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<base href="http://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - clang does not throw away unused dynamic_cast"
href="http://llvm.org/bugs/show_bug.cgi?id=16136">16136</a>
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</tr>
<tr>
<th>Summary</th>
<td>clang does not throw away unused dynamic_cast
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>3.2
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>C++
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>yozh@mx1.ru
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Code:
===
struct aaa { virtual ~aaa() {} } ;
struct bbb : public aaa {};
void foo(aaa* aaa) {
dynamic_cast<bbb*>(aaa);
}
===
GCC -O3 produces code:
===
0000000000000000 <_Z3fooP3aaa>:
0: f3 c3 repz retq
===
Clang 3.2 -O3:
===
0000000000000000 <_Z3fooP3aaa>:
0: 48 85 ff test %rdi,%rdi
3: 74 16 je 1b <_Z3fooP3aaa+0x1b>
5: be 00 00 00 00 mov $0x0,%esi
a: ba 00 00 00 00 mov $0x0,%edx
f: 48 c7 c1 ff ff ff ff mov $0xffffffffffffffff,%rcx
16: e9 00 00 00 00 jmpq 1b <_Z3fooP3aaa+0x1b>
1b: c3 retq
===
So it looks like clang does not throw dynamic_cast away, when result of
dynamic_cast is unused.</pre>
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</p>
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