[LLVM] Simplify GPU runtimes flag handling (llvm#159802)

Summary:
The AMDGPU hack can be removed, and we no longer need to skip 90% of the
`HandleLLVMOptions` if we work around NVPTX earlier. Simplifies the
interface by removing duplicated logic and keeps the GPU targets from
being weirdly divergent on some flags.

Author: jhuber6

compiler-rt/cmake/Modules/CompilerRTUtils.cmake

@@ -418,11 +418,9 @@ macro(construct_compiler_rt_default_triple)
     # Pass the necessary flags to make flag detection work.
     if("${COMPILER_RT_DEFAULT_TARGET_ARCH}" MATCHES "amdgcn")
       set(COMPILER_RT_GPU_BUILD ON)
-      set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nogpulib")
     elseif("${COMPILER_RT_DEFAULT_TARGET_ARCH}" MATCHES "nvptx")
       set(COMPILER_RT_GPU_BUILD ON)
-      set(CMAKE_REQUIRED_FLAGS
-          "${CMAKE_REQUIRED_FLAGS} -flto -c -Wno-unused-command-line-argument")
+      set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -flto -c")
     endif()
   endif()
 

flang-rt/CMakeLists.txt

@@ -221,15 +221,6 @@ endif()
 # System Introspection #
 ########################
 
-# The GPU targets require a few mandatory arguments to make the standard CMake
-# check flags happy.
-if ("${LLVM_RUNTIMES_TARGET}" MATCHES "^amdgcn")
-  set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nogpulib")
-elseif ("${LLVM_RUNTIMES_TARGET}" MATCHES "^nvptx")
-  set(CMAKE_REQUIRED_FLAGS
-      "${CMAKE_REQUIRED_FLAGS} -flto -c -Wno-unused-command-line-argument")
-endif()
-
 include(CheckCXXSymbolExists)
 include(CheckCXXSourceCompiles)
 check_cxx_symbol_exists(strerror_r string.h HAVE_STRERROR_R)

libc/cmake/modules/prepare_libc_gpu_build.cmake

@@ -20,12 +20,6 @@ endif()
 if(LIBC_TARGET_TRIPLE)
   set(CMAKE_REQUIRED_FLAGS "--target=${LIBC_TARGET_TRIPLE}")
 endif()
-if(LIBC_TARGET_ARCHITECTURE_IS_AMDGPU)
-  set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nogpulib")
-elseif(LIBC_TARGET_ARCHITECTURE_IS_NVPTX)
-  set(CMAKE_REQUIRED_FLAGS
-      "${CMAKE_REQUIRED_FLAGS} -flto -c -Wno-unused-command-line-argument")
-endif()
 
 # Optionally set up a job pool to limit the number of GPU tests run in parallel.
 # This is sometimes necessary as running too many tests in parallel can cause

llvm/cmake/modules/HandleLLVMOptions.cmake

@@ -144,12 +144,6 @@ if( LLVM_ENABLE_ASSERTIONS )
   endif()
 endif()
 
-# If we are targeting a GPU architecture in a runtimes build we want to ignore
-# all the standard flag handling.
-if(LLVM_RUNTIMES_GPU_BUILD)
-  return()
-endif()
-
 if(LLVM_ENABLE_EXPENSIVE_CHECKS)
   # When LLVM_ENABLE_EXPENSIVE_CHECKS is ON, LLVM will intercept errors
   # using assert(). An explicit check is performed here.

openmp/CMakeLists.txt

@@ -99,14 +99,6 @@ else()
   set(CMAKE_CXX_EXTENSIONS NO)
 endif()
 
-# Targeting the GPU directly requires a few flags to make CMake happy.
-if("${CMAKE_CXX_COMPILER_TARGET}" MATCHES "^amdgcn")
-  set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nogpulib")
-elseif("${CMAKE_CXX_COMPILER_TARGET}" MATCHES "^nvptx")
-  set(CMAKE_REQUIRED_FLAGS
-      "${CMAKE_REQUIRED_FLAGS} -flto -c -Wno-unused-command-line-argument")
-endif()
-
 # Check and set up common compiler flags.
 include(config-ix)
 include(HandleOpenMPOptions)

runtimes/CMakeLists.txt

@@ -181,15 +181,14 @@ if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
   endif()
 endif()
 
+# The NVPTX target needs to override linking to pass compiler flag checks.
+if("${LLVM_RUNTIMES_TARGET}" MATCHES "^nvptx")
+  set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -flto -c")
+endif()
+
 # Avoid checking whether the compiler is working.
 set(LLVM_COMPILER_CHECKED ON)
 
-# This can be used to detect whether we're targeting a GPU architecture.
-if("${LLVM_RUNTIMES_TARGET}" MATCHES "^amdgcn" OR
-   "${LLVM_RUNTIMES_TARGET}" MATCHES "^nvptx64")
-  set(LLVM_RUNTIMES_GPU_BUILD ON)
-endif()
-
 # Handle common options used by all runtimes.
 include(AddLLVM)
 include(HandleLLVMOptions)