Add a bit to HObjectAccess to encode immutable fields.

src/hydrogen-instructions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 5895 matching lines @@
   }
 
   inline Representation representation() const {
     return Representation::FromKind(RepresentationField::decode(value_));
   }
 
   inline Handle<String> name() const {
     return name_;
   }
 
+  inline bool immutable() const {
+    return ImmutableField::decode(value_);
+  }
+
   inline HObjectAccess WithRepresentation(Representation representation) {
     return HObjectAccess(portion(), offset(), representation, name());
   }
 
   static HObjectAccess ForHeapNumberValue() {
     return HObjectAccess(
         kDouble, HeapNumber::kValueOffset, Representation::Double());
   }
 
   static HObjectAccess ForHeapNumberValueLowestBits() {
@@ skipping 210 matching lines @@
     kStringLengths,    // the length of a string
     kElementsPointer,  // elements pointer
     kBackingStore,     // some field in the backing store
     kDouble,           // some double field
     kInobject,         // some other in-object field
     kExternalMemory    // some field in external memory
   };
 
   HObjectAccess(Portion portion, int offset,
                 Representation representation = Representation::Tagged(),
-                Handle<String> name = Handle<String>::null())
+                Handle<String> name = Handle<String>::null(),
+                bool immutable = false)
     : value_(PortionField::encode(portion) |
              RepresentationField::encode(representation.kind()) |
+             ImmutableField::encode(immutable ? 1 : 0) |
              OffsetField::encode(offset)),
       name_(name) {
     // assert that the fields decode correctly
     ASSERT(this->offset() == offset);
     ASSERT(this->portion() == portion);
+    ASSERT(this->immutable() == immutable);
     ASSERT(RepresentationField::decode(value_) == representation.kind());
   }
 
   class PortionField : public BitField<Portion, 0, 3> {};
   class RepresentationField : public BitField<Representation::Kind, 3, 4> {};
-  class OffsetField : public BitField<int, 7, 25> {};
+  class ImmutableField : public BitField<int, 7, 1> {};

[Igor Sheludko, 2013/12/06 09:18:54]

Wouldn't it be better to define it as a BitField<bool, ...> instead?

+  class OffsetField : public BitField<int, 8, 24> {};
 
   uint32_t value_;  // encodes portion, representation, and offset
   Handle<String> name_;
 
   friend class HLoadNamedField;
   friend class HStoreNamedField;
 
   inline Portion portion() const {
     return PortionField::decode(value_);
   }
@@ skipping 1319 matching lines @@
   virtual bool IsDeletable() const V8_OVERRIDE { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_