[og11] Rework indirect struct handling for OpenACC in gimplify.c

[og11] Rework indirect struct handling for OpenACC in gimplify.c

This patch reworks indirect struct handling in gimplify.c (i.e. for
struct components mapped with "mystruct->a[0:n]", "mystruct->b", etc.),
for OpenACC.  The key observation leading to these changes was that
component mappings of references-to-structures is already implemented
and working, and indirect struct component handling via a pointer can
work quite similarly.  That lets us remove some earlier, special-case
handling for mapping indirect struct component accesses for OpenACC,
which required the pointed-to struct to be manually mapped before the
indirect component mapping.

With this patch, you can map struct components directly (e.g. an array
slice "mystruct->a[0:n]") just like you can map a non-indirect struct
component slice ("mystruct.a[0:n]"). Both references-to-pointers (with
the former syntax) and references to structs (with the latter syntax)
work now.

For Fortran class pointers, we no longer re-use GOMP_MAP_TO_PSET for the
class metadata (the structure that points to the class data and vptr)
-- it is instead treated as any other struct.

For C++, the struct handling also works for class members ("this->foo"),
without having to explicitly map "this[:1]" first.

For OpenACC, we permit chained indirect component references
("mystruct->a->b[0:n]"), though only the last part of such mappings will
trigger an attach/detach operation.  To properly use such a construct
on the target, you must still manually map "mystruct->a[:1]" first --
but there's no need to map "mystruct[:1]" explicitly before that.

This version of the patch avoids altering code paths for OpenMP,
where possible.

2021-06-02  Julian Brown  <julian@codesourcery.com>

gcc/fortran/
	* trans-openmp.cc (gfc_trans_omp_clauses): Don't create GOMP_MAP_TO_PSET
	mappings for class metadata, nor GOMP_MAP_POINTER mappings for
	POINTER_TYPE_P decls.

gcc/
	* gimplify.cc (extract_base_bit_offset): Add BASE_IND and OPENMP
	parameters.  Handle pointer-typed indirect references for OpenACC
	alongside reference-typed ones.
	(strip_components_and_deref, aggregate_base_p): New functions.
	(build_struct_group): Add pointer type indirect ref handling,
	including chained references, for OpenACC.  Also handle references to
	structs for OpenACC.  Conditionalise bits for OpenMP only where
	appropriate.
	(gimplify_scan_omp_clauses): Rework pointer-type indirect structure
	access handling to work more like the reference-typed handling for
	OpenACC only.
	* omp-low.cc (scan_sharing_clauses): Handle pointer-type indirect struct
	references, and references to pointers to structs also.

gcc/testsuite/
	* g++.dg/goacc/member-array-acc.C: New test.
	* g++.dg/gomp/member-array-omp.C: New test.

libgomp/
	* testsuite/libgomp.oacc-c-c++-common/deep-copy-15.c: New test.
	* testsuite/libgomp.oacc-c-c++-common/deep-copy-16.c: New test.
	* testsuite/libgomp.oacc-c++/deep-copy-17.C: New test.