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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Optimization bug with member function return a rvalue in a class template"
href="https://llvm.org/bugs/show_bug.cgi?id=26189">26189</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Optimization bug with member function return a rvalue in a class template
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>3.7
</td>
</tr>
<tr>
<th>Hardware</th>
<td>Macintosh
</td>
</tr>
<tr>
<th>OS</th>
<td>MacOS X
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>C++11
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>waistcoatwm@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>I have a simple piece of code as follows:
#include <map>
#include <iostream>
template <typename LocType, typename Base>
class MapWrapper {
public:
Base&& get_and_erase(LocType x) {
Base ret = std::move(_data[x]);
_data.erase(x);
// Uncomment the cout will give correct result
// std::cout << "retval = " << ret << std::endl;
return std::move(ret);
}
void increase(const LocType& x, const Base& w) {
if (w == 0.0) {
return;
}
_data[x] += w;
}
private:
std::map<LocType, Base> _data;
};
int main() {
MapWrapper<int, double> a;
a.increase(1, 1.0);
double w = a.get_and_erase(1);
std::cout << "w = " << w << std::endl;
return 0;
}
I think the output should be 1, but when I use my MAC with
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin14.5.0
Thread model: posix
and compile it with: g++ --std=c++11 -O2 debug.cpp -o debug
What I get is : w = 2.64619e-260
The only way I can make it correct is to turn off -O2 or force an output by
uncomment the `std::cout` in the code.
Any ideas?</pre>
</div>
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