[libcxx][libcxxabi] Remove the unused CMake checks

[phosek]

Summary

These seemed to have been used in the past but were since replaced
by the add_compile_flags_if_supported function that combine these
these checks and adding the flag, but the original checks were never
removed.

[phosek]

Alternative would be to avoid add_compile_flags_if_supported altogether and instead the combination of check_cxx_compiler_flag and append_if as is used in libunwind (https://github.com/llvm/llvm-project/blob/master/libunwind/CMakeLists.txt#L274). The advantage of the latter is that we could in theory have different config-ix.cmake files (e.g. pre-populated ones for the runtimes build).

[ldionne]

libcxxabi/cmake/config-ix.cmake

52

Why are we keeping this one?

[phosek]

libcxxabi/cmake/config-ix.cmake

52

It's the only one that's being used in CMakeLists.txt, see https://github.com/llvm/llvm-project/blob/master/libcxxabi/CMakeLists.txt#L264

[phosek]

Does anyone have any opinion on add_compile_flags_if_supported vs check_cxx_compiler_flag + append_if? If not I'm going to land this as is.

[ldionne]

In D62566#1521730, @phosek wrote:

Does anyone have any opinion on add_compile_flags_if_supported vs check_cxx_compiler_flag + append_if? If not I'm going to land this as is.

I have a strong preference for add_compile_flags_if_supported until we have the use case you described above. I'm not saying it's not a good/real use case, just that if we're not taking advantage of it right now, we should just simplify things.

libcxx/cmake/config-ix.cmake

if (CMAKE_C_FLAGS MATCHES -fsanitize-coverage OR CMAKE_CXX_FLAGS MATCHES -fsanitize-coverage)
     set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -fno-sanitize-coverage=edge,trace-cmp,indirect-calls,8bit-counters")
   endif ()
 endif ()
 
 if(NOT WIN32 OR MINGW)
   include(CheckLibcxxAtomic)
 endif()
 
-# Check compiler flags
-
-check_cxx_compiler_flag(/WX                     LIBCXX_HAS_WX_FLAG)
-check_cxx_compiler_flag(/WX-                    LIBCXX_HAS_NO_WX_FLAG)
-check_cxx_compiler_flag(/EHsc                   LIBCXX_HAS_EHSC_FLAG)
-check_cxx_compiler_flag(/EHs-                   LIBCXX_HAS_NO_EHS_FLAG)
-check_cxx_compiler_flag(/EHa-                   LIBCXX_HAS_NO_EHA_FLAG)
-check_cxx_compiler_flag(/GR-                    LIBCXX_HAS_NO_GR_FLAG)
-
-
 # Check libraries
 if(WIN32 AND NOT MINGW)
   # TODO(compnerd) do we want to support an emulation layer that allows for the
   # use of pthread-win32 or similar libraries to emulate pthreads on Windows?
   set(LIBCXX_HAS_PTHREAD_LIB NO)
   set(LIBCXX_HAS_M_LIB NO)
   set(LIBCXX_HAS_RT_LIB NO)
   set(LIBCXX_HAS_SYSTEM_LIB NO)

libcxxabi/cmake/config-ix.cmake

if (CMAKE_C_FLAGS MATCHES -fsanitize OR CMAKE_CXX_FLAGS MATCHES -fsanitize)
     set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -fno-sanitize=all")
   endif ()
   if (CMAKE_C_FLAGS MATCHES -fsanitize-coverage OR CMAKE_CXX_FLAGS MATCHES -fsanitize-coverage)
     set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -fno-sanitize-coverage=edge,trace-cmp,indirect-calls,8bit-counters")
   endif ()
 endif ()
 
 # Check compiler flags
-check_c_compiler_flag(-funwind-tables         LIBCXXABI_HAS_FUNWIND_TABLES)
-check_cxx_compiler_flag(-fno-exceptions       LIBCXXABI_HAS_NO_EXCEPTIONS_FLAG)
-check_cxx_compiler_flag(-fno-rtti             LIBCXXABI_HAS_NO_RTTI_FLAG)
-check_cxx_compiler_flag(-fstrict-aliasing     LIBCXXABI_HAS_FSTRICT_ALIASING_FLAG)
-check_cxx_compiler_flag(-nostdinc++           LIBCXXABI_HAS_NOSTDINCXX_FLAG)
-check_cxx_compiler_flag(-Wall                 LIBCXXABI_HAS_WALL_FLAG)
-check_cxx_compiler_flag(-W                    LIBCXXABI_HAS_W_FLAG)
-check_cxx_compiler_flag(-Wunused-function     LIBCXXABI_HAS_WUNUSED_FUNCTION_FLAG)
-check_cxx_compiler_flag(-Wunused-variable     LIBCXXABI_HAS_WUNUSED_VARIABLE_FLAG)
-check_cxx_compiler_flag(-Wunused-parameter    LIBCXXABI_HAS_WUNUSED_PARAMETER_FLAG)
-check_cxx_compiler_flag(-Wstrict-aliasing     LIBCXXABI_HAS_WSTRICT_ALIASING_FLAG)
-check_cxx_compiler_flag(-Wstrict-overflow     LIBCXXABI_HAS_WSTRICT_OVERFLOW_FLAG)
-check_cxx_compiler_flag(-Wwrite-strings       LIBCXXABI_HAS_WWRITE_STRINGS_FLAG)
-check_cxx_compiler_flag(-Wchar-subscripts     LIBCXXABI_HAS_WCHAR_SUBSCRIPTS_FLAG)
-check_cxx_compiler_flag(-Wmismatched-tags     LIBCXXABI_HAS_WMISMATCHED_TAGS_FLAG)
-check_cxx_compiler_flag(-Wmissing-braces      LIBCXXABI_HAS_WMISSING_BRACES_FLAG)
-check_cxx_compiler_flag(-Wshorten-64-to-32    LIBCXXABI_HAS_WSHORTEN_64_TO_32_FLAG)
-check_cxx_compiler_flag(-Wsign-conversion     LIBCXXABI_HAS_WSIGN_CONVERSION_FLAG)
-check_cxx_compiler_flag(-Wsign-compare        LIBCXXABI_HAS_WSIGN_COMPARE_FLAG)
-check_cxx_compiler_flag(-Wshadow              LIBCXXABI_HAS_WSHADOW_FLAG)
-check_cxx_compiler_flag(-Wconversion          LIBCXXABI_HAS_WCONVERSION_FLAG)
-check_cxx_compiler_flag(-Wnewline-eof         LIBCXXABI_HAS_WNEWLINE_EOF_FLAG)
-check_cxx_compiler_flag(-Wundef               LIBCXXABI_HAS_WUNDEF_FLAG)
-check_cxx_compiler_flag(-pedantic             LIBCXXABI_HAS_PEDANTIC_FLAG)
-check_cxx_compiler_flag(-Werror               LIBCXXABI_HAS_WERROR_FLAG)
-check_cxx_compiler_flag(-Wno-error            LIBCXXABI_HAS_WNO_ERROR_FLAG)
-check_cxx_compiler_flag(/WX                   LIBCXXABI_HAS_WX_FLAG)
-check_cxx_compiler_flag(/WX-                  LIBCXXABI_HAS_NO_WX_FLAG)
-check_cxx_compiler_flag(/EHsc                 LIBCXXABI_HAS_EHSC_FLAG)
-check_cxx_compiler_flag(/EHs-                 LIBCXXABI_HAS_NO_EHS_FLAG)
-check_cxx_compiler_flag(/EHa-                 LIBCXXABI_HAS_NO_EHA_FLAG)
-check_cxx_compiler_flag(/GR-                  LIBCXXABI_HAS_NO_GR_FLAG)
+check_cxx_compiler_flag(-nostdinc++ LIBCXXABI_HAS_NOSTDINCXX_FLAG)
 
 # Check libraries
 check_library_exists(dl dladdr "" LIBCXXABI_HAS_DL_LIB)
 check_library_exists(pthread pthread_once "" LIBCXXABI_HAS_PTHREAD_LIB)
 check_library_exists(c __cxa_thread_atexit_impl ""
   LIBCXXABI_HAS_CXA_THREAD_ATEXIT_IMPL)