[vm] Carry over argdescriptors from vm-isolate

When bootstrapping isolate group copy over immutable list constants
from vm-isolate. These are used to represent argdescriptors used in
stubs generated into vm-isolate. Copying them over into freshly
created isolate group allows us to reuse them instead of creating
new ones with the same content.

TEST=ci

Change-Id: I0c6c89b190868cc8a295041da6c794d322b1788f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/438521
Commit-Queue: Slava Egorov <[email protected]>
Reviewed-by: Martin Kustermann <[email protected]>

Author: mraleph

runtime/vm/object.cc

@@ -1808,8 +1808,11 @@ ErrorPtr Object::Init(IsolateGroup* isolate_group,
     SafepointWriteRwLocker ml(thread, isolate_group->program_lock());
 
     Class& cls = Class::Handle(zone);
+    Class& vm_isolate_cls = Class::Handle(zone);
     Type& type = Type::Handle(zone);
+    Object& obj = Object::Handle(zone);
     Array& array = Array::Handle(zone);
+    Array& array2 = Array::Handle(zone);
     WeakArray& weak_array = WeakArray::Handle(zone);
     Library& lib = Library::Handle(zone);
     TypeArguments& type_args = TypeArguments::Handle(zone);
@@ -1938,6 +1941,24 @@ ErrorPtr Object::Init(IsolateGroup* isolate_group,
     pending_classes.Add(cls);
 
     cls = Class::New<Array, RTN::Array>(kImmutableArrayCid, isolate_group);
+
+    // Carry over immutable array constants from vm-isolate: vm-isolate contains
+    // stubs and those use argument descriptor objects represented as
+    // canonical immutable arrays. To avoid duplicating these again prepopulate
+    // constants set by copying it over from vm-isolate.
+    vm_isolate_cls =
+        Dart::vm_isolate_group()->object_store()->immutable_array_class();
+    array = vm_isolate_cls.constants();
+    if (!array.IsNull()) {
+      const auto length = array.Length();
+      array2 = Array::New(length, Heap::kOld);
+      for (intptr_t i = 0; i < length; i++) {
+        obj = array.At(i);
+        array2.SetAt(i, obj);
+      }
+      cls.set_constants(array2);
+    }
+
     object_store->set_immutable_array_class(cls);
     cls.set_type_arguments_field_offset(Array::type_arguments_offset(),
                                         RTN::Array::type_arguments_offset());