OpenMP: Noncontiguous "target update" for Fortran

(Note: On OG14 branch, this was tacked on to "OpenMP: Array shaping
operator and strided "target update" for C", losing its original
commit message from OG13; I've restored it as a separate patch for
OG15, and merged with "Strided/rectangular 'target update'
out-of-bounds array lookup fix" and the Fortran part of "Dimension
ordering for array-shaping operator for C and C++".)

This patch implements noncontiguous "target update" for Fortran.
The existing middle end/runtime bits relating to C++ support are reused,
with some small adjustments, e.g.:

  1. The node used to map the OMP "array descriptor" (from omp-low.cc
     onwards) now uses the OMP_CLAUSE_SIZE field as a bias (the difference
     between the "virtual origin" element with zero indices in each
     dimension and the first element actually stored in memory).

  2. The OMP_CLAUSE_SIZE field of a GOMP_MAP_DIM_STRIDE node may now be
     used to store a "span", which is the distance in bytes between
     two adjacent elements in an array (with unit stride) when that is
     different from the element size, as it can be in Fortran.

The implementation goes to some effort to massage Fortran array metadata
(array descriptors) into a form that can ultimately be consumed by
omp_target_memcpy_rect_worker. The method for doing this is described
in comments in the patch body.

2023-07-03  Julian Brown  <julian@codesourcery.com>

gcc/ChangeLog
	* gimplify.cc (gimplify_adjust_omp_clauses): Don't gimplify
	VIEW_CONVERT_EXPR away in GOMP_MAP_TO_GRID/GOMP_MAP_FROM_GRID clauses.
	* omp-low.cc (omp_noncontig_descriptor_type): Add SPAN field.
	(scan_sharing_clauses): Don't store descriptor size in its
	OMP_CLAUSE_SIZE field.
	(lower_omp_target): Add missing OMP_CLAUSE_MAP check.  Add special-case
	string handling.  Handle span and bias.  Use low bound instead of zero
	as index for trailing full dimensions.

gcc/fortran/ChangeLog
	* trans-openmp.cc (gfc_omp_deep_map_kind_p): Handle
	GOMP_MAP_{TO,FROM}_GRID, GOMP_MAP_GRID_{DIM,STRIDE}.
	(gfc_trans_omp_arrayshape_type, gfc_omp_calculate_gcd,
	gfc_desc_to_omp_noncontig_array, gfc_omp_contiguous_update_p): New
	functions.
	(gfc_trans_omp_clauses): Handle noncontiguous to/from clauses for OMP
	"target update" directives.

gcc/testsuite/ChangeLog
	* gfortran.dg/gomp/noncontig-updates-1.f90: New test.
	* gfortran.dg/gomp/noncontig-updates-2.f90: New test.
	* gfortran.dg/gomp/noncontig-updates-3.f90: New test.
	* gfortran.dg/gomp/noncontig-updates-4.f90: New test.

libgomp/ChangeLog
	* libgomp.h (omp_noncontig_array_desc): Add span field.
	* target.c (omp_target_memcpy_rect_worker): Add span parameter. Update
	forward declaration. Handle span != element_size.
	(gomp_update): Handle bias in descriptor's size slot.  Update calls to
	omp_target_memcpy_rect_worker.
	* testsuite/libgomp.fortran/noncontig-updates-1.f90: New test.
	* testsuite/libgomp.fortran/noncontig-updates-2.f90: New test.
	* testsuite/libgomp.fortran/noncontig-updates-3.f90: New test.
	* testsuite/libgomp.fortran/noncontig-updates-4.f90: New test.
	* testsuite/libgomp.fortran/noncontig-updates-5.f90: New test.
	* testsuite/libgomp.fortran/noncontig-updates-6.f90: New test.
	* testsuite/libgomp.fortran/noncontig-updates-7.f90: New test.
	* testsuite/libgomp.fortran/noncontig-updates-8.f90: New test.
	* testsuite/libgomp.fortran/noncontig-updates-9.f90: New test.
	* testsuite/libgomp.fortran/noncontig-updates-10.f90: New test.
	* testsuite/libgomp.fortran/noncontig-updates-11.f90: New test.
	* testsuite/libgomp.fortran/noncontig-updates-12.f90: New test.
	* testsuite/libgomp.fortran/noncontig-updates-13.f90: New test.

Co-Authored-By: Sandra Loosemore <sloosemore@baylibre.com>

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