Use MPI_IN_PLACE (AMReX-Codes#3428)

WeiqunZhang · Jul 19, 2023 · fc32f3e · fc32f3e
1 parent 10b6cb2
commit fc32f3e
Showing 1 changed file with 4 additions and 3 deletions.
diff --git a/Src/Base/AMReX_ParallelReduce.H b/Src/Base/AMReX_ParallelReduce.H
@@ -36,14 +36,15 @@ namespace detail {
  inline void Reduce (ReduceOp op, T* v, int cnt, int root, MPI_Comm comm)
  {
  auto mpi_op = mpi_ops[static_cast<int>(op)]; // NOLINT
- Vector<T> tmp(v, v+cnt);
  if (root == -1) {
  // TODO: add BL_COMM_PROFILE commands
- MPI_Allreduce(tmp.data(), v, cnt, ParallelDescriptor::Mpi_typemap<T>::type(),
+ MPI_Allreduce(MPI_IN_PLACE, v, cnt, ParallelDescriptor::Mpi_typemap<T>::type(),
  mpi_op, comm);
  } else {
  // TODO: add BL_COMM_PROFILE commands
- MPI_Reduce(tmp.data(), v, cnt, ParallelDescriptor::Mpi_typemap<T>::type(),
+ const auto* sendbuf = (ParallelDescriptor::MyProc(comm) == root) ?
+ (void const*)(MPI_IN_PLACE) : (void const*) v;
+ MPI_Reduce(sendbuf, v, cnt, ParallelDescriptor::Mpi_typemap<T>::type(),
  mpi_op, root, comm);
  }
  }