Remove unused-but-set variables in gloo/mpi/example/main_unmanaged.cc +1

Summary:
This diff removes a variable that was set, but which was not used.

LLVM-15 has a warning `-Wunused-but-set-variable` which we treat as an error because it's so often diagnostic of a code issue. Unused but set variables often indicate a programming mistake, but can also just be unnecessary cruft that harms readability and performance.

Removing this variable will not change how your code works, but the unused variable may indicate your code isn't working the way you thought it was. If you feel the diff needs changes before landing, **please commandeer** and make appropriate changes: there are hundreds of these and responding to them individually is challenging.

For questions/comments, contact r-barnes.

 - If you approve of this diff, please use the "Accept & Ship" button :-)

Reviewed By: palmje

Differential Revision: D57793834

fbshipit-source-id: 464397c542c61d6838285d4c90cbbe81767953b3

Author: r-barnes

gloo/mpi/example/main_unmanaged.cc

@@ -8,16 +8,17 @@
 
 #include <cassert>
 #include <iostream>
+#include <stdexcept>
 
 #include "gloo/mpi/context.h"
 #include "gloo/transport/tcp/device.h"
 #include "gloo/allreduce_ring.h"
 
 int main(int argc, char** argv) {
-  int rv;
-
-  rv = MPI_Init(&argc, &argv);
-  assert(rv == MPI_SUCCESS);
+  auto rv = MPI_Init(&argc, &argv);
+  if(rv != MPI_SUCCESS) {
+    throw std::runtime_error("Failed to initialize MPI");
+  }
 
   // We'll use the TCP transport in this example
   auto dev = gloo::transport::tcp::CreateDevice("localhost");
@@ -36,6 +37,9 @@ int main(int argc, char** argv) {
   }
 
   rv = MPI_Finalize();
-  assert(rv == MPI_SUCCESS);
+  if(rv != MPI_SUCCESS) {
+    throw std::runtime_error("Failed to Finalize MPI");
+  }
+
   return 0;
 }