<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/60946>60946</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Clang ignores the `min_vector_width` attribute
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          He3lixxx
      </td>
    </tr>
</table>

<pre>
    Consider this code snippet ([godbolt](https://godbolt.org/z/b59MvarKq)):
```c++
void test(uint64_t* input_, uint64_t* output_) __attribute__((min_vector_width(512))) {
    uint64_t* __restrict input = std::assume_aligned<64>(input_);
    uint64_t* __restrict output = std::assume_aligned<64>(output_);
    
    for (size_t i = 0; i < 64; ++i) {
        output[i] = input[i] * 16;
    }
}
```

When compiling on x86 with `-std=c++20 -O3 -march=icelake-server`, this resulting assembly does not use the 512-bit registers (`zmm`), but the AVX2 256-bit registers (`ymm`).

I understand that clang defaults to `-mprefer-vector-width=256`, but [according to the documentation](https://clang.llvm.org/docs/AttributeReference.html#min-vector-width), the `min_vector_width` attribute should overrule this default.

With `-mprefer-vector-width=512`, clang [uses the `zmm` registers](https://godbolt.org/z/eEoPE96xT).
</pre>
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