vtk-m/docs/changelog/EnableUnityBuild.md

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.