<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/57032>57032</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            ubsan reports a misalignment error for operator new[] invocations to build 0-length array instance
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          RobertHenry6bev
      </td>
    </tr>
</table>

<pre>
    Consider this C++ snippet where a deliberate misalignment of data is passed to operator new

      class Thing {int a, b; ....}
      size_t delta = 1;
      unsigned char buf[sizeof(int)*20] ;
      Thing *pThing = new (buf + delta) Thing[0];

clang++-14 builds a binary which at runtime says:
runtime error: constructor call on misaligned address 0x7fffffffe3a1 for type 'Thing', which requires 4 byte alignment

This error message is incorrect.  The constructor Thing::Thing will never be called since the invocation of operator new[] asked for 0 Things.

The error message should only be generated  prior to calling the constructor, not upon return from operator new.

g++-12 seems to get this right.

g++-12 does not seem to test for this.

I have not looked at the clang-14 test suite to see if this situation is explicitly tested.

</pre>
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