Do not use guarded cid on externalizable cid-s (one and two byte strings).

runtime/vm/object.h

 // 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.
 
 #ifndef VM_OBJECT_H_
 #define VM_OBJECT_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/utils.h"
@@ skipping 1943 matching lines @@
     return HasInitializerBit::decode(raw_ptr()->kind_bits_);
   }
   void set_has_initializer(bool has_initializer) const {
     set_kind_bits(HasInitializerBit::update(has_initializer,
                                             raw_ptr()->kind_bits_));
   }
 
   // Return class id that any non-null value read from this field is guaranteed
   // to have or kDynamicCid if such class id is not known.
   // Stores to this field must update this information hence the name.
-  intptr_t guarded_cid() const { return raw_ptr()->guarded_cid_; }
+  intptr_t guarded_cid() const {

[Vyacheslav Egorov (Google), 2013/08/07 17:56:09]

Please add assertion in the place where we infer CompileType for LoadField.

[srdjan, 2013/08/07 18:27:48]

Done.

+    const intptr_t cid = raw_ptr()->guarded_cid_;
+    if (IsExternalizableCid(cid)) {
+      return kDynamicCid;
+    } else {
+      return cid;
+    }
+  }
   void set_guarded_cid(intptr_t cid) const {
     raw_ptr()->guarded_cid_ = cid;
   }
   static intptr_t guarded_cid_offset() {
     return OFFSET_OF(RawField, guarded_cid_);
   }
 
+  static bool IsExternalizableCid(intptr_t cid) {
+    return (cid == kOneByteStringCid) || (cid == kTwoByteStringCid);
+  }
+
   // Returns false if any value read from this field is guaranteed to be
   // not null.
   // Internally we is_nullable_ field contains either kNullCid (nullable) or
   // any other value (non-nullable) instead of boolean. This is done to simplify
   // guarding sequence in the generated code.
   bool is_nullable() const {
     return raw_ptr()->is_nullable_ == kNullCid;
   }
   void set_is_nullable(bool val) const {
     raw_ptr()->is_nullable_ = val ? kNullCid : kIllegalCid;
@@ skipping 4057 matching lines @@
 
 
 RawObject* MegamorphicCache::GetTargetFunction(const Array& array,
                                                intptr_t index) {
   return array.At((index * kEntryLength) + kTargetFunctionIndex);
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_