[vm] Fix late field store bug

Late field stores were being incorrectly marked as initializations,
causing them to be incorrectly optimised out in some cases.

Change-Id: I7487d24238af3b3922e76a9ca6ae6df4bf5ab849
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/138566
Reviewed-by: Alexander Markov <[email protected]>
Reviewed-by: Liam Appelbe <[email protected]>
Commit-Queue: Liam Appelbe <[email protected]>

Author: liamappelbe

runtime/vm/compiler/frontend/kernel_to_il.cc

@@ -566,8 +566,7 @@ Fragment FlowGraphBuilder::StoreLateField(const Field& field,
   if (is_static) {
     instructions += StoreStaticField(position, field);
   } else {
-    instructions += StoreInstanceFieldGuarded(
-        field, StoreInstanceFieldInstr::Kind::kInitializing);
+    instructions += StoreInstanceFieldGuarded(field);
   }
 
   return instructions;

tests/language/nnbd/syntax/late_modifier_non_final_field_test.dart

@@ -17,6 +17,7 @@ class A {
   late int fieldWithTrivialInit = 123;
   late int? fieldWithNullInit = null;
   late int fieldWithNoInit;
+  late int? nullableFieldWithNoInit;
 }
 
 main() {
@@ -29,22 +30,28 @@ main() {
     Expect.equals(null, a.fieldWithNullInit);
     Expect.throws(
         () => a.fieldWithNoInit, (error) => error is LateInitializationError);
+    Expect.throws(() => a.nullableFieldWithNoInit,
+        (error) => error is LateInitializationError);
     Expect.equals(1, initCalls);
     Expect.equals(123, a.fieldWithInit);
     Expect.equals(123, a.fieldWithTrivialInit);
     Expect.equals(null, a.fieldWithNullInit);
     Expect.throws(
         () => a.fieldWithNoInit, (error) => error is LateInitializationError);
+    Expect.throws(() => a.nullableFieldWithNoInit,
+        (error) => error is LateInitializationError);
     Expect.equals(1, initCalls);
     a.fieldWithInit = 456;
     a.fieldWithTrivialInit = 456;
     a.fieldWithNullInit = 456;
     a.fieldWithNoInit = 456;
+    a.nullableFieldWithNoInit = null;
     Expect.equals(1, initCalls);
     Expect.equals(456, a.fieldWithInit);
     Expect.equals(456, a.fieldWithTrivialInit);
     Expect.equals(456, a.fieldWithNullInit);
     Expect.equals(456, a.fieldWithNoInit);
+    Expect.equals(null, a.nullableFieldWithNoInit);
     Expect.equals(1, initCalls);
     initCalls = 0;