/// Make use of the padding bits by allowing derived class to store data here.
  /// NOTE: Derived classes are expected to initialize the bitfields.
  LLVM_PACKED(union Bits {
    Bits() : raw() {}
    // Raw bits (to zero-init the union)
    char raw[7];
    // NamedDecl bits
    struct {
      bool illegalRedeclaration : 1;
      union {
        // VarDecl bits
        struct {
          bool isMutable : 1;
        } varDecl;
        // FuncDecl bits
        struct {
          bool bodyChecked : 1;
        } funcDecl;
      };
    } namedDecl;
  });
  static_assert(sizeof(Bits) == 7, "Bits is too large!");