCast<core::num>(:result);
-        if(!self::caughtFutureNum)
-          throw "Uncaught async return";
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
diff --git a/pkg/front_end/testcases/nnbd/return_null.dart.strong.expect b/pkg/front_end/testcases/nnbd/return_null.dart.strong.expect
index dab461b..70d918b 100644
--- a/pkg/front_end/testcases/nnbd/return_null.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/return_null.dart.strong.expect
@@ -103,7 +103,7 @@
 static method returnAsync4() → FutureOr<core::int?> async {}
 static method returnAsync5() → dynamic async {}
 static method returnAsync6() → asy::Future<core::int?> async {
-  return let final Null #t6 = null in #t6 is asy::Future<core::int?> ?{FutureOr<core::int?>} await #t6 : #t6;
+  return null;
 }
 static method returnAsync7() → asy::Future<core::int?> async {}
 static method yieldSync() → core::Iterable<dynamic> sync* {}
@@ -133,7 +133,7 @@
     default:
       {}
   }
-  return let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:54:6: Error: A non-null value must be returned since the return type 'Enum' doesn't allow null.
+  return let final<BottomType> #t6 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:54:6: Error: A non-null value must be returned since the return type 'Enum' doesn't allow null.
  - 'Enum' is from 'pkg/front_end/testcases/nnbd/return_null.dart'.
 Enum caseReturn2(Enum e) /* error */ {
      ^" in null;
@@ -141,38 +141,38 @@
 static method localFunctions() → dynamic {
   function returnImplicit() → core::String {
     core::print("foo");
-    return let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:63:3: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:63:3: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String returnImplicit() /* error */ {
   ^" in null;
   }
   function returnExplicit() → core::String {
     core::print("foo");
-    return let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:69:12: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
+    return let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:69:12: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
     return null; // error
            ^" in null as{TypeError,ForNonNullableByDefault} core::String;
   }
   function returnMixed(core::bool b) → core::String {
     if(b) {
       core::print("foo");
-      return let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:75:14: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
+      return let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:75:14: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
       return null; // error
              ^" in null as{TypeError,ForNonNullableByDefault} core::String;
     }
-    return let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:72:3: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:72:3: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String returnMixed(bool b) /* error */ {
   ^" in null;
   }
   function returnAsync1() → asy::Future<dynamic> async {}
   function returnAsync2() → FutureOr<dynamic> async {}
   function returnAsync3() → FutureOr<core::int> async {
-    return let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:83:3: Error: A non-null value must be returned since the return type 'int' doesn't allow null.
+    return let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:83:3: Error: A non-null value must be returned since the return type 'int' doesn't allow null.
   FutureOr<int> returnAsync3() async {} // error
   ^" in null;
   }
   function returnAsync4() → FutureOr<core::int?> async {}
   function returnAsync5() → asy::Future<Null> async {}
   function returnAsync6() → asy::Future<core::int?> async {
-    return let final Null #t13 = null in #t13 is asy::Future<core::int?> ?{FutureOr<core::int?>} await #t13 : #t13;
+    return null;
   }
   function returnAsync7() → asy::Future<core::int?> async {}
   function yieldSync() → core::Iterable<dynamic> sync* {}
@@ -202,7 +202,7 @@
       default:
         {}
     }
-    return let final<BottomType> #t14 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:108:3: Error: A non-null value must be returned since the return type 'Enum' doesn't allow null.
+    return let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:108:3: Error: A non-null value must be returned since the return type 'Enum' doesn't allow null.
  - 'Enum' is from 'pkg/front_end/testcases/nnbd/return_null.dart'.
   Enum caseReturn2(Enum e) /* error */ {
   ^" in null;
diff --git a/pkg/front_end/testcases/nnbd/return_null.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/return_null.dart.strong.transformed.expect
index af2d2ae..2b1a3dc 100644
--- a/pkg/front_end/testcases/nnbd/return_null.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/return_null.dart.strong.transformed.expect
@@ -55,7 +55,6 @@
 import self as self;
 import "dart:core" as core;
 import "dart:async" as asy;
-import "dart:_internal" as _in;
 
 import "dart:async";
 
@@ -227,21 +226,11 @@
   (core::Object, core::StackTrace) → dynamic :async_op_error;
   core::int :await_jump_var = 0;
   dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  FutureOr<core::int?>:async_temporary_0;
   function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
     try {
       #L6:
       {
-        final Null #t8 = null;
-        if(#t8 is asy::Future<core::int?>) {
-          [yield] let dynamic #t9 = asy::_awaitHelper(#t8, :async_op_then, :async_op_error, :async_op) in null;
-          :async_temporary_0 = _in::unsafeCast<Null>(:result);
-        }
-        else {
-          :async_temporary_0 = #t8;
-        }
-        :return_value = :async_temporary_0;
+        :return_value = null;
         break #L6;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -343,7 +332,7 @@
     default:
       {}
   }
-  return let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:54:6: Error: A non-null value must be returned since the return type 'Enum' doesn't allow null.
+  return let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:54:6: Error: A non-null value must be returned since the return type 'Enum' doesn't allow null.
  - 'Enum' is from 'pkg/front_end/testcases/nnbd/return_null.dart'.
 Enum caseReturn2(Enum e) /* error */ {
      ^" in null;
@@ -351,24 +340,24 @@
 static method localFunctions() → dynamic {
   function returnImplicit() → core::String {
     core::print("foo");
-    return let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:63:3: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:63:3: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String returnImplicit() /* error */ {
   ^" in null;
   }
   function returnExplicit() → core::String {
     core::print("foo");
-    return let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:69:12: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
+    return let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:69:12: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
     return null; // error
-           ^" in let Null #t13 = null in #t13.==(null) ?{core::String} #t13 as{TypeError,ForNonNullableByDefault} core::String : #t13{core::String};
+           ^" in let Null #t11 = null in #t11.==(null) ?{core::String} #t11 as{TypeError,ForNonNullableByDefault} core::String : #t11{core::String};
   }
   function returnMixed(core::bool b) → core::String {
     if(b) {
       core::print("foo");
-      return let final<BottomType> #t14 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:75:14: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
+      return let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:75:14: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
       return null; // error
-             ^" in let Null #t15 = null in #t15.==(null) ?{core::String} #t15 as{TypeError,ForNonNullableByDefault} core::String : #t15{core::String};
+             ^" in let Null #t13 = null in #t13.==(null) ?{core::String} #t13 as{TypeError,ForNonNullableByDefault} core::String : #t13{core::String};
     }
-    return let final<BottomType> #t16 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:72:3: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t14 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:72:3: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String returnMixed(bool b) /* error */ {
   ^" in null;
   }
@@ -432,7 +421,7 @@
       try {
         #L15:
         {
-          :return_value = let final<BottomType> #t17 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:83:3: Error: A non-null value must be returned since the return type 'int' doesn't allow null.
+          :return_value = let final<BottomType> #t15 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:83:3: Error: A non-null value must be returned since the return type 'int' doesn't allow null.
   FutureOr<int> returnAsync3() async {} // error
   ^" in null;
           break #L15;
@@ -505,21 +494,11 @@
     (core::Object, core::StackTrace) → dynamic :async_op_error;
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
-    dynamic :saved_try_context_var0;
-    FutureOr<core::int?>:async_temporary_0;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L18:
         {
-          final Null #t18 = null;
-          if(#t18 is asy::Future<core::int?>) {
-            [yield] let dynamic #t19 = asy::_awaitHelper(#t18, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<Null>(:result);
-          }
-          else {
-            :async_temporary_0 = #t18;
-          }
-          :return_value = :async_temporary_0;
+          :return_value = null;
           break #L18;
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -621,7 +600,7 @@
       default:
         {}
     }
-    return let final<BottomType> #t20 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:108:3: Error: A non-null value must be returned since the return type 'Enum' doesn't allow null.
+    return let final<BottomType> #t16 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:108:3: Error: A non-null value must be returned since the return type 'Enum' doesn't allow null.
  - 'Enum' is from 'pkg/front_end/testcases/nnbd/return_null.dart'.
   Enum caseReturn2(Enum e) /* error */ {
   ^" in null;
@@ -663,7 +642,7 @@
 Evaluated: MethodInvocation @ org-dartlang-testcase:///return_null.dart:75:14 -> BoolConstant(true)
 Evaluated: VariableGet @ org-dartlang-testcase:///return_null.dart:75:14 -> NullConstant(null)
 Evaluated: VariableGet @ org-dartlang-testcase:///return_null.dart:75:14 -> NullConstant(null)
-Extra constant evaluation: evaluated: 422, effectively constant: 12
+Extra constant evaluation: evaluated: 394, effectively constant: 12
 
 
 Constructor coverage from constants:
diff --git a/pkg/front_end/testcases/nnbd/return_null.dart.weak.expect b/pkg/front_end/testcases/nnbd/return_null.dart.weak.expect
index aef28a4..0513741 100644
--- a/pkg/front_end/testcases/nnbd/return_null.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/return_null.dart.weak.expect
@@ -104,7 +104,7 @@
 static method returnAsync4() → FutureOr<core::int?> async {}
 static method returnAsync5() → dynamic async {}
 static method returnAsync6() → asy::Future<core::int?> async {
-  return let final Null #t6 = null in #t6 is asy::Future<core::int?> ?{FutureOr<core::int?>} await #t6 : #t6;
+  return null;
 }
 static method returnAsync7() → asy::Future<core::int?> async {}
 static method yieldSync() → core::Iterable<dynamic> sync* {}
@@ -137,7 +137,7 @@
     default:
       {}
   }
-  return let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:54:6: Error: A non-null value must be returned since the return type 'Enum' doesn't allow null.
+  return let final<BottomType> #t6 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:54:6: Error: A non-null value must be returned since the return type 'Enum' doesn't allow null.
  - 'Enum' is from 'pkg/front_end/testcases/nnbd/return_null.dart'.
 Enum caseReturn2(Enum e) /* error */ {
      ^" in null;
@@ -145,38 +145,38 @@
 static method localFunctions() → dynamic {
   function returnImplicit() → core::String {
     core::print("foo");
-    return let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:63:3: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:63:3: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String returnImplicit() /* error */ {
   ^" in null;
   }
   function returnExplicit() → core::String {
     core::print("foo");
-    return let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:69:12: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
+    return let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:69:12: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
     return null; // error
            ^" in null as{TypeError,ForNonNullableByDefault} core::String;
   }
   function returnMixed(core::bool b) → core::String {
     if(b) {
       core::print("foo");
-      return let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:75:14: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
+      return let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:75:14: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
       return null; // error
              ^" in null as{TypeError,ForNonNullableByDefault} core::String;
     }
-    return let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:72:3: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:72:3: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String returnMixed(bool b) /* error */ {
   ^" in null;
   }
   function returnAsync1() → asy::Future<dynamic> async {}
   function returnAsync2() → FutureOr<dynamic> async {}
   function returnAsync3() → FutureOr<core::int> async {
-    return let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:83:3: Error: A non-null value must be returned since the return type 'int' doesn't allow null.
+    return let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:83:3: Error: A non-null value must be returned since the return type 'int' doesn't allow null.
   FutureOr<int> returnAsync3() async {} // error
   ^" in null;
   }
   function returnAsync4() → FutureOr<core::int?> async {}
   function returnAsync5() → asy::Future<Null> async {}
   function returnAsync6() → asy::Future<core::int?> async {
-    return let final Null #t13 = null in #t13 is asy::Future<core::int?> ?{FutureOr<core::int?>} await #t13 : #t13;
+    return null;
   }
   function returnAsync7() → asy::Future<core::int?> async {}
   function yieldSync() → core::Iterable<dynamic> sync* {}
@@ -209,7 +209,7 @@
       default:
         {}
     }
-    return let final<BottomType> #t14 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:108:3: Error: A non-null value must be returned since the return type 'Enum' doesn't allow null.
+    return let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:108:3: Error: A non-null value must be returned since the return type 'Enum' doesn't allow null.
  - 'Enum' is from 'pkg/front_end/testcases/nnbd/return_null.dart'.
   Enum caseReturn2(Enum e) /* error */ {
   ^" in null;
diff --git a/pkg/front_end/testcases/nnbd/return_null.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/return_null.dart.weak.transformed.expect
index dba40e5..3643cf7 100644
--- a/pkg/front_end/testcases/nnbd/return_null.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/return_null.dart.weak.transformed.expect
@@ -227,21 +227,11 @@
   (core::Object, core::StackTrace) → dynamic :async_op_error;
   core::int :await_jump_var = 0;
   dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  FutureOr<core::int?>:async_temporary_0;
   function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
     try {
       #L6:
       {
-        final Null #t6 = null;
-        if(#t6 is asy::Future<core::int?>) {
-          [yield] let dynamic #t7 = asy::_awaitHelper(#t6, :async_op_then, :async_op_error, :async_op) in null;
-          :async_temporary_0 = _in::unsafeCast<Null>(:result);
-        }
-        else {
-          :async_temporary_0 = #t6;
-        }
-        :return_value = :async_temporary_0;
+        :return_value = null;
         break #L6;
       }
       asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -346,7 +336,7 @@
     default:
       {}
   }
-  return let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:54:6: Error: A non-null value must be returned since the return type 'Enum' doesn't allow null.
+  return let final<BottomType> #t6 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:54:6: Error: A non-null value must be returned since the return type 'Enum' doesn't allow null.
  - 'Enum' is from 'pkg/front_end/testcases/nnbd/return_null.dart'.
 Enum caseReturn2(Enum e) /* error */ {
      ^" in null;
@@ -354,24 +344,24 @@
 static method localFunctions() → dynamic {
   function returnImplicit() → core::String {
     core::print("foo");
-    return let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:63:3: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:63:3: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String returnImplicit() /* error */ {
   ^" in null;
   }
   function returnExplicit() → core::String {
     core::print("foo");
-    return let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:69:12: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
+    return let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:69:12: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
     return null; // error
            ^" in null;
   }
   function returnMixed(core::bool b) → core::String {
     if(b) {
       core::print("foo");
-      return let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:75:14: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
+      return let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:75:14: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
       return null; // error
              ^" in null;
     }
-    return let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:72:3: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
+    return let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:72:3: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
   String returnMixed(bool b) /* error */ {
   ^" in null;
   }
@@ -435,7 +425,7 @@
       try {
         #L16:
         {
-          :return_value = let final<BottomType> #t13 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:83:3: Error: A non-null value must be returned since the return type 'int' doesn't allow null.
+          :return_value = let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:83:3: Error: A non-null value must be returned since the return type 'int' doesn't allow null.
   FutureOr<int> returnAsync3() async {} // error
   ^" in null;
           break #L16;
@@ -508,21 +498,11 @@
     (core::Object, core::StackTrace) → dynamic :async_op_error;
     core::int :await_jump_var = 0;
     dynamic :await_ctx_var;
-    dynamic :saved_try_context_var0;
-    FutureOr<core::int?>:async_temporary_0;
     function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
       try {
         #L19:
         {
-          final Null #t14 = null;
-          if(#t14 is asy::Future<core::int?>) {
-            [yield] let dynamic #t15 = asy::_awaitHelper(#t14, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<Null>(:result);
-          }
-          else {
-            :async_temporary_0 = #t14;
-          }
-          :return_value = :async_temporary_0;
+          :return_value = null;
           break #L19;
         }
         asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
@@ -627,7 +607,7 @@
       default:
         {}
     }
-    return let final<BottomType> #t16 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:108:3: Error: A non-null value must be returned since the return type 'Enum' doesn't allow null.
+    return let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:108:3: Error: A non-null value must be returned since the return type 'Enum' doesn't allow null.
  - 'Enum' is from 'pkg/front_end/testcases/nnbd/return_null.dart'.
   Enum caseReturn2(Enum e) /* error */ {
   ^" in null;
diff --git a/pkg/front_end/testcases/nnbd_mixed/return_from_async.dart b/pkg/front_end/testcases/nnbd_mixed/return_from_async.dart
deleted file mode 100644
index 5b167d0..0000000
--- a/pkg/front_end/testcases/nnbd_mixed/return_from_async.dart
+++ /dev/null
@@ -1,92 +0,0 @@
-// Copyright (c) 2020, 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.
-
-import 'dart:async';
-import 'return_from_async_lib.dart';
-
-abstract class Class {
-  FutureOr<int> throwFutureOrInt();
-
-  int throwInt();
-
-  Future<int> throwFutureInt();
-
-  dynamic throwDynamic();
-
-  Future<num> throwFutureNum();
-}
-
-bool caughtFutureOrInt = false;
-
-Future<int> callFutureOrInt(Class c) async {
-  try {
-    return c.throwFutureOrInt();
-  } catch (e) {
-    print('Caught "$e"');
-    caughtFutureOrInt = true;
-    return 0;
-  }
-}
-
-bool caughtInt = false;
-
-Future<int> callInt(Class c) async {
-  try {
-    return c.throwInt();
-  } catch (e) {
-    print('Caught "$e"');
-    caughtInt = true;
-    return 0;
-  }
-}
-
-bool caughtFutureInt = false;
-
-Future<int> callFutureInt(Class c) async {
-  try {
-    return c.throwFutureInt();
-  } catch (e) {
-    print('Caught "$e"');
-    caughtFutureInt = true;
-    return 0;
-  }
-}
-
-bool caughtDynamic = false;
-
-Future<int> callDynamic(Class c) async {
-  try {
-    return c.throwDynamic();
-  } catch (e) {
-    print('Caught "$e"');
-    caughtDynamic = true;
-    return 0;
-  }
-}
-
-bool caughtFutureNum = false;
-
-Future<num> callFutureNum(Class c) async {
-  try {
-    return c.throwFutureNum();
-  } catch (e) {
-    print('Caught "$e"');
-    caughtFutureNum = true;
-    return 0;
-  }
-}
-
-void main() async {
-  Class c = new Subclass();
-  await callFutureOrInt(c);
-  if (!caughtFutureOrInt) throw 'Uncaught async return';
-  await callInt(c);
-  if (!caughtInt) throw 'Uncaught async return';
-  await callFutureInt(c);
-  if (!caughtFutureInt) throw 'Uncaught async return';
-  await callDynamic(c);
-  if (!caughtDynamic) throw 'Uncaught async return';
-  await callFutureNum(c);
-  if (!caughtFutureNum) throw 'Uncaught async return';
-}
diff --git a/pkg/front_end/testcases/nnbd_mixed/return_from_async.dart.textual_outline.expect b/pkg/front_end/testcases/nnbd_mixed/return_from_async.dart.textual_outline.expect
deleted file mode 100644
index 66339b5..0000000
--- a/pkg/front_end/testcases/nnbd_mixed/return_from_async.dart.textual_outline.expect
+++ /dev/null
@@ -1,22 +0,0 @@
-import 'dart:async';
-import 'return_from_async_lib.dart';
-
-abstract class Class {
-  FutureOr<int> throwFutureOrInt();
-  int throwInt();
-  Future<int> throwFutureInt();
-  dynamic throwDynamic();
-  Future<num> throwFutureNum();
-}
-
-bool caughtFutureOrInt = false;
-Future<int> callFutureOrInt(Class c) async {}
-bool caughtInt = false;
-Future<int> callInt(Class c) async {}
-bool caughtFutureInt = false;
-Future<int> callFutureInt(Class c) async {}
-bool caughtDynamic = false;
-Future<int> callDynamic(Class c) async {}
-bool caughtFutureNum = false;
-Future<num> callFutureNum(Class c) async {}
-void main() async {}
diff --git a/pkg/front_end/testcases/nnbd_mixed/return_from_async.dart.textual_outline_modelled.expect b/pkg/front_end/testcases/nnbd_mixed/return_from_async.dart.textual_outline_modelled.expect
deleted file mode 100644
index 3c8dcd7..0000000
--- a/pkg/front_end/testcases/nnbd_mixed/return_from_async.dart.textual_outline_modelled.expect
+++ /dev/null
@@ -1,23 +0,0 @@
-import 'dart:async';
-import 'return_from_async_lib.dart';
-
-Future<int> callDynamic(Class c) async {}
-Future<int> callFutureInt(Class c) async {}
-Future<int> callFutureOrInt(Class c) async {}
-Future<int> callInt(Class c) async {}
-Future<num> callFutureNum(Class c) async {}
-
-abstract class Class {
-  Future<int> throwFutureInt();
-  Future<num> throwFutureNum();
-  FutureOr<int> throwFutureOrInt();
-  dynamic throwDynamic();
-  int throwInt();
-}
-
-bool caughtDynamic = false;
-bool caughtFutureInt = false;
-bool caughtFutureNum = false;
-bool caughtFutureOrInt = false;
-bool caughtInt = false;
-void main() async {}
diff --git a/pkg/front_end/testcases/nnbd_mixed/return_from_async.dart.weak.expect b/pkg/front_end/testcases/nnbd_mixed/return_from_async.dart.weak.expect
deleted file mode 100644
index 0a614de..0000000
--- a/pkg/front_end/testcases/nnbd_mixed/return_from_async.dart.weak.expect
+++ /dev/null
@@ -1,122 +0,0 @@
-library /*isNonNullableByDefault*/;
-import self as self;
-import "dart:core" as core;
-import "dart:async" as asy;
-import "return_from_async_lib.dart" as ret;
-
-import "dart:async";
-import "org-dartlang-testcase:///return_from_async_lib.dart";
-
-abstract class Class extends core::Object {
-  synthetic constructor •() → self::Class
-    : super core::Object::•()
-    ;
-  abstract method throwFutureOrInt() → FutureOr<core::int>;
-  abstract method throwInt() → core::int;
-  abstract method throwFutureInt() → asy::Future<core::int>;
-  abstract method throwDynamic() → dynamic;
-  abstract method throwFutureNum() → asy::Future<core::num>;
-}
-static field core::bool caughtFutureOrInt = false;
-static field core::bool caughtInt = false;
-static field core::bool caughtFutureInt = false;
-static field core::bool caughtDynamic = false;
-static field core::bool caughtFutureNum = false;
-static method callFutureOrInt(self::Class c) → asy::Future<core::int> async {
-  try {
-    return let final FutureOr<core::int>#t1 = c.{self::Class::throwFutureOrInt}() in #t1 is asy::Future<core::int> ?{FutureOr<core::int>} await #t1 : #t1;
-  }
-  on core::Object catch(final core::Object e) {
-    core::print("Caught \"${e}\"");
-    self::caughtFutureOrInt = true;
-    return let final core::int #t2 = 0 in #t2 is asy::Future<core::int> ?{FutureOr<core::int>} await #t2 : #t2;
-  }
-}
-static method callInt(self::Class c) → asy::Future<core::int> async {
-  try {
-    return let final core::int #t3 = c.{self::Class::throwInt}() in #t3 is asy::Future<core::int> ?{FutureOr<core::int>} await #t3 : #t3;
-  }
-  on core::Object catch(final core::Object e) {
-    core::print("Caught \"${e}\"");
-    self::caughtInt = true;
-    return let final core::int #t4 = 0 in #t4 is asy::Future<core::int> ?{FutureOr<core::int>} await #t4 : #t4;
-  }
-}
-static method callFutureInt(self::Class c) → asy::Future<core::int> async {
-  try {
-    return let final asy::Future<core::int> #t5 = c.{self::Class::throwFutureInt}() in #t5 is asy::Future<core::int> ?{FutureOr<core::int>} await #t5 : #t5;
-  }
-  on core::Object catch(final core::Object e) {
-    core::print("Caught \"${e}\"");
-    self::caughtFutureInt = true;
-    return let final core::int #t6 = 0 in #t6 is asy::Future<core::int> ?{FutureOr<core::int>} await #t6 : #t6;
-  }
-}
-static method callDynamic(self::Class c) → asy::Future<core::int> async {
-  try {
-    return let final dynamic #t7 = c.{self::Class::throwDynamic}() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::int> in #t7 is asy::Future<core::int> ?{FutureOr<core::int>} await #t7 : #t7;
-  }
-  on core::Object catch(final core::Object e) {
-    core::print("Caught \"${e}\"");
-    self::caughtDynamic = true;
-    return let final core::int #t8 = 0 in #t8 is asy::Future<core::int> ?{FutureOr<core::int>} await #t8 : #t8;
-  }
-}
-static method callFutureNum(self::Class c) → asy::Future<core::num> async {
-  try {
-    return let final asy::Future<core::num> #t9 = c.{self::Class::throwFutureNum}() in #t9 is asy::Future<core::num> ?{FutureOr<core::num>} await #t9 : #t9;
-  }
-  on core::Object catch(final core::Object e) {
-    core::print("Caught \"${e}\"");
-    self::caughtFutureNum = true;
-    return let final core::int #t10 = 0 in #t10 is asy::Future<core::num> ?{FutureOr<core::num>} await #t10 : #t10;
-  }
-}
-static method main() → void async {
-  self::Class c = new ret::Subclass::•();
-  await self::callFutureOrInt(c);
-  if(!self::caughtFutureOrInt)
-    throw "Uncaught async return";
-  await self::callInt(c);
-  if(!self::caughtInt)
-    throw "Uncaught async return";
-  await self::callFutureInt(c);
-  if(!self::caughtFutureInt)
-    throw "Uncaught async return";
-  await self::callDynamic(c);
-  if(!self::caughtDynamic)
-    throw "Uncaught async return";
-  await self::callFutureNum(c);
-  if(!self::caughtFutureNum)
-    throw "Uncaught async return";
-}
-
-library /*isNonNullableByDefault*/;
-import self as ret;
-import "dart:core" as core;
-import "return_from_async.dart" as self;
-import "dart:async" as asy;
-
-import "dart:async";
-import "org-dartlang-testcase:///return_from_async.dart";
-
-class Subclass extends core::Object implements self::Class {
-  synthetic constructor •() → ret::Subclass
-    : super core::Object::•()
-    ;
-  method throwFutureOrInt() → FutureOr<core::int> async {
-    throw "FutureOr<int>";
-  }
-  method throwInt() → core::int {
-    throw "int";
-  }
-  method throwFutureInt() → asy::Future<core::int> async {
-    throw "Future<int>";
-  }
-  method throwDynamic() → dynamic {
-    throw "dynamic";
-  }
-  method throwFutureNum() → asy::Future<core::num> async {
-    throw "Future<num>";
-  }
-}
diff --git a/pkg/front_end/testcases/nnbd_mixed/return_from_async.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd_mixed/return_from_async.dart.weak.transformed.expect
deleted file mode 100644
index 1924b7e..0000000
--- a/pkg/front_end/testcases/nnbd_mixed/return_from_async.dart.weak.transformed.expect
+++ /dev/null
@@ -1,461 +0,0 @@
-library /*isNonNullableByDefault*/;
-import self as self;
-import "dart:core" as core;
-import "dart:async" as asy;
-import "dart:_internal" as _in;
-import "return_from_async_lib.dart" as ret;
-
-import "dart:async";
-import "org-dartlang-testcase:///return_from_async_lib.dart";
-
-abstract class Class extends core::Object {
-  synthetic constructor •() → self::Class
-    : super core::Object::•()
-    ;
-  abstract method throwFutureOrInt() → FutureOr<core::int>;
-  abstract method throwInt() → core::int;
-  abstract method throwFutureInt() → asy::Future<core::int>;
-  abstract method throwDynamic() → dynamic;
-  abstract method throwFutureNum() → asy::Future<core::num>;
-}
-static field core::bool caughtFutureOrInt = false;
-static field core::bool caughtInt = false;
-static field core::bool caughtFutureInt = false;
-static field core::bool caughtDynamic = false;
-static field core::bool caughtFutureNum = false;
-static method callFutureOrInt(self::Class c) → asy::Future<core::int> /* originally async */ {
-  final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
-  core::bool* :is_sync = false;
-  FutureOr<core::int>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  dynamic :saved_try_context_var1;
-  dynamic :exception0;
-  dynamic :stack_trace0;
-  FutureOr<core::int>:async_temporary_0;
-  FutureOr<core::int>:async_temporary_1;
-  FutureOr<core::int>:async_temporary_2;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L1:
-      {
-        try {
-          final FutureOr<core::int>#t1 = c.{self::Class::throwFutureOrInt}();
-          if(#t1 is asy::Future<core::int>) {
-            [yield] let dynamic #t2 = asy::_awaitHelper(#t1, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_0 = #t1;
-          }
-          :return_value = :async_temporary_0;
-          break #L1;
-        }
-        on core::Object catch(final core::Object e) {
-          core::print("Caught \"${e}\"");
-          self::caughtFutureOrInt = true;
-          final core::int #t3 = 0;
-          if(#t3 is asy::Future<core::int>) {
-            [yield] let dynamic #t4 = asy::_awaitHelper(#t3, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_2 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_2 = #t3;
-          }
-          :return_value = :async_temporary_2;
-          break #L1;
-        }
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method callInt(self::Class c) → asy::Future<core::int> /* originally async */ {
-  final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
-  core::bool* :is_sync = false;
-  FutureOr<core::int>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  dynamic :saved_try_context_var1;
-  dynamic :exception0;
-  dynamic :stack_trace0;
-  FutureOr<core::int>:async_temporary_0;
-  FutureOr<core::int>:async_temporary_1;
-  FutureOr<core::int>:async_temporary_2;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L2:
-      {
-        try {
-          final core::int #t5 = c.{self::Class::throwInt}();
-          if(#t5 is asy::Future<core::int>) {
-            [yield] let dynamic #t6 = asy::_awaitHelper(#t5, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_0 = #t5;
-          }
-          :return_value = :async_temporary_0;
-          break #L2;
-        }
-        on core::Object catch(final core::Object e) {
-          core::print("Caught \"${e}\"");
-          self::caughtInt = true;
-          final core::int #t7 = 0;
-          if(#t7 is asy::Future<core::int>) {
-            [yield] let dynamic #t8 = asy::_awaitHelper(#t7, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_2 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_2 = #t7;
-          }
-          :return_value = :async_temporary_2;
-          break #L2;
-        }
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method callFutureInt(self::Class c) → asy::Future<core::int> /* originally async */ {
-  final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
-  core::bool* :is_sync = false;
-  FutureOr<core::int>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  dynamic :saved_try_context_var1;
-  dynamic :exception0;
-  dynamic :stack_trace0;
-  FutureOr<core::int>:async_temporary_0;
-  FutureOr<core::int>:async_temporary_1;
-  FutureOr<core::int>:async_temporary_2;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L3:
-      {
-        try {
-          final asy::Future<core::int> #t9 = c.{self::Class::throwFutureInt}();
-          if(#t9 is asy::Future<core::int>) {
-            [yield] let dynamic #t10 = asy::_awaitHelper(#t9, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_0 = #t9;
-          }
-          :return_value = :async_temporary_0;
-          break #L3;
-        }
-        on core::Object catch(final core::Object e) {
-          core::print("Caught \"${e}\"");
-          self::caughtFutureInt = true;
-          final core::int #t11 = 0;
-          if(#t11 is asy::Future<core::int>) {
-            [yield] let dynamic #t12 = asy::_awaitHelper(#t11, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_2 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_2 = #t11;
-          }
-          :return_value = :async_temporary_2;
-          break #L3;
-        }
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method callDynamic(self::Class c) → asy::Future<core::int> /* originally async */ {
-  final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
-  core::bool* :is_sync = false;
-  FutureOr<core::int>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  dynamic :saved_try_context_var1;
-  dynamic :exception0;
-  dynamic :stack_trace0;
-  FutureOr<core::int>:async_temporary_0;
-  FutureOr<core::int>:async_temporary_1;
-  FutureOr<core::int>:async_temporary_2;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L4:
-      {
-        try {
-          final FutureOr<core::int>#t13 = c.{self::Class::throwDynamic}() as{TypeError,ForDynamic,ForNonNullableByDefault} FutureOr<core::int>;
-          if(#t13 is asy::Future<core::int>) {
-            [yield] let dynamic #t14 = asy::_awaitHelper(#t13, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_0 = #t13;
-          }
-          :return_value = :async_temporary_0;
-          break #L4;
-        }
-        on core::Object catch(final core::Object e) {
-          core::print("Caught \"${e}\"");
-          self::caughtDynamic = true;
-          final core::int #t15 = 0;
-          if(#t15 is asy::Future<core::int>) {
-            [yield] let dynamic #t16 = asy::_awaitHelper(#t15, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_2 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_2 = #t15;
-          }
-          :return_value = :async_temporary_2;
-          break #L4;
-        }
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method callFutureNum(self::Class c) → asy::Future<core::num> /* originally async */ {
-  final asy::_Future<core::num> :async_future = new asy::_Future::•<core::num>();
-  core::bool* :is_sync = false;
-  FutureOr<core::num>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  dynamic :saved_try_context_var1;
-  dynamic :exception0;
-  dynamic :stack_trace0;
-  FutureOr<core::num>:async_temporary_0;
-  FutureOr<core::num>:async_temporary_1;
-  FutureOr<core::num>:async_temporary_2;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L5:
-      {
-        try {
-          final asy::Future<core::num> #t17 = c.{self::Class::throwFutureNum}();
-          if(#t17 is asy::Future<core::num>) {
-            [yield] let dynamic #t18 = asy::_awaitHelper(#t17, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_0 = _in::unsafeCast<core::num>(:result);
-          }
-          else {
-            :async_temporary_0 = #t17;
-          }
-          :return_value = :async_temporary_0;
-          break #L5;
-        }
-        on core::Object catch(final core::Object e) {
-          core::print("Caught \"${e}\"");
-          self::caughtFutureNum = true;
-          final core::int #t19 = 0;
-          if(#t19 is asy::Future<core::num>) {
-            [yield] let dynamic #t20 = asy::_awaitHelper(#t19, :async_op_then, :async_op_error, :async_op) in null;
-            :async_temporary_2 = _in::unsafeCast<core::int>(:result);
-          }
-          else {
-            :async_temporary_2 = #t19;
-          }
-          :return_value = :async_temporary_2;
-          break #L5;
-        }
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-static method main() → void /* originally async */ {
-  final asy::_Future<dynamic> :async_future = new asy::_Future::•<dynamic>();
-  core::bool* :is_sync = false;
-  FutureOr<dynamic>? :return_value;
-  (dynamic) → dynamic :async_op_then;
-  (core::Object, core::StackTrace) → dynamic :async_op_error;
-  core::int :await_jump_var = 0;
-  dynamic :await_ctx_var;
-  dynamic :saved_try_context_var0;
-  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-    try {
-      #L6:
-      {
-        self::Class c = new ret::Subclass::•();
-        [yield] let dynamic #t21 = asy::_awaitHelper(self::callFutureOrInt(c), :async_op_then, :async_op_error, :async_op) in null;
-        _in::unsafeCast<core::int>(:result);
-        if(!self::caughtFutureOrInt)
-          throw "Uncaught async return";
-        [yield] let dynamic #t22 = asy::_awaitHelper(self::callInt(c), :async_op_then, :async_op_error, :async_op) in null;
-        _in::unsafeCast<core::int>(:result);
-        if(!self::caughtInt)
-          throw "Uncaught async return";
-        [yield] let dynamic #t23 = asy::_awaitHelper(self::callFutureInt(c), :async_op_then, :async_op_error, :async_op) in null;
-        _in::unsafeCast<core::int>(:result);
-        if(!self::caughtFutureInt)
-          throw "Uncaught async return";
-        [yield] let dynamic #t24 = asy::_awaitHelper(self::callDynamic(c), :async_op_then, :async_op_error, :async_op) in null;
-        _in::unsafeCast<core::int>(:result);
-        if(!self::caughtDynamic)
-          throw "Uncaught async return";
-        [yield] let dynamic #t25 = asy::_awaitHelper(self::callFutureNum(c), :async_op_then, :async_op_error, :async_op) in null;
-        _in::unsafeCast<core::num>(:result);
-        if(!self::caughtFutureNum)
-          throw "Uncaught async return";
-      }
-      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-      return;
-    }
-    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-    }
-  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-  :async_op.call();
-  :is_sync = true;
-  return :async_future;
-}
-
-library /*isNonNullableByDefault*/;
-import self as ret;
-import "dart:core" as core;
-import "return_from_async.dart" as self;
-import "dart:async" as asy;
-
-import "dart:async";
-import "org-dartlang-testcase:///return_from_async.dart";
-
-class Subclass extends core::Object implements self::Class {
-  synthetic constructor •() → ret::Subclass
-    : super core::Object::•()
-    ;
-  method throwFutureOrInt() → FutureOr<core::int> /* originally async */ {
-    final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
-    core::bool* :is_sync = false;
-    FutureOr<core::int>? :return_value;
-    (dynamic) → dynamic :async_op_then;
-    (core::Object, core::StackTrace) → dynamic :async_op_error;
-    core::int :await_jump_var = 0;
-    dynamic :await_ctx_var;
-    function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-      try {
-        #L7:
-        {
-          throw "FutureOr<int>";
-        }
-        asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-        return;
-      }
-      on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-        asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-      }
-    :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-    :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-    :async_op.call();
-    :is_sync = true;
-    return :async_future;
-  }
-  method throwInt() → core::int {
-    throw "int";
-  }
-  method throwFutureInt() → asy::Future<core::int> /* originally async */ {
-    final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
-    core::bool* :is_sync = false;
-    FutureOr<core::int>? :return_value;
-    (dynamic) → dynamic :async_op_then;
-    (core::Object, core::StackTrace) → dynamic :async_op_error;
-    core::int :await_jump_var = 0;
-    dynamic :await_ctx_var;
-    function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-      try {
-        #L8:
-        {
-          throw "Future<int>";
-        }
-        asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-        return;
-      }
-      on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-        asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-      }
-    :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-    :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-    :async_op.call();
-    :is_sync = true;
-    return :async_future;
-  }
-  method throwDynamic() → dynamic {
-    throw "dynamic";
-  }
-  method throwFutureNum() → asy::Future<core::num> /* originally async */ {
-    final asy::_Future<core::num> :async_future = new asy::_Future::•<core::num>();
-    core::bool* :is_sync = false;
-    FutureOr<core::num>? :return_value;
-    (dynamic) → dynamic :async_op_then;
-    (core::Object, core::StackTrace) → dynamic :async_op_error;
-    core::int :await_jump_var = 0;
-    dynamic :await_ctx_var;
-    function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
-      try {
-        #L9:
-        {
-          throw "Future<num>";
-        }
-        asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
-        return;
-      }
-      on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-        asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
-      }
-    :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-    :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-    :async_op.call();
-    :is_sync = true;
-    return :async_future;
-  }
-}
diff --git a/pkg/front_end/testcases/nnbd_mixed/return_from_async_lib.dart b/pkg/front_end/testcases/nnbd_mixed/return_from_async_lib.dart
deleted file mode 100644
index 0e4cbb7..0000000
--- a/pkg/front_end/testcases/nnbd_mixed/return_from_async_lib.dart
+++ /dev/null
@@ -1,28 +0,0 @@
-// Copyright (c) 2020, 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.
-
-import 'dart:async';
-import 'return_from_async.dart';
-
-class Subclass implements Class {
-  FutureOr<int> throwFutureOrInt() async {
-    throw 'FutureOr<int>';
-  }
-
-  int throwInt() {
-    throw 'int';
-  }
-
-  Future<int> throwFutureInt() async {
-    throw 'Future<int>';
-  }
-
-  dynamic throwDynamic() {
-    throw 'dynamic';
-  }
-
-  Future<num> throwFutureNum() async {
-    throw 'Future<num>';
-  }
-}
diff --git a/pkg/front_end/testcases/strong.status b/pkg/front_end/testcases/strong.status
index bbb5c64..2e35c64 100644
--- a/pkg/front_end/testcases/strong.status
+++ b/pkg/front_end/testcases/strong.status
@@ -171,6 +171,7 @@
 nnbd/covariant_late_field: TypeCheckError
 nnbd/getter_vs_setter_type: TypeCheckError
 nnbd/issue41180: RuntimeError # Strong mode runtime checking fails due to mixed strong mode.
+nnbd/issue42546: TypeCheckError
 nnbd/issue42603: TypeCheckError
 nnbd/no_support_for_old_null_aware_index_access_syntax: RuntimeError # Expected.
 nnbd/nullable_object_access: TypeCheckError
diff --git a/pkg/front_end/testcases/text_serialization.status b/pkg/front_end/testcases/text_serialization.status
index c21c124..a59dfcd 100644
--- a/pkg/front_end/testcases/text_serialization.status
+++ b/pkg/front_end/testcases/text_serialization.status
@@ -171,6 +171,7 @@
 nnbd/covariant_late_field: TypeCheckError
 nnbd/getter_vs_setter_type: TypeCheckError
 nnbd/issue41180: RuntimeError
+nnbd/issue42546: TypeCheckError
 nnbd/issue42603: TypeCheckError
 nnbd/no_support_for_old_null_aware_index_access_syntax: RuntimeError # Expected.
 nnbd/nullable_object_access: TypeCheckError
diff --git a/pkg/front_end/testcases/weak.status b/pkg/front_end/testcases/weak.status
index 731df3e..56c47dc 100644
--- a/pkg/front_end/testcases/weak.status
+++ b/pkg/front_end/testcases/weak.status
@@ -58,6 +58,7 @@
 late_lowering/covariant_late_field: TypeCheckError
 nnbd/covariant_late_field: TypeCheckError
 nnbd/getter_vs_setter_type: TypeCheckError
+nnbd/issue42546: TypeCheckError
 nnbd/issue42603: TypeCheckError
 nnbd/no_support_for_old_null_aware_index_access_syntax: RuntimeError # Expected.
 nnbd/nullable_object_access: TypeCheckError
diff --git a/pkg/vm_service/test/async_single_step_out_test.dart b/pkg/vm_service/test/async_single_step_out_test.dart
index 7e5f200..a0a3d83 100644
--- a/pkg/vm_service/test/async_single_step_out_test.dart
+++ b/pkg/vm_service/test/async_single_step_out_test.dart
@@ -44,10 +44,6 @@
   stepInto, // exit helper via a single step.
 
   hasStoppedAtBreakpoint,
-  stoppedAtLine(LINE_B), // await helper
-  stepInto,
-
-  hasStoppedAtBreakpoint,
   stoppedAtLine(20), // return null (weird dispatching)
   stepInto, // exit helper via a single step.
 
diff --git a/runtime/observatory/tests/service/async_single_step_out_test.dart b/runtime/observatory/tests/service/async_single_step_out_test.dart
index 3c6de1b..cfeac6c 100644
--- a/runtime/observatory/tests/service/async_single_step_out_test.dart
+++ b/runtime/observatory/tests/service/async_single_step_out_test.dart
@@ -44,10 +44,6 @@
   stepInto, // exit helper via a single step.
 
   hasStoppedAtBreakpoint,
-  stoppedAtLine(LINE_B), // await helper
-  stepInto,
-
-  hasStoppedAtBreakpoint,
   stoppedAtLine(20), // return null (weird dispatching)
   stepInto, // exit helper via a single step.
 
diff --git a/runtime/tests/vm/dart/causal_stacks/utils.dart b/runtime/tests/vm/dart/causal_stacks/utils.dart
index fdebc07..6995e01 100644
--- a/runtime/tests/vm/dart/causal_stacks/utils.dart
+++ b/runtime/tests/vm/dart/causal_stacks/utils.dart
@@ -720,22 +720,20 @@
   final mixedYieldsExpected = const <String>[
     r'^#0      throwAsync \(.*/utils.dart:21(:3)?\)$',
     r'^<asynchronous suspension>$',
-    r'^#1      mixedYields3 \(.*/utils.dart:70(:3)?\)$',
+    r'^#1      mixedYields2 \(.*/utils.dart:66(:3)?\)$',
     r'^<asynchronous suspension>$',
-    r'^#2      mixedYields2 \(.*/utils.dart:66(:3)?\)$',
-    r'^<asynchronous suspension>$',
-    r'^#3      mixedYields \(.*/utils.dart:61(:3)?\)$',
+    r'^#2      mixedYields \(.*/utils.dart:61(:3)?\)$',
     r'^<asynchronous suspension>$',
   ];
   await doTestAwait(
       mixedYields,
       mixedYieldsExpected +
           const <String>[
-            r'^#4      doTestAwait ',
+            r'^#3      doTestAwait ',
             r'^<asynchronous suspension>$',
-            r'^#5      doTestsLazy ',
+            r'^#4      doTestsLazy ',
             r'^<asynchronous suspension>$',
-            r'^#6      main ',
+            r'^#5      main ',
             r'^<asynchronous suspension>$',
           ],
       debugInfoFilename);
@@ -743,7 +741,7 @@
       mixedYields,
       mixedYieldsExpected +
           const <String>[
-            r'^#4      doTestAwaitThen.<anonymous closure> ',
+            r'^#3      doTestAwaitThen.<anonymous closure> ',
             r'^<asynchronous suspension>$',
           ],
       debugInfoFilename);
@@ -784,22 +782,20 @@
   final nonAsyncNoStackExpected = const <String>[
     r'^#0      throwAsync \(.*/utils.dart:21(:3)?\)$',
     r'^<asynchronous suspension>$',
-    r'^#1      nonAsyncNoStack2 \(.*/utils.dart:97(:36)?\)$',
+    r'^#1      nonAsyncNoStack1 \(.*/utils.dart:95(:36)?\)$',
     r'^<asynchronous suspension>$',
-    r'^#2      nonAsyncNoStack1 \(.*/utils.dart:95(:36)?\)$',
-    r'^<asynchronous suspension>$',
-    r'^#3      nonAsyncNoStack \(.*/utils.dart:93(:35)?\)$',
+    r'^#2      nonAsyncNoStack \(.*/utils.dart:93(:35)?\)$',
     r'^<asynchronous suspension>$',
   ];
   await doTestAwait(
       nonAsyncNoStack,
       nonAsyncNoStackExpected +
           const <String>[
-            r'^#4      doTestAwait ',
+            r'^#3      doTestAwait ',
             r'^<asynchronous suspension>$',
-            r'^#5      doTestsLazy ',
+            r'^#4      doTestsLazy ',
             r'^<asynchronous suspension>$',
-            r'^#6      main ',
+            r'^#5      main ',
             r'^<asynchronous suspension>$',
           ],
       debugInfoFilename);
@@ -807,7 +803,7 @@
       nonAsyncNoStack,
       nonAsyncNoStackExpected +
           const <String>[
-            r'^#4      doTestAwaitThen.<anonymous closure> ',
+            r'^#3      doTestAwaitThen.<anonymous closure> ',
             r'^<asynchronous suspension>$',
           ],
       debugInfoFilename);
@@ -968,7 +964,6 @@
           ],
       debugInfoFilename);
   await doTestAwaitCatchError(awaitWait, awaitWaitExpected, debugInfoFilename);
-
   {
     final expected = const <String>[
       r'^#0      throwAsync \(.*/utils.dart:21(:3)?\)$',
diff --git a/runtime/tests/vm/dart/split_literals.dart b/runtime/tests/vm/dart/split_literals.dart
deleted file mode 100644
index b71e9bd..0000000
--- a/runtime/tests/vm/dart/split_literals.dart
+++ /dev/null
@@ -1,21 +0,0 @@
-// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-import "split_literals_deferred.dart" deferred as lib;
-
-class Box {
-  final contents;
-  const Box(this.contents);
-  String toString() => "Box($contents)";
-}
-
-main() async {
-  print("Root literal!");
-  print(const <String>["Root literal in a list!"]);
-  print(const <String, String>{"key": "Root literal in a map!"});
-  print(const Box("Root literal in a box!"));
-
-  await lib.loadLibrary();
-  lib.foo();
-}
diff --git a/runtime/tests/vm/dart/split_literals_deferred.dart b/runtime/tests/vm/dart/split_literals_deferred.dart
deleted file mode 100644
index 015ae1d..0000000
--- a/runtime/tests/vm/dart/split_literals_deferred.dart
+++ /dev/null
@@ -1,12 +0,0 @@
-// Copyright (c) 2020, 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.
-
-import "split_literals.dart";
-
-void foo() {
-  print("Deferred literal!");
-  print(const <String>["Deferred literal in a list!"]);
-  print(const <String, String>{"key": "Deferred literal in a map!"});
-  print(const Box("Deferred literal in a box!"));
-}
diff --git a/runtime/tests/vm/dart/split_literals_test.dart b/runtime/tests/vm/dart/split_literals_test.dart
deleted file mode 100644
index 6cbc01b..0000000
--- a/runtime/tests/vm/dart/split_literals_test.dart
+++ /dev/null
@@ -1,115 +0,0 @@
-// Copyright (c) 2020, 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.
-
-import "dart:convert";
-import "dart:io";
-
-import "package:expect/expect.dart";
-import "package:path/path.dart" as path;
-
-import "use_flag_test_helper.dart";
-
-main(List<String> args) async {
-  if (!isAOTRuntime) {
-    return; // Running in JIT: AOT binaries not available.
-  }
-
-  if (Platform.isAndroid) {
-    return; // SDK tree not available on the test device.
-  }
-
-  // These are the tools we need to be available to run on a given platform:
-  if (!File(platformDill).existsSync()) {
-    throw "Cannot run test as $platformDill does not exist";
-  }
-  if (!await testExecutable(genSnapshot)) {
-    throw "Cannot run test as $genSnapshot not available";
-  }
-
-  sanitizedPartitioning(manifest) {
-    // Filter core libraries, relativize URIs, and sort to make the results less
-    // sensitive to compiler or test harness changes.
-    print(manifest);
-    var units = <List<String>>[];
-    for (var unit in manifest['loadingUnits']) {
-      var uris = <String>[];
-      for (var uri in unit['libraries']) {
-        if (uri.startsWith("dart:")) continue;
-        uris.add(Uri.parse(uri).pathSegments.last);
-      }
-      uris.sort((a, b) => a.compareTo(b));
-      units.add(uris);
-    }
-    units.sort((a, b) => a.first.compareTo(b.first));
-    print(units);
-    return units;
-  }
-
-  await withTempDir("split-literals-test", (String tempDir) async {
-    final source =
-        path.join(sdkDir, "runtime/tests/vm/dart_2/split_literals.dart");
-    final dill = path.join(tempDir, "split_literals.dart.dill");
-    final snapshot = path.join(tempDir, "split_literals.so");
-    final manifest = path.join(tempDir, "split_literals.txt");
-    final deferredSnapshot = snapshot + "-2.part.so";
-
-    // Compile source to kernel.
-    await run(genKernel, <String>[
-      "--aot",
-      "--platform=$platformDill",
-      "-o",
-      dill,
-      source,
-    ]);
-
-    // Compile kernel to ELF.
-    await run(genSnapshot, <String>[
-      "--use_bare_instructions=false", //# object: ok
-      "--use_bare_instructions=true", //# bare: ok
-      "--snapshot-kind=app-aot-elf",
-      "--elf=$snapshot",
-      "--loading-unit-manifest=$manifest",
-      dill,
-    ]);
-    var manifestContent = jsonDecode(await new File(manifest).readAsString());
-    Expect.equals(2, manifestContent["loadingUnits"].length);
-    // Note package:expect doesn't do deep equals on collections.
-    Expect.equals(
-        "[[split_literals.dart],"
-        " [split_literals_deferred.dart]]",
-        sanitizedPartitioning(manifestContent).toString());
-    Expect.isTrue(await new File(deferredSnapshot).exists());
-
-    bool containsSubsequence(haystack, needle) {
-      outer:
-      for (var i = 0, n = haystack.length - needle.length; i < n; i++) {
-        for (var j = 0; j < needle.length; j++) {
-          if (haystack[i + j] != needle.codeUnitAt(j)) continue outer;
-        }
-        return true;
-      }
-      return false;
-    }
-
-    var unit_1 = await new File(snapshot).readAsBytes();
-    Expect.isTrue(containsSubsequence(unit_1, "Root literal!"));
-    Expect.isTrue(containsSubsequence(unit_1, "Root literal in a list!"));
-    Expect.isTrue(containsSubsequence(unit_1, "Root literal in a map!"));
-    Expect.isTrue(containsSubsequence(unit_1, "Root literal in a box!"));
-    Expect.isTrue(!containsSubsequence(unit_1, "Deferred literal!"));
-    Expect.isTrue(!containsSubsequence(unit_1, "Deferred literal in a list!"));
-    Expect.isTrue(!containsSubsequence(unit_1, "Deferred literal in a map!"));
-    Expect.isTrue(!containsSubsequence(unit_1, "Deferred literal in a box!"));
-
-    var unit_2 = await new File(deferredSnapshot).readAsBytes();
-    Expect.isTrue(!containsSubsequence(unit_2, "Root literal!"));
-    Expect.isTrue(!containsSubsequence(unit_2, "Root literal in a list!"));
-    Expect.isTrue(!containsSubsequence(unit_2, "Root literal in a map!"));
-    Expect.isTrue(!containsSubsequence(unit_2, "Root literal in a box!"));
-    Expect.isTrue(containsSubsequence(unit_2, "Deferred literal!"));
-    Expect.isTrue(containsSubsequence(unit_2, "Deferred literal in a list!"));
-    Expect.isTrue(containsSubsequence(unit_2, "Deferred literal in a map!"));
-    Expect.isTrue(containsSubsequence(unit_2, "Deferred literal in a box!"));
-  });
-}
diff --git a/runtime/tests/vm/dart_2/split_literals.dart b/runtime/tests/vm/dart_2/split_literals.dart
deleted file mode 100644
index b71e9bd..0000000
--- a/runtime/tests/vm/dart_2/split_literals.dart
+++ /dev/null
@@ -1,21 +0,0 @@
-// Copyright (c) 2020, 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.
-
-import "split_literals_deferred.dart" deferred as lib;
-
-class Box {
-  final contents;
-  const Box(this.contents);
-  String toString() => "Box($contents)";
-}
-
-main() async {
-  print("Root literal!");
-  print(const <String>["Root literal in a list!"]);
-  print(const <String, String>{"key": "Root literal in a map!"});
-  print(const Box("Root literal in a box!"));
-
-  await lib.loadLibrary();
-  lib.foo();
-}
diff --git a/runtime/tests/vm/dart_2/split_literals_deferred.dart b/runtime/tests/vm/dart_2/split_literals_deferred.dart
deleted file mode 100644
index 015ae1d..0000000
--- a/runtime/tests/vm/dart_2/split_literals_deferred.dart
+++ /dev/null
@@ -1,12 +0,0 @@
-// Copyright (c) 2020, 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.
-
-import "split_literals.dart";
-
-void foo() {
-  print("Deferred literal!");
-  print(const <String>["Deferred literal in a list!"]);
-  print(const <String, String>{"key": "Deferred literal in a map!"});
-  print(const Box("Deferred literal in a box!"));
-}
diff --git a/runtime/tests/vm/dart_2/split_literals_test.dart b/runtime/tests/vm/dart_2/split_literals_test.dart
deleted file mode 100644
index 6cbc01b..0000000
--- a/runtime/tests/vm/dart_2/split_literals_test.dart
+++ /dev/null
@@ -1,115 +0,0 @@
-// Copyright (c) 2020, 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.
-
-import "dart:convert";
-import "dart:io";
-
-import "package:expect/expect.dart";
-import "package:path/path.dart" as path;
-
-import "use_flag_test_helper.dart";
-
-main(List<String> args) async {
-  if (!isAOTRuntime) {
-    return; // Running in JIT: AOT binaries not available.
-  }
-
-  if (Platform.isAndroid) {
-    return; // SDK tree not available on the test device.
-  }
-
-  // These are the tools we need to be available to run on a given platform:
-  if (!File(platformDill).existsSync()) {
-    throw "Cannot run test as $platformDill does not exist";
-  }
-  if (!await testExecutable(genSnapshot)) {
-    throw "Cannot run test as $genSnapshot not available";
-  }
-
-  sanitizedPartitioning(manifest) {
-    // Filter core libraries, relativize URIs, and sort to make the results less
-    // sensitive to compiler or test harness changes.
-    print(manifest);
-    var units = <List<String>>[];
-    for (var unit in manifest['loadingUnits']) {
-      var uris = <String>[];
-      for (var uri in unit['libraries']) {
-        if (uri.startsWith("dart:")) continue;
-        uris.add(Uri.parse(uri).pathSegments.last);
-      }
-      uris.sort((a, b) => a.compareTo(b));
-      units.add(uris);
-    }
-    units.sort((a, b) => a.first.compareTo(b.first));
-    print(units);
-    return units;
-  }
-
-  await withTempDir("split-literals-test", (String tempDir) async {
-    final source =
-        path.join(sdkDir, "runtime/tests/vm/dart_2/split_literals.dart");
-    final dill = path.join(tempDir, "split_literals.dart.dill");
-    final snapshot = path.join(tempDir, "split_literals.so");
-    final manifest = path.join(tempDir, "split_literals.txt");
-    final deferredSnapshot = snapshot + "-2.part.so";
-
-    // Compile source to kernel.
-    await run(genKernel, <String>[
-      "--aot",
-      "--platform=$platformDill",
-      "-o",
-      dill,
-      source,
-    ]);
-
-    // Compile kernel to ELF.
-    await run(genSnapshot, <String>[
-      "--use_bare_instructions=false", //# object: ok
-      "--use_bare_instructions=true", //# bare: ok
-      "--snapshot-kind=app-aot-elf",
-      "--elf=$snapshot",
-      "--loading-unit-manifest=$manifest",
-      dill,
-    ]);
-    var manifestContent = jsonDecode(await new File(manifest).readAsString());
-    Expect.equals(2, manifestContent["loadingUnits"].length);
-    // Note package:expect doesn't do deep equals on collections.
-    Expect.equals(
-        "[[split_literals.dart],"
-        " [split_literals_deferred.dart]]",
-        sanitizedPartitioning(manifestContent).toString());
-    Expect.isTrue(await new File(deferredSnapshot).exists());
-
-    bool containsSubsequence(haystack, needle) {
-      outer:
-      for (var i = 0, n = haystack.length - needle.length; i < n; i++) {
-        for (var j = 0; j < needle.length; j++) {
-          if (haystack[i + j] != needle.codeUnitAt(j)) continue outer;
-        }
-        return true;
-      }
-      return false;
-    }
-
-    var unit_1 = await new File(snapshot).readAsBytes();
-    Expect.isTrue(containsSubsequence(unit_1, "Root literal!"));
-    Expect.isTrue(containsSubsequence(unit_1, "Root literal in a list!"));
-    Expect.isTrue(containsSubsequence(unit_1, "Root literal in a map!"));
-    Expect.isTrue(containsSubsequence(unit_1, "Root literal in a box!"));
-    Expect.isTrue(!containsSubsequence(unit_1, "Deferred literal!"));
-    Expect.isTrue(!containsSubsequence(unit_1, "Deferred literal in a list!"));
-    Expect.isTrue(!containsSubsequence(unit_1, "Deferred literal in a map!"));
-    Expect.isTrue(!containsSubsequence(unit_1, "Deferred literal in a box!"));
-
-    var unit_2 = await new File(deferredSnapshot).readAsBytes();
-    Expect.isTrue(!containsSubsequence(unit_2, "Root literal!"));
-    Expect.isTrue(!containsSubsequence(unit_2, "Root literal in a list!"));
-    Expect.isTrue(!containsSubsequence(unit_2, "Root literal in a map!"));
-    Expect.isTrue(!containsSubsequence(unit_2, "Root literal in a box!"));
-    Expect.isTrue(containsSubsequence(unit_2, "Deferred literal!"));
-    Expect.isTrue(containsSubsequence(unit_2, "Deferred literal in a list!"));
-    Expect.isTrue(containsSubsequence(unit_2, "Deferred literal in a map!"));
-    Expect.isTrue(containsSubsequence(unit_2, "Deferred literal in a box!"));
-  });
-}
diff --git a/runtime/vm/clustered_snapshot.cc b/runtime/vm/clustered_snapshot.cc
index 12ec76e..ef22f90 100644
--- a/runtime/vm/clustered_snapshot.cc
+++ b/runtime/vm/clustered_snapshot.cc
@@ -289,7 +289,7 @@
   ClassDeserializationCluster() : DeserializationCluster("Class") {}
   ~ClassDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     predefined_start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     intptr_t count = d->ReadUnsigned();
@@ -311,7 +311,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
+  void ReadFill(Deserializer* d, bool is_canonical) {
     ClassTable* table = d->isolate_group()->class_table();
 
     for (intptr_t id = predefined_start_index_; id < predefined_stop_index_;
@@ -464,7 +464,7 @@
       : DeserializationCluster("TypeArguments") {}
   ~TypeArgumentsDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -476,13 +476,13 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       TypeArgumentsPtr type_args = static_cast<TypeArgumentsPtr>(d->Ref(id));
       const intptr_t length = d->ReadUnsigned();
       Deserializer::InitializeHeader(type_args, kTypeArgumentsCid,
                                      TypeArguments::InstanceSize(length),
-                                     stamp_canonical);
+                                     is_canonical);
       type_args->untag()->length_ = Smi::New(length);
       type_args->untag()->hash_ = Smi::New(d->Read<int32_t>());
       type_args->untag()->nullability_ = Smi::New(d->ReadUnsigned());
@@ -494,15 +494,22 @@
     }
   }
 
-  void PostLoad(Deserializer* d, const Array& refs, bool canonicalize) {
-    if (canonicalize) {
-      Thread* thread = Thread::Current();
+  void PostLoad(Deserializer* d, const Array& refs, bool is_canonical) {
+    if (is_canonical && (d->isolate() != Dart::vm_isolate())) {
+      CanonicalTypeArgumentsSet table(
+          d->zone(),
+          d->isolate_group()->object_store()->canonical_type_arguments());
       TypeArguments& type_arg = TypeArguments::Handle(d->zone());
       for (intptr_t i = start_index_; i < stop_index_; i++) {
         type_arg ^= refs.At(i);
-        type_arg = type_arg.Canonicalize(thread, nullptr);
-        refs.SetAt(i, type_arg);
+        ASSERT(type_arg.IsCanonical());
+        bool present = table.Insert(type_arg);
+        // Two recursive types with different topology (and hashes) may be
+        // equal.
+        ASSERT(!present || type_arg.IsRecursive());
       }
+      d->isolate_group()->object_store()->set_canonical_type_arguments(
+          table.Release());
     }
   }
 };
@@ -551,7 +558,7 @@
   PatchClassDeserializationCluster() : DeserializationCluster("PatchClass") {}
   ~PatchClassDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -562,8 +569,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       PatchClassPtr cls = static_cast<PatchClassPtr>(d->Ref(id));
       Deserializer::InitializeHeader(cls, kPatchClassCid,
@@ -661,7 +667,7 @@
   FunctionDeserializationCluster() : DeserializationCluster("Function") {}
   ~FunctionDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -671,8 +677,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     Snapshot::Kind kind = d->kind();
 
     for (intptr_t id = start_index_; id < stop_index_; id++) {
@@ -720,7 +725,7 @@
     }
   }
 
-  void PostLoad(Deserializer* d, const Array& refs, bool canonicalize) {
+  void PostLoad(Deserializer* d, const Array& refs, bool is_canonical) {
     if (d->kind() == Snapshot::kFullAOT) {
       Function& func = Function::Handle(d->zone());
       for (intptr_t i = start_index_; i < stop_index_; i++) {
@@ -811,7 +816,7 @@
   ClosureDataDeserializationCluster() : DeserializationCluster("ClosureData") {}
   ~ClosureDataDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -822,8 +827,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       ClosureDataPtr data = static_cast<ClosureDataPtr>(d->Ref(id));
       Deserializer::InitializeHeader(data, kClosureDataCid,
@@ -893,7 +897,7 @@
       : DeserializationCluster("FfiTrampolineData") {}
   ~FfiTrampolineDataDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -904,8 +908,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       FfiTrampolineDataPtr data = static_cast<FfiTrampolineDataPtr>(d->Ref(id));
       Deserializer::InitializeHeader(data, kFfiTrampolineDataCid,
@@ -1012,7 +1015,7 @@
   FieldDeserializationCluster() : DeserializationCluster("Field") {}
   ~FieldDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -1022,8 +1025,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     Snapshot::Kind kind = d->kind();
 
     for (intptr_t id = start_index_; id < stop_index_; id++) {
@@ -1079,7 +1081,7 @@
     }
   }
 
-  void PostLoad(Deserializer* d, const Array& refs, bool canonicalize) {
+  void PostLoad(Deserializer* d, const Array& refs, bool is_canonical) {
     Field& field = Field::Handle(d->zone());
     if (!IsolateGroup::Current()->use_field_guards()) {
       for (intptr_t i = start_index_; i < stop_index_; i++) {
@@ -1155,7 +1157,7 @@
   ScriptDeserializationCluster() : DeserializationCluster("Script") {}
   ~ScriptDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -1165,8 +1167,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       ScriptPtr script = static_cast<ScriptPtr>(d->Ref(id));
       Deserializer::InitializeHeader(script, kScriptCid,
@@ -1231,7 +1232,7 @@
   LibraryDeserializationCluster() : DeserializationCluster("Library") {}
   ~LibraryDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -1241,8 +1242,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       LibraryPtr lib = static_cast<LibraryPtr>(d->Ref(id));
       Deserializer::InitializeHeader(lib, kLibraryCid, Library::InstanceSize());
@@ -1304,7 +1304,7 @@
   NamespaceDeserializationCluster() : DeserializationCluster("Namespace") {}
   ~NamespaceDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -1314,8 +1314,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       NamespacePtr ns = static_cast<NamespacePtr>(d->Ref(id));
       Deserializer::InitializeHeader(ns, kNamespaceCid,
@@ -1371,7 +1370,7 @@
       : DeserializationCluster("KernelProgramInfo") {}
   ~KernelProgramInfoDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -1382,8 +1381,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       KernelProgramInfoPtr info = static_cast<KernelProgramInfoPtr>(d->Ref(id));
       Deserializer::InitializeHeader(info, kKernelProgramInfoCid,
@@ -1393,7 +1391,7 @@
     }
   }
 
-  void PostLoad(Deserializer* d, const Array& refs, bool canonicalize) {
+  void PostLoad(Deserializer* d, const Array& refs, bool is_canonical) {
     Array& array = Array::Handle(d->zone());
     KernelProgramInfo& info = KernelProgramInfo::Handle(d->zone());
     for (intptr_t id = start_index_; id < stop_index_; id++) {
@@ -1419,26 +1417,9 @@
       objects_.Add(code);
     }
 
-    if (s->kind() == Snapshot::kFullAOT && FLAG_use_bare_instructions) {
-      if (FLAG_retain_function_objects) {
-        ObjectPoolPtr pool = code->untag()->object_pool_;
-        if ((pool != ObjectPool::null()) && s->InCurrentLoadingUnit(code)) {
-          const intptr_t length = pool->untag()->length_;
-          uint8_t* entry_bits = pool->untag()->entry_bits();
-          for (intptr_t i = 0; i < length; i++) {
-            auto entry_type = ObjectPool::TypeBits::decode(entry_bits[i]);
-            if (entry_type == ObjectPool::EntryType::kTaggedObject) {
-              s->Push(pool->untag()->data()[i].raw_obj_);
-            }
-          }
-        }
-      }
-    } else {
-      if (s->InCurrentLoadingUnit(code->untag()->object_pool_)) {
-        s->Push(code->untag()->object_pool_);
-      }
+    if (!(s->kind() == Snapshot::kFullAOT && FLAG_use_bare_instructions)) {
+      s->Push(code->untag()->object_pool_);
     }
-
     s->Push(code->untag()->owner_);
     s->Push(code->untag()->exception_handlers_);
     s->Push(code->untag()->pc_descriptors_);
@@ -1550,6 +1531,20 @@
   }
 
   void WriteAlloc(Serializer* s) {
+    Sort(&objects_);
+    auto loading_units = s->loading_units();
+    if (loading_units != nullptr) {
+      for (intptr_t i = LoadingUnit::kRootId + 1; i < loading_units->length();
+           i++) {
+        auto unit_objects = loading_units->At(i)->deferred_objects();
+        Sort(unit_objects);
+        for (intptr_t j = 0; j < unit_objects->length(); j++) {
+          deferred_objects_.Add(unit_objects->At(j)->ptr());
+        }
+      }
+    }
+    s->PrepareInstructions(&objects_);
+
     s->WriteCid(kCodeCid);
     const intptr_t count = objects_.length();
     s->WriteUnsigned(count);
@@ -1610,11 +1605,7 @@
     // No need to write object pool out if we are producing full AOT
     // snapshot with bare instructions.
     if (!(kind == Snapshot::kFullAOT && FLAG_use_bare_instructions)) {
-      if (s->InCurrentLoadingUnit(code->untag()->object_pool_)) {
-        WriteField(code, object_pool_);
-      } else {
-        WriteFieldValue(object_pool_, ObjectPool::null());
-      }
+      WriteField(code, object_pool_);
 #if defined(DART_PRECOMPILER)
     } else if (FLAG_write_v8_snapshot_profile_to != nullptr &&
                code->untag()->object_pool_ != ObjectPool::null()) {
@@ -1695,8 +1686,7 @@
     s->Write<int32_t>(code->untag()->state_bits_);
   }
 
-  GrowableArray<CodePtr>* objects() { return &objects_; }
-  GrowableArray<CodePtr>* deferred_objects() { return &deferred_objects_; }
+  GrowableArray<CodePtr>* discovered_objects() { return &objects_; }
 
   // Some code objects would have their owners dropped from the snapshot,
   // which makes it is impossible to recover program structure when
@@ -1742,7 +1732,7 @@
   CodeDeserializationCluster() : DeserializationCluster("Code") {}
   ~CodeDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     PageSpace* old_space = d->heap()->old_space();
     start_index_ = d->next_index();
     const intptr_t count = d->ReadUnsigned();
@@ -1760,8 +1750,7 @@
     deferred_stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       ReadFill(d, id, false);
     }
@@ -1816,7 +1805,7 @@
     code->untag()->state_bits_ = d->Read<int32_t>();
   }
 
-  void PostLoad(Deserializer* d, const Array& refs, bool canonicalize) {
+  void PostLoad(Deserializer* d, const Array& refs, bool is_canonical) {
     d->EndInstructions(refs, start_index_, stop_index_);
 
 #if !defined(PRODUCT)
@@ -1864,17 +1853,12 @@
     ObjectPoolPtr pool = ObjectPool::RawCast(object);
     objects_.Add(pool);
 
-    if (s->kind() == Snapshot::kFullAOT && FLAG_use_bare_instructions &&
-        FLAG_retain_function_objects) {
-      // Treat pool as weak.
-    } else {
-      const intptr_t length = pool->untag()->length_;
-      uint8_t* entry_bits = pool->untag()->entry_bits();
-      for (intptr_t i = 0; i < length; i++) {
-        auto entry_type = ObjectPool::TypeBits::decode(entry_bits[i]);
-        if (entry_type == ObjectPool::EntryType::kTaggedObject) {
-          s->Push(pool->untag()->data()[i].raw_obj_);
-        }
+    const intptr_t length = pool->untag()->length_;
+    uint8_t* entry_bits = pool->untag()->entry_bits();
+    for (intptr_t i = 0; i < length; i++) {
+      auto entry_type = ObjectPool::TypeBits::decode(entry_bits[i]);
+      if (entry_type == ObjectPool::EntryType::kTaggedObject) {
+        s->Push(pool->untag()->data()[i].raw_obj_);
       }
     }
   }
@@ -1893,9 +1877,6 @@
   }
 
   void WriteFill(Serializer* s) {
-    bool weak = s->kind() == Snapshot::kFullAOT && FLAG_use_bare_instructions &&
-                FLAG_retain_function_objects;
-
     const intptr_t count = objects_.length();
     for (intptr_t i = 0; i < count; i++) {
       ObjectPoolPtr pool = objects_[i];
@@ -1916,12 +1897,7 @@
               s->WriteElementRef(StubCode::CallBootstrapNative().ptr(), j);
               break;
             }
-            if (weak && !s->HasRef(entry.raw_obj_)) {
-              // Any value will do, but null has the shortest id.
-              s->WriteElementRef(Object::null(), j);
-            } else {
-              s->WriteElementRef(entry.raw_obj_, j);
-            }
+            s->WriteElementRef(entry.raw_obj_, j);
             break;
           }
           case ObjectPool::EntryType::kImmediate: {
@@ -1950,7 +1926,7 @@
   ObjectPoolDeserializationCluster() : DeserializationCluster("ObjectPool") {}
   ~ObjectPoolDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -1962,10 +1938,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
-    fill_position_ = d->position();
-
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id += 1) {
       const intptr_t length = d->ReadUnsigned();
       ObjectPoolPtr pool = static_cast<ObjectPoolPtr>(d->Ref(id + 0));
@@ -1995,41 +1968,6 @@
       }
     }
   }
-
-  void PostLoad(Deserializer* d, const Array& refs, bool canonicalize) {
-    intptr_t restore_position = d->position();
-    d->set_position(fill_position_);
-
-    ObjectPool& pool = ObjectPool::Handle();
-    Object& entry = Object::Handle();
-    for (intptr_t id = start_index_; id < stop_index_; id += 1) {
-      pool ^= refs.At(id);
-      const intptr_t length = d->ReadUnsigned();
-      for (intptr_t j = 0; j < length; j++) {
-        const uint8_t entry_bits = d->Read<uint8_t>();
-        switch (ObjectPool::TypeBits::decode(entry_bits)) {
-          case ObjectPool::EntryType::kTaggedObject:
-            entry = refs.At(d->ReadUnsigned());
-            pool.SetObjectAt(j, entry);
-            break;
-          case ObjectPool::EntryType::kImmediate:
-            d->Read<intptr_t>();
-            break;
-          case ObjectPool::EntryType::kNativeFunction: {
-            // Read nothing.
-            break;
-          }
-          default:
-            UNREACHABLE();
-        }
-      }
-    }
-
-    d->set_position(restore_position);
-  }
-
- private:
-  intptr_t fill_position_ = 0;
 };
 
 #if defined(DART_PRECOMPILER)
@@ -2152,7 +2090,7 @@
       : DeserializationCluster("WeakSerializationReference") {}
   ~WeakSerializationReferenceDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -2166,8 +2104,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       auto const ref = static_cast<WeakSerializationReferencePtr>(d->Ref(id));
       Deserializer::InitializeHeader(
@@ -2226,7 +2163,7 @@
       : DeserializationCluster("PcDescriptors") {}
   ~PcDescriptorsDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -2238,8 +2175,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id += 1) {
       const intptr_t length = d->ReadUnsigned();
       PcDescriptorsPtr desc = static_cast<PcDescriptorsPtr>(d->Ref(id));
@@ -2321,7 +2257,7 @@
       : DeserializationCluster("ROData"), cid_(cid) {}
   ~RODataDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     intptr_t count = d->ReadUnsigned();
     uint32_t running_offset = 0;
@@ -2332,25 +2268,21 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
+  void ReadFill(Deserializer* d, bool is_canonical) {
     // No-op.
   }
 
-  void PostLoad(Deserializer* d, const Array& refs, bool canonicalize) {
-    if (canonicalize && IsStringClassId(cid_)) {
+  void PostLoad(Deserializer* d, const Array& refs, bool is_canonical) {
+    if (is_canonical && IsStringClassId(cid_) &&
+        (d->isolate() != Dart::vm_isolate())) {
       CanonicalStringSet table(
           d->zone(), d->isolate_group()->object_store()->symbol_table());
       String& str = String::Handle(d->zone());
-      String& str2 = String::Handle(d->zone());
       for (intptr_t i = start_index_; i < stop_index_; i++) {
         str ^= refs.At(i);
-        str2 ^= table.InsertOrGet(str);
-        if (str.ptr() == str2.ptr()) {
-          // str.SetCanonical();
-        } else {
-          FATAL("Lost canonicalization race");
-          refs.SetAt(i, str2);
-        }
+        ASSERT(str.IsCanonical());
+        bool present = table.Insert(str);
+        ASSERT(!present);
       }
       d->isolate_group()->object_store()->set_symbol_table(table.Release());
     }
@@ -2417,7 +2349,7 @@
       : DeserializationCluster("ExceptionHandlers") {}
   ~ExceptionHandlersDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -2429,8 +2361,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       ExceptionHandlersPtr handlers =
           static_cast<ExceptionHandlersPtr>(d->Ref(id));
@@ -2506,7 +2437,7 @@
   ContextDeserializationCluster() : DeserializationCluster("Context") {}
   ~ContextDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -2518,8 +2449,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       ContextPtr context = static_cast<ContextPtr>(d->Ref(id));
       const intptr_t length = d->ReadUnsigned();
@@ -2584,7 +2514,7 @@
       : DeserializationCluster("ContextScope") {}
   ~ContextScopeDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -2596,8 +2526,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       ContextScopePtr scope = static_cast<ContextScopePtr>(d->Ref(id));
       const intptr_t length = d->ReadUnsigned();
@@ -2653,7 +2582,7 @@
       : DeserializationCluster("UnlinkedCall") {}
   ~UnlinkedCallDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -2664,8 +2593,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       UnlinkedCallPtr unlinked = static_cast<UnlinkedCallPtr>(d->Ref(id));
       Deserializer::InitializeHeader(unlinked, kUnlinkedCallCid,
@@ -2722,7 +2650,7 @@
   ICDataDeserializationCluster() : DeserializationCluster("ICData") {}
   ~ICDataDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -2732,8 +2660,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       ICDataPtr ic = static_cast<ICDataPtr>(d->Ref(id));
       Deserializer::InitializeHeader(ic, kICDataCid, ICData::InstanceSize());
@@ -2788,7 +2715,7 @@
       : DeserializationCluster("MegamorphicCache") {}
   ~MegamorphicCacheDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -2799,8 +2726,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       MegamorphicCachePtr cache = static_cast<MegamorphicCachePtr>(d->Ref(id));
       Deserializer::InitializeHeader(cache, kMegamorphicCacheCid,
@@ -2811,7 +2737,7 @@
   }
 
 #if defined(DART_PRECOMPILED_RUNTIME)
-  void PostLoad(Deserializer* d, const Array& refs, bool canonicalize) {
+  void PostLoad(Deserializer* d, const Array& refs, bool is_canonical) {
     if (FLAG_use_bare_instructions) {
       // By default, every megamorphic call site will load the target
       // [Function] from the hash table and call indirectly via loading the
@@ -2880,7 +2806,7 @@
       : DeserializationCluster("SubtypeTestCache") {}
   ~SubtypeTestCacheDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -2891,8 +2817,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       SubtypeTestCachePtr cache = static_cast<SubtypeTestCachePtr>(d->Ref(id));
       Deserializer::InitializeHeader(cache, kSubtypeTestCacheCid,
@@ -2944,7 +2869,7 @@
   LoadingUnitDeserializationCluster() : DeserializationCluster("LoadingUnit") {}
   ~LoadingUnitDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -2955,8 +2880,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       LoadingUnitPtr unit = static_cast<LoadingUnitPtr>(d->Ref(id));
       Deserializer::InitializeHeader(unit, kLoadingUnitCid,
@@ -3015,7 +2939,7 @@
       : DeserializationCluster("LanguageError") {}
   ~LanguageErrorDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -3026,8 +2950,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       LanguageErrorPtr error = static_cast<LanguageErrorPtr>(d->Ref(id));
       Deserializer::InitializeHeader(error, kLanguageErrorCid,
@@ -3083,7 +3006,7 @@
       : DeserializationCluster("UnhandledException") {}
   ~UnhandledExceptionDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -3094,8 +3017,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       UnhandledExceptionPtr exception =
           static_cast<UnhandledExceptionPtr>(d->Ref(id));
@@ -3204,35 +3126,13 @@
 };
 #endif  // !DART_PRECOMPILED_RUNTIME
 
-class AbstractInstanceDeserializationCluster : public DeserializationCluster {
- protected:
-  explicit AbstractInstanceDeserializationCluster(const char* name)
-      : DeserializationCluster(name) {}
-
- public:
-  void PostLoad(Deserializer* d, const Array& refs, bool canonicalize) {
-    if (canonicalize) {
-      Thread* thread = Thread::Current();
-      SafepointMutexLocker ml(
-          thread->isolate_group()->constant_canonicalization_mutex());
-      Instance& instance = Instance::Handle(d->zone());
-      for (intptr_t i = start_index_; i < stop_index_; i++) {
-        instance ^= refs.At(i);
-        instance = instance.CanonicalizeLocked(thread);
-        refs.SetAt(i, instance);
-      }
-    }
-  }
-};
-
-class InstanceDeserializationCluster
-    : public AbstractInstanceDeserializationCluster {
+class InstanceDeserializationCluster : public DeserializationCluster {
  public:
   explicit InstanceDeserializationCluster(intptr_t cid)
-      : AbstractInstanceDeserializationCluster("Instance"), cid_(cid) {}
+      : DeserializationCluster("Instance"), cid_(cid) {}
   ~InstanceDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -3246,7 +3146,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
+  void ReadFill(Deserializer* d, bool is_canonical) {
     intptr_t next_field_offset = next_field_offset_in_words_ << kWordSizeLog2;
     intptr_t instance_size =
         Object::RoundedAllocationSize(instance_size_in_words_ * kWordSize);
@@ -3255,7 +3155,7 @@
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       InstancePtr instance = static_cast<InstancePtr>(d->Ref(id));
       Deserializer::InitializeHeader(instance, cid_, instance_size,
-                                     stamp_canonical);
+                                     is_canonical);
       intptr_t offset = Instance::NextFieldOffset();
       while (offset < next_field_offset) {
         if (unboxed_fields_bitmap.Get(offset / kWordSize)) {
@@ -3330,7 +3230,7 @@
       : DeserializationCluster("LibraryPrefix") {}
   ~LibraryPrefixDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -3341,8 +3241,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       LibraryPrefixPtr prefix = static_cast<LibraryPrefixPtr>(d->Ref(id));
       Deserializer::InitializeHeader(prefix, kLibraryPrefixCid,
@@ -3425,7 +3324,7 @@
   TypeDeserializationCluster() : DeserializationCluster("Type") {}
   ~TypeDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -3435,11 +3334,11 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       TypePtr type = static_cast<TypePtr>(d->Ref(id));
       Deserializer::InitializeHeader(type, kTypeCid, Type::InstanceSize(),
-                                     stamp_canonical);
+                                     is_canonical);
       ReadFromTo(type);
       const uint8_t combined = d->Read<uint8_t>();
       type->untag()->type_state_ = combined >> kNullabilityBitSize;
@@ -3447,15 +3346,20 @@
     }
   }
 
-  void PostLoad(Deserializer* d, const Array& refs, bool canonicalize) {
-    if (canonicalize) {
-      Thread* thread = Thread::Current();
-      AbstractType& type = AbstractType::Handle(d->zone());
+  void PostLoad(Deserializer* d, const Array& refs, bool is_canonical) {
+    if (is_canonical && (d->isolate() != Dart::vm_isolate())) {
+      CanonicalTypeSet table(
+          d->zone(), d->isolate_group()->object_store()->canonical_types());
+      Type& type = Type::Handle(d->zone());
       for (intptr_t i = start_index_; i < stop_index_; i++) {
         type ^= refs.At(i);
-        type = type.Canonicalize(thread, nullptr);
-        refs.SetAt(i, type);
+        ASSERT(type.IsCanonical());
+        bool present = table.Insert(type);
+        // Two recursive types with different topology (and hashes) may be
+        // equal.
+        ASSERT(!present || type.IsRecursive());
       }
+      d->isolate_group()->object_store()->set_canonical_types(table.Release());
     }
 
     Type& type = Type::Handle(d->zone());
@@ -3536,7 +3440,7 @@
       : DeserializationCluster("FunctionType") {}
   ~FunctionTypeDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -3547,12 +3451,11 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       FunctionTypePtr type = static_cast<FunctionTypePtr>(d->Ref(id));
-      Deserializer::InitializeHeader(type, kFunctionTypeCid,
-                                     FunctionType::InstanceSize(),
-                                     stamp_canonical);
+      Deserializer::InitializeHeader(
+          type, kFunctionTypeCid, FunctionType::InstanceSize(), is_canonical);
       ReadFromTo(type);
       const uint8_t combined = d->Read<uint8_t>();
       type->untag()->type_state_ = combined >> kNullabilityBitSize;
@@ -3561,15 +3464,22 @@
     }
   }
 
-  void PostLoad(Deserializer* d, const Array& refs, bool canonicalize) {
-    if (canonicalize) {
-      Thread* thread = Thread::Current();
-      AbstractType& type = AbstractType::Handle(d->zone());
+  void PostLoad(Deserializer* d, const Array& refs, bool is_canonical) {
+    if (is_canonical && (d->isolate() != Dart::vm_isolate())) {
+      CanonicalFunctionTypeSet table(
+          d->zone(),
+          d->isolate_group()->object_store()->canonical_function_types());
+      FunctionType& type = FunctionType::Handle(d->zone());
       for (intptr_t i = start_index_; i < stop_index_; i++) {
         type ^= refs.At(i);
-        type = type.Canonicalize(thread, nullptr);
-        refs.SetAt(i, type);
+        ASSERT(type.IsCanonical());
+        bool present = table.Insert(type);
+        // Two recursive types with different topology (and hashes) may be
+        // equal.
+        ASSERT(!present || type.IsRecursive());
       }
+      d->isolate_group()->object_store()->set_canonical_function_types(
+          table.Release());
     }
 
     FunctionType& type = FunctionType::Handle(d->zone());
@@ -3632,7 +3542,7 @@
   TypeRefDeserializationCluster() : DeserializationCluster("TypeRef") {}
   ~TypeRefDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -3642,16 +3552,16 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       TypeRefPtr type = static_cast<TypeRefPtr>(d->Ref(id));
-      Deserializer::InitializeHeader(type, kTypeRefCid, TypeRef::InstanceSize(),
-                                     stamp_canonical);
+      Deserializer::InitializeHeader(type, kTypeRefCid,
+                                     TypeRef::InstanceSize());
       ReadFromTo(type);
     }
   }
 
-  void PostLoad(Deserializer* d, const Array& refs, bool canonicalize) {
+  void PostLoad(Deserializer* d, const Array& refs, bool is_canonical) {
     TypeRef& type_ref = TypeRef::Handle(d->zone());
     Code& stub = Code::Handle(d->zone());
 
@@ -3731,7 +3641,7 @@
       : DeserializationCluster("TypeParameter") {}
   ~TypeParameterDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -3742,12 +3652,11 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       TypeParameterPtr type = static_cast<TypeParameterPtr>(d->Ref(id));
-      Deserializer::InitializeHeader(type, kTypeParameterCid,
-                                     TypeParameter::InstanceSize(),
-                                     stamp_canonical);
+      Deserializer::InitializeHeader(
+          type, kTypeParameterCid, TypeParameter::InstanceSize(), is_canonical);
       ReadFromTo(type);
       type->untag()->parameterized_class_id_ = d->Read<int32_t>();
       type->untag()->base_ = d->Read<uint16_t>();
@@ -3758,15 +3667,20 @@
     }
   }
 
-  void PostLoad(Deserializer* d, const Array& refs, bool canonicalize) {
-    if (canonicalize) {
-      Thread* thread = Thread::Current();
+  void PostLoad(Deserializer* d, const Array& refs, bool is_canonical) {
+    if (is_canonical && (d->isolate() != Dart::vm_isolate())) {
+      CanonicalTypeParameterSet table(
+          d->zone(),
+          d->isolate_group()->object_store()->canonical_type_parameters());
       TypeParameter& type_param = TypeParameter::Handle(d->zone());
       for (intptr_t i = start_index_; i < stop_index_; i++) {
         type_param ^= refs.At(i);
-        type_param ^= type_param.Canonicalize(thread, nullptr);
-        refs.SetAt(i, type_param);
+        ASSERT(type_param.IsCanonical());
+        bool present = table.Insert(type_param);
+        ASSERT(!present);
       }
+      d->isolate_group()->object_store()->set_canonical_type_parameters(
+          table.Release());
     }
 
     TypeParameter& type_param = TypeParameter::Handle(d->zone());
@@ -3825,14 +3739,12 @@
 };
 #endif  // !DART_PRECOMPILED_RUNTIME
 
-class ClosureDeserializationCluster
-    : public AbstractInstanceDeserializationCluster {
+class ClosureDeserializationCluster : public DeserializationCluster {
  public:
-  ClosureDeserializationCluster()
-      : AbstractInstanceDeserializationCluster("Closure") {}
+  ClosureDeserializationCluster() : DeserializationCluster("Closure") {}
   ~ClosureDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -3842,11 +3754,11 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       ClosurePtr closure = static_cast<ClosurePtr>(d->Ref(id));
       Deserializer::InitializeHeader(closure, kClosureCid,
-                                     Closure::InstanceSize(), stamp_canonical);
+                                     Closure::InstanceSize(), is_canonical);
       ReadFromTo(closure);
     }
   }
@@ -3899,7 +3811,7 @@
   MintDeserializationCluster() : DeserializationCluster("int") {}
   ~MintDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     PageSpace* old_space = d->heap()->old_space();
 
     start_index_ = d->next_index();
@@ -3912,7 +3824,7 @@
         MintPtr mint = static_cast<MintPtr>(
             AllocateUninitialized(old_space, Mint::InstanceSize()));
         Deserializer::InitializeHeader(mint, kMintCid, Mint::InstanceSize(),
-                                       stamp_canonical);
+                                       is_canonical);
         mint->untag()->value_ = value;
         d->AssignRef(mint);
       }
@@ -3920,24 +3832,19 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {}
+  void ReadFill(Deserializer* d, bool is_canonical) {}
 
-  void PostLoad(Deserializer* d, const Array& refs, bool canonicalize) {
-    if (canonicalize) {
+  void PostLoad(Deserializer* d, const Array& refs, bool is_canonical) {
+    if (is_canonical && (d->isolate() != Dart::vm_isolate())) {
       const Class& mint_cls = Class::Handle(
-          d->zone(), d->isolate_group()->object_store()->mint_class());
+          d->zone(), IsolateGroup::Current()->object_store()->mint_class());
+      mint_cls.set_constants(Object::null_array());
       Object& number = Object::Handle(d->zone());
-      Mint& number2 = Mint::Handle(d->zone());
       for (intptr_t i = start_index_; i < stop_index_; i++) {
         number = refs.At(i);
-        if (!number.IsMint()) continue;
-        number2 =
-            mint_cls.LookupCanonicalMint(d->zone(), Mint::Cast(number).value());
-        if (number2.IsNull()) {
-          number.SetCanonical();
+        if (number.IsMint()) {
+          ASSERT(number.IsCanonical());
           mint_cls.InsertCanonicalMint(d->zone(), Mint::Cast(number));
-        } else {
-          refs.SetAt(i, number2);
         }
       }
     }
@@ -3984,7 +3891,7 @@
   DoubleDeserializationCluster() : DeserializationCluster("double") {}
   ~DoubleDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -3994,35 +3901,14 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       DoublePtr dbl = static_cast<DoublePtr>(d->Ref(id));
       Deserializer::InitializeHeader(dbl, kDoubleCid, Double::InstanceSize(),
-                                     stamp_canonical);
+                                     is_canonical);
       dbl->untag()->value_ = d->Read<double>();
     }
   }
-
-  void PostLoad(Deserializer* d, const Array& refs, bool canonicalize) {
-    if (canonicalize) {
-      const Class& cls = Class::Handle(
-          d->zone(), d->isolate_group()->object_store()->double_class());
-      SafepointMutexLocker ml(
-          d->isolate_group()->constant_canonicalization_mutex());
-      Double& dbl = Double::Handle(d->zone());
-      Double& dbl2 = Double::Handle(d->zone());
-      for (intptr_t i = start_index_; i < stop_index_; i++) {
-        dbl ^= refs.At(i);
-        dbl2 = cls.LookupCanonicalDouble(d->zone(), dbl.value());
-        if (dbl2.IsNull()) {
-          dbl.SetCanonical();
-          cls.InsertCanonicalDouble(d->zone(), dbl);
-        } else {
-          refs.SetAt(i, dbl2);
-        }
-      }
-    }
-  }
 };
 
 #if !defined(DART_PRECOMPILED_RUNTIME)
@@ -4069,7 +3955,7 @@
       : DeserializationCluster("GrowableObjectArray") {}
   ~GrowableObjectArrayDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -4080,13 +3966,13 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       GrowableObjectArrayPtr list =
           static_cast<GrowableObjectArrayPtr>(d->Ref(id));
       Deserializer::InitializeHeader(list, kGrowableObjectArrayCid,
                                      GrowableObjectArray::InstanceSize(),
-                                     stamp_canonical);
+                                     is_canonical);
       ReadFromTo(list);
     }
   }
@@ -4142,7 +4028,7 @@
       : DeserializationCluster("TypedData"), cid_(cid) {}
   ~TypedDataDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -4155,17 +4041,15 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     intptr_t element_size = TypedData::ElementSizeInBytes(cid_);
 
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       TypedDataPtr data = static_cast<TypedDataPtr>(d->Ref(id));
       const intptr_t length = d->ReadUnsigned();
       const intptr_t length_in_bytes = length * element_size;
-      Deserializer::InitializeHeader(data, cid_,
-                                     TypedData::InstanceSize(length_in_bytes),
-                                     stamp_canonical);
+      Deserializer::InitializeHeader(
+          data, cid_, TypedData::InstanceSize(length_in_bytes), is_canonical);
       data->untag()->length_ = Smi::New(length);
       data->untag()->RecomputeDataField();
       uint8_t* cdata = reinterpret_cast<uint8_t*>(data->untag()->data());
@@ -4222,7 +4106,7 @@
       : DeserializationCluster("TypedDataView"), cid_(cid) {}
   ~TypedDataViewDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -4233,17 +4117,16 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       TypedDataViewPtr view = static_cast<TypedDataViewPtr>(d->Ref(id));
-      Deserializer::InitializeHeader(view, cid_, TypedDataView::InstanceSize());
+      Deserializer::InitializeHeader(view, cid_, TypedDataView::InstanceSize(),
+                                     is_canonical);
       ReadFromTo(view);
     }
   }
 
-  void PostLoad(Deserializer* d, const Array& refs, bool canonicalize) {
-    ASSERT(!canonicalize);
+  void PostLoad(Deserializer* d, const Array& refs, bool is_canonical) {
     auto& view = TypedDataView::Handle(d->zone());
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       view ^= refs.At(id);
@@ -4303,7 +4186,7 @@
       : DeserializationCluster("ExternalTypedData"), cid_(cid) {}
   ~ExternalTypedDataDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -4314,8 +4197,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     intptr_t element_size = ExternalTypedData::ElementSizeInBytes(cid_);
 
     for (intptr_t id = start_index_; id < stop_index_; id++) {
@@ -4376,7 +4258,7 @@
   StackTraceDeserializationCluster() : DeserializationCluster("StackTrace") {}
   ~StackTraceDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -4387,8 +4269,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       StackTracePtr trace = static_cast<StackTracePtr>(d->Ref(id));
       Deserializer::InitializeHeader(trace, kStackTraceCid,
@@ -4442,7 +4323,7 @@
   RegExpDeserializationCluster() : DeserializationCluster("RegExp") {}
   ~RegExpDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -4452,8 +4333,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       RegExpPtr regexp = static_cast<RegExpPtr>(d->Ref(id));
       Deserializer::InitializeHeader(regexp, kRegExpCid,
@@ -4508,7 +4388,7 @@
       : DeserializationCluster("WeakProperty") {}
   ~WeakPropertyDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -4519,8 +4399,7 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
-    ASSERT(!stamp_canonical);  // Never canonical.
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       WeakPropertyPtr property = static_cast<WeakPropertyPtr>(d->Ref(id));
       Deserializer::InitializeHeader(property, kWeakPropertyCid,
@@ -4599,14 +4478,13 @@
 };
 #endif  // !DART_PRECOMPILED_RUNTIME
 
-class LinkedHashMapDeserializationCluster
-    : public AbstractInstanceDeserializationCluster {
+class LinkedHashMapDeserializationCluster : public DeserializationCluster {
  public:
   LinkedHashMapDeserializationCluster()
-      : AbstractInstanceDeserializationCluster("LinkedHashMap") {}
+      : DeserializationCluster("LinkedHashMap") {}
   ~LinkedHashMapDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -4617,14 +4495,13 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
+  void ReadFill(Deserializer* d, bool is_canonical) {
     PageSpace* old_space = d->heap()->old_space();
 
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       LinkedHashMapPtr map = static_cast<LinkedHashMapPtr>(d->Ref(id));
-      Deserializer::InitializeHeader(map, kLinkedHashMapCid,
-                                     LinkedHashMap::InstanceSize(),
-                                     stamp_canonical);
+      Deserializer::InitializeHeader(
+          map, kLinkedHashMapCid, LinkedHashMap::InstanceSize(), is_canonical);
 
       map->untag()->type_arguments_ =
           static_cast<TypeArgumentsPtr>(d->ReadRef());
@@ -4708,14 +4585,13 @@
 };
 #endif  // !DART_PRECOMPILED_RUNTIME
 
-class ArrayDeserializationCluster
-    : public AbstractInstanceDeserializationCluster {
+class ArrayDeserializationCluster : public DeserializationCluster {
  public:
   explicit ArrayDeserializationCluster(intptr_t cid)
-      : AbstractInstanceDeserializationCluster("Array"), cid_(cid) {}
+      : DeserializationCluster("Array"), cid_(cid) {}
   ~ArrayDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -4727,12 +4603,12 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       ArrayPtr array = static_cast<ArrayPtr>(d->Ref(id));
       const intptr_t length = d->ReadUnsigned();
       Deserializer::InitializeHeader(array, cid_, Array::InstanceSize(length),
-                                     stamp_canonical);
+                                     is_canonical);
       array->untag()->type_arguments_ =
           static_cast<TypeArgumentsPtr>(d->ReadRef());
       array->untag()->length_ = Smi::New(length);
@@ -4787,40 +4663,13 @@
 };
 #endif  // !DART_PRECOMPILED_RUNTIME
 
-class StringDeserializationCluster : public DeserializationCluster {
- protected:
-  explicit StringDeserializationCluster(const char* name)
-      : DeserializationCluster(name) {}
-
- public:
-  void PostLoad(Deserializer* d, const Array& refs, bool canonicalize) {
-    if (canonicalize) {
-      CanonicalStringSet table(
-          d->zone(), d->isolate_group()->object_store()->symbol_table());
-      String& str = String::Handle(d->zone());
-      String& str2 = String::Handle(d->zone());
-      for (intptr_t i = start_index_; i < stop_index_; i++) {
-        str ^= refs.At(i);
-        str2 ^= table.InsertOrGet(str);
-        if (str.ptr() == str2.ptr()) {
-          str.SetCanonical();
-        } else {
-          refs.SetAt(i, str2);
-        }
-      }
-      d->isolate_group()->object_store()->set_symbol_table(table.Release());
-    }
-  }
-};
-
-class OneByteStringDeserializationCluster
-    : public StringDeserializationCluster {
+class OneByteStringDeserializationCluster : public DeserializationCluster {
  public:
   OneByteStringDeserializationCluster()
-      : StringDeserializationCluster("OneByteString") {}
+      : DeserializationCluster("OneByteString") {}
   ~OneByteStringDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -4832,13 +4681,13 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       OneByteStringPtr str = static_cast<OneByteStringPtr>(d->Ref(id));
       const intptr_t length = d->ReadUnsigned();
       Deserializer::InitializeHeader(str, kOneByteStringCid,
                                      OneByteString::InstanceSize(length),
-                                     stamp_canonical);
+                                     is_canonical);
       str->untag()->length_ = Smi::New(length);
       StringHasher hasher;
       for (intptr_t j = 0; j < length; j++) {
@@ -4849,6 +4698,21 @@
       String::SetCachedHash(str, hasher.Finalize());
     }
   }
+
+  void PostLoad(Deserializer* d, const Array& refs, bool is_canonical) {
+    if (is_canonical && (d->isolate() != Dart::vm_isolate())) {
+      CanonicalStringSet table(
+          d->zone(), d->isolate_group()->object_store()->symbol_table());
+      String& str = String::Handle(d->zone());
+      for (intptr_t i = start_index_; i < stop_index_; i++) {
+        str ^= refs.At(i);
+        ASSERT(str.IsCanonical());
+        bool present = table.Insert(str);
+        ASSERT(!present);
+      }
+      d->isolate_group()->object_store()->set_symbol_table(table.Release());
+    }
+  }
 };
 
 #if !defined(DART_PRECOMPILED_RUNTIME)
@@ -4893,14 +4757,13 @@
 };
 #endif  // !DART_PRECOMPILED_RUNTIME
 
-class TwoByteStringDeserializationCluster
-    : public StringDeserializationCluster {
+class TwoByteStringDeserializationCluster : public DeserializationCluster {
  public:
   TwoByteStringDeserializationCluster()
-      : StringDeserializationCluster("TwoByteString") {}
+      : DeserializationCluster("TwoByteString") {}
   ~TwoByteStringDeserializationCluster() {}
 
-  void ReadAlloc(Deserializer* d, bool stamp_canonical) {
+  void ReadAlloc(Deserializer* d, bool is_canonical) {
     start_index_ = d->next_index();
     PageSpace* old_space = d->heap()->old_space();
     const intptr_t count = d->ReadUnsigned();
@@ -4912,13 +4775,13 @@
     stop_index_ = d->next_index();
   }
 
-  void ReadFill(Deserializer* d, bool stamp_canonical) {
+  void ReadFill(Deserializer* d, bool is_canonical) {
     for (intptr_t id = start_index_; id < stop_index_; id++) {
       TwoByteStringPtr str = static_cast<TwoByteStringPtr>(d->Ref(id));
       const intptr_t length = d->ReadUnsigned();
       Deserializer::InitializeHeader(str, kTwoByteStringCid,
                                      TwoByteString::InstanceSize(length),
-                                     stamp_canonical);
+                                     is_canonical);
       str->untag()->length_ = Smi::New(length);
       StringHasher hasher;
       for (intptr_t j = 0; j < length; j++) {
@@ -4930,6 +4793,21 @@
       String::SetCachedHash(str, hasher.Finalize());
     }
   }
+
+  void PostLoad(Deserializer* d, const Array& refs, bool is_canonical) {
+    if (is_canonical && (d->isolate() != Dart::vm_isolate())) {
+      CanonicalStringSet table(
+          d->zone(), d->isolate_group()->object_store()->symbol_table());
+      String& str = String::Handle(d->zone());
+      for (intptr_t i = start_index_; i < stop_index_; i++) {
+        str ^= refs.At(i);
+        ASSERT(str.IsCanonical());
+        bool present = table.Insert(str);
+        ASSERT(!present);
+      }
+      d->isolate_group()->object_store()->set_symbol_table(table.Release());
+    }
+  }
 };
 
 #if !defined(DART_PRECOMPILED_RUNTIME)
@@ -5309,26 +5187,16 @@
       const Object* deferred_object = (*unit_->deferred_objects())[i];
       ASSERT(deferred_object->IsCode());
       CodePtr code = static_cast<CodePtr>(deferred_object->ptr());
-      if (FLAG_use_bare_instructions) {
-        if (FLAG_retain_function_objects) {
-          ObjectPoolPtr pool = code->untag()->object_pool_;
-          if (pool != ObjectPool::null()) {
-            const intptr_t length = pool->untag()->length_;
-            uint8_t* entry_bits = pool->untag()->entry_bits();
-            for (intptr_t i = 0; i < length; i++) {
-              auto entry_type = ObjectPool::TypeBits::decode(entry_bits[i]);
-              if (entry_type == ObjectPool::EntryType::kTaggedObject) {
-                s->Push(pool->untag()->data()[i].raw_obj_);
-              }
-            }
-          }
-        }
-      } else {
-        s->Push(code->untag()->object_pool_);
-      }
       s->Push(code->untag()->compressed_stackmaps_);
       s->Push(code->untag()->code_source_map_);
     }
+    {
+      GrowableArray<CodePtr> raw_codes(num_deferred_objects);
+      for (intptr_t i = 0; i < num_deferred_objects; i++) {
+        raw_codes.Add((*unit_->deferred_objects())[i]->ptr());
+      }
+      s->PrepareInstructions(&raw_codes);
+    }
   }
 
   void WriteRoots(Serializer* s) {
@@ -5348,33 +5216,9 @@
       ASSERT(s->RefId(code) == (start_index + i));
       s->WriteInstructions(code->untag()->instructions_,
                            code->untag()->unchecked_offset_, code, false);
-      if (!FLAG_use_bare_instructions) {
-        s->WriteRootRef(code->untag()->object_pool_, "deferred-code");
-      }
       s->WriteRootRef(code->untag()->compressed_stackmaps_, "deferred-code");
       s->WriteRootRef(code->untag()->code_source_map_, "deferred-code");
     }
-
-    if (FLAG_use_bare_instructions && FLAG_retain_function_objects) {
-      ObjectPoolPtr pool =
-          s->isolate_group()->object_store()->global_object_pool();
-      const intptr_t length = pool->untag()->length_;
-      uint8_t* entry_bits = pool->untag()->entry_bits();
-      intptr_t last_write = 0;
-      for (intptr_t i = 0; i < length; i++) {
-        auto entry_type = ObjectPool::TypeBits::decode(entry_bits[i]);
-        if (entry_type == ObjectPool::EntryType::kTaggedObject) {
-          if (s->IsWritten(pool->untag()->data()[i].raw_obj_)) {
-            intptr_t skip = i - last_write;
-            s->WriteUnsigned(skip);
-            s->WriteRootRef(pool->untag()->data()[i].raw_obj_,
-                            "deferred-literal");
-            last_write = i;
-          }
-        }
-      }
-      s->WriteUnsigned(length - last_write);
-    }
 #endif
   }
 
@@ -5410,29 +5254,12 @@
         ASSERT(unchecked_entry_point != 0);
         func->untag()->unchecked_entry_point_ = unchecked_entry_point;
       }
-      if (!FLAG_use_bare_instructions) {
-        code->untag()->object_pool_ = static_cast<ObjectPoolPtr>(d->ReadRef());
-      }
       code->untag()->compressed_stackmaps_ =
           static_cast<CompressedStackMapsPtr>(d->ReadRef());
       code->untag()->code_source_map_ =
           static_cast<CodeSourceMapPtr>(d->ReadRef());
     }
 
-    if (FLAG_use_bare_instructions && FLAG_retain_function_objects) {
-      ObjectPoolPtr pool =
-          d->isolate_group()->object_store()->global_object_pool();
-      const intptr_t length = pool->untag()->length_;
-      uint8_t* entry_bits = pool->untag()->entry_bits();
-      for (intptr_t i = d->ReadUnsigned(); i < length; i += d->ReadUnsigned()) {
-        auto entry_type = ObjectPool::TypeBits::decode(entry_bits[i]);
-        ASSERT(entry_type == ObjectPool::EntryType::kTaggedObject);
-        // The existing entry will usually be null, but it might also be an
-        // equivalent object that was duplicated in another loading unit.
-        pool->untag()->data()[i].raw_obj_ = d->ReadRef();
-      }
-    }
-
     // Reinitialize the dispatch table by rereading the table's serialization
     // in the root snapshot.
     IsolateGroup* group = d->thread()->isolate()->group();
@@ -5845,9 +5672,6 @@
     // TODO(41974): Are these always type testing stubs?
     unit_id = LoadingUnit::kRootId;
   }
-  if (unit_id == LoadingUnit::kRootId) {
-    return true;
-  }
   if (unit_id != current_loading_unit_id_) {
     if (record) {
       (*loading_units_)[unit_id]->AddDeferredObject(static_cast<CodePtr>(obj));
@@ -5858,58 +5682,11 @@
 }
 
 #if !defined(DART_PRECOMPILED_RUNTIME)
-void Serializer::PrepareInstructions() {
-  if (!Snapshot::IncludesCode(kind())) return;
-
-  CodeSerializationCluster* cluster =
-      static_cast<CodeSerializationCluster*>(clusters_by_cid_[kCodeCid]);
-
-  // Code objects that have identical/duplicate instructions must be adjacent in
-  // the order that Code objects are written because the encoding of the
-  // reference from the Code to the Instructions assumes monotonically
-  // increasing offsets as part of a delta encoding. Also the code order table
-  // that allows for mapping return addresses back to Code objects depends on
-  // this sorting.
-  if (cluster != nullptr) {
-    CodeSerializationCluster::Sort(cluster->objects());
-  }
-  if ((loading_units_ != nullptr) &&
-      (current_loading_unit_id_ == LoadingUnit::kRootId)) {
-    for (intptr_t i = LoadingUnit::kRootId + 1; i < loading_units_->length();
-         i++) {
-      auto unit_objects = loading_units_->At(i)->deferred_objects();
-      CodeSerializationCluster::Sort(unit_objects);
-      for (intptr_t j = 0; j < unit_objects->length(); j++) {
-        cluster->deferred_objects()->Add(unit_objects->At(j)->ptr());
-      }
-    }
-  }
-
+void Serializer::PrepareInstructions(GrowableArray<CodePtr>* code_objects) {
 #if defined(DART_PRECOMPILER) && !defined(TARGET_ARCH_IA32)
   if ((kind() == Snapshot::kFullAOT) && FLAG_use_bare_instructions) {
-    // Group the code objects whose instructions are not being deferred in this
-    // snapshot unit in the order they will be written: first the code objects
-    // encountered for this first time in this unit being written by the
-    // CodeSerializationCluster, then code object previously deferred whose
-    // instructions are now written by UnitSerializationRoots. This order needs
-    // to be known to finalize bare-instructions-mode's PC-relative calls.
-    GrowableArray<CodePtr> code_objects;
-    if (cluster != nullptr) {
-      auto in = cluster->objects();
-      for (intptr_t i = 0; i < in->length(); i++) {
-        code_objects.Add(in->At(i));
-      }
-    }
-    if (loading_units_ != nullptr) {
-      auto in =
-          loading_units_->At(current_loading_unit_id_)->deferred_objects();
-      for (intptr_t i = 0; i < in->length(); i++) {
-        code_objects.Add(in->At(i)->ptr());
-      }
-    }
-
     GrowableArray<ImageWriterCommand> writer_commands;
-    RelocateCodeObjects(vm_, &code_objects, &writer_commands);
+    RelocateCodeObjects(vm_, code_objects, &writer_commands);
     image_writer_->PrepareForSerialization(&writer_commands);
   }
 #endif  // defined(DART_PRECOMPILER) && !defined(TARGET_ARCH_IA32)
@@ -6117,22 +5894,6 @@
   }
 
   GrowableArray<SerializationCluster*> canonical_clusters;
-  // The order that PostLoad runs matters for some classes. Explicitly place
-  // these clusters first, then add the rest ordered by class id.
-#define ADD_NEXT(cid)                                                          \
-  if (canonical_clusters_by_cid_[cid] != nullptr) {                            \
-    canonical_clusters.Add(canonical_clusters_by_cid_[cid]);                   \
-    canonical_clusters_by_cid_[cid] = nullptr;                                 \
-  }
-  ADD_NEXT(kOneByteStringCid)
-  ADD_NEXT(kTwoByteStringCid)
-  ADD_NEXT(kMintCid)
-  ADD_NEXT(kDoubleCid)
-  ADD_NEXT(kTypeParameterCid)
-  ADD_NEXT(kTypeCid)
-  ADD_NEXT(kTypeArgumentsCid)
-  ADD_NEXT(kClosureCid)
-#undef ADD_NEXT
   for (intptr_t cid = 0; cid < num_cids_; cid++) {
     if (canonical_clusters_by_cid_[cid] != nullptr) {
       canonical_clusters.Add(canonical_clusters_by_cid_[cid]);
@@ -6159,8 +5920,6 @@
   }
 #endif
 
-  PrepareInstructions();
-
   intptr_t num_objects = num_base_objects_ + num_written_objects_;
 #if defined(ARCH_IS_64_BIT)
   if (!Utils::IsInt(32, num_objects)) {
@@ -6278,7 +6037,8 @@
   ASSERT(code_cluster != nullptr);
   // Reference IDs in a cluster are allocated sequentially, so we can use the
   // first code object's reference ID to calculate the cluster index.
-  const intptr_t first_code_id = RefId(code_cluster->objects()->At(0));
+  const intptr_t first_code_id =
+      RefId(code_cluster->discovered_objects()->At(0));
   // The first object in the code cluster must have its reference ID allocated.
   ASSERT(IsAllocatedReference(first_code_id));
 
@@ -6968,17 +6728,18 @@
     ASSERT_EQUAL(next_ref_index_ - kFirstReference, num_objects_);
 
     {
-      TIMELINE_DURATION(thread(), Isolate, "PostLoad");
+      TIMELINE_DURATION(thread(), Isolate, "ReadFill");
       for (intptr_t i = 0; i < num_canonical_clusters_; i++) {
-        bool stamp_canonical = isolate() == Dart::vm_isolate();
-        canonical_clusters_[i]->ReadFill(this, stamp_canonical);
+        TIMELINE_DURATION(thread(), Isolate, canonical_clusters_[i]->name());
+        canonical_clusters_[i]->ReadFill(this, /*is_canonical*/ true);
 #if defined(DEBUG)
         int32_t section_marker = Read<int32_t>();
         ASSERT(section_marker == kSectionMarker);
 #endif
       }
       for (intptr_t i = 0; i < num_clusters_; i++) {
-        clusters_[i]->ReadFill(this, /*stamp_canonical*/ false);
+        TIMELINE_DURATION(thread(), Isolate, clusters_[i]->name());
+        clusters_[i]->ReadFill(this, /*is_canonical*/ false);
 #if defined(DEBUG)
         int32_t section_marker = Read<int32_t>();
         ASSERT(section_marker == kSectionMarker);
@@ -6999,22 +6760,26 @@
   roots->PostLoad(this, refs);
 
 #if defined(DEBUG)
-  isolate()->ValidateClassTable();
-  if (isolate() != Dart::vm_isolate()) {
-    isolate_group()->heap()->Verify();
+  Isolate* isolate = thread()->isolate();
+  isolate->ValidateClassTable();
+  if (isolate != Dart::vm_isolate()) {
+    isolate->group()->heap()->Verify();
   }
 #endif
 
+  // TODO(rmacnak): When splitting literals, load clusters requiring
+  // canonicalization first, canonicalize and update the ref array, the load
+  // the remaining clusters to avoid a full heap walk to update references to
+  // the losers of any canonicalization races.
   {
     TIMELINE_DURATION(thread(), Isolate, "PostLoad");
     for (intptr_t i = 0; i < num_canonical_clusters_; i++) {
       TIMELINE_DURATION(thread(), Isolate, canonical_clusters_[i]->name());
-      bool canonicalize = isolate() != Dart::vm_isolate();
-      canonical_clusters_[i]->PostLoad(this, refs, canonicalize);
+      canonical_clusters_[i]->PostLoad(this, refs, /*is_canonical*/ true);
     }
     for (intptr_t i = 0; i < num_clusters_; i++) {
       TIMELINE_DURATION(thread(), Isolate, clusters_[i]->name());
-      clusters_[i]->PostLoad(this, refs, /*canonicalize*/ false);
+      clusters_[i]->PostLoad(this, refs, /*is_canonical*/ false);
     }
   }
 }
diff --git a/runtime/vm/clustered_snapshot.h b/runtime/vm/clustered_snapshot.h
index d35b83a..ac72aed 100644
--- a/runtime/vm/clustered_snapshot.h
+++ b/runtime/vm/clustered_snapshot.h
@@ -116,20 +116,16 @@
 
   // Allocate memory for all objects in the cluster and write their addresses
   // into the ref array. Do not touch this memory.
-  virtual void ReadAlloc(Deserializer* deserializer, bool stamp_canonical) = 0;
+  virtual void ReadAlloc(Deserializer* deserializer, bool is_canonical) = 0;
 
   // Initialize the cluster's objects. Do not touch the memory of other objects.
-  virtual void ReadFill(Deserializer* deserializer, bool stamp_canonical) = 0;
+  virtual void ReadFill(Deserializer* deserializer, bool is_canonical) = 0;
 
   // Complete any action that requires the full graph to be deserialized, such
   // as rehashing.
   virtual void PostLoad(Deserializer* deserializer,
                         const Array& refs,
-                        bool canonicalize) {
-    if (canonicalize) {
-      FATAL1("%s needs canonicalization but doesn't define PostLoad", name());
-    }
-  }
+                        bool is_canonical) {}
 
   const char* name() const { return name_; }
 
@@ -351,7 +347,7 @@
     Write<int32_t>(cid);
   }
 
-  void PrepareInstructions();
+  void PrepareInstructions(GrowableArray<CodePtr>* codes);
   void WriteInstructions(InstructionsPtr instr,
                          uint32_t unchecked_offset,
                          CodePtr code,
@@ -384,7 +380,6 @@
   void set_loading_units(GrowableArray<LoadingUnitSerializationData*>* units) {
     loading_units_ = units;
   }
-  intptr_t current_loading_unit_id() { return current_loading_unit_id_; }
   void set_current_loading_unit_id(intptr_t id) {
     current_loading_unit_id_ = id;
   }
@@ -419,13 +414,6 @@
     FATAL("Missing ref");
   }
 
-  bool HasRef(ObjectPtr object) const {
-    return heap_->GetObjectId(object) != kUnreachableReference;
-  }
-  bool IsWritten(ObjectPtr object) const {
-    return heap_->GetObjectId(object) > num_base_objects_;
-  }
-
  private:
   const char* ReadOnlyObjectType(intptr_t cid);
 
@@ -585,8 +573,6 @@
 
   uword ReadWordWith32BitReads() { return stream_.ReadWordWith32BitReads(); }
 
-  intptr_t position() const { return stream_.Position(); }
-  void set_position(intptr_t p) { stream_.SetPosition(p); }
   const uint8_t* CurrentBufferAddress() const {
     return stream_.AddressOfCurrentPosition();
   }
diff --git a/runtime/vm/compiler/relocation.cc b/runtime/vm/compiler/relocation.cc
index ff5ea61..f19bbbd 100644
--- a/runtime/vm/compiler/relocation.cc
+++ b/runtime/vm/compiler/relocation.cc
@@ -71,15 +71,8 @@
   // We're guaranteed to have all calls resolved, since
   //   * backwards calls are resolved eagerly
   //   * forward calls are resolved once the target is written
-  if (!all_unresolved_calls_.IsEmpty()) {
-    for (auto call : all_unresolved_calls_) {
-      OS::PrintErr("Unresolved call to %s from %s\n",
-                   Object::Handle(call->callee).ToCString(),
-                   Object::Handle(call->caller).ToCString());
-    }
-  }
-  RELEASE_ASSERT(all_unresolved_calls_.IsEmpty());
-  RELEASE_ASSERT(unresolved_calls_by_destination_.IsEmpty());
+  ASSERT(all_unresolved_calls_.IsEmpty());
+  ASSERT(unresolved_calls_by_destination_.IsEmpty());
 
   // Any trampolines we created must be patched with the right offsets.
   auto it = trampolines_by_destination_.GetIterator();
diff --git a/runtime/vm/compiler/runtime_offsets_extracted.h b/runtime/vm/compiler/runtime_offsets_extracted.h
index 9694444..5bdddc8 100644
--- a/runtime/vm/compiler/runtime_offsets_extracted.h
+++ b/runtime/vm/compiler/runtime_offsets_extracted.h
@@ -86,7 +86,7 @@
 static constexpr dart::compiler::target::word Array_tags_offset = 0;
 static constexpr dart::compiler::target::word Array_type_arguments_offset = 4;
 static constexpr dart::compiler::target::word Class_declaration_type_offset =
-    48;
+    52;
 static constexpr dart::compiler::target::word Class_num_type_arguments_offset =
     88;
 static constexpr dart::compiler::target::word Class_super_type_offset = 44;
@@ -611,7 +611,7 @@
 static constexpr dart::compiler::target::word Array_tags_offset = 0;
 static constexpr dart::compiler::target::word Array_type_arguments_offset = 8;
 static constexpr dart::compiler::target::word Class_declaration_type_offset =
-    96;
+    104;
 static constexpr dart::compiler::target::word Class_num_type_arguments_offset =
     164;
 static constexpr dart::compiler::target::word Class_super_type_offset = 88;
@@ -1140,7 +1140,7 @@
 static constexpr dart::compiler::target::word Array_tags_offset = 0;
 static constexpr dart::compiler::target::word Array_type_arguments_offset = 4;
 static constexpr dart::compiler::target::word Class_declaration_type_offset =
-    48;
+    52;
 static constexpr dart::compiler::target::word Class_num_type_arguments_offset =
     88;
 static constexpr dart::compiler::target::word Class_super_type_offset = 44;
@@ -1662,7 +1662,7 @@
 static constexpr dart::compiler::target::word Array_tags_offset = 0;
 static constexpr dart::compiler::target::word Array_type_arguments_offset = 8;
 static constexpr dart::compiler::target::word Class_declaration_type_offset =
-    96;
+    104;
 static constexpr dart::compiler::target::word Class_num_type_arguments_offset =
     164;
 static constexpr dart::compiler::target::word Class_super_type_offset = 88;
@@ -2194,7 +2194,7 @@
 static constexpr dart::compiler::target::word Array_tags_offset = 0;
 static constexpr dart::compiler::target::word Array_type_arguments_offset = 4;
 static constexpr dart::compiler::target::word Class_declaration_type_offset =
-    48;
+    52;
 static constexpr dart::compiler::target::word Class_num_type_arguments_offset =
     88;
 static constexpr dart::compiler::target::word Class_super_type_offset = 44;
@@ -2713,7 +2713,7 @@
 static constexpr dart::compiler::target::word Array_tags_offset = 0;
 static constexpr dart::compiler::target::word Array_type_arguments_offset = 8;
 static constexpr dart::compiler::target::word Class_declaration_type_offset =
-    96;
+    104;
 static constexpr dart::compiler::target::word Class_num_type_arguments_offset =
     164;
 static constexpr dart::compiler::target::word Class_super_type_offset = 88;
@@ -3236,7 +3236,7 @@
 static constexpr dart::compiler::target::word Array_tags_offset = 0;
 static constexpr dart::compiler::target::word Array_type_arguments_offset = 4;
 static constexpr dart::compiler::target::word Class_declaration_type_offset =
-    48;
+    52;
 static constexpr dart::compiler::target::word Class_num_type_arguments_offset =
     88;
 static constexpr dart::compiler::target::word Class_super_type_offset = 44;
@@ -3752,7 +3752,7 @@
 static constexpr dart::compiler::target::word Array_tags_offset = 0;
 static constexpr dart::compiler::target::word Array_type_arguments_offset = 8;
 static constexpr dart::compiler::target::word Class_declaration_type_offset =
-    96;
+    104;
 static constexpr dart::compiler::target::word Class_num_type_arguments_offset =
     164;
 static constexpr dart::compiler::target::word Class_super_type_offset = 88;
@@ -4280,7 +4280,7 @@
 static constexpr dart::compiler::target::word AOT_Array_type_arguments_offset =
     4;
 static constexpr dart::compiler::target::word
-    AOT_Class_declaration_type_offset = 48;
+    AOT_Class_declaration_type_offset = 52;
 static constexpr dart::compiler::target::word
     AOT_Class_num_type_arguments_offset = 88;
 static constexpr dart::compiler::target::word AOT_Class_super_type_offset = 44;
@@ -4864,7 +4864,7 @@
 static constexpr dart::compiler::target::word AOT_Array_type_arguments_offset =
     8;
 static constexpr dart::compiler::target::word
-    AOT_Class_declaration_type_offset = 96;
+    AOT_Class_declaration_type_offset = 104;
 static constexpr dart::compiler::target::word
     AOT_Class_num_type_arguments_offset = 164;
 static constexpr dart::compiler::target::word AOT_Class_super_type_offset = 88;
@@ -5454,7 +5454,7 @@
 static constexpr dart::compiler::target::word AOT_Array_type_arguments_offset =
     8;
 static constexpr dart::compiler::target::word
-    AOT_Class_declaration_type_offset = 96;
+    AOT_Class_declaration_type_offset = 104;
 static constexpr dart::compiler::target::word
     AOT_Class_num_type_arguments_offset = 164;
 static constexpr dart::compiler::target::word AOT_Class_super_type_offset = 88;
@@ -6043,7 +6043,7 @@
 static constexpr dart::compiler::target::word AOT_Array_type_arguments_offset =
     4;
 static constexpr dart::compiler::target::word
-    AOT_Class_declaration_type_offset = 48;
+    AOT_Class_declaration_type_offset = 52;
 static constexpr dart::compiler::target::word
     AOT_Class_num_type_arguments_offset = 88;
 static constexpr dart::compiler::target::word AOT_Class_super_type_offset = 44;
@@ -6620,7 +6620,7 @@
 static constexpr dart::compiler::target::word AOT_Array_type_arguments_offset =
     8;
 static constexpr dart::compiler::target::word
-    AOT_Class_declaration_type_offset = 96;
+    AOT_Class_declaration_type_offset = 104;
 static constexpr dart::compiler::target::word
     AOT_Class_num_type_arguments_offset = 164;
 static constexpr dart::compiler::target::word AOT_Class_super_type_offset = 88;
@@ -7203,7 +7203,7 @@
 static constexpr dart::compiler::target::word AOT_Array_type_arguments_offset =
     8;
 static constexpr dart::compiler::target::word
-    AOT_Class_declaration_type_offset = 96;
+    AOT_Class_declaration_type_offset = 104;
 static constexpr dart::compiler::target::word
     AOT_Class_num_type_arguments_offset = 164;
 static constexpr dart::compiler::target::word AOT_Class_super_type_offset = 88;
diff --git a/runtime/vm/compiler/type_testing_stubs_arm.cc b/runtime/vm/compiler/type_testing_stubs_arm.cc
index ccd9d36..ed1ace2 100644
--- a/runtime/vm/compiler/type_testing_stubs_arm.cc
+++ b/runtime/vm/compiler/type_testing_stubs_arm.cc
@@ -20,8 +20,16 @@
     const Type& type,
     const Class& type_class) {
   BuildOptimizedTypeTestStubFastCases(assembler, hi, type, type_class);
-  __ Branch(compiler::Address(
-      THR, compiler::target::Thread::slow_type_test_entry_point_offset()));
+  if (!compiler::IsSameObject(
+          compiler::NullObject(),
+          compiler::CastHandle<Object>(slow_type_test_stub))) {
+    __ GenerateUnRelocatedPcRelativeTailCall();
+    unresolved_calls->Add(new compiler::UnresolvedPcRelativeCall(
+        __ CodeSize(), slow_type_test_stub, /*is_tail_call=*/true));
+  } else {
+    __ Branch(compiler::Address(
+        THR, compiler::target::Thread::slow_type_test_entry_point_offset()));
+  }
 }
 
 }  // namespace dart
diff --git a/runtime/vm/compiler/type_testing_stubs_arm64.cc b/runtime/vm/compiler/type_testing_stubs_arm64.cc
index 850b198..0540b01 100644
--- a/runtime/vm/compiler/type_testing_stubs_arm64.cc
+++ b/runtime/vm/compiler/type_testing_stubs_arm64.cc
@@ -20,11 +20,19 @@
     const Type& type,
     const Class& type_class) {
   BuildOptimizedTypeTestStubFastCases(assembler, hi, type, type_class);
-  __ ldr(
-      TMP,
-      compiler::Address(
-          THR, compiler::target::Thread::slow_type_test_entry_point_offset()));
-  __ br(TMP);
+  if (!compiler::IsSameObject(
+          compiler::NullObject(),
+          compiler::CastHandle<Object>(slow_type_test_stub))) {
+    __ GenerateUnRelocatedPcRelativeTailCall();
+    unresolved_calls->Add(new compiler::UnresolvedPcRelativeCall(
+        __ CodeSize(), slow_type_test_stub, /*is_tail_call=*/true));
+  } else {
+    __ ldr(TMP,
+           compiler::Address(
+               THR,
+               compiler::target::Thread::slow_type_test_entry_point_offset()));
+    __ br(TMP);
+  }
 }
 
 }  // namespace dart
diff --git a/runtime/vm/compiler/type_testing_stubs_x64.cc b/runtime/vm/compiler/type_testing_stubs_x64.cc
index 7722cee..f7a974c 100644
--- a/runtime/vm/compiler/type_testing_stubs_x64.cc
+++ b/runtime/vm/compiler/type_testing_stubs_x64.cc
@@ -20,8 +20,16 @@
     const Type& type,
     const Class& type_class) {
   BuildOptimizedTypeTestStubFastCases(assembler, hi, type, type_class);
-  __ jmp(compiler::Address(
-      THR, compiler::target::Thread::slow_type_test_entry_point_offset()));
+  if (!compiler::IsSameObject(
+          compiler::NullObject(),
+          compiler::CastHandle<Object>(slow_type_test_stub))) {
+    __ GenerateUnRelocatedPcRelativeTailCall();
+    unresolved_calls->Add(new compiler::UnresolvedPcRelativeCall(
+        __ CodeSize(), slow_type_test_stub, /*is_tail_call=*/true));
+  } else {
+    __ jmp(compiler::Address(
+        THR, compiler::target::Thread::slow_type_test_entry_point_offset()));
+  }
 }
 
 }  // namespace dart
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index fae18df..d98aa2d 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -20212,11 +20212,9 @@
       }
     }
     ASSERT(this->Equals(type));
-    // TODO(rmacnak): Revisit immediately returning type after to changes to
-    // recanonicalization on load for literal splitting.
-    if (type.IsCanonical()) {
-      return type.ptr();
-    }
+    ASSERT(type.IsCanonical());
+    ASSERT(type.IsOld());
+    return type.ptr();
   }
 
   Type& type = Type::Handle(zone);
diff --git a/runtime/vm/program_visitor.cc b/runtime/vm/program_visitor.cc
index b8e3de1..9082979 100644
--- a/runtime/vm/program_visitor.cc
+++ b/runtime/vm/program_visitor.cc
@@ -1371,15 +1371,9 @@
     MergeAssignment(obj_, id);
     obj_ = code.compressed_stackmaps();
     MergeAssignment(obj_, id);
-    if (!FLAG_use_bare_instructions) {
-      obj_ = code.object_pool();
-      MergeAssignment(obj_, id);
-    }
   }
 
   void MergeAssignment(const Object& obj, intptr_t id) {
-    if (obj.IsNull()) return;
-
     intptr_t old_id = heap_->GetLoadingUnit(obj_.ptr());
     if (old_id == WeakTable::kNoValue) {
       heap_->SetLoadingUnit(obj_.ptr(), id);
diff --git a/runtime/vm/raw_object.h b/runtime/vm/raw_object.h
index 8a02e59..d209ad2 100644
--- a/runtime/vm/raw_object.h
+++ b/runtime/vm/raw_object.h
@@ -28,8 +28,8 @@
 //  * Target architecture
 //  * DART_PRECOMPILED_RUNTIME (i.e, AOT vs. JIT)
 //
-// That is, fields in UntaggedObject and its subclasses should only be included or
-// excluded conditionally based on these factors. Otherwise, the generated
+// That is, fields in UntaggedObject and its subclasses should only be included
+// or excluded conditionally based on these factors. Otherwise, the generated
 // offsets can be wrong (which should be caught by offset checking in dart.cc).
 //
 // TODO(dartbug.com/43646): Add DART_PRECOMPILER as another axis.
@@ -819,6 +819,8 @@
   POINTER_FIELD(LibraryPtr, library)
   POINTER_FIELD(TypeArgumentsPtr, type_parameters)  // Array of TypeParameter.
   POINTER_FIELD(AbstractTypePtr, super_type)
+  POINTER_FIELD(ArrayPtr,
+                constants)  // Canonicalized const instances of this class.
   POINTER_FIELD(TypePtr, declaration_type)  // Declaration type for this class.
   POINTER_FIELD(ArrayPtr,
                 invocation_dispatcher_cache)  // Cache for dispatcher functions.
@@ -828,9 +830,7 @@
                 direct_implementors)                        // Array of Class.
   POINTER_FIELD(GrowableObjectArrayPtr, direct_subclasses)  // Array of Class.
   POINTER_FIELD(ArrayPtr, dependent_code)  // CHA optimized codes.
-  POINTER_FIELD(ArrayPtr,
-                constants)  // Canonicalized const instances of this class.
-  VISIT_TO(ObjectPtr, constants)
+  VISIT_TO(ObjectPtr, dependent_code)
   ObjectPtr* to_snapshot(Snapshot::Kind kind) {
     switch (kind) {
       case Snapshot::kFullAOT:
@@ -1642,8 +1642,6 @@
 
   friend class Object;
   friend class CodeSerializationCluster;
-  friend class UnitSerializationRoots;
-  friend class UnitDeserializationRoots;
 };
 
 class UntaggedInstructions : public UntaggedObject {
diff --git a/tests/ffi/structs_test.dart b/tests/ffi/structs_test.dart
index 6bc1ed1..a38c241 100644
--- a/tests/ffi/structs_test.dart
+++ b/tests/ffi/structs_test.dart
@@ -24,6 +24,7 @@
     testBareStruct();
     testTypeTest();
     testUtf8();
+    testDotDotRef();
   }
 }
 
@@ -135,3 +136,10 @@
   Expect.equals(test, Utf8.fromUtf8(medium));
   calloc.free(medium);
 }
+
+void testDotDotRef() {
+  final pointer = calloc<Coordinate>()
+    ..ref.x = 1
+    ..ref.y = 1;
+  calloc.free(pointer);
+}
diff --git a/tests/ffi_2/structs_test.dart b/tests/ffi_2/structs_test.dart
index 2759056..57bdbc6 100644
--- a/tests/ffi_2/structs_test.dart
+++ b/tests/ffi_2/structs_test.dart
@@ -24,6 +24,7 @@
     testBareStruct();
     testTypeTest();
     testUtf8();
+    testDotDotRef();
   }
 }
 
@@ -135,3 +136,10 @@
   Expect.equals(test, Utf8.fromUtf8(medium));
   calloc.free(medium);
 }
+
+void testDotDotRef() {
+  final pointer = calloc<Coordinate>()
+    ..ref.x = 1
+    ..ref.y = 1;
+  calloc.free(pointer);
+}
diff --git a/tests/language/async/explicit_await_test.dart b/tests/language/async/explicit_await_test.dart
deleted file mode 100644
index 545e5c5..0000000
--- a/tests/language/async/explicit_await_test.dart
+++ /dev/null
@@ -1,48 +0,0 @@
-// Copyright (c) 2021, 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.
-
-import 'package:expect/expect.dart';
-
-bool caughtInMethod1 = false;
-bool caughtInMethod2 = false;
-bool caughtInMain = false;
-
-Future<Object> f() {
-  return new Future<Future<Object>>.value(new Future<Object>.delayed(
-      const Duration(seconds: 1), () => throw 'foo'));
-}
-
-Future<Object> method1() async {
-  try {
-    return await f();
-  } catch (e) {
-    print('caught in method1: $e');
-    caughtInMethod1 = true;
-  }
-  return new Object();
-}
-
-Future<Object> method2() async {
-  try {
-    return method1();
-  } catch (e) {
-    print('caught in method2: $e');
-    caughtInMethod2 = true;
-  }
-  return new Object();
-}
-
-void main() async {
-  try {
-    print(await method2());
-    print('Done');
-  } catch (e) {
-    print('caught in main: $e');
-    caughtInMain = true;
-  }
-  Expect.isTrue(caughtInMethod1, "Exception should be caught in 'method1'.");
-  Expect.isFalse(
-      caughtInMethod2, "Exception should not be caught in 'method2'.");
-  Expect.isFalse(caughtInMain, "Exception should not be caught in 'main'.");
-}
diff --git a/tests/language/async/implicit_await_test.dart b/tests/language/async/implicit_await_test.dart
deleted file mode 100644
index 9c79259..0000000
--- a/tests/language/async/implicit_await_test.dart
+++ /dev/null
@@ -1,36 +0,0 @@
-// Copyright (c) 2021, 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.
-
-import 'package:expect/expect.dart';
-
-bool caughtInF = false;
-bool caughtInMain = false;
-
-class A {}
-
-class AAndFutureOfA implements A, Future<A> {
-  noSuchMethod(Invocation i) => throw 0;
-}
-
-Future<A> f(A a) async {
-  try {
-    // Statically looks like no `await` is needed, but dynamically it is needed.
-    // So we should check dynamically whether to await.
-    return a;
-  } catch (e) {
-    caughtInF = true;
-  }
-  return new A();
-}
-
-void main() async {
-  try {
-    print(await f(AAndFutureOfA()));
-    print('Done');
-  } catch (e) {
-    caughtInMain = true;
-  }
-  Expect.isTrue(caughtInF, "Exception should be caught in 'f'.");
-  Expect.isFalse(caughtInMain, "Exception should not be caught in 'main'.");
-}
diff --git a/tools/VERSION b/tools/VERSION
index 9270cb0..5e91b59 100644
--- a/tools/VERSION
+++ b/tools/VERSION
@@ -28,4 +28,4 @@
 MINOR 12
 PATCH 0
 PRERELEASE 259
-PRERELEASE_PATCH 1
\ No newline at end of file
+PRERELEASE_PATCH 8
\ No newline at end of file