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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Lifetime of temporaries inconsistently extending when optiimzations are enabled"
href="https://bugs.llvm.org/show_bug.cgi?id=47861">47861</a>
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<th>Summary</th>
<td>Lifetime of temporaries inconsistently extending when optiimzations are enabled
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>11.0
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</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
</td>
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<th>Reporter</th>
<td>chris@chrissavoie.com
</td>
</tr>
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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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<p>
<div>
<pre>Godbolt example: <a href="https://godbolt.org/z/fssed1">https://godbolt.org/z/fssed1</a>
The following code:
struct A {
__attribute__((noinline))
A(int i) : data(i) {}
A& operator+=(int i) { data += i; return *this; }
int data;
};
int main() {
A const& b = A(5) += 5;
A c(6);
return b.data + c.data; // 16 expected
}
Will return 16 when compiled without optimizations, 11 when compiled with
optimizations (-O2 or greater).
Browsing versions on godbolt it looks like the difference appeared between
versions 6.0.0 and 7.0.0.
I realize that this is generally undefined behavior, but the differences
between optimization levels caught me off guard. I'm not sure if there's either
a way to return to the pre-7 behavior or to make the non-optimized version more
obviously incorrect.</pre>
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