[PATCH, OpenACC] Fortran "declare create"/allocate support for OpenACC

Thu Oct 4 13:04:00 GMT 2018

On Sun, 23 Sep 2018 10:48:52 +0200
Bernhard Reutner-Fischer <rep.dot.nop@gmail.com> wrote:

> On Sat, 22 Sep 2018 at 00:32, Julian Brown <julian@codesourcery.com>
> wrote:
> 
> @@ -6218,13 +6221,20 @@ add_clause (gfc_symbol *sym, gfc_omp_map_op
> map_op) {
>    gfc_omp_namelist *n;
> 
> +  if (!module_oacc_clauses)
> +    module_oacc_clauses = gfc_get_omp_clauses ();
> +
> +  if (sym->backend_decl == NULL)
> +    gfc_get_symbol_decl (sym);
> +
> +  for (n = module_oacc_clauses->lists[OMP_LIST_MAP]; n != NULL; n =
> n->next)
> +    if (n->sym->backend_decl == sym->backend_decl)
> +      return;
> +
> 
> Didn't look too close, but should this throw an error instead of
> silently returning, or was the error emitted earlier?

The purpose of this fragment seems not to have been to do with error
reporting at all, but rather to do with de-duplicating symbols that
are listed (once) in clauses of "declare" directives in module blocks.
Variables that are listed twice are diagnosed elsewhere.

As for why the de-duplication is necessary, it seems to be because of
the way that modules are instantiated in programs and in subroutines.
E.g. in declare-allocatable-1.f90, we have something along the lines of:

  module vars
    implicit none
    integer, parameter :: n = 100
    real*8, allocatable :: b(:)
   !$acc declare create (b)
  end module vars

  program test
    use vars
    ...
  end program test

  subroutine sub1
    use vars
    ...
  end subroutine sub1

  subroutine sub2
    use vars
    ...
  end subroutine sub2

The function find_module_oacc_declare_clauses is called for each of
'test', 'sub1' and 'sub2'. But in trans-decl.c:finish_oacc_declare, the
new declare clauses are only attached to the namespace for a FL_PROGRAM
(i.e. 'test'), not for the subroutines. The module_oacc_clauses global
variable is reset only after moving the clauses to a FL_PROGRAM's
namespace, otherwise it accumulates.

Hence, with the above code, we'd scan 'test', find declare clauses, and
attach them to the namespace for 'test'. We'd then reset
module_oacc_clauses.

Then, we'd scan 'sub1', and accumulate declare clauses from 'vars' into
a fresh module_oacc_clauses.

Then we'd scan 'sub2', and accumulate declare clauses from 'vars'
again: this is why the de-duplication in the patch seemed to be
necessary.

This seems wrong to me though, and admits the possibility of clauses
instantiated in a subroutine "leaking" into a subsequent program block.
As a tentative fix, I've tried resetting module_oacc_clauses before
each time the find_module_oacc_declare_clauses traversal takes place,
and removing the de-duplication code.

This seems to work fine for the current tests in the testsuite, but I
wonder the reason that things weren't done like like that to start
with? The code dates back to 2015 (by James Norris):

https://gcc.gnu.org/ml/gcc-patches/2015-11/msg02367.html

> Furthermore the testcase uses "call abort" which is non-standard.
> We recently moved to "STOP n" in the testsuite, please adjust the new
> testcases accordingly.

Fixed. Re-tested with offloading to NVPTX and bootstrapped. OK?

Thank you,

Julian

ChangeLog

	gcc/
	* omp-low.c (scan_sharing_clauses): Update handling of OpenACC declare
	create, declare copyin and declare deviceptr to have local lifetimes.
	(convert_to_firstprivate_int): Handle pointer types.
	(convert_from_firstprivate_int): Likewise.  Create local storage for
	the values being pointed to.  Add new orig_type argument.
	(lower_omp_target): Handle GOMP_MAP_DECLARE_{ALLOCATE,DEALLOCATE}.
	Add orig_type argument to convert_from_firstprivate_int call.
	Allow pointer types with GOMP_MAP_FIRSTPRIVATE_INT.  Don't privatize
	firstprivate VLAs.
	* tree-pretty-print.c (dump_omp_clause): Handle
	GOMP_MAP_DECLARE_{ALLOCATE,DEALLOCATE}.

	gcc/fortran/
	* gfortran.h (enum gfc_omp_map_op): Add OMP_MAP_DECLARE_ALLOCATE,
	OMP_MAP_DECLARE_DEALLOCATE.
	(gfc_omp_clauses): Add update_allocatable.
	* trans-array.c (gfc_array_allocate): Call
	gfc_trans_oacc_declare_allocate for decls that have oacc_declare_create
	attribute set.
	* trans-decl.c (add_attributes_to_decl): Enable lowering of OpenACC
	declare create, declare copyin and declare deviceptr clauses.
	(find_module_oacc_declare_clauses): Relax oacc_declare_create to
	OMP_MAP_ALLOC, and oacc_declare_copyin to OMP_MAP_TO, in order to
	match OpenACC 2.5 semantics.
	(finish_oacc_declare): Reset module_oacc_clauses before scanning each
	namespace.
	* trans-openmp.c (gfc_trans_omp_clauses): Use GOMP_MAP_ALWAYS_POINTER
	(for update directive) or GOMP_MAP_FIRSTPRIVATE_POINTER (otherwise) for
	allocatable scalar decls.  Handle OMP_MAP_DECLARE_{ALLOCATE,DEALLOCATE}
	clauses.
	(gfc_trans_oacc_executable_directive): Use GOMP_MAP_ALWAYS_POINTER
	for allocatable scalar data clauses inside acc update directives.
	(gfc_trans_oacc_declare_allocate): New function.
	* trans-stmt.c (gfc_trans_allocate): Call
	gfc_trans_oacc_declare_allocate for decls with oacc_declare_create
	attribute set.
	(gfc_trans_deallocate): Likewise.
	* trans.h (gfc_trans_oacc_declare_allocate): Declare.

	gcc/testsuite/
	* gfortran.dg/goacc/declare-allocatable-1.f90: New test.

	include/
	* gomp-constants.h (enum gomp_map_kind): Define
	GOMP_MAP_DECLARE_{ALLOCATE,DEALLOCATE} and GOMP_MAP_FLAG_SPECIAL_4.

	libgomp/
	* oacc-mem.c (gomp_acc_declare_allocate): New function.
	* oacc-parallel.c (GOACC_enter_exit_data): Handle
	GOMP_MAP_DECLARE_{ALLOCATE,DEALLOCATE}.
	* testsuite/libgomp.oacc-fortran/allocatable-array.f90: New test.
	* testsuite/libgomp.oacc-fortran/allocatable-scalar.f90: New test.
	* testsuite/libgomp.oacc-fortran/declare-allocatable-1.f90: New test.
	* testsuite/libgomp.oacc-fortran/declare-allocatable-2.f90: New test.
	* testsuite/libgomp.oacc-fortran/declare-allocatable-3.f90: New test.
	* testsuite/libgomp.oacc-fortran/declare-allocatable-4.f90: New test.
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