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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Error with ThinLTO: Invalid function metadata: outgoing forward refs"
href="https://bugs.llvm.org/show_bug.cgi?id=35472">35472</a>
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<th>Summary</th>
<td>Error with ThinLTO: Invalid function metadata: outgoing forward refs
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>LLVM Codegen
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>sunil_srivastava@playstation.sony.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>As shown below, a ThinLTO run fails with an assertion failure on two simple
files, trimmed from a larger code.
The attribute nodebug on ~Echo() is needed for this crash to occur. In this
trimmed example the ~Echo() default declaration has been added to be able to
put that attribute.
-------------------------------------------------------------------------------
$ clang++ --version
clang version 6.0.0 (trunk 319376)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: ....
$ clang++ -c a.cpp -o a.bc --std=c++11 -O0 -g -flto=thin
$ clang++ -c b.cpp -o b.bc --std=c++11 -O0 -g -flto=thin
$ llvm-lto -thinlto-action=run a.bc b.bc
ThinLTO: b.bc: error: Invalid function metadata: outgoing forward refs
(Producer: 'LLVM6.0.0svn' Reader: 'LLVM 6.0.0svn')
LLVM ERROR: importFunctions failed
$ cat a.cpp
struct Charlie {
__attribute__((__always_inline__)) ~Charlie() { Golf = 0; }
int Golf;
};
struct Delta {
Charlie Foxtrot;
};
struct Echo {
Charlie Foxtrot;
__attribute__((nodebug)) ~Echo() = default;
};
extern void Bravo();
void Bravo() {
Delta Hotel;
Echo India;
}
$ cat b.cpp
extern void Bravo();
extern void Alpha();
void Alpha() { Bravo(); }
$
--------------------------------------------------------------------------
The crash occurs in BitcodeReader.cpp at a point where it expects all Metadata
forward-refs to be resolved, but they are not. Around line 4615:
// Unexpected unresolved metadata about to be dropped.
if (MDLoader->hasFwdRefs())
return error("Invalid function metadata: outgoing forward refs");
I am filing this bug under clang/CodeGen under the assumption that the incoming
IR at this point is defective. If not, please go ahead and assign it to another
component.</pre>
</div>
</p>
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