Use Unique<Map> in CompareMap.

src/unique.h

 // Copyright 2013 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 11 matching lines @@
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #ifndef V8_HYDROGEN_UNIQUE_H_
 #define V8_HYDROGEN_UNIQUE_H_
 
 #include "handles.h"
+#include "objects.h"
 #include "utils.h"
 #include "zone.h"
 
 namespace v8 {
 namespace internal {
 
 
 template <typename T>
 class UniqueSet;
 
 
 // Represents a handle to an object on the heap, but with the additional
 // ability of checking for equality and hashing without accessing the heap.
 //
 // Creating a Unique<T> requires first dereferencing the handle to obtain
 // the address of the object, which is used as the hashcode and the basis for
 // comparison. The object can be moved later by the GC, but comparison
 // and hashing use the old address of the object, without dereferencing it.
 //
 // Careful! Comparison of two Uniques is only correct if both were created
 // in the same "era" of GC or if at least one is a non-movable object.
 template <typename T>
 class Unique V8_FINAL {
  public:
-  // TODO(titzer): make private and introduce some builder/owner class.
+  // TODO(titzer): make private and introduce a factory.
   explicit Unique(Handle<T> handle) {
     if (handle.is_null()) {
       raw_address_ = NULL;
     } else {
+      // This is a best-effort check to prevent comparing Unique<T>'s created
+      // in different GC eras; we require heap allocation to be disallowed at
+      // creation time.
+      // NOTE: we currently consider maps to be non-movable, so no special
+      // assurance is required for creating a Unique<Map>.
+      // TODO(titzer): other immortable immovable objects are also fine.
+      ASSERT(!AllowHeapAllocation::IsAllowed() || handle->IsMap());
       raw_address_ = reinterpret_cast<Address>(*handle);
-      ASSERT_NE(raw_address_, NULL);
+      ASSERT_NE(raw_address_, NULL);  // Non-null should imply non-zero address.
     }
     handle_ = handle;
   }
 
   // TODO(titzer): this is a hack to migrate to Unique<T> incrementally.
   Unique(Address raw_address, Handle<T> handle)
     : raw_address_(raw_address), handle_(handle) { }
 
   // Constructor for handling automatic up casting.
-  // Ex. Unique<JSFunction> can be passed when Unique<Object> is expected.
+  // Eg. Unique<JSFunction> can be passed when Unique<Object> is expected.
   template <class S> Unique(Unique<S> uniq) {
 #ifdef DEBUG
     T* a = NULL;
     S* b = NULL;
     a = b;  // Fake assignment to enforce type checks.
     USE(a);
 #endif
     raw_address_ = uniq.raw_address_;
-    handle_ = uniq.handle_;  // Creates a new handle sharing the same location.
+    handle_ = uniq.handle_;
   }
 
   template <typename U>
   bool operator==(const Unique<U>& other) const {
     ASSERT(IsInitialized() && other.IsInitialized());
     return raw_address_ == other.raw_address_;
   }
 
   template <typename U>
   bool operator!=(const Unique<U>& other) const {
@@ skipping 196 matching lines @@
       capacity_ = new_capacity;
       array_ = new_array;
     }
   }
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_UNIQUE_H_