Fix issue #23914: do not attempt to make an already immutable array immutable

runtime/vm/object.cc

 // Copyright (c) 2012, 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.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 617 matching lines @@
   // need it when reading in the token stream of bootstrap classes in the VM
   // isolate.
   Class::NewExternalTypedDataClass(kExternalTypedDataUint8ArrayCid);
 
   // Needed for object pools of VM isolate stubs.
   Class::NewTypedDataClass(kTypedDataInt8ArrayCid);
 
   // Allocate and initialize the empty_array instance.
   {
     uword address = heap->Allocate(Array::InstanceSize(0), Heap::kOld);
-    InitializeObject(address, kArrayCid, Array::InstanceSize(0));
+    InitializeObject(address, kImmutableArrayCid, Array::InstanceSize(0));
     Array::initializeHandle(
         empty_array_,
         reinterpret_cast<RawArray*>(address + kHeapObjectTag));
     empty_array_->StoreSmi(&empty_array_->raw_ptr()->length_, Smi::New(0));
   }
 
   Smi& smi = Smi::Handle();
   // Allocate and initialize the zero_array instance.
   {
     uword address = heap->Allocate(Array::InstanceSize(1), Heap::kOld);
-    InitializeObject(address, kArrayCid, Array::InstanceSize(1));
+    InitializeObject(address, kImmutableArrayCid, Array::InstanceSize(1));
     Array::initializeHandle(
         zero_array_,
         reinterpret_cast<RawArray*>(address + kHeapObjectTag));
     zero_array_->StoreSmi(&zero_array_->raw_ptr()->length_, Smi::New(1));
     smi = Smi::New(0);
     zero_array_->SetAt(0, smi);
   }
 
   // Allocate and initialize the canonical empty object pool object.
   {
@@ skipping 19066 matching lines @@
 
   if (with_type_argument) {
     dest.SetTypeArguments(TypeArguments::Handle(GetTypeArguments()));
   }
 
   return dest.raw();
 }
 
 
 void Array::MakeImmutable() const {
+  if (IsImmutable()) return;
   NoSafepointScope no_safepoint;
   uword tags = raw_ptr()->tags_;
   uword old_tags;
   do {
     old_tags = tags;
     uword new_tags = RawObject::ClassIdTag::update(kImmutableArrayCid,
                                                    old_tags);
     tags = CompareAndSwapTags(old_tags, new_tags);
   } while (tags != old_tags);
 }
@@ skipping 1528 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Instance::PrintJSONImpl(stream, ref);
 }
 
 
 }  // namespace dart