<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/123208>123208</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            AMDGPU silently converts incorrect physical register asm constraint to virtual register
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            backend:AMDGPU,
            accepts-invalid
      </td>
    </tr>

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

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

<pre>
    ```
; RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx940 < %s

define void @invalid_sgpr(<2 x i32> inreg %arg0) {
  call void asm sideeffect "; use $0", "{s[1:2]}"(<2 x i32> %arg0)
  ret void
}

```

s[1:2] is not a valid SGPR reference as 64-bit SGPRs require even alignment. This is silently accepted, and appears to be treated as a virtual register constraint. In -stop-after=finalize-isel, I see:

```
    %10:sreg_64 = COPY %11
 INLINEASM &"; use $0", 1 /* sideeffect attdialect */, 3997705 /* reguse:SReg_64 */, %10
```
</pre>
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