VMS Help MACRO, /MIGRATION, Compiler Directives, .PRESERVE, Example  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  INCW 1(R0)

      This instruction, when compiled with .PRESERVE GRANULARITY,
      retries the insertion of the new word value, if it is
      interrupted. However, when compiled with .PRESERVE ATOMICITY,
      it will also refetch the initial value and increment it, if
      interrupted. If both options are specified, it will do the
      latter.