<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/143171>143171</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [HLSL][SPIRV] 64bit firstbitlow returns incorrect values
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            HLSL,
            clang:HLSL:SPIRV
      </td>
    </tr>

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

    <tr>
      <th>Reporter</th>
      <td>
          V-FEXrt
      </td>
    </tr>
</table>

<pre>
    Discovered while running the offload-test-suite. The values returned imply an incorrect lowering for the 64bit overload. This only occurs for the Vulkan target which makes sense as it has the most complex lowering. The errors are all off by 32 so its probably an error related to the bit offseting to  account for splitting a i64 into i32x2

```
# .---command stderr------------
# | Test failed: Test1
# | Expected:
# | ---
# | Name:            ExpectedOut
# | Format:          UInt32
# | Stride:          16
# | Data:            [ 4294967295, 3, 0, 63, 4294967295, 3, 0, 63, 4294967295, 
# | 2, 3, 4294967295 ]
# | OutputProps:
# |   Height:          0
# | Width:           0
# |   Depth:           0
# | ...
# | Got:
# | ---
# | Name:            Out
# | Format:          UInt32
# | Stride:          16
# | Data:            [ 4294967295, 35, 32, 63, 4294967295, 35, 32, 63, 4294967295, 
# |                    34, 35, 4294967295 ]
# | OutputProps:
# |   Height:          0
# |   Width:           0
# | Depth:           0
# | ...
# | 
# `-----------------------------
```

See https://github.com/llvm/offload-test-suite/pull/210 for more context
</pre>
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