<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/63019>63019</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Invalid optimization around loops
        </td>
    </tr>

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

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

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

<pre>
    come from https://github.com/rust-lang/rust/issues/112061

alive2 complains about an optimization in the LLVM IR: https://alive2.llvm.org/ce/z/fyzhJ3

The code is quite big and I have made attempts to minimize it, but I didn't quite figure out the tooling, so I'm not sure whether my not very good minimizations would be useful. Everything can be found on https://github.com/Nilstrieb/rlo-issue-112061 if desired.

The program prints `11` on O0/O1 and `22` on O2.

This small helper must be linked in to run the program:
```c
#include <stdio.h>
#include <stdint.h>

void print_var(uint8_t x) {
 printf("%d", x);
}

void fn12_rs();

int main() {
 fn12_rs();
}
```

I can't say for sure that the IR emitted by rustc is free of UB, but I suspect that this is the case. The code is really sensitive to small changes and rustc's constant propagation pass actually masks the miscompilation and has to be disabled.
</pre>
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