Fix the target specific "-msse3" flag check in CMake. NFC

[sgundapa]

Summary

msse3 is a target dependent flag and must be guarded as check_cxx_compiler_flag()
checks only for compiler error messages and ignores warnings. Earlier COMPILER_RT_HAS_MSSE3_FLAG
is set to "TRUE" for all targets as clang emits warnings and the compilation spits unnecessary
warnings for non-X86 targets. This issue is fixed by coupling the flag with "-Werror"

[seurer]

The use of the flag is causing errors in the sanitizer buildbot runs (for power at least) so assuming this patch fixes that it would be great to get this in ASAP.

Building CXX object lib/asan/CMakeFiles/RTAsan_dynamic.powerpc64le.dir/asan_interceptors.cc.o
clang-3.8: error: argument unused during compilation: '-msse3'

[samsonov]

Would smth. along the lines of

check_cxx_compiler_flag("-Werror -msse3" COMPILER_RT_HAS_MSSE3_FLAG)

work?

[sgundapa]

But classifying the flag under the specific target makes more sense to me. I am okay with "-Werror" fix too. Let me know. Feel free to ping me in IRC @ sgundapa

[samsonov]

Let's use the -Werror approach. We already use it to detect presence of warnings, and I'd rather not hardcode targets. E.g. what if this flag is not supported (produces warning) by your host compiler on x86?

[sgundapa]

Have no clue on what "msse3" flag does and when this flag is added. Agree with you and pushed a new patch set

[samsonov]

LGTM

compiler-rt/trunk/cmake/config-ix.cmake

 check_cxx_compiler_flag(-fno-sanitize=safe-stack COMPILER_RT_HAS_FNO_SANITIZE_SAFE_STACK_FLAG)
 check_cxx_compiler_flag(-fvisibility=hidden  COMPILER_RT_HAS_FVISIBILITY_HIDDEN_FLAG)
 check_cxx_compiler_flag(-fno-rtti            COMPILER_RT_HAS_FNO_RTTI_FLAG)
 check_cxx_compiler_flag(-ffreestanding       COMPILER_RT_HAS_FFREESTANDING_FLAG)
 check_cxx_compiler_flag("-Werror -fno-function-sections" COMPILER_RT_HAS_FNO_FUNCTION_SECTIONS_FLAG)
 check_cxx_compiler_flag(-std=c++11           COMPILER_RT_HAS_STD_CXX11_FLAG)
 check_cxx_compiler_flag(-ftls-model=initial-exec COMPILER_RT_HAS_FTLS_MODEL_INITIAL_EXEC)
 check_cxx_compiler_flag(-fno-lto             COMPILER_RT_HAS_FNO_LTO_FLAG)
-check_cxx_compiler_flag(-msse3               COMPILER_RT_HAS_MSSE3_FLAG)
+check_cxx_compiler_flag("-Werror -msse3" COMPILER_RT_HAS_MSSE3_FLAG)
 check_cxx_compiler_flag(-std=c99             COMPILER_RT_HAS_STD_C99_FLAG)
 check_cxx_compiler_flag(--sysroot=.          COMPILER_RT_HAS_SYSROOT_FLAG)
 
 if(NOT WIN32 AND NOT CYGWIN)
   # MinGW warns if -fvisibility-inlines-hidden is used.
   check_cxx_compiler_flag("-fvisibility-inlines-hidden" COMPILER_RT_HAS_FVISIBILITY_INLINES_HIDDEN_FLAG)
 endif()
 

 
 if (COMPILER_RT_HAS_SANITIZER_COMMON AND UBSAN_SUPPORTED_ARCH AND
     OS_NAME MATCHES "Darwin|Linux|FreeBSD|Windows")
   set(COMPILER_RT_HAS_UBSAN TRUE)
 else()
   set(COMPILER_RT_HAS_UBSAN FALSE)
 endif()
 
-# -msse3 flag is not valid for Mips therefore clang gives a warning
-# message with -msse3. But check_c_compiler_flags() checks only for
-# compiler error messages. Therefore COMPILER_RT_HAS_MSSE3_FLAG turns out to be
-# true on Mips, so we make it false here.
-if("${COMPILER_RT_DEFAULT_TARGET_ARCH}" MATCHES "mips")
-  set(COMPILER_RT_HAS_MSSE3_FLAG FALSE)
-endif()
-
 if (COMPILER_RT_HAS_SANITIZER_COMMON AND SAFESTACK_SUPPORTED_ARCH AND
     OS_NAME MATCHES "Darwin|Linux|FreeBSD")
   set(COMPILER_RT_HAS_SAFESTACK TRUE)
 else()
   set(COMPILER_RT_HAS_SAFESTACK FALSE)
 endif()