https://github.com/wenju-he created
https://github.com/llvm/llvm-project/pull/177754
When an incompatible opencl-c-base.h exists in CPATH, libclc build fails with:
oclgpu/Kobuk-25.40.35563.7/include/opencl-c-base.h:53:6:
error: '__OPENCL_CPP_VERSION__' is not defined, evaluates to 0
[-Werror,-Wundef]
53 | #if (__OPENCL_CPP_VERSION__ == 100 || __OPENCL_C_VERSION__ == 200)
This occurs because clang's header search order is:
1. Command line -I flags
2. CPATH directories
3. Builtin resource directories (added automatically)
The CPATH version shadows clang's built-in header, causing compilation errors.
Simply adding the resource directory with -I is insufficient because clang
still adds builtin directories after CPATH.
Fix by:
1. Adding -nostdinc to disable automatic builtin directory inclusion
2. Explicitly adding clang's resource include directory with -I
This ensures clang's opencl-c-base.h is found before any CPATH version and
prevents automatic builtin directories from interfering.
>From b05c5008565767c0e4026b9092bb89d085a9cb43 Mon Sep 17 00:00:00 2001
From: Wenju He <[email protected]>
Date: Sat, 24 Jan 2026 12:22:55 +0100
Subject: [PATCH] [libclc][NFC] Prioritize clang's built-in opencl-c-base.h
over CPATH versions
When an incompatible opencl-c-base.h exists in CPATH, libclc build fails with:
oclgpu/Kobuk-25.40.35563.7/include/opencl-c-base.h:53:6:
error: '__OPENCL_CPP_VERSION__' is not defined, evaluates to 0
[-Werror,-Wundef]
53 | #if (__OPENCL_CPP_VERSION__ == 100 || __OPENCL_C_VERSION__ == 200)
This occurs because clang's header search order is:
1. Command line -I flags
2. CPATH directories
3. Builtin resource directories (added automatically)
The CPATH version shadows clang's built-in header, causing compilation errors.
Simply adding the resource directory with -I is insufficient because clang
still adds builtin directories after CPATH.
Fix by:
1. Adding -nostdinc to disable automatic builtin directory inclusion
2. Explicitly adding clang's resource include directory with -I
This ensures clang's opencl-c-base.h is found before any CPATH version
and prevents automatic builtin directories from interfering.
---
libclc/CMakeLists.txt | 21 ++++++++++++++++-----
1 file changed, 16 insertions(+), 5 deletions(-)
diff --git a/libclc/CMakeLists.txt b/libclc/CMakeLists.txt
index 88a32797d5915..af53dd236a543 100644
--- a/libclc/CMakeLists.txt
+++ b/libclc/CMakeLists.txt
@@ -80,6 +80,12 @@ if( LIBCLC_STANDALONE_BUILD OR CMAKE_SOURCE_DIR STREQUAL
CMAKE_CURRENT_SOURCE_DI
endforeach()
endif()
+ cmake_path( GET clang_exe PARENT_PATH CLANG_PARENT_PATH )
+ cmake_path( GET CLANG_PARENT_PATH PARENT_PATH CLANG_GRANDPARENT_PATH )
+ cmake_path( APPEND LIBCLC_CLANG_RESOURCE_INCLUDE_DIR
${CLANG_GRANDPARENT_PATH}
+ lib${LLVM_LIBDIR_SUFFIX}/clang/${LLVM_VERSION_MAJOR}
+ include)
+
# Setup the paths where libclc runtimes should be stored.
set( LIBCLC_OUTPUT_LIBRARY_DIR ${CMAKE_CURRENT_BINARY_DIR} )
set( LIBCLC_INSTALL_DIR ${CMAKE_INSTALL_DATADIR}/clc )
@@ -106,9 +112,12 @@ else()
get_host_tool_path( opt OPT opt_exe opt_target )
endif()
+ include(GetClangResourceDir)
+ get_clang_resource_dir(LIBCLC_CLANG_RESOURCE_INCLUDE_DIR
+ PREFIX ${LLVM_LIBRARY_OUTPUT_INTDIR}/.. SUBDIR include)
+
# Setup the paths where libclc runtimes should be stored. By default, in an
# in-tree build we place the libraries in clang's resource driectory.
- include(GetClangResourceDir)
get_clang_resource_dir( LIBCLC_INSTALL_DIR )
cmake_path( APPEND LIBCLC_INSTALL_DIR "lib" "libclc" )
@@ -411,7 +420,7 @@ foreach( t ${LIBCLC_TARGETS_TO_BUILD} )
-I${CMAKE_CURRENT_SOURCE_DIR}/clc/include
# Error on undefined macros
-Werror=undef
- -fdiscard-value-names
+ -fdiscard-value-names -nostdinc
)
if( NOT "${cpu}" STREQUAL "" )
@@ -453,16 +462,18 @@ foreach( t ${LIBCLC_TARGETS_TO_BUILD} )
LIB_FILES ${clc_lib_files}
)
- list( APPEND build_flags
- -Xclang -fdeclare-opencl-builtins -Xclang -finclude-default-header
+ set( opencl_build_flags ${build_flags}
-I${CMAKE_CURRENT_SOURCE_DIR}/opencl/include
+ -Xclang -fdeclare-opencl-builtins -Xclang -finclude-default-header
+ # Ensure clang's opencl-c-base.h is found before CPATH directories.
+ -I${LIBCLC_CLANG_RESOURCE_INCLUDE_DIR}
)
add_libclc_builtin_set(
ARCH ${ARCH}
ARCH_SUFFIX ${arch_suffix}
TRIPLE ${clang_triple}
- COMPILE_FLAGS ${build_flags}
+ COMPILE_FLAGS ${opencl_build_flags}
OPT_FLAGS ${opt_flags}
LIB_FILES ${opencl_lib_files}
ALIASES ${${d}_aliases}
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