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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Clang generates wrong optimized code for std::rotate followed by std::min_element with libc++"
href="https://bugs.llvm.org/show_bug.cgi?id=40641">40641</a>
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<th>Summary</th>
<td>Clang generates wrong optimized code for std::rotate followed by std::min_element with libc++
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>7.0
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<th>Hardware</th>
<td>PC
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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
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>C++
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>steffen.muething@iwr.uni-heidelberg.de
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<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<pre>Created <span class=""><a href="attachment.cgi?id=21442" name="attach_21442" title="Failing code, check return code to see if it worked">attachment 21442</a> <a href="attachment.cgi?id=21442&action=edit" title="Failing code, check return code to see if it worked">[details]</a></span>
Failing code, check return code to see if it worked
When compiling with clang 7 "-std=libc++ -O3", the attached program generates
wrong output on x86_64 (both Linux and macOS). In particular, the rotated
sequence contains one of the items twice, and one item has disappeared.
I did some testing with the following outcomes:
- The code only fails in optimized mode
- The code only fails when using libc++, when compiling with the GCC 8
libstdc++, the generated code is correct
- On the other hand, when compiling the code with GCC 8 and libc++, the
generated code is also correct
- The code only fails when the output of std::min_element is used as the middle
parameter of std:rotate</pre>
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