Decompose OpenACC 'kernels' constructs into parts, a sequence of compute constructs

Decompose OpenACC 'kernels' constructs into parts, a sequence of compute constructs

Not yet enabled by default: for now, the current mode of OpenACC 'kernels'
constructs handling still remains '-fopenacc-kernels=parloops', but that is to
change later.

	gcc/
	* omp-oacc-kernels-decompose.cc: New.
	* Makefile.in (OBJS): Add it.
	* passes.def: Instantiate it.
	* tree-pass.h (make_pass_omp_oacc_kernels_decompose): Declare.
	* flag-types.h (enum openacc_kernels): Add.
	* doc/invoke.texi (-fopenacc-kernels): Document.
	* gimple.h (enum gf_mask): Add
	'GF_OMP_TARGET_KIND_OACC_PARALLEL_KERNELS_PARALLELIZED',
	'GF_OMP_TARGET_KIND_OACC_PARALLEL_KERNELS_GANG_SINGLE',
	'GF_OMP_TARGET_KIND_OACC_DATA_KERNELS'.
	(is_gimple_omp_oacc, is_gimple_omp_offloaded): Handle these.
	* gimple-pretty-print.c (dump_gimple_omp_target): Likewise.
	* omp-expand.c (expand_omp_target, build_omp_regions_1)
	(omp_make_gimple_edges): Likewise.
	* omp-low.c (scan_sharing_clauses, scan_omp_for)
	(check_omp_nesting_restrictions, lower_oacc_reductions)
	(lower_oacc_head_mark, lower_omp_target): Likewise.
	* omp-offload.c (execute_oacc_device_lower): Likewise.
	gcc/c-family/
	* c.opt (fopenacc-kernels): Add.
	gcc/fortran/
	* lang.opt (fopenacc-kernels): Add.
	gcc/testsuite/
	* c-c++-common/goacc/kernels-decompose-1.c: New.
	* c-c++-common/goacc/kernels-decompose-2.c: New.
	* c-c++-common/goacc/kernels-decompose-ice-1.c: New.
	* c-c++-common/goacc/kernels-decompose-ice-2.c: New.
	* gfortran.dg/goacc/kernels-decompose-1.f95: New.
	* gfortran.dg/goacc/kernels-decompose-2.f95: New.
	* c-c++-common/goacc/if-clause-2.c: Adjust.
	* gfortran.dg/goacc/kernels-tree.f95: Likewise.
	libgomp/
	* testsuite/libgomp.oacc-c-c++-common/declare-vla-kernels-decompose-ice-1.c:
	New.
	* testsuite/libgomp.oacc-c-c++-common/declare-vla-kernels-decompose.c:
	Likewise.
	* testsuite/libgomp.oacc-c-c++-common/kernels-decompose-1.c:
	Likewise.
	* testsuite/libgomp.oacc-c-c++-common/declare-vla.c: Adjust.
	* testsuite/libgomp.oacc-fortran/pr94358-1.f90: Likewise.

Co-authored-by: Thomas Schwinge <thomas@codesourcery.com>