In addition, I suggest guarding these definitions. Leaving these in increases the total number of symbols in an example executable linking PETSc by a factor of 2. (They're all read-only, but they're still there.) Clang is smart enough to remove these, presumably because it understands the special attributes.

static const MPI_Datatype mpich_mpi_float_int       MPICH_ATTR_TYPE_TAG_LAYOUT_COMPATIBLE(struct mpich_struct_mpi_float_int)       = MPI_FLOAT_INT;
static const MPI_Datatype mpich_mpi_double_int      MPICH_ATTR_TYPE_TAG_LAYOUT_COMPATIBLE(struct mpich_struct_mpi_double_int)      = MPI_DOUBLE_INT;
static const MPI_Datatype mpich_mpi_long_int        MPICH_ATTR_TYPE_TAG_LAYOUT_COMPATIBLE(struct mpich_struct_mpi_long_int)        = MPI_LONG_INT;
static const MPI_Datatype mpich_mpi_short_int       MPICH_ATTR_TYPE_TAG_LAYOUT_COMPATIBLE(struct mpich_struct_mpi_short_int)       = MPI_SHORT_INT;
static const MPI_Datatype mpich_mpi_2int            MPICH_ATTR_TYPE_TAG_LAYOUT_COMPATIBLE(struct mpich_struct_mpi_2int)            = MPI_2INT;
static const MPI_Datatype mpich_mpi_long_double_int MPICH_ATTR_TYPE_TAG_LAYOUT_COMPATIBLE(struct mpich_struct_mpi_long_double_int) = MPI_LONG_DOUBLE_INT;

On Tue, Jan 1, 2013 at 11:48 AM, Jed Brown <jedbrown@mcs.anl.gov> wrote:

---
 src/include/mpi.h.in | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)