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

src/ia32/macro-assembler-ia32.h

Index: src/ia32/macro-assembler-ia32.h
diff --git a/src/ia32/macro-assembler-ia32.h b/src/ia32/macro-assembler-ia32.h
index 8ec3652deb3f4a27530ed2ae19dcfd5eadaae664..7d475e7d7edf0b0462c72a8b45f9ddbe41409b17 100644
--- a/src/ia32/macro-assembler-ia32.h
+++ b/src/ia32/macro-assembler-ia32.h
@@ -492,7 +492,15 @@ class MacroAssembler: public Assembler {
   }
 
   void LoadInstanceDescriptors(Register map, Register descriptors);
-
+  void EnumLength(Register dst, Register map);
+
+  template<typename Field>
+  void DecodeField(Register reg) {
+    static const int full_shift = Field::kShift + kSmiTagSize;
+    static const int low_mask = Field::kMask >> Field::kShift;
+    sar(reg, full_shift);
+    and_(reg, Immediate(low_mask));
+  }
   void LoadPowerOf2(XMMRegister dst, Register scratch, int power);
 
   // Abort execution if argument is not a number. Used in debug code.