<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/137739>137739</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            UB optimization leads to really bad code gen
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

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

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

<pre>
    Linux has some code that may result in dividing by zero or shifting by negative numbers. For instance, in one of the ARMGPU drivers, a "divide by zero" results in a fall through into the following function.

```
drivers/gpu/drm/amd/amdgpu/../display/dc/basics/fixpt31_32.o:
 warning: objtool: dc_fixpt_recip() falls through to next function dc_fixpt_sinc()

drivers/gpu/drm/amd/amdgpu/../display/dc/sspl/spl_fixpt31_32.o:
 warning: objtool: spl_fixpt_recip() falls through to next function spl_fixpt_sinc()
```

It is undefined behavior, but in these cases it will silently generate incorrect code. It's far better to generate the bad code so that it signals/traps/whatever.
</pre>
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