<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/116629>116629</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [X86] Missing support for ‘z’ asm operand modifier
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            backend:X86,
            inline-asm
      </td>
    </tr>

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

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

<pre>
    As initially reported on LKML: https://lore.kernel.org/202411180620.8uhr11le-lkp@intel.com/

```c
void foo(unsigned char *var)
{
    asm("shr%z1 %1" : "+m"(*var));
}
```

```
$ gcc -c -o /dev/null test.c

$ clang -c -o /dev/null test.c
test.c:3:6: error: invalid operand in inline asm: 'shr${1:z} $1'
    3 |         asm("shr%z1 %1" : "+m"(*var));
      |             ^
test.c:3:6: error: ambiguous instructions require an explicit suffix (could be 'shrb', 'shrw', 'shrl', or 'shrq')
<inline asm>:1:2: note: instantiated into assembly here
    1 |         shr (%rax)
      |         ^
2 errors generated.
```

https://godbolt.org/z/o6bWzfh9x

>From [the GCC documentation](https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#x86-Operand-Modifiers):

`z` | Print the opcode suffix for the size of the current integer operand (one of `b/w/l/q`). | `%z0` | `l`
-- | -- | -- | --

I see where the X86 specific modifiers are implemented in `X86AsmPrinter::PrintAsmOperand()` but I am not entirely sure how to implement this there. I am happy to try with any guidance.
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJykVU-T4rgP_TTioiKVKCEkBw5puvnV1G-mdm87VycRxDuOnbGdbuDTb9mE_rdbO4ftarBkbOnp-ckWzsmTZt7B5gE2jysx-8HYnRZ-ELoLH161pr_sGodSSy-FUhe0PBnruUej8ev_v32FvMHB-8lB3gAdgA7KWE5-sNWsEmNPQAdKqciyrEpLSpNqHmyWKV6rHxMUqdSeVdKZMWxOHyFtlu8yvf13N__ZyB6PxgBVs47Ae-wGYRGoeRYWqF72bR9uBiKicCNQBURusECba4ZAmwyIMMAGIqCHMQ7VWxiqIX-4B3v8hOYfIS4uFXjqOlx3uDYIdOj5GeigZ6XQs_NJ92EzFdgpoU-_XL_YeZND3pQBOFtrbDCkfhZK9mgmtkL3KDVKraTmWHkscRtLL2D7kEHeXGH7iEBFBrR9oylH2O7x_vdfSbtFeR8x-punX5YjxlaeZjMHvTlv585Lox1a_jlLyyg08nlSspMe3Xw8yjMCVZ2ZVY8tL7W2oTLaL97LB08tnrHLxM84cVdOvn9P3hPkTaCMAjJtPN8Id15oL0XoAKm9QeEcj6264MCW3wjIPhDghpCxAtpYcX5N-HeiXkmiGykOT6zZhmzJvwjxY_-dTN8a5ZfeuwIdTNn-cT0O9fn9poM1I8LmwQ-M_9vvsTfdPLL2IpAOm0eg6lPcrktOel7imkhVbzp3-wno8HT2rHvu140bk8GPCig_V-X6t5s6199ML4-SrYtqaT610hXKNJLxu5XaY4Blps70fD_ro7Fx1skrozlGu5utZe3DUfCJ7WsjAFVGh1WwJ2gCXy3Q4SXcTkCHn4E_qpOYLtqba3pPD2WqXvldr-Pc5-E99C_omPElHH-E9L0q0U3cyaPscLyXjMIyynFSHDiO4gmZvldl48ZYMYcWgLyJTuPGhbUomzqAa2ePX1CMQYzI2kvL6oJutoyDeUFv3uKjH6QLaCwntz2DmKZLWOPtBV-kH1DoC55m2Yd7Pln1u7yv81qseJdt86zO6yrNVsOuqHohiIqCtm2RUl-JvhXtsSz6bdbnVbqSu_vtnhWUU5qURbc5tsWxK2qxKbMCipRHIVWi1PMYxLOSzs28y7KypHqlRMvKxTeIqBXdD9Y95M33qoxXzB6Ibl25jvcShZfK7kKsdTufHBSpks67t-heehXftBBi84jfpHNSn9DNU3i5oozgiaBKoa6ud6sOTf8qn_uxrWardp-6QPphbpcHKyRdhvVkzZ_ceaBDrC-0xVLi847-CgAA__-P6ic3">