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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Missed optimization of functions deduplication"
href="https://bugs.llvm.org/show_bug.cgi?id=38335">38335</a>
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<th>Summary</th>
<td>Missed optimization of functions deduplication
</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>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>C++
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>antoshkka@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>dgregor@apple.com, llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>If two functions have the same body Clang does not deduplicate the functions.
Consider the following example:
void mutate0(int&);
template <int I>
int foo_template(int b) {
mutate0(b); mutate0(b); mutate0(b); mutate0(b);
mutate0(b); mutate0(b); mutate0(b); mutate0(b);
mutate0(b); mutate0(b); mutate0(b); mutate0(b);
return b;
}
int foo0(int b) {
return foo_template<0>(b);
}
int foo1(int b) {
return foo_template<1>(b);
}
GCC deduplicates the function bodies and foo1 and foo2 and call the same
template instantiation:
_Z4foo0i:
jmp _Z12foo_templateILi0EEii
_Z4foo1i:
jmp _Z12foo_templateILi0EEii # Same as above
Clang instead produces functions that call different template instantiations:
_Z4foo0i:
jmp _Z12foo_templateILi0EEii
_Z4foo1i:
jmp _Z12foo_templateILi1EEii # Differs from above!
This results in a two times bigger assembly on Clang.</pre>
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