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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] Consider mov-to-push also at -O2?"
href="https://llvm.org/bugs/show_bug.cgi?id=26325">26325</a>
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<th>Summary</th>
<td>[x86] Consider mov-to-push also at -O2?
</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>
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<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>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>hans@chromium.org
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, michael.kuperstein@gmail.com
</td>
</tr>
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<th>Blocks</th>
<td>26299
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>On Windows, most of Chromium builds with /O1 /Os (optimize for size), but some
of it builds with /O2 /Ot (optimize for speed).
For this code:
void f(int x, int y);
void g(int x) {
f(x, 1);
}
clang -target i686-pc-win32 -Os generates:
00000000 <?g@@YAXH@Z>:
0: 6a 01 push $0x1
2: ff 74 24 08 pushl 0x8(%esp)
6: e8 00 00 00 00 call b <?g@@YAXH@Z+0xb>
b: 83 c4 08 add $0x8,%esp
e: c3 ret
but with -O2 it generates:
00000000 <?g@@YAXH@Z>:
0: 83 ec 08 sub $0x8,%esp
3: 8b 44 24 0c mov 0xc(%esp),%eax
7: 89 04 24 mov %eax,(%esp)
a: c7 44 24 04 01 00 00 movl $0x1,0x4(%esp)
11: 00
12: e8 00 00 00 00 call 17 <?g@@YAXH@Z+0x17>
17: 83 c4 08 add $0x8,%esp
1a: c3 ret
Is the -O2 version actually faster enough to justify the size increase here?</pre>
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