Hi Tobias, Thomas,
this patch adds support for Fortran to use arrays and struct(record) types in OpenACC reductions.

There is still some shortcomings in the current state, mainly that only explicit-shaped arrays can be used (like its C counterpart). Anything else is currently a bit more complicated in the middle-end, since the existing reduction code creates an "init-op" (literal of initial values) which can't be done when say TYPE_MAX_VALUE (TYPE_DOMAIN (array_type)) is not a tree constant. I think we'll be on the hook to solve this later, but I think the current state is okay to submit.

Tested without regressions on mainline (on top of first struct/array reduction patch[1])

Thanks,
Chung-Lin

[1] https://gcc.gnu.org/pipermail/gcc-patches/2024-January/641669.html

2024-02-08  Chung-Lin Tang  <cltang@baylibre.com>

gcc/fortran/ChangeLog:
	* openmp.cc (oacc_reduction_defined_type_p): New function.
	(resolve_omp_clauses): Adjust OpenACC array reduction error case. Use
	oacc_reduction_defined_type_p for OpenACC.
	* trans-openmp.cc (gfc_trans_omp_array_reduction_or_udr):
	Add 'bool openacc' parameter, adjust part of function to be !openacc
	only.
	(gfc_trans_omp_reduction_list): Add 'bool openacc' parameter, pass to
	calls to gfc_trans_omp_array_reduction_or_udr.
	(gfc_trans_omp_clauses): Add 'openacc' argument to calls to
	gfc_trans_omp_reduction_list.
	(gfc_trans_omp_do): Pass 'op == EXEC_OACC_LOOP' as 'bool openacc'
	parameter in call to gfc_trans_omp_clauses.

gcc/ChangeLog:
	* omp-low.cc (omp_reduction_init_op): Add checking if reduced array
	has constant bounds.
	(lower_oacc_reductions): Add handling of error_mark_node.

gcc/testsuite/ChangeLog:
	* gfortran.dg/goacc/array-reduction.f90: Adjust testcase.
	* gfortran.dg/goacc/reduction.f95: Likewise.

libgomp/ChangeLog:
	* libgomp/testsuite/libgomp.oacc-fortran/reduction-9.f90: New testcase.
	* libgomp/testsuite/libgomp.oacc-fortran/reduction-10.f90: Likewise.
	* libgomp/testsuite/libgomp.oacc-fortran/reduction-11.f90: Likewise.
	* libgomp/testsuite/libgomp.oacc-fortran/reduction-12.f90: Likewise.
	* libgomp/testsuite/libgomp.oacc-fortran/reduction-13.f90: Likewise.