Hi Jakub,
this patch implements the uses_allocators clause for OpenMP target regions.

For user defined allocator handles, this allows target regions to assign
memory space and traits to allocators, and automatically calls
omp_init/destroy_allocator() in the beginning/end of the target region.

For pre-defined allocators (i.e. omp_..._mem_alloc names), this is a no-op,
such clauses are not created.

Asides from the front-end portions, the target region transforms are
done in gimplify_omp_workshare.

This patch also includes added changes to enforce the "allocate allocator
must be also in a uses_allocator clause", as to mentioned in[1].
This is done during gimplify_scan_omp_clauses.

[1] https://gcc.gnu.org/pipermail/gcc-patches/2022-May/594039.html

Tested on mainline, please see if this is okay.

Thanks,
Chung-Lin

2022-05-06  Chung-Lin Tang  <cltang@codesourcery.com>

gcc/c-family/ChangeLog:

	* c-omp.cc (c_omp_split_clauses): Add OMP_CLAUSE_USES_ALLOCATORS case.
	* c-pragma.h (enum pragma_omp_clause): Add PRAGMA_OMP_CLAUSE_USES_ALLOCATORS.

gcc/c/ChangeLog:

	* c-parser.cc (c_parser_omp_clause_name): Add case for uses_allocators
	clause.
	(c_parser_omp_clause_uses_allocators): New function.
	(c_parser_omp_all_clauses): Add PRAGMA_OMP_CLAUSE_USES_ALLOCATORS case.
	(OMP_TARGET_CLAUSE_MASK): Add PRAGMA_OMP_CLAUSE_USES_ALLOCATORS to mask.
	* c-typeck.cc (c_finish_omp_clauses): Add case handling for
	OMP_CLAUSE_USES_ALLOCATORS.

gcc/cp/ChangeLog:

	* parser.cc (cp_parser_omp_clause_name): Add case for uses_allocators
	clause.
	(cp_parser_omp_clause_uses_allocators): New function.
	(cp_parser_omp_all_clauses): Add PRAGMA_OMP_CLAUSE_USES_ALLOCATORS case.
	(OMP_TARGET_CLAUSE_MASK): Add PRAGMA_OMP_CLAUSE_USES_ALLOCATORS to mask.
	* semantics.cc (finish_omp_clauses): Add case handling for
	OMP_CLAUSE_USES_ALLOCATORS.

fortran/ChangeLog:

	* gfortran.h (struct gfc_omp_namelist): Add memspace_sym, traits_sym
	fields.
	(OMP_LIST_USES_ALLOCATORS): New list enum.
	* openmp.cc (enum omp_mask2): Add OMP_CLAUSE_USES_ALLOCATORS.
	(gfc_match_omp_clause_uses_allocators): New function.
	(gfc_match_omp_clauses): Add case to handle OMP_CLAUSE_USES_ALLOCATORS.
	(OMP_TARGET_CLAUSES): Add OMP_CLAUSE_USES_ALLOCATORS.
	(resolve_omp_clauses): Add "USES_ALLOCATORS" to clause_names[].
	* trans-array.cc (gfc_conv_array_initializer): Adjust array index
	to always be a created tree expression instead of NULL_TREE when zero.
	* trans-openmp.cc (gfc_trans_omp_clauses): For ALLOCATE clause, handle
	using gfc_trans_omp_variable for EXPR_VARIABLE exprs.
	Add handling of OMP_LIST_USES_ALLOCATORS case.
	* types.def (BT_FN_VOID_PTRMODE): Define.
	(BT_FN_PTRMODE_PTRMODE_INT_PTR): Define.

gcc/ChangeLog:

	* builtin-types.def (BT_FN_VOID_PTRMODE): Define.
	(BT_FN_PTRMODE_PTRMODE_INT_PTR): Define.
	* omp-builtins.def (BUILT_IN_OMP_INIT_ALLOCATOR): Define.
	(BUILT_IN_OMP_DESTROY_ALLOCATOR): Define.
	* tree-core.h (enum omp_clause_code): Add OMP_CLAUSE_USES_ALLOCATORS.
	* tree-pretty-print.cc (dump_omp_clause): Handle OMP_CLAUSE_USES_ALLOCATORS.
	* tree.h (OMP_CLAUSE_USES_ALLOCATORS_ALLOCATOR): New macro.
	(OMP_CLAUSE_USES_ALLOCATORS_MEMSPACE): New macro.
	(OMP_CLAUSE_USES_ALLOCATORS_TRAITS): New macro.
	* tree.cc (omp_clause_num_ops): Add OMP_CLAUSE_USES_ALLOCATORS.
	(omp_clause_code_name): Add "uses_allocators".

	* gimplify.cc (gimplify_scan_omp_clauses): Add checking of OpenMP target
	region allocate	clauses, to require a uses_allocators clause to exist
	for allocators.
	(gimplify_omp_workshare): Add handling of OMP_CLAUSE_USES_ALLOCATORS
	for OpenMP target regions; create calls of omp_init/destroy_allocator
	around target region body.

gcc/testsuite/ChangeLog:

	* c-c++-common/gomp/uses_allocators-1.c: New test.
	* c-c++-common/gomp/uses_allocators-2.c: New test.
	* gfortran.dg/gomp/uses_allocators-1.f90: New test.
	* gfortran.dg/gomp/uses_allocators-2.f90: New test.
	* gfortran.dg/gomp/uses_allocators-3.f90: New test.