Add CMake option to build with external CCCL

CMakeLists.txt

@@ -75,6 +75,7 @@ option(USE_NCCL  "Build with NCCL to enable distributed GPU support." OFF)
 # This is specifically designed for PyPI binary release and should be disabled for most of the cases.
 option(USE_DLOPEN_NCCL "Whether to load nccl dynamically." OFF)
 option(BUILD_WITH_SHARED_NCCL "Build with shared NCCL library." OFF)
+option(BUILD_WITH_EXTERNAL_CCCL "Build with external CCCL instead of one from CTK" OFF)
 
 if(USE_CUDA)
   if(NOT DEFINED CMAKE_CUDA_ARCHITECTURES AND NOT DEFINED ENV{CUDAARCHS})
@@ -221,6 +222,10 @@ if(USE_CUDA)
   add_subdirectory(${PROJECT_SOURCE_DIR}/gputreeshap)
 
   find_package(CUDAToolkit REQUIRED)
+
+  if(BUILD_WITH_EXTERNAL_CCCL)
+    find_package(CCCL REQUIRED CONFIG COMPONENTS cub)
+  endif()
 endif()
 
 if(FORCE_COLORED_OUTPUT AND (CMAKE_GENERATOR STREQUAL "Ninja") AND
@@ -427,6 +432,9 @@ else()
     set(INSTALL_TARGETS xgboost)
   endif()
 endif()
+if(BUILD_WITH_EXTERNAL_CCCL)
+  list(APPEND INSTALL_TARGETS _CUB_CUB _CUB_libcudacxx)
+endif()
 
 install(TARGETS ${INSTALL_TARGETS}
   EXPORT XGBoostTargets

cmake/Utils.cmake

@@ -104,6 +104,11 @@ function(xgboost_set_cuda_flags target)
     target_compile_definitions(${target} PRIVATE -DXGBOOST_USE_NVTX=1)
   endif()
 
+  if(BUILD_WITH_EXTERNAL_CCCL)
+    target_compile_definitions(${target} PRIVATE -DTHRUST_IGNORE_CUB_VERSION_CHECK=1)
+    target_link_libraries(${target} PRIVATE CCCL::CUB)
+  endif()
+
   target_compile_definitions(${target} PRIVATE -DXGBOOST_USE_CUDA=1)
   target_include_directories(
     ${target} PRIVATE