[Bug middle-end/127178] New: [OpenMP] With requires unified_shared_memory/self_maps: missing implicit declare target (link) for variables

[burnus at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127178

            Bug ID: 127178
           Summary: [OpenMP] With requires
                    unified_shared_memory/self_maps: missing implicit
                    declare target (link) for variables
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Keywords: openmp, rejects-valid
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: burnus at gcc dot gnu.org
  Target Milestone: ---

OpenMP states for 'unified_shared_memory' (in OpenMP 6.1):

"The use of declare target directives in an OpenMP program is optional for
referencing variables with static storage duration in device procedures."

The wording is a bit ambiguous about where the variable is defined - inside the
device procedure or not, but it seems to imply global static variables - and,
hence, implicit declare target.

[BTW: The 5.0 wording was: "The unified_shared_memory clause makes the map
clause optional on target constructs and the declare target directive optional
for static lifetime variables accessed inside declare target functions.]

Currently, GCC only handles implicit 'declare target' for functions, seems as
if this needs to be extended to variables as well.

Note: With USM/self_maps, 'declare target' implies the 'link' clause such that
the runtime can make the device side point to the host variable during image
load time.