[mpich2-dev] Fortran, MPI_SEND_INIT, and the Intel test suite

[David Gingold]

MPICH2 folks --

I was chasing a problem in one of the Intel MPI tests, and stumbled  
on the following issue.  I'm wondering whether it is something that  
has come up before.

The test in question (which is fortran/persist_request/functional/ 
MPI_Send_init_overtake in the Intel test suite) does something like  
this:

       INTEGER NUMSHORT
       PARAMETER (NUMSHORT=20)

       INTEGER SHORTB(NUMSHORT)
C
C         Send a number of short messages
C
           CALL MPI_SEND_INIT(SHORTB(1), 1, MPI_INTEGER, 1, 1,
      $         MPI_COMM_WORLD, REQUEST(2), IERR)

           DO 200 I=1, NUMSHORT
             CALL MPI_START(REQUEST(2), IERR)

             CALL MPI_WAIT(REQUEST(2), STAT, IERR)

             SHORTB(1) = SHORTB(1) + 1
  200      CONTINUE

With the optimizer turned on, our compiler optimizes away the  
statement "SHORTB(1) = SHORTB(1) + 1".  That causes the test to fail.

Our compiler team tells me that this is a legal optimization for a  
Fortran compiler to make.  The code has no further references to  
SHORTB in this branch, and because MPI_START and MPI_WAIT do not  
reference SHORTB, the compiler is allowed to assume that the  
statement would have no effect.

If that's correct, then this is an invalid test.  But it also  
suggests that the Fortran interface for persistent sends is ill- 
defined in MPI.  The code above is the natural way to use persistent  
sends, after all.  I think there could also be corresponding trouble  
with persistent receives.

-dg

--
David Gingold
Principal Software Engineer
SiCortex
Three Clock Tower Place, Suite 210
Maynard MA 01754
(978) 897-0214 x224



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