[libc][gpu][NFC] Move CMake logic to prepare GPU build to a separate file.

[jhuber6]

I appreciate it, I was thinking about adding a file like this just now for the testing or for detecting the user's setup. Basically query what GPUs the user has installed locally and see if we can run any tests on it. We already so something similar elsewhere. I'll probably add that capability to this file once you land it.

libc/CMakeLists.txt

else()
   message(STATUS "COMPILER_RESOURCE_DIR not set
                   --print-resource-dir not supported by host compiler")
 endif()
 
 option(LLVM_LIBC_FULL_BUILD "Build and test LLVM libc as if it is the full libc" OFF)
 option(LLVM_LIBC_IMPLEMENTATION_DEFINED_TEST_BEHAVIOR "Build LLVM libc tests assuming our implementation-defined behavior" ON)
 option(LLVM_LIBC_ENABLE_LINTING "Enables linting of libc source files" OFF)
 
-# Set up the target architectures to build for the GPU
-set(ALL_GPU_ARCHITECTURES "sm_35;sm_37;sm_50;sm_52;sm_53;sm_60;sm_61;sm_62;sm_70;sm_72;sm_75;sm_80;sm_86;gfx700;gfx701;gfx801;gfx803;gfx900;gfx902;gfx906;gfx908;gfx90a;gfx90c;gfx940;gfx1010;gfx1030;gfx1031;gfx1032;gfx1033;gfx1034;gfx1035;gfx1036;gfx1100;gfx1101;gfx1102;gfx1103")
-set(LLVM_LIBC_GPU_ARCHITECTURES ${ALL_GPU_ARCHITECTURES} CACHE STRING "List of GPU architectures to support in LLVM libc")
-if (LLVM_LIBC_GPU_ARCHITECTURES STREQUAL "all")
-  set(LIBC_GPU_ARCHITECTURES ${ALL_GPU_ARCHITECTURES})
-else()
-  set(LIBC_GPU_ARCHITECTURES ${LLVM_LIBC_GPU_ARCHITECTURES})
-endif()
-
 set(LLVM_LIBC_TARGET_OS ${CMAKE_SYSTEM_NAME} CACHE STRING "Target operating system for LLVM libc")
 string(TOLOWER ${LLVM_LIBC_TARGET_OS} LIBC_TARGET_OS)
 
 # Defines LIBC_TARGET_ARCHITECTURE and associated macros.
 include(LLVMLibCArchitectures)
 include(LLVMLibCCheckMPFR)
 
-# Ensure the compiler is a valid clang when building the GPU target.
-if(LIBC_TARGET_ARCHITECTURE_IS_GPU AND NOT (CMAKE_CXX_COMPILER_ID MATCHES "[Cc]lang" AND 
-  ${CMAKE_CXX_COMPILER_VERSION} VERSION_EQUAL "${LLVM_VERSION_MAJOR}.${LLVM_VERSION_MINOR}.${LLVM_VERSION_PATCH}"))
-  message(FATAL_ERROR "Cannot build GPU library, CMake compiler '${CMAKE_CXX_COMPILER_ID} ${CMAKE_CXX_COMPILER_VERSION}' is not `Clang ${LLVM_VERSION_MAJOR}.${LLVM_VERSION_MINOR}.${LLVM_VERSION_PATCH}`")
-endif()
-if(LIBC_TARGET_ARCHITECTURE_IS_GPU AND NOT LLVM_LIBC_FULL_BUILD)
-  message(FATAL_ERROR "Cannot build GPU library, LLVM_LIBC_FULL_BUILD must be enabled")
+if(LIBC_TARGET_ARCHITECTURE_IS_GPU)
+  include(prepare_libc_gpu_build)
 endif()
 
 if(LLVM_LIBC_CLANG_TIDY)
   set(LLVM_LIBC_ENABLE_LINTING ON)
 endif()
 
 if(LLVM_LIBC_ENABLE_LINTING)
   if(NOT CMAKE_CXX_COMPILER_ID STREQUAL "Clang")

libc/cmake/modules/prepare_libc_gpu_build.cmake

+# Set up the target architectures to build the GPU libc for.
+set(all_gpu_architectures "sm_35;sm_37;sm_50;sm_52;sm_53;sm_60;sm_61;sm_62;"
+                          "sm_70;sm_72;sm_75;sm_80;sm_86;gfx700;gfx701;gfx801;"
+                          "gfx803;gfx900;gfx902;gfx906;gfx908;gfx90a;gfx90c;"
+                          "gfx940;gfx1010;gfx1030;gfx1031;gfx1032;gfx1033;"
+                          "gfx1034;gfx1035;gfx1036;gfx1100;gfx1101;gfx1102;"
+                          "gfx1103")
+set(LIBC_GPU_ARCHITECTURES ${all_gpu_architectures} CACHE STRING
+    "List of GPU architectures to build the libc for.")
+if(LIBC_GPU_ARCHITECTURES STREQUAL "all")
+  set(LIBC_GPU_ARCHITECTURES ${all_gpu_architectures} FORCE)
+endif()
+
+# Ensure the compiler is a valid clang when building the GPU target.
+set(req_ver "${LLVM_VERSION_MAJOR}.${LLVM_VERSION_MINOR}.${LLVM_VERSION_PATCH}")
+if(LIBC_TARGET_ARCHITECTURE_IS_GPU AND
+   NOT (CMAKE_CXX_COMPILER_ID MATCHES "[Cc]lang" AND
+       ${CMAKE_CXX_COMPILER_VERSION} VERSION_EQUAL "${req_ver}"))
+  message(FATAL_ERROR "Cannot build libc for GPU. CMake compiler "
+                      "'${CMAKE_CXX_COMPILER_ID} ${CMAKE_CXX_COMPILER_VERSION}' "
+                      " is not `Clang ${req_ver}.")
+endif()
+if(LLVM_LIBC_FULL_BUILD)
+  message(FATAL_ERROR "LLVM_LIBC_FULL_BUILD must be enabled to build libc for "
+                      "GPU.")
+endif()