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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - std::string::push_back is 3.4x slower than on libstdc++"
href="https://bugs.llvm.org/show_bug.cgi?id=33840">33840</a>
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<th>Summary</th>
<td>std::string::push_back is 3.4x slower than on libstdc++
</td>
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<th>Product</th>
<td>libc++
</td>
</tr>
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<th>Version</th>
<td>unspecified
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>All Bugs
</td>
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<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>thomasanderson@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
</td>
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<p>
<div>
<pre>Simple program that demonstrates the issue:
----test.cpp----
#include <string>
int main(void) {
std::string s;
for(volatile int i = 0; i < 500000000; i++) {
s.push_back('a');
}
return 0;
}
----test.cpp----
$ clang++ main.cpp -stdlib=libstdc++ && time ./a.out
real 0m2.451s
$ clang++ main.cpp -stdlib=libc++ && time ./a.out
real 0m8.535s
I've verified that it is always a constant factor of 3.4x slower than libstdc++
regardless of the input size.</pre>
</div>
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