Remove HType::HeapNumber from mutable heap numbers.

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 8e0858dca7ea91be64f320d0f83392c592cbf8d9..41e241050a3e05d551604816fe5c9f0cbb963a45 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -5446,7 +5446,6 @@ HInstruction* HOptimizedGraphBuilder::BuildLoadNamedField(
     checked_object = Add<HLoadNamedField>(
         checked_object, static_cast<HValue*>(NULL),
         access.WithRepresentation(Representation::Tagged()));
-    checked_object->set_type(HType::HeapNumber());
     // Load the double value from it.
     access = HObjectAccess::ForHeapNumberValue();
   }
@@ -5485,8 +5484,11 @@ HInstruction* HOptimizedGraphBuilder::BuildStoreNamedField(
       PretenureFlag pretenure_flag = !FLAG_allocation_site_pretenuring ?
           isolate()->heap()->GetPretenureMode() : NOT_TENURED;
 
+      // Mark mutable heap numbers as Tagged rather than HeapNumber, since
+      // unlike immutable heap numbers, the identity of mutable heap numbers
+      // matters.
       HInstruction* heap_number = Add<HAllocate>(heap_number_size,
-          HType::HeapNumber(),
+          HType::Tagged(),
           pretenure_flag,
           HEAP_NUMBER_TYPE);
       AddStoreMapConstant(heap_number, isolate()->factory()->heap_number_map());
@@ -5499,7 +5501,6 @@ HInstruction* HOptimizedGraphBuilder::BuildStoreNamedField(
       // Already holds a HeapNumber; load the box and write its value field.
       HInstruction* heap_number = Add<HLoadNamedField>(
           checked_object, static_cast<HValue*>(NULL), heap_number_access);
-      heap_number->set_type(HType::HeapNumber());
       instr = New<HStoreNamedField>(heap_number,
                                     HObjectAccess::ForHeapNumberValue(),
                                     value, STORE_TO_INITIALIZED_ENTRY);