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d0
    The d0 option will generate no debugging information.  This is the
    default option.

d1
    The d1 option will generate debugging information for global symbols and
    line numbers.

d1+
    The d1+ option will generate debugging information for global symbols
    and line numbers, and typing information for local structs and arrays.

d2
    The d2 option will generate the most debugging information that is
    normally needed, including global information, line numbers, types, and
    local variables.

d2i
    The d2i option is identical to d2 but does not permit inlining of
    functions.  This option can result in larger object and/or executable
    files (we are discussing both "code" and "file" size here).

d2t
    The d2t option is identical to d2 but does not include type name
    debugging information.  This option can result in smaller object and/or
    executable files (we are discussing "file" size here).

d3
    The d3 option will generate all debugging information generated by d2.
     In addition, it will generate information about all types defined in a
    compilation unit, regardless of whether they are used in that
    compilation unit.  This option will create very large objects and
    executable files.  Do not use it unless you want to have access to types
    that have no variables associated with them.