Use a special EnumLength field to indicate number of valid enum cache values.

src/arm/lithium-arm.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 114 matching lines @@
   V(LoadFunctionPrototype)                      \
   V(LoadGlobalCell)                             \
   V(LoadGlobalGeneric)                          \
   V(LoadKeyedFastDoubleElement)                 \
   V(LoadKeyedFastElement)                       \
   V(LoadKeyedGeneric)                           \
   V(LoadKeyedSpecializedArrayElement)           \
   V(LoadNamedField)                             \
   V(LoadNamedFieldPolymorphic)                  \
   V(LoadNamedGeneric)                           \
+  V(MapEnumLength)                              \
   V(MathFloorOfDiv)                             \
   V(MathMinMax)                                 \
   V(ModI)                                       \
   V(MulI)                                       \
   V(NumberTagD)                                 \
   V(NumberTagI)                                 \
   V(NumberTagU)                                 \
   V(NumberUntagD)                               \
   V(ObjectLiteral)                              \
   V(OsrEntry)                                   \
@@ skipping 850 matching lines @@
   explicit LFixedArrayBaseLength(LOperand* value) {
     inputs_[0] = value;
   }
 
   DECLARE_CONCRETE_INSTRUCTION(FixedArrayBaseLength,
                                "fixed-array-base-length")
   DECLARE_HYDROGEN_ACCESSOR(FixedArrayBaseLength)
 };
 
 
+class LMapEnumLength: public LTemplateInstruction<1, 1, 0> {
+ public:
+  explicit LMapEnumLength(LOperand* value) {
+    inputs_[0] = value;
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(MapEnumLength, "map-enum-length")
+};
+
+
 class LElementsKind: public LTemplateInstruction<1, 1, 0> {
  public:
   explicit LElementsKind(LOperand* value) {
     inputs_[0] = value;
   }
 
   DECLARE_CONCRETE_INSTRUCTION(ElementsKind, "elements-kind")
   DECLARE_HYDROGEN_ACCESSOR(ElementsKind)
 };
 
@@ skipping 1413 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(LChunkBuilder);
 };
 
 #undef DECLARE_HYDROGEN_ACCESSOR
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_ARM_LITHIUM_ARM_H_