As described in Section Problems with Code Movement and Register Optimization, a dummy call may be necessary to tell the compiler that registers are to be flushed for a given buffer or that accesses to a buffer may not be moved across a given point in the execution sequence. Only a Fortran binding exists for this call.
| MPI_F_SYNC_REG(buf) | |
| INOUT buf | initial address of buffer (choice) |
This routine has no executable statements. It must be compiled in the MPI library in such a manner that a Fortran compiler cannot detect in the module that the routine has an empty body. It is used only to force the compiler to flush a cached register value of a variable or buffer back to memory (when necessary), or to invalidate the register value.
Rationale.
This function is not available in other languages
because it would not be useful.
This routine has no ierror return argument because
there is no operation that can fail.
( End of rationale.)
Advice
to implementors.
This routine can be bound to a C routine to minimize
the risk that the Fortran compiler can learn that this routine is empty
(and that the call to this routine can be removed
as part of an optimization).
However, it is explicitly allowed to implement this routine within the
mpi_f08 module according to the definition
for the mpi module or mpif.h to circumvent
the overhead of building the internal dope vector to handle
the assumed-type, assumed-rank argument.
( End of advice to implementors.)
Rationale.
This routine is not defined with TYPE(*), DIMENSION(*),
i.e., assumed size instead of assumed rank, because this
would restrict the usability to ``simply contiguous'' arrays
and would require overloading with another interface for
scalar arguments.
( End of rationale.)
Advice to users.
If only a part of an array (e.g., defined by a subscript triplet)
is used in a nonblocking routine,
it is recommended to pass the whole array to MPI_F_SYNC_REG
anyway to minimize the overhead of this no-operation call.
Note that this routine need not be called
if MPI_ASYNC_PROTECTS_NONBLOCKING is .TRUE. and
the application fully uses the facilities of ASYNCHRONOUS arrays.
( End of advice to users.)