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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Erroneous -Wunreachable-code in some cases when C++20 `[[likely]]`/`[[unlikely]]` are used."
href="https://bugs.llvm.org/show_bug.cgi?id=49425">49425</a>
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<th>Summary</th>
<td>Erroneous -Wunreachable-code in some cases when C++20 `[[likely]]`/`[[unlikely]]` are used.
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>unspecified
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<th>Hardware</th>
<td>All
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>C++2a
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>ian@geometrian.com
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<th>CC</th>
<td>blitzrakete@gmail.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<pre>Consider the following simple, complete example:
//Compile with "-std=c++20 -Wunreachable-code -O3"
bool foo();
int bar() {
if (foo()) [[likely]] return 1;
else return 0;
}
The compiler of course cannot tell what `foo()` returns in this translation
unit. However, clang (tested 13.0.0) complains:
<source>:4:13: warning: code will never be executed [-Wunreachable-code]
if (foo()) [[likely]] return 1;
^~~~~~~~~~~~~~~~~~~
This is an incorrect claim. Note that the generated code is correct, and in
particular the positive branch is correctly implemented. Removing `[[likely]]`
also removes the warning (which makes no sense since `[[likely]]` is a hint);
the generated code in that case happens to be the same.</pre>
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