Re: [PATCH] [gfortran] Add support for allocate clause (OpenMP 5.0).

[Tobias Burnus <tobias@codesourcery.com>]

On 21.01.22 18:15, Thomas Schwinge wrote:
>      source-gcc/libgomp/testsuite/libgomp.fortran/allocate-1.f90:11:47:
>
>         11 |     integer(c_int) function is_64bit_aligned (a) bind(C)
>            |                                               1
>      Warning: Variable ‘a’ at (1) is a dummy argument of the BIND(C) procedure ‘is_64bit_aligned’ but may not be C interoperable [-Wc-binding-type]
>
> Is that something to worry about?

I think it is not very elegant – but should be okay.

On the Fortran side:

     integer(c_int) function is_64bit_aligned (a) bind(C)
       import :: c_int
       integer  :: a
     end

that matches  'int is_64bit_aligned (int *a);'
While 'integer' in principle may not be 'int',
the call by reference makes this independent of the
actually used integer kind.

HOWEVER: That interface it not used! While it
defines that interface in 'module m', there is
no 'use m' in 'subroutine foo'.

(or alternatively: 'foo' being after 'contains' inside
the 'module m' - and then 'use m' in the main program)



That means that 'is_64bit_aligned(...)' gets implicitly
types as 'integer' with unknown arguments, which get
passed by value. By gfortran convention, that function
has a tailing underscore.

That matches the C side, which such an underscore:

int
is_64bit_aligned_ (uintptr_t a)
{
   return ( (a & 0x3f) == 0);
}

With pass by reference, a pointer is passed, which
should be handled by 'uintptr_t'.

  * * *

Side remark: I really recommend 'implicit none'
when writing Fortran code - which disables implicit
typing. I personally have started to use
   implicit none (type, external)
which also rejects 'call something()' unless
'something' has been explicitly declared, e.g. by
an interface block.

  * * *

Side remark: A Fortran-only variant has been used in
libgomp/testsuite/libgomp.fortran/alloc-11.f90:

if (mod (TRANSFER (p, iptr), 64) /= 0)

As optimization, also 'iand(..., z'3f') == 0' would work ;-)

Tobias

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