Add mutable double boxes for fields.

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 2124 matching lines @@
   void set_guarded_list_length(intptr_t list_length) const;
   static intptr_t guarded_list_length_offset() {
     return OFFSET_OF(RawField, guarded_list_length_);
   }
   bool needs_length_check() const {
     const bool r = guarded_list_length() >= Field::kUnknownFixedLength;
     ASSERT(!r || is_final());
     return r;
   }
 
+  bool IsUnboxedField() const {
+    return is_unboxing_candidate()
+        && !is_final()
+        && (guarded_cid() == kDoubleCid && !is_nullable());
+  }
+
+  bool IsPotentialUnboxedField() const {
+    return is_unboxing_candidate()
+        && (IsUnboxedField() ||
+            (!is_final() && (guarded_cid() == kIllegalCid)));
+  }
+
+  bool is_unboxing_candidate() const {
+    return UnboxingCandidateBit::decode(raw_ptr()->kind_bits_);
+  }
+  void set_is_unboxing_candidate(bool b) const {
+    set_kind_bits(UnboxingCandidateBit::update(b, raw_ptr()->kind_bits_));
+  }
+
   static bool IsExternalizableCid(intptr_t cid) {
     return (cid == kOneByteStringCid) || (cid == kTwoByteStringCid);
   }
 
   enum {
     kUnknownFixedLength = -1,
     kNoFixedLength = -2,
   };
   // Returns false if any value read from this field is guaranteed to be
   // not null.
@@ skipping 44 matching lines @@
   // instance to be supplied here.
   virtual void PrintToJSONStreamWithInstance(
       JSONStream* stream, const Instance& instance, bool ref) const;
 
  private:
   enum {
     kConstBit = 1,
     kStaticBit,
     kFinalBit,
     kHasInitializerBit,
+    kUnboxingCandidateBit
   };
   class ConstBit : public BitField<bool, kConstBit, 1> {};
   class StaticBit : public BitField<bool, kStaticBit, 1> {};
   class FinalBit : public BitField<bool, kFinalBit, 1> {};
   class HasInitializerBit : public BitField<bool, kHasInitializerBit, 1> {};
+  class UnboxingCandidateBit : public BitField<bool,
+                                               kUnboxingCandidateBit, 1> {
+  };
 
   // Update guarded class id and nullability of the field to reflect assignment
   // of the value with the given class id to this field. Returns true, if
   // deoptimization of dependent code is required.
   bool UpdateCid(intptr_t cid) const;
 
   // Update guarded class length of the field to reflect assignment of the
   // value with the given length. Returns true if deoptimization of dependent
   // code is required.
   bool UpdateLength(intptr_t length) const;
@@ skipping 4299 matching lines @@
 
 
 RawObject* MegamorphicCache::GetTargetFunction(const Array& array,
                                                intptr_t index) {
   return array.At((index * kEntryLength) + kTargetFunctionIndex);
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_