[Clang] Remove `CLANG_OPENMP_NVPTX_DEFAULT_ARCH` CMake option.

[jhuber6]

Summary

The CLANG_OPENMP_NVPTX_DEFAULT_ARCH is a static build configuration to
set the default OpenMP value. This was replaced in D141708 with the use
of the nvptx-arch tool which lets us query this at runtime instead.
This makes the behaviour between AMD and NVIDIA be more consisten and
allows users to have a default architecture that does not rely on
whoever configured the LLVM build.

Depends on D141708

[tschuett]

Up right you will find Edit Related Revisions....

[MaskRay]

Removing a CMAKE_*_DEFAULT_* makes me happy:)

clang/CMakeLists.txt

 endif()
 
 set(CLANG_DEFAULT_OBJCOPY "objcopy" CACHE STRING
   "Default objcopy executable to use.")
 
 set(CLANG_DEFAULT_OPENMP_RUNTIME "libomp" CACHE STRING
   "Default OpenMP runtime used by -fopenmp.")
 
-# OpenMP offloading requires at least sm_35 because we use shuffle instructions
-# to generate efficient code for reductions and the atomicMax instruction on
-# 64-bit integers in the implementation of conditional lastprivate.
-set(CUDA_ARCH_FLAGS "sm_35")
-
-# Try to find the highest Nvidia GPU architecture the system supports
-if (NOT DEFINED CLANG_OPENMP_NVPTX_DEFAULT_ARCH)
-  find_package(CUDA QUIET)
-  if (CUDA_FOUND)
-    cuda_select_nvcc_arch_flags(CUDA_ARCH_FLAGS)
-  endif()
-else()
-  set(CUDA_ARCH_FLAGS ${CLANG_OPENMP_NVPTX_DEFAULT_ARCH})
-endif()
-
-string(REGEX MATCH "sm_([0-9]+)" CUDA_ARCH_MATCH ${CUDA_ARCH_FLAGS})
-if (NOT DEFINED CUDA_ARCH_MATCH OR "${CMAKE_MATCH_1}" LESS 35)
-  set(CLANG_OPENMP_NVPTX_DEFAULT_ARCH "sm_35" CACHE STRING
-    "Default architecture for OpenMP offloading to Nvidia GPUs." FORCE)
-  message(WARNING "Resetting default architecture for OpenMP offloading to Nvidia GPUs to sm_35")
-else()
-  set(CLANG_OPENMP_NVPTX_DEFAULT_ARCH ${CUDA_ARCH_MATCH} CACHE STRING
-    "Default architecture for OpenMP offloading to Nvidia GPUs.")
-endif()
-
 set(CLANG_SYSTEMZ_DEFAULT_ARCH "z10" CACHE STRING "SystemZ Default Arch")
 
 set(CLANG_VENDOR ${PACKAGE_VENDOR} CACHE STRING
   "Vendor-specific text for showing with version information.")
 
 set(CLANG_REPOSITORY_STRING "" CACHE STRING
   "Vendor-specific text for showing the repository the source is taken from.")
 

clang/include/clang/Config/config.h.cmake

 #define CLANG_DEFAULT_UNWINDLIB "${CLANG_DEFAULT_UNWINDLIB}"
 
 /* Default objcopy to use */
 #define CLANG_DEFAULT_OBJCOPY "${CLANG_DEFAULT_OBJCOPY}"
 
 /* Default OpenMP runtime used by -fopenmp. */
 #define CLANG_DEFAULT_OPENMP_RUNTIME "${CLANG_DEFAULT_OPENMP_RUNTIME}"
 
-/* Default architecture for OpenMP offloading to Nvidia GPUs. */
-#define CLANG_OPENMP_NVPTX_DEFAULT_ARCH "${CLANG_OPENMP_NVPTX_DEFAULT_ARCH}"
-
 /* Default architecture for SystemZ. */
 #define CLANG_SYSTEMZ_DEFAULT_ARCH "${CLANG_SYSTEMZ_DEFAULT_ARCH}"
 
 /* Multilib basename for libdir. */
 #define CLANG_INSTALL_LIBDIR_BASENAME "${CLANG_INSTALL_LIBDIR_BASENAME}"
 
 /* Relative directory for resource files */
 #define CLANG_RESOURCE_DIR "${CLANG_RESOURCE_DIR}"

llvm/utils/gn/secondary/clang/include/clang/Config/BUILD.gn

values = [
     "CLANG_DEFAULT_PIE_ON_LINUX=1",
     "CLANG_DEFAULT_LINKER=",
     "CLANG_DEFAULT_CXX_STDLIB=",
     "CLANG_DEFAULT_RTLIB=",
     "CLANG_DEFAULT_OBJCOPY=objcopy",
     "CLANG_DEFAULT_OPENMP_RUNTIME=libomp",
     "CLANG_DEFAULT_UNWINDLIB=",
     "CLANG_INSTALL_LIBDIR_BASENAME=lib",
-    "CLANG_OPENMP_NVPTX_DEFAULT_ARCH=sm_35",
     "CLANG_RESOURCE_DIR=",
     "C_INCLUDE_DIRS=",
     "CLANG_CONFIG_FILE_SYSTEM_DIR=",
     "CLANG_CONFIG_FILE_USER_DIR=",
     "CLANG_SPAWN_CC1=",
     "DEFAULT_SYSROOT=",
     "GCC_INSTALL_PREFIX=",
     "ENABLE_LINKER_BUILD_ID=",

utils/bazel/llvm-project-overlay/clang/include/clang/Config/config.h

 #define CLANG_DEFAULT_UNWINDLIB ""
 
 /* Default objcopy to use */
 #define CLANG_DEFAULT_OBJCOPY "objcopy"
 
 /* Default OpenMP runtime used by -fopenmp. */
 #define CLANG_DEFAULT_OPENMP_RUNTIME "libomp"
 
-/* Default architecture for OpenMP offloading to Nvidia GPUs. */
-#define CLANG_OPENMP_NVPTX_DEFAULT_ARCH "sm_35"
-
 /* Default architecture for SystemZ. */
 #define CLANG_SYSTEMZ_DEFAULT_ARCH "z10"
 
 /* Multilib basename for libdir. */
 #define CLANG_INSTALL_LIBDIR_BASENAME "lib"
 
 /* Relative directory for resource files */
 #define CLANG_RESOURCE_DIR ""