<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=http://email.email.llvm.org/c/eJytVVuPozYU_jXwYhWBExJ44CGz01ajzkPVRuruU2XsE_CMY0e2SSbz63sw5MZm1JF2UQIcOJfvfOdCbcSxitLHKF393dVm5-WWKcKNALIxlngmUWJKoaSUOYAg9ZF02gLjLasVDKbjeZGOvyAK4IpZIHsjBYnmae8GIKKFXMwjWl5bCthIfdEELdxB-vbf60DBjkQ0T9GYRMsHgsdg3t9dkN6Ld7K76H-fw_LxM5As-M7qn40GvQbNKZRbRtetdOTpL4JnbrY7qbAczJEasDLJGL31fuei2Sqiv-GvMaI2yifGNii94__38sX--v7N_HM3wl3mZwHi5Ijo7MNSndPqj13n2pAie7t9EegZr8jMPP3zeT1BMZJ9F8BdFKPBTZyX7Y5M43zsbb16ev6yen6-S8_1ed3iiHSae2k06QGQHgFB3XPx8f5mblA-FxpfcWTMgyPsql1OPhB0cg770HlyaEET_2HMm0n50ntn_eMTir5jQjSBdUAvONkt04POOfgl4BNxXdOA8wRd6kbqhmys2V579Oa7VGGPEOXmcyiTCalPyFSnBRojVulcB5gydjiOhjNq30Po_Zr6xRujIrp0WK5CSd29kVewGoZnw8uSHJjVATYusSh_eMzSPFuUUf6IRrcjYmEv4eASpfbbcU5O2rRMRnAbcjQdOtW-T5y3wF8HOFYiO7gxd9ZgUlvkPmhyJBf3hwhKFkTHkfk9WNdTYgaKBtTDrmWe_N_gum9va6fb_A_C0G8DGmyoJ-6D4IIbjdUISU_6oW-GqX-m5B7oddIcToHe22b1kMSimolyVrKYdb41tmqPYHRz7F7lNu6sqiaAscRdneBeQqF3O15-QWZegHsUQ1Ud3uSzLCvitqIFXcJciCVGmS2LTbmoiyLPaC7mUNZMxIrhbnMVFjCitGb8FbsJI34tFihjMeMfRyErmlKaZlmWzvKc0qRYpMuUF8DLDJZzyvv1ssU2P3MV2yq4rLvG4Uslnb90T8yck40GCKARoZdeQTX5tmL1Pvd5jQPaKkD9D6OuWKY>53118</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Suboptimal codegen for tail call followed by unreachable
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            backend:X86
      </td>
    </tr>

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

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

<pre>
    
Suboptimal code for tail call followed by unreachable

```
declare void @callee(i64)

define void @endswith_unreachable(i64 %0) {    
    tail call void @callee(i64 %0)
    unreachable
}

define void @endswith_return(i64 %0) {    
    tail call void @callee(i64 %0)
    ret void
}
```
This IR is compiled as below. 
https://godbolt.org/z/G9jrEzYoW
```
endswith_unreachable:                   # @endswith_unreachable
        push    rax
        call    callee@PLT
endswith_return:                        # @endswith_return
        jmp     callee@PLT                      # TAILCALL
```


The function ends with `tail call` followed by `ret void` creates a tail call with `jmp.`
But when the function ends with `unreachable,` a `call` is created rather than a `tail call.`
I suggest changing from `call` to `tail call` even if the function ends with `unreachable.`

I found this issue while resolving the objtool's (linux kernel's tool) warning for [D105169](https://reviews.llvm.org/D105169).
If you want to check the original problem, you can find the reduced version of the kernel code at https://godbolt.org/z/sYxTsnh5K and generated IR code containing `unreachable` at https://alive2.llvm.org/ce/z/szhgAB.
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJytVUuPqzYU_jWwsYqMMyRhwSJzp61GnUXVRmrvqjLmBDzj2JEfyWR-fQ-GvLgZdRZFCXDgPL7znQe1aY5VQp8Suvoz1Gbn5ZYrIkwDZGMs8VyixJVCSSlzgIbURxK0BS46XisYTMfznI6_KDYgFLdA9kY2JHmgvRuAhC3l_CFh5bVlAxupL5qgG3eQvvvnOlC0IwkrKBqTZPFI8BjM-7sL0nvxTnYX_R9zWDx9BZIFH6z-v9Gg16g5hXLL6LqTjjz_QfAszHYnFZaDO1IDViYbo3fe71wyWyXsF_y1pqmN8pmxLUof-P-1fLU_f3w3f92NcJf5WYQ4ORI2-7RU57T6YxdcF1Pk77cvIj3jFZl5oL-_rCcoRrLvAriLYjS4ifO63ZFpnM-9rVfPL99WLy936bk-rzsckaCFl0aTHgDpERDUPRcf72_mBuVzofGVQMY8OMKv2uXkA0Fn57CPwZNDB5r4T2PeTMq33jvvH59Q9B0TozVYB_SCk91xPeicg18CPhMX2hacJ-hSt1K3ZGPN9tqjNz-kCnuEKDdfQ5lNSH1GpoJu0BixSucCYMrY4Tgazqh9D6H3a-pXb4xK2MJhuZZK6vBO3sBqGJ4NL0ty4FZH2LjEkuLxKadFPi-T4gmNbkfEwl7CwWVK7bfjnJy0WZmN4DbkaAI61b5PXHQg3gY4ViI7uDF31mBSW-Q-agokF_dHE5UsNEEg83uwrqfEDBQNqIddyz35r8F139_XTnfFb4Sj3xY02FhP3AfRhTAaqxGTnvRD3wxT_1zJPbDrpAWcAn107eoxS5tq1pSzkqdeegXV5POAAL72hUiDVdUkOWyHUGe4w1DoIYyXn5DFVxAexdgBDm-KWZ4v065qNkU5B1FSAFEUDRWU1yVb5Jwu6QKvqeK4B12FxU4Yq7l4w87DiH8v5yhj4VNZMcoYzfOczoqCsWw5pwsqlug0h8UDE_0i2WI6Z1ZSW0VYdWgdvlTS-UufpNw52WqAGBL98-A7Y6vuCEa3x_Amt2nMooop_AthikNH">