From: Wolfgang Bangerth <bangerth@colostate.edu>
Date: Wed, 10 Jan 2024 22:21:28 +0000 (-0700)
Subject: Avoid using two temporary vectors when not necessary.
X-Git-Tag: relicensing~179^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F16454%2Fhead;p=dealii.git

Avoid using two temporary vectors when not necessary.
---

diff --git a/include/deal.II/numerics/data_out_dof_data.templates.h b/include/deal.II/numerics/data_out_dof_data.templates.h
index 32ce2c2212..92e019b511 100644
--- a/include/deal.II/numerics/data_out_dof_data.templates.h
+++ b/include/deal.II/numerics/data_out_dof_data.templates.h
@@ -803,15 +803,33 @@ namespace internal
         const VectorType                           &src,
         LinearAlgebra::distributed::Vector<Number> &dst)
       {
-        LinearAlgebra::ReadWriteVector<typename VectorType::value_type> temp;
-        temp.reinit(src.locally_owned_elements());
-        temp.import_elements(src, VectorOperation::insert);
+        // If source and destination vector have the same underlying scalar,
+        // we can directly import elements by using only one temporary vector:
+        if constexpr (std::is_same_v<typename VectorType::value_type, Number>)
+          {
+            LinearAlgebra::ReadWriteVector<typename VectorType::value_type>
+              temp;
+            temp.reinit(src.locally_owned_elements());
+            temp.import_elements(src, VectorOperation::insert);
 
-        LinearAlgebra::ReadWriteVector<Number> temp2;
-        temp2.reinit(temp, true);
-        temp2 = temp;
+            dst.import_elements(temp, VectorOperation::insert);
+          }
+        else
+          // The source and destination vector have different scalar types. We
+          // need to split the parallel import and local copy operations into
+          // two phases
+          {
+            LinearAlgebra::ReadWriteVector<typename VectorType::value_type>
+              temp;
+            temp.reinit(src.locally_owned_elements());
+            temp.import_elements(src, VectorOperation::insert);
 
-        dst.import_elements(temp2, VectorOperation::insert);
+            LinearAlgebra::ReadWriteVector<Number> temp2;
+            temp2.reinit(temp, true);
+            temp2 = temp;
+
+            dst.import_elements(temp2, VectorOperation::insert);
+          }
       }
 
 #ifdef DEAL_II_WITH_TRILINOS