<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/128071>128071</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [DirectX] Error if unknown intrinsic makes it to DXILOpLowering.cpp
        </td>
    </tr>

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

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

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

<pre>
    
For the purposes of this ticket an unknown intrinsic is defined as any intrinsics not defined in `llvm/lib/Target/DirectX/DXIL.td`. In other words intrinsics not mapped to a DXIL Op.

Today we are letting these intrinsics slip through and we only catch the failure in the DXIL validator. 

> Why is this a problem?
Clang builtins are usable in HLSL mode so intrinsics we never intended to support could also make their way to the DirectX backend.

Example:
https://hlsl.godbolt.org/z/13rPj18vn

This is because we don't error in the default case, we just skip it if we don't know what to do with it.
https://github.com/llvm/llvm-project/blob/87bf23216fc1257e88e0d38730df2d0187ff5bc6/llvm/lib/Target/DirectX/DXILOpLowering.cpp#L788-L789

Solution we should return some diagnositcs so the User knows the builtin and its coresponding llvm codegen is not valid when targeting the DirectX backend.


</pre>
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