From 7992e1b6bf737430af8f917c8ae5b7e8a5d317a6 Mon Sep 17 00:00:00 2001
From: Kenneth Moreland <morelandkd@ornl.gov>
Date: Thu, 31 Aug 2023 14:03:30 -0500
Subject: [PATCH] Store constant AMR arrays with less memory

The `AmrArrays` filter generates some cell fields that specify information
about the hierarchy, which are constant across all cells in a partition.
These were previously stored as an array with the same value throughout.
Now, the field is stored as an `ArrayHandleConstant`, which does not
require any real storage. Recent changes to VTK-m allow code to extract the
array as a component efficiently without knowing the storage type.

Fixes #794
---
 docs/changelog/constant-amr-arrays.md |  8 ++++++++
 vtkm/filter/multi_block/AmrArrays.cxx | 20 +++++++-------------
 2 files changed, 15 insertions(+), 13 deletions(-)
 create mode 100644 docs/changelog/constant-amr-arrays.md

diff --git a/docs/changelog/constant-amr-arrays.md b/docs/changelog/constant-amr-arrays.md
new file mode 100644
index 000000000..c2afda9df
--- /dev/null
+++ b/docs/changelog/constant-amr-arrays.md
@@ -0,0 +1,8 @@
+# Store constant AMR arrays with less memory
+
+The `AmrArrays` filter generates some cell fields that specify information
+about the hierarchy, which are constant across all cells in a partition.
+These were previously stored as an array with the same value throughout.
+Now, the field is stored as an `ArrayHandleConstant`, which does not
+require any real storage. Recent changes to VTK-m allow code to extract the
+array as a component efficiently without knowing the storage type.
diff --git a/vtkm/filter/multi_block/AmrArrays.cxx b/vtkm/filter/multi_block/AmrArrays.cxx
index ec2c49b40..6962e180e 100644
--- a/vtkm/filter/multi_block/AmrArrays.cxx
+++ b/vtkm/filter/multi_block/AmrArrays.cxx
@@ -274,21 +274,15 @@ void AmrArrays::GenerateIndexArrays()
     {
       vtkm::cont::DataSet partition = this->AmrDataSet.GetPartition(this->PartitionIds.at(l).at(b));
 
-      vtkm::cont::ArrayHandle<vtkm::Id> fieldAmrLevel;
-      vtkm::cont::ArrayCopy(
-        vtkm::cont::ArrayHandleConstant<vtkm::Id>(l, partition.GetNumberOfCells()), fieldAmrLevel);
-      partition.AddCellField("vtkAmrLevel", fieldAmrLevel);
+      partition.AddCellField(
+        "vtkAmrLevel", vtkm::cont::ArrayHandleConstant<vtkm::Id>(l, partition.GetNumberOfCells()));
 
-      vtkm::cont::ArrayHandle<vtkm::Id> fieldBlockId;
-      vtkm::cont::ArrayCopy(
-        vtkm::cont::ArrayHandleConstant<vtkm::Id>(b, partition.GetNumberOfCells()), fieldBlockId);
-      partition.AddCellField("vtkAmrIndex", fieldBlockId);
+      partition.AddCellField(
+        "vtkAmrIndex", vtkm::cont::ArrayHandleConstant<vtkm::Id>(b, partition.GetNumberOfCells()));
 
-      vtkm::cont::ArrayHandle<vtkm::Id> fieldPartitionIndex;
-      vtkm::cont::ArrayCopy(vtkm::cont::ArrayHandleConstant<vtkm::Id>(
-                              this->PartitionIds.at(l).at(b), partition.GetNumberOfCells()),
-                            fieldPartitionIndex);
-      partition.AddCellField("vtkCompositeIndex", fieldPartitionIndex);
+      partition.AddCellField("vtkCompositeIndex",
+                             vtkm::cont::ArrayHandleConstant<vtkm::Id>(
+                               this->PartitionIds.at(l).at(b), partition.GetNumberOfCells()));
 
       this->AmrDataSet.ReplacePartition(this->PartitionIds.at(l).at(b), partition);
     }