Pass the complete number type information into the GenericBinaryOpStub....

src/number-info.h

 // Copyright 2010 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 28 matching lines @@
     kSmi = 3,
     kHeapNumber = 5,
     kUninitialized = 7
   };
 
   // Return the weakest (least precise) common type.
   static Type Combine(Type a, Type b) {
     // Make use of the order of enum values.
     return static_cast<Type>(a & b);
   }
+
+  static bool IsNumber(Type a) {
+    ASSERT(a != kUninitialized);
+    return ((a & kNumber) != 0);
+  }
+
+  static const char* ToString(Type a) {
+    switch (a) {
+      case kUnknown: return "UnknownType";
+      case kNumber: return "NumberType";
+      case kSmi: return "SmiType";
+      case kHeapNumber: return "HeapNumberType";
+      case kUninitialized:
+        UNREACHABLE();
+        return "UninitializedType";
+    }
+    UNREACHABLE();
+    return "Unreachable code";
+  }
+
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_NUMBER_INFO_H_