[libcxx-commits] [libcxx] [libcxx] Add necessary compile flags for targeting the GPU (PR #99333)

[via libcxx-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: Joseph Huber (jhuber6)

<details>
<summary>Changes</summary>

Summary:
The GPU target will always be a sufficiently new `clang`, so we can
assume these flags are present. We need to first set
`CMAKE_REQUIRED_FLAGS` to these values so that the
`check_cxx_compile_flag` utilities work. Then, we need to add several
things to the compiler flags that are necessary for correctness and
optimal code output.


---
Full diff: https://github.com/llvm/llvm-project/pull/99333.diff


1 Files Affected:

- (modified) libcxx/CMakeLists.txt (+9) 


``````````diff
diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
index 190a97db9462f..a72e5aca0903f 100644
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -491,6 +491,15 @@ include(HandleLibcxxFlags)
 # 'config-ix' use them during feature checks. It also adds them to both
 # 'LIBCXX_COMPILE_FLAGS' and 'LIBCXX_LINK_FLAGS'
 
+# Targeting the GPU requires a clang compiler and several extra flags.
+if (${LLVM_RUNTIMES_TARGET} MATCHES "^amdgcn")
+  set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nogpulib")
+  add_flags("-nogpulib" "-flto" "-fconvergent-functions" "-Xclang" "-mcode-object-version=none")
+elseif (${LLVM_RUNTIMES_TARGET} MATCHES "^nvptx")
+  set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -flto -c -Wno-unused-command-line-argument")
+  add_flags("-nogpulib" "-flto" "-fconvergent-functions" "--cuda-feature=+ptx63")
+endif()
+
 if (${CMAKE_SYSTEM_NAME} MATCHES "AIX")
   add_flags_if_supported("-mdefault-visibility-export-mapping=explicit")
   set(CMAKE_AIX_EXPORT_ALL_SYMBOLS OFF)

``````````

</details>


https://github.com/llvm/llvm-project/pull/99333