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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [X86] Redundant zext when returning from i8 function"
href="https://llvm.org/bugs/show_bug.cgi?id=26300">26300</a>
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<th>Summary</th>
<td>[X86] Redundant zext when returning from i8 function
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</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>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>hans@chromium.org
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Blocks</th>
<td>26299
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>For the following C++ code:
bool f(int x, int y) {
return x == y;
}
clang -Os will generate:
00000000 <_Z1fii>:
0: 8b 44 24 04 mov 0x4(%esp),%eax
4: 3b 44 24 08 cmp 0x8(%esp),%eax
8: 0f 94 c0 sete %al
b: 0f b6 c0 movzbl %al,%eax
e: c3 ret.
The movzbl seems redundant, and neither GCC nor MSVC will generate it.
I suppose the motivation for clearing the high bits is breaking any potential
partial register dependency, but I don't think we should do that at -Os.</pre>
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</p>
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