Refactor CMAKE_CUDA_ARCHITECTURES handling

Improve how we handle CUDA arch settings by moving
some of the logic into the root CMakeLists. This
will allow us to specify CUDA as a language in our project()
call once we require CMake 3.20.

CMakeLists.txt

@@ -13,6 +13,19 @@
 # =============================================================================
 cmake_minimum_required(VERSION 3.18...3.18 FATAL_ERROR)
 
+# If `CMAKE_CUDA_ARCHITECTURES` is not defined, build for all supported architectures. If
+# `CMAKE_CUDA_ARCHITECTURES` is set to an empty string (""), build for only the current
+# architecture. If `CMAKE_CUDA_ARCHITECTURES` is specified by the user, use user setting.
+
+# This needs to be run before enabling the CUDA language due to the default initialization behavior
+# of `CMAKE_CUDA_ARCHITECTURES`, https://gitlab.kitware.com/cmake/cmake/-/issues/21302
+if(NOT DEFINED CMAKE_CUDA_ARCHITECTURES)
+  set(RMM_BUILD_FOR_ALL_ARCHS TRUE)
+elseif(CMAKE_CUDA_ARCHITECTURES STREQUAL "")
+  unset(CMAKE_CUDA_ARCHITECTURES CACHE)
+  set(RMM_BUILD_FOR_DETECTED_ARCHS TRUE)
+endif()
+
 project(
   RMM
   VERSION 0.19.0
@@ -85,10 +98,9 @@ message(STATUS "RMM: RMM_LOGGING_LEVEL = '${RMM_LOGGING_LEVEL}'")
 
 if(BUILD_TESTS OR BUILD_BENCHMARKS)
   # Auto-detect available GPU compute architectures
+  enable_language(CUDA)
   include(${RMM_SOURCE_DIR}/cmake/Modules/SetGPUArchs.cmake)
   message(STATUS "RMM: Building benchmarks with GPU Architectures: ${CMAKE_CUDA_ARCHITECTURES}")
-  # Only enable the CUDA language after including SetGPUArchs.cmake
-  enable_language(CUDA)
 endif()
 
 # optionally build tests

cmake/Modules/EvalGPUArchs.cmake

@@ -10,8 +10,6 @@
 # or implied. See the License for the specific language governing permissions and limitations under
 # the License.
 
-enable_language(CUDA)
-
 # Function uses the CUDA runtime API to query the compute capability of the device, so if a user
 # doesn't pass any architecture options to CMake we only build the current architecture
 function(evaluate_gpu_archs gpu_archs)

cmake/Modules/SetGPUArchs.cmake

@@ -48,23 +48,12 @@ if(CUDAToolkit_VERSION_MAJOR LESS 9)
   list(REMOVE_ITEM SUPPORTED_CUDA_ARCHITECTURES "70")
 endif()
 
-# If `CMAKE_CUDA_ARCHITECTURES` is not defined, build for all supported architectures. If
-# `CMAKE_CUDA_ARCHITECTURES` is set to an empty string (""), build for only the current
-# architecture. If `CMAKE_CUDA_ARCHITECTURES` is specified by the user, use user setting.
-
-# This needs to be run before enabling the CUDA language due to the default initialization behavior
-# of `CMAKE_CUDA_ARCHITECTURES`, https://gitlab.kitware.com/cmake/cmake/-/issues/21302
-
-if(NOT DEFINED CMAKE_CUDA_ARCHITECTURES)
+if(${PROJECT_NAME}_BUILD_FOR_ALL_ARCHS)
   set(CMAKE_CUDA_ARCHITECTURES ${SUPPORTED_CUDA_ARCHITECTURES})
-endif(NOT DEFINED CMAKE_CUDA_ARCHITECTURES)
-
-if(CMAKE_CUDA_ARCHITECTURES STREQUAL "")
-  unset(CMAKE_CUDA_ARCHITECTURES)
-  unset(CMAKE_CUDA_ARCHITECTURES CACHE)
-  include(${RMM_SOURCE_DIR}/cmake/Modules/EvalGPUArchs.cmake)
+elseif(${PROJECT_NAME}_BUILD_FOR_DETECTED_ARCHS)
+  include(${PROJECT_SOURCE_DIR}/cmake/Modules/EvalGPUArchs.cmake)
   evaluate_gpu_archs(CMAKE_CUDA_ARCHITECTURES)
-endif(CMAKE_CUDA_ARCHITECTURES STREQUAL "")
+endif()
 
 # CMake architecture list entry of "80" means to build compute and sm. What we want is for the
 # newest arch only to build that way while the rest built only for sm.