<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/145438>145438</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [DirectX] RootSignature's `v2::DescriptorRange` is misordered
        </td>
    </tr>

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

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

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

<pre>
    We currently have the `v2::DescriptorRange` inherit from the `v1::DescriptorRange` and add a `Flags` field, but this is incorrect. In both the 1.0 and 1.1 root signature formats, the `OffsetInDescriptorsFromTableStart` comes last. That is, `v1::DescriptorRange` is laid out as follows:
```c++
struct DescriptorRange {
  uint32_t RangeType;
  uint32_t NumDescriptors;
  uint32_t BaseShaderRegister;
  uint32_t RegisterSpace;
  uint32_t OffsetInDescriptorsFromTableStart;
};
```

This matches what we have today, but `v2::DescriptorRange` is laid out like so:
```c++
struct DescriptorRange {
  uint32_t RangeType;
  uint32_t NumDescriptors;
 uint32_t BaseShaderRegister;
  uint32_t RegisterSpace;
  uint32_t Flags;
 uint32_t OffsetInDescriptorsFromTableStart;
};
```

This *does not* match what we have today, as we have the `OffsetInDescriptorsFromTableStart` and `Flags` fields reversed. This causes obvious issues when we feed shaders that have root signatures with descriptor ranges into any driver.
</pre>
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