Hi Jakub,
attached is a rebased version of this "OpenMP fixes/adjustments" patch.

This version removes some of the (ort == C_ORT_OMP || ort == C_ORT_ACC) stuff that's not needed
in handle_omp_array_sections_1 and [c_]finish_omp_clauses.

Note that this is meant to be patched atop of the recent also posted C++ PR92120 v5 patch:
https://gcc.gnu.org/pipermail/gcc-patches/2021-November/584602.html

Again, tested without regressions (together with the PR92120 patch), awaiting review.

Thanks,
Chung-Lin

(ChangeLog updated below)

On 2021/5/25 9:36 PM, Chung-Lin Tang wrote:
> 
> This patch largely implements three pieces of functionality:
> 
> (1) Per discussion and clarification on the omp-lang mailing list,
> standards conforming behavior for mapping array sections should *NOT* also map the base-pointer,
> i.e for this code:
> 
>      struct S { int *ptr; ... };
>      struct S s;
>      #pragma omp target enter data map(to: s.ptr[:100])
> 
> Currently we generate after gimplify:
> #pragma omp target enter data map(struct:s [len: 1]) map(alloc:s.ptr [len: 8]) \
>                                 map(to:*_1 [len: 400]) map(attach:s.ptr [bias: 0])
> 
> which is deemed incorrect. After this patch, the gimplify results are now adjusted to:
> #pragma omp target enter data map(to:*_1 [len: 400]) map(attach:s.ptr [bias: 0])
> (the attach operation is still generated, and if s.ptr is already mapped prior, attachment will happen)
> 
> The correct way of achieving the base-pointer-also-mapped behavior would be to use:
> #pragma omp target enter data map(to: s.ptr, s.ptr[:100])
> 
> This adjustment in behavior required a number of small adjustments here and there in gimplify, including
> to accomodate map sequences for C++ references.
> 
> There is also a small Fortran front-end patch involved (hence CCing Tobias and fortran@).
> The new gimplify processing changed behavior in handling GOMP_MAP_ALWAYS_POINTER maps such that
> the libgomp.fortran/struct-elem-map-1.f90 regressed. It appeared that the Fortran FE was generating
> a GOMP_MAP_ALWAYS_POINTER for array types, which didn't seem quite correct, and the pre-patch behavior
> was removing this map anyways. I have a small change in trans-openmp.c:gfc_trans_omp_array_section
> to not generate the map in this case, and so far no bad test results.
> 
> (2) The second part (though kind of related to the first above) are fixes in libgomp/target.c
> to not overwrite attached pointers when handling device<->host copies, mainly for the "always" case.
> This behavior is also noted in the 5.0 spec, but not yet properly coded before.
> 
> (3) The third is a set of changes to the C/C++ front-ends to extend the allowed component access syntax
> in map clauses. This is actually mainly an effort to allow SPEC HPC to compile, so despite in the long
> term the entire map clause syntax parsing is probably going to be revamped, we're still adding this in
> for now. These changes are enabled for both OpenACC and OpenMP.


2021-11-19  Chung-Lin Tang  <cltang@codesourcery.com>

gcc/c/ChangeLog:

	* c-parser.c (struct omp_dim): New struct type for use inside
	c_parser_omp_variable_list.
	(c_parser_omp_variable_list): Allow multiple levels of array and
	component accesses in array section base-pointer expression.
	(c_parser_omp_clause_to): Set 'allow_deref' to true in call to
	c_parser_omp_var_list_parens.
	(c_parser_omp_clause_from): Likewise.
	* c-typeck.c (handle_omp_array_sections_1): Extend allowed range
	of base-pointer expressions involving INDIRECT/MEM/ARRAY_REF and
	POINTER_PLUS_EXPR.
	(c_finish_omp_clauses): Extend allowed ranged of expressions
	involving INDIRECT/MEM/ARRAY_REF and POINTER_PLUS_EXPR.

gcc/cp/ChangeLog:

	* parser.c (struct omp_dim): New struct type for use inside
	cp_parser_omp_var_list_no_open.
	(cp_parser_omp_var_list_no_open): Allow multiple levels of array and
	component accesses in array section base-pointer expression.
	(cp_parser_omp_all_clauses): Set 'allow_deref' to true in call to
	cp_parser_omp_var_list for to/from clauses.
	* semantics.c (handle_omp_array_sections_1): Extend allowed range
	of base-pointer expressions involving INDIRECT/MEM/ARRAY_REF and
	POINTER_PLUS_EXPR.
	(handle_omp_array_sections): Adjust pointer map generation of
	references.
	(finish_omp_clauses): Extend allowed ranged of expressions
	involving INDIRECT/MEM/ARRAY_REF and POINTER_PLUS_EXPR.

gcc/fortran/ChangeLog:

	* trans-openmp.c (gfc_trans_omp_array_section): Do not generate
	GOMP_MAP_ALWAYS_POINTER map for main array maps of ARRAY_TYPE type.

gcc/ChangeLog:

	* gimplify.c (extract_base_bit_offset): Add 'tree *offsetp' parameter,
	accomodate case where 'offset' return of get_inner_reference is
	non-NULL.
	(is_or_contains_p): Further robustify conditions.
	(omp_target_reorder_clauses): In alloc/to/from sorting phase, also
	move following GOMP_MAP_ALWAYS_POINTER maps along.  Add new sorting
	phase where we make sure pointers with an attach/detach map are ordered
	correctly.
	(gimplify_scan_omp_clauses): Add modifications to avoid creating
	GOMP_MAP_STRUCT and associated alloc map for attach/detach maps.

gcc/testsuite/ChangeLog:

	* c-c++-common/goacc/deep-copy-arrayofstruct.c: Adjust testcase.
	* c-c++-common/gomp/target-enter-data-1.c: New testcase.
	* c-c++-common/gomp/target-implicit-map-2.c: New testcase.

libgomp/ChangeLog:

	* target.c (gomp_map_vars_existing): Make sure attached pointer is
	not overwritten during cross-host/device copying.
	(gomp_update): Likewise.
	(gomp_exit_data): Likewise.
	* testsuite/libgomp.c++/target-11.C: Adjust testcase.
	* testsuite/libgomp.c++/target-12.C: Likewise.
	* testsuite/libgomp.c++/target-15.C: Likewise.
	* testsuite/libgomp.c++/target-16.C: Likewise.
	* testsuite/libgomp.c++/target-17.C: Likewise.
	* testsuite/libgomp.c++/target-21.C: Likewise.
	* testsuite/libgomp.c++/target-23.C: Likewise.
	* testsuite/libgomp.c/target-23.c: Likewise.
	* testsuite/libgomp.c/target-29.c: Likewise.
	* testsuite/libgomp.c-c++-common/target-implicit-map-2.c: New testcase.