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This option instructs the compiler to generate function prologue and
epilogue sequences that save and restore any segment registers that are
modified by the function.  Caution should be exercised when using this
option.  If the value of the segment register being restored matches the
value of a segment that was freed within the function, a general protection
fault will occur in protected-mode environments.  By default, the compiler
does not generate code to save and restore segment registers.  This option
is provided for compatibility with the version 8.0 release.  The macro
__SW_R will be predefined if "r" is selected.