[mpich-discuss] Fwd: Erroneous MPI type tag warning

[Junchao Zhang]

On Wed, Dec 25, 2013 at 9:36 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> Junchao Zhang <jczhang at mcs.anl.gov> writes:
>
> > To strictly obey MPI standard, we should declare MPI_2INT's type
> attribute
> > as
> >
> > typedef int mpich_array_mpi_2int[2];
> > static const MPI_Datatype mpich_mpi_2int
> > MPICH_ATTR_TYPE_TAG_LAYOUT_COMPATIBLE (mpich_array_mpi_2int) =
> > MPI_2INT;
>
> Why would you want this?  How is this a more "strict" interpretation of
> the standard?  Note that for heterogeneous pairs, such as
> MPI_DOUBLE_INT, the struct definition is the only one that really makes
> sense and gets padding correct.
>
> I tried to literally interpret "MPI_TYPE_CONTIGUOUS(2, MPI_REAL,
MPI_2REAL)" stated in the standard. I agree in reality it is not more
strict.


>  > The warning happens again. In reality, struct {int value; int loc; }
> should
> > have the same layout as int[2].
>
> Guaranteed to be the same, yes.
>
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