Fix collective alias checks to look for zero-sized buffers

If the size of the input buffers is 0, don't bother to check if they are
aliased.

Fixes #2124
Signed-off-by: Antonio J. Pena <apenya@mcs.anl.gov>

src/mpi/coll/exscan.c

@@ -371,7 +371,7 @@ int MPI_Exscan(const void *sendbuf, void *recvbuf, int count, MPI_Datatype datat
             }
             if (mpi_errno != MPI_SUCCESS) goto fn_fail;
 
-            if (sendbuf != MPI_IN_PLACE)
+            if (sendbuf != MPI_IN_PLACE && count != 0)
                 MPIR_ERRTEST_ALIAS_COLL(sendbuf, recvbuf, mpi_errno);
         }
         MPID_END_ERROR_CHECKS;

src/mpi/coll/iexscan.c

@@ -306,7 +306,7 @@ int MPI_Iexscan(const void *sendbuf, void *recvbuf, int count, MPI_Datatype data
 
             MPIR_ERRTEST_ARGNULL(request,"request", mpi_errno);
 
-            if (sendbuf != MPI_IN_PLACE)
+            if (sendbuf != MPI_IN_PLACE && count != 0)
                 MPIR_ERRTEST_ALIAS_COLL(sendbuf, recvbuf, mpi_errno);
             /* TODO more checks may be appropriate (counts, in_place, etc) */
         }

src/mpi/coll/ired_scat.c

@@ -1082,6 +1082,7 @@ int MPI_Ireduce_scatter(const void *sendbuf, void *recvbuf, const int recvcounts
     int mpi_errno = MPI_SUCCESS;
     MPID_Comm *comm_ptr = NULL;
     MPID_MPI_STATE_DECL(MPID_STATE_MPI_IREDUCE_SCATTER);
+    int i = 0;
 
     MPIU_THREAD_CS_ENTER(ALLFUNC,);
     MPID_MPI_FUNC_ENTER(MPID_STATE_MPI_IREDUCE_SCATTER);
@@ -1134,7 +1135,9 @@ int MPI_Ireduce_scatter(const void *sendbuf, void *recvbuf, const int recvcounts
 
             MPIR_ERRTEST_ARGNULL(request,"request", mpi_errno);
 
-            if (comm_ptr->comm_kind == MPID_INTRACOMM && sendbuf != MPI_IN_PLACE)
+            while (i < comm_ptr->remote_size && recvcounts[i] == 0) ++i;
+
+            if (comm_ptr->comm_kind == MPID_INTRACOMM && sendbuf != MPI_IN_PLACE && i < comm_ptr->remote_size)
                 MPIR_ERRTEST_ALIAS_COLL(sendbuf, recvbuf, mpi_errno)
             /* TODO more checks may be appropriate (counts, in_place, etc) */
         }

src/mpi/coll/ired_scat_block.c

@@ -1035,7 +1035,7 @@ int MPI_Ireduce_scatter_block(const void *sendbuf, void *recvbuf,
 
             MPIR_ERRTEST_ARGNULL(request,"request", mpi_errno);
 
-            if (comm_ptr->comm_kind == MPID_INTRACOMM && sendbuf != MPI_IN_PLACE)
+            if (comm_ptr->comm_kind == MPID_INTRACOMM && sendbuf != MPI_IN_PLACE && recvcount != 0)
                 MPIR_ERRTEST_ALIAS_COLL(sendbuf, recvbuf, mpi_errno)
             /* TODO more checks may be appropriate (counts, in_place, etc) */
         }

src/mpi/coll/iscan.c

@@ -442,7 +442,7 @@ int MPI_Iscan(const void *sendbuf, void *recvbuf, int count, MPI_Datatype dataty
 
             MPIR_ERRTEST_ARGNULL(request,"request", mpi_errno);
 
-            if (sendbuf != MPI_IN_PLACE)
+            if (sendbuf != MPI_IN_PLACE && count != 0)
                 MPIR_ERRTEST_ALIAS_COLL(sendbuf, recvbuf, mpi_errno);
             /* TODO more checks may be appropriate (counts, in_place, etc) */
         }

src/mpi/coll/red_scat.c

@@ -1174,7 +1174,7 @@ int MPI_Reduce_scatter(const void *sendbuf, void *recvbuf, const int recvcounts[
             MPIR_ERRTEST_RECVBUF_INPLACE(recvbuf, recvcounts[comm_ptr->rank], mpi_errno);
             if (comm_ptr->comm_kind == MPID_INTERCOMM) {
                 MPIR_ERRTEST_SENDBUF_INPLACE(sendbuf, sum, mpi_errno);
-            } else if (sendbuf != MPI_IN_PLACE)
+            } else if (sendbuf != MPI_IN_PLACE && sum != 0)
                 MPIR_ERRTEST_ALIAS_COLL(sendbuf, recvbuf, mpi_errno)
 
             MPIR_ERRTEST_USERBUFFER(recvbuf,recvcounts[comm_ptr->rank],datatype,mpi_errno);

src/mpi/coll/red_scat_block.c

@@ -1138,7 +1138,7 @@ int MPI_Reduce_scatter_block(const void *sendbuf, void *recvbuf,
             MPIR_ERRTEST_RECVBUF_INPLACE(recvbuf, recvcount, mpi_errno);
             if (comm_ptr->comm_kind == MPID_INTERCOMM) {
                 MPIR_ERRTEST_SENDBUF_INPLACE(sendbuf, recvcount, mpi_errno);
-            } else if (sendbuf != MPI_IN_PLACE)
+            } else if (sendbuf != MPI_IN_PLACE && recvcount != 0)
                 MPIR_ERRTEST_ALIAS_COLL(sendbuf, recvbuf, mpi_errno)
 
             MPIR_ERRTEST_USERBUFFER(recvbuf,recvcount,datatype,mpi_errno);

src/mpi/coll/scan.c

@@ -549,7 +549,7 @@ int MPI_Scan(const void *sendbuf, void *recvbuf, int count, MPI_Datatype datatyp
             }
             if (mpi_errno != MPI_SUCCESS) goto fn_fail;
 
-            if (sendbuf != MPI_IN_PLACE)
+            if (sendbuf != MPI_IN_PLACE && count != 0)
                 MPIR_ERRTEST_ALIAS_COLL(sendbuf, recvbuf, mpi_errno);
         }
         MPID_END_ERROR_CHECKS;