[Bug middle-end/115279] New: [OpenMP] Fix USM/unified-shared memory handling of 'declare target enter(global_var)'

[burnus at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115279

            Bug ID: 115279
           Summary: [OpenMP] Fix USM/unified-shared memory handling of
                    'declare target enter(global_var)'
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Keywords: openmp
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: burnus at gcc dot gnu.org
  Target Milestone: ---

Created attachment 58309
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58309&action=edit
C testcase using USM + a static declare-target variable

For 'omp requires unified_shared_memory', OpenMP is a bit unclear but for
'omp required self_maps' OpenMP is rather clear: it should just work.

(Note: The 'enter' clause is (only) permitted for 'declare target')

OpenMP pre-TR13 states:

"If required evaluates to true, the 'self_maps' clause implies the
unified_shared_memory clause, inheriting all of its behaviors. Additionally,
map-entering clauses in the compilation unit behave as if all resulting mapping
operations are self maps, and"

Now it comes:

"all corresponding list items created by the enter clauses specified by declare
target directives in the compilation unit share storage with the original list
items."


In my understanding, the attached program is therefore valid.

It seems as if the way to handle is to generate different code with
'unified_shared_address' and 'self', namely, to replace the variable by a
pointer to the real variable (indirection) – similar to the link clause – and
then associate the device side link-clause pointer with the host pointer.