From c2e19b77b517484a4d9382e456900bbdf4e04047 Mon Sep 17 00:00:00 2001
From: Julian Roth <mathmerizing@gmail.com>
Date: Sat, 6 Jun 2020 22:17:13 +0200
Subject: [PATCH] Moved copy of vector into if block

---
 source/multigrid/mg_transfer_prebuilt.cc | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/source/multigrid/mg_transfer_prebuilt.cc b/source/multigrid/mg_transfer_prebuilt.cc
index c250fefb37..d7d3669aca 100644
--- a/source/multigrid/mg_transfer_prebuilt.cc
+++ b/source/multigrid/mg_transfer_prebuilt.cc
@@ -85,14 +85,20 @@ MGTransferPrebuilt<VectorType>::prolongate(const unsigned int to_level,
   Assert((to_level >= 1) && (to_level <= prolongation_matrices.size()),
          ExcIndexRange(to_level, 1, prolongation_matrices.size() + 1));
 
-  VectorType copy_src(src);
   if (this->mg_constrained_dofs != nullptr &&
       this->mg_constrained_dofs->get_user_constraint_matrix(to_level - 1)
           .get_local_lines()
           .size() > 0)
-    this->mg_constrained_dofs->get_user_constraint_matrix(to_level - 1)
-      .distribute(copy_src);
-  prolongation_matrices[to_level - 1]->vmult(dst, copy_src);
+    {
+      VectorType copy_src(src);
+      this->mg_constrained_dofs->get_user_constraint_matrix(to_level - 1)
+        .distribute(copy_src);
+      prolongation_matrices[to_level - 1]->vmult(dst, copy_src);
+    }
+  else
+    {
+      prolongation_matrices[to_level - 1]->vmult(dst, src);
+    }
 }
 
 
-- 
2.39.5