<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/56778>56778</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Wrong warning about linker input unused
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          Fedr
      </td>
    </tr>
</table>

<pre>
    Building this program
```
#include <spdlog/spdlog.h>
#include <spdlog/fmt/ostr.h>
#include <thread>

int main() {
    spdlog::info( "{}", std::this_thread::get_id() );
}
```
in Clang 14.0.0 with command line options `-std=c++20 -Wall -Wextra -pedantic-errors -lpthread` produces the warning:
```
clang-14: warning: -lpthread: 'linker' input unused [-Wunused-command-line-argument]
```

But if one removes `-lpthread` option, then the build fails with the errors:
```
/opt/compiler-explorer/gcc-11.2.0/lib/gcc/x86_64-linux-gnu/11.2.0/../../../../x86_64-linux-gnu/bin/ld: ./libspdlogd.a(async.cpp.o): in function `std::thread::thread<spdlog::details::periodic_worker::periodic_worker(std::function<void ()> const&, std::chrono::duration<long, std::ratio<1l, 1l> >)::$_0, , void>(spdlog::details::periodic_worker::periodic_worker(std::function<void ()> const&, std::chrono::duration<long, std::ratio<1l, 1l> >)::$_0&&)':
async.cpp:(.text+0xdc1): undefined reference to `pthread_create'
/opt/compiler-explorer/gcc-11.2.0/lib/gcc/x86_64-linux-gnu/11.2.0/../../../../x86_64-linux-gnu/bin/ld: ./libspdlogd.a(async.cpp.o): in function `std::thread::thread<spdlog::details::thread_pool::thread_pool(unsigned long, unsigned long, std::function<void ()>)::$_1, , void>(spdlog::details::thread_pool::thread_pool(unsigned long, unsigned long, std::function<void ()>)::$_1&&)':
async.cpp:(.text+0x2191): undefined reference to `pthread_create'
```
So the option is not "unused".

Online demo: https://gcc.godbolt.org/z/qxoWe8fzd


</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzlVkuT4yYQ_jXShZJKQrYeBx3GM_E1hxzm6EKAZRIMCqAZ7_76dCN5xpPxJrW5bNXGhTB0t5p-fE1rsOJLv5uVFsqMJJyUJ5Ozo2PnpHhKioekLtaxbGmlDNezkCSpHv0ktB0Tul8W-SmpfvlHueM5wGx9cN-UDScnmXhnxlmZQM5MmYS2Ce1I0uwWOoHfqrx6gKHM0YIMSShFmeYJF_SR-CAWAXTwcD0CCaMMByWuemmXVKtqfPleBJQhj5pBrMpNXuQFeVXhRLg9n5kRRCsjiZ2CssYTeCWLBz_xhO5g0IJkz0xrmOUlOEaySQpmguKZdM46TzI9rcbVBeZBzFx6yIokr8wZyBAafc8qjiZl5Qb4N6I3-mCT0Abs-0M6WBBlpjmQ2cxeCpJsd9nzss5WVzJ0JWNunM_ShGR7PxjLvANN6kgs-O7k2b7IxfdbX5aYYCrAGRM9GhB05MiU9ksQkbjE4VteInYmRBAYOSktXSYvk7YOXdqPnGdlmdO8gI1Ww0KC-dLWh3qDDs2XbDQzkN7k8vzzdEd-QOjtdQxjvqhfYCdyBthh_ovhOZ-m3EYIPUB4yXE2HJ3GWNzg7x161_XjLYKFDBiRZTNJp6xQ_PBqHebtLpG2b9qvR4LOF6sgrxHWUEsAUOMhcPWHYuAnZ41dz50dW1_VFsBzKxc5wCg1kmEGhVig0VUcdHMokIUPHhyZ7U_iVh1HB0XzBsu3fEepNg9QzlDfxUXwcgXAbIQ8QgkJKImjdNJwSYJFLKxVceAwB4lq_5fYXqMwWas_E2g7G69GDN81bZ8I_w6PD5ksvwOgP8C270EZLbv_DrOPN-pvNl67y_VMoPkbG7B7Ls0AFvntRf-riQ1OwCWPh59CmGLE6H4BZD5aMVgdcuuw23-F58-LfZbt8au41ZPKvqy3XVGWRdmmoq9EV3UsDSpo2T9D9Y7XJkbYYKG7LH3rQ9NKZ6f7v1kAXWQecigghLF-uf5l0El_lxyLS3k_Sw-Lbd00bXrq67ZpBz40xVZ2cthuh062omorVtKuZsUm1WyQ2vfQIiEaRr6SqAK_K7ZPqeppQWnR0LaktKrqvGKbDS1b2HJBG1klm0LCh4vO0Q4MS-r6aNIwjx6YWvng35nMRyDJeBzoZ3M4WdfvpXBpPLePdv8FBTbsww">