<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/91380>91380</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            AllocaInst::getAllocationSize/AllocaInst::getAllocationSizeInBits should check for overflow
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            good first issue
      </td>
    </tr>

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

    <tr>
      <th>Reporter</th>
      <td>
          efriedma-quic
      </td>
    </tr>
</table>

<pre>
    Currently, the code just blindly multiplies the size, and can therefore return a nonsense result.  (The behavior isn't really defined in the overflow case, but reasoning based on the overflowed computation is likely to lead to weird results.)

https://github.com/llvm/llvm-project/blob/7115ed0fff027b65fa76fdfae215ed1382ed1473/llvm/lib/Transforms/Utils/InlineFunction.cpp#L2622 has code to compute the allocation size while conservatively checking for overflow; we should use similar logic, then make the inliner call getAllocationSize().  Maybe use the multiply-with-overflow helper from CheckedArithmetic.h instead of writing out that code.
</pre>
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