To: J3                                                     J3/21-154
From: Bill Long
Subject: OpenMP Liaison Report
Date: 2021-June-21

M224 OpenMP Liaison report:


Since last February, the committee has primarily been focused on
releasing version 5.2 of the specification. OpenMP 5.2 doesn't add any
new features to the OpenMP specification. Instead, the committee
decided to release a minor version that reorganizes the way in which
directives are specified in the document to reduce redundancy in the
spec, fix various inconsistencies in how directives are specified, and
prevent such inconsistencies from cropping up in the future. Here is a
list of planned changes that would actually affect users/implementers:

- OMPD: a few new routines were added to the debugging interface to
  improve use on target devices.

- OMPT: clarify order of tool interface events for device constructs

- miscellaneous clarifications for how clauses are applied to combined
  constructs

- disallow mapping complex part designators in Fortran (need to map
  the full complex variable)

- clarify that a type-name list item should be a Fortran type-spec
  (not a declaration-type-spec)

- clarify implicit data-scoping rules for dispatch construct

- allow specifying locality clauses for DO CONCURRENT constructs
  inside OpenMP regions (previously unspecified behavior)

- clarify restrictions on threadprivate variables appearing in OpenMP
  clauses (list items shouldn't refer to them)

- clarifications for mapping C++ class objects of polymorphic type

- add symbolic alias for the initial device number
  (omp_initial_device), equal to -1

- clarify default device that an implementation may choose when
  OMP_TARGET_OFFLOAD=mandatory is set.

- clarify that a program may abort for C++ exceptions caught inside a
  target region

- clarify that impure elemental functions aren't allowed in WORKSHARE
  construct

- clarify that list items cannot be substrings or be array sections of
  substrings

- clarify restrictions for event handle variables in a detach clause
  (for Fortran, no pointer, and allocatables must be allocated)

- allow explicit map type to be ommitted from target enter data and
  target exit data map clauses

- Syntax changes:

 - deprecate allocate directives on a Fortran allocate statement,
   replaced with an allocators construct

 - deprecate modifier syntax for linear clause (val, uval, ref),
   replaced with post-modifier syntax

 - deprecate depend clause on ordered construct for doacross loops,
   replace with doacross clause

 - deprecate old uses_allocators syntax for target construct, adds
   memspace and traits modifiers to the clause

 - deprecate minus operator for reduction clause (use plus operator
   instead)

 - require "::"" type separator for iterators

A comment draft for OpenMP 5.2 is planned for release end of this
month or early next month. The final release will likely happen in
November.

At the same time, the committee has been discussing topics slated for
OpenMP 6.0 -- due to be released in November 2023. Among them are:

- "free agent" threads that are free to execute tasks generated by any
  thread team.

- dependences on taskloop construct

- allocators for managed memory that is accessible from multiple
  devices

- scoped atomics

- various improvements to OMPT and OMPD interfaces

- improved support for controlling execution across multiple devices
  and controlling affinity within target devices

A TR draft for OpenMP 6.0 likely will not be released this year, given
most of the time will be spent on finalizing OpenMP 5.2.