openacc: No attach/detach present/release mappings for array descriptors

openacc: No attach/detach present/release mappings for array descriptors

Standalone attach and detach clauses should not create present/release
mappings for Fortran array descriptors (e.g. used when we have a pointer
to an array), both because it is unnecessary and because those mappings
will be incorrectly subject to reference counting. Simply omitting the
mappings means we just use GOMP_MAP_TO_PSET and GOMP_MAP_{ATTACH,DETACH}
mappings for array descriptors.

That requires a tweak in gimplify.c, since we may now see GOMP_MAP_TO_PSET
without a preceding data-movement mapping.

2020-08-03  Julian Brown  <julian@codesourcery.com>
	    Thomas Schwinge  <thomas@codesourcery.com>

gcc/fortran/
	* trans-openmp.c (gfc_trans_omp_clauses): Don't create present/release
	mappings for array descriptors.

gcc/
	* gimplify.c (gimplify_omp_target_update): Allow GOMP_MAP_TO_PSET
	without a preceding data-movement mapping.

gcc/testsuite/
	* gfortran.dg/goacc/attach-descriptor.f90: Update pattern output. Add
	scanning of gimplify dump.

libgomp/
	* testsuite/libgomp.oacc-fortran/attach-descriptor-1.f90: Don't run for
	shared-memory devices.  Extend with further checking.

Co-Authored-By: Thomas Schwinge <thomas@codesourcery.com>