<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/78512>78512</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Clang does not propagate __builtin_expect probability information outside of function
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang
      </td>
    </tr>

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

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

<pre>
    Hi, I've created a small test to see how __builtin_expect variants work in Clang and GCC and noticed the difference which can be seen here https://godbolt.org/z/8ccTP7rY1

The gist of it is as follows: function `f` returns bool with expectation. Function `g` uses this bool in if statement where in both branches something non-trivial is executed. I expected Clang to propagate probability info outside of `f` function but in this case it does not, both probabilities 0 and 1 produce the same code. GCC produces different code for these cases, swapping branches when probability is flipped.

Optimizations are turned on, `f` is inlined in `g`. I also tried LTO with the same result.

If I manually inline `f` in `g`, Clang starts using probability info https://godbolt.org/z/1qvfbjbqG

Is my testcase too simple for Clang? Is it a problem in Clang, or maybe a known and expected difference in implementations between Clang and GCC?
</pre>
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