<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/90954>90954</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [X86] Crash when building SingleSource/UnitTests/Matrix/AMXINT8/t_gemm_bf16.cpp: Assertion `RegNo && RegNo < 388 && "Invalid register number!"'
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            backend:X86,
            llvm:crash,
            crash-on-valid
      </td>
    </tr>

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

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

<pre>
    Building the tests in `SingleSource/UnitTests/Matrix/AMXINT8/` added in [afc7e6588b3b43351e49f697fe48283ec5056c11](https://github.com/llvm/llvm-test-suite/commit/afc7e6588b3b43351e49f697fe48283ec5056c11) crashes `clang` with a `skylake-avx512` CPU.

I think this has been happening for a while. 

Reduced IR reproducer:
https://llvm.godbolt.org/z/ax36ojxj5
</pre>
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