<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/86192>86192</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [DXIL] Add `log`, `log2`, and `log10` intrinsic Lowering
        </td>
    </tr>

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

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

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

<pre>
    
Needs to cover the float and half case for all three: https://godbolt.org/z/64fzEq3nd

This is a perfect candidate for [instruction expansion](https://github.com/llvm/llvm-project/blob/main/llvm/lib/Target/DirectX/DXILIntrinsicExpansion.cpp):

- `log2`
  - This is the simplest case just call  unary dxilop 23
- `log`
  - Call `log2` DXIL op (ie 23)
  -  Create a ln2 const value 
     -  `M_LN2_F`       `0.693147180559945309417232121458176568f`
 -  `M_LN2_H`      `0.693147180559945309417232121458176568h`
  -  Floating point multiply the value of M_LN2 with the return value of `log2`
  - [Reference implementation](https://github.com/microsoft/DirectXShaderCompiler/blob/main/lib/HLSL/HLOperationLower.cpp#L2238C1-L2253C2)
- `log10` 
  - Define M_LN10
    - `M_LN10_F` `2.30258509299404568401799145468436421f`
    - `M_LN10_H` `2.30258509299404568401799145468436421h`
  - Call `log2` DXIL op (ie 23)
  -  Create a  `log2_10Const` = `M_LN2` / `M_LN10`  const value 
 - Floating point multiply the value of `log2_10Const` with the return value of `log2`
  -  [Reference implementation](https://github.com/microsoft/DirectXShaderCompiler/blob/main/lib/HLSL/HLOperationLower.cpp#L2255C1-L2271C2)
</pre>
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