clang-tidy & SSE with GCC toolchain


I have a project which is compiled with GCC (7) and Clang (5.0). The clang built uses the GCC tool chain, like this (Red Hat 7 with devtoolset-7):

clang++ -gcc-toolchain /opt/rh/devtoolset-7/root/usr […]

The code compiles and runs fine, but running clang-tidy (using the same compiler flags) chokes on the SSE built-ins in GCC’s headers:

/opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/7/include/xmmintrin.h:54:3: error: argument to ‘__builtin_prefetch’ must be a constant integer [clang-diagnostic-error]

__builtin_prefetch (__P, (__I & 0x4) >> 2, __I & 0x3);


/opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/7/include/xmmintrin.h:130:19: error: use of undeclared identifier ‘__builtin_ia32_addss’ [clang-diagnostic-error]

return (__m128) __builtin_ia32_addss ((__v4sf)__A, (__v4sf)__B);


/opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/7/include/xmmintrin.h:136:19: error: use of undeclared identifier ‘__builtin_ia32_subss’ [clang-diagnostic-error]

return (__m128) __builtin_ia32_subss ((__v4sf)__A, (__v4sf)__B);

[more errors following…]

This happens as soon as I include <xmmintrin.h> (e.g. indirectly via Boost.UUID).

I’m wondering that the clang compiler accepts the code, while clang-tidy doesn’t.

Any ideas how to fix this? My current workaround is to disable SSE-support in Boost.UUID via macro for clang-tidy, but the problem will re-appear as soon as some other lib tries to use SSE instructions.


Daniel Evers

The gcc version of xmmintrin.h is not compatible with clang. Clang has its own version. Maybe you need to explicitly add the clang include directory to your command line?

check the original compilation with -H to see which xmmintrin.h got compiled.

Does clang-tidy understand -gcc-toolchain?



Thanks for the tip. I checked the output and clang++ uses its own includes instead of the GCC headers.
Does the compiler add some pre-defined include paths that the clang-based tools don't have by default?

Clang-tidy at least doesn't complain about -gcc-toolchain :wink: But I'm not sure if it's relevant here.


There used to (not sure if it's still there) a special relative lookup
for the builtins, something like
$dirname(driver-binary)/../lib/clang-6.0/include. So if your
clang-tidy is not in /usr/bin, it might not find the builtins.

- Kim

Hi @all,

Thanks again for all help - it turned out the problem was home-grown after all :frowning:
Somewhere in the script to generate the compilation database, the GCC include were explicitly added. This brought in the problems. (seems like we needed this for an older version were clang was installed in a different directory than clang-tidy)

I fixed it to pass the Clang parameters as-is and all problems were gone... Same flags for clang-tidy and clang++ and it works as expected.

Sorry & thanks again!