[vm/shared] Replace static final _emptyList with getter.

static final _emptyList can't be used in isolategroup mutator code, so the code that uses lists didn't work in that setting neither.
Having natively-implemented _emptyList getter fixes this issue.

TEST=run_isolate_group_run_test

Change-Id: Iad422231829d1dc0994863632521f50f2f8247ab
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/443146
Reviewed-by: Alexander Markov <[email protected]>
Commit-Queue: Alexander Aprelev <[email protected]>

Author: aam

runtime/vm/compiler/frontend/kernel_to_il.cc

@@ -1103,6 +1103,7 @@ bool FlowGraphBuilder::IsRecognizedMethodForFlowGraph(
     case MethodRecognizer::kClassIDgetID:
     case MethodRecognizer::kGrowableArrayAllocateWithData:
     case MethodRecognizer::kGrowableArrayCapacity:
+    case MethodRecognizer::kGrowableArrayGetEmptyList:
     case MethodRecognizer::kObjectArrayAllocate:
     case MethodRecognizer::kCopyRangeFromUint8ListToOneByteString:
     case MethodRecognizer::kImmutableLinkedHashBase_setIndexStoreRelease:
@@ -1482,6 +1483,9 @@ FlowGraph* FlowGraphBuilder::BuildGraphOfRecognizedMethod(
       body += LoadNativeField(Slot::GrowableObjectArray_data());
       body += LoadNativeField(Slot::Array_length());
       break;
+    case MethodRecognizer::kGrowableArrayGetEmptyList:
+      body += Constant(Object::mutable_empty_array());
+      break;
     case MethodRecognizer::kObjectArrayAllocate:
       ASSERT(function.IsFactory() && (function.NumParameters() == 2));
       body += LoadLocal(parsed_function_->RawParameterVariable(0));

runtime/vm/compiler/recognized_methods_list.h

@@ -38,6 +38,8 @@ namespace dart {
   V(CoreLibrary, _GrowableList, ._withData, GrowableArrayAllocateWithData,     \
     0x192ac0e1)                                                                \
   V(CoreLibrary, _GrowableList, []=, GrowableArraySetIndexed, 0x3a23c6fa)      \
+  V(CoreLibrary, _GrowableList, get:_emptyList, GrowableArrayGetEmptyList,     \
+    0x735785f0)                                                                \
   V(CoreLibrary, _Record, get:_fieldNames, Record_fieldNames, 0x68c8319e)      \
   V(CoreLibrary, _Record, get:_numFields, Record_numFields, 0x7ba4f393)        \
   V(CoreLibrary, _Record, get:_shape, Record_shape, 0x70c40933)                \

runtime/vm/object.cc

@@ -781,6 +781,7 @@ void Object::Init(IsolateGroup* isolate_group) {
   *empty_array_ = Array::null();
   *empty_instantiations_cache_array_ = Array::null();
   *empty_subtype_test_cache_array_ = Array::null();
+  *mutable_empty_array_ = Array::null();
 
   Class& cls = Class::Handle();
 
@@ -1036,6 +1037,14 @@ void Object::Init(IsolateGroup* isolate_group) {
     empty_array_->untag()->set_length(Smi::New(0));
     empty_array_->SetCanonical();
   }
+  {
+    uword address = heap->Allocate(thread, Array::InstanceSize(0), Heap::kOld);
+    InitializeObjectVariant<Array>(address, kArrayCid, 0);
+    Array::initializeHandle(mutable_empty_array_,
+                            static_cast<ArrayPtr>(address + kHeapObjectTag));
+    mutable_empty_array_->untag()->set_length(Smi::New(0));
+    mutable_empty_array_->SetCanonical();
+  }
 
   Smi& smi = Smi::Handle();
   // Allocate and initialize the empty instantiations cache array instance,

runtime/vm/object.h

@@ -514,6 +514,7 @@ class Object {
   V(Array, empty_array)                                                        \
   V(Array, empty_instantiations_cache_array)                                   \
   V(Array, empty_subtype_test_cache_array)                                     \
+  V(Array, mutable_empty_array)                                                \
   V(ContextScope, empty_context_scope)                                         \
   V(ObjectPool, empty_object_pool)                                             \
   V(CompressedStackMaps, empty_compressed_stackmaps)                           \

sdk/lib/_internal/vm/lib/growable_array.dart

@@ -364,7 +364,10 @@ class _GrowableList<T> extends ListBase<T> {
   }
 
   // Shared array used as backing for new empty growable arrays.
-  static final _List _emptyList = _List(0);
+  @pragma("vm:prefer-inline")
+  @pragma("vm:recognized", "other")
+  @pragma("vm:exact-result-type", "dart:core#_List")
+  external static _List get _emptyList;
 
   static _List _allocateData(int capacity) {
     if (capacity == 0) {

tests/ffi/run_isolate_group_run_test.dart

@@ -44,7 +44,19 @@ bar() {
   Baz.foo = 42;
 }
 
+@pragma('vm:shared')
+var list_length = 0;
+
 main() {
+  IsolateGroup.runSync(() {
+    final l = <int>[];
+    for (int i = 0; i < 100; i++) {
+      l.add(i);
+    }
+    list_length = l.length;
+  });
+  Expect.equals(100, list_length);
+
   Expect.equals(42, IsolateGroup.runSync(() => 42));
 
   Expect.listEquals([1, 2, 3], IsolateGroup.runSync(() => [1, 2, 3]));