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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - -Wunused-but-set-variable fails to see variable is used"
href="https://bugs.llvm.org/show_bug.cgi?id=51595">51595</a>
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<th>Summary</th>
<td>-Wunused-but-set-variable fails to see variable is used
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
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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
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>mprivozn@redhat.com
</td>
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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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<pre>I've updated my Rawhide and as a result clang-13.0.0~rc1-1.fc35.x86_64 was
installed. But that version broke build of libvirt. In libvirt we use glib and
its g_autoptr() and g_autofree to automatically free memory when variable goes
out of scope. An example of failure can be seen in our CI:
<a href="https://gitlab.com/libvirt/libvirt/-/jobs/1528604467">https://gitlab.com/libvirt/libvirt/-/jobs/1528604467</a>
The corresponding code can be seen here:
<a href="https://gitlab.com/libvirt/libvirt/-/blob/master/src/util/viridentity.c#L135">https://gitlab.com/libvirt/libvirt/-/blob/master/src/util/viridentity.c#L135</a>
Another location that triggers the warning:
<a href="https://gitlab.com/libvirt/libvirt/-/blob/master/src/rpc/virnetclient.c#L883">https://gitlab.com/libvirt/libvirt/-/blob/master/src/rpc/virnetclient.c#L883</a>
The code can be simplified to the following:
// clang $(pkg-config --cflags --libs glib-2.0) -Wunused-but-set-variable
repro.c -o repro
#include <glib.h>
int main(int argc, char *argv[])
{
g_autoptr(GSource) source = NULL;
source = g_source_new(NULL, 0);
}
I don't think that the warning should be emitted in this case, because the
variable is actually used - in the cleanup function. Please note that this
scenario is different to plain: g_autoptr(GSource) source = NULL; (that is
leaving the g_source_new() line out) in which case the warning is warranted.</pre>
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