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<body><span class="vcard"><a class="email" href="mailto:nok.raven@gmail.com" title="Nikita Kniazev <nok.raven@gmail.com>"> <span class="fn">Nikita Kniazev</span></a>
</span> changed
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED DUPLICATE - Clang always emits a library call for unaligned atomics"
href="https://bugs.llvm.org/show_bug.cgi?id=25335">bug 25335</a>
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<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>What</th>
<th>Removed</th>
<th>Added</th>
</tr>
<tr>
<td style="text-align:right;">Product</td>
<td>new-bugs
</td>
<td>clang
</td>
</tr>
<tr>
<td style="text-align:right;">CC</td>
<td>
</td>
<td>neeilans@live.com, nok.raven@gmail.com, richard-llvm@metafoo.co.uk
</td>
</tr>
<tr>
<td style="text-align:right;">Status</td>
<td>NEW
</td>
<td>RESOLVED
</td>
</tr>
<tr>
<td style="text-align:right;">Assignee</td>
<td>unassignedbugs@nondot.org
</td>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<td style="text-align:right;">Summary</td>
<td>atomics are 20x slower compared to gcc if atomic<T>'s T is a packed struct
</td>
<td>Clang always emits a library call for unaligned atomics
</td>
</tr>
<tr>
<td style="text-align:right;">Component</td>
<td>new bugs
</td>
<td>Frontend
</td>
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<td style="text-align:right;">Resolution</td>
<td>---
</td>
<td>DUPLICATE
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<b><a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED DUPLICATE - Clang always emits a library call for unaligned atomics"
href="https://bugs.llvm.org/show_bug.cgi?id=25335#c2">Comment # 2</a>
on <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED DUPLICATE - Clang always emits a library call for unaligned atomics"
href="https://bugs.llvm.org/show_bug.cgi?id=25335">bug 25335</a>
from <span class="vcard"><a class="email" href="mailto:nok.raven@gmail.com" title="Nikita Kniazev <nok.raven@gmail.com>"> <span class="fn">Nikita Kniazev</span></a>
</span></b>
<pre>Clang always emits a library call for unaligned atomics by design
<a href="https://github.com/llvm/llvm-project/blob/32e2729e337640e547bb6e8bd3dbe43ac36daa81/clang/lib/CodeGen/CGAtomic.cpp#L809-L810">https://github.com/llvm/llvm-project/blob/32e2729e337640e547bb6e8bd3dbe43ac36daa81/clang/lib/CodeGen/CGAtomic.cpp#L809-L810</a>
<a href="https://godbolt.org/z/Gz4srWKqT">https://godbolt.org/z/Gz4srWKqT</a>
I am marking this as a duplicate of <a class="bz_bug_link
bz_status_NEW "
title="NEW - LLVM lowers __atomic builtin to a function call when lowering __sync builtin to a single instruction with LOCK prefix"
href="show_bug.cgi?id=38846">bug 38846</a> which has a discussion.
*** This bug has been marked as a duplicate of <a class="bz_bug_link
bz_status_NEW "
title="NEW - LLVM lowers __atomic builtin to a function call when lowering __sync builtin to a single instruction with LOCK prefix"
href="show_bug.cgi?id=38846">bug 38846</a> ***</pre>
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