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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - vtable linkage in key function TU differs between clang and gcc"
href="https://llvm.org/bugs/show_bug.cgi?id=22992">22992</a>
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<th>Summary</th>
<td>vtable linkage in key function TU differs between clang and gcc
</td>
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<th>Product</th>
<td>new-bugs
</td>
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<th>Version</th>
<td>trunk
</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>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>new bugs
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>yaron.keren@gmail.com
</td>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
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<th>Classification</th>
<td>Unclassified
</td>
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<p>
<div>
<pre>Using gcc version 4.9.1 and clang trunk under Windows 7, the following C++
program creates COMDAT linkage for vtable and typeinfo in gcc but not in clang.
class C {
public:
virtual void f();
};
void C::f() {}
<span class="quote">>g++ -c v.cpp & dumpbin /headers v.o | grep COMDAT</span >
COMDAT; sym= __ZTV1C
COMDAT; sym= __ZTI1C
COMDAT; sym= __ZTS1C
<span class="quote">>clang++ -target i686-pc-windows-gnu -c v.cpp & dumpbin /headers v.o | grep COMDAT</span >
The difference is probably not related to Windows but the result of
CodeGenModule::getVTableLinkage returning ExternalLinkage for class C. This is
OK as the vtable will not be emitted in other TUs at least with clang.
However, I am not sure if mixed compiling with clang and gcc-compiled objects
would not bomb in some situations.
There may be a reason why gcc produces weak vtables.
If it makes sense matching gcc behaviour, a patch would be to return
WeakODRLinkage instead of ExternalLinkage.</pre>
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