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Re: [PATCH 2/5, OpenACC] Support Fortran optional arguments in the firstprivate clause
Am 17.07.19 um 19:53 schrieb Kwok Cheung Yeung:
> On 12/07/2019 12:41 pm, Jakub Jelinek wrote:
>> This should be done through a langhook.
>> Are really all PARM_DECLs wtih DECL_BY_REFERENCE and pointer type
>> optional
>> arguments? I mean, POINTER_TYPE is used for a lot of cases.
>
> Hmmm... I thought it was the case that if you pass an argument in by
> reference (the default) in Fortran, the PARM_DECL will always be a
> reference to the argument type if non-optional, or a pointer if
> optional. However, fixed-shape arrays are passed in via a pointer
> whether optional or not...
[I have to admit that I have not yet read the OpenACC (nor OpenMP 5)
spec to know the semantics and whether it matters if something is a true
pointer or just optional.]
The following is a rather special case (matching a C "void *" pointer),
which is useless without later casting the argument ("c_f_pointer"
call), but it is a pointer argument which is not by reference and not
optional.
use iso_c_binding
implicit none
call foo(c_null_ptr)
contains
subroutine foo(x)
type(c_ptr), value :: x ! Matches a C 'void *' pointer
end subroutine foo
end
Maybe there are more methods, but that requires some pondering.
> In the Fortran FE, optional arguments are indicated by setting
> attr.optional on the gfc_symbol for the parameter, but the OMP
> lowering works on a tree - is it somehow possible to get from the tree
> back to the gfc_symbol? If so, that would be a more reliable method of
> detecting optional arguments.
The gfc_symbol etc. is gone. The only possibility is to store some extra
data in the language-dependent part of the tree, i.e. using
DECL_LANG_SPECIFIC. Cf. lang_decl in trans.h and the various #defines
which use DECL_LANG_SPECIFIC.
Cheers,
Tobias