Enable using Thrust from CCCL

src/thrust/model.cmake

@@ -1,13 +1,13 @@
 
 register_flag_optional(THRUST_IMPL
         "Which Thrust implementation to use, supported options include:
-         - CUDA (via https://github.com/NVIDIA/thrust)
+         - CUDA (via https://github.com/NVIDIA/thrust or https://github.com/NVIDIA/CCCL)
          - ROCM (via https://github.com/ROCmSoftwarePlatform/rocThrust)
         "
         "CUDA")
 
 register_flag_optional(SDK_DIR
-        "Path to the selected Thrust implementation (e.g `/opt/nvidia/hpc_sdk/Linux_x86_64/21.9/cuda/include` for NVHPC, `/opt/rocm` for ROCm)"
+        "Path to the installation prefix for CCCL or Thrust (e.g `/opt/nvidia/hpc_sdk/Linux_x86_64/24.5/cuda/12.4/lib64/cmake` for NVHPC, or `/usr/local/cuda-12.5/lib64/cmake` for nvcc, or `/usr/local/cuda-11.4/include` for older nvcc, or `/opt/rocm` for ROCm)"
         "")
 
 register_flag_optional(BACKEND
@@ -18,7 +18,7 @@ register_flag_optional(BACKEND
         "
         "CUDA")
 
-      register_flag_optional(MANAGED "Enabled managed memory mode."
+register_flag_optional(MANAGED "Enabled managed memory mode."
         "OFF")
 
 register_flag_optional(CMAKE_CUDA_COMPILER
@@ -34,6 +34,9 @@ register_flag_optional(CUDA_EXTRA_FLAGS
         "[THRUST_IMPL==CUDA] Additional CUDA flags passed to nvcc, this is appended after `CUDA_ARCH`"
         "")
 
+option(FETCH_CCCL "Fetch (download) the CCCL library. This uses CMake's FetchContent feature.
+                   Specify version by setting FETCH_CCCL_VERSION" OFF)
+set(FETCH_CCCL_VERSION "v2.4.0" CACHE STRING "Specify version of CCCL to use if FETCH_CCCL is ON")
 
 macro(setup)
     set(CMAKE_CXX_STANDARD 14)
@@ -42,44 +45,48 @@ macro(setup)
     endif ()
 
     if (${THRUST_IMPL} STREQUAL "CUDA")
-
-        # see CUDA.cmake, we're only adding a few Thrust related libraries here
-
         if (POLICY CMP0104)
             cmake_policy(SET CMP0104 NEW)
         endif ()
-
         set(CMAKE_CUDA_ARCHITECTURES  ${CUDA_ARCH})
-        # add -forward-unknown-to-host-compiler for compatibility reasons
         set(CMAKE_CUDA_FLAGS ${CMAKE_CUDA_FLAGS} "--expt-extended-lambda " ${CUDA_EXTRA_FLAGS})
         enable_language(CUDA)
-        # CMake defaults to -O2 for CUDA at Release, let's wipe that and use the global RELEASE_FLAG
-        # appended later
+        # CMake defaults to -O2 for CUDA at Release, let's wipe that and use the global RELEASE_FLAG appended later
         wipe_gcc_style_optimisation_flags(CMAKE_CUDA_FLAGS_${BUILD_TYPE})
 
         message(STATUS "NVCC flags: ${CMAKE_CUDA_FLAGS} ${CMAKE_CUDA_FLAGS_${BUILD_TYPE}}")
 
-
-        # XXX NVHPC <= 21.9 has cub-config in `Linux_x86_64/21.9/cuda/11.4/include/cub/cmake`
-        # XXX NVHPC >= 22.3 has cub-config in `Linux_x86_64/22.3/cuda/11.6/lib64/cmake/cub/`
-        # same thing for thrust
         if (SDK_DIR)
+            # CMake tries several subdirectories below SDK_DIR, see documentation:
+            # https://cmake.org/cmake/help/latest/command/find_package.html#config-mode-search-procedure
             list(APPEND CMAKE_PREFIX_PATH ${SDK_DIR})
-            find_package(CUB REQUIRED CONFIG PATHS ${SDK_DIR}/cub)
-            find_package(Thrust REQUIRED CONFIG PATHS ${SDK_DIR}/thrust)
-        else ()
-            find_package(CUB REQUIRED CONFIG)
-            find_package(Thrust REQUIRED CONFIG)
         endif ()
 
-        message(STATUS "Using Thrust backend: ${BACKEND}")
-
-        # this creates the interface that we can link to
-        thrust_create_target(Thrust${BACKEND}
-                HOST CPP
-                DEVICE ${BACKEND})
-
-        register_link_library(Thrust${BACKEND})
+        set(CCCL_THRUST_DEVICE_SYSTEM ${BACKEND} CACHE STRING "" FORCE)
+
+        # fetch CCCL if user wants to
+        if (FETCH_CCCL)
+            FetchContent_Declare(
+                    CCCL
+                    GIT_REPOSITORY https://github.com/nvidia/cccl.git
+                    GIT_TAG "${FETCH_CCCL_VERSION}"
+            )
+            FetchContent_MakeAvailable(CCCL)
+            register_link_library(CCCL::CCCL)
+        else()
+            # try to find CCCL locally
+            find_package(CCCL CONFIG)
+            if (CCCL_FOUND)
+                register_link_library(CCCL::CCCL)
+            else()
+                # backup: find legacy projects separately
+                message(WARNING "No CCCL found on your system. Trying Thrust and CUB legacy targets.")
+                find_package(CUB REQUIRED CONFIG)
+                find_package(Thrust REQUIRED CONFIG)
+                thrust_create_target(Thrust${BACKEND} HOST CPP DEVICE ${BACKEND})
+                register_link_library(Thrust${BACKEND})
+            endif()
+        endif()
     elseif (${THRUST_IMPL} STREQUAL "ROCM")
         if (SDK_DIR)
             find_package(rocprim REQUIRED CONFIG PATHS ${SDK_DIR}/rocprim)