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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] Unnecessary copy when taking address of function parameter"
href="https://llvm.org/bugs/show_bug.cgi?id=26328">26328</a>
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<tr>
<th>Summary</th>
<td>[x86] Unnecessary copy when taking address of function parameter
</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>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Consider:
void f(int*);
void g(int x) {
f(&x);
}
at -Os, Clang generates:
pushl %eax
movl 8(%esp), %eax
movl %eax, (%esp)
leal (%esp), %eax
pushl %eax
calll "?f@@YAXPAH@Z"
addl $4, %esp
popl %eax
retl
MSVC generates:
00000000: 8D 44 24 04 lea eax,[esp+4]
00000004: 50 push eax
00000005: E8 00 00 00 00 call ?f@@YAXPAH@Z
0000000A: 59 pop ecx
0000000B: C3 ret
It seems Clang is wasting two instructions copying x to g's stack frame,
whereas MSVC just uses the address of the parameter directly.</pre>
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</p>
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