[libc] Use CMAKE_CROSSCOMPILING_EMULATOR instead searching for `llvm-gpu-loader' (#189417)

Summary:
We already handle this with other targets, we should be able to unify
the handling here.

libc/CMakeLists.txt

@@ -34,7 +34,6 @@ if (CMAKE_BUILD_TYPE STREQUAL "Debug")
   add_definitions("-D_DEBUG")
 endif()
 
-
 # Default to C++17
 set(CMAKE_CXX_STANDARD 17)
 

libc/cmake/modules/LLVMLibCTestRules.cmake

@@ -643,12 +643,6 @@ function(add_integration_test test_name)
                    libc.test.IntegrationTest.test
                    ${INTEGRATION_TEST_DEPENDS})
 
-  # Tests on the GPU require an external loader utility to launch the kernel.
-  if(TARGET libc.utils.gpu.loader)
-    add_dependencies(${fq_build_target_name} libc.utils.gpu.loader)
-    get_target_property(gpu_loader_exe libc.utils.gpu.loader "EXECUTABLE")
-  endif()
-
   # We have to use a separate var to store the command as a list because
   # the COMMAND option of `add_custom_target` cannot handle empty vars in the
   # command. For example, if INTEGRATION_TEST_ENV is empty, the actual
@@ -658,7 +652,6 @@ function(add_integration_test test_name)
   set(test_cmd
       ${INTEGRATION_TEST_ENV}
       $<$<BOOL:${LIBC_TARGET_ARCHITECTURE_IS_NVPTX}>:LIBOMPTARGET_STACK_SIZE=3072>
-      $<$<BOOL:${LIBC_TARGET_OS_IS_GPU}>:${gpu_loader_exe}>
       ${CMAKE_CROSSCOMPILING_EMULATOR}
       ${INTEGRATION_TEST_LOADER_ARGS}
       $<TARGET_FILE:${fq_build_target_name}> ${INTEGRATION_TEST_ARGS})
@@ -896,12 +889,6 @@ function(add_libc_hermetic test_name)
     )
   endif()
 
-  # Tests on the GPU require an external loader utility to launch the kernel.
-  if(TARGET libc.utils.gpu.loader)
-    add_dependencies(${fq_build_target_name} libc.utils.gpu.loader)
-    get_target_property(gpu_loader_exe libc.utils.gpu.loader "EXECUTABLE")
-  endif()
-
   if(NOT HERMETIC_TEST_NO_RUN_POSTBUILD)
     if (LIBC_TEST_CMD)
       # In the form of "<command> binary=@BINARY@", e.g. "qemu-system-arm -loader$<COMMA>file=@BINARY@"
@@ -910,7 +897,7 @@ function(add_libc_hermetic test_name)
     else()
       set(test_cmd ${HERMETIC_TEST_ENV}
         $<$<BOOL:${LIBC_TARGET_ARCHITECTURE_IS_NVPTX}>:LIBOMPTARGET_STACK_SIZE=3072>
-        $<$<BOOL:${LIBC_TARGET_OS_IS_GPU}>:${gpu_loader_exe}> ${CMAKE_CROSSCOMPILING_EMULATOR} ${HERMETIC_TEST_LOADER_ARGS}
+        ${CMAKE_CROSSCOMPILING_EMULATOR} ${HERMETIC_TEST_LOADER_ARGS}
         $<TARGET_FILE:${fq_build_target_name}> ${HERMETIC_TEST_ARGS})
     endif()
 

libc/cmake/modules/prepare_libc_gpu_build.cmake

@@ -66,24 +66,6 @@ else()
 endif()
 set(LIBC_GPU_TARGET_ARCHITECTURE "${gpu_test_architecture}")
 
-# Identify the GPU loader utility used to run tests.
-set(LIBC_GPU_LOADER_EXECUTABLE "" CACHE STRING "Executable for the GPU loader.")
-if(LIBC_GPU_LOADER_EXECUTABLE)
-  set(gpu_loader_executable ${LIBC_GPU_LOADER_EXECUTABLE})
-else()
-  find_program(gpu_loader_executable
-               NAMES llvm-gpu-loader NO_DEFAULT_PATH
-               PATHS ${LLVM_BINARY_DIR}/bin ${compiler_path})
-endif()
-if(NOT TARGET libc.utils.gpu.loader AND gpu_loader_executable)
-  add_custom_target(libc.utils.gpu.loader)
-  set_target_properties(
-    libc.utils.gpu.loader
-    PROPERTIES
-      EXECUTABLE "${gpu_loader_executable}"
-  )
-endif()
-
 # The AMDGPU environment uses different code objects to encode the ABI for
 # kernel calls and intrinsic functions. We want to expose this to conform to
 # whatever the test suite was built to handle.

libc/docs/gpu/building.rst

@@ -195,6 +195,7 @@ standard runtime build.
   commonly run out of resources if this is not constrained so it is recommended
   to keep it low. The default value is a single thread.
 
-**LIBC_GPU_LOADER_EXECUTABLE**:STRING
-  Overrides the default loader used for running GPU tests. If this is not
-  provided the standard one will be built.
+**CMAKE_CROSSCOMPILING_EMULATOR**:STRING
+  Overrides the default loader used for running GPU tests. This is set
+  automatically to ``llvm-gpu-loader`` for GPU runtime targets when building
+  via the runtimes build.

libc/docs/gpu/testing.rst

@@ -94,7 +94,7 @@ Running tests
 
 Tests will only be built and run if a GPU target architecture is set and the
 corresponding loader utility was built. These can be overridden with the
-``LIBC_GPU_TEST_ARCHITECTURE`` and ``LIBC_GPU_LOADER_EXECUTABLE`` :ref:`CMake
+``LIBC_GPU_TEST_ARCHITECTURE`` and ``CMAKE_CROSSCOMPILING_EMULATOR`` :ref:`CMake
 options <gpu_cmake_options>`. Once built, they can be run like any other tests.
 The CMake target depends on how the library was built.
 

libc/test/CMakeLists.txt

@@ -16,11 +16,6 @@ add_custom_target(libc-hermetic-tests-build)
 add_custom_target(libc-integration-tests-build)
 add_custom_target(libc_include_tests-build)
 
-# Resolve the GPU loader executable path for the lit site config.
-if(TARGET libc.utils.gpu.loader)
-  get_target_property(LIBC_GPU_LOADER_EXECUTABLE libc.utils.gpu.loader "EXECUTABLE")
-endif()
-
 # Configure the site config file for lit
 configure_lit_site_cfg(
   ${LIBC_SOURCE_DIR}/test/lit.site.cfg.py.in
@@ -34,7 +29,7 @@ configure_lit_site_cfg(
   "LLVM_LIBS_DIR"
   "LIBC_SOURCE_DIR"
   "LIBC_BUILD_DIR"
-  "LIBC_GPU_LOADER_EXECUTABLE"
+  "CMAKE_CROSSCOMPILING_EMULATOR"
 )
 
 add_lit_testsuite(check-libc-lit
@@ -46,8 +41,8 @@ add_lit_testsuite(check-libc-lit
 add_subdirectory(UnitTest)
 
 if(LIBC_TARGET_OS_IS_GPU)
-  if(NOT TARGET libc.utils.gpu.loader)
-    message(WARNING "Cannot build libc GPU tests, missing loader.")
+  if(NOT CMAKE_CROSSCOMPILING_EMULATOR)
+    message(WARNING "Cannot build libc GPU tests, set CMAKE_CROSS_COMPILING_EMULATOR.")
     return()
   elseif(LIBC_GPU_TESTS_DISABLED)
     message(WARNING "Cannot build libc GPU tests, missing target architecture.")

libc/test/lit.site.cfg.py.in

@@ -8,11 +8,11 @@ config.llvm_tools_dir = lit_config.substitute(path(r"@LLVM_TOOLS_DIR@"))
 config.libc_src_root = path(r"@LIBC_SOURCE_DIR@")
 config.libc_obj_root = path(r"@LIBC_BUILD_DIR@")
 config.libc_test_cmd = "@LIBC_TEST_CMD@"
-config.libc_gpu_loader = path(r"@LIBC_GPU_LOADER_EXECUTABLE@")
+config.libc_crosscompiling_emulator = path(r"@CMAKE_CROSSCOMPILING_EMULATOR@")
 
-# If running GPU tests and no explicit test command is set, use the GPU loader.
-if not config.libc_test_cmd and config.libc_gpu_loader:
-    config.libc_test_cmd = config.libc_gpu_loader + " @BINARY@"
+# If no explicit test command is set, use the cross-compiling emulator.
+if not config.libc_test_cmd and config.libc_crosscompiling_emulator:
+    config.libc_test_cmd = config.libc_crosscompiling_emulator + " @BINARY@"
 
 # Add libc's utils directory to the path so we can import the test format.
 site.addsitedir(os.path.join(config.libc_src_root, "utils"))

llvm/runtimes/CMakeLists.txt

@@ -591,6 +591,12 @@ if(build_runtimes)
     endforeach()
   endif()
   if(LLVM_LIBC_GPU_BUILD)
+    set(_gpu_loader "${LLVM_TOOLS_BINARY_DIR}/llvm-gpu-loader${CMAKE_EXECUTABLE_SUFFIX}")
+    foreach(name ${LLVM_RUNTIME_TARGETS})
+      if(name MATCHES "^(amdgcn|nvptx)")
+        set(RUNTIMES_${name}_CMAKE_CROSSCOMPILING_EMULATOR "${_gpu_loader}" CACHE STRING "")
+      endif()
+    endforeach()
     list(APPEND extra_cmake_args "-DLLVM_LIBC_GPU_BUILD=ON")
     if(TARGET llvm-offload-binary)
       list(APPEND extra_deps llvm-offload-binary)