OpenMP: middle-end support for dispatch + adjust_args

OpenMP: middle-end support for dispatch + adjust_args

This patch adds middle-end support for the `dispatch` construct and the
`adjust_args` clause. The heavy lifting is done in `gimplify_omp_dispatch` and
`gimplify_call_expr` respectively. For `adjust_args`, this mostly consists in
emitting a call to `omp_get_mapped_ptr` for the adequate device.

For dispatch, the following steps are performed:

* Handle the device clause, if any: set the default-device ICV at the top of the
dispatch region and restore its previous value at the end.

* Handle novariants and nocontext clauses, if any. Evaluate compile-time
constants and select a variant, if possible. Otherwise, emit code to handle all
possible cases at run time.

gcc/ChangeLog:

	* builtins.cc (builtin_fnspec): Handle BUILT_IN_OMP_GET_MAPPED_PTR.
	* gimple-low.cc (lower_stmt): Handle GIMPLE_OMP_DISPATCH.
	* gimple-pretty-print.cc (dump_gimple_omp_dispatch): New function.
	(pp_gimple_stmt_1): Handle GIMPLE_OMP_DISPATCH.
	* gimple-walk.cc (walk_gimple_stmt): Likewise.
	* gimple.cc (gimple_build_omp_dispatch): New function.
	(gimple_copy): Handle GIMPLE_OMP_DISPATCH.
	* gimple.def (GIMPLE_OMP_DISPATCH): Define.
	* gimple.h (gimple_build_omp_dispatch): Declare.
	(gimple_has_substatements): Handle GIMPLE_OMP_DISPATCH.
	(gimple_omp_dispatch_clauses): New function.
	(gimple_omp_dispatch_clauses_ptr): Likewise.
	(gimple_omp_dispatch_set_clauses): Likewise.
	(gimple_return_set_retval): Handle GIMPLE_OMP_DISPATCH.
	* gimplify.cc (enum omp_region_type): Add ORT_DISPATCH.
	(struct gimplify_omp_ctx): Add in_call_args.
	(gimplify_call_expr): Handle need_device_ptr arguments.
	(is_gimple_stmt): Handle OMP_DISPATCH.
	(gimplify_scan_omp_clauses): Handle OMP_CLAUSE_DEVICE in a dispatch
	construct. Handle OMP_CLAUSE_NOVARIANTS and OMP_CLAUSE_NOCONTEXT.
	(omp_has_novariants): New function.
	(omp_has_nocontext): Likewise.
	(omp_construct_selector_matches): Handle OMP_DISPATCH with nocontext
	clause.
	(find_ifn_gomp_dispatch): New function.
	(gimplify_omp_dispatch): Likewise.
	(gimplify_expr): Handle OMP_DISPATCH.
	* gimplify.h (omp_has_novariants): Declare.
	* internal-fn.cc (expand_GOMP_DISPATCH): New function.
	* internal-fn.def (GOMP_DISPATCH): Define.
	* omp-builtins.def (BUILT_IN_OMP_GET_MAPPED_PTR): Define.
	(BUILT_IN_OMP_GET_DEFAULT_DEVICE): Define.
	(BUILT_IN_OMP_SET_DEFAULT_DEVICE): Define.
	* omp-general.cc (omp_construct_traits_to_codes): Add OMP_DISPATCH.
	(struct omp_ts_info): Add dispatch.
	(omp_resolve_declare_variant): Handle novariants. Adjust
	DECL_ASSEMBLER_NAME.
	* omp-low.cc (scan_omp_1_stmt): Handle GIMPLE_OMP_DISPATCH.
	(lower_omp_dispatch): New function.
	(lower_omp_1): Call it.
	* tree-inline.cc (remap_gimple_stmt): Handle GIMPLE_OMP_DISPATCH.
	(estimate_num_insns): Handle GIMPLE_OMP_DISPATCH.