Re: MPI_STATUS_IGNORE etc.

William Gropp (gropp@mcs.anl.gov)
Tue, 20 May 1997 08:42:33 -0500

| - Optional arguments require a run time determination of whether
| an argument exists. This is in critical path code.

But detecting the presence of MPI_STATUS_IGNORE also requires a test; in some
cases, this test will be MORE expensive than testing for the presence of an
optional argument (testing the presence of the optional arg is probably a test
of a local register; testing in Fortran for the address of MPI_STATUS_IGNORE
may require testing against a globally known address, which often requires a
separate load). The varargs case in C is weaker, but having MPI_STATUS_IGNORE
already mandates a test that was not necessary (though may often have been
performed to catch user errors) in MPI 1.x.

Bill