[Bug middle-end/110639] [OpenMP][5.1] Predefined firstprivate for pointers - attachment missing

["burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110639

--- Comment #2 from Tobias Burnus <burnus at gcc dot gnu.org> ---
> If 'a' is already present on the device (e.g. 'omp target enter data map(a)'), it works.

This applies to both the comment 0 example where only a section of 'a' is
mapped start > 0 and for the comment 1 example where the whole of 'a' is
mapped.

It also works fine if 'p' points inside 'A'.

* * *

As spec ref:

TR12 states in "14.8 target Construct" [379:8-10]:

"[C/C++] If a list item in a map clause has a base pointer that is
predetermined firstprivate (see Section 6.1.1) and on entry to the target
region the list item is mapped, the firstprivate pointer is updated via
corresponding base pointer initialization."


OpenMP 5.1 has in the mentioned C/C++-only section "2.21.7.2 Pointer
Initialization for Device Data Environments" that is too long to be quoted.


[The TR12 wording 'on entry to the target region' makes it clear that
effectively ordering needs to happen. The 5.1 wording is a bit unclear whether
it can be mapped with that very target construct - or the storage needs to be
present before the target directive. - However, the examples in OpenMP issue
#1796 implies that also 5.1 permit mapping the data and the pointer be on the
same directive.]

* * *

The implicit handling of the 'p' in this example happens in gimplify.cc's
gimplify_adjust_omp_clauses_1 for 'else if (code == OMP_CLAUSE_MAP && (flags &
GOVD_MAP_0LEN_ARRAY) != 0)'.