[cfe] Change late lowering to handle unsound null values

Change-Id: I91d3f0ee4350816ee4e80713b4d975085f8b3915
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/163345
Reviewed-by: Dmitry Stefantsov <dmitryas@google.com>
Commit-Queue: Johnni Winther <johnniwinther@google.com>

pkg/front_end/lib/src/fasta/builder/field_builder.dart

@@ -10,6 +10,8 @@ import 'package:kernel/ast.dart' hide MapEntry;
 import 'package:kernel/core_types.dart';
 import 'package:kernel/src/legacy_erasure.dart';
 
+import '../../base/nnbd_mode.dart';
+
 import '../constant_context.dart' show ConstantContext;
 
 import '../fasta_codes.dart' show messageInternalProblemAlreadyInitialized;
@@ -122,6 +124,9 @@ class SourceFieldBuilder extends MemberBuilderImpl implements FieldBuilder {
       Procedure setterReferenceFrom)
       : super(libraryBuilder, charOffset) {
     Uri fileUri = libraryBuilder?.fileUri;
+    // If in mixed mode, late lowerings cannot use `null` as a sentinel on
+    // non-nullable fields since they can be assigned from legacy code.
+    bool forceUseIsSetField = libraryBuilder.loader.nnbdMode != NnbdMode.Strong;
     if (isAbstract || isExternal) {
       _fieldEncoding = new AbstractOrExternalFieldEncoding(fileUri, charOffset,
           charEndOffset, getterReferenceFrom, setterReferenceFrom,
@@ -143,7 +148,8 @@ class SourceFieldBuilder extends MemberBuilderImpl implements FieldBuilder {
               lateIsSetReferenceFrom,
               getterReferenceFrom,
               setterReferenceFrom,
-              isCovariant);
+              isCovariant,
+              forceUseIsSetField);
         } else {
           _fieldEncoding = new LateFieldWithInitializerEncoding(
               name,
@@ -154,7 +160,8 @@ class SourceFieldBuilder extends MemberBuilderImpl implements FieldBuilder {
               lateIsSetReferenceFrom,
               getterReferenceFrom,
               setterReferenceFrom,
-              isCovariant);
+              isCovariant,
+              forceUseIsSetField);
         }
       } else {
         if (isFinal) {
@@ -167,7 +174,8 @@ class SourceFieldBuilder extends MemberBuilderImpl implements FieldBuilder {
               lateIsSetReferenceFrom,
               getterReferenceFrom,
               setterReferenceFrom,
-              isCovariant);
+              isCovariant,
+              forceUseIsSetField);
         } else {
           _fieldEncoding = new LateFieldWithoutInitializerEncoding(
               name,
@@ -178,7 +186,8 @@ class SourceFieldBuilder extends MemberBuilderImpl implements FieldBuilder {
               lateIsSetReferenceFrom,
               getterReferenceFrom,
               setterReferenceFrom,
-              isCovariant);
+              isCovariant,
+              forceUseIsSetField);
         }
       }
     } else if (libraryBuilder.isNonNullableByDefault &&
@@ -196,7 +205,8 @@ class SourceFieldBuilder extends MemberBuilderImpl implements FieldBuilder {
             lateIsSetReferenceFrom,
             getterReferenceFrom,
             setterReferenceFrom,
-            isCovariant);
+            isCovariant,
+            forceUseIsSetField);
       } else {
         _fieldEncoding = new LateFieldWithInitializerEncoding(
             name,
@@ -207,7 +217,8 @@ class SourceFieldBuilder extends MemberBuilderImpl implements FieldBuilder {
             lateIsSetReferenceFrom,
             getterReferenceFrom,
             setterReferenceFrom,
-            isCovariant);
+            isCovariant,
+            forceUseIsSetField);
       }
     } else {
       assert(lateIsSetReferenceFrom == null);
@@ -714,11 +725,21 @@ abstract class AbstractLateFieldEncoding implements FieldEncoding {
   Procedure _lateGetter;
   Procedure _lateSetter;
 
+  // If `true`, an isSet field is used even when the type of the field is
+  // not potentially nullable.
+  //
+  // This is used to force use isSet fields in mixed mode encoding since
+  // we cannot trust non-nullable fields to be initialized with non-null values.
+  bool _forceUseIsSetField;
+
   // If `true`, the is-set field was register before the type was known to be
   // nullable or non-nullable. In this case we do not try to remove it from
   // the generated AST to avoid inconsistency between the class hierarchy used
   // during and after inference.
-  bool _forceIncludeIsSetField = false;
+  //
+  // This is also used to force use isSet fields in mixed mode encoding since
+  // we cannot trust non-nullable fields to be initialized with non-null values.
+  bool _forceIncludeIsSetField;
 
   AbstractLateFieldEncoding(
       this.name,
@@ -729,8 +750,11 @@ abstract class AbstractLateFieldEncoding implements FieldEncoding {
       Field lateIsSetReferenceFrom,
       Procedure getterReferenceFrom,
       Procedure setterReferenceFrom,
-      bool isCovariant)
-      : fileOffset = charOffset {
+      bool isCovariant,
+      bool forceUseIsSetField)
+      : fileOffset = charOffset,
+        _forceUseIsSetField = forceUseIsSetField,
+        _forceIncludeIsSetField = forceUseIsSetField {
     _field =
         new Field(null, fileUri: fileUri, reference: referenceFrom?.reference)
           ..fileOffset = charOffset
@@ -1048,7 +1072,8 @@ mixin NonFinalLate on AbstractLateFieldEncoding {
         createVariableWrite: (Expression value) =>
             _createFieldSet(_field, value),
         createIsSetWrite: (Expression value) =>
-            _createFieldSet(_lateIsSetField, value));
+            _createFieldSet(_lateIsSetField, value),
+        useIsSetField: _forceUseIsSetField || type.isPotentiallyNullable);
   }
 }
 
@@ -1060,7 +1085,8 @@ mixin LateWithoutInitializer on AbstractLateFieldEncoding {
     return late_lowering.createGetterBodyWithoutInitializer(
         coreTypes, fileOffset, name, type, 'Field',
         createVariableRead: _createFieldRead,
-        createIsSetRead: () => _createFieldGet(_lateIsSetField));
+        createIsSetRead: () => _createFieldGet(_lateIsSetField),
+        useIsSetField: _forceUseIsSetField || type.isPotentiallyNullable);
   }
 }
 
@@ -1075,7 +1101,8 @@ class LateFieldWithoutInitializerEncoding extends AbstractLateFieldEncoding
       Field lateIsSetReferenceFrom,
       Procedure getterReferenceFrom,
       Procedure setterReferenceFrom,
-      bool isCovariant)
+      bool isCovariant,
+      bool forceUseIsSetField)
       : super(
             name,
             fileUri,
@@ -1085,7 +1112,8 @@ class LateFieldWithoutInitializerEncoding extends AbstractLateFieldEncoding
             lateIsSetReferenceFrom,
             getterReferenceFrom,
             setterReferenceFrom,
-            isCovariant);
+            isCovariant,
+            forceUseIsSetField);
 }
 
 class LateFieldWithInitializerEncoding extends AbstractLateFieldEncoding
@@ -1099,7 +1127,8 @@ class LateFieldWithInitializerEncoding extends AbstractLateFieldEncoding
       Field lateIsSetReferenceFrom,
       Procedure getterReferenceFrom,
       Procedure setterReferenceFrom,
-      bool isCovariant)
+      bool isCovariant,
+      bool forceUseIsSetField)
       : super(
             name,
             fileUri,
@@ -1109,7 +1138,8 @@ class LateFieldWithInitializerEncoding extends AbstractLateFieldEncoding
             lateIsSetReferenceFrom,
             getterReferenceFrom,
             setterReferenceFrom,
-            isCovariant);
+            isCovariant,
+            forceUseIsSetField);
 
   @override
   Statement _createGetterBody(
@@ -1122,7 +1152,8 @@ class LateFieldWithInitializerEncoding extends AbstractLateFieldEncoding
             _createFieldSet(_field, value),
         createIsSetRead: () => _createFieldGet(_lateIsSetField),
         createIsSetWrite: (Expression value) =>
-            _createFieldSet(_lateIsSetField, value));
+            _createFieldSet(_lateIsSetField, value),
+        useIsSetField: _forceUseIsSetField || type.isPotentiallyNullable);
   }
 }
 
@@ -1137,7 +1168,8 @@ class LateFinalFieldWithoutInitializerEncoding extends AbstractLateFieldEncoding
       Field lateIsSetReferenceFrom,
       Procedure getterReferenceFrom,
       Procedure setterReferenceFrom,
-      bool isCovariant)
+      bool isCovariant,
+      bool forceUseIsSetField)
       : super(
             name,
             fileUri,
@@ -1147,7 +1179,8 @@ class LateFinalFieldWithoutInitializerEncoding extends AbstractLateFieldEncoding
             lateIsSetReferenceFrom,
             getterReferenceFrom,
             setterReferenceFrom,
-            isCovariant);
+            isCovariant,
+            forceUseIsSetField);
 
   @override
   Statement _createSetterBody(
@@ -1161,7 +1194,8 @@ class LateFinalFieldWithoutInitializerEncoding extends AbstractLateFieldEncoding
             _createFieldSet(_field, value),
         createIsSetRead: () => _createFieldGet(_lateIsSetField),
         createIsSetWrite: (Expression value) =>
-            _createFieldSet(_lateIsSetField, value));
+            _createFieldSet(_lateIsSetField, value),
+        useIsSetField: _forceUseIsSetField || type.isPotentiallyNullable);
   }
 }
 
@@ -1175,7 +1209,8 @@ class LateFinalFieldWithInitializerEncoding extends AbstractLateFieldEncoding {
       Field lateIsSetReferenceFrom,
       Procedure getterReferenceFrom,
       Procedure setterReferenceFrom,
-      bool isCovariant)
+      bool isCovariant,
+      bool forceUseIsSetField)
       : super(
             name,
             fileUri,
@@ -1185,7 +1220,8 @@ class LateFinalFieldWithInitializerEncoding extends AbstractLateFieldEncoding {
             lateIsSetReferenceFrom,
             getterReferenceFrom,
             setterReferenceFrom,
-            isCovariant);
+            isCovariant,
+            forceUseIsSetField);
   @override
   Statement _createGetterBody(
       CoreTypes coreTypes, String name, Expression initializer) {

pkg/front_end/lib/src/fasta/kernel/inference_visitor.dart

@@ -15,6 +15,7 @@ import '../../base/instrumentation.dart'
         InstrumentationValueForMember,
         InstrumentationValueForType,
         InstrumentationValueForTypeArgs;
+import '../../base/nnbd_mode.dart';
 import '../fasta_codes.dart';
 import '../names.dart';
 import '../problems.dart' show unhandled;
@@ -5634,7 +5635,11 @@ class InferenceVisitor
       result.add(node);
 
       VariableDeclaration isSetVariable;
-      if (node.type.isPotentiallyNullable) {
+      if (node.type.isPotentiallyNullable ||
+          // We cannot trust that non-nullable locals are not initialized to
+          // `null` in mixed mode, so we use an `isSet` variable here.
+          (inferrer.isNonNullableByDefault &&
+              inferrer.nnbdMode != NnbdMode.Strong)) {
         isSetVariable = new VariableDeclaration(
             '${late_lowering.lateLocalPrefix}'
             '${node.name}'
@@ -5676,7 +5681,8 @@ class InferenceVisitor
                       node.type,
                       'Local',
                       createVariableRead: createVariableRead,
-                      createIsSetRead: createIsSetRead)
+                      createIsSetRead: createIsSetRead,
+                      useIsSetField: isSetVariable != null)
                   : late_lowering.createGetterWithInitializer(
                       inferrer.coreTypes,
                       fileOffset,
@@ -5686,7 +5692,8 @@ class InferenceVisitor
                       createVariableRead: createVariableRead,
                       createVariableWrite: createVariableWrite,
                       createIsSetRead: createIsSetRead,
-                      createIsSetWrite: createIsSetWrite),
+                      createIsSetWrite: createIsSetWrite,
+                      useIsSetField: isSetVariable != null),
               returnType: node.type))
         ..fileOffset = fileOffset;
       getVariable.type =
@@ -5720,12 +5727,14 @@ class InferenceVisitor
                             createVariableRead: createVariableRead,
                             createVariableWrite: createVariableWrite,
                             createIsSetRead: createIsSetRead,
-                            createIsSetWrite: createIsSetWrite)
+                            createIsSetWrite: createIsSetWrite,
+                            useIsSetField: isSetVariable != null)
                         : late_lowering.createSetterBody(inferrer.coreTypes,
                             fileOffset, node.name, setterParameter, node.type,
                             shouldReturnValue: true,
                             createVariableWrite: createVariableWrite,
-                            createIsSetWrite: createIsSetWrite)
+                            createIsSetWrite: createIsSetWrite,
+                            useIsSetField: isSetVariable != null)
                       ..fileOffset = fileOffset,
                     positionalParameters: <VariableDeclaration>[
                       setterParameter

pkg/front_end/lib/src/fasta/kernel/late_lowering.dart

@@ -26,8 +26,10 @@ Statement createGetterWithInitializer(CoreTypes coreTypes, int fileOffset,
     {Expression createVariableRead({bool needsPromotion}),
     Expression createVariableWrite(Expression value),
     Expression createIsSetRead(),
-    Expression createIsSetWrite(Expression value)}) {
-  if (type.isPotentiallyNullable) {
+    Expression createIsSetWrite(Expression value),
+    bool useIsSetField}) {
+  assert(useIsSetField != null);
+  if (useIsSetField) {
     // Generate:
     //
     //    if (!_#isSet#field) {
@@ -213,7 +215,9 @@ Statement createGetterWithInitializerWithRecheck(
 Statement createGetterBodyWithoutInitializer(CoreTypes coreTypes,
     int fileOffset, String name, DartType type, String variableKindName,
     {Expression createVariableRead({bool needsPromotion}),
-    Expression createIsSetRead()}) {
+    Expression createIsSetRead(),
+    bool useIsSetField}) {
+  assert(useIsSetField != null);
   Expression exception = new Throw(new ConstructorInvocation(
       coreTypes.lateInitializationErrorConstructor,
       new Arguments(<Expression>[
@@ -224,7 +228,7 @@ Statement createGetterBodyWithoutInitializer(CoreTypes coreTypes,
         ..fileOffset = fileOffset)
     ..fileOffset = fileOffset)
     ..fileOffset = fileOffset;
-  if (type.isPotentiallyNullable) {
+  if (useIsSetField) {
     // Generate:
     //
     //    return _#isSet#field ? _#field : throw '...';
@@ -272,7 +276,9 @@ Statement createSetterBody(CoreTypes coreTypes, int fileOffset, String name,
     VariableDeclaration parameter, DartType type,
     {bool shouldReturnValue,
     Expression createVariableWrite(Expression value),
-    Expression createIsSetWrite(Expression value)}) {
+    Expression createIsSetWrite(Expression value),
+    bool useIsSetField}) {
+  assert(useIsSetField != null);
   Statement createReturn(Expression value) {
     if (shouldReturnValue) {
       return new ReturnStatement(value)..fileOffset = fileOffset;
@@ -285,7 +291,7 @@ Statement createSetterBody(CoreTypes coreTypes, int fileOffset, String name,
       createVariableWrite(new VariableGet(parameter)..fileOffset = fileOffset)
         ..fileOffset = fileOffset);
 
-  if (type.isPotentiallyNullable) {
+  if (useIsSetField) {
     // Generate:
     //
     //    _#isSet#field = true;
@@ -321,7 +327,9 @@ Statement createSetterBodyFinal(
     Expression createVariableRead(),
     Expression createVariableWrite(Expression value),
     Expression createIsSetRead(),
-    Expression createIsSetWrite(Expression value)}) {
+    Expression createIsSetWrite(Expression value),
+    bool useIsSetField}) {
+  assert(useIsSetField != null);
   Expression exception = new Throw(new ConstructorInvocation(
       coreTypes.lateInitializationErrorConstructor,
       new Arguments(<Expression>[
@@ -341,7 +349,7 @@ Statement createSetterBodyFinal(
     }
   }
 
-  if (type.isPotentiallyNullable) {
+  if (useIsSetField) {
     // Generate:
     //
     //    if (_#isSet#field) {

pkg/front_end/test/predicates/data/late.dart

@@ -5,10 +5,12 @@
 /*member: _#topLevelNonNullableWithoutInitializer:lateField*/
 /*member: topLevelNonNullableWithoutInitializer:lateFieldGetter*/
 /*member: topLevelNonNullableWithoutInitializer=:lateFieldSetter*/
+/*member: _#topLevelNonNullableWithoutInitializer#isSet:lateIsSetField*/
 late int topLevelNonNullableWithoutInitializer;
 /*member: _#finalTopLevelNonNullableWithoutInitializer:lateField*/
 /*member: finalTopLevelNonNullableWithoutInitializer:lateFieldGetter*/
 /*member: finalTopLevelNonNullableWithoutInitializer=:lateFieldSetter*/
+/*member: _#finalTopLevelNonNullableWithoutInitializer#isSet:lateIsSetField*/
 late final int finalTopLevelNonNullableWithoutInitializer;
 /*member: _#topLevelNullableWithoutInitializer:lateField*/
 /*member: _#topLevelNullableWithoutInitializer#isSet:lateIsSetField*/
@@ -23,9 +25,11 @@ late final int? finalTopLevelNullableWithoutInitializer;
 /*member: _#topLevelNonNullableWithInitializer:lateField*/
 /*member: topLevelNonNullableWithInitializer:lateFieldGetter*/
 /*member: topLevelNonNullableWithInitializer=:lateFieldSetter*/
+/*member: _#topLevelNonNullableWithInitializer#isSet:lateIsSetField*/
 late int topLevelNonNullableWithInitializer = 0;
 /*member: _#finalTopLevelNonNullableWithInitializer:lateField*/
 /*member: finalTopLevelNonNullableWithInitializer:lateFieldGetter*/
+/*member: _#finalTopLevelNonNullableWithInitializer#isSet:lateIsSetField*/
 late final int finalTopLevelNonNullableWithInitializer = 0;
 /*member: _#topLevelNullableWithInitializer:lateField*/
 /*member: _#topLevelNullableWithInitializer#isSet:lateIsSetField*/
@@ -38,10 +42,12 @@ late int? topLevelNullableWithInitializer = 0;
 late final int? finalTopLevelNullableWithInitializer = 0;
 
 class Class {
+  /*member: Class._#Class#instanceNonNullableWithoutInitializer#isSet:lateIsSetField*/
   /*member: Class._#Class#instanceNonNullableWithoutInitializer:lateField*/
   /*member: Class.instanceNonNullableWithoutInitializer:lateFieldGetter*/
   /*member: Class.instanceNonNullableWithoutInitializer=:lateFieldSetter*/
   late int instanceNonNullableWithoutInitializer;
+  /*member: Class._#Class#finalInstanceNonNullableWithoutInitializer#isSet:lateIsSetField*/
   /*member: Class._#Class#finalInstanceNonNullableWithoutInitializer:lateField*/
   /*member: Class.finalInstanceNonNullableWithoutInitializer:lateFieldGetter*/
   /*member: Class.finalInstanceNonNullableWithoutInitializer=:lateFieldSetter*/
@@ -56,10 +62,12 @@ class Class {
   /*member: Class.finalInstanceNullableWithoutInitializer:lateFieldGetter*/
   /*member: Class.finalInstanceNullableWithoutInitializer=:lateFieldSetter*/
   late final int? finalInstanceNullableWithoutInitializer;
+  /*member: Class._#Class#instanceNonNullableWithInitializer#isSet:lateIsSetField*/
   /*member: Class._#Class#instanceNonNullableWithInitializer:lateField*/
   /*member: Class.instanceNonNullableWithInitializer:lateFieldGetter*/
   /*member: Class.instanceNonNullableWithInitializer=:lateFieldSetter*/
   late int instanceNonNullableWithInitializer = 0;
+  /*member: Class._#Class#finalInstanceNonNullableWithInitializer#isSet:lateIsSetField*/
   /*member: Class._#Class#finalInstanceNonNullableWithInitializer:lateField*/
   /*member: Class.finalInstanceNonNullableWithInitializer:lateFieldGetter*/
   late final int finalInstanceNonNullableWithInitializer = 0;
@@ -73,10 +81,12 @@ class Class {
   /*member: Class.finalInstanceNullableWithInitializer:lateFieldGetter*/
   late final int? finalInstanceNullableWithInitializer = 0;
 
+  /*member: Class._#staticNonNullableWithoutInitializer#isSet:lateIsSetField*/
   /*member: Class._#staticNonNullableWithoutInitializer:lateField*/
   /*member: Class.staticNonNullableWithoutInitializer:lateFieldGetter*/
   /*member: Class.staticNonNullableWithoutInitializer=:lateFieldSetter*/
   static late int staticNonNullableWithoutInitializer;
+  /*member: Class._#finalStaticNonNullableWithoutInitializer#isSet:lateIsSetField*/
   /*member: Class._#finalStaticNonNullableWithoutInitializer:lateField*/
   /*member: Class.finalStaticNonNullableWithoutInitializer:lateFieldGetter*/
   /*member: Class.finalStaticNonNullableWithoutInitializer=:lateFieldSetter*/
@@ -91,10 +101,12 @@ class Class {
   /*member: Class.finalStaticNullableWithoutInitializer:lateFieldGetter*/
   /*member: Class.finalStaticNullableWithoutInitializer=:lateFieldSetter*/
   static late final int? finalStaticNullableWithoutInitializer;
+  /*member: Class._#staticNonNullableWithInitializer#isSet:lateIsSetField*/
   /*member: Class._#staticNonNullableWithInitializer:lateField*/
   /*member: Class.staticNonNullableWithInitializer:lateFieldGetter*/
   /*member: Class.staticNonNullableWithInitializer=:lateFieldSetter*/
   static late int staticNonNullableWithInitializer = 0;
+  /*member: Class._#finalStaticNonNullableWithInitializer#isSet:lateIsSetField*/
   /*member: Class._#finalStaticNonNullableWithInitializer:lateField*/
   /*member: Class.finalStaticNonNullableWithInitializer:lateFieldGetter*/
   static late final int finalStaticNonNullableWithInitializer = 0;

pkg/front_end/testcases/late_lowering/compound.dart.weak.expect

@@ -12,33 +12,47 @@ import "dart:_internal" as _in;
 
 static method main() → dynamic {
   core::int? local1;
+  core::bool #local1#isSet = false;
   function #local1#get() → core::int
-    return let final core::int? #t1 = local1 in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local1' has not been initialized.") : #t1{core::int};
-  function #local1#set(core::int #t2) → dynamic
-    return local1 = #t2;
+    return #local1#isSet ?{core::int} local1{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local1' has not been initialized.");
+  function #local1#set(core::int #t1) → dynamic {
+    #local1#isSet = true;
+    return local1 = #t1;
+  }
   #local1#set.call(0);
   self::expect(0, #local1#get.call());
   #local1#set.call(#local1#get.call().{core::num::+}(2));
   self::expect(2, #local1#get.call());
   core::int? local2;
-  function #local2#get() → core::int
-    return let final core::int? #t3 = local2 in #t3.==(null) ?{core::int} local2 = 1 : #t3{core::int};
-  function #local2#set(core::int #t4) → dynamic
-    return local2 = #t4;
+  core::bool #local2#isSet = false;
+  function #local2#get() → core::int {
+    if(!#local2#isSet) {
+      local2 = 1;
+      #local2#isSet = true;
+    }
+    return local2{core::int};
+  }
+  function #local2#set(core::int #t2) → dynamic {
+    #local2#isSet = true;
+    return local2 = #t2;
+  }
   self::expect(1, #local2#get.call());
   #local2#set.call(#local2#get.call().{core::num::+}(2));
   self::expect(3, #local2#get.call());
 }
 static method error() → dynamic {
   final core::int? local;
+  core::bool #local#isSet = false;
   function #local#get() → core::int
-    return let final core::int? #t5 = local in #t5.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local' has not been initialized.") : #t5{core::int};
-  function #local#set(core::int #t6) → dynamic
-    if(local.==(null))
-      return local = #t6;
-    else
+    return #local#isSet ?{core::int} local{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local' has not been initialized.");
+  function #local#set(core::int #t3) → dynamic
+    if(#local#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local' has already been initialized.");
-  #local#set.call((let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/late_lowering/compound.dart:20:3: Error: Non-nullable late variable 'local' without initializer is definitely unassigned.
+    else {
+      #local#isSet = true;
+      return local = #t3;
+    }
+  #local#set.call((let final<BottomType> #t4 = invalid-expression "pkg/front_end/testcases/late_lowering/compound.dart:20:3: Error: Non-nullable late variable 'local' without initializer is definitely unassigned.
   local += 0;
   ^^^^^" in #local#get.call()).{core::num::+}(0));
 }

pkg/front_end/testcases/late_lowering/compound.dart.weak.transformed.expect

@@ -12,33 +12,47 @@ import "dart:_internal" as _in;
 
 static method main() → dynamic {
   core::int? local1;
+  core::bool #local1#isSet = false;
   function #local1#get() → core::int
-    return let final core::int? #t1 = local1 in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local1' has not been initialized.") : #t1{core::int};
-  function #local1#set(core::int #t2) → dynamic
-    return local1 = #t2;
+    return #local1#isSet ?{core::int} local1{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local1' has not been initialized.");
+  function #local1#set(core::int #t1) → dynamic {
+    #local1#isSet = true;
+    return local1 = #t1;
+  }
   #local1#set.call(0);
   self::expect(0, #local1#get.call());
   #local1#set.call(#local1#get.call().{core::num::+}(2));
   self::expect(2, #local1#get.call());
   core::int? local2;
-  function #local2#get() → core::int
-    return let final core::int? #t3 = local2 in #t3.==(null) ?{core::int} local2 = 1 : #t3{core::int};
-  function #local2#set(core::int #t4) → dynamic
-    return local2 = #t4;
+  core::bool #local2#isSet = false;
+  function #local2#get() → core::int {
+    if(!#local2#isSet) {
+      local2 = 1;
+      #local2#isSet = true;
+    }
+    return local2{core::int};
+  }
+  function #local2#set(core::int #t2) → dynamic {
+    #local2#isSet = true;
+    return local2 = #t2;
+  }
   self::expect(1, #local2#get.call());
   #local2#set.call(#local2#get.call().{core::num::+}(2));
   self::expect(3, #local2#get.call());
 }
 static method error() → dynamic {
   final core::int? local;
+  core::bool #local#isSet = false;
   function #local#get() → core::int
-    return let final core::int? #t5 = local in #t5.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local' has not been initialized.") : #t5{core::int};
-  function #local#set(core::int #t6) → dynamic
-    if(local.==(null))
-      return local = #t6;
-    else
+    return #local#isSet ?{core::int} local{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local' has not been initialized.");
+  function #local#set(core::int #t3) → dynamic
+    if(#local#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local' has already been initialized.");
-  #local#set.call((let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/late_lowering/compound.dart:20:3: Error: Non-nullable late variable 'local' without initializer is definitely unassigned.
+    else {
+      #local#isSet = true;
+      return local = #t3;
+    }
+  #local#set.call((let final<BottomType> #t4 = invalid-expression "pkg/front_end/testcases/late_lowering/compound.dart:20:3: Error: Non-nullable late variable 'local' without initializer is definitely unassigned.
   local += 0;
   ^^^^^" in #local#get.call()).{core::num::+}(0));
 }

pkg/front_end/testcases/late_lowering/covariant_late_field.dart.weak.expect

@@ -16,18 +16,24 @@ import "dart:_internal" as _in;
 
 class A extends core::Object {
   field core::num? _#A#invariantField = null;
+  field core::bool _#A#invariantField#isSet = false;
   field core::num? _#A#covariantField = null;
+  field core::bool _#A#covariantField#isSet = false;
   synthetic constructor •() → self::A
     : super core::Object::•()
     ;
   get invariantField() → core::num
-    return let final core::num? #t1 = this.{self::A::_#A#invariantField} in #t1.==(null) ?{core::num} throw new _in::LateInitializationErrorImpl::•("Field 'invariantField' has not been initialized.") : #t1{core::num};
-  set invariantField(core::num #t2) → void
+    return this.{self::A::_#A#invariantField#isSet} ?{core::num} let final core::num? #t1 = this.{self::A::_#A#invariantField} in #t1{core::num} : throw new _in::LateInitializationErrorImpl::•("Field 'invariantField' has not been initialized.");
+  set invariantField(core::num #t2) → void {
+    this.{self::A::_#A#invariantField#isSet} = true;
     this.{self::A::_#A#invariantField} = #t2;
+  }
   get covariantField() → core::num
-    return let final core::num? #t3 = this.{self::A::_#A#covariantField} in #t3.==(null) ?{core::num} throw new _in::LateInitializationErrorImpl::•("Field 'covariantField' has not been initialized.") : #t3{core::num};
-  set covariantField(covariant core::num #t4) → void
+    return this.{self::A::_#A#covariantField#isSet} ?{core::num} let final core::num? #t3 = this.{self::A::_#A#covariantField} in #t3{core::num} : throw new _in::LateInitializationErrorImpl::•("Field 'covariantField' has not been initialized.");
+  set covariantField(covariant core::num #t4) → void {
+    this.{self::A::_#A#covariantField#isSet} = true;
     this.{self::A::_#A#covariantField} = #t4;
+  }
 }
 abstract class B extends core::Object implements self::A {
   synthetic constructor •() → self::B

pkg/front_end/testcases/late_lowering/definitely_assigned.dart.weak.expect

@@ -77,31 +77,37 @@ static field <T extends core::Object? = dynamic>(T%) → core::Null? fieldDirect
       return local2 = #t1;
     }
   final core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t2 = local4 in #t2.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t2{core::int};
-  function #local4#set(core::int #t3) → dynamic
-    if(local4.==(null))
-      return local4 = #t3;
-    else
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t2) → dynamic
+    if(#local4#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local4' has already been initialized.");
+    else {
+      #local4#isSet = true;
+      return local4 = #t2;
+    }
   final FutureOr<core::int>? local6;
+  core::bool #local6#isSet = false;
   function #local6#get() → FutureOr<core::int>
-    return let final FutureOr<core::int>? #t4 = local6 in #t4.==(null) ?{FutureOr<core::int>} throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.") : #t4{FutureOr<core::int>};
-  function #local6#set(FutureOr<core::int>#t5) → dynamic
-    if(local6.==(null))
-      return local6 = #t5;
-    else
+    return #local6#isSet ?{FutureOr<core::int>} local6{FutureOr<core::int>} : throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.");
+  function #local6#set(FutureOr<core::int>#t3) → dynamic
+    if(#local6#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local6' has already been initialized.");
+    else {
+      #local6#isSet = true;
+      return local6 = #t3;
+    }
   #local2#set.call(value);
   #local4#set.call(0);
   #local6#set.call(0);
-  let final<BottomType> #t6 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:30:3: Error: Non-nullable late final variable 'local2' definitely assigned.
+  let final<BottomType> #t4 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:30:3: Error: Non-nullable late final variable 'local2' definitely assigned.
   local2 = value; // error
   ^^^^^^" in #local2#set.call(value);
-  let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:31:3: Error: Non-nullable late final variable 'local4' definitely assigned.
+  let final<BottomType> #t5 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:31:3: Error: Non-nullable late final variable 'local4' definitely assigned.
   local4 = 0; // error
   ^^^^^^" in #local4#set.call(0);
-  let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:32:3: Error: Non-nullable late final variable 'local6' definitely assigned.
+  let final<BottomType> #t6 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:32:3: Error: Non-nullable late final variable 'local6' definitely assigned.
   local6 = 0; // error
   ^^^^^^" in #local6#set.call(0);
 };
@@ -110,29 +116,35 @@ static field <T extends core::Object? = dynamic>(core::bool, T%) → core::Null?
   core::bool #local2#isSet = false;
   function #local2#get() → T%
     return #local2#isSet ?{T%} local2{T%} : throw new _in::LateInitializationErrorImpl::•("Local 'local2' has not been initialized.");
-  function #local2#set(T% #t9) → dynamic
+  function #local2#set(T% #t7) → dynamic
     if(#local2#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local2' has already been initialized.");
     else {
       #local2#isSet = true;
-      return local2 = #t9;
+      return local2 = #t7;
     }
   final core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t10 = local4 in #t10.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t10{core::int};
-  function #local4#set(core::int #t11) → dynamic
-    if(local4.==(null))
-      return local4 = #t11;
-    else
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t8) → dynamic
+    if(#local4#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local4' has already been initialized.");
+    else {
+      #local4#isSet = true;
+      return local4 = #t8;
+    }
   final FutureOr<core::int>? local6;
+  core::bool #local6#isSet = false;
   function #local6#get() → FutureOr<core::int>
-    return let final FutureOr<core::int>? #t12 = local6 in #t12.==(null) ?{FutureOr<core::int>} throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.") : #t12{FutureOr<core::int>};
-  function #local6#set(FutureOr<core::int>#t13) → dynamic
-    if(local6.==(null))
-      return local6 = #t13;
-    else
+    return #local6#isSet ?{FutureOr<core::int>} local6{FutureOr<core::int>} : throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.");
+  function #local6#set(FutureOr<core::int>#t9) → dynamic
+    if(#local6#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local6' has already been initialized.");
+    else {
+      #local6#isSet = true;
+      return local6 = #t9;
+    }
   if(b) {
     #local2#set.call(value);
     #local4#set.call(0);
@@ -141,27 +153,30 @@ static field <T extends core::Object? = dynamic>(core::bool, T%) → core::Null?
   #local2#set.call(value);
   #local4#set.call(0);
   #local6#set.call(0);
-  let final<BottomType> #t14 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:70:3: Error: Non-nullable late final variable 'local2' definitely assigned.
+  let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:70:3: Error: Non-nullable late final variable 'local2' definitely assigned.
   local2 = value; // error
   ^^^^^^" in #local2#set.call(value);
-  let final<BottomType> #t15 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:71:3: Error: Non-nullable late final variable 'local4' definitely assigned.
+  let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:71:3: Error: Non-nullable late final variable 'local4' definitely assigned.
   local4 = 0; // error
   ^^^^^^" in #local4#set.call(0);
-  let final<BottomType> #t16 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:72:3: Error: Non-nullable late final variable 'local6' definitely assigned.
+  let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:72:3: Error: Non-nullable late final variable 'local6' definitely assigned.
   local6 = 0; // error
   ^^^^^^" in #local6#set.call(0);
 };
 static field () → core::Null? fieldCompound = () → core::Null? {
   final core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t17 = local4 in #t17.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t17{core::int};
-  function #local4#set(core::int #t18) → dynamic
-    if(local4.==(null))
-      return local4 = #t18;
-    else
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t13) → dynamic
+    if(#local4#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local4' has already been initialized.");
+    else {
+      #local4#isSet = true;
+      return local4 = #t13;
+    }
   #local4#set.call(0);
-  let final<BottomType> #t19 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:88:3: Error: Non-nullable late final variable 'local4' definitely assigned.
+  let final<BottomType> #t14 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:88:3: Error: Non-nullable late final variable 'local4' definitely assigned.
   local4 += 0; // error
   ^^^^^^" in #local4#set.call(#local4#get.call().{core::num::+}(0));
 };
@@ -170,39 +185,45 @@ static method methodDirect<T extends core::Object? = dynamic>(self::methodDirect
   core::bool #local2#isSet = false;
   function #local2#get() → self::methodDirect::T%
     return #local2#isSet ?{self::methodDirect::T%} local2{self::methodDirect::T%} : throw new _in::LateInitializationErrorImpl::•("Local 'local2' has not been initialized.");
-  function #local2#set(self::methodDirect::T% #t20) → dynamic
+  function #local2#set(self::methodDirect::T% #t15) → dynamic
     if(#local2#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local2' has already been initialized.");
     else {
       #local2#isSet = true;
-      return local2 = #t20;
+      return local2 = #t15;
     }
   final core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t21 = local4 in #t21.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t21{core::int};
-  function #local4#set(core::int #t22) → dynamic
-    if(local4.==(null))
-      return local4 = #t22;
-    else
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t16) → dynamic
+    if(#local4#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local4' has already been initialized.");
+    else {
+      #local4#isSet = true;
+      return local4 = #t16;
+    }
   final FutureOr<core::int>? local6;
+  core::bool #local6#isSet = false;
   function #local6#get() → FutureOr<core::int>
-    return let final FutureOr<core::int>? #t23 = local6 in #t23.==(null) ?{FutureOr<core::int>} throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.") : #t23{FutureOr<core::int>};
-  function #local6#set(FutureOr<core::int>#t24) → dynamic
-    if(local6.==(null))
-      return local6 = #t24;
-    else
+    return #local6#isSet ?{FutureOr<core::int>} local6{FutureOr<core::int>} : throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.");
+  function #local6#set(FutureOr<core::int>#t17) → dynamic
+    if(#local6#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local6' has already been initialized.");
+    else {
+      #local6#isSet = true;
+      return local6 = #t17;
+    }
   #local2#set.call(value);
   #local4#set.call(0);
   #local6#set.call(0);
-  let final<BottomType> #t25 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:16:3: Error: Non-nullable late final variable 'local2' definitely assigned.
+  let final<BottomType> #t18 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:16:3: Error: Non-nullable late final variable 'local2' definitely assigned.
   local2 = value; // error
   ^^^^^^" in #local2#set.call(value);
-  let final<BottomType> #t26 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:17:3: Error: Non-nullable late final variable 'local4' definitely assigned.
+  let final<BottomType> #t19 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:17:3: Error: Non-nullable late final variable 'local4' definitely assigned.
   local4 = 0; // error
   ^^^^^^" in #local4#set.call(0);
-  let final<BottomType> #t27 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:18:3: Error: Non-nullable late final variable 'local6' definitely assigned.
+  let final<BottomType> #t20 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:18:3: Error: Non-nullable late final variable 'local6' definitely assigned.
   local6 = 0; // error
   ^^^^^^" in #local6#set.call(0);
 }
@@ -211,29 +232,35 @@ static method methodConditional<T extends core::Object? = dynamic>(core::bool b,
   core::bool #local2#isSet = false;
   function #local2#get() → self::methodConditional::T%
     return #local2#isSet ?{self::methodConditional::T%} local2{self::methodConditional::T%} : throw new _in::LateInitializationErrorImpl::•("Local 'local2' has not been initialized.");
-  function #local2#set(self::methodConditional::T% #t28) → dynamic
+  function #local2#set(self::methodConditional::T% #t21) → dynamic
     if(#local2#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local2' has already been initialized.");
     else {
       #local2#isSet = true;
-      return local2 = #t28;
+      return local2 = #t21;
     }
   final core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t29 = local4 in #t29.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t29{core::int};
-  function #local4#set(core::int #t30) → dynamic
-    if(local4.==(null))
-      return local4 = #t30;
-    else
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t22) → dynamic
+    if(#local4#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local4' has already been initialized.");
+    else {
+      #local4#isSet = true;
+      return local4 = #t22;
+    }
   final FutureOr<core::int>? local6;
+  core::bool #local6#isSet = false;
   function #local6#get() → FutureOr<core::int>
-    return let final FutureOr<core::int>? #t31 = local6 in #t31.==(null) ?{FutureOr<core::int>} throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.") : #t31{FutureOr<core::int>};
-  function #local6#set(FutureOr<core::int>#t32) → dynamic
-    if(local6.==(null))
-      return local6 = #t32;
-    else
+    return #local6#isSet ?{FutureOr<core::int>} local6{FutureOr<core::int>} : throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.");
+  function #local6#set(FutureOr<core::int>#t23) → dynamic
+    if(#local6#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local6' has already been initialized.");
+    else {
+      #local6#isSet = true;
+      return local6 = #t23;
+    }
   if(b) {
     #local2#set.call(value);
     #local4#set.call(0);
@@ -242,27 +269,30 @@ static method methodConditional<T extends core::Object? = dynamic>(core::bool b,
   #local2#set.call(value);
   #local4#set.call(0);
   #local6#set.call(0);
-  let final<BottomType> #t33 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:50:3: Error: Non-nullable late final variable 'local2' definitely assigned.
+  let final<BottomType> #t24 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:50:3: Error: Non-nullable late final variable 'local2' definitely assigned.
   local2 = value; // error
   ^^^^^^" in #local2#set.call(value);
-  let final<BottomType> #t34 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:51:3: Error: Non-nullable late final variable 'local4' definitely assigned.
+  let final<BottomType> #t25 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:51:3: Error: Non-nullable late final variable 'local4' definitely assigned.
   local4 = 0; // error
   ^^^^^^" in #local4#set.call(0);
-  let final<BottomType> #t35 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:52:3: Error: Non-nullable late final variable 'local6' definitely assigned.
+  let final<BottomType> #t26 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:52:3: Error: Non-nullable late final variable 'local6' definitely assigned.
   local6 = 0; // error
   ^^^^^^" in #local6#set.call(0);
 }
 static method methodCompound() → dynamic {
   final core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t36 = local4 in #t36.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t36{core::int};
-  function #local4#set(core::int #t37) → dynamic
-    if(local4.==(null))
-      return local4 = #t37;
-    else
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t27) → dynamic
+    if(#local4#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local4' has already been initialized.");
+    else {
+      #local4#isSet = true;
+      return local4 = #t27;
+    }
   #local4#set.call(0);
-  let final<BottomType> #t38 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:80:3: Error: Non-nullable late final variable 'local4' definitely assigned.
+  let final<BottomType> #t28 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:80:3: Error: Non-nullable late final variable 'local4' definitely assigned.
   local4 += 0; // error
   ^^^^^^" in #local4#set.call(#local4#get.call().{core::num::+}(0));
 }

pkg/front_end/testcases/late_lowering/definitely_assigned.dart.weak.transformed.expect

@@ -77,31 +77,37 @@ static field <T extends core::Object? = dynamic>(T%) → core::Null? fieldDirect
       return local2 = #t1;
     }
   final core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t2 = local4 in #t2.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t2{core::int};
-  function #local4#set(core::int #t3) → dynamic
-    if(local4.==(null))
-      return local4 = #t3;
-    else
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t2) → dynamic
+    if(#local4#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local4' has already been initialized.");
+    else {
+      #local4#isSet = true;
+      return local4 = #t2;
+    }
   final FutureOr<core::int>? local6;
+  core::bool #local6#isSet = false;
   function #local6#get() → FutureOr<core::int>
-    return let final FutureOr<core::int>? #t4 = local6 in #t4.==(null) ?{FutureOr<core::int>} throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.") : #t4{FutureOr<core::int>};
-  function #local6#set(FutureOr<core::int>#t5) → dynamic
-    if(local6.==(null))
-      return local6 = #t5;
-    else
+    return #local6#isSet ?{FutureOr<core::int>} local6{FutureOr<core::int>} : throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.");
+  function #local6#set(FutureOr<core::int>#t3) → dynamic
+    if(#local6#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local6' has already been initialized.");
+    else {
+      #local6#isSet = true;
+      return local6 = #t3;
+    }
   #local2#set.call(value);
   #local4#set.call(0);
   #local6#set.call(0);
-  let final<BottomType> #t6 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:30:3: Error: Non-nullable late final variable 'local2' definitely assigned.
+  let final<BottomType> #t4 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:30:3: Error: Non-nullable late final variable 'local2' definitely assigned.
   local2 = value; // error
   ^^^^^^" in #local2#set.call(value);
-  let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:31:3: Error: Non-nullable late final variable 'local4' definitely assigned.
+  let final<BottomType> #t5 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:31:3: Error: Non-nullable late final variable 'local4' definitely assigned.
   local4 = 0; // error
   ^^^^^^" in #local4#set.call(0);
-  let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:32:3: Error: Non-nullable late final variable 'local6' definitely assigned.
+  let final<BottomType> #t6 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:32:3: Error: Non-nullable late final variable 'local6' definitely assigned.
   local6 = 0; // error
   ^^^^^^" in #local6#set.call(0);
 };
@@ -110,29 +116,35 @@ static field <T extends core::Object? = dynamic>(core::bool, T%) → core::Null?
   core::bool #local2#isSet = false;
   function #local2#get() → T%
     return #local2#isSet ?{T%} local2{T%} : throw new _in::LateInitializationErrorImpl::•("Local 'local2' has not been initialized.");
-  function #local2#set(T% #t9) → dynamic
+  function #local2#set(T% #t7) → dynamic
     if(#local2#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local2' has already been initialized.");
     else {
       #local2#isSet = true;
-      return local2 = #t9;
+      return local2 = #t7;
     }
   final core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t10 = local4 in #t10.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t10{core::int};
-  function #local4#set(core::int #t11) → dynamic
-    if(local4.==(null))
-      return local4 = #t11;
-    else
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t8) → dynamic
+    if(#local4#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local4' has already been initialized.");
+    else {
+      #local4#isSet = true;
+      return local4 = #t8;
+    }
   final FutureOr<core::int>? local6;
+  core::bool #local6#isSet = false;
   function #local6#get() → FutureOr<core::int>
-    return let final FutureOr<core::int>? #t12 = local6 in #t12.==(null) ?{FutureOr<core::int>} throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.") : #t12{FutureOr<core::int>};
-  function #local6#set(FutureOr<core::int>#t13) → dynamic
-    if(local6.==(null))
-      return local6 = #t13;
-    else
+    return #local6#isSet ?{FutureOr<core::int>} local6{FutureOr<core::int>} : throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.");
+  function #local6#set(FutureOr<core::int>#t9) → dynamic
+    if(#local6#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local6' has already been initialized.");
+    else {
+      #local6#isSet = true;
+      return local6 = #t9;
+    }
   if(b) {
     #local2#set.call(value);
     #local4#set.call(0);
@@ -141,27 +153,30 @@ static field <T extends core::Object? = dynamic>(core::bool, T%) → core::Null?
   #local2#set.call(value);
   #local4#set.call(0);
   #local6#set.call(0);
-  let final<BottomType> #t14 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:70:3: Error: Non-nullable late final variable 'local2' definitely assigned.
+  let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:70:3: Error: Non-nullable late final variable 'local2' definitely assigned.
   local2 = value; // error
   ^^^^^^" in #local2#set.call(value);
-  let final<BottomType> #t15 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:71:3: Error: Non-nullable late final variable 'local4' definitely assigned.
+  let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:71:3: Error: Non-nullable late final variable 'local4' definitely assigned.
   local4 = 0; // error
   ^^^^^^" in #local4#set.call(0);
-  let final<BottomType> #t16 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:72:3: Error: Non-nullable late final variable 'local6' definitely assigned.
+  let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:72:3: Error: Non-nullable late final variable 'local6' definitely assigned.
   local6 = 0; // error
   ^^^^^^" in #local6#set.call(0);
 };
 static field () → core::Null? fieldCompound = () → core::Null? {
   final core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t17 = local4 in #t17.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t17{core::int};
-  function #local4#set(core::int #t18) → dynamic
-    if(local4.==(null))
-      return local4 = #t18;
-    else
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t13) → dynamic
+    if(#local4#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local4' has already been initialized.");
+    else {
+      #local4#isSet = true;
+      return local4 = #t13;
+    }
   #local4#set.call(0);
-  let final<BottomType> #t19 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:88:3: Error: Non-nullable late final variable 'local4' definitely assigned.
+  let final<BottomType> #t14 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:88:3: Error: Non-nullable late final variable 'local4' definitely assigned.
   local4 += 0; // error
   ^^^^^^" in #local4#set.call(#local4#get.call().{core::num::+}(0));
 };
@@ -170,39 +185,45 @@ static method methodDirect<T extends core::Object? = dynamic>(self::methodDirect
   core::bool #local2#isSet = false;
   function #local2#get() → self::methodDirect::T%
     return #local2#isSet ?{self::methodDirect::T%} local2{self::methodDirect::T%} : throw new _in::LateInitializationErrorImpl::•("Local 'local2' has not been initialized.");
-  function #local2#set(self::methodDirect::T% #t20) → dynamic
+  function #local2#set(self::methodDirect::T% #t15) → dynamic
     if(#local2#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local2' has already been initialized.");
     else {
       #local2#isSet = true;
-      return local2 = #t20;
+      return local2 = #t15;
     }
   final core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t21 = local4 in #t21.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t21{core::int};
-  function #local4#set(core::int #t22) → dynamic
-    if(local4.==(null))
-      return local4 = #t22;
-    else
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t16) → dynamic
+    if(#local4#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local4' has already been initialized.");
+    else {
+      #local4#isSet = true;
+      return local4 = #t16;
+    }
   final FutureOr<core::int>? local6;
+  core::bool #local6#isSet = false;
   function #local6#get() → FutureOr<core::int>
-    return let final FutureOr<core::int>? #t23 = local6 in #t23.==(null) ?{FutureOr<core::int>} throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.") : #t23{FutureOr<core::int>};
-  function #local6#set(FutureOr<core::int>#t24) → dynamic
-    if(local6.==(null))
-      return local6 = #t24;
-    else
+    return #local6#isSet ?{FutureOr<core::int>} local6{FutureOr<core::int>} : throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.");
+  function #local6#set(FutureOr<core::int>#t17) → dynamic
+    if(#local6#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local6' has already been initialized.");
+    else {
+      #local6#isSet = true;
+      return local6 = #t17;
+    }
   #local2#set.call(value);
   #local4#set.call(0);
   #local6#set.call(0);
-  let final<BottomType> #t25 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:16:3: Error: Non-nullable late final variable 'local2' definitely assigned.
+  let final<BottomType> #t18 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:16:3: Error: Non-nullable late final variable 'local2' definitely assigned.
   local2 = value; // error
   ^^^^^^" in #local2#set.call(value);
-  let final<BottomType> #t26 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:17:3: Error: Non-nullable late final variable 'local4' definitely assigned.
+  let final<BottomType> #t19 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:17:3: Error: Non-nullable late final variable 'local4' definitely assigned.
   local4 = 0; // error
   ^^^^^^" in #local4#set.call(0);
-  let final<BottomType> #t27 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:18:3: Error: Non-nullable late final variable 'local6' definitely assigned.
+  let final<BottomType> #t20 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:18:3: Error: Non-nullable late final variable 'local6' definitely assigned.
   local6 = 0; // error
   ^^^^^^" in #local6#set.call(0);
 }
@@ -211,29 +232,35 @@ static method methodConditional<T extends core::Object? = dynamic>(core::bool b,
   core::bool #local2#isSet = false;
   function #local2#get() → self::methodConditional::T%
     return #local2#isSet ?{self::methodConditional::T%} local2{self::methodConditional::T%} : throw new _in::LateInitializationErrorImpl::•("Local 'local2' has not been initialized.");
-  function #local2#set(self::methodConditional::T% #t28) → dynamic
+  function #local2#set(self::methodConditional::T% #t21) → dynamic
     if(#local2#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local2' has already been initialized.");
     else {
       #local2#isSet = true;
-      return local2 = #t28;
+      return local2 = #t21;
     }
   final core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t29 = local4 in #t29.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t29{core::int};
-  function #local4#set(core::int #t30) → dynamic
-    if(local4.==(null))
-      return local4 = #t30;
-    else
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t22) → dynamic
+    if(#local4#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local4' has already been initialized.");
+    else {
+      #local4#isSet = true;
+      return local4 = #t22;
+    }
   final FutureOr<core::int>? local6;
+  core::bool #local6#isSet = false;
   function #local6#get() → FutureOr<core::int>
-    return let final FutureOr<core::int>? #t31 = local6 in #t31.==(null) ?{FutureOr<core::int>} throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.") : #t31{FutureOr<core::int>};
-  function #local6#set(FutureOr<core::int>#t32) → dynamic
-    if(local6.==(null))
-      return local6 = #t32;
-    else
+    return #local6#isSet ?{FutureOr<core::int>} local6{FutureOr<core::int>} : throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.");
+  function #local6#set(FutureOr<core::int>#t23) → dynamic
+    if(#local6#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local6' has already been initialized.");
+    else {
+      #local6#isSet = true;
+      return local6 = #t23;
+    }
   if(b) {
     #local2#set.call(value);
     #local4#set.call(0);
@@ -242,27 +269,30 @@ static method methodConditional<T extends core::Object? = dynamic>(core::bool b,
   #local2#set.call(value);
   #local4#set.call(0);
   #local6#set.call(0);
-  let final<BottomType> #t33 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:50:3: Error: Non-nullable late final variable 'local2' definitely assigned.
+  let final<BottomType> #t24 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:50:3: Error: Non-nullable late final variable 'local2' definitely assigned.
   local2 = value; // error
   ^^^^^^" in #local2#set.call(value);
-  let final<BottomType> #t34 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:51:3: Error: Non-nullable late final variable 'local4' definitely assigned.
+  let final<BottomType> #t25 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:51:3: Error: Non-nullable late final variable 'local4' definitely assigned.
   local4 = 0; // error
   ^^^^^^" in #local4#set.call(0);
-  let final<BottomType> #t35 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:52:3: Error: Non-nullable late final variable 'local6' definitely assigned.
+  let final<BottomType> #t26 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:52:3: Error: Non-nullable late final variable 'local6' definitely assigned.
   local6 = 0; // error
   ^^^^^^" in #local6#set.call(0);
 }
 static method methodCompound() → dynamic {
   final core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t36 = local4 in #t36.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t36{core::int};
-  function #local4#set(core::int #t37) → dynamic
-    if(local4.==(null))
-      return local4 = #t37;
-    else
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t27) → dynamic
+    if(#local4#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'local4' has already been initialized.");
+    else {
+      #local4#isSet = true;
+      return local4 = #t27;
+    }
   #local4#set.call(0);
-  let final<BottomType> #t38 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:80:3: Error: Non-nullable late final variable 'local4' definitely assigned.
+  let final<BottomType> #t28 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_assigned.dart:80:3: Error: Non-nullable late final variable 'local4' definitely assigned.
   local4 += 0; // error
   ^^^^^^" in #local4#set.call(#local4#get.call().{core::num::+}(0));
 }

pkg/front_end/testcases/late_lowering/definitely_unassigned.dart.weak.expect

@@ -108,16 +108,22 @@ static field <T extends core::Object? = dynamic>(T%) → core::Null? fieldDirect
   }
   core::int local3;
   core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t2 = local4 in #t2.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t2{core::int};
-  function #local4#set(core::int #t3) → dynamic
-    return local4 = #t3;
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t2) → dynamic {
+    #local4#isSet = true;
+    return local4 = #t2;
+  }
   FutureOr<core::int>local5;
   FutureOr<core::int>? local6;
+  core::bool #local6#isSet = false;
   function #local6#get() → FutureOr<core::int>
-    return let final FutureOr<core::int>? #t4 = local6 in #t4.==(null) ?{FutureOr<core::int>} throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.") : #t4{FutureOr<core::int>};
-  function #local6#set(FutureOr<core::int>#t5) → dynamic
-    return local6 = #t5;
+    return #local6#isSet ?{FutureOr<core::int>} local6{FutureOr<core::int>} : throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.");
+  function #local6#set(FutureOr<core::int>#t3) → dynamic {
+    #local6#isSet = true;
+    return local6 = #t3;
+  }
   T? local7;
   core::bool #local7#isSet = false;
   function #local7#get() → T% {
@@ -127,26 +133,26 @@ static field <T extends core::Object? = dynamic>(T%) → core::Null? fieldDirect
     }
     return local7{T%};
   }
-  function #local7#set(T% #t6) → dynamic {
+  function #local7#set(T% #t4) → dynamic {
     #local7#isSet = true;
-    return local7 = #t6;
+    return local7 = #t4;
   }
-  let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:34:3: Error: Non-nullable variable 'local1' must be assigned before it can be used.
+  let final<BottomType> #t5 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:34:3: Error: Non-nullable variable 'local1' must be assigned before it can be used.
   local1; // error
   ^^^^^^" in local1;
-  let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:35:3: Error: Non-nullable late variable 'local2' without initializer is definitely unassigned.
+  let final<BottomType> #t6 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:35:3: Error: Non-nullable late variable 'local2' without initializer is definitely unassigned.
   local2; // error
   ^^^^^^" in #local2#get.call();
-  let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:36:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
+  let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:36:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
   local3; // error
   ^^^^^^" in local3;
-  let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:37:3: Error: Non-nullable late variable 'local4' without initializer is definitely unassigned.
+  let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:37:3: Error: Non-nullable late variable 'local4' without initializer is definitely unassigned.
   local4; // error
   ^^^^^^" in #local4#get.call();
-  let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:38:3: Error: Non-nullable variable 'local5' must be assigned before it can be used.
+  let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:38:3: Error: Non-nullable variable 'local5' must be assigned before it can be used.
   local5; // error
   ^^^^^^" in local5;
-  let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:39:3: Error: Non-nullable late variable 'local6' without initializer is definitely unassigned.
+  let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:39:3: Error: Non-nullable late variable 'local6' without initializer is definitely unassigned.
   local6; // error
   ^^^^^^" in #local6#get.call();
   #local7#get.call();
@@ -157,22 +163,28 @@ static field <T extends core::Object? = dynamic>(core::bool, T%) → core::Null?
   core::bool #local2#isSet = false;
   function #local2#get() → T%
     return #local2#isSet ?{T%} local2{T%} : throw new _in::LateInitializationErrorImpl::•("Local 'local2' has not been initialized.");
-  function #local2#set(T% #t13) → dynamic {
+  function #local2#set(T% #t11) → dynamic {
     #local2#isSet = true;
-    return local2 = #t13;
+    return local2 = #t11;
   }
   core::int local3;
   core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t14 = local4 in #t14.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t14{core::int};
-  function #local4#set(core::int #t15) → dynamic
-    return local4 = #t15;
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t12) → dynamic {
+    #local4#isSet = true;
+    return local4 = #t12;
+  }
   FutureOr<core::int>local5;
   FutureOr<core::int>? local6;
+  core::bool #local6#isSet = false;
   function #local6#get() → FutureOr<core::int>
-    return let final FutureOr<core::int>? #t16 = local6 in #t16.==(null) ?{FutureOr<core::int>} throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.") : #t16{FutureOr<core::int>};
-  function #local6#set(FutureOr<core::int>#t17) → dynamic
-    return local6 = #t17;
+    return #local6#isSet ?{FutureOr<core::int>} local6{FutureOr<core::int>} : throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.");
+  function #local6#set(FutureOr<core::int>#t13) → dynamic {
+    #local6#isSet = true;
+    return local6 = #t13;
+  }
   T? local7;
   core::bool #local7#isSet = false;
   function #local7#get() → T% {
@@ -182,9 +194,9 @@ static field <T extends core::Object? = dynamic>(core::bool, T%) → core::Null?
     }
     return local7{T%};
   }
-  function #local7#set(T% #t18) → dynamic {
+  function #local7#set(T% #t14) → dynamic {
     #local7#isSet = true;
-    return local7 = #t18;
+    return local7 = #t14;
   }
   if(b) {
     local1 = value;
@@ -195,15 +207,15 @@ static field <T extends core::Object? = dynamic>(core::bool, T%) → core::Null?
     #local6#set.call(0);
     #local7#get.call();
   }
-  let final<BottomType> #t19 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:90:3: Error: Non-nullable variable 'local1' must be assigned before it can be used.
+  let final<BottomType> #t15 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:90:3: Error: Non-nullable variable 'local1' must be assigned before it can be used.
   local1; // error
   ^^^^^^" in local1;
   #local2#get.call();
-  let final<BottomType> #t20 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:92:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
+  let final<BottomType> #t16 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:92:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
   local3; // error
   ^^^^^^" in local3;
   #local4#get.call();
-  let final<BottomType> #t21 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:94:3: Error: Non-nullable variable 'local5' must be assigned before it can be used.
+  let final<BottomType> #t17 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:94:3: Error: Non-nullable variable 'local5' must be assigned before it can be used.
   local5; // error
   ^^^^^^" in local5;
   #local6#get.call();
@@ -212,14 +224,17 @@ static field <T extends core::Object? = dynamic>(core::bool, T%) → core::Null?
 static field () → core::Null? fieldCompound = () → core::Null? {
   core::int local3;
   core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t22 = local4 in #t22.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t22{core::int};
-  function #local4#set(core::int #t23) → dynamic
-    return local4 = #t23;
-  local3 = (let final<BottomType> #t24 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:111:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t18) → dynamic {
+    #local4#isSet = true;
+    return local4 = #t18;
+  }
+  local3 = (let final<BottomType> #t19 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:111:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
   local3 += 0; // error
   ^^^^^^" in local3).{core::num::+}(0);
-  #local4#set.call((let final<BottomType> #t25 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:112:3: Error: Non-nullable late variable 'local4' without initializer is definitely unassigned.
+  #local4#set.call((let final<BottomType> #t20 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:112:3: Error: Non-nullable late variable 'local4' without initializer is definitely unassigned.
   local4 += 0; // error
   ^^^^^^" in #local4#get.call()).{core::num::+}(0));
 };
@@ -229,22 +244,28 @@ static method methodDirect<T extends core::Object? = dynamic>(self::methodDirect
   core::bool #local2#isSet = false;
   function #local2#get() → self::methodDirect::T%
     return #local2#isSet ?{self::methodDirect::T%} local2{self::methodDirect::T%} : throw new _in::LateInitializationErrorImpl::•("Local 'local2' has not been initialized.");
-  function #local2#set(self::methodDirect::T% #t26) → dynamic {
+  function #local2#set(self::methodDirect::T% #t21) → dynamic {
     #local2#isSet = true;
-    return local2 = #t26;
+    return local2 = #t21;
   }
   core::int local3;
   core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t27 = local4 in #t27.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t27{core::int};
-  function #local4#set(core::int #t28) → dynamic
-    return local4 = #t28;
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t22) → dynamic {
+    #local4#isSet = true;
+    return local4 = #t22;
+  }
   FutureOr<core::int>local5;
   FutureOr<core::int>? local6;
+  core::bool #local6#isSet = false;
   function #local6#get() → FutureOr<core::int>
-    return let final FutureOr<core::int>? #t29 = local6 in #t29.==(null) ?{FutureOr<core::int>} throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.") : #t29{FutureOr<core::int>};
-  function #local6#set(FutureOr<core::int>#t30) → dynamic
-    return local6 = #t30;
+    return #local6#isSet ?{FutureOr<core::int>} local6{FutureOr<core::int>} : throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.");
+  function #local6#set(FutureOr<core::int>#t23) → dynamic {
+    #local6#isSet = true;
+    return local6 = #t23;
+  }
   self::methodDirect::T? local7;
   core::bool #local7#isSet = false;
   function #local7#get() → self::methodDirect::T% {
@@ -254,26 +275,26 @@ static method methodDirect<T extends core::Object? = dynamic>(self::methodDirect
     }
     return local7{self::methodDirect::T%};
   }
-  function #local7#set(self::methodDirect::T% #t31) → dynamic {
+  function #local7#set(self::methodDirect::T% #t24) → dynamic {
     #local7#isSet = true;
-    return local7 = #t31;
+    return local7 = #t24;
   }
-  let final<BottomType> #t32 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:16:3: Error: Non-nullable variable 'local1' must be assigned before it can be used.
+  let final<BottomType> #t25 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:16:3: Error: Non-nullable variable 'local1' must be assigned before it can be used.
   local1; // error
   ^^^^^^" in local1;
-  let final<BottomType> #t33 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:17:3: Error: Non-nullable late variable 'local2' without initializer is definitely unassigned.
+  let final<BottomType> #t26 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:17:3: Error: Non-nullable late variable 'local2' without initializer is definitely unassigned.
   local2; // error
   ^^^^^^" in #local2#get.call();
-  let final<BottomType> #t34 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:18:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
+  let final<BottomType> #t27 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:18:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
   local3; // error
   ^^^^^^" in local3;
-  let final<BottomType> #t35 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:19:3: Error: Non-nullable late variable 'local4' without initializer is definitely unassigned.
+  let final<BottomType> #t28 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:19:3: Error: Non-nullable late variable 'local4' without initializer is definitely unassigned.
   local4; // error
   ^^^^^^" in #local4#get.call();
-  let final<BottomType> #t36 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:20:3: Error: Non-nullable variable 'local5' must be assigned before it can be used.
+  let final<BottomType> #t29 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:20:3: Error: Non-nullable variable 'local5' must be assigned before it can be used.
   local5; // error
   ^^^^^^" in local5;
-  let final<BottomType> #t37 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:21:3: Error: Non-nullable late variable 'local6' without initializer is definitely unassigned.
+  let final<BottomType> #t30 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:21:3: Error: Non-nullable late variable 'local6' without initializer is definitely unassigned.
   local6; // error
   ^^^^^^" in #local6#get.call();
   #local7#get.call();
@@ -284,22 +305,28 @@ static method methodConditional<T extends core::Object? = dynamic>(core::bool b,
   core::bool #local2#isSet = false;
   function #local2#get() → self::methodConditional::T%
     return #local2#isSet ?{self::methodConditional::T%} local2{self::methodConditional::T%} : throw new _in::LateInitializationErrorImpl::•("Local 'local2' has not been initialized.");
-  function #local2#set(self::methodConditional::T% #t38) → dynamic {
+  function #local2#set(self::methodConditional::T% #t31) → dynamic {
     #local2#isSet = true;
-    return local2 = #t38;
+    return local2 = #t31;
   }
   core::int local3;
   core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t39 = local4 in #t39.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t39{core::int};
-  function #local4#set(core::int #t40) → dynamic
-    return local4 = #t40;
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t32) → dynamic {
+    #local4#isSet = true;
+    return local4 = #t32;
+  }
   FutureOr<core::int>local5;
   FutureOr<core::int>? local6;
+  core::bool #local6#isSet = false;
   function #local6#get() → FutureOr<core::int>
-    return let final FutureOr<core::int>? #t41 = local6 in #t41.==(null) ?{FutureOr<core::int>} throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.") : #t41{FutureOr<core::int>};
-  function #local6#set(FutureOr<core::int>#t42) → dynamic
-    return local6 = #t42;
+    return #local6#isSet ?{FutureOr<core::int>} local6{FutureOr<core::int>} : throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.");
+  function #local6#set(FutureOr<core::int>#t33) → dynamic {
+    #local6#isSet = true;
+    return local6 = #t33;
+  }
   self::methodConditional::T? local7;
   core::bool #local7#isSet = false;
   function #local7#get() → self::methodConditional::T% {
@@ -309,9 +336,9 @@ static method methodConditional<T extends core::Object? = dynamic>(core::bool b,
     }
     return local7{self::methodConditional::T%};
   }
-  function #local7#set(self::methodConditional::T% #t43) → dynamic {
+  function #local7#set(self::methodConditional::T% #t34) → dynamic {
     #local7#isSet = true;
-    return local7 = #t43;
+    return local7 = #t34;
   }
   if(b) {
     local1 = value;
@@ -322,15 +349,15 @@ static method methodConditional<T extends core::Object? = dynamic>(core::bool b,
     #local6#set.call(0);
     #local7#set.call(value);
   }
-  let final<BottomType> #t44 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:62:3: Error: Non-nullable variable 'local1' must be assigned before it can be used.
+  let final<BottomType> #t35 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:62:3: Error: Non-nullable variable 'local1' must be assigned before it can be used.
   local1; // error
   ^^^^^^" in local1;
   #local2#get.call();
-  let final<BottomType> #t45 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:64:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
+  let final<BottomType> #t36 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:64:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
   local3; // error
   ^^^^^^" in local3;
   #local4#get.call();
-  let final<BottomType> #t46 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:66:3: Error: Non-nullable variable 'local5' must be assigned before it can be used.
+  let final<BottomType> #t37 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:66:3: Error: Non-nullable variable 'local5' must be assigned before it can be used.
   local5; // error
   ^^^^^^" in local5;
   #local6#get.call();
@@ -339,14 +366,17 @@ static method methodConditional<T extends core::Object? = dynamic>(core::bool b,
 static method methodCompound() → dynamic {
   core::int local3;
   core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t47 = local4 in #t47.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t47{core::int};
-  function #local4#set(core::int #t48) → dynamic
-    return local4 = #t48;
-  local3 = (let final<BottomType> #t49 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:103:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t38) → dynamic {
+    #local4#isSet = true;
+    return local4 = #t38;
+  }
+  local3 = (let final<BottomType> #t39 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:103:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
   local3 += 0; // error
   ^^^^^^" in local3).{core::num::+}(0);
-  #local4#set.call((let final<BottomType> #t50 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:104:3: Error: Non-nullable late variable 'local4' without initializer is definitely unassigned.
+  #local4#set.call((let final<BottomType> #t40 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:104:3: Error: Non-nullable late variable 'local4' without initializer is definitely unassigned.
   local4 += 0; // error
   ^^^^^^" in #local4#get.call()).{core::num::+}(0));
 }

pkg/front_end/testcases/late_lowering/definitely_unassigned.dart.weak.transformed.expect

@@ -108,16 +108,22 @@ static field <T extends core::Object? = dynamic>(T%) → core::Null? fieldDirect
   }
   core::int local3;
   core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t2 = local4 in #t2.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t2{core::int};
-  function #local4#set(core::int #t3) → dynamic
-    return local4 = #t3;
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t2) → dynamic {
+    #local4#isSet = true;
+    return local4 = #t2;
+  }
   FutureOr<core::int>local5;
   FutureOr<core::int>? local6;
+  core::bool #local6#isSet = false;
   function #local6#get() → FutureOr<core::int>
-    return let final FutureOr<core::int>? #t4 = local6 in #t4.==(null) ?{FutureOr<core::int>} throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.") : #t4{FutureOr<core::int>};
-  function #local6#set(FutureOr<core::int>#t5) → dynamic
-    return local6 = #t5;
+    return #local6#isSet ?{FutureOr<core::int>} local6{FutureOr<core::int>} : throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.");
+  function #local6#set(FutureOr<core::int>#t3) → dynamic {
+    #local6#isSet = true;
+    return local6 = #t3;
+  }
   T? local7;
   core::bool #local7#isSet = false;
   function #local7#get() → T% {
@@ -127,26 +133,26 @@ static field <T extends core::Object? = dynamic>(T%) → core::Null? fieldDirect
     }
     return local7{T%};
   }
-  function #local7#set(T% #t6) → dynamic {
+  function #local7#set(T% #t4) → dynamic {
     #local7#isSet = true;
-    return local7 = #t6;
+    return local7 = #t4;
   }
-  let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:34:3: Error: Non-nullable variable 'local1' must be assigned before it can be used.
+  let final<BottomType> #t5 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:34:3: Error: Non-nullable variable 'local1' must be assigned before it can be used.
   local1; // error
   ^^^^^^" in local1;
-  let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:35:3: Error: Non-nullable late variable 'local2' without initializer is definitely unassigned.
+  let final<BottomType> #t6 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:35:3: Error: Non-nullable late variable 'local2' without initializer is definitely unassigned.
   local2; // error
   ^^^^^^" in #local2#get.call();
-  let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:36:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
+  let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:36:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
   local3; // error
   ^^^^^^" in local3;
-  let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:37:3: Error: Non-nullable late variable 'local4' without initializer is definitely unassigned.
+  let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:37:3: Error: Non-nullable late variable 'local4' without initializer is definitely unassigned.
   local4; // error
   ^^^^^^" in #local4#get.call();
-  let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:38:3: Error: Non-nullable variable 'local5' must be assigned before it can be used.
+  let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:38:3: Error: Non-nullable variable 'local5' must be assigned before it can be used.
   local5; // error
   ^^^^^^" in local5;
-  let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:39:3: Error: Non-nullable late variable 'local6' without initializer is definitely unassigned.
+  let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:39:3: Error: Non-nullable late variable 'local6' without initializer is definitely unassigned.
   local6; // error
   ^^^^^^" in #local6#get.call();
   #local7#get.call();
@@ -157,22 +163,28 @@ static field <T extends core::Object? = dynamic>(core::bool, T%) → core::Null?
   core::bool #local2#isSet = false;
   function #local2#get() → T%
     return #local2#isSet ?{T%} local2{T%} : throw new _in::LateInitializationErrorImpl::•("Local 'local2' has not been initialized.");
-  function #local2#set(T% #t13) → dynamic {
+  function #local2#set(T% #t11) → dynamic {
     #local2#isSet = true;
-    return local2 = #t13;
+    return local2 = #t11;
   }
   core::int local3;
   core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t14 = local4 in #t14.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t14{core::int};
-  function #local4#set(core::int #t15) → dynamic
-    return local4 = #t15;
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t12) → dynamic {
+    #local4#isSet = true;
+    return local4 = #t12;
+  }
   FutureOr<core::int>local5;
   FutureOr<core::int>? local6;
+  core::bool #local6#isSet = false;
   function #local6#get() → FutureOr<core::int>
-    return let final FutureOr<core::int>? #t16 = local6 in #t16.==(null) ?{FutureOr<core::int>} throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.") : #t16{FutureOr<core::int>};
-  function #local6#set(FutureOr<core::int>#t17) → dynamic
-    return local6 = #t17;
+    return #local6#isSet ?{FutureOr<core::int>} local6{FutureOr<core::int>} : throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.");
+  function #local6#set(FutureOr<core::int>#t13) → dynamic {
+    #local6#isSet = true;
+    return local6 = #t13;
+  }
   T? local7;
   core::bool #local7#isSet = false;
   function #local7#get() → T% {
@@ -182,9 +194,9 @@ static field <T extends core::Object? = dynamic>(core::bool, T%) → core::Null?
     }
     return local7{T%};
   }
-  function #local7#set(T% #t18) → dynamic {
+  function #local7#set(T% #t14) → dynamic {
     #local7#isSet = true;
-    return local7 = #t18;
+    return local7 = #t14;
   }
   if(b) {
     local1 = value;
@@ -195,15 +207,15 @@ static field <T extends core::Object? = dynamic>(core::bool, T%) → core::Null?
     #local6#set.call(0);
     #local7#get.call();
   }
-  let final<BottomType> #t19 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:90:3: Error: Non-nullable variable 'local1' must be assigned before it can be used.
+  let final<BottomType> #t15 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:90:3: Error: Non-nullable variable 'local1' must be assigned before it can be used.
   local1; // error
   ^^^^^^" in local1;
   #local2#get.call();
-  let final<BottomType> #t20 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:92:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
+  let final<BottomType> #t16 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:92:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
   local3; // error
   ^^^^^^" in local3;
   #local4#get.call();
-  let final<BottomType> #t21 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:94:3: Error: Non-nullable variable 'local5' must be assigned before it can be used.
+  let final<BottomType> #t17 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:94:3: Error: Non-nullable variable 'local5' must be assigned before it can be used.
   local5; // error
   ^^^^^^" in local5;
   #local6#get.call();
@@ -212,14 +224,17 @@ static field <T extends core::Object? = dynamic>(core::bool, T%) → core::Null?
 static field () → core::Null? fieldCompound = () → core::Null? {
   core::int local3;
   core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t22 = local4 in #t22.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t22{core::int};
-  function #local4#set(core::int #t23) → dynamic
-    return local4 = #t23;
-  local3 = (let final<BottomType> #t24 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:111:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t18) → dynamic {
+    #local4#isSet = true;
+    return local4 = #t18;
+  }
+  local3 = (let final<BottomType> #t19 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:111:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
   local3 += 0; // error
   ^^^^^^" in local3).{core::num::+}(0);
-  #local4#set.call((let final<BottomType> #t25 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:112:3: Error: Non-nullable late variable 'local4' without initializer is definitely unassigned.
+  #local4#set.call((let final<BottomType> #t20 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:112:3: Error: Non-nullable late variable 'local4' without initializer is definitely unassigned.
   local4 += 0; // error
   ^^^^^^" in #local4#get.call()).{core::num::+}(0));
 };
@@ -229,22 +244,28 @@ static method methodDirect<T extends core::Object? = dynamic>(self::methodDirect
   core::bool #local2#isSet = false;
   function #local2#get() → self::methodDirect::T%
     return #local2#isSet ?{self::methodDirect::T%} local2{self::methodDirect::T%} : throw new _in::LateInitializationErrorImpl::•("Local 'local2' has not been initialized.");
-  function #local2#set(self::methodDirect::T% #t26) → dynamic {
+  function #local2#set(self::methodDirect::T% #t21) → dynamic {
     #local2#isSet = true;
-    return local2 = #t26;
+    return local2 = #t21;
   }
   core::int local3;
   core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t27 = local4 in #t27.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t27{core::int};
-  function #local4#set(core::int #t28) → dynamic
-    return local4 = #t28;
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t22) → dynamic {
+    #local4#isSet = true;
+    return local4 = #t22;
+  }
   FutureOr<core::int>local5;
   FutureOr<core::int>? local6;
+  core::bool #local6#isSet = false;
   function #local6#get() → FutureOr<core::int>
-    return let final FutureOr<core::int>? #t29 = local6 in #t29.==(null) ?{FutureOr<core::int>} throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.") : #t29{FutureOr<core::int>};
-  function #local6#set(FutureOr<core::int>#t30) → dynamic
-    return local6 = #t30;
+    return #local6#isSet ?{FutureOr<core::int>} local6{FutureOr<core::int>} : throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.");
+  function #local6#set(FutureOr<core::int>#t23) → dynamic {
+    #local6#isSet = true;
+    return local6 = #t23;
+  }
   self::methodDirect::T? local7;
   core::bool #local7#isSet = false;
   function #local7#get() → self::methodDirect::T% {
@@ -254,26 +275,26 @@ static method methodDirect<T extends core::Object? = dynamic>(self::methodDirect
     }
     return local7{self::methodDirect::T%};
   }
-  function #local7#set(self::methodDirect::T% #t31) → dynamic {
+  function #local7#set(self::methodDirect::T% #t24) → dynamic {
     #local7#isSet = true;
-    return local7 = #t31;
+    return local7 = #t24;
   }
-  let final<BottomType> #t32 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:16:3: Error: Non-nullable variable 'local1' must be assigned before it can be used.
+  let final<BottomType> #t25 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:16:3: Error: Non-nullable variable 'local1' must be assigned before it can be used.
   local1; // error
   ^^^^^^" in local1;
-  let final<BottomType> #t33 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:17:3: Error: Non-nullable late variable 'local2' without initializer is definitely unassigned.
+  let final<BottomType> #t26 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:17:3: Error: Non-nullable late variable 'local2' without initializer is definitely unassigned.
   local2; // error
   ^^^^^^" in #local2#get.call();
-  let final<BottomType> #t34 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:18:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
+  let final<BottomType> #t27 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:18:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
   local3; // error
   ^^^^^^" in local3;
-  let final<BottomType> #t35 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:19:3: Error: Non-nullable late variable 'local4' without initializer is definitely unassigned.
+  let final<BottomType> #t28 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:19:3: Error: Non-nullable late variable 'local4' without initializer is definitely unassigned.
   local4; // error
   ^^^^^^" in #local4#get.call();
-  let final<BottomType> #t36 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:20:3: Error: Non-nullable variable 'local5' must be assigned before it can be used.
+  let final<BottomType> #t29 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:20:3: Error: Non-nullable variable 'local5' must be assigned before it can be used.
   local5; // error
   ^^^^^^" in local5;
-  let final<BottomType> #t37 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:21:3: Error: Non-nullable late variable 'local6' without initializer is definitely unassigned.
+  let final<BottomType> #t30 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:21:3: Error: Non-nullable late variable 'local6' without initializer is definitely unassigned.
   local6; // error
   ^^^^^^" in #local6#get.call();
   #local7#get.call();
@@ -284,22 +305,28 @@ static method methodConditional<T extends core::Object? = dynamic>(core::bool b,
   core::bool #local2#isSet = false;
   function #local2#get() → self::methodConditional::T%
     return #local2#isSet ?{self::methodConditional::T%} local2{self::methodConditional::T%} : throw new _in::LateInitializationErrorImpl::•("Local 'local2' has not been initialized.");
-  function #local2#set(self::methodConditional::T% #t38) → dynamic {
+  function #local2#set(self::methodConditional::T% #t31) → dynamic {
     #local2#isSet = true;
-    return local2 = #t38;
+    return local2 = #t31;
   }
   core::int local3;
   core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t39 = local4 in #t39.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t39{core::int};
-  function #local4#set(core::int #t40) → dynamic
-    return local4 = #t40;
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t32) → dynamic {
+    #local4#isSet = true;
+    return local4 = #t32;
+  }
   FutureOr<core::int>local5;
   FutureOr<core::int>? local6;
+  core::bool #local6#isSet = false;
   function #local6#get() → FutureOr<core::int>
-    return let final FutureOr<core::int>? #t41 = local6 in #t41.==(null) ?{FutureOr<core::int>} throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.") : #t41{FutureOr<core::int>};
-  function #local6#set(FutureOr<core::int>#t42) → dynamic
-    return local6 = #t42;
+    return #local6#isSet ?{FutureOr<core::int>} local6{FutureOr<core::int>} : throw new _in::LateInitializationErrorImpl::•("Local 'local6' has not been initialized.");
+  function #local6#set(FutureOr<core::int>#t33) → dynamic {
+    #local6#isSet = true;
+    return local6 = #t33;
+  }
   self::methodConditional::T? local7;
   core::bool #local7#isSet = false;
   function #local7#get() → self::methodConditional::T% {
@@ -309,9 +336,9 @@ static method methodConditional<T extends core::Object? = dynamic>(core::bool b,
     }
     return local7{self::methodConditional::T%};
   }
-  function #local7#set(self::methodConditional::T% #t43) → dynamic {
+  function #local7#set(self::methodConditional::T% #t34) → dynamic {
     #local7#isSet = true;
-    return local7 = #t43;
+    return local7 = #t34;
   }
   if(b) {
     local1 = value;
@@ -322,15 +349,15 @@ static method methodConditional<T extends core::Object? = dynamic>(core::bool b,
     #local6#set.call(0);
     #local7#set.call(value);
   }
-  let final<BottomType> #t44 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:62:3: Error: Non-nullable variable 'local1' must be assigned before it can be used.
+  let final<BottomType> #t35 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:62:3: Error: Non-nullable variable 'local1' must be assigned before it can be used.
   local1; // error
   ^^^^^^" in local1;
   #local2#get.call();
-  let final<BottomType> #t45 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:64:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
+  let final<BottomType> #t36 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:64:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
   local3; // error
   ^^^^^^" in local3;
   #local4#get.call();
-  let final<BottomType> #t46 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:66:3: Error: Non-nullable variable 'local5' must be assigned before it can be used.
+  let final<BottomType> #t37 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:66:3: Error: Non-nullable variable 'local5' must be assigned before it can be used.
   local5; // error
   ^^^^^^" in local5;
   #local6#get.call();
@@ -339,14 +366,17 @@ static method methodConditional<T extends core::Object? = dynamic>(core::bool b,
 static method methodCompound() → dynamic {
   core::int local3;
   core::int? local4;
+  core::bool #local4#isSet = false;
   function #local4#get() → core::int
-    return let final core::int? #t47 = local4 in #t47.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.") : #t47{core::int};
-  function #local4#set(core::int #t48) → dynamic
-    return local4 = #t48;
-  local3 = (let final<BottomType> #t49 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:103:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
+    return #local4#isSet ?{core::int} local4{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local4' has not been initialized.");
+  function #local4#set(core::int #t38) → dynamic {
+    #local4#isSet = true;
+    return local4 = #t38;
+  }
+  local3 = (let final<BottomType> #t39 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:103:3: Error: Non-nullable variable 'local3' must be assigned before it can be used.
   local3 += 0; // error
   ^^^^^^" in local3).{core::num::+}(0);
-  #local4#set.call((let final<BottomType> #t50 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:104:3: Error: Non-nullable late variable 'local4' without initializer is definitely unassigned.
+  #local4#set.call((let final<BottomType> #t40 = invalid-expression "pkg/front_end/testcases/late_lowering/definitely_unassigned.dart:104:3: Error: Non-nullable late variable 'local4' without initializer is definitely unassigned.
   local4 += 0; // error
   ^^^^^^" in #local4#get.call()).{core::num::+}(0));
 }

pkg/front_end/testcases/late_lowering/infer_from_late_variable.dart.weak.expect

@@ -7,9 +7,12 @@ static method f<T extends core::Object? = dynamic>(self::f::T% t) → self::f::T
   return t;
 static method main() → dynamic {
   core::int? local;
+  core::bool #local#isSet = false;
   function #local#get() → core::int
-    return let final core::int? #t1 = local in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local' has not been initialized.") : #t1{core::int};
-  function #local#set(core::int #t2) → dynamic
-    return local = #t2;
+    return #local#isSet ?{core::int} local{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local' has not been initialized.");
+  function #local#set(core::int #t1) → dynamic {
+    #local#isSet = true;
+    return local = #t1;
+  }
   #local#set.call(self::f<core::int>(0));
 }

pkg/front_end/testcases/late_lowering/infer_from_late_variable.dart.weak.transformed.expect

@@ -7,9 +7,12 @@ static method f<T extends core::Object? = dynamic>(self::f::T% t) → self::f::T
   return t;
 static method main() → dynamic {
   core::int? local;
+  core::bool #local#isSet = false;
   function #local#get() → core::int
-    return let final core::int? #t1 = local in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local' has not been initialized.") : #t1{core::int};
-  function #local#set(core::int #t2) → dynamic
-    return local = #t2;
+    return #local#isSet ?{core::int} local{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local' has not been initialized.");
+  function #local#set(core::int #t1) → dynamic {
+    #local#isSet = true;
+    return local = #t1;
+  }
   #local#set.call(self::f<core::int>(0));
 }

pkg/front_end/testcases/late_lowering/initializer_rewrite.dart.weak.expect

@@ -6,11 +6,13 @@ import "dart:_internal" as _in;
 class Class extends core::Object {
   static field core::int nonNullableStaticFieldReads = 0;
   static field core::int? _#nonNullableStaticField = null;
+  static field core::bool _#nonNullableStaticField#isSet = false;
   static field core::int nullableStaticFieldReads = 0;
   static field core::int? _#nullableStaticField = null;
   static field core::bool _#nullableStaticField#isSet = false;
   field core::int nonNullableInstanceFieldReads = 0;
   field core::int? _#Class#nonNullableInstanceField = null;
+  field core::bool _#Class#nonNullableInstanceField#isSet = false;
   field core::int nullableInstanceFieldReads = 0;
   field core::int? _#Class#nullableInstanceField = null;
   field core::bool _#Class#nullableInstanceField#isSet = false;
@@ -44,6 +46,7 @@ class Class extends core::Object {
 }
 static field core::int nonNullableTopLevelFieldReads = 0;
 static field core::int? _#nonNullableTopLevelField = null;
+static field core::bool _#nonNullableTopLevelField#isSet = false;
 static field core::int nullableTopLevelFieldReads = 0;
 static field core::int? _#nullableTopLevelField = null;
 static field core::bool _#nullableTopLevelField#isSet = false;

pkg/front_end/testcases/late_lowering/initializer_rewrite.dart.weak.transformed.expect

@@ -6,11 +6,13 @@ import "dart:_internal" as _in;
 class Class extends core::Object {
   static field core::int nonNullableStaticFieldReads = 0;
   static field core::int? _#nonNullableStaticField = null;
+  static field core::bool _#nonNullableStaticField#isSet = false;
   static field core::int nullableStaticFieldReads = 0;
   static field core::int? _#nullableStaticField = null;
   static field core::bool _#nullableStaticField#isSet = false;
   field core::int nonNullableInstanceFieldReads = 0;
   field core::int? _#Class#nonNullableInstanceField = null;
+  field core::bool _#Class#nonNullableInstanceField#isSet = false;
   field core::int nullableInstanceFieldReads = 0;
   field core::int? _#Class#nullableInstanceField = null;
   field core::bool _#Class#nullableInstanceField#isSet = false;
@@ -44,6 +46,7 @@ class Class extends core::Object {
 }
 static field core::int nonNullableTopLevelFieldReads = 0;
 static field core::int? _#nonNullableTopLevelField = null;
+static field core::bool _#nonNullableTopLevelField#isSet = false;
 static field core::int nullableTopLevelFieldReads = 0;
 static field core::int? _#nullableTopLevelField = null;
 static field core::bool _#nullableTopLevelField#isSet = false;

pkg/front_end/testcases/late_lowering/injected_late_field_checks/main.dart.weak.expect

@@ -15,16 +15,19 @@ import "dart:_internal";
 @#C1
 class Class extends core::Object {
   field core::int? _#Class#foo = null /* from org-dartlang-testcase:///patch_lib.dart */;
+  field core::bool _#Class#foo#isSet = false /* from org-dartlang-testcase:///patch_lib.dart */;
   constructor bar() → self2::Class
     : super core::Object::•()
     ;
   constructor baz(core::int foo) → self2::Class
-    : self2::Class::_#Class#foo = foo, super core::Object::•()
+    : self2::Class::_#Class#foo#isSet = true, self2::Class::_#Class#foo = foo, super core::Object::•()
     ;
   get /* from org-dartlang-testcase:///patch_lib.dart */ foo() → core::int
-    return let final core::int? #t1 = this.{self2::Class::_#Class#foo} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'foo' has not been initialized.") : #t1{core::int};
-  set /* from org-dartlang-testcase:///patch_lib.dart */ foo(core::int #t2) → void
+    return this.{self2::Class::_#Class#foo#isSet} ?{core::int} let final core::int? #t1 = this.{self2::Class::_#Class#foo} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'foo' has not been initialized.");
+  set /* from org-dartlang-testcase:///patch_lib.dart */ foo(core::int #t2) → void {
+    this.{self2::Class::_#Class#foo#isSet} = true;
     this.{self2::Class::_#Class#foo} = #t2;
+  }
 }
 
 constants  {

pkg/front_end/testcases/late_lowering/injected_late_field_checks/main.dart.weak.transformed.expect

@@ -15,16 +15,19 @@ import "dart:_internal";
 @#C1
 class Class extends core::Object {
   field core::int? _#Class#foo = null /* from org-dartlang-testcase:///patch_lib.dart */;
+  field core::bool _#Class#foo#isSet = false /* from org-dartlang-testcase:///patch_lib.dart */;
   constructor bar() → self2::Class
     : super core::Object::•()
     ;
   constructor baz(core::int foo) → self2::Class
-    : self2::Class::_#Class#foo = foo, super core::Object::•()
+    : self2::Class::_#Class#foo#isSet = true, self2::Class::_#Class#foo = foo, super core::Object::•()
     ;
   get /* from org-dartlang-testcase:///patch_lib.dart */ foo() → core::int
-    return let final core::int? #t1 = this.{self2::Class::_#Class#foo} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'foo' has not been initialized.") : #t1{core::int};
-  set /* from org-dartlang-testcase:///patch_lib.dart */ foo(core::int #t2) → void
+    return this.{self2::Class::_#Class#foo#isSet} ?{core::int} let final core::int? #t1 = this.{self2::Class::_#Class#foo} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'foo' has not been initialized.");
+  set /* from org-dartlang-testcase:///patch_lib.dart */ foo(core::int #t2) → void {
+    this.{self2::Class::_#Class#foo#isSet} = true;
     this.{self2::Class::_#Class#foo} = #t2;
+  }
 }
 
 constants  {

pkg/front_end/testcases/late_lowering/instance_field_with_initializer.dart.weak.expect

@@ -4,22 +4,30 @@ import "dart:core" as core;
 
 class Class extends core::Object {
   field core::int? _#Class#field = null;
+  field core::bool _#Class#field#isSet = false;
   constructor constructor1() → self::Class
     : super core::Object::•()
     ;
   constructor constructor2(core::int field) → self::Class
-    : self::Class::_#Class#field = field, super core::Object::•()
+    : self::Class::_#Class#field#isSet = true, self::Class::_#Class#field = field, super core::Object::•()
     ;
   constructor constructor3(core::int value) → self::Class
-    : self::Class::_#Class#field = value.{core::num::+}(1), super core::Object::•()
+    : self::Class::_#Class#field#isSet = true, self::Class::_#Class#field = value.{core::num::+}(1), super core::Object::•()
     ;
   constructor constructor4([core::int field = #C1]) → self::Class
-    : self::Class::_#Class#field = field, super core::Object::•()
+    : self::Class::_#Class#field#isSet = true, self::Class::_#Class#field = field, super core::Object::•()
     ;
-  get field() → core::int
-    return let final core::int? #t1 = this.{self::Class::_#Class#field} in #t1.==(null) ?{core::int} this.{self::Class::_#Class#field} = 10 : #t1{core::int};
-  set field(core::int #t2) → void
+  get field() → core::int {
+    if(!this.{self::Class::_#Class#field#isSet}) {
+      this.{self::Class::_#Class#field} = 10;
+      this.{self::Class::_#Class#field#isSet} = true;
+    }
+    return let final core::int? #t1 = this.{self::Class::_#Class#field} in #t1{core::int};
+  }
+  set field(core::int #t2) → void {
+    this.{self::Class::_#Class#field#isSet} = true;
     this.{self::Class::_#Class#field} = #t2;
+  }
 }
 class Subclass extends self::Class {
   constructor constructor1() → self::Subclass

pkg/front_end/testcases/late_lowering/instance_field_with_initializer.dart.weak.transformed.expect

@@ -4,22 +4,30 @@ import "dart:core" as core;
 
 class Class extends core::Object {
   field core::int? _#Class#field = null;
+  field core::bool _#Class#field#isSet = false;
   constructor constructor1() → self::Class
     : super core::Object::•()
     ;
   constructor constructor2(core::int field) → self::Class
-    : self::Class::_#Class#field = field, super core::Object::•()
+    : self::Class::_#Class#field#isSet = true, self::Class::_#Class#field = field, super core::Object::•()
     ;
   constructor constructor3(core::int value) → self::Class
-    : self::Class::_#Class#field = value.{core::num::+}(1), super core::Object::•()
+    : self::Class::_#Class#field#isSet = true, self::Class::_#Class#field = value.{core::num::+}(1), super core::Object::•()
     ;
   constructor constructor4([core::int field = #C1]) → self::Class
-    : self::Class::_#Class#field = field, super core::Object::•()
+    : self::Class::_#Class#field#isSet = true, self::Class::_#Class#field = field, super core::Object::•()
     ;
-  get field() → core::int
-    return let final core::int? #t1 = this.{self::Class::_#Class#field} in #t1.==(null) ?{core::int} this.{self::Class::_#Class#field} = 10 : #t1{core::int};
-  set field(core::int #t2) → void
+  get field() → core::int {
+    if(!this.{self::Class::_#Class#field#isSet}) {
+      this.{self::Class::_#Class#field} = 10;
+      this.{self::Class::_#Class#field#isSet} = true;
+    }
+    return let final core::int? #t1 = this.{self::Class::_#Class#field} in #t1{core::int};
+  }
+  set field(core::int #t2) → void {
+    this.{self::Class::_#Class#field#isSet} = true;
     this.{self::Class::_#Class#field} = #t2;
+  }
 }
 class Subclass extends self::Class {
   constructor constructor1() → self::Subclass

pkg/front_end/testcases/late_lowering/instance_field_without_initializer.dart.weak.expect

@@ -5,22 +5,25 @@ import "dart:_internal" as _in;
 
 class Class extends core::Object {
   field core::int? _#Class#field = null;
+  field core::bool _#Class#field#isSet = false;
   constructor constructor1() → self::Class
     : super core::Object::•()
     ;
   constructor constructor2(core::int field) → self::Class
-    : self::Class::_#Class#field = field, super core::Object::•()
+    : self::Class::_#Class#field#isSet = true, self::Class::_#Class#field = field, super core::Object::•()
     ;
   constructor constructor3(core::int value) → self::Class
-    : self::Class::_#Class#field = value.{core::num::+}(1), super core::Object::•()
+    : self::Class::_#Class#field#isSet = true, self::Class::_#Class#field = value.{core::num::+}(1), super core::Object::•()
     ;
   constructor constructor4([core::int field = #C1]) → self::Class
-    : self::Class::_#Class#field = field, super core::Object::•()
+    : self::Class::_#Class#field#isSet = true, self::Class::_#Class#field = field, super core::Object::•()
     ;
   get field() → core::int
-    return let final core::int? #t1 = this.{self::Class::_#Class#field} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'field' has not been initialized.") : #t1{core::int};
-  set field(core::int #t2) → void
+    return this.{self::Class::_#Class#field#isSet} ?{core::int} let final core::int? #t1 = this.{self::Class::_#Class#field} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'field' has not been initialized.");
+  set field(core::int #t2) → void {
+    this.{self::Class::_#Class#field#isSet} = true;
     this.{self::Class::_#Class#field} = #t2;
+  }
 }
 class Subclass extends self::Class {
   constructor constructor1() → self::Subclass

pkg/front_end/testcases/late_lowering/instance_field_without_initializer.dart.weak.transformed.expect

@@ -5,22 +5,25 @@ import "dart:_internal" as _in;
 
 class Class extends core::Object {
   field core::int? _#Class#field = null;
+  field core::bool _#Class#field#isSet = false;
   constructor constructor1() → self::Class
     : super core::Object::•()
     ;
   constructor constructor2(core::int field) → self::Class
-    : self::Class::_#Class#field = field, super core::Object::•()
+    : self::Class::_#Class#field#isSet = true, self::Class::_#Class#field = field, super core::Object::•()
     ;
   constructor constructor3(core::int value) → self::Class
-    : self::Class::_#Class#field = value.{core::num::+}(1), super core::Object::•()
+    : self::Class::_#Class#field#isSet = true, self::Class::_#Class#field = value.{core::num::+}(1), super core::Object::•()
     ;
   constructor constructor4([core::int field = #C1]) → self::Class
-    : self::Class::_#Class#field = field, super core::Object::•()
+    : self::Class::_#Class#field#isSet = true, self::Class::_#Class#field = field, super core::Object::•()
     ;
   get field() → core::int
-    return let final core::int? #t1 = this.{self::Class::_#Class#field} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'field' has not been initialized.") : #t1{core::int};
-  set field(core::int #t2) → void
+    return this.{self::Class::_#Class#field#isSet} ?{core::int} let final core::int? #t1 = this.{self::Class::_#Class#field} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'field' has not been initialized.");
+  set field(core::int #t2) → void {
+    this.{self::Class::_#Class#field#isSet} = true;
     this.{self::Class::_#Class#field} = #t2;
+  }
 }
 class Subclass extends self::Class {
   constructor constructor1() → self::Subclass

pkg/front_end/testcases/late_lowering/instance_final_field_without_initializer.dart.weak.expect

@@ -5,25 +5,28 @@ import "dart:_internal" as _in;
 
 class Class extends core::Object {
   field core::int? _#Class#field = null;
+  field core::bool _#Class#field#isSet = false;
   constructor constructor1() → self::Class
     : super core::Object::•()
     ;
   constructor constructor2(core::int field) → self::Class
-    : self::Class::_#Class#field = field, super core::Object::•()
+    : self::Class::_#Class#field#isSet = true, self::Class::_#Class#field = field, super core::Object::•()
     ;
   constructor constructor3(core::int value) → self::Class
-    : self::Class::_#Class#field = value.{core::num::+}(1), super core::Object::•()
+    : self::Class::_#Class#field#isSet = true, self::Class::_#Class#field = value.{core::num::+}(1), super core::Object::•()
     ;
   constructor constructor4([core::int field = #C1]) → self::Class
-    : self::Class::_#Class#field = field, super core::Object::•()
+    : self::Class::_#Class#field#isSet = true, self::Class::_#Class#field = field, super core::Object::•()
     ;
   get field() → core::int
-    return let final core::int? #t1 = this.{self::Class::_#Class#field} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'field' has not been initialized.") : #t1{core::int};
+    return this.{self::Class::_#Class#field#isSet} ?{core::int} let final core::int? #t1 = this.{self::Class::_#Class#field} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'field' has not been initialized.");
   set field(core::int #t2) → void
-    if(this.{self::Class::_#Class#field}.==(null))
-      this.{self::Class::_#Class#field} = #t2;
-    else
+    if(this.{self::Class::_#Class#field#isSet})
       throw new _in::LateInitializationErrorImpl::•("Field 'field' has already been initialized.");
+    else {
+      this.{self::Class::_#Class#field#isSet} = true;
+      this.{self::Class::_#Class#field} = #t2;
+    }
 }
 class Subclass extends self::Class {
   constructor constructor1() → self::Subclass

pkg/front_end/testcases/late_lowering/instance_final_field_without_initializer.dart.weak.transformed.expect

@@ -5,25 +5,28 @@ import "dart:_internal" as _in;
 
 class Class extends core::Object {
   field core::int? _#Class#field = null;
+  field core::bool _#Class#field#isSet = false;
   constructor constructor1() → self::Class
     : super core::Object::•()
     ;
   constructor constructor2(core::int field) → self::Class
-    : self::Class::_#Class#field = field, super core::Object::•()
+    : self::Class::_#Class#field#isSet = true, self::Class::_#Class#field = field, super core::Object::•()
     ;
   constructor constructor3(core::int value) → self::Class
-    : self::Class::_#Class#field = value.{core::num::+}(1), super core::Object::•()
+    : self::Class::_#Class#field#isSet = true, self::Class::_#Class#field = value.{core::num::+}(1), super core::Object::•()
     ;
   constructor constructor4([core::int field = #C1]) → self::Class
-    : self::Class::_#Class#field = field, super core::Object::•()
+    : self::Class::_#Class#field#isSet = true, self::Class::_#Class#field = field, super core::Object::•()
     ;
   get field() → core::int
-    return let final core::int? #t1 = this.{self::Class::_#Class#field} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'field' has not been initialized.") : #t1{core::int};
+    return this.{self::Class::_#Class#field#isSet} ?{core::int} let final core::int? #t1 = this.{self::Class::_#Class#field} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'field' has not been initialized.");
   set field(core::int #t2) → void
-    if(this.{self::Class::_#Class#field}.==(null))
-      this.{self::Class::_#Class#field} = #t2;
-    else
+    if(this.{self::Class::_#Class#field#isSet})
       throw new _in::LateInitializationErrorImpl::•("Field 'field' has already been initialized.");
+    else {
+      this.{self::Class::_#Class#field#isSet} = true;
+      this.{self::Class::_#Class#field} = #t2;
+    }
 }
 class Subclass extends self::Class {
   constructor constructor1() → self::Subclass

pkg/front_end/testcases/late_lowering/issue40373.dart.weak.expect

@@ -6,15 +6,23 @@ import "dart:_internal" as _in;
 class C extends core::Object {
   field core::num pi = 3.14;
   field core::num? _#C#p1 = null;
+  field core::bool _#C#p1#isSet = false;
   field core::num? _#C#p2 = null;
   field core::bool _#C#p2#isSet = false;
   synthetic constructor •() → self::C
     : super core::Object::•()
     ;
-  get p1() → core::num
-    return let final core::num? #t1 = this.{self::C::_#C#p1} in #t1.==(null) ?{core::num} this.{self::C::_#C#p1} = this.{self::C::pi} : #t1{core::num};
-  set p1(core::num #t2) → void
+  get p1() → core::num {
+    if(!this.{self::C::_#C#p1#isSet}) {
+      this.{self::C::_#C#p1} = this.{self::C::pi};
+      this.{self::C::_#C#p1#isSet} = true;
+    }
+    return let final core::num? #t1 = this.{self::C::_#C#p1} in #t1{core::num};
+  }
+  set p1(core::num #t2) → void {
+    this.{self::C::_#C#p1#isSet} = true;
     this.{self::C::_#C#p1} = #t2;
+  }
   get p2() → core::num
     return let final core::num? #t3 = this.{self::C::_#C#p2} in #t3.==(null) ?{core::num} let final core::num #t4 = this.{self::C::pi} in this.{self::C::_#C#p2}.==(null) ?{core::num} this.{self::C::_#C#p2} = #t4 : throw new _in::LateInitializationErrorImpl::•("Field 'p2' has been assigned during initialization.") : #t3{core::num};
 }

pkg/front_end/testcases/late_lowering/issue40373.dart.weak.transformed.expect

@@ -6,15 +6,23 @@ import "dart:_internal" as _in;
 class C extends core::Object {
   field core::num pi = 3.14;
   field core::num? _#C#p1 = null;
+  field core::bool _#C#p1#isSet = false;
   field core::num? _#C#p2 = null;
   field core::bool _#C#p2#isSet = false;
   synthetic constructor •() → self::C
     : super core::Object::•()
     ;
-  get p1() → core::num
-    return let final core::num? #t1 = this.{self::C::_#C#p1} in #t1.==(null) ?{core::num} this.{self::C::_#C#p1} = this.{self::C::pi} : #t1{core::num};
-  set p1(core::num #t2) → void
+  get p1() → core::num {
+    if(!this.{self::C::_#C#p1#isSet}) {
+      this.{self::C::_#C#p1} = this.{self::C::pi};
+      this.{self::C::_#C#p1#isSet} = true;
+    }
+    return let final core::num? #t1 = this.{self::C::_#C#p1} in #t1{core::num};
+  }
+  set p1(core::num #t2) → void {
+    this.{self::C::_#C#p1#isSet} = true;
     this.{self::C::_#C#p1} = #t2;
+  }
   get p2() → core::num
     return let final core::num? #t3 = this.{self::C::_#C#p2} in #t3.==(null) ?{core::num} let final core::num #t4 = this.{self::C::pi} in this.{self::C::_#C#p2}.==(null) ?{core::num} this.{self::C::_#C#p2} = #t4 : throw new _in::LateInitializationErrorImpl::•("Field 'p2' has been assigned during initialization.") : #t3{core::num};
 }

pkg/front_end/testcases/late_lowering/issue40805.dart.weak.expect

@@ -5,16 +5,19 @@ import "dart:_internal" as _in;
 
 class C extends core::Object {
   field core::int? _#C#x = null;
+  field core::bool _#C#x#isSet = false;
   synthetic constructor •() → self::C
     : super core::Object::•()
     ;
   get x() → core::int
-    return let final core::int? #t1 = this.{self::C::_#C#x} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.") : #t1{core::int};
+    return this.{self::C::_#C#x#isSet} ?{core::int} let final core::int? #t1 = this.{self::C::_#C#x} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.");
   set x(covariant core::int #t2) → void
-    if(this.{self::C::_#C#x}.==(null))
-      this.{self::C::_#C#x} = #t2;
-    else
+    if(this.{self::C::_#C#x#isSet})
       throw new _in::LateInitializationErrorImpl::•("Field 'x' has already been initialized.");
+    else {
+      this.{self::C::_#C#x#isSet} = true;
+      this.{self::C::_#C#x} = #t2;
+    }
 }
 class D extends self::C {
   synthetic constructor •() → self::D

pkg/front_end/testcases/late_lowering/issue40805.dart.weak.transformed.expect

@@ -5,16 +5,19 @@ import "dart:_internal" as _in;
 
 class C extends core::Object {
   field core::int? _#C#x = null;
+  field core::bool _#C#x#isSet = false;
   synthetic constructor •() → self::C
     : super core::Object::•()
     ;
   get x() → core::int
-    return let final core::int? #t1 = this.{self::C::_#C#x} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.") : #t1{core::int};
+    return this.{self::C::_#C#x#isSet} ?{core::int} let final core::int? #t1 = this.{self::C::_#C#x} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.");
   set x(covariant core::int #t2) → void
-    if(this.{self::C::_#C#x}.==(null))
-      this.{self::C::_#C#x} = #t2;
-    else
+    if(this.{self::C::_#C#x#isSet})
       throw new _in::LateInitializationErrorImpl::•("Field 'x' has already been initialized.");
+    else {
+      this.{self::C::_#C#x#isSet} = true;
+      this.{self::C::_#C#x} = #t2;
+    }
 }
 class D extends self::C {
   synthetic constructor •() → self::D

pkg/front_end/testcases/late_lowering/issue41436/issue41436.dart.weak.expect

@@ -15,13 +15,16 @@ import "dart:_internal" as _in;
 
 abstract class A extends core::Object {
   field core::int? _#A#x = null;
+  field core::bool _#A#x#isSet = false;
   synthetic constructor •() → test::A
     : super core::Object::•()
     ;
   get x() → core::int
-    return let final core::int? #t1 = this.{test::A::_#A#x} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.") : #t1{core::int};
-  set x(core::int #t2) → void
+    return this.{test::A::_#A#x#isSet} ?{core::int} let final core::int? #t1 = this.{test::A::_#A#x} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.");
+  set x(core::int #t2) → void {
+    this.{test::A::_#A#x#isSet} = true;
     this.{test::A::_#A#x} = #t2;
+  }
 }
 class _B extends core::Object implements test::A {
   field core::int x = 3;

pkg/front_end/testcases/late_lowering/issue41436/issue41436.dart.weak.transformed.expect

@@ -15,13 +15,16 @@ import "dart:_internal" as _in;
 
 abstract class A extends core::Object {
   field core::int? _#A#x = null;
+  field core::bool _#A#x#isSet = false;
   synthetic constructor •() → test::A
     : super core::Object::•()
     ;
   get x() → core::int
-    return let final core::int? #t1 = this.{test::A::_#A#x} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.") : #t1{core::int};
-  set x(core::int #t2) → void
+    return this.{test::A::_#A#x#isSet} ?{core::int} let final core::int? #t1 = this.{test::A::_#A#x} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.");
+  set x(core::int #t2) → void {
+    this.{test::A::_#A#x#isSet} = true;
     this.{test::A::_#A#x} = #t2;
+  }
 }
 class _B extends core::Object implements test::A {
   field core::int x = 3;

pkg/front_end/testcases/late_lowering/issue41436b.dart.weak.expect

@@ -5,13 +5,16 @@ import "dart:_internal" as _in;
 
 abstract class A extends core::Object {
   field core::int? _#A#x = null;
+  field core::bool _#A#x#isSet = false;
   synthetic constructor •() → self::A
     : super core::Object::•()
     ;
   get x() → core::int
-    return let final core::int? #t1 = this.{self::A::_#A#x} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.") : #t1{core::int};
-  set x(core::int #t2) → void
+    return this.{self::A::_#A#x#isSet} ?{core::int} let final core::int? #t1 = this.{self::A::_#A#x} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.");
+  set x(core::int #t2) → void {
+    this.{self::A::_#A#x#isSet} = true;
     this.{self::A::_#A#x} = #t2;
+  }
 }
 class _B extends core::Object implements self::A {
   field core::int x = 3;

pkg/front_end/testcases/late_lowering/issue41436b.dart.weak.transformed.expect

@@ -5,13 +5,16 @@ import "dart:_internal" as _in;
 
 abstract class A extends core::Object {
   field core::int? _#A#x = null;
+  field core::bool _#A#x#isSet = false;
   synthetic constructor •() → self::A
     : super core::Object::•()
     ;
   get x() → core::int
-    return let final core::int? #t1 = this.{self::A::_#A#x} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.") : #t1{core::int};
-  set x(core::int #t2) → void
+    return this.{self::A::_#A#x#isSet} ?{core::int} let final core::int? #t1 = this.{self::A::_#A#x} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.");
+  set x(core::int #t2) → void {
+    this.{self::A::_#A#x#isSet} = true;
     this.{self::A::_#A#x} = #t2;
+  }
 }
 class _B extends core::Object implements self::A {
   field core::int x = 3;

pkg/front_end/testcases/late_lowering/issue41436c/issue41436c.dart.weak.expect

@@ -9,10 +9,14 @@ class C extends iss::B {
   synthetic constructor •() → self::C
     : super iss::B::•()
     ;
+  no-such-method-forwarder get /* from org-dartlang-testcase:///issue41436c_lib.dart */ _#A#x#isSet() → core::bool
+    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#C1, 1, #C2, #C3, core::Map::unmodifiable<core::Symbol*, dynamic>(#C4))) as{TypeError,ForDynamic,ForNonNullableByDefault} core::bool;
   no-such-method-forwarder get /* from org-dartlang-testcase:///issue41436c_lib.dart */ _#A#x() → core::int?
-    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#C1, 1, #C2, #C3, core::Map::unmodifiable<core::Symbol*, dynamic>(#C4))) as{TypeError,ForDynamic,ForNonNullableByDefault} core::int?;
+    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#C5, 1, #C2, #C3, core::Map::unmodifiable<core::Symbol*, dynamic>(#C4))) as{TypeError,ForDynamic,ForNonNullableByDefault} core::int?;
+  no-such-method-forwarder set /* from org-dartlang-testcase:///issue41436c_lib.dart */ _#A#x#isSet(core::bool value) → void
+    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#C6, 2, #C2, core::List::unmodifiable<dynamic>(<dynamic>[value]), core::Map::unmodifiable<core::Symbol*, dynamic>(#C4)));
   no-such-method-forwarder set /* from org-dartlang-testcase:///issue41436c_lib.dart */ _#A#x(core::int? value) → void
-    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#C5, 2, #C2, core::List::unmodifiable<dynamic>(<dynamic>[value]), core::Map::unmodifiable<core::Symbol*, dynamic>(#C4)));
+    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#C7, 2, #C2, core::List::unmodifiable<dynamic>(<dynamic>[value]), core::Map::unmodifiable<core::Symbol*, dynamic>(#C4)));
 }
 static method main() → dynamic {
   new self::C::•();
@@ -25,13 +29,16 @@ import "dart:_internal" as _in;
 
 abstract class A extends core::Object {
   field core::int? _#A#x = null;
+  field core::bool _#A#x#isSet = false;
   synthetic constructor •() → iss::A
     : super core::Object::•()
     ;
   get x() → core::int
-    return let final core::int? #t1 = this.{iss::A::_#A#x} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.") : #t1{core::int};
-  set x(core::int #t2) → void
+    return this.{iss::A::_#A#x#isSet} ?{core::int} let final core::int? #t1 = this.{iss::A::_#A#x} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.");
+  set x(core::int #t2) → void {
+    this.{iss::A::_#A#x#isSet} = true;
     this.{iss::A::_#A#x} = #t2;
+  }
 }
 class B extends core::Object implements iss::A {
   field core::int x = 3;
@@ -41,9 +48,11 @@ class B extends core::Object implements iss::A {
 }
 
 constants  {
-  #C1 = #org-dartlang-testcase:///issue41436c.dart::_#A#x
+  #C1 = #org-dartlang-testcase:///issue41436c.dart::_#A#x#isSet
   #C2 = <core::Type*>[]
   #C3 = <dynamic>[]
   #C4 = core::_ImmutableMap<core::Symbol*, dynamic> {_kvPairs:#C3}
-  #C5 = #org-dartlang-testcase:///issue41436c.dart::_#A#x=
+  #C5 = #org-dartlang-testcase:///issue41436c.dart::_#A#x
+  #C6 = #org-dartlang-testcase:///issue41436c.dart::_#A#x#isSet=
+  #C7 = #org-dartlang-testcase:///issue41436c.dart::_#A#x=
 }

pkg/front_end/testcases/late_lowering/issue41436c/issue41436c.dart.weak.transformed.expect

@@ -9,10 +9,14 @@ class C extends iss::B {
   synthetic constructor •() → self::C
     : super iss::B::•()
     ;
+  no-such-method-forwarder get /* from org-dartlang-testcase:///issue41436c_lib.dart */ _#A#x#isSet() → core::bool
+    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#C1, 1, #C2, #C3, core::Map::unmodifiable<core::Symbol*, dynamic>(#C4))) as{TypeError,ForDynamic,ForNonNullableByDefault} core::bool;
   no-such-method-forwarder get /* from org-dartlang-testcase:///issue41436c_lib.dart */ _#A#x() → core::int?
-    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#C1, 1, #C2, #C3, core::Map::unmodifiable<core::Symbol*, dynamic>(#C4))) as{TypeError,ForDynamic,ForNonNullableByDefault} core::int?;
+    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#C5, 1, #C2, #C3, core::Map::unmodifiable<core::Symbol*, dynamic>(#C4))) as{TypeError,ForDynamic,ForNonNullableByDefault} core::int?;
+  no-such-method-forwarder set /* from org-dartlang-testcase:///issue41436c_lib.dart */ _#A#x#isSet(core::bool value) → void
+    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#C6, 2, #C2, core::List::unmodifiable<dynamic>(<dynamic>[value]), core::Map::unmodifiable<core::Symbol*, dynamic>(#C4)));
   no-such-method-forwarder set /* from org-dartlang-testcase:///issue41436c_lib.dart */ _#A#x(core::int? value) → void
-    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#C5, 2, #C2, core::List::unmodifiable<dynamic>(<dynamic>[value]), core::Map::unmodifiable<core::Symbol*, dynamic>(#C4)));
+    return this.{core::Object::noSuchMethod}(new core::_InvocationMirror::_withType(#C7, 2, #C2, core::List::unmodifiable<dynamic>(<dynamic>[value]), core::Map::unmodifiable<core::Symbol*, dynamic>(#C4)));
 }
 static method main() → dynamic {
   new self::C::•();
@@ -25,13 +29,16 @@ import "dart:_internal" as _in;
 
 abstract class A extends core::Object {
   field core::int? _#A#x = null;
+  field core::bool _#A#x#isSet = false;
   synthetic constructor •() → iss::A
     : super core::Object::•()
     ;
   get x() → core::int
-    return let final core::int? #t1 = this.{iss::A::_#A#x} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.") : #t1{core::int};
-  set x(core::int #t2) → void
+    return this.{iss::A::_#A#x#isSet} ?{core::int} let final core::int? #t1 = this.{iss::A::_#A#x} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.");
+  set x(core::int #t2) → void {
+    this.{iss::A::_#A#x#isSet} = true;
     this.{iss::A::_#A#x} = #t2;
+  }
 }
 class B extends core::Object implements iss::A {
   field core::int x = 3;
@@ -41,9 +48,11 @@ class B extends core::Object implements iss::A {
 }
 
 constants  {
-  #C1 = #org-dartlang-testcase:///issue41436c.dart::_#A#x
+  #C1 = #org-dartlang-testcase:///issue41436c.dart::_#A#x#isSet
   #C2 = <core::Type*>[]
   #C3 = <dynamic>[]
   #C4 = core::_ImmutableMap<core::Symbol*, dynamic> {_kvPairs:#C3}
-  #C5 = #org-dartlang-testcase:///issue41436c.dart::_#A#x=
+  #C5 = #org-dartlang-testcase:///issue41436c.dart::_#A#x
+  #C6 = #org-dartlang-testcase:///issue41436c.dart::_#A#x#isSet=
+  #C7 = #org-dartlang-testcase:///issue41436c.dart::_#A#x=
 }

pkg/front_end/testcases/late_lowering/late_annotations.dart.weak.expect

@@ -10,158 +10,209 @@ class Annotation extends core::Object /*hasConstConstructor*/  {
 }
 class A extends core::Object {
   field core::int? _#A#instanceField = null;
+  field core::bool _#A#instanceField#isSet = false;
   field core::int? _#A#finalInstanceField = null;
+  field core::bool _#A#finalInstanceField#isSet = false;
   field core::int? _#A#finalInstanceFieldWithInitializer = null;
+  field core::bool _#A#finalInstanceFieldWithInitializer#isSet = false;
   field core::num? _#A#covariantInstanceField = null;
+  field core::bool _#A#covariantInstanceField#isSet = false;
   static field core::int? _#staticField = null;
+  static field core::bool _#staticField#isSet = false;
   static field core::int? _#finalStaticField = null;
+  static field core::bool _#finalStaticField#isSet = false;
   static field core::int? _#finalStaticFieldWithInitializer = null;
+  static field core::bool _#finalStaticFieldWithInitializer#isSet = false;
   synthetic constructor •() → self::A
     : super core::Object::•()
     ;
   @#C1
   get instanceField() → core::int
-    return let final core::int? #t1 = this.{self::A::_#A#instanceField} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'instanceField' has not been initialized.") : #t1{core::int};
+    return this.{self::A::_#A#instanceField#isSet} ?{core::int} let final core::int? #t1 = this.{self::A::_#A#instanceField} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'instanceField' has not been initialized.");
   @#C1
-  set instanceField(core::int #t2) → void
+  set instanceField(core::int #t2) → void {
+    this.{self::A::_#A#instanceField#isSet} = true;
     this.{self::A::_#A#instanceField} = #t2;
+  }
   @#C1
   get finalInstanceField() → core::int
-    return let final core::int? #t3 = this.{self::A::_#A#finalInstanceField} in #t3.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceField' has not been initialized.") : #t3{core::int};
+    return this.{self::A::_#A#finalInstanceField#isSet} ?{core::int} let final core::int? #t3 = this.{self::A::_#A#finalInstanceField} in #t3{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceField' has not been initialized.");
   @#C1
   set finalInstanceField(core::int #t4) → void
-    if(this.{self::A::_#A#finalInstanceField}.==(null))
-      this.{self::A::_#A#finalInstanceField} = #t4;
-    else
+    if(this.{self::A::_#A#finalInstanceField#isSet})
       throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceField' has already been initialized.");
+    else {
+      this.{self::A::_#A#finalInstanceField#isSet} = true;
+      this.{self::A::_#A#finalInstanceField} = #t4;
+    }
   @#C1
   get finalInstanceFieldWithInitializer() → core::int
     return let final core::int? #t5 = this.{self::A::_#A#finalInstanceFieldWithInitializer} in #t5.==(null) ?{core::int} let final core::int #t6 = 0 in this.{self::A::_#A#finalInstanceFieldWithInitializer}.==(null) ?{core::int} this.{self::A::_#A#finalInstanceFieldWithInitializer} = #t6 : throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceFieldWithInitializer' has been assigned during initialization.") : #t5{core::int};
   @#C1
   get covariantInstanceField() → core::num
-    return let final core::num? #t7 = this.{self::A::_#A#covariantInstanceField} in #t7.==(null) ?{core::num} throw new _in::LateInitializationErrorImpl::•("Field 'covariantInstanceField' has not been initialized.") : #t7{core::num};
+    return this.{self::A::_#A#covariantInstanceField#isSet} ?{core::num} let final core::num? #t7 = this.{self::A::_#A#covariantInstanceField} in #t7{core::num} : throw new _in::LateInitializationErrorImpl::•("Field 'covariantInstanceField' has not been initialized.");
   @#C1
-  set covariantInstanceField(covariant core::num #t8) → void
+  set covariantInstanceField(covariant core::num #t8) → void {
+    this.{self::A::_#A#covariantInstanceField#isSet} = true;
     this.{self::A::_#A#covariantInstanceField} = #t8;
+  }
   @#C1
   static get staticField() → core::int
-    return let final core::int? #t9 = self::A::_#staticField in #t9.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'staticField' has not been initialized.") : #t9{core::int};
+    return self::A::_#staticField#isSet ?{core::int} let final core::int? #t9 = self::A::_#staticField in #t9{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'staticField' has not been initialized.");
   @#C1
-  static set staticField(core::int #t10) → void
+  static set staticField(core::int #t10) → void {
+    self::A::_#staticField#isSet = true;
     self::A::_#staticField = #t10;
+  }
   @#C1
   static get finalStaticField() → core::int
-    return let final core::int? #t11 = self::A::_#finalStaticField in #t11.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'finalStaticField' has not been initialized.") : #t11{core::int};
+    return self::A::_#finalStaticField#isSet ?{core::int} let final core::int? #t11 = self::A::_#finalStaticField in #t11{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'finalStaticField' has not been initialized.");
   @#C1
   static set finalStaticField(core::int #t12) → void
-    if(self::A::_#finalStaticField.==(null))
-      self::A::_#finalStaticField = #t12;
-    else
+    if(self::A::_#finalStaticField#isSet)
       throw new _in::LateInitializationErrorImpl::•("Field 'finalStaticField' has already been initialized.");
+    else {
+      self::A::_#finalStaticField#isSet = true;
+      self::A::_#finalStaticField = #t12;
+    }
   @#C1
   static get finalStaticFieldWithInitializer() → core::int
     return let final core::int? #t13 = self::A::_#finalStaticFieldWithInitializer in #t13.==(null) ?{core::int} let final core::int #t14 = 0 in self::A::_#finalStaticFieldWithInitializer.==(null) ?{core::int} self::A::_#finalStaticFieldWithInitializer = #t14 : throw new _in::LateInitializationErrorImpl::•("Field 'finalStaticFieldWithInitializer' has been assigned during initialization.") : #t13{core::int};
 }
 abstract class B extends core::Object /*isMixinDeclaration*/  {
   field core::int? _#B#instanceField = null;
+  field core::bool _#B#instanceField#isSet = false;
   field core::int? _#B#finalInstanceField = null;
+  field core::bool _#B#finalInstanceField#isSet = false;
   field core::int? _#B#finalInstanceFieldWithInitializer = null;
+  field core::bool _#B#finalInstanceFieldWithInitializer#isSet = false;
   field core::num? _#B#covariantInstanceField = null;
+  field core::bool _#B#covariantInstanceField#isSet = false;
   static field core::int? _#staticField = null;
+  static field core::bool _#staticField#isSet = false;
   static field core::int? _#finalStaticField = null;
+  static field core::bool _#finalStaticField#isSet = false;
   static field core::int? _#finalStaticFieldWithInitializer = null;
+  static field core::bool _#finalStaticFieldWithInitializer#isSet = false;
   @#C1
   get instanceField() → core::int
-    return let final core::int? #t15 = this.{self::B::_#B#instanceField} in #t15.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'instanceField' has not been initialized.") : #t15{core::int};
+    return this.{self::B::_#B#instanceField#isSet} ?{core::int} let final core::int? #t15 = this.{self::B::_#B#instanceField} in #t15{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'instanceField' has not been initialized.");
   @#C1
-  set instanceField(core::int #t16) → void
+  set instanceField(core::int #t16) → void {
+    this.{self::B::_#B#instanceField#isSet} = true;
     this.{self::B::_#B#instanceField} = #t16;
+  }
   @#C1
   get finalInstanceField() → core::int
-    return let final core::int? #t17 = this.{self::B::_#B#finalInstanceField} in #t17.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceField' has not been initialized.") : #t17{core::int};
+    return this.{self::B::_#B#finalInstanceField#isSet} ?{core::int} let final core::int? #t17 = this.{self::B::_#B#finalInstanceField} in #t17{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceField' has not been initialized.");
   @#C1
   set finalInstanceField(core::int #t18) → void
-    if(this.{self::B::_#B#finalInstanceField}.==(null))
-      this.{self::B::_#B#finalInstanceField} = #t18;
-    else
+    if(this.{self::B::_#B#finalInstanceField#isSet})
       throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceField' has already been initialized.");
+    else {
+      this.{self::B::_#B#finalInstanceField#isSet} = true;
+      this.{self::B::_#B#finalInstanceField} = #t18;
+    }
   @#C1
   get finalInstanceFieldWithInitializer() → core::int
     return let final core::int? #t19 = this.{self::B::_#B#finalInstanceFieldWithInitializer} in #t19.==(null) ?{core::int} let final core::int #t20 = 0 in this.{self::B::_#B#finalInstanceFieldWithInitializer}.==(null) ?{core::int} this.{self::B::_#B#finalInstanceFieldWithInitializer} = #t20 : throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceFieldWithInitializer' has been assigned during initialization.") : #t19{core::int};
   @#C1
   get covariantInstanceField() → core::num
-    return let final core::num? #t21 = this.{self::B::_#B#covariantInstanceField} in #t21.==(null) ?{core::num} throw new _in::LateInitializationErrorImpl::•("Field 'covariantInstanceField' has not been initialized.") : #t21{core::num};
+    return this.{self::B::_#B#covariantInstanceField#isSet} ?{core::num} let final core::num? #t21 = this.{self::B::_#B#covariantInstanceField} in #t21{core::num} : throw new _in::LateInitializationErrorImpl::•("Field 'covariantInstanceField' has not been initialized.");
   @#C1
-  set covariantInstanceField(covariant core::num #t22) → void
+  set covariantInstanceField(covariant core::num #t22) → void {
+    this.{self::B::_#B#covariantInstanceField#isSet} = true;
     this.{self::B::_#B#covariantInstanceField} = #t22;
+  }
   @#C1
   static get staticField() → core::int
-    return let final core::int? #t23 = self::B::_#staticField in #t23.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'staticField' has not been initialized.") : #t23{core::int};
+    return self::B::_#staticField#isSet ?{core::int} let final core::int? #t23 = self::B::_#staticField in #t23{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'staticField' has not been initialized.");
   @#C1
-  static set staticField(core::int #t24) → void
+  static set staticField(core::int #t24) → void {
+    self::B::_#staticField#isSet = true;
     self::B::_#staticField = #t24;
+  }
   @#C1
   static get finalStaticField() → core::int
-    return let final core::int? #t25 = self::B::_#finalStaticField in #t25.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'finalStaticField' has not been initialized.") : #t25{core::int};
+    return self::B::_#finalStaticField#isSet ?{core::int} let final core::int? #t25 = self::B::_#finalStaticField in #t25{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'finalStaticField' has not been initialized.");
   @#C1
   static set finalStaticField(core::int #t26) → void
-    if(self::B::_#finalStaticField.==(null))
-      self::B::_#finalStaticField = #t26;
-    else
+    if(self::B::_#finalStaticField#isSet)
       throw new _in::LateInitializationErrorImpl::•("Field 'finalStaticField' has already been initialized.");
+    else {
+      self::B::_#finalStaticField#isSet = true;
+      self::B::_#finalStaticField = #t26;
+    }
   @#C1
   static get finalStaticFieldWithInitializer() → core::int
     return let final core::int? #t27 = self::B::_#finalStaticFieldWithInitializer in #t27.==(null) ?{core::int} let final core::int #t28 = 0 in self::B::_#finalStaticFieldWithInitializer.==(null) ?{core::int} self::B::_#finalStaticFieldWithInitializer = #t28 : throw new _in::LateInitializationErrorImpl::•("Field 'finalStaticFieldWithInitializer' has been assigned during initialization.") : #t27{core::int};
 }
 extension Extension on self::A {
   static field extensionStaticField = self::_#Extension|extensionStaticField;
+  static field extensionStaticField = self::_#Extension|extensionStaticField#isSet;
   static get extensionStaticField = get self::Extension|extensionStaticField;
   static set extensionStaticField = set self::Extension|extensionStaticField;
   static field finalExtensionStaticField = self::_#Extension|finalExtensionStaticField;
+  static field finalExtensionStaticField = self::_#Extension|finalExtensionStaticField#isSet;
   static get finalExtensionStaticField = get self::Extension|finalExtensionStaticField;
   static set finalExtensionStaticField = set self::Extension|finalExtensionStaticField;
   static field finalExtensionStaticFieldWithInitializer = self::_#Extension|finalExtensionStaticFieldWithInitializer;
+  static field finalExtensionStaticFieldWithInitializer = self::_#Extension|finalExtensionStaticFieldWithInitializer#isSet;
   static get finalExtensionStaticFieldWithInitializer = get self::Extension|finalExtensionStaticFieldWithInitializer;
 }
 static field core::int? _#topLevelField = null;
+static field core::bool _#topLevelField#isSet = false;
 static field core::int? _#finalTopLevelField = null;
+static field core::bool _#finalTopLevelField#isSet = false;
 static field core::int? _#finalTopLevelFieldWithInitializer = null;
+static field core::bool _#finalTopLevelFieldWithInitializer#isSet = false;
 static field core::int? _#Extension|extensionStaticField = null;
+static field core::bool _#Extension|extensionStaticField#isSet = false;
 static field core::int? _#Extension|finalExtensionStaticField = null;
+static field core::bool _#Extension|finalExtensionStaticField#isSet = false;
 static field core::int? _#Extension|finalExtensionStaticFieldWithInitializer = null;
+static field core::bool _#Extension|finalExtensionStaticFieldWithInitializer#isSet = false;
 @#C1
 static get topLevelField() → core::int
-  return let final core::int? #t29 = self::_#topLevelField in #t29.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'topLevelField' has not been initialized.") : #t29{core::int};
+  return self::_#topLevelField#isSet ?{core::int} let final core::int? #t29 = self::_#topLevelField in #t29{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'topLevelField' has not been initialized.");
 @#C1
-static set topLevelField(core::int #t30) → void
+static set topLevelField(core::int #t30) → void {
+  self::_#topLevelField#isSet = true;
   self::_#topLevelField = #t30;
+}
 @#C1
 static get finalTopLevelField() → core::int
-  return let final core::int? #t31 = self::_#finalTopLevelField in #t31.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'finalTopLevelField' has not been initialized.") : #t31{core::int};
+  return self::_#finalTopLevelField#isSet ?{core::int} let final core::int? #t31 = self::_#finalTopLevelField in #t31{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'finalTopLevelField' has not been initialized.");
 @#C1
 static set finalTopLevelField(core::int #t32) → void
-  if(self::_#finalTopLevelField.==(null))
-    self::_#finalTopLevelField = #t32;
-  else
+  if(self::_#finalTopLevelField#isSet)
     throw new _in::LateInitializationErrorImpl::•("Field 'finalTopLevelField' has already been initialized.");
+  else {
+    self::_#finalTopLevelField#isSet = true;
+    self::_#finalTopLevelField = #t32;
+  }
 @#C1
 static get finalTopLevelFieldWithInitializer() → core::int
   return let final core::int? #t33 = self::_#finalTopLevelFieldWithInitializer in #t33.==(null) ?{core::int} let final core::int #t34 = 0 in self::_#finalTopLevelFieldWithInitializer.==(null) ?{core::int} self::_#finalTopLevelFieldWithInitializer = #t34 : throw new _in::LateInitializationErrorImpl::•("Field 'finalTopLevelFieldWithInitializer' has been assigned during initialization.") : #t33{core::int};
 @#C1
 static get Extension|extensionStaticField() → core::int
-  return let final core::int? #t35 = self::_#Extension|extensionStaticField in #t35.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'extensionStaticField' has not been initialized.") : #t35{core::int};
+  return self::_#Extension|extensionStaticField#isSet ?{core::int} let final core::int? #t35 = self::_#Extension|extensionStaticField in #t35{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'extensionStaticField' has not been initialized.");
 @#C1
-static set Extension|extensionStaticField(core::int #t36) → void
+static set Extension|extensionStaticField(core::int #t36) → void {
+  self::_#Extension|extensionStaticField#isSet = true;
   self::_#Extension|extensionStaticField = #t36;
+}
 @#C1
 static get Extension|finalExtensionStaticField() → core::int
-  return let final core::int? #t37 = self::_#Extension|finalExtensionStaticField in #t37.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'finalExtensionStaticField' has not been initialized.") : #t37{core::int};
+  return self::_#Extension|finalExtensionStaticField#isSet ?{core::int} let final core::int? #t37 = self::_#Extension|finalExtensionStaticField in #t37{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'finalExtensionStaticField' has not been initialized.");
 @#C1
 static set Extension|finalExtensionStaticField(core::int #t38) → void
-  if(self::_#Extension|finalExtensionStaticField.==(null))
-    self::_#Extension|finalExtensionStaticField = #t38;
-  else
+  if(self::_#Extension|finalExtensionStaticField#isSet)
     throw new _in::LateInitializationErrorImpl::•("Field 'finalExtensionStaticField' has already been initialized.");
+  else {
+    self::_#Extension|finalExtensionStaticField#isSet = true;
+    self::_#Extension|finalExtensionStaticField = #t38;
+  }
 @#C1
 static get Extension|finalExtensionStaticFieldWithInitializer() → core::int
   return let final core::int? #t39 = self::_#Extension|finalExtensionStaticFieldWithInitializer in #t39.==(null) ?{core::int} let final core::int #t40 = 0 in self::_#Extension|finalExtensionStaticFieldWithInitializer.==(null) ?{core::int} self::_#Extension|finalExtensionStaticFieldWithInitializer = #t40 : throw new _in::LateInitializationErrorImpl::•("Field 'finalExtensionStaticFieldWithInitializer' has been assigned during initialization.") : #t39{core::int};

pkg/front_end/testcases/late_lowering/late_annotations.dart.weak.transformed.expect

@@ -10,158 +10,209 @@ class Annotation extends core::Object /*hasConstConstructor*/  {
 }
 class A extends core::Object {
   field core::int? _#A#instanceField = null;
+  field core::bool _#A#instanceField#isSet = false;
   field core::int? _#A#finalInstanceField = null;
+  field core::bool _#A#finalInstanceField#isSet = false;
   field core::int? _#A#finalInstanceFieldWithInitializer = null;
+  field core::bool _#A#finalInstanceFieldWithInitializer#isSet = false;
   field core::num? _#A#covariantInstanceField = null;
+  field core::bool _#A#covariantInstanceField#isSet = false;
   static field core::int? _#staticField = null;
+  static field core::bool _#staticField#isSet = false;
   static field core::int? _#finalStaticField = null;
+  static field core::bool _#finalStaticField#isSet = false;
   static field core::int? _#finalStaticFieldWithInitializer = null;
+  static field core::bool _#finalStaticFieldWithInitializer#isSet = false;
   synthetic constructor •() → self::A
     : super core::Object::•()
     ;
   @#C1
   get instanceField() → core::int
-    return let final core::int? #t1 = this.{self::A::_#A#instanceField} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'instanceField' has not been initialized.") : #t1{core::int};
+    return this.{self::A::_#A#instanceField#isSet} ?{core::int} let final core::int? #t1 = this.{self::A::_#A#instanceField} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'instanceField' has not been initialized.");
   @#C1
-  set instanceField(core::int #t2) → void
+  set instanceField(core::int #t2) → void {
+    this.{self::A::_#A#instanceField#isSet} = true;
     this.{self::A::_#A#instanceField} = #t2;
+  }
   @#C1
   get finalInstanceField() → core::int
-    return let final core::int? #t3 = this.{self::A::_#A#finalInstanceField} in #t3.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceField' has not been initialized.") : #t3{core::int};
+    return this.{self::A::_#A#finalInstanceField#isSet} ?{core::int} let final core::int? #t3 = this.{self::A::_#A#finalInstanceField} in #t3{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceField' has not been initialized.");
   @#C1
   set finalInstanceField(core::int #t4) → void
-    if(this.{self::A::_#A#finalInstanceField}.==(null))
-      this.{self::A::_#A#finalInstanceField} = #t4;
-    else
+    if(this.{self::A::_#A#finalInstanceField#isSet})
       throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceField' has already been initialized.");
+    else {
+      this.{self::A::_#A#finalInstanceField#isSet} = true;
+      this.{self::A::_#A#finalInstanceField} = #t4;
+    }
   @#C1
   get finalInstanceFieldWithInitializer() → core::int
     return let final core::int? #t5 = this.{self::A::_#A#finalInstanceFieldWithInitializer} in #t5.==(null) ?{core::int} let final core::int #t6 = 0 in this.{self::A::_#A#finalInstanceFieldWithInitializer}.==(null) ?{core::int} this.{self::A::_#A#finalInstanceFieldWithInitializer} = #t6 : throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceFieldWithInitializer' has been assigned during initialization.") : #t5{core::int};
   @#C1
   get covariantInstanceField() → core::num
-    return let final core::num? #t7 = this.{self::A::_#A#covariantInstanceField} in #t7.==(null) ?{core::num} throw new _in::LateInitializationErrorImpl::•("Field 'covariantInstanceField' has not been initialized.") : #t7{core::num};
+    return this.{self::A::_#A#covariantInstanceField#isSet} ?{core::num} let final core::num? #t7 = this.{self::A::_#A#covariantInstanceField} in #t7{core::num} : throw new _in::LateInitializationErrorImpl::•("Field 'covariantInstanceField' has not been initialized.");
   @#C1
-  set covariantInstanceField(covariant core::num #t8) → void
+  set covariantInstanceField(covariant core::num #t8) → void {
+    this.{self::A::_#A#covariantInstanceField#isSet} = true;
     this.{self::A::_#A#covariantInstanceField} = #t8;
+  }
   @#C1
   static get staticField() → core::int
-    return let final core::int? #t9 = self::A::_#staticField in #t9.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'staticField' has not been initialized.") : #t9{core::int};
+    return self::A::_#staticField#isSet ?{core::int} let final core::int? #t9 = self::A::_#staticField in #t9{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'staticField' has not been initialized.");
   @#C1
-  static set staticField(core::int #t10) → void
+  static set staticField(core::int #t10) → void {
+    self::A::_#staticField#isSet = true;
     self::A::_#staticField = #t10;
+  }
   @#C1
   static get finalStaticField() → core::int
-    return let final core::int? #t11 = self::A::_#finalStaticField in #t11.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'finalStaticField' has not been initialized.") : #t11{core::int};
+    return self::A::_#finalStaticField#isSet ?{core::int} let final core::int? #t11 = self::A::_#finalStaticField in #t11{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'finalStaticField' has not been initialized.");
   @#C1
   static set finalStaticField(core::int #t12) → void
-    if(self::A::_#finalStaticField.==(null))
-      self::A::_#finalStaticField = #t12;
-    else
+    if(self::A::_#finalStaticField#isSet)
       throw new _in::LateInitializationErrorImpl::•("Field 'finalStaticField' has already been initialized.");
+    else {
+      self::A::_#finalStaticField#isSet = true;
+      self::A::_#finalStaticField = #t12;
+    }
   @#C1
   static get finalStaticFieldWithInitializer() → core::int
     return let final core::int? #t13 = self::A::_#finalStaticFieldWithInitializer in #t13.==(null) ?{core::int} let final core::int #t14 = 0 in self::A::_#finalStaticFieldWithInitializer.==(null) ?{core::int} self::A::_#finalStaticFieldWithInitializer = #t14 : throw new _in::LateInitializationErrorImpl::•("Field 'finalStaticFieldWithInitializer' has been assigned during initialization.") : #t13{core::int};
 }
 abstract class B extends core::Object /*isMixinDeclaration*/  {
   field core::int? _#B#instanceField = null;
+  field core::bool _#B#instanceField#isSet = false;
   field core::int? _#B#finalInstanceField = null;
+  field core::bool _#B#finalInstanceField#isSet = false;
   field core::int? _#B#finalInstanceFieldWithInitializer = null;
+  field core::bool _#B#finalInstanceFieldWithInitializer#isSet = false;
   field core::num? _#B#covariantInstanceField = null;
+  field core::bool _#B#covariantInstanceField#isSet = false;
   static field core::int? _#staticField = null;
+  static field core::bool _#staticField#isSet = false;
   static field core::int? _#finalStaticField = null;
+  static field core::bool _#finalStaticField#isSet = false;
   static field core::int? _#finalStaticFieldWithInitializer = null;
+  static field core::bool _#finalStaticFieldWithInitializer#isSet = false;
   @#C1
   get instanceField() → core::int
-    return let final core::int? #t15 = this.{self::B::_#B#instanceField} in #t15.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'instanceField' has not been initialized.") : #t15{core::int};
+    return this.{self::B::_#B#instanceField#isSet} ?{core::int} let final core::int? #t15 = this.{self::B::_#B#instanceField} in #t15{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'instanceField' has not been initialized.");
   @#C1
-  set instanceField(core::int #t16) → void
+  set instanceField(core::int #t16) → void {
+    this.{self::B::_#B#instanceField#isSet} = true;
     this.{self::B::_#B#instanceField} = #t16;
+  }
   @#C1
   get finalInstanceField() → core::int
-    return let final core::int? #t17 = this.{self::B::_#B#finalInstanceField} in #t17.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceField' has not been initialized.") : #t17{core::int};
+    return this.{self::B::_#B#finalInstanceField#isSet} ?{core::int} let final core::int? #t17 = this.{self::B::_#B#finalInstanceField} in #t17{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceField' has not been initialized.");
   @#C1
   set finalInstanceField(core::int #t18) → void
-    if(this.{self::B::_#B#finalInstanceField}.==(null))
-      this.{self::B::_#B#finalInstanceField} = #t18;
-    else
+    if(this.{self::B::_#B#finalInstanceField#isSet})
       throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceField' has already been initialized.");
+    else {
+      this.{self::B::_#B#finalInstanceField#isSet} = true;
+      this.{self::B::_#B#finalInstanceField} = #t18;
+    }
   @#C1
   get finalInstanceFieldWithInitializer() → core::int
     return let final core::int? #t19 = this.{self::B::_#B#finalInstanceFieldWithInitializer} in #t19.==(null) ?{core::int} let final core::int #t20 = 0 in this.{self::B::_#B#finalInstanceFieldWithInitializer}.==(null) ?{core::int} this.{self::B::_#B#finalInstanceFieldWithInitializer} = #t20 : throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceFieldWithInitializer' has been assigned during initialization.") : #t19{core::int};
   @#C1
   get covariantInstanceField() → core::num
-    return let final core::num? #t21 = this.{self::B::_#B#covariantInstanceField} in #t21.==(null) ?{core::num} throw new _in::LateInitializationErrorImpl::•("Field 'covariantInstanceField' has not been initialized.") : #t21{core::num};
+    return this.{self::B::_#B#covariantInstanceField#isSet} ?{core::num} let final core::num? #t21 = this.{self::B::_#B#covariantInstanceField} in #t21{core::num} : throw new _in::LateInitializationErrorImpl::•("Field 'covariantInstanceField' has not been initialized.");
   @#C1
-  set covariantInstanceField(covariant core::num #t22) → void
+  set covariantInstanceField(covariant core::num #t22) → void {
+    this.{self::B::_#B#covariantInstanceField#isSet} = true;
     this.{self::B::_#B#covariantInstanceField} = #t22;
+  }
   @#C1
   static get staticField() → core::int
-    return let final core::int? #t23 = self::B::_#staticField in #t23.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'staticField' has not been initialized.") : #t23{core::int};
+    return self::B::_#staticField#isSet ?{core::int} let final core::int? #t23 = self::B::_#staticField in #t23{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'staticField' has not been initialized.");
   @#C1
-  static set staticField(core::int #t24) → void
+  static set staticField(core::int #t24) → void {
+    self::B::_#staticField#isSet = true;
     self::B::_#staticField = #t24;
+  }
   @#C1
   static get finalStaticField() → core::int
-    return let final core::int? #t25 = self::B::_#finalStaticField in #t25.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'finalStaticField' has not been initialized.") : #t25{core::int};
+    return self::B::_#finalStaticField#isSet ?{core::int} let final core::int? #t25 = self::B::_#finalStaticField in #t25{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'finalStaticField' has not been initialized.");
   @#C1
   static set finalStaticField(core::int #t26) → void
-    if(self::B::_#finalStaticField.==(null))
-      self::B::_#finalStaticField = #t26;
-    else
+    if(self::B::_#finalStaticField#isSet)
       throw new _in::LateInitializationErrorImpl::•("Field 'finalStaticField' has already been initialized.");
+    else {
+      self::B::_#finalStaticField#isSet = true;
+      self::B::_#finalStaticField = #t26;
+    }
   @#C1
   static get finalStaticFieldWithInitializer() → core::int
     return let final core::int? #t27 = self::B::_#finalStaticFieldWithInitializer in #t27.==(null) ?{core::int} let final core::int #t28 = 0 in self::B::_#finalStaticFieldWithInitializer.==(null) ?{core::int} self::B::_#finalStaticFieldWithInitializer = #t28 : throw new _in::LateInitializationErrorImpl::•("Field 'finalStaticFieldWithInitializer' has been assigned during initialization.") : #t27{core::int};
 }
 extension Extension on self::A {
   static field extensionStaticField = self::_#Extension|extensionStaticField;
+  static field extensionStaticField = self::_#Extension|extensionStaticField#isSet;
   static get extensionStaticField = get self::Extension|extensionStaticField;
   static set extensionStaticField = set self::Extension|extensionStaticField;
   static field finalExtensionStaticField = self::_#Extension|finalExtensionStaticField;
+  static field finalExtensionStaticField = self::_#Extension|finalExtensionStaticField#isSet;
   static get finalExtensionStaticField = get self::Extension|finalExtensionStaticField;
   static set finalExtensionStaticField = set self::Extension|finalExtensionStaticField;
   static field finalExtensionStaticFieldWithInitializer = self::_#Extension|finalExtensionStaticFieldWithInitializer;
+  static field finalExtensionStaticFieldWithInitializer = self::_#Extension|finalExtensionStaticFieldWithInitializer#isSet;
   static get finalExtensionStaticFieldWithInitializer = get self::Extension|finalExtensionStaticFieldWithInitializer;
 }
 static field core::int? _#topLevelField = null;
+static field core::bool _#topLevelField#isSet = false;
 static field core::int? _#finalTopLevelField = null;
+static field core::bool _#finalTopLevelField#isSet = false;
 static field core::int? _#finalTopLevelFieldWithInitializer = null;
+static field core::bool _#finalTopLevelFieldWithInitializer#isSet = false;
 static field core::int? _#Extension|extensionStaticField = null;
+static field core::bool _#Extension|extensionStaticField#isSet = false;
 static field core::int? _#Extension|finalExtensionStaticField = null;
+static field core::bool _#Extension|finalExtensionStaticField#isSet = false;
 static field core::int? _#Extension|finalExtensionStaticFieldWithInitializer = null;
+static field core::bool _#Extension|finalExtensionStaticFieldWithInitializer#isSet = false;
 @#C1
 static get topLevelField() → core::int
-  return let final core::int? #t29 = self::_#topLevelField in #t29.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'topLevelField' has not been initialized.") : #t29{core::int};
+  return self::_#topLevelField#isSet ?{core::int} let final core::int? #t29 = self::_#topLevelField in #t29{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'topLevelField' has not been initialized.");
 @#C1
-static set topLevelField(core::int #t30) → void
+static set topLevelField(core::int #t30) → void {
+  self::_#topLevelField#isSet = true;
   self::_#topLevelField = #t30;
+}
 @#C1
 static get finalTopLevelField() → core::int
-  return let final core::int? #t31 = self::_#finalTopLevelField in #t31.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'finalTopLevelField' has not been initialized.") : #t31{core::int};
+  return self::_#finalTopLevelField#isSet ?{core::int} let final core::int? #t31 = self::_#finalTopLevelField in #t31{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'finalTopLevelField' has not been initialized.");
 @#C1
 static set finalTopLevelField(core::int #t32) → void
-  if(self::_#finalTopLevelField.==(null))
-    self::_#finalTopLevelField = #t32;
-  else
+  if(self::_#finalTopLevelField#isSet)
     throw new _in::LateInitializationErrorImpl::•("Field 'finalTopLevelField' has already been initialized.");
+  else {
+    self::_#finalTopLevelField#isSet = true;
+    self::_#finalTopLevelField = #t32;
+  }
 @#C1
 static get finalTopLevelFieldWithInitializer() → core::int
   return let final core::int? #t33 = self::_#finalTopLevelFieldWithInitializer in #t33.==(null) ?{core::int} let final core::int #t34 = 0 in self::_#finalTopLevelFieldWithInitializer.==(null) ?{core::int} self::_#finalTopLevelFieldWithInitializer = #t34 : throw new _in::LateInitializationErrorImpl::•("Field 'finalTopLevelFieldWithInitializer' has been assigned during initialization.") : #t33{core::int};
 @#C1
 static get Extension|extensionStaticField() → core::int
-  return let final core::int? #t35 = self::_#Extension|extensionStaticField in #t35.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'extensionStaticField' has not been initialized.") : #t35{core::int};
+  return self::_#Extension|extensionStaticField#isSet ?{core::int} let final core::int? #t35 = self::_#Extension|extensionStaticField in #t35{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'extensionStaticField' has not been initialized.");
 @#C1
-static set Extension|extensionStaticField(core::int #t36) → void
+static set Extension|extensionStaticField(core::int #t36) → void {
+  self::_#Extension|extensionStaticField#isSet = true;
   self::_#Extension|extensionStaticField = #t36;
+}
 @#C1
 static get Extension|finalExtensionStaticField() → core::int
-  return let final core::int? #t37 = self::_#Extension|finalExtensionStaticField in #t37.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'finalExtensionStaticField' has not been initialized.") : #t37{core::int};
+  return self::_#Extension|finalExtensionStaticField#isSet ?{core::int} let final core::int? #t37 = self::_#Extension|finalExtensionStaticField in #t37{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'finalExtensionStaticField' has not been initialized.");
 @#C1
 static set Extension|finalExtensionStaticField(core::int #t38) → void
-  if(self::_#Extension|finalExtensionStaticField.==(null))
-    self::_#Extension|finalExtensionStaticField = #t38;
-  else
+  if(self::_#Extension|finalExtensionStaticField#isSet)
     throw new _in::LateInitializationErrorImpl::•("Field 'finalExtensionStaticField' has already been initialized.");
+  else {
+    self::_#Extension|finalExtensionStaticField#isSet = true;
+    self::_#Extension|finalExtensionStaticField = #t38;
+  }
 @#C1
 static get Extension|finalExtensionStaticFieldWithInitializer() → core::int
   return let final core::int? #t39 = self::_#Extension|finalExtensionStaticFieldWithInitializer in #t39.==(null) ?{core::int} let final core::int #t40 = 0 in self::_#Extension|finalExtensionStaticFieldWithInitializer.==(null) ?{core::int} self::_#Extension|finalExtensionStaticFieldWithInitializer = #t40 : throw new _in::LateInitializationErrorImpl::•("Field 'finalExtensionStaticFieldWithInitializer' has been assigned during initialization.") : #t39{core::int};

pkg/front_end/testcases/late_lowering/late_field_inference.dart.weak.expect

@@ -14,10 +14,17 @@ class A extends core::Object {
   synthetic constructor •() → self::A
     : super core::Object::•()
     ;
-  get nonNullableInstanceField() → core::int
-    return let final core::int? #t1 = this.{self::A::_#A#nonNullableInstanceField} in #t1.==(null) ?{core::int} this.{self::A::_#A#nonNullableInstanceField} = 0 : #t1{core::int};
-  set nonNullableInstanceField(core::int #t2) → void
+  get nonNullableInstanceField() → core::int {
+    if(!this.{self::A::_#A#nonNullableInstanceField#isSet}) {
+      this.{self::A::_#A#nonNullableInstanceField} = 0;
+      this.{self::A::_#A#nonNullableInstanceField#isSet} = true;
+    }
+    return let final core::int? #t1 = this.{self::A::_#A#nonNullableInstanceField} in #t1{core::int};
+  }
+  set nonNullableInstanceField(core::int #t2) → void {
+    this.{self::A::_#A#nonNullableInstanceField#isSet} = true;
     this.{self::A::_#A#nonNullableInstanceField} = #t2;
+  }
   get nullableInstanceField() → core::int? {
     if(!this.{self::A::_#A#nullableInstanceField#isSet}) {
       this.{self::A::_#A#nullableInstanceField} = self::method();
@@ -29,10 +36,17 @@ class A extends core::Object {
     this.{self::A::_#A#nullableInstanceField#isSet} = true;
     this.{self::A::_#A#nullableInstanceField} = #t3;
   }
-  static get nonNullableStaticField() → core::int
-    return let final core::int? #t4 = self::A::_#nonNullableStaticField in #t4.==(null) ?{core::int} self::A::_#nonNullableStaticField = 0 : #t4{core::int};
-  static set nonNullableStaticField(core::int #t5) → void
+  static get nonNullableStaticField() → core::int {
+    if(!self::A::_#nonNullableStaticField#isSet) {
+      self::A::_#nonNullableStaticField = 0;
+      self::A::_#nonNullableStaticField#isSet = true;
+    }
+    return let final core::int? #t4 = self::A::_#nonNullableStaticField in #t4{core::int};
+  }
+  static set nonNullableStaticField(core::int #t5) → void {
+    self::A::_#nonNullableStaticField#isSet = true;
     self::A::_#nonNullableStaticField = #t5;
+  }
   static get nullableStaticField() → core::int? {
     if(!self::A::_#nullableStaticField#isSet) {
       self::A::_#nullableStaticField = self::method();
@@ -62,10 +76,17 @@ static field core::int? _#nullableTopLevelField = null;
 static field core::bool _#nullableTopLevelField#isSet = false;
 static method method() → core::int?
   return null;
-static get nonNullableTopLevelField() → core::int
-  return let final core::int? #t7 = self::_#nonNullableTopLevelField in #t7.==(null) ?{core::int} self::_#nonNullableTopLevelField = 0 : #t7{core::int};
-static set nonNullableTopLevelField(core::int #t8) → void
+static get nonNullableTopLevelField() → core::int {
+  if(!self::_#nonNullableTopLevelField#isSet) {
+    self::_#nonNullableTopLevelField = 0;
+    self::_#nonNullableTopLevelField#isSet = true;
+  }
+  return let final core::int? #t7 = self::_#nonNullableTopLevelField in #t7{core::int};
+}
+static set nonNullableTopLevelField(core::int #t8) → void {
+  self::_#nonNullableTopLevelField#isSet = true;
   self::_#nonNullableTopLevelField = #t8;
+}
 static get nullableTopLevelField() → core::int? {
   if(!self::_#nullableTopLevelField#isSet) {
     self::_#nullableTopLevelField = self::method();

pkg/front_end/testcases/late_lowering/late_field_inference.dart.weak.transformed.expect

@@ -14,10 +14,17 @@ class A extends core::Object {
   synthetic constructor •() → self::A
     : super core::Object::•()
     ;
-  get nonNullableInstanceField() → core::int
-    return let final core::int? #t1 = this.{self::A::_#A#nonNullableInstanceField} in #t1.==(null) ?{core::int} this.{self::A::_#A#nonNullableInstanceField} = 0 : #t1{core::int};
-  set nonNullableInstanceField(core::int #t2) → void
+  get nonNullableInstanceField() → core::int {
+    if(!this.{self::A::_#A#nonNullableInstanceField#isSet}) {
+      this.{self::A::_#A#nonNullableInstanceField} = 0;
+      this.{self::A::_#A#nonNullableInstanceField#isSet} = true;
+    }
+    return let final core::int? #t1 = this.{self::A::_#A#nonNullableInstanceField} in #t1{core::int};
+  }
+  set nonNullableInstanceField(core::int #t2) → void {
+    this.{self::A::_#A#nonNullableInstanceField#isSet} = true;
     this.{self::A::_#A#nonNullableInstanceField} = #t2;
+  }
   get nullableInstanceField() → core::int? {
     if(!this.{self::A::_#A#nullableInstanceField#isSet}) {
       this.{self::A::_#A#nullableInstanceField} = self::method();
@@ -29,10 +36,17 @@ class A extends core::Object {
     this.{self::A::_#A#nullableInstanceField#isSet} = true;
     this.{self::A::_#A#nullableInstanceField} = #t3;
   }
-  static get nonNullableStaticField() → core::int
-    return let final core::int? #t4 = self::A::_#nonNullableStaticField in #t4.==(null) ?{core::int} self::A::_#nonNullableStaticField = 0 : #t4{core::int};
-  static set nonNullableStaticField(core::int #t5) → void
+  static get nonNullableStaticField() → core::int {
+    if(!self::A::_#nonNullableStaticField#isSet) {
+      self::A::_#nonNullableStaticField = 0;
+      self::A::_#nonNullableStaticField#isSet = true;
+    }
+    return let final core::int? #t4 = self::A::_#nonNullableStaticField in #t4{core::int};
+  }
+  static set nonNullableStaticField(core::int #t5) → void {
+    self::A::_#nonNullableStaticField#isSet = true;
     self::A::_#nonNullableStaticField = #t5;
+  }
   static get nullableStaticField() → core::int? {
     if(!self::A::_#nullableStaticField#isSet) {
       self::A::_#nullableStaticField = self::method();
@@ -62,10 +76,17 @@ static field core::int? _#nullableTopLevelField = null;
 static field core::bool _#nullableTopLevelField#isSet = false;
 static method method() → core::int?
   return null;
-static get nonNullableTopLevelField() → core::int
-  return let final core::int? #t7 = self::_#nonNullableTopLevelField in #t7.==(null) ?{core::int} self::_#nonNullableTopLevelField = 0 : #t7{core::int};
-static set nonNullableTopLevelField(core::int #t8) → void
+static get nonNullableTopLevelField() → core::int {
+  if(!self::_#nonNullableTopLevelField#isSet) {
+    self::_#nonNullableTopLevelField = 0;
+    self::_#nonNullableTopLevelField#isSet = true;
+  }
+  return let final core::int? #t7 = self::_#nonNullableTopLevelField in #t7{core::int};
+}
+static set nonNullableTopLevelField(core::int #t8) → void {
+  self::_#nonNullableTopLevelField#isSet = true;
   self::_#nonNullableTopLevelField = #t8;
+}
 static get nullableTopLevelField() → core::int? {
   if(!self::_#nullableTopLevelField#isSet) {
     self::_#nullableTopLevelField = self::method();

pkg/front_end/testcases/late_lowering/late_field_with_initializer.dart.weak.expect

@@ -4,8 +4,11 @@ import "dart:core" as core;
 
 class Class<T extends core::Object? = dynamic> extends core::Object {
   static field core::int? _#lateStaticField1 = null;
+  static field core::bool _#lateStaticField1#isSet = false;
   static field core::int? _#lateStaticField2 = null;
+  static field core::bool _#lateStaticField2#isSet = false;
   field core::int? _#Class#lateInstanceField = null;
+  field core::bool _#Class#lateInstanceField#isSet = false;
   final field self::Class::T% field;
   generic-covariant-impl field self::Class::T? _#Class#lateGenericField1 = null;
   field core::bool _#Class#lateGenericField1#isSet = false;
@@ -14,23 +17,44 @@ class Class<T extends core::Object? = dynamic> extends core::Object {
   constructor •(self::Class::T% field) → self::Class<self::Class::T%>
     : self::Class::field = field, super core::Object::•()
     ;
-  static get lateStaticField1() → core::int
-    return let final core::int? #t1 = self::Class::_#lateStaticField1 in #t1.==(null) ?{core::int} self::Class::_#lateStaticField1 = 87 : #t1{core::int};
-  static set lateStaticField1(core::int #t2) → void
+  static get lateStaticField1() → core::int {
+    if(!self::Class::_#lateStaticField1#isSet) {
+      self::Class::_#lateStaticField1 = 87;
+      self::Class::_#lateStaticField1#isSet = true;
+    }
+    return let final core::int? #t1 = self::Class::_#lateStaticField1 in #t1{core::int};
+  }
+  static set lateStaticField1(core::int #t2) → void {
+    self::Class::_#lateStaticField1#isSet = true;
     self::Class::_#lateStaticField1 = #t2;
-  static get lateStaticField2() → core::int
-    return let final core::int? #t3 = self::Class::_#lateStaticField2 in #t3.==(null) ?{core::int} self::Class::_#lateStaticField2 = 42 : #t3{core::int};
-  static set lateStaticField2(core::int #t4) → void
+  }
+  static get lateStaticField2() → core::int {
+    if(!self::Class::_#lateStaticField2#isSet) {
+      self::Class::_#lateStaticField2 = 42;
+      self::Class::_#lateStaticField2#isSet = true;
+    }
+    return let final core::int? #t3 = self::Class::_#lateStaticField2 in #t3{core::int};
+  }
+  static set lateStaticField2(core::int #t4) → void {
+    self::Class::_#lateStaticField2#isSet = true;
     self::Class::_#lateStaticField2 = #t4;
+  }
   static method staticMethod() → dynamic {
     self::expect(42, self::Class::lateStaticField2);
     self::Class::lateStaticField2 = 43;
     self::expect(43, self::Class::lateStaticField2);
   }
-  get lateInstanceField() → core::int
-    return let final core::int? #t5 = this.{self::Class::_#Class#lateInstanceField} in #t5.==(null) ?{core::int} this.{self::Class::_#Class#lateInstanceField} = 16 : #t5{core::int};
-  set lateInstanceField(core::int #t6) → void
+  get lateInstanceField() → core::int {
+    if(!this.{self::Class::_#Class#lateInstanceField#isSet}) {
+      this.{self::Class::_#Class#lateInstanceField} = 16;
+      this.{self::Class::_#Class#lateInstanceField#isSet} = true;
+    }
+    return let final core::int? #t5 = this.{self::Class::_#Class#lateInstanceField} in #t5{core::int};
+  }
+  set lateInstanceField(core::int #t6) → void {
+    this.{self::Class::_#Class#lateInstanceField#isSet} = true;
     this.{self::Class::_#Class#lateInstanceField} = #t6;
+  }
   get lateGenericField1() → self::Class::T% {
     if(!this.{self::Class::_#Class#lateGenericField1#isSet}) {
       this.{self::Class::_#Class#lateGenericField1} = this.{self::Class::field};
@@ -66,28 +90,54 @@ class Class<T extends core::Object? = dynamic> extends core::Object {
 }
 extension Extension<T extends core::Object? = dynamic> on self::Class<T%> {
   static field lateExtensionField1 = self::_#Extension|lateExtensionField1;
+  static field lateExtensionField1 = self::_#Extension|lateExtensionField1#isSet;
   static get lateExtensionField1 = get self::Extension|lateExtensionField1;
   static set lateExtensionField1 = set self::Extension|lateExtensionField1;
   static field lateExtensionField2 = self::_#Extension|lateExtensionField2;
+  static field lateExtensionField2 = self::_#Extension|lateExtensionField2#isSet;
   static get lateExtensionField2 = get self::Extension|lateExtensionField2;
   static set lateExtensionField2 = set self::Extension|lateExtensionField2;
   static method staticMethod = self::Extension|staticMethod;
 }
 static field core::int? _#lateTopLevelField1 = null;
+static field core::bool _#lateTopLevelField1#isSet = false;
 static field core::int? _#Extension|lateExtensionField1 = null;
+static field core::bool _#Extension|lateExtensionField1#isSet = false;
 static field core::int? _#Extension|lateExtensionField2 = null;
-static get lateTopLevelField1() → core::int
-  return let final core::int? #t11 = self::_#lateTopLevelField1 in #t11.==(null) ?{core::int} self::_#lateTopLevelField1 = 123 : #t11{core::int};
-static set lateTopLevelField1(core::int #t12) → void
+static field core::bool _#Extension|lateExtensionField2#isSet = false;
+static get lateTopLevelField1() → core::int {
+  if(!self::_#lateTopLevelField1#isSet) {
+    self::_#lateTopLevelField1 = 123;
+    self::_#lateTopLevelField1#isSet = true;
+  }
+  return let final core::int? #t11 = self::_#lateTopLevelField1 in #t11{core::int};
+}
+static set lateTopLevelField1(core::int #t12) → void {
+  self::_#lateTopLevelField1#isSet = true;
   self::_#lateTopLevelField1 = #t12;
-static get Extension|lateExtensionField1() → core::int
-  return let final core::int? #t13 = self::_#Extension|lateExtensionField1 in #t13.==(null) ?{core::int} self::_#Extension|lateExtensionField1 = 87 : #t13{core::int};
-static set Extension|lateExtensionField1(core::int #t14) → void
+}
+static get Extension|lateExtensionField1() → core::int {
+  if(!self::_#Extension|lateExtensionField1#isSet) {
+    self::_#Extension|lateExtensionField1 = 87;
+    self::_#Extension|lateExtensionField1#isSet = true;
+  }
+  return let final core::int? #t13 = self::_#Extension|lateExtensionField1 in #t13{core::int};
+}
+static set Extension|lateExtensionField1(core::int #t14) → void {
+  self::_#Extension|lateExtensionField1#isSet = true;
   self::_#Extension|lateExtensionField1 = #t14;
-static get Extension|lateExtensionField2() → core::int
-  return let final core::int? #t15 = self::_#Extension|lateExtensionField2 in #t15.==(null) ?{core::int} self::_#Extension|lateExtensionField2 = 42 : #t15{core::int};
-static set Extension|lateExtensionField2(core::int #t16) → void
+}
+static get Extension|lateExtensionField2() → core::int {
+  if(!self::_#Extension|lateExtensionField2#isSet) {
+    self::_#Extension|lateExtensionField2 = 42;
+    self::_#Extension|lateExtensionField2#isSet = true;
+  }
+  return let final core::int? #t15 = self::_#Extension|lateExtensionField2 in #t15{core::int};
+}
+static set Extension|lateExtensionField2(core::int #t16) → void {
+  self::_#Extension|lateExtensionField2#isSet = true;
   self::_#Extension|lateExtensionField2 = #t16;
+}
 static method Extension|staticMethod() → dynamic {
   self::expect(42, self::Extension|lateExtensionField2);
   self::Extension|lateExtensionField2 = 43;

pkg/front_end/testcases/late_lowering/late_field_with_initializer.dart.weak.transformed.expect

@@ -4,8 +4,11 @@ import "dart:core" as core;
 
 class Class<T extends core::Object? = dynamic> extends core::Object {
   static field core::int? _#lateStaticField1 = null;
+  static field core::bool _#lateStaticField1#isSet = false;
   static field core::int? _#lateStaticField2 = null;
+  static field core::bool _#lateStaticField2#isSet = false;
   field core::int? _#Class#lateInstanceField = null;
+  field core::bool _#Class#lateInstanceField#isSet = false;
   final field self::Class::T% field;
   generic-covariant-impl field self::Class::T? _#Class#lateGenericField1 = null;
   field core::bool _#Class#lateGenericField1#isSet = false;
@@ -14,23 +17,44 @@ class Class<T extends core::Object? = dynamic> extends core::Object {
   constructor •(self::Class::T% field) → self::Class<self::Class::T%>
     : self::Class::field = field, super core::Object::•()
     ;
-  static get lateStaticField1() → core::int
-    return let final core::int? #t1 = self::Class::_#lateStaticField1 in #t1.==(null) ?{core::int} self::Class::_#lateStaticField1 = 87 : #t1{core::int};
-  static set lateStaticField1(core::int #t2) → void
+  static get lateStaticField1() → core::int {
+    if(!self::Class::_#lateStaticField1#isSet) {
+      self::Class::_#lateStaticField1 = 87;
+      self::Class::_#lateStaticField1#isSet = true;
+    }
+    return let final core::int? #t1 = self::Class::_#lateStaticField1 in #t1{core::int};
+  }
+  static set lateStaticField1(core::int #t2) → void {
+    self::Class::_#lateStaticField1#isSet = true;
     self::Class::_#lateStaticField1 = #t2;
-  static get lateStaticField2() → core::int
-    return let final core::int? #t3 = self::Class::_#lateStaticField2 in #t3.==(null) ?{core::int} self::Class::_#lateStaticField2 = 42 : #t3{core::int};
-  static set lateStaticField2(core::int #t4) → void
+  }
+  static get lateStaticField2() → core::int {
+    if(!self::Class::_#lateStaticField2#isSet) {
+      self::Class::_#lateStaticField2 = 42;
+      self::Class::_#lateStaticField2#isSet = true;
+    }
+    return let final core::int? #t3 = self::Class::_#lateStaticField2 in #t3{core::int};
+  }
+  static set lateStaticField2(core::int #t4) → void {
+    self::Class::_#lateStaticField2#isSet = true;
     self::Class::_#lateStaticField2 = #t4;
+  }
   static method staticMethod() → dynamic {
     self::expect(42, self::Class::lateStaticField2);
     self::Class::lateStaticField2 = 43;
     self::expect(43, self::Class::lateStaticField2);
   }
-  get lateInstanceField() → core::int
-    return let final core::int? #t5 = this.{self::Class::_#Class#lateInstanceField} in #t5.==(null) ?{core::int} this.{self::Class::_#Class#lateInstanceField} = 16 : #t5{core::int};
-  set lateInstanceField(core::int #t6) → void
+  get lateInstanceField() → core::int {
+    if(!this.{self::Class::_#Class#lateInstanceField#isSet}) {
+      this.{self::Class::_#Class#lateInstanceField} = 16;
+      this.{self::Class::_#Class#lateInstanceField#isSet} = true;
+    }
+    return let final core::int? #t5 = this.{self::Class::_#Class#lateInstanceField} in #t5{core::int};
+  }
+  set lateInstanceField(core::int #t6) → void {
+    this.{self::Class::_#Class#lateInstanceField#isSet} = true;
     this.{self::Class::_#Class#lateInstanceField} = #t6;
+  }
   get lateGenericField1() → self::Class::T% {
     if(!this.{self::Class::_#Class#lateGenericField1#isSet}) {
       this.{self::Class::_#Class#lateGenericField1} = this.{self::Class::field};
@@ -66,28 +90,54 @@ class Class<T extends core::Object? = dynamic> extends core::Object {
 }
 extension Extension<T extends core::Object? = dynamic> on self::Class<T%> {
   static field lateExtensionField1 = self::_#Extension|lateExtensionField1;
+  static field lateExtensionField1 = self::_#Extension|lateExtensionField1#isSet;
   static get lateExtensionField1 = get self::Extension|lateExtensionField1;
   static set lateExtensionField1 = set self::Extension|lateExtensionField1;
   static field lateExtensionField2 = self::_#Extension|lateExtensionField2;
+  static field lateExtensionField2 = self::_#Extension|lateExtensionField2#isSet;
   static get lateExtensionField2 = get self::Extension|lateExtensionField2;
   static set lateExtensionField2 = set self::Extension|lateExtensionField2;
   static method staticMethod = self::Extension|staticMethod;
 }
 static field core::int? _#lateTopLevelField1 = null;
+static field core::bool _#lateTopLevelField1#isSet = false;
 static field core::int? _#Extension|lateExtensionField1 = null;
+static field core::bool _#Extension|lateExtensionField1#isSet = false;
 static field core::int? _#Extension|lateExtensionField2 = null;
-static get lateTopLevelField1() → core::int
-  return let final core::int? #t11 = self::_#lateTopLevelField1 in #t11.==(null) ?{core::int} self::_#lateTopLevelField1 = 123 : #t11{core::int};
-static set lateTopLevelField1(core::int #t12) → void
+static field core::bool _#Extension|lateExtensionField2#isSet = false;
+static get lateTopLevelField1() → core::int {
+  if(!self::_#lateTopLevelField1#isSet) {
+    self::_#lateTopLevelField1 = 123;
+    self::_#lateTopLevelField1#isSet = true;
+  }
+  return let final core::int? #t11 = self::_#lateTopLevelField1 in #t11{core::int};
+}
+static set lateTopLevelField1(core::int #t12) → void {
+  self::_#lateTopLevelField1#isSet = true;
   self::_#lateTopLevelField1 = #t12;
-static get Extension|lateExtensionField1() → core::int
-  return let final core::int? #t13 = self::_#Extension|lateExtensionField1 in #t13.==(null) ?{core::int} self::_#Extension|lateExtensionField1 = 87 : #t13{core::int};
-static set Extension|lateExtensionField1(core::int #t14) → void
+}
+static get Extension|lateExtensionField1() → core::int {
+  if(!self::_#Extension|lateExtensionField1#isSet) {
+    self::_#Extension|lateExtensionField1 = 87;
+    self::_#Extension|lateExtensionField1#isSet = true;
+  }
+  return let final core::int? #t13 = self::_#Extension|lateExtensionField1 in #t13{core::int};
+}
+static set Extension|lateExtensionField1(core::int #t14) → void {
+  self::_#Extension|lateExtensionField1#isSet = true;
   self::_#Extension|lateExtensionField1 = #t14;
-static get Extension|lateExtensionField2() → core::int
-  return let final core::int? #t15 = self::_#Extension|lateExtensionField2 in #t15.==(null) ?{core::int} self::_#Extension|lateExtensionField2 = 42 : #t15{core::int};
-static set Extension|lateExtensionField2(core::int #t16) → void
+}
+static get Extension|lateExtensionField2() → core::int {
+  if(!self::_#Extension|lateExtensionField2#isSet) {
+    self::_#Extension|lateExtensionField2 = 42;
+    self::_#Extension|lateExtensionField2#isSet = true;
+  }
+  return let final core::int? #t15 = self::_#Extension|lateExtensionField2 in #t15{core::int};
+}
+static set Extension|lateExtensionField2(core::int #t16) → void {
+  self::_#Extension|lateExtensionField2#isSet = true;
   self::_#Extension|lateExtensionField2 = #t16;
+}
 static method Extension|staticMethod() → dynamic {
   self::expect(42, self::Extension|lateExtensionField2);
   self::Extension|lateExtensionField2 = 43;

pkg/front_end/testcases/late_lowering/late_field_without_initializer.dart.weak.expect

@@ -5,30 +5,39 @@ import "dart:_internal" as _in;
 
 class Class<T extends core::Object? = dynamic> extends core::Object {
   static field core::int? _#lateStaticField1 = null;
+  static field core::bool _#lateStaticField1#isSet = false;
   static field core::int? _#lateStaticField2 = null;
+  static field core::bool _#lateStaticField2#isSet = false;
   field core::int? _#Class#lateInstanceField = null;
+  field core::bool _#Class#lateInstanceField#isSet = false;
   generic-covariant-impl field self::Class::T? _#Class#lateGenericInstanceField = null;
   field core::bool _#Class#lateGenericInstanceField#isSet = false;
   synthetic constructor •() → self::Class<self::Class::T%>
     : super core::Object::•()
     ;
   static get lateStaticField1() → core::int
-    return let final core::int? #t1 = self::Class::_#lateStaticField1 in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateStaticField1' has not been initialized.") : #t1{core::int};
-  static set lateStaticField1(core::int #t2) → void
+    return self::Class::_#lateStaticField1#isSet ?{core::int} let final core::int? #t1 = self::Class::_#lateStaticField1 in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateStaticField1' has not been initialized.");
+  static set lateStaticField1(core::int #t2) → void {
+    self::Class::_#lateStaticField1#isSet = true;
     self::Class::_#lateStaticField1 = #t2;
+  }
   static get lateStaticField2() → core::int
-    return let final core::int? #t3 = self::Class::_#lateStaticField2 in #t3.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateStaticField2' has not been initialized.") : #t3{core::int};
-  static set lateStaticField2(core::int #t4) → void
+    return self::Class::_#lateStaticField2#isSet ?{core::int} let final core::int? #t3 = self::Class::_#lateStaticField2 in #t3{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateStaticField2' has not been initialized.");
+  static set lateStaticField2(core::int #t4) → void {
+    self::Class::_#lateStaticField2#isSet = true;
     self::Class::_#lateStaticField2 = #t4;
+  }
   static method staticMethod() → dynamic {
     self::throws(() → core::int => self::Class::lateStaticField2, "Read value from uninitialized Class.lateStaticField2");
     self::Class::lateStaticField2 = 42;
     self::expect(42, self::Class::lateStaticField2);
   }
   get lateInstanceField() → core::int
-    return let final core::int? #t5 = this.{self::Class::_#Class#lateInstanceField} in #t5.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateInstanceField' has not been initialized.") : #t5{core::int};
-  set lateInstanceField(core::int #t6) → void
+    return this.{self::Class::_#Class#lateInstanceField#isSet} ?{core::int} let final core::int? #t5 = this.{self::Class::_#Class#lateInstanceField} in #t5{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateInstanceField' has not been initialized.");
+  set lateInstanceField(core::int #t6) → void {
+    this.{self::Class::_#Class#lateInstanceField#isSet} = true;
     this.{self::Class::_#Class#lateInstanceField} = #t6;
+  }
   get lateGenericInstanceField() → self::Class::T%
     return this.{self::Class::_#Class#lateGenericInstanceField#isSet} ?{self::Class::T%} let final self::Class::T? #t7 = this.{self::Class::_#Class#lateGenericInstanceField} in #t7{self::Class::T%} : throw new _in::LateInitializationErrorImpl::•("Field 'lateGenericInstanceField' has not been initialized.");
   set lateGenericInstanceField(generic-covariant-impl self::Class::T% #t8) → void {
@@ -46,28 +55,39 @@ class Class<T extends core::Object? = dynamic> extends core::Object {
 }
 extension Extension<T extends core::Object? = dynamic> on self::Class<T%> {
   static field lateExtensionField1 = self::_#Extension|lateExtensionField1;
+  static field lateExtensionField1 = self::_#Extension|lateExtensionField1#isSet;
   static get lateExtensionField1 = get self::Extension|lateExtensionField1;
   static set lateExtensionField1 = set self::Extension|lateExtensionField1;
   static field lateExtensionField2 = self::_#Extension|lateExtensionField2;
+  static field lateExtensionField2 = self::_#Extension|lateExtensionField2#isSet;
   static get lateExtensionField2 = get self::Extension|lateExtensionField2;
   static set lateExtensionField2 = set self::Extension|lateExtensionField2;
   static method staticMethod = self::Extension|staticMethod;
 }
 static field core::int? _#lateTopLevelField = null;
+static field core::bool _#lateTopLevelField#isSet = false;
 static field core::int? _#Extension|lateExtensionField1 = null;
+static field core::bool _#Extension|lateExtensionField1#isSet = false;
 static field core::int? _#Extension|lateExtensionField2 = null;
+static field core::bool _#Extension|lateExtensionField2#isSet = false;
 static get lateTopLevelField() → core::int
-  return let final core::int? #t9 = self::_#lateTopLevelField in #t9.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateTopLevelField' has not been initialized.") : #t9{core::int};
-static set lateTopLevelField(core::int #t10) → void
+  return self::_#lateTopLevelField#isSet ?{core::int} let final core::int? #t9 = self::_#lateTopLevelField in #t9{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateTopLevelField' has not been initialized.");
+static set lateTopLevelField(core::int #t10) → void {
+  self::_#lateTopLevelField#isSet = true;
   self::_#lateTopLevelField = #t10;
+}
 static get Extension|lateExtensionField1() → core::int
-  return let final core::int? #t11 = self::_#Extension|lateExtensionField1 in #t11.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateExtensionField1' has not been initialized.") : #t11{core::int};
-static set Extension|lateExtensionField1(core::int #t12) → void
+  return self::_#Extension|lateExtensionField1#isSet ?{core::int} let final core::int? #t11 = self::_#Extension|lateExtensionField1 in #t11{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateExtensionField1' has not been initialized.");
+static set Extension|lateExtensionField1(core::int #t12) → void {
+  self::_#Extension|lateExtensionField1#isSet = true;
   self::_#Extension|lateExtensionField1 = #t12;
+}
 static get Extension|lateExtensionField2() → core::int
-  return let final core::int? #t13 = self::_#Extension|lateExtensionField2 in #t13.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateExtensionField2' has not been initialized.") : #t13{core::int};
-static set Extension|lateExtensionField2(core::int #t14) → void
+  return self::_#Extension|lateExtensionField2#isSet ?{core::int} let final core::int? #t13 = self::_#Extension|lateExtensionField2 in #t13{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateExtensionField2' has not been initialized.");
+static set Extension|lateExtensionField2(core::int #t14) → void {
+  self::_#Extension|lateExtensionField2#isSet = true;
   self::_#Extension|lateExtensionField2 = #t14;
+}
 static method Extension|staticMethod() → dynamic {
   self::throws(() → core::int => self::Extension|lateExtensionField2, "Read value from uninitialized Class.lateExtensionField2");
   self::Extension|lateExtensionField2 = 42;

pkg/front_end/testcases/late_lowering/late_field_without_initializer.dart.weak.transformed.expect

@@ -5,30 +5,39 @@ import "dart:_internal" as _in;
 
 class Class<T extends core::Object? = dynamic> extends core::Object {
   static field core::int? _#lateStaticField1 = null;
+  static field core::bool _#lateStaticField1#isSet = false;
   static field core::int? _#lateStaticField2 = null;
+  static field core::bool _#lateStaticField2#isSet = false;
   field core::int? _#Class#lateInstanceField = null;
+  field core::bool _#Class#lateInstanceField#isSet = false;
   generic-covariant-impl field self::Class::T? _#Class#lateGenericInstanceField = null;
   field core::bool _#Class#lateGenericInstanceField#isSet = false;
   synthetic constructor •() → self::Class<self::Class::T%>
     : super core::Object::•()
     ;
   static get lateStaticField1() → core::int
-    return let final core::int? #t1 = self::Class::_#lateStaticField1 in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateStaticField1' has not been initialized.") : #t1{core::int};
-  static set lateStaticField1(core::int #t2) → void
+    return self::Class::_#lateStaticField1#isSet ?{core::int} let final core::int? #t1 = self::Class::_#lateStaticField1 in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateStaticField1' has not been initialized.");
+  static set lateStaticField1(core::int #t2) → void {
+    self::Class::_#lateStaticField1#isSet = true;
     self::Class::_#lateStaticField1 = #t2;
+  }
   static get lateStaticField2() → core::int
-    return let final core::int? #t3 = self::Class::_#lateStaticField2 in #t3.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateStaticField2' has not been initialized.") : #t3{core::int};
-  static set lateStaticField2(core::int #t4) → void
+    return self::Class::_#lateStaticField2#isSet ?{core::int} let final core::int? #t3 = self::Class::_#lateStaticField2 in #t3{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateStaticField2' has not been initialized.");
+  static set lateStaticField2(core::int #t4) → void {
+    self::Class::_#lateStaticField2#isSet = true;
     self::Class::_#lateStaticField2 = #t4;
+  }
   static method staticMethod() → dynamic {
     self::throws(() → core::int => self::Class::lateStaticField2, "Read value from uninitialized Class.lateStaticField2");
     self::Class::lateStaticField2 = 42;
     self::expect(42, self::Class::lateStaticField2);
   }
   get lateInstanceField() → core::int
-    return let final core::int? #t5 = this.{self::Class::_#Class#lateInstanceField} in #t5.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateInstanceField' has not been initialized.") : #t5{core::int};
-  set lateInstanceField(core::int #t6) → void
+    return this.{self::Class::_#Class#lateInstanceField#isSet} ?{core::int} let final core::int? #t5 = this.{self::Class::_#Class#lateInstanceField} in #t5{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateInstanceField' has not been initialized.");
+  set lateInstanceField(core::int #t6) → void {
+    this.{self::Class::_#Class#lateInstanceField#isSet} = true;
     this.{self::Class::_#Class#lateInstanceField} = #t6;
+  }
   get lateGenericInstanceField() → self::Class::T%
     return this.{self::Class::_#Class#lateGenericInstanceField#isSet} ?{self::Class::T%} let final self::Class::T? #t7 = this.{self::Class::_#Class#lateGenericInstanceField} in #t7{self::Class::T%} : throw new _in::LateInitializationErrorImpl::•("Field 'lateGenericInstanceField' has not been initialized.");
   set lateGenericInstanceField(generic-covariant-impl self::Class::T% #t8) → void {
@@ -46,28 +55,39 @@ class Class<T extends core::Object? = dynamic> extends core::Object {
 }
 extension Extension<T extends core::Object? = dynamic> on self::Class<T%> {
   static field lateExtensionField1 = self::_#Extension|lateExtensionField1;
+  static field lateExtensionField1 = self::_#Extension|lateExtensionField1#isSet;
   static get lateExtensionField1 = get self::Extension|lateExtensionField1;
   static set lateExtensionField1 = set self::Extension|lateExtensionField1;
   static field lateExtensionField2 = self::_#Extension|lateExtensionField2;
+  static field lateExtensionField2 = self::_#Extension|lateExtensionField2#isSet;
   static get lateExtensionField2 = get self::Extension|lateExtensionField2;
   static set lateExtensionField2 = set self::Extension|lateExtensionField2;
   static method staticMethod = self::Extension|staticMethod;
 }
 static field core::int? _#lateTopLevelField = null;
+static field core::bool _#lateTopLevelField#isSet = false;
 static field core::int? _#Extension|lateExtensionField1 = null;
+static field core::bool _#Extension|lateExtensionField1#isSet = false;
 static field core::int? _#Extension|lateExtensionField2 = null;
+static field core::bool _#Extension|lateExtensionField2#isSet = false;
 static get lateTopLevelField() → core::int
-  return let final core::int? #t9 = self::_#lateTopLevelField in #t9.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateTopLevelField' has not been initialized.") : #t9{core::int};
-static set lateTopLevelField(core::int #t10) → void
+  return self::_#lateTopLevelField#isSet ?{core::int} let final core::int? #t9 = self::_#lateTopLevelField in #t9{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateTopLevelField' has not been initialized.");
+static set lateTopLevelField(core::int #t10) → void {
+  self::_#lateTopLevelField#isSet = true;
   self::_#lateTopLevelField = #t10;
+}
 static get Extension|lateExtensionField1() → core::int
-  return let final core::int? #t11 = self::_#Extension|lateExtensionField1 in #t11.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateExtensionField1' has not been initialized.") : #t11{core::int};
-static set Extension|lateExtensionField1(core::int #t12) → void
+  return self::_#Extension|lateExtensionField1#isSet ?{core::int} let final core::int? #t11 = self::_#Extension|lateExtensionField1 in #t11{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateExtensionField1' has not been initialized.");
+static set Extension|lateExtensionField1(core::int #t12) → void {
+  self::_#Extension|lateExtensionField1#isSet = true;
   self::_#Extension|lateExtensionField1 = #t12;
+}
 static get Extension|lateExtensionField2() → core::int
-  return let final core::int? #t13 = self::_#Extension|lateExtensionField2 in #t13.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateExtensionField2' has not been initialized.") : #t13{core::int};
-static set Extension|lateExtensionField2(core::int #t14) → void
+  return self::_#Extension|lateExtensionField2#isSet ?{core::int} let final core::int? #t13 = self::_#Extension|lateExtensionField2 in #t13{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateExtensionField2' has not been initialized.");
+static set Extension|lateExtensionField2(core::int #t14) → void {
+  self::_#Extension|lateExtensionField2#isSet = true;
   self::_#Extension|lateExtensionField2 = #t14;
+}
 static method Extension|staticMethod() → dynamic {
   self::throws(() → core::int => self::Extension|lateExtensionField2, "Read value from uninitialized Class.lateExtensionField2");
   self::Extension|lateExtensionField2 = 42;

pkg/front_end/testcases/late_lowering/late_final_field_with_initializer.dart.weak.expect

@@ -23,10 +23,13 @@ class C extends self::B {
 class Class<T extends core::Object? = dynamic> extends core::Object {
   static field core::int? lateStaticField1Init = null;
   static field core::int? _#lateStaticField1 = null;
+  static field core::bool _#lateStaticField1#isSet = false;
   static field core::int? lateStaticField2Init = null;
   static field core::int? _#lateStaticField2 = null;
+  static field core::bool _#lateStaticField2#isSet = false;
   field core::int? lateInstanceFieldInit = null;
   field core::int? _#Class#lateInstanceField = null;
+  field core::bool _#Class#lateInstanceField#isSet = false;
   generic-covariant-impl field self::Class::T? lateGenericFieldInit = null;
   final field self::Class::T% field;
   field self::Class::T? _#Class#lateGenericField = null;
@@ -80,19 +83,24 @@ extension Extension<T extends core::Object? = dynamic> on self::Class<T%> {
   static field lateExtensionField1Init = self::Extension|lateExtensionField1Init;
   static method initLateExtensionField1 = self::Extension|initLateExtensionField1;
   static field lateExtensionField1 = self::_#Extension|lateExtensionField1;
+  static field lateExtensionField1 = self::_#Extension|lateExtensionField1#isSet;
   static get lateExtensionField1 = get self::Extension|lateExtensionField1;
   static field lateExtensionField2Init = self::Extension|lateExtensionField2Init;
   static method initLateExtensionField2 = self::Extension|initLateExtensionField2;
   static field lateExtensionField2 = self::_#Extension|lateExtensionField2;
+  static field lateExtensionField2 = self::_#Extension|lateExtensionField2#isSet;
   static get lateExtensionField2 = get self::Extension|lateExtensionField2;
   static method staticMethod = self::Extension|staticMethod;
 }
 static field core::int? lateTopLevelField1Init;
 static field core::int? _#lateTopLevelField1 = null;
+static field core::bool _#lateTopLevelField1#isSet = false;
 static field core::int? Extension|lateExtensionField1Init;
 static field core::int? _#Extension|lateExtensionField1 = null;
+static field core::bool _#Extension|lateExtensionField1#isSet = false;
 static field core::int? Extension|lateExtensionField2Init;
 static field core::int? _#Extension|lateExtensionField2 = null;
+static field core::bool _#Extension|lateExtensionField2#isSet = false;
 static method initLateTopLevelField1(core::int value) → core::int {
   return self::lateTopLevelField1Init = value;
 }

pkg/front_end/testcases/late_lowering/late_final_field_with_initializer.dart.weak.transformed.expect

@@ -23,10 +23,13 @@ class C extends self::B {
 class Class<T extends core::Object? = dynamic> extends core::Object {
   static field core::int? lateStaticField1Init = null;
   static field core::int? _#lateStaticField1 = null;
+  static field core::bool _#lateStaticField1#isSet = false;
   static field core::int? lateStaticField2Init = null;
   static field core::int? _#lateStaticField2 = null;
+  static field core::bool _#lateStaticField2#isSet = false;
   field core::int? lateInstanceFieldInit = null;
   field core::int? _#Class#lateInstanceField = null;
+  field core::bool _#Class#lateInstanceField#isSet = false;
   generic-covariant-impl field self::Class::T? lateGenericFieldInit = null;
   final field self::Class::T% field;
   field self::Class::T? _#Class#lateGenericField = null;
@@ -80,19 +83,24 @@ extension Extension<T extends core::Object? = dynamic> on self::Class<T%> {
   static field lateExtensionField1Init = self::Extension|lateExtensionField1Init;
   static method initLateExtensionField1 = self::Extension|initLateExtensionField1;
   static field lateExtensionField1 = self::_#Extension|lateExtensionField1;
+  static field lateExtensionField1 = self::_#Extension|lateExtensionField1#isSet;
   static get lateExtensionField1 = get self::Extension|lateExtensionField1;
   static field lateExtensionField2Init = self::Extension|lateExtensionField2Init;
   static method initLateExtensionField2 = self::Extension|initLateExtensionField2;
   static field lateExtensionField2 = self::_#Extension|lateExtensionField2;
+  static field lateExtensionField2 = self::_#Extension|lateExtensionField2#isSet;
   static get lateExtensionField2 = get self::Extension|lateExtensionField2;
   static method staticMethod = self::Extension|staticMethod;
 }
 static field core::int? lateTopLevelField1Init;
 static field core::int? _#lateTopLevelField1 = null;
+static field core::bool _#lateTopLevelField1#isSet = false;
 static field core::int? Extension|lateExtensionField1Init;
 static field core::int? _#Extension|lateExtensionField1 = null;
+static field core::bool _#Extension|lateExtensionField1#isSet = false;
 static field core::int? Extension|lateExtensionField2Init;
 static field core::int? _#Extension|lateExtensionField2 = null;
+static field core::bool _#Extension|lateExtensionField2#isSet = false;
 static method initLateTopLevelField1(core::int value) → core::int {
   return self::lateTopLevelField1Init = value;
 }

pkg/front_end/testcases/late_lowering/late_final_field_without_initializer.dart.weak.expect

@@ -5,25 +5,32 @@ import "dart:_internal" as _in;
 
 class Class extends core::Object {
   static field core::int? _#lateStaticField1 = null;
+  static field core::bool _#lateStaticField1#isSet = false;
   static field core::int? _#lateStaticField2 = null;
+  static field core::bool _#lateStaticField2#isSet = false;
   field core::int? _#Class#lateInstanceField = null;
+  field core::bool _#Class#lateInstanceField#isSet = false;
   synthetic constructor •() → self::Class
     : super core::Object::•()
     ;
   static get lateStaticField1() → core::int
-    return let final core::int? #t1 = self::Class::_#lateStaticField1 in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateStaticField1' has not been initialized.") : #t1{core::int};
+    return self::Class::_#lateStaticField1#isSet ?{core::int} let final core::int? #t1 = self::Class::_#lateStaticField1 in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateStaticField1' has not been initialized.");
   static set lateStaticField1(core::int #t2) → void
-    if(self::Class::_#lateStaticField1.==(null))
-      self::Class::_#lateStaticField1 = #t2;
-    else
+    if(self::Class::_#lateStaticField1#isSet)
       throw new _in::LateInitializationErrorImpl::•("Field 'lateStaticField1' has already been initialized.");
+    else {
+      self::Class::_#lateStaticField1#isSet = true;
+      self::Class::_#lateStaticField1 = #t2;
+    }
   static get lateStaticField2() → core::int
-    return let final core::int? #t3 = self::Class::_#lateStaticField2 in #t3.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateStaticField2' has not been initialized.") : #t3{core::int};
+    return self::Class::_#lateStaticField2#isSet ?{core::int} let final core::int? #t3 = self::Class::_#lateStaticField2 in #t3{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateStaticField2' has not been initialized.");
   static set lateStaticField2(core::int #t4) → void
-    if(self::Class::_#lateStaticField2.==(null))
-      self::Class::_#lateStaticField2 = #t4;
-    else
+    if(self::Class::_#lateStaticField2#isSet)
       throw new _in::LateInitializationErrorImpl::•("Field 'lateStaticField2' has already been initialized.");
+    else {
+      self::Class::_#lateStaticField2#isSet = true;
+      self::Class::_#lateStaticField2 = #t4;
+    }
   static method staticMethod() → dynamic {
     self::throws(() → core::int => self::Class::lateStaticField2, "Read value from uninitialized Class.lateStaticField2");
     self::Class::lateStaticField2 = 42;
@@ -31,12 +38,14 @@ class Class extends core::Object {
     self::throws(() → core::int => self::Class::lateStaticField2 = 43, "Write value to initialized Class.lateStaticField2");
   }
   get lateInstanceField() → core::int
-    return let final core::int? #t5 = this.{self::Class::_#Class#lateInstanceField} in #t5.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateInstanceField' has not been initialized.") : #t5{core::int};
+    return this.{self::Class::_#Class#lateInstanceField#isSet} ?{core::int} let final core::int? #t5 = this.{self::Class::_#Class#lateInstanceField} in #t5{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateInstanceField' has not been initialized.");
   set lateInstanceField(core::int #t6) → void
-    if(this.{self::Class::_#Class#lateInstanceField}.==(null))
-      this.{self::Class::_#Class#lateInstanceField} = #t6;
-    else
+    if(this.{self::Class::_#Class#lateInstanceField#isSet})
       throw new _in::LateInitializationErrorImpl::•("Field 'lateInstanceField' has already been initialized.");
+    else {
+      this.{self::Class::_#Class#lateInstanceField#isSet} = true;
+      this.{self::Class::_#Class#lateInstanceField} = #t6;
+    }
   method instanceMethod() → dynamic {
     self::throws(() → core::int => this.{self::Class::lateInstanceField}, "Read value from uninitialized Class.lateInstanceField");
     this.{self::Class::lateInstanceField} = 16;
@@ -46,37 +55,48 @@ class Class extends core::Object {
 }
 extension Extension on self::Class {
   static field lateExtensionField1 = self::_#Extension|lateExtensionField1;
+  static field lateExtensionField1 = self::_#Extension|lateExtensionField1#isSet;
   static get lateExtensionField1 = get self::Extension|lateExtensionField1;
   static set lateExtensionField1 = set self::Extension|lateExtensionField1;
   static field lateExtensionField2 = self::_#Extension|lateExtensionField2;
+  static field lateExtensionField2 = self::_#Extension|lateExtensionField2#isSet;
   static get lateExtensionField2 = get self::Extension|lateExtensionField2;
   static set lateExtensionField2 = set self::Extension|lateExtensionField2;
   static method staticMethod = self::Extension|staticMethod;
 }
 static field core::int? _#lateTopLevelField = null;
+static field core::bool _#lateTopLevelField#isSet = false;
 static field core::int? _#Extension|lateExtensionField1 = null;
+static field core::bool _#Extension|lateExtensionField1#isSet = false;
 static field core::int? _#Extension|lateExtensionField2 = null;
+static field core::bool _#Extension|lateExtensionField2#isSet = false;
 static get lateTopLevelField() → core::int
-  return let final core::int? #t7 = self::_#lateTopLevelField in #t7.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateTopLevelField' has not been initialized.") : #t7{core::int};
+  return self::_#lateTopLevelField#isSet ?{core::int} let final core::int? #t7 = self::_#lateTopLevelField in #t7{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateTopLevelField' has not been initialized.");
 static set lateTopLevelField(core::int #t8) → void
-  if(self::_#lateTopLevelField.==(null))
-    self::_#lateTopLevelField = #t8;
-  else
+  if(self::_#lateTopLevelField#isSet)
     throw new _in::LateInitializationErrorImpl::•("Field 'lateTopLevelField' has already been initialized.");
+  else {
+    self::_#lateTopLevelField#isSet = true;
+    self::_#lateTopLevelField = #t8;
+  }
 static get Extension|lateExtensionField1() → core::int
-  return let final core::int? #t9 = self::_#Extension|lateExtensionField1 in #t9.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateExtensionField1' has not been initialized.") : #t9{core::int};
+  return self::_#Extension|lateExtensionField1#isSet ?{core::int} let final core::int? #t9 = self::_#Extension|lateExtensionField1 in #t9{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateExtensionField1' has not been initialized.");
 static set Extension|lateExtensionField1(core::int #t10) → void
-  if(self::_#Extension|lateExtensionField1.==(null))
-    self::_#Extension|lateExtensionField1 = #t10;
-  else
+  if(self::_#Extension|lateExtensionField1#isSet)
     throw new _in::LateInitializationErrorImpl::•("Field 'lateExtensionField1' has already been initialized.");
+  else {
+    self::_#Extension|lateExtensionField1#isSet = true;
+    self::_#Extension|lateExtensionField1 = #t10;
+  }
 static get Extension|lateExtensionField2() → core::int
-  return let final core::int? #t11 = self::_#Extension|lateExtensionField2 in #t11.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateExtensionField2' has not been initialized.") : #t11{core::int};
+  return self::_#Extension|lateExtensionField2#isSet ?{core::int} let final core::int? #t11 = self::_#Extension|lateExtensionField2 in #t11{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateExtensionField2' has not been initialized.");
 static set Extension|lateExtensionField2(core::int #t12) → void
-  if(self::_#Extension|lateExtensionField2.==(null))
-    self::_#Extension|lateExtensionField2 = #t12;
-  else
+  if(self::_#Extension|lateExtensionField2#isSet)
     throw new _in::LateInitializationErrorImpl::•("Field 'lateExtensionField2' has already been initialized.");
+  else {
+    self::_#Extension|lateExtensionField2#isSet = true;
+    self::_#Extension|lateExtensionField2 = #t12;
+  }
 static method Extension|staticMethod() → dynamic {
   self::throws(() → core::int => self::Extension|lateExtensionField2, "Read value from uninitialized Class.lateExtensionField2");
   self::Extension|lateExtensionField2 = 42;

pkg/front_end/testcases/late_lowering/late_final_field_without_initializer.dart.weak.transformed.expect

@@ -5,25 +5,32 @@ import "dart:_internal" as _in;
 
 class Class extends core::Object {
   static field core::int? _#lateStaticField1 = null;
+  static field core::bool _#lateStaticField1#isSet = false;
   static field core::int? _#lateStaticField2 = null;
+  static field core::bool _#lateStaticField2#isSet = false;
   field core::int? _#Class#lateInstanceField = null;
+  field core::bool _#Class#lateInstanceField#isSet = false;
   synthetic constructor •() → self::Class
     : super core::Object::•()
     ;
   static get lateStaticField1() → core::int
-    return let final core::int? #t1 = self::Class::_#lateStaticField1 in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateStaticField1' has not been initialized.") : #t1{core::int};
+    return self::Class::_#lateStaticField1#isSet ?{core::int} let final core::int? #t1 = self::Class::_#lateStaticField1 in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateStaticField1' has not been initialized.");
   static set lateStaticField1(core::int #t2) → void
-    if(self::Class::_#lateStaticField1.==(null))
-      self::Class::_#lateStaticField1 = #t2;
-    else
+    if(self::Class::_#lateStaticField1#isSet)
       throw new _in::LateInitializationErrorImpl::•("Field 'lateStaticField1' has already been initialized.");
+    else {
+      self::Class::_#lateStaticField1#isSet = true;
+      self::Class::_#lateStaticField1 = #t2;
+    }
   static get lateStaticField2() → core::int
-    return let final core::int? #t3 = self::Class::_#lateStaticField2 in #t3.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateStaticField2' has not been initialized.") : #t3{core::int};
+    return self::Class::_#lateStaticField2#isSet ?{core::int} let final core::int? #t3 = self::Class::_#lateStaticField2 in #t3{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateStaticField2' has not been initialized.");
   static set lateStaticField2(core::int #t4) → void
-    if(self::Class::_#lateStaticField2.==(null))
-      self::Class::_#lateStaticField2 = #t4;
-    else
+    if(self::Class::_#lateStaticField2#isSet)
       throw new _in::LateInitializationErrorImpl::•("Field 'lateStaticField2' has already been initialized.");
+    else {
+      self::Class::_#lateStaticField2#isSet = true;
+      self::Class::_#lateStaticField2 = #t4;
+    }
   static method staticMethod() → dynamic {
     self::throws(() → core::int => self::Class::lateStaticField2, "Read value from uninitialized Class.lateStaticField2");
     self::Class::lateStaticField2 = 42;
@@ -31,12 +38,14 @@ class Class extends core::Object {
     self::throws(() → core::int => self::Class::lateStaticField2 = 43, "Write value to initialized Class.lateStaticField2");
   }
   get lateInstanceField() → core::int
-    return let final core::int? #t5 = this.{self::Class::_#Class#lateInstanceField} in #t5.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateInstanceField' has not been initialized.") : #t5{core::int};
+    return this.{self::Class::_#Class#lateInstanceField#isSet} ?{core::int} let final core::int? #t5 = this.{self::Class::_#Class#lateInstanceField} in #t5{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateInstanceField' has not been initialized.");
   set lateInstanceField(core::int #t6) → void
-    if(this.{self::Class::_#Class#lateInstanceField}.==(null))
-      this.{self::Class::_#Class#lateInstanceField} = #t6;
-    else
+    if(this.{self::Class::_#Class#lateInstanceField#isSet})
       throw new _in::LateInitializationErrorImpl::•("Field 'lateInstanceField' has already been initialized.");
+    else {
+      this.{self::Class::_#Class#lateInstanceField#isSet} = true;
+      this.{self::Class::_#Class#lateInstanceField} = #t6;
+    }
   method instanceMethod() → dynamic {
     self::throws(() → core::int => this.{self::Class::lateInstanceField}, "Read value from uninitialized Class.lateInstanceField");
     this.{self::Class::lateInstanceField} = 16;
@@ -46,37 +55,48 @@ class Class extends core::Object {
 }
 extension Extension on self::Class {
   static field lateExtensionField1 = self::_#Extension|lateExtensionField1;
+  static field lateExtensionField1 = self::_#Extension|lateExtensionField1#isSet;
   static get lateExtensionField1 = get self::Extension|lateExtensionField1;
   static set lateExtensionField1 = set self::Extension|lateExtensionField1;
   static field lateExtensionField2 = self::_#Extension|lateExtensionField2;
+  static field lateExtensionField2 = self::_#Extension|lateExtensionField2#isSet;
   static get lateExtensionField2 = get self::Extension|lateExtensionField2;
   static set lateExtensionField2 = set self::Extension|lateExtensionField2;
   static method staticMethod = self::Extension|staticMethod;
 }
 static field core::int? _#lateTopLevelField = null;
+static field core::bool _#lateTopLevelField#isSet = false;
 static field core::int? _#Extension|lateExtensionField1 = null;
+static field core::bool _#Extension|lateExtensionField1#isSet = false;
 static field core::int? _#Extension|lateExtensionField2 = null;
+static field core::bool _#Extension|lateExtensionField2#isSet = false;
 static get lateTopLevelField() → core::int
-  return let final core::int? #t7 = self::_#lateTopLevelField in #t7.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateTopLevelField' has not been initialized.") : #t7{core::int};
+  return self::_#lateTopLevelField#isSet ?{core::int} let final core::int? #t7 = self::_#lateTopLevelField in #t7{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateTopLevelField' has not been initialized.");
 static set lateTopLevelField(core::int #t8) → void
-  if(self::_#lateTopLevelField.==(null))
-    self::_#lateTopLevelField = #t8;
-  else
+  if(self::_#lateTopLevelField#isSet)
     throw new _in::LateInitializationErrorImpl::•("Field 'lateTopLevelField' has already been initialized.");
+  else {
+    self::_#lateTopLevelField#isSet = true;
+    self::_#lateTopLevelField = #t8;
+  }
 static get Extension|lateExtensionField1() → core::int
-  return let final core::int? #t9 = self::_#Extension|lateExtensionField1 in #t9.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateExtensionField1' has not been initialized.") : #t9{core::int};
+  return self::_#Extension|lateExtensionField1#isSet ?{core::int} let final core::int? #t9 = self::_#Extension|lateExtensionField1 in #t9{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateExtensionField1' has not been initialized.");
 static set Extension|lateExtensionField1(core::int #t10) → void
-  if(self::_#Extension|lateExtensionField1.==(null))
-    self::_#Extension|lateExtensionField1 = #t10;
-  else
+  if(self::_#Extension|lateExtensionField1#isSet)
     throw new _in::LateInitializationErrorImpl::•("Field 'lateExtensionField1' has already been initialized.");
+  else {
+    self::_#Extension|lateExtensionField1#isSet = true;
+    self::_#Extension|lateExtensionField1 = #t10;
+  }
 static get Extension|lateExtensionField2() → core::int
-  return let final core::int? #t11 = self::_#Extension|lateExtensionField2 in #t11.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'lateExtensionField2' has not been initialized.") : #t11{core::int};
+  return self::_#Extension|lateExtensionField2#isSet ?{core::int} let final core::int? #t11 = self::_#Extension|lateExtensionField2 in #t11{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'lateExtensionField2' has not been initialized.");
 static set Extension|lateExtensionField2(core::int #t12) → void
-  if(self::_#Extension|lateExtensionField2.==(null))
-    self::_#Extension|lateExtensionField2 = #t12;
-  else
+  if(self::_#Extension|lateExtensionField2#isSet)
     throw new _in::LateInitializationErrorImpl::•("Field 'lateExtensionField2' has already been initialized.");
+  else {
+    self::_#Extension|lateExtensionField2#isSet = true;
+    self::_#Extension|lateExtensionField2 = #t12;
+  }
 static method Extension|staticMethod() → dynamic {
   self::throws(() → core::int => self::Extension|lateExtensionField2, "Read value from uninitialized Class.lateExtensionField2");
   self::Extension|lateExtensionField2 = 42;

pkg/front_end/testcases/late_lowering/late_final_local_with_initializer.dart.weak.expect

@@ -8,8 +8,14 @@ static method main() → dynamic {
     return lateLocalInit = value;
   }
   final core::int? lateLocal;
-  function #lateLocal#get() → core::int
-    return let final core::int? #t1 = lateLocal in #t1.==(null) ?{core::int} lateLocal = initLateLocal.call(123) : #t1{core::int};
+  core::bool #lateLocal#isSet = false;
+  function #lateLocal#get() → core::int {
+    if(!#lateLocal#isSet) {
+      lateLocal = initLateLocal.call(123);
+      #lateLocal#isSet = true;
+    }
+    return lateLocal{core::int};
+  }
   self::expect(null, lateLocalInit);
   self::expect(123, #lateLocal#get.call());
   self::expect(123, lateLocalInit);

pkg/front_end/testcases/late_lowering/late_final_local_with_initializer.dart.weak.transformed.expect

@@ -8,8 +8,14 @@ static method main() → dynamic {
     return lateLocalInit = value;
   }
   final core::int? lateLocal;
-  function #lateLocal#get() → core::int
-    return let final core::int? #t1 = lateLocal in #t1.==(null) ?{core::int} lateLocal = initLateLocal.call(123) : #t1{core::int};
+  core::bool #lateLocal#isSet = false;
+  function #lateLocal#get() → core::int {
+    if(!#lateLocal#isSet) {
+      lateLocal = initLateLocal.call(123);
+      #lateLocal#isSet = true;
+    }
+    return lateLocal{core::int};
+  }
   self::expect(null, lateLocalInit);
   self::expect(123, #lateLocal#get.call());
   self::expect(123, lateLocalInit);

pkg/front_end/testcases/late_lowering/late_final_local_without_initializer.dart.weak.expect

@@ -6,13 +6,16 @@ import "dart:_internal" as _in;
 static method main() → dynamic {
   core::bool b = false;
   final core::int? lateLocal;
+  core::bool #lateLocal#isSet = false;
   function #lateLocal#get() → core::int
-    return let final core::int? #t1 = lateLocal in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'lateLocal' has not been initialized.") : #t1{core::int};
-  function #lateLocal#set(core::int #t2) → dynamic
-    if(lateLocal.==(null))
-      return lateLocal = #t2;
-    else
+    return #lateLocal#isSet ?{core::int} lateLocal{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'lateLocal' has not been initialized.");
+  function #lateLocal#set(core::int #t1) → dynamic
+    if(#lateLocal#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'lateLocal' has already been initialized.");
+    else {
+      #lateLocal#isSet = true;
+      return lateLocal = #t1;
+    }
   if(b) {
     #lateLocal#set.call(123);
   }
@@ -27,12 +30,12 @@ static method main() → dynamic {
     core::bool #lateGenericLocal#isSet = false;
     function #lateGenericLocal#get() → T%
       return #lateGenericLocal#isSet ?{T%} lateGenericLocal{T%} : throw new _in::LateInitializationErrorImpl::•("Local 'lateGenericLocal' has not been initialized.");
-    function #lateGenericLocal#set(T% #t3) → dynamic
+    function #lateGenericLocal#set(T% #t2) → dynamic
       if(#lateGenericLocal#isSet)
         throw new _in::LateInitializationErrorImpl::•("Local 'lateGenericLocal' has already been initialized.");
       else {
         #lateGenericLocal#isSet = true;
-        return lateGenericLocal = #t3;
+        return lateGenericLocal = #t2;
       }
     if(b) {
       #lateGenericLocal#set.call(value);

pkg/front_end/testcases/late_lowering/late_final_local_without_initializer.dart.weak.transformed.expect

@@ -6,13 +6,16 @@ import "dart:_internal" as _in;
 static method main() → dynamic {
   core::bool b = false;
   final core::int? lateLocal;
+  core::bool #lateLocal#isSet = false;
   function #lateLocal#get() → core::int
-    return let final core::int? #t1 = lateLocal in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'lateLocal' has not been initialized.") : #t1{core::int};
-  function #lateLocal#set(core::int #t2) → dynamic
-    if(lateLocal.==(null))
-      return lateLocal = #t2;
-    else
+    return #lateLocal#isSet ?{core::int} lateLocal{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'lateLocal' has not been initialized.");
+  function #lateLocal#set(core::int #t1) → dynamic
+    if(#lateLocal#isSet)
       throw new _in::LateInitializationErrorImpl::•("Local 'lateLocal' has already been initialized.");
+    else {
+      #lateLocal#isSet = true;
+      return lateLocal = #t1;
+    }
   if(b) {
     #lateLocal#set.call(123);
   }
@@ -27,12 +30,12 @@ static method main() → dynamic {
     core::bool #lateGenericLocal#isSet = false;
     function #lateGenericLocal#get() → T%
       return #lateGenericLocal#isSet ?{T%} lateGenericLocal{T%} : throw new _in::LateInitializationErrorImpl::•("Local 'lateGenericLocal' has not been initialized.");
-    function #lateGenericLocal#set(T% #t3) → dynamic
+    function #lateGenericLocal#set(T% #t2) → dynamic
       if(#lateGenericLocal#isSet)
         throw new _in::LateInitializationErrorImpl::•("Local 'lateGenericLocal' has already been initialized.");
       else {
         #lateGenericLocal#isSet = true;
-        return lateGenericLocal = #t3;
+        return lateGenericLocal = #t2;
       }
     if(b) {
       #lateGenericLocal#set.call(value);

pkg/front_end/testcases/late_lowering/late_future_or.dart.weak.expect

@@ -149,10 +149,17 @@ static set field3(FutureOr<dynamic>#t14) → void {
   self::_#field3#isSet = true;
   self::_#field3 = #t14;
 }
-static get field4() → FutureOr<core::int>
-  return let final FutureOr<core::int>? #t15 = self::_#field4 in #t15.==(null) ?{FutureOr<core::int>} self::_#field4 = self::method4() : #t15{FutureOr<core::int>};
-static set field4(FutureOr<core::int>#t16) → void
+static get field4() → FutureOr<core::int> {
+  if(!self::_#field4#isSet) {
+    self::_#field4 = self::method4();
+    self::_#field4#isSet = true;
+  }
+  return let final FutureOr<core::int>? #t15 = self::_#field4 in #t15{FutureOr<core::int>};
+}
+static set field4(FutureOr<core::int>#t16) → void {
+  self::_#field4#isSet = true;
   self::_#field4 = #t16;
+}
 static get field5() → FutureOr<core::int?> {
   if(!self::_#field5#isSet) {
     self::_#field5 = self::method5();

pkg/front_end/testcases/late_lowering/late_future_or.dart.weak.transformed.expect

@@ -149,10 +149,17 @@ static set field3(FutureOr<dynamic>#t14) → void {
   self::_#field3#isSet = true;
   self::_#field3 = #t14;
 }
-static get field4() → FutureOr<core::int>
-  return let final FutureOr<core::int>? #t15 = self::_#field4 in #t15.==(null) ?{FutureOr<core::int>} self::_#field4 = self::method4() : #t15{FutureOr<core::int>};
-static set field4(FutureOr<core::int>#t16) → void
+static get field4() → FutureOr<core::int> {
+  if(!self::_#field4#isSet) {
+    self::_#field4 = self::method4();
+    self::_#field4#isSet = true;
+  }
+  return let final FutureOr<core::int>? #t15 = self::_#field4 in #t15{FutureOr<core::int>};
+}
+static set field4(FutureOr<core::int>#t16) → void {
+  self::_#field4#isSet = true;
   self::_#field4 = #t16;
+}
 static get field5() → FutureOr<core::int?> {
   if(!self::_#field5#isSet) {
     self::_#field5 = self::method5();

pkg/front_end/testcases/late_lowering/late_local_with_initializer.dart.weak.expect

@@ -4,10 +4,18 @@ import "dart:core" as core;
 
 static method main() → dynamic {
   core::int? lateLocal;
-  function #lateLocal#get() → core::int
-    return let final core::int? #t1 = lateLocal in #t1.==(null) ?{core::int} lateLocal = 123 : #t1{core::int};
-  function #lateLocal#set(core::int #t2) → dynamic
-    return lateLocal = #t2;
+  core::bool #lateLocal#isSet = false;
+  function #lateLocal#get() → core::int {
+    if(!#lateLocal#isSet) {
+      lateLocal = 123;
+      #lateLocal#isSet = true;
+    }
+    return lateLocal{core::int};
+  }
+  function #lateLocal#set(core::int #t1) → dynamic {
+    #lateLocal#isSet = true;
+    return lateLocal = #t1;
+  }
   self::expect(123, #lateLocal#get.call());
   self::expect(124, #lateLocal#set.call(124));
   self::expect(124, #lateLocal#get.call());
@@ -21,9 +29,9 @@ static method main() → dynamic {
       }
       return lateGenericLocal{T%};
     }
-    function #lateGenericLocal#set(T% #t3) → dynamic {
+    function #lateGenericLocal#set(T% #t2) → dynamic {
       #lateGenericLocal#isSet = true;
-      return lateGenericLocal = #t3;
+      return lateGenericLocal = #t2;
     }
     self::expect(value1, #lateGenericLocal#get.call());
     self::expect(value2, #lateGenericLocal#set.call(value2));

pkg/front_end/testcases/late_lowering/late_local_with_initializer.dart.weak.transformed.expect

@@ -4,10 +4,18 @@ import "dart:core" as core;
 
 static method main() → dynamic {
   core::int? lateLocal;
-  function #lateLocal#get() → core::int
-    return let final core::int? #t1 = lateLocal in #t1.==(null) ?{core::int} lateLocal = 123 : #t1{core::int};
-  function #lateLocal#set(core::int #t2) → dynamic
-    return lateLocal = #t2;
+  core::bool #lateLocal#isSet = false;
+  function #lateLocal#get() → core::int {
+    if(!#lateLocal#isSet) {
+      lateLocal = 123;
+      #lateLocal#isSet = true;
+    }
+    return lateLocal{core::int};
+  }
+  function #lateLocal#set(core::int #t1) → dynamic {
+    #lateLocal#isSet = true;
+    return lateLocal = #t1;
+  }
   self::expect(123, #lateLocal#get.call());
   self::expect(124, #lateLocal#set.call(124));
   self::expect(124, #lateLocal#get.call());
@@ -21,9 +29,9 @@ static method main() → dynamic {
       }
       return lateGenericLocal{T%};
     }
-    function #lateGenericLocal#set(T% #t3) → dynamic {
+    function #lateGenericLocal#set(T% #t2) → dynamic {
       #lateGenericLocal#isSet = true;
-      return lateGenericLocal = #t3;
+      return lateGenericLocal = #t2;
     }
     self::expect(value1, #lateGenericLocal#get.call());
     self::expect(value2, #lateGenericLocal#set.call(value2));

pkg/front_end/testcases/late_lowering/late_local_without_initializer.dart.weak.expect

@@ -5,10 +5,13 @@ import "dart:_internal" as _in;
 
 static method main() → dynamic {
   core::int? lateLocal;
+  core::bool #lateLocal#isSet = false;
   function #lateLocal#get() → core::int
-    return let final core::int? #t1 = lateLocal in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'lateLocal' has not been initialized.") : #t1{core::int};
-  function #lateLocal#set(core::int #t2) → dynamic
-    return lateLocal = #t2;
+    return #lateLocal#isSet ?{core::int} lateLocal{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'lateLocal' has not been initialized.");
+  function #lateLocal#set(core::int #t1) → dynamic {
+    #lateLocal#isSet = true;
+    return lateLocal = #t1;
+  }
   self::throws(() → core::int => #lateLocal#get.call(), "Read value from uninitialized lateLocal");
   self::expect(123, #lateLocal#set.call(123));
   self::expect(123, #lateLocal#get.call());
@@ -17,9 +20,9 @@ static method main() → dynamic {
     core::bool #lateGenericLocal#isSet = false;
     function #lateGenericLocal#get() → T%
       return #lateGenericLocal#isSet ?{T%} lateGenericLocal{T%} : throw new _in::LateInitializationErrorImpl::•("Local 'lateGenericLocal' has not been initialized.");
-    function #lateGenericLocal#set(T% #t3) → dynamic {
+    function #lateGenericLocal#set(T% #t2) → dynamic {
       #lateGenericLocal#isSet = true;
-      return lateGenericLocal = #t3;
+      return lateGenericLocal = #t2;
     }
     self::throws(() → T% => #lateGenericLocal#get.call(), "Read value from uninitialized lateGenericLocal");
     self::expect(value, #lateGenericLocal#set.call(value));

pkg/front_end/testcases/late_lowering/late_local_without_initializer.dart.weak.transformed.expect

@@ -5,10 +5,13 @@ import "dart:_internal" as _in;
 
 static method main() → dynamic {
   core::int? lateLocal;
+  core::bool #lateLocal#isSet = false;
   function #lateLocal#get() → core::int
-    return let final core::int? #t1 = lateLocal in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'lateLocal' has not been initialized.") : #t1{core::int};
-  function #lateLocal#set(core::int #t2) → dynamic
-    return lateLocal = #t2;
+    return #lateLocal#isSet ?{core::int} lateLocal{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'lateLocal' has not been initialized.");
+  function #lateLocal#set(core::int #t1) → dynamic {
+    #lateLocal#isSet = true;
+    return lateLocal = #t1;
+  }
   self::throws(() → core::int => #lateLocal#get.call(), "Read value from uninitialized lateLocal");
   self::expect(123, #lateLocal#set.call(123));
   self::expect(123, #lateLocal#get.call());
@@ -17,9 +20,9 @@ static method main() → dynamic {
     core::bool #lateGenericLocal#isSet = false;
     function #lateGenericLocal#get() → T%
       return #lateGenericLocal#isSet ?{T%} lateGenericLocal{T%} : throw new _in::LateInitializationErrorImpl::•("Local 'lateGenericLocal' has not been initialized.");
-    function #lateGenericLocal#set(T% #t3) → dynamic {
+    function #lateGenericLocal#set(T% #t2) → dynamic {
       #lateGenericLocal#isSet = true;
-      return lateGenericLocal = #t3;
+      return lateGenericLocal = #t2;
     }
     self::throws(() → T% => #lateGenericLocal#get.call(), "Read value from uninitialized lateGenericLocal");
     self::expect(value, #lateGenericLocal#set.call(value));

pkg/front_end/testcases/late_lowering/later.dart.weak.expect

@@ -70,17 +70,26 @@ import "dart:async" as asy;
 class A extends core::Object {
   field core::int a = 42;
   field core::int? _#A#b = null;
+  field core::bool _#A#b#isSet = false;
   synthetic constructor •() → self::A
     : super core::Object::•()
     ;
-  get b() → core::int
-    return let final core::int? #t1 = this.{self::A::_#A#b} in #t1.==(null) ?{core::int} this.{self::A::_#A#b} = this.{self::A::a}.{core::num::*}(2).{core::int::>>}(1) : #t1{core::int};
-  set b(core::int #t2) → void
+  get b() → core::int {
+    if(!this.{self::A::_#A#b#isSet}) {
+      this.{self::A::_#A#b} = this.{self::A::a}.{core::num::*}(2).{core::int::>>}(1);
+      this.{self::A::_#A#b#isSet} = true;
+    }
+    return let final core::int? #t1 = this.{self::A::_#A#b} in #t1{core::int};
+  }
+  set b(core::int #t2) → void {
+    this.{self::A::_#A#b#isSet} = true;
     this.{self::A::_#A#b} = #t2;
+  }
   method foo(core::int x) → dynamic {}
 }
 class B extends core::Object /*hasConstConstructor*/  {
   field core::int? _#B#x = null;
+  field core::bool _#B#x#isSet = false;
   const constructor •() → self::B
     : super core::Object::•()
     ;
@@ -89,16 +98,19 @@ class B extends core::Object /*hasConstConstructor*/  {
 }
 class C extends core::Object {
   field core::int? _#C#x = null;
+  field core::bool _#C#x#isSet = false;
   synthetic constructor •() → self::C
     : super core::Object::•()
     ;
   get x() → core::int
-    return let final core::int? #t5 = this.{self::C::_#C#x} in #t5.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.") : #t5{core::int};
+    return this.{self::C::_#C#x#isSet} ?{core::int} let final core::int? #t5 = this.{self::C::_#C#x} in #t5{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.");
   set x(core::int #t6) → void
-    if(this.{self::C::_#C#x}.==(null))
-      this.{self::C::_#C#x} = #t6;
-    else
+    if(this.{self::C::_#C#x#isSet})
       throw new _in::LateInitializationErrorImpl::•("Field 'x' has already been initialized.");
+    else {
+      this.{self::C::_#C#x#isSet} = true;
+      this.{self::C::_#C#x} = #t6;
+    }
   method initVars() → dynamic {
     this.{self::C::x} = 42;
   }
@@ -138,24 +150,48 @@ static method hest() → dynamic async {
 }
 static method fisk() → dynamic async {
   core::String? s1;
-  function #s1#get() → core::String
-    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.
+  core::bool #s1#isSet = false;
+  function #s1#get() → core::String {
+    if(!#s1#isSet) {
+      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 : #t8{core::String};
-  function #s1#set(core::String #t9) → dynamic
-    return s1 = #t9;
+                   ^^^^^" as{TypeError,ForDynamic,ForNonNullableByDefault} core::String;
+      #s1#isSet = true;
+    }
+    return s1{core::String};
+  }
+  function #s1#set(core::String #t8) → dynamic {
+    #s1#isSet = true;
+    return s1 = #t8;
+  }
   core::String? s2;
-  function #s2#get() → core::String
-    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.
+  core::bool #s2#isSet = false;
+  function #s2#get() → core::String {
+    if(!#s2#isSet) {
+      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.
-                             ^^^^^"}${#C1}" : #t10{core::String};
-  function #s2#set(core::String #t11) → dynamic
-    return s2 = #t11;
+                             ^^^^^"}${#C1}";
+      #s2#isSet = true;
+    }
+    return s2{core::String};
+  }
+  function #s2#set(core::String #t9) → dynamic {
+    #s2#isSet = true;
+    return s2 = #t9;
+  }
   core::Function? f;
-  function #f#get() → core::Function
-    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;
+  core::bool #f#isSet = false;
+  function #f#get() → core::Function {
+    if(!#f#isSet) {
+      f = () → asy::Future<dynamic> async => await self::hest();
+      #f#isSet = true;
+    }
+    return f{core::Function};
+  }
+  function #f#set(core::Function #t10) → dynamic {
+    #f#isSet = true;
+    return f = #t10;
+  }
 }
 static method main() → dynamic {}
 

pkg/front_end/testcases/late_lowering/later.dart.weak.transformed.expect

@@ -70,17 +70,26 @@ import "dart:async" as asy;
 class A extends core::Object {
   field core::int a = 42;
   field core::int? _#A#b = null;
+  field core::bool _#A#b#isSet = false;
   synthetic constructor •() → self::A
     : super core::Object::•()
     ;
-  get b() → core::int
-    return let final core::int? #t1 = this.{self::A::_#A#b} in #t1.==(null) ?{core::int} this.{self::A::_#A#b} = this.{self::A::a}.{core::num::*}(2).{core::int::>>}(1) : #t1{core::int};
-  set b(core::int #t2) → void
+  get b() → core::int {
+    if(!this.{self::A::_#A#b#isSet}) {
+      this.{self::A::_#A#b} = this.{self::A::a}.{core::num::*}(2).{core::int::>>}(1);
+      this.{self::A::_#A#b#isSet} = true;
+    }
+    return let final core::int? #t1 = this.{self::A::_#A#b} in #t1{core::int};
+  }
+  set b(core::int #t2) → void {
+    this.{self::A::_#A#b#isSet} = true;
     this.{self::A::_#A#b} = #t2;
+  }
   method foo(core::int x) → dynamic {}
 }
 class B extends core::Object /*hasConstConstructor*/  {
   field core::int? _#B#x = null;
+  field core::bool _#B#x#isSet = false;
   const constructor •() → self::B
     : super core::Object::•()
     ;
@@ -89,16 +98,19 @@ class B extends core::Object /*hasConstConstructor*/  {
 }
 class C extends core::Object {
   field core::int? _#C#x = null;
+  field core::bool _#C#x#isSet = false;
   synthetic constructor •() → self::C
     : super core::Object::•()
     ;
   get x() → core::int
-    return let final core::int? #t5 = this.{self::C::_#C#x} in #t5.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.") : #t5{core::int};
+    return this.{self::C::_#C#x#isSet} ?{core::int} let final core::int? #t5 = this.{self::C::_#C#x} in #t5{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.");
   set x(core::int #t6) → void
-    if(this.{self::C::_#C#x}.==(null))
-      this.{self::C::_#C#x} = #t6;
-    else
+    if(this.{self::C::_#C#x#isSet})
       throw new _in::LateInitializationErrorImpl::•("Field 'x' has already been initialized.");
+    else {
+      this.{self::C::_#C#x#isSet} = true;
+      this.{self::C::_#C#x} = #t6;
+    }
   method initVars() → dynamic {
     this.{self::C::x} = 42;
   }
@@ -204,52 +216,76 @@ static method fisk() → dynamic /* originally async */ {
       #L3:
       {
         core::String? s1;
-        function #s1#get() → core::String
-          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.
+        core::bool #s1#isSet = false;
+        function #s1#get() → core::String {
+          if(!#s1#isSet) {
+            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.
-                   ^^^^^" : #t11{core::String};
-        function #s1#set(core::String #t12) → dynamic
-          return s1 = #t12;
+                   ^^^^^";
+            #s1#isSet = true;
+          }
+          return s1{core::String};
+        }
+        function #s1#set(core::String #t11) → dynamic {
+          #s1#isSet = true;
+          return s1 = #t11;
+        }
         core::String? s2;
-        function #s2#get() → core::String
-          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.
+        core::bool #s2#isSet = false;
+        function #s2#get() → core::String {
+          if(!#s2#isSet) {
+            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.
-                             ^^^^^"}${#C1}" : #t13{core::String};
-        function #s2#set(core::String #t14) → dynamic
-          return s2 = #t14;
+                             ^^^^^"}${#C1}";
+            #s2#isSet = true;
+          }
+          return s2{core::String};
+        }
+        function #s2#set(core::String #t12) → dynamic {
+          #s2#isSet = true;
+          return s2 = #t12;
+        }
         core::Function? f;
-        function #f#get() → core::Function
-          return let final core::Function? #t15 = f in #t15.==(null) ?{core::Function} f = () → asy::Future<dynamic> /* originally async */ {
-            final asy::_AsyncAwaitCompleter<dynamic> :async_completer = new asy::_AsyncAwaitCompleter::•<dynamic>();
-            FutureOr<dynamic>? :return_value;
-            dynamic :async_stack_trace;
-            (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 {
-                #L4:
-                {
-                  [yield] let dynamic #t16 = asy::_awaitHelper(self::hest(), :async_op_then, :async_op_error, :async_op) in null;
-                  :return_value = :result;
-                  break #L4;
+        core::bool #f#isSet = false;
+        function #f#get() → core::Function {
+          if(!#f#isSet) {
+            f = () → asy::Future<dynamic> /* originally async */ {
+              final asy::_AsyncAwaitCompleter<dynamic> :async_completer = new asy::_AsyncAwaitCompleter::•<dynamic>();
+              FutureOr<dynamic>? :return_value;
+              dynamic :async_stack_trace;
+              (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 {
+                  #L4:
+                  {
+                    [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_completer, :return_value);
+                  return;
                 }
-                asy::_completeOnAsyncReturn(:async_completer, :return_value);
-                return;
-              }
-              on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
-                :async_completer.{asy::Completer::completeError}(exception, stack_trace);
-              }
-            :async_stack_trace = asy::_asyncStackTraceHelper(:async_op);
-            :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
-            :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
-            :async_completer.{asy::_AsyncAwaitCompleter::start}(:async_op);
-            return :async_completer.{asy::Completer::future};
-          } : #t15{core::Function};
-        function #f#set(core::Function #t17) → dynamic
-          return f = #t17;
+                on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
+                  :async_completer.{asy::Completer::completeError}(exception, stack_trace);
+                }
+              :async_stack_trace = asy::_asyncStackTraceHelper(:async_op);
+              :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
+              :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
+              :async_completer.{asy::_AsyncAwaitCompleter::start}(:async_op);
+              return :async_completer.{asy::Completer::future};
+            };
+            #f#isSet = true;
+          }
+          return f{core::Function};
+        }
+        function #f#set(core::Function #t14) → dynamic {
+          #f#isSet = true;
+          return f = #t14;
+        }
       }
       asy::_completeOnAsyncReturn(:async_completer, :return_value);
       return;

pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart

@@ -0,0 +1,37 @@
+// 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.
+
+// @dart=2.8
+
+import 'non_nullable_from_opt_out_lib.dart';
+
+main() {
+  topLevelField = null;
+  finalTopLevelField = null;
+
+  var c = new Class<int>();
+  c.instanceField = null;
+  c.finalInstanceField = null;
+  c.instanceTypeVariable = null;
+  c.finalInstanceTypeVariable = null;
+
+  Class.staticField = null;
+  Class.staticFinalField = null;
+
+  expect(null, topLevelField);
+  expect(null, finalTopLevelField);
+  expect(null, c.instanceField);
+  expect(null, c.finalInstanceField);
+  expect(null, c.instanceTypeVariable);
+  expect(null, c.finalInstanceTypeVariable);
+  expect(null, Class.staticField);
+  expect(null, Class.staticFinalField);
+
+  throws(() => finalTopLevelField = null);
+  throws(() => c.finalInstanceField = null);
+  throws(() => c.finalInstanceTypeVariable = null);
+  throws(() => Class.staticFinalField = null);
+
+  method(true, null, null);
+}

pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart.outline.expect

@@ -0,0 +1,56 @@
+library /*isNonNullableByDefault*/;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:5:1: Error: A library can't opt out of null safety by default, when using sound null safety.
+// // @dart=2.8
+// ^^^^^^^^^^^^
+//
+import self as self;
+
+import "org-dartlang-testcase:///non_nullable_from_opt_out_lib.dart";
+
+static method main() → dynamic
+  ;
+
+library /*isNonNullableByDefault*/;
+import self as self2;
+import "dart:core" as core;
+
+class Class<T extends core::Object = core::Object> extends core::Object {
+  field core::int? _#Class#instanceField;
+  field dynamic _#Class#finalInstanceField;
+  field core::bool _#Class#finalInstanceField#isSet;
+  generic-covariant-impl field self2::Class::T? _#Class#instanceTypeVariable;
+  field self2::Class::T? _#Class#finalInstanceTypeVariable;
+  static field core::int? _#staticField;
+  static field dynamic _#staticFinalField;
+  static field core::bool _#staticFinalField#isSet;
+  synthetic constructor •() → self2::Class<self2::Class::T>
+    ;
+  get instanceField() → core::int;
+  set instanceField(core::int #t1) → void;
+  get finalInstanceField() → dynamic;
+  set finalInstanceField(dynamic #t2) → void;
+  get instanceTypeVariable() → self2::Class::T;
+  set instanceTypeVariable(generic-covariant-impl self2::Class::T #t3) → void;
+  get finalInstanceTypeVariable() → self2::Class::T;
+  set finalInstanceTypeVariable(self2::Class::T #t4) → void;
+  static get staticField() → core::int;
+  static set staticField(core::int #t5) → void;
+  static get staticFinalField() → dynamic;
+  static set staticFinalField(dynamic #t6) → void;
+}
+static field core::int? _#topLevelField;
+static field dynamic _#finalTopLevelField;
+static field core::bool _#finalTopLevelField#isSet;
+static get topLevelField() → core::int;
+static set topLevelField(core::int #t7) → void;
+static get finalTopLevelField() → dynamic;
+static set finalTopLevelField(dynamic #t8) → void;
+static method method<T extends core::Object = core::Object>(core::bool b, core::int i, self2::method::T t) → dynamic
+  ;
+static method expect(dynamic expected, dynamic actual) → dynamic
+  ;
+static method throws(() → void f) → dynamic
+  ;

pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart.strong.expect

@@ -0,0 +1,217 @@
+library /*isNonNullableByDefault*/;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:5:1: Error: A library can't opt out of null safety by default, when using sound null safety.
+// // @dart=2.8
+// ^^^^^^^^^^^^
+//
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:10:19: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+//   topLevelField = null;
+//                   ^
+//
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:14:21: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+//   c.instanceField = null;
+//                     ^
+//
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:16:28: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+//   c.instanceTypeVariable = null;
+//                            ^
+//
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:17:33: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+//   c.finalInstanceTypeVariable = null;
+//                                 ^
+//
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:19:23: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+//   Class.staticField = null;
+//                       ^
+//
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:33:46: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+//   throws(() => c.finalInstanceTypeVariable = null);
+//                                              ^
+//
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:36:16: Error: The argument type 'Null' can't be assigned to the parameter type 'int'.
+//   method(true, null, null);
+//                ^
+//
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:36:3: Error: Inferred type argument 'Null' doesn't conform to the bound 'Object' of the type variable 'T' on 'method'.
+//  - 'Object' is from 'dart:core'.
+// Try specifying type arguments explicitly so that they conform to the bounds.
+//   method(true, null, null);
+//   ^
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out_lib.dart:18:8: Context: This is the type variable whose bound isn't conformed to.
+// method<T extends Object>(bool b, int i, T t) {
+//        ^
+//
+import self as self;
+import "non_nullable_from_opt_out_lib.dart" as non;
+import "dart:core" as core;
+
+import "org-dartlang-testcase:///non_nullable_from_opt_out_lib.dart";
+
+static method main() → dynamic {
+  non::topLevelField = let final<BottomType> #t1 = invalid-expression "pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:10:19: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+  topLevelField = null;
+                  ^" in null as{TypeError,ForNonNullableByDefault} core::int;
+  non::finalTopLevelField = null;
+  non::Class<core::int> c = new non::Class::•<core::int>();
+  c.{non::Class::instanceField} = let final<BottomType> #t2 = invalid-expression "pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:14:21: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+  c.instanceField = null;
+                    ^" in null as{TypeError,ForNonNullableByDefault} core::int;
+  c.{non::Class::finalInstanceField} = null;
+  c.{non::Class::instanceTypeVariable} = let final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:16:28: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+  c.instanceTypeVariable = null;
+                           ^" in null as{TypeError,ForNonNullableByDefault} core::int;
+  c.{non::Class::finalInstanceTypeVariable} = let final<BottomType> #t4 = invalid-expression "pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:17:33: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+  c.finalInstanceTypeVariable = null;
+                                ^" in null as{TypeError,ForNonNullableByDefault} core::int;
+  non::Class::staticField = let final<BottomType> #t5 = invalid-expression "pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:19:23: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+  Class.staticField = null;
+                      ^" in null as{TypeError,ForNonNullableByDefault} core::int;
+  non::Class::staticFinalField = null;
+  non::expect(null, non::topLevelField);
+  non::expect(null, non::finalTopLevelField);
+  non::expect(null, c.{non::Class::instanceField});
+  non::expect(null, c.{non::Class::finalInstanceField});
+  non::expect(null, c.{non::Class::instanceTypeVariable});
+  non::expect(null, c.{non::Class::finalInstanceTypeVariable});
+  non::expect(null, non::Class::staticField);
+  non::expect(null, non::Class::staticFinalField);
+  non::throws(() → core::Null? => non::finalTopLevelField = null);
+  non::throws(() → core::Null? => c.{non::Class::finalInstanceField} = null);
+  non::throws(() → core::Null? => c.{non::Class::finalInstanceTypeVariable} = let final<BottomType> #t6 = invalid-expression "pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:33:46: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+  throws(() => c.finalInstanceTypeVariable = null);
+                                             ^" in null as{TypeError,ForNonNullableByDefault} core::int);
+  non::throws(() → core::Null? => non::Class::staticFinalField = null);
+  non::method<core::Null?>(true, let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:36:16: Error: The argument type 'Null' can't be assigned to the parameter type 'int'.
+  method(true, null, null);
+               ^" in null as{TypeError,ForNonNullableByDefault} core::int, null);
+}
+
+library /*isNonNullableByDefault*/;
+import self as non;
+import "dart:core" as core;
+import "dart:_internal" as _in;
+
+class Class<T extends core::Object = core::Object> extends core::Object {
+  field core::int? _#Class#instanceField = null;
+  field dynamic _#Class#finalInstanceField = null;
+  field core::bool _#Class#finalInstanceField#isSet = false;
+  generic-covariant-impl field non::Class::T? _#Class#instanceTypeVariable = null;
+  field non::Class::T? _#Class#finalInstanceTypeVariable = null;
+  static field core::int? _#staticField = null;
+  static field dynamic _#staticFinalField = null;
+  static field core::bool _#staticFinalField#isSet = false;
+  synthetic constructor •() → non::Class<non::Class::T>
+    : super core::Object::•()
+    ;
+  get instanceField() → core::int
+    return let final core::int? #t8 = this.{non::Class::_#Class#instanceField} in #t8.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'instanceField' has not been initialized.") : #t8{core::int};
+  set instanceField(core::int #t9) → void
+    this.{non::Class::_#Class#instanceField} = #t9;
+  get finalInstanceField() → dynamic
+    return this.{non::Class::_#Class#finalInstanceField#isSet} ?{dynamic} this.{non::Class::_#Class#finalInstanceField} : throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceField' has not been initialized.");
+  set finalInstanceField(dynamic #t10) → void
+    if(this.{non::Class::_#Class#finalInstanceField#isSet})
+      throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceField' has already been initialized.");
+    else {
+      this.{non::Class::_#Class#finalInstanceField#isSet} = true;
+      this.{non::Class::_#Class#finalInstanceField} = #t10;
+    }
+  get instanceTypeVariable() → non::Class::T
+    return let final non::Class::T? #t11 = this.{non::Class::_#Class#instanceTypeVariable} in #t11.==(null) ?{non::Class::T} throw new _in::LateInitializationErrorImpl::•("Field 'instanceTypeVariable' has not been initialized.") : #t11{non::Class::T};
+  set instanceTypeVariable(generic-covariant-impl non::Class::T #t12) → void
+    this.{non::Class::_#Class#instanceTypeVariable} = #t12;
+  get finalInstanceTypeVariable() → non::Class::T
+    return let final non::Class::T? #t13 = this.{non::Class::_#Class#finalInstanceTypeVariable} in #t13.==(null) ?{non::Class::T} throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceTypeVariable' has not been initialized.") : #t13{non::Class::T};
+  set finalInstanceTypeVariable(non::Class::T #t14) → void
+    if(this.{non::Class::_#Class#finalInstanceTypeVariable}.==(null))
+      this.{non::Class::_#Class#finalInstanceTypeVariable} = #t14;
+    else
+      throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceTypeVariable' has already been initialized.");
+  static get staticField() → core::int
+    return let final core::int? #t15 = non::Class::_#staticField in #t15.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'staticField' has not been initialized.") : #t15{core::int};
+  static set staticField(core::int #t16) → void
+    non::Class::_#staticField = #t16;
+  static get staticFinalField() → dynamic
+    return non::Class::_#staticFinalField#isSet ?{dynamic} non::Class::_#staticFinalField : throw new _in::LateInitializationErrorImpl::•("Field 'staticFinalField' has not been initialized.");
+  static set staticFinalField(dynamic #t17) → void
+    if(non::Class::_#staticFinalField#isSet)
+      throw new _in::LateInitializationErrorImpl::•("Field 'staticFinalField' has already been initialized.");
+    else {
+      non::Class::_#staticFinalField#isSet = true;
+      non::Class::_#staticFinalField = #t17;
+    }
+}
+static field core::int? _#topLevelField = null;
+static field dynamic _#finalTopLevelField = null;
+static field core::bool _#finalTopLevelField#isSet = false;
+static get topLevelField() → core::int
+  return let final core::int? #t18 = non::_#topLevelField in #t18.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'topLevelField' has not been initialized.") : #t18{core::int};
+static set topLevelField(core::int #t19) → void
+  non::_#topLevelField = #t19;
+static get finalTopLevelField() → dynamic
+  return non::_#finalTopLevelField#isSet ?{dynamic} non::_#finalTopLevelField : throw new _in::LateInitializationErrorImpl::•("Field 'finalTopLevelField' has not been initialized.");
+static set finalTopLevelField(dynamic #t20) → void
+  if(non::_#finalTopLevelField#isSet)
+    throw new _in::LateInitializationErrorImpl::•("Field 'finalTopLevelField' has already been initialized.");
+  else {
+    non::_#finalTopLevelField#isSet = true;
+    non::_#finalTopLevelField = #t20;
+  }
+static method method<T extends core::Object = core::Object>(core::bool b, core::int i, non::method::T t) → dynamic {
+  core::int? local;
+  function #local#get() → core::int
+    return let final core::int? #t21 = local in #t21.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local' has not been initialized.") : #t21{core::int};
+  function #local#set(core::int #t22) → dynamic
+    return local = #t22;
+  final dynamic finalLocal;
+  core::bool #finalLocal#isSet = false;
+  function #finalLocal#get() → dynamic
+    return #finalLocal#isSet ?{dynamic} finalLocal : throw new _in::LateInitializationErrorImpl::•("Local 'finalLocal' has not been initialized.");
+  function #finalLocal#set(dynamic #t23) → dynamic
+    if(#finalLocal#isSet)
+      throw new _in::LateInitializationErrorImpl::•("Local 'finalLocal' has already been initialized.");
+    else {
+      #finalLocal#isSet = true;
+      return finalLocal = #t23;
+    }
+  non::method::T? localTypeVariable;
+  function #localTypeVariable#get() → non::method::T
+    return let final non::method::T? #t24 = localTypeVariable in #t24.==(null) ?{non::method::T} throw new _in::LateInitializationErrorImpl::•("Local 'localTypeVariable' has not been initialized.") : #t24{non::method::T};
+  function #localTypeVariable#set(non::method::T #t25) → dynamic
+    return localTypeVariable = #t25;
+  final non::method::T? finalLocalTypeVariable;
+  function #finalLocalTypeVariable#get() → non::method::T
+    return let final non::method::T? #t26 = finalLocalTypeVariable in #t26.==(null) ?{non::method::T} throw new _in::LateInitializationErrorImpl::•("Local 'finalLocalTypeVariable' has not been initialized.") : #t26{non::method::T};
+  function #finalLocalTypeVariable#set(non::method::T #t27) → dynamic
+    if(finalLocalTypeVariable.==(null))
+      return finalLocalTypeVariable = #t27;
+    else
+      throw new _in::LateInitializationErrorImpl::•("Local 'finalLocalTypeVariable' has already been initialized.");
+  if(b) {
+    #local#set.call(i);
+    #finalLocal#set.call(i);
+    #localTypeVariable#set.call(t);
+    #finalLocalTypeVariable#set.call(t);
+    non::expect(i, #local#get.call());
+    non::expect(i, #finalLocal#get.call());
+    non::expect(t, #localTypeVariable#get.call());
+    non::expect(t, #finalLocalTypeVariable#get.call());
+  }
+  non::throws(() → core::int => #finalLocal#set.call(i));
+  non::throws(() → non::method::T => #finalLocalTypeVariable#set.call(t));
+}
+static method expect(dynamic expected, dynamic actual) → dynamic {
+  if(!expected.{core::Object::==}(actual))
+    throw "Expected ${expected}, actual ${actual}";
+}
+static method throws(() → void f) → dynamic {
+  try {
+    f.call();
+  }
+  on core::Object catch(final core::Object _) {
+    return;
+  }
+  throw "Missing exception";
+}

pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart.strong.transformed.expect

@@ -0,0 +1,217 @@
+library /*isNonNullableByDefault*/;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:5:1: Error: A library can't opt out of null safety by default, when using sound null safety.
+// // @dart=2.8
+// ^^^^^^^^^^^^
+//
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:10:19: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+//   topLevelField = null;
+//                   ^
+//
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:14:21: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+//   c.instanceField = null;
+//                     ^
+//
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:16:28: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+//   c.instanceTypeVariable = null;
+//                            ^
+//
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:17:33: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+//   c.finalInstanceTypeVariable = null;
+//                                 ^
+//
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:19:23: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+//   Class.staticField = null;
+//                       ^
+//
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:33:46: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+//   throws(() => c.finalInstanceTypeVariable = null);
+//                                              ^
+//
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:36:16: Error: The argument type 'Null' can't be assigned to the parameter type 'int'.
+//   method(true, null, null);
+//                ^
+//
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:36:3: Error: Inferred type argument 'Null' doesn't conform to the bound 'Object' of the type variable 'T' on 'method'.
+//  - 'Object' is from 'dart:core'.
+// Try specifying type arguments explicitly so that they conform to the bounds.
+//   method(true, null, null);
+//   ^
+// pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out_lib.dart:18:8: Context: This is the type variable whose bound isn't conformed to.
+// method<T extends Object>(bool b, int i, T t) {
+//        ^
+//
+import self as self;
+import "non_nullable_from_opt_out_lib.dart" as non;
+import "dart:core" as core;
+
+import "org-dartlang-testcase:///non_nullable_from_opt_out_lib.dart";
+
+static method main() → dynamic {
+  non::topLevelField = let final<BottomType> #t1 = invalid-expression "pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:10:19: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+  topLevelField = null;
+                  ^" in let core::Null? #t2 = null in #t2.==(null) ?{core::int} #t2 as{TypeError,ForNonNullableByDefault} core::int : #t2{core::int};
+  non::finalTopLevelField = null;
+  non::Class<core::int> c = new non::Class::•<core::int>();
+  c.{non::Class::instanceField} = let final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:14:21: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+  c.instanceField = null;
+                    ^" in let core::Null? #t4 = null in #t4.==(null) ?{core::int} #t4 as{TypeError,ForNonNullableByDefault} core::int : #t4{core::int};
+  c.{non::Class::finalInstanceField} = null;
+  c.{non::Class::instanceTypeVariable} = let final<BottomType> #t5 = invalid-expression "pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:16:28: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+  c.instanceTypeVariable = null;
+                           ^" in let core::Null? #t6 = null in #t6.==(null) ?{core::int} #t6 as{TypeError,ForNonNullableByDefault} core::int : #t6{core::int};
+  c.{non::Class::finalInstanceTypeVariable} = let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:17:33: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+  c.finalInstanceTypeVariable = null;
+                                ^" in let core::Null? #t8 = null in #t8.==(null) ?{core::int} #t8 as{TypeError,ForNonNullableByDefault} core::int : #t8{core::int};
+  non::Class::staticField = let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:19:23: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+  Class.staticField = null;
+                      ^" in let core::Null? #t10 = null in #t10.==(null) ?{core::int} #t10 as{TypeError,ForNonNullableByDefault} core::int : #t10{core::int};
+  non::Class::staticFinalField = null;
+  non::expect(null, non::topLevelField);
+  non::expect(null, non::finalTopLevelField);
+  non::expect(null, c.{non::Class::instanceField});
+  non::expect(null, c.{non::Class::finalInstanceField});
+  non::expect(null, c.{non::Class::instanceTypeVariable});
+  non::expect(null, c.{non::Class::finalInstanceTypeVariable});
+  non::expect(null, non::Class::staticField);
+  non::expect(null, non::Class::staticFinalField);
+  non::throws(() → core::Null? => non::finalTopLevelField = null);
+  non::throws(() → core::Null? => c.{non::Class::finalInstanceField} = null);
+  non::throws(() → core::Null? => c.{non::Class::finalInstanceTypeVariable} = let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:33:46: Error: A value of type 'Null' can't be assigned to a variable of type 'int'.
+  throws(() => c.finalInstanceTypeVariable = null);
+                                             ^" in let core::Null? #t12 = null in #t12.==(null) ?{core::int} #t12 as{TypeError,ForNonNullableByDefault} core::int : #t12{core::int});
+  non::throws(() → core::Null? => non::Class::staticFinalField = null);
+  non::method<core::Null?>(true, let final<BottomType> #t13 = invalid-expression "pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart:36:16: Error: The argument type 'Null' can't be assigned to the parameter type 'int'.
+  method(true, null, null);
+               ^" in let core::Null? #t14 = null in #t14.==(null) ?{core::int} #t14 as{TypeError,ForNonNullableByDefault} core::int : #t14{core::int}, null);
+}
+
+library /*isNonNullableByDefault*/;
+import self as non;
+import "dart:core" as core;
+import "dart:_internal" as _in;
+
+class Class<T extends core::Object = core::Object> extends core::Object {
+  field core::int? _#Class#instanceField = null;
+  field dynamic _#Class#finalInstanceField = null;
+  field core::bool _#Class#finalInstanceField#isSet = false;
+  generic-covariant-impl field non::Class::T? _#Class#instanceTypeVariable = null;
+  field non::Class::T? _#Class#finalInstanceTypeVariable = null;
+  static field core::int? _#staticField = null;
+  static field dynamic _#staticFinalField = null;
+  static field core::bool _#staticFinalField#isSet = false;
+  synthetic constructor •() → non::Class<non::Class::T>
+    : super core::Object::•()
+    ;
+  get instanceField() → core::int
+    return let final core::int? #t15 = this.{non::Class::_#Class#instanceField} in #t15.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'instanceField' has not been initialized.") : #t15{core::int};
+  set instanceField(core::int #t16) → void
+    this.{non::Class::_#Class#instanceField} = #t16;
+  get finalInstanceField() → dynamic
+    return this.{non::Class::_#Class#finalInstanceField#isSet} ?{dynamic} this.{non::Class::_#Class#finalInstanceField} : throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceField' has not been initialized.");
+  set finalInstanceField(dynamic #t17) → void
+    if(this.{non::Class::_#Class#finalInstanceField#isSet})
+      throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceField' has already been initialized.");
+    else {
+      this.{non::Class::_#Class#finalInstanceField#isSet} = true;
+      this.{non::Class::_#Class#finalInstanceField} = #t17;
+    }
+  get instanceTypeVariable() → non::Class::T
+    return let final non::Class::T? #t18 = this.{non::Class::_#Class#instanceTypeVariable} in #t18.==(null) ?{non::Class::T} throw new _in::LateInitializationErrorImpl::•("Field 'instanceTypeVariable' has not been initialized.") : #t18{non::Class::T};
+  set instanceTypeVariable(generic-covariant-impl non::Class::T #t19) → void
+    this.{non::Class::_#Class#instanceTypeVariable} = #t19;
+  get finalInstanceTypeVariable() → non::Class::T
+    return let final non::Class::T? #t20 = this.{non::Class::_#Class#finalInstanceTypeVariable} in #t20.==(null) ?{non::Class::T} throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceTypeVariable' has not been initialized.") : #t20{non::Class::T};
+  set finalInstanceTypeVariable(non::Class::T #t21) → void
+    if(this.{non::Class::_#Class#finalInstanceTypeVariable}.==(null))
+      this.{non::Class::_#Class#finalInstanceTypeVariable} = #t21;
+    else
+      throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceTypeVariable' has already been initialized.");
+  static get staticField() → core::int
+    return let final core::int? #t22 = non::Class::_#staticField in #t22.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'staticField' has not been initialized.") : #t22{core::int};
+  static set staticField(core::int #t23) → void
+    non::Class::_#staticField = #t23;
+  static get staticFinalField() → dynamic
+    return non::Class::_#staticFinalField#isSet ?{dynamic} non::Class::_#staticFinalField : throw new _in::LateInitializationErrorImpl::•("Field 'staticFinalField' has not been initialized.");
+  static set staticFinalField(dynamic #t24) → void
+    if(non::Class::_#staticFinalField#isSet)
+      throw new _in::LateInitializationErrorImpl::•("Field 'staticFinalField' has already been initialized.");
+    else {
+      non::Class::_#staticFinalField#isSet = true;
+      non::Class::_#staticFinalField = #t24;
+    }
+}
+static field core::int? _#topLevelField = null;
+static field dynamic _#finalTopLevelField = null;
+static field core::bool _#finalTopLevelField#isSet = false;
+static get topLevelField() → core::int
+  return let final core::int? #t25 = non::_#topLevelField in #t25.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'topLevelField' has not been initialized.") : #t25{core::int};
+static set topLevelField(core::int #t26) → void
+  non::_#topLevelField = #t26;
+static get finalTopLevelField() → dynamic
+  return non::_#finalTopLevelField#isSet ?{dynamic} non::_#finalTopLevelField : throw new _in::LateInitializationErrorImpl::•("Field 'finalTopLevelField' has not been initialized.");
+static set finalTopLevelField(dynamic #t27) → void
+  if(non::_#finalTopLevelField#isSet)
+    throw new _in::LateInitializationErrorImpl::•("Field 'finalTopLevelField' has already been initialized.");
+  else {
+    non::_#finalTopLevelField#isSet = true;
+    non::_#finalTopLevelField = #t27;
+  }
+static method method<T extends core::Object = core::Object>(core::bool b, core::int i, non::method::T t) → dynamic {
+  core::int? local;
+  function #local#get() → core::int
+    return let final core::int? #t28 = local in #t28.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Local 'local' has not been initialized.") : #t28{core::int};
+  function #local#set(core::int #t29) → dynamic
+    return local = #t29;
+  final dynamic finalLocal;
+  core::bool #finalLocal#isSet = false;
+  function #finalLocal#get() → dynamic
+    return #finalLocal#isSet ?{dynamic} finalLocal : throw new _in::LateInitializationErrorImpl::•("Local 'finalLocal' has not been initialized.");
+  function #finalLocal#set(dynamic #t30) → dynamic
+    if(#finalLocal#isSet)
+      throw new _in::LateInitializationErrorImpl::•("Local 'finalLocal' has already been initialized.");
+    else {
+      #finalLocal#isSet = true;
+      return finalLocal = #t30;
+    }
+  non::method::T? localTypeVariable;
+  function #localTypeVariable#get() → non::method::T
+    return let final non::method::T? #t31 = localTypeVariable in #t31.==(null) ?{non::method::T} throw new _in::LateInitializationErrorImpl::•("Local 'localTypeVariable' has not been initialized.") : #t31{non::method::T};
+  function #localTypeVariable#set(non::method::T #t32) → dynamic
+    return localTypeVariable = #t32;
+  final non::method::T? finalLocalTypeVariable;
+  function #finalLocalTypeVariable#get() → non::method::T
+    return let final non::method::T? #t33 = finalLocalTypeVariable in #t33.==(null) ?{non::method::T} throw new _in::LateInitializationErrorImpl::•("Local 'finalLocalTypeVariable' has not been initialized.") : #t33{non::method::T};
+  function #finalLocalTypeVariable#set(non::method::T #t34) → dynamic
+    if(finalLocalTypeVariable.==(null))
+      return finalLocalTypeVariable = #t34;
+    else
+      throw new _in::LateInitializationErrorImpl::•("Local 'finalLocalTypeVariable' has already been initialized.");
+  if(b) {
+    #local#set.call(i);
+    #finalLocal#set.call(i);
+    #localTypeVariable#set.call(t);
+    #finalLocalTypeVariable#set.call(t);
+    non::expect(i, #local#get.call());
+    non::expect(i, #finalLocal#get.call());
+    non::expect(t, #localTypeVariable#get.call());
+    non::expect(t, #finalLocalTypeVariable#get.call());
+  }
+  non::throws(() → core::int => #finalLocal#set.call(i));
+  non::throws(() → non::method::T => #finalLocalTypeVariable#set.call(t));
+}
+static method expect(dynamic expected, dynamic actual) → dynamic {
+  if(!expected.{core::Object::==}(actual))
+    throw "Expected ${expected}, actual ${actual}";
+}
+static method throws(() → void f) → dynamic {
+  try {
+    f.call();
+  }
+  on core::Object catch(final core::Object _) {
+    return;
+  }
+  throw "Missing exception";
+}

pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart.textual_outline.expect

@@ -0,0 +1,4 @@
+// @dart = 2.8
+import 'non_nullable_from_opt_out_lib.dart';
+
+main() {}

pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart.textual_outline_modelled.expect

@@ -0,0 +1,4 @@
+// @dart = 2.8
+import 'non_nullable_from_opt_out_lib.dart';
+
+main() {}

pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart.weak.expect

@@ -0,0 +1,183 @@
+library;
+import self as self;
+import "non_nullable_from_opt_out_lib.dart" as non;
+import "dart:core" as core;
+
+import "org-dartlang-testcase:///non_nullable_from_opt_out_lib.dart";
+
+static method main() → dynamic {
+  non::topLevelField = null;
+  non::finalTopLevelField = null;
+  non::Class<core::int*>* c = new non::Class::•<core::int*>();
+  c.{non::Class::instanceField} = null;
+  c.{non::Class::finalInstanceField} = null;
+  c.{non::Class::instanceTypeVariable} = null;
+  c.{non::Class::finalInstanceTypeVariable} = null;
+  non::Class::staticField = null;
+  non::Class::staticFinalField = null;
+  non::expect(null, non::topLevelField);
+  non::expect(null, non::finalTopLevelField);
+  non::expect(null, c.{non::Class::instanceField});
+  non::expect(null, c.{non::Class::finalInstanceField});
+  non::expect(null, c.{non::Class::instanceTypeVariable});
+  non::expect(null, c.{non::Class::finalInstanceTypeVariable});
+  non::expect(null, non::Class::staticField);
+  non::expect(null, non::Class::staticFinalField);
+  non::throws(() → core::Null? => non::finalTopLevelField = null);
+  non::throws(() → core::Null? => c.{non::Class::finalInstanceField} = null);
+  non::throws(() → core::Null? => c.{non::Class::finalInstanceTypeVariable} = null);
+  non::throws(() → core::Null? => non::Class::staticFinalField = null);
+  non::method<core::Null?>(true, null, null);
+}
+
+library /*isNonNullableByDefault*/;
+import self as non;
+import "dart:core" as core;
+import "dart:_internal" as _in;
+
+class Class<T extends core::Object = core::Object> extends core::Object {
+  field core::int? _#Class#instanceField = null;
+  field core::bool _#Class#instanceField#isSet = false;
+  field dynamic _#Class#finalInstanceField = null;
+  field core::bool _#Class#finalInstanceField#isSet = false;
+  generic-covariant-impl field non::Class::T? _#Class#instanceTypeVariable = null;
+  field core::bool _#Class#instanceTypeVariable#isSet = false;
+  field non::Class::T? _#Class#finalInstanceTypeVariable = null;
+  field core::bool _#Class#finalInstanceTypeVariable#isSet = false;
+  static field core::int? _#staticField = null;
+  static field core::bool _#staticField#isSet = false;
+  static field dynamic _#staticFinalField = null;
+  static field core::bool _#staticFinalField#isSet = false;
+  synthetic constructor •() → non::Class<non::Class::T>
+    : super core::Object::•()
+    ;
+  get instanceField() → core::int
+    return this.{non::Class::_#Class#instanceField#isSet} ?{core::int} let final core::int? #t1 = this.{non::Class::_#Class#instanceField} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'instanceField' has not been initialized.");
+  set instanceField(core::int #t2) → void {
+    this.{non::Class::_#Class#instanceField#isSet} = true;
+    this.{non::Class::_#Class#instanceField} = #t2;
+  }
+  get finalInstanceField() → dynamic
+    return this.{non::Class::_#Class#finalInstanceField#isSet} ?{dynamic} this.{non::Class::_#Class#finalInstanceField} : throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceField' has not been initialized.");
+  set finalInstanceField(dynamic #t3) → void
+    if(this.{non::Class::_#Class#finalInstanceField#isSet})
+      throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceField' has already been initialized.");
+    else {
+      this.{non::Class::_#Class#finalInstanceField#isSet} = true;
+      this.{non::Class::_#Class#finalInstanceField} = #t3;
+    }
+  get instanceTypeVariable() → non::Class::T
+    return this.{non::Class::_#Class#instanceTypeVariable#isSet} ?{non::Class::T} let final non::Class::T? #t4 = this.{non::Class::_#Class#instanceTypeVariable} in #t4{non::Class::T} : throw new _in::LateInitializationErrorImpl::•("Field 'instanceTypeVariable' has not been initialized.");
+  set instanceTypeVariable(generic-covariant-impl non::Class::T #t5) → void {
+    this.{non::Class::_#Class#instanceTypeVariable#isSet} = true;
+    this.{non::Class::_#Class#instanceTypeVariable} = #t5;
+  }
+  get finalInstanceTypeVariable() → non::Class::T
+    return this.{non::Class::_#Class#finalInstanceTypeVariable#isSet} ?{non::Class::T} let final non::Class::T? #t6 = this.{non::Class::_#Class#finalInstanceTypeVariable} in #t6{non::Class::T} : throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceTypeVariable' has not been initialized.");
+  set finalInstanceTypeVariable(non::Class::T #t7) → void
+    if(this.{non::Class::_#Class#finalInstanceTypeVariable#isSet})
+      throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceTypeVariable' has already been initialized.");
+    else {
+      this.{non::Class::_#Class#finalInstanceTypeVariable#isSet} = true;
+      this.{non::Class::_#Class#finalInstanceTypeVariable} = #t7;
+    }
+  static get staticField() → core::int
+    return non::Class::_#staticField#isSet ?{core::int} let final core::int? #t8 = non::Class::_#staticField in #t8{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'staticField' has not been initialized.");
+  static set staticField(core::int #t9) → void {
+    non::Class::_#staticField#isSet = true;
+    non::Class::_#staticField = #t9;
+  }
+  static get staticFinalField() → dynamic
+    return non::Class::_#staticFinalField#isSet ?{dynamic} non::Class::_#staticFinalField : throw new _in::LateInitializationErrorImpl::•("Field 'staticFinalField' has not been initialized.");
+  static set staticFinalField(dynamic #t10) → void
+    if(non::Class::_#staticFinalField#isSet)
+      throw new _in::LateInitializationErrorImpl::•("Field 'staticFinalField' has already been initialized.");
+    else {
+      non::Class::_#staticFinalField#isSet = true;
+      non::Class::_#staticFinalField = #t10;
+    }
+}
+static field core::int? _#topLevelField = null;
+static field core::bool _#topLevelField#isSet = false;
+static field dynamic _#finalTopLevelField = null;
+static field core::bool _#finalTopLevelField#isSet = false;
+static get topLevelField() → core::int
+  return non::_#topLevelField#isSet ?{core::int} let final core::int? #t11 = non::_#topLevelField in #t11{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'topLevelField' has not been initialized.");
+static set topLevelField(core::int #t12) → void {
+  non::_#topLevelField#isSet = true;
+  non::_#topLevelField = #t12;
+}
+static get finalTopLevelField() → dynamic
+  return non::_#finalTopLevelField#isSet ?{dynamic} non::_#finalTopLevelField : throw new _in::LateInitializationErrorImpl::•("Field 'finalTopLevelField' has not been initialized.");
+static set finalTopLevelField(dynamic #t13) → void
+  if(non::_#finalTopLevelField#isSet)
+    throw new _in::LateInitializationErrorImpl::•("Field 'finalTopLevelField' has already been initialized.");
+  else {
+    non::_#finalTopLevelField#isSet = true;
+    non::_#finalTopLevelField = #t13;
+  }
+static method method<T extends core::Object = core::Object>(core::bool b, core::int i, non::method::T t) → dynamic {
+  core::int? local;
+  core::bool #local#isSet = false;
+  function #local#get() → core::int
+    return #local#isSet ?{core::int} local{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local' has not been initialized.");
+  function #local#set(core::int #t14) → dynamic {
+    #local#isSet = true;
+    return local = #t14;
+  }
+  final dynamic finalLocal;
+  core::bool #finalLocal#isSet = false;
+  function #finalLocal#get() → dynamic
+    return #finalLocal#isSet ?{dynamic} finalLocal : throw new _in::LateInitializationErrorImpl::•("Local 'finalLocal' has not been initialized.");
+  function #finalLocal#set(dynamic #t15) → dynamic
+    if(#finalLocal#isSet)
+      throw new _in::LateInitializationErrorImpl::•("Local 'finalLocal' has already been initialized.");
+    else {
+      #finalLocal#isSet = true;
+      return finalLocal = #t15;
+    }
+  non::method::T? localTypeVariable;
+  core::bool #localTypeVariable#isSet = false;
+  function #localTypeVariable#get() → non::method::T
+    return #localTypeVariable#isSet ?{non::method::T} localTypeVariable{non::method::T} : throw new _in::LateInitializationErrorImpl::•("Local 'localTypeVariable' has not been initialized.");
+  function #localTypeVariable#set(non::method::T #t16) → dynamic {
+    #localTypeVariable#isSet = true;
+    return localTypeVariable = #t16;
+  }
+  final non::method::T? finalLocalTypeVariable;
+  core::bool #finalLocalTypeVariable#isSet = false;
+  function #finalLocalTypeVariable#get() → non::method::T
+    return #finalLocalTypeVariable#isSet ?{non::method::T} finalLocalTypeVariable{non::method::T} : throw new _in::LateInitializationErrorImpl::•("Local 'finalLocalTypeVariable' has not been initialized.");
+  function #finalLocalTypeVariable#set(non::method::T #t17) → dynamic
+    if(#finalLocalTypeVariable#isSet)
+      throw new _in::LateInitializationErrorImpl::•("Local 'finalLocalTypeVariable' has already been initialized.");
+    else {
+      #finalLocalTypeVariable#isSet = true;
+      return finalLocalTypeVariable = #t17;
+    }
+  if(b) {
+    #local#set.call(i);
+    #finalLocal#set.call(i);
+    #localTypeVariable#set.call(t);
+    #finalLocalTypeVariable#set.call(t);
+    non::expect(i, #local#get.call());
+    non::expect(i, #finalLocal#get.call());
+    non::expect(t, #localTypeVariable#get.call());
+    non::expect(t, #finalLocalTypeVariable#get.call());
+  }
+  non::throws(() → core::int => #finalLocal#set.call(i));
+  non::throws(() → non::method::T => #finalLocalTypeVariable#set.call(t));
+}
+static method expect(dynamic expected, dynamic actual) → dynamic {
+  if(!expected.{core::Object::==}(actual))
+    throw "Expected ${expected}, actual ${actual}";
+}
+static method throws(() → void f) → dynamic {
+  try {
+    f.call();
+  }
+  on core::Object catch(final core::Object _) {
+    return;
+  }
+  throw "Missing exception";
+}

pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out.dart.weak.transformed.expect

@@ -0,0 +1,183 @@
+library;
+import self as self;
+import "non_nullable_from_opt_out_lib.dart" as non;
+import "dart:core" as core;
+
+import "org-dartlang-testcase:///non_nullable_from_opt_out_lib.dart";
+
+static method main() → dynamic {
+  non::topLevelField = null;
+  non::finalTopLevelField = null;
+  non::Class<core::int*>* c = new non::Class::•<core::int*>();
+  c.{non::Class::instanceField} = null;
+  c.{non::Class::finalInstanceField} = null;
+  c.{non::Class::instanceTypeVariable} = null;
+  c.{non::Class::finalInstanceTypeVariable} = null;
+  non::Class::staticField = null;
+  non::Class::staticFinalField = null;
+  non::expect(null, non::topLevelField);
+  non::expect(null, non::finalTopLevelField);
+  non::expect(null, c.{non::Class::instanceField});
+  non::expect(null, c.{non::Class::finalInstanceField});
+  non::expect(null, c.{non::Class::instanceTypeVariable});
+  non::expect(null, c.{non::Class::finalInstanceTypeVariable});
+  non::expect(null, non::Class::staticField);
+  non::expect(null, non::Class::staticFinalField);
+  non::throws(() → core::Null? => non::finalTopLevelField = null);
+  non::throws(() → core::Null? => c.{non::Class::finalInstanceField} = null);
+  non::throws(() → core::Null? => c.{non::Class::finalInstanceTypeVariable} = null);
+  non::throws(() → core::Null? => non::Class::staticFinalField = null);
+  non::method<core::Null?>(true, null, null);
+}
+
+library /*isNonNullableByDefault*/;
+import self as non;
+import "dart:core" as core;
+import "dart:_internal" as _in;
+
+class Class<T extends core::Object = core::Object> extends core::Object {
+  field core::int? _#Class#instanceField = null;
+  field core::bool _#Class#instanceField#isSet = false;
+  field dynamic _#Class#finalInstanceField = null;
+  field core::bool _#Class#finalInstanceField#isSet = false;
+  generic-covariant-impl field non::Class::T? _#Class#instanceTypeVariable = null;
+  field core::bool _#Class#instanceTypeVariable#isSet = false;
+  field non::Class::T? _#Class#finalInstanceTypeVariable = null;
+  field core::bool _#Class#finalInstanceTypeVariable#isSet = false;
+  static field core::int? _#staticField = null;
+  static field core::bool _#staticField#isSet = false;
+  static field dynamic _#staticFinalField = null;
+  static field core::bool _#staticFinalField#isSet = false;
+  synthetic constructor •() → non::Class<non::Class::T>
+    : super core::Object::•()
+    ;
+  get instanceField() → core::int
+    return this.{non::Class::_#Class#instanceField#isSet} ?{core::int} let final core::int? #t1 = this.{non::Class::_#Class#instanceField} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'instanceField' has not been initialized.");
+  set instanceField(core::int #t2) → void {
+    this.{non::Class::_#Class#instanceField#isSet} = true;
+    this.{non::Class::_#Class#instanceField} = #t2;
+  }
+  get finalInstanceField() → dynamic
+    return this.{non::Class::_#Class#finalInstanceField#isSet} ?{dynamic} this.{non::Class::_#Class#finalInstanceField} : throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceField' has not been initialized.");
+  set finalInstanceField(dynamic #t3) → void
+    if(this.{non::Class::_#Class#finalInstanceField#isSet})
+      throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceField' has already been initialized.");
+    else {
+      this.{non::Class::_#Class#finalInstanceField#isSet} = true;
+      this.{non::Class::_#Class#finalInstanceField} = #t3;
+    }
+  get instanceTypeVariable() → non::Class::T
+    return this.{non::Class::_#Class#instanceTypeVariable#isSet} ?{non::Class::T} let final non::Class::T? #t4 = this.{non::Class::_#Class#instanceTypeVariable} in #t4{non::Class::T} : throw new _in::LateInitializationErrorImpl::•("Field 'instanceTypeVariable' has not been initialized.");
+  set instanceTypeVariable(generic-covariant-impl non::Class::T #t5) → void {
+    this.{non::Class::_#Class#instanceTypeVariable#isSet} = true;
+    this.{non::Class::_#Class#instanceTypeVariable} = #t5;
+  }
+  get finalInstanceTypeVariable() → non::Class::T
+    return this.{non::Class::_#Class#finalInstanceTypeVariable#isSet} ?{non::Class::T} let final non::Class::T? #t6 = this.{non::Class::_#Class#finalInstanceTypeVariable} in #t6{non::Class::T} : throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceTypeVariable' has not been initialized.");
+  set finalInstanceTypeVariable(non::Class::T #t7) → void
+    if(this.{non::Class::_#Class#finalInstanceTypeVariable#isSet})
+      throw new _in::LateInitializationErrorImpl::•("Field 'finalInstanceTypeVariable' has already been initialized.");
+    else {
+      this.{non::Class::_#Class#finalInstanceTypeVariable#isSet} = true;
+      this.{non::Class::_#Class#finalInstanceTypeVariable} = #t7;
+    }
+  static get staticField() → core::int
+    return non::Class::_#staticField#isSet ?{core::int} let final core::int? #t8 = non::Class::_#staticField in #t8{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'staticField' has not been initialized.");
+  static set staticField(core::int #t9) → void {
+    non::Class::_#staticField#isSet = true;
+    non::Class::_#staticField = #t9;
+  }
+  static get staticFinalField() → dynamic
+    return non::Class::_#staticFinalField#isSet ?{dynamic} non::Class::_#staticFinalField : throw new _in::LateInitializationErrorImpl::•("Field 'staticFinalField' has not been initialized.");
+  static set staticFinalField(dynamic #t10) → void
+    if(non::Class::_#staticFinalField#isSet)
+      throw new _in::LateInitializationErrorImpl::•("Field 'staticFinalField' has already been initialized.");
+    else {
+      non::Class::_#staticFinalField#isSet = true;
+      non::Class::_#staticFinalField = #t10;
+    }
+}
+static field core::int? _#topLevelField = null;
+static field core::bool _#topLevelField#isSet = false;
+static field dynamic _#finalTopLevelField = null;
+static field core::bool _#finalTopLevelField#isSet = false;
+static get topLevelField() → core::int
+  return non::_#topLevelField#isSet ?{core::int} let final core::int? #t11 = non::_#topLevelField in #t11{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'topLevelField' has not been initialized.");
+static set topLevelField(core::int #t12) → void {
+  non::_#topLevelField#isSet = true;
+  non::_#topLevelField = #t12;
+}
+static get finalTopLevelField() → dynamic
+  return non::_#finalTopLevelField#isSet ?{dynamic} non::_#finalTopLevelField : throw new _in::LateInitializationErrorImpl::•("Field 'finalTopLevelField' has not been initialized.");
+static set finalTopLevelField(dynamic #t13) → void
+  if(non::_#finalTopLevelField#isSet)
+    throw new _in::LateInitializationErrorImpl::•("Field 'finalTopLevelField' has already been initialized.");
+  else {
+    non::_#finalTopLevelField#isSet = true;
+    non::_#finalTopLevelField = #t13;
+  }
+static method method<T extends core::Object = core::Object>(core::bool b, core::int i, non::method::T t) → dynamic {
+  core::int? local;
+  core::bool #local#isSet = false;
+  function #local#get() → core::int
+    return #local#isSet ?{core::int} local{core::int} : throw new _in::LateInitializationErrorImpl::•("Local 'local' has not been initialized.");
+  function #local#set(core::int #t14) → dynamic {
+    #local#isSet = true;
+    return local = #t14;
+  }
+  final dynamic finalLocal;
+  core::bool #finalLocal#isSet = false;
+  function #finalLocal#get() → dynamic
+    return #finalLocal#isSet ?{dynamic} finalLocal : throw new _in::LateInitializationErrorImpl::•("Local 'finalLocal' has not been initialized.");
+  function #finalLocal#set(dynamic #t15) → dynamic
+    if(#finalLocal#isSet)
+      throw new _in::LateInitializationErrorImpl::•("Local 'finalLocal' has already been initialized.");
+    else {
+      #finalLocal#isSet = true;
+      return finalLocal = #t15;
+    }
+  non::method::T? localTypeVariable;
+  core::bool #localTypeVariable#isSet = false;
+  function #localTypeVariable#get() → non::method::T
+    return #localTypeVariable#isSet ?{non::method::T} localTypeVariable{non::method::T} : throw new _in::LateInitializationErrorImpl::•("Local 'localTypeVariable' has not been initialized.");
+  function #localTypeVariable#set(non::method::T #t16) → dynamic {
+    #localTypeVariable#isSet = true;
+    return localTypeVariable = #t16;
+  }
+  final non::method::T? finalLocalTypeVariable;
+  core::bool #finalLocalTypeVariable#isSet = false;
+  function #finalLocalTypeVariable#get() → non::method::T
+    return #finalLocalTypeVariable#isSet ?{non::method::T} finalLocalTypeVariable{non::method::T} : throw new _in::LateInitializationErrorImpl::•("Local 'finalLocalTypeVariable' has not been initialized.");
+  function #finalLocalTypeVariable#set(non::method::T #t17) → dynamic
+    if(#finalLocalTypeVariable#isSet)
+      throw new _in::LateInitializationErrorImpl::•("Local 'finalLocalTypeVariable' has already been initialized.");
+    else {
+      #finalLocalTypeVariable#isSet = true;
+      return finalLocalTypeVariable = #t17;
+    }
+  if(b) {
+    #local#set.call(i);
+    #finalLocal#set.call(i);
+    #localTypeVariable#set.call(t);
+    #finalLocalTypeVariable#set.call(t);
+    non::expect(i, #local#get.call());
+    non::expect(i, #finalLocal#get.call());
+    non::expect(t, #localTypeVariable#get.call());
+    non::expect(t, #finalLocalTypeVariable#get.call());
+  }
+  non::throws(() → core::int => #finalLocal#set.call(i));
+  non::throws(() → non::method::T => #finalLocalTypeVariable#set.call(t));
+}
+static method expect(dynamic expected, dynamic actual) → dynamic {
+  if(!expected.{core::Object::==}(actual))
+    throw "Expected ${expected}, actual ${actual}";
+}
+static method throws(() → void f) → dynamic {
+  try {
+    f.call();
+  }
+  on core::Object catch(final core::Object _) {
+    return;
+  }
+  throw "Missing exception";
+}

pkg/front_end/testcases/late_lowering/non_nullable_from_opt_out_lib.dart

@@ -0,0 +1,52 @@
+// 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.
+
+late int topLevelField;
+late final finalTopLevelField;
+
+class Class<T extends Object> {
+  late int instanceField;
+  late final finalInstanceField;
+  late T instanceTypeVariable;
+  late final T finalInstanceTypeVariable;
+
+  static late int staticField;
+  static late final staticFinalField;
+}
+
+method<T extends Object>(bool b, int i, T t) {
+  late int local;
+  late final finalLocal;
+  late T localTypeVariable;
+  late final T finalLocalTypeVariable;
+
+  if (b) {
+    // Ensure assignments below are not definitely assigned.
+    local = i;
+    finalLocal = i;
+    localTypeVariable = t;
+    finalLocalTypeVariable = t;
+
+    expect(i, local);
+    expect(i, finalLocal);
+    expect(t, localTypeVariable);
+    expect(t, finalLocalTypeVariable);
+  }
+
+  throws(() => finalLocal = i);
+  throws(() => finalLocalTypeVariable = t);
+}
+
+expect(expected, actual) {
+  if (expected != actual) throw 'Expected $expected, actual $actual';
+}
+
+throws(void Function() f) {
+  try {
+    f();
+  } catch (_) {
+    return;
+  }
+  throw 'Missing exception';
+}

pkg/front_end/testcases/late_lowering/override.dart.weak.expect

@@ -5,58 +5,85 @@ import "dart:_internal" as _in;
 
 class Class extends core::Object {
   field core::int? _#Class#field1 = null;
+  field core::bool _#Class#field1#isSet = false;
   field core::int? _#Class#field2 = null;
+  field core::bool _#Class#field2#isSet = false;
   field core::int? _#Class#field3 = null;
+  field core::bool _#Class#field3#isSet = false;
   field core::int? _#Class#field4 = null;
+  field core::bool _#Class#field4#isSet = false;
   synthetic constructor •() → self::Class
     : super core::Object::•()
     ;
   get field1() → core::int
-    return let final core::int? #t1 = this.{self::Class::_#Class#field1} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'field1' has not been initialized.") : #t1{core::int};
-  set field1(core::int #t2) → void
+    return this.{self::Class::_#Class#field1#isSet} ?{core::int} let final core::int? #t1 = this.{self::Class::_#Class#field1} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'field1' has not been initialized.");
+  set field1(core::int #t2) → void {
+    this.{self::Class::_#Class#field1#isSet} = true;
     this.{self::Class::_#Class#field1} = #t2;
+  }
   get field2() → core::int
-    return let final core::int? #t3 = this.{self::Class::_#Class#field2} in #t3.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'field2' has not been initialized.") : #t3{core::int};
-  set field2(core::int #t4) → void
+    return this.{self::Class::_#Class#field2#isSet} ?{core::int} let final core::int? #t3 = this.{self::Class::_#Class#field2} in #t3{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'field2' has not been initialized.");
+  set field2(core::int #t4) → void {
+    this.{self::Class::_#Class#field2#isSet} = true;
     this.{self::Class::_#Class#field2} = #t4;
+  }
   get field3() → core::int
-    return let final core::int? #t5 = this.{self::Class::_#Class#field3} in #t5.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'field3' has not been initialized.") : #t5{core::int};
+    return this.{self::Class::_#Class#field3#isSet} ?{core::int} let final core::int? #t5 = this.{self::Class::_#Class#field3} in #t5{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'field3' has not been initialized.");
   set field3(core::int #t6) → void
-    if(this.{self::Class::_#Class#field3}.==(null))
-      this.{self::Class::_#Class#field3} = #t6;
-    else
+    if(this.{self::Class::_#Class#field3#isSet})
       throw new _in::LateInitializationErrorImpl::•("Field 'field3' has already been initialized.");
+    else {
+      this.{self::Class::_#Class#field3#isSet} = true;
+      this.{self::Class::_#Class#field3} = #t6;
+    }
   get field4() → core::int
-    return let final core::int? #t7 = this.{self::Class::_#Class#field4} in #t7.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'field4' has not been initialized.") : #t7{core::int};
+    return this.{self::Class::_#Class#field4#isSet} ?{core::int} let final core::int? #t7 = this.{self::Class::_#Class#field4} in #t7{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'field4' has not been initialized.");
   set field4(core::int #t8) → void
-    if(this.{self::Class::_#Class#field4}.==(null))
-      this.{self::Class::_#Class#field4} = #t8;
-    else
+    if(this.{self::Class::_#Class#field4#isSet})
       throw new _in::LateInitializationErrorImpl::•("Field 'field4' has already been initialized.");
+    else {
+      this.{self::Class::_#Class#field4#isSet} = true;
+      this.{self::Class::_#Class#field4} = #t8;
+    }
 }
 class SubClass extends self::Class {
   field core::int? _#SubClass#field1 = null;
+  field core::bool _#SubClass#field1#isSet = false;
   field core::int? _#SubClass#field2 = null;
+  field core::bool _#SubClass#field2#isSet = false;
   field core::int? _#SubClass#field3 = null;
+  field core::bool _#SubClass#field3#isSet = false;
   field core::int? _#SubClass#field4 = null;
+  field core::bool _#SubClass#field4#isSet = false;
   synthetic constructor •() → self::SubClass
     : super self::Class::•()
     ;
   get field1() → core::int
-    return let final core::int? #t9 = this.{self::SubClass::_#SubClass#field1} in #t9.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'field1' has not been initialized.") : #t9{core::int};
-  set field1(core::int #t10) → void
+    return this.{self::SubClass::_#SubClass#field1#isSet} ?{core::int} let final core::int? #t9 = this.{self::SubClass::_#SubClass#field1} in #t9{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'field1' has not been initialized.");
+  set field1(core::int #t10) → void {
+    this.{self::SubClass::_#SubClass#field1#isSet} = true;
     this.{self::SubClass::_#SubClass#field1} = #t10;
-  get field2() → core::int
-    return let final core::int? #t11 = this.{self::SubClass::_#SubClass#field2} in #t11.==(null) ?{core::int} this.{self::SubClass::_#SubClass#field2} = 0 : #t11{core::int};
-  set field2(core::int #t12) → void
+  }
+  get field2() → core::int {
+    if(!this.{self::SubClass::_#SubClass#field2#isSet}) {
+      this.{self::SubClass::_#SubClass#field2} = 0;
+      this.{self::SubClass::_#SubClass#field2#isSet} = true;
+    }
+    return let final core::int? #t11 = this.{self::SubClass::_#SubClass#field2} in #t11{core::int};
+  }
+  set field2(core::int #t12) → void {
+    this.{self::SubClass::_#SubClass#field2#isSet} = true;
     this.{self::SubClass::_#SubClass#field2} = #t12;
+  }
   get field3() → core::int
-    return let final core::int? #t13 = this.{self::SubClass::_#SubClass#field3} in #t13.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'field3' has not been initialized.") : #t13{core::int};
+    return this.{self::SubClass::_#SubClass#field3#isSet} ?{core::int} let final core::int? #t13 = this.{self::SubClass::_#SubClass#field3} in #t13{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'field3' has not been initialized.");
   set field3(core::int #t14) → void
-    if(this.{self::SubClass::_#SubClass#field3}.==(null))
-      this.{self::SubClass::_#SubClass#field3} = #t14;
-    else
+    if(this.{self::SubClass::_#SubClass#field3#isSet})
       throw new _in::LateInitializationErrorImpl::•("Field 'field3' has already been initialized.");
+    else {
+      this.{self::SubClass::_#SubClass#field3#isSet} = true;
+      this.{self::SubClass::_#SubClass#field3} = #t14;
+    }
   get field4() → core::int
     return let final core::int? #t15 = this.{self::SubClass::_#SubClass#field4} in #t15.==(null) ?{core::int} let final core::int #t16 = 0 in this.{self::SubClass::_#SubClass#field4}.==(null) ?{core::int} this.{self::SubClass::_#SubClass#field4} = #t16 : throw new _in::LateInitializationErrorImpl::•("Field 'field4' has been assigned during initialization.") : #t15{core::int};
   get directField1() → core::int

pkg/front_end/testcases/late_lowering/override.dart.weak.transformed.expect

@@ -5,58 +5,85 @@ import "dart:_internal" as _in;
 
 class Class extends core::Object {
   field core::int? _#Class#field1 = null;
+  field core::bool _#Class#field1#isSet = false;
   field core::int? _#Class#field2 = null;
+  field core::bool _#Class#field2#isSet = false;
   field core::int? _#Class#field3 = null;
+  field core::bool _#Class#field3#isSet = false;
   field core::int? _#Class#field4 = null;
+  field core::bool _#Class#field4#isSet = false;
   synthetic constructor •() → self::Class
     : super core::Object::•()
     ;
   get field1() → core::int
-    return let final core::int? #t1 = this.{self::Class::_#Class#field1} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'field1' has not been initialized.") : #t1{core::int};
-  set field1(core::int #t2) → void
+    return this.{self::Class::_#Class#field1#isSet} ?{core::int} let final core::int? #t1 = this.{self::Class::_#Class#field1} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'field1' has not been initialized.");
+  set field1(core::int #t2) → void {
+    this.{self::Class::_#Class#field1#isSet} = true;
     this.{self::Class::_#Class#field1} = #t2;
+  }
   get field2() → core::int
-    return let final core::int? #t3 = this.{self::Class::_#Class#field2} in #t3.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'field2' has not been initialized.") : #t3{core::int};
-  set field2(core::int #t4) → void
+    return this.{self::Class::_#Class#field2#isSet} ?{core::int} let final core::int? #t3 = this.{self::Class::_#Class#field2} in #t3{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'field2' has not been initialized.");
+  set field2(core::int #t4) → void {
+    this.{self::Class::_#Class#field2#isSet} = true;
     this.{self::Class::_#Class#field2} = #t4;
+  }
   get field3() → core::int
-    return let final core::int? #t5 = this.{self::Class::_#Class#field3} in #t5.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'field3' has not been initialized.") : #t5{core::int};
+    return this.{self::Class::_#Class#field3#isSet} ?{core::int} let final core::int? #t5 = this.{self::Class::_#Class#field3} in #t5{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'field3' has not been initialized.");
   set field3(core::int #t6) → void
-    if(this.{self::Class::_#Class#field3}.==(null))
-      this.{self::Class::_#Class#field3} = #t6;
-    else
+    if(this.{self::Class::_#Class#field3#isSet})
       throw new _in::LateInitializationErrorImpl::•("Field 'field3' has already been initialized.");
+    else {
+      this.{self::Class::_#Class#field3#isSet} = true;
+      this.{self::Class::_#Class#field3} = #t6;
+    }
   get field4() → core::int
-    return let final core::int? #t7 = this.{self::Class::_#Class#field4} in #t7.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'field4' has not been initialized.") : #t7{core::int};
+    return this.{self::Class::_#Class#field4#isSet} ?{core::int} let final core::int? #t7 = this.{self::Class::_#Class#field4} in #t7{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'field4' has not been initialized.");
   set field4(core::int #t8) → void
-    if(this.{self::Class::_#Class#field4}.==(null))
-      this.{self::Class::_#Class#field4} = #t8;
-    else
+    if(this.{self::Class::_#Class#field4#isSet})
       throw new _in::LateInitializationErrorImpl::•("Field 'field4' has already been initialized.");
+    else {
+      this.{self::Class::_#Class#field4#isSet} = true;
+      this.{self::Class::_#Class#field4} = #t8;
+    }
 }
 class SubClass extends self::Class {
   field core::int? _#SubClass#field1 = null;
+  field core::bool _#SubClass#field1#isSet = false;
   field core::int? _#SubClass#field2 = null;
+  field core::bool _#SubClass#field2#isSet = false;
   field core::int? _#SubClass#field3 = null;
+  field core::bool _#SubClass#field3#isSet = false;
   field core::int? _#SubClass#field4 = null;
+  field core::bool _#SubClass#field4#isSet = false;
   synthetic constructor •() → self::SubClass
     : super self::Class::•()
     ;
   get field1() → core::int
-    return let final core::int? #t9 = this.{self::SubClass::_#SubClass#field1} in #t9.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'field1' has not been initialized.") : #t9{core::int};
-  set field1(core::int #t10) → void
+    return this.{self::SubClass::_#SubClass#field1#isSet} ?{core::int} let final core::int? #t9 = this.{self::SubClass::_#SubClass#field1} in #t9{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'field1' has not been initialized.");
+  set field1(core::int #t10) → void {
+    this.{self::SubClass::_#SubClass#field1#isSet} = true;
     this.{self::SubClass::_#SubClass#field1} = #t10;
-  get field2() → core::int
-    return let final core::int? #t11 = this.{self::SubClass::_#SubClass#field2} in #t11.==(null) ?{core::int} this.{self::SubClass::_#SubClass#field2} = 0 : #t11{core::int};
-  set field2(core::int #t12) → void
+  }
+  get field2() → core::int {
+    if(!this.{self::SubClass::_#SubClass#field2#isSet}) {
+      this.{self::SubClass::_#SubClass#field2} = 0;
+      this.{self::SubClass::_#SubClass#field2#isSet} = true;
+    }
+    return let final core::int? #t11 = this.{self::SubClass::_#SubClass#field2} in #t11{core::int};
+  }
+  set field2(core::int #t12) → void {
+    this.{self::SubClass::_#SubClass#field2#isSet} = true;
     this.{self::SubClass::_#SubClass#field2} = #t12;
+  }
   get field3() → core::int
-    return let final core::int? #t13 = this.{self::SubClass::_#SubClass#field3} in #t13.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'field3' has not been initialized.") : #t13{core::int};
+    return this.{self::SubClass::_#SubClass#field3#isSet} ?{core::int} let final core::int? #t13 = this.{self::SubClass::_#SubClass#field3} in #t13{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'field3' has not been initialized.");
   set field3(core::int #t14) → void
-    if(this.{self::SubClass::_#SubClass#field3}.==(null))
-      this.{self::SubClass::_#SubClass#field3} = #t14;
-    else
+    if(this.{self::SubClass::_#SubClass#field3#isSet})
       throw new _in::LateInitializationErrorImpl::•("Field 'field3' has already been initialized.");
+    else {
+      this.{self::SubClass::_#SubClass#field3#isSet} = true;
+      this.{self::SubClass::_#SubClass#field3} = #t14;
+    }
   get field4() → core::int
     return let final core::int? #t15 = this.{self::SubClass::_#SubClass#field4} in #t15.==(null) ?{core::int} let final core::int #t16 = 0 in this.{self::SubClass::_#SubClass#field4}.==(null) ?{core::int} this.{self::SubClass::_#SubClass#field4} = #t16 : throw new _in::LateInitializationErrorImpl::•("Field 'field4' has been assigned during initialization.") : #t15{core::int};
   get directField1() → core::int

pkg/front_end/testcases/late_lowering/override_getter_setter.dart.weak.expect

@@ -5,18 +5,21 @@ import "dart:_internal" as _in;
 
 class A extends core::Object {
   field core::int? _#A#x = null;
+  field core::bool _#A#x#isSet = false;
   field core::int? _#A#y = null;
   field core::bool _#A#y#isSet = false;
   synthetic constructor •() → self::A
     : super core::Object::•()
     ;
   get x() → core::int
-    return let final core::int? #t1 = this.{self::A::_#A#x} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.") : #t1{core::int};
+    return this.{self::A::_#A#x#isSet} ?{core::int} let final core::int? #t1 = this.{self::A::_#A#x} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.");
   set x(core::int #t2) → void
-    if(this.{self::A::_#A#x}.==(null))
-      this.{self::A::_#A#x} = #t2;
-    else
+    if(this.{self::A::_#A#x#isSet})
       throw new _in::LateInitializationErrorImpl::•("Field 'x' has already been initialized.");
+    else {
+      this.{self::A::_#A#x#isSet} = true;
+      this.{self::A::_#A#x} = #t2;
+    }
   get y() → core::int?
     return this.{self::A::_#A#y#isSet} ?{core::int?} this.{self::A::_#A#y} : throw new _in::LateInitializationErrorImpl::•("Field 'y' has not been initialized.");
   set y(core::int? #t3) → void
@@ -38,6 +41,7 @@ class B extends self::A {
 }
 class C extends self::A {
   field core::int? _#C#x = null;
+  field core::bool _#C#x#isSet = false;
   field core::int? _#C#y = null;
   field core::bool _#C#y#isSet = false;
   synthetic constructor •() → self::C

pkg/front_end/testcases/late_lowering/override_getter_setter.dart.weak.transformed.expect

@@ -5,18 +5,21 @@ import "dart:_internal" as _in;
 
 class A extends core::Object {
   field core::int? _#A#x = null;
+  field core::bool _#A#x#isSet = false;
   field core::int? _#A#y = null;
   field core::bool _#A#y#isSet = false;
   synthetic constructor •() → self::A
     : super core::Object::•()
     ;
   get x() → core::int
-    return let final core::int? #t1 = this.{self::A::_#A#x} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.") : #t1{core::int};
+    return this.{self::A::_#A#x#isSet} ?{core::int} let final core::int? #t1 = this.{self::A::_#A#x} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.");
   set x(core::int #t2) → void
-    if(this.{self::A::_#A#x}.==(null))
-      this.{self::A::_#A#x} = #t2;
-    else
+    if(this.{self::A::_#A#x#isSet})
       throw new _in::LateInitializationErrorImpl::•("Field 'x' has already been initialized.");
+    else {
+      this.{self::A::_#A#x#isSet} = true;
+      this.{self::A::_#A#x} = #t2;
+    }
   get y() → core::int?
     return this.{self::A::_#A#y#isSet} ?{core::int?} this.{self::A::_#A#y} : throw new _in::LateInitializationErrorImpl::•("Field 'y' has not been initialized.");
   set y(core::int? #t3) → void
@@ -38,6 +41,7 @@ class B extends self::A {
 }
 class C extends self::A {
   field core::int? _#C#x = null;
+  field core::bool _#C#x#isSet = false;
   field core::int? _#C#y = null;
   field core::bool _#C#y#isSet = false;
   synthetic constructor •() → self::C

pkg/front_end/testcases/late_lowering/return_late.dart.weak.expect

@@ -26,10 +26,18 @@ class Class<E extends core::Object? = dynamic> extends core::Object {
 }
 static method returnNonNullable(core::int value) → core::int {
   core::int? result;
-  function #result#get() → core::int
-    return let final core::int? #t2 = result in #t2.==(null) ?{core::int} result = value : #t2{core::int};
-  function #result#set(core::int #t3) → dynamic
-    return result = #t3;
+  core::bool #result#isSet = false;
+  function #result#get() → core::int {
+    if(!#result#isSet) {
+      result = value;
+      #result#isSet = true;
+    }
+    return result{core::int};
+  }
+  function #result#set(core::int #t2) → dynamic {
+    #result#isSet = true;
+    return result = #t2;
+  }
   return #result#get.call();
 }
 static method returnNullable(core::int? value) → core::int? {
@@ -42,9 +50,9 @@ static method returnNullable(core::int? value) → core::int? {
     }
     return result;
   }
-  function #result#set(core::int? #t4) → dynamic {
+  function #result#set(core::int? #t3) → dynamic {
     #result#isSet = true;
-    return result = #t4;
+    return result = #t3;
   }
   return #result#get.call();
 }

pkg/front_end/testcases/late_lowering/return_late.dart.weak.transformed.expect

@@ -26,10 +26,18 @@ class Class<E extends core::Object? = dynamic> extends core::Object {
 }
 static method returnNonNullable(core::int value) → core::int {
   core::int? result;
-  function #result#get() → core::int
-    return let final core::int? #t2 = result in #t2.==(null) ?{core::int} result = value : #t2{core::int};
-  function #result#set(core::int #t3) → dynamic
-    return result = #t3;
+  core::bool #result#isSet = false;
+  function #result#get() → core::int {
+    if(!#result#isSet) {
+      result = value;
+      #result#isSet = true;
+    }
+    return result{core::int};
+  }
+  function #result#set(core::int #t2) → dynamic {
+    #result#isSet = true;
+    return result = #t2;
+  }
   return #result#get.call();
 }
 static method returnNullable(core::int? value) → core::int? {
@@ -42,9 +50,9 @@ static method returnNullable(core::int? value) → core::int? {
     }
     return result;
   }
-  function #result#set(core::int? #t4) → dynamic {
+  function #result#set(core::int? #t3) → dynamic {
     #result#isSet = true;
-    return result = #t4;
+    return result = #t3;
   }
   return #result#get.call();
 }

pkg/front_end/testcases/late_lowering/uninitialized_non_nullable_late_fields.dart.weak.expect

@@ -5,15 +5,18 @@ import "dart:_internal" as _in;
 
 class A extends core::Object {
   field core::int? _#A#x = null;
+  field core::bool _#A#x#isSet = false;
   constructor foo(core::int x) → self::A
-    : self::A::_#A#x = x, super core::Object::•()
+    : self::A::_#A#x#isSet = true, self::A::_#A#x = x, super core::Object::•()
     ;
   constructor bar() → self::A
     : super core::Object::•()
     ;
   get x() → core::int
-    return let final core::int? #t1 = this.{self::A::_#A#x} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.") : #t1{core::int};
-  set x(core::int #t2) → void
+    return this.{self::A::_#A#x#isSet} ?{core::int} let final core::int? #t1 = this.{self::A::_#A#x} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.");
+  set x(core::int #t2) → void {
+    this.{self::A::_#A#x#isSet} = true;
     this.{self::A::_#A#x} = #t2;
+  }
 }
 static method main() → dynamic {}

pkg/front_end/testcases/late_lowering/uninitialized_non_nullable_late_fields.dart.weak.transformed.expect

@@ -5,15 +5,18 @@ import "dart:_internal" as _in;
 
 class A extends core::Object {
   field core::int? _#A#x = null;
+  field core::bool _#A#x#isSet = false;
   constructor foo(core::int x) → self::A
-    : self::A::_#A#x = x, super core::Object::•()
+    : self::A::_#A#x#isSet = true, self::A::_#A#x = x, super core::Object::•()
     ;
   constructor bar() → self::A
     : super core::Object::•()
     ;
   get x() → core::int
-    return let final core::int? #t1 = this.{self::A::_#A#x} in #t1.==(null) ?{core::int} throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.") : #t1{core::int};
-  set x(core::int #t2) → void
+    return this.{self::A::_#A#x#isSet} ?{core::int} let final core::int? #t1 = this.{self::A::_#A#x} in #t1{core::int} : throw new _in::LateInitializationErrorImpl::•("Field 'x' has not been initialized.");
+  set x(core::int #t2) → void {
+    this.{self::A::_#A#x#isSet} = true;
     this.{self::A::_#A#x} = #t2;
+  }
 }
 static method main() → dynamic {}

pkg/front_end/testcases/static_field_lowering/opt_in.dart.weak.expect

@@ -9,26 +9,39 @@ class Class extends core::Object {
   field core::int nonNullableInstanceFieldWithInitializer = self::init<core::int>(55);
   field core::int? nullableInstanceFieldWithInitializer = self::init<core::int?>(17);
   static field core::int? _#nonNullableStaticFieldWithInitializer1 = null;
+  static field core::bool _#nonNullableStaticFieldWithInitializer1#isSet = false;
   static field core::int? _#nullableStaticFieldWithInitializer1 = null;
   static field core::bool _#nullableStaticFieldWithInitializer1#isSet = false;
   static field core::int? _#nonNullableStaticFieldWithInitializer2 = null;
+  static field core::bool _#nonNullableStaticFieldWithInitializer2#isSet = false;
   static field core::int? _#nullableStaticFieldWithInitializer2 = null;
   static field core::bool _#nullableStaticFieldWithInitializer2#isSet = false;
   static field core::int? _#nonNullableStaticFinalFieldWithInitializer1 = null;
+  static field core::bool _#nonNullableStaticFinalFieldWithInitializer1#isSet = false;
   static field core::int? _#nullableStaticFinalFieldWithInitializer1 = null;
   static field core::bool _#nullableStaticFinalFieldWithInitializer1#isSet = false;
   static field core::int? _#nonNullableStaticFinalFieldWithInitializer2Init = null;
+  static field core::bool _#nonNullableStaticFinalFieldWithInitializer2Init#isSet = false;
   static field core::int? _#nonNullableStaticFinalFieldWithInitializer2 = null;
+  static field core::bool _#nonNullableStaticFinalFieldWithInitializer2#isSet = false;
   static field core::int? _#nullableStaticFinalFieldWithInitializer2Init = null;
+  static field core::bool _#nullableStaticFinalFieldWithInitializer2Init#isSet = false;
   static field core::int? _#nullableStaticFinalFieldWithInitializer2 = null;
   static field core::bool _#nullableStaticFinalFieldWithInitializer2#isSet = false;
   synthetic constructor •() → self::Class
     : super core::Object::•()
     ;
-  static get nonNullableStaticFieldWithInitializer1() → core::int
-    return let final core::int? #t1 = self::Class::_#nonNullableStaticFieldWithInitializer1 in #t1.==(null) ?{core::int} self::Class::_#nonNullableStaticFieldWithInitializer1 = self::init<core::int>(55) : #t1{core::int};
-  static set nonNullableStaticFieldWithInitializer1(core::int #t2) → void
+  static get nonNullableStaticFieldWithInitializer1() → core::int {
+    if(!self::Class::_#nonNullableStaticFieldWithInitializer1#isSet) {
+      self::Class::_#nonNullableStaticFieldWithInitializer1 = self::init<core::int>(55);
+      self::Class::_#nonNullableStaticFieldWithInitializer1#isSet = true;
+    }
+    return let final core::int? #t1 = self::Class::_#nonNullableStaticFieldWithInitializer1 in #t1{core::int};
+  }
+  static set nonNullableStaticFieldWithInitializer1(core::int #t2) → void {
+    self::Class::_#nonNullableStaticFieldWithInitializer1#isSet = true;
     self::Class::_#nonNullableStaticFieldWithInitializer1 = #t2;
+  }
   static get nullableStaticFieldWithInitializer1() → core::int? {
     if(!self::Class::_#nullableStaticFieldWithInitializer1#isSet) {
       self::Class::_#nullableStaticFieldWithInitializer1 = self::init<core::int?>(17);
@@ -40,10 +53,17 @@ class Class extends core::Object {
     self::Class::_#nullableStaticFieldWithInitializer1#isSet = true;
     self::Class::_#nullableStaticFieldWithInitializer1 = #t3;
   }
-  static get nonNullableStaticFieldWithInitializer2() → core::int
-    return let final core::int? #t4 = self::Class::_#nonNullableStaticFieldWithInitializer2 in #t4.==(null) ?{core::int} self::Class::_#nonNullableStaticFieldWithInitializer2 = self::init<core::int>(55) : #t4{core::int};
-  static set nonNullableStaticFieldWithInitializer2(core::int #t5) → void
+  static get nonNullableStaticFieldWithInitializer2() → core::int {
+    if(!self::Class::_#nonNullableStaticFieldWithInitializer2#isSet) {
+      self::Class::_#nonNullableStaticFieldWithInitializer2 = self::init<core::int>(55);
+      self::Class::_#nonNullableStaticFieldWithInitializer2#isSet = true;
+    }
+    return let final core::int? #t4 = self::Class::_#nonNullableStaticFieldWithInitializer2 in #t4{core::int};
+  }
+  static set nonNullableStaticFieldWithInitializer2(core::int #t5) → void {
+    self::Class::_#nonNullableStaticFieldWithInitializer2#isSet = true;
     self::Class::_#nonNullableStaticFieldWithInitializer2 = #t5;
+  }
   static get nullableStaticFieldWithInitializer2() → core::int? {
     if(!self::Class::_#nullableStaticFieldWithInitializer2#isSet) {
       self::Class::_#nullableStaticFieldWithInitializer2 = self::init<core::int?>(17);
@@ -67,16 +87,30 @@ class Class extends core::Object {
     }
     return self::Class::_#nullableStaticFinalFieldWithInitializer1;
   }
-  static get nonNullableStaticFinalFieldWithInitializer2Init() → core::int
-    return let final core::int? #t10 = self::Class::_#nonNullableStaticFinalFieldWithInitializer2Init in #t10.==(null) ?{core::int} self::Class::_#nonNullableStaticFinalFieldWithInitializer2Init = 0 : #t10{core::int};
-  static set nonNullableStaticFinalFieldWithInitializer2Init(core::int #t11) → void
+  static get nonNullableStaticFinalFieldWithInitializer2Init() → core::int {
+    if(!self::Class::_#nonNullableStaticFinalFieldWithInitializer2Init#isSet) {
+      self::Class::_#nonNullableStaticFinalFieldWithInitializer2Init = 0;
+      self::Class::_#nonNullableStaticFinalFieldWithInitializer2Init#isSet = true;
+    }
+    return let final core::int? #t10 = self::Class::_#nonNullableStaticFinalFieldWithInitializer2Init in #t10{core::int};
+  }
+  static set nonNullableStaticFinalFieldWithInitializer2Init(core::int #t11) → void {
+    self::Class::_#nonNullableStaticFinalFieldWithInitializer2Init#isSet = true;
     self::Class::_#nonNullableStaticFinalFieldWithInitializer2Init = #t11;
+  }
   static get nonNullableStaticFinalFieldWithInitializer2() → core::int
     return let final core::int? #t12 = self::Class::_#nonNullableStaticFinalFieldWithInitializer2 in #t12.==(null) ?{core::int} let final core::int #t13 = (let final core::int #t14 = self::Class::nonNullableStaticFinalFieldWithInitializer2Init in let final core::int #t15 = self::Class::nonNullableStaticFinalFieldWithInitializer2Init = #t14.{core::num::+}(1) in #t14).{core::num::==}(0) ?{core::int} self::Class::nonNullableStaticFinalFieldWithInitializer2.{core::num::+}(1) : 87 in self::Class::_#nonNullableStaticFinalFieldWithInitializer2.==(null) ?{core::int} self::Class::_#nonNullableStaticFinalFieldWithInitializer2 = #t13 : throw new _in::LateInitializationErrorImpl::•("Field 'nonNullableStaticFinalFieldWithInitializer2' has been assigned during initialization.") : #t12{core::int};
-  static get nullableStaticFinalFieldWithInitializer2Init() → core::int
-    return let final core::int? #t16 = self::Class::_#nullableStaticFinalFieldWithInitializer2Init in #t16.==(null) ?{core::int} self::Class::_#nullableStaticFinalFieldWithInitializer2Init = 0 : #t16{core::int};
-  static set nullableStaticFinalFieldWithInitializer2Init(core::int #t17) → void
+  static get nullableStaticFinalFieldWithInitializer2Init() → core::int {
+    if(!self::Class::_#nullableStaticFinalFieldWithInitializer2Init#isSet) {
+      self::Class::_#nullableStaticFinalFieldWithInitializer2Init = 0;
+      self::Class::_#nullableStaticFinalFieldWithInitializer2Init#isSet = true;
+    }
+    return let final core::int? #t16 = self::Class::_#nullableStaticFinalFieldWithInitializer2Init in #t16{core::int};
+  }
+  static set nullableStaticFinalFieldWithInitializer2Init(core::int #t17) → void {
+    self::Class::_#nullableStaticFinalFieldWithInitializer2Init#isSet = true;
     self::Class::_#nullableStaticFinalFieldWithInitializer2Init = #t17;
+  }
   static get nullableStaticFinalFieldWithInitializer2() → core::int? {
     if(!self::Class::_#nullableStaticFinalFieldWithInitializer2#isSet) {
       final core::int? #t18 = (let final core::int #t19 = self::Class::nullableStaticFinalFieldWithInitializer2Init in let final core::int #t20 = self::Class::nullableStaticFinalFieldWithInitializer2Init = #t19.{core::num::+}(1) in #t19).{core::num::==}(0) ?{core::int} self::Class::nullableStaticFinalFieldWithInitializer2!.{core::num::+}(1) : 32;
@@ -92,27 +126,40 @@ static field dynamic lastInit;
 static const field core::int constTopLevelField = #C2;
 static field core::int? topLevelFieldWithoutInitializer;
 static field core::int? _#nonNullableTopLevelFieldWithInitializer1 = null;
+static field core::bool _#nonNullableTopLevelFieldWithInitializer1#isSet = false;
 static field core::int? _#nullableTopLevelFieldWithInitializer = null;
 static field core::bool _#nullableTopLevelFieldWithInitializer#isSet = false;
 static field core::int? _#nonNullableTopLevelFieldWithInitializer2 = null;
+static field core::bool _#nonNullableTopLevelFieldWithInitializer2#isSet = false;
 static field core::int? _#nullableTopLevelFieldWithInitializer2 = null;
 static field core::bool _#nullableTopLevelFieldWithInitializer2#isSet = false;
 static field core::int? _#nonNullableFinalTopLevelFieldWithInitializer1 = null;
+static field core::bool _#nonNullableFinalTopLevelFieldWithInitializer1#isSet = false;
 static field core::int? _#nullableFinalTopLevelFieldWithInitializer1 = null;
 static field core::bool _#nullableFinalTopLevelFieldWithInitializer1#isSet = false;
 static field core::int? _#nonNullableFinalTopLevelFieldWithInitializer2Init = null;
+static field core::bool _#nonNullableFinalTopLevelFieldWithInitializer2Init#isSet = false;
 static field core::int? _#nonNullableFinalTopLevelFieldWithInitializer2 = null;
+static field core::bool _#nonNullableFinalTopLevelFieldWithInitializer2#isSet = false;
 static field core::int? _#nullableFinalTopLevelFieldWithInitializer2Init = null;
+static field core::bool _#nullableFinalTopLevelFieldWithInitializer2Init#isSet = false;
 static field core::int? _#nullableFinalTopLevelFieldWithInitializer2 = null;
 static field core::bool _#nullableFinalTopLevelFieldWithInitializer2#isSet = false;
 static method init<T extends core::Object? = dynamic>(self::init::T% value) → self::init::T% {
   self::lastInit = value;
   return value;
 }
-static get nonNullableTopLevelFieldWithInitializer1() → core::int
-  return let final core::int? #t21 = self::_#nonNullableTopLevelFieldWithInitializer1 in #t21.==(null) ?{core::int} self::_#nonNullableTopLevelFieldWithInitializer1 = self::init<core::int>(42) : #t21{core::int};
-static set nonNullableTopLevelFieldWithInitializer1(core::int #t22) → void
+static get nonNullableTopLevelFieldWithInitializer1() → core::int {
+  if(!self::_#nonNullableTopLevelFieldWithInitializer1#isSet) {
+    self::_#nonNullableTopLevelFieldWithInitializer1 = self::init<core::int>(42);
+    self::_#nonNullableTopLevelFieldWithInitializer1#isSet = true;
+  }
+  return let final core::int? #t21 = self::_#nonNullableTopLevelFieldWithInitializer1 in #t21{core::int};
+}
+static set nonNullableTopLevelFieldWithInitializer1(core::int #t22) → void {
+  self::_#nonNullableTopLevelFieldWithInitializer1#isSet = true;
   self::_#nonNullableTopLevelFieldWithInitializer1 = #t22;
+}
 static get nullableTopLevelFieldWithInitializer() → core::int? {
   if(!self::_#nullableTopLevelFieldWithInitializer#isSet) {
     self::_#nullableTopLevelFieldWithInitializer = self::init<core::int?>(123);
@@ -124,10 +171,17 @@ static set nullableTopLevelFieldWithInitializer(core::int? #t23) → void {
   self::_#nullableTopLevelFieldWithInitializer#isSet = true;
   self::_#nullableTopLevelFieldWithInitializer = #t23;
 }
-static get nonNullableTopLevelFieldWithInitializer2() → core::int
-  return let final core::int? #t24 = self::_#nonNullableTopLevelFieldWithInitializer2 in #t24.==(null) ?{core::int} self::_#nonNullableTopLevelFieldWithInitializer2 = self::init<core::int>(42) : #t24{core::int};
-static set nonNullableTopLevelFieldWithInitializer2(core::int #t25) → void
+static get nonNullableTopLevelFieldWithInitializer2() → core::int {
+  if(!self::_#nonNullableTopLevelFieldWithInitializer2#isSet) {
+    self::_#nonNullableTopLevelFieldWithInitializer2 = self::init<core::int>(42);
+    self::_#nonNullableTopLevelFieldWithInitializer2#isSet = true;
+  }
+  return let final core::int? #t24 = self::_#nonNullableTopLevelFieldWithInitializer2 in #t24{core::int};
+}
+static set nonNullableTopLevelFieldWithInitializer2(core::int #t25) → void {
+  self::_#nonNullableTopLevelFieldWithInitializer2#isSet = true;
   self::_#nonNullableTopLevelFieldWithInitializer2 = #t25;
+}
 static get nullableTopLevelFieldWithInitializer2() → core::int? {
   if(!self::_#nullableTopLevelFieldWithInitializer2#isSet) {
     self::_#nullableTopLevelFieldWithInitializer2 = self::init<core::int?>(123);
@@ -151,16 +205,30 @@ static get nullableFinalTopLevelFieldWithInitializer1() → core::int? {
   }
   return self::_#nullableFinalTopLevelFieldWithInitializer1;
 }
-static get nonNullableFinalTopLevelFieldWithInitializer2Init() → core::int
-  return let final core::int? #t30 = self::_#nonNullableFinalTopLevelFieldWithInitializer2Init in #t30.==(null) ?{core::int} self::_#nonNullableFinalTopLevelFieldWithInitializer2Init = 0 : #t30{core::int};
-static set nonNullableFinalTopLevelFieldWithInitializer2Init(core::int #t31) → void
+static get nonNullableFinalTopLevelFieldWithInitializer2Init() → core::int {
+  if(!self::_#nonNullableFinalTopLevelFieldWithInitializer2Init#isSet) {
+    self::_#nonNullableFinalTopLevelFieldWithInitializer2Init = 0;
+    self::_#nonNullableFinalTopLevelFieldWithInitializer2Init#isSet = true;
+  }
+  return let final core::int? #t30 = self::_#nonNullableFinalTopLevelFieldWithInitializer2Init in #t30{core::int};
+}
+static set nonNullableFinalTopLevelFieldWithInitializer2Init(core::int #t31) → void {
+  self::_#nonNullableFinalTopLevelFieldWithInitializer2Init#isSet = true;
   self::_#nonNullableFinalTopLevelFieldWithInitializer2Init = #t31;
+}
 static get nonNullableFinalTopLevelFieldWithInitializer2() → core::int
   return let final core::int? #t32 = self::_#nonNullableFinalTopLevelFieldWithInitializer2 in #t32.==(null) ?{core::int} let final core::int #t33 = (let final core::int #t34 = self::nonNullableFinalTopLevelFieldWithInitializer2Init in let final core::int #t35 = self::nonNullableFinalTopLevelFieldWithInitializer2Init = #t34.{core::num::+}(1) in #t34).{core::num::==}(0) ?{core::int} self::nonNullableFinalTopLevelFieldWithInitializer2.{core::num::+}(1) : 87 in self::_#nonNullableFinalTopLevelFieldWithInitializer2.==(null) ?{core::int} self::_#nonNullableFinalTopLevelFieldWithInitializer2 = #t33 : throw new _in::LateInitializationErrorImpl::•("Field 'nonNullableFinalTopLevelFieldWithInitializer2' has been assigned during initialization.") : #t32{core::int};
-static get nullableFinalTopLevelFieldWithInitializer2Init() → core::int
-  return let final core::int? #t36 = self::_#nullableFinalTopLevelFieldWithInitializer2Init in #t36.==(null) ?{core::int} self::_#nullableFinalTopLevelFieldWithInitializer2Init = 0 : #t36{core::int};
-static set nullableFinalTopLevelFieldWithInitializer2Init(core::int #t37) → void
+static get nullableFinalTopLevelFieldWithInitializer2Init() → core::int {
+  if(!self::_#nullableFinalTopLevelFieldWithInitializer2Init#isSet) {
+    self::_#nullableFinalTopLevelFieldWithInitializer2Init = 0;
+    self::_#nullableFinalTopLevelFieldWithInitializer2Init#isSet = true;
+  }
+  return let final core::int? #t36 = self::_#nullableFinalTopLevelFieldWithInitializer2Init in #t36{core::int};
+}
+static set nullableFinalTopLevelFieldWithInitializer2Init(core::int #t37) → void {
+  self::_#nullableFinalTopLevelFieldWithInitializer2Init#isSet = true;
   self::_#nullableFinalTopLevelFieldWithInitializer2Init = #t37;
+}
 static get nullableFinalTopLevelFieldWithInitializer2() → core::int? {
   if(!self::_#nullableFinalTopLevelFieldWithInitializer2#isSet) {
     final core::int? #t38 = (let final core::int #t39 = self::nullableFinalTopLevelFieldWithInitializer2Init in let final core::int #t40 = self::nullableFinalTopLevelFieldWithInitializer2Init = #t39.{core::num::+}(1) in #t39).{core::num::==}(0) ?{core::int} self::nullableFinalTopLevelFieldWithInitializer2!.{core::num::+}(1) : 32;

pkg/front_end/testcases/static_field_lowering/opt_in.dart.weak.transformed.expect

@@ -9,26 +9,39 @@ class Class extends core::Object {
   field core::int nonNullableInstanceFieldWithInitializer = self::init<core::int>(55);
   field core::int? nullableInstanceFieldWithInitializer = self::init<core::int?>(17);
   static field core::int? _#nonNullableStaticFieldWithInitializer1 = null;
+  static field core::bool _#nonNullableStaticFieldWithInitializer1#isSet = false;
   static field core::int? _#nullableStaticFieldWithInitializer1 = null;
   static field core::bool _#nullableStaticFieldWithInitializer1#isSet = false;
   static field core::int? _#nonNullableStaticFieldWithInitializer2 = null;
+  static field core::bool _#nonNullableStaticFieldWithInitializer2#isSet = false;
   static field core::int? _#nullableStaticFieldWithInitializer2 = null;
   static field core::bool _#nullableStaticFieldWithInitializer2#isSet = false;
   static field core::int? _#nonNullableStaticFinalFieldWithInitializer1 = null;
+  static field core::bool _#nonNullableStaticFinalFieldWithInitializer1#isSet = false;
   static field core::int? _#nullableStaticFinalFieldWithInitializer1 = null;
   static field core::bool _#nullableStaticFinalFieldWithInitializer1#isSet = false;
   static field core::int? _#nonNullableStaticFinalFieldWithInitializer2Init = null;
+  static field core::bool _#nonNullableStaticFinalFieldWithInitializer2Init#isSet = false;
   static field core::int? _#nonNullableStaticFinalFieldWithInitializer2 = null;
+  static field core::bool _#nonNullableStaticFinalFieldWithInitializer2#isSet = false;
   static field core::int? _#nullableStaticFinalFieldWithInitializer2Init = null;
+  static field core::bool _#nullableStaticFinalFieldWithInitializer2Init#isSet = false;
   static field core::int? _#nullableStaticFinalFieldWithInitializer2 = null;
   static field core::bool _#nullableStaticFinalFieldWithInitializer2#isSet = false;
   synthetic constructor •() → self::Class
     : super core::Object::•()
     ;
-  static get nonNullableStaticFieldWithInitializer1() → core::int
-    return let final core::int? #t1 = self::Class::_#nonNullableStaticFieldWithInitializer1 in #t1.==(null) ?{core::int} self::Class::_#nonNullableStaticFieldWithInitializer1 = self::init<core::int>(55) : #t1{core::int};
-  static set nonNullableStaticFieldWithInitializer1(core::int #t2) → void
+  static get nonNullableStaticFieldWithInitializer1() → core::int {
+    if(!self::Class::_#nonNullableStaticFieldWithInitializer1#isSet) {
+      self::Class::_#nonNullableStaticFieldWithInitializer1 = self::init<core::int>(55);
+      self::Class::_#nonNullableStaticFieldWithInitializer1#isSet = true;
+    }
+    return let final core::int? #t1 = self::Class::_#nonNullableStaticFieldWithInitializer1 in #t1{core::int};
+  }
+  static set nonNullableStaticFieldWithInitializer1(core::int #t2) → void {
+    self::Class::_#nonNullableStaticFieldWithInitializer1#isSet = true;
     self::Class::_#nonNullableStaticFieldWithInitializer1 = #t2;
+  }
   static get nullableStaticFieldWithInitializer1() → core::int? {
     if(!self::Class::_#nullableStaticFieldWithInitializer1#isSet) {
       self::Class::_#nullableStaticFieldWithInitializer1 = self::init<core::int?>(17);
@@ -40,10 +53,17 @@ class Class extends core::Object {
     self::Class::_#nullableStaticFieldWithInitializer1#isSet = true;
     self::Class::_#nullableStaticFieldWithInitializer1 = #t3;
   }
-  static get nonNullableStaticFieldWithInitializer2() → core::int
-    return let final core::int? #t4 = self::Class::_#nonNullableStaticFieldWithInitializer2 in #t4.==(null) ?{core::int} self::Class::_#nonNullableStaticFieldWithInitializer2 = self::init<core::int>(55) : #t4{core::int};
-  static set nonNullableStaticFieldWithInitializer2(core::int #t5) → void
+  static get nonNullableStaticFieldWithInitializer2() → core::int {
+    if(!self::Class::_#nonNullableStaticFieldWithInitializer2#isSet) {
+      self::Class::_#nonNullableStaticFieldWithInitializer2 = self::init<core::int>(55);
+      self::Class::_#nonNullableStaticFieldWithInitializer2#isSet = true;
+    }
+    return let final core::int? #t4 = self::Class::_#nonNullableStaticFieldWithInitializer2 in #t4{core::int};
+  }
+  static set nonNullableStaticFieldWithInitializer2(core::int #t5) → void {
+    self::Class::_#nonNullableStaticFieldWithInitializer2#isSet = true;
     self::Class::_#nonNullableStaticFieldWithInitializer2 = #t5;
+  }
   static get nullableStaticFieldWithInitializer2() → core::int? {
     if(!self::Class::_#nullableStaticFieldWithInitializer2#isSet) {
       self::Class::_#nullableStaticFieldWithInitializer2 = self::init<core::int?>(17);
@@ -67,16 +87,30 @@ class Class extends core::Object {
     }
     return self::Class::_#nullableStaticFinalFieldWithInitializer1;
   }
-  static get nonNullableStaticFinalFieldWithInitializer2Init() → core::int
-    return let final core::int? #t10 = self::Class::_#nonNullableStaticFinalFieldWithInitializer2Init in #t10.==(null) ?{core::int} self::Class::_#nonNullableStaticFinalFieldWithInitializer2Init = 0 : #t10{core::int};
-  static set nonNullableStaticFinalFieldWithInitializer2Init(core::int #t11) → void
+  static get nonNullableStaticFinalFieldWithInitializer2Init() → core::int {
+    if(!self::Class::_#nonNullableStaticFinalFieldWithInitializer2Init#isSet) {
+      self::Class::_#nonNullableStaticFinalFieldWithInitializer2Init = 0;
+      self::Class::_#nonNullableStaticFinalFieldWithInitializer2Init#isSet = true;
+    }
+    return let final core::int? #t10 = self::Class::_#nonNullableStaticFinalFieldWithInitializer2Init in #t10{core::int};
+  }
+  static set nonNullableStaticFinalFieldWithInitializer2Init(core::int #t11) → void {
+    self::Class::_#nonNullableStaticFinalFieldWithInitializer2Init#isSet = true;
     self::Class::_#nonNullableStaticFinalFieldWithInitializer2Init = #t11;
+  }
   static get nonNullableStaticFinalFieldWithInitializer2() → core::int
     return let final core::int? #t12 = self::Class::_#nonNullableStaticFinalFieldWithInitializer2 in #t12.==(null) ?{core::int} let final core::int #t13 = (let final core::int #t14 = self::Class::nonNullableStaticFinalFieldWithInitializer2Init in let final core::int #t15 = self::Class::nonNullableStaticFinalFieldWithInitializer2Init = #t14.{core::num::+}(1) in #t14).{core::num::==}(0) ?{core::int} self::Class::nonNullableStaticFinalFieldWithInitializer2.{core::num::+}(1) : 87 in self::Class::_#nonNullableStaticFinalFieldWithInitializer2.==(null) ?{core::int} self::Class::_#nonNullableStaticFinalFieldWithInitializer2 = #t13 : throw new _in::LateInitializationErrorImpl::•("Field 'nonNullableStaticFinalFieldWithInitializer2' has been assigned during initialization.") : #t12{core::int};
-  static get nullableStaticFinalFieldWithInitializer2Init() → core::int
-    return let final core::int? #t16 = self::Class::_#nullableStaticFinalFieldWithInitializer2Init in #t16.==(null) ?{core::int} self::Class::_#nullableStaticFinalFieldWithInitializer2Init = 0 : #t16{core::int};
-  static set nullableStaticFinalFieldWithInitializer2Init(core::int #t17) → void
+  static get nullableStaticFinalFieldWithInitializer2Init() → core::int {
+    if(!self::Class::_#nullableStaticFinalFieldWithInitializer2Init#isSet) {
+      self::Class::_#nullableStaticFinalFieldWithInitializer2Init = 0;
+      self::Class::_#nullableStaticFinalFieldWithInitializer2Init#isSet = true;
+    }
+    return let final core::int? #t16 = self::Class::_#nullableStaticFinalFieldWithInitializer2Init in #t16{core::int};
+  }
+  static set nullableStaticFinalFieldWithInitializer2Init(core::int #t17) → void {
+    self::Class::_#nullableStaticFinalFieldWithInitializer2Init#isSet = true;
     self::Class::_#nullableStaticFinalFieldWithInitializer2Init = #t17;
+  }
   static get nullableStaticFinalFieldWithInitializer2() → core::int? {
     if(!self::Class::_#nullableStaticFinalFieldWithInitializer2#isSet) {
       final core::int? #t18 = (let final core::int #t19 = self::Class::nullableStaticFinalFieldWithInitializer2Init in let final core::int #t20 = self::Class::nullableStaticFinalFieldWithInitializer2Init = #t19.{core::num::+}(1) in #t19).{core::num::==}(0) ?{core::int} self::Class::nullableStaticFinalFieldWithInitializer2!.{core::num::+}(1) : 32;
@@ -92,27 +126,40 @@ static field dynamic lastInit;
 static const field core::int constTopLevelField = #C2;
 static field core::int? topLevelFieldWithoutInitializer;
 static field core::int? _#nonNullableTopLevelFieldWithInitializer1 = null;
+static field core::bool _#nonNullableTopLevelFieldWithInitializer1#isSet = false;
 static field core::int? _#nullableTopLevelFieldWithInitializer = null;
 static field core::bool _#nullableTopLevelFieldWithInitializer#isSet = false;
 static field core::int? _#nonNullableTopLevelFieldWithInitializer2 = null;
+static field core::bool _#nonNullableTopLevelFieldWithInitializer2#isSet = false;
 static field core::int? _#nullableTopLevelFieldWithInitializer2 = null;
 static field core::bool _#nullableTopLevelFieldWithInitializer2#isSet = false;
 static field core::int? _#nonNullableFinalTopLevelFieldWithInitializer1 = null;
+static field core::bool _#nonNullableFinalTopLevelFieldWithInitializer1#isSet = false;
 static field core::int? _#nullableFinalTopLevelFieldWithInitializer1 = null;
 static field core::bool _#nullableFinalTopLevelFieldWithInitializer1#isSet = false;
 static field core::int? _#nonNullableFinalTopLevelFieldWithInitializer2Init = null;
+static field core::bool _#nonNullableFinalTopLevelFieldWithInitializer2Init#isSet = false;
 static field core::int? _#nonNullableFinalTopLevelFieldWithInitializer2 = null;
+static field core::bool _#nonNullableFinalTopLevelFieldWithInitializer2#isSet = false;
 static field core::int? _#nullableFinalTopLevelFieldWithInitializer2Init = null;
+static field core::bool _#nullableFinalTopLevelFieldWithInitializer2Init#isSet = false;
 static field core::int? _#nullableFinalTopLevelFieldWithInitializer2 = null;
 static field core::bool _#nullableFinalTopLevelFieldWithInitializer2#isSet = false;
 static method init<T extends core::Object? = dynamic>(self::init::T% value) → self::init::T% {
   self::lastInit = value;
   return value;
 }
-static get nonNullableTopLevelFieldWithInitializer1() → core::int
-  return let final core::int? #t21 = self::_#nonNullableTopLevelFieldWithInitializer1 in #t21.==(null) ?{core::int} self::_#nonNullableTopLevelFieldWithInitializer1 = self::init<core::int>(42) : #t21{core::int};
-static set nonNullableTopLevelFieldWithInitializer1(core::int #t22) → void
+static get nonNullableTopLevelFieldWithInitializer1() → core::int {
+  if(!self::_#nonNullableTopLevelFieldWithInitializer1#isSet) {
+    self::_#nonNullableTopLevelFieldWithInitializer1 = self::init<core::int>(42);
+    self::_#nonNullableTopLevelFieldWithInitializer1#isSet = true;
+  }
+  return let final core::int? #t21 = self::_#nonNullableTopLevelFieldWithInitializer1 in #t21{core::int};
+}
+static set nonNullableTopLevelFieldWithInitializer1(core::int #t22) → void {
+  self::_#nonNullableTopLevelFieldWithInitializer1#isSet = true;
   self::_#nonNullableTopLevelFieldWithInitializer1 = #t22;
+}
 static get nullableTopLevelFieldWithInitializer() → core::int? {
   if(!self::_#nullableTopLevelFieldWithInitializer#isSet) {
     self::_#nullableTopLevelFieldWithInitializer = self::init<core::int?>(123);
@@ -124,10 +171,17 @@ static set nullableTopLevelFieldWithInitializer(core::int? #t23) → void {
   self::_#nullableTopLevelFieldWithInitializer#isSet = true;
   self::_#nullableTopLevelFieldWithInitializer = #t23;
 }
-static get nonNullableTopLevelFieldWithInitializer2() → core::int
-  return let final core::int? #t24 = self::_#nonNullableTopLevelFieldWithInitializer2 in #t24.==(null) ?{core::int} self::_#nonNullableTopLevelFieldWithInitializer2 = self::init<core::int>(42) : #t24{core::int};
-static set nonNullableTopLevelFieldWithInitializer2(core::int #t25) → void
+static get nonNullableTopLevelFieldWithInitializer2() → core::int {
+  if(!self::_#nonNullableTopLevelFieldWithInitializer2#isSet) {
+    self::_#nonNullableTopLevelFieldWithInitializer2 = self::init<core::int>(42);
+    self::_#nonNullableTopLevelFieldWithInitializer2#isSet = true;
+  }
+  return let final core::int? #t24 = self::_#nonNullableTopLevelFieldWithInitializer2 in #t24{core::int};
+}
+static set nonNullableTopLevelFieldWithInitializer2(core::int #t25) → void {
+  self::_#nonNullableTopLevelFieldWithInitializer2#isSet = true;
   self::_#nonNullableTopLevelFieldWithInitializer2 = #t25;
+}
 static get nullableTopLevelFieldWithInitializer2() → core::int? {
   if(!self::_#nullableTopLevelFieldWithInitializer2#isSet) {
     self::_#nullableTopLevelFieldWithInitializer2 = self::init<core::int?>(123);
@@ -151,16 +205,30 @@ static get nullableFinalTopLevelFieldWithInitializer1() → core::int? {
   }
   return self::_#nullableFinalTopLevelFieldWithInitializer1;
 }
-static get nonNullableFinalTopLevelFieldWithInitializer2Init() → core::int
-  return let final core::int? #t30 = self::_#nonNullableFinalTopLevelFieldWithInitializer2Init in #t30.==(null) ?{core::int} self::_#nonNullableFinalTopLevelFieldWithInitializer2Init = 0 : #t30{core::int};
-static set nonNullableFinalTopLevelFieldWithInitializer2Init(core::int #t31) → void
+static get nonNullableFinalTopLevelFieldWithInitializer2Init() → core::int {
+  if(!self::_#nonNullableFinalTopLevelFieldWithInitializer2Init#isSet) {
+    self::_#nonNullableFinalTopLevelFieldWithInitializer2Init = 0;
+    self::_#nonNullableFinalTopLevelFieldWithInitializer2Init#isSet = true;
+  }
+  return let final core::int? #t30 = self::_#nonNullableFinalTopLevelFieldWithInitializer2Init in #t30{core::int};
+}
+static set nonNullableFinalTopLevelFieldWithInitializer2Init(core::int #t31) → void {
+  self::_#nonNullableFinalTopLevelFieldWithInitializer2Init#isSet = true;
   self::_#nonNullableFinalTopLevelFieldWithInitializer2Init = #t31;
+}
 static get nonNullableFinalTopLevelFieldWithInitializer2() → core::int
   return let final core::int? #t32 = self::_#nonNullableFinalTopLevelFieldWithInitializer2 in #t32.==(null) ?{core::int} let final core::int #t33 = (let final core::int #t34 = self::nonNullableFinalTopLevelFieldWithInitializer2Init in let final core::int #t35 = self::nonNullableFinalTopLevelFieldWithInitializer2Init = #t34.{core::num::+}(1) in #t34).{core::num::==}(0) ?{core::int} self::nonNullableFinalTopLevelFieldWithInitializer2.{core::num::+}(1) : 87 in self::_#nonNullableFinalTopLevelFieldWithInitializer2.==(null) ?{core::int} self::_#nonNullableFinalTopLevelFieldWithInitializer2 = #t33 : throw new _in::LateInitializationErrorImpl::•("Field 'nonNullableFinalTopLevelFieldWithInitializer2' has been assigned during initialization.") : #t32{core::int};
-static get nullableFinalTopLevelFieldWithInitializer2Init() → core::int
-  return let final core::int? #t36 = self::_#nullableFinalTopLevelFieldWithInitializer2Init in #t36.==(null) ?{core::int} self::_#nullableFinalTopLevelFieldWithInitializer2Init = 0 : #t36{core::int};
-static set nullableFinalTopLevelFieldWithInitializer2Init(core::int #t37) → void
+static get nullableFinalTopLevelFieldWithInitializer2Init() → core::int {
+  if(!self::_#nullableFinalTopLevelFieldWithInitializer2Init#isSet) {
+    self::_#nullableFinalTopLevelFieldWithInitializer2Init = 0;
+    self::_#nullableFinalTopLevelFieldWithInitializer2Init#isSet = true;
+  }
+  return let final core::int? #t36 = self::_#nullableFinalTopLevelFieldWithInitializer2Init in #t36{core::int};
+}
+static set nullableFinalTopLevelFieldWithInitializer2Init(core::int #t37) → void {
+  self::_#nullableFinalTopLevelFieldWithInitializer2Init#isSet = true;
   self::_#nullableFinalTopLevelFieldWithInitializer2Init = #t37;
+}
 static get nullableFinalTopLevelFieldWithInitializer2() → core::int? {
   if(!self::_#nullableFinalTopLevelFieldWithInitializer2#isSet) {
     final core::int? #t38 = (let final core::int #t39 = self::nullableFinalTopLevelFieldWithInitializer2Init in let final core::int #t40 = self::nullableFinalTopLevelFieldWithInitializer2Init = #t39.{core::num::+}(1) in #t39).{core::num::==}(0) ?{core::int} self::nullableFinalTopLevelFieldWithInitializer2!.{core::num::+}(1) : 32;

pkg/front_end/testcases/strong.status

@@ -171,6 +171,7 @@ inference_new/invalid_assignment_during_toplevel_inference: TypeCheckError
 instantiate_to_bound/non_simple_class_parametrized_typedef_cycle: RuntimeError # Expected
 instantiate_to_bound/non_simple_generic_function_in_bound_regress: RuntimeError # Expected
 late_lowering/covariant_late_field: TypeCheckError
+late_lowering/non_nullable_from_opt_out: RuntimeError # Test is inherently mixed mode
 nnbd/covariant_late_field: TypeCheckError
 nnbd/issue41180: RuntimeError # Strong mode runtime checking fails due to mixed strong mode.
 nnbd/issue42546: TypeCheckError

pkg/front_end/testcases/text_serialization.status

@@ -169,6 +169,7 @@ inference_new/invalid_assignment_during_toplevel_inference: TypeCheckError
 instantiate_to_bound/non_simple_class_parametrized_typedef_cycle: RuntimeError
 instantiate_to_bound/non_simple_generic_function_in_bound_regress: RuntimeError
 late_lowering/covariant_late_field: TypeCheckError
+late_lowering/non_nullable_from_opt_out: RuntimeError # Test is inherently mixed mode
 nnbd/covariant_late_field: TypeCheckError
 nnbd/issue41180: RuntimeError
 nnbd/issue42546: TypeCheckError