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[flang-rt] Use -Wp to undefine macros (#156034)

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If the macro was previously defined with `-Wp,-D` then a later `-U` is
*not* going to take effect, the `-Wp` flag takes precedence.

Instead use `-Wp,-U`. This works regardless of whether the original
definition was provided via `-D` or `-Wp,-D`.

Also make sure these flags only get passed to the C++ compiler -- they
are only relevant there, and flang does not support `-Wp`.
This commit is contained in:
Nikita Popov 2025-09-11 15:47:25 +02:00 committed by GitHub
parent 23302a2aac
commit e1aa2dff8a
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2 changed files with 6 additions and 4 deletions
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4
flang-rt/CMakeLists.txt
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@ -255,11 +255,11 @@ if (UNIX AND CMAKE_SYSTEM_NAME MATCHES "AIX")
add_compile_definitions(_LARGE_FILE_API)
endif ()
# Check whether the compiler can undefine a macro using the "-U" flag.
# Check whether the compiler can undefine a macro using the "-Wp,-U" flag.
# Aternatively, we could use
# CMAKE_CXX_COMPILER_FRONTEND_VARIANT STREQUAL "GNU"
# but some older versions of CMake don't define it for GCC itself.
check_cxx_compiler_flag("-UTESTFLAG" FLANG_RT_SUPPORTS_UNDEFINE_FLAG)
check_cxx_compiler_flag("-Wp,-UTESTFLAG" FLANG_RT_SUPPORTS_UNDEFINE_FLAG)
# Check whether -fno-lto is supported.
check_cxx_compiler_flag(-fno-lto FLANG_RT_HAS_FNO_LTO_FLAG)

6
flang-rt/cmake/modules/AddFlangRT.cmake
View File

@ -283,8 +283,10 @@ function (add_flangrt_library name)
# build, to avoid an unwanted dependency on libstdc++/libc++.so.
target_compile_definitions(${tgtname} PUBLIC _GLIBCXX_NO_ASSERTIONS)
if (FLANG_RT_SUPPORTS_UNDEFINE_FLAG)
target_compile_options(${tgtname} PUBLIC -U_GLIBCXX_ASSERTIONS)
target_compile_options(${tgtname} PUBLIC -U_LIBCPP_ENABLE_ASSERTIONS)
target_compile_options(${tgtname} PUBLIC
"$<$<COMPILE_LANGUAGE:CXX>:-Wp,-U_GLIBCXX_ASSERTIONS>")
target_compile_options(${tgtname} PUBLIC
"$<$<COMPILE_LANGUAGE:CXX>:-Wp,-U_LIBCPP_ENABLE_ASSERTIONS>")
endif ()
# Non-GTest unittests depend on LLVMSupport