From acd964309dd41b95c81d63fd5a480797d76a4ed2 Mon Sep 17 00:00:00 2001
From: Urs Ganse <urs.ganse@helsinki.fi>
Date: Wed, 3 May 2023 15:07:44 +0300
Subject: [PATCH] Patch for undefined behaviour (nullpointer reference).

Discovered by GCC12's undefined behaviour sanitizer.
---
 dccrg_mpi_support.hpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/dccrg_mpi_support.hpp b/dccrg_mpi_support.hpp
index fe7a5d2..96f2af7 100644
--- a/dccrg_mpi_support.hpp
+++ b/dccrg_mpi_support.hpp
@@ -185,6 +185,10 @@ class All_Gather
 			total_send_count += (uint64_t) send_count;
 		}
 
+		if(total_send_count == 0) {
+			//Early abort if there is nothing to communicate.
+			return;
+		}
 		std::vector<uint64_t> temp_result(total_send_count, std::numeric_limits<uint64_t>::max());
 
 		// give a sane address to gatherv also when nothing to send