<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/59891>59891</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Assertion `DAG.isGuaranteedNotToBeUndefOrPoison(R, false) && "Can't create node that may be undef/poison!"' failed.
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            backend:AArch64,
            llvm:codegen,
            crash-on-valid
      </td>
    </tr>

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

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

<pre>
    this function:

```llvm
target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
target triple = "aarch64-linux-gnu"

define i8 @f(i64 %0) {
  %2 = freeze i64 %0
  %3 = trunc i64 %2 to i1
  %4 = trunc i64 %0 to i1
  %5 = xor i1 %3, %4
  %6 = freeze i1 %5
  %7 = zext i1 %6 to i8
  ret i8 %7
}
```

when passed to the default AArch64 backend, crashes with an assertion violation: https://gcc.godbolt.org/z/s3eeE7jj4

perhaps it is useful to know that we saw this one get triggered last summer: https://github.com/llvm/llvm-project/issues/57402

</pre>
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