/sys$common/syshlp/helplib.hlb FORTRAN, /SHOW, LOOPS  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Controls whether the listing file includes loop structure and
  statement execution order chosen by dependence analysis, automatic
  decomposition, and vectorization.

  The reported loop structures can be scalar, vector, parallel
  section, parallel chunk, or serial.  The loop summary listing is
  described in greater detail in your performance guide.