From 555013cdda270f2387b22909f6fd57456e7cbbec Mon Sep 17 00:00:00 2001
From: Vicente Adolfo Bolea Sanchez <vicente.bolea@kitware.com>
Date: Wed, 10 Nov 2021 15:03:11 -0500
Subject: [PATCH 1/2] CMAKE: add unity builds support

---
 CMake/VTKmWrappers.cmake           | 16 ++++++++++++++--
 CMakeLists.txt                     |  8 ++++++++
 docs/changelog/EnableUnityBuild.md | 12 ++++++++++++
 vtkm/filter/CMakeLists.txt         |  8 ++++----
 4 files changed, 38 insertions(+), 6 deletions(-)
 create mode 100644 docs/changelog/EnableUnityBuild.md

diff --git a/CMake/VTKmWrappers.cmake b/CMake/VTKmWrappers.cmake
index ac4872197..ebb5e780a 100644
--- a/CMake/VTKmWrappers.cmake
+++ b/CMake/VTKmWrappers.cmake
@@ -464,6 +464,16 @@ function(vtkm_library)
     set(VTKm_LIB_type SHARED)
   endif()
 
+  # Skip unity builds unless explicitly asked
+  foreach(source IN LISTS VTKm_LIB_SOURCES VTKm_LIB_DEVICE_SOURCES)
+    get_source_file_property(is_candidate ${source} UNITY_BUILD_CANDIDATE)
+    if (NOT is_candidate)
+      list(APPEND non_unity_sources ${source})
+    endif()
+  endforeach()
+
+  set_source_files_properties(${non_unity_sources} PROPERTIES SKIP_UNITY_BUILD_INCLUSION ON)
+
   add_library(${lib_name}
               ${VTKm_LIB_type}
               ${VTKm_LIB_SOURCES}
@@ -615,8 +625,10 @@ function(vtkm_add_instantiations instantiations_list)
     math(EXPR counter "${counter} + 1")
   endforeach(instantiation)
 
-  set_source_files_properties(${_instantiations_list}
-    PROPERTIES SKIP_UNITY_BUILD_INCLUSION ON
+  # Force unity builds here
+  set_source_files_properties(${_instantiations_list} PROPERTIES
+    SKIP_UNITY_BUILD_INCLUSION OFF
+    UNITY_BUILD_CANDIDATE ON
     )
   set(${instantiations_list} ${_instantiations_list} PARENT_SCOPE)
 endfunction(vtkm_add_instantiations)
diff --git a/CMakeLists.txt b/CMakeLists.txt
index d039b8e09..99b3efe32 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -24,6 +24,14 @@ set(CMAKE_CXX_EXTENSIONS OFF)
 set(VTKm_CMAKE_MODULE_PATH ${VTKm_SOURCE_DIR}/CMake)
 set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} ${VTKm_CMAKE_MODULE_PATH})
 
+# While disabled system-wide, VTK-m uses UNITY builds in some modules
+set(CMAKE_UNITY_BUILD OFF)
+
+# By default effectively disable unity builds
+if (NOT DEFINED CMAKE_UNITY_BUILD_BATCH_SIZE)
+  set(CMAKE_UNITY_BUILD_BATCH_SIZE 1)
+endif()
+
 # Determine VTK-m version
 include(Utilities/Git/Git.cmake)
 include(VTKmDetermineVersion)
diff --git a/docs/changelog/EnableUnityBuild.md b/docs/changelog/EnableUnityBuild.md
new file mode 100644
index 000000000..4f8adbfbb
--- /dev/null
+++ b/docs/changelog/EnableUnityBuild.md
@@ -0,0 +1,12 @@
+## Enable Unity build ##
+
+VTK-m now partially supports unity builds in a subset its sources files which
+are known to take the longer time/memory to build. Particularly, this enables
+you to speedup compilation in VTK-m not memory intensive builds (HIP, CUDA) in a
+system with sufficient resources.
+
+We use `BATCH` unity builds type and the number of source files per batch can be
+controlled by the canonical _CMake_ variable: `CMAKE_UNITY_BUILD_BATCH_SIZE`.
+
+Unity builds requires _CMake_ >= 3.16, if using a older version, unity build
+will be disabled a regular build will be performed.
diff --git a/vtkm/filter/CMakeLists.txt b/vtkm/filter/CMakeLists.txt
index a46fdffbe..fc9829d56 100644
--- a/vtkm/filter/CMakeLists.txt
+++ b/vtkm/filter/CMakeLists.txt
@@ -234,8 +234,6 @@ set(gradient_sources_device
 vtkm_pyexpander_generated_file(ClipWithFieldExternInstantiations.h)
 vtkm_pyexpander_generated_file(ClipWithImplicitFunctionExternInstantiations.h)
 
-set_source_files_properties(Contour.cxx ExtractStructured.cxx PROPERTIES SKIP_UNITY_BUILD_INCLUSION ON)
-
 add_library(vtkm_filter INTERFACE)
 
 vtkm_library(
@@ -270,12 +268,14 @@ vtkm_library(
   USE_VTKM_JOB_POOL
   )
 
-set_property(TARGET
+set_target_properties(
   vtkm_filter_common
   vtkm_filter_extra
   vtkm_filter_contour
   vtkm_filter_gradient
-  PROPERTY UNITY_BUILD_MODE GROUP
+  PROPERTIES
+  UNITY_BUILD ON
+  UNITY_BUILD_MODE BATCH
   )
 
 target_link_libraries(vtkm_filter_common PUBLIC vtkm_worklet)

From b680269811da1b24840aa588e9508e037354dc4e Mon Sep 17 00:00:00 2001
From: Vicente Adolfo Bolea Sanchez <vicente.bolea@kitware.com>
Date: Fri, 19 Nov 2021 15:57:21 -0500
Subject: [PATCH 2/2] CI: use latest master GBench

---
 .gitlab/ci/config/google_benchmarks.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/.gitlab/ci/config/google_benchmarks.sh b/.gitlab/ci/config/google_benchmarks.sh
index 3cd69cde8..9866ed4c7 100755
--- a/.gitlab/ci/config/google_benchmarks.sh
+++ b/.gitlab/ci/config/google_benchmarks.sh
@@ -2,10 +2,10 @@
 
 set -xe
 
-readonly version="v1.5.2"
+readonly version="91ed7eea6856f8785139c58fbcc827e82579243c"
 readonly tarball="$version.tar.gz"
 readonly url="https://github.com/google/benchmark/archive/$tarball"
-readonly sha256sum="dccbdab796baa1043f04982147e67bb6e118fe610da2c65f88912d73987e700c"
+readonly sha256sum="039054b7919b0af1082b121df35f4c24fccdd97f308e3dc28f36a0d3a3c64c69"
 readonly install_dir="$HOME/gbench"
 
 if ! [[ "$VTKM_SETTINGS" =~ "benchmarks" ]]; then