Automatic internal conversion of indices to index

When a data-item declared in Working-Storage or Local-Storage is used to access the elements of a table (OCCURS), and is not used to access other tables (data-item dedicated to a table), this data-item could be automatically converted to INDEX format at the binary code level.

The conditions necessary for this automatic internal conversion would be:
- the optimization level requested for the program is greater than 0
- the data-item can not be accessed outside the scope of the code of the current program
-> the data-item is declared in Working-Storage or Local-Storage (not in Linkage or File Section)
-> the data-item is not declared EXTERNAL
-> the data-item is not declared VOLATILE
-> the data-item is not declared GLOBAL
- the data-item is not manipulated through a structure: all access to the data-item is done directly by direct reference to this data-item
-> the data-item is not the subject of a REDEFINES
-> the data-item is not loaded or read using a MOVE on a higher level structure (but it may be dependent on a higher level structure, see use case)
- the data-item is not used to access more than one table, but it can be used in calculations as a source or destination
-> all source level instructions using this data-item must be adapted to the INDEX format: MOVE replaced by SET TO, ADD and SUBSTRACT replaced by SET UP / DOWN BY, etc.

Alternative: (for debugging or simpler implementation mechanism), the internal representation in memory of the data-item could be kept and duplicated with the INDEX format associated with the table
- statements modifying the value of the data-item would then immediately be followed by an internal statement "SET format-index TO format-native".
- all accesses to the table associated with the data-item would be made with the INDEX format associated with the data-item

Note: These automatic indexes must support the assignment corresponding to indices of value 0, or even of negative value. The value of the index will be checked when accessing the table according to the SSRANGE compilation option.