$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/8/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 8-20170923-1ubuntu2' --with-bugurl=file:///usr/share/doc/gcc-8/README.Bugs --enable-languages=c,c++,go,brig,fortran,objc,obj-c++ --prefix=/usr --with-gcc-major-version-only --program-suffix=-8 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie --with-system-zlib --enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 8.0.0 20170923 (experimental) [trunk revision 253118] (Ubuntu 8-20170923-1ubuntu2)

$ cat small.c
__attribute__((target_clones("arch=slm","default")))
int foo1 (int a, int b) {
  return a + b;
}

int foo2 (int a, int b) {
  return a + b;
}

int main() {
  foo1(1, 1);
  foo2(1, 1);
  return 1;
}

$ gcc --coverage small.c; ./a.out; gcov-8 small.c; cat small.c.gcov
File 'small.c'
Lines executed:88.89% of 9
Creating 'small.c.gcov'

        -:    0:Source:small.c
        -:    0:Graph:small.gcno
        -:    0:Data:small.gcda
        -:    0:Runs:1
        -:    0:Programs:1
        -:    1:__attribute__((target_clones("arch=slm","default")))
    #####:    2:int foo1 (int a, int b) {
        1:    3:  return a + b;
        -:    4:}
        -:    5:
        1:    6:int foo2 (int a, int b) {
        1:    7:  return a + b;
        -:    8:}
        -:    9:
        1:   10:int main() {
        1:   11:  foo1(1, 1);
        1:   12:  foo2(1, 1);
        1:   13:  return 1;
        1:   14:}


Line #2 is wrongly marked as not executed with "#####". 
Function foo2 is with no attribute, the coverage of function foo2 is correct.