<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/72300>72300</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            clang-tidy check `misc-unused-using-decls` appears to be quite slow
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
      </td>
    </tr>

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

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

<pre>
    The `misc-unused-using-decls` check constantly comes up as one of the top 3 expensive checks in our code base (it usually takes about 5% of the total time). Considering it is not providing that much in terms of its findings compared to other checks it seems a bit excessive.

```
  ---User Time---   --System Time--   --User+System--   ---Wall Time---  --- Name ---
   0.8125 ( 11.9%)   0.0000 (  0.0%)   0.8125 (  7.4%)   0.7912 ( 7.2%)  bugprone-reserved-identifier
   0.4531 (  6.6%)   0.3125 (  7.6%) 0.7656 (  7.0%)   0.6002 (  5.5%)  misc-unused-using-decls
   0.2344 ( 3.4%)   0.0938 (  2.3%)   0.3281 (  3.0%)   0.4317 (  3.9%) bugprone-use-after-move
```

```
   0.7969 ( 11.6%)   0.0312 ( 0.8%)   0.8281 (  7.5%)   0.8204 (  7.5%)  bugprone-reserved-identifier
 0.2969 (  4.3%)   0.3125 (  7.7%)   0.6094 (  5.6%)   0.6044 (  5.5%) misc-unused-using-decls
   0.4219 (  6.1%)   0.1094 (  2.7%)   0.5312 ( 4.8%)   0.4172 (  3.8%)  bugprone-use-after-move
```

```
 0.5781 (  5.0%)   0.4688 (  4.9%)   1.0469 (  5.0%)   1.1171 (  5.3%) misc-unused-using-decls
   0.8750 (  7.6%)   0.0938 (  1.0%)   0.9688 ( 4.6%)   0.9738 (  4.6%)  bugprone-reserved-identifier
   0.7969 (  6.9%) 0.2344 (  2.5%)   1.0312 (  4.9%)   0.8989 (  4.3%) bugprone-use-after-move
```
</pre>
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