Never hchange nan-hole to hole or hole to nan-hole.

src/hydrogen-representation-changes.cc

Index: src/hydrogen-representation-changes.cc
diff --git a/src/hydrogen-representation-changes.cc b/src/hydrogen-representation-changes.cc
index 63b7b4d6ec8e326a2900e1be3c8b4557fabe70f5..d6745bb2e758c7bb2dade3997e48378268f0a08e 100644
--- a/src/hydrogen-representation-changes.cc
+++ b/src/hydrogen-representation-changes.cc
@@ -47,8 +47,6 @@ void HRepresentationChangesPhase::InsertRepresentationChangeForUse(
   HInstruction* new_value = NULL;
   bool is_truncating_to_smi = use_value->CheckFlag(HValue::kTruncatingToSmi);
   bool is_truncating_to_int = use_value->CheckFlag(HValue::kTruncatingToInt32);
-  bool allow_undefined_as_nan =
-      use_value->CheckFlag(HValue::kAllowUndefinedAsNaN);
   if (value->IsConstant()) {
     HConstant* constant = HConstant::cast(value);
     // Try to create a new copy of the constant with the new representation.
@@ -61,10 +59,8 @@ void HRepresentationChangesPhase::InsertRepresentationChangeForUse(
   }
 
   if (new_value == NULL) {
-    new_value = new(graph()->zone()) HChange(value, to,
-                                             is_truncating_to_smi,
-                                             is_truncating_to_int,
-                                             allow_undefined_as_nan);
+    new_value = new(graph()->zone()) HChange(
+        value, to, is_truncating_to_smi, is_truncating_to_int);
   }
 
   new_value->InsertBefore(next);