[libc-commits] [libc] [libc] Remove CUDA Toolkit dependency for NVPTX build (PR #208497)

[Joseph Huber via libc-commits]

https://github.com/jhuber6 created https://github.com/llvm/llvm-project/pull/208497

Summary:
This was problemtatic because these CMake headers were never intended to
be used from a GPu target. We had to hack around this to suppress
threads, but all this is used for is getting the default CUDA path, so
just do this directly.


>From 6c77399a243d91dbe56678bf964d3ad06eca3821 Mon Sep 17 00:00:00 2001
From: Joseph Huber <huberjn at outlook.com>
Date: Thu, 9 Jul 2026 11:15:39 -0500
Subject: [PATCH] [libc] Remove CUDA Toolkit dependency for NVPTX build

Summary:
This was problemtatic because these CMake headers were never intended to
be used from a GPu target. We had to hack around this to suppress
threads, but all this is used for is getting the default CUDA path, so
just do this directly.
---
 .../modules/prepare_libc_gpu_build.cmake      | 20 ++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/libc/cmake/modules/prepare_libc_gpu_build.cmake b/libc/cmake/modules/prepare_libc_gpu_build.cmake
index 36ab321e4994c..aba4d11bf41a1 100644
--- a/libc/cmake/modules/prepare_libc_gpu_build.cmake
+++ b/libc/cmake/modules/prepare_libc_gpu_build.cmake
@@ -73,12 +73,18 @@ set(LIBC_GPU_TARGET_ARCHITECTURE "${gpu_test_architecture}")
 set(LIBC_GPU_CODE_OBJECT_VERSION "6" CACHE STRING "AMDGPU Code object ABI to use")
 
 if(LIBC_TARGET_ARCHITECTURE_IS_NVPTX)
-  # FIXME: This is a hack required to keep the CUDA package from trying to find
-  #        pthreads. We only link the CUDA driver, so this is unneeded.
-  add_library(CUDA::cudart_static_deps IMPORTED INTERFACE)
-
-  find_package(CUDAToolkit QUIET)
-  if(CUDAToolkit_FOUND)
-    get_filename_component(LIBC_CUDA_ROOT "${CUDAToolkit_BIN_DIR}" DIRECTORY ABSOLUTE)
+  # Respect the standard CUDAToolkit_ROOT override if the user provided one,
+  # otherwise ask the compiler which CUDA installation it detected.
+  if(CUDAToolkit_ROOT)
+    set(LIBC_CUDA_ROOT "${CUDAToolkit_ROOT}")
+  else()
+    execute_process(
+      COMMAND ${CMAKE_CXX_COMPILER} -v --print-resource-dir
+      OUTPUT_QUIET ERROR_VARIABLE cuda_search_output)
+    string(REGEX MATCH "Found CUDA installation: ([^,]+), version"
+      cuda_search_match "${cuda_search_output}")
+    if(CMAKE_MATCH_1)
+      set(LIBC_CUDA_ROOT "${CMAKE_MATCH_1}")
+    endif()
   endif()
 endif()