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[runtimes] Append -nostd*++ flags only for Clang #151930

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Aug 12, 2025
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[runtimes] Append -nostd*++ flags only for Clang #151930

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27 changes: 20 additions & 7 deletions runtimes/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -160,13 +160,26 @@ endif()
# Check for -nostdlib++ first; if there's no C++ standard library yet,
# all check_cxx_compiler_flag commands will fail until we add -nostdlib++
# (or -nodefaultlibs).
llvm_check_compiler_linker_flag(CXX "-nostdlib++" CXX_SUPPORTS_NOSTDLIBXX_FLAG)
if (CXX_SUPPORTS_NOSTDLIBXX_FLAG)
set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nostdlib++")
endif()
check_cxx_compiler_flag(-nostdinc++ CXX_SUPPORTS_NOSTDINCXX_FLAG)
if (CXX_SUPPORTS_NOSTDINCXX_FLAG)
set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nostdinc++")
#
# CMAKE_REQUIRED_FLAGS is used both for C and C++ compilation. This breaks
# compiling with GCC (and we should not need to force -nostd* for GCC anyway),
# so apply it only with Clang. However, since there are cases when appending
# the flag actually breaks the build, still perform the checks rather than
# appending it unconditionally.
#
# TODO: find a better solution. See the discussion on:
# https://github.com/llvm/llvm-project/issues/90332
# https://github.com/llvm/llvm-project/pull/108357

if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
llvm_check_compiler_linker_flag(CXX "-nostdlib++" CXX_SUPPORTS_NOSTDLIBXX_FLAG)
if (CXX_SUPPORTS_NOSTDLIBXX_FLAG)
set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nostdlib++")
endif()
check_cxx_compiler_flag(-nostdinc++ CXX_SUPPORTS_NOSTDINCXX_FLAG)
if (CXX_SUPPORTS_NOSTDINCXX_FLAG)
set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nostdinc++")
endif()
endif()

# Avoid checking whether the compiler is working.
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