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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Miscompilation of C++ constructors"
href="https://bugs.llvm.org/show_bug.cgi?id=40118">40118</a>
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<th>Summary</th>
<td>Miscompilation of C++ constructors
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>7.0
</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>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>-New Bugs
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>tebbi@chromium.org
</td>
</tr>
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<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
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<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=21259" name="attach_21259" title="minimized repro for the bug">attachment 21259</a> <a href="attachment.cgi?id=21259&action=edit" title="minimized repro for the bug">[details]</a></span>
minimized repro for the bug
The following (minimized) code is miscompiled in Clang 7.0, as well as the
trunk version currently used in Chromium (clang version 8.0.0 (trunk 346388),
Target: x86_64-pc-windows-msvc, Thread model: posix), when compiled with
optimizations, on Windows, and in 32 bit mode.
#include <memory>
#include <string>
#include <iostream>
struct Foo {
Foo(std::string s) : x(std::move(s)){}
std::string x;
};
struct Container {
Container(Foo foo) : storage(new Foo(std::move(foo))) {}
std::unique_ptr<Foo> storage;
};
int main() {
Container c(Foo("hi there!"));
std::cout << c.storage->x.size() << std::endl;
}
The compiled program crashes with memory corruption, the std::string accessed
in the last line points to random memory.
I can reproduce it by compiling as follows:
clang-cl.exe -D_HAS_ITERATOR_DEBUGGING=0 -m32 /MTd /O2 clang-bug.cc
At the moment, we work around the bug by writing the constructor as
Foo(std::string s) { x = std::move(s); }
which strangely enough seems to make a difference.</pre>
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