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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 --- - X86CallFrameOptimization leads to generation of two consecutive `subl $8, %esp` (instead of a single `subl $16, %esp)"
href="https://llvm.org/bugs/show_bug.cgi?id=28542">28542</a>
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<tr>
<th>Summary</th>
<td>X86CallFrameOptimization leads to generation of two consecutive `subl $8, %esp` (instead of a single `subl $16, %esp)
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>nicolasweber@gmx.de
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>$ cat fastisel.cc
struct S {
void f(int a);
};
void g() {
S s;
s.f(43);
}
$ bin/clang -m32 -O2 -c fastisel.cc -S -o - -mllvm -no-x86-call-frame-opt
...
pushl %ebp
movl %esp, %ebp
subl $24, %esp
leal -8(%ebp), %eax
movl %eax, (%esp)
movl $43, 4(%esp)
calll __ZN1S1fEi
...
This looks reasonable. Now:
$ bin/clang -m32 -O2 -c fastisel.cc -S -o -
...
pushl %ebp
movl %esp, %ebp
subl $8, %esp
subl $8, %esp
leal -8(%ebp), %eax
pushl $43
pushl %eax
calll __ZN1S1fEi
This would look much better if it said `subl $16, %esp` instead.</pre>
</div>
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