OpenMP 5.0: Implement relaxation of implicit map vs. existing device mappings

OpenMP 5.0: Implement relaxation of implicit map vs. existing device mappings

This patch implements relaxing the requirements when a map with the implicit
attribute encounters an overlapping existing map. As the OpenMP 5.0 spec
describes on page 320, lines 18-27 (and 5.1 spec, page 352, lines 13-22):

"If a single contiguous part of the original storage of a list item with an
 implicit data-mapping attribute has corresponding storage in the device data
 environment prior to a task encountering the construct that is associated with
 the map clause, only that part of the original storage will have corresponding
 storage in the device data environment as a result of the map clause."

Also tracked in the OpenMP spec context as issue #1463:
https://github.com/OpenMP/spec/issues/1463

2021-05-05  Chung-Lin Tang  <cltang@codesourcery.com>

include/ChangeLog:

	* gomp-constants.h (GOMP_MAP_IMPLICIT): New special map kind bits value.
	(GOMP_MAP_FLAG_SPECIAL_BITS): Define helper mask for whole set of
	special map kind bits.
	(GOMP_MAP_NONCONTIG_ARRAY_P): Adjust test for non-contiguous array map
	kind bits to be more specific.
	(GOMP_MAP_IMPLICIT_P): New predicate macro for implicit map kinds.

gcc/ChangeLog:

	* tree.h (OMP_CLAUSE_MAP_IMPLICIT_P): New access macro for 'implicit'
	bit, using 'base.deprecated_flag' field of tree_node.
	* tree-pretty-print.c (dump_omp_clause): Add support for printing
	implicit attribute in tree dumping.
	* gimplify.c (gimplify_adjust_omp_clauses_1):
	Set OMP_CLAUSE_MAP_IMPLICIT_P to 1 if map clause is implicitly created.
	(gimplify_adjust_omp_clauses): Adjust place of adding implicitly created
	clauses, from simple append, to starting of list, after non-map clauses.
	* omp-low.c (lower_omp_target): Add GOMP_MAP_IMPLICIT bits into kind
	values passed to libgomp for implicit maps.

gcc/testsuite/ChangeLog:

	* c-c++-common/gomp/target-implicit-map-1.c: New test.
	* c-c++-common/goacc/combined-reduction.c: Adjust scan test pattern.
	* c-c++-common/goacc/firstprivate-mappings-1.c: Likewise.
	* c-c++-common/goacc/mdc-1.c: Likewise.
        * c-c++-common/goacc/reduction-1.c: Likewise.
        * c-c++-common/goacc/reduction-2.c: Likewise.
        * c-c++-common/goacc/reduction-3.c: Likewise.
        * c-c++-common/goacc/reduction-4.c: Likewise.
        * c-c++-common/goacc/reduction-8.c: Likewise.
        * g++.dg/goacc/firstprivate-mappings-1.C: Likewise.
        * g++.dg/gomp/target-lambda-1.C: Likewise.
        * g++.dg/gomp/target-this-3.C: Likewise.
        * g++.dg/gomp/target-this-4.C: Likewise.
        * gfortran.dg/goacc/common-block-3.f90: Likewise.
        * gfortran.dg/goacc/loop-tree-1.f90: Likewise.
        * gfortran.dg/goacc/private-explicit-kernels-1.f95: Likewise.
	* gfortran.dg/goacc/private-predetermined-kernels-1.f95: Likewise.

libgomp/ChangeLog:

	* target.c (gomp_map_vars_existing): Add 'bool implicit' parameter, add
	implicit map handling to allow a "superset" existing map as valid case.
	(get_kind): Adjust to filter out GOMP_MAP_IMPLICIT bits in return value.
	(get_implicit): New function to extract implicit status.
	(gomp_map_fields_existing): Adjust arguments in calls to
	gomp_map_vars_existing, and add uses of get_implicit.
	(gomp_map_vars_internal): Likewise.

	* testsuite/libgomp.c-c++-common/target-implicit-map-1.c: New test.