Unknown OpenMP flags for clang

[moravveji]

Hey guys

I am trying to build libFLAME on our AMD Naples machines using the AOCC v.2.2.0 compilers (clang, clang++, flang). We run CentOS 7.8 on our compute nodes.

Here is the configure options that I pass:

# CFLAGS are set identical to OpenBLAS
cflags='-O3 -march=native -fopenmp=libiomp5 -mavx2 -fvectorize -mfma -m3dnow -floop-unswitch-aggressive'
fflags='-O3 -march=native -fopenmp=libiomp5 -mavx -frecursive'

./configure --prefix=$dir_install \
            --enable-max-arg-list-hack \
            --enable-static-build \
            --enable-dynamic-build \
            --enable-lapack2flame \
            --disable-external-lapack-for-subproblems \
            --disable-external-lapack-interfaces \
            --enable-multithreading=openmp \
            --enable-supermatrix \
            --enable-vector-intrinsics=sse \
            --enable-cblas-interfaces \
            --with-cc=clang \
            EXTRA_CFLAGS="$cflags" \
            F77=flang \
            FFLAGS="$fflags"

However, I get the following complaint over OpenMP flags:

checking user-requested multithreading model... openmp
checking for (guessing) OpenMP flags for clang... unknown
configure: error: configure doesn't know what flag to give clang in order to enable OpenMP support. Please submit a bug report to the FLAME developers.

I have played with the cflags and fflags variables above, e.g. with/without -fopenmp, or -fopenmp=libomp or -fopenmp=libiomp5; however, all have failed. Seems like the configure is not listening to the EXTRA_CLFAGS argument passed to it.

Do you have any idea how to fix this?

Regards
Ehsan

[moravveji]

A gentle reminder about this issue.

[dnparikh]

Clang does not support openmp. Use pthreads instead.

[pradeeptrgit]

Hi,

You can try adding following line in the 'configure' file to include -fopenmp option for clang
clang)
fla_c_openmp_flags='-fopenmp'
;;

            { $as_echo "$as_me:${as_lineno-$LINENO}: checking for (guessing) OpenMP flags for ${CC_VENDOR}" >&5 $as_echo_n "checking for (guessing) OpenMP flags for ${CC_VENDOR}... " >&6; }

            case ${CC_VENDOR} in
                            icc)
                    fla_c_openmp_flags='-qopenmp'
            ;;
                            gcc)
                    fla_c_openmp_flags='-fopenmp'
            ;;
                            clang)
                    fla_c_openmp_flags='-fopenmp'
            ;;
                            pathcc)
                    fla_c_openmp_flags='-mp'
            ;;
                            pgcc)
                    fla_c_openmp_flags='-mp'
            ;;
                            sxcc)
                    fla_c_openmp_flags='-P openmp'
            ;;
                            *xlc*)
                    fla_c_openmp_flags='-qsmp=omp'
            ;;
                            *)
                    fla_c_openmp_flags='unknown'
            ;;
    esac