private RegisterSpecList getResult() {
      if (regSpecList.isImmutable()) {
        result.setImmutable();
      }

      return result;
    }
Returns an instance that is identical to this one, except that all incompatible register
numbers are renumbered sequentially from the given base, with the first number duplicated if
indicated. If a null BitSet is given, it indicates all registers are incompatible.

@param base the base register number
@param duplicateFirst whether to duplicate the first number
@param compatRegs {@code null-ok;} either a {@code non-null} set of compatible registers, or
    {@code null} to indicate all registers are incompatible
@return {@code non-null;} an appropriately-constructed instance
android/android_framework/dex-maker/src/main/java/com/android/dx/rop/code/RegisterSpecList.java