Hi!
Given the following reduced code, from a bigger test case that I'm
currently writing:
program main
use openacc
implicit none
integer, allocatable :: ar(:,:,:)
logical :: l
if (allocated (ar)) stop 10 ! just for illustration
l = acc_is_present (ar)
print *, l
end program main
..., this results in a list of '-Wuninitialized' diagnostics (have not
checked if also bad/"unexpected" code gnerated), and from the
'*.original' dump it's clear where that's coming from:
__attribute__((fn spec (". ")))
void MAIN__ ()
{
struct array03_integer(kind=4) ar;
logical(kind=4) l;
ar.data = 0B;
ar.dtype = {.elem_len=4, .rank=3, .type=1};
if ((integer(kind=4)[0:] * restrict) ar.data != 0B)
{
_gfortran_stop_numeric (10, 0);
}
L.1:;
{
integer(kind=8) D.4260;
integer(kind=8) D.4261;
integer(kind=8) D.4262;
integer(kind=8) D.4263;
integer(kind=8) D.4264;
integer(kind=8) D.4265;
struct array03_integer(kind=4) parm.0;
integer(kind=8) D.4272;
integer(kind=8) D.4273;
D.4260 = ar.dim[0].lbound;
D.4261 = ar.dim[0].ubound;
D.4262 = ar.dim[1].lbound;
D.4263 = ar.dim[1].ubound;
D.4264 = ar.dim[2].lbound;
D.4265 = ar.dim[2].ubound;
parm.0.span = 4;
parm.0.dtype = {.elem_len=4, .rank=3, .type=1};
parm.0.dim[0].lbound = 1;
parm.0.dim[0].ubound = (1 - D.4260) + D.4261;
parm.0.dim[0].stride = 1;
D.4272 = ar.dim[1].stride;
parm.0.dim[1].lbound = 1;
parm.0.dim[1].ubound = (1 - D.4262) + D.4263;
parm.0.dim[1].stride = NON_LVALUE_EXPR <D.4272>;
D.4273 = ar.dim[2].stride;
parm.0.dim[2].lbound = 1;
parm.0.dim[2].ubound = (1 - D.4264) + D.4265;
parm.0.dim[2].stride = NON_LVALUE_EXPR <D.4273>;
parm.0.data = (void *) &(*(integer(kind=4)[0:] * restrict)
ar.data)[((D.4260 - ar.dim[0].lbound) + (D.4262 - ar.dim[1].lbound) * D.4272) +
(D.4264 - ar.dim[2].lbound) * D.4273];
parm.0.offset = ~NON_LVALUE_EXPR <D.4272> - NON_LVALUE_EXPR <D.4273>;
l = acc_is_present_array_h (&parm.0);
}
[...]
Note 'D.4260 = ar.dim[0].lbound;', etc., with these 'ar' fields not
having been initialized.
For reference, OpenACC 'acc_is_present' is implemented in
'libgomp/openacc.f90':
[...]
72 module openacc_internal
73 use openacc_kinds
74 implicit none
75
76 interface
[...]
360 function acc_is_present_array_h (a)
361 logical acc_is_present_array_h
362 type (*), dimension (..), contiguous :: a
363 end function
[...]
508 end interface
509
510 interface
[...]
698 function acc_is_present_l (a, len) &
699 bind (C, name = "acc_is_present")
700 use iso_c_binding, only: c_int32_t, c_size_t
701 !GCC$ ATTRIBUTES NO_ARG_CHECK :: a
702 integer (c_int32_t) :: acc_is_present_l
703 type (*), dimension (*) :: a
704 integer (c_size_t), value :: len
705 end function
[...]
760 end interface
761 end module openacc_internal
762
763 module openacc
764 use openacc_kinds
765 use openacc_internal
766 implicit none
767
768 private
[...]
793 public :: [...], acc_is_present
[...]
961 interface acc_is_present
962 procedure :: acc_is_present_32_h
963 procedure :: acc_is_present_64_h
964 procedure :: acc_is_present_array_h
965 end interface
[...]
1006 end module openacc
[...]
1413 function acc_is_present_array_h (a)
1414 use openacc_internal, only: acc_is_present_l
1415 logical acc_is_present_array_h
1416 type (*), dimension (..), contiguous :: a
1417 acc_is_present_array_h = acc_is_present_l (a, sizeof (a)) /= 0
1418 end function
[...]
GCC currently implements OpenACC 2.6,
<https://www.openacc.org/sites/default/files/inline-files/OpenACC.2.6.final.pdf>,
which in 3.2.30. "acc_is_present" states:
*Summary* The 'acc_is_present' routine tests whether a host variable or
array region is present
on the device.
*Format*
C or C++:
int acc_is_present( h_void*, size_t );
Fortran:
logical function acc_is_present( a )
logical function acc_is_present( a, len )
type(*), dimension(..) :: a
integer :: len
*Description* The 'acc_is_present' routine tests whether the specified host
data is present
on the device. In C, the arguments are a pointer to the data and length in
bytes; the function
returns nonzero if the specified data is fully present, and zero otherwise.
In Fortran, two forms are
supported. In the first, the argument is a contiguous array section of
intrinsic type. In the second,
the first argument is a variable or array element and the second is the
length in bytes. The function
returns '.true.' if the specified data is fully present, and '.false.'
otherwise. If the byte length is
zero, the function returns nonzero in C or '.true.' in Fortran if the given
address is present at all
on the device.
I may certainly be wrong on that -- still not too much of a Fortran
programmer... ;'-| -- but just like an "inquiry function"
'if (allocated (ar))', I would have expected 'acc_is_present (ar)' to
also work fine on un-allocated data (act as if called with a C/C++ 'NULL'
pointer). Well, and maybe that's even what's happening, but there's the
'len' calculation that's firing here. Should that one simply be put into
'if (ar.data != NULL)', and 'else' calculate a length of zero?
So, is the problem (a) in the user code, (b) in the GCC implementation --
and/or (c) in the OpenACC specification even?
Grüße
Thomas
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