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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Unnecessary use of local dynamic on x86_64"
href="http://llvm.org/bugs/show_bug.cgi?id=17581">17581</a>
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<th>Summary</th>
<td>Unnecessary use of local dynamic on x86_64
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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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>Backend: X86
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
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<th>Reporter</th>
<td>rafael.espindola@gmail.com
</td>
</tr>
<tr>
<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>Local dynamic is not any better than general dynamic when there is only one
access. Given
__attribute__((visibility("hidden"))) __thread int obj;
int test() {
return ((int)&obj) > 0;
}
clang produces
leaq obj@TLSLD(%rip), %rdi
callq __tls_get_addr@PLT
movq $obj@DTPOFF, %rcx
addl %eax, %ecx
which is 21 bytes
without the hidden attribute clang itself produces
data16
leaq obj@TLSGD(%rip), %rdi
data16
data16
rex64
callq __tls_get_addr@PLT
which is 16 bytes.</pre>
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</p>
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